A Semi-Active Occupational Shoulder Exoskeleton for Overhead Work with Free Mode and Personalized Assistive Torque

Abstract

Current passive or semi-active shoulder exoskeletons for overhead work provide fixed assistive torque for all participants and tasks, which lacks adaptability. In addition, due to the need to store energy at low elevation angles, they may increase physical demand on the user when assistance is not required. This study presents a novel semi-active shoulder exoskeleton that can provide the free mode (i.e., no assistance) and personalized assistive torque to assist overhead work. The exoskeleton includes the motorized torque generator and hybrid control strategy. The motorized torque generator equipped with servo motor and encoder is characterized by its ability to electrically adjust the peak assistive torque angle and peak torque. In addition, we propose a hybrid control strategy with free and assistive modes. The free mode allows the exoskeleton to not interfere with movements that do not require assistance. The assistive mode provides personalized torque with three levels based on the height and weight of the user. Experimental results validated the exoskeleton's mechanical performance (e.g., high backdrivability) and its assistive effectiveness. The results showed that the exoskeleton could reduce shoulder muscle activation by up to 55.03% and demonstrated a significant difference compared to fixed assistance.