Reader / writer and method of controlling the same

Abstract

To reduce the possibility of affecting communication between other reader / writers and other RFID tags.SOLUTION: A reader / writer (1) is provided, comprising a voltage adjustment unit (14) configured to adjust a transmission voltage of a transmission signal when writing to an RFID tag (2) according to a reception voltage of a reception signal received when reading the RFID (2) that allowed normal reading of data.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a reader / writer and a control method thereof. [Background technology]

[0002] Conventionally, there is known an RFID (Radio Frequency Identification) technology that performs short-distance wireless communication using electromagnetic waves or magnetic fields. In the RFID technology, a reader / writer communicates with an RFID tag to read data from the RFID tag and write data to the RFID tag.

[0003] It is known that more power is consumed when writing data to an RFID tag than when reading data from the RFID tag. Therefore, the communication distance between a reader / writer and an RFID tag at which data can be written is shorter than the communication distance between a reader / writer and an RFID tag at which data can be read. If the transmission power used when reading data is the same as the transmission power used when writing data, the reader / writer may be able to read data from an RFID tag located at a specific position but may not be able to write data to it.

[0004] For example, Patent Document 1 discloses a technique for differentiating the transmission power of an inquiry signal for detecting a contactless IC card that can communicate and a data signal when writing. In Patent Document 1, the IC card reader / writer lowers the transmission power of the inquiry signal and increases the transmission power of the data signal when writing. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2004-220492 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, the IC card reader / writer in Patent Document 1 always transmits a higher output power of the data signal during writing than the output power of the inquiry signal. Therefore, if the output power of the data signal during writing is increased, the communication distance over which the IC card reader / writer can write data always increases.

[0007] For example, as the communication distance at which a reader / writer can communicate increases, it is possible that other reader / writers and other RFID tags may exist within the communication range of the reader / writer. In such a situation, the electromagnetic waves or magnetic fields transmitted from the reader / writer when communicating with an RFID tag may interfere with the electromagnetic waves or magnetic fields transmitted by the other reader / writer when communicating with another RFID tag. As a result, communication between the other reader / writer and the other RFID tag may fail.

[0008] An object of one embodiment of the present disclosure is to realize a reader / writer that can appropriately communicate when writing data. [Means for solving the problem]

[0009] In order to solve the above problems, a reader / writer according to one embodiment of the present disclosure includes a voltage measuring unit that measures a received voltage of a received signal received from an RFID tag when reading the RFID tag, and a voltage adjusting unit that adjusts a transmission voltage of a transmission signal to be sent to the RFID tag when writing to the RFID tag, and the voltage adjusting unit adjusts the transmission voltage when writing to the RFID tag in accordance with the received voltage when reading the RFID tag from which data was able to be read successfully.

[0010] According to the above configuration, the transmission voltage when writing data can be increased as necessary. This reduces the possibility of affecting communication between other reader / writers and other RFID tags when writing data. This allows proper communication with RFIDs.

[0011] The voltage adjustment unit may set the transmission voltage when writing to the RFID tag higher than the transmission voltage when reading the RFID tag when the measured reception voltage when reading is less than a threshold value.

[0012] According to the above configuration, when the receiving voltage is equal to or higher than the threshold, the voltage adjusting unit does not adjust the transmitting voltage, thereby reducing the possibility that communication between other reader / writers and other RFID tags is affected when writing data.

[0013] The voltage adjustment unit may increase the transmission voltage during writing as the measured reception voltage becomes lower than the threshold. According to this configuration, the voltage adjustment unit adjusts the transmission voltage so that the transmission voltage becomes higher according to the lower reception voltage. This makes it possible to reduce the possibility that data will not be written to the RFID tag.

[0014] The device may further include a communication unit that communicates with the RFID tag by electromagnetic waves or AC magnetic fields having a frequency in the LF band.

[0015] In order to solve the above problems, a reader / writer control method according to one embodiment of the present disclosure is a control method for controlling a reader / writer that communicates with an RFID tag, and includes a voltage measurement process for measuring a reception voltage of a reception signal received from an RFID tag when reading the RFID tag, and a voltage adjustment process for adjusting a transmission voltage of a transmission signal to be transmitted to the RFID tag when writing to the RFID tag, in which the transmission voltage when writing to the RFID tag is adjusted in the voltage adjustment process according to the reception voltage when reading the RFID tag from which it was possible to normally read data of the reception signal. Effect of the Invention

[0016] According to one embodiment of the present disclosure, a reader / writer capable of appropriately communicating when writing data can be realized. [Brief description of the drawings]

[0017] [Figure 1] 1 is a block diagram showing a configuration of a main part of an RFID system including a reader / writer according to a first embodiment of the present disclosure. [Diagram 2] 13 is a flowchart showing an example of control by the reader / writer. [Diagram 3] 13 is a flowchart showing an example of control by a reader / writer according to a modified example of the first embodiment of the present disclosure. [Figure 4] FIG. 13 is a graph showing the relationship between the reception voltage and the transmission voltage contained in the transmission voltage table. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] [Embodiment 1] Hereinafter, one embodiment of the present disclosure will be described in detail.

[0019] §1 Examples of application Fig. 1 is a block diagram showing the configuration of a main part of an RFID system 100 including a reader / writer 1. An example of a situation to which the present disclosure is applied will be described with reference to Fig. 1.

[0020] The RFID system 100 includes a reader / writer 1, an RFID tag 2, and a PLC (Programmable Logic Controller) 3. The reader / writer 1 is capable of communicating data with the PLC 3, which is a higher-level device, and is controlled by the PLC 3. The reader / writer 1 transmits and receives (communicates) data with the RFID tag 2 in a non-contact manner based on commands transmitted from the PLC 3.

[0021] The reader / writer 1 communicates with the RFID tag 2 by electromagnetic waves or AC magnetic fields. An antenna 4 that realizes communication with the RFID tag 2 is connected to the reader / writer 1. The reader / writer 1 performs at least one of reading and / or reading data from the RFID tag 2 located in a position where communication is possible.

[0022] The RFID tag 2 is attached to an article. For example, the RFID tag 2 may be attached to a workpiece, which is an example of an article, passing through a production line in a factory, etc. Data related to the article to which the RFID tag 2 is attached is stored in the RFID tag 2.

[0023] The RFID tag 2 does not have to move relative to the reader / writer 1 during communication. That is, the position of the RFID tag 2 relative to the reader / writer 1 when writing data may be the same as the position of the RFID tag 2 relative to the reader / writer 1 when reading data. In this case, there is no change in the communication distance between the reader / writer 1 and the RFID tag 2. Also, the RFID tag 2 may move relative to the reader / writer 1 during communication. That is, the position of the RFID tag 2 relative to the reader / writer 1 when writing data may be different from the position of the RFID tag 2 relative to the reader / writer 1 when reading data. In this case, there is a change in the communication distance between the reader / writer 1 and the RFID tag 2.

[0024] The reader / writer 1 of the present disclosure is particularly effective in cases where if the transmission power when reading data from an RFID tag 2 is the same as the transmission power when writing data to the RFID tag 2, the communication distance when writing would be shorter than the communication distance when reading.

[0025] §2 Configuration Example The configuration of the RFID system 100 according to this embodiment will be described in detail below with reference to FIG.

[0026] (Reader / writer configuration) 1, the reader / writer 1 includes a communication unit 11, a communications unit 12, a voltage measurement unit 13, and a voltage adjustment unit 14. The reader / writer 1 may further include a storage unit 15.

[0027] The communication unit 11 transmits and receives data between the reader / writer 1 and the PLC 3. The communication unit 11 also transmits and receives data with the communication unit 12. The communication unit 11 transmits commands received from the PLC 3 to the communication unit 12, the voltage measurement unit 13, and the voltage adjustment unit 14. The communication unit 11 also transmits data related to communication with the RFID tag 2 received from the communication unit 12 to the PLC 3.

[0028] The communication unit 12 communicates with the tag communication unit 21 of the RFID tag 2 based on a command received from the PLC 3 via the communication unit 11. When the communication unit 12 receives a command from the PLC 3, the communication unit 12 at least reads data or writes data via the tag communication unit 21. When reading data, the communication unit 12 may demodulate a reception signal received from the tag communication unit 21 to acquire data included in the reception signal. The communication unit 12 modulates the AC voltage of the transmission voltage generated by the voltage adjustment unit 14 and transmits it to the tag communication unit 21 as a transmission signal.

[0029] The communication unit 12 communicates with the tag communication unit 21 by electromagnetic waves or AC magnetic fields. The communication unit 12 may use electromagnetic waves or AC magnetic fields with a frequency belonging to the LF band (long wave band). The frequency of the electromagnetic waves or AC magnetic fields used by the communication unit 12 is not limited to the frequency belonging to the LF band, and may be a frequency belonging to another band.

[0030] The voltage measurement unit 13 measures the reception voltage of the reception signal received from the RFID tag 2. The voltage measurement unit 13 acquires the reception signal received from the tag communication unit 21 from the communication unit 12. The voltage measurement unit 13 includes a voltage detection circuit that detects the reception voltage of the reception signal. The voltage measurement unit 13 converts the reception voltage of the reception signal detected by the voltage detection circuit into a digital value and stores it in the memory unit 15.

[0031] The voltage measurement unit 13 measures, as the received voltage, any one of the amplitude width of the received signal, the maximum voltage value of the received signal, and the difference between the maximum and minimum voltage values ​​of the received signal. The voltage of the received signal measured by the voltage measurement unit 13 is any one of (i) the voltage at the start of reception of the received signal received from the RFID tag 2, i.e., the voltage of the first bit of the received signal, (ii) the voltage at the end of reception of the received signal received from the RFID tag 2, i.e., the voltage of the last bit of the received signal, or (iii) the average voltage of the entire received signal.

[0032] The voltage adjusting unit 14 adjusts the transmission voltage of the transmission signal to be transmitted to the RFID tag 2. The voltage adjusting unit 14 includes a voltage adjusting circuit that increases the transmission voltage of the transmission signal to be transmitted to the RFID tag 2. The voltage adjusting unit 14 outputs to the communication unit 12 an AC voltage of the transmission voltage generated by the voltage adjusting circuit.

[0033] The voltage adjustment unit 14 sets the transmission voltage to a preset default value when reading the RFID tag 2 and writing to the RFID tag 2. Furthermore, the voltage adjustment unit 14 reads out data of the reception voltage measured by the voltage measurement unit 13 from the storage unit 15 when writing to the RFID tag 2. The voltage adjustment unit 14 identifies the reception voltage of the reception signal when reading the RFID tag 2 from which data could be read normally, and adjusts the transmission voltage when writing to the RFID tag 2 according to the identified reception voltage. That is, the voltage adjustment unit 14 changes the transmission voltage when writing from the default value to a voltage value different from the default value according to the identified reception voltage. The voltage adjustment unit 14 controls the voltage adjustment circuit to adjust the transmission voltage of the transmission signal according to the digital value of the identified reception voltage stored in the storage unit 15.

[0034] The storage unit 15 is a medium that accumulates data such as a program recorded therein by electrical, magnetic, optical, mechanical, or chemical action so that the data can be read by a computer or other device, machine, etc. The storage unit 15 stores data related to communication with the RFID tag 2. The data related to communication is, for example, data read from the RFID tag 2, data to be written to the RFID tag 2, and data related to the transmission voltage during communication.

[0035] (RFID tag configuration) 1, the RFID tag 2 has a tag communication unit 21. The tag communication unit 21 communicates with the communication unit 12 of the reader / writer 1. When the tag communication unit 21 successfully communicates with the reader / writer 1, it transmits a tag ID, which is an identifier indicating the RFID tag 2, to the communication unit 12 of the reader / writer 1 along with a response indicating successful communication.

[0036] The tag communication unit 21 receives a command to read data from the RFID tag 2 or a command to write data to the RFID tag 2 from the communication unit 12 of the reader / writer 1. After receiving a command from the communication unit 12, the tag communication unit 21 transmits a successful processing response for each process when the data read process and data write process are completed. The data read by the reader / writer 1 is stored in a tag memory unit of the RFID tag 2 (not shown). In addition, the data transmitted from the reader / writer 1 is written to the tag memory unit of the RFID tag 2.

[0037] §3 Example of operation 2 is a flow chart showing an example of control by the reader / writer 1. An example of processing by the reader / writer 1 will be described below with reference to FIG.

[0038] First, the communication unit 11 receives a write command to the RFID tag 2 transmitted from the PLC 3 (S1). In step S1, the communication unit 11 transmits the write command received from the PLC 3 to the communication unit 12, the voltage measurement unit 13, and the voltage adjustment unit 14. Upon receiving the write command from the communication unit 11, the voltage adjustment unit 14 sets the transmission voltage of a transmission signal to be transmitted to the RFID tag 2 when writing to the RFID tag 2 to the same voltage as the transmission voltage of a transmission signal to be transmitted to the RFID tag 2 when reading from the RFID tag 2 (S2).

[0039] Next, the communication unit 12 communicates with the RFID tag 2 and reads the tag ID of the RFID tag 2 (S3). In step S3, the communication unit 12 transmits a command to the RFID tag 2 to read the tag ID. In step S3, the transmission voltage of the transmission signal when transmitting the command is a default value set by the voltage adjustment unit 14. In step S3, if the communication is successful, the communication unit 12 receives a reception signal including the tag ID as a response from the tag communication unit 21. Also, in step S3, the voltage measurement unit 13 measures the reception voltage of the reception signal received from the tag communication unit 21. In step S3, the voltage measurement unit 13 stores the measured reception voltage of the reception signal as a digital value in the memory unit 15.

[0040] Next, the communication unit 12 determines whether or not there has been a reply from the RFID tag 2 (S4). In step S4, the communication unit 12 determines whether or not there has been a response from the tag communication unit 21. If there has been no reply from the RFID tag 2 (S4: NO), the communication unit 12 transmits to the communication unit 11 a message indicating that there has been no reply from the RFID tag 2. In S4, the communication unit 11 determines that there is no RFID tag 2 within a range where the reader / writer 1 can communicate with the reader / writer 1, and transmits an RFID tag 2 absence error to the PLC 3. Thereafter, the reader / writer 1 ends the processing of the flowchart shown in FIG. 2.

[0041] If there is a reply from the RFID tag 2 (S4: YES), the communication unit 12 determines whether or not the signal received from the tag communication unit 21 of the RFID tag 2 can be normally demodulated (S6).

[0042] If demodulation is not successful (S6: NO), the communication unit 12 transmits to the communication unit 11 a message indicating that communication with the RFID tag 2 is not possible. In step S6, the communication unit 11 transmits a communication error to the PLC 3, indicating that the communication unit 12 is unable to communicate with the RFID tag 2. Thereafter, the reader / writer 1 ends the process of the flowchart shown in FIG.

[0043] If normal demodulation is possible (S6: YES), the voltage adjustment unit 14 identifies the reception voltage of the reception signal when reading the RFID tag 2 from which data could be read normally (S8). In step S8, the voltage adjustment unit 14 identifies the reception voltage of the reception signal when reading the RFID tag 2, which was measured by the voltage measurement unit 13 in step S3.

[0044] Note that in step S8, the voltage adjustment unit 14 may specify the reception voltage of the reception signal measured by the voltage measurement unit 13 when reading the RFID tag 2 before the communication unit 11 receives the write command from the PLC 3. That is, in step S8, the voltage adjustment unit 14 may specify the reception voltage of the reception signal received when reading data from the same RFID tag 2 as the RFID tag 2 to which data is to be written.

[0045] Next, the voltage adjustment unit 14 judges whether the reception voltage specified in step S8 is equal to or higher than a threshold value (S9). The threshold value may be higher than a reception voltage value at which writing to the RFID tag 2 may be impossible when the RFID tag 2 is located at a specific position relative to the reader / writer 1 and when the transmission voltage at the time of writing and the transmission voltage at the time of reading are the same. The threshold value may be set to a different value between a case where the RFID tag 2 does not move relative to the reader / writer 1 during communication and a case where the RFID tag 2 moves relative to the reader / writer 1 during communication. In step S9, the voltage adjustment unit 14 reads out the digital value of the specified reception voltage from the storage unit 15. In step S9, the voltage adjustment unit 14 compares the read digital value of the reception voltage with the threshold value.

[0046] If the received voltage is less than the threshold (S9: NO), the voltage adjustment unit 14 adjusts the transmission voltage when writing to the RFID tag 2 to a predetermined adjustment value (S10). Here, the adjustment value is a voltage value higher than the transmission voltage when reading the RFID tag 2. In step S10, the voltage adjustment unit 14 generates an AC voltage by the voltage adjustment circuit, using the transmission voltage of the transmission signal as the adjustment value, and outputs the generated AC voltage of the adjustment value to the communication unit 12. After step S10, the reader / writer 1 executes step S11.

[0047] If the received voltage is equal to or higher than the threshold (S9: YES), the reader / writer 1 executes step S11. That is, the voltage adjustment unit 14 outputs an AC voltage from the voltage adjustment circuit as the transmission voltage adjusted in step S2 to be the transmission voltage during writing.

[0048] Next, the communication unit 12 writes data to the RFID tag 2 (S11). In step S11, the communication unit 12 transmits a write command to the tag communication unit 21 of the RFID tag 2 at the transmission voltage output by the voltage adjustment circuit of the voltage adjustment unit 14. In step S11, the communication unit 12 writes data to the RFID tag 2 by specifying the tag ID read in step S3.

[0049] Next, the communication unit 12 determines whether or not the writing to the RFID tag 2 was successful (S12). In step S12, the communication unit 12 determines whether or not a response indicating that the writing was successful is received from the tag communication unit 21 of the RFID tag 2. If the writing was not successful (S12: NO), the reader / writer 1 executes step S7. If the writing was successful (S12: YES), the reader / writer 1 ends the process of the flowchart shown in FIG.

[0050] According to the configuration in which the voltage adjustment unit 14 adjusts the transmission voltage in response to the reception voltage measured by the voltage measurement unit 13, the transmission voltage when writing data can be increased when necessary. Furthermore, the voltage adjustment unit 14 does not need to increase the transmission voltage when writing data higher than the transmission voltage when reading data when it is not necessary. The voltage adjustment unit 14 may set the transmission voltage when writing data to the same as the transmission voltage when reading data when it is not necessary. This makes it possible to realize a reader / writer 1 that can appropriately communicate when writing data to the RFID tag 2 by the reader / writer 1.

[0051] Furthermore, if the voltage adjustment unit 14 is configured to set the transmission voltage during writing higher than the transmission voltage during reading when the receiving voltage is below the threshold, the voltage adjustment unit does not adjust the transmission voltage when the receiving voltage is equal to or higher than the threshold. This reduces the possibility that communication between other reader / writers and other RFID tags will be affected when the reader / writer 1 writes data to the RFID tag 2.

[0052] § 4 Variations Fig. 3 is a flowchart showing an example of control by the reader / writer 1 according to a modified example of the first embodiment of the present disclosure. A modified example of the first embodiment (hereinafter also referred to as "this modified example") will be described with reference to Fig. 3. This modified example differs from the above-described embodiment in that the voltage adjustment unit 14 adjusts the transmission voltage when writing to the RFID tag 2 according to a transmission voltage table. For ease of explanation, the same reference numerals are used to designate members having the same functions as those described in the above embodiment, and their explanations will not be repeated.

[0053] The process by the reader / writer 1 according to this modification will be described below with reference to Fig. 3. Steps S21 to S28 shown in Fig. 3 are similar to steps S1 to S8 in the flowchart shown in Fig. 2, and therefore will not be described. After step S28, the voltage adjustment unit 14 adjusts the transmission voltage when writing to the RFID tag 2 according to the transmission voltage table (S29). In step S29, the voltage adjustment unit 14 adjusts the transmission voltage when writing, based on the digital value of the reception voltage confirmed in step S29.

[0054] Fig. 4 is a diagram showing a graph 40 showing the relationship between the received voltage and the transmitted voltage contained in the transmitted voltage table. An example of the transmitted voltage table will be described with reference to Fig. 4. The transmitted voltage table may be stored in the memory unit 15 of the reader / writer 1. The horizontal axis of the graph 40 relating to the transmitted voltage table corresponds to the received voltage measured by the voltage measuring unit 13, with the received voltage increasing toward the right. The vertical axis of the graph 40 corresponds to the transmitted voltage of the transmitted signal transmitted by the communication unit 12 to the tag communication unit 21 of the RFID tag 2, with the transmitted voltage increasing toward the top.

[0055] The received voltage value Vr shown in graph 40 is the limit value of the received voltage at which writing is possible with the transmission voltage at the time of reading for an RFID tag 2 located at a specific position. The received voltage value Vr is an example of a threshold. Note that the received voltage value Vr only needs to be higher than the limit value of the received voltage at which writing is possible with the transmission voltage at the time of reading for an RFID tag 2 located at a specific position.

[0056] In graph 40, when the received voltage is equal to or greater than the value Vr, the transmitted voltage is set to a constant value Vt1. When the received voltage measured by voltage measurement unit 13 is equal to or greater than the value Vr, voltage adjustment unit 14 sets the transmitted voltage of the transmitted signal to tag communication unit 21 when writing to RFID tag 2 to value Vt1 in accordance with the transmitted voltage table. The transmitted voltage value Vt1 is the same as the default value of the transmitted voltage when reading RFID tag 2. Voltage adjustment unit 14 generates an AC voltage by a voltage adjustment circuit with the transmitted voltage at the time of writing set to value Vt1, and outputs the generated AC voltage of value Vt1 to communication unit 12.

[0057] In graph 40, when the received voltage is less than value Vr, the lower the received voltage is from value Vr, the higher the transmission voltage is set to be above value Vt1. That is, when the received voltage is less than value Vr, the transmission voltage is higher than the transmission voltage when reading the RFID tag 2. When the received voltage is less than value Vr, the voltage adjustment unit 14 adjusts the transmission voltage of the transmission signal transmitted from the communication unit 12 to the tag communication unit 21 of the RFID tag 2 when writing to the RFID tag 2 to a value higher than value Vt1 according to the transmission voltage table. The voltage adjustment unit 14 sets the transmission voltage when writing to a value higher than value Vt1 according to the transmission voltage table, and outputs an AC voltage by the voltage adjustment circuit.

[0058] In the graph 40, the maximum value Vt2 of the transmission voltage when the reception voltage is less than the value Vr is set to a value arbitrarily set by the user or a value regulated by the Radio Act. In addition, in the transmission voltage table, when the reception voltage is less than the value Vr, the transmission voltage may be set to be higher than the value Vt1 in multiple stages as the reception voltage becomes lower than the value Vr.

[0059] As shown in Fig. 3, after step S29, the reader / writer 1 executes steps S30 and S31. Steps S30 and S31 shown in Fig. 3 are similar to steps S11 and S12 shown in Fig. 2, respectively, and therefore will not be described.

[0060] According to the configuration in which the voltage adjusting unit 14 adjusts the transmission voltage during writing in accordance with the transmission data table, the voltage adjusting unit 14 adjusts the transmission voltage so that the transmission voltage becomes higher according to the lowering of the receiving voltage. This makes it possible to reduce the possibility that data will not be written to the RFID tag 2.

[0061] 〔summary〕 A reader / writer according to aspect 1 of the present disclosure includes a voltage measuring unit that measures a received voltage of a received signal that is received from an RFID tag when reading the RFID tag and that enables data to be read successfully, and a voltage adjusting unit that adjusts a transmission voltage of a transmission signal that is sent to the RFID tag when writing to the RFID tag, and the voltage adjusting unit adjusts the transmission voltage when writing to the RFID tag in accordance with the measured received voltage when reading the RFID tag.

[0062] In the reader / writer of aspect 2 of the present disclosure, in the above aspect 1, when the measured received voltage at the time of reading is less than a threshold value, the voltage adjustment unit makes the transmission voltage at the time of writing to the RFID tag higher than the transmission voltage at the time of reading the RFID tag.

[0063] In the reader / writer according to aspect 3 of the present disclosure, in accordance with aspect 2 above, the voltage adjustment unit increases the transmission voltage during writing as the measured reception voltage becomes lower than the threshold.

[0064] The reader / writer according to a fourth aspect of the present disclosure is any one of the first to third aspects, further comprising a communication unit that communicates with the RFID tag by electromagnetic waves or AC magnetic fields having a frequency in the LF band.

[0065] A reader / writer control method according to aspect 5 of the present disclosure is a control method for controlling a reader / writer that communicates with an RFID tag, and includes a voltage measurement process for measuring a received voltage of a received signal received from the RFID tag when reading the RFID tag, and a voltage adjustment process for adjusting a transmission voltage of a transmission signal to be transmitted to the RFID tag when writing to the RFID tag, in which the voltage adjustment process adjusts the transmission voltage when writing to the RFID tag in accordance with the received voltage when reading the RFID tag from which it was possible to normally read data of the received signal.

[0066] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present disclosure. [Explanation of symbols]

[0067] 1 Reader / writer 2. RFID tags 3. PLC 4 Antennas 11 Communications Department 12 Communication Section 13 Voltage measurement section 14 Voltage regulator 15 Storage section 21 Tag communication section 100 RFID Systems

Claims

1. a voltage measuring unit that measures a reception voltage of a reception signal received from the RFID tag when reading the RFID tag; a voltage adjusting unit that adjusts a transmission voltage of a transmission signal to be transmitted to the RFID tag when writing to the RFID tag, The voltage adjustment unit adjusts the transmission voltage when writing to the RFID tag, depending on the reception voltage when reading the RFID tag from which data could be normally read.

2. The reader / writer according to claim 1 , wherein the voltage adjustment unit increases the transmission voltage when writing to the RFID tag higher than the transmission voltage when reading the RFID tag when the measured reception voltage when reading is less than a threshold value.

3. The reader / writer according to claim 2 , wherein the voltage adjustment section increases the transmission voltage during writing as the measured reception voltage becomes lower than the threshold value.

4. 4. The reader / writer according to claim 1, further comprising a communication unit that communicates with the RFID tag by electromagnetic waves or AC magnetic fields having a frequency in the LF band.

5. A control method for controlling a reader / writer that communicates with an RFID tag, comprising: a voltage measurement process for measuring a reception voltage of a reception signal received from the RFID tag when reading the RFID tag; a voltage adjustment process for adjusting a transmission voltage of a transmission signal transmitted to the RFID tag when writing to the RFID tag, A reader / writer control method, comprising: adjusting the transmission voltage when writing to the RFID tag in accordance with the receiving voltage when reading the RFID tag from which the data of the received signal was able to be read normally in the voltage adjustment process.

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