Magnet design for active damping of disk drive actuator

Details Magnet design for active damping of disk drive actuator Magnet design for active damping of disk drive actuator

2000-06-30

2002-05-21

Heinz, A. J. (Department: 2652)

Dynamic magnetic information storage or retrieval

Head mounting

For shifting head between tracks

Reexamination Certificate

active

06392845

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a disk drive, an actuator, and a stator magnet configuring a voice coil motor (hereinafter, a VCM) of the actuator, and in particular, to a configuration for improving a breathing phenomenon of a coil occurring during the operation of the VCM.
2. Description of the Related Art
FIG. 10
is a schematic of an actuator
100
used in a conventional hard disk drive. An actuator arm
101
is configured by a suspension
102
and a coil support part
103
in one piece, is rotatably supported by a rotary shaft
104
setting on a base (not shown), and is driven by a VCM, described later, in the direction shown by an arrow J or K.
A slider
109
is supported in an edge of the suspension
102
, and respective heads for reading and writing that are not shown are provided on this slider
109
. When the actuator arm
101
is positioned on a recording surface of a hard disk (not shown) rotating, the actuator
100
is configured so that the heads face the recording surface with keeping a predetermined gap between the recording surface and themselves by the slider
109
flying over the recording surface of the disk.
In the actuator arm
101
, the slider
109
is supported in the edge of the suspension
102
as described above. Nevertheless, a pair of coil supports
103
a
and
103
b
for sandwiching a flat coil
105
configuring the VCM is formed in the coil support part
103
positioned in the opposite side of the slider
109
against the rotation shaft
104
. A lower stator magnet retention plate
106
fixed on the base retains a stator magnet
107
below the flat coil
105
. The stator magnet
107
has a north pole
107
a
and a south pole
107
b
, and these are formed with making a boundary
107
c
a borderline. The VCM is configured by these flat coil
105
and stator magnet
107
, and the actuator
100
is configured by this VCM and the actuator arm
101
.
In the configuration described above, the flat coil
105
obtains a force in a rotational direction shown by an arrow H in each of the side edges
105
a
and
105
b
. This is because the flat coil
105
is located so that an electromagnetic action may occur between the flat coil
105
and stator magnet
107
. Therefore, the actuator arm
101
obtains a rotary force in a clockwise direction if current in the direction shown by an arrow m passes through the flat coil
105
. On the contrary, if the current passes through the flat coil
105
in the direction shown by an arrow n, the actuator arm
101
obtains a rotary force in the counterclockwise direction. This is because the flat coil
105
obtains a force in the rotary direction shown by an arrow I in each of the side edges
105
a
and
105
b.
On the other hand, an outer edge
105
c
of the flat coil
105
is not supported by the coil support part
103
because of lightening and miniaturizing the coil support part
103
, and further making a torque small. Nevertheless, the outer edge
105
c
receives a force in a radial direction shown by an arrow F or G according to the direction of the current passing and its rotary position.
FIGS. 11 and 12
are operational diagrams for explaining a force that the outer edge
105
c
of the flat coil
105
receives, but the suspension
102
of the actuator arm
101
(
FIG. 10
) is omitted.
FIG. 11
shows such a state that the actuator arm
101
is present at a position (hereinafter, this is called an OD position) where the actuator arm
101
rotates at most in the direction, shown by an arrow H, within its rotatable range. At this position, the outer edge
105
c
of the flat coil
105
is present above the north pole
107
a
of the stator magnet
107
. Therefore, if current in the direction shown by an arrow m passes through the flat coil
105
, the outer edge
105
c
receives a force in the direction shown by an arrow F that heads from the shaft center of the rotary shaft
104
to the outside. On the contrary, if current in the direction shown by an arrow n, the outer edge
105
c
receives a force in the direction shown by an arrow G that heads toward the shaft center of the rotary shaft
104
.
FIG. 12
shows such a state that the actuator arm
101
is present at a position (hereinafter, this is called an ID position) where the actuator arm
101
rotates at most in the direction, shown by an arrow I, within its rotatable range. At this position, the outer edge
105
c
of the flat coil
105
is present above the south pole
107
b
of the stator magnet
107
. Therefore, if current in the direction shown by an arrow m passes through the flat coil
105
, the outer edge
105
c
receives a force in the direction shown by an arrow G. On the contrary, if current in the direction shown by an arrow n, the outer edge
105
c
receives a force in the direction shown by an arrow F.
FIGS. 13 and 14
are drawings of analyzing the deformation of the flat coil
105
and coil supports
103
a
and
103
b
, sandwiching the flat coil
105
, when the flat coil
105
resonates at a predetermined frequency by alternately receiving forces in the directions shown by No arrows F and G, by numerical simulation using a finite-element method (FEM). As shown in
FIG. 13
, when the outer edge
105
c
of the flat coil
105
protrudes in the direction shown by an arrow F and hence the flat coil
105
is extended, an angle between the coil supports
103
a
and
103
b
sandwiching this decreases. On the other hand, as shown in
FIG. 14
, when the outer edge
105
c
of the flat coil
105
dents in the direction shown by an arrow G and hence the flat coil
105
is shrunk, an angle between the coil supports
103
a
and
103
b
sandwiching this increases.
Such a vibration mode wherein a coil is extended and shrunk is called a coil-breathing mode. A piezoelectric element
108
(
FIG. 10
) detects an amount of extension or shrinkage of the coil support
103
b
where the piezoelectric element
108
is fixed. In addition, as
FIG. 13
, the piezoelectric element
108
detects extension when the flat coil
105
is extended and hence the angle between the coil supports
103
a
and
103
b
decreases. Furthermore, the piezoelectric element
108
outputs, for example, plus voltage at a level according to the extension amount. On the contrary, as shown in
FIG. 14
, the piezoelectric element
108
detects shrinkage when the flat coil
105
is shrunk and hence the angle between the coil supports
103
a
and
103
b
increases. Furthermore, the piezoelectric element
108
outputs, for example, minus voltage at a level according to the shrinkage amount. In addition, a fixed position of the piezoelectric element
108
(
FIG. 10
) is determined so that it is possible to detect warpage occurring when the actuator arm
101
receives acceleration in a rotary direction.
FIGS. 15
a
and
15
b
show frequency characteristics of a transfer function from the drive current of the flat coil
105
to the output voltage of the piezoelectric element
108
in the actuator
100
(
FIG. 10
) configured as described above. In the frequency characteristic charts, the horizontal axis shows frequencies from 2 kHz to 16 kHz that are linearly graduated. In addition, the vertical axis in FIG.
15
(
a
) shows gains expressed in decibels, and the vertical axis in FIG.
15
(
b
) shows phases. Furthermore, dotted lines show frequency characteristics of a transfer function A
2
od(s) at the time when the actuator arm
101
is near the OD position shown in FIG.
11
. Moreover, continuous lines show frequency characteristics of a transfer function A
2
id(s) at the time when the actuator arm
101
is near the ID position shown in FIG.
12
.
As being apparent from
FIG. 15
, although the actuator
100
resonates at nearly 4 kHz, this is butterfly resonance caused by the warpage of the actuator arm
101
. In addition, although the phase largely changes near this frequency, two phases at different rotary positions of the actuator arm, that is, the OD position and ID position become the same.
On the other hand, resonance at nearly 10 kHz is coil-breathing resona

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