Time-varying nonsingular terminal sliding mode control for uncertain second-order nonlinear systems with prespecified time

This article proposes a time-varying nonsingular terminal sliding mode (TSM) control for a class of uncertain second-order nonlinear system and its application to n-links rigid robotic manipulators. First, a time-varying nonsingular terminal sliding manifold is developed by incorporating a piecewise-defined function of time into a nonsingular TSM manifold. As a result, the singularity problem is avoided and the reaching phase existing in conventional TSM control is totally suppressed which ensures the global robustness of the system against uncertainties and disturbances. Moreover, adaptive tuning laws are developed to omit the requirement of prior knowledge of the upper bound of the lumped uncertainty. In particular, an effective method is provided for the parameters selection to meet a prespecified convergence time. Hence, the convergence time to the origin of the tracking errors can be specified in advance according to the mission requirements. The formulation of the controllers and the stability analysis are verified by Lyapunov theory. Simulation results and comparative studies are presented to demonstrate the effectiveness and the superiority of the proposed algorithms.