Fixed-time/predefined-time control for robotic systems with unknown system dynamics estimator

In this paper, the integration of the unknown system dynamics estimator (USDE) with robust fixed-time/predefined-time control is proposed for robotic systems while effectively eliminating the influence of nonlinear uncertainties and enhancing the overall control performance. Specifically, a USDE that requires adjustment of only one parameter is designed to provide a lumped estimation of both unknown dynamics and disturbances. Then, to achieve rapid convergence of the control errors, the fixed-time/predefined-time control is designed, which ensures the fixed-time/predefined-time convergence of the tracking error to a compact region during both the reaching mode and sliding mode phases. By introducing an adjustable parameter, both the exact convergence time and the size of the convergence region can be precisely regulated simultaneously for the predefined-time control. The stability of the closed-loop system is rigorously proved via Lyapunov theory. Comparative simulations and experiments on a Baxter robot validate the superior convergence speed and tracking accuracy of the proposed schemes.