Feed forward compensation for fly height control in a disk drive

1. A method of selecting a dynamic fly height (DFH) control setting for a head in a disk drive, the method comprising:

servoing the head over a disk;

generating a fly height measurement for the head;

extracting a frequency component from the fly height measurement; and

adjusting the DFH control setting for the head in response to the extracted frequency component.

2. The method as recited in claim 1 , wherein:

the disk is clamped to a spindle motor with a number of screws; and

the frequency component is based on the number of screws.

3. The method as recited in claim 2 , wherein the frequency component is based on the number of screws multiplied by the rotation frequency of the disk.

4. The method as recited in claim 1 , wherein adjusting the DFH control setting comprises:

calibrating a nominal DFH control setting; and

adjusting the nominal DFH control setting in response to the extracted frequency component.

5. The method as recited in claim 4 , wherein adjusting the DFH control setting further comprises:

comparing the nominal DFH control setting to a feedback signal to generate an error signal;

filtering the error signal to generate a control signal; and

applying feed forward compensation to the control signal in response to the extracted frequency component.

6. The method as recited in claim 1 , wherein:

servo data is recorded on the disk;

the servo data comprises a plurality of servo sectors; and

a fly height measurement is generated as the head passes over each servo sector.

7. The method as recited in claim 6 , wherein:

the servo sectors are read to generate a read signal; and

the fly height measurement is generated in response to the read signal.

8. The method as recited in claim 1 , wherein extracting the frequency component from the fly height measurement comprises:

evaluating an amplitude deviation of the fly height measurement over a range of frequencies; and

selecting a frequency component having the maximum amplitude deviation.

9. The method as recited in claim 1 , wherein extracting the frequency component from the fly height measurement comprises evaluating an amplitude deviation of the fly height measurement over a predetermined frequency range.

10. The method as recited in claim 9 , wherein:

the disk is clamped to a spindle motor with a number of screws; and

the predetermined frequency range is based on the number of screws.

11. The method as recited in claim 1 , wherein:

servo data is recorded on the disk;

the servo data comprises a plurality of spiral tracks; and

a fly height measurement is generated as the head passes over each spiral track.

12. A disk drive comprising:

a disk;

a head actuated over the disk; and

control circuitry operable to select a dynamic fly height (DFH) control setting for the head by:

servoing the head over the disk;

generating a fly height measurement for the head;

extracting a frequency component from the fly height measurement; and

adjusting the DFH control setting for the head in response to the extracted frequency component.

13. The disk drive as recited in claim 12 , wherein:

the disk is clamped to a spindle motor with a number of screws; and

the frequency component is based on the number of screws.

14. The disk drive as recited in claim 13 , wherein the frequency component is based on the number of screws multiplied by the rotation frequency of the disk.

15. The disk drive as recited in claim 12 , wherein the control circuitry is further operable to adjust the DFH control setting by:

calibrating a nominal DFH control setting; and

adjusting the nominal DFH control setting in response to the extracted frequency component.

16. The disk drive as recited in claim 15 , wherein the control circuitry is further operable to adjust the DFH control setting by:

comparing the nominal DFH control setting to a feedback signal to generate an error signal;

filtering the error signal to generate a control signal; and

applying feed forward compensation to the control signal in response to the extracted frequency component.

17. The disk drive as recited in claim 12 , wherein:

servo data is recorded on the disk;

the servo data comprises a plurality of servo sectors; and

the control circuitry is further operable to generate a fly height measurement as the head passes over each servo sector.

18. The disk drive as recited in claim 17 , wherein the control circuitry is further operable to:

read the servo sectors to generate a read signal; and

generate the fly height measurement in response to the read signal.

19. The disk drive as recited in claim 12 , wherein the control circuitry is further operable to extract the frequency component from the fly height measurement by:

evaluating an amplitude deviation of the fly height measurement over a range of frequencies; and

selecting a frequency component having the maximum amplitude deviation.

20. The disk drive as recited in claim 12 , wherein the control circuitry is further operable to extract the frequency component from the fly height measurement by evaluating an amplitude deviation of the fly height measurement over a predetermined frequency range.

21. The disk drive as recited in claim 20 , wherein:

the disk is clamped to a spindle motor with a number of screws; and

the predetermined frequency range is based on the number of screws.

22. The disk drive as recited in claim 12 , wherein:

servo data is recorded on the disk;

the servo data comprises a plurality of spiral tracks; and

the control circuitry is further operable to generate a fly height measurement as the head passes over each spiral track.

23. A disk drive comprising:

a disk;

a head actuated over the disk; and

a means for servoing the head over the disk;

a means for generating a fly height measurement for the head;

a means for extracting a frequency component from the fly height measurement; and

a means for adjusting a DFH control setting for the head in response to the extracted frequency component.