We consider the robust tip position control problem for the flexible arm by using the sliding mode method. The model of the flexible arms is described as a nonminimum phase system, in which the higher order modes, the model uncertainty, the disturbance etc., are considered as the system uncertainty. The upper and lower bounds of the uncertainty, which can hardly be obtained in practice, are adaptively updated. The stability of the closed-loop system is analyzed based on this approach, where the fact that a part of the control input is the approximate estimate of the uncertainty is employed. Experimental results show the robustness of the proposed method, where only the strain moment and motor angular position in the arm root are measured.
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