Improved Sliding‐Mode Control for High‐Dynamic‐Accuracy EHA in Exoskeleton Joint

ABSTRACT To address the time‐varying parameters, nonlinear friction, leakage, and load disturbances inherent to electro‐hydrostatic actuator (EHA), and the exoskeleton robot's demands for handling strong coupling and achieving high trajectory accuracy, we design an adaptive variable‐damping sliding‐mode controller (ADV‐SMC) that suppresses chattering while improving the dynamic response of the joint EHA. Because most existing studies overlook the higher‐order characteristics of composite disturbances, this work incorporates an improved nonlinear extended disturbance observer (INEDOB) into the controller design. By constructing a novel surrogate function to circumvent the differentiability constraint of the saturation function, the INEDOB enables accurate estimation of time‐varying external disturbances and their higher‐order derivatives. On the basis of a rigorous stability proof, the effectiveness of the newly designed controller is further analyzed and validated. This integrated control scheme markedly enhances system robustness and trajectory‐tracking accuracy, providing a new avenue for high‐dynamic‐precision control of exoskeleton robots.