Measuring and testing – Specimen stress or strain – or testing by stress or strain... – Specified electrical sensor or system
Reexamination Certificate
2001-03-08
2003-03-18
Noori, Max (Department: 2855)
Measuring and testing
Specimen stress or strain, or testing by stress or strain...
Specified electrical sensor or system
Reexamination Certificate
active
06532824
ABSTRACT:
TECHNICAL FIELD
This invention relates to a strain sensor formed on a surface of an elastic body for detecting strain produced due to bending of the elastic body and, in particular, to a capacitive strain sensor for detecting the produced strain as a change in capacitance, to a method of using the same for detecting an internal pressure of a hollow-cylindrical closed container made of the above-mentioned elastic body with reference to expansion/depression in its upper flat end portion, for detecting cylinder torsion produced on an outer peripheral surface of a bar-like cylindrical elastic body, and for detecting an acceleration, and to a method of detecting the strain and correcting the same.
BACKGROUND ART
As a strain sensor formed on a surface of an elastic body for detecting strain produced due to bending of the elastic body, there has been well known a so-called strain gauge having an electric resistance changing in value in response to the strain.
FIG. 1
is a perspective view showing an example of the state of use of a conventional strain sensor.
FIG. 2
is a perspective view showing an example of a strain gauge used as the conventional strain sensor.
In
FIG. 1
, a cylindrical elastic body
20
is placed on one surface of a mount table
10
with a strain gauge
30
A adhered to a center area of an upper end surface
21
of the elastic body
20
and a strain gauge
30
B adhered to an outer peripheral side surface
22
so that its strain detection axis is inclined by 45° with respect to a center axis direction of the elastic body
20
to coincide with a strain direction.
The strain gauge
30
shown in
FIG. 2
is one identical with the strain gauges
30
A and
30
B shown in FIG.
1
and comprises a resistance wire
31
having a parallel-line thin film pattern made of an Fe—Ni alloy and formed by making a plurality of turns, and terminals
32
and
33
arranged at opposite ends thereof.
At first, the strain sensor
30
A shown in
FIG. 1
will be described in connection with the case where the cylindrical elastic body
20
is a closed container and the strain sensor is used in detecting an internal pressure of the closed container elastic body
20
.
When the internal pressure of the closed container elastic body
20
is increased from a normal condition, the closed container elastic body
20
is deformed and expands in the upper end surface
21
, the outer peripheral side surface
22
and a lower end surface thereof. When the internal pressure of the closed container elastic body
20
is decreased from the normal condition, the elastic body
20
is deformed and is depressed in the upper end surface
21
, the peripheral side surface
22
and the lower end surface thereof. Accordingly, if the wall thickness of the upper end
21
with the strain gauge
30
A adhered thereonto is slightly reduced within a safety range as compared with those of the peripheral side and the bottom end, the variation in internal pressure can be converged to the deformation of the upper end
21
.
The strain gauge
30
shown in
FIG. 2
is a sensor in which a resistance value of a conductor formed in the thin film pattern changes under the strain applied thereto. When the internal pressure of the closed container elastic body
20
shown in
FIG. 1
is varied, the upper end
21
is at first deformed so that the strain gauge
30
A adhered thereto is similarly deformed. This results in variation in electrical resistance between the both terminals
32
and
33
of the resistance wire
31
of the strain gauge
30
. Thus, it is possible to detect the internal pressure of the closed container made of the elastic body
20
.
Next, the strain sensor
30
B shown in
FIG. 1
will be described in connection with the case where the elastic body
20
having a cylindrical shape, that is, the cylindrical elastic body
20
is a cylinder having a circular-shaped cross section in the outer peripheral surface and the strain sensor is used in detecting torsion of the cylinder.
In the above-mentioned state, it is assumed that the torsional strain of the cylindrical elastic body
20
is detected by the use of the strain gauge
30
B. When a torsional moment is applied to the cylindrical elastic body
20
to produce the torsional strain in the cylindrical elastic body
20
, an extension strain in a direction inclined by 45° with respect to the center axis direction of the cylindrical elastic body
20
and a compressive strain in a direction perpendicular thereto are produced at the portion where the strain gauge
30
is adhered. Therefore, it is possible to detect the torsional strain of the cylindrical elastic body
20
by detecting the change in resistance value depending on the extension strain and the compressive strain.
On the other hand, the strain sensor can be used as an acceleration sensor. The acceleration sensor is used in detecting the vibration of a car and the acceleration upon collision thereof, the vibration and the acceleration applied to an electronic apparatus when it is carried, and the abnormal vibration of a motor and various kinds of machines. In order to detect the vibration and the impact of those machines, many kinds of acceleration sensors have been used. Depending on the magnitude and a frequency range of the acceleration to be detected, use has been made of a selected one of the acceleration sensors which is suitable for the application.
Next, referring to
FIGS. 3
to
5
, description will be made about a conventional acceleration sensor which is used, for example, in detecting the vibration caused by knocking of a car engine or the vibration of a machine.
An acceleration sensor
40
shown in
FIG. 3
has a structure in which two piezoelectric rings
41
and
42
are stacked so that their polarization directions are opposite to each other and are fixed by a fixing screw
44
together with a weight
43
comprising a hollow metal cylinder, and is used in detecting the acceleration of the order of several Gal to several tens of Gal. The acceleration sensor
40
is provided with a case
45
generally connected to the ground, specifically, connected via a mounting screw
47
to a ground terminal of an object to be detected, together with a terminal
46
similarly grounded.
In the acceleration sensor
40
of
FIG. 3
, when an acceleration &agr;
4
is applied from the outside, the piezoelectric rings
41
and
42
are subjected to the force “F
4
=M
4
&agr;
4
”. Herein, M
4
represents the mass of the weight
43
. Each of the piezoelectric rings
41
and
42
is an element which produces an electric voltage under a pressure applied thereto, as is self-explanatory, and produces the electric voltage given by “V=k·g·F
4
”. Herein, “k” and “g” represent a constant determined by the shape and the size of the acceleration sensor and another constant determined by a piezoelectric material, respectively. Thus, the principle of an operation of a piezoelectric-type acceleration sensor represented by the acceleration sensor
40
shown in
FIG. 3
is that an applied acceleration acts on the weight
43
to produce a force and the piezoelectric rings
41
and
42
are deformed under the force to produce the electric voltage.
Recently, development has been made of a capacitive acceleration sensor of a so-called micromachine type produced by making the most of a semiconductor micromachining technique. This sensor can detect the acceleration on a d.c. basis and can accommodate a wide range from a small acceleration not greater than 1 Gal to a large acceleration of several tens of Gal upon collision of the car by designing a resonant frequency of a mechanical vibration system and a mechanical strength of each part to meet such a requirement.
FIG. 4
is a schematic perspective view showing an example of a structure of a capacitive acceleration sensor
50
using the micromachining technique. The capacitive acceleration sensor
50
comprises an Si single crystal plate
51
which is formed, by a surface micromachining technique, with movable electrodes
55
(X) integral with a movable plate
54
which serves as a
Mori Kazuya
Ueno Toru
Yoshida Tetsuo
Frishauf Holtz Goodman & Chick P.C.
Noori Max
Tokin Corporation
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