Variable-Stiffness Leg Prosthesis for Gait-Phase Energy Return
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Solution Overview
Problem
Existing ankle foot prostheses lack the ability to adapt stiffness and energy release timing dynamically, leading to improper walking behaviors, increased musculature demands, and excessive joint loads due to fixed stiffness and energy dissipation mechanisms.
Innovation Solution
A hybrid closed-loop pneumatic and hydraulic system is integrated into the prosthesis to adjust stiffness and energy return timing in real time, using a variable stiffness module with a motor-controlled pneumatic cylinder and accumulator to modulate fluid volume and pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single stiffness carbon fiber blade is used, then the prosthesis is simple and lightweight, but it cannot adapt to various walking conditions and provides improper walking behaviors
Solution Approach 1:
The patent implements a variable stiffness mechanism that dynamically adjusts the stiffness of the carbon fiber blade during the gait cycle. A motor-driven fulcrum positioner changes the fulcrum position along the blade, transitioning the blade from a flexible state during loading response to a stiffer state during terminal stance, enabling adaptation to different walking conditions while maintaining a relatively simple overall structure
Solution Approach 2:
The patent changes the physical parameter of stiffness by modifying the fulcrum position on the carbon fiber blade. By adjusting the fulcrum position, the effective stiffness of the blade is altered without changing the blade material or geometry, allowing the prosthesis to adapt to various walking conditions through parameter modulation
2Adaptability or versatility
If a hydraulic cylinder is used to adjust ankle impedance, then the level of stiffness can be controlled, but energy is dissipated and cannot be modulated for energy return
Solution Approach 1:
The patent employs a pneumatic artificial muscle (PAM) actuator instead of a traditional hydraulic cylinder. The PAM uses pneumatic pressure to generate force while maintaining compliance and energy efficiency. The pneumatic system can store and release energy elastically, avoiding the energy dissipation inherent in hydraulic systems while providing adjustable stiffness control
3Adaptability or versatility
If pneumatic actuators are used in pairs to control plantarflexion and dorsiflexion, then adjustable stiffness is achieved, but device weight and size increase
Solution Approach 1:
The patent merges the functions of multiple actuators into a single pneumatic artificial muscle by using a parallel cable-driven mechanism. One PAM actuator controls both plantarflexion and dorsiflexion through a cable-pulley system, eliminating the need for paired actuators and significantly reducing device weight and size while maintaining adjustable stiffness capability
4Adaptability or versatility
If the fulcrum position is changed to adjust stiffness, then continuously adaptable stiffness is achieved, but the maneuvering speed is limited due to acme screw mechanism
Solution Approach 1:
The patent replaces the slow acme screw mechanism with a pneumatic artificial muscle actuator that can rapidly reposition the fulcrum along the carbon fiber blade. The PAM's rapid response capability enables fast stiffness transitions, achieving both continuous adaptability and high maneuvering speed
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system provides adaptable stiffness and energy return timing, enhancing walking efficiency and comfort by dynamically adjusting to various gait phases, speeds, and surfaces, while maintaining a compact and lightweight design.
Implementation Method 1
A semi-active mechanism to provide a wide range of motion for different activities uses a pneumatic cylinder with an interior region that can be pressurized
Implementation Method 2
hydraulic component to provide custom stiffness or absorb impact during heel contact
Implementation Method 3
The apparatus includes a motor configured to reduce the volume of the interior region from the first value to a second value during a second gait phase after the first gait phase
Data Source
AI summary
A method and an apparatus for enhancing operation of a leg prothesis is provided. The apparatus includes a variable stiffness module configured to be attached between a first portion and a second portion of a leg prothesis. The first portion is configured to move relative to the second portion in a first plane during a first gait phase. The variable stiffness module defines an interior region configured to store pressurized fluid. A motor is configured to reduce a volume of the interior region during a second gait phase to increased an amount of stored energy of the pressurized fluid. The amount of stored energy is released during a third gait phase to assist a subject wearing the leg prothesis during the third gait phase.