JP7725836B2 - Control device, reader/writer, and control method - Google Patents

Description

The present invention relates to a reader/writer that communicates with moving RFID tags.

At production sites, it is necessary to identify the location of finished products. For example, at automobile production sites, it is necessary to distinguish between vehicles that require rework after production is complete and vehicles that are waiting to be shipped, and to identify their locations. Without knowing the locations of vehicles that require rework and vehicles waiting to be shipped, accurate shipping plans cannot be made. In addition, the amount of work required by workers to identify the locations of vehicles is enormous.

Patent Document 1 discloses a technology for identifying the location of products (items) at a production site (work site) using a system that uses UHF (Ultra-High Frequency) RFID (Radio Frequency Identifier).

JP 2014-078211 A

However, when RFID tags are attached to automobiles, the target products are mobile and can move on their own, so the products move across the detection areas of each antenna, making communication with the RFID tag unstable and making it difficult to identify their location. Because the RFID tag is moving, if the RFID tag moves while communicating with another RFID tag, the RFID tag may be temporarily lost.

Furthermore, because there are overlapping areas in the communication areas of multiple antennas, products may be detected in those areas. Furthermore, due to radio wave reflection and fading, RFID tags in unintended areas may be detected by unintended antennas. Therefore, when the same RFID tag is detected by multiple antennas, it is difficult to determine which antenna should be used for communication, i.e., to identify which communication area the RFID tag is in and to determine the location of the RFID tag.

One aspect of the present invention aims to realize a system that can stably communicate with RFID tags that move across the communication areas of multiple reader/writers (antennas).

In order to solve the above problem, one aspect of the present invention provides a control device that controls multiple reader/writers that communicate with RFID tags, and includes a communication strength determination unit that determines the communication strength between the RFID tag and each reader/writer, and a switching unit that switches the reader/writer that communicates data with the RFID tag depending on the communication strength during data communication with the RFID tag.

With the above configuration, communication strength can be determined (specified) and the appropriate reader/writer can be dynamically switched to each time. Therefore, even if an RFID tag is attached to a moving object, stable communication is possible, and the location of the moving object can be identified from the physical placement of the reader/writer.

The control device may time-share control the scan period, during which the communication strength is measured, and the communication period, during which data is exchanged with the RFID tag.

With the above configuration, a scanning period is set up in advance to measure the communication strength before communication can be performed, and based on the results, communication with the RFID can be performed during the communication period while switching the RFID to communicate with each time.

The communication strength determination unit may calculate the communication strength from a first reception strength when the RFID tag receives from the reader/writer and a second reception strength when the reader/writer receives from the RFID tag.

With the above configuration, communication strength can be determined by comprehensively considering the reception strength of the RFID tag and the reception strength of the reader/writer.

The system may include a distance determination unit that determines the distance between the RFID tag and the reader/writer based on the communication strength, and the switching unit may switch the reader/writer that communicates the data with the RFID tag depending on the distance.

With the above configuration, the distance between the reader/writer and the RFID tag may be determined from the communication strength, and the reader/writer to be used for communication may be determined based on that distance.

The communication strength determination unit may measure the communication strength only for multiple reader/writers within a predetermined range that includes the reader/writer exchanging data with the RFID tag during the period in which the communication strength is measured.

With the above configuration, the reader/writers that measure communication strength can be limited to those within a specified range, including the reader/writer communicating with the RFID tag. Therefore, even in a system using multiple reader/writers, only a limited number of reader/writers that should be able to stably detect the RFID tag in question will be in operation, reducing lost time during the scanning period.

The switching unit may switch to the reader/writer with the highest communication strength.

With the above configuration, the reader/writer suitable for an RFID tag can be the one with the highest communication strength. This makes it easy to uniquely identify the reader/writer.

The switching unit does not need to switch the reader/writer if the communication strength of the reader/writer communicating with the RFID tag during the communication period is greater than the communication strength of the other reader/writer and the difference is within a predetermined range.

With the above configuration, even if there is a reader/writer suitable for the RFID tag with a stronger communication strength than the reader/writer already communicating, if the difference is smaller than a predetermined value, there is no need to switch reader/writers. This minimizes the period of invalid communication that occurs when switching reader/writers.

If there are multiple reader/writers whose communication strength with the RFID tag is equal to or greater than a predetermined value, the switching unit may switch the reader/writers so as to reduce the difference in the number of RFID tags with which the multiple reader/writers are communicating.

RFID tags may be concentrated on a specific reader/writer. In such cases, processing by that reader/writer alone may become excessive, which may result in RFID tags not being detected. To reduce this risk, reader/writers suitable for RFID tags may be designed to balance the load of the reader/writers so that the difference in the number of RFID tags each reader/writer is communicating with is reduced, provided that the communication strength is within a specified range.

During the scanning period, it is not necessary to measure the communication strength of the reader/writer that communicated with the RFID tag during the most recent communication period.

With the above configuration, by using the communication strength during the communication period, it is possible to reduce the number of readers/writers that perform scanning during the scan period.

During the communication period, the communication strength determination unit may determine the communication strength based on the reception strength obtained by the multiple reader/writers receiving communication from the RFID tag.

With the above configuration, during the communication period, other reader/writers receive communication from the RFID tag and measure the communication strength, thereby reducing the scanning period.

A reader/writer according to another aspect of the present invention is a reader/writer connected to multiple antennas that communicate with RFID tags, and includes a communication strength determination unit that determines the communication strength between the RFID tag and each antenna, and a switching unit that switches the antenna that communicates data with the RFID tag depending on the communication strength during data communication with the RFID tag.

The above configuration may be a system that detects RFID tags using a single reader/writer connected to multiple antennas.

A control method for a control device according to another aspect of the present invention is a method for controlling multiple reader/writers that communicate with RFID tags, and includes a communication strength determination step for determining the communication strength between the RFID tag and each reader/writer, and a switching step for switching the reader/writer that communicates data with the RFID tag in accordance with the communication strength during data communication with the RFID tag.

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

One aspect of the present invention enables stable communication with RFID tags that move across the communication areas of multiple reader/writers (antennas).

1 is a block diagram showing a configuration of a main part of an RFID system according to a first embodiment. 4 is a flowchart illustrating an example of the operation of the RFID system according to the first embodiment. 5 is a flowchart showing a method for selecting a reader/writer in a switching unit according to the first embodiment. 10 is a specific example showing switching between the first reader/writer and the second reader/writer according to the first embodiment. 10 is a graph showing changes in communication intensity between a first interrogator and a second interrogator. FIG. 10 is a block diagram showing the configuration of a main part of an RFID system according to a second embodiment. FIG. 10 is a block diagram showing the configuration of a main part of an RFID system according to a third embodiment. 10 is a specific example showing a method for switching a reader/writer according to the fourth embodiment. 10 is a specific example showing another reader/writer switching method according to the fourth embodiment. FIG. 1 is a conceptual diagram showing the positional relationship between an RFID tag and multiple reader/writers.

[Embodiment 1]
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.

§1. Application Example Fig. 1 is a block diagram showing the configuration of the main parts of an RFID system 100 according to embodiment 1. The RFID system 100 is a system in which an upper control device 10 that controls a plurality of reader/writers 20 in an integrated manner detects and communicates with an RFID tag 30 using an appropriate reader/writer 20.

RFID tags 30 are attached to moving objects such as automobiles, and move over time. Therefore, if only one reader/writer 20 is used, the RFID tag may move out of the detection range of that reader/writer 20. Therefore, the communication strength of multiple reader/writers with the RFID tag 30 is measured, and communication is performed by dynamically switching to the most appropriate reader/writer 20 each time. This allows for stable communication even with RFID tags 30 attached to moving objects.

§2. Configuration example (Configuration of RFID system 100)
1, an RFID system 100 includes multiple reader/writers 20 under the control of a single host control device 10 (control device). Each reader/writer 20 includes an antenna and can detect RFID tags within the antenna's detection range. Multiple RFID tags 30 may exist within the detection range.

(Configuration of the upper control device 10)
The upper control device 10 includes a communication unit 11 , a communication strength determination unit 12 , and a switching unit 13 .

The communication unit 11 acquires information about the RFID tag 30 with which each reader/writer 20 is communicating by having the upper-level control device 10 communicate with the reader/writer 20. The communication unit 11 also transmits the communication content determined by the upper-level control device 10 to the RFID tag 30 via the reader/writer 20. The communication unit 11 outputs the communication content to the communication strength determination unit 12.

The communication strength determination unit 12 acquires the reception strength measured by the reader/writer 20 and the RFID tag 30. The communication strength determination unit 12 is a functional block that determines the communication strength of each RFID tag 30 using the reception strength measured by the reader/writer 20 and the RFID tag 30. The communication strength determination unit 12 outputs the determined communication strength to the switching unit 13.

The switching unit 13 uses the determined communication strength to determine the appropriate reader/writer 20 for each RFID tag 30, and switches the reader/writer 20 to be used for communication during data communication with the RFID tag. The switching unit 13 outputs the selected reader/writer 20 to the communication unit 11.

§3. Operational Example Fig. 2 is a flowchart showing an operational example of the RFID system 100 according to the first embodiment.

In S11, the communication unit 11 communicates with the RFID tag 30 using the reader/writer 20 (first reader/writer) that is currently communicating data, and performs a scan. Here, scanning refers to communication that measures the communication strength between the reader/writer 20 and the RFID tag 30.

First, in accordance with an instruction from the communication unit 11, the reader/writer 20 issues an instruction to the RFID tag 30 to measure the reception strength. In response to this instruction, the RFID tag 30 measures the received UHF radio wave strength and returns the measured radio wave strength to the reader/writer 20 as the first reception strength. The reader/writer 20 measures the received UHF radio wave strength and returns the measured radio wave strength as the second reception strength. This series of operations between the reader/writer 20 and the RFID tag 30 for a given RFID tag is called a scan. Scans may be performed multiple times (for example, N times) consecutively for a given pair of reader/writer 20 and RFID tag 30.

In S12, the communication unit 11 checks whether there is an unscanned reader/writer 20 (second reader/writer) other than the first reader/writer. If there is a second reader/writer (Yes in S12), the process proceeds to S13; if there is no second reader/writer (No in S12), the process proceeds to S14.

In S13, the communication unit 11 scans the RFID tag 30 using the second reader/writer. Then, the process returns to S12. That is, the processes of S12 and S13 are repeated until all second reader/writers have been scanned.

In S14, the communication strength determination unit 12 determines the communication strength for each reader/writer 20. The method for determining the communication strength will be described in detail below. The communication strength determination unit 12 then outputs the communication strength for each combination of reader/writer 20 and RFID tag 30 to the switching unit 13.

In S15, the switching unit 13 selects an appropriate reader/writer for each RFID tag 30 based on the communication strength. The selected RFID tag 30 is then indicated to the communication unit 11. The method for selecting an appropriate reader/writer 20 will be described later.

At S16, the communication unit 11 communicates with the RFID tag 30 using the instructed reader/writer 20.

Here, the period from S11 to S13 is collectively referred to as the scanning period, during which the communication strength for each combination of reader/writer 20 and RFID tag 30 is measured and the appropriate reader/writer 20 is determined. In contrast, the period corresponding to S16 is collectively referred to as the communication period, during which data is actually exchanged between the reader/writer 20 and RFID tag 30 using the reader/writer 20 selected by the switching unit 13 based on communication strength.

(Method of determining communication strength: reception strength)
An example of a method for determining the communication strength will be described below. The reader/writer 20 measures the received signal strength indicator (RSSI) of the communication received by itself. That is, it measures the second reception strength described above.

Here, communication strength can be expressed as Dlvl in the following equation:

Dlvl=ΣRSSI(n)/N
Here, RSSI(n) is the value of the second reception strength at the nth scan, and the number of scans for each combination of reader/writer 20 and RFID tag 30 is N. Σ represents the sum of N scans. In other words, the communication strength Dlvl calculated by this formula is the average value of the second reception strength. The communication strength can also be used as an index representing the distance between the reader/writer 20 and the RFID tag 30.

(Method for selecting a suitable reader/writer 20)
A method for selecting an appropriate reader/writer 20 in the switching unit 13 will now be described.

Figure 3 is a flowchart showing how the switching unit 13 selects the reader/writer 20 in embodiment 1.

In S21, the switching unit 13 compares the communication strength between the first reader/writer (the reader/writer 20 currently communicating) and the second reader/writer (the unscanned reader/writers 20 excluding the first reader/writer). If the communication strength of the first reader/writer is greater than that of the second reader/writer, the process proceeds to S24; if the communication strength of the second reader/writer is equal to or greater than that of the first reader/writer, the process proceeds to S22.

In S22, the switching unit 13 determines whether the difference between the communication strength of the second reader/writer and the communication strength of the first reader/writer is smaller than a predetermined value. If the difference is smaller than the predetermined value, the process proceeds to S24; if the difference is equal to or greater than the predetermined value, the process proceeds to S23.

In S23, the switching unit 13 outputs an instruction to the communication unit 11 to switch to communication using the second reader/writer.

In S24, the switching unit 13 outputs an instruction to the communication unit 11 to continue communication using the first reader/writer.

Therefore, if the difference between the communication strength of the first reader/writer and the communication strength of the second reader/writer is small, or if the communication strength of the first reader/writer is greater, communication continues with the first reader/writer. On the other hand, if the communication strength of the second reader/writer is sufficiently greater than that of the first reader/writer, communication is switched to the second reader/writer. This is a measure to reduce the number of times the reader/writer that communicates with the RFID tag is switched while maintaining sufficient communication strength.

(Example of switching between the first reader/writer and the second reader/writer)
Fig. 4 is a specific example showing switching between the first reader/writer and the second reader/writer according to the first embodiment. Fig. 5 is a graph showing changes in communication strength between the first reader/writer and the second reader/writer. The horizontal axis of Fig. 5 represents time for the RFID tag 30, and the vertical axis represents communication strength. The RFID tag 30 is moving, and its position changes from tag position A to tag position B over time.

As shown in Figure 4, from reference numeral 51 to reference numeral 56, the reader/writer 20 used to communicate with the RFID tag 30 switches from the first reader/writer to the second reader/writer.

At reference numeral 51, during the scan period, the communication unit 11 has the first reader/writer and the second reader/writer each scan the same RFID tag 30. The result of this scan is reference numeral 61 in Figure 5. At reference numeral 52, the communication strength determination unit 12 determines the communication strength, and the switching unit 13 selects to continue using the first reader/writer. Thereafter, at reference numeral 53, the first reader/writer communicates data with the RFID tag 30 for a predetermined period. Data communication by the first reader/writer refers to the transmission of data to be written to the RFID tag 30 or the reception of data read from the RFID tag 30.

At reference numeral 54, during the scan period, the communication unit 11 again has the first reader/writer and the second reader/writer each scan the same RFID tag 30. The result of this scan is reference numeral 62 in Figure 5. At reference numeral 55, the communication strength determination unit 12 determines the communication strength, and the switching unit 13 selects to switch to the second reader/writer. Thereafter, at reference numeral 56, the second reader/writer communicates with the RFID tag 30 for a predetermined period.

The size of the transmitted and received data may be large, requiring a communication period longer than the scanning period. Furthermore, it is possible that the RFID tag 30 may move during the communication period. As shown in FIG. 5 , since the RFID tag 30 is attached to a moving object, the distance from the reader/writer 20 varies. Therefore, the communication strength also changes. The switching unit 13 switches to a reader/writer 20 suitable for communicating with the RFID tag 30 (e.g., reference numeral 55) between periods of data communication (e.g., reference numeral 53) and periods of data communication (e.g., reference numeral 56).

§4. Actions and Effects After measuring the communication strength, it is possible to dynamically switch to the reader/writer 20 that is best suited for communication with the RFID tag 30. Therefore, even if the RFID tag 30 is attached to a moving object, stable communication can be maintained. Furthermore, it is possible to identify the location of the moving object from the switching of the reader/writer 20 that can perform stable communication and the physical location of the reader/writer.

By clearly differentiating the roles of communication between the RFID tag 30 and the reader/writer 20 during the scanning period and the communication period, communication with the RFID tag 30 can be performed while maintaining sufficient communication strength.

The communication strength during the scan period can be measured using either the RFID tag reception strength, the reader/writer reception strength, or the reader/writer transmission strength, allowing for a comprehensive assessment.

Based on the results of measuring communication strength during the scan period, the switching unit 13 can select a suitable reader/writer based on the communication strength. Even if a suitable reader/writer has a stronger communication strength than the currently communicating reader/writer, if the difference is smaller than a predetermined value, there is no need to switch reader/writers. This minimizes the period of invalid communication that accompanies reader/writer switching.

Furthermore, the method for selecting an appropriate reader/writer is not limited to this method; for example, it is also possible to switch from multiple reader/writers to the one with the highest communication strength.

(Modification)
The function of the upper control device 10 may be included in any one of the multiple reader/writers 20. In this case, a specific reader/writer 20 having the function of the upper control device 10 communicates with the other reader/writers 20. The specific reader/writer 20 determines which reader/writer 20, including itself, to use to communicate with the RFID tag 30.

[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 6 is a block diagram showing the configuration of the main parts of an RFID system 101 according to embodiment 2. The RFID system 101 is a system in which a reader/writer 20a connected to multiple antennas 21 detects an RFID tag 30 using an appropriate antenna 21 and communicates with the appropriate antenna 21.

In embodiment 2, the reader/writer 20 of embodiment 1 is replaced by an antenna 21, and the upper control device 10 is replaced by a reader/writer 20a. The reader/writer 20a includes a communication unit 11, a communication strength determination unit 12, and a switching unit 13. The reader/writer 20a is connected to multiple antennas 21. In other words, the switching unit 13 of the reader/writer 20a selects one of the multiple antennas based on the communication strength determined by the communication strength determination unit 12.

[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.

Figure 7 is a block diagram showing the configuration of the main parts of an RFID system 102 according to embodiment 3. The RFID system 102 uses an upper control device 10b connected to multiple reader/writers 20 to select an appropriate reader/writer 20 to read an RFID tag 30 and communicate with it.

The host control device 10b of embodiment 3 differs from the host control device 10 of embodiment 1 in that it includes a distance determination unit 14. The distance determination unit 14 inputs the communication strength from the communication strength determination unit 12 and determines the distance of the RFID tag 30 from the reader/writer 20. The switching unit 13 selects the reader/writer 20 to use for communication based on the determined distance, rather than the communication strength. The distance determination unit 14 may also determine the position of the RFID tag using the distance of the same RFID tag 30 from multiple reader/writers 20.

(Method of determining communication strength: Friis's transmission formula)
Specifically, the RFID tag 30 measures the strength of the received signal in communication received by itself (i.e., measures the first received signal strength described above), and the reader/writer 20 measures the transmission power in scanning itself.

Here, communication strength can also be expressed as Dlvl in the following equation:

Dlvl=Σ10^{(Tx_rw(n)-RSSI_tag(n))/20}/N
Here, Tx_rw(n) is the value of the transmission power in the reader/writer 20 at the nth scan, and RSSI_tag(n) is the value of the first reception strength in the RFID tag 30 at the nth scan. "10^x" represents 10 to the xth power. However, the number of scans for each combination of reader/writer 20 and RFID tag 30 is N. Σ represents the sum of N scans. This calculation formula is a simplified formula for distance conversion based on the Friis propagation formula, and communication strength is also an index of the distance between the reader/writer 20 and RFID tag 30.

Calculating communication strength using this formula, which is based on the Friis transmission formula, provides a more accurate indicator of distance than the communication strength calculation method using only the second reception strength described above in embodiment 1. This allows the distance between the reader/writer 20 and the RFID tag 30 to be determined with high accuracy, making it easier to identify the location of the product to which the RFID tag 30 is attached.

[Embodiment 4]
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.

(Method to shorten scan period: Use the most recent communication)
The scanning period becomes long when there are a large number of reader/writers 20. Therefore, a method for shortening the scanning period using the most recent existing communication results will be described.

Figure 8 shows a specific example of a method for switching a reader/writer 20 according to embodiment 4. Unlike Figure 4, Figure 8 is a method for limiting the number of reader/writers 20 to be scanned during a scanning period based on the results of the most recent communication period.

Specifically, the first reader/writer used for communication during the most recent communication period (reference numeral 71 in FIG. 8) is considered to have already finished measuring its communication strength, and is not scanned during the scan period (reference numeral 72 in FIG. 8). The communication unit 11 scans the other reader/writers 20 (the second and third reader/writers in the example of FIG. 8), and the communication strength determination unit 12 measures their communication strength. Based on the results, the switching unit 13 selects the reader/writer 20 to use (reference numeral 73 in FIG. 8). In the example shown in FIG. 8, the third reader/writer is selected (reference numeral 74 in FIG. 8).

This allows for a reduction in the number of readers/writers scanned during a scan period, shortening the scan period.

(Method to shorten the scan period: Use communication with other reader/writers)
Another method for shortening the scan period will be described.

Figure 9 is a specific example showing another reader/writer 20 switching method according to embodiment 4. Unlike Figure 4, Figure 9 shows a method in which communication from an RFID tag 30 to a certain reader/writer 20 during the most recent communication period is received by another reader/writer 20, and processing is performed that is deemed to be a scan based on the received reception strength.

Specifically, the first reader/writer used for communication during the most recent communication period (reference numeral 81 in FIG. 9) is considered to have already finished measuring the communication strength. The control device 10 does not allow the first reader/writer to measure the communication strength during the scanning period. Furthermore, the communication strength determination unit 12 of the other reader/writers 20 (the second and third reader/writers in the example of FIG. 9) measures the communication strength upon receiving a reply (communication) from the RFID tag 30 to the first reader/writer. The switching unit 13 then selects the reader/writer 20 to be used (reference numeral 82 in FIG. 9). In the example shown in FIG. 9, the third reader/writer is selected (reference numeral 83 in FIG. 9).

Therefore, by using the communication period as the scanning period, the scanning period can be eliminated except for the initial scan.

(Method to shorten the scanning period: limit the number of readers/writers)
In the above two methods for shortening the scan period, the scan period is shortened by changing the processing during the scan period. In contrast to these, another method for shortening the scan period will be described.

Figure 10 is a conceptual diagram showing the positional relationship between an RFID tag 30 and multiple reader/writers 20. As shown in Figure 10, there are multiple reader/writers 20 (reader/writers A to L in Figure 10), and each reader/writer 20 can communicate with RFID tags within its communication range 91.

Let us assume that reader/writer E is currently communicating with RFID tag 30. At this time, even if RFID tag 30 is moving during the scanning period, it is believed that RFID tag 30 can be detected by scanning only reader/writers 20 whose communication ranges 91 are adjacent to the communication range 91 of the reader/writer with which communication is currently possible. Therefore, scanning can be performed using reader/writers A to I that are within a predetermined range 92 that includes reader/writer E. In other words, reader/writers J to L that are not within the predetermined range 92 are not scanned.

As a result, the reader/writers that perform scanning during the scanning period can be limited to only those within a specified range 92, including the reader/writer communicating with the RFID tag. As a result, even in systems that use a large number of reader/writers, the scanning period is shortened, allowing for stable detection of the target RFID tag.

[Embodiment 5]
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.

In embodiment 1, the reader/writer 20 that will communicate with the RFID tag 30 is determined using only the communication strength, but this is not limited to this. For example, the reader/writer 20 that will communicate may also be determined taking into consideration the number of RFID tags 30 that are communicating.

For example, suppose a first reader/writer and a second reader/writer are connected to the upper control device 10, and there is an overlapping range between the communication ranges of the first reader/writer and the second reader/writer. In this case, suppose there are three RFID tags within the communication range of only the first reader/writer, no RFID tags within the communication range of only the second reader/writer, and one RFID tag within the overlapping range. Both the first reader/writer and the second reader/writer have sufficient communication strength with the RFID tag in the overlapping range, but the communication strength of the first reader/writer is stronger.

If the reader/writer is determined based solely on communication strength, the first reader/writer will also communicate with RFID tags within the overlapping range. However, the number of RFID tags communicating with each reader/writer may be averaged. In other words, since the second reader/writer also has sufficient communication strength and is already communicating with multiple RFID tags 30, in embodiment 5, communication is performed using the second reader/writer rather than the first reader/writer.

Therefore, in embodiment 5, if the communication strength of the reader/writer 20 is equal to or greater than a predetermined value, the switching unit 13 may select a reader/writer 20 so as to reduce the difference in the number of RFID tags 30 with which the reader/writer 20 is communicating. This makes it possible to balance the load among multiple reader/writers 20 and prevent RFID tags 30 from going undetected.

[Software implementation example]
The functions of the upper control device 10 and the reader/writer 20a (hereinafter referred to as "devices") are programs for causing a computer to function as the devices, and can be realized by programs for causing a computer to function as each control block of the devices (particularly each part included in the upper control device 10 and the reader/writer 20a).

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 this control device and storage device.

The above program may be stored non-transitory on one or more computer-readable storage media. These storage 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 each of the above control blocks can be realized by logic circuits. For example, integrated circuits incorporating logic circuits that function as each of the above control blocks are also included in the scope of the present invention. In addition, the functions of each of the above control blocks can also be realized by, for example, a quantum computer.

Furthermore, each process described in each of the above embodiments may be executed by AI (Artificial Intelligence). In this case, the AI may run on the control device, or on another device (for example, an edge computer or a cloud server).

[Additional Notes]
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.

10, 10b Upper control device (control device)
REFERENCE SIGNS LIST 11 communication unit 12 communication strength determination unit 13 switching unit 14 distance determination unit 20, 20a reader/writer 21 antenna 30 RFID tag 100, 101, 102 RFID system

Claims (5)

A control device that controls a plurality of reader/writers that communicate with RFID tags,
a communication strength determination unit that determines the communication strength between the RFID tag and each reader/writer;
a switching unit that switches the reader/writer that communicates data with the RFID tag in accordance with the communication strength during data communication with the RFID tag,
The control device controls a scan period, which is a period for measuring the communication strength, and a communication period, which is a period for communicating the data with the RFID tag, in a time-division manner. The control device described in claim 1, wherein the switching unit does not switch the reader/writer if the communication strength of the reader/writer communicating with the RFID tag during the communication period is greater than the communication strength of another reader/writer and the difference is within a predetermined range. 3. The control device according to claim 1, wherein during the scanning period, the measurement of the communication strength of the reader/writer that has communicated with the RFID tag during the most recent communication period is not performed. The control device according to any one of claims 1 to 3, wherein the communication strength determination unit determines the communication strength based on the reception strength obtained by the plurality of reader/writers receiving communication from the RFID tag during the communication period. A control method for controlling a plurality of reader/writers that communicate with an RFID tag, comprising:
a communication strength determination step of determining communication strength between the RFID tag and each reader/writer;
a switching step of switching the reader/writer that communicates data with the RFID tag in accordance with the communication strength during data communication with the RFID tag,
In the control method, a scan period during which the communication strength is measured and a communication period during which the data is communicated with the RFID tag are controlled in a time-division manner.