Fictitious Target-Trajectory Forming Control for Redundant Manipulator and Active Regulation of Impulsive Forces

Task-space control by FTTF method This paper describes a new control method for stable robot positioning by means of a three degree-of-freedom robotic manipulator that consists of six wire-driven actuators located at each rotational joint. The actuator contains a direct-current (DC) motor capable of pulling a wire to which a high-stiffness spring is connected in series. We demonstrate that the positioning control method used by the redundant robot, which is based on task-space control given in Cartesian coordinates, works well in the vertical plane under gravity. With the use of the reliable positioning controller, we propose a simple algorithm to absorb impulsive forces exerted on the tip position of the robot. In addition, we reveal that the control method presented in this study enables the redundant robot to change its stable posture while maintaining the tip position on which a heavy load is placed. We finally verify that a simple algorithm, based on positioning control, which involves suspending and restarting the switching of the integral controller forming a fictitious target-trajectory of joint angles, realizes recovery motion towards a former posture attained before the impulsive force.