Quasi-Passive Pneumatic Ankle Prosthesis Stiffness Control
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Solution Overview
Problem
Conventional energy storage and release (ESR) prosthetic feet for transtibial amputees fail to replicate biologically appropriate torque and stiffness profiles during walking, leading to increased metabolic energy expenditure and reduced mobility due to their cantilever design, which opposes the natural mechanical behavior of the biological ankle joint.
Innovation Solution
A quasi-passive pneumatic ankle-foot prosthesis with a piston, valve, and bending spring mechanism that stores energy during dorsiflexion and releases it during plantarflexion, mimicking the stiffness and torque behavior of a biological ankle, allowing for customizable and biologically inspired mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a cantilever leaf spring design is used in ESR prosthetic feet, then energy storage and release function is achieved, but the stiffness decreases exponentially during stance phase which opposes biological ankle behavior
Solution Approach 1:
The patent inverts the traditional cantilever approach by using a parallel architecture where the pogo spring and A-F foot spring work together in parallel. This inversion allows the system to achieve increasing stiffness during stance phase, matching biological ankle behavior, while still providing effective energy storage and release through the coordinated action of both springs.
Solution Approach 2:
The patent implements dynamic stiffness adjustment through the interaction of the pogo spring and A-F foot spring in parallel. The system transitions from a static cantilever design to a dynamic system where the effective stiffness changes during the gait cycle, increasing during stance phase to match biological ankle characteristics while maintaining energy storage functionality.
2Power
If an anthropomorphic cantilever design is used, then energy return at terminal stance is achieved, but the torque-angle and stiffness properties are non-biological
Solution Approach 1:
The patent changes the fundamental parameters of the prosthetic design by transitioning from a cantilever configuration to a parallel configuration with a pogo spring and A-F foot spring. This parameter change enables the system to produce biologically appropriate torque-angle and stiffness properties while maintaining effective energy return at terminal stance through the coordinated deformation of both springs.
Solution Approach 2:
The pogo spring acts as an intermediary element between the ground reaction force and the A-F foot spring. It mediates the force transmission in a way that allows the system to achieve both biological appropriateness in torque-angle properties and effective energy return, by distributing and coordinating the mechanical work between the two spring elements.
3Device complexity
If conventional passive ESR prosthetic feet are used, then simple structure is maintained, but metabolic energy expenditure increases by at least 20%
Solution Approach 1:
The patent introduces a pneumatic or hydraulic damper in parallel with the spring elements to control the damping characteristics of the prosthetic foot. This allows passive energy dissipation and active energy return through the damping mechanism, reducing metabolic energy expenditure while maintaining a relatively simple overall structure that builds upon the conventional ESR design.
Solution Approach 2:
The patent recovers energy that would otherwise be lost during the gait cycle by using the damper to capture and return energy during push-off. This energy recovery mechanism reduces the metabolic burden on the user while maintaining structural simplicity by integrating the damping function into the existing spring-based ESR prosthetic framework.
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 prosthesis provides biomechanically appropriate ankle walking kinetics and kinematics, reducing metabolic energy consumption and improving mobility by replicating the natural stiffness and torque profiles of a biological ankle, thus enhancing the walking efficiency of transtibial amputees.
Implementation Method 1
a bending spring mechanism that stores energy during dorsiflexion and releases it during plantarflexion
Implementation Method 2
A quasi-passive pneumatic ankle-foot prosthesis with a piston, valve, and bending spring mechanism
Data Source
AI summary
Implementations of a quasi-passive assistive device are disclosed. Such a device may comprise a spring mechanism that increases stiffness similar to a biological ankle. In one implementation, the spring mechanism may comprise a piston, valve, springs, or other elements to match a biological stiffness profile similar to that of a biological ankle. In one implementation, an apparatus for an artificial ankle is disclosed, comprising a piston coupled to a spring and the piston connected to a valve. The spring and the piston may store energy during dorsiflexion of the ankle and the spring and the piston release energy during plantarflexion of the ankle. The piston may store and release energy through the use of the valve.