Method and apparatus for positioning a transducer using embedded servo

Abstract

A system and method for accurately positioning a transducer means radially in alignment with a selected data track on a magnetic disc and maintaining it in radially alignment is described. Sectored servo tracks radially interspersed with data tracks on a magnetic disc, are uniquely encoded within groups, the code comprising the location of recorded servo signals at either a first or second position within a plurality of data frames located on the servo tracks. The recorded servo signals are detected by a transducer and compared with a D.C. voltage in a comparator in order to produce a series of clock pulses for a shift register. A predetermined sequence of pulses corresponding to possible locations for recorded servo signals within the data frame in a sector is the data input to the shift register. The output of the shift register is a binary number corresponding to the servo track or the data track with which the transducer is radially aligned. This information is processed to identify the radial location of the transducer and to provide, if required, a signal to move the transducer radially. The use of a unique encoding scheme wherein the encoding on the successively positioned servo tracks for any data frame is allowed to change only once every N number of tracks, where N is the number of data frames per track, enhances the abiity of a second position detecting means to maintain the transducer in radial alignment with the selected data track. This is accomplished by circuitry which compares the peaks of the signals corresponding to the first and second locations within a selected data frame, the selection of the data frame depending upon the selected data track, and applying the signal to move the transducer radially, if necessary.