Variable Stiffness Ankle Cam System for Prosthetic Gait
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Solution Overview
Problem
Ankle-foot prostheses fail to accurately mimic the torque-angle relationship of able-bodied walking, leading to hindered tibial progression, reduced stability, and abnormal gait patterns in amputees due to their high stiffness during stance phases and inability to modulate mechanical properties for various mobility tasks.
Innovation Solution
A cam-based transmission system with a customizable torque-angle profile, utilizing a cam profile and follower with a leaf spring, where the stiffness is adjustable via a sliding element, allowing for continuous variation of ankle stiffness to match human biomechanics during different phases of gait and mobility tasks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If ESR feet are used to provide energy storage and return, then energy efficiency is improved, but the quasi-stiffness during stance phase becomes too high, hindering tibial progression and reducing stability
Solution Approach 1:
The patent applies a cam mechanism that dynamically adjusts the stiffness of the prosthetic ankle during the gait cycle. The cam profile is designed to vary the mechanical properties continuously, providing low quasi-stiffness during early stance to allow tibial progression, then increasing stiffness before heel-off to capture energy, thereby resolving the contradiction between energy efficiency and tibial progression
Solution Approach 2:
The invention changes the stiffness parameter of the prosthetic ankle throughout the gait cycle using a cam-based transmission system. The cam profile transforms the constant stiffness of a spring into a variable stiffness output, matching the natural quasi-stiffness curve of a human ankle, thus allowing the system to provide appropriate stiffness at different phases without compromising energy storage and return
2Use of energy by moving object
If ESR feet are used to provide energy storage and return, then energy efficiency is improved, but the range of motion during stair traversal is reduced due to high stiffness
Solution Approach 1:
The cam mechanism dynamically adjusts stiffness based on the gait phase, allowing the prosthetic to provide low quasi-stiffness during stair traversal to enable adequate range of motion, while maintaining high energy storage and return capabilities during level walking through the same variable stiffness mechanism
3Stability of the object's composition
If damping characteristics are varied to improve stability, then stability is improved, but energy is removed from the ankle joint, reducing forward propulsion
Solution Approach 1:
Instead of varying damping, the invention changes the stiffness parameter through the cam mechanism. This allows the system to provide appropriate mechanical support for stability during stance phase while preserving energy for forward propulsion, as the cam-transformed spring system stores and returns energy rather than dissipating it through damping
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 enables improved stability, reduced energy dissipation, and enhanced range of motion during walking and stair traversal by closely matching human biomechanics, reducing the risk of socket pain and joint diseases in amputees.
Implementation Method 1
The cam follower may roll along the curved outer edge of the cam profile from dorsiflexion to plantarflexion of the assistive device
Implementation Method 2
The cam follower may be coupled to a leaf spring of the assistive device
Data Source
Figure 1~2A
Figure 2B~3B
Figure 2C~12
AI summary
A cam system for an assistive device and related methods are disclosed. The cam system may comprise a cam profile (252) and a cam follower (254). The cam profile has a curved outer edge comprising a concave portion. The cam follower is positioned within the concave portion when the assistive device is in an equilibrium position. The assistive device may further comprise a spring (210) that deflects in response to a force applied by the cam system. The assistive device may have a sliding element (220) to adjust the stiffness of the spring in deflection. The assistive device may take the form of a prosthesis or an orthosis.