Design and Control of a Novel Active Shoulder Exoskeleton for Overhead Work Assistance

This article presents a novel active shoulder exoskeleton to assist overhead work. The exoskeleton has its actuators, control electronics, and the battery packed in a drive unit located on the user's back. Bowden cables are used to transmit the forces from the drive unit to the shoulder joints of two lightweight arm support structures. Due to the flexibility of the Bowden cable, the exoskeleton can adapt to complex shoulder joint movements. Linear series elastic actuators are used to achieve force control instead of position control for overhead work assistance. The design specifications achieve a portable and compliant system. In addition, a multimodal assistive strategy has been developed to handle different working conditions with seamless switching between different modes: free mode with zero torque tracking when no assistance is needed, assist mode during overhead work, and safe mode when a sudden impact load is detected. Experimental studies conducted in simulated overhead work conditions demonstrated the usability and effectiveness of the system. Statistical analysis of the electromyography signals from the key shoulder muscles indicated that the exoskeleton could reduce the level of shoulder muscle activation by up to 40%.