Passive Ankle Prosthesis Spring Torque Conversion
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Solution Overview
Problem
Current prosthetic ankle and foot devices rely on passive leaf springs that absorb and release energy during walking, but they store insufficient energy to propel the body forward efficiently, leading to slower walking speeds and increased energy expenditure for amputees, and existing active designs are hindered by large and heavy actuators.
Innovation Solution
A two-degree of freedom mechanism utilizing a network of conventional springs that converts the force generated during walking into ankle torque for propulsion, allowing for active behavior without the need for sensors or actuators, by releasing stored energy along a different degree of freedom to achieve natural ankle mechanical characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If passive leaf springs are used in prosthetic ankles, then the device structure remains simple and lightweight, but the energy storage capacity is insufficient to propel the body forward efficiently
Solution Approach 1:
The patent introduces a second degree of freedom (rotational movement) in addition to the traditional single degree of freedom (compression). This dimensional change allows the spring mechanism to store and release energy more effectively by converting linear compression forces into rotational torque at the ankle joint, thereby increasing energy storage capacity without requiring complex active components.
Solution Approach 2:
The patent employs a dynamic spring mechanism that transitions between compression and rotation during the gait cycle. The spring dynamically adapts its configuration, compressing during weight acceptance and rotating during push-off, allowing the passive structure to deliver active-like energy return characteristics without motors or sensors.
2Use of energy by moving object
If active components (motors) are used to assist propulsion, then the desired mechanical characteristics and energy return are achieved, but the size and weight of the ankle prosthesis increase significantly
Solution Approach 1:
The spring mechanism serves itself by automatically converting compression energy into rotational torque without external control systems. The stored elastic energy in the compressed spring directly drives the rotational movement during push-off, eliminating the need for motors, batteries, or control electronics that would add weight and complexity.
Solution Approach 2:
The patent replaces the active mechanical system (motors and actuators) with a passive mechanical system (spring-based energy storage and conversion). This substitution maintains the desired energy return characteristics while dramatically reducing the weight and complexity of the prosthesis by eliminating electronic actuation components.
3Use of energy by moving object
If active components (motors) are used to assist propulsion, then the desired mechanical characteristics and energy return are achieved, but the size of the ankle prosthesis increases significantly
Solution Approach 1:
The spring mechanism serves itself by automatically converting compression energy into rotational torque without external control systems. The stored elastic energy in the compressed spring directly drives the rotational movement during push-off, eliminating the need for motors, batteries, or control electronics that would add weight and complexity.
Solution Approach 2:
The patent replaces the active mechanical system (motors and actuators) with a passive mechanical system (spring-based energy storage and conversion). This substitution maintains the desired energy return characteristics while dramatically reducing the weight and complexity of the prosthesis by eliminating electronic actuation components.
4Use of energy by moving object
If more energy is extracted from the ankle than was provided in ankle deflection, then active behavior is achieved, but this requires active components that increase device complexity
Solution Approach 1:
The patent introduces a second degree of freedom (rotational movement) in addition to the traditional single degree of freedom (compression). This dimensional change allows the spring mechanism to store and release energy more effectively by converting linear compression forces into rotational torque at the ankle joint, thereby increasing energy storage capacity without requiring complex active components.
Solution Approach 2:
The patent employs a dynamic spring mechanism that transitions between compression and rotation during the gait cycle. The spring dynamically adapts its configuration, compressing during weight acceptance and rotating during push-off, allowing the passive structure to deliver active-like energy return characteristics without motors or sensors.
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
This approach enables a lightweight prosthetic ankle to release more energy than stored in ankle deflection, reducing the need for large motors and allowing amputees to walk with a near-normal gait, while maintaining mechanical characteristics similar to a natural ankle.
Implementation Method 1
a spring mechanism (3) between the top body (C) and the middle body (B)... The force generated along the leg during walking is converted into ankle torque used to propel the body forward during push-off
Implementation Method 2
The energy stored along one degree of freedom (generated by the weight of the amputee) is released along a different degree of freedom to achieve mechanical characteristics very similar to a natural ankle
Data Source
AI summary
Disclosed are passive lower limb prosthetic devices comprising at least a two degree of freedom mechanism and a network of compression springs.