Contact-Induced Vibration in Dual-Stage HDD Servo Systems and Its Compensation Using PQ Method and Peak Filters

Abstract

Other than many well-known vibration sources in high density hard disk drive (HDD) servo systems, contact-induced vibration (CIV) is a new vibration source due to continuous contact of the read/write head with the media. This paper presents the experimental observation on the characteristics of CIV and its compensator design under dual-stage servo structure. By lowering the fly-height between the slider and the recording media artificially, the effects of CIV are investigated at different fly-heights, different rotation speeds, and different tracks. We found that, unlike the airflow disturbance that affects all frequencies of HDD, the CIVs excite and amplify only the resonance modes of the system, namely, the modes at 441 Hz, 2110 Hz and 2800 Hz in our experimental setup. Moreover, consistent relationships between the center frequencies and magnitudes of the CIV modes and the tested fly-height, rotation speed and track position are clearly observed and analyzed. In what follows, to facilitate the compensator design for CIV in dual-stage HDD system that is actually a dual-input single-output system, the so-called PQ method is adopted to reduce the problem to two single-input single-output design problems. As such, the relative contributions to system output from the voice coil motor (VCM) and lead-zirconium-titanate (PZT) actuator subsystems can be well assigned in the frequency domain. Meanwhile, based on the prior CIV investigation, two well-designed peak filters are incorporated in parallel with the PZT loop to further shape the whole sensitivity loop. In the end, the remarkable performance of the proposed method in CIV compensation is demonstrated by simulation.