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Overtwisting and Coiling Highly Enhance Strain Generation of Twisted String Actuators
Revanth Konda1, David Bombara1, Jun Zhang1
1Department of Mechanical Engineering, University of Nevada, Reno, Nevada, USA.
Soft Robotics
|May 16, 2023
Summary
Researchers achieved significantly higher strain in twisted string actuators (TSAs) by developing a method for consistent overtwisting and coiling. This breakthrough enhances TSA performance for robotic applications, enabling greater movement and compliance.
Area of Science:
- Robotics
- Materials Science
- Mechanical Engineering
Background:
- Twisted string actuators (TSAs) offer high force but struggle with consistent strain generation and compliance.
- Overtwisting in TSAs typically leads to undesirable knots and coils, creating unstable structures.
- Achieving uniform coiling during overtwisting is crucial for enhancing TSA strain capabilities.
Purpose of the Study:
- To investigate and realize uniform and consistent coil formation in overtwisted TSAs.
- To enhance strain generation in TSAs through controlled overtwisting and coiling.
- To systematically train strings for uniform coil formation in overtwisted TSAs.
Main Methods:
- Experimental investigation of overtwisting in TSAs with varying string stiffnesses (ultrahigh molecular-weight polyethylene and supercoiled polymers).
- Development of a systematic string "training" procedure to ensure uniform coil formation.
- Characterization of strain, force, velocity, and torque in overtwisted TSAs.
Main Results:
- Consistent uniform coil formation was achieved in overtwisted TSAs for the first time.
- Overtwisting and coiling resulted in approximately 70% strain for stiff TSAs and 60% for compliant TSAs.
- Achieved strain is more than double that of conventional twisting methods.
Conclusions:
- Controlled overtwisting and uniform coiling significantly enhance TSA strain capabilities.
- The developed string training method enables consistent performance in overtwisted TSAs.
- Demonstrated the successful application of an overtwisted TSA in a robotic bicep, showcasing its potential.
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