Analysis of the magnetic field and vibration of permanent magnet motors with rotor eccentricit

The drive motor is the most important element in many precision spindle applications and also a frequent source of vibration. Vibrations of magnetically induced origin are becoming more serious with the advent of new high-energy magnets together with the trend of high speed use in smaller and lighter portable applications. These trends place a significant emphasis on motor design and manufacturing processes. Rotor eccentricity is a problem which may result from working allowances or errors in manufacturing processes. It is also an inherent rotating mode of motors supported by fluid film bearings, which has relationship with runouts and stability problems of the rotor. Therefore, it is necessary to examine the effects of rotor eccentricity on the performance and dynamic characteristics of motors.;This dissertation presents a magnetic field analysis technique of permanent magnet motors with rotor eccentricity and vibration effects. The magnetic field associated with rotor eccentricity is modeled by a perturbation of the corresponding Maxwell's equations and boundary conditions. Static rotor eccentricity and dynamic rotor eccentricity are considered. Analytical solutions for predicting the instantaneous magnetic field distribution in the air gap region of permanent magnet motors are given by the perturbation method and verified by the corresponding finite element method.;Stator slotting effects are introduced to the perturbation analysis by solving a boundary value problem of Maxwell's equations with a redefined boundary condition at the stator surface. A regular first order perturbation solution is sufficient to describe the flux density distribution and agrees with what the corresponding finite element method predicts. The solution is given in a harmonic series in the temporal and spectral coordinates, which may be a difficulty in the finite element solution. The analytical solution is more advantageous for applications to the future problem of the rotor dynamics coupled with magnetic forces.;Analytical expressions of force imbalance and cogging torque in a permanent magnet motor are derived by the Maxwell's stress method taking into account of the analytical flux density distribution in the air gap region of the motor. The frequency contents of the force imbalance and cogging torque are examined and characterized to give a design criterion for better vibration performance. The effect of rotor eccentricity on the force imbalance and cogging torque is also examined.