U.S. patent application number 11/495140 was filed with the patent office on 2007-02-22 for artificial ankle-foot system with spring, variable-damping, and series-elastic actuator components.
This patent application is currently assigned to Massachusetts Institute of Technology. Invention is credited to Samuel K. Au, Peter Dilworth, Hugh M. Herr, Daniel Joseph Paluska.
Application Number | 20070043449 11/495140 |
Document ID | / |
Family ID | 46325804 |
Filed Date | 2007-02-22 |
United States Patent
Application |
20070043449 |
Kind Code |
A1 |
Herr; Hugh M. ; et
al. |
February 22, 2007 |
Artificial ankle-foot system with spring, variable-damping, and
series-elastic actuator components
Abstract
An artificial foot and ankle joint consisting of a curved leaf
spring foot member that defines a heel extremity and a toe
extremity, and a flexible elastic ankle member that connects said
foot member for rotation at the ankle joint. An actuator motor
applies torque to the ankle joint to orient the foot when it is not
in contact with the support surface and to store energy in a
catapult spring that is released along with the energy stored in
the leaf spring to propel the wearer forward. A ribbon clutch
prevents the foot member from rotating in one direction beyond a
predetermined limit position, and a controllable damper is employed
to lock the ankle joint or to absorb mechanical energy as needed.
The controller and a sensing mechanisms control both the actuator
motor and the controllable damper at different times during the
walking cycle for level walking, stair ascent and stair
descent.
Inventors: |
Herr; Hugh M.; (Somerville,
MA) ; Au; Samuel K.; (Cambridge, MA) ;
Dilworth; Peter; (Brighton, MA) ; Paluska; Daniel
Joseph; (Somerville, MA) |
Correspondence
Address: |
CHARLES G. CALL
68 HORSE POND ROAD
WEST YARMOUTH
MA
02673-2516
US
|
Assignee: |
Massachusetts Institute of
Technology
Cambridge
MA
|
Family ID: |
46325804 |
Appl. No.: |
11/495140 |
Filed: |
July 29, 2006 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11395448 |
Mar 31, 2006 |
|
|
|
11495140 |
Jul 29, 2006 |
|
|
|
60704517 |
Aug 1, 2005 |
|
|
|
60666876 |
Mar 31, 2005 |
|
|
|
60704517 |
Aug 1, 2005 |
|
|
|
Current U.S.
Class: |
623/24 ;
623/52 |
Current CPC
Class: |
A61F 2002/509 20130101;
A61F 2/605 20130101; B25J 19/0008 20130101; A61F 2002/5004
20130101; A61F 2002/5006 20130101; A61F 2002/5079 20130101; A61F
2/6607 20130101; A61F 2/70 20130101; A61F 2002/6657 20130101; A61F
2002/704 20130101; A61F 2/60 20130101; A61F 2002/7625 20130101;
A61F 2002/7645 20130101; A61F 2002/503 20130101; A61F 2002/7635
20130101; A61F 2002/6678 20130101; A61F 2002/5073 20130101; A61F
2002/6818 20130101; B62D 57/032 20130101; A61F 2002/5075 20130101;
A61F 2/64 20130101; A61F 2002/5033 20130101; A61F 2002/763
20130101; A61F 2002/764 20130101; A61F 2002/701 20130101 |
Class at
Publication: |
623/024 ;
623/052 |
International
Class: |
A61F 2/48 20060101
A61F002/48 |
Claims
1. An artificial ankle comprising, in combination, a shin member, a
foot and ankle structure coupled for rotation with respect to said
shin member at an ankle joint, said foot and ankle structure
comprising: a curved flexible elastic foot member that defines a
heel extremity and a toe extremity, and a flexible elastic ankle
member that connects said foot member to said ankle joint, and a
variable damper element for arresting the motion of said foot and
ankle structure with respect to said shin member under
predetermined conditions.
2. An artificial ankle as set forth in claim 1 further comprising a
motor for applying torque to said ankle joint to rotate said foot
and ankle structure with respect to said shin member.
3. An artificial ankle as set forth in claim 2 further including an
elastic member operatively connected in series with said motor
between said shin member and said foot and ankle structure to store
energy when the relative motion of said foot and ankle structure
and said shin member is being arrested by said variable damper and
to thereafter apply an additional torque to said ankle joint when
the relative motion of said foot and ankle structure with respect
to said shin member is no longer arrested by said controllable
variable damping element.
4. An artificial ankle as set forth in claim 3 further including a
controller for operating said motor to store energy in said elastic
member when the relative motion of said foot and ankle structure
and said shin member is being arrested by said variable damper.
5. An artificial ankle as set forth in claim 2 wherein said
variable damper includes a stop mechanism for preventing said ankle
and foot structure from rotating beyond a maximum limiting
rotational position.
6. An artificial ankle as set forth in claim 2 wherein said motor
adjusts the position of said foot and ankle structure relative to
said shin member when said foot and ankle member is not in contact
with a support surface.
7. An artificial ankle as set forth in claim 6 further comprising a
inertial sensing means for determining the relative elevation of
said foot and angle structure and for actuating said motor in
response to changes in said relative elevation.
8. An artificial ankle as set forth in claim 1 further including an
elastic member operatively connected in series with said motor
between said shin member and said foot and ankle structure to store
energy when the relative motion of said foot and ankle structure
and said shin member is being arrested by said controllable
variable damping element and to thereafter apply an additional
torque to said ankle joint when the relative motion of said foot
and ankle structure with respect to said shin member is no longer
arrested by said controllable variable damping element.
9. An artificial ankle as set forth in claim 8 wherein said
variable damper includes a stop mechanism for preventing said ankle
and foot structure from rotating beyond a maximum limiting
rotational position.
10. An artificial ankle as set forth in claim 1, wherein said
variable damper includes a stop mechanism for preventing said ankle
and foot structure from rotating beyond a maximum limiting
rotational position.
11. An artificial ankle as set forth in claim 10 wherein said
variable damper further includes a controllable damping element for
arresting the motion of said foot and ankle structure with respect
to said shin member when said foot and ankle structure is storing
and releasing energy.
12. An artificial ankle as set forth in claim 1 wherein said
variable damper element includes a controllable variable damper and
a controller for actuating said controllable variable damper to
arrest the motion of said foot and ankle structure with respect to
said shin member under predetermined conditions.
13. An artificial ankle as set forth in claim 12 wherein said
controller actuates said controllable variable damper to arrest the
motion of said foot and ankle structure when said foot and ankle
structure is storing and releasing energy.
14. An artificial ankle as set forth in claim 13 further comprising
a motor for applying torque to said ankle joint to rotate said foot
and ankle structure with respect to said shin and wherein said
motor adjusts the position of said foot and ankle structure
relative to said shin member when said foot and ankle member is not
in contact with a support surface.
15. An artificial ankle comprising, in combination, a shin member,
a foot and ankle structure coupled for rotation with respect to
said shin member at an ankle joint, said foot and ankle structure
comprising: a curved flexible elastic foot member that defines a
heel extremity and a toe extremity, and a flexible elastic ankle
member that connects said foot member to said ankle joint, and a
motor connected for applying torque to said ankle joint to rotate
said foot and ankle structure with respect to said shin member at
controllable times.
16. An artificial ankle as set forth in claim 15 further including
an elastic member operatively connected in series with said motor
between said shin member and said foot and ankle structure to store
energy when the relative motion of said foot and ankle structure
and said shin member is being arrested by said controllable
variable damping element and to thereafter apply an additional
torque to said ankle joint when the relative motion of said foot
and ankle structure with respect to said shin member is no longer
arrested by said controllable variable damping element.
17. An artificial ankle as set forth in claim 16 further including
a stop mechanism for preventing said ankle and foot structure from
rotating beyond a maximum limiting rotational position.
18. An artificial ankle as set forth in claim 16 further including
a controller for operating said motor to store energy in said
elastic member when the relative motion of said foot and ankle
structure and said shin member is being arrested by said variable
damper.
19. An artificial ankle and foot system for supporting a human
wearer as said wearer walks on a support surface comprising, in
combination, an elastic ankle and foot structure for storing energy
during a dorsiflexion period as the weight of said wearer displaces
said elastic ankle and foot structure and for releasing energy
during a powered plantarflexion period as said elastic foot and
ankle structure urges said wearer in a forward direction with
respect to said support surface, a shin member, an ankle joint for
connecting said ankle and shin structure for rotational motion with
respect to said shin member, a motor for applying a torque to said
ankle joint tending to move said ankle and foot structure with
respect to said shin member, a stop mechanism coupled between said
ankle and foot structure and said shin member for preventing the
rotation of said ankle and foot structure with respect to said shin
member beyond a limiting position, a controllable variable damper
coupled to said ankle joint for arresting the motion of said ankle
and foot structure with respect to said shin member under
predetermined conditions, and a controller connected to operate
said motor and said controllable variable damper at predetermined
times relative to said dorsiflexion period and said plantarflexion
period.
20. An artificial ankle and foot system as set forth in claim 19
wherein said controller operates said controllable variable damper
to arrest the motion of said ankle and foot structure with respect
to said shin member during said powered plantarflexion period.
21. An artificial ankle and foot system as set forth in claim 20
wherein said controller operates said motor to reorient said foot
and ankle structure with respect to said shin member when said
ankle and foot structure is not in contact with said support
surface.
22. An artificial ankle and foot system as set forth in claim 21
further including an additional elastic member for storing energy
from said electric motor prior to each,powered plantarflexion
period and for releasing energy during said powered plantarflexion
period.
23. An artificial ankle and foot system as set forth in claim 19
wherein said controller operates said motor to reorient said foot
and ankle structure with respect to said shin member when said
ankle and foot structure is not in contact with said support
surface.
24. An artificial ankle and foot system as set forth in claim 23
further including an additional elastic member for storing energy
from said electric motor prior to each powered plantarflexion
period and for releasing energy during said powered plantarflexion
period.
25. An artificial ankle and foot system as set forth in claim 19
further including an additional elastic member for storing energy
from said electric motor prior to each powered plantarflexion
period and for releasing energy during said powered plantarflexion
period.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation in part of, and claims
the benefit of the filing date of, U.S. patent application Ser. No.
11/395,448 filed on Mar. 31, 2006. application Ser. No. 11/395,448
was a non-provisional of, and claimed the benefit of the filing
date of, U.S. Provisional Patent Application Ser. No. 60/666,876
filed on Mar. 3, 2005 and U.S. Provisional Patent Application Ser.
No. 60/704,517 filed on Aug. 1. 2005.
[0002] This application is a non-provisional of, and also claims
the benefit of the filing date of U.S. Provisional Patent
Application Ser. No. 60/704,517 filed on Aug. 1, 2005.
[0003] This application incorporates the disclosures of each of the
foregoing application herein by reference.
FIELD OF THE INVENTION
[0004] This invention relates generally to prosthetic devices and
artificial limb and joint systems, including robotic, orthotic,
exoskeletal limbs, and more particularly, although in its broader
aspects not exclusively, to artificial feet and ankle joints.
BACKGROUND OF THE INVENTION
[0005] In the course of the following description, reference will
be made to the papers, patents and publications presented in a list
of references at the conclusion of this specification. When cited,
each listed reference will be identified by a numeral within
curly-braces indicating its position within this list.
[0006] As noted in {1} {2} {3}, an artificial ankle-foot system
ideally needs to fulfill a diverse set of requirements. The
artificial system must be a reasonable weight and have a natural
morphological shape, but still have an operational time between
refueling or battery recharges of at least one full day. The system
must also be capable of varying its position, impedance, and motive
power in a comparable manner to that of a normal, healthy
biological limb. Still further, the system must be adaptive,
changing its characteristics given such environmental disturbances
as walking speed and terrain variation. The embodiments of the
invention which are described in this specification employ novel
architectures capable of achieving these many requirements.
[0007] From recent biomechanical studies {1} {2} {3}, researchers
have determined researchers have determined that early stance
period ankle stiffness varies from step-to-step in wag.
Furthermore, researchers have discovered that the human ankle
performs more positive mechanical work than negative work,
especially at moderate to fast wag speeds {1} {2}{3}. The added
ankle power is important for providing adequate forward progression
of the body at the end of each stance period. In distinction, for
stair descent, the ankle behaves as a variable damper during the
first half of stance, absorbing impact energies {2}. These
biomechanical findings suggest that in order to mimic the actual
behavior of the human ankle, joint stiffness, motive power, and
damping must be actively controlled in the context of an efficient,
high cycle-life, quiet and cosmetic ankle-foot artificial
joint.
[0008] For level ground ambulation, the ankle behaves as a variable
stiffness device during the early to midstance period, storing and
releasing impact energies. Throughout terminal stance, the ankle
acts as a torque source to power the body forward. In distinction,
the ankle varies damping rather than stiffness during the early
stance period of stair descent. These biomechanical findings
suggest that in order to mimic the actual behavior of a human joint
or joints, stiffness, damping, and nonconservative, motive power
must be actively controlled in the context of an efficient, high
cycle-life, quiet and cosmetic biomimetic limb system, be it for a
prosthetic or orthotic device. This is also the case for a
biomimetic robotic limb since it will need to satisfy the same
mechanical and physical laws as its biological counterpart, and
will benefit from the same techniques for power and weight
savings.
[0009] In the discussion immediately below, the biomechanical
properties of the ankle will be described in some detail to explain
the insights that have guided the design and development of the
specific embodiments of the invention and to define selected terms
that will be used in this specification.
[0010] Joint Biomechanics: The Human Ankle
[0011] Understanding normal walking biomechanics provides the basis
for the design and development of the artificial ankle joint and
ankle-foot structures that embody the invention. Specifically, the
function of human ankle under sagittal plane rotation is described
below for different locomotor conditions including level-ground
walking and stair/slope ascent and descent. From these
biomechanical descriptions, the justifications for key mechanical
components and configurations of the artificial ankle structures
and functions embodying the invention may be better understood.
[0012] Level-Ground Walking
[0013] A level-ground walking gait cycle is typically defined as
beginning with the heel strike of one foot and ending at the next
heel strike of the same foot {8}. The main subdivisions of the gait
cycle are the stance phase (about 60% of the cycle) and the
subsequent swing phase (about 40% of the cycle) as shown in FIG. 1.
The swing phase represents the portion of the gait cycle when the
foot is off the ground. The stance phase begins at heel-strike when
the heel touches the floor and ends at toe-off when the same foot
rises from the ground surface. Additionally, we can further divide
the stance phase into three sub-phases: Controlled Plantar flexion
(CP), Controlled Dorsiflexion (CD), and Powered Plantar flexion
(PP).
[0014] Each phase and the corresponding ankle functions which occur
when walking on level ground are illustrated in FIG. 1. The
subdivisions of the stance phase of walking, in order from first to
last, are: the Controlled Plantar flexion (CP) phase, the
Controlled Dorsiflexion (CD) phase, and the Powered Plantar flexion
(PP) phase.
[0015] CP begins at heel-strike illustrated at 103 and ends at
foot-flat at 105. Simply speaking, CP describes the process by
which the heel and forefoot initially make contact with the ground.
In {1, 12}, researchers showed that CP ankle joint behavior was
consistent with a linear spring response where joint torque is
proportional to joint position. The spring behavior is, however,
variable; joint stiffness is continuously modulated by the body
from step to step.
[0016] After the CP period, the CD phase continues until the ankle
reaches a state of maximum dorsiflexion and begins powered
plantarflexion PP as illustrated at 107. Ankle torque versus
position during the CD period can often be described as a nonlinear
spring where stiffness increases with increasing ankle position.
The main function of the ankle during CD is to store the elastic
energy necessary to propel the body upwards and forwards during the
PP phase {9} {3}.
[0017] The PP phase begins after CD and ends at the instant of
toe-off illustrated at 109. During PP, the ankle can be modeled as
a catapult in series or in parallel with the CD spring or springs.
Here the catapult component includes a motor that does work on a
series spring during the latter half of the CD phase and/or during
the first half of the PP phase. The catapult energy is then
released along with the spring energy stored during the CD phase to
achieve the high plantar flexion power during late stance. This
catapult behavior is necessary because the work generated during PP
is more than the negative work absorbed during the CP and CD phases
for moderate to fast walking speeds {1} {2} {3} {9}.
[0018] During he swing phase, the final 40% of the gait cycle,
which extends from toe-off at 109 until the next heel strike at
113, the foot is lifted off the ground.
[0019] Stair Ascent and Descent
[0020] Because the kinematic and kinetic patterns at the ankle
during stair ascent/descent are significantly different from that
of level-ground walking {2}, a separate description of the
ankle-foot biomechanics is presented in FIGS. 2 and 3.
[0021] FIG. 2 shows the human ankle biomechanics during stair
ascent. The first phase of stair ascent is called Controlled
Dorsiflexion 1 (CD 1), which begins with foot strike in a
dorsiflexed position seen at 201 and continues to dorsiflex until
the heel contacts the step surface at 203. In this phase, the ankle
can be modeled as a linear spring.
[0022] The second phase is Powered Plantar flexion 1 (PP 1), which
begins at the instant of foot flat (when the ankle reaches its
maximum dorsiflexion at 203) and ends when dorsiflexion begins once
again at 205. The human ankle behaves as a torque actuator to
provide extra energy to support the body weight.
[0023] The third phase is Controlled Dorsiflexion 2 (CD 2), in
which the ankle dorsiflexes until heel-off at 207. For the CD 2
phase, the ankle can be modeled as a linear spring.
[0024] The fourth and final phase is Powered Plantar flexion 2 (PP
2) which begins at heel-off 207 and continues as the foot pushes
off the step, acting as a torque actuator in parallel with the CD 2
spring to propel the body upwards and forwards, and ends when the
toe leaves the surface at 209 to being the swing phase that ends at
213.
[0025] FIG. 3 shows the human ankle-foot biomechanics for stair
descent. The stance phase of stair descent is divided into three
sub-phases: Controlled Dorsiflexion 1 (CD1), Controlled
Dorsiflexion 2 (CD2), and Powered Plantar flexion (PP).
[0026] CD1 begins at foot strike illustrated at 303 and ends at
foot-flat 305. In this phase, the human ankle can be modeled as a
variable damper. In CD2, the ankle continues to dorsiflex forward
until it reaches a maximum dorsiflexion posture seen at 307. Here
the ankle acts as a linear spring, storing energy throughout CD2.
During PP, which begins at 307, the ankle plantar flexes until the
foot lifts from the step at 309. In this final PP phase, the ankle
releases stored CD2 energy, propelling the body upwards and
forwards. After toe-off at 309, the foot is positioned controlled
through the swing phase until the next foot strike at 313.
[0027] For stair ascent depicted in FIG. 2, the human ankle-foot
can be effectively modeled using a combination of an actuator and a
variable stiffness mechanism. However, for stair descent, depicted
in FIG. 3, a variable damper needs also to be included for modeling
the ankle-foot complex; the power absorbed by the human ankle is
much greater during stair descent than the power released by 2.3 to
11.2 J/kg {2}. Hence, it is reasonable to model the ankle as a
combination of a variable-damper and spring for stair descent
{2}.
SUMMARY OF THE INVENTION
[0028] The preferred embodiments of the present invention take the
form of an artificial ankle system capable of providing
biologically-realistic dynamic behaviors. The key mechanical
components of these embodiments, and their general functions, may
be summarized as follows: [0029] 1. One or more passive springs--to
store and release elastic energy for propulsion; [0030] 2. One or
more series-elastic actuators (muscle-tendon)--to control the
position of the ankle, provide additional elastic energy storage
for propulsion, and to control joint stiffness; and [0031] 3. One
or more variable dampers--to absorb mechanical energy during stair
and slope descent.
[0032] The above-identified U.S. patent application Ser. No.
11/395,448 filed on Mar. 31, 2006 describes related artificial
limbs and joints that employ passive and series-elastic elements
and variable-damping elements, and in addition employ active motor
elements in arrangements called "Biomimetic Hybrid Actuators"
forming biologically-inspired musculoskeletal architectures. The
electric motor used in the hybrid actuators supply positive energy
to and store negative energy from one or more joints which connect
skeletal members, as well as elastic elements such as springs, and
controllable variable damper components, for passively storing and
releasing energy and providing adaptive impedance to accommodate
level ground walking as well as movement on stairs and surfaces
having different slopes.
[0033] As described in application Ser. No. 11/395,448, an
artificial ankle may employ an elastic member operatively connected
in series with the motor between the shin member and the foot
member to store energy when the relative motion of the foot and
shin members is being arrested by a controllable variable damping
element and to thereafter apply an additional torque to the ankle
joint when the variable damping element no longer arrests the
relative motion of the two members.
[0034] As further described in application Ser. No. 11/395,448, An
artificial ankle may include an elastic member operatively
connected in series with the motor between the shin and foot
members to store energy when the foot member is moved toward the
shin member and to release energy and apply an additional torque to
the ankle joint that assists the motor to move the foot member away
from the shin member. A controllable damping member may be employed
to arrest the motion of the motor to control the amount of energy
absorbed by the motor when the foot member is moved toward the shin
member.
[0035] The Flex-Foot, made by Ossur of Reykjavik, Iceland, is a
passive carbon-fiber energy storage device that replicates the
ankle joint for amputees. The Flex-Foot is described in U.S. Pat.
No. 6,071,313 issued to Van L. Phillips entitled "Split foot
prosthesis" and in Phillips' earlier U.S. Pat. Nos. 5,776,205,
5,514,185 and No. 5,181,933, the disclosures of which are
incorporated herein by reference. The Flex-foot is a foot
prosthesis for supporting an amputee relative to a support surface
and consists of a leaf spring having multiple flexing portions
configured to flex substantially independently of one another
substantially completely along their length. The Flex-Foot has an
equilibrium position of 90 degrees and a single nominal stiffness
value. In the embodiments described below, a hybrid actuator
mechanism of the kind described in the above-noted application Ser.
No. 11/395,448 is used to augment a flexing foot member such as the
Flex-Foot by allowing the equilibrium position to be set to an
arbitrary angle by a motor and locking, or arresting the relative
movement of, the foot member with respect to the shin member using
a clutch or variable damper. Furthermore, the embodiment of the
invention to be described can also change the stiffness and damping
of the prosthesis dynamically.
[0036] Preferred embodiments of the present invention take the form
of an artificial ankle and foot system in which a foot and ankle
structure is mounted for rotation with respect to a shin member at
an ankle joint. The foot and ankle structure preferably comprises a
curved flexible elastic foot member that defines an arch between a
heel extremity and a toe extremity, and a flexible elastic ankle
member that connects said foot member for rotation at the ankle
joint. A variable damper is employed to arresting the motion of
said foot and ankle structure with respect to said shin member
under predetermined conditions, and preferably includes a stop
mechanism that prevents the foot and ankle structure from rotating
with respect to the shin member beyond a predetermined limit
position. The variable damper may further include a controllable
damper, such as a magnetorheological (MR) brake, which arrests the
rotation of the ankle joint by controllable amount at controlled
times during the walking cycle. Preferred embodiments of the ankle
and foot system further include an actuator motor for applying
torque to the ankle joint to rotate said foot and ankle structure
with respect to said shin member.
[0037] In addition, embodiments of the invention may include a
catapult mechanism comprising a series elastic member operatively
connected in series with the motor between the shin member and the
foot and ankle structure. The series elastic member stores energy
from the motor during a first portion of each walking cycle and
then releases the stored energy to help propel the user forward
over the walking surface at a later time in each walking cycle. The
preferred embodiments of the invention may employ a controller for
operating both the motor and the controllable damper such that the
motor stores energy in the series elastic member as the shin member
is being arrested by the controllable damper.
[0038] The actuator motor which applies torque to the ankle joint
may be employed to adjust the position of the foot and ankle
structure relative to the shin member when the foot and ankle
member is not in contact with a support surface. Inertial sensing
means are preferably employed to determine the relative elevation
of the foot and angle structure and to actuate the motor in
response to changes in the relative elevation, thereby
automatically positioning the foot member for toe first engagement
if the wearer is descending stairs.
[0039] These and other features and advantages of the present
invention will be better understood by considering the following
detailed description of two illustrative embodiments of the
invention. In course of this description, frequent reference will
be made to the attached drawings which are briefly described
below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] FIG. 1 illustrates the different phases of a walking cycle
experienced by a human ankle and foot during level ground
walking;
[0041] FIG. 2 depicts the phases of a walking cycle experienced by
a human ankle and foot when ascending stairs;
[0042] FIG. 3 depicts the phases of a walking cycle experienced by
a human ankle and foot during stair descent;
[0043] FIG. 4 shows the mechanical design of an anterior view of
embodiment 1;
[0044] FIG. 5 shows a posterior view of embodiment 1;
[0045] FIG. 6 shows a side elevational view of embodiment 1;
[0046] FIG. 7 is a schematic depiction of embodiment 1;
[0047] FIG. 8 depicts a lumped parameter model of embodiment 1;
[0048] FIGS. 9-12 show the control sequence for embodiment 1 during
ground level walking;
[0049] FIGS. 13-15 show the control sequence for embodiment 1
during stair ascent;
[0050] FIGS. 16-19 show the control sequence for embodiment 1
during stair descent;
[0051] FIG. 20 shows the mechanical design of an anterior view of
embodiment 2;
[0052] FIG. 21 shows a posterior view of embodiment 2;
[0053] FIG. 22 shows a side elevational view of embodiment 2;
[0054] FIG. 23 is a schematic depiction of embodiment 2;
[0055] FIG. 24 depicts a lumped parameter model of embodiment
2;
[0056] FIGS. 25-28 show the control sequence for embodiment 1
during ground level walking;
[0057] FIG. 29 is a schematic block diagram of a sensing and
control mechanism used to control the operation of the motors and
dampers in ankle foot systems embodying the invention.
DETAILED DESCRIPTION
[0058] Two embodiments of an ankle-foot system contemplated by the
present invention are described in detail below. The first
embodiment (Embodiment 1) provides for elastic energy storage,
variable-damping and a variable-orientation foot control. In
addition to these capabilities, the second embodiment to be
described includes a motor in series with a spring for providing
joint spring stiffness control during the CP and CD phases, and a
motive torque control during the PP phase of the walking cycle as
described above.
Embodiment 1
[0059] Mechanical Components
[0060] The mechanical design of embodiment 1 is seen in FIGS. 4-6
and the corresponding schematic and lumped parameter model of
embodiment 1 are shown in FIGS. 7 and 8, respectively. As seen in
the side elevation view of FIG. 6, there are four main mechanical
elements in this embodiment: an elastic leaf spring structure 601,
a dorsiflexion clutch (Ribbon Stop) seen at 603, a variable damper
(MR brake) seen at 605, and an actuator system comprising a small
motor seen at 607. As seen in the schematic of FIG. 7, these four
main mechanical elements are shown as an elastic leaf spring
structure 701, a dorsiflexion clutch (Ribbon Stop) 703, a variable
damper 705, and a motor actuator system 707.
[0061] The elastic leaf spring seen at 601 and 701 can be made from
a lightweight, efficient spring material such as carbon composite,
fiberglass or a material of similar properties. As seen in FIG. 6,
and as described in Phillips' U.S. Pat. No. 6,071,313 issued on
Jun. 6, 2000, the elastic leaf spring structure includes a heel,
portion seen at 609 and a toe portion seen at 660. A curved,
flexible ankle section 680 is attached at its upper end to a brake
mount member 690 which is mounts the flexible foot for rotation
about the axis of the ankle joint which, in FIG. 6, is located at
the center of the MR brake 605.
[0062] The variable-damper mechanism seen at 605 and 705 can be
implemented using magnetorheological (MR), electrorheological (ER),
dry magnetic particles, hydraulic, pneumatic, friction, or any
similar strategy to control joint damping. For embodiment 1, a MR
system is employed. Here MR fluid is used in the shear mode where a
set of rotary plates shear thin layers of MR fluid. When a magnetic
field is induced across the MR layers, iron particles suspended in
carrier fluid form chains, increasing the shear viscosity and joint
damping.
[0063] The ribbon stop seen at 603 and 703 prevents the ankle joint
from dorsiflexing beyond a certain maximum dorsiflexion limit,
ranging from 0 to 30 degrees depending on ankle performance
requirements. The ribbon stop is uni-directional, preventing
dorsiflexion but not impeding plantarflexion movements.
[0064] The actuator motor seen at 607 and 707 is a small, low-power
electromagnetic motor that provides foot orientation control. The
motor can exert a torque about the ankle joint (indicated at 711)
to re-position the foot (the elastic leaf spring 601, 701) relative
to the shank depicted at 713 when the foot is not in contact with
the ground. As seen in FIGS. 4-6, the shank frame for the
ankle-foot assembly attaches to a shin member (not shown) using a
standard pyramid mount seen at 613 which may be used to attach the
shank frame to the shin portion of an artificial limb or the
wearer's stump. As will be understood, both of the artificial foot
and ankle joint embodiments described in this specification may be
used in combination with artificial limb structures such as the
artificial knees and hips described in the above-noted U.S. patent
application Ser. No. 11/395,448.
[0065] Control System
[0066] For a better understanding of the control sequence of the
artificial ankle, a simplified 1D lumped parameter model of
embodiment 1 seen in FIG. 8 is used to explain the behavior of the
ankle-foot system under different walking conditions.
[0067] From FIG. 7, it may be noted that the bending angle of the
elastic leaf spring 701 is independent of the ankle angle of the
pin joint, therefore the lumped parameter model includes two
degrees of freedom: one for the displacement of the foot, X.sub.1,
and the other for the displacement of the shank X.sub.2 as shown in
FIG. 8. The leaf spring structure, seen at 601 in FIG. 6 and at 701
in FIG. 7, is modeled as a nonlinear spring shown at 801 in FIG. 8
with a stiffness that varies with X.sub.1, the foot bending angle
(displacement of the foot). The actuator motor seen at 807, the
variable-damper 805, and the ribbon stop seen at 803 act between
the mass of the shank at 820 and the mass of the foot at 830. The
loading force F.sub.load(t) due to body weight varies dynamically
during the stance phase of each gait cycle.
[0068] Level-Ground Walking
[0069] The control sequence of Embodiment 1 for level-ground
walking is depicted in FIGS. 9-12. During level-ground walking, the
variable-damper is set at a high damping level to essentially lock
the ankle joint during early to midstance, allowing the leaf spring
structure to store and release elastic energy. Once a critical
dorsiflexion angle is achieved (between 0 to 30 degrees), the
ribbon stop becomes taught during the remainder of the CD phase.
When the ribbon is engaged, the leaf spring and shank can be
treated as one single component because the ribbon behaves as a
clutch (FIG. 10). From heel strike to maximum dorisflexion, the
leaf spring structure stores elastic energy (Ax, 0, &.sub.2=0).
In PP, as the loading from the body weight decreases, the spring
structure releases its stored elastic energy, rotating in a plantar
flexion direction and propelling the body upwards and forwards
(FIG. 11). After toe-off, the actuator controls the equilibrium
position of the foot to achieve foot clearance during the swing
phase and to maintain a proper landing of the foot for the next
gait cycle (FIG. 12).
[0070] The state of each element of the ankle-foot system during
the four phases of a level ground walking cycle are listed
below:
[0071] Controlled Plantar Flexion (FIG. 9) [0072] 1. Actuator motor
is OFF [0073] 2. Ribbon clutch is OFF [0074] 3. Damper is ON [0075]
4. Leaf spring heel portion at 609 is being compressed
[0076] Controlled Dorsiflexion (FIG. 10) [0077] 1. Actuator motor
is OFF [0078] 2. Ribbon clutch is ON [0079] 3. Damper is OFF [0080]
4. Leaf spring toe section 660 is being compressed
[0081] Powered Plantar Flexion (FIG. 11) [0082] 1. Actuator motor
is OFF [0083] 2. Ribbon clutch is ON [0084] 3. Damper is OFF [0085]
4. Leaf spring ankle section 660 is releasing energy
[0086] Swing Phase (FIG. 12) [0087] 1. Actuator motor is ON
(changing foot orientation) [0088] 2. Ribbon clutch is OFF [0089]
3. Damper is OFF [0090] 4. Foot leaf spring is slack
[0091] The maximum dorsiflexion ankle torque during level-ground
walking is in the range from 1.5 Ng to 2 Nm/kg, i.e. around 150 Nm
for a 100 kg person {2}. With current technology, a variable-damper
that can provide such high damping torque and additionally very low
damping levels is difficult to build at a reasonable weight and
size. Fortunately, the maximum controlled plantar flexion torque is
small, typically in the range of 0.3 Nm/kg to 0.4 Ng. Because of
these factors, a ribbon stop that engages at a small dorsiflexion
angle such as 5 degrees would lower the peak torque requirements of
the variable-damper since the peak controlled plantar flexion
torque is considerably smaller than the peak dorsiflexion
torque.
[0092] During stair descent/downhill walking, the human ankle
behaves like a damper from foot strike to 90.degree. of
dorsiflexion {11}. Beyond that, the ankle behaves like a non-linear
spring, storing elastic energy during controlled dorsiflexion.
Taking advantage of the biomechanics of the human ankle, it is
reasonable to add a passive clutch for resisting dorsiflexion
movements beyond 90.degree., thus allowing for a smaller sized
variable damper. A ribbon stop is preferred as a unidirectional
clutch because it is lightweight with considerable strength in
tension.
[0093] Stair Ascent
[0094] FIGS. 13-15 depict the control sequence of embodiment 1 for
stair ascent. It is noted here that there are only three control
phases/modes for stair ascent, although the gait cycle for stair
ascent can be divided into 5 sub-phases, including Controlled
Dorsiflexion 1 (CD1), Powered Plantarflexion 1 (PP1), Controlled
Dorsiflexion 2 (CD2), Powered Plantarflexion 1 (PP1), and Swing
Phase. The main-reason is that in terms of control, we can combine
phases PP1, CD2, and PP2 into one single phase since all three
phases may be described using the same control law. For ascending a
stair, the clutch is engaged and the leaf spring is compressed
throughout ground contact (FIG. 13) because the toe strikes the
ground first, engaging the ribbon stop during CD (Ax, 0,
&.sub.2=0). After the heel strikes the ground and then lifts
off the ground, the toe leaf spring begins releasing its energy,
supplying forward propulsion to the body (FIG. 14). The variable
damper may be activated to control the process of energy release
from the leaf spring, but in general, the damper is turned off so
that all the stored elastic energy is used to propel the body
upwards and forwards (Ax, 0, &.sub.2 0). After toe-off, the
actuator controls the equilibrium position of the ankle in
preparation for the next step (FIG. 15).
[0095] The state of each element of the ankle-foot system during
these three phases of a stair ascent are listed below:
[0096] Controlled Dorsiflexion (FIG. 13) [0097] 1. Actuator motor
is OFF [0098] 2. Ribbon clutch is ON [0099] 3. Damper is OFF [0100]
4. Leaf spring toe section 660 is being compressed
[0101] Powered Plantar Flexion (FIG. 14) [0102] 1. Actuator motor
is OFF [0103] 2. Ribbon clutch is-ON [0104] 3. Damper is OFF [0105]
4. Leaf spring toe section 660 is releasing energy
[0106] Swing Phase (FIG. 15) [0107] 1. Actuator motor is ON
(changing foot orientation) [0108] 2. Ribbon clutch is OFF [0109]
3. Damper is OFF [0110] 4. Foot leaf spring is slack
[0111] Stair Descent
[0112] The control sequence for embodiment 1 for stair descent is
depicted in FIGS. 16-19. After forefoot contact, the body has to be
lowered until the heel makes contact with the stair tread {11}
(FIG. 16). Therefore, the variable damper is activated as energy is
dissipated during controlled dorsiflexion (.DELTA.X.sub.1<=0,
.DELTA.X.sub.2<=0). As is shown in FIG. 17, when the foot
becomes flat on the ground, the ribbon stop becomes taunt,
compressing the toe leaf spring (.DELTA.X.sub.1<=0,
.DELTA.X.sub.2=0). During PP, the toe leaf spring releases its
energy, propelling the body upwards and forwards (FIG. 18).
[0113] The state of each element of the ankle-foot system during
the four phases of stair descent are listed below:
[0114] Controlled Dorsiflexion 1 (FIG. 16) [0115] 1. Actuator motor
is OFF [0116] 2. Ribbon clutch is OFF [0117] 3. Damper is ON [0118]
4. Leaf spring toe section 660 is being compressed
[0119] Controlled Dorsiflexion 2 (FIG. 17) [0120] 1. Actuator motor
is OFF [0121] 2. Ribbon clutch is ON [0122] 3. Damper is OFF [0123]
4. Leaf spring toe section 660 is being compressed
[0124] Powered Plantar Flexion (FIG. 18) [0125] 1. Actuator motor
is OFF [0126] 2. Ribbon clutch is ON [0127] 3. Damper is OFF [0128]
4. Leaf spring toe section 660 is releasing energy
[0129] Swing Phase (FIG. 19) [0130] 1. Actuator motor is ON
(changing foot orientation) [0131] 2. Ribbon clutch is OFF [0132]
3. Damper is OFF [0133] 4. Foot leaf spring is slack
Sensing for Embodiment 1
[0134] The ankle foot system preferably employs an inertial
navigation system (INS) for the control of an active artificial
ankle joint to achieve a more natural gait and improved comfort
over the range of human walking and climbing activities.
[0135] To achieve these advantages, an artificial ankle joint must
be controlled to behave like a normal human ankle. For instance,
during normal level ground walking, the heel strikes the ground
first; but when descending stairs, it is the toe which first
touches the ground. Walking up or down an incline, either the toe
or the heel may strike the ground first, depending upon the
steepness of the incline.
[0136] A difficult aspect of the artificial ankle control problem
is that the ankle joint angle must be established before the foot
reaches the ground, so that the heel or toe will strike first, as
appropriate to the activity. Reliable determination of which
activity is underway while the foot is still in the air presents
implacable difficulties for sensor systems presently employed on
lower leg artificial devices.
[0137] The present invention addresses this difficulty by attaching
an inertial navigation system below the knee joint, either on the
lower leg segment or on the artificial foot. This system is then
used to determine the foot's change in elevation since it last left
the ground. This change in elevation may be used to discriminate
between level ground walking and descending stairs or steep
inclines. The ankle joint angle may then be controlled during the
foot's aerial phase to provide heel strike for level ground walking
or toe strike upon detection of negative elevation, as would be
encountered descending stairs or walking down a steep incline.
[0138] Inertial navigation systems rely upon accelerometers and
gyroscopes jointly attached to a rigid assembly to detect the
assembly's motion and change of orientation. In accordance with the
laws of mechanics, these changes may be integrated to measure
changes of the system's position and orientation, relative to its
initial position and orientation. In practice, however, it is found
that errors of the accelerometers and gyros produce ever-increasing
errors in the system's estimated position. Inertial navigation
systems can address this problem in one of two ways: by the use of
expensive, high precision accelerometers and gyroscopes, and by
incorporating other, external sources of information about position
and orientation, for instance GPS, to augment the purely inertial
information. But using either of these alternatives would make the
resulting system unattractive for an artificial ankle device.
[0139] However, we have found that an unaugmented, purely inertial
system based on available low cost accelerometers and rate gyros
can provide sufficiently accurate trajectory information to support
proper control of the angle of an actuated artificial ankle
system.
[0140] An Illustrative Control Algorithm
[0141] Control of an actuated artificial ankle joint may be
implemented as follows: [0142] A. During the foot flat (controlled
dorsiflexion) phase of the walking cycle, reset and maintain the
measured elevation to zero. When the foot is flat on the ground,
its velocity and acceleration are zero. Thus, this particular foot
posture serves as a reset point for the integration of angular and
linear velocities in the estimation of absolute positions. [0143]
B. During the push off phase, when powered plantarflexion begins,
measure the upward and downward movements to determine the current
elevation relative to the initial zero elevation during the flat
foot phase; [0144] C. As long as the elevation remains above zero,
maintain the foot orientation that will provide heelstrike; and
[0145] D. If the elevation decreases below zero, reorient the angle
ankle to provide toe-first contact.
[0146] The foot flat phase may be detected by the absence of
non-centrifugal, non-gravitational, linear acceleration along the
length axis,of the lower leg. Push off phase may be detected by the
upward acceleration along the axis of the,lower leg. Elevation
>0 and elevation <0 phases are recognized from the change in
relative elevation computed by the INS since the end of foot flat
phase.
Embodiment 2
[0147] Mechanical Design
[0148] The mechanical design of Embodiment 2 is shown in FIGS.
20-23. As seen in FIG. 22, the foot and ankle system includes an
elastic leaf spring structure that provides a heel spring as seen
at 2201 and a toe spring as seen at 2206, the elastic leaf spring
structure attaches to a brake mount member 2202 that rotates with
respect to an ankle joint shank frame 2203 and a tibial side
bracket 2204 about a pivot axis at the center of the MR brake seen
at 2205. The actuator motor 2207 is mounted within the tibial side
bracket 2204 and its drive shaft is coupled through a drive gear
(not shown) to rotate the elastic leaf spring structure 2201 and
2206 with respect to the shank frame 2203 and side bracket 2204
about the ankle joint. A catapult mechanism to provide powered
plantar flexion during late stance is employed that consists of a
series elastic spring element seen at 2210 having an internal
slider 2212 that attaches to the brake mount 2202 at the lower
actuator mount 2213, and the spring element 2210 attaches to the
upper actuator mount 2216 at the top of the tibial side bracket
2204. A standard pyramid mount 2230 at the top of the tibial side
bracket 2294 provides a connection to the shin member (not
shown).
[0149] The corresponding schematic of Embodiment 2 is seen in FIG.
23 and is similar to that of Embodiment 1, including the heel and
toe leaf spring 2301, variable damper 2305, and ribbon stop 2303.
The series elastic spring element is seen at 2310 connected in
series with the actuator motor 2307 to form the catapult.
[0150] One of the main challenges in the design of an artificial
ankle is to have a relatively low-mass actuation system that can
provide a large instantaneous output power upwards of 200 Watts
during Powered Plantar Flexion (PP) {2,11} Fortunately, the
duration of PP is only 15% of the entire gait cycle, and the
average power output of the human ankle during the stance phase is
much lower than the instantaneous output power during PP. Hence, a
catapult mechanism is a compelling solution to this problem.
[0151] The catapult mechanism is mainly composed of three
components: an actuator motor, a variable damper and/or clutch and
an energy storage element. The actuator can be any type of motor
system, including electric, shape memory alloy, hydraulic or
pneumatic devices, and the series energy storage element can be any
elastic element capable of storing elastic energy when compressed
or stretched. The damper can be any type of device including
hydraulic, magnetorheological, pneumatic, or
electrorheological.
[0152] With the parallel damper seen at 2305 in FIG. 23 activated
to a high damping level or with the parallel clutch 2303 activated,
the series elastic spring element 2310 can be compressed or
stretched by the actuator 2307 in series to the spring 2310 without
the joint rotating. The spring 2310 will provide a large amount of
instantaneous output power once the parallel damping device 2305 or
clutch 2303 is deactivated, allowing the elastic element 2310 to
release its energy. If the actuator 2307 has a relatively long
period of time to compress or stretch the elastic element 2310, its
mass can be kept relatively low, decreasing the overall weight of
the artificial ankle device. In Embodiment 2, the catapult system
comprises a magnetorheological variable damper 2305 placed in
parallel to the series elastic electric motor system.
[0153] Control System
[0154] The lumped parameter model of Embodiment 2 is shown in FIG.
24. It is basically the same as the model of Embodiment 1 as
depicted in FIG. 8, except that we now place a spring element 2410
in series with the actuator 2407 and the foot mass structure 2430.
The main idea here is that if the variable MR damper seen at 2405
outputs high damping, locking the ankle joint, the foot and the
shank become one single component. Once the joint is locked, the
actuator 2407 compresses or stretches the spring element 2310. Once
joint damping is minimized, the spring element 2410 will then push
against the shank 2420 to provide forward propulsion during powered
plantar flexion.
[0155] The control sequence of Embodiment 2 for level-ground
walking will be discussed in the next section. Stair ascent/descent
can be deduced from the earlier descriptions for embodiment 1, and
thus, will not be described herein.
[0156] Level-Ground Walking
[0157] The control sequence of Embodiment 2 for level-ground
walking is depicted in FIGS. 25-28. During CP, the actuator
controls the stiffness of the ankle by controlling the displacement
of the series spring (FIG. 25). During CD, the toe carbon fiber
leaf spring 2206 is compressed due to the loading of body weight,
while the actuator compresses the series spring to store additional
elastic energy in the system (FIG. 26). In this control scheme,
inertia and body weight hold the joint in a dorsiflexed posture,
enabling the motor to elongate the series spring. In a second
control approach, where body weight and inertia are insufficient to
lock the joint, the MR variable damper would output a high damping
value to essentially lock the ankle joint while the motor stores
elastic energy in the series spring. Independent of the catapult
control approach, during PP as seen in FIG. 27, as the load from
body weight decreases, both the leaf spring and the series catapult
spring begin releasing stored elastic energy, supplying high ankle
output powers. After toe-off, the actuator controls the position of
the foot while both the series spring and the leaf springs are
slack as depicted in FIG. 28.
[0158] The state of each element of Embodiment 2 of the ankle foot
system during the four phases of a level ground walking cycle are
listed below:
[0159] Controlled Plantar Flexion (FIG. 25) [0160] 1. Actuator
motor is ON [0161] 2. Ribbon clutch is OFF [0162] 3. Damper is OFF
[0163] 4. Leaf spring heel portion at 2201 is being compressed
[0164] Controlled Dorsiflexion (FIG. 26) [0165] 1. Actuator motor
is ON [0166] 2. Ribbon clutch is ON [0167] 3. Damper is OFF [0168]
4. Leaf spring toe section 2206 is being compressed
[0169] Powered Plantar Flexion (FIG. 27) [0170] 1. Actuator motor
is ON [0171] 2. Ribbon clutch is OFF [0172] 3. Damper is OFF [0173]
4. Leaf spring toe section 2206 is releasing energy
[0174] Swing Phase (FIG. 28) [0175] 1. Actuator motor is ON
(changing foot orientation) [0176] 2. Ribbon clutch is OFF [0177]
3. Damper is OFF [0178] 4. Foot leaf spring structure is slack
Sensing for Embodiment 2
[0179] As with Embodiment 1, an inertial navigation system for the
control of the active artificial ankle joint will be employed to
achieve a more natural gait and improved comfort over the range of
human walking and climbing activities. The manner in which these
navigation sensors will be used is similar to that described for
Embodiment 1.
[0180] Sensing and Control
[0181] As described above, investigations of the biomechanics of
human limbs have revealed the functions performed by the ankle
during normal walking over level ground, and when ascending or
descending a slope or stairs. As discussed above, these functions
may be performed in an artificial ankle joint using motors to act
as torque actuators and to position the foot relative to the shin
member during a specific times of walking cycle, using springs in
combination with controllable dampers to act as linear springs and
provide controllable damping at other times in the walking cycle.
The timing of these different functions occurs during the walking
cycle at times described in detail above. The specific mechanical
structures, that is the combinations of motors, springs and
controllable dampers used in these embodiments are specifically
adapted to perform the functions needed, a variety of techniques
may be employed to automatically control the motor and controllable
dampers at the times needed to perform the functions illustrated,
and any suitable control mechanism may be employed. FIG. 29 depicts
the general form of a typical control mechanism in which a multiple
sensors are employed to determine the dynamic status of the
skeletal structure and the components of the hybrid actuator and
deliver data indicative of that status to a processor seen at 2900
which produces control outputs to operate the motor actuator and to
control the variable dampers.
[0182] The sensors used to enable general actuator operation and
control can include: [0183] (1) Position sensors seen at 2902 in
FIG. 29 located at the ankle joint axis to measure joint angle (a
rotary potentiometer), and at the motor rotor to measure total
displacement of the motor's drive shaft (as indicated at 2904) and
additionally the motor's velocity (as indicated at 2906). A single
shaft encoder may be employed to sense instantaneous position, from
which motor displacement and velocity may be calculated by the
processor 2900. [0184] (2) A force sensor (strain gauges) to
measure the actual torque borne by the joint as indicated at 2908.
[0185] (3) Velocity sensors on each of the dampers (rotary
encoders) as indicated at 2910 in order to get a true reading of
damper velocity. [0186] (4) A displacement sensor on each spring
(motor series spring and global damper spring) as indicated at 2912
in order to measure the amount of energy stored. [0187] (5) One or
more Inertial Measurement Units (IMUs) seen at 2914 which can take
the form of accelerometers positioned on skeletal members from
which the processor 2900 can compute absolute orientations and
displacements of the artificial joint system. For example, the IMU
may sense the relative vertical movement of the foot member
relative to its foot flat position during the walking cycle to
control foot orientation as discussed above. [0188] (6) One or more
control inputs manipulatable by a person, such a wearer of a
prosthetic joint or the operator of a robotic system, to control
such things as walking speed, terrain changes, etc.
[0189] The processor 2900 preferably comprises a microprocessor
which is carried on the ankle-foot system and typically operated
from the same battery power source 2920 used to power the motor
2930 and the controllable dampers 2932 and 2934. A non-volatile
program memory 2941 stores the executable programs that control the
processing of the data from the sensors and input controls to
produce the timed control signals which govern the operation of the
actuator motor and the dampers. An additional data memory seen at
2942 may be used to supplement the available random access memory
in the microprocessor 2900.
[0190] Instead of directly measuring the deflection of the motor
series springs as noted at (4) above, sensory information from the
position sensors (1) can be employed. By subtracting the ankle
joint angle from the motor output shaft angle, it is possible to
calculate the amount of energy stored in the motor series spring.
Also, the motor series spring displacement sensor can be used to
measure the torque borne by the joint because joint torque can be
calculated from the motor series output force.
[0191] Many variations exist in the particular sensing
methodologies employed in the measurement of the listed parameters.
Although this specification describes preferred sensing methods,
each has the goal of determining the energy state of the spring
elements, the velocities of interior points, and the absolute
movement pattern of the ankle joint itself.
REFERENCES
[0192] The following published materials provide background
information relating to the invention. Individual items are cited
above by using the reference numerals which appear below and in the
citations in curley brackets. [0193] {1} Palmer, Michael. Sagittal
Plane Characterization of Normal Human Ankle Function across a
Range of Walking Gait Speeds. Massachusetts Institute of Technology
Master's Thesis, 2002. [0194] {2} Gates Deanna H., Characterizing
ankle function during stair ascent, descent, and level walking for
ankle prosthesis and orthosis design. Master thesis, Boston
University, 2004. [0195] {3} Hansen, A., Childress, D. Miff, S.
Gard, S. and Mesplay, K., The human ankle during walking:
implication for the design of biomimetric ankle prosthesis, Journal
of Biomechanics (In Press). [0196] {4} Koganezawa, K. and Kato, I.,
Control aspects of artifical leg, IFAC Control Aspects of
Biomedical Engineering, 1987, pp. 71-85. [0197] {5} Herr H,
Wilkenfeld A. User-Adaptive Control of a Magnetorheological
Prosthetic Knee. Industrial Robot: An International Journal 2003;
30: 42-55. [0198] {6} Seymour Ron, Prosthetics and Orthotics: Lower
limb and Spinal, Lippincott Williams & Wilkins, 2002. [0199]
{7} G. A. Pratt and M. M. Williamson, "Series Elastic Actuators,"
presented at 1995 IEEE/RSJ International Conference on Intelligent
Robots and Systems, Pittsburgh, Pa., [0200] {8} Inman V T, Ralston
H J, Todd F. Human walking. Baltimore: Williams and Wilkins; 1981.
[0201] {9} Hof. A. L. Geelen B. A., and Berg, J w. Van den, "Calf
muscle moment, work and efficiency in level walking; role of series
elasticity," Journal of Biomechanics, Vol 16, No. 7, pp. 523-537,
1983. [0202] {10} Gregoire, L., and et al, Role of mono- and
bi-articular muscles in explosive movements, International Journal
of Sports Medicine 5, 614-630. [0203] {11} Koganezawa, K. and Kato,
I., Control aspects of artifical leg, IFAC Control Aspects of
Biomedical Engineering, 1987, pp. 71-85. [0204] {12} U.S. Pat. No.
6,517,503 issued Feb. 11, 203.
CONCLUSION
[0205] It is to be understood that the methods and apparatus which
have been described above are merely illustrative applications of
the principles of the invention. Numerous modifications may be made
by those skilled in the art without departing from the true spirit
and scope of the invention.
* * * * *