Artificial Muscle Structure for High-Contraction Wearable Robotics

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Solution Overview

Problem

Pneumatic artificial muscles, such as the McKibben muscle, face challenges in achieving high contraction ratios while minimizing discomfort and maintaining user mobility due to radial expansion and increasing stiffness during pressurization, which interferes with user movements and causes skin discomfort.

Innovation Solution

The design features densely wound tension members with expansion members placed on one side to reduce squeezing and pinching, and a modular structure that adjusts stiffness and output characteristics, allowing for a convex output curve to maintain user comfort and mobility, with adjustable sectional geometry of the tube to optimize performance for specific muscle groups.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Length of moving object

If radial expansion of the muscle is increased to achieve higher contraction ratio, then contraction ratio is improved, but the expansion interferes with user movements and causes skin discomfort

Engineering Contradiction:

Improvecontraction ratioVSAvoidskin discomfort and movement interference

Core Design Contradiction:

Length of moving objectVSObject-affected harmful factors

Solution Approach 1:

The muscle is divided into multiple segments along its length, with tension members wound at different angular positions in each segment. This segmentation allows the radial expansion to be distributed and controlled, reducing localized skin pressure while maintaining overall contraction capability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Tension members are wound at different angular positions around the circumference of the muscle in different segments, creating an asymmetric distribution. This asymmetric winding pattern allows the expansion to occur preferentially in certain directions, minimizing interference with user movements and reducing skin discomfort while achieving high contraction ratios.

Inventive Principle:

Principle #4Asymmetry

2Strength

If stiffness of the muscle is increased during pressurization to maintain structural integrity, then strength is improved, but user comfort is reduced

Engineering Contradiction:

Improvemuscle strengthVSAvoiduser discomfort

Core Design Contradiction:

StrengthVSObject-affected harmful factors

Solution Approach 1:

The muscle structure transitions from a static to a dynamic configuration during pressurization. The tension members are arranged to allow progressive engagement as pressure increases, with different segments activating at different pressure levels. This dynamic behavior allows the muscle to maintain structural integrity and strength while adapting its stiffness characteristics to minimize user discomfort.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

Different segments of the muscle have different tension member winding patterns and local structural properties. This local quality variation allows certain regions to be stiffer for structural support while other regions remain more compliant for user comfort, resolving the contradiction between strength and comfort.

Inventive Principle:

Principle #3Local quality

3Productivity

If densely wound tension members are used to achieve high contraction ratio, then productivity is improved, but device complexity increases

Engineering Contradiction:

Improvecontraction ratioVSAvoidstructure complexity

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The complex winding pattern is divided into multiple simpler segments along the muscle length. Each segment has a manageable winding configuration that can be manufactured separately, reducing overall device complexity while achieving the high contraction ratio through the cumulative effect of all segments working together.

Inventive Principle:

Principle #1Segmentation

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 solution achieves a higher contraction ratio of 40% or more, reduces user discomfort, and maintains mobility by minimizing stiffness increase during pressurization, providing a comfortable and effective assistive muscle for wearable robots.

Implementation Method 1

Braided net can be used to wrap an inflatable tube, so that the radial expansion of tube is transformed into axial contraction

Methodology Applied

Scientific EffectRadial expansion transformation:

Implementation Method 2

a hollow pressurized expansion tube... configured to change shape with pressurized expansion

Methodology Applied

Scientific EffectPressure expansion: Pressure Increase

Data Source

PatentUS11788562B1Artificial muscle for robotic systems

Publication Date: 2023.10.17 THE CHINESE UNIVERSITY OF HONG KONG

AI summary

The subject invention pertains to a pneumatic, hydraulic, or otherwise inflatable or pressurized artificial muscle. Also provided are methods for making, controlling, and using such a muscle useful for prostheses, movement aids, or wearable robots to assist the movement of impaired subjects or to improve the function of healthy subjects. Muscles can be made by densely winding tension wires around pressurized expandable tubes having one or more specific geometric shapes removed from the tube cross section. The curve of output characteristics such as output force vs. contraction ratio can be adjustable by changing parameters of the sectional view of the tube. The appropriate shape of tube and related output characteristics can be selected according to application area or body part to be assisted to achieve the most flexible and optimal design for one or more muscle groups.