Synthesis of a hybrid super-twisting and adaptive fractional-order sliding-mode control law for the gimbal seeker ensuring disturbance rejection and high accuracy

Abstract

This paper investigates the synthesis of an Adaptive Fractional-Order Super-Twisting Sliding Mode Control (AFOSTSMC) law to improve line-of-sight (LOS) stabilization performance for the two-axis gimbal drive system of an electro-optical seeker. The gimbal system has strongly nonlinear dynamics and is affected by angle-dependent varying moments of inertia, cross-coupling between the Yaw and Pitch channels, and uncertain disturbances. The proposed controller combines three techniques: (1) the Caputo fractional-order derivative, which accelerates convergence and smooths the error response; (2) the Super-Twisting Algorithm (STA), which suppresses chattering; and (3) an adaptive mechanism, which automatically tunes the controller gains online to compensate for disturbance components with unknown bounds. System stability is proven using Lyapunov theory and the Mittag-Leffler convergence criterion. Simulation results on a compact drive-system model demonstrate the advantages of the hybrid AFOSTSMC law over Super-Twisting Sliding Mode Control (STSMC) and Adaptive Fractional-Order Sliding Mode Control (AFOSMC) methods.