Wireless communication system and control method therefor

Abstract

This wireless communication system (2) is provided with a communication unit (18) mounted on a transport carriage (6), and a plurality of communication devices (8) that performs wireless communication with the communication unit (18). The communication unit (18) and the plurality of communication devices (8) change communication channels for each prescribed hopping cycle, and each of the plurality of communication devices (8) performs wireless communication with the communication unit (18) using a plurality of communication slots obtained by time-dividing the prescribed hopping cycle. The plurality of communication devices, which belongs to each of a plurality of groups, each change the communication channel for each prescribed hopping cycle so as to perform wireless communication with the communication unit (18) using a plurality of communication channels different from each other in the prescribed hopping cycle.

Description

Wireless communication system and control method thereof

[0001] The present invention relates to a wireless communication system and a control method thereof.

[0002] BACKGROUND ART A semiconductor manufacturing system is known that includes an overhead transport vehicle for transporting front opening unified pods (FOUPs) storing semiconductor wafers, and semiconductor manufacturing equipment for processing the semiconductor wafers.

[0003] The E84 communication sequence of SEMI (Semiconductor Equipment and Materials International) is applied to wireless communication between the transport vehicle and a communication device communicatively connected to a port of the semiconductor manufacturing equipment. When transferring a FOUP between the transport vehicle and the port, control signals are exchanged between the transport vehicle and the communication device according to the E84 communication sequence.

[0004] Incidentally, Patent Document 1 discloses a wireless unit that specifies a communication slot and a hopping pattern to be used for wireless communication with each controlled device based on unique information set for each controlled device. Each controlled device performs wireless communication with the wireless unit using the communication slot specified by the wireless unit.

[0005] Japanese Patent Application Laid-Open No. 2006-121392

[0006] When the wireless communication technology disclosed in Patent Document 1 is applied to the semiconductor manufacturing system described above, the following problem arises: When a large number of semiconductor manufacturing devices are densely arranged in a semiconductor manufacturing factory (for example, about 100 devices within a radius of 10 meters), it is necessary to increase the number of communication channels in order to avoid radio wave interference between the transport carts and the communication devices, or to increase the number of communication slots that realize time-division communication according to the number of communication devices.

[0007] However, there is a limit to the number of available communication channels, and simply increasing the number of communication slots would lengthen the period of wireless communication between one transport vehicle and one communication device, which could result in the inability to properly exchange control signals between the transport vehicle and the communication device.

[0008] The present invention has been made in consideration of such problems, and its purpose is to provide a wireless communication system and a control method thereof that can perform wireless communication between a communication unit and a communication device normally while suppressing an increase in the number of communication slots.

[0009] (Technology 1) A wireless communication system comprising: a communication unit mounted on a transport vehicle that transports articles by traveling along a track; and a plurality of communication devices that are communicatively connected to a plurality of ports through which the articles are transferred to and from the transport vehicle and that perform wireless communication with the communication unit, wherein the communication unit and the plurality of communication devices change communication channels at every predetermined hopping period, and each of the plurality of communication devices performs wireless communication with the communication unit using a plurality of communication slots that time-divide the predetermined hopping period, and when a trigger signal is received from the communication unit, each of the plurality of communication devices performs interlock communication with the communication unit to permit the transport vehicle to transfer the articles to and from the plurality of ports, the plurality of communication devices are grouped into a plurality of mutually different groups, each of the plurality of groups including a group of communication devices that are arranged in proximity to each other, and the plurality of communication device groups that belong to each of the plurality of groups change communication channels at every predetermined hopping period so as to perform wireless communication with the communication unit using a plurality of mutually different communication channels in the predetermined hopping period.

[0010] According to Technology 1, a plurality of communication devices belonging to a plurality of groups each change their communication channel at each predetermined hopping period so as to communicate wirelessly with the communication unit using a plurality of different communication channels in the predetermined hopping period. Furthermore, each of the plurality of communication devices belonging to each group communicates wirelessly with the communication unit using a plurality of communication slots obtained by time-dividing the predetermined hopping period. This allows the number of communication channels to be increased artificially, thereby minimizing the number of communication slots and preventing the period for wireless communication between the communication unit and the communication devices from becoming longer. Therefore, wireless communication between the communication unit and the communication devices can be performed normally while preventing an increase in the number of communication slots.

[0011] (Technology 2) The wireless communication system described in Technology 1, wherein the plurality of communication device groups belonging to each of the plurality of groups change the communication channel at each predetermined hopping period so that the same communication channel is used within the same group, and different communication channels are used between different groups at any point in time to perform wireless communication with the communication unit.

[0012] According to the second technique, wireless communication between the communication unit and the communication device can be performed normally while suppressing an increase in the number of communication slots.

[0013] (Technology 3) The wireless communication system according to Technology 1 or 2, wherein each of the plurality of communication device groups includes a first communication device and a second communication device, the first communication device performs wireless communication with the communication unit at a first timing in a specific communication slot among the plurality of communication slots, and the second communication device performs wireless communication with the communication unit at a second timing different from the first timing in the specific communication slot.

[0014] According to the third technique, wireless communication between the communication unit and the communication device can be further multiplexed within the same time division slot.

[0015] (Technology 4) The wireless communication system according to any one of Technologies 1 to 3, wherein at least one of the plurality of communication devices is a master communication device that is set as a master, and performs time synchronization with a slave communication device that is set as a slave other than the at least one communication device.

[0016] According to Technique 4, by performing time synchronization among a plurality of communication devices, it is possible to improve the accuracy of communication using frequency hopping and time division slots by a plurality of communication devices.

[0017] (Technology 5) The wireless communication system according to Technology 4, wherein, if one of the slave communication devices cannot receive time synchronization information from the master communication device for a predetermined period of time, the slave communication device performs time synchronization with other communication devices as the master communication device.

[0018] According to Technology 5, even if one of the slave communication devices is unable to receive time synchronization information from the master communication device for a predetermined period of time, it can become the master communication device and continue to perform time synchronization with multiple communication devices.

[0019] (Technology 6) The wireless communication system according to Technology 4 or 5, wherein the plurality of communication devices wirelessly transmit and receive data to and from each other.

[0020] According to Technique 6, it is possible to perform time synchronization between a plurality of communication devices by wireless communication.

[0021] (Technology 7) A wireless communication system according to any one of Technologies 1 to 6, wherein, before the transport vehicle equipped with the communication unit delivers or receives the item to a specific port among the plurality of ports, the communication unit (i) first monitors for at least one cycle of the predetermined hopping period to check whether or not any of the plurality of communication slots is not being used for the interlock communication by any other transport vehicle other than the transport vehicle in question, and (ii) then transmits the trigger signal to the communication device using the communication slot that has been confirmed by the monitoring to be not being used for the interlock communication by any other transport vehicle.

[0022] According to Technology 7, the communication unit sends a trigger signal to the communication device using a communication slot that has been confirmed through monitoring to be not being used for interlock communication by other transport vehicles, thereby suppressing collisions in interlock communication.

[0023] (Technology 8) A control method for a wireless communication system including a communication unit mounted on a transport vehicle that transports an article by traveling along a track, and a plurality of communication devices that are communicatively connected to a plurality of ports through which the article is transferred to and from the transport vehicle and that perform wireless communication with the communication unit, wherein each of the plurality of communication devices performs interlock communication with the communication unit to permit the transport vehicle to transfer the article to and from the plurality of ports when a trigger signal is received from the communication unit, and the plurality of communication devices are grouped into a plurality of mutually different groups, each of which includes a group of communication devices that are arranged in close proximity to one another, the control method includes the steps of: (a) the communication unit and the plurality of communication devices changing a communication channel at every predetermined hopping period, and each of the plurality of communication devices performing wireless communication with the communication unit using a plurality of communication slots that time-divide the predetermined hopping period, and in (a), the communication channel is changed at every predetermined hopping period so that each of the plurality of communication device groups respectively belonging to the plurality of groups performs wireless communication with the communication unit using a plurality of communication channels that are mutually different from one another in the predetermined hopping period.

[0024] According to Technology 8, a plurality of communication devices belonging to a plurality of groups each change their communication channel at each predetermined hopping period so as to communicate wirelessly with the communication unit using a plurality of different communication channels in the predetermined hopping period. Furthermore, each of the plurality of communication devices belonging to each group communicates wirelessly with the communication unit using a plurality of communication slots obtained by time-dividing the predetermined hopping period. This allows the number of communication channels to be increased artificially, thereby minimizing the number of communication slots and preventing the period for wireless communication between the communication unit and the communication devices from becoming longer. Therefore, wireless communication between the communication unit and the communication devices can be performed normally while preventing an increase in the number of communication slots.

[0025] The present invention can be realized not only as an apparatus, but also as a method in which the processing means constituting the apparatus are steps, as a program that causes a computer to execute those steps, as a computer-readable recording medium such as a CD-ROM on which the program is recorded, or as information, data, or signals that represent the program.These programs, information, data, and signals may be distributed via a communication network such as the Internet.

[0026] According to a wireless communication system and the like relating to one aspect of the present invention, wireless communication between a communication unit and a communication device can be performed normally while suppressing an increase in the number of communication slots.

[0027] 1 is a schematic diagram showing an overview of a wireless communication system according to an embodiment; FIG. 2 is a block diagram showing a functional configuration of a wireless communication system according to an embodiment; FIG. 3 is a diagram for explaining an example of frequency hopping in a wireless communication system according to an embodiment; FIG. 4 is a diagram showing an example of a configuration of a wireless communication system according to an embodiment; FIG. 5 is a diagram showing an example of setting contents of a plurality of communication devices according to an embodiment; FIG. 6 is a sequence diagram showing a flow of operation of a wireless communication system according to an embodiment; FIG. 7 is a flowchart showing a flow of operation of a wireless communication system according to an embodiment; FIG. 8 is a flowchart showing a flow of operation of a wireless communication system according to an embodiment; FIG. 9 is a diagram for explaining operation of a wireless communication system according to an embodiment; FIG. 10 is a timing chart for explaining operation of a wireless communication system according to a first modification of an embodiment; FIG. 11 is a timing chart for explaining operation of a wireless communication system according to a second modification of an embodiment;

[0028] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the embodiments described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, component placement and connection forms, steps, step order, etc. shown in the following embodiments are merely examples and are not intended to limit the present invention. Furthermore, among the components in the following embodiments, components not recited in independent claims will be described as optional components.

[0029] (Embodiment) [1. Overview of Wireless Communication System] First, an overview of a wireless communication system 2 according to an embodiment will be described with reference to Fig. 1. Fig. 1 is a schematic diagram showing an overview of a wireless communication system 2 according to an embodiment.

[0030] 1, the wireless communication system 2 is a system constructed in, for example, a semiconductor manufacturing factory. The semiconductor manufacturing factory is equipped with a plurality of semiconductor manufacturing apparatuses 4. The wireless communication system 2 includes a plurality of transport vehicles 6 and a plurality of communication devices 8.

[0031] In a semiconductor manufacturing factory, a large number of transport vehicles 6 (for example, hundreds to thousands) are actually operated, but for the sake of convenience, only two transport vehicles 6 are shown in Fig. 1. In addition, in a semiconductor manufacturing factory, a large number of semiconductor manufacturing devices 4 (for example, thousands) are actually installed, but for the sake of convenience, only three semiconductor manufacturing devices 4 are shown in Fig. 1.

[0032] Each of the plurality of transport vehicles 6 is an overhead traveling transport vehicle, known as an OHT (Overhead Hoist Transfer), for transporting a FOUP 10 (an example of an article) storing semiconductor wafers. Each of the plurality of transport vehicles 6 travels unmanned along a track 12 or a track 14 installed on the ceiling of the semiconductor manufacturing factory.

[0033] The tracks 12 and 14 are disposed at different positions in the vertical direction directly above a plurality of ports 22 (described later) of the semiconductor manufacturing equipment 4. In the example shown in Fig. 1, the track 14 is disposed above (directly above) the track 12. Note that instead of this arrangement, only one of the tracks 12 and 14 may be disposed directly above the plurality of ports 22 of the semiconductor manufacturing equipment 4. Furthermore, the track 12 or the track 14 is not limited to a linear track as shown in Fig. 1, and may be a track of any shape.

[0034] A gripper 16 for gripping a FOUP 10 is mounted inside each of the multiple transport vehicles 6. The gripper 16 is movable up and down relative to the transport vehicle 6. When a FOUP 10 is transferred between the transport vehicle 6 and a port 22 of the semiconductor manufacturing equipment 4, the gripper 16 descends from the transport vehicle 6 to the vicinity of the port 22 while the transport vehicle 6 is stopped in a position directly above the port 22. When the transfer of the FOUP 10 is complete, the gripper 16 ascends from the vicinity of the port 22 to the transport vehicle 6 and is stored inside the transport vehicle 6.

[0035] Each of the plurality of transport vehicles 6 is equipped with a communication unit 18. The communication unit 18 performs wireless communication with each of the plurality of communication devices 8 by short-range wireless communication such as BLE (Bluetooth (registered trademark) Low Energy).

[0036] The semiconductor manufacturing equipment 4 is an apparatus for performing various processes on the semiconductor wafers stored in the FOUP 10, and is installed below the tracks 12 and 14. The semiconductor manufacturing equipment 4 has a plurality of loading / unloading openings 20 for loading / unloading the semiconductor wafers into and out of the semiconductor manufacturing equipment 4, and a plurality of ports 22 respectively disposed near the plurality of loading / unloading openings 20.

[0037] Each of the plurality of ports 22 is a load port for placing a FOUP 10. The FOUP 10 is transferred between each of the plurality of ports 22 and the gripper 16 of the transport vehicle 6. Then, the semiconductor wafers stored in the FOUP 10 are transferred between the ports 22 and the semiconductor manufacturing equipment 4 through the loading / unloading opening 20.

[0038] Although the semiconductor manufacturing equipment 4 has four ports 22 in FIG. 1, the number of ports 22 is not limited to four, and the equipment may have three or fewer ports 22 or five or more ports 22 .

[0039] Each of the multiple communication devices 8 is a device server that mediates communication between the communication unit 18 of the transport cart 6 and the port 22 of the semiconductor manufacturing equipment 4. The communication device 8 is disposed, for example, on the top surface of the semiconductor manufacturing equipment 4, and is communicatively connected to the port 22 of the semiconductor manufacturing equipment 4 via a parallel cable (not shown). As a result, the communication device 8 performs wired communication with the port 22 of the semiconductor manufacturing equipment 4 via the parallel cable. Note that the communication device 8 may be disposed in a location other than the top surface of the semiconductor manufacturing equipment 4, such as on the side surface of the semiconductor manufacturing equipment 4. Furthermore, each of the multiple communication devices 8 performs wireless communication with the communication unit 18 of the transport cart 6 via short-range wireless communication such as BLE. Furthermore, each of the multiple communication devices 8 performs wireless communication with other communication devices 8 other than the communication device 8 via short-range wireless communication such as BLE.

[0040] When a FOUP 10 is to be transferred between the transport vehicle 6 and a port 22 of the semiconductor manufacturing equipment 4, the communication unit 18 of the transport vehicle 6 transmits a trigger signal to the communication device 8 connected to the port 22. This causes synchronization of interlock communication between the communication unit 18 and the communication device 8 in accordance with the SEMI E84 interlock sequence for permitting the transport vehicle 6 to transfer the FOUP 10 to the port 22. Thereafter, a control signal is exchanged between the communication unit 18 and the communication device 8 through interlock communication. The E84 interlock sequence employs an interlock sequence in which specific control signals are turned on and off to perform a plurality of processes when a FOUP 10 is to be transferred between the transport vehicle 6 and the port 22.

[0041] 2. Functional Configuration of Wireless Communication System Next, a functional configuration of the wireless communication system 2 according to the embodiment will be described with reference to Fig. 2. Fig. 2 is a block diagram showing the functional configuration of the wireless communication system 2 according to the embodiment.

[0042] As shown in Fig. 2, the transport vehicle 6 has, as its functional components, a communication unit 18 and a control unit 24. Note that, since each of the multiple transport vehicles 6 shown in Fig. 1 has the same functional components, only the functional components of one transport vehicle 6 will be described here.

[0043] The communication unit 18 transmits and receives trigger signals, control signals, and the like relating to interlock communication to and from the communication device 8 via wireless communication.

[0044] The control unit 24 executes various processes by controlling the travel of the transport vehicle 6 and the communication unit 18. The control unit 24 is realized, for example, by a processor reading and executing a software program recorded on a recording medium such as a hard disk or a semiconductor memory.

[0045] Furthermore, the communication device 8 has, as its functional configuration, a communication unit 26 and a control unit 28. Note that, since each of the multiple communication devices 8 shown in Fig. 1 has the same functional configuration, only the functional configuration of one communication device 8 will be described here.

[0046] The communication unit 26 transmits and receives trigger signals, control signals, and the like related to interlock communication via wireless communication with the communication unit 18 of the transport cart 6. The communication unit 26 also transmits and receives control signals, which are parallel signals, with the port 22 of the semiconductor manufacturing equipment 4 via a parallel cable. The communication unit 26 also transmits and receives data via wireless communication with the communication unit 26 of another communication device 8 other than the communication device 8, thereby performing time synchronization (described later) between the two communication devices 8.

[0047] The control unit 28 executes various processes by controlling the communication unit 26. The control unit 28 is realized, for example, by a processor reading and executing a software program recorded on a recording medium such as a hard disk or a semiconductor memory.

[0048] The semiconductor manufacturing apparatus 4 also has, as its functional components, a control unit 32 and a communication unit 30 corresponding to each port 22. Note that each of the multiple ports 22 shown in Fig. 1 has the same functional component, and therefore only the functional component of one port 22 will be described here.

[0049] The communication unit 30 transmits and receives control signals, which are parallel signals, to and from the communication device 8 via a parallel cable.

[0050] The control unit 32 executes various processes by controlling the communication unit 30. Specifically, the control unit 32 executes an interlock process for transferring the FOUP 10 to and from the transport vehicle 6 based on a control signal from the communication device 8. The control unit 32 also executes a process for transferring the FOUP 10 to and from the semiconductor manufacturing apparatus 4 through the loading / unloading opening 20. The control unit 32 is realized, for example, by a processor reading and executing a software program recorded on a recording medium such as a hard disk or semiconductor memory.

[0051] Here, characteristic functions of the wireless communication system 2 according to the embodiment will be described with reference to Fig. 3. Fig. 3 is a diagram for explaining an example of frequency hopping in the wireless communication system 2 according to the embodiment.

[0052] The following description focuses on one of the multiple transport vehicles 6 and the multiple communication devices 8.

[0053] As shown in FIG. 3, the plurality of communication devices 8 are grouped into, for example, three different groups (hereinafter also referred to as "group 1," "group 2," and "group 3"). Each group includes a group of communication devices that are located near each other. That is, a communication device group is a collection of two or more communication devices 8 that are located within a range where they can wirelessly communicate with each other. In this embodiment, each of groups 1 to 3 includes ten communication devices 8 (hereinafter also referred to as "communication device D1," "communication device D2," ..., "communication device D10") as the communication device group.

[0054] The communication unit 18 of the transport cart 6 and the communication unit 26 of each of the ten communication devices D1 to D10 change (frequency hop) the communication channel (communication frequency) to one of three different communication channels (hereinafter also referred to as "channel CH1," "channel CH2," and "channel CH3") every predetermined hopping period (e.g., 10 ms).

[0055] In this embodiment, the frequency hopping between the communication unit 18 of the transport cart 6 and the communication unit 26 of each communication device is changed to one of three different communication channels, but this is not limited to this and the frequency hopping may be changed to one of four or more communication channels.

[0056] Furthermore, the ten communication devices D1 to D10 belonging to each group each use ten communication slots obtained by time-dividing a predetermined hopping period to perform wireless communication with the communication unit 18 of the transporting carriage 6. The ten communication slots are assigned slot numbers "1," "2," ..., "10," respectively, and the length (time) of each communication slot is, for example, 1 ms.

[0057] In this embodiment, the predetermined hopping period is time-divided into 10 communication slots, but this is not limited to this and the period may be time-divided into any number of communication slots. Also, in this embodiment, the length (time) of each communication slot is 1 ms, but this is not limited to this and the length may be less than 1 ms or longer than 1 ms.

[0058] The three communication device groups belonging to groups 1 to 3 respectively change the communication channel at each predetermined hopping period so as to use the three communication channels in the predetermined hopping period to perform wireless communication with the communication unit 18 of the transport vehicle 6. In other words, the three communication device groups belonging to groups 1 to 3 respectively use the same communication channel within the same group, and change the communication channel at each predetermined hopping period so that different groups use different communication channels at any time to perform wireless communication with the communication unit 18.

[0059] 3 , in the first predetermined hopping period (a period from 0 ms to 10 ms), the ten communication devices D1 to D10 belonging to group 1 each use channel CH1 as a communication channel and ten communication slots with slot numbers "1," "2," ..., "10" obtained by time-dividing the predetermined hopping period to perform wireless communication with the communication unit 18 of the transporting vehicle 6. Meanwhile, the ten communication devices D1 to D10 belonging to group 2 each use channel CH3 as a communication channel and ten communication slots with slot numbers "1," "2," ..., "10" obtained by time-dividing the predetermined hopping period to perform wireless communication with the communication unit 18 of the transporting vehicle 6. Meanwhile, the ten communication devices D1 to D10 belonging to group 3 each use channel CH2 as a communication channel and ten communication slots with slot numbers "1," "2," ..., "10" obtained by time-dividing the predetermined hopping period to perform wireless communication with the communication unit 18 of the transporting vehicle 6.

[0060] Next, in a second predetermined hopping period (a period of 10 ms to 20 ms), the ten communication devices D1 to D10 belonging to group 1 each change the communication channel they use from channel CH1 to channel CH2, and use ten communication slots with slot numbers "1," "2," ..., "10," which are obtained by time-dividing the predetermined hopping period, to perform wireless communication with the communication unit 18 of the transporting vehicle 6. Furthermore, the ten communication devices D1 to D10 belonging to group 2 each change the communication channel they use from channel CH3 to channel CH1, and use ten communication slots with slot numbers "1," "2," ..., "10," which are obtained by time-dividing the predetermined hopping period, to perform wireless communication with the communication unit 18 of the transporting vehicle 6. In addition, each of the 10 communication devices D1 to D10 belonging to group 3 changes the communication channel used from channel CH2 to channel CH3, and performs wireless communication with the communication unit 18 of the transport cart 6 using 10 communication slots with slot numbers "1," "2," ..., "10," which are obtained by time-dividing a predetermined hopping period.

[0061] Next, in the third predetermined hopping period (a period of 20 ms to 30 ms), each of the ten communication devices D1 to D10 belonging to group 1 changes the communication channel they use from channel CH2 to channel CH3, and uses ten communication slots with slot numbers "1," "2," ..., "10," which are obtained by time-dividing the predetermined hopping period, to perform wireless communication with the communication unit 18 of the transporting vehicle 6. Also, each of the ten communication devices D1 to D10 belonging to group 2 changes the communication channel they use from channel CH1 to channel CH2, and uses ten communication slots with slot numbers "1," "2," ..., "10," which are obtained by time-dividing the predetermined hopping period, to perform wireless communication with the communication unit 18 of the transporting vehicle 6. In addition, each of the 10 communication devices D1 to D10 belonging to group 3 changes the communication channel used from channel CH3 to channel CH1, and performs wireless communication with the communication unit 18 of the transport cart 6 using 10 communication slots with slot numbers "1," "2," ..., "10," which are obtained by time-dividing a predetermined hopping period.

[0062] Similarly, each of the 10 communication devices D1 to D10 belonging to group 1 simultaneously changes the communication channel they use in the order of "Channel CH1 → Channel CH2 → Channel CH3 → Channel CH1 → ..." at each predetermined hopping period. Also, each of the 10 communication devices D1 to D10 belonging to group 2 simultaneously changes the communication channel they use in the order of "Channel CH3 → Channel CH1 → Channel CH2 → Channel CH3 → ..." at each predetermined hopping period. Also, each of the 10 communication devices D1 to D10 belonging to group 3 simultaneously changes the communication channel they use in the order of "Channel CH2 → Channel CH3 → Channel CH1 → Channel CH2 → ..." at each predetermined hopping period.

[0063] Furthermore, the communication unit 18 of the transporting vehicle 6 synchronizes interlock communications with the ten communication devices D1 to D10 belonging to each group using a communication channel (e.g., channel CH1) used by the communication device of the other party to which the FOUP 10 is being transferred. Thereafter, for example, when the communication unit 18 of the transporting vehicle 6 performs interlock communications with the communication device D1 belonging to group 1, the communication channel to be used is changed in the order of "channel CH1 → channel CH2 → channel CH3 → channel CH1 → ..." at each predetermined hopping period in accordance with the frequency hopping of the communication device D1 shown in FIG. 3. Furthermore, for example, when the communication unit 18 of the transporting vehicle 6 performs interlock communications with the communication device D1 belonging to group 2, the communication channel to be used is changed in the order of "channel CH3 → channel CH1 → channel CH2 → channel CH3 → ..." at each predetermined hopping period, similar to the above. For example, when the communication unit 18 of the transport cart 6 performs interlock communication with the communication device D1 belonging to group 3, the communication channel to be used is changed in the following order at each predetermined hopping period, as described above: "Channel CH2 → Channel CH3 → Channel CH1 → Channel CH2 → ...".

[0064] [3. Operation of Wireless Communication System] Next, the operation of the wireless communication system 2 according to the embodiment will be described with reference to Figs. 4 to 9. Fig. 4 is a diagram showing an example of the configuration of the wireless communication system 2 according to the embodiment. Fig. 5 is a diagram showing an example of the setting contents of each of the multiple communication devices 8 according to the embodiment. Fig. 6 is a sequence diagram showing the flow of operation of the wireless communication system 2 according to the embodiment. Figs. 7 and 8 are flowcharts showing the flow of operation of the wireless communication system 2 according to the embodiment. Fig. 9 is a diagram for explaining the operation of the wireless communication system 2 according to the embodiment.

[0065] The following describes a wireless communication system 2 configured as shown in Fig. 4. As shown in Fig. 4, seven semiconductor manufacturing devices 4 (hereinafter also referred to as "semiconductor manufacturing device EQ1," "semiconductor manufacturing device EQ2," ..., "semiconductor manufacturing device EQ7") are installed in a semiconductor manufacturing factory.

[0066] The semiconductor manufacturing equipment EQ1 has two ports 22 (hereinafter also referred to as "port LP1" and "port LP2"). Two communication devices 8 (hereinafter also referred to as "communication device EQ1-LP1" and "communication device EQ1-LP2") are communicatively connected to the ports LP1 and LP2, respectively.

[0067] The semiconductor manufacturing equipment EQ2 has four ports 22 (hereinafter also referred to as "port LP1," "port LP2," "port LP3," and "port LP4"). Four communication devices 8 (hereinafter also referred to as "communication device EQ2-LP1," "communication device EQ2-LP2," "communication device EQ2-LP3," and "communication device EQ2-LP4") are communicatively connected to the ports LP1 to LP4, respectively.

[0068] The semiconductor manufacturing equipment EQ3 has two ports 22 (hereinafter also referred to as "port LP1" and "port LP2"). Two communication devices 8 (hereinafter also referred to as "communication device EQ3-LP1" and "communication device EQ3-LP2") are communicatively connected to the ports LP1 and LP2, respectively.

[0069] The semiconductor manufacturing equipment EQ4 has two ports 22 (hereinafter also referred to as "port LP1" and "port LP2"). Two communication devices 8 (hereinafter also referred to as "communication device EQ4-LP1" and "communication device EQ4-LP2") are communicatively connected to the ports LP1 and LP2, respectively.

[0070] The semiconductor manufacturing equipment EQ5 has three ports 22 (hereinafter also referred to as "port LP1," "port LP2," and "port LP3"). Three communication devices 8 (hereinafter also referred to as "communication device EQ5-LP1," "communication device EQ5-LP2," and "communication device EQ5-LP3") are communicatively connected to the ports LP1 to LP3, respectively.

[0071] The semiconductor manufacturing equipment EQ6 has four ports 22 (hereinafter also referred to as "port LP1," "port LP2," "port LP3," and "port LP4"). Four communication devices 8 (hereinafter also referred to as "communication device EQ6-LP1," "communication device EQ6-LP2," "communication device EQ6-LP3," and "communication device EQ6-LP4") are communicatively connected to the ports LP1 to LP4, respectively.

[0072] The semiconductor manufacturing equipment EQ7 has three ports 22 (hereinafter also referred to as "port LP1," "port LP2," and "port LP3"). Three communication devices 8 (hereinafter also referred to as "communication device EQ7-LP1," "communication device EQ7-LP2," and "communication device EQ7-LP3") are communicatively connected to the ports LP1 to LP3, respectively.

[0073] Of the 20 communication devices EQ1-LP1, ..., EQ7-LP3 mentioned above, 10 communication devices EQ1-LP1, ..., EQ4-LP2 are grouped into group 1, and the remaining 10 communication devices EQ5-LP1, ..., EQ7-LP3 are grouped into group 2.

[0074] In this embodiment, communication devices are grouped into groups of 10 as described above, but the number of communication devices per group is linked to the number of communication slots in a given hopping cycle (10). Therefore, if the number of communication slots in a given hopping cycle is changed, the number of communication devices per group will also change accordingly.

[0075] Furthermore, each of the 20 communication devices EQ1-LP1, ..., EQ7-LP3 is set as shown in Fig. 5. As shown in Fig. 5, each of the 10 communication devices EQ1-LP1, ..., EQ4-LP2 belonging to group 1 starts frequency hopping from channel CH1, and each of the 10 communication devices EQ5-LP1, ..., EQ7-LP3 belonging to group 2 starts frequency hopping from channel CH3.

[0076] 5, the communication device EQ1-LP1 is a master communication device set as the first master (1st master) of time synchronization, and the communication device EQ1-LP2 is a master communication device set as the second master (2nd master) of time synchronization. Each of the remaining 18 communication devices EQ2-LP1 to EQ7-LP3 is a slave communication device set as a slave of time synchronization. Note that the second master functions as a slave of time synchronization when the first master is normal, but has the role of becoming the master of time synchronization (new first master) in place of the original first master if the first master becomes abnormal.

[0077] First, time synchronization is performed between the communication device EQ1-LP1 set as the first master and the remaining 19 communication devices EQ1-LP2, . . . , EQ7-LP3 as follows.

[0078] As shown in FIG. 6, first, each of the 20 communication devices EQ1-LP1, ..., EQ7-LP3 starts counting up its soft counter (internal timer) almost simultaneously (S101: at this point, time synchronization has not yet been achieved between the communication devices).

[0079] Next, the communication device EQ1-LP1 set as the first master transmits the soft counter value (xx01) of its own soft counter to the communication device EQ1-LP2 set as the second master (S102).

[0080] Next, the communication device EQ1-LP2 updates the soft counter value of its own soft counter to the received soft counter value (xx01) (S103).

[0081] Next, the communications device EQ1-LP2 transmits the updated soft counter value (xx01) as a response to the communications device EQ1-LP1 (S104), thereby completing time synchronization of the soft counters between the communications devices EQ1-LP1 and EQ1-LP2.

[0082] Next, the communication device EQ1-LP1 set as the first master transmits the soft counter value (xx02) of its own soft counter to the communication device EQ2-LP1 set as the slave (S105).

[0083] Next, the communication device EQ2-LP1 updates the soft counter value of its own soft counter to the received soft counter value (xx02) (S106).

[0084] Next, the communications device EQ2-LP1 transmits the updated soft counter value (xx02) as a response to the communications device EQ1-LP1 (S107), thereby completing time synchronization of the soft counters between the communications devices EQ1-LP1 and EQ2-LP1.

[0085] Next, although illustration of each step is omitted, in the same manner as described above, time synchronization of each soft counter is performed between the communication device EQ1-LP1 and the communication devices EQ2-LP2, . . . , EQ7-LP2.

[0086] Finally, the communication device EQ1-LP1 set as the first master transmits the soft counter value (xx19) of its own soft counter to the communication device EQ7-LP3 set as the slave (S108).

[0087] Next, the communication device EQ7-LP3 updates the soft counter value of its own soft counter to the received soft counter value (xx19) (S109).

[0088] Next, the communications device EQ7-LP3 transmits the updated soft counter value (xx19) to the communications device EQ7-LP3 as a response (S110), thereby completing time synchronization of the soft counters between the communications devices EQ1-LP1 and EQ7-LP3.

[0089] In this way, time synchronization is completed between the communication device EQ1-LP1 set as the first master and the remaining 19 communication devices EQ1-LP2, ..., EQ7-LP3. This allows the frequency hopping timing to be synchronized among the 20 communication devices EQ1-LP1, ..., EQ7-LP3.

[0090] Here, with reference to FIG. 7, the operation of time synchronization communication of the communication device EQ1-LP1 set as the first master (hereinafter also referred to as the "time synchronization master communication device") will be described.

[0091] When the initial time setting (time synchronization of the software counter) shown in FIG. 6 is completed, the communication device serving as the time synchronization master starts time synchronization communication as shown in FIG. 7 (S201).

[0092] Next, the time synchronization master communication device EQ1-LP1 determines whether a predetermined time (for example, 15 seconds) has elapsed since the start of time synchronization communication (S202). If the predetermined time has not elapsed since the start of time synchronization communication (NO in S202), step S202 is executed again.

[0093] If a predetermined time has elapsed since the start of time synchronization communication (YES in S202), the time synchronization master communication device EQ1-LP1 determines whether the soft counter value of the soft counter is an integer multiple of a predetermined hopping period (S203). If the soft counter value of the soft counter is not an integer multiple of the predetermined hopping period (NO in S203), step S203 is executed again.

[0094] If the soft counter value of the soft counter is an integer multiple of a predetermined hopping period (YES in S203), the time synchronization master communication device EQ1-LP1 transmits the soft counter value on channel CH1 (or channel CH3) to the communication device EQ1-LP2 set as the second master (hereinafter also referred to as the "second master communication device") and the communication devices EQ2-LP1, ... EQ7-LP3 set as slaves (hereinafter each of these will also be referred to as the "time synchronization slave communication device") (S204).

[0095] If time synchronization communication has not been performed with the second master communication device and all the time synchronization slave communication devices (NO in S205), the above-described step S204 is executed again.

[0096] Thereafter, when time synchronization communication has been performed with the second master communication device and all the time synchronization slave communication devices (YES in S205), the time synchronization master communication device ends the time synchronization communication (S206).

[0097] Here, the operation of time synchronization communication of a time synchronization slave communication device (including a time synchronization slave communication device set as a second master) will be described with reference to FIG.

[0098] As shown in FIG. 8, the time synchronization slave communication device determines whether or not it has received a soft counter value from the time synchronization master communication device (S301).

[0099] If the time synchronization slave communication device has not received a soft counter value from the time synchronization master communication device (NO in S301) and a predetermined time (e.g., 15 seconds) has not elapsed since the start of time synchronization communication (NO in S302), step S301 is executed again.

[0100] On the other hand, if the time synchronization slave communication device has not received a soft counter value from the time synchronization master communication device (NO in S301) and a predetermined time has elapsed since the start of time synchronization communication (YES in S302), the time synchronization slave communication device determines whether it is set as the second master (S303).

[0101] If the time synchronization slave communication device is not set as the second master (NO in S303), step S301 is executed again.

[0102] On the other hand, in step S303, if the time synchronization slave communication device is set as the second master (YES in S303), the time synchronization slave communication device changes itself from the second master to the first master (S304) and ends the process. At this time, among the other time synchronization slave communication devices, a communication device whose order has been determined in advance (for example, in the case of FIG. 5, communication device EQ2-LP1) is set as the new second master. As a result, even if, for example, communication device EQ1-LP1 set as the first master is malfunctioning, time synchronization communication can be continued between the new first master communication device and the time synchronization slave communication device.

[0103] Returning to step S301, when the time synchronization slave communication device receives a soft counter value from the time synchronization master communication device (YES in S301), it determines whether the difference between the received soft counter value and its own soft counter value is greater than or equal to a threshold value (e.g., 5 ms) (S305).

[0104] If the difference between the received soft counter value and its own soft counter value is equal to or greater than the threshold value (YES in S305), the time synchronization slave communication device stores the restart instruction (S306) and then proceeds to step S307.

[0105] On the other hand, if the difference between the received soft counter value and its own soft counter value is less than the threshold value (NO in S305), the process proceeds to step S307, and the time synchronization slave communication device updates its own soft counter value to the received soft counter value (S307).

[0106] Next, in step S308, if the time synchronization slave communication device has not stored a restart instruction in step S306 (NO in S308), the time synchronization slave communication device ends the time synchronization communication.

[0107] On the other hand, if the time synchronization slave communication device has stored a restart instruction in step S306 (YES in S308), it determines whether its own soft counter value is an integer multiple of a predetermined hopping period (S309).

[0108] If the soft counter value is not an integer multiple of the predetermined hopping period (NO in S309), step S309 is executed again.

[0109] On the other hand, if the soft counter value is an integer multiple of the predetermined hopping period (YES in S309), the time synchronization slave communication device determines whether interlock communication is being performed (S310).

[0110] If interlock communication is being performed (YES in S310), step S309 is executed again.

[0111] If interlock communication is not being performed (NO in S310), the time synchronization slave communication device restarts itself (S311) and ends the process.

[0112] After the time-synchronized communication is completed in the manner described above, the 20 communication devices EQ1-LP1, ..., EQ7-LP3 each perform interlock communication with the 20 transport carts 6 (hereinafter also referred to as "transport cart T1," "transport cart T2," ..., "transport cart T20").

[0113] Specifically, as shown in Fig. 9, each of the ten communication devices EQ1-LP1, ..., EQ4-LP2 belonging to group 1 first performs interlock communication using channel CH1, and thereafter performs frequency hopping every 10 ms in the order shown in Fig. 3. Also, each of the ten communication devices EQ5-LP1, ..., EQ7-LP3 belonging to group 2 first performs interlock communication using channel CH3, and thereafter performs frequency hopping every 10 ms in the order shown in Fig. 3.

[0114] The communication device EQ1-LP1 belonging to group 1 performs interlock communication with the transporting vehicle T1 using the communication slot of channel CH1 and slot number "1" (time t = 0 to 1 ms) during the time period t = 0 to 1 ms. Note that the communication state "↓↑" in Fig. 9 means that interlock communication is performed between the communication device and the transporting vehicle.

[0115] Next, the communication device EQ1-LP2 belonging to group 1 performs interlock communication with the transport cart T2 using the communication slot with channel CH1 and slot number "2" (time t = 1 to 2 ms) during the time period t = 1 to 2 ms.

[0116] Next, although not shown in the figure, similarly to the above, the communication devices EQ2-LP1, ..., EQ4-LP2 belonging to group 1 each perform interlock communication with transport vehicles T3, ..., T10 using channel CH1 and communication slots with slot numbers "3", ..., and "10" during the time period t = 2 to 3 ms, ..., and the time period t = 9 to 10 ms.

[0117] In addition, the communication device EQ5-LP1 belonging to group 2 performs interlock communication with the transport cart T11 using the communication slot with channel CH3 and slot number "1" (time t = 0 to 1 ms) during the time period t = 0 to 1 ms.

[0118] Next, the communication device EQ5-LP2 belonging to group 2 performs interlock communication with the transport cart T12 using the communication slot with channel CH3 and slot number "2" (time t = 1 to 2 ms) during the time period t = 1 to 2 ms.

[0119] Next, although not shown in the figure, similarly to the above, the communication devices EQ5-LP3, ..., EQ7-LP3 belonging to group 2 each perform interlock communication with the transport carts T13, ..., T20 using the communication slots of channel CH3 and slot numbers "3", ..., "10" during the time period t = 2 to 3 ms, ..., 9 to 10 ms.

[0120] Thereafter, at time t=10 ms, each of the ten communication devices EQ1-LP1, ..., EQ4-LP2 belonging to group 1 frequency hops from channel CH1 to channel CH2. Also, at time t=10 ms, each of the ten communication devices EQ5-LP1, ..., EQ7-LP3 belonging to group 2 frequency hops from channel CH3 to channel CH1.

[0121] As a result, the communication device EQ1-LP1 belonging to group 1 performs interlock communication with the transport cart T1 using the communication slot with channel CH2 and slot number "1" (time t = 10 to 11 ms) during the time period t = 10 to 11 ms.

[0122] Next, communication device EQ1-LP2 belonging to group 1 performs interlock communication with transport cart T2 using channel CH2 and communication slot number "2" (time t = 11 to 12 ms) during the time period t = 11 to 12 ms.

[0123] Next, although not shown in the figure, similarly to the above, the communication devices EQ2-LP1, ..., EQ4-LP2 belonging to group 1 each perform interlock communication with transport vehicles T3, ..., T10 using channel CH2 and communication slots with slot numbers "3", ..., and "10" during the time period t = 12 to 13 ms, ..., t = 19 to 20 ms.

[0124] In addition, the communication device EQ5-LP1 belonging to group 2 performs interlock communication with the transport cart T11 using the communication slot with channel CH1 and slot number "1" (time t = 10 to 11 ms) during the time period t = 10 to 11 ms.

[0125] Next, the communication device EQ5-LP2 belonging to group 2 performs interlock communication with the transport cart T2 using the communication slot with channel CH1 and slot number "2" (time t = 11 to 12 ms) during the time period t = 11 to 12 ms.

[0126] Next, although not shown in the figure, similarly to the above, the communication devices EQ5-LP3, ..., EQ7-LP3 belonging to group 2 each perform interlock communication with the transport vehicles T13, ..., T20 using the communication slots of channel CH1 and slot numbers "3", ..., "10" during the time period t = 12 to 13 ms, ..., t = 19 to 20 ms.

[0127] [4. Effects] In this embodiment, a plurality of communication device groups respectively belonging to a plurality of groups change the communication channel at each predetermined hopping period so as to perform wireless communication with the communication unit 18 of the transporting vehicle 6 using a plurality of different communication channels in the predetermined hopping period. Furthermore, a plurality of communication devices 8 belonging to each group each perform wireless communication with the communication unit 18 of the transporting vehicle 6 using one of a plurality of communication slots obtained by time-dividing the predetermined hopping period. This allows the number of communication channels to be increased artificially, and therefore, by minimizing the number of communication slots, it is possible to prevent the period for wireless communication between the communication unit 18 of the transporting vehicle 6 and the communication devices 8 from becoming longer. Therefore, wireless communication between the communication unit 18 of the transporting vehicle 6 and the communication devices 8 can be performed normally while suppressing an increase in the number of communication slots.

[0128] [5. Modification 1] Next, the operation of the wireless communication system 2 according to Modification 1 of the embodiment will be described with reference to Fig. 10 and Fig. 11. Fig. 10 and Fig. 11 are timing charts for explaining the operation of the wireless communication system 2 according to Modification 1 of the embodiment.

[0129] 10(a), for example, the communication device D1 starts frequency hopping at a first timing (hereinafter also referred to as "1st Timing") in a specific communication slot (e.g., 1000 μs) on channel CH1, and performs interlock communication with the communication unit 18 of the transporting vehicle 6. Here, the first timing is a timing that coincides with the start timing of the specific communication slot, and is set in advance for the communication device D1.

[0130] 10A, the interlock communication includes command communication (TX) in which the communication unit 18 of the transporting vehicle 6 transmits a command signal to the communication device D1, and response communication (RX) in which the communication device D1 transmits a response signal to the communication unit 18 of the transporting vehicle 6. For example, the period of the command communication is 170 μs, and the period of the response communication is 180 μs. Furthermore, for example, the period between the command communication and the response communication in a specific communication slot is 300 μs, and the period between the response communication in a specific communication slot and the command communication in the next communication slot is 350 μs.

[0131] 10(b), another communication device D2 belonging to the same group as the communication device D1 starts frequency hopping at a second timing (hereinafter also referred to as "2nd Timing") in a specific communication slot (e.g., 1000 μs) on channel CH1, and performs interlock communication with the communication unit 18 of the transporting carriage 6. Here, the second timing is a timing different from the first timing, i.e., a timing delayed by 200 μs from the start timing of the specific communication slot, and is set in advance for the communication device D2. As a result, the communication device D2 performs command communication in the period between the command communication and response communication in the specific communication slot by the communication device D1, and also performs response communication in the period between the response communication in the specific communication slot by the communication device D1 and the command communication in the next communication slot.

[0132] 10(b), the interlock communication includes command communication (TX) in which the communication unit 18 of the transporting vehicle 6 transmits a command signal to the communication device D2, and response communication (RX) in which the communication device D2 transmits a response signal to the communication unit 18 of the transporting vehicle 6. For example, the period of the command communication is 170 μs, and the period of the response communication is 180 μs. Furthermore, for example, the period between the command communication and the response communication in a specific communication slot is 300 μs, and the period between the response communication in a specific communication slot and the command communication in the next communication slot is 350 μs.

[0133] As a result, even if the communication devices D1 and D2 belong to the same group, they perform command communication and response communication at timings that do not overlap with each other in the communication slots, thereby enabling further multiplexing.

[0134] 11A, for example, the communication device D3 starts frequency hopping at a first timing (hereinafter also referred to as "1st Timing") in a specific communication slot (e.g., 1000 μs) on channel CH1, and performs interlock communication with the communication unit 18 of the transporting vehicle 6. Here, the first timing is a timing that coincides with the start timing of the specific communication slot, and is set in advance for the communication device D3.

[0135] 11A, the interlock communication includes command communication (TX) in which the communication unit 18 of the transporting vehicle 6 transmits a command signal to the communication device D3, and response communication (RX) in which the communication device D3 transmits a response signal to the communication unit 18 of the transporting vehicle 6. For example, the period of the command communication is 170 μs, and the period of the response communication is 180 μs. Also, for example, the period between the command communication and the response communication in a specific communication slot is 100 μs, and the period between the response communication in a specific communication slot and the command communication in the next communication slot is 550 μs.

[0136] 11(b), another communication device D4 belonging to the same group as the communication device D3 starts frequency hopping at a second timing (hereinafter also referred to as "2nd Timing") in a specific communication slot (e.g., 1000 μs) on channel CH1, and performs interlock communication with the communication unit 18 of the transporting carriage 6. Here, the second timing is a timing different from the first timing, i.e., a timing delayed by 500 μs from the start timing of the specific communication slot, and is set in advance for the communication device D4. As a result, the communication device D4 performs command communication and response communication in the period between the response communication by the communication device D3 in the specific communication slot and the command communication in the next communication slot.

[0137] 11(b), the interlock communication includes command communication (TX) in which the communication unit 18 of the transporting vehicle 6 transmits a command signal to the communication device D4, and response communication (RX) in which the communication device D2 transmits a response signal to the communication unit 18 of the transporting vehicle 6. For example, the period of the command communication is 170 μs, and the period of the response communication is 180 μs. Also, for example, the period between the command communication and the response communication in a specific communication slot is 100 μs, and the period between the response communication in a specific communication slot and the command communication in the next communication slot is 550 μs.

[0138] As a result, even if the communication devices D3 and D4 belong to the same group, they perform command communication and response communication at timings that do not overlap with each other in the communication slots, thereby enabling further multiplexing.

[0139] [6. Modification 2] Next, an operation of the wireless communication system 2 according to Modification 2 of the embodiment will be described with reference to Fig. 12. Fig. 12 is a timing chart for explaining the operation of the wireless communication system 2 according to Modification 2 of the embodiment.

[0140] 12, each of the nine communication devices D1, ..., D9 performs interlock communication with the nine transport vehicles T1, ..., T9 while changing the communication channel it uses in the following order at each predetermined hopping period: "Channel CH1 → Channel CH2 → Channel CH3 → Channel CH1 → ..." Also, each of the nine communication devices D1, ..., D9 uses communication slots with slot numbers "1", ..., "9", and the communication slot with slot number "10" is unused.

[0141] In this situation, suppose that the tenth transport vehicle T10 receives a command from a higher-level device to transfer a FOUP 10 to a specific port 22 among the multiple ports 22. Before the transfer, the communication unit 18 of the transport vehicle T10 first checks whether any of the communication slots with slot numbers "1" to "9" are available for interlock communication between the transport vehicles T1 to T9. Specifically, the communication unit 18 of the transport vehicle T10 starts monitoring the RSSI (Received Signal Strength Indicator) on channel CH1, starts a count-up timer, and clears the communication slot usage counter to zero. As a result, the communication unit 18 of the transport vehicle T10 monitors the RSSI on channel CH1 for each communication slot (i.e., at 1 ms intervals) and calculates an average RSSI value over 1 ms based on the monitored RSSI.

[0142] If the calculated average RSSI value is equal to or greater than a threshold value (for example, −77 dbm), the communication unit 18 of the transporting vehicle T10 increments the communication slot usage counter by “1”.

[0143] The communication unit 18 of the transporting vehicle T10 monitors the RSSI for each communication slot for three predetermined hopping periods (channel CH1 → channel CH2 → channel CH3). That is, the communication unit 18 of the transporting vehicle T10 reads out the counter value of the communication slot counter and the measurement value of the count-up timer after repeating the RSSI monitoring 30 times in total (= the number of predetermined hopping periods "3" × the number of communication slots "10").

[0144] Then, if the counter value of the communication slot counter has reached "30", the communication unit 18 of the transporting platform T10 determines that there are no available communication slots, and performs the above-mentioned RSSI monitoring again.

[0145] On the other hand, if the counter value of the communication slot counter has not reached "30," the communication unit 18 of the transporting vehicle T10 determines that there is an available communication slot and stops monitoring the RSSI. Then, if the measurement value of the count-up timer is 30 ms or more (= the predetermined hopping period "10 ms" x 3 periods), the communication unit 18 of the transporting vehicle T10 starts the countdown timer with the difference between 30 ms and the measurement value of the count-up timer. Then, when the time counted down by the countdown timer (i.e., the transmission execution waiting period for channel CH1) has elapsed, the communication unit 18 of the transporting vehicle T10 uses the available communication slot with slot number "10" to transmit a trigger signal to the communication device D10.

[0146] As a result, the communication unit 18 of the transport cart T10 sends a trigger signal to the communication device D10 using the communication slot with slot number "10", which has been confirmed through monitoring to be not being used for interlock communication by other transport carts T1, ..., T9, thereby preventing collisions in interlock communication.

[0147] In this modified example, the communication unit 18 of the transport cart T10 monitors the RSSI for three cycles of the specified hopping period, but this is not limited to this, and the RSSI may be monitored for at least one cycle of the specified hopping period.

[0148] (Other Modifications, etc.) While the wireless communication system of the present invention has been described above based on the above embodiment, the present invention is not limited to the above embodiment. The present invention also includes modifications that can be made to the above embodiment by those skilled in the art, and other modifications that can be realized by arbitrarily combining the components of the above embodiment.

[0149] In the above-described embodiments, each component may be configured with dedicated hardware, or may be realized by executing a software program suitable for each component. Each component may be realized by a program execution unit such as a CPU or processor reading and executing a software program recorded on a recording medium such as a hard disk or semiconductor memory.

[0150] The wireless communication system according to the present invention can be applied to, for example, a semiconductor manufacturing system for transporting FOUPs by a transport cart that travels along a track installed on the ceiling.

[0151] 2 Wireless communication system 4 Semiconductor manufacturing equipment 6 Transport vehicle 8 Communication device 10 FOUP 12, 14 Track 16 Gripper 18, 26, 30 Communication unit 20 Loading / unloading port 22 Port 24, 28, 32 Control unit

Claims

1. A wireless communication system comprising: a communication unit mounted on a transport vehicle that transports articles by traveling along a track; and a plurality of communication devices that are communicatively connected to a plurality of ports through which the articles are transferred to and from the transport vehicle and that perform wireless communication with the communication unit, wherein the communication unit and the plurality of communication devices change communication channels at each predetermined hopping period, and each of the plurality of communication devices performs wireless communication with the communication unit using a plurality of communication slots that time-divide the predetermined hopping period, and when a trigger signal is received from the communication unit, each of the plurality of communication devices performs interlock communication with the communication unit to permit the transport vehicle to transfer the articles to and from the plurality of ports, the plurality of communication devices are grouped into a plurality of mutually different groups, each of the plurality of groups including a group of communication devices that are arranged in close proximity to each other, and the plurality of communication device groups that belong to each of the plurality of groups change communication channels at each predetermined hopping period so as to perform wireless communication with the communication unit using a plurality of mutually different communication channels in the predetermined hopping period.

2. The wireless communication system according to claim 1, wherein the plurality of communication device groups belonging to each of the plurality of groups change the communication channel at each predetermined hopping period so that the same communication channel is used within the same group, and different communication channels are used between different groups at any given time to perform wireless communication with the communication unit.

3. The wireless communication system of claim 1, wherein each of the plurality of communication device groups includes a first communication device and a second communication device, the first communication device performs wireless communication with the communication unit at a first timing in a specific communication slot among the plurality of communication slots, and the second communication device performs wireless communication with the communication unit at a second timing different from the first timing in the specific communication slot.

4. The wireless communication system according to claim 1, wherein at least one of the plurality of communication devices is a master communication device that is set as a master, and performs time synchronization with slave communication devices that are set as slaves other than the at least one communication device.

5. The wireless communication system according to claim 4, wherein if one of the slave communication devices is unable to receive time synchronization information from the master communication device for a predetermined period of time, it acts as the master communication device and performs time synchronization with other communication devices.

6. The wireless communication system according to claim 4, wherein the plurality of communication devices transmit and receive data to and from each other wirelessly.

7. A wireless communication system according to any one of claims 1 to 6, wherein before the transport vehicle equipped with the communication unit delivers or receives the item to a specific port among the plurality of ports, the communication unit (i) first monitors for at least one cycle of the predetermined hopping period to check whether or not there is a communication slot among the plurality of communication slots that is not being used for the interlock communication by another transport vehicle other than the transport vehicle in question, and (ii) then transmits the trigger signal to the communication device using a communication slot that has been confirmed by the monitoring to be not being used for the interlock communication by the other transport vehicle.

8. A control method for a wireless communication system including a communication unit mounted on a transport vehicle that transports articles by traveling along a track, and a plurality of communication devices that are communicatively connected to a plurality of ports through which the articles are transferred to and from the transport vehicle and that perform wireless communication with the communication unit, wherein each of the plurality of communication devices, upon receiving a trigger signal from the communication unit, performs interlock communication with the communication unit to permit the transport vehicle to transfer the articles to and from the plurality of ports, and the plurality of communication devices are grouped into a plurality of mutually different groups, each of which includes a group of communication devices that are arranged in close proximity to one another, the control method comprising the steps of: (a) the communication unit and the plurality of communication devices changing communication channels at every predetermined hopping period, and each of the plurality of communication devices performing wireless communication with the communication unit using a plurality of communication slots that time-divide the predetermined hopping period, and in (a), changing the communication channel at every predetermined hopping period so that the plurality of communication device groups respectively belonging to the plurality of groups perform wireless communication with the communication unit using a plurality of communication channels that are mutually different from one another in the predetermined hopping period.

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