Experimental Study on Electromagnetic Force Induced Vibration and Noise from Universal Motor with Off-Centered Rotor

Abstract

There are many harmonic components in the electromagnetic force caused by electrical motors. The harmonic components induce the structural vibration and noise, frequently. The amplitude of harmonic components is also affected by magnitude and angle of the eccentricity of rotor. The unbalanced electromagnetic attractive force is generated between the rotor and the stator when the rotor is not corresponding to the center of the stator, that is, eccentric in the electrical motor. The unbalanced electromagnetic attractive force causes vibration and noise. In the paper, electromagnetic vibration and noise from universal motor with rotor eccentricity are experimentally discussed comparing with normal rotor. The magnitude of eccentricity is 0.2mm against air gap 0.4mm and, angle of eccentricity is 0, 45, 90, and 135 deg. The vibration and the noise of the motor grow by the frequency of the electromagnetic force agreement with structural natural frequency, that is, resonance. As for eccentricity magnitude 0.2mm and the angle 90 deg, maximum value of vibration amplitude doubles roughly and the noise is about 9 dB larger than those of normal motor. The amplitude of vibration and noise depend on eccentric angle. The vibration and the noise depend on the angle of rotor eccentricity.