Waist-assistive exoskeleton powered by a singular actuation mechanism for prevention of back-injury

This paper proposes the design of an electrically-powered waist assistive exoskeleton wire-driven only by one actuator and its control method. The developed exoskeleton is intended to reduce muscle fatigue and further prevent back-injury of industrial workers who undergo repeated, intensive waist motions. Considering requirements specially for industrial purposes, system performances related to cost, weight, operational time, and system endurance & maintainability of the robot have to be specially pursued. Therefore, reduction in the number of actuators without deteriorating the robot's main function can be an effective approach. Along with this concept, only the single actuator mounted on the back part of the robot is proposed to simultaneously drive both legs by wire through a differential gear mechanism. The applied differential mechanism allows natural motions generally observed in human walking with almost zero mechanical impedance, but the waist motion for lifting-up heavy objects can be assisted by the powered extension of both legs. A current control algorithm embedded in a micro-controller is specially designed to achieve objectives of the robot. In order to evaluate the waist assistance provided by the developed robot, activation signals of electromyography (EMG) on main muscles of working wearers related to waist motions were measured. Further, the usability was evaluated using the responses of a questionnaire survey. Thus, the proposed method for waist assistance by a singular actuator is verified to be conclusively effective. (C) 2018 Elsevier B.V. All rights reserved.