JP5198897B2 - RFID tag reader - Google Patents

Description

  The present invention relates to an RFID tag reader that reads a unique identifier set in an RFID tag in a non-contact manner from an RFID tag affixed to a distribution item in fields such as logistics and inventory management.

This type of RFID tag reader (hereinafter simply referred to as “reader”) is an essential component of an antenna for communication with an RFID tag and a high-frequency circuit connected to the antenna. For these components, various mounting forms are adopted depending on the intended use of the reader. For example, as shown in Patent Document 1, when the purpose is to read an RFID tag attached to a product displayed on a store shelf, the top surface or the bottom surface of the shelf plate has substantially the same area as the shelf plate. A thin antenna unit is attached. The high-frequency circuit is housed in a housing attached to an appropriate location on the shelf. The high frequency circuit and the antenna unit are connected by a coaxial cable having a predetermined characteristic impedance. The antenna unit includes a loop antenna and a matching circuit for impedance matching. In such a reader, RFID tags are sequentially read for a large number of products displayed on the shelf, and the read data is transmitted to a device such as a computer.
JP 2001-118037 A

  However, in the system as described above, if the position and angle of the RFID tag affixed to each product and the display direction of each product on the shelf are not stable, all RFID tags can be read stably. It was difficult. This is because the antenna of the RFID tag usually has directivity in a specific direction, and it may be difficult to read depending on the angle of the RFID tag and the antenna.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an RFID tag reader capable of stably reading an RFID tag.

  To achieve the above object, the present invention provides an RFID tag comprising an antenna for communication with an RFID tag and a high-frequency transmission / reception circuit for performing communication using the antenna, and reading a unique identifier from the RFID tag. In the reading apparatus, the antenna includes first to third loop antennas whose directing directions are orthogonal to each other, and distributes the high-frequency signal from the high-frequency transmission / reception circuit into three to the first to third loop antennas. Distributing means for supplying, fluctuation means for periodically changing the intensity or phase of the distributed high-frequency signal supplied to the first loop antenna, distributed high-frequency signal supplied to the second loop antenna, and third loop antenna A phase shift means for generating a phase difference with the distributed high-frequency signal supplied to is provided.

  According to the present invention, since a phase difference is generated between the supply signal to the second loop antenna and the third loop antenna and the supply signal, the combined magnetic field formed by the second and third loop antennas. Is a rotating magnetic field that rotates in a plane defined by the directivity direction of the second loop antenna and the directivity direction of the third loop antenna. Furthermore, the supply signal to the first loop antenna is obtained by periodically changing the intensity or phase of the high frequency signal from the high frequency transmission / reception circuit. Therefore, the first to third loop antennas are combined with the rotating magnetic fields generated by the second and third loop antennas by synthesizing a magnetic field whose intensity or phase is periodically changed by the first loop antenna. The resultant magnetic field is oriented in all directions over time. In other words, it becomes a three-dimensional rotating magnetic field. Accordingly, stable reading can be performed without being affected by the direction in which the RFID tag is placed.

  As an example of a preferred aspect of the present invention, the changing means includes an oscillating means for outputting a high-frequency signal separated by a frequency corresponding to a changing period with respect to a carrier frequency in a high-frequency transmitting / receiving circuit, and a first loop antenna. And a mixing unit that mixes a high-frequency signal from the oscillation unit with a distributed high-frequency signal to be supplied. According to the present invention, the supply signal to the first loop antenna is a mixed signal (synthesized signal) of the high-frequency signal from the high-frequency transmitting / receiving circuit and the high-frequency signal from the oscillating means. The mixed signal has an amplitude (intensity) that increases or decreases at a predetermined frequency. In other words, the mixed signal is a signal with a predetermined period of beat. The beat frequency is determined by the frequency difference between the high frequency signal from the high frequency transmission / reception circuit and the high frequency signal from the oscillation means.

  As an example of a more specific aspect of the present invention, the second loop antenna is supplied with the distributed high frequency signal distributed by the distributing means while maintaining the phase, and the phase shift means is distributed by the distributing means. The distributed high-frequency signal is supplied to the third loop antenna with the phase shifted. According to the present invention, it is possible to reliably generate a phase difference between the high-frequency signal supplied to the second loop antenna and the high-frequency signal supplied to the third loop antenna.

  Also, as an example of a preferred aspect of the present invention, the fluctuation means includes an oscillation means for outputting a signal having a frequency corresponding to the fluctuation period, and the oscillation for the distributed high-frequency signal supplied to the first loop antenna. A phase modulation means for performing phase modulation using a signal from the means is proposed. According to the present invention, the supply signal to the first loop antenna is obtained by changing the phase of the high-frequency signal from the high-frequency transmission / reception circuit with the period of the signal from the oscillation means.

  As an example of the phase variation means, a branch line hybrid coupler (hereinafter simply referred to as “BHC”) is provided, and a distributed high-frequency signal is input to the first port of the BHC and is opposed to the first port. The second port and the third port on the diagonal line of the first port are terminated via an impedance circuit, and a high frequency signal output from the fourth port is supplied to the first loop antenna, and the impedance is An example of the circuit is one that varies the impedance based on a signal from the oscillation means. An example of the impedance circuit includes a circuit including a variable capacitance diode.

  As described above, according to the present invention, the magnetic field in which the intensity or phase of the first loop antenna is periodically changed is synthesized with the rotating magnetic field of the second and third loop antennas. The combined magnetic field formed by the first to third loop antennas becomes a three-dimensional rotating magnetic field that faces all directions over time. Accordingly, stable reading can be performed without being affected by the direction in which the RFID tag is placed.

(First embodiment)
An RFID tag reader according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of an RFID tag reader. In this embodiment, a device that reads a unique identifier from an RFID tag of a product displayed on a product shelf such as a showcase will be described. In this embodiment, the RFID tag and the reading procedure thereof conform to JIS standard X6323.

  As shown in FIG. 1, the RFID tag reading apparatus includes a main control unit 10 that generates a high-frequency signal for communication and reading processing of an RFID tag, and a high-frequency process that processes a high-frequency signal supplied from the main control unit 10. A unit 20 and three loop antennas 31, 32, 33 are provided.

  The main control unit 10 performs a reading process based on an instruction from another device (hereinafter referred to as “higher device”). As shown in FIG. 1, the main control unit 10 includes an interface circuit 11 for connecting to a host device, a reading control unit 12 for controlling reading processing of the RFID tag, and an RF circuit unit including a high-frequency signal transmission / reception circuit. 13. The reading control unit 12 performs reading processing of the RFID tag based on an instruction from the host device, and transmits a reading result (list of unique identifiers of the RFID tag) to the host device. The RF circuit unit 13 is a high frequency transmission / reception circuit using 13.56 MHz as a carrier wave, and includes an oscillation circuit, a modulation circuit, a detection circuit, a demodulation circuit, and the like. The RF circuit unit 13 is connected to the high-frequency processing unit 20 via the coaxial cable 15.

  The high-frequency processing unit 20 distributes the high-frequency signal output from the RF circuit unit 13 of the main control unit 10 into three, the oscillator 22 that outputs an 11 MHz sine wave, and the output signal of the distributor 21 A mixer 23 that mixes (combines) one output signal with the output signal of the oscillator 22 and a phase shifter 24 that shifts the phase of one of the output signals of the distributor 21 are provided. The phase shifter 24 shifts the fundamental frequency of one output signal out of the outputs of the distributor 21, that is, backward by ¼ wavelength (90 °) in the frequency of the carrier wave in the RF circuit unit 13. An output signal from the mixer 23 is supplied to the first loop antenna 31. The output signal from the phase shifter 24 is supplied to the third loop antenna 33. The output signal from the other distributor 21 is supplied to the second loop antenna 32 while maintaining the phase.

  The first to third loop antennas 31, 32, and 33 are arranged at the peripheral edge of the reading area of the RFID tag, and are arranged so that the directivity directions thereof are orthogonal to each other. In other words, as shown in FIG. 1, the first loop antenna 31 is arranged so that the directions of the magnetic fields passing through the first to third loop antennas 31, 32, 33 are orthogonal to each other. Are arranged in the xz plane, the second loop antenna 32 is arranged in the yz plane, and the third loop antenna 33 is arranged in the xy plane.

  The operation of the RFID tag reader according to the present embodiment will be described in particular with respect to the operation of the high-frequency processing unit 20 including the characteristic features of the present invention. FIG. 2 shows an output signal of the RF circuit unit 13. This output signal is a signal obtained by modulating a signal from the reading control unit 12 with respect to a 13.56 MHz carrier wave. Therefore, the center frequency is the same as the frequency of the carrier wave. FIG. 3 shows the output signal of the mixer 23. As shown in FIG. 3, the output signal of the mixer 23 is obtained by increasing or decreasing the amplitude of the high-frequency signal shown in FIG. 2 at a predetermined cycle. In other words, the output signal of the mixer 23 is accompanied by a beat (beat) of a predetermined frequency. The center frequency of the output signal of the mixer 23 is approximately between the frequency of the carrier wave and the frequency of the output signal of the oscillator 22. On the other hand, the beat frequency is approximately equal to the difference between the carrier frequency and the output signal frequency of the oscillator 22. In FIG. 2 and FIG. 3, the description of the modulation component modulated on the carrier wave is omitted.

  Next, magnetic field intensity distribution by the RFID tag reader according to the present embodiment will be described with reference to FIGS. 4 to 6 show a region where the magnetic field strength is high in the region surrounded by the first to third loop antennas 31, 32 and 33. 4 shows the magnetic field strength in the xz plane, FIG. 5 shows the magnetic field strength in the xy plane, and FIG. 6 shows the magnetic field strength in the yz plane.

  As shown in FIG. 4, the distribution of the magnetic field strength draws a circle on the xz plane. This is because the phase of the second loop antenna 32 and the third loop antenna 33 is shifted by ¼ wavelength (90 °). The period of drawing the circle of the magnetic field strength, that is, the period of change with time coincides with the period of the carrier wave. On the other hand, as shown in FIGS. 5 and 6, the magnetic field strength in the xy plane and the yz plane changes periodically in the region indicated by the oblique lines in each figure. The period of change in magnetic field strength over time coincides with the beat frequency.

  As described above, according to the RFID tag reading apparatus of the present embodiment, the direction of the magnetic field strength changes with time in the region surrounded by the first to third loop antennas 31, 32, 33. Moreover, the direction of the magnetic field strength changes in almost all directions of the three-dimensional space. Thereby, it is possible to communicate with the RFID tag regardless of the orientation of the RFID tag, thereby performing a stable and reliable reading process.

  In the above embodiment, only a high-frequency signal supplied to the first loop antenna 31 has a beat (beat), but for example, a plurality of loops such as a first loop antenna 32 and a second loop antenna 33 are used. You may make it supply the high frequency signal accompanying a beat to an antenna.

(Second Embodiment)
An RFID tag reader according to a second embodiment of the present invention will be described with reference to the drawings. FIG. 7 is a configuration diagram of the RFID tag reader. In the figure, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  The RFID tag reader according to the present embodiment is different from the first embodiment in the high frequency signal supplied to the first loop antenna 31. Specifically, in the first embodiment, the first loop antenna 31 receives a high-frequency signal whose amplitude (intensity) fluctuates periodically, that is, a high-frequency signal accompanied by a beat (beat). In the present embodiment, the first loop antenna 31 is input with a high-frequency signal whose phase periodically varies. Hereinafter, the differences will be described in detail.

  As shown in FIG. 7, the high-frequency processing unit 20 of the RFID tag reader according to the present embodiment includes a distributor 21 that distributes the high-frequency signal output from the RF circuit unit 13 of the main control unit 10 into three parts, An oscillator 25 that outputs a low-frequency sine wave of about 800 Hz, a phase modulator 26 that performs phase modulation on one of the output signals of the distributor 21 using the output signal of the oscillator 25, and an output signal of the distributor 21 And a phase shifter 24 for shifting the phase of the output signal. The phase shifter 24 shifts the fundamental frequency of one output signal out of the outputs of the distributor 21, that is, backward by ¼ wavelength (90 °) in the frequency of the carrier wave in the RF circuit unit 13. An output signal from the phase modulator 26 is supplied to the first loop antenna 31. The output signal from the phase shifter 24 is supplied to the third loop antenna 33. The output signal from the other distributor 21 is supplied to the second loop antenna 32 while maintaining the phase.

  The phase modulator 26 will be described with reference to FIG. FIG. 8 is a circuit diagram of the phase modulator. As shown in FIG. 8, the phase modulator 26 includes a branch line hybrid coupler 261. The BHC 261 has four ports 261a to 261d. (A) The signal phase delay amount between the opposing ports (between the ports 261a-261b and between the ports 261c-261d) is 90 °, and (b) on the diagonal line. The signal phase delay amount between ports (between ports 261a-261c and between ports 261b-261d) is 180 °, and (c) no signal is transmitted between adjacent ports (between ports 261a-261d and between ports 261b-261c). (D) The signal transmission characteristic is bidirectional. The output signal of the distributor 21 is input to the port 261a of the BHC 261. The port 261d of the BHC 261 is connected to the first loop antenna 31. The ports 261b and 261c of the BHC 261 are connected to the ground via variable capacitance diodes 262 and 263, respectively.

  The phase modulator 26 includes a DC bias application circuit 264 that applies a predetermined voltage bias to the low-frequency output signal from the oscillator 25. The low frequency signal to which the DC bias is applied by the DC bias applying circuit 264 is supplied to the variable capacitance diodes 262 and 263 through the high frequency choke coils 265 and 266. The high frequency choke coils 265 and 266 are for preventing high frequency signals output from the ports 261b and 261c from being transmitted to the oscillator 25 side.

  According to such a phase modulator 26, the high frequency signal input from the port 261 a of the BHC 261 is output from the port 261 d in a state where the phase is shifted according to the impedance (capacitive reactance) by the variable capacitance diodes 262 and 263. The Here, the reverse bias voltage value to the variable capacitance diodes 262 and 263 periodically changes according to the low frequency signal from the oscillator 25. Thereby, the impedance (capacitive reactance) by the variable capacitance diodes 262 and 263 also periodically changes. Therefore, the signal supplied to the first loop antenna 31 has a phase that varies with the period of the oscillator 25 with respect to the high-frequency signal distributed by the distributor 21.

  According to the RFID tag reader according to the present embodiment, the phase of the supply signal to the second loop antenna 32, the third loop antenna 33, and the supply signal is 90 °, as in the first embodiment. Since they are shifted, the combined magnetic field formed by the second and third loop antennas 32 and 33 becomes a rotating magnetic field. Further, since the signal supplied to the first loop antenna 31 changes in phase with the period of the oscillator 25 as described above, the combined magnetic field formed by the first to third loop antennas 31 to 33 is Turn in all directions over time. In other words, it becomes a three-dimensional rotating magnetic field. Accordingly, stable reading can be performed without being affected by the direction in which the RFID tag is placed.

  Although the first and second embodiments of the present invention have been described in detail above, the present invention is not limited to this. For example, in each of the above embodiments, the phase difference between the supply signal to the second loop antenna 32 and the supply signal to the third loop antenna 33 is set to ¼ wavelength (90 °). There may be. In that case, the magnetic field strength draws an ellipse on the xz plane.

  In each of the above embodiments, only the supply signal to the third loop antenna is shifted in order to cause a phase difference between the supply signal to the second loop antenna 32 and the supply signal to the third loop antenna 33. Although the phase is shifted using the phase shifter 24, the phase of both the signals supplied to the second and third loop antennas 32 and 33 may be shifted if a phase difference occurs between them.

  In each of the above embodiments, the main control unit 10 and the high frequency processing unit 20 are separately mounted. However, these may be mounted in one.

Configuration diagram of RFID tag reader The figure explaining the output signal of RF circuit part The figure explaining the output signal of a mixer The figure explaining magnetic field intensity distribution in xz plane The figure explaining magnetic field strength distribution in xy plane The figure explaining magnetic field strength distribution in a yz plane Configuration diagram of RFID tag reader Configuration diagram of phase modulator

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Main control part, 11 ... Interface circuit, 12 ... Reading control part, 13 ... RF circuit part, 20 ... High frequency processing part, 21 ... Distributor, 22 ... Oscillator, 23 ... Mixer, 24 ... Phase shifter, DESCRIPTION OF SYMBOLS 25 ... Oscillator, 26 ... Phase modulator, 261 ... Branch line hybrid coupler, 262, 263 ... Variable capacity diode, 264 ... DC bias application circuit, 265, 266 ... High frequency choke coil, 31, 32, 33 ... Loop antenna

Claims (5)

An RFID tag reader comprising an antenna for communication with an RFID tag and a high-frequency transmission / reception circuit for performing communication using the antenna, and reading a unique identifier from the RFID tag,
The antenna includes first to third loop antennas whose directing directions are orthogonal to each other,
Distributing means for distributing the high-frequency signal from the high-frequency transmitting / receiving circuit into three and supplying the high-frequency signal to the first to third loop antennas;
Fluctuating means for periodically fluctuating the intensity or phase of the distributed high-frequency signal supplied to the first loop antenna;
Phase shift means for generating a phase difference between the distributed high-frequency signal supplied to the second loop antenna and the distributed high-frequency signal supplied to the third loop antenna ;
The fluctuation means outputs an high-frequency signal separated by a frequency corresponding to a fluctuation period with respect to a carrier frequency in the high-frequency transmission / reception circuit, and the oscillation for the distributed high-frequency signal supplied to the first loop antenna An RFID tag reader comprising: mixing means for mixing high-frequency signals from the means . The second loop antenna is supplied with the distributed high frequency signal distributed by the distributing means while maintaining the phase,
It said phase shifting means reading the RFID tag of claim 1, wherein the supply to the third loop antenna by shifting the phase of dispensing high-frequency signal distributed by the distribution unit device. The RFID tag reader according to claim 1 or 2, wherein an absolute value of a phase difference in the phase shift means is 90 °. An RFID tag reader comprising an antenna for communication with an RFID tag and a high-frequency transmission / reception circuit for performing communication using the antenna, and reading a unique identifier from the RFID tag,
The antenna includes first to third loop antennas whose directing directions are orthogonal to each other,
Distributing means for distributing the high-frequency signal from the high-frequency transmitting / receiving circuit into three and supplying the high-frequency signal to the first to third loop antennas;
Fluctuating means for periodically fluctuating the intensity or phase of the distributed high-frequency signal supplied to the first loop antenna;
Phase shift means for generating a phase difference between the distributed high-frequency signal supplied to the second loop antenna and the distributed high-frequency signal supplied to the third loop antenna ;
The fluctuation means includes an oscillation means for outputting a signal having a frequency corresponding to the fluctuation period, and phase modulation for performing phase modulation on the distributed high-frequency signal supplied to the first loop antenna using the signal from the oscillation means Means and
The phase modulation means includes a branch line hybrid coupler (hereinafter simply referred to as a “coupler”), and inputs a distributed high-frequency signal to the first port of the coupler and a second opposite to the first port. A third port on the diagonal of the first port and the first port is terminated via an impedance circuit, and a high-frequency signal output from the fourth port is supplied to the first loop antenna;
The RFID tag reader, wherein the impedance circuit varies impedance based on a signal from the oscillating means . The RFID tag reader according to claim 4, wherein the impedance circuit includes a variable capacitance diode.

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