Walking Assist Device Torque Amplification Mechanism
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Solution Overview
Problem
Existing walking assist devices face challenges in reducing the inertial moment of the leg link while maintaining the required assist force, as lighter rotary actuators struggle to generate sufficient torque, and increasing crank arm length slows down telescopic velocity, affecting controllability.
Innovation Solution
The walking assist device employs a drive mechanism with a rotary actuator, a drive crank arm, and a driven crank arm, where the connection link's pivot line obliquely crosses the actuator and joint shaft connection line, varying rotational angular velocities to amplify torque and reduce the required output torque from the rotary actuator, allowing for a lighter actuator without compromising assist function.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the rotary actuator is made lighter to reduce the inertial moment of the leg link, then the load on the free leg during forward swing is reduced, but the output torque becomes insufficient to generate the desired assist force
Solution Approach 1:
A connection link is introduced as an intermediary mechanical element between the drive crank arm and driven crank arm. This link creates a lever system that amplifies the output torque from the rotary actuator, allowing a lighter actuator to generate sufficient assist force through mechanical advantage rather than increasing actuator weight or power
Solution Approach 2:
The drive mechanism uses variable crank arm lengths (drive crank arm and driven crank arm with different lengths) to dynamically adjust the torque amplification ratio throughout the walking cycle. The angular velocity ratio between drive and driven crank arms varies dynamically, providing higher torque amplification when needed while maintaining adequate telescopic velocity for controllability
2Force
If the crank arm length is increased to amplify torque, then the output torque is increased, but the telescopic velocity of the leg link slows down, affecting controllability
Solution Approach 1:
The mechanism employs dynamically varying crank arm lengths and angular velocities rather than fixed dimensions. The drive crank arm and driven crank arm have different lengths that create a time-varying torque amplification effect, ensuring high telescopic velocity during critical phases of walking while providing torque amplification when needed
Solution Approach 2:
The drive mechanism utilizes periodic variation in the angular velocity ratio between drive and driven crank arms throughout the walking cycle. This periodic action provides torque amplification during specific phases of the gait cycle while maintaining high telescopic velocity during other phases, resolving the contradiction between force and speed requirements
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 configuration reduces the inertial moment of the leg link, alleviates load on the free leg during forward swing, and maintains controllability by optimizing torque and velocity ratios, enabling a lighter rotary actuator without impairing walking assist functionality.
Implementation Method 1
a connection link with one end pivoted at the drive crank arm and the other end pivoted at the driven crank arm, and the connection line connecting a pivot portion of the connection link at which the drive crank arm is pivotally mounted and a pivot portion of the connection link at which the driven crank arm is pivotally mounted obliquely crosses a connection line connecting the output shaft of the rotary actuator and the joint shaft of the third joint portion
Data Source
AI summary
An actuator is reduced in weight without impairing a walking assist function, and this reduces the inertial moment of a leg link. A drive crank arm on the output shaft of the actuator and a driven crank arm fixed to a second link portion so as to be concentric to the joint shaft of a third joint portion are connected to each other via a connection link. The connection link is placed so that a line connecting a pivot portion at which the drive crank arm is pivotally mounted and a pivot portion at which the driven crank arm is pivotally mounted obliquely crosses a line connecting the output shaft of the actuator and the joint shaft of the third joint portion.