A Novel Detent Force Reduction Method Based on Primary Modular Twice Offset for Alternating Pole Permanent Magnet Linear Motor

Aimed at achieving low detent force and minimal permanent magnet usage, this paper discusses a novel design of a Primary Modular Twice Offset Alternating Pole Permanent Magnet Linear Motor (PMTO-APPMLM). The four-segment unit motors are offset twice to different degrees so that the detent force components cancel each other out, which ultimately reduces the detent force of the entire linear motor. Additionally, the twice alternating pole structure is implemented to further cut down development costs by maintaining motor performance with a minimal number of magnets. An innovative unequal iron pole structure is proposed to optimize the width of the soft magnets in the secondary, resulting in lower detent force. The obtained results indicate a substantial weakening of the linear motor detent force, with a final value of 1.4 N, and a thrust ripple of only 0.67%. The proposed linear motor is compared with the common skewed-pole optimization method, which has the minimum thrust loss with the positioning force weakened to the same value. Finally, the prototype and testing platforms are set up and the experimental results validate that the proposed PMTO-APPMLM can achieve low detent force.