A Lightweight Shoulder Exoskeleton With a Series Elastic Actuator for Assisting Overhead Work

This article presents a novel active shoulder exoskeleton (SE) with a series elastic actuator (SEA) to assist overhead work. By proposing a differential drive approach and a clutch system, we make it possible to use only one actuator to assist different types of overhead work (one-handed and two-handed). This design offers the outstanding advantage of low device weight (comparable to the weight of a passive SE), which is the major challenge with current active SEs. In two-handed work, the SE can provide the same assistive torque to both shoulder joints and accommodate differences in their flexion angles. To provide adequate assistive torque to the user, we propose an intelligent assistive strategy with two seamless switchable control modes: Free mode with active backdrivability when the user rests the arm for daily activities (such as siting and walking), and assist mode with an impedance controller during overhead work. Experimental studies verified the good usability and effectiveness of the device. Statistical analysis of the electromyography (EMG) signals showed that the exoskeleton could reduce shoulder muscle activation levels by up to 30%.