Adaptive Global Fixed-Time Terminal Sliding Mode Control for Trajectory Tracking of Disturbed Robot Systems

This article investigates the problem of globally fixed-time trajectory tracking for uncertain robot manipulators with the lumped uncertainty, which includes the external disturbance and system uncertainties. At first, a novel fixed-time sliding manifold incorporating an auxiliary function is proposed. Building upon this manifold, a nonsingular fixed-time terminal sliding mode control (NFTSMC) approach is designed to achieve the globally fixed-time convergence of the trajectory tracking error, where the settling time shows independence from the initial states of robot system. Furthermore, an adaptive NFTSMC (A-NFTSMC) approach is developed to handle the practical scenario where the upper bound of the lumped uncertainty is unknown, thereby enhancing its robustness. The proposed approach simultaneously resolves the inherent singularity and algebraic loop problems associated with conventional terminal sliding mode designs, while achieving faster transient as well as superior steady-state precision. In the end, simulative and experimental results serve to verify the effectiveness and performance improvements of the proposed A-NFTSMC.