Robust Control Design For 3 Degree Of Freedom Fully Actuated Upper Limb Exoskeleton

In this paper, a robust position control design for a 3 DOF upper limb exoskeleton is proposed. Starting with the nonlinear equations of motion for the exoskeleton, a state feedback controller based on traditional Sliding Mode Control (SMC) is designed which stabilizes the system and tracks a constant (desired) angle in a finite time. The controller ensures asymptotic stability of the closed loop system in the presence of coupling effect and model uncertainties. Stability analysis is carried out using the Lyapunov methods. Furthermore, state feedback control design is then extended to an output feedback control design by incorporating a High-Gain Observer (HGO) to estimate the states of the system. It is shown that the states of the closed-loop system under output feedback control approach an invariant manifold in finite time, and stay there then after. The efficacy of the proposed control strategies is evaluated with the help of numerical simulations.