Granted Patent B1

US 8,941,939 · App. 14/090,732 · Granted Jan 27, 2015

Abstract

Claims (71)

1. A disk drive comprising:

a disk;

a head;

a voice coil motor (VCM) configured to actuate the head over the disk; and

control circuitry configured to:

control the VCM to seek the head over the disk during a first seek;

measure a back electromotive force (BEMF) voltage generated by the VCM during the first seek;

generate feed-forward compensation based on the measured BEMF voltage;

control the VCM to seek the head over the disk during a second seek using the feed-forward compensation; and

write servo data to the disk during the second seek.

2. The disk drive as recited in claim 1 , wherein the control circuitry is further configured to:

control the VCM based on a target profile during the first seek;

measure a seek time of the first seek; and

adjust the target profile based on the measured seek time.

3. The disk drive as recited in claim 1 , wherein the control circuitry is further configured to:

periodically measure the BEMF voltage during the first seek to generate BEMF samples;

compute a derivative of the BEMF samples to generate a measured acceleration of the VCM; and

generate the feed-forward compensation based on the measured acceleration of the VCM.

4. The disk drive as recited in claim 3 , wherein the control circuitry is further configured to:

filter the measured acceleration with an inverse of a plant representing the VCM to generate a bias control signal; and

generate the feed-forward compensation based on the bias control signal.

5. The disk drive as recited in claim 4 , wherein the control circuitry is further configured to:

filter the bias control signal with a low pass filer to generate a filtered bias control signal; and

generate the feed-forward compensation based on the filtered bias control signal.

6. The disk drive as recited in claim 1 , wherein after executing the first seek and prior to executing the second seek the control circuitry is further configured to:

control the VCM to seek the head over the disk during a third seek using the feed-forward compensation;

adapt the feed-forward compensation based on the BEMF voltage measured during the third seek.

7. The disk drive as recited in claim 6 , wherein the control circuitry is further configured to adapt the feed-forward compensation based on:

u bias ( i+ 1 ,k )= u bias ( i,k )+ g 2 *G LPF ( G VCM −1 ( v ( i,k )− v ( i,k− 1)))

where:

u bias (i,k) represents the feed-forward compensation generated based on the BEMF voltage measured during the first seek;

g 2 represents a learning coefficient;

G LPF represents a low pass filter;

G VCM −1 represents an inverse of a plant representing the VCM;

v(i,k+1) and v(i,k) represent consecutive BEMF voltage measurements during the third seek; and

u bias (i+1,k) represents the adapted feed-forward compensation.

8. The disk drive as recited in claim 1 , wherein the servo data comprises a spiral track written substantially over an entire radius of the disk during the second seek.

9. A method of operating a disk drive, the method comprising:

controlling a voice coil motor (VCM) to seek a head over a disk during a first seek;

measuring a back electromotive force (BEMF) voltage generated by the VCM during the first seek;

generating feed-forward compensation based on the measured BEMF voltage;

controlling the VCM to seek the head over the disk during a second seek using the feed-forward compensation; and

writing servo data to the disk during the second seek.

10. The method as recited in claim 9 , further comprising:

controlling the VCM based on a target profile during the first seek;

measuring a seek time of the first seek; and

adjusting the target profile based on the measured seek time.

11. The method as recited in claim 9 , further comprising:

periodically measuring the BEMF voltage during the first seek to generate BEMF samples;

computing a derivative of the BEMF samples to generate a measured acceleration of the VCM; and

generating the feed-forward compensation based on the measured acceleration of the VCM.

12. The method as recited in claim 11 , further comprising:

filtering the measured acceleration with an inverse of a plant representing the VCM to generate a bias control signal; and

generating the feed-forward compensation based on the bias control signal.

13. The method as recited in claim 12 , further comprising:

filtering the bias control signal with a low pass filer to generate a filtered bias control signal; and

generating the feed-forward compensation based on the filtered bias control signal.

14. The method as recited in claim 9 , further comprising:

after executing the first seek and prior to executing the second seek,

controlling the VCM to seek the head over the disk during a third seek using the feed-forward compensation; and

adapting the feed-forward compensation based on the BEMF voltage measured during the third seek.

15. The method as recited in claim 14 , further comprising adapting the feed-forward compensation based on:

u bias ( i+ 1 ,k )= u bias ( i,k )+ g 2 *G LPF ( G VCM −1 ( v ( i,k )− v ( i,k− 1)))

where:

u bias (i,k) represents the feed-forward compensation generated based on the BEMF voltage measured during the first seek;

g 2 represents a learning coefficient;

G LPF represents a low pass filter;

G VCM −1 represents an inverse of a plant representing the VCM;

v(i,k+1) and v(i,k) represent consecutive BEMF voltage measurements during the third seek; and

u bias (i+1,k) represents the adapted feed-forward compensation.

16. The method as recited in claim 9 , wherein the servo data comprises a spiral track written substantially over an entire radius of the disk during the second seek.

Assignments (8)