One of the causes behind motor vibration and noise is the eccentricity of the rotor. It is well known that the torque in a motor is generated when the electromagnetic attraction and repulsion are produced by the stator and rotor, but the attraction force between the rotor and stator is not well recognized. This is because generally the rotor and stator are positioned at the center which makes it look as if the attraction is balanced out. Therefore an error occurs in the calculation for the parts that support the shaft or stator and the concentric circle is not supported in which the attraction is not canceled. The radial load is constantly moving which generates friction loss in the bearing when an electromagnetic force is unbalanced causing vibration and sound. Also, the tolerance needs to be calculated to a certain extent in the mechanical process. The tradeoff between the amount of eccentricity and the electromagnetic force needs to be specified in the design.
The error in calculation is not large to the point where parts cannot be constructed, but a very small difference of 1/10mm occurs in the eccentricity amount when constructing. To evaluate the small difference in the geometry, a magnetic field analysis using a finite element method with a level of detail in shape deformation that can respond to the accuracy needs to be calculated.
This note presents how electromagnetic force changes when modifying the eccentricity amount for a rotor.
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