Disk drive estimating repeatable runout of reference pattern based on repeatable runout of phase error
View Patent ↗A disk drive is disclosed comprising head actuated over a disk comprising a reference pattern. The head is positioned at a first radial location, a first phase error is measured in response to the reference pattern at the first radial location, and a first repeatable runout (RRO) of the first phase error is measured. The head is positioned at a second radial location, a second phase error is measured in response to the reference pattern at the second radial location, and a second repeatable runout (RRO) of the second phase error is measured. The first and second RROs are processed to estimate an offset r 0 representing a difference between an axial rotation of the disk and an axial rotation of the reference pattern.
1. A disk drive comprising:
a disk comprising a reference pattern;
a head actuated over the disk; and
control circuitry operable to:
position the head at a first radial location;
measure a first phase error in response to the reference pattern at the first radial location;
measure a first repeatable runout (RRO) of the first phase error;
position the head at a second radial location;
measure a second phase error in response to the reference pattern at the second radial location;
measure a second repeatable runout (RRO) of the second phase error; and
process the first and second RROs to estimate an offset r 0 representing a difference between an axial rotation of the disk and an axial rotation of the reference pattern.
2. The disk drive as recited in claim 1 , wherein the reference pattern comprises a plurality of spiral tracks.
3. The disk drive as recited in claim 1 , wherein the control circuitry is operable to:
generate timing compensation values;
generate a control signal in response to the first phase error and the timing compensation values; and
adjust a frequency of an oscillator in response to the control signal.
4. The disk drive as recited in claim 3 , wherein the control circuitry is operable to:
generate the timing compensation values as feed-forward timing compensation values;
adjust the control signal using the feed-forward timing compensation values to generate an adjusted control signal; and
adjust the frequency of the oscillator in response to the adjusted control signal.
5. The disk drive as recited in claim 3 , wherein the control circuitry is operable to adapt coefficients of a sinusoid in response to the first phase error to generate the timing compensation values.
6. The disk drive as recited in claim 5 , wherein the control circuitry is operable to measure a first peak Ψ 1 in the first RRO based on the coefficients.
7. The disk drive as recited in claim 1 , wherein the control circuitry is operable to:
measure a first peak Ψ 1 in the first RRO;
measure a second peak Ψ 2 in the second RRO; and
estimate the offset r 0 in response to the first peak Ψ 1 and the second peak Ψ 2 .
8. The disk drive as recited in claim 7 , wherein the control circuitry is further operable to estimate the offset r 0 according to:
(
R
2
-
R
1
)
(
1
/
tan
ψ
2
-
1
/
tan
ψ
1
)
where:
R 1 is the first radial location; and
R 2 is the second radial location.
9. A method of operating a disk drive, the disk drive comprising a disk comprising a reference pattern, a head actuated over the disk, the method comprising:
positioning the head at a first radial location;
measuring a first phase error in response to the reference pattern at the first radial location;
measuring a first repeatable runout (RRO) of the first phase error;
positioning the head at a second radial location;
measuring a second phase error in response to the reference pattern at the second radial location;
measuring a second repeatable runout (RRO) of the second phase error; and
processing the first and second RROs to estimate an offset r 0 representing a difference between an axial rotation of the disk and an axial rotation of the reference pattern.
10. The method as recited in claim 9 , wherein the reference pattern comprises a plurality of spiral tracks.
11. The method as recited in claim 9 , further comprising:
generating timing compensation values;
generating a control signal in response to the first phase error and the timing compensation values; and
adjusting a frequency of an oscillator in response to the control signal.
12. The method as recited in claim 11 , further comprising:
generating the timing compensation values as feed-forward timing compensation values;
adjusting the control signal using the feed-forward timing compensation values to generate an adjusted control signal; and
adjusting the frequency of the oscillator in response to the adjusted control signal.
13. The method as recited in claim 11 , further comprising adapting coefficients of a sinusoid in response to the first phase error to generate the timing compensation values.
14. The method as recited in claim 13 , further comprising measuring a first peak Ψ 1 in the first RRO based on the coefficients.
15. The method as recited in claim 9 , further comprising:
measuring a first peak Ψ 1 in the first RRO;
measuring a second peak Ψ 2 in the second RRO; and
estimating the offset r 0 in response to the first peak Ψ 1 and the second peak Ψ 2 .
16. The method as recited in claim 15 , further comprising estimating the offset r 0 according to:
(
R
2
-
R
1
)
(
1
/
tan
ψ
2
-
1
/
tan
ψ
1
)
where:
R 1 is the first radial location; and
R 2 is the second radial location.