A data-based approach is presented for modeling and controller design of a dual-stage servo actuator in a hard disk drive. The servo actuator in this hard disk drive consists of a conventional voice coil motor and a piezo-electrically actuated suspension. A weighted Hankel matrix based realization algorithm that uses frequency domain data is applied to estimate a discrete-time model of the voice coil motor and the piezoelectric actuator. Based on the discrete-time models, different dual-stage track-following controllers were designed using classic and H ∞ loop shaping techniques. The controllers were implemented in real-time in the investigated hard disk drive. A stable feed-back control and good agreement between measurements and simulations show the promising result of data based modeling and control.

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We have implemented the design of a dual-stage actuator tape head for enhanced reduction of lateral tape motion (LTM) disturbance. Our design consists of a conventional voice coil motor (VCM) and a micro-actuator for coarse and fine positioning, respectively. The micro-actuator, which is mounted on the VCM, uses a piezo crystal and allows following LTM up to the kHz regime, while the VCM follows low frequency LTM. Using step response measurements and a realization algorithm, we have created a multi-input discrete-time model of the dual-stage actuator. Based on the model, we designed and implemented a dual-stage controller, using a dual-input single-output approach based on a PQ method. The dual-stage controller controls the position of both actuators and enables an increased track-following bandwidth along with a control signal that is smaller in magnitude than that for a conventional single-stage tape head.

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