Robust fractional-order fixed-time terminal sliding mode control for robot manipulators

This paper addresses the robust trajectory tracking problem for robotic manipulators in the presence of parametric uncertainties and external disturbances. A novel fractional-order sliding manifold is constructed to guarantee fixed-time convergence independent of initial conditions. The proposed control strategy combines fractional-order calculus with fixed-time terminal sliding mode control, thereby ensuring global finite-time stability while significantly enhancing robustness against modeling uncertainties and perturbations. The stability analysis based on Lyapunov theory confirms fixed-time convergence of the closed-loop system. To alleviate chattering and improve control smoothness, the discontinuous signum function in the control law is replaced by a continuously differentiable nonlinear function, leading to optimized gain adaptation and reduced control oscillations. The proposed method achieves superior tracking accuracy, faster convergence, and substantial chattering attenuation compared with existing approaches. Comprehensive numerical simulations and comparative studies validate the effectiveness and robustness of the proposed controller.