Disk drive adjusting microactuator gain by injecting a sinusoid into a servo control system
View Patent ↗A disk drive is disclosed comprising a head, a disk surface, and a dual stage actuator (DSA) servo loop comprising a voice coil motor (VCM) servo loop and a microactuator servo loop operable to actuate the head over the disk surface. A microactuator compensator in the microactuator servo loop is disabled, a sinusoid is injected into a control signal applied to the microactuator, and coefficients of a corresponding sinusoidal response in a DSA error signal of the DSA servo loop is measured. The sinusoid is injected into a model of the microactuator to generate a compensation signal. A gain of the microactuator is adjusted based on a VCM error signal and the coefficients of the sinusoidal response in the DSA error signal.
1. A disk drive comprising:
a head;
a disk surface;
a dual stage actuator (DSA) servo loop comprising a voice coil motor (VCM) servo loop comprising a VCM and a microactuator servo loop comprising a microactuator operable to actuate the head over the disk surface; and
control circuitry operable to:
disable a microactuator compensator in the microactuator servo loop; and
after disabling the microactuator compensator:
inject a sinusoid into a control signal applied to the microactuator and measure coefficients of a corresponding sinusoidal response in a DSA error signal of the DSA servo loop;
inject the sinusoid into a model of the microactuator to generate a compensation signal;
generate a VCM error signal of the VCM servo loop based on the DSA error signal and the compensation signal;
generate a VCM control signal based on the VCM error signal; and
adjust a gain of the microactuator based on the VCM error signal and the coefficients of the sinusoidal response in the DSA error signal.
2. The disk drive as recited in claim 1 , wherein the control circuitry is operable to disable the model of the microactuator while measuring the coefficients of the sinusoidal response in the DSA error signal.
3. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to adjust the gain of the microactuator based on:
K 0 ( k )=(1−γ( k )) K 0 ( k− 1)−γ( k ) e v ( k )( a·d m ( k )+ b·d m c ( k ))
where:
K 0 is the gain of the microactuator;
γ is a learning coefficient;
d m is the sinusoid;
d m c equals
d
m
·
ⅇ
-
j
π
2
;
a and b are the coefficients of the sinusoidal response in the DSA error signal; and
e v is the VCM error signal.
4. The disk drive as recited in claim 3 , wherein the control circuitry is operable to adjust the gain of the microactuator until the VCM error signal falls below a threshold.
5. The disk drive as recited in claim 3 , wherein the control circuitry is operable to adjust the gain of the microactuator to substantially match a gain of the model of the microactuator.
6. The disk drive as recited in claim 1 , wherein the control circuitry is operable to adjust the gain of the microactuator to substantially match a gain of the model of the microactuator.
7. A disk drive comprising:
a head;
a disk surface;
a dual stage actuator (DSA) servo loop comprising a voice coil motor (VCM) servo loop comprising a VCM and a microactuator servo loop comprising a microactuator operable to actuate the head over the disk surface; and
control circuitry operable to:
initialize a gain of the microactuator;
inject a sinusoid into the microactuator servo loop and generate a corresponding feed-forward control signal in the VCM servo loop that compensates for an effect of the sinusoid on a DSA error signal; and
detect a change in the gain of the microactuator in response to the DSA error signal.
8. The disk drive as recited in claim 7 , wherein the control circuitry is operable to:
measure coefficients of a sinusoidal response of the DSA servo loop; and
detect the change in the gain of the microactuator in response to the DSA error signal and the coefficients of the sinusoidal response of the DSA servo loop.
9. The disk drive as recited in claim 8 , wherein the control circuitry is operable to detect the change in the gain of the microactuator based on:
2
N
(
a
2
+
b
2
)
d
m
2
∑
k
=
1
N
ⅇ
(
k
)
(
a
·
d
m
(
k
)
+
b
·
d
m
c
(
k
)
)
where:
d m is the sinusoid;
d m c equals
d
m
·
ⅇ
-
j
π
2
;
a and b are the coefficients of the sinusoidal response of the DSA servo loop;
e is the DSA error signal; and
N is an integer number of samples of the DSA error signal.
10. The disk drive as recited in claim 8 , wherein the control circuitry is operable to generate the feed-forward control signal in the VCM servo loop in response to the coefficients of the sinusoidal response of the DSA servo loop.
11. The disk drive as recited in claim 7 , wherein the control circuitry is operable to:
measure coefficients of a sinusoidal response of the DSA servo loop; and
adjust the gain of the microactuator in response to the DSA error signal and the coefficients of the sinusoidal response of the DSA servo loop.
12. The disk drive as recited in claim 11 , wherein the control circuitry is operable to adjust the gain of the microactuator based on:
K 0 ( k )=(1−γ( k )) K 0 ( k− 1)−γ( k ) e ( k )( a·d m ( k )+ b·d m c ( k ))
where:
K 0 is the gain of the microactuator;
γ is a learning coefficient;
d m is the sinusoid;
d m c equals
d
m
·
ⅇ
-
j
π
2
;
a and b are the coefficients of the sinusoidal response of the DSA servo loop; and
e is the DSA error signal.
13. A method of operating a disk drive, the disk drive comprising a head, a disk surface, and a dual stage actuator (DSA) servo loop comprising a voice coil motor (VCM) servo loop comprising a VCM and a microactuator servo loop comprising a microactuator operable to actuate the head over the disk surface, the method comprising:
disabling a microactuator compensator in the microactuator servo loop; and
after disabling the microactuator compensator:
injecting a sinusoid into a control signal applied to the microactuator and measure coefficients of a corresponding sinusoidal response in a DSA error signal of the DSA servo loop;
injecting the sinusoid into a model of the microactuator to generate a compensation signal;
generating a VCM error signal of the VCM servo loop based on the DSA error signal and the compensation signal;
generating a VCM control signal based on the VCM error signal; and
adjusting a gain of the microactuator based on the VCM error signal and the coefficients of the sinusoidal response in the DSA error signal.
14. The method as recited in claim 13 , further comprising disabling the model of the microactuator while measuring the coefficients of the sinusoidal response in the DSA error signal.
15. The method as recited in claim 13 , further comprising adjusting the gain of the microactuator based on:
K 0 ( k )=(1−γ( k )) K 0 ( k− 1)−γ( k ) e v ( k )( a·d m ( k )+ b·d m c ( k ))
where:
K 0 is the gain of the microactuator;
γ is a learning coefficient;
d m is the sinusoid;
d m c equals
d
m
·
ⅇ
-
j
π
2
;
a and b are the coefficients of the sinusoidal response in the DSA error signal; and
e v is the VCM error signal.
16. The method as recited in claim 15 , further comprising adjusting the gain of the microactuator until the VCM error signal falls below a threshold.
17. The method as recited in claim 15 , further comprising adjusting the gain of the microactuator to substantially match a gain of the model of the microactuator.
18. The method as recited in claim 13 , further comprising adjusting the gain of the microactuator to substantially match a gain of the model of the microactuator.
19. A method of operating a disk drive, the disk drive comprising a head, a disk surface, and a dual stage actuator (DSA) servo loop comprising a voice coil motor (VCM) servo loop comprising a VCM and a microactuator servo loop comprising a microactuator operable to actuate the head over the disk surface, the method comprising:
initializing a gain of the microactuator;
injecting a sinusoid into the microactuator servo loop and generate a corresponding feed-forward control signal in the VCM servo loop that compensates for an effect of the sinusoid on a DSA error signal; and
detecting a change in the gain of the microactuator in response to the DSA error signal.
20. The method as recited in claim 19 , further comprising:
measuring coefficients of a sinusoidal response of the DSA servo loop; and
detecting the change in the gain of the microactuator in response to the DSA error signal and the coefficients of the sinusoidal response of the DSA servo loop.
21. The method as recited in claim 20 , further comprising detecting the change in the gain of the microactuator based on:
2
N
(
a
2
+
b
2
)
d
m
2
∑
k
=
1
N
ⅇ
(
k
)
(
a
·
d
m
(
k
)
+
b
·
d
m
c
(
k
)
)
where:
d m is the sinusoid;
d m c equals
d
m
·
ⅇ
-
j
π
2
;
a and b are the coefficients of the sinusoidal response of the DSA servo loop;
e is the DSA error signal; and
N is an integer number of samples of the DSA error signal.
22. The method as recited in claim 20 , further comprising generating the feed-forward control signal in the VCM servo loop in response to the coefficients of the sinusoidal response of the DSA servo loop.
23. The method as recited in claim 19 , further comprising:
measure coefficients of a sinusoidal response of the DSA servo loop; and
adjust the gain of the microactuator in response to the DSA error signal and the coefficients of the sinusoidal response of the DSA servo loop.
24. The method as recited in claim 23 , further comprising adjusting the gain of the microactuator based on:
K 0 ( k )=(1−γ( k )) K 0 ( k− 1)−γ( k ) e ( k )( a·d m ( k )+ b·d m c ( k ))
where:
K 0 is the gain of the microactuator;
γ is a learning coefficient;
d m is the sinusoid;
d m c equals
d
m
·
ⅇ
-
j
π
2
;
a and b are the coefficients of the sinusoidal response of the DSA servo loop; and
e is the DSA error signal.