Head control unit in a disk apparatus

A head control unit in a disk apparatus having a rotation driving section for driving a disk, a head facing a recording surface of the disk, head feeding means for feeding the head in a direction in which the head traverses tracks on the disk, a detection section for generating a detection output changed according to the movement of the head, and a control section for controlling the head feeding means according to the detection output obtained by the detection section,

• wherein the detection section outputs phase-A and phase-B detection outputs having different phases and having polarities changing at an interval of half the period according to the movement of the head are transmitted to the control section;
• and the control section controls such that it is determined from a combination of the polarity of the phase-A detection output and that of the phase-B detection output whether the head has been moved to an adjacent track, the track number of the current head position is incremented or decremented by 1, an intra-track deviation from the current head position to the center of the track is detected by the control section by the use of either the phase-A detection output or the phase-B detection output, a deviation from the current head position to the center of the target track is calculated from the track number and the detected intra-track deviation, said phase-A and phase-B detection outputs have a relative phase-shift tolerance, and whichever of the phase-A or phase-B detection outputs used for detecting outputs used for detecting the intra-track deviation is provided with a dead zone where the relative phase-shift tolerance may be generated and detected values are fixed and a signal is sent to the head feeding means instructing it to move the head according to the deviation from the current head position to the center of the target track.