Abstract:
In a traveling vehicle system, traveling vehicles travel along a travel route under the control of at least one controller. Each of the traveling vehicles includes a first traveling vehicle position determining section arranged to determine a position of the respective traveling vehicle, and a second traveling vehicle position determining section arranged to determine a position of at least one other of the traveling vehicles by communication, and a distance sensor arranged to detect a distance between the respective traveling vehicle and the at least one other of the traveling vehicles. The at least one controller and the traveling vehicles are configured to control velocities of the traveling vehicles in an inter-vehicle control area by determining inter-vehicle distances between the traveling vehicles based on the position of the at least one other of the traveling vehicles obtained by the communication in the second traveling vehicle position determining section, and the position of the respective traveling vehicle determined by the first traveling vehicle position determining section, and to control the velocities of the traveling vehicles in areas of the traveling route other than in the inter-vehicle control area based on distances detected by the distance sensor.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to traveling vehicles such as an overhead traveling vehicle (OHT), an automated guided vehicle (AGV), a rail guided vehicle (RGV), or the like. In particular, the present invention relates to a technique of implementing control in a diverging section or a merging section of such a traveling vehicle. 
         [0003]    2. Description of the Related Art 
         [0004]    In a technique disclosed in JP2005-284779A, a collision prevention sensor is provided in a traveling vehicle such as an overhead traveling vehicle to monitor a leading traveling vehicle for preventing interference with the leading traveling vehicle. Further, a ground controller restricts entry of the traveling vehicle into a diverging section and a merging section to ensure that only one traveling vehicle can enter the diverging section or the merging section. Hereinafter, control where the ground controller&#39;s permission is required for the traveling vehicle to enter a certain area, and the number of traveling vehicles that can be present in the certain area is limited to one or less is referred to as the blocking control. Further, an area where entry of the traveling vehicle is restricted by blocking control is referred to as the blocking area. 
         [0005]    In general, the conventional blocking area is several times longer than the vehicle length of one traveling vehicle for the following reasons. For example, in the case of the diverging section, it is difficult to detect a traveling vehicle diverging from the diverging section by a collision prevention sensor from a position upstream of the diverging section. Further, it is difficult for a traveling vehicle in a curve segment at the exit of the diverging section to monitor traveling vehicles in a straight segment downstream of the diverging section by the collision prevention sensor. Likewise, in the case of the merging section, it is difficult for a traveling vehicle curving at an entrance of the merging section for entering the merging section, to detect traveling vehicles in the merging section using the collision prevention sensor. Therefore, a region upstream of the merging section is also included in the blocking area. Further, it is difficult for a traveling vehicle curving in the merging section to detect traveling vehicles at the exit of the merging section by the collision prevention sensor. Therefore, a region at the merging section is included in the blocking area as well. Under the circumstances, the blocking area becomes large. Since the number of traveling vehicles that can pass through the blocking area per unit time is substantially inversely proportional to the size of the blocking area, the efficiency of the traveling vehicle system is low. 
       SUMMARY OF THE INVENTION 
       [0006]    Preferred embodiments of the present invention provide a system and method to increase the number of traveling vehicles that can pass through a diverging section or a merging section. 
         [0007]    According to a preferred embodiment of the present invention, a system for a plurality of traveling vehicles traveling along a travel route including a diverging section and a merging section under control of at least one controller is provided. 
         [0008]    Each of the traveling vehicles preferably includes a first traveling vehicle position determining section arranged to determine a position of the respective traveling vehicle, and a second traveling vehicle position determining section arranged to determine a position of at least one other of the traveling vehicles by communication. 
         [0009]    A certain area of the travel route, which includes a diverging section and a merging section, is designated as a blocking area. An area including the blocking area, which is larger than the blocking area, is designated as an inter-vehicle distance control area. 
         [0010]    In the inter-vehicle distance control area, velocity control of the respective traveling vehicle is implemented by determining an inter-vehicle distance between the respective traveling vehicle and the at least one other of the traveling vehicles based on the position of the at least one other of the traveling vehicles obtained by communication and the position of the first traveling vehicle determined by the first traveling vehicle position determining section. The first traveling vehicle is configured to enter the blocking area after obtaining permission from the at least one controller. 
         [0011]    Further, according to a preferred embodiment of the present invention, a travel control method in a traveling vehicle system for a plurality of traveling vehicles traveling along a travel route including a diverging section and a merging section under control of at least one controller is provided. The method includes the steps of designating a certain area of the travel route including a diverging section and a merging section as a blocking area; designating an area that includes the blocking area and is larger than the blocking area as an inter-vehicle distance control area; allowing a first traveling vehicle to travel along the travel route, the first traveling vehicle including a distance sensor arranged to detect a distance to a second traveling vehicle ahead of the first traveling vehicle, a first traveling vehicle position determining section arranged to determine a position of the first traveling vehicle, and a second traveling vehicle position determining section arranged to determine a position of the second traveling vehicle by communication; allowing the first traveling vehicle in the inter-vehicle distance control area to determine an inter-vehicle distance between the first and second traveling vehicles from the position of the second traveling vehicle obtained by communication and the position of the first traveling vehicle determined by the first traveling vehicle position determining section to implement velocity control of the first traveling vehicle to avoid interference with the second traveling vehicle; allowing the first traveling vehicle to request permission from the at least one controller before entering into the blocking area, and allowing the first traveling vehicle to enter the blocking area after obtaining the requested permission; and allowing the first traveling vehicle in a travel route other than the inter-vehicle distance control area to implement velocity control of the first traveling vehicle based on the distance determined by the distance sensor to avoid interference with the second traveling vehicle. 
         [0012]    In this specification, description regarding the traveling vehicle system is directly applicable to the travel control method. 
         [0013]    Preferably, the first traveling vehicle further includes a distance sensor arranged to detect a distance to the second traveling vehicle ahead of the first traveling vehicle, and velocity control of the first traveling vehicle in a travel route other than the inter-vehicle distance control area is implemented based on a distance determined by the distance sensor instead of the position of the second traveling vehicle obtained by communication. 
         [0014]    Further, preferably, the first traveling vehicle is configured to request permission from the controller before entering into the merging section, and the controller is configured to provide permissions for entry into the merging section, preferentially to traveling vehicles coming from a same direction regardless of an arrival order of the request, to allow the traveling vehicles coming from the same direction to successively enter the merging section. 
         [0015]    In particular, preferably, marks are provided along the travel route and the first traveling vehicle position determining section reads the marks to recognize the position of the first traveling vehicle, the first traveling vehicle further includes a communication section arranged to transmit the position of the first traveling vehicle to the controller on the ground, and the second traveling vehicle position determining section arranged to determine a position of the second traveling vehicle by communication intercepts communication of the transmission to the controller on the ground to obtain the position of the second traveling vehicle. 
         [0016]    In a preferred embodiment of the present invention, since the size of the blocking area can be minimized, the number of traveling vehicles that can pass the diverging section or the merging section can be increased, and improvement in the system efficiency is achieved. 
         [0017]    Further, in the travel route other than the inter-vehicle distance control area, by implementing only velocity control based on the distance determined by the distance sensor, the control can be simplified since it is not required to obtain the inter-vehicle distance to the leading traveling vehicle by communication. 
         [0018]    Further, by giving permissions for entry into the merging section, preferentially to traveling vehicles coming from a same direction regardless of an arrival order of the request, to allow the traveling vehicles coming from the same direction to successively enter the merging section, the number of traveling vehicles that can pass the merging section can be further increased. 
         [0019]    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 
         [0020]      FIG. 1  is a diagram schematically showing a layout of overhead traveling vehicles according to a preferred embodiment of the present invention. 
           [0021]      FIG. 2  is a diagram showing a blocking area and an inter-vehicle distance control area in a diverging section in a preferred embodiment of the present invention. 
           [0022]      FIG. 3  is a diagram showing a blocking area and an inter-vehicle distance control area in a merging section in a preferred embodiment of the present invention. 
           [0023]      FIG. 4  is a diagram showing a curve segment in a preferred embodiment of the present invention. 
           [0024]      FIG. 5  is a diagram showing the relationship between a controller and overhead traveling vehicles in a preferred embodiment of the present invention. 
           [0025]      FIG. 6  is a diagram showing a pattern of traveling vehicles passing through the merging section in a preferred embodiment of the present invention. 
       
    
    
     DESCRIPTION OF THE NUMERALS 
       [0000]    
       
           2 : overhead traveling vehicle system 
           4 : inter-bay route 
           6 : intra-bay route 
           8 ,  10 : shortcut 
           12 : ground controller 
           14 : overhead traveling vehicle 
           20 ,  30 : blocking area 
           21 ,  31 : inter-vehicle distance control area 
           22 : exit of diverging lane 
           23 : exit of merging lane 
           24 : entrance of diverging lane 
           32 : entrance of merging lane 
           33 : entrance of straight lane 
           34 : exit of merging lane 
           50 : LAN 
           51 : controller body 
           52 : communication interface 
           53 : blocking controller 
           54 : optical distance sensor 
           55 : absolute position sensor 
           56 : mark 
           61  to  64 : permission request from straight lane 
           65  to  67 : permission request from merging lane 
           68 : travel permission pattern in embodiment 
           69 : travel permission pattern in conventional example 
         D: diverging section 
         D 1  to D 15 : diverging section 
         M: merging section 
         M 1  to M 15 : merging section 
         C: curve segment 
         C 1  to C 4 : curve segment 
       
     
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0057]    Hereinafter, preferred embodiments for carrying out the present invention will be described. 
         [0058]      FIGS. 1 to 6  show an overhead traveling vehicle system  2  according to a preferred embodiment of the present invention. It should be noted that other types of overhead traveling vehicles may be used. For example, rail guided vehicles that travel on the ground or automated guided vehicles that travel without any rail may be used.  FIG. 1  shows a non-limiting example of an overall layout of the overhead traveling vehicle system. A reference numeral  4  denotes an inter-bay route of a semiconductor factory or the like, reference numerals  6  denote intra-bay routes, and reference numerals  8  and  10  denote shortcuts. The overall control of the system  2  is implemented by a ground controller  12 . A plurality of overhead traveling vehicles  14  travel to circulate along the routes  4 ,  6  or the like in one direction. The routes  4 ,  6  include straight segments, diverging sections D 1  to D 15 , merging sections M 1  to M 15 , and curve segments C 1  to C 4 . 
         [0059]      FIG. 2  shows control in the diverging section D. Control in the diverging section D is applicable to each of the diverging sections D 1  to D 15  shown in  FIG. 1 . A reference numeral  20  denotes a blocking area. For entry into the blocking area  20 , the overhead traveling vehicle  14  requires permission from the ground controller  12 . An inter-vehicle distance control area  21  including the blocking area  20 , which is larger than the blocking area  20 , is provided. The inter-vehicle distance control area  21  is extended along the entrance of the blocking area  20  and an exit  22  of a diverging lane. No inter-vehicle distance control area is provided at an exit  23  of a straight lane. Further, in the inter-vehicle distance control area  21  including the blocking area  20 , the overhead traveling vehicle  14  obtains the inter-vehicle distance to a leading traveling vehicle by communication. The overhead traveling vehicle  14  implements velocity control based on the inter-vehicle distance to avoid interference with the leading traveling vehicle. By performing blocking control, two overhead traveling vehicles  14  do not enter the blocking area  20  at the same time. 
         [0060]    The overhead traveling vehicle  14  determines an inter-vehicle distance with a leading overhead traveling vehicle preferably by an optical distance sensor  54  as described later, and implements velocity control to avoid interference. This control is implemented in the straight segment. Further, in the curve segment, since it is difficult to detect the leading traveling vehicle by the optical distance sensor, the curve segment is also included in the inter-vehicle distance control area. The inter-vehicle distance with the leading traveling vehicle is obtained by communication, and velocity control is implemented to avoid interference or the like. 
         [0061]    The range of the inter-vehicle distance control area  21  will be described. At the entrance  24  of the diverging lane, it may be difficult to detect an overhead traveling vehicle  14   a  diverging from the blocking area  20  by the optical distance sensor. Therefore, it is preferable to obtain the inter-vehicle distance by communication. Further, it may be difficult for an overhead traveling vehicle  14   c  in the middle of transition from straight movement to curving movement at the exit of the diverging lane, to detect a leading overhead traveling vehicle by the optical distance sensor. Therefore, likewise, it is preferable to obtain the inter-vehicle distance by communication. In contrast, the overhead traveling vehicle  14   d  at the exit  23  of the straight lane can detect the leading traveling vehicle by the optical distance sensor. Therefore, no inter-vehicle distance control area is required at the exit  23  of the straight lane. Further, the blocking area  20  is included in the inter-vehicle distance control area  21 , and the overhead traveling vehicle  14   a  in the blocking area  20  obtains the position of the leading overhead traveling vehicle  14   c  by communication. 
         [0062]    In the inter-vehicle distance control area  21  including the blocking area  20 , each of the overhead traveling vehicles  14   a  to  14   c  obtains the distance to the leading overhead traveling vehicle by communication, and implements velocity control in accordance with the distance. When the overhead traveling vehicle enters the blocking area  20  from the entrance of the diverging lane, the overhead traveling vehicle obtains permission from the ground controller  12 . When the overhead traveling vehicle exits the blocking area  20 , the overhead traveling vehicle reports the current position and velocity to the ground controller  12 , and the ground controller  12  detects that the blocking area  20  has become vacant. 
         [0063]      FIG. 3  shows control in the merging section M. This control is commonly applicable to the merging sections M 1  to M 15 . A reference numeral  30  denotes a blocking area. When the overhead traveling vehicle  14  enters the blocking area  30 , permission from the ground controller  12  is required beforehand. An inter-vehicle distance control area  31  is present over an area including the blocking area  30 , and is larger than the blocking area  30 . The inter-vehicle distance control area  31  includes an area at the entrance  32  of a merging lane of the blocking area  30  and an area at the exit  34  of the blocking area  30 . Since the entrance  32  of the merging lane is provided in a curve segment, the entrance  32  of the merging lane is included in the inter-vehicle control area  31 . It should be noted that the entrance  33  of the straight lane of the blocking area  30  is not included in the inter-vehicle distance control area  31 . 
         [0064]    In each of the cases of  FIG. 2  and  FIG. 3 , the length along the traveling path of the blocking area  20  or the blocking area  30  is substantially equal to the length of the vehicle body of the overhead traveling vehicle  14 , and this length is the minimum size for avoiding interference between the 1 overhead traveling vehicles  14 . Further, in the inter-vehicle distance control areas  21 ,  31 , the overhead traveling vehicle  14  obtains the distance to the leading transportation vehicle by communication, and implements velocity control based on the distance to avoid interference. The entrance  33  of the straight lane of the blocking area  30  is not included in the inter-vehicle distance control area  31 . It is because, in the presence of the blocking area  30 , the traveling vehicle that has traveled in the straight segment can avoid interference with the leading traveling vehicle. Further, when the overhead traveling vehicle  14   g  that travels at the exit  34  of the merging lane comes from the entrance  32  of the merging lane, the leading traveling vehicle may not be detected until the vehicle body is oriented so as to be completely straight. Therefore, the exit  34  of the merging lane is included in the inter-vehicle distance control area  31 . 
         [0065]      FIG. 4  shows control in the curve segment C. In the straight segment, as described above, the overhead traveling vehicle  14  determines the distance to the leading transportation vehicle by the optical distance sensor to implement velocity control. In the curve segment C, since it may be difficult to detect the leading transportation vehicle by the optical distance sensor, the inter-vehicle distance is determined by communication to implement velocity control. 
         [0066]    As a result of these operations, in the straight segment, basically, interference avoidance by the optical distance sensor is performed. In the curve segment, the diverging section, or the merging section, interference avoidance based on the inter-vehicle distance determined by communication is performed. Blocking control is implemented only in the minimum requisite range, i.e., in the blocking areas  20 ,  30 . In general, since only one overhead traveling vehicle  14  can travel in one blocking area at one time, the size of the blocking area is inversely proportional to the number of overhead traveling vehicles  14  that can pass through the blocking area. In the present preferred embodiment, the number of overhead traveling vehicles  14  that can travel within the blocking area  20  or the blocking area  30  is increased to improve the throughput of the system  2 . 
         [0067]      FIG. 5  shows the relationship between the ground controller  12  and the overhead traveling vehicle  14 . A reference numeral  50  denotes a wired or wireless LAN. For example, a feeder cable or a non-contact feeder cable may be included in a wired LAN. A wireless LAN may be adopted instead of the wired LAN. The ground controller  12  includes a communication interface and a blocking controller  53 . The blocking controller  53  stores data as to whether the blocking area  20  or the blocking area  30  is occupied or not. When the blocking controller  53  receives permission requests from the overhead traveling vehicles  14 , the blocking controller  53  issues travel permissions in accordance with a predetermined order. 
         [0068]    In the areas other than the inter-vehicle control area, the overhead traveling vehicle  14  determines the inter-vehicle distance to the leading overhead traveling vehicle using an optical distance sensor  54  such as a laser distance sensor, for example. It should be noted that a supersonic distance sensor, a microwave distance sensor or the like may be used instead of the optical distance sensor. Marks  56  such as magnetic marks are provided along the travel rail or the like of the overhead traveling vehicle  14 , and an absolute position sensor  55  is preferably used to detect the marks  56  for determining an absolute position of the overhead traveling vehicle  14 . Alternatively, comb teeth like marks may be used as the marks  56 . The overhead traveling vehicle  14  reports its own position and velocity determined by the absolute position sensor  55  to the ground controller  12  through the LAN  50 . The overhead traveling vehicle  14  intercepts the current position and velocity of the other overhead traveling vehicle  14  to determine the inter-vehicle distance, and implement velocity control to avoid interference. 
         [0069]      FIG. 6  shows a pattern of permissions issued in response to blocking requests to the merging section M. There are two options for the merging section M, i.e., whether a priority is given to the overhead traveling vehicle coming from the merging lane or the overhead traveling vehicle coming from the straight lane. A reference numeral  69  denotes a velocity permission pattern in a conventional example. Permissions are given to travel permission requests in the order of the earliest reception. In contrast, a reference numeral  68  denotes a velocity permission pattern in the present preferred embodiment of the present invention. Permissions are preferentially given to permission requests coming from the same lane where permission has already been given. 
         [0070]    As shown on the lower side of  FIG. 6 , it is assumed that permission requests  61  to  67  have reached the controller  12  separately. Reference numerals  61  to  64  denote permission requests from the straight lane, and reference numerals  65  to  67  denote permission requests from the merging lane. Since the blocking controller  53  firstly received the permission request  61  from the straight lane, the blocking controller  53  gives permission in response to the request, and performs blocking. It is assumed that the permission request  65  from the merging lane is received initially, and thereafter, the permission request  62  from the straight lane is received. In this case, a priority is given to the permission request  62  from straight lane where permission has been given to the previous request. In the absence of any other permission request before blocking for the permission request  62  is released, permission is given to the permission request  65  from the merging lane. Since the permission request  63  from the straight lane and the permission request  66  from the merging lane have reached before blocking for the permission request  65  is released, permission is given to the permission request  66  from the merging lane. After blocking for the permission request  66  is released, permission is given to the permission request  63  from the straight lane. In the meantime, if any permission request  67  from the merging lane is received, such a permission request is suspended, and a priority is given to the permission request  64  from the straight lane. 
         [0071]    In the algorithm of processing, a priority is given to the permission request from the lane where permission has already been given to the previous permission request. In this manner, since permissions are given successively to permission requests from the same lane, the overhead traveling vehicles  14  can travel more efficiently in the blocking area  30 . 
         [0072]    In the present preferred embodiment of the present invention, the following advantages are obtained. 
         [0073]    Since the sizes of the blocking areas  20 ,  30  are minimized, the number of overhead traveling vehicles  14  that can pass through the blocking areas  20 ,  30  per unit time is increased, and improvement in the transportation efficiency is achieved. 
         [0074]    In the straight segment, since interference is avoided using the optical distance sensor  54 , processing is simplified. 
         [0075]    In the inter-vehicle distance control area such as the curve segment, the diverging section, and the merging section, reports of positions of overhead traveling vehicles to the controller are intercepted by communication to implement inter-vehicle distance control. In the system, in comparison with the case of adopting direct communication between the traveling vehicles  14 , communication traffic of the LAN  50  is reduced. 
         [0076]    In the merging section, blocking permissions are given preferentially to the overhead traveling vehicles that enter the merging section from the same lane. Therefore, the overhead traveling vehicles can travel through the merging section more efficiently. 
         [0077]    It should be noted that the overhead traveling vehicle  14  reports its own position to the ground controller  12 , and such a report may be made only in the inter-vehicle distance control areas  21 ,  31 . 
         [0078]    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 the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.