Patent Publication Number: US-2023143085-A1

Title: Article Transport Facility

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is claims priority to Japanese Patent Application Nos. 2021-181421 filed Nov. 5, 2021, 2021-181422 filed Nov. 5, 2021, and 2021-181423 filed Nov. 5, 2021, the disclosures of which are hereby incorporated by reference in their entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an article transport facility including a transport vehicle for transporting an article. 
     2. Description of the Related Art 
     An example of such an article transport facility is disclosed in Japanese Patent Application Laid-Open No. 2017-150005 (Patent Document 1). In the following description of the background art, reference numerals in parentheses refer to Patent Document 1. 
     The article transport facility disclosed in Patent Document 1 includes a travel rail ( 4 ) on which a transport vehicle ( 8 ) travels. A first rail ( 9 ) and a second rail ( 11 ) extending in different directions intersect in the same horizontal plane to form the travel rail ( 4 ). The transport vehicle ( 8 ) is configured to be able to travel along the first rail ( 9 ) and to travel along the second rail ( 11 ). That is, the transport vehicle ( 8 ) can travel in two different directions. 
     In the article transport facility disclosed in Patent Document 1, two travel routes, that is, the first rail ( 9 ) and the second rail ( 11 ), intersect in the same horizontal plane, and therefore a level difference is likely to be formed at an intersection portion ( 14 ) where both rails intersect. For this reason, there is a high likelihood that the transport vehicle ( 8 ) will vibrate when passing through the intersection portion ( 14 ). Also, for example, if the travel rail ( 4 ) is integrally formed in such a manner that there is no seam between the first rail ( 9 ) and the second rail ( 11 ) that intersect each other, this causes an increase in the size of the travel rail ( 4 ). In this case, there are more restrictions when installing the travel rail ( 4 ) in the article transport facility. 
     SUMMARY OF THE INVENTION 
     In view of the above-mentioned situation, it is desired that vibration of the transport vehicle is suppressed and a degree of freedom in setting the travel route is ensured in an article transport facility including a travel route in which a plurality of routes with different extension directions intersect each other. 
     A technique for solving the above problems is as follows. 
     An article transport facility including a transport vehicle configured to transport an article, the article transport facility including: 
     at least one first rail including a first travel surface; and 
     at least one second rail including a second travel surface, 
     in which the at least one second rail is spaced upward relative to the at least one first rail and intersects the at least one first rail in a view in an up-down direction, 
     the transport vehicle includes a vehicle body disposed between the at least one first rail and the at least one second rail in the up-down direction, a first traveling unit configured to cause the vehicle body to travel along a first direction corresponding to a direction in which the at least one first rail extends, a second traveling unit configured to cause the vehicle body to travel along a second direction corresponding to a direction in the at least one second rail extends, and a control unit configured to control operations of the first traveling unit and the second traveling unit, 
     the first traveling unit includes a first wheel and a first orientation changing mechanism configured to change an orientation of the first wheel relative to the vehicle body, and the first traveling unit is configured to perform an orientation change between a first wheel placement orientation, in which the first wheel is placed on the first travel surface, and a first wheel retraction orientation, in which the first wheel is separated from the first travel surface, 
     the second traveling unit includes a second wheel and a second orientation changing mechanism configured to change an orientation of the second wheel relative to the vehicle body, and the second traveling unit is configured to perform an orientation change between a second wheel placement orientation, in which the second wheel is placed on the second travel surface, and a second wheel retraction orientation, in which the second wheel is separated from the second travel surface, and 
     the control unit is configured to change in mode between (i) a first mode of causing the vehicle body to travel along the at least one first rail with the first traveling unit in the first wheel placement orientation and the second traveling unit in the second wheel retraction orientation, and (ii) a second mode of causing the vehicle body to travel along the at least one second rail with the second traveling unit in the second wheel placement orientation and the first traveling unit in the first wheel retraction orientation. 
     According to this configuration, it is possible to cause the transport vehicle to travel in the first direction along the first rail, and to cause the transport vehicle to travel in the second direction along the second rail. The second rail is spaced upward relative to the first rail. That is, the first rail and the second rail are disposed at different positions in the up-down direction. As a result, the travel route along the first rail and the travel route along the second rail can be disposed in different horizontal planes while intersecting each other in a view in the up-down direction. Accordingly, with this configuration, there is no seam between the first rail and the second rail, and no level difference is formed due to the existence of the seam, and therefore it is possible to prevent vibration that occurs when the transport vehicle travels in the portion where both rails intersect. Also, since the first rail and the second rail are physically spaced apart from each other, the first rail and the second rail can be installed at different times. Accordingly, it is possible to ensure a degree of freedom when installing the travel route constituted by the first rail and the second rail in the article transport facility. As described above, according to this configuration, it is possible to suppress vibration of the transport vehicle and to ensure a degree of freedom in the installation of the travel route in the article transport facility including the travel route in which a plurality of routes with different extension directions intersect each other. 
     Further features and advantages of the technique according to the present disclosure will become evident from the following description of exemplary and non-limiting embodiments described with reference to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a plan view showing an intersection area of an article transport facility. 
         FIG.  2    is a view of a transport vehicle in a first direction during execution of a first mode. 
         FIG.  3    is a view of the transport vehicle in a second direction during execution of a second mode. 
         FIG.  4    is an illustrative diagram of a case where a transfer operation is performed with respect to a transfer target location. 
         FIG.  5    is an illustrative diagram of a case where a transfer operation is performed with respect to a storage shelf. 
         FIG.  6    is a diagram showing a structure of an engaging portion and an engaged portion. 
         FIG.  7    is a view in a first direction showing a state in which the transport vehicle is executing the first mode and a second transport vehicle is executing a fourth mode in a second embodiment. 
         FIG.  8    is a view in a second direction showing a state in which the transport vehicle is executing the first mode and the second transport vehicle is executing the fourth mode in the second embodiment. 
         FIG.  9    is a diagram showing another example of the engaging portion and the engaged portion. 
         FIG.  10    is a diagram showing another example of the engaging portion and the engaged portion. 
         FIG.  11    is a diagram showing another example of the engaging portion and the engaged portion. 
         FIG.  12    is a diagram showing another example of the engaging portion and the engaged portion. 
         FIG.  13    is a view in a second direction showing another example of a second rail. 
         FIG.  14    is a view in a second direction showing another example of the second rail. 
         FIG.  15    is a view in a second direction showing another example of the second rail. 
         FIG.  16    is a diagram showing another example of an elevating apparatus. 
         FIG.  17    is a diagram showing another example of the elevating apparatus. 
         FIG.  18    is a plan view showing a route connecting two intersection areas. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     Embodiments of an article transport facility will be described below with reference to the drawings. 
     As shown in  FIGS.  1  to  3   , an article transport facility  100  includes transport vehicles V for transporting an article G, first rails R 1  including first travel surfaces Fr 1 , and second rails R 2  including second travel surfaces Fr 2 . The transport vehicles V can travel along the first rails R 1  and travel along the second rails R 2 . That is, the travel route of the transport vehicles V is set along the first rails R 1  and the second rails R 2 . 
     Hereinafter, the extension direction of the first rails R 1  is a first direction X, and the extension direction of the second rails R 2  is a second direction Y. Also, a direction orthogonal to the first direction X in a view along an up-down direction is a first width direction Xw, and a direction orthogonal to the second direction Y in a view in the up-down direction is a second width direction Yw. In this embodiment, the first direction X and the second direction Y are orthogonal to each other in a view in the up-down direction. That is, in the present embodiment, the first width direction Xw orthogonal to the first direction X in a view in the up-down direction is equal to the second direction Y. Also, the second width direction Yw orthogonal to the second direction Y in a view in the up-down direction is equal to the first direction X. 
     In the present embodiment, the location where the article G is transferred to and from the transport vehicle V is a transfer target location S, and the article transport facility  100  includes a plurality of transfer target locations S (see  FIGS.  4  and  5   ). As shown in  FIG.  4   , the transfer target location S includes a mounting platform  91 . The article G is transported to the mounting platform  91  for a specific purpose. This particular purpose differs depending on the type and state of the article G, and the like. Also, as shown in  FIG.  5   , the article transport facility  100  includes a storage shelf  8  capable of holding the article G. In this example, the transfer target location S also includes this storage shelf  8 . The storage shelf  8  is provided at an intermediate position on the route along which the article G is transported. As a result, the article G can be temporarily or long-term stored on the storage shelf  8  while the article G is being transported by the transport vehicle V. Note that although detailed illustration is omitted, the transfer target location S includes, for example, a conveyor for entering and leaving an article storeroom. 
     The article transport facility  100  is used, for example, in a semiconductor manufacturing factory. As shown in  FIG.  4   , in the present embodiment, the article transport facility  100  includes a processing apparatus  90  that processes the article G, and the above-described mounting platform  91  is arranged adjacent to the processing apparatus  90 . 
     In this embodiment, the transport vehicle V transports the article G that has not yet been processed by the processing apparatus  90  to the mounting platform  91 , and transports the article G that has been processed by the processing apparatus  90  from the mounting platform  91  to a specified transport destination. For example, the article G is a container that contains a processing target object to be processed by the processing apparatus  90 , and the above-mentioned “processing performed on the article G” means processing performed on the processing target object contained in the article G. 
     Examples of the article G include a wafer accommodating container for accommodating a wafer (a so-called FOUP: Front Opening Unified Pod) and a reticle accommodating container for accommodating a reticle (a so-called reticle pod). If the article G is a FOUP, the processing target object is a wafer. If the article G is a reticle pod, the processing target object is a reticle. In the semiconductor manufacturing factory illustrated here, the processing apparatus  90  performs various processes such as thin film formation, photolithography, and etching on a semiconductor substrate. 
     As shown in  FIGS.  2  and  3   , the second rail R 2  is spaced upward from the first rail R 1  and intersects the first rail R 1  in a view in an up-down direction. That is, the first rail R 1  and the second rail R 2  are disposed at different positions in the up-down direction. As a result, the travel route along the first rail R 1  and the travel route along the second rail R 2  can be disposed in different horizontal planes while intersecting each other in a view in the up-down direction. 
     According to this configuration, the first rail R 1  and the second rail R 2  are not connected to each other, and therefore there is no seam between the first rail R 1  and the second rail R 2 . Accordingly, since there is no level difference resulting from the presence of a seam, it is possible to prevent vibration from occurring when the transport vehicle V travels through the portion where both rails (R 1 , R 2 ) intersect each other. Also, since the first rail R 1  and the second rail R 2  are physically separated from each other, the first rail R 1  and the second rail R 2  can be installed at different times. Accordingly, it is possible to ensure a degree of freedom in the task when installing the travel route constituted by the first rail R 1  and the second rail R 2  in the article transport facility  100 . 
     As shown in  FIG.  1   , in the present embodiment, the article transport facility  100  has an intersection area CA where the travel route along the first rail R 1  and the travel route along the second rail R 2  intersect each other. In this example, the first rail R 1  and the second rail R 2  are orthogonal in a view in the up-down direction. The plurality of first rails R 1  are disposed side by side in the direction (first width direction Xw, second direction Y) orthogonal to the first direction X in a view in the up-down direction, and the plurality of second rails R 2  are disposed side by side in the direction (second width direction Yw, first direction X) orthogonal to the second direction Y in a view in the up-down direction. As a result, in this example, a travel route in which the plurality of first rails R 1  and the plurality of second rails R 2  form a lattice in a view in the up-down direction is provided in the intersection area CA. 
     As described above, the first rail R 1  includes the first travel surfaces Fr 1  on which the transport vehicle V travels along the first direction X. As shown in  FIGS.  2  and  3   , in the present embodiment, the first rail R 1  includes first guide surfaces Fg 1  facing a direction (in this example, the second direction Y) orthogonal to the first direction X in a view in the up-down direction. In other words, the first rail R 1  includes the first guide surfaces Fg 1  facing the first width direction Xw. The first guide surfaces Fg 1  are surfaces for guiding the transport vehicle V along the first direction X. 
     Also, as described above, the second rail R 2  includes the second travel surfaces Fr 2  on which the transport vehicle V travels along the second direction Y. In this embodiment, the second rail R 2  includes second guide surfaces Fg 2  that face a direction (in this example, the first direction X) orthogonal to the second direction Y in a view in an up-down direction. 
     In other words, the second rail R 2  includes the second guide surfaces Fg 2  facing the second width direction Yw. 
     The second guide surfaces Fg 2  are surfaces for guiding the transport vehicle V along the second direction Y. 
     As shown in  FIG.  2   , in this embodiment, the first rail R 1  includes a pair of first rail bodies RB 1  spaced apart in a first width direction Xw. In this example, each of the plurality of first rails R 1  disposed side by side in the first width direction Xw includes a pair of first rail bodies RB 1  spaced apart in the first width direction Xw. That is, one first rail R 1  is constituted by a pair of first rail bodies RB 1  spaced apart in the first width direction Xw, and a plurality of first rails R 1  are disposed side by side in the first width direction Xw. 
     In the present embodiment, two first rails R 1  adjacent to each other in the first width direction Xw share one first rail body RB 1 , and the first rail body RB 1  has a pair of first travel surfaces Fr 1  formed thereon that respectively belong to the two first rails R 1  adjacent to each other in the first width direction Xw. As a result, the number of first rail bodies RB 1  to be installed can be reduced in the entire facility. Accordingly, it is easy to reduce the number of man-hours when installing the first rails R 1 . 
     In the present embodiment, the first rail body RB 1  includes a first main body portion R 11  extending along the first direction X, and a first wall portion R 12  that protrudes upward from the first main body portion R 11  and extends along the first direction X. The first travel surfaces Fr 1  are formed by the upward-facing surface of the first main body portion R 11 . In this example, the first travel surfaces Fr 1  are disposed on both sides of the first wall portion R 12  in the first width direction Xw. The first guide surfaces Fg 1  are formed by surfaces of the first wall portion R 12  facing both sides in the first width direction Xw. 
     With the above-described configuration, it is possible to cause both the transport vehicle V that travels on one side of the first wall portion R 12  in the first width direction Xw and the other transport vehicle V that travels on the other side of the first wall portion R 12  in the first width direction Xw to appropriately travel using the pair of first travel surfaces Fri included on one first rail body RB 1 , and it is possible to appropriately guide both of the transport vehicles V using the pair of first guide surfaces Fg 1  included on one first rail body RB 1 . In this example, the cross-section of the first rail body RB 1  orthogonal to the first direction X is in an inverted T shape. 
     As shown in  FIG.  3   , in the present embodiment, the second rail R 2  includes a pair of second rail bodies RB 2  spaced apart in the second width direction Yw. In this example, each of the plurality of second rails R 2  disposed side by side in the second width direction Yw includes a pair of second rail bodies RB 2  spaced apart in the second width direction Yw. That is, one second rail R 2  is constituted by a pair of second rail bodies RB 2  spaced apart in the second width direction Yw, and a plurality of second rails R 2  are disposed side by side in the second width direction Yw. 
     In the present embodiment, two second rails R 2  adjacent to each other in the second width direction Yw share one second rail body RB 2 , and a pair of second travel surfaces Fr 2  that respectively belong to the two rails R 2  adjacent to each other in the second width direction Yw are formed on the second rail body RB 2 . This makes it possible to reduce the number of second rail bodies RB 2  to be installed in the entire facility. Accordingly, it is easy to reduce the number of man-hours when installing the second rails R 2 . 
     In the present embodiment, the second rail body RB 2  includes a second main body portion R 21  extending along the second direction Y, and a second wall portion R 22  that protrudes upward from the second main body portion R 21  and extends along the second direction Y. The second travel surfaces Fr 2  are formed by the upward-facing surface of the second main body portion R 21 . In this example, the second travel surfaces Fr 2  are disposed on both sides of the second wall portion R 22  in the second width direction Yw. The second guide surfaces Fg 2  are formed by surfaces of the second wall portion R 22  facing both sides in the second width direction Yw. 
     With the above-described configuration, it is possible to cause both the transport vehicle V that travels on one side of the second wall portion R 22  in the second width direction Yw and the other transport vehicle V that travels on the other side of the second wall portion R 22  in the second width direction Yw to appropriately travel using the pair of second travel surfaces Fr 2  included on one second rail body RB 2 , and it is possible to appropriately guide both of the transport vehicles V using the pair of second guide surfaces Fg 2  included on one second rail body RB 2 . In this example, the cross-section of the second rail body RB 2  orthogonal to the second direction Y is in an inverted T shape. 
     As shown in  FIGS.  2  and  3   , the transport vehicle V includes a vehicle body Va, a first traveling unit U 1  that causes the vehicle body Va to travel along the first direction X, a second traveling unit U 2  that causes the vehicle body Va to travel along the second direction Y, and a control unit C that controls the operations of the first traveling unit U 1  and the second traveling unit U 2 . The vehicle body Va is disposed between the first rail R 1  and the second rail R 2  in the up-down direction. Specifically, the vehicle body Va is disposed between an upper end of the first rail body RB 1  (an upper end of the first wall portion R 12 ) and a lower end of the second rail body RB 2  (the lower end of the second main body portion R 21 ) in the up-down direction. 
     In this embodiment, the transport vehicle V includes an accommodation portion Vb that accommodates the article G during travel. The accommodation portion Vb is provided in the vehicle body Va. In this example, the transport vehicle V includes an elevating body Vc coupled to the vehicle body Va, an elevating apparatus Vd that raises and lowers the elevating body Vc relative to the vehicle body Va, and a holding section Ve that is supported by the elevating body Vc and holds the article G. 
     In this embodiment, the vehicle body Va has a shape that covers the article G accommodated in the accommodation portion Vb from a plurality of directions. In this example, the vehicle body Va has a shape that covers the upper side and both sides in the second direction Y of the article G accommodated in the accommodation portion Vb. For this reason, the lower side and both sides in the first direction X of the article G accommodated in the accommodation portion Vb are open. These open portions are used when the article G is transferred to and from the mounting platform  91  or the storage shelf  8 . The details of the transfer of the article G will be described later. 
     The first traveling unit U 1  includes a first wheel  11  and a first orientation changing mechanism  13  that changes the orientation of the first wheel  11  relative to the vehicle body Va, and the first traveling unit U 1  performs an orientation change between a first wheel placement orientation, in which the first wheel  11  is placed on the first travel surface Fr 1 , and a first wheel retraction orientation, in which the first wheel  11  is separated from the first travel surface Fr 1 . In this embodiment, the first wheel  11  is rotationally driven. As a result, a propulsive force by which the vehicle body Va travels along the first direction X is generated. Note that  FIG.  2    shows the first wheel placement orientation of the first traveling unit U 1 .  FIG.  3    shows the first wheel retraction orientation of the first traveling unit U 1 . 
     In this embodiment, the first traveling unit U 1  includes a first guide wheel  12  guided by the first guide surface Fg 1 . The first guide wheel  12  is in contact with the first guide surface Fg 1  while the first traveling unit U 1  is in the first wheel placement orientation, and is separated from the first guide surface Fg 1  while the first traveling unit U 1  is in the first wheel retraction orientation. With such a configuration, when the first traveling unit U 1  causes the vehicle body Va to travel along the first rail R 1  in the first wheel placement orientation, the first guide wheel  12  can appropriately guide the vehicle body Va along the first rail R 1 . 
     In the present embodiment, while the first traveling unit U 1  is in the first wheel placement orientation, the first wheel  11  is placed on the first travel surface Fr 1  with the rotation axis of the first wheel  11  directed in the first width direction Xw (the second direction Y). Also, while the first traveling unit U 1  is in the first wheel placement orientation, the first guide wheel  12  is in contact with the first guide surface Fg 1  with the rotation axis of the first guide wheel  12  directed in the up-down direction. 
     In this embodiment, the transport vehicle V includes a plurality of first traveling units U 1 . The transport vehicle V travels along the first rail R 1  using the plurality of first traveling units U 1 . As described above, the first rail R 1  on which the transport vehicle V travels along the first direction X includes the pair of first rail bodies RB 1  spaced apart in the first width direction Xw. In this embodiment, the first traveling units U 1  are provided corresponding to the pair of first rail bodies RB 1  spaced apart in the first width direction Xw. Also, in this example, the pair of first traveling units U 1  are separated from each other in the first direction X on the two side portions of the vehicle body Va in the first width direction Xw (second direction Y) (see  FIG.  3   ). That is, in this example, the transport vehicle V includes a total of four first traveling units U 1 . 
     The second traveling unit U 2  includes a second wheel  21  and a second orientation changing mechanism  23  that changes the orientation of the second wheels  21  relative to the vehicle body Va, and the second traveling unit U 2  performs an orientation change between a second wheel placement orientation, in which the second wheel  21  is placed on the second travel surface Fr 2 , and a second wheel retraction orientation, in which the second wheel  21  is separated from the second travel surface Fr 2 . In this embodiment, the second wheel  21  is rotationally driven. As a result, a propulsive force for causing the vehicle body Va to travel along the second direction Y is generated. Note that  FIG.  2    shows the second wheel retraction orientation of the second traveling unit U 2 .  FIG.  3    shows the second wheel placement orientation of the second traveling unit U 2 . 
     As shown in  FIG.  3   , in this embodiment, the second traveling unit U 2  includes a second guide wheel  22  guided by the second guide surface Fg 2 . The second guide wheel  22  is in contact with the second guide surface Fg 2  while the second traveling unit U 2  is in the second wheel placement orientation, and is separated from the second guide surface Fg 2  while the second traveling unit U 2  is in the second wheel retraction orientation. With such a configuration, when the second traveling unit U 2  causes the vehicle body Va to travel along the second rail R 2  in the second wheel placement orientation, the second guide wheel  22  can appropriately guide the vehicle body Va along the second rail R 2 . 
     In the present embodiment, while the second traveling unit U 2  is in the second wheel placement orientation, the second wheel  21  is placed on the second travel surface Fr 2  with the rotation axis of the second wheel  21  directed in the second width direction Yw (first direction X). Also, while the second traveling unit U 2  is in the second wheel placement orientation, the second guide wheel  22  is in contact with the second guide surface Fg 2  with the rotation axis of the second guide wheel  22  directed in the up-down direction. 
     In this embodiment, the transport vehicle V includes a plurality of second traveling units U 2 . The transport vehicle V travels along the second rail R 2  using the plurality of second traveling units U 2 . As described above, the second rail R 2  on which the transport vehicle V travels along the second direction Y includes a pair of second rail bodies RB 2  spaced apart in the second width direction Yw. In this embodiment, the second traveling units U 2  are provided so as to respectively correspond to the pair of second rail bodies RB 2  spaced apart in the second width direction Yw. Also, in this example, a pair of second traveling units U 2  are separated from each other in the first direction X on both side portions of the vehicle body Va in the first width direction Xw (second direction Y) (see  FIG.  3   ). That is, in this example, the transport vehicle V has a total of four second traveling units U 2 . 
     The control unit C can change in mode between a first mode of causing the vehicle body Va to travel along the first rail R 1  with the first traveling units U 1  in the first wheel placement orientation and the second traveling units U 2  in the second wheel retraction orientation, and a second mode of causing the vehicle body Va to travel along the second rail R 2  with the second traveling units U 2  in the second wheel placement orientation and the first traveling units U 1  in the first wheel retraction orientation.  FIG.  2    shows a state in which the control unit C is executing the first mode.  FIG.  3    shows a state in which the control unit C is executing the second mode. 
     In the present embodiment, before changing between the first mode and the second mode, the control unit C is in a double-supported state in which the vehicle body Va is supported by both the first rail R 1  and the second rail R 2  with the first traveling units U 1  in the first wheel placement orientation and the second traveling units U 2  in the first wheel placement orientation. When the first mode is to be executed, the control unit C changes the second traveling units U 2  from the double-supported state to the second wheel retraction orientation. Also, when the second mode is to be executed, the control unit C changes the first traveling units U 1  from the double-supported state to the first wheel retraction orientation. With such a configuration, the mode can be changed while appropriately supporting the vehicle body Va. Note that the mode change between the first mode and the second mode is executed while the vehicle body Va is at the intersection location where the first rail R 1  and the second rail R 2  intersect in a view in the up-down direction. 
     In the present embodiment, the first wheels  11  and the first guide wheels  12  are above the first rail R 1  while the first traveling units U 1  are in the first wheel retraction orientation (see  FIG.  3   ). As a result, when the control unit C executes the second mode and the transport vehicle V travels along the second direction Y, the first wheels  11  and the first guide wheels  12  can be prevented from interfering with the first rail R 1 . Accordingly, it is possible to cause the transport vehicle V to travel appropriately along the second direction Y. 
     In the present embodiment, when the second traveling units U 2  is in the second wheel retraction orientation, the second wheels  21  and the second guide wheels  22  are below the second rail R 2  (see  FIG.  2   ). As a result, when the control unit C executes the first mode and the transport vehicle V travels along the first direction X, the second wheels  21  and the second guide wheels  22  can be prevented from interfering with the second rail R 2 . Accordingly, it is possible to cause the transport vehicle V to travel appropriately along the first direction X. 
     In the present embodiment, the first orientation changing mechanism  13  includes a first support arm  131  that is swingably coupled to the vehicle body Va and supports the first wheel  11 , and a first drive unit  132  that drives the first support arm  131 . 
     In this embodiment, the first support arm  131  supports the first guide wheel  12  in addition to the first wheel  11 . The first support arm  131  rotatably supports both the first wheel  11  and the first guide wheel  12  such that the rotation axis of the first wheel  11  and the rotation axis of the first guide wheel  12  extend along different directions. More specifically, the first support arm  131  supports the first wheel  11  and the first guide wheel  12  such that the direction along the rotation axis of the first wheel  11  and the direction along the rotation axis of the first guide wheel  12  are orthogonal to each other. 
     In this embodiment, the first drive unit  132  swings the first support arm  131  about a first swing axis Ax 1  extending in the second direction Y to change the orientation of the first wheel  11  relative to the vehicle body Va. In this example, the first drive unit  132  also changes the orientation of the first guide wheel  12  relative to the vehicle body Va by swinging the first support arm  131  about the first swing axis Ax 1 . The first drive unit  132  includes, for example, a motor. 
     In this embodiment, the positions of the first wheels  11  and the first guide wheels  12  (indicated by the solid lines in  FIG.  3   ) when the first traveling units U 1  are in the first wheel retraction orientation are arranged toward the center of the vehicle body Va in the first direction X relative to the positions of the first wheels  11  and the first guide wheels  12  when the first traveling units U 1  are in the first wheel placement orientation (indicated by the broken lines in  FIG.  3   ). In this example, the first wheels  11  and the first guide wheels  12  when the first traveling units U 1  are in the first wheel retraction orientation are at positions overlapping with the vehicle body Va in a view in the second direction Y. This makes it easier to reduce the size of the transport vehicle V in the first direction X when the first traveling units U 1  are in the first wheel retraction orientation. 
     In this embodiment, the second orientation changing mechanism  23  includes a second support arm  231  that is swingably coupled to the vehicle body Va and supports the second wheel  21 , and a second drive unit  232  that drives the second support arm  231 . 
     In this embodiment, the second support arm  231  supports the second guide wheel  22  in addition to the second wheel  21 . The second support arm  231  rotatably supports both the second wheel  21  and the second guide wheel  22  such that the rotation axis of the second wheel  21  and the rotation axis of the second guide wheel  22  extend in different directions. More specifically, the second support arm  231  supports the second wheel  21  and the second guide wheel  22  such that the direction along the rotation axis of the second wheel  21  and the direction along the rotation axis of the second guide wheel  22  are orthogonal to each other. 
     In the present embodiment, the second drive unit  232  swings the second support arm  231  about a second swing axis Ax 2  extending in the second direction Y to change the orientation of the second wheel  21  relative to the vehicle body Va. In this example, the second drive unit  232  also changes the orientation of the second guide wheel  22  relative to the vehicle body Va by swinging the second support arm  231  about the second swing axis Ax 2 . The second drive unit  232  includes, for example, a motor. 
     In the present embodiment, the positions of the second wheels  21  and the second guide wheels  22  when the second traveling units U 2  are in the second wheel retraction orientation (indicated by the broken lines in  FIG.  3   ) are closer to the center of the vehicle body Va in the first direction X relative to the positions of the second wheels  21  and the second guide wheels  22  when the second traveling units U 2  are in the second wheel placement orientation (indicated by the solid lines in  FIG.  3   ). In this example, the second wheels  21  and the second guide wheels  22  when the second traveling units U 2  are in the second wheel retraction orientation are at positions overlapping with the vehicle body Va in a view in the second direction Y. This makes it easier to reduce the size of the transport vehicle V in the first direction X when the second traveling unit U 2  is in the second wheel retraction orientation. 
     As shown in the partially-enlarged view of  FIG.  3   , in the present embodiment, when the second orientation changing mechanism  23  changes the orientation of the second traveling unit U 2  from the second wheel retraction orientation to the second wheel placement orientation, the second wheel  21  is placed on the second travel surface Fr 2  at a position past an uppermost position Pt of a movement path along which the second wheel  21  due to swinging of the second support arm  231 . This makes it possible to place the second wheel  21  on the second travel surface Fr 2  by approaching the second travel surface Fr 2  from above. Accordingly, when the orientation is changed from the second wheel retraction orientation to the second wheel placement orientation, the orientation can be appropriately changed while reducing friction between the second wheel  21  and the second travel surface Fr 2 . By doing so, wearing of the second wheel  21  and the generation of dust can be suppressed. 
     With the configuration described above, it is possible to cause the transport vehicle V to travel in the first direction X along the first rail R 1  and to cause the transport vehicle V to travel in the second direction Y along the second rail R 2 . 
     Next, the configuration by which the transport vehicle V transfers the article G will be described mainly with reference to  FIGS.  4  and  5   . 
     As described above, in the present embodiment, the transport vehicle V includes the elevating body Vc coupled to the vehicle body Va, the elevating apparatus Vd that raises and lowers the elevating body Vc relative to the vehicle body Va, and the holding section Ve that is supported by the elevating body Vc and holds the article G, and the transport vehicle V transfers the article G to and from the mounting platform  91  and the storage shelf  8 . 
     In this embodiment, the elevation apparatus Vd includes a belt Vda coupled to the elevating body Vc, and an elevation drive unit Vdb that drives the belt Vda. Although detailed illustration is omitted, the elevation drive unit Vdb includes a pulley around which the belt Vda is wound, and a motor that rotationally drives the pulley. 
     In this embodiment, the holding section Ve performs an orientation change between a holding orientation, in which the article G is held, and a release orientation, in which the article G is released. In this example, the holding section Ve includes a pair of holding claws Vea that approach or separate from each other, and a holding drive unit Veb that drives the pair of holding claws Vea. The pair of holding claws Vea enter the holding orientation by approaching each other, and enter the holding release orientation by separating from each other. 
     In this embodiment, the elevation apparatus Vd raises and lowers the elevating body Vc between the pair of first rail bodies RB 1  in the first width direction Xw in a view in the up-down direction. In this example, the control unit C allows the elevating apparatus Vd to raise and lower the lifting body Vc during execution of the first mode. 
     To add further description, when the control unit C is executing the first mode, the vehicle body Va is disposed between the pair of first rail bodies RB 1  in the first width direction Xw in a view in the up-down direction. That is, when the control unit C is executing the first mode, the elevating body Vc is disposed at a position that does not overlap with the first rail body RB 1  in a view in the up-down direction. In this case, the elevating body Vc can be raised and lowered without interfering with the first rail body RB 1 . 
     Here, it is preferable that the control unit C prohibits the raising and lowering of the lifting body Vc by the lifting device Vd during execution of the second mode. To add further description, when the control unit C is executing the second mode, the position of the elevating body Vc in the second direction Y is determined according to the current position of the vehicle body Va traveling along the second rail R 2 . For this reason, the first rail body RB 1  can be disposed directly below the elevating body Vc. If the elevating body Vc is lowered in this state, the elevating body Vc and the first rail body RB 1  interfere with each other. However, by prohibiting the raising and lowering of the elevating body Vc by the lifting device Vd during the execution of the second mode, the control unit C can avoid such a situation where the elevating body Vc and the first rail body RB 1  interfere with each other. Note that even during execution of the second mode, the raising and lowering of the elevating body Vc by the lifting device Vd may also be permitted on the condition that the first rail body RB 1  is not arranged directly below the elevating body Vc. In this case, it is possible to confirm that the first rail body RB 1  is not disposed directly below the elevating body Vc by detecting the position of the first rail body RB 1  relative to the vehicle body Va with use of a sensor, for example. 
     The transport vehicle V further includes a slide apparatus Vf that slides the holding portion Ve along the horizontal direction relative to the elevating body Vc, and an engaging apparatus Vg that is supported by the elevating body Vc. 
     In this embodiment, the slide apparatus Vf includes a slide body Vfa that supports the holding section Ve and extends and retracts along the horizontal direction, and a slide drive unit (not shown) that drives the slide body Vfa to extend and retract. By extending and retracting the slide body Vfa, the holding section Ve supported by the slide body Vfa can be displaced in the horizontal direction. In this embodiment, the slide apparatus Vf slides the holding section Ve along the second direction Y. As a result, as shown in  FIG.  4   , even if the mounting platform  91  is disposed at a position shifted in the first width direction Xw (second direction Y) relative to the first rail R 1 , it is possible to appropriately transfer the article G to and from the mounting platform  91 . Also, as shown in  FIG.  5   , in this embodiment, the storage shelf  8  is disposed at a position shifted in the first width direction Xw (second direction Y) relative to the first rail R 1 . Accordingly, the slide apparatus Vf can appropriately transfer the article G to and from such a storage shelf  8 . Note that the storage shelf  8  is supported by the first rail R 1  below the first rail R 1 . In the illustrated example, the storage shelf  8  is supported by a pair of first rail bodies RB 1  belonging to another first rail R 1  adjacent in the first width direction Xw (second direction Y) to the first rail R 1  on which the transport vehicle V is present. 
     In this embodiment, the transport vehicle V further includes a second elevating apparatus Vd 2  that raises and lowers the holding section Ve relative to the slide apparatus Vf, below the slide apparatus Vf. The elevating apparatus Vd and the second elevating apparatus Vd 2  are different apparatuses. The elevating apparatus Vd may also be referred to as a “first elevating apparatus Vd” to distinguish it from the second elevating apparatus Vd 2 . 
     If the maximum elevation range in which the elevating apparatus Vd can raise and lower the elevating body Vc is a first elevation range and the maximum elevation range in which the second elevating apparatus Vd 2  can raise and lower the holding section Ve is a second elevation range, in the present embodiment, the first elevation range and the second elevation range are different from each other. In this example, the first elevation range is shorter than the second elevation range. That is, the range in which the elevating body Vc can be raised and lowered is shorter than the range in which the holding section Ve can be raised and lowered. 
     In this embodiment, the second elevating apparatus Vd 2  includes a belt Vd 2   a  coupled to the holding section Ve, and an elevation drive unit (not shown) that drives the belt Vd 2   a.  Although detailed illustration is omitted, the elevation drive unit of the second elevating apparatus Vd 2  includes a pulley around which the belt Vd 2   a  is wound, and a motor that rotationally drives the pulley. 
     Here, the first rail R 1  has an engaged portion Rg. In the present embodiment, the engaged portion Rg is disposed at a position corresponding to the transfer target location S in the first direction X. In this example, the engaged portion Rg is disposed at a position corresponding to the mounting platform  91  in the first direction X and a position corresponding to the storage shelf  8  in the first direction X. 
     The engaged portion Rg is provided on at least one of the pair of first rail bodies RB 1 . In this embodiment, the engaged portions Rg are provided on both of the pair of first rail bodies RB 1 . The engaged portions Rg provided on the pair of first rail bodies RB 1  are disposed at the same position in the first direction X. Specifically, the engaged portions Rg provided on the pair of first rail bodies RB 1  are disposed at the same position in the first direction X and the up-down direction. 
     In other words, the engaged portions Rg provided on the pair of first rail bodies RB 1  face each other in the second direction Y. 
     In this embodiment, the engaged portions Rg are fixed to the first rail R 1 , below the first travel surfaces Fr 1 . Specifically, the engaged portions Rg are fixed to the pair of first rail bodies RB 1  spaced apart in the first width direction Xw. The engaged portions Rg are provided so as to protrude downward from the first rail bodies RB 1 . 
     As shown in  FIG.  6   , in the present embodiment, the engaged portion Rg includes a block portion Rga in a block shape and an engaged hole Rgb formed in the block portion Rga. The engaged hole Rgb is open to the surface of the block portion Rga facing inward in the first width direction Xw (second direction Y). In this example, the engaged hole Rgb is formed such that the opening area narrows from the inner side in the first width direction Xw (second direction Y) toward the outer side in the first width direction Xw (second direction Y). In the illustrated example, the engaged hole Rgb is formed in a conical shape. 
     As shown in  FIGS.  4  and  5   , the engaging apparatus Vg is supported by the elevating body Vc. The engaging apparatus Vg includes an engaging portion Vga that engages with the engaged portion Rg, and an engagement drive unit Vgb that changes the orientation of the engaging portion Vga between an engagement orientation and a release orientation. 
     In this embodiment, the engaging apparatus Vg has a pair of engaging portions Vga. The pair of engaging portions Vga protrude outward in the first width direction Xw (second direction Y) relative to the elevating body Vc in at least the engagement orientation. In this example, each of the pair of engaging portions Vga is formed in a bar shape and is supported by the elevating body Vc in an orientation extending along the first width direction Xw (second direction Y). In this example, the leading end of each of the pair of engaging portions Vga is formed so as to taper toward the outer side (toward the engaged hole Rgb) in the first width direction Xw (the second direction Y). In the illustrated example, the leading end of the engaging portion Vga is formed in a hemispherical shape. 
     The engagement drive unit Vgb moves the engaging portion Vga back and forth along the first width direction Xw (the second direction Y), thereby changing the orientation of the engaging portion Vga between the engagement orientation and the release orientation. In this example, the engagement drive unit Vgb changes the orientation of the pair of engaging portions Vga. The engagement drive unit Vgb preferably includes, for example, a known mechanism such as a ball screw mechanism or a link mechanism for moving an object (the engaging portion Vga). 
     In the engagement orientation, the engaging portion Vga engages with the engaged portion Rg to restrict raising, lowering, and tilting of the elevating body Vc, and in the release orientation, the engaging portion Vga is separated from the engaged portion Rg to allow raising and lowering of the elevating body Vc.  FIGS.  4  and  5    show the engagement orientation of the engaging portion Vga. Note that  FIG.  2    shows the release orientation of the engaging portion Vga. 
     The control unit C sets the engaging portion Vga to the release orientation when the elevating apparatus Vd is to raise or lower the elevating body Vc, and sets the engaging portion Vga to the engagement orientation when the slide apparatus Vf is to cause the holding section Ve to protrude from the elevating body Vc in the horizontal direction. In the present embodiment, the control unit C sets the engaging portion Vga to the engagement orientation, and causes the holding section Ve to protrude in the first width direction Xw (the second direction Y) relative to the elevating body Vc by the slide apparatus Vf, or causes the holding section Ve to retract in the first width direction Xw (second direction Y) relative to the elevating body Vc. With the above configuration, when the article G is transferred to a position shifted in the horizontal direction from directly below the transport vehicle V, tilting of the elevating body Vc can be restricted by setting the engaging portion Vga to the engagement orientation. As a result, it is possible to appropriately transfer the article G to a position shifted in the horizontal direction from directly below the transport vehicle V. Note that the engaging portion Vga also positions the elevating body Vc in the first direction X in the engagement orientation. Accordingly, when the article G is transferred to and from the mounting platform  91  or the storage shelf  8 , positioning in the first direction X can also be easily performed. 
     In this embodiment, the transport vehicle V can execute a delivery operation of delivering the article G to the mounting platform  91  and a receiving operation of receiving the article G from the mounting platform  91  by sliding the holding section Ve with the slide apparatus Vf. 
     As shown in  FIG.  4   , when causing the transport vehicle V to deliver the article G to the mounting platform  91 , the control unit C lowers the elevating body Vc with the elevating apparatus Vd and sets the engaging portion Vga to the engagement orientation. Then, the control unit C causes the holding section Ve to protrude in the first width direction Xw (the second direction Y) relative to the elevating body Vc with the slide apparatus Vf, and disposes the holding section Ve directly above the mounting platform  91 . Thereafter, the control unit C lowers the holding section Ve with the second elevating apparatus Vd 2  and places the article G on the mounting platform  91  with the holding section Ve in the release orientation. When the control unit C causes the transport vehicle V to perform the operation of receiving the article G from the mounting platform  91 , the control unit C causes the apparatuses to perform operations opposite to those described above. 
     Note that if the mounting platform  91  is not disposed at a position shifted in the first width direction Xw (second direction Y) relative to the first rail R 1 , but at a position overlapping with the first rail R 1  in a view in the up-down direction (immediately below the transport vehicle V), there is no need to slide the holding section Ve with the slide apparatus Vf. In this case, the control unit C transfers the article G to and from the mounting platform  91  disposed directly below the transport vehicle V by operating at least one of the elevating apparatus Vd and the second elevating apparatus Vd 2 . In this case, depending on the situation, the engagement portion Vga may be in the engagement orientation or in the release orientation. 
     As described above, the transport vehicle V transfers the article G to and from the storage shelf  8  in addition to the mounting platform  91 . That is, in the present embodiment, the transport vehicle V can execute the delivery operation of delivering the article G to the storage shelf  8  and the receiving operation of receiving the article G from the storage shelf  8  by sliding the holding section Ve with the slide apparatus Vf. 
     As shown in  FIG.  5   , when the transport vehicle V is to perform a delivery operation or a receiving operation of the article G to or from the storage shelf  8 , the control unit C causes the elevating apparatus Vd to raise the elevating body Vc to a height corresponding to the storage shelf  8  and sets the engaging portion Vga to the engagement orientation. In the present embodiment, when the transport vehicle V is to execute a delivery operation of the article G to the storage shelf  8 , the control unit C lowers the elevating body Vc with the elevating apparatus Vd and sets the engagement portion Vga to the engagement orientation. Then, the control unit C causes the holding section Ve to protrude in the first width direction Xw (the second direction Y) relative to the elevating body Vc with the slide apparatus Vf, and disposes the holding section Ve directly above the storage shelf  8 . Thereafter, the control unit C lowers the holding section Ve with the second elevating apparatus Vd 2  and places the article G on the storage shelf  8  with the holding section Ve in the release orientation. When the transport vehicle V is to execute the reception operation of the article G from the storage rack  8 , the control unit C causes each apparatus to perform an operation opposite to that described above. 
     Second Embodiment 
     Next, a second embodiment of the article transport facility  100  will be described with reference to  FIGS.  7  and  8   . Differences from the first embodiment will be mainly described below. Points that are not particularly described are the same as those of the first embodiment. 
     As shown in  FIGS.  7  and  8   , the article transport facility  100  according to this embodiment includes a second transport vehicle V 2 , a third rail R 3  including third travel surfaces Fr 3 , and a fourth rail R 4  including fourth travel surfaces Fr 4 . 
     The second transport vehicle V 2  travels on a different travel route from that of the transport vehicle V. Specifically, the second transport vehicle V 2  can travel along the third rail R 3  and along the fourth rail R 4 . That is, the travel route of the second transport vehicle V 2  is set along each of the third rail R 3  and the fourth rail R 4 . 
     The third rail R 3  is spaced downward relative to the first rail R 1  and intersects the first rail R 1  in a view in the up-down direction. In this example, the third rail R 3  is arranged parallel to the second rail R 2 . That is, in this example, the third rail R 3  extends along the second direction Y, and is orthogonal to the first rail R 1  in a view in the up-down direction. 
     The fourth rail R 4  is disposed between the first rail R 1  and the third rail R 3  in the up-down direction, and is parallel to the first rail R 1  in a view in the up-down direction. That is, in this example, the fourth rail R 4  extends along the first direction X, and intersects both the second rail R 2  and the third rail R 3  in a view in the up-down direction. 
     Thus, in this embodiment, the third rail R 3  extends along the second direction Y, and the fourth rail R 4  extends along the first direction X. For this reason, the third rail R 3  and the fourth rail R 4  are orthogonal to each other in a view in the up-down direction. A plurality of third rails R 3  are disposed side by side in the second width direction Yw (first direction X). Also, a plurality of fourth rails R 4  are disposed side by side in the first width direction Xw (second direction Y). As a result, in this example, a travel route in which the plurality of third rails R 3  and the plurality of fourth rails R 4  form a lattice in a view in the up-down direction is provided in the intersection area CA. 
     As described above, the fourth rail R 4  includes the fourth travel surfaces Fr 4  on which the second transport vehicle V 2  travels along the first direction X. In the present embodiment, the fourth rail R 4  includes fourth guide surfaces Fg 4  facing a direction (in this example, the second direction Y) orthogonal to the first direction X in a view from above. 
     In other words, the fourth rail R 4  includes the fourth guide surfaces Fg 4  facing the first width direction Xw.
 
The fourth guide surfaces Fg 4  are surfaces for guiding the second transport vehicle V 2  along the first direction X.
 
     Also, as described above, the third rail R 3  includes the third travel surfaces Fr 3  on which the second transport vehicle V 2  travels along the second direction Y. In this embodiment, the third rail R 3  includes third guide surfaces Fg 3  facing a direction (in this example, the first direction X) orthogonal to the second direction Y in a view from above. In other words, the third rail R 3  includes the third guide surfaces Fg 3  facing the second width direction Yw. The third guide surfaces Fg 3  are surfaces for guiding the second transport vehicle V 2  along the second Y direction. 
     As shown in  FIG.  7   , in this embodiment, the fourth rail R 4  includes a pair of fourth rail bodies RB 4  spaced apart in the first width direction Xw. In this example, each of the plurality of fourth rails R 4  disposed side by side in the first width direction Xw includes a pair of fourth rail bodies RB 4  spaced apart in the first width direction Xw. That is, one fourth rail R 4  is constituted by a pair of fourth rail bodies RB 4  spaced apart in the first width direction Xw, and a plurality of the fourth rails R 4  are disposed side by side in the first width direction Xw. 
     In this embodiment, two fourth rails R 4  that are adjacent to each other in the first width direction Xw share one fourth rail body RB 4 , and a pair of fourth travel surfaces Fr 4  belonging to the two fourth rails R 4  that are adjacent to each other in the first width direction Xw are formed in the fourth rail body RB 4 . As a result, the number of fourth rail bodies RB 4  to be installed can be reduced in the entire facility. Accordingly, it is easy to reduce the number of man-hours when installing the fourth rails R 4 . 
     In this embodiment, the fourth rail body RB 4  and the first rail body RB 1  adjacent above the fourth rail body RB 4  are formed in one piece. As a result, it is possible to reduce the number of first rail bodies RB 1  and fourth rail bodies RB 4  to be installed in the entire facility while realizing a configuration in which the transport vehicle V and the second transport vehicle V 2  travel at different positions in the up-down direction. Accordingly, it is easy to reduce the number of man-hours when installing the first rails R 1  and the fourth rails R 4 . 
     In the present embodiment, the fourth rail body RB 4  includes a fourth main body portion R 41  extending along the first direction X, and a fourth wall portion R 42  that protrudes upward from the fourth main body portion R 41  and extends along the first direction X. The fourth travel surfaces Fr 4  are formed by the upward-facing surface of the fourth main body portion R 41 . In this example, the fourth travel surfaces Fr 4  are disposed on both sides of the fourth wall portion R 42  in the first width direction Xw. The fourth guide surfaces Fg 4  are formed by the surfaces of the fourth wall portion R 42  facing both sides in the first width direction Xw. 
     With the above configuration, it is possible to cause both the second transport vehicle V 2  that travels on one side of the fourth wall R 42  in the first width direction Xw and the second transport vehicle V 2  (not shown) that travels on the other side of the fourth wall R 42  in the first width direction Xw to appropriately travel with the pair of fourth travel surfaces Fr 4  provided on one fourth rail body RB 4 , and it is possible to appropriately guide the second transport vehicles V 2  with the pair of fourth guide surfaces Fg 4  provided on one fourth rail body RB 4 . 
     As described above, in the present embodiment, the fourth rail body RB 4  and the first rail body RB 1  adjacent above the fourth rail body RB 4  are formed in one piece. In this example, the fourth wall portion R 42  of the fourth rail body RB 4  is coupled to the first main body portion R 11  of the first rail body RB 1  from below. As a result, the fourth rail body RB 4  and the first rail body RB 1  are formed in one piece. For example, the fourth rail body RB 4  and the first rail body RB 1  may be formed in one piece by coupling a member forming the fourth rail body RB 4  and another member forming the first rail body RB 1  to each other. Alternatively, the fourth rail body RB 4  and the first rail body RB 1  may be composed of one identical member. In other words, part of the identical member may constitute the fourth rail body RB 4  and another part may constitute the first rail body RB 1 . 
     As shown in  FIG.  8   , in the present embodiment, the third rail R 3  includes a pair of third rail bodies RB 3  spaced apart in the second width direction Yw. In this example, each of the plurality of third rails R 3  disposed side by side in the second width direction Yw includes a pair of third rail bodies RB 3  spaced apart in the second width direction Yw. That is, one third rail R 3  is constituted by a pair of third rail bodies RB 3  spaced apart in the second width direction Yw, and the plurality of third rails R 3  are disposed side by side in the second width direction Yw. 
     In this embodiment, two third rails R 3  adjacent to each other in the second width direction Yw share one third rail body RB 3 , and a pair of third travel surfaces Fr 3  belonging to each of the two third rails R 3  adjacent to each other in the second with direction Yw are formed in the third rail body RB 3 . As a result, the number of third rail bodies RB 3  to be installed can be reduced in the entire facility. Accordingly, it is easy to reduce the number of man-hours when installing the third rails R 3 . 
     In this embodiment, the third rail body RB 3  includes a third main body portion R 31  extending along the second direction Y, and a third wall portion R 32  that protrudes upward from the third main body portion R 31  and extends along the second direction Y. The third travel surfaces Fr 3  are formed by the upward-facing surface of the third main body portion R 31 . In this example, the third travel surfaces Fr 3  are arranged on both sides of the third wall portion R 32  in the second width direction Yw. The third guide surfaces Fg 3  are formed by the surfaces of the third wall portion R 32  facing both sides in the second width direction Yw. 
     With the above-described configuration, it is possible to cause both the second transport vehicle V 2  traveling on one side of the third wall portion R 32  in the second width direction Yw, and the second transport vehicle V 2  (not shown) traveling on the other side of the third wall portion R 32  in the second width direction Yw to appropriately travel with the pair of third travel surfaces Fr 3  provided on one third rail body RB 3 , and it is possible to appropriately guide the pair of transport vehicles V 2  with the pair of third guide surfaces Fg 3  provided on one third rail body RB 3 . In this example, the cross section of the third rail body RB 3  orthogonal to the second direction Y is formed in an inverted T shape. 
     The second transport vehicle V 2  includes a second vehicle body V 2   a,  a third traveling unit U 3  that causes the second vehicle body V 2   a  to travel along a third rail R 3 , a fourth traveling unit U 4  that causes the second vehicle body V 2   a  to travel along a fourth rail R 4 , and a second control unit C 2  (see  FIG.  8   ) that controls the operations of the third traveling unit U 3  and the fourth traveling unit U 4 . The second vehicle body V 2   a  is disposed between the third rail R 3  and the fourth rail R 4  in the up-down direction. Specifically, the second vehicle body V 2   a  is disposed between the upper end of the third rail body RB 3  (the upper end of the third wall portion R 32 ) and the lower end of the fourth rail body RB 4  (the lower end of the fourth main body portion R 41 ) in the up-down direction. The other configurations of the second transport vehicle V 2  (e.g., the configuration for transferring the article G) may be the same as or partially different from the configuration of the transport vehicle V described above. 
     The third traveling unit U 3  includes a third wheel  31  and a third orientation changing mechanism  33  that changes the orientation of the third wheel  31  relative to the second vehicle body V 2   a,  and the third traveling unit U 3  performs an orientation change between a third wheel placement orientation, in which the third wheel is placed on the third traveling surface Fr 3 , and a third wheel retraction orientation, in which the third wheel  31  is separated from the third travel surface Fr 3 .  FIGS.  7  and  8    show the third wheel retraction orientation of the third traveling unit U 3 . 
     In this embodiment, the third traveling unit U 3  includes a third guide wheel  32  guided by the third guide surface Fg 3 . The third guide wheel  32  is in contact with the third guide surfaces Fg 3  while the third traveling unit U 3  is in the third wheel placement orientation, and is separated from the third guide surface Fg 3  while the third traveling unit U 3  is in the third wheel retraction orientation. With such a configuration, when the third traveling unit U 3  causes the second vehicle body V 2   a  to travel along the third rail R 3  in the third wheel placement orientation, the third guide wheel  32  appropriately guides the second vehicle body V 2   a  along the third rail R 3 . 
     Although detailed illustration is omitted, in the present embodiment, while the third traveling unit U 3  is in the third wheel placement orientation, the third wheel  31  is placed on the third travel surface Fr 3  with the rotation axis of the third wheel  31  directed in the second width direction Yw (first direction X). Also, while the third traveling unit U 3  is in the third wheel placement orientation, the third guide wheel  32  is in contact with the third guide surface Fg 3  with the rotation axis of the third guide wheel  32  directed in the up-down direction. 
     In this embodiment, the second transport vehicle V 2  includes a plurality of third traveling units U 3 . The second transport vehicle V 2  travels along the third rail R 3  using the plurality of third traveling units U 3 . As described above, the third rail R 3  on which the second transport vehicle V 2  travels along the second direction Y includes a pair of third rail bodies RB 3  spaced apart in the second width direction Yw (see  FIG.  8   ). In this embodiment, the third traveling units U 3  are provided corresponding to the pair of third rail bodies RB 3  spaced apart in the second width direction Yw. Also, in this example, a pair of third traveling units U 3  are separated from each other in the second direction Y on both side portions in the second width direction Yw (first direction X) of the second vehicle body V 2   a  (see  FIG.  7   ). That is, in this example, the second transport vehicle V 2  has a total of four third traveling units U 3 . 
     The fourth traveling unit U 4  includes a fourth wheel  41  and a fourth orientation changing mechanism  43  that changes the orientation of the fourth wheels  41  relative to the second vehicle body V 2   a,  and the fourth traveling unit U 4  performs an orientation change between a fourth wheel placement orientation, in which the fourth wheel is placed on the fourth travel surface Fr 4 , and a fourth wheel retraction orientation, in which the fourth wheel  41  is separated from the fourth travel surface Fr 4 .  FIGS.  7  and  8    show the fourth wheel placement orientation of the fourth traveling unit U 4 . 
     In this embodiment, the fourth traveling unit U 4  includes a fourth guide wheel  42  guided by the fourth guide surface Fg 4 . The fourth guide wheel  42  is in contact with the fourth guide surface Fg 4  while the fourth traveling unit U 4  is in the fourth wheel placement orientation, and is separated from the fourth guide surface Fg 4  while the fourth traveling unit U 4  is in the fourth wheel retraction orientation. With such a configuration, when the fourth traveling unit U 4  causes the second vehicle body V 2   a  to travel along the fourth rail R 4  in the fourth wheel placement orientation, the fourth guide wheel  42  can appropriately guide the second vehicle body V 2   a  along the fourth rail R 4 . 
     In the present embodiment, while the fourth traveling unit U 4  is in the fourth wheel placement orientation, the fourth wheel  41  is placed on the fourth travel surface Fr 4  with the rotation axis of the fourth wheel  41  directed in the first width direction Xw (second direction Y). Also, while the fourth traveling unit U 4  is in the fourth wheel placement orientation, the fourth guide wheel  42  is in contact with the fourth guide surface Fg 4  with the rotation axis of the fourth guide wheel  42  directed in the up-down direction. 
     In this embodiment, the second transport vehicle V 2  includes a plurality of fourth traveling units U 4 . The second transport vehicle V 2  travels along the fourth rail R 4  using a plurality of fourth traveling units U 4 . As described above, the fourth rail R 4  on which the second transport vehicle V 2  travels along the first direction X includes a pair of fourth rail bodies RB 4  spaced apart other in the first width direction Xw (see  FIG.  7   ). In this embodiment, the fourth traveling units U 4  are provided corresponding to the pair of fourth rail bodies RB 4  spaced apart in the first width direction Xw. Also, in this example, a pair of fourth traveling units U 4  are separated from each other in the second direction Y on both side portions in the second width direction Yw (first direction X) of the second vehicle body V 2   a  (see  FIG.  7   ). That is, in this example, the second transport vehicle V 2  has a total of four fourth traveling units U 4 . 
     The second control unit C 2  can change in mode between a third mode of causing the second vehicle V 2   a  to travel along the third rail R 3  with the third traveling unit U 3  in the third wheel placement orientation and the fourth traveling unit U 4  in the fourth wheel retraction orientation, and a fourth mode of causing the second vehicle body V 2   a  to travel along the fourth rail R 4  with the fourth traveling unit U 4  in the fourth wheel placement orientation and the third traveling unit U 3  in the third wheel retraction orientation.  FIGS.  7  and  8    show a state in which the second control unit C 2  is executing the fourth mode. Note that the mode change between the third mode and the fourth mode is executed while the second vehicle body V 2   a  is arranged at the intersection of the third rail R 3  and the fourth rail R 4  in a view in the up-down direction. 
     In this embodiment, the third wheel  31  and the third guide wheel  32  are above the third rail R 3  in the third wheel retraction orientation of the third traveling unit U 3 . As a result, when the second control unit C 2  executes the fourth mode and the second transport vehicle V 2  travels along the first direction X, the third wheels  31  and the third guide wheels  32  can be prevented from interfering with the third rail R 3 . Accordingly, it is possible to cause the second transport vehicle V 2  to appropriately travel along the first direction X. 
     Although detailed illustration is omitted, in this embodiment, the fourth wheels  41  and the fourth guide wheels  42  are below the fourth rail R 4  when the fourth traveling unit U 4  is in the fourth wheel retraction orientation. 
     As a result, when the second control unit C 2  executes the third mode and the second transport vehicle V 2  travels along the second direction Y, the fourth wheels  41  and the fourth guide wheels  42  can be prevented from interfering with the fourth rail R 4 . Accordingly, it is possible to cause the second transport vehicle V 2  to appropriately travel along the second Y direction. 
     In this embodiment, the third orientation changing mechanism  33  includes a third support arms  331  that are swingably coupled to the second vehicle body V 2   a  and support the third wheels  31 , and third drive units  332  that drive the third support arms  331 . 
     In this embodiment, the third support arm  331  supports the third guide wheel  32  in addition to the third wheel  31 . The third support arm  331  rotatably supports both the third wheel  31  and the third guide wheel  32  such that the rotation axis of the third wheel  31  and the rotation axis of the third guide wheel  32  extend in different directions. More specifically, the third support arm  331  supports the third wheel  31  and the third guide wheel  32  such that the direction along the rotation axis of the third wheel  31  and the direction along the rotation axis of the third guide wheel  32  are orthogonal to each other. 
     In the present embodiment, the third drive unit  332  swings the third support arm  331  about a third swing axis Ax 3  extending in the first direction X to change the orientation of the third wheel  31  relative to the second vehicle body V 2   a.  In this example, the third drive unit  332  also changes the orientation of the third guide wheel  32  relative to the second vehicle body V 2   a  by swinging the third support arm  331  about the third swing axis Ax 3 . The third drive unit  332  includes, for example, a motor. 
     In this embodiment, the fourth orientation changing mechanism  43  drives a fourth support arm  431  that is swingably coupled to the second vehicle body V 2   a  and supports the fourth wheel  41 , and a fourth drive unit  432  that drives the fourth support arm  431 . 
     In this embodiment, the fourth support arm  431  supports the fourth guide wheel  42  in addition to the fourth wheel  41 . The fourth support arm  431  rotatably supports both the fourth wheel  41  and the fourth guide wheel  42  such that the rotation axis of the fourth wheel  41  and the rotation axis of the fourth guide wheel  42  extend in different directions. More specifically, the fourth support arm  431  supports the fourth wheel  41  and the fourth guide wheel  42  such that the direction along the rotation axis of the fourth wheel  41  and the direction along the rotation axis of the fourth guide wheel  42  are orthogonal to each other. 
     In the present embodiment, the fourth drive unit  432  swings the fourth support arm  431  about the fourth swing axis Ax 4  along the first direction X to change the orientation of the fourth wheel  41  relative to the second vehicle body V 2   a.  In this example, the fourth drive unit  432  also changes the orientation of the fourth guide wheel  42  relative to the second vehicle body V 2   a  by swinging the fourth support arm  431  about the fourth swing axis Ax 4 . The fourth drive unit  432  includes, for example, a motor. 
     Other Embodiments 
     Next, another embodiment of the article transport facility will be described. 
     (1) In the above embodiment, an example was described in which the engaged portion Rg includes the block portion Rga and the engaged hole Rgb formed in the block portion Rga, and the engaged hole Rgb is formed in a conical shape. However, there is no limitation to such an example, and for example, as shown in  FIG.  9   , the engaged portion Rg may include a through hole Rgc passing through the plate-shaped member. In this case, it is preferable that the engaging portion Vga of the engagement apparatus Vg has, for example, a hook Vgaa that is engaged with the engaged portion Rg. In this case, the engaging portion Vga enters the engaged orientation when the hook Vgaa is engaged with the engaged portion Rg. 
     As another example of the engaging portion Vga and the engaged portion Rg, as shown in  FIG.  10   , one of the engaged portion Rg and the engaging portion Vga may be constituted by a magnetic member, and the other may be constituted by a magnet (a permanent magnet or an electromagnet). In this case, the engaging portion Vga enters the engagement orientation by being attracted to the engaged portion Rg by magnetic force. 
     Also, as another example of the engaging portion Vga and the engaged portion Rg, the engaged portion Rg may include an attraction surface Rgd that attracts the engaging portion Vga, as shown in  FIG.  11   . In this case, the engaging portion Vga preferably has a suction portion Vgab that generates a suction force. In this case, the engaging portion Vga enters the engagement orientation by being attracted to the attraction surface Rgd of the engaged portion Rg by the suction force of the suction portion Vgab. As the suction portion Vgab, for example, a pump or the like that generates negative pressure can be used. 
     Also, as another example of the engaging portion Vga and the engaged portion Rg, as shown in  FIG.  12   , the engaging portion Vga may include a roller Vgac and the engaged portion Rg may include an opening Rge that guides the roller Vgac. In this case, the engagement portion Vga enters the engagement orientation due to the roller Vgac being inserted into the opening Rge. 
     (2) In the above embodiment, an example was described in which the second rail R 2  includes the second travel surfaces Fr 2  and the second guide surfaces Fg 2 . However, there is no limitation to such an example, and the second rail R 2  need not include the second guide surfaces Fg 2 . In this case, for example, as shown in  FIG.  13   , the second travel surfaces Fr 2  may incline downward toward the inner side in the second width direction Yw. It is preferable that the second rail R 2  includes a fall prevention portion R 23  that prevents the second wheel  21  from falling off the second travel surface Fr 2 . In the example shown in  FIG.  13   , the fall prevention portion R 23  is formed to rise upward from the inner end of the second travel surface Fr 2  in the second width direction Yw. Note that the second traveling units U 2  need not include the second guide wheels  22  in the configuration described above. The above also applies to the first rail R 1  and the first traveling units U 1 . That is, the first rail R 1  need not include the first guide surfaces Fg 1 , and the first traveling units U 1  need not include the first guide wheels  12 . In this case, it is preferable that the first travel surface Fr 1  is formed so as to be inclined with respect to the first width direction Xw, and the first rail R 1  includes a fall prevention portion that prevents the first wheel  11  from falling off. 
     (3) In the above-described embodiment, an example was described in which one second rail R 2  is constituted by a pair of second rail bodies RB 2  spaced apart in the second width direction Yw. However, there is no limitation to such an example, and one second rail R 2  may be constituted by one second rail body RB 2 . In this case, for example, as shown in  FIG.  14   , the cross section of the second rail body RB 2  orthogonal to the second direction Y may be formed in an inverted L shape. Also, it is preferable that the second traveling unit U 2  includes a plurality of second wheels  21  (two second wheels  21  in the illustrated example) arranged side by side in the second width direction Yw (the first direction X) in the second wheel placement orientation, and the plurality of second wheels  21  are placed on the second travel surface Fr 2 . According to this configuration, while the second traveling unit U 2  is in the second wheel placement orientation, the orientation of the transport vehicle V is easy to stabilize even though the transport vehicle V is suspended and supported by a single second rail body RB 2 . 
     As another example of the second rail R 2  constituted by one second rail body RB 2 , as shown in  FIG.  15   , the second rail body RB 2  may be formed in a tubular shape that is open downward, and may include a pair of second travel surfaces Fr 2  spaced apart in the second width direction Yw. In this case, it is preferable that the second traveling unit U 2  includes a pair of second wheels  21  spaced apart in the second width direction Yw, raises and lowers the pair of second wheels  21 , and moves the pair of second wheels  21  toward or away from each other along the second width direction Yw. By raising the pair of second wheels  21 , the second traveling unit U 2  aligns the pair of second wheels  21  and the pair of second traveling surfaces Fr 2  in the up-down direction. Then, the second traveling unit U 2  aligns the pair of second wheels  21  and the pair of second traveling surfaces Fr 2  in the second width direction Yw by moving the pair of second wheels  21  away from each other. As a result, the second traveling unit U 2  enters the second wheel placement orientation. Note that although detailed illustration is omitted, the first rail R 1  may also similarly be constituted by one first rail body RB 1  instead of two first rail bodies RB 1 . 
     (4) In the above-described embodiment, an example was described in which the elevating apparatus Vd raises and lowers the elevating body Vc by means of the belt Vda coupled to the elevating body Vc and the elevation drive unit Vdb that drives the belt Vda. However, there is no limitation to such an example, and for example, as shown in  FIG.  16   , the elevating apparatus Vd may raise and lower the elevating body Vc by means of a ball screw mechanism Vdc. In this case, the elevating apparatus Vd preferably includes a driving source such as a motor for rotating the screw portion of the ball screw mechanism Vdc. 
     As another example of the elevating apparatus Vd, as shown in  FIG.  17   , the elevating apparatus Vd may raise and lower the elevating body Vc by means of a pantograph Vdd. Although detailed illustration is omitted, the elevating apparatus Vd may raise and lower the elevating body Vc with use of a cross link or the like. 
     (5) In the above-described embodiment, an example was described in which the article transport facility  100  includes the intersection area CA where the travel route along the first rail R 1  and the travel route along the second rail R 2  intersect each other. For example, as shown in  FIG.  18   , the article transport facility  100  may include a plurality of intersection areas CA. In this case, the article transport facility  100  is preferably provided with a connection route CR that connects the plurality of intersection areas CA. The connection route CR may be formed by extending the first rail R 1  or the second rail R 2  provided in the intersection area CA (in the illustrated example, the first rail R 1  is extended). Also, as illustrated, the connection route CR may include a straight section and a curved section. 
     (6) In the above-described embodiment, an example was described in which the first rail R 1  and the second rail R 2  are orthogonal to each other in a view in the up-down direction. However, the first rail R 1  and the second rail R 2  need only intersect in a view in the up-down direction, and need not be orthogonal. 
     (7) In the above embodiment, an example was described in which the first rail body RB 1  includes the first main body portion R 11  and the first wall portion R 12 , and the cross section of the first rail body RB 1  orthogonal to the first direction X is in an inverted T-shape. However, there is no limitation to such an example, and the first rail body RB 1  need only be provided with a first travel surface Fr 1  on which the transport vehicle V travels along the first direction X, and the first rail body RB 1  may have any kind of cross-sectional shape. 
     (8) In the above-described embodiment, an example was described in which the second rail body RB 2  includes the second main body portion R 21  and the second wall portion R 22 , and the cross section of the second rail body RB 2  orthogonal to the second direction Y is in an inverted T shape. However, there is no limitation to such an example, and the second rail body RB 2  need only be provided with a second travel surface Fr 2  on which the transport vehicle V travels along the second direction Y, and the second rail body RB 2  may have any kind of cross-sectional shape. 
     (9) In the above-described embodiment, an example was described in which the fourth rail body RB 4  and the first rail body RB 1  adjacent above the fourth rail body RB 4  are formed in one piece. However, there is no limitation to such an example, and the fourth rail body RB 4  and the first rail body RB 1  adjacent above the fourth rail body RB 4  may be separated from each other in the up-down direction. 
     (10) In the above-described embodiment, an example was described in which the engaged portions Rg are fixed to the first rail R 1  below the first travel surfaces Fr 1 . However, there is no limitation to such an example, and the engaged portions Rg may be disposed above the first travel surfaces Fr 1  instead of below the first travel surfaces Fr 1 . Also, the engaged portions Rg may be fixed to a member other than the first rail R 1 . The other member may be, for example, a frame or bracket coupled to the first rail R 1 . 
     (11) In the above-described embodiment, an example was described in which the first drive unit  132  swings the first support arm  131  about the first swing axis Ax 1  extending in the second direction Y, to change the orientation of the first wheel  11  relative to the vehicle body Va. However, there is no limitation to such an example, and the configuration for changing the orientation of the first wheels  11  relative to the vehicle body Va need only realize the first wheel placement orientation and the first wheel retraction orientation of the first traveling unit U 1 . For example, the first drive unit  132  may change the orientation of the first wheel  11  relative to the vehicle body Va by sliding the first wheel  11  in the up-down direction or swinging the first wheel  11  about an axis different from that in the above embodiment. 
     (12) In the above-described embodiment, an example was described in which the second drive unit  232  changes the orientation of the second wheel  21  relative to the vehicle body Va by swinging the second support arm  231  about the second swing axis Ax 2  extending in the second direction Y. However, there is no limitation to such an example, and the configuration for changing the orientation of the second wheel  21  relative to the vehicle body Va need only realize the second wheel placement orientation and the second wheel retraction orientation of the second traveling unit U 2 . For example, the second drive unit  232  may change the orientation of the second wheel  21  relative to the vehicle body Va by sliding the second wheel  21  in the up-down direction and the horizontal direction, or swinging the second wheel  21  about an axis different from that in the above embodiment. 
     (13) In the above-described embodiment, an example was described in which the first drive unit  132  changes the orientation of the first wheel  11  and the orientation of the first guide wheel  12  relative to the vehicle body Va by swinging the first support arm  131 . However, there is no limitation to such an example, and the orientation of the first guide wheel  12  may also be changed using a drive source other than the first drive unit  132  or a member other than the first support arm  131 . 
     (14) In the above-described embodiment, an example was described in which the second drive unit  232  changes the orientation of the second wheel  21  and the orientation of the second guide wheel  22  relative to the vehicle body Va by swinging the second support arm  231 . However, there is no limitation to such an example, and the orientation of the second guide wheel  22  may be changed using a drive source other than the second drive unit  232  or a member other than the second support arm  231 . 
     (15) In the above-described embodiment, an example was described in which the first wheel  11  is rotationally driven, thereby generating a propulsion force by which the vehicle body Va travels along the first direction X. However, there is no limitation to such an example, and the propulsive force by which the vehicle body Va travels along the first direction X may be generated by another configuration. For example, the engagement between a rack provided along the first rail R 1  and a gear provided on the vehicle body Va may be utilized, and the propulsive force may be generated by driving the gear. Alternatively, a linear motor may be used to generate the driving force. A similar configuration can also be used when generating a propulsive force by which the vehicle body Va travels along the second direction Y. 
     (16) Note that the configurations disclosed in the above-described embodiments can also be applied in combination with configurations disclosed in other embodiments as long as there is no contradiction. Regarding other configurations as well, the embodiments disclosed in this specification are merely examples in all respects. Accordingly, various modifications can be made as appropriate without departing from the spirit of the present disclosure. 
     Overview of the Embodiments 
     The article transport facility described above will be described hereinafter. 
     An article transport facility including a transport vehicle configured to transport an article, the article transport facility including: 
     at least one first rail including a first travel surface; and 
     at least one second rail including a second travel surface, 
     in which the at least one second rail is spaced upward relative to the at least one first rail and intersects the at least one first rail in a view in an up-down direction, 
     the transport vehicle includes a vehicle body disposed between the at least one first rail and the at least one second rail in the up-down direction, a first traveling unit configured to cause the vehicle body to travel along a first direction corresponding to a direction in which the at least one first rail extends, a second traveling unit configured to cause the vehicle body to travel along a second direction corresponding to a direction in the at least one second rail extends, and a control unit configured to control operations of the first traveling unit and the second traveling unit, 
     the first traveling unit includes a first wheel and a first orientation changing mechanism configured to change an orientation of the first wheel relative to the vehicle body, and the first traveling unit is configured to perform an orientation change between a first wheel placement orientation, in which the first wheel is placed on the first travel surface, and a first wheel retraction orientation, in which the first wheel is separated from the first travel surface, 
     the second traveling unit includes a second wheel and a second orientation changing mechanism configured to change an orientation of the second wheel relative to the vehicle body, and the second traveling unit is configured to perform an orientation change between a second wheel placement orientation, in which the second wheel is placed on the second travel surface, and a second wheel retraction orientation, in which the second wheel is separated from the second travel surface, and 
     the control unit is configured to change in mode between (i) a first mode of causing the vehicle body to travel along the at least one first rail with the first traveling unit in the first wheel placement orientation and the second traveling unit in the second wheel retraction orientation, and (ii) a second mode of causing the vehicle body to travel along the at least one second rail with the second traveling unit in the second wheel placement orientation and the first traveling unit in the first wheel retraction orientation. 
     According to this configuration, it is possible to cause the transport vehicle to travel in the first direction along the first rail and to cause the transport vehicle to travel in the second direction along the second rail. The second rail is spaced upward from the first rail. That is, the first rail and the second rail are disposed at different positions in the up-down direction. As a result, the travel route along the first rail and the travel route along the second rail can be disposed in different horizontal planes while intersecting each other in a view in the up-down direction. Accordingly, with this configuration, there is no seam between the first rail and the second rail, and no level difference occurs due to the existence of the seam, and therefore it is possible to prevent the occurrence of vibration when the transport vehicle travels in the portion where both rails intersect. Also, since the first rail and the second rail are physically separated, the first rail and the second rail can be installed at different times. Accordingly, it is possible to ensure a degree of freedom when installing the travel route constituted by the first rail and the second rail in the article transport facility. As described above, with this configuration, it is possible to suppress the vibration of the transport vehicle and to ensure a degree of freedom in the installation of the travel route in the article transport facility having the travel route where a plurality of routes with different extension directions intersect. 
     It is preferable that the transport vehicle includes an accommodation portion configured to accommodate the article during travel, and 
     the accommodation portion is provided in the vehicle body. 
     According to this configuration, the vehicle body disposed between the first rail and the second rail in the up-down direction is provided with the accommodation portion for accommodating the article. As a result, the control unit can make the distance from the wheel supporting the vehicle body to the article approximately the same even when executing the first mode of causing the vehicle body to travel along the first rail or the second mode of causing the vehicle body to travel along the second rail. Accordingly, with this configuration, the article can be conveyed while being stably held. 
     It is preferable that the second orientation changing mechanism includes a second support arm that is swingably coupled to the vehicle body and supports the second wheel, and a second drive unit configured to drive the second support arm, and 
     the second drive unit changes the orientation of the second wheel relative to the vehicle body by swinging the second support arm about a second swing axis extending in the second direction. 
     According to this configuration, the second wheel can be appropriately placed on the second travel surface of the second rail disposed above the vehicle body, and the second wheel can be appropriately separated from the second travel surface. 
     It is preferable that in response to the second orientation changing mechanism changing the orientation of the second traveling unit from the second wheel retraction orientation to the second wheel placement orientation, the second wheel is placed on the second travel surface at a position past an uppermost position of a movement path along which the second wheel moves due to swinging of the second support arm. 
     According to this configuration, the second wheel can be placed on the second travel surface by approaching the second travel surface from above. Accordingly, with this configuration, when the orientation is changed from the second wheel retraction orientation to the second wheel placement orientation, the orientation can be appropriately changed while reducing the friction between the second wheel and the second travel surface. 
     It is preferable that the first orientation changing mechanism includes a first support arm that is swingably coupled to the vehicle body and supports the first wheel, and a first drive unit configured to drive the first support arm, and 
     the first drive unit changes the orientation of the first wheel relative to the vehicle body by swinging the first support arm about a first swing axis extending in the second direction. 
     According to this configuration, the first swing axis, which is the swing center of the first support arm, and the second swing axis, which is the swing center of the second support arm, can be disposed in parallel along the second direction. For this reason, it is possible to make it difficult for the movement ranges of both the first support arm and the second support arm to expand in the second direction. There is also an advantage in that, for example, the first drive unit and the second drive unit can be easily used in common due to the first swing axis and the second swing axis being disposed parallel to each other. 
     It is preferable that the at least one first rail includes a first guide surface facing a direction intersecting the first direction in a view in the up-down direction, 
     the at least one second rail includes a second guide surface facing a direction intersecting the second direction in a view in the up-down direction, 
     the first traveling unit includes a first guide wheel configured to be guided on the first guide surface, 
     the first guide wheel is configured to be in contact with the first guide surface while the first traveling unit is in the first wheel placement orientation, and to be separated from the first guide surface while the first traveling unit is in the first wheel retraction orientation, 
     the second traveling unit includes a second guide wheel configured to be guided on the second guide surface, and 
     the second guide wheel is configured to be in contact with the second guide surface while the second traveling unit is in the second wheel placement orientation, and to be separated from the second guide surface while the second traveling unit is in the second wheel retraction orientation. 
     According to this configuration, when the first traveling unit causes the vehicle body to travel along the first rail in the first wheel placement orientation, the first guide wheels can appropriately guide the vehicle body along the first rail. Also, when the second traveling unit causes the vehicle body to travel along the second rail in the second wheel placement orientation, the second guide wheels can appropriately guide the vehicle body along the second rail. 
     It is preferable that the at least one first rail includes a plurality of first rails disposed side by side in a direction intersecting the first direction in a view in the up-down direction, and 
     the at least one second rail includes a plurality of second rails disposed side by side in a direction intersecting the second direction in a view in the up-down direction. 
     According to this configuration, it is possible to ensure a wide traveling range of the transport vehicle over the range extending in the first direction and the second direction. 
     It is preferable that the transport vehicle includes an elevating body coupled to the vehicle body, an elevating apparatus configured to raise and lower the elevating body relative to the vehicle body, and a holding section supported by the elevating body and configured to hold the article. 
     According to this configuration, the article can be transferred to a position spaced apart in the up-down direction relative to the transport vehicle. 
     It is preferable that the transport vehicle includes an elevating body coupled to the vehicle body, an elevating apparatus configured to raise and lower the elevating body relative to the vehicle body, a holding section supported by the elevating body and configured to hold the article, a slide apparatus configured to slide the holding section in a horizontal direction relative to the elevating body, and an engagement apparatus supported by the elevating body, 
     the at least one first rail includes an engaged portion, 
     the engagement apparatus includes an engaging portion configured to engage with the engaged portion, and an engagement drive unit configured to change an orientation of the engaging portion between an engagement orientation and a release orientation, 
     while the engaging portion is in the engagement orientation, the engaging portion is engaged with the engaged portion to restrict raising, lowering, and tilting of the elevating body, and while the engaging portion is in the release orientation, the engaging portion is separated from the engaged portion to allow raising and lowering of the elevating body, and 
     the control unit causes the engaging portion to have the release orientation in response to the elevating apparatus raising or lowering the elevating body, and causes the engaging portion to have the engagement orientation in response to the slide apparatus causing the holding section to protrude in the horizontal direction relative to the elevating body. 
     According to this configuration, it is possible to cause the transport vehicle to travel in the first direction along the first rail and to cause the transport vehicle to travel in the second direction along the second rail. The second rail is spaced upward from the first rail. That is, the first rail and the second rail are disposed at different positions in the up-down direction. As a result, the travel route along the first rail and the travel route along the second rail can be disposed in different horizontal planes while intersecting each other in a view in the up-down direction. Accordingly, with this configuration, there is no seam between the first rail and the second rail, and no level difference occurs due to the existence of the seam, and therefore it is possible to prevent the occurrence of vibration when the transport vehicle travels in the portion where both rails intersect. Also, according to this configuration, the article held by the holding section can be disposed at a position shifted in the horizontal direction relative to the elevating body due to the operation of the slide apparatus. For this reason, it is possible to transfer the article to a position shifted in the horizontal direction from directly below the transport vehicle. Also, when such transfer is performed, tilting of the elevating body can be restricted by causing the engaging portion to have the engagement orientation. As a result, it is possible to appropriately transfer the article to a position shifted in the horizontal direction from directly below the transport vehicle. As described above, according to this configuration, in an article transport facility having a travel route where a plurality of routes with different extension directions intersect each other, vibration of the transport vehicle can be suppressed, and the article can be transferred to a position shifted in the horizontal direction from directly below the transfer vehicle. 
     It is preferable that a storage shelf configured to hold the article is further included, 
     in which the storage shelf is supported by the at least one first rail, below the at least one first rail, 
     the transport vehicle is configured to be capable of executing a delivery operation of delivering the article to the storage shelf and a reception operation of receiving the article from the storage shelf, by the slide apparatus sliding the holding section, and 
     in response to the control unit causing the transport vehicle to execute the delivery operation or the reception operation, the control unit causes the elevating mechanism to position the elevating body at a height corresponding to the storage shelf and causes the engaging portion to have the engagement orientation. 
     According to this configuration, the storage shelf for temporary or long-term storage of an article can be disposed using the space below the first rail. When an article is transferred to and from the storage shelf, it is possible to use an elevating operation of the elevating body by the elevating device and a sliding operation of the holding section by the sliding device. Also, when the holding section is slid, it is possible to suppress tilting of the elevating body since the engaging portion is in the engagement orientation. Accordingly, it is possible to appropriately transfer the article to the storage shelf. 
     It is preferable that the engaged portion is at a position corresponding to a transfer target location where the article is transferred to or from the vehicle, in the first direction, and 
     the engaging portion also performs positioning of the elevating body in the first direction while in the engagement orientation. 
     According to this configuration, by causing the engaging portion to have the engagement orientation, the elevating body can be positioned in the first direction at the position corresponding to the transfer target location in the first direction. This makes it easier to accurately transfer the article to the transfer target location. 
     It is preferable that the transport vehicle further includes a second elevation apparatus configured to raise and lower the holding section relative to the slide apparatus, below the slide apparatus. 
     According to this configuration, the second elevating apparatus can raise and lower the holding section from a position where the slide apparatus causes the holding section to protrude in the horizontal direction relative to the elevating body. Accordingly, with this configuration, it is possible to increase the number of locations where the articles can be transferred by the transport vehicle, and it is possible to improve the versatility of the transfer target locations of the article. 
     It is preferable that the at least one first rail includes a pair of first rail bodies spaced apart in a first width direction intersecting the first direction in a view in the up-down direction, 
     the elevating apparatus raises and lowers the elevating body between the pair of first rail bodies in the first width direction in a view in the up-down direction, 
     the engaged portion is provided on at least one of the pair of first rail bodies, and 
     the engagement drive unit changes the orientation of the engaging portion between the engagement orientation and the release orientation by extending and retracting the engaging portion in the first width direction. 
     According to this configuration, in the configuration in which the elevating body is disposed between the pair of first rail bodies in the first width direction, the engaging device supported by the elevating body can appropriately cause the engaging portion to engage with and separate from the engaged portion provided on at least one of the pair of first rail bodies by causing the engaging portion to extend and retract along the first width direction. 
     It is preferable that the engaged portion is fixed to the at least one first rail below the first travel surface. 
     According to this configuration, the engaged portion can be disposed at a position that does not interfere with the first travel wheel placed on the first travel surface. Also, since the engaged portion is fixed to the first rail, the structure for supporting the engaged portion can be simplified. 
     It is preferable that the at least one first rail includes a plurality of first rails disposed side by side in a first width direction intersecting the first direction in a view in the up-down direction, 
     each of the plurality of first rails includes a pair of first rail bodies spaced apart in the first width direction, and 
     two of the first rails adjacent to each other in the first width direction share one of the first rail bodies, and a pair of the first travel surfaces belonging to each of the two first rails adjacent to each other in the first width direction are formed in the first rail body. 
     According to this configuration, it is possible to cause the transport vehicle to travel in the first direction along the first rail and to cause the transport vehicle to travel in the second direction along the second rail. The second rail is spaced upward from the first rail. That is, the first rail and the second rail are disposed at different positions in the up-down direction. As a result, the travel route along the first rail and the travel route along the second rail can be disposed in different horizontal planes while intersecting each other in a view in the up-down direction. Accordingly, with this configuration, there is no seam between the first rail and the second rail, and no level difference occurs due to the existence of the seam, and therefore it is possible to prevent the occurrence of vibration when the transport vehicle travels in the portion where both rails intersect. Also, according to this configuration, since two first rails adjacent to each other in the first width direction share one first rail body, it is possible to reduce the number of first rail bodies to be installed in the entire facility. Thus, it is easy to reduce the number of man-hours when installing the first rail. As described above, according to the present configuration, in an article transport facility including a travel route on which a plurality of routes extending in different directions intersect each other, it is possible to suppress vibration of the transport vehicle and to reduce man-hours for installing the travel route. 
     It is preferable that each of the first rails includes a first guide surface facing the first width direction, 
     the first traveling unit includes a first guide wheel configured to be guided on the first guide surface, 
     the first guide wheel is configured to be in contact with the first guide surface while the first traveling unit is in the first wheel placement orientation, and to be separated from the first guide surface while the first traveling unit is in the first wheel retraction orientation, 
     each of the first rail bodies includes a first main body portion extending in the first direction, and a first wall portion protruding upward from the first main body portion and extending in the first direction, 
     the first travel surfaces are formed by an upward-facing surface of the first main body portion, 
     the first travel surfaces are disposed on opposite sides of the first wall portion in the first width direction, and 
     the first guide surfaces are formed by surfaces of the first wall portion that face opposite sides in the first width direction. 
     According to this configuration, when the first traveling unit causes the vehicle body to travel along the first rail in the first wheel placement orientation, the first guide wheels can appropriately guide the vehicle body along the first rail. The first guide surface for guiding the first guide wheel is formed on each of the surfaces of the first wall portion of the first rail body facing both sides in the first width direction. As a result, both the first guide wheel used for the transport vehicle traveling on one side of the first wall portion in the first width direction and the first guide wheel provided on the other transport vehicle traveling on the other side of the first wall portion in the first width direction can be appropriately guided by the pair of first guide surfaces provided on one first rail body. 
     It is preferable that the at least one second rail includes a plurality of second rails disposed side by side in a second width direction intersecting the second direction in a view in the up-down direction, 
     each of the plurality of second rails includes a pair of second rail bodies spaced apart in the second width direction, and 
     two of the second rails adjacent to each other in the second width direction share one of the second rail bodies, and a pair of the second travel surfaces belonging to each of the two second rails adjacent to each other in the second width direction are formed in the second rail body. 
     According to this configuration, two second rails adjacent to each other in the second width direction share one second rail body, and therefore the number of second rail bodies to be installed can be reduced in the entire facility. Thus, the number of man-hours for installing the second rail can be easily suppressed. 
     It is preferable that each of the second rails includes a second guide surface facing the second width direction, 
     the second traveling unit includes a second guide wheel configured to be guided on the second guide surface, 
     the second guide wheel is configured to be in contact with the second guide surface while the second traveling unit is in the second wheel placement orientation, and to be separated from the second guide surface while the second traveling unit is in the second wheel retraction orientation, 
     each of the second rail bodies includes a second main body portion extending in the second direction, and a second wall portion protruding upward from the second main body portion and extending in the second direction, 
     the second travel surfaces are formed by an upward-facing surface of the second main body portion, 
     the second travel surfaces are disposed on opposite sides of the second wall portion in the second width direction, and 
     the second guide surfaces are formed by surfaces of the second wall portion that face opposite sides in the second width direction. 
     According to this configuration, when the second traveling unit causes the vehicle body to travel along the second rail in the second wheel placement orientation, the second guide wheels can appropriately guide the vehicle body along the second rail. Also, second guide surfaces for guiding the second guide wheels are formed on the surfaces facing both sides in the second width direction of the second wall portion of the second rail body. As a result, both the second guide wheel used for the transport vehicle traveling on one side of the second wall in the second width direction and the second guide wheel used for the other transport vehicle traveling on the other side of the second wall in the second width direction can be appropriately guided by the pair of second guide surfaces provided on one second rail body. 
     It is preferable that a second transport vehicle; 
     a third rail including a third travel surface; and 
     at least one fourth rail including a fourth travel surface are further included, 
     in which the third rail is spaced downward relative to the at least one first rail and intersects the at least one first rail in a view in an up-down direction, 
     the at least one fourth rail is disposed between the at least one first rail and the third rail in the up-down direction and is disposed parallel to the at least one first rail in the up-down direction, 
     the transport vehicle includes a second vehicle body, a third traveling unit configured to cause the second vehicle body to travel along the third rail, a fourth traveling unit configured to cause the second vehicle body to travel along the at least one fourth rail, and a second control unit configured to control the third traveling unit and the fourth traveling unit, 
     the third traveling unit includes a third wheel and a third orientation changing mechanism configured to change an orientation of the third wheel relative to the second vehicle body, and is configured to perform an orientation change between a third wheel placement orientation, in which the third wheel is placed on the third travel surface, and a third wheel retraction orientation, in which the third wheel is separated from the third travel surface, 
     the fourth traveling unit includes a fourth wheel and a fourth orientation changing mechanism configured to change the orientation of the fourth wheel relative to the second vehicle body, and is configured to perform an orientation change between a fourth wheel placement orientation, in which the fourth wheel is placed on the fourth travel surface, and a fourth wheel retraction orientation, in which the fourth wheel is separated from the fourth travel surface, 
     the second control unit is configured to change in mode between (i) a third mode of causing the second vehicle body to travel along the third rail with the third traveling unit in the third wheel placement orientation and the fourth traveling unit in the fourth wheel retraction orientation, and (ii) a fourth mode of causing the second vehicle body to travel along the at least one fourth rail with the fourth traveling unit in the fourth wheel placement orientation and the third traveling unit in the third wheel retraction orientation, 
     the at least one fourth rail includes a plurality of fourth rails disposed side by side in the first width direction, 
     each of the plurality of fourth rails includes a pair of fourth rail bodies spaced apart in the first width direction, and 
     for each of the fourth rail bodies, the fourth rail body and a corresponding first rail body adjacent above the fourth rail body are formed in one piece. 
     According to this configuration, it is possible to cause the second transport vehicle to travel between the third rail and the fourth rail in the up-down direction, separately from the transport vehicle that travels between the first rail and the second rail in the up-down direction. Also, the second transport vehicle can be caused to travel along the third rail, and the second transport vehicle can be caused to travel along the fourth rail. Also, according to this configuration, since the first rail body and the fourth rail body, which are adjacent to each other in the up-down direction, are formed in one piece, the number of first rail bodies and fourth rail bodies to be installed can be reduced in the entire facility while realizing the configuration where the transport vehicle and the second transport vehicle are caused to travel at different positions in the up-down direction. Thus, it is easy to reduce the number of man-hours when installing the first rail and the fourth rail. 
     It is preferable that two of the fourth rails adjacent to each other in the first width direction share one of the fourth rail bodies, and a pair of the fourth travel surfaces belonging to each of the two fourth rails adjacent to each other in the first width direction are formed in the fourth rail body. 
     According to this configuration, two fourth rails adjacent to each other in the first width direction share one fourth rail body, and therefore the number of fourth rail bodies to be installed can be reduced in the entire facility. Thus, it is easy to reduce the number of man-hours when installing the fourth rail. 
     INDUSTRIAL APPLICABILITY 
     The technology according to the present disclosure can be used in an article transport facility including a transport vehicle that transports articles.