A Novel Bilateral Underactuated Upper Limb Exoskeleton for Post-Stroke Bimanual ADL Training

This paper introduces a lightweight bilateral underactuated upper limb exoskeleton (UULE) designed to assist chronic stroke patients with distal joint (Elbow-Wrist) impairments during bimanual activities of daily living (ADL). The UULE aims to assist patients in shoulder flexion/extension, elbow flexion/extension, forearm pronation/supination, and wrist flexion/extension. Notable features include (i) a cable-driven mechanism maintaining a lightweight structure (1.783 kg); (ii) passive joints conforming to less-impaired proximal joints, reducing restrictions on their movements; (iii) a compact design with passive ball joints enabling bilateral configuration for scapula protraction/retraction; and (iv) implementation of the master-slave joint assistance training strategy in an underactuated exoskeleton, achieving symmetric robot joint motion in bimanual ADL. Experiments with ten healthy subjects demonstrated the UULE's effectiveness by revealing significant reductions in muscle activity in a symmetric bimanual ADL task. These advancements address critical limitations of current exoskeletons, showcasing the UULE as a promising contribution to lightweight and effective robotic rehabilitation strategies for chronic stroke patients.