Adaptive Servo Control of Vibration Induced Error

Abstract

Vibration degrades the effective data rate of a disk drive. Any imbalance of a rotating disk platter can produce periodic vibration. Multiple disk drives cumulatively emit a mixture of periodic and random vibration. Track-following precision of a drive therefore becomes impaired. The frequency of the external vibration pattern is not always known a priori. An adaptive algorithm to determine the periodicity and strength of a cross vibration component is developed and demonstrated. A second order digital peak filter, driven by vibration afflicted position error signal (V-PES), in an open loop configuration forms the basis for detection method. Filter coefficients expressed as a function of a frequency dependent parameter selectively amplifies the V-PES signal. By sweeping through an anticipated frequency range, critical vibration components are first identified. Subsequently V-PES components with rich spectral contribution are compensated by the corresponding filter bank in feedback configuration. The demonstrated algorithm circumvents a need for Fourier analysis to identify V-PES frequency components, facilitating ease of implementation in cost-sensitive products.