In this paper, we have developed a disturbance observer (DOB) based on robust control method for a class of nonlinear robot manipulators with time-varying uncertainty. To facilitate digital implementation of the controller, the robot system is formulated in discrete time. The DOB controller is design to compensate for uncertainty and disturbance by bounding both all states and observed uncertain function in a control region. The robust stability of closed-loop robot system can be well guaranteed by applying Schur complement theory and Lyapunov analysis, such that parameters of the DOB controller are derived using linear matrix inequalities (LMIs) theory. Simulation studies have been performed to test and verify the proposed control scheme, which results in supreme robust control and satisfied trajectory tracking performance for robot manipulators with time-varying uncertainty.
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