Communication system, master station, slave station, communication method, and communication program

Abstract

To provide a communication system, a master station, a slave station, a communication method, and a communication program capable of suppressing power consumption and preventing deterioration of response in roaming in which the master station corresponding to the slave station is switched.SOLUTION: In a communication system, a first slave station transmits a search signal to search for another master station when the stability of communication with a first master station associated with the first slave station falls below a threshold. Each of a plurality of master stations that have received the search signal transmits a report including identification information on the master station, identification information on the first slave station, and signal information about the search signal to a management server. The management server determines a second master station to be associated with the first slave station from among the plurality of master stations based on the plurality of reports received from each of the plurality of master stations, and switches the master station to be associated with the first slave station from the first master station to the second master station.SELECTED DRAWING: Figure 21

Description

Technical Field

[0001] The present invention relates to a communication system, a master station, a slave station, a communication method, and a communication program.

Background Art

[0002] Conventionally, there is known a communication method (TDMA; Time Division Multiple Access) in which one master station (also referred to as a controller, host, etc.) occupies one channel and sequentially communicates with a plurality of slave stations (also referred to as slaves) assigned to the master station in a time division manner. For each slave station, a certain period immediately after receiving communication (transmission data) from the master station is assigned as the communication available time with the host.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in factories, warehouses, etc., workers perform picking operations to pick up items stored on storage shelves. Conventionally, a picking system for improving the efficiency of the picking operation has been introduced. In the picking system, a plurality of storage shelves, slave stations (tags having a communication function) installed on each storage shelf, and a master station (controller) for controlling a plurality of tags are arranged in a work area. The controller transmits a command (which may include a lighting command) to the tag of the storage shelf where the item to be picked is stored, and lights a lamp (LED) mounted on the tag. The worker picks up the target item from the storage shelf with the lit lamp button.

[0005] In the aforementioned picking system, when constructing numerous star-topology networks consisting of a master station and multiple slave stations, it is necessary to associate each of the multiple slave stations with a specific master station that has stable communication. Furthermore, if the communication environment between a slave station and a master station deteriorates after the slave station has been associated with a master station, a process (roaming) is required to switch to a master station with a better communication environment.

[0006] Conventional roaming systems typically employ a method where a slave station receives beacons from other base stations and directly queries the base station with the best reception to switch. However, this method increases the load on the slave station, leading to increased power consumption and temporary lag in response times.

[0007] The object of the present invention is to provide a communication system, a master station, a slave station, a communication method, and a communication program that can suppress power consumption and prevent deterioration of response in roaming, which involves switching between master stations corresponding to slave stations. [Means for solving the problem]

[0008] A communication system according to an embodiment of the present invention is a communication system including a management server, a plurality of master stations, and a plurality of slave stations, wherein the first slave station transmits a search signal to search for other master stations when the stability of communication with the first master station associated with the first slave station falls below a threshold, and each of the plurality of master stations that receive the search signal transmits a report to the management server including the identification information of the master station, the identification information of the first slave station, and signal information relating to the search signal, and the management server determines a second master station to associate with the first slave station from among the plurality of master stations based on the plurality of reports received from each of the plurality of master stations, and switches the master station associated with the first slave station from the first master station to the second master station.

[0009] A master station according to an embodiment of the present invention is a master station that communicates with a management server and a plurality of slave stations, and when the stability of communication with the first master station associated with the first slave station falls below a threshold, the master station receives a search signal from the first slave station for searching for other master stations, and sends a report to the management server that includes the identification information of the master station, the identification information of the first slave station, and signal information relating to the search signal. When the master station receives an instruction from the management server to switch the master station associated with the first slave station from the first master station to the second master station, the master station transmits information relating to the second master station to the first slave station.

[0010] A slave station according to an embodiment of the present invention is a slave station that communicates with a management server and a plurality of master stations, and when the stability of communication with a first master station associated with the slave station falls below a threshold, it transmits a search signal to search for other master stations, and when the management server determines a second master station to be associated with the slave station, it switches the master station associated with the slave station from the first master station to the second master station.

[0011] A communication method according to an embodiment of the present invention is a communication method in which a management server, a plurality of master stations, and a plurality of slave stations perform wireless communication, and one or more processors perform the following steps: when the stability of communication between a first slave station and a first master station associated with the first slave station falls below a threshold, one or more processors transmit a search signal for searching for other master stations; each of the plurality of master stations that have received the search signal transmits a report to the management server that includes the identification information of the master station, the identification information of the first slave station, and signal information relating to the search signal; and the management server determines a second master station to associate with the first slave station from among the plurality of master stations based on the plurality of reports received from each of the plurality of master stations, and switches the master station associated with the first slave station from the first master station to the second master station.

[0012] A communication program according to an embodiment of the present invention is a communication program that causes one or more processors to execute the following steps: a first slave transmits a search signal to search for other slaves when the stability of communication with the first slave associated with the first slave falls below a threshold; each of the plurality of slaves that have received the search signal transmits a report to the management server that includes the identification information of the slave, the identification information of the first slave, and signal information relating to the search signal; and the management server determines a second slave to associate with the first slave from among the plurality of slaves based on the plurality of reports received from each of the plurality of slaves, and switches the slave associated with the first slave from the first slave to the second slave. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a communication system, a master station, a slave station, a communication method, and a communication program that can suppress power consumption and prevent deterioration of response in roaming where a master station corresponding to a slave station is switched. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is a functional block diagram showing the schematic configuration of a communication system according to Embodiment 1 of the present invention. [Figure 2] Figure 2 is an external view of a storage shelf according to an embodiment of the present invention. [Figure 3A] Figure 3A shows the configuration of tags installed in a storage shelf according to an embodiment of the present invention. [Figure 3B] Figure 3B is a bottom view of a tag according to an embodiment of the present invention. [Figure 4] Figure 4 shows an example of tag information stored in the storage unit of a communication system according to an embodiment of the present invention. [Figure 5] Figure 5 shows an example of related information stored in the storage unit of a communication system according to an embodiment of the present invention. [Figure 6] FIG. 6 is a diagram showing the correspondence relationship between the controller and the tag according to an embodiment of the present invention. [Figure 7] FIG. 7 is a diagram showing an example of a time division to which the controller according to an embodiment of the present invention is assigned. [Figure 8] FIG. 8 is a diagram showing a specific example of the communication method according to an embodiment of the present invention. [Figure 9] FIG. 9 is a diagram showing a specific example of the communication method according to an embodiment of the present invention. [Figure 10] [[ID=1 / 3]]FIG. 10 is a flowchart for explaining an example of the procedure of communication processing executed in the communication system according to Embodiment 1 of the present invention. [Figure 11] FIG. 11 is a diagram showing the correspondence relationship between the controller and the communication area according to an embodiment of the present invention. [Figure 12] FIG. 12 is a diagram showing a state in which each of a plurality of controllers according to an embodiment of the present invention is assigned to a channel and a time division. [Figure 13] FIG. 13 is a functional block diagram showing a schematic configuration of the communication system according to Embodiment 2 of the present invention. [Figure 14] FIG. 14 is a diagram showing a specific example of the association process in the communication system according to Embodiment 2 of the present invention. [Figure 15] FIG. 15 shows an example of the procedure of the association process between the management server, a plurality of controllers, and the target tag in the communication system according to Embodiment 2 of the present invention. [Figure 16] [ FIG. 16 is a flowchart for explaining an example of the procedure of the association process executed in the target tag according to Embodiment 2 of the present invention. [Figure 17] FIG. 17 is a flowchart for explaining an example of the procedure of the association process executed in the controller according to Embodiment 2 of the present invention. [Figure 18] [ FIG. 18 is a flowchart for explaining an example of the procedure of the association process executed in the management server according to Embodiment 2 of the present invention. [Figure 19] Figure 19 is a functional block diagram showing the schematic configuration of a communication system according to Embodiment 3 of the present invention. [Figure 20] Figure 20 is an external view of a trolley according to Embodiment 3 of the present invention. [Figure 21] Figure 21 is a diagram showing a specific example of association processing in a communication system according to Embodiment 3 of the present invention. [Figure 22] Figure 22 shows an example of a roaming procedure between a management server, multiple controllers, and target tags in a communication system according to Embodiment 3 of the present invention. [Figure 23A] Figure 23A is a flowchart illustrating an example of a roaming procedure performed in a target tag according to Embodiment 3 of the present invention. [Figure 23B] Figure 23B is a flowchart illustrating an example of a roaming procedure performed in a target tag according to Embodiment 3 of the present invention. [Figure 24] Figure 24 is a flowchart illustrating an example of a roaming procedure performed in a controller according to Embodiment 3 of the present invention. [Figure 25] Figure 25 is a flowchart illustrating an example of a roaming procedure performed in a management server according to Embodiment 3 of the present invention. [Modes for carrying out the invention]

[0015] Embodiments of the present invention will be described below with reference to the attached drawings. Note that the following embodiments are merely examples of the present invention and do not limit the technical scope of the present invention.

[0016] [Embodiment 1] Figure 1 is a functional block diagram showing the schematic configuration of a communication system 10 according to Embodiment 1 of the present invention.

[0017] The communication system 10 includes a management server 1, a controller 2, and a tag Tg. The communication system 10 is introduced, for example, to a work site (factory, warehouse, etc.) where workers pick the desired items from storage shelves 3 (see Figure 2) where items are stored. The items are not particularly limited and include items from various fields such as parts, retail goods, pharmaceuticals, books, documents, and miscellaneous goods. In this embodiment, as an example of the items, parts used in the assembly of a predetermined product (vehicle, electrical appliance, etc.) are given. That is, the communication system 10 in this embodiment is introduced to a facility F1 (factory, etc.) where workers pick the desired parts from storage shelves 3 where parts are stored.

[0018] The management server 1 and controller 2 are connected to each other via network N1. Network N1 is a communication network such as the Internet, LAN, WAN, or public telephone line. Controller 2 and tag Tg are connected by this communication method using radio waves. Tag Tg is installed in each storage shelf 31 of storage shelf 3 (see Figure 2). As shown in Figure 3A, tag Tg includes a display unit (LCD) that displays the part name, etc., a lamp button B1 that lights up, blinks, and turns off in multiple colors, and a communication unit (not shown) that communicates with controller 2. Lamp button B1 also has a button function as a user interface. Tag Tg can display predetermined information on the display unit or light up or turn off lamp button B1 according to commands (transmitted data) from controller 2. For example, an operator picks a part from storage shelf 31 where a tag Tg with the lamp button B1 lit is installed. Tag Tg notifies controller 2 that lamp button B1 has been pressed using this communication method, and controller 2 notifies management server 1 of this. If the management server 1 confirms that tag Tg corresponds to the correct part, it uses this communication method to notify the controller 2 of a signal to the tag Tg corresponding to the next part to be picked, causing lamp button B1 to blink at a predetermined interval. Figure 3A shows tag 1 in the lit state. The management server 1 controls each controller 2 collectively and outputs a transmission instruction (such as a command to light up tag Tg) to the designated controller 2 based on the information of the picking target.

[0019] Multiple storage shelves 3 are arranged within facility F1. Multiple controllers 2 are installed distributed throughout facility F1, and these multiple controllers 2 communicate with the tags Tg on the multiple storage shelves 3 located within facility F1. In this way, the communication system 10 constructs the picking system for facility F1 by controlling the multiple tags Tg located within facility F1 using multiple controllers 2. Specifically, the communication system 10 is a system that manages radio communication between the multiple controllers 2 and the multiple tags Tg to occur at predetermined intervals.

[0020] Management Server 1 functions as an arbitration station that manages and controls Controller 2, Controller 2 functions as a host device, and Tag Tg functions as a slave device. Controller 2 is an example of a master station of the present invention, and Tag Tg is an example of a slave station of the present invention.

[0021] [Management Server 1] As shown in Figure 1, the management server 1 includes a control unit 11, a storage unit 12, an operation display unit 13, and a communication unit 14, etc. The management server 1 may be an information processing device such as a personal computer. Alternatively, the management server 1 may be configured as a cloud server.

[0022] The communication unit 14 connects the management server 1 to the network N1 by wire or wireless connection and performs data communication with the controller 2 via the network N1 in accordance with a predetermined communication protocol.

[0023] The operation display unit 13 is a user interface comprising a display unit such as a liquid crystal display or an organic EL display that displays various types of information, and an operation unit such as a touch panel, mouse, or keyboard that accepts operations.

[0024] The storage unit 12 is a non-volatile storage unit such as an HDD (Hard Disk Drive), SSD (Solid State Drive), or flash memory that stores various types of information. Data such as tag information D1 and related information D2 are stored in the storage unit 12.

[0025] Figure 4 shows an example of tag information D1. Tag information D1 registers information about all tags Tg placed in facility F1. Specifically, tag information D1 includes information such as tag ID, location information, and part name. The tag ID is the identification information of tag Tg. The location information is the location information of the place where tag Tg is installed, such as the location of storage shelf 3, the shelf number of storage shelf 3 (storage shelf 31), and the coordinates of facility F1 on a map. The part name is the name of the part stored in storage shelf 31 where tag Tg is installed.

[0026] Tag information D1 is registered, for example, by the administrator of facility F1. Tag information D1 may also be stored on a server different from management server 1.

[0027] Figure 5 shows an example of related information D2. Related information D2 is information that identifies the tag Tg associated with each of the multiple controllers 2. Specifically, related information D2 includes information such as controller ID and tag ID. The controller ID is the identification information of controller 2, and the tag ID is the identification information of tag Tg. In reality, each controller 2 is associated with the tag Tg that provides the most stable communication, so the IDs of tag Tg are random and have no regularity.

[0028] As shown in Figure 6, multiple tags Tg are associated with one controller 2. Each controller 2 can communicate with multiple tags Tg, and each tag Tg can communicate with one controller 2. For example, controller A can communicate with tags Tg in communication area AR1, and controller B can communicate with tags Tg in communication area AR2. In practice, to ensure sufficient communication stability, a single tag Tg is often located within the communication area AR of multiple controllers 2, as shown in Figure 11. Each tag Tg is associated with the controller 2 that provides the most stable communication among the multiple controllers 2, but this area experiences radio interference from the multiple controllers 2, as shown in Figure 11. In this embodiment, five controllers 2 (controllers A to E) are configured to cover the entire work area of ​​facility F1 and enable communication with all tags Tg within facility F1. Related information D2 is registered by the processing of the control unit 11 (described later).

[0029] Furthermore, the storage unit 12 may store picking information, including the order in which parts are picked. For each part to be picked, the picking information is registered with associated information such as tag ID, location information, and picking status. The management server 1 registers the information to be picked in the picking information based on the picking instructions. The management server 1 may obtain the picking instructions from a server that manages the product manufacturing process, or it may generate the picking information based on the manufacturing process stored in the storage unit 12.

[0030] Furthermore, the storage unit 12 stores control programs, such as communication programs, that cause the control unit 11 to execute the communication processing described later (see Figure 10). For example, the communication program is non-temporarily recorded on a computer-readable recording medium such as a CD or DVD, and is read by a reading device (not shown), such as a CD drive or DVD drive, which is electrically connected to the management server 1, and stored in the storage unit 12.

[0031] The control unit 11 includes control equipment such as a CPU. The CPU is a processor that performs various arithmetic operations. The control unit 11 controls the management server 1 by executing various control programs pre-stored in the storage unit 12 using the CPU.

[0032] Specifically, the control unit 11 includes various processing units such as the related processing unit 111, the allocation processing unit 112, and the communication processing unit 113. The control unit 11 functions as these various processing units by executing various processes according to the communication program using the CPU. Some or all of the processing units included in the control unit 11 may be composed of electronic circuits. The communication program may be a program that causes multiple processors to function as these various processing units.

[0033] The association processing unit 111 associates each of the multiple tags Tg with one of the multiple controllers 2.

[0034] For example, as shown in Figure 5, the association processing unit 111 associates multiple tags Tg with tag IDs "tg0001 to tg0100" located in communication area AR1 with controller A, controller ID "c0001", located in communication area AR1. The association processing unit 111 also associates multiple tags Tg with tag IDs "tg0101 to tg0200" located in communication area AR2 with controller B, controller ID "c0002", located in communication area AR2. Furthermore, the association processing unit 111 associates multiple tags Tg with tag IDs "tg0201 to tg0300" located in communication area AR3 with controller C, controller ID "c0003", located in communication area AR3. Furthermore, the related processing unit 111 associates multiple tags Tg with tag IDs "tg0301 to tg0400" located in communication area AR4 with controller D with controller ID "c0004" located in communication area AR4. Also, the related processing unit 111 associates multiple tags Tg with tag IDs "tg0401 to tg0500" located in communication area AR5 with controller E with controller ID "c0005" located in communication area AR5.

[0035] The above association is the result of associating each tag Tg with the controller 2 that provides the most stable communication, and then assigning an appropriate number. In this invention, each of the multiple slave stations may be pre-associated with one of the multiple master stations. Another method (association process) for associating each of the multiple slave stations with one of the multiple master stations will be described in Embodiment 2. Furthermore, a method (roaming) for changing (switching) the master station associated with a slave station will be described in Embodiment 3.

[0036] The association processing unit 111 registers information about the associated controller 2 and tag Tg in the association information D2 (see Figure 5).

[0037] The allocation processing unit 112 assigns each of the multiple controllers 2 to one of several time slots (time divisions) obtained by dividing a predetermined period within a predetermined channel. For example, as shown in Figure 7, if the period is "C1", the period C1 is divided into multiple time slots. Here, the period C1 is divided into five time slots t1 to t5. Also, here it is assumed that one predetermined channel CH1 is used. A number of controllers 2 capable of communicating with multiple tags Tg within a predetermined period are assigned to channel CH1. For example, the allocation processing unit 112 assigns controller A to the first time slot t1, controller B to the second time slot t2, controller C to the third time slot t3, controller D to the fourth time slot t4, and controller E to the fifth time slot t5.

[0038] The allocation processing unit 112 assigns controllers A to E to time segments t1 to t5 in order for each period C1.

[0039] The communication processing unit 113 causes the controller 2 and the multiple tags Tg associated with the controller 2 by the related processing unit 111 to communicate within each of the multiple time segments. A specific example of the communication method will be explained with reference to Figure 8.

[0040] In the example shown in Figure 8, the period C1 in channel CH1 is set to "200ms", and the time width of each time segment t1 to t5 is set to "40ms". The communication processing unit 113 outputs a transmission instruction to the controller A for transmission data in the first time segment t1 of period C1. The transmission data is, for example, a beacon.

[0041] Here, as shown in Figure 9, the transmitted data includes command information (command information) that causes a tag Tg to execute a predetermined process, and identification information (destination information) that identifies the tag Tg that will execute the command. Specifically, the transmitted data includes destination information for each of a predetermined number of tags Tg, and command information that causes each of the predetermined number of tags Tg to execute a predetermined command. For example, Figure 9 shows an example of transmitted data transmitted by controller A. The communication processing unit 113 identifies five tags Tg (see Figure 4) associated with the five parts to be picked from among a plurality of tags Tg (see Figure 5) associated with controller A, and outputs a transmission instruction to controller A for transmitted data that includes the identified five tags 1 to 5 as destinations.

[0042] In other words, the communication processing unit 113 causes controller A to send transmission data to a predetermined number of tags Tg among a plurality of tags Tg associated with controller A. Controller A also sends the transmission data to a predetermined number of tags Tg that can communicate with controller A within a time interval.

[0043] When Controller A receives the transmission instruction from Management Server 1, it transmits the transmission data (see Figure 9) to all tags Tg (see Figure 5) associated with Controller A in the first time segment t1 (see Figure 8).

[0044] Each tag Tg associated with controller A, upon receiving the transmission data, checks the destination included in the transmission data and executes a predetermined process if it contains a command addressed to itself. For example, if tag 1 receives the transmission data containing a command addressed to itself to turn on lamp button B1 (see Figure 3A), it turns on lamp button B1 (see Figure 3A). Tag 1 also sends a response (acknowledgment) to controller A when it executes the command. Similarly, each of tags 2 to 5, upon receiving the transmission data, turns on lamp button B1 (see Figure 3A) and sends a response (acknowledgment) to controller A because it contains a command addressed to itself. Controller A receives responses from each of tags 1 to 5 (see Figure 9). At this time, tags 1 to 5 send their responses appropriately at timings that do not conflict with each other, depending on the position of the command addressed to them in the transmission data. In this embodiment, each tag Tg sends an acknowledgment of the same size in the order in which the commands were found, and a time interval that takes into account the time required for each acknowledgment transmission and a predetermined margin is added to prevent the acknowledgment signals from colliding.

[0045] Furthermore, in this embodiment, the design ensures that after all five units have sent acknowledgments within the time segment, there is remaining tag data reception period R1 (Figure 9). When the button function of the lamp is pressed, the tag Tg transmits using the CSMA / CA method during the subsequent tag data reception period R1. The tag data reception period R1 shown in Figure 9 is the uplink period from tag Tg to controller 2 using the CSMA / CA method.

[0046] Furthermore, the aforementioned confirmation response is not limited to button press information; if other user interfaces are available, it may also be the content of those operations. Additionally, if the tag Tg has a sensor function, it may be configured to transmit a measurement spontaneously when the measurement value meets predetermined conditions.

[0047] Controller A transmits the transmission data to tags 1-5 in the first time segment t1 (40ms) of period C1 (200ms). Once the execution of the commands for tags 1-5 is complete, the communication processing unit 113 outputs a transmission instruction to controller B for the transmission data in the next second time segment t2 of period C1 (200ms) (see Figure 8). The transmission data includes the destinations and commands for tags 6-10.

[0048] Each tag Tg associated with controller B, upon receiving the transmission data, checks the destination included in the transmission data and executes a predetermined process if it contains a command addressed to itself. For example, if tag 6 receives the transmission data containing a command addressed to itself to turn on lamp button B1 (see Figure 3A), it turns on lamp button B1 (see Figure 3A) because it contains a command addressed to itself. Tag 6 also sends a response (acknowledgment) to controller B when it executes the command. Similarly, each of tags 7 to 10, upon receiving the transmission data, turns on lamp button B1 (see Figure 3A) and sends a response (acknowledgment) to controller B because it contains a command addressed to itself. Controller B receives responses from each of tags 6 to 10.

[0049] When controller B transmits the transmission data to tags 6-10 in the second time segment t2 (40ms) of period C1 (200ms), and the execution of the commands for tags 6-10 is completed, the communication processing unit 113 outputs a transmission instruction to controller C in the next third time segment t3 of period C1 (200ms). The transmission data includes the destinations and commands for tags 11-15 (see Figure 8).

[0050] Each tag Tg associated with controller C, upon receiving the transmission data, checks the destination included in the transmission data and executes a predetermined process if it contains a command addressed to itself. For example, if tag 11 receives the transmission data containing a command addressed to itself to turn on lamp button B1 (see Figure 3A), it turns on lamp button B1 (see Figure 3A) because it contains a command addressed to itself. Tag 11 also sends a response (acknowledgment) to controller C when it executes the command. Similarly, each of tags 12 to 15, upon receiving the transmission data, turns on lamp button B1 (see Figure 3A) and sends a response (acknowledgment) to controller C because it contains a command addressed to itself. Controller C receives responses from each of tags 11 to 15 (see Figure 8).

[0051] Controller C transmits the transmission data to tags 11-15 in the third time segment t3 (40ms) of period C1 (200ms). Once the execution of the commands for tags 11-15 is complete, the communication processing unit 113 outputs a transmission instruction to controller D for the transmission data in the next fourth time segment t4 of period C1 (200ms). The transmission data includes the destinations and commands for tags 16-20.

[0052] Each tag Tg associated with controller D, upon receiving the transmission data, checks the destination included in the transmission data and executes a predetermined process if it contains a command addressed to itself. For example, if tag 16 receives the transmission data containing a command addressed to itself to turn on lamp button B1 (see Figure 3A), it turns on lamp button B1 (see Figure 3A) because it contains a command addressed to itself. Tag 16 also sends a response (acknowledgment) to controller D when it has executed the command. Similarly, each of tags 17 to 20, upon receiving the transmission data, turns on lamp button B1 (see Figure 3A) and sends a response (acknowledgment) to controller D because it contains a command addressed to itself. Controller D receives responses from each of tags 16 to 20 (see Figure 8).

[0053] When controller D transmits the transmission data to tags 16-20 in the fourth time segment t4 (40ms) of period C1 (200ms), and the execution of the commands on tags 16-20 is completed, communication processing unit 113 outputs a transmission instruction to controller E in the next fifth time segment t5 of period C1 (200ms). The transmission data includes the destinations and commands for tags 21-25.

[0054] Each tag Tg associated with controller E, upon receiving the transmission data, checks the destination included in the transmission data and executes a predetermined process if it contains a command addressed to itself. For example, if tag 21 receives the transmission data containing a command addressed to itself to turn on lamp button B1 (see Figure 3A), it turns on lamp button B1 (see Figure 3A) because it contains a command addressed to itself. Tag 21 also sends a response (acknowledgment) to controller E when it executes the command. Similarly, each of tags 22 to 25, upon receiving the transmission data, turns on lamp button B1 (see Figure 3A) and sends a response (acknowledgment) to controller E because it contains a command addressed to itself. Controller E receives responses from each of tags 21 to 25 (see Figure 8).

[0055] When controller E transmits the transmission data to tags 21-25 in the fifth time segment t5 (40ms) of period C1 (200ms), and the execution of the commands on tags 21-25 is completed, communication processing unit 113 outputs a transmission instruction to controller A again in the first time segment t1 of the next period C1 (200ms). The transmission data includes the destinations and commands for tags 1-5.

[0056] Each tag Tg associated with controller A, upon receiving the transmission data, checks the destination included in the transmission data and executes a predetermined process if it contains a command addressed to itself. For example, if tag 1 receives the transmission data containing a command addressed to itself to turn on lamp button B1 (see Figure 3A), it turns on lamp button B1 (see Figure 3A) because it contains a command addressed to itself. Tag 1 also sends a response (acknowledgment) to controller A when it executes the command. Similarly, each of tags 2 to 5, upon receiving the transmission data, turns on lamp button B1 (see Figure 3A) and sends a response (acknowledgment) to controller A because it contains a command addressed to itself. Controller A receives responses from each of tags 1 to 5 (see Figure 8).

[0057] As described above, the communication processing unit 113 causes the controller 2 and the multiple tags Tg associated with the controller 2 to communicate within each of the multiple time segments. The communication processing unit 113 also outputs transmission instructions for the transmission data to each of the multiple controllers 2 in the order of the time segments. As a result, for example, each of the controllers A to E communicates with the tags Tg controlled by each controller in the order of time segments t1 to t5.

[0058] For example, after controller A transmits the transmission data to five tags 1 to 5 of the multiple tags Tg associated with controller A in the first time segment t1, controller B transmits the transmission data to five tags 6 to 10 of the multiple tags Tg associated with controller B in the second time segment t2 following the first time segment t1.

[0059] Furthermore, in the first time segment t1, controller A transmits the transmission data to tags 1 to 5, and after controller A receives responses from tags 1 to 5, controller B transmits the transmission data to tags 6 to 10 in the second time segment t2.

[0060] Here, the control unit 11 executes a process to synchronize (time synchronize) the management server 1 and each controller. Also, each controller 2 executes a process to synchronize (time synchronize) with the corresponding tag Tg. As a result, each controller 2 sends transmission data to the tag Tg at a predetermined period (e.g., 200ms), and each tag Tg receives the transmission data at a predetermined period (e.g., 200ms). For example, each tag Tg starts up in accordance with the time of reception of the transmission data and starts receiving the transmission data at that reception time. Also, each tag Tg completes the reception process at the time when the transmission of the transmission data is completed by the controller 2, and performs time synchronization after the completion of the reception process. Each tag Tg sets a timer and waits (power save) until the time of reception of the next transmission data.

[0061] Time synchronization between the controllers 2 may be performed autonomously, for example, using the IEEE 1588 Precision Time Protocol. Alternatively, the communication processing unit 113 may notify each controller 2 of the period C1 and time segments t1 to t5, and control each controller 2 to communicate at the timings shown in Figure 7.

[0062] [Communication Processing] Hereinafter, with reference to Figure 10, an example of the procedure for communication processing performed in the communication system 10 according to Embodiment 1 will be described.

[0063] Furthermore, the present invention can be understood as an invention of a communication method that performs one or more steps included in the communication process, and the one or more steps included in the communication process described herein may be omitted as appropriate. In addition, the execution order of each step in the communication process may differ to the extent that similar effects are produced. Moreover, although the case in which each step in the communication process is executed by the management server 1 and the controller 2 is described here as an example, a communication method in which multiple processors distribute and execute each step in the communication process can also be considered as another embodiment.

[0064] Here, we will explain using the communication method shown in Figures 8 and 9 above as an example. The control unit 11 of the management server 1 uses a predetermined channel CH1 to output transmission instructions for transmission data (see Figure 8) to each of the controllers A to E that are assigned to each of the five time divisions t1 to t5 (40ms each) obtained by time-dividing a predetermined period (200ms).

[0065] First, when the first cycle (N=1) begins (S1), in step S2, the control unit 11 determines whether or not the first time segment t1 has started. If the first time segment t1 has started (S2: Yes), in step S3, the control unit 11 outputs a transmission instruction for the transmission data to the controller A. When the controller A receives the transmission instruction, it sends the transmission data, which includes the tags Tg (e.g., tags 1 to 5) that will execute the command, to all tags Tg associated with the controller A (see Figure 5).

[0066] Next, in step S4, the control unit 11 determines whether or not it has received a response (acknowledgment) from tag Tg. For example, when tags 1 to 5 receive the transmission data, execute a command (lighting command), and send a response to controller A, controller A sends the received response to management server 1. As a result, the control unit 11 of management server 1 receives the response. When the control unit 11 receives the response (S4: Yes), the process moves to step S5.

[0067] In step S5, the control unit 11 determines whether the second time segment t2 has started. If the second time segment t2 has started (S5: Yes), in step S6, the control unit 11 outputs a transmission instruction for the transmission data to the controller B. When the controller B receives the transmission instruction, it sends the transmission data, which includes the tags Tg (e.g., tags 6 to 10) that will execute the command, to all tags Tg associated with the controller B (see Figure 5).

[0068] Next, in step S7, the control unit 11 determines whether or not it has received a response from tag Tg. For example, when tags 6 to 10 receive the transmission data, execute a command (lighting command), and send a response to controller B, controller B sends the received response to management server 1. As a result, the control unit 11 of management server 1 receives the response. If the control unit 11 receives the response (S7: Yes), the process proceeds to step S8.

[0069] In step S8, the control unit 11 determines whether the third time segment t3 has started. If the third time segment t3 has started (S8: Yes), in step S9, the control unit 11 outputs a transmission instruction to the controller C for the transmission data. When the controller C receives the transmission instruction, it sends the transmission data, which includes the tags Tg (e.g., tags 11-15) that will execute the command, to all tags Tg associated with the controller C (see Figure 5).

[0070] Next, in step S10, the control unit 11 determines whether or not it has received a response from tag Tg. For example, when tags 11 to 15 receive the transmission data, execute a command (lighting command), and send a response to controller C, controller C sends the received response to management server 1. As a result, the control unit 11 of management server 1 receives the response. When the control unit 11 receives the response (S10: Yes), the process proceeds to step S11.

[0071] In step S11, the control unit 11 determines whether the fourth time segment t4 has started. If the fourth time segment t4 has started (S11: Yes), in step S12, the control unit 11 outputs a transmission instruction for the transmission data to the controller D. When the controller D receives the transmission instruction, it sends the transmission data, which includes the tag Tg (e.g., tags 16-20) that will execute the command, to all tags Tg associated with the controller D (see Figure 5).

[0072] Next, in step S13, the control unit 11 determines whether or not it has received a response from tag Tg. For example, when tags 16 to 20 receive the transmission data, execute a command (lighting command), and send a response to controller D, controller D sends the received response to management server 1. As a result, the control unit 11 of management server 1 receives the response. When the control unit 11 receives the response (S13: Yes), the process moves to step S14.

[0073] In step S14, the control unit 11 determines whether the fifth time period t5 has started. If the fifth time period t5 has started (S14: Yes), in step S15, the control unit 11 outputs a transmission instruction for the transmission data to the controller E. When the controller E receives the transmission instruction, it sends the transmission data, which includes the tags Tg (e.g., tags 21-25) that will execute the command, to all tags Tg associated with the controller E (see Figure 5).

[0074] Next, in step S16, the control unit 11 determines whether or not it has received a response from tag Tg. For example, when tags 21 to 25 receive the transmission data and execute a command (lighting command), and send a response to controller E, controller E sends the received response to management server 1. As a result, the control unit 11 of management server 1 receives the response. If the control unit 11 receives the response (S16: Yes), the process returns to step S1.

[0075] Returning to step S1, the second cycle (N=2) begins. In step S2, the control unit 11 determines whether the first time segment t1 has started. If the first time segment t1 has started (S2: Yes), in step S3, the control unit 11 outputs a transmission instruction for the transmission data to controller A. Upon receiving the transmission instruction, controller A sends the transmission data, which includes the tag Tg (e.g., tags 1-5) that will execute the command, to all tags Tg associated with controller A (see Figure 5). The process thereafter is the same as described above. In this manner, the communication system 10 executes the communication process.

[0076] As described above, the communication system 10 according to this embodiment 1 is a communication system in which a plurality of controllers 2 (master stations) and a plurality of tags Tg (slave stations) perform wireless communication at a predetermined period. The communication system 10 associates each of the plurality of tags Tg with one of the plurality of controllers 2. The communication system 10 also assigns each of the plurality of controllers 2 to each of a plurality of time divisions (time slots) obtained by dividing the predetermined period into time segments on a predetermined channel. The communication system 10 also causes the controller 2 and the plurality of tags Tg associated with the controller 2 to communicate within each of the plurality of time segments.

[0077] In the above configuration, each controller 2 uses radio waves only during the time segment (40 ms) within the period (e.g., 200 ms). Furthermore, by allocating (adjusting) the radio wave usage times of the controllers 2 so that they do not overlap, one channel (CH1) can be shared by up to 5 controllers 2. This makes it possible to install a large number of controllers 2 even when their communication areas AR overlap, as shown in Figure 11. For example, if there are 20 frequency channels, it is possible to install 100 controllers 2, which is five times the number of channels, even in areas where they radio-interfere with each other.

[0078] Furthermore, depending on the factory layout and the type of each line, it may be desirable to allocate channels while being mindful of the maximum number of channels that each controller 2 can share. In such cases, a display screen (UI) may be provided that allows the number of each controller (here, for example, "1" to "64") to be mapped to a table with axes representing time slots (slot numbers) and channels (frequency channels), as shown in Figure 12. In other words, the control unit 11 may visually display the predetermined channels and predetermined time divisions to which each of the multiple controllers 2 (master stations) has been assigned.

[0079] Furthermore, the transmitted data includes destination information for multiple tags Tg. With the above configuration, using a single channel, each controller 2 can communicate with multiple tags Tg in each time segment assigned to each controller 2 in each cycle. Therefore, a large number of tags Tg can be installed over a wide area. In addition, the amount of communication can be increased in the communication system 10. Thus, it is possible to install a large number of tags Tg while ensuring high-speed response of communication between the controller 2 and the tags Tg.

[0080] In the communication system 10 according to this embodiment, the multiple controllers 2 (master stations) synchronize their time with each other and communicate within the time slots assigned by the allocation processing unit 112. Furthermore, the multiple controllers 2 may be connected to each other via wired communication.

[0081] Furthermore, when data to be transmitted is generated in the tag Tg (slave station), the communication processing unit 113 causes the controller 2 to which the tag Tg is associated to transmit the data within the time slot allocated to that controller 2.

[0082] Furthermore, the data to be transmitted by tag Tg is the data observed by that tag Tg. The data observed by tag Tg is data corresponding to the user interface operations performed on that tag Tg.

[0083] The present invention is not limited to the embodiments described above, and may also be provided in the following embodiments. For example, the communication system 10 may include multiple channels. In this case, the allocation processing unit 112 assigns each of the multiple controllers 2 to each of the multiple time divisions for each channel. As a result, for example, five controllers A to E share channel CH1, five controllers F to J share channel CH2, five controllers K to O share channel CH3, five controllers P to T share channel CH4, and five controllers U to Y share channel CH5. Each controller 2 communicates with multiple tags Tg in each of the multiple time divisions obtained by dividing a predetermined period into time divisions, as in the embodiments described above. With this configuration, the number of controllers 2 can be increased according to the number of available channels, making it possible to install more tags Tg.

[0084] Furthermore, the above embodiment shows an example where a 200ms period is divided into five 40ms slots, but this is just one example. The period, number of divisions, and slot time should be appropriately set considering the time response, power consumption, number of slave stations, number of available frequency channels, communication speed, etc., required for each application.

[0085] Furthermore, in the above-described embodiment, the management server 1 (arbitration station) controls the multiple controllers 2, but in another embodiment, a specific controller 2 among the multiple controllers 2 may also perform the functions of the management server 1. In this case, the specific controller 2 functions as the master controller, and the other controllers 2 function as slave controllers. The master controller performs an assignment process to assign each of the multiple slave controllers to each of a plurality of time divisions on a predetermined channel, and a communication process to cause the slave controllers to communicate with the plurality of tags Tg in each of the plurality of time divisions. The master controller transmits the transmission data to each slave controller in the order of the time divisions. Note that the controller 2 that functions as the master controller may be changed as appropriate depending on the communication status of the entire communication system 10.

[0086] [Embodiment 2] A communication system 10 according to Embodiment 2 of the present invention will now be described. In the following, the same reference numerals will be used for components and processes that are the same as those in the communication system 10 according to Embodiment 1, and their descriptions will be omitted as appropriate.

[0087] The communication system 10 according to Embodiment 2 is a system that enables the association of multiple tags Tg with a specific controller 2 that provides stable communication, in a simple configuration, when constructing a large number of star topology networks consisting of controllers 2 and multiple tags Tg. Each tag Tg is associated with one of the controllers 2. The "association" of a tag Tg and a controller 2 is also called "linking" or "binding".

[0088] Figure 13 is a functional block diagram showing the schematic configuration of a communication system 10 according to Embodiment 2 of the present invention. In the configuration shown in Figure 13, each of the multiple tags Tg is shown before being associated with one of the controllers 2. In contrast, the configuration shown in Figure 1 shows the state after each of the multiple tags Tg has been associated with one of the controllers 2.

[0089] The communication system 10 includes a management server 1, a plurality of controllers 2, and a plurality of tags Tg. One or more of the plurality of controllers 2 may also perform the functions of the management server 1. In other words, the management server 1 may also be a controller 2.

[0090] For example, among multiple tags Tg, tag Tg1 (an example of a first slave station in the present invention) transmits a search signal containing the identification information (tag ID) of tag Tg1 in order to identify the controller 2 (an example of a first master station in the present invention) corresponding to tag Tg1. When each of the multiple controllers 2 receives the search signal transmitted from tag Tg1, it sends an analysis report to the management server 1 containing its own identification information (controller ID), the identification information (tag ID) of tag Tg1, and signal information related to the search signal (e.g., the received strength of the search signal). Based on the multiple analysis reports received from the multiple controllers 2, the management server 1 determines the controller 2 (e.g., controller A) corresponding to tag Tg1 from among the multiple controllers 2 and associates tag Tg1 and controller A with each other. The communication system 10 performs the above process for each tag Tg and associates each tag Tg with one of the controllers 2.

[0091] The specific configuration of the communication system 10 according to Embodiment 2 will be described below. In Embodiment 2, a 200ms period is divided into 16 slots of 12.5ms each. That is, one frequency channel can be shared by up to 16 controllers.

[0092] Figure 14 shows a specific example of the association process for the target tag Tg (target tag Tg) to be associated with any of the controllers 2. Figure 15 shows an example of the procedure for associating the management server 1 with multiple controllers 2 and the target tag Tg. Note that Figure 14 is annotated with step numbers (s1, s5, s6, s9, s10) corresponding to the processing steps in Figure 15.

[0093] In Figure 14, for example, Controller A sends transmission data (commands) to a predetermined number (up to 5) of the multiple tags Tg already associated with Controller A in the Operation channel, where a "12.5ms" slot is set. Controller A switches the "187.5ms" of the "200ms" (excluding "12.5ms") to the search channel. Controller A becomes capable of receiving search signals transmitted from target tags Tg in the search channel (reception standby state). Controller B and other controllers have the same configuration as Controller A.

[0094] In the association process described above, first, the target tag Tg transmits a search signal (step s1 in Figure 15). Specifically, the target tag Tg transmits a search signal when it receives a predetermined user operation. For example, when a user presses the bottom button E1 of the target tag Tg (see Figure 3B), the target tag Tg receives the user's press operation and transmits a search signal. The target tag Tg transmits the search signal on the search channel. The target tag Tg also transmits the search signal multiple times at time intervals longer than the slot time in time-division communication assigned to each controller 2 (here, "12.5ms") (for example, at "15ms" intervals). Here, the target tag Tg transmits the search signal four times at "15ms" intervals on the search channel. In this way, the controller 2 performs time-division communication with the tag Tg, and the tag Tg transmits the search signal multiple times at time intervals longer than the slot time in the time-division communication. By making the transmission interval of the search signal longer than the slot time, all controllers 2 can receive the search signal at least multiple times.

[0095] Each of the multiple controllers 2 receives the search signal transmitted from the target tag Tg while in a waiting state for the search channel to receive. For example, among all the controllers 2 installed in facility F1, multiple controllers 2 installed in locations where the signal from the target tag Tg can reach will receive the search signal.

[0096] Each of the multiple controllers 2, upon receiving the search signal, sends an analysis report to the management server 1 that includes the controller 2's identification information (controller ID), the target tag Tg's identification information (tag ID), and signal information related to the search signal (e.g., received strength) (step s2 in Figure 15). The analysis report also includes the time the search signal was received and the search signal number (if there were 4 transmissions, information indicating which of the 4 transmissions it is). Based on this, the management server 1 can obtain the reception start time when the tag Tg begins receiving on the announcement channel. Since it is desirable that the target tag Tg be associated with a controller 2 that provides sufficiently stable communication, the controller 2 may be configured not to send an analysis report corresponding to the search signal whose received strength is below a predetermined value.

[0097] When the management server 1 receives the analysis report from each controller 2, it determines which controller 2 to associate with the target tag Tg (step s3 in Figure 15). Specifically, the association processing unit 111 of the management server 1 determines which controller 2 to associate with the target tag Tg based on the stability of the search signal. For example, the association processing unit 111 aggregates the analysis reports corresponding to the target tag Tg and determines which controller 2 has the most stable search signal if it has received, for example, three or more of the search signals from the first to the last (in this case, the fourth) of all the search signals. The association processing unit 111 calculates the stability of the search signal based on the average value of the signal intensity of the search signal. Alternatively, the association processing unit 111 may calculate the stability of the search signal based on the average value of the signal intensity, the minimum intensity, the variance of the signal intensity, etc.

[0098] When the association processing unit 111 determines the controller 2, it sends an association schedule (Bind schedule) for associating the target tag Tg to the controller 2 (step s4 in Figure 15). Here, the association processing unit 111 determines controller B as the controller 2 to which the target tag Tg will be associated, and sends the association schedule to controller B. The association schedule includes at least the address of controller B and the reception start time when the target tag Tg will begin receiving on the Announce channel (1 second after the time the last search signal was sent). It is preferable to perform the transmission process of the association schedule within a predetermined time immediately after the slot time, as this reduces the possibility of multiple collisions with the search signals sent at 15ms intervals.

[0099] When controller B receives the association schedule from management server 1, it sends an association instruction (Bind instruction) to the target tag Tg via the announcement channel at the reception start time included in the association schedule (step s5 in Figure 15). The association instruction includes at least the address of the target tag and the address of controller B to be associated, and if there are multiple operating channels, it also includes information on the operating channel assigned to controller B.

[0100] When the reception start time arrives, the target tag Tg receives the association instruction on the announcement channel. Upon receiving the association instruction addressed to its own address, the target tag Tg switches to the designated operating channel and periodically receives beacons (which may include a lighting command) output by controller B. After switching to the operating channel, when the target tag Tg receives a command addressed to it, it executes the command and sends an acknowledgment signal back to controller B (step s6 in Figure 15).

[0101] When Controller B receives the confirmation signal from the target tag Tg, it sends a confirmation notification to Management Server 1 (step s7 in Figure 15). When Management Server 1 receives the confirmation notification from Controller B, it replies with a completion instruction to Controller B (step s8 in Figure 15). When Controller B receives the completion instruction from Management Server 1, it sends a completion display instruction to the target tag Tg (step s9 in Figure 15).

[0102] When the target tag Tg receives the completion display instruction from controller B, it sends an acknowledgment signal back to controller B (step s10 in Figure 15) and displays completion (step s11 in Figure 15). For example, the target tag Tg lights up lamp button B1 (see Figure 3A).

[0103] Finally, the management server 1 registers the association information between the target tag Tg and controller B in the related information D2 (see Figure 5) (step s12 in Figure 15). Note that registration to the management server 1 may also be performed when the management server 1 receives the confirmation notification (step s7 in Figure 15).

[0104] The communication system 10 performs the above processing for each tag Tg and associates one controller 2 with each tag Tg. In this way, the management server 1 notifies the target tag Tg of at least the identifier or communication channel of controller B, and the target tag Tg communicates with controller B based on at least the identifier or communication channel of controller B. Furthermore, in the communication system 10, the channel through which the target tag Tg transmits the search signal is different from the channel through which the target tag Tg communicates with controller B after being associated with controller B.

[0105] [Association process] The following describes an example of the association processing procedure performed in the communication system 10 according to Embodiment 2, with reference to Figures 16 to 18. Figure 16 shows an example of the association processing procedure performed on the target tag Tg, Figure 17 shows an example of the association processing procedure performed on the controller 2, and Figure 18 shows an example of the association processing procedure performed on the management server 1.

[0106] [Association processing for target tag Tg] The target tag Tg is initially in a nearly dormant state, and in step S21 shown in Figure 16, it determines whether or not the bottom button E1 has been pressed. If the bottom button E1 is pressed (S21: Yes), the target tag Tg becomes active and proceeds to step S22. The target tag Tg waits in a dormant state until the bottom button E1 is pressed (S21: No).

[0107] In step S22, the target tag Tg switches to the search channel. In the following step S23, the target tag Tg transmits the search signal multiple times at predetermined intervals (step s1 in Figure 15). For example, the target tag Tg transmits the search signal four times at 15ms intervals on the search channel. After transmitting the last (fourth) search signal, the target tag Tg waits for a predetermined time (1 second) to elapse (S24).

[0108] Next, in step S25, the target tag Tg switches from the search channel to the announcement channel. Next, in step S26, the target tag Tg attempts to receive the association instruction from controller 2 (controller B determined by management server 1) for 500ms. If the target tag Tg receives the association instruction (S26:Yes) (step s5 in Figure 15), it proceeds to step S27. On the other hand, if the target tag Tg does not receive the association instruction during the above 500ms (S26:No), it proceeds to step S21.

[0109] In step S27, the target tag Tg switches from the announcement channel to the operation channel specified in the association instruction, and receives beacons from controller B in synchronization based on the controller B address obtained in the association instruction.

[0110] Next, in step S28, the target tag Tg determines whether or not it has received a command addressed to it from controller B. If the target tag Tg has received a command addressed to it from controller B (S29: Yes), it proceeds to step S30. On the other hand, if the target tag Tg has not received a command addressed to it from controller B (S29: No), it proceeds to step S21.

[0111] Next, in step S30, the target tag Tg transmits the confirmation signal to the controller B (step s6 in Figure 15). After that, when the target tag Tg receives the completion display instruction from the controller B, it sends the confirmation signal back to the controller B and lights up the lamp button B1 (see Figure 3A) (S30) (steps s9 and s10 in Figure 15).

[0112] [Association process in Controller 2] In step S31 shown in Figure 17, controller 2 (controller B is used as an example here) sets the operation channel assigned to it. Next, in step S32, controller B executes the operation process instructed by management server 1. For example, controller B sends transmission data (commands) to a predetermined number of tags Tg from among the multiple tags Tg that are already associated.

[0113] Next, when the predetermined operating time (slot time "12.5ms") ends (S33:Yes), controller B moves the process to step S34.

[0114] In step S34, controller B determines whether the reception start time (1 second after the time when the target tag Tg sent the last search signal) has arrived for the target tag Tg to begin receiving on the announcement channel. If the reception start time arrives (S34: Yes), controller B switches from the operation channel to the announcement channel (S35) and sends the association instruction to the target tag Tg (S36) (step s5 in Figure 15). If the reception start time has not arrived (S34: No), controller B proceeds to step S37.

[0115] In step S37, controller B switches from the announcement channel to the search channel. Next, in step S38, controller B determines whether or not it has received the search signal from the target tag Tg. If controller B has received the search signal (S38: Yes), it proceeds to step S39. If controller B has not received the search signal (S38: No), it proceeds to step S40.

[0116] In step S39, controller B sends the analysis report to management server 1 (step s2 in Figure 15). For example, controller B sends four analysis reports to management server 1.

[0117] Next, in step S40, controller B determines whether or not it is time to start operation. If it is time to start operation (S40: Yes), controller B returns to step S31 and switches to the operation channel. Controller B repeats the processes in steps S38 and S39 until it is time to start operation (S40: No). Each controller 2 repeatedly executes the above process.

[0118] [Association process on management server 1] In step S41 shown in Figure 18, the management server 1 determines whether or not it has received the analysis reports from the multiple controllers 2. For example, the management server 1 receives multiple analysis reports (for 3 to 4 search signals) from controller B.

[0119] When the management server 1 receives multiple analysis reports from multiple controllers 2 (S41: Yes), it aggregates the multiple analysis reports (S42) and determines which controller 2 to associate with the target tag Tg (S43) (step s3 in Figure 15). For example, the management server 1 identifies the lowest received strength of multiple search signals for each controller 2 and determines which controller 2 has the highest lowest received strength. The management server 1 then determines which controller 2 has the highest lowest received strength to associate with the target tag Tg.

[0120] When the management server 1 determines one controller 2 (in this case, controller B) (S43), in step S44, it sends an association plan (Bind plan) for associating the target tag Tg to controller B (step s4 in Figure 15).

[0121] When Controller B receives the association schedule, it sends an association instruction (Bind instruction) to the target tag Tg to perform the association with the target tag Tg. This process corresponds to the communication process in step S36 of Figure 17.

[0122] Once the management server 1 has completed verifying the association between the target tag Tg and controller B, it registers the association information between the target tag Tg and controller B in related information D2 (see Figure 5) (S45) (step s12 in Figure 15). The management server 1 repeatedly performs the above process each time it receives the analysis report from controller 2.

[0123] As described above, the communication system 10 according to this embodiment 2 is a communication system that includes a management server 1, a plurality of controllers 2 (master stations), and a plurality of tags Tg (slave stations). The first tag Tg transmits a search signal to identify the first controller 2 corresponding to the first tag Tg. When each of the plurality of controllers 2 receives the search signal, it sends an analysis report to the management server 1 that includes the identification information of the controller 2, the identification information of the first tag Tg, and signal information related to the search signal. Based on the plurality of analysis reports received from each of the plurality of controllers 2, the management server 1 determines the first controller 2 corresponding to the first tag Tg from among the plurality of controllers 2 and associates the first tag Tg and the first controller 2 with each other.

[0124] With the above configuration, by aggregating analysis reports from the controller 2 that receive search signals transmitted from the tags Tg in response to predetermined events (e.g., user operation), it becomes possible to associate multiple tags Tg with simple operations such as pressing a button on the tag Tg. In other words, the controller 2 and multiple tags Tg can be associated with each other with a simple configuration. Furthermore, since the tags Tg only need to receive association instructions within a predetermined time after transmitting search signals multiple times, the communication load on the tags Tg and battery consumption can be reduced. In addition, battery consumption can be further reduced by having the tags enter sleep (hibernation mode) as needed when not communicating.

[0125] In another embodiment of the present invention, the tag Tg may transmit the search signal when it receives a predetermined signal. For example, the tag Tg transmits the search signal when it receives an instruction to transmit the search signal from the management server 1.

[0126] Furthermore, the tag Tg may transmit the search signal after a predetermined time has elapsed. For example, the tag Tg transmits the search signal after a preset time has elapsed. This allows the tag Tg to periodically perform the association process and associate with the optimal controller 2.

[0127] Furthermore, the tag Tg may transmit the search signal if communication becomes unstable. For example, the tag Tg transmits the search signal when the reception of the beacon deteriorates, that is, when the received signal level falls below a predetermined state, or when beacon reception fails under predetermined conditions. This allows the tag Tg to be associated with the optimal controller 2 even if the situation changes due to a change in location, and prevents situations where it becomes inoperable.

[0128] Furthermore, when transmitting the search signal, the tag Tg may perform carrier sensing and transmit only if it is available, and retry if it is not available. This makes it possible to efficiently associate multiple tags Tg simultaneously.

[0129] Furthermore, it is even preferable to generate a random number and perform a random backoff during the above retry.

[0130] Thus, the tag Tg transmits the search signal when it receives a user operation, when it receives a predetermined signal, when the stability of the signal from the controller 2 associated with the tag Tg reaches a predetermined state, or when a predetermined time has elapsed.

[0131] As described above, the communication system of the present invention may consist of an entire communication system 10 (see Figure 1) including a management server 1, a controller 2, and a tag Tg, or it may consist of the management server 1 and the controller 2, or it may consist of the management server 1 alone or the controller 2 alone.

[0132] Furthermore, the channel (frequency channel) of the present invention can also be applied to communication methods such as frequency hopping and direct spread spectrum.

[0133] Furthermore, in this invention, the channel used to send commands to the tag Tg (slave station) via the beacon for control (operation channel) and the channel used to send the search signal (search channel) are different. By separating the channels used in this way, it is possible to avoid affecting normal operation.

[0134] Furthermore, the present invention also includes a channel (announcement channel) that transmits a signal instructing the association between the tag Tg and the controller 2, and the announcement channel is different from the operation channel and the search channel. By separating the channels used in this way, it is possible to avoid affecting normal operation.

[0135] Furthermore, in this invention, if communication between the first slave station and the first master station becomes unstable, the tag Tg transmits the search signal to re-establish the association. This makes it possible to re-associate with a better controller 2 in response to environmental changes such as relocation of the installation site.

[0136] [Embodiment 3] A communication system 10 according to Embodiment 3 of the present invention will now be described. In the following, descriptions of the same configuration and processing as those of the communication system 10 according to Embodiments 1 and 2 will be omitted as appropriate.

[0137] The communication system 10 according to Embodiment 3 is a system that, after a tag Tg has been associated with a specific controller 2, performs a process (roaming) to switch to a controller 2 with a better communication environment if the communication environment between the tag Tg and the controller 2 deteriorates. Here, each tag Tg is assumed to be associated with one of the controllers 2.

[0138] Figure 19 is a functional block diagram showing the schematic configuration of a communication system 10 according to Embodiment 3 of the present invention. In the configuration shown in Figure 19, a plurality of storage shelves 3 (see Figure 2) are arranged in facility F1, and a plurality of trolleys 4 that can travel within facility F1 are also arranged. As shown in Figure 2, the storage shelves 3 include a plurality of storage shelves 31, and each storage shelf 31 is equipped with a tag Tg (see Figures 3A and 3B).

[0139] Figure 20 shows an example of a trolley 4. The trolley 4 is, for example, an autonomously mobile robot (AGV, etc.) that can move autonomously in response to instructions sent from the management server 1. The trolley 4 also includes one or more storage shelves 41, and each storage shelf 41 is equipped with a tag Tg. The tag Tg installed on the storage shelf 41 is the same as the tag Tg installed on the storage shelf 31 (see Figures 3A and 3B).

[0140] The tag Tg of storage shelf 3, when associated with a controller 2 corresponding to the communication area including the location where storage shelf 3 is installed, will always communicate with that controller 2. On the other hand, the tag Tg of trolley 4 will communicate with controller X if stable communication with controller X is possible, for example, and will communicate with controller Y if stable communication with controller Y becomes possible when trolley 4 moves compared to controller X.

[0141] In this way, the tag Tg on the trolley 4 communicates with the controller 2, which has a high level of communication stability, as the trolley 4 moves. The communication system 10 according to Embodiment 3 performs a process (roaming) to switch to the controller 2, which has a good communication environment (high communication stability), when the communication environment between the tag Tg (slave station) and the controller 2 (master station) deteriorates (communication stability decreases).

[0142] The specific configuration of the communication system 10 according to Embodiment 3 will be described below. In Embodiment 3, similar to Embodiment 2, the 200ms period is divided into 16 slots of 12.5ms each. That is, one frequency channel can be shared by up to 16 controllers.

[0143] Figure 21 shows a specific example of the switching process (roaming) of the target tag Tg (target tag Tg) when switching the controller 2 to which communication is being performed. Figure 22 shows an example of the roaming procedure between the management server 1, multiple controllers 2, and the target tag Tg. Note that Figure 21 is annotated with step numbers (s1, s5, s6, s9, s10) corresponding to the processing steps in Figure 22.

[0144] In Figure 21, for example, controller X sends transmission data (commands) to a predetermined number (up to 5) of tags Tg already associated with controller X in the operation channel where a "12.5ms" slot is set. Controller X switches the "187.5ms" of the "200ms" (excluding "12.5ms") to the search channel. Controller X becomes capable of receiving search signals transmitted from target tags Tg in the search channel (reception standby state). Controller Y and other controllers have the same configuration as controller X.

[0145] Here, we assume that the target tag Tg is associated with controller X and communicates with controller X. For example, when controller X receives a transmit command from management server 1, it sends the transmit data (see Figure 9) to all tags Tg (see Figure 5) associated with controller X via the operation channel.

[0146] When each tag Tg associated with controller X receives the transmission data, it checks the destination included in the transmission data and performs a predetermined process if it contains a command addressed to itself. For example, if a target tag Tg receives the transmission data containing a command addressed to itself to turn on lamp button B1 (see Figure 3A), it turns on lamp button B1.

[0147] If the trolley 4 carrying the target tag Tg moves and the stability of communication with the controller X decreases, the communication system 10 performs the roaming described below.

[0148] First, the target tag Tg transmits a search signal (step s201 in Figures 21 and 22). Specifically, the target tag Tg transmits a search signal to search for other controllers 2 when the stability of communication with the controller X associated with the target tag Tg falls below a threshold. For example, the target tag Tg transmits a search signal when the average value of the received intensity of the last 10 signals (beacons) received from controller X on the operating channel falls below -70 dB (an example of the threshold). The target tag Tg is an example of a first slave station of the present invention, and controller X is an example of a first master station of the present invention.

[0149] Furthermore, the target tag Tg switches the channel from the operation channel to the search channel and transmits a search signal. The target tag Tg also transmits the search signal multiple times at time intervals longer than the slot time in time-division communication allocated to each controller 2 (here, "12.5ms") (for example, at "15ms" intervals). In this case, the target tag Tg transmits the search signal four times at "15ms" intervals on the search channel. In this way, the controller 2 performs time-division communication with the tag Tg, and the tag Tg transmits the search signal multiple times at time intervals longer than the slot time in the time-division communication. By making the transmission interval of the search signal longer than the slot time, all controllers 2 can receive the search signal at least multiple times.

[0150] Each of the multiple controllers 2 receives the search signal transmitted from the target tag Tg while in a waiting state for the search channel to receive. For example, among all the controllers 2 installed in facility F1, multiple controllers 2 installed in locations where the signal from the target tag Tg can reach will receive the search signal.

[0151] Each of the multiple controllers 2, upon receiving the search signal, sends an analysis report (an example of the report of the present invention) to the management server 1, which includes its own identification information (controller ID), the identification information of the target tag Tg (tag ID), and signal information related to the search signal (e.g., received strength) (step s202 in Figure 22). The analysis report also includes the time the search signal was received and the number of the search signal (if the number of transmissions is 4, information indicating which of the 4 transmissions it is). Since it is desirable that the target tag Tg be associated with a controller 2 that provides sufficiently stable communication, the controller 2 may be configured not to send an analysis report corresponding to the search signal whose received strength is below a predetermined value.

[0152] When the management server 1 receives the analysis report from each controller 2, it determines the controller 2 to which the target tag Tg will be associated, in this case controller X, and the controller to which it will switch (roaming destination) (step s203 in Figure 22). Specifically, the switching processing unit 114 of the management server 1 (see Figure 19) determines the controller 2 to which the target tag Tg will switch based on the stability of the search signal. For example, the switching processing unit 114 aggregates the analysis reports corresponding to the target tag Tg and, if it has received, for example, three or more of the search signals from the first to the last (in this case, the fourth) of the search signals, it determines the controller 2 with the most stable search signal. The switching processing unit 114 also calculates the stability of the search signal based on the average value of the signal strength of the search signal. Alternatively, the switching processing unit 114 may calculate the stability of the search signal based on the average value of the signal strength of the search signal, the minimum strength, the variance of the signal strength, etc.

[0153] When the switching processing unit 114 determines the controller 2 (controller Y), it sends a master station change instruction (roaming instruction) to the original controller 2 (controller X) to switch to the controller corresponding to the target tag Tg (step s204 in Figure 22). Here, the switching processing unit 114 determines controller Y as the destination controller 2 corresponding to the target tag Tg and sends the master station change instruction to controller Y. The change instruction includes the address of the target tag Tg, the address of controller X, and the start time when the target tag Tg begins receiving on the operation channel.

[0154] When the management server 1 (switching processing unit 114) determines the new linked controller 2 (for example, controller Y), it sends a parent station change instruction for the target tag Tg to the original linked controller X (step s204 in Figure 22).

[0155] When controller Y receives the master station change instruction from management server 1, it stores the master station change instruction in a beacon that it outputs at 200ms intervals and sends it to the target tag Tg (step s205 in Figure 22).

[0156] The target tag Tg receives beacons from the original controller X, while intermittently activating at 200ms intervals to conserve power. When it finds a master station change instruction addressed to itself stored in the received beacon, it sends an Acknowledge for the master station change instruction (hereinafter referred to as "master station change Ack") to controller X at the predetermined timing mentioned above (step s206 in Figure 22).

[0157] When controller X receives a master station change Ack from the target tag Tg, it reports the receipt of the master station change Ack to management server 1 via Ethernet communication (step s207 in Figure 22).

[0158] When management server 1 receives a master station change Ack from controller X, it determines that the target tag Tg has been confirmed to roam to the new controller Y. The master station change instruction includes information such as the operation channel (frequency) of controller Y, the communication address of controller Y, and the timing of the beacon that controller Y outputs at 200ms intervals.

[0159] Next, the management server 1 (switching processing unit 114) sends a change confirmation instruction to the controller Y for the target tag Tg (step s208 in Figure 22).

[0160] Upon receiving the aforementioned change confirmation instruction, controller Y stores the instruction in a beacon that is output at 200ms intervals and transmits it to the target tag Tg (step s209 in Figure 22).

[0161] On the other hand, after receiving the master station change instruction, the target tag Tg switches to the operation channel (frequency) of controller Y based on the information stored in the master station change instruction, and attempts to receive the beacon containing the communication address of controller Y at the timing of the beacon that controller Y outputs every 200ms, and thus receives the change confirmation instruction mentioned above.

[0162] The target tag Tg is deemed to have confirmed roaming to the new controller Y at the time it receives the aforementioned change confirmation instruction.

[0163] The target tag Tg sends an Acknowledge (hereinafter referred to as "Change Confirmation Ack") for the previous change confirmation instruction to controller Y (step s210 in Figure 22).

[0164] When controller Y receives a change confirmation Ack from the target tag Tg, it reports the receipt of the change confirmation Ack to management server 1 via Ethernet communication (step s211 in Figure 22).

[0165] Finally, the management server 1 registers the association information between the target tag Tg and controller Y in the related information D2 (see Figure 5), and completes the roaming process.

[0166] In the above process, it is assumed that retries and timeouts are set as appropriate. If the management server 1 does not reach "roaming confirmation" even after the maximum number of retries or the timeout period has elapsed, the management server 1 will discard this roaming process, and the target tag Tg will continue to operate as if it were linked to the original controller X.

[0167] Furthermore, if the target tag Tg does not reach "roaming confirmation" even after exceeding the retry limit or timeout period, the target tag Tg performs the binding process described above. In the binding process described above, information about the controller to be newly associated is transmitted via the Announce channel, and since a large number of tags Tg may be associated simultaneously, the tags need to receive the Announce channel for a certain period of time. On the other hand, in this roaming process, this information is transmitted via the beacon of the normal control channel, and the target tag Tg that receives it can immediately switch to the next controller's beacon reception timing. This makes it possible to switch controllers while maintaining a response time of up to 200ms, which is the beacon period, almost.

[0168] In this embodiment, the timing of the beacon output by controller Y at a 200ms cycle was included in the master station change instruction, but this may be omitted. In that case, the target tag Tg should attempt to receive the beacon on the specified channel for a longer period than the beacon cycle, for example, 220ms.

[0169] The communication system 10 executes the above process each time the communication stability of tag Tg falls below a threshold, and switches the controller 2 associated with tag Tg to a controller 2 with stable communication.

[0170] [Controller switching process (roaming)] The following describes an example of a roaming procedure performed in the communication system 10 according to Embodiment 3, with reference to Figures 23 to 25. Figures 23A and 23B show an example of a roaming procedure performed in the target tag Tg, Figure 24 shows an example of a roaming procedure performed in the controller 2, and Figure 25 shows an example of a roaming procedure performed in the management server 1.

[0171] [Roaming for the target tag Tg] Similar to the example above, here we assume that the target tag Tg (slave station) is associated with controller X (master station) and is communicating with controller X.

[0172] In step S51 shown in Figure 23A, the target tag Tg, which is a slave station, sets the channel to the operating channel. Next, in step S52, the target tag Tg attempts to receive a beacon from controller 2 (controller X, which is currently communicating). If the target tag Tg receives the beacon (S52:Yes), it proceeds to step S53. The target tag Tg continues to attempt to receive the beacon until it receives it (S52:No).

[0173] In step S53, the target tag Tg determines whether or not it has received a command addressed to it from controller X. If the target tag Tg has received a command addressed to it from controller X (S53: Yes), it proceeds to step S54. On the other hand, if the target tag Tg has not received a command addressed to it from controller X (S53: No), it proceeds to step S56.

[0174] In step S54, the target tag Tg determines whether the command addressed to it contains the master station change instruction. If the command addressed to it does not contain the master station change instruction (S54: No), the target tag Tg proceeds to step S55. On the other hand, if the command addressed to it contains the master station change instruction (S54: Yes), the target tag Tg proceeds to step S541 (see Figure 23B).

[0175] In step S55, the target tag Tg executes the command and, at a predetermined timing, sends a master station change Ack (confirmation signal) in response to the master station change instruction to the controller X.

[0176] Next, the target tag Tg checks the communication status (S56) and determines whether the communication status has deteriorated or not (S57). For example, if the stability of communication with controller X falls below a threshold (S57: Yes), the target tag Tg moves the process to step S571. If the stability of communication with controller X is above the threshold (S57: No), the target tag Tg communicates with controller X and waits until the next beacon (S58).

[0177] In step S571, the target tag Tg determines whether 10 seconds or more have passed since the last search signal was output. If the target tag Tg determines that 10 seconds or more have passed since the last search signal was output (S571:Yes), it proceeds to step S572. If the target tag Tg determines that 10 seconds or more have not passed since the last search signal was output (S571:No), it proceeds to step S58.

[0178] In step S572, the target tag Tg sets the channel to the search channel. Next, in step S573, the target tag Tg transmits a search signal to search for other controllers 2. After transmitting the search signal, the target tag Tg waits until the next beacon time (S574).

[0179] In step S54, if the command addressed to itself contains the master station change instruction (S54: Yes), the process proceeds to step S541 (see Figure 23B), and the target tag Tg sends a master station change Ack (acknowledgment signal) in response to the master station change instruction to controller X.

[0180] Next, in step S542, the target tag Tg sets the channel to a new operating channel (new operating channel (see Figure 21)). Then, in step S543, the target tag Tg receives a beacon on the operating channel at the specified time.

[0181] Next, in step S544, the target tag Tg determines whether the beacon contains the change confirmation instruction. If the beacon contains the change confirmation instruction (S544: Yes), the target tag Tg proceeds to step S58. On the other hand, if the beacon does not contain the change confirmation instruction (S544: No), the target tag Tg proceeds to step S545.

[0182] In step S545, if the target tag Tg determines that the timeout period has elapsed (S545:Yes), the binding process described above is executed in step S546.

[0183] [Roaming in Controller 2] In steps S61 and S62 shown in Figure 24, when the start time for operation arrives (S61: Yes), the master controller 2 sets itself to the operating channel assigned to it (S62).

[0184] Next, in step S63, the controller 2 determines whether or not it has received a master station change instruction (roaming instruction) from the management server 1 to switch the controller corresponding to the target tag Tg. If the controller 2 receives the master station change instruction (S63: Yes), it proceeds to step S64. On the other hand, if the controller 2 does not receive the master station change instruction (S63: No), it proceeds to step S67.

[0185] In step S64, the controller 2 transmits the master station change instruction received from the management server 1 to the target tag Tg.

[0186] In step S65, controller 2 determines whether it has received a change confirmation instruction from management server 1 to identify the controller corresponding to the target tag Tg. If controller 2 receives the change confirmation instruction (S65: Yes), it proceeds to step S66. On the other hand, if controller 2 does not receive the change confirmation instruction (S65: No), it proceeds to step S67.

[0187] In step S66, the controller 2 sends the change confirmation instruction received from the management server 1 to the target tag Tg.

[0188] In step S67, controller 2 performs normal operation processing. When the operation time ends (S68: Yes), controller 2 moves the process to step S69.

[0189] In step S69, the controller 2 sets the channel to the search channel and determines whether or not it has received the search signal transmitted from the tag Tg (S70). If the controller 2 receives the search signal (S70: Yes), it proceeds to step S71. On the other hand, if the controller 2 does not receive the search signal (S70: No), it proceeds to step S72.

[0190] In step S71, the controller 2 analyzes the search signal, including obtaining the ID of the tag Tg (slave station) and measuring the signal strength, and sends the analysis results (analysis report) to the management server 1.

[0191] In step S72, controller 2 determines whether or not it is time to start operation. If it is time to start operation (S72: Yes), controller 2 proceeds to step S62 and repeats the processes of steps S70 and S71 until it is time to start operation (S72: No).

[0192] [Roaming on Management Server 1] In step S81 shown in Figure 25, the management server 1 determines whether or not it has received the analysis reports from multiple controllers 2. For example, the management server 1 receives multiple analysis reports (for 3 to 4 search signals) from controller Y.

[0193] When the management server 1 receives multiple analysis reports from multiple controllers 2 (S81: Yes), it aggregates the multiple analysis reports (S82) to determine the controller 2 to which the target tag Tg will be switched. For example, the management server 1 identifies the lowest received strength of multiple search signals for each controller 2 and determines the controller 2 with the highest lowest received strength. The management server 1 then determines the controller 2 with the highest lowest received strength to be the controller 2 to which the target tag Tg will be switched.

[0194] If there is a target controller 2 (S83: Yes), management server 1 proceeds to step S84. On the other hand, if there is no target controller 2 (S83: No), management server 1 proceeds to step S81.

[0195] In step S84, the management server 1 sends the master station change instruction to the original controller 2 (in this case, controller X), which includes information indicating the new operating channel and the controller 2 to which the switch will be made (in this case, controller Y).

[0196] Next, in step S85, the management server 1 determines whether or not it has received the master station change Ack from controller X. If the management server 1 receives the master station change Ack from controller X (S85: Yes), it proceeds to step S86. On the other hand, if the management server 1 does not receive the master station change Ack from controller X (S85: No), it proceeds to step S88.

[0197] In step S86, the management server 1 confirms the switch from controller X to controller Y (master station change), and in step S87, it sends the change confirmation instruction to controller Y.

[0198] If the management server 1 does not receive the master station change Ack from controller X in step S85 (S85: No), in step S88, it cancels the master station change process.

[0199] Furthermore, when the management server 1 confirms that the controller corresponding to the target tag Tg has been switched to controller Y, it registers the association information between the target tag Tg and controller Y in the related information D2 (see Figure 5). The management server 1 repeatedly performs the above process each time it receives the analysis report from controller 2.

[0200] As described above, the communication system 10 according to this embodiment 3 is a communication system that includes a management server 1, a plurality of controllers (master stations), and a plurality of tags Tg (slave stations). Furthermore, the first tag Tg transmits a search signal to search for other controllers 2 when the stability of communication with the first controller 2 associated with the first tag Tg falls below a threshold. In addition, each of the plurality of controllers 2 that receives the search signal transmits an analysis report to the management server 1 that includes the identification information of the controller 2, the identification information of the first tag Tg, and signal information related to the search signal. Based on the plurality of analysis reports received from each of the plurality of controllers 2, the management server 1 determines which second controller 2 to associate with the first tag Tg from among the plurality of controllers 2, and associates the first tag Tg with the second controller 2.

[0201] Furthermore, the management server 1 determines the second controller 2 to be the controller 2 that receives the search signal with a higher stability than the search signal received from the first controller 2. In addition, in the above configuration, the channel through which the first tag Tg transmits the search signal (search channel) and the channel through which the first tag Tg communicates with the second controller 2 after being associated with the second controller 2 (operation channel) are different.

[0202] Furthermore, the management server 1 transmits at least the identifier or channel information of the second controller 2 to the first tag Tg, and the first tag Tg communicates with the second controller 2 based at least the identifier or channel information of the second controller 2.

[0203] Furthermore, when the controller 2 of the present invention receives a search signal from the first tag Tg to search for another controller 2 when the stability of communication with the first controller 2 associated with the first tag Tg falls below a threshold, it sends an analysis report to the management server 1 that includes the identification information of the controller 2, the identification information of the first tag Tg, and signal information related to the search signal. When the controller 2 receives an instruction from the management server 1 to switch the controller 2 associated with the first tag Tg from the first controller 2 to the second controller 2, it sends information about the second controller 2 (the master station change instruction) to the first tag Tg.

[0204] Furthermore, the present invention transmits a search signal to search for another master station when the stability of communication with the first controller 2 associated with the tag Tg falls below a threshold, and switches the controller 2 associated with the tag Tg from the first controller 2 to the second controller 2 when the management server 1 determines that the second controller 2 is the controller 2 to associate with the tag Tg.

[0205] With the above configuration, if the communication environment between the tag Tg and controller 2 deteriorates, it is possible to switch to a controller 2 with a better communication environment. In this way, when the communication conditions deteriorate, the tag Tg sends a search signal on a predetermined channel, and only if a better controller 2 is found, it is instructed to switch to the new controller 2 in communication with the currently communicating controller 2. Therefore, the tag Tg only needs to switch to the new channel according to the instruction. This makes it possible to suppress power consumption and avoid deterioration of response time.

[0206] In another embodiment of the present invention, among the plurality of controllers 2 that have received the search signal from the target tag Tg, only the controller 2 whose search signal stability is higher than the stability of the search signal received by controller X from the target tag Tg may send the analysis report to the management server 1. This makes it possible to avoid receiving from controller 2 that is unlikely to become the switch destination, thereby reducing communication traffic and load.

[0207] In another embodiment, the target tag Tg may transmit the search signal with a signal strength weaker than that during normal communication (for example, when receiving a beacon from controller X), and the management server 1 may calculate the stability of the search signal by correcting the amount by which the signal strength has been weakened. This can reduce communication traffic and load. It can also reduce the probability of signal collisions.

[0208] In another embodiment, one of the controllers 2 among the multiple controllers 2 may also have the functionality of a management server 1.

[0209] Furthermore, the communication system of the present invention may be configured to perform both the binding process according to Embodiment 2 and the roaming process according to Embodiment 3. For example, if the communication environment between the tag Tg and the controller 2 deteriorates and the stability of communication decreases, the communication system 1 performs a process (roaming) to switch to a controller 2 with higher communication stability, and if the communication environment further deteriorates and the stability of communication decreases or communication is interrupted, it performs a process (binding) to associate with a controller 2 that can communicate.

[0210] For example, the target tag Tg transmits a search signal and performs roaming (processing in Embodiment 3 (see Figures 21 and 22)) when the average value of the received signal strength of the past 10 signals (beacons) received from the controller X on the operating channel falls below -70 dB (an example of a first threshold). Alternatively, the target tag Tg transmits a search signal and performs binding (processing in Embodiment 2 (see Figures 14 and 15)) when the average value of the received signal strength falls below -90 dB (an example of a second threshold).

[0211] [Notes on the invention] The following is an overview of the invention extracted from the above-described embodiments. Note that each configuration and processing function described below can be selected and combined as desired.

[0212] <Note 1> A communication system including a management server, multiple master stations, and multiple slave stations, The first slave station, when the stability of its communication with the first master station associated with it falls below a threshold, transmits a search signal to search for other master stations. Each of the multiple master stations that has received the search signal sends a report to the management server that includes the identification information of the master station, the identification information of the first slave station, and the signal information relating to the search signal. The management server determines which second master station to associate with the first slave station from among the multiple master stations based on the multiple reports received from each of the multiple master stations, and switches the master station associated with the first slave station from the first master station to the second master station. Communication system.

[0213] <Note 2> The management server determines that the second master station is the master station that receives the search signal with a stability higher than the stability of the search signal received from the first master station. The communication system described in Appendix 1.

[0214] <Note 3> The channel on which the first slave station transmits the search signal and the channel on which the first slave station communicates with the second master station after it has become associated with the second master station are different. The communication system described in Appendix 1 or 2.

[0215] <Note 4> The management server transmits at least the identifier or channel information of the second master station to the first slave station. The first slave station communicates with the second master station based at least on the identifier of the second master station or the channel information. A communication system as described in any of the appendices 1 to 3.

[0216] <Note 5> The aforementioned master station performs time-division multiplex communication with the aforementioned slave station. The first slave station transmits the search signal multiple times at time intervals longer than the slot time in the time-division communication. A communication system as described in any of the appendices 1 to 4.

[0217] <Note 6> The stability of the search signal is calculated based on either the signal intensity value of the search signal or the average value of the signal intensity. The communication system described in Appendix 2.

[0218] <Note 7> Of the multiple master stations that have received the search signal, only the master station whose search signal stability is higher than the search signal stability received by the first master station from the first slave station will send the report to the management server. A communication system as described in any of the appendices 1 to 6.

[0219] <Note 8> The first slave station transmits the search signal with a signal strength weaker than that used during normal communication. The management server calculates the stability of the search signal by correcting the amount by which the signal strength was weakened. A communication system as described in any of the appendices 1 to 7.

[0220] <Note 9> One of the aforementioned multiple master stations is equipped with the management server function. A communication system as described in any of the appendices 1 to 8.

[0221] Furthermore, the communication system according to the present invention can also be constructed by freely combining the embodiments described above within the scope of the invention described in each claim, or by appropriately modifying or omitting parts of each embodiment. [Explanation of Symbols]

[0222] 1: Management Server 2: Controller 3: Storage shelves 4: Dolly 10: Communication Systems 111: Related Processing Unit 112: Assignment Processing Unit 113: Communication Processing Unit 114: Switching Processing Unit Tg: Tag

Claims

1. A communication system comprising a management server, multiple master stations, and multiple slave stations, wherein the master stations perform time-division multiplex communication with the slave stations, If the stability of communication between the first slave station and the first master station associated with the first slave station falls below a threshold, the first slave station transmits a search signal to search for other master stations at time intervals longer than the slot time in the time-division communication. Each of the multiple master stations that received the search signal sends a report to the management server that includes the identification information of the master station, the identification information of the first slave station, and the received strength of the search signal. The management server determines, based on the multiple reports received from each of the multiple master stations, which master station to associate with the first slave station, and switches the master station associated with the first slave station from the first master station to the second master station. Communication system.

2. The management server calculates the stability of the search signal based on either the signal strength value or the average signal strength, and determines the second master station to receive the search signal with a stability higher than the calculated stability. The communication system according to claim 1.

3. The channel on which the first slave station transmits the search signal and the channel on which the first slave station communicates with the second master station after it has become associated with the second master station are different. The communication system according to claim 1.

4. The management server transmits at least the identifier or channel information of the second master station to the first slave station. The first slave station communicates with the second master station based at least on the identifier of the second master station or the channel information. A communication system according to any one of claims 1 to 3.

5. One of the aforementioned multiple master stations is equipped with the management server function. A communication system according to any one of claims 1 to 3.

6. A communication system including a management server, multiple master stations, and multiple slave stations, If the stability of communication between the first slave station and the first master station associated with the first slave station falls below a threshold, the first slave station transmits a search signal to search for other master stations. Of the multiple master stations that have received the search signal, only the master station whose search signal stability is higher than the search signal stability received by the first master station from the first slave station sends a report to the management server including the identification information of the master station, the identification information of the first slave station, and the received strength of the search signal. The management server determines, based on the multiple reports received from each of the multiple master stations, which master station to associate with the first slave station, and switches the master station associated with the first slave station from the first master station to the second master station. Communication system.

7. A communication system including a management server, multiple master stations, and multiple slave stations, If the stability of communication between the first slave station and the first master station associated with the first slave station falls below a threshold, the first slave station transmits a search signal to search for other master stations, with a signal strength weaker than that used during normal communication. Each of the multiple master stations that received the search signal sends a report to the management server that includes the identification information of the master station, the identification information of the first slave station, and the received strength of the search signal. The management server, based on the multiple reports received from each of the multiple master stations, determines which of the multiple master stations to associate with the first slave station, and switches the master station associated with the first slave station from the first master station to the second master station. The management server calculates the stability of the search signal by correcting the amount by which the signal strength was weakened. Communication system.

8. A master station that communicates with a management server and multiple slave stations, and performs time-division multiplexing communication with the said slave stations, When the stability of communication between the first slave station and the first master station associated with the first slave station falls below a threshold, and the first slave station receives a search signal from the first slave station that is transmitted at time intervals longer than the slot time in the time-division communication, the management server is sent a report including the identification information of the master station, the identification information of the first slave station, and the received strength of the search signal. A master station that, upon receiving an instruction from the management server to switch the master station associated with the first slave station from the first master station to the second master station, transmits information about the second master station to the first slave station.

9. A slave station that communicates with a management server and multiple master stations, and performs time-division multiplexing communication with the master stations, If the stability of communication between the slave station and the first master station associated with the slave station falls below a threshold, a search signal for searching for other master stations is transmitted at time intervals longer than the slot time in the time-division communication. A child station that, when the management server determines that the second parent station is the parent station to be associated with the child station, switches the parent station associated with the child station from the first parent station to the second parent station.

10. A communication method in which a management server, multiple master stations, and multiple slave stations perform wireless communication, and the master stations perform time-division multiplex communication with the slave stations, One or more processors In the first slave station, if the stability of communication with the first master station associated with the first slave station falls below a threshold, the step of sending a search signal for searching for other master stations at time intervals longer than the slot time in the time-division communication, The steps include: each of the multiple master stations that have received the search signal transmits a report to the management server that includes the identification information of the master station, the identification information of the first slave station, and the received strength of the search signal; The management server, based on the multiple reports received from each of the multiple master stations, determines which of the multiple master stations to associate with the first slave station, and switches the master station associated with the first slave station from the first master station to the second master station. A communication method for performing [this action].

11. A communication program in which a management server, multiple master stations, and multiple slave stations perform wireless communication, and the master stations perform time-division multiplex communication with the slave stations, In the first slave station, if the stability of communication with the first master station associated with the first slave station falls below a threshold, the step of sending a search signal for searching for other master stations at time intervals longer than the slot time in the time-division communication, The steps include: each of the multiple master stations that have received the search signal transmits a report to the management server that includes the identification information of the master station, the identification information of the first slave station, and the received strength of the search signal; The management server, based on the multiple reports received from each of the multiple master stations, determines which of the multiple master stations to associate with the first slave station, and switches the master station associated with the first slave station from the first master station to the second master station. A communication program that causes one or more processors to execute.

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