Overview
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An outer rotor motor has a magnetic rotor that rotates around a stator.
An outer rotor motor can produce a larger amount of torque than an inner
rotor motor with the same diameter because the radius of the outer rotor
is larger.
Vibrations produced by electromagnetic force can be produced as the motor
rotates. The fabrication of the motor can be modified, such as adding and
fabricating holes in the rotor core to change the eigenfrequency reducing
the amount of electromagnetic vibrations that can cause noise or damage
the motor.
This example presentsthe use of a magnetic field analysis and structural
analysis to obtain the sound pressure caused by electromagnetic vibrations
in an outer rotor motor with holes fabricated in the rotor core. |
Electromagnetic Force Distribution
| The electromagnetic force distribution at the measuring point as the maximum
is indicated in Fig. 1. The frequency component of the electromagnetic
force for the point indicated in Fig. 1 is indicated in Fig. 2. The frequency
components of the electromagnetic force are concentrated at 180 Hz and
the electromagnetic force is larger between the rotor core and poles. |
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Eigenmode
| The eigenmode for a rotor core with and without fabricated holes are indicated
in Fig. 3. The minimum vibrations of the mode in the radial direction with
fabricated holes is 647 Hz and without fabricated holes is 675 Hz. A large
amount of vibration is generated by the resonance phenomenon of the eigenfrequency
and the electromagnetic force. |
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Acceleration (Intensity) Distribution and Sound Pressure Level Distribution
| The acceleration (intensity) distribution at 720 Hz is indicated in Fig.
4 and the sound pressure level distribution at 720 Hz is indicated in Fig.
5. The movement of the electromagnetic force and the large acceleration
and high sound pressure level distribution cause by the resonance phenomenon
at an eigenfrequency near 720 Hz is apparent. The noise can be reduced
for this outer rotor motor by fabricating holes in the rotor core as indicated
in Fig. 5. |
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