Analytical techniques for magnetically induced vibration in brushless permanent-magnet motors

This paper discusses an analytical method for predicting the force imbalanc e and cogging torque in a radial field permanent-magnet motor. Explicit for ms of the force-imbalance and cogging-torque expressions are derived based on a two-dimensional model, taking account of the effects of magnetic flux fringing at the stator slots. The Maxwell stress method is directly used fo r the force calculation. Dynamic characteristics of the force imbalance and cogging torque are explained in terms of the frequency content. Fast desig n criteria are suggested for motors used mostly in hard-disk drives, from a vibration-control viewpoint.