Twisted string actuation is an actuation concept which uses the twisting motion of strings to convert the rotational motion of a motor into a linear motion. By replacing the heavy, high friction, and high-cost gearheads with light, silent, compliant, and low-cost strings, twisted string actuators (TSAs) can provide powerful tendon-based transmission, making it a unique solution for human-robot interactive tasks. Despite such advantages, TSAs exhibit highly nonlinear force/displacement characteristics when compared to conventional geared motors, thus limiting their performance in bidirectional joints. In order to implement TSAs in a bidirectional joint, two motors had to be used to compensate for the nonlinearities, which eventually increased the control complexity, weight, and overall cost of the robotic system. In addition, TSAs show poor durability, which also limits its applicability. To address these issues, a high-performance bidirectional joint has been proposed by implementing optimized TSAs with lubrication, and a variable radius pulley (VRP). By implementation of specially designed TSAs, we achieved 1) extended service time of the strings. Furthermore, by replacing the conventional circular pulley with a VRP, we achieved 2) improved range of motion; 3) increased payload; and 4) better tracking performance, even with a single motor.
Bibliographical noteFunding Information:
Manuscript received June 26, 2018; revised February 12, 2019, July 26, 2019, and October 15, 2019; accepted December 9, 2019. Date of publication December 19, 2019; date of current version February 13, 2020. Recommended by Technical Editor C.-C. Lan. This work was supported in part by the Ministry of Trade, Industry & Energy (Korea) under the Industrial Technology Innovation Program no. 10062636, “Development of Compact, Lightweight, High-Performance, Highly Durable, Safe Twisted String Actuation Module Using Reinforced Strings, Variable Radius Pulleys, and Hybrid Actuation Control,” in part by Chung-Ang University Research Scholarship Grants in 2017, and in part by the Convergence Technology Development Program for bionic arm funded by the Korea Government (MSIT) (NRF-2017M3C1B2085321). (Corresponding author: Dongjun Shin.) The authors are with the Chung-Ang University, Seoul 06974, South Korea (e-mail: firstname.lastname@example.org; email@example.com; firstname.lastname@example.org; email@example.com; firstname.lastname@example.org).
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All Science Journal Classification (ASJC) codes
- Control and Systems Engineering
- Computer Science Applications
- Electrical and Electronic Engineering