CONTROL OF A 2-DOF MANIPULATOR WITH A FLEXIBLE FOREARM

In this paper we present experimental results on the position and vibr ation control of the end-effector of a 2-DOF parallelogram manipulator with a flexible forearm. A dynamic model of the manipulator is first obtained. Control strategies are implemented to control the manipulato r. The first control strategy uses the computed torque method based on a reduced-order dynamic model of the manipulator which is obtained by assuming that all the links are rigid. This method is referred to as the reduced-order computed torque (ROCT) method, Experimental results demonstrate that such a strategy is not good for vibration control of the end-effector of the manipulator. The second control strategy is a state feedback control law designed based on a local linearization of the nonlinear dynamic model. Experimental results show that this contr ol strategy achieves good vibration control of the end-effector of the manipulator. However, since the strategy is based on local linearizat ion, it is valid only in a neighbourhood of the operating point. A hyb rid controller that uses the ROCT method for the initial large movemen t of the manipulator is then implemented. Based on a switching rule, t he controller is switched to the state feedback controller based on th e linearized model when the manipulator is sufficiently close to the e quilibrium state. Experimental results are reported and the successful performance of the controller in dampening out end-point vibrations i s demonstrated.