Disk drive compensating for laser induced head protrusion in heat assisted magnetic recording
A disk drive is disclosed comprising a head actuated over a disk comprising a plurality of data tracks defined by servo sectors. The head comprises a laser operable to heat the disk while writing data to the disk and a fly height actuator operable to adjust a fly height of the head over the disk. When the head approaches a target data sector of a write command, the fly height of the actuator adjusts the fly height of the head to a target pre-heat fly height during a pre-heat interval. After the pre-heat interval and during a pre-laser interval, the fly height actuator increases the fly height of the head. After the pre-laser interval, a power applied to the laser is increased to heat the disk, wherein the pre-laser interval compensates for a protrusion transient of the head toward the disk due to increasing the power applied to the laser.
1. A disk drive comprising:
a disk comprising a plurality of data tracks defined by servo sectors, wherein each data track comprises a plurality of data sectors;
a head actuated over the disk, wherein the head comprises a laser operable to heat the disk while writing data to the disk and a fly height actuator operable to adjust a fly height of the head over the disk; and
control circuitry operable to:
receive a write command to write data to a target data sector of a target data track;
position the head over the target data track; and
when the head approaches the target data sector:
during a pre-heat interval, control the fly height of the actuator to adjust the fly height of the head to a target pre-heat fly height;
after the pre-heat interval and during a pre-laser interval, control the fly height actuator to increase the fly height of the head;
after the pre-laser interval, increase a power applied to the laser to heat the disk, wherein the pre-laser interval compensates for a protrusion transient of the head toward the disk due to increasing the power applied to the laser; and
after increasing the power applied to the laser, write the data to the disk.
2. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to control the fly height actuator during the pre-laser interval by decreasing a power applied to the fly height actuator during the pre-laser interval.
3. The disk drive as recited in claim 1 , wherein after the pre-laser interval the control circuitry is further operable to control the fly height actuator to maintain a target write fly height while writing the data to the disk.
4. The disk drive as recited in claim 3 , wherein the control circuitry is operable to:
control the fly height actuator during the pre-laser interval by decreasing a power applied to the fly height actuator during the pre-laser interval; and
after the pre-laser interval, increase the power applied to the fly height actuator to maintain the target write fly height while writing data to the disk.
5. The disk drive as recited in claim 1 , wherein the control circuitry is operable to write the data to the disk during the protrusion transient.
6. The disk drive as recited in claim 1 , wherein the control circuitry is operable to write the data to the disk after the protrusion transient has substantially settled.
7. The disk drive as recited in claim 1 , wherein:
increasing power applied to the fly height actuator causes the head to protrude toward the disk based on a first time constant; and
increasing power applied to the laser causes the head to protrude toward the disk based on a second time constant different from the first time constant.
8. The disk drive as recited in claim 7 , wherein the first time constant is greater than the second time constant.
9. The disk drive as recited in claim 7 , wherein the pre-laser interval is based on the first time constant and the second time constant.
10. The disk drive as recited in claim 9 , wherein the pre-laser interval is based on a ratio of the first time constant to the second time constant.
11. A method of operating a disk drive, the disk drive comprising a head actuated over a disk comprising a plurality of data tracks defined by servo sectors, wherein each data track comprises a plurality of data sectors, wherein the head comprises a laser operable to heat the disk while writing data to the disk and a fly height actuator operable to adjust a fly height of the head over the disk, the method comprising:
receiving a write command to write data to a target data sector of a target data track;
positioning the head over the target data track; and
when the head approaches the target data sector:
during a pre-heat interval, controlling the fly height of the actuator to adjust the fly height of the head to a target pre-heat fly height;
after the pre-heat interval and during a pre-laser interval, controlling the fly height actuator to increase the fly height of the head;
after the pre-laser interval, increasing a power applied to the laser to heat the disk, wherein the pre-laser interval compensates for a protrusion transient of the head toward the disk due to increasing the power applied to the laser; and
after increasing the power applied to the laser, writing the data to the disk.
12. The method as recited in claim 11 , further comprising controlling the fly height actuator during the pre-laser interval by decreasing a power applied to the fly height actuator during the pre-laser interval.
13. The method as recited in claim 11 , wherein after the pre-laser interval further comprising controlling the fly height actuator to maintain a target write fly height while writing the data to the disk.
14. The method as recited in claim 13 , further comprising:
controlling the fly height actuator during the pre-laser interval by decreasing a power applied to the fly height actuator during the pre-laser interval; and
after the pre-laser interval, increasing the power applied to the fly height actuator to maintain the target write fly height while writing data to the disk.
15. The method as recited in claim 11 , further comprising writing the data to the disk during the protrusion transient.
16. The method as recited in claim 11 , further comprising writing the data to the disk after the protrusion transient has substantially settled.
17. The method as recited in claim 11 , wherein:
increasing power applied to the fly height actuator causes the head to protrude toward the disk based on a first time constant; and
increasing power applied to the laser causes the head to protrude toward the disk based on a second time constant different from the first time constant.
18. The method as recited in claim 17 , wherein the first time constant is greater than the second time constant.
19. The method as recited in claim 17 , wherein the pre-laser interval is based on the first time constant and the second time constant.
20. The method as recited in claim 19 , wherein the pre-laser interval is based on a ratio of the first time constant to the second time constant.