A Parallel-Elastic Actuator for a Torque-Controlled Back-Support Exoskeleton

An actuated back-support exoskeleton to assist manual handling is presented. Its objective is to provide a significant portion of the forces necessary to carry out the physical task, thereby reducing the compressive loads on the lumbar spine and the associated risk of injury. The design rationale for a parallel-elastic actuator (PEA) is proposed to match the asymmetrical torque requirements associated to the target task. The parallel spring relaxes the maximum motor torque requirements, with substantial effects on the resulting torque-control performance. A formal analysis and experimen- tal evaluation is presented with the goal of documenting the improvement in performance. To this end, the proposed PEA is compared with a more traditional configuration without the parallel spring. The analytical and experimental results highlight the importance of the motor inertia reflected through the gearbox, and indicate two- to six-fold improvements in the proposed measures of torque-control performance.