Disk drive initializing a coil temperature estimation algorithm using a resistance of the coil estimated during a load operation

1. A disk drive comprising:

a disk;

a head coupled to a distal end of an actuator arm;

a voice coil motor (VCM) operable to rotate the actuator arm about a pivot to actuate the head radially over the disk, the VCM comprising a coil;

a ramp; and

control circuitry operable to:

measure a load resistance of the coil prior to executing a load operation, wherein the load operation moves the actuator arm off the ramp to load the head onto the disk;

measure a calibrated ambient temperature (Tcal_amb) using a temperature sensor;

measure a calibrated ambient resistance (Rcal_amb) of the coil at the calibrated ambient temperature (Tcal_amb); and

convert the load resistance of the coil into an initial coil temperature estimate according to:

1

α

⁢

(

Rcoil

-

R

⁢

cal

⁢

_

⁢

amb

)

+

T

⁢

cal_amb

where:

α is a coefficient; and

Rcoil is the load resistance of the coil.

2. The disk drive as recited in claim 1 , wherein the control circuitry measures the calibrated ambient resistance (Rcal_amb) of the coil after the VCM has been idle for a predetermined interval.

3. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to calibrate the coefficient α according to:

Rtemp

⁢

⁢

1

-

Rtemp

⁢

⁢

2

temp

⁢

⁢

1

-

temp

⁢

⁢

2

where:

temp 1 is a first ambient temperature;

temp 2 is a second ambient temperature;

Rtemp 1 is a measured coil resistance at temp 1 ; and

Rtemp 2 is a measured coil resistance at temp 2 .

4. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to estimate a change in the coil temperature according to:

1

K

t

⁢

(

K

r

⁢

P

r

+

Tamb

-

Tcoil

)

where:

K t and K r are coefficients;

P r is a heating power of the coil;

Tamb is an ambient temperature measured with a temperature sensor; and

Tcoil is a previous coil temperature estimate.

5. The disk drive as recited in claim 4 , wherein the heating power of the coil Pr is estimated according to:

R c I c 2

where:

R c is an estimated resistance of the coil; and

I c is a measured current flowing through the coil.

6. The disk drive as recited in claim 5 , wherein the resistance of the coil R c is estimated according to:

Rcal_amb[1+α(Tcoil−Tcal_amb)].

7. The disk drive as recited in claim 4 , wherein the control circuitry is further operable to convert the coil temperature estimate into an unload resistance of the coil prior to executing an unload operation.

8. The disk drive as recited in claim 7 , wherein the control circuitry is further operable to convert the coil temperature estimate into the unload resistance of the coil according to:

Rcal_amb[1+α(Tcoil−Tcal_amb)].

9. A method of operating a disk drive, the disk drive comprising a disk, a head coupled to a distal end of an actuator arm, a voice coil motor (VCM) operable to rotate the actuator arm about a pivot to actuate the head radially over the disk, the VCM comprising a coil, and a ramp, the method comprising:

measuring a load resistance of the coil prior to executing a load operation, wherein the load operation moves the actuator arm off the ramp to load the head onto the disk;

measuring a calibrated ambient temperature (Tcal_amb) using a temperature sensor;

measuring a calibrated ambient resistance (Rcal_amb) of the coil at the calibrated ambient temperature (Tcal_amb); and

converting the load resistance of the coil into an initial coil temperature estimate according to:

1

α

⁢

(

Rcoil

-

R

⁢

cal

⁢

_

⁢

amb

)

+

T

⁢

cal_amb

where:

α is a coefficient; and

Rcoil is the load resistance of the coil.

10. The method as recited in claim 9 , wherein measuring the calibrated ambient resistance (Rcal_amb) of the coil is performed after the VCM has been idle for a predetermined interval.

11. The method as recited in claim 9 , further comprising calibrating the coefficient α according to:

Rtemp

⁢

⁢

1

-

Rtemp

⁢

⁢

2

temp

⁢

⁢

1

-

temp

⁢

⁢

2

where:

temp 1 is a first ambient temperature;

temp 2 is a second ambient temperature;

Rtemp 1 is a measured coil resistance at temp 1 ; and

Rtemp 2 is a measured coil resistance at temp 2 .

12. The method as recited in claim 9 , further comprising estimating a change in the coil temperature according to:

1

K

t

⁢

(

K

r

⁢

P

r

+

Tamb

-

Tcoil

)

where:

K t and K r are coefficients;

P r is a heating power of the coil;

Tamb is an ambient temperature measured with a temperature sensor; and

Tcoil is a previous coil temperature estimate.

13. The method as recited in claim 12 , wherein the heating power of the coil Pr is estimated according to:

R c I c 2

where:

R c is an estimated resistance of the coil; and

I c is a measured current flowing through the coil.

14. The method as recited in claim 13 , wherein the resistance of the coil R c is estimated according to:

Rcal_amb[1+α(Tcoil−Tcal_amb)].

15. The method as recited in claim 12 , further comprising converting the coil temperature estimate into an unload resistance of the coil prior to executing an unload operation.

16. The method as recited in claim 15 , wherein the coil temperature estimate is converted into the unload resistance of the coil according to:

Rcal_amb[1+α(Tcoil−Tcal_amb)].

17. A disk drive comprising:

a disk;

a head coupled to a distal end of an actuator arm;

a voice coil motor (VCM) operable to rotate the actuator arm about a pivot to actuate the head radially over the disk, the VCM comprising a coil;

a ramp;

a means for measuring a load resistance of the coil prior to executing a load operation, wherein the load operation moves the actuator arm off the ramp to load the head onto the disk;

a means for measuring a calibrated ambient temperature (Tcal_amb) using a temperature sensor;

a means for measuring a calibrated ambient resistance (Rcal_amb) of the coil at the calibrated ambient temperature (Tcal_amb); and

a means for converting the load resistance of the coil into an initial coil temperature estimate according to:

1

α

⁢

(

Rcoil

-

R

⁢

cal

⁢

_

⁢

amb

)

+

T

⁢

cal_amb

where:

α is a coefficient; and

Rcoil is the load resistance of the coil.

18. A disk drive comprising:

a disk;

a head coupled to a distal end of an actuator arm;

a voice coil motor (VCM) operable to rotate the actuator arm about a pivot to actuate the head radially over the disk, the VCM comprising a coil;

a ramp; and

control circuitry operable to:

measure a load resistance of the coil prior to executing a load operation, wherein the load operation moves the actuator arm off the ramp to load the head onto the disk;

convert the load resistance of the coil into an initial coil temperature estimate;

update the coil temperature estimate after the load operation; and

convert the updated coil temperature estimate into an unload resistance of the coil prior to executing an unload operation, wherein the unload operation moves the actuator arm onto the ramp.

19. A method of operating a disk drive, the disk drive comprising a disk, a head coupled to a distal end of an actuator arm, a voice coil motor (VCM) operable to rotate the actuator arm about a pivot to actuate the head radially over the disk, the VCM comprising a coil, and a ramp, the method comprising:

measuring a load resistance of the coil prior to executing a load operation, wherein the load operation moves the actuator arm off the ramp to load the head onto the disk;

converting the load resistance of the coil into an initial coil temperature estimate;

updating the coil temperature estimate after the load operation; and

converting the updated coil temperature estimate into an unload resistance of the coil prior to executing an unload operation, wherein the unload operation moves the actuator arm onto the ramp.