Disk drive defining non-circular data tracks relative to a rotation axis of the disk
View Patent ↗A disk drive is disclosed comprising a disk having a plurality of servo tracks defined by servo sectors, and a head actuated over the disk. The disk drive further comprises control circuitry comprising a servo control system operable to position the head over the disk. A disturbance is induced in the servo control system, and while positioning the head over the disk, a data track is accessed. The disturbance induced in the servo control system causes the data track to be non-circular relative to a rotation axis of the disk such that the non-circular data track crosses multiple of the servo tracks over a revolution of the disk.
1. A disk drive comprising:
a disk comprising a plurality of servo tracks defined by servo sectors;
a head actuated over the disk; and
control circuitry comprising 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 further operable to:
induce a disturbance in the servo control system; and
while positioning the head over the disk in response to the control signal, access a data track, wherein the disturbance induced in the servo control system causes the data track to be non-circular relative to a rotation axis of the disk such that a center of the non-circular data track crosses multiple of the servo tracks over a revolution of the disk.
2. The disk drive as recited in claim 1 , wherein the center of the non-circular data track crosses at least three of the servo tracks over the revolution of the disk.
3. The disk drive as recited in claim 1 , wherein the servo control system is further operable to:
induce the disturbance in 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 disk drive as recited in claim 1 , wherein the disturbance comprises a sinusoid.
5. The disk drive as recited in claim 4 , wherein a frequency of the sinusoid comprises a rotation frequency of the disk.
6. The disk drive as recited in claim 4 , wherein a frequency of the sinusoid comprises a multiple of a rotation frequency of the disk.
7. The disk drive as recited in claim 1 , wherein the servo tracks are substantially circular relative to the rotation axis of the disk.
8. The disk drive as recited in claim 1 , wherein the servo tracks are substantially non-circular relative to the rotation axis of the disk.
9. The disk drive as recited in claim 8 , wherein the disturbance comprises a phase substantially opposite a phase of the non-circular servo tracks.
10. A method of operating a disk drive, the disk drive comprising a disk comprising a plurality of servo tracks defined by servo sectors, and a head actuated over the disk, 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;
processing the PES with a servo compensator to generate a control signal; and
positioning the head over the disk in response to the control signal;
induce a disturbance in the PES to generate a modified PES; and
while positioning the head over the disk in response to the control signal, access a data track, wherein the disturbance induced in the PES causes the data track to be non-circular relative to a rotation axis of the disk such that a center of the non-circular data track crosses multiple of the servo tracks over a revolution of the disk.
11. The method as recited in claim 10 , wherein the center of the non-circular data track crosses at least three of the servo tracks over a revolution of the disk.
12. The method as recited in claim 10 , 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.
13. The method as recited in claim 10 , wherein the disturbance comprises a sinusoid.
14. The method as recited in claim 13 , wherein a frequency of the sinusoid comprises a rotation frequency of the disk.
15. The method as recited in claim 13 , wherein a frequency of the sinusoid comprises a multiple of a rotation frequency of the disk.
16. The method as recited in claim 10 , wherein the servo tracks are substantially circular relative to the rotation axis of the disk.
17. The method as recited in claim 10 , wherein the servo tracks are substantially non-circular relative to the rotation axis of the disk.
18. The method as recited in claim 17 , wherein the disturbance comprises a phase substantially opposite a phase of the non-circular servo tracks.