JP2018055634A - Rfid gate system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an RFID gate system suppressing the reading of an RFID tag outside of a gate without using a shield structure of an electric wave in a passing direction of the gate.SOLUTION: An RFID gate system includes: a metallic gate 10 opened at both ends and having a cylindrical wall in which a cavity space is provided; and one or more antennas 50 installed in the inner surface of the gate 10 that communicates with an RFID tag 40 provided by an article when the article passes through an inner part of the gate 10 by emitting an electric wave by a preset transmission output. A gain of the antenna 50 is set to the maximum value in an emission angle vertical to an installation surface with the inner surface of the gate 10 installed with the antenna 50 as an installation surface and with a lower limit value of the electric wave level capable of communicating with the RFID tag 40 as a level lower limit value, and a level of a radiation wave in the outside of the opening is set to the value that becomes lower than the level lower limit value.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an RFID gate system that performs wireless communication with an RFID tag included in an article that passes through a gate.

  The RFID gate system is a system that reads information from an RFID tag by performing wireless communication with an RFID tag included in an article passing through the gate via an antenna. In this type of system, since only the RFID tag included in the article inside the gate is to be read, a technique for suppressing reading of the RFID tag included in the article outside the gate has been proposed. For example, in the inspection system described in Patent Document 1, a shield curtain made of a radio wave shielding material or a radio wave absorber is provided at the entrance and exit of a tunnel-shaped gate, and radio waves are emitted outside the entrance and exit of the gate. Suppressing radiation.

JP 2009-155108 A

  In the inspection system, a shield curtain, which is a radio wave shielding structure, must be provided at the entrance and exit of the gate, which increases the number of parts and thus increases the cost. In addition, since the shield curtain is provided, there is a problem that smooth passage of the article through the gate is suppressed as compared with the case where there is no shield curtain.

  The present invention has been made in view of the above circumstances, and has as its main object to provide an RFID gate system that suppresses reading of an RFID tag outside the gate without using a radio wave shielding structure in the passage direction of the gate. To do.

  The invention according to claim 1 is an RFID gate system, which is installed on a metal gate having a cylindrical wall having both ends open and hollow inside, and an inner surface of the cylindrical wall, One or more antennas that radiate radio waves with a set transmission output and communicate with an RFID tag included in the article when the article passes through the inside of the gate, and the gain of the antenna is The inner surface where the antenna is installed is the installation surface, the lower limit value of the radio wave level that can communicate with the RFID tag is the lower limit value, and is set to the maximum value at the radiation angle perpendicular to the installation surface of the antenna, In a radiation angle range in which the radiated wave radiated from the antenna leaks out from the opening, the level of the radiated wave outside the opening is lower than the level lower limit value. It is set to a value such, characterized in that.

  The invention according to claim 2 is the RFID gate system according to claim 1, wherein the gain of the antenna is radiated from the antenna with the inner surface of the cylindrical wall facing the installation surface as an opposing surface. The level of the reflected wave outside the opening is lower than the level lower limit value in a range of radiation angles where the reflected wave is reflected by the facing surface and the reflected wave leaks out from the opening. It is set to such a value.

  The invention according to claim 3 is the RFID gate system according to claim 1 or 2, wherein the antenna is installed so that a center in a passing direction of the gate coincides with a center of the antenna. It is characterized by that.

  A fourth aspect of the present invention is the RFID gate system according to any one of the first to third aspects, wherein the gate is formed of a material that transmits radio waves, and is a floor of the cylindrical wall. It is formed of a plate-shaped spacer installed on the inner surface of the part and a material that transmits radio waves, and is installed on the spacer to convey the article from one opening to the other opening. And a slider configured to do so.

  A fifth aspect of the present invention is the RFID gate system according to any one of the first to fourth aspects, wherein the reader is connected to the antenna and configured to read data of the RFID tag. A processing device configured to process the data read by the reading device, wherein the processing device has a radio wave reception intensity by the antenna lower than a preset reception threshold value. It is configured to remove data.

  The invention according to claim 6 is the RFID gate system according to claim 5, wherein the reception threshold is set to a higher value as the performance of the RFID tag or the reader is higher. Features.

  The invention according to claim 7 is the RFID gate system according to claim 5 or 6, wherein the reader is installed on an outer surface of the cylindrical wall and is connected to the antenna by a connection line. The gate has a metal protective cover that covers the connection line on an outer surface of the cylindrical wall, and the protective cover is electrically grounded to the ground. .

  According to an eighth aspect of the present invention, the cylindrical wall is a square cylindrical wall, and the antenna is installed on each of the ceiling portion and the two side wall portions of the rectangular cylindrical wall. It is characterized by that.

  According to the first aspect of the present invention, since the gain of the antenna is maximized at a radiation angle perpendicular to the installation surface, communication can be performed between the antenna and the RFID tag in the gate. On the other hand, since the antenna gain is suppressed at the radiation angle toward the outside of the gate, communication between the antenna and the RFID tag outside the gate is suppressed. Therefore, reading of the RFID tag outside the gate can be suppressed without using a radio wave shielding structure in the direction of passage of the gate.

  According to the second aspect of the present invention, communication between the antenna and the RFID tag by the reflected wave as well as the radiated wave is suppressed outside the gate. Therefore, reading of the RFID tag outside the gate can be further suppressed.

According to the third aspect of the present invention, the gain of the antenna can be maximized at the center in the passage direction of the gate, and the gain can be suppressed at the entrance and the exit.
According to the invention of claim 4, since the spacer is installed between the floor portion and the slider, even if the RFID tag is installed on the bottom of the article, the RFID tag and the metal floor portion A distance can be secured between them. For this reason, it is possible to prevent communication between the RFID tag and the antenna from being disabled as the RFID tag 40 and the floor 14 approach each other.

  According to the fifth aspect of the present invention, the data of the RFID tag outside the gate is removed even if the data of the RFID tag outside the gate is read by removing the data whose reception intensity is lower than the reception threshold. Therefore, it is not confused with the data of the RFID tag inside the gate. The processing device may be provided integrally with the reading device or may be provided separately. In the case of a general planar antenna, if data lower than the reception threshold is removed, not only the outside of the gate but also the data of the RFID tag inside the gate is removed.

  According to the sixth aspect of the present invention, the performance of the RFID tag and the reading device is high, and even when the data of the RFID tag outside the gate is read, the reception threshold is set to a high value. The data outside can be appropriately removed. Note that the performance corresponds to, for example, reception sensitivity.

  According to the seventh aspect of the present invention, since the external noise is absorbed from the protective cover to the ground and does not enter the protective cover, the connection line can be effectively protected from the disturbance of the external noise.

  According to the eighth aspect of the invention, communication failure due to reflected waves or the like is suppressed, and communication with the RFID tag can be made no matter where the RFID tag passes inside the gate.

It is a perspective view which shows the external appearance of a gate. It is a perspective view which shows the inside of a gate. It is a vertical sectional view showing the floor portion of the gate entrance. It is a block diagram which shows the data flow of a RFID gate system. It is a top view showing the external appearance of the narrow directivity antenna which concerns on this embodiment. It is a rear view showing the external appearance of the narrow directivity antenna concerning this embodiment. It is a horizontal sectional view of the gate which shows the radiation angle of a radiated wave in case the radiated wave radiated | emitted in the gate goes to the opening of a gate. It is a horizontal sectional view of a gate which shows the radiation angle of a radiated wave in case a radiated wave is reflected in a gate and the reflected wave goes to the opening of a gate. It is a figure which shows the gain with respect to the radiation angle of the narrow directivity antenna which concerns on this embodiment, and a general planar antenna. It is a figure which shows the range which can communicate with an RFID tag in the outer side of the gate in which the general planar antenna was installed. It is a figure which shows the range which can communicate with a RFID tag in the outer side of the gate in which the narrow directivity antenna which concerns on this embodiment was installed. It is a flowchart which shows the process sequence of a data reception process.

Hereinafter, embodiments for carrying out the invention will be described with reference to the drawings.
[1. Configuration of RFID gate system]
First, the configuration of the RFID gate system 100 according to the present embodiment will be described with reference to FIGS. The RFID gate system 100 includes a gate 10, an antenna 50, and a reader / writer 60. RFID is an abbreviation for Radio Frequency Identification.

  The gate 10 is a portable metal tunnel-type gate that has a rectangular tube-shaped wall that is open at both ends and hollow inside, and through which an article with an RFID tag passes. The square cylindrical wall of the gate 10 includes two opposing side walls 11 and 13, a ceiling 12, and a floor 14 facing the ceiling. Here, the direction perpendicular to the openings at both ends, that is, the passing direction of the article is defined as the front-rear direction. Further, a direction perpendicular to the ceiling 12 and the floor 14 is defined as an up-down direction, and a direction perpendicular to the side walls 11, 13 is defined as a left-right direction. Moreover, in FIG.1 and FIG.2, let the opening of the front side be an entrance, and let the opening of the rear side be an exit.

On the outer surface of the ceiling 12, handles 17 and 18 are provided on the front side and the rear side, respectively. The gate 10 can be carried by holding the grips 17 and 18.
On the inner surfaces of the ceiling 12 and the side wall 13, an antenna 50 is assembled with screws. Although not shown in FIG. 2, the antenna 50 is also assembled on the inner surface of the side wall 11. That is, among the four inner surfaces of the gate 10, the antenna 50 is installed on the left and right and the upper three surfaces.

  As shown in FIG. 3, a plate-like spacer 30 having a predetermined thickness is installed on the inner surface of the floor 14. A slider 20 is further provided on the spacer 30. The slider 20 is assembled to the floor 14 with screws with the spacer 30 in between. The slider 20 and the spacer 30 are made of a material that transmits radio waves such as resin and rubber, and the length in the front-rear direction is slightly shorter than that of the floor 14.

  The slider 20 is a transport mechanism that includes a plurality of rollers whose rotation axes are in the left-right direction, and is configured to transport an article from the entrance to the exit of the gate 10. The article pushed in from the entrance of the gate 10 slides on the slider 20 and is conveyed to the exit.

  The spacer 30 is a member provided to ensure a distance between the floor 14 and the RFID tag 40 attached to the article. If the spacer 30 is not installed, when the RFID tag 40 is attached to the bottom surface of the article, the RFID tag 40 and the metal floor 14 approach each other. As a result, radio waves radiated from the RFID tag may be guided to the floor 14 and communication between the RFID tag 40 and the antenna 50 may not be possible. On the other hand, by installing the spacer 30, even when the RFID tag 40 is attached to the bottom of the article, a distance is secured between the RFID tag 40 and the floor 14, and the RFID tag 40 and the antenna 50 are Inability to communicate with each other is suppressed. The thickness of the slider 20 is 9 mm, for example, and the thickness of the spacer 30 is 10 mm, for example.

  Normally, there is a gap between the article passing through the gate 10 and the side walls 11, 13 and the ceiling 12. Antennas 50 are installed on the side walls 11 and 13 and the ceiling. Therefore, when the RFID tag is attached to a part other than the bottom surface of the article, there is a low possibility that communication between the RFID tag 40 and the antenna 50 is impossible.

  Further, as shown in FIG. 3, a rubber mat 25 is attached to the outer surface of the floor 14. The rubber mat 25 has both a function of releasing a screw for assembling the slider 20 to the floor 14 and a function of preventing the gate 10 from slipping.

  Furthermore, a slope 15 is attached to the inlet side end of the floor 14, and a slope 16 is attached to the outlet side end of the floor 14. The slope 15 has a slope that becomes higher toward the entrance of the gate 10, and the slope 16 has a slope that becomes lower as it goes away from the exit of the gate 10. The slopes 15 and 16 smoothly connect the steps between the installation surface when the gate 10 is installed on a table and the transport surface of the slider 20.

  The antenna 50 is a narrow directivity antenna that transmits and receives radio waves to and from the RFID tag. In the present embodiment, the antenna 50 uses the UHF band and radiates radio waves with a preset transmission output. In this embodiment, the antenna 50 is a rectangular planar antenna and is installed in the gate 10 so that the short side is perpendicular to the ceiling 12 and the floor 14 and the long side is perpendicular to the entrance and the exit. ing. Details of the configuration and directivity of the antenna 50 will be described later.

  As shown in FIG. 4, the antenna 50 is connected to the reader / writer 60, and the reader / writer 60 is connected to the PC 70. The PC 70 is a known computer including a CPU, a ROM, and a semiconductor memory such as a flash memory. The reader / writer 60 is a device that reads information stored in the RFID tag 40 from a signal received by the antenna 50. The RFID tag 40 is a passive tag including a semiconductor chip and an antenna. The semiconductor chip of the RFID tag 40 stores information including ID information of an article to which the RFID tag 40 is attached (hereinafter referred to as ID information).

  When reading the ID information from the RFID tag 40, the PC 70 transmits a reading command to the reader / writer 60. When the reader / writer 60 receives a read command from the PC 70, the reader / writer 60 transmits the read command from the antenna 50 as a radio signal. The RFID tag 40 is supplied with power and receives a command from a radio signal transmitted from the antenna 50. The RFID tag 40 interprets the received command, modulates and transmits a radio signal with ID information stored in the semiconductor chip. The reader / writer 60 demodulates the radio signal received by the antenna 50 to acquire ID information, and transmits the acquired ID information to the PC 70. The PC 70 collates the ID information received from the reader / writer 60 with an internal or network database, and executes a predetermined operation. Similarly, when writing information to the RFID tag 40, the PC 70 transmits a write command and write information to the reader / writer 60. The reader / writer 60 transmits the write command and write information received from the PC 70 from the antenna 50 as radio signals. The RFID tag 40 receives a radio signal transmitted from the antenna 50 and stores write information in the semiconductor chip.

  The reader / writer 60 is supported on two mounting brackets 61 provided on the outer surface of the side wall 11 and is installed on the outer surface of the gate 10. The reader / writer 60 is connected to each antenna 50 by three coaxial cables 51. One end of each coaxial cable 51 is connected to the output terminal of each antenna 50 in the gate 10, and the other end is drawn out from three holes provided in the side wall 11. Each terminal is connected.

  The gate 10 includes a protective cover 19 on the outer surface of the side wall 11 that covers the portion of the coaxial cable 51 that is exposed to the outside of the gate 10. The protective cover 19 is installed on the upper side of the reader / writer 60 supported by the mounting bracket 61, and surrounds the three surfaces of the front side, the rear side, and the upper side of the coaxial cable 51. The protective cover 19 is made of metal, and is electrically grounded to the ground in order to protect the coaxial cable 51 from disturbance of external noise. In the present embodiment, the reader / writer 60 corresponds to a reading device and a processing device, and the coaxial cable 51 corresponds to a connection line.

[2. Antenna configuration]
Next, the configuration of the antenna 50 will be described with reference to FIG. As shown in FIGS. 5 and 6, the antenna 50 includes a reflector 51, three radiators 521 to 523, a distributor 540, and three feeding circuits 531 to 533. The antenna 50 is housed in a resin antenna case capable of transmitting radio waves and is installed inside the gate 10.

  The reflector 51 is a parasitic element made of a rectangular metal plate. As shown in FIG. 5, three radiators 521 to 523 are installed on the surface 51A of the reflector 51 with air or a dielectric interposed therebetween, and the reflector 51 is radiated from the radiators 521 to 523. Reflect radio waves. As shown in FIG. 6, a distributor 540 and power supply circuits 531 to 533 are installed on the back surface 51 </ b> B of the reflector 51. The distributor 540 divides the high-frequency signal input to the antenna 50 into three equal parts. The feeding circuits 531 and 533 receive the distributed high-frequency signal via the attenuators 561 and 562 and the coaxial cables 551 and 552, respectively, and excite the radiators 521 and 523, respectively. In addition, the power feeding circuit 532 receives the supply of the high frequency signal distributed via the line 553 on the substrate and excites the radiator 522. The distributor 540 functions as a mixer when transmitting a radio signal received by the antenna 50 to the reader / writer 60. Hereinafter, the high frequency signal supplied to the radiator 521 is S1, the high frequency signal supplied to the radiator 522 is S2, and the high frequency signal supplied to the radiator 523 is S3.

  Radiators 521 to 523 are patch antennas formed in a rectangular shape. Radiators 521 to 523 are arranged at equal intervals on surface 51A along the longitudinal direction of reflector 51 to constitute an array antenna. Specifically, with respect to radiator 522, radiator 521 is disposed on the left side and 523 is disposed on both ends on the right side. On the other hand, the back surface 51 </ b> B side of the antenna 50 has a bilaterally symmetric configuration with the feeding circuit 532 as the center. The antenna 50 is installed so that the passage direction of the article is the direction in which the radiators 521 to 523 are arranged, and the surface 51A of the reflector 51 faces the inside of the gate 10, and the radio wave is directed toward the inside of the gate 10. Radiate.

  The output of the antenna 50 is a mixed output in which the outputs of the radiators 521 to 523 are mixed. From the characteristics of the array antenna, when the phases of the outputs of the radiators 521 to 523 are all the same, the half-value angle of the antenna 50 is narrower than the half-value angle when there is one radiator. Therefore, the three high-frequency signals S1 to S3 supplied to the radiators 521 to 523 are set to have the same phase so that the outputs of the radiators 521 to 523 have the same phase. Specifically, the lengths of the coaxial cables 551 and 552 are adjusted so that the phases of the high-frequency signals S1 and S3 are matched with the phase of the high-frequency signal S2.

  Although the directivity of the main lobe is narrowed by the configuration of the array antenna, side lobes are generated. Along with the generation of the side lobe, there arises a problem that the ID information of the RFID tag that is not to be read (hereinafter referred to as a non-target tag) is erroneously read by the side lobe. Therefore, in the case of the antenna 50 according to the present embodiment, the output power of the outer radiators 521 and 523 is more than the output power of the central radiator 522 in order to further suppress the directivity side lobe of the antenna 50. The powers of the three high-frequency signals S1 to S3 are adjusted so as to be smaller. That is, the three high frequency signals S1 to S3 are weighted so that the power of the high frequency signals S1 and S3 is smaller than the power of the high frequency signal S2.

  Specifically, when the high-frequency signals S1 and S3 pass through the coaxial cables 551 and 552, a passage loss occurs. Therefore, the length of the coaxial cables 551 and 552 and the attenuation amount of the attenuators 561 and 562 are adjusted, and the high-frequency signals The power of S1 and S3 is made smaller than the power of the high-frequency signal S2. That is, in this embodiment, the lengths of the coaxial cables 551 and 552 and the attenuation amounts of the attenuators 561 and 562 are adjusted so that the output phases of the radiators 521 to 523 are the same phase and the radiators 521 and 523 have the same phase. The output power is set to be smaller than the output power of the radiator 522. In this way, the narrow directivity of the antenna 50 described below is realized.

[3. Antenna directivity]
Next, the directivity of the antenna 50 will be described with reference to FIGS. Since the square cylindrical wall of the gate 10 is made of metal, radio waves radiated from the antenna 50 do not leak from the square cylindrical wall. However, the entrance and exit of the gate 10 are open, and radio waves may leak from the opening. If radio waves leak from the opening of the gate 10, the antenna 50 may communicate with a non-target tag outside the gate 10 and read ID information of the non-target tag. Therefore, the antenna 50 is a narrow directional antenna in which the level of radio waves leaking from the opening of the gate 10 is suppressed to a level at which communication with the RFID tag 40 is impossible so that the antenna 50 cannot communicate with the non-target tag.

  Specifically, the gain of the antenna 50 is set to a maximum value at a radiation angle perpendicular to the installation surface with the inner surface of the gate 10 on which the antenna 50 is installed as the installation surface. The level of the radiation wave radiated at the radiation angle of 0 ° at which the gain is maximized is equal to or higher than the level lower limit value L1. The level lower limit value L1 is a lower limit value of the radio wave level that can be communicated with the RFID tag 40 set in advance, and the radio wave level is an electric field strength indicating the strength of the radio wave. That is, inside the gate 10, communication is possible between the antenna 50 and the RFID tag 40 at least at a radiation angle of 0 °.

  Here, a radiation angle range in which a radiated wave radiated from the antenna 50 leaks outward from the opening of the gate 10 is defined as a first leakage range. In the present embodiment, by adjusting the phase and power of the high-frequency signals S1 to S3, the gain of the antenna 50 is adjusted so that the radio wave is emitted outside the opening when a radio wave is radiated with a preset transmission output in the first leakage range. Is set to a value such that the level of the radiated wave leaking to the lower limit is lower than the level lower limit L1.

  As shown in FIG. 7, in this embodiment, the antenna 50 is installed such that the center of the antenna 50 coincides with the center C in the front-rear direction of the gate 10. In the present embodiment, the length of the gate 10 in the front-rear direction is 1080 mm and the length in the left-right direction is 625 mm. The radiation angle perpendicular to the installation surface is 0 °, and the gate 10 faces the installation surface. The radiation angle toward the opening end of the opposing surface is 41 °. That is, in the present embodiment, the first leakage range is a radiation angle of 41 ° or more. Therefore, in the present embodiment, when the radio wave is radiated with a preset transmission output, the level of the radiated wave outside the opening of the gate 10 is lower than the level lower limit. The value is set to be lower than the value L1, specifically, -15 dB or less.

  Further, even when the radiated wave does not leak from the opening of the gate 10, the radiated wave may be reflected by the facing surface and the reflected wave may leak from the opening of the gate 10. Here, the radiation angle range in which the radiated wave radiated from the antenna 50 is reflected by the opposing surface and the reflected wave leaks outward from the opening of the gate 10 is defined as a second leakage range. In the present embodiment, by adjusting the phase and power of the high-frequency signals S1 to S3, the gain of the antenna 50 is adjusted so that the radio wave is emitted outside the opening when a radio wave is radiated with a preset transmission output in the second leakage range. Is set to a value such that the level of the reflected wave leaking to the lower level is lower than the level lower limit L1.

  As shown in FIG. 8, in this embodiment, when a radiation wave having a radiation angle of 23 ° is reflected by the facing surface, the reflected wave is directed toward the opening end of the installation surface. If the radiation angle is less than 23 °, the reflected wave does not leak to the outside of the gate 10 even if the radiation wave is reflected on the facing surface, and if the radiation angle is 41 ° or more, the radiation wave is not reflected on the facing surface. That is, in the present embodiment, the second leakage range is a radiation angle of 23 ° to 41 °. Therefore, in the present embodiment, when a radio wave is radiated at a preset transmission output with a gain in the range of a radiation angle of 23 ° to 41 °, the level of the reflected wave outside the opening of the gate 10 is the level lower limit value. The value is set to be lower than L1, specifically, -10 dB or less.

  In FIG. 9, the directivity of the antenna 50 according to the present embodiment is indicated by a solid line, and the directivity of a general planar antenna is indicated by a broken line. Both the antenna 50 and the general planar antenna have the maximum gain in the radiation direction perpendicular to the installation surface, but the directivity width of the antenna 50 is larger than the directivity width of the general planar antenna. Is very narrow. That is, the antenna 50 has a sharper directivity than a general planar antenna.

  FIG. 10 shows a range in which the RFID gate system 300 in which a general planar antenna is installed in the gate 10 can communicate with the RFID tag 40 in the vicinity of the entrance or the exit. Further, FIG. 11 shows a range in which the RFID gate system 100 in which the antenna 50 is installed in the gate 10 can communicate with the RFID tag 40 in the vicinity of the entrance or the exit. 10 and 11, the number of installed antennas, the transmission output, and the RFID tag 40 are made equal.

  As shown in FIG. 10, in the RFID gate system 300, since the width of the directivity of the planar antenna is wide, the levels of the radiated wave and the reflected wave are not suppressed outside the gate 10, and the RFID tag 40 communicates with the RFID tag 40 in a wide range. It is possible. That is, the RFID gate system 300 can read even the ID information of the non-target tag.

  On the other hand, as shown in FIG. 11, in the RFID gate system 100, since the antenna 50 has a narrow directivity, the level of the radiated wave and the reflected wave is suppressed outside the gate 10, and communication with the RFID tag 40 is performed. The possible range is very narrow. That is, in the RFID gate system 100, reading of the ID information of the non-target tag is extremely suppressed.

  Further, in the present embodiment, reading the ID information of the non-target tag is further suppressed by the data processing by suppressing the reading of the ID information of the non-target tag by setting the antenna 50 to have a narrow directivity.

[4. Data processing]
Next, data processing executed by the reader / writer 60 will be described with reference to the flowchart of FIG. This processing procedure is repeatedly executed by the reader / writer 60 at predetermined intervals.

First, in step S10, a radio signal received by the antenna 50 is acquired as reception data.
Subsequently, in step S20, it is determined whether or not the reception intensity of the reception data acquired in step S10 is equal to or greater than a preset reception threshold value. The antenna 50 is a narrow directivity antenna with sharp directivity. Therefore, even if the ID information of the non-target tag outside the gate 10 is read, compared to the case where the ID information of the RFID tag (hereinafter, target tag) to be read inside the gate 10 is read, The reception intensity of received data becomes very small. Therefore, the reception intensity of the reception data is compared with the reception threshold value to determine whether the reception data is ID information of the target tag or non-target tag ID information.

  Here, the reception threshold value is set according to the directivity of the antenna 50 to a value that can determine whether the received data is the ID information of the target tag or the non-target tag. The reception threshold is set to a higher value as the performance of the RFID tag 40 or the reader / writer 60 is higher. The performance here corresponds to, for example, tag reception sensitivity.

  In step S20, when the reception intensity of the received data is equal to or higher than the reception threshold, the process proceeds to step S30, where it is determined that the received data is data read from the RFID tag 40 existing in the gate 10, and normal processing is performed. I do. That is, the received data is demodulated and the demodulated received data is transmitted to the PC 70.

  On the other hand, when the reception intensity of the reception data is less than the reception threshold value in step S20, the process proceeds to step S40, where it is determined that the reception data is data read from the non-target tag, and the reception data is removed. The process is temporarily terminated as described above.

  In addition, when a general planar antenna having a wide directivity is used, even if the received data is the ID information of the non-target tag, the received strength is higher than when the received data is the ID information of the target tag. There is no big difference. Therefore, when a general planar antenna is used, if data having a reception intensity lower than the reception threshold is removed, even the ID information of the target tag is removed.

[5. effect]
According to the embodiment described above in detail, the following effects can be obtained.
(1) The gain of the antenna 50 becomes maximum at a radiation angle of 0 °, and decreases sharply at the radiation angle toward the outside of the gate 10, so that the antenna 50 and the RFID tag 40 can communicate with each other inside the gate 10, Outside the gate 10, communication between the antenna 50 and the RFID tag 40 is suppressed. Therefore, it is possible to suppress reading of RFID tags that are not to be read existing outside the gate 10 without using a radio wave shielding structure in the passage direction of the gate 10.

  (2) Since the gain of the antenna 50 is greatly reduced even at the radiation angle at which the reflected wave goes to the outside of the gate 10, the antenna 50 and the RFID tag 40 not only by the reflected wave but also by the reflected wave are outside the gate 10. Communication is also suppressed. Therefore, reading of the RFID tag 40 outside the gate 10 can be further suppressed.

  (3) Since the center C in the front-rear direction of the gate 10 and the center of the antenna 50 coincide with each other, the gain of the antenna 50 is maximized at the center of the gate 10 and the gain is suppressed at the entrance and the exit. Can do.

  (4) Since the spacer 30 is installed between the floor 14 and the slider 20, even if the RFID tag 40 is installed at the bottom of the object, the distance between the RFID tag 40 and the metal floor 14 is increased. Can be secured. As a result, it is possible to prevent the RFID tag 40 and the antenna 50 from communicating with each other as the RFID tag 40 and the floor 14 approach each other.

  (5) Even if the ID information of the non-target tag is read by removing the data whose reception intensity is lower than the reception threshold, the ID information of the non-target tag is removed, so it is confused with the ID information of the target tag. There is nothing.

  (6) Even when the performance of the RFID tag 40 or the reader / writer 60 is high and the ID information of the non-target tag is read, the reception threshold is set to a high value. Can be removed.

  (7) The protective cover 19 covering the coaxial cable 51 is electrically grounded to the ground. Therefore, the external noise is absorbed from the protective cover 19 to the ground and does not enter the protective cover 19, so that the coaxial cable 51 can be effectively protected from the disturbance of the external noise.

  (8) Since the antenna 50 is installed on each of the side walls 11 and 13 of the gate 10 and the inner surface of the ceiling 12, no matter where the RFID tag 40 passes inside the gate 10, poor communication due to reflected waves or the like. And the ID information of the RFID tag 40 can be read.

(Other embodiments)
As mentioned above, although the form for implementing this invention was demonstrated, this invention is not limited to the above-mentioned embodiment, It can implement in various deformation | transformation.

  (A) Although three radiators are arranged in the antenna 50 in the above embodiment, four or more radiators may be arranged. Even when four or more radiators are arranged, the output power of each radiator is in phase, and the output power of at least the outermost radiator is smaller than the output power of the other radiators. In this way, the phase and power of each distributed high-frequency signal may be adjusted.

  (B) In the above embodiment, the reader / writer 60 executes the flowchart of FIG. 12, but the PC 70 may execute the flowchart of FIG. The data acquired in S10 is data demodulated by the reader / writer 60. In this case, the RFID gate system 100 includes a PC 70, the reader / writer 60 corresponds to a reading device, and the PC 70 corresponds to a processing device.

  (C) In the above embodiment, a total of three antennas 50 are installed on the inner surfaces of the left and right side walls 11, 12 and the ceiling 12, but the number of antennas 50 is not limited to three, and at least one antenna 50 is included. Install it. Also, a total of four or more antennas 50 may be installed on the inner surfaces of the left and right side walls 11 and 12 and the ceiling 12.

  (D) In the above embodiment, the antenna 50 is installed on the inner surfaces of the left and right side walls 11, 12 and the ceiling 12, but the antenna 50 may also be installed on the inner surface of the floor 14. In this case, the spacer 30 and the slider 20 or only the slider 20 may be installed on the antenna 50 installed on the inner surface of the floor 14. By installing the antenna 50 on the inner surface of the floor 14, it becomes easier to read the ID information of the RFID tag 40 when the RFID tag 40 is attached to the bottom of the article.

  (E) In the above embodiment, the gate 10 is formed in a square tube shape, but is not limited to a square tube shape. For example, the shape of the gate 10 may be a polygonal cylinder shape or a semi-cylindrical shape.

  (F) A plurality of functions of one constituent element in the above embodiment may be realized by a plurality of constituent elements, or a single function of one constituent element may be realized by a plurality of constituent elements. . Further, a plurality of functions possessed by a plurality of constituent elements may be realized by one constituent element, or one function realized by a plurality of constituent elements may be realized by one constituent element. Moreover, you may abbreviate | omit a part of structure of the said embodiment. In addition, at least a part of the configuration of the above embodiment may be added to or replaced with the configuration of the other embodiment. In addition, all the aspects included in the technical idea specified only by the wording described in the claim are embodiment of this invention.

  (G) In addition to the RFID gate system described above, the present invention can be implemented in various forms such as a tag information acquisition method.

  DESCRIPTION OF SYMBOLS 10 ... Gate, 11, 13 ... Side wall, 12 ... Ceiling, 14 ... Floor, 15, 16 ... Slope, 19 ... Protective cover, 20 ... Slider, 30 ... Spacer, 40 ... RFID tag, 50 ... Antenna, 51 ... Coaxial cable , 60 ... Reader / writer, 70 ... PC, 100 ... Gate system.

Claims (8)

An RFID gate system,
A metal gate having a cylindrical wall with both ends open and hollow inside;
One or more installed on the inner surface of the cylindrical wall, radiating radio waves with a preset transmission output, and communicating with an RFID tag included in the article when the article passes through the gate With the antenna
With
The antenna gain is
The inner surface where the antenna is installed is the installation surface, the lower limit value of the radio wave level that can communicate with the RFID tag is the lower limit value, and the radiation angle perpendicular to the installation surface of the antenna is set to the maximum value. The level of the radiation wave outside the opening is set to a value lower than the level lower limit value in a range of radiation angles where the radiation wave radiated from the antenna leaks out from the opening. Yes,
RFID gate system characterized by the above. The antenna gain is
With the inner surface of the cylindrical wall facing the installation surface as the facing surface, the radiation angle is such that the radiated wave radiated from the antenna is reflected by the facing surface and the reflected wave leaks out from the opening. In the range, the level of the reflected wave outside the opening is set to a value that is lower than the level lower limit value,
The RFID gate system according to claim 1. The antenna is installed so that the center in the direction of passage of the gate coincides with the center of the antenna.
The RFID gate system according to claim 1 or 2, wherein The gate is
A plate-shaped spacer formed of a material that transmits radio waves and installed on the inner surface of the floor portion of the cylindrical wall;
A slider that is formed of a material that transmits radio waves and that is installed on the spacer and configured to convey the article from one of the openings to the other opening;
Having
The RFID gate system according to any one of claims 1 to 3, wherein A reader connected to the antenna and configured to read data of the RFID tag;
A processing device configured to process the data read by the reading device;
With
The processing device is configured to remove the data whose radio wave reception intensity by the antenna is lower than a preset reception threshold value,
The RFID gate system according to any one of claims 1 to 4, wherein The reception threshold is set to a higher value as the performance of the RFID tag or the reading device is higher.
The RFID gate system according to claim 5. The reader is installed on the outer surface of the cylindrical wall, and is connected to the antenna by a connection line;
The gate has a metal protective cover that covers the connection line on the outer surface of the cylindrical wall,
The protective cover is electrically grounded to the ground,
The RFID gate system according to claim 5 or 6, wherein The gate has a square cylindrical wall,
The antenna is installed on each of the ceiling portion and the two side wall portions of the square cylindrical wall,
The RFID gate system according to claim 1, wherein: