Ankle Prosthesis Load-Directing Cam Mechanism for Lighter Gait Support
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Solution Overview
Problem
Existing lower limb prostheses, both passive and powered, face challenges in providing adequate functionality for various activities while maintaining a lightweight and compact design, with powered devices being heavy and requiring continuous power, and passive devices lacking versatility.
Innovation Solution
A semi-active ankle prosthesis with a load directing mechanism that redirects loads away from the actuator during weight-bearing phases, using a cam transmission and actuator to manage ankle position during non-weight bearing activities, allowing for a smaller and lighter design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a powered prosthesis with motorized actuators is used to provide power generation and joint positioning for various activities, then the user can perform more activities including stairs and ramps, but the weight increases 2-4 times and the device requires continuous battery charging and produces noise
Solution Approach 1:
The prosthesis is segmented into passive structural components and active control elements. The ankle joint uses a passive cam-based transmission mechanism for structural support while separating the actuator's role to only provide positioning control during non-weight-bearing phases, eliminating the need for heavy-duty motors required for weight-bearing support
Solution Approach 2:
The system dynamically switches between passive structural support during weight-bearing phases and active actuated control during non-weight-bearing phases. The cam transmission mechanism passively absorbs and redirects loads during standing and walking, while the actuator activates only when needed for joint positioning, creating a dynamic hybrid operation mode
2Adaptability or versatility
If a powered prosthesis with continuous actuation is used to assist with a wide range of activities, then the user can perform more functions, but the device consumes power even during zero net energy tasks such as walking and standing
Solution Approach 1:
The actuator operates periodically only during non-weight-bearing phases of the gait cycle rather than continuously. The passive cam transmission handles structural support during weight-bearing phases without energy consumption, while the actuator activates intermittently for positioning adjustments, creating a periodic operation pattern that eliminates wasted energy
Solution Approach 2:
The passive cam-based transmission mechanism self-activates to handle load redirection and structural support during weight-bearing phases without requiring external power. The mechanism automatically engages and disengages based on the gait cycle phase, making the system self-regulating and eliminating the need for continuous powered assistance
3Weight of moving object
If a passive prosthesis with constant or variable resistance is used to maintain lightweight and robust design, then the device remains lightweight and quiet, but it provides limited function for activities such as stairs and ramps and requires user compensation
Solution Approach 1:
The passive cam transmission mechanism serves multiple functions: it provides structural support during weight-bearing phases, redirects reaction torques to the frame, and enables joint movement. The same mechanism works across various activities from level walking to stairs and ramps, making the lightweight design universally applicable without requiring activity-specific heavy actuators
4Adaptability or versatility
If a powered prosthesis uses actuators that accommodate a wide range of speeds and torques to assist with a wide range of activities, then the user can perform diverse activities, but the device requires power over the course of an entire day and increases weight significantly
Solution Approach 1:
The heavy-duty actuation capability is extracted from the continuous operation requirement and concentrated only into the brief non-weight-bearing phases. The passive cam transmission takes out the weight-bearing support function entirely from the actuator, allowing the use of a much lighter actuator that only needs to provide brief positioning assistance
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 ankle prosthesis provides enhanced stability and comfort on different terrains while reducing the actuator's power requirements, resulting in a 50% shorter and 30% lighter form factor with improved mobility and reduced fatigue.
Implementation Method 1
a biasing component that biases the cam roller of the cam transmission against the cam follower of the cam transmission
Implementation Method 2
a cam transmission including a cam follower, wherein the cam transmission pivots the ankle joint about the ankle axis
Implementation Method 3
the load directing mechanism directs a load imposed upon the ankle prosthesis into the structural frame during a loaded state
Data Source
AI summary
The ankle prosthesis of the present disclosure includes a load directing mechanism that alters the internal load path during weight bearing, guiding the load directly into the structural frame. By changing the load path with the load directing mechanism, both vertical and horizontal loads can be supported directly by the ankle's structure through a cam roller.