Disturbance Observer-Based Terminal Sliding Mode Control of a 5-DOF Upper-Limb Exoskeleton Robot

In this paper, a finite-time control strategy composed of disturbance observer and sliding mode controller is investigated for five-degree of freedom (5-DOF) upper-limb exoskeleton subject to system uncertainties and external disturbances. First, a new finite-time disturbance observer (FTDO) is constructed to handle unknown disturbances and modeling uncertainties. Second, a nonsingular fast terminal sliding mode (TSM) approach is presented to follow the desired joint angles. By combining the novel FTDO and the nonsingular fast TSM technology, the exoskeleton angle tracking errors can be forced to zero within a finite time. Furthermore, the stability of the exoskeleton system is illustrated via Lyapunov. Finally, the tracking performance of the proposed control scheme is verified by simulations.