Translational Research on a Soft Upper Limb Rehabilitation Robot Driven by Twisted String Actuators

1. Funding Agency

Ministry of Health and Welfare of the Republic of Korea

2. Motivation

Conventional rehabilitation robots rely on bulky and expensive high-stiffness motors and gear systems, limiting their use to clinical settings and making continuous rehabilitation in daily life difficult. This is particularly problematic for upper-limb rehabilitation, which requires flexible and high-degree-of-freedom movements. Although there is growing interest in lightweight, high power-density twisted string actuators (TSAs), their application in rehabilitation robots remains unexplored. There is thus an urgent need for accessible, lightweight, and affordable rehabilitation devices that can be integrated into patients’ everyday lives.

3. Objectives

This project aims to develop an upper-limb rehabilitation robot utilizing twisted string actuators, offering a lightweight, low-cost, and highly flexible wearable system. By enabling personalized and quantitative rehabilitation therapy, the proposed device supports repetitive training at home, ultimately improving clinical outcomes and enhancing the quality of life for patients beyond traditional healthcare environments.

4. Results

This study presents the advancement of a lightweight, high-output actuator module based on Twisted String Actuation (TSA), achieving a peak performance of 10 Nm and 45 deg/s. The actuator’s operational durability was validated under a load of 100 N, 20% stroke, and 500 cycles per day over 35 days. A 2-degree-of-freedom (2-DOF) rehabilitation robot for the elbow and wrist was developed, integrating the TSA modules into a compact system weighing 1.996 kg. A nonlinear stiffness modulation and bidirectional position control algorithm were implemented to ensure precise and adaptive motion control. Safety functions—including motion-synchronized exercise based on contralateral IMU data, therapist-driven remote operation, emergency stop, and spasticity response mechanisms—were developed. Furthermore, two exercise scenarios and a game-based rehabilitation interface were completed through feedback from patients and clinical experts. As a result, core components such as the position control algorithm, the 2-DOF exoskeleton prototype, TSA modules, and the motion-synchronized exercise (MSE) system were successfully established, leading to the filing of two patent applications.

5. Related Publications

• Continuously Variable Transmission based Twisted String Actuator (Korean Patent Application No. 1020230147716)

6. Contact

• Jaehyung Jang