JP7032065B2 - Wireless communication equipment - Google Patents

Description

The present invention relates to a wireless communication device using an RF tag.

RF tags may be used to identify and manage products in manufacturing factories. An RF tag in which unique information is embedded is attached to a product or the like, and a reader / writer exchanges information with the RF tag by wireless communication, so that distribution management and location management of the product or the like can be realized.

There are two types of RF tags: an active type that is driven by a built-in battery and a passive type that does not have a battery and is driven by radio waves received from the outside as an energy source. Active RF tags can have a long communication distance, but the unit price is high and it is necessary to know the remaining capacity of the built-in battery, so most of the manufacturing factories that handle a large number of products etc. Not adopted. On the other hand, the passive type RF tag is often adopted in manufacturing factories and the like because the unit price is low and it is not necessary to manage the remaining capacity of the battery.

Japanese Unexamined Patent Publication No. 2008-177739

The passive type RF tag generally has a communication distance of about 5 to 6 [m], and it is required to extend the communication distance depending on the application.
In order to extend the communication distance of the RF tag, for example, it is conceivable to improve the area, length, shape, etc. of the antenna inside the RF tag, but it will be handled by the manufacturer of the RF tag, and the unit price will increase. It ends up.

To extend the communication distance, it is possible to increase the directivity. For example, in Patent Document 1, for the purpose of easily changing the directivity of an existing RFID tag, a base plate in which a tag mounting position for mounting an RFID tag is pre-marked and a non-feeding element provided in advance on the base plate are provided. Attachments for RFID tags with and are disclosed. The base plate is formed of a printed substrate material, and the pattern of the antenna element of the non-feeding element is formed on the printed substrate material by etching. However, a two-dimensional structure such as constructing an antenna element on a printed substrate material as in Patent Document 1 can only support linear polarization (horizontal polarization or vertical polarization), and the frequency and shape of the RF tag. Depending on the case, the RFID tags that can be supported may be limited, and the wireless communication function is limited.

The present invention has been made in view of the above points, and an object of the present invention is to extend a communication distance and improve a wireless communication function by using an existing general RF tag.

The gist of the present invention for solving the above problems is as follows.
[1] Passive RF tags and
A first metal round bar that functions as a reflector and is placed away from the RF tag.
A second metal round bar that functions as a director and is arranged on the opposite side of the RF tag from the RF tag on the opposite side to the first round bar.
The RF tag, the first round bar material, and a support for supporting the second round bar material are provided.
The first round bar and the second round bar are arranged in parallel, and the first round bar is arranged in parallel.
The RF tag, the first round bar, and the second round bar are orthogonal to the length direction of the first round bar and the length direction of the second round bar. Arranged line-symmetrically with respect to a straight line
The directivity direction of the RF tag is made to coincide with the length direction of the first round bar and the direction orthogonal to the length direction of the second round bar, and the first round bar is used to the second round bar. In a configuration that strengthens the directivity in the direction toward the round bar material
The support is a wireless communication device that slidably supports the first round bar and the second round bar in a direction in which the directivity is strengthened .
[2] The wireless communication device according to [1], wherein the second round bar material has a plurality of rods and is arranged at predetermined intervals in a direction for strengthening the directivity.
[3] The wireless communication according to [1] or [2], wherein the second round bar member is arranged so as to extend in four directions perpendicular to the direction in which the directivity is strengthened. machine.
[4] Any one of [1] to [3], wherein the first round bar member is arranged so as to extend in four directions perpendicular to the direction in which the directivity is strengthened. The wireless communication device described in.

According to the present invention, the existing general RF tag can be used to extend the communication distance and improve the wireless communication function.

It is a figure which shows the structure of the wireless communication device which concerns on embodiment. It is a characteristic diagram which shows an example of the relationship between the position of a reflector with respect to an RF tag, and a communication distance. It is a schematic diagram for demonstrating the use example of the wireless communication apparatus which concerns on embodiment. It is a schematic diagram for demonstrating the modification of the wireless communication apparatus to which this invention is applied. It is a figure which shows the configuration example which arranges a round bar material so that it crosses.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 shows the configuration of the wireless communication device 1 according to the embodiment. 1A is a plan view of the wireless communication device 1 according to the embodiment, and FIG. 1B is a left side view. The wireless communication device 1 according to the embodiment is configured such that a director and a reflector are arranged before and after the RF tag. In the present application, the directivity of the RF tag can be strengthened as described in detail below, and each direction will be described with the directivity direction D (see the arrow in FIG. 1) as the front.

As shown in FIG. 1, for example, a tag stage 3 is provided on the upper surface of a support 2 made of a prismatic material, and an RF tag 4 in which unique information is embedded is installed in the tag stage 3. When installing the RF tag 4, its directivity is aligned with the longitudinal direction of the support 2. As the RF tag 4, an existing commercially available one may be used, and in this embodiment, all passive RF tags whose frequency band includes the UHF band are used. The RF tag shown in FIG. 1 is only an example, and its shape and size are not limited, and it is possible to deal with a wide variety of differences in the shape and size of the RF tag. Further, when the RF tag 4 is installed on the tag stage 3, the RF tag 4 may be fixed by using a screw or the like, but the method of installing the RF tag 4 is not limited.

Behind the RF tag 4, a metal round bar 5 that functions as a reflector is arranged. The round bar member 5 is held by the holding member 6 mounted on the upper surface of the support 2, and as shown in FIG. 1A, is orthogonal to the support 2 in a plan view. The round bar 5 is arranged at a predetermined distance L ₁ from the RF tag 4. As the round bar material 5, for example, a pipe material made of an aluminum alloy is used, and has an appropriate length H ₁ and a diameter. The round bar 5 corresponds to the first round bar in the present invention.

Further, two metal round bars 7a and 7b functioning as directors are arranged on the opposite side of the round bar 5 with the RF tag 4 interposed therebetween, that is, in front of the RF tag 4. The round bar members 7a and 7b are held by the holding member 8 mounted on the upper surface of the support 2, and as shown in FIG. 1A, are orthogonal to the support 2 in a plan view. That is, the round bar members 7a and 7b are arranged in parallel with the round bar member 5. The round bar 7a is arranged at a predetermined distance L ₂ from the RF tag 4. Further, the round bar member 7b is arranged at a predetermined distance L ₂ from the round bar member 7a. When a plurality of round bar members 7a, 7b, ... Are arranged in this way, they are arranged at intervals of a distance L ₂ from the RF tag 4 in the directivity direction D. As the round bar members 7a and 7b, for example, a pipe material made of an aluminum alloy is used, and has an appropriate length H ₂ (<length H ₁ of the round bar member 5) and a diameter. The round bar members 7a and 7b correspond to the second round bar member in the present invention.

As shown in FIG. 1 (b), the round bar 5 and the round bars 7a and 7b are set to the same height position in the side view, and are set to appropriate height positions with respect to the RF tag 4. It is arranged so as to be.

Next, the structural design parameters of the wireless communication device 1 will be described in detail. The structural design parameters of the wireless communication device 1 are set according to the frequency band λ of the RF tag 4. In the following, the round bar member 5 may be referred to as a reflector 5, and the round bar members 7a and 7b may be referred to as directors 7a and 7b. Further, the directors may be collectively described by using reference numeral 7.
The distance L ₁ between the RF tag 4 and the reflector 5 is set to about λ / 4 wavelength. For example, if the frequency band of the RF tag 4 is 920 MHz, L ₁ = 80 [mm] ± tolerance. FIG. 2 shows an example of the relationship between the position of the reflector with respect to the RF tag and the communication distance. FIG. 2 shows the results of experimentally obtaining the communication distance when the position of the reflector made of a metal round bar is changed with respect to the RF tag in the 920 MHz band (see the characteristic line 201). The characteristic line 202 represents the distance in the case of only the RF tag (without the reflector). As can be seen from this result, if the distance L ₁ is set to around 80 [mm], the communication distance can be extended most.
Further, the distance L ₂ between the RF tag 4 and the director 7a and the distance L ₂ between the director 7a and the director 7b are also about λ / 4 wavelength (L ₂ = 80 [mm] ± tolerance. ) Is set.

The length H ₁ of the reflector 5 is set to be longer than the λ / 2 wavelength (160 [mm]), and is set to 175 [mm] in this embodiment. On the other hand, the length H ₂ of the directors 7a and 7b is set shorter than the λ / 2 wavelength (160 [mm]), and is set to 137 [mm] in this embodiment.
The diameter of the reflector 5 and the diameters of the directors 7a and 7b are both set to a diameter of 4 [mm] in this embodiment.

By providing the reflector 5 and the directors 7a and 7b in the wireless communication device 1 as described above, the existing RF tag 4 can be used to enhance the directivity and extend the communication distance. As shown by the arrow D in FIG. 1, the direction from the reflector 5 toward the RF tag 4 and the directors 7a and 7b, in other words, the longitudinal direction of the support 2 is the directing direction D.
As a result of experiments by the present inventor, when neither the reflector 5 nor the directors 7a and 7b are installed, that is, when the communication distance of the RF tag 4 itself is set to 1, the reflector 5 is installed (guided in FIG. 1). (When the waveguides 7a and 7b are omitted), the communication distance is about 1.5 times longer. Further, when the reflector 5 and one director 7a are installed (when the director 7b is omitted in FIG. 1), the communication distance is about 2.0 times. Further, as shown in FIG. 1, when the reflector 5 and the two directors 7a and 7b are installed, the communication distance is about 3.0 times. As described above, if the communication distance of the RF tag 4 is about 5 to 6 [m], the communication distance can be set to exceed 10 [m], and the communication distance can be dramatically extended.

The configuration of the wireless communication device 1 shown in FIG. 1 is an example, and the shape and the like of each part are not limited. Since the communication distance can be extended only by the reflector 5, the director 7 may be omitted. Further, when it is desired to further extend the communication distance, the number of directors 7 may be three or more.

Further, in FIG. 1, the holding members 6 and 8 are mounted on the upper surface of the support 2 to hold the round bar members 5, 7a and 7b, but the configuration is not limited. For example, the round bar members 5, 7a, and 7b may be held so as to penetrate the left and right side surfaces of the support 2.

Further, the holding member 6 for holding the reflector 5 may be slidable in the longitudinal direction of the support 2, and the position (distance L ₁ ) of the reflector 5 may be made variable. Similarly, the holding member 8 that holds the director 7 may be slidable in the longitudinal direction of the support 2, and the position (distance L ₂ ) of the director 7 may be variable. In this case, the positions of the reflector 5 and the director 7 can be arbitrarily changed according to the frequency band of the mounted RF tag 4, and therefore, regardless of the type of RF tag 4 that can be used, a request from a manufacturing factory or the like is required. It becomes possible to suit the matter.

Next, a usage example of the wireless communication device 1 will be described with reference to FIG. In the wireless communication device 1, since the directivity can be strengthened and the communication distance can be extended, for example, it can be suitably used for identifying objects lined up in a row.
The example of FIG. 3 is a usage example in which the connection and disconnection of the freight car 101 traveling on the rail can be identified.
A wireless communication device 1 is installed in each freight car 101. When the freight cars 101 can be connected either front or back, a pair of wireless communication devices 1 are installed in one freight car 101 so that one has directivity in the forward direction and the other has directivity in the rear direction. Let me do it. Further, the reader 103 is installed on the towing vehicle 102. As the antenna 104 of the reader 103, for example, a Yagi-Uda antenna is used in order to have directivity. The wireless communication device 1 and the antenna 104 are installed so as to be at height positions where they can communicate with each other.

In such a usage example, the reader 103 identifies the freight car 101 connected to (or intends to be connected to) the towing vehicle 102 by exchanging information with the RF tag 4 of each wireless communication device 1 by wireless communication. Can be done. In this case, if a pair of wireless communication devices 1 are installed on one freight car 101 as described above, it is possible to identify which of the front and rear freight cars 101 is facing the direction of the towing vehicle 102 for each freight car 101. ..
It is also possible to estimate the distance between the reader 103 and the wireless communication device 1 based on the strength of the radio wave that wirelessly communicates with each other, and in what order the freight cars 101 are lined up with respect to the tow vehicle 102. Can be identified.

Hereinafter, the wireless communication function of the wireless communication device to which the present invention is applied will be described. It should be noted that each component will be described with a reference numeral common to that of the wireless communication device 1 of the embodiment.
First, the wireless communication device 1 to which the present invention is applied can cope with the inclination of the wireless communication device 1 and the antenna 104. This point will be described.
When the polarization characteristic of the RF tag 4 is linear polarization (horizontal polarization or vertical polarization), as shown in FIG. 4A, the reflector 5 extending in the horizontal direction and the reflector 5 extending in the horizontal direction extend in the horizontal direction. In the wireless communication device 1 provided with the waveguide 7, the RF tag 4 can be reliably detected if the polarization directions are aligned with the antenna 104.
However, as shown in FIG. 4B, when the wireless communication device 1 and the antenna 104 are relatively tilted in the rotation direction about the directivity direction D, the polarization between the wireless communication device 1 and the antenna 104 The direction shifts and the communication distance gradually shortens. As described above, the RF tag 4 may not be detected depending on the relative inclination of the wireless communication device 1 and the antenna 104.

Therefore, as shown in FIG. 4C, the polarization characteristic of the RF tag 4 is circularly polarized, and the reflector 5 and the director 7 are arranged so as to cross each other, that is, the reflector 5 and The directors 7 are arranged so as to extend in four directions perpendicular to the direction D. Even when the reflectors 5 and the directors 7 are arranged so as to cross each other, the reflectors 5 and the directors 7 are arranged in parallel with each other. By making the antenna cross-antenna in this way, even if the wireless communication device 1 and the antenna 104 are relatively tilted in the rotation direction about the directivity direction D (for example, as shown in FIG. 4C), the antenna 104 That is, even if the polarization direction deviates between the wireless communication device 1 and the antenna 104, the RF tag 4 can be reliably detected.

FIG. 5 shows a configuration example in which the reflector 5 and the director 7 are arranged so as to cross each other. The reflector 5 (or director 7) is arranged so as to penetrate the left and right side surfaces of the support 2, and the reflector 5 (or director 7) is arranged so as to penetrate the upper and lower surfaces of the support 2. ) Is arranged. The crossing position is preferably the same position in the directivity direction D, but as shown in FIG. 5, there may be a deviation in the directivity direction D as long as it can be regarded as substantially the same position. This is because, as shown in FIG. 2, even if the position of the reflector with respect to the RF tag is slightly displaced, the communication distance is not affected (the same applies to the director).

As described above, the structure using the reflector 5 and the director 7 made of a round bar can cope with circular polarization, which was difficult with the two-dimensional structure as described in Patent Document 1, and the wireless communication device 1 and the like. It becomes possible to cope with the inclination of the antenna 104. In a usage environment where the inclination of the wireless communication device 1 or the antenna 104 fluctuates, a cross antenna may be used as described with reference to FIG. 4 (c). In the case of the usage example described with reference to FIG. 3, the wireless communication device 1 and the antenna 104 installed in the freight car 101 and the towing vehicle 102 do not significantly tilt in the rotation direction with the directivity direction D as the axis. And the form described in FIG. 4 (a) can be used.

Next, in the wireless communication device 1 to which the present invention is applied, the bandwidth of the frequencies that can be supported can be widened so that the RFID tags 4 that can be used are not limited. This point will be described.
The RF tag 4 has a range in frequency for the purpose of preventing interference. For example, an RF tag in the f ₀ = 920 MHz band has a range of 910 MHz to 922 MHz.
Here, the resonance condition (the condition where the current flowing through the circuit becomes the largest = the condition where the radio wave from the RF tag 4 becomes the largest) is as follows. The notation of √ (LC) is assumed to be √ above (LC).
f ₀ (resonance frequency) = 1 / 2π√ (LC)
ω ₀ (resonance angular frequency) = 2πf ₀
In this way, the resonance frequency f ₀ is determined by the inductance component L and the capacitance component C. The inductance component L indicates the magnitude of the ability to store electromagnetic energy and is determined by the properties of the substance. Capacitance C indicates the magnitude of the ability to store electrical energy and is determined by the nature of the substance.

Whether it is a two-dimensional structure as described in Patent Document 1 or a structure using a reflector 5 made of a round bar or a director 7 as in the present invention, if the lengths are the same, the inductance component L is the same. It is regarded. On the other hand, in a structure using a reflector 5 or a director 7 made of a round bar material, when the diameter or surface area thereof is increased, the capacitance of the inductance component L increases due to the stray capacity such as stray capacitance. As a result, the capacitance C tends to increase. Compared to the two-dimensional structure, in the case of a structure using a reflector 5 made of a round bar or a director 7, the surface area is 3.14 times larger and has a larger capacitance if the width is the same. can.

Here, the Q value is expressed as follows, and the Q value decreases when the capacitance C increases. The resistance component R indicates the magnitude of the ability to consume electric energy, and is determined by the properties of the substance. The notation of √ (L / C) is assumed to be √ above (L / C).
Q = ω ₀ L / R = 1 / ω ₀ CR = 1 / R ・ √ (L / C)

The Q value is expressed as follows.
Q = ω ₀ / ω ₂ －ω ₁
ω ₀ : Central angle frequency (resonance angle frequency)
ω ₂ : Upper limit angular frequency ω ₁ : Lower limit angle frequency The decrease in Q value is equivalent to a large difference between the upper limit angle frequency ω ₂ and the lower limit angle frequency ω ₁ (called the half width), so the bandwidth is It will be wider.

As described above, in the two-dimensional structure, the difference between the upper limit angle frequency ω ₂ and the lower limit angle frequency ω ₁ is small, the bandwidth of the frequencies that can be supported is narrowed, and the usable RFID tags are limited. As described above, for example, even an RF tag in the 920 MHz band has a range of 910 MHz to 922 MHz, but there is a risk that the wireless communication function will deteriorate due to the difference in frequency in that range.
On the other hand, due to the structure using the reflector 5 and the director 7 made of a round bar material, the capacitance C increases, and as a result, the Q value decreases. In other words, since the difference between the upper limit angular frequency ω ₂ and the lower limit angular frequency ω ₁ becomes large, the bandwidth of the frequencies that can be supported can be widened so that the usable RFID tag 4 is not limited.

Although the present invention has been described above with the embodiments, the above embodiments are merely examples of embodiment of the present invention, and the technical scope of the present invention is limitedly interpreted by these. It shouldn't be. That is, the present invention can be implemented in various forms without departing from the technical idea or its main features.
For example, the usage example described with reference to FIG. 3 is only an example, and the wireless communication device to which the present invention is applied can be widely used for physical distribution management and location management of products and the like.

1: Wireless communication equipment, 2: Support, 3: Tag stage, 4: RF tag, 5: Reflector (round bar material), 6: Holding member, 7, 7a, 7b: Waveguide (round bar material) ), 8: Holding member

Claims (4)

Passive RF tags and
A first metal round bar that functions as a reflector and is placed away from the RF tag.
A second metal round bar that functions as a director and is arranged on the opposite side of the RF tag from the RF tag on the opposite side to the first round bar.
The RF tag, the first round bar material, and a support for supporting the second round bar material are provided.
The first round bar and the second round bar are arranged in parallel, and the first round bar is arranged in parallel.
The RF tag, the first round bar, and the second round bar are orthogonal to the length direction of the first round bar and the length direction of the second round bar. Arranged line-symmetrically with respect to a straight line
The directivity direction of the RF tag is made to coincide with the length direction of the first round bar and the direction orthogonal to the length direction of the second round bar, and the first round bar is used to the second round bar. It is configured to strengthen the directivity in the direction toward the round bar material .
The support is a wireless communication device that slidably supports the first round bar and the second round bar in a direction in which the directivity is strengthened . The wireless communication device according to claim 1, wherein the second round bar material has a plurality of rods and is arranged at predetermined intervals in a direction for strengthening the directivity. The wireless communication device according to claim 1 or 2, wherein the second round bar member is arranged so as to extend in four directions perpendicular to the direction in which the directivity is strengthened. The wireless communication according to any one of claims 1 to 3, wherein the first round bar member is arranged so as to extend in four directions perpendicular to the direction in which the directivity is strengthened. machine.

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