Adaptive Robust Finite-Time Sliding-Mode Tracker Combined with Damping Functions for Robot Manipulator under Disturbance and Input Delay

This study examines the challenge of achieving finite-time stability and enhancing transient response in robotic manipulators subjected to uncertainties, disturbances, and input delay. Inspired by the damping features of some nonlinear functions, a tracking strategy is proposed based on adaptive sliding-mode control (SMC). To handle input delay, a suitable coordinate transformation is introduced, which converts the original delayed system model into a delay-free form in new coordinates. Having known upper-bounds of the combined uncertainty, a robust SMC coupled with an extra nonlinear term is first designed for the transformed system. Subsequently, an adaptive SMC scheme including damping functions is derived for the more practical scenario where this bound is unknown but constant. The adaptive mechanism continuously estimates the uncertainty bound to adjust the controller gain accordingly. Both control schemes guarantee convergence of the sliding variables in finite-time and stability of the overall equations. Some simulations reflect the robustness and effectiveness of the planned tracking method, showing superior performance in contrast to similar techniques.