Design and Evaluation of a 3-DOF TSA-Driven Wrist Exoskeleton with Minimal Actuation

This paper presents a lightweight, tendon-actuated exoskeleton for wrist rehabilitation. The device employs four twisted string actuators (TSAs) to actuate three degrees of freedom, supporting flexion/extension, abduction/adduction, and pronation/supination of the wrist. Its modular and compact structure allows easy adaptation to different users and integration with additional hand modules. A tracking system based on two inertial measurement units (IMUs) captures the orientation of the hand relative to the forearm, enabling both recording and playback of physiotherapist-guided exercises. The exoskeleton was evaluated with two healthy subjects and a user with impaired wrist mobility. Results demonstrate accurate replication of wrist motion, with low root mean square errors across all degrees of freedom, and a significant increase in the end-user's range of motion. The system represents a wearable, portable, and user-friendly platform for both clinical and home-based rehabilitation, highlighting the potential of TSA-based exoskeletons for individualized therapy.