Disk drive decreasing a settle delay based on speed that a settle parameter adapts

1. A disk drive comprising:

a disk comprising a plurality of tracks;

a head actuated over the disk; and

control circuitry operable to:

(a) seek the head to a target track and settle the head on the target track during a settle time;

(b) adapt a settle parameter used to settle the head on the target track;

(c) access the target track after an access delay;

(d) decrease the access delay based on a speed that the settle parameter adapts; and

(e) repeat (a) through (d) at least once.

2. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to measure the speed that the settle parameter adapts by measuring a difference between the settle parameter over an interval.

3. The disk drive as recited in claim 2 , wherein the control circuitry is further operable to measure the speed that the settle parameter adapts according to:

speed[ k ]=(1−α)speed[ k− 1]+α( p[k]−p[k− 1])

wherein:

k−1 and k present a beginning and end of the interval;

α is a scalar; and

p is the settle parameter.

4. The disk drive as recited in claim 2 , wherein the interval spans at least part of a single settle time for a single seek.

5. The disk drive as recited in claim 4 , wherein the interval spans at least part of multiple settle times for multiple seeks.

6. The disk drive as recited in claim 1 , wherein the settle parameter comprises a magnitude of a sinusoid that estimates a repeatable runout (RRO) of the disk.

7. the disk drive as recited in claim 1 , wherein the control circuitry is further operable to:

adapt the settle parameter over an adapting delay of the settle time;

save the settle parameter after the adapting delay of a first settle time of a first seek;

further adapt the saved settle parameter over the adapting delay of a second settle time of a second seek; and

decrease the adapting delay based on the speed that the settle parameter adapts.

8. The disk drive as recited in claim 7 , wherein the adapting delay substantially equals the access delay.

9. A method of operating a disk drive comprising, the disk drive comprising a head actuated over a disk comprising a plurality of tracks, the method comprising:

(a) seeking the head to a target track and settle the head on the target track during a settle time;

(b) adapting a settle parameter used to settle the head on the target track;

(c) accessing the target track after an access delay;

(d) decreasing the access delay based on a speed that the settle parameter adapts; and

(e) repeating (a) through (d) at least once.

10. The method as recited in claim 9 , further comprising measuring the speed that the settle parameter adapts by measuring a difference between the settle parameter over an interval.

11. The method as recited in claim 10 , further comprising measuring the speed that the settle parameter adapts according to:

speed[ k ]=(1−α)speed[ k− 1]+α( p[k]−p[k− 1])

wherein:

k−1 and k present a beginning and end of the interval;

α is a scalar; and

p is the settle parameter.

12. The method as recited in claim 10 , wherein the interval spans at least part of a single settle time for a single seek.

13. The method as recited in claim 12 , wherein the interval spans at least part of multiple settle times for multiple seeks.

14. The method as recited in claim 9 , wherein the settle parameter comprises a magnitude of a sinusoid that estimates a repeatable runout (RRO) of the disk.

15. the method as recited in claim 9 , further comprising:

adapting the settle parameter over an adapting delay of the settle time;

saving the settle parameter after the adapting delay of a first settle time of a first seek;

further adapting the saved settle parameter over the adapting delay of a second settle time of a second seek; and

decreasing the adapting delay based on the speed that the settle parameter adapts.

16. The method as recited in claim 15 , wherein the adapting delay substantially equals the access delay.