Disk drive detecting head touchdown from microactuator signal
A disk drive is disclosed comprising a head actuated over a disk surface by a microactuator, and a fly height actuator operable to adjust a fly height of the head. A servo control voltage is applied to the microactuator, and the fly height actuator is adjusted to decrease a fly height of the head. The servo control voltage is filtered to generate a filtered voltage. A touchdown signal is generated in response to the microactuator and the filtered voltage, wherein the touchdown signal indicates when the head contacts the disk.
1. A disk drive comprising:
a disk comprising first surface and a second surface;
a first head actuated over the first surface by a first microactuator;
a second head actuated over the second surface by a second microactuator;
a fly height actuator operable to adjust a fly height of the first head; and
control circuitry operable to:
apply a servo control voltage to the first and second microactuators;
adjust the fly height actuator to decrease a fly height of the first head; and
generate a touchdown signal in response to a difference between a first voltage output by the first microactuator and a second voltage output by the second microactuator, wherein the touchdown signal indicates when the first head contacts the first disk surface.
2. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to filter the touchdown signal to substantially cancel an effect of the servo control voltage on the touchdown signal.
3. The disk drive as recited in claim 1 , wherein the control circuitry comprises:
a first impedance coupling the output of the first microactuator to ground; and
a second impedance coupling the output of the second microactuator to ground.
4. The disk drive as recited in claim 3 , wherein the control circuitry generates the touchdown signal according to:
Z
1
·
Za
2
-
Z
2
·
Za
1
(
Za
2
+
Z
2
)
(
Za
1
+
Z
1
)
·
Vc
+
Z
1
Za
1
+
Z
1
·
Va
1
where:
Z 1 is the first impedance;
Z 2 is the second impedance;
Va 1 is the first voltage output by the first microactuator;
Za 1 is an impedance of the first microactuator;
Za 2 is an impedance of the second microactuator; and
Vc is the servo control voltage.
5. The disk drive as recited in claim 4 , wherein Z 1 and Z 2 comprise values such that the term (Z 1 ·Za 2 −Z 2 ·Za 1 ) is approximately zero.
6. The disk drive as recited in claim 4 , wherein Z 1 and Z 2 comprise values such that the term:
Z
1
·
Za
2
-
Z
2
·
Za
1
(
Za
2
+
Z
2
)
(
Za
1
+
Z
1
)
attenuates low frequencies.
7. A disk drive comprising:
a disk surface;
a head actuated over the disk surface by a microactuator;
a fly height actuator operable to adjust a fly height of the head; and
control circuitry operable to:
apply a servo control voltage to the microactuator;
adjust the fly height actuator to decrease a fly height of the head;
filter the servo control voltage to generate a filtered voltage; and
generate a touchdown signal in response to the microactuator and the filtered voltage, wherein the touchdown signal indicates when the head contacts the disk surface.
8. The disk drive as recited in claim 7 , wherein the control circuitry is further operable to generate the touchdown signal in response to a difference between a voltage output by the microactuator and the filtered voltage.
9. The disk drive as recited in claim 7 , wherein the control circuitry is further operable to generate the touchdown signal in response to a difference between a voltage input into the microactuator and the filtered voltage.
10. The disk drive as recited in claim 7 , wherein the control circuitry is further operable to filter the touchdown signal to substantially cancel an effect of the servo control voltage on the touchdown signal.
11. The disk drive as recited in claim 8 , wherein:
the control circuitry comprises a filter for filtering the servo control voltage;
the filter comprises a first impedance coupled to the servo control voltage;
the filter comprises a second impedance coupling the first impedance to ground; and
the filtered voltage is generated between the first and second impedance.
12. The disk drive as recited in claim 11 , wherein the control circuitry comprises a third impedance for coupling the output of the microactuator to ground.
13. The disk drive as recited in claim 12 , wherein the control circuitry generates the touchdown signal according to:
Z
1
·
Za
2
-
Z
2
·
Za
1
(
Za
2
+
Z
2
)
(
Za
1
+
Z
1
)
·
Vc
+
Z
1
Za
1
+
Z
1
·
Va
1
where:
Z 0 is the first impedance;
Z 2 is the second impedance;
Z 1 is the third impedance;
Va 1 is the voltage output by the microactuator;
Za 1 is an impedance of the microactuator; and
Vc is the servo control voltage.
14. The disk drive as recited in claim 13 , wherein Z 0 , Z 1 and Z 2 comprise values such that the term (Z 1 ·Z 0 −Z 2 ·Za 1 ) is approximately zero.
15. The disk drive as recited in claim 13 , wherein Z 1 and Z 2 comprise values such that the term:
Z
1
·
Za
2
-
Z
2
·
Za
1
(
Za
2
+
Z
2
)
(
Za
1
+
Z
1
)
attenuates low frequencies.
16. The disk drive as recited in claim 9 , wherein:
the control circuitry comprises a filter for filtering the servo control voltage;
the filter comprises a first impedance coupled to the servo control voltage;
the filter comprises a second impedance coupling the first impedance to ground; and
the filtered voltage is generated between the first and second impedance.
17. The disk drive as recited in claim 16 , wherein the control circuitry comprises a third impedance for coupling the servo control voltage to the input of the microactuator.
18. The disk drive as recited in claim 17 , wherein the control circuitry generates the touchdown signal according to:
Z
1
·
Za
2
-
Z
2
·
Za
1
(
Za
2
+
Z
2
)
(
Za
1
+
Z
1
)
·
Vc
+
Z
1
Za
1
+
Z
1
·
Va
1
where:
Z 2 is the first impedance;
Z 0 is the second impedance;
Z 1 is the third impedance;
Va 1 is the voltage output by the microactuator;
Za 1 is an impedance of the microactuator; and
Vc is the servo control voltage.
19. The disk drive as recited in claim 18 , wherein Z 0 , Z 1 and Z 2 comprise values such that the term (Za 1 ·Z 2 −Z 0 ·Z 1 ) is approximately zero.
20. The disk drive as recited in claim 18 , wherein Z 1 and Z 2 comprise values such that the term:
Z
1
·
Za
2
-
Z
2
·
Za
1
(
Za
2
+
Z
2
)
(
Za
1
+
Z
1
)
attenuates low frequencies.
21. A method of operating a disk drive comprising a disk comprising first surface and a second surface, a first head actuated over the first surface by a first microactuator, a second head actuated over the second surface by a second microactuator, and a fly height actuator operable to adjust a fly height of the first head, the method comprising:
applying a servo control voltage to the first and second microactuators;
adjusting the fly height actuator to decrease a fly height of the first head; and
generating a touchdown signal in response to a difference between a first voltage output by the first microactuator and a second voltage output by the second microactuator, wherein the touchdown signal indicates when the first head contacts the first disk surface.
22. A method of operating disk drive comprising a disk surface, a head actuated over the disk surface by a microactuator, and a fly height actuator operable to adjust a fly height of the head, the method comprising:
applying a servo control voltage to the microactuator;
adjusting the fly height actuator to decrease a fly height of the head;
filtering the servo control voltage to generate a filtered voltage; and
generating a touchdown signal in response to the microactuator and the filtered voltage, wherein the touchdown signal indicates when the head contacts the disk surface.