Source and reduction of uneven magnetization of a permanent magnet of a HDD spindle motor

Uneven magnetization of a permanent magnet (PM) generates the cogging torque with slot harmonics and the unbalanced magnetic force which are the major sources of vibration and noise in a HDD spindle motor. This research investigates the several sources of uneven magnetization of a ring-shaped PM by analyzing the transient finite element analysis in a capacitor-discharge impulse magnetizer. Developed simulation model is verified by comparing the simulated surface magnetic flux density along the ring-shaped PM with measured one. This research shows that the positioning error of magnetizing coil in the magnetizing yoke is dominant source of the uneven magnetization. High magnetic field intensity in the magnetization moment due to high magnetizing voltage or back yoke decreases the uneven magnetization of PM by compensating the coil positioning.