DISK DRIVE WITH IMPROVED SPIN-UP CONTROL

1 . A disk drive comprising:

a head actuated over a disk;

a spindle motor operable to rotate the disk, wherein:

the spindle motor operates according to a plurality of electrical cycles over a single revolution of the spindle motor; and

each electrical cycle spans a cycle period; and

control circuitry operable to:

measure a plurality of the cycle periods;

combine at least two of the cycle periods; and

measure a rotation speed of the spindle motor based on the combined cycle periods.

2 . The disk drive as recited in claim 1 , wherein the spindle motor operates according to N electrical cycles over a single revolution, and the control circuitry is further operable to generate the combined cycle periods by summing N consecutive cycle periods.

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

update the combined cycle periods by summing a running N consecutive cycle periods as each new cycle period is measured; and

update the measured rotation speed based on the updated combined cycle periods.

4 . A disk drive comprising:

a head actuated over a disk;

a spindle motor operable to rotate the disk; and

control circuitry operable to:

measure a rotation speed of the spindle motor;

generate a gain as a function of the measured rotation speed, wherein the function comprises a polynomial having a degree greater than one; and

spin-up the spindle motor based on the gain.

5 . The disk drive as recited in claim 4 , wherein the gain comprises a feedback gain operable to amplify a feedback error signal.

6 . The disk drive as recited in claim 5 , wherein the feedback error signal represents a difference between the measured rotation speed and a target rotation speed.

7 . A disk drive comprising:

a head actuated over a disk;

a spindle motor operable to rotate the disk; and

control circuitry operable to:

measure a rotation speed of the spindle motor;

generate a feed-forward control based on the measured rotation speed; and

spin-up the spindle motor based on the feed-forward control.

8 . The disk drive as recited in claim 7 , wherein the control circuitry is operable to generate the feed-forward control based on the measured rotation speed and an ambient temperature of the disk drive.

9 . The disk drive as recited in claim 7 , wherein the control circuitry is operable to generate the feed-forward control proportional to the measured rotation speed.

10 . The disk drive as recited in claim 9 , wherein the feed-forward control compensates for a back electromotive force of the spindle motor.

11 . The disk drive as recited in claim 7 , wherein the feed-forward control compensates for a drag torque of the spindle motor.

12 . The disk drive as recited in claim 11 , wherein the control circuitry is operable to generate the feed-forward control based on the measured rotation speed and an ambient temperature of the disk drive.

13 . A disk drive comprising:

a head actuated over a disk;

a spindle motor operable to rotate the disk; and

control circuitry operable to:

measure a rotation speed of the spindle motor;

generate a control signal based on the measured rotation speed and a speed command profile; and

spin-up the spindle motor based on the control signal, wherein the speed command profile ensures a minimum spin-up time and a limited power consumption under a worst case environmental condition.

14 . The disk drive as recited in claim 13 , wherein the environmental condition comprises an ambient temperature of the disk drive.

15 . The disk drive as recited in claim 13 , wherein the speed command profile accounts for a maximum current draw of the spindle motor.

16 . A disk drive comprising:

a head actuated over a disk;

a spindle motor operable to rotate the disk; and

control circuitry operable to:

measure a rotation speed of the spindle motor;

generate a control signal based on a difference between the measured rotation speed and a target rotation speed; and

spin-up the spindle motor based on the control signal generated over a second fraction of a spin-up time;

wherein:

the target rotation speed is generated based on a speed command profile and the second fraction of the spin-up time; and

the control circuitry is operable to determine the second fraction of the spin-up time based on an initial measured rotation speed of the spindle motor prior to generating the control signal.

17 . The disk drive as recited in claim 16 , wherein the control circuitry is operable to initialize the second fraction of the spin-up time so that an initial target rotation speed is greater than the initial measured rotation speed.

18 . The disk drive as recited in claim 17 , wherein the initial target rotation speed ensures the spindle motor continues accelerating from the initial measured rotation speed when the control signal is generated.

19 . The disk drive as recited in claim 18 , wherein the control circuitry is further operable to:

initially control the spindle motor independent of the control signal for a first fraction of the spin-up time; and

after the first fraction of the spin-up time, control the spindle motor based on the control signal for the second fraction of the spin-up time.

20 . A disk drive comprising:

a head actuated over a disk;

a spindle motor operable to rotate the disk; and

control circuitry operable to:

spin up the spindle motor to a target rotation speed using a spin-up controller;

after spinning up the spindle motor, initialize an integrator based on a state of the spin-up controller; and

control the spindle motor using a constant-speed controller comprising the integrator.

21 . The disk drive as recited in claim 20 , wherein the state of the spin-up controller comprises an acceleration control signal applied to the spindle motor.

22 . The disk drive as recited in claim 21 , wherein the control circuitry is operable to initialize the integrator according to:

Accel− Kp ·Speed Err

where:

Accel represents the acceleration control signal;

Kp represents a gain of the constant-speed controller; and

SpeedErr represents a difference between a measured rotation speed of the spindle motor and a target rotation speed.

23 . A method of operating a disk drive comprising a head actuated over a disk, and a spindle motor operable to rotate the disk, wherein the spindle motor operates according to a plurality of electrical cycles over a single revolution of the spindle motor, and each electrical cycle spans a cycle period, the method comprising:

measuring a plurality of the cycle periods;

combining at least two of the cycle periods; and

measuring a rotation speed of the spindle motor based on the combined cycle periods.

24 . The method as recited in claim 23 , wherein the spindle motor operates according to N electrical cycles over a single revolution, and the method further comprising generating the combined cycle periods by summing N consecutive cycle periods.

25 . The method as recited in claim 23 , wherein the method further comprises:

updating the combined cycle periods by summing a running N consecutive cycle periods as each new cycle period is measured; and

updating the measured rotation speed based on the updated combined cycle periods.

26 . A method of operating a disk drive comprising a head actuated over a disk, and a spindle motor operable to rotate the disk, the method comprising:

measuring a rotation speed of the spindle motor;

generating a gain as a function of the measured rotation speed, wherein the function comprises a polynomial having a degree greater than one; and

spinning up the spindle motor based on the gain.

27 . The method as recited in claim 26 , wherein the gain comprises a feedback gain operable to amplify a feedback error signal.

28 . The method as recited in claim 27 , wherein the feedback error signal represents a difference between the measured rotation speed and a target rotation speed.

29 . A method of operating a disk drive comprising a head actuated over a disk, and a spindle motor operable to rotate the disk, the method comprising:

measuring a rotation speed of the spindle motor;

generating a feed-forward control based on the measured rotation speed; and

spinning up the spindle motor based on the feed-forward control.

30 . The method as recited in claim 29 , further comprising generating the feed-forward control based on the measured rotation speed and an ambient temperature of the disk drive.

31 . The method as recited in claim 29 , further comprising generating the feed-forward control proportional to the measured rotation speed.

32 . The method as recited in claim 31 , wherein the feed-forward control compensates for a back electromotive force of the spindle motor.

33 . The method as recited in claim 29 , wherein the feed-forward control compensates for a drag torque of the spindle motor.

34 . The method as recited in claim 33 , further comprising generating the feed-forward control based on the measured rotation speed and an ambient temperature of the disk drive.

35 . A method of operating a disk drive comprising a head actuated over a disk, and a spindle motor operable to rotate the disk, the method comprising:

measuring a rotation speed of the spindle motor;

generating a control signal based on the measured rotation speed and a speed command profile; and

spinning up the spindle motor based on the control signal, wherein the speed command profile ensures a minimum spin-up time and a limited power consumption under a worst case environmental condition.

36 . The method as recited in claim 35 , wherein the environmental condition comprises an ambient temperature of the disk drive.

38 . The method as recited in claim 35 , wherein the speed command profile accounts for a maximum current draw of the spindle motor.

39 . A method of operating a disk drive comprising a head actuated over a disk, and a spindle motor operable to rotate the disk, the method comprising:

measuring a rotation speed of the spindle motor;

generating a control signal based on a difference between the measured rotation speed and a target rotation speed; and

spinning up the spindle motor based on the control signal generated over a second fraction of a spin-up time;

wherein:

the target rotation speed is generated based on a speed command profile and the second fraction of the spin-up time; and

the method further comprises determining the second fraction of the spin-up time based on an initial measured rotation speed of the spindle motor prior to generating the control signal.

40 . The method as recited in claim 39 , further comprising initializing the second fraction of the spin-up time so that an initial target rotation speed is greater than the initial measured rotation speed.

41 . The method as recited in claim 40 , wherein the initial target rotation speed ensures the spindle motor continues accelerating from the initial measured rotation speed when the control signal is generated.

42 . The method as recited in claim 41 , further comprising:

initially controlling the spindle motor independent of the control signal for a first fraction of the spin-up time; and

after the first fraction of the spin-up time, controlling the spindle motor based on the control signal for the second fraction of the spin-up time.

43 . A method of operating a disk drive comprising a head actuated over a disk, and a spindle motor operable to rotate the disk, the method comprising:

spinning up the spindle motor to a target rotation speed using a spin-up controller;

after spinning up the spindle motor, initializing an integrator based on a state of the spin-up controller; and

controlling the spindle motor using a constant-speed controller comprising the integrator.

44 . The method as recited in claim 43 , wherein the state of the spin-up controller comprises an acceleration control signal applied to the spindle motor.

45 . The method as recited in claim 44 , further comprising initializing the integrator according to:

Accel− Kp ·Speed Err

where:

Accel represents the acceleration control signal;

Kp represents a gain of the constant-speed controller; and

SpeedErr represents a difference between a measured rotation speed of the spindle motor and a target rotation speed.