U.S. patent application number 16/518895 was filed with the patent office on 2020-01-23 for system and method for monitoring a person via an analog multi-zone pressure sensitive pad.
This patent application is currently assigned to J. BRASCH CO., LLC. The applicant listed for this patent is J. BRASCH CO., LLC. Invention is credited to John Joseph Brasch, James R. Leacock, Yuanjian Li, Gordon Smith, JR..
Application Number | 20200022643 16/518895 |
Document ID | / |
Family ID | 57319525 |
Filed Date | 2020-01-23 |
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United States Patent
Application |
20200022643 |
Kind Code |
A1 |
Smith, JR.; Gordon ; et
al. |
January 23, 2020 |
System And Method For Monitoring A Person Via An Analog Multi-Zone
Pressure Sensitive Pad
Abstract
A pressure sensitive pad, generally planar in shape for
placement underneath a mattress or cushion, capable of outputting a
spectrum of signals depending on the pressure applied on the pad,
comprising a plurality of sensitive zones, each zone being
connected to a respective controller, configured to measure the
pressure on each zone. The pressure sensitive pad comprising two
electrically conductive layers; a variable conductive foam layer
between the two conductive layers; and a non-conductive layer
comprising a plurality of holes, disposed between a first of the
two electrically conductive layers and the conductive foam layer. A
system operable with the pad calibrates to detect absence and
presence of a person for a range of mattress types and mattress
weights and person weights; and determines a relative weight and
position of the person while the person is on the mattress.
Inventors: |
Smith, JR.; Gordon;
(Lincoln, NE) ; Brasch; John Joseph; (Lincoln,
NE) ; Leacock; James R.; (Lincoln, NE) ; Li;
Yuanjian; (Chengdu City, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
J. BRASCH CO., LLC |
Lincoln |
NE |
US |
|
|
Assignee: |
J. BRASCH CO., LLC
Lincoln
NE
|
Family ID: |
57319525 |
Appl. No.: |
16/518895 |
Filed: |
July 22, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
15574479 |
Nov 15, 2017 |
10357197 |
|
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PCT/IB2016/052835 |
May 16, 2016 |
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16518895 |
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62161903 |
May 15, 2015 |
|
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62307774 |
Mar 14, 2016 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61G 2203/44 20130101;
G08B 21/22 20130101; A61B 5/1115 20130101; A61B 5/6891 20130101;
A61B 2562/066 20130101; A61B 5/447 20130101; A61G 7/108 20130101;
A61B 5/746 20130101; A61B 5/00 20130101; A61G 7/057 20130101; A61B
5/1036 20130101; A61G 7/0527 20161101; A61B 2562/06 20130101; A61B
5/445 20130101; A61B 5/4815 20130101; A61G 2203/34 20130101; A61B
5/6892 20130101; A61B 5/7282 20130101; A61B 2562/0247 20130101 |
International
Class: |
A61B 5/00 20060101
A61B005/00; A61B 5/11 20060101 A61B005/11; A61B 5/103 20060101
A61B005/103; G08B 21/22 20060101 G08B021/22; A61G 7/05 20060101
A61G007/05; A61G 7/057 20060101 A61G007/057; A61G 7/10 20060101
A61G007/10 |
Claims
1. A pressure sensitive pad, generally planar in shape for
placement underneath a mattress or cushion, capable of outputting a
spectrum of signals depending on the pressure applied on the
pad.
2. The pressure sensitive pad of claim 1 configured for
substantially not deforming the mattress or cushion.
3. The pressure sensitive pad of claim 1, comprising at least one
of: a conductive film; a conductive foam; a conductive ink; and a
strain gauge.
4. The pressure sensitive pad of claim 1, comprising a plurality of
sensitive zones, each zone being connected to a respective
controller, configured to measure the pressure on each zone.
5. The pressure sensitive pad of claim 1, comprising: two
electrically conductive layers; a variable conductive layer between
the two conductive layers, configured such that a resistance of the
variable conductive layer decreases when pressure is applied on the
variable conductive layer and the variable conductive layer is
compressed; wherein the two electrically conductive layers are
separated by the variable conductive layer, such that the
electrical resistance between the two conducting layers decreases
as pressure is applied to the pad, by way of increasing electrical
conductivity between the two conducting layers as mechanical
pressure increases on the pad and the variable conductive layer is
compressed.
6. The pressure sensitive pad of claim 5, wherein the variable
conductive layer is a conductive foam layer.
7. The pressure sensitive pad of claim 6, comprising a
non-conductive layer comprising a plurality of holes, disposed
between a first of the two electrically conductive layers and the
conductive foam layer; wherein pressure applied to the pad
increases contact between the first conductive layer and the
conductive foam, thereby easing electrical conductivity between the
two electrically conductive layers.
8. The pressure sensitive pad of claim 5, comprising a controller
connected to the two conducting layers and configured to input a
signal that passes through the two electrically conductive layers
to read an output signal resulting from the input signal passing
through the electrically conductive layers; and two sheath layers
that contain and protect the electrically conductive layers.
9. A system for detecting weight of a person or weight changes over
time or movements of a person on a mattress, comprising: an analog
pressure sensitive pad; and a control unit configured for
processing data received from the pad, and the control unit
operable to: (a) calibrate the system to detect absence and
presence of a person for a range of mattress types and mattress
weights and person weights; and (b) determine a relative weight of
the person while the person is on the mattress.
10. The system of claim 9, wherein the control is operable to: (c)
send processed data to a remote system; (d) emit an alarm if an
undesirable situation concerning the person's presence/absence
occurs; and (e) stop the alarm if a certain input is received.
11. The system of claim 9, wherein the pressure sensitive pad is a
variable pressure sensitive pad configured for placement under a
mattress.
12. The system of claim 10, comprising a local output unit
configured for emitting an alarm in response to an undesirable
condition of the person occurring based on information from the
pad.
13. The system of claim 10, further comprising a local input
configured for receiving a termination signal, communicated to the
controller, whereby the controller if configured to terminate an
emitted alarm.
14. The system of claim 10, comprising a remote communication unit
configured to transmit data processed by the control unit to a
remote system.
15. The system of claim 14, wherein the data transmitted is alert
data.
16. The system of claim 14, wherein the data is weight data.
17. A method for calibrating a variable pressure sensitive pad to
detect a person's weight with the pad of claim 1 placed beneath a
mattress of an unknown weight and the person is on the mattress,
the calibration comprising: a) placing the pressure variable
pressure sensitive pad undress a mattress; b) measuring a high, a
low, a last reading and an average reading from the pad; c) if the
difference is smaller than a threshold, gathering more data until
threshold is passed; d) if the difference is greater than the
threshold: i) determining a deactivated zone, wherein the
deactivated zone is a range of values from the high to a value that
is a function of the low and high; ii) determining an activated
zone, wherein the activated zone is a range of values from the low
to a value that is a second function of the low and high; and iii)
determining a transition zone, wherein the transition zone is range
between the highest value of the activated zone and the lowest of
deactivated zone; e) if the average value is in the transitioning
region, then performing an iterative process of lowering the record
high by a second amount that is a third function of the previous
record highs and lows and increasing the record low by a third
amount that is a fourth function of the previous record highs and
lows, until the last reading is out of the transitioning
region.
18. The method of claim 17, wherein the second amount and the third
amount are equal to each other.
19. A method for determining a person's relative weight using the
pad of claim 1, on a mattress of unknown weight, while the pad is
beneath the mattress of an unknown weight and the person is on the
mattress, comprising measuring an output voltage of the pad and
determining the relative weight of the person based on the output
voltage.
20. A method for determining the movement of a person on a
mattress, using the pad of claim 4 under the mattress, comprising
comparing measurements of an output from each of the sensitive
zones over time and determining whether an output from a first zone
is higher than an adjacent zone over time.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] The present application claims priority from U.S.
Provisional Application Ser. No. 62/161,903 filed on May 15, 2015
and U.S. Provisional Application Ser. No. 62/307,774 filed on Mar.
14, 2016, both of which are hereby incorporated herein by reference
in their respective entirety.
BACKGROUND OF INVENTION
[0002] Pressure pads are used in the medical field to sense the
presence of a monitored person on a surface, like a chair or a
bed.
[0003] Pressure pads may be used under the mattress/cushion or on
the mattress/cushion. Pressure pads located on the mattress can be
exposed to bodily fluids. It is sometimes also a concern to nurse
managers because of possible subtle changes in pressure on the
skin, leading to decubitus ulcers.
[0004] The inventors have found that pressure switch pads known in
the industry are not very reliable when used under a
mattress/cushion. Variations in thickness, softness, and internal
structure of the mattress/cushion result in sporadic behavior,
which results in unreliable detection of the presence or absence of
monitored person. One reason for this lies in the fact that basic
pressure pads are created to have a specific force sensitivity,
which has to be carefully selected. If the pressure pad is too
sensitive, the mattress/cushion alone could trigger the pad. If the
pressure pad is too lenient, the pad may not detect the presence of
a light person. This is further complicated by the fact that
different models of mattresses have varying masses and distributing
the weight of an individual over different areas.
BRIEF SUMMARY OF THE INVENTION
[0005] To solve the above problem, the present invention makes use
of an analog pressure pad, which can measure a wide range of
pressures and convey data instead of a simple on/off switch. This
data can then be read by a controller and processed, for example by
evaluated over time and/or being compared on previous readings.
This processing enables automatic calibration of the same analog
pressure pad for different types of mattresses and different
weights of users. In this manner, the presence of a user on a bed
can be detected for a wide range of mattress/cushion types and
weights and for a wide range of users. In some embodiments of the
present invention, the pressure pad has a tare (relative weight)
function, for allowing the monitor connected to the pressure pad to
take into account the weight of the mattress/cushion in use and
subtract that weight from a calculated total to get a weight
measurement of the user.
[0006] In other embodiments of the present invention, the
controller is configured for periodically taking automatic
measurements from the pad, and averaging them over an inactive time
period (i.e., a time in which it is known that the person is not on
the mattress) to auto calibrate the tare weight. This, combined
with some intelligent thresholds, could account for weight
differences due to changes in bedding, pillows, etc. over time.
[0007] This solution has the added benefit of being able to produce
a relative weight measurement of an individual simply by them going
to bed during the day or for the night. Relative weight
measurements could be used to detect weight gain or loss of the
user over time and possibly, if calibrated correctly, supply an
actual weight measurement (pounds, kilograms, etc). Historical
relative weight measurements could also aid in the detection of
pets which might jump into bed, such as a dog, which might
otherwise have triggered a basic pressure pad.
[0008] It should be noted that the pad of the present invention may
be used under any kind of mattress cushion. In the following
sections of the document, the term "mattress" is meant to include
any kind of mattress, cushion, or support on which a person may sit
or lie.
[0009] (1) In a variant, a pressure sensitive pad is generally
planar in shape for placement underneath a mattress or cushion, and
is capable of outputting a spectrum of signals depending on the
pressure applied on the pad.
[0010] (2) In another variant, the pressure sensitive pad is
configured for substantially not deforming the mattress or
cushion.
[0011] (3) In a further variant, the pressure sensitive pad
comprises at least one of: a conductive film; a conductive foam; a
conductive ink; and a strain gauge.
[0012] (4) In still another variant, the pressure sensitive pad
comprises a plurality of sensitive zones, each zone being connected
to a respective controller, configured to measure the pressure on
each zone.
[0013] (5) In yet a further variant, the pressure sensitive pad
comprises two electrically conductive layers. A variable conductive
layer is disposed between the two conductive layers, configured
such that a resistance of the variable conductive layer decreases
when pressure is applied on the variable conductive layer and the
variable conductive layer is compressed. The two electrically
conductive layers are separated by the variable conductive layer,
such that the electrical resistance between the two conducting
layers decreases as pressure is applied to the pad, by way of
increasing electrical conductivity between the two conducting
layers as mechanical pressure increases on the pad and the variable
conductive layer is compressed.
[0014] (6) In a variant of the pressure sensitive pad, the variable
conductive layer is a conductive foam layer.
[0015] (7) In another variant, the pressure sensitive pad comprises
a non-conductive layer comprising a plurality of holes, disposed
between a first of the two electrically conductive layers and the
conductive foam layer. Pressure applied to the pad increases
contact between the first conductive layer and the conductive foam,
thereby easing electrical conductivity between the two electrically
conductive layers.
[0016] (8) In a further variant, the pressure sensitive pad
comprises a controller connected to the two conducting layers and
configured to input a signal that passes through the two
electrically conductive layers to read an output signal resulting
from the input signal passing through the electrically conductive
layers; and two sheath layers that contain and protect the
electrically conductive layers.
[0017] (9) In still another variant, s system for detecting weight
of a person or weight changes over time or movements of a person on
a mattress, comprises: an analog pressure sensitive pad; and a
control unit configured for processing data received from the pad,
and the control unit operable to: (a) calibrate the system to
detect absence and presence of a person for a range of mattress
types and mattress weights and person weights; and (b) determine a
relative weight of the person while the person is on the
mattress.
[0018] (10) In yet a further variant of the system, the control is
operable to: (c) send processed data to a remote system; (d) emit
an alarm if an undesirable situation concerning the person's
presence/absence occurs; and (e) stop the alarm if a certain input
is received.
[0019] (11) In a variant of the system, the pressure sensitive pad
is a variable pressure sensitive pad configured for placement under
a mattress.
[0020] (12) In another variant, the system comprises a local output
unit configured for emitting an alarm in response to an undesirable
condition of the person occurring based on information from the
pad.
[0021] (13) In a further variant, the system comprises a local
input configured for receiving a termination signal, communicated
to the controller, whereby the controller if configured to
terminate an emitted alarm.
[0022] (14) In still another variant, the system comprises a remote
communication unit configured to transmit data processed by the
control unit to a remote system.
[0023] (15) In yet a further variant of the system, the data
transmitted is alert data.
[0024] (16) In another variant of the system, the data is weight
data.
[0025] (17) In a variant, a method for calibrating a variable
pressure sensitive pad to detect a person's weight with the analog
pressure sensitive pad placed beneath a mattress of an unknown
weight and the person is on the mattress, the calibration
comprising: a) placing the pressure variable pressure sensitive pad
undress a mattress; b) measuring a high, a low, a last reading and
an average reading from the pad; c) if the difference is smaller
than a threshold, gathering more data until threshold is passed; d)
if the difference is greater than the threshold: determining a
deactivated zone, wherein the deactivated zone is a range of values
from the high to a value that is a function of the low and high;
determining an activated zone, wherein the activated zone is a
range of values from the low to a value that is a second function
of the low and high; and determining a transition zone, wherein the
transition zone is range between the highest value of the activated
zone and the lowest of deactivated zone; e) if the average value is
in the transitioning region, then performing an iterative process
of lowering the record high by a second amount that is a third
function of the previous record highs and lows and increasing the
record low by a third amount that is a fourth function of the
previous record highs and lows, until the last reading is out of
the transitioning region.
[0026] (18) In another variant of the method, the second amount and
the third amount are equal to each other.
[0027] (19) In a further variant, a method for determining a
person's relative weight using the pressure sensitive pad, on a
mattress of unknown weight, while the pad is beneath the mattress
of an unknown weight and the person is on the mattress, comprises
measuring an output voltage of the pad and determining the relative
weight of the person based on the output voltage.
[0028] (20) In still another variant, the method for determining
the movement of a person on a mattress, using the pressure
sensitive pad under the mattress, comprises comparing measurements
of an output from each of the sensitive zones over time and
determining whether an output from a first zone is higher than an
adjacent zone over time.
BRIEF DESCRIPTION OF DRAWINGS
[0029] The present invention, in accordance with one or more
various embodiments, is described in detail with reference to the
following figures. The drawings are provided for purposes of
illustration only and merely depict typical or example embodiments
of the invention. These drawings are provided to facilitate the
reader's understanding of the invention and shall not be considered
limiting of the breadth, scope, or applicability of the invention.
It should be noted that for clarity and ease of illustration these
drawings are not necessarily made to scale.
[0030] Some of the figures included herein illustrate various
embodiments of the invention from different viewing angles.
Although the accompanying descriptive text may refer to such views
as "top," "bottom" or "side" views, such references are merely
descriptive and do not imply or require that the invention be
implemented or used in a particular spatial orientation unless
explicitly stated otherwise.
[0031] FIG. 1 is a block diagram illustrating a monitoring
apparatus comprising an analog pad, according to some embodiments
of the present invention;
[0032] FIG. 2 is a schematic drawing illustrating a zone of the
analog pressure pad of FIG. 1, or a pressure pad according to FIG.
1 that is not divided in zones, according to some embodiments of
the present invention;
[0033] FIGS. 3 and 4 are schematic drawing illustrating an example
of the structure of the pressure pad of FIG. 1 or of a zone of a
pressure pad of FIG. 1, according to some embodiments of the
present invention;
[0034] FIGS. 5 and 6 are schematic drawings of an electrical
circuit which includes the pad of FIGS. 3 and 4, according to some
embodiments of the present invention;
[0035] FIG. 7 is a flowchart illustrating a method used by the
control unit of FIG. 1 for processing data received from the analog
pressure pad;
[0036] FIG. 8 is a flowchart illustrating a method of some
embodiments of the present invention, for dynamic calibration of a
pressure sensitive pad according to FIG. 1, to any mattress and/or
person; and
[0037] FIG. 9 is a resistance vs. time graph, illustrating the
calibration of a pad of FIG. 1 over time, according to the method
of FIG. 8; and
[0038] FIG. 10 is a block diagram illustrating a system of the
present invention, in which the control unit is in communication
with a wireless scale.
[0039] The figures are not intended to be exhaustive or to limit
the invention to the precise form disclosed. It should be
understood that the invention can be practiced with modification
and alteration, and that the invention be limited only by the
claims and the equivalents thereof.
DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION
[0040] From time-to-time, the present invention is described herein
in terms of example environments. Description in terms of these
environments is provided to allow the various features and
embodiments of the invention to be portrayed in the context of an
exemplary application. After reading this description, it will
become apparent to one of ordinary skill in the art how the
invention can be implemented in different and alternative
environments.
[0041] Unless defined otherwise, all technical and scientific terms
used herein have the same meaning as is commonly understood by one
of ordinary skill in the art to which this invention belongs. All
patents, applications, published applications and other
publications referred to herein are incorporated by reference in
their entirety. If a definition set forth in this section is
contrary to or otherwise inconsistent with a definition set forth
in applications, published applications and other publications that
are herein incorporated by reference, the definition set forth in
this document prevails over the definition that is incorporated
herein by reference.
[0042] FIG. 1 is a box diagram illustrating a monitoring apparatus
according to some embodiments of the present invention. The
monitoring apparatus includes a pressure pad 102, and a control
unit 104. Optionally, the control unit is in communication with a
local memory unit 105, for storing data received from the pressure
pad, or uses a remote communication unit 110 to transfer data to a
remote system 112, which is configured for storing and/or analyzing
the received data. Optionally, the system includes a local output
unit 106 and a local input unit 108. The local output unit is
configured for emitting a warning locally, when an undesirable
condition relating to the user's absence or presence is detected.
The local input unit is configured for enabling the user or anyone
nearby to turn off the warning. Optionally, the remote system 112
is configured for sending the warning to one or more predefined
persons, to inform them of the undesirable condition.
[0043] In some embodiments of the present invention, the remote
system 112 is accessible to medical personnel to analyze conditions
of the user, such as frequent sleep interruptions or rapid weight
gain. These conditions may be indicative of heart failure, as will
be described below.
[0044] In some embodiments of the present invention, the control
unit analyzes the data indicative of the user's frequency of sleep
interruptions and/or rapid gain weight. If the control unit
determines that the frequency of sleep interruptions is too high
and/or if the person's weight gain is too rapid, according to
predetermined thresholds, a notification is sent via the
communication unit 110 to a remote system accessible to medical
personnel. Optionally, a warning is also emitted by the local
output unit to inform the person of a health-related risk.
[0045] In some embodiments of the present invention, the pressure
pad 102 is configured for being located under the user's mattress,
and includes a varying resistance conductive material. This
material is electrically conductive, like a wire, but has a
resistance which decreases as pressure is applied. This allows for
a resistance measuring circuit, such as a voltage divider, to be
used with an Analog to Digital Converter (ADC) of a micro
controller (MCU) to obtain weight measurements. In some embodiments
of the present invention, the variable resistance material of the
present invention may include one or more of a conductive film
(e.g., a film called Velostat and produced by 3M, or any similar
material), conductive foam, strain gauges which generate varying
resistance when deformed, and conductive ink. Optionally, the pad
is integral with a mattress/cushion, such the pressure sensitive
part is a sheet or layer of the mattress or cushion.
[0046] In an embodiment of the present invention, the analog pad
102 is divided up into zones, which in effect act like many little
analog pads in a grid pattern covering the surface area of the pad.
Each zone is attached to a separate ADC on the micro controller and
measured independently allowing for software to determine
specifically where on the pad pressure is, how much pressure is
present, and as the user moves, how the pressure changes from zone
to zone. FIG. 2 shows a zone of the analog pressure pad 102, or a
pressure pad 102 that is not divided in zones.
[0047] The relevance of detecting position and movement is that
nursing staff can be alerted when a person is in a position for too
long, thus leading to possible decubitus ulcers. Moreover,
caretakers can be alerted at an earlier moment the user reaches the
side of the bed, in order to exit the bed. A local alert may be
emitted if a user who is not supposed to leave the bed is at the
edge of the bed.
[0048] Individual signals are transmitted from each pad to the
control unit 110 before processing the signal in a CPU (which may
be in the control unit 110 or in the remote system 112), comparing
magnitudes of changes in weight. Optionally, the signals are
amplified before being received by the control unit 110. Some
embodiments of the present invention relate to techniques for
determining when the user is starting to leave a bed, departs from
bed, when the user has been in place for too long a period, and
optionally, evidence of changes in a person's body weight from day
to day (of diagnostic value for several conditions including
congestive heart failure). Relative weight measurements could be
used to detect weight gain or loss of the user over time and
possibly, if calibrated correctly, supply an actual weight
measurement (pounds, kilograms, etc). Historical relative weight
measurements could also aid in the detection of pets that might
jump into bed, such as a dog, which might otherwise have triggered
an alarm in basic pressure pad.
[0049] FIGS. 3 and 4 are schematic drawing illustrating an example
of the structure of the pressure pad of FIG. 1 or of a zone of a
pressure pad of FIG. 1, according to some embodiments of the
present invention.
[0050] The pad 102 relies on an electrical circuit having
pressure-sensitive resistance. The pad 102 includes two
electrically conductive layers 8 and 9 (e.g., Aluminum foil PET
Mylar) separated by a non-conductive layer 13 (e.g. Mylar with die
cuts) and a layer of conductive foam 12. Optionally the pad 102
includes a sheath (layers 7 and 10) that contains and seals the
conductive layers 8 and 9, the non-conductive layer 13, and the
conductive foam 12. Optionally the sheath is an RF-welded vinyl
cover. Optionally the pad 102 is fully sealed and water proof.
[0051] Electrical wires 50 are connected to each of the
electrically conductive layers, and run to a circuit board 51 that
connects to the micro-controller unit (MCU) which may be part of
the control unit 104 of FIG. 1, or may be in communication with the
control unit 104 of FIG. 1. In some embodiments of the present
invention, a limitation resistor 52 is connected to circuit board
and is parallel to each of the electrically conductive layers. The
apparatus which includes the conductive layers, non-conductive
layer, and foam layer operates as a pressure-sensitive resistor
which is in parallel with the limitation resistor 52.
[0052] Optionally, the output of MCU runs to a modular connector
that connects to the fall alarm.
[0053] The upper conductive layer 8 and upper face of conductive
foam 12 are separated by the non-conductive layer 13. The lower
conductive layer 9 is in contact with the lower face of conductive
foam 12.
[0054] When no pressure is applied on the pad 102 or if the weight
is lower than a certain threshold pressure, the upper conductive
layer 8 and the upper face of conductive foam 12 are still
separated by the non-conductive layer. The resistance present
between the conductive layer 8 and 9 is very high or approaches
infinity.
[0055] The output resistance R.sub.OUT of the pad is equal to:
R.sub.OUT=(1/R.sub.VAR+1/R.sub.LIM).sup.-1
[0056] where, R.sub.VAR is the variable resistance between the
conductive layers 8 and 9, while R.sub.LIM is the resistance of the
limitation resistor 52.
[0057] Thus, when the pressure applied to the pad is lower than a
certain pressure, R.sub.OUT is equal to value of limitation
resister.
[0058] When weight/pressure present on the pad increases, the upper
conductive layer 8 is compressed, allowing the upper conductive
layer 8 and upper face of conductive foam 12 to make contact via
the holes 14 in the non-conductive layer 13. The increased
weight/pressure also compresses the conductive foam. As the
conductive foam is sandwiched between two conductive layers, the
resistance of conductive foam 12 between two conductive layers
decreases. As the weight/pressure on the sensor pad increases more,
the conductive foam is compressed more and causes the resistance of
conductive foam 12 to decrease more, therefore decreasing the
resistance R.sub.VAR between the two conductive layers 8 and 9.
[0059] As R.sub.VAR decreases, the output resistance of the pad,
R.sub.OUT decreases as well. When weight/pressure on the pad
decreases, the conductive foam recovers its original shape the
resistance of the foam increases, thereby increasing the resistance
R.sub.VAR between the conductive layers 8 and 9. Therefore,
R.sub.OUT increases as well.
[0060] When the weight/pressure is removed from the pad, the upper
conductive layer 8 and upper face of conductive foam 12 are
separated by the non-conductive layer 13. R.sub.VAR therefore rises
toward infinity, and R.sub.OUT is equal to value of limitation
resister. By tracking R.sub.OUT, R.sub.VAR can be calculated, and
the pressure on the pad can be determined.
[0061] FIGS. 5 and 6 are schematic drawings of an electrical
circuit which includes the pad of FIGS. 3 and 4, according to some
embodiments of the present invention;
[0062] The circuit includes the variable resistor R.sub.VAR of the
pad as described above, and the limiting resistor R.sub.LIM, a
power source PWR, and a reading point at which V.sub.OUT is
read.
[0063] In the example of FIG. 5, there is no pressure on the pad,
so R.sub.VAR is very high (e.g. 100 M.OMEGA.), compared to the
resistance of R.sub.LIM (for example, 10 k.OMEGA.). In this
example, V.sub.OUT will be about the same as the voltage provided
by the power source (e.g., 5V).
[0064] In the example of FIG. 6, there is a high pressure on the
pad, so R.sub.VAR is very low (e.g. 1.OMEGA.), compared to the
resistance of R.sub.LIM (for example, 10 k.OMEGA.). In this
example, V.sub.OUT will be about 499.95 .mu..OMEGA., which is much
lower that the voltage provided by the pow source (e.g., 5V) and
approaches 0.
[0065] In some embodiments of the present invention, the pad does
not include the non-conductive layer. This pad uses more power, but
still operates correctly.
[0066] In some embodiments of the present invention, the micro
controller which reads the zones and calculates the
in-bed/out-of-bed determination, is separate from the control unit.
This places the micro controller within the pad, on the cord for
the pad, at the connector for the pad, or as an adapter which the
pad plugs into or connects to wirelessly. This allows for a simple
monitor with limited processing capabilities to work with the
pad.
[0067] FIG. 7 is a flowchart illustrating a method used by the
control unit of FIG. 1 for processing data received from the analog
pressure pad described above. It should be noted that any pressure
pad may be used, in which variable resistance of the pad or its
sections relates to the pressure applied on the pad or its
sections. The left branch of the flowchart relates to processing
analysis of the data taken by all the zones of the pressure pad.
The right branch of the flowchart relates to separately analyzing
data from each zone of the pressure pad.
[0068] At 500, the control unit is turned on. At 502, data
indicative of pressure(s) is read from the analog pressure pad.
[0069] At 504, a check is made to determine if only the mattress is
present. When no weight is applied, the resistance through the pad
is very high and approaches infinite. Without the weight of a
mattress, the resistance of the pad becomes very high and causes
Vout is to be very close to the input voltage. Thus, when Vout is
close to the input voltage, it can be assumed that no mattress is
present. If this is the case, the pressure readings due to the
mattress' presence are stored. A mattress threshold is set at 506
and the control unit is calibrated accordingly at 508. There are
two methods in which the mattress weight can be calibrated. In the
first method, a reset button or reset mechanism can be used by a
staff member when the pad is first placed under a mattress, to
force an immediate recalibration by zeroing out the currently
applied weight. In the second method, the calibration occurs
automatically via the method of FIG. 8 after the first person uses
the mattress with the pad installed.
[0070] If a person is on the mattress, a check is made to determine
whether the person is still at 510. If this is the case, the
pressure readings due to the presence of the mattress and the
person are stored. A person's threshold is set at 512 and the
control unit is calibrated accordingly at 514. Since the pressure
due to the mattress is known, a relative weight of the person can
be determined by comparing the pressure due to the presence of the
mattress and the pressure due to the presence of the mattress and
the person at 516.
[0071] If the person is not still, the control unit records that
the person is moving at 518. Movement of the person can be detected
when a number of readings taken at predetermined intervals (e.g., 4
readings at intervals of 0.5 s) vary substantially in relation to
each other. If the variance of the readings is under a
predetermined threshold, it is determined that the person is
still.
[0072] On the right branch of the flowchart, data from each zone of
the pressure pad is processed separately at 520, and a check is
made to determine whether the person is exiting the bed at 522. If
this analysis determines that the person is exiting from the bed,
an exiting notification is recorded at 524, and optionally a
warning is issued. If exiting is not detected, the raw zone
readings are recorded for later analysis at 526.
[0073] In some embodiments of the present invention, the apparatus
100 of FIG. 1 is configured for helping diagnose a health condition
of the user. In a non-limiting example, nocturnal polyuria and
rapid weight gain may be diagnosed by using data from the pressure
pad.
[0074] Nocturnal polyuria is a condition in which a person wakes up
frequently during the night to urinate. A healthy person should be
able to sleep six to eight hours during the night without having to
get up to go to the bathroom. People suffering from nocturnal
polyuria wake up more than once a night to urinate. This can cause
disruptions in a normal sleep cycle. Causes of nocturnal polyuria
may include congestive heart failure.
[0075] By utilizing the apparatus according to FIG. 1 (with a
regular or an analog pressure pad) to keep a nocturnal diary, it is
possible to reliably track how many times the user rises during the
night. While the apparatus may not detect whether the user has
woken up to use the bathroom, data relating to frequent
interruptions in the user's sleep may be an indicator that
something might be wrong.
[0076] Rapid weight gain is commonly experienced by people
suffering from heart failure. In fact, if a person's heart failure
is causing fluid accumulation, the person will gain weight in a
short time period.
[0077] People who are at risk for heart failure should weight
themselves every day at the same time, and to report to medical
personnel, if the weight increases quickly (for example, by more
than 2 kilograms in 3 days, or by more than 3 pounds in 3
days).
[0078] By using the apparatus of FIG. 1, the relative weight of the
user each night is recorded while they are asleep. The measurements
are relative weight, but since we are interested in weight gain
these relative measurements can be compared to each other from day
to day to detect rapid weight changes. This removes the element of
forgetfulness on the part of the user to weigh himself or herself
daily, and negates observation bias by dealing with discrete
recorded measurements instead of the user's memory of past
weights.
[0079] FIG. 8 is a flowchart 600, illustrating a method of some
embodiments of the present invention, for dynamic calibration of a
pressure sensitive pad according to FIG. 1, to any mattress and/or
person. The method may be implemented by the control unit of FIG.
1.
[0080] At 600, a new cycle is started. At 602, a resistance reading
from the pad is recorded by the control unit. The recorded reading
is called LastReading. At 603, LastReading is compared to previous
readings, to determine RecordHigh and RecordLow, which are
respectively the highest and lowest resistances recorded over a
predetermined time period.
[0081] At 604, an average reading is calculated. The average
reading may be an average of the readings recorded over a certain
time period, or may be weighted average, in which the current
LastReading weighs more than previous readings.
[0082] At 606, a check is made to determine whether a difference
between the RecordHigh and RecordLow is greater than a certain
threshold. At this point the control unit needs to make a decision
if it has gathered enough data in order to execute the remaining
logic or if it needs to go back to sleep. This is required because
a newly initialized control unit will have a
RecordHigh=RecordLow=AverageReading and if they aren't exactly
equal they will be very close in value which creates an error
condition. In this state a large enough range of pressures have not
been recorded. Therefore, an in bed (person on mattress) or out of
bed (person off mattress) condition cannot be determined. In some
embodiments of the present invention, the threshold value is
hardcoded and depends on the responsiveness of the pad material
used.
[0083] If the difference between RecordHigh and RecordLow is
smaller than the threshold, the cycle is ended at 620. If the
difference between RecordHigh and RecordLow is larger than the
threshold, three ranges or regions are determined at 608: the
activated region, the deactivated region, and the transition
region.
[0084] The activated region includes a range of values, such that
if the last reading or average reading is within the activated
region, it is determined that the person is in bed. The lowest
value of the activated region is RecordLow (as low resistance
corresponds to high pressure on the pad). The highest value of the
activated region is a first function of RecordHigh and RecordLow.
For example, the highest value of the activated region may be:
RecordLow+f.sub.1(RecordHigh, RecordLow), where f.sub.1 is a first
function.
[0085] The deactivated region includes a range of values, such that
if the last reading or average reading is within the deactivated
region, it is determined that the person is out bed. The highest
value of the deactivated region is RecordHigh (as high resistance
corresponds to low pressure on the pad). The lowest value of the
activated region is a second function of RecordHigh and RecordLow.
For example, the highest value of the activated region may be:
RecordHigh-f.sub.2(RecordHigh, RecordLow), where f.sub.2 is a
second function.
[0086] The transitional region corresponds to a range of values
higher than the highest value of the activated region and lower
than the lowest value of the deactivated region.
[0087] At 610, a check is made to determine whether the
AverageReading is within the activated region. Alternatively, the
check of 610 is made to determine whether the LastReading is within
the activated region. If the check is positive, an "In Bed" signal
is output at 612. This signal may be sent to a remote station, or
used by the control unit to determine whether the fact that the
person is in bed is a desirable or undesirable condition, and act
accordingly.
[0088] If the check of 610 is negative, another check is made at
614 to determine whether the AverageReading is within the
deactivated region. Alternatively, the check of 614 is made to
determine whether the LastReading is within the deactivated region.
If the check of 614 is positive, an "Out of Bed" signal is output
at 616. This signal may be sent to a remote station, or used by the
control unit to determine whether the fact that the person is out
bed is a desirable or undesirable condition, and act
accordingly.
[0089] In an ideal situation the above stated steps would be
sufficient for full pad operation. If this was the case, recordHigh
would be the tare weight of the mattress and recordLow would
represent the weight of the patient plus mattress. During real
world usage, events occur which push the recordHigh and recordLow
briefly to extremes which do not represent their intended
representations. This could be as simple as a staff member remaking
a bed who accidentally leans too hard on the mattress while tucking
in the far corner. If these outliers were not accounted for the pad
would function for a time, but slowly become less and less reliable
until it stops seeing the patient all together.
[0090] In order to rectify this, the transition region calculated
earlier is used to adjust the record values. Thus, if the check of
614 is negative, then the AverageReading (alternatively, the
LastReading) is in the transitional zone. Thus, for every wake
cycle in which the averageReading (alternatively, the LastReading)
is within the transition region the RecordHigh is decreased by a
first amount and the RecordLow is increased by a second amount at
618. The first and second amounts may be calculated by third and
fourth functions, each function taking into account both RecordHigh
and RecordLow.
[0091] The increase or RecordLow and the decrease or RecordHigh
decreases the distance between these values. If a much lower high
or much high low is observed than previously these record values
will start to converge until the AverageReading (alternatively,
LastReading) is once again within either the Activated or
Deactivated region. In some cases this convergence may take a
minute if sampling occurs every 0.5 s, but it prevents the staff
from needing to manually intervene in the calibration process.
[0092] At 620, the cycle ends. A new cycle begins according to a
predetermined sampling time. The time interval between cycles may
be 1 seconds, 100 milliseconds, 10 milliseconds, or any other value
that is deemed desirable.
[0093] The method of FIG. 6 can be used to dynamically calibrate a
pad to new conditions, such as a new mattress and a new person
having a different weight. Depending on the sampling time and on
the period over which the AverageReading, RecordHigh, and RecordLow
are determined, and on the formula used for calculating
AverageReading, a pad can be calibrated to new conditions within a
minute when sampling occurs every 0.5 s. Alternatively, a pad can
be initialized to start a new calibration via the control unit each
time the pad is transferred to anew mattress or a new person.
[0094] FIG. 9 is a resistance vs. time graph, illustrating the
calibration of a pad of FIG. 1 over time, according to the method
of FIG. 8. The green lines represent the Activated region while the
red lines represent the Deactivated region. As the LastReading
(black) changes the AverageReading (blue) follows it, but slightly
lagging behind. In the last half of the graph the LastReading drops
to 700 which is in the Transition Region. At this point the red and
green regions begin to converge until the red region captures the
current AverageReading. According to some embodiments of the
present invention, the control unit of FIG. 1 keeps track of the
relative of weight of the person to be monitored when the person is
on the bed. The relative weight eight is relative because it
depends on the weight and structure of the mattress and on the
weight of the person. Readings from the pad would differ even if
the same person were to lie on two different mattresses.
[0095] In the simplest embodiment of a system, measuring the
relative weight the pad of FIG. 1 includes one single zone. In this
embodiment, the entire weight of the individual is applied to the
single sensor zone. This weight is distributed unevenly based on
the position and stance of the monitored person, but the unevenness
is not detected since all the pressure measured by the pad is all
contained within a single zone.
[0096] In a slightly more complex embodiment of a system, measuring
the relative weight the pad of FIG. 1 includes two sensor zones, in
which the dividing line runs through the center of the pad. If the
person's center of mass is along the dividing line, the same amount
of pressure is being applied to the pad as a whole, but now half of
that pressure resides on each zone. All other things remaining the
same, the voltage drop across each zone is reduced by a certain
coefficient as the pressure resistance of each zone is doubled
compared to the single zone example The coefficient depends on the
structure of the pad, on the structures and weight of the mattress,
and on the stance and weight of the person.
[0097] This example can be extended out again by dividing each of
those zones in half but this time divided parallel to the first
division. This provides four zones extending across a bed. However,
the pressure is no longer equally distributed among the zones. For
example, 1/5 of the pressure may be on the outer zones and the
remaining 4/5 on the central zones. The voltage drops (directly
proportional to the resistances) at each zone change according to
the ratio of the total pressure applied on the zone. This allows
for the addition of the voltage drops for a multi-zone pad to
simulate a single zone for presence. In one embodiment, total
pressure=f(Vout 1)+f(Vout 2)+f(Vout 3)+ . . . +f(Vout n) for n
zones. For example, f=Vout/(Vcc/1024). In another example the
function f is a logarithmic function and the total pressure is
related logarithmically to the output voltage. For the single zone
pad, total pressure=f(Vout). The multi-zone pad, however, provides
zone granularity to determine bed location and position. It is
important to remember all of these voltage drops represent relative
weights and not absolute measurements. The material and composition
of the mattress will affect pressure dispersement. This means
reading between mattresses cannot be compared. Multiple readings
from the same mattress are comparable, and allow tracking the
relative weight of the monitored person.
[0098] It should be noted that the weight distribution across the
different zones allows the determination of the person's position
on the mattress. For example, if most of the weight is concentrated
on the outer sides of the bed for a prolonged time, there may be a
chance that the person is trying to get up or is about to fall.
[0099] The other item to keep in mind is patient movement when
using readings for relative weight measurements. If the patient is
actively shifting or fidgeting, the kinetic energy imparted to the
mattress appears as additional pressure to the sensors and
therefore additional weight. To account for this, multiple
measurements should be taken over several seconds for each zone and
each of the zone reading should be compared to itself over that
time period. If little to no fluctuation in the readings over
several seconds are observed the algorithm can assume the
individual is lying still. Otherwise the system should delay
several minutes before reattempting another relative weight
measurement. On the other hand, a failed relative weight
measurement is also an active individual measurement if presence
has already been determined. A failed weight measurement in this
case is due to the patient moving too much. This has the benefit of
determining the monitored person is moving, which can be used as an
indication of restlessness, shifting, or the possibility of waking
from sleep, if it is preceded by an extended period of stillness in
the middle of the night.
[0100] In one example, the relative weight is determined by the sum
of the voltage drops from all zones. f=pressure
reading=Vout/(Vcc/1024) In some embodiments of the present
invention, the micro controller (MCU) of each zone reads each zone
as a 10 bit value between the reference voltage (for example, 5V)
and ground. Optionally, the micro controllers are configured to
create an even more fine grained reading (for example 12 bits and
14 bits). At a 10 bit resolution, the MCU is able to measure in
approximately 4.88 mV increments of the maximum voltage drop, where
the maximum voltage drop is 5V. The addition of these four zones
provides a relative range between 4092 increments (of the maximal
voltage drop) with no pressure (resistance is infinite, thus
voltage drop is maximal) and theoretically 0 increments at an
infinite pressure (at infinite pressure, the resistance is 0, so
the voltage drop is 0).
[0101] FIG. 10 is a block diagram illustrating a system of the
present invention, in which the control unit is in communication
with a wireless scale. The apparatus of FIG. 10 is similar to the
apparatus of FIG. 1. However, in FIG. 8, a wireless scale 114 is in
communication with the control unit. The wireless scale records the
weight of the person, and sends data indicative of the person's
weight to the control unit. The control unit records the weight and
the time of the weighing. The data is either analyzed locally and
sent to medical personnel only if a threshold is reached, or is
directly sent to medical personnel, as described above. The weight
data may be able indicate whether the user is at risk for heart
failure. The calibrated weight from a scale can be used by the
control unit to assist in calibrating the pressure pad's relative
weights into absolute weights (pounds or kilograms).
[0102] It should be noted that the inventors have found that
different variably resistive materials perform differently under a
mattress. A first material (conductive film) appears to be very
reliable for "in bed" and "out of bed" detection, while a second
material (conductive foam) is more reliable at providing a relative
weight once a user is in bed and lying still. Therefore, in some
embodiments of the present invention, the analog pad with includes
two types of variably resistive materials in communication with the
control unit. Data from the first material is used for in bed and
movement detection. Once the movement stills data from the second
material is sampled for determining weights. As soon as movement is
detected again, the control unit analyzes data from the first
material again.
* * * * *