Head position controlling circuit for disk unit including servo head selection

Claim 1

A head position controlling circuit for a disk unit, which comprises: a plurality of disk-shaped recording media arranged in planes spaced along a common axis of rotation, each recording medium having a plurality of concentric tracks; a plurality of heads each opposed to a recording face of each said recording medium for reading and writing information from and into said tracks; a carriage for collectively moving said heads toward or away from said axis of rotation; a position information detecting circuit for detecting position information which indicates a position of each track read out with each of said heads; a positioning error detecting circuit responsive to said position information of said position information detecting circuit to detect a deviation of a head with respect to a specified track; a carriage driving circuit to move said carriage to a specified track; a timer for enabling said positioning error detecting circuit at predetermined intervals to detect deviations of said heads with respect to specified tracks; a memory for storing said deviations of said respective heads detected by said positioning error detecting circuit; means for selecting a reference head from said heads; and means provided in said carriage driving circuit for reading, when a head and a track from which data is read out are specified, from said memory, a first deviation of said specified head and a second deviation of said reference head which has been selected from said heads and feeding a difference between said first and second deviations to said carriage driving circuit to move said carriage so that said difference is minimized.