Stability Guaranteed Time-Delay Control of Manipulators Using Nonlinear Damping and Terminal Sliding Mode

Time-delay control has been verified as a simple and robust controller for robot manipulators. However, time-delay estimation (TDE) error inherently exists and critically affects both the closed-loop stability and control performance. In this paper, we propose a remedy for the TDE error that involves a combination of a nonlinear damping component and a novel fast-convergent error dynamics. Nonlinear damping incorporated with a backstepping design is adopted to counteract TDE error and ensure closed-loop stability. The fast-convergent error dynamics, constructed by means of terminal sliding mode (TSM), is introduced to enhance the control performance degraded by the TDE error. Through a rigorous stability analysis, it is proved that the tracking error of the closed-loop system due to the proposed control scheme is globally uniformly ultimately bounded. Through simulations and experiments, it is verified that the nonlinear damping counteracts the TDE error, while the TSM speeds up the convergence of the error dynamics. Finally, these two elements together substantially enhance the control accuracy.