Simulink-Based Comparative Study and Selection of a Controller for a Waist-Assistive Exoskeleton

This paper describes the conceptual design and comparative simulation study of three controller strategies—Proportional Integral Derivative (PID), PD-based Computed Torque Control and PD-based Sliding Mode Control (SMC) for a waist-assistive exoskeleton. The exoskeleton is modelled in Simulink, and its joint control is simulated for a predefined desired trajectory. The motor, joint and link parameters are incorporated into the Simulink model to match the properties and evaluate the performance similar to the real-time system. In addition, MSC ADAMS-based simulation study is also performed to validate the dynamic model of the exoskeleton. The preliminary study indicates that the SMC controller shows better tracking accuracy than the other two strategies. The proposed exoskeleton is designed to reduce the effort taken by the user during regular sit-to-stand and weight-lifting operations. It is intended to lower the strain the lumbar muscles take during standing and lifting operations over the long run.