Ankle-foot prosthesis for automatic adaptation to sloped walking surfaces
Inventors
Hansen, Andrew H. • Nickel, Eric A.
Assignees
US Department of Veterans Affairs • University of Minnesota System
Publication Number
US-10105243-B2
Publication Date
2018-10-23
Expiration Date
2033-09-10
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Abstract
An ankle-foot prosthesis includes a foot plate, an ankle frame attached to the foot plate, a yoke pivotally connected to the ankle frame and including a member for attaching to a leg, a damper having a first end connected to the yoke and a second end connected to the ankle frame, and a control mechanism for switching the damper between low and high settings.
Core Innovation
The invention is an ankle-foot prosthesis that automatically adapts to level and sloped walking surfaces, providing lower limb amputees with a more natural and stable gait. The device includes a foot plate, an ankle frame, a yoke pivotally connected to the ankle frame for attaching to a leg, a damper connected between the yoke and ankle frame, and a control mechanism for switching the damper between low and high damping settings. This allows the prosthesis to adjust its behavior on every step, adapting to different terrain and providing stability during walking and standing tasks.
The problem being solved is that existing prosthetic ankle devices typically operate about a single equilibrium point which works acceptably on level surfaces but causes instability on sloped surfaces. Prior systems that use hydraulic dampers or powered motors have drawbacks such as energy loss, delayed adaptation requiring multiple steps to adjust, high power requirements, expense, and bulkiness. The invention addresses these issues by providing a prosthesis that can automatically adapt to sloped walking surfaces on every step, with simple mechanical and hydraulic components, low or no maintenance, and low energy consumption.
Specifically, the invention employs a hydraulic damper with variable extension damping controlled by a cutoff valve and optionally variable flow resistors, along with a spring arranged in parallel. The control mechanism switches the damper between high extension damping during stance phase and low extension damping during toe-off and swing phase to allow natural ankle motion and quick return to neutral position. The design also includes a curved roll-over surface that limits dorsiflexion and ensures biomimetic ankle-foot rollover motion. The system offers a standing mode with high damping in both directions for increased stability while standing or swaying.
Claims Coverage
The patent includes multiple independent claims describing an ankle-foot prosthesis with integrated foot plate, ankle frame, yoke, hydraulic damper with spring, and fluid control circuit features. The main inventive features are identified below.
Hydraulic damper with fluid control circuit for controlled extension and compression
The prosthesis incorporates a hydraulic damper pivotally connected between the yoke and ankle frame, working with a spring in parallel. A fluid control circuit controls damper extension and compression with valves such as check valves allowing only compression or extension, and a cutoff valve that permits extension during specific gait intervals.
Automatic switching of damper extension damping during gait cycle
The prosthesis switches the cutoff valve to allow damper extension during prosthetic side toe off and up to 0 to 0.13 seconds thereafter, and closes it at or before the next prosthetic side foot flat. This enables the ankle to move naturally during swing phase and locks extension during stance.
Roll-over curved surface limiting dorsiflexion on foot plate
The anterior portion of the ankle frame includes a curved, upwardly inclined roll-over surface that directly engages and limits dorsiflexion of the forward deflectable portion of the foot plate, providing biomimetic ankle-foot rollover shape.
Mode switching for walking and standing stability
The fluid control circuit is capable of preventing compression and extension of the damper during standing mode to increase stability, and allowing compression and extension during walking mode cycles.
Inclusion of adjustable fluid-flow resistors to tune damping
The fluid control circuit may include variable fluid-flow resistors to adjust hydraulic fluid resistance selectively in dorsiflexion, plantarflexion, or both, allowing customization of damping characteristics.
Mechanical or actuator-controlled cutoff valve triggered by load
The cutoff valve opening and closing can be actuated mechanically by a load applied during walking (e.g., via spring-loaded hinge or telescoping element) or actuated electronically, enabling passive or semi-active control of the damper.
Overall, the claims cover a prosthetic ankle-foot device featuring a hydraulic damper and spring assembly with a fluid control circuit that regulates damping dynamically throughout the gait cycle, employs a roll-over surface to mimic natural ankle motion, and switches between walking and standing modes for optimized user stability and adaptability.
Stated Advantages
Provides a more natural and comfortable gait for the user.
Increases energy efficiency during walking or other gait activities.
Simple design using fewer parts resulting in low or no maintenance.
Compact and more durable with reduced mechanical failure risk.
Prevents undesirable backward swing that could cause imbalance or injury.
Quieter, lighter, less clumsy, enhancing user friendliness.
Automatically adapts to different sloped walking surfaces on every step.
Easily switches to a stable mode for standing or swaying tasks.
Documented Applications
Used by lower limb amputees for walking over various sloped terrain with improved stability and confidence.
Provides stability during standing or swaying tasks such as washing dishes.
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