Disk drive tuning speed control loop for a spindle motor
View Patent ↗A disk drive is disclosed comprising a head actuated over a disk, a spindle motor operable to rotate the disk, and control circuitry comprising a speed control loop operable to control a rotation speed of the disk. A rotation speed of the disk is measured, and a speed error is generated in response to the measured rotation speed. The speed error is processed with a compensator to generate a control signal, a disturbance is injected into the control signal to generate a modified control signal, and the modified control signal is applied to the spindle motor. An amplitude of the disturbance is ramped, and after ramping the amplitude of the disturbance, an open-loop gain of the speed control loop is estimated at a frequency of the disturbance, and at least one parameter of the compensator is adjusted in response to the estimated open-loop gain.
1. A disk drive comprising:
a disk;
a head actuated over the disk;
a spindle motor operable to rotate the disk; and
control circuitry comprising a speed control loop operable to:
measure a rotation speed of the disk;
generate a speed error in response to the measured rotation speed;
process the speed error with a compensator to generate a control signal;
inject a disturbance into the control signal to generate a modified control signal; and
apply the modified control signal to the spindle motor;
wherein the control circuitry is operable to:
ramp an amplitude of the disturbance while injecting the disturbance into the control signal; and
after ramping the amplitude of the disturbance, estimate an open-loop gain of the speed control loop at a frequency of the disturbance and adjust at least one parameter of the compensator in response to the estimated open-loop gain.
2. The disk drive as recited in claim 1 , wherein the control circuitry is operable to ramp the amplitude of the disturbance until the speed control loop generates a response that exceeds a threshold.
3. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to adjust a gain of the compensator in response to the estimated open-loop gain.
4. The disk drive as recited in claim 3 , wherein the control circuitry is operable to adjust the gain of the compensator according to:
K
p
[
i
+
1
]
=
K
p
[
i
]
OLG
i
where:
K p represents the gain of the compensator; and
OLG i represents the estimated open-loop gain of the speed control loop at the frequency of the disturbance corresponding to K p [i].
5. The disk drive as recited in claim 3 , wherein the control circuitry is operable to adjust the gain of the compensator according to:
K
p
[
i
+
1
]
=
K
p
[
i
]
×
(
1
-
α
)
+
K
p
[
i
]
OLG
i
×
α
where:
K p represents the gain of the compensator;
OLG i represents the estimated open-loop gain of the speed control loop at the frequency of the disturbance corresponding to K p [i]; and
α is a positive scalar less than one.
6. The disk drive as recited in claim 3 , wherein prior to ramping the amplitude of the disturbance, the control circuitry is further operable to initialize the gain of the compensator according to:
K
p
=
ω
olbw
K
d
K
t
(
ω
olbw
J
spindle
R
w
)
2
+
(
K
t
K
e
)
2
ω
olbw
2
+
K
i
2
where:
K p represents the gain of the compensator;
ω olbw is a desired bandwidth frequency of the speed control loop;
K d is a gain of a spindle motor driver operable to drive the spindle motor;
K t represents a motor torque constant of the spindle motor;
K e represents a back electromotive force constant of the spindle motor;
J spindle represents a total rotational inertia of the spindle motor;
R w represents a winding resistance of the spindle motor; and
K i represents a ratio of an integral gain to a proportional gain of the compensator.
7. The disk drive as recited in claim 3 , wherein the control circuitry is further operable to adjust the gain of the compensator until the open-loop gain of the speed control loop substantially matches a target value.
8. The disk drive as recited in claim 7 , wherein the control circuitry is further operable to configure the gain with a default value when the open-loop gain of the speed control loop does not converge to the target value.
9. The disk drive as recited in claim 8 , wherein the default value comprises:
K
p
=
ω
olbw
K
d
K
t
(
ω
olbw
J
spindle
R
w
)
2
+
(
K
t
K
e
)
2
ω
olbw
2
+
K
i
2
where:
K p represents the gain of the compensator;
ω olbw is a desired bandwidth frequency of the speed control loop;
K d is a gain of a spindle motor driver operable to drive the spindle motor;
K t represents a motor torque constant of the spindle motor;
K e represents a back electromotive force constant of the spindle motor;
J spindle represents a total rotational inertia of the spindle motor;
R w represents a winding resistance of the spindle motor; and
K i represents a ratio of an integral gain to a proportional gain of the compensator.
10. A method of operating a disk drive, the disk drive comprising a head actuated over a disk, a spindle motor operable to rotate the disk, and control circuitry comprising a speed control loop operable to control a rotation speed of the disk, the method comprising:
measuring a rotation speed of the disk;
generating a speed error in response to the measured rotation speed;
processing the speed error with a compensator to generate a control signal;
injecting a disturbance into the control signal to generate a modified control signal; and
applying the modified control signal to the spindle motor;
ramping an amplitude of the disturbance while injecting the disturbance into the control signal; and
after ramping the amplitude of the disturbance, estimating an open-loop gain of the speed control loop at a frequency of the disturbance and adjusting at least one parameter of the compensator in response to the estimated open-loop gain.
11. The method as recited in claim 10 , wherein the amplitude of the disturbance is ramped until the speed control loop generates a response that exceeds a threshold.
12. The method as recited in claim 10 , further comprising adjusting a gain of the compensator in response to the estimated open-loop gain.
13. The method as recited in claim 12 , wherein the gain of the compensator is adjusted according to:
K
p
[
i
+
1
]
=
K
p
[
i
]
OLG
i
where:
K p represents the gain of the compensator; and
OLG i represents the estimated open-loop gain of the speed control loop at the frequency of the disturbance corresponding to K p [i].
14. The method as recited in claim 12 , wherein the gain of the compensator is adjusted according to:
K
p
[
i
+
1
]
=
K
p
[
i
]
×
(
1
-
α
)
+
K
p
[
i
]
OLG
i
×
α
where:
K p represents the gain of the compensator;
OLG i represents the estimated open-loop gain of the speed control loop at the frequency of the disturbance corresponding to K p [i]; and
α is a positive scalar less than one.
15. The method as recited in claim 12 , wherein prior to ramping the amplitude of the disturbance, further comprising initializing the gain of the compensator according to:
K
p
=
ω
olbw
K
d
K
t
(
ω
olbw
J
spindle
R
w
)
2
+
(
K
t
K
e
)
2
ω
olbw
2
+
K
i
2
where:
K p represents the gain of the compensator;
ω olbw is a desired bandwidth frequency of the speed control loop;
K d is a gain of a spindle motor driver operable to drive the spindle motor;
K t represents a motor torque constant of the spindle motor;
K e represents a back electromotive force constant of the spindle motor;
J spindle represents a total rotational inertia of the spindle motor;
R w represents a winding resistance of the spindle motor; and
K i represents a ratio of an integral gain to a proportional gain of the compensator.
16. The method as recited in claim 12 , wherein the gain of the compensator is adjusted until the open-loop gain of the speed control loop substantially matches a target value.
17. The method as recited in claim 16 , further comprising configuring the gain with a default value when the open-loop gain of the speed control loop does not converge to the target value.
18. The method as recited in claim 17 , wherein the default value comprises:
K
p
=
ω
olbw
K
d
K
t
(
ω
olbw
J
spindle
R
w
)
2
+
(
K
t
K
e
)
2
ω
olbw
2
+
K
i
2
where:
K p represents the gain of the compensator;
ω olbw is a desired bandwidth frequency of the speed control loop;
K d is a gain of a spindle motor driver operable to drive the spindle motor;
K t represents a motor torque constant of the spindle motor;
K e represents a back electromotive force constant of the spindle motor;
J spindle represents a total rotational inertia of the spindle motor;
R w represents a winding resistance of the spindle motor; and
K i represents a ratio of an integral gain to a proportional gain of the compensator.