Servo position error signal calibration in a hard disc drive

摘要

A method for calibrating the position error signal in a servo system of a disc drive. The disc drive comprises a disc and an actuator adjacent the disc, the actuator including a head which is controllably positionable relative to data tracks on the surface of the disc using a servo position error signal generated using a scale factor generally indicative of the ratio of the width of the head to the width of the tracks on the disc. The head is positioned at the center of a selected track using an initial scale factor for the position error signal, the selected track having servo position fields comprising a plurality of burst patterns. The burst patterns include a first burst pattern extending radially from a first track boundary to a second track boundary of the selected track, a second burst pattern extending radially from the center of the selected track to the first track boundary and a third burst pattern extending radially from the center of the selected track to the second track boundary. At the center of the selected track, the magnitude of burst signals read by the head from the second and third burst patterns is nominally equal, and from this location the head is swept towards the first track boundary until the magnitude of burst signals from the second burst pattern is nominally equal to the magnitude of burst signals from the first burst pattern, identifying a quarter-track location halfway between the center of the selected track and the first track boundary. A calibration scale factor for the position error signal is determined from the ratio of the expected position error signal to the actual position error signal obtained at the quarter-track location. Alternatively, the initial scale factor is incremented and the head is repositioned towards until the quarter-track location until the magnitude of burst signals from the second burst pattern is nominally equal to the magnitude of burst signals from the first burst pattern, after which the incremented scale factor is stored as the calibration scale factor.