Compensating for voice coil motor and microactuator disturbance in a hard drive

1. A method comprising:

applying a voice coil motor (VCM) input signal to a voice coil motor and a microactuator (PZT) input signal to a microactuator in response to positioning a read/write head of a hard drive;

determining a position signal in response to positioning the read/write head;

decoupling a PZT component from the position signal to determine an estimated VCM response, the estimated VCM response used to determine an estimated VCM disturbance;

decoupling a VCM component from the position signal to determine an estimated PZT response, the estimated PZT response used to determine an estimated PZT disturbance; and

modifying the VCM input signal and the PZT input signal respectively to compensate for the estimated VCM disturbance and the estimated PZT disturbance.

2. The method of claim 1 , further comprising adaptively filtering the estimated VCM disturbance and the estimated PZT disturbance.

3. The method of claim 2 , wherein adaptively filtering comprises using one of a lattice filter, Goertzel filter, and discrete Fourier transform to estimate disturb frequencies.

4. The method of claim 2 , wherein adaptively filtering comprises using at least one of joint process estimator and finite impulse response filter.

5. The method of claim 1 , further comprising modifying the VCM input signal further via a feed-forward compensator to compensate for measured VCM disturbance.

6. An apparatus comprising:

a servo controller configured to:

apply a voice coil motor (VCM) input signal to a VCM and a microactuator (PZT) input signal to a PZT to position a read/write head of a hard drive;

determine a position signal in response to positioning the read/write head;

decouple a PZT component from the position signal to determine an estimated VCM response, the estimated VCM response used to determine an estimated VCM disturbance;

decouple a VCM component from the position signal to determine an estimated PZT response, the estimated PZT response used to determine and an estimated PZT disturbance; and

modify the VCM input signal and the PZT input signal respectively to compensate for the estimated VCM disturbance and the estimated PZT disturbance.

7. The apparatus of claim 6 , wherein the servo controller is further configured to adaptively filter the estimated VCM disturbance and the estimated PZT disturbance.

8. The apparatus of claim 7 , wherein adaptively filtering comprises using one of a lattice filter, Goertzel filter, and discrete Fourier transform to estimate disturb frequencies.

9. The apparatus of claim 7 , wherein adaptively filtering comprises using at least one of joint process estimator and finite impulse response filter.

10. The apparatus of claim 6 , wherein the servo controller is further configured to:

transform the VCM input signal via a VCM model to obtain an estimated VCM component of the position signal;

transform a difference between the estimated VCM component and the position signal via a denominator of a PZT transform function to obtain a PZT plus disturb component of the position signal;

transform the PZT input signal via a numerator of the PZT transform function to obtain an estimated PZT component of the position signal; and

subtract the estimated PZT component from the PZT plus disturb component to obtain the estimated PZT disturbance.

11. The apparatus of claim 10 , wherein the servo control processor is further configured to adaptively filter the estimated PZT disturbance.

12. The apparatus of claim 11 , wherein adaptively filtering comprises using one of a lattice filter, Goertzel filter, and discrete Fourier transform to estimate disturb frequencies.

13. The apparatus of claim 6 , wherein the servo controller is further configured to:

transform the PZT input signal via a PZT model to obtain an estimated PZT component of the position signal;

transform a difference between the estimated PZT component and the position signal via a denominator of a VCM transform function to obtain a VCM plus disturb component of the position signal;

transform the VCM input signal via a numerator of the VCM transform function to obtain an estimated VCM component of the position signal; and

subtract the estimated VCM component from the VCM plus disturb component to obtain the estimated VCM disturbance.

14. The apparatus of claim 13 , wherein the servo controller is further configured to adaptively filter the estimated VCM disturbance.

15. The apparatus of claim 14 , wherein adaptively filtering comprises using one of a lattice filter, Goertzel filter, and discrete Fourier transform to estimate disturb frequencies.

16. An apparatus comprising:

a servo controller configured to:

receive a position error signal in response to positioning a read/write head of a hard drive via a dual-stage controller that drives a voice coil motor and a microactuator;

determine a disturbance compensation signal using a Q-parameterization that comprises a plant model of the dual-stage controller, the voice coil motor, and the microactuator, the Q-parameterization comprising selecting a stabilizing feedback controller for the plant model as function of a single parameter;

modify an input signal to the dual-stage controller using the disturbance compensation signal.

17. The apparatus of claim 16 , wherein the Q-parameterization determines the disturbance compensation signal based on the input signal and the modified input signal.

18. The apparatus of claim 16 , wherein the servo control processor is further configured to adaptively filter the disturbance compensation signal.

19. The apparatus of claim 18 , wherein adaptively filtering comprises using one of a lattice filter, Goertzel filter, and discrete Fourier transform to estimate disturb frequencies.

20. The apparatus of claim 18 , wherein adaptively filtering comprises using at least one of joint process estimator and finite impulse response filter.