Torsional displacement compensation in position control for machining centers

Abstract In a CNC machining center, each axis of an XY table is linked to a motor through a ballscrew. Since the stiffness of the ballscrew is finite, there exists a torsional displacement resulting in a difference between the position of the motor and the corresponding position of the table. For more precise position control of the table, methods using measuring instruments such as a laser interferometer can be used, but this is too expensive to be implemented in a commercial CNC machining center. In this paper, a method is proposed to reduce the error of the table's position without directly measuring the position of the table. The method consists of a torsional displacement feedback algorithm and an estimation of the torsional displacement. The proposed method is tested in a CNC machining center and shows significant reduction in the error of the table position.