Disk drive evaluating burst metric
View Patent ↗A disk drive is disclosed comprising a disk and a head actuated over the disk. A burst metric is generated in response to a burst read signal. The burst metric comprises at least one of an alpha metric comprising a ratio of a first burst amplitude of a first phased based servo burst measured at a first radial offset to a second burst amplitude of a second phased based servo burst measured at a second radial offset, a harmonic metric comprising a ratio of a first harmonic of the burst read signal as the head is moved radially over the disk to a higher harmonic of the burst read signal as the head is moved radially over the disk, and a spiral track crossing metric comprising a first and second interval each representing a partial duration of the read element crossing a spiral track.
1. A disk drive comprising:
a disk;
a head actuated over the disk, the head comprising a read element and a write element; and
control circuitry operable to:
read at least one servo burst from the disk to generate a burst read signal; and
generate a burst metric in response to the burst read signal, wherein the burst metric comprises at least one of:
an alpha metric comprising a ratio of a first burst amplitude of a first phased based servo burst measured while the head is positioned at a first radial offset to a second burst amplitude of a second phased based servo burst measured while the head is positioned at a second radial offset different from the first radial offset; and
a harmonic metric comprising a ratio of a first harmonic of the burst read signal representing an off-track profile as the head is moved radially over the disk to a higher harmonic of the burst read signal representing the off-track profile as the head is moved radially over the disk.
2. The disk drive as recited in claim 1 , wherein the burst metric comprises the alpha metric.
3. The disk drive as recited in claim 2 , wherein:
the first radial offset corresponds to when an amplitude of the first phase based servo burst substantially equals an amplitude of the second phase based servo burst; and
the second radial offset corresponds to when an amplitude of the second phase based servo burst is substantially at a minimum.
4. The disk drive as recited in claim 2 , wherein the burst metric further comprises a beta metric comprising a ratio:
m
-
l
h
-
m
where:
h is a first burst amplitude of a first amplitude based servo burst;
I is a second burst amplitude of a second amplitude based servo burst; and
m is a third burst amplitude of a third amplitude based servo burst.
5. The disk drive as recited in claim 1 , wherein the burst metric comprises the harmonic metric.
6. The disk drive as recited in claim 5 , wherein the higher harmonic comprises a third harmonic of the burst read signal.
7. The disk drive as recited in claim 6 , wherein the at least one servo burst comprises an amplitude based servo burst.
8. A method of operating a disk drive, the disk drive comprising a disk and a head actuated over the disk, the head comprising a read element and a write element, the method comprising:
reading at least one servo burst from the disk to generate a burst read signal; and
generating a burst metric in response to the burst read signal, wherein the burst metric comprises at least one of:
an alpha metric comprising a ratio of a first burst amplitude of a first phased based servo burst measured while the head is positioned at a first radial offset to a second burst amplitude of a second phased based servo burst measured while the head is positioned at a second radial offset different from the first radial offset; and
a harmonic metric comprising a ratio of a first harmonic of the burst read signal representing an off-track profile as the head is moved radially over the disk to a higher harmonic of the burst read signal representing the off-track profile as the head is moved radially over the disk.
9. The method as recited in claim 8 , wherein the burst metric comprises the alpha metric.
10. The method as recited in claim 9 , wherein:
the first radial offset corresponds to when an amplitude of the first phase based servo burst substantially equals an amplitude of the second phase based servo burst; and
the second radial offset corresponds to when an amplitude of the second phase based servo burst is substantially at a minimum.
11. The method as recited in claim 9 , wherein the burst metric further comprises a beta metric comprising a ratio:
m
-
l
h
-
m
where:
h is a first burst amplitude of a first amplitude based servo burst;
I is a second burst amplitude of a second amplitude based servo burst; and
m is a third burst amplitude of a third amplitude based servo burst.
12. The method as recited in claim 8 , wherein the burst metric comprises the harmonic metric.
13. The method as recited in claim 12 , wherein the higher harmonic comprises a third harmonic of the burst read signal.
14. The method as recited in claim 13 , wherein the at least one servo burst comprises an amplitude based servo burst.