JP5611511B2 - Reader / writer and article sorting system - Google Patents

Description

  The present invention relates to a reader / writer and an article sorting system. More specifically, the present invention relates to a reader / writer that reads / writes information from / to a non-contact information recording medium that communicates using a microwave method, and is arranged in a vertical and horizontal manner. The present invention relates to a contact information recording medium and an information identification technique for collectively reading information of a plurality of moving non-contact information recording media.

An RFID system using radio waves has a long communicable distance of several tens of centimeters to several meters even for a passive non-contact IC tag having no power source. However, since the communicable distance with the non-contact IC tag is determined by the characteristics of the antenna mounted on the non-contact IC tag, it is difficult to realize a small antenna with a narrow directivity (such as a UHF band of 1 GHz or less). In the RFID system using the ID, it is difficult to accurately detect the direction in which the non-contact IC tag exists.
Patent Document 1 discloses a tag communication antenna that can cover a wide communication area having no communication impossible portion with a small number of highly directional antennas.
JP 2006-20083 A

However, in the prior art disclosed in Patent Document 1, the tag communication antenna used in the RFID reader / writer is a beam scan antenna that can scan a beam of radio waves to be transmitted, and the beam has directivity in the scan direction. Because there are many constraints such as being a strong beam, and scanning the beam so that the plane including the scan direction intersects the floor surface, which is the reflective surface where the strongest reflected wave is generated, depending on the location, the antenna may be There is a problem that it cannot be installed in an optimal position.
The present invention has been made in view of such problems, and includes a plurality of antennas, and from each antenna to the RDID tag based on the delay time of the radio wave transmitted from the reader / writer and the radio wave reflected from the RFID tag. It is an object of the present invention to provide a reader / writer that can identify the direction in which an RFID tag exists by determining the difference in distance between the RFID tags.

In order to solve this problem, the present invention provides a reader / writer that reads and writes information from and to a non-contact information recording medium using radio waves, and modulates and transmits the radio waves to the non-contact information recording medium. A transmission means ; a reception means for receiving and demodulating a reflected wave obtained by modulating a part of the radio wave by the non-contact information recording medium; an arithmetic means; a plurality of antennas; and a control means. Communicating between each antenna and the non-contact information recording medium, and each antenna from a delay time corresponding to a phase difference of a backscattered wave between the antenna and the non-contact information recording medium at that time The direction in which the non-contact information recording medium exists is determined using a calculation result of the calculating means for calculating a difference in distance between the non-contact recording medium and the non-contact recording medium.
The present invention is a reader / writer in a microwave system that communicates with a non-contact information recording medium using microwaves, and radio waves (microwaves) transmitted from the reader / writer are radiated from a plurality of antennas and contactless information. Modulated by the recording medium and received as a reflected wave by each antenna. At this time, a delay time corresponding to the distance occurs between the transmitted radio wave and the reflected wave. According to the present invention, the direction in which the non-contact information recording medium exists is determined by calculating the difference in distance between each antenna and the non-contact information recording medium at that time by calculating means. Thereby, the position of the non-contact information recording medium can be specified without depending on the directivity of the antenna. Also, for applications where narrow-directional antennas have been required in the past, such as identification of luggage transported on a belt conveyor, identification of luggage arranged vertically and horizontally, and realization of a linear identification area. Therefore, it is possible to apply a system using a wide directivity antenna, and it is easy to use it in such an application even in an RFID system using a band where it is difficult to realize a small antenna with a narrow directivity. . In addition, it is possible to set a range to be identified more flexibly than when a narrow-directional antenna is used for the same purpose. It is also possible to simultaneously perform an operation of reading a wide range of non-contact information recording media at once and an operation of identifying non-contact information recording media in a specific range.

According to a second aspect of the present invention, the control means performs communication between two antennas and the non-contact information recording medium, and a phase difference of backscattered waves between the antennas and the non-contact information recording medium at that time The calculation means calculates a difference in distance between each antenna and the non-contact recording medium from a delay time according to the difference between the two antennas based on the calculated difference in distance. A direction in which the non-contact information recording medium is present is determined by calculating an angle formed by a straight line connecting the non-contact information recording medium.
According to a third aspect of the present invention, when the calculation means calculates a difference in distance between each antenna and the non-contact information recording medium, the reflection has a delay proportional to the distance between the non-contact information recording medium and the antenna. It is characterized by measuring using waves.
In an RFID system using radio waves, a non-contact information recording medium modulates and returns a part of a radio wave (CW wave) applied to the non-contact information recording medium (reflects by changing the amplitude and phase). The communication from the non-contact information recording medium to the reader / writer is performed. The reflected wave (backscattered wave) of the radio wave transmitted by itself will return to the reader / writer, but this backscattered wave has a delay proportional to the distance between the non-contact information recording medium and the antenna. It is a wave. Thereby, the difference of the distance between the two antennas and the non-contact information recording medium can be easily calculated by the calculation means.

According to a fourth aspect of the present invention, a specific non-contact information recording medium is designated from among the plurality of non-contact information recording media communicating by an anti-collision protocol that detects a plurality of non-contact information recording media within a detection range without collision. The direction in which the non-contact information recording medium exists is determined.
When communicating using the anti-collision protocol, a specific non-contact information recording medium can be designated from a plurality of non-contact information recording media. Therefore, in the present invention, a specific non-contact information recording medium is designated from a plurality of non-contact information recording media, and the position of the non-contact information recording medium is determined. Thereby, the direction in which the specific non-contact information recording medium selected from the plurality of non-contact information recording media exists can be determined.
According to a fifth aspect of the present invention, when calculating a difference in distance between the two antennas and the non-contact information recording medium, an angle formed by a straight line connecting the midpoint of the distance between the two antennas and the non-contact information recording medium The reader / writer according to any one of claims 1 to 4 , wherein the distance between the antennas is arranged as narrow as possible so that the angle becomes ± 90 degrees or less .
In the measurement of the difference in distance between the non-contact information recording medium and the plurality of antennas, the probability of erroneous detection increases as the distance between the plurality of antennas increases. Therefore, in the present invention, the distance between the antennas is arranged as narrow as possible. Thereby, the probability of erroneous detection can be lowered.

According to a sixth aspect of the present invention, the direction in which the distance difference between each antenna and the non-contact information recording medium increases by giving each antenna a predetermined directivity characteristic is out of the communication range with the non-contact information recording medium. It is characterized by that.
When the distance difference d between the non-contact information recording medium and the two antennas is smallest, the non-contact information recording medium exists at the midpoint between the two antennas. Therefore, an antenna having a certain degree of directivity is used instead of an omnidirectional antenna, and the direction in which the distance difference d increases is out of the communication range with the non-contact information recording medium. Thereby, either the left or right direction from the midpoint can be out of the communication range, and the positional relationship between the non-contact information recording medium and the antenna can be limited.
According to a seventh aspect of the present invention, the distance difference between each antenna and the non-contact information recording medium is calculated from the reception intensity of each antenna under the condition that each antenna has a front directivity characteristic and is arranged at a predetermined interval. It is characterized by correcting.
For example, the antenna 1 and the antenna 2 are antennas having front directivity, and the antennas are arranged at intervals such that θ does not become a value of −3π or less or + 3π or more. If there is no difference in the received intensity between the antenna 1 and the antenna 2 under these conditions, it can be determined that the difference of θ is a value between −π and + π. Further, when the difference between the reception strengths of the antenna 1 and the antenna 2 is large, it is determined that if the reception on the antenna 1 side is large, + π or more and + 3π or less, and if the reception on the antenna 2 side is large, it is −π or less and −3π or more. . Thereby, the distance difference between each antenna and the non-contact information recording medium can be easily corrected from the received intensity.

According to an eighth aspect of the present invention, the control unit measures the difference in phase difference calculated by the calculation unit and obtains a change in the distance between the antenna and the non-contact information recording medium, whereby the non-contact information recording medium Identifies the timing at which the antenna is closest to the antenna.
The timing when the non-contact information recording medium comes closest to the antenna is immediately before the direction of the vector changes. That is, the minimum point of the quadratic function derived from the relationship between distance and time is when the non-contact information recording medium is closest to the antenna. Thereby, the time when the non-contact information recording medium passes through the antenna can be individually managed.
According to a ninth aspect of the present invention, two antennas are arranged in a range where the non-contact information recording medium can exist so that a phase difference of backscattered waves between the antennas indicates a unique direction. A relative speed calculation unit that calculates a relative speed between the antenna and the non-contact information recording medium, and obtains a phase difference by using passage detection by the relative speed calculation unit; By obtaining a point closest to the antenna, a direction in which the non-contact information recording medium exists is obtained, and it is determined that the non-contact information recording medium has passed through the front of the antenna.
In order to make the phase difference indicate a unique direction, it is sufficient to narrow the antenna interval and make the antenna interval <wavelength. However, the influence of the error at the time of phase acquisition becomes large, and the accuracy decreases. Therefore, in the present invention, the accuracy is improved by using both the passage detection based on the relative velocity and the direction detection so that a unique direction can be obtained even under the condition of antenna interval> wavelength. For this purpose, the antenna is installed so that the phase difference in the antenna interval indicates a unique direction in a range where the tag can exist. Then, by using the passage detection based on the relative velocity between the non-contact information recording medium and the antenna, the closest point α to the one antenna of the non-contact information recording medium and the other antenna at the same time as obtaining the phase difference. Find the approach point β. When the non-contact information recording medium moves so as to be orthogonal to the antenna, α is a point on one antenna, and β is a point on the other antenna. And since it can be said that the phase difference indicates a unique direction at the antenna interval, a direction in which the tag is considered to be present can be obtained from the phase difference between α and β.

According to a tenth aspect of the present invention, there may be a specific non-contact information recording medium among the plurality of non-contact information recording media that communicates by an anti-collision protocol that detects a plurality of non-contact information recording media within a detection range without collision. Two antennas are arranged in a range such that the phase difference of the backscattered wave between the antennas indicates a unique direction, and the control means determines a relative velocity between each antenna and the specific non-contact information recording medium. A relative speed calculation unit for calculating, and using the detection of passage by the relative speed calculation unit to obtain a phase difference, by obtaining the point at which the specific non-contact information recording medium is closest to each antenna, A direction in which the specific non-contact information recording medium exists is acquired, and it is determined that the specific non-contact information recording medium has passed through the front of the antenna.
When communicating using the anti-collision protocol, a specific non-contact information recording medium can be designated from a plurality of non-contact information recording media. Therefore, in the present invention, a specific non-contact information recording medium is designated from a plurality of non-contact information recording media, and the position of the non-contact information recording medium is determined. Thereby, the position of a specific non-contact information recording medium selected from a plurality of non-contact information recording media can be determined .

An eleventh aspect of the present invention is an article attached with the reader / writer according to any one of the first to tenth aspects, a plurality of antennas that mediate transmission and reception of radio waves, and a non-contact information recording medium that records information on the article. A conveying means for conveying the article, a detecting means for detecting passage of the article conveyed by the conveying means, a sorting means for sorting the articles conveyed by the conveying means, and a control means, The control means obtains a change in the distance between each antenna and the article by measuring a difference in delay time computed by the computing means, and identifies a transport order of the article and a moving direction with respect to the antenna. When the detection means detects the passage of the article, it is determined that the leading article has passed, and the sorting of the article is executed.
The present invention relates to a sorting system that automatically identifies and sorts moving articles. That is, the reader / writer of the present invention is provided, for example, an antenna is arranged in the vicinity of the belt conveyor, and information is exchanged with a non-contact information recording medium attached to the article. Identifies the direction of travel from Moreover, in order to sort those articles | goods, the detection means which detects that the articles | goods passed and the sorter which actually sorts articles | goods are provided. And the control means comprised from PC etc. memorize | stores the arrangement | sequence order and a moving direction, and if a detection means detects passage of articles | goods, it will judge that the top article | item of arrangement | sequence order passed, the said articles | goods The sorting according to is executed. Thereby, even if the articles in the reading area move, the arrangement order can be accurately grasped and sorted correctly.

According to the present invention, the direction in which the non-contact information recording medium is present is identified by calculating the difference in distance between each antenna and the non-contact information recording medium by calculating means, and therefore depends on the directivity of the antenna. The direction in which the non-contact information recording medium is present can be specified without the need. Also, for applications where narrow-directional antennas have been required in the past, such as identification of luggage transported on a belt conveyor, identification of luggage arranged vertically and horizontally, and realization of a linear identification area. Therefore, it is possible to apply a system using a wide directivity antenna, and it is easy to use it in such an application even in an RFID system using a band where it is difficult to realize a small antenna with a narrow directivity. . In addition, it is possible to set a range to be identified more flexibly than when a narrow-directional antenna is used for the same purpose. It is also possible to simultaneously perform an operation of reading a wide range of non-contact information recording media at once and an operation of identifying non-contact information recording media in a specific range.
Further, the backscattered wave is a wave having a delay proportional to the distance between the non-contact information recording medium and the antenna. Thereby, the difference of the distance between the two antennas and the non-contact information recording medium can be easily calculated by the calculation means.

In addition, since a specific non-contact information recording medium is designated from among a plurality of non-contact information recording media and the direction in which the non-contact information recording medium exists is identified, the specific selected from the plurality of non-contact information recording media The direction in which the non-contact information recording medium exists can be identified.
Also, an antenna having a certain degree of directivity is used instead of an omnidirectional antenna, and the direction in which the distance difference d increases is outside the communication range with the non-contact information recording medium. Can be out of the communication range, and the positional relationship between the non-contact information recording medium and the antenna can be limited.
In addition, since the distance difference between each antenna and the non-contact information recording medium is corrected from the directivity and reception intensity of each antenna, the distance difference between each antenna and the non-contact information recording medium can be easily corrected from the reception intensity. Can do.

In addition, by using one transmission antenna or one reception antenna and performing only reception / transmission with multiple antennas, the difference between the round trip distance from the tag and the reception antenna can be reduced. Since it can be a one-way distance difference between the two, it is possible to identify with higher accuracy.
Also, even when the phase difference indicates multiple directions, it is possible to obtain a unique direction for the moving tag by obtaining the closest point (α point, β point) for the two antennas from the relative speed with the antenna. Is possible. If the error at the time of phase acquisition is constant, the accuracy can be increased as the antenna interval is increased, so that more accurate direction detection and passage detection are possible.
In addition, the difference between the phase difference at the α point and the phase difference at the β point is obtained, and in the vicinity of the middle point, the direction near the antenna intermediate point is indicated. It is.
Furthermore, by providing information such as the tag moving speed and the distance to the tag, tag movement can be predicted based on the α and β points, and the direction of the tag can be estimated from there. On top of that, it is possible to improve the accuracy by obtaining a unique direction.

Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings. However, the components, types, combinations, shapes, relative arrangements, and the like described in this embodiment are merely illustrative examples and not intended to limit the scope of the present invention only unless otherwise specified. .
FIG. 1 is a block diagram of a reader / writer according to an embodiment of the present invention. The reader / writer 50 synchronizes the phase of the output signal of the VCO 2 with the phase of the reference input signal, the VCO 2 that oscillates at a predetermined frequency based on the control voltage of the PLL circuit 1, and the transmission from the VCO 2. A modulator 3 that modulates the received signal into microwaves (radio waves), an amplifier 4 that amplifies the microwaves, a circulator 5 that determines the direction according to the direction of the microwaves, and a non-contact IC tag that transmits microwaves ( Hereinafter, antennas 6a and 6b that receive reflected waves from 7), an amplifier 8 that amplifies the synthesized wave synthesized by the circulator 5, and the VCO2 signal and the signal amplified by the amplifier 8 are added and superimposed. Then, the mixer 9 that demodulates the sin wave, the signal obtained by shifting the signal of the VCO 2 by the 90 ° phase shifter 10 and the signal amplified by the amplifier 8 are added and overlapped. Then, the mixer 11 that demodulates the cos wave, the BPF 12 that passes only a predetermined frequency component from the signal of the mixer 9, the BPF 13 that passes only the predetermined frequency component from the signal of the mixer 11, and the output signal of the BPF 12 are digital signals. An A / D converter 14 that converts the output signal of the BPF 13 into a digital signal, and an arithmetic unit 15 that calculates a phase from the A / D converter 14 and the A / D converter 16. Configured.

In an RFID system using radio waves, a part of the radio waves (CW waves) given to the tag 7 is modulated back by the tag 7 (reflected by changing the amplitude and phase), and then the reader / writer from the tag 7 is read. 50 communication.
The “reflected wave (backscattered wave) of the radio wave transmitted by itself” is returned to the reader / writer 50. This backscattered wave is a wave reciprocated between the tag 7 and the antenna 6a or 6b. It can be considered that the wave has a delay proportional to the distance between the tag 7 and the antenna 6a or 6b with respect to the radio wave transmitted by itself.
In the present embodiment, a plurality of antennas 6a and 6b are used to measure the delay of the backscattered wave from the tag 7 and the difference in distance between the antennas 6a and 6b to the tag 7 is known. Get the direction in which 7 exists.

・・・（１）
とした時（Ａとθ_Cは回路による決まる一定値）、同じアンテナで受信されるタグ７からの後方散乱波は、以下のように表せる。

・・・（２）
ｌ［ｍ］はタグ−アンテナ間の距離、ｃは電波の速度［ｍ／ｓ］、Ｂは空間やタグでの減衰を表す係数、θ_Tはタグでの反射時の位相変化である。電波を利用するＲＦＩＤにおいては、タグ７からリーダライタ５０への通信を行う際、タグ７で加えられる変調により、このＢとθ_Tが変化する。 FIG. 2 is a schematic diagram showing the relationship between the distance between the antenna and the tag when the article a, the article b, and the article c to which the tag 7 is attached are arranged side by side. In this figure, it is assumed that the article a, the article b, and the article c to which the tag 7 is attached are arranged at a predetermined interval. In FIG. 2, the tag 7a of the article a is on the antenna 6a side. The tag 7b of the article b is at the midpoint between the antenna 6a and the antenna 6b. The tag 7c of the article c is on the antenna 6b side.
Here, CW waves transmitted from the antennas 6a and 6b connected to the reader / writer 50 are

... (1)
(A and θ _C are constant values determined by the circuit), the backscattered wave from the tag 7 received by the same antenna can be expressed as follows.

... (2)
l [m] is the distance between the tag and the antenna, c is the velocity of the radio wave [m / s], B is a coefficient representing the attenuation in the space or the tag, and θ _T is the phase change upon reflection at the tag. In RFID using radio waves, when communication from the tag 7 to the reader / writer 50 is performed, B and θ _T change due to modulation applied by the tag 7.

Here, when communication between the tag 7 and the reader / writer 50 is performed by ASK modulation, the delay time is measured in synchronization with a symbol representing 1. Thereby, θ _T can be set to a certain value specific to the tag.
In the case of BPSK modulation, it is assumed that the delay time is measured in synchronization with a symbol representing 1 or 0. Thus, θ _T can be set to a certain value θ _T1 unique to the tag or θ _T2 (= θ _T1 + π). Similarly, in other phase modulations, θ _T can be set to a certain value specific to the tag by measuring the delay time in synchronization with a certain symbol.
Thus, when communicating with the tag 7, the phase when reflected by the tag 7 is stabilized by measuring the delay time in synchronization with the symbol, and θ _T can be regarded as a constant value. it can.
In addition, by measuring the modulated backscattered wave, it becomes possible to remove the backscattered wave (reflected wave) having no change by the BPF, and there is no surrounding metal object or communication state. The influence of reflection from the tag can be eliminated.
Further, since the delay time is measured when the communication from the tag 7 to the reader / writer 50 is performed, under the protocol having the anti-collision function, the communication partner is limited to one tag. It is possible to measure the delay time, and even in an environment where there are a plurality of tags, only the backscattered wave of a specific tag is selected to measure the delay time, and the data (ID ) And the delay time can be managed in association with each other.

・・・（３）
を使用して、直交検波を行うことによって行う。
これにより、以下のＩＱ信号が得られる。

・・・（４）

・・・（５）
ここで、Ｃとθ_Rは、直交検波の操作により付加される変数であるが、Ｃは回路により決まる値であるため一定値と考える事ができる。また、ローカル信号とＣＷ波は、同じ信号源からの信号であるため、その位相差を回路により決まる一定値とみなすことができ、これにより、θ_Rも回路により決まる一定値とみなすことができる。 The measurement of the delay time of the backscattered wave is a local signal generated from the same signal source as the CW wave.

... (3)
Is used to perform quadrature detection.
Thereby, the following IQ signals are obtained.

... (4)

... (5)
Here, C and θ _R are variables added by the operation of quadrature detection, but C is a value determined by the circuit and can be considered as a constant value. Further, since the local signal and the CW wave are signals from the same signal source, the phase difference can be regarded as a constant value determined by the circuit, and thus θ _R can also be regarded as a constant value determined by the circuit. .

・・・（６）
ただし、θ_Rは回路による固有値であるため、使用するアンテナによって、値が異なる場合がある。そこで、あらかじめそれぞれのアンテナを使用した際のθ_constの値を得ておき、各アンテナにおいて測定されたθ_rから、固有のオフセット量θ_constを減算することで補正を行うこととし、その補正後の値をθ_ANTnとする。

・・・（７） Here, since θ _c · θ _T · θ _R can be regarded as constant values, θ _r can be expressed as follows.

... (6)
However, since θ _R is an eigenvalue by the circuit, the value may differ depending on the antenna to be used. Therefore, the value of θ _const when using each antenna is obtained in advance, and correction is performed by subtracting the specific offset amount θ _const from θ _r measured at each antenna. _Let θ _ANTn be the value of.

... (7)

・・・（８）
このとき、θ_ANT1とθ_ANT2の測定を行う間にタグ７が移動すると、その移動量が誤差となるが、この場合、θ_ANT2の測定後に、再度θ_ANT1の測定を行い平均化することで、誤差を補正できる。 It is assumed that radio waves are transmitted to the tag 7 from the antenna 6a and the antenna 6b, respectively, and the delay of the backscattered wave is obtained by the same antenna. At this time, the difference d = l ₁ −l ₂ between the distance l ₁ of the tag 7 and the antenna 6a and the distance l ₂ of the tag 7 and the antenna 6b can be obtained by θ _ANT1 −θ _ANT2 .

... (8)
At this time, if the tag 7 moves during the measurement of θ _ANT1 and θ _ANT2 , the amount of movement becomes an error. In this case, after the measurement of θ _ANT2 , the measurement of θ _ANT1 is performed again and averaged. The error can be corrected.

・・・（９）
そして、回路による固有値であるθ_Rの補正を、前記と同様に行い、その補正後の値をθ_ANTmnとする。

・・・（１０）
ここで、タグ７への電波の送信をあるアンテナａから行い、その後方散乱波の遅延をアンテナ６ａとアンテナ６ｂで得たとすれば、θ_ANTa1−θ_ANTa2により、タグ７−アンテナ６ａの距離ｌ₁とタグ７−アンテナ６ｂの距離ｌ₂の差のｄ＝ｌ₁−ｌ₂を得る事ができる（アンテナａはアンテナ６ａもしくはアンテナ６ｂであっても構わない）。

・・・（１１）
この場合には、二組の直交検波回路を使用して同時にθ_ANTa1とθ_ANTa2の取得を行うこともできる。また、１つの直交検波回路とアンテナ切替回路を用いて、アンテナ６ａにおいてθ_ANTa1の測定を行った後で、アンテナ切替を行い、アンテナ６ｂにおいてθ_ANTa2の取得を行ってもよい。
後者の手段を用いる場合は、θ_ANTa1とθ_ANTa2の測定を行う間にタグ７が移動すると、その差が誤差となるが、この場合、θ_ANTa2の測定後に、再度θ_ANTa1の測定を行い平均化することで、誤差を補正できる。 When transmission is performed with antenna m and reception is performed with different antenna n, when the distance between antenna m and tag 7 is 1 _m and the distance between antenna n and tag is 1 _n , Can be represented.

... (9)
Then, the correction of θ _R , which is an eigenvalue by the circuit, is performed in the same manner as described above, and the corrected value is set to θ _ANTmn .

(10)
Here, if transmission of radio waves to the tag 7 is performed from an antenna a and the delay of the backscattered wave is obtained by the antenna 6a and the antenna 6b, the distance l between the tag 7 and the antenna 6a is _obtained by _{θANTa1− θANTa2. It} is possible to obtain d = l ₁ −l ₂ which is the difference between the distance l ₂ between ₁ and the tag 7 -antenna 6b (the antenna a may be the antenna 6a or the antenna 6b).

(11)
In this case, θ _ANTa1 and θ _ANTa2 can be simultaneously acquired using two sets of quadrature detection circuits. Further, by using one of the quadrature detection circuit and the antenna switching circuit, after performing measurement of theta _ANTa1 the antenna 6a, it performs the antenna switching may be performed to acquire theta _ANTa2 the antenna 6b.
When using the latter means, the tag 7 is moved during the measurement of theta _ANTa1 and theta _ANTa2, but the difference becomes an error, in this case, after measurement of the theta _ANTa2, average was measured again theta _ANTa1 By making it, error can be corrected.

Next, referring to FIG. 3, the tag direction is determined from the distance difference d.
Here, it is assumed that the antenna 6a and the antenna 6b are installed at a distance w, the midpoint of the antenna 6a and the antenna 6b is an origin, and a straight line connecting the antenna 6a and the antenna 6b is an x-axis. At this time, the coordinates of the antenna 6a can be expressed as (w / 2, 0, 0), and the coordinates of the antenna 6b can be expressed as (−w / 2, 0, 0).
Further, the z axis is determined so that the tag 7 exists on the xy plane. At this time, the position of the tag 7 can be expressed as (x, y, 0).
Then, consider triangles having apexes A1, A2, and T as positions of the antenna 6a, the antenna 6b, and the tag 7, respectively.

・・・（１２）
と考えることができる。そして、

・・・（１３）
からθ_bを得ることができる。ここで、直線αと直線βの交わる点をＣ、直線βとｘ軸の交わる点をＢ、点Ａ１−点Ｃ間の距離をｐ、点Ａ１−点Ｂ間の距離をｑとすると、三角形Ａ１−Ｂ−Ｃと、三角形Ａ１−Ａ２−Ｄは、相似の関係にあるため、

・・・（１４）
となる。このため、直線βは原点付近でｘ軸と交わるということができ、２つのアンテナの中点からみて角度θ_bの方向にタグがあると考えることができる。

In the case of d> 0, by drawing a straight line α connecting a point on the side T-A2 that is separated from the position of the antenna A2 by d and the vertex A1, an isosceles triangle having the side T-A1 as one equilateral side can be drawn.
A straight line β that equally divides the apex angle of the isosceles triangle is drawn, the angle obtained by equally dividing the apex angle is θ _a , and the angle between the equally divided line and the y axis is θ _b . At this time, the angle between the base of the isosceles triangle and the x axis can also be expressed as θ _b .
A straight line passing through the vertex A2 and parallel to the straight line β is considered, and the distance between the intersection D of the straight line and the straight line α and the vertex A2 is d ′.
Here, if the distance w between the antennas is relatively small compared to l, the angle θ _a is also small.

(12)
Can be considered. And

... (13)
Θ _b can be obtained from Here, a point where the line α and the line β intersect is C, a point where the line β and the x axis intersect is B, a distance between the points A1 and C is p, and a distance between the points A1 and B is q. Since A1-B-C and the triangle A1-A2-D are in a similar relationship,

(14)
It becomes. For this reason, it can be said that the straight line β intersects the x-axis near the origin, and it can be considered that there is a tag in the direction of the angle θ _{b when} viewed from the midpoint of the two antennas.

Similarly, when d <0, it can be considered that there is a tag in the direction of the angle −θ _{b when} viewed from the midpoint of the two antennas. If d = 0, the tags are the antenna A1 and the antenna A2. It can be said that it lies on a straight line on the midpoint perpendicular to the x axis.
Since the difference of θ is used in the measurement of d, there is a possibility of erroneous detection when θ is −π or less or + π or more. In order to prevent this, the possible range of d is limited by the following method.
1. The distance between the antennas to be measured is narrowed (because the maximum value of d is the distance between the antennas).
2. An antenna having a certain degree of directivity is used instead of an omnidirectional antenna, and the direction in which d increases (the x-axis direction in the above example) is out of the communication range with the tag.

In addition, by using one transmission antenna or one reception antenna and performing only reception / transmission with multiple antennas, the difference between the round trip distance from the tag and the reception antenna can be reduced. Since it can be a one-way distance difference between the two, it is possible to identify with higher accuracy.
Then, the range of difference of θ may be selected by combining the reception intensity at each antenna and the directivity characteristic of the antenna.
For example, the antenna 1 and the antenna 2 are antennas having front directivity, and the antennas are arranged at intervals such that θ does not become a value of −3π or less or + 3π or more. If there is no difference in the received intensity between the antenna 1 and the antenna 2 under these conditions, it can be determined that the difference of θ is a value between −π and + π. Further, when the difference in reception strength between the antenna A1 and the antenna A2 is large, it is determined that if the reception on the antenna A1 side is large, + π or more and + 3π or less, and if the reception on the antenna A2 side is large, it is −π or less and −3π or more. .

  That is, the present invention is a microwave reader / writer that communicates with a non-contact information recording medium using microwaves, and radio waves (microwaves) transmitted from the reader / writer 50 are transmitted from a plurality of antennas 6a and 6b. It is radiated and modulated by the tag 7, and is received by the respective antennas 6a and 6b as reflected waves. At this time, a delay time corresponding to the distance occurs between the transmitted radio wave and the reflected wave. In the present invention, the direction in which the tag 7 exists is identified by calculating the difference in distance between the antennas 6a, 6b and the tag 7 at that time by calculating means. Thereby, the direction in which the tag 7 exists can be specified without depending on the directivity of the antennas 6a and 6b. Also, for applications where narrow-directional antennas have been required in the past, such as identification of luggage transported on a belt conveyor, identification of luggage arranged vertically and horizontally, and realization of a linear identification area. Therefore, it is possible to apply a system using a wide directivity antenna, and it is easy to use it in such an application even in an RFID system using a band where it is difficult to realize a small antenna with a narrow directivity. . In addition, it is possible to set a range to be identified more flexibly than when a narrow-directional antenna is used for the same purpose. Then, it is possible to simultaneously perform the operation of collectively reading the tags 7 in a wide range and the operation of identifying the tags in a specific range among them.

Further, in the RFID system using radio waves, a part of the radio waves (CW waves) given to the tag 7 is modulated back by the tag 7 (reflected by changing the amplitude and phase), so that the tag 7 Communication with the reader / writer 50 is performed. The “reflected wave (backscattered wave) of the radio wave transmitted by itself” is returned to the reader / writer 50. This backscattered wave has a delay proportional to the distance between the tag 7 and the antennas 6a and 6b. It is a wave. Thereby, the difference of the distance between the two antennas 6a and 6b and the tag 7 can be easily calculated by the calculation means.
In addition, when communicating using the anti-collision protocol, a specific tag can be designated from a plurality of tags. Therefore, in the present invention, a specific tag is designated from a plurality of tags, and the direction in which the tag exists is identified. Thereby, the direction where the specific tag selected from the some tag exists can be identified.

The distance d between the tag 7 and the two antennas 6a and 6b is the smallest when the tag 7 exists at the midpoint between the two antennas 6a and 6b. Therefore, an antenna having a certain degree of directivity is used instead of an omnidirectional antenna, and the direction in which the distance difference d increases is out of the communication range with the tag 7. As a result, either the left or right direction from the midpoint can be out of the communication range, and the positional relationship between the tag 7 and the antennas 6a and 6b can be limited.
Further, for example, the antenna 6a and the antenna 6b are antennas having front directivity, and are arranged at intervals such that θ does not become a value of −3π or less or + 3π or more. Under these conditions, if there is no difference in the reception intensity between the antenna 6a and the antenna 6b, it can be determined that the difference in θ is a value between −π and + π. Further, when the difference in reception intensity between the antenna 6a and the antenna 6b is large, it is determined that if the reception on the antenna 6a side is large, + π or more and + 3π or less, and if the reception on the antenna 6b side is large, it is −π or less and −3π or more. . Thereby, the distance difference between each antenna 6a, 6b and the tag 7 can be easily corrected from the received intensity.
In addition, by using one transmission antenna or one reception antenna and performing only reception / transmission with a plurality of antennas, the difference from the round-trip distance with the tag 7 can be reduced. Since it can be a one-way distance difference to the receiving antenna, more accurate identification is possible.
In the above description, the antenna distance difference d is limited so that a unique direction can be obtained from the phase difference. However, in this case, the influence of the error at the time of phase acquisition becomes large and the accuracy decreases. To do. Therefore, accuracy can be improved by using both passage detection based on relative speed and direction detection so that a unique direction can be obtained even under a condition where the phase difference indicates a plurality of directions.

In this embodiment, by increasing the distance between the antennas when the direction is obtained by the phase difference between the two antennas, the ratio of the phase difference / direction difference is increased, and the influence of the error during the phase difference measurement is suppressed. . For example, if the entire antenna front direction is a readable range and the reading range of 180 degrees is represented by a unique phase, the phase difference assigned to the front direction of 10 degrees is 20 degrees or less. If the antenna front direction 30 degrees is represented by a unique phase, the phase difference assigned to the front direction 10 degrees at that time is 120 degrees or less. In this case, the influence of the phase error can be reduced to 1/6.
As a result, when a tag in a direction other than 30 degrees in the antenna front direction is read, the uniqueness between the phase difference and the direction is lost, but in the moving tag, the change in the distance between the antenna and the tag (relative speed). From the fact that the relative velocity (distance change / time) is 0 near the front of the antenna, the passage of the tag in front of the antenna can be detected. From this, by separately detecting that the tag is near the front of the antenna by detecting the closest approach of the two antennas, the direction in which the tag exists is narrowed down to obtain a unique direction.
In FIG. 4, the backscattered wave from the tag of the radio wave emitted from ANT (a) is received by ANT (a) and ANT (b), and the phase difference between the received waves is obtained, so that the tag exists. You can know the direction.
In the front direction of the antenna, when d = phase difference θ [degree] × wavelength λ [m], the direction θb in which the tag exists can be obtained as shown in Expression (13).

However, if the antenna interval w [m] is w> λ with respect to the wavelength λ of the radio wave to be used, there may be a plurality of directions having the same phase difference, and therefore, it is not uniquely determined. In FIG. 4, the black circle points are all points having the same phase difference, and it can be said that points having at least the same phase difference exist in the three directions A, B, and C.
Therefore, in the range 30 where the tag can exist, the antenna is installed so that the phase difference between xy indicates a unique direction. Then, using the passage detection based on the relative speed between the tag and the antenna, the closest point α to the tag ANT (a) and the closest point β to the ANT (b) are obtained simultaneously with the acquisition of the phase difference. If the tag moves perpendicular to the antenna, α is a point on x and β is a point on y. Since it can be said that the phase difference indicates a unique direction between xy, the direction in which the tag is considered to be present can be obtained from the phase difference between α and β.
Thereby, even if w> λ, a unique direction can be obtained from the phase difference near the front of the antenna. And if the error at the time of phase acquisition is constant, the accuracy can be increased as w increases, so that more accurate direction detection and passage detection are possible.

In addition, by predicting tag movement based on α point and β point, or correcting the direction of tag presence, the condition that the phase difference between xy points in a unique direction becomes unnecessary, and more accuracy is achieved. It is also possible to raise. For example, it is possible to obtain the predicted passing time of the antenna intermediate point from the passing times of the α point and the β point, and obtain a unique direction from the condition that the phase difference at that time indicates the direction near the antenna intermediate point. it can.
Further, a difference between the phase difference at the α point and the phase difference at the β point is obtained, and a unique direction can be obtained in the vicinity of the middle, assuming that the direction near the antenna middle point is indicated.
Furthermore, by providing information such as the tag moving speed and the distance to the tag, tag movement can be predicted based on the α and β points, and the direction of the tag can be estimated from there. And then you can get a unique direction.

FIG. 5 is a block diagram showing the configuration of the article sorting system of the present invention. The same components will be described with the same reference numerals as in FIG. This article sorting system 100 includes a reader / writer 50 shown in FIG. 1, antennas 6a and 6b that mediate transmission / reception of radio waves, and a sensor (detection means) 21 that detects passage of articles conveyed by a conveyance means (not shown). And a sorting machine (sorting means) 22 for sorting the articles conveyed by the conveying means, and a PC (control means) 20, and the PC 20 measures the difference in delay time calculated by the calculating means. The change in the distance between the antennas 6a and 6b and the article is obtained, the arrangement order of the articles and the moving direction from the antennas 6a and 6b are identified, and when the sensor 21 detects the passage of the article, the top article in the arrangement order is It is determined that the product has passed, and sorting for the article is executed.
That is, this embodiment is an invention related to a sorting system that automatically identifies and sorts moving articles. That is, the reader / writer 50 shown in FIG. 1 is provided. For example, the antennas 6a and 6b are arranged in the vicinity of the belt conveyor to exchange information with the tag 7 attached to the article. The moving direction from 6a, 6b is identified. Moreover, in order to sort those articles | goods, the sensor 21 which detects that the articles | goods passed and the sorter 22 which actually sorts articles | goods are provided. Then, the PC 20 stores the arrangement order and the moving direction, and when the sensor 21 detects the passage of the article, the PC 20 determines that the top article in the arrangement order has passed, and executes sorting related to the article. Thereby, even if the articles in the reading area move, the arrangement order can be accurately grasped and sorted correctly.

  FIG. 6 is a schematic diagram for explaining an example of the operation of the sorting system of the present invention. The same components will be described with the same reference numerals as those in FIGS. 1 and 5. In the present embodiment, in order to simplify the description, articles a to d are placed on the belt conveyor 23, and tags 7 each storing information (tag ID, route information, etc.) relating to the article are attached. It has been. The order of the articles is a, b, c, d from the top. The belt conveyor 23 moves in the direction of arrow A. The readable area of the antennas 6a and 6b is 6c.

  FIG. 7 is a flowchart for explaining the operation of the sorting system of FIG. This will be described with reference to FIG. The reader / writer 50 collectively reads the information of the tags 7 of the articles a, b, and c in the readable area 6a (S1). The PC 20 calculates the delay time of each tag from the information read by the reader / writer 50 (S2). Further, the PC 20 obtains the distance and direction to each article a, b, c from the difference in delay time (S3). In this figure, it is recognized that the article a is moving away from the antenna 6, the article b is closest to the antenna 6, and the article c is approaching the antenna 6. Then, it is recognized from these calculation results that the order of the articles is a, b, c from the top (S4). This information is stored in the memory in the PC 20 (S5) (see FIG. 8). Here, it is checked whether the sensor 21 has detected an article (S6). Since it is not known when this check will occur, it is preferably performed by interrupt processing. When the sensor 21 is OFF in step S6 (NO in S6), the process returns to step S1 and is repeated. When the sensor 21 is ON in step S6 (YES in S6), the route destination is determined from the top article name a stored in the memory (S7). In this example, since the route destination of the article a is B, the sorting machine 22 performs a sorting operation so that the article a becomes the route B (S8) (see FIG. 8A). Next, since the data of the finished article a is not necessary, it is deleted, and the next article b is moved up to the head as shown in FIG. 8B, and the process returns to S1 and repeats (S9).

  FIG. 8 is a view showing the arrangement order of articles stored in the memory in the PC. In this memory, for example, the stored contents in the case of FIG. In FIG. 8A, the article name 24 is stored as “a” and the route destination 25 is stored as “B” at the start address (AA) of the memory. The address (BB) stores the article name 24 as “b” and the route destination 25 as “A”. In the address (CC), the article name 24 is stored as “c”, and the route destination 25 is stored as “C”. Next, when the sorting of the article a is completed, as shown in FIG. 8B, the article a stored at the address (AA) is deleted, and the article b stored at the address “BB” is changed to the address “ Move up to "AA" and store. Thereafter, the data are sequentially moved up and stored. As a result, the article b is newly placed at the head.

1 is a block diagram of a reader / writer according to an embodiment of the present invention. It is a schematic diagram which shows the relationship between the distance of an antenna and a tag when the goods a, the goods b, and the goods c to which the tag 7 is attached are arranged horizontally. It is a figure which calculates | requires the direction of a tag from the distance difference d. It is a figure explaining the relationship between a tag and an antenna at the time of extending an antenna space | interval. It is a block diagram which shows the structure of the goods sorting system of this invention. It is a schematic diagram for demonstrating an example of operation | movement of the sorting system of this invention. It is a flowchart explaining operation | movement of the sorting system of FIG. It is a figure which shows the arrangement | sequence order of the articles | goods memorize | stored in the memory in PC.

Explanation of symbols

  1 PLL circuit, 2 VCO, 3 modulator, 4, 8 amplifier, 5 circulator, 6a, 6b antenna, 7 tag, 9, 11 mixer, 12, 13 BPF, 14, 16 A / D converter, 15 calculator, 50 Reader / writer

Claims (11)

A reader / writer that reads and writes information on a non-contact information recording medium using radio waves,
Transmitting means for modulating and transmitting radio waves to the non-contact information recording medium, receiving means for receiving and demodulating a reflected wave modulated by the non-contact information recording medium, a part of the radio waves, arithmetic means, and a plurality of antennas And a control means,
The control means performs communication between each antenna and the non-contact information recording medium, and a delay time corresponding to a phase difference of a backscattered wave between each antenna and the non-contact information recording medium at that time A reader / writer for determining a direction in which the non-contact information recording medium exists by using a calculation result of the calculation means for calculating a difference in distance between each antenna and the non-contact recording medium. The control means performs communication between two antennas and the non-contact information recording medium, and a delay time corresponding to a phase difference of backscattered waves between the antennas and the non-contact information recording medium at that time To calculate the difference in distance between each antenna and the non-contact recording medium by the calculating means, and based on the calculated distance difference, the midpoint of the distance between the two antennas and the non-contact information recording 2. The reader / writer according to claim 1, wherein a direction in which the non-contact information recording medium exists is determined by calculating an angle formed by a straight line connecting to the medium.   When the calculation means calculates a difference in distance between each antenna and the non-contact information recording medium, measurement is performed using a reflected wave having a delay proportional to the distance between the non-contact information recording medium and the antenna. The reader / writer according to claim 1, wherein:   A specific non-contact information recording medium is designated from the plurality of non-contact information recording media communicating by an anti-collision protocol for detecting a plurality of non-contact information recording media within a detection range without collision. 4. The reader / writer according to claim 1, wherein the direction in which the medium exists is determined.   When calculating the difference in distance between the two antennas and the non-contact information recording medium, an angle formed by a straight line connecting the midpoint of the distance between the two antennas and the non-contact information recording medium is ± 90 degrees or less. The reader / writer according to any one of claims 1 to 4, wherein the distance between the antennas is arranged to be as narrow as possible.   By giving each antenna a predetermined directivity characteristic, a direction in which a distance difference between each antenna and the non-contact information recording medium increases is outside a communication range with the non-contact information recording medium. The reader / writer according to any one of claims 1 to 5.   The distance difference between each antenna and the non-contact information recording medium is corrected from the reception intensity of each antenna under the condition that each antenna has a front directivity characteristic and is arranged at a predetermined interval. The reader / writer according to any one of claims 1 to 6.   The control means measures the difference of the phase difference calculated by the calculation means and obtains a change in the distance between the antenna and the non-contact information recording medium, so that the non-contact information recording medium reaches the antenna. 3. The reader / writer according to claim 1, wherein the approach timing is identified. Two antennas are arranged in a range where the non-contact information recording medium can exist so that the phase difference of the backscattered wave between the antennas indicates a unique direction, and the control means is configured to contact each antenna and the non-contact A relative speed calculation unit that calculates a relative speed with the information recording medium is provided, and a phase difference is obtained by using passage detection by the relative speed calculation unit, and the non-contact information recording medium is closest to each antenna. 2. The point in which the non-contact information recording medium exists is obtained by obtaining a point, and it is determined that the non-contact information recording medium has passed through the front of the antenna. Or the reader / writer of 8. The antenna is within a range in which a specific non-contact information recording medium can exist among the plurality of non-contact information recording media communicating by an anti-collision protocol that detects a plurality of non-contact information recording media within a detection range without collision. Two antennas are arranged so that the phase difference of backscattered waves between them indicates a unique direction, and the control means calculates a relative speed between each antenna and the specific non-contact information recording medium. And obtaining the phase difference using the passage detection by the relative velocity calculation unit, and obtaining the specific non-contact information recording medium by obtaining a point at which the specific non-contact information recording medium is closest to each antenna. The direction in which the information recording medium exists is acquired, and it is determined that the specific non-contact information recording medium has passed through the front of the antenna. Writer described.   An article to which the reader / writer according to any one of claims 1 to 10, a plurality of antennas that mediate transmission / reception of radio waves, a non-contact information recording medium that records information about the article, and the article are conveyed Conveying means, detecting means for detecting passage of articles conveyed by the conveying means, sorting means for sorting the articles conveyed by the conveying means, and control means,
  The control means obtains a change in the distance between each antenna and the article by measuring a difference in delay time computed by the computing means, and identifies a transport order of the article and a moving direction with respect to the antenna. When the detection means detects the passage of the article, it is determined that the leading article has passed, and the sorting of the article is executed.

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