Patent Publication Number: US-11383383-B2

Title: Vehicle transport apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2019-034651 filed on Feb. 27, 2019, the contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a vehicle transport apparatus for transporting a vehicle within a prescribed region. 
     Description of the Related Art 
     Japanese Laid-Open Patent Publication No. 08-028085 discloses an apparatus that loads a vehicle onto a pallet and transports the vehicle within a multistory parking lot in which pieces of equipment such as rails and pallets are provided. 
     SUMMARY OF THE INVENTION 
     A vehicle transport apparatus, which is different than the transport apparatus serving as the equipment described in Japanese Laid-Open Patent Publication No. 08-028085 and that can travel within the vehicle transport region (parking lot, cargo ship, harbor, or the like) has been developed. There is a desire that such a vehicle transport apparatus be made smaller and be capable of travelling freely within the vehicle transport region. 
     The present invention takes the above problems into consideration, and it is an object of the present invention to provide a small vehicle transport apparatus that can travel freely within a prescribed region. 
     The present invention is a vehicle transport apparatus that transports a vehicle by lifting up wheels of the vehicle, including a first robot configured to enter underneath the vehicle, lift up front wheels of the vehicle, and travel; and a second robot configured to enter underneath the vehicle, lift up rear wheels of the vehicle, and travel, wherein the first robot and the second robot each include omnidirectional wheels configured to cause a body to freely travel and turn omnidirectionally, by operating in cooperation with each other; a drive force transmitting mechanism configured to transmit a drive force to the omnidirectional wheels; a right contact portion configured to contact a contact surface on one of a front side and a back side of one wheel of the wheels; a right lifting arm configured to be freely rotationally movable between a right storage position at which a tip thereof points toward a center of the body in a width direction and a right expanded position at which the tip points toward a right side of the body in the width direction, and lift up the one wheel by drawing near the right contact portion while in contact with a contact surface on the other of the front side and the back side of the one wheel at the right expanded position; a left contact portion configured to contact a contact surface on one of a front side and a back side of the other wheel; a left lifting arm configured to be freely rotationally movable between a left storage position at which a tip thereof points toward the center of the body in the width direction and a left expanded position at which the tip points toward a left side of the body in the width direction, and lift up the other wheel by drawing near the left contact portion while in contact with a contact surface on the other of the front side and the back side of the other wheel at the left expanded position; a right rotational force transmitting mechanism configured to transmit a rotational force to the right lifting arm; and a left rotational force transmitting mechanism configured to transmit a rotational force to the left lifting arm. 
     According to the present embodiment, the apparatus can be made smaller and can also move freely within the prescribed region. 
     The above and other objects features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which preferred embodiments of the present invention are shown by way of illustrative example. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are each a schematic view of a vehicle transport apparatus that transports a vehicle; 
         FIG. 2  is a perspective view of a transport robot with the upper cover removed; 
         FIG. 3  is a top view of the transport robot with the upper cover removed; 
         FIG. 4  shows a block configuration of a control system and a power system of the transport robot; 
         FIG. 5  is a schematic view of the transport robot at a stage of aligning with the vehicle; 
         FIGS. 6A and 6B  are each a schematic view of the transport robot before lifting up the wheels; 
         FIGS. 7A and 7B  are each a schematic view of the transport robot after lifting up the wheels; 
         FIG. 8  shows a system configuration of a vehicle transport system; 
         FIG. 9  is a schematic view of a parking list; 
         FIG. 10  is a schematic view of a charging reservation list; 
         FIG. 11  is a sequence diagram showing an entry process in which the vehicle enters a charging spot; 
         FIG. 12  is a sequence diagram showing a transport-in process in which the vehicle is transported into a charging space; 
         FIG. 13  is a sequence diagram showing a transport-out process in which the vehicle is transported out from the charging space; and 
         FIG. 14  is a sequence diagram showing an exit process in which the vehicle exits the charging spot. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following describes in detail preferred embodiments of a vehicle transport apparatus according to the present invention, while referencing the accompanying drawings. 
     [1. Vehicle Transport Apparatus  10 ] 
     As shown in  FIGS. 1A and 1B , the vehicle transport apparatus  10  includes a set of transport robots  12  (first robot  12   a  and second robot  12   b ) that can travel autonomously within a prescribed region where transport of a vehicle  94  is required. The first robot  12   a  can enter underneath the vehicle  94 , lift up front wheels  96   f  of the vehicle  94 , and move autonomously within the prescribed region. The second robot  12   b  can enter underneath the vehicle  94 , lift up rear wheels  96   r  of the vehicle  94 , and travel autonomously within the prescribed region. The first robot  12   a  and the second robot  12   b  have the same structure. However, the first robot  12   a  is a master device, and the second robot  12   b  is a slave device. 
     [1.1. Structure of the Transport Robots  12 ] 
     The following describes the structure of a transport robot  12  (first robot  12   a  or second robot  12   b ), using  FIGS. 2 and 3 .  FIGS. 2 and 3  show the transport robot  12  in a state where an upper cover  14  (see  FIG. 1A ) that covers the top portion of the body  16  is removed. In this specification, in order to aid the description, each direction used as a reference for the transport robot  12  is defined as shown below. A direction in which a right contact portion  48 R and a left contact portion  48 L are arranged relative to a right lifting arm  42 R and a left lifting arm  42 L, which are described further below, is a forward direction, and the opposite of this direction is a backward direction. Furthermore, in this specification, a direction in which a right load-bearing mechanism  30 R, which is described further below, is arranged relative to a center position (referred to below as the center line C) in a width direction of the transport robot  12  is the right direction, and the direction in which a left load-bearing mechanism  30 L, which is described further below, is arranged relative to the center line C is the left direction. In the following description, unless otherwise specified, forward, backward, right, and left refer to the forward, backward, right, and left directions of the transport robot  12 . 
     The transport robot  12  basically includes the body  16 , four sets of drive mechanisms  20  arranged inside the body  16 , the right load-bearing mechanism  30 R arranged on the right side of the body  16 , and the left load-bearing mechanism  30 L arranged on the left side of the body  16 . The right load-bearing mechanism  30 R is arranged on the right side of the transport robot  12 . The left load-bearing mechanism  30 L is arranged on the left side of the transport robot  12 . The four sets of drive mechanisms  20  are arranged in the center of the transport robot  12  between the right load-bearing mechanism  30 R and the left load-bearing mechanism  30 L. The body  16  is a frame that forms the transport robot  12  and supports each component. 
     The first set of drive mechanisms  20  includes a drive force transmitting mechanism  22  and an omnidirectional wheel  28 . The drive force transmitting mechanism  22  includes a travel motor  24  and a drive-side reduction gear (speed reducer)  26 . The four sets of drive mechanisms  20  are separated into two groups, which are arranged respectively on the left and right of the center line C. The two sets of drive mechanisms  20  on the left side and the two sets of drive mechanisms  20  on the right side are arranged to be linearly symmetric, with the center line C as the axis. Furthermore, the two sets of drive mechanisms  20  on the front side and the two sets of drive mechanisms  20  on the rear side are arranged to be linearly symmetric, with a line (not shown in the drawings) parallel to the width direction of the transport robot  12  as the axis. The travel motor  24 , the drive-side reduction gear  26 , and the omnidirectional wheel  28  in each set are arranged in the stated order from the center line C toward the outside in the width direction. Furthermore, the travel motor  24 , the drive-side reduction gear  26 , and the omnidirectional wheel  28  in each set are arranged such that the axes thereof coincide with each other. 
     The travel motor  24  is an electric motor. An output shaft of the travel motor  24  is connected to an input shaft of the drive-side reduction gear  26 . The drive-side reduction gear  26  includes the input shaft and an output shaft on the same line, and includes a planetary gear reducer, for example. The output shaft of the drive-side reduction gear  26  is connected to the omnidirectional wheel  28 . 
     The omnidirectional wheel  28  is a Mecanum wheel. The Mecanum wheel provided to each set can move the body  16  omnidirectionally (in a holonomic manner with 2 degrees of freedom in a plane) by operating in cooperation with each other to drive the body  16 . Each drive mechanism  20  in the present embodiment includes a Mecanum wheel, but may instead include another type of wheel capable of omnidirectional driving. For example, each drive mechanism  20  may include an Omni wheel instead of the Mecanum wheel. Since the body  16  can travel omnidirectionally and turn freely if three Omni wheels are included, it is only necessary to provide three sets of drive mechanisms  20 . The transport robot  12  may include an auxiliary wheel along with the omnidirectional wheels  28 , in order to stabilize the orientation in the horizontal direction. 
     The right load-bearing mechanism  30 R includes the right rotational force transmitting mechanism  32 R, the right lifting arm  42 R, and the right contact portion  48 R. The left load-bearing mechanism  30 L includes the left rotational force transmitting mechanism  32 L, the left lifting arm  42 L, and the left contact portion  48 L. The right load-bearing mechanism  30 R and the left load-bearing mechanism  30 L are arranged to be linearly symmetrical, with the center line C as the axis. The right rotational force transmitting mechanism  32 R and the left rotational force transmitting mechanism  32 L each include a loading motor  34 , a brake  36 , a loading-side speed reducer  38 , and a link member  40 . The loading motor  34 , the brake  36 , the loading-side speed reducer  38 , and the link member  40  are arranged in the stated order in a direction toward the rear of the transport robot  12 . The link member  40  is arranged at the rear end of the transport robot  12 . Since the right load-bearing mechanism  30 R and the left load-bearing mechanism  30 L have the same structure, the following describes only the right load-bearing mechanism  30 R. The description of the right load-bearing mechanism  30 R can also be applied to the left load-bearing mechanism  30 L, by switching the term “right” for “left” and switching “R” for “L” in the reference numerals. 
     The loading motor  34  is an electric motor. The output shaft of the loading motor  34  is connected to the input shaft of the brake  36 . The brake  36  is an electromagnetic brake, for example. The output shaft of the brake  36  is connected to the input shaft of the loading-side speed reducer  38 . The loading-side speed reducer  38  has the input shaft and the output shaft that are orthogonal to each other, and it is a bevel gear, for example. The output shaft of the loading-side speed reducer  38  is connected to the link member  40 . This output shaft is parallel to the up-down direction. The link member  40  includes a top plate part and a bottom plate part that are parallel to the front-rear direction and the width direction, and a side plate part that is connected to an end portion of the top plate part and an end portion of the bottom plate part and is parallel to the up-down direction. The top plate part is connected to the output shaft of the loading-side speed reducer  38 , and the bottom plate part is connected to the body  16  in a rotatable manner. 
     The right lifting arm  42 R is a rotating rod that includes a shaft member that is parallel to the front-rear direction and the width direction and a cylindrical member that is concentric with the shaft member and rotatable centered on the shaft member. A base portion  44 R of the shaft member of the right lifting arm  42 R is connected to the side plate part of the link member  40 . The right lifting arm  42 R moves rotationally between a right storage position  76 R where a tip  46 R points at the center of the body  16  in the width direction and a right expanded position  78 R where the tip  46 R points at the outside of the body  16  in the width direction (the right direction), in accordance with the rotational operation of the link member  40 . 
     The right storage position  76 R and the right expanded position  78 R are positions where the shaft member of the right lifting arm  42 R is parallel to the width direction. In other words, the right storage position  76 R is the position of the right lifting arm  42 R after the right lifting arm  42 R has been rotated 180 degrees from the right expanded position  78 R in a plane parallel to the front-rear direction and the width direction. On the other hand, the right expanded position  78 R is the position of the right lifting arm  42 R after the right lifting arm  42 R has been rotated 180 degrees from the right storage position  76 R in the plane parallel to the front-rear direction and the width direction. 
     The right contact portion  48 R is a rotating rod that includes a shaft member extending from the body  16  toward the outside in the width direction and a cylindrical member that is concentric with the shaft member and rotatable centered on the shaft member. Both ends of the shaft member of the right contact portion  48 R are fixed to the body  16 . The shaft member is arranged on an extension line of the axes of the two sets of drive mechanisms  20  on the front side. 
     The transport robot  12  can enter underneath the vehicle  94 , lift up the vehicle  94 , and travel underneath the vehicle  94 . Therefore, the total height of the transport robot  12  is preferably as low as possible. The total height of the transport robot  12  is preferably less than 150 mm, more preferably less than 140 mm, and even more preferably less than 130 mm. According to safety regulations in Japan, the lower limit for the height of the vehicle  94  from the ground is determined to be 90 mm, and therefore the total height of the transport robot  12  is most preferably less than 90 mm. 
     [1.2. Configuration of the Control System and Power System of the Transport Robots  12 ] 
     The following describes the configuration of the control system and power system of a transport robot  12 , using  FIG. 4 . A portion of the configuration shown in  FIG. 4  is also shown in  FIGS. 1A and 3 . The transport robot  12  includes, as the control system, a sensor group  50 , a communicating section  62 , a robot computing section  64 , a robot storage section  66 , a motor driver  70 , a power relay  72 , and a DC/DC converter  74 . The sensor group  50  includes a camera  52 , a distance sensor (ranging sensor)  54 , a limit switch  56 , a Hall element  58 , an encoder  59 , a positioning section  60 , and a line sensor  61 . 
     The camera  52  captures an image of the surroundings of the transport robot  12 . The distance sensor  54  is a PSD sensor, radar, LiDAR, LRF, TOF sensor, or the like, for example, and detects the distance to an object in the vicinity of the transport robot  12 . A plurality of the cameras  52  and a plurality of the distance sensors  54  are provided, in order to detect targets in all directions of the transport robot  12 . As shown in  FIG. 1A , in the present embodiment, four sets of a camera  52  and a distance sensor  54  are attached to the upper cover  14 . The attachment positions are a front right portion, a front left portion, a rear right portion, and a rear left portion of the upper cover  14 . The number, arrangement, and orientation of the cameras  52  are suitably set according to the range in which the cameras  52  are capable of capturing images. Similarly, the number, arrangement, and orientation of the distance sensors  54  are suitably set according to the range in which the distance sensors  54  are to be capable of detection. 
     The limit switch  56  limits the movement range of the right lifting arm  42 R and the left lifting arm  42 L. One limit switch  56  is provided at each of a position in front of the right expanded position  78 R, a position in front of the right storage position  76 R, a position in front of a left expanded position  78 L, and a position in front of a left storage position  76 L. The Hall element  58  detects rotation speeds of the four travel motors  24  and the two loading motors  34 . The Hall element  58  is provided to each motor. The encoder  59  detects the rotational angle of the omnidirectional wheel  28 . The encoder  59  is provided on the shaft of the omnidirectional wheel  28 . The positioning section  60  includes a GNSS module, an acceleration sensor, a gyro sensor, and the like, for example, and detects the position and orientation of the transport robot  12  using at least one of satellite navigation and inertial navigation. The line sensor  61  captures an image of the ground surfaces (floor surface) on which the transport robot  12  travels. 
     The communicating section  62  includes a communication apparatus and an antenna for performing wireless communication with an external communication device. The external communication device is a server  102  (see  FIG. 8 ) described further below, for example, and is a communicating section  62  of another transport robot  12  forming a pair with the transport robot  12 . The communicating section  62  includes a communication module that performs wireless communication, via a public network, with a communication module for performing close-range wireless communication or Near-Field Communication. 
     The robot computing section  64  is formed by a processor that includes a CPU, an MPU, and the like, for example. The robot computing section  64  realizes various functions by executing programs stored in the robot storage section  66 . The robot storage section  66  is formed by a RAM, a ROM, and the like, for example. The robot storage section  66  stores various programs, various types of information used in the processes performed by the robot computing section  64 , and map information of the region in which the transport robot  12  travels. 
     A motor driver  70  is provided individually for each of the four travel motors  24  and the two loading motors  34 . The input side of each motor driver  70  is connected to the battery  68 , and the output side of each motor driver  70  is connected to the corresponding travel motor  24  or loading motor  34 . The motor driver  70  performs a transformation operation according to a control signal output from the robot computing section  64 . The battery  68  is connected to the input side of the power relay  72 , and the brake  36  is connected to the output side of the power relay  72 . The power relay  72  switches between supplying and cutting off the power from the battery  68 , according to an ON signal or an OFF signal output from the robot computing section  64 . The input side of the DC/DC converter  74  is connected to the battery  68 , and the output side of the DC/DC converter  74  is connected to each electronic device. The DC/DC converter  74  has the power from the battery  68  input thereto, drops this power to a certain voltage, and supplies the resulting power to the sensor group  50  and the robot computing section  64 . 
     [1.3. Loading Operation of the Transport Robot  12 ] 
     Here, a description is provided of the loading operation of the first robot  12   a  that lifts up front wheels  96   f,  of the two robots that are the transport robots  12 . Before lifting up a vehicle  94 , the right lifting arm  42 R is stored at the right storage position  76 R and the left lifting arm  42 L is stored at the left storage position  76 L. 
     As shown in  FIG. 5 , the robot computing section  64  recognizes the orientation of the vehicle  94  to be transported based on the image information captured by the camera  52  and the information detected by the distance sensor  54 , moves the first robot  12   a  to a position in front of the vehicle  94 , and causes the rear portion of the first robot  12   a  to face the front portion of the vehicle  94 . At this time, the robot computing section  64  may receive the image information from cameras (external cameras) that are not the cameras of the robot, to recognize the orientation of the vehicle  94  to be transported based on this image information. Furthermore, the robot computing section  64  recognizes the width of the vehicle  94  (vehicle width) and also recognizes the center position (center line Co) in the vehicle width direction, based on the image information. In order to align the center position (center line C) of the first robot  12   a  in the width direction with the center position (center line Co) of the vehicle  94 , the robot computing section  64  outputs a control signal to the motor driver  70  to drive each travel motor  24 . At this time, each travel motor  24  operates cooperatively to move the first robot  12   a  in the width direction (either right or left). After the positional alignment, the robot computing section  64  outputs a control signal to the motor driver  70  to drive each travel motor  24 , in order to cause the first robot  12   a  to move backward. At this time, each travel motor  24  operates cooperatively to move the first robot  12   a  backward so that the first robot  12   a  enters underneath the vehicle  94 . 
     As shown in  FIGS. 6A and 6B , when each of the right contact portion  48 R and the left contact portion  48 L contacts or comes close to (within several centimeters) the contact surface on the front side of each of the left and right front wheels  96   f,  the robot computing section  64  outputs a control signal to the motor driver  70  to stop each travel motor  24 . The robot computing section  64  recognizes that the right contact portion  48 R and the left contact portion  48 L have contacted or become close to the front wheels  96   f  based on at least one of the image information captured by the camera  52  and the information detected by the distance sensor  54 . Alternatively, the robot computing section  64  also can recognize that the right contact portion  48 R and the left contact portion  48 L have contacted the front wheels  96   f,  based on the loads of the travel motors  24  (load&gt;prescribed value). Yet further, before moving the first robot  12   a  backward, the robot computing section  64  may calculate the distance between the right and left contact portions  48 R,  48 L and the front wheels  96   f  based on the information detected by the distance sensor  54 , and cause the first robot  12   a  to move backward by this distance. 
     As shown in  FIGS. 7A and 7B , the robot computing section  64  outputs a control signal to the motor driver  70  to cause the left and right loading motors  34  to operate. Since the operation of the right load-bearing mechanism  30 R and the operation of the left load-bearing mechanism  30 L are substantially the same, the following describes only the operation of the left load-bearing mechanism  30 L. When the loading motor  34  of the left rotational force transmitting mechanism  32 L operates, the left lifting arm  42 L rotationally moves from the left storage position  76 L to the left expanded position  78 L and contacts the contact surface on the rear side of the front wheel  96   f . When the loading motor  34  continues to operate, the left lifting arm  42 L draws near the left contact portion  48 L while the cylindrical member rotates. When this happens, the front wheel  96   f  on the left side is lifted up. When the loading motor  34  continues to operate, the left lifting arm  42 L contacts the limit switch  56  at the position where the left lifting arm  42 L has been rotated by 180 degrees, or 180 degrees plus or minus a few degrees, from the storage position. The robot computing section  64  detects the signal output from the limit switch  56 , and outputs a control signal to the motor driver  70  to stop the loading motor  34 . At the same time, the robot computing section  64  outputs a control signal to the power relay  72  to cause the brake  36  to operate. 
     When the first robot  12   a  is to lower the front wheels  96   f,  the robot computing section  64  causes the loading motor  34  to operate, thereby moving the left lifting arm  42 L away from the left contact portion  48 L. When this happens, the front wheel  96   f  on the left side is lowered to the ground. When the loading motor  34  continues to operate, the left lifting arm  42 L moves rotationally from the left expanded position  78 L to the left storage position  76 L. The left lifting arm  42 L at the left storage position  76 L contacts the limit switch  56 . The robot computing section  64  detects the signal output from the limit switch  56 , and outputs a control signal to the motor driver  70  to stop the loading motor  34 . 
     The above is a description of the loading operation of the first robot  12   a . The loading operation of the second robot  12   b  is the same. However, as shown in  FIGS. 1A and 1B , in the present embodiment, the front, rear, left, and right directions of the first robot  12   a  match the front, rear, left, and right directions of the vehicle  94 , but the front, rear, left, and right directions of the second robot  12   b  are the opposite of the front, rear, left, and right directions of the vehicle  94 . Therefore, for the loading operation of the second robot  12   b,  the front, rear, left, and right directions are the opposite of the front, rear, left, and right directions in the loading operation of the first robot  12   a  described above. 
     It should be noted that the front and rear directions of the first robot  12   a  and the second robot  12   b  relative to the vehicle  94  are not particularly limited. The front and rear directions of the first robot  12   a  may match the front and rear directions of the vehicle  94 , or may be the opposite of these direction. Similarly, the front and rear directions of the second robot  12   b  may match the front and rear directions of the vehicle  94 , or may be the opposite of these direction. 
     The robot computing section  64  of the first robot  12   a  and the robot computing section  64  of the second robot  12   b  can perform the loading operation of the first robot  12   a  and the loading operation of the second robot  12   b  at the same timing, or at different timings. For example, the robot computing section  64  of the first robot  12   a  may transmit a loading completion signal with the communicating section  62 , after the loading operation is completed. In this case, the robot computing section  64  of the second robot  12   b  starts the loading operation (lifting and lowering the rear wheels  96   r ) upon receiving the loading completion signal with the communicating section  62 . Alternatively, the loading operation of the first robot  12   a  may start after the loading operation of the second robot  12   b  has been completed. Furthermore, the robot computing section  64  may detect information indicating the weight distribution of the vehicle  94  and then determine the timing of the loading operation of the first robot  12   a  and the timing of the loading operation of the second robot  12   b  based on this detection result. The information indicating the weight distribution of the vehicle  94  may be transmitted from the vehicle  94 , or may be transmitted from an external apparatus other than the vehicle  94 . 
     [1.4. Travel Operation of the Transport Robots  12 ] 
     The robot computing section  64  of the first robot  12   a  causes the first robot  12   a  to travel along a travel route generated in advance, regardless of whether the vehicle  94  to be transported is present. The information of the travel route may be generated by the robot computing section  64  of the first robot  12   a,  or may be generated by the external server  102  (see  FIG. 8 ). The information of the travel route is generated by arranging positions through which the first robot  12   a  is to travel (positions in the region), in order of time. The robot computing section  64  of the first robot  12   a  performs travel control by comparing the generated travel route to the position detected by at least one of the sensor group  50  and an external camera. It should be noted that, while the first robot  12   a  is travelling, the robot computing section  64  of the first robot  12   a  adjusts the travel route such that the distance between the first robot  12   a  and an obstacle is greater than or equal to a prescribed value, based on the image information captured by the camera  52  and the information detected by the distance sensor  54 . 
     The robot computing section  64  of the first robot  12   a  may cause the first robot  12   a  to travel with a travel posture that is generated in advance. The first robot  12   a  can freely adjust its travel posture by individually adjusting the drive amounts and drive directions of the omnidirectional wheels  28 . The information of the travel posture may be generated by the robot computing section  64  of the first robot  12   a,  or may be generated by the external server  102  ( FIG. 8 ). The robot computing section  64  of the first robot  12   a  performs posture control by comparing the generated travel posture to the posture detected by the positioning section  60 . It should be noted that, while the first robot  12   a  is travelling, the robot computing section  64  of the first robot  12   a  adjusts the travel posture such that the distance between the first robot  12   a  and an obstacle is greater than or equal to a prescribed value, based on the image information captured by the camera  52  and the information detected by the distance sensor  54 . 
     The robot computing section  64  of the second robot  12   b  causes the second robot  12   b  to travel along the trajectory (travel trajectory) on which the first robot  12   a  travelled. At this time, the robot computing section  64  of the second robot  12   b  may acquire the information of the travel trajectory from the first robot  12   a  via the communicating section  62 , or may calculate the travel trajectory of the first robot  12   a  based on the image information captured by the camera  52 . In the same manner as in the first robot  12   a , the robot computing section  64  of the second robot  12   b  adjusts the travel route (or the travel trajectory) such that the distance between the second robot  12   b  and an obstacle is greater than or equal to a prescribed value, based on the image information captured by the camera  52  and the information detected by the distance sensor  54 . 
     Furthermore, the robot computing section  64  of the second robot  12   b  performs the travel control such that a certain space is maintained between the second robot  12   b  and the first robot  12   a.    
     [2. Usage Example of the Vehicle Transport Apparatus  10 ] 
     The vehicle transport apparatus  10  can be used in a prescribed region where transport of a vehicle  94  is necessary, such as a parking lot, a charging spot  80 , a cargo ship, or a port and harbor, for example. Here, a vehicle transport system  100  is described that uses the vehicle transport apparatus  10  at a charging spot  80 . 
     [2.1. Charging Spot  80 ] 
     As shown in  FIG. 8 , the charging spot  80  serves as both a charging facility and a parking lot, and includes an entry space  82 , an exit space  84 , a parking space  86 , a standby space  88 , and a charging space  90 . 
     The entry space  82  is the entrance to the charging spot  80 , and is also a space where the vehicle transport apparatus  10  lifts up the vehicle  94 . The exit space  84  is the exit from the charging spot  80 , and is a space where the vehicle transport apparatus  10  lowers the vehicle  94 . The parking space  86  is a space where the vehicle  94  parks when the user of the vehicle  94  wants to park. The standby space  88  is a space where the vehicle transport apparatus  10  is in standby, and includes equipment for non-contact charging of the transport robot  12 . The charging space  90  is a space for charging the battery of a vehicle  94  that travels using an electric motor, such as an electric vehicle or a hybrid vehicle. In this specification, it is envisioned that equipment for non-contact charging is provided in the charging space  90 , but equipment that performs contact charging may be provided instead. The parking space  86  and the charging space  90  are spaces for a single vehicle, and one or more of these spaces are provided at the charging spot  80 . 
     [2.2. Configuration of the Vehicle Transport System  100 ] 
     The vehicle transport system  100  constructed at the charging spot  80  includes one or more vehicle transport apparatuses  10 , the server  102 , a vehicle sensor  108 , a monitoring camera  110 , and a charging apparatus  112 . 
     The server  102  is a computer that includes a server computing section  104  and a server storage section  106 . The server computing section  104  is formed by a processor including a CPU, an MPU, and the like. The server computing section  104  performs various functions by executing programs stored in the server storage section  106 . The server storage section  106  is formed by a RAM, a ROM, and the like. The server storage section  106  stores various programs, various types of information used in the processes performed by the server computing section  104 , map information of the inside of the charging spot  80 , a parking list  120  (see  FIG. 9 ), and a charging reservation list  130  (see  FIG. 10 ). 
     As shown in  FIG. 9 , position information  122  indicating the number (serial number) and position of each parking space  86  and identification information  124  of a user that is to receive a parking service are stored in the parking list  120  in association with each other. The identification information  124  is information for identifying a vehicle  94  at the charging spot  80 . Here, information indicating the contact information of a terminal apparatus  140  possessed by the user of the vehicle  94 , a number set arbitrarily by the user, and the like are used as the identification information  124 . 
     As shown in  FIG. 10 , reservation number information  132  indicating the order in which charging reservations were received, the identification information  124  of a user that is to receive a charging service, and a charging completion flag  134  indicating whether charging has been completed are stored in the charging reservation list  130  in association with each other. Battery charging is performed in the order in which charging reservations were received. Essentially, the reservation number information  132  indicates the charging order. 
     The description continues below while returning to  FIG. 8 . The server  102  transmits and receives information through wireless communication to and from the transport robot  12  and manages the actions of the transport robot  12 . The server  102  performs wired or wireless communication with the charging apparatus  112 , and manages the charging process. Furthermore, the server  102  performs wireless communication with the vehicle  94  that is stopped in the charging space  90 , to monitor the charging state of the battery of the vehicle  94 . Furthermore, the server  102  performs wired or wireless communication with the vehicle sensor  108  and the monitoring camera  110 , to monitor whether a vehicle has entered the charging spot  80  and the parking state. Yet further, the server  102  performs communication with the terminal apparatus  140  possessed by the user of the vehicle  94 , receives requests for charging from the user, and provides various notifications to the user, using close-range wireless communication or a public network. 
     A vehicle sensor  108  is provided to the parking space  86  and to the charging space  90 . Upon detecting the vehicle  94  stopped in the corresponding parking space  86  or charging space  90 , the vehicle sensor  108  transmits a detection signal to the server  102 . The monitoring camera  110  is provided to the entry space  82 . The monitoring camera  110  transmits image information obtained by capturing an image of the entry space  82  to the server  102 . The charging apparatus  112  includes a power transmission coil  114  and a power supply apparatus  116 . The power transmission coil  114  is arranged on the ground surface (floor surface) or below the ground surface (floor surface), facing a power reception coil of the vehicle  94 . The power supply apparatus  116  supplies power to the power transmission coil  114 . 
     The terminal apparatus  140  possessed by the user is a smartphone, a tablet, or the like, for example. The terminal apparatus  140  has a function of being able to perform communication using a public network or a function of being able to perform close-range wireless communication, such as Bluetooth (Registered Trademark). Software for using the charging spot  80  is installed in advance in the terminal apparatus  140 . 
     [2.3. Each Process Performed by the Vehicle Transport System  100 ] 
     The following describes each process (entry process, transport-in process, transport-out process, and exit process) performed by the vehicle transport system  100 . 
     [A. Entry Process of the Vehicle  94  Entering the Charging Spot  80 ] 
     The following describes the flow of the entry process in which the vehicle  94  enters the charging spot  80 , using  FIG. 11 . A user who wants to enter the charging spot  80  with their vehicle applies for vehicle entry using the terminal apparatus  140 , after stopping the vehicle  94  in the entry space  82 . 
     At step S 1 , the terminal apparatus  140  transmits an entry request to the server  102 . At this time, the terminal apparatus  140  transmits the identification information  124  (see  FIG. 9 ) along with the request. 
     At step S 2 , the server computing section  104  checks the image information captured by the monitoring camera  110  in response to the entry request, and detects the vehicle  94 . At step S 3 , the server computing section  104  refers to the parking list  120  (see  FIG. 9 ) and assigns the vehicle  94  to an empty parking space  86 . At step S 4 , the server computing section  104  generates the shortest travel route from the standby space  88  to the entry space  82  and the shortest travel route from the entry space  82  to the parking space  86 . At this time, an optimal travel posture may be generated. At step S 5 , the server computing section  104  transmits route information indicating the generated travel routes and transport-in instructions to the first robot  12   a  of the transport robots  12 . When transmitting the travel route information, the server computing section  104  may also transmit the travel posture information. In the following, at any time when the vehicle  94  is not being transported, the server computing section  104  may generate and transmit the travel posture information in the same manner. 
     At step S 6 , the first robot  12   a  and the second robot  12   b  travel along the travel route and transport the vehicle  94  in. Specifically, the robot computing section  64  of the first robot  12   a  refers to the travel route from the standby space  88  to the entry space  82  and performs travel control of the first robot  12   a  and the second robot  12   b  (see section [1.4] above). When the first robot  12   a  and the second robot  12   b  arrive at the entry space  82 , each robot computing section  64  lifts up the vehicle  94  (see section [1.3] above). When the loading operation is completed, the robot computing section  64  of the first robot  12   a  refers to the travel route from the entry space  82  to the parking space  86  and performs travel control of the first robot  12   a  and the second robot  12   b  (see section [1.4] above). When the first robot  12   a  and the second robot  12   b  arrive at the parking space  86 , each robot computing section  64  lowers the vehicle  94  (see section [1.3] above). At step S 7 , the robot computing section  64  of the first robot  12   a  transmits a transport-in completion notification to the server  102 . 
     At step S 8 , the server computing section  104  transmits parking completion notification to the terminal apparatus  140  of the user, and also transmits the position information  122  of the parking space  86 , e.g., the number of the parking space  86 , to the terminal apparatus  140 . 
     At step S 9 , the server computing section  104  updates the parking list  120  by associating the identification information  124  transmitted from the terminal apparatus  140  at step S 1  with the position information  122  of the parking space  86  where the vehicle  94  parked. At step S 10 , the server computing section  104  generates the shortest travel route from the parking space  86  to the standby space  88 . At step S 11 , the server computing section  104  transmits the route information indicating the generated travel route and return instructions to the first robot  12   a.    
     At step S 12 , the first robot  12   a  and the second robot  12   b  travel along the travel route. Specifically, the robot computing section  64  of the first robot  12   a  refers to the travel route from the parking space  86  to the standby space  88  and performs travel control of the first robot  12   a  and the second robot  12   b  (see section [1.4] above). At step S 13 , when the first robot  12   a  and the second robot  12   b  arrive at the standby space  88 , the robot computing section  64  of the first robot  12   a  transmits a return notification to the server  102 . 
     A user who wants to park at the charging spot  80  and also perform charging applies for the parking service and also applies for the charging service, using the terminal apparatus  140 . In this case, at step S 1 , the terminal apparatus  140  transmits the charging request to the server  102 . 
     Furthermore, at step S 9 , the server computing section  104  updates the charging reservation list  130  (see  FIG. 10 ). Here, the server computing section  104  creates data in which the reservation number information  132  indicating the newest receipt number, the identification information  124  transmitted from the terminal apparatus  140  at step S 1 , and the charging completion flag  134  indicating that the charging is incomplete are associated with each other, and updates the charging reservation list  130 . 
     [B. Transport-In Process for Transporting the Vehicle  94  into the Charging Space  90 ] 
     The following describes the flow of the transport-in process for transporting the vehicle  94  into the charging space  90 , using  FIG. 12 . The server computing section  104  periodically judges whether a vehicle  94  is waiting to be charged, based on the charging completion flag  134  of the charging reservation list  130 . If there is a vehicle  94  waiting to be charged, the following process is performed. 
     At step S 21 , the server computing section  104  confirms that no vehicle  94  is stopped in the charging space  90 , based on the detection result of the vehicle sensor  108  provided to the charging space  90 . At step S 22 , the server computing section  104  specifies the vehicle  94  to be charged next. Here, the server computing section  104  refers to the charging reservation list  130 , selects a piece of data that has the lowest number for the reservation number information  132  and in which the charging completion flag  134  indicates that the charging is incomplete, and extracts the identification information  124  from this data. At step S 23 , the server computing section  104  specifies the parking position of the vehicle  94  to be charged next. Here, the server computing section  104  refers to the parking list  120 , selects the data that includes the identification information  124  extracted at step S 22 , and specifies the parking space  86  in which the vehicle  94  is parked from the position information  122  of this data. At step S 24 , the server computing section  104  generates the shortest travel route from the standby space  88  to the parking space  86  and the shortest travel route from the parking space  86  to the charging space  90 . At step S 25 , the server computing section  104  transmits the route information indicating the generated travel routes and the transport-in instructions to the first robot  12   a  of the transport robots  12 . 
     At step S 26 , the first robot  12   a  and the second robot  12   b  travel along the travel route, to transport the vehicle  94  in. Specifically, the robot computing section  64  of the first robot  12   a  refers to the travel route from the standby space  88  to the parking space  86  and performs travel control of the first robot  12   a  and the second robot  12   b  (see section [1.4] above). When the first robot  12   a  and the second robot  12   b  arrive at the parking space  86 , each robot computing section  64  lifts up the vehicle  94  (see section [1.3] above). When the loading operation is completed, the robot computing section  64  of the first robot  12   a  refers to the travel route from the parking space  86  to the charging space  90  and performs travel control of the first robot  12   a  and the second robot  12   b  (see section [1.4] above). When the first robot  12   a  and the second robot  12   b  arrive at the charging space  90 , each robot computing section  64  lowers the vehicle  94  (see section [1.3] above). At this time, the robot computing section  64  of the first robot  12   a  checks and confirms the position of the power transmission coil  114 , based on the image information captured by the camera  52 , and determines the position where the vehicle  94  is to be lowered. At this time, the robot computing section  64  may check and confirm the power transmission coil  114  itself, or may check and confirm a prescribed reference position provided in the charging space  90  and calculate the position of the power transmission coil  114  relative to the reference position. At step S 27 , the robot computing section  64  of the first robot  12   a  transmits the transport-in completion notification to the server  102 . 
     At step S 28 , the server computing section  104  instructs the power supply apparatus  116  to start the supply of power. 
     The flow from step S 29  to step S 32  is substantially the same as the flow from step S 10  to step S 13  shown in  FIG. 11 . However, here, the travel route from the charging space  90  to the standby space  88  is generated. 
     [C. Transport-Out Process for Transporting the Vehicle  94  Out from the Charging Space  90 ] 
     The following describes the transport-out process for transporting the vehicle  94  out from the charging space  90 , using  FIG. 13 . The ECU of the vehicle  94  monitors the state of charge during the charging of the battery. 
     At step S 41 , the ECU of the vehicle  94  transmits the state of charge information indicating the state of charge to the server  102 . The state of charge information may be information indicating the charge amount of the battery, or may be information providing notification that the charge amount of the battery has reached a prescribed value. 
     At step S 42 , the server computing section  104  detects that the charging of the battery has ended (charge amount &gt;prescribed value), based on the state of charge information. At step S 43 , the server computing section  104  instructs the power supply apparatus  116  to stop the supply of power. At step S 44 , the server computing section  104  generates the shortest travel route from the standby space  88  to the charging space  90  and the shortest travel route from the charging space  90  to the parking space  86  where the vehicle  94  was parked before the charging. At step S 45 , the server computing section  104  transmits the travel route information indicating the generated travel routes and the transport-out instructions to the first robot  12   a  of the transport robots  12 . 
     At step S 46 , the first robot  12   a  and the second robot  12   b  travel along the travel route, to transport the vehicle  94  out. Specifically, the robot computing section  64  of the first robot  12   a  refers to the travel route from the standby space  88  to the charging space  90  and performs travel control of the first robot  12   a  and the second robot  12   b  (see section [1.4] above). When the first robot  12   a  and the second robot  12   b  arrive at the charging space  90 , each robot computing section  64  lifts up the vehicle  94  (see section [1.3] above. When the loading process is completed, the robot computing section  64  of the first robot  12   a  refers to the travel route from the charging space  90  to the parking space  86  and performs travel control of the first robot  12   a  and the second robot  12   b  (see section [1.4] above). When the first robot  12   a  and the second robot  12   b  arrive at the parking space  86 , each robot computing section  64  lowers the vehicle  94  (see section [1.3] above). At step S 47 , the robot computing section  64  of the first robot  12   a  transmits a transport-out completion notification to the server  102 . 
     At step S 48 , the server computing section  104  transmits a charging end notification to the terminal apparatus  140  of the user. 
     The flow from step S 49  to step S 52  is the same as the flow from step S 10  to step S 13  shown in  FIG. 11 . 
     [D. Exit Process of the Vehicle  94  Exiting the Charging Spot  80 ] 
     The following describes the flow of the exit process in which the vehicle  94  exits the charging spot  80 , using  FIG. 14 . A user who wants to exit from the charging spot  80  with their vehicle applies for exit using the terminal apparatus  140 . 
     At step S 61 , the terminal apparatus  140  transmits an exit request to the server  102 . At this time, the terminal apparatus  140  transmits the identification information  124  (see  FIG. 9 ) along with the request. 
     At step S 62 , the server computing section  104  specifies the parking position (parking space  86 ) of the vehicle  94  that is to exit. Here, the server computing section  104  refers to the parking list  120  and specifies the parking position corresponding to the identification information  124  transmitted from the terminal apparatus  140  at step S 61 . At step S 63 , the server computing section  104  generates the shortest travel route from the standby space  88  to the parking space  86  and the shortest travel route from the parking space  86  to the exit space  84 . At step S 64 , the server computing section  104  transmits the route information indicating the generated travel routes and the transport-out instructions to the first robot  12   a  of the transport robots  12 . 
     At step S 65 , the first robot  12   a  and the second robot  12   b  travel along the travel route, to transport the vehicle  94 . Specifically, the robot computing section  64  of the first robot  12   a  refers to the travel route from the standby space  88  to the parking space  86  and performs travel control of the first robot  12   a  and the second robot  12   b  (see section [1.4] above). When the first robot  12   a  and the second robot  12   b  arrive at the parking space  86 , each robot computing section  64  lifts up the vehicle  94  (see section [1.3] above). When the loading operation is completed, the robot computing section  64  of the first robot  12   a  refers to the travel route from the parking space  86  to the exit space  84  and performs travel control of the first robot  12   a  and the second robot  12   b  (see section [1.4] above). When the first robot  12   a  and the second robot  12   b  reach the exit space  84 , each robot computing section  64  lowers the vehicle  94  (see section [1.3] above). At step S 66 , the robot computing section  64  of the first robot  12   a  transmits a transport-out completion notification to the server  102 . 
     At step S 67 , the server computing section  104  transmits an exit notification to the terminal apparatus  140  of the user. 
     The flow from step S 68  to step S 71  is the same as the flow from step S 10  to step S 13  shown in  FIG. 11 . However, here, the travel route from the exit space  84  to the standby space  88  is generated. 
     [3. Modifications and Other Additional Functions] 
     When the robot computing section  64  checks its own position and posture based on inertial navigation, it is preferable to adjust the position and posture of the robot computing section  64  checked at a prescribed timing or a certain timing. For example, the charging spot  80  (standby space  88  or the like) is provided with an indicator at a prescribed position, and this prescribed position is stored in each robot storage section  66 . The robot computing section  64  adjusts its own position and posture checked at this point of time by using the prescribed position stored in the robot storage section  66  and a direction and distance of the indicator relative to the body  16  detected by the camera  52  and the distance sensor  54 . 
     With the vehicle transport system  100  shown in  FIG. 8 , it is possible to provide maintenance information to the user of the vehicle  94  parked in the charging spot  80 . For example, when the robot computing section  64  enters underneath the vehicle  94  or passes underneath the vehicle  94 , an image of the bottom surface or the tires of the vehicle  94  is captured by the camera  52 . Then, the robot computing section  64  associates the image information with the position information  122  and the identification information  124  of the vehicle  94 . The robot computing section  64  analyzes the image information to detect scratches or the like on the bottom surface or to check the wear and damage of the tires. In a case where the left and right contact portions and lifting arms are provided with sheet-shaped pressure sensors, the robot computing section  64  judges whether the air pressure in the tires is insufficient, based on the detection results of the pressure sensors. The robot computing section  64  transmits these pieces of maintenance information to the terminal apparatus  140 . 
     [4. Technical Concepts that Can Be Realized from the Embodiments] 
     The technical concepts that can be understood from the embodiments described above are described below. 
     An aspect of the present invention is a vehicle transport apparatus  10  that transports a vehicle  94  by lifting up wheels  96  of the vehicle  94 , including:
         a first robot  12   a  configured to enter underneath the vehicle  94 , lift up front wheels  96   f  of the vehicle  94 , and travel; and   a second robot  12   b  configured to enter underneath the vehicle  94 , lift up rear wheels  96   r  of the vehicle  94 , and travel, wherein   the first robot  12   a  and the second robot  12   b  each include:
           omnidirectional wheels  28  configured to cause a body  16  to freely travel and turn omnidirectionally, by operating in cooperation with each other;   a drive force transmitting mechanism  22  configured to transmit a drive force to the omnidirectional wheels  28 ;   a right contact portion  48 R configured to contact a contact surface on one of a front side and a back side of one wheel of the wheels  96  (the front wheels or the rear wheels);   a right lifting arm  42 R configured to be freely rotationally movable between a right storage position  76 R at which a tip  46 R thereof points toward a center of the body  16  in a width direction and a right expanded position  78 R at which the tip  46 R points toward a right side of the body  16  in the width direction, and lifts up the one wheel  96  by drawing near the right contact portion  48 R while in contact with a contact surface on the other of the front side and the back side of the one wheel  96  at the right expanded position  78 R;   a left contact portion  48 L configured to contact a contact surface on one of a front side and a back side of the other wheel  96 ;   a left lifting arm  42 L configured to be freely rotationally movable between a left storage position  76 L at which a tip  46 L thereof points toward the center of the body  16  in the width direction and a left expanded position  78 L at which the tip  46 L points toward a left side of the body  16  in the width direction, and lifts up the other wheel  96  by drawing near the left contact portion  48 L while in contact with a contact surface on the other of the front side and the back side of the other wheel  96  at the left expanded position  78 L;   a right rotational force transmitting mechanism  32 R configured to transmit a rotational force to the right lifting arm  42 R; and   a left rotational force transmitting mechanism  32 L configured to transmit a rotational force to the left lifting arm  42 L.   
               

     According to the above configuration, the vehicle transport apparatus  10  is divided into the first robot  12   a  and the second robot  12   b,  and therefore the overall apparatus is made smaller and can turn in a small space. Furthermore, according to the above configuration, the tips  46 L and  46 R of the left and right arms point toward the center in the width direction when at the storage positions and point toward the outside in the width direction when at the expanded positions, and therefore the lengths of the first robot  12   a  and the second robot  12   b  in the front-rear direction are shortened. As a result, there is no need for a wide region in which to store the first robot  12   a  and the second robot  12   b.    
     Furthermore, according to the above configuration, the first robot  12   a  and the second robot  12   b  can enter underneath the vehicle  94 . In other words, the first robot  12   a  and the second robot  12   b  can travel underneath the vehicle  94 , and therefore the travel routes of the first robot  12   a  and the second robot  12   b  can be set in the parking position of the vehicle  94 . As a result, the first robot  12   a  and the second robot  12   b  can move across the shortest distance toward the destination (parking position of the vehicle  94  to be transported or the like). 
     Furthermore, according to the above configuration, the first robot  12   a  and the second robot  12   b  include the omnidirectional wheels  28 , and therefore the first robot  12   a  and the second robot  12   b  can move freely in all directions. Therefore, no matter what posture the vehicle  94  to be transported stops in, the first robot  12   a  and the second robot  12   b  can easily enter underneath the vehicle  94  and lift up the vehicle  94 . Furthermore, even when the transport path or the parking space  86  is narrow, the first robot  12   a  and the second robot  12   b  can easily perform the travelling and loading. 
     In this aspect of the present invention, 
     the right rotational force transmitting mechanism  32 R may rotate the right lifting arm  42 R 180 degrees in a plane parallel to a ground surface, and 
     the left rotational force transmitting mechanism  32 L may rotate the left lifting arm  42 L 180 degrees in the plane parallel to the ground surface. 
     According to the above configuration, the lengths of the first robot  12   a  and the second robot  12   b  in the front-rear direction can be further shortened. 
     In this aspect of the present invention, 
     the right contact portion  48 R may be shaped as a rod that is fixed to the body  16  and extends to the right side of the body  16  in the width direction, and 
     the left contact portion  48 L may be shaped as a rod that is fixed to the body  16  and extends to the left side of the body  16  in the width direction. 
     According to the above configuration, the contact portions are fixed, and therefore the operation of lifting up the wheels  96  is stabilized. 
     In this aspect of the present invention, 
     the first robot  12   a  may be a master device, and 
     the second robot  12   b  may be a slave device. 
     According to the above configuration, the first robot  12   a  and the second robot  12   b  can easily perform cooperative operations. Furthermore, the computational load of the second robot  12   b  is reduced. 
     In this aspect of the present invention, 
     operation timings of the right rotational force transmitting mechanism  32 R and the left rotational force transmitting mechanism  32 L of the first robot  12   a  may differ from operation timings of the right rotational force transmitting mechanism  32 R and the left rotational force transmitting mechanism  32 L of the second robot  12   b.    
     In this aspect of the present invention, 
     a total height of the first robot  12   a  and a total height of the second robot  12   b  may each be less than 150 mm. 
     According to the above configuration, the first robot  12   a  and the second robot  12   b  can enter underneath the vehicle  94  that is at a height of at least 150 mm from the ground. 
     In this aspect of the present invention, 
     a drive mechanism  20  is formed by the omnidirectional wheels  28  and the drive force transmitting mechanism  22 , 
     a right load-bearing mechanism  30 R is formed by the right contact portion  48 R, the right lifting arm  42 R, and the right rotational force transmitting mechanism  32 R, 
     a left load-bearing mechanism  30 L is formed by the left contact portion  48 L, the left lifting arm  42 L, and the left rotational force transmitting mechanism  32 L, 
     the right load-bearing mechanism  30 R is arranged on the right side of the first robot  12   a  and the second robot  12   b , 
     the left load-bearing mechanism  30 L is arranged on the left side of the first robot  12   a  and the second robot  12   b , and 
     the drive mechanism  20  is arranged between the right load-bearing mechanism  30 R and the left load-bearing mechanism  30 L. 
     According to the above configuration, the drive mechanism  20  is arranged between the right load-bearing mechanism  30 R and the left load-bearing mechanism  30 L, and therefore the lengths of the first robot  12   a  and the second robot  12   b  in the front-rear direction are shortened. 
     While the preferred embodiments of the present invention have been described above, the technical scope of the invention is not limited to the above described embodiments, and various configuration can be included in the technical scope of the invention.