Disk drive detecting defective spiral servo track
View Patent ↗A disk drive is disclosed comprising a disk and a head actuated over the disk, wherein the disk comprises a plurality of spiral tracks, each comprising a high frequency signal interrupted by a sync mark at a sync mark interval. The head is used to read a spiral track to generate a spiral track crossing signal g(x n ), where x n is a time in a demodulation window. A position error signal (PES) is determined in response to g(x n ), and a deviation index is computed by correlating g(x n ) with a nominal track crossing signal shifted by the PES. When the deviation index is less than a threshold, the PES is used to servo the head over the disk.
1. A disk drive comprising:
a disk comprising a plurality of spiral tracks, wherein each spiral track comprises a high frequency signal interrupted by a sync mark at a sync mark interval;
a head actuated over the disk; and
control circuitry operable to:
use the head to read a spiral track to generate a spiral track crossing signal g(x n ), where x n is a time in a demodulation window;
determine a position error signal (PES) in response to g(x n );
compute a deviation index by correlating g(x n ) with a nominal track crossing signal shifted by the PES; and
when the deviation index is less than a threshold, use the PES to servo the head over the disk.
2. The disk drive as recited in claim 1 , wherein the control circuitry is operable to compute the deviation index according to:
d
i
=
∑
n
=
1
N
(
g
(
x
n
)
-
f
(
x
n
-
x
0
+
PES
)
)
2
where di is the deviation index and f(x n −x 0 +PES) represents the nominal track crossing signal shifted by the PES.
3. The disk drive as recited in claim 1 , where the control circuitry is further operable to utilize a previously generated PES to servo the head when the deviation index exceeds the threshold.
4. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to write product servo sectors to the disk while servoing the head in response to the PES.
5. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to position the head at an initial radial location in order to estimate an initial nominal track crossing signal.
6. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to update the nominal track crossing signal as the head moves radially over the disk.
7. The disk drive as recited in claim 6 , wherein the control circuitry is further operable to update the nominal track crossing signal when the average deviation index is greater than a first threshold.
8. The disk drive as recited in claim 7 , wherein the control circuitry is further operable to update the nominal track crossing signal when the deviation index is less than a second threshold.
9. A method of operating a disk drive, the disk drive comprising a disk and a head actuated over the disk, wherein the disk comprises a plurality of spiral tracks each comprising a high frequency signal interrupted by a sync mark at a sync mark interval, the method comprising:
using the head to read a spiral track to generate a spiral track crossing signal g(x n ), where x n is a time in a demodulation window;
determining a position error signal (PES) in response to g(x n );
computing a deviation index by correlating g(x n ) with a nominal track crossing signal shifted by the PES; and
when the deviation index is less than a threshold, using the PES to servo the head over the disk.
10. The method as recited in claim 9 , wherein the deviation index is computed according to:
d
i
=
∑
n
=
1
N
(
g
(
x
n
)
-
f
(
x
n
-
x
0
+
PES
)
)
2
where di is the deviation index and f(x n −x 0 +PES) represents the nominal track crossing signal shifted by the PES.
11. The method as recited in claim 9 , further comprising utilizing a previously generated PES to servo the head when the deviation index exceeds the threshold.
12. The method as recited in claim 9 , further comprising writing product servo sectors to the disk while servoing the head in response to the PES.
13. The method as recited in claim 9 , further comprising positioning the head at an initial radial location in order to estimate an initial nominal track crossing signal.
14. The method as recited in claim 9 , further comprising updating the nominal track crossing signal as the head moves radially over the disk.
15. The method as recited in claim 14 , further comprising updating the nominal track crossing signal when the average deviation index is greater than a first threshold.
16. The method as recited in claim 15 , further comprising updating the nominal track crossing signal when the deviation index is less than a second threshold.