Equilibrium-point prosthetic and orthotic ankle-foot systems and devices
Inventors
Hansen, Andrew H. • Gard, Steven A. • Childress, Dudley S. • Ruhe, Brian • Williams, Ryan
Assignees
Northwestern University • US Department of Veterans Affairs
Publication Number
US-8597369-B2
Publication Date
2013-12-03
Expiration Date
2027-10-17
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Abstract
The present invention relates to a system for use in rehabilitation and/or physical therapy for the treatment of injury or disease. The system can enable an amputee to proceed over any surface without overbalancing. In particular the system is self-adapting to adjust the torque moment depending upon the motion, the extent of inclination, and the surface topography.
Core Innovation
The invention provides an equilibrium-point prosthetic and orthotic ankle-foot device designed to assist human gait and prevent compromising balance. The device uses an ankle member comprising a reversible engagement means, torsion means, and a joint, and during use, a torsion curve plot of ankle moment against ankle dorsiflexion angle includes at least one transition point or multiple equilibrium points. This mechanism automatically adapts to different surface conditions, such as varying terrain inclinations and shoe heel heights, without requiring mechanical adjustments.
The invention addresses problems in prior art where prosthetic ankle devices either do not allow ankle motion or incorporate a single equilibrium point that does not change automatically. Existing devices tend to be rigid or depend on damping control, which removes energy, rather than stiffness control that stores and releases energy efficiently. The invention uses stiffness-based control with minimal sensors, enabling biomimetic ankle-foot roll-over shapes and plantarflexion beyond neutral in late stance, improving energy return and walking efficiency for amputees.
Claims Coverage
The patent includes one independent claim and covers several inventive features related to the structure and operation of the prosthetic/orthotic ankle-foot system.
Ankle-foot system with reversible dual-cam locking mechanism
A prosthetic/orthotic ankle-foot system comprising a foot member, a shaft serving as an axis of rotation, a support arm rotatably secured to the shaft, a first bumper maintaining the support arm's neutral position, a first cam rotatably secured to the shaft, a second bumper between the first cam and foot member, and a second cam rotatably secured to the support arm that engages with the first cam. The system further includes an upper housing movably secured to the support arm and a link pivotally secured to the upper housing and second cam so that movement of the upper housing causes rotation of the second cam into contact with the first cam, with ankle dorsiflexion causing rotation of the first cam and compression of the second bumper.
Spring-loaded adjustable upper housing with compression member
The system further includes an elongated bolt secured to the support arm, with the upper housing slidingly received on this bolt. A compression member, such as a spring received on the bolt, is interposed between the upper housing and support arm to resist movement of the upper housing toward the support arm. Spacers may be used to limit motion of the upper housing toward the support arm.
Cam geometry ratios for controlled locking engagement
The first cam and second cam have radii of curvature where the ratio of the first cam's radius to the second cam's radius ranges between 2:1 to 10:1, with a preferred ratio of about 4:1. This geometry supports effective locking and unlocking action during gait.
Adaptability for prosthetic pylon attachment and differential bumper stiffness
The upper housing is configured for attachment to a prosthetic pylon, enabling integration with lower limb prosthetic systems. Additionally, the second bumper is relatively stiffer than the first bumper to support the variable ankle joint stiffness during different gait phases.
The claims collectively cover a prosthetic ankle-foot system with a reversible dual-cam locking mechanism coordinated via a link and upper housing movement, supported by spring-loaded components to control lock engagement. The cam geometry and differential bumper stiffness enable adaptive stiffness modulation accommodating natural gait dynamics and prosthetic integration.
Stated Advantages
The device automatically adapts to various surface inclinations and shoe heel heights without manual adjustments.
The system utilizes stiffness-based control that allows for storage and return of energy during walking, increasing walking efficiency.
The prosthetic device more closely mimics the able-bodied ankle-foot mechanism by achieving plantarflexion beyond neutral during late stance.
The invention supports biomimetic ankle-foot roll-over shapes, improving the naturalness of gait.
The system uses minimal sensing devices compared to prior art, allowing simpler and possibly more reliable control.
Documented Applications
Use in ankle-foot prostheses and orthoses to improve mobility for persons with disabilities by automatic adaptation to walking surfaces and shoe heel heights.
Implementation in walking machines, legged robots, and toys that require adaptive ankle-foot mechanisms.
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