Disk drive modifying estimated seek times for a rotational position optimization algorithm based on change in estimated seek time parameter

1. A disk drive comprising:

(a) a disk comprising a plurality of tracks, wherein each track comprises a plurality of data sectors and a plurality of embedded servo sectors;

(b) a head;

(c) a voice coil motor (VCM) for actuating the head over the disk;

(d) a command queue for storing a plurality of disk access commands; and

(e) a disk controller for executing a rotational position optimization (RPO) algorithm to select a disk access command from the command queue as the next command to execute relative to an estimated seek time required to seek the head to a target track for each command in the command queue, wherein:

the disk controller estimates a seek time parameter;

the disk controller modifies the estimated seek time for each command in the command queue by:

computing a seek time delta in response to the estimated seek time parameter; and

adding the seek time delta to a nominal estimated seek time; and

the disk controller executes the RPO algorithm using the modified estimated seek times.

2. The disk drive as recited in claim 1 , wherein the estimated seek time parameter comprises an estimated motor capability of the VCM.

3. The disk drive as recited in claim 2 , wherein the disk controller modifies the estimated seek time for each command in the command queue according to:

est_st=est_st 0 +k*D (st( L ))/ D ( a )* da

where:

est_st is the modified estimated seek time;

est_st 0 is the nominal estimated seek time;

L is a seek distance;

st(L) is a seek time as a function of the seek distance L;

a is the estimated motor capability;

a 0 is a nominal motor capability;

da is the difference between a and a 0 ; and

k is a discounting scalar.

4. The disk drive as recited in claim 3 , wherein:

(a) Lamin is a minimum seek distance that uses full motor capability of the VCM;

(b) Lvmin is a minimum seek distance that reaches a maximum allowed constant velocity for the VCM;

(c) for seek distances Lamin<L<Lvmin the sensitivity measurement D(st(L))/D(a) comprises −0.5*st/a; and

(d) for seek distances L>=Lvmin the sensitivity measurement D(st(L))/D(a) comprises−0.5*(st(Lvmin))/a.

5. The disk drive as recited in claim 2 , wherein the disk controller determines the estimated motor capability by measuring a velocity of the VCM relative to a current flowing through the VCM.

6. The disk drive as recited in claim 3 , wherein the nominal estimated seek time is determined statistically over a subset of disk drives.

7. The disk drive as recited in claim 3 , wherein the nominal estimated seek time is measured during manufacture of the disk drive.

8. The disk drive as recited in claim 1 , wherein:

(a) the estimated seek time comprises an estimated settle time;

(b) during the estimated settle time, the disk controller processes the embedded servo sectors to generate a position error signal (PES) representing a position error between the head and the target track;

(c) the estimated seek time parameter comprises an estimated track mis-registration (TMR) value representing a probability that a magnitude of the PES will exceed a predetermined threshold; and

(d) the estimated settle time is computed in response to the estimated TMR value.

9. The disk drive as recited in claim 8 , wherein the disk controller modifies the estimated settle time for each command in the command queue according to:

est_settle est_settle 0 +k*D (settle( TMR ))/ D ( TMR )* dTMR

where:

est_settle is the modified estimated settle time;

est_settles is a nominal estimated settle time;

settle(TMR) is a settle time as a function of the TMR;

TMR is the estimated track mis-registration (TMR);

TMR 0 is a nominal TMR;

dTMR is the difference between TMR and TMR 0 ; and

k is a discounting scalar.

10. The disk drive as recited in claim 9 , wherein the sensitivity measurement D(settle(TMR))/D(TMR) comprises:

k 1 /(ON_TRACK_LIMIT−TMR)

where k 1 is a predetermined gain value and ON_TRACK_LIMIT is a threshold wherein the settle time ends if the PES remains within the ON_TRACK_LIMIT for a predetermined interval.

11. The disk drive as recited in claim 9 , wherein the nominal estimated settle time is determined statistically over a subset of disk drives.

12. The disk drive as recited in claim 9 , wherein the nominal estimated settle time is measured during manufacture of the disk drive.

13. A method of executing a rotational position optimization (RPO) algorithm in a disk drive for selecting a disk access command from a command queue as the next command to execute relative to an estimated seek time required to seek a head to a target track of a disk for each command in the command queue, wherein a voice coil motor (VCM) actuates the head over the disk, the method comprising the steps of:

(a) estimating a seek time parameter;

(b) modifying the estimated seek time for each command in the command queue by:

computing a seek time delta in response to the estimated seek time parameter; and

adding the seek time delta to a nominal estimated seek time; and

(c) executing the RPO algorithm using the modified estimated seek times.

14. The method as recited in claim 13 , wherein the estimated seek time parameter comprises an estimated motor capability of the VCM.

15. The method as recited in claim 13 , wherein the estimated seek time for each command in the command queue is modified according to:

est_st=est_st 0 +k*D (st( L ))/ D ( a )* da

where:

est_st is the modified estimated seek time;

est_st 0 is the nominal estimated seek time;

st(L) is a seek time as a function of the seek distance L;

a is the estimated motor capability;

a 0 is a nominal motor capability;

da is the difference between a and a 0 ; and

k is a discounting scalar.

16. The method as recited in claim 15 , wherein:

(a) Lamin is a minimum seek distance that uses full motor capability of the VCM;

(b) Lvmin is a minimum seek distance that reaches a maximum allowed constant velocity for the VCM;

(c) for seek distances Lamin<L<Lvmin the sensitivity measurement D(st(L))/D(a) is computed as −0.5*st/a; and

(d) for seek distances L>=Lvmin the sensitivity measurement D(st(L))/D(a) is computed as −0.5*(st(Lvmin))/a.

17. The method as recited in claim 14 , wherein the nominal estimated seek time is determined statistically over a subset of disk drives.

18. The method as recited in claim 15 , wherein the nominal estimated seek time is measured during manufacture of the disk drive.

19. The method as recited in claim 15 , wherein the step of estimating the motor capability comprises the step of measuring a velocity of the VCM relative to a current flowing through the VCM.

20. The method as recited in claim 13 , wherein:

(a) the estimated seek time comprises an estimated settle time;

(b) during the estimated settle time, the disk controller processes the embedded servo sectors to generate a position error signal (PES) representing a position error between the head and the target track;

(c) the estimated seek time parameter comprises an estimated track mis-registration (TMR) value representing a probability that a magnitude of the PES will exceed a predetermined threshold; and

(d) the estimated settle time is computed in response to the estimated TMR value.

21. The method as recited in claim 20 , wherein the estimated settle time for each command in the command queue is modified according to:

est_settle=est_settle 0 +k*D (settle( TMR ))/ D ( TMR )* dTMR

where:

est_settle is the modified estimated settle time;

est_settle 0 is a nominal estimated settle time;

settle(TMR) is a settle time as a function of the TMR;

TMR is the estimated track mis-registration (TMR);

TMR 0 is a nominal TMR;

dTMR is the difference between TMR and TMR 0 ; and

k is a discounting scalar.

22. The method as recited in claim 21 , wherein the sensitivity measurement D(settle(TMR))/D(TMR) comprises:

k 1 /(ON_TRACK_LIMIT−TMR)

where k 1 is a predetermined gain value and ON_TRACK_LIMIT is a threshold wherein the settle time ends if the PES remains within the ON_TRACK_LIMIT for a predetermined interval.

23. The method as recited in claim 21 , wherein the nominal estimated settle time is determined statistically over a subset of disk drives.

24. The method as recited in claim 21 , wherein the nominal estimated settle time is measured during manufacture of the disk drive.