Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
2001-03-27
2002-09-24
Hofsass, Jeffery (Department: 2632)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S561000, C340S660000, C340S635000, C340S654000, C340S664000, C340S541000, C340S550000, C256S010000, C256S048000, C324S071100, C324S658000
Reexamination Certificate
active
06456198
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a fence sensor, and more particularly to a crime prevention sensor for a fence which can detect the presence of an object that approaches or makes contact with the fence.
BACKGROUND OF THE INVENTION
Among the conventional crime prevention sensors for a fence for detecting an intruder, there has been known an electric field formation type sensor as disclosed in Japanese Patent Laid-Open Publication No. 9-237389. This is a type in which an electric field is generated by supplying sinusoidal current to electric wires embedded in the fence, and an alarm device is actuated when a change of the electrostatic capacity is detected that occurs due to an intrude approaching the fence.
In addition, there has also been known a crime prevention sensor in which an emitting part of infrared rays and a receiving part for receiving the emitted infrared rays are installed in the vicinity of the fence in order to establish an infrared ray detection region along the fence. In this sensor, when an interception of infrared rays by an intruder is detected, an alarm device is actuated.
The electric field formation type sensor uses a sinusoidal wave to generate an electric field, so it has a problem that it becomes a source of noise in telephone lines or electronic circuits found in the vicinity of the fence. Accordingly, installation sites for the sensor are limited.
Moreover, the electric field formation type sensor has a detection region defined by the region where electric wires are laid within the fence, so that it has a problem that it gives restrictions on the fence design.
Besides, the electric field formation type sensor has another problem that the power consumption increases due to the necessity that the electric field has to be maintained all the time.
Furthermore, with respect to the infrared sensor, the detection region between the light emitting part and the light receiving part needs to be formed in a linear shape, so that it has a problem that a detection region cannot be formed along a fence having a curved surface structure.
It is an object of the present invention to provide a fence sensor with an excellent detection stability that resolves the problems associated with the electric field formation type sensor and the infrared sensor described above without requiring electric current for generating an electric field or infrared rays.
SUMMARY OF THE INVENTION
A fence sensor defined by claim
1
comprises:
a detection electrode;
a reference electrode insulated from the detection electrode;
a chargeable member insulated from both of the detection electrode and the reference electrode, the chargeable member being arranged such that at least a part of the chargeable member is situated within a detection region of the detection electrode, and the chargeable member being formed from a conductor; and
a detection circuit for detecting a change in the electrostatic capacitance between the detection electrode and the reference electrode that is generated by the presence of an object to be detected within the detection region.
In this structure, when the electrical charges on the chargeable member are increased by the presence of the object within the detection region of the chargeable member, the electrostatic capacitance between the detection electrode and the reference electrode is changed. According to the present invention described above, the fence sensor can detect the presence of the object within the detection region by detecting such a change in the electrostatic capacitance between the detection electrode and the reference electrode. Accordingly, the fence sensor of this invention does not require the formation of an electric field or the use of infrared rays.
For example, if an intruder approaches the detection region, electrostatic induction is generated in the conductive chargeable member due to the charge on the body of the intruder, thus increasing the amount of the charge on the chargeable member. Since the chargeable member is insulated from both of the detection electrode and the reference electrode, the charges on the chargeable member will not move directly to these electrodes as currents. However, since the chargeable member is found within the detection region of the detection electrode, the increase in the charges on the chargeable member forms an electric field in the detection region of the detection electrode, and causes an increase in the charge on the detection electrode. Consequently, the electrostatic capacitance between the detection electrode and the reference electrode is increased. When the increase in the electrostatic capacitance exceeds a detection threshold of the detection circuit, the detection circuit outputs a detection signal.
Further, the use of the chargeable member makes it possible to form a detection region with wider area. For example, when a wide area of the sidewall of the fence is formed as a detection region, the increase in the detection region can simply be achieved by the installation of a chargeable member on the entire sidewall of the fence. However, if the detection electrode and the reference electrode are installed over a wide area, the electrostatic capacitance between the detection electrode and the reference electrode becomes extremely large in the case of absence (static state) of an object in the detection region of the detection electrode.
When the electrostatic capacitance between the detection electrode and the reference electrode is extremely large as in the above, the increased amount of the charge on the detection electrode in the charged state (that is, in a state that an object is found within the detection region) will be relatively extremely small compared with the amount of the charge in the static state. Because of this, the detection circuit has to detect an extremely large increase, relatively speaking, in the amount of the charge, thus impairing detection stability or causing inability of detection. For these reasons, the fence sensor of this invention utilizes the chargeable member. According to such a fence sensor, it is possible to stably detect an object within a wide detection region. Further, it is also possible to achieve the detection without being accompanied by an increase in the electrostatic capacitance between the detection electrode and the reference electrode in the static state.
Here, there is no limitation on a fence in which the fence sensor of this invention is to be installed. Examples of such a fence includes a wall formed of concrete or stone; a palisade formed from support pillars arranged with a prescribed distance apart and a metallic net spread between the support pillars; and the like. Further, such a fence may be installed indoors, and may also be installed outdoors. In addition, the fence sensor of this invention may be installed in a fence so that the detection region covers the entirety of the fence. Further, the fence sensor may also be installed so that the detection region covers a part of the fence (e.g., handrails of the fence).
Further, the use of the fence sensor is not limited to the purpose of crime prevention. For example, a fence sensor of this invention may be installed on a fence in the rear of a parking lot in order to give a warning about the approach of a vehicle to the fence. According to such a fence sensor, it is possible to prevent collision of a vehicle with the fence.
The fence sensor defined by claim
2
further comprises water film separation means for separating a water film on the surface of the chargeable member from a water film grounded to the earth.
A fence sensor defined by claim
3
comprises:
a detection electrode;
a reference electrode insulated from the detection electrode;
a chargeable member arranged such that at least a part of the chargeable member is situated within a detection region of the detection electrode, the chargeable member being formed from an insulator; and
a detection circuit for detecting a change in the electrostatic capacitance between the detection electrode and the refer
Kamiyama Kunihide
Kato Hideto
Kato Ryochi
Seino Kiichi
Brinks Hofer Gilson & Lione
KS Techno Co., Ltd.
Nguyen Tai T.
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