A Novel Back-Support Exoskeleton with a Differential Series Elastic Actuator for Lifting Assistance

Compared to conventional back-support exoskeletons (BSEs) with two motors, BSEs driven by a single motor have the advantage of light weight. However, current single-motor BSEs have problems with accommodating asynchronous hip movements, achieving precise force control and efficient force transmission, and giving autonomy to users when walking. In this article, we propose a novel BSE with a differential series elastic actuator (D-SEA) for lifting assistance. The unique differential working principle can accommodate the angular difference between the hip joints and provide the same assistive torque at both hip joints. The D-SEA achieves precise force control with a custom controller based on accurate spring deflection feedback, and drives the hip joints via an efficient cable-roller mechanism. Taking advantage of the active backdrivability of the D-SEA, we proposed an intelligent assistive strategy that automatically provides adequate support for lifting tasks and grants autonomy to users during walking. In experi- ments, the BSE reduced the activation level of the back muscles by up to 40% during lifting, without increasing the activation of the back and leg muscles during walking.