Disk drive adjusting demodulation window for spiral track using timing feed-forward compensation
View Patent ↗A disk drive is disclosed comprising a head actuated over a disk comprising a plurality of spiral tracks, each spiral track comprising a high frequency signal interrupted at a predetermined interval by a sync mark. The head is used to read the spiral tracks to generate a read signal representing spiral track crossings. A position error signal (PES) is generated in response to the spiral track crossings, and the head is servoed over the disk in response to the PES. Timing feed-forward compensation values are generated in response to the PES, and the timing feed-forward compensation values are used to open a demodulation window at each spiral track crossing, wherein the timing feed-forward compensation values compensate for a repeatable runout (RRO) of the spiral tracks.
1. A disk drive comprising:
a disk comprising a plurality of spiral tracks, each spiral track comprising a high frequency signal interrupted at a predetermined interval by a sync mark;
a head actuated over the disk; and
control circuitry operable to:
use the head to read the spiral tracks to generate a read signal representing spiral track crossings;
generate a position error signal (PES) in response to the spiral track crossings;
servo the head over the disk in response to the PES;
generate timing feed-forward compensation values in response to the PES; and
use the timing feed-forward compensation values to open a demodulation window at each spiral track crossing, wherein the timing feed-forward compensation values compensate for a repeatable runout (RRO) of the spiral tracks.
2. The disk drive as recited in claim 1 , wherein the control circuitry is operable to generate the timing feed-forward compensation values by generating first coefficients of a first sinusoid.
3. The disk drive as recited in claim 2 , wherein the control circuitry is further operable to generate the timing feed-forward compensation values according to:
a
1
cos
(
(
2
π
·
(
k
N
)
)
+
(
2
π
·
r
r
1
)
)
+
b
1
sin
(
(
2
π
·
(
k
N
)
)
+
(
2
π
·
r
r
1
)
)
where:
a1 and b1 are the first coefficients;
k is the kth spiral track out of N spiral tracks;
r is the radial location of the head; and
r 1 represents a part of the radius of the disk spanned by a complete revolution of the spiral tracks.
4. The disk drive as recited in claim 2 , wherein the control circuitry is further operable to adjust the PES based on the first sinusoid in order to cancel at least part of the RRO in the PES.
5. The disk drive as recited in claim 3 , wherein the control circuitry is further operable to adjust the PES based on the first sinusoid in order to cancel at least part of the RRO in the PES.
6. The disk drive as recited in claim 5 , wherein the control circuitry is further operable to:
generate position feed-forward compensation values in response to the PES by generating second coefficients of a second sinusoid;
servo the head over the disk in response to the adjusted PES and the position feed-forward compensation values to cause the head to follow at least part of the RRO in the PES; and
reduce the second coefficients and adapt the first coefficients to account for a corresponding increase of the RRO in the PES.
7. The disk drive as recited in claim 6 , wherein the control circuitry is further operable to:
incrementally reduce the second coefficients until reaching a target amount of RRO in the PES; and
allow the first coefficients to adapt after each incremental reduction of the second coefficients.
8. A disk drive comprising:
a disk comprising a plurality of spiral tracks, each spiral track comprising a high frequency signal interrupted at a predetermined interval by a sync mark;
a head actuated over the disk; and
control circuitry operable to:
use the head to read the spiral tracks to generate a read signal representing spiral track crossings;
generate a position error signal (PES) in response to the spiral track crossings;
adjust the PES based on first coefficients of a first sinusoid in order to cancel at least part of a repeatable runout (RRO) in the PES;
generate position feed-forward compensation values in response to the PES by generating second coefficients of a second sinusoid; and
servo the head over the disk in response to the adjusted PES and the position feed-forward compensation values to cause the head to follow at least part of the RRO in the PES.
9. The disk drive as recited in claim 8 , wherein the control circuitry is further operable to generate the first sinusoid according to:
a
1
cos
(
(
2
π
·
(
k
N
)
)
+
(
2
π
·
r
r
1
)
)
+
b
1
sin
(
(
2
π
·
(
k
N
)
)
+
(
2
π
·
r
r
1
)
)
where:
a1 and b1 are the first coefficients;
k is the kth spiral track out of N spiral tracks;
r is the radial location of the head; and
r 1 represents a part of the radius of the disk spanned by a complete revolution of the spiral tracks.
10. The disk drive as recited in claim 8 , wherein the control circuitry is further operable to:
generate timing feed-forward compensation values in response to the second coefficients of the second sinusoid; and
use the timing feed-forward compensation values to open a demodulation window at each spiral track crossing, wherein the timing feed-forward compensation values compensate for the RRO in the PES.
11. The disk drive as recited in claim 8 , wherein the control circuitry is further operable to reduce the second coefficients and adapt the first coefficients to account for a corresponding increase of the RRO in the PES.
12. The disk drive as recited in claim 11 , wherein the control circuitry is further operable to:
incrementally reduce the second coefficients until reaching a target amount of RRO in the PES; and
allow the first coefficients to adapt after each incremental reduction of the second coefficients.
13. A method of operating a disk drive, the disk drive comprising a head actuated over a disk comprising a plurality of spiral tracks, each spiral track comprising a high frequency signal interrupted at a predetermined interval by a sync mark, the method comprising:
using the head to read the spiral tracks to generate a read signal representing spiral track crossings;
generating a position error signal (PES) in response to the spiral track crossings;
servoing the head over the disk in response to the PES;
generating timing feed-forward compensation values in response to the PES; and
using the timing feed-forward compensation values to open a demodulation window at each spiral track crossing, wherein the timing feed-forward compensation values compensate for a repeatable runout (RRO) of the spiral tracks.
14. The method as recited in claim 13 , further comprising generating the timing feed-forward compensation values by generating first coefficients of a first sinusoid.
15. The method as recited in claim 14 , further comprising generating the timing feed-forward compensation values according to:
a
1
cos
(
(
2
π
·
(
k
N
)
)
+
(
2
π
·
r
r
1
)
)
+
b
1
sin
(
(
2
π
·
(
k
N
)
)
+
(
2
π
·
r
r
1
)
)
where:
a1 and b1 are the first coefficients;
k is the kth spiral track out of N spiral tracks;
r is the radial location of the head; and
r 1 represents a part of the radius of the disk spanned by a complete revolution of the spiral tracks.
16. The method as recited in claim 14 , further comprising adjusting the PES based on the first sinusoid in order to cancel at least part of the RRO in the PES.
17. The method as recited in claim 15 , further comprising adjusting the PES based on the first sinusoid in order to cancel at least part of the RRO in the PES.
18. The method as recited in claim 17 , further comprising:
generating position feed-forward compensation values in response to the PES by generating second coefficients of a second sinusoid;
servoing the head over the disk in response to the adjusted PES and the position feed-forward compensation values to cause the head to follow at least part of the RRO in the PES; and
reducing the second coefficients and adapt the first coefficients to account for a corresponding increase of the RRO in the PES.
19. The method as recited in claim 18 , further comprising:
incrementally reducing the second coefficients until reaching a target amount of RRO in the PES; and
allowing the first coefficients to adapt after each incremental reduction of the second coefficients.
20. A method of operating a disk drive, the disk drive comprising a head actuated over a disk comprising a plurality of spiral tracks, each spiral track comprising a high frequency signal interrupted at a predetermined interval by a sync mark, the method comprising:
using the head to read the spiral tracks to generate a read signal representing spiral track crossings;
generating a position error signal (PES) in response to the spiral track crossings;
adjusting the PES based on first coefficients of a first sinusoid in order to cancel at least part of a repeatable runout (RRO) in the PES;
generating position feed-forward compensation values in response to the PES by generating second coefficients of a second sinusoid; and
servoing the head over the disk in response to the adjusted PES and the position feed-forward compensation values to cause the head to follow at least part of the RRO in the PES.
21. The method as recited in claim 20 , further comprising generating the first sinusoid according to:
a
1
cos
(
(
2
π
·
(
k
N
)
)
+
(
2
π
·
r
r
1
)
)
+
b
1
sin
(
(
2
π
·
(
k
N
)
)
+
(
2
π
·
r
r
1
)
)
where:
a1 and b1 are the first coefficients;
k is the kth spiral track out of N spiral tracks;
r is the radial location of the head; and
r 1 represents a part of the radius of the disk spanned by a complete revolution of the spiral tracks.
22. The method as recited in claim 20 , further comprising:
generating timing feed-forward compensation values in response to the second coefficients of the second sinusoid; and
using the timing feed-forward compensation values to open a demodulation window at each spiral track crossing, wherein the timing feed-forward compensation values compensate for the RRO in the PES.
23. The method as recited in claim 20 , further comprising reducing the second coefficients and adapt the first coefficients to account for a corresponding increase of the RRO in the PES.
24. The method as recited in claim 23 , further comprising:
incrementally reducing the second coefficients until reaching a target amount of RRO in the PES; and
allowing the first coefficients to adapt after each incremental reduction of the second coefficients.
25. A disk drive comprising:
a disk comprising a plurality of spiral tracks, each spiral track comprising a high frequency signal interrupted at a predetermined interval by a sync mark;
a head actuated over the disk; and
control circuitry operable to:
estimate an offset r 0 representing a difference between an axial rotation of the disk and an axial rotation of the spiral tracks;
use the head to read the spiral tracks to generate a read signal representing spiral track crossings;
generate a position error signal (PES) in response to the spiral track crossings;
servo the head over the disk in response to the PES;
generate timing feed-forward compensation values in response to the estimated offset r 0 ; and
use the timing feed-forward compensation values to open a demodulation window at each spiral track crossing, wherein the timing feed-forward compensation values compensate for a repeatable runout (RRO) of the spiral tracks.
26. A method of operating a disk drive, the disk drive comprising a head actuated over a disk comprising a plurality of spiral tracks, each spiral track comprising a high frequency signal interrupted at a predetermined interval by a sync mark, the method comprising:
estimating an offset r 0 representing a difference between an axial rotation of the disk and an axial rotation of the spiral tracks;
using the head to read the spiral tracks to generate a read signal representing spiral track crossings;
generating a position error signal (PES) in response to the spiral track crossings;
servoing the head over the disk in response to the PES;
generating timing feed-forward compensation values in response to the estimated offset r 0 ; and
using the timing feed-forward compensation values to open a demodulation window at each spiral track crossing, wherein the timing feed-forward compensation values compensate for a repeatable runout (RRO) of the spiral tracks.