Granted Patent B1

US 9,001,454 · App. 13/862,320 · Granted Apr 7, 2015

Abstract

Claims (162)

1. A disk drive comprising:

a disk comprising tracks defined by servo sectors;

a head; and

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

configure the servo control system into a first state so as to comprise a first input sensitivity function;

generate a position error signal (PES) representing a difference between a target location for the head and a measured location for the head;

generate an actuator control signal in response to the PES;

adapt a feed-forward control signal in response to the servo sectors;

adjust the actuator control signal using the feed-forward control signal;

configure the servo control system from the first state to a second state so as to comprise a second input sensitivity function different from the first input sensitivity function; and

adjust a phase of the adaptation of the feed-forward control signal based on the second state.

2. The disk drive as recited in claim 1 , wherein the feed-forward control signal comprises a sinusoidal control signal.

3. The disk drive as recited in claim 2 , wherein the feed-forward control signal compensates for a repeatable runout (RRO) of the servo sectors.

4. The disk drive as recited in claim 3 , wherein the feed-forward control signal compensates for a harmonic of the repeatable runout (RRO).

5. The disk drive as recited in claim 2 , wherein the control circuitry is further operable to initialize the phase of the adaptation of the feed-forward control signal based on a first phase response of the first input sensitivity function of the servo control system when configured into the first state.

6. The disk drive as recited in claim 5 , wherein the control circuitry is further operable to adjust the phase of the adaptation of the feed-forward control signal based on a second phase response of the second input sensitivity function of the servo control system when configured into the second state.

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

prior to configuring the servo control system into the second state, save the phase of the adaptation of the feed-forward control signal;

configure the servo control system from the second state to the first state; and

restore the phase of the adaptation of the feed-forward control signal based on the saved phase.

8. The disk drive as recited in claim 7 , wherein the control circuitry is further operable to:

configure the servo control system into the second state by enabling a disturbance compensator; and

configure the servo control system into the first state by disabling the disturbance compensator.

9. The disk drive as recited in claim 8 , wherein the disturbance compensator comprises a disturbance observer operable to adjust the actuator control signal based on an observed disturbance.

10. The disk drive as recited in claim 9 , wherein the control circuitry is further operable to adjust the phase of the adaptation of the feed-forward control signal based on the phase response of:

1 −Q ( e jω i )

where:

Q represents a disturbance observer filter; and

ω i represents a target frequency of the observed disturbance.

11. The disk drive as recited in claim 10 , wherein the control circuitry is further operable to adjust the phase of the adaptation of the feed-forward control signal based on:

arc

⁢

⁢

tan

⁢

g

⁢

⁢

X

R

i

⁢

X

I

i

(

1

-

g

)

⁢



X

R

i



2

+



X

I

i



2

where:

X R i =(1 −b 2 )sin ω i ;

X l i =b 1 +b 2 cos ω i ;

g represents a gain of the disturbance observer filter; and

b 1 and b 2 represent coefficients of the disturbance observer filter.

12. The disk drive as recited in claim 11 , wherein b 1 and b 2 establish a center frequency and bandwidth of the disturbance observer filter.

13. A method of operating a disk drive comprising a disk comprising tracks defined by servo sectors, a head, and control circuitry comprising a servo control system operable to actuate the head over the disk in response to the servo sectors, the method comprising:

configuring the servo control system into a first state so as to comprise a first input sensitivity function;

generating a position error signal (PES) representing a difference between a target location for the head and a measured location for the head;

generating an actuator control signal in response to the PES;

adapting a feed-forward control signal in response to the servo sectors;

adjusting the actuator control signal using the feed-forward control signal;

configuring the servo control system from the first state to a second state so as to comprise a second input sensitivity function different from the first input sensitivity function; and

adjusting a phase of the adaptation of the feed-forward control signal based on the second state.

14. The method as recited in claim 13 , wherein the feed-forward control signal comprises a sinusoidal control signal.

15. The method as recited in claim 14 , wherein the feed-forward control signal compensates for a repeatable runout (RRO) of the servo sectors.

16. The method as recited in claim 15 , wherein the feed-forward control signal compensates for a harmonic of the repeatable runout (RRO).

17. The method as recited in claim 14 , further comprising initializing the phase of the adaptation of the feed-forward control signal based on a first phase response of the first input sensitivity function of the servo control system when configured into the first state.

18. The method as recited in claim 17 , further comprising adjusting the phase of the adaptation of the feed-forward control signal based on a second phase response of the second input sensitivity function of the servo control system when configured into the second state.

19. The method as recited in claim 13 , further comprising:

prior to configuring the servo control system into the second state, saving the phase of the adaptation of the feed-forward control signal;

configuring the servo control system from the second state to the first state; and

restoring the phase of the adaptation of the feed-forward control signal based on the saved phase.

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

configuring the servo control system into the second state by enabling a disturbance compensator; and

configuring the servo control system into the first state by disabling the disturbance compensator.

21. The method as recited in claim 20 , wherein the disturbance compensator comprises a disturbance observer operable to adjust the actuator control signal based on an observed disturbance.

22. The method as recited in claim 21 , further comprising adjusting the phase of the adaptation of the feed-forward control signal based on the phase response of:

1 −Q ( e jω i )

where:

Q represents a disturbance observer filter; and

ω i represents a target frequency of the observed disturbance.

23. The method as recited in claim 22 , further comprising adjusting the phase of the adaptation of the feed-forward control signal based on:

arc

⁢

⁢

tan

⁢

g

⁢

⁢

X

R

i

⁢

X

I

i

(

1

-

g

)

⁢



X

R

i



2

+



X

I

i



2

where:

X R i =(1−b 2 )sin ω i ;

X I i =b 1 +b 2 cos ω i ;

g represents a gain of the disturbance observer filter; and

b 1 and b 2 represent coefficients of the disturbance observer filter.

24. The method as recited in claim 23 , wherein b 1 and b 2 establish a center frequency and bandwidth of the disturbance observer filter.

25. A disk drive comprising:

a disk comprising tracks defined by servo sectors;

a head; and

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

configure the servo control system into a first state;

generate a position error signal (PES) representing a difference between a target location for the head and a measured location for the head;

generate an actuator control signal in response to the PES;

adapt a feed-forward control signal in response to the servo sectors;

adjust the actuator control signal using the feed-forward control signal;

configure the servo control system from the first state to a second state;

adjust a phase of the adaptation of the feed-forward control signal based on the second state;

prior to configuring the servo control system into the second state, save the phase of the adaptation of the feed-forward control signal;

configure the servo control system from the second state to the first state; and

restore the phase of the adaptation of the feed-forward control signal based on the saved phase.

26. A method of operating a disk drive comprising a disk comprising tracks defined by servo sectors, a head, and control circuitry comprising a servo control system operable to actuate the head over the disk in response to the servo sectors, the method comprising:

configuring the servo control system into a first state;

generating a position error signal (PES) representing a difference between a target location for the head and a measured location for the head;

generating an actuator control signal in response to the PES;

adapting a feed-forward control signal in response to the servo sectors;

adjusting the actuator control signal using the feed-forward control signal;

configuring the servo control system from the first state to a second state;

adjusting a phase of the adaptation of the feed-forward control signal based on the second state;

prior to configuring the servo control system into the second state, saving the phase of the adaptation of the feed-forward control signal;

configuring the servo control system from the second state to the first state; and

restoring the phase of the adaptation of the feed-forward control signal based on the saved phase.

Assignments (8)