Modeling and control of an SMA-based upper limb exoskeleton rehabilitation robot: a pilot study

Abstract

With the increasing aging population and the growing prevalence of upper-limb motor impairments, conventional rehabilitation approaches face limitations in terms of labor demand and long-term training continuity. This study presents a shape memory alloy (SMA)-driven upper-limb rehabilitation exoskeleton for assisting elbow and wrist joint motions. The system integrates an SMA actuator with a Bowden cable transmission mechanism to achieve a lightweight and compliant actuation design for human–robot interaction. A nonlinear SMA model based on the Liang–Rogers formulation is adopted to describe phase transformation behavior and hysteresis characteristics. A PWM-based PID control strategy was implemented to regulate joint motion and improve tracking performance under the inherent thermal delay of SMA actuation. The proposed system is evaluated through MATLAB/Simulink simulations and experimental testing. The results demonstrate that the exoskeleton can achieve stable trajectory tracking for elbow and wrist rehabilitation motions. The study confirms the feasibility of SMA-based lightweight rehabilitation systems while highlighting the influence of SMA thermal dynamics on system performance.