Twisted String Actuation Module for Compact Robotic Finger with Extended Stroke, Reduced Hysteresis, and Bidirectional Operation
Chunghyeon Lee, Bhivraj Suthar, Seokhwan Jeong
AI summary
Problem
Practical twisted string actuators are hindered by nonlinear twisting hysteresis, limited contraction stroke, and inherently unidirectional motion, which prevent their reliable use in compact robotic systems.
Approach
The authors implement a single-motor-driven antagonistic string pair that uses adaptive tensioning to suppress hysteresis, combined with asymmetrically shifted finger channels and adjustable pre-tension to compensate for kinematic asymmetry and enable true bidirectional operation.
Key results
- Suppression of twisting hysteresis via antagonistic tensioning
- Extended effective stroke through asymmetric axis shift design
- Accurate bidirectional bending control across ±180°
- Compact kinematic model validated for multi-finger gripper integration
Why it matters
Offers a scalable, gear-free actuation solution for compact robotic hands and dexterous manipulation systems requiring precise reversible motion.
Abstract
Twisted String Actuators (TSAs) are promising alternatives to conventional gear-based transmissions due to their high reduction ratios and compact form factors. However, practical limitations such as nonlinear hysteresis, limited stroke, and inherently unidirectional motion hinder their deployment in robotic systems. In this work, we propose a novel bidirectional TSA mechanism that addresses all three limitations simultane- ously through an antagonistic configuration, asymmetric axis shift (AAS), and pre-tension tuning. This mechanism enables reliable bidirectional actuation by compensating for asymmetric contraction-extension behavior, suppresses hysteresis via adaptive tensioning, and extends the effective stroke. We implement the proposed design in a continuum finger module and derive a compact kinematic model for control. Extensive experiments validate the effectiveness of the approach, demonstrating the attenuation of the hysteresis, accurate bidirectional bending control across a wide range (±180°), and the feasibility of integration into multi-finger grippers for dexterous manipulation. The results suggest that the proposed actuator design serves as a practical and scalable solution for compact robotic systems requiring precise and reversible motion.