A Passive Upper Limb Exoskeleton With Tilted and Offset Shoulder Joints for Assisting Overhead Tasks

Overhead tasks, mostly in the industrial sector, frequently cause upper limb work-related musculoskeletal disorders (WMSDs) leading to low productivity. Although passive upper limb exoskeletons have been used in industry to decrease upper limb WMSDs, they are limited to assist in overhead tasks, as they lack sufficient range of motion (ROM), assistive performance, and wearability. Here, we propose a passive upper limb exoskeleton with tilted and offset shoulder joints, enhanced ROM, and assistive mechanisms to effectively assist the upper limb. The ROM of the shoulder joint, tilted and offset to the rear of the user to increase the range, was sufficient at a 165° elevation angle, revealed by simulations and experiments. The assistive mechanism loads and unloads a spring to passively generate assistive torque. Our results showed that 9.5 N·m of maximum assistive torque was generated at 120°, which is sufficient to assist overhead task with a 1-kg tool. The assistive torque profile can be adjusted by changing the design parameters. Finally, assistance performance was evaluated by user verifications via electromyography experiments in welding-like tasks. The muscle activities of the anterior deltoid and lateral deltoid, the main muscles of shoulder flexion, were reduced to 32.4% and 45.2%, respectively.