Metal working – Piezoelectric device making
Reexamination Certificate
1998-03-05
2001-05-22
Young, Lee (Department: 3729)
Metal working
Piezoelectric device making
C029S594000, C427S100000
Reexamination Certificate
active
06233801
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a mounting arrangement of acceleration detecting elements used in detecting impact.
BACKGROUND OF THE INVENTION
A conventional example of an acceleration detecting element is constituted by a bimorph element of a double end fixing type. For example, a conventional example of an acceleration sensor
20
a
, shown in
FIG. 11
in a simplified manner, includes a bimorph element
1
serving as an acceleration detecting element and an insulating case
2
containing the element positioned therein. The case is fixedly attached on a sensor attaching surface
3
such as a circuit board.
The bimorph element
1
is formed in a rectangular plate shape and is integrated by laminating two piezoelectric ceramics plates
6
. Each plate
6
has a signal electrode
4
and an intermediate electrode
5
formed on its top and bottom faces, respectively. The piezoelectric ceramics plates
6
are bonded to each other via the intermediate electrode
5
and are polarized along their thickness direction, each plate being polarized in a direction opposite to that of the other piezoelectric ceramics plate
6
. The broken line arrow marks in
FIG. 11
designate the directions of polarization. The respective signal electrodes
4
in this example are formed along the longitudinal direction of the respective piezoelectric ceramics plates
6
and are extended to both opposite end portions of each plate.
The insulating case
2
is constituted by a pair of clamp frames
7
having a channel-like shape when seen in a plan view, clamping together both longitudinal end portions in the thickness direction of the bimorph element
1
; and also by a pair of case lids
8
enclosing open faces formed by the bimorph element
1
and the clamp frames
7
arranged on opposite sides of the element. The respective signal electrodes
4
of the bimorph element
1
contained in the insulating case
2
are connected to external electrodes (not shown) formed at a pair of opposite outer end faces of the insulating case
2
.
An outer surface of the clamp frames
7
or the case lids
8
constituting the insulating case
2
is positioned and fixed on the sensor attaching surface
3
thereby attaching the acceleration sensor. The respective signal electrodes
4
of the bimorph element
1
are connected to wiring patterns (not shown) on the sensor attaching surface
3
via the external electrodes formed on the insulating case
2
. These wiring patterns are connected to a signal processing circuit (not shown). The signal processing circuit detects acceleration caused by impact by processing electric signals outputted from the acceleration sensor.
FIG. 12
shows another conventional example of such an acceleration detecting element which is different from the conventional example of
FIG. 11
in respect of its polarization.
FIG. 12
illustrates electrodes and the like in more detail than in the acceleration detecting element in FIG.
11
.
The acceleration sensor
20
b
includes piezoelectric ceramics bodies
23
in a rectangular plate shape on the main surfaces of which signal output electrodes
21
are formed and wherein an inner electrode
22
in parallel with the signal output electrodes
21
is embedded. Each of the signal output electrodes
21
is constituted by three surface electrodes
24
arranged separately at a center location and end locations along the longitudinal direction of the piezoelectric ceramics bodies
23
and a connecting electrode
25
covering parts of all three surface electrodes
24
.
An acceleration detecting element is constituted by the signal output electrodes
21
and the piezoelectric ceramics bodies
23
.
One side electrode
24
of the signal output electrodes
21
(one of those on the top side in
FIG. 12
) is extended to one outer end surface (on the left side in
FIG. 12
) of the piezoelectric ceramics bodies
23
. Also, one of the signal output electrodes
21
on the other side (the bottom side in
FIG. 12
) is extended to the other outer end surface (on the right side in FIG.
12
). Further, ceramics regions
26
and
27
constituting the piezoelectric ceramics bodies
23
, which oppose each other on opposite sides of the inner electrode
22
, are respectively divided into three portions in the longitudinal direction, namely, center portions
26
a
and
27
a
and end portions
26
b
and
27
b
, the center portions being divided from the end portions via boundaries where stresses caused by the operation of acceleration are changed. The center portions
26
a
and
27
a
and the end portions
26
b
and
27
b
are polarized in the thickness direction with senses different from each other by a polarization process using the inner electrode
22
and the surface electrodes
24
.
More specifically, the center portion
26
a
and the left and right end portions
26
b
constituting the ceramics region
26
are provided with senses of polarization which are different from each other, as indicated by the arrows H and I. Likewise, the center portion
27
a
and the left and right end portions
27
b
constituting the ceramics region
27
are provided with senses J and K of polarization which are different from each other, as indicated by the arrows J and K. Further, in this case, for example, the senses of polarization H and J of the center portions
26
a
and
27
a
are inward senses wherein the senses are directed toward each other, and the senses of polarization I and K of the end portions
26
b
and
27
b
are outward senses wherein the senses are directed apart from each other.
Both edges in the longitudinal direction of the acceleration sensor
20
b
are fixedly supported by a pair of clamp frames
28
having a channel-like shape when seen in a side view. The respective signal output electrodes
21
formed on main surfaces of the piezoelectric ceramics bodies
23
are connected to external output electrodes
29
and
30
formed on different outer end surfaces of the piezoelectric ceramics bodies
23
and the clamp frames
28
.
The acceleration sensor
20
b
having such a structure operates as follows. When acceleration operates on the acceleration sensor
20
b
, which includes the acceleration detecting element constituted by the signal output electrodes
21
and the piezoelectric ceramics bodies
23
, the center portions
26
a
and
27
a
and the end portions
26
b
and
27
b
in the ceramics regions
26
and
27
constituting the piezoelectric ceramics bodies
23
are deformed by the operation of inertial force. In this case the respective portions
26
a
,
27
a
,
26
b
and
27
b
receive tensile stresses or compressive stresses caused by the deformation. In the respective portions
26
a
,
27
a
,
26
b
and
27
b
an amount of charge generation is enhanced by a synergistic effect of the respective senses of polarization H through K and the received stresses, and an amount of charge generation of the overall acceleration sensor
20
b
is enhanced, which promotes the detection sensitivity of the acceleration sensor.
In the acceleration sensor
20
a
or
20
b
, a maximum electric signal is outputted when acceleration operates in a direction orthogonal to the surface of the piezoelectric ceramics plate
6
or
23
, that is, in the thickness direction. Further, an electric signal having the same maximum absolute value with an inverse plus/minus sign is outputted when acceleration operates in a sense inverse thereto, that is, rotated by 180°. In these cases, the direction of the operation of acceleration is in the direction causing the maximum sensitivity, that is, the maximum sensitivity direction P, which is called a main axis of the acceleration sensor. No electric signal is outputted when acceleration operates in a direction tangential to the surface of the piezoelectric ceramics plates
6
or
23
in the acceleration sensor
20
a
or
20
b
and accordingly, the detection sensitivity is nullified. Meanwhile, when acceleration operates in a direction between the orthogonal direction and the tangential direction, a detection sensitivity has a value corres
Inoue Jiro
Tabota Jun
Unami Toshihiko
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
Tugbang A. Dexter
Young Lee
LandOfFree
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