Overview
Closeup |
Eccentricity can occur on the center axis or the rotation axis of a motor.
It is advantageous to evaluate the effects of eccentricity because it can
cause vibrations and noise and break the symmetry of the magnetic flux
density distribution and the electromagnetic force.
This example presents the use of a magnetic field analysis to obtain the
cogging torque and electromagnetic force with and without eccentricity. |
Cogging Torque
Closeup |
The cogging torque is indicated in Fig. 1, the frequency components of
the cogging torque with eccentricity are indicted in Fig. 2, and the frequency
components of the cogging torque without eccentricity are indicated in
Fig. 3.
The periodicity worsens as the cogging torque gets larger when there is
eccentricity, as indicated in Fig. 1. The dominate frequency components
are 240 Hz with eccentricity and 2160 Hz without eccentricity, as indicated
in Fig. 2 and Fig. 3. For this reason, the periodicity of the cogging torque
is 5 degrees and 45 degrees. Furthermore, the frequency component at 2160
Hz originates in the slot combination while the frequency component at
240 Hz originates in the poles. |
Closeup |
Closeup |
Electromagnetic Force Acting on the Rotor and Teeth
The direction component (X component) of the eccentricity for the electromagnetic
force acting on the rotor with and without eccentricity is indicated in
Fig. 4 and the orthogonal direction component (Y component) of the eccentricity
is indicated in Fig. 5. The X and Y direction components of the electromagnet
force acting in the teeth as the gap thins when there is eccentricity is
indicated in Fig. 6 and Fig. 7. The -X axis direction component of the
electromagnetic force acting on the teeth is indicated as positive values.
The X direction component of the electromagnetic force for the rotor as
well as the teeth gets larger with eccentricity as indicated in Fig. 4
and Fig. 6. This is caused by the increasing effects of the magnet poles
when the gap thins because of the eccentricity in the X-axis direction.
Therefore, the periodicity of the cogging torque is effected.
The force without eccentricity has a periodicity of 45 degrees produced
by the slot combination. Eccentricity occurs in the magnetic flux and the
electromagnetic force can not be eliminated because the geometry and magnetic
field do not have symmetry. |
Closeup |
Closeup |
Closeup |
Closeup |
Closeup |
|
  |
