Patent Publication Number: US-11642688-B2

Title: Paint system and paint method

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2020-095191 filed on Jun. 1, 2020, incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a paint system that paints an object to be painted such as a vehicle body of an automobile and a paint method in which the paint system is used, for example. In particular, the present disclosure relates to a paint system and a paint method in which at least two paint robots are provided on the same side with respect to a predetermined reference plane. 
     2. Description of Related Art 
     Japanese Unexamined Patent Application Publication No. 1-266870 (JP 1-266870 A) discloses a known paint system in which paint in a mist form is sprayed onto an object to be painted such as a vehicle body of an automobile to paint the object to be painted. In the paint system according to JP 1-266870 A, a plurality of paint robots is disposed along a transfer path for the object to be painted, and the respective arrangement height positions of the paint robots are offset in the up-down direction. In a specific example disclosed, a first paint robot that paints an upper surface of the object to be painted and a second paint robot that paints a side surface of the object to be painted are provided, the arrangement height position of the first paint robot is set to be higher than the arrangement height position of the second paint robot, and the arrangement position of the first paint robot is set to the outer side (farther side from the transfer path) with respect to the arrangement position of the second paint robot. That is, in the paint system according to JP 1-266870 A, each region of the object to be painted (the upper surface and the side surface of the object to be painted) is painted through combined use of a paint robot (first paint robot described above) that paints a region (e.g. the middle portion of the upper surface of the object to be painted) of the object to be painted that is closer to the middle portion of the transfer path and a paint robot (second paint robot described above) that paints a region (e.g. the side surface of the object to be painted) of the object to be painted that is farther from the middle portion of the transfer path. 
     SUMMARY 
     In general, a paint robot includes a robot base and a robot arm mounted on the robot base to extend toward an object to be painted on a transfer path. As disclosed in JP 1-266870 A, when the first paint robot which paints a region of the object to be painted that is closer to the middle portion of the transfer path and the second paint robot which paints a region of the object to be painted that is farther from the middle portion of the transfer path are used in combination with each other, it is necessary that the robot arm of the first paint robot should be elongated so that a spray gun provided at the distal end of the robot arm reaches the middle portion of the upper surface of the object to be painted. When the robot arm is elongated, however, the first paint robot may be increased in size, which may incur an increase in the size of the paint system. An increase in the size of the paint system leads to an increase in equipment cost and running cost, and therefore is not preferable. 
     As means for avoiding elongation of the robot arm, it is conceivable to set the position of the robot base of the first paint robot to a position that is close to the transfer path. In this case, however, simply setting the position of the robot base of the first paint robot to a position that is close to the transfer path could result in the movable range of the robot arm of the second paint robot being limited by the first paint robot (the movable range of the robot arm of the second paint robot being limited such that the second paint robot does not interfere with the first paint robot), which could adversely affect paint on the side surface of the object to be painted. 
     In this manner, it has been difficult, in a paint system in which a plurality of paint robots is disposed along a transfer path, to reduce the size of the paint robots and increase the movable range of robot arms at the same time. 
     The present disclosure provides a paint system that makes it possible to reduce the size of paint robots and increase the movable range of robot arms at the same time, and a paint method in which the paint system is used. 
     A first aspect of the present disclosure relates to a paint system. The paint system includes a paint unit that has a first paint robot configured to paint an upper region of an object to be painted and a second paint robot configured to paint a lower region of the object to be painted on a lower side with respect to the upper region. The first paint robot includes a first robot base and a first robot arm operably mounted on the first robot base. The second paint robot includes a second robot base and a second robot arm operably mounted on the second robot base. The object to be painted and the paint unit are movable relative to each other along a horizontal direction. When a virtual plane that extends in a vertical direction and along a direction of relative movement between the object to be painted and the paint unit is defined as a reference plane, the first paint robot and the second paint robot are disposed on the same side with respect to the reference plane. A distance between the first robot base and the reference plane is set to be shorter than a distance between the second robot base and the reference plane. An arrangement height position of the first robot base is set to be higher than an arrangement height position of the second robot base. A robot arm passage range that allows passage of the second robot arm is provided under the first robot base. 
     With the first aspect, when the paint system paints the object to be painted, the first paint robot paints the upper region of the object to be painted, and the second paint robot paints the lower region of the object to be painted on the lower side with respect to the upper region. In this event, the second paint robot, the second robot base of which is positioned below the arrangement height position of the first robot base (the distance of which from the reference plane is set to be shorter than the distance of the second robot base of the second paint robot from the reference plane) of the first paint robot, paints the lower region of the object to be painted (on the lower side with respect to the region painted by the first paint robot) with the second robot arm passing through the robot arm passage range which is provided under the first robot base. That is, the second robot arm paints the lower region on the lower side with respect to the region painted by the first paint robot without interfering with the first paint robot and with a sufficient movable range secured, even though the position of the first robot base is set to a position that is close to the transfer path (a position that is closer to the reference plane than the position of the second robot base). That is, a sufficient movable range of the second robot arm can be secured while reducing the length of the first robot arm by setting the position of the first robot base to a position that is close to the reference plane to reduce the distance between the object to be painted and the first robot base. Therefore, it is possible to reduce the size of the paint robots (in particular, the first paint robot) and increase the movable range of the robot arms (in particular, the second robot arm) at the same time. As a result, it is possible to reduce the size of the paint system along with a reduction in the size of the paint robots, and reduce the equipment cost and the running cost. It is also possible to reduce carbon dioxide (CO 2 ) because of a reduction in the size of the paint system. It is also possible to paint well the lower region of the object to be painted (on the lower side with respect to the region painted by the first paint robot) because of an increase in the movable range of the second robot arm. 
     The paint system according to the first aspect may further include a single control device configured to control both operation of the first paint robot and operation of the second paint robot. 
     With the configuration described above, it is possible to reduce the size of the control unit (unit for controlling the paint robots, including the control device) as a whole compared to the case where a plurality of control devices is provided to individually control respective operations of the paint robots, thereby contributing to a reduction in the size of the paint system. 
     The paint system according to the above aspect may further include a paint booth that constitutes a painting space that houses a transfer path for the object to be painted and the paint unit and that is blocked from outside. The control device may be arranged outside the paint booth. 
     With the configuration described above, it is possible to reduce the size of the internal space required for the paint booth compared to the case where the control device is arranged inside the paint booth. In a paint booth, in general, air conditioning is performed so as to generate a flow of air that causes a good flow of paint particles inside the paint booth (a flow of air for suppressing diffusion of paint particles that have not been applied). With the internal space of the paint booth reduced in size, however, it is possible to reduce the size of a space in which such an air flow is generated, and reduce the size of an air conditioning device for generating the air flow or reduce energy consumption. 
     In the above aspect, the first robot arm and the second robot arm may each include a spray gun configured to spray paint toward the object to be painted. At least one of the spray guns may be configured to electrostatically atomize the paint and spray the paint toward the object to be painted. 
     With the configuration described above, it is possible to improve the efficiency in applying the paint to the object to be painted, and reduce the range in which the paint sprayed toward the object to be painted is splashed back. Therefore, it is not necessary that the paint robots should be arranged at positions significantly away from the object to be painted so that the paint splashed back does not adhere to the paint robots, and the arrangement positions of the paint robots can be set to positions that are close to the object to be painted. As a result, it is possible to reduce the size of the paint system in the horizontal direction which is orthogonal to the direction of relative movement between the object to be painted and the paint unit, and reduce the equipment cost and the running cost. It is also possible to reduce CO 2  because of a reduction in the size of the paint system. 
     In the above aspect, A plurality of the paints unit may be arranged on a first side and a second side with respect to the reference plane. The paint unit which is arranged on the first side with respect to the reference plane may be configured such that the first paint robot paints a region, on the first side, of an upper surface of the object to be painted and the second paint robot paints a side surface, on the first side, of the object to be painted. The paint unit which is arranged on the second side with respect to the reference plane may be configured such that the first paint robot paints a region, on the second side, of the upper surface of the object to be painted and the second paint robot paints a side surface, on the second side, of the object to be painted. 
     With the configuration described above, it is possible to paint regions of the object to be painted on one side and the other side with respect to the reference plane well using the paint robots of the paint units, and finish the painted surfaces of the object to be painted well. 
     The paint system according to the above aspect may further include a rail configured to allow the first paint robot or the second paint robot to move along a transfer direction of the object to be painted. 
     In the paint system according to the first aspect, the first paint robot and the second paint robot may be configured to paint the object to be painted by spraying paint toward the object to be painted. 
     A second aspect of the present disclosure relates to a paint method in which the paint system according to the above aspect of the present disclosure is used. The method includes: the first paint robot painting the upper region of the object to be painted while the object to be painted and the paint unit are moved relative to each other along the horizontal direction; and the second paint robot painting the lower region of the object to be painted on the lower side with respect to the upper region. 
     With the second aspect, a sufficient movable range of the second robot arm can be secured by providing the robot arm passage range which allows passage of the second robot arm under the first robot base, while reducing the length of the first robot arm by setting the position of the first robot base to a position that is close to the reference plane to reduce the distance between the object to be painted and the first robot base. Therefore, it is possible to reduce the size of the paint robots and increase the movable range of the robot arms at the same time. 
     In the aspects of the present disclosure, the distance between the first robot base of the first paint robot, which paints the upper region of the object to be painted, and the reference plane (a virtual plane that extends in the vertical direction and along the direction of relative movement between the object to be painted and the paint unit) is set to be shorter than the distance between the second robot base of the second paint robot, which paints the lower region of the object to be painted on the lower side with respect to the upper region, and the reference plane, and the robot arm passage range which allows passage of the second robot arm of the second paint robot is provided under the first robot base. Consequently, it is possible to secure a sufficient movable range of the second robot arm while reducing the length of the first robot arm of the first paint robot. As a result, it is possible to reduce the size of the paint robots and increase the movable range of the robot arms at the same time. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, advantages, and technical and industrial significance of exemplary embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like signs denote like elements, and wherein: 
         FIG.  1    is a plan view illustrating a paint system according to a first embodiment; 
         FIG.  2    is a front view illustrating the paint system according to the first embodiment; 
         FIG.  3    is a sectional view illustrating a spray gun provided in a paint robot; 
         FIG.  4    is a perspective view illustrating the distal end of a rotary head of the spray gun; 
         FIG.  5    is a schematic diagram illustrating electrostatic atomization of paint; 
         FIG.  6    is a block diagram illustrating a schematic configuration of a control system for the paint system; 
         FIG.  7    is a plan view illustrating the respective movable ranges of a first robot arm and a second robot arm; 
         FIG.  8    is a front view illustrating the respective movable ranges of spray guns; 
         FIG.  9    is a plan view illustrating a paint system according to a second embodiment; 
         FIG.  10    is a front view illustrating the paint system according to the second embodiment; 
         FIG.  11    is a plan view illustrating a paint system according to a third embodiment; 
         FIG.  12    is a plan view illustrating a paint system according to a fourth embodiment; 
       and 
         FIG.  13    is a front view illustrating a paint system according to a fifth embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     A plurality of embodiments of the present disclosure will be described below with reference to the drawings. In the following first to fourth embodiments, the present disclosure is implemented as a paint system that paints a vehicle body of an automobile and a paint method in which the paint system is used. In a fifth embodiment, meanwhile, a paint system paints an object to be painted other than a vehicle body. 
     First Embodiment 
     A first embodiment is described first.  FIG.  1    is a plan view illustrating a paint system PS according to the present embodiment.  FIG.  2    is a front view (a view seen in the direction of the arrow II in  FIG.  1   ) illustrating the paint system PS according to the present embodiment. As illustrated in the drawings, the paint system PS includes a paint booth  100 , and a plurality of paint units PU 1 , PU 2 , PU 3 , and PU 4  is installed inside the paint booth  100 . Auxiliary booths  201  and  202  are installed on opposite outer sides (opposite outer sides in the horizontal direction) of the paint booth  100 . 
     In  FIGS.  1  and  2   , the X direction corresponds to the width direction of the paint system PS, the Y direction corresponds to the length direction of the paint system PS (the transfer direction of a vehicle body  150  as an object to be painted), and the Z direction corresponds to the height direction of the paint system PS (up-down direction). 
     The paint booth  100  includes a transfer device  5  that transfers the vehicle body  150 . Two of the paint units PU 1 , PU 2 , PU 3 , and PU 4  are installed on each side of the transfer device  5  (each of both sides in a direction that is orthogonal to the transfer direction). 
     When the vehicle body  150  is transferred as indicated by the arrow A in  FIG.  1    (when the vehicle body  150  is transferred by the transfer device  5  from the upper side toward the lower side in  FIG.  1   ), the paint units PU 1  and PU 2  (more specifically, paint robots  1 A and  1 B that constitute the paint unit PU 1 , and paint robots  1 A and  1 B that constitute the paint unit PU 2 ) which are positioned on the downstream side in the transfer direction mainly paint the front half of the vehicle body  150 . That is, the paint unit PU 1  (hereinafter referred to as “first paint unit PU 1 ”) which is positioned on the left side when facing the transfer direction (right side in  FIG.  1   ) mainly paints the left half of an engine hood, a left front fender, a left front door, and the front half of the left side of a roof of the vehicle body  150 . Meanwhile, the paint unit PU 2  (hereinafter referred to as “second paint unit PU 2 ”) which is positioned on the right side when facing the transfer direction (left side in  FIG.  1   ) mainly paints the right half of the engine hood, a right front fender, a right front door, and the front half of the right side of the roof of the vehicle body  150 . 
     On the other hand, the paint units PU 3  and PU 4  (more specifically, paint robots  1 A and  1 B that constitute the paint unit PU 3 , and paint robots  1 A and  1 B that constitute the paint unit PU 4 ) which are positioned on the upstream side in the transfer direction mainly paint the rear half of the vehicle body  150 . That is, the paint unit PU 3  (hereinafter referred to as “third paint unit PU 3 ”) which is positioned on the left side when facing the transfer direction (right side in  FIG.  1   ) mainly paints a left rear fender, a left rear door, and the rear half of the left side of the roof of the vehicle body  150 . Meanwhile, the paint unit PU 4  (hereinafter referred to as “fourth paint unit PU 4 ”) which is positioned on the right side when facing the transfer direction (left side in  FIG.  1   ) mainly paints a right rear fender, a right rear door, and the rear half of the right side of the roof of the vehicle body  150 . 
     The paint units PU 1  to PU 4  have the same configuration as each other.  FIG.  2    illustrates only the first paint unit PU 1  and the second paint unit PU 2 . 
     The paint booth  100 , the paint units PU 1  to PU 4 , and the auxiliary booths  201  and  202  which constitute the paint system PS according to the present embodiment will be described below. 
     Paint Booth 
     The paint booth  100  is equipment for painting the vehicle body  150 . The paint booth  100  includes a paint chamber (painting space)  2  in which the paint units PU 1  to PU 4  are installed, an air supply chamber  3  disposed above the paint chamber  2 , a recovery chamber  4  disposed below the paint chamber  2 , and the transfer device  5  which transfers the vehicle body  150 . 
     The paint chamber  2  is supported by a support frame  6 . A space for disposing the recovery chamber  4  is secured below the paint chamber  2 . An introduction port  21   a  for introducing air is formed in a part of a ceiling portion  21  of the paint chamber  2 . A discharge port  22   a  for discharging air is formed in a part of a floor portion  22  of the paint chamber  2 . The introduction port  21   a  is provided with a filter  23 . The discharge port  22   a  is provided with a grid plate  24 . The filter  23  is provided in order to remove dust etc. in the air introduced into the paint chamber  2 . 
     The air supply chamber  3  is provided in order to supply the paint chamber  2  with air for ventilation. An air supply duct  7  is connected to the air supply chamber  3 . Air from an air conditioner (not illustrated) at an adjusted temperature and an adjusted humidity flows into the air supply chamber  3  via the air supply duct  7 . The air supply chamber  3  has a function to rectify air that flows in from the air supply duct  7 . An air amount adjustment mechanism  31  is provided in the internal space of the air supply chamber  3 . Therefore, the internal space of the air supply chamber  3  is partitioned by the air amount adjustment mechanism  31  into an upstream space  3   a  and a downstream space  3   b . The upstream space  3   a  communicates with the air supply duct  7 . The downstream space  3   b  communicates with the paint chamber  2  via the filter  23  at the introduction port  21   a . The air amount adjustment mechanism  31  is configured to adjust the amount of air in the air supply chamber  3  such that the amount of air around the vehicle body  150  is equal to a value set in advance. 
     The recovery chamber  4  is provided in order to recover paint particles in the air discharged from the paint chamber  2 . An air discharge duct  8  is connected to the recovery chamber  4 . The recovery chamber  4  communicates with the outside via the air discharge duct  8 . A filter  41  and an air amount adjustment mechanism  42  are provided in the internal space of the recovery chamber  4 . Therefore, the internal space of the recovery chamber  4  is partitioned by the filter  41  and the air amount adjustment mechanism  42  into an upstream space  4   a  and a downstream space  4   b . The filter  41  is disposed on the upper side of the air amount adjustment mechanism  42  so that the filter  41  faces the upstream space  4   a  and the air amount adjustment mechanism  42  faces the downstream space  4   b . The upstream space  4   a  communicates with the paint chamber  2  via the grid plate  24  at the discharge port  22   a . The downstream space  4   b  communicates with the air discharge duct  8 . The filter  41  is a thin dry-type filter, and is provided in order to remove paint particles in the air. The air amount adjustment mechanism  42  is configured to adjust the amount of air in the recovery chamber  4  such that the amount of air around the vehicle body  150  is equal to a value set in advance. 
     The transfer device  5  is provided in order to transfer the vehicle body  150  into the paint chamber  2  and transfer the vehicle body  150  out of the paint chamber  2 . The transfer device  5  is configured to transfer the vehicle body  150  toward a front side of  FIG.  2    when viewed on a paper, for example. 
     The paint booth  100  according to the present embodiment is configured such that air directed from the air supply chamber  3  toward the recovery chamber  4  flows through a predetermined region Ri in the paint chamber  2 , and the air directed from the air supply chamber  3  toward the recovery chamber  4  does not flow through an area Ro outside the predetermined region in the paint chamber  2 . The predetermined region Ri includes a passage region Rp through which the vehicle body  150  passes in the paint chamber  2 , and an area around the passage region Rp (a range in which paint particles that have not been applied to the vehicle body  150  are suspended during painting). The area Ro outside the predetermined region is a region in the paint chamber  2  other than the predetermined region Ri, and is disposed on the outer side in the width direction (X direction) with respect to the predetermined region Ri. 
     Specifically, the introduction port  21   a  of the paint chamber  2  is disposed so as to correspond to the passage region Rp for the vehicle body  150 . The width (length in the X direction) of the introduction port  21   a  is larger than the width of the vehicle body  150 , and smaller than the width of the paint chamber  2 . For example, the width of the introduction port  21   a  is set based on the width of the vehicle body  150 , the range in which paint particles (overspray mist) that have not been applied to the vehicle body  150  are suspended during painting, etc. That is, the width of the introduction port  21   a  is set such that the range of generation of overspray mist is included in the predetermined region Ri through which air flows while forming the area Ro outside the predetermined region through which air does not flow. The introduction port  21   a  is provided over the entire length of the paint chamber  2  in the length direction (Y direction). 
     The discharge port  22   a  of the paint chamber  2  is disposed so as to correspond to the passage region Rp for the vehicle body  150 . The width (length in the X direction) of the discharge port  22   a  is set to be the same as the width of the introduction port  21   a , for example. The width of the discharge port  22   a  is set such that the range of generation of overspray mist is included in the predetermined region Ri through which air flows while forming the area Ro outside the predetermined region through which air does not flow. The discharge port  22   a  is provided over the entire length of the paint chamber  2  in the length direction. 
     At this time, air directed from the introduction port  21   a  toward the discharge port  22   a  mainly passes through a space between a long dashed double-short dashed line La that connects between a first end portion of the introduction port  21   a  in the width direction and a first end portion of the discharge port  22   a  in the width direction and a long dashed double-short dashed line Lb that connects between a second end portion of the introduction port  21   a  in the width direction and a second end portion of the discharge port  22   a  in the width direction. Therefore, the predetermined region Ri is a region that includes the space between the long dashed double-short dashed lines La and Lb and that additionally includes an area in which the air flow is spread, for example. 
     Paint Units 
     The paint units PU 1  to PU 4  each include two paint robots  1 A and  1 B. That is, the paint system PS is configured to include eight paint robots  1 A,  1 B, . . . . The paint robots  1 A,  1 B, . . . are air-driven multi joint robots of the same configuration, and are configured to atomize paint and apply the atomized paint to the vehicle body  150 . The paint robots  1 A,  1 B, . . . each include a spray gun  11 A,  11 B that atomizes paint, a robot arm  12 A,  12 B that moves the spray gun  11 A,  11 B, a robot base  13 A,  13 B that supports the robot arm  12 A,  12 B, and a support column  14 A,  14 B to which the robot base  13 A,  13 B is attached. The support column  14 A,  14 B is formed so as to extend upward from the floor portion  22  of the paint chamber  2 . 
     The two paint robots  1 A and  1 B provided in each of the paint units PU 1  to PU 4  are installed in different states, and accordingly have different roles. The paint robots  1 A and  1 B provided in each of the paint units PU 1  to PU 4  include a first paint robot  1 A that mainly paints the upper region of the vehicle body  150  and a second paint robot  1 B that mainly paints a region from the side region to the lower region of the vehicle body  150 . For example, in the first paint unit PU 1  and the second paint unit PU 2 , the first paint robot  1 A mainly paints the roof and the engine hood of the vehicle body  150 , while the second paint robot  1 B mainly paints the front fender and the front door of the vehicle body  150 . 
     Hereinafter, the robot arm  12 A of the first paint robot  1 A will be referred to as a first robot arm  12 A, and the robot arm  12 B of the second paint robot  1 B will be referred to as a second robot arm  12 B. The robot base  13 A of the first paint robot  1 A will be referred to as a first robot base  13 A, and the robot base  13 B of the second paint robot  1 B will be referred to as a second robot base  13 B. 
     In the present embodiment, the first paint robot  1 A and the second paint robot  1 B in each of the paint units PU 1  to PU 4  are arranged such that the first paint robot  1 A is arranged downstream (on the lower side in  FIG.  1   ) of the second paint robot  1 B in the transfer direction of the vehicle body  150  as illustrated in  FIG.  1   . 
     As one feature of the present embodiment, the installation position of the support column  14 A of the first paint robot  1 A in each of the paint units PU 1  to PU 4  is set to a position that is closer to the transfer device  5  than the installation position of the support column  14 B of the second paint robot  1 B. In other words, when a virtual plane (a virtual plane that passes through the center of the vehicle body  150 ) that extends in the vertical direction and along the direction of transfer of the vehicle body  150  by the transfer device  5  is defined as a reference plane L, the distance (distance in the horizontal direction) between the installation position of the support column  14 A of the first paint robot  1 A in each of the paint units PU 1  to PU 4  and the reference plane L is set to be shorter than the distance between the installation position of the support column  14 B of the second paint robot  1 B and the reference plane L. When the respective installation positions of the support columns  14 A and  14 B are described specifically, the installation position of the support column  14 A of the first paint robot  1 A is determined slightly on the outer side in the width direction with respect to the discharge port  22   a . That is, the support column  14 A is disposed at a position not overlapping the introduction port  21   a  and the discharge port  22   a  (a position displaced from the introduction port  21   a  and the discharge port  22   a ) as seen in plan. On the contrary, the installation position of the support column  14 B of the second paint robot  1 B is determined on the outer side in the width direction with respect to the discharge port  22   a  by a predetermined dimension. That is, the support column  14 B of the second paint robot  1 B is disposed on the outer side with respect to the support column  14 A of the first paint robot  1 A. That is, the respective support columns  14 A and  14 B of the paint robots  1 A and  1 B (the paint robots  1 A and  1 B which are disposed on the same side with respect to the reference plane L) are disposed at positions not overlapping the introduction port  21   a  and the discharge port  22   a  (positions displaced from the introduction port  21   a  and the discharge port  22   a ) as seen in plan, and disposed in the area Ro outside the predetermined region, and the installation position of the support column  14 B of the second paint robot  1 B is set on the outer side with respect to the installation position of the support column  14 A of the first paint robot  1 A. 
     As discussed earlier, the robot bases (first robot base and second robot base)  13 A and  13 B are attached to the respective upper ends of the support columns  14 A and  14 B in the paint robots  1 A and  1 B. Therefore, by setting the respective installation positions of the support columns  14 A and  14 B as discussed earlier, the distance between the first robot base  13 A in each of the paint units PU 1  to PU 4  and the reference plane L is set to be shorter than the distance between the second robot base  13 B in each of the paint units PU 1  to PU 4  and the reference plane L. 
     As another feature of the present embodiment, the height dimension of the support column  14 A of the first paint robot  1 A in each of the paint units PU 1  to PU 4  is set to be larger than the height dimension of the support column  14 B of the second paint robot  1 B. Therefore, the arrangement height position of the first robot base  13 A is set to be higher than the arrangement height position of the second robot base  13 B. As a result, the installation position of the first robot arm  12 A is also higher than the installation position of the second robot arm  12 B, and the first paint robot  1 A plays a role in painting the upper region of the vehicle body  150 , and the second paint robot  1 B plays a role in painting the lower region on the lower side with respect to the region painted by the first paint robot  1 A. In particular, the first paint robot  1 A paints the roof of the vehicle body  150 , and thus paints the middle portion (middle portion in the vehicle width direction) of the roof. As a result, a region (in particular, the roof) of the vehicle body  150  to be painted by the first paint robot  1 A includes a region that is closer to the reference plane L than a region of the vehicle body  150  to be painted by the second paint robot  1 B. 
     Since the paint robots  1 A and  1 B are installed in this manner, the respective first paint robots  1 A and  1 A of the first paint unit PU 1  and the second paint unit PU 2  are disposed so as to face each other with the passage region Rp for the vehicle body  150  interposed therebetween in the width direction, as illustrated in  FIG.  2   . Similarly, the respective second paint robots  1 B and  1 B of the first paint unit PU 1  and the second paint unit PU 2  are also disposed so as to face each other with the passage region Rp for the vehicle body  150  interposed therebetween in the width direction. In addition, the respective first paint robots  1 A and  1 A of the third paint unit PU 3  and the fourth paint unit PU 4  are disposed so as to face each other with the passage region Rp for the vehicle body  150  interposed therebetween in the width direction. Similarly, the respective second paint robots  1 B and  1 B of the third paint unit PU 3  and the fourth paint unit PU 4  are also disposed so as to face each other with the passage region Rp for the vehicle body  150  interposed therebetween in the width direction. 
     The width (dimension in the X direction) of the robot bases  13 A and  13 B of the paint robots  1 A and  1 B is set to be larger than the width of the support columns  14 A and  14 B. The robot bases  13 A and  13 B are attached to the upper portions of the support columns  14 A and  14 B with the outer ends of the robot bases  13 A and  13 B in the width direction aligned with the outer ends of the support columns  14 A and  14 B in the width direction. That is, the robot bases  13 A and  13 B extend toward the central side in the width direction from the upper portion of the support columns  14 A and  14 B. Therefore, the support columns  14 A and  14 B do not exist in a region under the extending portion of the robot bases  13 A and  13 B. For the first paint robot  1 A, a range (space) under the extending portion is secured as a passage range (robot arm passage range according to the present disclosure) MS for the second robot arm  12 B during paint work. Specifically, the arrangement height position of the first robot base  13 A is higher than the upper end of the fenders of the vehicle body  150 , whereby the passage range MS is extended to the upper side of the fenders. 
     The spray guns  11 A and  11 B provided in the paint robots  1 A and  1 B will be described. The spray guns  11 A and  11 B of the paint robots  1 A and  1 B are of the same configuration, and thus the spray gun  11 A provided in the first paint robot  1 A will be described in representation. 
       FIG.  3    is a sectional view illustrating the spray gun  11 A.  FIG.  4    is a perspective view illustrating the distal end of a rotary head  51  of the spray gun  11 A.  FIG.  5    is a schematic diagram illustrating electrostatic atomization of paint. 
     The spray gun  11 A is configured to release streaks of paint P 1  from the rotary head  51 , form paint particles (atomized paint) P 2  when the streaks of paint P 1  are electrostatically atomized, and apply the paint particles P 2  to the vehicle body  150 . 
     As illustrated in  FIG.  3   , the spray gun  11 A includes the rotary head  51 , an air motor (not illustrated) that rotates the rotary head  51 , a cap  52  that covers the outer peripheral surface of the rotary head  51 , a paint supply pipe  53  that supplies paint to the rotary head  51 , and a voltage generator  54  (see  FIG.  5   ) that applies a negative high voltage to the rotary head  51 . 
     The rotary head  51  is configured to be supplied with liquid paint and release the paint using a centrifugal force. A hub  511  is attached to the rotary head  51  to form a paint space S. The paint is supplied from the paint supply pipe  53  to the paint space S. A plurality of outflow holes  511   a  is formed in the outer edge portion of the hub  511  to allow the paint to flow out of the paint space S. 
     A diffusion surface  51   a  over which the paint is diffused by a centrifugal force is formed on the rotary head  51  on the outer side in the radial direction with respect to the outflow holes  511   a . The diffusion surface  51   a  is formed so as to become larger in diameter toward the distal end of the rotary head  51 , and configured to form the paint that has flowed out from the outflow holes  511   a  into a film form. As illustrated in  FIG.  4   , groove portions  51   c  are formed at an outer edge portion  51   b  of the diffusion surface  51   a  to form the paint in the film form into streaks and release the streaks of paint. In  FIG.  3   , the groove portions  51   c  are not illustrated in consideration of viewability. 
     The groove portions  51   c  are formed so as to extend in the radial direction when seen in the axial direction. A plurality of groove portions  51   c  is provided in the circumferential direction. That is, the groove portions  51   c  are formed in the outer edge portion  51   b  of the diffusion surface  51   a  so as to extend in the direction of inclination of the diffusion surface  51   a . The groove portions  51   c  are formed so as to reach the outer end portion, in the radial direction, of the rotary head  51 . Therefore, the distal end of the rotary head  51  is in a recessed and projected shape as seen from the side of the outer peripheral surface. 
     In the spray gun  11 A, as illustrated in  FIG.  5   , the voltage generator  54  applies a negative high voltage to the rotary head  51  to charge the streaks of paint P 1  released from the groove portions  51   c  of the rotary head  51 . The streaks of paint P 1  are atomized into the paint particles P 2  using a repulsive force due to the electrical charge. That is, the streaks of paint P 1  released from the groove portions  51   c  of the rotary head  51  are electrostatically atomized into the paint particles P 2 . That is, the paint robots  1 A and  1 B are not provided with an air discharging portion that discharges shaping air, and therefore the paint particles P 2  are formed without using shaping air. Thus, the paint robots  1 A and  1 B are of an electrostatic atomization type that does not use shaping air, and do not generate a rise of paint particles due to shaping air. Thus, generation of overspray mist is suppressed, and the range of generation of overspray mist is narrowed. 
     The paint booth  100  also includes cartridge stockers  205  ( 206 ) that each house a paint cartridge (not illustrated) to be loaded into the spray guns  11 A and  11 B of the paint robots  1 A and  1 B. The cartridge stockers  205  ( 206 ) house a plurality of types of paint cartridges that matches the types of paint to be used for painting in the paint system PS. When the amount of paint remaining in the paint cartridge loaded into the spray guns  11 A and  11 B has become small, or when the type of paint to be used for paining of the vehicle body  150  to be transferred into the paint system PS next is changed (e.g. for a color change) after the paint work in the paint system PS is ended, a desired paint cartridge is transferred from the cartridge stocker  205  ( 206 ) toward the spray guns  11 A and  11 B in order to replace the paint cartridge loaded into the spray guns  11 A and  11 B. The paint cartridge is transferred by a transfer robot (not illustrated), for example. 
     Although not described in detail, paint supply piping is connected to the cartridge stocker  205  ( 206 ) to individually inject (supply) predetermined paint to each paint cartridge housed, so that paint to be used for the next painting is injected into the paint cartridge housed in the cartridge stocker  205  ( 206 ). 
     Auxiliary Booths 
     The auxiliary booths  201  and  202  are arranged on opposite outer sides (opposite outer sides in the horizontal direction) of the paint booth  100 . The auxiliary booth  201  positioned on the right side in  FIG.  2    will be referred to as a “first auxiliary booth”. The auxiliary booth  202  positioned on the left side in  FIG.  2    will be referred to as a “second auxiliary booth”. 
     The auxiliary booths  201  and  202  are constituted as a space surrounded by frames  203  and  204 . The auxiliary booths  201  and  202  include control devices  303 A,  303 B,  303 C, and  303 D that control the devices provided in the paint units PU 1  to PU 4 . That is, a first control device  303 A that controls the devices provided in the first paint unit PU 1  and a third control device  303 C that controls the devices provided in the third paint unit PU 3  are arranged in the first auxiliary booth  201 . Meanwhile, a second control device  303 B that controls the devices provided in the second paint unit PU 2  and a fourth control device  303 D that controls the devices provided in the fourth paint unit PU 4  are arranged in the second auxiliary booth  202 . In the present embodiment, the control devices  303 A to  303 D are supported on a side surface of the frames  203  and  204  (a side surface of the auxiliary booths  201  and  202  that faces inward). 
     In this manner, the control devices  303 A to  303 D are provided in correspondence with the paint units PU 1  to PU 4 , respectively. The paint units PU 1  to PU 4  each include two paint robots  1 A and  1 B. Therefore, the control devices  303 A to  303 D each have a function to control both the two paint robots  1 A and  1 B. In other words, the control devices  303 A to  303 D are each a single (for each of the paint units PU 1  to PU 4 ) control device  303 A ( 303 B,  303 C,  303 D) that controls both operation of the first paint robot  1 A and operation of the second paint robot  1 B. As discussed earlier, the paint robots  1 A,  1 B, . . . are air-driven multi joint robots. Therefore, the control devices  303 A,  303 B,  303 C, and  303 D are each configured to include a pneumatic panel that controls the paint robot  1 A ( 1 B). The control devices  303 A,  303 B,  303 C, and  303 D may each include a circuit board. 
     Configuration of Control System 
     Next, a control system for the paint units will be described.  FIG.  6    is a block diagram illustrating a schematic configuration of the control system for the paint system PS according to the present embodiment. In the control system for the paint system PS, as illustrated in  FIG.  6   , a central processing device  300  that integrally controls the paint system PS, a start switch (start SW)  301 , a transfer device controller  302 , the first to fourth control devices  303 A to  303 D, and the first to fourth paint units PU 1  to PU 4  are electrically connected to each other to enable transmission and reception of various signals such as command signals. 
     The start switch  301  transmits a start command signal for the paint system PS to the central processing device  300  in accordance with an operation by an operator. When the start command signal is received, the paint system PS is started to start paint operation to be discussed later. 
     The transfer device controller  302  controls transfer of the vehicle body  150  by the transfer device  5 . Specifically, the transfer device  5  is actuated until the vehicle body  150  reaches a predetermined position (the position indicated in  FIG.  1   ) in the paint booth  100 , and since then, the vehicle body  150  is moved at a predetermined transfer speed (a speed set in advance and suited for paint operation). After the predetermined time has elapsed since painting of the vehicle body  150  was finished, the transfer device  5  is actuated such that the vehicle body  150  is transferred from the paint booth  100  toward the next station at a speed for vehicle body transfer and a new vehicle body  150  to be painted next is transferred to the paint booth  100 . 
     The control devices  303 A to  303 D receive a command signal from the central processing device  300 , and output a control command signal to the paint units PU 1  to PU 4 , respectively, in accordance with the control command signal. That is, the first control device  303 A outputs a control command signal to the paint robots (first paint robot  1 A and second paint robot  1 B) of the first paint unit PU 1 , the second control device  303 B outputs a control command signal to the paint robots  1 A and  1 B of the second paint unit PU 2 , the third control device  303 C outputs a control command signal to the paint robots  1 A and  1 B of the third paint unit PU 3 , and the fourth control device  303 D outputs a control command signal to the paint robots  1 A and  1 B of the fourth paint unit PU 4 . Upon receiving the control command signal, the paint robots  1 A and  1 B of each of the paint units PU 1  to PU 4  paint the vehicle body  150  in accordance with information on teaching performed in advance. 
     Operation During Painting 
     Next, paint operation (paint method) by the paint system PS will be described. The paint operation is performed without humans in the paint chamber  2 . 
     First, the paint system PS is started as the start switch  301  is operated. As the paint system PS is started, air at an adjusted temperature and an adjusted humidity flows from the air conditioner (not illustrated) into the air supply chamber  3  via the air supply duct  7  before the paint operation is started. In the air supply chamber  3 , the amount of air is adjusted by the air amount adjustment mechanism  31 , and the air is introduced into the paint chamber  2  via the filter  23  at the introduction port  21   a.    
     In the paint chamber  2 , air directed from the air supply chamber  3  toward the recovery chamber  4  flows through the predetermined region Ri. That is, a flow (downward flow) of air directed downward from the introduction port  21   a  toward the discharge port  22   a  is formed in the predetermined region Ri. 
     The air that has passed through the predetermined region Ri of the paint chamber  2  is discharged to the recovery chamber  4  via the grid plate  24  at the discharge port  22   a . In the recovery chamber  4 , the amount of air is adjusted by the air amount adjustment mechanism  42 , and the air is released to the outside via the air discharge duct  8 . 
     Next, the transfer device  5  is actuated in accordance with a command signal from the transfer device controller  302 , to move the vehicle body  150  to be painted until the vehicle body  150  reaches a predetermined position (the position indicated in  FIG.  1   ) in the paint booth  100 . The vehicle body  150  is painted with the paint robots  1 A and  1 B of each of the paint units PU 1  to PU 4  operating in accordance with the command signal from the control devices  303 A to  303 D while the vehicle body  150  is transferred at a predetermined speed. 
     In painting the vehicle body  150 , the upper region of the vehicle body  150  is painted by the respective first paint robots  1 A of the paint units PU 1  to PU 4 , and the lower region of the vehicle body  150  on the lower side with respect to the upper region is painted by the respective second paint robots  1 B of the paint units PU 1  to PU 4 . Specifically, the respective first paint robots  1 A,  1 A of the first paint unit PU 1  and the second paint unit PU 2  mainly paint the front half of the roof and the engine hood of the vehicle body  150 , and the respective second paint robots  1 B,  1 B of the first paint unit PU 1  and the second paint unit PU 2  mainly paint the front fender and the front door of the vehicle body  150 . Meanwhile, the respective first paint robots  1 A,  1 A of the third paint unit PU 3  and the fourth paint unit PU 4  mainly paint the rear half of the roof of the vehicle body  150 , and the respective second paint robots  1 B,  1 B of the third paint unit PU 3  and the fourth paint unit PU 4  mainly paint the rear fender and the rear door of the vehicle body  150 . In the paint operation performed by the paint robots  1 A and  1 B, the vehicle body  150  is painted with the paint robot arms  12 A and  12 B operating such that the spray guns  11 A and  11 B are moved along a predetermined track (a predetermined track based on teaching information) while facing a region to be painted by the paint robots  1 A and  1 B. 
     In this event, the second robot arm  12 B of the second paint robot  1 B, the second robot base  13 B of which is positioned below the arrangement height position of the first robot base  13 A, paints the lower region on the lower side with respect to the region painted by the first paint robot  1 A while passing through the passage range MS which is provided under the first robot base  13 A.  FIG.  7    is a plan view illustrating the respective movable ranges of the robot arms  12 A and  12 B of the paint robots  1 A and  1 B (the respective movable ranges of the robot arms  12 A and  12 B determined using the respective base end positions of the robot arms  12 A and  12 B as base points, including the respective movable ranges of the spray guns  11 A and  11 B) during painting.  FIG.  8    is a front view illustrating the respective movable ranges of the spray guns  11 A and  11 B of the paint robots  1 A and  1 B during painting. The regions inside the dashed lines in the drawings represent the movable ranges. As illustrated in  FIGS.  7  and  8   , the movable range of the second robot arm  12 B and the movable range of the spray gun  11 B include the passage range MS which is provided under the robot base  13 A of the first paint robot  1 A, and the lower region of the vehicle body  150  (the region on the lower side with respect to the region painted by the first paint robot  1 A) is painted while the second robot arm  12 B and the spray gun  11 B are passing through the passage range MS. 
     In this manner, the second robot arm  12 B paints the lower region on the lower side with respect to the region painted by the first paint robot  1 A without interfering with the first paint robot  1 A and with a sufficient movable range secured, even if the position of the first robot base  13 A is set to a position that is close to the transfer path (a position that is closer to the reference plane L than the position of the second robot base  13 B). 
     In the paint operation, more specifically, the paint robots  1 A and  1 B perform painting in an electrostatic atomization method in which shaping air is not used. Specifically, as illustrated in  FIG.  5   , the rotary head  51  is rotated by an air motor (not illustrated) with the voltage generator  54  applying a negative high voltage to the rotary head  51  and with the vehicle body  150  grounded. The distance between the rotary head  51  and the vehicle body  150  is adjusted by the robot arms  12 A and  12 B. As illustrated in  FIG.  3   , liquid paint is supplied from the paint supply pipe  53  to the paint space S, and the paint flows out through the outflow holes  511   a  because of a centrifugal force. 
     The paint that has flowed out through the outflow holes  511   a  flows outward in the radial direction along the diffusion surface  51   a  because of a centrifugal force. The paint that flows along the diffusion surface  51   a  is formed into a film form, and reaches the outer edge portion  51   b  to be supplied to the plurality of groove portions  51   c  (see  FIG.  4   ). Paint in each groove portion  51   c  is separated from paint in adjacent groove portions  51   c . The paint passing through the groove portions  51   c  is formed into streaks to be released from the outer end portion, in the radial direction, of the rotary head  51  (the groove portions  51   c  at the outer peripheral surface of the rotary head  51 ). 
     As illustrated in  FIG.  5   , the streaks of paint P 1  released from the rotary head  51  are electrostatically atomized to form paint particles P 2 . An electric field is formed between the rotary head  51  and the vehicle body  150 , and the paint particles P 2  which are negatively charged are drawn toward the vehicle body  150 . Therefore, the paint particles P 2  are applied to the vehicle body  150  to form a paint film (not illustrated) on the surface of the vehicle body  150 . 
     In the paint robots  1 A and  1 B, as illustrated in  FIG.  1   , the robot arms  12 A and  12 B move the spray guns  11 A and  11 B along the surface of the vehicle body  150  while the spray guns  11 A and  11 B are painting. Therefore, the paint robots  1 A and  1 B paint respective regions of the surface of the vehicle body  150 . Consequently, the entire surface of the vehicle body  150  is painted. 
     During the painting, paint particles (overspray mist) that have not been applied to the vehicle body  150  are generated. The range of generation of the overspray mist is included in the predetermined region Ri. Thus, the overspray mist generated during the painting is carried downward by a downward flow to be discharged into the recovery chamber  4 . In the recovery chamber  4 , the overspray mist is recovered by the filter  41 . That is, the filter  41  removes the paint particles that have not been applied to the vehicle body  150  from the air to purify the air to be fed to the air discharge duct  8 . 
     When the entire surface of the vehicle body  150  is painted in this manner to complete the paint operation, the vehicle body  150  is transferred out of the paint booth  100  by the transfer device  5 , and a next vehicle body  150  to be painted is transferred into the paint booth  100  to be subjected to similar paint operation. When the amount of paint remaining in the paint cartridge loaded into the spray guns  11 A and  11 B has become small as paint operation on the new vehicle body  150  is started, or when the type of paint to be used for paining of the new vehicle body  150  is changed, a desired paint cartridge is transferred from the cartridge stockers  205  and  206  toward the spray guns  11 A and  11 B in order to replace the paint cartridge loaded into the spray guns  11 A and  11 B. 
     Effects of Embodiment 
     In the present embodiment, as described above, the distance between the first robot base  13 A of the first paint robot  1 A, which paints the upper region of the vehicle body  150 , and the reference plane L is set to be shorter than the distance between the second robot base  13 B of the second paint robot  1 B, which paints the lower region of the vehicle body  150  on the lower side with respect to the upper region, and the reference plane L. In addition, the passage range MS which allows passage of the second robot arm  12 B of the second paint robot  1 B is provided under the first robot base  13 A. That is, the second robot arm  12 B can paint the lower region on the lower side with respect to the region painted by the first paint robot  1 A without interfering with the first paint robot  1 A and with a sufficient movable range secured, even though the position of the first robot base  13 A is set to a position that is close to the transfer device  5  (a position that is closer to the reference plane L than the position of the second robot base  13 B). That is, a sufficient movable range of the second robot arm  12 B can be secured while reducing the length of the first robot arm  12 A by reducing the distance between the vehicle body  150  and the first robot base  13 A by setting the position of the first robot base  13 A to a position that is close to the reference plane L. Therefore, it is possible to reduce the size of the paint robots (in particular, the first paint robot  1 A) and increase the movable range of the robot arms (in particular, the second robot arm  12 B) at the same time. As a result, it is possible to reduce the size of the paint system PS along with a reduction in the size of the paint robots, and reduce the equipment cost and the running cost. It is also possible to reduce CO 2  because of a reduction in the size of the paint system PS. It is also possible to paint well the lower region on the lower side with respect to the region painted by the first paint robot  1 A because of an increase in the movable range of the second robot arm  12 B. Since the length of the first robot arm  12 A can be reduced, the paint robots  1 A and  1 B can be of the same configuration as discussed earlier. This also allows a reduction in the equipment cost. 
     In the present embodiment, the second robot arm  12 B passes through the passage range MS, which is provided under the first robot base  13 A, to avoid interference with the first paint robot  1 A. Therefore, the arrangement position of the first paint robot  1 A and the arrangement position of the second paint robot  1 B in the length direction (Y direction) of the paint chamber  2  can be brought close to each other. Therefore, it is possible to reduce the size of the internal space required for the paint booth  100 . In the paint booth  100 , as discussed earlier, a downward flow of air is formed so that a good flow of paint particles can be obtained inside the paint booth  100 . With the internal space of the paint booth  100  reduced in size, however, it is possible to reduce the size of a space in which such a downward flow is generated, and reduce the size of an air conditioning device for generating the downward flow or reduce energy consumption. 
     In the present embodiment, a single control device  303 A ( 303 B,  303 C,  303 D) is provided to control both operation of the first paint robot  1 A and operation of the second paint robot  1 B. Therefore, it is possible to reduce the size of the control unit (a unit for paint robot control, including the control devices  303 A to  303 D) as a whole compared to the case where a plurality of control devices is provided to individually control operation of the paint robots  1 A and  1 B, thereby contributing to a reduction in the size of the paint system PS. 
     In the present embodiment, the control devices  303 A to  303 D are housed in the auxiliary booths  201  and  202  which are arranged outside the paint booth  100 . Therefore, it is possible to reduce the size of the internal space required for the paint booth  100  compared to the case where the control devices are arranged inside the paint booth  100 . This also makes it possible to reduce the size of a space in which a downward flow discussed earlier is generated, and reduce the size of an air conditioning device for generating the downward flow or reduce energy consumption. 
     In the paint system PS according to the present embodiment, the plurality of paint units PU 1  to PU 4  is arranged on opposite sides of the reference plane L. Therefore, it is possible to paint regions of the vehicle body  150  on one side (a first side) and the other side (a second side) with respect to the reference plane L well using the paint robots  1 A,  1 B, . . . of each of the paint units PU 1  to PU 4 , and finish the painted surfaces of the vehicle body  150  well. 
     In the present embodiment, the spray guns  11 A and  11 B electrostatically atomize paint and spray the paint toward the vehicle body  150 . Therefore, it is possible to improve the efficiency in applying the paint to the vehicle body  150 , and reduce the range in which the paint sprayed toward the vehicle body  150  is splashed back. Therefore, it is not necessary that the paint robots  1 A and  1 B should be arranged at positions significantly away from the vehicle body  150  so that the paint splashed back does not adhere to the paint robots  1 A and  1 B, and the arrangement positions of the paint robots  1 A and  1 B can be set to positions that are close to the vehicle body  150 . As a result, it is possible to reduce the size of the paint system PS by reducing the length of the paint system PS in the width direction. It is also possible to reduce CO 2  because of a reduction in the size of the paint system PS. 
     Second Embodiment 
     Next, a second embodiment will be described. In the present embodiment, the manner of arrangement of the paint robots  1 A and  1 B in each of the paint units PU 1  to PU 4  is different from that according to the first embodiment. 
       FIG.  9    is a plan view illustrating a paint system PS according to the present embodiment.  FIG.  10    is a front view illustrating the paint system PS according to the present embodiment. In each of the paint units PU 1  to PU 4  of the paint system PS according to the present embodiment, as illustrated in the drawings, the first paint robot  1 A and the second paint robot  1 B are arranged such that the first paint robot  1 A is arranged upstream of the second paint robot  1 B in the transfer direction of the vehicle body  150 . Also in the present embodiment, as in the first embodiment discussed earlier, the distance between the installation position of the support column  14 A of the first paint robot  1 A in each of the paint units PU 1  to PU 4  and the reference plane L is set to be shorter than the distance between the installation position of the support column  14 B of the second paint robot  1 B and the reference plane L. The arrangement height position of the first robot base  13 A is set to be higher than the arrangement height position of the second robot base  13 B. This allows the range provided under the first robot base  13 A to be secured as the passage range MS for the second robot arm  12 B during paint work. 
     Therefore, also with the present embodiment, a sufficient movable range of the second robot arm  12 B can be secured while reducing the length of the first robot arm  12 A by setting the position of the first robot base  13 A to a position that is close to the reference plane L to reduce the distance between the vehicle body  150  and the first robot base  13 A. As a result, it is possible to reduce the size of the paint robots (in particular, the first paint robot  1 A) and increase the movable range of the robot arms (in particular, the second robot arm  12 B) at the same time. 
     Third Embodiment 
     Next, a third embodiment will be described. In the embodiments discussed earlier, paint operation is performed while the vehicle body  150  is transferred by the transfer device  5 . In the present embodiment, instead, paint operation is performed while the paint units PU 1  to PU 4  are moved along the horizontal direction. 
       FIG.  11    is a plan view illustrating a paint system PS according to the present embodiment. In the present embodiment, as illustrated in  FIG.  11   , the first paint robot  1 A and the second paint robot  1 B in each of the paint units PU 1  to PU 4  are arranged such that the first paint robot  1 A is arranged downstream of the second paint robot  1 B in the transfer direction of the vehicle body  150  (the same manner of arrangement as in the first embodiment), and the paint robots  1 A and  1 B are movable on rails  15 A and  15 B (see the arrows B in  FIG.  11   ). In a specific example, wheels (not illustrated) arranged at the lower portion of the support columns  14 A and  14 B of the paint robots  1 A and  1 B are placed so as to be able to travel on the rails  15 A and  15 B, and configured to include an electric motor that applies power for travel to the wheels. The other components are the same as those according to the embodiments discussed earlier. 
     In the paint operation according to the present embodiment, the transfer device  5  is stopped when the vehicle body  150  reaches a predetermined position (the position indicated in  FIG.  11   ) in the paint booth  100  through actuation of the transfer device  5 . In this state, the vehicle body  150  is painted with the paint robots  1 A and  1 B of each of the paint units PU 1  to PU 4  operating in accordance with a command signal from the control devices  303 A to  303 D while the paint robots  1 A and  1 B are traveling on the rails  15 A and  15 B (e.g. traveling from the front side toward the rear side of the vehicle body  150 ). 
     Also with the present embodiment, the same effects as those of the embodiments discussed earlier can be achieved. 
     Fourth Embodiment 
     Next, a fourth embodiment will be described. Also in the present embodiment, paint operation is performed while the paint units PU 1  to PU 4  are moved along the horizontal direction. 
       FIG.  12    is a plan view illustrating a paint system PS according to the present embodiment. In the present embodiment, as illustrated in  FIG.  12   , the first paint robot  1 A and the second paint robot  1 B in each of the paint units PU 1  to PU 4  are arranged such that the first paint robot  1 A is arranged upstream of the second paint robot  1 B in the transfer direction of the vehicle body  150  (the same manner of arrangement as in the second embodiment), and the paint robots  1 A and  1 B are movable on the rails  15 A and  15 B (see the arrows B in  FIG.  12   ) as in the third embodiment discussed earlier. The other components are the same as those according to the embodiments discussed earlier. In addition, the paint operation according to the present embodiment is the same as that according to the third embodiment discussed earlier. 
     Also with the present embodiment, the same effects as those of the embodiments discussed earlier can be achieved. 
     Fifth Embodiment 
     Next, a fifth embodiment will be described. In the embodiments discussed earlier, the object to be painted is the vehicle body  150 , and the first paint robot  1 A paints a horizontal surface such as a roof. In the present embodiment, instead, both the first paint robot  1 A and the second paint robot  1 B paint a vertical surface, and a region to be painted by the first paint robot  1 A is located above a region to be painted by the second paint robot  1 B. 
       FIG.  13    is a front view illustrating a paint system PS according to the present embodiment. As illustrated in  FIG.  13   , an object to be painted  151  according to the present embodiment includes a body portion  151   a  and a projecting portion  151   b  that projects upward from the upper surface of the body portion  151   a , and the width of the body portion  151   a  is larger than the width of the projecting portion  151   b . A side surface of the body portion  151   a  is painted by the second paint robot  1 B. A side surface of the projecting portion  151   b  is painted by the first paint robot  1 A. 
     Also with the present embodiment, the same effects as those of the embodiments discussed earlier can be achieved. 
     Other Embodiments 
     The present disclosure is not limited to the embodiments described above, and can be modified and applied in all manners that fall within the scope of the claims and the scope of equivalence thereto. 
     For example, while the object to be painted is the vehicle body  150  in the first to fourth embodiments and the object to be painted  151  which includes the body portion  151   a  and the projecting portion  151   b  is to be painted in the fifth embodiment, the present disclosure is also applicable to a case where a different object is to be painted. 
     In the embodiments described above, the paint system PS includes eight paint robots  1 A,  1 B, . . . . However, the number of the paint robots  1 A,  1 B, . . . is not limited thereto. In the embodiments described above, each of the paint units PU 1  to PU 4  includes two paint robots  1 A and  1 B. However, each of the paint units may include three or more paint robots. Also in this case, at least two of the three or more paint robots that constitute the paint unit have the relationship according to the present disclosure (a configuration in which the distance between the first robot base  13 A and the reference plane L is set to be shorter than the distance between the second robot base  13 B and the reference plane L and the passage range MS which allows passage of the second robot arm  12 B is provided under the first robot base  13 A). 
     In the embodiments described above, painting is performed while the object to be painted (the vehicle body  150  or the object to be painted  151 ) and the paint units PU 1  to PU 4  are moving relative to each other. The present disclosure is not limited thereto. The present disclosure is also applicable to a case where painting is performed without the object to be painted  150 ,  151  and the paint units PU 1  to PU 4  being moved relative to each other. 
     In the embodiments described above, the respective first paint robots  1 A and  1 A of the first paint unit PU 1  and the second paint unit PU 2  are configured to face each other with the passage region Rp interposed therebetween, and the respective second paint robots  1 B and  1 B of the first paint unit PU 1  and the second paint unit PU 2  are configured to face each other with the passage region Rp interposed therebetween. Similarly, the respective first paint robots  1 A and  1 A of the third paint unit PU 3  and the fourth paint unit PU 4  are configured to face each other with the passage region Rp interposed therebetween, and the respective second paint robots  1 B and  1 B of the third paint unit PU 3  and the fourth paint unit PU 4  are configured to face each other with the passage region Rp interposed therebetween. The present disclosure is not limited thereto. The respective first paint robots  1 A and  1 A may be configured not to face each other with the passage region Rp interposed therebetween, or the respective second paint robots  1 B and  1 B may be configured not to face each other with the passage region Rp interposed therebetween. For example, the first paint unit PU 1  and the third paint unit PU 3  may be configured in accordance with the layout according to the first embodiment (a layout in which the first paint robot  1 A is arranged downstream of the second paint robot  1 B in the transfer direction of the vehicle body  150 ; see  FIG.  1   ), and the second paint unit PU 2  and the fourth paint unit PU 4  may be configured in accordance with the layout according to the second embodiment (a layout in which the first paint robot  1 A is arranged upstream of the second paint robot  1 B in the transfer direction of the vehicle body  150 ; see  FIG.  9   ). Alternatively, the first paint unit PU 1  and the third paint unit PU 3  may be configured in accordance with the layout according to the second embodiment (a layout in which the first paint robot  1 A is arranged upstream of the second paint robot  1 B in the transfer direction of the vehicle body  150 ), and the second paint unit PU 2  and the fourth paint unit PU 4  may be configured in accordance with the layout according to the first embodiment (a layout in which the first paint robot  1 A is arranged downstream of the second paint robot  1 B in the transfer direction of the vehicle body  150 ). With this configuration, it is possible to reduce the possibility that the first paint robots  1 A and  1 A interfere with each other when painting the middle portion of the roof etc. 
     In the embodiments described above, the paint may be water-based paint, or may be solvent-based paint. 
     The present disclosure is applicable to a paint system that includes a plurality of paint units, in each of which a first paint robot that paints an upper region of a vehicle body and a second paint robot that paints a lower region of the vehicle body on the lower side with respect to the upper region are disposed on the same side with respect to a predetermined reference plane.