Novel Configuration of the Magnetizing Fixture for a Brushless Permanent-Magnet Motor

The permanent magnet spindle motor for a hard disk or an optical disk drive is outer rotor type and the permanent magnet is mounted on the inner surface of the rotor. Because the motor is very small, the magnet for the motor is not a premagnetized segmented-magnet but a ring magnet which should be magnetized on the magnetization fixture. The magnetization distribution of the magnet is settled by a configuration of the fixture and magnetizing current. In many cases, the magnet is not fully magnetized on the whole regions because of the limitation of the magnetizing. current. The magnetization distribution of the magnet influences the air-gap flux density distribution of the motor and the flux density distribution influences the cogging torque and the back electromotive force of the spindle motor. In this paper, the effects of configuration of the fixture on performance of the spindle motors are specified and alternative configuration for more complete magnetization is suggested.