Flexible Control Strategy for Upper-Limb Rehabilitation Exoskeleton Based on Virtual Spring Damper Hypothesis

The focus of this work is to design a control strategy with the dynamic characteristics spring damping realize virtual flexibility and softness rigid-joint exoskeleton without installing real, physical elastic devices. basic idea “virtual softening strategy” for single rigid joint that damper (VSD) installed between motor output shaft. By designing signal motor, torque actuator softened so has elasticity variable stiffness. transfer velocity profile human limbs reaching from one posture another always presents as bell-shaped. According characteristic, we constructed trajectory planning method point-to-point position-tracking controller based on normal distribution function, it was successfully applied 5-DoF upper-limb rehabilitation exoskeleton. A multi-joint cooperative flexible hypothesis (VSDH) solve constrained problem exoskeletons self-motion caused by redundant degrees freedom (DoFs). stability closed-loop controlled system theoretically proven use scalar energy function gradient Riemann metric convergence analysis method.