Disk drive initializing position feedforward compensation with velocity feedforward compensation
View Patent ↗A disk drive is disclosed comprising a head actuated over a disk comprising a plurality of spiral tracks, wherein each spiral track comprises a high frequency signal interrupted by a sync mark at a sync mark interval. The head is positioned over the disk and used to read the spiral tracks to detect a plurality of spiral-to-spiral times each representing a time between consecutive spiral crossings. A velocity of the head is estimated in response to the spiral-to-spiral times, and velocity feedforward compensation values are generated from the estimated head velocity. A control signal is generated to position the head over the disk in response to the velocity feedforward compensation values. When the detected spiral-to-spiral times are substantially constant, position feedforward compensation values are initialized in response to the velocity feedforward compensation values.
1. A disk drive comprising:
a disk comprising a plurality of spiral tracks, wherein each spiral track comprises a high frequency signal interrupted by a sync mark at a sync mark interval;
a head actuated over the disk; and
control circuitry operable to:
position the head over the disk;
use the head to read the spiral tracks to detect a plurality of spiral-to-spiral times each representing a time between consecutive spiral crossings;
estimate a velocity of the head in response to the spiral-to-spiral times;
generate velocity feedforward compensation values from the estimated head velocity;
generate a control signal to position the head over the disk in response to the velocity feedforward compensation values;
when the detected spiral-to-spiral times are substantially constant, initialize position feedforward compensation values in response to the velocity feedforward compensation values;
estimate a position of the head in response to the spiral tracks; and
servo the head in response to the estimated head position and the position feedforward compensation values.
2. The disk drive as recited in claim 1 , wherein the velocity feedforward compensation values cause the head to substantially follow a repeatable runout of the disk.
3. The disk drive as recited in claim 2 , wherein the velocity feedforward compensation values cause the head to substantially follow a once-around repeatable runout of the disk.
4. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to:
generate a position error signal in response to a difference between the estimated head position and a reference position; and
servo the head in response to the position error signal.
5. The disk drive as recited in claim 4 , wherein the control circuitry is further operable to adapt the position feedforward compensation values in response to the position error signal.
6. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to:
generate a flex bias compensation value in response to the control signal; and
servo the head in response to the estimated head position, the position feedforward compensation values, and the flex bias compensation value.
7. A method of operating a disk drive, the disk drive comprising a head actuated over a disk comprising a plurality of spiral tracks, wherein each spiral track comprises a high frequency signal interrupted by a sync mark at a sync mark interval, the method comprising:
positioning the head over the disk;
using the head to read the spiral tracks to detect a plurality of spiral-to-spiral times each representing a time between consecutive spiral crossings;
estimating a velocity of the head in response to the spiral-to-spiral times;
generating velocity feedforward compensation values from the estimated head velocity;
generating a control signal to position the head over the disk in response to the velocity feedforward compensation values;
when the detected spiral-to-spiral times are substantially constant, initializing position feedforward compensation values in response to the velocity feedforward compensation values;
estimating a position of the head in response to the spiral tracks; and
serving the head in response to the estimated head position and the position feedforward compensation values.
8. The method as recited in claim 7 , wherein the velocity feedforward compensation values cause the head to substantially follow a repeatable runout of the disk.
9. The method as recited in claim 8 , wherein the velocity feedforward compensation values cause the head to substantially follow a once-around repeatable runout of the disk.
10. The method as recited in claim 7 , further comprising:
generating a position error signal in response to a difference between the estimated head position and a reference position; and
serving the head in response to the position error signal.
11. The method as recited in claim 10 , further comprising adapting the position feedforward compensation values in response to the position error signal.
12. The method as recited in claim 7 , further comprising:
generating a flex bias compensation value in response to the control signal; and
serving the head in response to the estimated head position, the position feedforward compensation values, and the flex bias compensation value.