U.S. patent application number 11/201578 was filed with the patent office on 2006-03-02 for methods and devices for reducing stance energy for rehabilitation and to enhance physical performance.
Invention is credited to Jahangir S. Rastegar, Thomas Spinelli.
Application Number | 20060046910 11/201578 |
Document ID | / |
Family ID | 35944186 |
Filed Date | 2006-03-02 |
United States Patent
Application |
20060046910 |
Kind Code |
A1 |
Rastegar; Jahangir S. ; et
al. |
March 2, 2006 |
Methods and devices for reducing stance energy for rehabilitation
and to enhance physical performance
Abstract
A method for reducing stance energy is provided. The method
including: storing energy during one or more periods of a periodic
motion of a joint in which energy is absorbed by the muscles; at
least partially returning the stored energy to the muscles during
one or more periods in which the muscles are performing work; and
producing a resisting moment at the joint in addition to a moment
necessary for the storing. A method for rehabilitating muscles
acting across a joint is also provided in which an amount of the
storing is adjusted to provide a desired rehabilitative effect.
Also provided is a method for enhancing performance of a physical
activity where energy is absorbed by muscles associated with the
motion and the stored energy is at least partially returned to the
muscles during one or more periods of the motion in which the
muscles are performing work.
Inventors: |
Rastegar; Jahangir S.;
(Stony Brook, NY) ; Spinelli; Thomas; (East
Northport, NY) |
Correspondence
Address: |
Thomas Spinelli
2 Sipala Court
East Northport
NY
11731
US
|
Family ID: |
35944186 |
Appl. No.: |
11/201578 |
Filed: |
August 11, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60600456 |
Aug 11, 2004 |
|
|
|
Current U.S.
Class: |
482/91 ;
482/148 |
Current CPC
Class: |
A63B 21/002 20130101;
A61H 3/00 20130101; A63B 23/04 20130101; A63B 21/4025 20151001 |
Class at
Publication: |
482/091 ;
482/148 |
International
Class: |
A63B 21/002 20060101
A63B021/002; A63B 23/00 20060101 A63B023/00 |
Claims
1. A method for reducing stance energy during standing, walking or
running, the method comprising: storing energy during one or more
periods of a periodic motion of a joint in which energy is absorbed
by the muscles; at least partially returning the stored energy to
the muscles during one or more periods of the periodic motion in
which the muscles are performing work; and producing a resisting
moment at the joint, the resisting moment being in addition to a
moment necessary for the storing.
2. The method of claim 1, wherein the resisting moment is derived
from a non-linear moment versus angular rotation relationship.
3. The method of claim 1, further comprising adjusting the
resisting moment.
4. The method of claim 3, wherein the adjusting is done
manually.
5. The method of claim 3, wherein the adjusting is done
automatically in response to one or more sensory inputs.
6. The method of claim 5, wherein the one or more sensory inputs
are used to predict an outset of stance instability.
7. The method of claim 5, wherein the one or more sensory inputs
are used to measure a load carried by a user.
8. A method for rehabilitating muscles acting across a joint, the
method comprising: storing energy during one or more periods of a
periodic motion of the joint in which energy is absorbed by the
muscles; at least partially returning the stored energy to the
muscles during one or more periods of the periodic motion in which
the muscles are performing work, and adjusting an amount of the
storing to provide a desired rehabilitative effect.
9. The method of claim 8, wherein the joint is the ankle.
10. The method of claim 8, wherein the joint is the knee.
11. The method of claim 8, wherein the periodic motion is
walking.
12. The method of claim 8, wherein the periodic motion is
running.
13. A method for enhancing performance of a physical activity, the
method comprising: storing energy during one or more periods of a
motion associated with the physical activity in which energy is
absorbed by one or more muscles associated with the motion; and at
least partially returning the stored energy to the one or more
muscles during one or more periods of the motion in which the one
or more muscles are performing work.
14. The method of claim 13, wherein the joint is the ankle.
15. The method of claim 13, wherein the joint is the knee.
16. The method of claim 13, wherein the physical activity is one of
walking, running, bicycling, rowing, and swimming.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to earlier filed U.S.
provisional application, Ser. No. 60/600,456 filed on Aug. 11,
2004, the entire contents of which is incorporated herein by its
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to walk-assist and
power generation devices and methods, and more particularly, to
devices, which generate power and/or assist movement when worn.
[0004] 2. Prior Art
[0005] During walking on a flat, rigid and horizontal surface, a
human subject spends energy and tires. On the other hand, if the
human subject were instead riding a bicycle that is in good
condition, the subject has to spend a significantly less amount of
energy to travel the same amount of distance. And in general, the
faster the person walks (or runs), the difference between the
amount of energy that has to be spent to travel a certain distance
on foot or on bicycle becomes greater. The reason for this
significant difference in the amount of energy that a person has to
spend to travel a certain amount of distance can be described as
follows. Here, the objective is to account for the major sources of
energy expenditure and for the secondary and generally less
significant but complex processes that demand energy expenditure
during locomotion.
[0006] During normal walking (gait), there are two main sources of
energy expenditure. Firstly, due to the structure of the human
body, energy is spent to sequentially accelerate and decelerate the
lower limbs and to a lesser degree certain other parts of the body
(e.g., pumping arms) to achieve locomotion. This component of the
energy spend by a person during the process of locomotion is
hereinafter called the "locomotion energy". This is the case even
during a highly efficient mode of locomotion along a straight path
in which the trunk moves at a nearly constant velocity. During
normal walking, the motion of the lower limb is nearly periodic.
During each cycle of gait, the muscles acting on the lower limbs
are responsible for both accelerating and decelerating the limb
segments. The muscles consume energy to apply the forces required
to accelerate the limb segments and they consume energy to apply
the forces required to decelerate the limb segments. In comparison,
if the person were riding a bicycle, following initial acceleration
to a constant travel velocity, the person has to provide minimal
energy to the human-bicycle system since no significant inertia has
to be sequentially accelerated and decelerated (neglecting the
small friction forces, aerodynamic drag, etc.).
[0007] Secondly, muscle forces have to provide the required forces
across the various joints of the lower extremities and the back and
neck to keep the body upright (or on the seat of the bicycle) and
to provide for a stable posture. Thereby the person has to spend
energy to provide such muscle forces. This component of the energy
spent by a person during the process of locomotion is hereinafter
called the "stance energy". The amount of energy required for this
purpose is usually significantly higher than the required minimum
since the muscle groups generally act together and provide opposing
(isometric) forces that provide joint preloads that in turn provide
for extra stability margin.
[0008] Thus, in order to more significantly reduce the amount of
energy that a person has to spend during locomotion, the amount of
aforementioned "locomotion energy" and "stance energy" that is
consumed by the muscles has to be reduced. Currently, certain
devices are known in the art that are used to reduce joint loads
and/or to reduce muscle forces (mostly in the lower extremities)
that are required for stance stability. These devices do reduce the
"stance energy", some a very small amount and some slightly more,
and are discussed below. There is, however, no device currently
available for directly reducing the "locomotion energy".
[0009] To provide or supplement muscle forces in achieving a stable
stance, various assist or support devices have been developed. Such
stance or support assist devices generally help to reduce the
muscle forces that are required to keep the body upright and to
provide stance (sitting) stability. As a result, such devices also
help reduce the aforementioned "stance energy" requirements during
locomotion to various degrees. A person may use one or more of such
assist or support devices due to the lack of adequate muscle force
levels or control due to age, joint disease, soft or hard tissue
injury or operation, etc. These devices include various braces,
walkers, canes, crutches, and the like. As a result, the forces
that the muscles have to provide and the forces across the various
joints of the lower extremities are generally reduced. The
currently available assist devices may be divided into the
following two categories. Here, various shoe inserts, components
incorporated into the shoes, etc., are not considered since they
are primarily used to modify force distribution on the foot and its
joints by providing certain type of interface between the foot and
the shoe (ground). [0010] 1. Various bracing devices used to bridge
one or more joints, for the primary purpose of reducing the load
transmitted through the joint. The level of muscle forces that act
across the joint to provide joint stability is also reduced,
thereby further reducing the joint forces. Depending on the
effectiveness of the bracing in providing joint (stance) stability,
the "stance energy" is reduced by a certain amount. [0011] 2.
Various walk assist devices such as walkers, canes, crutches, etc.,
for the primary purpose of reducing load on one or both lower
extremities. When such assist devices are used, other muscles,
usually the arm and shoulder and certain upper body muscles, must
then provide the forces needed to assist stance stability and
locomotion. The person obviously has to spend energy to provide the
latter muscle forces. The currently available assist devices do not
significantly reduce the total stance energy expended but merely
transfer the load from the lower limb muscles to the muscles of the
arm and the upper body.
SUMMARY OF THE INVENTION
[0012] The present invention provides methods and devices to reduce
both "locomotion energy" and the "stance energy". Such methods have
been developed e.g., based on the inherent characteristics of gate
and the work done by the muscle forces to affect locomotion and
stance stability. Based on such methods, devices are disclosed for
the following exemplary applications: [0013] 1. Methods and devices
to reduce "locomotion energy". A number of embodiments are
disclosed that provide a wide rage of locomotion energy reduction.
Such devices can be simple and totally passive to eliminate smaller
portions of the locomotion energy. More complex devices can be used
to eliminate larger portions of the locomotion energy. The
complexity in the latter devices can be in terms of the mechanisms
to be used and the active components and controls that are needed
to make them highly effective. By reducing the amount of locomotion
energy that the user has to provide during locomotion (walking and
running), the user becomes less fatigued. A user may, therefore,
use these devices for the purpose of walking while getting less
fatigued, or walking or running longer distances or with heavier
loads with essentially the same level of induced fatigue.
Embodiments with only passive elements and those with active
elements and also microprocessor-controlled versions to achieve
higher efficiency, adaptability and programmable operation are also
disclosed. [0014] 2. A modified version of the above methods to
reduce "locomotion energy" that allows the conversion of at least a
portion of the saved energy to electrical energy which can be
stored and/or directly used to power a device. A number of related
embodiments are also disclosed. By using the disclosed devices, a
user reduces locomotion energy, thereby gets less fatigued during
walking and/or running, while at the same time can generate
electrical energy that can be used directly or stored for later
use. Embodiments with active elements (in addition to the
electrical power generation elements and related electronics) to
achieve higher efficiency and those operated by programmable
microprocessors are also disclosed. [0015] 3. A modified version of
the above methods to reduce both "locomotion energy" and "stance
energy". Embodiments with only passive elements and those with
active elements, including those operated by programmable
microprocessors are also disclosed. The latter embodiments include
those with sensors for measuring a level of stance stability and
fatigue to adapt the parameters of the active components of the
device. [0016] 4. A modified version of the aforementioned methods
to reduce "locomotion energy" in which the phases of operation are
reversed, i.e., certain levels of accelerating forces are provided
to the limbs while the muscle forces are attempting to decelerate
them and decelerating forces are provided while the muscle forces
are attempting to accelerate the limbs. The forces applied to
oppose the action of the muscle forces help the user exercise the
affected muscles. The opposing forces are hereinafter called
"exercising forces", the energy spent by the user to provide their
action is hereinafter called "exercise energy", and such devices
are hereinafter "exercising devices". Embodiments that allow
selective application of "exercising forces" to exercise one or a
group of muscles and to allow the user to vary the level of the
exercising forces are also disclosed. Embodiments capable of
providing a programmed sequence of "exercising forces" and/or their
levels for selected group or groups of muscles are also
disclosed.
[0017] Embodiments are also disclosed in which the above
"exercising devices" are modified to reduce certain joint contact,
ligament or muscle forces. The reductions are achieved by reducing
"locomotion energy", and/or the "stance energy", and/or a certain
muscle or muscle group forces, and/or the forces transmitted across
certain joint or joints. Such embodiments are intended mainly for
physical therapy and rehabilitation purposes by providing means to
adjust the level of muscle, ligament or joint contact forces.
Embodiments capable of providing a programmable variation of the
aforementioned forces are also disclosed.
[0018] Accordingly, a method for reducing stance energy during
standing, walking or running is provided. The method comprising:
storing energy during one or more periods of a periodic motion of a
joint in which energy is absorbed by the muscles; at least
partially returning the stored energy to the muscles during one or
more periods of the periodic motion in which the muscles are
performing work; and producing a resisting moment at the joint, the
resisting moment being in addition to a moment necessary for the
storing.
[0019] The resisting moment can be derived from a non-linear moment
versus angular rotation relationship.
[0020] The method can further comprise adjusting the resisting
moment. The adjusting can be done manually or automatically in
response to one or more sensory inputs. When done automatically,
the one or more sensory inputs can be used to predict an outset of
stance instability or to measure a load carried by a user.
[0021] Also provided is a method for rehabilitating muscles acting
across a joint. The method comprising: storing energy during one or
more periods of a periodic motion of the joint in which energy is
absorbed by the muscles; at least partially returning the stored
energy to the muscles during one or more periods of the periodic
motion in which the muscles are performing work, and adjusting an
amount of the storing to provide a desired rehabilitative
effect.
[0022] The joint can be the ankle or the knee.
[0023] The periodic motion can be walking or running.
[0024] Still yet provided is a method for enhancing performance of
a physical activity. The method comprising: storing energy during
one or more periods of a motion associated with the physical
activity in which energy is absorbed by one or more muscles
associated with the motion; and at least partially returning the
stored energy to the one or more muscles during one or more periods
of the motion in which the one or more muscles are performing
work.
[0025] The joint can be the ankle or knee.
[0026] The physical activity can be one of walking, running,
bicycling, rowing, and swimming.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] These and other features, aspects, and advantages of the
apparatus and methods of the present invention will become better
understood with regard to the following description, appended
claims, and accompanying drawings where:
[0028] FIG. 1 illustrates a schematic of a lateral view of a right
leg.
[0029] FIGS. 2a-2d illustrate graphs showing measurements of
average lower extremity joints motion and the required net muscle
induced torques for a 80 kg male.
[0030] FIG. 3 illustrates a schematic of a right leg, indicating
the ankle joint angle .theta..sub.3 as measured from the foot to
the leg.
[0031] FIGS. 4a-4d illustrate plots of the relative joint angle
.theta..sub.3, the corresponding joint angular velocity
.omega..sub.3, the net moment of force acting on the ankle joint
M.sub.A and the corresponding mechanical power P.sub.A,
respectively, during normal gait as a function of stride.
[0032] FIGS. 5 and 6 illustrate plots of the ankle joint angle
.theta..sub.3 and the moment M.sub.A about the ankle joint against
during one stride, respectively, from the plots of FIGS. 4a-4d.
[0033] FIGS. 7 and 8 illustrate a plot of the ankle joint angle
.theta..sub.3 versus the moment about the ankle joint M.sub.A.
[0034] FIG. 9 illustrates a schematic of an embodiment of a
walk-assist device for use on an ankle.
[0035] FIGS. 10, 11 and 12 illustrate schematics of the embodiment
of FIG. 9 with a torsional spring, a linear spring and an elastic
element, respectively.
[0036] FIG. 13 illustrates a schematic of another embodiment of a
walk-assist device for use on an ankle.
[0037] FIG. 14 illustrates a schematic of two relatively rigid
links and attached by a rotary joint.
[0038] FIG. 15 illustrates a schematic of the two links of FIG. 14
with an added elastic (spring) element.
[0039] FIG. 16 illustrates a sliding joint having a braking element
that allows relative displacement of two relatively rigid
components.
[0040] FIG. 17 illustrates a section view of the sliding joint of
FIG. 16 as taken along line 17-17 of FIG. 16.
[0041] FIG. 18 illustrates a schematic of a simple linkage
mechanism.
[0042] FIG. 19a illustrates two of the links of FIG. 18. FIG. 19b
is a diagram showing links 190 and 191 of FIG. 19a and FIG. 19c is
a diagram showing links 191 and 192.
[0043] FIG. 20a illustrates a schematic showing three elements
connected in series and FIG. 20b illustrates a brake element and
spring element connected in series.
[0044] FIG. 21 illustrates a plot of the force versus displacement
for the three elements connected in series of FIG. 20a
[0045] FIG. 22 illustrates an embodiment of a power generating
walk-assist device.
[0046] FIGS. 23a and 23b illustrate a piezoelectric material based
power-generating element. In FIG. 23a, the piezo generator is
attached to the elastic element with a parallel configuration. In
FIG. 23b, the piezo generator is attached in series to the elastic
element.
[0047] FIG. 24a illustrates a schematic of a piezo generator. FIGS.
24b and 24c illustrates bending elements of the piezo generator of
FIG. 24a.
[0048] FIG. 25 illustrates a schematic of the piezo generator of
FIG. 24a under an applied pair of tensile forces.
[0049] FIG. 26 illustrates a schematic of an electric power
generator and its electrical energy collection and regulation
electronics.
[0050] FIG. 27 illustrates a schematic of an elastic element and
piezo generator element assembly with a brake element positioned in
parallel with the power generator where the power generator is
placed in parallel with the elastic element.
[0051] FIG. 28 illustrates a schematic of an elastic element and
piezo generator element assembly with a brake element positioned in
series with a power generator.
[0052] FIG. 29 illustrates a schematic of an embodiment of a device
configured to exercise muscles.
[0053] FIG. 30 illustrates a plot of moment (torque) .tau. versus
angular rotation .theta. for a spring element.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0054] The present invention provides methods and devices to reduce
"locomotion energy" and/or "stance energy", or obtain other novel
variations as enumerated above. As it is described below, the
disclosed novel method is based on the inherent characteristics of
gate and the work done by the muscle forces to affect locomotion
and stance stability. In this disclosure, for the sake of
simplicity, this method is first described by its application to a
device for the human knee, which allows the user to reduce the
component of the "locomotion energy" associated with the muscles
acting across the knee joint during locomotion (walking or
running). It is then shown how the muscle forces required for
stance stability across the knee joint can also be reduced. The
method is general and applicable to the other joints of the
subject, both individually and as a group. The method also applies
to other linear and/or rotational motion of other segments of the
body. The description of the aforementioned related methods and
devices and their various embodiments are provided next.
[0055] A schematic of the lateral view of a right leg is shown in
FIG. 1. For the sake of simplicity it is assumed that locomotion is
occurring in a fixed vertical plane and is represented by a simple
model. The thigh 101 is modeled as a link 102 connected to the
trunk (not shown) and the knee by rotary joints 103 and 104,
respectively. Similarly, the lower leg 105 is modeled as a link 106
connected to the knee joint 104 and an ankle joint 107. The foot is
indicated by reference numeral 108 and is also connected to the
ankle joint 107. In this simple model, the angle .theta. (109)
between the thigh 102 and the leg 106 is essentially between the
femur (link 102) and the tibia (link 106) in the direction shown in
FIG. 1, and is hereinafter referred to as the knee angle.
[0056] The torque .tau. (110) is the total torque produced by the
muscles acting on the knee joint 104 to produce or maintain the
angle .theta. (109). The torque .tau. (110) is hereinafter referred
to as the knee torque or knee moment.
[0057] The net mechanical power P at any given point of time due to
the torque .tau. (110) acting at the knee joint rotating with the
angular velocity V.sub..theta. is given by: P=.tau.V.sub..theta.
(1)
[0058] In periods in which the power P, equation (1), is positive,
the knee torque and angular velocity have the same sense and the
input of energy by the leg muscles into the (leg) system at the
knee joint 104 is positive. On the other hand, when the power P is
negative, the leg muscles are taking energy out of the (leg)
system, i.e., are absorbing energy. In either case, the muscles
spend energy, and as a result, the subject gets fatigued. In
general, if the subject is walking on a horizontal surface, the
above energy consists mostly of kinetic energy.
[0059] In any range of angular rotation, the mechanical work U done
by the knee torque .tau. can be found directly by integrating the
product of the torque and angular rotation over the specified range
of knee motion. Alternatively, the mechanical work U over an
interval of time may be determined by integrating the power P,
equation (1), over the specified interval of time as: U = .intg. t
initial t final .times. P .times. d t ( 2 ) ##EQU1##
[0060] Consider a subject walking with a fixed cyclic gate. The
kinematics and dynamics of such cyclic gates for humans have been
extensively studied and reported in the published literature, such
as in Bresler, B., Frankel, J. P., "The forces and moments in the
leg during level walking," Trans. ASME 72:27-36 (1950); Cappozzo,
A., Leo, T., Pedotti, A., "A general computing method for the
analysis of human locomotion," J. Biomechanics, 8:307-320 (1975);
Chao, E. Y., "Justification of triaxial goniometer for the
measurement of joint rotation," J. Biomechanics, 13:989-1006
(1980); David A. Winter, The Biomechanics and Motor Control of
Human Gait: Normal, Elderly and Pathological, Second Edition,
University of Waterloo Press (1991); and Winter, D. A., Sidwall, H.
G., Hobson, D. A., "Measurement and reduction of noise in
kinematics of locomotion," J. Biomechanics, 7:157-159 (1974).
[0061] For example, measurements of average lower extremity joints
motion and the required net muscle induced torques are presented in
FIGS. 2a-2d for an 80 kg male. The average rotation at the knee
joint 104 during the "stride period" of a natural "cadence" is
shown in FIG. 2a, with the intervals in which the knee is extending
(straightening) and flexing (bending) clearly indicated. "Stride
Period" is defined as the time between two consecutive initial
contacts between the right heel and the ground during natural
walking. "Cadence" is the number of steps per unit time. Natural
Cadence is the number of steps per unit time when the person is
walking at their natural pace.
[0062] The corresponding angular velocity of the knee V.sub..theta.
and knee torque .tau. are also shown in FIGS. 2b and 2c,
respectively. The corresponding power P is shown in FIG. 2d.
[0063] As can be seen in FIG. 2d, there are four intervals, labeled
as N1 (from time t.sub.1 to time t.sub.2), N2 (from time t.sub.3 to
time t.sub.4), N3 (from time t.sub.5 to time t.sub.6), and N4 (from
time t.sub.7 to time t.sub.8), within which the input power is
negative. During the intervals N1, N2, N3 and N4, the leg muscles,
as a whole, are absorbing energy and the knee torque (moment) and
angular velocity are in opposing directions. In the other intervals
N5 (from time t.sub.6 to time t.sub.1), N6 (from time t.sub.2 to
time t.sub.7) and N7 (from time t.sub.8 to time t.sub.3), however,
the muscles are doing work to mostly add to the kinetic and
potential energy of the leg system. During locomotion, muscle
forces in a similar manner act on other lower extremity joints (and
to a lesser degree other body segments) to accelerate and then to
decelerate them during each cycle of gate (in certain cases, e.g.,
at the knee joint 104, several such intervals are present during
each cycle of gait). In addition, the muscle forces also do work to
raise certain segments of the body, for example the foot and the
leg, thereby increasing and later decreasing their potential
energy. It is also noted that many muscles act on more than one
joint and that different segments of the body, e.g., the lower
extremities, undergo a more complex pattern of simultaneous
motions.
[0064] Now consider the case in which the energy to be absorbed
during the intervals N1, N2, N3 and N4 is stored in certain
mechanical (or electrical) storage devices and partially or wholly
returned to the leg system during the N5, N6 and N7 intervals to
partially or wholly eliminate the need for the leg muscles to input
the required energy during the latter intervals. In a similar
manner, the energy absorbed by the muscle forces acting across
other joints such as ankle and the hip joints may be stored (as
electrical energy and/or mechanical energy) and returned to the leg
system when the muscle forces are required to provide energy to the
affected body segments.
[0065] Such a device is a walk-assist device that significantly
reduces the amount of work that the leg muscles have to do during
walking or running, i.e., it would significantly reduce the
aforementioned "locomotion energy". As a result, the walk-assist
device significantly reduces the amount of work that the leg
muscles have to do during walking or running.
[0066] In fact, if a subject is walking on a horizontal surface and
if friction losses at the joints, friction losses between the shoes
and the ground, aerodynamic drag on the body, etc., are neglected,
it is theoretically possible to totally eliminate the
aforementioned "locomotion energy". This can be done using the
aforementioned method to construct a walk-assist device that
operates simultaneously across all the joints of the lower
extremities, storing e.g., mechanical energy that the muscles have
to provide to absorb kinetic and/or potential energy from the limbs
and providing the stored mechanical energy to the limbs when they
need to increase their kinetic and/or potential energy. Such a
system can operate across all the joints of the lower extremities.
The subject using such a device need only provide "stance energy"
and energy to overcome dissipation of energy due to friction,
aerodynamic drag, etc., similar to when the subject rides a bicycle
on a flat horizontal surface.
[0067] In general, and is shown in FIG. 2d, the input work by the
leg muscles as a function of angular rotation of the knee and
therefore time has a complex profile. Thus, the resulting
walk-assist devices can require mechanisms with mechanical elements
such as brakes and clutches and sensors and control units to allow
the device to take full advantage of the available energy during
different intervals of the locomotion. However, totally passive
devices that would eliminate at least part of the work that the leg
muscles have to do during walking or running are also possible. The
subject using such a walk-assist device can then walk while
spending less energy, thereby getting less tired. Alternatively,
the subject can walk longer distances or for longer periods of
times without getting more tired than he/she would for a shorter
distance without the present device. In addition, as it is shown
later in this disclosure, simple modification of such walk-assist
devices would allow them to also support the static and dynamic
loads due to the weight of the user and the load that is being
carried by the user. As a result, the "stance energy" that the user
has to spend is also significantly reduced. Such a walk-assist
device would then allow the user to walk while spending even less
energy, or to walk longer distances and/or to carry heavier
loads.
Methods and Devices to Reduce "Locomotion Energy"
[0068] The application of the aforementioned basic method to the
development of walk-assist devices for the ankle joint to reduce
the "locomotion energy" is now described. The method is, however,
general and applicable to other joints of the lower extremity and
to walk-assist devices extending across more than one joint. The
method also applies to other periodic linear and/or rotational
motion of other segments of the body during walking and/or running.
For such periodic linear and/or rotational motions, devices that
operate in a manner similar to those for the lower extremity joints
can be constructed to reduce the amount of mechanical energy that
the related muscles have to provide during walking or running.
[0069] FIG. 3 shows the schematics of a right leg, indicating the
ankle joint angle .theta..sub.3 (121), as measured from the foot to
the leg. The plots of the relative joint angle .theta..sub.3 (121),
the corresponding joint angular velocity .omega..sub.3, the net
moment of force acting on the ankle joint M.sub.A and the
corresponding mechanical power P.sub.A during normal gait as a
function of the stride can be obtained from the known methods of
the prior art and are shown in FIGS. 4a-4d, respectively. The
stride begins at heel contact, HC, and continues until the next
consecutive heel contact of the same foot. Toe off, TO, occurs
after about 0.64 of the stride and is indicated by the dashed
vertical line. The first 0.64 of the stride represents a stance
phase for the leg, while the remainder of the stride represents a
swing phase.
[0070] As can be seen in the plot of the mechanical power P.sub.A
in FIG. 4d, following the heel contact (point HC), the mechanical
power assumes a negative value starting from around the point A and
remains negative until the point B (the region between the points A
and B are shown bounded between two solid vertical lines). In this
region, the mechanical power is negative, i.e. the moment of force
and angular velocity have opposite directions. During this
interval, the angular velocity .omega..sub.3 is always positive
(FIG. 4b), indicating that the foot is rotating counterclockwise
with respect to the shank. Since the foot is in contact with the
ground, one can also picture the foot as being fixed flat on the
ground and the shank rotating clockwise relative to the foot. The
moment M.sub.A (FIG. 4c) about the ankle joint is negative during
this portion of the stride; therefore it has a clockwise direction.
Now if the foot is considered to be fixed, the moment M.sub.A is
then seen to be acting in a counterclockwise direction, thereby
making the mechanical power P.sub.A negative, which means that
during this period, the muscles acting on the ankle joint are
absorbing energy.
[0071] In FIGS. 5 and 6, the plots of the ankle joint angle
.theta..sub.3 (121) and the moment M.sub.A about the ankle joint
against during one stride are shown again from the plots of FIGS.
4a-4d. In FIG. 6, the point A at which the moment M.sub.A is
shown.
[0072] From the joint angle .theta..sub.3 (121) and the moment
M.sub.A about the ankle joint during one stride, FIGS. 5 and 6, the
moment M.sub.A can be plotted against the ankle joint angle
.theta..sub.3 (121), as shown in FIG. 7. The points A and B (where
the mechanical power P.sub.A is zero), the toe off TO and heal
contact HC are marked. If the curve is traversed from the point of
heel contact to point A, we find that point A occurs when the
moment M.sub.A is zero, thereby making the mechanical power P.sub.A
zero. Continuing downward and in the direction of Arrow 122 we
reach the point B. We find that point B is located at an extreme
angular position, corresponding to a zero value of angular
velocity, thereby again making the mechanical power P.sub.A zero.
In the region between the points A and B the mechanical power is
negative, i.e., the muscles acting on the ankle joint are absorbing
energy of the leg system, thereby tending to reduce the total
kinetic and potential energy of the leg. On the other hand, in the
region between B and toe off TO, the mechanical power is positive,
i.e., the muscles acting on the ankle joint are adding energy to
the leg system, thereby tending to reduce the total kinetic and
potential energy of the leg.
[0073] It can also be observed from FIG. 7 that the area between
the curve from the point A to B along the arrow 122 and the zero
moment (M.sub.A) line is the work that the leg muscles have to do
to absorb the kinetic and potential energy of the leg during the
corresponding portion of the stride. On the other hand, the area
under the curve from the point B to near the TO and the zero moment
(M.sub.A) line is the work that the leg muscles have to do to add
kinetic and/or potential energy to the leg system during the
corresponding portion of the stride. Therefore, the amount of
energy that is to be absorbed by the leg muscles is smaller than
the amount of the energy to be provided by the leg muscles.
Neglecting the energy lost to friction, aerodynamic drag, etc., and
also assuming that the trunk is moving at a constant speed, then
the extra input energy is mostly to increase the kinetic and/or
potential energy of the other segments of the lower limb and/or
absorb the same. In actual walking, some energy is actually lost,
and a certain amount of energy is transferred to the trunk to allow
for its translational and rotational "oscillations", which similar
to the leg, require input and output (energy absorption) from the
body muscles.
[0074] The ankle joint angle .theta..sub.3 (121) versus the moment
about the ankle joint M.sub.A is shown again in FIG. 8. In FIG. 8,
the point P5 corresponds to the moment of heel contact (HC in FIGS.
4-6), following which the ankle joint angle .theta..sub.3 versus
ankle joint moment M.sub.A goes through the points P6 through P17.
The area under the above curve from the point P6 to the point P9
and the zero moment (M.sub.A) line is the aforementioned work
(hereinafter referred to as W.sub.ab) that the leg muscles have to
do to absorb the kinetic and potential energy of the leg during the
corresponding portion of the stride. The area under the above curve
from the point P9 to the point P15 and the zero moment (M.sub.A)
line is the aforementioned work (hereinafter referred to as
W.sub.add) that the leg muscles have to do to add kinetic and/or
potential energy to the leg system during the corresponding portion
of the stride.
[0075] As can be clearly observed in FIG. 8, the work W.sub.add is
significantly greater than the work W.sub.ab. This means that for
the case of the ankle, a passive (no input energy device such as a
motor) walk-assist device that is to store the absorbed work
W.sub.ab and pass it back to the leg through the ankle joint to
reduce the work W.sub.add by the same amount (here, we are assuming
an ideal system for the sake of describing the present method and
related devices) is limited to a total energy exchange level of
W.sub.ab. Such a device can have a spring element with a
(non-linear) spring rate k.sub.M, given by
M.sub.A=k.sub.M.theta..sub.3 (3)
[0076] The ideal spring rate would yield an ankle joint moment
M.sub.A versus ankle joint angle .theta..sub.3 that traces the
curve from the point P6 to the point P9 and back as the ankle joint
.theta..sub.3 is varied in the corresponding range of ankle joint
angles shown in FIG. 8.
[0077] A schematic of one embodiment is shown in FIG. 9. The
walk-assist device 130 comprises two parts, one of which is a cuff
132 that is worn, preferably relatively tightly, on the leg 105. A
second part 131 is worn on the foot, also preferably relatively
tightly, and covers part or preferably the entire foot as a shoe or
a boot.
[0078] The two parts 131 and the 132 are hinged at the ankle joint
by the hinge 135, which may be provided through intermediate
elements 133 and 134, which are fixed to the leg part 132 and foot
part 131, respectively, by any means known in the art. A torsional
(linear, etc.) spring 136 (not shown in this schematic for clarity,
shown in FIG. 10) is provided at the joint 135 and provides the
aforementioned non-linear ankle joint moment M.sub.A versus ankle
joint angle .theta..sub.3 curve characteristic.
[0079] As can be seen in FIG. 8, the walk assist device 130
generates the aforementioned ankle joint moment M.sub.A versus
ankle joint angle .theta..sub.3 from the point P6 to P9, and zero
ankle joint moment M.sub.A in the remainder range of ankle joint
angle .theta..sub.3, i.e., from the point P9 to P15. Here, the
small zero moment range from the point P5 (P17) to the point P6 is
neglected, but such multi-tracked ranges of joint motion are
addressed below. The aforementioned zero ankle joint moment M.sub.A
in one part and nonzero moment M.sub.A in another part of the range
of ankle joint angle .theta..sub.3 (without multi-tracked ranges)
can be achieved using a variety of methods, including the following
(in the following schematics, only the hinge joint 135 and its
intermediate elements, i.e., the relatively rigid elements 133 and
134 and in certain cases the leg and foot worn parts 132 and 131
are shown).
[0080] During the ankle rotation, the spring element 136 (either
torsional, linear, etc.) engages the connecting parts 133 and 134
in the range that moment is to be generated and disengages in the
remaining (zero moment) range of ankle motion. The schematic of
this embodiment with torsional and linear springs are shown in
FIGS. 10 and 11, respectively. Other types of springs may be
employed in a similar manner. In FIG. 10, the link 133 is free to
rotate relative to link 134 about the rotary joint 135 without
generating resistance to rotation by the torsional spring 136 (a
torsional springs can make a significantly larger arc, and may even
make several turns, however, a short arc is shown in FIG. 10 for
clarity), unless it enters the range 137 (starting from the
position 138 to the link 134). A similar embodiment is shown in
FIG. 11, in which a compressive linear spring 143 is used to
connect the link 134 to a third link 141. The link 133 is free to
rotate until it reaches an extension 142 of link 141, at which
time, the spring 143 begins to provide resistance to further
rotation of the link 133 within the range 144. In the embodiments
of FIGS. 10 and 11, the link 133 is considered to be prevented by
the link 134 to rotate counter clockwise past the link 134. It is
appreciated by those skilled in the art that other types of springs
(e.g., tensile helical springs, or those working in bending and
even the structural flexibility of the two links 133 and 134) and
other joints, such as living rotary joints, and linkage
configurations could be used to perform the aforementioned
tasks.
[0081] An elastic element 145 such as a natural or synthetic
elastomer can also be attached to the links 133 and 134 as shown in
FIG. 12. The link 133 is free to rotate relative to the link 134
from close to the link 134 in the counter clockwise direction until
it reaches the position 146, at which time the elastic element 145
becomes taut (position 147), and begins to deform elastically with
further counter clockwise rotation of the link 133 relative to the
link 134, thereby generating a restoring moment. The links 133 and
134 and the elastic element 145 can be integral, and are attached
directly to the foot and leg worn components 132 and 131,
respectively. In one embodiment, the links 133 and 134, the elastic
element 145 and the leg and foot components 132 and 131 are
integral and in the form of a shoe with leg brace or preferably as
a boot.
[0082] In the above embodiments, the spring rate may be constant or
a non-linear function of displacement (FIGS. 11 and 1 ) or angular
rotation (FIG. 10). If the torsional spring 136, FIG. 10, has a
constant rate, then the corresponding ankle joint moment M.sub.A
versus ankle joint angle .theta..sub.3 becomes linear and similar
to the line 150 shown in FIG. 8. The slope of the line 150
indicates the spring rate and for the one shown in FIG. 8 it is
chosen to cover the entire aforementioned range of rotation, i.e.,
the range corresponding to the range of points P6 to P9 with
minimal amount of moment above the indicated curve. The spring rate
is also selected such that the moment-rotation line 150 covers as
much of the area under the curve between the points P6 and P9,
i.e., to store as much energy as possible when using a linear
spring. In addition, the moment-rotation line begins from zero
moment, indicating that the torsional spring 136 is not preloaded,
which in certain cases can increase the total amount of energy that
could be stored in the spring element.
[0083] If the spring element 143 in the joint mechanism shown in
FIG. 11 has a near constant spring rate and if the range of
rotation 144 is relatively small (such as about 12 deg. as seen in
FIG. 8 for the ankle joint), then the resulting ankle joint moment
M.sub.A versus ankle joint angle .theta..sub.3 relationship becomes
nearly linear. For larger ranges of angular rotation, the above
relationship becomes a function of the angle 144 (FIG. 11).
[0084] In the three embodiments shown in FIGS. 10-12, the spring
rate may be selected not to be constant. An advantage of using
non-linear springs is that the spring force (moment) versus
displacement (rotation) characteristics may be selected such that
the resulting ankle joint moment M.sub.A versus ankle joint angle
.theta..sub.3 curves become close to the curve from the point P6 to
P9, FIG. 8. As an example, the curve 151 shown in FIG. 8 results in
the storage of most of the energy available during the ankle
rotation from P6 to P9 and can be readily produced by an
elastomeric element used in the embodiment of FIG. 12. In addition,
by using springs with appropriate non-linear force (moment) versus
displacement (rotation) characteristics, the embodiments of FIGS.
11 and 10 may produce ankle joint moment M.sub.A versus ankle joint
angle .theta..sub.3 curves that are very close to that of curve 151
in FIG. 8.
[0085] Furthermore, instead of using non-linear spring (elastic)
elements, one may use linkage mechanisms (preferably made with
living joints) or cams to achieve the desired force (moment) versus
displacement (rotation) characteristics. The corresponding devices
may, however, become more complex and are not the preferred choice
whenever simple spring or elastic elements could suffice, even
though more complex force (moment) versus displacement (rotation)
characteristics could be obtained using cams and more complex
mechanisms.
[0086] In the embodiment shown in FIG. 9, the ankle joint is shown
as essentially fixed relative to the foot and the leg. However, the
actual instantaneous axis of rotation of the ankle (and the knee)
joints is neither fixed nor always perpendicular to the plane of
locomotion. As a result, it is highly preferable to provide
embodiments in which the instantaneous axis of rotation is allowed
to float and tilt in order to follow the actual unconstrained axis
of rotation as closely as possible. In practice, since the axes of
joint rotations undergo relatively small displacements and tilting
angles, therefore, they require minimal range of displacement and
tilting freedom. The axes of joint rotations is discussed in e.g.,
Rastegar, J., Miller, N., and Barmada, R., "An Apparatus for
Measuring the Load-Displacement and Load-Dependent Kinematic
Characteristics of Articulating Joints. Application to the Human
Ankle Joint," ASME Journal of Biomechanical Engineering 102, pp.
208-213 (1980); Rastegar, J., Piziali, R., L., Nagel, D. A., and
Schurnan, D. J., "Effect of Fixed Axis of Rotation on the
Varus-Valgus and Torsional Load-Displacement Characteristics of the
In-Vitro Human Knee," ASME Journal of Biomechanical Engineering 101
(1979); Piziali, R. L., Rastegar, J., and Nagel, D. A., "The
Contribution of the Cruciate Ligaments to the Load-Displacement
Characteristics of the Human Knee," ASME Journal of Biomechanical
Engineering 102, pp. 277-283 (1980); Piziali, R. L., Rastegar, J.,
and Nagel, D. A., "Measurement of the Non-Linear, Coupled Stiffness
Characteristics of the Human Knee," Journal of Biomechanics 10,
(1977); Rastegar, J., Miller, N., and Barmada, R., "Relative Motion
of the Tibia With Respect to the Foot During Internal-External
Rotation of a Human Ankle Joint," ASME Paper No. 79-Bio-4;
Rastegar, J., Miller, N., and Barmada, R., "Measurement of the
Internal-External Load-Displacement Characteristics of the In-Vitro
Human Ankle Joint," ASME Paper No. 79-Bio-3; Miller, N., Rastegar,
J., and Barmada, R., "Torsional Characteristics of the Human Knee
and its Passive Elements Under Simulated Anatomical Conditions,"
ASME Advances In Bioengineering, pp. 91-93 (1979); Rastegar, J.,
Miller, N., and Barmada, R., "Relative Motion of the Tibia With
Respect to the Foot During Internal-External Rotation of a Human
Ankle Joint," ASME Summer Conference (1979); Miller, N., Rastegar,
J., and Barmada, R., "Internal-External Load-Displacement
Characteristics of the In-Vitro Human Ankle Joint," ASME Summer
Conference (1979); Piziali, R. L., Rastegar, J., and Nagel, D. A.,
"The Axis of Varus-Valgus Rotation of the In-Vitro Human Knee
Joint," Proceedings of 24.sup.th Orthopaedic Research Society
(1978); Rastegar, J., Piziali, R. L., and Nagel, D. A.,
"Varus-Valgus Stiffness of the In-Vitro Human Knee Joint,"
Proceedings of 23.sup.rd Orthopaedic Research Society (1977);
Rastegar, J., Piziali, R. L., and Nagel, D. A., "Torsional
Load-Displacement Characteristics of the In-Vitro Human Knee,"
Proceedings of 30.sup.th ACEMB (1977); Piziali, R. L., Rastegar,
J., Nagel, D. A., and Hight, T., "Knee Mechanics and Analytical
Modeling in Lower Limb Injuries," Proceedings of 2.sup.nd
International Conference on Ski Trauma and Ski Safety, Spain
(1977); Rastegar, J., Piziali, R. L., and Nagel, D. A.,
"Varus-Valgus Stiffness of the In-Vitro Human Knee," ASME Winter
Annual Meeting (1976); and Rastegar, J., Piziali, R. L., Seering,
W. P., and Nagel, D. A., "The Function of the Passive Knee
Structures in Anterior-Posterior Tibial Displacement," Proceedings
of 28.sup.th ACEMB (1975).
[0087] In the embodiment of FIG. 13, the walk-assist device 160 for
the ankle joint consists of the aforementioned leg cuff 132 and
foot worn part 131 (preferably shoe or boot, hereinafter referred
to as shoe 131) elements. A relatively flat element 161 is fixed to
the leg cuff 132. The element 161 is relatively thin but rigid in
bending in its own plane, i.e., in the plane of the illustration,
but is relatively flexible in bending out of the plane of the
illustration. Two elastic elements 162 and 163 are fixed to the
shoe 131 on one side (162a, 163a) and fixed to the element 161 on
the other side (162b, 163b) as shown in FIG. 13. Thus, as the leg
105 rotates clockwise relative to the foot, the two elastic
elements 162 and 163 are stretched, thereby generating a couple
(moment) about a center of rotation 164. One advantage of this
embodiment is that the two elastic elements 162 and 163 provide a
moment about the center of rotation 164 and generate minimal joint
forces. This embodiment may be modified by not fixing the element
161 to the leg cuff 132, but constraining it loosely within a
pocket (not shown) so that it is free to displace laterally within
a certain range of leg rotation relative to the foot and force
relative rotation of the element 161 relative to the foot in
another range of such rotation to obtain ankle joint moment M.sub.A
versus ankle joint angle .theta..sub.3 curves close to the curve
from point P6 to P9 shown in FIG. 8. This modification has also an
advantage of allowing the instantaneous center of rotation 164
(together with the element 161) to displace laterally to near the
actual instantaneous center of rotation since the elastic elements
162 and 163 have minimal resistance to lateral bending. Similarly,
since the element 161 and the elastic elements 162 and 163 have
minimal resistance to bending and torsion in and out of the plane
of illustration, the instantaneous axis of rotation (normally
perpendicular to the plane of illustration) can be tilted up and
down and/or to the right and left a small amount to closely follow
the actual instantaneous axis of ankle rotation. In addition, since
the center of rotation 164 is located central to the elastic
elements 162 and 163, the center of rotation 164 may be floated up
along the stem 165 of the element 161 or below the stem 165 while
minimally affecting the nearly pure couple nature of the forces
generated in the elastic elements 162 and 163.
[0088] In general, other coupling elements that allow relatively
free displacement of the axis of rotation of the ankle joint and
its slight tilting could be used together with preferably couple
producing elastic elements or torsional springs to provide the
aforementioned joint moment versus angular rotation. Such couplings
are well known in the art and are used regularly to couple shafts
such that they can tolerate relatively small offsets and angular
misalignment. Such couplings are, however, generally bulky and
occupy a considerable space, which is not desirable for the present
applications. Therefore embodiments such as the one shown in FIG.
13 are more appropriate and could be made as a compact device that
could readily be integrated into boots or as a lightweight bracing.
The best mechanism design for the aforementioned purpose is one
that operates such that the loads applied to the passive ankle
joint elements such as ligaments and the joint surface contacts are
minimally altered or reduced and not increased.
[0089] It should be noted that in the schematics of FIGS. 9 and 13,
only one lateral joint mechanism for energy storage and release is
shown. In general, however, the preferred embodiments use one such
mechanism on both sides of the ankle (and the knee) joint to
provide a more uniform and symmetric moment across the joint.
[0090] In the above embodiments, the portion of the ankle joint
moment M.sub.A versus ankle joint angle .theta..sub.3 curve from
point P6 to point P5 (P17) was neglected and the aforementioned
embodiments would produce the curves 150 or 155 without the segment
corresponding to the segment P6 to P5 (P17). If it is desired to
keep the segment P6 to P5 (P17) with same passive mechanisms, then
the mechanisms shown in FIGS. 9-13 and the others described above
must only produce the portion of the ankle joint moment M.sub.A
versus ankle joint angle .theta..sub.3 curve positioned to the
right of the vertical line 166, FIG. 8, to the point P9. For
example, the spring (elastic) elements that produce the 150 and 151
curves can still be used, but for the aforementioned range, i.e.,
from the vertical line 166 to the point P9. The corresponding
spring (elastic) elements must, however, be preloaded to the line
167, FIG. 8, using a number of methods known in the art, e.g., by
providing a stop to prevent a preloaded spring or elastic element
from moving back to its no-load configuration.
[0091] From FIG. 8, the amount of energy to that the muscles have
to spend to absorb the leg kinetic and or potential energy, i.e.,
approximately the area under the curve to the zero moment line from
the point P6 to P9 may be estimated by simply counting the number
of grid squares, in this case about 5.1 squares. From the units in
FIG. 8, it is readily seen that each square corresponds to 20 N-m
times 5 degrees or about 1.75 N-m or Joules of energy. The energy
that the muscles have to spend to add kinetic and or potential
energy to the leg system, i.e., approximately the area under the
curve to the zero moment line from the point P9 to P15 may be
similarly estimated to be 15 squares. Thus, the total energy that
the muscles have to provide about the ankle joint is about 20.1
squares, i.e., 20.1.times.1.75=35.175 J. With the aforementioned
embodiments using an elastic element with the spring rate 151, FIG.
8, 5.1 squares, i.e., 5.1.times.1.75=8.925 J of energy is stored in
the elastic element while walk-assist device is absorbing kinetic
and/or potential energy from the leg system (from the point P5 to
P9, FIG. 8) and would provide it back to the leg system during the
portion of the stride that kinetic and/or potential energy has to
be increased (from the point P9 to P15, FIG. 8). Thus, up to
2.times.8.935=17.85 J out of the above 35.175 J, or up to 50.7
percent of energy spent by the muscles forces at the ankle joints
could be saved by using the disclosed walk-assist devices. In
practice, however, due to friction losses and other inefficiencies,
the actual energy savings should be expected to be lower, but as
can be seen, is significant nonetheless.
[0092] In addition, as shown below, the total savings in the energy
spent by the muscles acting at the ankle joints can be
significantly increased by providing a walk-assist device that
operates as a total leg system on all the joints of the lower
extremity. For the case of the ankle joint, such a device would
store energy that has to be absorbed by the muscles acting at the
other joints of the leg and transfer the energy to the ankle joints
during the ankle joint rotation from the point P9 to P15, FIG.
8.
[0093] With passive elastic (spring) elements, whether with linear
or non-linear load (force, moment, torque, etc.) versus
displacement (linear displacement, bending displacement, rotation,
etc.) characteristics, hereinafter referred to as simply the
load-displacement characteristics, it is impossible to obtain
complex rate characteristics that are required to follow the type
characteristics shown for the ankle joint in FIG. 8. As can be seen
in FIG. 8, during the stride, the ankle joint moment versus ankle
joint rotation curve starts from the point P5; becomes slightly
positive as the angle is reduced, then comes back to zero at the
point P6; then reverses its slope providing increasing levels of
moment (negative in sign) with increasing angle .theta..sub.3 up to
around the point P9; then as the ankle joint angle decreased, it
follows the branch from the point P9 through P10-P14, ending up at
the point P15, this time at higher (more negative) moment levels
for corresponding angles (within the range of P5 to P9); the ankle
joint is then returned to the starting point P5 (indicated also as
P17 in FIG. 8), at near zero moment levels following the line from
the point P15 through P16 to the point P17.
[0094] Another characteristic of the load-displacement
characteristics of the type shown for the ankle joint in FIG. 8
(similar types of load-displacement characteristics during gate are
found at the knee and the hip joints) is that the total amount of
the energy that is absorbed by the muscles (effectively the area
under the curve from the point P6 to the point P9 and the zero
moment line) is not the same as the amount of the energy that the
muscles have to provide to increase the kinetic and/or potential
energy of the system (effectively the area under the curve from the
point P9 to the point P15 and the zero moment line). In this case,
more energy is provided by the muscles through the ankle joint then
is absorbed. As a result, to provide part or all the extra needed
energy from the energy stored from walk-assist device components
mounted on the other joints of the body such as the knee and the
hip joints, the ankle joint device must be coupled (preferably)
mechanically to the devices at those joints. Such coupling is
possible but is very difficult to accomplish without the use of any
active elements. Here, by active elements it is meant powered
elements, such as those that are powered electrically,
pneumatically or by fluid power and without regards to the source
of power, whether internally or externally generated. The use of
purely passive elements for this task is made more difficult
considering the fact that the subject wearing the walk-assist
device may use various gate patterns, therefore requiring the
parameters of the walk-assist device to be capable of adapting to
varying gate patterns.
[0095] It must, however, be noted that with pure passive elements,
as it was shown above for the case of the ankle joint, walk-assist
devices can still significantly reduce the amount of energy that
the muscles have to provide during locomotion. However, to increase
their efficiency even more and to expand the application of such
devices to several other fields as described below, some or all the
aforementioned shortcomings of purely passive constructions can be
overcome. In the following, a number of embodiments that use very
simple and low power active elements are disclosed that can be used
to construct walk-assist devices without the aforementioned
shortcomings.
[0096] The basic active element of the aforementioned embodiments
is a braking (or locking) element. Such braking elements are used
to stop linear or rotary motions of relatively rigid parts, and for
this reason may be more appropriate to call them locking elements.
Such braking elements may in certain case also act as a clutch. In
the present disclosure these elements are generally referred to as
braking elements. The main purpose of using such brake elements is
to at times "lock" an extended (compressed) spring in place,
thereby preventing it from applying a pulling (pushing) force
(similarly for torsional or other types of springs) to the
components that the spring is attached to; or at times lock two or
more relatively rigid parts together, thereby preventing their
relative motion; or at times unlock the aforementioned extended
(compressed) spring, allowing it to exert pulling (pushing) force
to the components that the spring is attached to; or at times
unlock and allow the relative motion of aforementioned two or more
relatively rigid parts. The aforementioned relative motions may be
translational or rotational or may be a combination of the two.
[0097] In FIG. 14, two relatively rigid links 170 and 171 are shown
attached by a rotary joint 172. The two links are free to rotate
relative to each other, thereby varying the angle 173. By
positioning a braking element (not shown) at the joint 172, the
links 170 and 171 can be locked together, thereby forming a
relatively rigid structure at any desired angle 173.
[0098] In the schematic of FIG. 15, the two links 170 and 171 shown
in FIG. 14 are shown with an added elastic (spring) element 174.
The aforementioned braking element (not shown) is still considered
to be present at or about the joint 172. At any point in time and
while the elastic element 174 is in tension or compression, if the
braking element locks the joint 172, i.e., prevents the relative
motion between the two links 170 and 171, then the two links 170
and 171 would form a structure and the potential energy stored in
the elastic element 174 becomes an internal energy to the resulting
structure, and potential energy could no longer be transferred to
the spring element through the links or from the spring element to
the links.
[0099] It is appreciated by those skilled in the art that even
though in the embodiment of FIG. 15 a helical spring 174 is shown
with the rotary joint 172, similar braking elements may be used to
lock and later release relative motion between two or more elements
joined with other types of joints and with more than one
degree-of-freedom (which is the case for the rotary joint 172), and
lock in and later release potential energy stored in any type of
elastic element, even those provided by the flexibility of the
structure of the related devices. For example, a sliding, planar,
cylindrical or spherical joint may have been used instead of the
rotary joint 172; or torsional, bending type or elastomeric
elements may have been used in place of the helical spring 174.
[0100] The braking aforementioned element may be of any type known
in the art, such as a magnetic or brake shoe type operated
electrically, pneumatically or hydraulically that locks either the
two links together or directly locks the joint 172. Such braking
devices usually rely on friction-generated force (moment or torque)
to provide the aforementioned braking (locking) force (moment or
torque). A typical such braking element is shown in the schematics
of FIGS. 16 and 17. A sliding joint that allows their relative
displacement in the direction 186 connects the two relatively rigid
components 180 and 181 as shown in FIG. 16. A cross-section of the
sliding joint is shown in FIG. 17. The inner component 181 is seen
to be free to move relative to the outer component 180 in the axial
direction, i.e., in the direction indicated by Arrow 186 (the
clearance between the two components is exaggerated for the sake of
clarity). The inner component 181 is provided with a recess with
sides 187 to allow for the mounting of at least one braking
element. The braking element consists of at least one braking pad
183 and a displacement actuator 184, which imparts back and forth
motion to the braking pad 183. The actuation device may be
electrically operated such as like a solenoid, or may be
pneumatically or hydraulically operated, or operated by a
piezoelectric actuation device, or any other type of actuation
device known in the art. To lock the sliding joint, the actuator
184 is activated and used to press the braking pad 183 against the
surface 185 of the inner component 181. As a result, the sliding
motion of the inner component 181 relative to the outer component
180 is no longer possible. The amount of force applied by the
actuator 184 and the friction coefficient between the braking pad
183 and the surface 185 of the inner component 181 determines how
much axial force in the direction 186 this braking element(s) can
resist before slippage. Such braking elements can therefore provide
a limit on the amount of force (moment or torque) that the joint
must resist before allowing slippage. This characteristic of these
embodiments may be used, for example, to limit the amount of
potential energy to be stored in elastic elements or the maximum
force (moment or torque) that a locked joint should resist.
[0101] The aforementioned braking elements may be normally open,
i.e., apply no braking force without an input actuator force
(moment or torque), or may be normally closed, i.e., the applied
force (moment or torque) is used to disengage the braking element.
In general, either type of braking element may be used in the
walk-assist devices. However, it is preferable that appropriate
types be used so that in the case of loss of actuation power, the
walk-assist device does not hinder walking (running) in any way or
provide a destabilizing joint force, or increase the probability of
injury or become unsafe.
[0102] Other embodiments of braking elements that are particularly
suitable for the disclosed walk-assist devices are described
below.
[0103] Using an appropriate number of the aforementioned braking
elements and elastic elements with linear and/or non-linear spring
rates and together with relatively rigid links and joints,
assemblies with load-displacement characteristics that approximate
that of almost any of the lower extremity joints, such as that of
the ankle joint shown in FIG. 7, may be obtained. The braking
elements, elastic elements and links may be configured in parallel
and/or in series. Here, the load is intended to also mean moment or
torque, and displacement is intended to also mean angular
displacement.
[0104] As an example, consider the schematic of the simple linkage
mechanism 200 shown in FIG. 18. The mechanism consists of
relatively rigid links 190, 191 and 193. The links 191 and 192 and
the links 192 and 193 are connected by sliding joints (not shown)
that allow each pair of links to undergo a sliding motion in the
direction of Arrow 198. The link 190 at its end 193 and the link
192 at its end 194 are attached to two objects that can undergo
relative motion. For example, the mechanism 200 may replace the
spring element 174 in FIG. 15 (in this application, the mechanism
200 has to be attached to the links 170 and 171 by rotary joints)
to provide a combination of free rotation, rigid constraint or
spring element between the links 170 and 171. The mechanism 200
provides such flexibility as follows.
[0105] Braking elements 196 and 197 similar to those described
above are provided between the links 190 and 191 and the links 191
and 192, respectively. When activated, the brake element 196 (197)
locks the two links 190 and 191 (191 and 192) together, thereby
preventing their relative displacement. In this configuration, the
links 190 and 191 (191 and 192) form a relatively rigid structure.
When the brake element 196 (197) is deactivated, the links 190 and
191 (191 and 192) are free to undergo relative sliding motion in
direction 198. For the case of the pair of links 190 and 191, the
two links are connected by the spring element 195, which when the
braking element is deactivated, would provide a force resisting the
relative displacement of the two links, and could be used to store
potential energy or to extract the stored potential energy at the
desired range of motion, and in other ranges of motion to either
make the mechanism 200 act as a structure or allow free motion
between the connected objects in the direction of mechanism 200
displacement. It is noted that in the mechanism 200, once the
spring element 195 is deformed (in tension or in compression), a
corresponding amount of potential energy is stored in the elastic
element. All or part of this potential energy may, however, be
released by disengaging the brake elements 196 and 197, and thereby
allowing the link 191 to displace, in which case an energy
dissipative element such as a friction pad or a viscous or
viscoelastic damping element is preferably used to attach either or
both of the link pairs 190 and 191 and/or 191 and 192 in order to
minimize vibration of the released link 191.
[0106] In a modification of this embodiment, a second spring
element (not shown), preferably with a spring rate different from
that of spring element 195, is used to attach the links 191 and
192. As a result, by sequentially locking each spring element, the
mechanism 200 is used to provide an effective spring with three
possible spring rates The first spring rate (the spring rate of the
spring element 195) is obtained by the activation of the brake
element 197 and deactivation of the braking element 196. The second
spring rate (the spring rate of the aforementioned spring attached
to the links 191 and 192) is obtained by the activation of the
brake element 196 and deactivation of the brake element 197. The
third spring rate (the spring rate being equal to the inverse of
the sum of the inverses of the above two spring rates) is obtained
by the deactivation of both of the brake elements 196 and 197.
[0107] For the sake of simplicity, the links 190 and 191 and the
spring 195 and brake element 196 of the mechanism 200, FIG. 18 and
also redrawn in FIG. 19a, are shown in the simple diagram of FIG.
19b and marked as the assembly 210. Similarly, the links 191 and
192 and the brake element 197 are shown as the schematic of FIG.
19c and marked as the assembly 211. Two or more elements 210 and
211 may then be connected in series, in parallel or their
combination to obtain almost any desired force (moment or torque)
versus displacement (rotation) characteristics, such as the one
shown in FIG. 7.
[0108] For example, consider the schematic of FIG. 20a showing
three elements 210 (indicated as 210a, 210b and 210c) being
connected in series to obtain the assembly 220. In FIG. 20a, the
displacements .DELTA.x.sub.1, .DELTA.x.sub.2 and .DELTA.x.sub.3 are
associated with the elements 210a, 210b and 210c, respectively. Let
all three springs elements 195a, 195b, 195c of the elements 210
have a spring rate k. If the three brake elements 196a, 196b, 196c
are activated, then the assembly acts as a structure. However, if
all the three brake elements are deactivated, the effective spring
rate K.sub.e is then given by 1/K.sub.e=3/k or K.sub.e=k/3 (4)
[0109] Now consider the situation in which the three springs
elements 195a, 195b, 195c are at their undeformed lengths. One end
of the assembly 220 is fixed to the ground 201 and the end 207 is
pulled by applying a force F in the indicated direction. Initially,
all the three brake elements 196a, 196b, 196c are considered to be
deactivated, while the end 207 is displaced an amount X (from the
point 202 to 203) as shown in the plot of FIG. 21. During this
period, the equivalent spring rate has the lowest value as given
above, i.e., K.sub.e=k/3, and the force-displacement plot is linear
(all three springs are considered to have constant spring rates k)
as shown in the plot of FIG. 21. From the point 203 to the point
204, one of the three brake elements is activated, thereby
increasing the equivalent spring rate to k/2. From the point 204 to
205, two of the brake elements are activated, thereby increasing
the equivalent spring rate further to k. The force-displacement
plots for the latter two ranges of motion are also shown in the
plot of FIG. 21. As can be seen, the assembly of three elements 210
allows the user to approximate a curve of arbitrary shape.
Obviously, by using more elements 210 and also adding elements, and
utilizing both serial (FIG. 20a) and parallel (FIG. 20b)
configurations, almost any force (moment or torque) versus
displacement (rotation) curve could be achieved.
[0110] It will be appreciated by those skilled in the art that for
proper sequence of brake element activation and deactivation,
sensory devices can be employed to measure the relative
displacement of the joint (the connected objects). In addition,
since the walk-assist devices, for example the aforementioned one
attached to the ankle joint, must undergo more than one back and
forth motion during each cycle of stride (see FIG. 7), and as a
result, at one ankle joint angle several instantaneous spring rates
and instantaneous joint moments have to be present, therefore a
control unit, preferably based on a programmable microprocessor, is
needed to provide the proper sequence of brake element activation
and deactivation (and potential energy release if required).
[0111] It is also noted that in most cases, at the end of each
stride cycle, a balance of potential energy may be present in one
or more of the spring elements of the walk-assist device. This was
not the case for the aforementioned isolated walk-assist device
used on a subject ankle since the amount of energy absorbed by the
leg muscles acting on the ankle joint was shown to be smaller than
the amount of energy that the leg muscles have to provide to
increase the potential and/or kinetic energy of the leg. Since some
of the joints are like the former and some like the latter, a whole
leg or body mounted walk-assist device needs to link the joints,
preferably by passive mechanisms or at most by mechanisms equipped
with brake (clutch) elements, and utilize a control system
(preferably operated by a programmable microprocessor) to
sequentially activate and deactivate the brake (clutch) elements to
tend to balance the aforementioned energy requirements at each
joint.
[0112] In addition, a walk-assist device that is equipped with a
microprocessor control can use sensory information from the joint
angles (such as potentiometer or optical encoder type of sensors)
to optimally time the aforementioned sequence of activation and
deactivation of the brake and clutch elements as, for example, the
subject changes the pace of walking, or is walking on an inclined
(up or down) surface, etc. In another embodiment, at least one
accelerometer (e.g., a MEMS based tri-axial type accelerometer) is
also used (mounted on the subject body, such as on the waist
together with the programmable control unit) to further tune the
aforementioned operation of the walk-assist device. The operation
of the walk-assist device can be improved further by providing at
least one gyro (such as a MEMS type) to measure changes in the body
angle and use it in the determination of the optimal timing of the
activation and deactivation of the brake elements.
[0113] In one embodiment of this invention, the programmable
microprocessor is used for the aforementioned purpose of timing
brake element activation and deactivation to achieve proper force
(moment or torque) versus displacement (rotation) characteristics
for proper operation of the walk-assist device as described above.
The brake element activation and deactivation timing is based on
one or more of the aforementioned joint angle and/or body
acceleration sensory information.
[0114] In another embodiment, the programmable microprocessor is
used for the aforementioned purpose as well as for adapting to the
variations in the walking pattern, walking up and down stairs,
walking up or down an inclined surface, etc.
[0115] In another embodiment, the programmable microprocessor is
used for one or both of the aforementioned purposes as well as
allowing the user to adjust the control parameters and the brake
element activation and deactivation sequencing to increase or
decrease the effectiveness of the walk-assist device in reducing
the amount of work that is done by the muscles during walking or
running in order to allow the muscles to get certain amount of
exercise.
[0116] The role of the aforementioned programmable microprocessor
and the control unit in other embodiments is described below.
[0117] In an alternative embodiment, manual or automatic gearing
and/or cam mechanisms, similar to a gear on a bicycle, is used
instead of programmable microprocessor based control unit to adjust
the pattern and level of forces (moments and torque) generated by
the passive elements so as to provide the desired level of assist
and match it to the changing pattern of walking or running, such as
moving up or down a sloped surface or stairs.
[0118] In FIGS. 19b and 19c, the elements 210 and 211 are shown to
have a finite, even though preferably small, size. However, the
elements 2 1 0 and 211 are preferably very small and a relatively
large number of them used in the construction of walk-assist
devices, and as such act as quasi-distributed brake and clutch
systems. Such quasi-distributed brake and clutch systems could be
constructed using active materials such as piezoelectric films and
fibers and magnetorheological fluids.
[0119] In the above embodiments, power activated brake elements
such as the element 197 is used to engage or disengage the
walk-assist device by isolating the spring elements of the system
such as shown in FIG. 20b. In FIG. 20b, 191 and 192 are the
aforementioned components that are connected to the walk-assist
device to allow deformation of the spring element 195 during its
operation. By positioning the brake element 197 in series with the
spring element 195, the spring element 195 can be isolated by
deactivating (disengaging) the brake element 197.
[0120] In the embodiment shown in FIG. 20b, however, a power
operated engagement/disengagement clutch is used for the
aforementioned purpose instead of brake element 197, partly to
minimize electrical power consumption. In general, whenever
possible, engagement/disengagement clutches are preferable to
braking elements. However, when smooth transition from the engaged
to the disengaged states is desired, brake elements are preferable
since the applied braking force can be regulated. In addition,
braking elements can also be used to limit the transmitted force
unlike clutches with positive engagement/disengagement
mechanisms.
[0121] In the embodiment shown in FIG. 20b, the brake element is
replaced with a manually operated engagement/disengagement clutch,
which are well known in the art. This is particularly suitable for
walk-assist devices with partly or wholly passive elements.
[0122] In the above embodiments, spring elements are directly and
without intermediate mechanisms to store mechanical energy to be
absorbed by the walk-assist device and return it in the same manner
to the leg system. The mechanical energy may, however, be directed
to the spring element via a certain mechanism, such as a ratchet
type of mechanism for the purpose of storing energy during several
cycles of gate and releasing it at a desired portion of the stride,
or once a desired level of potential energy is stored in the
spring, or as programmed in the microprocessor control unit. The
higher levels of potential energy may be required to increase the
efficiency of the device receiving the released potential energy,
such as the efficiency of a boot integrated cooling device.
[0123] In this section of the disclosure, the present method and
related devices are described as applied to one joint of the lower
extremity, across two or more joints, or across all the joints of
the lower extremity. It is readily seen by those skilled in the art
that the proposed walk-assist devices can be designed to cover both
lower extremity and interconnected to provide added stance
stability and transfer energy from one leg to the other to further
reduce the "locomotion energy" and the "stance energy". Such
walk-assist devices can be equipped with the aforementioned active
elements and their operation is controlled by programmable
microprocessors.
Methods and Devices to Generate Electrical Energy While Reducing
Fatigue
[0124] Various devices have been made to allow a human to generate
useful electrical power. The most common such device is the bicycle
dynamo that is brought into contact with the tire to generate
electrical energy to power lights and certain other electrical and
electronic devices. Dynamos rotated by hands through a handle have
been used for various purposes including for powering fielded
communication devices. In recent years, attempt has also been made
to generate electrical energy during walking, for example by
incorporating piezoelectric elements directly or through other
mechanical devices in the sole of the shoes to utilize pressure
exerted by the weight of the subject to deform an elastic element
or pressurize certain fluid and use the stored potential and/or
kinetic energy to generate electrical energy.
[0125] However, in all the methods considered to date for
generating electrical energy by a human subject, the subject has to
spend energy to produce the mechanical energy that is used by the
energy conversion device or system. As a result, the subject
becomes tired, particularly if power has to be generated over a
considerable amount of time. In addition, due to the inherent
inefficiency of all energy conversion systems, the subject has to
spend a significantly higher amount of energy than is produced by
the energy conversion system. This is the primary reason why such
power generation methods and developed devices have not found
widespread usage, except for extremely low power levels such as
very low power implanted sensors and devices, and for emergency
situations.
[0126] In this disclosure, methods are presented for generating
electrical power by a human subject while participating in a
variety of activities such as walking or running. The primary
difference between the disclosed methods and all other currently
available methods is that with the methods disclosed herein, a
subject can generate electrical power while walking or running,
while at the same time reducing his/her fatigue by reducing the
aforementioned "locomotion energy". In other words, a subject using
a power generating device based on the disclosed methods can
generate electrical energy while walking or running, while at the
same time saving energy, i.e., getting less tired than he/she would
have become if he/she were not wearing the device.
[0127] The electrical energy generating devices constructed based
on the disclosed method can be attached to one or more of the
joints of the lower extremities. These devices would preferably be
similar to low profile braces worn on the knee, ankle or the hip
joints. The size of each device is related to the amount of
available mechanical energy at the joint and the amount of
electrical power that needs to be produced. For example, for low
power requirements, the device may closely resemble an elastic
joint support, that is worn under the garment. The preferable
joints for such devices are the knee joint for low power
requirements and the ankle joint for higher power requirements.
This is generally the case since for the knee joint, the device
could be built as a knee pad, and for the ankle joint, the device
could be built into a boot (or shoe). For maximum electrical power
generation, the aforementioned walk-assist mechanisms that
interconnect all the lower extremity joints can be used. The
mechanical to electrical energy conversion may utilize
piezoelectric polymers or fibers, coil and magnet, or any other
similar energy conversion components.
[0128] In the following segment of this disclosure, the present
methods are described by their application to an electrical energy
generation device for a human ankle joint, which allows the user to
generate electrical energy during walking while at the same time
getting less tired. However, the method is general, and can be used
similarly to construct devices for other joints, such as the knee
or hip joints or to be used with the aforementioned walk-assist
devices that interconnect all the lower extremity joints. The
method also applies to other periodic linear and/or rotational
motion of other segments of the body during walking or running. For
such periodic linear and/or rotational motions, devices that
operate in a manner similar to those for the lower extremity joints
can be constructed to generate electrical energy while reducing the
amount of mechanical energy that the related muscles have to
provide.
[0129] For the ankle joint, the plots of FIGS. 4, 7 and 8 were
shown to indicate that the muscles acting at the ankle joint have
to do work to absorb potential and/or kinetic energy of the leg in
the range A to B, FIGS. 4 and 7, corresponding to the range P6 to
P9 along Arrow 120 in FIG. 8, of the stride. The muscles acting at
the ankle joint also work to increase the potential and/or kinetic
energy of the leg in the range B to C, FIG. 4, corresponding to the
range P9 to P15, FIG. 8, of the stride. It was shown that the area
under the joint angle versus joint moment curve from point P6 to
point P9 and the zero moment (M.sub.A) line is the aforementioned
work (referred to as W.sub.ab) that the leg muscles have to do to
absorb the kinetic and/or potential energy of the leg during the
corresponding portion of the stride. The area under the above curve
from point P9 to point P15 and the zero moment (M.sub.A) line is
the aforementioned work (referred to as W.sub.add) that the leg
muscles have to do to add kinetic and/or potential energy to the
leg system during the corresponding portion of the stride.
[0130] Similar intervals were also shown for the knee joint in FIG.
2d. As can be seen in FIG. 2d, there are three intervals, labeled
as N1, N2, N3 and N4, within which the input power is negative.
During these intervals, the leg muscles, as a whole, are absorbing
energy and the knee torque (moment), FIG. 2c, and angular velocity,
FIG. 2b, are in opposing directions.
[0131] The net mechanical work done by the muscles acting on the
knee joint to absorb the energy during each of the N1, N2 and N3
intervals is determined by equation (2) for the time interval
t.sub.1 to t.sub.2, t.sub.3 to t.sub.4 and t.sub.5 to t.sub.6,
respectively, and are given in Table 1. The internal N4 relatively
small and is not included in Table 1. As can be seen in Table 1,
the right leg muscles absorb a total of approximately 250 mJ of
energy during each stride. The amount of energy absorbed by the leg
muscles acting on the ankle joint can be similarly determined.
TABLE-US-00001 TABLE 1 Work Done to Absorb Power at the Knee
Interval Time interval Work (mJ) N1 t.sub.1-t.sub.2 55.4 N2
t.sub.3-t.sub.4 85.1 N3 t.sub.5-t.sub.6 110
[0132] From the data presented in Table 1, the walking subject is
seen to need to spend 250 mJ of energy in the time interval t.sub.1
to t.sub.2, t.sub.3 to t.sub.4 and t.sub.5 to t.sub.6 by the
muscles acting on the knee joint to sustain gate. This energy is
spent for the purpose of absorbing kinetic and potential energy of
the leg. The electrical energy generation method being disclosed is
based on providing external means to absorb this energy rather than
requiring the subject to spend energy via the leg muscles.
[0133] In one embodiment, such an external device is attached to
the leg at the knee joint, and transforms the aforementioned
mechanical energy into electrical energy using an appropriate
mechanical to electrical energy conversion system such as a magnet
and coil or an appropriate piezoelectric based mechanism.
[0134] In a similar manner, the kinetic and/or energy to be
absorbed by the muscles acting at the ankle joint during the
portion of the stride from point A to point B, FIG. 4
(corresponding to the range P6 to P9 along the arrow 120 in FIG.
8), can be transformed into electrical energy using a similar
external electrical power generating device.
[0135] When the energy to be absorbed by the leg muscles is
absorbed by an external means such as the disclosed electrical
power generating system, the walking subject has to spend less
energy and is thereby less fatigued during walking.
[0136] In general, one may not want to convert all the available
mechanical energy to electrical energy. The remaining mechanical
energy is then stored in the aforementioned "locomotion energy"
reducing devices to reduce the required locomotion energy as
previously described. Thus, the methods and devices disclosed here
can reduce fatigue as wells as generate electrical energy. This is
particularly useful in light of the fact that the amount of
electrical energy that is generally needed by handheld electronics
devices is much less than the total mechanical energy to be
absorbed by the leg muscles during walking. Therefore in most
situations, only a portion of the aforementioned mechanical energy
needs to be converted to electrical energy. Secondly, partial
conversion of the available mechanical energy to electrical energy
can be achieved using a very simple conversion system as described
below. Lastly, the unused portion of the available mechanical
energy is not wasted but used to reduce the locomotion energy as
was previously described.
[0137] It is noted that walk-assist devices may be constructed with
only the energy absorbing components. Such devices would only
reduce or eliminate the need for the muscles to work to absorb the
aforementioned kinetic and/or potential energy of the leg during
walking and running. In other words, such walk-assist devices,
unlike the aforementioned "locomotion energy" reducing walk-assist
devices, do not store and return the absorbed mechanical energy to
the limbs. The absorbed energy is, however, available for other
uses, e.g., for generating electrical energy as previously
described. For this reason, hereinafter, this method of
constructing walk-assist devices is referred to as the "energy
dissipative" method. A number of embodiments of such walk-assist
devices are provided below.
[0138] In one embodiment of such a device, the mechanical
energy-absorbing element is an electrical energy generator.
[0139] In another embodiment of such a device, the mechanical
energy-absorbing element transforms the mechanical energy into heat
using, for example, a braking device.
[0140] In yet another embodiment of such a device, the mechanical
energy-absorbing element transforms the mechanical energy into
another form of mechanical energy such as potential energy of a
pressurized fluid or kinetic energy of a flywheel. The pressurized
fluid may then be used to run a micro-turbine to generate
electrical energy or the like. The kinetic energy stored in the
flywheel may also be used for similar purposes.
[0141] In yet another embodiment of such a device, the mechanical
energy-absorbing element transfers the energy directly to another
energy consuming system such as a personal cooling system. In one
embodiment, the entire system is integrated into the subject's
boots. In another embodiment, the head, and/or the upper body are
cooled with the disclosed system. When the source of cooling is
positioned relatively far from the intended cooling region, for
example if the cooling system is integrated into the boots and the
head is intended to be cooled, then it may be more efficient to
convert the mechanical energy first to electrical energy and then
use electrical energy to cool the head using solid state cooling or
the like. In yet another embodiment, drinking fluid or food is
cooled by the system.
[0142] In yet another embodiment of such a device, the mechanical
energy-absorbing element transfers the energy directly to another
energy consuming system such as a personal heating system,
particularly for warming the most vulnerable limbs such as feet and
toes, hands, etc.
[0143] In yet another embodiment of such a device, the mechanical
energy-absorbing element is a combination of two or more of the
aforementioned elements. In one embodiment of such a device, a
control (switching) unit is provided to either regulate the amount
of energy transferred to each element, e.g., to keep the body at
certain temperature. The control unit is preferably operated by a
programmable microprocessor.
[0144] The above embodiments provide walk-assist devices that
besides providing the intended benefits, for example heating or
cooling the body, they would also reduce the user fatigue by
reducing the amount of muscle work that the user has to
perform.
[0145] Similar to the aforementioned embodiments for power
generation, one may not want to transfer all the available
mechanical energy to the above elements (brake, cooling, heating,
etc. elements). In which case, the remaining mechanical energy is
then stored in the aforementioned "locomotion energy" reducing
devices and used to reduce the required locomotion energy as
previously described.
[0146] The aforementioned power generating walk-assist embodiments
is described first for a walk-assist device mounted at the ankle
joint similar to that of FIG. 9. The links 133 and 134 are still
joined by the rotary joint 135 and are fixed to the leg cuff 132
and the foot piece (shoe) 131, respectively. In FIG. 22, the links
133 and 134 are shown alone. The links 133 and 134 are provided by
structural means for attaching the power generating elements, in
this case by stems 220 and 221, respectively. In an embodiment, an
elastic element 223 (band, strip, spring, etc.) is used to connect
the stems 220 and 221. At some point along the element 223, an
electric power-generating device 224, the operation of which is
described later in this disclosure, is mounted. The characteristics
of the elastic element 223 and its free length are selected
according to the aforementioned procedure described for the
"locomotion energy" reducing walk-assist devices. The length of the
elastic element allows it to become loose (no tension) at the link
133 position 222 and onward as the link 133 is rotated clockwise,
thereby providing no resistance to the ankle joint rotation (this
range starts from around the point P6 to P5, continuing to point
P15, as shown in FIG. 8). However, starting from the point P6, the
elastic element 223 becomes taut (shown in broken line), and as the
link 133 is rotated counterclockwise, the elastic element provides
a moment about the ankle joint, which would in the best possible
situation, follow the ankle joint angle versus moment curve shown
in FIG. 8 from the point P6 all the way or part of the way to the
point P9 in the direction 122.
[0147] In one embodiment of this invention, the power-generating
element 224 is constructed using piezoelectric materials. One such
piezoelectric material based power-generating element 224
(hereinafter, referred to as the piezo generator) is shown in the
schematics of FIGS. 23a and 23b. In FIG. 23a, the piezo generator
224 is attached to the elastic element 223 with a parallel
configuration by the attachment means 225, which can be made out of
the same elastic material as elastic element 223. In FIG. 23b, the
piezo generator 224 is attached in series to the elastic element
223. In general, the effective spring rate of the piezo generator
224 is desired to be close to that of the elastic element 223 to
maximize the amount of mechanical energy to be converted to
electrical energy by the piezo generator 224. It is noted that by
applying tensile or compressive stress to a piezoelectric element,
a charge is generated that could then be harvested by well known
electronics circuits and stored in capacitors or used to charge
rechargeable batteries. During each cycle of stride, the mechanical
energy that is not converted to electrical energy is returned to
the leg system to reduce the work of the muscles while they need to
increase the kinetic and/or potential energy of the leg system.
[0148] The piezo generator may be a stacked type; a thin film type
with a flexible backing; fiber type, particularly of the type that
are formed to significantly increase allowable elongation; made as
a stack 230 of bending beams as shown in FIG. 24a, with each beam
covered by a sheet of piezoelectric material; or any other numerous
configurations that are known in the art. In general, the
piezoelectric elements must be prevented from being subjected to a
considerable amount of tensile force since they are fairly brittle
and could easily be fractured. This can be done by the design of
the piezo generator or by preloading said elements in compression
to a level that with the applied tensile force the element still
remains under compressive loading.
[0149] The piezo generator embodiment 230 shown schematically in
FIG. 24a is designed to subject piezoelectric elements (preferably
in thin strips) to compressive loading achieved through bending.
Each piezo generator 230 is constructed with basic bending elements
236 and 237 shown in FIGS. 24b and 24c, respectively. Each element
236 and 237 consists of a relatively long bending beam 231, over
which a strip of piezoelectric material is bonded using preferably
a thin layer of relatively stiff epoxy or other similar bonding
agent. In one embodiment, the bonding material is conducting and
forms one of the electrodes of the piezoelectric strip element as
described below. Each of the beam elements 231 are provided with
steps 233 that extend above the surface of the piezoelectric strips
232. The difference between the two bending elements 236 and 237 is
the position of the step, for the element 236 the step 233 is on
the left side and for the element 237 the step 233 is on the right
side, FIGS. 24b and 24c, respectively. The two elements 236 and 237
are preferably symmetrical so that one would only need to be
rotated to form the other. The elements 236 and 237 are then
stacked, one on the top of the other, to form the basic assembly of
the piezo generator 230, FIG. 24a. The stacks are attached by
attaching one step 233 to the appropriate surface of the other beam
as shown in FIG. 24a. The steps may be attached to the beams by
fasteners, adhesive bonding, or any other available method known in
the art. In one embodiment, the step and the beam are attached by
sliding one into a provided guide (e.g., a dove tail or square
shaped type- not shown in FIGS. 24a-24c), which are preferably
locked by an appropriate bonding material such as epoxy. In another
embodiment, the beams and steps are constructed from a single strip
of beam material, preferably aluminum. The piezoelectric strips 232
are first bonded at appropriate positions and then bended into the
form of the piezo generator 230. The steps 233 may also be
eliminated to simplify the parts and the bending process. However,
noting that one of the functions of the steps in 230 is to make the
ends of the deflecting beams more rigid, thereby maximizing the
amount of the bending of the beams in areas that are covered by the
piezoelectric strips. This function may, however, be provided in
the case of a strip of beam material with uniform thickness
(without the step 233), for example, by making the bent areas
wider, thereby stiffer.
[0150] During walking, as the elastic element 223, FIG. 22, is
stretched, the piezo generator is stretched, and a pair of forces
235 are applied to the piezo generator 230, subjecting the beams
231 to bending, thereby subjecting the outer layer of the beam,
i.e., the piezoelectric strip to compressive stress. The
piezoelectric strips would thereby produce a voltage and charge,
which can then be harvested as described below. The schematic of
the piezo generator under the applied pair of tensile forces 235
(provided by the elastic elements 223, 225) is shown in FIG. 25. In
general, the piezoelectric strip is preferably preloaded in
compression to avoid subjecting it to tensile forces. To make the
attachment of the piezo generator to the elastic elements 223 or
225 or any other element, relatively rigid end pieces 234 can be
provided.
[0151] Under the applied pair of tensile forces 235, the beam
elements 231 bend as shown in FIG. 25, thereby allowing the total
length of the piezo generator 230 to increase. The total amount of
work done by the force 235 over the elongation of the piezo
generator length is equal to the maximum amount of energy that is
ideally available to be harvested. However, a considerable portion
of the available mechanical energy is stored in the beam elements
and other structural elements of the piezo generator 230 and the
piezoelectric strips as strain energy, and is not available as
electrical charge for harvesting as electrical energy. For the case
of the beams and connecting structures of the piezo generator 230,
the aforementioned strain is due to the deformation pattern of the
whole structure as a spring. The piezoelectric strips, as deformed,
act as part of the structure of the piezo generator 230 to resist
the applied load. The deformation of the piezo generators would
also induce internal charges that tend to increase the resistance
of the piezoelectric strips to the aforementioned deformation,
thereby making them effectively stiffer. The amount of work that
the applied forces 235 have performed to overcome the
aforementioned internal resistance of the piezoelectric strips is
the amount of energy available for harvesting. In general, the rule
of thumb is that when an external force deforms a piezoelectric
element, about one-third of the work done by the external forces is
stored as electric potential in the piezoelectric element, i.e.,
about one-third of the input mechanical energy could be harvested
as electrical energy. Using the same rule of thumb, during each
cycle of stride, less than one-third of available mechanical energy
stored in the piezo generator 230 is available for conversion into
electrical energy. It can therefore be observed that in the ideal
situation, the beam and connecting structures of the piezo
generator 230 are desired to provide minimal resistance to
deformation as a result of the applied forces 235, thereby
transferring maximum mechanical energy to the piezoelectric
elements.
[0152] The agent bonding the piezoelectric strips 232 to the beams
231 is preferably very thin and has stiffness similar to that of
the beam 231 and has low damping so that the strain on the beam
surface is efficiently transmitted to the piezoelectric strip 232.
The piezoelectric strip is preferably poled such that as a result
of compressive stress along the length of the strip, charge is
produced on the two surfaces of the strip, where the conducting
electrodes are positioned. In one embodiment, the bonding agent is
conductive, and thereby makes the beam structure as the conducting
medium connecting one of the electrodes of a bank of piezoelectric
strip elements together in parallel, this method of wiring such
electrical power generators provide relatively high voltage output.
Conductive bonding agents such as epoxy are commonly used in
practice. The electric power generator and its electrical energy
collection and regulation electronics can then be configured as is
common practice in the art, such as shown in the schematic of FIG.
26. In FIG. 26, each piezoelectric element is shown schematically
as a capacitor 240, neglecting other smaller effects such as
resistance, etc. The capacitors are shown to be connected in
series, even though they could be wired in series or partly in
parallel and in series in various configurations, depending on the
number of piezoelectric elements and their capacitance in each
particular case, and depending on the electrical energy collection
and regulation element 241 and the storage device 242, which could
be capacitive, a rechargeable battery or their combination.
Alternatively, the electrical energy collection and regulation
element 241 may direct all or part of the collected electrical
energy to some terminal electrical or electronics loads (not shown)
such as lighting, communications devices, heating elements,
etc.
[0153] It is noted that piezoelectric elements may be constructed
in a variety of configurations, a number of which could be used to
design piezo generators similar to the element 230, in particular
when the objective is not to maximize electrical power generation
of the walk-assist device. It general, however, it is noted that to
maximize the amount of the electrical energy that could be
generated, the piezoelectric elements can provide nearly the same
amount to the stiffness of the piezo generator 230. Similarly, the
piezo generator 224 can provide nearly the same amount to the
equivalent spring rate of the assemblies shown in FIGS. 23a and 23b
as the elastic element 223.
[0154] In the assemblies of FIGS. 23a and 23b, an elastic element
223 is assembled in parallel or in series with a piezo generator
224. Alternatively, at least one piezo generator such as element
224, may be configured with at least one element 210 and/or at
least one element 211, FIGS. 19b and 19c, with or without other
elastic (spring) elements, for use in place of the elements 223 and
224 in a walk-assist device provided at one joint of the subject,
FIG. 22, or in the aforementioned assemblies connecting more than
one lower extremity of the subject. The most appropriate
configuration is dependent on each specific application. In a
manner similar to that described for the "locomotion energy"
reducing embodiments, a control unit equipped with a programmable
microprocessor may be used to determine the sequence of activate
and deactivate of the brake elements during walking. The
programmable microprocessor also allows the user to vary the
parameters of the control algorithm such as the rate of electrical
power generation or turn it off completely. Some of the major
related embodiments are disclosed below. However, it is appreciated
by those skilled in the art that numerous other combinations are
possible, each of which could provide slightly or significantly
different characteristics.
[0155] In one embodiment, the elastic element 223 and piezo
generator 224 element assembly shown in FIG. 23a is modified with a
brake element 211 positioned in series with the piezo generator 224
as shown in FIG. 27, and indicated as element 250. As a result, by
activating the brake element 211, the generator is placed in
parallel with the elastic element 223, and the assembly 250
operates as previously described for the schematic of FIG. 23a,
i.e., as a power generating walk-assist device that reduces the
required "locomotion energy". However, by deactivating the brake
element 211, no power is generated and the device becomes a pure
walk-assist device for reducing the "locomotion energy".
[0156] In another embodiment 251 shown in FIG. 28, the brake
element 211 is positioned in series with a power generator 243.
When the brake element 211 is activated, the power generator 243 is
operated and generates electrical power. Otherwise the power
generator 243 is deactivated. In walk-assist devices with passive
elements only, manual engagement/disengagement clutches, a number
of which are known in the art, can be used. Alternatively, power
operated engagement/disengagement clutches, a number of which are
known in the art, may be used instead of the brake element 211. The
power generator 243 can be a dynamo type since if properly
selected, it would allow the walk-assist device to operate at
various speeds and its output can readily be controlled by the
system programmable microprocessor to provide optimal resistance
during walking and or running.
[0157] In yet another embodiment, another of the aforementioned
devices, such as heating and or cooling elements are used in place
of the power generator 243, FIG. 28, the operation of which could
be controlled as described above with the system programmable
microcomputer.
[0158] In the embodiments of the disclosed electrical power
generating walk-assist devices that are used on isolated lower
extremity joints such as the ankle or the knee joints, the device
can be readily incorporated into wearable units already used widely
for other purposes. For example, the electrical power generating
walk-assist device used at the ankle joint is readily incorporated
into the boots being worn by the subject. Or the electrical power
generating walk-assist device for the knee joint can be constructed
as a flexible knee bracing that, which strapped to the thigh and
leg sides of the knee, which could also serve as a kneepad. In most
of these cases, the mechanical to electrical energy conversion
component of the electrical energy generator is preferably
constructed with piezoelectric polymers or fibers to reduce
complexity, weight and volume and make it resistant to impact
loading.
[0159] All the aforementioned embodiments may be constructed to be
adjustable, both in physical size so as to match different subject
geometries and also in their operating characteristics, e.g., the
level of power to be produced during walking or the amount of walk
assistance it should provide. Such devices may be designed with a
very specific task in mind, for example a knee brace type device
might be designed for a hiker with a built-in GPS system. Or a
device could be designed to power an MP3 player, while a person is
roller-blading, etc.
Methods and Devices for Selective Exercising of Muscles
[0160] The aforementioned "locomotion energy" reducing walk-assist
methods and related devices are based on storing the mechanical
energy to be absorbed by the leg muscles as mechanical energy in
elements such as springs, and providing it to the leg system when
the leg muscles need to work to increase the kinetic and/or
potential energy of the leg system. As a result, the total energy
that the leg muscles have to spend during walking is reduced.
[0161] Now consider the situation in which the disclosed
walk-assist device for reducing the "locomotion energy" is modified
so that it would absorb energy while the leg muscles are doing work
to increase the kinetic and/or potential energy of the leg system
and that it inputs energy into the leg system while the leg muscles
are required to absorb energy. The subject using the resulting
device must then spend more energy to walk then they would without
the device. As a result, the previously walk-assist device is
turned into an exercise device and will hereinafter be referred to
as an "exercise device" or a "muscle exercise device".
[0162] In a manner similar to the disclosed "locomotion energy"
reducing devices, the "exercise devices" may be constructed for
individual joints or for more than one joint, including as a
mechanism worn on both legs, including the hip joints.
[0163] By wearing the "exercise device" on one particular joint and
by selectively activating it during certain intervals of the
joint(s) motions, one or a group of muscles are required to
increase their work during walking and/or running, thereby turning
the device into a selective "muscle exercise device" to strengthen
a particular set of muscles or simply for aerobic purposes.
[0164] In one embodiment, the device is designed to absorb energy
only while the leg muscles are doing work to increase the kinetic
and/or potential energy of the leg system. The energy to be
absorbed can be transferred to any number of elements, including
those described in the electrical power generating walk-assist
devices. For example, the energy to be absorbed is transformed into
heat using braking or damping elements, or used to generate
electrical energy, or used to run a cooling system, etc.
[0165] In another embodiment, the disclosed walk-assist device for
reducing the "locomotion energy" is modified and a mechanical
energy storage device such as a spring is used to absorb energy in
the form of potential energy during the interval of the stride that
the leg muscles are doing work to increase the kinetic and/or
potential energy of the leg system. Then during the interval of the
stride that the leg muscles are used to absorb mechanical energy to
reduce kinetic and/or potential energy of the leg system, the
potential energy stored in the aforementioned mechanical energy
storage device is transferred to the leg system.
[0166] In yet another embodiment, the above two embodiments are
combined such that energy is absorbed by transferring it partly to
one of the aforementioned mechanical energy using devices such as
electrical power generators and is partly stored as potential
energy and transferred to the leg system while the leg muscles are
working to absorb kinetic and/or potential energy from the leg
system.
[0167] In yet another embodiment, energy may be absorbed during
walking by providing energy absorbing elements in the shoes or
boots (e.g., shoe sole or bottom surface utilizing bending
deformation) to get exercise similar to walking and/or running on
sand. The device can have means to adjust the rate of energy
absorption. Such energy absorbing means include viscous or other
friction elements used to generate heat, or other devices known in
the art for heating or cooling the feet and/or some other segments
of the body.
[0168] All embodiments of this invention can be equipped with
programmable microprocessors that can be used by the user to
activate or deactivate the exercising device; to select a
particular muscle or a muscle group for exercise; and to increase
or decrease the level of severity of the exercise. In devices
equipped with mechanical energy absorbing elements that provide
certain output, e.g., generate electrical energy or provide heating
or cooling functions, such programmable microprocessor can be used
to adjust their parameters. In another embodiment, manually
operated engagement/disengagement clutches or other similar
elements are used to activate or deactivate the exercising devices;
select a particular muscle or a muscle group for exercise; or to
adjust the level of exercise.
[0169] The methods and devices used to exercise selected muscles or
muscle groups is described mainly with their application to the
lower extremity joints, in particular the ankle joint. The
disclosed methods are, however, general and applicable to the other
joints of the body, both individually and as a group. The method
also applies to other linear and/or rotational motion of other
segments of the body that undergo nearly periodic motion during
walking or running.
[0170] Another embodiment illustrates how a walk-assist device for
the ankle joint is modified into an exercise device. Consider the
walk-assist device shown schematically in FIG. 9. In FIG. 29, the
links 133 and 134 are shown alone. The links 133 and 134 are
provided by structural means 252 and 253 for attaching a mechanical
energy consuming element, in this case the assembly 251, FIG. 28.
During walking, in the entire range of ankle joint motion except in
the range corresponding to the ankle joint moment versus ankle
joint angle curve from the point P9 to the pint P15 (during which
time the muscles acting at the ankle joint are doing work to
increase the kinetic and/or potential energy of the leg system),
the brake element 211 is deactivated. In part or the entire range
of ankle motion from the point P9 to the point P15, the brake
element 211 is activated. As a result, during this phase of the
stride, i.e., while the muscles are working about the ankle joint
to increase the kinetic and/or potential energy of the leg system,
the muscles have to work even harder to overcome the resistance of
the mechanical energy consuming element, in this case the
electrical power generator 243. Alternatively, other mechanical
energy consuming elements such as cooling, heat generating elements
such as viscous dampers or slipping brakes, etc., may be positioned
together or instead of the electrical power generating element 243.
The aforementioned programmable microprocessor control unit is
preferably used to activate and deactivate the brake element 211,
preferably based on a signal from an ankle joint sensor. The
programmable microprocessor preferably allows the user to adjust
the level of energy that is consumed by the mechanical energy
consuming element by either varying the brake element 211
activation and deactivation timing, or by adjusting the parameters
of the mechanical energy consuming element. The braking element 211
may be replaced by an engagement/disengagement clutch.
[0171] Such an embodiment is similar to the disclosed walk-assist
device for reducing the "locomotion energy", such as those shown
schematically in FIGS. 9 or 13 for the ankle joint, except for the
reversed action of the elastic mechanical (potential) energy
storage elements. In this embodiment, the elastic elements are
selected and positioned such that during the interval of the stride
that the muscles are doing work to increase the kinetic and/or
potential energy of the leg system, energy is also being
transferred to the present device elastic element(s) as potential
energy. And during the interval of the stride that the muscles are
working to absorb the kinetic and/or potential energy of the leg
system, the potential energy stored in the elastic element(s) of
the device is returned to the leg system. As a result, during both
of the above intervals of the stride, the leg muscles have to work
harder to also supply potential energy to the elastic element(s) of
the device, and later absorb the same potential energy.
[0172] Another embodiment is a combination of the above two
embodiments. For the ankle joint alone, such a device is very
similar to the embodiment shown in the schematic of FIG. 29, except
that in place of the element 251, either one of the elements shown
in FIGS. 23a, 23b or 27 or elements with similar characteristics is
used. The objective here is to return part of the available energy
to the leg and transfer the remainder to a mechanical energy
consuming element such as an electrical energy generating
element.
Methods and Devices to Reduce "Stance Energy"
[0173] During locomotion, the weight of the subject body and the
load that he/she is carrying (gravity generated loads) and the
dynamics forces due to the inertia of the body and the load are
supported partly by the muscle forces and partly by the resisting
forces, moments (torques) across these joints, which are provided
mostly by the passive components of the joints such as ligaments
and other connective tissues and the contact forces between the
condyles.
[0174] The motion across the joints of the lower extremities may be
divided into two basic groups. The first group consists of the
joint rotations with minimal connective tissue resistance except
for minimal friction forces, such as the knee joint rotation 109
and the ankle rotation 121, FIG. 3. These joint rotations are
hereinafter called the "unconstrained joint rotations". The
remaining joint rotations and displacements (e.g., axial and
shearing) are constrained, to various degrees, by the resistance of
the connective tissues such as ligaments and the contact forces
between the affected condyles. These joint rotations and
displacements are hereinafter called the "constrained joint
rotations" and "constrained joint displacements", respectively.
[0175] During walking, the required shearing, compressive and
tensile forces across the "constrained joints", i.e., the forces
required to stabilize the aforementioned "constrained joint
displacements", and the required moments and torques about the
"constrained joints", i.e., moments and torques required to
stabilize the aforementioned "constrained joint rotations", are
provided mostly by the ligaments and other passive connective
tissues and the contact forces between the joint condyles. The
ligaments and other connective tissues and the contact forces
between the condyles provide the required resisting (stabilizing)
forces, moments and torques across the "constrained joints" in
response to the components of the aforementioned static or dynamic
forces and moment and torques across these joints.
[0176] In normal conditions, the muscles generally contribute less
to the aforementioned resistive or stabilizing forces, moments and
torques. This is particularly the case when the forces generated by
the muscles expanding across a joint do not provide a significant
component in the direction of a "constrained joint displacement" or
moment or torque about a "constrained joint rotation". The muscles,
however, are used to provide additional moments to provide a margin
of stability to the aforementioned "unconstrained joint rotations",
and to a varying degree to the "constrained joint displacements"
and "constrained joint rotations". Stabilizing moments about the
"unconstrained joints" are also required to overcome static or
nearly static forces during standing or during very slow walking
such as walking with walkers, or while performing certain tasks
while standing in place or moving very slowly, or the like. In
general, while a subject uses his/her muscles to apply stabilizing
moments across the unconstrained joints, the subject usually also
applies stabilizing forces, moments and torques across the
"constrained joints". Hereinafter, the work done by the muscles to
provide the aforementioned stabilizing forces across both the
unconstrained and the constrained joints of the lower extremities
is called the "stance energy".
[0177] In the "locomotion energy" reducing embodiments, the
disclosed "walk-assist" devices provide the means to reduce the
required work of the muscles in providing moment about the
aforementioned "unconstrained joints" during walking. The objective
is to introduce methods and related devices for "walk-assist" or
"stance-assist" devices that can be used to reduce the
aforementioned "stance energy" during walking or during slow
movements or standing still upright.
[0178] In general, the aforementioned "locomotion energy" reducing
embodiments also help to reduce the "stance energy" in the
following manner. The work that the muscles have to perform to
increase the kinetic and/or potential energy during certain
portions of the stride and then absorb the kinetic and/or potential
energy during certain other portions of the stride include the work
needed to support the weight of the body. Therefore the "locomotion
energy" reducing embodiments also reduce certain amount of "stance
energy" that the muscles have to provide. In addition, the
potential energy storage elements, e.g., the elastic or spring
elements, used in all "locomotion energy" reducing embodiments
would resist a certain amount of rotation at the "unconstrained
joints", thereby increasing stance stability and reducing the need
for muscles to provide this portion of stabilizing moments about
the "unconstrained joints". Here, only those embodiments are
considered that do not use clutch and/or brake elements to isolate
the above elastic and spring elements from the joint when the
subject is not walking or running.
[0179] The basic method being disclosed for reducing "stance
energy" is based on providing stabilizing moments about the
"unconstrained joints" to at least support the weight of the
subject, and preferably also supports the weight of the load that
is being carried by the subject. In general, depending on the
circumstances facing the subject, it might be desirable to provide
more stabilizing moments than the required minimum to create a
certain amount of stability margin. Similarly, it is sometimes
desirable to provide certain amount of added stabilizing forces
and/or moments and/or torques to the "constrained joints" of the
subject. In general, all the above stabilizing forces, moments and
torques are preferably nonlinear functions of their respective
displacements and rotations, providing at least the minimum amount
of stabilizing force, moment and torque about the preferred
positioning of the joint, and increasing with an accelerated rate
with deviation from such preferred positioning of the joint. This
nonlinear characteristic of the stabilizing joint forces (moments
and toques) are described in more detail in the remaining portion
of this disclosure.
[0180] In general, the aforementioned "locomotion energy" reducing
walk assist devices do also reduce the "stance energy" by a certain
amount depending on their moment versus joint angle characteristics
of the spring elements used to store and release potential energy
during locomotion. With "locomotion energy" reducing walk-assist
devices, a subject reduces "stance energy" during walking and
running as well as while standing still or walking very slowly.
This is the case since during walking, the spring element supports
at least part of the subject weight and provides additional force,
moment and torque across the "constrained joints". While standing
still, the spring elements resist joint rotation to some extent as
the "unconstrained joints" rotate away from the position at which,
or range(s) of positions within which, the spring elements are
designed not to provide resisting moments.
[0181] The above discussion applies to all the disclosed
walk-assist embodiments for reducing "locomotion energy" that are
constructed primarily with passive elements. For those embodiments
that are constructed with braking (clutch) elements, including
those that are operated by microprocessor-controlled, walk-assist
devices that significantly reduce both the "locomotion energy" and
the "stance energy", including "stance energy" during very slow
walking or even while standing still, and that ensures stance
stability with an appropriate amount of stability margin can be
constructed as is described later in this section.
[0182] In one embodiment of the above walk-assist devices
constructed with passive elements, the springs are designed to
produce nonlinear moment (torque) .tau. versus angular rotation 0
characteristic similar to that shown in FIG. 30. The moment
(torque) shown in FIG. 30 is in addition to the moment (torque)
that in the previous section of this disclosure was shown to be
required by the walk-assist embodiments for reducing "locomotion
energy" and/or for utilizing the energy to be absorbed by the
muscles to generate electrical energy or for some other purposes.
The purpose of the added joint moment (torque) is to provide or
increase stance stability during walking and running and/or as
standing still or walking very slowly. As can be seen in FIG. 30,
in certain range of joint rotation .DELTA., the added moment
(torque) could be zero, but beyond that range (in one or both
directions of rotation), the added moment (torque) is shown to
increase with an accelerated rate. At relatively large angular
rotations of the joint, the added moment (torque) becomes
relatively large, thereby effectively stopping any further joint
rotation in that direction. Such "maximum" allowable joint
rotations may be manually adjustable.
[0183] In another embodiment, the "maximum" allowable joint
rotation, the no moment (torque) range .DELTA., and even the shape
of the curve are made adjustable utilizing the aforementioned
brakes (clutches) and spring element assemblies, such as those
shown in FIGS. 18-20 or disclosed previously. The adjustments may
be done manually. A microprocessor controller with sensory inputs
however, can also control the adjustments. Such sensory inputs
could be accelerometers and/or gyros attached to the subject body
or sensors measuring joint angles and their rates to predict an
outset of stance instability.
[0184] In a variation of the above embodiment, the microprocessor
control of the walk-assist device, particularly one that acts on
all three joints of the leg, provides adjustments to the resisting
moment (torque) at the "unconstrained joints" to provide support
for the weight of the subject and to load being carried by the
subject. The adjustment is preferably with input from a total
weight-measuring sensor, such as one provided in the shoes or the
boots. The subject using such a device can then carry a larger load
while being assisted by the present walk-assist device during
walking or running.
[0185] In yet another embodiment of the present invention, the
aforementioned sensory input are used to predict outset of stance
instability and make appropriate adjustment to the resisting joint
moment (torque) to prevent the subject from suddenly falling or
collapsing. In general, the stability is provided by an increase in
the resisting joint moments (torques), eventually locking them in
place to support the subject weight in a highly stable and
comfortable posture. As such, the walk-assist device acts also as
an emergency stance stability control device as well. Once the
subject is in full control of the situation, he/she or someone
assisting the subject would operate the microprocessor control with
input(s) to allow the subject to regain fill mobility, or be helped
to sit or lay down, etc., by varying the resisting moment (torque)
acting on the "unconstraint joints".
[0186] In all the above embodiments, the microprocessor control may
be used to automatically adapt the walk-assist device to provide
stance stability or increase in response to an input from one or
more of the aforementioned sensors or sensors measuring parameters
indicating fatigue, such as pulse rate, blood oxygen, EKG or the
like. The microprocessor controller can be programmable to run
various stored or input programs.
Methods and Devices for Rehabilitation
[0187] Almost all the walk-assist devices described in the previous
sections can be readily turned into rehabilitation devices designed
to perform one or more of the following tasks: [0188] 1. Reduce one
or more of the "constrained joint" forces, moments or torque to
reduce connective tissue and/or contact forces. [0189] 2. Reduce
forces applied to one or a group of specific ligaments or other
connective tissues. [0190] 3. Reduce condular contact forces,
partially or entirely, at a lower extremity joint. [0191] 4. Reduce
forces transmitted by one or a group of muscles acting across one
or more of the lower extremity joints. [0192] 5. Reduce certain
force, moment or torque that is transmitted across a limb, e.g.,
the leg or the thigh. [0193] 6. Provide the means to adjust the
above joint, connective tissue, muscles and limb force, moment and
torque.
[0194] The primary objective of the disclosed method and related
devices is to affect forces, moments and torques that are
transmitted across the lower extremity joints and/or limbs or their
various components without significantly affecting the subject
locomotion capabilities. This is generally done for therapeutic
and/or rehabilitative purposes, or to allow locomotion in the
presence of injury to one or more of the above, or following
certain surgical procedures or the like. For this reason, it is
highly desirable that the aforementioned reduction or increase in
the joint, limb, connective tissue, muscle, etc., be adjustable. In
this section of the disclosure, the present method is described by
its application to one of the embodiments of the present
invention.
[0195] In the most effective embodiment, an aforementioned
walk-assist for reducing "locomotion energy" and "stance energy"
with several active elements such as units 210 and 211 and
with-microprocessor control is modified as follows to provide the
desired rehabilitative or therapeutic effect. The embodiment is
described as employed on a single joint of the lower extremity. The
disclosed embodiment can similarly be applied to devices covering
two or more of the lower extremity joints.
[0196] In one embodiment, several spring and (brake) clutch
elements and units similar to 210 and 211 are connected in parallel
and/or in series as previously described and their actions are
controlled by a microprocessor. The primary function of the
microprocessor control unit is to activate and deactivate the brake
and clutch elements so that the ranges of motion in which the
device absorbs or provides energy to the leg system are selected
such that the amount of force that a certain muscle or a group of
muscles must apply (and tendons must bear) and/or the reaction
forces at the condular surfaces of the joint, joint ligaments or
other connective tissues. The method of reducing muscle forces
during locomotion and stance was described above. The condular
contact over the entire surface of the joint or a portion of it
(e.g., on the lateral or the medial side) is generally reduced by
allowing the walk-assist device to provide spring-generated loads
on the appropriate side of the joint. For example, if condular
contact on the lateral side of the knee joint is to be reduced, the
walk-assist device provides appropriate amounts of spring force
during each range of the joint motion. The condular contact forces
may be similarly increased. The load across the joint ligaments and
other soft tissues are similarly controlled.
[0197] In certain situations, the preloading of the spring elements
of the above embodiment may have to be initially adjusted to allow
the walk-assist device to provide the appropriate force levels
during the entire cycle of the gate.
[0198] The rehabilitation devices disclosed herein can be
controlled by a programmable microprocessor to achieve a prescribed
pattern of muscle, tendon, ligament and condular forces. The force
levels can then be varied over time to achieve the desired
rehabilitative effects. In particular, such devices can be used for
rehabilitation or for general muscle strengthening purposes. For
example, such devices can be designed to allow a patient to reduce
load on a specific joint or a muscle or a group of muscles or
ligaments, with the potential of enabling a patient with injury to
a hard and/or soft tissue to gain early mobility, and allow gradual
increased loading of the injured members as they heal and as a
means to enhance the healing process.
[0199] In an alternative embodiment, particularly if the
walk-assist device does not have to vary the above connective
tissue, contact force or muscle force patterns in a complex manner,
for example if it only need to reduce the entire condular contact
force or reduce the force transmitted through a specific ligament,
then a walk-assist with only passive elements may suffice. In such
walk-assist devices, the spring loads and preloading and other
parameters of the device are preferably adjustable to match a wide
range of adjustments.
Other Applications For the Disclosed Methods and Devices
[0200] The methods and devices disclosed in the previous sections
can directly and with minor modifications be applied to certain
sports activities to enhance performance or for training. For
example, the aforementioned "locomotion energy" reducing method and
devices can directly be used to reduce the energy spent during
bicycling. The only modification needed is the adaptation of the
joint moment (torque) versus angle characteristics from those of
walking (e.g., FIGS. 2 and 4-8) to those of bicycling. In many
sports, for example, cycling, swimming, rowing and the like, the
disclosed "sport assist" devices are preferably passive. As it was
shown previously in this disclosure, even totally passive devices
could cover at least a certain portion of the activity cycle,
thereby making a significant improvement in performance.
[0201] In one embodiment, the "sport assist" devices are designed
to increase the performance of the user in bicycling.
[0202] In another embodiment, the "sport assist" devices are
designed to increase the performance of the user in rowing.
[0203] In yet another embodiment, the "sport assist" devices are
designed to increase the performance of the user in swimming.
[0204] In yet another embodiment, the "sport assist" devices are
designed to increase the performance of the user in swimming under
water with fins.
[0205] In yet another embodiment, the "sport assist" devices are
designed to be adjustable so that its performance could be readily
matched to the individual user.
[0206] In yet another embodiment, the "sport assist" devices are
designed for exercising certain muscles and muscle groups important
to a specific sport.
[0207] In addition, the walk-assist devices designed to reduce
"locomotion energy" and "stance energy" and which span both legs of
the subject may also be used to minimize or even eliminate the need
for the leg muscle to do work during normal walking. Such devices
can be designed with stance stability and allow input energy by
powered actuation devices or preferably by the arms or muscles of
the subject's upper body. In such devices, mechanical energy is
readily transferred by the arms or upper body muscles by simply
extending or compressing one or more of the potential energy
storage springs of the walk-assist device. The aforementioned
active elements can then be used to direct the stored potential
energy to the required joints. The amount of mechanical energy
needed from the external sources, the arms or the upper body
muscles is minimal during walking on a flat surface, since the
disclosed walk-assist devices for reducing "locomotion energy" and
"stance energy" were shown to be capable of significantly reducing
the need for work by the leg muscles. Such walk-assist devices are
preferably equipped with the aforementioned active elements and
their operation is controlled by programmable microprocessors to
make them highly efficient. Such walk-assist devices will require a
relatively small amount of input energy by the arms or the upper
body muscles, and could be used by those who have minimal or even
no use of their lower extremity muscles, and older people as a
replacement for walkers of different types. In such applications,
the walk-assist device is preferably equipped with the
aforementioned sensor activated stance stability braking
devices.
[0208] While there has been shown and described what is considered
to be preferred embodiments of the invention, it will, of course,
be understood that various modifications and changes in form or
detail could readily be made without departing from the spirit of
the invention. It is therefore intended that the invention be not
limited to the exact forms described and illustrated, but should be
constructed to cover all modifications that may fall within the
scope of the appended claims.
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