Disk drive resetting fly height reference generated from a degrading calibration track
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 in response to a fly height control signal. A touchdown operation is executed to set an operating fly height control signal by adjusting the fly height control signal until the head contacts the disk. A fly height calibration track is then read to set a fly height reference. When calibrating the operating fly height control signal, the fly height calibration track is read and the operating fly height control signal is adjusted in response to the fly height reference. When the adjusted operating fly height control signal is invalid, the touchdown operation is re-executed to reset the operating fly height control signal and then the fly height calibration track is read to reset the fly height reference.
1. A disk drive comprising:
a disk comprising a plurality of tracks including a fly height calibration track;
a head actuated over the disk;
a fly height actuator operable to control a fly height of the head in response to a fly height control signal; and
control circuitry operable to:
execute a touchdown operation to set an operating fly height control signal by adjusting the fly height control signal until the head contacts the disk;
read the fly height calibration track to set a fly height reference;
when calibrating the operating fly height control signal, read the fly height calibration track and adjust the operating fly height control signal in response to the fly height reference;
determine whether the adjusted operating fly height control signal is valid; and
when the adjusted operating fly height control signal is invalid, re-execute the touchdown operation to reset the operating fly height control signal and reread the fly height calibration track to reset the fly height reference.
2. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to execute the touchdown operation by reading a touchdown track.
3. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to determine that the adjusted operating fly height control signal is invalid by:
adding a margin to the adjusted operating fly height control signal to generate a margined fly height control signal; and
detecting a touchdown of the head in response to the margined fly height control signal.
4. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to determine that the adjusted operating fly height control signal is invalid by evaluating a channel metric when reading data from the disk.
5. The disk drive as recited in claim 4 , wherein the channel metric comprises an error correction code (ECC) metric.
6. The disk drive as recited in claim 4 , wherein the channel metric comprises an sequence detector metric.
7. The disk drive as recited in claim 1 , wherein the disk comprises a plurality of zones, each zone comprises a plurality of tracks including a fly height calibration track, and the control circuitry is further operable to:
execute the touchdown operation to set an operating fly height control signal for each zone;
read the fly height calibration track in each zone to set a fly height reference for each zone;
when calibrating the operating fly height control signal for a target zone, read the fly height calibration track in the target zone and adjust the operating fly height control signal in response to the fly height reference for the target zone;
determine whether the adjusted operating fly height control signal for the target zone is valid; and
when the adjusted operating fly height control signal for the target zone is valid, adjust the operating fly height control signal for the other zones in response to the adjustment to the operating fly height control signal for the target zone.
8. The disk drive as recited in claim 7 , wherein when the adjusted operating fly height control signal for the target zone is invalid, the control circuitry is further operable to:
re-execute the touchdown operation to reset the operating fly height control signal and reread the fly height calibration track in the target zone to adjust the fly height reference for the target zone; and
adjust the operating fly height reference for the other zones in response to the adjustment to the fly height reference for the target zone.
9. The disk drive as recited in claim 1 , wherein the disk drive comprises a plurality of disk surfaces, each disk surface comprises a plurality of tracks including a fly height calibration track, and the control circuitry is further operable to:
execute the touchdown operation to set an operating fly height control signal for each disk surface;
read the fly height calibration track on each disk surface to set a fly height reference for each disk surface;
when calibrating the operating fly height control signal for a target disk surface, read the fly height calibration track on the target disk surface and adjust the operating fly height control signal in response to the fly height reference for the target disk surface;
determine whether the adjusted operating fly height control signal for the target disk surface is valid; and
when the adjusted operating fly height control signal for the target disk surface is valid, adjust the operating fly height control signal for the other disk surfaces in response to the adjustment to the operating fly height control signal for the target disk surface.
10. The disk drive as recited in claim 9 , wherein when the adjusted operating fly height control signal for the target disk surface is invalid, the control circuitry is further operable to:
re-execute the touchdown operation to reset the operating fly height control signal and reread the fly height calibration track on the target disk surface to adjust the fly height reference for the target disk surface; and
adjust the operating fly height reference for the other disk surfaces in response to the adjustment to the operating fly height reference for the target disk surface.
11. A method of operating a disk drive, the disk drive comprising a head actuated over a disk comprising a plurality of tracks including a fly height calibration track, and a fly height actuator operable to control a fly height of the head in response to a fly height control signal, the method comprising:
executing a touchdown operation to set an operating fly height control signal by adjusting the fly height control signal until the head contacts the disk;
reading the fly height calibration track to set a fly height reference;
when calibrating the operating fly height control signal, reading the fly height calibration track and adjust the operating fly height control signal in response to the fly height reference;
determining whether the adjusted operating fly height control signal is valid; and
when the adjusted operating fly height control signal is invalid, re-executing the touchdown operation to reset the operating fly height control signal and reread the fly height calibration track to reset the fly height reference.
12. The method as recited in claim 11 , further comprising executing the touchdown operation by reading a touchdown track.
13. The method as recited in claim 11 , further comprising determining that the adjusted operating fly height control signal is invalid by:
adding a margin to the adjusted operating fly height control signal to generate a margined fly height control signal; and
detecting a touchdown of the head in response to the margined fly height control signal.
14. The method as recited in claim 11 , further comprising determining that the adjusted operating fly height control signal is invalid by evaluating a channel metric when reading data from the disk.
15. The method as recited in claim 14 , wherein the channel metric comprises an error correction code (ECC) metric.
16. The method as recited in claim 14 , wherein the channel metric comprises a sequence detector metric.
17. The method as recited in claim 11 , wherein the disk comprises a plurality of zones, each zone comprises a plurality of tracks including a fly height calibration track, and the method further comprises:
executing the touchdown operation to set an operating fly height control signal for each zone;
reading the fly height calibration track in each zone to set a fly height reference for each zone;
when calibrating the operating fly height control signal for a target zone, reading the fly height calibration track in the target zone and adjust the operating fly height control signal in response to the fly height reference for the target zone;
determining whether the adjusted operating fly height control signal for the target zone is valid; and
when the adjusted operating fly height control signal for the target zone is valid, adjusting the operating fly height control signal for the other zones in response to the adjustment to the operating fly height control signal for the target zone.
18. The method as recited in claim 17 , wherein when the adjusted operating fly height control signal for the target zone is invalid, the method further comprises:
re-executing the touchdown operation to reset the operating fly height control signal and reread the fly height calibration track in the target zone to adjust the fly height reference for the target zone; and
adjusting the operating fly height reference for the other zones in response to the adjustment to the fly height reference for the target zone.
19. The method as recited in claim 11 , wherein the disk drive comprises a plurality of disk surfaces, each disk surface comprises a plurality of tracks including a fly height calibration track, and the method further comprises:
executing the touchdown operation to set an operating fly height control signal for each disk surface;
reading the fly height calibration track on each disk surface to set a fly height reference for each disk surface;
when calibrating the operating fly height control signal for a target disk surface, reading the fly height calibration track on the target disk surface and adjust the operating fly height control signal in response to the fly height reference for the target disk surface;
determining whether the adjusted operating fly height control signal for the target disk surface is valid; and
when the adjusted operating fly height control signal for the target disk surface is valid, adjusting the operating fly height control signal for the other disk surfaces in response to the adjustment to the operating fly height control signal for the target disk surface.
20. The disk drive as recited in claim 19 , wherein when the adjusted operating fly height control signal for the target disk surface is invalid, the method further comprises:
re-executing the touchdown operation to reset the operating fly height control signal and reread the fly height calibration track on the target disk surface to adjust the fly height reference for the target disk surface; and
adjusting the operating fly height reference for the other disk surfaces in response to the adjustment to the operating fly height reference for the target disk surface.