Disk drive measuring a resonance mode by injecting sinusoids into a servo control system
View Patent ↗A disk drive is disclosed comprising a disk comprising a plurality of servo tracks defined by servo sectors recorded around the circumference of the disk at a servo sampling frequency, and a servo control system operable to actuate a head over the disk by generating a control signal applied to an actuator. A first sinusoid is injected into the servo control system and a first DC component (dc1) is measured in the control signal. A second sinusoid is injected into the servo control system and a second DC component (dc2) is measured in the control signal, wherein the second sinusoid comprises a phase offset from the first sinusoid. A resonance mode of the servo control system is measured based on dc1 and dc2.
1. A disk drive comprising:
a disk comprising a plurality of servo tracks defined by servo sectors recorded around the circumference of the disk at a servo sampling frequency;
a head;
an actuator operable to actuate the head over the disk; and
control circuitry comprising a servo control system operable to generate a control signal applied to the actuator, the control circuitry operable to:
inject a first sinusoid into the servo control system and measure a first DC component dc1, in the control signal;
inject a second sinusoid into the servo control system and measure a second DC component dc2, in the control signal, wherein the second sinusoid comprises a phase offset from the first sinusoid; and
measure a resonance mode of the servo control system based on the dc1 and the dc2.
2. The disk drive as recited in claim 1 , wherein a frequency of the sinusoid substantially matches the servo sampling frequency.
3. The disk drive as recited in claim 2 , wherein the resonance mode is measured at substantially the servo sampling frequency.
4. The disk drive as recited in claim 2 , wherein the control circuitry is further operable to:
measure a third DC component dc0, in the control signal without injecting a sinusoid into the servo control system; and
measure the dc1 and the dc2 relative to the dc0.
5. The disk drive as recited in claim 4 , wherein the control circuitry is further operable to measure the resonance mode of the servo control system based on:
k
(
dc
1
)
2
+
(
dc
2
)
2
where k represents a DC gain of the servo control system.
6. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to measure the resonance mode of the servo control system based on:
k
(
dc
1
)
2
+
(
dc
2
)
2
where k represents a DC gain of the servo control system.
7. The disk drive as recited in claim 1 , wherein the phase offset comprises nπ/2 where n is an odd integer.
8. A method of operating a disk drive, the disk drive comprising a disk comprising a plurality of servo tracks defined by servo sectors recorded around the circumference of the disk at a servo sampling frequency, and a servo control system operable to actuate a head over the disk in response to a control signal, the method comprising:
injecting a first sinusoid into the servo control system and measure a first DC component dc1, in the control signal;
injecting a second sinusoid into the servo control system and measure a second DC component dc2, in the control signal, wherein the second sinusoid comprises a phase offset from the first sinusoid; and
measuring a resonance mode of the servo control system based on the dc1 and the dc2.
9. The method as recited in claim 8 , wherein a frequency of the sinusoid substantially matches the servo sampling frequency.
10. The method as recited in claim 9 , wherein the resonance mode is measured at substantially the servo sampling frequency.
11. The method as recited in claim 9 , further comprising:
measuring a third DC component dc0, in the control signal without injecting a sinusoid into the servo control system; and
measuring the dc1 and the dc2 relative to the dc0.
12. The method as recited in claim 11 , further comprising measuring the resonance mode of the servo control system based on:
k
(
dc
1
)
2
+
(
dc
2
)
2
where k represents a DC gain of the servo control system.
13. The method as recited in claim 8 , further comprising measuring the resonance mode of the servo control system based on:
k
(
dc
1
)
2
+
(
dc
2
)
2
where k represents a DC gain of the servo control system.
14. The method as recited in claim 8 , wherein the phase offset comprises nπ/2 where n is an odd integer.