Prosthetic Foot Spring Assembly With Speed-Dependent Stiffness
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Solution Overview
Problem
Existing prosthetic feet lack adaptability in stiffness to varying gait speeds, often optimized for either high damping or energy efficiency but not both, and may compromise stability or weight with complex electronic components.
Innovation Solution
A spring assembly with a carbon fiber structure and non-Newtonian polyurethane material layers that adjust stiffness based on gait speed, providing high damping at slower speeds and high energy return at faster speeds without the need for electronic components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If high energy returning materials such as carbon fiber are used in passive prosthetic feet, then greater energy return is achieved at higher walking speeds, but stability is reduced at slower walking speeds
Solution Approach 1:
The prosthetic foot combines carbon fiber composite materials with variable stiffness characteristics. The carbon fiber provides high energy return at faster walking speeds while the variable stiffness mechanism maintains stability at slower speeds, creating a composite structure that resolves the contradiction between energy efficiency and stability across different gait speeds.
2Stability of the object's composition
If low energy returning materials such as wood or polyurethane foams are used in passive prosthetic feet, then stability is improved at slower walking speeds, but energy return is significantly reduced at higher walking speeds
Solution Approach 1:
The prosthetic foot incorporates variable stiffness mechanisms that dynamically adjust the structural properties based on loading conditions and gait speed. This dynamic adaptation allows the foot to exhibit stability characteristics at slower speeds when needed and energy return characteristics at faster speeds, resolving the static contradiction between these two performance requirements.
3Adaptability or versatility
If electronically controlled and actuated components are added to prosthetic feet to enable variable ankle joint angle and positive energy push-off, then energy efficiency and adaptability are improved, but device complexity and weight increase
Solution Approach 1:
The prosthetic foot employs passive variable stiffness mechanisms that automatically adapt to different gait conditions without requiring external power sources or control systems. The material and structural design enable the device to self-regulate its stiffness and energy return characteristics based on the applied loads and gait speed, achieving adaptability while maintaining simplicity and reducing weight.
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 solution enables a prosthetic foot that automatically adjusts stiffness with gait speed, enhancing energy efficiency and stability across different walking speeds while maintaining a lightweight and simple design.
Implementation Method 1
The second material can be a non-Newtonian material
Implementation Method 2
one or more layers of a time-dependent second material disposed in the gap
Implementation Method 3
a first elongate member extending along a length and made of a first material; a second elongate member extending generally parallel to the first elongate member
Data Source
AI summary
A variable stiffness spring assembly includes first and second members made of a first material and separated by a gap along at least a portion of their lengths, and one or more layers made of a second material disposed in the gap. The variable stiffness spring assembly can be incorporated into or take the form of a limb support assembly, such as a prosthetic foot. The second material disposed between the first and second members is rate-sensitive or speed-dependent, such that the material exhibits different properties when the user of the prosthetic foot is walking at high or fast walking speeds compared to low or slow walking speeds. The prosthetic foot can exhibit high damping and energy absorption, and therefore stability, at slow speeds, and high energy return at faster speeds.