Fuzzy Fractional Reaching Law Based Sliding Mode Control for Rehabilitation Exoskeletons

ABSTRACT This paper presents a robust Fuzzy Logic Parameter Tuning‐based Fractional Reaching Law Sliding Mode Control strategy designed for lower‐limb rehabilitation exoskeletons. The proposed control scheme integrates the robustness of fractional‐Reaching law sliding mode control (FRSMC) with the adaptability of fuzzy logic, optimizing the trade‐off between torque generation and trajectory tracking. This work originally applies fractional‐order dynamics to the sliding mode reaching phase, where the non‐integer differentiation is effectuated in a fuzzy‐adaptive manner, which significantly enhances the management of dynamic behavior in the exoskeleton. This fusion of robust controllers achieves an optimal balance between transient and steady‐state performance by significantly reducing torque peaks while maintaining a rapid transient response, thus ensuring smooth operation throughout the rehabilitation task. A comprehensive stability analysis confirms the asymptotic convergence of the sliding function and the elimination of tracking errors, demonstrating the controller's efficiency. Simulation results on a three degrees‐of‐freedom (DOF) lower‐limb exoskeleton validate the strategy's effectiveness of the proposed controller.