Disk drive detecting head touchdown by computing anti-correlation in sensor signal
View Patent ↗A disk drive is disclosed comprising a head actuated over a disk, a dynamic fly height (DFH) actuator operable to control a fly height of the head over the disk, and a touchdown (TD) sensor operable to generate a TD signal. A periodic control signal is applied to the DFH actuator to generate a periodic response in the TD signal comprising at least one cycle, wherein the cycle comprises a first half cycle and a second half cycle. An anti-correlation is computed between the first half cycle and the second half cycle of the TD signal, and the head contacting the disk is detected in response to the anti-correlation.
1. A disk drive comprising:
a disk;
a head actuated over the disk;
a dynamic fly height (DFH) actuator operable to control a fly height of the head over the disk;
a touchdown (TD) sensor operable to generate a TD signal; and
control circuitry operable to:
apply a periodic control signal to the DFH actuator to generate a periodic response in the TD signal comprising at least one cycle, wherein the cycle comprises a first half cycle and a second half cycle;
compute an anti-correlation between the first half cycle and the second half cycle of the TD signal; and
detect the head contacting the disk in response to the anti-correlation.
2. The disk drive as recited in claim 1 , wherein the TD signal represents a thermal response of the TD sensor.
3. The disk drive as recited in claim 1 , wherein the at least one cycle comprises a plurality of cycles, the control circuitry is further operable to:
first average the first half cycles in the plurality of cycles and second average the second half cycles in the plurality of cycles; and
compute the anti-correlation between the first average and the second average.
4. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to incrementally increase a direct current (DC) offset of the periodic control signal until the head contacting the disk is detected.
5. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to detect the head contacting the disk when the anti-correlation falls below a threshold.
6. The disk drive as recited in claim 1 , wherein the TD sensor comprises a magnetoresistive (MR) element.
7. The disk drive as recited in claim 6 , wherein the control circuitry is further operable to bias the MR element with a direct current (DC) control signal when applying the periodic control signal.
8. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to calibrate a phase offset between the periodic control signal and the TD signal.
9. The disk drive as recited in claim 8 , wherein the control circuitry is further operable to calibrate the phase offset by adjusting the phase offset until the anti-correlation is substantially maximum.
10. A method of operating a disk drive, the disk drive comprising a head actuated over a disk, a dynamic fly height (DFH) actuator operable to control a fly height of the head over the disk, and a touchdown (TD) sensor operable to generate a TD signal, the method comprising:
applying a periodic control signal to the DFH actuator to generate a periodic response in the TD signal comprising at least one cycle, wherein the cycle comprises a first half cycle and a second half cycle;
computing an anti-correlation between the first half cycle and the second half cycle of the TD signal; and
detecting the head contacting the disk in response to the anti-correlation.
11. The method as recited in claim 10 , wherein the TD signal represents a thermal response of the TD sensor.
12. The method as recited in claim 10 , wherein the at least one cycle comprises a plurality of cycles, the method further comprising:
first averaging the first half cycles in the plurality of cycles and second average the second half cycles in the plurality of cycles; and
computing the anti-correlation between the first average and the second average.
13. The method as recited in claim 10 , further comprising incrementally increasing a direct current (DC) offset of the periodic control signal until the head contacting the disk is detected.
14. The method as recited in claim 10 , further comprising detecting the head contacting the disk when the anti-correlation falls below a threshold.
15. The method as recited in claim 10 , wherein the TD sensor comprises a magnetoresistive (MR) element.
16. The method as recited in claim 15 , further comprising biasing the MR element with a direct current (DC) control signal when applying the periodic control signal.
17. The method as recited in claim 10 , further comprising calibrating a phase offset between the periodic control signal and the TD signal.
18. The method as recited in claim 17 , further comprising calibrating the phase offset by adjusting the phase offset until the anti-correlation is substantially maximum.