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[0001] This patent application claims priorety of Provisional Patent Application No. 60/395,938, filed Jul. 15, 2002.
[0002] The invention relates generally to the fields of legged robotics, orthotic leg devices and prosthetic leg joints, and more specifically to artificial limbs with time-variable mechanical parameters.
[0003] Prosthetic limbs have come a long way since the days of simple wooden “peg legs”. Today, amputee men running on a prosthetic leg can beat race times of the best unimpaired women runners. It is believed that new advances in prosthetic limbs (such as those embodied in the present invention) will soon lead to amputees being able to out-perform the best unimpaired athletes of the same sex in sports such as running. It is an object of the present invention to advance the state of prosthetic limbs to a new level, providing increased athletic performance, increased control, and reduced body strain. It is a further object of the present invention to provide essential elements needed for making prosthetic limbs that more accurately mimic the mechanical behavior of healthy human limbs.
[0004] Description of Normal, Level-ground Walking:
[0005] In order to establish terminology used in this document, the basic walking progression from heel strike to toe off is first explained. There are three distinct phases to a walking stance-period as depicted in
[0006] Saggital Plane Knee Phases
[0007] 1. Beginning with heel strike, the stance knee begins to flex slightly (Sequence 1-3). This flexion allows for shock absorption upon impact as well as keeping the body's center of gravity at a more constant vertical level throughout stance.
[0008] 2. After maximum flexion is reached in the stance knee, the joint begins to extend again, until full extension is reached (Sequence 3-5).
[0009] 3. During late stance, the knee of the supporting leg begins to flex again in preparation for the swing phase (Sequence 5-7). This is referred to in the literature as “knee break”. At this time, the adjacent foot strikes the ground and the body is in “double support mode” (that is to say, both legs are supporting body weight).
[0010] Saggital Plane Ankle Phases
[0011] 1. Beginning with heel strike, the ankle undergoes a controlled plantar-flexion phase where the foot rotates towards the ground until the forefoot makes contact (Sequence 1-2).
[0012] 2. After controlled plantar-flexion, the ankle undergoes a controlled dorsi-flexion phase where the tibia rotates forwardly while the foot remains in contact with the ground (Sequence 2-5).
[0013] 3. During late stance, the ankle undergoes a powered plantar-flexion phase where the forefoot presses against the ground raising the heel from the ground (Sequence 5-7). This final phase of walking delivers a maximal level of mechanical power to the walking step to slow the fall of the body prior to heel strike of the adjacent, forwardly positioned leg.
[0014] The development of artificial leg systems that exhibit natural knee and ankle movements has been a long standing goal for designers of legged robots, prostheses and orthoses. In recent years, significant progress has been made in this area. The current state-of-the-art in prosthetic knee technology, the Otto Bock C-Leg, enables amputees to walk with early stance knee flexion and extension, and the state-of-the-art in ankle-foot systems (such as the Össur Flex-Foot) allow for ankle controlled plantar-flexion and dorsi-flexion. Although these systems restore a high level of functionality to leg amputees, they nonetheless fail to restore normal levels of ankle powered plantar-flexion, a movement considered important not only for biological realism but also for walking economy. In
[0015] Artificial legs with a mechanical impedance that can be modeled as a spring in parallel with a damper are known in the art. Some prostheses with non-linear spring rates or variable damping rates are also known in the art. Unfortunately, any simple linear or non-linear spring action cannot adequately mimic a natural limb that puts out positive power during part of the gait cycle. A simple non-linear spring function is monotonic, and the force vs. displacement function is the same while loading the spring as while unloading the spring. It is an object of the present invention to provide actively electronically controlled prosthetic limbs which improve significantly on the performance of artificial legs known in the art, and which require minimal power from batteries and the like. It is a further object of the present invention to provide advanced electronically-controlled artificial legs which still function reasonably well should the active control function fail (for instance due to power to the electronics of the limb being lost). Still further, it is an object of the present invention to provide artificial legs capable of delivering power at places in the gait cycle where a normal biological ankle delivers power. And finally, it is an object of the present invention to provide prosthetic legs with a controlled mechanical impedance and the ability to deliver power, while minimizing the inertial moment of the limb about the point where it attaches to the residual biological limb.
[0016] During use, biological limbs can be modeled as a variable spring-rate spring in parallel with a variable damping-rate damper in parallel with a variable-power-output forcing function (as shown in
[0017] Muscle tissue can be controlled through nerve impulses to provide variable spring rate, variable damping rate, and variable forcing function. It is an objective of the present invention to better emulate the wide range of controllability of damping rate, spring rate, and forcing function provided by human muscles, and in some cases to provide combination of these functions which are outside the range of natural muscles.
[0018] There are two major classes of embodiments of the present invention. The first major class provides for actively controlled passive mechanical parameters (actively controlled spring rate and damping rate). This major class of embodiments will be referred to as variable-stiffness embodiments. Three sub-classes of variable-stiffness embodiments are disclosed:
[0019] 1) Multiple parallel interlockable springs.
[0020] 2) Variable mechanical advantage.
[0021] 3) Pressure-variable pneumatics.
[0022] The second major class of embodiments of the present invention allows for the controlled storage and release of mechanical energy within a gait cycle according to any arbitrary function, including functions not available through simple nonlinear springs. Within this second major class of embodiments, energy can be stored and released at rates which are variable under active control. Thus for a given joint, the force vs. displacement function is not constrained to be monotonic or single-valued. Within this class of embodiments, energy (from either muscle or a separate on-board power source) can be stored and released along arbitrarily defined functions of joint angular or linear displacement, force, etc. This major subclass of embodiments shall be referred to herein as energy transfer embodiments. Two sub-classes of energy transfer embodiments are disclosed:
[0023] 1) Bi-articular embodiments (which transfer energy from a proximal joint to a distal joint to mimic the presence of a missing joint).
[0024] 2) Catapult embodiments (which store energy from a power source over one span of time and release it over another span of time to aid locomotion).
[0025] The present invention makes possible prostheses that have mechanical impedance components (damping and spring rate) and power output components that are actively controllable as functions of joint position, angular velocity, and phase of gait. When used in a prosthetic leg, the present invention makes possible control of mechanical parameters as a function of how fast the user is walking or running, and as a function of where within a particular step the prosthetic leg is operating.
[0026] It is often necessary to apply positive mechanical power in running shoes or in orthotic and prosthetic (O&P) leg joints to increase locomotory speed, to jump higher, or to produce a more natural walking or running gait. For example, when walking at moderate to high speeds, the ankle generates mechanical power to propel the lower leg upwards and forwards during swing phase initiation. In
[0027] Two catapult embodiments of the present invention are described in which elastic strain energy is stored during a walking, running or jumping phase and later used to power joint movements. In a first embodiment, catapult systems are described in which storage and release of stored elastic energy occurs without delay. In a second embodiment, elastic strain energy is stored and held for some time period before release. In each Embodiment, mechanism architecture, sensing and control systems are described for shoe and O&P leg devices. Although just a few devices are described herein, it is to be understood that the principles could be used for a wide variety of applications within the fields of human-machine systems or legged robots. Examples of these first and second catapult embodiments are shown in
[0028] One bi-articular embodiment of the invention described herein comprises a system of knee-ankle springs and clutches that afford a transfer of energy from hip muscle extensor work to artificial ankle work to power late stance plantar-flexion. Since the energy for ankle plantar-flexion originates from muscle activity about the hip, a motor and power supply need not be placed at the ankle, lowering the total mass of the knee-ankle prosthesis and consequently the metabolic cost associated with accelerating the legs in walking. Examples of these embodiments are shown in
[0029] Several variable-stiffness embodiments are described herein in which variable spring-rate structures are constructed by varying the length of a moment arm which attaches to a spring element about a pivot axis, thus providing a variable rotational spring rate about the pivot axis. Examples of such embodiments are depicted in
[0030] Variable-stiffness embodiments of the present invention employing multiple interlockable parallel spring elements are depicted in
[0031] The multiple parallel spring elements in
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[0058] A powered-catapult embodiment of the present invention is shown in
[0059] A mechanical implementation of lumped-element diagram
[0060] During the powered plantar-flexion phase of the gait cycle, the control system releases clutch
[0061] In an alternate embodiment, motor
[0062] In an alternate embodiment,
[0063] For catapult embodiments depicted in both
[0064]
[0065] Two bi-articular embodiments of the present invention are shown in
[0066] It should be understood that the bi-articular knee-ankle invention of embodiment I (
[0067] In a second embodiment (
[0068] It should be understood that the bi-articular knee-ankle invention of embodiment II (
[0069] The mechanical system in
[0070]
[0071] A variable stiffness ankle-foot prosthesis embodiment according to the present invention is shown in
[0072]
[0073] In a preferred embodiment, the slope discontinuities in function
[0074] In a preferred embodiment, coupling spring
[0075]
[0076] Utilizing a nonlinear dissipative coupling between pairs of elements in a multiple-parallel-element spring allows joint spring rates in a prosthetic limb which are a function of velocity. Thus, a joint spring rate can automatically become stiffer when running than it is while walking.
[0077] In one preferred embodiment, chamber
[0078]
[0079] In an immediate-energy-transfer embodiment of the present invention according to
[0080]
[0081] In one embodiment of the present invention (shown in
[0082] A pneumatic embodiment of a variable-stiffness spring for a prosthesis is shown in
[0083] In one mode of operation, valve
[0084] In a preferred embodiment of a variable-stiffness leg prosthesis according to the present invention is implemented through the pneumatic system of
[0085] The pneumatic system shown in
[0086] In a preferred embodiment of the present invention, a pneumatic prosthetic leg element according to
[0087] The foregoing discussion should be understood as illustrative and should not be considered to be limiting in any sense. While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the claims.