Nonsingular Predefined‐Time Terminal Sliding Mode Controller for Position Servo System

Position servo systems are essential in key industrial sectors, where fast convergence, high tracking accuracy, and strong disturbance rejection are core performance demands. However, traditional linear control delivers poor disturbance rejection under complex operating conditions; existing predefined‐time terminal sliding mode schemes suffer from inherent singularity due to fractional negative powers; and independent tuning of observers and controllers in composite frameworks frequently causes compensation phase lag, weakening recovery performance under abrupt load disturbances. To solve these problems, this paper proposes a novel predefined‐time terminal sliding mode controller with arbitrarily presettable settling time. Flexible parameter tuning breaks the inherent limitations of conventional finite‐time and fixed‐time control and avoids complex parameter coupling. The controller independently optimizes the convergence rates of the sliding surface and tracking error, balancing fast transient response and chattering suppression. A saturation function is embedded to ensure control continuity, supported by a rigorous alternative stability proof. To further enhance disturbance rejection, the controller is combined with a predefined‐time disturbance observer to form a globally stable anti‐disturbance framework. The observer is set with a shorter convergence time window than the outer‐loop controller, eliminating phase lag and enabling real‐time feedforward compensation. The scheme requires no prior disturbance information or derivative bounds and achieves fast tracking recovery under sudden load torque changes. Comparative simulation and hardware experimental results validate the effectiveness and practicability of the proposed control strategy.