Low Cost Active Magnetic Bearings for Hard Disk Drive Spindle Motors

This paper presents the design and implementation of a contact free Active Magnetic Bearing (AMB) and a vector controlled permanent magnet synchronous motor-bearing combination in a conventional Hard Disk Drive (HDD). The suspension and drive unit fits into the space formerly occupied by the spindle ball bearings. The controller design has to take into account the dynamics of the disks mounted on the rotor which can cause instability of the AMB due to strong gyroscopic effects and vibration of the disks. Rotational speeds higher than 10.000 rpm have been achieved without stability problems. The total power losses of the first prototype magnetically borne motor are in the same order of magnitude as motors with conventional bearings running at this speed.