Patent ID: 7787210

Claim:
A method for operating a magnetic hard disk drive comprising: providing the disk drive, said disk drive including a motor driven rotating spindle on which a magnetic hard disk is mounted, a movable actuator assembly, a read/write transducer mounted on said actuator assembly and positionable at selected target locations on said disk by the movement of said actuator assembly and reading information stored within servo wedges thereat, and an electro-mechanical closed loop servo-control mechanism, for responding to a position error signal that contains information describing both repeatable runout and non repeatable runout and, a digital to analog converter, for controllably positioning said read/write transducer at said target disk locations; wherein said magnetic hard disk is characterized by a first plurality of radially spaced annular data tracks, which may be further subdivided into a second plurality of radial zones, wherein each said data track is located within a zone and wherein each said data track has, formed therein, a third plurality of said servo wedges, that are regularly spaced circumferentially and of small angular width, wherein said servo wedges contain embedded information defining radial and angular positions within a track; then, rotating said disk at a rotational frequency and a. selecting a zone; b. selecting a data track within said zone; c. sending said transducer to a target position at a servo wedge, “n”, on said data track and determining a position error signal value at said target position; then d. acquiring a repeatable runout correction term at said servo wedge “n” target position and adding said correction term to said position error signal value at a summing junction, whereby the effects of a repeatable runout component of motion of said transducer at said target position is compensated; then, while still at said target position “n”, e. using a Bode plot of amplitude and phase performance characteristic of said HDD, computing N g feed-forward gain coefficients for N h harmonics characterizing a repeatable runout correction term for an immediately following servo wedge; then f. using said feed-forward gain coefficients computing a feed-forward repeatable runout correction term characterizing repeatable runout for said immediately following servo wedge; then g. feeding forward and storing said correction term for use at said immediately following servo wedge.