Twisted String Actuation
Overview of the TSA Robot Arm with TSA Spine Robot (left), Detailed Schematic of Single TSA Module (right)

   For the development of human-friendly robots that are capable of collaborating with humans, it is essential to employ suitable actuators, which must be inherently safe, compact, light, and cost-effective at the same time. Owing to its actuation characteristics, twisted string actuators (TSAs) have been implemented as a promising solution for various human-robot interactive applications. However, due to its nonlinear actuation characteristics, lengthy design constraint (force output is proportional to its length), poor durability, and creep property of the TSA strings due to its inherent compliance, there was a need for a novel solution. To address these problems, we have developed new approaches in 1) mechanism design, 2) control, and 3) string fabrication: 1) variable radius pulley, parallel-bundle driven actuation, and creep compensator, 2) adaptive force control based on hybrid actuation framework, and 3) reinforced strings using specially treated lubrication technique with a replacement cartridge. Unlike conventional TSA robot joints, we were able to develop a modular robot joint that can be: 1) driven bidirectionally even with a single motor with a 47% reduction in length, 2) enhance the control bandwidth from 4.0 Hz to 6.0 Hz, and 3) significantly increase the lifecycle of the strings by over 100%.

Related Publications

A Spine Assistive Robot With a Routed Twisted String Actuator and a Flat-Back Alleviation Mechanism for Lumbar-Degenerative Flat Back

D. Lee, S. H. Kim, H. Park, S. Kim, and D. Shin
IEEE/ASME Transactions on Mechatronics, vol. 27, no. 6, pp. 5185-5196, Dec. 2022

A Compact, High-Torque, Twisted String Actuator Using Parallel Bundle-Driven Actuation with an Asymmetric Behavior Compensator

S. R. Lee, Y. J. Kim, D Lee, and D. Shin
AIM Conference, Royton Sapporo, Sapporo, Hokkaido, Japan, July 2022

A Compact, High-Torque, Twisted String Actuator Using Parallel Bundle-Driven Actuation with an Asymmetric Behavior Compensator

S. R. Lee, D. Lee, Y. J. Kim, and D. Shin
IEEE/ASME Transactions on Mechatronics, Online, 2021.

A Precise Twisted String Actuator Using Hybrid Actuation Concept for Robotic Arms

S. R. Lee, D. Lee, Y. Kim, and D. Shin
UR On-going work, Online presentation, July 2021.

Highly Durable Bidirectional Joint with Twisted String Actuators and Variable Radius Pulley

D. Lee, D. H. Kim, C. H. Che, J. B. In, and D. Shin
IEEE/ASME Transactions on Mechatronics, Vol. 25, No. 1, pp. 360-370, 2020.

Design of Creep Compensator to Prevent Performance Degradation of Twisted String Actuators (TSAs)

Y. J. Kim and D. Shin
In Proceedings of KSPE Autumn Conference, Jeju Island, Korea, October 2019.

A Compact, High-Torque, Twisted String Actuation with a Novel Mechanism Compensating for Nonlinear Behavior

S. R. Lee, Y. J. Kim, and D. Shin
In Proceedings of KSPE Spring Conference, Jeju Island, Korea, May 2019.

A Parallel Mechanism for Compact Twisted String Actuators

S. R. Lee, Y. J. Kim, and D. Shin
In Proceedings of KROS Conference, Pyeongchang, Korea, January 2019.

Design and Control of A Twisted String Actuator with Variable Radius Pulley

D. Lee and D. Shin
In Proceedings of KSPE Autumn Conference, Yeo-Su, Korea, Oct 2016.

Awards

KSPE 2019 춘계 최우수 논문 : 이승열, 김영진
KSPE 2016 추계 최우수 논문 : 이동언