U.S. patent application number 11/809206 was filed with the patent office on 2008-01-03 for cable driven joint actuator and method.
This patent application is currently assigned to Northwestern University. Invention is credited to James L. Patton, Michael A. Peshkin, James S. Sulzer.
Application Number | 20080000317 11/809206 |
Document ID | / |
Family ID | 38875241 |
Filed Date | 2008-01-03 |
United States Patent
Application |
20080000317 |
Kind Code |
A1 |
Patton; James L. ; et
al. |
January 3, 2008 |
Cable driven joint actuator and method
Abstract
A cable driven actuator and actuator method involve a movable
link that is movable about a path by a cable connected to the link,
and a movable support member having a cable routing element. The
support member is movable in a manner to change a moment arm of the
cable acting on the link to control torque applied to the
joint.
Inventors: |
Patton; James L.; (Winnetka,
IL) ; Peshkin; Michael A.; (Evanston, IL) ;
Sulzer; James S.; (Chicago, IL) |
Correspondence
Address: |
Mr. Edward J. Timmer
P.O. Box 770
Richland
MI
49083-0770
US
|
Assignee: |
Northwestern University
|
Family ID: |
38875241 |
Appl. No.: |
11/809206 |
Filed: |
May 31, 2007 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60809698 |
May 31, 2006 |
|
|
|
Current U.S.
Class: |
74/500.5 ; 254/1;
623/32; 623/57 |
Current CPC
Class: |
A61H 2201/1635 20130101;
A61H 2201/163 20130101; A61H 2201/1642 20130101; A61H 1/0237
20130101; Y10T 74/20402 20150115; F16H 19/06 20130101; A61F 5/0102
20130101; A61F 5/0125 20130101; A61H 2201/165 20130101; A63B
21/0058 20130101; A63B 21/155 20130101; A63B 2220/51 20130101; A61H
3/00 20130101; A63B 2220/17 20130101; A61H 1/0274 20130101; A61H
2201/1676 20130101; A61H 2201/1215 20130101 |
Class at
Publication: |
074/500.5 ;
254/001; 623/032; 623/057 |
International
Class: |
F16C 1/10 20060101
F16C001/10; A61F 2/60 20060101 A61F002/60; A61F 2/66 20060101
A61F002/66; B66F 11/00 20060101 B66F011/00 |
Goverment Interests
CONTRACTUAL ORIGIN OF THE INVENTION
[0002] This invention was supported by funding from the Federal
Government through the National Institute of Health Science under
Grant/Contract No. 5T32 HD 07418. The Government may have certain
rights in the invention.
Claims
1. A cable driven actuator, comprising a movable link that is moved
about a path in response to a cable connected to the link, and a
movable support member having a cable routing element disposed
thereon wherein said support member is movable in a manner to
change a moment arm of the cable acting on the link.
2. The actuator of claim 1 wherein the support member is rotatable
to cause the cable routing element thereon to change the moment
arm.
3. The actuator of claim 2 wherein the support member is rotatable
about an axis that is coaxial with a pivot axis of the link.
4. The actuator of claim 1 wherein the support member moves in a
translatable path to cause the cable routing element thereon to
change the moment arm.
5. The actuator of claim 1 wherein the cable is substantially
inelastic or elastic.
6. A cable driven joint actuator comprising a pivotal link that is
adapted to be operatively coupled to a joint to be actuated and
that is pivoted about a pivot axis by a length of cable engaging a
pulley on the link remote from the pivot axis and having an end
coupled to the link, a pulley-support member having a cable
positioning pulley and being rotatable by a motor about an axis
that is coaxial with said pivot axis to cause the pulley to
position the cable in a manner to change the moment arm of the
cable acting on the link to control torque applied to the joint,
and a device to maintain a substantially constant tension on the
cable.
7. The actuator of claim 6 wherein the tensioner device comprises a
cable spool and a second motor to rotate the spool.
8. The actuator of claim 6 wherein the tensioner device comprises a
spring or bungee cord.
9. The actuator of claim 6 wherein said pulley of said link and
said pulley of said pulley support member form a block and tackle
to amplify torque applied to the joint.
10. A cable driven actuator for human limb, comprising a cable
connected to a human limb that comprises a pivotal link to be
actuated and that is moved about a pivot axis by the cable, the
cable being connected to the human limb remote from the pivot axis,
and a movable support member having an axis generally centered on
the pivot axis and having a cable routing element disposed thereon
wherein said support member is movable in a manner to change a
moment arm of the cable acting on the human limb to control torque
applied to the joint.
11. A robotic training or rehabilitating machine for a human user
comprising the actuator of claim 1 having a handle on the link for
grasping by the user.
12. A method of actuating a link, comprising providing a movable
link that is movable about a path by a cable connected to the link
and moving the link by moving a cable routing element in a manner
to change a moment arm of the cable acting on the link.
13. The method of claim 12 including moving the cable routing
element in a circular path.
14. The method of claim 12 wherein an axis of the circular path is
coaxial with a pivot axis of the link.
15. The method of claim 12 including moving the cable routing
element in a linear path.
16. The method of claim 12 wherein the movable link is a human
limb.
17. The method of claim 12 wherein the movable link is a mechanical
link.
18. The method of claim 12 where the cable routing element fixes an
elastic cable to a pulley support member.
Description
[0001] This application claims benefits and priority of provisional
application Ser. No. 60/809,698 filed May 31, 2006, the disclosure
of which is incorporated herein by reference.
FIELD OF THE INVENTION
[0003] The present invention relates to a cable driven actuator and
method incorporating moment arm adjustment features.
BACKGROUND OF THE INVENTION
[0004] In rehabilitation robotic, orthotic, or prosthetic
applications, devices have been used to apply forces including
torques to various points on the human body in order to manipulate
those points. When such devices apply forces or torques under
programmable computer control, it is said that the human body is
subject to robotic manipulation.
[0005] Current robotic manipulation can be used to provide benefits
to clinicians and patients that include, but are not limited to,
assessment, motor control studies, and therapy of both healthy
people and people with neuromuscular difficulties. However, the
robotic machines developed to date have been limited for use in a
laboratory setting.
[0006] A robotic machine capable of training or rehabilitating its
human user at home or otherwise outside of a laboratory has the
potential to be used more often and thus be more effective. Such a
robotic machine should be lightweight, inexpensive, and portable,
which current rehabilitation robotic machines cannot offer.
[0007] Rehabilitation robotic devices known as the STRING-MAN
device (Surdilovic et al. "STRING-MAN: A New Wire Robotic System
For Gait Rehabilitation", Proc. 8.sup.th International Conference
on Rehabilitation Robotics, 2003) and MACARM device (Mayhew et al.
"Development of the MACARM--a Novel Cable Robot for Upper Limb
Neurorehabilitation". Proceedings of the 2005 IEEE, 9.sup.th
International Conference on Rehabilitation Robotics, Chicago, Ill.
2005) use cables to actuate a human user's joints. The torque on
the human user's joint is controlled by changing the tension in the
wires.
[0008] The MIT Manus device uses a five-bar linkage and two torque
motors to produce a planar haptic interface (Hogan et al.
"MIT-MANUS: a workstation for manual therapy and training", IEEE
International Workshop on Robot and Human Communication", pp.
161-165, Tokyo, Japan 1992). As a linkage, where the individual
bars are of fixed length, motion pathways are prescribed by the
motions of the joints and by design and size of the linkage.
[0009] Several human interactive robots have embodied Bowden cables
guided by pulleys or drums. For example, such a robot is described
by Jacobsen et al. in "Design of the Utah/MIT Dextrous Hand", Proc.
IEEE International Conference on Robotics and Automation (ICRA),
San Francisco 1986. Also see Salisbury et al. "The Design and
Control of an Experimental Whole-Arm Manipulator", Proc. 5.sup.th
Int. Symp On Robotics Research 1989; and Perry et al. "Design of a
7-Degree-of-Freedom Upper-Limb Powered Exoskeleton", Proc. Int.
Conf. of Biomedical Robotics and Biomechatronics, Pisa, Italy
2006.
[0010] A robotic actuator for dynamic legged locomotion using a
cable-driven series elastic actuator is described by Hurst et al.
in "An Actuator with Physically Variable Stiffness for Highly
Dynamic Legged Locomotion", International Conference on Robotics
and Automation, New Orleans 2004). Also see Veneman et al. "Design
of a Series Elastic and Bowden cable-based actuation system for use
as torque-actuator in exoskeleton-type training", International
Conference on Rehabilitation Robotics, Chicago, Ill. 2005).
[0011] A robotic machine that embodies two elastic bands connected
to a passive (non-driven) circular disk and that relies on torque
unbalance to cause the passive disk to jump between positions is
described by Zeeman in "Catastrophe Theory: Selected Papers",
Addison-Wesley 1972-1977.
SUMMARY OF THE INVENTION
[0012] The present invention provides a cable driven actuator
mechanism that includes moment arm adjustment features to
manipulate the position of the moment arm relative to a movable
link.
[0013] In an illustrative embodiment of the present invention, a
cable driven joint actuator includes a movable link that can be
operatively coupled to a joint to be actuated and that is movable
about a path by a cable connected to the link. A cable routing
element is provided on a movable support member that is rotated
and/or translated in a manner to change the moment arm of the cable
acting on the link to control torque applied to the joint. The
joint can include but is not limited to, a human user's joint or a
mechanical joint of a mechanical device.
[0014] In a particular illustrative embodiment of the present
invention, the cable driven joint actuator includes a pivotal link
that is adapted to be operatively coupled to a joint to be actuated
and that is pivoted about a pivot axis by a length of cable
engaging a pulley on the link remote from the pivot axis and having
an end coupled to the link. One or more cable positioning pulleys
is/are provided on a rotatable pulley-support member that is
rotated about an axis that is coaxial with the pivot axis to cause
the cable positioning pulley to reposition the cable in a manner to
change the moment arm of the cable acting on the link to control
torque applied to the joint. The rotatable pulley support member is
rotatable by a first motor. A device is provided to maintain a
substantially constant tension on the cable. The device can
comprise a cable spool and a second motor to rotate the spool. The
pulley on the link and the cable positioning pulley on the movable
pulley-support member can be configured as a block and tackle to
amplify torque applied to the joint.
[0015] The present invention is useful as a robotic training or
rehabilitating machine, prosthetic machine, or orthotic machine for
human patient use at home or otherwise outside of a laboratory as a
result of its being lightweight, inexpensive, and portable.
[0016] The present invention envisions a cable driven actuator for
a human limb comprising a cable connected to a human limb that
comprises a pivotal link to be actuated and that is pivoted about
an axis by the cable, the cable being connected to the human limb
remote from the axis. A movable support member includes a cable
routing element wherein the support member is movable in a manner
to change a moment arm of the cable acting on the human limb to
control torque applied about the joint.
[0017] The present invention envisions a cable driven actuator for
a garage door or other mechanical link wherein the position of the
moment arm relative to a mechanical link is manipulated.
[0018] These and other features and advantages of the present
invention will be set forth in the following detailed description
taken with the following drawings.
DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is perspective view of a cable driven joint actuator
in accordance with an illustrative embodiment of the invention.
[0020] FIG. 2 is an enlarged perspective view of the rotator and
the cable tensioner of the cable driven joint actuator of FIG.
1.
[0021] FIG. 3 is a simplified top view meant to show the variables
involved in calculating torque exerted in the joint.
[0022] FIG. 4 is a schematic view of a human user grasping the
handle for use in training or rehabilitation where the actuator
applies a torque about the elbow joint.
[0023] FIGS. 5A is a schematic view of a human user having a cable
driven actuator to apply torque about the knee joint to move the
user's leg. FIG. 5B is an enlarged view of the region boxed-in by
dashed lines in FIG. 5A.
[0024] FIG. 6 is a view of the opposite side of the knee
orthosis.
[0025] FIG. 7A and 7B are schematic views of a garage door opener
mechanism in "door going up" position, where the moment arm in the
cable is set to lift the door up.
DESCRIPTION OF THE INVENTION
[0026] In one illustrative embodiment, the present invention
provides a cable driven joint actuator mechanism that includes
moment arm adjustment features to control torque applied to a
joint. The joint to be actuated can include, but is not limited to,
a human user's joint such as an elbow joint, a mechanical joint of
a mechanical device, or any other joint.
[0027] In a particular embodiment of the present invention offered
for purposes of illustration and not limitation with respect to
FIGS. 1 and 2, the cable driven joint actuator includes a pivotal
link 4 that is adapted to be operatively coupled to a joint to be
actuated and that is pivoted about a pivot axis 5 by a discrete
length of substantially inelastic cable 12 engaging one or more
pulleys 6 disposed on the link 4 remote from the pivot axis 5 and
having a cable end coupled to the link as explained below. One or
more cable positioning pulleys 8 is/are provided on a rotatable
pulley-support member 7 that is rotated about a center axis that is
coaxial with the pivot axis 5 to cause the one or more cable
positioning pulleys 8 to position the cable in a manner to change
the moment arm of the cable acting on the link to control torque
applied to the joint. Moment arm is defined using geometry from
FIG. 3. The angle of the cable positioning pulleys 8 relative to a
datum, .PHI., and the angle of the pulleys of link 4 relative to
the same datum, .THETA., are combined with the radius of the link 4
and the cable positioning pulleys 8, R.sub.L and R.sub.p,
respectively. The equation for the moment arm, R, is shown below: R
= R L .times. R p R L 2 + R p 2 - 2 .times. R L .times. R p .times.
.times. cos .function. ( .THETA. - .PHI. ) .times. sin .function. (
.THETA. - .PHI. ) . ##EQU1##
[0028] The rotatable pulley support member 7 is rotatable by a
first motor M1. A cable tensioner device 10 is provided to maintain
a substantially constant tension on the cable 12. The tensioner
device 10 can comprise a cable spool 11 and a second motor M2 to
rotate the spool 11. In FIGS. 1 and 2, two cable pulleys 6 are
shown disposed on the link 4 and two cable pulleys 8 are shown
disposed on the pulley-support member 7 configured to form a block
and tackle to amplify torque applied to the joint. The various
components of the actuator are disposed on a base plate B having a
base plate frame E. The end 4a of the link 4 is rotatably mounted
between the frame plates E1, E2 of the frame E.
[0029] A particular illustrative working embodiment of the
invention is now described in more detail with respect to FIGS. 1
and 2. The link 4 rotates about the pivot axis 5 defined by a link
pivot shaft 4s sandwiched between two 1/2 inch inner diameter ABEC
1 bearings from McMaster-Carr Supply Company and mounted between
the frame plates E1, E2. The angular position (.THETA.) of the link
4 is measured by a 10 k.OMEGA. conductive plastic potentiometer 14
from Spectrum Sensors and Controls, Inc. with a resolution of
0.03.degree. (0.0005 radians). The potentiometer is rotated by the
rotatable link shaft 4s that rotates about axis 5.
[0030] An adjustable handle 3 is provided and can slide across a
track on the link 4 to fit a variety of user arm lengths. Two link
pulleys 6 are shown located at the remote end of the link 4 so as
to form the distal portion of the cable block and tackle. The
pulleys 6 comprise 5/8 inch outer diameter pulleys from
McMaster-Carr Supply Company and are mounted atop one another on
the link by a 3/16 inch diameter steel shaft. All machined
components (except for steel shafts) are made of 6061 aluminum
alloy.
[0031] The pulley-support member 7 comprises a six inch pitch
diameter, steel sprocket (Stock Drive Products, Sterling
Instrument, 0.25 inch pitch) rotating about its center axis that is
coaxial with pivot axis 5 and a roller chain 13 (0.25 inch pitch).
The sprocket is rigidly connected to a support hub 7a to prevent
wobbling of the sprocket. The member 7 and hub 7a are rotatably
mounted on two 0.5 inch inner diameter ABEC 1 bearings from
McMaster-Carr Supply Company on a steel shaft 7s fixed to ground
(i.e. base plate B). The shaft 4s and the shaft 7s have the same
center of rotation. The pulleys 8 (both 5/8 inch outer diameter)
are positioned by a spacer SP to be roughly at the same height as
the link 4 for efficient cable-wrapping. Each pulley 8 uses a 1/4
inch inner diameter ABEC 1 bearing from McMaster-Carr Supply
Company. The pulleys 8 are fastened in a fixed position on the
member 7 (1.9375 inches from the sprocket center) on fixed shaft
7s. The angular position (.PHI.) of the pulleys 6 is measured by
the drive motor M1 with an encoder described below. The larger
rotating member (sprocket) 7 and the pulleys 8 disposed thereon for
rotation are known together as the rotator 7'.
[0032] The rotator 7' is driven by a roller chain 13 and sprocket
15 from Stock Drive Products, Sterling Instrument having a 0.25
inch pitch, 0.6 inch pitch diameter coupled to a drive motor M1,
which comprises a Yaskawa AC servomotor (SGM-02B312) with 0.637 Nm
continuous torque. The sprocket drive motor M1 is provided with an
encoder with 8192 counts/revolution that is used as feedback to
measure pulley angle .PHI.. Through the transmission ratio of 10,
the resulting resolution of the position is 0.016.degree. (0.0003
radian). The transmission ratio of 10 results from the ratio of the
drive motor coupler (not shown of 0.6 inch diameter) to the
sprocket (6 inch diameter). Consistent with cable design
principles, the angle of incidence of the cable (the fleet angle)
does not exceed 2.degree., the cable does not reverse wrapping, and
the pulleys are above the minimum diameter as described by Oberg et
al., Machinery's Handbook, 26.sup.th Edition: Industrial Press Inc.
which is incorporated herein by reference to this end.
[0033] The rotator 7' and the link 4 are mechanically coupled by a
steel aircraft cable 12 from Sava Industries ( 1/32 inch diameter,
7.times.19 strands) that wraps around the rotator pulleys 8 and the
link pulleys 6 in a block and tackle configuration to amplify the
effective tension of the cable by four, resulting in a four-fold
increase in torque and cable excursion. The path of wrapping of the
cable from the tensioner device 10 passes through the bottom pulley
of the cable positioning pulleys 8, then through the bottom pulley
of the link pulleys 6, back to the top pulley of the cable
positioning pulleys 8, and then back to the top pulley of the link
pulleys 6 until it is anchored back at the shaft 7s of the cable
positioning pulleys 8 by anchor 12b. To account for the increased
excursion, cable tensioner device 10 is provided on the base plate
B and comprises a spool 11 driven by a tensioner motor M2, which is
also a Yaskawa AC servomotor (SGM-02B312) for multiple cable wraps.
The cable 12 wraps around the spool 11 which couples to the
tensioner motor M2 with a resolution of 0.16 N, which includes the
transmission ratio. Since the cable 12 enters the spool at a large
fleet angle but a small fleet angle is desired for better wrapping,
a device that decreases the fleet angle at any wrapping level is
necessary. This embodiment uses a follower 17 with the same pitch
and thread diameter that guides the cable into the spool 11. Since
the follower needs to rise and fall with the level of cable on the
spool yet maintain consistent orientation, a post 19 is provided
with one end fixed to the follower and the other end translatable
vertically in the base plate B. The follower 17 is similar to a
follower employed on a fishing reel. Proximate one end, the cable
12 runs against the follower 17 and wraps up to the spool 11 as it
rotates. Exiting from the follower, the cable needs to match up to
the height of the rotator's pulleys 8. As a result, the cable 12
travels through a cable guidance system that comprises of four
pulleys 9 provided to both raise the cable to the proper constant
height when approaching the rotator pulleys 8 and also to measure
cable tension. The pulleys 9 comprise 1/2 inch diameter pulleys
from McMaster-Carr Supply Company disposed on fixed support block
10b. There are provided two strain gauges (strain gauge SG 1 being
shown on block 10b and the other strain gauge being located
therebelow on the underlying block surface 10s) that are disposed
on the pulley support block 10b in a manner to detect cable tension
and provide an optional feedback loop with the tensioner motor M2.
The strain gauges can comprise 350 .OMEGA. resistance strain gauges
SG from Omega Engineering, Inc. Cables for use in practice of the
invention can include, but are not limited to, steel aircraft cable
or other substantially inelastic cables. Elastic cables can be used
as well such as one or more bungee cords within the scope of the
invention. As used herein, the term cable or cables is intended to
include a cable, cord, strand, rope, belt, or other substantially
inelastic or flexible, elastic elements.
[0034] In lieu of the cable being connected to the tensioner device
10 as described above, the cable can be connected to a source of
energy storage such as including, but not limited to, a spring,
FIG. 7A, 7B, or even an energy dissipation element, such as a
damper and bungee cord.
[0035] From the above description, it is evident that the drive
motor M1 controls the rotational path of the cable positioning
pulleys 8 such that the rotator 7' is driven remotely, and the
other tensioner motor M2 controls the tension in the cable 12.
Moreover, the rotator (disk 7 with pulleys 8) and the link 4 rotate
independently from one another, coupled only by the cable 12.
[0036] An advantage of the cable driven joint actuator described
above is its simple control strategy. Using a real time operating
system, the data comprised of the angular positions of the link 4
and of the rotator 7' (disk 7 with pulleys 8) are sampled at 2 kHz.
The drive motor M1 which controls the rotator 7' is operated in a
torque mode, using encoder feedback and controls position. The
tensioner motor M2 is operated in open loop torque mode when the
strain gages SG 1, etc. are not used, where a voltage command
determines the desired tension in the cable. A general-purpose,
procedural, imperative computer programming language, such as C++,
and that interrupts in a semaphore structure to control the
actuator motors M1 and M2 of FIGS. 1, 2, and 3.
[0037] The desired torque to be applied to a joint is created by
setting the position of rotator 7' to create the proper relative
angle between itself and the link 4. For example, the torque per
unit tension is the derivative of the excursion according to the
position of the link 4 pursuant to: The torque on the arm is the
product of the moment arm and the effective tension, which through
the block and tackle, is four times the tension: .tau.=R*4T. where
.tau. is torque, T is tension in the cable, R is the moment arm
defined above. Endpoint stiffness can be manipulated in the same
manner. It is noted that changing the rotator position is
equivalent to changing the equilibrium position of the actuator.
The link position (determined from the potentiometer) and the
rotator position (determined from the motor encoder) are the only
feedback components necessary for control of the actuator, since
the tension of the cable 12 is held constant in this particular
working embodiment. Hard mechanical stops (not shown) are provided
to prevent the link 4 from surpassing the user's range of motion. A
chain guard (also not shown) can be provided to cover the exposed
portion of the roller chain 13 to prevent any interference.
[0038] The cable driven joint actuator described above can be used
in an illustrative embodiment as a robotic training or
rehabilitating machine, FIG. 4, for a human user who grasps the
handle 3 on the link 4 so that torque is applied by the actuator
about the elbow joint of the user, centered at the pivot point 5.
The Table below shows illustrative design parameters for such use.
In the Table, the user's forearm length refers to an actual user's
forearm, on which the length of the link 4 is sized and adjusted,
if necessary. TABLE-US-00001 TABLE Quantitative Design Parameters
Range of Motion User Forearm Torque Speed from full extension (rad)
Length (m) (N m) (rad/s) Minimum 0 0.28 0 0 Maximum 3.pi./4 0.4 10
50
[0039] The above range of torques is based on a 25 N endpoint
force, and the maximum speed is based on an 8 Hz movement. The
training or rehabilitating machine can be used in various modes of
operation; for example, in a Guidance mode where the actuator
torque pushes the user's arm/hand about the elbow joint toward the
desired trajectory of movement using a linear force field of 8
Nm/radian; in an Error Augmentation mode where the actuator torque
pushes the user's arm/hand about the elbow joint away from the
desired trajectory of movement using a linear force field of 8 N
m/radian; and in a Control mode where there is no haptic feedback
(actuator motor M1 not energized). In summary, the device can be
used to control either position or exert any accurate torque on its
user as long as the bandwidth and maximum torque are within
specifications.
[0040] In lieu of using the rotator 7' described above to
manipulate the moment arm, the invention envisions using a slide or
compound slide (not shown) having one or more cable positioning
pulleys disposed thereof to engage and position the cable. The
slide or compound slide can be moved linearly by a motor of any
type in a direction to manipulate the moment arm. In fact, the
invention envisions manipulating the moment arm in any given path,
whether it be linear, rotational, or a combination of the two.
[0041] FIGS. 5A, 5B and 6 are schematic views of a human user
having a cable driven actuator to apply torque about the knee joint
in a manner to move the user's leg pursuant to another illustrative
embodiment of the invention. The cable driven actuator is attached
by straps ST to the leg of the user. FIG. 6 provides a view of the
device from the opposite side. FIG. 6 shows a rotator 107 having
cable wrapping surface 107w and having a fixed shaft 108a that is
connected to a proximal bungee cord anchor 110 which fixes the ends
of two bungee cords 112 and that allows the anchor 110 to rotate
about the shaft 108a. In this embodiment, the cable routing element
is the proximal bungee cord anchor 110. The other ends of the
bungee cords are fixed in a distal bungee cord anchor 111 that
connects to a fixed shaft 114 distally located on a rigid leg
support member 115 in a manner that allows the anchor 111 to rotate
about the shaft. The rotator 107 is centered at the knee, and moves
in a rotational manner about its rotator shaft, thus moving the
proximal bungee cord anchor 110 in a rotational manner.
[0042] The position of the rotator 107 is controlled by cable 119
that wraps around the rotator surface 107w and then passes through
sheaths 119s to a motor M11 on a belt B donned by the user. One end
of each cable sheath 119s is anchored to an anchor plate 122 of a
rigid thigh support member 124 and referred to as a Bowden sheath
anchor. The other end of each sheath 1119s is rigidly connected to
the motor M 11 which wraps the other end of the cable. The members
115, 124 relatively rotate about the rotator shaft during leg
movement. The user's belt B also can include a controller C and
power source S, such as a battery pack.
[0043] The rotational path of the proximal bungee anchor 110 varies
both the length of the bungee cord and the moment arm, altering the
torque exerted on the knee. There are two angular position sensors
(goniometers) 125 that detect the position of both the rotator 107
and the leg relative to the thigh. Since the torque varies based on
rotator position relative to knee flexion angle, the position of
the rotator can be varied relative to the leg, and thus a
controlled torque can be provided at the knee. The torque could be
used for any number of embodiments, including assistive and
resistive strategies.
[0044] In another illustrative embodiment of the present invention,
a cable driven actuator mechanism is provided that includes moment
arm adjustment features to manipulate the position of the moment
arm relative to a movable link. For purposes of illustration and
not limitation, FIGS. 7A and 7B show a cable driven joint actuator
according to this embodiment for use as a garage door opener
device. In this embodiment, an inelastic cable 212 attached on one
end to an extension spring S1 fixed to ground, passes through a
fixed pulley 214 and then through another pulley 215 attached to a
linearly movable bearing 220 for linear movement therewith. The
pulley 215 comprises a cable routing element. The linearly movable
bearing 220 provides a movable support member for the cable
positioning pulley 215. The bearing 220 is moved in linear manner
by lead screw 222 driven by motor M111. The cable 212 then attaches
to the bottom of a conventional multi-hinged garage door D. The
garage door has wheels W that rotate around each hinge and travel
along a fixed track T, which provides a path for movement of the
garage door. The garage door itself or the door sections is
considered a movable link.
[0045] The device works by manipulating the moment arm of the cable
212 relative to the position of the door D. To open a closed door,
motor M111 moves the linear bearing 220 (with cable positioning
pulley 215 thereon) along a horizontal path towards the door,
modifying the cable's line of action it creates with the door and
thus the spring tension in the cable in the vertical direction is
larger than the weight of the door causing the door to rise. To
close an open door, the motor M111 will move the linear bearing 220
(with cable positioning pulley 215 thereon) away from the door
until the weight of the door is greater than the vertical direction
of the tension in the cable.
[0046] While certain embodiments of the invention have been
described in detail above, those skilled in the art will appreciate
that changes and modifications can be made therein within the scope
of the invention as set forth in the appended claims.
* * * * *