U.S. patent application number 17/525495 was filed with the patent office on 2022-06-09 for lower limb prosthesis.
The applicant listed for this patent is BLATCHFORD PRODUCTS LIMITED. Invention is credited to David Moser, Nadine Stech, Andrew John Sykes, Mir Saeed Zahedi.
Application Number | 20220175559 17/525495 |
Document ID | / |
Family ID | |
Filed Date | 2022-06-09 |
United States Patent
Application |
20220175559 |
Kind Code |
A1 |
Zahedi; Mir Saeed ; et
al. |
June 9, 2022 |
LOWER LIMB PROSTHESIS
Abstract
A lower limb prosthesis comprises an attachment section (10), a
shin section (12), a foot section (14), a knee joint (16) pivotally
connecting the attachment section (10) and the shin section (12),
and an ankle joint (22) pivotally connecting the shin section (12)
and the foot section (14). The knee joint includes a dynamically
adjustable knee flexion control device (18) for damping knee
flexion. The prosthesis further comprises a plurality of sensors
(52, 53, 54, 85, 87) each arranged to generate sensor signals
indicative of at least one respective kinetic or kinematic
parameter of locomotion or of walking environment, and an
electronic control system (100) coupled to the sensors (52, 53, 54,
85, 87) and to the knee flexion control device (18) in order
dynamically and automatically to modify the flexion control setting
of the knee joint (16) in response to signals from the sensors.
When the inclination sensor signals indicate descent of a downward
incline, the damping resistance of the knee flexion control device
(18) is set to a first level during a major part of the stance
phase of the gait cycle and to a second, lower level during a major
part of the swing phase of the gait cycle. During an interval
including a latter part of the stance phase, the knee flexion
control device (18) is adjusted so that the damping resistance to
knee flexion is between the first and second levels.
Inventors: |
Zahedi; Mir Saeed; (London,
GB) ; Stech; Nadine; (Hampshire, GB) ; Moser;
David; (Southampton, GB) ; Sykes; Andrew John;
(Surrey, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BLATCHFORD PRODUCTS LIMITED |
Basingstoke |
|
GB |
|
|
Appl. No.: |
17/525495 |
Filed: |
November 12, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16403025 |
May 3, 2019 |
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17525495 |
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14364637 |
Jun 11, 2014 |
10285827 |
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PCT/GB2012/053106 |
Dec 12, 2012 |
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16403025 |
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61580887 |
Dec 28, 2011 |
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61647016 |
May 15, 2012 |
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International
Class: |
A61F 2/76 20060101
A61F002/76; A61F 2/64 20060101 A61F002/64; A61F 2/66 20060101
A61F002/66; A61F 2/70 20060101 A61F002/70; A61F 2/60 20060101
A61F002/60 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 13, 2011 |
GB |
1121437.6 |
May 14, 2012 |
GB |
1208410.9 |
Claims
1-16. (canceled)
17. A lower limb prosthesis comprising: an attachment section, a
shin section, a foot section, a knee joint pivotally connecting the
attachment section and the shin section, the knee joint including a
dynamically adjustable knee flexion control device for damping knee
flexion, an ankle joint pivotally connecting the shin section and
the foot section, the ankle joint including a dynamically
adjustable ankle flexion control device for damping ankle flexion,
a first sensor associated with the ankle joint and which is
operable to generate inclination sensor signals indicative of
ground inclination, a second sensor associated with the knee joint
and which is operable to generate speed sensor signals indicative
of speed of locomotion, and an electronic control system coupled to
the sensors and to the knee and ankle flexion control devices in
order dynamically and automatically to modify a flexion control
setting of the knee joint and a flexion control setting of the
ankle joint in response to signals from the sensors, wherein
arrangement of the sensors, the electronic control system and the
knee and ankle flexion control device is such that when the
inclination sensor signals indicate walking on an incline the
damping resistance of the knee flexion control device and the
damping resistance of the ankle flexion control device are each
adjusted jointly based on the ground inclination and the speed of
locomotion.
18. A lower limb prosthesis as claimed in claim 17, further
comprising one or more further sensor associated with the ankle
joint and one or more further sensor associated with the knee
joint.
19. A lower limb prosthesis as claimed in claim 18, wherein one or
more of the further sensors generate a sensor signal indicative of
a shin or ankle bending moment, the arrangement of the sensors, the
electronic control devices and the electronic control system being
such that, during locomotion, the flexion control settings of the
knee joint are adjusted in response to the shin or ankle bending
moment.
20. A lower limb prosthesis as claimed in claim 18, wherein one of
the sensors associated with the ankle joint is an accelerometer
mounted on a prosthetic foot section, the flexion control setting
of the knee joint being adjusted in response to signal from the
accelerometer.
21. A lower limb prosthesis as claimed in claim 18, wherein signals
representative of stride length and/or step rate are generated in
the electronic control system in response to signals from the
sensors associated with the ankle joint.
22. A lower limb prosthesis as claimed in claim 17, wherein the
knee flexion control device comprises a pneumatic piston mounted on
a piston rod which is reciprocable in a pneumatic piston chamber
having upper and lower parts on opposite sides of the pneumatic
piston.
23. A lower limb prosthesis as claimed in claim 22, wherein
resistance of the pneumatic piston to flexion is controlled by a
needle valve in a passage interconnecting the upper and lower parts
of the pneumatic piston chamber, the needle valve having a needle
member and being adjustable by an electrical stepper motor and an
associated screw-threaded shaft connected to the needle member of
the needle valve.
24. A lower limb prosthesis as claimed in claim 22, wherein the
pneumatic piston contains a pneumatic bypass passage including a
non-return valve which is oriented such that the pneumatic piston
provides negligible resistance to knee extension.
25. A lower limb prosthesis as claimed in claim 22, wherein the
knee flexion control device further comprises a hydraulic piston
mounted on the piston rod which is reciprocable in a hydraulic
piston chamber.
26. A lower limb prosthesis as claimed in claim 25, wherein during
a stance phase of a walking gait cycle, the knee flexion control
device provides predominantly hydraulically controlled flexion and
extension and during a swing phase of the walking gait cycle the
knee flexion control device provides predominantly pneumatic
controlled flexion.
27. A lower limb prosthesis as claimed in claim 17, wherein the
ankle joint includes a dynamically adjustable hydraulic ankle
flexion control device having a piston which is reciprocable in a
cylinder to define upper and lower chambers which are linked by a
pair of passages, the hydraulic ankle flexion control device being
arranged to provide independent adjustment of dorsi-flexion and
plantar-flexion damping resistance.
28. A lower limb prosthesis as claimed in claim 27, wherein the
electronic control system is further coupled to the ankle flexion
control device in order dynamically and automatically to modify the
flexion control setting of the ankle joint in response to signals
from the sensors, wherein arrangement of the sensors, the
electronic control system and the ankle flexion control device is
such that when the inclination sensor signals indicate ascent of
the upward incline, the dorsi-flexion damping resistance of the
ankle flexion control device decreases as the speed of locomotion
increases.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 16/403,025 (published as U.S. 2019/0358061) filed on May 3,
2019 and entitled "Lower Limb Prosthesis", which application is a
continuation of U.S. application Ser. No. 14/364,637 (published as
U.S. 2014/0379096 and issued as U.S. Pat. No. 10,285,827 on May 14,
2019) filed Jun. 11, 2014 and entitled "Lower Limb Prosthesis with
Knee Flexion Control during Descent of a Downward Incline," which
application is a national stage application filed under 35 U.S.C.
371 of International Application No. PCT/GB2012/053106 filed Dec.
12, 2012, which application claims priority from each of GB
1121437.6 filed Dec. 13, 2011; GB 1208410.9 filed May 14, 2012;
U.S. Provisional Application No. 61/580,887 filed Dec. 28, 2011;
and U.S. Provisional Application No. 61/647,016 filed May 15, 2012.
Each of the foregoing applications and priority documents is hereby
incorporated by reference herein in its entirety.
[0002] This invention relates to a lower limb prosthesis including
a knee joint and an ankle joint. Both the knee joint and the ankle
joint include respective flexion control devices actuated by an
electronic control system.
[0003] Known lower limb prostheses for above-knee amputees include
prostheses with adaptive control systems for controlling knee
flexion during both stance and swing phases of the walking cycle.
Such a prosthesis is disclosed in WO99/08621. In this example, the
control system includes sensors for sensing shin bending moment and
knee flexion angle, corresponding electrical signals being fed to a
processing circuit for automatically adjusting hydraulic and
pneumatic flexion control devices. Knee flexion is controlled in
the stance phase in response to the activity mode of the amputee,
i.e. in response to changes between level walking, walking uphill,
and walking downhill, and in the swing phase in response to walking
speed. The disclosure of WO99/08621 is incorporated herein by
reference.
[0004] It is also known to provide dynamically variable damping of
a prosthetic ankle joint as in, for example, WO2008/103917 and
related U.S. application Ser. No. 13/150,694 filed Jun. 1, 2011,
the disclosure of which is incorporated herein by reference. In
this example, the ankle joint includes an hydraulic piston and
cylinder assembly providing independent variation of damping
resistance in dorsi-flexion and plantar-flexion directions in
response to, e.g., ground inclination.
[0005] It is an object of the present invention to provide
above-knee amputees with an electronically controlled prosthesis
with improved limb function in a wide range of conditions.
[0006] According to a first aspect of the invention, a lower limb
prosthesis comprises an attachment section, a shin section, a foot
section, a knee joint linking the attachment section and the shin
section, and an ankle joint linking the shin section and foot
section, wherein the knee joint includes a knee flexion control
device and the ankle joint includes an ankle flexion control
device, the prosthesis further comprising at least one sensor
associated with the knee joint and at least one sensor associated
with the ankle joint, each such sensor being arranged to generate
sensor signals indicative of at least one respective kinetic or
kinematic parameter of activity or locomotion, or of walking
environment, wherein the prosthesis further comprises an electronic
control system coupled to the said sensors to receive the sensor
signals and to the flexion control devices to feed control signals
to the said control devices in order dynamically and automatically
to modify the flexion control settings of the knee joint and the
ankle joint in response to the sensor signals, and wherein the
arrangement of the sensors, the control devices and the electronic
control system is such that, during locomotion, the flexion control
settings of the knee joint and those of the ankle joint are each
determined jointly by the sensor signals from the sensor or sensors
associated with the knee joint and the sensor signals from the
sensor or sensors associated with the ankle joint. In this way, it
is possible to provide a lower limb prosthesis for an above-knee or
through-knee disarticulation amputee with integrated microprocessor
control. In particular, the limb may combine microprocessor control
of a hybrid hydraulic, yielding stance and pneumatic swing control
device in the knee together with hydraulic control and
dorsi-flexion damping (and, preferably, plantar-flexion damping) of
the ankle joint, bringing advantages in terms of coordinated
adjustment at both knee and ankle levels based on signals from
sensors placed at optimum positions within the prosthesis,
according to the respective sensed parameters. References to
"flexion control" in this specification are to be interpreted in
the general sense of including control of flexion and/or extension
(rather than merely in the sense of increasing bending of a
joint).
[0007] Integration of the control functions for the knee joint and
the ankle joint, using inputs from sensors at the level of the knee
and the level of the ankle, allows more accurate measurement of
kinetic and kinematic parameters associated with locomotion. For
instance, sensors at the level of the ankle joint or foot are best
suited to detecting changes in surface inclination whereas sensors
associated with the knee joint are best suited for sensing certain
velocity and period parameters.
[0008] Integrated control may be achieved in a prosthesis with, for
instance, fibre-reinforced composite leaf springs, and axial
springs for absorbing mechanical energy, for improved function on a
variety of terrains and at different speeds of locomotion.
[0009] In one embodiment of the invention, the prosthesis has a
sensor associated with the ankle joint for generating a sensor
signal indicative of a shin or ankle bending moment, the
arrangement of the sensors, the control devices and the electronic
control system being such that, during locomotion, the flexion
control settings of the knee joint are adjusted in response to the
shin or ankle bending moment. Alternatively, or in addition, the
prosthesis may have a sensor associated with the ankle joint in the
form of an accelerometer mounted, e.g., on the prosthetic foot
section, the flexion control settings of the knee joint being
adjusted in response to signals from the accelerometer.
[0010] The arrangement is preferably such that, during locomotion,
the flexion control settings of the knee joint are determined in
response to settings of the ankle flexion control device, the
latter being a damping device providing variable damping
resistance. Signals representative of walking speed, e.g. signals
representative of stride length and/or step rate, may be generated
in the electronic control system in response to sensor signals from
the sensor or sensors associated with the knee joint and the sensor
signals from the sensor or sensors associated with the ankle joint.
Generally, the arrangement is such that the flexion control
settings of the ankle joint are determined in response to such
walking speed signals.
[0011] Additionally, in the preferred prosthesis, the flexion
control settings of the knee joint are modified in response to
sensor signals indicative of ground inclination, such signals being
derived from an accelerometer associated with the ankle joint.
Indeed, the flexion control settings of the knee joint may be
modified in response to a combination of sensor signals
representative of both ground inclination and the flexion control
settings of the ankle joint. It is preferred that control device
settings effective to control flexion resistance at the knee during
both the stance phase and the swing phase are adjusted in response
to sensed walking speed.
[0012] A gyroscopic sensor may be mounted, for instance, on the
shin section, i.e. at a location between the knee joint axis and
the ankle joint axis. Alternatively, the gyroscope sensor may be
mounted in the sagittal plane on the socket, or on the knee above
the knee joint axis, or below the ankle joint axis, e.g. on the
foot. The sensor measures angular velocity.
[0013] Other sensors forming part of the prosthesis may include at
least one sensor measuring real time loads, e.g. externally applied
bending moments and/or axial forces. Such sensors may be strain
gauges. Shear forces on the foot components may be measured in this
way using strain gauges in the foot. Shear forces in the shin may
be measured, e.g. by strain gauges at the knee level, typically on
the upper part of the shin, such as on a shin cradle connecting
knee joint components to a shin tube. Sensors may also be included
to detect both linear displacement and angular motion at the knee
and at the ankle/foot level. Where velocity, orientation or
acceleration measurements are required, accelerometers and
gyroscopic sensors are preferred. Such measurements may be used to
detect different environments, such as ramps and stairs, as well as
predicting changes in speed of locomotion, changes in stride length
and events such as coming to a standstill, sitting down, starting
and stopping locomotion, turning and maneuvering around
obstacles.
[0014] Thus, the arrangement of the preferred electronic control
system allows definition of a climbing stairs mode. The sensors may
include an ankle angle sensor and a knee angle sensor, the system
being further arranged such that the climbing stairs mode is
activated when signals from the ankle angle sensor and the knee
angle sensor are indicative of the ankle joint being dorsi-flexed
beyond a first dorsi-flexion threshold in conjunction with the knee
joint being flexed beyond a first knee flexion threshold.
[0015] Other activity modes may further comprise fast and slow
walking modes and a descending stairs mode.
[0016] The arrangement of the sensors, the control devices and the
electronic control system is preferably such that the flexion
control settings of the knee joint are responsive to activity mode.
Similarly, the flexion control settings of the ankle joint may be
responsive to activity mode.
[0017] Typically, the flexion control settings of the knee joint
and those of the ankle joint are responsive to sensor signals
indicative of shin bending moment, knee flexion angle, ankle
flexion angle, and ground inclination. Signals indicative of stride
length and angular velocity may also be used.
[0018] The arrangement may also be such that, during locomotion,
the flexion control settings of the ankle joint are modified to
achieve a predetermined shin bending moment profile, preferably one
in which, during the stance phase of the gait cycle, a graph
plotting bending moment with time has a stepped shape. More than
one preferred bending moment profile can be used, depending on,
e.g., activity mode, a detected gait parameter such as walking
speed or stride length, or ground inclination. The stepped shape of
the bending moment profile is characterised by a first period in
which the bending moment increases with a first gradient, followed
by a second period in which the moment increases with a second
gradient which is less than the first gradient, followed by a third
period in which the gradient reverts to a level similar to that of
the first period, the arrangement being such that if the bending
moment profile does not exhibit the said stepped shape, the stance
phase plantar-flexion resistance of the ankle flexion control
device is increased and/or the stance phase dorsi-flexion
resistance of the ankle flexion control device is decreased.
Typically, the duration of the third period of the stepped bending
moment profile shape is at least half, preferably at least 80
percent of that of the second period. The control settings may be
adjusted to achieve different bending moments for different
activities including, for instance, ground inclination, step rate
or stride length.
[0019] In the case of the prosthesis including an ankle flexion
angle sensor, the control system may be arranged such that, if the
area under the dorsi-flexion curve with respect to time during the
stance phase exceeds a respective predetermined area threshold, the
stance phase plantar-flexion resistance of the ankle flexion
control device is increased and/or the stance phase dorsi-flexion
resistance of the ankle flexion control device is decreased.
[0020] The arrangement may be such that the plantar-flexion and
dorsi-flexion resistance at the ankle are dynamically and
automatically adjusted during locomotion to cause the shin bending
moment profile to exhibit a step-shaped increase during the stance
phase and/or to reduce the ankle dorsi-flexion amplitude during the
stance phase.
[0021] Modifications or adjustments of the ankle joint flexion
resistance or resistances are typically performed in a calibration
mode of the electronic control system, thereby to establish flexion
resistance settings which are used during subsequent locomotion in
response to sensor output signals representative of the
above-mentioned kinetic or kinematic parameter or parameters of
locomotion, or of walking environment.
[0022] With regard to the composition of the electronic control
system, a single microprocessor controller may be used or there may
be a central controller and one or more subsidiary controllers. At
least one of such controllers receives signals from the sensors,
the respective measured parameters being used to define activity
modes, such as level walking, walking up a ramp, walking down a
ramp, fast walking, slow walking, etc., as input values to a
multiple-layer matrix containing control output values to form the
basis for selected output signals for setting mechanical control
devices in the knee joint and ankle joint. Combinations of such
modes are allowed by the multi-layer matrix. The activity mode may
distinguish between stride length and step rate, given that any
particular speed of locomotion may be achieved by the combination
of a low step rate and a large stride length or that of a high step
rate and a small stride length. Activity modes may, therefore,
include slow short steps, fast short steps, slow long steps, and
fast long steps. Starting and stopping steps may also be sensed and
taken into account. In particular, each activity mode, detected by
processing the sensor signals, has associated matrix values
defining ankle joint and knee joint flexion resistance settings
pre-selected for that mode. In the preferred prosthesis, the
settings relate to hydraulic and pneumatic control devices for the
knee joint, controlling flexion resistance in the stance phase and
swing phase respectively, and a control device or devices for
resisting plantar- and dorsi-flexion of the ankle joint. Such
devices may comprise linear or rotary pistons or vanes which are
reciprocable in chambers containing a fluid medium, whether liquid
or gas. Valves and motors allow damping to be varied by controlling
the flow of fluid and, thereby, the movement of the piston and vane
in each case.
[0023] Settings are preferably established during a teaching or
calibration mode which may be under the control of a prosthetist or
are carried out according to an automatic calibration process.
EP2334891 and WO2007/110585 disclose techniques for setting swing
phase resistance automatically. The disclosures of these published
patent applications and equivalent U.S. application Ser. No.
12/282,541 filed Sep. 11, 2008 are expressly incorporated in the
present application by reference.
[0024] During the calibration mode, individual locomotion
characteristics are detected and optimum values for, e.g., stance
yield (flexion resistance), the degree of heel rise during the
swing phase, the degree of plantar-flexion resistance and
dorsi-flexion resistance at preferred walking speeds and terrain
conditions are established. This calibration data can be refined
further in an automatic manner through manual adjustment via input
commands to the electronic control system using interface switches
or via wireless or wired remote control.
[0025] In the preferred prosthesis, the control system adjusts the
control device settings according to activity mode in order to
achieve safe yield control of the knee joint as it is being loaded,
optimum release of the yield to initiate swing with minimum user
effort, and correct braking of the ankle joint to enable natural
movement and progression of the centre of mass of the amputee. Both
plantar-flexion and dorsi-flexion are damped according to activity
mode, to maximise the propulsion push-off force from energy-storing
elements of the prosthesis so that an energy-efficient, safe and
comfortable movement is provided for the user. Initially, settings
are established for level walking at a preferred walking speed. The
level of compensation and abnormal adjustment by the user is
minimised as far as possible so as to give the perception of being
pushed or assisted forward, the limb braking or assisting to
control speed in as natural a manner as possible as the prosthesis
strikes the ground. The matrix values established for level walking
at the preferred walking speed are then adjusted to provide new
matrix values for slopes, different speeds, and non-walking modes.
In the preferred prosthesis, the sensors and the remainder of the
control system can detect and distinguish between ascending and
descending ramps, the degree of inclination of the ramps, ascending
and descending stairs, the speed of ascent or descent, the speed of
walking from the slowest the amputee walks to the fastest, as well
as sitting, standing-up from chairs, and other modes such as
maneuvering to avoid an obstacle. The matrix has a number of matrix
levels, at least one for each activity mode.
[0026] According to a second aspect of the invention, there is
provided a lower limb prosthesis comprising an attachment section,
a shin section, a foot section, a knee joint linking the attachment
section and the shin section, and an ankle joint linking the shin
section and foot section, wherein the knee joint includes a knee
flexion control device and the ankle joint includes an ankle
flexion control device, the prosthesis further comprising a
plurality of sensors arranged to generate sensor signals indicative
of at least one respective kinetic or kinematic parameter of
locomotion, or of walking environment, the prosthesis further
comprising an electronic control system coupled to the said sensors
to receive the sensor signals and to the flexion control devices to
feed control signals to the said control devices in order
dynamically and automatically to modify the flexion control
settings of the knee joint and the ankle joint in response to the
sensor signals, and wherein, the sensors include a sensor
associated with the shin section which is arranged, in combination
with the electronic control system, to generate signals
representative of a shin section bending moment, and to feed
control signals to the ankle flexion control device in response to
the signals representative of the shin section bending moment.
Preferably, the ankle damping resistance is varied in response to
the sensed bending moment and, more preferably, the knee damping
resistance as well.
[0027] According to a third aspect of the invention, there is
provided a lower limb prosthesis comprising an attachment section,
a shin section, a foot section, a knee joint pivotally connecting
the attachment section and the shin section, and an ankle joint
pivotally connecting the shin section and the foot section, the
knee joint including a dynamically adjustable knee flexion control
device for damping knee flexion, wherein the prosthesis further
comprises an inclination sensor associated with the ankle joint or
foot section and operable to generate inclination sensor signals
indicative of ground inclination, and an electronic control system
coupled to the inclination sensor and to the knee flexion control
device, the arrangement of the sensor, the electronic control
system and the knee flexion control device being such that the
damping resistance of the knee flexion control device is variable
in response to the inclination sensor signals. The damping
resistance at the knee may be controlled in part, also, by the
values produced by the electronic control system for ankle joint
damping resistance. In a particular embodiment of the invention,
the control system is arranged such that when the inclination
sensor signals indicate descent, the stance phase resistance to
flexion, in this case to bending of knee, is decreased during the
stance phase. Thus, whereas during an initial part of the stance
phase, the resistance to flexion is high such that the knee may be
nearly locked in order to provide stability during stance, in a
subsequent part of the stance phase the resistance is decreased to
allow greater yielding under the load imposed by the amputee's
weight in order to prepare for the swing phase. The reduction in
resistance may be stepped or progressive.
[0028] According to a fourth aspect of the invention, there is
provided a lower limb prosthesis comprising an attachment section,
a shin section, a foot section, a knee joint linking the attachment
section and the shin section, and an ankle joint linking the shin
section and foot section, wherein the knee joint includes a knee
flexion control device and the ankle joint includes an ankle
flexion control device, the prosthesis further comprising a sensor
associated with the knee joint which is coupled to the electronic
control system and is arranged, in combination with the electronic
control system, to generate signals indicative of a speed of
locomotion, wherein the ankle flexion control device is a device
capable of variably damping ankle joint flexion and arranged in
combination with electronic control system to alter the resistance
to ankle flexion damping in response to the signals indicative of
speed of locomotion.
[0029] According to a fifth aspect of the invention, there is
provided a lower limb prosthesis comprising an attachment section,
a shin section, a foot section, a knee joint pivotally connecting
the attachment section and the shin section, and an ankle joint
pivotally connecting the shin section and the foot section, the
knee joint including a dynamically adjustable knee flexion control
device for damping knee flexion, wherein the prosthesis further
comprises a plurality of sensors each arranged to generate sensor
signals indicative of at least one respective kinetic or kinematic
parameter of locomotion or of walking environment, and an
electronic control system coupled to the sensors and to the knee
flexion control device in order dynamically and automatically to
modify the flexion control setting of the knee joint in response to
signals from the sensors, including from one of the said sensors
which is operable to generate inclination sensor signals indicative
of ground inclination, and wherein the arrangement of the sensors,
the electronic control system and the knee flexion control device
is such that when the inclination sensor signals indicate descent
of a downward incline, the damping resistance of the knee flexion
control device is set to a first level during a major part of the
stance phase of the gait cycle and to a second, lower level during
a major part of the swing phase of the gait cycle, and wherein,
during an interval including a latter part of the stance phase, the
knee flexion control device is adjusted so that the damping
resistance to knee flexion is between the first and second
levels.
[0030] In contrast, in the preferred embodiment, the arrangement is
such that in a level walking mode or ramp-up mode, the damping
resistance of the knee flexion control device is switched
substantially directly from the first level or one similar thereto
to the second level or one similar thereto. In other words,
switching of the knee flexion damping resistance to the second
level is delayed in the ramp-down mode, as compared to the
switching in the level walking mode, by virtue of an adjustment of
the knee flexion control device to one or more intermediate
resistance levels. This allows to give some additional support at
the end of stance phase while not preventing the initiation of
swing phase in a controlled manner.
[0031] It is preferred that signals fed to the knee flexion control
device cause the flexion resistance to be reduced in a step change
at the start of the said interval to a third, predetermined
intermediate level between the first level and the second level,
and to be reduced in a further step change at the end of the said
interval to the second level. Alternatively, the signals fed to the
knee flexion control device during the said interval cause the knee
flexion damping resistance to be progressively reduced from the
first level to the second level.
[0032] Typically, the duration of the said interval is at least 10
percent of the duration of the stance phase (the stance phase
ending at toe-off, i.e. the point at which the foot section leaves
the ground). More preferably, the interval is at least 15 percent
of the stance phase duration and may be in excess of 20 percent. It
is also preferred that the interval spans the toe-off point,
beginning at or shortly after a shin bending moment maximum and
ending as the knee flexion angle is increasing during the swing
phase of the gait cycle. In the preferred embodiment, the interval
ends when the knee flexion angle has increased to a predetermined
threshold at between 30 percent and 70 percent of the maximum knee
flexion angle achieved in the swing phase.
[0033] In the ramp down mode, the electronic control system
preferably follows a ramp down resistance program controlling
switching of the knee flexion control device from the first level
to the third level and from the third level to the second level.
Switching of the knee flexion damping resistance from the first
level to the third level may be performed in response to a measured
kinetic parameter, e.g. a moment or force, preferably the shin
bending moment. Switching of the knee flexion damping resistance to
the second level at the end of the interval is preferably performed
in response to a measured kinematic parameter, e.g. a relative
linear or angular displacement of one limb segment with respect to
another, or related derivatives, e.g. velocities or accelerations.
In the preferred embodiment, the kinematic parameter is the
measured knee angle or an equivalent thereof.
[0034] The invention will now be described by way of example with
reference to the drawings, in which:--
[0035] FIG. 1A is a side elevation of a lower limb prosthesis in
accordance with the invention;
[0036] FIG. 1B is a longitudinal cross-section of a knee joint of
the prosthesis of FIG. 1A;
[0037] FIG. 1C is a schematic representation of hydraulic and
pneumatic circuits in a knee flexion control device in the knee
joint of FIG. 1B.
[0038] FIG. 1D is a longitudinal cross-section of a foot/ankle
assembly of the prosthesis of FIG. 1A;
[0039] FIG. 2 is a block diagram of an electronic control system,
together with sensors, for the prosthesis of FIG. 1;
[0040] FIG. 3A is a Venn diagram indicating different activity
modes defined within the electronic control system, and their
interrelationships;
[0041] FIG. 3B is a finite state diagram indicating the different
activity modes defined within the electronic control system, and
transitions between the modes;
[0042] FIG. 3C is a flow chart illustrating a typical set of
operations performed by the electronic control system and flexion
control devices of the prosthesis;
[0043] FIG. 3D is a first series of more detailed finite state
diagrams used by the electronic control system;
[0044] FIG. 3E is a second series of more detailed finite state
diagrams used by the electronic control system;
[0045] FIGS. 4A to 4D are representations of a multiple-layer
matrix group defining relationships between input conditions
derived, e.g., from sensed kinetic and kinematic parameters of
locomotion, and outputs for flexion control devices forming part of
the prosthesis of FIG. 1, FIG. 4A showing a main matrix and FIGS.
4B, 4C and 4D showing lower-level matrices for, respectively,
walking up a ramp, walking down a ramp, and walking at different
speeds on a level surface;
[0046] FIGS. 5A to 5D are graphs illustrating the variation of
selected parameters over the course of the walking gait cycle;
and
[0047] FIG. 6 is a composite graph illustrating the variation of
knee flexion damping resistance in a ramp down mode.
[0048] Referring to FIG. 1A, a lower limb prosthesis in accordance
with the invention has an attachment section 10 for attaching the
prosthesis to, for instance, a stump socket (not shown), a shin
section 12 and a foot section 14. The shin section 12 is linked to
the attachment section 10 by a knee joint 16 which, in this case,
is a uniaxial knee joint incorporating a flexion control device 18
housed in a knee cradle 20 to which the shin section 12 is
attached. Linking the foot section 14 to the shin section 12 is an
ankle joint 22 incorporating an ankle flexion control device which
will be described hereinafter.
[0049] The knee joint 16 is shown in more detail in FIG. 1B.
Referring to FIG. 1B, the knee joint has a knee chassis 25 to which
the attachment section 10 is rigidly mounted and carries a pivot 27
defining a knee axis 28. The shin cradle 20 is attached to the knee
chassis 25 by the pivot 27 so that, when the knee joint is flexed,
the shin cradle 20 pivots relative to the attachment section 10
about the knee axis 28.
[0050] Pivotally coupled to a posterior part of the knee chassis 25
and to a lower part of the shin cradle 20 by upper and lower
control device pivots 30, 32, the knee flexion control device 18 is
in the form of a hybrid pneumatic and hydraulic piston and cylinder
assembly for controlling both flexion and extension of the knee
joint. Being a hybrid control device, it comprises a housing having
two cylinders and two pistons, the latter both being mounted on a
common piston rod 18R. Referring to FIG. 1B in conjunction with
FIG. 1C, a first piston 18A, hereinafter referred to as the
"pneumatic piston" is reciprocable in a first pneumatic piston
chamber 18B, and a second piston 18C, hereinafter referred to as
the "hydraulic piston" is reciprocable in a second, hydraulic
chamber 18D. The arrangement and function of the pneumatic piston
18A and associated parts of the flexion control device are
generally similar to those of the piston and cylinder assembly
disclosed in published British Patent Application GB2280609A. The
pneumatic piston 18A contains a bypass passage 18E including a
non-return valve which is oriented such that the pneumatic piston
18A resists movement of the piston rod 18R much more during flexion
of the knee joint than during extension. Indeed, in this region,
resistance to extension is negligible. Resistance of the pneumatic
part of the control device 18 to flexion at the knee joint is
controlled by a needle valve 18N which is adjustable by a first
electrical stepper motor 34 and an associated screw-threaded shaft
34A connected to the needle member of the needle valve. The needle
valve 18N lies in a passage 18P in a lower housing part 18F of the
control device 18, the passage interconnecting the upper and lower
parts of the pneumatic chamber 18B on opposite respective sides of
the pneumatic piston 18A, and emerging to the outside at a port
(not shown) at the top of the pneumatic chamber 18B. Operation of
the motor 34 causes the shaft 34A to move axially so that the
needle member moves into or out of a passageway forming part of the
passage 18P to vary the orifice area.
[0051] The passage 18P constitutes a second bypass passage
interconnecting the chamber spaces on opposite sides of the
pneumatic piston 18A. It will be understood, then, that the flexion
resistance provided by differential pressure across the piston 18A
depends largely on the restriction created by the setting of the
needle valve 18N by the motor 34.
[0052] A first hydraulic bypass passage 18L contains a non-return
valve 18M oriented so as to close the passage during knee extension
movements. The passage 18L also contains an adjustable rotary valve
18O connected via a gear mechanism to a second electric motor 50
mounted on the side of the housing 18F of the knee flexion control
device 18. Variable valve 18O has a through-passage which
communicates with the bore of the bypass passage 18L to a varying
degree depending on the angular position of the valve 18O, the
cross-section of the passage being shaped to provide a progressive
change in orifice area as the rotatable part of the valve is driven
by the motor 50.
[0053] Owing to the orientation of the non-return valve 18M, the
first hydraulic bypass passage 18L and its associated adjustable
valve 18O control the level of knee flexion resistance due to the
hydraulic part of the control device 18 according to the electrical
signals controlling the motor 50.
[0054] A second hydraulic bypass passage 18Q in the hydraulic part
of the control device 18 has a non-return valve 18S which is
oppositely oriented to that of the first bypass passage 18L such
that a second rotary valve 18T, which restricts the flow of
hydraulic fluid through passage 18Q, controls the resistance to
knee extension when activated. In this embodiment of the invention,
the second rotary valve 18T is manually presettable.
[0055] The second hydraulic bypass passage 18NQ is branched into
two passages 18QA, 18QB which are ported into the hydraulic chamber
18D at different locations so that one of the branches 18QA is
covered by the piston 18C as the knee joint nears full extension.
The other branch 18QB remains uncovered substantially to full
extension. This second branch 18QB has a restriction 18U, whereas
the first branch 18QA is open, so that as the piston 18C nears the
full extension position, the restriction 18U takes effect over a
final portion of the piston stroke, as the piston itself restricts
fluid flow through passage 18QB, to provide progressive terminal
impact damping. The base resistance to extension is determined by
the setting of the manually adjustable second rotary valve 18T.
[0056] Activation of the hydraulic valve 18O is controlled by an
electronic control system, as described below, in order that, at
least during the stance phase of the walking gait cycle, the knee
flexion control device provides predominantly hydraulically
controlled flexion and extension, whereas during the swing phase,
the control is predominantly pneumatic.
[0057] As part of the electronic control system, the shin cradle 20
carries two strain gauges 52, 53, one mounted on an anterior wall
of the cradle 20 and the other on an opposite posterior wall. These
sensors are used for measuring the shin bending moment when the
prosthesis is loaded. The knee joint also carries a knee angle
sensor in the form of a magnetoresistive transducer 54A mounted on
the side of the knee control device housing 18F and a magnet 54B on
the piston 18A.
[0058] In the upper anterior part of the shin cradle, space is
provided for a battery 56 for powering the electronic control
system.
[0059] Referring now to FIG. 1D, the preferred prosthesis has a
foot keel 62 comprising a rigid carrier 62A. Independently coupled
to the rigid carrier 62A are a toe spring 62B and a heel spring
62C. The keel 62 is largely formed from carbon fibre composite
material and can be surrounded by a foam cosmetic covering (not
shown).
[0060] Coupled to the foot keel 62 is the ankle joint 22 which is
substantially cylindrical in shape and coaxial with the shin
section 12 (see FIG. 1A), the ankle joint carrying an upper
alignment interface 64 in the form of a pyramid-shaped shin
connection interface 64 which defines a longitudinal shin
connection axis 66. The ankle joint 22 connects the shin section 12
to the foot keel 62A of the foot 60, the mounting to the foot keel
62A being by way of an ankle flexion pivot 70 defining an ankle
flexion axis 70A.
[0061] The ankle joint 22 has an ankle joint body 22B which forms
the cylinder of an ankle joint piston and cylinder assembly having
a piston 74 with upper and lower piston rods 74A, 74B, the lower
piston rod being pivotally connected to the foot keel 62A at a
second pivotal connection 76, this second pivotal connection
defining a second medial-lateral axis which is spaced, in this
case, posteriorly from the flexion axis 70A. It will be seen that,
as the ankle joint body 22B pivots about the flexion axis 70A, the
piston 74 moves substantially linearly in the cylinder formed by
the body.
[0062] The cylinder is divided into upper and lower chambers 78A,
78B. These chambers are linked by two bypass passages 80 in the
ankle joint body 22B, one of which is visible in FIG. 1D. The other
passage does not appear in FIG. 1D since it is located in front of
the sectional plane. However, its configuration is almost
identical. These two bypass passages 80 each communicate with both
the upper chamber 78A and the lower chamber 78B of the cylinder via
two valves. Each contains a respective damping resistance control
valve 82 which has an associated actuator in the form of a servo
motor 84. Operation of the servo motor 84 rotates a valve member of
the valve 82 progressively to increase or decrease the orifice area
of the valve 82. Each bypass passage 80 also contains a respective
non-return valve 86. This adjustable-area orifice valve 82 and the
non-return valve 86 are arranged in series in the bypass passage
80, between the upper and lower cylinder chambers 78A, 78B.
[0063] The bypass passage 80 appearing in FIG. 1D has its
non-return valve 86 oriented to allow the flow of hydraulic fluid
from the lower chamber 78B to the upper chamber 78A. The other
bypass passage (not shown) has its non-return valve oriented in the
opposite direction. Accordingly, one of the passages 80 is
operative during dorsi-flexion and the other during
plantar-flexion. Continuous yielding movement of the foot component
14 relative to the ankle joint body 22B about the flexion axis 70A
is possible between dorsi-flexion and plantar-flexion limits
defined by the abutment of the piston 74 with, respectively, the
lower wall and the upper wall of the cylinder containing the piston
74. The level of damping for dorsi-flexion and plantar-flexion is
independently and automatically presettable by the respective
adjustable-area orifices by means of the electronic control system
described below.
[0064] The electronic control system has a sensor 85 in the form of
an accelerometer mounted on the foot keel 62A and a two-part ankle
flexion angle sensor 87A, 87B, the two parts being mounted in
registry with each other on the ankle joint body 22B and the foot
keel 62A. The ankle joint casing 22C not only houses the two servo
motors 84 for the adjustable damping resistance control valves 82;
they also provide space for a processor board 90 and a second
battery 92. Wires 94 link the ankle flexion angle sensor 87A, 87B
to the processor board 90. Other wires (not shown) link the other
sensors, the batteries, and the motors of the knee joint to the
processor board 90.
[0065] Referring, now, to FIG. 2, the preferred electronic control
system comprises a processor section 100 with three 8-bit
microprocessor controllers. (16-bit controllers may be used as an
alternative.) The controllers comprise a main controller 102
coupled to two slave controllers, these being a knee controller 104
and an ankle controller 106. Coupled to an input port 102A of the
main controller 102 is an analogue to digital converter 108 with a
plurality of inputs shown as an input port 108A in FIG. 2. These
comprise analogue inputs for receiving sensor signals from the
above-described sensors located in different parts of the
prosthesis. Accordingly, the data received by the controller 102 is
representative of a number of kinetic and kinematic parameters
associated with use of the limb in different activity modes. The
activity modes, such as level walking, walking on an incline,
standing, sitting down, etc. are detected on the basis of such
parameters by the main controller 102, as described below, in
accordance with preset rules.
[0066] According to further rules stored in the main controller
102, instructions are fed therefrom to the knee controller 104 and
the ankle controller 106 which generate control signals for knee
and ankle motor drivers 110, 112. The motors 34, 50 associated with
the knee joint, as described above with reference to FIG. 1B,
exchange signals with the processor section 100 via connections 114
with the first of the drivers 110, including driver signals for
driving the knee motors to required positions which are verified by
feedback signals via the connections 114. As described above, the
knee motors 34, 50 set the valves controlling the movement of the
pneumatic piston and the hydraulic piston in the respective parts
18P, 18L of the knee control device 18 (see FIG. 1B).
[0067] Similarly, the ankle motors 84 (described above with
reference to FIG. 1D) exchange signals with the processor section
100 via connections 116 to the second driver 112, the signals
comprising driving signals and feedback signals in order that the
ankle motors 84 set the valves controlling the movement of the
hydraulic piston in the ankle joint control device 22H contained in
the ankle joint 22, as described above with reference to FIG.
1D.
[0068] A user interface 120, coupled to the processor section 100,
comprises a wireless communication section for exchanging wireless
signals with a PC or tablet computing device. Programming can also
be done by a defined HMI (operator interface) using, e.g. two
buttons, an LED, and a beeper, indicating the status of
programming.
[0069] The control system uses open architecture, both in hardware
and software terms to allow parts to be added or to accommodate,
for instance, alternative or additional input and output signals,
e.g. for signals from another electronic control system in, e.g. a
second lower limb prosthesis in the case of a bilateral amputee.
This open architecture provides a technology platform with plug-in
modules that can be changed according to requirements. For
instance, in the case of a bi-lateral amputee information about the
second limb is provided. Sensor data from other sensors may be
provided. However, the bilateral option shall not only include
communication possibilities for a double transfemoral (above-knee)
amputee, for example, but also communication between a transfemoral
prosthesis and a transtibial (below-knee) prosthesis which means,
in effect, communication between a processor-controlled foot/ankle
joint is possible as this is beneficial for the overall gait
performance and coordination. Overall sharing of information
between different joints and/or components in various combinations
and configurations is possible owing to the open-architecture
approach.
[0070] The main controller 102 is programmed to derive from the
digital representations of the sensor signals kinetic or kinematic
parameters of locomotion thereby to measure gait characteristics
such as velocity including information about the relevant
parameters step rate and stride length, and gait phase, and the
step-to-step variability in such characteristics, thereby to
produce control signals from the knee and ankle controllers 104,
106 to modify the settings of the knee and ankle joint control
devices so as to optimise the gait of the amputee.
[0071] Included in the programming of the main controller 102 is a
self-calibrating routine, as described in the above-mentioned
EP1334891 and WO2007/110585, for convenient and straightforward
modification of the control characteristics for the individual
amputee. Velocity, i.e. the speed of locomotion, in particular
walking speed or gait cycle frequency, and gait phase are
preferably computed from the outputs of the knee angle sensor 54A
and the bending moment strain gauges 52, 53, although in some
circumstances, these parameters may be derived from the outputs of
a gyroscope 88 mounted, e.g. on the shin section and the
accelerometer 85 mounted at the foot level. Changes in the walking
surface and the velocity of the foot in the global reference frame
(kinematic changes) are preferably measured using the signals from
the accelerometer 85 and the ankle angle sensor 87 to drive
modification of the settings of the control device of the ankle
joint 22 (FIG. 1D), as described in the above-mentioned
WO2008/103917.
[0072] The main controller 102, collecting data derived from the
outputs of sensors associated with both the knee joint and the
ankle joint, i.e. from different regions of the prosthesis, allows
improved control of the knee joint and ankle joint control devices
and advanced analysis of gait and mode based on a combined
representation of data relating to different regions of the
prosthesis. The main controller 102 sends direct commands and
additional gait-related information to the knee controller 104 and
the ankle controller 106 which act, effectively, as slave
controllers in a hierarchical, distributed control system. The knee
controller 104 and the ankle controller 106 do, however, have some
autonomy for safety should, for instance, no valid signals be
forthcoming from the main controller 102.
[0073] The main controller 102 has a non-volatile memory for
storing values of a limb control matrix relating input conditions
derived from the sensor signals and output data which is used by
the main controller and the slave controllers 104, 106 to determine
the control signals for the flexion control devices 18A, 18C, 74.
Matrix values can be downloaded for external storage and
communication via the user interface 120 as well as being reloaded
from external devices. Alternatively, control matrix values may be
stored locally in the non-volatile memory of the slave controllers
104, 106, the main controller 102 having access to these values and
the ability to change them.
[0074] The processor section 100 operates on a finite-state control
basis. Referring to FIG. 3A, the status of the main controller 102
(FIG. 2) is defined according to a series of activity modes. These
activity modes are grouped as modes 124 associated with level
walking, ramp modes 125, standing modes 126, stairs modes 127, and
other modes 128, such as an obstacle mode, a special mode, and an
error mode. The intersections of the Venn diagram areas are
indicative of the transitions which may be made from one mode to
another. Other transitions such as going from ramp down to ramp up
directly are also possible. The preferred finite-state control
possibilities are shown more clearly in FIG. 3B. In this case, the
modes include a Normal Walking mode 130, a Ramp Up mode 132, a Ramp
Down mode 134, and so on, as shown in the diagram. The list of
modes in the diagram is not exhaustive. The Normal Walking mode is
configures as the central point of the diagram. As shown by the
interconnections between the different modes, the main controller
switches or transitions from one mode to another, according to
sensor inputs received as sensor data from the analogue to digital
converter (ADC) 108 (FIG. 2). The rules programmed into the main
controller 102 then determine how the knee motors 34, 50 and ankle
motors 84 (FIG. 2) are driven in response to the change of mode and
in response to other changes in the data obtained from the
sensors.
[0075] Thus, for instance, as shown in FIG. 3C, the commencement of
walking down an incline after a period of walking on the level may
be detected and responded to by the following steps: [0076] The
foot sensors (the accelerometer 85 and the ankle flexion angle
sensor 87 (FIGS. 1D, 2)) generate sensor signals indicative of a
change in ground inclination (step 140). [0077] The main controller
102 and/or the ankle controller 106 analyze the digitized versions
of the sensor signals and determine that the surface has changed to
a downwardly inclined ramp (step 142). [0078] Based on a stored
matrix of relationships between, on the one hand, activity mode and
kinetic or kinematic parameter values and, on the other hand,
respective flexion control resistances, the change in mode is
translated into new settings for the knee and ankle motors (step
144). [0079] Via the motor drivers 110, 112, the knee motors 34, 50
and ankle motors 84 (FIG. 2) are driven to the new respective
settings which, in this case, involves driving the servomotor 50 to
a new setting in which the hydraulic part of the knee joint control
device 18 is set to provide intermediate yield in the Ramp Down
mode and the pneumatic part of the control device 18 is driven to
different settings according to walking speed, in the same way as
in the level walking (normal walking) mode (step 146).
Concurrently, the ankle motor settings are changed to increase the
dorsi-flexion resistance provided by the ankle joint control device
and to reduce the plantar-flexion resistance (step 148).
[0080] Similar basic sequences apply to the other mode transitions
shown in FIG. 3B, the sensors used and the actions performed being
governed according to the sensed modes. In this embodiment, the
settings to which the actuators are driven are governed by a
6.times.5 main matrix, as shown in FIG. 4A, and three N.times.5
lower level matrices, as shown in FIGS. 4B, 4C and 4D. The matrix
rows correspond to different activity modes (listed in the
left-hand column in each case), and the matrix columns indicate the
settings of the four above-described flexion resistance control
device parts, those of the hydraulic part of the knee control
device being indicated for the swing and stance phases separately
The five primary resistance settings are adapted according to the
individual amputee. The normal settings for the ankle joint (foot)
plantar-flexion and dorsi-flexion resistances in the FIG. 4A matrix
are moderate resistance settings for normal, medium-speed Level
Walking as shown in FIG. 4D. The normal setting of the knee joint
is that shown in a "Level Velocity" mode in FIG. 4A and is
characterised by high hydraulic resistance during stance and low
hydraulic resistance during swing, and variation of pneumatic
flexion resistance according to walking speed.
[0081] In practice, the matrix for each mode or event is composed
of five primary values, as shown in the columns of the tables of
FIGS. 4A to 4D. In several instances, bands of values are
pre-programmed to provide a range of values from which a particular
value is selected in each case to suit the amputee.
[0082] The main modes are those appearing in the left-hand column
of FIG. 4A, i.e. Ramp Up, Ramp Down, Level Velocity (Level Walk),
Stairs Down, Stand Relaxed, and Sitting. In FIG. 4A, the asterisk
(*) indicates the existence of sub-modes, these appearing in FIGS.
4B, 4C and 4D respectively. The values in the body of each matrix
represent the level to which flexion (or extension) of the
respective joint is resisted. Thus, "VL" means very low resistance,
"L" means low resistance, "M" means medium resistance, "H" means
high resistance, and "VH" means very high resistance. "M/H" means a
resistance level between medium and high resistance, while "H-" is
resistance which is a little bit less than high resistance, and
"H+" means resistance a little higher than a high resistance.
"VL-", "L-", "L+" and "VH+" are to be correspondingly
interpreted.
[0083] With regard to the knee hydraulic settings, the dollar sign
$ at the head of the respective columns means that when the knee
control device resistance value is not indicated explicitly (i.e.
by a single value) the resistance is switched between two levels,
(a) between typically H or H- and M or (b) as the toe is loaded to
select the lower value, and as the limb is extended to select the
higher value. With regard to the setting of the pneumatic part of
the knee control device, the hash sign # at the head of the column
indicates that when the resistance value is not explicitly
indicated, the pneumatic part of the control device adapts
automatically to the speed of walking, regardless of the surface or
other conditions.
[0084] Accordingly, in the "Level Velocity" mode, for level
walking, the resistance due to the pneumatic part of the knee
control device varies from low to high according to walking speed,
as shown in FIG. 4D. Indeed, the pneumatic resistance may increase
to VH for very fast level walking. Resistance to plantar-flexion
and dorsi-flexion at the ankle during the velocity/level walking
mode, as indicated in FIG. 4D, according to speed.
[0085] Referring back to the main matrix of FIG. 4A, it will be
seen that the resistance values for Ramp Up and Ramp Down differ in
certain respects to those for the Velocity/Level Walk mode. Thus,
for instance, the resistance to plantar-flexion at the ankle is
lower, generally, when descending a ramp than during level walking,
and higher when ascending a ramp. Dorsi-flexion resistance at the
ankle tends to be higher when descending a ramp and lower when
ascending. However, at the same time, these values vary according
to speed/velocity and according to the steepness of the ramp, and
during transitions between modes, as indicated in the sub-matrices
of FIGS. 4B and 4C.
[0086] Referring to FIG. 4C, in both the stance and swing phases of
the Ramp Down mode, an intermediate hydraulic resistance level (M)
is indicated. This level is set by the knee flexion control device
to occur during an interval comprising a latter part of the stance
phase and an initial part of the swing phase. Thus, during each
gait cycle in the Ramp Down mode, the transition from stance to
swing is characterised by a stepwise reduction from the high (H or
H-) level to the low (L) level, the interval during which the
intermediate (M) level applies spanning the toe-off point at the
end of the stance phase. This increased yielding of the knee joint
towards the end of the stance phase aids descent. The main benefit
in the ramp down mode is that the change between the flexion
resistances between high and low (which is the normal profile in
other modes) is reduced (high to intermediate and then to low
during the end part of the stance phase). This creates, firstly,
some extra support as the amputee has some added resistance at the
end of stance. Able-bodied people then tend to use their muscles to
brake slowly going down a ramp so that they don't accelerate or
only accelerate in a controlled matter. The amputee doesn't have
this ability with the prosthetic limb. Secondly, the foot and ankle
already brake going down a ramp but the additional resistance at
the knee at end of the stance phase gives the amputee a feeling of
extra security and grip and has the potential beneficially to
decelerate the amputee.
[0087] It should be noted that no reduction of flexion damping
resistance occurs at the knee during descent of a steep ramp, as
shown by the Steep Ramp sub-modes in FIG. 4C. In this sub-mode,
there is little or no loading of the toe because the amputee uses
knee yield to descend the steep ramp.
[0088] Each basic mode described above with reference to FIGS. 3A
and 3B and FIGS. 4A to 4D has associated transition states, as
indicated by the more detailed finite state diagram of FIGS. 3D and
3E. In addition, in this embodiment, the basic modes are divided
into further sub-modes. To give examples from FIGS. 3D and 3E,
therefore, the normal walking mode 130 has three such sub-modes:
Normal Steps 130A, Small Steps 130B and Large Steps 130C. There are
respective transitions 130T between these sub-modes. As just
mentioned, other basic modes include transition states. For
example, referring to FIGS. 3E and 4C, the Ramp Down mode 134, in
addition to being divided into sub-modes Ramp Down 134A and Steep
Ramp Down 134B, has a transition state Transition Ramp Down 134C to
allow definition of intermediate settings of the flexion control
devices to provide a smoother transition from the Ramp Down mode
134 to the Normal Walking mode 130, and vice-versa. Transitions
normally have associated values which are set by interpolation
between the values of the starting mode and those of the finishing
mode in each case. Additional Ramp Down sub-modes are provided for
slow and fast walking velocities.
[0089] Similar sub-modes exist for the Ramp Up mode (see FIG.
3E).
[0090] Additional transition states and corresponding actuator
settings (i.e. control device settings) are related to each other
in further layers (not shown) of the matrix represented by the
table of FIG. 4A. For example, getting up from a chair, as
illustrated by the Sit-Down-Stand-Up Mode state 155 in the finite
state diagram of FIG. 3D, uses a set of output settings from one
layer of the matrix and then, moving to the Stand Relaxed mode 157,
from another matrix layer, or moving to the Slow Walking mode (a
sub-mode 160A of a Velocity mode 160 (in effect walking which is
other than normal walking)) require transition states Transition
Sit 155A, Stand Up 155B, and Transition Walking (a sub-mode 157C of
the Stand Relaxed mode 157) These transitions avoid the need to
compensate for or accommodate sudden changes so that the limb
operation is as nearly possible seamless and smooth as the amputee
moves from one activity mode to the other. Each matrix has a set of
relationships associating and linking modes, events and transitions
with different control settings for implementation in real
time.
[0091] The control system open architecture allows the programming
of additional matrices, e.g. for defining control functions
associated with additional events or activities, as well as
integration of additional data streams.
[0092] In general, when the control system is operating to indicate
a particular activity mode, it will continue to indicate that same
mode until it receives a sensor signal which is interpreted as
indicating a transition to a different mode.
[0093] The settings stored in the matrices described above with
reference to FIGS. 4A to 4D, and the settings at other matrix
levels (not shown) of the matrix are adjusted to suit the
individual amputee during a calibration program mode. A typical
calibration routine for establishing the matrix settings
includes:-- [0094] 1. Level walking with different velocities
[0095] 2. Level walking--starting and stopping [0096] 3. Walking up
and down a ramp at different velocities and with different
gradients [0097] 4. Walking up and down stairs [0098] 5. Level
walking with different disturbances [0099] 6. Sitting down and
getting up from and to walking and standing [0100] 7. Other
activity modes
[0101] The system does allow for calibration on the basis of tests
1., 2., and, preferably, 3. above only, default values for bands of
values that are adjusted according to the level walking values
being set for activities associated with tests which have not been
carried out, e.g. owing to a lack of facilities.
[0102] The calibration may be performed by a prosthetist feeding
settings to the prosthesis using the user interface 120 (FIG. 2).
As an alternative, or in addition, depending on the mode of
activity in question, a self-adjustment, self-programming or
automatic calibration phase may be included whereby the control
system provides a series of trial settings for particular activity
modes.
[0103] A particular technique used in the calibration program mode
of the preferred embodiment makes use of the variation of the shin
section bending moment, as sensed by the strain gauges 52, 53 (FIG.
1B) to set plantar-flexion resistance and dorsi-flexion resistance
of the ankle flexion control device. In particular, one or both
flexion control settings of the ankle joint are modified to achieve
a predetermined shin bending moment profile, i.e. the variation of
the sensed shin bending moment with time during individual stance
phases of the walking gait cycles. Similarly, the ankle joint
plantar-flexion resistance and/or dorsi-flexion resistance may be
changed in response to the sensed foot angle, as sensed by the
angle sensor 87A, 87B (FIG. 1C) at the ankle joint to achieve a
predetermined foot angle profile, i.e. variation of foot angle
during the stance phase of the walking gait cycle. In some
circumstances, the sensed knee angle and foot acceleration may also
be used.
[0104] FIGS. 5A to 5D indicate typical profiles for the knee angle,
the foot angle, the shin section bending moment, and the global
foot acceleration during the gait cycle. The horizontal axis in
each graph is time within a gait cycle nominated to the value 1, so
that the profile begins with heel contact, progresses through the
stance phase to push off (at about 0.6), then continues through the
swing phase, and returns to heel contact at 1. Each graph has four
plots relating to different combinations of plantar-flexion (PF)
and dorsi-flexion (DF) resistance settings, as indicated, a higher
number designation for the plots representing higher flexion
resistance and a lower number representing a lower respective
flexion resistance. The applicants have found that the higher the
setting for plantar-flexion resistance, the sharper and more peaked
is the foot angle profile (see FIG. 5C). In addition, with high
plantar-flexion resistance, the area below the foot angle profile
plot is smaller. With higher dorsi-flexion resistance, the area
below the foot angle curve becomes rounder and larger. Also, the
ratio of plantar-flexion resistance to dorsi-flexion resistance
affects the symmetry of the curve and its integral beneath it from
a normal value up to the peak, and back to the normal value again.
The applicants have found that the combinations of plantar-flexion
and dorsi-flexion resistance settings which are preferred, in terms
of amputee comfort and effort, were PF6 DF6 and PF8 DF4 which, as
can be seen from FIG. 5B, produce lower ankle dorsi-flexion
amplitude profiles, both in terms of peak dorsi-flexion and the
area under the respective part of the angle profile in the stance
phase.
[0105] The electronic control system, described above with
reference to FIG. 2, makes use of the sensed foot angle profile by
measuring both peak foot angle and the dorsi-flexion integral in a
process similar to that described above with reference to FIG. 3B
to achieve the preferred foot angle profile by adjusting the ankle
joint control device flexion resistances. Accordingly, if the peak
dorsi-flexion of the ankle joint during the stance phase exceeds a
predetermined threshold value, or the area (corresponding to the
integral) under the dorsi-flexion curve with respect to time during
the stance phase exceeds a predetermined area threshold, the
plantar-flexion resistance of the ankle flexion control device is
increased and the stance phase dorsi-flexion resistance is
decreased. Similarly, if these peak and area values are too low,
the plantar-flexion and dorsi-flexion resistances are driven in the
opposite respective directions.
[0106] In the present embodiment, integrals of the foot angle curve
(i.e. dorsi-flexion angle of the ankle) are computed as follows:
[0107] A first integral, Integral 1, from a first foot angle value
up to the peak [0108] A second integral, Integral 2, from the peak
down to the crossing of the first foot angle value line again
[0109] The ratios of Integral 1 to Integral 2 and the sum of the
two integrals obtained for different plantar-flexion and
dorsi-flexion resistances are typically as shown in Table 1
TABLE-US-00001 [0109] TABLE 1 Integral 1/Integral 2 Integral 1 +
Integral 2 "PF 3 DF8" 0.71 56.49 "PF 2 DF 2" 0.83 47.9 "PF 6 DF 6"
0.94 44.85 "PF 8 DF 8".sup.1 1.09 40.58 "PF 8 DF 4" 1.2 34.19
[0110] The ankle joint control device resistances are driven to
achieve a ratio of Integral 1 to Integral 2 of around 1 when both
settings are in an equal range, i.e. bigger than 1 if the
plantar-flexion resistance is greater than the dorsi-flexion
resistance and smaller than 1 if the dorsi-flexion resistance is
greater than the plantar-flexion resistance. The sum of both
integrals is larger the larger is the sum of the dorsi-flexion
resistance and the smaller is the plantar-flexion resistance. When
both plantar-flexion and dorsi-flexion resistance are approximately
equal, the lower the settings the larger is the sum.
[0111] Accordingly, the system also uses the ratio of different
areas beneath the foot angle profile, respectively when the
dorsi-flexion angle is increasing and when it is decreasing, as an
input variable for setting the dorsi-flexion and plantar-flexion
resistances.
[0112] With regard to the shin bending moment profile shown in FIG.
5B, this is significantly affected by the plantar-flexion and
dorsi-flexion resistance settings at the ankle joint. With
moderately low plantar-flexion resistance and high dorsi-flexion
resistance (PF3 DF8), the moment increases rapidly during the early
part of the stance phase and then, towards mid-stance, the gradient
is relatively small so that the peak moment is relatively late in
the stance phase. In contrast, with relatively high plantar-flexion
resistance and somewhat lower dorsi-flexion resistance (PF6 DF6),
for example, the gradient in the early stance phase is less steep
and there is a step in the region towards mid-stance followed by
another period of rapidly increasing moment to the bending moment
peak. The area under the bending moment curve during the stance
phase is affected by these different profiles, as indicated in
Table 2 below, which tabulates the ratio of the curve area for the
first, second and third resistance combinations shown in FIG. 5B
relative to that for the fourth combination, PF6 DF6. (For
completeness, similar ratios are tabulated in Table 2 for the foot
angle and the ratio between the foot angle and shin bending
moment.)
TABLE-US-00002 TABLE 2 Foot angle ratio in Bending moment ratio
Ratio between relation to in relation to foot angle and "PF 6 DF 6"
"PF 6 DF 6" bending moment "PF 3 DF 8" 1.34 1.08 0.78 "PF 2 DF 2"
1.15 1.02 0.71 "PF 8 DF 4" 0.83 0.93 0.56
[0113] The electronic control system of FIG. 2 computes the shin
bending moment area using signals from the strain gauges 52, 53
(FIG. 1B) to provide an input for setting plantar-flexion and
dorsi-flexion resistances.
[0114] An option in the preferred electronic control system is to
divide the sensed shin section bending moment profile before the
peak into three periods. Thus, the preferred profile has a first
period in which the moment increases with a first gradient,
followed by a second period in which the moment increases with a
second gradient which is significantly less than the first
gradient, followed by a third period in which the gradient reverts
to a level similar to that of the first period. This is the profile
which the applicants have found is most comfortable for the typical
amputee. Iterative adjustments of the stance phase plantar-flexion
resistance and dorsi-flexion resistance are made to achieve the
preferred profile. The preferred profile is also characterised by
the third period being at least 80 percent of the second period, in
terms of duration.
[0115] In the present embodiment, where the settings indicated by
the sensed foot angle are different from those indicated by the
sensed bending moment, it is the settings indicated by the bending
moment which are given precedence. It is possible, in variants of
the invention, to dispense with the sensed foot angle as a control
input.
[0116] The adjustments in control device settings described above
are performed during the calibration program mode so that
subsequently, during locomotion, the plantar-flexion and
dorsi-flexion resistances are automatically and dynamically set
according to activity mode.
[0117] The control functions described above with reference to
FIGS. 5A to 5D are ones performed during level walking. These
functions are performed in the same way when walking up slopes and
walking down slopes although, under those conditions, values of the
parameters illustrated in FIGS. 5A to 5D are different.
[0118] Described above is the stepwise reduction of the knee
flexion damping resistance in the Ramp Down mode. Referring to FIG.
6, the variation in the damping resistance at the knee in the Ramp
Down mode is illustrated in conjunction with knee angle, shin
bending moment, foot angle, and foot acceleration curves. As shown,
the flexion resistance 200 is high during the major part of the
stance phase. At or immediately after the maximum of the shin
bending moment, indicated by the arrow M, the knee flexion
resistance is reduced to the intermediate level or an interval
which ends at or very shortly after the end of the stance phase
indicated by the arrow N, whereupon a further reduction in knee
flexion resistance is effected to reduce the resistance level to
the low (L) level indicated in FIG. 4C. The flexion resistance
reverts to the high level in late swing, to prepare for
commencement of the stance phase at heel strike, indicated by the
arrow. Actuation of the first step wise reduction in resistance is
performed in response to detection of a negative-gradient bending
moment, derived from strain gauges mounted on the shin section. The
second step wise reduction in flexion resistance is actuated in
response to the knee angle reaching a predetermined knee angle
threshold in the early part of the swing phase, as sensed, for
instance by a piston/senor. Typically, the threshold at which the
second step wise reduction in knee flexion resistance is a knee
angle of 50 percent of the maximum knee angle achieved during the
swing phase. This programmed step wise reduction in knee flexion
resistance is not performed in the level velocity or Ramp Up modes.
In those modes switching occurs instantaneously between high and
low resistance settings towards the end of the stance phase. The
duration of the interval during which the flexion resistance is at
the intermediate level in the ramp down mode is typically 25
percent of the stance phase duration.
[0119] As shown in FIG. 6, and described above with respect to the
stepwise changes in resistance, in some embodiments, the damping
resistance of the knee flexion control device may be configured to
remain at a single, constant resistance level corresponding to the
second, intermediate resistance level (M) for a second period of
time.
[0120] In the preferred embodiment described above, the electronic
control system has a master microprocessor controller and two slave
microprocessor controllers, one for the knee joint and one for the
ankle joint. Alternative arrangements are possible. Indeed, all
control functions may be performed by a single microprocessor
controller, preferably mounted at the knee level, the single
controller collecting data from sensors associated with both
joints, as in the preferred embodiment, i.e. from different areas
of the prosthesis. The single controller would perform advanced
analysis of gait and circumstances (i.e. environment, including
ground inclination) based on sensor signals from two or more areas
of the prosthesis. Additionally, a single controller would monitor
the feedback signals from the knee and ankle adjustment motors
rather than having such functions performed by slave
controllers.
[0121] In a variant of the above-described prosthesis, the
electronic control system has a bi-lateral mode to allow
intercommunication of two limb prostheses for bilateral amputees.
In this case, the user interface 120 (FIG. 2) incorporates a
hard-wired interconnection incorporating a UART port for
communication with the second prosthesis. A wireless communication
port may be used instead. The matrices of FIGS. 4A to 4D are
expanded for the bi-lateral mode so that both prostheses are
synchronised to provide correct damping levels at the knee and the
ankle in each case. The high-yield resistance setting for stance
control release is timed to be in phase with the initiation of
high-yield resistance in the other prosthesis. Similarly, pneumatic
swing controls are also adjusted for different speeds for right and
left limbs. Plantar-flexion damping of the ankle is synchronised
with dorsi-flexion damping of the other limb to provide natural
progression and optimum function.
* * * * *