Dynamic magnetic information storage or retrieval – Head mounting – For adjusting head position
Reexamination Certificate
1999-07-20
2001-07-10
Ometz, David L. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head mounting
For adjusting head position
Reexamination Certificate
active
06259584
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an integrated device comprising a semiconductor material microactuator. In particular, the integrated device according to the present invention is used advantageously, but not exclusively, for actuation of hard disk read/write heads.
BACKGROUND OF THE INVENTION
As is known, for reading and writing a hard disk, use is generally made of a suspension that faces a surface of the hard disk when in an operative condition, so as to perform roll and pitch movements and to follow the surface of the hard disk.
It is also known to actuate a head by means of a double actuation stage, wherein a first actuation stage carries out a coarse movement of the head during tracking, and a second actuation stage performs finer adjustment of the head position. To implement the second actuation stage, it has been proposed to use an integrated microactuator of a rotary electrostatic type, interposed between the suspension and the head, to control the position of the head with micrometric accuracy.
An integrated microactuator
1
of an electrostatic type is shown schematically in FIG.
1
. For a more detailed description of a structure of an integrated, rotary electrostatic microactuator, see for example U.S. Pat. No. 5,025,346. As shown in
FIG. 1
, the microactuator
1
comprises an outer stator
2
, which is connected when in use to a suspension (not shown), and an inner rotor
4
electrostatically coupled to the stator
2
and supporting a read/write head (not shown).
The rotor
4
comprises a suspended mass
6
with a substantially circular shape, and a plurality of mobile arms
8
extending radially towards the exterior, starting from the suspended mass
6
, and identical to one another and angularly equidistant from one another. Each mobile arm
8
supports a plurality of mobile electrodes
10
that extend in a substantially circumferential direction on both sides of the respective mobile arm
8
.
The rotor
4
additionally comprises anchorages
14
and resilient suspension elements (shown as springs
12
), resiliently connecting the suspended mass
6
to the anchorage regions
14
, through which the rotor
4
and the mobile electrodes
10
are biased.
The stator
2
(only a part thereof is shown in full, owing to the symmetry of the structure) comprises a plurality of pairs of first and second fixed arms
20
a
,
20
b
arranged alternately to each other and extending radially towards the suspended mass
6
, starting from fixed regions
22
a
,
22
b
disposed circumferentially around the rotor
4
and intercalated with the anchorage regions
14
. The fixed regions
22
a
are connected to each other, as are the fixed regions
22
b
, as explained in detail hereinafter. These fixed regions
22
a
,
22
b
thus electrically define two nodes, which for simplicity are shown hereinafter as a first node
22
a
and a second node
22
b.
The pairs of fixed arms
20
a
,
20
b
are associated with the mobile arms
8
, such that a mobile arm
8
of the rotor
4
is arranged between two fixed arms
20
a
,
20
b
of each pair. Each fixed arm
20
a
,
20
b
also supports a plurality of fixed electrodes
24
extending in a substantially circumferential direction towards a corresponding mobile arm
8
. The fixed electrodes
24
are interdigitated with the mobile electrodes
10
of the respective mobile arms
8
. In the microactuator
1
, the first fixed arms
20
a
, arranged on a same side of the respective mobile arms
8
(in the example illustrated in
FIG. 1
, the first fixed arms
20
a
are located to the right of the mobile arms
8
), are all connected to the first node
22
a
, and are thus all biased to a same first potential. The second fixed arms
20
b
, arranged on the other side of the respective mobile arms
8
(in the example illustrated in
FIG. 1
, the second fixed arms
20
b
are located to the left of the mobile arms
8
), are all connected to the second node
22
b
, and are thus all biased to a same second potential. A capacitive coupling is thereby provided between each fixed electrode
24
and the respective mobile electrode
10
. The structure is electrically equivalent to a first plurality of capacitors connected in parallel between the first node
22
a
and the suspended mass
6
, and to a second plurality of capacitors connected in parallel between the suspended mass
6
and the second node
22
b.
The microactuator
1
is connected via the nodes
22
a
,
22
b
to a drive stage
30
(shown in FIG.
2
), the purpose of which is to apply potential differences between the fixed arms
20
a
,
20
b
and the respective mobile arm
8
, so as to rotate the rotor
4
with respect to the stator
2
. In particular, due to capacitive coupling between each mobile arm
8
and the respective pair of fixed arms
20
a
,
20
b
, the suspended mass
6
is subjected to a transverse force that is proportional to the number of pairs of fixed arms
20
a
,
20
b
and mobile arms
24
associated with each other. This force tends to space the mobile arm
8
from a fixed arm
20
a
,
20
b
having a lower potential difference, and to draw the mobile arm
8
closer to a fixed arm
20
b
,
20
a
having a higher potential difference. Thus a rotation of the suspended mass
6
is caused to consequently actuate the read/write head.
In prototypes of microactuators proposed hitherto, the nodes
22
a
,
22
b
are also used to obtain data relating to the relative positions of the rotor
4
and the stator
2
. The nodes
22
a
,
22
b
are thus simultaneously drive nodes and measure nodes. A position signal obtained thereby is then used in a feedback loop to carry out adjustment of the position of the read/write head. Therefore, it is possible to increase a mechanical band of a microactuator-head system and to read data recorded on increasingly narrow and dense tracks of the hard disk. This solution is described for example in an article entitled “Magnetic Recording Head Positioning at Very High Track Densities Using a Microactuator-Based Two-Stage Servo System” by Long-Sheng Fan, Hal H. Ottensen, Timothy C. Reiley and Roger W. Wood, IEEE Transaction on Industrial Electronics, vol. 42, no. 3, June 1995.
However, since voltages generated by the drive stage
30
have relatively high amplitudes of approximately 80 V, and on the other hand a stage downstream (shown as a measure stage
32
in
FIG. 2
) that processes the obtained position data operates with much lower voltages of approximately 5 V, it is often necessary to arrange an uncoupling structure
34
between the nodes
22
a
,
22
b
and the measure stage
32
to obtain required displacements of the rotor
4
.
FIG. 2
shows an electrical equivalent of the microactuator
1
, comprising two variable capacitors
40
,
42
arranged in series and representing respective capacitive coupling between the electrodes
24
,
10
of the first fixed arms
20
a
and the mobile arm
8
, respectively, and between the electrodes
10
,
24
of the mobile arm
8
and the second fixed arms
20
b
, respectively. In particular, in
FIG. 2
, an intermediate node
6
between the two variable capacitors
40
,
42
represents the suspended mass
6
of the rotor
4
.
The uncoupling structure
34
comprises two disconnection capacitors
44
,
46
. In particular, the disconnection capacitor
44
is arranged between the first node
22
a
and a first input of the measure stage
32
(represented as an operational amplifier), and the disconnection capacitor
46
is arranged between the second node
22
a
and a second input of the measure stage
32
. In practice, the disconnection capacitors
44
,
46
are arranged on a path of a signal containing data related to a position of the rotor
4
with respect to the stator
2
. In these proposed microactuators, the uncoupling capacitors
44
,
46
are formed through two metal layers at different levels, so as to both prevent distortion of the signal containing the data related the position of the rotor
4
and to withstand high ohmic drops present in the structure.
The microactuators proposed hitherto have many disadva
Cini Dario
Vigna Benedetto
Castro Angel
Galanthay Theodore E.
Iannucci Robert
Ometz David L.
Seed IP Law Group PLLC
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