Finite-Time Output Control for Uncertain Robotic Manipulators With Time-Varying Output Constraints

This paper proposes a finite-time output controller to realize the tracking control of n degrees of freedom (n-DOF) manipulator, which can address the time-varying output constraints and uncertainties, such as modeling error, unknown frictions, and external disturbance. A nonlinear mapping is conducted to convert the constrained manipulator dynamics into unconstrained dynamics. Based on the unconstrained dynamics, a finite-time output controller is established based on the output-feedback control scheme and nonlinear extended state observer (NESO). Fractional order terms are exploited to obtain finite-time convergence, and the switching law is developed for the NESO to estimate both the unmeasured states and uncertainties. The superiority of the NESO and the stability of the overall system are theoretically demonstrated by using the Lyapunov approach. The effectiveness of the proposed controller is illustrated by conducting simulations and experiments with robot manipulators and comparing the obtained results with those of the existing techniques.