Advance Servo Control for Hard Disk Drive in Mobile Application

Abstract

This thesis provided solutions to the following three major problems that HDD servo system encountered in the application of mobile consumer devices: acoustic noise and residual vibrations problem induced from track seeking, smooth settling problem during mode-switching, and disturbances rejection problem for high precision tracking accuracy. To reduce the seeking acoustic noise, a pseudo sinusoidal current profile for any seeking span was designed for the 2DOF seeking controller with consideration of driver saturation, and a design method was derived to chose a set of proper values of the parameters for the current profile such that the residual vibrations due to the dominant structural resonances can be minimized. To achieve the smooth and fast settling for dual stage servo systems which are the servo mechanism for next generation high density HDD, a feedforward compensator was proposed based on zero phase error tracking control. This feedforward compensator can be used to cancel the undesired transitions due to the non-zero initial states of VCM actuators, and hence achieve smooth and fast settling while switching from seeking mode to following mode. To achieve better tracking accuracy, an approach combining the KYP lemma together with H2 optimal method was proposed. This method can be used to shape the sensitivity function of the HDD servo loop to attenuate a few dominant disturbances at a specific frequency range and achieve the minimization of overall track misregistration of the servo system.