Dynamic magnetic information storage or retrieval – Head mounting – For shifting head between tracks
Reexamination Certificate
2000-10-31
2002-10-08
Tupper, Robert S. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head mounting
For shifting head between tracks
C310S154090
Reexamination Certificate
active
06462914
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to disk drives for computer systems. More particularly, the present invention relates to a disk drive employing a voice coil motor comprising a voice coil wrapped around a rotary voice coil yoke comprising a low reluctance end and a high reluctance end.
2. Description of the Prior Art
Referring to
FIG. 1
, a conventional disk drive typically comprises a disk
2
for storing data in a plurality of radially spaced, concentric tracks
4
. A head
6
is actuated radially over the disk
2
in order to write data to or read data from a target track
4
. The head
6
is typically attached to a suspension
8
which biases the head
6
toward the surface of the disk
2
. The suspension
8
is attached to the distal end of an actuator arm
10
which is rotated about a pivot
12
by a voice coil motor
14
. The disk
2
typically has recorded thereon embedded servo wedges
16
which store coarse and fine head position information for positioning the head
6
over a centerline of a target track
4
.
As shown in
FIG. 2A
, a conventional voice coil motor
14
typically comprises a voice coil
18
in the shape of a trapezoid comprising a first side
20
A opposite a second side
20
B. A current is passed through the voice coil
18
to induce a first magnetic flux
22
A and a second magnetic flux
22
B along the length of each side (
20
A and
20
B). Because the voice coil
18
is wound up one leg and down the other, the direction of the magnetic flux
22
A induced along the first side
20
A is opposite the direction of the magnetic flux
22
B induced along the second side
20
B. A first magnet
24
A and a second magnet
24
B induce respective magnetic fluxes into and out of the page which are orthogonal to the magnetic fluxes (
22
A and
22
B) induced by the voice coil
18
. The orthogonal magnetic fluxes induce a horizontal force on the voice coil
18
, thereby rotating the actuator arm
10
about the pivot
12
to move the head
6
radially over the disk
2
. The actuator arm's direction of rotation (clockwise or counter-clockwise) depends on the direction of the current passing through the voice coil
18
(clockwise or counter-clockwise). Thus, the direction of the head
6
is reversed by reversing the direction of the current passing through the voice coil
18
.
Because the direction of the magnetic flux
22
A induced along the first side
20
A of the is voice coil
18
is opposite the direction of the magnetic flux
22
B induced along the second side
20
B, the first magnet
24
A is magnetized from top to bottom with a magnetic polarity (N/S or S/N) that is opposite that of the second magnet
24
B so that the magnetic fluxes
24
A and
24
B are aligned in the appropriate direction. In one embodiment, the first and second magnets (
24
A and
24
B) are manufactured from separate pieces of magnetic material and then magnetized with the appropriate polarity N/S or S/N. In alternative embodiment, the first and second magnets (
24
A and
24
B) are manufactured from a single piece of magnetic material and then magnetized with the appropriate polarity (N/S and S/N). Thus, the dashed line between the first and second magnets (
24
A and
24
B) shown in
FIG. 2
may represent a border between two separate pieces of magnet material, or a polarity border delineating two separate magnetized regions of a single piece of magnetic material.
The first and second magnets (
24
A and
24
B) are housed within a rotary voice coil yoke
26
, further details for which are illustrated in a perspective view in FIG.
2
B and in a plane view in FIG.
2
C. The yoke
26
comprises a top magnetic flux conductor
28
A and a bottom magnetic flux conductor
28
B. The first and second magnets (
24
A and
24
B) are attached to an interior surface
30
of the top magnetic flux conductor
28
A. The yoke
26
may further comprise a third magnet
32
A and a forth magnet
32
B attached to an interior surface
31
of the bottom magnetic flux conductor
28
B. As shown in
FIG. 2C
, the top magnetic flux conductor
28
A and the bottom magnetic flux conductor
28
B form an air gap
34
between the magnets (
24
A,
24
B,
32
A and
32
B). The polarity (N/S) of the magnets (
24
A,
24
B,
32
A and
32
B) generates a multidirectional magnetic flux
36
A and
36
B with respect to the air gap
34
. In the example shown in
FIG. 2C
, the direction of magnetic flux
36
A is upward from magnet
32
A to magnet
24
A, and the direction of magnetic flux
36
B is downward from magnet
24
B to magnet
32
B. The magnetic flux
36
A interacts with the magnetic flux
22
A of
FIG. 2B
generated by the first side
20
A of the voice coil
18
, and the magnetic flux
36
B interacts with the magnetic flux
22
B generated by the second side
20
B of the voice coil
18
.
There are drawbacks associated with the conventional rotary voice coil yoke design of
FIGS. 2B and 2C
. Namely, the magnets
24
A,
24
B,
32
A and
32
B represent a significant cost of the overall actuator assembly. In particular, the magnetic material itself is expensive and there is expense involved with magnetizing the magnetic material. In addition, the conventional two-piece yoke design increases the manufacturing cost of the disk drive due to the three step process required to manufacture the actuator assembly. First, the bottom magnetic flux conductor
28
B is fastened to the base of the disk drive (e.g., glued or screwed down). Next, the actuator arm
10
is fastened onto the pivot
12
such that the voice coil
18
is positioned over the second and third magnet
32
A and
32
B. Finally, the top magnetic flux conductor
28
A is fastened to the bottom magnetic flux conductor
28
B (e.g., glued or screwed down) such that the first and second magnets
24
A and
24
B are positioned over the voice coil
18
. This three step process increases the manufacturing time and therefore the manufacturing cost of the disk drive.
The cost of the rotary voice coil yoke design of
FIGS. 2B and 2C
can be reduced by eliminating the top magnets
24
A and
24
B or the bottom magnets
32
A and
32
B. However, the stray flux emanating from the top and bottom sides of the magnets interact with the top and bottom sides of the trapezoidal coil
18
shown in
FIG. 2A
which can excite resonances in the system leading to poor performance. Thus, the prior art typically employs top and bottom magnets so that the stray magnetic flux emanating from the top and bottom sides of the magnets is canceled.
It is also known to construct a voice coil motor by wrapping a voice coil around a middle conductor within a closed-ended yoke (low reluctance on both ends) comprising a top and bottom plate connected at the ends to form a closed housing for the middle conductor. This is illustrated in
FIG. 3A
which shows a top view of a closed-ended yoke
38
and a first and second voice coil
40
A and
40
B wrapped around a middle conductor
42
. The first and second voice coils
40
A and
40
B are wrapped in opposite directions and magnets
44
A and
44
B are magnetized with opposite polarity. The construction of the closed-ended yoke
38
is similar to the yoke shown in
FIG. 2A
with the addition of a middle conductor
42
connected at both ends of the yoke within the housing.
FIG. 3A
also shows that two additional magnets
46
A and
46
B are attached to the back side of the closed-ended yoke
38
to generate flux which interacts with the back side of the voice coils
40
A and
40
B. A plane view of the closed-ended yoke
38
of
FIG. 3A
is shown in FIG.
3
B. Only the first voice coil
40
A is shown wrapped around the middle conductor
42
.
FIG. 3B
also illustrates the bottom magnet
48
A attached to the bottom plate of the closed-ended yoke
38
.
With the closed-ended yoke structure of
FIGS. 3A and 3B
, guiding the magnetic flux through both ends of the yoke
38
increases the inductance of the voice coils
40
A and
40
B, thereby reducing performance of the voice coil motor by increasing the rise time of current through the
Casey Shawn E.
Dougherty Mitchell D.
Oveyssi Kamran
Weaver Jason T.
Shara, Esq. Milad G.
Tupper Robert S.
Western Digital Technologies Inc.
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