The closest centroid and physical center of inertia of the rotor shaft is called the eccentricity, the rotor does not balance the eccentricity caused when the rotor is rotated due to the centrifugal force generated in the shaft mount a force formed by the vibration, and the vibration is transmitted to the base path via each mechanical part. When if "Micro Cooling Fan" physical rotation of the rotor shaft and the center of mass center of inertia of the rotor is not on the same axis, it will cause the rotor imbalance.