Reducing estimation period for repeatable runout errors in a disk drive
A method for reducing an estimation period for repeatable runout (RRO) errors in a disk drive comprising a head, a disk surface having a track partitioned by servo-wedges, and a servo control system for controlling the movement of the head relative to a track during revolutions of the disk. The method includes estimating the RRO errors of the track based on a) a series of position error signal values obtained during a current revolution of the disk surface, and b) a previous estimation of the RRO errors of the track obtained during a previous revolution of the disk surface and determining a differential value between a first measure of the estimated RRO errors and a second measure of the previous estimation of RRO errors, and repeating the estimating and determining for subsequent revolutions of the disk surface until the determined differential value is smaller than a pre-selected threshold value.
1. A method for reducing an estimation period for repeatable runout (RRO) errors in a disk drive comprising a head, a disk surface having a track partitioned by a plurality of servo-wedges, and a servo control system for controlling the movement of the head relative to a track during revolutions of the disk, the method comprising:
estimating the RRO errors of the track based on a) a series of position error signal values obtained during a current revolution of the disk surface, and b) a previous estimation of the RRO errors of the track obtained during a previous revolution of the disk surface;
determining a differential value between a first measure of the estimated RRO errors and a second measure of the previous estimation of the RRO errors; and
repeating the estimating and determining for subsequent revolutions of the disk surface until the determined differential value is smaller than a pre-selected threshold value.
2. The method as claimed in claim 1 , wherein the previous estimation of the RRO errors of the track is based on a series of position error signal values obtained during the previous revolution of the disk surface.
3. The method as claimed in claim 2 , wherein the previous estimation of the RRO errors of the track is based on a series of position error signal values obtained during a plurality of previous revolutions of the disk surface.
4. The method as claimed in claim 3 , wherein the first measure comprises:
calculating a first sum of absolute values for the RRO errors estimated during the current revolution of the disk surface.
5. The method as claimed in claim 4 , wherein the second measure comprises:
calculating a second sum of absolute values for the RRO errors estimated during the previous revolution of the disk surface.
6. The method as claimed in claim 5 , wherein the determining further comprises:
determining the differential value based on the calculated first and second sums.
7. The method as claimed in claim 6 , wherein the pre-selected threshold value is based on the number of servo-wedges in the plurality of the servo-wedges in the track.
8. The method as claimed in claim 7 , wherein the absolute values for the RRO errors estimated during the current revolution of the disk surface are digital count expressions.
9. The method as claimed in claim 8 , wherein the absolute values for the RRO errors estimated during the previous revolution of the disk surface are digital count expressions.
10. The method as claimed in claim 9 , wherein the plurality of servo-wedges is in the range of 164 to 180 servo-wedges.
11. The method as claimed in claim 10 , wherein the pre-selected threshold value is approximately 200.
12. The method as claimed in claim 9 , wherein the plurality of servo-wedges is in the range of 240 to 260 servo-wedges.
13. The method as claimed in claim 12 , wherein the pre-selected threshold value is approximately 252.
14. The method as claimed in claim 1 , wherein the disk surface comprises a plurality of tracks partitioned by a plurality of servo-wedges, and wherein the estimating the determining and the repeating is performed for each track in the plurality of tracks.
15. The method as claimed in claim 1 , wherein the disk surface comprises a plurality of tracks partitioned by a plurality of servo-wedges, and wherein the estimating the determining and the repeating is performed for each track in a subset of the plurality of tracks.