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

This paper 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$1^{\circ }$</tex-math></inline-formula>). The exoskeleton effectively achieves the desired wrist range of motion-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$115^{\circ }$</tex-math></inline-formula> for flexion/extension, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$70^{\circ }$</tex-math></inline-formula> for radial/ulnar deviation, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$150^{\circ }$</tex-math></inline-formula> 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).