Disk drive adjusting estimated reader/writer offset to achieve target burst crossing signal amplitude when propagating servo sectors
View Patent ↗A disk drive is disclosed comprising control circuitry for self servo writing a disk. An estimated reader/writer offset is initialized, servo bursts in a first servo track are read, the head is moved radially using the estimated reader/writer offset, and propagated servo bursts are written to a target servo track. The propagated servo bursts are read from the target servo track to generate a read signal, the read signal is processed to generate a burst crossing signal (BCS), and the estimated reader/writer offset is adjusted in response to the BCS.
1. A disk drive comprising:
a disk;
a head actuated over the disk, the head comprising a read element offset radially from a write element forming a reader/writer offset; and
control circuitry operable to self servo write the disk by:
(a) initializing an estimated reader/writer offset;
(b) reading servo bursts in a first servo track;
(c) moving the head radially using the estimated reader/writer offset;
(d) writing propagated servo bursts to a target servo track;
(e) reading the propagated servo bursts from the target servo track to generate a read signal;
(f) processing the read signal to generate a burst crossing signal (BCS);
(g) adjusting the estimated reader/writer offset in response to the BCS; and
(h) repeating (c) through (g) at least once.
2. The disk drive as recited in claim 1 , wherein the control circuitry decreases the estimated reader writer offset if the BCS is greater than a burst crossing threshold.
3. The disk drive as recited in claim 1 , wherein the control circuitry increases the estimated reader writer offset if the BCS is less than a burst crossing threshold.
4. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to self servo write the disk by:
measuring a plurality of BCSs from reading the propagated servo bursts; and
adjusting the estimated reader/writer offset in response to the plurality of BCSs.
5. The disk drive as recited in claim 4 , wherein the control circuitry is further operable to self servo write the disk by:
computing a delta as a function of the plurality of BCSs; and
adjusting the estimated reader/writer offset in response to the delta.
6. The disk drive as recited in claim 5 , wherein the control circuitry is further operable to compute the delta by weighting each BCS with a respective scalar.
7. The disk drive as recited in claim 5 , wherein the control circuitry is further operable to compute the delta by:
computing a difference between each BCS and a corresponding burst crossing threshold; and
computing an average of the differences.
8. The disk drive as recited in claim 1 , wherein the control circuitry is operable to adjust the estimated reader/writer offset by:
generating a delta as a function of the BCS;
scaling the delta with a gain value; and
adding the scaled delta to the estimated reader/writer offset.
9. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to self servo write the disk by:
calibrating a burst crossing threshold;
comparing the BCS to the burst crossing threshold; and
adjusting the estimated reader/writer offset in response to the comparison.
10. The disk drive as recited in claim 9 , wherein the control circuitry is further operable to calibrate the burst crossing threshold in response to a plurality of seed servo bursts written to the disk.
11. A method of servo writing a disk of a disk drive, the disk drive comprising the disk, a head actuated over the disk, the head comprising a read element offset radially from a write element forming a reader/writer offset, the method comprising:
(a) initializing an estimated reader/writer offset;
(b) reading servo bursts in a first servo track;
(c) moving the head radially using the estimated reader/writer offset;
(d) writing propagated servo bursts to a target servo track;
(e) reading the propagated servo bursts from the target servo track to generate a read signal;
(f) processing the read signal to generate a burst crossing signal (BCS);
(g) adjusting the estimated reader/writer offset in response to the BCS; and
(h) repeating (c) through (g) at least once.
12. The method as recited in claim 11 , wherein adjusting the estimated reader writer offset comprises decreasing the estimated reader writer offset if the BCS is greater than a burst crossing threshold.
13. The method as recited in claim 11 , wherein adjusting the estimated reader writer offset comprises increasing the estimated reader writer offset if the BCS is less than a burst crossing threshold.
14. The method as recited in claim 11 , further comprising:
measuring a plurality of BCSs from reading the propagated servo bursts; and
adjusting the estimated reader/writer offset in response to the plurality of BCSs.
15. The method as recited in claim 14 , further comprising:
computing a delta as a function of the plurality of BCSs; and
adjusting the estimated reader/writer offset in response to the delta.
16. The method as recited in claim 15 , wherein computing the delta comprises weighting each BCS with a respective scalar.
17. The method as recited in claim 15 , wherein computing the delta comprises:
computing a difference between each BCS and a corresponding burst crossing threshold; and
computing an average of the differences.
18. The method as recited in claim 11 , wherein adjusting the estimated reader/writer offset comprises:
generating a delta as a function of the BCS;
scaling the delta with a gain value; and
adding the scaled delta to the estimated reader/writer offset.
19. The method as recited in claim 11 , further comprising:
calibrating a burst crossing threshold;
comparing the BCS to the burst crossing threshold; and
adjusting the estimated reader/writer offset in response to the comparison.
20. The method as recited in claim 19 , wherein the burst crossing threshold is calibrated in response to a plurality of seed servo bursts written to the disk.