Adaptive track follow control
View Patent ↗A disk drive comprises a track follow control system having a plurality of selectable frequency modes, the track follow control system configured to receive a position error signal and to output a control signal based on the position error signal, wherein the control signal is used by a head assembly to position a head over a disk. The disk drive also comprises a state estimator configured to receive the control signal and a position signal indicating a position of the head, to estimate a disturbance based on the control signal and the position signal, and to output an estimated disturbance signal based on the estimated disturbance. The disk drive further comprises a disturbance evaluator configured to receive the estimated disturbance signal, and to select one of the frequency modes of the track follow control system based on the estimated disturbance signal.
1. A disk drive, comprising:
a track follow control system having a plurality of selectable frequency modes, the track follow control system configured to receive a position error signal and to output a control signal based on the position error signal, wherein the control signal is used by a head assembly to position a head over a disk;
a state estimator configured to receive the control signal and a position signal indicating a position of the head, to estimate a disturbance based on the control signal and the position signal, and to output an estimated disturbance signal based on the estimated disturbance; and
a disturbance evaluator configured to receive the estimated disturbance signal, and to select one of the frequency modes of the track follow control system based on the estimated disturbance signal.
2. The disk drive of claim 1 , wherein the state estimator is configured to estimate a position of the head based on the control signal, to compute an error between the estimated position of the head and the position signal, and to estimate the disturbance based on the computed error.
3. The disk drive of claim 2 , wherein the state estimator is configured to estimate a bias state of the head based on the computed error and to estimate the disturbance based on the estimated bias state and the computed error.
4. The disk drive of claim 3 , wherein a transfer function of the state estimator relating the estimated disturbance to the disturbance has a substantially flat gain over a frequency range of at least two kilohertz.
5. The disk drive of claim 1 , wherein the estimated disturbance signal is substantially independent of the frequency modes of the track follow control system.
6. The disk drive of claim 1 , wherein, in each frequency mode, the track follow control system is configured to reject disturbances within a different frequency band.
7. The disk drive of claim 1 , wherein the disturbance comprises vibrations applied to the head assembly.
8. The disk drive of claim 1 , wherein the disturbance evaluator comprises:
a plurality of filters configured to pass the estimated disturbance signal within different frequency bands to obtain a plurality of filtered estimated disturbance signals; and
a decision unit configured to receive the filtered estimated disturbance signals and to select one of the frequency modes of the track follow control system based on the filtered estimated disturbance signals.
9. The disk drive of claim 8 , wherein one of the filters comprises a low pass filter and another one of the filters comprises a band pass filter.
10. The disk drive of claim 8 , wherein the decision unit is configured to compute a value for each of the filtered estimated disturbance signals, and to select one of the frequency modes of the track follow control system based on the computed values for the filtered estimated disturbance signals.
11. The disk drive of claim 10 , wherein each of the computed values comprises energy of the respective filtered estimated disturbance signal.
12. The disk drive of claim 10 , wherein the decision unit is configured to compare each of the computed values to a respective threshold value, and to select one of the frequency modes of the track follow control system based on the comparisons.
13. The disk drive of claim 1 , wherein the track follow control system comprises:
a track follow controller configured to receive the position error signal and to output a nominal control signal based on the position error signal; and
a frequency mode controller configured to apply different filers to the nominal control signal for the different frequency modes of the track follow control system.
14. A method for adaptive track following in a disk drive, the disk drive including a track follow control system having a plurality of selectable frequency modes, the method comprising:
receiving a control signal from the track follow control system, wherein the control signal is used by a head assembly to position a head over a disk;
receiving a position signal indicating a position of the head;
estimating a disturbance based on the control signal and the position signal;
outputting an estimated disturbance signal based on the estimated disturbance; and
selecting one of the frequency modes of the track follow control system based on the estimated disturbance signal.
15. The method of claim 14 , wherein the estimating the disturbance comprises:
estimating a position of the head based on the control signal;
computing an error between the estimated position of the head and the position signal; and
estimating the disturbance based on the computed error.
16. The method of claim 15 , wherein the estimating the disturbance comprises:
estimating a bias state of the head based on the computed error; and
estimating the disturbance based on the estimated bias state and the computed error.
17. The method of claim 14 , wherein the estimating the disturbance is substantially independent of the frequency modes of the track follow control system.
18. The method of claim 14 , wherein, in each frequency mode, the track follow control system is configured to reject disturbances within a different frequency band.
19. The method of claim 14 , wherein the disturbance comprises vibrations applied to the head assembly.
20. The method of claim 14 , further comprising filtering the estimated disturbance signal with a plurality of filters configured to pass the estimated disturbance signal within different frequency bands to obtain a plurality of filtered estimated disturbance signals, wherein the selecting one of the frequency modes of the track follow control system is based on the filtered estimated disturbance signals.
21. The method of claim 20 , further comprising computing a value for each of the filtered estimated disturbance signals, wherein the selecting one of the frequency modes of the track follow control system is based on the computed values for the filtered estimated disturbance signals.
22. The method of claim 21 , wherein each of the computed values comprises energy of the respective filtered estimated disturbance signal.
23. The method of claim 21 , further comprising comparing each of the computed values to a respective threshold value, wherein the selecting one of the frequency modes of the track follow control system is based on the comparisons.