U.S. patent application number 13/663072 was filed with the patent office on 2013-02-28 for prosthetic sensing systems and methods.
The applicant listed for this patent is Frank J. Fedel, Richard H. Harrington, Michael G. Leydet, Michael Link, Joshua J. Street. Invention is credited to Frank J. Fedel, Richard H. Harrington, Michael G. Leydet, Michael Link, Joshua J. Street.
Application Number | 20130053979 13/663072 |
Document ID | / |
Family ID | 38649352 |
Filed Date | 2013-02-28 |
United States Patent
Application |
20130053979 |
Kind Code |
A1 |
Leydet; Michael G. ; et
al. |
February 28, 2013 |
PROSTHETIC SENSING SYSTEMS AND METHODS
Abstract
Systems and methods are disclosed for sensing forces, moments,
temperature, inclination, acceleration and other parameters
associated with prosthetic limbs. The system is capable of
measuring forces in three designated axes, and moments about the
same designated axes, for a total of six possible degrees of
freedom. The system can be readily fitted onto a conventional
prosthetic limb with no, or relatively minor, modification thereto.
A plurality of sensor arrays are disposed on a support member, each
array including a plurality of strain gauge sensors, each sensor
outputting an electrical signal responsive to loading imposed on
the support member through the prosthetic limb. Electronic
circuitry in communication with the gauges is operative to receive
the electrical signals from the strain gauges and provide a signal
useful in the form, fit or function of the prosthetic limb.
Inventors: |
Leydet; Michael G.; (St.
Clair Shores, MI) ; Harrington; Richard H.; (Dexter,
MI) ; Fedel; Frank J.; (Dearborn Heights, MI)
; Link; Michael; (Chesterfield, MI) ; Street;
Joshua J.; (Livonia, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Leydet; Michael G.
Harrington; Richard H.
Fedel; Frank J.
Link; Michael
Street; Joshua J. |
St. Clair Shores
Dexter
Dearborn Heights
Chesterfield
Livonia |
MI
MI
MI
MI
MI |
US
US
US
US
US |
|
|
Family ID: |
38649352 |
Appl. No.: |
13/663072 |
Filed: |
October 29, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11741397 |
Apr 27, 2007 |
8298293 |
|
|
13663072 |
|
|
|
|
60796301 |
Apr 28, 2006 |
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Current U.S.
Class: |
623/25 ; 600/587;
623/27 |
Current CPC
Class: |
A61F 2/60 20130101; G01B
7/18 20130101; A61F 2002/7665 20130101; A61F 2002/705 20130101;
A61F 2002/7695 20130101; A61F 2002/7645 20130101; A61F 2/54
20130101; A61F 2002/7635 20130101; A61F 2002/7625 20130101; A61F
2/76 20130101; A61F 2/70 20130101; A61F 2002/764 20130101 |
Class at
Publication: |
623/25 ; 623/27;
600/587 |
International
Class: |
A61F 2/72 20060101
A61F002/72; A61B 5/103 20060101 A61B005/103; A61F 2/60 20060101
A61F002/60 |
Claims
1. A sensing system for use with a prosthetic limb, comprising: a
support member having a length axis configured for attachment to a
prosthetic limb; a plurality of sensor arrays disposed on the
support member, each array including a plurality of strain gauge
sensors, each sensor outputting an electrical signal responsive to
loading imposed on the support member through the prosthetic limb;
the plurality of sensor arrays including at least one array having
a sensor aligned with the length axis of the support member; and
electronic circuitry in communication with the gauges, the
electronic circuitry being operative to receive the electrical
signals from the strain gauges and provide a signal useful in the
form, fit or function of the prosthetic limb.
2. The system of claim 1, wherein each strain gauge array includes
a plurality of strain gauge sensors oriented to sense loads along
three independent axes and the moments associated therewith so as
to determine all six subcomponents needed to fully describe a load
applied to the prosthetic limb.
3. The system of claim 1, further including an array having a gauge
oriented along the length axis of the support member and a pair of
gauges oriented at angles on either side of the axially oriented
gauge.
4. The system of claim 3, wherein the pair of strain gauges are
oriented at 45 degree angles relative to the axially oriented
gauge.
5. The system of claim 1, wherein the support member is a rigid
tube having a first end configured for attachment to the socket of
a prosthetic limb, and a second end configured for attachment to a
pylon of a prosthetic limb.
6. The system of claim 1, wherein: the support member is configured
for attachment to a prosthetic leg; and the placement of the
support member is: between the foot and a pylon, or between the
pylon and a knee device, or above a knee device, or between a knee
device and an above-the-knee socket.
7. The system of claim 1, wherein the electronic circuitry is
configured such that the strain gauges generate positive and
negative (signed) voltages.
8. The system of claim 7, wherein the electronic circuitry is
operative to determine moments and shear forces based upon the
signed voltages generated by the strain gauges.
9. The system of claim 7, wherein the electronic circuitry is
operative to compensate for off-center loading using the signed
voltages.
10. The system of claim 1, further including analog or digital
switches operative to activate the strain gauges as necessary to
conserve power or reduce heat generation.
11. The system of claim 1, wherein the electronic circuitry
includes an analog multiplexer interconnecting the strain gauges to
a common instrumentation amplifier such that the gains of the
strain gages are substantially equalized.
12. The system of claim 1, further including: an inclinometer and
accelerometer; and wherein the signal provided by the electronic
circuitry is used to analyze the gait of a user.
13. The system of claim 1, further including: a pair of
inclinometers, one disposed on either side of an articulating
joint; and wherein the electronic circuitry is operative to receive
signals from the inclinometers and output data approximating a
goniometer.
14. The system of claim 13, wherein the inclinometers are disposed
on either side of an ankle joint.
15. The system of claim 1, further including a data collection
module for receiving the signal from the electronic circuitry.
16. The system of claim 15, wherein the module receives the signal
from the electronic circuitry through a wired or wireless
connection.
17. The system of claim 15, further including: an unaffected limb
electronics package (ULEP) including an inclinometer and
accelerometer; and wherein the module for collecting data is
further operative to receive data from the inclinometer and
accelerometer of the ULEP to analyze the gait of a user.
18. The system of claim 15, further including: an unaffected limb
electronics package (ULEP) including a pair of inclinometers, one
disposed on either side of an articulating joint; and wherein the
module for collecting data is further operative to output data
approximating that of a goniometer associated with the unaffected
limb.
19. The system of claim 1, wherein the electronic circuitry is
powered by a generator associated with said prosthetic limb.
20. The system of claim 19, wherein the generator is a
piezoelectric generator or a moving magnet generator.
21. The system of claim 1, wherein the electronic circuitry
operates on an intermittent basis to conserve power.
22. The system of claim 1, further including a motion detector
operative to activate the electronic circuitry when motion is
detected.
23. The system of claim 1, wherein the data provided by the
electronic circuitry is operative to control a component of the
prosthetic limb.
24. The system of claim 1, wherein the data provided by the
electronic circuitry is operative to provide an alarm indicating
malfunction of the prosthetic limb.
25. The system of claim 1, wherein the support member is
flexible.
26. The system of claim 25, wherein the support member comprises a
sheet of flexible polymeric material which is affixable to the
prosthetic limb.
27. The system of claim 1, wherein the prosthetic limb is a leg or
an arm.
28. A method of analyzing a user's gait, said method comprising the
steps of: providing the system of claim 1; disposing the system on
a prosthetic leg or arm worn by the user; having the user walk; and
analyzing the data provided by the electronic circuitry.
29. A method of controlling the operation of a prosthetic limb,
comprising the steps of: providing a prosthetic leg or arm having
an electronically controllable component thereupon; providing the
system of claim 1; affixing the system to the prosthetic leg or arm
worn by a user; having the user walk; and using the data provided
by the electronic circuitry to control the operation of the
electronically controllable component.
Description
REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. patent
application Ser. No. 11/741,397, readable filed Apr. 27, 2007,
readable which claims priority of U.S. Provisional Patent
Application Ser. No. 60/796,301, readable filed Apr. 28, 2006,
readable the entire content of both of which is incorporated herein
by reference.
FIELD OF THE INVENTION
[0002] This invention relates to systems and methods for sensing
forces, moments, temperature, inclination, acceleration and other
parameters associated with prosthetic limbs. More specifically, the
invention relates to systems capable of measuring forces in three
designated axes, and moments about the same designated axes, for a
total of six possible degrees of freedom that can be associated to
the object in three-dimensional space.
BACKGROUND OF THE INVENTION
[0003] It is often desirable to measure stresses and strains caused
by loads or loading which occur in the use of prosthetic limbs. It
may also be desirable to measure the inclination and acceleration
of the prosthesis which are also critical to promote better gait.
Such measurement may be made in connection with the design of
prosthetic limb systems or with the fitting or adjustment of limbs,
or the analysis of the user's motion in the course of operating a
limb, as for example in the case of gait analysis. In other
instances, loads may be measured or detected as part of an alarm
system which indicates malfunction in a prosthetic limb. In yet
other instances, such measurements may be used to control the
operation of a component of a limb such as a motion damper, an
electronically controllable joint, or other such structure.
[0004] In response to needs and applications such as the
aforedescribed, the prior art has implemented various approaches to
systems for measuring loads in prosthetic limbs. Some measurement
systems rely upon the use of devices external to the limbs such as
pressure plates and the like. Such systems are often difficult to
use, and can interfere with a normal range of motion by the user;
furthermore, such systems generally provide relatively limited
data. Various onboard systems have been implemented; however, such
systems generally require significant modification of a prosthetic
limb. Hence they are not readily utilizable in connection with
diagnosis of persons using preexisting limb systems. Furthermore,
their complexity generally restricts their use to dedicated
research applications.
SUMMARY OF THE INVENTION
[0005] This invention relates to systems and methods for sensing
forces, moments, temperature, inclination, acceleration and other
parameters associated with prosthetic limbs. In the preferred
embodiment the system is capable of measuring forces in three
designated axes, and moments about the same designated axes, for a
total of six possible degrees of freedom.
[0006] The system comprises a plurality of sensor arrays disposed
on a support member, each array including a plurality of strain
gauge sensors, each sensor outputting an electrical signal
responsive to loading imposed on the support member through the
prosthetic limb. Electronic circuitry in communication with the
gauges is operative to receive the electrical signals from the
strain gauges and provide a signal useful in the form, fit or
function of the prosthetic limb.
[0007] In accord with the preferred embodiment, each strain gauge
array includes a plurality of strain gauge sensors oriented to
sense loads along three independent axes and the moments associated
therewith so as to determine all six subcomponents needed to fully
describe a load applied to the prosthetic limb. In one disclosed
configuration for accomplishing this, the gauges of the array
include an axially oriented gauge and a pair of gauges oriented at
angles such as +/-45 degrees on either side of the axially oriented
gauge.
[0008] The support member may be a flexible panel or a rigid tube
having a first end configured for attachment to the socket of a
prosthetic limb, and a second end configured for attachment to a
pylon of a prosthetic limb. If used with a prosthetic leg, for
example, the support member may be placed between the foot and a
pylon, between the pylon and a knee device, above a knee device, or
between a knee device and an above-the-knee socket.
[0009] The electronic circuitry may be configured so that the
strain gauges generate positive and negative (signed) voltages.
This allows the circuitry to determine moments and shear forces
based upon the signed voltages generated by the strain gauges,
providing the ability to compensate for off-center loading. Analog
or digital switches may be provided to activate the strain gauges
as necessary to conserve power or reduce heat generation. An analog
multiplexer may be provided to interconnect the strain gauges to a
common instrumentation amplifier such that the gains of the strain
gages are substantially equalized.
[0010] In addition to the strain gauges, the system may receive
inputs from an inclinometer and accelerometer, in which case the
signal provided by the electronic circuitry may be used to analyze
the gait of a user. A pair of inclinometers may be provided, one
disposed on either side of an articulating joint such as an ankle
joint, in which case the electronic circuitry is operative to
receive signals from the inclinometers and output data
approximating a goiniometer.
[0011] To enhance versatility, the system may include a data
collection module for receiving the signal from the electronic
circuitry. The module may be remotely located and may communicate
with the electronic circuitry through a wired or wireless
connection. In addition to the affected limb system, the module may
receive signals from an unaffected limb electronics package
including an inclinometer or accelerometer, in which case the
module may analyze a more complex gait pattern. The unaffected limb
electronics package may also include a pair of inclinometers to
implement a goiniometer function associated with the unaffected
limb.
[0012] The may be powered by a generator associated with said
prosthetic limb such as a piezoelectric generator or a moving
magnet generator. The electronic circuitry may operate on an
intermittent basis so as to conserve power. A motion detector may
be provided such that when motion is detected, operation of the
electronic circuitry is initiated.
[0013] The data provided by the electronic circuitry may be used
for a variety of purposes. For example, it may be used to control a
component of the prosthetic limb or provide an alarm indicating
malfunction of the prosthetic limb. A method of analyzing the gait
of a user includes the steps of disposing the system on a
prosthetic leg or arm worn by the user, having the user walk, and
analyzing the signal provided by the electronic circuitry. Other
methods are disclosed, including methods of controlling the
operation of an electronically controllable component associated
with the prosthetic limb.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a front view of a system optimized for use with a
prosthetic leg according to the invention;
[0015] FIG. 2 is a back view of a system optimized for use with a
prosthetic leg according to the invention;
[0016] FIG. 3 shows an embodiment of the invention in which a
relatively flexible support member for sensors and an electronics
package;
[0017] FIG. 4 shows a portion of a prosthetic limb, in this
instance a pylon, having the flexible support mounted
thereupon;
[0018] FIG. 5 shows a sensing system wherein the flexible substrate
portion is formed into a cylinder;
[0019] FIG. 6 shows a rosette strain gauge array comprising three
strain sensors sensitive to strains along three axes;
[0020] FIG. 7 shows four instrumentation amplifiers, one associated
with a bridge configuration, the outputs of which are summed by an
operational amplifier;
[0021] FIG. 8 is a block diagram of an electronics package for an
intelligent tube clamp adapter (ITCA) according to the
invention;
[0022] FIG. 9 is a simplified block diagram depicting an unaffected
limb electronics package (ULEP) according to the invention;
[0023] FIG. 10 is a block diagram of a data-collection module, or
DCM, used for collecting the data from the ITCA(s), and the
ULEP(s), as provided; and
[0024] FIG. 11 is a diagram that shows how an ITCA and DCM may be
used in conjunction with a ULEP to form an intelligent prosthetic
endo component system (IPECS).
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] This invention relates to systems and methods for sensing
forces, moments, temperature, inclination, acceleration and other
parameters associated with prosthetic limbs. The preferred
embodiments are capable of measuring forces relative to three
designated axes, and moments about the same designated axes, for a
total of six possible degrees of freedom associated with the object
in three-dimensional space. The invention is applicable to legs and
arms, with amputation or deficiency occurring at any point
facilitating a workable coupling. In all cases a goal is to provide
a sensing system that attaches to a prosthetic limb with no, or
relatively minor, modification thereto.
[0026] One disclosed embodiment includes a support member to which
a plurality of strain gauge sensors are affixed in a preselected
pattern. Each strain gauge is operative to provide a change in one
of its detectable characteristics, typically electrical resistance,
in response to a strain imposed on the member. The system further
includes an electronics package which is in communication with the
gauges. The electronics package is operative to detect the change
in detectable characteristics of the strain gauges and to provide
data in response thereto, such data being useful in the form, fit
or function of the prosthetic limb.
[0027] The sensing system may replace a support member of the
prosthetic limb with an Intelligent Tube Clamp Adapter (ITCA).
Alternatively, the system may be integrated to an existing
prosthetic component. The support member may be rigid, semi-rigid,
or may comprise a body of flexible material such as a polymeric
sheet which may be affixed to the limb, for example, by the use of
an adhesive. The electronics package may be mounted either on the
support member or on the limb itself. As explained in greater
detail herein, the electronics package may be operative to process
and/or store sensor signals, and in some instances, communicate
them via a wired or wireless link to a computer or data collection
module (DCM). The DCM may also receive signals from an unaffected
limb electronics package (ULEP) according to the invention to form
an intelligent prosthetic endo component system (IPECS) providing,
among other functions, a virtual goiniometer capability.
[0028] FIGS. 1 and 2 are respective front and back views of one
specific embodiment of the invention. As shown, the device includes
a support member 10, which in this instance is a rigid housing
configured for attachment to a prosthetic limb. The housing is
configured so that a first end 12 is affixable to the socket
portion of a prosthetic limb via set screws 14. A second end 16 is
configured to clamp onto a pylon portion of the limb, and as such
includes a split sidewall operative in cooperation with a screw 18.
As shown in these drawings, the support member 10 is configured to
clamp onto a pylon having a circular cross section. It is to be
understood that the support member 10 may likewise engage a pylon
having another configuration of cross section, such as an oval
cross section, a polygonal cross section or an irregular cross
section.
[0029] In the use of the system of FIGS. 1 and 2, the housing 10 is
joined to the socket portion of the prosthetic limb, which socket
portion engages the stump of the limb. In the case of a leg
prosthesis, the pylon has a prosthetic foot joined to the second
end 16. In those instances where the user is an above-the-knee
amputee, an artificial knee joint mechanism may be included in the
assembly, and the sensor of the present invention is typically
incorporated in the below the knee joint portion; although, in some
applications, it may alternatively be disposed above the knee
joint.
[0030] The system illustrated in FIGS. 1 and 2 may be readily
incorporated into a pylon of a prosthetic limb with minor
modification. The housing is configured so that the first end 12
fits onto a conventional socket in a similar manner to a typical
pylon connection. Therefore, no modification of the socket need be
carried out. The second end of the housing is configured to fit
onto a standard pylon, and again no modification is needed. The
housing itself will occupy some length of the limb, and typically
the length of the pylon will be adjusted to accommodate for the
length of the housing. If it is desired to remove the system after
measurements have been made, a conventional pylon of standard
length may be substituted for the shortened pylon, and the
prosthetic limb returned to use with no further modification being
required.
[0031] The sensor system includes a plurality of strain gauges
which are, in this embodiment, affixed to the housing, and in FIGS.
1 and 2, two of these strain gauges 22, 24 are shown. The housing
may have markings thereupon to aid in the proper placement of the
strain gauges 22, 24. Although not visible in these figures,
further strain gauges may be incorporated onto the housing 10 as
described elsewhere herein. In the illustrated embodiment, the
electronics package is disposed on a circuit board 26 affixed to
the housing. The housing includes a connector 28 that allows the
electronics package to be in communication with another electronic
device such as a data processor, mass data storage device or the
like. This other device may be disposed on the limb or off the limb
as described in further detail herein.
[0032] As is known in the art, the strain gauges may be adhesively
affixed to the ITCA or, as for example, to the pylon. After
affixation, the strain gauges may be adjusted by physical
calibration processes such as laser trimming; alternatively,
dynamic calibration processes, implemented through software and/or
hardware in the electronics package, may be used to accommodate
variations in sensor response and/or sensor placement. A dynamic
trimming procedure is described in further detail herein below.
[0033] While embodiments of the invention position the strain
gauges and electronics package onto a relatively rigid member which
is coupled to a prosthetic limb system, other embodiments of the
present invention are contemplated. For example, FIG. 3 shows an
embodiment of the invention in which a relatively flexible support
member 40 supports the sensors and electronics package. The support
member 40 is generally made from a polymeric material of the type
used for flexible printed circuit boards, and such material
includes polyimide polymers such as Kapton.RTM., polyesters,
polysulfones, polyethers, and other relatively stable, flexible
polymers. Disposed upon the flexible member 40 are strain gauges,
which in this instance are similar to the strain gauges 22 and 24
previously described. Also included is an electronics package 42
which is in communication with the sensors.
[0034] As illustrated in FIG. 3, the electronics package includes
terminals 44, 46 associated therewith, and these terminals, as well
as further terminals, may be used to establish connection to the
electronics package for data transfer, power supply and the like.
Circuitry for the electronics package may be formed directly on the
support member 40, and techniques such as chip onboard technology
may be utilized as is known in the art.
[0035] In the use of the system of FIG. 3, the flexible support
member 40 is mounted onto a portion of a prosthetic limb, such as
the pylon or other portions of limb structures. Mounting is
typically accomplished by the use of an adhesive material, and
adhesives which form a rigid bond are generally favored so that
transfer of limb loading is efficiently accomplished. Such
adhesives may include curable adhesives such as epoxies, urethanes
and the like. To aid in alignment of the sensing system on the
prosthetic limb, alignment markings such as markings 48 are
included on the substrate 40.
[0036] FIG. 4 shows a portion of a prosthetic limb, in this
instance a pylon having the flexible support 40 mounted thereupon.
As will be noted, the alignment marks 48 on the flexible member 40
are aligned with corresponding marks 52 on the pylon. In some
instances it may be advantageous to preform the sensing system so
as to conform to the substrate upon which it will be disposed. FIG.
5 shows a sensing system wherein the flexible substrate portion 40
is formed into a cylinder. Other such preformed shapes will also be
apparent to those of skill in the art.
[0037] Different types of strain gauges may be used according to
the invention. Gauges 22, for example, are unidirectional gauges
disposed so as to measure loading in the X and Y (horizontal) axis
of the limb when it is in use. Diametrically opposed strain gauges
24, each include two strain variable resistors and each forms a
full Wheatstone bridge. In this embodiment, these paired gauges are
used to measure loading in the Z axis, which is generally aligned
with the length axis of the prosthetic limb.
[0038] In the preferred embodiment, however, all of the strain
gauges are rosette strain gauge arrays comprised of at least three
strain sensors. In this manner, each of the arrays will be
sensitive to strains along three axes. One such gauge is shown in
FIG. 6 at reference numeral 60. This gauge 60 includes three
resistive components 62, 64 and 66, and is mounted on the
prosthetic limb so that the direction of strain gauge 64 is
generally parallel to the Z axis for the highest sensitivity. At
least two other gauge elements, 62, 66 are placed on either side of
element 64 and oriented for the highest sensitivity orientations of
45 degrees and -45 degrees off-axis, respectively. Other gauge
clusters are similarly disposed about the ITCA. Using an
arrangement as described, normal strain as measured by the gauge at
a given point can be translated into shear strain at the same
location utilizing the following equation:
.gamma..sub.xy=.epsilon..sub.1-.epsilon..sub.3
where .epsilon..sub.1 is the strain sensed by element 64 and
.epsilon..sub.3 is the strain sensed by element 62.
[0039] Utilizing strain gauge arrangements of the types described
above, it is possible to represent direct relationships between
normal strain and contributing force and moment components of
applied loads. Therefore, by the use of appropriately positioned
strain gauges, it is possible to determine all six subcomponents
needed to fully describe an applied load on a prosthetic limb.
Systems of this type may be adapted to regular structures such as
circular pylons, as well as to structures having noncircular but
symmetrical cross sections, particularly if consistent
circumferential placement is used.
[0040] Different placements of the gauges afford certain
advantages. For example, strain gauges spaced equidistantly from
the centroid of the loaded member facilitates off-center load
rejection. According to this embodiment, four strain gauges are
placed on the tube to measure X and Y bending forces. These gauges
are placed at 0 degrees, 180 degrees for the Y bending force, and
at 90 and 270 degrees to measure the X bending force. To handle the
addition and subtraction of strain values each gauge subcomponent
180, 182, 184, 186 is in a quarter Wheatstone bridge setup 190,
192, 194, 196 as shown in FIG. 7. A microprocessor associated with
the electronics portion of the system handles the necessary
mathematics.
[0041] The accepted method for transducer applications typically
use half or full Wheatstone bridge configurations to measure
strain. The benefits include automatic temperature compensation and
improved signal-to-noise ratio. For example, a conventional
approach is to use two T-rosette gauges in a full Wheatstone bridge
configuration. The gauges typically have two gauge patterns that
are perpendicular to each other. The gauges are typically placed
with one gauge pattern along the Z axis and the other along the X
axis. The gauge in the X axis senses the Poisson's strain which is
very small compared to the axial strain, typically about 3% of the
axial strain and is used for temperature compensation.
[0042] When an on-center load is applied to the end of the tube (Z
axis), the two axial gauges of the 2 T-rosette gauges will be in
compression, and when used in the standard Wheatstone bridge
configuration, the full bridge which uses all elements of two
T-rosette gauges will produce a voltage proportional to the applied
force. However, when an off-center force is applied, an error
occurs. The reason for the error arises from the way in which the
bridge is set up, in that signed numbers are not taken into
account. As such, the full Wheatstone bridge using axial and
lateral gauges does not perform the proper math to give correct
off-center load results.
[0043] An alternative approach is to use a different bridge
configuration using four gauges and summing the signed result. When
an off-center load is applied to the column, the gauges applied to
the same side of the column will be in compression and gauges
opposed to the ones in compression will be in tension. The proposed
strain gauge circuit provides a negative voltage for compression, a
positive voltage for tension and then when summed together, they
produce a result consistent with the applied load. The summation
can be done in an analog fashion using a summing operational
amplifier, or more complex calculations can be done with a computer
after an A/D conversion is done.
[0044] Referring again to FIG. 7, four instrumentation amplifiers
200, 202, 204, 206, one associated with each bridge configuration,
provide outputs which are summed by operational amplifier 210.
Alternatively, as shown in FIG. 8, one instrumentation amp may be
used if the outputs of the bridges are multiplexed under
microprocessor control. After performing the A/D conversion of the
gauges, an algebraic addition can be used to solve for the Z axis.
Since only one instrumentation amp is used, the error in that amp
will be the same for all readings, and if a precision reference and
ground are provided to the multiplexer, the absolute value from the
gauges may be determined with the instrumentation amp gain error
being removed from the error equation.
[0045] An additional benefit of multiplexing is automatic
temperature compensation. If all strain gauges track with
temperature, for instance the resistance of the gauges rises by the
same amount with an increase in temperature, the net result as seen
by the A/D converter will be same for all the gauges. The
instrumentation amp is a differential amplifier and only amplifies
the difference in the strain gauge resistances, so the
instrumentation amp output will not change. In FIG. 8, signal 92 is
one of the two inputs to the instrumentation amp. This signal is
the strain gauge excitation voltage divided by two plus an offset
calculated by the microprocessor to make this voltage compatible
with the strain gauge that is being selected by the
multiplexer.
[0046] With four gauges at 0, 90, 180 and 270 degrees, the
electronics package can be used to solve X moments and Y bending
moments. The math for solving X and Y bending is to reverse the
sign of one of the X or Y measurements and then add the two values
together. The sign reversal is necessary because with an on-center
load application, to X and Y outputs would both be positive and in
proportion to the applied force. Reversing the sign of one of the
gauges and then adding corrects the problem. Zero output at on
center loading and either negative or positive depending on force
application, such that with four gauges, Z axial and X and Y
moments may be determined. Additional gauges may also be
multiplexed into the same instrumentation amplifier.
[0047] Calibration of the load cell can be accomplished using an
automated process, applying known forces, and performing the gain
correction and zero correction using the embedded micro in the load
cell. However, more often than not, small adjustments to the bridge
resistors are necessary to produce a voltage that will not cause
the associated instrumentation amplifier to go into saturation, or
not be within the working range of the analog-to-digital (A/D)
converter. The overall gain of the instrumentation amplifier block
is often 1,000 or more, and the strain gauges are produced to a
typical absolute resistance of 0.3% and the resistors that are in
series with the gauges have a 0.1% tolerance. This tolerance
stack-up will produce a 10 volt error after being amplified 1,000
times. This error must be reduced before it can go to the A/D.]
[0048] This dynamic trimming is used instead of having to add small
resistance wire in series with the strain gauges so that the
Wheatstone bridge can be balanced. The dynamic trimming is done in
the following way: the microprocessor executes a routine that
selects a strain gauge with no load and looks at the A/D voltage
for that gauge. Using successive approximation, the processor
calculates the proper off-set value for each gauge. These values
will be stored in flash memory for use each time that gauge is
being selected, and will be used by the DAC that produces the
off-Set value. This voltage will force the voltage at the one of
the instrumentation amplifier's inputs to a value that makes the
input to the A/D converter in the working range.
Intelligent Tube Clamp Adapter (ITCA) Operation
[0049] The electronics package may be variously configured
depending upon the particular application. In the embodiment of
FIGS. 8, 12 to 16 strain gauges 70 are bonded to the intelligent
tube clamp adapter (ITCA), for measuring forces and moments. Each
strain gauge has two resistors in series, which equal the strain
gauge resistance. A group of four strain gauges and their
corresponding resistors are tied to a common point, shown as blocks
A, B, C, and D on the block diagram. These points are connected to
power MOSFETS (also not shown), powered by programmable power
supply 71. The power MOSFETS have a very low drain-source (D-S) ON
resistance (120 m Ohms max). They should not effect the strain
gauge measurement as long as the D-S ON resistance is accounted for
during calibration. Block activation is used at 72 through SELECT
lines 74 to save on power and reduce the self-heating of the ITCA
by strain gauges. The strain gauge circuits draw 57 mA per block of
4 strain gauges/resistors. If all the strain gauges were on all the
time, 228 mA would be needed and it would produce 1.7 Watts of
power.
[0050] The A/D converter 76 located in the microprocessor 78 can
only perform one conversion at a time, so an analog multiplexer 82
is provided to accommodate the large number of channels. The
outputs of the strain gauges/resistors are connected to a
16-channel analog multiplexer which is addressed by the
microprocessor 78 via path 84. The multiplexed voltages will be
.about.1/2 of the strain gauge excitation voltage. The strain gauge
excitation voltage is controlled by the microprocessor by changing
the voltage output on 68 and 86. The output of the 16-channel
analog multiplexer 82 is fed to instrumentation amplifier on path
90 along with a signal on path 92 equal to 1/2 the strain gauge
excitation voltage and a bias voltage which is controlled by the
microprocessor. This bias voltage is produced by D/A converter 94.
The offset on 96 is then fed to voltage divider and summer 98. The
reason for this is that, more often than not, small adjustments to
the bridge resistors are necessary to produce a voltage that will
not cause the instrumentation amplifier to go into saturation. This
improved method makes the small adjustments to the bridge resistors
unnecessary, and will force the instrumentation amp output voltage
to be in the working range of the A/D converter.
[0051] The strain gauges in this embodiment are arranged as 16,
1/4-bridge configurations (100); however, in reality they form at a
minimum a 1/2 bridge configuration. This is a very important fact
because of the benefits obtained by the 1/2 or full bridge over
that of a 1/4 bridge. Consider two axial strain gauges located 180
degrees apart on the ITCA. The two gauges get transferred to a
single instrumentation amplifier (which provides the added benefit
that all the strain gauges can have the exactly the amplification
factor applied) and then to programmable gain amplifier 102, which
will be set to the same gain while looking at the two opposed
gauges. The microprocessor performs mathematics on the various
gauges to make a composite value. In the case of an on-axis load,
the resultant output will be four times greater than a single 1/4
bridge because there are four gauges used for this equation. If the
four axial gauges were connected in the conventional full
Wheatstone bridge, it would have zero output with on-center load
because all the gauges would be at the same resistance, so the
voltage going into the instrumentation amplifier would be zero.
[0052] Another benefit is automatic temperature compensation which
is a considerable problem for a 1/4 bridge. Using the multiplexer,
a single instrumentation amplifier and programmable gain amplifier,
temperature compensation will be accomplished (assuming the whole
ITCA tube is at the same temperature) because the strain gauges
will track each other with temperature. If one gauge goes up in
resistance, the opposing gauge located on the other side of the
tube should go up approximately the same amount. The
instrumentation amplifier is a differential amplifier, and will
amplify only the difference between the signals, which in the case
of both gauges going up in value will cause the voltage at the
gauge/fixed resistor point junction to go down slightly. The gauge
located on the other side of the tube will also increase in
resistance, and the same thing will occur at its gauge/fixed
resistor point. The instrumentation amplifier output will not
change because there was no voltage differential.
[0053] Yet another benefit of the strain gauge amp configuration is
the ability to produce signed values. This is necessary because the
mathematics that calculates the forces and moments needs signed
numbers to generate properly. Without signed values, off-center
load cannot be properly calculated. Other calculations for forces
and moments need signed values as well. The signed values are
produced initially by the instrumentation amplifier, going both in
the negative and positive quadrant.
[0054] As discussed, the output of the instrumentation amplifier 88
is fed to the programmable gain amplifier 102. This amplifier's
gain is controlled by the microprocessor with 4 bits that make up
the GAIN SELECT bus 104. This allows for the gain to be changed in
16 steps for gains of 1 to 100. The gain word/gain factor is
linear. The overall gain for the strain gauges is equal to the gain
product of the instrumentation amplifier and the programmable gain
amplifier. The gain of the instrumentation amplifier is 50 and the
gain of the programmable gain amplifier is 1 to 100, so the overall
strain gauge gain is equal to 50 to 5,000.
[0055] Tri-axial inclinometers and accelerometers, depicted at
block 106, provide signals to analog multiplexer 80. The actual
part is MEMS technology with static as well as dynamic capability.
The MEMS device has small weights attached to it so that it
responds to the earth's gravity. In this way, it can be used as a
tilt sensor, with the output relating to how the chip is positioned
in relationship to the Earth's gravity.
[0056] The inclinometers and accelerometers may be included either
in the housing itself, or in association with the limb. These
inclinometers will provide a signal indicative of side-to-side and
fore/aft motion of the limb and may be used in conjunction with
strain gauge data to provide for a full range of motion analysis.
The accelerometers will provide a signal indicative of acceleration
and the direction of the limb's motion and may be used in
conjunction with strain gauge sensor and inclination data to
provide for a full range of motion analysis.
[0057] In yet other instances, measurement of the toe in/toe out
position of the prosthetic foot relative to the remainder of the
limb may be made, either by an onboard position sensor or by
mechanical or other measurements made at the time that the limb is
fitted. If the tilt sensors are located on the foot and on the
limb, the microprocessor may analyze the signals and compute the
angle between the foot and limb, thereby creating an electronic or
`virtual` goniometer. This analog multiplexer is addressed through
path 84 with the same address lines as the strain gauge mux with
the tilt mux output (110) going to a second A/D port pin located on
the microprocessor so that no conflict with the strain gauge
multiplexer is encountered.
[0058] The various components receive power from a rechargeable Li
battery and an automatic switch to a super capacitor if the battery
suddenly looses power. This condition will alert the data
collection module (DCM) described later that the ITCA battery needs
recharging, and will also send the last data available to the DCM.
The battery voltage will be used by the various power supplies to
produce the necessary voltages the ITCA needs, such as +10/+5V for
the strain gauges, the +/-15 volts needed by the multiplexers, the
+3.6V needed by the microprocessor.
[0059] USB communications is accomplished by connecting a UART/USB
bridge chip 114 to the microprocessor UART port along path 116. A
standard USB mini connector 118 is mounted on the ITCA PC board.
The RF multi-channel transceiver 120 located on the ITCA
communicates with the data collection module (DCM). The DCM will
determine when the ITCA should transmit so that collisions do not
occur. The ITCA performs signal averaging so that only necessary
data transfer occurs. The multi-channel approach has been chosen so
that multiple ITCAs can operate in the same space, and also to
avoid being swamped by signals not associated with the
ITCA/DCM.
Unaffected Limb Electronics Package (ULEP)
[0060] FIG. 9 is a simplified block diagram depicting an unaffected
limb electronics package (ULEP) generally at 128. The ULEP is
connected to inclinometers/accelerometers 132, 134 that are mounted
typically on the foot and on the limb or ITCA to measure both the
ground surface tilt, and also the angle between the foot and the
limb (virtual goinometer). The ULEP system is controlled by a
separate processor 140. A USB translator 142 is interfaced to a USB
port 144 for hard-wired communication. In the normal mode of
operation, only the RF transceiver link 130 to the DCM will be
used.
Data Collection Module (DCM)
[0061] The data-collection module, or DCM, shown generally at 148
in FIG. 10, is used for collecting the data from the ITCA(s), and
the ULEP(s), as provided. This is done over an RF Link using a
transceiver 150 based upon low-power frequency hopping spread
spectrum chips. With this technology, multiple units (multiple DCMs
and their ITCA and ULEP) can be operated in the same radio space
with little interference. The core of this technology is a
frequency agile transmitter and receiver that change their
frequency in a predictable method so that the entire system knows
what the next frequency will be, and when to change. This RF link
operates on the 915 MHz scientific and medical/short-range device
(ISM/SRD) band.
[0062] The DCM is the master and assigns time slots for the ITCA
and the ULEP to send their data to the DCM. This is called a
deterministic system, which avoids collisions because of the strict
rules regarding time slots. A second method of transmitting is
clear-channel assessment (CCA) where the transceivers listen before
transmitting so that they do not have two transmitters transmitting
on the same frequency at the same time.
[0063] The DCM has optional BLUETOOTH, and/or 802.11b transceiver
modules 152, 154 to transfer data the DCM gathered to PCs, PDAs,
laptops and wireless hot spots. The data will be encrypted for
security reasons. The optional modules will be turned on only when
directed to do so by the person using the DCM. The reason for this
is battery savings as well as security.
[0064] Time synchronization between the DCM and the two remotes
(ITCA, ULEP) is critical because the forces, moments and angles
need to be time stamped. Initially the DCM sends a time block to
update the timing registers to permit time synchronization. The DCM
and the remotes all have crystal clocks that are running at
approximately the same frequency. However with an elapsed time of
an hour (for instance), the clocks will drift. Periodically, the
DCM will send a new absolute time block to the remotes so that time
synchronization is maintained. Shorter time sync blocks will be
sent by the DCM so that the remotes can make small adjustments to
their clocks by updating a register that get incremented by a timer
located in the CPU of the remote. When the remotes upload their
data to the DCM, an abbreviated time stamp will be sent. This will
ensure that the DCM can associate a force, moment or tilt angle
with time. This timing information will be extremely helpful to the
researchers and prosthetist. If the DCM senses that a remote is
having time problems, it will download a full absolute time block
to that remote.
[0065] The DCM has a backlit LCD display 156 to monitor critical
functions such as equipment degradation or impending failure. Also
included is a beeper and a vibrator to alert the user. Other
functions that can be displayed are battery life, remaining memory
capacity, forces: average and peak, moments: average and peak, and
tilt: average and peak. A keypad 158 enables the user to pick the
various functions listed in the LCD section.
[0066] A USB 2.0 port 160 is available for connecting the DCM to a
PC, PDA, MEMORY STICKS 162. Using the USB connection, a custom
application program will upload the latest DCM data into a database
and will allow the person to see how they are walking, if excessive
forces were encountered. This program will show trends which will
be beneficial to the user, the researcher and the prosthetist. Also
available in this application will be select forces/select
moments/select angles/select all; display average; display PEAKS;
and display over-laid gate patterns (will ask how many steps).
[0067] For the gate labs, a 7-channel D/A port will be available
for connecting the DCM directly to a data gathering system. This
data will be 12 bit resolution analog signals that are single
ended. A separate processor 170 provides system control functions.
The DCM case has rounded edges so that it can fit into a pocket
easily. A detachable clip can be used for attaching the DCM to a
belt.
Intelligent Prosthetic Endo Component System (IPECS)
[0068] The ITCA and DCM may be used in conjunction with the
unaffected limb electronics package (ULEP) to form an intelligent
prosthetic endo component system (IPECS). FIG. 11 is a simplified
block diagram showing one ITCA, one ULEP and one DCM. The system is
composed of: one or two intelligent tube clamp adapters (ITCA), one
ITCA if one ULEP used, one data collection module (DCM), and one or
two unaffected limb electronics package (ULEP), one ULEP if one
ITCA is used.
[0069] While the foregoing has been described primarily with
reference to a system which is affixed to a prosthetic limb,
similar systems may be affixed to prosthetic arms and the like. In
view of the foregoing, numerous modifications and variations of the
system will be apparent to those of skill in the art. The foregoing
drawings, discussion and description are illustrative of specific
embodiments, but they are not meant to be limitations upon the
practice thereof. It is the following claims, including all
equivalents, which define the scope of the invention.
* * * * *