Ankle-Foot Prosthesis with Cam-Actuated Spring
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing ankle-foot prostheses face challenges in providing net positive work during gait, leading to non-symmetric gait patterns and high metabolic costs in amputees, with powered prostheses struggling to meet torque and power requirements while maintaining size and weight constraints due to battery energy density limitations.
Innovation Solution
An ankle-foot prosthesis combining an actuator with elastic elements, such as a spring mechanism and cam profile, to store and release negative mechanical energy, reducing system energy consumption and torque/power requirements, allowing for a more natural gait even in passive mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If powered prostheses use actuators to deliver net positive energy, then metabolic cost decreases and gait naturalness improves, but torque and power requirements increase making size and weight constraints difficult to meet
Solution Approach 1:
The spring mechanism stores energy during the dorsiflexion phase when the actuator is inactive, and releases it during the push-off phase. This periodic energy storage and release reduces the actuator's continuous power requirement while maintaining net positive work delivery, thus resolving the contradiction between metabolic cost reduction and actuator power requirements.
Solution Approach 2:
The spring is pre-loaded during the dorsiflexion phase before the push-off phase begins. This preliminary energy storage in the spring reduces the instantaneous power demand on the actuator during push-off, allowing the actuator to be downsized while still providing sufficient propulsion to reduce metabolic cost.
2Duration of action of moving object
If commercial batteries are used to supply energy for daily walking, then powered prosthesis function is achieved, but battery size and weight increase due to energy density limitations
Solution Approach 1:
By implementing periodic energy storage and release through the spring mechanism, the system reduces peak power demands on the battery. This allows the battery to be smaller and lighter while still providing sufficient energy for daily walking, thus resolving the contradiction between operating duration and battery weight.
Solution Approach 2:
The spring mechanism changes the power delivery parameters by smoothing out peak demands and extending the effective operating duration of the battery. This parameter transformation allows a lighter, smaller battery to provide equivalent energy over a longer period, resolving the contradiction between battery operating duration and weight.
3Ease of operation
If passive prostheses use spring-clutch mechanisms, then ankle angle adjustment is achieved, but net positive work cannot be supplied resulting in non-symmetric gait patterns
Solution Approach 1:
The invention merges the spring-clutch mechanism with an active actuator in a hybrid system. The spring provides passive ankle angle adjustment and energy storage, while the actuator provides active net positive work during push-off. This combination resolves the contradiction by integrating both passive adjustment capability and active work production.
Solution Approach 2:
The hybrid actuator-spring system performs multiple functions: the spring provides passive adjustment and energy storage, while the actuator provides active propulsion. Together they achieve both ankle angle adjustment and net positive work supply, resolving the contradiction between ease of operation and power delivery.
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 significantly decreases energy consumption, reduces actuator torque and power needs, and enables a nearly normal gait by using the elastic components to reproduce human ankle stiffness and propulsion, improving energy efficiency and extending battery life.
Implementation Method 1
employing an actuator in combination with elastic elements used to store and release negative mechanical energy
Implementation Method 2
The elastic components are embodied as a spring mechanism, such as linear springs, which are coupled with a cam and configured in parallel to the actuator
Data Source
AI summary
A powered ankle-foot prosthesis and associated methods of use are described herein. Such prostheses can employ an actuator and elastic components, the actuator being controlled to deliver net positive work to propel the wearing amputee forward and the elastic components being used to store and release negative energy to improve efficiency. Elastic components can be linear springs coupled with a cam and configured in parallel to the actuator. The cam profile can be designed to generate a desired spring torque versus angle curve rather than a spring stroke versus angle curve, thereby reproducing human ankle controlled dorsiflexion stiffness. Such configurations improve system energy efficiency and reduce both actuator torque and power requirements. Such prostheses can also operate in a passive mode, in which a nearly normal gait can be achieved even without powered assist.