Abstract
A system for monitoring a patient on a hospital bed includes load
cells and a controller for detecting patient movement on, exit from,
and impending exit from the hospital bed, including movement across
or outside a virtual boundary or region located on the bed. The controller
is configured to detect changes in the distribution of patient weight
among the load cells. The controller is also configured to accommodate
the installation or removal of medical equipment or other tare weights
on the bed, head incline adjustment, and bed frame deformation or
other changes in the system causing redistribution of weight among
the load cells, while minimizing false alarms. A caregiver may select
between various patient monitoring modes and remotely monitor patient
movement relative to a reference load cell distribution, impending
patient exit from the bed and patient exit from the bed.
Claims
1. A method of monitoring a patient in a hospital bed having at least
three load cells positioned about a periphery of the bed, each load
cell producing a signal corresponding to a distribution of patient
weight on that load cell, the method comprising the steps of: establishing
a plurality of sets of exit conditions about a periphery of the bed,
each of the plurality of sets of exit conditions defining threshold
values for each of the load cells, determining a current distribution
of patient weight on each of the load cells, and determining that
the patient is about to exit the bed if the current distribution of
weight on at least some of the load cells exceeds corresponding ones
of the threshold values of one of the sets of exit conditions.
2. The method of claim 1 further including the step of activating
an alarm local to the bed if the patient is about to exit the bed.
3. The method of claim 1 further including the step of activating
an alarm remote from the bed if the patient is about to exit the
bed.
4. The method of claim 1 wherein the step of establishing a plurality
of sets of exit conditions includes: placing an object having a
predefined calibration weight near one edge of the bed, measuring
a current distribution of the calibration weight on each of the
load cells, defining as one of the plurality of sets of exit conditions
a set of normalized threshold values corresponding to the current
distribution of the calibration weight on each of the load cells,
and moving the calibration weight about the periphery of the bed
and executing the measuring and defining steps at each discrete
placement of the calibration weight.
5. The method of claim 4 wherein the step of establishing a plurality
of sets of exit conditions further includes forming a data table
populated by the plurality of sets of exit conditions with each
of the plurality of sets of exit conditions defined by a corresponding
set of the normalized threshold values for each of the load cells.
6. The method of claim 4 wherein the step of determining that the
patient is about to exit the bed includes: determining from the
current distribution of patient weight on each of the load cells
a total patient weight on the bed, multiplying selected ones of
the normalized threshold values of one of the plurality of sets
of exit conditions by a ratio of the total patient weight and the
calibration weight to define computed threshold values, comparing
the current distribution of patient weight on the load cells that
correspond to the selected ones of the normalized threshold values
with corresponding ones of the computed threshold values, and deciding
that the patient is about to exit the bed if the current distribution
of weight on the load cells that correspond to the selected ones
of the normalized threshold values exceed the corresponding ones
of the computed threshold values.
7. The method of claim 6 wherein the step of determining that the
patient is about to exit the bed further includes: selecting a subset
of the plurality of sets of exit conditions; and executing the multiplying,
comparing and deciding steps for each set of exit conditions in
the subset of the plurality of sets of exit conditions.
8. The method of claim 6 wherein the step of determining a total
patient weight on the bed includes: determining a zero weight distribution
on each of the load cells when the bed is empty, determining a current
distribution of weight on each of the load cells when the patient
is supported by the bed, determining the current distribution of
patient weight on each of the load cells by subtracting the current
distribution of weight on each of the load cells when the patient
is supported by the bed from the zero weight distribution on each
of the load cells when the bed is empty, and computing the total
patient weight as a function of the current distribution of patient
weight on each of the load cells.
9. The method of claim 1 wherein the bed includes four load cells
each positioned near a different corner of the bed, and wherein
the plurality of sets of exit conditions includes a first plurality
of sets of exit conditions defined along a first side of the bed,
a second plurality of sets of exit conditions defined along a second
side of the bed opposite to the first side, a third plurality of
sets of exit conditions defined along a head end of the bed and
a fourth plurality of sets of exit conditions defined along a foot
end of the bed, and wherein the method further includes the steps
of: processing the current distribution of patient weight on some
the load cells to determine only one of the first and second plurality
of sets of exit conditions to monitor; and monitoring the one of
the first and second plurality of sets of exit conditions to determine
whether the patient is about to exit the bed.
10. The method of claim 9 wherein the processing step includes:
determining from the current distribution of patient weight on the
some of the load cells the one of the first and second sides of
the bed that patient exit is most likely to occur, and selecting
the one of the first and second plurality of sets of exit conditions
associated with the one of the first and second sides of the bed
that patient exit is more likely to occur.
11. The method of claim 9 wherein the step of determining that
the patient is about to exit the bed includes: comparing the current
distribution of patient weight on the load cells at the head and
foot ends of the one of the first and second sides that patient
exit is most likely to occur with corresponding ones of the threshold
values of each of the selected one of the first and second plurality
of sets of exit conditions, and deciding that the patient is about
to exit the bed if the current distribution of weight on the load
cells at the head and foot ends of the one of the first and second
sides that patient exit is most likely to occur exceed corresponding
head end and foot end threshold values of one of the selected one
of the first and second plurality of sets of exit conditions.
12. The method of claim 9 wherein the step of establishing a plurality
of sets of exit conditions includes: placing an object having a
predefined calibration weight near one edge of the bed, measuring
a current distribution of the calibration weight on each of the
load cells, defining as one of the plurality of sets of exit conditions
a set of normalized threshold values corresponding to the current
distribution of the calibration weight on each of the load cells,
and discretely moving the calibration weight about the periphery
of the bed and executing the measuring and defining steps at each
discrete placement of the calibration weight.
13. The method of claim 12 wherein the step of determining that
the patient is about to exit the bed includes: determining from
the current distribution of patient weight on each of the load cells
a total patient weight on the bed, for one of the selected one of
the first and second plurality of sets of exit conditions, multiplying
the normalized threshold values that correspond the head and foot
end load cells of the one of the first and second sides of the bed
that patient exit is most likely to occur by a ratio of the total
patient weight and the calibration weight to define computed head
and foot end threshold values, comparing the current distribution
of patient weight on the load cells at the head and foot ends of
the one of the first and second sides that patient exit is most
likely to occur with corresponding ones of the computed head and
foot end threshold values, deciding that the patient is about to
exit the bed if the current distribution of patient weight on the
load cells at the head and foot ends of the one of the first and
second sides that patient exit is most likely to occur exceed the
corresponding ones of the computed head and foot end threshold values,
and executing the multiplying, comparing and deciding steps for
remaining ones of the selected one of the first and second plurality
of sets of exit conditions.
14. The method of claim 9 wherein the step of determining that
the patient is about to exit the bed includes: comparing the current
distribution of patient weight on the load cells at the head and
foot ends of the one of the first and second sides of the bed that
patient exit is most likely to occur with corresponding head and
foot end threshold values of each of the selected one of the first
and second plurality of sets of exit conditions, of the selected
one of the first and second plurality of sets of exit conditions,
determining a first set of exit conditions where the current distribution
of patient weight on the load cell at the head end of the one of
the first and second sides of the bed that patient exit is most
likely to occur exceeds a corresponding head end threshold value,
of the selected one of the first and second plurality of sets of
exit conditions, determining a second set of exit conditions where
the current distribution of patient weight on the load cell at the
foot end of the one of the first and second sides of the bed that
patient exit is most likely to occur exceeds a corresponding foot
end threshold value, identifying a third set of exit conditions,
among the selected one of the first and second plurality of sets
of exit conditions, that is defined between the first and second
sets of exit conditions, and deciding that the patient is about
to exit the bed as a function of the current distribution of weight
on each of the load cells and of each of the third set of exit conditions.
15. The method of claim 14 wherein the deciding step includes:
computing a first difference between the distribution of patient
weight on the load cell at the head end of the one of the first
and second sides of the bed that patient exit is most likely to
occur and the distribution of patient weight on the load cell at
the head end of the other of the first and second sides of the bed,
computing a second difference between the head end threshold value
of the third set of exit conditions that corresponds to the load
cell at the head end of the one of the first and second sides of
the bed that patient exit is most likely to occur and the head end
threshold value of the third set of exit conditions that corresponds
to the load cell at the head end of the other of the first and second
sides of the bed, computing a third difference between the distribution
of patient weight on the load cell at the foot end of the one of
the first and second sides of the bed that patient exit is most
likely to occur and the distribution of patient weight on the load
cell at the foot end of the other of the first and second sides
of the bed, computing a fourth difference between the foot end threshold
value of the third set of exit conditions that corresponds to the
load cell at the foot end of the one of the first and second sides
of the bed that patient exit is most likely to occur and the foot
end threshold value of the third set of exit conditions that corresponds
to the load cell at the foot end of the other of the first and second
sides of the bed, and determining that the patient is about to exit
the bed if a sum of a difference between the first and second differences
and a difference between the third and fourth differences is greater
than zero.
16. The method of claim 15 further including: determining a fifth
difference between the head end threshold value of the third set
of exit conditions that corresponds to the load cell at the head
end of the one of the first and second sides of the bed that patient
exit is most likely to occur and the distribution of patient weight
on the load cell at the head end of the one of the first and second
sides of the bed that patient exit is most likely to occur, determining
a sixth difference between the distribution of patient weight on
the load cell at the foot end of the other of the first and second
sides of the bed that patient exit is most likely to occur and the
foot end threshold value of the third set of exit conditions that
corresponds to the load cell at the foot end of the other of the
first and second sides of the bed, computing an exit adjust value
as a ratio of the fifth and sixth differences, computing an exit
adjust clamp value as a function of the exit adjust value and one
or more of a total patient weight on the bed, a total weight on
the bed and a location of the third set of exit conditions relative
to the one of the first and second plurality of sets of exit conditions,
and multiplying the second and fourth differences by the exit adjust
clamp value prior to the step of determining that the patient is
about to exit the bed.
17. The method of claim 9 further includes the steps of: processing
the current distribution of patient weight on each of the load cells
to determine only one of the third and fourth plurality of sets
of exit conditions to monitor; and monitoring the one of the third
and fourth plurality of sets of exit conditions to determine whether
the patient is about to exit the bed.
18. The method of claim 17 wherein the processing step includes:
determining from the current distribution of patient weight on each
of the load cells the one of the head and foot ends of the bed that
patient exit is most likely to occur, and selecting the one of the
third and fourth plurality of sets of exit conditions associated
with the one of the head and foot ends that patient exit is more
likely to occur.
19. The method of claim 17 wherein the step of determining that
the patient is about to exit the bed includes: comparing the current
distribution of patient weight on the load cells at the one of the
head and foot ends of the bed that patient exit is most likely to
occur with corresponding ones of the threshold values of each of
the selected one of the third and fourth plurality of sets of exit
conditions, and deciding that the patient is about to exit the bed
if the current distribution of weight on the load cells at the one
of the head and foot ends of the bed that patient exit is most likely
to occur exceed corresponding threshold values of one of the selected
one of the third and fourth plurality of sets of exit conditions.
20. The method of claim 17 wherein the step of establishing a plurality
of sets of exit conditions includes: placing an object having a
predefined calibration weight near one edge of the bed, measuring
a current distribution of the calibration weight on each of the
load cells, defining as one of the plurality of sets of exit conditions
a set of normalized threshold values corresponding to the current
distribution of the calibration weight on each of the load cells,
and moving the calibration weight about the periphery of the bed
and executing the measuring and defining steps at each discrete
placement of the calibration weight.
21. The method of claim 20 wherein the step of determining that
the patient is about to exit the bed includes: determining from
the current distribution of patient weight on each of the load cells
a total patient weight on the bed, for one of the selected one of
the third and fourth plurality of sets of exit conditions, multiplying
the normalized threshold values that correspond the load cells on
either side of the one of the head and foot ends of the bed that
patient exit is most likely to occur by a ratio of the total patient
weight and the calibration weight to define computed first and second
side threshold values, comparing the current distribution of patient
weight on the load cells at the first and second sides of the one
of the head and foot ends of the bed that patient exit is most likely
to occur with corresponding ones of the computed first and second
side threshold values, deciding that the patient is about to exit
the bed if the current distribution of patient weight on the load
cells at the first and second sides of the one of the head and foot
ends of the bed that patient exit is most likely to occur exceed
the corresponding ones of the computed first and second side threshold
values, and executing the multiplying, comparing and deciding steps
for remaining ones of the selected one of the third and fourth plurality
of sets of exit conditions.
22. The method of claim 1 wherein the step of determining that
the patient is about to exit the bed if the current distribution
of weight on at least some of the load cells exceeds corresponding
ones of the threshold values of one of the sets of exit conditions
includes determining that the patient is about to exit the bed only
if the current distribution of weight on at least some of the load
cells exceeds corresponding ones of the threshold values of one
of the sets of exit conditions for a predefined time period.
23. The method of claim 1 wherein the threshold values of each
of the plurality of sets of exit conditions are threshold weight
values.
24. The method of claim 1 wherein the threshold values of each
of the plurality of sets of exit conditions are threshold weight
percentage values.
25. A system for monitoring a patient, comprising: a patient support
surface configured to support the patient, at least three load cells
each configured to produce a signal indicative of weight impressed
on that load cell via the patient support surface, and a controller
responsive to the signals produced by each of the at least three
load cells to determine a current distribution of patient weight
on each of the load cells, the controller determining that the patient
is about to exit the bed if the current distribution of weight on
at least some of the at least three load cells exceeds corresponding
threshold values comprising one of a plurality of sets of exit conditions.
26. The system of claim 25 further including a memory having stored
therein the plurality of sets of exit conditions defined about a
periphery of the patient support surface, each of the plurality
of sets of exit conditions defining threshold values for each of
the load cells.
27. The system of claim 25 wherein the patient support surface
is a hospital bed.
28. The system of claim 25 further including an alarm local to
the bed, the controller activating the alarm if the patient is about
to exit the bed.
29. The system of claim 25 further including an alarm remote from
the bed, the controller activating the alarm if the patient is about
to exit the bed.
30. A method of monitoring a patient in a hospital bed having at
least three load cells positioned about a periphery of the bed,
each load cell producing a signal corresponding to a distribution
of patient weight on that load cell, the method comprising the steps
of: establishing a first plurality of sets of excessive patient
movement conditions, each of the first plurality of sets of excessive
patient movement conditions defining first threshold values for
each of the at least three load cells, determining a total patient
weight on the bed, for each of the first plurality of sets of excessive
patient movement conditions, computing weight change values for
each of the at least three load cells according to a patient movement
model as a function of the total patient weight on the bed, and
determining that patient movement is excessive if at least some
of the weight change values exceed corresponding ones of the first
threshold values for at least one of the first plurality of sets
of excessive patient movement conditions.
31. The method of claim 30 wherein the step of computing weight
change values further includes computing weight change values for
each of the at least three load cells according to the patient movement
model further as a function of a patient movement sensitivity value.
32. The method of claim 30 further including the step of activating
an alarm remote from the bed if the patient movement is excessive.
33. The method of claim 30 wherein the first threshold values are
percentage weight values and the weight change values are percentage
weight change values.
34. The method of claim 30 wherein the bed includes four load cells
each positioned near a different corner of the bed, and wherein
the step of determining that patient movement is excessive includes
determining that patient movement is excessive if at least three
of the weight change values exceed corresponding ones of the first
threshold values for at least one of the first plurality of sets
of excessive patient movement conditions.
35. The method of claim 30 further including the steps of: establishing
a second plurality of sets of excessive patient movement conditions,
each of the second plurality of sets of excessive patient movement
conditions defining normalized threshold values for each of the
at least three load cells, determining a current distribution of
patient weight on each of the at least three load cells, for each
of the second plurality of sets of excessive patient movement conditions,
computing second threshold values for each of the at least three
load cells each as a function of a corresponding one of the normalized
threshold values and the total patient weight on the bed, and computing
weight differential values for each of the at least three load cells
as a function of the current distribution of patient weight on that
load cell and a reference weight for that load cell, and determining
that patient movement is excessive if at least some of the weight
differential values exceed corresponding ones of the second threshold
values for at least one of the second plurality of sets of excessive
patient movement conditions.
36. The method of claim 35 wherein the step of computing second
threshold values further includes computing the second threshold
values for each of the at least three load cells further as a function
of a patient movement sensitivity value.
37. The method of claim 35 wherein the second threshold values
are percentage weight values and the weight differential values
are percentage weight differential values.
38. The method of claim 35 wherein the bed includes four load cells
each positioned near a different corner of the bed, and wherein
the step of determining that patient movement is excessive includes
determining that patient movement is excessive if at least three
of the weight differential values exceed corresponding ones of the
second threshold values for at least one of the second plurality
of sets of excessive patient movement conditions.
39. The method of claim 35 wherein the bed includes four load cells
each positioned near a different corner of the bed, and wherein
the step of determining that patient movement is excessive includes
determining that patient movement is excessive if at least two of
the weight differential values exceed corresponding ones of the
second threshold values for at least one of the second plurality
of sets of excessive patient movement conditions.
40. The method of claim 35 further including the step of determining
that patient movement is excessive if at least one of the weight
differential values is less than a corresponding one of the second
threshold values while at least another of the weight differential
values exceeds a corresponding one of the second threshold values
for at least one of the second plurality of sets of excessive patient
movement conditions.
41. A system for monitoring a patient, comprising: a patient support
surface configured to support the patient, at least three load cells
each configured to produce a signal indicative of weight impressed
on that load cell via the patient support surface, and a controller
responsive to the signals produced by each of the at least three
load cells to determine a total patient weight on the patient support
surface, the controller computing weight change values for each
of the at least three load cells according to a patient movement
model as a function of the total patient weight on the bed for each
of a plurality of sets of excessive patient movement conditions,
the controller determining that patient movement is excessive if
at least some of the weight change values exceed corresponding ones
of the first threshold values for at least one of the plurality
of sets of excessive patient movement conditions.
42. The system of claim 41 further including a memory having stored
therein the plurality of sets of excessive patient movement conditions,
each of the plurality of sets of excessive patient movement conditions
defining threshold values for each of the load cells.
43. The system of claim 41 wherein the patient support surface
is a hospital bed.
44. The system of claim 41 further including an alarm remote from
the bed, the controller activating the alarm if the patient is about
to exit the bed.
45. A method of monitoring a patient in a hospital bed, the method
comprising the steps of: determining whether the patient is within
a safe arming zone of the hospital bed, and enabling monitoring
of the patient in the hospital bed only if the patient is within
the safe arming zone.
46. The method of claim 45 wherein the hospital bed has at least
three load cells positioned about a periphery of the bed, each load
cell producing a signal corresponding to a distribution of patient
weight on that load cell, and wherein the determining step includes:
determining a current distribution of patient weight on each of
the load cells, and determining that the patient is not within the
safe arming zone of the hospital bed if the current distribution
of patient weight on each the load cells exceed corresponding load
cell threshold values of one of a plurality of sets of arming conditions
defined about a periphery of the bed.
47. The method of claim 46 wherein the method of monitoring a patient
includes a patient exit mode configured to determine whether the
patient is about to exit the hospital bed, and wherein the enabling
step includes enabling activation of the patient exit mode only
if the patient is within the safe arming zone.
48. The method of claim 47 wherein the patient exit mode includes:
establishing a plurality of sets of exit conditions about a periphery
of the bed, each of the plurality of sets of exit conditions defining
threshold values for each of the load cells, determining a current
distribution of patient weight on each of the load cells, and determining
that the patient is about to exit the bed if the current distribution
of weight on at least some of the load cells exceeds corresponding
ones of the threshold values of one of the sets of exit conditions.
49. The method of claim 48 further including determining the one
of a plurality of sets of arming conditions by scaling a corresponding
one of the plurality of sets of exit conditions by a first predefined
scaling factor.
50. The method of claim 48 wherein the method of monitoring a patient
includes a patient movement mode configured to determine whether
the patient movement relative to a reference distribution of weight
on the load cells is excessive, and wherein the enabling step includes
enabling activation of the patient movement mode only if the patient
is within the safe arming zone.
51. The method of claim 50 wherein the patient movement mode includes:
establishing a first plurality of sets of excessive patient movement
conditions, each of the first plurality of sets of excessive patient
movement conditions defining first threshold values for each of
the at least three load cells, determining a total patient weight
on the bed, for each of the first plurality of sets of excessive
patient movement conditions, computing weight change values for
each of the at least three load cells according to a patient movement
model as a function of the total patient weight on the bed, and
determining that patient movement is excessive if at least some
of the weight change values exceed corresponding ones of the first
threshold values for at least one of the first plurality of sets
of excessive patient movement conditions.
52. The method of claim 51 further including determining the one
of a plurality of sets of arming conditions by scaling a corresponding
one of the plurality of sets of exit conditions by a second predefined
scaling factor.
53. The method of claim 45 wherein the method of monitoring a patient
includes a patient exit mode configured to determine whether the
patient is about to exit the hospital bed, and wherein the enabling
step includes enabling activation of the patient exit mode only
if the patient is within the safe arming zone.
54. The method of claim 45 wherein the method of monitoring a patient
includes a patient movement mode configured to determine whether
the patient movement relative to a reference distribution of weight
on the load cells is excessive, and wherein the enabling step includes
enabling activation of the patient movement mode only if the patient
is within the safe arming zone.
55. The method of claim 45 further including determining a total
patient weight on the bed, and wherein the enabling step is further
conditioned upon the total patient weight being less than a maximum
total patient weight.
56. The method of claim 45 further including determining a total
patient weight on the bed, and wherein the enabling step is further
conditioned upon the total patient weight being greater than a minimum
total patient weight.
57. The method of claim 56 wherein the enabling step is further
conditioned upon the total patient weight being less than a maximum
total patient weight.
58. A method of monitoring a patient in a hospital bed having a
head section that may be controllably elevated, the method comprising
the steps of: determining a total patient weight on the bed, and
enabling monitoring of the patient in the hospital bed if the total
patient weight is greater than about 50 pounds and the head section
of the bed is elevated in excess of 45 degrees relative to bed flat.
59. The method of claim 58 wherein the head section of the hospital
bed may be controllably elevated to a maximum head angle of at least
about 65 degrees relative to bed flat, and wherein the enabling
step includes enabling monitoring of the patient in the hospital
bed if the total patient weight is greater than about 50 pounds
and the head section is elevated anywhere between bed flat and the
maximum head angle.
61. The method of claim 58 further including the step of determining
whether the patient is within a safe arming zone of the hospital
bed, and wherein the enabling step is further conditioned upon the
patient being within the safe arming zone of the hospital bed.
62. A method of monitoring a patient in a hospital bed according
to a patient movement mode configured to determine whether patient
movement relative to a reference distribution of weight on the bed
is excessive, the bed having a head section that may be controllably
elevated to a maximum head angle of at least about 65 degrees relative
to bed flat, the method comprising the steps of: enabling monitoring
of the patient according to the patient movement mode regardless
of elevation of the head section of the bed relative to bed flat,
and continuing to monitor the patient according to the patient movement
mode without activating an alarm if the head section is articulated
to an elevation, between the maximum head angle and bed flat, that
is different than the elevation of the head section when the patient
movement mode was enabled.
63. The method of claim 62 further including determining a total
patient weight on the bed, and wherein the enabling step is conditioned
upon the total patient weight being greater than a minimum total
patient weight.
64. The method of claim 62 further including determining a total
patient weight on the bed, and wherein the enabling step is conditioned
upon the total patient weight being less than a maximum total patient
weight.
65. The method of claim 62 further including determining whether
the patient is within a safe arming zone of the bed, and wherein
the enabling step is conditioned upon the patient being within the
safe arming zone of the bed.
66. The method of claim 62 further including: determining a total
patient weight on the bed, and determining whether the patient is
within a safe arming zone of the bed, and wherein the enabling step
is conditioned upon the total patient weight being greater than
a minimum total patient weight, on the total patient weight being
less than a maximum total patient weight and on the patient being
within the safe arming zone of the bed.
67. The method of claim 62 wherein the continuing step is conditioned
upon articulating the head section via a control panel mounted to
the bed.
68. The method of claim 62 further including the step of activating
an alarm if the head section is articulated to the elevation that
is between the maximum head angle and bed flat via a patient control
pendant.
69. A method of monitoring a patient in a hospital bed according
to a patient movement mode configured to determine whether patient
movement relative to a reference distribution of weight on the bed
is excessive, the method comprising the steps of: enabling monitoring
of the patient according to the patient movement mode, and continuing
to monitor the patient according to the patient movement mode without
activating an alarm after further weight, less than a maximum further
weight, is added to the bed regardless of total patient weight on
the bed prior to adding the further weight.
70. The method of claim 69 further including determining the total
patient weight on the bed, and wherein the enabling step is conditioned
upon the total patient weight being greater than a minimum total
patient weight.
71. The method of claim 69 further including determining the total
patient weight on the bed, and wherein the enabling step is conditioned
upon the total patient weight being less than a maximum total patient
weight.
72. The method of claim 69 further including determining whether
the patient is within a safe arming zone of the bed, and wherein
the enabling step is conditioned upon the patient being within the
safe arming zone of the bed.
73. The method of claim 69 further including: determining the total
patient weight on the bed, and determining whether the patient is
within a safe arming zone of the bed, and wherein the enabling step
is conditioned upon the total patient weight being greater than
a minimum total patient weight, on the total patient weight being
less than a maximum total patient weight and on the patient being
within the safe arming zone of the bed.
74. The method of claim 69 wherein the maximum further weight is
about 30 pounds.
75. A method of monitoring a patient in a hospital bed according
to a patient exit mode configured to determine whether the patient
is about to exit the bed, the method comprising the steps of: determining
a bed zero weight without the patient supported by the bed, determining
a total patient weight on the bed as a function of the bed zero
weight when the patient is supported by the bed, enabling monitoring
of the patient in the bed according to the patient exit mode, and
continuing to monitor the patient according to the patient exit
mode without activating an alarm after further weight, less than
a maximum further weight, is added to the bed after determining
the bed zero weight.
76. The method of claim 75 wherein the maximum further weight is
about 30 pounds.
77. The method of claim 75 wherein the bed includes a head end
and a foot end, and wherein the further weight is added to one of
the head and foot ends.
78. The method of claim 75 wherein the enabling step is conditioned
upon the total patient weight being greater than a minimum total
patient weight.
79. The method of claim 75 wherein the enabling step is conditioned
upon the total patient weight being less than a maximum total patient
weight.
80. The method of claim 75 further including determining whether
the patient is within a safe arming zone of the bed, and wherein
the enabling step is conditioned upon the patient being within the
safe arming zone of the bed.
81. The method of claim 75 further including determining whether
the patient is within a safe arming zone of the bed, and wherein
the enabling step is conditioned upon the total patient weight being
greater than a minimum total patient weight, on the total patient
weight being less than a maximum total patient weight and on the
patient being within the safe arming zone of the bed.
82. A system for controlling air pressure in a number of different
zones of an air mattress supporting an occupant, comprising: a plurality
of load cells each configured to produce a signal indicative of
weight impressed upon that load cell via the air mattress, and a
controller responsive to the signals produced by the plurality of
load cells to determine a current distribution of occupant weight
on each of the load cells, the controller controlling air pressure
within any one or more of the number of different zones of the air
mattress based on the current distribution of occupant weight on
at least some of the plurality of load cells.
Description
CROSS-REFERENCE TO RELATED U.S. PATENT APPLICATIONS
[0001] This patent application claims priority to and the benefit
of U.S. Provisional Patent Application Ser. No. 60/599,558, filed
Aug. 9, 2004, and U.S. Provisional Patent Application Ser. No. 60/615,031,
filed Oct. 1, 2004, the disclosures of which are each incorporated
herein by reference.
FIELD OF THE INVENTION
[0002] This invention relates generally to systems for monitoring
and detecting movement of a mass on a platform, and more specifically
to methods and systems for detecting patient movement on, exit from,
or impending exit from a patient support system such as a hospital
bed.
BACKGROUND
[0003] When a patient is required to stay in a hospital bed at
a hospital or other patient care facility, it is desirable for a
caregiver to be able to monitor the presence, absence, and movement
of the patient on the bed platform, generally a mattress, and to
monitor the patient's activity level. Caregivers are generally responsible
for a number of patient-related activities, examples of which include
monitoring the presence or absence of patients on their hospital
beds and/or monitoring patient movement relative to their hospital
beds.
[0004] One system for monitoring patient movement on a hospital
bed is disclosed by U.S. Pat. No. 5,276,432, issued Jan. 4, 1994,
to Travis. The disclosed system calculates the center of gravity
of a patient within a two-dimensional Cartesian coordinate-based
region defined relative to the patient-supporting surface of the
bed mattress. The center of gravity of the patient relative to the
region is determined using data from load cells coupled to the hospital
bed frame. Patient movement relative to the region is detected by
monitoring movement of the center of gravity of the patient, and
by determining the location of the patient's center of gravity relative
to the region.
[0005] Alternative methods and systems for monitoring patient movement
on, exit from and/or impending exit from, a hospital bed are desirable.
SUMMARY
[0006] The present invention may comprise one or more of the features
recited in the appended claims and/or one or more of the following
features or combinations thereof. A system for monitoring a patient
on a patient support, such as a hospital bed or stretcher having
a support surface, may comprise a plurality of load cells positioned
to weigh the support surface and the patient supported thereon.
In one exemplary embodiment, four such load cells may be mounted
at or near each of the four corners of the support, one at each
right and left side at or near the head of the support and one at
each right and left side at or near the foot of the support. Output
signals of the load cells, which may typically be voltage or current
level outputs, may be digitized for processing by a control system
computer.
[0007] Various algorithms may utilize various combinations of the
load cell output signals to determine the weight of the patient
on the support surface, exit of the patient from the support surface,
impending exit of the patient from the support surface and/or movement
of the patient relative to reference load cell distribution values.
[0008] One such algorithm, for example, may be configured to determine
when the patient is in process of exiting the support surface. When,
for example, the sum of output signals of all four cells is substantially
less than, e.g., by 30 pounds to 60 pounds, the established weight
of the patient, this may be indicative that the patient has transferred
at least some of the patient's total weight off the support surface
onto some other support surface or structure that supports the missing
weight.
[0009] Another algorithm, for example, may determine when a patient's
movement on the support surface exceeds any of a number of predetermined
load cell thresholds. A collection of weight distribution threshold
percentages for each of the four cells RH, LH, RF and LF is stored
in memory and continually compared against the current load cell
values after arming of the system. When the distribution of weight
among two or three of the four cells changes by more than one of
the corresponding stored collection of weight distribution threshold
percentages as a result of excessive patient movement subsequent
to the system being armed, an alarm is triggered.
[0010] Yet another algorithm, for example, will determine when
a patient is about to exit the support surface. A collection of
load cells thresholds for each of the four cells RH, LH, RF and
LF is stored in memory, and the current load cell values are compared
to selected portions of the load cell threshold collection. When
the measured distribution of weight among the four cells RH, LH,
RF and LF exceeds a set of load cell thresholds forming the collection
of load cell thresholds as a result of impending patient exit from
the support surface, an alarm is triggered.
[0011] The above briefly described algorithms of the system do
not determine the center of gravity of a patient. Nor do the algorithms
determine the actual position of a patient relative to a reference
position. Nor do the algorithms require a measured length or width
of the support surface. Nor do the algorithms determine or use any
information relating to the physical locations of the various load
cells relative to a reference position, or any information relating
to distances between such load cells. The actual locations of the
various load cells are arbitrary, and the locations of the load
cells shown in the illustrated embodiments are provided only by
way of example. The locations of the load cells may therefore be
different for different applications.
[0012] The briefly described algorithms monitor the distribution
of patient weight supported by each of the four cells RH, LH, RF
and LF, and compare the resulting load cell weights to empirically
determined and/or model-based collections of load cell threshold
data. Changes in patient weight distribution among two, three or
four of the load cells relative to the one or more collections of
load cell threshold data are then used in a decision process to
detect excessive patient movement and/or impending exit from, and/or
exit from, the support surface. The algorithms accomplish this without
reference to a patient center of gravity, an actual patient position
relative to a reference position or a coordinate axis, actual locations
of one or more of the load cells relative to a reference position
or distance between any such load cells.
[0013] These and other features of the present invention will become
more apparent from the following description of the illustrated
embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1A is a perspective view of a hospital bed including
an exemplary embodiment of a system for monitoring patient movement
on, exit from, and impending exit from, the bed.
[0015] FIG. 1B is a block diagram illustrating exemplary locations
of a number of load cells relative to the bed of FIG. 1A.
[0016] FIG. 1C is a perspective view illustrating the hospital
bed of FIG. 1A with the foot end of the bed shown in an extended
position.
[0017] FIG. 2 is a perspective view of one of the siderails of
the bed shown in FIG. 1A having a control and display panel mounted
thereto.
[0018] FIG. 3 is a partial cutaway view of the circled portion
3 of FIG. 1A illustrating control circuitry and one of the load
cells carried by the bed.
[0019] FIG. 4 is a block diagram of one exemplary embodiment of
a monitoring system for monitoring patient movement on, exit from,
and impending exit from, the bed illustrated in FIGS. 1A-3.
[0020] FIG. 5 is a combined flowchart and state diagram illustrating
one exemplary embodiment of a software algorithm for monitoring
patient movement on, exit from, and impending exit from, the bed
illustrated in FIGS. 1A-3.
[0021] FIG. 6 is a flowchart illustrating an exemplary embodiment
of the state machine preparation routine forming part of the algorithm
of FIG. 5.
[0022] FIGS. 7A-7C show a flowchart illustrating an exemplary embodiment
of a software routine for executing the PM Off State that forms
part of the state machine of FIG. 5.
[0023] FIG. 8 is a flowchart illustrating an exemplary embodiment
of a software routine for executing the PM Zero State that forms
part of the state machine of FIG. 5.
[0024] FIG. 9 is a flowchart illustrating an exemplary embodiment
of the zero capture software routine called by the PM Zero State
routine of FIG. 8.
[0025] FIGS. 10A-10B show a flowchart illustrating an exemplary
embodiment of a software routine for executing the PM Movement/Exit
Transition State that forms part of the state machine of FIG. 5.
[0026] FIGS. 11A-11C show a flowchart illustrating an exemplary
embodiment of a software routine for executing the PM Active State
that forms part of the state machine of FIG. 5.
[0027] FIG. 12 is a flowchart illustrating an exemplary embodiment
of a software routine for executing the PM Active State that forms
part of the state machine of FIG. 5.
[0028] FIG. 13 is a block diagram illustrating one example construction
of an exit condition threshold table for use by a patent exit routine
called by the PM Active STATE software routine of FIGS. 11A-11C.
[0029] FIGS. 14A-14C show a flowchart illustrating an exemplary
embodiment of the exit mode routine called by the PM Active State
software routine of FIGS. 11A-11C.
[0030] FIG. 15 is a diagram illustrating a mathematical model of
vertical movement of a patient in the hospital bed of FIGS. 1A-1C.
[0031] FIG. 16 is a diagram illustrated a mathematical model of
horizontal movement of a patient in the hospital bed of FIGS. 1A-1C.
[0032] FIG. 17 is a block diagram illustrating one example construction
of a movement condition threshold table for use by a patent movement
routine called by the PM Active STATE software routine of FIGS.
11A-11C.
[0033] FIG. 18 is a flowchart illustrating an exemplary embodiment
of the movement mode routine called by the PM Active State software
routine of FIGS. 11A-11C.
[0034] FIG. 19 is a flowchart illustrating an exemplary embodiment
of the out-of-bed mode routine called by the PM Active State software
routine of FIGS. 11A-11C.
DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS
[0035] For the purposes of promoting an understanding of the principles
of the invention, reference will now be made to one or more illustrative
embodiments shown in the drawings and specific language will be
used to describe the same. It will nevertheless be understood that
no limitation of the scope of the invention is thereby intended.
[0036] Referring now to FIGS. 1A-1C, one illustrative embodiment
of a hospital bed 50 is shown. The bed 50 is implemented in the
context of a hospital bed and patient monitoring apparatus generally
of the type described in U.S. Pat. No. 6,208,250, issued Mar. 27,
2001, and entitled Patient Position Detection Apparatus for a Bed,
which is assigned to the assignee of the present invention, and
the disclosure of which is incorporated herein by reference. In
the exemplary embodiment shown and described herein, the hospital
bed 50 may illustratively be a VersaCare.RTM. hospital bed, which
is commercially available from Hill-Rom Company, Inc. of Batesville,
Ind. It will be appreciated, however, that this implementation and
the illustrated embodiment is provided only by way of example, and
that the concepts illustrated and described herein are applicable
to other patient support systems, including for example, but not
limited to, stretchers, wheelchairs, or other patient-supporting
apparatus. Any such other systems utilizing the concepts illustrated
and described herein are contemplated by this disclosure.
[0037] The exemplary hospital bed 50 includes a stationary base
54 coupled to a weigh frame 56 that is mounted via frame members
57a and 57b to an adjustably positionable mattress support frame
or deck 58 configured to support a conventional foam mattress 60.
The mattress 60 defines a patient support surface 65 bounded by
a head end 60a positioned adjacent to a headboard 62 mounted to
the mattress support frame 58 at a head end 62 of the bed 50, a
foot end 60b positioned adjacent to a footboard 64b mounted to the
mattress support frame 58 at a foot end 64 of the bed 50, a left
side 60c and a right side 60d. A pair of siderails 66a and 66c are
mounted to the mattress support frame 58 adjacent to one side 60c
of the mattress 60, and another pair of siderails 66b and 66d are
mounted to the mattress support frame 58 adjacent to the opposite
side 60d of the mattress 60. The siderail 66a supports a patient
monitoring control panel 70, and the siderail 66b supports a mattress
position control panel 70. The bed 50 is generally configured to
adjustably position the mattress support 58 relative to the base
54.
[0038] Conventional structures and devices may be provided to adjustably
position the mattress support 58, and such conventional structures
and devices may include, for example, linkages, drives, and other
movement members and devices coupled between base 54 and the weigh
frame 56, and/or between weigh frame 56 and mattress support frame
58. Control of the position of the mattress support frame 58 and
mattress 60 relative to the base 54 or weigh frame 56 is provided,
for example, by a patient control pendant (not shown), a mattress
position control panel 69, and/or a number of mattress positioning
pedals 55. The mattress support frame 58 may, for example, be adjustably
positioned in a general incline from the head end 62 to the foot
end 64 or vice versa. Additionally, the mattress support 58 may
be adjustably positioned such that the head end 60a of the mattress
60 is positioned between minimum and maximum incline angles, e.g.,
0-65 degrees, relative to horizontal or bed flat, and the mattress
support 58 may also be adjustably positioned such that the thigh
area 60f of the mattress 60 is positioned between minimum and maximum
bend angles, e.g., 0-35 degrees, relative to horizontal or bed flat.
Those skilled in the art will recognize that the mattress support
frame 58 or portions thereof may be adjustably positioned in other
orientations, and such other orientations are contemplated by this
disclosure.
[0039] A number of load cells are positioned between the weigh
frame 56 and the base 54, wherein each load cell is configured to
produce a voltage or current signal indicative of a weight impressed
on that load cell from the weigh frame 56 relative to the base 54.
In the illustrated embodiment, four such load cells are positioned
between the weigh frame 56 and the base 54; one each near a different
corner of the bed 50. Two such load cells 68a and 68c are shown
in FIG. 1A, and all four are shown in FIG. 1B. Some of the structural
components of the bed 50 will be designated hereinafter as "right",
"left", "head" and "foot" from the
reference point of an individual lying on the individual's back
on the support surface 65 of the mattress with the individual's
head oriented toward the head end 62 of the bed 50 and the individual's
feet oriented toward the foot end 64 of the bed 50. For example,
the weigh frame 56 illustrated in FIG. 1B includes a head end frame
member 56c mounted at one end to one end of a right side weigh frame
member 56a and at an opposite end to one end of a left side frame
member 56b. Opposite ends of the right side weigh frame member 56a
and the left side weigh frame member 56b are mounted to a foot end
frame member 56d. A middle weigh frame member 56e is mounted at
opposite ends to the right and left side weigh frame members 56a
and 56b respectively between the head end and foot end frame members
56c and 56d. The frame member 57a is shown mounted between the right
side frame member 56a and the mattress support frame 58, and the
frame member 57b is shown mounted between the left side frame member
56b and the mattress support frame 58. It will be understood that
other structural support is provided between the weigh frame member
56 and the mattress support frame 58, although only the frame members
57a and 57b are shown in FIGS. 1A-1C for ease of illustration.
[0040] A right head load cell (RHLC) 68a is illustratively positioned
near the right head end of the bed 50 between a base support frame
54a secured to the base 54 near the head end 62 of the bed and the
junction of the head end frame member 56c and the right side frame
member 56a, as shown in the block diagram of FIG. 1B. A left head
load cell (LHLC) 68b is illustratively positioned near the left
head end of the bed 50 between the base support frame 54a and the
junction of the head end frame member 56c and the left side frame
member 56b, as illustrated in FIGS. 1A-1C and 3. A right foot load
cell (RFLC) 68c is illustratively positioned near the right foot
end of the bed 50 between a base support frame 54b secured to the
base 54 near the foot end 64 of the bed 50 and the junction of the
foot end frame member 56d and the right side frame member 56a, as
shown in the block diagram of FIG. 1B. A left foot load cell (LFLC)
68d is illustratively positioned near the left foot end of the bed
50 between the base support frame 54b and the junction of the foot
end frame member 56d and the left side frame member 56b, as illustrated
in FIGS. 1A-1C. It should be noted that in FIGS. 1A and 1C, the
base support frame 54b coupled to the left foot load cell 68d is
not shown so that the exemplary position of the load cell 68d relative
to the weigh frame 56, and to the bed 50 generally, can be seen.
In the exemplary embodiment illustrated in FIG. 1B, the four corners
of the mattress support frame 58 are shown extending beyond the
four corners of the weigh frame 56, and hence beyond the positions
of the four load cells 68a-68d.
[0041] In the illustrated embodiment, each of the load cells 68a-d
are weight sensors of the type having resistive strain gauges coupled
to a deflectable block (not shown), and structurally couple the
weigh frame 56 to the base 54. It will be appreciated, however,
that other weight detection devices may alternatively be used, wherein
such alternative devices may be or include, but are not limited
to, linear variable displacement transducers (LVDTS) and/or other
weight detection devices operable in accordance with known capacitive,
inductive, or other physical principles. In any case, all such alternative
weight detection devices are contemplated by this disclosure.
[0042] As shown in FIG. 1C, one exemplary embodiment of the hospital
bed 50 includes a foot end 64 that may be moved between a retracted
position, as shown in FIG. 1A, and an extended position, as shown
in FIG. 1C. The extended position of foot end 64 may be used, for
example, to accommodate varying patient sizes and/or to provide
a support surface between the foot end 60b of the mattress 60 and
the footboard 64b to accommodate placement thereon of medical or
other equipment.
[0043] Referring to FIG. 2, details of one exemplary control panel
70 mounted to the siderail 66a of the bed 50 of FIGS. 1A-1C is shown.
The control panel 70 includes various user-interface components
including, for example, a zero select switch 72, an enable or key
switch 74, a volume control switch 76, a volume strength indicator
78, a movement mode switch 80, an exit mode switch 82 and an out-of-bed
mode switch 84. The zero select switch 72 may be actuated to calibrate
an empty bed weight; i.e., with out a patient on the mattress 60,
and the enable or key switch 74 is used to enable various patient
monitoring functions as will be described in greater detail hereinafter.
The volume control switch 76 may be actuated to control the volume
of a local alarm; i.e., an audible, visual and/or other alarm (not
shown) mounted to or near the bed 50, and the volume strength indicator
78 may, for example, include a number, e.g., 3, of visual indicators,
e.g., LED's, that are selectively activated to indicate a volume
level of the local alarm. The mode switches 80-84 may be individually
actuated to select between various patient monitoring modes. For
example, actuation of the movement mode switch 80 selects a patient
movement monitoring mode that monitors certain patient movement
within the bed 50. Actuation of the exit mode switch 82 selects
a patient exit, which may also be referred to as a bed exit, monitoring
mode that monitors impending exit of the patient from the bed 50,
and actuation of the out-of-bed mode switch 84 selects an out-of-bed
(OOB) monitoring mode that monitors when at least a portion of the
patient's weight is not supported by the weigh frame 56, thereby
indicating that the patient is exiting, or has exited, the bed 50.
Further details relating to the operation of each of these patient
monitoring modes will be described in greater detail hereinafter.
The control panel 70 illustrated in FIG. 2 includes additional switches
and other components that provide for monitoring and control of
other features of the bed 50.
[0044] Referring now to FIG. 3, the right side frame member 56a
of the weigh frame 56 includes a housing mounted thereto adjacent
to the base support frame 54a. The housing is configured to carry
a processor module 86 and a logic module 96 electrically coupled
thereto. In the exemplary embodiment, the processor module 86 forms
part of a patient monitoring control system and includes a number
of executable software algorithms for controlling operation of the
system, and one illustrative embodiment of such a patient monitoring
system 75 is shown in FIG. 4. The patient monitoring system 75 includes
the processor module 86 electrically coupled to the logic module
96, the load cells 68a-68d, the control panel 70, a local alarm
98 (mounted to or near the bed 50) and a remote alarm 99. The remote
alarm 99 is located near a caregiver or other patient monitoring
individual, and is controlled by the processor module 86 to alert
the remote caregiver or other patient monitoring individual via
an audible and/or visual or other alarm (not shown) of certain patient
movement activities as will be described in greater detail hereinafter.
[0045] The processor module 86 includes a microprocessor-based
controller 88 having a Flash memory unit 90 and a local RAM memory
unit 92. The module 86 further includes an auxiliary memory unit
94, which may be an EEPROM or other conventional memory unit that
is electrically connected to the controller 88. The logic module
96 and load cells 68a-68d are electrically connected to the controller
88, and in the exemplary embodiment the logic module 96 is configured
to continually determine a height of the bed 50 via one or more
conventional sensors and to supply the bed height information to
the controller 88. Alternatively, the controller 88 may be operable
to determine the height of the bed 50 via any one or more conventional
techniques. In any case, the controller 88 is also electrically
connected to the local alarm 98 and to the remote alarm 99, and
the controller 88 is configured to control operation of such alarms
98 and 99 in a conventional manner. The control panel 70 is also
electrically connected to the controller 88 to communicate information
from the various switches and other input devices 72-76 and 80-84
from the control panel 70 to the controller 88, and to communicate
information from the controller 88 to the volume strength indicator
78.
[0046] In the illustrated embodiment, the Flash memory 90 of the
processor module 86 includes a number of software algorithms and
other data that are executable by the controller 88 to monitor patient
movement relative to a reference load cell distribution, impending
exit from the mattress 60 and/or exit from the mattress 60. An exemplary
main software algorithm 100 for managing such functions is illustrated
in FIG. 5 in the form of a combined flowchart and state machine
120. The software algorithm 100 is executed periodically by the
controller 88, e.g., once every 200 ms, to monitor patient movement
relative to a reference load cell distribution, impending exit from
the mattress 60 and/or exit from the mattress 60. Referring to FIG.
5, the software algorithm 100 begins at step 102 where the controller
88 is operable to determine whether an invalid bed zero warning
is active upon power up, wherein an invalid bed zero warning indicates
that the zero reference weight of the bed 50, e.g., the total weight
impressed upon the weigh frame 56 without a patient supported by
the mattress 60, may not be current or accurate. If, at step 102,
the controller 88 determines that an invalid bed zero warning is
active upon power up, algorithm execution advances to a Freeze State
126 of the state machine 120. The controller 88 is operable in the
Freeze State 126 to wait until a bed weight zeroing process is activated
as will be described below. If, at step 102, the controller 88 instead
determines that an invalid bed zero warning is not active upon power
up, execution of the algorithm 100 advances to step 104 where the
controller 88 is operable to determine whether the patient monitoring
system 75 was armed, i.e., whether one of the patient monitoring
modes was active, before the last power down of the system 75. The
system 75 is operable to save the current data to the memory unit
94 at power down, and to recall such data from the memory unit 94
upon subsequent power up so that the controller 88 may make the
determination illustrated in step 104.
[0047] The patient monitoring modes include a patient movement
(PM) mode wherein the system 75 is operable to monitor movement
of a patient on the mattress 60 by monitoring weight distribution
among two or three of the four load cells 68a-68b relative to a
predefined set of PM load cell threshold data, a patient exit (PE)
mode wherein the system 75 is operable to monitor impending exit
from the mattress 60 by monitoring weight distribution of the four
load cells relative to a predefined set of PE load cell threshold
data, and a patient out-of-bed (OOB) mode wherein the system 75
is operable to monitor exit of the patient from the mattress 60
by monitoring the patient weight distributed over the four load
cells relative to an armed patient weight, wherein the armed weight
corresponds to the patient weight distributed over the four load
cells when the patient monitoring mode was armed as will be described
in greater detail hereinafter. In any case, if the controller 88
determines at step 104 that the system 75 was not armed before the
last system power down, execution of the algorithm 100 advances
to step 110 where the controller 88 is operable to execute a state
machine preparation routine. If, at step 104, the controller 88
instead determines that the system 75 was armed before the last
system power down, execution of the algorithm 100 advances to an
Arming From Power Up Transition State 138 of the state machine 120
where the patient weight is processed to determine whether it is
contained within a defined armed range prior to advancing to the
PM Active State 130 of the state machine 120 to resume operation
of the patient monitoring mode that was active at the last system
power down.
[0048] After executing the state machine preparation routine at
step 110, execution of the algorithm 100 advances to the state machine
120. In the first execution of the algorithm 100, the state machine
120 is started at the PM Off State 122. In further executions of
the algorithm 100, the state machine 120 will be entered from step
110 at its current operational state. In addition to the operating
and transition states just described, the state machine 120 further
includes a PM Movement/Exit Transition State 128 that is selected
for operation following the PM Off State 122 when either a request
for Patient Monitoring (PM) Mode or Patient Exit (PE) Mode is received
via the control panel switch 80 or 82 respectively. From the PM
Movement/Exit Transition State 128, the state machine 120 advances
to the PM active state 130 where the controller 88 is operable to
actively monitor patient activity pursuant to the PM mode or PE
mode respectively. The state machine 120 also includes a PM OOB
Transition State 132, that is similar to the PM Movement/Exit Transition
State 128 and that is selected for operation following the PM Off
State 122 when a request for out-of-bed (OOB) mode is received via
the control panel switch 84. From the PM OOB Transition State 132,
the state machine 120 advances to the PM active state 130 where
the controller 88 is operable to actively monitor patient activity
pursuant to the OOB mode.
[0049] From either of the PM Movement/Exit Transition state 128
or the PM OOB Transition State 132, the state machine 120 advances
to a PM Failed Arming State 134 if either of the transition states
128 or 132 failed the arming function; i.e., failed to arm the system
75 by determining a total patient weight. From the PM Failed Arming
state 134, the state machine 120 advances back to the PM Off State
where the patient may be repositioned relative to the mattress 60,
followed by selection of the PM, PE or OOB mode.
[0050] From either of the PM Active state 130 or the Arming from
Power Up State 138, the state machine 120 advances to a PM Alarm
State 136 if any alarm conditions are met in the PM Active State
130 or the patient weight arming conditions are not met in the Arming
from Power Up State 138. From the PM Alarm State 136, the state
machine 120 advances to the PM Off State 122 where the alarm condition
may be remedied and/or the patient may be repositioned relative
to the mattress 60 before re-selecting the PM or PE mode. The state
machine 120 further includes a PM Zero State 124 that is selected
to compute a new zero weight bed reference upon actuation of a predefined
combination of the switches forming part of the control panel 70
as will be described below.
[0051] Referring now to FIG. 6, a flowchart is shown of one illustrative
embodiment of the state machine preparation routine called by step
112 of the algorithm 100 of FIG. 5. In the illustrated embodiment,
the state machine preparation routine begins at step 150 where the
controller 88 is operable to acquire new load cell data, LCD, by
sampling the signals produced by the load cells 68a-68d. Thereafter
at step 152, the controller 88 is operable to correct the load cell
data, LCD, as a function of the current bed height. In the illustrated
embodiment, the various structures and mechanisms used to raise
and lower the height of the mattress support frame 58 relative to
the base 54 to cause the weights measured by the load cells 68a-68d
to vary as a function of bed height. In this embodiment, the logic
module 96 is coupled to one or more sensors from which the logic
module is operable to determine bed height in a known manner, and
the logic module 96 supplies the bed height information to the process
module 86. Alternatively, the controller 88 may be operable to determine
the height of the bed 50 via any one or more conventional techniques.
In any case, the memory unit 90 illustratively includes a bed height
conversion function in the form of a lookup table or other conversion
function mapping the bed height information to load cell signal
correction information. In one embodiment, for example, the lookup
table maps discrete bed height values to corresponding offset values,
and the offset value corresponding to the current bed height is
then used to correct the load cell data, LCD, by adding the offset
value to the values produced by two diagonally opposed pairs of
the load cells 68a-68d, and subtracting the offset value from the
values produced by the remaining two diagonally opposed pairs of
the load cells 68a-68d. Those skilled in the art will recognize
other techniques for correcting the signals or values produced by
the load cells 68a-68d as a function of bed height, and such other
techniques are intended to fall within the scope of claims appended
hereto.
[0052] Following step 152, the controller 88 is operable at step
154 of the state machine preparation routine to convert the corrected
load cell data signals to load cell weight values. Hereinafter,
the term "RH" may be used to identify the bed height-corrected
weight value produced by the right head load cell 68a, the term
"LH" may be used to identify the bed height-corrected
weight value produced by the left head load cell 68b, the term "RF"
may be used to identify the bed height-corrected weight value produced
by the right foot load cell 68c, and the term "LF" may
be used to identify the bed height-corrected weight value produced
by the left foot load cell 68d. In the illustrated embodiment, the
load cell signals produced by the load cells 68a-68d are analog
current or voltage signals, and the amplitudes of these analog signals
are converted via analog-to-digital inputs of the controller 88
to corresponding discrete, raw "count" values. The controller
88 is then operable at step 152 to add or subtract an offset count
value to or from the various discrete, raw count values, as just
described, to produce bed height-corrected count values for each
of the load cells 68a-68d. At step 154, the controller 88 then multiplies
the corrected count values of each the load cell by a predefined
conversion constant to convert the corrected count values of each
load cell to a corresponding weight value, LH, LF, RH and RF.
[0053] Following step 154, the controller 88 is operable at step
156 to correct the load cell weight values, LH, RH, LF and RF based
on the current PM State of the state machine 120. For example, if
the state machine 120 is currently in the PM Off State 122, the
controller 88 is operable to correct the load cell weight values
by subtracting tare weights in the form of original zero weight
(OZ) values, and then by correcting these weight difference values
by a trend angle, or reverse trend angle, factor, TAF. In one embodiment,
the controller 88 is operable to determine a trend angle or reverse
angle, .alpha., corresponding to the angle of incline or decline
of the entire mattress 60 from the head end 62 of the bed 50 to
the foot end 64 of the bed 50, as a function of bed height difference
between the head end 62 and foot end 64 of the bed 50. In this embodiment,
the logic module 96 supplies the bed height information to the processor
module 86, and the controller 88 is operable to determine the trend
angle, .alpha., as a known function of the bed height difference
between the head end 62 and foot end 64 of the bed 50. Alternatively,
the controller 88 may be configured to determine a via conventional
techniques. In any case, with the trend angle, .alpha., determined,
the controller 88 is then operable to compute the trend angle factor
according to the relationship TAF=cos .alpha.. As illustrated in
step 156, the controller 88 is thus operable to correct the load
cell weight values when the state machine 120 is in the PM Off State
122 according to the equations LH=(LH-OZLH)/TAF, RH=(RH-OZRH)/TAF,
LF=(LF-OZLF)/TAF and RF=(RF-OZRF)/TAF.
[0054] If, at step 156, the state machine 120 is instead in the
PM Zero State 124, the controller 88 is operable to correct the
load cell weight values by the trend angle, or reverse trend angle,
factor, TAF. As illustrated in step 156, the controller 88 is operable
to correct the load cell weight values when the state machine 120
is in the PM Zero State 124 according to the equations LH=LH/TAF,
RH=RH/TAF, LF=LF/TAF and RF=RF/TAF.
[0055] If, at step 156, the state machine 120 is instead in either
of the PM Movement/Exit Transition state 128 or the PM Active State
130, the controller 88 is operable to correct the load cell weight
values by tare weights in the form of auto zero (AZ) weight values.
As illustrated in step 156, the controller 88 is operable to correct
the load cell weight values when the state machine 120 is in the
PM Movement/Exit Transition State 128 or the PM Active State 130
according to the equations LH=LH-AZLH, RH=RH-AZRH, LF=LF-AZLF and
RF=RF-AZRF.
[0056] Following step 156, the controller 88 is operable to compute
a corrected total patient weight, CTPW, corresponding to a total
bed weight impressed upon the load cells 68a-68d by a patient. In
one embodiment, the controller 88 is operable to execute step 156
by computing the total patient weight, CTPW, as an average of the
sum of the corrected load cell weight values, or CTPW=(LH+RH+LF+RF)/4.
It may also be desirable to further correct CTPW, as a function
of the trend angle or reverse trend angle, .alpha., when CTPW is
determined from load cell weight values when the state machine 120
is in either the PM Movement/Exit Transition State 128 or the PM
Active State 130. In such cases, the controller 88 may further be
operable at step 158 to compute CTPW=CTPW/cos .alpha..
[0057] Following step 158, the controller 88 is operable at step
160 to compute a number of total patient weight running averages
using any one or more conventional sample averaging techniques.
In the illustrated embodiment, for example, the controller 88 is
operable at step 160 to compute a total patient weight slow running
average, SRA, and a total patient weight fast running average, FRA,
using conventional averaging techniques, although other sample averaging
techniques may be used to provide other patient weight running average
values. At step 162, the controller 88 is operable to determine
whether the corrected total patient weight, CTPW, is greater than
a minimum total patient weight threshold, MINTPW. The minimum total
patient weight threshold, MINTPW, may be selected to fit the particular
application, and one example value of MINTPW may be, but should
not be limited to, 50 lbs. If the controller 88 determines at step
162 that CTPW is greater than MINTPW, execution of the state machine
preparation routine advances to step 164 where the controller 88
is operable to compute a sensitivity to minimum weight change, SMWC,
as a function of the corrected total patient weight, CTPW, wherein
the minimum weight change may result from adding weight to the support
surface 65 of the mattress 60 and/or to the region of the mattress
support frame 58 between the end 60b of the mattress and the foot
end 64 of the bed 50 as illustrated in FIG. 1C. The sensitivity
to minimum weight change is used, as will be described in detail
hereinafter, to determine a maximum amount of weight change in the
patient movement (PM) mode that will be tolerated before temporarily
disabling the PM mode until the change in weight settles.
[0058] In one embodiment, for example, the controller 88 is operable
to execute step 164 by computing SMWC according to the equation
SMWC=MWCHBNR+(CTPW-MINTPW)*WCHS, where SMWC is the sensitivity to
minimum weight change, MWCHBNR is a minimum weight change before
new reference value, e.g., 5 lbs., CTPW is the corrected total patient
weight, MINTPW is the minimum total patient weight threshold and
WCHS is a weight change sensitivity value, e.g., 0.05. One example
implementation of this equation may thus result in SMWC=5+(CTPW-50)*0.05,
although other values of MWCHBNR, MINTPW and WCHS may be used. In
any case, execution of the state machine preparation routine advances
from step 164 and from the "NO" branch of step 162 to
step 166 where algorithm execution is returned to step 110 of the
main algorithm 100 of FIG. 5.
[0059] Following completion of the state machine preparation routine
at step 110, execution of the algorithm 100 advances to the current
state of the state machine 120. One such state may be, for example,
the PM Off State 122. Referring now to FIGS. 7A-7C, a flowchart
is shown of one illustrative embodiment of a software algorithm
or routine for executing the PM Off State 122 of the state machine
120. The PM Off State routine begins at step 180 where the controller
88 is operable to determine whether the corrected total patient
weight, CTPW, is stable. In one embodiment, the controller 88 is
operable at step 180 to determine whether CTPW is stable by comparing
CTPW to a sum and difference of a last weight settling snapshot,
LWSS, and an arming weight settle constant, AWSC, wherein the last
weight settling snapshot corresponds to the total weight impressed
upon the load cells 68a-68d at the most recent determination that
CTPW was stable. Specifically, the controller 88 is operable in
the illustrated embodiment to determine that CTPW is unstable if
CTPW>(LWSS+AWSC) OR CTPW<(LWSS-AWSC). If the controller 88
determines at step 180 that either of these conditions is met, execution
of the routine advances to step 182 where the controller 88 is operable
to reset a weight stable timer and capture a new weight reference
snap shot. Thereafter at step 184, the controller 88 is operable
to set the last weight settling snapshot, LWSS, to the corrected
total patient weight, CTPW.
[0060] Execution of the PM Off State routine advances from the
"YES" branch of step 180, which is indicative of CTPW
satisfying neither of the above inequalities and therefore being
considered to be stable, and from step 184 to step 186 where the
controller 88 is operable to execute the Exit Mode routine, which
will be described in detail hereinafter, to determine whether the
patient weight is contained within a safe arming zone of the mattress
60. Thereafter at step 188, the controller 88 is operable to determine
whether any patient monitoring mode requests; i.e., the patient
movement (PM) mode, patient exit (PE) exit mode or patient out-of-bed
(OOB) mode, are active. If so, execution of the PM Off State routine
advances to step 190 where the controller 88 is operable to determine
whether the patient monitoring mode request corresponds to either
of the patient movement (PM) or patient exit (PE) monitoring modes.
If so, the operating state of the state machine 120 moves to the
PM Movement/Exit Transition State 128 and the controller 88 is operable
at step 192 to execute a PM Movement/Exit Transition State routine,
one example of which will be described below with reference to FIGS.
10A-10B. If, on the other hand, the controller 88 determines at
step 190 that the patient monitoring mode request corresponds to
the patient out-of-bed (OOB) monitoring mode, the operating state
of the state machine 120 moves to the PM OOB Transition State 132
of the state machine 120 and the controller 88 is operable at step
194 to execute a PM OOB Transition State routine similar to the
PM Movement/Exit Transition State routine, one embodiment of which
will be described below with reference to FIGS. 10A-10B.
[0061] In the illustrated embodiment, the PM OOB Transition State
routine may be identical to the PM Movement/Exit Transition State
routine illustrated in FIGS. 10A-10B with the exception that step
362 is omitted and the Exit mode routine is therefore not executed
to determine whether the patient weight is within the safe arming
zone of the mattress 60. In all other respects, the PM OOB Transition
State routine in the illustrated embodiment is identical to the
PM Movement/Exit Transition State routine of FIGS. 10A-10B. A flowchart
and description of the details such a PM OOB Transition State routine
would thus be repetitious of the PM Movement/Exit Transition State
routine of FIGS. 10A-10B, and is accordingly omitted from this document
for brevity.
[0062] Returning to the PM Off State routine of FIGS. 7A-7C, execution
of this routine advances from the "NO" branch of step
188 to step 196 where the controller 88 is operable to determine
whether a common zero request flag, CZR, is active. This flag is
set when a user pushes the enable switch 74 and thereafter pushes
the zero select switch 72, thereby manually requesting zeroing of
the bed weight. If the controller 88 determines at step 196 that
CZR is "true", the operating state of the state machine
120 moves to the PM Zero State 124 and the controller 88 is operable
at step 198 to execute a PM Zero State routine to zero the bed weight,
and one example of such a PM Zero State routine will be described
below with reference to FIG. 8.
[0063] Execution of the PM Off State routine advances from the
"NO" branch of step 196 to step 200 where the controller
88 is operable to determine whether the corrected total patient
weight, CTPW, is between a minimum auto-zero weight value, MINAZW,
and a maximum auto-zero weight value, MAXAZW. When the state machine
120 is in the PM Off State the controller 88 executes steps 200
and beyond of the PM Off State routine to determine whether to perform
an auto-zeroing process, or an automatic bed zeroing. MINAZW may
be in the range of -4 to -5 lbs., and MAXAZW may be in the range
of 4-5 lbs., although it will be understood that these values are
provided only by way of example, and that MINAZW and MAXAZW may
take on any desired values. The auto-zeroing process of steps 200
and beyond is conducted because the weight distribution between
the load cells 68a-68d may have shifted since the last bed zeroing
event. Such a shift may have occurred for any number of reasons
including, for example, a visitor sits on the corner of the bed
for a brief time period, someone leans against one of the siderails
66a-66d, medical monitoring equipment may have been briefly stored
on the mattress 60 or between the end 60b of the mattress 60 and
the foot end 64 of the bed 50, or the like. In any of these cases,
the total bed weight after one or more such occurrences may remain
at or near the zeroed bed weight, but the distribution of the weight
between the various load cells 68a-68d may have shifted significantly.
Such weight shifting between the load cells 68a-68d may compromise
subsequent calculations made by the system 75, and it is accordingly
desirable to carry out an auto-zeroing process whenever the state
machine 120 is in the PM Off State 122 and conditions indicate that
auto-zeroing is desirable.
[0064] In any case, if the controller 88 determines at step 200
that CTPW does not fall between MINAZW and MAXAZW, CTPW is too high
to consider auto-zeroing and execution of the routine advances to
step 254 for execution of a warning algorithm. If, on the other
hand, the controller 88 determines at step 200 that CTPW falls between
MINAZW and MAXAZW, the controller 88 is thereafter operable at step
202 to determine whether the auto-zero weight conditions are satisfied.
In one embodiment, the controller 88 is operable at step 202 to
determine whether the auto-zero weight conditions are satisfied
by determining whether a patient exiting zone flag, PEZ, is false,
thereby indicating that the patient is within the safe arming zone
of the mattress, or whether the corrected total patient weight,
CTPW is greater than a minimum auto-zero trigger weight, MINAZTW,
or that CTPW is less than a maximum auto-zero trigger weight, MAXAZTW.
As examples, MINAZTW may be in the range of -4 to -5 lbs., e.g.,
-4.1 lbs., and MAXAZTW may be in the range of 4-5 lbs., e.g., 4.1
lbs., although it will be understood that these values are provided
only by way of example, and that MINAZTW and MAXAZTW may take on
any desired values. In any case, if the controller 88 determines
at step 202 that any of these conditions is met, execution of the
routine advances to step 204 where the controller 88 is operable
to determine whether an auto-zero (AZ) timer should be reset. If,
on the other hand, the controller 88 determines at step 202 that
none of the foregoing conditions are met, the weight conditions
for auto-zeroing are not satisfied and execution of the routine
advances to step 254 for execution of a warning algorithm.
[0065] Generally, it is not desirable to reset the auto-zero timer
and to therefore avoid executing an auto-zeroing process if it appears
that CTPW has not shifted recently. In one embodiment of step 204,
if the current state of the auto-zero timer indicates that sufficient
time, e.g., 700 ms, has elapsed since the last time an auto-zero
was considered, if the bed 50 has not been articulated within a
sufficient time period, e.g., 1 second, and if CTPW has been stable
within a specified weight window, e.g., +/-2.5 lbs., for a specified
time period, e.g., 1 second, the auto-zero timer is reset. If all
of these conditions are not satisfied in this exemplary embodiment,
execution of the routine advances to step 254 for execution of a
warning algorithm. If, however, all of these conditions are satisfied
in the exemplary embodiment of step 204, execution of the routine
advances to step 206 where the controller 88 resets the auto-zero
timer.
[0066] Following step 206, the controller 88 is operable at step
208 to determine whether an auto-zero has not occurred since the
last patient exit from the bed 50, whether the corrected total patient
weight, CTPW, is less by a pound than the last auto-zero weight,
LAZW, and whether the change in the absolute sum of LF and RF since
the bed 50 was last zeroed by the user is greater than a head angle
threshold value, HATH. Generally, the angle of the head section
60e of the mattress relative to horizontal will affect the weight
distribution among the load cells 68a-68d. It is accordingly desirable
to account for the possibility that that head 60e of the mattress
60 may positioned at some angle other than what is was the last
time a bed weight zeroing process was executed. In the illustrated
embodiment, a change of the angle of the head section 60e of the
mattress 60 from zero to maximum head section elevation, e.g., 65
degrees, may significantly change the distribution of weight between
the head end load cells 68a and 68b and the foot end load cells
68c and 68. This can be detected by monitoring a change in the absolute
value of the weight impressed upon the foot end load cells 68c and
68d. In this embodiment, the head angle threshold value, HATH, is
chosen to be slightly less than one-half of this value, e.g., 8
lbs., since the head section 60e may have been at an elevated position
during the last bed zeroing process. In any case, if none of the
conditions of step 208 are satisfied, it is unlikely that the head
section 60e of the mattress 60 has moved since the last bed zeroing
event, and execution of the routine advances to step 254 for execution
a warning algorithm. If, however, the controller 88 determines that
any of the conditions of step 208 are satisfied, it is likely that
the head section 60e of the mattress 60 has moved since the last
bed zeroing event and steps 210-224 are then executed to determine
an appropriate head angle weight compensation value.
[0067] At step 210, the controller 88 tests the change in the absolute
sum of LF and RF against the head angle threshold value, HATH, to
determine if the head angle has increased since the last bed zeroing
event. If the change in the absolute sum of LF and RF exceeds HATH,
the head angle has increased since the last bed zeroing event and
execution of the routine advances to step 212 where the controller
88 is operable to determine whether the difference in the absolute
sum of LF and RF is between the head angle threshold value, HATH,
e.g., 8 lbs., and a higher head angle threshold, HHATH, e.g., 12
lbs. If so, a dynamic compensation weight, DCW, which will be added
to the bed zero weight at the end of the auto-zeroing process, is
assigned a first weight value, W1, e.g., 2 lbs., at step 214. If
not, the dynamic compensation weight, DCW, is assigned a second
greater weight value, W2, e.g., 3 lbs., at step 216.
[0068] If, at step 210, the controller 88 determines that a change
in the absolute sum of LF and RF is not greater than HATH, execution
of the routine advances to step 218 where the controller 88 tests
the change in the absolute sum of LF and RF against the negative
of the head angle threshold value, HATH, to determine if the head
angle has decreased since the last bed zeroing event. If the change
in the absolute sum of LF and RF is less than -HATH, the head angle
has decreased since the last bed zeroing event and execution of
the routine advances to step 220 where the controller 88 is operable
to determine whether the difference in the absolute sum of LF and
RF is between the negative head angle threshold value, -HATH, e.g.,
-8 lbs., and a lower head angle threshold, -LHATH, e.g., -12 lbs.
If so, a dynamic compensation weight, DCW, which will be added to
the bed zero weight at the end of the auto-zeroing process, is assigned
a negative first weight value, -W1, e.g., -2 lbs., at step 222.
If not, the dynamic compensation weight, DCW, is assigned a second
lesser negative weight value, -W2, e.g., -3 lbs., at step 224. It
will be understood that while numerical values are given above for
parameters such as HATH, HHATH, LHATH, W1 and W2, such numerical
values are provided only by way of example and each of these parameters
may alternatively be assigned different values.
[0069] Execution of the PM Off State algorithm advances from steps
214, 216, 222 and 224, as well as from the "NO" branch
of step 218, to step 226 where the controller 88 is operable to
determine the absolute weight on each of the load cells 68a-68d,
resulting in the absolute weight values ALH, ALF, ARH and ARF. In
the illustrated embodiment, the ALH, ALF, ARH and ARF values are
determined from values obtained during the state machine preparation
routine of FIG. 6, although these values may be updated at step
226 by taking new weight measurements. In any case, the controller
88 is operable following step 226 at step 228 to determine whether
a first auto-zero attempt flag, FAZA, is "false." If not,
this is the first execution of step 228 and a set of last auto-zero
weight variables may not be updated. Execution of the routine accordingly
advances from the "NO" branch of step 228 to step 230
where the controller updates the last auto-zero weight variables
with the current absolute weight values by setting LAZLH=ALH, LAZLF=ALF,
LAZRH=RH and LAZRF=ARF. The controller 88 is also operable at step
230 to set FAZA="false" so that the next execution of
step 228 results in the routine advancing to step 232. Execution
of the routine advances from step 230 to step 254 for execution
of a warning algorithm.
[0070] At step 232, the controller 88 is operable to set current
auto-zero weight values to the last auto-zero weight values by setting
AZLH=LAZLH, AZLF=LAZLF, AZRH=LAZRH and AZRF=LAZRF. Thereafter at
step 233, the controller 88 is operable to again update the last
auto-zero weight variables with the current absolute weight values
by setting LAZLH=ALH, LAZLF=ALF, LAZRH=RH and LAZRF=ARF. Thereafter
at step 234, the controller 88 is operable to determine whether
a constant head angle correction factor flag, CHACF, is "true."
If so, this indicates that a significant positive shift exists between
the head end load cells 68a-68b and the foot end load cells 68c-68d,
and that the sum of LH and RH are thus greater than their bed flat
values. The constant head angle correction flag, CHACF, is reset
("false") when a significant positive shift exists between
the foot end load cells 68c-68d and the head end load cells 68a-68b,
and the sum of LF and RF are thus greater than their bed flat values.
In any case, execution of the routine advances from the "YES"
branch of step 234 to step 236 where the current auto-zero weight
values, AZLH, AZLF, AZRH and AZRF, are computed each as a sum of
its current value, a constant head angle factor, CHAF, and the dynamic
head angle factor, DCW. The constant head angle factor, CHAF, is
a constant weight value indicative of added bed weight due to raising
of the head section 60e of the mattress 60, and an example value
may be 5.0 lbs., although it will be understood that other values
may be used. Following step 236, execution of the routine advances
to step 237 where the controller 88 is operable to determine whether
the dynamic head angle factor, DHAF, is greater than a minimum dynamic
head angle factor, MDHAF, e.g., 5. If so, the controller 88 is operable
thereafter at step 239 to set the constant head angle correction
flag, CHACF, to "false." From step 239, and from the "NO"
branch of step 237, execution of the routine advances to step 254
for execution of a warning algorithm.
[0071] If, at step 234, the constant head angle correction flag,
CHACF, is "false, a significant positive shift does not exist
between the head end load cells 68a-68b and the foot end load cells
68c-68d, and execution of the routine advances to step 238 where
the controller 88 is operable to compute a dynamic head angle factor,
DHAF, as a function of auto-zero weights, AZW, and bed flat zero
weights, BFZW. In one embodiment, DHAF=[(AZLF-BFLF)+(AZRF-BFRF)-(AZRH-BFRH)-(AZLH-BFLH)]/4,
where BFLH, BFLF, BFRH and BFRF correspond to bed flat LH, LF, RH
and RF values determined during a bed flat zero request as will
be described hereinafter with respect to FIG. 8. In any case, execution
of the routine advances from step 238 to step 240 where the controller
88 is operable to compare the dynamic head angle factor, DHAF, to
the sum of a maximum dynamic head angle factor value, MAXDHAF, and
the current value of the dynamic compensation weight, DCW. If the
controller 88 determines at step 240 that DHAF>MAXDHAF+DCW, execution
of the routine advances to step 242 where the controller is operable
to clamp the value of the dynamic head angle factor, DHAF, to MAXDHAF+DCW.
In one embodiment, MAXDHAF is chosen to correspond to a maximum
of 45 degree head section angle relative to horizontal.
[0072] If, at step 240 the controller 88 determines that DHAF is
not greater than MAXDHAF+DCW, execution of the routine advances
to step 244 where the controller 88 is operable to determine whether
the dynamic head angle factor, DHAF, is less than an unsafe maximum
dynamic head angle factor, USMAXDHAF. If so, the controller 88 is
operable thereafter at step 246 to set the constant head angle correction
flag, CHACF, to "true." If not, the controller 88 is operable
at steps 248 and 250 to clamp DHAF at zero if DHAF is less than
zero.
[0073] Execution of the PM Off State routine advances from steps
246 and 250, and from the "NO" branch of step 248, to
step 252 where the controller 88 is operable to update current values
of the auto-zero weights, AZLH, AZLF, AZRH and AZRF, each as a sum
of corresponding ones of the individual original zero weights, OZLH,
OZLF, OZRH and OZRF, and the dynamic head angle factor, DHAF. Following
step 252, the controller 88 is operable at step 254 to execute a
warning algorithm by comparing a difference between a common zero
total weight, CZTW, and the corrected total patient weight, CTPW,
to a first weight value, and to compare an absolute difference between
the corrected total patient weight, CTPW, and the frame weight,
FW, i.e., the weight of the mattress support frame 58 (see FIG.
9), to a second weight value, W2. If, at step 254 the controller
determines that (CZTW-CTPW)>W1 AND abs(CTPW-FW)>W2, the controller
88 activates a warning mechanism, e.g., visual or audible alarm,
at step 256 and thereafter at step 258 goes to the Freeze State
126 of the state machine 120 until the warning condition is addressed.
Alternatively, the controller 88 may wait or delay for some timer
period before activating the warning mechanism at step 256. In any
case, if both of these conditions are not met at step 254, execution
of the PM Off State routine advances to the return step 260. In
one embodiment, W1=4.5 lbs., W2=19 lbs., although other values may
be used. The warning algorithm of step 254 is intended to detect
removal of the mattress 60, as it activates a warning only if the
corrected total patient weight, CTPW, has decreased by at least
4.5 lbs. and the difference between CTPW and FW is more than 19
lbs. (the mattress may add at least 25 lbs. to the frame weight).
[0074] Referring now to FIG. 8, a flowchart is shown illustrating
an exemplary embodiment of a software routine for executing the
PM Zero State 124 of the state machine 120 of FIG. 5. The PM Zero
State routine begins at step 270 where the controller 88 is operable
to determine whether the routine was called pursuant to a common
zero request, CZR. A common zero request, CZR, is made manually
via pressing a specified combination of the switches forming part
of the control panel 70 (FIG. 2). In one embodiment, for example,
a common zero request is made by pressing the enable switch 74 for
at least 0.5 seconds and then releasing the enable switch 74, followed
by pressing the zero select switch 72 for at least 0.5 seconds.
It will be appreciated that other combinations of switches and switch
activation scenarios may be used to activate a common zero request,
and any such other switch combinations and/or switch activation
scenarios are intended to fall within the scope of the appended
claims. For example, the zero switch hold time may be a function
of the corrected total patient weight, CTPW, slow running average,
SRA, or fast running average, FRA, such that the time required for
the zero select switch 72 to be pressed in order to complete a common
zero request is a function of patient weight. In one embodiment,
the zero switch hold time may be directly proportional to patient
weight so that longer zero switch hold times are required as patient
weight increases, although other functional relationships between
the zero switch hold time and the patient weight may be used.
[0075] If, at step 270, the controller 88 determines that a common
zero request, CZR, is active, execution of the routine advances
to steps 272 and 274 where the controller 88 is operable to verify
that the zero switch 72 was activated for T1 seconds, e.g., T1=0.5
seconds, and thereafter released. If so, the controller 88 is operable
at step 276 to determine whether the weight impressed upon the load
cells 68a-68d is stable using one or more of the techniques described
hereinabove with respect to the PM Off State. If the controller
88 determines at step 276 that the weight is not stable, the controller
88 is thereafter operable at steps 282 and 284 to reset the weight
stable timer and set the last weight settling snapshot, LWSS, equal
to the corrected total patient weight, CTPW. Execution of the PM
Zero State routine advances from step 284 to a return step 286.
[0076] If, at step 276 the controller 88 determines that the weight
has been stable for a specified time period, execution of the routine
advances to step 278 where the controller 88 executes a zero capture
routine. An exemplary embodiment of the zero capture routine will
be described below with respect to FIG. 9. Following execution of
the zero capture routine at step 278, the controller 88 is operable
to clear the common zero request, CZR, and clear any frozen status
in case the PM Zero State routine was called when the state machine
120 was in the Freeze State 126.
[0077] If, at step 270, the controller 88 determines that a common
zero request, CZR, is not active, execution of the PM Zero State
routine advances to step 288 to determine whether a bed flat zero
request, BFZR, is active. A bed flat zero request, BFZR, is made
manually via pressing a specified combination of the switches forming
part of the control panel 70. In one embodiment, for example, a
bed flat zero request, BFZR, is made by pressing the volume switch
76 for at least 3.0 seconds, followed by pressing the OOB mode switch
84, and then releasing either the OOB mode switch 84 or the volume
switch 76 if that is also pressed. It will be appreciated that other
combinations of switches and switch activation scenarios may be
used to activate a bed flat zero request, and any such other switch
combinations and/or switch activation scenarios are intended to
fall within the scope of the appended claims.
[0078] If, at step 288, the controller 88 determines that a bed
flat zero request, BFZR, is active, execution of the routine advances
to step 290 where the controller 88 executes the zero capture routine,
an exemplary embodiment of which will be described below with respect
to FIG. 9. Following execution of the zero capture routine at step
290, the controller 88 is operable at step 292 to clear the bed
flat zero request, BFZR, and clear any frozen status in case the
PM Zero State routine was called when the state machine 120 was
in the Freeze State 126.
[0079] If, at step 288, the controller 88 determines that a bed
flat zero request, BFZR, is not active, execution of the PM Zero
State routine advances to step 294 to determine whether a frame
zero request, FZR, is active. A frame zero request, FZR, is made
manually via pressing a specified combination of the switches forming
part of the control panel 70. In one embodiment, for example, a
frame zero request, FZR, is made by pressing the volume switch 76
for at least 3.0 seconds, followed by pressing the Exit mode switch
82 for at least 10.0 seconds, and then releasing either the Exit
mode switch 82 or the volume switch 76 if that is also pressed.
It will be appreciated that other combinations of switches and switch
activation scenarios may be used to activate a frame zero request,
and any such other switch combinations and/or switch activation
scenarios are intended to fall within the scope of the appended
claims.
[0080] If, at step 294, the controller 88 determines that a frame
zero request, FZR, is active, execution of the routine advances
to step 296 where the controller 88 executes the zero capture routine,
an exemplary embodiment of which will be described below with respect
to FIG. 9. It will be understood that since the zero capture routine
is executed at step 296 for the purpose of obtaining a frame zero
weight, the mattress 60 will naturally be removed from the mattress
support frame 58 prior to step 296. Thereafter, the mattress 60
may be returned to the mattress support frame 58. If, at step 294,
the controller 88 determines that the frame zero mode, FZR, is not
active, execution of the routine advances to the return step 286.
Following steps 280, 292 and 296, as well as the "NO"
branch of step 272, execution of the PM Zero State routine advances
to step 298 where the state machine 120 advances to the PM Off State
122, and controller 88 is thus operable to execute the PM Off State
routine of FIGS. 7A-7C.
[0081] Referring now to FIG. 9, a flowchart is shown illustrating
an exemplary embodiment of the zero capture software routine called
at steps 278, 290 and 296 of the PM Zero State routine of FIG. 8.
The zero capture routine begins at step 310 where the controller
88 is operable to determine current load cell weight values, LH,
LF, RH and RF. Thereafter at step 312, the controller 88 is operable
to determine whether a frame zero request, FZR, is active. If so,
execution of the routine advances to step 314 where the controller
88 is operable to calculate the frame weight, FW, as a known function
of LH, LF, RH and RF. If, at step 312, the controller 88 determines
that a Frame zero request, FZR, is not active execution of the routine
advances to step 316 where the controller 88 is operable to calculate
an absolute value of the sum of LF and RF. Thereafter at step 318,
the controller 88 is operable to determine whether a bed flat zero
(BFZ) request is active. If so, execution of the routine advances
to step 320 where the controller 88 is operable to set original
zero (OZ) values and auto zero (AZ) values for each of the load
cells 68a-68d to current values of LH, LF, RH and RF, e.g., OZLH=AZLH=LH,
OZLF=AZLF=LF, OZRH=AZRH=RH and OZRF=AZRF=RF. If, at step 318, the
controller 88 determines that a bed flat zero (BFZ) request is not
active, a common zero request must be active and execution of the
routine advances to step 322 where the controller 88 is operable
to set original zero (OZ) values for each of the load cells 68a-68d
to current values of LH, LF, RH and RF, e.g., OZLH=LH, OZLF=LF,
OZRH=RH and OZRF=RF, and correct these original zero values for
head angle as described hereinabove with respect to the auto-zeroing
portion of the PM Off State routine of FIGS. 7A-7C. If the head
angle correction was dynamic and is entering the constant mode,
set the constant head angle correction flag, CHACF, to "true".
If, on the other hand, the head angle correction was constant and
is entering the dynamic mode, set CHACF to "false." In
either case, the controller is also at step 322 to compute a common
zero total weight, CZTW, as described hereinabove with respect to
the auto-zeroing portion of the PM Off State routine of FIGS. 7A-7C.
Following any of the steps 314, 320 and 322, execution of the routine
advances to step 324 where the zero capture routine is returned
to its calling routine.
[0082] Referring now to FIGS. 10A-10B, a flowchart is shown of
one illustrative embodiment of a software algorithm or routine for
executing the PM Movement/Exit Transition State 128 of the state
machine 120. The PM Movement/Exit Transition State routine begins
at step 350 where the controller 88 is operable to determine whether
the current execution of step 350 constitutes the first execution
of the PM Movement/Exit Transition routine. If so, execution of
the routine advances to step 352 where the controller 88 is operable
to reset a general active (GA) timer. Execution of the routine advances
from step 352, and from the "NO" branch of step 350, to
step 354 where the controller 88 is operable to determine whether
the GA timer is less than a settling time, T.sub.S. If so, execution
of the routine advances to step 356 where the controller 88 is operable
to set the last weight settling snapshot, LWSS, equal to the corrected
total patient weight, CTPW. Steps 354 and 356 allow T.sub.S seconds
between capturing of new load cell data before the weight stability
check will continue. In one embodiment, T.sub.S=140 ms, although
T.sub.S may alternatively be set at other desired values.
[0083] Execution of the PM Movement/Exit Transition State routine
advances from step 356, and from the "NO" branch of step
354, to step 358 where the controller 88 is operable to compare
the corrected total patient weight, CTPW, to a sum of, and a difference
between, the last weight settling snapshot, LWSS, and an arming
weight settle constant, AWSC. In the illustrated embodiment, if
the controller 88 determines at step 358 that CTPW>LWSS+AWSC
AND CTPW<LWSS-AWSC, this is an indication that the weight on
the mattress 60 is unstable and execution of the routine advances
to step 360 where the controller 88 is operable to set LWSS equal
to CTPW and to reset the weight stable timer.
[0084] Execution of the PM Movement/Exit Transition State routine
advances from step 360, and from the "NO" branch of step
358, to step 362 where the controller 88 is operable to execute
the exit mode routine to determine whether the patient is within
the safe arming zone of the mattress 60. Thereafter at step 364,
the controller 88 is operable to determine whether the patient exit
(PE) or patient movement (PM) mode switch enable time is satisfied.
In one embodiment of the system 75, the mode switches 80-84 must
be depressed for at least a selected time period, e.g., 0.5 seconds,
and then released to successively activate a patient monitoring
mode. It will be appreciated that combinations of switches and/or
different switch activation scenarios may be used to activate the
various patient monitoring modes, and any such other switch combinations
and/or switch activation scenarios are intended to fall within the
scope of the appended claims.
[0085] In any case, if the controller 88 determines at step 364
that either of the patient exit (PE) or patient movement (PM) modes
have been successfully selected, execution of the routine advances
to step 366. If not, the selected switch has not been depressed
long enough before release and execution of the routine thus advances
to step 376 where the controller 88 is operable to make this determination.
If, at step 376, the controller 88 determines that the selected
mode switch has been released before successfully selecting the
patient exit (PE) mode or the patient movement (PM) mode, then the
selected mode was not successively activated and execution of the
routine advances to step 378 where the state machine 120 moves to
the PM Off State 122 and the controller 88 is thus operable to execute
the PM Off State routine of FIGS. 7A 7C. If the controller 88 determines
at step 376 that the selected switch has not been released, then
execution of the routine advances to the return step 380.
[0086] At step 366, the controller 88 has determined that one of
the patient exit (PE) or patient movement (PM) modes have been successfully
selected and the controller 88 is operable to determine whether
execution of the exit mode routine at step 362 determined that the
patient is within the safe arming zone of the mattress 60. If so,
the patient exiting zone flag, PEZ, was set equal to "false"
by the exit mode algorithm. The controller 88 is further operable
at step 366 to determine whether the corrected total patient weight,
CTPW, is between a minimum patient weight, MINPW, and a maximum
patient weight, MAXPW. In one embodiment, for example, MINPW=50
lbs. and MAXPW=500 lbs., although these values are provided only
by way of example and other values of MINPW and MAXPW. For example,
MINPW may be set to a value greater than 50 lbs., or may be set
to a value less than 50 lbs. to accommodate lighter-weight patients
such as toddlers and/or infants. Likewise, MAXPW may be set to a
value less than 500 lbs., or may be set to a value greater than
500 lbs. to accommodate bariatric patients. In any case, if the
controller 88 determines that all three of the conditions are met,
i.e., that the patient is in the safe arming zone of the mattress
60, CTPW>MINPW and CTPW<MAXPW, execution of the routine advances
to step 368 where the controller 88 is operable to compare the weight
settling timer to a predefined settling time, T.sub.ST, e.g., 5
seconds.
[0087] If the weight settling timer is greater than T.sub.ST, indicating
that the weight has been stable for at least T.sub.ST, execution
of the routine advances to step 370 where the controller 88 is operable
to set a last armed weight, LAW, and an armed weight, AW, equal
to the total patient weight slow running average, SRA, to set the
acquire new arming weight request flag, ANAWR, to "false",
to reset the weight settling (WS) timer, to set a waiting for weight
settling flag, WFWS, to "true", to capture new reference
load cell values, RLH, RLF, RRH and RRF, and compute a new corrected
total patient weight, CTPW, from RLH, RLF, RRH and RRF as described
hereinabove, to set the last weight settling snapshot, LWSS, to
the new corrected total patient weight, CTPW, and to reset an active
state timer. If, at step 368 the controller 88 determines that the
weight has not been stable for at least TST, execution of the routine
advances to step 372 where the controller 88 is operable to set
the last armed weight, LAW, and the armed weight, AW, equal to the
total patient weight slow running average, SRA, to set the acquire
new arming weight request flag, ANAWR, to "true", to reset
the weight settling timer, set a waiting for weight settling flag,
WFWS, to "true", to capture new reference load cell values,
RLH, RLF, RRH and RRF, and compute a new corrected total patient
weight, CTPW, from RLH, RLF, RRH and RRF as described hereinabove,
to set the last weight settling snapshot, LWSS, to the new corrected
total patient weight, CTPW, and to reset an the active state timer.
Alternatively, the controller 88 may be operable at either of steps
370 and 372 to set the last armed weight, LAW, and/or the armed
weight, AW, equal to the total patient weight fast running average,
FRA, or corrected total patient weight, CTPW. It will be noted that
the armed weight, AW, differs from the last armed weight, LAW. The
armed weight value, AW, is an armed weight value used by the out-of-bed
(OOB) mode routine, as will be described in detail hereinafter with
respect to FIG. 19, and may change during execution of the PM Exit/Movement
Transition State routine as just described and/or during execution
of the PM Active State routine as will be described in detail with
respect to FIGS. 11A-11C. The last armed weight value, LAW, on the
other hand, changes whenever weight greater than the sensitivity
to minimum weight change value, SMWC, or less than -SMWC, is added
to the bed 50. In any case, execution of the PM Movement/Exit Transition
State routine advances from either of the steps 370 and 372 to step
374 where the state machine 120 moves to the PM Active State 150
and the controller 88 thus executes a PM Active State routine, an
example of which will be described with respect to FIGS. 11A-11C.
[0088] The PM Movement/Exit Transition State 128 just described
is thus operable to ensure that the patient weight is between specified
minimum and maximum patient weight values, and to ensure that the
patient is within the safe arming zone of the mattress 60, when
the patient movement (PM) or patient exit (PE) mode is activated.
If these conditions are met and the patient movement (PM) or patient
(PE) is successfully activated, the system 75 is armed and the state
machine moves to the PM Active State, thereby indicating that one
of the patient monitoring modes is currently active with a patient
supported by the mattress 60. It should be noted that the arming
conditions are not dependent on other bed-related parameters such
as head angle or elevation, leg elevation, or the like. In fact,
as long as the foregoing arming conditions are met, the PE or PM
patient monitoring modes will be enabled regardless of whether the
head section of the bed is elevated anywhere between bed flat, i.e.,
horizontal, and the maximum head elevation angle, e.g., 65 degrees,
and/or regardless of whether the leg section is elevated anywhere
between its minimum and maximum leg elevation angles. Moreover,
when the system is armed as just described pursuant to enablement
of either the PE mode or the PM mode, the head section may thereafter
be articulated to any elevation between bed flat at the maxim head
elevation angle without activating a patient exit alarm or a patient
movement alarm. Likewise, the leg section may thereafter be articulated
anywhere between its two extreme elevations without triggering a
patient exit alarm or patient movement alarm. In an alternate embodiment,
it is desirable to distinguish between patient articulation of the
head section and/or the leg section after the system is armed. In
this embodiment, the system may be configured to allow such head
section and/or leg section articulation is executed via the control
panel 70, but to activate an alarm if such head section and/or leg
section articulation is executed via a patient control pendant.
[0089] Referring now to FIGS. 11A-11C, a flowchart is shown of
one illustrative embodiment of a software algorithm or routine for
executing the PM Active State 130 of the state machine 120. The
PM Active State routine begins at step 400 where the controller
88 is operable to determine whether the PM Active State has been
active for less than an active time, T.sub.A, e.g., 3 seconds. If
so, execution of the routine advances to step 402 where the controller
88 is operable to determine whether the corrected total patient
weight, CTPW, has changed by more than a weight change value, W.sub.CH,
since the armed weight, AW, was established when system 75 was armed
pursuant to the PM Movement/Exit Transition State 128 (see FIGS.
10A-10B). The weight change value, W.sub.CH, is, in one embodiment,
set to a weight value above which may be typical of someone leaning
against and applying some additional weight to the weigh frame 56
or other structure coupled to the weigh frame 56, e.g., an armrail
66a-66d. In any case, if the controller 88 determines at step 402
that CTPW has changed by more than W.sub.CH since the armed weight,
AW, was established, execution of the routine advances to step 404
where the controller 88 is operable to set the acquire new armed
weight request flag, ANAWR, to "true", to set the waiting
for weight settling flag, WFWS, to "true" and to set the
last weight settling snapshot, LWSS, equal to the corrected total
patient weight, CTPW.
[0090] Execution of the PM Active State routine advances from step
404, and from the "NO" branches of steps 400 and 402,
to step 406 where the controller 88 is operable to compare the total
patient weight fast running average, FRA, to a sum and difference
of the last armed weight, LAW, and the sensitivity to minimum weight
change value, SMWC, established by the state machine preparation
routine of FIG. 6. If the controller 88 determines at step 406 that
FRA>(LAW+SMWC) or FRA<(LAW-SMWC), this indicates that the
bed weight has increased sufficiently to warrant verification that
weight was added to or removed from the weigh frame 56. Thus if
the total patient weight fast running average, FRA, exceeds (LAW+SMWC)
or falls below (LAW-SMWC), execution of the routine advances to
step 414 where the controller 88 is operable to reset the weight
settling timer and to set the last weight settling snapshot, LWSS,
equal to the current corrected total patient weight, CTPW. Alternatively,
the controller 88 may be operable at step 406 to compare the total
patient weight slow running average, SRA, or corrected total patient
weight, CTPW, to the sum and difference of the last armed weight,
LAW, and the sensitivity to minimum weight change value, SMWC.
[0091] Execution of the PM Active State routine advances from step
414, and from the "NO" branch of step 412, to step 416
where the controller 88 is operable to compute a temporary weight
value, TEMPW as a difference between the corrected total patient
weight, CTPW, and the last armed weight, LAW. Thereafter at step
418, the controller 88 is operable to determine whether the bed
weight has stabilized by testing the status of the waiting for weight
settling flag, WFWS, and the status of the weight settling timer.
If, at step 418, the controller 88 determines that WFWS is "true"
and the weight settling timer has timed out, execution of the routine
advances to step 419 where the controller 88 is operable to set
WFWS to "false." Otherwise, execution of the routine advances
to step 452 where the state machine 120 moves to the PM Alarm State
where the controller 88 is operable to execute a PM Alarm State
routine of the type illustrated in FIG. 12
[0092] Execution of the PM Active State routine advances from step
419 to step 420 where the controller 88 is operable to determine
the status of the acquire new arming weight request flag, ANAWR.
If the controller 88 determines at step 420 that ANAWR is "true",
execution of the routine advances to steps 422, 424 and 426 where
the controller 88 is operable to capture new reference load cell
values, compute a new corrected total patient weight, CTPW, and
determine a new armed weight. In the illustrated embodiment, the
controller 88 is operable to accomplish this by first setting ANAWR
to "false" at step 422, and then capturing new reference
load cell values, RLH, RLF, RRH and RRF, and computing a new corrected
total patient weight, CTPW, from RLH, RLF, RRH and RRF as described
hereinabove, and setting the last armed weight, LAW, and the Armed
weight, AW, to the current corrected total patient weight, CTPW
at step 426, if CTPW is determined at step 424 to be between a minimum
armed weight, MINAW, and a maximum armed weight, MAXAW. If the controller
88 determines at step 424 that CTPW is not between MINAW and MAXAW,
however, execution of the routine advances to step 452 where the
state machine 120 moves to the PM Alarm State where the controller
88 is operable to execute a PM Alarm State routine of the type illustrated
in FIG. 12.
[0093] If, at step 420, the controller 88 determines that the acquire
new armed weight request flag, ANAWR is "false", execution
of the routine advances to step 428 where the controller 88 is operable
to compare the temporary weight value, TEMPW, determined at step
416 to the sensitivity to minimum weight change value, SMWC. TEMPW
represents a difference between the current corrected total patient
weight, CTPW, and the last armed weight value, LAW, and if this
difference value exceeds SMWC in either direction the controller
88 determines that a sufficient amount of weight has been added
to or removed from the weigh frame 56 to require new total patient
weight information. Thus, if the controller 88 determines at step
428 that TEMPW>SMWC OR TEMPW<-SMWC, execution of the routine
advances to step 430 where the controller 88 is operable to capture
new reference load cell values, RLH, RLF, RRH and RRF, to compute
a new corrected total patient weight, CTPW, from RLH, RLF, RRH and
RRF as described hereinabove, and to set the last armed weight,
LAW, equal to the newly computed corrected total patient weight,
CTPW. If, on the other hand, the controller 88 determines at step
428 that TEMPW falls between -SMWC and SMWC, this is an indication
that the bed weight has stabilized but not enough weight has been
added to or removed from the weigh frame 56 to justify calculation
of a new corrected total patient weight, CTPW. In this case, execution
of the routine thus advances to step 432 where the controller 88
is operable to set the waiting for weight settling flag, WFWS, to
"false."
[0094] Execution of the PM Active State routine advances from steps
426, 430 and 432 to step 434 where the controller 88 is operable
to determine whether a bed articulation timer is less than an articulation
stabilized time, AST. If so, the bed 50 is either articulating or
has articulated in the last second or so, and the controller 88
is thus operable at step 436 to capture new reference load cell
values, RLH, RLF, RRH and RRF.
[0095] Execution of the PM Active State routine advances from step
436, and from the "NO" branch of step 434, to step 438
where the controller 88 is operable to determine whether either
of the patient exit (PE) and patient movement (PM) modes are currently
active. If either of these modes is currently active, execution
of the routine advances to step 439 where the controller 88 is operable
to determine the status of a weight added flag, WA. If the weight
added flag, WA, is "false", execution of the routine advances
to step 440 where the controller 88 is operable to execute an exit
mode routine and a movement mode routine, examples of which will
be described in greater detail hereinafter with respect to FIGS.
13-18. Execution of the routine advances from step 440, and from
the "NO" branch of step 439, to step 442 where the controller
88 is operable to execute an out-of-bed (OOB) mode routine, one
example of which will be described in greater detail hereinafter
with respect to FIG. 19. Thereafter at step 444, the controller
88 is operable to determine whether an alarm condition is met (is
active) as a result of execution of either of the exit mode routine,
the movement mode routine or the out-of-bed mode routine. If so,
execution of the PM Active State routine advances to step 452 where
the state machine 120 moves to the PM Alarm State 136. If, at step
444, the controller 88 determines that no alarm conditions are currently
active, execution of the routine advances to step 446 where the
controller 88 is operable to determine whether any of the PM mode
switches 80-84 have been pressed. If not, execution of the routine
advances to a return step 450. If, at step 446, the controller 88
determines that at least one of the PM mode switches 80-84 has been
pressed, or some other predefined combination of switches has been
pressed, execution of the routine advances to step 448 where the
state machine 120 moves to the PM Off State, and the controller
88 is operable to execute a PM Off State routine of the type illustrated
in FIGS. 7A-7C.
[0096] The PM Active State 130 just described is thus operable
to monitor addition of weight to, and/or removal of weight from,
the weigh frame 56, and to call appropriate ones of the patient
monitoring modes. If sufficient weight is added to, or removed from,
the weigh frame 56 during the PM Active mode, a new corrected total
patient weight is then computed. As will become more apparent hereinafter,
the patient exit (PE) and patient movement (PM) modes will continue
to monitor patient movement after the system 75 is armed either
pursuant to selecting PE mode or PM mode, without activating an
alarm if further weight, less than 30 lbs., for example, is added
to the bed regardless of the total patient weight on the bed prior
to adding the further weight, as long as CTPW is between MINPW and
MAXPW. Likewise, the patient exit (PE) and patient movement (PM)
modes will continue to monitor patient movement after the system
75 is armed either pursuant to selecting PE mode or PM mode, without
activating an alarm if further weight, less than 30 lbs., for example,
is added to the bed after determining a bed zero weight, as long
as CTPW, determined as a function of the bed zero weight, is between
MINPW and MAXPW.
[0097] Referring now to FIG. 12, a flowchart is shown of one illustrative
embodiment of a software algorithm or routine for executing the
PM Alarm State 136 of the state machine 120. The PM Alarm State
routine begins at step 460 where the controller 88 is operable to
activate an appropriate alarm. Either one or both of the local alarm
98 and the remote alarm 99 may be flagged for activation, and the
controller 88 is accordingly operable at step 460 to activate any
alarm or alarms that are currently flagged for activation. Thereafter
at step 462, the controller 88 is operable to determine whether
any of the patient monitoring mode switches 80-84 have been pressed
to thereby deactivate any active alarms. If not, execution of the
routine advances to the return step 466. If, however, the controller
88 determines at step 462 that any of the patient monitoring mode
switches 80-84 have been flagged for activation, execution of the
routine advances to step 464 where the controller 88 is operable
to deactivate either, or both, of the alarms 98 and 99, and to set
an appropriate one, or both, of the alarms flags to an inactive
state. Thereafter at step 468, the state machine 120 moves to the
PM Off State, and the controller 88 is operable to execute a PM
Off State routine of the type illustrated in FIGS. 7A-7C.
[0098] In one exemplary embodiment of the system 75, the controller
88 is configured, pursuant to the patient exit (PE) mode of the
PM Active State 130, to determine impending exit by the patient
from the mattress 60 by comparing the current distribution of the
patient's weight over the four load cells 68a-68d to a predefined
collection of load cell exit threshold data. In the illustrated
embodiment, this predefined collection of load cell exit data is
provided in the form of a table of a number of sets of load cell
exit threshold values, although the collection of load cell exit
data may alternatively be provided in the form of one or more equations,
graphs, charts or the like. Referring now to FIG. 13, a diagram
of the bed 50 is shown illustrating one example implementation and
construction of such a table of load cell exit threshold values.
In this example, empirical load cell threshold data is established
by discretely moving a predefined calibration weight, e.g., 100
lbs., about a periphery of the mattress 60 or mattress support frame
58 and recording the corresponding readings, LH, LF, RF, RH, of
the four load cells 68a-68d into an exit condition threshold table.
Each such reading corresponds to a set of exit condition threshold
values, LHTN, LFTN, RFTN and RHTN, normalized to the predefined
calibration weight, and above which defines an exit condition at
the current location for the predefined calibration weight. The
exit condition threshold table may be sized to contain any number
of sets of exit condition threshold values, wherein the total number
of such sets used to populate the table will typically be dependent
upon the resolution requirements of the system 75.
[0099] In the example illustrated in FIG. 13, the exit condition
threshold table is populated with 78 such sets of exit condition
threshold values, E0-E77 defined about the periphery of the mattress
support frame 58. Each set of normalized exit condition threshold
values, LHTN, LFTN, RFTN and RHTN, may be provided in the form of
individual weight values, e.g., lbs., percentage of the total weight
on each of the load cells 68a-68d, ratios of load cell weights relative
to each other or to an armed weight, or the like. The following
Table 1 illustrates a portion of an example exit condition threshold
table wherein each set of normalized exit condition threshold values,
LHTN, LFTN, RFTN and RHTN, is provided in the form of individual
weight values. The example exit condition threshold table illustrated
in Table 1 is populated with a total of 78 sets of exit condition
threshold values (although only 10 such sets are shown) obtained
by discretely moving a 100 lb. calibration weight, CW, in approximately
equally-spaced location increments along the perimeter of the mattress
support frame 58, approximately 2.5 inches from each of the sides
and approximately one foot from each of the head and foot ends,
and recording the corresponding weight values or weight percentages
impressed upon each of the load cells 68a-68d. It will be understood,
however, that the data represented in Table 1, along with the particular
manner in which it is generated, is provided only by way of example,
and that Table 1 may alternatively be generated using other data
types, other predefined calibration weight values, other equally-spaced
or non-equally-spaced location increments, other spacings between
the calibration weight and the sides and/or ends of the mattress
support frame 58, and/or different total number of sets of exit
condition threshold values. Any such alternate implementation of
the exit condition threshold table, graph, chart or one or more
mathematical equations, is contemplated by this disclosure. TABLE-US-00001
TABLE 1 Exit Location LHTN (lbs.) LFTN (lbs.) RFTN (lbs.) RHTN (lbs.)
E0 92 15 -48 41 E1 88 19 -44 37 E2 84 24 -40 33 E3 79 29 -36 29
E4 75 33 -32 24 E5 71 38 -28 20 E6 66 42 -24 17 E7 62 46 -20 13
. . . . . . . . . . . . . . . E76 83 54 -41 10 E77 87 59 -45 5
[0100] Referring now to FIGS. 14A-14C, a flowchart is shown of
one illustrative embodiment of a software algorithm or routine for
executing the exit mode routine called by step 186 of the PM Off
State routine of FIGS. 7A-7C, by step 362 of the PM Exit/Movement
Transition State routine of FIGS. 10A and 10B and by step 452 of
the PM Active State routine of FIGS. 11A-11C. In the illustrated
embodiment, the exit mode algorithm or routine is configured to
implement two different decision criteria. One such decision criterion
eliminates one side 60c or 60d and either the head end 60a or foot
end 60b of the mattress 60, and scans the remaining side and end
for current load cell data. The controller 88 compares for each
selected side and end the current load cell values, LH, LF, RF,
and/or RH, for that side or end with corresponding computed exit
condition threshold values, LHT, LFT, RFT, and RHT, to determine
whether an exit condition is met. The exit condition threshold values,
LHT, LFT, RFT, and RHT, are computed by multiplying the normalized
exit condition threshold values, LHTN, LFTN, RFTN and RHTN, in the
exit condition threshold table, e.g., Table 1, by a ratio of the
corrected total patient weight, CTPW, and the calibration weight,
CW.
[0101] A second decision criterion implements a "difference
formula" that is applied only to the selected side 60c or 60d
of the mattress 60. As illustrated by example in FIG. 13, a total
weight 484.sub.1,2 of 80 lbs. may result from the sum of a 50 lb.
patient 480.sub.1,2 supported by the mattress 60 and a 30 lb. static
weight 482, e.g., in the form of medical equipment or other stationary
weight, supported by the mattress support frame 58 between the foot
end 60b of the mattress 60 and the foot end 64 of the bed 50. It
will be understood that the static weight 482 may alternatively
be supported by the mattress 60, the mattress support frame 58,
and/or the footboard 64b. In any case, the first decision criterion
reacts to movement of the total weight on the mattress 60, and does
not distinguish between the moving patient weight and stationary,
static weight 482. Thus, if the 50 lb. patient 480.sub.1,2 moves
from a first position 480.sub.1 on the mattress 60 to a second position
4802 adjacent to the right edge 60c of the mattress 60, e.g., at
E64, the first decision criterion will detect only movement of the
combined 80 lbs. of weight 484.sub.1,2 from a first position 484.sub.1
to a second position 484.sub.2 toward E52 which is not near the
edge of the mattress 60. Consequently, the first decision criterion
may not detect actual impending exit from the bed 50 of a lightweight
patient when a sufficient static weight 482 is also impressed on
the mattress 60, mattress support frame 58 and/or footboard 64b,
as illustrated by example in FIG. 13. This phenomenon becomes more
pronounced as the patient weight nears the static weight. The second
decision criterion using the aforementioned "difference formula"
is accordingly implemented to account for non-moving weight that
may be included in the total patent weight as illustrated by example
in FIG. 13. It will be appreciated that the difference formula may
alternatively be configured to account for static weight positioned
at or around the head end 62 of the bed 50, or at or around any
other particular location of the mattress, and any such modifications
to the software algorithms and/or routines described herein to accommodate
such alternative positioning of the static weight 482 are contemplated
by this disclosure. In any case, however, it will be noted that
the controller 88 is at no time operable to compute an actual position
of the patient 480.sub.1,2, the static weight 482, or the combined
weight 484.sub.1,2 relative to a reference position. Rather, the
scenario illustrated in FIG. 13 with respect to the patient 480.sub.1,2,
the static weight 482, and the combined weight 484.sub.1,2 is provided
only by way of example to illustrate a patient exit scenario that
the PE mode routine of FIGS. 14A and 14B is designed to address.
[0102] Referring again to FIGS. 14A and 14B, the exit routine begins
at step 500 where the controller 88 is operable to execute a sensitivity
determination routine. The exit mode routine illustrated in FIGS.
14A-14B may be called during any of several operating states of
the state machine 120. It is desirable to configure the sensitivity
of the exit mode routine differently depending upon which of the
operating states of the state machine 120 calls the exit mode routine,
and the sensitivity determination routine is accordingly operable
to scale the sensitivity of the first and second decision criteria
to the current values of the load cell weight values.
[0103] Referring to FIG. 14C, one illustrative embodiment of the
sensitivity determination routine of step 500 is shown. In the illustrated
embodiment, the sensitivity determination routine begins at step
531 where the controller 88 is operable to determine whether the
state machine 120 is currently in the PM Off State 122. If so, execution
of the routine advances to step 533 where the controller 88 is operable
to set a scale factor, SC, to a first scale factor value, SC1. The
scale factor, SC, scales the sensitivity of the first decision criterion
of the exit mode algorithm to current load cell weight values, as
will be described in greater detail hereinafter. In any case, the
controller 88 is further operable at step 533 to define equations
for a second left side exit adjust clamp value, EXAL.sub.CL2 and
also for a second right side exit adjust clamp value, EXAR.sub.CL2.
In the illustrated embodiment, EXAL.sub.CL2 and EXAR.sub.CL2 are
generally defined as a function of one or more constants, represented
by the constant vector, A, and the corrected total patient weight.
In one specific embodiment, EXAL.sub.CL2=EXAR.sub.CL2=A1 when CTPW>W.sub.TH,
and otherwise EXAL.sub.CL2=EXAR.sub.CL2=A2, where A1 and A2 are
constants, and W.sub.TH is a threshold weight value, e.g., 40 lbs.
EXAL.sub.CL2 and EXAR.sub.CL2 scale the sensitivity of the second
decision criterion of the exit mode algorithm to current load cell
weight values, as will be described in greater detail hereinafter.
It will be appreciated that EXAL.sub.CL2 and EXAR.sub.CL2 may alternatively
be defined according to other functions of A and CTPW, and/or according
to functions of additional or different parameters, without detracting
from the scope of the claims appended hereto. In any case, if the
controller 88 determines at step 531 that the state machine 120
is not currently in the PM Off State 122, execution of the routine
advances to step 535 where the controller 88 is operable to determine
whether the state machine 120 is currently in the PM Movement/Exit
Transition State 128.
[0104] If, at step 535, the controller 88 determines that the state
machine 120 is currently in the PM Movement/Exit Transition State
128, execution of the routine advances to step 537 where the controller
88 is operable to determine whether the PM mode or the PE mode has
been selected in the PM Movement/Exit Transition State 128. If the
patient movement (PM) mode has been selected, execution of the routine
advances to step 539 where the controller 88 is operable to set
the scale factor, SC, to a second scale factor value, SC2. The controller
88 is further operable at step 539 to define equations for the second
left side exit adjust clamp value, EXAL.sub.CL2 and also for the
second right side exit adjust clamp value, EXAR.sub.CL2. In the
illustrated embodiment, EXAL.sub.CL2 and EXAR.sub.CL2 are generally
defined as a function of one or more constants, represented by the
constant vector, B, and the corrected total patient weight. In one
specific embodiment, EXAL.sub.CL2=EXAR.sub.CL2=B1 when CTPW>W.sub.TH,
and otherwise EXAL.sub.CL2=EXAR.sub.CL2=B2, where B1 and B2 are
constants, and W.sub.TH is a threshold weight value, e.g., 40 lbs.
It will be appreciated that EXAL.sub.CL2 and EXAR.sub.CL2 may alternatively
be defined according to other functions of B and CTPW, and/or according
to functions of additional or different parameters, without detracting
from the scope of the claims appended hereto. In any case, if the
controller 88 determines step 537 that the PE mode was instead selected
in the PM Movement/Exit Transition State 128, execution of the routine
advances to step 541 where the controller 88 is operable to set
the scale factor, SC, to a third scale factor value, SC3. The controller
88 is further operable at step 541 to define equations for the second
left side exit adjust clamp value, EXAL.sub.CL2 and also for the
second right side exit adjust clamp value, EXAR.sub.CL2. In the
illustrated embodiment, EXAL.sub.CL2 and EXAR.sub.CL2 are generally
defined as a function of one or more constants, represented by the
constant vector, C, and the corrected total patient weight. In one
specific embodiment, EXAL.sub.CL2=EXAR.sub.CL2=C1 when CTPW>W.sub.TH,
and otherwise EXAL.sub.CL2=EXAR.sub.CL2=C2, where C1 and C2 are
constants, and W.sub.TH is a threshold weight value, e.g., 40 lbs.
It will be appreciated that EXAL.sub.CL2 and EXAR.sub.CL2 may alternatively
be defined according to other functions of C and CTPW, and/or according
to functions of additional or different parameters, without detracting
from the scope of the claims appended hereto. It will be further
appreciated that any two or more of SC1, SC2 and SC3 may have identical
values or they may instead all have different values. Likewise,
any two or more of the constant vectors A, B and C may contain identical
constant values, or they may instead all contain different constant
values. In any case, if the controller 88 determines at step 535
that the state machine 120 is not current in the PM Movement/Exit
Transition State 128, execution of the routine advances to step
543 where the controller 88 is operable to determine whether the
state machine 120 is currently in the PM Active State 130.
[0105] If, at step 543, the controller 88 determines that the state
machine 120 is currently in the PM Active State 130, execution of
the routine advances to step 545 where the controller 88 is operable
to determine whether the PM mode is being executed in the PM Active
State 128. If so, execution of the routine advances to step 547
where the controller 88 is operable to set the scale factor, SC,
to a fourth scale factor value, SC4. The controller 88 is further
operable at step 547 to define equations for the second left side
exit adjust clamp value, EXAL.sub.CL2 and also for the second right
side exit adjust clamp value, EXAR.sub.CL2. In the illustrated embodiment,
EXAL.sub.CL2 is generally defined as a function of one or more constants,
represented by the constant vector, D, and as a function of a first
left side exit adjust clamp value, EXAL.sub.CL1, and EXAR.sub.CL2
is generally defined as a function of D and as a function of a first
right side exit adjust clamp value, EXAR.sub.CL1. In one specific
embodiment, EXAL.sub.CL2=EXAL.sub.CL- 1-D1, and if EXALCL.sub.2<D2
then EXAL.sub.CL2=D2 and if EXAL.sub.CL2>D3 then EXAL.sub.CL2=D3,
where D1, D2 and D3 are constants. In this embodiment, EXAR.sub.CL2
is similarly defined according to the equations EXAR.sub.CL2=EXAR.sub.CL1-D1,
and if EXAR.sub.CL2<D2 then EXAR.sub.CL2=D2 and if EXAR.sub.CL2>D3
then EXAR.sub.CL2=D3. It will be appreciated that EXAL.sub.CL2 and
EXAR.sub.CL2 may alternatively be defined according to other functions
of D, EXAL.sub.CL1 and EXAR.sub.CL1, and/or according to functions
of additional or different parameters, without detracting from the
scope of the claims appended hereto. In any case, if the controller
88 determines step 545 that the PM mode is not being executed in
the PM Active State 130, execution of the routine advances to step
549 where the controller 88 is operable to determine whether the
patient exit (PE) mode is being executed in the PM Active State
130.
[0106] If the controller determines at step 549 that the PE mode
is being executed in the PM Active state 130, execution of the routine
advances to step 551 where the controller 88 is operable to set
the scale factor, SC, to a fourth scale factor value, SC5. The controller
88 is further operable at step 551 to define equations for the second
left side exit adjust clamp value, EXAL.sub.CL2 and also for the
second right side exit adjust clamp value, EXAR.sub.CL2. In the
illustrated embodiment, EXAL.sub.CL2 and EXAR.sub.CL2 are generally
defined as a function of one or more constants, represented by the
constant vector, E, and as a function of the corrected total patient
weight, CTPW. In one specific embodiment, EXAL.sub.CL2=EXAR.sub.CL2=(E1-CTPW)/E2
if CTPW<E3, and EXAL.sub.CL2=EXAR.sub.CL2=(CTPW-E4)/(MAW-E5)
if CTPW>E6, where E1-E6 are constants and MAW is a maximum armed
weight value. It will be appreciated that EXAL.sub.CL2 and EXAR.sub.CL2
may alternatively be defined according to other functions of E and
CTPW, and/or according to functions of additional or different parameters,
without detracting from the scope of the claims appended hereto.
It will be further appreciated that any two or more of SC1, SC2,
SC3, SC4 and SC5 may have identical values or they may instead all
have different values. Likewise, any two or more of the constant
vectors A, B, C, D and E may contain one or more identical constant
values, or they may instead all contain different constant values.
In any case, execution of the sensitivity determination routine
advances from steps 533, 539, 541, 547, 551 and the "NO"
branches of steps 543 and 549 to the return step 553.
[0107] The sensitivities of the first and second decision criteria
of the Exit Mode routine of FIGS. 14A-14B are thus determined by
the sensitivity determination routine of FIG. 14C. As the sensitivities
of the first and second decision criteria increase, the movement
required by the patient toward any edge of the bed 50 before any
of the exit conditions are violated will decrease. Conversely, as
the sensitivities of the first and second decision criteria decrease,
the movement required by the patient toward any edge of the bed
50 before any of the exit conditions are violated will increase.
When arming the system in the PM Movement/Exit Transition State
128 for subsequent execution of either of the patient exit (PE)
or patient movement (PM) modes, the sensitivities of the first and
second decision criteria are increased over what they would otherwise
be when executing the PM or PE modes. This makes the first and second
decision criteria very sensitive to movement of the patient toward
any edge of the bed and thereby effectively defines the safe arming
zone as a region of the mattress 60 that is remote from any edge
of the bed 50 and therefore substantially central to the mattress
60. To arm the system for transition of the state machine 120 from
the PM Movement/Exit Transition State 128 to the PM Active State
130, the patient will accordingly be required to be positioned approximately
centrally on the mattress 60. If the patient is instead outside
of the safe arming zone when attempting to arm the system, the local
alarm will chirp some number of times and the state machine 120
will return to the PM Off State 122 as illustrated in the flowchart
of FIGS. 10A-10C. In order to properly arm the system for transition
of the state machine 120 from the PM Movement/Exit Transition State
128 to the PM Active State 130, it will be necessary for a caregiver
to position or reposition the patient approximately centrally on
the mattress 60.
[0108] Referring again to FIG. 14A, the exit mode routine advances
from step 500 to step 501 where the controller 88 is operable to
determine which load cells to monitor for potential exit conditions
relating to one side or the other of the mattress 60. In the illustrated
embodiment, the controller 88 is operable to determine whether RF>LF
and RH>LF. If not, execution of the routine advances to step
502 where the controller 88 is operable to scan a subset of the
exit condition threshold table having sets of exit condition threshold
values defined at the left side 60d of the mattress 60. Thereafter
at step 503, the controller 88 is operable to execute the first
decision criterion by comparing the current left head load cell
value, LH, with a scaled representation of the Ith left head load
cell threshold value, SC*LHT_I, in the scan, where LHT_I=LHTN(I)*(CTPW/CW),
and where LHTN(I) is the LHTN value in the Ith set of exit condition
threshold values of the exit condition threshold table, e.g., Table
1. The controller 88 is further operable at step 503 to compare
the current left foot load cell value, LF, with a scaled representation
of the Ith left foot load cell threshold value, SC*LFT_I, in the
scan, where LFT_I=LFTN(I)*(CTPW/CW), and where LFTN(I) is the LFTN
value in the Ith set of exit condition threshold values of the exit
condition threshold table, e.g., Table 1. In any case, if both conditions
are met, i.e., if LH>SC*LHT_I and LF>LFT_I, execution of the
routine advances to step 544 where the controller 88 is operable
to compare an exit counter to a counter limit, CL. If the exit counter
is greater than CL, execution of the routine advances to step 546
where the controller 88 is operable to set a patient exiting zone
flag, PEZ, to "true" to thereby indicate that the patient
is not in the safe arming zone of the bed 50 as described hereinabove.
Thereafter at step 547, the controller 88 is operable to determine
whether the state machine 120 is currently operating in the PM Active
State 130. If not, no alarms will be activated and execution of
the routine instead advances to the return step 552. If, on the
other hand, the controller 88 determines at step 547 that the state
machine 120 is currently operating in the PM Active State 130, execution
of the routine advances to step 548 where the controller 88 is operable
to set the remote alarm flag to an active state and to set the local
alarm flag to an active state. Thereafter at step 549 the state
machine moves to the PM Alarm State 136, and the controller 88 is
accordingly operable to execute the PM Alarm State routine of FIG.
12. If, at step 544, the controller 88 determines that the exit
counter is not greater than the counter limit, CL, execution of
the routine advances to step 550 where the controller 88 is operable
to increment the exit counter. Thereafter, execution of the exit
mode routine advances to the return step 552.
[0109] If, at step 503 the controller 88 determines that at least
one of the illustrated conditions is not true, execution of the
routine advances to step 504 where the controller 88 is operable
to execute the second decision criterion by comparing the current
left foot load cell value, LF, with a scaled representation of the
Ith left foot load cell threshold value, SC*LFT_I, in the scan,
where LFT_I=LFTN(I)*(CTPW/CW), and LFTN(I) is the LFTN value in
the Ith set of exit condition threshold values of the exit condition
threshold table, e.g., Table 1. The controller 88 is then operable
to set a foot variable, FOOT_I, equal to the current value of "I"
if LF is greater than SC*LFT_I. Thereafter at step 506, the controller
88 is likewise operable to compare the current left head load cell
value, LH, with a scaled representation of the Ith left head load
cell threshold value, SC*LHT_I, in the scan, where LHT_I=LHTN(I)*(CTPW/CW),
and LHTN(I) is the LHTN value in the Ith set of exit condition threshold
values of the exit condition threshold table, e.g., Table 1. The
controller 88 is then operable to set a head variable, HEAD_I, equal
to the current value of "I" if LH is greater than SC*LHT_I.
Thereafter at step 508, the controller 88 is operable to compute
a possible left side exit condition as an average of FOOT_I and
HEAD_I, e.g., according to the equation AVGI=(FOOT_I-HEAD_I)/2.
In an alternative embodiment of the exit mode routine, step 503
may be implemented after step 508 where the AVGI value is computed.
[0110] From step 508, execution of the routine advances to step
510 where the controller 88 is operable to compute a left-side exit
adjust value, EXAL, where EXAL is inversely proportional to the
amount of static load located at the foot end 64 of the bed 50.
In the illustrated embodiment, the controller 88 is operable to
compute EXAL according to the equation EXAL=[(LHT_AVGI-LH)/(RF-RFT_AVGI)]/EXAC,
where LHT_AVGI=LHTN_AVGI*CTPW/CW- , RFT_AVGI=RFTN_AVGI*CTPW/CW,
EXAC is an exit adjust constant, and LHTN_AVGI and RFTN_AVGI are
the LHTN and RFTN values in the Ith set of exit condition threshold
values of the exit condition threshold table, e.g., Table 1. It
will be understood that this formula for EXAL represents a specific
implementation of a more general equation for EXAL for one specific
type of hospital bed 50, i.e., the VersaCare bed described hereinabove.
A more general EXAL formula that may be applied to other embodiments
of the bed 50 is EXAL=[[(LHT_AVGI-LH)/(RF-RFT_AVGI)]+[(- RHT_AVGI-RH)/(LF-LFT_AVGI)]]/EXAC,
where LHT_AVGI=LHTN_AVGI*CTPW/CW, RFT_AVGI=RFTN_AVGI*CTPW/CW, RHT_AVGI=RHTN_AVGI*CTPW/CW,
LFT_AVGI=LFTN_AVGI*CTPW/CW, EXAC is the exit adjust constant, and
LHTN_AVGI, RFTN_AVGI, RHTN_AVGI and LFTN_AVGI are the LHTN, RFTN,
RHTN and LFTN values in the Ith set of exit condition threshold
values of the exit condition threshold table, e.g., Table 1.
[0111] Execution of the routine advances from step 510 to step
512 where the controller 88 is operable to compute the percentage
of LF relative to the corrected total patient weight, CTPW according
to the equation LF %=LF/CTPW, and to then determine a first clamped
left-side exit adjust value, EXAL.sub.CL1, as a function of LF %.
In one embodiment, the function of LF % is configured such that
EXAL.sub.CL1 is decreased as LF % increases. EXAL.sub.CL1 may be
alternatively or additionally determined as a function of AVGI,
for example, according to the equation EXAL.sub.CL1=EXAL.sub.CL1-K1*(AVGI-K2),
where K1 and K2 are constants. EXAL.sub.CL1 may be alternatively
or additionally still determined as a function of the corrected
total patient weight, CTPW, for example, according to the equation
EXAL.sub.CL1=EXAL.sub.CL1+K3*(CTPW-K4), where K3 and K4 are constants.
[0112] In any case, execution of the exit mode routine advances
from step 512 to step 513 where the controller 88 is operable to
compute the second clamped left side exit adjust value, EXAL.sub.CL2,
according to an appropriate one of the equations established by
the sensitivity determination routine of FIG. 14C. Thereafter at
step 514, the controller 88 is operable in one embodiment to compute
the following values, TA=(LH-RH), TB=EXAL.sub.CL2*(LHT_AVGI-RHT_AVGI),
TC=LF-RF and TD=EXAL.sub.CL2*(LFT_AVGI-RFT_AVGI), where LHT_AVGI,
LFT_AVGI, RHT_AVGI, and RFT_AVGI correspond to the AVGIth set of
LHTN, RHTN, LFTN and RFTN exit condition threshold values in the
exit condition threshold table, e.g., Table 1, each multiplied by
(CTPW*CW). In an alternative embodiment, the equations for TB and
TD may omit EXAL.sub.CL2 so that TB=(LHT_AVGI-RHT_AVG_I) and TD=(LFT_AVGI-RFT_AVGI).
In any case, execution of the routine advances to step 516 where
the controller 88 is operable to compare the relationship (TA-TB)+(TC-TD)
to zero. If the controller 88 determines at step 516 that (TA-TB)+(TC-TD)>0,
a potential impending exit condition is identified and execution
of the routine advances to step 544. If, at step 516, the controller
88 determines that (TA-TB)+(TC-TD) is not greater than zero, an
impending exit condition is not identified and execution of the
routine advances to step 554 where the controller 88 is operable
to clear the exit counter. The controller 88 is operable thereafter
at step 555 to set the patient exiting zone flag, PEZ, to "false",
to thereby indicate that the patient is in the safe arming zone
of the bed 50 as described hereinabove. Execution of the exit state
routine advances from step 555 to the return step 552.
[0113] If, at step 500, the controller 88 determines that RF>LF
AND RH>LF, execution of the routine advances to step 518 where
the controller 88 is operable to scan a subset of the exit condition
threshold table having sets of exit condition threshold values defined
at the right side 60c of the mattress 60. Thereafter at step 519,
the controller 88 is operable to execute the first decision criterion
by comparing the current right head load cell value, RH, with a
scaled representation of the Ith right head load cell threshold
value, SC*RHT_I, in the scan, where RHT_I=RHTN(I)*(CTPW/CW), and
where RHTN(I) is the RHTN value in the Ith set of exit condition
threshold values of the exit condition threshold table, e.g., Table
1. The controller 88 is further operable at step 519 to compare
the current right foot load cell value, RF, with a scaled representation
of the Ith right foot load cell threshold value, SC*RFT_I, in the
scan, where RFT_I=RFTN(I)*(CTPW/CW), and where RFTN(I) is the RFTN
value in the Ith set of exit condition threshold values of the exit
condition threshold table, e.g., Table 1. In any case, if both conditions
are met, i.e., if RH>SC*RHT_I and RF>RFT_I, execution of the
routine advances to step 544.
[0114] If, at step 519 the controller 88 determines that at least
one of the illustrated conditions is not true, execution of the
routine advances to step 520 where the controller 88 is operable
to execute the second decision criterion by comparing the current
right foot load cell value, RF, with a scaled representation of
the Ith right foot load cell threshold value, SC* RFT_I, in the
scan, where RFT_I=RFTN(I)*(CTPW/CW), and RFTN(I) is the RFTN value
in the Ith set of exit condition threshold values of the exit condition
threshold table, e.g., Table 1. The controller 88 is then operable
to set a foot variable, FOOT_I, equal to the current value of "I"
if RF is greater than SC*RFT_I. Thereafter at step 522, the controller
88 is likewise operable to compare the current left head load cell
value, RH, with a scaled representation of the Ith right head load
cell threshold value, SC*RHT_I, in the scan, where RHT_I=RHTN(I)*
(CTPW/CW), and RHTN(I) is the RHTN value in the Ith set of exit
condition threshold values of the exit condition threshold table,
e.g., Table 1. The controller 88 is then operable to set a head
variable, HEAD_I, equal to the current value of "I" if
RH is greater than SC*RHT_I. Thereafter at step 524, the controller
88 is operable to compute a possible right side exit condition as
an average of FOOT_I and HEAD_I, e.g., according to the equation
AVGI=(FOOT_I-HEAD_I)/2. In an alternative embodiment of the exit
mode routine, step 519 may be implemented after step 524 where the
AVGI value is computed.
[0115] From step 524, execution of the routine advances to step
526 where the controller 88 is operable to compute a right-side
exit adjust value, EXAR, where EXAR is inversely proportional to
the amount of static load located at the foot end 64 of the bed
50. In the illustrated embodiment, the controller 88 is operable
to compute EXAR according to the equation EXAR=[(RHT_AVGI-RH)/(LF-LFT_AVGI)]/EXAC,
where RHT_AVGI=RHTN_AVGI*CTPW/CW- , LFT_AVGI=LFTN_AVGI*CTPW/CW,
EXAC is an exit adjust constant, and RHTN_AVGI and LFTN_AVGI are
the RHTN and LFTN values in the Ith set of exit condition threshold
values of the exit condition threshold table, e.g., Table 1. It
will be understood that this formula for EXAR represents a specific
implementation of a more general equation for EXAR for one specific
type of hospital bed 50, i.e., the VersaCare bed described hereinabove.
A more general EXAR formula that may be applied to other embodiments
of the bed 50 is EXAR=[[(RHT_AVGI-RH)/(LF-LFT_AVGI)]+[(- LHT_AVGI-LH)/(RF-RFT_AVGI)]]/EXAC,
where RHT_AVGI=RHTN_AVGI*CTPW/CW, LFT_AVGI=LFTN_AVGI*CTPW/CW, LHT_AVGI=LHTN_AVGI*CTPW/CW,
RFT_AVGI=RFTN_AVGI*CTPW/CW, EXAC is the exit adjust constant, and
RHTN_AVGI, LFTN_AVGI, LHTN_AVGI and RFTN_AVGI are the RHTN, LFTN,
LHTN and RFTN values in the Ith set of exit condition threshold
values of the exit condition threshold table, e.g., Table 1.
[0116] Execution of the routine advances from step 526 to step
528 where the controller 88 is operable to compute the percentage
of RF relative to the corrected total patient weight, CTPW according
to the equation RF %=RF/CTPW, and to then determine a first clamped
right-side exit adjust value, EXAR.sub.CL1, as a function of RF
%. In one embodiment, the function of RF % is configured such that
EXAR.sub.CL1 is decreased as RF % increases. EXAR.sub.CL1 may be
alternatively or additionally determined as a function of AVGI,
for example, according to the equation EXAR.sub.CL1=EXAR.sub.CL1-K1*(AVGI-K2),
where K1 and K2 are constants. EXAR.sub.CL1 may be alternatively
or additionally still determined as a function of the corrected
total patient weight, CTPW, for example, according to the equation
EXAR.sub.CL1=EXAR.sub.CL1+K3*(CTPW-K4), where K3 and K4 are constants.
[0117] Execution of the exit mode routine advances from step 528
to step 529 where the controller 88 is operable to determine the
second clamped right-side exit adjust value, EXAR.sub.CL2, according
to an appropriate one of the equations established by the sensitivity
determination routine of FIG. 14C Execution of the routine then
advances from step 529 to step 530 where the controller 88 is operable
to compute the following values, TA=(RH-LH), TB=EXAR.sub.CL2*(RHT_AVGI-LHT_AVGI),
TC=RF-LF and TD=EXAR.sub.CL2*(RFT_AVGI-LFT_AVGI), where LHT_AVGI,
LFT_AVGI, RHT_AVGI, and RFT_AVGI correspond to the AVGIth set of
LHTN, RHTN, LFTN and RFTN exit condition threshold values in the
exit condition threshold table, e.g., Table 1, each multiplied by
(CTPW*CW). In an alternative embodiment, the equations for TB and
TD may omit EXAR.sub.CL2 so that TB=(RHT_AVGI-LHT_AVG_I) and TD=(RFT_AVGI-LFT_AVGI).
In any case, execution of the routine advances to step 532 where
the controller 88 is operable to compare the relationship (TA-TB)+(TC-TD)
to zero. If the controller 88 determines at step 532 that (TA-TB)+(TC-TD)>0,
a potential impending exit condition is identified and execution
of the routine advances to step 544. If, at step 532, the controller
88 determines that (TA-TB)+(TC-TD) is not greater than zero, an
impending exit condition is not identified and execution of the
routine advances to step 554.
[0118] Along with step 501, the controller 88 is operable to execute
step 534 where the controller 88 is operable to determine which
load cells to monitor for potential exit conditions relating to
the head end 60a or the foot end 60b of the mattress 60. In the
illustrated embodiment, the controller 88 is operable at step 534
to determine whether RF>RH AND LF>LH. If so, execution of
the routine advances to step 536 where the controller 88 is operable
to scan a subset of the exit condition threshold table having sets
of exit condition threshold values defined at the foot end 60b of
the mattress 60. Thereafter at step 538, the controller 88 is operable
to execute the first decision criterion by comparing the current
right foot load cell value, RF, with a scaled representation of
the Ith right foot load cell threshold value, SC*RFT_I, in the scan,
where RFT_I=RFTN(I)*(CTPW/CW), and where RFTN(I) is the RFTN value
in the Ith set of exit condition threshold values of the exit condition
threshold table, e.g., Table 1. The controller 88 is further operable
at step 538 to compare the current left foot load cell value, LF,
with a scaled representation of the Ith left foot load cell threshold
value, SC*LFT_I, in the scan, where LFT_I=LFTN(I)*(CTPW/CW), and
where LFTN(I) is the LFTN value in the Ith set of exit condition
threshold values of the exit condition threshold table, e.g., Table
1. If both conditions are met, i.e., if RF>SC*RFT_I and RH>SC*RHT_I,
execution of the routine advances to step 544. If, at step 538 the
controller 88 determines that at least one of the illustrated conditions
is not true, execution of the routine advances to step 554.
[0119] If, at step 534, the controller 88 determines that at least
one of the illustrated conditions is not true, execution of the
routine advances to step 540 where the controller 88 is operable
to scan a subset of the exit condition threshold table having sets
of exit condition threshold values defined at the head end 60a of
the mattress 60. Thereafter at step 542, the controller 88 is operable
to execute the first decision criterion by comparing the current
right head load cell value, RH, with a scaled representation of
the Ith right head load cell threshold value, SC*RHT_I, in the scan,
where RHT_I=RHTN(I)*(CTPW/CW), and where RHTN(I) is the RHTN value
in the Ith set of exit condition threshold values of the exit condition
threshold table, e.g., Table 1. The controller 88 is further operable
at step 542 to compare the current left head load cell value, LH,
with a scaled representation of the Ith left head load cell threshold
value, SC*LHT_I, in the scan, where LHT_I=LHTN(I)*(CTPW/CW), and
where LHTN(I) is the LHTN value in the Ith set of exit condition
threshold values of the exit condition threshold table, e.g., Table
1. If both conditions are met, i.e., if RH>SC*RHT_I and LH>SC*LHT_I,
execution of the routine advances to step 544. If, at step 538 the
controller 88 determines that at least one of the illustrated conditions
is not true, execution of the routine advances to step 554.
[0120] In one exemplary embodiment of the system 75, the controller
88 is configured, pursuant to the patient movement (PM) mode of
the PM Active State 130, to identify excessive movement of the patient
relative to a reference load cell distribution by comparing the
current distribution of the patient's weight over the two or three
of the load cells 68a-68d to a predefined collection of load cell
movement threshold data. In the illustrated embodiment, this predefined
collection of load cell movement data is provided in the form of
a number of tables of a number of sets of load cell movement threshold
values, although the collection of load cell movement data may alternatively
provided in the form of one or more equations, graphs, charts or
the like.
[0121] Referring now to FIGS. 15-17, a diagram of the bed 50 is
shown illustrating one example implementation and construction of
two such tables of load cell movement threshold values. In this
example, load cell movement threshold data for the first load cell
movement threshold table, Table 2, is established according to a
model of patient movement within a hospital bed such as the hospital
bed 50 illustrated and described hereinabove with respect to FIGS.
1A-1C. Referring specifically to FIG. 15, a patient 570 is shown
elevating an upper body portion from a prone position to an incline
position, with an angular displacement therebetween of approximately
AX=45 degrees. UPW is defined as the portion of the corrected total
patient weight, CTPW, attributable to the upper body portion of
the patient 570, and LPW is defined as the portion of CTPW attributable
to the lower body portion of the patient 570. WRP is defined as
the reaction force of the mattress 60 to the patient's weight, CTPW,
and XA is defined as the distance between M, the bending point of
patient 570, and WRP. PL is defined as the length, or height, of
the patient from head to feet. Assuming that LPW is approximately
equal to UPW, and assuming that the length of the patient from the
patient's waist to the patient's feet is 2*PL/3 and the length of
the patient from the patient's waist to the top of the patient's
head is PL/3, it can be shown via known physical principles that
the patient's weight shifts a distance of approximately 0.024 PL,
or approximately 2.4% of the patient's length in the X direction,
which is parallel to the length of the patient, when the patient
sits up from a prone position to about 45 degrees as illustrated
in FIG. 15.
[0122] Referring specifically to FIG. 16, the patient 570 of width
PW is shown rolling approximately 45 degrees to one side. Assuming
PW=PL/4, it can be shown via known physical principles that the
patient's weight shifts a distance of approximately 0.036 PL, or
approximately 3.5% of the patient's length in the Y direction, which
is transverse to the length of the patient, when the patient rolls
sideways from a prone position, with the patient's back lying on
the mattress 60, to a position of about 45 degrees from the prone
position as illustrated in FIG. 16.
[0123] Patient movement in a hospital bed is modeled as a combination
of the two different movement types illustrated in FIGS. 15 and
16. In other words, typical movement of a patient lying in a hospital
bed is modeled as a combination of side-rolling and raising of the
upper body portion. From the above relationships, the ratio of patient
movement in the X direction relative to the Y direction is thus
approximately 1.5:1.
[0124] Depending upon the bed type, the distance between the load
cells 68a and 68c (or 68b and 68d) may be 2-3 times more than the
distance between the load cells 68a and 68b (or 68c and 68d). Assuming
that this distance ratio is 1:2, then it takes twice as much movement
from the head end 60a toward the foot end 60b (or vice versa) of
the mattress 60 as compared with movement from the side 60c to the
side 60d (or vice versa) of the mattress 60 to get the same amount
of weight distribution.
[0125] Combining these two effects, the ratio of redistribution
of weight on the load cells 68a-68d is approximately 3:1 when the
patient moves in the X direction relative to the Y direction. In
the head-raising model, it was assumed that LPW:UPW=1:1, although
it should be noted that when a sick patient exits a hospital bed
the back is generally curved when the head is raised. A more realistic
assumption for LPW:UPW is thus between 1:1 and 1:2, resulting in
a net effective load cell redistribution ratio of approximately
4:1, which implies that the patient weight shift seen by the load
cells 68a-68d will be approximately 4 times as great when the patient
rolls approximately 45 degrees to the side as compared to when the
patient sits up at approximately 45 degrees.
[0126] Implementing the above relationships in a patient movement
model, the effect on the four load cells 68a-68d of patient movement
in any direction is modeled as a combination of movement in the
X direction (sine) and movement in the Y direction (cosine) according
to an equation of the form PCLC=+/-((CTPW/4)*(1/S)*Cos(A))+/-((CTPW/4)*(1/S)*(1/4)*Sin(A-
)), wherein PCLC corresponds to the percentage weight change seen
by any of the four load cells 68a-68d, CTPW is the corrected total
patient weight, "S" is a sensitivity value, and "A"
is the angle of patient movement relative to a reference direction.
CTPW/4 represents the approximated average of total weight seen
by each of the four load cells, and the additional 1/4 factor multiplying
the sine function represents the 4:1 net effective load cell ratio
just described.
[0127] Referring specifically to FIG. 17, the above equation is
applied to the surface of the mattress 60 or mattress support frame
58, resulting in the following four equations relating the above
PCLC relationship to the percentage weight change seen by each of
the load cells RHLC, RFLC, LFLC and LHLC, PCRH=((CTPW/4)*(1/S)*Cos(A))+((CTPW/4)*(1/S)*(1/4)*Sin(A))
(1), PCRF=((CTPW/4)*(1/S)*Cos(A))-((CTPW/4)*(1/S)*(1/4)*Sin(A))
(2), PCLF=-((CTPW/4)*(1/S)*Cos(A)/)-((CTPW/4)*(1/S)*(1/4)*Sin(A))
(3), PCLH=-((CTPW/4)*(1/S)*Cos(A))+((CTPW/4)*(1/S)*(1/4)*Sin(A))
(4).
[0128] By applying equations (1)-(4) to an arbitrary point on the
surface 65 of the mattress 60, patent movement in any direction
about a periphery 580 of that arbitrary point may be monitored.
Resolution of such patient movement monitoring is determined by
the number of sectors defining a 360-degree virtual boundary about
the arbitrary point, and the total number of sectors is determined
by the increment value used for the angle "A." In the
illustrated example, the angle "A" is advanced at 5-degree
increments, thereby creating 72 sectors radiating outwardly from
an arbitrary and unknown point. More or fewer sectors may be defined
via an appropriate choice of increments of the angle, "A."
[0129] To establish threshold violation criteria for equations
(1)-(4), the corrected total patient weight, CTPW, sensitivity,
S, and constant values in these equations are represented by constants,
K1 and K2, such that the above set of equations are reduced to the
following set of calibration equations: RHT=K1*Cos(A)+K2*Sin(A)
(5), RFT=K1*Cos(A)-K2*Sin(A) (6), LFT=-K1*Cos(A)-K2*Sin(A) (7),
LHT=-K1*Cos(A)+K2*Sin(A) (8), [0130] where PCRH, PCRF, PCLF and
PCLH are replaced in equations (5)-(8) with corresponding threshold
values, RHT, RFT, LFT and LHT.
[0131] The calibration equations (5)-(8) are used to generate a
first one of the tables, Table 2, of load cell movement threshold
values. More particularly, Table 2 is populated by a number of sets
of movement threshold values forming the load cell movement threshold
data, wherein equations (5)-(8) are used to define each set of movement
threshold values for a given angle, "A." The following
example of Table 2 illustrates a portion of a first collection of
movement condition threshold value sets, wherein each set of the
movement condition threshold values, RHT, RFT, LFT and LHT, is provided
in the form of a percentage value. In the illustrated example, K1=132
and K2=33, although it will be understood that other values may
be used. Specific values for K1 and K2 will typically depend upon
the application, and may be determined experimentally. The K1 and
K2 values may further be refined using one or more conventional
optimization techniques. In any case, the example movement condition
threshold table illustrated by Table 2 is populated with a total
of 72 sets of movement condition threshold values (although only
10 such sets are shown) using angle increments of 5 degrees. It
will be understood, however, that the data represented in Table
2, along with the particular manner in which it is generated, is
provided only by way of example, and that Table 2 may alternatively
be generated using other data types, other angle increment values,
and more, fewer and/or different models and/or model parameters.
Any such alternate implementation of the illustrated movement condition
threshold table, graph, chart or one or more mathematical equations,
is contemplated by this disclosure. TABLE-US-00002 TABLE 2 Angle/Sector
RHT (%) RFT (%) LFT (%) LHT (%) 0/0 132 132 -132 -132 5/1 134 129
-134 -129 10/2 136 124 -136 -124 15/3 136 119 -36 -119 20/4 135
113 -135 -113 25/5 134 106 -34 -106 30/6 131 98 -131 -98 45/7 127
89 -127 -89 . . . . . . . . . . . . . . . 350/70 124 136 -124 -136
355/71 129 134 -129 -134
[0132] If any three of the four percentage weight change values,
PCRH, PCRF, PCLF and PCLH, computed by equations (1)-(4) are greater
than corresponding three of the four percentage movement condition
threshold values of any one set of movement condition threshold
values of Table 2 for a given corrected total patient weight, CTPW,
and sensitivity value, S, the controller 88 determines that a "bounded
movement condition" is satisfied and the controller 88 is operable
to activate an alarm as will be described more fully hereinafter
with respect to the patient movement (PM) mode routine illustrated
by example in FIG. 18. Optionally, the corrected total patient weight,
CTPW, may be reduced by a specified weight value before calculating
any of equations (1)-(4) for the purpose of reducing the thresholds,
RHT, RFT, LFT, LHT, that would be expected in the case of light
weight patients in the presence of relatively heavy equipment 482
on the bed 50. In any case, Table 2 may thus be referred to hereinafter
as a "bounded movement condition threshold" table, data
set or collection of data.
[0133] It may further be desirable to specify an upper boundary
to avoid prematurely satisfying bounded conditions of neighboring
sectors. As one specific example of an implementation using an upper
boundary, UB, a given set of sector conditions may be satisfied
by any three of the following four conditions:
[0134] LH has increased by at least 11% of CTPW but by no more
than 11%+(UB/4)% since armed,
[0135] LF has increased by at least 11% of CTPW but by no more
than 11%+(UB/4)% since armed,
[0136] RH has decreased by at least 11% of CTPW but by no more
than 11%+(UB/4)% since armed, and [0137] RF has decreased by at
least 11% of CTPW but by no more than 11%+(UB/4)% since armed.
[0138] If a patient changes position at a rate that is higher than
the response time of the system 75, it is possible that certain
ones of the bounded set of conditions may not detected. To address
such possibilities, an unbounded set of conditions is also examined.
The number of unbounded conditions will typically be small in any
implementation, and any one collection of unbounded movement condition
threshold sets may require only two or three load cell conditions
to be satisfied. Thresholds are determined experimentally by considering
a number, e.g., 12, of different directions in which the patient
can move. Table 3 below illustrates a second collection of movement
condition threshold value sets, wherein each set of the movement
condition threshold values, RHTN, RFTN, LFTN and LHTN, is provided
in the form of a normalized percentage value: TABLE-US-00003 TABLE
3 LHTN LFTN RFTN (%) (%) (%) RHTN (%) Movement Detected 25 -25 0
0 from head -25 25 0 0 from foot 0 111 -111 0 from left 0 -111 111
0 from right 0 0 25 -25 from foot 0 0 -25 25 from head -111 0 0
111 right roll 111 0 0 -111 left roll -35 0 35 -1 diagonal to right
front sit up -1 35 0 -35 diagonal to left front sit up 25 <10
-25 0 diagonal to left reverse slide 0 -25 <10 25 diagonal to
right reverse slide
[0139] For each set of unbounded movement condition threshold values
in Table 3, the controller is operable to compute unbounded movement
condition threshold values, RHT, RFT, LFT and LHT, from the normalized
movement condition threshold values, RHTN, RFTN, LFTN and LHTN,
as a function of the corrected total patient weight, CTPW, and the
sensitivity value, S, an to compare the computed unbounded movement
condition threshold values with weight differentials between the
current and reference weight values of corresponding ones of the
various load cells. Each set of the unbounded movement condition
threshold values are computed according to the equations: LHT=LHTN*(CTPW/4)*(1/S)
(9), LFT=LFTN*(CTPW/4)*(1/S) (10), RFT=RFTN*(CTPW/4)*(1/S) (11),
RHT=RHTN*(CTPW/4)*(1/S) (12).
[0140] The weight differentials between the current and reference
weight values of the cells are computed by the controller 88 according
to the equations:: LHWD=C*(LH-RLH) (13), LFWD=C*(LF-RLF) (14), RFWD=C*(RF-RFR)
(15), RHWD=C*(RH-RHR) (16),
[0141] where RLH, RLF, RFR and RHR are individual load cell reference
weight values computed at various times during the PM Exit/Movement
Transition State routine of FIGS. 10A-10B and the PM Active State
routine of FIGS. 11A-11C, LH, LF, RF and RH are the current weight
values measure by the corresponding load cells 68a-68d, "C"
is a constant, e.g., 1000, and LHWD, LFWD, RFWD and RHWD are individual
load cell weight differentials relative to the corresponding reference
weight values. The controller 88 is operable to compare the individual
load cell weight differentials computed according to equations (13)-(16)
with each corresponding set of the computed unbounded movement condition
threshold values computed according to equations (9)-(12) to determine
whether an "unbounded movement condition" is satisfied.
More specifically, the controller 88 is operable to determine that
an unbounded movement condition is satisfied if at least two or
three of the four weight differential values are greater than corresponding
unbounded movement threshold values of any one set of unbounded
movement threshold data if the unbounded movement threshold values
are greater than zero, or are less than corresponding unbounded
movement threshold values of any one set of unbounded movement threshold
data if the unbounded movement threshold values are less than zero.
Two exceptions to this rule apply as noted in Table 3, one for the
"diagonal to left reverse slide" unbounded condition and
one for the "diagonal to right reverse slide" unbounded
condition. Otherwise, for sets of unbounded movement threshold values
having two non-zero values, an unbounded movement condition is satisfied
if the two non-zero weight differentials satisfy the inequality
relative to the two unbounded movement threshold values. For sets
of unbounded movement threshold values having three non-zero values,
an unbounded movement condition is satisfied if the three non-zero
weight differentials satisfy the inequality relative to the three
unbounded movement threshold values. For example, using the first
entry in Table 3, an unbounded condition is satisfied if LHWD>LHT
and LFWD<LFT.
[0142] Referring now to FIG. 18, a flowchart is shown of one illustrative
embodiment of a software algorithm or routine for executing the
movement mode routine called by step 440 of the PM Active State
routine illustrated in FIGS. 11A-11C. In the illustrated embodiment,
the movement mode algorithm or routine begins at step 580 where
the controller 88 is operable to determine whether the exit mode
is currently selected. If so, execution of the routine advances
to step 582 where the controller 88 is operable to set the sensitivity
value, S, equal to a first sensitivity value, S1. If, at step 580,
the controller 88 determines that the exit mode is not currently
active, then the controller 88 is operable to set the sensitivity
value, S, to a second sensitivity value, S2, wherein S1 is less
than S2. In the illustrated embodiment, the sensitivity value, S,
for the bounded movement condition threshold data collection, e.g.,
Table 2, is set lower, so that the movement mode routine is more
sensitive, when the movement mode is selected via the movement mode
selection switch 80 than when the exit mode is selected via the
exit mode selection switch 84. Thus while both the exit and movement
mode routines run in the exit and movement modes, the sensitivity
value, S, of the movement mode routine is set to a lower value when
the movement mode is selected via the selection switch 80. As examples,
S1 may set to 1/29 and S2 may be set to 1/6-1/5, although it will
be appreciated that other values of S1 and S2 may be used, and that
S1 may alternatively be set less than or equal to S2.
[0143] In any case, execution of the movement mode routine advances
from step 582, and from the "NO" branch of step 584, to
step 586 where the controller 88 is operable to reset the sector
to zero. Thereafter at step 588, the controller 88 is operable to
determine a movement condition threshold value set for the current
sector from the bounded movement threshold table, Table 2. Thereafter
at step 590, the controller 88 is operable to determine whether
the bounded condition is satisfied by the current load cell data,
RH, RF, LF and LH, for at least three of the load cell threshold
values, RHT, RFT, LFT and LHT of the movement condition threshold
value set for the current sector by plugging RH, RF, LF and LH into
the above equations and comparing the results with the movement
condition threshold value set for the current sector. If the controller
88 determines at step 690 that for the current sector at least three
of the equations (1)-(4) above produce corresponding current percent
weight change values, PCRH, PCRF, PCLF and PCLH, that are greater
than three corresponding entries in the bounded movement threshold
table, Table 2, a bounded condition is satisfied. If the controller
88 determines at step 590 that a bounded condition is satisfied,
execution of the routine advances to step 594 where the controller
88 is operable to determine whether the waiting for weight stabilization
(WFWS) flag is "false" or the temporary weight value,
TEMPW, computed at step 416 of the PM Active State routine of FIGS.
11A-11C is between positive and negative values of the sensitivity
to weight change value, SMWC. If both conditions are satisfied,
execution of the routine advances to step 596 where the controller
88 is operable to set the remote alarm flag active. Thereafter at
step 598, execution of the routine advances to the step 598 where
the state machine 120 moves to the PM Alarm State and the controller
88 is operable to execute the PM Alarm State routine of FIG. 12.
If, at step 594, neither of the illustrated conditions is satisfied,
execution of the routine advances to step 604 where the controller
88 is operable to increment the sector counter by incrementing the
angle, "A", by the angle increment value, and then loop
back to step 588.
[0144] If, at step 590 the controller 88 determines that the bounded
condition is not satisfied for at least three of the four load cells,
execution of the routine advances to step 592 where the controller
88 is operable to determine whether the unbounded condition is satisfied
as described hereinabove. Thereafter at step 600, if the controller
88 determines that the unbounded condition is satisfied for at least
two or three of the four load cells, execution of the routine advances
to step 596 where the controller 88 is operable to set the remote
alarm flag to an active state. If, at step 600 the controller 88
determines that the unbounded condition is not satisfied, execution
of the routine advances to step 602 where the controller 88 is operable
to determine whether all of the sectors have been checked. If not,
execution of the routine advances to step 604 where the controller
88 is operable to increment the sector number by incrementing the
angle, "A", by the angle increment value. If, at step
602 the controller 88 determines that all sectors have been checked,
execution of the routine advances to return step 616.
[0145] Referring now to FIG. 19, a flowchart is shown of one illustrative
embodiment of a software algorithm or routine for executing the
out-of-bed (OOB) mode routine called by step 452 of the PM Active
State routine illustrated in FIGS. 11A-11C. In the illustrated embodiment,
the OOB mode algorithm or routine begins at step 620 where the controller
88 is operable to compute a weight change, WC, as a difference between
the total patient weight fast running average, FRA, and the armed
weight, AW. Alternatively, the controller 88 may be operable at
step 620 to compute WC as a difference between the total patient
weight slow running average, SRA, and the armed weight, AW, or the
corrected total patient weight, CTPW, and the armed weight. In any
case, execution of the routine advances to step 621 where the controller
88 is operable to compare the corrected total patient weight, CTPW,
to a low patient weight value, W.sub.LP. In one embodiment, W.sub.LP
is 40 lbs., although other values may be used. In any case, if the
controller 88 determines at step 621 that CTPW<W.sub.LP, execution
of the routine advances to step 630 where the controller 88 is operable
to set the local alarm flag to an active state and to set the remote
alarm flag to an active state. Thereafter at step 632 the state
machine moves to the PM Alarm State 136, and the controller 88 is
operable to execute the PM Alarm State routine of FIG. 12. In an
alternative embodiment, the "YES" branch of step 621 may
advance to step 624.
[0146] If, at step 621, the controller 88 determines that CTPW
is not less than W.sub.LP, execution of the routine advances to
step 622 where the controller 88 is operable to compare the absolute
weight change value, abs(WC), to an excess weight value, W.sub.E.
In one embodiment, W.sub.E is set equal to approximately 30 lbs.,
although other values of W.sub.E may be used. In any case, if the
controller 88 determines at step 622 that the absolute value of
the weight change, WC, exceeds the excess weight value, WE, this
indicates that the total patient weight has changed from the armed
weight by an amount sufficient to warrant investigation of the weight
change. After expiration of a weight settling timer at step 624,
the controller 88 is operable at step 626 to determine whether the
detected weight change is due to an addition or subtraction of weight
from the weigh frame 56. The timeout value of the weight settling
timer may be a constant value, or may instead by a dynamic variable
that increases proportionally to CTPW, SRA or FRA. In any case execution
of the OOB mode routine advances from the "NO" branches
of steps 622 and 624 to the return step 628.
[0147] At step 626, the controller 88 is operable to compare the
weight change, WC, to the excess weight value, W.sub.E, and determine
whether WC is less than -W.sub.E. If so, this indicates that the
patient has transferred at least a significant portion of the patient's
weight to a support surface other than the weigh frame 56, and execution
of the routine advances to step 630. If, at step 626, the controller
88 determines that the weight change value, WC, is not less than
-W.sub.E, execution of the routine advances to step 634 where the
controller 88 is operable to determine whether WC>W.sub.E. If
so, execution of the routine advances to step 636 where the controller
88 is operable to activate a visual and/or audible local alarm,
and thereafter to step 638 where the controller 88 is operable to
set the weight added flag to "true." Following step 638,
the controller 88 is operable at step 640 to determine whether the
local alarm activated at step 636 has been active for longer than
a local alarm time, T.sub.LA. In one embodiment, T.sub.LA is approximately
seven seconds, although other values may be used. In any case, if
the controller 88 determines at step 640 that the local alarm activated
at step 636 has been active for more than T.sub.LA, execution of
the routine advances to step 632. Otherwise, execution of the routine
advances to the return step 628. If, at step 634, the controller
88 determines that WC is not greater than W.sub.E, execution of
the routine advances to step 642 where the controller 88 is operable
to set the weight added flag to "true." Execution of the
routine advances from step 642 to the return step 638.
[0148] Further details relating to one implementation of the OOB
mode routine illustrated and described with respect to FIG. 19 are
disclosed in U.S. Pat. No. 6,208,250, which is assigned to the assignee
of the present invention, and the disclosure of which is incorporated
herein by reference.
[0149] While the invention has been illustrated and described in
detailed in the foregoing drawings and descriptions, the same is
to be considered as illustrative and not restrictive in character,
it being understood that only illustrative embodiments thereof have
been shown and described and that all changes and modifications
that come within the spirit of the invention are desired to be protected.
For example, while the concepts illustrated and described herein
have been disclosed in the context of a hospital bed 50 having a
conventional mattress 60, they are also applicable to other types
of hospital beds including, but not limited to, air mattress-based
beds and the like. As one specific example, one or more of the concepts
described herein may be used to control air pressures at different
zones of an air mattress as a function of one or more of total patient
weight, the distribution of total patient weight on each the plurality
of load cells, and the like. As another example, the bed 50 has
been illustrated and described as having four load cells 68a-68d,
with one each positioned near or toward a different corner of the
mattress support frame 58. Alternative embodiments of the bed 50
may include more or fewer load cells. In embodiments including fewer
load cells, as few as three may be positioned about the periphery
of the mattress support frame 58, and modifications to the various
algorithms and routines described herein to accommodate a three
load cell system would be a mechanical step for a skilled software
programmer. As yet another example, while a number of patient monitoring
modes have been described herein, e.g., exit, potential exit and/or
movement monitoring modes, those skilled in the art will recognize
other patient monitoring modes may be implemented either alone or
in combination with other patient monitoring modes. As one specific
example, it may be desirable to implement, either alone or in combination
with another patient monitoring mode, a highly sensitive patient
movement monitoring mode. Such a patient monitoring mode may be
implemented using the concepts described hereinabove with respect
to FIGS. 15-17 with an appropriate sensitivity value, S.
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