Finite time extended state observer based nonsingular fast terminal sliding mode control of flexible-joint manipulators with unknown disturbance

To solve the problems concerning with finite time trajectory tracking of the flexible-joint manipulator subject to unknown disturbance, a singular perturbation theory (SPT) based decoupling controller is proposed in this paper. SPT is employed to decouple the basic dynamic model of the flexible-joint manipulator into a fast subsystem and a slow subsystem. For the slow subsystem, a finite time extended state observer (FTESO) is proposed to estimate the unknown disturbance. In order to avoid the singularity and accelerate the convergence speed of terminal sliding mode controller (TSMC), a novel nonsingular fast terminal sliding mode controller (NFTSMC) is designed to achieve finite time trajectory tracking. Besides, to attenuate the chattering effect, a nonsingular terminal sliding mode controller (NTSMC) is introduced for the fast subsystem. Finally, the finite time stability of the closed-loop system is proven by means of the Lyapunov theory and some comparative simulations are performed to verify the effectiveness of the proposed controller.