U.S. patent application number 15/600930 was filed with the patent office on 2017-12-14 for terrain adaptive powered joint orthosis.
The applicant listed for this patent is BionX Medical Technologies, Inc.. Invention is credited to Christopher Eric Barnhart, Richard James Casler, JR., Zhixiu HAN, Hugh M. Herr, Jeff Anthony Weber, Christopher Williams.
Application Number | 20170354529 15/600930 |
Document ID | / |
Family ID | 45567129 |
Filed Date | 2017-12-14 |
United States Patent
Application |
20170354529 |
Kind Code |
A1 |
HAN; Zhixiu ; et
al. |
December 14, 2017 |
TERRAIN ADAPTIVE POWERED JOINT ORTHOSIS
Abstract
A powered device augments a joint function of a human during a
gait cycle using a powered actuator that supplies an augmentation
torque, an impedance, or both to a joint. A controller estimates
terrain slope and modulates the augmentation torque and the
impedance according to a phase of the gait cycle and the estimated
terrain slope to provide at least a biomimetic response. The
controller may also modulate a joint equilibrium. Accordingly, the
device is capable of normalizing or augmenting human biomechanical
function, responsive to a wearer's activity, regardless of speed
and terrain, and can be used, for example, as a knee orthosis,
prosthesis, or exoskeleton.
Inventors: |
HAN; Zhixiu; (Acton, MA)
; Williams; Christopher; (Pittsburgh, PA) ; Weber;
Jeff Anthony; (San Francisco, CA) ; Barnhart;
Christopher Eric; (Carlisle, MA) ; Herr; Hugh M.;
(Somerville, MA) ; Casler, JR.; Richard James;
(Lowell, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BionX Medical Technologies, Inc. |
Bedford |
MA |
US |
|
|
Family ID: |
45567129 |
Appl. No.: |
15/600930 |
Filed: |
May 22, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13356230 |
Jan 23, 2012 |
9687377 |
|
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15600930 |
|
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|
61435045 |
Jan 21, 2011 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61F 5/0125 20130101;
A61H 2201/165 20130101; A61H 2201/1642 20130101; A61H 3/00
20130101; A61H 2201/5097 20130101; A61H 2205/102 20130101; A61H
2205/10 20130101; A61H 2003/001 20130101; A61H 2201/5064 20130101;
A61H 2201/5084 20130101; A61H 1/024 20130101; A61H 2201/5007
20130101 |
International
Class: |
A61F 5/01 20060101
A61F005/01; A61H 1/02 20060101 A61H001/02; A61H 3/00 20060101
A61H003/00 |
Claims
1. A method for assisting a person walking on a surface with a
powered human augmentation device including a controller, the
method comprising the steps of: determining a phase of a gait
cycle; estimating within the gait cycle, a slope of the surface;
supplying to a joint at least one of an augmentation torque and an
impedance comprising a linear spring component and a damping
component; and modulating the augmentation torque and the impedance
based on the phase of the gait cycle and the estimated slope to
provide at least a biomimetic response.
2. The method of claim 1, wherein the estimated slope is indicative
of a walking mode such that level-ground walking mode corresponds
to a substantially zero slope, downslope walking mode corresponds
to a negative slope, and upslope walking mode corresponds to a
positive slope.
3. The method of claim 2, wherein the downslope walking mode
comprises descending stairs and the upslope walking mode comprises
ascending stairs.
4. The method of claim 1, wherein the joint is a knee.
5. The method of claim 1 further comprising estimating walking
speed, wherein at least one of the augmentation torque and the
impedance is based on the estimated walking speed.
6. The method of claim 1, wherein if the phase of the gait cycle is
determined to be one of early stance and mid stance and the
estimated slope is substantially zero, the impedance is modulated
such that contribution of the linear spring component to the
modulated impedance is greater than contribution of the damping
component.
7. The method of claim 1, wherein if the phase of the gait cycle is
determined to be one of early stance and mid stance and the
estimated slope is negative, the impedance is modulated such that
contribution of the damping component is increased substantially
compared to contribution thereof if slope is estimated to be
substantially zero.
8. The method of claim 7, wherein modulating comprises varying the
damping component according to the negative slope.
9. The method of claim 1, wherein the augmentation torque comprises
a non-conservative propulsive torque; and if the phase of the gait
cycle is determined to be one of early stance and mid stance and
the estimated slope is positive, providing the non-conservative
propulsive torque such that the modulated augmentation torque is
greater than the modulated augmentation torque applied if the slope
is estimated to be substantially zero.
10. The method of claim 1, wherein if the phase of the gait cycle
is determined to be late stance, the augmentation torque is
modulated to correspond to a reflex torque that is related to the
estimated slope.
11. The method of claim 1 further comprising the step of modeling,
during a swing phase of the gait cycle, a joint equilibrium as a
second-order response to a joint-position goal to be achieved prior
to a next phase of the gait cycle.
12. The method of claim 11 further comprising the step of
determining if the joint is substantially fully flexed, during a
swing phase of the gait cycle, wherein modulating comprises
adjusting both the augmentation torque and the impedance to be
substantially zero, if the joint is determined to be substantially
fully flexed.
13. The method of claim 11, wherein if the phase of the gait cycle
is determined to be early swing, the augmentation torque is
modulated according to the joint-equilibrium model such that a
joint equilibrium corresponds to the joint-position goal.
14. The method of claim 11, wherein if the phase of the gait cycle
is determined to be early swing, the impedance is modulated
according to the joint-equilibrium model such that a joint
equilibrium corresponds to the joint-position goal.
15. The method of claim 1, wherein estimating the slope comprises
kinematically reconstructing a path of the joint within the gait
cycle.
16. The method of claim 15 further comprising the steps of:
kinematically reconstructing a path of another joint within the
gait cycle; and associating the path of the other joint with the
path of the joint to estimate the slope.
17. The method of claim 15, wherein the kinematic reconstruction
comprises computing a pose and an origin of a co-ordinate frame
associated with a link connected to at least one of the joint and
another joint proximal to the joint.
18. The method of claim 17, wherein computing the pose comprises
creating a homogeneous transformation of the co-ordinate frame.
19. The method of claim 18, wherein the homogeneous transformation
comprises: a 3.times.1 vector defining an origin of the co-ordinate
frame; and a 3.times.3 matrix comprising unit vectors of the
co-ordinate frame.
20. The method of claim 17, wherein at least one point within the
co-ordinate frame corresponds to a link connected to at least one
of the joint and another joint proximal to the joint.
21. The method of claim 20, wherein the another joint is an ankle
joint and the at least one point is at least one of a distal end
and a proximal end of a tibia connected to the ankle.
22. The method of claim 1, wherein the augmentation torque is
modulated according to a positive-force feedback.
23. The method of claim 22, wherein the augmentation torque
modulated according to the positive-force feedback, in combination
with a natural joint torque supplied by the human, approximates at
least a normal joint torque.
24. The method of claim 22, wherein the positive-force feedback
comprises a gain and an exponent.
25. The method of claim 24, wherein modulating comprises adjusting
at least one of the gain and the exponent according to at least one
of the estimated slope and walking speed.
26. The method of claim 1, wherein the augmentation torque is
modulated according to a scaling factor.
27. The method of claim 1 further comprising the step of
attenuating the augmentation torque to be applied according to a
protocol.
28. The method of claim 1, wherein the augmentation torque is
supplied in addition to natural joint torque supplied by the person
to achieve at least a pre-determined total joint torque
response.
29. The method of claim 1, wherein modulating comprises applying a
closed-loop torque control at the joint.
30. The method of claim 29 further comprising: modeling the joint
torque; and determining the phase of the gait cycle based on the
joint torque model.
31. The method of claim 1, wherein the augmentation torque, the
impedance, and a joint equilibrium are modulated in order to
achieve at least a target walking speed.
32. The method of claim 1, wherein the augmentation torque, the
impedance, and a joint equilibrium are modulated in order to
substantially achieve a metabolic economy in accordance with a
normative reference across at least one of walking speed and
terrain.
33-62. (canceled)
Description
RELATED APPLICATIONS
[0001] This application claims priority to and benefit of U.S.
Provisional Patent Application Ser. No. 61/435,045, filed on Jan.
21, 2011, the entire content of which is hereby incorporated by
reference in its entirety.
FIELD OF THE INVENTION
[0002] This invention relates generally to powered human
augmentation devices, such as lower-extremity prosthetic, orthotic,
or exoskelton apparatus, designed to emulate human biomechanics and
to normalize function, components thereof, and methods for
controlling the same.
BACKGROUND
[0003] Approximately 65% of service members seriously injured in
Iraq and Afghanistan sustain injuries to their extremities. Many of
these individuals experience muscle tissue loss and/or nerve
injury, resulting in the loss of limb function or substantial
reduction thereof. Many devices used for the treatment of
lower-extremity pathology, e.g., knee orthoses, are passive
devices. Increasingly, robotic technology is employed in the
treatment of individuals suffering from limb pathology, either for
the advancement of therapy tools or as permanent assistive devices.
Upper-extremity robotic devices provide assistance and therapy for
improved reaching and manipulation and, lower-extremity robotic
devices have been developed for the enhancement of locomotor
function.
[0004] Although decades of research has been conducted in the area
of active permanent assistive devices for the treatment of
lower-extremity pathology, these devices are not designed to
produce a biomimetic response, generally described in terms of
joint torque, joint angle, and other related parameters as observed
in a human not having substantial muscle tissue injury and not
using any device to assist in ambulation. Therefore, the robotic
devices usually result in unnatural ambulation and may even cause
significant discomfort to the wearer.
[0005] As such, many commercially available knee orthoses remain
passive and non-adaptive to the wearer even today. These devices
typically stabilize the knee joint medial-laterally, and limit the
extent of knee flexion and extension. As such, they do not provide
power or significant assistance to the user in walking, getting out
of a chair, and ascending slopes and stairs, etc.
[0006] In level-ground walking, a healthy biological knee generally
behaves like a spring during early to mid-stance, where knee torque
is proportional to knee angular position. Further, during slope
descent, the biological knee generally behaves like a variable
damper, dissipating mechanical energy as heat to lower the body's
center of mass with each step. Still further, during slope ascent,
the biological knee behaves like a torque source, applying a
non-conservative propulsive torque throughout early to mid-stance
to lift the body's center of mass upwards with each step.
[0007] Some common major complications of knee extensor weakness
are an inability to apply: 1) damping control during slope/stair
descent, 2) spring stiffness control during early to mid-stance in
level-ground walking, and 3) non-conservative propulsive torque
control for slope/stair ascent and sit-to-stand maneuvers. Due to
these various complications, a patient with knee extensor weakness
frequently experiences a decrease in self-selected walking speed
for level-ground and slope/stair ground surfaces, as well as an
increase in walking metabolism while traversing these ground
surfaces. Therefore, there is a need for improved systems and
methods of permanent assistive devices for the treatment of
lower-extremity pathology.
SUMMARY
[0008] In various embodiments, the present invention provides
devices and methods for operating/controlling such devices so as to
assist humans with knee extensor weakness, normalizing and/or
enhancing the wearer's self-selected walking speed and metabolic
economy. This is achieved using a type of device called Powered
Knee Othosis (PKO); the PKO devices are capable of capable of
spring stiffness control, dissipative damping control, and
non-conservative torque control in both knee flexion and extension
directions, in accordance with the gait-cycle, terrain (e.g.,
ground slope and stairs), and walking speed. As such, the PKO
devices can adaptively provide a non-conservative propulsive torque
to assist the user in walking, getting out of a chair, and
ascending slopes and stairs.
[0009] The PKO devices can also augment knee torque during late
stance, particularly during slope and/or stair ascent. Thus, the
PKO devices can provide at least a biomimetic response and
optionally can be used to enhance normal biomechanical response.
Offering control enhancement for both stance and swing phases, a
PKO device can be used as a permanent assistive device where
actuation, sensing, power, and computation are all packaged within
a small, lightweight, autonomous, manufacturable, and high
cycle-life package that can readily fit within a normal pant leg,
and can assist humans with weak or absent quadriceps. PKO devices
can also assist humans having uninjured leg musculature in
activities such as carrying a heavy load over a long distance
and/or increasing elevation, to enhance their strength and
endurance.
[0010] In one aspect, a method for assisting a person walking on a
surface with a powered human augmentation device includes a
controller. The method includes using the controller for
determining a phase of a gait cycle, and estimating within the gait
cycle, a slope of the surface. The method also includes supplying
to a joint (e.g., knee) an augmentation torque, an impedance, or
both. The impedance includes a linear spring component and a
damping component. The method also includes modulating the
augmentation torque and the impedance based on the phase of the
gait cycle and the estimated slope, to provide at least a
biomimetic response.
[0011] In some embodiments, the estimated slope is indicative of a
walking mode such that level-ground walking mode corresponds to a
substantially zero slope, downslope walking mode corresponds to a
negative slope, and upslope walking mode corresponds to a positive
slope. The downslope walking mode may include descending stairs and
the upslope walking mode may include ascending stairs. The joint
may be a knee.
[0012] In some embodiments, the method includes estimating walking
speed, and the augmentation torque and/or the impedance may be
based on the estimated walking speed. If the phase of the gait
cycle is determined to be one of early stance and mid stance and
the estimated slope is substantially zero, the impedance may be
modulated such that contribution of the linear spring component to
the modulated impedance is greater than contribution of the damping
component. If the phase of the gait cycle is determined to be one
of early stance and mid stance and the estimated slope is negative,
however, the impedance is modulated such that contribution of the
damping component is increased substantially compared to
contribution thereof if slope is estimated to be substantially
zero. Modulating the impedance may include varying the damping
component according to the negative slope.
[0013] In some embodiments, the augmentation torque includes a
non-conservative propulsive torque. If the phase of the gait cycle
is determined to be one of early stance and mid stance and the
estimated slope is positive, the non-conservative propulsive torque
is provided such that the modulated augmentation torque is greater
than the modulated augmentation torque applied if the slope is
estimated to be substantially zero. If the phase of the gait cycle
is determined to be late stance, the augmentation torque may be
modulated to correspond to a reflex torque that is related to the
estimated slope.
[0014] The method may include the step of modeling a joint
equilibrium as a second-order response to a joint-position goal to
be achieved prior to a next phase of the gait cycle. The modeling
may be performed during a swing phase of the gait cycle. The method
may also include determining if the joint is substantially fully
flexed, during a swing phase of the gait cycle. If the joint is
determined to be substantially fully flexed, modulating includes
adjusting both the augmentation torque and the impedance to be
substantially zero. In some embodiments, if the phase of the gait
cycle is determined to be early swing, the augmentation torque is
modulated according to the joint-equilibrium model such that a
joint equilibrium corresponds to the joint-position goal. The
impedance may be modulated according to the joint-equilibrium model
such that a joint equilibrium corresponds to the joint-position
goal.
[0015] In some embodiments, estimating the slope includes
kinematically reconstructing a path of the joint (e.g., a knee)
within the gait cycle. The method may also include kinematically
reconstructing a path of another joint (e.g., an ankle) within the
gait cycle, and associating the path of the other joint with the
path of the joint to estimate the slope. The kinematic
reconstruction may include computing a pose and an origin of a
co-ordinate frame associated with a link connected to at least one
of the joint and another joint proximal to the joint. The step of
computing the pose may include creating a homogeneous
transformation of the co-ordinate frame. In some embodiments, the
homogeneous transformation includes a 3.times.1 vector defining an
origin of the co-ordinate frame, and a 3.times.3 matrix comprising
unit vectors of the co-ordinate frame. At least one point within
the co-ordinate frame may correspond to a link connected to the
joint and/or another joint proximal to the joint. The another joint
may be an ankle joint and one point within the co-ordinate frame
can be a distal end and/or a proximal end of a tibia connected to
the ankle.
[0016] In some embodiments, the augmentation torque is modulated
according to a positive-force feedback. The augmentation torque
modulated according to the positive-force feedback, in combination
with a natural joint torque supplied by the human, may approximate
at least a normal joint torque. The positive-force feedback may
include a gain and an exponent, and modulating may include
adjusting the gain or the exponent, or both, according to the
estimated slope and/or walking speed. The augmentation torque may
be modulated according to a scaling factor and/or may be attenuated
according to a protocol. The augmentation torque may be supplied in
addition to natural joint torque supplied by the person to achieve
at least a pre-determined total joint torque response.
[0017] In some embodiments, modulating includes applying a
closed-loop torque control at the joint. To this end, the method
may include modeling the joint torque, and determining the phase of
the gait cycle based on the joint torque model. The augmentation
torque, the impedance, and a joint equilibrium may be modulated in
order to achieve at least a target walking speed, such as a walking
speed desirable to the person. The augmentation torque, the
impedance, and a joint equilibrium may also be modulated in order
to substantially achieve a metabolic economy in accordance with a
normative reference across at least one of walking speed and
terrain.
[0018] In another aspect, embodiments of the invention feature a
powered human augmentation device for assisting a person walking on
a surface. The device includes a powered actuator for supplying to
a joint an augmentation torque and/or an impedance that includes a
linear spring component and a damping component. The device also
includes a controller for (i) determining a phase of a gait cycle,
(ii) estimating within the gait cycle a slope of the surface, and
(iii) modulating the augmentation torque and the impedance based on
the phase of the gait cycle and the estimated slope to provide at
least a biomimetic response.
[0019] In some embodiments, the estimated slope is indicative of a
walking mode, such that level-ground walking mode corresponds to a
substantially zero slope, downslope walking mode corresponds to a
negative slope, and upslope walking mode corresponds to a positive
slope. The downslope walking mode may include descending stairs and
the upslope walking mode may include ascending stairs. The joint
may be a knee.
[0020] In some embodiments, the controller is adapted to estimate
walking speed, and the augmentation torque, the impedance, or both
may be based on the estimated walking speed. If the controller
determines the phase of the gait cycle to be one of early stance
and mid stance and the estimated slope is substantially zero, the
powered actuator may be adapted to provide the modulated impedance
such that contribution of the linear spring component to the
modulated impedance is greater than contribution of the damping
component. If the controller determines the phase of the gait cycle
to be one of early stance and mid stance and the estimated slope is
negative, the powered actuator may be adapted to provide the
modulated impedance such that contribution of the damping component
is increased substantially compared to contribution thereof if
slope is estimated to be substantially zero. The controller may
also be adapted to modulate the damping component according to the
negative slope.
[0021] In some embodiments, the augmentation torque includes a
non-conservative propulsive torque and, if the controller
determines the phase of the gait cycle to be one of early stance
and mid stance and the estimated slope is positive, the powered
actuator may be adapted to provide the non-conservative propulsive
torque such that the modulated augmentation torque is greater than
the modulated augmentation torque applied if the slope is estimated
to be substantially zero. If the controller determines the phase of
the gait cycle to be late stance, the powered actuator may be
adapted to provide the modulated augmentation torque, such that the
modulated augmentation torque corresponds to a reflex torque that
is related to the estimated slope.
[0022] In some embodiments, the controller is adapted to model,
during a swing phase of the gait cycle, a joint equilibrium as a
second-order response to a joint-position goal to be achieved prior
to a next phase of the gait cycle. The device may include a joint
angle sensor to provide a joint angle signal to the controller. If
the controller determines, based on the joint angle signal, that
the joint is substantially fully flexed, the powered actuator may
adapted to adjust both the augmentation torque and the impedance to
be substantially zero, during a swing phase of the gait cycle. If
the controller determines the phase of the gait cycle to be early
swing, the augmentation torque, impedance, or both may be modulated
according to the joint-equilibrium model such that a joint
equilibrium corresponds to the joint-position goal.
[0023] In some embodiments, the device includes an inertial
measurement unit (IMU), and the controller may be adapted to
kinematically reconstruct a path of the joint within the gait cycle
based on a signal from the IMU. The controller may also be adapted
to estimate the slope based on the kinematic reconstruction. The
IMU may include an accelerometer and/or a gyroscope. The IMU may
also include a first set of sensors associated with the joint
(e.g., a knee) and a second set of sensors associated with another
joint (e.g., an ankle). The controller may be adapted to
kinematically reconstruct a path of the other joint within the gait
cycle based on signals from the second set of sensors, and to
associate the path of the other joint with the path of the joint to
estimate the slope of the terrain.
[0024] The augmentation torque may be modulated according to a
positive-force feedback. The augmentation torque modulated
according to the positive-force feedback, in combination with a
natural joint torque supplied by the human, may approximate at
least a normal joint torque. The positive-force feedback may
include a gain and an exponent, and modulating may include
adjusting the gain, the exponent, or both according to the
estimated slope and/or walking speed. The controller may be adapted
to modulate the augmentation torque according to a scaling factor.
In some embodiments, the device includes a communication interface
for receiving a protocol, and the controller may be adapted to
attenuate the augmentation torque according to the received
protocol. The augmentation torque may be supplied in addition to
natural joint torque supplied by the person to achieve at least a
pre-determined total joint torque response.
[0025] In some embodiments, the controller is adapted to apply a
closed-loop torque control at the joint. The controller may be
adapted to model the joint torque, and to determine the phase of
the gait cycle based on the joint torque model. The powered
actuator may include a series-elastic actuator, and the
series-elastic actuator may include a transverse-flux motor. In
some embodiments, the series-elastic actuator includes a bilateral
spring and a cable drive. The series-elastic actuator may also
include a buckled beam and/or a unidirectional spring.
[0026] These and other objects, along with advantages and features
of the embodiments of the present invention herein disclosed, will
become more apparent through reference to the following
description, the accompanying drawings, and the claims.
Furthermore, it is to be understood that the features of the
various embodiments described herein are not mutually exclusive and
can exist in various combinations and permutations. As used herein,
the term "substantially" means.+-.10% and, in some embodiments,
.+-.5%.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] In the drawings, like reference characters generally refer
to the same parts throughout the different views. Also, the
drawings are not necessarily to scale, emphasis instead generally
being placed upon illustrating the principles of the invention. In
the following description, various embodiments of the present
invention are described with reference to the following drawings,
in which:
[0028] FIG. 1 illustrates biological knee function of an average
human in the stance and swing phases of a human gait cycle during
level-ground ambulation;
[0029] FIG. 2 illustrates how the knee response of an average
human, described in terms of angle, moment (i.e., torque), and
power, changes as a function of terrain slope;
[0030] FIG. 3a illustrates how the knee response may become
impaired when the quadriceps extensors are weakened;
[0031] FIG. 3b illustrates how the knee response of FIG. 3a can be
augmented, according to one embodiment;
[0032] FIGS. 4a and 4b schematically illustrate, during early
stance and late stance, respectively, the terrain-based modulation
of various components of knee extensor torque supplied by a powered
augmentation device so as to normalize the knee response, according
to one embodiment;
[0033] FIG. 4c shows adjustment of various torque and impedance
parameters according to terrain and/or walking speed, according to
one embodiment;
[0034] FIG. 5 schematically depicts a powered augmentation device
according to one embodiment;
[0035] FIG. 6 illustrates the operation of a state machine of a
powered augmentation device according to one embodiment;
[0036] FIG. 7 illustrates the operation of a powered augmentation
device implementing the state machine of FIG. 6, according to one
embodiment;
[0037] FIGS. 8a-8c schematically depict a powered augmentation
device according to another embodiment;
[0038] FIGS. 8d and 8e illustrate closed-loop control of the
powered augmentation device depicted in FIGS. 8a-8c, according to
two embodiments, respectively;
[0039] FIG. 9 illustrates seamless integration of a powered
augmentation device with a leg of a human, according to one
embodiment;
[0040] FIG. 10 depicts kinematic reconstruction by a controller for
controlling a powered augmentation device according to one
embodiment; and
[0041] FIGS. 11a and 11b depict ankle and knee paths, respectively,
each derived using measurements from an inertial measurement unit,
according to one embodiment.
DESCRIPTION
[0042] The entire contents of each of U.S. patent application Ser.
No. 12/157,727 "Powered Ankle-Foot Prosthesis" filed on Jun. 12,
2008 (Publication No. US2011/0257764 A1); U.S. patent application
Ser. No. 12/552,013 "Hybrid Terrain-Adaptive Lower-Extremity
Systems" filed on Sep. 1, 2009 (Publication No. US2010/0179668 A1);
U.S. patent application Ser. No. 13/079,564 "Controlling Power in a
Prosthesis or Orthosis Based on Predicted Walking Speed or
Surrogate for Same" filed on Apr. 4, 2011; and U.S. patent
application Ser. No. 13/079,571 "Controlling Torque in a Prosthesis
or Orthosis Based on a Deflection of Series Elastic Element" filed
on Apr. 4, 2011 are incorporated herein by reference.
[0043] FIG. 1 illustrates biological knee function in the stance
and swing phases of a human gait cycle during level-ground
ambulation. Throughout early stance 102 to mid stance 104 the knee
120 typically responds as a linear spring. This form of mechanical
impedance (which can take the form of a spring, inertia or damper,
acting alone or in combination) serves to cushion the foot-strike
impact in accordance with the gait speed. In late-stance 106, the
knee 120 generally behaves as a torque source in the form of a
reflex to lift the lower leg 122 off the ground surface 130 during
initiation portion 108 of the swing phase. The reflex release may
arise from a positive force feedback mechanism within the
gastrocnemius muscle. In the terminal portion 110 of the swing
phase, the knee 120 first brakes the swinging lower leg 122 to
limit heel rise after toe-off and then positions the lower leg 122
optimally for absorbing energy prior to foot strike initiation in
the next gait cycle.
[0044] Typically, the human gait adapts to terrain modality, e.g.,
ground slope and whether the human is ascending or descending
stairs, and to walking speed so as to maintain balance and to
achieve a metabolically economical movement pattern. FIG. 2
illustrates how the knee response, described in terms of angle,
moment (torque), and power, changes as a function of terrain slope.
For example, during level-ground walking depicted by curve 202, the
biological knee behaves like a spring, where knee torque is
proportional to knee angular position, during early to mid-stance
212. During slope descent, depicted by curve 204, the biological
knee behaves like a variable damper, dissipating mechanical energy
as heat to lower the body's center of mass with each step, during
early to mid-stance 212. The variable damping generally increases
as the declination angle increases. Such behavior may also be
invoked during stair descent. During slope ascent, depicted by
curve 206, the biological knee behaves like a torque source,
applying a non-conservative propulsive torque throughout early to
mid-stance 212 to lift the body's center of mass upwards with each
step. Such behavior is usually also invoked upon stair ascent. A
slope-dependent reflex is applied in late stance 214.
[0045] Flexion angle in the swing phase also shows terrain
dependence. In slope ascent, the flexion angle just prior to
foot-strike, i.e., late swing 222 of the curve 232 increases with
the slope of ascent, whereas the knee flexion is invariant with the
slope of descent, as depicted by the curve 234. To achieve
sufficient toe clearance on descent, the knee flexion angle
increases in early swing 224 as the descent becomes steeper. Though
the data presented in FIG. 2 are captured at a substantially
constant gait speed, it is understood that the above impedance and
torque response on level ground and slopes typically changes with
gait speed, in part, to account for changes in the body momentum
and to deliver/absorb power accordingly.
[0046] PKO platforms 500, 800 described with reference to FIGS. 5
and 8, respectively, can discriminate terrain modality and speed
within a gait cycle (intra-cycle), and can also adapt the
impedance, reflex, and position response in accordance with that
terrain and gait speed. Intra-cycle sensing is advantageous,
because during an average walk terrain and walking speed may change
frequently. The platforms 500, 800 employ a six-degree-of-freedom
inertial measurement unit (IMU) capable of computing the path of
the ankle joint and the distal-end of the femur (knee), from which
the IMU can discriminate and discern terrain modality, including
stairs and slopes, as illustrated with reference to FIG. 11b. The
path of the hip can be used to augment the information from the
knee and ankle. For instance, in stair ascent, the hip is generally
stationary as the knee flexes, a precursor that is not evident when
a wearer is traversing sloping and/or level ground.
[0047] FIG. 3a illustrates how the knee response may become
impaired when the quadriceps extensors are weakened. In early
stance 302, the knee stiffness can be insufficient to absorb energy
either as a spring as in level-ground ambulation or as a damper in
steep descent. In late stance 304, the knee torque is insufficient
to "brake" the knee and to deliver sufficient reflex particularly
in steep ascent and descent.
[0048] When worn by a wearer with weakened quadriceps extensors,
the PKO platforms 500, 800 deliver an augmentation torque,
.GAMMA..sub.augment, to normalize the response, i.e., to produce a
response that may be produced by a joint (e.g., knee) of average
humans not having weakened muscle tissue (e.g., quadriceps
extensors) and not wearing any powered prosthetic/orthotic devices.
With reference to FIG. 3b, just prior to foot-strike in early
stance 312, the PKO platforms 500, 800 apply a computed knee
flexion angle and set the impedance, for energy absorption, in
accordance with terrain slope. The terrain slope can be inferred
from the ankle and knee trajectories and with instantaneous gait
speed inferred from the IMU-computed angular pitch rate of the
femur and tibia.
[0049] Once the foot strikes the ground in early stance 312, the
PKO platforms 500, 800 apply appropriate knee extensor torque,
.tau..sub.extensor, to achieve an impedance relation of the
form:
.tau..sub.extensor=.GAMMA..sub.0(.phi.,{dot over
(s)})-k.sub..phi.,{dot over
(s)}(.theta.-.theta..sub.0)-b.sub..phi.{dot over (s)}{dot over
(.theta.)}
in accordance with the computed terrain slope and speed. In late
stance 314, the PKO platforms 500, 800 apply additional torque and
reflex in accordance with the terrain slope and the instantaneous
gait speed inferred by femur and tibia pitch rates. In late stance
314, the knee extensor torque corresponds to a
biologically-conceived, non-linear, positive torque feedback
relation of the form:
.tau. extensor = P ff .phi. , s . ( .GAMMA. knee .GAMMA. 0 ) N
.phi. , s . ##EQU00001##
where the gain, P.sub.ff.phi.,{dot over (s)} is a function of
terrain slope, .phi., and gait speed, and the exponent,
N.sub..phi.{dot over (s)}, is also a function of terrain slope and
gait speed. .GAMMA..sub.knee is an intrinsic measure of knee torque
in the above relation that includes the contribution of both the
"locking torque" of the knee and the normalized extensor/flexor
contribution. In general, both the gain and the exponent are
increased to achieve the higher reflex torques needed as the slope
of ascent and descent increase.
[0050] With reference to FIG. 4a, in early stance, during
level-ground walking, the linear spring component k 402 of the
extensor torque applied by the PKO platforms 500, 800 is
significant. While descending slope, the linear spring component k
402 is decreased and the damping component b 404 is increased, such
that the damping component b 404 is significant. While ascending
slope, both the linear spring k 402 and damping component b 404 are
decreased and a non-conservative propulsive torque component
.tau..sub.0 406 is increased.
[0051] With reference to FIG. 4b, in late stance, during
level-ground walking, the knee extensor torque applied by the PKO
platforms 500, 800 corresponds to non-linear, positive torque
feedback determined by gain 412 and exponent 414. While descending
slope, the gain 412 is decreased and the exponent 414 is increased.
While ascending slope, both the gain 412 and exponent 414 are
increased. Adjustment of various torque and impedance parameters
according to terrain and/or walking speed is described in a Table
in FIG. 4c. Thus, the PKO platforms 500, 800 can emulate human knee
behavior during the gait cycle by biomimetically applying
impedance, torque, and joint equilibrium control in accordance with
the gait cycle and speed, and augment the knee torque of the wearer
to provide at least a normalized knee response.
[0052] With reference to FIG. 5, the PKO platform 500 uses a quiet,
light-weight, and rugged actuator 502. A modular battery 504 having
a 3000 step capacity (typically for a wearer weighing about 70 kg
with significant quadriceps extensor weakness) is used. A typical
wearer may need to replace this lightweight battery pack 504
between one and two times per day. The actuator 502 can deliver at
least biomimetic torque and angle response within a gait speed
range from about 0 up to about 1.75 m/sec.
[0053] Optionally, the Platform 500 may employ one or two embedded
wireless interfaces 506. A Bluetooth.RTM. interface may be used as
the pathway for PDA-based tuning by clinicians and researchers to
normalize the torque response, e.g., by specifically programming
the PKO platform 500 to deliver augmentation torque
.GAMMA..sub.augment as required in each phase of the gait cycle as
described below with reference to FIG. 7. A smart WiFi interface
may serve as the pathway for researchers to acquire control state
variables and sensory feedback from the PKO platform 500 and to
synchronize this telemetry with external biomechanical
instrumentation.
[0054] The actuator 502 of the PKO platform 500 can be a
series-elastic actuator (SEA) to drive the powered orthosis. See,
for example, U.S. Pat. No. 5,650,704 "Elastic Actuator for Precise
Force Control" the disclosure of which is incorporated herein by
reference. A multi-processor control system (State and Actuator
Controller) 508 uses feedback from the SEA to deliver the
appropriate response in accordance with the phase of the gait
cycle, the terrain, and the walking speed. A three-phase brushless
motor driver (Motor Driver) 522 interfaces to the State and
Actuator Controller 508 to accomplish closed-loop torque control of
the SEA 502. An Inertial Measurement Unit (IMU) 510, employing a
three-axis rate gyro and a three-axis accelerometer, provides
feedback to sense transitions between phases of the gait cycle, to
measure gait speed, and to discriminate terrain modality. The
WiFi/Bluetooth.RTM. communication module 506 is employed to
interface directly to the State Controller and Actuator Controller
508 to facilitate data acquisition and PDA-based clinician
tuning.
[0055] The SEA 502 may employ a robust ball-screw mechanism 524
driven by the high-rpm brushless motor 522 through a redundant
aramid fiber twin belt transmission 526. The ball-nut 524 of the
SEA 502 drives the knee 540 through a bilateral spring assembly 528
and a redundant aramid fiber cable drive 530. The bilateral spring
assembly 528 can exhibit a weak stiffness in flexion and a stiffer
spring in extension as would be applied in locking the knee joint.
Thus in this embodiment, the bilateral spring 528 is used (i) to
store energy in late stance for later release in the reflex
response and (ii) to serve as a sensing means for achieving
closed-loop torque control of the actuator 502. By storing energy
for later release, the peak power and, hence, size and weight of
the motor 522 are reduced by over 40% compared to an actuator
without the spring storage, in this embodiment. Displacement of the
spring 528 can be used to estimate and thereby control drive torque
in a way that attenuates the effect of friction, enabling a
backdrivable means of actuation that replicates biological knee
operation.
[0056] A knee sensor 532, a motor-position sensor 534, and a
ball-screw position sensor 536 embedded in the actuator 502 are
employed to determine a state of the actuator 502 and to provide a
basis for brushless motor control and for modulation of impedance,
torque, and position in accordance with the phase of the gait cycle
and gait speed. To this end, the State Controller and Actuator
Controller 508 implements a state machine.
[0057] With reference to FIG. 6, during early stance state 602, the
state machine 600 adapts the PKO platform 500 to apply a linear
spring and damping impedance in accordance with the gait speed and
terrain angle, given by:
.tau..sub.extensor=.GAMMA..sub.0(.phi.,{dot over
(s)})-k.sub..phi.,{dot over
(s)}(.theta.-.theta..sub.0)-b.sub..phi.{dot over (s)}{dot over
(.theta.)}
[0058] k.sub.cp=k.sub.cp(.phi.{dot over (s)});
b.sub.cp=b.sub.cp(.phi., {dot over (s)})
Where
[0059] .tau..sub.extensor is the commanded SEA motor torque
[0060] .theta. is the ankle angle,
[0061] .phi. is the terrain angle, and
[0062] {dot over (s)} the estimated gait speed at foot-strike
estimated by the IMU
[0063] Transition into the early stance state 602 is accomplished
by sensing by the IMU 510 the distinctive vibration that occurs
when the foot strikes the ground. The impedance is configured and
scaled so as to prevent buckling of the knee in accordance with
walking speed and the response needed to at least normalize the
augmented response of the wearer.
[0064] Transition into the late stance state 604 generally occurs
when the detected knee extension angle velocity changes from
negative to positive. In this state 604, a reflex response can be
achieved through non-linear positive feedback as described by the
relation:
.tau. extensor = P ff .phi. , s . ( .GAMMA. knee .GAMMA. 0 ) N
.phi. , s . ##EQU00002##
In this, the reflex gain, P.sub.ff(.phi., {dot over (s)}) and the
exponent (non-linear spring), N(.phi.,{dot over (s)}) are each a
function of the terrain angle, .phi., and the estimated gait speed,
{dot over (s)}={dot over (s)}){dot over (.phi.)}.sub.femur, {dot
over (.phi.)}.sub.tibia), which is a function of the instantaneous
angular rate of the tibia and femur at the time of entry in to the
late stance state 604. A hard stop spring model for extreme knee
extension, .GAMMA..sub.knee (.theta.), is used to model the wearer
torque response at extremes of extension (.theta.>0) while the
knee is locked so that at least a biomimetic response is
achieved.
[0065] Transition into early swing state 606 occurs when the
detected SEA 502 torque, .GAMMA..sub.SEA, approaches a programmable
percentage of peak torque. In this state 606, position control is
employed to brake the knee flexion velocity, to achieve proper
ground clearance and heel rise during the early to mid swing phase
through use of an organically-derived trajectory, .theta..sub.0(t)
that smoothly decelerates to a goal position in a nearly ballistic
trajectory (i.e., small torque corresponding to a lightly damped
pendulum),
.theta..sub.goal=.theta..sub.goal.sub.0=.theta..sub.goal.sub.0({circumfle-
x over (.phi.)}|.sub.ls,{dot over (s)}):
.tau..sub.extensor=-k.sub.esw(.theta.-.theta..sub.0)-b.sub.esw({dot
over (.beta.)}.sub.motor-{dot over (.beta.)}.sub.motor.sub.0)
.tau..sub.trajectory.sup.2{umlaut over
(.theta.)}.sub.0+2.tau..sub.trajectory{dot over
(.theta.)}.sub.0+.theta..sub.0=.theta..sub.goal.sub.0.sub.
.theta..sub.goal.sub.0=.theta..sub.goal.sub.0({circumflex over
(.phi.)}|.sub.ls,{dot over (s)}); {dot over
(.beta.)}=J.sup.-1(.theta.){dot over (.theta.)}
where .beta..sub.motor is the motor angle corresponding to a knee
angle with zero SEA spring displacement. and
[0066] {circumflex over (.phi.)}|.sub.ls is estimated terrain angle
as estimated at the end of late stance using the inertial tibia and
femur angular velocities.
[0067] Also in the early swing state 606, the inertial ankle and
knee trajectories are computed and used to discriminate between the
three modalities, i.e., slope/stair ascent, slope/stair descent,
and walking on substantially level ground. This early
discrimination may be used to adjust the control parameters of the
State Controller and Actuator Controller 508 in advance of foot
strike to achieve seamless response across the swing-stance
transition.
[0068] Transition into late swing state 608 occurs when the IMU 510
detects a negative, vertical Cartesian (world-frame referenced)
ankle pivot velocity, .sup.WV.sub.ankle pivot.sub.z In this state
608, position control is used with a smooth trajectory that
converges to a time-varying goal point, .theta..sub.goal, that is a
function of gait speed and terrain slope, each estimated by the IMU
510 which in some embodiments uses only intra-gait-cycle
information. The impedance (stiffness and damping) applied to
position and velocity errors referenced to the trajectory
(equilibrium), .theta..sub.0(t) may be preferably set in accordance
with gait speed and terrain angle.
[0069] FIG. 7 illustrates how the PKO platform 500 can augment the
torque of a wearer to achieve at least a normalized biomimetic
response. In some embodiments, a powered augmentation device can
augment the torque and adjust impedance to achieve a response that
can enable a wearer who does not have a diminished natural joint
function to perform activities such as walking or running a long
distance, carrying a heavy load, climbing steep slopes, etc. The
state machine 600 modulates the SEA 502 impedance, reflex, and
position control response in accordance with gait speed and terrain
modality inputs from the IMU 510. The SEA 502 control internally
computes at least the normalized biomimetic torque, .GAMMA.*, in
each state of the gait cycle. State-specific attenuation, set by
the clinician, then scales .GAMMA.* and drives the SEA 502 to
deliver just the right torque, .GAMMA..sub.augment, add to the
wearer's natural torque response, .GAMMA..sub.wearer, to
approximate .GAMMA.*, i.e., the desired normalized biomimetic
response or an enhanced response that may allow a person to
undertake activities such as walking fast (e.g., 2 m/sec.) for a
long time e.g., about 6 hours.
[0070] Battery conservation is important in wearable PKO devices.
In the absence of battery energy, or when the walking state machine
(e.g., the state machine 600, illustrated with reference to FIG. 6)
detects that the wearer has stopped walking (which can be
determined by absence of gait-cycle phase transition for over
approximately two seconds), the control system shorts the motor
leads to ground using power electronics. In this special damping
mode the motor leads are shorted together, creating a dynamic brake
with damping torque,
.tau. motor = - b sl .omega. = - ( k g k t ) 2 R .omega. ,
##EQU00003##
where b.sub.sl is the shorted leads damping, k.sub.g is the gear
ratio between the motor and joint output, k.sub.t is the motor
constant in Nm/A and R is the motor resistance, and .omega. is the
rotation rate of the joint. In the "shorted leads" operation, the
time constant, .tau..sub.sl, that describes the first-order
spring-damper actuator dynamics comprising the series-spring,
k.sub.SEA and the intrinsic actuator damping, b.sub.sl, is given by
the relation,
.tau. sl = b sl k SEA . ##EQU00004##
In transverse-flux and other high-torque motor actuators, the
.tau..sub.sl may be on the order of about 500 msec or more. For
time intervals, e.g., less than 1/3 of the time constant, the
actuator 502 in "shorted leads" mimics a static clutch, taking no
energy from the battery. By matching the series-stiffness with that
required in early stance flexion, the motor clutch is engaged at
the desired joint equilibrium so as to approximate the biomimetic
linear spring response without requiring any battery energy. This
affords significant advantage in system design, response, and
economy of operation.
[0071] FIGS. 8a-8c depict a PKO device 800 that employs a buckled
beam 812 as the series-elastic element of the SEA 802. The SEA 802
includes a high RPM brushless, permanent magnet motor 814 having an
integral heat sink and an insulator. The motor 814 can be a radial
motor, a transverse-flux motor, a stepping motor, etc. The SEA 802
also includes a sealed ball-screw mechanism 816 having a 14 mm
diameter and 3 mm lead, in this embodiment. It should be understood
that these dimensions are illustrative only and are not
limiting.
[0072] The motor 814 is coupled to the buckled beam via a flexural
coupling 818 to protect the ball-screw mechanism 816 from moment
load, a reverse-cam linkage 820, and sealed needle bearings 824.
The needle bearings 824 typically have L1 design life of over five
million cycles (i.e., a design whereby 99% of a population survive
longer than the reported design life with 95% statistical
confidence). The PKO 800 also includes an integral pivot scaffold
SEA support 826, coupled to the motor 814, and a foot support 828
(e.g., a custom nylon foot support), coupled to the buckled beam
812. The reverse-cam linkage 820 includes an encoder 830 that may
be used to determine the SEA torque based on a torque-angular
displacement model. The encoder 830 can be a 13-bit absolute
encoder having a torque resolution of about 8 bits.
[0073] In one embodiment, the motor 814 is controlled in a closed
loop. FIG. 8d illustrates one embodiment of an implementation of
the closed-loop torque control in the PKO 800, in which the Joint
Torque Command Generator 852 computes the commanded joint torque,
.tau..sub.joint, from terrain, .phi., walking speed, {dot over
(s)}, and gait-cycle phase as these are supplied from a State
Controller (e.g., State and Actuator Controller 508, described with
reference to FIG. 5). The Joint-Torque Model 854 estimates the
actual applied joint torque, .tau..sub.joint, from wearer knee
extension, wearer extensor-flexor and buckling-beam 812 (for
series-elasticity) torque contributions. The wearer contributions
may be assumed to be a percentage of a normative amount or a
percentage of the command torque. The contribution of the
buckling-beam 812 (series elastic component of the SEA 802, in
general) may be estimated from off-wearer calibration during
testing of the PKO device 800.
[0074] The difference in the commanded and applied torque,
.delta..GAMMA..sub.joint, is scaled by the nominal stiffness of the
buckling beam 812 (generally, the SEA) and is passed through a
proportional-integral-derivative (PID) compensator 856,
G.sub.1(z.sup.-1), to compute a commanded value of deflection,
.beta.-.theta., where .theta. is the joint angle and .beta. is the
joint angle specified by the actuator for approximately zero
buckled beam (SEA) deflection. G.sub.1 is designed with at least
integral compensation with saturation error limits to force
substantially zero steady-state torque error and may typically
include proportional and derivative terms. The sensed joint angle,
.theta..sub.sense, is added by an adder 858 to the deflection
command to compute a commanded actuator angle,
.beta..sub.commanded.
[0075] The estimated actuator displacement is derived by actuator
kinematics 860 by sensing the motor angle, p, which is used in a
computational model, .beta.(p), of the actuator kinematics 860. The
actuator error is supplied to a second PID compensator 862 with
actuator range of motion limits to deliver a motor torque,
.tau..sub.motor, to drive the actuator 802. A brushless, permanent
magnet motor, either radial, transverse flux, or stepping motor, is
commutated electronically using a multiphase motor driver that
delivers a torque-producing current component, i.sub.q, to achieve
the desired motor torque via the relation
.tau..sub.motor=k.sub.ti.sub.q, where k.sub.t is the motor torque
constant in Nm/A. If a stepping motor is used, the motor can be
stepped in a closed-loop fashion to align with the position
command.
[0076] In another embodiment illustrated with reference to FIG. 8e,
the Joint Torque Model 854 supplies and estimated joint torque to
the Joint Torque Command generator 852, which determines the
augmentation torque command, .GAMMA..sub.joint. The torque command
is passed through a command shaping filter 864, having a transfer
function G.sub.1(z.sup.-1) and a torque de-scaling,
1 k SEA , ##EQU00005##
to create a high-fidelity deflection signal. The command shaping
filter 864 may be a low-pass filter to ensure that the inner
deflection control loop has sufficient response bandwidth to follow
the command. Other embodiments may be implemented by those skilled
in the art to deliver a joint torque response that closely matches
the desired biomechanical response as this is achieved through
modulation of impedance, joint equilibrium, and torque in
accordance with gait-cycle phase, terrain and walking speed.
[0077] Seamless integration of the PKO platform 500 onto a wearer
is desirable to ensure that the torque supplied by the PKO platform
500 is coupled efficiently to the joint (knee, ankle, etc.). With
reference to FIG. 9, in some embodiments, a process is provided for
custom manufacturing an upper cuff assembly 902 and a lower cuff
assembly 904 to conform/couple directly to the wearer. For each
wearer a three-dimensional scanning tool is employed to measure
those body surfaces that must integrate with the PKO platform 500.
From these surface measurements, lightweight titanium forms can be
printed (e.g., using a direct-write process). These can be
functionalized through heat treating to create the scaffold upon
which a custom 3-D printed elastomer, with spatially-varying
durometer, can be bonded to achieve the desired custom
integration.
[0078] In some embodiments, the State and Actuator Controller 508
is adapted to kinematically reconstruct a joint path. Such
reconstruction can be used to determine the terrain (e.g., whether
the terrain is level ground, sloping ground, or stairs), and
activity (i.e., whether the wearer is walking on level ground,
upslope, or downslope, or walking up or down the stairs). The
modulation of the toque, impedance, and joint equilibrium may be
based on the terrain and activity as determined via the kinematic
reconstruction.
[0079] FIG. 10 illustrates a method for determining, via kinematic
reconstruction, ankle joint 1000, heel 1012 and toe 1016 paths
while using any PKO device (e.g., the PKO platforms 500, 800) based
on the inertial pose of a lower leg member 1020 coupled to the
ankle joint 1000, and the angle between the lower leg member 1020
and foot member 1008. Pose is the position and orientation of a
coordinate system. The IMU (e.g., the IMU 510) may be coupled to
the lower leg member 1020. The IMU may include a three-axis rate
gyro for measuring angular rate and a three-axis accelerometer for
measuring acceleration. Placing the inertial measurement unit on
the lower leg member 1020 collocates the measurement of angular
rate and acceleration for all three axes of the lower leg member
1020. The inertial measurement unit provides a
six-degree-of-freedom estimate of the lower leg member 1020 pose,
inertial (world frame referenced) orientation and ankle-joint 1000
(center of rotation of the ankle-foot) location.
[0080] In some embodiments, the lower leg member 1020 pose is used
to compute the instantaneous location of the knee joint. By using
knowledge of the ankle joint 1000 angle (.theta.) the instantaneous
pose of the bottom of the foot 1008 can be computed, including
location of the heel 1012 and toe 1016. This information in turn
can be used when the foot member 1008 is flat to measure the
terrain angle in the plane defined by the rotational axis of the
ankle joint/foot member. Mounting the inertial measurement unit on
the lower leg member 1020 has advantages over other potential
locations. Unlike if it were mounted on the foot member 1008, the
lower leg member 1020 mounting protects against physical abuse and
keeps it away from water exposure. Further, it eliminates the cable
tether that would otherwise be needed if it were on the foot member
1008 thereby ensuring mechanical and electrical integrity. Finally,
the lower leg member 1020 is centrally located within the kinematic
chain of a hybrid system facilitating the computation of the thigh
and torso pose with a minimum of additional sensors.
[0081] The inertial measurement unit can be used to calculate the
orientation, .sub.ankle.sup.wO, position, .sub.ankle.sup.wP, and
velocity, .sub.ankle.sup.wV, of the PKO platform in a
ground-referenced world frame. .sub.ankle.sup.wO may be represented
by a quaternion or by a 3.times.3 matrix of unit vectors that
define the orientation of the x, y and z axes of the ankle joint in
relation to the world frame. The ankle joint 1000 coordinate frame
is defined to be positioned at the center of the ankle joint axis
of rotation with its orientation tied to the lower leg member 1020.
From this central point, the position, velocity and acceleration
can be computed. For points of interest in, for example, the foot
(e.g., the heel 1012 or toe 1016), a foot member-to-ankle joint
orientation transformation, .sub.foot.sup.ankleO(.theta.) is used
to derive the position using the following relation:
.sub.point-of-interest.sup.wp=.sub.ankle.sup.wp+.sub.ankle.sup.wO(.gamma-
.).sub.foot.sup.ankleO(.theta.)(.sup.footr.sub.point-of-interest)
where
foot ankle O ( .gamma. ) = [ 1 0 0 0 cos ( .gamma. ) - sin (
.gamma. ) 0 sin ( .gamma. ) cos ( .gamma. ) ] ##EQU00006##
where .gamma. is the inertial lower leg member angle, and
foot ankle O ( .theta. ) = [ 1 0 0 0 cos ( .theta. ) - sin (
.theta. ) 0 sin ( .theta. ) cos ( .theta. ) ] ##EQU00007##
where .theta. is the ankle joint angle.
[0082] In this embodiment, the inertial measurement unit, including
the three-axis accelerometer and three-axis rate gyro, is located
on the forward face at the top of the lower leg member 1020. It is
advantageous to remove the effect of scale, drift and
cross-coupling on the world-frame orientation, velocity and
position estimates introduced by numerical integrations of the
accelerometer and rate gyro signals
[0083] Inertial navigation systems typically employ a zero-velocity
update (ZVUP) periodically by averaging over an extended period of
time, usually seconds to minutes. This placement of the inertial
measurement unit is almost never stationary in the lower-extremity
devices such as a PKO. However, the bottom of the foot is the only
stationary location, and then only during the controlled
dorsiflexion state of the gait cycle. An exemplary zero-velocity
update method, which is not impacted by this limitation, for use
with various embodiments of the invention is described further
below.
[0084] To solve this problem, orientation, velocity and position
integration of ankle joint is performed. After digitizing the
inertial measurement unit acceleration, IMU.sub.a, the ankle joint
acceleration (.sup.IMUa.sub.ankle) is derived with the following
rigid body dynamic equation:
.sup.IMUa.sub.ankle=.sup.IMUa+.sup.IMU{right arrow over
(.omega.)}X.sup.IMU{right arrow over
(.omega.)}X.sub.ankle.sup.IMU{right arrow over (r)}+{right arrow
over ({dot over (.omega.)})}X.sub.ankle.sup.IMU{right arrow over
(r)}
where IMU{right arrow over (.omega.)} and IMU{right arrow over
({dot over (.omega.)})} are the vectors of angular rate and angular
acceleration, respectively, in the inertial measurement unit frame
and X denotes the cross-product.
[0085] The relationship is solved .sub.ankle.sup.wO=.sub.IMU.sup.wO
similarly as in the equations above using standard strapdown
inertial measurement unit integration methods, in accordance with
the following relationships known to one skilled in the art:
.sub.ankle.sup.w{circumflex over (.PHI.)}=.sup.w{circumflex over
(.OMEGA.)}(.sup.w{circumflex over
(.omega.)}).sub.ankle.sup.w{circumflex over (.PHI.)}
.sup.w{circumflex over
(V)}.sub.ankle=.sup.wa.sub.ankle-[0,0,g]T
.sup.w{circumflex over (p)}.sub.ankle=.sup.w{circumflex over
(v)}.sub.ankle
.sub.foot.sup.w{circumflex over
(.PHI.)}=.sub.ankle.sup.w{circumflex over
(.PHI.)}.sub.foot.sup.ankle{circumflex over
(.PHI.)}=.sub.ankle.sup.w{circumflex over
(.PHI.)}Rotation.sub.x({circumflex over (.THETA.)})
.sup.w{circumflex over (v)}.sub.heel=.sup.w{circumflex over
(v)}.sub.ankle+.sup.w{circumflex over
(.OMEGA.)}(.sub.ankle.sup.w{circumflex over (.PHI.)}[{circumflex
over ({dot over (.THETA.)})}0 0].sup.T).sup.wr.sub.heel-ankle
.sup.w{circumflex over (v)}.sub.toe=.sup.w{circumflex over
(v)}.sub.ankle+.sup.w{circumflex over
(.OMEGA.)}(.sub.ankle.sup.w{circumflex over (.PHI.)}[{circumflex
over ({dot over (.THETA.)})}0 0].sup.T).sup.wr.sub.toe-ankle
.sup.w{circumflex over (p)}.sub.heel=.sup.w{circumflex over
(p)}.sub.ankle+.sup.wr.sub.heel-ankle
.sup.w{circumflex over (p)}.sub.toe=.sup.w{circumflex over
(p)}.sub.ankle+.sup.wr.sub.toe-ankle
.sup.wr.sub.heel-ankle=.sub.foot.sup.w{circumflex over
(.PHI.)}.sup.foot(r.sub.heel-r.sub.ankle)
.sup.wr.sub.toe-ankle=.sub.foot.sup.w{circumflex over
(.PHI.)}.sup.foot(r.sub.toe-r.sub.ankle)
[0086] In the equations above, the matrix, {circumflex over
(.PHI.)}, will be used interchangeably with the orientation matrix,
.sub.IMU.sup.wO. The world frame-referenced ankle joint velocity
and position are then derived at a point in time after the time of
the previous zero-velocity update (i-th zero-velocity update) based
on the following:
.sup.wv.sub.ankle(t)=.intg..sub.ZVUP(i).sup.t(.sub.IMU.sup.wO).sup.IMUa.-
sub.ankledt
.sup.wp.sub.ankle(t)=.intg..sub.ZVUP(i).sup.twv.sub.ankkledt
where .sup.wp.sub.ankle(t=ZVUP(i)) is reset to zero for all i.
[0087] The six-degree-of-freedom inertial measurement unit (IMU)
510 of the PKO platform 500 or the IMU of the PKO device 800 is
capable of computing the path of the ankle joint and the distal-end
of the femur (knee) from which the IMU can discriminate and discern
terrain modality including stairs and slopes. With reference to
FIG. 11a, inertially referenced ankle joint paths 1102,
.sup.wp.sub.ankle joint(t), and ankle-velocity-attack-angle 1104,
.sup.wV.sub.ankle joint, on stairs and sloping ground can be used
to discriminate stair ascent/descent from ascent/descent on sloping
ground. The slope, .phi., can be estimated as {circumflex over
(.phi.)} in swing using the relation:
{circumflex over (.phi.)}=tan.sup.-1(.sup.wp.sub.ankle
joint.sub.z(t), .sup.wp.sub.ankle joint.sub.y)
[0088] With reference to FIG. 11b, inertially-referenced knee path
shape can be used to detect stair ascent/descent shortly after
toe-off enabling knee impedance and torque response to be
configured prior to foot-strike on the stair. The "kink" 1110 in
the knee path may signal impending foot strike on sloping ground,
enabling a prediction of terrain slope using the ankle joint slope
prediction described above with reference to FIG. 11a. Using the
joint slope, speed and ankle velocity angle-of-attack, the joint
equilibrium and impedance can be adjusted in preparation for the
foot strike.
[0089] While the invention has been particularly shown and
described with reference to specific embodiments, it will be
understood by those skilled in the art that various changes in form
and detail may be made therein without departing from the spirit
and scope of the invention as defined by the appended claims. The
scope of the invention is thus indicated by the appended claims and
all changes that come within the meaning and range of equivalency
of the claims are therefore intended to be embraced.
* * * * *