RFID Systems

Abstract

To detect deterioration of an antenna of an RFID tag in advance and avoid a situation where the RFID tag cannot communicate.SOLUTION: An RFID communication device (3) receives a signal (S) from an RFID tag (2). A signal strength measuring unit (306) measures signal strength received from the RFID tag (2). A disconnection detection unit (307) refers to a log table (312) to detect whether the signal strength of the signal (S) does not change. When the signal strength changes, a notification unit (308) notifies a user that the RFID tag (2) has deteriorated.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an RFID system and an RFID communication device. [Background technology]

[0002] In recent years, the technique of managing objects using RFID (Radio Frequency Identification) tags has become widespread and is used across a wide range of industries, for example, production management in factories, and material management in warehouses and logistics. An RFID system consists of a large number of RFID tags and a reader / writer, which is a parent device that communicates between the RFID tags. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2006-352750 A Summary of the Invention [Problem to be solved by the invention]

[0004] Especially in production management and product testing management in factories, RFID tags are sometimes used in harsh environments such as high temperatures and environments with rapid temperature changes. As a result, the antenna of the RFID tag may break due to changes in the surrounding environment. If the antenna breaks unexpectedly, communication with the reader / writer becomes impossible, and the system using the RFID system may suddenly stop. In production sites using RFID systems, sudden system stoppages must be avoided because they can cause major losses.

[0005] The conventional technology in Patent Document 1 discloses a technology in which the antenna coils of the RF tag are arranged in parallel so that communication is not interrupted even if the antenna coils are partially broken. However, as the antenna deteriorates, communication will eventually become impossible, and it is unavoidable that communication with the reader / writer will suddenly become impossible.

[0006] The present invention has been made in consideration of the above-mentioned problems, and has an object to realize an RFID system that can detect antenna deterioration in an RFID tag before the antenna deteriorates and communication becomes impossible. [Means for solving the problem]

[0007] In order to solve the above problems, an RFID system according to a first aspect of the present invention is an RFID system comprising an RFID tag and an RFID communication device, wherein the RFID tag comprises an antenna having a plurality of loop-shaped antenna wires connected in parallel, and a tag transceiver unit that holds identification information and communicates with the RFID communication device using the antenna, and the RFID communication device comprises a master station antenna, a master station transceiver unit that communicates with the RFID tag using the master station antenna, and a control unit, wherein the control unit comprises an identification unit that acquires the identification information of the RFID tag from a signal received from the RFID tag by the master station transceiver unit, a signal strength measurement unit that measures the strength of the signal received from the RFID tag by the master station transceiver unit, a break detection unit that detects a break in the antenna wire of the RFID tag from the strength of the signal received from the RFID tag measured by the signal strength measurement unit, and a notification unit that executes a notification that there is an abnormality in the RFID tag when the break detection unit detects a break in the antenna wire of the RFID tag.

[0008] According to the above configuration, it is possible to detect when some of the multiple antenna wires of the RFID tag are broken, thereby avoiding a situation in which the RFID tag continues to be used until all of the antenna wires of the RFID tag are broken and communication is impossible.

[0009] An RFID system according to aspect 2 of the present invention is characterized in that, in aspect 1, the RFID communication device further includes a memory unit for storing information, and the control unit further includes a log generation unit for storing in the memory unit a log table that chronologically records information regarding the strength of the signal received from the RFID tag, linked to the identification information of the RFID tag acquired by the identification unit.

[0010] According to the above configuration, the RFID system can store the signal strength in chronological order in the storage unit as a log table, linked to the identification information.

[0011] An RFID system according to aspect 3 of the present invention is characterized in that, in aspect 2, the break detection unit detects a break in the antenna wire of the RFID tag by comparing the strength of the signal received from the RFID tag measured by the signal strength measuring unit with information regarding the signal strength for the RFID tag in the log table stored in the memory unit.

[0012] According to the above configuration, the RFID system detects a break in the antenna wire of the RFID tag by comparing the signal strength of the signal received from the RFID tag with information about the signal strength in the log table.

[0013] An RFID system according to a fourth aspect of the present invention is characterized in that, in any one of the first to third aspects, the multiple antenna wires in the RFID tag include antenna wires having different parameters that affect the strength of the antenna wires.

[0014] According to the above configuration, when a weak part of the antenna wire of the RFID tag breaks, the user can know that the RFID tag is placed in a harsh environment and the antenna is about to break, causing communication to be impossible. Parameters that affect the strength of the antenna wire include the cross-sectional area and material of the antenna wire.

[0015] In order to solve the above problems, an RFID communication device of aspect 5 of the present invention comprises a master station antenna, a master station transceiver unit that communicates with an RFID tag using the master station antenna, and a control unit, wherein the RFID tag is provided with an antenna having multiple loop-shaped antenna wires connected in parallel, and a tag transceiver unit that holds identification information and communicates with the RFID communication device using the antenna, and the control unit is characterized in that it has an identification unit that acquires the identification information of the RFID tag from a signal received from the RFID tag by the master station transceiver unit, a signal strength measurement unit that measures the strength of the signal received from the RFID tag by the master station transceiver unit, a break detection unit that detects a break in the antenna wire of the RFID tag from the strength of the signal received from the RFID tag measured by the signal strength measurement unit, and a notification unit that executes a notification that there is an abnormality in the RFID tag when the break detection unit detects a break in the antenna wire of the RFID tag.

[0016] According to the above configuration, it is possible to detect when some of the multiple antenna wires of the RFID tag are broken, thereby avoiding a situation in which the RFID tag continues to be used until all of the antenna wires of the RFID tag are broken and communication is impossible.

[0017] The RFID communication device according to each aspect of the present invention may be realized by a computer. In this case, the control program for the RFID communication device, which causes a computer to operate as each part (software element) of the RFID communication device, and the computer-readable recording medium on which the control program is recorded, also fall within the scope of the present invention. Effect of the Invention

[0018] According to one aspect of the present invention, an RFID system can detect antenna deterioration in an RFID tag before the antenna deteriorates and becomes unable to communicate with an RFID communication device, thereby avoiding a situation in which an RFID tag is used continuously until the antenna deteriorates to the point where communication is impossible. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a functional configuration diagram of an RFID system according to a first embodiment. [Diagram 2] 2 is a functional configuration diagram of a master station transmitting / receiving unit of the RFID system according to the first embodiment. FIG. [Diagram 3] 1 is a schematic structural diagram of an RFID tag in an RFID system according to a first embodiment. [Figure 4] 1 is a circuit diagram of an RFID tag in an RFID system according to a first embodiment. [Diagram 5] FIG. 2 is a schematic structural diagram of an RFID tag in the RFID system according to the first embodiment, showing a state in which a part of the antenna wire is broken. [Figure 6] 1 is a circuit diagram of an RFID tag in an RFID system according to a first embodiment, showing an equivalent circuit when a part of an antenna wire is broken. [Figure 7] FIG. 1 is a diagram showing frequency dependence of antenna gain of an RFID tag. [Figure 8] 4 is a flowchart of a detection process in which the RFID communication device according to the first embodiment detects a break in an antenna wire. [Figure 9] 4 is a schematic diagram of a log table stored in a storage unit of the RFID communication device according to the first embodiment. FIG. [Figure 10] 10 is a flowchart of a detection process in which the RFID communication device according to the second embodiment detects a break in an antenna wire. [Figure 11] 13 shows an example of a log table for threshold setting method 2. [Figure 12] 13 shows another example of the log table for threshold setting method 2. [Figure 13]13 shows an example of a log table for threshold setting method 3. [Figure 14] 13 shows another example of the log table for threshold setting method 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] [Embodiment 1] Hereinafter, the first embodiment of the present invention will be described in detail.

[0021] §1 Examples of application First, an example of a situation in which the present invention is applied will be described. The RFID communication system according to the application example of the present invention is applied to a management system for managing objects by using a large number of RFID tags, for example, a production management system in a factory, an item management system in a warehouse, or in logistics.

[0022] FIG. 1 is a diagram showing a schematic configuration of an RFID system 1 according to an application example of the first embodiment. The RFID system 1 includes an RFID tag 2 and an RFID communication device 3. The RFID tag 2 includes an antenna 201 and a tag transceiver 202. The antenna 201 is configured by connecting a plurality of loop-shaped antenna wires in parallel. The antenna 201 converts high-frequency waves transmitted from the RFID communication device 3 into power and transmits the power to the tag transceiver 202. The tag transceiver 202 holds identification information 203 and communicates with the RFID communication device 3 using the antenna 201.

[0023] The RFID communication device 3 includes a master station antenna 301, a master station transceiver unit 302, a control unit 303, and a storage unit 311. The control unit 303 includes an identification unit 304, a signal strength measurement unit 306, a disconnection detection unit 307, and a notification unit 308. The identification unit 304 acquires the identification information 203 of the RFID tag 2 from the signal S received from the RFID tag 2 by the master station transceiver unit 302. The signal strength measurement unit 306 measures the strength of the signal received from the RFID tag 2.

[0024] The disconnection detection unit 307 compares the signal strength measured by the signal strength measurement unit 306 with the information on the signal strength related to the RFID tag 2 in the log table 312 stored in the storage unit 311. Thereby, disconnection of the antenna element wire of the RFID tag 2 is detected.

[0025] When the disconnection detection unit 307 detects disconnection of the antenna element wire of the RFID tag 2, the notification unit 308 executes a notification indicating that there is an abnormality in the RFID tag 2. The storage unit 311 stores, in the storage unit 311, a log table 312 that records information on the signal strength received from the RFID tag 2 in time series, linked to the identification information 203 of the RFID tag 2 acquired by the identification unit 304. The log generation unit 305 generates the log table 312.

[0026] With the above configuration, when the antenna of the RFID tag 2 deteriorates, a part of the antenna element wires connected in parallel is disconnected. When a part of the antenna element wire is disconnected, the signal strength received from the RFID tag 2 decreases. The signal strength measurement unit 306 of the RFID communication device 3 measures the signal strength received from the RFID tag 2. The disconnection detection unit 307 compares the record in the log table 312 stored in the storage unit 311 with the signal strength measured by the signal strength measurement unit 306 to detect that a part of the antenna element wire of the RFID tag 2 is disconnected. The notification unit 308 notifies the user that the RFID tag is deteriorated.

[0027] In this way, in the RFID system 1 of this application example, the disconnection detection unit 307 detects a decrease in the signal strength received from the RFID tag 2, and the notification unit 308 notifies the user that the RFID tag 2 is deteriorated. The user can avoid a situation where the RFID tag 2 becomes incommunicable by replacing it with a non-deteriorated RFID tag 2 and using it until the RFID tag 2 becomes incommunicable.

[0028] §2 Configuration Example <Functional Configuration of RFID System 1> Fig. 1 shows a functional configuration diagram of the RFID system 1 according to Embodiment 1. The RFID system 1 includes an RFID tag 2 and an RFID communication device 3.

[0029] The RFID tag 2 includes an antenna 201 and a tag transceiver 202. The tag transceiver 202 is a circuit for communicating with the RFID communication device 3, which is a master station, using the antenna 201. The tag transceiver 202 stores identification information 203. The identification information 203 is an identification code uniquely assigned to each device of the RFID tag 2.

[0030] The RFID communication device 3 includes a master station antenna 301, a master station transmitting / receiving unit 302, a control unit 303, and a storage unit 311. The master station transmitting / receiving unit 302 is a circuit for communicating with the RFID tag 2 using the master station antenna 301. The storage unit 311 is a memory that can store, hold, and read out information.

[0031] The storage unit 311 stores a log table 312, which will be described later. The control unit 303 includes a command receiving unit 309, a transmission / reception control unit 310, an identification unit 304, a signal strength measurement unit 306, a log generating unit 305, a disconnection detection unit 307, and a notification unit 308. Details of each of these functional blocks included in the control unit 303 will be described later.

[0032] 2 is a diagram showing the functional configuration of the master station transceiver unit 302 according to the first embodiment. The master station antenna 301 receives a signal S from the RFID tag 2. The signal S is a signal obtained by modulating a carrier having a frequency of 13.56 MHz with a modulation signal. The signal S is sent in sequence to a matching circuit 302A, a filter 302B, a detection unit 302C, and an amplifier 302D, and the modulated signal is extracted.

[0033] The signal S is composed of an LSB (Lower Side Band) with a frequency of 13.134 MHz and an USB (Upper Side Band) with a frequency of 13.984 MHz. In this embodiment, the carrier frequency is described as 13.56 MHz, but the carrier frequency is not limited to 13.56 MHz. RFID systems with other frequency bands may be used.

[0034] The filter 302B blocks the LSB. The detector 302C extracts the USB component from the carrier and USB and shifts the frequency to 424 kHz. The amplifier 302D amplifies the USB. The amplified USB is decoded by the decoder 302E, and the identification unit 304 obtains the identification information 203 of the RFID tag 2 from the decoded data string. The signal strength measurement unit 306 measures the signal strength of the signal output from the amplifier 302D.

[0035] <Principle of disconnection detection> Fig. 3 is a schematic diagram showing an example of the configuration of the RFID tag 2. Fig. 4 is a circuit diagram showing the circuit configuration of the RFID tag 2. The RFID tag 2 is a passive type tag that receives a carrier transmitted by an RFID communication device 3 and operates by generating power based on the carrier.

[0036] The RFID tag 2 comprises a housing 4, an antenna 201, and a tag transceiver unit 202. The antenna 201 and the tag transceiver unit 202 are built into the housing 4. The tag transceiver unit 202 and the antenna 201 are electrically connected. The antenna 201 is composed of an antenna wire A1 and an antenna wire A2. The antenna wire is a loop-shaped coil formed from a wire of a conductive material such as iron or copper. The antenna wire may be wound once or multiple times.

[0037] 4, the antenna wire A1 and the antenna wire A2 are electrically connected in parallel to the tag transceiver unit 202. In this embodiment, the number of antenna wires constituting the antenna 201 is two, but is not limited to this and may be three or more. For example, ten antenna wires may be connected in parallel to the tag transceiver unit 202.

[0038] The tag transceiver 202 includes a tag IC 5 and a capacitor 6. The capacitor 6, the antenna wire A1, and the antenna wire A2 are connected in parallel to the input / output section of the tag IC 5. The capacitance of the capacitor 6 is represented by C, the inductance of the antenna wire A1 is represented by L1, and the inductance of the antenna wire A2 is represented by L2. The capacitor 6 is thus externally attached to the tag IC 5 in order to adjust the resonant frequency fc.

[0039] When the antenna wire A1 and the antenna wire A2 receive a carrier signal from the RFID communication device 3, they generate power to operate the tag IC 5. In the RFID tag 2, the values ​​of the capacitor C of the capacitor 6, the inductance L1 of the antenna wire A1, and the inductance L2 of the antenna wire A2 are determined so that the RFID tag 2 resonates at the frequency of the carrier signal transmitted from the RFID communication device 3. The resonant frequency fc is derived by the following equation.

[0040]

number

[0041] In this embodiment, the resonant frequency fc is 13.56 MHz. The RFID communication device 3 sets the resonant frequency fc to match the frequency of the carrier transmitted to the RFID tag. The RFID tag superimposes a signal S on the carrier and transmits the signal S to the RFID communication device.

[0042] Fig. 5 is a schematic diagram showing an example of the configuration of an RFID tag 2 in which the antenna wire A1 of the antenna 201 is broken. Fig. 6 is a circuit diagram showing an equivalent circuit configuration of an RFID tag 2 in which the antenna wire A1 of the antenna 201 is broken. Even if the antenna wire A1 is broken, the RFID tag 2 can communicate with the RFID communication device 3 through the antenna wire A2.

[0043] A capacitor 6 and an inductance L2 of the antenna wire A2 are connected in parallel to both ends of the tag IC 5. Since the antenna wire A1 is disconnected, the inductance of the antenna wire A1 is infinite and is represented as an open circuit in the circuit diagram as shown in FIG. 6. When the antenna wire A2 receives a carrier from the RFID communication device 3, it generates power to operate the tag IC 5. At this time, the resonant frequency fd is derived from the capacitance C of the capacitor 6 and the inductance L2 of the antenna wire A2 by the following equation.

[0044]

number

[0045] Fig. 7 is a diagram showing the frequency dependence of the gain of the antenna 201 of the RFID tag 2. The output line S2-1 shows the frequency dependence of the gain of the antenna 201 of the RFID tag 2 in the circuit diagram shown in Fig. 6 when the antenna wire A1 of the RFID tag 2 is broken. The output line S2 shows the frequency dependence of the gain of the antenna 201 of the RFID tag 2 in the circuit diagram shown in Fig. 4 when the antenna wire A1 of the RFID tag 2 is not broken. The resonant frequency fd is smaller than the resonant frequency fc.

[0046] When the antenna wire A1 of the RFID tag 2 is not broken, the RFID communication device 3 receives the signal S transmitted at the gain peak. At this time, the signal strength measured by the signal strength measurement unit 306 is V1. In contrast, even when the antenna wire A1 of the RFID tag 2 is broken, the RFID communication device 3 receives the signal S transmitted at a time shifted from the gain peak. Therefore, in the RFID communication device 3, the signal strength measured by the signal strength measurement unit 306 is V2, which is lower than V1.

[0047] The RFID communication device 3 detects a decrease in the signal strength of the received signal S when a part of the antenna 201 of the RFID tag 2 is disconnected. By detecting a decrease in the signal strength of the signal S transmitted by the RFID tag 2, the RFID communication device 3 can know that a part of the antenna element of the antenna 201 of the RFID tag 2 is disconnected. Thereby, it is possible to prevent a situation where the RFID tag 2 continues to be used until all the antenna elements of the antenna 201 of the RFID tag 2 are disconnected and the antenna 201 cannot perform its function.

[0048] <Detection Process of RFID System> FIG. 8 shows the detection process of the RFID system 1 according to Embodiment 1.

[0049] Step S101: When the RFID communication device 3 issues a communication command to communicate with the RFID tag 2 from the upper system, the command reception unit 309 receives the communication command.

[0050] Step S102: According to the communication command from the upper system, the transmission / reception control unit 310 controls the master station transmission / reception unit 302 to cause the master station transmission / reception unit 302 to transmit a communication command to the RFID tag 2 via the master station antenna 301.

[0051] Step S103: The tag transmission / reception unit 202 that has received the communication command via the antenna 201 returns a signal S including identification information to the RFID communication device 3. The master station transmission / reception unit 302 receives the signal S via the master station antenna 301.

[0052] Step S104: The identification unit 304 acquires the identification information 203 from the data string decoded by the master station transmission / reception unit 302 for the signal S.

[0053] Step S105: The signal strength measurement unit 306 measures the signal strength of the signal output by the amplifier 302D of the master station transmission / reception unit 302. The signal strength is the value of the voltage with respect to the predetermined frequency.

[0054] Step S106: The log generating unit 305 records the identification information 203 and the signal strength in a log table 312 stored in the storage unit 311 every time communication is made with an RFID tag 2. The log table 312 is information in which the signal strength from the RFID tag 2 is recorded in chronological order in association with the identification information 203 for each RFID tag 2.

[0055] 9 is an example of the log table 312. The horizontal items in the log table 312 are unique identification information 203 assigned to each RFID tag 2. The identification information UID1, the identification information UID2, and the identification information UID3 each have different unique identification information 203. The vertical items in the log table 312 are the number of communications.

[0056] In the example shown in Figure 9, the signal strength of identification information UID1 is 1V when communication is performed for the first time. After that, when communication is performed for the second time, the signal strength of identification information UID1 is 1V. Similarly, when communication is performed for the third, fourth, and fifth times, the signal strength of identification information UID1 is 1V. From the first to fifth communication, the signal strength of identification information UID1 remains unchanged at 1V. This causes disconnection detection unit 307 to detect that the RFID tag has not deteriorated.

[0057] For the identification information UID2, the signal strength is 0.8 V during the first communication. During the second to fifth communications, the signal strength of the identification information UID2 remains unchanged at 0.8 V. This causes the disconnection detection unit 307 to detect that the RFID tag has not deteriorated. As long as the antenna 201 of the RFID tag 2 has not deteriorated, the signal strength received from the RFID tag will be approximately the same.

[0058] For the identification information UID3, when the communication count is the first, second, third, and fourth, the signal strength for the identification information UID3 is 1.2V.

[0059] However, at the fifth communication, the signal strength of the identification information UID3 is 0.4 V. This signal strength has decreased compared to the signal strength of 1.2 V of the identification information UID3 measured before the fourth communication. The disconnection detection unit 307 refers to the record in the log table 312 and detects that the measured signal strength associated with the same identification information 203 has changed. This indicates that the RFID tag 2 has deteriorated.

[0060] Step S107: When the disconnection detection unit 307 refers to the record in the log table 312 stored in the storage unit 311 and detects that the measured signal strength has not changed compared to the signal strength of a past communication associated with the same identification information 203 (Yes in S107), the disconnection detection unit 307 proceeds to step S108. Otherwise (No in S107), the disconnection detection unit 307 proceeds to step S109.

[0061] Step S108: When the flow reaches step S108, it is determined that there is no deterioration in the antenna 201 of the RFID tag 2, and the flow ends.

[0062] Step S109: When the flow reaches step S109, it is determined that the antenna 201 of the RFID tag 2 is degraded. The disconnection detection unit 307 transmits a detection signal to the notification unit 308. The notification unit 308 notifies the user or the upper system that the RFID tag is degraded. As a method of notification, appropriate methods such as notification by sound, notification on the display screen of the upper system, notification by lighting a lamp, etc. can be applied. Then, the flow ends.

[0063] <Actions and Effects> If all of the antenna wires of the antenna 201 of the RFID tag 2 are broken, the RFID communication device 3 will be unable to communicate with the RFID tag 2. Before this happens, the break detection unit 307 detects a decrease in the signal strength of the signal S, and the notification unit 308 notifies the user that the RFID tag 2 has deteriorated. The user can avoid a situation in which the RFID tag is used until it becomes unable to communicate by replacing it with a non-deteriorated RFID tag.

[0064] [Embodiment 2] Other embodiments of the present invention will be described below. For ease of explanation, the same reference numerals are given to members having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0065] Fig. 10 shows a detection process in which the RFID communication device 3 according to the second embodiment detects a break in an antenna wire. The detection process in the second embodiment is the same as that in the first embodiment shown in Fig. 8, except that step S107 is changed. Steps S201 to S209 of the detection process in the second embodiment correspond to steps S101 to S109 of the detection process in the first embodiment, respectively.

[0066] Step S207: The disconnection detection unit 307 refers to the record in the log table 312 stored in the storage unit 311, and if the measured signal strength is compared with the threshold value stored in the storage unit 311 of the RFID communication device 3 and the signal strength is equal to or greater than the threshold value (Yes in step S207), the process proceeds to step S208. Otherwise (No in step S207), the process proceeds to step S209.

[0067] Here, a method for setting the threshold value will be described.

[0068] Threshold setting method 1: The threshold is set as a fixed value by default. The threshold is stored in the storage unit 311 of the RFID communication device 3. It is assumed that the threshold for detecting a state in which the antenna 201 of the RFID tag 2 is deteriorated is set to 0.6 V. A specific description will be given using an example of the log table 312 in FIG. 9.

[0069] 9, the signal strength of the RFID tag 2 having the identification information UID3 is 0.4 V when the communication count is 5. At this time, the signal strength is smaller than the threshold value of 0.6 V stored in the memory unit 311. The disconnection detection unit 307 detects that the antenna 201 of the RFID tag 2 is deteriorated based on the measured signal strength.

[0070] Threshold setting method 2: The administrator can set the threshold value as the lowest value of signal strength by referring to past records in the log table 312A when communicating with the RFID tag 2. This will be explained using the example of the log table 312A in FIG.

[0071] For example, when communication with each RFID tag 2 has been performed up to the second time, the administrator refers to the past records in the log table 312A. The administrator then finds that the lowest signal strength is 0.4V, which is the signal strength D2 during the second communication with the RFID tag 2 having the identification information UID1 attached. Therefore, the administrator sets the threshold to 0.4V and stores it in the memory unit 311 of the RFID communication device 3.

[0072] Then, from the third communication with each RFID tag 2 onwards, the signal strength D1 of the RFID tag 2 with identification information UID2 becomes 0.3 V in the fourth communication, and it is detected that the antenna 201 has deteriorated. The signal strength D3 of the RFID tag 2 with identification information UID3 becomes 0.6 V in the fifth communication, and it is detected that the antenna 201 has not deteriorated.

[0073] Furthermore, the threshold may be set for each RFID tag 2. An example will be described using the log table 312A in Fig. 12. Similarly, if the threshold is set from the record of the second communication with each RFID tag 2, in this case, the following thresholds will be set for each RFID tag 2. The threshold for the RFID tag 2 with identification information UID1 is set to 0.4V. The threshold for the RFID tag 2 with identification information UID2 is set to 0.6V. The threshold for the RFID tag 2 with identification information UID3 is set to 1.2V.

[0074] Then, for the third and subsequent communications with each RFID tag, in the RFID tag 2 with identification information UID2, the signal strength D1 in the fourth communication is 0.3 V, and the antenna 201 is detected as degraded. Also, in the RFID tag 2 with identification information UID3, the signal strength D3 in the fifth communication is 0.6 V, and the antenna 201 is detected as degraded.

[0075] Threshold setting method 3: The administrator can set a threshold using a statistical method based on the signal strengths recorded in the log table 312B. An example of an administrator setting a threshold will be described with reference to the log table 312B in FIG. 13. For example, the administrator calculates the average value of each signal strength D4 recorded in the log table 312B. The administrator then determines the threshold value as the average value minus a predetermined value. The predetermined value is, for example, a numerical value obtained by multiplying the standard deviation of each signal strength D4 by 3.

[0076] Furthermore, the threshold may be set for each RFID tag 2. An example will be described using the log table 312B in FIG. 14. For example, the administrator calculates the average values ​​of the signal strengths D5 of the RFID tag 2 to which the identification information UID1 is attached, the signal strengths D6 of the RFID tag 2 to which the identification information UID2 is attached, and the signal strengths D7 of the RFID tag 2 to which the identification information UID3 is attached, all of which are recorded in the log table 312B. Then, the administrator sets the threshold value to a value obtained by subtracting each predetermined value from each average value. Each predetermined value is a numerical value obtained by multiplying the standard deviation of each of the signal strengths D5 to D7 by 3.

[0077] In the above threshold setting methods 2 and 3, the example in which the administrator calculates the threshold has been described. However, the control unit 303 of the RFID communication device 3 may be configured to refer to the log table 312 and calculate the threshold in the same manner as above.

[0078] Other embodiments The strength of the antenna wires may be changed by varying at least one of the cross-sectional area or material of the multiple antenna wires constituting the antenna 201. Furthermore, other parameters that affect the strength of each of the multiple antenna wires may be made different from each other, not limited to the cross-sectional area or material of the antenna wires.

[0079] When the RFID tag 2 is exposed to a harsh environment, the weaker antenna wire breaks. When the weaker antenna wire of the RFID tag 2 breaks, the user can know that the RFID tag 2 has been placed in a harsh environment and the antenna is about to break, which will cause communication to become impossible.

[0080] [Software implementation example] The control blocks of the RFID communication device 3 (particularly the functional blocks of the control unit 303) may be realized by a logic circuit (hardware) formed in an integrated circuit (IC chip) or the like, or may be realized by software.

[0081] In the latter case, the RFID communication device 3 includes a computer that executes instructions of a program, which is software that realizes each function. This computer includes, for example, one or more processors, and a computer-readable recording medium that stores the program. In the computer, the processor reads the program from the recording medium and executes it, thereby achieving the object of the present invention.

[0082] The processor may be, for example, a CPU (Central Processing Unit). The recording medium may be a "non-transitory tangible medium" such as a ROM (Read Only Memory), a tape, a disk, a card, a semiconductor memory, a programmable logic circuit, or the like. The device may further include a RAM (Random Access Memory) for expanding the program.

[0083] The program may be supplied to the computer via any transmission medium capable of transmitting the program (such as a communication network or a broadcast wave). Note that one aspect of the present invention may also be realized in the form of a data signal embedded in a carrier wave, in which the program is embodied by electronic transmission.

[0084] The present invention 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 invention. [Explanation of symbols]

[0085] 1. RFID System 2. RFID tags 3. RFID communication device 4. Chassis 5. Tag IC 6 Capacitors 201 Antenna 202 Tag Transmitter / Receiver 203 Identification Information 301 Master Station Antenna 302 Master station transmitter / receiver 303 Control Unit 304 Identification Unit 305 Log Generator 306 Signal Strength Measurement Unit 307 Disconnection detection unit 308 Information Department 309 Command Reception Department 310 Transmission and reception control section 311 Storage section 312, 312A, 312B Log Table A1 Antenna wire A2 Antenna wire

Claims

1. An RFID tag; An RFID system comprising: The RFID tag comprises: an antenna in which a plurality of loop-shaped antenna wires are connected in parallel; a tag transceiver unit that holds identification information and communicates with the RFID communication device using the antenna, The RFID communication device includes: A master station antenna; a master station transceiver unit that communicates with the RFID tag using the master station antenna; A control unit, The control unit is an identification unit that acquires the identification information of the RFID tag from the signal received from the RFID tag by the master station transceiver unit; a signal strength measuring unit for measuring the strength of a signal received by the master station transceiver unit from the RFID tag; a disconnection detection unit that detects a disconnection of the antenna wire of the RFID tag based on the strength of the signal received from the RFID tag measured by the signal strength measurement unit; a notification unit that, when the disconnection detection unit detects a disconnection of the antenna wire of the RFID tag, issues a notification that an abnormality exists in the RFID tag; An RFID system, wherein the plurality of antenna wires in the RFID tag include antenna wires having mutually different parameters that affect the strength of the antenna wires.

2. The RFID communication device includes: Further comprising a storage unit for storing information, The control unit further 2. The RFID system according to claim 1, further comprising: a log generating unit that causes the memory unit to store a log table that records, in chronological order, information regarding the strength of the signal received from the RFID tag, linked to the identification information of the RFID tag acquired by the identification unit.

3. 3. The RFID system of claim 2, wherein the break detection unit detects a break in the antenna wire of the RFID tag by comparing the strength of the signal received from the RFID tag measured by the signal strength measurement unit with information about the strength of the signal for the RFID tag in the log table stored in the memory unit.

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