Disk drive predicting off-track error due to disturbances occurring over different frequency ranges

1. A disk drive comprising:

a disk;

a head; and

control circuitry comprising a servo control system operable to actuate the head over the disk, the control circuitry operable to:

measure a vibration signal VS(k) representing a disturbance in the servo control system;

predict a first future value of the vibration signal VS(k) based on:

VS1( k+ 1)=α 1 [VS( k )−VS( k− 1)]+VS( k )

where α 1 is a first scalar corresponding to a first frequency range; and

predict a second future value of the vibration signal VS(k) based on:

VS2( k+ 1)=α 2 [VS( k )−VS( k− 1)]+VS( k )

where α 2 is a second scalar corresponding to a second frequency range different from the first frequency range.

2. The disk drive as recited in claim 1 , wherein:

the first frequency range corresponds to a physical vibration; and

the second frequency range corresponds to a thermal popping.

3. The disk drive as recited in claim 1 , wherein the second frequency range is higher than the first frequency range.

4. The disk drive as recited in claim 3 , wherein:

α 1 is less than a half; and

α 2 is greater than a half.

5. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to:

abort a write operation when the first future value exceeds a first threshold; and

abort the write operation when the second future value exceeds a second threshold different than the first threshold.

6. The disk drive as recited in claim 1 , wherein the disk comprises a plurality of servo tracks, each servo track comprises a plurality of servo sectors, and the control circuitry is further operable to:

generate a position error signal by reading the servo sectors; and

generate the vibration signal based on the position error signal.

7. The disk drive as recited in claim 1 , wherein the disk comprises a plurality of servo tracks, each servo track comprises a plurality of servo sectors, and the control circuitry is further operable to:

measure a wedge-to-wedge time representing an interval between the head passing over consecutive servo sectors; and

generate the vibration signal based on the wedge-to-wedge time.

8. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to:

generate a disk-locked clock synchronized to a rotation of the disk; and

generate the vibration signal based on a control signal used to generate the disk locked clock.

9. The disk drive as recited in claim 8 , wherein the control circuitry is further operable to generate the vibrating signal by filtering the control signal to induce a phase lead into the control signal.

10. The disk drive as recited in claim 9 , wherein the control circuitry is further operable to:

prior to predicting the first future value of the vibration signal, first filter the control signal to induce a first phase lead into the control signal proximate the first frequency range; and

prior to predicting the second future value of the vibration signal, second filter the control signal to induce a second phase lead into the control signal proximate the second frequency range.

11. A method of operating a disk drive comprising a head, a disk, and a servo control system operable to actuate the head over the disk, the method comprising:

measuring a vibration signal VS(k) representing a disturbance in the servo control system;

predicting a first future value of the vibration signal VS(k) based on:

VS1( k+ 1)=α 1 [VS( k )−VS( k− 1)]+VS( k )

where α 1 is a first scalar corresponding to a first frequency range; and

predicting a second future value of the vibration signal VS(k) based on:

VS2( k+ 1)=α 2 [VS( k )−VS( k− 1)]+VS( k )

where α 2 is a second scalar corresponding to a second frequency range different from the first frequency range.

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

the first frequency range corresponds to a physical vibration; and

the second frequency range corresponds to a thermal popping.

13. The method as recited in claim 11 , wherein the second frequency range is higher than the first frequency range.

14. The method as recited in claim 13 , wherein:

α 1 is less than a half; and

α 2 is greater than a half.

15. The method as recited in claim 11 , further comprising:

aborting a write operation when the first future value exceeds a first threshold; and

aborting the write operation when the second future value exceeds a second threshold different than the first threshold.

16. The method as recited in claim 11 , wherein the disk comprises a plurality of servo tracks, each servo track comprises a plurality of servo sectors, and the method further comprises:

generating a position error signal by reading the servo sectors; and

generating the vibration signal based on the position error signal.

17. The method as recited in claim 11 , wherein the disk comprises a plurality of servo tracks, each servo track comprises a plurality of servo sectors, and the method further comprises:

measuring a wedge-to-wedge time representing an interval between the head passing over consecutive servo sectors; and

generating the vibration signal based on the wedge-to-wedge time.

18. The method as recited in claim 11 , further comprising:

generating a disk-locked clock synchronized to a rotation of the disk; and

generating the vibration signal based on a control signal used to generate the disk locked clock.

19. The method as recited in claim 18 , further comprising generating the vibrating signal by filtering the control signal to induce a phase lead into the control signal.

20. The method as recited in claim 19 , further comprising:

prior to predicting the first future value of the vibration signal, first filtering the control signal to induce a first phase lead into the control signal proximate the first frequency range; and

prior to predicting the second future value of the vibration signal, second filtering the control signal to induce a second phase lead into the control signal proximate the second frequency range.