Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SPECIFICATION
TITLE OF THg INVENTION
ELECTROSTATIC CAPACITY SENSOR .
IrI OF THE INVErPrION
The present invention relates to an electrostatic capacity
sensor.
BACKGRODND OF TIC INVBrITI~N
An electrostatic capacity sensor which is capable of detecting
approach of an ob ject to be detected has been known . A conventional
electrostatic capacity sensor is provided with an electrode part
and a detection circuit which is connected to the electrode part.
The electrode part is constructed from a detection electrode for
detecting approach of an object to be detected (hereinafter, this
is also referred to simply as "object" ) and a ground electrode grounded
to a predetermined part.
In such an electrostatic capacity sensor, the capacitance of
the detection electrode is increased as the object approaches the
detection electrode. In this way, approach of the object is sensed
by detecting the change in the capacitance of the detection electrode
with the detection circuit.
Practically In reality, however, in the electrostatic capacity
sensor, not only the capacitance of the detection electrode, but also
the capacitance of the electrode part and the capacitance of the
detection circuit and the like are also detected. Moreover, the
capacitance varies with the changes in the ambient conditions such
as the temperature and humidity, or vibration, which act as noises
in the measurement. Because of this, the conventional electrostatic
capacity sensor has low detection precision. Besides, the
electrostatic capacity sensor is liable to malfunction when the
ambient conditions vary., In particular, when the electrostatic
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capacity sensor is.used in outdoors, the detection precision is
deteriorated further since the temperature and the humidity vary
drastically with the season, time of the day, weather, or the like.
Furthermore, in the conventional electrostatic capacity sensor,
the sensitivity of the electrode part itself is low and unstable,
so that it has been difficult to increase the detection distance from
the detection electrode to an object to be detected (hereinafter,
referred to as "detection distance").
In particular, the variations in the capacitance of the
electrode part due to the changes in the ambient conditions become
larger in the case where the detection plane of the detection electrode
has a large area. As a result, noises are increased, so that the
detection precision of the electrostatic capacity sensor is reduced.
Further, when the area of the detection plane of the detection
electrode is relatively large, the threshold of the detection circuit
should be set at a high level in order to improve the detection
precision. However, this increases influence of noise, so that it
is difficult to set the detection distance at a sufficiently large
value.
bUMdAtiY Ulr ltil~ II~IVENTIUN
It is an object of the present invention, irrespective of the
size of the detection electrode, to provide an electrostatic capacity
sensor with high detection precision and high sensitivity.
In order to achieve the above object, the electrostatic
capacity sensor according to the present invention comprises an
electrostatic capacity type detection element in which a detection
electrode, a ground electrode and a charge plate interposed between
the detection electrode and the ground electrode are arranged in a
state that they are isolated to each other; a detection circuit for
detecting changes in capacitance of the detection electrode caused
by an object to be detected;, and a power supply for supplying electrical
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power to the detection circuit.
It is preferable that the ground electrode is electrically
connected to a negative termtnal of the power supply.
The ground electrode may be electrically connected to a
negative terminal of the power supply via a relay circuit. In this
case, it is preferable that the relay circuit includes a resistor.
Further, it is more preferable that the resister is a variable
resister.
Moreover, it is preferable that the relay circuit includes a
capacitor. Further, it is more preferable that the capacitor is a
variable capacitor. In this case, the relay circuit has a function
that adjusts sensitivity of the electrostatic capacity sensor.
Further, the relay circuit also has a function that stabilizes
sensitivity of the electrostatic capacity sensor.
In the electrostatic capacity sensor according to the present
invention, the sensitivity of the electrostatic capacity sensor Can
be adjusted by adjusting the distance between the charge plate and
the ground electrode.
It is preferable that the distance between the charge plate
and the ground electrode is set so as. to be larger than the distance
between the detection electrode and the charge plate.
Moreover, it is also preferable that the detection electrode
has a first surface that functions as a detection plane and a second
surface which is opposite to the first surface. and the detection
circuit is provided on the second surface of the detection electrode.
Further, it is also preferable that a plurality of charge plates
are arranged along the direction of the thickness of the detection
element.
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BRIEF D$SCRIPTION OF THE DRAWING6
Fig. 1 is a schematic side view showing a first embodiment of
an electrostatic capacity sensor according to the present invention.
Fig. 2 is a block diagram showing an example of configuration
of the detection circuit of the electrostatic capacity sensor
according to the present invention.
Fig. 3 is a schematic side view showing a second embodiment
of the electrostatic capacity sensor according to the present
invention.
Fig. 4 is a schematic side view showing a third embodiment of
the electrostatic capacity sensor according to the present
invention.
Fig. 5 is a schematic side view showing a fourth embodiment
of the electrostatic capacity sensor according to the present
invention.
Fig. 6 is a schematic side view showing a fifth embodiment of
the electrostatic capacity sensor according to the present
invention.
Fig. 7 is a schematic side view showing a sixth embodiment of.
the electrostatic capacity sensor according to the present
invention.
Fig. 8 is a schematic side view showing a seventh embodiment
of the electrostatic capacity sensor according to the present
invention.
Fig. 9 is a schematic side view showing an eighth embodiment
of the electrostatic capacity sensor according to the present
invention.
Fig. 10 is a schematic side view showing a ninth embodiment
of the electrostatic capacity sensor according to the present
lllvention .
Fig. 11 is a schematic side view showing a 10th embodiment of
the electrostatic capacity sensor according to the present invention.
Fig. 12 is a schematic side view showing an 11th embodiment
of the electrostatic capacity sensor according to the present
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invention.
Hereinbelow, an electrostatic capacity sensor according to
the present invention will be described in detail based on the
preferred embodiments illustrated in the accompanying drawings.
Fig. 1 is a schematic side view showing a first embodiment of
the electrostatic capacity sensor of this invention.
As shown in Fig . 1, an electrostatic capacity sensor la includes
an electrostatic capacity type detection element (electrode part)
2, a circuit board 6 on which a detection circuit is mounted, and
a power supply (DC power supply) 7.
The detection element 2 is mainly composed of a detection
electrode 3, a charge plate 4 and a ground electrode 5. The charge
plate 4 is positioned between the detection electrode 3 and the ground
electrode 5. The detection electrode 3, the charge plate 4 and the
ground electrode 5 are arranged in a state that they are isolated
to each other. In this case, it is preferable that the detection
electrode 3 , the charge plate 4 and the ground electrode 5 are arranged
in parallel with each other.
The detection electrode 3, the charge plate 4 and the ground
electrode 5 are supported at their end portions by support members
made of an insulating material ( not shown in the drawings ) . In this
embodiment, a space is formed between the detection electrode 3 and
the charge plate 4, and between the charge plate 4 and the ground
electrode 5, respectively.
In this invention, an insulating layer (for example,
plate-like insulating member) which mutually isolates the detection
electrode 3 and the charge plate 4 may be interposed therebetween.
Similarly, an insulating layer may be interposed between the charge
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plate 4 and the ground electrode 5.
In this embodiment, the detection electrode 3 is formed into
a plate shape, but no particular limitation is imposed upon the shape
of the detection electrode 3.
For the constituent material of the detection electrode 3,
there are no particular limitations. Various kinds of metallic
materials or conductive materials can be employed so long as they
can function as a detection electrode. Examples of the constituent
material for the detection electrode 3 include an aluminunn, an
aluminum alloy, a copper, a copper alloy, a stainless steel, a
conductive film, a conductive rubber, a conductive vinyl chloride
and the like.
In this embodiment, the charge plate 4 is formed into a plate
shape , but no particular limitation is imposed upon the shape of the
charge plate 4.
For the constituent material of the charge plate 4 , there are
no particular limitations. Various kinds of metallic materials or
conductive materials can be employed so long as they can function
to store sufficient amount of electric charge as a charge plate.
Examples of the constituent material for the charge plate 4 include
an aluminum, an aluminum alloy, a copper, a copper alloy, a stainless
steel, a conductive film, a conductive rubber, a conductive vinyl
chloride and the like.
In this embodiment, the ground electrode 5 is formed into a
plate shape, but no particular limitation is imposed upon the shape
of the ground electrode 5.
For the constituent material for the ground electrode 5 , there
are no particular limitations . Various kinds of metallic materials
or conductive materials can be employed so long as they can function
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as a ground electrode. Examples of the constituent material for
the ground electrode 5 include an aluminum, an aluminum alloy, a
copper, a copper alloy, a stainless steel, a conductive film, a
conductive rubber, a conductive vinyl chloride and the like.
Further, examples of the constituent material for the
insulating material and the insulating layer mentioned above include
various kinds of resin materials and the like.
As described in the above, since the detection element 2 of
the electrostatic capacity sensor la has the charge plate 4, it is
considered that a capacitor is formed between the detection electrode
3 and the charge plate 4. This charge plate 4 supplies charge to
the detection electrode 3 or absorbs charge from the detection
electrode 3 in response to the amount of charge stored in the detection
electrode 3 ( in other words , the charge plate 4 functions as a charge
supply and absorption part for the detection electrode 3 j _ In this
way, certain amount of charge can always be quickly replenished and
stored, so that the sensitivity of the detection element 2 can be
improved and stabilized.
Further, it is considered that serially connected two
capacitors are formed between the detection eleotrode 3 and the charge
plate 4 and between the charge plate 4 and the ground electrode 5,
respectively. With this result, the capacitance of each capacitor
is lowered in comparison with the case when no charge plate is provided.
Therefore, noises generated by the variations in the capacitance
caused by the changes in the ambient conditions (such as changes in
the temperature or humidity and vibration and the like ) is reduced .
In other words, since the ratio of the signal to noise generated by
the changes in the ambient conditions ( the ratio of S/N) is increased,
the detection precision of the electrostatic capacity sensor la is
improved.
The circuit board 6 is provided on the plane 32 opposite to
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the detection plane 31 of the detection electrode 2. In this case,
the circuit board 6 is insulated from the charge plate 4.
Since the circuit board 6 is provided on the opposite plane
32 of the detection electrode 3 as described above, it is considered
that two capacitors are additionally formed between the circuit
board 6 and the detection electrode 3 and between the circuit board
6 and the charge plate 4, respectively. These capacitors are also
considered to be a part of a serially connected plurality of
capacitors (which are comprised of the capacitors formed between the
object 9 and the detection electrode 3, between the detection
electrode 3 and the charge plate 4, and between the charge plate 4
and the ground electrode 5, respectively). Accordingly. the circuit
board 6 is not likely to be affected by the changes in the ambient
conditions, and this means that the detection precision of the
electrostatic capacity sensor la is not likely to be affected by
the changes in the ambient conditions.
Besides, since the circuit board 6 is not provided on the
detection plane 31 of the detection electrode 3, it is possible to
make the detection surface 31 planar.
The detection circuit provided in the circuit board 6 is
connected electrically to a positive terminal 71 and a negative
terminal 72 of the power supply 7, and power is supplied from the
power supply 7 to the detection circuit. Hereinafter, "electrical
connection" will be simply referred to as "connection°. The
detection circuit will be described in more detail later.
Now, in the case where a detection element of an electrostatic
capacity sensor includes a detection electrode which has the area
of the detection plane of mere than 30 cmZ, in particular more than
100 cm2, and in more particular more than 300 cmz, it is necessary
to further reduce the variations of the capacitance of the detection
electrode 3 due to changes in the ambient conditions . However, since
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the detection element 2 in this invention has the charge plate 4,
it is possible to suppress the variations in the capacitance of the
detection electrode 3 due to the changes in the ambient conditions
as mentioned above.
Hereinafter, the detection distance from the detection plane
31 of the detection electrode 3 to the object 9 is referred to as
"L1° . The distance between the detection electrode 3 and the charge
plate 4 is referred to as "L2" . The distance between the charge plate
4 and the ground electrode 5 is referred to as "L3".
In the electrostatic capacity sensor la, the sensitivity of
the detection element (the sensitivity of the electrostatic capacity
sensor la) is more improved as the distance L, is set to be a larger
value. As a result, it is possible to increase the detection distance
Ll. This is due to the following reasons. The capacitance of the
capacitor formed by the charge plate 4 and the ground electrode 5
is reduced if the distance L3 is set to be a larger value. Therefore,
the discharge of the charge on the charge plate 4 to the ground
electrode 5 is suppressed, and the migration of the charge on the
charge plate 4 to the detection electrode 3 is facilitated. In this
way, a certain amount of charge is stored quickly and surely on the
detection electrode 3.
For this reason, the distance L, between the charge plate 4
and the ground electrode 5 is preferably sat to be larger than the
distance L2, and more preferably set so as to be larger than twice
L2.
Moreover, in the electrostatic capacity sensor la, the
sensitivity of the detection element 2 (the sensitivity of the
electrostatic capacity sensor la) can be adjusted by adjusting the
distance L3. Further, the detection distance Ll can be also adjusted
by adjusting the sensitivity of the detection element 2, as will be
described later.
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In this case, with the increase in the distance L,, the
sensitivity of the detection element 2 is improved. On the other hand,
however, the detection precision of the electrostatic capacity sensor
la deteriorates. Therefore, it is necessary that the distance L3
should be appropriately determined by taking this fact into
consideration.
Furthermore, in order to realize an electrostatic capacity
sensor of the reduced size having the equivalent performance with
those of the electrostatic capacity sensors described above, it is
pref erred that each of the detection electrode 3 , the charge plate
4 and the ground electrode 5 is formed so as to have substantially
the same area.
In providing the electrostatic capacity sensor la, the ground
electrode 5 is fixed at a predetermined position of the attaching
part 8. In this case, the ground electrode 5 is grounded to the
attaching part 8 or directly to the earth, or grounded to the earth
via the attaching part 8.
Next, the detection circuit of the electrostatic capacity
sensor la will be described. Fig. 2 is a block diagram showing an
example of configuration of the detection circuit la of the
electrostatic capacity sensor 1a.
As shown in Fig. 2, a detection circuit 60 generally includes
a pulse signal generation circuit 61, a resistor 62, a differential
amplifier 64, an AC-DC converter 65 which converts an AC voltage to
a DC voltage, and a comparator 66.
The pulse generation circuit 61, the resistor 62, the
differential amplifier 64 , the AC-DC converter 65 and the comparator
66 are connected in this order.
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The detection electrode 3 is connected to one end of the
resistor 62 . The resistor 62 and the detection electrode 3 ( detection
element 2) form an attenuator 63.
The pulse signal generating circuit 61 outputs a pulse signal
with voltage Vl. This pulse signal from the pulse signal generating
circuit 61 is inputted to the attenuator 63 and the negative terminal
of the differential amplifier 64, respectively. The capacitance C
of the detection electrode 3 (in other words, capacitance of the
detection element 2) is increased as the object approaches the
detection plane 31 of the detection electrode 3. On the other hand,
The capacitance C is decreased as the object moves away from the
detection plane 31 of the detection electrode 3.
Further, in response to the capacitance C of the detection
electrode 3, the output signal from the pulse signal generation
circuit 61 is attenuated by the attenuator 63. The attenuated output
signal from the attenuator 63 is inputted to the positive terminal
of the differential amplifier 64. In'this case, the attenuator 63
outputs the signal with voltage VZ ("voltage VZ° is potential
difference of the earth and the detection electrode 3).
The differential amplifier 64 amplifies the difference between
the voltages V1 and VZ, and outputs a signal with voltage V3. This
output signal from the differential amplifier 64 is inputted to the
AC-DC converter 65 where it is converted from an AC voltage into a
DC voltage. The AC-DC converter 65 outputs the signal with voltage
V4 .
The output signal is inputted into the comparator 66 to be
compared with a predetermined threshold ( reference voltage ) set in
advance. When the voltage V, is greater than the threshold, a
high-level signal (H) is outputted from the comparator 66. On the
other hand, when the voltage V4 is smaller than the threshold, a
low-level signal (L) is outputted from the comparator 66.
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As the object 9 approaches the detection plane 31 of the
detection electrode 3, the capacitance C of the detection circuit
3 is increased. This causes the voltage VZ of the output signal from
the attenuator 63 to be decreased. Further, as the voltage Vz is
decreased, the voltage V3 of the output signal from the differential
amplifier 64 is increased. This causes the voltage V4 of the output
signal from the AC-DC converter 65 to be increased. Accordingly,
a low level signal (L) is outputted from the detection circuit 60
until the voltage V, becomes equal to the threshold . Then , when the
voltage V, exceeds the threshold, a high-level signal (H) is output
f..rom the detection circuit 60. Therefore, this detection signal can
be utilized for detecting the approach of the object 9.
In this electrostatic capacity sensor la, the detection
distance L1 is determined depend upon the combination of the
sensitivity of the detection element 2 and the threshold. In this
case, it is preferred that the adjustment of the detection distance
L1 is carried out by adjusting the sensitivity of the detection
element 2 appropriately under the state that the threshold is being
sat at a predetermined level. This is due to the following reasons.
In order to make the threshold variable, it is necessary for
the comparator 66 to have a variable resistor for adjusting the
threshold. However, since the variable resistor has a relatively
large capacitance , the variations in the capacitance of the variable
resistor due to the changes in the ambient conditions are liable to
appear as noises . These noises give adverse effects to the detection
of the capacitance of the detection electrode 3 in some cases. On
the other hand, however, in the case where the threshold is set
to be a predetermined value, the variable resister can be
eliminated from the comparator 66. With this result, it is possible
to suppress the generation of such noises, so that the detection
precision of the electrostatic capacity sensor la can be improved.
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As described in the above, according to this electrostatic
capacity sensor la, since the detection element 2 has the charge plate
4, it is possible to improve the sensitivity of the detection element
2, thereby increasing the detection distance Ll. In addition, the
variations in the capacitance of the detection element 2 due to the
changes in the ambient conda.tions can be reduced . As a result , the
ratio of the signal to noise ( the ratio of S/N) is increased, so that
the detection precision of the electrostatic capacity sensor 1a is
improved.
Next, a second embodiment of the electrostatic capacity sensor
according to the present invention will be described.
Fig. 3 is a schematic side view showing the second embodiment
of the electrostatic capacity sensor of this invention. In the
following, the structures and elements of this embodiment which
are in common with those of the above-mentioned electrostatic capacity
sensor la will be omi..tted, and only the principal differences
therebetween will be described.
As shown in Fig. 3, in an electrostatic capacity sensor 1b,
the ground electrode 5 is connected to the negative terminal 72 of
the power supply 7. The remaining construction of the electrostatic
capacity sensor 1b is almost the same as in the electrostatic capacity
sensor la of the first embodiment described above.
In this electrostatic capacity sensor 1b, it is possible to
discharge the charge more effectively from the ground electrode 5
than in the case where the ground electrode 5 is not connected to
the negative terminal 72 of the power supply 7. In this way, the
sensitivity of the detection element 2 is improved.
In addition, the ground electrode 5 becomes substantially free
from the influence of charges existing in the atmosphere and the
influence of the capacitance existing between the earth and the ground
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electrode (for example, the capacitance in and around the attaching
table 8 ) . Therefore , the noise due to variations of the capacitance
is reduced, so that the detection precision of the sensor 1b is
improved.
Moreover, according to the electrostatic capacity sensor 1b,
the detection element 2 has the charge plate 4 in the same manner
as the above-mentioned electrostatic capacity sensor la. Therefore,
the sensitivity of the detection element 2 can be improved, so that
the detection distance L1 can be increased. In addition, the
variations in the capacitance of the detection element 2 due to the
changes in the ambient conditions are reduced. In this way, the ratio
of S/N is increased, thereby enabling to improve the detection
precision of the electrostatic capacity sensor 1b.
Next , a third embodiment of the electrostatic capacity sensor
according to the present invention will be described.
Fig. 4 is a schematic side view showing the third embodiment
of the electrostatic capacity sensor lc of this invention. In the
following, the structures and elements of this embodiment which
are in common with those of the above-mentioned electrostatic capacity
sensor 1b are omitted, and only the principal differences
therebetween will be described.
As shown in Fig. 4, in an electrostatic capacity sensor lc,
the ground electrode 5 is connected to the negative terminal 72 of
the power supply 7 via a relay circuit 11. It is preferable that
the relay circuit 11 is arranged apart from the detection element
2 by a predetermined distance so that its capacitance does not give
any influence to the detection circuit 6O. The remaining
construction of the electrostatic capacity sensor lc is almost the
same as in the electrostatic capacity sensor 1b of the second
embodiment described above.
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The relay circuit 11 of the electrostatic capacity sensor 1c
has a resistor 12.
By providing the resistor 12 between the ground electrode 5
and the negative terminal 72 , it is possible to make the sensitivity
of the ground electrode 5 to be sufficiently small in comparison
with the sensitivity of the detection electrode 3. This means that
it becomes possible to prevent the ground electrode 5 from functioning
as a detection electrode. In this way, the sensitivity of the
detection electrode 2 is stabilized, thereby enabling to improve
the detection precision of the electrostatic capacity sensor 1c.
In the electrostatic capacity sensor lc, with the increase
in the resistance of the resistor 12 , the sensitivity of the detection
element 2 is stabilized. On the other hand, however, the sensitivity
of the detection element 2 is deteriorated. Therefore, the
resistance of the resistor 12 should be appropriately determined by
taking this fact into consideration.
According to the electrostatic capacity sensor lc, the
detection element 2 has the charge plate 4 in the same manner as
the electrostatic capacity sensor 1b of the second embodiment
described above. Therefore, the sensitivity of the detection element
2 can be improved, so that it is possible to increase the detection
distance L1. In addition, the variations in the capacitance of the
detection element due to the changes in the ambient conditions are
reduced. In this way, the ratio of S/N is increased, thereby
enabling to improve the detection precision of the electrostatic
capacity sensor lc.
Next, a fourth embodiment of the electrostatic capacity sensor
of according to the present invention will be described.
Fig. 5 is a schematic side view showing the fourth embodiment
of the electrostatic capacity sensor 1d of this invention. In the
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following, the structures and elements of this embodiment which
are in common with those of the above-mentioned electrostatic capacity
sensor lc are omitted, and only the principal differences
therebetween will be described.
As shown in Fig. 5, in an electrostatic capacity sensor 1d,
the relay circuit 11 includes a variable resistor 13. The remaining
construction of the electrostatic capacity sensor 1d is almost the
same as in the electrostatic capacity sensor lc of the third embodiment
described above.
In the electrostatic capacity sensor 1d, since the variable
resistor 13 is used, it is possible to adjust the se~si.tivity of the
detection element 2 and the stability of the sensitivity easily by
adjusting the resistance of the variable resistor 13 such that the
optimum sensitivity and stability can be obtained.
Moreover, according to the electrostatic capacity sensor 1d,
the detection element 2 has the charge plate 4 in the same manner
as the electrostatic capacity sensor lc of the third embodiment
described above. Therefore, the sensitivity of the detection element
2 can be improved, thereby enabling to increase the detection
da.stance L1. In addition, the variations in the capacitance of the
detection element 2 due to the changes in the ambient conditions are
reduced. In this way, the ratio of S/N is increased, so that it is
possible to improve the detection precision of the electrostatic
capacity sensor 1d.
Next, a fifth embodiment of the electrostatic capacity sensor
according to the present invention will be described.
Fig. 6 is a schematic side view showing the fifth embodiment
of the electrostatic capacity sensor 1e of this invention. In the
following, the structures and elements of this embodiment which
are in common with those of the above-mentioned electrostatic capacity
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sensor 1c are omitted, and only the principal differences
therebetween will be described.
As shown in Fig. 6, in an electrostatic capacity sensor 1e,
the relay circuit 11 includes a capacitor 14, and the remaining
construction of the sensor 1e is almost the same as in the
electrostatic capacity sensor is of the third embodiment described
above.
By providing a capacitor 14 between the ground electrode 5 and
the negative terminal 72 of the power supply 7, the sensitivity of
the detection element 2 is improved-
In particular, it is possible to improve the sensitivity of
the detection element 2 while keeping the distance L3 constant , that
is, without making the distance L, large. This is advantageous in
reducing the thickness of the electrostatic capacity sensor 1e (the
thickness of detection element 2).
In the electrostatic capacity sensor 1e, the adjustment of
the sensitivity of the detection element 2 is achieved by adjusting
the capacitance of the capacitor 14 . In this case, as mentioned above,
it is preferable that the setting of the detection distance L1 is
carried out by the adjustment of the sensitivity of the detection
element 2.
In this case, with the increase in the capacitance of the
capacitor 14 , the sensitivity of the detection element 2 is improved.
On the other hand, however, the detection precision of the
electrostatic capacity sensor 1e is deteriorated. Therefore, the
capacitance of the capacitor 14 should be determined appropriately
by taking this fact into consideration.
According to the electrostatic capacity sensor 1e, the
detection element 2 has the charge plate 4 in the same manner as
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the electrostatic capacity sensor lc of the third embodiment described
above. Therefore. the sensitivity of the detection element 2 can be
improved, so that it is possible to increase the detection distance
Ll. In addition, the variations in the capacitance of the detection
element 2 due to the changes in the ambient conditions are reduced.
In this way, the ratio of S/N is increased, thereby enabling to improve
the detection precision of the electrostatic capacity sensor 1e.
Next, a sixth embodiment of the electrostatic capacity sensor
according to the present invention will be described.
Fig. 7 is a schematic side view showing the sixth embodiment
of the electrostatic capacity sensor of this invention. In the
following, the structures and elements of this embodiment which
are in common with those of the above-mentioned electrostatic-capacity
sensor 1e are omitted, and only the principal differences
therebetween will be described.
As shown in Fig. 7, in an electrostatic capacity sensor 1f,
the relay circuit 11 includes a variable capacitor 15, and the
remaining construction of the electrostatic capacity sensor 1f is
almost the same as in the electrostatic capacity sensor 1e of the
fifth embodiment described above.
In the electrostatic capacity sensor 1f, since the variable
capacitor 15 is used, it is possible to adjust the sensitivity of
the detection element 2, that is, the detection distance L1 readily
by adjusting the capacitance of the variable capacitor 15.
Moreover, according to the electrostatic capacity sensor 1f,
the detection element 2 has the charge plate 4 in the same manner
as the above-mentioned electrostatic capacity sensor 1e. Therefore,
the sensitivity of the detection element 2 can be improved, so that
it is possible to increase the detection distance L,~. In addition,
the variations in the capacitance of the detection element 2 due to
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the changes in the ambient conditions are reduced. In this way, the
ratio of S/N is increased, thereby enabling to improve the detection
precision of the electrostatic capacity sensor 1f. Further, this
is advantageous in reducing the thickness of the electrostatic
capacity sensor.
Next, a seventh embodiment of the electrostatic capacity sensor
according to the present invention will be described.
Fig. 8 is a schematic side view showing the seventh embodiment
of the electrostatic capacity sensor of this invention. In the
following, the structures and elements of this embodiment which
are in common with those of the above-mentioned electrostatic capacity
sensor if are omitted, and only the principal differences
therebetween will be described.
As shown in Fig. 8, in an electrostatic capacity sensor 1g,
the relay circuit 11 includes a resistor 12 and a capacitor 14 that
are connected in series. The remaining construction of the
electrostatic capacity sensor 1g is almost the same as in the
electrostatic capacity sensor 1e of the fifth embodiment described
above.
In the electrostatic capacity sensor 1g, in the same manner
as the above-mentioned electrostatic capacity sensor 1e, the
sensitivity of the detection element 2 is improved by the provision
of the capacitor 14.
Moreover, in the same manner as the above-mentioned
electrostatic capacity sensor 1c, the sensitivity of the ground
electrode 5 is made sufficiently small compared with the sensitivity
of the detection electrode 3 by the provision of the resistor 12,
thereby enabling to prevent the ground electrode 5 from functioning
as a detection electrode. In this way, the sensitivity of the
detection element 2 is stabilized, and the detection precision of
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the electrostatic capacity sensor 1g is improved.
Furthermore, according to the electrostatic capacity sensor
1g, in the same manner as the above-mentioned electrostatic capacity
sensor 1e, the detection element 2 has the charge plate 4. Therefore,
the sensitivity of the detection element 2 can be improved, so that
it is possible to increase the detection distance L1. In addition,
the variations in the capacitance of the detection element 2 due to
the changes in the ambient conditions are reduced. In this way, the
ratio of S/N is increased, thereby enabling to improve the detection
precision of the electrostatic capacity sensor 1g. Further, this
is also advantageous in reducing the thickness of the electrostatic
capacity sensor 1g.
Next, an eighth embodiment of the electrostatic capacity sensor
according to the present invention will be described.
Fig. 9 is a schematic side view showing the eighth embodiment
of the electrostatic capacity sensor of this invention. In the
following, the structures and elements of this embodiment which
are in common with those of the above-mentioned electrostatic capacity
sensor 1g are omitted, and only the principal differences
therebetween will be described.
As shown in Fig. 9, in an electrostatic capacity sensor 1h,
the relay circuit 11 includes the variable resistor 13 and the
variable capacitor 15 which are connected in series . The remaining
construction of the electrostatic capacity sensor 1h is almost the
same as in the electrostatic capacity sensor 1g of the seventh
embodiment described above.
In this electrostatic capacity sensor 1h, since the variable
resistor 13 is used, it is possible to adjust the sensitivity of the
detection element 2 and the stability of the sensitivity easily by
adjusting the resistance of the variable resistor 13 such that the
CA 02266026 2005-08-15
optimum sensitivity and the stability can be obtained. Further,
since the variable capacitor 15 is also used, it is possible to adjust
the sensitivity of the detection element 2, that is, the detection
distance L1 readily by adjusting the capacitance of the variable
capacitor 15.
Moreover, according to the electrostatic capacity sensor 1h,
in the same manner as the above-mentioned electrostatic capacity
sensor 1g, the detection element 2 has the charge plate 4. Therefore,
the sensitivity of the detection element 2 can be improved, so that
it is possible to increase the detection distance Ll. In addition,
the variations in the capacitance of the detection element 2 due to
the changes in the :ambient conditions are reduced. In this way, the
ratio of S/N is increased, thereby enabling to improve the detection
precision of the electrostatic capacity sensor 1h. Further, this
is also advantageous in reducing the thic)~ess of the electrostatic
capacity sensor 1~.
Next, a ninth embodiment of the electrostatic capacity sensor
according to the present invention will be described.
Fig. 10 is a schematic side view showing the ninth embodiment
of the electrostatic capacity sensor of this invention. In the
following, the structures and elements of this embodiment which
are in common with those of the above-mentioned electrostatic capacity
sensor 1g are omitted, and only the principal differences
therebetween wily be described.
As shown in Fig. 10, in an electrostatic capacity sensor 1i,
the relay circuit 11 includes the resistor 12 and the capacitor 14
which are connected in parallel. The remaining construction of the
electrostatic capacity sensor 1i is almost the same as in the
electrostatic capacity sensor 1g of the seventh embodiment described
above.
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CA 02266026 2005-08-15
In the electrostatic capacity sensor 1i, since the capacitor
14 is used in the same manner as the above-mentioned electrostatic
capacity sensor 1g, the sensitivity of the detection element 2 is
improved.
Further, the sensitivity of the ground electrode 5 is made
sufficiently small compared with the sensitivity of the detection
electrode 3 by the provision of the resistor 12. Therefore, it is
possible to prevent the ground electrode 5 from functioning as a
detection electrode. In this way, the sensitivity of the detection
element 2 is stabilized, thereby enabling to improve the detection
precision of the electrostatic capacity sensor 1i.
Furthermore, according to the electrostatic capacity sensor
1i, the detection element 2 has the charge plate 4 has in the same
manner as the above-mentioned electrostatic capacity sensor 1h.
Therefore, the sensitivity of the detection element 2 can be improved,
so that it is possible to increase the detection distance Ll. In
addition, the variations in the capacitance of the detection element
2 are reduced. In this way, the ratio of S/N is increased, thereby
enabling to improve the detection precision of the electrostatic
capacity sensor 1i. Further, this is also advantageous in reducing
the thickness of the electrostatic capacity sensor 1i.
Next, a 10th embodiment of the electrostatic capacity sensor
according to the present invention will be described.
Fig. 11 is a schematic side view of the 10th embodiment of the
electrostatic capacity sensor of this invention. In the following,
the structures and elements of this embodiment which are in common
with those of the above-mentioned electrostatic capacity sensor 1h
are omitted, and only the principal differences therebetween will
be described.
As shown in Fig. 11, in an electrostatic capacity sensor 1j;
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CA 02266026 2005-08-15
the relay circuit 1l includes the variable resistor 13 and the
variable capacitor 15 that are connected in parallel. The remaining
construction of the sensor 1j is almost the same as in the
electrostatic capacity sensor 1h of the eighth embodiment described
above.
In this electrostatic capacity sensor 1j, since the variable
resistor 13 is used, it is possible to adjust the sensitivity of the
detection element 2 and the stability of the sensitivity easily by
adjusting the resistance of the variable resistor 13 such that the
optimum sensitivity and stability can be obtained. Further, since
the variable capacitor 15 is also used, it is -possible to adjust the
sensitivity of the detection element 2, that is, the detection
distance L1 readily by adjusting the capacitance of the variable
capacitor 15.
Moreover, according to the electrostatic capacity sensor 1j,
the detection element 2 has the charge plate 4 in the same manner
as the above-mentioned electrostatic capacity sensor 1h. Therefore,
the sensitivity of the detection element 2 can be improved, so that
it is possible to increase the detection distance L1. In addition,
the variations in the capacitance of the detection element 2 due to
the changes in the ambient conditions are reduced : In this way, the
ratio of S/N is increased, thereby enabling to improve the detection
precision of the electrostatic capacity sensor 1j. Further, this
is also advantageous in reducing the thickness of the electrostatic
capacity sensor 1j.
Next, an llth embodiment of the electrostatic capacity sensor
according to the present invention will be described.
Fig. 12 is a schematic side view of the 11th embodiment of the
electrostatic capacity sensor of this invention. In the following,
the structures and elements of this embodiment which are in common
with those of the above-mentioned electrostatic capacity sensor 1h
23
CA 02266026 2005-08-15
are omitted, and only the principal differences therebetween will
be described.
As shown in Fig.l2, an electrostatic capacity sensor 1k is
different from the above-mentioned electrostatic capacity sensor 1h
in the structure of the detection element 2. The remaining
construction of the electrostatic capacity sensor 1h is almost the
same as in the sensor 1g of the seventh embodiment described above.
The detection element 2 of the electrostatic capacity sensor
1k includes two charge plates constructed from a first charge plate
41 and a second charge plate 42, the detection electrode 3, and the
ground electrode 5. In this case, the charge plates 41 and 42 are
arranged in the direction of the thickness of the detection element
2 (in the vertical direction of Fig. 12) so as to have the charge
plate 41 closer to the detection electrode 3 and the charge plate
42 closer to the ground electrode 5.
In this embodiment, hereinafter, the distance between the
detection electrode 3 and the charge plate 41 is referred to as
"distance L2", and tha distance between the charge plate 42 and the
ground electrode 5 is referred to as "distance L3".
In the electrostatic capacity sensor 1k, the detection
electrode 3 and the charge plate 41 form a first capacitor. The first
charge plate 41 and the second charge plate 42 form a second capacitor.
The second charge plate 42 and the ground electrode 5 foirn a third
capacitor. Accordingly, the electrostatic capacity sensor 1k has
larger number of serially connected capacitors than in the case of
the electrostatic capacity sensor 1h. Therefore, in comparison with
the electrostatic capacity sensor 1h, the sensitivity of the detection
element 2 is further improved, so that it is possible to increase
the detection distance Li further. In addition, it is possible to
reduce noises due to the changes in the ambient conditions , thereby
enabling to improve the detection precision of the electrostatic
24
CA 02266026 2005-08-15
capacity sensor 1k further.
Moreover, in this electrostatic capacity sensor 1k, since the
variable resistor 13 is used in the same manner as the above-mentioned
electrostatic capacity sensor 1h, it .is possible to adjust the
sensitivity of the detection element 2 and the stability of the
sensitivity easily by adjusting the resistance of the variable
resistor 13 such that the optimum sensitivity and stability can be
obtained. Further, since the variable capacitor 15 is also used,
it is possible to adjust the sensitivity of the detection element
2, that is, the detection distance Ll readily by adjusting the
capacitance of the variable capacitor 15. Furthermore, the
sensitivity of the detection element 2 can be improved while fixing
the distance L" and this is advantageous in reducing the thickness
of the electrostatic capacity sensor 1k.
In this invention, the electrostatic capacity sensor may
include three charge plates or more.
In this invention, with the increase of the number of the charge
plates, the number of the serially connected capacitors is also
increased. Therefore, from the viewpoint of improving the
detection precision, it is preferable that the electrostatic capacity
sensor has a larger number of the charge plates. On the other hand,
however, with the increase of the number of the charge plates, the
thickness of the electrostatic capacity sensor (the vertical length
in Fig. 12) is increased.
Under these circumstances, it is preferable that the number
of the charge plates is about 2 to 10, and more preferably about 2
to 5.
Moreover, similar to the electrostatic capacity sensor 1k,
it is preferable that the electrostatic capacity sensors la to 1g
and 1i and 1j also include a plurality of the charge plates.
CA 02266026 2005-08-15
The use of the electrostatic capacity sensor is not
particularly limited. For example, the electrostatic capacity
sensor of the present invention may be applied for various kinds
of sensors such as a proximity switch (non contact switch) , distance
sensor, touch sensor, displacement gauge, thickness meter and the
like.
When the present invention is applied for the proximity
sensor, it can be provided on, for example, an elevator, escalator,
toilet seat, automobile bumper, lift mechanism and the like.
Next , more specific descriptions of the electrostatic capacity
sensor will be given.
(Example 1)
The electrostatic capacity sensor 1b shown in Fig. 3 was
manufactured with the following conditions.
[Detection Electrode]
Material: Aluminum alloy
Dimensions of the Detection Plane: 3 cm x 150 cm (450 cmz)
Thickness: 0.2 cm
[Charge Plate]
Material: Aluminum alloy
Dimensions: 3 cm x 150 cm (450 any)
Thickness: 0.2 cm
[Ground Electrode]
Material: Aluminum alloy
Dimensions: 3 cm x 150 cm (450 cm2)
Thickness: 0.2 cm
[Support Material for Detection Electrode, Charge Plate and Ground
26
CA 02266026 2005-08-15
Electrode]
Material: Acrylonitrile-butadiene-styrene copolymer (ABS
resin)
[Distance LZ between Detection Electrode and Charge Plate]
L2: 0.2 cm
[Distance L3 between Charge Plate and Ground Electrode]
L,: 1.5 cm
(Example 2)
An electrostatic capacity sensor 1b was manufactured in the
same way as in Example 1 except that the distance L3 between the charge
plate and the ground electrode was changed to 2.0 cm.
(Example 3)
The electrostatic capacity sensor 1h was manufactured in the
same conditions as in Example 2.
(Comparative Example 1)
An electrostatic capacity sensor was manufactured in the same
way as in Example 1 except that the charge plate was omitted, and
the dimensions of the detection electrode was changed to 3cm x 3cm
( 9 cm2 ) .
<Experiment>
For the electrostatic capacity sensors of Examples 1 to 3 and
Comparative Example 1, the detection distance L1 was measured. In
this Experiment , the threshold for the comparator 66 of the detection
circuit 60 was set equal for all of them. Further, in the
electrostatic capacity sensor 1h of Example 3 , the resistance of the
variable resistor 13 was set at 0 S2 short-circuiting, and the
capacitance of the variable capacitor 15 was set at 500 a F in one case
and was set at 1000 J-~ F in the other case . The result of the experiment
was as shown in Table 1 below.
27
CA 02266026 2005-08-15
Table 1
AREA OF CAPACITANCE RESISTANCE DETE~TI~1
OF OF
DETEGTIQIJ PLANg DISTANCEVARIAHYE VARIAHLS DISTANCE
OF
DETECTION ELECTRODELZ CAPACITOR RESISTER Li
tao~1 taul tuFl t~1
6X. C,IiARGE
1
PLATE 450 1.5 --- ---
E7C. CHARGE
2
450 2.0 --- --- 4
ax. 500 O 8
3
P~ 450 2.0
100 O 12
co. No
EX. CHARGE ~ ___ ,__ ___
1 2
PLATE
As shown in Table 1, each of the electrostatic capacity sensors
of Examples 1 to 3 had large value for the detection distance Ll since
they are equipped with the charge plate. In, contrast, the
electrostatic capacity sensor of Comparative Example 1 had a smaller
value for the detection distance L,_
Further, though the detection plane of the detection electrode
has the area of 450cm2, each of the electrostatic capacity sensors
of Examples 1 to 3 had constant values for the detection distance.
In contrast, though the detection plane of the detection electrode
has the area of 9cm2, the electrostatic capacity sensor of Comparative
Example 1 had dispersion in the detection distance L1 and the low
detection precision.
(Example 4)
An experiment was carried out for each of examples 1 to 3 in
the same way as in the above, using two charge plates arranged in
the thickness direction of the detection element. In this experiment,
the detection distance L1 was further increased, and the detection
precision was further improved.
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In the above, the electrostatic capacity sensor according to
the present invention has been described based on the respective
embodiments , but this invention is not limited to these embodiments .
For example, in this invention, the structure of the detection
circuit 60 is not limited those shown in the figures.
Further, in this invention, the function of the relay circuit
11 is not limited to those described above. In addition, the relay
circuit 11 is not limited to a circuit having a function of stabilizing
the sensitivity of the electrostatic capacity sensor, and a Circuit
having a function of adjusting the sensitivity of the electrostatic
capacity sensor. The relay circuit 11 can be used for achieving any
other purposes.
Moreover, in this invention, the circuit board may be provided
on a section ( for example , on the back face , on the side face of the
attaching table 8, or the like) other than the plane 32 of the detection
electrode 3.
As described in the above, according to the electrostatic
capacity sensor of the present invention, the detection element
includes the charge plate. Therefore, the sensitivity of the
detection element is improved, so that it is possible to increase
the detection distance. In addition, the variations in the
capacitance of the detection element due to the changes in the ambient
conditions can be reduced. In this way, the ratio of signal to noise
( the ratio of S/N ) can be increased, thereby enabling to improve the
detection precision of the electrostatic capacity sensor.
In particular, when a plurality of charge plates are arranged
in the direction of the thickness of the detection element, the
sensitivity of the detection element is higher than the case where
a single charge plate is used. Consequently, it becomes possible
29
CA 02266026 2005-08-15
to increase the detection distance and to improve the detection
precision of the electrostatic capacity sensor.
Further, when the distance between the charge plate and the
ground electrode is set to be larger than the distance between the
detection electrode and the charge plate, the discharge of charge
on the charge plate toward the ground electrode can be suppressed.
Therefore, the migration of charge on the charge plate toward the
detection electrode is effectively carried out, so that the
sensitivity of the detection element can be improved, thereby enabling
to increase the detection distance.
Furthermore, when the ground electrode is connected
electrically to the negative terminal of the power supply, in
particular, when the ground electrode is connected electrically to
the negative terminal of the power supply via a relay circuit , charge
can be discharged from the ground electrode more effectively compared
with the case where the ground electrode is not connected to the
negative terminal of the power supply. In this way, the sensitivity
of the detection element can be improved. Therefore, the ground
electrode becomes substantially free from the influence of the
electric charges existing in the atmosphere and the influence of the
capacitance between the ground electrode and the ground. As a result,
noise due to the variations in the capacitance is reduced, thereby
enabling to improve the detection precision of the electrostatic
capacity sensor.
