Methods and devices for extracting off-track motion using microactuators

1. An apparatus comprising:

a first set of piezoelectric (PZT) elements poled in the same direction as a second set of PZT elements, the first and second sets of PZT elements configured to be driven while simultaneously sensing motion, wherein the first set of PZT elements is located on a first suspension on a first side of a disk, and wherein the second set of PZT elements is located on a second suspension on a second side of the disk; and

a circuit configured to add outputs of the first and second sets of PZT elements, extract the sensed motion, and detect off-track motion from the extracted sensed motion.

2. The apparatus of claim 1 , wherein a sensing signal is responsive to the sensing motion of the first and second PZT elements, and wherein the first and second PZT elements are responsive to a drive signal.

3. The apparatus of claim 2 , wherein the circuit farther comprises:

a filter configured to filter the drive and sensing signals of the first and second PZT elements into separate frequencies to allow the sensing signal o be isolated from the drive signal.

4. T The apparatus of claim 3 , wherein the filter is configured to filter the drive signal into a low frequency band and a high frequency band.

5. The apparatus of claim 1 , wherein the first and second PZT elements are located near a distal end of a suspension in a hard disk drive.

6. The apparatus of claim 1 wherein the first and second PZT elements are located between a first distal end of the suspension and an opposite, second distal end of the suspension.

7. The apparatus of claim 1 ,herein the first and second PZT elements are driven asymmetrically.

8. The apparatus of claim 7 , wherein the first PZT element is configured to sense motion while the second PZT element is configured to be driven, during track-follow operations.

9. The apparatus of claim 1 , wherein the circuit is configured to subtract signals from the first and second PZT elements from each other in a differential mode to reduce common-mode noise.

10. A method comprising:

sensing a sensing signal responsive to a motion of a first set of PZT elements while simultaneously driving a second set of PZT elements responsive to a driving signal;

combining the sensing signal and the driving signal to create a composite signal;

extracting sensed motion from the composite signal; and

detecting off-track motion from the extracted sensed motion,

wherein the first set of PZT elements is located on a first suspension on a first side of a disk in a hard disk drive, and wherein the second set of PZT elements is located on a second suspension on a second side of the disk.

11. The method of claim 10 , further comprising:

filtering a driving signal of the plurality of PZT elements and a sensing signal of the plurality of PZT elements into separate frequencies to allow the sensing signal to be isolated from the driving signal.

12. The method of claim 11 , wherein the filtering includes filtering the driving signal into a low frequency band and a high frequency band.

13. An apparatus comprising:

a first and second microactuator configured to be driven while simultaneously sensing motion, the first microactuator configured to output a first sensing signal responsive to a first microactuator deformation, the second microactuator configured to output a second sensing signal responsive to a second microactuator deformation;

a third microactuator element configured to output a third sensing signal responsive to a third microactuator deformation; and

a controller configured to subtract the third sensing signal from combined first and second sensing signals to generate a composite signal to detect off-track motion.

14. The apparatus of claim 13 , wherein the first and second microactuators are driven asymmetrically.