Digital Control of Position and Force of a Direct-Drive Robot with a Variable Table.

Abstract

In this paper, the hybrid control of position and force of a direct-drive (DD) robot with a variable table is proposed. The DD robot has six degrees of freedom (d. o. f. ) and consists of a three-d. o. f. articulated DD robot arm and a three-d. o. f. DD variable table. A six-d. o. f. motion of an end effector on the robot arm and the internal force of the object on the table can be obtained by the DD robot arm in cooperation with the variable table. The motion and the internal force are specified using a task-oriented Cartesian coordinate system fixed on the table, and achieved by a set of three-d. o. f. hybrid controllers : one is a controller of position and force and the other is a controller of orientation and moment. The control of position and orientation is based on the stiffness control, thus the proposed control algorithm is kinematically stable and easy to calculate. It is also possible to replace one of the hybrid controllers with a joint-independent controller to simplify the algorithm. The effectiveness of the proposed control algorithm is demonstrated by the experiment on the control of both the position of an end effector and the contact force on the constraint surface of the object.