Metabolically efficient leg brace Number:7,393,335 from the United States Patent and Trademark Office (PTO) owispatent

Title: Metabolically efficient leg brace

Abstract: Embodiments of the invention relate to walking/running braces and to devices for enhancing locomotion, specifically human bipedal locomotion. More particularly, it relates to a controlled mechanical device which provides support of the torso via the hip sockets, reduces the metabolic energy associated with walking/running and reduces the incidence of falls caused by insufficient leg thrust. Embodiments of the invention also relates to reducing the strain and metabolic energy consumption associated with walking/running with a heavy backpack or other significant carried load.

Patent Number: 7,393,335 Issued on 07/01/2008 to Carvey,   et al.

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Inventors:	Carvey; Matthew R. (Bedford, MA), Carvey; Andrew W. (Bedford, MA), Carvey; Philip P. (Bedford, MA), Howard; Nicholas S. (Bedford, MA)
Appl. No.:	11/120,503
Filed:	May 3, 2005

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Related U.S. Patent Documents

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	Application Number	Filing Date	Patent Number	Issue Date
	60568773	May., 2004

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Current U.S. Class:	602/26 ; 602/16
Current International Class:	A61F 5/00 (20060101)
Field of Search:	602/26,24,5,16,20-29,62 632/39-40,42-45,27,30 482/4,51,901 601/35 607/62,66 700/245,253 318/568.11,568.12,568.17 701/23 901/23,24 128/878,892

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References Cited [Referenced By]

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U.S. Patent Documents

2010482	August 1935	Cobb
2632440	March 1953	Hauser et al.
3315406	April 1967	Ryan
4413713	November 1983	West
4771872	September 1988	Kampf
5011136	April 1991	Rennex
5052379	October 1991	Airy et al.
5230700	July 1993	Humbert et al.
5476441	December 1995	Durfee et al.
5575764	November 1996	Van Dyne
5636805	June 1997	Fukuzawa
5830166	November 1998	Klopf
6024713	February 2000	Barney
6471664	October 2002	Campbell et al.
6500138	December 2002	Irby et al.
6666796	December 2003	MacCready, Jr.
6834752	December 2004	Irby et al.
7153242	December 2006	Goffer
2002/0094919	July 2002	Rennex et al.
2003/0062241	April 2003	Irby et al.

Foreign Patent Documents

	44 00 820 A 1		Jul., 1995		DE
	WO 94/09727		May., 1994		WO

Primary Examiner: Yu; Justine R
Assistant Examiner: Ali; Shumaya B
Attorney, Agent or Firm: Proskauer Rose LLP

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Parent Case Text

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RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No. 60/568,773, filed on May 6, 2004, the entire teachings of which are herein incorporated by reference.

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Claims

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What is claimed is:

1. A metabolically efficient leg brace, comprising: a shank frame for transferring forces between a wearer's tibia/fibula and the shank frame; a thigh frame for transferring forces between a wearer's femur and the thigh frame; at least one knee joint rotatably coupling the shank frame to the thigh frame; at least one torsion spring having a torsional axis at the at least one knee joint, a first arm of the torsion spring coupled to the shank frame, and a second arm of the torsion spring coupled to an input arbor of a thigh clutch; an output arbor of the thigh clutch coupled to the thigh frame; a first activation mechanism for actuating and releasing the thigh clutch; and an electronics control module controlling the first activation mechanism during periods governed by the wearer's gait.

2. The leg brace of claim 1, further comprising: a shoe frame rotatably coupled to the shank frame at an ankle joint for transferring forces between the wearer's shoe/foot and the shoe frame.

3. The leg brace of claim 1, further comprising: a second leg brace; and an attached mass support frame rotatably coupled at a hip joint to respective thigh frames of each leg brace for transmitting forces between attached masses and the coupled leg braces.

4. The leg brace of claim 1, wherein the first activation mechanism is a cam optimized for reduced energy consumption.

5. A metabolically efficient leg brace, comprising: a shank frame for transferring forces between a wearer's tibia/fibula and the shank frame; a thigh frame for transferring forces between a wearer's femur and the thigh frame; at least one knee joint rotatably coupling the shank frame to the thigh frame; at least one torsion spring having a torsional axis at the at least one knee joint, a first arm of the torsion spring coupled to the shank frame, and a second arm of the torsion spring coupled to an input arbor of a thigh clutch; an output arbor of the thigh clutch coupled to the thigh frame; and a first activation mechanism for actuating and releasing the thigh clutch during periods governed by the wearer's gait; a spring clutch having an input arbor coupled to the first arm of the at least one torsion spring and an output arbor coupled to the shank frame; and a second activation mechanism for actuating and releasing the spring clutch during periods governed by the wearer's gait.

6. The leg brace of claim 5, wherein the spring clutch is a one-way clutch with an orientation selected such that its free direction of rotation occurs during the wearer's knee flexion.

7. The leg brace of claim 5, wherein the clutch is a one-way two-state clutch with an orientation selected such that its direction of rotation occurs during the wearer's knee flexion.

8. The leg brace of claim 5, wherein the second activation mechanism is a cam optimized for reduced energy consumption.

9. The leg brace of claim 5, wherein the at least one torsion spring is a non-linear hardening torsion spring.

10. The leg brace of claim 5, wherein the thigh clutch is a one-way two-state clutch whose hard direction occurs during a wearer's knee flexion.

11. The leg brace of claim 5, wherein the first activation mechanism is a cam optimized for reduced energy consumption.

12. A metabolically efficient leg brace, comprising: a shank frame for transferring forces between a wearer's tibia/fibula and the shank frame; a thigh frame for transferring forces between a wearer's femur and the thigh frame; at least one knee joint rotatably coupling the shank frame to the thigh frame; at least one torsion spring having a torsional axis at the at least one knee joint, a first arm of the torsion spring coupled to the shank frame, and a second arm of the torsion spring coupled to an input arbor of a thigh clutch; an output arbor of the thigh clutch coupled to the thigh frame; and a first activation mechanism for actuating and releasing the thigh clutch during periods governed by the wearer's gait; wherein the thigh clutch transfers torque between slipping input and output arbors of the thigh clutch and the activation mechanism activates the thigh clutch to achieve constant power dissipation.

13. A metabolically efficient leg brace, comprising: a shank frame for transferring forces between a wearer's tibia/fibula and the shank frame; a thigh frame for transferring forces between a wearer's femur and the thigh frame; at least one knee joint rotatably coupling the shank frame to the thigh frame; at least one torsion spring having a torsional axis at the at least one knee joint, a first arm of the torsion spring coupled to the shank frame, and a second arm of the torsion spring coupled to an input arbor of a thigh clutch; an output arbor of the thigh clutch coupled to the thigh frame; and a first activation mechanism for actuating and releasing the thigh clutch during periods governed by the wearer's gait.

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Description

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BACKGROUND OF THE INVENTION

Ground Reaction Force (GRF) is defined as a force vector applied by the ground to a person at a point on a person's footprint called the Center of Pressure (COP). The GRF direction can be modeled by a force vector colinear with a line connecting ankle and hip. Neglecting air friction, the average horizontal component of the GRF must exactly equal zero for a person walking/running at constant average velocity regardless of ground slope. If this were not the case, then a person's torso would increase or decrease its average horizontal velocity. Similarly, the average vertical component of the GRF must be exactly equal to body weight regardless of the ground slope. If this were not the case, then the average distance from the torso to the ground would increase or decrease.

The function of the legs in human bipedal locomotion (hereafter locomotion) is to make periodic ground contact with a foot during each step for the purpose of transferring the GRF to the torso. By making the average horizontal GRF less than or greater than zero, the torso can be accelerated or decelerated. The locomotion process is one whereby the torso weight is supported alternately between one leg and the other. Each step consists of a support epoch during which one leg supports the torso weight while the alternate leg is swinging forward preparing for the next step. Each support epoch is followed by a transition epoch where the torso weight transitions between the current support leg to the new support leg.

Others have created locomotion assist devices throughout recorded history mostly with the intention of mitigating leg dysfunction. Locomotion assist devices are currently in widespread use today in the form of crutches, canes, and a variety of knee braces. Some locomotion assist devices include wheeled devices, such as bicycles, wheelchairs, scooters, and other alternatives to human bipedal locomotion. These devices transfer the GRF to the torso from points on the ground which are constantly moving.

Canes and crutches are devices that allow a user to transfer a portion (up to all) of the GRF to the torso via the arm sockets. These devices are effective in reducing the gait problems caused by one or both dysfunctional legs and are commonly employed. Unfortunately these devices are problematic for long term use, over uneven terrain, or where the arm sockets are not suitable for transferring substantial portions of the GRT to the torso.

Locking knee braces are another class of device commonly used to transfer the GRF to the torso. Unlike canes and crutches, locking knee braces transfer the GRF to the torso via the hip sockets. Since this is the normal mechanism for humans to transfer GRF to the torso, it is a preferred mechanism. Common locking knee braces consist of a shank and thigh frame coupled together with a hinge that can be locked at an explicit knee angle when torso support is required. Knee braces are widely used to reduce knee joint stresses and provide knee immobilization following surgery. In general they are not employed as walking enhancement devices because the fixed knee angle greatly impedes normal action of the leg during walking/running.

There exists several intelligent, electronic knee braces used to control resistive torque or damping about the knee joint. These knee braces are primarily intended to mitigate leg dysfunction caused by amputation. Using sensory information, these active braces can discriminate between early and late support phases thereby allowing amputees to flex their knee just after heel strike. This feature is important for shock absorption and is not possible with prior mechanically passive prosthesis. Electronic knees can also supply different levels of damping during swing and support dependent on walking speeds using adaptive algorithms. Several of these electronically controlled knee braces have been commercialized, such as the Otto Bock's C-leg and Ossur's Rheo Knee.

U.S. Pat. Nos. 6,500,138, 6,834,752, and U.S. Patent Publication 2003/0062241 disclose a knee brace which provides support while allowing unimpeded knee angle flexion during leg swing. This device, called an auto-locking knee brace, employs a microprocessor controlled one-way clutch at the knee joint of a common knee-ankle-foot-orthotic. This device has two modes of operation. In one mode, the one-way clutch is inactivated thereby allowing free rotation of the foot/shank and thigh frames. One-way clutches have a well known property that when activated they have an easy rotation direction where only a small amount of torque can be coupled from input to output and a hard direction where an arbitrarily large amount of torque can be coupled from input to output. This feature of the one-way clutch is exploited in the auto-locking brace to allow relatively unimpeded leg extension prior to heel strike while providing full support following heel strike. Activation of the one-way clutch utilizes a solenoid. For polio and stroke patients, the auto-locking knee has shown significant improvements including reducing metabolic energy consumption of wearers of the device.

Numerous mobility assist devices have been developed over the years employing mechanisms which incorporate means for temporarily storing and releasing the energy generated and needed during each step. U.S. Pat. Nos. 420,178 and 420,179 disclosed a device employing bow springs attached to a shoulder and a pelvis. The '179 Patent incorporates a foot-lift mechanism to enable swing leg foot clearance, however does not teach a workable mechanism for activating the foot-lift mechanism.

U.S. Pat. No. 4,872,665 discloses a running brace that employs a telescoping gas spring and a swing leg foot clearance mechanism employing a ratchet joint. The disclosure does not discuss practical methods for release of the ratchet joint. The primary problem with the device is there is no mechanism for controlling the natural release of the energy stored in the gas spring phase locked to the gait cycle selected by the wearer. In particular, assuming that an embodiment of the device is possible, a wearer must adjust his gait cycle to the natural frequency dictated by the physical parameters of the device.

U.S. Pat. No. 5,016,869 discloses a running assist device for enhanced mobility and reduced metabolic energy consumption. In this device, the GRF is coupled to the torso mass directly through the legs without any mechanism working in parallel with the legs. Accordingly, the device cannot store energy available during the period of time when the distance between hip socket and ankle is decreasing. In effect, the device acts as a mechanism for transferring GRF to the soles of the wearer's feet, not the torso.

U.S. Pat. Nos. 4,967,734, 5,011,136, and U.S. Patent Publication 2002/0094919, disclose energy-efficient running braces employing a mechanical spring which temporarily stores the energy during the period when the distance between torso center of mass and the ground is decreasing and releases the energy during the period when that distance is increasing. These devices support the torso via a torso harness and refer to means for generating a constant leg thrust. Measurement of the GRF reveal that the required leg thrust increases substantially as running speed is increased, reaching up to five times body weight during sprinting. Benefits of these devices do not appear to be achievable by a wearer suffering single leg dysfunction. The devices also appear to require extensive periods of time to doff and don. All of the above-mentioned designs couple the GRF to the torso via a torso harness.

SUMMARY OF THE INVENTION

One embodiment of the invention supports the torso by fixing one arm of a torsion spring to a shank frame and coupling the other arm of the torsion spring to a thigh frame. The shank and thigh frames are coupled to the wearer's shank and thigh via padded half shells and Velcro straps. The shank and thigh frames are passively hinged at the knee axis. This configuration supports the torso by working in parallel with the wearer's legs to transfer the Ground Reaction Force (GRF) from ground to the torso via the wearer's hip sockets for all knee angles. At zero knee angle, 100% of the torso weight is supported via the wearer's leg skeleton. As the knee angle increases, the percentage of torso weight supported by an embodiment of the invention increases while the percentage supported by the wearer's leg skeleton decreases. The brace allows the wearer to supplement the torso support features of an embodiment of the invention to any extent desired via natural contracting of the wearer's quadricep muscles. Note that a conventional locking knee brace only provides this support at one knee angle and does not allow the wearer to supplement the torso support via contracting the wearer's quadricep muscles. The addition of an attached mass support frame, hinged to braces worn on both legs and shoe frames, hinged at the ankle, results in the attached mass being fully supported by the braces. Unlike torso and carried load support, support of the attached mass does not increase pressures applied by the brace to the wearer's shank and thigh.

The metabolic energy reduction benefit of an embodiment of the invention is based on the observation that during each gait cycle, the support leg knee flexes and extends. During support leg knee flexion, the distance between hip and ankle decreases. This results in energy being extracted from the torso. Similarly, during support leg knee extension, the distance between hip and ankle increases. This results in energy being added to the torso.

Without use of the principles of the embodiments of invention, the torso energy decrease during knee flexion is converted into heat by muscle activity of the support leg. The torso energy increase required during knee extension must be supplied from muscle activity of the support leg. With use of the principles of the embodiments of invention, most of the torso energy decrease during knee flexion is stored as potential energy in a torsion spring. Since the energy stored need not be converted into heat by the muscle activity of the support leg, the muscle activity during knee flexion is substantially reduced. During knee extension, the brace releases the stored energy of the spring. Since the energy sourced from the spring replaces most of the normal muscle activity during knee extension, overall metabolic energy is reduced.

It should be clearly understood that the brace is mechanically passive. While it employs batteries to power the sensing and control electronics, none of the energy drawn from the batteries is injected into the system. Since any physical embodiment of the invention will result in frictional and other energy losses, the brace will never be 100% efficient. Accordingly, the wearer must supply metabolic energy to compensate for these inefficiencies. Since an embodiment of the invention reduces the metabolic energy during both knee flexion and knee extension, a double benefit is gained. For example, if the brace is 83% efficient, overall metabolic energy consumption decreases by a factor of six.

When the wearer dons the brace, the simplified system comprises a spring and mass. This system results in a natural motion exclusively dictated by the physical parameters of the spring, mass and starting conditions. This natural motion would normally require that the wearer adapt his gait to the physical parameters of an embodiment of the invention. Though it has been shown experimentally that wearers of embodiments of the invention can adapt their gait to the brace, the adjustment period is fairly lengthy and the system is somewhat difficult to control.

A novel mechanism enables an embodiment of the invention to adapt to the gait selected by the wearer rather than vice versa. An embodiment employs a controlled one-way clutch to mechanically freeze the knee angle at that point where the stored energy is maximum. After the body has progressed to the optimal leg angle, the control unfreezes the energy stored in the spring. The energy of the torsion spring then naturally flows into torso. This same mechanism works identically for the attached mass.

A preferred embodiment comprises shoe frame, shank frame, thigh frame, torsion spring, two controlled one-way clutches and control electronics. The shoe frame is passively hinged to the distal end of the shank frame at the ankle joint. The distal end of the thigh frame is passively hinged to the proximal end of the shank frame at the knee joint. The shoe frame is fixed to the wearer shoe via a quick connect/disconnect mechanism. Shank and thigh frames are coupled to the wearer's shank and thigh via straps and padded shells. A mechanism called an actuated knee couples the shank and thigh frames at the knee joint. It is composed of a torsion spring in series with a one-way dual-state clutch called the thigh clutch. A second one-way dual-state clutch called the spring clutch operates in parallel with the torsion spring.

In a preferred embodiment, one arm of the torsion spring is directly coupled to the shank frame while the other end of the torsion spring is coupled to both the input arbor of the thigh clutch and the input arbor of the spring clutch. The thigh clutch output arbor is directly coupled to the thigh frame. The thigh clutch allows for torque produced by the thigh frame to be coupled to the torsion spring. The spring clutch output arbor is directly coupled to the shank frame. The spring clutch provides a mechanism for freezing the torsion spring at that point where maximum energy is stored. It should be noted that if one arm of the torsion spring is directly coupled to the thigh frame and the use of the two clutches is interchanged, identical behavior occurs.

In a preferred embodiment, many components of the shoe, shank and thigh frames as well as spring and clutches are replicated on both the inner side and outer side of the leg. Hence, a preferred embodiment employs two torsion springs, two thigh clutches and two spring clutches. One actuator is employed to control both thigh clutches and a second actuator is employed to control both spring clutches. This balanced scheme allows the large forces produced at the hip socket to be transferred to ground without creating axial torques on the brace. It should be noted that an unbalanced scheme employing only a single torsion spring, single thigh clutch and single spring clutch also implements all principles of operation of various embodiments of the invention.

In a preferred embodiment, a half cylindrical padded shell, positioned at the upper front of the wearer's shank, couples the inner and outer struts of the shank frame. This shell allows the wearer to transfer a fraction of the hip socket force to the shank frame. Similarly, a half cylindrical padded shell, positioned at the upper back of the wearer's thigh, couples the inner and outer struts of the thigh frame. This shell allows the wearer to transfer a fraction of the hip socket to the thigh frame.

One embodiment of the invention utilizes well known clutches called one-way, dual-state clutches. These clutches are characterized by having two states, activated and released. In the activated state, these clutches have a hard rotation direction and an easy rotation direction. In the hard direction a large torque can be coupled from input to output arbors before slippage occurs. In the easy direction, only a small torque can be coupled between input and output arbors before slippage occurs. The hard direction of the thigh clutch occurs during knee flexion and hard direction of the spring clutch occurs during knee extension. In the released state, approximately zero torque can be coupled between input and output arbors before slippage occurs.

The spring clutch employs a variant of a well known class of one-way clutches called spring wrap clutches. Spring wrap clutches employ a wire coiled in a helix as the means for transferring torque from input to output arbors. One end of the wire coil is fixed to the output arbor and the other end is used for control. When zero control force is applied, the input and output arbors rotate freely. When a force is applied to the control end of the wire coil, a large torque can be transferred from input to output arbors in the hard direction.

The thigh clutch employs a novel variant of the spring wrap clutch. It couples torque from the thigh frame to one arm of the torsion spring. When in the released state, the knee is free to flex and extend. When in the activated state, the wearer will experience only a small back torque when extending his knee. During knee flexion on level or ascending terrain, all of the torque produced by the thigh frame is coupled to the torsion spring without slippage. During knee flexion on descending terrain, again all of the torque produced by the thigh frame is coupled to the torsion spring, but the microprocessor allows controlled slippage. This slippage implies that the thigh clutch must be able to dissipate energy like the brakes on a bicycle.

A preferred embodiment utilizes two motor/gearbox driven CAMs to supply a force to the control side of each of the one-way clutches. In normal operation, the CAM makes one revolution for each step cycle. The control CAM has an engineered shape with several important properties. First, the control force can be varied from zero to maximum over any time period. Second, the force can be changed from maximum to zero almost instantaneously. Lastly, the shape minimizes the power drain from the battery.

In order to clarify the action of an embodiment of the invention, the concept of a Seg is introduced. A Seg is an imaginary line connecting ankle and hip. Its length and angle with respect to vertical vary throughout the step. A brief description of brace operation during level walking starts with the system just prior to the swing phase of the braced leg. This transition is detected by detecting a negative Seg angle together with a change of foot pressure to near zero. Just prior to the start of the swing phase, the spring clutch is in its released state and the thigh clutch is in its activated state. At the start of the swing phase, the thigh clutch activation CAM is rotated slightly causing a quick transition of the thigh clutch to its released state. After the transition, the wearer can easily flex the braced leg and swing it forward. Some time later, the swing leg Seg angle becomes positive and the wearer starts extending the swing leg. This initiates rotation of the CAMs until both clutches reach their fully activated states. Properly engineered, both clutches will be in their fully activated state by the time heel strike occurs. Following heel-strike, increasing flexion of the knee causes torsion spring energy to increase until the maximum knee angle is sensed. At that time, the Seg angle is recorded and stored in the microprocessor's .beta..sub.crit register. The hip socket of the support leg will continue to rotate at a fixed distance from the support leg ankle until the Seg angle reaches -.beta..sub.crit. At that point, the microprocessor causes the spring clutch CAM rotate slightly causing the spring clutch to transition to released state. This action allows the energy stored in the torsion spring to be released into the system.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.

FIG. 1 shows a side view of a person wearing the one embodiment of the present invention;

FIGS. 2A-2D show computed normalized forces at three brace/human contact areas versus 1/2 knee angle of a wearer of the invention of FIG. 1;

FIG. 3 shows is a side view of the invention of FIG. 1 augmented with an attached mass support frame;

FIG. 4 shows a perspective view of a person employing the embodiment of FIG. 1 on both legs;

FIG. 5 shows a perspective view of a person employing the embodiment of FIG. 3;

FIG. 6 shows a side view of one embodiment of an actuated knee;

FIG. 7 shows a perspective view of a transfer arbor assembly of the actuated knee of FIG. 6;

FIGS. 8A-8C shows a torsion spring relationship with the thigh clutch arbor and shank frame at three different knee angles;

FIG. 9 shows a perspective view of one embodiment of a spring clutch of an embodiment of the present invention;

FIGS. 10A-10C show elements of a spring clutch activator in its partially activated state, its fully released state and its fully activated state;

FIG. 11 shows a side view of a thigh clutch;

FIG. 12 shows a perspective view of a thigh clutch shoe;

FIG. 13 shows a sensorized insole for use in a wearer's shoe; and

FIG. 14 is a block diagram of an electronics control module.

FIG. 15 shows geometry, forces and torques in a simplified model having a massless leg and a point mass torso;

FIG. 16 shows measurements of maximum knee torque of a human versus knee angle at four different knee angular velocities;

FIG. 17A shows the leg thrust produced at the hip sockets of a wearer of the invention of FIG. 1 versus knee angle for one variant of torsion spring;

FIG. 17B shows the torsion spring energy versus knee angle relationship of the invention of FIG. 1 versus knee angle for one variant of torsion spring;

FIG. 18 shows angles, forces, and velocity definitions of a Seg model;

FIG. 19A shows the Seg angle versus time during one step of a simulation model walking at 1.38 meters/second over level ground;

FIG. 19B shows the Seg thrust versus time during one step of a simulation model walking at 1.38 meters/second over level ground;

FIG. 19C shows the horizontal component of the torso velocity versus time during one step of a simulation model walking at 1.38 meters/second over level ground;

FIG. 19D shows the vertical component of the torso velocity versus time during one step of a simulation model walking at 1.38 meters/second over level ground;

FIG. 20A shows the normalized torso kinetic energy versus time;

FIG. 20B shows the normalized torso potential energy versus time;

FIG. 20C shows the normalized knee spring energy versus time;

FIG. 21 shows the position of the torso and the Seg at 20 millisecond intervals over two successive steps; and

FIGS. 22A-22C show the position of the torso and Seg at 40 millisecond intervals over two successive steps walking on level ground, on ascending stairs and on descending stairs.

DETAILED DESCRIPTION OF THE INVENTION

A description of preferred embodiments of the invention follows.

In the following discussion, the present invention shall be referenced as a leg brace or brace. When a wearer of the present invention dons the brace, the Ground Reaction Force (GRF) is transferred to the wearer's hip socket via two parallel structures. One structure is the wearer's femur, tibia, and foot skeletal bones. The other structure is the brace's thigh, shank, and shoe frames.

One embodiment of the invention addresses the problem of supporting the torso weight, supporting the weight of a carried load, and/or supporting the weight of an attached mass while standing, walking or running on any terrain. In addition to supporting the torso/carried load/attached mass weight, an embodiment of the invention also extracts and stores energy produced by the torso and/or carried load and/or attached mass during the period when the distance from a hip socket to an ankle is decreasing and then releases the stored energy during a period when the distance from the hip socket to the ankle is increasing. An embodiment of the present invention enables a wearer to reduce the amount of metabolic energy that would be normally required by the wearer without use of the embodiment of the present invention during walking and running activities. There is also provided a control mechanism for yielding the support and reduced metabolic energy consumption benefits at any speed and step length selected by the wearer over level or descending terrain.

In another embodiment, when a user of the brace wears a conventional backpack; support of that backpack weight must originate from the user's hip sockets. In effect, carrying extra weight simply adds mass to the torso (a carried load). By adding an attached mass support frame to braces worn on each leg, the weight of an attached mass such as a backpack is supported by the leg braces and not by the user's hip sockets. An attached mass support frame is likely to be a preferred usage of an embodiment of the invention when one adds a mass to the system since it reduces the stresses created on the wearer's skeleton and joints. Following discussions will utilize the term torso to mean wearer's torso system (comprising head, thorax, pelvis, and arms), a carried load, an attached mass, or any combination of the three.

To understand the full benefits of embodiments of the present invention, it is important to understand what is meant by support. One should first visualize a torso supported by legs wearing embodiments of the invention. One or both feet make periodic contact with the ground with the purpose of maintaining a relatively fixed distance between the ground and the torso Center of Mass (COM). By providing net forward or reverse thrust on each of the legs, the torso can be accelerated, decelerated. All this can be accomplished over uneven terrain. Bipedal locomotion is a process whereby the torso weight is supported alternately between one leg and the other. In walking and running, each step consists of a support epoch during which one leg supports the torso weight while the alternate leg is swinging forward preparing for the next step. Each support epoch is followed by a transition epoch where the torso weight transitions between the current support leg to the new support leg.

Ground Reaction Force (GRF) is defined as a force vector applied by the ground to a person at a point on a footprint called the "Center of Pressure (COP)." While the COP moves from heel to toe during the support epoch, to a first order, we can approximate the COP as located directly under the ankle. Neglecting air friction, the average horizontal component of the GRF must exactly equal zero for a person walking/running at constant average velocity regardless of ground slope. Similarly, the average vertical component of the GRF must be exactly equal to body weight regardless of the ground slope. While the average values of horizontal and vertical GRF are fixed by these constraints, the magnitude and direction of the GRF vary substantially during each step period.

Numerous devices have been created to transfer the GRF to the torso. These devices include crutches, canes and leg braces. One of the most successful is the conventional knee brace. A conventional knee brace consists of a shank frame and a thigh frame coupled together with a hinge employing stops to fix the knee angle. Typically, these frames are semi-rigid, and include padded half shells with straps to provide a mechanism for coupling a wearer's shank and thigh to the brace's shank frame and thigh frame. Knee braces are widely used to reduce knee joint stresses and provide knee immobilization following surgery.

Knee braces, while widely used, are not normally employed as walking enhancement devices because they impede normal gait activity. An embodiment of the present invention extends the basic knee brace concept in several aspects and introduces the benefits of reduced metabolic energy consumption over level and downsloping terrain at wearer selectable gait speed and step lengths. These benefits are accrued while supporting the torso weight via the hip sockets. Knee brace extensions include an actuated knee joint coupling the shank frame and the thigh frame and the addition of a foot frame hinged to the shank frame. While many benefits of embodiments of the present invention result without the foot frame, incorporating both the actuated knee joint and foot frame maximizes the overall benefits.

FIG. 1 shows a side view of a person wearing the one embodiment of the present invention. The general brace includes a shank frame 2, a thigh frame 3 and an actuated knee joint 11. An alternate embodiment includes a shoe frame 1 for attaching to a wearer's shoe 4. The thigh frame 3 includes a thigh strap 5 and a padded thigh shell 6 for providing a means for coupling force F.sub.thigh 7 between the wearer's femur and the thigh frame 3. The shank frame 2 includes a shank strap 8 and a padded shank shell 9 for providing a means for coupling force F.sub.shank 10 between the wearer's tibia and the shank frame 2.

The actuated knee joint 11 produces a torque Trq.sub.knee 12 between the thigh frame 3 and the shank frame 2. The magnitude of Trq.sub.knee 12 is dependent on a knee angle A.sub.knee 13. Forces F.sub.ankle1 14 and F.sub.ankle2 15 are forces applied by the shoe frame 1 to the shank frame 2 at an ankle joint 16. F.sub.hip 17 is a force applied by the torso to the hip socket caused by the gravitational field and inertial forces. To a first order, we assume that the wearer creates no torque either at a knee or an ankle. Accordingly, F.sub.hip 17 has a direction pointing directly from hip socket 18 to ankle joint 16. The only direct coupling between GRF and the wearer's hip socket 18 is through the wearer's foot, tibia and femur. The brace, however, provides an indirect coupling between the GRF and the wearer's hip socket 18 which increases from zero to 100% as a function of the knee angle A.sub.knee 13.

To a first order, we can assume that the entire torso mass is concentrated as a point mass located at the hip socket 18 and the leg and the brace are massless. With this assumption, the support function of the one embodiment of the present invention can now be seen. At near zero shank angle A.sub.s 19, the GRF is transferred to the hip socket 18 exclusively through the wearer's skeleton. As the shank angle A.sub.s 19 increases, a portion of the GRF is transferred to the hip socket 18 directly by the wearer's skeleton and the remaining portion of the GRF is transferred to the hip socket 18 indirectly by the brace.

FIGS. 2A-2D show forces at three brace/human contact areas versus 1/2 knee angle of a wearer of the invention of FIG. 1. The forces F.sub.thigh 7, F.sub.shank 10, F.sub.ankle1 14 and F.sub.ankle2 15 are shown as functions of shank angle A.sub.s 19 as a fraction of F.sub.hip 17. FIG. 2A shows a normalized F.sub.thigh 7 force versus shank angle A.sub.s 19. As can be seen, F.sub.thigh 7 increases from zero to approximately 1.2 F.sub.hip 17 at maximum knee flexion. FIG. 2B shows a normalized F.sub.shank 10 force versus shank angle A.sub.s 19. As can be seen, F.sub.shank 10 increases from zero to approximately 1.05 F.sub.hip 17 at shank angle A.sub.s 19 of 0.55 and then decreases. FIG. 2C shows a normalized F.sub.ankle1 14 force versus shank angle A.sub.s 19. Because F.sub.ankle1 14 is perpendicular to the F.sub.hip 17 vector, there is an equal an opposite force between the wearer's foot and the wearer's shoe. As can be seen, F.sub.ankle1 14 first becomes negative and then becomes positive but never exceeds approximately 0.4 F.sub.hip 17. Lastly, FIG. 2D shows a normalized F.sub.ankle2 15 force versus shank angle A.sub.s 19. As can be seen, F.sub.ankle2 14 increases monotonically to equal F.sub.hip 17 at a shank angle A.sub.s 19 of approximately 0.6 radians. Since F.sub.ankle2 14 plus the foot force against the bottom of the shoe must equal F.sub.hip 17, the force of the foot against the bottom of the shoe decreases to zero at a shank angle A.sub.s 19 of approximately 0.6 radians and then becomes negative. A negative force implies that the wearer's foot applies an upward force on the top inside of the shoe. This analysis shows how the torso force applied to the hip socket 18 (FIG. 1) is indirectly supported by the brace.

FIG. 3 shows is a side view of the invention of FIG. 1 augmented with an attached mass support frame 20. The attached mass support frame 20 is hinged at a proximal end of the thigh frame 3. The attached mass support frame 20 includes chest strap 21 and waist strap 22 for providing a means for the attached mass support frame 20 to transmit inertial and gravitational forces to the wearer's torso. In addition to the chest strap 21 and waist strap 22, an attached mass support frame hinge 24 provides a means for the attached mass support frame 20 to transmit inertial and gravitational forces to the support leg brace. It is straightforward to see that if a backpack mass is concentrated at a point mass located at the attached mass support frame hinge 24, 100% of the GRF associated with the backpack is transmitted through the brace with no support via the wearer's skeletal structure. In effect, the gravitational and inertial forces of the attached mass F.sub.b 23 is added to the F.sub.hip 17 as an applied load to the support leg brace.

FIG. 4 shows a perspective view of a person employing the embodiment of FIG. 1 on both legs. Each brace includes a shoe frame 1, a shank frame 2, an actuated knee 11, a thigh frame 3, and a control module 25. Although a pair of braces is shown, it should be understood that a single brace can be employed including at least one actuated knee 11 and optionally including the shoe frame 1. As shown, both the left and right braces have similar components with mirror symmetry. The shoe frame 1 is coupled to the shank frame 2 via bilateral hinges colinear with the wearer's ankle joint 16 (FIG. 1). A proximal end of the shank frame 2 is also coupled to a distal end of the thigh frame 3 via bilateral hinges colinear with the wearer's knee joint. Each of the actuated knees 11 include two arms, one of which is fixed to the distal end of the thigh frame 3 and the other arm is fixed to the proximal end of the shank frame 2. A quick release mechanism can be employed to fix the shoe frame 1 to a wearer's shoe 4 (FIG. 1). The shank frame 2 and the thigh frame 3 are coupled to the wearer's shank and thigh using well known schemes employing straps and padded shells connecting inner and outer side struts of the respective frames. The brace control module 25 is preferably fixed to the shank frame 2.

FIG. 5 shows a perspective view of a person employing the embodiment of FIG. 3. The embodiment of FIG. 5 includes all the components of FIG. 4 coupled to an attached mass support frame 20 via hinges colinear with a wearer's hip socket 18 (FIG. 1). However the thigh frame 3 includes a quick release hinge on its outer side strut to allow hinged coupling of the thigh frame 3 to the attached mass support frame 20. The attached mass support frame 20 is conventional except for quick release hinges.

FIG. 6 shows a side view of one embodiment of an actuated knee 11 coupled to the thigh frame 3 (FIG. 1) and the shank frame 2 (FIG. 1). The actuated knee 11 includes a thigh clutch assembly, a spring clutch assembly, a transfer arbor assembly, and a torsion spring 70. The thigh clutch assembly includes a thigh clutch wire 73 (at output arbor of the thigh clutch) and a thigh clutch actuator 75. The thigh clutch assembly is a mechanism for transferring torque from the thigh frame 3 (FIG. 1) to the transfer arbor under microprocessor control. The spring clutch assembly includes a spring clutch wire 74 (at output arbor of the spring clutch) and a spring clutch actuator 76. The spring clutch assembly is a mechanism for transferring torque from one arm of the torsion spring to its other arm under microprocessor control. The transfer arbor assembly includes two side plates (not shown), a thigh clutch arbor 71 (at input arbor of the thigh clutch), a spring clutch arbor 72 (at input arbor of the spring clutch), and a transfer arbor pin 83. Knee axle 84 provides a means for the shank frame 2, thigh frame 3, and the transfer arbor to rotate around a single axis of rotation.

The thigh frame 3 includes a thigh frame side strut 77, a thigh frame side plate 78, and a thigh wire termination 79 that are fixed relative to one another. The shank frame 2 includes a shank frame side strut 80, a shank frame side plate 81, a torsion arm pin 82 that and are fixed relative to one another. One arm of the torsion spring is directly coupled to the shank frame 2 (FIG. 1) via the torsion arm pin 82 while the other arm of the torsion spring 70 is directly coupled to the thigh clutch arbor 71 via transfer arbor pin 83. The thigh frame 3, the shank frame 2, and the transfer arbor all rotate around a common axis of rotation. Stops prevent hyper extension of the knee joint and limit flexion of the knee to approximately 130 degrees.

FIG. 7 shows a perspective view of a transfer arbor assembly of the actuated knee 11 of FIG. 6. The transfer arbor includes a pair of transfer arbor side plates 90 (one shown), a thigh clutch arbor 71, a spring clutch arbor 72, and a transfer arbor pin 83. The transfer arbor side plates 90 couple the thigh clutch arbor 71, the spring clutch arbor 72, and the transfer arbor pin 83. In a preferred embodiment, a thin steel thigh clutch sleeve 91 is heat shrunk on an outer surface of the thigh clutch arbor 71 to form a thigh clutch face. Similarly, a thin steel spring clutch sleeve 85 is heat shrunk on an outer surface of the spring clutch arbor 72 to form a spring clutch face. The outer surfaces of the thigh clutch arbor 71 and spring clutch arbor 72 are circular with a center coincident with a knee axle 84. To create an arbitrary hyper linear spring, the inner surface of the thigh clutch arbor is not circular.

The transfer arbor assembly is shown with the torsion spring 70 at a knee angle of zero degrees. With the thigh clutch activated, the thigh frame 3 is coupled to the thigh clutch arbor 71. Accordingly, any knee flexion causes the thigh clutch arbor 71 to rotate counter clockwise around the knee axle 84. A torsion arm pin 82 provides a means for pinning one arm of the torsion spring 70 to a shank frame 2. The transfer arbor sideplate cutout 92 (FIG. 8A), allows the transfer arbor assembly to rotate counter clockwise around the knee axle 84 approximately 1.1 radian. A transfer arbor pin 83 provides a means for pinning the other end of the torsion spring 70 to the thigh clutch arbor 71.

FIGS. 8A-8C show the torsion spring 70 relationship with the thigh clutch arbor 71 and shank frame 2 (FIG. 1) at three different knee angles. FIG. 8A shows a side view of the transfer arbor assembly with the torsion spring 70 at a zero knee angle. The shape of torsion spring 70 and the inner surface contour of thigh clutch arbor 71 are engineered to achieve the non-linear hardening back torque versus knee angle function desired. While non-trivial to design, well known techniques can be employed to achieve almost any monotonic torque function. Many torque functions can be realized without contouring the inner surface of the thigh clutch arbor 71. As a general rule, hyper linear behavior is gained by providing continuous stops that reduce the length of steel allowed to sustain torsion. At a knee angle of zero, the entire length of the torsion spring is allowed to sustain torsion. FIG. 8B shows the torsion spring 70 sustaining torsion of 24 degrees. As can be seen, only about 70% of the spring length is allowed to sustain torsion since the remaining 30% is fixed to the inner surface of the thigh clutch arbor 71. FIG. 8C shows maximum spring where 100% of the spring length is in contact with the inner surface of the thigh clutch arbor 71. This knee angle is called the torsion spring angle limit. Knee flexion greater than the torsion spring angle limit is possible because the thigh clutch will allow slipping once its maximum torque limit is reached. The torsion spring 70 is cut from spring steel blank with a shape dictated by the non-linear hardening spring function desired.

In one embodiment, both a microprocessor activated thigh clutch and spring clutch are used during normal operation. Both clutches are variants of a class of clutches called one-way dual-state clutches. In all clutches, there is an input arbor and an output arbor and a means for coupling torque between input arbor and output arbor. In dual-state clutches, there are two states that can be called released and actuated. In its released state, negligible torque can be transferred from input arbor to output arbor before slippage occurs. In the actuated state, a large torque can be coupled from input arbor to output arbor before slippage occurs. Transition between states is affected either mechanically or electrically typically via a solenoid.

Operation of a one-way dual-state clutch (employed in an embodiment of the invention) is identical to a dual-state clutch in the released state. In the actuated state, operation of the one-way dual-state clutch differs because large amounts of torque can be transferred from input arbor to output arbor only in one rotational direction. This torque transfer direction is called the `hard direction`. When in the actuated state, only a small amount of torque can be transferred from input arbor to output arbor before slippage occurs in the other direction, called the `easy direction`. Note that in any physical implementation of a one-way dual-state clutch, the maximum torque transferable between the input arbor and the output arbor without slippage is limited by the physical parameters of the clutch. Moreover, easy direction torque will normally be much larger than release state transfer torque.

FIG. 9 shows a perspective view of one embodiment of a spring clutch of the present invention. Preferably, the spring clutch is a one-way dual-state clutch called a spring wrap clutch. The spring wrap clutch includes multiple turns of music wire 100 coiled around the spring clutch arbor 72. Spring clutch arbor 72 is fixed to transfer arbor 71 via transfer arbor sideplates 90. The coiled music wire 100 preferably has an inside diameter of about 0.5 millimeters larger than the spring clutch arbor 72 outside diameter. The termination end 101 of the music wire 100 is looped around a torsion arm pin 82 and secured by crimping a wire oval 102 as shown. A control end 103 of the music wire 100 is formed as shown allowing the control end 103 to exit the transfer arbor sideplate 90 through transfer arbor sideplate cutout 92. The control end 103 is also formed to allow a spring clutch control arm 104 to hinge at the control end 103 of music wire 100.

The spring wrap clutch utilizes the well known capstan effect. Activation and release state are controlled by the application of a control force F.sub.c 105 applied to the control end 103 of the coiled music wire 100 via the spring clutch control arm 104. With zero F.sub.c, the music wire 100 assumes an unstressed inside diameter slightly larger than the outside diameter of the spring clutch arbor 72. In this state, virtually no torque can be transferred between the shank frame 2 and the transfer arbor 71. As control force F.sub.c 105 increases, the inner diameter of the music wire 100 decreases. When the force F.sub.c 105 reaches a critical value called the activation force F.sub.a (preferably approximately 1.7 newtons), all coils of the music wire 100 are in contact with the outer surface of the spring clutch arbor 72. When F.sub.c is greater than F.sub.a, the difference is available to create a much larger holding force F.sub.h 106 at the termination end 101 of the music wire 100. The ratio of the holding force F.sub.h 106 to available control force (F.sub.c-F.sub.a) varies as the well known capstan effect formula: Exp[N.differential.], where N is the number of wire turns (in radians) making contact with the spring clutch arbor 72 outside surface; and .differential. is the coefficient of friction between music wire 100 and spring clutch arbor 72 outside surface.

In a capstan effect system, the peak force occurs at the termination end 101 and decreases exponentially. Accordingly, an implementer sizes the diameter of the music wire 100 based on the peak force. Assuming 150 newton meter maximum torsion spring 70 torque, a music wire 100 having a diameter of 2.311 millimeters is required to sustain the 3750 newton peak force in the wire. With this minimum wire diameter limitation, only 5.75 turns of 2.311 millimeter music wire will fit on the surface of spring clutch arbor 72. Assuming a control force 105 F.sub.c=6 newtons and a coefficient of friction of .differential.=0.18 yields a 4000 newton maximum holding force F.sub.h 106.

To efficiently generate the control force F.sub.c 105, an extension spring is used to couple the end of spring clutch control arm 104 and an actuator. The actuator is composed of a geared motor driving a CAM to rotate the activation arm. The CAM makes one full turn per step and utilizes a surface contour that allows very fast transition from the activated to the released states. The CAM contour is also engineered for constant battery current drain when transitioning between states; and no battery current drain after reaching either state.

The amount of power consumption is directly proportional to the tolerances that can be engineered. To allow for ageing and manufacturing tolerances, an extension spring length change of 4 millimeters is assumed. The amount of energy needed to extend an extension is 0.5 .DELTA.x F.sub.max, where .DELTA.x is the extension distance in meters and F.sub.max is the maximum force in newtons. Assuming a geared motor/CAM efficiency of 50% implies that 0.024 joules of energy will be drained from the battery for each step.

FIGS. 10A-10C show elements of a spring clutch activator in its partially activated state; it's fully activated state, and its released state. A direct current (DC) motor 110, with a pinion gear 111, drives a first stage compound gear 112 rotating on first stage gear axle 113. The first stage compound gear 112 drives a second stage compound gear 114 rotating on second stage gear axle 115. Finally, the second stage compound gear 114 drives a third stage simplex gear 116 rotating on CAM axle 117. A control CAM 118 is fixed to a gear axle 117 and drives a actuation roller 122. The overall gear ratio between motor and control CAM 118 is selected such that CAM can rotate one turn in 160 milliseconds. An actuation arm 120 pivots on an actuation arm axle 121. To allow only one activation mechanism per actuated knee pair, the actuation arm 120 is bent from a single aluminum rectangular with two activation arm axles 121, one for the inner actuated knee and one for the outer actuated knee. The single actuation roller 122 rides along the control CAM 118 causing the actuation arm 120 to rotate around the actuation axle 121. Finally, an actuation spring 123 couples the actuation arm 120 and a clutch control arm 104. The control CAM 118 normally rotates counter clockwise and is shown midway between released and activated states. FIG. 10B shows the spring clutch activator in its released state while FIG. 10C shows the spring clutch activator in its activated state. In the activated state, the control CAM 118 contour is engineered to prevent control force F.sub.c 105 from back driving the motor.

FIG. 11 shows a side view of a thigh clutch according to the principles of the present invention. The thigh clutch couples torque from the thigh frame 3 (FIG. 1) to the transfer arbor 71 (FIGS. 6-8). It must transition from its activated state to its release state in a few milliseconds or a wearer will sense knee binding following toe off. When in the released state, the thigh frame 3 and transfer arbor 71 must rotate freely relative to one another or the wearer will have difficulty flexing his knee. When activated, the wearer should experience only a small back torque when attempting to extend his knee. When activated, a microprocessor must be able to finely control the amount of torque transferred from thigh frame 3 to transfer arbor 71 to affect controlled slippage. This implies that the thigh clutch must dissipate energy. Since the thigh clutch is positioned on the outer surface of the transfer arbor 71, it must prevent contamination of the surface by environmental agents that could significantly change the clutch surface's coefficient of friction. Lastly, like the spring clutch, it must go through one activation/release cycle per step. Thus, the amount of battery power consumed per step must be small.

The thigh clutch includes preferably five identical clutch shoes 130, one end clutch shoe 131, a first turn wire 132, a last wire turns 133, and the thigh clutch actuator 75. Each of the six clutch shoes 130/131 slides in the channel formed by the outer surface of the thigh clutch arbor 71 and transfer arbor sideplates 90 (FIGS. 6-8). The first turn wire 132, is fixed to the thigh frame 3 (FIG. 1) via a thigh wire termination 79. The first turn wire 132 is then routed clockwise through channels in each of the five clutch shoes 130 and half way through a channel in end clutch shoe 131. The first turn wire 132 then wraps 1/2 turn around first turn termination post 134 and then is routed counter clockwise through a second