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| Example of the Week |
2012-01-23
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* Influence Analysis of Dimensional Tolerance using Morphing
The angle of the magnets in SPM motors use a fillet or chamfer. However, the fillet and chamfer of each product that is manufactured varies because to completely fabricate the same fillet or chamfer is difficult in the manufacturing process. Therefore, the dimensional tolerance is set so the motor performance is not affected by these variations.
This example presents the use of a magnetic field analysis to compare whether the cogging torque of the SPM motor is influenced by changing geometry in the tolerance range assuming the dimensional tolerance of the chamfer is ±0.4 mm.
· Cogging torque
The cogging torque waveform is indicated in Fig. 1 and the frequency components of the cogging torque are indicated in Fig. 2. The position of the peak value shifts as the dimensions of the chamfer change, but the peak value remains almost the same, as indicated in Fig. 1. The variations of the fundamental frequency of 360 Hz are smaller than the harmonic components, as indicated by the frequency components in Fig. 2.
Therefore, the variations of the geometry in the tolerance range of the chamfer only affect the cogging torque minimally.
· Back EMF
The back EMF waveform is indicated in Fig. 3 and the frequency components of the back EMF are indicated in Fig. 4. The value of the back EMF is almost the same even when the dimensions of the chamfer are changed, as indicated in Fig. 3. The variations of the fundamental frequency of 60 Hz are smaller than the harmonic components, as indicated by the frequency components in Fig. 4.
Therefore, the influence of the chamfer tolerance is minimal.
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