JP4160409B2 - Antenna and object detection device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an antenna for transmitting, receiving, or transmitting / receiving microwaves and an object detection apparatus using the antenna.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, object detection devices using laser light, infrared rays, or the like have been widely used in factory production sites, work sites, and the like to detect the presence and position of objects such as processed products. However, in such a method using light, for example, in a high temperature blast furnace, incinerator, or use environment where steam mist, oil mist, or the like exists, the sensitivity is remarkably lowered and detection is difficult. Therefore, as an object detection method under such a bad environment, a microwave is used as a detection medium instead of the conventional optical detection method.
[0003]
FIG. 5 is a schematic cross-sectional view showing an incinerator equipped with a level meter which is one of the object detection devices using microwaves. In the incinerator 5 shown in the figure, the combusted material 3 such as the introduced dust is deposited on the gravel bed portion 1, and an opening 7 is provided immediately above the combusted material 3, and a level meter 9 is provided in the opening 7. Is attached. The level meter 9 includes a controller 15 including a microwave transmitter, a microwave receiver, a calculation unit, and the like, and an antenna 11 connected from the controller 15 via a waveguide 13.
[0004]
The antenna 11 is formed by processing a metal plate into a horn shape whose diameter gradually increases toward the opening 17 at one end, and a flange 21 is integrally provided on the periphery of the opening 17. The antenna 11 is attached to the upper portion of the incinerator 5 by bolting the flange 21 of the opening 17 to the flange 23 of the opening 7 of the incinerator 5.
[0005]
In such a level meter 9, the transmission microwave 25 is emitted from the microwave transmitter via the antenna 11 so as to be perpendicularly incident on the upper surface of the combustion material 3, and the reflected microwave 25 a reflected by the combustion material 3 is emitted. Is received by the microwave receiver via the antenna 11 and the reception signal is calculated by the calculation unit of the controller 15 to detect the distance to the detected object, that is, the amount of accumulation of the combustion product 3 (for example, , See Patent Document 1).
[Patent Document 1]
JP-A-2001-158882 [0006]
[Problems to be solved by the invention]
However, in the incinerator 5, foreign matter or dust derived from the volatile components generated by the combustion of the combustion product 3 floats, enters inward from the opening 17 of the dust antenna 11, and adheres to the inner surface. As a result, the narrowing portion 19 on the connection side of the antenna 11 to the waveguide 13 is closed, and the detection accuracy is lowered, or in some cases, detection is impossible. Therefore, conventionally, the antenna 11 is periodically cleaned.
[0007]
In order to solve such a problem, as shown in FIG. 5, a material that transmits microwaves (for example, glass) is provided between the opening 7 provided in the upper part of the incinerator 5 and the opening 17 of the antenna 11. And a baffle plate 27 in which a plurality of through holes 29 are formed, and air or an inert gas is introduced into the space between the baffle plate 27 and the opening 17 of the antenna 11 from the air supply pipe 31. Thus, measures such as preventing the invasion of the vessel and dust derived from volatile components into the inside of the antenna 11 and removing the deposits on the inner surface of the baffle plate 27 have been proposed.
[0008]
However, due to the presence of the baffle plate 27, a decrease in microwave transmission / reception intensity is unavoidable, and in particular, when a low dielectric constant material is mixed in the combustion product 3, the microwave 25 is absorbed. Since the amount of reflection of the reflected microwave 25a is greatly reduced, the detection accuracy is greatly reduced.
[0009]
The present invention has been made in view of the above situation, does not require cleaning for maintaining detection accuracy, has no adhesion of foreign matters or dusts derived from volatile components, and lowers microwave transmission / reception strength. An object of the present invention is to provide an antenna that is not allowed to be detected, and an object detection device that includes the antenna and that can detect an object to be detected with high accuracy even in an environment where floating objects exist.
[0010]
[Means for Solving the Problems]
To achieve the above object, the present invention is an antenna for transmitting, receiving or transmitting / receiving microwaves,
An antenna main body that exhibits a horn shape or a parabolic shape that gradually expands toward an opening for transmitting, receiving, or transmitting and receiving microwaves ;
And an air chamber you encirclement entirely airtight except for the opening of the antenna body,
The antenna body has a plurality of vent holes formed over the entire surface,
The air chamber includes an air supply hole for introducing gas into a space formed by the antenna body,
There is provided an antenna characterized in that gas introduced into the air chamber is blown out toward the opening through a vent hole of the antenna body .
[0011]
In the antenna of the present invention, the antenna main body is breathable, and gas is supplied from the outer surface side of the antenna to the inner surface side through this ventilation hole, so that foreign matter can enter and enter the antenna without interposing a baffle plate. Adhesion to the inner surface can be prevented. Therefore, it is possible to detect an object to be detected with high sensitivity, and cleaning for maintaining detection accuracy is not required, and maintenance costs are not required.
[0012]
Further, the present invention is a method of emitting a microwave from a microwave transmitter toward an object to be measured, detecting the reflected microwave by the microwave receiver, and detecting the distance to the object to be measured or the object to be detected. An object detection apparatus for detecting the presence or absence of an object, wherein the microwave transmitter and the microwave receiver include the antenna according to claim 1 or 2. .
[0013]
The level meter of the present invention includes the antenna described above, and can detect a detection object with high accuracy over a long period of time without maintenance.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of an antenna and an object detection device according to the invention will be described in detail with reference to the drawings. In addition, as an object detection apparatus, the level meter used for an incinerator is illustrated and demonstrated.
[0015]
FIG. 1 is a schematic sectional view showing the configuration of an incinerator equipped with a level meter, which is an object detection apparatus according to the present invention, FIG. 2 is a block diagram showing the configuration of a controller, FIG. 3 is an explanatory diagram of the measurement principle, and FIG. FIG. 2 is an enlarged half sectional view of the antenna shown in FIG. 1. In addition, the same code | symbol is attached | subjected to the member same as the member shown in FIG.
[0016]
An opening 7 is provided in the upper part of the incinerator 5, and a level meter 41 including the antenna 53 of the present invention is attached to the opening 7. The level meter 41 is configured by connecting the controller 15 and the antenna 53 with the waveguide 13, and emits the transmission microwave 25 from the antenna 15 so as to be perpendicularly incident on the upper surface of the combustion product 3, and the reflection thereof. The microwave 25a is received by the antenna 15.
[0017]
For example, as shown in FIG. 2, the controller 15 includes a microwave transmitter 43, a microwave receiver 45, and a calculation unit 60. Although both the microwave transmitter 43 and the microwave receiver 45 may be known ones, the transmission microwave 25 and the reflected microwave 25a are rotated in either the clockwise or counterclockwise direction of the electric field. It is preferable to adopt a configuration in which the rotating wave is polarized. The upper surface of the combustion product 3 is generally a complex uneven surface, and the transmission microwave 25 incident on the combustion product 3 is reflected in multiple directions, and after it collides with the inner wall of the incinerator 5 and is reflected. There is also a reflected microwave 25 a incident on the antenna 53. As will be described later, the detection principle of the level meter 41 is based on the propagation time or propagation distance until the transmission microwave 25 is received. Therefore, the reflected microwave 25a reflected by the inner wall of the incinerator 5 propagates accordingly. Time or propagation distance becomes longer, resulting in noise. On the other hand, since the rotating wave has the property of reversing the direction of rotation of the electric field when reflected by a certain object, it is further reflected by the reflected microwave 25a reflected only by the combustion product 3 and the inner wall of the incinerator 5. The direction of rotation of the electric field is opposite to that of the reflected microwave 25a. Therefore, for example, a rotating wave (transmitting microwave 25) having a clockwise electric field is emitted from the microwave transmitter 43 via the antenna 53, and is counteracted in the rotating wave (reflected microwave 25a) received by the antenna 53. By adopting a configuration in which a rotating wave having a clockwise electric field is detected by the microwave receiver 45, it is possible to detect only the reflected microwave 25a caused by the combusted material 3 and to detect the amount of accumulation of the combusted material 3 with high accuracy. become.
[0018]
In order to perform the transmission / reception by the rotating wave as described above, as shown in FIG. 2, the microwave transmitter 43 operates the microwave oscillator 49 based on the modulation circuit 47 to transmit the microwave, and the transmitting microwave Is made to enter the polarization converter 51 to be polarized into a rotating wave. In addition, the microwave receiver 45 is configured so that the rotating wave received by the antenna 53 is incident on the polarization converter 57 and then incident on the microwave detector 59. Here, both the polarization converter 51 and the polarization converter 57 are flat plates made of a dielectric material. Further, the current application direction of the microwave oscillator 49 and the current application direction (detection direction) of the microwave detector 59 are arranged orthogonally, and accordingly, the polarization converter 51 has its end face applied to the microwave oscillator 49. The polarization converter 57 is arranged so that its end face coincides with the current application direction of the microwave detector 59.
[0019]
The microwave receiver 45 includes a low-frequency amplifier 61 that amplifies the signal detected by the microwave detector 59, a detection circuit 63 that performs waveform shaping and waveform adjustment, an output circuit 65, and the like. The received signal is output to the arithmetic unit 60 from On the other hand, the microwave transmitter 43 also oscillates microwaves through the modulation circuit 47 by a signal from the calculation unit 60. The calculation unit 60 includes, for example, calculation means (CPU), storage means (RAM / ROM), display means, and the like, and the transmission microwave 25 is transmitted from the antenna 53 by a predetermined processing program stored in the storage means (ROM). While firing, the distance to the combustible 3 is obtained based on the detection signal based on the received reflected microwave 25a, and the signal is output to the display means and the storage means. In addition, in the calculating part 60, the distance to the combustion thing 3 is measured as follows.
[0020]
That is, as shown in FIG. 3, when the transmission microwave 25 whose frequency increases linearly with respect to time is emitted toward the combustible 3, it is emitted at a certain frequency (f1) at a certain time (t1). The transmission microwave 25 is received after the time (Δt) required for reciprocation after being reflected by the combustible 3. On the other hand, the frequency of the reflected microwave 25a received at that time changes from f1 to f2. At this time, the frequency difference (Δf) between the transmission microwave 25 and the reflection microwave 25a is proportional to the distance (d). Therefore, the calculation unit 60 mixes the transmission microwave 25 and the reflected microwave 25a, extracts a reception signal waveform having a difference frequency, and obtains the difference frequency by performing FFT (Fast Fourier Transform) on the waveform. Output as a distance signal.
[0021]
As shown in FIG. 4, the antenna 53 of the present invention has a plurality of ventilation holes 75, an antenna main body 67 that defines a horn shape that gradually increases in diameter toward the opening 17 at one end, and the antenna main body 67. And an air chamber 71 that hermetically surrounds the outer surface side. The air chamber 71 is formed by processing a metal plate into a box shape with one end opened, and has an air supply hole 73 for introducing gas into a space 69 formed between the antenna body 67 and the air chamber 71. The antenna body 67 includes a flange 21 on the periphery on the opening 17 side, and is integrated with the flange 23 provided in the opening 7 of the incinerator 5 in a state where the flange 74 of the air chamber 71 is overlapped on the flange 21. Fixed.
[0022]
The antenna body 67 is obtained by processing a metal plate having a plurality of ventilation holes 75 into a predetermined antenna shape, for example, a horn shape or a parabolic shape. The opening diameter, the number of openings, and the arrangement of the vent holes 75 are not limited and can be set as appropriate. Further, the air holes 75 may be formed regularly, such as in a lattice shape, or may be formed randomly.
[0023]
The antenna body 67 can also be a metal net or cloth, or a porous metal plate.
[0024]
In the antenna 53 of the present invention, since the antenna main body 67 has air permeability, air or inert gas is introduced from the entire inner surface of the antenna main body 67 by introducing air or inert gas into the air chamber 71 through the air supply holes 73. It is blown out evenly. As a result, foreign matters, dusts and the like derived from the volatile components of the combustion product 3 cannot enter the antenna body 67 through the opening 17, and they do not adhere and accumulate. The amount of air or inert gas introduced is appropriately set according to the type and amount of the combustion product 3 (volatile component), the opening diameter of the vent hole 75, the number thereof, and the like.
[0025]
As described above, according to the level meter 41 of the present invention, it is possible to prevent adhesion and accumulation of foreign matters or dusts derived from volatile components on the antenna 53 without intervening the baffle plate 27 (see FIG. 5), and low dielectric constant. Even in the case of a combustion product 3 in which a large number of materials are mixed and the received power of microwaves is small, the amount of deposition can be detected with high accuracy without being affected by large unnecessary reflection by the baffle plate 27. can do.
[0026]
As described above, the case where the present invention is used in an incinerator has been described as an example. However, the antenna and the object detection device of the present invention are not limited to this, and can be suitably applied to an environment where suspended solids exist, for example, a melt surface in a blast furnace. It is also suitable for detecting the liquid level. In addition, the microwave transmitter and the microwave receiver were integrated into one, and the case of one antenna was shown. However, the microwave transmitter and the microwave receiver are separated, and each Of course, it is possible to mount the antenna of the present invention. In addition, various modifications other than the antenna can be made within a known range.
[0027]
【The invention's effect】
As described above in detail, the antenna of the present invention does not require cleaning for maintaining detection accuracy, does not adhere to foreign matters, and does not reduce microwave transmission / reception strength. Therefore, the object detection apparatus provided with this antenna can detect the detected object with high accuracy even in an environment where floating objects exist.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing the configuration of an incinerator equipped with a level meter that is an object detection apparatus according to the present invention.
FIG. 2 is a block diagram illustrating a configuration of a controller.
FIG. 3 is an explanatory diagram of a measurement principle.
4 is an enlarged half sectional view of the antenna shown in FIG.
FIG. 5 is a schematic cross-sectional view showing the configuration of an incinerator equipped with a conventional microwave level meter.
[Explanation of symbols]
15 Controller 17 Opening 25 Transmission Microwave 25a Reflected Microwave 41 Level Meter 43 Microwave Transmitter 45 Microwave Receiver 53 Antenna 67 Antenna Main Body 69 Sealed Space 71 Air Chamber 73 Air Supply Pipe 75 Vent

Claims (4)

An antenna for transmitting, receiving or transmitting / receiving microwaves,
An antenna body that exhibits a horn shape or a parabolic shape that gradually increases in diameter toward an opening for transmitting, receiving, or transmitting and receiving microwaves ;
And an air chamber you encirclement entirely airtight except for the opening of the antenna body,
The antenna body has a plurality of vent holes formed over the entire surface,
The air chamber includes an air supply hole for introducing gas into a space formed by the antenna body,
An antenna, wherein the gas introduced into the air chamber is blown out toward the opening through a vent hole of the antenna body .   The antenna according to claim 1, wherein the antenna body is made of a metal plate having a plurality of through holes, a metal net or cloth, or a porous metal plate. An object for detecting the distance to the object to be measured or the presence / absence of the object to be detected by emitting the microwave from the microwave transmitter toward the object to be measured and detecting the reflected microwave by the microwave receiver A detection device,
The object detection apparatus, wherein the microwave transmitter and the microwave receiver include the antenna according to claim 1.   3. The object detection apparatus according to claim 2, wherein the object detection apparatus is used for a level meter of an incinerator or a blast furnace.

Images