RFID reader / writer, control device

Abstract

To make it possible to appropriately communicate with RFID tags in a short time.SOLUTION: An RFID reader / writer includes: a first circuit (23) and a second circuit (24) provided on a path between a communication control unit (20A) and an antenna (21) and having mutually different amounts of signal phase delay; an acquisition unit (261) that acquires at least one of first information about the antenna, second information about an RFID tag (4), and third information about the length of a connection cable (22); and a selection unit (262) that selects either the first circuit or the second circuit based on the information acquired by the acquisition unit. The communication control unit transmits and receives signals to and from the antenna via a path passing through the circuit selected by the selection unit.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an RFID reader / writer and a control device. [Background technology]

[0002] RFID (Radio Frequency Identification) technology is a technology that uses an RFID reader / writer to wirelessly communicate with an RFID tag and read or write information from or to the RFID tag.

[0003] There are known RFID reader / writers that use a diode for amplitude demodulation to demodulate the superimposed signal of the transmitted signal from the transmitter circuit and the received signal from the RFID tag.However, under certain distance conditions, such RFID reader / writers may experience a problem where the received signal is weak and cannot be demodulated, even if the return signal from the RFID tag is strong enough, due to the RFID antenna cable length.

[0004] To enable demodulation of the received signal even when such a phenomenon occurs, an RFID reader / writer is known that is provided with a phase shift circuit that shifts the phase of the received signal and the transmitted signal, and that switches between demodulating a superimposed signal to which the phase shift by the phase shift circuit has been applied and demodulating a superimposed signal to which the phase shift has not been applied (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-033424 Summary of the Invention [Problem to be solved by the invention]

[0006] In the RFID reader / writer of Patent Document 1, if the demodulated signal obtained by demodulating the superimposed signal cannot be recognized within a predetermined time, the RFID reader / writer switches whether or not to apply a phase shift using a phase shift circuit. However, this switching method has the problem that it requires an attempt to communicate with the RFID tag, which increases the time required for communication.

[0007] One aspect of the present invention has been made in view of the above circumstances, and an object of the present invention is to provide an RFID reader / writer that can appropriately communicate with an RFID tag in a short time. [Means for solving the problem]

[0008] In order to solve the above problem, an RFID reader / writer according to one embodiment of the present invention comprises an antenna, a connection cable, a communication control unit to which the antenna is connected via the connection cable and which transmits and receives signals to and from the antenna when communicating with an RFID tag, a first circuit and a second circuit provided on a path between the communication control unit and the antenna and having different phase delay amounts for the signals, an acquisition unit which acquires at least one of first information about the antenna, second information about the RFID tag, and third information about the cable length of the connection cable, and a selection unit which selects either the first circuit or the second circuit based on the information acquired by the acquisition unit, and the communication control unit transmits and receives signals to and from the antenna via a path passing through the circuit selected by the selection unit from the first circuit and the second circuit.

[0009] According to the above configuration, the selection unit selects a circuit based on the information acquired by the acquisition unit, so that the circuit selection can be completed appropriately before communication with the RFID tag, thereby enabling appropriate communication with the RFID tag to be performed in a short time.

[0010] An RFID reader / writer according to one embodiment of the present invention may further include a first memory unit that stores at least one of the first information, the second information, and the third information in association with information regarding the circuit that the selection unit should select from the first circuit and the second circuit, wherein the acquisition unit acquires at least one of the first information, the second information, and the third information, and the selection unit selects either the first circuit or the second circuit by referring to the first memory unit based on the information acquired by the acquisition unit.

[0011] According to the above configuration, at least one of the first information, second information, and third information and information regarding the circuit that the selection unit should select from the first circuit and the second circuit are determined in advance, associated with each other, and stored, thereby making it possible to properly complete circuit selection before communication with the RFID tag.

[0012] The acquisition unit may acquire at least the third information, and the selection unit may switch the selection between the first circuit and the second circuit every time the cable length of the connection cable included in the third information changes by 1 / 8 times the wavelength of the signal.

[0013] During communication between an RFID reader / writer and an RFID tag, the communication distance of the RFID reader / writer's communication control unit may decrease. It is known that this decrease in communication distance occurs periodically every time the cable length of the antenna cable changes by 1 / 4 of the signal wavelength. With the above configuration, by switching the selection between the first circuit and the second circuit every time the cable length changes by 1 / 8 of the signal wavelength λ, it is possible to appropriately switch the selection between the first circuit and the second circuit in accordance with the period of the decrease in communication distance.

[0014] The antenna may have a second memory unit that stores at least one of the first information and the third information, the acquisition unit acquires the first information and the third information that is stored in the second memory unit, and the selection unit selects either the first circuit or the second circuit based on the information acquired by the acquisition unit.

[0015] According to the above configuration, since the information about the antenna and the like is acquired from the second storage unit of the antenna, it is possible to acquire error-free information about the antenna.

[0016] The acquisition unit may acquire information received by an input device that receives input of at least one of the first information, the second information, and the third information from the input device, and the selection unit may select either the first circuit or the second circuit based on the information received by the input device.

[0017] According to the above configuration, the input of at least one of the first information, the second information, and the third information is received by the input device, the information received by the input device is acquired, and either the first circuit or the second circuit is selected based on the information received by the input device. This configuration makes it easy for the user to make adjustments.

[0018] In an RFID reader / writer according to one embodiment of the present invention, the absolute value of the impedance of the path between the communication control unit including the first circuit and the antenna divided by the absolute value of the impedance of the path between the communication control unit including the second circuit and the antenna may be 0.9 or more and 1.1 or less, and the difference between the phase delay amount of the path passing through the first circuit and the phase delay amount of the path passing through the second circuit may not be an integer multiple of 90 degrees.

[0019] According to the above configuration, the absolute value of the impedance of the path between the antenna and the communication control unit including the first circuit divided by the absolute value of the impedance of the path between the antenna and the communication control unit including the second circuit is set to be 0.9 or more and 1.1 or less. This configuration allows the reflected wave generated at the antenna to be substantially the same when passing through a path including the first circuit and when passing through a path including the second circuit. Furthermore, according to the above configuration, the difference between the phase delay amount of the path through the first circuit and the phase delay amount of the path through the second circuit is not an integer multiple of 90 degrees. This configuration prevents a node of a standing wave from appearing at the receiving port of the communication control circuit when passing through at least one of the path including the first circuit and the path including the second circuit.

[0020] In order to solve the above problem, a control device according to one embodiment of the present invention is a control device that controls an RFID reader / writer to communicate with an RFID tag, the RFID reader / writer comprising: an antenna; a connection cable; a communication control unit to which the antenna is connected via the connection cable and that transmits and receives signals to and from the antenna when communicating with the RFID tag; and a first circuit and a second circuit that are provided in a path between the communication control unit and the antenna and have different phase delay amounts for the signals. The control device comprises: an acquisition unit that acquires at least one of first information about the antenna, second information about the RFID tag, and third information about the cable length of the connection cable; a selection unit that selects either the first circuit or the second circuit based on the information acquired by the acquisition unit; and a communication instruction unit that instructs the RFID reader / writer to transmit and receive the signals to and from the antenna via a path that passes through the circuit selected by the selection unit from the first circuit and the second circuit.

[0021] According to the above configuration, the control device, which is a higher-level device of the RFID reader / writer, can obtain information and select a circuit, so that circuit selection can be completed appropriately before communication with the RFID tag.

[0022] A control device according to one embodiment of the present invention may further include a first memory unit that stores at least one of the first information, the second information, and the third information in association with information regarding a circuit that the selection unit should select from the first circuit and the second circuit, and the selection unit may select either the first circuit or the second circuit by referring to the first memory unit based on the information acquired by the acquisition unit.

[0023] According to the above configuration, at least one of the first information, the second information, and the third information is stored in the first storage unit in association with information about a circuit that the selection unit should select from the first circuit and the second circuit. By previously determining and storing at least one of the first information, the second information, and the third information and information about a circuit that the selection unit should select from the first circuit and the second circuit in association with each other, it is possible to properly complete circuit selection before communication with the RFID tag.

[0024] The acquisition unit may acquire at least the third information, and the selection unit may switch the selection between the first circuit and the second circuit every time the cable length of the connection cable included in the third information changes by 1 / 8 times the wavelength of the signal.

[0025] According to the above configuration, by switching between the first circuit and the second circuit every time the cable length changes by 1 / 8 times the signal wavelength λ, it is possible to appropriately switch between the first circuit and the second circuit in accordance with the period of the decrease in the communication distance.

[0026] The antenna may have a second memory unit that stores at least one of the first information and the third information, the acquisition unit instructs the RFID reader / writer to acquire from the second memory unit which of the first information and the third information is stored in the second memory unit, and acquires from the RFID reader / writer which of the first information and the third information is stored in the second memory unit, and the selection unit may select either the first circuit or the second circuit based on the information acquired by the acquisition unit.

[0027] According to the above configuration, the antenna has a second storage unit that stores at least one of the first information and the third information, and the acquisition unit acquires the information from the second storage unit. As a result, the information about the antenna is acquired from the second storage unit of the antenna, and therefore, it is possible to acquire error-free information about the antenna.

[0028] The acquisition unit may acquire information received by an input device that receives input of at least one of the first information, the second information, and the third information from the input device, and the selection unit may select either the first circuit or the second circuit based on the information received by the input device.

[0029] According to the above configuration, the input of at least one of the first information, the second information, and the third information is received by the input device, the information received by the input device is acquired, and either the first circuit or the second circuit is selected based on the information received by the input device. This configuration makes it easy for the user to make adjustments. [Effects of the Invention]

[0030] According to one aspect of the present invention, an RFID reader / writer can communicate with an RFID tag appropriately in a short time. [Brief explanation of the drawings]

[0031] [Figure 1]1 is a diagram schematically illustrating a system environment of an RFID communication system including an RFID reader / writer according to a first embodiment of the present invention. [Figure 2] 1 is a block diagram showing a configuration of a main part of an RFID reader / writer according to a first embodiment of the present invention. [Figure 3] 3 is a circuit diagram showing a part of the circuit provided in the RFID reader / writer of FIG. 2 that communicates with an RFID tag. [Figure 4] 3 is a diagram showing an example of a path selection table that is referred to when the control unit in FIG. 2 functions as a selection unit. FIG. [Figure 5] 4 is a flowchart relating to a circuit selection process executed at the time of starting up the RFID communication system including the RFID reader / writer according to the first embodiment of the present invention. [Figure 6] FIG. 10 is a diagram illustrating an example of a simulation result. [Figure 7] FIG. 10 is a block diagram showing the configuration of a main part of an RFID reader / writer according to a second embodiment of the present invention. [Figure 8] FIG. 10 is a circuit diagram showing a portion of a circuit provided in an RFID reader / writer according to a second embodiment of the present invention that communicates with an RFID tag. [Figure 9] FIG. 10 is a block diagram showing the configuration of a main part of a control device according to a third embodiment of the present invention. [Figure 10] FIG. 11 is a diagram showing an example of a path selection table referred to by a control device according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0032] Hereinafter, an embodiment according to one aspect of the present invention (hereinafter also referred to as "the present embodiment") will be described with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and description thereof will not be repeated.

[0033] [Embodiment 1] §1. Application Examples FIG. 1 is a diagram showing a schematic diagram of a system environment using an RFID communication system 1 equipped with an RFID reader / writer 2A according to this embodiment.

[0034] 1, the RFID communication system 1 includes an RFID reader / writer 2A and its higher-level device, a programmable logic controller (PLC) 3. The RFID communication system 1 is a system for at least one of reading and writing data to and from RFID tags 4 used for managing individual items such as parts and products at, for example, a production site.

[0035] The RFID reader / writer 2A includes a communication control unit 20A and an antenna 21. The communication control unit 20A communicates with the RFID tag 4 via the antenna 21. The antenna 21 and the RFID tag 4 communicate with each other by electromagnetic coupling.

[0036] There are multiple types of RFID tags 4, and one of them is selected when the RFID communication system 1 is installed at a production site or the like. The inductance of the coil that constitutes the electromagnetic coupling antenna of each of the multiple RFID tags 4 is individually determined.

[0037] There are also multiple types of antennas 21, which can be detachably connected to the RFID reader / writer 2A via cables 22. The multiple types of antennas 21 each have their own inductance and other characteristics. The cables 22 are connecting cables extending from the antennas 21. The cable length of the cables 22 is determined individually for each type of antenna 21.

[0038] Because there are multiple RFID tags 4 and antennas 21, impedance mismatching may occur in communication between the communication control unit 20A and the RFID tags 4. When impedance mismatching occurs, a reflected wave is generated at the antenna 21. The reflected wave may cause a drop in the received voltage of the communication control unit 20A, resulting in a drop in the communication distance in communication via the antenna 21. This drop in the communication distance occurs periodically every time the cable length of the cable 22 of the antenna 21 changes by 1 / 4 of the signal wavelength λ, i.e., λ / 4.

[0039] Therefore, RFID reader / writer 2A provides multiple circuits with different signal phase delay amounts on the path for communication between communication control unit 20A and antenna 21, and selects one circuit from the multiple circuits for each antenna 21. By appropriately selecting a circuit from the multiple circuits, RFID reader / writer 2A suppresses drops in the receiving voltage of communication control unit 20A.

[0040] The RFID reader / writer 2A completes the above-described circuit selection before actually starting communication with the RFID tag 4. Specifically, when the RFID communication system 1 is started, the RFID reader / writer 2A acquires first information about the antenna 21, second information about the RFID tag 4, and third information about the cable length of the cable 22. The first information is, for example, information about the model of the antenna 21. The second information is, for example, information about the model of the RFID tag 4. Then, the RFID reader / writer 2A selects a circuit based on these pieces of information.

[0041] By completing the circuit selection before the start of communication with the RFID tag 4, communication can be performed appropriately during operation at a production site or the like where the RFID communication system 1 is installed. This allows communication between the RFID reader / writer 2A and the RFID tag 4 to be performed in a short time.

[0042] §2. Configuration example FIG. 2 is a block diagram showing the configuration of the main parts of the RFID reader / writer 2A according to the first embodiment of the present invention.

[0043] The RFID reader / writer 2A includes a communication control unit 20A, an antenna 21, a cable 22, a first circuit 23, a second circuit 24, a matching circuit 25, a control unit 26, a first storage unit 27, and an input unit .

[0044] The communication control unit 20A has a transmission port and two reception ports RX_IN1 and RX_IN2. The communication control unit 20A transmits signals from the transmission port to the RFID tag 4. The communication control unit 20A also receives signals from the RFID tag 4 at the two reception ports RX_IN1 and RX_IN2. Either the reception port RX_IN1 or the reception port RX_IN2 is selected by the communication control unit 20A under the control of the control unit 26.

[0045] The transmission port and reception port RX_IN1 of the communication control unit 20A are connected to a first circuit 23. Furthermore, the reception port RX_IN2 of the communication control unit 20A is connected to a second circuit 24. The first circuit 23 and the second circuit 24 are connected to a matching circuit 25. The matching circuit 25 is connected to an antenna 21 via a cable 22. A signal transmitted from the communication control unit 20A to the RFID tag 4 passes through the first circuit 23, the matching circuit 25, and the cable 22 to the antenna 21. When the reception port RX_IN1 is selected by the communication control unit 20A, a signal received from the RFID tag 4 passes from the antenna 21 through the cable 22, the matching circuit 25, and the first circuit 23 to the reception port RX_IN1. On the other hand, when the reception port RX_IN2 is selected by the communication control unit 20A, a signal received from the RFID tag 4 passes from the antenna 21 through the cable 22, the matching circuit 25, and the second circuit 24 to the reception port RX_IN2. In the following description, the path from the transmission port of the communication control unit 20A to the reception port RX_IN1 via the antenna 21 is referred to as the first path, and the path from the transmission port of the communication control unit 20A to the reception port RX_IN2 via the antenna 21 is referred to as the second path.

[0046] The matching circuit 25 is a circuit for achieving impedance matching in communication between the communication control unit 20A and the RFID tag 4. However, there are multiple RFID tags 4 and antennas 21, and it is not possible to perform appropriate impedance matching for all combinations of RFID tags 4, cable lengths, and antennas 21. If there is an error in the impedance matching by the matching circuit 25, a reflected wave may occur at the antenna 21, causing a drop in the voltage (received voltage) at the position of the receive port RX_IN1 or RX_IN2 of the communication control unit 20A.

[0047] The first circuit 23 and the second circuit 24 are designed so that the absolute value of the impedance of the first path divided by the absolute value of the impedance of the second path is 0.9 to 1.1. By designing them in this way, the reflected waves generated at the antenna when passing through a path including the first circuit can be made to be approximately the same as when passing through a path including the second circuit. In other words, regardless of whether the first circuit or the second circuit is selected, the RFID reader / writer 2A can communicate with the RFID tag 4 with matched impedances.

[0048] Furthermore, the first circuit 23 and the second circuit 24 are designed so that the difference between the phase delay amount of the first path and the phase delay amount of the second path is not an integer multiple of 90 degrees. In the following description, it is assumed that the difference between the phase delay amount of the first path and the phase delay amount of the second path is designed to be 45 degrees. By designing in this way, it is possible to prevent a node of a standing wave from appearing at the position of the receiving port of the communication control unit 20 when passing through at least one of the first path and the second path.

[0049] 3 is a circuit diagram showing a portion of the circuit provided in the RFID reader / writer 2A according to the first embodiment of the present invention that communicates with the RFID tag 4. In FIG. 3, the portions corresponding to the first circuit 23, the second circuit 24, and the matching circuit 25 are surrounded by dashed lines. In FIG. 3, the second circuit 24 is simply a wire.

[0050] 2 is configured with a CPU (Central Processing Unit) and the like, and functions as an acquisition unit 261 and a selection unit 262 by executing a control program stored in a first storage unit 27 configured with a non-volatile storage device. The acquisition unit 261 acquires first information about the antenna 21, second information about the RFID tag 4, and third information about the cable length of the cable 22. Then, the selection unit 262 selects either the first circuit 23 or the second circuit 24 based on the information acquired by the acquisition unit 261.

[0051] The first information acquired by the acquisition unit 261 is, for example, information relating to the model of the antenna 21. The antenna 21 has a second storage unit 211 which is a non-volatile storage device, and stores the first information in this second storage unit 211. The acquisition unit 261 acquires the first information from the second storage unit 211 of the antenna 21.

[0052] The second information acquired by the acquisition unit 261 is, for example, information relating to the type of the RFID tag 4. The control unit 26 can communicate with the PLC 3 via the input unit 28. The acquisition unit 261 acquires information relating to the type of the RFID tag 4 provided in the RFID communication system 1 from the PLC 3 via the input unit 28. A computer 5 (input device) is connected to the PLC 3. The computer 5 accepts input of information relating to the type of the RFID tag 4 by a system administrator of the RFID communication system 1. The computer 5 then stores the input information relating to the type of the RFID tag 4 in the PLC 3.

[0053] The third information acquired by the acquisition unit 261 is information relating to the cable length of the cable 22. The information relating to the cable length is stored together with the first information in the second storage unit 211 of the antenna 21. The acquisition unit 261 acquires the third information together with the first information from the second storage unit 211 of the antenna 21. Get.

[0054] The first storage unit 27 stores a route selection table that associates the first information, second information, and third information acquired by the acquisition unit 261 with information indicating a circuit to be selected by the selection unit 262 from the first circuit 23 and the second circuit 24. The selection unit 262 refers to the route selection table based on the first information, second information, and third information acquired by the acquisition unit 261, and selects a circuit to be selected from the first circuit 23 and the second circuit 24.

[0055] Fig. 4 shows an example of a path selection table. In the path selection table 271 shown in Fig. 4, information on the type of antenna 21, information on the type of RFID tag 4, and information on the cable length of cable 22 are associated with information on the circuit to be selected by the selection unit 262. In Fig. 4, the cable length X2 of cable 22 is the value obtained by adding 1 / 8 times the wavelength λ of the signal used in communication between the communication control unit 20 and the RFID tag 4 to the cable length X1. Furthermore, the cable length X3 of cable 22 is the value obtained by adding λ / 8 to the cable length X2. In the path selection table 271 shown in Fig. 4, information on the circuit to be selected by the selection unit 262 is set so that the circuit to be selected by the selection unit 262 is switched every time the cable length of cable 22 changes by λ / 8.

[0056] FIG. 5 is a flowchart showing a circuit selection process executed by the control unit 26 of the RFID reader / writer 2A when the RFID communication system 1 is started up.

[0057] When the RFID communication system 1 is started, the control unit 26 starts the process from step S100. In step S100, the control unit 26 controls the input unit 28 to acquire the second information on the RFID tag 4 from the PLC 3.

[0058] Subsequently, in step S101, the control unit 26 acquires the first information about the antenna and the third information about the cable length of the cable 22 from the second storage unit 211 of the antenna 21.

[0059] Next, in step S102, the control unit 26 selects a circuit by referring to the route selection table 271 stored in the first storage unit 27 based on the first information, second information, and third information acquired in steps S100 and S101. For example, if the type of the antenna 21 is the "first antenna," the type of the RFID tag 4 is the "first tag," and the cable length of the cable 22 is greater than X2 and equal to or less than X3, the second circuit 24 is selected.

[0060] Next, in step S103, the control unit 26 switches the circuit to be used for communication with the RFID tag 4 based on the selection result of step S102. Specifically, the control unit 26 instructs the communication control unit 20A which receiving port to use for communication. If the first circuit 23 is selected in step S102, the control unit 26 instructs the communication control unit 20A to use receiving port RX_IN1. On the other hand, if the second circuit 24 is selected in step S102, the control unit 26 instructs the communication control unit 20A to use receiving port RX_IN2.

[0061] Fig. 6 shows the results of a simulation of the communication distance of communication control unit 20A with respect to changes in the cable length of cable 22. In Fig. 6, the solid line shows the simulation results when communication is performed by selecting first circuit 23, and the dashed line shows the simulation results when communication is performed by selecting second circuit 24.

[0062] 6, the communication distance of communication control unit 20A periodically drops whether first circuit 23 or second circuit 24 is selected. In either case, the drop in communication distance occurs every time the cable length of cable 22 changes by approximately 1 / 4 of the signal wavelength λ. Here, signal wavelength λ is the wavelength of the signal in the wiring of cable 22, and is calculated by multiplying the reciprocal of the signal frequency by the speed of light in a vacuum and multiplying that product by the wavelength shortening rate of the wire in cable 22.

[0063] 6, the cable length at which a drop in the communication distance occurs differs depending on whether the first circuit 23 is selected or the second circuit 24 is selected, due to the difference in the amount of phase delay between the first circuit 23 and the second circuit 24. Therefore, by appropriately selecting the first circuit 23 and the second circuit 24, it is possible to prevent a drop in the communication distance.

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

[0065] Fig. 7 is a block diagram showing the configuration of a main part of an RFID reader / writer 2B according to embodiment 2. Fig. 8 is a circuit diagram showing a part of the circuit provided in the RFID reader / writer 2B according to embodiment 2 that communicates with an RFID tag 4.

[0066] The second embodiment differs from the first embodiment in that the circuit used for communication with the RFID tag 4 is switched by switches SW1 and SW2. The switch SW1 connects the communication port (receiving port) of the communication control unit 20B to the circuit selected by the selection unit 262. The switch SW2 connects the matching circuit 25 to the circuit selected by the selection unit 262.

[0067] In the second embodiment, when the control unit 26 selects a circuit in step S102 of FIG. 5, the control unit 26 controls the switches SW1 and SW2 to connect a path between the communication control unit 20B and the antenna 21 in step S103.

[0068] [Embodiment 3] Other embodiments of the present invention will be described below. For ease of explanation, the same reference numerals will be used to designate components having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0069] The third embodiment differs from the first embodiment in that the PLC 3 selects whether to use a path through the first circuit 23 or the second circuit 24 when communicating with the RFID tag 4.

[0070] 9 is a block diagram showing the essential configuration of an RFID reader / writer 2C according to a third embodiment and a PLC 3, which is a higher-level control device thereof. The PLC 3 functions as an acquisition unit 301, a selection unit 302, and a communication instruction unit 304 by executing a program stored in a third storage unit 303. The third storage unit 303 is a non-volatile storage device. In addition to the program executed by the PLC 3, the third storage unit 303 stores first information about the antenna 21, second information about the RFID tag 4, and third information about the cable length of the cable 22. The first information, second information, and third information stored in the third storage unit 303 are input to the PLC 3 by a system administrator of the RFID communication system 1 using the computer 5.

[0071] The acquiring unit 301 acquires the first information, the second information, and the third information from the third storage unit 303 .

[0072] The selection unit 302 selects one of the first circuit 23 and the second circuit 24 based on the first information, the second information, and the third information acquired by the acquisition unit 301 .

[0073] 10 is a diagram showing an example of a route selection table referred to by the selection unit 302. The route selection table 272 shown in FIG. 10 associates information about the type of antenna 21 and information about the type of RFID tag 4 with a parameter called constant A. Constant A is a numerical value determined based on the type of antenna 21 and the type of RFID tag 4. The selection unit 302 refers to the route selection table 272 based on the first information and second information acquired by the acquisition unit 301, and acquires constant A. Thereafter, the selection unit 302 calculates a judgment value B using the following calculation formula (1) based on the third information acquired by the acquisition unit 301 and constant A acquired from the route selection table 272. B = L / (λ / 8) + A (1)

[0074] λ is the signal wavelength, and as described above, is obtained by multiplying the reciprocal of the signal frequency by the speed of light in a vacuum and then multiplying the product by the wavelength shortening rate of the wire material of the cable 22. L is the cable length of the cable 22, and is acquired from the third information acquired by the acquisition unit 301.

[0075] After calculating the judgment value B, the selection unit 302 determines whether the integer part of the judgment value B is even or odd. If the integer part of the judgment value B is odd, the selection unit 302 selects the first circuit 23. On the other hand, if the integer part of the judgment value B is even, the selection unit 302 selects the second circuit 24.

[0076] The integer part of the judgment value B changes by 1 every time the cable length of the cable 22 changes by 1 / 8 times the signal wavelength λ. In other words, every time the cable length of the cable 22 changes by 1 / 8 times the signal wavelength λ, the even or odd state of the integer part of the judgment value B changes, and the selected circuit is switched.

[0077] As described above, a drop in the communication distance of communication control unit 20C occurs periodically every time the cable length of cable 22 changes by λ / 4. Because the value of judgment value B changes by 2 every time the cable length of cable 22 changes by λ / 4, the even or odd status of the integer part does not change, and a circuit that avoids a drop in the communication distance is selected.

[0078] The constant A is a numerical representation of the influence of the impedance of the antenna 21 and the impedance of the RFID tag 4. By correcting the judgment value B using this constant A, the correspondence between the cable length L of the cable 22 and the circuit selected by the selection unit 302 is corrected to an appropriate one.

[0079] The communication instruction unit 304 transmits information about the circuit selected by the selection unit 302 to the RFID reader / writer 2C. The control unit 26 of the RFID reader / writer 2C receives the information transmitted by the communication instruction unit 304 via the input unit 28. Based on the information received from the communication instruction unit 304, the control unit 26 selects, for the communication control unit 20C, which receiving port to use, receiving port RX_IN1 or receiving port RX_IN2. If the selection unit 302 selects the first circuit 23, the control unit 26 selects receiving port RX_IN1. On the other hand, if the selection unit 302 selects the second circuit 24, the control unit 26 selects receiving port RX_IN2. In other words, the communication instruction unit 304 instructs the RFID reader / writer 2C to transmit and receive signals to and from the antenna 21 via a path that passes through the circuit selected by the selection unit 302, of the first circuit 23 and the second circuit 24.

[0080] [Modification] In the first to third embodiments, information on the model of the antenna 21, information on the type of the antenna 21, etc. have been exemplified as the first information on the antenna 21. However, the first information on the antenna 21 is not limited to these pieces of information. For example, the first information on the antenna 21 may be information on the inductance or impedance of the antenna 21.

[0081] In the first to third embodiments, the second information about the RFID tag 4 is exemplified by information about the model of the RFID tag 4, information about the type of the RFID tag 4, etc. However, the second information about the RFID tag 4 is not limited to these pieces of information. For example, the second information about the RFID tag 4 may be information about the inductance or impedance of the RFID tag 4.

[0082] In the first to third embodiments, the cable 22 is a cable extending from the antenna 21. However, the cable 22 may be a component independent of the antenna 21, or may include an extension cable that extends the cable of the antenna 21. The cable 22 may also be designed so that the system administrator of the RFID communication system 1 can freely adjust its cable length. If the system administrator is allowed to adjust the cable length, it is preferable that third information regarding the cable length of the cable 22 be stored in the PLC 3. For example, the system administrator may input the third information regarding the cable length of the cable 22 via the computer 5, and the third information may be stored in the PLC 3.

[0083] In the first to third embodiments, the correspondence between the first information, the second information, and the third information acquired by the acquisition unit 261 etc. and the circuits selected by the selection unit 262 etc. is stored in a storage device such as the first storage unit 27 in a table format such as the path selection table 271 etc. However, as long as the correspondence between the first information etc. acquired by the acquisition unit 261 etc. and the circuits selected by the selection unit 262 etc. can be represented, it does not have to be in a table format.

[0084] In the first to third embodiments, the selection unit 262, 302 selects the circuit to be selected from the first circuit 23 and the second circuit 24 based on the first information, the second information, and the third information. However, the information used by the selection unit 262, 302 to select a circuit may include information regarding elements in the RFID communication system 1 that can be changed by a system administrator, and may include at least one of the first information, the second information, and the third information. For example, if the number of antennas 21 usable in the RFID communication system 1 is limited to one type, there is no need to provide an item related to the first information in the route selection table 271, 272, and there is no need to refer to the route selection table 271, 272 based on the first information. In this case, the acquisition unit 261, 301 does not need to acquire the first information. Similarly, if the number of RFID tags 4 usable in the RFID communication system 1 is limited to one type, there is no need to provide an item related to the second information in the route selection table 271, 272, and there is no need to refer to the route selection table 271, 272 based on the second information. In this case, the acquiring units 261, 301 do not need to acquire the second information. Furthermore, if the cable length of the cable 22 is predetermined at the design stage of the antenna 21, there is no need to provide an item related to the third information in the route selection table 271, and there is no need to refer to the route selection table 271 based on the third information. Furthermore, the information used by the selecting units 262, 302 to select a circuit may further include information other than the first information, the second information, and the third information.

[0085] In the first and second embodiments, the selection unit 262 refers to the route selection table 271 based on the first information, the second information, and the third information acquired by the acquisition unit 261. However, as in the third embodiment, the selection unit 262 may refer to the route selection table 272 based on the first information, the second information, and the third information. On the other hand, in the third embodiment, the selection unit 302 refers to the route selection table 272 based on the first information, the second information, and the third information acquired by the acquisition unit 301, but may refer to the route selection table 271.

[0086] In the first and second embodiments, the first information regarding the antenna 21 and the third information regarding the cable length of the cable 22 are stored in the second storage unit 211. The acquisition unit 261 acquires the first information and the third information from the second storage unit 211. However, the source of the first information and the third information is not limited to the second storage unit 211. For example, the first information and the third information may be stored in the first storage unit 27 or the PLC 3. The first information or the third information may be input by a system administrator of the RFID communication system 1 via the computer 5, and the first information or the third information may be stored in the PLC 3. In this case, the acquisition unit 261 may acquire the first information from the PLC 3 via the input unit 28.

[0087] The circuits shown in Figures 3 and 8 are merely examples, and the circuit configuration is not limited to the illustrated configuration. The first circuit 23 and the second circuit 24 are not limited to the illustrated configurations, as long as the absolute value of the impedance of the first path divided by the absolute value of the impedance of the second path is 0.9 to 1.1, and the difference between the phase delay of the first path and the phase delay of the second path is not an integer multiple of 90 degrees. A third circuit other than the first circuit 23 and the second circuit 24 may be provided on the path for updating between the communication control unit 20 and the antenna 21. The third circuit is preferably designed so that the absolute value of the impedance of the path passing through the third circuit divided by the absolute value of the impedance of the second path is 0.9 to 1.1. The path passing through the third circuit is preferably designed so that the difference between the phase delay of the first path and the phase delay of the second path is not an integer multiple of 90 degrees.

[0088] [Software implementation example] The functions of the RFID reader / writers 2A, 2B, PLC 3, and computer 5 (hereinafter referred to as "devices") can be realized by a program that causes the computer to function as the device, and causes the computer to function as each control block of the device (particularly the control unit 26, each unit included in PLC 3 (acquisition units 261, 301, selection units 262, 302, communication instruction unit 304), and input unit 28). In this case, the device includes a computer having at least one control device (e.g., a processor) and at least one storage device (e.g., a memory) as hardware for executing the program. The control device and storage device execute the program, thereby realizing the functions described in each of the above embodiments. The program may be non-transitory and may be recorded on one or more computer-readable recording media. The recording media may or may not be included in the device. In the latter case, the program may be supplied to the device via any wired or wireless transmission medium. Furthermore, some or all of the functions of the control blocks can be realized by logic circuits. For example, an integrated circuit in which a logic circuit that functions as each of the control blocks is formed is also included in the scope of the present invention. In addition, the functions of the control blocks can also be realized by, for example, a quantum computer.

[0089] 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]

[0090] 1. RFID communication system 20, 20A, 20B, 20C Communication control section 2A, 2B, 2C RFID reader / writer 3 PLC 4. RFID tags 5 Computer (input device) 21 Antenna 22 Cable 23 1st circuit 24 2nd circuit 25 Matching Circuit 26 Control Unit 27 1st memory section 28 Input section 211 2nd memory section 261, 301 Acquisition Department 262, 262, 302, 302 selection section 271, 272 Routing table 303 Third memory section 304 Communication Indicator

Claims

1. The antenna and A connection cable and a communication control unit connected to the antenna via the connection cable and transmitting and receiving signals to and from the antenna when communicating with an RFID tag; a first circuit and a second circuit, the first circuit and the second circuit being provided on a path between the communication control unit and the antenna, and having mutually different amounts of phase delay of the signal; an acquisition unit that acquires at least one of first information about the antenna, second information about the RFID tag, and third information about a cable length of the connection cable; a selection unit that selects either the first circuit or the second circuit based on the information acquired by the acquisition unit; Equipped with The communication control unit transmits and receives signals to and from the antenna via a path that passes through the circuit selected by the selection unit from the first circuit and the second circuit.

2. a first storage unit that stores at least one of the first information, the second information, and the third information and information regarding a circuit that the selection unit should select from the first circuit and the second circuit, in association with each other; the acquisition unit acquires at least one of the first information, the second information, and the third information; The RFID reader / writer according to claim 1 , wherein the selection unit selects either the first circuit or the second circuit by referring to the first storage unit based on the information acquired by the acquisition unit.

3. the acquisition unit acquires at least the third information, 2. The RFID reader / writer according to claim 1, wherein the selection unit switches the selection between the first circuit and the second circuit each time the cable length of the connection cable included in the third information changes by 1 / 8 times the wavelength of the signal.

4. the antenna has a second storage unit that stores at least one of the first information and the third information, the acquisition unit acquires the information stored in the second storage unit out of the first information and the third information, The RFID reader / writer according to claim 1 , wherein the selection unit selects either the first circuit or the second circuit based on the information acquired by the acquisition unit.

5. the acquisition unit acquires, from an input device that accepts input of at least one of the first information, the second information, and the third information, information accepted by the input device; The RFID reader / writer according to claim 1 , wherein the selection unit selects either the first circuit or the second circuit based on information received by the input device.

6. a value obtained by dividing the absolute value of the impedance of a path between the communication control unit including the first circuit and the antenna by the absolute value of the impedance of a path between the communication control unit including the second circuit and the antenna is 0.9 or more and 1.1 or less, The RFID reader / writer according to claim 1 , wherein a difference between a phase delay amount of the path passing through the first circuit and a phase delay amount of the path passing through the second circuit is not an integral multiple of 90 degrees.

7. A control device that controls an RFID reader / writer to communicate with an RFID tag, The RFID reader / writer includes: The antenna and A connection cable and a communication control unit connected to the antenna via the connection cable and transmitting and receiving signals to and from the antenna when communicating with the RFID tag; a first circuit and a second circuit, which are provided in a path between the communication control unit and the antenna, and which have mutually different amounts of phase delay of the signal; The control device an acquisition unit that acquires at least one of first information about the antenna, second information about the RFID tag, and third information about a cable length of the connection cable; a selection unit that selects either the first circuit or the second circuit based on the information acquired by the acquisition unit; a communication instruction unit that instructs the RFID reader / writer to transmit and receive the signal to and from the antenna via a path that passes through the circuit selected by the selection unit from among the first circuit and the second circuit.

8. a first storage unit that stores at least one of the first information, the second information, and the third information and information regarding a circuit that the selection unit should select from the first circuit and the second circuit, in association with each other; The control device according to claim 7 , wherein the selection unit selects either the first circuit or the second circuit by referring to the first storage unit based on the information acquired by the acquisition unit.

9. the acquisition unit acquires at least the third information, 8. The control device according to claim 7, wherein the selection unit switches the selection between the first circuit and the second circuit every time the cable length of the connection cable included in the third information changes by 1 / 8 times the wavelength of the signal.

10. the antenna has a second storage unit that stores at least one of the first information and the third information, The acquisition unit instructing the RFID reader / writer to acquire, from the second storage unit, the information stored in the second storage unit out of the first information and the third information; acquiring, from the RFID reader / writer, the information stored in the second storage unit out of the first information and the third information; The control device according to claim 7 , wherein the selection unit selects either the first circuit or the second circuit based on the information acquired by the acquisition unit.

11. the acquisition unit acquires, from an input device that accepts input of at least one of the first information, the second information, and the third information, information accepted by the input device; The control device according to claim 7 , wherein the selection unit selects either the first circuit or the second circuit based on information received by the input device.

Images