Abstract : This paper addresses the tracking control problem of an electro-hydraulic servo system with varying parameters and proposes a sliding mode robust controller design method with feedforward compensation. The asymptotic stability of the entire closed-loop system is proved using the Lyapunov method. This method is applied to the electro-hydraulic servo system of a fatigue testing machine, and its effectiveness is verified through simulation. Keywords : Uncertainty; Electro-hydraulic servo system; Sliding mode robust control 0 Introduction Strictly speaking, all real-world systems possess numerous uncertainties, such as variations in system parameters, external load disturbances, and uncertainties caused by system complexity and nonlinearity. The impact of these uncertainties is non-negligible for most systems we study. Therefore, control systems designed from a steady-state perspective often fail to achieve the desired performance and may even lead to system instability. Electro-hydraulic servo systems also exhibit many uncertainties, especially those caused by variations in system parameters (such as oil pressure, system overall stiffness, inertial mass, viscous friction of the actuator during movement, and oil temperature), which are the main factors affecting the performance of the entire control system. Therefore, the study of the uncertainty of parameters in hydraulic servo control systems has received great attention in recent years. Reference [3] applied the conventional variable structure control method to study the response of the hydraulic position servo system to the step reference signal when the parameters change. The simulation results show that the hydraulic system with optimal variable structure control not only has good dynamic characteristics, but also good robustness. Reference [4] applied sliding mode control to a pump pressure control system and studied the system response to the sinusoidal signal when the system parameter load flow changes by 50%. The simulation results show that the sliding mode control has good robustness to the changes in system parameters. This paper proposes a sliding mode control method with feedforward compensation based on the basic theory of sliding mode control for the tracking control problem of a certain uncertain electro-hydraulic position servo system with parameter changes. The simulation results show that the designed feedforward compensation robust controller can enable the system output to asymptotically track a certain desired signal and obtain satisfactory tracking accuracy for this type of uncertain electro-hydraulic servo system with parameter changes. At the same time, the controller has strong robustness to the changes in system parameters and disturbances, and has an obvious effect on weakening or eliminating the inherent chattering phenomenon of VSC. [b][align=center]For details, please click: Sliding Mode Robust Tracking Control for Uncertain Electro-hydraulic Position Servo Systems[/align][/b]