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It is known that the slot frequency vibration is the one of the main components in electromagnetic vibration spectrum of permanent magnet DC motors (PMDCM). After finding that the vibration reduction scheme of the piecewise varying pole width (PVPW) is only effective for the odd order harmonic of slot frequency vibrations by analytical method, the PM pole with sawtooth edge is put forward to reduce all harmonic components of slot frequency vibrations of PMDCM. In this article, after the air gap flux density and radial force density are analyzed, the two vibration sources, radial force and bending moment, are derived for the motor with sawtooth edge poles (SEP). Then the optimized pole shape is obtained to reduce all harmonic components of both the radial force and bending moment at the same time. Three dimensional finite element method of electromagnetic field and structure are used to calculate the magnetic flux density, radial force and vibration for the motors of PVPW and SEP. Three permanent magnet motors with fixed pole width (FPW), PVPW and SEP are manufactured and tested. The comparison and verification show that SEP is better than the other two schemes in general. [ABSTRACT FROM AUTHOR]

The electromagnetic vibration of permanent magnet brush dc (PMBDC) motors has its distinct feature, where only slot-frequency related components exist. Skew slot technique is naturally recalled to mitigate the slot-frequency vibration. Unfortunately, the straight skew slot normally used is not as effective as the mitigation of tooth harmonic electromotive force (EMF) or cogging torque. First, in this paper, the principle of vibration mitigation by straight skew is discussed and compared with mitigation of tooth harmonic EMF and cogging torque. The reason for poor effect of straight skew slot is illustrated by a specifically-designed experiment and finite-element method (FEM) simulation. In order to solve this problem, the zigzag skew PM pole technique is proposed for PMBDC motors for the first time, which overcomes the disadvantage of straight skew slot. The pulsating radial force and bending moment, two main causes of electromagnetic vibration, are derived and analyzed analytically and by the three-dimensional FEM for zigzag skew PM poles. At last, the experiments on two PMBDC motors, one with straight skew slots and the other with zigzag skew PM poles, are conducted to verify the effectiveness of the zigzag pole technique. [ABSTRACT FROM AUTHOR]