Adaptive Loop Shaping for Wideband Disturbances Attenuation in Precision Information Storage Systems

Modern hard disk drive (HDD) systems are subjected to various external disturbances. One particular category, defined as wide-band disturbances, can generate vibrations with their energy highly concentrated at several frequency bands. Such vibrations are commonly time-varying and strongly environment/product-dependent, and the wide spectral peaks can occur at frequencies above the servo bandwidth. This paper considers the attenuation of such challenging vibrations in the track-following problem of HDDs. Due to the fundamental limitation imposed by the Bode’s integral theorem, the attenuation of such wide-band disturbances may cause unacceptable amplifications at other frequencies. To achieve a good performance and an optimal tradeoff, an add-on adaptive vibration-compensation scheme is proposed in this paper. Through parameter adaptation algorithms that online identify both the center frequencies and the widths of the spectral peaks, the proposed control scheme automatically allocates the control efforts with respect to the real-time disturbance characteristics. The effect is that the position error signal in HDDs can be minimized with effective vibration cancelation. Evaluation of the proposed algorithm is performed by experiments on a voice-coil-driven flexible positioner system.