Method and apparatus for tracking radially-dependent repeatable run-out

A method of tracking coherent repeatable run-out in a data storage system having a servo loop for positioning a head over a rotatable disc having tracks, the method comprising:

• determining coherent repeatable run-out control components for at least a subset of the tracks;
• utilizing data representative of the coherent repeatable run-out control components to follow the tracks;
• and
• storing data representative of the coherent repeatable run-out control components,
• wherein utilizing data representative of the coherent repeatable run-out control components comprises utilizing the stored data representative of the coherent repeatable run-out control components, and
• wherein storing data representative of the coherent repeatable run-out components comprises storing polynomial coefficients representing coherent repeatable run-out control components in a memory.

A method of tracking coherent repeatable run-out in a data storage system having a servo loop for positioning a head over a rotatable disc having tracks, the method comprising:

• determining coherent repeatable run-out control components for at least a subset of the tracks;
• utilizing data representative of the coherent repeatable run-out control components to follow the tracks;
• and
• storing data representative of the coherent repeatable run-out control components,
• wherein utilizing data representative of the coherent repeatable run-out control components comprises utilizing the stored data representative of the coherent repeatable run-out control components, and
• wherein utilizing the stored data representative of the coherent repeatable run-out components comprises:
• reading data representative of a coherent repeatable run-out control component for a destination track to be followed from the stored data representative of the coherent repeatable run-out control components;
• determining a coherent repeatable run-out control signal for following the destination track as a function of the data representative of the coherent repeatable run-out control component for the destination track;
• and
• injecting the coherent repeatable run-out control signal into, the servo loop to thereby position the head to follow the destination track, and
• wherein reading data representative of the coherent repeatable run-out control component for the destination track is carried out during a seek operation for the destination track just prior to positioning the head to follow the destination track.

A method of tracking coherent repeatable run-out in a data storage system having a servo loop for positioning a head over a rotatable disc having tracks, the method comprising:

• determining coherent repeatable run-out control components for at least a subset of the tracks;
• and
• utilizing data representative of the coherent repeatable run-out control components to follow the tracks;
• wherein the coherent repeatable run-out control components are determined from a calibration procedure, and
• wherein the calibration procedure is a factory calibration procedure that is carried out during manufacture of the disc drive.

A data storage system comprising:

• a servo loop for positioning a head over a rotatable disk having tracks, the servo loop comprising:
• a repeatable run-out tracking module adapted to track coherent repeatable run-out in the servo loop by:
• determining coherent repeatable run-out control components for at least a subset of the tracks;
• and
• utilizing data representative of the coherent repeatable run-out control components to follow the tracks,
• wherein the repeatable run-out tracking module is further adapted to utilize the stored data representative of the coherent repeatable run-out components by:
• reading data representative of a coherent repeatable run-out control component for a destination track to be followed from the stored data representative of the coherent repeatable run-out control components;
• determining a coherent repeatable run-out control signal for following the destination track as a function of the data representative of the coherent repeatable run-out control component for the destination track;
• and
• injecting the coherent repeatable run-out control signal into the servo loop to thereby position the head to follow the destination track, and
• wherein the repeatable run-out tracking module is further adapted to read the data representative of the coherent repeatable run-out control component for the destination track during a seek operation for the destination track just prior to positioning the head to follow the destination track.

A data storage system comprising:

• a servo loop for positioning a head over a rotatable disk having tracks, the servo loop comprising:
• a repeatable run-out tracking module adapted to track coherent repeatable run-out in the servo loop by:
• determining coherent repeatable run-out control components for at least a subset of the tracks;
• and
• utilizing data representative of the coherent repeatable run-out control components to follow the tracks,
• wherein the repeatable run-out tracking module is further adapted to utilize the stored data representative of the coherent repeatable run-out components by:
• reading data representative of a coherent repeatable run-out control component for a destination track to be followed from the stored data representative of the coherent repeatable run-out control components;
• determining a coherent repeatable run-out control signal for following the destination track as a function of the data representative of the coherent repeatable run-out control component for the destination track;
• and
• injecting the coherent repeatable run-out. control signal into the servo loop to thereby position the head to follow the destination track, and
• wherein the repeatable run-out tracking module is further adapted to determine the coherent repeatable run-out control signal for following the destination track during the seek operation.