Measuring and testing – Fluid pressure gauge – Electrical
Reexamination Certificate
2002-06-20
2004-02-24
Oen, William (Department: 2855)
Measuring and testing
Fluid pressure gauge
Electrical
Reexamination Certificate
active
06694820
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a pressure sensor, and more particularly to a sensor electrode coated with an insulating body on a base plate, in which the dispersion in a coating thickness of the insulating body is decreased.
Referring to
FIGS. 3
to
6
, a related sensor of this type will be described below. In
FIG. 3
, a switch device
1
includes a pair of first electrodes
3
mounted on a base plate
2
, and a C-shaped second electrode
4
which is circumferentially arranged around the first electrodes
3
so as to be outwardly apart therefrom as shown in FIG.
4
. The first electrodes
3
and the second electrode
4
are covered with a resist
5
, and a pair of carbon electrodes
6
are provided on an upper face of the resist
5
and above the first electrodes
3
.
Moreover, there is provided a click rubber
7
above and opposed to the first electrodes
3
and the second electrode
4
. The click rubber
7
has a substantially cylindrical body
8
and a flexible leg
9
extending downwardly from an outer peripheral part of the cylindrical body
8
at a lower end thereof. In addition, a conductive rubber
10
substantially in a disc-like shape is provided in a center part of the lower end of the cylindrical body
8
. The conductive rubber
10
, the first electrodes
3
and the second electrode
4
constitute an electrostatic capacitance sensor
13
.
Further, a button
11
is mounted on an upper face of the click rubber
7
. An upper cover
12
for covering an upper part of the click rubber
7
, the first electrodes
3
and the second electrode
4
is provided to press down at a bottom parts
9
a
of the flexible leg
9
of the click rubber
7
, so that an upper part of the button
11
is projected through an opening
12
a
which is formed in an upper part of the upper cover
12
.
FIG. 5
shows a sensor circuit
14
of the switch device
1
. The sensor circuit
14
includes a resistor
16
for setting a resistance constant connected to a line extending from a clock power source
15
, and the resistor
16
is connected to one of input terminals of the Exclusive OR gate
17
. Then, an end of the sensor
13
is connected to the line between the resistor
16
and the Exclusive-OR gate
17
. The sensor
13
is composed of a capacitor
18
and a switch
19
connected in series, and the other end of the sensor
13
is grounded.
On the other hand a resistor
20
for setting a resistance constant os connected to another line extending from the clock power source
15
, and the resistor
20
is connected to the other input terminal of the Exclusive-OR gate
17
.
In this state, the capacitor
18
corresponds to a circuit constituted by the conductive rubber
10
, the first electrodes
3
and the second electrode
4
, while the switch
19
corresponds to a circuit constituted by the conductive rubber
10
and the carbon electrodes
6
.
Incidentally, when the button
11
is depressed, the flexible leg
9
of the click rubber
7
is flexed so that the conductive rubber
10
of the click rubber
7
is brought into contact with the carbon electrodes
6
to establish electrical connection between the carbon electrodes. As the button
11
continues to be pushed down, the conductive rubber
10
is pushed against the first electrodes
3
and the second electrode
4
which is covered with the resist
5
. According to the pressure contact, electrostatic capacitance in the conductive rubber
10
is varied so that output from the conductive rubber
10
is thereby changed.
In other words, after the switch
19
is turned on in the circuit
14
, the output of the Exclusive-OR gate
17
is changed in accordance with the variation of the electrostatic capacitance of the capacitory
18
.
FIG. 6
is a graph showing the relationship between pressure of the sensor provided by bringing the conductive rubber
10
into contact with the resist
5
and the output level therefrom. As shown by a solid line, the output level rises substantially in proportion to a rise of the pressure.
Howerver, in
FIG. 6
, there exists disersio
0
n in the output level for the pressure of the respective sensors
13
as shown by dotte lines. The dispersion may incur instability of the output level for the pressure of the sensor
13
so that reliabilty as the sensor
13
may be deteriorated.
It is considered that dispersion in a coating thickness of the resist
5
covering the first electrodes
3
and the second electrode
4
is one of the causes of the dispersion in the output level for the pressure. In fact, when the resist
5
having a coating thickness of 10 &mgr;m are resist-printed on copper patters of the first electrodes
3
and second electrode
4
, a coating thickness of the printed resist
5
will be 8 &mgr;m to 16 &mgr;m, and the dispersion in the output level for the pressure will occur.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a pressure sensor in which the dispersion in the output level for the pressure of the pressure sensor is decreased.
In order to achieve the above object, according to the present invention, there is provided a pressure sensor comprising:
a base plate;
a first electrode, formed on the base plate;
a insulating laminate material, which coats the first electrode;
a conductive rubber; and
a click rubber, on which the conductive rubber is attached, for bringing the conductive rubber into a pressure contact with the first electrode coated with the insulating laminate material.
Preferably, a coating thickness of the insulating laminate material is substantially constant.
Preferably, the first electrode is formed into a C-shape in a plane view.
In this configurations, the dispersion in the output level for the pressure of the pressure sensor can be decreased.
REFERENCES:
patent: 4533604 (1985-08-01), Honda et al.
patent: 4970446 (1990-11-01), Yaguchi
patent: 5045829 (1991-09-01), Kuramochi et al.
patent: 5090246 (1992-02-01), Colla et al.
patent: 5948990 (1999-09-01), Hashida
Mitsumi Electric Co. Ltd.
Oen William
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