Design, Control, and Validation of a Novel Cable-Driven Series Elastic Actuation System for a Flexible and Portable Back-Support Exoskeleton

Abstract

Various active back-support exoskeletons have been developed to assist manual materials handling work for low back injury prevention. Existing back-support exoskeleton actuation either suffers from rigid transmission structure, or fails to efficiently generate assistance via portable actuation system with flexible transmissions. In this article, a novel cable-driven series elastic actuation (CSEA) system is proposed to realize a flexible and portable back-support exoskeleton design with safe, efficient, and sufficient assistive torque output capability. The CSEA system realizes a flexible actuation based on cable transmission for an ergonomic human-exoskeleton interaction. Based on a torsion spring-support beam mechanism, it achieves an efficient assistance output capability to prevent high cable force demand and resultant lumbar compression, assuring a safe and synergistic operation for flexible exoskeleton actuation. Meanwhile, this mechanism enables the CSEA system to integrate series elastic actuator (SEA) with cable transmission and operates with multiple statuses to leverage SEA advantages and to overcome its torque output limitation. Dynamic model is established for the CSEA system, and a unified torque controller is designed for stable, continuous, and accurate torque control of the CSEA system despite its discontinuous dynamics during operation status transition. The efficacy of the closed-loop CSEA system to enable an ergonomic and efficient back-support exoskeleton actuation with the capability of accurately delivering desired level of assistance is verified via bench tests and human tests. Results verified that the CSEA system actuated exoskeleton can effectively reduce activity of relevant muscles during trunk flexion and extension motions compared to no exoskeleton case, validating successful application of the CSEA system on the exoskeleton for an effective back support effect.