Singular Perturbation Control for Vibration Rejection in HDDs Using the PZT Active Suspension as Fast Subsystem Observer

Currently, position sensors other than the read/write head are not embedded into current hard disk drives (HDDs) due to signal-to-noise ratio and nanometer resolution issues. Moreover, a noncollocated sensor fusion creates nonminimum phase zero dynamics which degrades the tracking performance. In this paper, the singular perturbation theory is applied to decompose the voice coil motor's (VCM's) and induced PZT active suspension's dynamics into fast and slow subsystems, respectively. The control system is decomposed into fast and slow time scales for controller designs, and control effectiveness is increased to tackle more degrees-of-freedom via an inner loop vibration suppression with measured high-frequency VCM's and PZT active suspension's dynamics from the piezoelectric elements in the suspension. Experimental results on a commercial HDD with a laser doppler vibrometer show the effective suppression of the VCM and PZT active suspension's flexible resonant modes, as well as an improvement of 39.9% in 3sigma position error signal during track following when compared to conventional notch-based servos