Patent Publication Number: US-2022223446-A1

Title: Transport system and transport control method

Description:
TECHNICAL FIELD 
     This disclosure relates to a transport system and a transport control method. 
     BACKGROUND 
     In a semiconductor device manufacturing factory or the like, articles accommodating, for example, semiconductor wafers or reticles are transported by a transport system. A transport system includes, for example, transport vehicles that travel on a track and a controller that controls the transport vehicles. The transport vehicles transmit information such as their current location to the controller by communication such as wireless communication. The controller determines a transport vehicle to execute transportation on the basis of the position of the transport vehicle, and assigns a transport instruction to cause the determined transport vehicle to pick up an article at a pickup port, transport the article picked up at the pickup port to an unloading port, and unload the article (for example, see Japanese Patent No. 6176399). 
     In the above transport system, in some situations, a part of the route from the current position of the transport vehicle to the pickup port or a part of the route from the pickup port to the unloading port may be closed for maintenance and other reasons. Also, another transport vehicle may be at a stop on the above route for reasons such as congestion or failure. In such a situation, the transport vehicle is unable to travel on the closed route or on the route on which another transport vehicle is at a stop. In the transport system mentioned above, a no-traveling section is set in the section in which a traveling route cannot be secured, and a transport instruction is suspended and not assigned to any transport vehicle until this no-traveling section is lifted. Therefore, for example, if a no-traveling section is set in a part of the route from the load port of a processing apparatus serving as the pickup port to the unloading port, the transport vehicle will not perform pickup at the load port of the processing apparatus. As a result, the article is left to remain at the load port of the processing apparatus, and the processing apparatus becomes unable to accept a new article, resulting in a reduction in the utilization rate of the processing apparatus. 
     It could therefore be helpful to provide a transport system and a transport control method capable of avoiding an article from being left to remain at a pickup port. 
     SUMMARY 
     I thus provide: 
     A transport system may comprise: a transport vehicle that travels along a track; and a controller that controls the transport vehicles, wherein the controller assigns a first transport instruction instead of a transport instruction, to cause the transport vehicle to pick up an article at a pickup port and travel to a specified point on the downstream side of the pickup port in a traveling direction of the transport vehicle at which a traveling route can be secured on the track when a traveling route for the transport vehicle from a pickup port to an unloading port designated by the transport instruction cannot be secured on the track, and the controller assigns a second transport instruction to cause the transport vehicle to travel from the specified point to the unloading port and unload the article at the unloading port when a traveling route from the specified point to the unloading port can be secured at the point in time at which the transport vehicle approaches or reaches the specified point. 
     The first transport instruction may be an instruction to cause the transport vehicle to travel to the specified point and hold but not unload the article. The specified point may be set immediately before a branching part or a merging part on the track. When the specified point is set immediately before the branching part, the branching part may be a branching part closest to the pickup port. 
     The controller may determine whether or not to assign the first transport instruction and the second transport instruction, according to the type of at least one of the pickup port and the unloading port. The controller may assign the first transport instruction and the second transport instruction to the transport vehicle when the pickup port is a load port of a processing apparatus. The controller may assign the first transport instruction and the second transport instruction to the transport vehicle when the pickup port is a load port of a stocker. 
     The controller may assign the first transport instruction and the second transport instruction when the pickup port is a buffer on which an article can be placed, and the unloading port is a load port of a processing apparatus, and the controller may not assign the first transport instruction and the second transport instruction when the pickup port is the buffer and the unloading port is other than a load port of a processing apparatus. The controller may be a transport controller that controls a plurality of the transport vehicles, or an in-vehicle controller fitted in the transport vehicle. 
     A transport control method may be a method that controls a transport vehicle traveling along a track, the method comprising: assigning a first transport instruction, instead of a transport instruction, to cause the transport vehicle to pick up an article at a pickup port and travel to a specified point on the downstream side of the pickup port in a traveling direction of the transport vehicle at which a traveling route can be secured on the track when a traveling route for the transport vehicle from a pickup port to an unloading port designated by the transport instruction cannot be secured on the track; and assigning a second transport instruction to cause the transport vehicle to travel from the specified point to the unloading port and unload the article at the unloading port when a traveling route from the specified point to the unloading port can be secured at the point in time at which the transport vehicle approaches or reaches the specified point. 
     According to the transport system and the transport control method, the transport vehicle is caused by the first transport instruction to pick up an article at a pickup port and travel to a specified point when a traveling route for the transport vehicle from the pickup port to the unloading port designated by the transport instruction cannot be secured on the track. As a result, an article can be quickly transported out from the pickup port, and another article can be placed at the pickup port from which the article has been transported out. When a traveling route to the unloading port can be secured before the transport vehicle approaches or reaches the specified point, the second transport instruction causes the transport vehicle to travel straight to the unloading port and unloads the article at the unloading port. As a result, the amount of time taken to transport an article is reduced and the efficiency of transporting articles can be improved compared to when a transport instruction is assigned to a transport vehicle when the entire traveling route for the transport vehicle has been secured. 
     In the configuration in which the first transport instruction is an instruction to cause the transport vehicle to travel to the specified point and hold but not unload the article, transport of an article can be performed quickly when a traveling route from the specified point to the unloading port can be secured compared to a configuration in which a transport vehicle having traveled to the specified point unloads the article once at a storage or the like. In the configuration in which the specified point is set immediately before a branching part or a merging part on the track, it is possible at the branching part to select a traveling route that can be traveled after the specified point, and it is possible at the merging part to secure a passage of another transport vehicle through the merging part. When the specified point is set immediately before the branching part, the branching part is a branching part closest to the pickup port, it is possible to easily change to another traveling route by the branching part while transporting an article from the pickup port. 
     In the configuration in which the controller determines whether or not to assign the first transport instruction and the second transport instruction, according to the type of at least one of the pickup port and the unloading port, the first transport instruction causes an article to be transported out quickly from the pickup port from which articles are required to be transported out promptly, and therefore, the processing load on the controller can be reduced. In the configuration in which the controller assigns the first transport instruction and the second transport instruction to the transport vehicle when the pickup port is a load port of a processing apparatus, an article is transported out quickly from the load port of the processing apparatus, and therefore, a new article can be placed on the load port of the processing apparatus, and the utilization rate of the processing apparatus can be improved. In the configuration in which the controller assigns the first transport instruction and the second transport instruction to the transport vehicle when the pickup port is a load port of a stocker, an article is transported out quickly from the load port of the stocker, and therefore, a new article can be placed on the load port of the stocker, and the utilization rate of the stocker can be improved. 
     In the configuration in which the controller assigns the first transport instruction and the second transport instruction when the pickup port is a buffer, on which an article can be placed, and the unloading port is a load port of a processing apparatus, and the controller does not assign the first transport instruction and the second transport instruction when the pickup port is the buffer and the unloading port is other than a load port of a processing apparatus, an article can be transported to the load port of the processing apparatus in a short period of time. In the configuration in which the controller is a transport controller that controls a plurality of the transport vehicles, or an in-vehicle controller fitted in the transport vehicle, the transport vehicles can be controlled efficiently. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing a transport system and a controller according to a first example. 
         FIG. 2  is a diagram showing an example of a functional block configuration of the controller. 
         FIG. 3  is a diagram showing an example of a configuration of a transport vehicle. 
         FIG. 4  is a diagram showing an operation flow of the controller according to the first example. 
         FIG. 5  is an explanatory diagram showing an operation of the transport vehicle in the first example. 
         FIG. 6  is an explanatory diagram that follows  FIG. 5 , showing an example of an operation of the transport vehicle. 
         FIG. 7  is an explanatory diagram that follows  FIG. 6 , showing an example of an operation of the transport vehicle. 
         FIG. 8  is a diagram showing an operation flow of a controller according to a second example. 
         FIG. 9  is an explanatory diagram showing an operation of a transport vehicle in the second example. 
         FIG. 10  is an explanatory diagram that follows  FIG. 9 , showing another example of an operation of the transport vehicle. 
         FIG. 11  is an explanatory diagram showing another example of the operation of the transport vehicle. 
         FIG. 12  is a diagram showing a functional block configuration of a controller according to a third example. 
         FIG. 13  is a diagram showing another operation flow of the controller according to the third example. 
         FIG. 14  is a table showing the relationship between the types of pickup ports and unloading ports, and the types of transport instructions to be assigned. 
         FIG. 15  is an explanatory diagram showing another operation of a transport vehicle in a fourth example. 
     
    
    
     DESCRIPTION OF REFERENCE SIGNS 
     
         
         P, P 1 , P 2 , P 3 : Specified point 
         BF: Buffer 
         V: Transport vehicle 
         W: Article 
         MC: Host controller 
         TA, TA 1 : Track 
         CR: Closed route 
         TC, TCA: Controller (transport controller) 
         PF 1 : Pickup port 
         PT 1 , PT 2 , PT 3 : Unloading port 
         VC: In-vehicle controller 
         SYS: Transport system 
           11 ,  11 A,  11 C,  11 D,  11 E: Branching part 
           12 ,  12 A,  12 B: Merging part 
           31 : Transport instruction generator 
           41 : Transport instruction receiver 
           42 : Transport vehicle selector 
           43 : Traveling route generator 
           44 : Route determiner 
           45 : Assignor 
           46 : State report receiver 
           47 : Transport completion reporter 
           48 : Position identifier 
           49 : Destination change requester 
           50 : Port determiner 
       
    
     DETAILED DESCRIPTION 
     The following describes examples of my systems and methods with reference to the drawings. However, this disclosure is not limited to the examples. In the drawings, scale is changed as necessary to illustrate the example such as by enlarging or by emphasizing a part. In  FIG. 3 , an XYZ coordinate system is used to describe directions in the figure. In this XYZ coordinate system, a plane that is parallel to a horizontal plane is defined as an XY plane. In this XY plane, a traveling direction of a transport vehicle V is denoted as an X direction, and a direction orthogonal to the X direction is denoted as a Y direction. A direction perpendicular to the XY plane is denoted as a Z direction. For each of the X direction, the Y direction, and the Z direction, description is made with a definition in which a direction indicated by an arrow is the positive (+) direction and a direction opposite to the direction indicated by the arrow is the negative (−) direction. 
     First Example 
       FIG. 1  is a diagram showing a transport system and a controller according to a first example. A transport system SYS according to the example is a system for transporting articles W by transport vehicles V. The transport system SYS is installed in, for example, a semiconductor manufacturing factory. The article W is, for example, a FOUP, a SMIF pod, a reticle pod, or the like capable of accommodating wafers, reticles or the like. The transport system SYS includes, for example, a host controller MC, a controller TC, and a plurality of transport vehicles V. The controller TC is a transport controller that controls the plurality of transport vehicles V. One of the plurality of transport vehicles V is shown. However, the other transport vehicles V are similar thereto. 
     Each transport vehicle V travels along a predetermined track TA (route) and transports an article W. The track TA includes branching parts  11  and merging parts  12 . Blocking areas BA 1  to BA 4  are set in the branching parts  11  and the merging parts  12 . The passage of the transport vehicle V is restricted in the blocking areas BA 1  to BA 4 . For example, when the transport vehicle V is to pass through the blocking areas BA 1  to BA 4 , the transport vehicle V transmits a passage request for the blocking areas BA 1  to BA 4  to a blocking controller not shown in the drawings. The transport vehicle V will pass through the blocking areas BA 1  to BA 4  if a passage permission is received from the blocking controller. However, the transport vehicle V will stop immediately before each of the blocking areas BA 1  to BA 4  and not enter the blocking areas BA 1  to BA 4  if the passage permission is not obtained. The track TA can be set arbitrarily, and is installed suspended from a ceiling  1  (see  FIG. 3 ) of a building, for example. Each transport vehicle V transports an article W according to a transport instruction assigned by the controller TC. 
       FIG. 2  is a diagram showing an example of a functional block configuration of the controller. The controller includes a host controller MC and a controller TC. The host controller MC includes, for example, a CPU, a main memory, a memory storage device, and a communication device, and performs tasks such as processing of various information, storing information, input and output of information, and communication (transmitting/receiving) of information. As the host controller MC, for example, a computer system is used. 
     The host controller MC instructs transportation of articles W in the transport system SYS. Each unit of the system including the controller TC transmits to the host controller MC information such as information related to the state of each pickup port PF 1  and each unloading port PT 1 , or information related to the state of an instruction transmitted from the host controller MC to the controller TC. The host controller MC manages information such as position information of each article W, information related to the state of each pickup port or each unloading port (for example, the operating state of a device, the state of the occupancy of articles W), or information related to the state of an instruction transmitted from the host controller MC to the controller TC (for example, being executed, execution completed, execution failed). 
     The host controller MC includes a host transport instruction generator (transport instruction generator)  31 . The host transport instruction generator  31  generates a host transport instruction to transport a predetermined article W from a pickup port PF 1 , which is the origin of the transportation, to an unloading port PT 1 , which is the destination of the transportation. The host controller MC transmits the host transport instruction generated by the host transport instruction generator  31  to the controller TC. The host transport instruction includes, for example, pickup port information indicating the position (pickup port PF 1 ) of the article W to be transported, unloading port information indicating the position (unloading port PT 1 ) at which the article W to be transported is to be unloaded, and an instruction to transport the article W at the pickup port PF 1  to the unloading port PT 1 . The controller TC assigns a transport instruction related to the transportation of the article W to a transport vehicle V, on the basis of the host transport instruction received from the host controller MC. That is to say, the controller TC assigns to one of transport vehicles V a transport instruction to pick up an article W at the pickup port PF 1  and unload the article W at the unloading port PT 1 . 
     The controller TC controls the transport vehicles V. The controller TC transmits various instructions to the transport vehicles V to thereby control the transport vehicles V. The controller TC includes, for example, a transport instruction receiver  41 , a transport vehicle selector  42 , a traveling route generator  43 , a route determiner  44 , an assignor  45 , a state report receiver  46 , a transport completion reporter  47 , a position identifier  48 , and a destination change requester  49 . The controller TC includes, for example, a CPU, a main memory, a memory storage device, and a communication device, and performs tasks such as processing of various information, storing information, input and output of information, and communication (transmitting/receiving) of information. As the controller TC, for example, a computer system is used. The controller TC stores information required to control each transport vehicle V (for example, route information, map information), and a control program in a storage device not shown in the drawings. The configuration of the controller TC is not limited to the configuration shown in  FIG. 2 , and may employ another configuration. 
     The transport instruction receiver  41  receives a host transport instruction transmitted from the host controller MC. As mentioned above, the host transport instruction transmitted from the host controller MC to the controller TC includes a pickup port PF 1  (From: transport origin) of an article W and an unloading port PT 1  (To: transport destination) of the article W. 
     The transport vehicle selector  42  selects a transport vehicle V to which the transport instruction is to be assigned. For example, the transport vehicle selector  42  selects empty vehicles (transport vehicles not currently transporting an article W) from the plurality of transport vehicles V, and selects, from the selected empty vehicles, a transport vehicle V that is to arrive at the pickup port PF 1  earliest. The traveling route generator  43  generates a traveling route on the track TA for the transport vehicle V from the pickup port PF 1  to the unloading port PT 1  designated in the transport instruction (host transport instruction). For example, the traveling route generator  43  selects the shortest route from the route information stored in a memory storage device not shown in the drawings, and generates a traveling route for the transport vehicle V. 
     The route determiner  44  determines whether or not the traveling route can be secured on the traveling route generated by the traveling route generator  43 . For example, the route determiner  44  detects whether or not a part of the traveling route is closed on the traveling route generated by the traveling route generator  43 . For example, damage to the track TA, presence of a failed vehicle, maintenance, and so forth can cause closure of a part of a traveling route, and an operator or the like inputs or transmits such closure to the controller TC. The closure of a traveling route is called “route down,” and is set for each route by, for example, an operator or the like. If closure is not detected, the route determiner  44  determines that the traveling route can be secured. If closure of a part of the traveling route is detected, the route determiner  44  determines that the traveling route cannot be secured. 
     The assignor  45  assigns one of a transport instruction, a first transport instruction, and a second transport instruction to a transport vehicle V selected by the transport vehicle selector  42 , on the basis of the determination result of the route determiner  44 . The assignor  45  assigns a transport instruction to a transport vehicle V to cause it to pick up an article W at the pickup port PF 1 , travel along the traveling route mentioned above, and unload the article W at the unloading port PT 1  when the traveling route for the transport vehicle V from the pickup port PF 1  to the unloading port PT 1  designated by the transport instruction can be secured on the track TA. 
     The controller TC generates a first transport instruction when the traveling route for the transport vehicle V from the pickup port PF 1  to the unloading port PT 1  designated by the transport instruction cannot be secured on the track TA. The assignor  45  assigns the transport instruction to the transport vehicle V instead of the previous transport instruction. The first transport instruction may be generated by the assignor  45 , or may be generated by a transport instruction generator (not shown in the drawings) that is included as a unit separate from the assignor  45  in the controller TC. The first transport instruction causes the transport vehicle V to pickup an article W at the pickup port PF 1 , travel to a specified point P 1  on the downstream side of the pickup port PF 1  in the traveling direction of the transport vehicle V, at which point the traveling route can be secured on the track TA, and hold but not unload the article W. 
     In the first transport instruction, the specified point P 1  is set immediately before the branching part  11  or the merging part  12  on the track TA. The specified point P 1  may be set, for example, by the traveling route generator  43  or by the assignor  45 . The specified point P 1  is set immediately before the branching part  11  that is on the downstream side of the pickup port PF 1  and is closest to the pickup port PF 1 . As a result of the specified point P 1  being set immediately before the branching part  11  or the merging part  12 , it is possible at the branching part  11  to select another traveling route that can be traveled after the specified point P 1  has been reached, and it is possible to secure a passage for another transport vehicle V through the merging part  12 . Since the transport vehicle V is moved from above the pickup port PF 1 , another transport vehicle V can unload an article W to the pickup port PF 1 . 
     The assignor  45  assigns a second transport instruction to the transport vehicle V when the traveling route from the specified point P 1  to the unloading port PT 1  can be secured at the point in time at which the transport vehicle V has approached or reached the specified point P 1  (or before it reaches the specified point P 1 ). That is to say, the assignor  45  assigns the second transport instruction to the transport vehicle V when the closure of the traveling route is lifted at the point in time at which the transport vehicle V has approached or reached the specified point P 1  such as when repair of the track TA has been completed, when a failed vehicle has been removed, or when maintenance has ended. The second transport instruction is an instruction that causes a transport vehicle V to travel from the specified point P 1  to the unloading port PT 1  and unload an article W to the unloading port PT 1 . 
     The state report receiver  46  receives a state report that is transmitted from an in-vehicle controller VC in response to a state report request transmitted from the controller TC. State reports transmitted from the in-vehicle controller VC to the controller TC include a position report reporting the position of a transport vehicle V, a pickup completion report reporting a transport vehicle V having completed pickup of an article W, and a transport completion report reporting a transport vehicle V having completed unloading of an article W, and further includes information such as traveling speed. The transport completion reporter  47  reports to the host controller MC that transportation of an article W to the unloading port PT 1  has been completed. 
     The position identifier  48  identifies the position of a transport vehicle V on the track TA, on the basis of a position report transmitted from the transport vehicle V. The destination change requester  49  reports that the destination of the transport vehicle V having received the first transport instruction has been changed to the specified point P 1 , and requests the host controller MC to newly determine an unloading port for the article W, taking the specified point P 1  as a reference. As described above, the assignor  45  assigns the second transport instruction to the transport vehicle V when the traveling route can be secured at the point in time at which the transport vehicle V has approached or reached the specified point P 1 . However, if the traveling route from the specified point P 1  to the unloading port PT 1  cannot be secured, the second transport instruction cannot be assigned and the transport vehicle V will remain stopped at the specified point P 1 . When the second transport instruction cannot be assigned, for example, the destination change requester  49  transmits a destination change request to the host controller MC to request a new unloading port for the article W. 
     The host controller MC determines a new unloading port for the article W on the basis of the request from the destination change requester  49 , and transmits the determination content related to the new unloading port for the article W to the controller TC. Upon receiving the determination content related to the new unloading port for the article W, the controller TC generates, in the traveling route generator  43 , a traveling route from the specified point P 1  to the new unloading port. The assignor  45  assigns to the transport vehicle V a third transport instruction to cause it to travel from the specified point P 1  to the new unloading port, and unload the article W at the new unloading port. 
     A configuration of the transport vehicle V will be described.  FIG. 3  is a diagram showing an example of the configuration of the transport vehicle V. The transport vehicle V is an overhead transport vehicle that, for example, travels in one direction (+X direction) along the track TA suspended from the ceiling  1  or the like of the building, picks up an article W at the pickup port PF 1  arranged on the lower side of (directly below) the track TA or on the lower and lateral side (in the Y direction) of the track TA, and unloads the article W at the unloading port PT 1  arranged on the lower side of the track TA or on the lower and lateral side of the track TA. 
     The transport vehicle V includes an in-vehicle controller VC. The in-vehicle controller VC controls various operations of the transport vehicle V (such as traveling, speed control (accelerating, decelerating, and stopping), operations related to execution of pickup, and operations related to execution of unloading). The in-vehicle controller VC controls the transport vehicle V according to instructions transmitted from the controller TC. The controller TC transmits to the transport vehicle V, for example, the transport instruction mentioned above, a move instruction described later, and so forth as instructions to control the transport vehicle V. The in-vehicle controller VC is a computer system that includes, for example, a CPU, a main memory, a memory storage device, and a communication device, and performs tasks such as processing of various information, storing information, input and output of information, and communication (transmitting/receiving) of information. 
     The in-vehicle controller VC manages state information that indicates the state of the transport vehicle V. The in-vehicle controller VC transmits the state information to the controller TC in a manner of responding to a state report request transmitted periodically from the controller TC. Communications related to the state report request and the state information (state report including state information) that are exchanged between the in-vehicle controller VC and the controller TC, are performed periodically at predetermined time intervals. The controller TC receives state information (state report including state information) from each transport vehicle V periodically, and thereby grasps and manages the latest state of the transport vehicles V under the management thereof and the latest state of various instructions transmitted to the transport vehicles V by the controller TC. 
     Examples of the state information of a transport vehicle V include information indicating the current location of a transport vehicle V (current location information), information on traveling (such as speed and stop state), information on whether or not an article W is held, and information on the state (status) of various instructions transmitted from (assigned by) the controller TC. Examples of the information on the state of various instructions in the state information include information indicating completion or failure (inexecutability) of assignment of various instructions, information indicating completion or failure of execution of various instructions (such as transport instruction and move instruction), and information indicating completion or failure of execution of operations or processes related to various instructions (such as traveling, pickup, unloading). By receiving the state information (state report including state information) transmitted periodically from the transport vehicles V, the controller TC grasps the state of the transport vehicles V and the execution state of instructions for the transport vehicles V, and manages and controls the transport vehicles V. The state information (state report including state information) transmitted from a transport vehicle V enables the controller TC to recognize the transport vehicle V approaching or reaching the specified point P 1 . 
     Each transport vehicle V includes a traveler M and a main body  3  as shown in  FIG. 3 . The traveler M includes wheels  4  and travels along the track TA (route) by a traveling driver not shown in the drawings. The main body  3  is provided in a state of being suspended below the traveler M. The main body  3  includes a transferer  5 . The transferer  5  includes an article holder  6  that holds an article W, a lift driver  7  that raises or lowers the article holder  6 , and a lateral extender  8  that moves the lift driver  7  in a direction lateral to (in the +Y direction or the −Y direction of) the track TA. 
     The article holder  6  is a chuck having claws  6   a  that can be advanced or retracted, and inserts the claws  6   a  under a flange Wa of the article W to thereby suspend and hold the article W. The article holder  6  is connected to suspenders  6   b  such as wires and belts. The lift driver  7  is, for example, a hoist, and raises or lowers the article holder  6  by feeding out or taking up the suspenders  6   b . The lateral extender  8  causes a plurality of movable plates to slide, thereby causing the article holder  6  and the lift driver  7  to move between a position for being stored in the main body  3  and a position for being projected toward a lateral side of the track TA. Pickup and unloading of an article W performed by the transport vehicle V is performed using the article holder  6 , or the lift driver  7  and the lateral extender  8  mentioned above. Operations of the article holder  6 , the lift driver  7 , and the lateral extender  8  are controlled by the in-vehicle controller VC. 
     When an article W is to be picked up at the pickup port PF 1 , the in-vehicle controller VC instructs the transport vehicle V to stop to align with the pickup port PF 1  and causes the lift driver  7 , or the lift driver  7  and the lateral extender  8  to operate and move the article holder  6  to a predetermined position, to thereby pick up the article W at the pickup port PF 1 . The pickup port PF 1  can be arbitrarily set in the transport system SYS. Examples of the pickup port PF 1  include a load port of a processing apparatus PA or a load port of a stocker ST, and an overhead buffer (referred to as buffer) BF provided with a shelf, on which an article W can be placed, suspended from the ceiling  1  of the building. Examples of the buffer BF include a side track buffer arranged below and to the side of the track TA and an under-track buffer arranged directly below the track TA. 
     When an article W is to be unloaded at the unloading port PT 1 , the in-vehicle controller VC instructs the transport vehicle V to stop to align with the unloading port PT 1  and causes the lift driver  7 , or the lift driver  7  and the lateral extender  8  to operate and move the article holder  6  to a predetermined position, to thereby unload the article W at the unloading port PT 1 . The unloading port PT 1  can be arbitrarily set in the transport system SYS. Examples of the unloading port PT 1  include a load port of the processing apparatus PA or the stocker ST, and the buffer BF provided with a shelf, on which an article W can be placed, suspended from the ceiling  1  of the building. 
     The controller TC and the in-vehicle controller VC are connected to communicate with each other in a wireless manner via a transmission path such as wireless LAN (Local Area Network) or feeder communication using a feeder line. The controller TC and the host controller MC are connected to communicate with each other via a transmission line such as a wired LAN or a wireless LAN. 
       FIG. 4  is a diagram showing an example of the operation flow of the controller TC. The operations performed when the controller TC assigns a transport instruction will be described, with reference to the operation flow shown in  FIG. 4 . In the description of this operation flow, reference will be made to  FIGS. 1 to 3  where appropriate. In transporting an article W present at the pickup port PF 1  to the unloading port PT 1 , the host controller MC transmits to the controller TC a transport instruction (host transport instruction) that instructs that a pickup target article W is present at the pickup port PF 1  and that the pickup target article W is to be transported to the unloading port PT 1 . 
     The transport instruction receiver  41  of the controller TC receives the transport instruction from the host controller MC (Step S 01 ). The transport instruction receiver  41  determines whether the data received from the host controller MC is a transport instruction by making reference to the header of the data received from the host controller MC, for example. After having received the transport instruction, the transport vehicle selector  42  of the controller TC selects a transport vehicle V to which the transport instruction is to be assigned (Step S 02 ). The traveling route generator  43  generates a traveling route for the transport vehicle V from the pickup port PF 1  to the unloading port PT 1  on the basis of the received transport instruction (Step S 03 ). 
     The route determiner  44  determines whether or not a part of the traveling route is closed on the traveling route generated by the traveling route generator  43  (Step S 04 ). If closure is not determined in Step S 04  (Step S 04 ; NO), a transport instruction including the traveling route generated by the traveling route generator  43  is assigned to the transport vehicle V (Step  505 ). 
     On the other hand, in Step S 04 , if it is determined that a part of the traveling route is closed and that no transport vehicle V that can execute the transport instruction from the host controller MC (that is, no transport vehicle V that can transport an article W from the pickup port PF 1  to the unloading port PT 1  designated in the transport instruction) is present within a predetermined range (Step S 04 ; YES), a first transport instruction, instead of the transport instruction from the host controller MC, is assigned to the transport vehicle V (Step S 06 ).  FIG. 5  is a diagram showing an example of the operation of the transport vehicle V. As shown in  FIG. 5 , when a closed route CR is set in a part of the traveling route on the track TA, the assignor  45  assigns to the transport vehicle V the first transport instruction that sets the transport origin (From) as the pickup port PF 1  and the transport destination (To) as the specified point P 1 . Upon receiving the first transport instruction, the transport vehicle V, according to the first transport instruction, picks up the article W at the pickup port PF 1  and then travels toward the specified point P 1 . 
     At the point in time at which the transport vehicle V has approached or reached the specified point P 1 , the route determiner  44  determines whether or not a traveling route from the specified point P 1  to the unloading port PT 1  can be secured (Step S 07 ). If it is determined in Step S 07  that a traveling route can be secured (Step S 07 ; YES), a second transport instruction is assigned to the transport vehicle V (Step S 08 ). 
       FIG. 6  is an explanatory diagram that follows  FIG. 5 , showing an example of the operation of the transport vehicle V. As shown in  FIG. 6 , at the point in time at which the transport vehicle V reaches the specified point P 1 , the closed route CR has been lifted and traveling is allowed. Therefore, there is no closed route on the traveling route for the transport vehicle V from the specified point P 1  to the unloading port PT 1 , and the traveling route can be secured. In such a situation, the assignor  45  assigns to the transport vehicle V the second transport instruction that sets the transport origin (From) as the specified point P 1  or the transport vehicle V itself and the transport destination (To) as the unloading port PT 1 . If the second transport instruction is received, the transport vehicle V, according to the second transport instruction, travels from the specified point P 1  toward the unloading port PT 1 . 
       FIG. 7  is an explanatory diagram that follows  FIG. 6 , showing an example of the operation of the transport vehicle V. As shown in  FIG. 7 , when traveling from the specified point P 1  toward the unloading port PT 1  through the branching part  11  and the merging part  12 , the transport vehicle V is to pass through the blocking areas BA 1  to BA 4 . When the transport vehicle V is to pass through the blocking areas BA 1  to BA 4 , the transport vehicle V transmits a passage request for the blocking areas BA 1  to BA 4  to a blocking controller not shown in the drawings. The transport vehicle V will pass through the blocking areas BA 1  to BA 4  if a passage permission is received from the blocking controller. Upon arriving at the unloading port PT 1 , the transport vehicle V unloads the article W.  FIG. 7  shows a state where the transport vehicle V has moved to the downstream side after the article W has been unloaded at the unloading port PT 1 . 
     If it is determined in Step S 07  that the traveling route cannot be secured (Step S 07 ; NO), the transport vehicle V is brought into a stop state at the specified point P 1 . Since the first transport instruction is an instruction to hold but not unload the article W, it does not allow the article W to be unloaded even if the transport vehicle V arrives at the specified point P 1 . 
     As described above, according to this example, when the traveling route for the transport vehicle V from the pickup port PF 1  to the unloading port PT 1  designated by the transport instruction cannot be secured on the track TA, the first transport instruction causes the transport vehicle V to pick up the article W at the pickup port PF 1  and then travel to the specified point P 1 . Therefore, the article W can be quickly transported out from the pickup port PF 1 , and another article W can be placed at the pickup port PF 1  from which the article W has been transported out. As a result, it is possible to prevent a reduction in the efficiency of the processing of the processing apparatus PA or the like. 
     When it becomes possible to secure a traveling route to the unloading port PT 1  before the transport vehicle V approaches or reaches the specified point P 1 , the second transport instruction causes the transport vehicle V to travel straight to the unloading port PT 1  and unloads the article W at the unloading port PT 1 . As a result, the amount of time taken to transport the article W is reduced and the efficiency of transporting articles W can be improved compared to when a transport instruction is assigned to a transport vehicle V when the entire traveling route for the transport vehicle V has been secured. This example corresponds to a configuration in which a host transport instruction from the host controller MC is divided into a first transport instruction and a second transport instruction by the controller TC, and the second transport instruction is assigned to the transport vehicle V after the first transport instruction has been assigned to the transport vehicle V. 
     Second Example 
     Next, a second example is described.  FIG. 8  is a diagram showing the operation flow of a controller TC according to the second example. In the operation flow shown in  FIG. 8 , the operations of Step S 01  to Step S 06 , YES of Step S 07 , and Step S 08  are similar to those in the operation flow of the above example. In this example, as shown in  FIG. 8 , if it is determined in Step S 07  that a traveling route cannot be secured (Step S 07 ; NO), the destination change requester  49  reports to the host controller MC that the destination of the transport vehicle V having received the first transport instruction has been changed to the specified point P 1 , and requests the host controller MC to newly determine an unloading port for the article W, taking the specified point P 1  as a reference (Step S 11 ). The host controller MC determines a new unloading port PT 2  for the article W on the basis of the request from the destination change requester  49 , and transmits the determination content related to the new unloading port PT 2  for the article W to the controller TC. 
     The controller TC receives a new transport instruction related to the new unloading port PT 2  for the article W (Step S 12 ). Upon receiving the new transport instruction, the controller TC generates, in the traveling route generator  43 , a traveling route from the specified point P 1  to the unloading port PT 2  (Step S 13 ). After Step S 13 , the route determiner  44  may determine whether or not a traveling route from the specified point P 1  to the unloading port PT 2  can be secured. The assignor  45  assigns to the transport vehicle V a third transport instruction that causes the transport vehicle V to travel from the specified point P 1  to the unloading port PT 2  and perform unloading at the unloading port PT 2  (Step S 14 ). 
       FIGS. 9 and 10  are explanatory diagrams showing the operation of the transport vehicle V in the second example. As shown in  FIG. 9 , at the point in time at which the transport vehicle V reaches the specified point P 1 , the closed route CR still remains as it was set. In such a situation, the destination change requester  49  requests the host controller MC to change the destination as in Step S 11  above. In response to this request, the host controller MC transmits to the controller TC a transport instruction (host transport instruction) that designates the transport origin (From) as the specified point P 1  and the transport destination (To) as the unloading port PT 2 . 
     Upon receiving the transport instruction, on the basis of this transport instruction, the controller TC generates and assigns to the transport vehicle V a third transport instruction that designates the transport origin (From) as the specified point P 1  and the transport destination (To) as the unloading port PT 2 . Upon receiving the third transport instruction, the transport vehicle V, according to the third transport instruction, travels from the specified point P 1  to the unloading port PT 2  through the branching part  11  and the merging part  12 A, and unloads the article W at the unloading port PT 2  as shown in  FIG. 10 . In such a situation, the transport vehicle V passes through the blocking areas BA 1 , BA 5 . When the transport vehicle V is to pass through the blocking areas BA 1 , BA 5 , the transport vehicle V transmits a passage request for the blocking areas BA 1 , BA 5  to a blocking controller not shown in the drawings. The transport vehicle V will pass through the blocking areas BA 1 , BA 5  if a passage permission is received from the blocking controller.  FIG. 10  shows a state where the transport vehicle V has moved to the downstream side after the article W has been unloaded at the unloading port PT 2 . 
       FIG. 11  is an explanatory diagram showing another example of the operation of the transport vehicle V. As shown in  FIG. 11 , this example is similar to the example described above in that the closed route CR is set in the state where the transport vehicle V has reached the specified point P 1 . In such a situation, the destination change requester  49  requests the host controller MC to change the destination. In response to this request, the host controller MC may transmit to the controller TC a transport instruction (host transport instruction) that designates the transport origin (From) as the specified point P 1  and the transport destination (To) as circling travel. 
     Upon receiving the transport instruction, on the basis of this transport instruction, the controller TC generates and assigns to the transport vehicle V a fourth transport instruction that designates the transport origin (From) as the specified point P 1  and the transport destination (To) as a circling route C (circling travel). Upon receiving the fourth transport instruction, according to the fourth transport instruction, the transport vehicle V travels along the circling route C from the specified point P 1  through the branching part  11 , the merging part  12 A, the branching part  11 A, and the merging part  12 B, while holding the article W. When information that indicates the closed route CR having become available for traveling while the transport vehicle V is traveling along the circling route C, the controller TC may assign to the transport vehicle V a fifth transport instruction that designates the transport origin as the circling route C and the transport destination as the unloading port PT 1 . 
     The controller TC may request the host controller MC to change the destination by the destination change requester  49  after the transport vehicle V has traveled in circles along the circling route C for a predetermined length of time. In response to this request, the host controller MC may transmit to the controller TC a transport instruction (host transport instruction) that designates the transport origin (From) as the circling route C and the transport destination (To) as the unloading port PT 2 . 
     As described above, according to this example, even when the second transport instruction cannot be assigned to the transport vehicle V (where the closed route CR remains set), it is possible to avoid the transport vehicle V from remaining in a stop state at the specified point P 1 , and avoid the transport vehicle V from causing hindrance to another transport vehicle V passing through the specified point P 1 . 
     Third Example 
       FIG. 12  is a diagram showing a functional block configuration of the host controller MC and a controller TCA according to a third example. As shown in  FIG. 12 , the controller TCA includes a port determiner  50  in addition to the configuration of the controller TC described above. The port determiner  50  determines the type of at least one of the pickup port PF 1  being the transport origin and the unloading port PT 1  being the transport destination. 
       FIG. 13  is a diagram showing the operation flow of the controller TCA according to the third example. In the operation flow shown in  FIG. 13 , the flow of Step S 01  to Step S 03 , NO of Step S 04 , Step S 05  and thereafter are similar to that in the operation flow of the above example. In the operation flow of this example, if it is determined in Step S 04  that a part of the traveling route is closed (Step S 04 ; YES), the port determiner  50  determines whether or not the pickup port PF 1  is a specified pickup port (Step S 21 ). 
     If the pickup port PF 1  is a specific pickup port (Step S 21 ; YES), the assignor  45  assigns a first transport instruction to the transport vehicle V (Step S 06 ). If the pickup port PF 1  is not a specified pickup port (Step S 21 ; NO), the port determiner  50  determines whether or not the unloading port PT 1  is a specified unloading port (Step S 22 ). 
     If the unloading port PT 1  is a specific unloading port (Step S 22 ; YES), the assignor  45  assigns a first transport instruction to the transport vehicle V (Step S 06 ). If the unloading port PT 1  is not a specific unloading port (Step S 22 ; NO), the assignor  45  suspends the transport instruction until the traveling route can be secured (Step S 23 ). 
       FIG. 14  is a table showing the relationship between the types of the pickup port PF 1  and unloading port PT 1  in the determinations of Step S 21  and Step S 22 , and the types of transport instructions to be assigned. As shown in  FIG. 14 , when the pickup port PF 1  is a load port of the processing apparatus PA (see  FIG. 3 ) or a load port of the stocker ST (see  FIG. 3 ), the first transport instruction is assigned when a traveling route cannot be secured, regardless of the type of the unloading port PT 1 . When the pickup port PF 1  is a buffer BF, the type of the instruction to be assigned differs, depending on the type of the unloading port PT 1 . That is to say, when the type of the unloading port PT 1  is a load port of the processing apparatus PA, a first transport instruction is assigned when the traveling route cannot be secured. 
     When the type of the unloading port PT 1  is a load port of a stocker ST or a buffer BF (see  FIG. 3 ), assignment of the transport instruction is suspended when the traveling route cannot be secured. That is to say, neither the transport instruction nor the first transport instruction is assigned to the transport vehicle V, and the transport instruction from the host controller MC is suspended in the controller TC. As shown in the table of  FIG. 14 , when a traveling route can be secured, a normal transport instruction is assigned to the transport vehicle V in any event. 
     As described above, according to this example, the first transport instruction causes an article W to be transported out quickly from the pickup port PF 1  (processing apparatus PA, stocker ST) from which articles W are required to be transported out promptly, and therefore, the next article W can be placed at the pickup port PF 1  (processing apparatus PA, stocker ST) from which an article W has already been transported out, and a reduction can be avoided in the utilization rate of the processing apparatus PA or the stocker ST. 
     When the pickup port PF 1  is a buffer BF on which an article W can be placed and the unloading port PT 1  is a load port of the processing apparatus PA, the controller TC assigns a first transport instruction and a second transport instruction, and therefore, an article W can be transported to the load port of the processing apparatus PA in a short period of time. When the pickup port PF 1  is a buffer BF and the unloading port PT 1  is other than a load port of the processing apparatus PA, a first transport instruction and a second transport instruction are not assigned, and therefore, the processing load on the controller TC can be reduced. 
     Fourth Example 
       FIG. 15  is an explanatory diagram showing the operation of the transport vehicle V in a fourth example. The track TA shown in  FIG. 15  includes a branching part  11 C, a branching part  11 D, and a branching part  11 E on the downstream side of the pickup port PF 1 . A closed route CR is set on the downstream side of the branching part  11 E, and the unloading port PT 1  is arranged on the downstream side of the closed route CR. 
     In the above example, the specified point P 1  is set immediately before the branching part  11  closest to the pickup port PF 1 . However, this disclosure is not limited to this example. For example, a specified point P 2  may be set immediately before the branching part  11 E closest to the closed path CR. In such a situation, the transport vehicle V travels to the specified point P 2  and then stops, and accordingly, the transport vehicle V stands by at a position closest possible to the unloading port PT 1 . As a result, when the closed route CR is lifted, the transport vehicle V can quickly reach the unloading port PT 1  and unload the article W at the unloading port PT 1 . 
     A specified point P 3  may be set immediately before the branching part  11 D, on the track TA 1  on the downstream side of which another unloading port PT 3  is arranged. In such a situation, when requesting a change of destination after a first transport instruction has been assigned, it is possible to unload the article W from the specified point P 3  in a short period of time by setting the new destination of the article W as the unloading port PT 3  close to the specified point P 3 . As a result, the next transport instruction can be assigned to the transport vehicle V and a reduction can be prevented in the efficiency of transporting articles W. 
     Examples of my systems and methods have been described above. However, the technical scope of this disclosure is not limited to the description of the above examples. It is also apparent to those skilled in the art that various modifications or improvements can be added to the above examples. The technical scope of this disclosure also encompasses one or more of such modifications or improvements. The order of executing processes shown in the examples can be realized in an arbitrary order unless an output of the previous processing is used in the following processing. While operations in the above examples have been described with expressions such as “first,” “next” and “subsequently” for the sake of convenience, the operations need not always be implemented in that order. 
     Furthermore, in the above examples, the configuration has been described as an example in which a host controller MC and a controller TC are provided in the transport system SYS. However, this disclosure is not limited to this configuration. For example, a single controller may include the functions of both the host controller MC and the controller TC. In the above examples, the configuration has been described as an example in which the controller TC is provided as a unit separate from the in-vehicle controller VC of the transport vehicle V. However, this disclosure is not limited to this configuration. For example, the function of the controller TC may be realized as a part of the function of the in-vehicle controller VC. 
     One or more of the requirements described in the above examples may be omitted when appropriate. One or more of the requirements described in the above examples may be combined where appropriate. The contents of Japanese Patent Application No. 2019-091260 and all documents cited in this disclosure are incorporated herein by reference.