Patent Publication Number: US-2016236869-A1

Title: Transfer Robot System

Description:
TECHNICAL FIELD 
     The present invention relates to a transfer robot system using a transfer robot that transfers a rack having an article stored therein. 
     BACKGROUND ART 
     A robot which takes in charge of a transfer operation of moving an article from a position to another position is called an automated guided vehicle or an AGV and is widely introduced to facilities, such as warehouses, factories, and harbors. 
     In addition, the robot can be used in combination with a loading and unloading device which automatically performs an operation of exchanging articles between an article storage place and a transfer robot, that is, a loading and unloading operation to automate most of the commodity distribution operations in facilities. 
     In recent years, the number of warehouses that store a wide variety of products in small quantities, such as mail-order warehouses, has increased with the diversification of customer needs. As a result, it takes a lot of time, labor, and cost to search for articles and to load the articles in terms of the properties of commodity management. For this reason, there is a demand for automating a distribution operation in facilities, such as warehouses which treat single articles in large quantities. 
     Patent Document 1 discloses a system in which movable storage racks are arranged in a space, such as a warehouse, and a transfer robot is combined with a rack having a necessary article or part stored therein and transfers each storage rack to a workshop in which articles are packed or products are assembled, as an example of the transfer of articles in a mail-order warehouse which treats a wide variety of products or a factory which produces a wide variety of products in small quantities. 
     Patent Document 2 discloses a warehouse system which includes a transfer robot and an automatic loading and unloading device. In the system, the loading and unloading device which moves an article from a rack to the transfer robot is attached to a storage rack. When the transfer robot is connected to the loading and unloading device, the robot supplies power to the loading and unloading device and controls the loading and unloading device. In this way, it is possible to automate a loading and unloading operation, without providing a power supply in the loading and unloading device. 
     Patent Document 3 discloses a technique which stores wafers that are produced in large quantities in a factory in a multi-stage storage rack provided in a transfer robot and transfers the wafers at one time. 
     CITATION LIST 
     Patent Document 
     Patent Document 1: JP 2009-539727 A 
     Patent Document 2: JP 4-333404 A 
     Patent Document 3: JP 10-303274 A 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     The method disclosed in Patent Document 1 has to transfer all of the articles stored in a rack at the same time when a certain article stored in the rack is required. 
     When most of the articles stored in the rack are not necessary, the consumption of energy increases by an amount corresponding to the weight of unnecessary articles. 
     As such, in Patent Document 1, a technique which individually transfers only a necessary article or only a tray having the necessary article stored therein is not considered. 
     When a plurality of necessary articles are separately stored in different racks, all of the racks need to be transferred to the workshop. 
     Therefore, it is necessary to perform a transfer operation between a storage area and a work area a number of times corresponding to the number of racks. As a result, transfer time efficiency and energy efficiency are not high. 
     In contrast, in the method disclosed in Patent Document 2, a necessary article or tray is stored in the storage space of the transfer robot. Therefore, it is possible to transfer only a necessary article. However, there is a limit in the article storage capacity of the robot and the number of articles which can be transferred at one time is limited. 
     In the technique disclosed in Patent Document 3, the multi-stage storage space is provided in the robot. Therefore, it is possible to transfer a plurality of articles. However, the multi-stage storage space is a portion of the robot. When the robot is moved without storing a necessary article, it is necessary to continuously hold the multi-stage storage rack which is a heavy rack. 
     Therefore, when a robot which can transfer a large number of articles is moved in a normal mode in which the robot does not transfer an article or a tray, a total carrying weight including the weight of the robot increases, which results in a reduction in energy efficiency. 
     In the techniques according to the related art, it is necessary to carry an excessively heavy article in at least one of the normal movement mode in which no article is carried and the article transfer mode. 
     The invention has been made in view of the above-mentioned problems and an object of the invention is to provide a transfer robot system which automatically transfers a large number of articles at one time and has high transfer time efficiency and high energy efficiency in both a normal movement mode and an article transfer mode. 
     Solutions to Problems 
     In order to achieve the object, according to the invention, there is provided a transfer robot system including: a plurality of movable racks each of which includes a transfer unit for moving a stored article; at least one robot that is capable of transferring a predetermined rack to a predetermined position; and a management terminal that issues a transfer instruction to the robot. The robot detachably holds the rack and includes a connection portion that is electrically connected to the rack, a driving unit, and a control unit. The control unit moves the robot to a vicinity of a first rack, using the driving unit, connects the robot to the first rack through the connection portion, moves the robot and the first rack to a vicinity of a second rack, supplies power to the transfer unit of the first rack or/and the second rack through the connection portion, operates the transfer unit corresponding to a position where an article to be moved is placed, and moves the article to be moved from a rack in which the article to be moved is placed to a predetermined position of another rack. 
     Effects of the Invention 
     According to the invention, in the transfer robot system which can carry a large number of articles at one time, it is possible to achieve an automatic transfer technique which has high transfer time efficiency and high energy efficiency in both a normal movement mode and an article transfer mode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating an example of the structure of a transfer robot system  10   a  according to Embodiment 1. 
         FIG. 2  is a flowchart illustrating an example of the overall operation of the transfer robot system  10  for one task  902   x  in Embodiment 1. 
         FIG. 3  is a diagram illustrating an example of the structure of a rack  100   a  in Embodiment 1. 
         FIG. 4  is a diagram illustrating an example of the structure of a contacted surface  103  in Embodiment 1. 
         FIG. 5  is a diagram illustrating an example of the structure of a rack  100   b  in Embodiment 1. 
         FIG. 6  is a diagram illustrating an example of the structure of a robot  200  in Embodiment 1. 
         FIG. 7  is a diagram illustrating an example of the structure of a contact surface  207  in Embodiment 1. 
         FIG. 8  is a diagram schematically illustrating an aspect in which a connected portion  102  and a connection portion  202  are connected to each other in Embodiment 1. 
         FIG. 9  is a diagram schematically illustrating an aspect in which a rack  100   x  is prepared in Embodiment 1. 
         FIG. 10  is a flowchart illustrating an example of the operation of a robot  200   x  and a robot  200   y  when the rack  100   x  is prepared in Embodiment 1. 
         FIG. 11  is a diagram illustrating an example of the structure of rack information  905  related to the rack  100  which is checked by a management terminal  300  in Embodiment 1. 
         FIG. 12  is a diagram illustrating an example of the structure of an order  900  which is input to the management terminal  300  in Embodiment 1. 
         FIG. 13  is a diagram illustrating an example of the structure of a task  902  which is created by the management terminal  300  in Embodiment 1. 
         FIG. 14  is a diagram illustrating an example of the structure of state transition information  915  of the rack  100  in Embodiment 1. 
         FIG. 15  is a diagram schematically illustrating an aspect in which articles are exchanged between storage spaces with different heights in Embodiment 1. 
         FIG. 16  is a diagram illustrating an example of the structure of a transfer robot system  10   b  according to Embodiment 2. 
         FIG. 17  is a diagram illustrating an example of the structure of a stage change transfer rack  600  in Embodiment 2. 
         FIG. 18  is a diagram schematically illustrating an aspect in which articles are exchanged between storage spaces with different heights in Embodiment 2. 
         FIG. 19  is a diagram schematically illustrating an aspect in which one robot  200   x  controls the operation of the racks  100   x  and  100   y  in Embodiment 1. 
         FIG. 20  is a diagram illustrating the structure of a management terminal function  310  of the management terminal  300  in Embodiment 1. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, embodiments will be described with reference to the drawings. 
     Embodiment 1 
     In this embodiment, an example of a transfer robot system  10   a  which transfers articles between racks will be described on the assumption that articles are stored in or delivered from a mail-order warehouse or a factory that manufactures a wide variety of products in small quantities. In this embodiment, a mail-order warehouse is given as a preferred example. In the invention, the number of articles or the type of article is not particularly limited. In addition, the invention may be applied to all manufacturing factories. 
       FIG. 1  is a diagram illustrating an example of the structure of the transfer robot system  10   a  according to this embodiment. The transfer robot system  10   a  includes two or more racks  100 , one or more robots  200 , a management terminal (hereinafter, also referred to as a management computer)  300 , a user interface  400 , and a charging station  500 . 
     In this embodiment, an example in which two or more racks  100  and two or more robots are provided in a warehouse will be described, if not otherwise specified. 
     A plurality of racks  100  are installed in a storage area  1000 . A plurality of articles are stored in some racks and no article is stored in some racks. The user interface  400  is installed in a work area  2000 . An operator  20  performs, for example, an operation of taking out articles from a rack  100   x  transferred by a robot  200   x  or an operation of supplementing articles. 
     The user interface  400  is, for example, a PC. The management computer  300  and the user interface  400  can communicate with each other wirelessly or in a wired manner and each include a transmitting unit and a receiving unit (not illustrated). In addition, the management computer  300  and the robot  200  can wirelessly communicate with each other. The robot  200  includes a transmitting unit and a receiving unit (not illustrated). 
     The management computer  300  manages and operates the entire transfer robot system  10   a . It is assumed that the function of the management computer  300  is referred to as a management terminal function  310 .  FIG. 20  is a diagram illustrating an example of the structure of the management terminal function  310  in this embodiment. The management terminal function  310  is mainly classified into a task list creation function  320  that creates a task list  903  in which the state transition of the rack  100  is described in detail, a system operation planning function  330  that plans the operation of the robot  200  or the user interface  400  in the transfer robot system  10   a , and a task list execution management function  340  that manages the execution state of the task list  903  by the transfer robot system  10   a.    
     First, the task list creation function  320  will be described. An administrator  30  of the transfer robot system  10   a  inputs an order list  901  of all orders  900  to be executed for a predetermined period of time, for example, for a day to the management computer  300 , using an order list input function  321  of the management computer  300 . 
     The order  900  is ordering or supplementing articles or parts. For example, the management computer  300  reorders the order list  901 , using an order list reordering function  322 , plans a plurality of tasks  902  for executing all of the orders, and creates the task list  903 . The task  902  is a series of operations of the transfer robot system  10   a  for the operation of the operator  20  for one rack  100 . In this embodiment, it is assumed that, when the task list  903  is created, how to allocate the robot  200  to the task  902  or the charging time of the robot  200  has not been determined. However, the allocation and the charging time may be determined when the task list  903  is created. 
     In this embodiment, when creating the task list  903 , first, the management computer  300  checks each order  900  in the order list  901  and performs a reordering process of collecting the orders  900  for the same type of articles (order list reordering function  322 ). When the transfer robot system  10   a  is introduced, for the same type of articles, small-size articles  120  are stored in a single tray  110  and the tray  110  and the medium-size articles  130  are stored in a single rack  100  in advance. The reordering process makes it possible to prevent the same rack  100  from being transferred many times, particularly, during a delivery operation. As a result, it is possible to improve transfer efficiency. 
     Then, a list of the racks  100  in which the articles described in a plurality of collected orders  900  are to be stored is drawn up (target article storage rack list drawing function  323 ). A rack  100   x  to be moved to the work area  200  and a rack  100   y  which exchanges articles with the rack  100   x  are selected from the list of the racks  100  (target rack selection function  324 ). Only one rack  100   x  is selected. However, the number of racks  100   y  is not particularly limited. The articles to be stored in the rack  100   x  are compared with the articles which are currently stored in the rack  100   x . When there is no difference therebetween, the rack  100   y  is not selected. 
     As a method for selecting the rack  100   x  during a delivery operation, for example, a method is considered which selects, as the rack  100   x , a rack  100  including a large number of transfer units  101  having necessary articles stored therein. In this case, the number of times articles are transferred between the racks  100  is reduced and it is possible to improve transfer efficiency. When there are a plurality of racks including the same number of transfer units  101  having necessary articles stored therein, a rack  100  including a larger number of transfer units  101  in which no article is stored may be selected as the rack  100   x . In this case, the number of times an unnecessary article is transferred to other racks  100   y  is reduced and it is possible to improve transfer efficiency. In some cases, some of the transfer units  101  are removed in order to store a large-size article  140 , which will be described in detail below with reference to  FIG. 5 . When it is necessary to store the large-size article  140  and there are a small number of racks  100  capable of storing the large-size article  140 , the rack  100  having the large-size article  140  stored therein needs to be preferentially selected as the rack  100   x.    
     As a method for selecting the rack  100   x  during a storage operation, a method is considered which selects, the rack  100   x , a rack  100  including a large number of empty transfer units  101 . In this case, it is possible to store a large number of articles in one rack  100   x  in the work area  2000 . However, when a small-size article  120  which is not stored in the tray  110  is stored, the rack  100  including the tray  110  in which the same type of small-size articles  120  are stored needs to be selected as the rack  100   x . When the large-size article  140  is stored and there are a small number of racks  100  capable of storing the large-size article  140 , a rack  100  having an empty storage space capable of storing the large-size article  140  needs to be preferentially selected as the rack  100   x.    
     For a storage operation, a method is also considered which preferentially stores the same type of articles in one rack  100 . For example, when there are a small number of articles which are the same type and are to be stored or when a small number of trays  110 , each of which has a large number of small-size articles  120 , are stored, a method is considered which selects, as the rack  100   x , a rack  100  which stores a large number of articles of the same type and in which all of the transfer units  101  are not full of the same type of articles. In this case, the storage operation can be performed such that the same type of articles is collected in a single rack  100 . As described above, it is possible to improve transfer efficiency during a delivery operation. 
     The target rack selection function  324  may select the candidates of the rack  100  to be used for the task  902 , narrow down the candidates, using the function  325  of examining the exchange of articles between the target racks, and finally select the rack  100 . As a method for selecting the candidates of the rack  100   y  during the delivery operation, for example, a method is considered which selects, as the candidate of the rack  100   y , a rack  100  including an empty transfer unit  101  among the racks  100  which are required for the delivery operation and have the articles that are not stored in the rack  100   x . It is possible to transfer an article which is unnecessary for the rack  100   x  from the rack  100   x  to the candidate of the rack  100   y  and to transfer an article which is necessary for the rack  100   x  from the candidate of the rack  100   y  to the rack  100   x . When the candidate of the rack  100   y  is selected, it is examined in detail whether a target article can be exchanged (the function  325  of examining the exchange of articles between the target racks). When there are a plurality of candidates of the rack  100   y  which can exchange a target article, the distances between the rack  100   x  and the candidates of the rack  100   y  and the distances between the candidates of the rack  100   y  and the work area  2000  are calculated. Then, the candidate of the rack  100   y  having the minimum sum of the distances is selected as the rack  100   y . Therefore, the moving distance of the robot  200   x  is reduced and it is possible to improve transfer efficiency. In addition, when a group of a plurality of racks  100   y  is selected, the distances between the rack  100   x  and the candidates of the rack  100   y  which is circulated first, the distance between the candidates of the rack  100   y , and the distances between the work area  2000  and the candidates of the rack  100   y  which is finally circulated are calculated. Then, a group of the candidates of the rack  100   y  having the minimum sum of the distances is selected as a group of the racks  100   y.    
     During the storage operation, the rack  100   y  is not necessarily selected. However, when the same type of articles is preferentially stored in one rack  100 , it is preferable to move a small number of articles or trays  110 , which are stored in the rack  100   x  and are a different type from the stored articles, from the rack  100   x  to another rack  100 . A method is considered which selects, as the candidate of the rack  100   y  with which the rack  100   x  exchanges articles, a rack  100  that stores a large number of articles of the same type as the articles to be moved from the rack  100   x  and includes an empty transfer unit  101 . In this case, it is possible to move the articles to be moved from the rack  100   x  to the candidate of the rack  100   y  that stores the articles of the same type as those. Therefore, it is possible to collect the same type of articles and to store the same type of articles in one rack. When the candidates of the rack  100   y  are selected, it is examined in detail whether a target article can be exchanged, similarly to the delivery operation. When there are a plurality of candidates of the rack  100   y  which can exchange the target article, the distances between the rack  100   x , the rack  100   y , and the work area  2000  are calculated and the candidate of the rack  100   y  having the minimum sum of the distances is selected as the rack  100   y.    
     The rack state transition information items  915   x  and  915   y  of the racks  100   x  and  100   y  are generated (rack state transition information generation function  326 ) from the selection results of the racks  100   x  and  100   y  and the results of examining the exchange of articles between the rack  100   x  and the rack  100   y  and are collected as a task  902   x.    
     The system operation planning function  330  is actually used when the task  902  is executed and includes a robot selection function  331  which selects the robot  200  for executing the task  902 , a robot operation planning function  332  which plans the operation of the robot  200  in order to change, for example, the position of the rack  100  or the arrangement of articles described in the rack state transition information  915  of the task  902 , and a user interface operation planning function  333  which plans the operation of the user interface  400  in order to inform the operator  20  of an operation for the rack  100  that has been transferred to the work area  2000  by the robot  200 . 
     The task list execution management function  340  includes a task list progress management function  341  that manages whether each task  902  in the task list  903  has been completed, is being executed, or has not been executed, an individual task progress management function  342  which checks a current rack state  907  for the task  902  that is currently being executed, a robot state management function  344  which checks whether each robot  200  is executing the task or is being charged, and a rack information update function  344  which updates the rack state  907  of each rack  100  according to the progress situation of each task  902 . In addition, the task list execution management function  340  includes a communication function  345  of the robot  200  and a communication function  346  of the user interface  400  for executing the tasks in the task list  90 . 
       FIG. 2  is a flowchart illustrating an example of the overall operation of the transfer robot system  10   a  for one task  902   x  in this embodiment. First, the management computer  300  determines whether to perform the task  902   x  when it is checked that the rack  100  related to the task  902   x  is not used by other tasks  902  and the number of robots  200  to which no task  902  is allocated is equal to or greater than a value required for performing the task  902   x . The process illustrated in  FIG. 2  starts at the time when the execution of the task  902   x  is determined. 
     First, the management computer  300  determines the robot  200  related to the task  902   x , using the robot selection function  331 , plans the operation of the robot  200 , using the robot operation planning function  332 , and transmits the planned operation to the robot  200 , using wireless communication (S 100 ). 
     In this embodiment, two robots  200  are allocated. That is, a first robot  200   x  that transfers the rack  100   x  and a second robot  200   y  that supports the exchange of articles are allocated. However, a plurality of robots  200  which support the exchange of articles may be provided. 
     The robot is allocated to the rack  100   x  to be transferred as follows. The number of articles to be stored is compared with the number of stored articles. When there is no difference therebetween, only the first robot  200   x  is allocated. On the other hand, when there is a difference therebetween, two robots, that is, the first robot  200   x  and the second robot  200   y  are allocated. 
     In addition, even when there is a difference therebetween, one robot may be allocated, the rack  100   x  and the rack  100   y  may be electrically connected to each other, and both the rack  100   x  and the rack  100   y  may receive a control instruction from the robot  200   x.    
     Furthermore, the rack  100   x  and the  100   y  may not be electrically connected to each other and the transfer unit of the rack  100   x  or the rack  100   y  may be driven on the basis of a control instruction from the robot  200   x  to transfer an article to the rack which is not driven. 
     The plan for the operation includes, for example, the moving paths  904   x  and  904   y  of the robots  200   x  and  200   y , the time when the rack is loaded and installed, and the control flow and time of the transfer unit  101  of the rack  100 . After planning the operation, the management computer  300  instructs the robots  200   x  and  200   y  to perform the planned operation through wireless communication. 
     When receiving the instruction, the robots  200   x  and  200   y  prepare the rack  100   x  in the storage area  1000  (S 101 ). First, the robots  200   x  and  200   y  are moved to the storage area  1000  in which the rack  100  is present along the moving paths  904   x  and  904   y  included in the instruction. When arriving in the storage area  1000 , the robot  200  prepares the rack  100   x  to be transferred to the work area  2000  on the basis of the instructed operation. 
     Specifically, the robot  200   x  is moved to the position of the rack  100   x  to be transferred and is loaded with the rack  100   x . When the exchange of articles between the rack  100   x  and another rack  100   y  is needed, the robot  200   x  transfers the rack  100   x  to the position where the rack  100   x  can exchange articles with the rack  100   y  and the robot  200   y  is moved to the position of the rack  100   y . Then, the robot  200   x  operates the transfer unit  101  of the rack  100   x  and the robot  200   y  operates the transfer unit  101  of the rack  100   y  to exchange articles. After the articles are exchanged, the rack  100   x  and the rack  100   y  have a relative position relationship capable of exchanging articles, or the robot  200   y  may transfer the rack  100   y  such that the relative positional relationship is established. After the preparation of the rack  100   x  is completed, the robot  200   y  notifies the management computer  300  that the preparation of the rack  100   x  has been completed. Then, the operation of the robot  200   y  ends. 
     In the above-mentioned example, one robot  200  is allocated to one rack  100  and articles are exchanged between the racks  100 . However, as illustrated in  FIG. 19 , the robot  200   x  may transfer the rack  100   x  to the vicinity of the rack  100   y  and electrically connect the rack  100   x  and the rack  100   y . Then, the robot  200   x  may control both the transfer units  101   x  of the rack  100   x  and the transfer units  101   y  of the rack  100   y  at the same time. In this case, it is possible to exchange articles between the racks  1000  and to perform the task  902   x , using only one robot  200 . 
     Then, the robot  200   x  transfers the rack  100   x  to the work area  2000  and notifies the management computer  300  that the transfer of the rack  100   x  has been completed immediately after arriving in the work area  2000  (S 102 ). 
     Immediately after the rack  100   x  arrives in the work area  2000 , the operator  20  performs an operation for the rack  100   x  (S 103 ). First, the management computer  300  instructs the operator  20  to perform an operation for the rack  100   x  through the user interface  400 . The operator  20  performs the operation for the rack  100   x  on the basis of the instruction displayed on the screen of the user interface  400 . After completing the operation, the operator  20  inputs information indicating the completion of the operation to the management computer  300  through the user interface  400 . 
     Immediately after the operation of the rack  100   x  ends, the robot  200   x  returns the rack  100   x  to the storage area  1000  (S 104 ). 
     First, when checking the completion of the operation in the task  902   x , the management computer  300  instructs the robot  200   x  to resume movement. 
     Then, the robot  200   x  transfers the rack  100   x  to the storage area  1000  and places the rack  100   x  at the instructed position. Immediately after the placement of the rack  100   x  is completed, the robot  200   x  notifies the management computer  300  that the placement of the rack  100   x  has been completed. When the management computer  300  accepts the notice, the task  902   x  ends. 
     When determining that charging is required, the robot  200  transmits information indicating that charging is required to the management computer  300 . When it is determined that the task  902  is being executed, the robot  200  transmits the information and a notice indicating that the placement of the rack has been completed at the same time. Then, the management computer  300  plans the moving path  904  of the robot  200  to the charging station  500  and transmits the moving path  904  to the robot  200 . When receiving the moving path  904 , the robot  200  is moved along the moving path  904 , arrives in the charging station  500 , and is electrically connected to the charging station. Then, a power supply  204  is charged. When charging is completed, the robot  200  transmits information indicating the completion of charging to the management computer  300  and waits for an instruction from the management computer  300 . 
     In this embodiment, the charging station  500  is provided separately from the rack  100 . However, the invention is not limited thereto. For example, an arbitrary rack may be provided with a rechargeable battery. 
     Next, the characteristics of this embodiment will be described in detail with reference to  FIGS. 3 to 15 . 
       FIG. 3  is a diagram illustrating an example of the structure of a rack  100   a  in this embodiment. 
     A left figure illustrates a state in which no article is stored in a storage space and a right figure illustrates a state in which articles are stored in a storage space. In the left and right figures, for convenience of explanation, an upper plate is transparent such that the inside of the rack is seen. However, the upper plate is not necessarily transparent. 
     The rack  100   a  includes three stages of storage spaces. Each stage of storage space includes 2×2 sets of transfer units  101   a . That is, the rack  100   a  includes a total of 12 sets of transfer units  101   a A to  101   a L. As such, since a plurality of transfer units  101  are provided, it is possible to individually move articles. When a large-size article is moved, a plurality of transfer units  101  may be operated at the same time. The number of stages of storage spaces and the number of sets of transfer units  101  in one stage of storage space are not particularly limited. 
     The transfer unit  101  is a mechanism which moves an article between the racks. It is preferable to mount, as the transfer unit  101 , a sliding mechanism, such as a roller conveyer, a belt conveyer, or a mechanism in which a surface on which an article is placed is slippery and is inclined. 
     The mounting of these mechanisms makes it unnecessary to attach a mechanism, such as a fork or a manipulator, to the outside of the storage space of the rack and makes it possible to reduce the size of the system. Therefore, it is possible to maintain the storage ratio or the mobile power of the robot  200  at a high level. 
     It is preferable to control the reversal of the transfer direction of the transfer unit  101  in order to move articles in two directions. It is preferable that the transfer speed be variable in order to adjust the transfer speed according to the size or weight of an article. 
     For example, a method is considered which can perform control according to the reversal of the potential of power supplied to the transfer unit  101 , a potential difference, or the amount of current. A method is considered which adjusts the amount of current using pulse width modulation control (PWM control). 
     The rack  100  can hold an article in the storage space. A small-size article  120  that is smaller than one set of the transfer units  101  is stored in a tray  110  having the same size as one set of the transfer units  101  and one set of the transfer units  101  is allocated to one tray  110 . One set of the transfer units  101  is allocated to a medium-size article  130  having the same size as one set of the transfer units  101 . A plurality of sets of the transfer units  101  are allocated to a large-size article  130  that is larger than one set of the transfer units  101 . 
     A connected portion  102  which is electrically connected to the robot  200  is provided on a contacted surface  103  which comes into contact with the robot  200  when the robot  200  loads the rack  100  and is provided below the bottom of the transfer unit  101  of the rack  100 . Therefore, it is not necessary to separately provide a touch surface and it is possible to reduce manufacturing limitations by an amount corresponding to the touch surface. 
     In this embodiment, the robot  200  gets under the rack  100 , lifts the bottom of the rack  100 , and holds the rack  100 . Therefore, the bottom of the rack  100  becomes the contacted surface  103 . However, the invention is not limited thereto. Since the connected portion  102  is provided on the bottom of the rack  100  as the contacted surface  103 , it is possible to connect the robot  200 , without damaging the mobile power of the robot  200 . 
     For example, it is considered that the rack is connected to the side surface of the robot  200 . In this case, it is necessary to attach a plate between the legs of the rack  100 , which makes it difficult for the robot to move in a certain direction of the plate. However, in the structure according to this embodiment, the mobile power of the robot  200  is not lost. 
       FIG. 4  is a diagram illustrating an example of the structure of the contacted surface  103  of the rack  100  in this embodiment. The contacted surface  103  includes the connected portions  102  corresponding to the number of sets of the transfer units  101 ×2. In this embodiment, the contacted surface  103  includes 24 connected portions  102 . The connected portion  102  is a metal surface that conducts electricity and is electrically connected to the transfer unit  101 . A cable which connects the connected portion  102  and the transfer unit  101  is provided in a frame forming the rack  100 . 
     It is preferable that the connected portion  102  have a size greater than the average value of the movement control errors of the robot  200  in order to allow the movement control errors of the robot  200  when the connected portions  102  are connected to the robot  200 . 
     The arrangement of the connected portions  102  on the contacted surface  103  illustrated in  FIG. 4  is illustrative and the invention is not limited thereto. However, as illustrated in  FIG. 4 , it is preferable that the connected portions  102  be arranged in the same pattern in all directions. Similarly, connection portions  202  of the robot  200  are arranged in the same pattern in all directions. According to this structure, when the robot  200  gets under the rack  100  in any direction, it is possible to exactly allocate the connection portions  202  to all of the connected portions  102 . Therefore, when the robot  200  accesses the rack  100  in any direction, it is possible to control any of the transfer units  101  of the rack  100 , without performing the posture control of the robot  200  below the rack  100  due to a turning operation, while minimizing the number of connected portions  102  and the number of connection portions  202 . 
     In  FIG. 3 , capital letters described in the connected portions  102  correspond to those of the transfer units  101  illustrated in  FIG. 3 . Among the connected portions  102  having the same capital letters, when potential is applied between a connected portion  102   a  having a small “a” and a connected portion  102   b  having a small “b”, a current flows through a corresponding transfer unit  101 . 
     The upper right corner of the contacted surface  103  illustrated in  FIG. 4  corresponds to the corner of the rack  100  in a direction in which the transfer units  101 A,  101 E, and  101 I are provided in  FIG. 3 . 
     In this embodiment, a direction from the transfer unit  101 A to the transfer unit  101 C, in which articles are moved, in  FIG. 3  is a forward direction. In a case in which the reversal of the moving direction of the transfer unit  101  can be controlled, for example, when the potential of the connected portion  102   a  is higher than that of the connected portion  102   b , the transfer unit  101  may be operated so as to move an article in the forward direction. When the potential between the connected portions  102   a  and  102   b  is reversed, the transfer unit  101  may be operated so as to move an article in a reverse direction. When the transfer speed of the transfer unit  101  is variable, for example, the transfer speed may change depending on the potential difference between the connected portions  102   a  and  102   b  or the absolute value of the amount of current. 
     It is considered that the robot  200  gets under the rack  100  in four directions. It is preferable to symmetrically arrange the connected portions  102  in four directions in order to appropriately control the transfer units  101  of the rack  100  when the robot  200  gets under the rack  100  in any direction. 
     Similarly, the connection portions  202  of the robot  200  are symmetrically arranged in four directions. Therefore, when the robot  200  gets under the rack  100  in any direction, the connection portions of the robot  200  can be connected to the corresponding connected portions  102 , while the robot maintains its posture, without being rotated. According to this structure, the robot  200  can check its direction with respect to the rack  100 . Therefore, it is possible to check the operational relationship between the connection portion  202  to which a current will flow and the transfer unit  101  to be operated and thus to appropriately control the transfer units  101  of the rack  100 . 
     In a case in which the robot  200  is loaded with the rack  100 , when there is a structure capable of recognizing a rack ID  906  of the rack  100  to be loaded, it is possible to check whether the robot  200  is loaded with the rack  100  corresponding to an instruction from the management computer  300 . When the loaded rack  100  does not correspond to the instruction, the robot  200  can issue an alarm to the management computer  300 . 
     When there is a structure in which the robot  200  can recognize a relative positional relationship with the rack  100 , it is possible to check whether the connection portions  202  of the robot  200  can be connected to the connected portions  102  of the rack  100 . When it is recognized that there is a connection load, the robot  200  can finely adjust its position. In order to achieve the structure, the rack  100  according to this embodiment includes a rack bottom marker  104  on the bottom of the rack. The rack bottom marker  104  is provided as, for example, a two-dimensional barcode. 
     Preferably, the rack  100  is a mechanism in which a plurality of transfer units  101  and a member that supports the transfer units  101  are detached from each other, in order to store the large-size article  140  that is larger than the storage space corresponding to one stage in a height direction. 
     In addition, it is preferable that the remaining transfer units  101  be controlled by the same method as the rack  100   a . For example,  FIG. 5  is a diagram illustrating an example of the structure of a rack  100   b  obtained by detaching transfer units  101 E to  101 H from the rack  100   a  illustrated in  FIG. 3 . A left figure illustrates a state in which no article is stored in the storage space and a right figure illustrates a state in which articles are stored in the storage space. In both the figures, an upper plate is transparent such that the inside of the rack is seen. As such, the transfer robot system  100   a  may include a plurality of types of racks  100 , such as the general rack  100   a  and the rack  100   b  for storing a large-size article  140 AH that is not accommodated in a storage space corresponding to one stage. 
       FIG. 6  is a diagram illustrating an example of the structure of the robot  200  according to this embodiment. A left figure is a diagram illustrating the outward appearance of the robot  200  and a right figure is a front view illustrating the internal structure of the robot  200 , as viewed from a direction opposite to a traveling direction  250  of the robot. In this embodiment, a control unit  211  that controls the operation of the robot  200  is divided into a robot main computer  206  and a connection portion feeding controller  205 . However, the robot main computer  206  and connection portion feeding controller  205  may be integrated into one device. 
     In this embodiment, the robot  200  gets under the rack  100  and operates a loading and unloading unit  201  to lift the rack  100 . The loading and unloading unit  201  is a mechanism which is provided at the upper part of the robot  200  and is operated to lift the rack  100 , and includes a motor, a motor controller, a gear and a shaft that convert a rotational motion into an up-and-down motion in the vertical direction, a controller that controls the motor, and an upper plate. 
     The loading and unloading unit  201  is connected to the power supply  204  and the robot main computer  206  and controls its motor to lift the upper plate on the basis of an instruction from the robot main computer  206 . The number of components other than the upper plate may be two or more. It is preferable that a plurality of motors be synchronized with each other to have the same motion, in order to keep the upper plate horizontal. 
     When the robot  200  lifts the rack  100 , first, the robot main computer  206  controls a driving unit  203  such that the robot  200  gets under the rack  100 . In this state, the robot main computer  206  instructs the loading and unloading unit  201  to control the motor such that the upper plate is lifted. The loading and unloading unit  201  gradually lifts the upper plate in response to the instruction. Then, the surface of the upper plate of the loading and unloading unit  201  reaches the height of the contacted surface  103  which is the bottom of the rack  100  and comes into contact with the contacted surface  103 . The surface of the upper plate of the loading and unloading unit  201  is referred to as a contact surface  207  since it comes into contact with the contacted surface  103  of the rack  100 . In addition, when the upper plate of the loading and unloading unit  201  is lifted, the legs of the rack  100  are separated from the ground and the rack  100  is in a lifted state. That is, the robot  200  is loaded with the rack  100  by the loading and unloading unit  201 . 
     When the rack  100  is installed while being loaded on the robot  200 , first, the robot main computer  206  controls the driving unit  203  such that the robot  200  is moved to the position where the rack  100  is installed. After the robot  200  arrives at the position, the robot main computer  206  instructs the loading and unloading unit  201  to control the motor such that the upper plate is dropped. The loading and unloading unit  201  drops the rack  100  while gradually dropping the upper plate in response to the instruction. Then, the legs of the rack  100  reach the ground and come into contact with the ground. When the upper plate of the loading and unloading unit  201  is dropped, the contact surface  207  of the robot  200  is separated from the contacted surface  103  of the rack  100  and the installation of the rack  100  is completed. 
     A plurality of connection portions  202  which are electrically connected to the connected portions  102  of the rack  100  are attached to the upper plate of the loading and unloading unit  201 . 
     In this embodiment, 24 connection portions  202   a  to  202   x  are attached, similarly to the number of connected portions  102  of the rack  100 . The connection portions  202  are connected to the connection portion feeding controller  205  through cables. In addition, a plurality of connection terminals  208  for charging which are electrically connected to connection terminals  501  for charging of the charging station  500  are attached to the upper plate of the loading and unloading unit  201 . In this embodiment, four connection terminals  208  for charging are attached and are connected to the power supply  204  through cables. 
     As such, according to the structure in which the robot is electrically connected to the rack  100  or the charging station  500  at the same time as it comes into contact with the rack  100  or the charging station  500  during a loading and unloading operation, it is not necessary to separately provide a contact portion and it is possible to reduce manufacturing limitations by an amount corresponding to the contact portion. In addition, the mobile power of the robot  200  which gets under the rack  100  is not lost. A method for connecting the robot  200  and the rack  100  and a method for connecting the robot  200  and the charging station  500  may be the same in order to simplify the mounting of the transfer robot system  10   a.    
     In this embodiment, the robot  200  operates the driving unit  203  to move. The driving unit  203  includes, for example, a motor, a motor controller, and wheels. In addition, the driving unit  203  may be provided with a rotary encoder for measuring the rotation of the wheels. 
     At least two motors and three wheels which are independently operated are required to achieve the two-dimensional movement of the robot  200 . For example, a structure is considered in which the robot  200  includes a left wheel and a right wheel, a motor and a motor controller for independently controlling the left and right wheels, and one caster. In this case, the robot  200  rotates the left and right wheels at the same speed to go straight and rotates the left and right wheels in the opposite direction to turn. The driving unit  203  is connected to the power supply  204  and the robot main computer  206  and controls its motor to move the robot  200  on the basis of an instruction from the robot main computer  206 . 
     The power supply  204  is, for example, a battery. The power supply  204  supplies power to the loading and unloading unit  201 , the driving unit  203 , the connection portion feeding controller  205 , the robot main computer  206 , a rack recognition sensor  209 , and a self-position recognition sensor  210  of the robot  200 . In this embodiment, power is indirectly supplied to the rack recognition sensor  209  and the self-position recognition sensor  210  through the robot main computer  206 . However, it may be determined whether to indirectly or directly supply power to each device, on the basis of the mounting of the device. 
     When the robot  200  operates the transfer units  101  of the rack  100 , the power supply  204  supplies power to the transfer units  101  of the rack  100  through the connection portion feeding controller  205 , the connection portions  202 , and the connected portions  102  of the rack  100 . In addition, the power supply  204  is connected to the connection terminal  208  for charging which is attached to the upper plate of the loading and unloading unit  201  through a cable. The connection terminal  208  for charging is provided on the assumption that it is connected to the connection terminal  501  for charging in the charging station  500 . The charging station  500  applies a potential difference between the connection terminals  208  for charging in the robot  200  through the connection terminals  501  for connection to change the power supply  204  of the robot  200 . In  FIG. 5 , the robot  200  includes two power supplies  204 . However, the number of power supplies  204  is not particularly limited. 
     In this embodiment, the robot  200  operates the connection portion feeding controller  205  to control the transfer units  101  of the rack  100 . The connection portion feeding controller  205  is connected to the connection portions  202 , the power supply  204 , and the robot main computer  206  and applies potential to each connection portion  202 , using the power supply  204 , in response to an instruction from the robot main computer  206 . When the connection portions  202  are connected to the connected portions  102  of the rack  100  and the connection portion feeding controller  205  applies potential to each connected portion  102 , a potential difference is generated between the connected portions  102   a  and  102   b  corresponding to the transfer unit  101 . Then, the transfer unit  101  is operated. In  FIG. 5 , the robot  200  includes two connection portion feeding controllers  205  which take charge of different groups of the connection portions  202 . However, the number of connection portion feeding controllers  205  is not particularly limited. 
     The robot main computer  206  is a combination of a CPU, a RAM, an external storage medium, and a wireless communication function. The external storage medium is, for example, an HDD or a flash memory and the wireless communication function is, for example, a wireless LAN. The robot main computer  206  is supplied with power from the power supply  204  and controls other devices in the robot  200 , that is, the loading and unloading unit  201 , the driving unit  203 , the connection portion feeding controller  205 , the rack recognition sensor  209 , and the self-position recognition sensor  210 . In addition, the robot main computer  206  communicates with the management computer  300 , using the wireless communication function to receive an operation command and to transmit an operation state. In addition, when the robot  200  transfers articles between the racks  100  together with other robots  200 , the robot main computer  206  communicates with other robots  200 , using the wireless communication function, to report situations. 
     In order to move the robot  200  along the moving path  904  received from the management computer  300 , the robot main computer  206  calculates the position and posture of the robot on the basis of the measurement result acquired by the self-position recognition sensor  210 , calculates the difference between the posture of the robot  200  based on the calculation results of the position and posture of the robot and the moving path  904  and a target moving direction, and determines the latest operation parameters of the driving unit  203  on the basis of the calculation result of the difference. 
     Here, the measurement result of the rotary encoder which is a component of the driving unit  203  may be acquired and used for self-position recognition or the determination of the operation parameters. In addition, in order to check the rack ID  906  of the rack  100  which will be transferred or has the transfer units  101  to be operated and to check the shift of the position and posture of the robot relative to the rack  100 , the rack bottom marker  104  of the rack  100  is read on the basis of the measurement result acquired by the rack recognition sensor  209 , the rack ID  906  of the rack  100  is recognized, and the shift of the position and posture of the robot  200  relative to the rack  100  is calculated. 
     The rack recognition sensor  209  is provided such that it can measure information on the upper side in the vertical direction in order to measure the rack bottom marker  104  of the rack  100  when the robot  200  gets under the rack  100 . The rack recognition sensor is selected according to the characteristics of the rack bottom marker  104 . For example, when the rack bottom marker  104  is a two-dimensional barcode, the rack recognition sensor  209  is, for example, a monochrome camera or a color camera. The rack recognition sensor  209  is connected to the robot main computer  206  performs measurement in response to an instruction from the robot main computer  206  and transmits the measurement result to the robot main computer  206 . 
     The self-position recognition sensor  210  is provided in order to recognize the position of the robot  200  when the robot  200  is moved along the moving path  904 , to check the shift of the robot  200  from the moving path  904 , and to calculate a control parameter to be transmitted to the driving unit  203 . The self-position recognition sensor  210  is selected according to a self-position recognition method. 
     For example, when a method is used which attaches floor markers  3001 , such as two-dimensional barcodes, to a floor  3000  in a lattice shape, reads the floor marker  3001 , and recognizes a position and posture, the self-position recognition sensor  210  is, for example, a monochrome camera or a color camera which is attached so as to face the floor. 
     When a method is used which acquires the configuration map of the entire space, calculates which part of the configuration map the shape of a part of the space measured by the robot  200  is matched with, and recognizes a position and posture, the self-position recognition sensor  210  is, for example, a laser distance sensor or a sonar that is attached in order to measure obstacles on the horizontal plane. A plurality of self-position estimation sensors  210  may be provided and the space measured by the robots  200  may be different types. 
     The rack recognition sensor  210  is connected to the robot main computer  206 , performs measurement in response to an instruction from the robot main computer  206 , and transmits the measurement result to the robot main computer  206 . 
     In this embodiment, the control unit  211  which controls the operation of the robot  200  is divided into the robot main computer  206  and the connection portion feeding controller  205  that controls the supply of power to the connection portions. However, the invention includes the structures described in other embodiments and is not limited thereto. The control unit  211  in which the robot main computer  206  and the connection portion feeding controller  205  are integrated with each other may be provided 
       FIG. 7  is a diagram illustrating an example of the structure of the contact surface  207  of the robot  200  in this embodiment. The contact surface  207  includes the connection portions  202 , of which the number is equal to the number of connected portions  102  of the rack  100 . In this embodiment, the contact surface  207  includes 24 connection portions  202 . The connection portion  202  is a metal spring that conducts electricity and is electrically connected to the connection portion feeding controller  205 . It is preferable that the connection portion  202  be as thin as possible such that it does not protrude from the connected portion  102 , in order to allow the movement control error of the robot  200  when connected to the rack  100 . Two or more contact terminals  208  for charging are needed. In this embodiment, four contact terminals  208  for charging are provided. The contact terminal  208  for charging is a metal spring, similarly to the connection portion  202 , and is electrically connected to the power supply  204 . 
       FIG. 8  is a diagram schematically illustrating an aspect of the connection between the connected portion  102  of the rack  100  and the connection portion  202  of the robot  200 . In  FIG. 8 , a left figure illustrates a state before the connection and a right figure illustrates a state after the connection. When the robot  200  gets under the rack  100  and operates the loading and unloading unit  201  to lift the upper plate, first, the leading end of the connection portion  202  comes into contact with the surface of the connected portion  102  and is electrically connected thereto. When the upper plate is further lifted, the spring of the connection portion  202  is compressed and the contacted surface  103  of the rack  100  and the contact surface  207  of the robot come into contact with each other. According to this structure, a load which is applied to the connected portion  102  and the connection portion  202  is only restoring force corresponding to the compression of the spring of the connection portion  202  and the contacted surface  103  and the contact surface  207  are subjected to a load corresponding to the weight of the rack  100 . In addition, the connection terminal  501  for charging in the charging station  500  and the contact terminal  208  for charging in the robot  200  may be the same type as the connected portion  102  of the rack  100  and the connection portion  202  of the robot  200 . 
     Next, the preparation (S 101 ) of the rack  100   x  illustrated in  FIG. 2  will be described.  FIG. 9  is a diagram schematically illustrating an aspect in which the rack  100   x  according to this embodiment is prepared.  FIG. 10  is a flowchart illustrating an example of the operation of the robots  200   x  and  200   y  at that time.  FIGS. 9 and 10  illustrate only an example of one scene of the preparation (S 101 ) of the rack  100   x  in this embodiment. According to the structure of the invention, articles can be transferred between the racks in various scenes other than this scene. In this scene, articles are exchanged between the lower storage spaces of the racks  100 . Therefore, in  FIG. 9 , the upper storage space and the middle storage space of the rack  100  are not illustrated. 
     In this example, one robot  200  is allocated to one rack  100  and articles are exchanged between the racks  100 . However, as illustrated in  FIG. 19 , the robot  200   x  may transfer the rack  100   x  to the vicinity of the rack  100   y  and electrically connect the rack  100   x  and the rack  100   y . Then, the robot  200   x  may control both the transfer units  101   x  of the rack  100   x  and the transfer units  101   y  of the rack  100   y  at the same time. In this case, it is possible to exchange articles between the racks  10  and to perform the task  902   x , using only one robot  200 . 
     In this case, for example, inter-rack connected portions  105  and inter-rack connection portions  106  are provided in frames of the side surfaces of the rack  100   x  and the rack  100   y , respectively, such that the rack  100   x  and the rack  100   y  can be electrically connected to each other. According to this structure, the robot  200   x  can control the operation of the transfer units  101  of the rack  100   x  and the rack  100   y . At that time, it is preferable that the connected portions  102  for controlling the operation of each transfer unit  101  of two racks  100  be provided on the contacted surface  103  of the rack  100   x  or  100   y . It is desirable that the connection portions  202  corresponding to the connected portions  102  of the rack  100  be provided on the contact surface  207  of the robot  200   x.    
     However, when an article is unloaded from the rack  100   x , which is a transfer target, to the rack  100   y  that does not need to be transferred, only the transfer units  101  of the rack  100   x  are operated to exchange an unnecessary article and a necessary article with the rack  100   y.    
     As such, only one transfer robot  200   x  is used to perform a loading operation and an unloading operation. Therefore, for example, when there are an excessive number of operations, it is possible to instruct a transfer operation using only one robot. As a result, it is possible to perform a large number of transfer operations using a small number of robots. 
     In the scene illustrated in  FIG. 9 , the rack  100   y  is installed in the vicinity of a wall surface  3002 . When the rack  100   y  is not moved, it is difficult to install the rack  100   x  in the vicinity of the wall surface  3002  and to exchange articles. Both the rack  100   x  and the rack  100   y  are the same type as the rack  100   a  illustrated in  FIG. 3 . For each transfer unit  101 , the letter “a” illustrated in  FIG. 3  is replaced with the letter “y” or “x”. The directions of the rack  100   x  and the rack  100   y  in  FIG. 9  are the same as the direction of the rack  100   a  illustrated in  FIG. 3 . 
     The management computer  300  instructs the robots  200   x  and  200   y  illustrated in  FIG. 9  to transfer a medium-size article  130   c  stored in the rack  100   y  to the rack  100   x  and to transfer a medium-size article  130   a  stored in the rack  100   x  to the rack  100   y , thereby preparing the rack  100   x . This operation is a portion of the task  902 . The management computer  300  has already made a plan for, for example, the moving paths  904   x  and  904   y  of the robots  200   x  and  200   y , the loading and installation time of the racks  100   x  and  100   y , and the control procedure and time of the transfer units  101   x  and  101   y  of the racks  100   x  and  100   y  (S 100  in  FIG. 2 ). The robots  200   x  and  200   y  are operated according to the planned instruction to prepare the rack  100   x  (S 101 ). 
     In the scene illustrated in  FIG. 9 , a state in which the medium-size article  130   c  is interposed between the wall surface  3002  and the medium-size article  130   b  changes to a state in which only the medium-size article  130   c  is stored in the lowest storage space of the rack  100   x , which is a portion of the task  902 . As a method for achieving this operation, for example, the following methods are considered: a method which transfers the rack  100   y  so as to be separated from the wall surface  3002 ; and a method which moves the medium-size article  130   b  to the rack  100   x , moves a target medium-size article  130   c  to the rack  100   x , and returns the medium-size article  130   b  to the rack  100   y.    
       FIGS. 9 and 10  illustrate an example in which the latter method is selected as the method according to this embodiment. 
     First, the robots  200   x  and  200   y  are moved to the positions of the racks  100   x  and  100   y  along the instructed moving paths  904   xa  and  904   ya , respectively ( FIG. 9( a )  and S 200  and S 300  in  FIG. 10 ). When the robots  200   x  and  200   y  arrive at the positions of the racks  100   x  and  100   y , that is, when the robots  200   x  and  200   y  get under the racks  100   x  and  100   y , respectively, they operate the loading and unloading portions  201   x  and  201   y  to load the racks  100   x  and  100   y  ( FIGS. 9( b ) and 9( c )  and S 201  and S 301  in  FIG. 10 ). Then, the robot  200   x  transfers the rack  100   x  to the position where articles can be exchanged between the rack  100   x  and the rack  100   y  along the instructed moving path  904   xb  ( FIG. 9( c )  and S 202  in  FIG. 10 ). In this example, the robot  200   y  does not transfer the rack  100   y . However, the robot  200   y  is loaded with the rack  100   y  in order to align the height since the robot  200   x  is loaded with the rack. 
     Then, the robots  200   x  and  200   y  move an article, which is stored in the rack  100   y  and is to be transferred to the work area, from the rack  100   y  to the rack  100   x  and move an article, which is stored in the rack  100   x  and is not to be transferred to the work area  2000 , from the rack  100   x  to the rack  100   y  (S 203  to S 205  and S 302  to S 304  in  FIG. 10 ). In this embodiment, an operation which moves the medium-size article  103   c  stored in the rack  100   y  to the rack  100   x  and moves the medium-size article  130   a  stored in the rack  100   x  to the rack  100   y  is given as an example. The operation of the robots  200   x  and  200   y  will be described in detail. 
     First, the medium-size article  130   a  is moved from the rack  100   x  to the rack  100   y  and the medium-size article  130   b  is temporarily moved from the rack  100   y  to the rack  100   x  (FIG.  9 ( d ) and S 203  and S 302  in  FIG. 10 ). The reason why the medium-size article  130   b  is moved is as follows. As described above, the medium-size article  130   c  stored in a transfer unit  101   y B needs to be moved to the rack  100   x  through a transfer unit  101   y D and the medium-size article  130   b  stored in the transfer unit  101   y D blocks the movement of the medium-size article  130   c.    
     After being ready to control the transfer units  101   x  of the rack  100   x , the robot  200   x  transmits a message indicating that the robot  200   x  is ready to control the transfer units  101   x  to the robot  200   y , using the wireless communication function of the robot main computer  206   x . When receiving the message, the robot  200   y  transmits a message indicating that the robot  200   y  is ready to control the transfer units  101   y  of the rack  100   y  to the robot  200   x , using the wireless communication function, after being ready to control the transfer units  101   y . Then, the robot  200   x  receives the message and recognizes that the robot  200   y  is ready to perform control. 
     When receiving the message, the robot  200   x  starts to control the transfer units  101   x . When transmitting the message, the robot  200   y  starts to control the transfer units  101   y . It is necessary to synchronize the control flow of the transfer units  101   x  and  101   y  between the robots  200   x  and  200   y  in order to exchange articles between the rack  100   x  and the rack  100   y  using the transfer units  101   x  and  101   y  and the message is transmitted and received in order to achieve the synchronization. The distance between the robots  200   x  and  200   y  is small enough to neglect a delay in wireless communication. 
     When the robot  200  controls the transfer units  101  of the rack  100 , the connection portion  202  to which potential will be applied varies depending on the position of the robot  200  relative to the rack  100 . In this embodiment, when planning the operation of the robot  200 , the management computer  300  determines to which of the connection portions  202  potential is applied, considering the direction of the rack  100 , and adds the information to an operation command to be transmitted to the robot  200 . As another method, when it is difficult for the management computer  300  to recognize the direction of the rack  100 , the robot  200  may recognize the posture of the rack  100 , using the rack recognition sensor  209 , and determine the connection portion  202  to which potential will be applied. 
     In addition, the time required to move an article corresponding to one set of the transfer units  101  (half of the size or the rack  100  or half mass) is measured in advance, the robot  200  stores the time as a parameter in the external storage medium of the robot main computer  206  and uses the time as the operating time of the transfer unit  101 . 
     The robot  200   x  appropriately applies potential to the connection portion  202   x , using the connection portion feeding controller  205   x , to operate the transfer unit  101   x B of the rack  100   x  in the forward direction by a distance corresponding to one set of the transfer units  101  and to operate the transfer units  101   x A and  101   x C in the reverse direction by a distance corresponding to one set of the transfer units  101 . In the case of  FIG. 9( d ) , the potential of a connection portion  202   xg  is higher than that of a connection portion  202   xh  in order to operate the transfer unit  101   x B in the forward direction. The potential of a connection portion  202   xb  is higher than that of a connection portion  202   xa  in order to operate the transfer unit  101   x A in the reverse direction. In addition, the potential of a connection portion  202   xn  is higher than that of a connection portion  202   xm  in order to operate the transfer unit  101   x C in the reverse direction. 
     At the same time, the robot  200   y  appropriately applies potential to the connection portion  202   y , using the connection portion feeding controller  205   y , to operate the transfer units  101   y B and  101   y D of the rack  100   y  in the forward direction by a distance corresponding to one set of the transfer units  101 . In the case of  FIG. 9( d ) , the potential of a connection portion  202   yg  is higher than that of a connection portion  202   yh  in order to operate the transfer unit  101   y B in the forward direction. The potential of a connection portion  202   ys  is higher than that of a connection portion  202   yt  in order to operate the transfer unit  101   y D in the forward direction. 
     As a result, the medium-size article  130   a  is moved from the transfer unit  101   x C to the transfer unit  101   x A of the rack  100   x . The medium-size article  130   b  is moved from the transfer unit  101   y D of the rack  100   y  to the transfer unit  101   x B of the rack  100   x . The medium-size article  130   c  is moved from the transfer unit  101   y B to the transfer unit  101   y D of the rack  100   y.    
     In addition, the robot  200   x  operates the transfer unit  101   x A in the reverse direction by a distance corresponding to one set of the transfer units  101 , using the connection portion feeding controller  205   x . The robot  200   y  operates the transfer unit  101   y C in the reverse direction by a distance corresponding to one set of the transfer units  101 , using the connection portion feeding controller  205   y . In the robot  200   x , the potential of the connection portion  202   xb  is high between the connection portions  202   xa  and  202   xb . In the robot  200   y , the potential of the connection portion  202   yn  is high between the connection portions  202   ym  and  202   yn . As a result, the medium-size article  130   a  is moved between the transfer unit  101   x A of the rack  100   x  to the transfer unit  101   y C of the rack  100   y.    
     Then, the medium-size article  130   c  is moved from the rack  100   y  to the rack  100   x  ( FIGS. 9( e ) and 9( f )  and S 204  and S 303  in  FIG. 10 ). 
     First, the position of the rack  100   x  is shifted by a distance corresponding to half mass and the robot  200   x  transfers the rack  100   x  along the instructed moving path  904   xc  such that the transfer unit  101   y L of the rack  100   y  comes into contact with the transfer unit  101   x I of the rack  100   x  ( FIG. 9( e ) ). 
     Immediately after the movement of the robot  200   x  is completed, the transfer units  101   x A and  101   y D are operated to move the medium-size article  130   c  ( FIG. 9( f ) ). In this case, similarly to S 203  and S 302  in  FIG. 10 , the robots  200   x  and  200   y  exchange a message indicating that they are ready to control the transfer units. Then, the robot  200   x  operates the transfer unit  101   x A in the forward direction by a distance corresponding to one set of the transfer units  101 , using the connection portion feeding controller  205   x , and the robot  200   y  operates the transfer unit  101   y D in the forward direction by a distance corresponding to one set of the transfer units  101 , using the connection portion feeding controller  205   y . In this case, the operations of the robots  200   x  and  200   y  are synchronized with each other. In the robot  200   x , the potential of the connection portion  202   xa  is higher than that of the connection portion  202   xb . In the robot  200   y , the potential of the connection portion  202   ys  is higher than that of the connection portion  202   yt . As a result, the medium-size article  130   c  is moved from the transfer unit  101   y D of the rack  100   y  to the transfer unit  101   x A of the rack  100   x.    
     Finally, the medium-size article  130   b  which is temporarily stored in the rack  100   x  is returned to the rack  100   y  ( FIGS. 9( g ) and 9( h )  and S 205  and S 304  in  FIG. 10 ). 
     First, the position of the rack  100   x  is shifted by a distance corresponding to one mass and the robot  200   x  transfers the rack  100   x  along the instructed moving path  904   xd  such that the transfer unit  101   y C of the rack  100   y  comes into contact with the transfer unit  101   x B of the rack  100   x  ( FIG. 9( g ) ). 
     Immediately after the movement of the robot  200   x  is completed, similarly to S 203  and S 302  in  FIG. 10 , the robots  200   x  and  200   y  exchange a message indicating that they are ready to control the transfer units. In this way, the robot  200   x  operates the transfer unit  101   x B in the reverse direction by a distance corresponding to one set of the transfer units  101 , using the connection portion feeding controller  205   x , and the robot  200   y  operates the transfer units  101   y A and  101   y C in the reverse direction by a distance corresponding to one set of the transfer units  101 , using the connection portion feeding controller  205   y  ( FIG. 9( h ) ). In this case, the operations of the robots  200   x  and  200   y  are synchronized with each other. In the robot  200   x , the potential of the connection portion  202   xh  is higher than that of the connection portion  202   xg . In the robot  200   y , the potential of the connection portion  202   yb  is higher than that of the connection portion  202   ya  and the potential of the connection portion  202   yn  is higher than that of the connection portion  202   ym . As a result, the medium-size article  130   a  is moved from the transfer unit  101   y C to the transfer unit  101   y A of the rack  100   y  and the medium-size article  130   b  is moved from the transfer unit  101   x B of the rack  100   x  to the transfer unit  101   y C of the rack  100   y.    
     As a result of this series of operations, the medium-size article  130   c  is stored in the rack  100   x  and the medium-size articles  130   a  and  130   b  are stored in the rack  100   y . Finally, the robot  200   y  operates the loading and unloading unit  201   y  to install the rack  100   y  ( FIG. 9( i )  and S 305  in  FIG. 10 ). Then, the process ends. 
     As such, in the transfer robot system  10   a  according to this embodiment, the robot  200  can move articles between the racks  100 . 
       FIG. 11  is a diagram illustrating an example of the structure of rack information  905  related to the rack  100  which is checked by the management computer  300  according to this embodiment. The rack information  905  includes a rack ID  906 , a rack type ID  917 , and a rack state  907 . The rack ID  906  is numbers for identifying the rack  100  and the rack type ID  917  is numbers for identifying the type of rack when there are a plurality of types of racks. 
     In this embodiment, it is assumed that, since there is no substantial difference between the rack  100   a  illustrated in  FIG. 3  and the rack  100   b  illustrated in  FIG. 5 , the same rack type ID  917  is given to the racks  100   a  and  100   b , without distinction. The rack state  907  includes a rack X coordinate  908 , a rack Y coordinate  909 , a rack Z coordinate  910 , a rack Θ coordinate  911 , and the storage states  912 A to  912 L of the transfer units  101 . The number of storage states  912  of the transfer units  101  is equal to the number of transfer units  101  which can be provided in the rack  100 . In this embodiment, the number of storage states  912  of the transfer units  101  is 12. 
     The rack X coordinate  908  and the rack Y coordinate  909  indicate the position of the rack  100  in the two-dimensional plane and the rack Θ coordinate  911  indicates the direction of the rack  100  in the two-dimensional plane. The rack Z coordinate  910  is the coordinate of the rack  100  in the vertical direction and indicates a height in a state in which the legs of the rack floor  3000  are on the ground. 
     The storage state  912  of the transfer unit  101  indicates whether the transfer unit  101  is present, the type of article stored, and the number of articles. The rack  100   a  illustrated on the right side of  FIG. 3  will be described as an example. A storage state  912   a J of a transfer unit  101   a J indicates “present, a medium-size article  130 J, and one”. 
     When 20 small-size articles  120 H are stored in a tray  120 H, a storage state  912   a H of a transfer unit  101   a H indicates “present, the small-size article  120 H, and  20 ”. 
     In addition, no article is stored in a transfer unit  101   a I. In this case, a storage state  912   a I of the transfer unit  101   a I indicates “present, no article, and 0”. 
     When the large-size article  140  is stored using a plurality of transfer units  101 , the type of article and the number of articles are input for one main transfer unit  101  and the main transfer unit  101  is input for the other transfer units. That is, for the transfer units  101   a A and  101   a B in which a large-size article  140 AB is stored, the storage state  910   a A of the transfer unit  101   a A indicating “present, the large-size article  140 AB, and one” is input and the storage state  912   a B of the transfer unit  101   a B indicating “present, the transfer unit  101   a A, and 0” is input. 
     In the rack  100   b  illustrated in  FIG. 5 , the middle transfer units  101   b E to  101   b H are removed. Then, “absent” is input to the item indicating whether the transfer unit  101   b  is present in the storage states  912   b E to  912   b H of the transfer units  101   b . On the left side of  FIG. 5 , the storage states  912   b E to  912   b H of the transfer units  101   b  indicating “absent, no article, and 0” are input. On the right side of  FIG. 5 , when the middle transfer units  101   b E to  101   b H are not removed, it is difficult to store the large-size article  140 AH. In this case, it is considered that the middle transfer units  101   b E to  101   b H take charge of the transfer of the large-size article  140 AH. 
     Therefore, the storage states  912   b E to  912   b H of the transfer units  101   b  indicating “absent, the transfer unit  101   b A, and 0” are input. In the description of the storage states, when the large-size article  140 AH is desired to be moved from the rack  100   b  illustrated on the right side of  FIG. 5  to another rack  100 , the rack state  907   b  of the rack  100   b  is checked to determine the size of the storage space required to store the large-size article  140 AH. 
       FIG. 12  is a diagram illustrating an example of the structure of the order  900  which is input to the management computer  300  in this embodiment. The order  900  includes a storage and delivery flag  913  and target article information  914  corresponding to the number of article types. In  FIG. 12 , the number of target article information items  913  is 3. However, the invention is not limited thereto. The storage and delivery flag  913  is a flag for designating storage or delivery. The target article information  914  includes the type of article to be stored or delivered and the number of articles. A set of a plurality of orders  900  is the order list  901 . 
       FIG. 13  is a diagram illustrating an example of the structure of the task  902  which is created by the management computer  300  to execute the order  900  in this embodiment. The task  902  includes rack state transition information  915  corresponding to the number of related racks  100 .  FIG. 13  illustrates the task  902  when the rack  100   x  and the rack  100   y  are related. The number of related racks  100  is not particularly limited. 
       FIG. 14  is a diagram illustrating an example of the structure of the state transition information  915  of the rack  100  in this embodiment. The state transition information  915  of the rack  100  includes the rack ID  906 , the rack type ID  917 , the rack state  907 , and a synchronization control rack ID  916 . The state transition information  915  includes a plurality of rack states  907  and a plurality of synchronization control rack IDs  916 . The number of rack states  907  is one greater than the number of synchronization control rack IDs  916 .  FIG. 14  illustrates an example in which the number of rack states  907  is 7. However, the number of rack states  907  is not limited thereto. 
     How the rack state  907  of the rack  100  has changed is described in the state transition information  915  of the rack  100  and the state transition information  915  of the rack  100  includes the position ( 908  to  910 ) and direction ( 911 ) of the rack  100 , the number of times the article ( 912 ) stored in the transfer unit  101  is moved, and the rack state  907 . The rack state  907   a  of the rack  100  when the task  902  starts is certainly described. The movement of the rack  100  is represented by a combination of linear changes in the coordinates and the rack state  907  of each node is input. For example, when a series of motions of the rack  100  includes a first translational motion, turning, and a second translational motion, a total of four rack states  907   a  to  907   d , that is, a rack state  907   a  when the task  902  starts, a rack state  907   b  after the first translational motion, a rack state  907   c  after turning, and a rack state  907   d  after the second translational motion are described. 
     Here, when articles are exchanged between the racks  100   x  and  100   y , it is necessary to synchronize the operations of the racks, as described above. When the rack  100   x  changes from a rack state  907   xe  to a rack state  907   xf  after it is synchronized with another rack  100   y , the rack ID  906   y  of the rack  100   y  is input to the synchronization control rack ID  916   f  corresponding to the rack state  907   xf . In addition, for a synchronization control rack ID  916   xb  corresponding to a rack state  907   xb  of the rack  100   x  indicating the operation result of the rack  100   x  when the rack  100   x  is independently operated without any synchronization, a number indicating “nothing” is input. Here, when the transfer of the rack  100   x  to the work area  2000  by the robot  200   x  is completed, the robot  200   x  notifies the management computer  300  of the arrival of the rack. Then, after receiving information indicating the completion of an operation from the operator  20 , the management computer  300  instructs the robot  200   x  to resume movement and the robot  200   x  resumes movement. When a number indicating the user interface  400  which is installed in the work area  2000  is input to a synchronization control rack ID  916   xp  corresponding to a rack state  907   xp  indicating the transfer result of the rack  100   x  after the resumption of movement, it is possible to wait for a report on the completion of the operation from the operator  20  through the management computer  300 . 
     The management computer  300  determines a related robot  200  and plans the operation of the robot  200 , on the basis of the task  902  illustrated in  FIG. 13  (S 100 ). 
     According to the transfer robot system  10   a  of this embodiment, a lift height is shifted between the racks  100  by a value corresponding to the storage space. Therefore, it is possible to exchange articles between the storage spaces with different heights. 
       FIG. 15  is a diagram illustrating an aspect in which articles are exchanged between the storage spaces with different heights in this embodiment. In the scene illustrated in  FIG. 15 , in order to move a medium-size article  130   p  which is stored in a transfer unit  101   p I located at the top of the rack  100   p  to a transfer unit  101   p G located in the middle of the rack  100   q , a robot  200   q  operates the loading and unloading unit  201  to lift a rack  101   q  by a distance corresponding to the height of a storage space, thereby aligning the height of the top of the rack  100   p  with the height of the middle of the rack  100   q . In this state, the robot  200   p  operates a connection portion feeding controller  205   p  such that the transfer unit  101   p I of the rack  100   p  is operated in the reverse direction and the robot  200   q  operates a connection portion feeding controller  205   q  such that the transfer unit  101   q G of the rack  100   q  is operated in the reverse direction. In this way, it is possible to move the medium-size article  130   p  from the transfer unit  101   p I located at the top of the rack  100   p  to the transfer unit  101   q G located in the middle of the rack  100   q.    
     As illustrated in  FIG. 15 , the exchange of articles between the storage spaces with different heights is performed in stages a plurality of number of times. Therefore, when the loading and unloading unit  201  of the robot  200  can lift the rack  100  by a height corresponding to one storage space of the rack  100 , it is possible to move the article stored in the transfer unit  101  located at the top of the rack  100  to the transfer unit  101  located at the bottom of the rack  100 . 
     In the above-mentioned embodiment, a transfer robot system includes a plurality of movable racks each of which includes a transfer unit for moving a stored article, at least one robot that is capable of transferring a predetermined rack to a predetermined position, and a management terminal that issues a transfer instruction to the robot. The robot detachably holds the rack and includes a connection portion that can be electrically connected to the rack, a driving unit, and a control unit. The control unit moves the robot to a vicinity of a first rack, using the driving unit, connects the robot to the first rack through the connection portion, moves the robot and the first rack to a vicinity of a second rack, supplies power to the transfer unit of the first rack or/and the second rack through the connection portion, operates the transfer unit corresponding to a position where an article to be moved is placed, and moves the article to be moved from a rack in which the article to be moved is placed to a predetermined position of another rack. 
     As such, according to the above-described embodiment, in a normal movement mode, it is not necessary to carry a heavy body, such as a multi-stage storage space. In addition, when an article is transferred, it is possible to exchange the stored articles or trays between the racks and to transfer the rack in which a plurality of necessary articles or trays are stored. As such, in the transfer robot system which can carry a large number of articles at one time, it is possible to achieve an automated transfer technique which has high transfer time efficiency and high energy efficiency in both the normal movement mode and an article transfer mode. 
     Embodiment 2 
     In this embodiment, an example of a transfer robot system  10   b  which can exchange articles between storage spaces with different heights even when a loading and unloading unit  201  of a robot  200  does not have capability to lift a rack  100  by a height corresponding to one storage space of the rack  100  will be described. 
       FIG. 16  is a diagram illustrating an example of the structure of the transfer robot system  10   b  according to this embodiment. The transfer robot system  10   b  includes two or more racks  100 , two or more robots  200 , a management computer  300 , a user interface  400 , a charging station  500 , and a stage change transfer rack  600 . In this embodiment, the rack  100 , the robot  200 , the management computer  300 , the user interface  400 , and the charging station  500  have the same structure and basic function as those in Embodiment 1 and thus the description thereof will not be repeated. In addition, in this embodiment, a storage area  1000 , a work area  2000 , and an operator  20  are located at the same position as those in Embodiment 1 and thus the description thereof will not be repeated. 
     The transfer robot system  10   b  according to this embodiment differs from the transfer robot system  10   a  according to Embodiment 1 in that the stage change transfer rack  600  is newly provided and is used to exchange articles between storage spaces with different heights in two racks  100 . 
       FIG. 17  is a diagram illustrating an example of the structure of the stage change transfer rack  600  according to this embodiment. The stage change transfer rack  600  has a similar structure to the rack  100  and comes into contact with and is electrically connected to the robot  200 , similarly to the rack  100 . Therefore, a contacted surface  103 , a connected portion  102 , and a rack bottom marker  104  are the same as those in the rack  100 . In addition, the stage change transfer rack  600  has the same transfer units  101  as the rack  100 . The robot  200  transfers the stage change transfer rack  600 , using the loading and unloading unit  201  and the driving unit  203 , and controls the transfer unit  101  of the stage change transfer rack  600 , using the connection portion feeding controller  205 . A method for controlling the transfer unit  101  of the stage change transfer rack  600  is the same as the method for controlling the transfer unit  101  of the rack  100 . In this embodiment, the stage change transfer rack  600  includes 12 transfer units  101 , of which the number is equal to the number of transfer units  101  in the rack  100 . However, the numbers of transfer units may be different from each other. 
     The structure of the stage change transfer rack  600  differs from the structure of the rack  100  in that the transfer units  101  of the stage change transfer rack  600  can transfer articles to storage spaces with different heights and are provided so as to be inclined. In the stage change transfer rack  600  according to this embodiment, transfer units  101 A,  101 C, and  101 E can be operated in the forward direction to transfer an article from the middle to the bottom of the rack and can be operated in the reverse direction to transfer an article from the bottom to the middle of the rack. Similarly, transfer units  101 G,  101 I, and  101 K can be operated in the forward direction to transfer an article from the top to the middle of the rack and can be operated in the reverse direction to transfer an article from the middle to the top of the rack. 
       FIG. 18  is a diagram illustrating an aspect in which articles are exchanged between storage spaces with different heights in Embodiment 2. Specifically, a stage change transfer rack  600   v  is used to move a medium-size article  130   v  which is stored in a transfer unit  101   w K located at an upper storage space of a rack  100   w  to a transfer unit  101   u E located at a middle storage space of a rack  100   u  and to move a large-size article  140   v  which is stored in transfer units  101   w G and  101   w H located at a middle storage space of the rack  100   w  to transfer units  101   u A and  101   u B located at a lower storage space of the rack  100   u.    
     In this embodiment, the rack  100   u , the stage change transfer rack  600   v , and the rack  100   w  are operated by robots  200   u ,  200   v , and  200   w , respectively. 
     Here, the movement of the medium-size article  130   v  will be described. First, the robots  200   w  and  200   v  are synchronized with each other and simultaneously operate a transfer unit  101   w K of the rack  100   w  and a transfer unit  101   v K of the stage change transfer rack  600   v  in the forward direction by a distance corresponding to one set of the transfer units  101  to move the medium-size article  130   v  to the stage change transfer rack  600   v . Then, the robot  200   v  simultaneously operates the transfer units  101   v K and  101   v I of the stage change transfer rack  600   v  in the forward direction by a distance corresponding to one set of the transfer units  101 . Then, the robot  200   v  simultaneously operates the transfer units  101   v G and  101   v I in the forward direction by a distance corresponding to one set of the transfer units  101  and stops the transfer units at one time. 
     Then, the robots  200   v  and  200   u  are synchronized with each other and operate the transfer unit  101   v G of the stage change transfer rack  600   v  and a transfer unit  101   v A of the rack  100   v  in the forward direction by a distance corresponding to one set of the transfer units  101 . Then, the medium-size article  130   v  is moved to the transfer unit  101   v A of the rack  100   v . As a result, the object is achieved. The large-size article  140   v  can be moved by the same process as described above. The large-size article  140   v  may be moved at the same time as the medium-size article  130   v.    
     In this embodiment illustrated in  FIG. 18 , three robots  200  are used. However, only two robots  200  may be used to achieve the exchange of articles using the stage change transfer rack  600   v . For example, the robot  200   w  illustrated in  FIG. 18  also functions as the robot  200   u . The following method is considered. First, the robot  200   w  controls the transfer unit  101   w  of the rack  100   w , moves to the rack  100   u , and controls the transfer unit  101   u  of the rack  100   u.    
     In this embodiment, the stage change transfer rack  600  is treated as a kind of rack  100 . The stage change transfer rack  600  may also function as the rack  100  or the rack  100  may not be provided. When the transfer robot system  10   b  according to this embodiment uses the rack  100  illustrated in  FIG. 3  or  FIG. 5  and the stage change transfer rack  600  illustrated in  FIG. 17 , the rack  100  and the stage change transfer rack  600  are distinguished from each other by rack type IDs  917  included in rack information  905  or rack state transition information  915 . 
     In Embodiment 1, when articles are exchanged between the upper storage space of the rack  100   p  and the lower storage space of another rack  100   q , the robot  200  needs to lift the rack  100   q  by a height corresponding to at least one storage space and the loading and unloading unit  201  needs to have a stroke corresponding to the height. In this embodiment, since the stage change transfer rack  600  is introduced, the loading and unloading unit  201  has only a sufficient stroke to lift the rack  100  or the stage change transfer rack  600 . Therefore, it is possible to simplify the structure of the robot  200 . 
     REFERENCE SIGNS LIST 
     
         
         
           
               10  TRANSFER ROBOT SYSTEM 
               20  OPERATOR 
               30  ADMINISTRATOR 
               100  RACK 
               101  TRANSFER UNIT 
               102  CONNECTED PORTION 
               103  CONTACTED SURFACE 
               104  RACK BOTTOM MARKER 
               105  INTER-RACK CONNECTED PORTION 
               106  INTER-RACK CONNECTION PORTION 
               110  TRAY 
               120  SMALL-SIZE ARTICLE 
               130  MEDIUM-SIZE ARTICLE 
               140  LARGE-SIZE ARTICLE 
               200  ROBOT 
               201  LOADING AND UNLOADING UNIT 
               202  CONNECTION PORTION 
               203  DRIVING UNIT 
               204  POWER SUPPLY 
               205  CONNECTION PORTION FEEDING CONTROLLER 
               206  ROBOT MAIN COMPUTER 
               207  CONTACT SURFACE 
               208  CONNECTION TERMINAL FOR CHARGING 
               209  RACK RECOGNITION SENSOR 
               210  SELF-POSITION RECOGNITION SENSOR 
               211  CONTROL UNIT 
               250  ROBOT TRAVELING DIRECTION 
               300  MANAGEMENT TERMINAL 
               310  MANAGEMENT TERMINAL FUNCTION 
               320  TASK LIST CREATION FUNCTION 
               321  ORDER LIST INPUT FUNCTION 
               322  ORDER LIST REORDERING FUNCTION 
               323  TARGET ARTICLE STORAGE RACK LIST DRAWING FUNCTION 
               324  TARGET RACK SELECTION FUNCTION 
               325  FUNCTION OF EXAMINING EXCHANGE OF ARTICLES BETWEEN TARGET RACKS 
               326  RACK STATE TRANSITION INFORMATION GENERATION FUNCTION 
               330  SYSTEM OPERATION PLANNING FUNCTION 
               331  ROBOT SELECTION FUNCTION 
               332  ROBOT OPERATION PLANNING FUNCTION 
               333  USER INTERFACE OPERATION PLANNING FUNCTION 
               340  TASK LIST EXECUTION MANAGEMENT FUNCTION 
               341  TASK LIST PROGRESS MANAGEMENT FUNCTION 
               342  INDIVIDUAL TASK PROGRESS MANAGEMENT FUNCTION 
               343  ROBOT STATE MANAGEMENT FUNCTION 
               344  RACK INFORMATION UPDATE FUNCTION 
               345  ROBOT COMMUNICATION FUNCTION 
               346  USER INTERFACE COMMUNICATION FUNCTION 
               400  USER INTERFACE 
               500  CHARGING STATION 
               501  CONNECTION TERMINAL FOR CHARGING 
               600  STAGE CHANGE TRANSFER RACK 
               900  ORDER 
               901  ORDER LIST 
               902  TASK 
               903  TASK LIST 
               904  MOVING PATH 
               905  RACK INFORMATION 
               906  RACK ID 
               907  RACK STATE 
               908  RACK X COORDINATE 
               909  RACK Y COORDINATE 
               909  RACK Z COORDINATE 
               911  RACK  0  COORDINATE 
               912  STORAGE STATE OF TRANSFER UNIT 
               913  STORAGE AND DELIVERY FLAG 
               914  TARGET ARTICLE INFORMATION 
               915  RACK STATE TRANSITION INFORMATION 
               916  SYNCHRONIZATION CONTROL RACK ID 
               917  RACK TYPE ID 
               1000  STORAGE AREA 
               2000  WORK AREA 
               3000  FLOOR 
               3001  FLOOR MARKER 
               3002  WALL SURFACE