Disk drive servosystem using gray code

Claim 1

In a disk drive, a servo system for controlling the position of a magnetic head driven by an actuator relative to data tracks on a magnetic disk during the seek and track following modes of operation of a disk drive comprising: a first closed feedback path comprising said magnetic head and said actuator wherein said head is in transducing relation with said disk for detecting recorded signals on said disk; said first feedback path including a first position circuit coupled to said head for receiving recorded Gray coded position signals recorded along the data tracks of said disk and for providing a head position error signal; said first feedback path further including a microprocessor coupled to said first position circuit for providing selected track data and for comparing said position error signal to a position profile stored in said microprocessor; and a digital-to-analog converter coupled to said microprocessor for receiving a binary signal representative of a selected track to be accessed and for converting said binary signal to an analog signal; a second closed feedback path including a second position circuit coupled to said head for receiving quadrature servo signals recorded along servo tracks of said disk, said servo tracks being interposed between said data tracks; said second feedback path including a summer coupled to said digital-to-analog converter and said second position circuit for summing head position error signals calculated in said first and second feedback paths; and means for compensating for the head position errors coupled to said summer, wherein said first position circuit is active during said seek mode and inactive during said track following mode.