A New Cogging-Free Permanent-Magnet Linear Motor

The cogging force of a permanent-magnet linear motor (PMLM) is a major component of the detent force, but unfortunately makes a ripple in the thrust force and induces undesired vibration and acoustic noise. It also deteriorates the control characteristics, particularly in regard to precise speed and position control. In this paper, we propose a new PMLM having a 9-pole 10-slot structure in order to reduce the cogging force. Our PMLM is properly wound for three-phase driving. Through a theoretical and finite-element analysis, we show that the 9-pole 10-slot PMLM removes almost all of the cogging force while giving 10% and 23% larger back-electromotive force and thrust force, respectively, than a conventional 8-pole 12-slot PMLM under the same conditions of exciting current, total number of windings, and total PM volume.