Control of an Interior Permanent-Magnet Screw Motor With Power-Saving Axial-Gap Displacement Adjustment

This paper proposes position and force control of a screw motor with power-saving axial-gap displacement adjustment. The motor has a helical-shape mover, which moves in a helical-shape stator without contact. Due to the fabrication process, the actual helical shapes of the mover and the stator are not completely uniform, and the air-gap length between the mover and the stator slightly changes, depending on the mover rotation angle. The d-axis current remains a finite value, and copper loss arises even when the mover is located at the center between the stator cores. A power-saving axial-gap displacement adjustment method is proposed to solve this problem. The proposed control is experimentally verified.