A quasi-passive lockable shoulder exoskeleton with load adaptability for assisting both static and dynamic tasks

Passive shoulder exoskeletons are widely adopted to mitigate musculoskeletal injuries. However, conventional passive shoulder exoskeletons suffer from limited spring stiffness and insufficient assistive torque, resulting in poor adaptability. While lockable exoskeletons provide greater assistance, they fail to support dynamic tasks. This study presents a quasi-passive lockable shoulder exoskeleton that unifies these two design approaches and provides assistive torque for both dynamic and static tasks. The device integrates a lockable mechanism for static load support with a torque generator for dynamic assistance. Specifically, the lockable mechanism, actuated by an electromagnetic clutch, enables locking at desired shoulder angles. This allows the exoskeleton to fully compensate for arm gravity across different users and tools, thereby enhancing load adaptability and usability. Meanwhile, the torque generator driven by elastic elements improves performance during dynamic tasks. To the best of our knowledge, this is the first shoulder exoskeleton capable of both lockability and dynamic assistance. Experimental results demonstrated that the exoskeleton, with a sufficient range of motion, significantly reduced muscle activation in both static (up to 81.79%) and dynamic tasks (up to 45.39%). For static tasks, it also increased task duration by up to 148%. The exoskeleton showed good usability, with a score of 79.3 ±7.7, reduced perceived effort, but increased discomfort in the arms and hips. These findings indicate that the proposed exoskeleton can effectively assist both dynamic and static tasks and has the potential to reduce the risk of shoulder musculoskeletal disorders. The proposed design emphasizes multifunctionality and task adaptability, providing a promising solution for the practical application of exoskeletons.