Method and apparatus for tracking radially-dependent repeatable run-out
View Patent ↗An apparatus and method for tracking radially-dependent repeatable run-out in a disc drive having a servo loop for positioning a head over a rotating disc is provided. The disc includes multiple tracks. Radially-dependent repeatable run-out control components for at least a subset of the multiple tracks are first determined. Data representative of the radially-dependent repeatable run-out control components for the subset of the multiple tracks is then stored. The stored data representative of the radially-dependent repeatable run-out control components is retrieved before settling on the target track, and subsequently used to follow the selected track.
1. A disc drive comprising:
a disc mounted on a spindle motor, the disc having a plurality of tracks; and
tracking means, in a servo loop, for tracking coherent repeatable run-out in the servo loop.
2. The apparatus of claim 1 wherein the tracking means comprises a repeatable run-out tracking module adapted to track coherent repeatable run-out in the servo loop by:
(a) determining a coherent repeatable run-out control components for a subset of the plurality tracks;
(b) storing data representative of the coherent repeatable run-out control components for the subset of the plurality of tracks; and
(c) utilizing the stored data representative of the coherent repeatable run-out control components to follow different tracks of the plurality of tracks.
3. The apparatus of claim 1 wherein the tracking means comprises a repeatable run-out tracking module adapted to track coherent repeatable run-out in the servo loop by:
(a) storing several repeatable run-out control components each determined from a plurality of tracks on the disc surface;
(b) receiving a command initiating a seek to a selected target track on the disc surface;
(c) before settling on the target track, retrieving the control components stored in the storing step (a); and
(d) using the control components retrieved in the retrieving step (c) to follow the target track.
4. 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.
5. 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.
6. The method of claim 5 wherein determining the coherent repeatable run-out control signal for following the destination track is carried out during the seek operation.
7. 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.
8. 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.
9. 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.