Hybrid method of determining a fractional track position of a read

Abstract

A method used to implement a sampled servo control system in a magnetic disk drive for generating a fractional track portion of a position error signal to correctably maintain the alignment of a read transducer (or associated write transducer) relative to a centerline of one of a plurality of a concentric data tracks upon a rotating data storage disk. The system uses a hybrid approach of determining a fractional track position by using a two-burst algorithm when possible and using a multi-burst algorithm only when necessary. The system is particularly suited to determining fraction track position when jogging a relatively narrow magnetoresistive read transducer with a servo pattern normally useful only for wider transducers, namely a pattern of four angularly sequential servo bursts A, B, C, D that are 100% of a track pitch in width and are arranged in quadrature. In this context, the preferred system reads all four 100% servo bursts and then uniquely selects between a two-burst algorithm and a four-burst algorithm to generate a fractional track position relative to a two-burst centerline (A/B or C/D) or a four-burst centerline (N-Q or N+Q). In general, the servo system selects between the two-burst and the four-burst algorithms based on the transducer's passing through a two-burst zone or a four-burst zone, which preferably overlap, as determined from the relative burst amplitudes of all four servo bursts. When operating at a position in which the zones overlap, the preferred system is biased to select the zone corresponding to the algorithm used during the immediately previous servo sample in order to add stability.