JP4400539B2 - RFID system, reader and tag - Google Patents

Description

  The present invention relates to an RFID system including a reader that transmits predetermined power and a tag that operates by receiving the transmitted power, and a reader and tag used in the system.

RFID systems are widely used in fields such as logistics. Depending on the form of distribution, a plurality of products each having a tag may be stored in one container, and the container itself may be provided with an identification tag. In such a case, there is a problem that even if only the tag attached to the container is recognized by the reader, the tag of the product accommodated in the container is recognized.
For example, Patent Literature 1 discloses a wireless communication medium processing device that performs communication by setting a transmission power level according to the type of wireless communication medium corresponding to a tag.
JP 2002-368629 A

That is, Patent Document 1 is a technique based on the premise that different types of tags are used, and cannot solve the above-described problems that occur when the types of tags used are the same.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an RFID system in which a reader side can perform communication by limiting a communication target as necessary even when the types of tags to be used are the same. Another object of the present invention is to provide a reader and a tag used in the system.

According to the RFID system of the first aspect, the tag compares the received power transmitted by the reader with the lower limit value stored in the storage means, and when the received power is equal to or higher than the lower limit value, Response. In other words, when it is necessary for the reader to communicate only with a specific tag, the reader may perform transmission so as to give power equal to or higher than the lower limit value stored and held by the tag to be communicated. Therefore, even when the types of tags to be used are the same, it is possible for the reader side to communicate by limiting the communication target as necessary.
When the tag receives the power level setting command transmitted from the reader, the tag writes and sets the received power level arranged in the command frame in the storage means. Therefore, the reader can determine a tag to be selected as a communication target according to the time by transmitting a power level setting command.

  According to the RFID system of claim 2, the tag compares the received power transmitted by the reader with the upper limit value stored in the storage means, and the received power is not less than the lower limit value and not more than the upper limit value. In this case, a response is returned to the reader. Therefore, when it is necessary for the reader to communicate only with a specific tag, the reader may perform transmission so as to give power that is not less than the lower limit value stored in the tag to be communicated and less than the upper limit value. Therefore, exclusive control is facilitated when two or two or more groups of tags are set as different communication targets.

According to the RFID system of the third aspect, the comparison operation by the comparison means provided in the tag is configured to be effective when the command transmitted from the reader is a command other than the power level setting command. Therefore, when the reader transmits a power level setting command to the tag, the tag can accept the transmitted command regardless of the received power level.

According to the RFID system of the fourth aspect, the power detection means included in the tag A / D converts the operation power supply voltage of the tag obtained by the received power by the A / D conversion circuit and outputs the result to the comparison means. Therefore, the comparison unit can compare the detected value of the received power subjected to A / D conversion and the lower limit value and / or the upper limit value stored in the storage unit as digital data.

According to the RFID system of the fifth aspect, since the storage means provided in the tag is configured by a rewritable nonvolatile memory, the data once written and stored is cut off from the supply of power for operating the tag. Even if you can hold.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a functional block diagram showing an electrical configuration of an RFID tag reader (provided with a data writing function) 1. The reader (communication device) 1 is controlled by a CPU (microcomputer, control means) 2. The data encoding unit 3 encodes transmission data output from the CPU 2 into, for example, a Manchester code and outputs the encoded data to the ASK modulator 4.

  The ASK modulator 4 multiplies the carrier (carrier wave) output from the high-frequency oscillator 5 and the encoded transmission signal (modulated signal) output from the data encoding unit 3 to thereby multiply the ASK (Amplitude Shift Keying). The modulated modulated signal is output to the high frequency amplifier 6. The gain of the high-frequency amplifier 6 is controlled by the CPU 2, and the high-frequency amplifier 6 outputs the signal to the filter 7 when the input signal is amplified with the set gain. The filter 7 outputs the filtered transmission signal to the antenna (transmission means) 9 via the circulator 8. Then, a transmission signal is transmitted to the outside from the antenna 9 as an electromagnetic wave. The CPU 2 transmits a command to the RFID tag side by the above transmission system.

  The circulator 8 is connected to the input terminal of the filter 10 on the receiving side. The signal received via the antenna 9 and the circulator 8 is filtered and then fed to the mixer 11 which is a demodulator and demodulated. The The mixer 11 is given a carrier output from the frequency oscillator 5 for demodulation. When the demodulated signal is binarized by the binarization processing comparator 12, it is decoded by the data restoration unit 13. The decrypted received data is output to the CPU 2. That is, the CPU 2 receives a response (reply) from the RFID tag by the above receiving system.

  FIG. 2 is a functional block diagram showing an electrical configuration of the RFID tag 14. When the RFID tag 14 receives a signal transmitted by the reader 1 via the antenna (reception means) 15, the power supply regeneration circuit 16 rectifies and smoothes the received signal to regenerate the power supply. The regenerated power supply is supplied to the regulator 17 and the received power detector (power detection means) 18. The regulator 17 stabilizes the power regenerated by the power regeneration circuit 16 to a predetermined voltage and supplies it to each part of the RFID tag 14.

  The received signal is given to the demodulator / modulator 19 and demodulated, and the demodulated signal is output to the CPU / logic unit 20 (hereinafter simply referred to as CPU). The reception power detector 18 includes an A / D conversion circuit, and outputs data obtained by A / D converting the power supply voltage regenerated by the power regeneration circuit 16 to the comparison determination unit (comparison means) 21. The comparison determination unit 21 is composed of a magnitude comparator, and compares the data output from the received power detector 18 with the data written and output to the operation level storage memory (storage means) 22 by the CPU 20. Then, the comparison result between the two is output to the CPU 20.

The operation level storage memory 22 is a rewritable nonvolatile memory, and is composed of, for example, an EEPROM. Then, when an operation level setting command is transmitted by the reader 1 as will be described later, the CPU 20 writes and stores the operation power level value set in the command frame in the operation level storage memory 22. Yes.
Here, the “operating power level” is a lower limit power level (voltage value) for determining whether the RFID tag 14 executes a command and transmits a response when a command is transmitted by the reader 1. ). Therefore, the comparison determination unit 21 is configured to output to the CPU 20 a comparison determination signal that becomes active when the data output from the received power detector 18 is equal to or greater than the data written in the operation level storage memory 22. Has been.
Further, when the CPU 20 outputs transmission data to the demodulator / modulator 19, the demodulator / modulator 19 transmits response data to the reader 1 side by load-modulating the carrier wave transmitted by the reader 1. It has become.

Next, the operation of this embodiment will be described with reference to FIGS. FIG. 3 is a flowchart showing the contents of control by the CPU 20 of the RFID tag 14. The CPU 20 waits until a command is received from the reader 1 (step S1). When receiving the command (“YES”), the CPU 20 determines whether the received command is an operating power level setting command (step S2). .
When the operating power level setting command is received (step S2, “YES”), the CPU 20 proceeds to step S4 and executes the received command. In this case, as described above, the operating power level value set in the command frame is written and stored in the operating level storage memory 22. Then, a response is transmitted to the reader 1 (step S5).

Here, FIG. 4A shows an example of the frame configuration of the operating power level setting command. The command frame is configured as follows.
CMD1: Operating power level setting command code FLAG: Whether to send a command to all tags or a specific tag
Flag to select UID: ID of tag to set when selecting a specific tag
LEVEL: Operating power level value (lower limit)
CRC: Check code for frame error detection (Cyclic Redundancy Check)

FIG. 4B shows an example of a frame structure of a response transmitted by the RFID tag 14. The response frame is configured as follows.
FLAG: Flag indicating normal end or error end CODE: Code indicating error content when error ends CRC: Check code for frame error detection

FIG. 5 shows an example of the operating power level set by the reader 1 and the voltage setting value corresponding to each level. In this case, there are three levels “1 to 3”, and the voltage values corresponding to the respective levels are 3.5 V, 2.5 V, and 1.5 V.
FIG. 6 is a sequence diagram showing a flow of processing between the reader 1, the RFID tag 14, and the operation level storage memory 22 when the reader 1 transmits an operation power level setting command to the RFID tag 14.

  Refer to FIG. 3 again. As described above, it is assumed that the operating power level setting command is transmitted from the reader 1 and the RFID tag 14 writes and stores the operating power level value in the operating level storage memory 22. Thereafter, when a command other than the operating power level setting command is transmitted from the reader 1, the CPU 20 determines “NO” in step S2, and the comparison determination signal output from the comparison determination unit 21 becomes active. It is determined whether or not there is (step S3).

If the comparison determination signal is inactive (“NO”), since the received power level at that time is less than the set operating power level, the CPU 20 returns to step S1 without executing the transmitted command. On the other hand, if the comparison determination signal is active (“YES”), since the received power level at that time is equal to or higher than the set operating power level, the CPU 20 shifts to step S4 to execute the received command and execute a response. Is transmitted (step S5).
Therefore, when it is necessary to perform communication by limiting the communication target to some RFID tags 14, the reader 1 first transmits a command so as to set the operating power setting levels “1 to 3”. Then, first, the command is transmitted by setting the gain of the high-frequency amplifier 6 so that the transmission power level of itself is “3” or more and less than “2”. Then, only the RFID tag 14 whose operating power setting level is “3” responds to the transmission.

Then, the reader 1 transmits a command to “sleep” so that the RFID tag 14 whose operating power setting level is “3” does not respond, and then its own transmission power level is “2” or more and less than “1”. Set the gain so that Then, only the RFID tag 14 whose operating power setting level is “2” responds to the transmission.
Similarly, a command for “sleeping” is also transmitted to the RFID tag 14 whose operating power setting level is “2”, and then the gain is set so that its own transmission power level becomes “1” or more. If transmitted, only the RFID tag 14 whose operating power setting level is “1” responds to the transmission.

  As described above, according to the present embodiment, the RFID tag 14 compares the received power transmitted by the reader 1 with the lower limit value stored in the operation level storage memory 22, and the received power is equal to or higher than the lower limit value. In some cases, a response is returned to the reader 1. In other words, when it is necessary for the reader 1 to communicate only with a specific RFID tag 14, it is sufficient to perform transmission so as to give power equal to or higher than the lower limit value stored in the RFID tag 14. Even when the types of RFID tags 14 to be used are the same, the reader 1 side can perform communication by limiting the communication target as necessary.

Further, the reception power detector 18 of the RFID tag 14 A / D-converts the operating power supply voltage obtained from the reception power by the A / D conversion circuit and outputs it to the comparison determination unit 21. The detection value of the received power subjected to the / D conversion and the lower limit value stored in the operation level storage memory 22 can be compared with digital data. Since the operation level storage memory 22 included in the RFID tag 14 is composed of a rewritable nonvolatile memory, the data once written and stored can be stored even when the operation power supply of the RFID tag 14 is cut off. Can be held.
Furthermore, since the comparison operation by the comparison determination unit 21 included in the RFID tag 14 is valid when the command transmitted from the reader 1 is a command other than the power level setting command, the reader 1 transmits the power level setting command. In this case, the RFID tag 14 can accept the transmitted command regardless of the received power level at that time.

(Second embodiment)
7 to 10 show a second embodiment of the present invention. The same parts as those in the first embodiment are denoted by the same reference numerals and the description thereof will be omitted. Only different parts will be described below. The configuration of the second embodiment is basically the same as that of the first embodiment for the reader 1, but the configuration of the RFID tag 31 shown in FIG. 7 is slightly different. The reader 1 is also configured to set an upper limit value in addition to the lower limit value of the operating power level as in the first embodiment when transmitting an operating power level setting command to the RFID tag 31. Yes.

  As shown in FIG. 7, the upper limit value and the lower limit value of the operating power level are written by the CPU 33 into the operation level storage memory (storage means) 32 of the RFID tag 31, and these data are output to the comparison determination unit 34. Yes. The comparison / determination unit (comparison unit) 34 includes two comparators for lower limit comparison and upper limit comparison, and the data output from the received power detector 18 is greater than or equal to the lower limit value for each comparison determination signal. In this case, it is configured to be active and output to the CPU 33 when it is equal to or lower than the upper limit value.

Next, the operation of the second embodiment will be described with reference to FIGS. FIG. 8 shows the frame configuration of the operating power level setting command in FIG. 4 (a), and only the parts different from FIG. 4 (a) will be described.
CMD2: Operating power level setting command code LEVEL_MIN: Operating power level lower limit value LEVEL_MAX: Operating power level upper limit value In other words, the upper limit value of the operating power level is added in the frame. The response frame transmitted by the RFID tag 31 is the same as that shown in FIG.

  FIG. 9 is a view corresponding to FIG. In this case, there are two levels “1, 2”, and the voltage values corresponding to each level are 2.5 V to 3.0 V for level “1” and 1.5 V to 2.5 for level “2”. 2.0V. In the flowchart shown in FIG. 10, when the CPU 33 determines “YES” in step S 2, in step S 4, the lower limit value and upper limit value of the operating power level set in the command frame are stored in the operation level storage memory 32. Write and store.

  Thereafter, when a command other than the operating power level setting command is transmitted from the reader 1, the CPU 33 determines “NO” in step S2, and the lower limit comparison determination signal output from the comparison determination unit 34 becomes active. (Step S3 ′, substantially equal to step S3). If the lower limit comparison determination signal is active (“YES”), it is subsequently determined whether or not the upper limit comparison determination signal is active (step S6).

  If the upper limit comparison determination signal is inactive (“NO”) in step S6, the CPU 33 returns to step S1 without executing the transmitted command. On the other hand, if the upper limit comparison determination signal is active (“YES”), the received power level at that time is greater than or equal to the set lower limit value and less than or equal to the upper limit value, so the CPU 33 proceeds to step S4. The received command is executed and a response is transmitted (step S5).

Therefore, in the case of the second embodiment, the reader 1 first sets the operating power setting level “1, 2” when it is necessary to perform communication by limiting the communication target to some RFID tags 31. To send the command. Then, at first, the gain of the high-frequency amplifier 6 is set so that its own transmission power level is in a range corresponding to “1”, and a command is transmitted. Then, only the RFID tag 31 whose operating power setting level is set to “1” responds to the transmission.
Then, the reader 1 transmits a command with a gain set so that its own transmission power level is in a range corresponding to “2”. Then, only the RFID tag 31 whose operating power setting level is set to “2” responds to the transmission.

As described above, according to the second embodiment, the plurality of RFID tags 31 are configured so that the reception power ranges as the response conditions are different when the power transmitted by the reader 1 is received, When the reader 1 selects a target to be communicated from among a plurality of RFID tags 31, the reader 1 performs communication by setting a transmission power level corresponding to the communication target.
Therefore, even if the types of the plurality of RFID tags 31 are the same, the reader 1 can select some of them as communication targets by appropriately changing the power level transmitted by itself. When the reader 1 needs to communicate only with a specific RFID tag 31, the reader 1 applies power that is not less than the lower limit value stored in the RFID tag 31 to be communicated and less than the upper limit value. Since transmission may be performed, exclusive control is facilitated when two or more groups of RFID tags 31 are set as different communication targets.

Further, when the RFID tag 31 receives the power level setting command transmitted by the reader 1, the RFID tag 31 writes and sets the received power level arranged in the command frame in the operation level storage memory 32, so that the reader 1 The RFID tag 31 to be selected as a communication target can be determined depending on the time.
The power setting as in the above embodiment is particularly effective when the carrier frequency is in the UHF band (for example, about 953 MHz).

The present invention is not limited only to the embodiments described above且one drawing, it is possible following such modifications or extensions.
The set voltage of the power level is an example, and may be changed as appropriate according to the individual design.
In the second embodiment, the comparison / determination unit 34 makes the comparison / determination signal active when the data output from the received power detector 18 is greater than or equal to the lower limit and less than or equal to the upper limit by a combination of a comparator and logic circuit. May be output to the CPU 33. In this case, the determination process by the software of the CPU 33 can be reduced .

1 is a functional block diagram showing an electrical configuration of an RFID tag reader according to a first embodiment of the present invention. Functional block diagram showing the electrical configuration of the RFID tag Flow chart showing control contents of CPU of RFID tag (A) is a frame configuration of the operating power level setting command, (b) is a diagram showing an example of a response frame configuration transmitted by the RFID tag The figure which shows an example of the operating power level set by the reader | leader, and the voltage setting value corresponding to each level. Sequence diagram showing the flow of processing among the reader, RFID tag, and operation level storage memory when the reader transmits an operation power level setting command to the RFID tag FIG. 2 equivalent diagram showing a second embodiment of the present invention. Fig. 4 (a) equivalent Figure equivalent to FIG. 3 equivalent diagram

Explanation of symbols

  In the drawing, 1 is a reader, 9 is an antenna (transmission means), 14 is an RFID tag, 15 is an antenna (reception means), 18 is a received power detector (power detection means, A / D conversion circuit), and 21 is a comparative judgment. Section (comparison means), 22 is an operation level storage memory (storage means, nonvolatile memory), 31 is an RFID tag, 32 is an operation level storage memory (storage means, nonvolatile memory), and 34 is a comparison judgment section (comparison means). Indicates.

Claims (7)

A reader comprising a transmission means for transmitting predetermined power;
A receiving means for receiving the power transmitted by the reader, a power detecting means for detecting the received power, a storage means for storing a lower limit value of the received power, and a comparison for comparing the received power with the lower limit value And a tag that returns a response to the reader when the received power is greater than or equal to the lower limit value .
The reader transmits a power level setting command in which a received power level is arranged in a command frame,
When the tag receives the power level setting command, the tag writes and sets the received power level in the command frame in the storage means . The storage means also stores an upper limit value of received power,
The comparing means compares the received power with the upper limit value,
2. The RFID system according to claim 1, wherein the tag returns a response to the reader when the detected received power is not less than the lower limit value and not more than the upper limit value. 3. The comparison operation by the comparison unit is configured to be effective when a command transmitted from the reader is a command other than the power level setting command . RFID system. The power detection unit includes an A / D conversion circuit that performs A / D conversion on an operation power supply voltage of a tag obtained by the received power and outputs the A / D conversion circuit to the comparison unit. The RFID system according to any one of 1 to 3 . The RFID system according to claim 1 , wherein the storage unit includes a rewritable nonvolatile memory . A reader used in the RFID system according to claim 1. A tag used in the RFID system according to claim 1.

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