Disk drive detecting microactuator degradation by evaluating frequency component of servo signal
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 frequency component of a servo signal in the DSA servo loop is evaluated, wherein the frequency component is based on a peak frequency of an error rejection curve of the DSA servo loop. A degradation of the microactuator is detected based on the frequency component of the servo 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;
control circuitry operable to evaluate a first frequency component of a servo signal in the DSA servo loop, wherein the first frequency component is based on a peak frequency of an error rejection curve of the DSA servo loop; and
detect a degradation of the microactuator based on the first frequency component of the servo signal.
2. The disk drive as recited in claim 1 , wherein the servo signal comprises a position error signal representing a difference between a measured radial location of the head over the disk and a target radial location.
3. The disk drive as recited in claim 1 , wherein the DSA servo loop is operable to generate a control signal applied to the microactuator in response to the servo signal.
4. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to detect the degradation of the microactuator based on a number of times the first frequency component of the servo signal exceeds a threshold over a predetermined time window.
5. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to:
increment a counter while the first frequency component of the servo signal exceeds a first threshold;
decrement the counter toward zero while the first frequency component of the servo signal does not exceed the first threshold; and
detect degradation of the microactuator when the counter exceeds a second threshold.
6. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to ignore the first frequency component of the servo signal during a vibration event.
7. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to ignore the first frequency component of the servo signal while seeking the head to a target track on the disk surface.
8. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to:
disable the microactuator servo loop after detecting the degradation of the microactuator; and
after disabling the microactuator servo loop, evaluate a second frequency component of the servo signal to verify the degradation.
9. The disk drive as recited in claim 8 , wherein the second frequency component is different than the first frequency component due to a change in the error rejection curve after disabling the microactuator servo loop.
10. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to:
disable the microactuator servo loop after detecting the degradation of the microactuator; and
after disabling the microactuator servo loop, evaluate a second frequency component of the servo signal to verify the degradation;
wherein the degradation of the microactuator is verified based on a number of times the second frequency component of the servo signal falls below a first threshold.
11. The disk drive as recited in claim 10 , wherein the control circuitry is further operable to detect the degradation of the microactuator based on a number of times the first frequency component of the servo signal exceeds a second threshold different from the first threshold.
12. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to adjust a gain of the microactuator when the degradation of the microactuator is detected.
13. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to adjust a model of the microactuator in the microactuator servo loop when the degradation of the microactuator is detected.
14. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to excite the microactuator with a buzzing frequency when the degradation of the microactuator is detected.
15. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to rewrite data to the disk surface when the degradation of the microactuator is detected during a write operation.
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:
evaluating a first frequency component of a servo signal in the DSA servo loop, wherein the first frequency component is based on a peak frequency of an error rejection curve of the DSA servo loop; and
detecting a degradation of the microactuator based on the first frequency component of the servo signal.
17. The method as recited in claim 16 , wherein the servo signal comprises a position error signal representing a difference between a measured radial location of the head over the disk and a target radial location.
18. The method as recited in claim 16 , wherein the DSA servo loop is operable to generate a control signal applied to the microactuator in response to the servo signal.
19. The method as recited in claim 16 , wherein detecting the degradation of the microactuator is based on a number of times the first frequency component of the servo signal exceeds a threshold over a predetermined time window.
20. The method as recited in claim 16 , further comprising:
incrementing a counter while the first frequency component of the servo signal exceeds a first threshold;
decrementing the counter toward zero while the first frequency component of the servo signal does not exceed the first threshold; and
detecting degradation of the microactuator when the counter exceeds a second threshold.
21. The method as recited in claim 16 , further comprising ignoring the first frequency component of the servo signal during a vibration event.
22. The method as recited in claim 16 , further comprising ignoring the first frequency component of the servo signal while seeking the head to a target track on the disk surface.
23. The method as recited in claim 16 , further comprising:
disabling the microactuator servo loop after detecting the degradation of the microactuator; and
after disabling the microactuator servo loop, evaluating a second frequency component of the servo signal to verify the degradation.
24. The method as recited in claim 23 , wherein the second frequency component is different than the first frequency component due to a change in the error rejection curve after disabling the microactuator servo loop.
25. The method as recited in claim 16 , further comprising:
disabling the microactuator servo loop after detecting the degradation of the microactuator; and
after disabling the microactuator servo loop, evaluating a second frequency component of the servo signal to verify the degradation;
wherein the degradation of the microactuator is verified based on a number of times the second frequency component of the servo signal falls below a first threshold.
26. The method as recited in claim 25 , wherein the degradation of the microactuator is detected based on a number of times the first frequency component of the servo signal exceeds a second threshold different from the first threshold.
27. The method as recited in claim 16 , further comprising adjusting a gain of the microactuator when the degradation of the microactuator is detected.
28. The method as recited in claim 16 , further comprising adjusting a model of the microactuator in the microactuator servo loop when the degradation of the microactuator is detected.
29. The method as recited in claim 16 , further comprising exciting the microactuator with a buzzing frequency when the degradation of the microactuator is detected.
30. The method as recited in claim 16 , further comprising rewriting data to the disk surface when the degradation of the microactuator is detected during a write operation.