Disk file head positioning servo system incorporating adaptive saturated

Abstract

A data recording disk file includes rotatable disks with concentric data tracks thereon. The data disk file includes servo information recorded on at least one of the disks, at least one head for reading the servo information during rotation of the disk, and a voice coil motor (VCM) attached to the head for positioning the head relative to the data tracks. A servo is driven by signals read from the head to control the VCM. The servo includes a processor employing an estimator model for estimating the parameters of the VCM and for generating, from the estimated parameters and the servo information, a digital control signal. The digital control signal is converted to an analog control signal. The control signal is applied to a power amplifier which generates an input current for use by the VCM. The processor provides solely a single estimator model which operates in both saturated mode and linear mode depending on the magnitude of the digital PES. In the processor, a discrete model is formed by using a linear continuous model in which the effect of the back electromotive force (emf) is implicitly added into the model, and the current rise time in the VCM is ignored. The processor employs an adaptive estimator model which adjusts its calculations based on both calibrated overall servo gain and the VCM torque constant. The processor also employs a technique used during calibration to identify the average VCM torque constant. The processor employs a technique used during calibration to identify head offsets. The servo includes a short seek and head switch technique which adaptively adjusts the estimator position, the feed forward durations and magnitude based on the identified head offsets.