Patent Publication Number: US-2023152804-A1

Title: Control system, control method, and program

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese patent application No. 2021-185428, filed on Nov. 15, 2021, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     The present disclosure relates to a control system, a control method, and a program. 
     In recent years, techniques have been developed for transporting objects by autonomous mobile robots in factories, warehouses, or the like. For example, Japanese Unexamined Patent Application Publication No. 2021-099724 discloses an autonomous mobile robot having a placement part on which a load is placed. The autonomous mobile robot can then transport a load by moving in a state in which the load is placed on the placement part. A height of the placement part in the autonomous mobile robot can be changed. 
     SUMMARY 
     The posture of the autonomous mobile robot is less stable when the load is placed on the raised placement part than when it is not. Therefore, when the autonomous mobile robot moves in a state in which the load is placed on the raised placement part, there is a risk caused by the instability of the posture of the autonomous mobile robot, for example, falling. 
     The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a control system, a control method, and a program capable of reducing a risk due to lowering of the level of stability of a posture of an autonomous mobile robot having a placement part with a changeable height. 
     In an example aspect of the present disclosure in order to achieve the above object, a control system for controlling a movement of a carriage in which a load is housed includes: a determination unit configured to determine whether or not an autonomous mobile robot is planned to move toward the carriage in a state in which the load is raised to a predetermined height or higher by a placement part, the autonomous mobile robot including the placement part having a changeable height and being configured to house the load placed on the placement part in the carriage; and a carriage control unit configured to control the carriage so that the carriage moves toward the autonomous mobile robot when it is determined that the autonomous mobile robot is planned to move toward the carriage in a state in which the load is raised to the predetermined height or higher by the placement part. 
     Such control system reduces a distance that the autonomous mobile robot moves toward the carriage, because the carriage moves toward the autonomous mobile robot. Therefore, it is possible to reduce the distance that the autonomous mobile robot moves in a state where the load is placed on the raised placement part, that is, in an unstable state. It is thus possible to reduce the risk due to the lowering of the level of the stability of the posture of the autonomous mobile robot. 
     In the above example aspect, the determination unit may be configured to make the determination based on information indicating a height of the placement part detected by using a sensor or a height of the load above the placement part detected by using the sensor. 
     With such a configuration, a determination about whether or not the autonomous mobile robot is planned to move toward the carriage in a state in which the load is raised to the predetermined height or higher by the placement part can be easily made. 
     In the above example aspect, the determination unit may be configured to make the determination based on control information about the height of the placement part received from the autonomous mobile robot. 
     With such a configuration, a determination about whether or not the autonomous mobile robot is planned to move toward the carriage in a state in which the load is raised to the predetermined height or higher by the placement part can be easily made. 
     In the above example aspect, the determination unit may be configured to make the determination based on a planned housing position of the load in the carriage. 
     With such a configuration, regardless of whether or not the placement part has already been raised, a determination about whether or not the autonomous mobile robot is planned to move toward the carriage in a state in which the load is raised to the predetermined height or higher by the placement part can be easily made. 
     In the above example aspect, the load may include projections projecting in a horizontal direction on both sides of the load, the carriage may include an open chassis, the chassis may include therein a support part for supporting the projections, and the carriage control unit may be configured to move the carriage so that the placement part enters the chassis. 
     Such configuration enables the load to be housed in the carriage by the movement of the carriage, not by the movement of the autonomous mobile robot. Therefore, the risk due to the movement of the autonomous mobile robot for housing the load in the carriage can be reduced. 
     In another example aspect of the present disclosure in order to achieve the above object, a method for controlling a movement of a carriage in which a load is housed includes: determining whether or not an autonomous mobile robot is planned to move toward the carriage in a state in which the load is raised to a predetermined height or higher by a placement part, the autonomous mobile robot including the placement part having a changeable height and being configured to house the load placed on the placement part in the carriage; and controlling the carriage so that the carriage moves toward the autonomous mobile robot when it is determined that the autonomous mobile robot is planned to move toward the carriage in a state in which the load is raised to the predetermined height or higher by the placement part. 
     Such method reduces a distance that the autonomous mobile robot moves toward the carriage, because the carriage moves toward the autonomous mobile robot. Therefore, it is possible to reduce the distance that the autonomous mobile robot moves in a state where the load is placed on the raised placement part, that is, in an unstable state. It is thus possible to reduce the risk due to the lowering of the level of the stability of the posture of the autonomous mobile robot. 
     In another example aspect of the present disclosure to achieve the above object, a program for causing a computer for controlling a movement of a carriage in which a load is housed to execute: determining whether or not an autonomous mobile robot is planned to move toward the carriage in a state in which the load is raised to a predetermined height or higher by a placement part, the autonomous mobile robot including the placement part having a changeable height and being configured to house the load placed on the placement part in the carriage; and controlling the carriage so that the carriage moves toward the autonomous mobile robot when it is determined that the autonomous mobile robot is planned to move toward the carriage in a state in which the load is raised to the predetermined height or higher by the placement part. 
     Such program reduces a distance that the autonomous mobile robot moves toward the carriage, because the carriage moves toward the autonomous mobile robot. Therefore, it is possible to reduce the distance that the autonomous mobile robot moves in a state where the load is placed on the raised placement part, that is, in an unstable state. It is thus possible to reduce the risk due to the lowering of the level of the stability of the posture of the autonomous mobile robot. 
     According to the present disclosure, it is possible to provide a control system, a control method, and a program capable of reducing a risk due to lowering of the level of stability of a posture of an autonomous mobile robot having a placement part which can change its height. 
     The above and other objects, features and advantages of the present disclosure will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a schematic side view showing an example of an autonomous mobile robot according to a first embodiment; 
         FIG.  2    is a block diagram showing an overview of system configuration of an autonomous mobile robot according to the first embodiment; 
         FIG.  3    is a schematic perspective view showing an example of a carriage according to the first embodiment; 
         FIG.  4    is a block diagram showing an overview of a system configuration of the carriage according to the first embodiment; 
         FIG.  5    is a perspective view showing an example of a load housed in the carriage; 
         FIG.  6    is a schematic diagram showing an autonomous mobile robot entered in a chassis of the carriage; 
         FIG.  7    is a block diagram showing an example of a functional configuration of a control device of the carriage according to the first embodiment; 
         FIG.  8 A  is a schematic diagram showing a movement of the carriage under control of a carriage control unit; 
         FIG.  8 B  is a schematic diagram showing a movement of the carriage under the control of the carriage control unit; 
         FIG.  9    is a flowchart showing an example of a processing flow of the control device of the carriage according to the first embodiment; 
         FIG.  10    is a flowchart showing a processing flow of a determination unit according to the first embodiment; 
         FIG.  11    is a flowchart showing a processing flow of the determination unit according to a second embodiment; and 
         FIG.  12    is a flowchart showing a processing flow of the determination unit according to a third embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present disclosure will now be described with reference to the drawings. 
     First Embodiment 
     A transport system according to a first embodiment will be described. This transport system includes an autonomous mobile robot  10  and a carriage  20 . The transport system may include a plurality of autonomous mobile robots  10  or a plurality of carriages  20 . 
       FIG.  1    is a schematic side view showing an example of the autonomous mobile robot  10  according to this embodiment.  FIG.  2    is a block diagram showing an overview of a schematic system configuration of the autonomous mobile robot  10  according to this embodiment.  FIG.  3    is a schematic perspective view showing an example of the carriage  20  according to this embodiment. Specifically,  FIG.  3    is a perspective view showing a front surface of the carriage  20 . In addition to the carriage  20 , a load  90  housed in the carriage  20  is also shown in  FIG.  3   .  FIG.  4    is a block diagram showing an overview of a schematic system configuration of the carriage  20  according to this embodiment. 
     First, the autonomous mobile robot  10  will be described. The autonomous mobile robot  10  is a robot that moves autonomously in a mobile environment such as a house, a facility, a warehouse, a factory, or outdoors. In this embodiment, the autonomous mobile robot  10  is controlled by a control device  100 , which will be described later, but some or all of the control functions may be implemented by a device other than the autonomous mobile robot  10 , such as a server. 
     The autonomous mobile robot  10  includes a chassis  110  provided with a mobile device  111  for moving the autonomous mobile robot  10 , an extendable part  120  which is extendable and contractable in an up-down direction (in a vertical direction), a placement part  130  for supporting a load placed thereon, a control device  100  for controlling the autonomous mobile robot  10  including the control of the mobile device  111  and the extendable part  120 , and a radio communication unit  140 . 
     The mobile device  111  provided in the chassis  110  includes a pair of left and right driving wheels  112  rotatably provided on the chassis  110 , a pair of front and rear driven wheels  113  rotatably provided on the chassis  110 , and a pair of motors  114  for rotationally driving the driving wheels  112 . The motors  114  rotate the driving wheels  112  through a reduction gear or the like. The motors  114  rotate the driving wheels  112  in response to a control signal from the control device  100 , thereby enabling the autonomous mobile robot  10  to move forward, backward, and rotate. Thus, the autonomous mobile robot  10  can move to any position. The configuration of the mobile device  111  is an example and is not limited thereto. For example, the number of the driving wheels  112  and the driven wheels  113  of the mobile device  111  may be any number, and any configuration can be employed as long as the autonomous mobile robot  10  can be moved to any position. 
     The extendable part  120  is an extendable mechanism which can be extended and contracted in the up-down direction, and is a support pillar for supporting the placement part  130  above the chassis  110 . The extendable part  120  may be configured as a telescopic extendable mechanism. The placement part  130  is provided at an upper end of the extendable part  120 , and the placement part  130  is raised or lowered by an operation of the extendable part  120 . The extendable part  120  includes a driving device  121  such as a motor, and is extended or contracted by driving the driving device  121 . That is, the placement part  130  is raised or lowered by driving the driving device  121 . The driving device  121  is driven in response to a control signal from the control device  100 . In the autonomous mobile robot  10 , any known mechanism for controlling the height of the placement part  130  provided above the chassis  110  may be used instead of the extendable mechanism. 
     The placement part  130  is provided at an upper part (a leading end) of the extendable part  120 . That is, the placement part  130  is provided above the chassis  110  of the autonomous mobile robot  10  with the extendable part  120  interposed therebetween. The placement part  130  is raised and lowered by the driving device  121  such as a motor. In this embodiment, the placement part  130  is used to place a load to be transported by the autonomous mobile robot  10  or to support and raise the load. In order to transport the load, the autonomous mobile robot  10  moves with the load in a state in which the load is being supported by the placement part  130 . In this manner, the autonomous mobile robot  10  transports loads. 
     The placement part  130  is made of, for example, a plate material. In this embodiment, a shape of the plate material, that is, the shape of the placement part  130  is, for example, a flat disk shape, but it may be any other shape. As described above, the placement part  130  can be described as a plate whose height is changed by the driving device  121  (actuator). 
     The radio communication unit  140  is a circuit for radio communication in order to communicate with the carriage  20  or a server as needed, and includes, for example, a radio transmission and reception circuit and an antenna. If the autonomous mobile robot  10  does not communicate with other devices, the radio communication unit  140  may be omitted. 
     The control device  100  controls the autonomous mobile robot  10  and includes a processor  101 , a memory  102 , and an interface  103 . The processor  101 , the memory  102 , and the interface  103  are connected to each other via a data bus or the like. 
     The interface  103  is an input/output circuit used to communicate with other devices such as the mobile device  111 , the extendable part  120 , and the radio communication unit  140 . 
     The memory  102  is composed of, for example, a combination of a volatile memory and a non-volatile memory. The memory  102  is used to store software (computer program) including one or more instructions executed by the processor  101 , data used for various processing of the autonomous mobile robot  10 , and the like. 
     The processor  101  reads software (computer program) from the memory  102  and executes it to perform processing of the control device  100 . 
     The processor  101  may be, for example, a microprocessor, a Micro Processor Unit (MPU), or a central processing unit (CPU). The processor  101  may include a plurality of processors. 
     In this way, the control device  100  functions as a computer. 
     The program includes instructions (or software codes) that, when loaded into a computer, cause the computer to perform one or more of the functions described in the embodiments. The program may be housed in a non-transitory computer readable medium or a tangible housing medium. By way of example, and not a limitation, non-transitory computer readable media or tangible housing media can include a random-access memory (RAM), a read-only memory (ROM), a flash memory, a solid-state drive (SSD) or other types of memory technologies, a CD-ROM, a digital versatile disc (DVD), a Blu-ray disc or other types of optical disc housing, and magnetic cassettes, magnetic tape, magnetic disk housing or other types of magnetic housing devices. The program may be transmitted on a transitory computer readable medium or a communication medium. By way of example, and not a limitation, transitory computer readable media or communication media can include electrical, optical, acoustical, or other forms of propagated signals. 
     The above description of the program is the same as that of the program executed by the other devices such as the carriage  20 . 
     Next, the processing of the control device  100  will be described. 
     The control device  100  controls the operation of the autonomous mobile robot  10 . That is, the control device  100  controls the operations of the mobile device  111  and the extendable part  120 . The control device  100  can control the rotation of the driving wheels  112 , and move the autonomous mobile robot  10  to any position by transmitting a control signal to the motors  114  of the mobile device  111 . Furthermore, the control device  100  can control the height of the placement part  130  by transmitting a control signal to the driving device  121  of the extendable part  120 . 
     The control device  100  may control the movement of the autonomous mobile robot  10  by performing well-known control such as feedback control and robust control based on rotation information of the driving wheels  112  detected by rotation sensors provided on the driving wheels  112 . The control device  100  may control the mobile device  111  based on information including environmental information detected by a sensor such as a camera provided in the autonomous mobile robot  10  and map information of the mobile environment stored in the memory  102 , thereby controlling the autonomous mobile robot  10  to autonomously move. 
     In particular, the control device  100  performs control to transport the load placed on the placement part  130  to the carriage  20 . Thus, the control device  100  moves the autonomous mobile robot  10  to the position of the carriage  20  in order to transport the load to the carriage  20 . The position of the carriage  20  may be transmitted to the autonomous mobile robot  10  from another device (e.g., the server or the carriage  20 ) or may be specified based on the environmental information detected by a sensor provided in the autonomous mobile robot  10 . In addition, the control device  100  performs control so that the height of the placement part  130  becomes a height corresponding to the height of a position in the carriage  20  where the load is to be housed prior to housing the load in the carriage  20 . 
     Next, the carriage  20  will be described. The carriage  20  is also a robot that moves autonomously in the mobile environment such as a house, a facility, a warehouse, a factory, or outdoors, and its operation is controlled by a control system. In this embodiment, a control device  200  described later of the carriage  20  functions as a control system, but some or all functions of the control system may be implemented by a device other than the carriage  20 , such as a server. The sections where the carriage  20  move may be different from the sections where the autonomous mobile robot  10  move. For example, the autonomous mobile robot  10  may move within a local area, and the carriage  20  may move between a plurality of local areas. 
     The carriage  20  includes a chassis  210  (which may be referred to as a rack  210  or housing  210 ) provided with a mobile device  211  for moving the carriage  20 , the control device  200  for controlling the carriage  20  including the control of the mobile device  211 , a sensor  220 , and a radio communication unit  230 . 
     The mobile device  211  provided in the chassis  210  includes, for example, four driving wheels  212  rotatably provided on the chassis  210 , and a motor  213  for rotationally driving the driving wheels  212 . The motor  213  rotates the driving wheels  212  through a reduction gear or the like. The motor  213  rotates the driving wheels  212  in response to a control signal from the control device  200 , thereby enabling the carriage  20  to move forward, backward, and rotate. Thus, the carriage  20  can be moved to any position. A configuration of the mobile device  211  is an example, and is not limited thereto, and any configuration can be employed as long as the carriage  20  can be moved to any position. 
     The chassis  210  constitutes a vehicle body of the carriage  20 . The chassis  210  has a space inside. In the example shown in  FIG.  3   , the chassis  210  has a rectangular parallelepiped shape. A front surface of the chassis  210  has an inverted U-shaped and is opened. That is, a cross-sectional shape of the chassis  210  in a vertical direction is an inverted U-shape. Therefore, the load  90  can be put into a housing space in the chassis  210  and the load  90  can be taken out from the housing space in the chassis  210  through the opening. Here, the housing space means a space in the chassis  210  where the load  90  is housed. In particular, since the opening is opened to the traveling surface (a ground surface or a floor surface) of the carriage  20 , the autonomous mobile robot  10  with the load  90  placed on the placement part  130  can enter the inside of the chassis  210 . In other words, the carriage  20  can be moved to receive the autonomous mobile robot  10  into the chassis  210 . As described above, the chassis  210  is opened so that the autonomous mobile robot  10  can enter the chassis  210  together with the load  90  on the placement part  130 . Here, an open surface of the outer surface excluding the upper surface and the lower surface of the chassis  210  is referred to as the front surface. A rear surface of the chassis  210  may also be open in the same manner as the front surface. 
     The loads  90  are housed in the chassis  210 . In the example shown in  FIG.  3   , a plurality of loads  90  can be housed in the chassis  210  arranged along a vertical line. In the example shown in  FIG.  3   , the chassis  210  has one row of housing spaces, but a plurality of rows of housing spaces may be included by providing partition plates parallel to a vertical plane in the chassis  210 . 
     Pairs of rails  215   a  and  215   b  are provided on both sides of an inside of the chassis  210 , that is, in the housing space. Hereinafter, each pair of rails  215   a  and  215   b  will be referred to simply as rails  215 . More specifically, a plurality of pairs of rails  215  are arranged in the up-down direction. The rail  215   a  and the rail  215   b  are provided at the same height in parallel from the front surface to the rear surface of the chassis  210 . In the carriage  20  shown in  FIG.  3   , the plurality of pairs of rails  215  are provided in the up-down direction at a constant interval, but the interval may not be constant. By supporting the load  90  on the both sides thereof by the rails  215 , the load  90  is housed in the carriage  20 . More specifically, projections  91 , which will be described later, of the load  90  are supported by the rails  215 . The rail  215  is an example of a support part for supporting the projection  91  of the load  90 . In place of the rails  215 , grooves provided in parallel from the front surface to the rear surface of the chassis  210  may be used as support parts. That is, the chassis  210  may be provided with an optional support member for supporting both sides of the load  90 . 
     In this embodiment, the load  90  housed in the carriage  20  is a rectangular box, and articles can be housed therein.  FIG.  5    is a perspective view showing an example of the load  90  housed in the carriage  20 . More particularly,  FIG.  5    is a perspective view showing the front surface, bottom surface, and side surfaces of the load  90 . The projections  91  (flanges) projecting in the horizontal direction are provided on both sides of the load  90 . The projections  91  are provided on both sides of the load  90  from the front surface to the rear surface. The right and left projections  91  are supported from below by the rails  215  provided on the carriage  20 , whereby the load  90  is housed in the chassis  210 . For example, after the autonomous mobile robot  10  enters the chassis  210  in a state where the positions of the projections  91  of the load  90  on the placement part  130  of the autonomous mobile robot  10  are higher than the position of the rails  215  (see  FIG.  6   ), the autonomous mobile robot  10  lowers the placement part  130 , so that the projections  91  are caught by the rails  215  and the load  90  is housed in the carriage  20 . 
     Referring back to  FIG.  4   , the configuration of the carriage  20  will be described. 
     The sensor  220  is installed at any position of the carriage  20 . The sensor  220  is for detecting information about an external appearance of the autonomous mobile robot  10 . For example, the sensor  220  is a camera, and instead may be any sensor that detects the information about an external appearance of an object, such as a LiDAR (light detection and ranging) sensor. An output of the sensor  220  is input to the control device  200 . In this embodiment, the sensor  220  is used to specify the height of the placement part  130  of the autonomous mobile robot  10  or the height of the load  90  on the placement part  130 . The height of the placement part  130  means a vertical distance between the position where the placement part  130  is present and a ground surface or a floor surface. Similarly, the height of the load  90  above the placement part  130  refers to a vertical distance between the position where the load  90  is present and the ground surface or the floor surface. 
     The radio communication unit  230  is a circuit for radio communication in order to communicate with the autonomous mobile robot  10  or a server as needed, and includes, for example, a radio transmission and reception circuit and an antenna. If the carriage  20  does not communicate with other devices, the radio communication unit  230  may be omitted. 
     The control device  200  controls the carriage  20  and includes a processor  201 , a memory  202 , and an interface  203 . The processor  201 , the memory  202 , and the interface  203  are connected to each other via a data bus or the like. 
     The interface  203  is an input/output circuit used to communicate with other devices such as the mobile device  211 , the sensor  220 , and the radio communication unit  230 . 
     The memory  202  is composed of, for example, a combination of a volatile memory and a non-volatile memory. The memory  202  is used to store software (computer program) including one or more instructions executed by the processor  201 , data used for various processing of the carriage  20 , and the like. 
     The processor  201  reads software (computer program) from the memory  202  and executes it to perform processing of the control device  200 . 
     The processor  201  may be, for example, a microprocessor, MPU, or CPU. The processor  201  may include a plurality of processors. 
     In this way, the control device  200  functions as a computer. 
       FIG.  7    is a block diagram showing an example of a functional configuration of the control device  200  of the carriage  20 . As shown in  FIG.  7   , the control device  200  includes a determination unit  240  and a carriage control unit  241 . 
     The determination unit  240  determines whether or not the autonomous mobile robot  10  is planned to move toward the carriage  20  in a state in which the load  90  is raised to a predetermined height or higher by the placement part  130 . Since such a movement is a movement in a state in which the stability of the posture of the autonomous mobile robot  10  is lowered, the movement will hereinafter be referred to as an unstable movement. 
     The determination unit  240  determines whether or not the autonomous mobile robot  10  detected to be the autonomous mobile robot  10  for housing the load  90  placed on the placement part  130  in the carriage  20  is planned for an unstable movement. Note that the detection of the autonomous mobile robot  10  for housing the load  90  placed on the placement part  130  in the carriage  20  can be performed by any method. For example, such an autonomous mobile robot  10  may be detected based a notification from the autonomous mobile robot  10  that houses the load  90  placed on the placement part  130  in the carriage  20 . Alternatively, the autonomous mobile robot  10  present in an area within a predetermined distance from the carriage  20  may be detected as such an autonomous mobile robot  10 . 
     In this embodiment, the determination unit  240  determines whether or not an unstable movement is planned based on the information indicating the height of the placement part  130  detected by using the sensor  220  or the height of the load  90  on the placement part  130  detected by using the sensor  220 . For example, when the height of the placement part  130  of the autonomous mobile robot  10  specified from information about the output of the sensor  220  is greater than or equal to a predetermined threshold value, the determination unit  240  determines that the autonomous mobile robot  10  is planned for an unstable movement. When the height of the load  90  on the placement part  130  specified from the information about the output of the sensor  220  is greater than or equal to the predetermined threshold value, the determination unit  240  determines that the autonomous mobile robot  10  having the placement part  130  is planned for an unstable movement. 
     The carriage control unit  241  controls the movement of the carriage  20 . That is, the carriage control unit  241  controls the operation of the mobile device  211 . The carriage control unit  241  can control the rotation of the driving wheels  212 , and move the carriage  20  to any position by transmitting a control signal to the motor  213  of the mobile device  211 . 
     The carriage control unit  241  may control the movement of the carriage  20  by performing well-known control such as feedback control and robust control based on rotation information of the driving wheels  212  detected by rotation sensors provided on the driving wheels  212 . The carriage control unit  241  may control the mobile device  211  based on information including environmental information detected by a sensor such as a camera provided in the carriage  20  and map information of the mobile environment housed in the memory  202 , thereby controlling the carriage  20  to autonomously move. The sensor  220  used to specify the height of the placement part  130  of the autonomous mobile robot  10  or the height of the load  90  on the placement part  130  may be used to sense the mobile environment during the movement of the carriage  20 . 
     In particular, the carriage control unit  241  controls the carriage  20  so that the carriage  20  moves toward the autonomous mobile robot  10  when it is determined that the autonomous mobile robot  10  is planned to move toward the carriage  20  in a state in which the load  90  is raised to a predetermined height or higher by the placement part  130 . That is, when the determination unit  240  determines that the autonomous mobile robot  10  is planned for an unstable movement, the carriage control unit  241  controls the carriage  20  so that it moves toward the autonomous mobile robot  10 . Such control reduces the distance that the autonomous mobile robot  10  moves toward the carriage  20 , because the carriage  20  moves toward the autonomous mobile robot  10 . Therefore, it is possible to reduce the distance that the autonomous mobile robot  10  moves in a state where the load  90  is placed on the raised placement part  130 , that is, in an unstable state. It is thus possible to reduce the risk due to the lowering of the level of the stability of the posture of the autonomous mobile robot  10 . 
     If the determination unit  240  determines that the autonomous mobile robot  10  is planned for an unstable movement, the carriage control unit  241  may perform the following control for moving the carriage  20  toward the autonomous mobile robot  10 . That is, the carriage control unit  241  may move the carriage  20  so that the placement part  130  enters the chassis  210  (that is, the carriage control unit  241  may move the carriage  20  so as to realize a state in which the placement part  130  has entered the chassis  210 ). Here, the state in which the placement part  130  has entered means, for example, a state in which the load  90  on the placement part  130  has reached a position in the chassis  210  where a load is housed. Specifically, it can be said that the state in which the placement part  130  enters is a state in which the projections  91  on both sides of the load  90  are positioned directly above the pair of rails  215 . The state in which the placement part  130  has entered may be a state in which at least a part of the placement part  130  has entered. Such control is shown in  FIGS.  8 A and  8 B . When the determination unit  240  determines that the autonomous mobile robot  10  is planned for an unstable movement, as shown in  FIG.  8 A , the carriage control unit  241  controls the carriage  20  so that it moves toward the autonomous mobile robot  10 . At this time, the carriage control unit  241  may adjust an orientation of the carriage  20  so that the orientation of the pair of rails  215  relative to the projections  91  on both sides of the load  90  becomes the orientation required for housing. That is, the carriage control unit  241  may adjust the orientation of the carriage  20  so that the direction in which the rails  215  are extended match the direction in which the projections  91  are extended. The autonomous mobile robot  10  may adjust the orientation of the autonomous mobile robot  10 . Needless to say, if the relative orientation of the pair of rails  215  with respect to the projections  91  on both sides of the load  90  already match the orientation required for housing, no adjustment of the orientation of the carriage  20  or the autonomous mobile robot  10  is necessary. As shown in  FIG.  8 B , the carriage control unit  241  controls the carriage  20  so that it moves in such a way that the placement part  130  enters the chassis  210 . That is, the carriage control unit  241  moves the carriage  20  so as to receive the autonomous mobile robot  10  into the chassis  210 . In the state shown in  FIG.  8 B , when the autonomous mobile robot  10  lowers the placement part  130 , the projections  91  on both sides of the load  90  are caught by the rails  215 , and thus the load  90  is housed. The autonomous mobile robot  10  moves so as to get out of the carriage  20 . When the load  90  is housed in the carriage  20 , for example, the carriage control unit  241  moves the carriage  20  to the destination in order to transport the load  90  to the destination. 
     Such control enables the load  90  to be housed in the carriage  20  by the movement of the carriage  20 , not by the movement of the autonomous mobile robot  10 . Therefore, the risk due to the movement of the autonomous mobile robot  10  for housing the load  90  in the carriage  20  can be reduced. In order to house the load  90 , not only the carriage  20  but also the autonomous mobile robot  10  may move. That is, the carriage  20  and the autonomous mobile robot  10  may move in a direction approaching each other. 
     The housing of the load  90  in the carriage  20  may be achieved only by the movement of the autonomous mobile robot  10 . In this case, the control device  100  of the autonomous mobile robot  10  detects an opening of the carriage  20  (the chassis  210 ) by a sensor or the like, and controls the autonomous mobile robot  10  so that it moves from the opening into the chassis  210 . At this time, the control device  100  adjusts the orientation of the autonomous mobile robot  10  so that the orientation of the projections  91  on both sides of the load  90  with respect to the pair of rails  215  of the carriage  20  become the orientation required for housing. In this case, it is assumed that the orientation of the projections  91  of the load  90  on the placement part  130  is known to the autonomous mobile robot  10 . The orientation of the projection  91  of the load  90  on the placement part  130  may be detected by a sensor or the like provided in the autonomous mobile robot  10 . Further, an operational rule may be defined so that the orientation of the load  90  on the placement part  130  (the orientation of the projections  91 ) becomes constant, or the orientation of the load  90  may be physically limited. 
       FIG.  9    is a flowchart showing an example of a processing flow of the control device  200  of the carriage  20  according to this embodiment. The processing flow of the control device  200  of the carriage  20  will be described below with reference to the flowchart. 
     In Step S 10 , the determination unit  240  determines whether or not an unstable movement is planned. A specific process of Step S 10  according to this embodiment will be described with reference to  FIG.  10   .  FIG.  10    is a flowchart showing the processing flow of the determination unit  240  according to this embodiment. That is,  FIG.  10    is a flowchart showing a specific processing flow of Step S 10  according to this embodiment. 
     First, in Step S 100 , the determination unit  240  acquires information indicating the height of the placement part  130  (the height of the load  90  on the placement part  130 ) detected by using the sensor  220 . For example, the determination unit  240  obtains the height of the placement part  130  (the height of the load  90  on the placement part  130 ) by specifying the position of the placement part  130  (the position of the load  90  on the placement part  130 ) from the information about the output of the sensor  220 . In order to detect the height of the placement part  130  (the height of the load  90  on the placement part  130 ), a sensor provided in the mobile environment may be used instead of the sensor  220  provided on the carriage  20 . 
     Next, in Step S 101 , the determination unit  240  determines whether the height obtained in Step S 100  is greater than or equal to a predetermined threshold value. If the height acquired in Step S 100  is greater than or equal to the predetermined threshold value (Yes in Step S 101 ), the determination unit  240  determines in Step S 102  that an unstable movement is planned. On the other hand, if the height obtained in Step S 100  is less than the predetermined threshold value (No in Step S 101 ), the determination unit  240  determines in Step S 103  that no unstable movement is planned. 
     Referring back to  FIG.  9   , the processing after Step S 10  will be described. If it is determined in Step S 10  that an unstable movement is planned (Yes in Step S 20 ), the processing of Step S 30  is performed, and if it is determined in Step S 10  that an unstable movement is not planned (No in Step S 20 ), the processing of Step S 30  is not performed. 
     In Step S 30 , the carriage control unit  241  controls the carriage  20  so that it moves toward the autonomous mobile robot  10  which houses the load  90  in the carriage  20 . At this time, as described above, the carriage control unit  241  may move the carriage  20  so that the placement part  130  of the autonomous mobile robot  10  enters the chassis  210 . 
     The first embodiment has been described above. According to this embodiment, as described above, when an unstable movement of the autonomous mobile robot  10  is planned, the carriage  20  moves toward the autonomous mobile robot  10 , so that the risk due to the lowering of the level of the stability of the posture of the autonomous mobile robot  10  is reduced. 
     Second Embodiment 
     In this embodiment, a method for determining whether or not an unstable movement is planned is different from that of the above-described embodiment. Although the processing of the determination unit  240  of the control device  200  according to this embodiment is different from that according to the first embodiment, other processing and configuration according to this embodiment are the same as those according to the first embodiment. Hereinafter, the points of this embodiment different from those the first embodiment will be described, and the description overlapping with the first embodiment will be omitted. 
     In this embodiment, the determination unit  240  determines whether or not the autonomous mobile robot  10  is planned for an unstable movement based on control information about the height of the placement part  130  received from the autonomous mobile robot  10  which houses the load  90  in the carriage  20 . The control information about the height of the placement part  130  is information used by the control device  100  of the autonomous mobile robot  10 , and may be, for example, a control signal transmitted to the driving device  121  in order to change the height of the placement part  130 , or may be information indicating the current height of the placement part  130  managed by the control device  100 . In this embodiment, the control device  100  of the autonomous mobile robot  10  transmits such control information about the height of the placement part  130  to the carriage  20  where the load  90  is housed. The determination unit  240  of the carriage  20  which has received the control information specifies the height of the placement part  130  from the received control information. If the received information is a control signal, the determination unit  240  may specify the height of the placement part  130  from the control signal by referring to, for example, a predefined lookup table. 
     When the height of the specified placement part  130  is greater than or equal to a predetermined threshold value, the determination unit  240  determines that the autonomous mobile robot  10  is planned for an unstable movement. If it is determined by the determination unit  240  that the autonomous mobile robot  10  is planned for an unstable movement, the carriage control unit  241  performs the same control as that in the first embodiment. 
       FIG.  11    is a flowchart showing a processing flow of the determination unit  240  according to the second embodiment. That is,  FIG.  11    is a flowchart showing a specific processing flow of Step S 10  (see  FIG.  9   ) according to the second embodiment. In this embodiment, the processing from Step S 110  to Step S 113  is performed as the specific processing of Step S 10 . 
     First, in Step S 110 , the determination unit  240  acquires the control information about the height of the placement part  130  used by the control device  100  of the autonomous mobile robot  10 . Then, the determination unit  240  specifies the height of the placement part  130  from the acquired control information. 
     Next, in Step S 111 , the determination unit  240  determines whether or not the height specified in Step S 110  is greater than or equal to a predetermined threshold value. If the height specified in Step S 110  is greater than or equal to the predetermined threshold value (Yes in Step S 111 ), the determination unit  240  determines in Step S 112  that an unstable movement is planned. On the other hand, if the height obtained in Step S 110  is less than the predetermined threshold value (No in Step S 111 ), the determination unit  240  determines in Step S 113  that no unstable movement is planned. 
     The second embodiment has been described above. Also in this embodiment, when an unstable movement of the autonomous mobile robot  10  is planned, the carriage  20  moves toward the autonomous mobile robot  10 , so that the risk due to the lowering of the level of the stability of the posture of the autonomous mobile robot  10  is reduced. 
     Third Embodiment 
     Also in this embodiment, a method for determining whether or not an unstable movement is planned is different from those of the above-described embodiments. Although the processing of the determination unit  240  of the control device  200  according to this embodiment is different from that according to the first embodiment, other processing and configuration according to this embodiment are the same as those according to the first embodiment. Hereinafter, the points of this embodiment different from those of the first embodiment will be described, and the description overlapping with the first embodiment will be omitted. 
     In this embodiment, the determination unit  240  determines whether or not the autonomous mobile robot  10  is planned for an unstable movement based on a planned housing position of the load  90  in the carriage  20 . When the planned housing position of the load  90  is at a high position, it is expected that the autonomous mobile robot  10  will move in a state in which the placement part  130  raised high to house the load  90  at the planned housing position. Therefore, in this embodiment, it is determined whether or not the autonomous mobile robot  10  is planned for an unstable movement based on the planned housing position. The carriage  20  may receive the planned housing position from the autonomous mobile robot  10  which houses the load  90  in the carriage  20 , or may receive it from another server. Further, when the position in the chassis  210  where a load can be housed is managed, the planned housing position may be specified from information indicating the position where a load can be housed. In this case, for example, the determination unit  240  may specify the highest position where a load can be housed as the planned housing position. 
     If the height of the planned housing position of the load  90  housed by the autonomous mobile robot  10  is greater than or equal to a predetermined threshold value, the determination unit  240  determines that the autonomous mobile robot  10  is planned for an unstable movement. If it is determined by the determination unit  240  that the autonomous mobile robot  10  is planned for an unstable movement, the carriage control unit  241  performs the same control as that in the first embodiment. 
       FIG.  12    is a flowchart showing a processing flow of the determination unit  240  according to the third embodiment. That is,  FIG.  12    is a flowchart showing a specific processing flow of Step S 10  (see  FIG.  9   ) according to the third embodiment. In this embodiment, the processing from Step S 120  to Step S 123  is performed as the specific processing of Step S 10 . 
     First, in Step S 120 , the determination unit  240  acquires the planned housing position of the load  90  placed on the placement part  130  by the autonomous mobile robot  10 . 
     Next, in Step S 121 , the determination unit  240  determines whether or not the height of the planned housing position acquired in Step S 120  is greater than or equal to the predetermined threshold value. If the height of the planned housing position is greater than or equal to the predetermined threshold value (Yes in Step S 121 ), the determination unit  240  determines in Step S 122  that an unstable movement is planned. On the other hand, if the height of the planned housing position is less than the predetermined threshold value (No in Step S 121 ), the determination unit  240  determines in Step S 123  that no unstable movement is planned. 
     The third embodiment has been described above. Also in this embodiment, when an unstable movement of the autonomous mobile robot  10  is planned, the carriage  20  moves toward the autonomous mobile robot  10 , so that the risk due to the lowering of the level of the stability of the posture of the autonomous mobile robot  10  is reduced. In particular, in this embodiment, regardless of whether or not the placement part  130  has already been raised, a determination about whether or not the autonomous mobile robot  10  is planned to move toward the carriage  20  in a state in which the load is being raised to the predetermined height or higher by the placement part  130  can be easily made. In this embodiment, the carriage  20  can start moving in order to reduce the risk before the placement part  130  is raised. 
     The present disclosure is not limited to the above-described embodiments, and may be suitably modified without departing from the scope thereof. For example, some or all of the control processing of the carriage  20  or the autonomous mobile robot  10  may be implemented in a device such as a server. In the above-described embodiments, in order to reduce the risk, it has been explained that the control for moving the carriage  20  is performed so that the autonomous mobile robot  10  is positioned in the chassis  210  of the carriage  20 . However, the state in which the autonomous mobile robot  10  is positioned in the chassis  210  of the carriage  20  may not be achieved by the movement of the carriage  20 . In this case, with the autonomous mobile robot  10  positioned outside the chassis  210  of the carriage  20 , the load  90  may be housed in the carriage  20  by a manipulator or the like provided in the autonomous mobile robot  10 . The determination unit  240  may use together the determination methods described in the first to third embodiments. 
     From the disclosure thus described, it will be obvious that the embodiments of the disclosure may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure, and all such modifications as would be obvious to one skilled in the art are intended for inclusion within the scope of the following claims.