Disk drive adjusting gain of spindle motor compensator based on a ratio of spin speeds
View Patent ↗A disk drive is disclosed comprising a head actuated over a disk, a spindle motor for rotating the disk, and a spindle motor control system comprising a servo compensator operable to generate a control signal applied to the spindle motor, the servo compensator comprising a programmable gain term (PGT). The disk is spun at a first speed RPM — 1 using a first value PGT — 1 selected for the PGT, and the disk is spun at a second speed RPM — 2 using a second value PGT — 2 selected for the PGT, wherein the second value PGT — 2 is generated in response to the first value PGT — 1 scaled by a function of a ratio of RPM — 2 to RPM — 1.
1. A disk drive comprising:
a disk;
a head actuated over the disk;
a spindle motor for rotating the disk;
a spindle motor control system comprising a servo compensator operable to generate a control signal applied to the spindle motor, the servo compensator comprising a programmable gain term (PGT); and
control circuitry operable to:
spin the disk at a first speed RPM_ 1 using a first value PGT_ 1 selected for the PGT; and
spin the disk at a second speed RPM_ 2 using a second value PGT_ 2 selected for the PGT,
wherein the second value PGT_ 2 is generated in response to the first value PGT_ 1 scaled by a function of a ratio of RPM_ 2 to RPM_ 1 .
2. The disk drive as recited in claim 1 , wherein the RPM_ 2 is less than the RPM_ 1 .
3. The disk drive as recited in claim 1 , wherein the function comprises an exponentiation of the ratio.
4. The disk drive as recited in claim 3 , wherein the function comprises:
(
RPM_
2
RPM_
1
)
N
where N is greater than one.
5. The disk drive as recited in claim 4 , wherein the second value PGT_ 2 is generated according to:
PGT_
1
·
(
RPM_
2
RPM_
1
)
N
.
6. The disk drive as recited in claim 5 , wherein the second value PGT_ 2 is generated according to:
PGT_
1
·
(
RPM_
2
RPM_
1
)
2
.
7. The disk drive as recited in claim 5 , wherein the second value PGT_ 2 is generated according to:
PGT_
1
·
(
RPM_
2
RPM_
1
)
3
.
8. The disk drive as recited in claim 5 , wherein the second value PGT_ 2 is generated according to:
PGT_
1
·
(
RPM_
2
RPM_
1
)
N
·
(
(
RPM_
2
·
Ecycles
·
Lw
)
2
+
(
60
·
Ra
2
π
)
2
(
RPM_
1
·
Ecycles
·
Lw
)
2
+
(
60
·
Ra
2
π
)
2
)
where:
Ra represents a motor winding resistance of the spindle motor plus a driver resistance of the spindle motor control system;
Lw represents a spindle motor winding inductance; and
Ecycles represents a number of electrical cycles per mechanical cycle of the spindle motor.
9. The disk drive as recited in claim 3 , wherein the exponentiation of the ratio accounts for parameters of the spindle motor.
10. The disk drive as recited in claim 9 , wherein the exponentiation of the ratio accounts for the spindle motor winding resistance, the spindle motor winding inductance, and a number of electrical cycles per mechanical cycle of the spindle motor.
11. The disk drive as recited in claim 1 , wherein the function of the ratio results in a substantially constant bandwidth for the spindle motor control system across the first and second speeds.
12. The disk drive as recited in claim 1 , wherein the function of the ratio results in a substantially constant phase response for the spindle motor control system across the first and second speeds.
13. A method of operating a disk drive the disk drive comprising a head actuated over a disk, a spindle motor for rotating the disk, and a spindle motor control system comprising a servo compensator operable to generate a control signal applied to the spindle motor, the servo compensator comprising a programmable gain term (PGT), the method comprising:
spinning the disk at a first speed RPM_ 1 using a first value PGT_ 1 selected for the PGT; and
spinning the disk at a second speed RPM_ 2 using a second value PGT_ 2 selected for the PGT,
wherein the second value PGT_ 2 is generated in response to the first value PGT_ 1 scaled by a function of a ratio of RPM_ 2 to RPM_ 1 .
14. The method as recited in claim 13 , wherein the RPM_ 2 is less than the RPM_ 1 .
15. The method as recited in claim 13 , wherein the function comprises an exponentiation of the ratio.
16. The method as recited in claim 15 , wherein the function comprises:
(
RPM_
2
RPM_
1
)
N
where N is greater than one.
17. The method as recited in claim 16 , wherein the second value PGT_ 2 is generated according to:
PGT_
1
·
(
RPM_
2
RPM_
1
)
N
.
18. The method as recited in claim 17 , wherein the second value PGT_ 2 is generated according to:
PGT_
1
·
(
RPM_
2
RPM_
1
)
2
.
19. The method as recited in claim 17 , wherein the second value PGT_ 2 is generated according to:
PGT_
1
·
(
RPM_
2
RPM_
1
)
3
.
20. The method as recited in claim 17 , wherein the second value PGT_ 2 is generated according to:
PGT_
1
·
(
RPM_
2
RPM_
1
)
N
·
(
(
RPM_
2
·
Ecycles
·
Lw
)
2
+
(
60
·
Ra
2
π
)
2
(
RPM_
1
·
Ecycles
·
Lw
)
2
+
(
60
·
Ra
2
π
)
2
)
where:
Ra represents a motor winding resistance of the spindle motor plus a driver resistance of the spindle motor control system;
Lw represents a spindle motor winding inductance; and
Ecycles represents a number of electrical cycles per mechanical cycle of the spindle motor.
21. The method as recited in claim 15 , wherein the exponentiation of the ratio accounts for parameters of the spindle motor.
22. The method as recited in claim 21 , wherein the exponentiation of the ratio accounts for the spindle motor winding resistance, the spindle motor winding inductance, and a number of electrical cycles per mechanical cycle of the spindle motor.
23. The method recited in claim 13 , wherein the function of the ratio results in a substantially constant bandwidth for the spindle motor control system across the first and second speeds.
24. The method as recited in claim 13 , wherein the function of the ratio results in a substantially constant phase response for the spindle motor control system across the first and second speeds.