Patent Publication Number: US-2021179153-A1

Title: Conveyance vehicle system

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a transport vehicle system. 
     2. Description of the Related Art 
     As a conventional transport vehicle system, a transportation carriage system includes a track that extends over a plurality of areas, a plurality of overhead transport vehicles (transport vehicles) configured to travel in one direction along the track, a plurality of placement units (buffers) configured for each transport vehicle to deliver or receive an article thereto or therefrom, a plurality of area controllers (logic bay controllers) each configured to consider the corresponding one of the areas as a jurisdiction area and cause a transport vehicle in the jurisdiction area to execute various instructions, and a host controller (production controller) configured to transmit conveyance instructions to the area controllers is known (see Japanese Unexamined Patent Publication No. 2009-9365, for example). 
     In the system configured to control various operations of the transport vehicles individually for the areas as described above, an area boundary exists between one jurisdiction area and another jurisdiction area different from the one jurisdiction area. In one jurisdiction area, a special section that cannot be entered without passing through another jurisdiction area may exist. If a conveyance instruction the conveyance source of which is a placement unit belonging to such a special section is issued, this conveyance instruction cannot be handled efficiently, and the handling time for a transport vehicle to reach the placement unit to be loaded with an article tends to increase. 
     SUMMARY OF THE INVENTION 
     Preferred embodiments of the present invention provide transport vehicle systems that are each able to efficiently handle conveyance instruction, even when conveyance instructions are provided by placement units that belong to special sections. 
     A transport vehicle system according to a preferred embodiment of the present invention includes a track that extends over a plurality of areas, a plurality of transport vehicles that are able to travel in one direction along the track, a plurality of placement units provided along the track to deliver or receive an article to or from the placement units for each transport vehicle, a plurality of area controllers that each receive, from a host controller, a conveyance instruction to convey an article placed on one of the placement units, determine the corresponding one of the areas as a jurisdiction area, and control the transport vehicle in the jurisdiction area to execute various instructions. When, in one jurisdiction area, the placement unit belonging to a special section being a section that is unable to be entered without passing through a second jurisdiction area different from the one jurisdiction area is considered as a special placement unit, each area controller, in response to receiving from the host controller the conveyance instruction destined for the one special placement unit belonging to a first jurisdiction area that is a jurisdiction area of the area controller, transmits a movement instruction to control an empty transport vehicle to move toward the first jurisdiction area to another area controller configured to control the transport vehicle in the second jurisdiction area, and also controls an empty transport vehicle that has become available in the first jurisdiction area after transmission of the movement instruction to execute the conveyance instruction. 
     There is a situation in which, even after receiving a conveyance instruction the conveyance source of which is a special placement unit belonging to a first jurisdiction area, its area controller is not able to immediately control a transport vehicle to move to the special placement unit for loading. Thus, in a conventional transport vehicle system, the host controller transmits the conveyance instruction to another area controller having jurisdiction over another area, and this other area controller controls an empty transport vehicle in a second jurisdiction area to execute the conveyance instruction. However, in this case, even if an empty transport vehicle has become available in the special section of the first jurisdiction area before a transport vehicle in the second jurisdiction area reaches the special placement unit, the other area controller that has received the conveyance instruction is not able to control the transport vehicle in the first jurisdiction area over which it has no jurisdiction. Thus, the transport vehicle in the first jurisdiction area instead passes by the special placement unit even though the transport vehicle is an empty transport vehicle. Accordingly, a problem arises in which the conveyance efficiency is significantly reduced, and the handling time is significantly increased. The term “empty transport vehicle” herein indicates a transport vehicle that is loaded with no article and is able to be loaded with (is able to convey) an article. 
     According, in the transport vehicle system described above, when a conveyance instruction the conveyance source of which is a special placement unit in one area has been issued, the host controller transmits the conveyance instruction to an area controller having jurisdiction over an area to which the special placement unit belongs first, instead of transmitting the conveyance instruction to an area controller of another area to which the special placement unit does not belong. The area controller that has received the conveyance instruction transmits, to another area controller, a movement instruction to cause an empty transport vehicle to move toward the first jurisdiction area. Thus, the area controller having jurisdiction over the area to which the special placement unit belongs is able to control a transport vehicle in the first jurisdiction area to execute the conveyance instruction, and the conveyance instruction is able to be assigned to both of a transport vehicle (a transport vehicle in a second jurisdiction area) that is going to enter the first jurisdiction area in accordance with the preceding movement instruction and an empty transport vehicle that becomes available in the first jurisdiction area. Therefore, a reduction of the conveyance efficiency described above is able to be significantly reduced or prevented, and thus even when a conveyance instruction the conveyance source of which is a placement unit belonging to a special section has been issued, this conveyance instruction is able to be handled efficiently. 
     In the transport vehicle system according to a preferred embodiment of the present invention, the empty transport vehicle in the first jurisdiction area to be detected by the area controller after the transmission of the movement instruction may be an empty transport vehicle that enters the first jurisdiction area from the second jurisdiction area or an empty transport vehicle that becomes available by placing an article onto the special placement unit belonging to the first jurisdiction area. 
     In a transport vehicle system according to a preferred embodiment of the present invention, the area controller may delete the movement instruction transmitted to the other area controller after controlling the empty transport vehicle that has become available in the first jurisdiction area to execute the conveyance instruction. Accordingly, at the time when an empty transport vehicle has become available in the first jurisdiction area, movement of an empty transport vehicle traveling toward the first jurisdiction area is able to be canceled, and thus influence on the conveying capability in the other area is able to be significantly reduced. 
     In a transport vehicle system according to a preferred embodiment of the present invention, the area controller is able to detect whether an empty transport vehicle is present in the first jurisdiction area before transmitting the movement instruction to the other area controller. Accordingly, before transmitting the movement instruction to the other area controller, a necessity of the movement instruction is able to be checked, and thus influence on the conveying capability in the other area is able to be reduced or minimized. 
     In a transport vehicle system according to a preferred embodiment of the present invention, the area controller may detect whether an empty transport vehicle is present in the first jurisdiction area and upstream of the one special placement unit before transmitting the movement instruction to the other area controller. Accordingly, a check range of the necessity to transmit the movement instruction to the other area controller is able to reduced or minimized, and thus the handling speed is able to be improved. 
     According to preferred embodiments of the present invention, even when a conveyance instruction the conveyance source of which is a placement unit belonging to a special section has been issued, the conveyance instruction is able to be handled efficiently. 
     The above and other elements, features, steps, characteristics, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic plan view illustrating a transport vehicle system according to a preferred embodiment of the present invention. 
         FIG. 2  is a schematic side view illustrating a transport vehicle, a delivery port, and a buffer of the transport vehicle system shown in  FIG. 1 . 
         FIG. 3  is a plan view for describing a special section and non-special section in an area of the transport vehicle system shown in  FIG. 1 . 
         FIG. 4  is a sequence diagram of the transport vehicle system shown in  FIG. 1 . 
         FIG. 5  is a sequence diagram of the transport vehicle system shown in  FIG. 1 . 
         FIG. 6  is a sequence diagram of the transport vehicle system shown in  FIG. 1 . 
         FIG. 7  is a sequence diagram of the transport vehicle system shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will now be described in detail with reference to the drawings. In description of the drawings, like elements are designated by like reference signs, and duplicate description is omitted. The terms “upstream” and “downstream” used in the description of preferred embodiments of the present invention mean upstream and downstream in a traveling direction in which overhead transport vehicles (transport vehicles)  6  move along a one-way (unidirectional) track  4 . 
     As illustrated in  FIG. 1  and  FIG. 2 , a transport vehicle system  1  is a system in which the overhead transport vehicles  6  are able to move along the track to convey articles  10  between placement units  8 ,  8 . Examples of the articles  10  include containers, for example, a FOUP that stores a plurality of semiconductor wafers and a reticle pod that stores glass substrates, and general parts. The following describes an example of the transport vehicle system  1  in a factory, for example, in which the overhead transport vehicles  6  (hereinafter, simply called “transport vehicles  6 ”) travel along the one-way track  4  installed on, for example, a ceiling of the factory. As illustrated in  FIG. 1 , the transport vehicle system  1  includes the track  4 , the transport vehicles  6 , a plurality of placement units  8 , and a plurality of area controllers  50 A,  50 B,  50 C. 
     The track  4  extends over a plurality of areas A 1 , A 2 , A 3 . The track  4  is installed near the ceiling in a space overhead of an operator, for example. The track  4  is suspended from the ceiling, for example. The track  4  is a predetermined traveling path for the transport vehicles  6  to travel. The track  4  is supported by posts  40 ,  40 . 
     Each transport vehicle  6  travels along the track  4  to convey an article  10 . The transport vehicle  6  is able to transfer the article  10 . The transport vehicle  6  is an overhead-traveling automated guided transport vehicle. The number of the transport vehicles  6  that the transport vehicle system  1  includes is not limited to a particular number, and is preferably two or more, for example. 
     As illustrated in  FIG. 2 , each transport vehicle  6  includes a traveling device  18  that moves the transport vehicle  6  along the track  4  and a power-receiving communicator  20  that receives electric power from the track  4  by noncontact feeding, for example. The transport vehicle  6  uses a communication line (feeder line) of the track  4 , for example, to communicate with any one of the area controllers  50 A,  50 B,  50 C. Herein, the transport vehicle  6  may communicate with any one of the area controllers  50 A,  50 B,  50 C via an electric supply line provided along the track  4 . The transport vehicle  6  includes a body frame  22 , a cross-feeder  24 , a θ drive  26 , a lifting driver  28 , a lifting platform  30 , and a fall-prevention cover  33 . 
     The cross-feeder  24  laterally feeds the θ drive  26 , the lifting driver  28 , and the lifting platform  30  all together in a direction orthogonal or substantially orthogonal to the traveling direction of the track  4 . The θ drive  26  turns at least either one of the lifting driver  28  and the lifting platform  30  within a predetermined angle range in a horizontal plane. The lifting driver  28  winds or pays out suspensions, for example, wires, ropes, and belts, to raise or lower the lifting platform  30 . The lifting platform  30  is provided with a chuck to hold or release an article  10 . The fall-prevention cover  33  is provided in a pair to the front and the rear of the transport vehicle  6  in the traveling direction. The fall-prevention cover  33  extends and retracts claws (not illustrated), for example, to prevent the article  10  from falling during conveyance. 
     Each placement unit  8  to and from which a transport vehicle  6  delivers and receives an article  10  includes a buffer  8 A and a delivery port  8 B. The buffer  8 A is a placement unit on which the article  10  is temporarily placed. For example, on the buffer  8 A, an article  10  being conveyed by the transport vehicle  6  is temporarily placed when the article  10  is not able to be transferred onto a delivery port  8 B as a destination, for example, when another article  10  has already been placed on the delivery port  8 B. The delivery port  8 B is a placement unit to deliver and receive an article  10  to and from a semiconductor processing device  12  including, for example, cleaning equipment, deposition equipment, lithography equipment, etching equipment, thermal treatment equipment, and planarization equipment. Herein, the processing device  12  is not limited to a particular one, and may be a device of various types or a stocker, for example. 
     Each placement unit  8  is provided along the track  4 , and is provided in a position where an article  10  is able to be delivered to and received from a transport vehicle  6 . For example, the buffer  8 A is located beside the track  4  (see  FIG. 2 ). In this case, the transport vehicle  6  laterally feeds the lifting driver  28 , for example, with the cross-feeder  24 , and slightly raises and lowers the lifting platform  30  to deliver and receive the article  10  to and from the buffer  8 A. The buffer  8 A may be located directly below the track  4 . For example, the delivery port  8 B is located directly below the track  4  (see  FIG. 2 ). In this case, the transport vehicle  6  raises and lowers the lifting platform  30  to deliver and receive the article  10  to and from the delivery port  8 B. The delivery port  8 B may be located beside and below the track  4 . 
     The area controllers  50 A,  50 B,  50 C are each an electronic controller including a central processing unit (CPU), a read-only memory (ROM), and a random-access memory (RAM). The area controllers  50 A,  50 B,  50 C each may be defined by, for example, software including a program stored in the ROM and loaded into the RAM to be executed by the CPU. The area controllers  50 A,  50 B,  50 C each may be implemented as hardware, for example, an electronic circuit. 
     The area controllers  50 A,  50 B,  50 C are provided to the areas A 1 , A 2 , A 3 , respectively. The respective area controllers  50 A,  50 B,  50 C are provided to correspond to the respective areas A 1 , A 2 , A 3 . Specifically, the area controllers  50 A,  50 B,  50 C consider the areas A 1 , A 2 , A 3  respectively as jurisdiction areas, which are areas that the area controllers  50 A,  50 B,  50 C are in charge of controlling. In other words, one area controller considers one area as its jurisdiction area. The number of the area controllers is preferably the same as the number of the areas, for example. Thus, one area controller considers any one of the areas as its jurisdiction area. 
     The area controller  50 A communicates with a plurality of transport vehicles  6  in the jurisdiction area A 1  (hereinafter, also called “its first jurisdiction area A 1 ”) of the area controller  50 A to control the transport vehicles  6  in its first jurisdiction area A 1 . In other words, the area controller  50 A controls the transport vehicles  6  in the jurisdiction area A 1  to execute various instructions. Similar to the area controller  50 A, the area controller  50 B communicates with a plurality of transport vehicles in its first jurisdiction area A 2  to control the transport vehicles  6  in its first jurisdiction area A 2 . Also similar to the area controller  50 A, the area controller  50 C communicates with a plurality of transport vehicles  6  in its first jurisdiction area A 3  to control the transport vehicles  6  in its first jurisdiction area A 3 . The area controllers  50 A,  50 B,  50 C communicate with the host controller  60  by wire or radio. 
     The host controller  60  is an electronic controller including a CPU, a ROM, and a RAM. The host controller  60  may be defined by, for example, software including a program stored in the ROM is loaded into the RAM to be executed by the CPU. The host controller  60  may be implemented as hardware, for example, an electronic circuit. The host controller  60  communicates with any one of the area controllers  50 A,  50 B,  50 C by wire or radio, and transmits to any one of the area controllers  50 A,  50 B,  50 C a conveyance instruction to control a transport vehicle  6  to convey an article  10 . In the present preferred embodiment, the host controller  60  outputs to any one of the area controllers  50 A,  50 B,  50 C a conveyance instruction (the conveyance source of which is a placement unit  8 ) to convey an article  10  placed on the placement unit  8  to another predetermined placement unit  8 . 
     In  FIG. 1 , a layout of the track  4  according to the present preferred embodiment is illustrated. In the present preferred embodiment, the track  4  includes intra-bay traveling paths  42 ,  43  respectively provided in the areas A 2 , A 3  and one inter-bay traveling path  41  that provides a communication path between the two intra-bay traveling paths  42 ,  43 . The transport vehicles  6  are able to travel between the two intra-bay traveling paths  42 ,  43  by travelling on the inter-bay traveling path  41 . According to the structure of the intra-bay traveling paths  42 ,  43  and the inter-bay traveling path  41 , the transport vehicles  6  travel in one direction clockwise (directions indicated by arrows in  FIG. 1  and  FIG. 3 ). 
     In the predetermined traveling direction of the transport vehicles  6 , when a location where a track  4  branches off is a branch portion B, a location where tracks  4  merge is a merging portion C, and a boundary between areas is a boundary portion D, a track portion that is located between any pair among the branch portion B, the merging portion C, and the boundary portion D is defined as a “section”. 
     In the system as described above in which various operations of the transport vehicles  6  that are present in the areas A 1 , A 2 , A 3  are controlled respectively by the area controllers  50 A,  50 B,  50 C, in one area, there is a section that is not able to be entered without passing through another area that is different from the one area. This section is defined as “special section”. In the layout of the track  4  illustrated in  FIG. 1 , a section, in the area A 2 , which is not able to be entered without passing through the other area A 1  different from the area A 2  (section extending from a boundary portion D to the merging portion C in the traveling direction of the transport vehicles  6 ) and a section, in the area A 3 , which is not able to be entered without passing through the other area A 1  different from the area A 3  (section extending from a boundary portion D to the merging portion C in the traveling direction of the transport vehicles  6 ) correspond to special sections (see  FIG. 3 ). 
     As illustrated in  FIG. 3 , in each of the areas A 2 , A 3 , in the traveling direction of the transport vehicles  6 , a section L 2  extending from a merging portion C to a branch portion B, a section L 3  extending from the branch portion B to the merging portion C, and a section L 4  extending from the branch portion B to a boundary portion D are provided. The sections L 2 , L 3 , L 4  are able to be entered from another section in the same area. For example, in the area A 2 , the section L 2  is able to be entered from both the section L 1  and the section L 3  in the same area A 2 . The section L 3  and the section L 4  are able to be entered from the section L 2  in the same area A 2 . In the present preferred embodiment, the sections L 2 , L 3 , L 4  are defined as non-special sections. 
     In the section L 1 , which is a special section in each of the areas A 2 , A 3  (hereinafter, called “special section L 1 ”), placement units  8  are provided along this section. As illustrated in  FIG. 1 , in the present preferred embodiment, three placement units  8 ,  8 ,  8  are provided. In the present preferred embodiment, these placement units  8  belonging to the special section L 1  are referred to as special placement units  80 A,  80 B,  80 C from the upstream in the predetermined traveling direction of the transport vehicles  6 . 
     The following describes operation of the area controllers  50 B,  50 C in the above-described layout of the track  4 . The area controller  50 B ( 50 C), in response to receiving from the host controller  60  a conveyance instruction (the conveyance source of which is the special placement unit  80 C) to convey to a predetermined placement unit  8  an article  10  placed on one special placement unit (e.g.,  80 C) of the first jurisdiction area A 2  (A 3 ) that is its first jurisdiction area, transmits a movement instruction to control a transport vehicle  6  that is empty to move toward the first jurisdiction area A 2  (A 3 ) to the other area controller  50 A configured to control a transport vehicle  6  in the area A 1  that is adjacent to the special section L 1  where the special placement unit  80 C is positioned. The transport vehicle  6  that is empty (hereinafter, called “empty transport vehicle  6 ”) indicates a transport vehicle that is not loaded with (holds) any article  10  and is able to be loaded with an article  10 . 
     The area controller  50 B ( 50 C) in the present preferred embodiment detects whether an empty transport vehicle  6  is present in the first jurisdiction area A 2  (A 3 ) and upstream of the one special placement unit  80 C before transmitting the movement instruction to the other area controller  50 A. The area controller  50 B ( 50 C) transmits the above-described movement instruction to the area controller  50 A only when an empty transport vehicle  6  is not present in the first jurisdiction area A 2  (A 3 ) or upstream of the one special placement unit  80 C. If an empty transport vehicle  6  is present in the first jurisdiction area A 2  (A 3 ) and upstream of the one special placement unit  80 C, the area controller  50 B ( 50 C) controls this empty transport vehicle  6  to execute the conveyance instruction. 
     If the area controller  50 B ( 50 C) detects that an empty transport vehicle  6  has become available in the first jurisdiction area A 2  (A 3 ) after transmission of the above-described movement instruction, the area controller  50 B ( 50 C) controls the empty transport vehicle  6  in the first jurisdiction area A 2  (A 3 ) to execute the conveyance instruction. The expression “after transmission” herein includes a meaning of “at substantially the same time”. Candidates for an empty transport vehicle  6  in the first jurisdiction area A 2 (A 3 ) to be detected after transmission of the movement instruction by the area controller  50 B ( 50 C) include an empty transport vehicle  6  that enters the first jurisdiction area A 2  (A 3 ) from the second jurisdiction area A 1  and an empty transport vehicle  6  that becomes available by placing an article  10  onto a placement unit  8  belonging to the first jurisdiction area A 2  (A 3 ) (by completing a conveyance instruction). After controlling the empty transport vehicle  6  that has become available in the first jurisdiction area A 2  (A 3 ) to execute the conveyance instruction, the area controller  50 B ( 50 C) transmits to the other area controller  50 A an instruction to delete the movement instruction transmitted to the other area controller  50 A. 
     The following describes one example of processes performed by the transport vehicle system  1  with reference to sequence diagrams in  FIG. 4  to  FIG. 7 . Processes when a conveyance instruction (the conveyance source of which is the special placement unit  80 C) to convey an article  10  placed on the special placement unit  80 C in the area A 2  to a predetermined placement unit  8  are described below. In the following, a procedure of operation of the one area controller  50 B among the area controllers  50 A,  50 B,  50 C is described. 
     As illustrated in  FIG. 4 , the host controller  60  transmits, as a conveyance instruction, a loading instruction at the special placement unit  80 C in the area A 2  to the area controller  50 B having jurisdiction over the area A 2  (step S 1 ). The area controller  50 B, in response to receiving the loading instruction from the host controller  60 , transmits to the host controller  60  a signal to notify it of having received the loading instruction (step S 2 ). The area controller  50 B detects whether an empty transport vehicle  6  capable of moving toward the special placement unit  80 C is present in the first jurisdiction area A 2  (step S 3 ). Hereinafter, description is made on the assumption that such an empty transport vehicle  6  has been determined to be absent in the first jurisdiction area A 2 . 
     The area controller  50 B transmits a movement instruction destined for the area A 2  to the area controller  50 A having jurisdiction over the area A 1  that is different from the first jurisdiction area A 2  (step S 4 ). The area controller  50 A, in response to receiving the movement instruction from the area controller  50 B, transmits to the area controller  50 B a signal to notify the area controller  50 B of having received the movement instruction (step S 5 ). The area controller  50 A determines whether an empty transport vehicle  6  is present in the first jurisdiction area A 1  (step S 6 ). The area controller  50 A continuously communicates with all transport vehicles  6  that are present in the first jurisdiction area A 1  at predetermined intervals (e.g., several times per second), and receives a status report from each transport vehicle  6 . The area controller  50 A determines the states of all the transport vehicles  6  based on such status reports, and thus is able to determine whether an empty transport vehicle  6  is present in the first jurisdiction area A 1 . 
     The following describes a case when the area controller  50 A has determined that an empty transport vehicle  6  is present in the first jurisdiction area A 1  (step S 7 ). A case when the area controller  50 A has determined that no empty transport vehicle  6  is present will be described below. 
     If the area controller  50 A determines that an empty transport vehicle  6  is present in the first jurisdiction area A 1 , the area controller  50 A transmits to this empty transport vehicle  6  a movement instruction to move toward the area A 2  (step S 8 ). The transport vehicle  6 , in response to receiving the movement instruction from the area controller  50 A, transmits to the area controller  50 A a signal to notify it of having received the movement instruction (step S 9 ), and starts moving toward the area A 2  (step S 11 ). The area controller  50 A, in response to receiving the signal to notify it of having received the movement instruction from the transport vehicle  6 , deletes the movement instruction stored in a memory (not illustrated) that the area controller  50 A includes (step S 10 ). 
     As illustrated in  FIG. 5 , the transport vehicle  6  executes the movement instruction transmitted at step S 8 , and thus enters the area A 2  (step S 12 ). The transport vehicle  6  assigned with the movement instruction transmits a request for entry into the area A 2  to the area controller  50 A. The area controller  50 A communicates with the area controller  50 B, and also transmits an entry permission to the transport vehicle  6 . The transport vehicle  6  enters the area A 2  and transmits an entry report to the area controller  50 B (step S 13 ), and the area controller  50 B confirms (is notified) that the transport vehicle  6  has entered (step S 14 ). The entry report into the area A 2  is also transmitted to the area controller  50 A via the area controller  50 B. 
     The area controller  50 B, after confirming that the empty transport vehicle  6  has entered the first jurisdiction area A 2 , transmits an instruction to be loaded with the article  10  placed on the special placement unit  80 C to the transport vehicle  6  that has entered the area A 2  (step S 15 ). The transport vehicle  6 , in response to receiving this loading instruction from the area controller  50 B, transmits to the area controller  50 B a signal to notify the area controller  50 B of having received the loading instruction (step S 16 ), and continues moving toward the special placement unit  80 C. The transport vehicle  6  that has reached the special placement unit  80 C is loaded with the article  10  placed on the special placement unit  80 C, and conveys the article  10  to a predetermined location (step S 20 ). Herein, in the conveyance instruction including the loading instruction, information on a conveyance destination of the article  10  is included. 
     The area controller  50 B receives the signal to notify the area controller  50 B of having received the loading instruction from the transport vehicle  6 , thus confirming that the loading instruction has been assigned to the transport vehicle  6  (step S 17 ). Subsequently, the area controller  50 B transmits an assignment report to the host controller  60  (step S 18 ), and also causes the area controller  50 A to cancel the movement instruction transmitted thereto (step S 19 ). In the present preferred embodiment, because the movement instruction stored in the memory of the area controller  50 A has already been deleted in the process at step S 10 , no process will be performed in accordance with the movement instruction at step S 19 . Thus, a series of processes when a conveyance instruction to convey the article  10  placed on the special placement unit  80 C in the area A 2  to the predetermined placement unit  8  has been issued ends. 
     The following describes a case when the area controller  50 A has determined at step S 6  that no empty transport vehicle  6  is present with reference to  FIG. 6  and  FIG. 7 . Because processes up to step S 6  are the same as those described above, duplicate description is omitted. As illustrated in  FIG. 6 , if the area controller  50 A determines that no empty transport vehicle  6  is present in the first jurisdiction area A 1  (step S 30 ), the area controller  50 A is not able to issue a movement instruction to a transport vehicle  6 . Thus, the area controller  50 A continues monitoring the first jurisdiction area A 1  with the movement instruction being stored in the memory thereof. 
     Herein, at the special placement unit  80 A or  80 B upstream of the special placement unit  80 C in the area A 2 , when a transport vehicle  6  has been unloaded with an article  10  (step S 31 ), this empty transport vehicle  6  newly becomes available in the area A 2 , and thus an empty transport vehicle  6  becomes present. Thus, the area controller  50 B monitoring the area A 2  determines that an empty transport vehicle  6  able to move toward the special placement unit  80 C is present in the first jurisdiction area A 2  (step S 32 ). 
     As illustrated in  FIG. 7 , the area controller  50 B transmits a loading instruction at the special placement unit  80 C to the empty transport vehicle  6  that has newly become available in the area A 2  (step S 33 ). The transport vehicle  6 , in response to receiving the loading instruction from the area controller  50 B, transmits a signal to notify the area controller  50 B of having received the loading instruction to the area controller  50 B (step S 34 ), and starts moving toward the special placement unit  80 C. The transport vehicle  6  that has reached the special placement unit  80 C is loaded with the article  10  placed on the special placement unit  80 C, and conveys the article  10  to a predetermined location (step S 39 ). Herein, in the conveyance instruction including the loading instruction, information on a conveyance destination of the article  10  is included. 
     The area controller  50 B, after receiving the signal to notify area controller  50 B of having received the loading instruction from the transport vehicle  6 , confirms that the loading instruction has been assigned to the transport vehicle  6  (step S 35 ). Subsequently, the area controller  50 B transmits an assignment report to the host controller  60  (step S 36 ), and also controls the area controller  50 A to cancel the movement instruction (step S 37 ). In other words, the movement instruction stored in the memory of the area controller  50 A is deleted (step S 38 ). Thus, a series of processes when a conveyance instruction to convey the article  10  placed on the special placement unit  80 C in the area A 2  to the predetermined placement unit  8  has been issued ends. 
     Although detailed description is omitted, the area controller  50 C also implements the same or similar procedure of operation as the area controller  50 B. 
     The following describes features of the transport vehicle system  1  according to the preferred embodiment described above. A transport vehicle system  1  in which the area controllers  50 A,  50 B,  50 C respectively consider the areas A 1 , A 2 , A 3  as the jurisdiction areas A 1 , A 2 , A 3  and control various operations of transport vehicles  6  has problems described below. Specifically, each area controller  50 B ( 50 C) of the transport vehicle system  1 , even after receiving a conveyance instruction destined for the special placement unit  80 C in the first jurisdiction area A 2  (A 3 ), is not able to control a transport vehicle  6  to move to the special placement unit  80 C to be loaded in most cases. Thus, a conventional host controller  60  transmits the conveyance instruction to the other area controller  50 A having jurisdiction over the other area A 1 , and this other area controller  50 A controls an empty transport vehicle  6  in the jurisdiction area A 1  to execute the conveyance instruction. 
     However, in this case, even if an empty transport vehicle  6  has become available in the special section L 1  of the area A 2  (A 3 ) before a transport vehicle  6  in the second jurisdiction area A 1  reaches the special placement unit  80 C, the other area controller  50 A that has received the conveyance instruction is not able to control the transport vehicle  6  that has become available in the area A 2  over which it has no jurisdiction. Thus, the transport vehicle  6  in the first jurisdiction area A 2  (A 3 ) instead passes by the special placement unit  80 C even though the transport vehicle  6  is not loaded with an article  10  (that is, the transport vehicle  6  is empty). Accordingly, the conveyance efficiency is reduced, and the handling time is increased. 
     In the transport vehicle system  1  according to the preferred embodiment described above, when a conveyance instruction the conveyance source of which is the special placement unit  80 C in the area A 2  (A 3 ) has been issued, the host controller  60  first transmits the conveyance instruction to the area controller  50 B ( 50 C) having jurisdiction over the area A 2  (A 3 ) to which the special placement unit  80 C belongs, instead of transmitting the conveyance instruction to the other area controller  50 A to which the special placement unit  80 C does not belong. The area controller  50 B ( 50 C) that has received the conveyance instruction transmits, to the other area controller  50 A, a movement instruction to cause an empty transport vehicle  6  to move toward the area A 2 . According to the processes described above, the area controller  50 B ( 50 C) having jurisdiction over the area A 2  (A 3 ) to which the special placement unit  80 C belongs is able to control a transport vehicle  6  to execute the conveyance instruction, and the conveyance instruction is able to be assigned to both of a transport vehicle  6  (a transport vehicle  6  in the second jurisdiction area A 1 ) that is going to enter the area A 2  (A 3 ) in accordance with the preceding movement instruction and an empty transport vehicle  6  that becomes available in the area A 2  (A 3 ). Therefore, a reduction of the conveyance efficiency described above is able to be significantly reduced or prevented, and thus even when a conveyance instruction the conveyance source of which is a placement unit belonging to the special section L 1  has been issued, this conveyance instruction is able to be handled efficiently. 
     In the transport vehicle system  1  according to the preferred embodiment described above, the area controller  50 B ( 50 C) deletes the movement instruction transmitted to the area controller  50 A after causing the empty transport vehicle  6  that has become available in the first jurisdiction area A 2  (A 3 ) to execute the conveyance instruction. Accordingly, at the time when an empty transport vehicle  6  has become available in the area A 2  (A 3 ), movement of an empty transport vehicle  6  traveling toward the first jurisdiction area A 2  (A 3 ) is able to be canceled, and thus influence on the conveying capability in the other area A 1  is able to be significantly reduced. 
     In the transport vehicle system  1  according to the preferred embodiment described above, the area controller  50 B ( 50 C) detects whether an empty transport vehicle  6  is present in the first jurisdiction area A 2  (A 3 ) before transmitting the movement instruction to the area controller  50 A. Accordingly, before transmitting the movement instruction to the other area controller  50 A, a necessity of the transmission of the movement instruction is able to be checked, and thus influence on the conveying capability in the other area A 1  is able to be significantly reduced. 
     In the transport vehicle system  1  according to the preferred embodiment described above, the area controller  50 B ( 50 C) detects whether an empty transport vehicle  6  is present in the first jurisdiction area A 2  (A 3 ) and upstream of the one special placement unit  80 C before transmitting the movement instruction to the other area controller  50 A. Accordingly, a check range of the necessity to transmit the movement instruction to the other area controller  50 A is able to be significantly reduced, and a handling speed is able to be significantly improved. 
     Although preferred embodiments of the present invention have been described above, the present invention is not limited to the preferred embodiments, and various modifications may be made within the scope not departing from the gist of the present invention. 
     In the preferred embodiments described above, an example of control performed in layout of the track  4  as illustrated in  FIG. 1  has been described. However, the layout is not limited to this. Preferred embodiments of the present invention may be applied to any layout of the track  4  if the layout of the track  4  has a special section L 1 . 
     In the preferred embodiments described above, an example has been described in which the area controller  50 B ( 50 C), in response to receiving from the host controller  60  a conveyance instruction destined for the one special placement unit  80 C in the first jurisdiction area A 2  (A 3 ), transmits a movement instruction to the one area controller  50 A. However, the area controller  50 B ( 50 C) may transmit the movement instruction to a plurality of other area controllers. This modification may be implemented, for example, in a layout in which a merging portion is closer to the starting point of each special section L 1 . Accordingly, even if the layout in which a merging portion is closer to the starting point of each special section L 1  is provided, the movement instruction may be transmitted to a predetermined one of the other area controllers. Furthermore, the area controller  50 B ( 50 C) may transmit the movement instruction to area controllers having jurisdiction over not only the adjacent areas but also areas that are adjacent to the adjacent areas, for example, if the number of empty transport vehicles is relatively small. 
     In the preferred embodiments described above, an example has been described in which the area controller  50 B ( 50 C) transmits the movement instruction to the area controller  50 A only when an empty transport vehicle  6  is not present in the first jurisdiction area A 2  (A 3 ) or upstream of the one special placement unit  80 C. However, the present invention is not limited to this. For example, the area controller  50 B ( 50 C) may transmit the movement instruction to the other area controller  50 A without confirming that an empty transport vehicle  6  is present in the first jurisdiction area A 2  (A 3 ) and upstream of the one special placement unit  80 C. Even in this case, the movement instruction is deleted as soon as an empty transport vehicle  6  is found in the first jurisdiction area A 2  (A 3 ), and thus influence on the other area A 1  is able to be significantly reduced. 
     The transport vehicle systems  1  according to the preferred embodiments and the modifications have been described in which the traveling vehicles are transport vehicles  6  as one example. However, other examples of the traveling vehicles include automated guided traveling vehicles and stacker cranes configured to travel on a track installed on the ground or abutments. 
     While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.