Motion control of a two-link underactuated manipulator without state feedback of unactuated link (utilization of bifurcations under high-frequency excitation)

A motion control technique for a two-link underactuated manipulator without state feedback control of the unactuated link is proposed; the manipulator can be moved in the vertical plane and the first and second links are actuated and unactuated, respectively. The usual control methods of the underactuated manipulators are based on the feedback of states of not only active link but also unactuated link. On the other hand, the proposed method does not require the information with respect to the motion of the unactuated link and not utilize the state feedback control of the unactuated link. The various bifurcation phenomena are emerged in the unactuated link by high-frequency excitation of the actuated first link. By using the nonlinear characteristics it is carried out to swing up to the upright position which is statically unstable and to stabilize the position. Experimental results indicate the validity of the proposed method for the underactuated manipulator.