Patent Publication Number: US-2022229420-A1

Title: Identifier management method, and reading device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of PCT International Patent Application No. PCT/JP2020/037362 filed on Sep. 30, 2020, which claims the benefit of priority of Japanese Patent Application No. 2019-188157 filed on Oct. 11, 2019, the entire contents of which are incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to an identifier management method and a reading device. 
     BACKGROUND 
     JP-A-2017-102548 discloses a production management device that manages production performance information on a manufacturing line in which a plurality of manufacturing machines are arranged. The production management device detects which manufacturing machine a workpiece supplied to the manufacturing line is located in, generates an identifier unique to the workpiece when it is detected that the workpiece is located in any manufacturing machine, notifies the manufacturing 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 manufacturing machine. Each time the workpiece is sequentially moved to each of a plurality of manufacturing 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 an identifier management method and reading device which support more efficient management of an identifier of a workpiece manufactured in a process such as welding, an identification sign assignment device, and a weldment. 
     The present disclosure provides an identifier output method to be executed by a welding system, the identifier output method including: acquiring information on identifiers of a plurality of original workpieces to which identification signs are assigned, respectively, the identification signs being assigned such that information on the identifiers are readable; selecting, from the identifiers of the plurality of original workpieces according to a predetermined rule, an identifier to be set for a welded workpiece to be produced by a welding process using the plurality of original workpieces; and after the selecting, in a case in which any identification sign among the identification signs assigned to the plurality of original workpieces is read by the reading device, outputting, as an identifier of the welded workpiece, the information on the identifier that has been selected to the reading device. 
     The present disclosure provides a reading device configured to read identification signs assigned to a plurality of original workpieces to be used in a welding process performed by a welding system, the reading device including: a reading unit configured to read the identification signs capable of outputting information on respective identifiers of the plurality of original workpieces; a processor configured to acquire, based on an identification sign that has been read, information on an identifier associated with the identification sign from the welding system; and an output unit configured to output the information on the identifier that has been acquired. 
     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 the host device, a robot control device, and a reading device according to a first embodiment. 
         FIG. 3  is an explanatory diagram showing an example of an operation outline example at the time of welding using a workpiece with an ID “A” and a workpiece with an ID “B”. 
         FIG. 4  is an explanatory diagram showing an example of display of a reading result of an ID during welding using the workpiece of ID “A” and the workpiece with the ID “B”. 
         FIG. 5  is an explanatory diagram showing an example of the operation outline at the time of welding using the workpiece with the ID “A”, the workpiece with the ID “B”, a workpiece with an ID “C”, and a workpiece with an ID “D”. 
         FIG. 6  is a diagram showing an example of the correspondence table between the existing IDs and the management IDs. 
         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 and a robot control 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 an identifier management method and a reading device which support more efficient management of the identifier of the workpiece produced in a process such as welding will be described. 
     Hereinafter, embodiments specifically disclosing an identifier management method and a reading device 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 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 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 ), and a reading device  3 . 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 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 welding 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  FIGS. 3 and 5 ). 
     The host device  1  is connected to the monitor MN 1 , the input interface UI 1 , the reading device  3 , 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  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 of each of the plurality of the original workpieces 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  sets the ID of a welded workpiece (for example, a secondary workpiece) produced by the welding process to an ID selected in advance according to a predetermined rule. Further, the host device  1  generates the welding process logical data (see  FIGS. 3 and 5 ) corresponding to the set welded workpiece. 
     The host device  1  stores, in the external storage ST, the information on the identification sign that can be assigned to each original workpiece and that can read the information on the ID set in the original workpiece and the ID set in the original workpiece in association with each other. Further, when the ID is set for the welded workpiece, the host device  1  stores the ID of the welded workpiece and the welding process logical data in the external storage ST in association with the information on the identification signs of the plurality of original workpieces. At this time, the host device  1  does not overwrite and store the set IDs of the welded workpieces to the IDs of the plurality of original workpieces used for producing the welded workpieces, and stores the IDs as the IDs to be output to the reading device  3 . The information (data) stored in association with the identification sign is not limited to the information on the ID set for the plurality of original workpieces or welded workpieces and the welding process logical data, and may include, for example, welding-related information stored in association with the ID, and a management ID (see  FIG. 6 ). Accordingly, the host device  1  can appropriately manage the IDs of the welded workpieces produced by the welding process by various main welding robots, and can similarly manage the IDs of the plurality of original workpieces used for producing the welded workpieces. Details of an operation of the host device  1  will be described later with reference to the drawings. The host device  1  may display the welding process logical data including the ID of the welded workpiece on the monitor MN 1 . 
     The host device  1  receives information on the identification sign read by the reading device  3  from the reading device  3  capable of reading the identification sign arranged for each of the workpiece. Based on the received information on the identification sign, the host device  1  acquires information on the ID set for the plurality of original workpieces or the welded workpiece read by the reading device  3  from the external storage ST, and transmits the information to the reading device  3 . 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, welding-related information, welding process logical data, and management IDs (see  FIG. 6 ) stored in association with the IDs. 
     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 assigned (that is, marked) to the original workpiece by a laser, or may be assigned by attaching the IC tag or the RF tag. 
     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 welding-related information, or an input operation when a welding process execution command is transmitted to the robot control device  2   a.    
     The reading device  3  is a device that reads the identification sign arranged on 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  3  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  3  transmits the information on the read identification sign to the host device  1 . The reading device  3  displays (outputs) the ID of the original workpiece or the welded workpiece received from the host device  1 . The reading device  3  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, information on the identification sign arranged on each workpiece, data of welding-related information created for each welding process, and welding process logical data (see  FIGS. 3 and 5 ) 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 , the robot control device  2   a , and the reading device  3  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. 2 , 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. 
     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 host device  1  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 communication unit  10  is connected to the robot control device  2  and the external storage ST so that data can be communicated among the communication unit  10 , the robot control device  2   a , and the external storage ST. The communication unit  10  transmits a welding process execution command (see the above description) generated by the processor  11  to the robot control device  2   a . The communication unit  10  receives the ID of the welded work transmitted from the robot control device  2   a  and outputs the ID to the processor  11 . The welding process execution command may include, for example, a control signal for controlling each of the manipulator  200 , the wire feeding device  300 , and the power supply device  4  included in the main welding robot MC 1   a.    
     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 welding-related information read from the external storage ST, 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  FIGS. 3 and 5 ) 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  as the ID of the welded workpiece (secondary workpiece) produced by the welding process using each of the plurality of original workpieces, and stores the ID in the memory  12 . The ID setting management unit  14  may store the ID of the welded workpiece (secondary workpiece) and the welding process logical data (see the following description) in the external storage ST in association with the information on the identification sign Q. 
     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  FIGS. 3 and 5 ). Details of the welding process logical data will be described later with reference to  FIGS. 3 and 5 . The logical data generation unit  15  may store the ID of the welded workpiece (secondary workpiece) and the welding process logical data (see  FIG. 3 ) in the external storage ST in association with the information on the identification sign Q. 
     After the welding process using the plurality of original workpieces is completed, the ID selection unit  16  sets, according to a predetermined rule, the ID of the welded workpiece (secondary workpiece) selected in advance before the welding process is performed. Here, the ID and the predetermined rule will be described. In the present specification, the predetermined rule used for the selection of the ID is a rule to be selected by the ID strength (that is, the ID is strong and the ID is weak), a rule to be randomly selected from the IDs set for the plurality of original workpieces used for the production of the welded workpiece, and a rule to generate a new ID different from the IDs of the plurality of original workpieces. The ID selection unit  16  selects or generates the ID of the welded workpiece based on any one of the rules set by the user business operator, and sets the ID. 
     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 for example, different numbers of digits such as “TA001” and “RA001” shown in  FIG. 4  may be set. Hereinafter, the rules for selecting or generating the ID of the welded workpiece will be described. 
     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 stronger 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. 
     Next, the rule for randomly selecting any of the IDs of the plurality of original workpieces and determining the selected ID as the ID of the welded workpiece (secondary workpiece) will be described. In other words, when the IDs of the plurality of original workpieces are “A” and “B” (see  FIG. 3 ), the ID selection unit  16  randomly selects “A” or “B” as the ID of the welded workpiece (for example, the secondary workpiece). “Random” means that probability that the ID “A” is selected and probability that the ID “B” is selected at the time of selection may be equal (for example, 50% each) or may not be equal. A fact that the probabilities are not equal indicates that, for example, one of the IDs may be selected more unevenly or preferentially than other IDs. 
     Next, the rule for selecting or generating the new ID different from any ID among the IDs of the plurality of original workpieces and determining the ID as the ID of the welded workpiece (secondary workpiece) will be described. In other words, when the IDs of the plurality of original workpieces are “A” and “B”, the ID selection unit  16  generates a new ID such as “X” as the ID of the welded workpiece (for example, the secondary workpiece). Here, the original workpiece and the welded workpiece include a final weldment (for example, an n-th workpiece) produced by completing all the welding processes (for example, n welding processes (n is an integer of 3 or more)). The ID selection unit  16  may generate different new IDs for a plurality of welded workpieces to which the same welding process is completed. For example, the ID selection unit  16  may generate the ID of each of the three welded workpieces (secondary workpieces) produced by the execution of the secondary welding process, as “X”, “Y”, and “Z”. 
     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 (the secondary workpiece) produced by the welding process to the host device  1 . 
     Here, the secondary workpiece information includes, in addition to the ID of the welded workpiece (the secondary workpiece), at least workpiece information (for example, the ID and name of the original workpiece, 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 (the 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 . 
     The reading device  3  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  3  is used by the user business operator. The reading device  3  includes at least a communication unit  30 , a processor  31 , a memory  32 , a reading unit  33 , and an operation unit  35 . A monitor  34  may or may not be included in the reading device  3 . When the monitor  34  is implemented as a configuration that is not included in the reading device  3 , the monitor  34  is connected to the reading device  3  so as to be capable of wireless or wired communication. The reading device  3  may include a speaker (not shown) when the reading device  3  outputs information on the ID of the workpiece by voice. 
     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  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 reading result of the identification sign Q by the processor  31 . The communication unit  30  receives the ID of the welded workpiece transmitted from the host device  1 , and outputs the ID to the processor  31 . 
     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 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. Further, the memory  32  stores the information on the identification sign Q read from the reading unit  33 , 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  33  includes, for example, a camera for reading a two-dimensional barcode or a laser for reading a barcode. The reading unit  33  reads the identification sign Q assigned to the workpiece, and outputs information (data) read from the identification sign Q to the processor  31 . 
     The reading unit  33  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  33  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  33  outputs information (data) on the identification sign Q acquired as a result of the image analysis to the processor  31 . 
     The reading unit  33  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  33  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  33  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  31 . When the reading unit  33  is implemented by the RFID, the reading unit  33  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  34  serving as an example of an output unit is configured using, for example, a liquid crystal display (LCD) or an organic electroluminescence (EL). The monitor  34  outputs the ID of the workpiece received from the host device  1 . The monitor  34  may be a touch interface configured by a touch panel. In such a case, the monitor  34  has a function as an operation unit  35 , 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  31 . 
     The operation unit  35  receives the input operation by the user business operator and outputs the input operation to the processor  31 . The operation unit  35  generates the control signal based on the input operation by the user business operator and outputs the control signal to the processor  31 . The operation unit  35  may be implemented as a touch panel of the monitor  34  described above. 
       FIG. 3  is an explanatory diagram showing an example of an operation outline at the time of welding using a workpiece with an ID “A” and a workpiece with an ID “B”. In the example of  FIG. 3 , a process in which a welded workpiece (that is, the secondary workpiece Wk 3 ) is produced by joining a circular workpiece Wk 1  (original workpiece) having the ID “A” and a square workpiece Wk 2  (original workpiece) having the ID “B” in one welding process is shown. As described above, the IDs “A” and “B” are, for example, 12-digit alphabets and numerals, but are collectively represented by one alphabetic character in order to make the description of  FIG. 3  easy to understand. 
     In  FIG. 3 , the ID selection unit  16  selects the ID “A” as an ID read from each of the plurality of identification signs Q 1  and Q 2  assigned to the welded workpiece (that is, the secondary workpiece Wk 3 ). Here, when the ID selection unit  16  determines that the ID “A” is stronger than the ID “B” based on strength information on the set ID, 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 ). The ID selection unit  16  may randomly adopt one of the ID strength or the ID “A” and the ID “B” (see the above description), and select the ID “A” as the ID of the welded workpiece (that is, the secondary workpiece Wk 3 ). As described above, it is needless to say that the ID selection unit  16  may generate and adopt a new ID different from the ID of each of the workpieces Wk 1  and Wk 2  (original workpieces). 
     The ID setting management unit  14  sets the ID of the secondary workpiece Wk 3  selected by the ID selection unit  16  to the ID “A”. The ID setting management unit  14  associates the ID “A” set for the secondary workpiece Wk 3  with the identification sign Q 1  assigned to the workpiece Wk 1  (original workpiece) and the identification sign Q 2  assigned to the workpiece Wk 2  (original workpiece) as an ID to be output to the reading device  3 , and stores the ID “A” in the external storage ST. 
     When the reading device  3  reads the identification sign Q 1  assigned to the workpiece Wk 1  (original workpiece) before the first welding process, the reading device  3  receives the ID “A” of the workpiece Wk 1  (original workpiece) from the host device  1 , and outputs (displays) the ID “A” to a display screen R 11 . Similarly, when the reading device  3  reads the identification sign Q 2  assigned to the workpiece Wk 2  (original workpiece) before the first welding process, the reading device  3  receives the ID “B” of the workpiece Wk 2  (original workpiece) from the host device  1 , and outputs (displays) the ID “B” to a display screen R 21 . Further, the reading device  3  reads a plurality of identification signs Q 1  and Q 2  assigned to the secondary workpiece Wk 3  (welded workpiece) after the first welding process. At this time, the ID “A” of the secondary workpiece Wk 3  is set as the ID output to the reading device  3  by the plurality of identification signs Q 1  and Q 2 . Therefore, after the first welding process, the reading device  3  outputs (displays) the ID “A” on the display screen even when any of the plurality of identification signs Q 1  and Q 2  assigned to the secondary workpiece Wk 3  is read. Specifically, the reading device  3  outputs (displays) the ID “A” to the display screen R 12  when the identification sign Q 1  is read, and similarly outputs (displays) the ID “A” to the display screen R 22  when the identification sign Q 2  is read. In the display screen shown in  FIG. 3 , only the information on the ID displayed for easy understanding of the description of  FIG. 3  is shown in a simplified manner. In the description of  FIG. 3 , an output example of the reading device  3  is described for all the identification signs assigned to each workpiece. However, since the ID set in each welding process is set to be unified into one ID, the reading device  3  may read at least one identification sign among the plurality of identification sign assigned to each workpiece. 
     Accordingly, in the welding system  100  according to the first embodiment, even if the ID of the workpiece (that is, the secondary workpiece Wk 3 ) is randomly selected as the ID, if the ID “A” of the workpiece Wk 1  (original workpiece) and the ID “A” of the welded workpiece (that is, the secondary workpiece Wk 3 ) are the same, it may be complicated to manage whether the ID “A” is the ID of the workpiece Wk 1  (original workpiece) or the secondary workpiece Wk 3 . Therefore, in the welding system  100  according to the first embodiment, for example, in the welding process using the workpiece Wk 1  (original workpiece) having the ID “A” and the workpiece Wk 2  (original workpiece) having the ID “B”, the logical data generation unit  15  in the host device  1  generates welding process logical data “A-B” logically indicating a mutual relationship between the ID “A” of the workpiece Wk 1  (original workpiece), the ID “B” of the workpiece Wk 2  (original workpiece), and the ID “A” of the secondary workpiece Wk 3 . The logical data generation unit  15  stores the generated welding process logical data “A-B” in association with the ID of each of the plurality of workpieces Wk 1  and Wk 2  (original workpieces) stored in the external storage ST. 
     The welding process logical data “A-B” shown in  FIG. 3  is data having a logical structure in which the ID “A” is located at a higher level and the ID “B” is located at a lower level than the ID “A”. That is, the welding process logical data indicates, as viewed from the ID “A” of the secondary workpiece Wk 3 , which ID the original workpiece having is used and the secondary workpiece Wk 3  is produced by the welding process, and also indicates a list of IDs of the plurality of original workpieces used in the welding process and a temporal order in which the welding processes are executed when the plurality of welding processes exist. Accordingly, even after the welding process is completed, the user business operator can comprehensively grasp the data related to each of the original workpieces used for the production of the secondary workpiece Wk 3  without losing the information on the workpiece Wk 2  (original workpiece). 
     Further, the host device  1  generates a record TB 1  in which the ID “A” of the secondary workpiece Wk 3  and the welding process logical data “A-B” are associated with each other, and stores the record TB 1  in the external storage ST in association with each of the IDs of the plurality of workpieces Wk 1  and Wk 2  (original workpieces). The host device  1  may display, on the reading device  3  or the monitor MN 1 , a display screen showing the relationship between the ID “A” of the secondary workpiece Wk 3  and the welding process logical data “A-B”, or a display screen showing the relationship between the ID “B” of the secondary workpiece Wk 3  and the welding process logical data “A-B”. Accordingly, the user business operator can intuitively grasp details of the welding process that reaches the production of the secondary workpiece Wk 3 . Accordingly, even after the welding process is completed, the user business operator can comprehensively grasp the data related to each of the original workpieces used for the production of the secondary workpiece Wk 3  without losing the information on the workpiece Wk 1  (original workpiece). 
     The welding process logical data “A-B” is data having a logical structure in which the ID “B” is located at a higher level and the ID “A” is located at a lower level than the ID “B”. That is, the welding process logical data “A-B” indicates, as viewed from the ID “A” of the secondary workpiece Wk 3 , which ID the original workpiece having is used and the secondary workpiece Wk 3  is produced by the welding process, and also indicates a list of IDs of the plurality of original workpieces used in the welding process and a temporal order in which the welding processes are executed when the plurality of welding processes exist. 
       FIG. 4  is an explanatory diagram showing an example of display of a reading result of an ID during welding using the workpiece with the ID “A” and the workpiece with the ID “B”. The first welding process shown in  FIG. 4  is the same process as the first welding process described with reference to  FIG. 3 . In  FIG. 4 , an ID output to the reading device  3  when the ID of each workpiece before and after the first welding process is read will be described. Atiming at which the reading device  3  reads the ID of the workpiece may be only before the first welding process or only after the first welding process. 
     In  FIG. 4 , the host device  1  sets a management ID “TA001” that is set and used when actually managed in a user business operator (see the following description) for the ID “A” of the workpiece Wk 1  (original workpiece) shown in  FIG. 3 , and sets the management ID “RA001” for the ID “B” of the workpiece Wk 2  (original workpiece). The host device  1  further associates the management ID “TA001” set for the workpiece Wk 1  (original workpiece) with the identification sign Q 1 , and stores the management ID “TA001” in the external storage ST. Similarly, the host device  1  further associates the management ID “RA001” set for the workpiece Wk 2  (original workpiece) with the identification sign Q 2 , and stores the management ID “RA001” in the external storage ST. 
     In  FIG. 4 , the reading device  3  reads the ID of the workpiece before and after the first welding process. Before the first welding process, the reading device  3  reads the identification sign Q 1  assigned to the workpiece Wk 1  (original workpiece) having the ID “A” and the identification sign Q 2  assigned to the workpiece Wk 2  (original workpiece) having the ID “B” before the first welding process. 
     When the reading device  3  reads the identification sign Q 1  assigned to the workpiece Wk 1  (original workpiece) before the first welding process, the reading device  3  receives the ID “A” of the workpiece Wk 1  (original workpiece) from the host device  1 , and displays the management ID “TA001” on the display screen SR 11 . The display screen SR 11  includes a plurality of buttons “Detail” and “Back”, and when the button “Detail” is selected (input) by the user business operator operation, the display screen SR 11  displays various kinds of information stored in association with the information on the identification sign Q 1  (data of the welding-related information related to the first welding process read from the external storage ST, customer (supplier) information on the workpiece Wk 1  (the original workpiece), and the like). When the button “Back” is selected (input), the reading device  3  shifts to a screen (not shown) for reading the identification sign. 
     Similarly, when the reading device  3  reads the identification sign Q 2  assigned to the workpiece Wk 2  (original workpiece) before the first welding process, the reading device  3  receives the ID “B” of the workpiece Wk 2  (original workpiece) from the host device  1 , and displays the ID “RA001” to the display screen SR 21 . The display screen SR 21  includes a plurality of buttons “Detail” and “Back”, and when the button “Detail” is selected (input) by the user business operator operation, the display screen SR 21  displays various kinds of information stored in association with the information on the identification sign Q 2  (data of the welding-related information related to the first welding process read from the external storage ST, customer (supplier) information on the workpiece Wk 2  (the original workpiece), and the like). 
     The host device  1  selects and sets the ID “TA001” as the ID of the secondary workpiece Wk 3 . The host device  1  associates the set ID “TA001” with the identification signs Q 1  and Q 2  assigned to each of the workpieces Wk 1  and Wk 2  (original workpieces) used for the production of the secondary workpiece Wk 3  as an ID to be output to the reading device  3 , and stores the ID “TA001” in the external storage ST. When the reading device  3  reads the identification sign Q 1  assigned to the secondary workpiece Wk 3  after the first welding process, the reading device  3  receives the ID “TA001” set in the secondary workpiece Wk 3  from the host device  1 , and when the identification sign Q 2  is read, the reading device  3  receives the ID “TA001” set in the secondary workpiece Wk 3  from the host device  1 . The reading device  3  displays the received ID “TA001”. 
     The display screen SR 12  when the identification sign Q 1  of the secondary workpiece Wk 3  is read includes the ID “TA001” of the secondary workpiece Wk 3  and the plurality of buttons “Detail” and “Back”, and when the button “Detail” is selected (input) by the user business operator, the display screen SR 12  displays the welding process logical data of the secondary workpiece Wk 3  stored in association with the information on the identification sign Q 1 , the various kinds of information stored in association with the information on the identification sign Q 1  (data of the welding-related information related to the first welding process read from the external storage ST, the customer (supplier) information on the workpiece Wk 1  (the original workpiece), and the like). Similarly, the display screen SR 22  when the identification sign Q 2  of the secondary workpiece Wk 3  is read includes the ID “TA001” of the secondary workpiece Wk 3  and the plurality of buttons “Detail” and “Back”, and when the button “Detail” is selected (input) by the user business operator, the display screen SR 22  displays the welding process logical data of the secondary workpiece Wk 3  stored in association with the information on the identification sign Q 2 , the various kinds of information stored in association with the information on the identification sign Q 1  (data of the welding-related information related to the first welding process read from the external storage ST, the customer (supplier) information on the workpiece Wk 1  (the original workpiece), and the like). When the button “Back” is selected (input), the reading device  3  shifts to a screen (not shown) for reading the identification sign. 
     Accordingly, the reading device  3  according to the first embodiment can visualize the IDs of the workpieces and the welding process logical data before and after the welding process without losing the information on each of the workpieces Wk 1  and Wk 2  (original workpieces). As described above, even when any of the plurality of identification signs assigned to the n-th workpiece is read, the host device  1  according to the first embodiment uniformly sets the same ID so that the same ID is output (displayed). Therefore, it is possible to reduce the possibility that all the identification signs assigned to the n-th workpiece are unreadable due to, for example, dirt, or breakage. Further, the user business operator can comprehensively grasp the information on the plurality of workpieces Wk 1  and Wk 2  (original workpiece) or the secondary workpiece Wk 3  (for example, the ID or the management ID for each workpiece, the welding-related information for each welding process, and the welding process logical data in the n-th workpiece) from the information displayed on the reading device  3 . 
       FIG. 5  is an explanatory diagram showing an example of an operation outline at the time of welding using the workpiece with the ID “A”, the workpiece with the ID “B”, the workpiece with the ID “C”, and the workpiece with the ID “D”. In the example of  FIG. 5 , a triangular parallelepiped workpiece Wk 4  (original workpiece) having the ID “C” and a pentagonal workpiece Wk 5  (original workpiece) having the ID “D” are joined together in a first welding process to produce a welded workpiece (that is, a secondary workpiece Wk 6 ), a circular workpiece Wk 1  (original workpiece) having the ID “A” and a rectangular workpiece Wk 2  (original workpiece) having the ID “B” are joined together in a second 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. 5  easy to understand. 
     The ID selection unit  16  in  FIG. 5  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. 5 , 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 “C” is stronger than the ID “D”. In this case, the ID selection unit  16  adopts and selects the stronger ID “C” 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 “A” is stronger than the ID “C”. 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 tertiary workpiece Wk 7 ) which is the product of the third welding process. 
     However, if the ID “A” of the workpiece Wk 1  (original workpiece), the ID “A” of the welded workpiece (that is, the secondary workpiece Wk 3 ), and the ID “A” of the tertiary workpiece Wk 7  are all the same, it may be complicated to manage which ID “A” is the workpiece Wk 1  (original workpiece), the secondary workpiece Wk 3 , or the tertiary workpiece Wk 7 . Therefore, in the welding system  100  according to the first embodiment, for example, in the first welding process to the third welding process, the host device  1  generates the welding process logical data (see  FIG. 5 ) logically indicating a mutual relationship between the strongest ID “A” and other weak IDs “B”, “C”, and “D”, generates a record TB 2  in which the ID “A” of the tertiary workpiece Wk 7  and the welding process logical data are associated with each other, and stores the record TB 2  in the external storage ST. 
     The welding process logical data indicates, as viewed from the ID “A” 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 “A” 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 “C” is stronger than the ID “D”, 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 “C” 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 “A” of the tertiary workpiece Wk 7 , a position closer to the ID “A” indicates that a time at which the workpiece Wk 1  (original workpiece) or the secondary workpiece Wk 3  of the ID “A” is welded is older, and a position farther from the ID “A” indicates that the time at which the workpiece Wk 1  (original workpiece) or the secondary workpiece Wk 3  of the ID “A” 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 each of 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 weak ID in each welding process. 
     The ID of each workpiece displayed by reading each of the plurality of identification signs Q 1  to Q 4  assigned to each workpiece in the first welding process to the third welding process shown in  FIG. 5  will be described. Before the first welding process, the reading device  3  transmits the information on the identification sign Q 1  assigned to the workpiece Wk 1  (original workpiece) to the host device  1 , reads the ID “A” of the workpiece Wk 1  (original workpiece), and displays the display screen R 11  including the read ID “A”. The reading device  3  transmits the information on the identification sign Q 2  assigned to the workpiece Wk 2  (original workpiece) to the host device  1 , reads the ID “B” of the workpiece Wk 2  (original workpiece), and displays the display screen R 21  including the read ID “B”. In the first welding process, the host device  1  selects (sets) the ID “A” as the ID of the secondary workpiece Wk 3  based on the ID strength rule. Therefore, the reading device  3  reads the same ID “A” even when any information on the plurality of identification signs Q 1  and Q 2  assigned to the secondary workpiece Wk 3  is transmitted to the host device  1 . The reading device  3  displays the display screen R 12  including the ID “A” when the identification sign Q 1  assigned to the secondary workpiece Wk 3  is read, and displays the display screen R 22  including the ID “A” when the identification sign Q 2  is read. 
     Before the second welding process, the reading device  3  transmits the information on the identification sign Q 3  assigned to the workpiece Wk 4  (original workpiece) to the host device  1 , reads the ID “C” of the workpiece Wk 4  (original workpiece), and displays the display screen R 31  including the read ID “C”. The reading device  3  transmits the information on the identification sign Q 4  assigned to the workpiece Wk 5  (original workpiece) to the host device  1 , reads the ID “D” of the workpiece Wk 4  (original workpiece), and displays the display screen R 41  including the read ID “D”. In the second welding process, the host device  1  selects (sets) the ID “C” as the ID of the secondary workpiece Wk 6  based on the ID strength rule. Therefore, the reading device  3  reads the same ID “C” even when any information on the plurality of identification signs Q 1  and Q 2  assigned to the secondary workpiece Wk 6  is transmitted to the host device  1 . The reading device  3  displays the display screen R 32  including the ID “C” when the identification sign Q 3  assigned to the secondary workpiece Wk 6  is read, and displays the display screen R 42  including the ID “C” when the identification sign Q 4  is read. 
     In the third welding process, the host device  1  selects (sets) the ID “A” as the ID of the tertiary workpiece Wk 7  based on the ID strength rule. After the third welding process, the reading device  3  transmits the information on the identification sign Q 1  assigned to the tertiary workpiece Wk 7  to the host device  1 , reads the ID “A” of the tertiary workpiece Wk 7 , and displays the display screen R 13  including the read ID “A”. Similarly, the reading device  3  displays the display screen R 23  including the ID “A” read from the identification sign Q 2  assigned to the tertiary workpiece Wk 7 , displays the display screen R 33  including the ID “A” read from the identification sign Q 3 , and displays the display screen R 43  including the ID “A” read from the identification sign Q 4 . 
     In the description of  FIG. 5 , an output example of the reading device  3  is described for all the identification signs assigned to each workpiece. However, since the ID set in each welding process is set to be unified into one ID, the reading device  3  may read at least one identification sign among the plurality of identification sign assigned to the welded workpiece in each of the welded workpieces (the secondary workpiece Wk 6 , the secondary workpiece Wk 3 , and the tertiary workpiece Wk 7 ). 
     As described above, the reading device  3  according to the first embodiment can visualize the IDs of the workpieces and the welding process logical data before and after the welding process without losing information on the workpieces Wk 1 , Wk 2 , Wk 4 , and Wk 5  (original workpieces) and the plurality of secondary workpieces Wk 3  and Wk 6  (welded workpieces). As described above, even when any of the plurality of identification signs assigned to the n-th workpiece is read, the host device  1  according to the first embodiment uniformly sets the same ID so that the same ID is output (displayed). Therefore, it is possible to reduce the possibility that all the identification signs assigned to the n-th workpiece are unreadable due to, for example, dirt, or breakage. Further, the user business operator can comprehensively grasp the information related to each welding process (for example, the ID or the management ID for each workpiece, the welding-related information for each welding process, and the welding process logical data for the n-th workpiece) from the information displayed on the reading device  3 . 
       FIG. 6  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. 6 , 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. 6 , 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. 
     (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  3  with respect to the welding process using the plurality of workpieces Wk 1  and Wk 2  (original workpieces) shown in  FIG. 3  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, and the welding position of the original workpiece) including an ID of the plurality of workpieces Wk 1  and Wk 2  (original workpieces) to be subjected to the welding process (main welding) (St 1 ), and selects (generates) an ID adopted as an ID of the secondary workpiece Wk 3  (that is, the welded workpiece) after the welding process based on the predetermined rule (St 2 ). The ID of the secondary workpiece Wk 3  (the welded workpiece) selected (generated) here may be stored in the memory  12  of the host device  1 . The host device  1  transmits a 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 3 ). Here, in the processing of step St 2 , it is assumed that, for example, the ID “A” of the workpiece Wk 1  (original workpiece) is selected as the ID of the secondary workpiece Wk 3  (welded workpiece). 
     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  generates a welding process program executed by the main welding robot MC 1   a  using the workpiece information on each of the plurality of workpieces Wk 1  and Wk 2  (original workpieces) included in the execution command, and causes the main welding robot MC 1   a  to execute the main welding according to the program (St 4 ). 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 5 ), generates a main welding completion notification indicating the completion of the main welding every time the main welding of each of the plurality of workpieces Wk 1  and Wk 2  (original workpieces) is completed, and transmits the notification to the host device  1  (St 6 ). 
     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 (generated) in the processing of step St 2  to be output to the reading device  3  as the ID “A” of the secondary workpiece Wk 3  (welded workpiece), and generates the welding process logical data (see  FIGS. 3 and 5 ) related to the secondary workpiece Wk 3  (welded workpiece) (St 7 ). The host device  1  stores the ID “A” of the secondary workpiece Wk 3  (the welded workpiece) and the welding process logical data on the secondary workpiece Wk 3  (the welded workpiece) in association with each other in the external storage ST (St 8 ). 
     The reading device  3  reads one of the identification signs Q 1  and Q 2  assigned to the secondary workpiece Wk 3  (welded workpiece) produced by the completion of the main welding (St 9 ), and transmits the information on the read identification sign to the host device  1  (St 10 ). Here, the read identification sign is referred to as the identification sign Q 2 . 
     The host device  1  refers to the external storage ST based on the information on the identification sign Q 2  received from the reading device  3 , 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 2  (St 11 ). The host device  1  transmits the acquired ID “A” of the secondary workpiece Wk 3  (welded workpiece) to the reading device  3  (St 12 ). 
     The reading device  3  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  (Stl 3 ). 
     As described above, the welding system  100  according to the first embodiment acquires the information on the IDs of the plurality of original workpieces to which the identification signs are assigned, respectively, the identification signs being assigned such that the information on the IDs (identifiers) are readable; selects, from the IDs of the plurality of original workpieces according to the predetermined rule, the ID to be set for the welded workpiece to be produced by the welding process using the plurality of original workpieces; and after the selection, in a case in which any identification sign among the identification signs assigned to the plurality of original workpieces is read by the reading device, outputs, as the ID of the welded workpiece, the information on the selected ID to the reading device. 
     Accordingly, the welding system  100  according to the first embodiment can support more efficient management by uniformly setting the IDs of the workpieces (in other words, the welded workpieces) produced in the welding process in which the plurality of original workpieces are joined or the like and outputting the IDs to the reading device  3 . 
     In the welding system  100  according to the first embodiment, identification signs of the plurality of original workpieces are assigned to the welded workpiece so as to be readable by the reading device  3 . Accordingly, the welding system  100  according to the first embodiment can acquire information on the plurality of original workpieces used in the production of the workpiece by reading at least one of the plurality of identification signs assigned to the workpiece even when the identification sign assigned in the welding process is contaminated, damaged, or the like, by assigning the plurality of identification signs in which the unified ID is set to the welded 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 an 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  according to the first embodiment can easily set and 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. The predetermined rule includes randomly employing any one of the IDs of the plurality of original workpieces included in the welded workpiece in the selection of the ID to be set for the welded workpiece. Accordingly, the welding system  100  according to the first embodiment can easily set and 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. The predetermined rule includes adopting another ID different from the IDs of the plurality of original workpieces included in the welded workpiece in the selection of the ID to be set for the welded workpiece to be adopted. Accordingly, the welding system  100  according to the first embodiment can easily set and manage an ID different from any of the IDs of the plurality of original workpieces used for the production of the welded workpiece (for example, the secondary workpiece). 
     The reading device  3  according to the first embodiment is configured to read the identification signs assigned to the plurality of original workpieces to be used in the welding process performed by the welding system  100 , and includes the reading unit  33  configured to read the identification signs capable of outputting the information on the respective identifiers of the plurality of original workpieces, the processor  31  configured to acquire, based on an identification sign that has been read, the information on the identifier associated with the identification sign from the welding system, and the output unit (for example, the monitor  34 ) configured to output the information on the identifier that has been acquired. 
     Accordingly, the reading device  3  according to the first embodiment can output the ID of the welded workpiece by reading the identification sign assigned to each workpiece. Therefore, the user business operator can easily confirm the ID of the welded workpiece. 
     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  3  (that is, the example in which the ID of the workpiece is read by the reading device  3 ) 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  33   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  33   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  33   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  3  and cause the reading device  3  to display the acquired workpiece ID. 
     The reading unit  33   b  includes, for example, a camera for reading a two-dimensional barcode or a laser for reading a barcode. The reading unit  33   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  3  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  3  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  3 , the user business operator can select which of the robot control device  2   b  and the reading device  3  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. 2019-188157) filed on Oct. 11, 2019, and contents thereof are incorporated herein by reference. 
     The present disclosure is useful as an identifier management method and a reading device which support more efficient management of an identifier of a workpiece produced in a process such as welding.