Abstract:
After selecting a robot for carrying out a welding operation at a given welding spot, the cross-section of a welding gun with which that robot is provided and the cross-section of a workpiece at the welding spot are compared. Furthermore, a determination is made as to whether or not welding is possible without the welding gun and the workpiece coming into contact. When it is determined to be impossible, a substitute robot for carrying out the welding of the welding spot is selected. With the present invention, the automatic selection of the robot for carrying out the welding operation for the welding spot becomes possible. Therefore, the number of steps for robot selection can be reduced.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a robot selection method and a robot selection apparatus (device) for selecting a robot to perform welding of a welding spot. 
       BACKGROUND ART 
       [0002]    For example, Japanese Laid-Open Patent Publication No. 2012-091304 and Japanese Patent No. 5474739 disclose techniques relating to off-line teaching of a welding gun performing a welding operation. In the technique described in Japanese Patent Laid-Open No. 2012-091304, teaching data for existing workpieces is diverted as teaching data for similar new workpieces. In the technique described in Japanese Patent No. 5474739, interference between two robots is detected. 
       SUMMARY OF INVENTION 
       [0003]    A technique for automatically selecting a robot to perform a welding operation with respect to a welding spot is not disclosed, including Japanese Laid-Open Patent Publication No. 2012-091304 and Japanese Patent No. 5474739. In the present situation, for each welding spot, the operator performs the verification/selection operation of the robot that performs the welding operation on the welding spot. Excessive worker-hours are required for such an operation. 
         [0004]    The present invention has been made in consideration of such problems, and it is an object of the present invention to provide a robot selection method and a robot selection apparatus capable of automatically selecting a robot to perform a welding operation with respect to welding spots and reducing a worker-hour for selecting a robot. 
         [0005]    A method according to the present invention is a robot selection method for selecting a robot for each of a plurality of welding spots distributed in a workpiece to perform a welding operation with respect to the welding spots, the robot selecting method comprising: a robot selection step of selecting the robot to perform the welding operation on any of the welding spots; a welding capability determination step of determining whether it is possible to weld the welding spot without contact between a welding gun of the robot selected in the robot selection step and the workpiece by comparing a cross section of the welding gun and a cross section of the workpiece; and a substitution robot selection step of selecting a substitution robot that substitutes for welding at the welding spot in a case where the robot selected is determined to be incapable in the welding capability determination step. 
         [0006]    In the present invention, after selecting a robot to perform a welding operation at an arbitrary welding spot, the cross section of the welding gun of the robot is compared with the cross section of the workpiece at the welding spot. Then, it is determined whether welding can be performed without contact between the welding gun and the workpiece. If it is determined that it is not possible, a substitution robot that substitutes welding at the welding spot is selected. According to the present invention, by performing such a process, it is possible to select automatically a robot that performs a welding operation on a welding spot. As a result, it is possible to reduce worker-hours for robot selection. 
         [0007]    Further, in the present invention, in the substitution robot selection step, a candidate for the substitution robot is selected, a cross section of a welding gun of the candidate for the substitution robot and a cross section of the workpiece at the welding spot are compared, and the candidate for the substitution robot is selected as the substitution robot in a case where the welding spot can be welded using the welding gun of the candidate for the substitution robot without contact between the welding gun and the workpiece. In this way, by determining whether the substitution robot can be a fill-in, it is possible to select automatically a robot that performs a welding operation on the welding spot. 
         [0008]    In the present invention, in the substitution robot selection step, the substitution robot may be selected from the working station where the robot is installed. In this way, it is easy to select the substitution robot. 
         [0009]    In the present invention, in the substitution robot selection step, the substitution robot may be selected from a working station different from the working station where the robot is installed. In this way, the number of options of the substitution robot is increased, and the possibility of finding the substitution robot is increased. 
         [0010]    An apparatus according to the present invention is a robot selecting apparatus for selecting a robot for each of a plurality of welding spots distributed in a workpiece to perform a welding operation with respect to the welding spots, the apparatus comprising: a robot selecting unit configured to select the robot to perform the welding operation on any of the welding spots; a welding capability determination unit configured to determine whether it is possible to weld the welding spot without contact between a welding gun of the robot selected by the robot selecting unit and the workpiece, by comparing a cross section of the welding gun with a cross section of the workpiece at the welding spot; and a substitution robot selecting unit configured to select a substitution robot that substitutes for welding at the welding spot in a case where the robot selected is determined to be incapable by the welding capability determination unit. 
         [0011]    In the present invention, the substitution robot selection unit is configured to select a candidate for the substitution robot, compare a cross section of a welding gun of the candidate for the substitution robot with the cross section of the workpiece at the welding spot, and select the candidate as the substitution robot in a case where the welding spot can be welded using the welding gun of the substitution robot without contact between the welding gun and the workpiece. 
         [0012]    According to the present invention, it is possible to select automatically a robot that performs a welding operation with respect to a welding spot. Therefore, it is possible to reduce the worker-hour for robot selection. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0013]      FIG. 1  is a plan view of a production line with two working stations; 
           [0014]      FIG. 2  is an external view of the robot; 
           [0015]      FIG. 3  is a functional block diagram of a robot selecting apparatus according to the embodiment; 
           [0016]      FIG. 4  is a view showing an example of a welding spot-process table; 
           [0017]      FIG. 5  is a flowchart of a robot selection method according to the embodiment; 
           [0018]      FIG. 6  is a view for explaining a cross section of a welding gun; 
           [0019]      FIG. 7A  is a view showing a state in which a gun arm and the workpiece are not in contact, and  FIG. 7B  is a view showing a state in which the gun arm and the workpiece are in contact; and 
           [0020]      FIG. 8  is a flowchart of the substitution robot selection process. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0021]    Preferred embodiments of a robot selection method and a robot selection apparatus according to the present invention will be described in detail below with reference to the accompanying drawings. In the present embodiment, a vehicle body is assumed as the workpiece W, but the present invention is also applicable to a workpiece other than the vehicle body. 
       [Description of Production Line] 
       [0022]    Before describing a robot selection apparatus  40  according to the present invention, the production line L on which the welding operation of the workpiece W is performed will be described with reference to  FIG. 1 .  FIG. 1  shows a production line L with two working stations A, B. Each of the working stations A and B is provided for each operation step for the workpiece W. For convenience of explanation, the production line L having only two working stations A and B will be described, but the number of working stations provided in the production line L corresponds to the number of operation steps. In the production line L shown in  FIG. 1 , six robots  10  ( 10 A 1  to  10 A 6 ) are installed in the working station A and six robots  10  ( 10 B 1  to  10 B 6 ) are installed in the working station B. 
         [0023]    Here, with reference to  FIG. 2 , each robot  10  used in this embodiment will be described. The robot  10  is a multi-axis robot, and includes an installation section  12  and a turning section  14 , a first arm  16 , a second arm  18 , and a third arm  20  in this order with reference to the installation section  12 . The installation section  12  is installed at the predetermined installation sites in each working station A, B shown in  FIG. 1 . The turning section  14  is rotatably connected to the installation section  12  by a shaft J 1 . The first arm  16  is rotatably connected to the turning section  14  by a shaft J 2 . The second arm  18  is rotatably connected to the first arm  16  by a shaft J 3 . The second arm  18  can be twisted and rotated by the shaft J 4 . The third arm  20  is rotatably connected to the second arm  18  by a shaft J 5 . The third arm  20  can be twisted and rotated by the shaft J 6 . A welding gun  22  is detachably provided at a distal end of the third arm  20 . The welding gun  22  includes a gun arm  24  that can be opened and closed and electrode tips  26 . The controller  28  controls the operation of the robot  10  based on teaching data set in advance to process the workpiece. 
         [0024]    In this specification, all robots  10  installed in the working stations A and B are described as being the same, but robots installed in the working stations A and B may be different from each other. 
         [0025]    Returning to  FIG. 1 , the explanation will be continued. The workpiece W is conveyed to the working station A. The robots  10 A 1  to  10 A 6  installed to the working station A weld a part of welding spots in the workpiece W. Thereafter, the workpiece W is conveyed to the working station B. The robots  10 B 1  to  10 B 6  installed in the working station B weld the remaining welding spots other than the welding spots welded by the robots  10 A 1  to  10 A 6 . 
         [0026]    For example, the robot  10 A 1  can weld a welding spot included in the movable range FA 1 . However, if it is expected that the welding gun  22  and the workpiece W are in contact with each other when attempting to weld the welding spot with the welding gun  22 , the robot  10 A 1  cannot perform a welding operation on the welding spot. According to the present invention, as will be described later, the substitution robots  10 A 2  to  10 A 6  and  10 B 1  to  10 B 6  perform the welding operation on such welding spots. 
         [0027]    Like the robot  10 A 1 , the robots  10 A 2  to  10 A 6  can weld welding spots included in the movable ranges FA 2  to FA 6 . The robots  10 B 1  to  10 B 6  can weld welding spots included in the movable ranges FB 1  to FB 6 . In the present invention, when the first robot  10  cannot perform a welding operation with respect to the welding spot initially allocated, the second robot  10 , that is, the substitution robot  10  performs welding operation on the welding spot. The determination as to whether the welding operation with respect to the welding spot initially allocated can be performed and the selection of the second robot  10  are performed by the robot selecting apparatus  40  shown in  FIG. 3 . 
       [Configuration of Robot Selection Apparatus  40 ] 
       [0028]    The configuration of the robot selection apparatus  40  according to the present embodiment will be described with reference to  FIG. 3 . The robot selection apparatus  40  selects in advance which welding spot distributed in the workpiece W shown in  FIG. 1  is to be welded by which robot  10  ( 10 A 1  to  10 A 6 ,  10 B 1  to  10 B 6 ) prior to the welding operation. 
         [0029]    The robot selecting apparatus  40  includes a CPU that performs calculation processing, a memory that stores various data, an input/output device that inputs and outputs data, and the like, and is configured by, for example, a personal computer. The robot selection apparatus  40  functions as a robot selection unit  42 , a welding capability determination unit  44 , and a substitution robot selection unit  46  by executing a program stored inside or outside the apparatus. The functions of the robot selection unit  42 , the welding capability determination unit  44 , and the substitution robot selection unit  46  will be described later. 
         [0030]    The robot selecting apparatus  40  acquires existing data  52 , welding spot data  54 , and robot data  56 . The existing data  52  is data on an existing workpiece W′ (for example, an existing vehicle body) different from the workpiece W (for example, a new vehicle body). The existing data  52  is formed by associating the welding spot data  54  of the workpiece W′ with the robot  10 . The welding spot data  54  is data of each of the welding spots distributed in the workpiece W. The welding spot data  54  is formed by data, such as the spot number, welding operation process to be performed on the spot, the coordinates, the direction perpendicular to the plane of the spot (normal direction), the cross-sectional shape of the workpiece W at the welding spot, associated with each other. The robot data  56  is data of each robot  10  installed in the working stations A and B. The robot data  56  is constructed by data, such as a working station number to which the robot is to be installed, a movable range, a cross-sectional shape of the welding gun  22  of the robot  10 , and the like, associated with each other. 
         [0031]    In addition, the robot selection apparatus  40  includes a table storage unit  48 . The table storage unit  48  stores a welding spot-process table  62 .  FIG. 4  shows an example of the welding spot-process table  62 . In the welding spot-process table  62 , the spot number of each welding spot is associated with the operation process in which the welding operation of the welding spot can be performed. Specifically, in the welding spot-process table  62  shown in  FIG. 4 , the welding spots of the spot numbers  1001 ,  1002 ,  1003 ,  1004 ,  1005 , . . . are associated with the operation processes A, B, C, D, . . . . Operation processes A and B here correspond to working stations A and B shown in  FIG. 1 . For example, the welding spot of spot number  1001  is associated with the operation process A and the operation process B. This indicates that the welding spot of spot number  1001  distributed in the workpiece W can be welded in the operation process A and the operation process B. 
         [0032]    A display device  60  displays the result of the robot selection process performed by the robot selection apparatus  40  on the screen. 
       [Robot Selection Method] 
       [0033]    Next, the robot selection method according to this embodiment will be described with reference to  FIG. 5 . The following processing is performed for each welding spot. 
         [0034]    In step S 1 , the robot selecting apparatus  40  acquires the existing data  52 , the welding spot data  54 , and the robot data  56 . In step S 2 , the robot selection unit  42  selects the robot  10  ( 10 A 1  to  10 A 6 ,  10 B 1  to  10 B 6 ) that performs a welding operation with respect to an arbitrary welding spot. For example, when the coordinate of a certain welding spot included in the welding spot data  54  is similar to the coordinate of the welding spot included in the existing data  52 , the robot  10  included in the existing data  52  is selected. Alternatively, the coordinate and operation process of the welding spot included in the welding spot data  54  are collated with the working station number and the movable range of the robot  10  included in the robot data  56 , and the robot  10  that can perform the welding operation on the welding spot is selected. 
         [0035]    In step S 3 , the welding capability determination unit  44  compares the cross section  22 C of the welding gun  22  of the robot  10  selected by the robot selection unit  42  with the cross section WC of the workpiece W at the welding spot. The cross section  22 C of the welding gun  22  is acquired from the robot data  56 . The cross section WC of the workpiece W at the welding spot is acquired from the welding spot data  54 . 
         [0036]    Here, the cross section  22 C of the welding gun  22  will be described with reference to  FIG. 6 . The gun arm  24  of the welding gun  22  used in this embodiment has a first arm  24   a  and a second arm  24   b  which are openable and closable. The cross section  22 C of the welding gun  22  is defined based on the state in which the first arm  24   a  and the second arm  24   b  are closed. First, a rectangular outer frame OF surrounding the entire welding gun  22  is defined. At this time, the range on the tip end side of the gun arm  24  may extend up to the plane perpendicular axis, that is, the center axis of the electrode tips  26 . Next, the inner frame IF of the welding gun  22  is defined. The inner peripheral surface of the first arm  24   a  and the inner peripheral surface of the second arm  24   b  are parallel to each other. The length of a portion of the inner peripheral surface of the first arm  24   a  parallel to the inner peripheral surface of the second arm  24   b  is defined as B 1  and the length from the inner peripheral surface of the first arm  24   a  to the central axis C of the gun arm  24  is defined as H 1 . Similarly, the length of a portion of the inner peripheral surface of the second arm  24   b  parallel to the inner peripheral surface of the first arm  24   a  is defined as B 2 , and the length from the inner peripheral surface of the second arm  24   b  to the central axis C of the welding gun  22  is defined as H 2 . A rectangular frame surrounded by the length B 1  and the length H 1  and a rectangular frame surrounded by the length B 2  and the length H 2  are defined as the inner frame IF of the welding gun  22 . A portion of the welding gun  22  surrounded by the outer frame OF excluding a portion surrounded by the inner frame IF is defined as a cross section  22 C of the welding gun  22 . It is also possible to define the cross section  22 C by another method. 
         [0037]    In step S 4 , the welding capability determination unit  44  determines whether it is possible to weld the welding spot with the welding gun  22  of the robot  10 . Specifically, the following simulation is performed. The welding capability determination unit  44  assumes a state in which the posture of the welding gun  22  is adjusted based on the coordinates included in the welding spot data  54  and the direction perpendicular to the plane of the spot, and compares the cross section  22 C of the welding gun  22  and the cross section WC of the workpiece W with each other. As shown in  FIG. 7A , when the cross section  22 C of the welding gun  22  and the cross section WC of the workpiece W do not contact each other, the welding capability determination unit  44  determines that welding is possible (step S 4 : YES). At this time, the process proceeds to step S 6 . On the other hand, as shown in  FIG. 7B , when the cross section  22 C of the welding gun  22  makes contact with the cross section WC of the workpiece W, the welding capability determination unit  44  determines that welding is impossible (step S 4 : NO). At this time, the process proceeds to step S 5 , and the substitution robot selection process is performed. 
         [0038]    As shown in  FIG. 6 , when the first arm  24   a  and the second arm  24   b  are opened, the electrode tips  26 ,  26  are opened only by H 0 . In step S 4 , the welding capability determination unit  44  also determines whether the workpiece W to be placed between the gun arms  24  passes through the gun opening/closing height H 0 . When the height WH of the workpiece W is smaller than the gun opening/closing height H 0 , the welding capability determination unit  44  determines that welding is possible (step S 4 : YES). On the other hand, when the height WH of the workpiece W is larger than the gun opening/closing height H 0 , the welding capability determination unit  44  determines that welding is impossible (step S 4 : NO). 
         [0039]    In step S 6 , it is determined whether the robot  10  performing the welding operation with respect to the welding spot is selected. When the robot  10  that can be welded is selected by the robot selection unit  42  or the substitution robot selection unit  46  (step S 6 : YES), the series of processing ends. The welding capability determination unit  44  or the substitution robot selection unit  46  creates new data  58  in which the welding spot and the robot  10  performing the welding operation on the welding spot are associated. On the other hand, if the robot  10  capable of welding is not selected by the robot selection unit  42  or the substitution robot selection unit  46  (step S 6 : NO), the process proceeds to step S 7 . In step S 7 , the display device  60  displays an error indicating that the robot  10  has not been selected at the welding spot, and a series of processing is completed. 
         [0040]    Next, the substitution robot selection step shown in step S 5  in  FIG. 5  will be described with reference to  FIG. 8 . The substitution robot selection process is performed mainly by the substitution robot selection unit  46 . The substitution robot selection unit  46  selects the substitution robot  10  which substitutes for welding on the welding spot. 
         [0041]    In step S 11 , the substitution robot selection unit  46  searches candidates of the substitution robot  10  from the robots  10  installed in the same working station. In step S 12 , the substitution robot selection unit  46  determines whether there is a candidate for the substitution robot  10  in the same working station. When there is a candidate for the substitution robot  10  (step S 12 : YES), the process proceeds to step S 13 . When there is no candidate for the substitution robot  10  (step S 12 : NO), the process proceeds to step S 16 . 
         [0042]    Here, a specific process performed by the substitution robot selection unit  46  in steps S 11  and S 12  will be described with reference to  FIG. 1 . It is assumed that the robot  10 A 1  of the working station A cannot be welded to a certain welding spot. The substitution robot selection unit  46  determines whether the welding spot is included in the movable ranges FA 2  to FA 6  other than the movable range FA 1 . For example, when the welding spot is included in the movable range FA 2 , the substitution robot selection unit  46  selects the robot  10 A 2  as a candidate for the substitution robot  10 . 
         [0043]    In step S 13 , the substitution robot selection unit  46  compares the cross section  22 C of the welding gun  22  included in the candidate for the substitution robot  10  with the cross section WC of the workpiece W in the welding spot. Specifically, the process equivalent to the process performed by the welding capability determination unit  44  in step S 3  shown in  FIG. 5  is performed. 
         [0044]    In step S 14 , the substitution robot selection unit  46  determines whether it is possible to weld the welding spot with the welding gun  22  of the robot  10 . Specifically, the process equivalent to the process performed by the welding capability determination unit  44  is performed in step S 4  shown in  FIG. 5 . When the cross section  22 C of the welding gun  22  and the cross section WC of the workpiece W do not come into contact with each other, the substitution robot selection unit  46  determines that welding is possible (step S 14 : YES). At this time, the process proceeds to step S 15 . On the other hand, when the cross section  22 C of the welding gun  22  and the cross section WC of the workpiece W are to contact each other, the substitution robot selection section  46  determines that welding is impossible (step S 14 : NO). At this time, the process returns to step S 11 , and a search process of a further substitution robot  10  is performed. 
         [0045]    In step S 15 , the substitution robot selection unit  46  selects the candidate for the substitution robot  10  as the substitution robot  10 , and ends the substitution robot selection process. 
         [0046]    In step S 16 , a candidate for the substitution robot  10  is retrieved from among the robots  10  installed in another working station. In step S 17 , the substitution robot selection unit  46  determines whether there is a candidate for the substitution robot  10  in the other working station. When there is a candidate for the substitution robot  10  (step S 17 : YES), the process proceeds to step S 13 . When there is no candidate for the substitution robot  10  (step S 17 : NO), the substitution robot selection process is ended. 
         [0047]    Here, a specific process performed by the substitution robot selection unit  46  in steps S 16  and S 17  will be described with reference to  FIG. 1  and  FIG. 4 . It is assumed that the robot  10 A 1  of the working station A cannot be welded to a certain welding spot. The substitution robot selection unit  46  refers to the welding spot-process table  62  (see  FIG. 4 ) stored in the table storage unit  48 , and selects an operation process other than the operation process associated with the spot number, for example, the operation process A associated with the spot number  1001 . In the welding spot-process table  62  in  FIG. 4 , the spot number  1001  is associated with the operation process B in addition to the operation process A. In this case, the substitution robot selection unit  46  selects the operation process B. The substitution robot selection unit  46  then determines whether or not the welding spot is included in the movable ranges FB 1  to FB 6  of the robots  10 B 1  to  10 B 6  installed in the working station B. For example, when the welding spot is included in the movable range FB 1 , the substitution robot selection unit  46  selects the robot  10 B 1  as a candidate for the substitution robot  10 . Thereafter, the process proceeds to step S 13 , and the process is continued. 
       Summary of Present Embodiment 
       [0048]    Broadly speaking, a robot selection process, a welding capability determination process, and a substitution robot selection process are performed in the present embodiment. 
         [0049]    The robot selection process is performed by the robot selection unit  42  of the robot selection apparatus  40 . The robot selection unit  42  selects a robot  10  that performs a welding operation with respect to an arbitrary welding spot (step S 2 ). 
         [0050]    The welding capability determination step is performed by the welding capability determination part  44  of the robot selection apparatus  40 . The welding capability determination unit  44  compares the cross section  22 C of the welding gun  22  of the robot  10  selected in the robot selection step with the cross section WC of the workpiece W at the welding spot (step S 3 ). Then, it is determined whether the welding spot can be welded without contact between the welding gun  22  of the robot  10  and the workpiece W (step S 4 ). 
         [0051]    The substitution robot selection process is performed by the substitution robot selection unit  46  of the robot selection apparatus  40 . The substitution robot selection unit  46  selects the substitution robot  10  for substituting for the welding of the welding spot when it is determined that it is not possible to weld the welding spot without any contact between the welding gun  22  and the workpiece W in the welding capability determination step (step S 5 ). Specifically, the substitution robot selection unit  46  selects the candidate for the substitution robot  10  (step S 12 : YES, step S 17 : YES), and compares the cross section  22 C of the welding gun  22  included in the candidate for the substitution robot  10  with the cross section WC of the workpiece W (step S 13 ). When it is possible to weld the welding spot without any contact between the welding gun  22  included in the candidate for the substitution robot  10  and the workpiece W, the candidate for the substitution robot  10  is set as the substitution robot  10 . 
         [0052]    As described above, in the present embodiment, after selecting the robot  10  to perform the welding operation with respect to an arbitrary welding spot, the cross section of the welding gun of the robot  10  is compared with the cross section of the workpiece W at the welding spot. Then, it is determined whether welding can be performed without contact between the welding gun  22  and the workpiece W. If it is determined that it is not possible, the substitution robot  10  that substitutes the welding of the welding spot is selected. According to the present embodiment, by performing such a process, it is possible to select automatically the robot  10  that performs the welding operation on the welding spot. As a result, it is possible to reduce worker-hours for robot selection.