Motors are used in many appliances, and noise reduction is strongly demanded. One of the main causes of noise is electromagnetic excitation force and it is well known that the excitation force is increased by the eccentricity of the rotor to the stator. For this reason, it is very important to decrease the eccentricity, but there are limits because the eccentricity is due to inevitable manufacturing tolerances or assembly errors. So, we propose a method to estimate the eccentricity of the

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... in the process of manufacturing by using windings as a sensor. When the rotor and the stator are in an eccentric condition, the impedance of each winding is different. We developed an experimental apparatus that can set the amount of eccentricity and verified that the terminal voltage of each winding changes proportionally to the eccentricity. In order to produce motors with eccentricity of almost zero, we need to estimate the two-dimensional amount of eccentricity in a very short time. When the number of turns of each winding is different, there is interaction between each winding and so the accuracy of the estimation decreases. To solve these problem, we applied a different frequency of voltage to the winding located on the x axis and the winding located on the y axis, so that we can estimate the amount of eccentricity for the x direction and the y direction with high accuracy at the same time. We also developed a way to produce motors by using this technology. After detecting the terminal voltage of each winding under the tentative assembly situation, we adjust the amount of eccentricity to almost zero and fix the motor by laser welding. As a result, we were able to mass produce motors with eccentricity of under one micrometer and with a very low noise level.