Disk drive calibrating a velocity profile prior to writing a spiral track

1. A disk drive comprising:

a disk;

a head actuated over the disk;

a ramp near an outer diameter of the disk, wherein the ramp for unloading the head off the disk; and

control circuitry operable to:

position the head at an inner diameter of the disk;

move the head toward the ramp in response to a velocity profile;

measure an interval from a beginning of the movement until the head begins unloading onto the ramp;

adjust the velocity profile in response to the measured interval;

synchronize a disk locked clock to a rotation of the disk; and

measure the interval relative to the disk locked clock.

2. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to write a spiral track to the disk in response to the adjusted velocity profile.

3. The disk drive as recited in claim 1 , wherein the velocity profile comprises:

an acceleration segment for accelerating the head away from the inner diameter of the disk; and

a constant velocity segment for moving the head at a substantially constant velocity until the head begins unloading onto the ramp.

4. The disk drive as recited in claim 1 , further comprising a voice coil motor (VCM) for actuating the head over the disk, wherein the control circuitry is further operable to:

measure a VCM back electromotive force (BEMF) voltage generated by the VCM; and

move the head toward the ramp in response to the velocity profile and the VCM BEMF voltage.

5. The disk drive as recited in claim 1 , further comprising a spindle motor for rotating the disk, wherein the control circuitry is further operable to:

measure a spindle back electromotive force (BEMF) voltage generated by the spindle motor; and

synchronize the disk locked clock in response to the spindle BEMF voltage.

6. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to repeatedly move the head from the inner diameter of the disk to the ramp and adjust the velocity profile until the measured interval substantially matches a target interval.

7. A disk drive comprising:

a disk;

a head actuated over the disk;

a ramp near an outer diameter of the disk, wherein the ramp for unloading the head off the disk; and

control circuitry operable to:

position the head at an inner diameter of the disk;

write a spiral track while moving the head toward the ramp at a substantially constant velocity until the head contacts the ramp; and

after the head contacts the ramp, decelerate the head.

8. The disk drive as recited in claim 7 , wherein the control circuitry is further operable to accelerate the head away from the inner diameter of the disk while writing the spiral track.

9. The disk drive as recited in claim 8 , wherein the spiral track comprises an increasing slope while the head accelerates away from the inner diameter of the disk and a substantially constant slope until the head contacts the ramp.

10. A method of operating a disk drive, the disk drive comprising a head actuated over a disk, and a ramp near an outer diameter of the disk, wherein the ramp for unloading the head off the disk, the method comprising:

positioning the head at an inner diameter of the disk;

moving the head toward the ramp in response to a velocity profile;

measuring an interval from a beginning of the movement until the head begins unloading onto the ramp;

adjusting the velocity profile in response to the measured interval;

synchronizing a disk locked clock to a rotation of the disk; and

measuring the interval relative to the disk locked clock.

11. The method as recited in claim 10 , further comprising writing a spiral track to the disk in response to the adjusted velocity profile.

12. The method as recited in claim 10 , wherein the velocity profile comprises:

an acceleration segment for accelerating the head away from the inner diameter of the disk; and

a constant velocity segment for moving the head at a substantially constant velocity until the head begins unloading onto the ramp.

13. The method as recited in claim 10 , wherein the disk drive further comprises a voice coil motor (VCM) for actuating the head over the disk, the method further comprising:

measuring a VCM back electromotive force (BEMF) voltage generated by the VCM; and

moving the head toward the ramp in response to the velocity profile and the VCM BEMF voltage.

14. The method as recited in claim 10 , wherein the disk drive further comprises a spindle motor for rotating the disk, the method further comprising:

measuring a spindle back electromotive force (BEMF) voltage generated by the spindle motor; and

synchronizing the disk locked clock in response to the spindle BEMF voltage.

15. The method as recited in claim 10 , further comprising repeatedly moving the head from the inner diameter of the disk to the ramp and adjusting the velocity profile until the measured interval substantially matches a target interval.

16. A method of operating a disk drive, the disk drive comprising a head actuated over a disk, and a ramp near an outer diameter of the disk, wherein the ramp for unloading the head off the disk, the method comprising:

positioning the head at an inner diameter of the disk;

writing a spiral track while moving the head toward the ramp at a substantially constant velocity until the head contacts the ramp; and

after the head contacts the ramp, decelerating the head.

17. The method as recited in claim 16 , further comprising accelerating the head away from the inner diameter of the disk while writing the spiral track.

18. The method as recited in claim 17 , wherein the spiral track comprises an increasing slope while the head accelerates away from the inner diameter of the disk and a substantially constant slope until the head contacts the ramp.