Disk drive detecting touchdown event by evaluating frequency response of a touchdown metric
View Patent ↗A disk drive is disclosed comprising a head actuated over a disk, and a fly height actuator operable to control a fly height of the head over the disk. A periodic control signal is applied to the fly height actuator, a frequency response of a touchdown metric at a frequency of the periodic control signal is measured, and a touchdown event is detected in response to the frequency response of the touchdown metric.
1. A disk drive comprising:
a disk;
a head actuated over the disk;
a fly height actuator operable to control a fly height of the head over the disk; and
control circuitry operable to:
apply a periodic control signal to the fly height actuator;
measure a frequency response of a touchdown metric at a frequency of the periodic control signal; and
detect a touchdown event in response to the frequency response of the touchdown metric.
2. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to generate the periodic control signal by periodically decreasing the fly height for at least one revolution of the disk and increasing the fly height for at least one revolution of the disk.
3. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to detect the touchdown event in response to the frequency response of the touchdown metric by evaluating a phase response of the touchdown metric at the frequency of the periodic control signal.
4. The disk drive as recited in claim 1 , wherein:
the head is coupled to a distal end of an actuator arm; and
the touchdown metric comprises a bias force applied to the actuator arm.
5. The disk drive as recited in claim 4 , wherein the control circuitry is further operable to detect the head touching down on the disk when the touchdown metric is one of approximately in phase with the periodic control signal and approximately 180 degrees out of phase with the periodic control signal.
6. The disk drive as recited in claim 4 , wherein the control circuitry is further operable to detect the head contacting a contaminant on the disk when the touchdown metric is out of phase with the periodic control signal by a degree corresponding to a rotational delay of the disk after decreasing the fly height of the head until the head contacts the contaminant.
7. The disk drive as recited in claim 4 , wherein the control circuitry is further operable to detect a contaminant on the head contacting the disk when the touchdown metric is out of phase with the periodic control signal.
8. The disk drive as recited in claim 1 , wherein the touchdown metric comprises a spin rate of the disk.
9. The disk drive as recited in claim 8 , wherein the control circuitry is further operable to detect the head touching down on the disk when the touchdown metric is out of phase with the periodic control signal by approximately a first phase.
10. The disk drive as recited in claim 9 , wherein the first phase comprises one of 90 degrees and 270 degrees.
11. The disk drive as recited in claim 9 , wherein the control circuitry is further operable to detect the head contacting a contaminant on the disk when the touchdown metric is out of phase with the periodic control signal by a second phase different from the first phase.
12. The disk drive as recited in claim 11 , wherein the second phase differs from the first phase by approximately 180 degrees.
13. The disk drive as recited in claim 9 , wherein the control circuitry is further operable to detect a contaminant on the head contacting the disk when the touchdown metric is out of phase with the periodic control signal by approximately a second phase different from the first phase.
14. The disk drive as recited in claim 13 , wherein the second phase differs from the first phase by approximately 180 degrees.
15. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to:
compute a real part and an imaginary part of the touchdown metric at the frequency of the periodic control signal; and
detect the touchdown event in response to the real part and the imaginary part of the touchdown metric.
16. A method of operating a disk drive, the disk drive comprising a disk, a head actuated over the disk, and a fly height actuator operable to control a fly height of the head over the disk, the method comprising:
applying a periodic control signal to the fly height actuator;
measuring a frequency response of a touchdown metric at a frequency of the periodic control signal; and
detecting a touchdown event in response to the frequency response of the touchdown metric.
17. The method as recited in claim 16 , further comprising generating the periodic control signal by periodically decreasing the fly height for at least one revolution of the disk and increasing the fly height for at least one revolution of the disk.
18. The method as recited in claim 16 , further comprising detecting the touchdown event in response to the frequency response of the touchdown metric by evaluating a phase response of the touchdown metric at the frequency of the periodic control signal.
19. The method as recited in claim 16 , wherein:
the head is coupled to a distal end of an actuator arm; and
the touchdown metric comprises a bias force applied to the actuator arm.
20. The method as recited in claim 19 , further comprising detecting the head touching down on the disk when the touchdown metric is one of approximately in phase with the periodic control signal and approximately 180 degrees out of phase with the periodic control signal.
21. The method as recited in claim 19 , further comprising detecting the head contacting a contaminant on the disk when the touchdown metric is out of phase with the periodic control signal by a degree corresponding to a rotational delay of the disk after decreasing the fly height of the head until the head contacts the contaminant.
22. The method as recited in claim 19 , further comprising detecting a contaminant on the head contacting the disk when the touchdown metric is out of phase with the periodic control signal.
23. The method as recited in claim 16 , wherein the touchdown metric comprises a spin rate of the disk.
24. The method as recited in claim 23 , further comprising detecting the head touching down on the disk when the touchdown metric is out of phase with the periodic control signal by approximately a first phase.
25. The method as recited in claim 24 , wherein the first phase comprises one of 90 degrees and 270 degrees.
26. The method as recited in claim 24 , further comprising detecting the head contacting a contaminant on the disk when the touchdown metric is out of phase with the periodic control signal by a second phase different from the first phase.
27. The method as recited in claim 26 , wherein the second phase differs from the first phase by approximately 180 degrees.
28. The method as recited in claim 24 , further comprising detecting a contaminant on the head contacting the disk when the touchdown metric is out of phase with the periodic control signal by approximately a second phase different from the first phase.
29. The method as recited in claim 28 , wherein the second phase differs from the first phase by approximately 180 degrees.
30. The method as recited in claim 16 , further comprising:
computing a real part and an imaginary part of the touchdown metric at the frequency of the periodic control signal; and
detecting the touchdown event in response to the real part and the imaginary part of the touchdown metric.