Electrostatic capacitance sensor

Details Electrostatic capacitance sensor Electrostatic capacitance sensor

2002-04-19

2004-09-14

Nguyen, Vincent Q. (Department: 2858)

Electricity: measuring and testing

Impedance, admittance or other quantities representative of...

Lumped type parameters

C324S686000, C324S687000, C361S283300, C361S283400

Reexamination Certificate

active

06791342

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an electrostatic capacitance sensor, and more particularly to the electrostatic capacitance sensor in which a conductive rubber is abutted against electrodes covered with a resist, thereby to vary electrostatic capacitance of the conductive rubber, and to change output level with the variation of the electrostatic capacitance.
Referring to
FIGS. 4
to
7
, a related electrostatic capacitance sensor of this type will be described. In
FIG. 4
, a switch device
1
includes a pair of first electrodes
3
mounted on a base plate
2
, and a second electrode
4
in a C-shape as seen in a plan view which is circumferentially arranged around the first electrodes
3
so as to be apart therefrom. The first electrodes
3
and the second electrode
4
are covered with a resist
5
, and a pair of carbon electrodes
6
are mounted 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 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
.
FIGS. 5A and 5B
show particulars of the first electrodes
3
and the second electrode
4
. The first electrodes
3
are provided in a center of the C-shaped second electrode
4
so as to be apart from each other. The carbon electrodes
6
are mounted above the first electrodes
3
which are covered with the resist
5
. Lead lines
14
are respectively connected to the carbon electrodes
6
, and the one end of the one lead line
14
is grounded. Moreover, a lead line
15
is connected to the second electrode
4
. A two dotted chain line in
FIG. 5A
represents a range of an area upon which the conductive rubber
10
is brought into contact.
FIG. 6
shows a circuit
16
of the switch device
1
. The circuit
16
includes a clock power source
17
, resistors
18
,
19
, an ENOR gate
20
(also known as an exclusive NOR or XNOR gate), and an electrostatic capacitance sensor
13
. The electrostatic capacitance sensor
13
is composed of a capacitor
21
and a switch
22
connected in series. The resistors
18
,
19
are respectively connected to the clock power source
17
. The other end of the resistors
18
,
19
are respectively connected to two input terminals of the ENOR gate
20
. Then, one end of the electrostatic capacitance sensor
13
is connected to the resistor
18
and the ENOR gate
20
, and the other end of the electrostatic capacitance sensor
13
is grounded.
In this state, the capacitor
21
corresponds to a circuit constituted by the conductive rubber
10
, the first electrodes
3
and the second electrode
4
, while the switch
22
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 conduction between the carbon electrodes
6
. 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 are covered with the resist
5
. According to the pressure contact, the 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
22
has been turned on in the circuit
16
, the output of the ENOR gate
20
is changed in accordance with the variation of the electrostatic capacitance of the capacitor
21
.
FIG. 7
is a graph showing relationship between pressure of the electrostatic capacitance sensor
13
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.
However, in
FIG. 7
, there exists dispersion in the output level for the pressure as shown by dotted lines so that the output levels are deviated from an ideal output levels as shown by solid lines. The dispersion may incur instability of the output level of the electrostatic capacitance sensor
13
so that reliability as the electrostatic capacitance sensor
13
may be deteriorated.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an electrostatic capacitance sensor in which the dispersion of the output level for the pressure of the electrostatic capacitance sensor is decreased in order to stabilize the output level thereof.
In order to achieve the above object, according to the present invention, there is provided an electrostatic capacitance sensor comprising:
a base board;
an electrode, formed on the base board;
a resist, which covers the electrode;
a conductive rubber, including:
a first face having a first area, which is opposed to the resist; and
a second face which is opposed to the first face, the second face having a second area which is larger than the first area; and
a flexible click rubber, on which the second face of the conductive rubber is attached, for providing pressure contact of the conductive rubber with respect to the resist.
Preferably, the first face and the second face are parallel with each other, and a sectional area of the conductive rubber perpendicular to a direction in which the pressure contact is provided, is made minimum at the first face.
Here, it is preferable that a form of the conductive rubber is shaped into a frustum.
Preferably, a form of the conductive rubber is shaped into a frustum of a circular cone.
Preferably, a peripheral end portion of the first face of the conductive rubber is chamfered.
According to the present invention, there is also provided an electrostatic capacitance sensor comprising:
a base board;
an electrode, formed on the base board;
a resist, which covers with the electrode;
a conductive rubber, which is shaped into a semispherical shape; and
a flexible click rubber, on which a flat face portion of the semispherical conductive rubber is attached, for providing pressure contact of the semispherical conductive rubber with respect to the resist.
In the above configurations, dispersion in the output levels generated with a deformation of the conductive rubber of the electrostatic capacitance sensor can be decreased, and stabilization of the output levels can be attained.


REFERENCES:
patent: 6184865 (2001-02-01), Zimmerman et al.
patent: 6373265 (2002-04-01), Morimoto et al.

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