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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.

Wearable back-support exoskeletons can assist workers during heavy load lifting and lowering to reduce spinal loading. As these exoskeletons are worn by the user, they must be well designed to adapt to the natural movements of the human body. In this paper, the detailed design requirements of a back-support exoskeletons based on a biomechanical analysis of human bending motion is described. Following these requirements, a back-support exoskeleton with a novel cable-driven series parallel elastic actuation (SPEA) unit is proposed. A set of passive flexible elastic beams are used in parallel with an active cable-driven series-elastic actuator (CSEA) to lower the power and torque demand of the CSEA. Equipped with the proposed SPEA unit, the back-support exoskeleton interacts with human body only via flexible beams and cables. The possibility of misalignments or reduction of degrees of freedom of the body is minimized by the flexible interaction between human body and exoskeleton. Moreover, the design of the exoskeleton also permits the generation of axial twisting and lateral bending moments, which are key in supporting asymmetric lifting.