Evaluating distribution of peak signals representing reference track crossings to compensate for thermal expansion when writing spiral tracks to a disk

1. A method of writing a spiral track on a disk of a disk drive, the method comprising:

writing a plurality of reference tracks on the disk;

moving a head over the reference tracks to generate a read signal comprising a plurality of peak signals, wherein each peak signal corresponds to a reference track crossing;

adjusting at least one of a starting radial location and a velocity profile in response to a circumferential distribution of the peak signals; and

writing the spiral track on the disk using the starting radial location and the velocity profile.

2. The method as recited in claim 1 , wherein the head is moved over the reference tracks at a substantially constant velocity.

3. The method as recited in claim 1 , further comprising:

generating an encoder count representing a circumferential location of the head; and

correlating the read signal with the encoder count to generate the distribution of the peak signals.

4. The method as recited in claim 1 , wherein the head is moved over the reference tracks such that a reference track crossing spans fractionally more than one revolution of the disk.

5. The method as recited in claim 1 , wherein the head is moved over the reference tracks such that a reference track crossing spans fractionally less than one revolution of the disk.

6. The method as recited in claim 1 , wherein the distribution of the peak signals represents a uniform expansion of a mechanical component.

7. The method as recited in claim 1 , wherein the distribution of the peak signals represents a non-uniform expansion of a mechanical component.

8. The method as recited in claim 1 , wherein the distribution of the peak signals represents a uniform and a non-uniform expansion of a mechanical component.

9. The method as recited in claim 1 , further comprising comparing the distribution of the peak signals to an initial distribution of the peak signals to determine a shift in the peak signals, wherein at least one of the starting radial location and the velocity profile is adjusted in response to the shift in the peak signals.

10. The method as recited in claim 1 , further comprising averaging a plurality of the peak signals to attenuate noise in each peak signal.

11. The method as recited in claim 1 , wherein the plurality of reference tracks span a small fraction of the disk.

12. A spiral track writer for writing a spiral track on a disk of a disk drive, the spiral track writer comprising:

a head positioner operable to position a head radially over the disk; and

control circuitry operable to:

move the head over a plurality of reference tracks written on the disk to generate a read signal comprising a plurality of peak signals, wherein each peak signal corresponds to a reference track crossing;

adjust at least one of a starting radial location and a velocity profile in response to a circumferential distribution of the peak signals; and

write the spiral track on the disk using the starting radial location and the velocity profile.

13. The spiral track writer as recited in claim 12 , wherein the control circuitry moves the head over the reference tracks at a substantially constant velocity.

14. The spiral track writer as recited in claim 12 , wherein the control circuitry is further operable to:

generate an encoder count representing a circumferential location of the head; and

correlate the read signal with the encoder count to generate the distribution of the peak signals.

15. The spiral track writer as recited in claim 12 , wherein the control circuitry moves the head over the reference tracks such that a reference track crossing spans fractionally more than one revolution of the disk.

16. The spiral track writer as recited in claim 12 , wherein the control circuitry moves the head over the reference tracks such that a reference track crossing spans fractionally less than one revolution of the disk.

17. The spiral track writer as recited in claim 12 , wherein the distribution of the peak signals represents a uniform expansion of a mechanical component.

18. The spiral track writer as recited in claim 12 , wherein the distribution of the peak signals represents a non-uniform expansion of a mechanical component.

19. The spiral track writer as recited in claim 12 , wherein the distribution of the peak signals represents a uniform and a non-uniform expansion of a mechanical component.

20. The spiral track writer as recited in claim 12 , wherein the control circuitry is further operable to compare the distribution of the peak signals to an initial distribution of the peak signals to determine a shift in the peak signals, wherein at least one of the starting radial location and the velocity profile is adjusted in response to the shift in the peak signals.

21. The spiral track writer as recited in claim 12 , wherein the control circuitry is further operable to average a plurality of the peak signals to attenuate noise in each peak signal.

22. The spiral track writer as recited in claim 12 , wherein the plurality of reference tracks span a small fraction of the disk.

23. A disk drive comprising:

a disk;

a head actuated over the disk; and

control circuitry operable to:

move the head over a plurality of reference tracks written on the disk to generate a read signal comprising a plurality of peak signals, wherein each peak signal corresponds to a reference track crossing;

adjust at least one of a starting radial location and a velocity profile in response to a circumferential distribution of the peak signals; and

write a spiral track on the disk using the starting radial location and the velocity profile.

24. The disk drive as recited in claim 23 , wherein the plurality of reference tracks span a small fraction of the disk.