Disk drive updating compensation values for multiple servo sectors based on PES generated for current servo sector
View Patent ↗A disk drive is disclosed comprising a head actuated over a disk comprising a plurality of servo tracks defined by servo sectors. The head is positioned over a first servo track, and a first position error signal (PES) by reading a first servo sector during a first revolution of the disk and in response to a first compensation value. A second compensation value is updated for a second servo sector based on the first PES during the first revolution of the disk. A second PES is generated by reading the second servo sector during the first revolution of the disk and in response to the updated second compensation value. The first compensation value is updated for the first servo sector based on the second PES during the first revolution of the disk. The head is actuated over the disk in response to the first PES and the second PES.
1. A disk drive comprising:
a disk comprising a plurality of servo tracks, wherein each servo track comprises a plurality of servo sectors;
a head; and
control circuitry operable to:
position the head over a first servo track;
generate a first position error signal (PES) by reading a first servo sector during a first revolution of the disk and in response to a first compensation value;
update a second compensation value for a second servo sector based on the first PES during the first revolution of the disk;
generate a second PES by reading the second servo sector during the first revolution of the disk and in response to the updated second compensation value;
update the first compensation value for the first servo sector based on the second PES during the first revolution of the disk;
actuate the head over the disk in response to the first PES and the second PES.
2. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to:
update the first compensation value for the first servo sector based on the first PES during the first revolution of the disk; and
update the second compensation value for the second servo sector based on the second PES during the first revolution of the disk.
3. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to:
update a third compensation value for a third servo sector based on the first PES and the second PES during the first revolution of the disk;
generate a third PES for the third servo sector during the first revolution of the disk and in response to the third compensation value; and
actuate the head radially over the disk in response to the third PES during the first revolution of the disk.
4. The disk drive as recited in claim 3 , wherein the first, second, and third compensation values compensate for a repeatable disturbance when actuating the head.
5. The disk drive as recited in claim 1 , wherein the control circuitry is operable to update multiple compensation values for multiple of the servo sectors based on the first PES according to:
⌊
w
0
w
1
⋮
w
M
-
1
⌋
+=
α
·
PES
(
a
)
[
g
(
mod
(
M
-
a
,
M
)
)
g
(
mod
(
M
-
a
+
1
,
M
)
)
⋮
g
(
mod
(
M
-
a
-
1
,
M
)
)
]
where:
w 0 -w M-1 represent the multiple compensation values for the multiple servo sectors;
a represents the first servo sector;
PES(a) represents the first PES;
α is a learning coefficient;
g(x) represents an inverse error rejection function.
6. The disk drive as recited in claim 5 , wherein the control circuitry is operable to update multiple compensation values for multiple of the servo sectors based on the second PES according to:
[
w
0
w
1
⋮
w
M
-
1
]
+=
α
·
PES
(
b
)
[
g
(
mod
(
M
-
b
,
M
)
)
g
(
mod
(
M
-
b
+
1
,
M
)
)
⋮
g
(
mod
(
M
-
b
-
1
,
M
)
)
]
where:
w 0 -w M-1 represent the multiple compensation values for the multiple servo sectors;
b represents the second servo sector;
PES(b) represents the second PES;
α is a learning coefficient;
g(x) represents an inverse error rejection function.
7. The disk drive as recited in claim 6 , wherein the control circuitry is further operable to update the multiple compensation values w 0 -w M-1 after reading each of the multiple servo sectors based on the PES generated for each of the multiple servo sectors according to:
⌊
w
0
w
1
⋮
w
M
-
1
⌋
+=
α
·
PES
(
i
)
[
g
(
mod
(
M
-
i
,
M
)
)
g
(
mod
(
M
-
i
+
1
,
M
)
)
⋮
g
(
mod
(
M
-
i
-
1
,
M
)
)
]
where i represents each of the multiple servo sectors.
8. The disk drive as recited in claim 6 , wherein the control circuitry is further operable to update the multiple compensation values w 0 -w M-1 after reading each of the multiple servo sectors based on the PES generated for each of the multiple servo sectors during the first revolution of the disk.
9. The disk drive as recited in claim 5 , wherein the control circuitry is further operable to update the multiple compensation values w 0 -w M-1 after reading each of the multiple servo sectors based on the PES generated for each of the multiple servo sectors during a second revolution of the disk.
10. The disk drive as recited in claim 5 , wherein the learning coefficient α is greater than zero and less than two.
11. The disk drive as recited in claim 6 , wherein the learning coefficient α for the first PES is different than the learning coefficient α for the second PES.
12. The disk drive as recited in claim 7 , wherein the control circuitry is further operable to update the multiple compensation values w 0 -w M-1 until all of the PESs generated over a revolution of the disk are less than a threshold.
13. The disk drive as recited in claim 7 , wherein the control circuitry is further operable to update the multiple compensation values w 0 -w M-1 until a variance of the PESs falls below a threshold.
14. A method of operating a disk drive comprising a head actuated over a disk comprising a plurality of servo tracks, wherein each servo track comprises a plurality of servo sectors, the method comprising:
positioning the head over a first servo track;
generating a first position error signal (PES) by reading a first servo sector during a first revolution of the disk and in response to a first compensation value;
updating a second compensation value for a second servo sector based on the first PES during the first revolution of the disk;
generating a second PES by reading the second servo sector during the first revolution of the disk and in response to the updated second compensation value;
updating the first compensation value for the first servo sector based on the second PES during the first revolution of the disk;
actuating the head over the disk in response to the first PES and the second PES.
15. The method as recited in claim 14 , further comprising:
updating the first compensation value for the first servo sector based on the first PES during the first revolution of the disk; and
updating the second compensation value for the second servo sector based on the second PES during the first revolution of the disk.
16. The method as recited in claim 14 , further comprising:
updating a third compensation value for a third servo sector based on the first PES and the second PES during the first revolution of the disk;
generating a third PES for the third servo sector during the first revolution of the disk and in response to the third compensation value; and
actuating the head radially over the disk in response to the third PES during the first revolution of the disk.
17. The method as recited in claim 16 , wherein the first, second, and third compensation values compensate for a repeatable disturbance when actuating the head.
18. The method as recited in claim 14 , further comprising updating multiple compensation values for multiple of the servo sectors based on the first PES according to:
⌊
w
0
w
1
⋮
w
M
-
1
⌋
+=
α
·
PES
(
a
)
[
g
(
mod
(
M
-
a
,
M
)
)
g
(
mod
(
M
-
a
+
1
,
M
)
)
⋮
g
(
mod
(
M
-
a
-
1
,
M
)
)
]
where:
w 0 -w M-1 represent the multiple compensation values for the multiple servo sectors;
a represents the first servo sector;
PES(a) represents the first PES;
α is a learning coefficient;
g(x) represents an inverse error rejection function.
19. The method as recited in claim 18 , further comprising updating multiple compensation values for multiple of the servo sectors based on the second PES according to:
[
w
0
w
1
⋮
w
M
-
1
]
+=
α
·
PES
(
b
)
[
g
(
mod
(
M
-
b
,
M
)
)
g
(
mod
(
M
-
b
+
1
,
M
)
)
⋮
g
(
mod
(
M
-
b
-
1
,
M
)
)
]
where:
w 0 -w M-1 represent the multiple compensation values for the multiple servo sectors;
b represents the second servo sector;
PES(b) represents the second PES;
α is a learning coefficient;
g(x) represents an inverse error rejection function.
20. The method as recited in claim 19 , further comprising updating the multiple compensation values w 0 -w M-1 after reading each of the multiple servo sectors based on the PES generated for each of the multiple servo sectors according to:
⌊
w
0
w
1
⋮
w
M
-
1
⌋
+=
α
·
PES
(
i
)
[
g
(
mod
(
M
-
i
,
M
)
)
g
(
mod
(
M
-
i
+
1
,
M
)
)
⋮
g
(
mod
(
M
-
i
-
1
,
M
)
)
]
where i represents each of the multiple servo sectors.
21. The method as recited in claim 19 , further comprising updating the multiple compensation values w 0 -w M-1 after reading each of the multiple servo sectors based on the PES generated for each of the multiple servo sectors during the first revolution of the disk.
22. The method as recited in claim 18 , further comprising updating the multiple compensation values w 0 -w M-1 after reading each of the multiple servo sectors based on the PES generated for each of the multiple servo sectors during a second revolution of the disk.
23. The method as recited in claim 18 , wherein the learning coefficient α is greater than zero and less than two.
24. The method as recited in claim 19 , wherein the learning coefficient α for the first PES is different than the learning coefficient α for the second PES.
25. The method as recited in claim 20 , further comprising updating the multiple compensation values w 0 -w M-1 until all of the PESs generated over a revolution of the disk are less than a threshold.
26. The method as recited in claim 20 , further comprising updating the multiple compensation values w 0 -w M-1 until a variance of the PESs falls below a threshold.