A new feedback control law of task-oriented coordinates of manipulators is proposed. Although the conventional control law has some desirable features such as simple computation, suitability to the singular points, etc., it is difflcult to get a tolerable performance because the law has been introduced based on an ideal dynamic model. Moreover, as the system is considered to be described by a continuous time, the stability margin has not been clarified.
In this paper, a manipulator whose joints are rate-controlled to reduce the effects of frictional disturbances is considered. The rate-control makes the motion of the manipulator to be described by difference equations with a descrete time. The characteristics may be evaluated by the eigenvalues of the equations. First, a simplified model of a manipulator with 2 D.O.F. is introduced. Then the difficulty of the conventional control law is indicated. Second, a new control law that predicts the error and provides an effective feedback in order to improve the characteristics of the conventional law is proposed. Finally, the law is applied to a practical redundant manipulator with 7 D.O.F. The results of the experiments display good performances.