Disk drive compensating for track squeeze by writing non-circular servo tracks
View Patent ↗A servo writer is disclosed operable to write servo sectors on a disk to define non-circular servo tracks. The servo writer comprises control circuitry including a servo control system operable to measure a position of a head over the disk to generate a position signal, generate a position error signal (PES) representing a difference between the position signal and a reference signal, process the PES with a servo compensator to generate a control signal, and position the head over the disk in response to the control signal. A disturbance is induced into the servo control system, and while positioning the head over the disk in response to the control signal, a plurality of servo sectors are written on the disk to define a servo track, wherein the disturbance induced into the servo control system causes the servo track to be non-circular relative to a rotation axis of the disk.
1. A servo writer operable to write servo sectors on a disk to define non-circular servo tracks, the servo writer comprising control circuitry including a servo control system operable to:
measure a position of a head over the disk to generate a position signal;
generate a position error signal (PES) representing a difference between the position signal and a reference signal;
process the PES with a servo compensator to generate a control signal; and
position the head over the disk in response to the control signal;
wherein the control circuitry is operable to:
induce a disturbance into the servo control system; and
while positioning the head over the disk in response to the control signal, write a plurality of servo sectors on the disk to define a servo track, wherein the disturbance induced into the servo control system causes the servo track to be non-circular relative to a rotation axis of the disk.
2. The servo writer as recited in claim 1 , wherein after writing the non-circular servo tracks on the disk when the head is substantially stationary relative to the disk the head crosses over multiple of the non-circular servo tracks as the disk rotates.
3. The servo writer as recited in claim 1 , wherein the servo control system is further operable to:
induce the disturbance into the PES to generate a modified PES;
generate a feed-forward signal in response to the modified PES; and
adjust the control signal in response to the feed-forward signal, wherein the head is positioned over the disk using the adjusted control signal.
4. The servo writer as recited in claim 1 , wherein the disturbance comprises a sinusoid.
5. The servo writer as recited in claim 4 , wherein a frequency of the sinusoid comprises a rotation frequency of the disk.
6. The servo writer as recited in claim 4 , wherein a frequency of the sinusoid comprises a multiple of a rotation frequency of the disk.
7. The servo writer as recited in claim 1 , wherein the servo control system is further operable to read a reference pattern from the disk in order to measure the position of the head over the disk to generate the position signal.
8. The servo writer as recited in claim 7 , wherein the reference pattern is substantially circular relative to the rotation axis of the disk.
9. The servo writer as recited in claim 7 , wherein the reference pattern comprises a plurality of spiral tracks.
10. The servo writer as recited in claim 1 , wherein the disk is inserted into a disk drive after writing the servo sectors on the disk.
11. The servo writer as recited in claim 1 , wherein the disk is inserted into a disk drive prior to writing the servo sectors on the disk.
12. A method of writing servo sectors on a disk to define non-circular servo tracks, the method comprising:
measuring a position of a head over the disk to generate a position signal;
generating a position error signal (PES) representing a difference between the position signal and a reference signal;
inducing a disturbance into the PES to generate a modified PES;
processing the modified PES with a servo compensator to generate a control signal;
positioning the head over the disk in response to the control signal; and
while positioning the head over the disk in response to the control signal, writing a plurality of servo sectors on the disk to define a servo track, wherein the disturbance induced into the PES causes the servo track to be non-circular relative to a rotation axis of the disk.
13. The method as recited in claim 12 , wherein after writing the non-circular servo tracks on the disk when the head is substantially stationary relative to the disk the head crosses over multiple of the non-circular servo tracks as the disk rotates.
14. The method as recited in claim 12 , further comprising:
generating a feed-forward signal in response to the modified PES; and
adjusting the control signal in response to the feed-forward signal, wherein the head is positioned over the disk using the adjusted control signal.
15. The method as recited in claim 12 , wherein the disturbance comprises a sinusoid.
16. The method as recited in claim 15 , wherein a frequency of the sinusoid comprises a rotation frequency of the disk.
17. The method as recited in claim 15 , wherein a frequency of the sinusoid comprises a multiple of a rotation frequency of the disk.
18. The method as recited in claim 12 , further comprising reading a reference pattern from the disk in order to measure the position of the head over the disk to generate the position signal.
19. The method as recited in claim 18 , wherein the reference pattern is substantially circular relative to the rotation axis of the disk.
20. The method as recited in claim 18 , wherein the reference pattern comprises a plurality of spiral tracks.
21. The method as recited in claim 12 , further comprising inserting the disk into a disk drive after writing the servo sectors on the disk.
22. The method as recited in claim 12 , further comprising inserting the disk into a disk drive prior to writing the servo sectors on the disk.