JP7767951B2 - RFID reader/writer, control device - Google Patents

Description

The present invention relates to an RFID reader/writer and a control device.

RFID (Radio Frequency Identification) technology is a technology that uses an RFID reader/writer to wirelessly communicate with an RFID tag, reading and writing information from the RFID tag.

RFID reader/writers are known that use a diode to perform amplitude demodulation, demodulating the superimposed signal of the transmitted signal from the transmitter circuit and the received signal from the RFID tag. With such RFID reader/writers, under certain distance conditions where the RFID antenna cable length is too long, the received signal may be weak and unable to be demodulated, even if the return signal from the RFID tag is strong enough.

To ensure that the received signal can be demodulated even when such a phenomenon occurs, some RFID readers/writers are equipped with a phase-shift circuit that shifts the phase of the received and transmitted signals, and can switch between demodulating a superimposed signal that has undergone a phase shift by the phase-shift circuit and demodulating a superimposed signal that has not (see, for example, Patent Document 1).

JP 2009-033424 A

The RFID reader/writer in Patent Document 1 switches between applying and not applying a phase shift using a phase shift circuit when the demodulated signal obtained by demodulating the superimposed signal cannot be recognized within a specified time. However, this switching method requires attempts to communicate with the RFID tag, which increases the time required for communication.

One aspect of the present invention was made in consideration of the above-mentioned circumstances, and aims to realize an RFID reader/writer that can communicate with RFID tags appropriately in a short amount of time.

In order to solve the above problems, an RFID reader/writer according to one embodiment of the present invention comprises an antenna, a connection cable, 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 provided on a path between the communication control unit and the antenna and having different amounts of phase delay for the signals, 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, and a selection unit that 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 that passes through the circuit selected by the selection unit from the first circuit and the second circuit.

With the above configuration, the selection unit selects a circuit based on the information acquired by the acquisition unit, allowing circuit selection to be completed appropriately before communication with the RFID tag. This allows appropriate communication with the RFID tag to be performed in a short amount of time.

An RFID reader/writer according to one aspect of the present invention may further include a first storage 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, 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 storage unit based on the information acquired by the acquisition unit.

With the above configuration, at least one of the first information, second information, and third information is determined in advance, and information regarding the circuit that the selection unit should select from the first circuit and the second circuit is stored in association with each other. This allows appropriate circuit selection to be completed before communication with the RFID tag.

The acquisition unit may acquire at least the third information, and the selection unit may switch between the selection of 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.

During communication between an RFID reader/writer and an RFID tag, the communication distance of the RFID reader/writer's communication control unit can sometimes drop. It is known that this drop 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 between the first and second circuits every time the cable length changes by 1/8 of the signal wavelength λ, it is possible to appropriately switch between the first and second circuits in accordance with the period of the drop in communication distance.

The antenna may have a second storage 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 stored in the second storage unit, and the selection unit selects either the first circuit or the second circuit based on the information acquired by the acquisition unit.

With the above configuration, information about the antenna, etc. is obtained from the antenna's second storage unit, making it possible to obtain error-free information about the antenna.

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, and the selection unit may select either the first circuit or the second circuit based on the information received by the input device.

With the above configuration, the input of at least one of the first information, second information, and third information is accepted by the input device, the information accepted by the input device is obtained, and either the first circuit or the second circuit is selected based on the information accepted by the input device. This configuration makes it easy for the user to make adjustments.

In an RFID reader/writer according to one aspect of the present invention, 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 may be 0.9 or more and 1.1 or less, and the difference in phase delay between the path passing through the first circuit and the path passing through the second circuit may not be an integer multiple of 90 degrees.

With 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 between 0.9 and 1.1. This configuration makes it possible to make the reflected waves generated at the antenna approximately the same when passing through a path including the first circuit and when passing through a path including the second circuit. Furthermore, with the above configuration, the difference in phase delay between the path through the first circuit and the path through the second circuit is not an integer multiple of 90 degrees. With this configuration, it is possible to prevent a node of the 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.

In order to solve the above problem, one aspect of the present invention provides a control device that controls an RFID reader/writer to communicate with an RFID tag. The RFID reader/writer includes 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 also includes 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.

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

A control device according to one aspect of the present invention may further include a first storage 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, and the selection unit may select either the first circuit or the second circuit by referring to the first storage unit based on the information acquired by the acquisition unit.

With the above configuration, at least one of the first information, second information, and third information is associated with information about the circuit that the selection unit should select from the first circuit and the second circuit, and stored in the first storage unit. By determining in advance and associating and storing at least one of the first information, second information, and third information with information about the circuit that the selection unit should select from the first circuit and the second circuit, it is possible to properly complete circuit selection before communicating with the RFID tag.

The acquisition unit may acquire at least the third information, and the selection unit may switch between the selection of 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.

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

The antenna may have a second memory unit that stores at least one of the first information and the third information, and the acquisition unit may instruct 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 acquire 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.

With 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 information from the second storage unit. As a result, information about the antenna is acquired from the second storage unit of the antenna, and error-free information about the antenna can be acquired.

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, and the selection unit may select either the first circuit or the second circuit based on the information received by the input device.

With the above configuration, the input device receives input of at least one of the first information, second information, and third information, acquires the information received by the input device, and selects either the first circuit or the second circuit based on the information received by the input device. This configuration makes it easy for the user to make adjustments.

According to one aspect of the present invention, an RFID reader/writer can communicate with an RFID tag appropriately in a short period of time.

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. 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; 3 is a circuit diagram showing a portion of the circuit provided in the RFID reader/writer of FIG. 2 that communicates with an RFID tag. 3 is a diagram showing an example of a route selection table that is referred to when the control unit in FIG. 2 functions as a selection unit; FIG. 5 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. FIG. 10 is a diagram illustrating an example of a simulation result. FIG. 10 is a block diagram showing a configuration of a main part of an RFID reader/writer according to a second embodiment of the present invention. 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. 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. 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.

An embodiment of one aspect of the present invention (hereinafter also referred to as "the present embodiment") will be described below with reference to the drawings. Note that identical or corresponding parts in the drawings are designated by the same reference numerals, and their description will not be repeated.

[Embodiment 1]
§1. Application Example 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.

As shown in FIG. 1, RFID communication system 1 includes an RFID reader/writer 2A and its host device, a programmable logic controller (PLC) 3. RFID communication system 1 is a system for reading and/or writing data to and from RFID tags 4 used for managing individual items such as parts and products at production sites, for example.

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 using electromagnetic coupling.

There are multiple types of RFID tags 4, and one of these types is selected when the RFID communication system 1 is installed at a production site, etc. Each of the multiple RFID tags 4 has its own individually defined inductance and other characteristics for the coil that makes up the electromagnetic coupling antenna.

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

Because there are multiple RFID tags 4 and antennas 21, impedance mismatches may occur during communication between the communication control unit 20A and the RFID tags 4. When impedance mismatches occur, reflected waves are generated at the antenna 21. The reflected waves can cause the received voltage of the communication control unit 20A to drop, reducing the communication distance during 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.

The RFID reader/writer 2A therefore provides multiple circuits with different signal phase delays on the path for communication between the communication control unit 20A and the antenna 21, and selects one circuit from the multiple circuits for each antenna 21. By appropriately selecting one circuit from the multiple circuits, the RFID reader/writer 2A suppresses drops in the reception voltage of the communication control unit 20A.

The RFID reader/writer 2A completes the above-described circuit selection before communication with the RFID tag 4 actually begins. 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. The RFID reader/writer 2A then selects a circuit based on this information.

By completing circuit selection before communication with the RFID tag 4 begins, communication can be carried out appropriately when the RFID communication system 1 is installed in a production site or other facility where it is in operation. This allows communication between the RFID reader/writer 2A and the RFID tag 4 to be completed in a short period of time.

§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.

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 memory unit 27, and an input unit 28.

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

The transmit port and receive port RX_IN1 of the communication control unit 20A are connected to the first circuit 23. The receive port RX_IN2 of the communication control unit 20A is connected to the second circuit 24. The first circuit 23 and the second circuit 24 are connected to the matching circuit 25. The matching circuit 25 is connected to the antenna 21 via the 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 receive 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 receive port RX_IN1. On the other hand, when the communication control unit 20A selects the receiving port RX_IN2, the 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 receiving port RX_IN2. In the following explanation, the path from the transmitting port of the communication control unit 20A via the antenna 21 to the receiving port RX_IN1 will be referred to as the first path. Also, the path from the transmitting port of the communication control unit 20A via the antenna 21 to the receiving port RX_IN2 will be referred to as the second path.

The matching circuit 25 is a circuit used to achieve impedance matching during 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 properly match impedance for all combinations of RFID tags 4, cable lengths, and antennas 21. If there is an error in the impedance matching performed by the matching circuit 25, reflected waves may be generated at the antenna 21, causing a drop in the voltage (received voltage) at the receiving port RX_IN1 or RX_IN2 of the communication control unit 20A.

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 between 0.9 and 1.1. Designing them in this way makes it possible to ensure that the reflected waves generated at the antenna are comparable when passing through a path including the first circuit and 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.

Furthermore, the first circuit 23 and the second circuit 24 are 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. In the following explanation, it is assumed that they are designed so that the difference between the phase delay of the first path and the phase delay of the second path is 45 degrees. By designing them in this way, it is possible to prevent a node of the standing wave from appearing at the position of the receiving port of the communication control unit 20 when passing through either the first path or the second path.

Figure 3 is a circuit diagram showing the portion of the circuitry provided in the RFID reader/writer 2A according to embodiment 1 of the present invention that communicates with the RFID tag 4. In Figure 3, the areas corresponding to the first circuit 23, second circuit 24, and matching circuit 25 are surrounded by dashed lines. In Figure 3, the second circuit 24 is simply a wire.

The control unit 26 shown in FIG. 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 regarding the antenna 21, second information regarding the RFID tag 4, and third information regarding the cable length of the cable 22. The selection unit 262 then selects either the first circuit 23 or the second circuit 24 based on the information acquired by the acquisition unit 261.

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

The second information acquired by the acquisition unit 261 is, for example, information regarding the model 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 regarding the model 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 regarding the model of the RFID tag 4 from the system administrator of the RFID communication system 1. The computer 5 then stores the input information regarding the model of the RFID tag 4 in the PLC 3.

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.

The first memory 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 which circuit should be selected from the first circuit 23 and the second circuit 24 by the selection unit 262. 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 which circuit should be selected from the first circuit 23 and the second circuit 24.

Figure 4 shows an example of a path selection table. The path selection table 271 shown in Figure 4 associates information about the type of antenna 21, information about the type of RFID tag 4, and information about the cable length of cable 22 with information about the circuit to be selected by the selection unit 262. In Figure 4, the cable length X2 of cable 22 is the value obtained by adding 1/8 times the wavelength λ of the signal used for 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 Figure 4, information about the circuit to be selected by the selection unit 262 is set so that the circuit selected by the selection unit 262 switches every time the cable length of cable 22 changes by λ/8.

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

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

Next, in step S101, the control unit 26 acquires first information about the antenna and third information about the cable length of the cable 22 from the second memory unit 211 of the antenna 21.

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

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.

Figure 6 shows the simulation results of the communication distance of the communication control unit 20A as the cable length of the cable 22 changes. In Figure 6, the solid line shows the simulation results when communication is performed by selecting the first circuit 23, and the dashed line shows the simulation results when communication is performed by selecting the second circuit 24.

As shown in Figure 6, the communication distance of communication control unit 20A periodically drops whether the first circuit 23 or the 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 within cable 22, and is calculated by multiplying the inverse of the signal frequency by the speed of light in a vacuum and multiplying that product by the wavelength shortening rate of the wire material of cable 22.

As shown in Figure 6, the cable length at which a drop in communication distance occurs differs depending on whether the first circuit 23 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, a drop in communication distance can be prevented.

[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.

Figure 7 is a block diagram showing the main configuration of an RFID reader/writer 2B according to embodiment 2. Figure 8 is a circuit diagram showing the portion of the circuitry provided in the RFID reader/writer 2B according to embodiment 2 that communicates with an RFID tag 4.

Embodiment 2 differs from embodiment 1 in that the circuit used for communication with the RFID tag 4 is switched by switches SW1 and SW2. Switch SW1 connects the communication port (receiving port) of the communication control unit 20B to the circuit selected by the selection unit 262. Switch SW2 connects the matching circuit 25 to the circuit selected by the selection unit 262.

In embodiment 2, when the control unit 26 selects a circuit in step S102 of FIG. 5, in step S103, it controls switches SW1 and SW2 to connect a path between the communication control unit 20B and the antenna 21.

[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.

Embodiment 3 differs from embodiment 1 in that when communicating with the RFID tag 4, the PLC 3 selects whether to use a path through the first circuit 23 or the second circuit 24.

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

The acquisition unit 301 acquires the first information, second information, and third information from the third storage unit 303.

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

10 is a diagram showing an example of a route selection table referenced 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 references the route selection table 272 and acquires constant A based on the first information and second information acquired by the acquisition unit 301. 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)

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

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

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

As mentioned 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.

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 value.

The communication instruction unit 304 transmits information regarding 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 which receiving port, RX_IN1 or RX_IN2, to use for the communication control unit 20C. If the selection unit 302 selects the first circuit 23, the control unit 26 selects the receiving port RX_IN1. On the other hand, if the selection unit 302 selects the second circuit 24, the control unit 26 selects the 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, either the first circuit 23 or the second circuit 24.

[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.

In embodiments 1 to 3, information regarding the model of the RFID tag 4, information regarding the type of the RFID tag 4, etc. have been exemplified as the second information regarding the RFID tag 4. However, the second information regarding the RFID tag 4 is not limited to these types of information. For example, the second information regarding the RFID tag 4 may be information regarding the inductance or impedance of the RFID tag 4.

In embodiments 1 to 3, cable 22 is a cable extending from antenna 21. However, cable 22 may be a component independent of antenna 21, or may include an extension cable that extends the cable of antenna 21. Cable 22 may also be designed so that the system administrator of 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 cable 22 be stored in PLC 3. For example, the system administrator can input third information regarding the cable length of cable 22 via computer 5, and have the third information stored in PLC 3.

In embodiments 1 to 3, the correspondence between the first information, second information, and 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 a path selection table 271. 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.

In embodiments 1 to 3, 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, second information, and third information. However, the information used by the selection unit 262, 302 to select a circuit need only include information regarding elements in the RFID communication system 1 that can be changed by a system administrator, and need only include at least one of the first information, second information, and third information. For example, if the antennas 21 usable in the RFID communication system 1 are limited to one type, there is no need to include an item related to the first information in the route selection tables 271, 272, and there is no need to refer to the route selection tables 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 RFID tags 4 usable in the RFID communication system 1 are limited to one type, there is no need to include an item related to the second information in the route selection tables 271, 272, and there is no need to refer to the route selection tables 271, 272 based on the second information. In this case, the acquisition 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 for 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 selection units 262, 302 to select a circuit may further include information other than the first information, second information, and third information.

In embodiments 1 and 2, the selection unit 262 references the route selection table 271 based on the first information, second information, and third information acquired by the acquisition unit 261. However, as in embodiment 3, the selection unit 262 may reference the route selection table 272 based on the first information, second information, and third information. On the other hand, in embodiment 3, the selection unit 302 references the route selection table 272 based on the first information, second information, and third information acquired by the acquisition unit 301, but may also reference the route selection table 271.

In embodiments 1 and 2, the first information regarding the antenna 21 and the third information regarding the cable length of the cable 22 are stored in the second memory unit 211. The acquisition unit 261 acquires the first information and the third information from the second memory unit 211. However, the source of the first information and the third information is not limited to the second memory unit 211. For example, the first information and the third information may be stored in the first memory 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.

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 configuration, 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. Furthermore, a third circuit other than the first circuit 23 and the second circuit 24 may be provided on the path for performing updates between the communication control unit 20 and the antenna 21. It is preferable to design the third circuit 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. It is also preferable to design the path passing through the third circuit 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.

[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 for causing the computer to function as the device, and for causing 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), 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 functions described in each of the above embodiments are realized by executing the program using the control device and storage device.
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.

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.

1 RFID communication system 20, 20A, 20B, 20C communication control unit 2A, 2B, 2C RFID reader/writer 3 PLC
4 RFID tag 5 Computer (input device)
21 Antenna 22 Cable 23 First circuit 24 Second circuit 25 Matching circuit 26 Control unit 27 First storage unit 28 Input unit 211 Second storage unit 261, 301 Acquisition units 262, 262, 302, 302 Selection units 271, 272 Route selection table 303 Third storage unit 304 Communication instruction unit

Claims (11)

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. 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. 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. 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. 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. 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. 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 on a path between the communication control unit and the antenna, and which have mutually different phase delay amounts 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. 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. 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. 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. 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.