Analysis and measurement of torque hysteresis of pivot bearing in hard disk drive applications

During hard disk drive (HDD) operation in the track-following, short seek and seek settling modes, the motion of the actuator, which is supported by a pivot bearing cartridge, has very small amplitudes. The effect of hysteresis friction from the pivot bearing becomes significant, impacting servo performance. Often such effects are not well understood and thus, it is not being taken into consideration during servo design. A study of the hysteresis friction behaviour of pivot bearings is presented. An integrated test apparatus for pivot bearing analysis was designed and built where a Laser Doppler Vibrometer (LDV) was used to accurately measure the displacement and velocity of the actuator for feedback control. Using this test apparatus, the hysteresis friction behaviour in both frequency and time domain was analysed. The effects of pre-load, oscillating magnitude and oscillating frequency were investigated. The results obtained can now be used for servo design and pivot bearing evaluation.