Robust hub design to prevent mechanical contact between the hub and sleeve of FDBs in an HDD due to disc clamping force

We investigated the rotational harmonic source of the runout in a 2.5? hard disk drive (HDD) with a height of 5 mm, especially at low rotating speeds. After disassembling the HDD, circumferential scratches between the upper thrust surface of the hub and sleeve were observed. Through a finite element static analysis of the hub, the deflection resulting from disc clamping force was identified as a source of mechanical contact between the rotating hub and the stationary sleeve. This was determined to generate large-amplitude harmonics in the runout and flying height lower than design values. To prevent mechanical contact between these components, we propose a robust hub design in which the hub thickness radially decreases between the inner and outer thrusts. And HDD spindle motor was prototyped with the proposed hub. Experiments showed that the flying height is increased almost same as design value and the harmonics of the runout were significantly reduced, even at low rotating speeds. After disassembling the prototyped HDD spindle motor, we confirmed that there were no scratches on the surface of the thrust bearing.