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Numerical models are developed to predict the electromagnetic vibration and noise of permanent-magnet direct current (PMDC) commutator motors when both rotor eccentricities and glue effects are involved. Finite-element method (FEM) and boundary-element method (BEM) are combined to analyze the electromagnetic, mechanical, and acoustical characteristics of the studied motor. By using the finite-element method, an electromagnetic field considered as the electromagnetic vibration and noise sources of the motor is calculated in the two-dimensional air-gap region. Based on the electromagnetic field, the radial and tangential magnetic forces exciting the structure of the motor are then obtained in the time and frequency domains. Consequently, the transient responses (accelerations) of the motor are simulated by applying the magnetic forces on the three-dimensional dynamic-structure finite-element model of the motor. Furthermore, the sound pressures radiated from the vibrating surface of the motor can be obtained by using the boundary-element method in the frequency domain. The numerical results agree well with those measured in the laboratory. The present research reveals that the static eccentricity distorts the distribution of the magnetic forces in the spatial domain. And the distorted magnetic forces mainly exaggerate the accelerations of the motor for the frequency range which is lower than the natural frequencies of the motor. In addition, the epoxide-resin glue between the permanent magnets and the stator can influence the vibrational and the acoustical characteristics of the motor.
Date of Publication: May 2012