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