A light-weight passive upper arm assistive exoskeleton based on multi-linkage spring-energy dissipation mechanism for overhead tasks

This paper introduces a novel passive type upper arm exoskeletal vest for assisting overhead jobs in industrial environment such as automotive manufacturing centers. The developed upper arm exoskeleton named as Hyundai Vest Exoskeleton (H-VEX) proposes two key mechanical structural elements: (1) an energy-storage multi-linkage mechanism dissipating spring-loaded energy according to angle-increment of a wearer’s upper arm, and (2) a poly-centric shoulder joint mechanism on the transverse plane for its proper alignment with a wearer’s shoulder joint movement. Based on the proposed mechanical structures, H-VEX has effective ergonomic properties which enable it to provide a smooth-increasing upper arm assistive torque according to increment in a wearer’s arm angle up to its target angle without impeding movements in large ranges of motion (RoM). Especially, the critical design parameters of the energy-storage multi-linkage are able to be adjusted to generate customized assistive torque responses, and additionally, this mechanism can be covered in a thin cover frame for beneficial ergonomic & cosmetic reasons. Furthermore, industrial-purposed requirements such as mechanical endurance and cost-effectiveness can be achieved taking advantages of key structures. To verify the effectiveness of H-VEX on overhead works, activation signals of electromyography (EMG) on main corresponding muscles of ten subjects carrying out overhead manipulation tasks were measured and compared with cases without wearing the exoskeletal vest. The statistical analysis on acquired EMG signal indicates that assistive torque provided by H-VEX was shown to significantly decrease activation of the shoulder-related muscles during target tasks.