Design and Characterization of a Cable-Driven Series Elastic Actuator Based Torque Transmission for Back-Support Exoskeleton

Active back-support exoskeletons have been developed aiming to reduce human effort by providing assistive torque during human bending. However, most existing active back-support exoskeletons transmit assistive torque through rigid linkages connected to the human body, leading to restriction on natural motion. Several exoskeletons equipped with soft structures are less intrusive but cannot deliver sufficient assistive torque. In this paper, we present a cable-driven series elastic actuator (SEA) based torque transmission system that consists of a DC motor actuation unit, a cable-driven transmission, a support beam and a torsion spring for large assistive torque transmission of back-support exoskeletons. The moment arm of cable force is enlarged by the support beam for large assistive torque generation while SEA properties are obtained by connecting the support beam with a torsion spring. The torque transmission system is experimentally characterized to be able to achieve a large torque output of up to 81 Nm and torque control bandwidth of 1.9 Hz. Experimental results of impedance regulation for different level of desired impedance with low mechanical output impedance are also presented, showing the capability for back-support exoskeletons.