Servo writing a disk drive by writing spiral tracks using a mechanical position sensor

1. A disk drive comprising:

a head disk assembly (HDA) comprising a base and a cover for enclosing:

a disk;

an actuator arm;

a head attached to a distal end of the actuator arm;

a mechanical position sensor operable to generate a position signal representing a position of the head relative to the disk; and

a voice coil motor for rotating the actuator arm about a pivot; and

the disk drive further comprising control circuitry operable to:

rotate the disk at a predetermined velocity;

generate a control signal in response to the position signal generated by the mechanical position sensor;

apply the control signal to the voice coil motor in order to seek the head radially over the disk while writing a spiral track to the disk; and

process the spiral track to maintain the head along a servo track while writing product servo sectors along the servo track.

2. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to write a plurality of spiral tracks to the disk by seeking the head radially over the disk a number of times and writing one of the spiral tracks during each seek.

3. The disk drive as recited in claim 1 , wherein:

(a) the disk comprises a clock track for synchronizing a write clock; and

(b) the control circuitry is operable to process the write clock while writing the spiral track to the disk.

4. The disk drive as recited in claim 3 , wherein the disk drive further comprises a clock head for reading the clock track to synchronize the write clock.

5. The disk drive as recited in claim 1 , wherein

(a) the disk further comprises a first plurality of reference tracks written at an outer diameter of the disk and a second plurality of reference tracks written at an inner diameter of the disk; and

(b) the control circuitry is further operable to calibrate the mechanical position sensor by reading at least one of the first and second plurality of reference tracks.

6. The disk drive as recited in claim 5 , wherein the control circuitry is further operable to calibrate at least one of a gain and an offset of the mechanical position sensor by reading the at least one of the first and second plurality of reference tracks.

7. The disk drive as recited in claim 6 , wherein the control circuitry is further operable to determine a reference position representing a radial position of at least one of the first and second plurality of reference tracks.

8. The disk drive as recited in claim 6 , wherein the control circuitry is further operable to seek the head from a first diameter of the disk to a second diameter of the disk while writing the spiral track by:

(a) positioning the head near the first diameter of the disk;

(b) verifying the position of the head by reading at least one of the first and second plurality of reference tracks; and

(c) seeking the head toward the second diameter of the disk.

9. The disk drive as recited in claim 8 , wherein the control circuitry is further operable to:

(a) seek the head toward the second diameter of the disk in response to a predetermined velocity seek profile; and

(b) calibrate at least one of the gain and offset of the mechanical position sensor by reading at least one of the first and second plurality of reference tracks after seeking the head toward the second diameter of the disk.

10. The disk drive as recited in claim 1 , wherein the spiral track comprises a high frequency signal interrupted at a periodic interval by a sync mark.

11. The disk drive as recited in claim 1 , wherein the mechanical position sensor comprises an optical sensor.

12. A method of servo writing a disk drive, the disk drive comprising a head disk assembly (HDA) comprising a base and a cover for enclosing a disk, an actuator arm, a head attached to a distal end of the actuator arm, a mechanical position sensor operable to generate a position signal relative to a position of the actuator arm, and a voice coil motor for rotating the actuator arm about a pivot, the method comprising the steps of:

rotating the disk at a predetermined velocity;

generating a control signal in response to the position signal generated by the mechanical position sensor;

applying the control signal to the voice coil motor in order to seek the head radially over the disk while writing a spiral track to the disk; and

processing the spiral track to maintain the head along a servo track while writing product servo sectors along the servo track.

13. The method as recited in claim 12 , further comprising the step of writing a plurality of spiral tracks to the disk by seeking the head radially over the disk a number of times and writing one of the spiral tracks during each seek.

14. The method as recited in claim 12 , wherein the disk comprises a clock track for synchronizing a write clock, further comprising the step of processing the write clock while writing the spiral track to the disk.

15. The method as recited in claim 14 , wherein the disk drive further comprises a clock head for reading the clock track to synchronize the write clock.

16. The method as recited in claim 12 , wherein the disk further comprises a first plurality of reference tracks written at an outer diameter of the disk and a second plurality of reference tracks written at an inner diameter of the disk, further comprising the step of calibrating the mechanical position sensor by reading at least one of the first and second plurality of reference tracks.

17. The method as recited in claim 16 , wherein the step of calibrating the mechanical position sensor comprises the step of calibrating at least one of a gain and an offset of the mechanical position sensor by reading at least one of the first and second plurality of reference tracks.

18. The method as recited in claim 17 , wherein the step of calibrating the mechanical position sensor comprises the step of determining a reference position representing a radial position of at least one of the first and second plurality of reference tracks.

19. The method as recited in claim 17 , wherein the step of applying the control signal to the voice coil motor in order to seek the head radially over the disk while writing the spiral track to the disk comprises the steps of:

positioning the head near a first diameter of the disk;

verifying the position of the head by reading at least one of the first and second plurality of reference tracks; and

seeking the head toward a second diameter of the disk.

20. The method as recited in claim 19 , wherein the step of seeking the head toward the second diameter of the disk comprises the step of seeking the head toward the second diameter of the disk in response to a predetermined velocity seek profile, the method further comprising the step of calibrating at least one of the gain and offset of the mechanical position sensor by reading at least one of the first and second plurality of reference tracks after seeking the head toward the second diameter of the disk.

21. The method as recited in claim 12 , wherein the spiral track comprises a high frequency signal interrupted at a periodic interval by a sync mark.

22. The method as recited in claim 12 , wherein the mechanical position sensor comprises an optical sensor.