Disk drive employing system inversion for tuning seek to settle servo loop

1. A method of operating a disk drive, the disk drive comprising a disk comprising a plurality of tracks, a head, and a closed loop servo system comprising a seek servo loop and a settle servo loop for actuating the head over the disk, the method comprising:

seeking the head toward a target track using the seek servo loop; and

when the head approaches the target track, switching to the settle servo loop and settling the head on the target track in response to a reference signal generated in response to a system inversion of the settle servo loop.

2. The method as recited in claim 1 , wherein the reference signal is generated by:

applying a function h to the settle servo loop and measuring a corresponding output g of the settle servo loop; and

generating the reference signal in response to a summation of a plurality of the function h, wherein:

each of the plurality of the function h is shifted by an offset and scaled by a coefficient; and

the coefficients are generated in response to the measured output g.

3. The method as recited in claim 2 , wherein the coefficients are generated in response to a dual basis function generated using a discrete Fourier transform of the measured output g.

4. The method as recited in claim 2 , wherein the reference signal is generated by adapting the coefficients in response to a difference between a measured position of the head and a desired position of the head.

5. The method as recited in claim 3 , wherein the reference signal is generated by:

generating a difference between a measured position of the head and a desired position of the head; and

adapting the coefficients in response to the difference and the dual basis function.

6. The method as recited in claim 5 , wherein the desired position of the head is a target track.

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

seeking the head to the target track in response to a selected one of a plurality of seek profiles; and

when the head approaches the target track, switching to the settle servo loop and settling the head on the target track in response to the reference signal corresponding to the selected seek profile.

8. The method as recited in claim 7 , wherein each seek profile corresponds to a different seek length.

9. The method as recited in claim 7 , wherein each seek profile corresponds to a different maximum seek velocity.

10. A disk drive comprising:

a disk comprising a plurality of tracks;

a head; and

control circuitry comprising a closed loop servo system comprising a seek servo loop and a settle servo loop for actuating the head over the disk, the control circuitry operable to:

seek the head toward a target track using the seek servo loop; and

when the head approaches the target track, switch to the settle servo loop and settle the head on the target track in response to a reference signal generated in response to a system inversion of the settle servo loop.

11. The disk drive as recited in claim 10 , wherein the reference signal is generated by:

applying a function h to the settle servo loop and measuring a corresponding output g of the settle servo loop; and

generating the reference signal in response to a summation of a plurality of the function h, wherein:

each of the plurality of the function h is shifted by an offset and scaled by a coefficient; and

the coefficients are generated in response to the measured output g.

12. The disk drive as recited in claim 11 , wherein the coefficients are generated in response to a dual basis function generated using a discrete Fourier transform of the measured output g.

13. The disk drive as recited in claim 11 , wherein the reference signal is generated by adapting the coefficients in response to a difference between a measured position of the head and a desired position of the head.

14. The disk drive as recited in claim 12 , wherein the reference signal is generated by:

generating a difference between a measured position of the head and a desired position of the head; and

adapting the coefficients in response to the difference and the dual basis function.

15. The disk drive as recited in claim 14 , wherein the desired position of the head is a target track.

16. The disk drive as recited in claim 10 , wherein the control circuitry is further operable to:

seek the head to the target track in response to a selected one of a plurality of seek profiles; and

when the head approaches the target track, switch to the settle servo loop and settle the head on the target track in response to the reference signal corresponding to the selected seek profile.

17. The disk drive as recited in claim 16 , wherein each seek profile corresponds to a different seek length.

18. The disk drive as recited in claim 16 , wherein each seek profile corresponds to a different maximum seek velocity.