Disk drive employing a velocity profile and back EMF feedback to control a voice coil motor

1. A disk drive comprising:

(a) a disk comprising a plurality of tracks;

(b) an actuator arm;

(c) a head connected to a distal end of the actuator arm;

(d) a voice coil motor (VCM) for rotating the actuator arm about a pivot to actuate the head over the disk; and

(d) disk control circuitry for controlling the VCM by:

applying a driving current to the VCM;

detecting a back electromotive force (EMF) voltage generated by the VCM;

estimating a velocity of the VCM in response to the back EMF voltage;

comparing the estimated VCM velocity to a target velocity in a velocity profile, wherein the velocity profile comprises at least an acceleration component and a coast component;

adjusting the driving current in response to the comparison so that the velocity of the VCM substantially follows the velocity profile; and

estimating a latch distance corresponding to a distance the actuator arm travels during a latch operation by:

performing an unlatch operation to unlatch the actuator arm;

integrating the estimated VCM velocity during the unlatch operation to estimate an unlatch distance;

detecting an unlatch track ID corresponding to a position of the head after the unlatch operation;

performing a seek operation to seek the head from the unlatch track to an inner diameter track;

integrating the estimated VCM velocity during the seek operation to estimate a seek distance; and

subtracting the estimated seek distance from the estimated unlatch distance to estimate the latch distance.

2. The disk drive as recited in claim 1 , wherein the velocity profile comprises a deceleration component.

3. The disk drive as recited in claim 1 , wherein the acceleration component comprises a curve shape.

4. The disk drive as recited in claim 3 , wherein the acceleration component comprises an S shape.

5. The disk drive as recited in claim 1 , wherein the disk control circuitry for controlling the VCM to unlatch the actuator arm.

6. The disk drive as recited in claim 1 , wherein the disk control circuitry for latching the actuator arm by:

(a) performing a seek operation to seek the head to an inner diameter track;

(b) moving the actuator arm toward the latch according to the acceleration component and coast component of the velocity profile;

(c) integrating the estimated VCM velocity while moving the actuator arm to estimate a distance traveled; and

(d) when the estimated distance traveled equals the estimated latch distance minus an estimated deceleration distance, decelerating the actuator arm toward the latch according to the deceleration component of the velocity profile.

7. The disk drive as recited in claim 6 , wherein the estimated deceleration distance is the integral of the deceleration component of the velocity profile.

8. The disk drive as recited in claim 1 , further comprising a magnetic latch comprising a stationary magnet for attracting a metal component of the actuator arm, wherein:

(a) the magnet is covered at least partially with an insulating material; and

(b) at least part of the insulating material is between the magnet and the metal component of the actuator arm to reduce the maximum latching force of the magnet.

9. The disk drive as recited in claim 8 , wherein the insulating material comprises plastic.

10. The disk drive as recited in claim 8 , wherein the insulating material comprises rubber.

11. A method of controlling the motion of an actuator arm in a disk drive, the disk drive comprising a disk having a plurality of tracks, the actuator arm, a head connected to a distal end of the actuator arm, and a voice coil motor (VCM) for rotating the actuator arm about a pivot to actuate the head over the disk, the method comprising the steps of:

(a) applying a driving current to the VCM;

(b) detecting a back electromotive force (EMF) voltage generated by the VCM;

(c) estimating a velocity of the VCM in response to the back EMF voltage;

(d) comparing the estimated VCM velocity to a target velocity in a velocity profile, wherein the velocity profile comprises at least an acceleration component and a coast component;

(e) adjusting the driving current in response to the comparison so that the velocity of the VCM substantially follows the velocity profile; and

(f) estimating a latch distance corresponding to a distance the actuator arm travels during a latch operation by:

performing an unlatch operation to unlatch the actuator arm;

integrating the estimated VCM velocity during the unlatch operation to estimate an unlatch distance;

detecting an unlatch track ID corresponding to a position of the head after the unlatch operation;

performing a seek operation to seek the head from the unlatch track to an inner diameter track;

integrating the estimated VCM velocity during the seek operation to estimate a seek distance; and

subtracting the estimated seek distance from the estimated unlatch distance to estimate the latch distance.

12. The method as recited in claim 11 , wherein the velocity profile comprises a deceleration component.

13. The method as recited in claim 11 , wherein the acceleration component comprises a curve shape.

14. The method as recited in claim 13 , wherein the acceleration component comprises an S shape.

15. The method as recited in claim 11 , wherein controlling the motion of the actuator arm unlatches the actuator arm.

16. The method as recited in claim 11 , further comprising the step of latching the actuator arm comprising the steps of:

(a) performing a seek operation to seek the head to an inner diameter track;

(b) moving the actuator arm toward the latch according to the acceleration component and coast component of the velocity profile;

(c) integrating the estimated VCM velocity while moving the actuator arm to estimate a distance traveled; and

(d) when the estimated distance traveled equals the estimated latch distance minus an estimated deceleration distance, decelerating the actuator arm toward the latch according to the deceleration component of the velocity profile.

17. The method as recited in claim 16 , wherein the estimated deceleration distance is the integral of the deceleration component of the velocity profile.

18. The method as recited in claim 11 , wherein the disk drive further comprises a magnetic latch comprising a stationary magnet for attracting a metal component of the actuator arm, wherein:

(a) the magnet is covered at least partially with an insulating material; and

(b) at least part of the insulating material is between the magnet and the metal component of the actuator arm to reduce the maximum latching force of the magnet.

19. The method as recited in claim 18 , wherein the insulating material comprises plastic.

20. The method as recited in claim 18 , wherein the insulating material comprises rubber.

21. A disk drive comprising:

(a) a disk comprising a plurality of tracks;

(b) an actuator arm;

(c) a head connected to a distal end of the actuator arm;

(d) a voice coil motor (VCM) for rotating the actuator arm about a pivot to actuate the head over the disk; and

(e) disk control circuitry for controlling the VCM by performing the steps of:

applying a driving current to the VCM;

detecting a back EMF voltage generated by the VCM;

estimating a velocity of the VCM in response to the back EMF voltage;

comparing the estimated VCM velocity to a target velocity in a velocity profile, wherein the velocity profile comprises at least an acceleration component and a coast component;

adjusting the driving current in response to the comparison so that the velocity of the VCM substantially follows the velocity profile; and

estimating a latch distance corresponding to a distance the actuator arm travels during a latch operation by:

performing a seek operation to seek the head to an inner diameter track;

moving the actuator arm toward the latch;

integrating the estimated VCM velocity while moving the actuator arm to estimate the latch distance; and

stopping the integration when the back EMF voltage reverses polarity indicating that the actuator arm has latched.

22. A method of controlling the motion of an actuator arm in a disk drive, the disk drive comprising a disk having a plurality of tracks, the actuator arm, a head connected to a distal end of the actuator arm, and a voice coil motor (VCM) for rotating the actuator arm about a pivot to actuate the head over the disk, the method comprising the steps of:

(a) applying a driving current to the VCM;

(b) detecting a back EMF voltage generated by the VCM;

(c) estimating a velocity of the VCM in response to the back EMF voltage;

(d) comparing the estimated VCM velocity to a target velocity in a velocity profile, wherein the velocity profile comprises at least an acceleration component and a coast component;

(e) adjusting the driving current in response to the comparison so that the velocity of the VCM substantially follows the velocity profile; and

(f) estimating a latch distance corresponding to a distance the actuator arm travels during a latch operation by:

performing a seek operation to seek the head to an inner diameter track;

moving the actuator arm toward the latch according to the acceleration component and coast component of the velocity profile;

integrating the estimated VCM velocity while moving the actuator arm to estimate the latch distance; and

stopping the integration when the back EMF voltage reverses polarity indicating that the actuator arm has latched.