Patent Publication Number: US-2022226923-A1

Title: Welding method, identification sign assignment device, and weldment

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of PCT International Patent Application No. PCT/JP2020/037365 filed on Sep. 30, 2020, which claims the benefit of priority of Japanese Patent Application No. 2019-188154 filed on Oct. 11, 2019, the entire contents of which are incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to a welding method, an identification sign assignment device, and a weldment. 
     BACKGROUND 
     JP-A-2017-102548 discloses a production management device that manages production performance information on a production line in which a plurality of production machines are arranged. The production management device detects which production machine a workpiece supplied to the production line is located in, generates an identifier unique to the workpiece when it is detected that the workpiece is located in any production machine, notifies the production machine in which the workpiece is located, and receives and records the generated identifier and the production performance information at the time of processing the workpiece corresponding to the identifier from the production machine. Each time the workpiece is sequentially moved to each of a plurality of production machines, the production management device records a plurality of identifiers generated for the workpiece and identifiers of products completed by the workpiece in association with each other. 
     SUMMARY 
     The present disclosure provides a welding method that supports more efficient management of an identifier of a workpiece produced in a process such as welding, an identification sign assignment device, and a weldment. 
     The present disclosure provides a welding method to be executed by a welding system, wherein identification signs are arranged on a plurality of original workpieces to be used in a welding process, respectively, the identification signs on which identifiers of the respective original workpieces are readable, the welding method including: executing the welding process such that a part or an entire of an identification sign is hidden in a joint surface on which the plurality of original workpieces are joined in the welding process. 
     The present disclosure provides an identification sign assignment device configured to assign identification signs to a plurality of original workpieces to be used in a welding process executed by a welding system, respectively, the identification sign assignment device including: a communication unit configured to acquire welding information including information on identifiers of the respective original workpieces and information on an identifier that is not selected as an identifier of a welded workpiece to be produced in the welding process among the identifiers of the plurality of original workpieces; and a processor configured to control a laser oscillator, the laser oscillator being configured to assign the identification signs based on the received welding information, the identification signs on which information on the identifiers corresponding to the respective original workpieces are readable. The identification signs are assigned such that a part or an entire of an identification sign of an original workpiece having the identifier that is not selected as the identifier of the welded workpiece is located on a joint surface on which the plurality of original workpieces are joined by the welding process. 
     The present disclosure provides a weldment produced by execution of a welding process by a welding system, the weldment being produced by: a process of arranging identification signs on a plurality of original workpieces to be used in a welding process, the identification signs on which identifiers of the respective original workpieces are readable; and a process of executing the welding process so as to hide a part or an entire of an identification sign assigned at a position of a joint surface on which the plurality of original workpieces are joined in the welding process. 
     According to the present disclosure, it is possible to support more efficient management of an identifier of a workpiece produced in a process such as welding. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram showing a system configuration example of a welding system. 
         FIG. 2  is a diagram showing an internal configuration example of a host device and a laser device according to a first embodiment. 
         FIG. 3  is a diagram showing an internal configuration example of the host device, a robot control device, and a reading device according to the first embodiment. 
         FIG. 4  explanatory diagram showing an example of an operation outline at the time of welding using a workpiece with an ID “A”, a workpiece with an ID “B”, a workpiece with an ID “C”, and a workpiece with an ID “D”. 
         FIG. 5  is a diagram showing an example of a correspondence table between IDs of selected welded workpieces and management IDs. 
         FIG. 6  is a sequence diagram showing an arrangement setting procedure of an identification sign in the welding system according to the first embodiment. 
         FIG. 7  is a sequence diagram showing an example of an operation procedure of ID management in the welding system according to the first embodiment. 
         FIG. 8  is a diagram showing an internal configuration example of a host device, a robot control device, and a reading device according to a second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     (Introduction to Present Disclosure) 
     According to JP-A-2017-102548, a production management device can manage traceability data for each workpiece. However, in the configuration of JP-A-2017-102548, different identifiers are newly assigned each time the same workpiece is located in a plurality of different production machines. In other words, each time one workpiece is sequentially located on another production machine in a production line, the one workpiece has a plurality of different identifiers. Therefore, for example, when a plurality of workpieces are joined and another workpiece is produced as in a welding process, if a new identifier is assigned to the produced workpiece in accordance with JP-A-2017-102548, a relationship between an identifier of the workpiece used in the welding process and an identifier of the produced workpiece may be complicated, and thus it may be difficult to use traceability related to the produced workpiece. That is, management of the identifier of the workpiece is complicated, and work efficiency of a system administrator is deteriorated. 
     Therefore, in the following embodiments, examples of a welding method, an identification sign assignment device, and a weldment that support more efficient management of the identifier of the workpiece produced in a process such as welding will be described. 
     Hereinafter, embodiments specifically disclosing a welding method, an identification sign assignment device, and a weldment according to the present disclosure will be described in detail with reference to the drawings as appropriate. However, an unnecessarily detailed description may be omitted. For example, a detailed description of a well-known matter or a repeated description of substantially the same configuration may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate understanding of those skilled in the art. It should be noted that the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure, and are not intended to limit the range of the claims. 
     First Embodiment 
     The welding system according to the first embodiment acquires information on identifiers of a plurality of original workpieces, and selects an identifier to be adopted as an identifier of a produced welded workpiece (that is, a weldment, the same shall apply hereinafter.) according to a predetermined rule based on completion of execution of a welding process using the plurality of original workpieces. The welding system sets the selected identifier as the identifier of the welded workpiece produced in the welding process. Hereinafter, the workpiece used in the welding process is defined as an “original workpiece”, and the workpiece produced in the welding process (that is, the weldment) is defined as a “welded workpiece”. The “welded workpiece” may be referred to as a “secondary workpiece” or an “n-th workpiece” (n: an integer of 2 or more). 
     (Configuration of Welding System) 
       FIG. 1  is a schematic diagram showing a system configuration example of a welding system  100 . The welding system  100  includes a host device  1  connected to each of an external storage ST, an input interface UI 1 , and a monitor MN 1 , a plurality of robot control devices (for example, robot control devices  2   a  and  2   b ), a plurality of main welding robots (for example, main welding robots MC 1   a  and MC 1   b ), a laser device  3 , and a reading device  5 . The robot control device  2   a  is provided corresponding to the main welding robot MC 1   a , the robot control device  2   b  is provided corresponding to the main welding robot MC 1   b , and the same number of robot control devices are similarly provided corresponding to one main welding robot. The number of the laser devices  3  and the number of the reading devices  5  are not limited to one, and may be plural. 
     The host device  1  is connected to the monitor MN 1 , the input interface UI 1 , the laser device  3 , the reading device  5 , and the external storage ST so as to be able to input and output data, and is further connected to each of the plurality of robot control devices  2   a ,  2   b , and so on so as to be able to communicate data. The host device  1  may include a terminal device P 1  integrally including the monitor MN 1  and the input interface UI 1 , and may further integrally include the external storage ST. In this case, the terminal device P 1  is a personal computer (PC) used by a user business operator prior to execution of a welding process (for example, main welding). The terminal device P 1  is not limited to the PC described above, and may be a computer device having a communication function, such as a smartphone or a tablet terminal. 
     The host device  1  stores design data for each original workpiece or each welded workpiece input by the user business operator in the memory  12  or the external storage ST. The design data is data created using a design support tool such as computer aided design (CAD). The host device  1  acquires information on a joint surface of a welded workpiece based on workpiece-related information including information on a welding portion and a joint surface of the main welding (so-called welding process) executed by the main welding robots MC 1   a , MC 1   b , and so on, information on a supplier, information on a specification of the workpiece, and the like, and design data, and selects an ID of the welded workpiece (for example, a secondary workpiece, and a welded workpiece produced by two or more welding processes) from IDs of a plurality of original workpieces used for production of the welded workpiece in advance according to a predetermined rule. 
     The host device  1  acquires the design data of each of the plurality of original workpieces, and sets an arrangement position of an identification sign on which an ID of the original workpiece selected as an ID of the welded workpiece produced in a predetermined welding process is readable so as to be assigned at a position readable after the predetermined welding process. On the other hand, the host device  1  sets the identification sign on which an ID of the original workpiece unselected as the ID of the welded workpiece produced in the predetermined welding process is readable so that the identification sign is assigned in the joint surface on which the plurality of original workpieces are joined in the predetermined welding process at a position where the identification sign cannot be read. Further, the host device  1  generates a pattern of the identification sign assigned to each of the plurality of original workpieces, and stores the pattern in the external storage ST in association with the ID of each of the plurality of original workpieces. The host device  1  generates an execution command for assigning an identification sign having the generated pattern to the arrangement position of the identification sign set for each of the plurality of original workpieces, and transmits the execution command to the laser device  3 . The host device  1  may store the IDs of the plurality of original workpieces, the patterns of the identification signs on which the IDs can be read, and the information on the arrangement positions of the identification signs in the external storage ST in association with each other. 
     Here, the identification sign is an identification sign on which the ID set for the original workpiece or the welded workpiece is readable, and is, for example, a two-dimensional barcode, a QR code (registered trademark), a barcode, an IC tag, or an RF tag. The identification sign may be directly arranged (that is, marked) on the workpiece by a laser, or may be arranged by attaching the IC tag or the RF tag. The identification sign may be directly arranged (that is, marked) on the original workpiece by the laser device  3 , or may be arranged by attaching the IC tag or the RF tag by another robot (not shown). 
     The arrangement positions of the respective identification signs of the original workpiece set by the host device  1  will be described. The identification sign of the original workpiece having the ID unselected as the ID of the welded workpiece produced by the execution of the predetermined welding process is partially or entirely hidden on the joint surface to be joined by the execution of the predetermined welding process, and is arranged at an arrangement position that is unreadable after the execution of the predetermined welding process. When the code itself has an error correction function of restoring data when a part of the code is stained or lost, for example, a two-dimensional barcode, the host device  1  sets the arrangement position so that the error correction function of the identification code is disabled, that is, a part or an entire of the identification sign is assigned in the joint surface. Accordingly, the welding system  100  according to the first embodiment can prevent the identification sign of the original workpiece having the ID that is not erroneously selected from being read. 
     When the process of arranging the identification signs by the laser device  3  is completed, the host device  1  proceeds to the process of main welding using the workpiece on which the identification signs are arranged. The host device  1  integrally controls the execution of the main welding (so-called welding process) executed by the corresponding main welding robots MC 1   a , MC 1   b , and so on via each of the plurality of robot control devices  2   a ,  2   b , and so on. For example, the host device  1  reads, from the external storage ST, welding-related information input or set in advance by the user business operator (for example, a welding operator or a system administrator. The same applies hereinafter), generates a welding process execution command including a part of contents of the welding-related information based on the welding-related information, and transmits the generated execution command to the corresponding robot control device (for example, the robot control device  2   a ). The execution command of the main welding described above is not limited to being generated by the host device  1 , and may be generated by, for example, an operation panel (for example, a programmable logic controller (PLC)) of equipment in a factory or the like in which the main welding is performed, or an operation panel (for example, a teach Pendant (TP)) of the robot control devices  2   a ,  2   b , and so on. The teach pendant (TP) is a device for operating the main welding robots MC 1   a , MC 1   b , and so on connected to the robot control devices  2   a ,  2   b , and so on. 
     Here, the welding-related information is information indicating the content of the welding process executed for each main welding robot, and is created in advance for each welding process and registered in the external storage ST. The welding-related information includes, for example, the number of original workpieces required for the welding process, an identifier (hereinafter, abbreviated as “ID”) of the original workpiece used in the welding process, workpiece information including a name and a welding portion of the original workpiece, an execution scheduled date on which the welding process is scheduled to be executed, the number of welded workpieces, and various welding conditions at the time of the welding process. The welding-related information is not limited to data of items described above. The robot control device (for example, the robot control device  2   a ) causes the main welding robot (for example, the main welding robot MC 1   a ) to perform the welding process using the plurality of original workpieces designated by the execution command based on the execution command transmitted from the host device  1 . In the present specification, the type of the welding process is not limited, but in order to make the description easy to understand, a process of joining each of the plurality of original workpieces will be described as an example (see  FIG. 4 ). 
     The host device  1  acquires the above-described welding-related information from the external storage ST, generates the welding process execution command using the plurality of original workpieces based on the welding-related information, and transmits the execution command to the corresponding robot control devices  2   a ,  2   b , and so on. When the host device  1  is notified of the completion of the welding process from the corresponding robot control devices  2   a ,  2   b , and so on after the completion of the welding process by each of the main welding robots MC 1   a , MC 1   b , and so on, the host device  1  generates welding process logical data (see  FIG. 4 ) corresponding to the welding workpiece produced by the welding process. 
     When the welding process logical data corresponding to the welded workpiece is generated, the host device  1  stores the ID of the welded workpiece, the welding process logical data, and a management ID (see  FIG. 6 ) used by the user business operator in the external storage ST in association with each other. At this time, the host device  1  associates the workpiece-related information and the welding-related information on the unselected original workpiece with the ID of the unselected original workpiece indicated by the welding process logical data, and stores the information in the external storage ST. Accordingly, the host device  1  can appropriately manage the ID of the original workpiece having the ID unselected as the ID of the welded workpiece after the execution of the welding process, and can produce the weldment in which only one identification sign readable as the ID of the welded workpiece is arranged. Therefore, the user business operator limits the number of identification signs to be read at the time of reading the ID of the welded workpiece to one, thereby facilitating the ID management of the welded workpiece. Such a method of assigning the identification sign is more useful for the welded workpiece produced by executing a plurality of welding processes. 
     The host device  1  receives pattern information on the identification sign read by the reading device  5  from the reading device  5  capable of reading the identification sign arranged for each of the original workpiece and the welded workpiece. Based on the received pattern information on the identification sign, the host device  1  acquires information on the ID set for the original workpiece or the welded workpiece read by the reading device  5  from the external storage ST, and transmits the information to the reading device  5 . Here, the information acquired by the host device  1  is not limited to the information on the IDs set for the plurality of original workpieces or welded workpieces, and may include, for example, workpiece-related information, welding-related information, welding process logical data, and management IDs (see  FIG. 6 ) stored in association with the IDs. 
     The monitor MN 1  may be configured with a display device such as a liquid crystal display (LED) or an organic electroluminescence (EL). The monitor MN 1  may display, for example, a screen indicating the welding process logical data including the ID of the welded workpiece, which is output from the host device  1 . Instead of the monitor MN 1  or together with the monitor MN 1 , a speaker (not shown) may be connected to the host device  1 , and the host device  1  may output the ID included in the welding process logical data by voice via the speaker. 
     The input interface UI 1  is a user interface that detects an input operation of the user business operator and outputs the input operation to the host device  1 , and may be configured using, for example, a mouse, a keyboard, or a touch panel. The input interface UI 1  receives, for example, an input operation when the user business operator creates the workpiece-related information or the welding-related information, or an input operation when a welding process execution command is transmitted to the robot control device  2   a.    
     The laser device  3  as an example of the identification sign assignment device is a device that assigns the identification sign to the workpiece based on an execution instruction received from the host device  1 . In the welding system  100  according to the first embodiment, an example in which the identification sign is assigned to the workpiece by the laser device  3  will be described, whereas the device to which the identification sign is assigned is not limited to the laser device  3 . For example, when the identification sign is assigned by attaching to a workpiece such as the IC tag or the RF tag, the laser device  3  may be omitted, and the attachment of the IC tag or the RF tag may be implemented by another robot (not shown). 
     The reading device  5  is a device that reads the identification sign assigned to each workpiece and outputs information on the ID set for the original workpiece or the welded workpiece, and may include, for example, a camera, a charge coupled device (CCD) sensor, or a laser. The reading device  5  may be a terminal device capable of reading the identification sign by the operation of the user business operator, or may be a device that is provided in a robot that executes the welding process or a robot that executes an inspection of the welding portion and is capable of reading the identification sign based on a control command of the host device  1  before and after the welding process or the inspection process. The reading device  5  transmits the pattern information on the read identification sign to the host device  1 . The reading device  5  displays (outputs) the ID of the original workpiece or the welded workpiece received from the host device  1 . The reading device  5  may output the ID of the original workpiece or the welded workpiece by voice. 
     The external storage ST is configured using, for example, a hard disk drive (HDD) or a solid state drive (SSD). The external storage ST stores, for example, pattern information on the identification sign assigned to each workpiece, data of workpiece-related information created for each workpiece, data of welding-related information created for each welding process, and welding process logical data (see  FIG. 4 ) including the ID of the welded workpiece produced by the welding process. 
     The robot control devices  2   a ,  2   b , and so on are connected so as to be able to communicate data with the host device  1 , and are connected so as to be able to communicate data with each of the main welding robots MC 1   a , MC 1   b , and so on. When the robot control devices  2   a ,  2   b , and so on receive the welding process execution command sent from the host device  1 , the robot control devices  2   a ,  2   b , and so on control the corresponding main welding robots MC 1   a , MC 1   b , and so on based on the execution command to execute the welding process. When detecting the completion of the welding process, the robot control devices  2   a ,  2   b , and so on generate a welding completion notification indicating the completion of the welding process and transmit the welding completion notification to the host device  1 . Accordingly, the host device  1  can appropriately detect the completion of the welding process based on each of the robot control devices  2   a ,  2   b , and so on. The method of detecting the completion of the welding process by the robot control devices  2   a ,  2   b , and so on may be a method of determining the completion of the welding process based on a signal indicating the completion of the welding process from a sensor (not shown) included in, for example, a wire feeding device  300 , or may be a known method, and a content of the method of detecting the completion of the welding process is not limited. 
     The main welding robots MC 1   a , MC 1   b , and so on as an example of the welding robot are connected to the robot control devices  2   a ,  2   b , and so on so as to be able to communicate data with the robot control devices  2   a ,  2   b , and so on. The main welding robots MC 1   a , MC 1   b , and so on execute the welding process instructed by the host device  1  under the control of the corresponding robot control devices  2   a ,  2   b , and so on. 
       FIG. 2  is a diagram showing an internal configuration example of the host device  1  and the laser device  3  according to the first embodiment. In order to make the description easy to understand, in  FIG. 2 , illustration of the monitor MN 1 , the input interface UI 1 , the main welding robots MC 1   a , MC 1   b , and so on, the robot control devices  2   a ,  2   b , and so on, and the reading device  5  is omitted, and a process of assigning an identification sign Q before the welding process (hereinafter, referred to as an identification sign assigning process) will be described.  FIG. 3  is a diagram showing an internal configuration example of the host device  1 , the robot control device  2   a , and the reading device  5  according to the first embodiment. In order to make the description easy to understand, the monitor MN 1  and the input interface UI 1  are not shown in  FIG. 3 , the main welding robot MC 1   a  among the main welding robots MC 1   a , MC 1   b , and so on is exemplified, and further, the robot control device  2   a  among the robot control devices  2   a ,  2   b , and so on is exemplified, and the welding process executed after the identification sign assigning process will be described. 
     The host device  1  in the identification sign assigning process transmits, to the laser device  3 , an execution command for assigning the identification sign Q generated by using the design data of the original workpiece and the welded workpiece input in advance by the user business operator and information on the original workpiece having the ID selected as the ID of the welded workpiece. The host device  1  in the welding process generates the welding process execution command using each of the plurality of original workpieces by using the welding-related information input or set in advance by the user business operator, and transmits the execution command to the robot control device  2   a . The host device  1  includes at least a communication unit  10 , a processor  11 , and a memory  12 . 
     The processor  11  is configured using, for example, a central processing unit (CPU) or a field programmable gate array (FPGA), and performs various processing and control in cooperation with the memory  12 . Specifically, the processor  11  functionally implements a cell control unit  13 , an ID setting management unit  14 , a logical data generation unit  15 , and an ID selection unit  16  by referring to a program held in the memory  12  and executing the program. 
     The memory  12  includes, for example, a random access memory (RAM) as a workpiece memory used when processing of the processor  11  is executed, and a read only memory (ROM) for storing a program defining processing of the processor  11 . The RAM temporarily stores data generated or acquired by the processor  11 . A program that defines processing of the processor  11  is written into the ROM. The memory  12  stores the data of the workpiece-related information and the welding-related information read from the external storage ST, information on the arrangement position of the identification sign Q and information on the pattern, data of secondary workpiece information (see the following description) including the ID of the selected welded workpiece (secondary workpiece), and the welding process logical data (see  FIG. 4 ) of the secondary workpiece generated by the processor  11 . 
     The cell control unit  13  generates the execution command for executing the welding process using the plurality of original workpieces defined (in other words, set) in the welding-related information based on the welding-related information stored in the external storage ST. The cell control unit  13  may generate a different welding process execution command for each welding process executed by each of the main welding robots MC 1   a , MC 1   b , and so on. The welding process execution command generated by the cell control unit  13  is transmitted to the corresponding robot control devices  2   a ,  2   b , and so on via the communication unit  10 . 
     The ID setting management unit  14  sets the ID of the welded workpiece (secondary workpiece) output from the ID selection unit  16  to include information on the ID of the original workpiece unselected as the ID of the welded workpiece, and stores the information in the memory  12 . The ID setting management unit  14  may store, in the external storage ST, the workpiece-related information on the unselected original workpiece in association with the ID of the original workpiece unselected as the ID of the welded workpiece, which is included in the welding process logical data (see the following description) generated along with the completion of the welding process for producing the welded workpiece (secondary workpiece). 
     The logical data generation unit  15  uses the secondary workpiece information including the ID of the welded workpiece (secondary workpiece) transmitted from the robot control device (for example, the robot control device  2   a ) to generate the welding process logical data indicating a relationship between the ID of the secondary workpiece and the ID of each of the plurality of original workpieces used in the welding process (for example, a temporal order in which the welding process is performed on each of the plurality of original workpieces) (see  FIG. 4 ). Details of the welding process logical data will be described later with reference to  FIG. 4 . The logical data generation unit  15  may store the ID of the welded workpiece (secondary workpiece), the ID of the original workpiece which is used for production of the welded workpiece and unselected as the ID of the welded workpiece, and the welding process logical data (see  FIG. 4 ) in the external storage ST in association with the information on the identification sign Q. 
     The ID selection unit  16  determines the ID of the welded workpiece (secondary workpiece) according to a predetermined rule in the identification sign assigning process. Here, the ID and the predetermined rule will be described. The predetermined rule used for the selection of the ID is a rule for selecting any ID among the IDs of the plurality of original workpieces used for the production of the welded workpiece for each welding process, and is a rule for selecting based on ID strength (that is, the ID is strong and the ID is weak), a rule for selecting the IDs of the workpiece and the workpiece having a small influence (for example, heat) due to the execution of the welding process based on the welding-related information, a rule for selecting the IDs of the workpiece and the workpiece in which the identification sign Q is easily read in the welded workpiece (so-called weldment) produced for each welding process, or the like, and any rule may be selected by the user business operator. The ID selection unit  16  stores the ID of the original workpiece selected as the ID of the welded workpiece and the ID of the original workpiece unselected as the ID of the welded workpiece for each welding process in the memory  12 , and outputs the IDs to an identification sign arrangement unit  17 . 
     In the present specification, the ID is constituted by, for example, a combination of a plurality of types of character codes. The types are, for example, alphabets and numbers, and are not limited thereto. For example, “ABC001XYZ999” is indicated as the ID of the original workpiece. Here, in order to make the description easy to understand, the ID is shown as a 12-digit character code formed of “three digits of alphabets”, “three digits of numerals”, “three digits of alphabets”, and “three digits of numerals”, whereas the ID is not limited to the configuration examples. Among the 12-digit character codes, for example, the upper three digits of alphabets may indicate codes of a company or a customer (for example, a supplier or a shipping destination), and other “three digits of numerals”, “three digits of alphabets”, and “three digits of numerals” may indicate serial numbers. The numbers of digits of numbers and alphabets are not limited to the same number of digits, and different numbers of digits such as a character code formed of “two digits of alphabets” and “three digits of alphabets” may be set. 
     A rule for selecting the ID of the welded workpiece (secondary workpiece) according to ID strength will be described. As for the ID, the following two strength rules are defined as rules indicating the ID strength (that is, the ID is strong and the ID is weak). Hereinafter, the two strength rules will be described. 
     In a first strength rule, the ID selection unit  16  sets a division between an alphabet and a number for the ID of the original workpiece, and compares the strength of each part of the division. In a second strength rule, the ID selection unit  16  determines that, in one division between the alphabet or the number, the strength is stronger as the order of the alphabets is earlier and the strength is stronger as the number is larger. For example, it is determined that “A” is stronger than “B” in the alphabet and “2” is stronger than “1” in the number. 
     As a modification of the second strength rule, the ID selection unit  27  may determine that, in one division between the alphabet or the number, the strength is stronger as the order of the alphabets is later and the strength is stronger as the number is smaller. For example, it may be determined that “B” is stronger than “A” in the alphabet and “1” is stronger than “2” in the number. 
     Here, “ABC001XYZ999” and “ABD002XYW998” are shown as the IDs of the original workpieces to be compared. For example, the ID selection unit  16  provides divisions “ABC”, “001”, “XYZ”, and “999” for the ID “ABC001XYZ999”, and similarly provides divisions “ABD”, “002”, “XYW”, and “998” for the ID “ABD002XYW998”. 
     For example, the ID selection unit  16  compares the IDs of the segment parts provided in order from upper digits of the ID at any time, and determines that “ABC” is stronger than “ABD”, “001” is weaker than “002”, “XYZ” is weaker than “XYW”, and “999” is weaker than “998”. Furthermore, the ID selection unit  16  gives priority to the one with the stronger ID in the division of the upper digits and determines that the ID as a whole is strong. This is because, for example, the “alphabet” used in the upper digit of the ID does not often define the type of the original workpiece. Therefore, the ID selection unit  16  determines that the ID “ABC001XYZ999” is stronger than the ID “ABD002XYW998”. The above described strength rule is merely an example, and is not limited to the above described example, and it is needless to say that a rule for determining the ID strength may be provided. 
     Furthermore, the ID selection unit  16  may select a workpiece having a small influence (for example, heat) due to the execution of the welding process based on the welding-related information, or may select a workpiece for which the identification sign Q is easily read in the welded workpiece (so-called weldment) produced for each welding process. For this reason, the ID selection unit  16  adopts the ID of the selected workpiece as the ID of the welded workpiece. 
     The identification sign arrangement unit  17  sets the arrangement position of the identification sign Q assigned to each workpiece based on the ID of the original workpiece selected and the ID of the original workpiece unselected as the ID of the welded workpiece input by the ID selection unit  16 , and the design data of the welded workpiece stored in the external storage ST. When the welded workpiece is generated by executing a plurality of welding processes, the arrangement position of the identification sign Q of the original workpiece is set in accordance with the order of the welding processes. Specifically, the identification sign arrangement unit  17  sets the arrangement position of the identification sign Q to be assigned to the workpiece according to the order of the welding processes and so that the number of readable identification signs Q to be assigned to the welded workpiece after execution of each welding process is one. 
     The identification sign arrangement unit  17  generates a pattern for reading the ID of the workpiece for the identification sign of each workpiece. The identification sign arrangement unit  17  stores the ID of the workpiece, the information on the arrangement position of the identification sign assigned to the workpiece, and the information on the pattern generated for each identification sign in the external storage ST in association with each other, generates an execution command for assigning the identification sign based on the information on the arrangement position of the identification sign assigned to the workpiece and the information on the pattern generated for each identification sign, and transmits the execution command to the laser device  3 . 
     Accordingly, the welding system  100  according to the first embodiment can appropriately manage the ID of the original workpiece having the ID unselected as the ID of the welded workpiece after the execution of the welding process, and can produce the weldment to which only one identification sign readable as the ID of the welded workpiece is assigned. Therefore, the user business operator limits the number of identification sign to be read at the time of reading the ID of the welded workpiece to one, thereby facilitating the ID management of the welded workpiece. Such a method of assigning the identification sign is more useful for the welded workpiece produced by executing a plurality of welding processes. 
     The main welding robot MC 1   a  executes the welding process instructed from the host device  1  under the control of the robot control device  2   a . The main welding robot MC 1   a  performs, for example, arc welding in the welding process. However, the main welding robot MC 1   a  may perform welding (for example, laser welding) other than the arc welding. In this case, although not shown, a laser head may be connected to a laser oscillator via an optical fiber instead of a welding torch  400 . The main welding robot MC 1   a  includes at least a manipulator  200 , the wire feeding device  300 , a welding wire  301 , and the welding torch  400 . 
     The manipulator  200  includes an articulated arm, and moves each arm based on a control signal from a robot control unit  25  (see the following description) of the robot control device  2   a . Accordingly, the manipulator  200  can change a positional relationship between a workpiece Wk and the welding torch  400  (for example, an angle of the welding torch  400  with respect to the workpiece Wk) by the movement of the arm. 
     The wire feeding device  300  controls a feeding speed of the welding wire  301  based on a control signal (see the following description) from the robot control device  2   a . The wire feeding device  300  may include a sensor capable of detecting a remaining amount of the welding wire  301 . 
     The welding wire  301  is held by the welding torch  400 . When electric power is supplied from a power supply device  4  to the welding torch  400 , an arc is generated between a tip end of the welding wire  301  and the workpiece Wk, and the arc welding is performed. The illustration and description of a configuration and the like for supplying shielding gas to the welding torch  400  are omitted for the convenience of description. 
     The robot control device  2   a  controls the processing of the corresponding main welding robot MC 1   a  (specifically, the manipulator  200 , the wire feeding device  300 , and the power supply device  4 ) based on the welding process execution command sent from the host device  1 . The robot control device  2   a  includes at least a communication unit  20 , a processor  21 , and a memory  22 . 
     The communication unit  20  is connected to enable data communication between the host device  1  and the main welding robot MC 1   a . Although illustration is simplified in  FIG. 2 , data is transmitted and received between the robot control unit  25  and the manipulator  200 , between the robot control unit  25  and the wire feeding device  300 , and between a power supply control unit  26  and the power supply device  4  via the communication unit  20 . The communication unit  20  receives the welding process execution command transmitted from the host device  1 . The communication unit  20  transmits the secondary workpiece information including the ID of the welded workpiece (secondary workpiece) produced by the welding process to the host device  1 . 
     Here, the secondary workpiece information includes not only the ID of the welded workpiece (secondary workpiece), but also at least workpiece information (for example, the ID and name of the original workpiece, and the welding portion of the original workpiece) including the IDs of the plurality of original workpieces used in the welding process, and welding conditions at the time of execution of the welding process. The welding conditions include, for example, a material and a thickness of the original workpiece, a material and a wire diameter of the welding wire  301 , a type of the shielding gas, a flow rate of the shielding gas, a set average value of a welding current, a set average value of a welding voltage, a feeding speed and a feeding amount of the welding wire  301 , the number of times of welding, and a welding time. In addition to these, for example, information indicating a type of welding process (for example, TIG welding, MAG welding, or pulse welding), and a moving speed and a moving time of the manipulator  200  may be included. 
     The processor  21  is configured with, for example, a CPU or an FPGA, and executes various processing and controls in cooperation with the memory  22 . Specifically, the processor  21  functionally implements a program generation unit  23 , a calculation unit  24 , the robot control unit  25 , and the power supply control unit  26  by referring to a program held in the memory  22  and executing the program. 
     The memory  22  includes, for example, a RAM as a workpiece memory used when the processing of the processor  21  is executed, and a ROM that stores a program defining the processing of the processor  21 . The RAM temporarily stores data generated or acquired by the processor  21 . The program that defines processing of the processor  21  is written in the ROM. The memory  22  stores data of the welding process execution command transmitted from the host device  1 , data of the secondary workpiece information including the ID of the welded workpiece (secondary workpiece) generated by the welding process, and data of welding process logical data (see  FIGS. 3 and 4 ) of the secondary workpiece generated by the processor  21 . The memory  22  stores a welding process program executed by the main welding robots MC 1   a , MC 1   b , and so on. The welding process program is a program that defines a specific procedure (process) of the welding process of joining the plurality of original workpieces using the welding conditions in the welding process. The program may be created in the robot control device  2   a , or may be created by the host device  1 , transmitted in advance, and stored in the robot control device  2   a.    
     The program generation unit  23  generates a welding process program to be executed by the main welding robot (for example, the main welding robot MC 1   a ) using the workpiece information (for example, the ID, the name, and the welding portion of the original workpiece) of each of the plurality of original workpieces included in the execution command based on the welding process execution command transmitted from the host device  1  via the communication unit  20 . The program may include various parameters such as the welding current, the welding voltage, an offset amount, a welding speed, and a posture of the welding torch  400  for controlling the power supply device  4 , the manipulator  200 , the wire feeding device  300 , the welding torch  400 , and the like during the execution of the welding process. The generated program may be stored in the processor  21  or may be stored in the RAM in the memory  22 . 
     The calculation unit  24  performs various calculations. For example, the calculation unit  24  performs calculation or the like for controlling the main welding robot MC 1   a  (specifically, each of the manipulator  200 , the wire feeding device  300 , and the power supply device  4 ) controlled by the robot control unit  25  based on a welding process program generated by the program generation unit  23 . 
     The robot control unit  25  drives the main welding robot MC 1   a  (specifically, each of the manipulator  200 , the wire feeding device  300 , and the power supply device  4 ) based on the welding process program generated by the program generation unit  23 . 
     The power supply control unit  26  drives the power supply device  4  based on the welding process program generated by the program generation unit  23  and a calculation result of the calculation unit  24 . 
     In the identification sign assigning process, the laser device  3  assigns the identification sign Q on which the ID of the workpiece for each workpiece is readable based on the execution command for assigning the identification sign received from the host device  1 . The laser device  3  includes a communication unit  30 , a processor  31 , a memory  32 , and a laser oscillator  33 . 
     The communication unit  30  is connected to the host device  1  so as to be able to communicate data with the host device  1 . The communication unit  30  outputs, to the processor  31 , the information on the arrangement position of the identification sign assigned to the workpiece received from the host device and the information on the pattern generated for each identification sign. The communication unit  30  transmits, to the host device  1 , a notification generated when the execution of the identification sign assigning process by the laser oscillator  33  is completed. 
     The processor  31  is configured with, for example, a CPU or an FPGA, and executes various processing and controls in cooperation with the memory  32 . Specifically, the processor  31  implements functions of the processor  31  by referring to a program held in the memory  32  and executing the program. The processor  31  generates a control signal for assigning the identification sign to the workpiece based on the received information on the arrangement position of the identification sign assigned to the workpiece and the received information on the pattern generated for each identification sign, and executes control of the laser oscillator  33 . 
     The memory  32  includes, for example, a RAM as a workpiece memory used when the processing of the processor  31  is executed, and a ROM that stores a program defining the processing of the processor  31 . The RAM temporarily stores data generated or acquired by the processor  31 . The program that defines processing of the processor  31  is written in the ROM. 
     The laser oscillator  33  marks a pattern set at a predetermined arrangement position on the workpiece based on the execution command of assigning the identification sign received from the host device  1  for each workpiece, and executes assignment of the identification sign Q. The method of assigning the identification sign Q performed in the identification sign assigning process performed by the laser device  3  may be a known method, and the content of the method of assigning the identification sign Q is not limited. 
     The reading device  5  reads the identification sign Q assigned to the original workpiece used for the execution of the welding process or the welded workpiece produced by the execution of the welding process, and outputs the ID of the read workpiece. The reading device  5  is used by the user business operator. The reading device  5  includes at least a communication unit  50 , a processor  51 , a memory  52 , a reading unit  53 , and an operation unit  55 . A monitor  54  may or may not be included in the reading device  5 . When the monitor  54  is implemented as a configuration that is not included in the reading device  5 , the monitor  54  is connected to the reading device  5  so as to be capable of wireless or wired communication. The reading device  5  may include a speaker (not shown) when the information on the ID of the workpiece is output by voice. 
     The communication unit  50  is connected to the host device  1  so as to be able to communicate data with the host device  1 . The communication unit  50  transmits, to the host device  1 , a command for requesting information on the ID of the workpiece to which the read identification sign Q is assigned, based on a result of reading the identification sign Q by the processor  51  (that is, reading the information on the pattern of the identification sign Q). The communication unit  50  receives the ID of the welded workpiece transmitted from the host device  1  and outputs the ID to the processor  51 . 
     The processor  51  is configured with, for example, a CPU or an FPGA, and executes various processing and controls in cooperation with the memory  52 . Specifically, the processor  51  implements functions of the processor  51  by referring to a program held in the memory  52  and executing the program. 
     The memory  52  includes, for example, a RAM as a workpiece memory used when the processing of the processor  51  is executed, and a ROM that stores a program defining the processing of the processor  51 . The RAM temporarily stores data generated or acquired by the processor  51 . The program that defines processing of the processor  51  is written in the ROM. The memory  52  stores the information on the identification sign Q read from the reading unit  53 , the ID of the workpiece associated with the information on the identification sign Q transmitted from the host device  1 , and the like. 
     The reading unit  53  includes, for example, a camera for reading a two-dimensional barcode or a laser for reading a barcode. The reading unit  53  reads the identification sign Q assigned to the workpiece, and outputs information (data) read from the identification sign Q to the processor  51 . 
     The reading unit  53  implemented by using the camera is capable of reading, for example, the two-dimensional barcode, and includes at least a lens (not shown) and an image sensor (not shown). The image sensor is, for example, a solid-state imaging element of a charged-coupled device (CCD) or a complementary metal oxide semiconductor (CMOS), and converts an optical image formed on an imaging surface into an electric signal. The reading unit  53  implemented by the camera captures an image of the identification sign Q and performs image analysis on the captured identification sign Q. The reading unit  53  outputs information (data) on the identification sign Q acquired as a result of the image analysis to the processor  51 . 
     The reading unit  53  implemented by using the laser can optically read the identification sign Q (for example, the bar code, the IC tag, or the RF tag), and specifically, receives reflected light reflected by the identification sign Q by using the laser, and replaces a color included in the reflected light with a binary digital signal to acquire the information on the identification sign Q. The reading unit  53  includes a laser and a CCD reader capable of receiving the reflected light of the laser, or a laser and radio frequency identification (RFID). The reading unit  53  outputs information (data) on the barcode read by the CCD reader or information (data) on the IC tag, the RF tag, and the like read by the RFID to the processor  51 . When the reading unit  53  is implemented by the RFID, the reading unit  53  can read each of a plurality of IC tags or RF tags located in a range where radio waves reach at a time. 
     The monitor  54  is configured using, for example, a liquid crystal display (LCD) or an organic electroluminescence (EL). The monitor  54  outputs the ID of the workpiece received from the host device  1 . The monitor  54  may be a touch interface configured by a touch panel. In such a case, the monitor  54  has a function as the operation unit  55 , receives the input operation of the user business operator, generates a control signal based on the input operation, and outputs the control signal to the processor  51 . 
     The operation unit  55  receives the input operation by the user business operator and outputs the input operation to the processor  51 . The operation unit  55  generates the control signal based on the input operation by the user business operator and outputs the control signal to the processor  51 . The operation unit  55  may be implemented as a touch panel of the monitor  54  described above. 
       FIG. 4  is an explanatory diagram showing an example of an operation outline at the time of welding using the workpiece Wk 1  with the ID “A”, the workpiece Wk 2  with the ID “B”, the workpiece Wk 4  with the ID “C”, and the workpiece Wk 5  with the ID “D”. In the example of  FIG. 4 , a rectangular parallelepiped workpiece Wk 4  (original workpiece) having the ID “C” and a rectangular parallelepiped workpiece Wk 5  (original workpiece) having the ID “D” are joined together in a second welding process to produce a welded workpiece (that is, a secondary workpiece Wk 6 ), a cylindrical workpiece Wk 1  (original workpiece) having the ID “A” and a cylindrical workpiece Wk 2  (original workpiece) having the ID “B” are joined together in a first welding process to produce a welded workpiece (that is, a secondary workpiece Wk 3 ), and the secondary workpiece Wk 3  having the ID “A” and the secondary workpiece Wk 6  having the ID “C” are joined together in a third welding process to produce a welded workpiece (that is, a tertiary workpiece Wk 7 ). Similarly, the IDs “A”, “B”, “C”, and “D” are formed of, for example, 12-digit alphabets and numerals, but are collectively represented by one alphabetic character in order to make the description of  FIG. 4  easy to understand. 
     The ID selection unit  16  in  FIG. 4  selects an ID to be adopted for each of the secondary workpiece Wk 6 , the secondary workpiece Wk 3 , and the tertiary workpiece Wk 7  based on the ID strength rule. It is needless to say that the rule for selecting the ID is not limited thereto. In the example shown in  FIG. 4 , it is assumed that the ID selection unit  16  determines that the ID “A” is stronger than the ID “B”. In this case, the ID selection unit  16  adopts and selects the stronger ID “A” as it is (that is, without changing) as the ID of the welded workpiece (that is, the secondary workpiece Wk 3 ) which is a product of the first welding process. Similarly, it is assumed that the ID selection unit  16  determines that the ID “D” is stronger than the ID “C”. In this case, the ID selection unit  16  adopts and selects the stronger ID “D” as it is (that is, without changing) as the ID of the welded workpiece (that is, the secondary workpiece Wk 6 ) which is the product of the second welding process. Furthermore, it is assumed that the ID selection unit  16  determines that the ID “D” is stronger than the ID “A”. In this case, the ID selection unit  16  adopts and selects the stronger ID “D” as it is (that is, without changing) as the ID of the welded workpiece (that is, the tertiary workpiece Wk 7 ) which is the product of the third welding process. 
     The identification sign arrangement unit  17  receives, from the ID selection unit  16 , information on an ID selected as an ID of each of the secondary workpieces Wk 3  and Wk 6  (welded workpieces) and the tertiary workpiece Wk 7  (welded workpiece) produced by the first welding process to the third welding process. The identification sign arrangement unit  17  sets the arrangement positions of the identification signs of the plurality of workpieces Wk 1 , Wk 2 , Wk 4 , and Wk 5  (original workpieces) based on the IDs of the plurality of workpieces Wk 1 , Wk 2 , Wk 4 , and Wk 5  (original workpieces), information on the IDs selected as welded workpieces produced by the welding processes, information on the order in which the welding processes are executed, and information on joint surfaces to be joined in the welding processes. 
     Specifically, the identification sign arrangement unit  17  sets the arrangement positions so that an entire of the identification sign Q 3  on which the ID of the unselected workpiece Wk 4  (original workpiece) is readable are assigned in the joint surface to be joined in the first welding process. Similarly, the identification sign arrangement unit  17  sets the arrangement positions so that an entire of the identification sign Q 2  on which the ID of the unselected workpiece Wk 2  (original workpiece) is readable are assigned in the joint surface to be joined in the second welding process. Further, the identification sign arrangement unit  17  sets the arrangement positions so that an entire of the identification sign Q 1  on which the ID of the unselected workpiece Wk 1  (original workpiece) is readable are assigned in the joint surface to be joined in the third welding process, and sets the identification sign on which the ID of the tertiary workpiece Wk 7  (welded workpiece) is readable to the identification sign Q 4  only. Accordingly, since only one identification sign readable as the ID of the welded workpiece is assigned to the welded workpiece produced by the welding system  100  according to the first embodiment, it is not necessary to consider any one of the identification signs read when the ID is read by the user business operator. Such a method of assigning (arranging) the identification sign is more useful for the welded workpiece which is produced by executing a plurality of welding processes shown in  FIG. 4 . 
     However, when the ID “D” of the workpiece Wk 5  (original workpiece), the ID “D” of the welded workpiece (that is, the secondary workpiece Wk 6 ), and the ID “D” of the tertiary workpiece Wk 7  are all the same, the management of the ID “D” among the workpiece Wk 1  (original workpiece), the secondary workpiece Wk 3 , and the tertiary workpiece Wk 7  may be complicated. Furthermore, since the identification signs assigned to the secondary workpieces Wk 3  and Wk 6  (welded workpieces) and the tertiary workpiece Wk 7  (welded workpiece) are only the identification signs that enable the ID of the selected original workpiece to be read, it is not possible to read the information on the ID of the original workpiece or the ID of the workpiece unselected after the execution of each welding process. Therefore, in the welding system  100  according to the first embodiment, for example, when the host device  1  receives the notification of the completion of the welding process, in the first welding process to the third welding process, the host device  1  generates the welding process logical data (see  FIG. 4 ) logically indicating a mutual relationship between the strongest ID “D” and other weak IDs “A”, “B”, and “C”, generates a record TB 1  in which the ID “D” of the tertiary workpiece Wk 7  and the welding process logical data are associated with each other, and stores the record TB 1  in the external storage ST. 
     The welding process logical data indicates, as viewed from the ID “D” of the tertiary workpiece Wk 7 , which ID the original workpiece having which ID is used in which the welding process the tertiary workpiece Wk 7  is used and produced, and also indicates a strength relationship of the IDs of the plurality of original workpieces used in each of the welding processes, and a temporal order in which each process is executed. For example, the welding process logical data indicates that the tertiary workpiece Wk 7  having the ID “D” is produced through three welding processes (the first welding process to the third welding process). In the second welding process, the workpiece Wk 1  (original workpiece) having the ID “A” and the workpiece Wk 2  (original workpiece) having the ID “B” are welded to each other, and since the ID “A” is stronger than the ID “B”, the ID “A” is selected as the ID of the secondary workpiece Wk 3 . In the first welding process, the workpiece Wk 4  (original workpiece) having the ID “C” and the workpiece Wk 5  (original workpiece) having the ID “D” are welded, and since the ID “D” is stronger than the ID “C”, the ID “D” is selected as the ID of the secondary workpiece Wk 6 . In the third welding process, the secondary workpiece Wk 3  having the ID “A” and the secondary workpiece Wk 6  having the ID “D” are welded to each other, and since the ID “A” is strong, the ID “A” is selected as the ID of the tertiary workpiece Wk 7 . In the welding process logical data, when viewed from the ID “D” of the tertiary workpiece Wk 7 , a position closer to the ID “D” indicates that a time at which the workpiece Wk 5  (original workpiece) or the secondary workpiece Wk 6  of the ID “D” is welded is older, and a position farther from the ID “D” indicates that the time at which the workpiece Wk 5  (original workpiece) or the secondary workpiece Wk 6  of the ID “D” is welded is newer. Accordingly, even after all of the plurality of welding processes are completed, the user business operator can comprehensively grasp the data on the plurality of original workpieces used for the production of the tertiary workpiece Wk 7  without losing the information on the original workpiece or the secondary workpiece of the ID that is unreadable in each welding process. 
       FIG. 5  is a diagram showing an example of a correspondence table XTB 1  between a selection ID and a management ID. When a business operator (hereinafter, referred to as the “user business operator”) who executes the welding process starts the welding process, an original workpiece such as a steel material used in the welding process may be supplied (in other words, may be outsourced) from the supplier in advance. For this reason, when the user business operator outsources the original workpiece such as the steel material, an ID is often assigned to the original workpiece in advance at an outsource destination. In the following description, the ID of the original workpiece assigned in advance in the outsource destination as described above is referred to as a “selection ID”. When the supplied original workpiece is assigned a selection ID unique to the outsource destination, the use of the selection ID may not be suitable in terms of the management of the user business operator. 
     Therefore, as shown in  FIG. 5 , in the welding system  100  according to the first embodiment, when the selection ID is assigned to each of one or more original workpieces to be supplied from the outsource destination, the correspondence table XTB 1  (an example of the management table) indicating a relationship between the selection ID and the management ID of the user business operator is created by the user business operator and stored in the external storage ST. The correspondence table XTB 1  may be stored in the memory  12  of the host device  1 . 
     For example, in the correspondence table XTB 1  of  FIG. 5 , it is assumed that the user business operator supplies a plurality of original workpieces of the same type (for example, the same material supplied from the same supplier) from the outsource destination, and the management IDs “AAA001”, “BBB001”, “DDD001”, and the like corresponding to the selection IDs “RX85-1001”, “RX85-1002”, “RR90-0001”, and the like unique to the outsource destination are defined. “RX85-1001”, “RX85-1002”, “RR90-0001”, and so on are of the same type because “RX85” before hyphen in the ID is common, and are different from each other in branch number of “RX85” (number after the hyphen in the ID), so that the original workpieces (parts) are different. 
     (Arrangement Setting of Identification Sign) 
     Next, an arrangement setting procedure of the identification sign by the welding system  100  according to the first embodiment will be described with reference to  FIG. 6 .  FIG. 6  is a sequence diagram showing an arrangement setting procedure of the identification sign in the welding system  100  according to the first embodiment. In the description of  FIG. 6 , the arrangement setting procedure of the identification sign performed between the host device  1  and the laser device  3  in the second welding process using the plurality of workpieces Wk 1  and Wk 2  (original workpieces) shown in  FIG. 4  will be described as an example. The workpiece A shown in  FIG. 6  is the workpiece Wk 1  (original workpiece) having the ID “A”. Similarly, the workpiece B shown in  FIG. 6  is the workpiece Wk 2  (original workpiece) having the ID “B”. 
     In  FIG. 6 , the host device  1  acquires information (for example, the number of welding processes, and the order of the welding processes) related to the welding process (main welding) and workpiece information (for example, the ID, the name, and the welding portion of the original workpiece) including IDs of the plurality of workpieces Wk 1  and Wk 2  (original workpieces) to be subjected to the welding process (St 1 ), and further acquires information related to a joint surface of the plurality of workpieces Wk 1  and Wk 2  (original workpieces) to be joined (used) by the welding process for producing the welded workpiece (that is, the secondary workpiece Wk 3 ) (St 2 ). Here, the information related to the joint surfaces of the plurality of workpieces Wk 1  and Wk 2  (original workpieces) is, for example, design data of the welded workpiece in which the plurality of workpieces Wk 1  and Wk 2  (original workpieces) are joined in the welding process, or design data of each of the plurality of workpieces Wk 1  and Wk 2  (original workpieces). 
     The host device  1  selects an ID to be adopted as the ID of the secondary workpiece Wk 3  (that is, the welded workpiece) after the welding process based on a predetermined rule (St 3 ). The ID “A” of the secondary workpiece Wk 3  (welded workpiece) selected here may be stored in the memory  12  of the host device  1 . The host device  1  sets the arrangement positions of the identification signs assigned to the plurality of workpieces Wk 1  and Wk 2  (original workpieces), respectively, based on the information on the ID “A” selected by the processing of step St 3  and the unselected ID “B”, and the information on the joint surfaces of the plurality of workpieces Wk 1  and Wk 2  (original workpieces) to be joined (St 4 ). The host device  1  notifies the laser device  3  of the information on the arrangement position of the identification sign and the information on the pattern of the identification sign assigned to each of the plurality of set workpieces Wk 1  and Wk 2  (original workpieces) (St 5 ). 
     Based on the notification received from the host device  1 , the laser device  3  executes an assigning process of assigning an identification sign Q 1  to the workpiece Wk 1  (original workpiece), executes an assigning process of assigning an identification sign Q 2  to the workpiece Wk 2  (original workpiece) (St 6 ), and when completion of the assigning process of the identification sign is determined (St 7 ), generates an identification sign assignment completion notification indicating that the assignment of the identification sign is completed, and transmits the identification sign assignment completion notification to the host device  1  (St 8 ). The processing of steps St 6  to St 8  may be executed independently for each original workpiece. 
     As described above, the welding system  100  according to the first embodiment can produce a weldment to which only one readable identification sign is assigned as the ID of the welded workpiece. Therefore, the user business operator limits the number of identification signs to be read at the time of reading the ID of the welded workpiece to one, thereby facilitating the ID management of the welded workpiece. Such a method of assigning the identification sign is more useful for the welded workpiece produced by executing a plurality of welding processes. The arrangement setting procedure of the identification sign shown in  FIG. 6  is an example, and a processing order of the arrangement setting procedure is not limited thereto. 
     (Operation of Welding System) 
     Next, an operation procedure of the ID management by the welding system  100  according to the first embodiment will be described with reference to  FIG. 7 .  FIG. 7  is a sequence diagram showing an operation procedure example of the ID management in the welding system  100  according to the first embodiment. In the description of  FIG. 7 , an operation procedure performed among the host device  1 , the robot control device  2   a , and the reading device  5  with respect to the second welding process using the plurality of workpieces Wk 1  and Wk 2  (original workpieces) shown in  FIG. 4  will be described as an example, and an operation procedure performed among other robot control devices  2   b  will be omitted. The workpiece A shown in  FIG. 7  is the workpiece Wk 1  (original workpiece) having the ID “A”. Similarly, the workpiece B shown in  FIG. 7  is the workpiece Wk 2  (original workpiece) having the ID “B”. 
     In  FIG. 7 , the host device  1  acquires workpiece information (for example, the ID, the name of the workpiece, the arrangement position of the identification sign, and the welding portion of the original workpiece) including the IDs of the plurality of workpieces Wk 1  and Wk 2  (original workpieces) to be subjected to the welding process (main welding) (St 9 ), and transmits a second welding process execution command including the workpiece information on the workpiece Wk 1  (original workpiece) and the workpiece information on the workpiece Wk 2  (original workpiece) to the robot control device  2   a  (St 10 ). 
     When the robot control device  2   a  receives the welding process execution command transmitted from the host device  1 , the robot control device  2   a  causes the main welding robot MC 1   a  to execute the main welding in accordance with the workpiece information on each of the plurality of workpieces Wk 1  and Wk 2  (original workpieces) included in the execution command and the welding process program executed by the main welding robot MC 1   a  received together with the welding process execution command (SW). The robot control device  2   a  determines the completion of the main welding (welding process) by the main welding robot MC 1   a  by various known methods (St 12 ), generates a main welding completion notification indicating the completion of the main welding, and transmits the notification to the host device  1  (St 13 ). 
     When the main welding completion notification indicating that the main welding is completed is received from the robot control device  2   a , the host device  1  sets the ID “A” selected in the processing of step St 3  as the ID of the secondary workpiece Wk 3  (welded workpiece), and generates the welding process logical data (see  FIG. 4 ) related to the secondary workpiece Wk 3  (welded workpiece) (St 14 ). The host device  1  stores the information including the ID “A” of the secondary workpiece Wk 3  (welded workpiece), the ID “B” of the unselected workpiece Wk 2  (original workpiece), and the welding process logical data related to the secondary workpiece Wk 3  (welded workpiece) in the external storage ST in association with each other (St 15 ). 
     The reading device  5  reads the identification sign Q 1  assigned to the secondary workpiece Wk 3  (welded workpiece) produced by the completion of the main welding (St 16 ), and transmits information on the read identification sign to the host device  1  (St 17 ). 
     The host device  1  refers to the external storage ST based on the information on the identification sign Q 1  received from the reading device  5 , and acquires the information on the ID “A” as the ID of the secondary workpiece Wk 3  (welded workpiece) associated with the information on the identification sign Q 1  (St 18 ). The host device  1  transmits the acquired ID “A” of the secondary workpiece Wk 3  (welded workpiece) to the reading device  5  (St 19 ). 
     The reading device  5  outputs (displays) the ID “A” of the secondary workpiece Wk 3  (welded workpiece) which is received from the host device  1  and is associated with the identification sign Q 2  read in the processing of step St 9  (St 20 ). 
     In  FIG. 7 , an example in which the reading device  5  reads the identification sign Q 1  of the secondary workpiece Wk 3  (welded workpiece) after the execution of the second welding process is described, whereas a timing of reading the identification sign is not limited thereto. For example, the user business operator may execute the reading of the identification sign Q 2  of the workpiece Wk 2  (original workpiece) in view of a fact that the identification sign Q 2  of the workpiece Wk 2  (original workpiece) cannot be read after the execution of the second welding process. The user business operator may read the identification sign Q 1  of the workpiece Wk 1  (original workpiece) and the identification sign Q 2  of the workpiece Wk 2  (original workpiece) before the execution of the second welding process, and may read the identification sign Q 1  of the secondary workpiece Wk 3  (welded workpiece) after the execution of the second welding process. 
     Accordingly, the welding system  100  according to the first embodiment can appropriately manage the ID of the original workpiece having the ID unselected as the ID of the welded workpiece after the execution of the welding process, and can produce the weldment to which only one identification sign readable as the ID of the welded workpiece is assigned. Therefore, the user business operator limits the number of identification signs to be read at the time of reading the ID of the welded workpiece to one, thereby facilitating the ID management of the welded workpiece. Such a method of assigning the identification sign is more useful for the welded workpiece produced by executing a plurality of welding processes. 
     As described above, the welding system  100  according to the first embodiment in which the identification signs are arranged on the plurality of original workpieces to be used in the welding process, respectively, the identification signs on which identifiers of the respective original workpieces are readable, executes the welding process such that a part or an entire of the identification sign is hidden in the joint surface on which the plurality of original workpieces are joined by the welding process. 
     Accordingly, since only one identification sign readable as the ID of the welded workpiece is assigned to the welded workpiece produced by the welding system  100  according to the first embodiment, it is not necessary to consider any one of the identification sign read when the ID is read by the user business operator, and it is possible to support more efficient management of the identifier of the workpiece produced in the process of welding or the like. 
     The identifier in the welding system  100  according to the first embodiment selects, according to a predetermined rule, any one of the identifiers of the plurality of original workpieces to be adopted as the identifier of the welded workpiece to be produced by the welding process, and after the selection, the welding process is executed so as to hide a part or an entire of the identification sign of the original workpiece having the identifier that has not been selected as the identifier of the welded workpiece. Accordingly, the welding system  100  according to the first embodiment can easily and efficiently set the identifier to be adopted as the identifier of the welded workpiece based on the predetermined rule. Further, the welding system  100  according to the first embodiment can set the identification sign readable by the reading device  5  to the selected identification sign by executing the welding process so as to hide a part or an entire of the identification sign of the original workpiece having the identifier that is not set as the identifier of the welded workpiece. Therefore, it is possible to easily and efficiently manage the ID of the welded workpiece (for example, the secondary workpiece). 
     In the welding system  100  according to the first embodiment, each of the IDs includes a combination of a plurality of character codes, and is selected according to the ID strength rule defined for each type of character code. Specifically, the ID strength rule is defined for adopting an ID having a strong character code based on a comparison of strength among character codes constituting the IDs of the plurality of original workpieces included in the workpiece. The character codes include, for example, an alphabet and a number. Accordingly, the welding system  100  can easily set and manage the ID of the welded workpiece (for example, the secondary workpiece). 
     The welding system  100  according to the first embodiment acquires information on the identifier of each of the plurality of original workpieces after selecting the identifier of the welded workpiece. Accordingly, the user business operator can acquire and manage the IDs of the plurality of original workpieces without considering the welded workpiece to which the identification sign that becomes unreadable after the execution of the welding process is assigned. 
     The welding system  100  according to the first embodiment acquires information on the identifier which has not been selected after the identifier of the welded workpiece is selected. Accordingly, the user business operator can acquire only the ID of the original workpiece to which the identification sign that becomes unreadable after the execution of the welding process is assigned, and can omit reading and management of the identification sign of the workpiece having the same ID before and after the execution of the welding process. 
     The welding system  100  according to the first embodiment reads the identification signs assigned to the respective original workpieces to be used in the production of the welded workpiece, and generates and stores data (welding process logical data) indicating the relationship between the identifier that has been selected and the identifier that has not been selected. Accordingly, the welding system  100  according to the first embodiment can appropriately manage the ID of the original workpiece having the ID unselected as the ID of the welded workpiece after the execution of the welding process, and can produce the weldment to which only one identification sign readable as the ID of the welded workpiece is assigned. Therefore, the user business operator limits the number of identification sign to be read at the time of reading the ID of the welded workpiece to one, thereby facilitating the ID management of the welded workpiece. Such a method of assigning the identification sign is more useful for the welded workpiece produced by executing a plurality of welding processes. Therefore, even after all of the plurality of welding processes are completed, the user business operator can comprehensively grasp the data on the plurality of original workpieces used in the plurality of welding processes without losing the information on the original workpiece or the secondary workpiece of the ID that is unreadable in each welding process. 
     In the welding system  100  according to the first embodiment, in a case in which the welding process includes a plurality of welding processes, the data indicates the temporal order of the plurality of welding processes. Accordingly, the welding system  100  according to the first embodiment can visualize the relationship between the plurality of original workpieces used in the production of each of the plurality of welding processes, and can support more efficient management of the identifier of the workpiece produced in the process such as welding. Therefore, the user business operator can grasp the relationship between the plurality of original workpieces used in the production of each of the plurality of welding processes, and can comprehensively grasp the data on the plurality of original workpieces used in the plurality of welding processes without losing the information on the original workpiece or the secondary workpiece of the ID that is unreadable in each welding process. 
     As described above, the identification sign assignment device (that is, the laser device  3 ) in the welding system  100  according to the first embodiment is a device that assigns an identification sign to a plurality of original workpieces to be used in a welding process executed by the welding system, and includes the communication unit  30  that acquires welding information including information on an identifier of the respective original workpieces and information on an identifier that is not selected as an identifier of a welded workpiece to be produced in the welding process among the identifiers of the plurality of original workpieces, and the processor  31  that controls the laser oscillator  33  that assigns identification signs on which identifiers corresponding to the respective original workpieces are readable based on the received welding information. Among the identification signs assigned by the identification sign assignment device, the identification sign of the original workpiece having the identifier that is not selected as the identifier of the welded workpiece is assigned such that a part or an entire of the identification sign is located on the joint surface on which the plurality of original workpieces are joined by the welding process. 
     Accordingly, the welded workpiece produced by the welding system  100  according to the first embodiment is produced with only one identification sign that is readable as the ID of the welded workpiece being assigned. Therefore, the user business operator limits the number of identification signs to be read at the time of reading the ID of the welded workpiece to one, thereby facilitating the ID management of the welded workpiece. 
     In a case in which a plurality of welding processes are performed by the welding system  100  according to the first embodiment, the identification sign of the original workpiece having the identifier that is not selected for each welding process is assigned so as to be partially or entirely hidden. Accordingly, the welding system  100  according to the first embodiment can similarly produce the welded workpiece, which is produced by executing the plurality of welding processes, by assigning only one identification sign readable as the ID of the welded workpiece. Therefore, the user business operator limits the number of identification signs to be read at the time of reading the ID of the welded workpiece to one, thereby facilitating the ID management of the welded workpiece. 
     As described above, the weldment produced by the welding system  100  according to the first embodiment is a weldment produced by the execution of the welding process by the welding system, and is produced by the process of arranging the identification signs on which the information on the identifiers of the plurality of original workpieces to be used in the welding process is readable, and the process of executing the welding process based on the position information on the joint surface so as to hide a part or an entire of the identification sign assigned at the position of the joint surface on which the plurality of original workpieces are joined in the welding process. 
     Accordingly, since only one identification sign readable as the ID of the welded workpiece is assigned to the welded workpiece (weldment) produced by the welding system  100  according to the first embodiment, it is not necessary to consider any one of the identification sign read when the ID is read by the user business operator, and it is possible to support more efficient management of the identifier of the workpiece produced in the process of welding or the like. 
     Second Embodiment 
     In the welding system  100  according to the first embodiment, the example in which the identification sign Q is read by the reading device  5  (that is, the example in which the ID of the workpiece is read by the reading device  5 ) is described. In the welding system  100  according to the second embodiment, an example will be described in which the main welding robot further includes a reading unit capable of reading information on the identification sign Q assigned to the workpiece, and the robot control device has an ID reading function. 
       FIG. 8  is a diagram showing an internal configuration example of the host device  1  and the robot control device  2   b  according to the second embodiment. The welding system  100  according to the second embodiment has substantially the same configuration as the welding system  100  according to the first embodiment. Therefore, the same components as those of the first embodiment are denoted by the same reference numerals, and a description thereof will be omitted. In the description of  FIG. 8 , in order to make the description easy to understand, illustration of the monitor MN 1  and the input interface UI 1  is omitted, the main welding robot MC 1   b  among the main welding robots MC 1   a , MC 1   b , and so on is exemplified, and further, the robot control device  2   b  among the robot control devices  2   a ,  2   b , and so on is exemplified and described. 
     In the welding system  100  according to the second embodiment, the robot control device and the main welding robot having the function of reading the identification sign may be a part of the robot control device and the main welding robot selected by the user business operator. That is, in the welding system  100  according to the second embodiment, all of the robot control devices  2   a ,  2   b , and so on and the main welding robots MC 1   a , MC 1   b , and so on do not have to have the function of reading the identification sign. 
     The main welding robot MC 1   b  executes the welding process and the reading of the identification sign Q instructed from the host device  1  under the control of the robot control device  2   b . Before the welding process, the main welding robot MC 1   b  executes reading of the identification sign Q assigned to each of the plurality of original workpieces using a reading unit  53   b , and transmits information on the read identification sign Q to the robot control device  2   b . After reading the identification sign Q, the main welding robot MC 1   b  proceeds to the welding process, and performs, for example, arc welding in the welding process. The main welding robot MC 1   b  may perform welding (for example, laser welding) other than the arc welding. 
     The manipulator  200  includes an articulated arm, and moves each arm based on a control signal from the robot control unit  25  of the robot control device  2   b . Accordingly, the manipulator  200  can change the positional relationship between the reading unit  53   b  and the identification sign Q assigned to the workpiece Wk and the positional relationship between the workpiece Wk and the welding torch  400  by the movement of the arm. 
     The host device  1  generates an execution command for executing reading of the identification sign Q of each of the plurality of original workpieces based on the position information on the identification sign Q assigned to each of the plurality of original workpieces used in the welding process, and transmits the execution command to the robot control device  2   b . The host device  1  generates a welding process execution command using each of the plurality of original workpieces by using the welding-related information input or set in advance by the user business operator, and transmits the execution command to the robot control device  2   b.    
     The processor  11  in the host device  1  according to the second embodiment refers to the external storage ST based on a reading result of the identification sign Q read by the reading unit  53   b , and acquires the information on the ID of the workpiece to which the read identification sign Q is assigned. The processor  11  outputs the acquired workpiece ID to the monitor MN 1 . The processor  11  may transmit the acquired workpiece ID to the reading device  5  and cause the reading device  5  to display the acquired workpiece ID. 
     The reading unit  53   b  includes, for example, a camera for reading a two-dimensional barcode or a laser for reading a barcode. The reading unit  53   b  reads the identification sign Q assigned to the workpiece, and outputs information (data) read from the identification sign Q to the processor  21 . 
     As described above, the welding system  100  according to the second embodiment can not only read the identification sign Q using the reading device  5  but also read the identification sign Q using the main welding robot MC 1   b . Accordingly, the welding system  100  according to the second embodiment can read the IDs of a plurality of original workpieces or welded workpieces from the identification sign Q assigned to the workpiece Wk, for example, before, after, or both before and after the welding process, can display the read IDs of the workpieces on the reading device  5  owned by the user business operator, and can more efficiently read the IDs of the workpieces. 
     Since the ID of the workpiece can be read by the robot control device  2   b  and the reading device  5 , the user business operator can select which of the robot control device  2   b  and the reading device  5  reads the ID of the workpiece in accordance with a production process of the welded workpiece, such as a case where there are a plurality of welding processes or a case where the welding process is executed in a different cell. 
     Although the various embodiments are described above with reference to the drawings, it is needless to say that the present disclosure is not limited to such examples. It will be apparent to those skilled in the art that various alterations, modifications, substitutions, additions, deletions, and equivalents can be conceived within the scope of the claims, and it should be understood that such changes also belong to the technical scope of the present disclosure. Further, components in the various embodiments described above may be combined optionally in the range without deviating from the spirit of the invention. 
     The present application is based on Japanese Patent Application (Japanese Patent Application No. 2019-188154) filed on Oct. 11, 2019, and contents thereof are incorporated herein by reference. 
     The present disclosure is useful as a welding method, an identification sign assignment device, and a weldment that support more efficient management of an identifier of a workpiece produced in a process such as welding.