A 3 Degrees-of-Freedom Lightweight Flexible Twisted String Actuators (TSAs)-Based Exoskeleton for Wrist Rehabilitation

This letter introduces a lightweight, three-degrees-of-freedom exoskeleton for wrist rehabilitation powered by Twisted String Actuators (TSAs), specifically designed to support flexion/extension, radial/ulnar deviation, and pronation/supination movements. Leveraging the high power-to-weight ratio of TSA actuation system, the exoskeleton ensures effective, comfortable, and personalized rehabilitation exercises. The device comprises five TSAs arranged in a tendon-driven configuration, enabling precise control and adaptability to various user anatomies. The experimental evaluations was conducted on a prototype demonstrating the device's ability to accurately replicate wrist movements guided by a physiotherapist, achieving low tracking errors (RMSE $\leq$ 1$^{\circ }$). The exoskeleton effectively achieves the desired wrist range of motion—115$^{\circ }$ for flexion/extension, 70$^{\circ }$ for radial/ulnar deviation, and 150$^{\circ }$ for pronation/supination—with torque capabilities suitable for rehabilitation purposes (0.35 Nm for flexion/extension and radial/ulnar deviation, and 0.06 Nm for pronation/supination).