Design, Modelling and Experimental Evaluation of a Tendon-driven Wrist Abduction-Adduction Mechanism for an upper limb exoskeleton

Researchers at Aalborg University (Juwairiya S. Khan, Mostafa Mohammadi, John Rasmussen, Lotte N.S. Andreasen Struijk) have designed and experimentally validated a novel tendon-driven wrist abduction-adduction mechanism for upper limb exoskeletons. Published on arXiv (2604.20893) and submitted to IEEE/ASME Transactions on Mechatronics, the mechanism uses a single Bowden cable passively tensioned by a spiral torsional (clock) spring, eliminating the need for antagonistic actuation or heavy electric motors/pneumatics. This reduces weight, friction, and mechanical complexity—key challenges in wearable assistive devices.

Kinematic and dynamic modeling estimated required torque and identified optimal spring stiffness parameters, which were tested with three spring configurations on five participants with no motor disabilities (NMD) under varying arm positions and loading conditions. The nominal spring configuration achieved consistent agreement between simulation predictions and experimental results, balancing motion range, torque demand, and repeatability. The study demonstrates that simulation-informed stiffness selection can effectively guide compact, cable-driven wrist exoskeleton design, reducing reliance on empirical tuning and accelerating development of lightweight rehabilitation and assistive devices.