Disk drive applying feed-forward compensation when writing consecutive data tracks
View Patent ↗A disk drive is disclosed comprising a disk comprising a plurality of servo tracks defined by servo sectors, a head actuated over the disk, and control circuitry comprising a servo control system operable to servo the head over the disk. A plurality of data tracks are defined relative to the servo tracks, and a first data track is accessed while servoing the head over the first data track based on a position error signal X n−1 (k) generated at each servo sector of the first data track. Feed-forward compensation values are generated based on X n−1 (k), and a second, consecutive data track is accessed while servoing the head over the second data track based on a position error signal X n (k) generated at each servo sector of the second data track and based on the feed-forward compensation values.
1. A disk drive comprising:
a disk comprising a plurality of servo tracks defined by servo sectors;
a head actuated over the disk; and
control circuitry comprising a servo control system operable to servo the head over the disk, the control circuitry operable to:
define a plurality of data tracks relative to the servo tracks, wherein each data track comprises a plurality of data sectors;
access a first data track while servoing the head over the first data track based on a position error signal X n−1 (k) generated at each servo sector of the first data track;
generate first feed-forward compensation values based on X n−1 (k); and
access a second data track while servoing the head over the second data track based on a position error signal X n (k) generated at each servo sector of the second data track and based on the first feed-forward compensation values,
wherein:
the second data track is consecutive with the first data track;
the access of the first data track accesses at least one data sector in the first data track; and
the access of the second data track accesses at least one data sector in the second data track.
2. The disk drive as recited in claim 1 , wherein the control circuitry is operable to generate the first feed-forward compensation values based on a reference offset R n (k) generated based on
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where:
T o + represents a threshold toward the first data track;
T o − represents a threshold toward a next data track after the second data track;
Δ max + and Δ max − bound a maximum of |R n (k)|.
3. The disk drive as recited in claim 2 , wherein the control circuitry is operable to generate the first feed-forward compensation based on:
R n ( X n−1 )* S −1
wherein S −1 represents an inverse of a sensitivity function of the servo control system.
4. The disk drive as recited in claim 2 , wherein the control circuitry is operable to generate the position error signal X n (k) based on a nominal centerline of the second data track offset by the reference offset R n (k).
5. The disk drive as recited in claim 4 , wherein the control circuitry is further operable to:
generate a position error signal {circumflex over (X)} n (k) by adding X n (k) to R n (k);
generate a first unsafe threshold based on X n−1 (k); and
abort the access of the second data track based on the first unsafe threshold.
6. The disk drive as recited in claim 5 , wherein the control circuitry is operable to abort the access of the second data track when {circumflex over (X)} n (k) exceeds the first unsafe threshold.
7. The disk drive as recited in claim 6 , wherein the first unsafe threshold is based on:
[min( T w + ,W+X n−1 ( k )), T w − ]
where:
T w + represents a maximum threshold for {circumflex over (X)} n (k) toward the first data track;
T w − represents a maximum threshold for {circumflex over (X)} n (k) toward a next data track following the second data track; and
W is a predetermined constant based on a squeeze limit between the first and second data tracks.
8. The disk drive as recited in claim 5 , wherein the control circuitry is operable to:
generate a predicted position error signal {circumflex over (X)} n (k+1) based on {circumflex over (X)} n (k);
generate a second unsafe threshold based on X n−1 (k+1); and
abort the access of the second data track based on the second unsafe threshold.
9. The disk drive as recited in claim 8 , wherein the control circuitry is operable to abort the access of the second data track when {circumflex over (X)} n (k+1) exceeds the second unsafe threshold.
10. The disk drive as recited in claim 9 , wherein the second unsafe threshold is based on:
[min( T p + ,W+X n−1 ( k+ 1)), T p − ]
where:
T p + represents a maximum threshold for {circumflex over (X)} n (k+1) toward the first data track;
T p − represents a maximum threshold for {circumflex over (X)} n (k+1) toward a next data track following the second data track; and
W is a predetermined constant based on a squeeze limit between the first and second data tracks.
11. The disk drive as recited in claim 4 , wherein the control circuitry is operable to:
generate a position error signal {circumflex over (X)} n (k) by adding X n (k) to R n (k);
generate second feed-forward compensation values based on {circumflex over (X)} n (k); and
access a third data track while servoing the head over the second data track based on a position error signal X n+1 (k) generated at each servo sector of the third data track and based on the second feed-forward compensation values,
wherein the third data track is consecutive with the second data track.
12. A method of operating a disk drive comprising a disk comprising a plurality of servo tracks defined by servo sectors, a head actuated over the disk, and control circuitry comprising a servo control system operable to servo the head over the disk, the method comprising:
defining a plurality of data tracks relative to the servo tracks, wherein each data track comprises a plurality of data sectors;
accessing a first data track while servoing the head over the first data track based on a position error signal X n−1 (k) generated at each servo sector of the first data track;
generating first feed-forward compensation values based on X n−1 (k); and
accessing a second data track while servoing the head over the second data track based on a position error signal X n (k) generated at each servo sector of the second data track and based on the first feed-forward compensation values,
wherein:
the second data track is consecutive with the first data track;
the access of the first data track accesses at least one data sector in the first data track; and
the access of the second data track accesses at least one data sector in the second data track.
13. The method as recited in claim 12 , further comprising generating the first feed-forward compensation values based on a reference offset R n (k) generated based on
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where:
T o + represents a threshold toward the first data track;
T o − represents a threshold toward a next data track after the second data track;
Δ max + and Δ max − bound a maximum of |R n (k)|.
14. The method as recited in claim 13 , further comprising generating the first feed-forward compensation based on:
R n ( X n−1 )* S −1
wherein S −1 represents an inverse of a sensitivity function of the servo control system.
15. The method as recited in claim 13 , further comprising generating the position error signal X n (k) based on a nominal centerline of the second data track offset by the reference offset R n (k).
16. The method as recited in claim 15 , further comprising:
generating a position error signal {circumflex over (X)} n (k) by adding X n (k) to R n (k);
generating a first unsafe threshold based on X n−1 (k); and
aborting the access of the second data track based on the first unsafe threshold.
17. The method as recited in claim 16 , further comprising aborting the access of the second data track when {circumflex over (X)} n (k) exceeds the first unsafe threshold.
18. The method as recited in claim 17 , wherein the first unsafe threshold is based on:
[min( T w + ,W+X n−1 ( k )), T w − ]
where:
T w + represents a maximum threshold for {circumflex over (X)} n (k) toward the first data track;
T w − represents a maximum threshold for {circumflex over (X)} n (k) toward a next data track following the second data track; and
W is a predetermined constant based on a squeeze limit between the first and second data tracks.
19. The method as recited in claim 16 , further comprising:
generating a predicted position error signal {circumflex over (X)} n (k+1) based on {circumflex over (X)} n (k);
generating a second unsafe threshold based on X n−1 (k+1); and
aborting the access of the second data track based on the second unsafe threshold.
20. The method as recited in claim 19 , further comprising aborting the access of the second data track when {circumflex over (X)} n (k+1) exceeds the second unsafe threshold.
21. The method as recited in claim 20 , wherein the second unsafe threshold is based on:
[min( T p + ,W+X n−1 ( k )), T p − ]
where:
T p + represents a maximum threshold for {circumflex over (X)} n (k+1) toward the first data track;
T p − represents a maximum threshold for {circumflex over (X)} n (k+1) toward a next data track following the second data track; and
W is a predetermined constant based on a squeeze limit between the first and second data tracks.
22. The method as recited in claim 15 , further comprising:
generating a position error signal {circumflex over (X)} n (k) by adding X n (k) to R n (k);
generating second feed-forward compensation values based on {circumflex over (X)} n (k); and
accessing a third data track while servoing the head over the second data track based on a position error signal X n+1 (k) generated at each servo sector of the third data track and based on the second feed-forward compensation values,
wherein the third data track is consecutive with the second data track.