Joseph Cheng-Tsu Liu

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

Abstract 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.

Hinge pivot for disk drive

This paper discusses the findings of a hinge pivot for use in hard disk drives (HDD). The actuator assembly in a HDD is supported by a pivot cartridge and controlled by a servo system to perform seek and track following operations for data recording. The cartridge is composed of a pair of pre-loaded ball bearings. Due to the demand for thin hard disk drives and hence, the need to reduce the height of the actuator assembly, a hinge pivot is proposed to replace the set of bearings. The shaft of the pivot is connected to the sleeve with thin hinges made of ultra-high heat-resistant polyamide film, such as Upilex. Measurement showed that the hinge pivot did not exhibit the nonlinear effects during low frequency actuation, such was inherent for ball bearing pivots. Experiment also showed that at least a million life cycles can be achieved without any performance degradation.