Disk drive estimating microactuator gain by injecting a sinusoid into a closed loop servo 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 comprising a VCM and a microactuator servo loop comprising a microactuator operable to actuate the head over the disk surface. A microactuator compensator processes a position error signal (PES) to generate a first control signal, and a disturbance sinusoid is injected into the first control signal to generate a second control signal, wherein the microactuator is controlled in response to the second control signal. Feed-forward compensation is generated corresponding to the injected disturbance sinusoid, and a third control signal is generated in response to the PES and the feed-forward compensation, wherein the VCM is controlled in response to the third control signal. A gain of the microactuator is estimated in response to the feed-forward compensation.
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:
generate a position error signal (PES) representing a position of the head over the disk surface;
process the PES using a microactuator compensator to generate a first control signal;
inject a disturbance sinusoid into the first control signal to generate a second control signal;
control the microactuator in response to the second control signal;
generate first feed-forward compensation corresponding to the injected disturbance sinusoid;
generate a third control signal in response to the PES and the first feed-forward compensation;
control the VCM in response to the third control signal; and
estimate a gain of the microactuator in response to the first feed-forward compensation;
wherein prior to injecting the disturbance sinusoid into the first control signal the control circuitry is further operable to adapt a second feed-forward compensation according to:
A ( k+ 1)= A ( k )+μ·PES·cos( nk )
B ( k+ 1)= B ( k )+μ·PES·sin( nk )
where:
n represents a frequency of the disturbance sinusoid;
μ is a learning coefficient; and
A and B are coefficients of a second sinusoid used to generate the second feed-forward compensation; and
after injecting the disturbance sinusoid into the first control signal the control circuitry is further operable to adapt the first feed-forward compensation according to:
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where:
a and b are coefficients of a first sinusoid used to generate the first feed-forward compensation;
A 0 and B 0 are coefficients of the second sinusoid prior to injecting the disturbance sinusoid into the first control signal; and
A i and B i are coefficients of the second sinusoid generated over m samples of the PES after injecting the disturbance sinusoid into the first control signal.
2. The disk drive as recited in claim 1 , wherein the control circuitry is operable to estimate the gain of the microactuator according to:
U ff — d *P v ( jw )/ D m
where:
U ff — d represents the first feed-forward compensation;
P v (jω) represents a frequency response of the VCM; and
D m represents the disturbance sinusoid.
3. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to ramp an amplitude of the disturbance sinusoid toward a maximum amplitude in order to reduce a corresponding transient of the DSA servo loop.
4. The disk drive as recited in claim 3 , wherein the control circuitry is further operable to:
adapt the first feed-forward compensation using a first learning coefficient while ramping the amplitude of the disturbance sinusoid toward the maximum amplitude; and
adapt the first feed-forward compensation using a second learning coefficient after ramping the amplitude of the disturbance sinusoid toward the maximum amplitude, wherein the second learning coefficient is smaller than the first learning coefficient.
5. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to adjust the gain of the microactuator in response to the estimated gain of the microactuator.
6. The disk drive as recited in claim 1 , wherein the DSA servo loop comprises a model of the microactuator and the control circuitry is further operable to adjust a gain of the model of the microactuator in response to the estimated gain of the microactuator.
7. A method of operating a 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:
generating a position error signal (PES) representing a position of the head over the disk surface;
processing the PES using a microactuator compensator to generate a first control signal;
injecting a disturbance sinusoid into the first control signal to generate a second control signal;
controlling the microactuator in response to the second control signal;
generating first feed-forward compensation corresponding to the injected disturbance sinusoid;
generating a third control signal in response to the PES and the first feed-forward compensation;
controlling the VCM in response to the third control signal; and
estimating a gain of the microactuator in response to the first feed-forward compensation;
wherein prior to injecting the disturbance sinusoid into the first control signal the method further comprising adapting the second feed-forward compensation according to:
A ( k+ 1)= A ( k )+μ·PES·cos( nk )
B ( k+ 1)= B ( k )+μ·PES·sin( nk )
where:
n represents a frequency of the disturbance sinusoid;
μ is a learning coefficient; and
A and B are coefficients of a second sinusoid used to generate the second feed-forward compensation; and
after injecting the disturbance sinusoid into the first control signal the method further comprising adapting the first feed-forward compensation according to:
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where:
a and b are coefficients of a first sinusoid used to generate the first feed-forward compensation;
A 0 and B 0 are coefficients of the second sinusoid prior to injecting the disturbance sinusoid into the first control signal; and
A i and B i are coefficients of the second sinusoid generated over m samples of the PES after injecting the disturbance sinusoid into the first control signal.
8. The method as recited in claim 7 , further comprising estimating the gain of the microactuator according to:
U ff — d *P v ( jw )/ D m
where:
U ff — d represents the first feed-forward compensation;
P v (jω) represents a frequency response of the VCM; and
D m represents the disturbance sinusoid.
9. The method as recited in claim 7 , further comprising ramping an amplitude of the disturbance sinusoid toward a maximum amplitude in order to reduce a corresponding transient of the DSA servo loop.
10. The method as recited in claim 9 , further comprising:
adapting the first feed-forward compensation using a first learning coefficient while ramping the amplitude of the disturbance sinusoid toward the maximum amplitude; and
adapting the first feed-forward compensation using a second learning coefficient after ramping the amplitude of the disturbance sinusoid toward the maximum amplitude, wherein the second learning coefficient is smaller than the first learning coefficient.
11. The method as recited in claim 7 , further comprising adjusting the gain of the microactuator in response to the estimated gain of the microactuator.
12. The method as recited in claim 7 , wherein the DSA servo loop comprises a model of the microactuator and the method further comprises adjusting a gain of the model of the microactuator in response to the estimated gain of the microactuator.
13. 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:
generate a position error signal (PES) representing a position of the head over the disk surface;
process the PES using a microactuator compensator to generate a first control signal;
inject a disturbance sinusoid into the first control signal to generate a second control signal;
control the microactuator in response to the second control signal;
generate first feed-forward compensation corresponding to the injected disturbance sinusoid;
generate a third control signal in response to the PES and the first feed-forward compensation;
control the VCM in response to the third control signal; and
estimate a gain of the microactuator according to:
U ff — d *P v ( jw )/ D m
where:
U ff — d represents the first feed-forward compensation;
P v (jω) represents a frequency response of the VCM; and
D m represents the disturbance sinusoid.
14. 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:
generate a position error signal (PES) representing a position of the head over the disk surface;
process the PES using a microactuator compensator to generate a first control signal;
inject a disturbance sinusoid into the first control signal to generate a second control signal;
control the microactuator in response to the second control signal;
generate first feed-forward compensation corresponding to the injected disturbance sinusoid;
generate a third control signal in response to the PES and the first feed-forward compensation;
control the VCM in response to the third control signal;
estimate a gain of the microactuator in response to the first feed-forward compensation; and
ramp an amplitude of the disturbance sinusoid toward a maximum amplitude in order to reduce a corresponding transient of the DSA servo loop.
15. The disk drive as recited in claim 14 , wherein the control circuitry is further operable to:
adapt the first feed-forward compensation using a first learning coefficient while ramping the amplitude of the disturbance sinusoid toward the maximum amplitude; and
adapt the first feed-forward compensation using a second learning coefficient after ramping the amplitude of the disturbance sinusoid toward the maximum amplitude, wherein the second learning coefficient is smaller than the first learning coefficient.
16. A method of operating a 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:
generating a position error signal (PES) representing a position of the head over the disk surface;
processing the PES using a microactuator compensator to generate a first control signal;
injecting a disturbance sinusoid into the first control signal to generate a second control signal;
controlling the microactuator in response to the second control signal;
generating first feed-forward compensation corresponding to the injected disturbance sinusoid;
generating a third control signal in response to the PES and the first feed-forward compensation;
controlling the VCM in response to the third control signal; and
estimating the gain of the microactuator according to:
U ff — d *P v ( jw )/ D m
where:
U ff — d represents the first feed-forward compensation;
P v (jω) represents a frequency response of the VCM; and
D m represents the disturbance sinusoid.
17. A method of operating a 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:
generating a position error signal (PES) representing a position of the head over the disk surface;
processing the PES using a microactuator compensator to generate a first control signal;
injecting a disturbance sinusoid into the first control signal to generate a second control signal;
controlling the microactuator in response to the second control signal;
generating first feed-forward compensation corresponding to the injected disturbance sinusoid;
generating a third control signal in response to the PES and the first feed-forward compensation;
controlling the VCM in response to the third control signal;
estimating a gain of the microactuator in response to the first feed-forward compensation; and
ramping an amplitude of the disturbance sinusoid toward a maximum amplitude in order to reduce a corresponding transient of the DSA servo loop.
18. The method as recited in claim 17 , further comprising:
adapting the first feed-forward compensation using a first learning coefficient while ramping the amplitude of the disturbance sinusoid toward the maximum amplitude; and
adapting the first feed-forward compensation using a second learning coefficient after ramping the amplitude of the disturbance sinusoid toward the maximum amplitude, wherein the second learning coefficient is smaller than the first learning coefficient.