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Research on the Torque Ripple and Scanning Range of an Arc-Structure PMSM Used for Scanning System

A kind of arc-structure permanent-magnet synchronous machine (AS-PMSM) used for scanning system, which requires high positioning accuracy, high response performance, and wide scanning range, is proposed and researched in this paper. The AS-PMSM is able to replace the traditional rotary motor plus gear box to realize the directly driving and limited angular movement. To ensure the high positioning accuracy and high response performance, the torque characteristics are researched. A new method is proposed to detach the torque Tslot caused by slotting and the end torque Tend caused by stator end effect for AS-PMSM. Considering the large torque Tend, the average torque and especially torque ripple are optimized from the aspects of stator central angle and permanent-magnet (PM) shape. Furthermore, the edge PM mounted on the end of the rotor is optimized by adopting asymmetry shape to improve the smooth scanning range. After all the optimization, the smooth scanning range with a satisfying torque ripple limited in 3% is much increased by 19.5%.