Additional Cogging Torque Components in Permanent-Magnet Motors Due to Manufacturing Imperfections

This paper presents issues for reducing cogging torque of permanent-magnet motors. When proper methods are employed, it is theoretically possible to minimize its level or even to eliminate it. FFT analyses of cogging torque in mass-produced motors have shown additional harmonic components, which are in tight correlation with assembly tolerances and/or permanent-magnet imperfections. Finite element method has been used to study the sensitivity of different motor models relative to manufacturing tolerances and to determine rules for detecting imperfections in mass-production.