Patent Publication Number: US-11029254-B2

Title: Welding monitoring system and welding monitoring method

Description:
CLAIM OF PRIORITY 
     The present application is a divisional application of U.S. application Ser. No. 15/786,770, filed Oct. 18, 2017, which claims priority from Japanese Patent application serial no. 2016-205721, filed on Oct. 20, 2016, the content of which is hereby incorporated by reference into this application. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a quality monitoring system which uses optical means, and particularly to an efficient technology employed in quality monitoring of welded products having different sizes. 
     BACKGROUND ART 
     When managing the quality of a manufactured product by optical means, there is a case where it is necessary to capture an image not one surface of the manufactured product but multiple surfaces thereof at the same time. For example, in order to perform quality inspection of a welding portion in which two tubular members face each other, there is a case of imaging light emission of the entire circumference of the tube during the welding. In a case where such a light emitting monitoring system is provided on the inside of a welding machine, it is desirable that the imaging can be performed by one camera from the viewpoint of saving an installation space or simplifying a system configuration. 
     As a background art of the field of the technology, for example, there is a technology, such as Patent Literature 1. In Patent Literature 1, as a method for multidimensionally monitoring a subject by optical means, a method for keeping multiple observation target surfaces in an imaging viewing field of one camera by disposing a prism on the periphery, is disclosed. 
     CITATION LIST 
     Patent Literature 
     PTL 1: WO 2005/083399 
     SUMMARY OF INVENTION 
     Technical Problem 
     A case where components having different sizes exist together as components which flow in a manufacturing line of a welded product which is a subject, is considered. Even when an imaging target surface of the subject having a certain size is focused, the subject having another size is generally out of focus. In other words, in the imaging target, there is a point that approaches or becomes separated from the camera, and thus, an optical path length to the camera changes nonuniformly. Therefore, only by moving the position of the camera, it is not possible to focus on the entire imaging target region. In addition, in order to arrange the optical path lengths, when rearranging an optical system of the prism or the like in accordance with the size of the subject, extra time, machines, and human resources which are required for the rearrangement are necessary. 
     Above, even in a case of monitoring the subjects having different sizes, it is desirable to configure a system that inspects the quality by imaging the subjects by automatically focusing on the entire imaging target region in accordance with the size. 
     Here, an object of the present invention is to provide a welding monitoring system which multidimensionally monitors a welding portion with high accuracy and a monitoring method thereof, by using a relatively simple configuration. 
     Solution to Problem 
     In order to solve the above-described problem, according to the present invention, there is provided a welding monitoring system which monitors a subject, including: a mechanical portion; and an imaging portion, in which the mechanical portion includes a transport arm which transports the subject, a subject holding portion which holds the subject, and an energizing device which causes welding with respect to the subject to be performed, and in which the imaging portion includes imaging means for obtaining imaging data of the subject, a data recording portion which records the imaging data, an analyzing portion which extracts predetermined characteristics from the imaging data, a comparison determination portion which compares the extracted characteristics and normal characteristics to each other to determine the presence or absence of abnormality, and a determination result output portion which outputs a determination result by the comparison determination portion. 
     In addition, according to the present invention, there is provided a welding monitoring method for monitoring the subject, including: imaging the subject during attachment and transport to a subject holding portion; imaging the subject before welding, which is held by the subject holding portion; imaging the subject during the welding; imaging the subject after the welding, which is held by the subject holding portion; imaging the subject during detachment and transport from the subject holding portion; extracting predetermined characteristics from each piece of imaging data; determining the presence or absence of abnormality by comparing the extracted characteristics and normal characteristics to each other; and notifying a managing system or a manager of the determined result. 
     Advantageous Effects of Invention 
     According to the present invention, by using a relatively simple configuration, it is possible to realize a welding monitoring system which can multidimensionally monitor a welding portion with high accuracy, and a monitoring method thereof. 
     Other problems, configurations, and effects in addition to those described above will be apparent by the description of the following embodiments. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic view of a welding monitoring system according to a first embodiment of the present invention. 
         FIG. 2  is a view illustrating that cases where two subjects having different diameters are respectively set overlap each other, in the welding monitoring system of  FIG. 1 . 
         FIG. 3  is a schematic view of a subject picture imaged by the welding monitoring system of  FIG. 1 . 
         FIG. 4  is a schematic sectional view of a welding monitoring system according to a second embodiment of the present invention. 
         FIG. 5  is a schematic view of a welding monitoring system according to a third embodiment of the present invention. 
         FIG. 6  is a schematic view of a welding monitoring system according to a fourth embodiment of the present invention. 
         FIG. 7  is a schematic view of the periphery of the subject according to a fifth embodiment of the present invention. 
         FIG. 8  is a schematic view illustrating an operation of a welding monitoring system and a flow of imaging data processing according to a sixth embodiment of the present invention. 
         FIG. 9  is a flowchart illustrating a welding monitoring method according to the sixth embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an aspect (hereinafter, referred to as “embodiment”) for realizing the present invention will be described in detail with reference to the drawings. In addition, in each of the drawings, common parts will be given the same reference numerals, and the overlapping description will be omitted. 
     Example 1 
     First, a welding monitoring system according to a first embodiment of the present invention will be described with reference to  FIG. 1 .  FIG. 1  is a schematic view of a welding monitoring system  1  according to the embodiment. 
     The welding monitoring system  1  of the embodiment includes a welding machine  2 , an imaging portion  3 , a first holding portion  4 , a second holding portion  5 , and four mirrors (a first mirror  8 , a second mirror  9 , a third mirror  10 , and a fourth mirror  11 ). The imaging portion  3  includes a light receiving surface  6  for imaging a subject  20 . 
     The welding machine  2  (not illustrated) is transported to a welded product holding portion configured of the first holding portion  4  and the second holding portion  5  by a welded product gripping arm (not illustrated). A welded product (subject  20 ) during the welding and before and after the welding is captured by the imaging portion  3 , the quality is determined by analyzing the obtained image data, and the result thereof is output to a control system of a production system or is notified with respect to a field supervisor. In addition, in  FIG. 1 , as a part of the configuration of the welding machine  2 , the welding monitoring system  1  is illustrated. 
     Relative positions of the light receiving surface  6 , the first mirror  8 , and the third mirror  10  with respect to the first holding portion  4  are fixed, by a method, such as fastening. Relative positions of the second mirror  9  and the fourth mirror  11  with respect to the second holding portion  5  are fixed by a method, such as fastening. 
     A method for keeping the entire circumference of the side surface of the subject  20  within an imaging viewing field by one light receiving surface  6 , will be described. 
     In order to make it easy to understand the description, as a surface that becomes an imaging target, a virtual square pole side surfaces that are externally in contact with the subject  20  are considered, and one of the surfaces is referred to as a subject front surface  21 , surfaces orthogonal to the subject front surface  21  are referred to as a subject first side surface  22  and a subject second side surface  23 , and a surface which opposes the subject front surface  21  is referred to as a subject rear surface  24 . 
     The subject front surface  21  opposes the light receiving surface  6  substantially to be parallel thereto, and is kept within the imaging viewing field. Hereinafter, a direction which is parallel to a normal line of the subject front surface  21  and is oriented toward the light receiving surface  6  from the subject front surface  21  is referred to as a first direction  25 . In addition, a direction which is parallel to a normal line of the subject first side surface  22  and is oriented toward the subject first side surface  22  from the subject second side surface  23  is referred to as a second direction  26 . 
     The first mirror  8  is installed such that the light receiving surface  6  keeps the subject first side surface  22  in the viewing field. In other words, the first mirror  8  is installed to be substantially parallel to a bisector of the first direction  25  and the second direction  26 . 
     The second mirror  9  is installed such that the light receiving surface  6  keeps the subject second side surface  23  in the viewing field. In other words, the second mirror  9  is installed to be substantially parallel to a bisector of a direction opposite to the first direction  25 , and the second direction  26 . 
     The third mirror  10  and the fourth mirror  11  are installed such that the light receiving surface  6  keeps the subject rear surface  24  in the viewing field. In other words, the third mirror  10  is installed substantially to be parallel to the first mirror, and the fourth mirror  11  is installed to be substantially parallel to the second mirror  9 . 
     In  FIG. 1 , paths through which light to be generated on four surfaces that surround the subject  20  reaches the light receiving surface  6  are illustrated as optical paths  27 A to  27 D. 
     The welding monitoring system  1  includes optical path length adjustment portions  28 A to  28 D in front of the light receiving surface  6  on the path through which the optical paths  27 A to  27 D pass. The optical path length adjustment portions  28 A to  28 D use a transparent material (for example, glass or crystal) of which a refractive index is equal to or greater than 1. When the light passes through the material of which the refractive index is equal to or greater than 1, by using the optical path length obtained by multiplying the refractive index by the length of the material, focusing is performed. In other words, in accordance with the optical path to the light receiving surface  6  from each of the side surfaces of the subject  20 , by adjusting the optical path lengths of the optical path length adjustment portions  28 A to  28 D, the optical lengths of the optical paths  27 A to  27 D are arranged. 
     By the above-described configuration, it is possible to keep the entire circumference of the subject in the imaging viewing field of the imaging portion  3 , and to simultaneously image the entire circumference by one camera (imaging portion  3 ). 
     Next, a method for fixing a position of the subject  20  will be described. A driving mechanism is provided in the first holding portion  4  or in the second holding portion  5 , or in both of the first holding portion  4  and the second holding portion  5 , and the second holding portion  5  can relatively move along the first direction  25  with respect to the first holding portion  4 . By the movement, the subject  20  is interposed and held by the first holding portion  4  and the second holding portion  5 . By the holding method, the subject front surface  21  is in contact with a front surface holding surface  13  of the first holding portion  4 , and the subject rear surface  24  is in contact with a rear surface holding surface  14  of the second holding portion  5 . 
     In addition, the welding monitoring system  1  includes a load applying mechanism  12  which applies a load to the subject  20  along the second direction  26 . By the action of the load applying mechanism  12 , when the subject  20  is held, the subject  20  receives the load in the second direction  26  and is in contact with a side surface holding surface  15  of the first holding portion  4 . 
     In this manner, the subject  20  is held by the first holding portion  4  and the second holding portion  5 , and the position thereof is determined. 
     Next, the reason why the images on four surfaces are focused even in a case of components having different sectional sizes, will be described with reference to  FIG. 2 . 
     By the configuration described above, the first mirror to the fourth mirror (reference numbers  8  to  11 ) and the optical path length adjustment portions  28 A to  28 D (not illustrated in  FIG. 2 ) are installed to be focused in a case where the subject  20  having a certain diameter (radius r) is set. In  FIG. 2 , the situation is illustrated by dotted lines. Here, a case where components having different radiuses (r+Δ) are set in the welding monitoring system  1  is considered. In  FIG. 2 , the situation is illustrated by solid lines. A case where the optical path lengths of the optical paths  27 A to  27 D from each of the side surfaces (the subject front surface  21 , the subject first side surface  22 , the subject second side surface  23 , and the subject rear surface  24 ) of the subject  20  to the light receiving surface  6  do not respectively change, will be described hereinafter. 
     First, the focus of the subject front surface  21  will be described. The subject front surface  21  is in contact with the first holding portion  4 , and thus, there is no relative displacement with respect to the first holding portion  4  along the first direction  25 . In addition, the relative positional relationship between the light receiving surface  6  and the first holding portion  4  is fixed. Therefore, even when the sectional size of the subject  20  changes, a state of being in focus without changing the distance between the subject front surface  21  and the light receiving surface  6 , can be held. 
     Next, the focus of the subject first side surface  22  will be described. The subject first side surface  22  is relatively displaced substantially only by Δ with respect to the first holding portion  4  in a direction reverse to the second direction  26 . In addition, the subject first side surface  22  is not relatively displaced with respect to the first holding portion  4  along the second direction  26 . On the optical path  27 D, a point on the subject first side surface  22  is D 1 , a point reflected by the first mirror  8  is D 2 , and a point that has reached the light receiving surface is D 3 . 
     By changing the sectional size of the subject  20 , the distance between D 1  and D 2  is shortened by Δ, and the distance between D 2  and D 3  extends by Δ, and thus, the sum of the distance becomes exactly zero. Therefore, even when the sectional size of the subject  20  changes, it is possible to hold a state of being in focus without changing the distance between the subject first side surface  22  and the light receiving surface  6 . 
     Next, focus on the subject second side surface  23  will be described. The subject second side surface  23  is relatively displaced substantially by Δ with respect to the first holding portion  4  in the direction reverse to the first direction  25 . In addition, the subject second side surface  23  is relatively displaced substantially by 2Δ with respect to the first holding portion  4  in the direction reverse to the second direction  26 . Furthermore, the second mirror  9  which is on the optical path  27 A is relatively displaced substantially by 2Δ with respect to the first holding portion  4  in the direction reverse to the first direction  25 . 
     On the optical path  27 A, a point on the subject second side surface  23  is A 1 , a point reflected by the second mirror  9  is A 2 , and a point that has reached the light receiving surface is A 3 . 
     By changing the sectional size of the subject  20 , the distance between A 1  and A 2  extends by Δ, the distance between A 2  and A 3  is shortened by Δ, and thus, the sum of the distance becomes exactly zero. Therefore, even when the sectional size of the subject  20  changes, it is possible to hold a state of being in focus without changing the distance between the subject second side surface  23  and the light receiving surface  6 . 
     Next, focus on the subject rear surface  24  will be described. The subject rear surface  24  is relatively displaced substantially by 2Δ with respect to the first holding portion  4  in the direction reverse to the first direction  25 . In addition, the subject rear surface  24  is relatively displaced substantially by Δ with respect to the first holding portion  4  in the direction reverse to the second direction  26 . Furthermore, the third mirror  10  which is on the optical path  27 B is relatively displaced substantially by 2Δ with respect to the first holding portion  4  in the direction reverse to the first direction  25 . 
     On the optical path  27 B, a point on the subject rear surface  24  is B 1 , a point reflected by the third mirror  10  is B 2 , a point reflected by the fourth mirror  11  is B 3 , and a point that has reached the light receiving surface is B 4 . 
     By changing the sectional size of the subject  20 , the distance between B 1  and B 2  extends by Δ, the distance between B 2  and B 3  is shortened by 4Δ, the distance between B 3  and B 4  extends by 3Δ, and thus, the sum of the distance becomes exactly zero. Therefore, even when the sectional size of the subject  20  changes, it is possible to hold a state of being in focus without changing the distance between the subject rear surface  24  and the light receiving surface  6 . 
     A picture in a process from the setting of the subject  20  in the subject holding portion to the welding is illustrated in  FIG. 3 . The process is arranged in a time-series order from top (T 1 ) to bottom (T 4 ) of  FIG. 3 , and in T 1 , in a state where the subject  20  is not set, only the mirrors (reference numbers  8 ,  9 , and  11 ) are kept within the imaging viewing field. In addition, before the subject  20  is set, the first holding portion  4  and the second holding portion  5  are separated from each other, and thus, compared to the first mirror  8  fixed to the first holding portion  4 , the second mirror  9  and the fourth mirror  11  which are fixed to the second holding portion  5  are projected to be small. 
     In T 2 , a picture in the middle of movement of the subject  20  by a transport arm toward the right side from the left side on a paper surface of  FIG. 2  is illustrated. An arrow illustrated in T 2  illustrates a moving direction of the subject  20 . In addition, a symbol X illustrates a direction toward the near side from the far side on the paper surface. 
     In T 3 , a state where the movement of the transport arm is finished is illustrated. T 4  illustrates a state after the second holding portion  5  relatively moves with respect to the first holding portion  4 , and holds the subject  20 . As the second mirror  9  and the fourth mirror  11  approach the first holding portion  4 , the entire side surface of the subject  20  enters the imaging viewing field, and the preparation of imaging during the welding is completed. After the welding, the picture to be reproduced is recorded from T 4  to T 1  in reverse. 
     Action and Effect 
     In this manner, in the welding monitoring system  1  according to the first embodiment, the mirror for keeping the entire circumference of the subject within the viewing field of the light receiving surface can automatically perform the focusing by moving in accordance with the sectional size of the subject  20 . In other words, by cancelling the displacement of the optical path caused by the change in subject size by the displacement of the subject holding portion, the entire circumference of the subject can be focused. 
     Example 2 
     A welding monitoring system according to a second embodiment of the present invention will be described with reference to  FIG. 4 .  FIG. 4  is a schematic view of the welding monitoring system  1  according to the embodiment. 
     The welding monitoring system  1  according to the embodiment is different from the configuration of the welding monitoring system  1  according to the first embodiment in the configuration of the optical path length adjustment portion  28 . Since other configurations of the welding monitoring system  1  according to the embodiment are the same as those of the welding monitoring system  1  according to the first embodiment, the description thereof will be omitted. 
     In the welding monitoring system  1  according to embodiment, an optical path length adjustment portion  7  includes a plurality of optical path length extending mirrors  29  instead of the transparent material of which the refractive index is equal to or greater than 1. Without changing a start point (subject  20 ) of the optical paths  27 A to  27 D, each of the reflection points by the first mirror  8  to the fourth mirror  11 , and a final point (light receiving surface  6 ), the optical path length extending mirror  29  is installed to make the optical path lengths uniform by extending the optical path lengths by bending the middle part of the path. Accordingly, a function of making the optical path lengths of optical paths  27  uniform can be realized by bending the optical path not only in a linear space between the imaging target part and the light receiving surface  6  but also in the direction perpendicular thereto, and the installation space can be more efficiently used. 
     Action and Effect 
     In this manner, in the welding monitoring system  1  according to the second embodiment, not only the effects similar to those of the welding monitoring system according to the first embodiment can be obtained, but also it is possible to more efficiently use the installation space of the configuration member of the welding monitoring system  1  by configuring the optical path length adjustment portion  7  by the plurality of optical path length extending mirrors  29 . 
     Example 3 
     A welding monitoring system according to a third embodiment of the present invention will be described with reference to  FIG. 5 .  FIG. 5  is a schematic view of the welding monitoring system  1  according to the embodiment. 
     The welding monitoring system  1  according to the embodiment is different from the configuration of the welding monitoring system  1  according to the first embodiment in that the second holding portion  5  also functions as the load applying mechanism  12 . Since other configurations of the welding monitoring system  1  according to the embodiment are the same as those of the welding monitoring system  1  according to the first embodiment, the description thereof will be omitted. 
     In the welding monitoring system  1  according to the embodiment, the applying of the load in the second direction  26  of the subject  20  which is an action of the load applying mechanism  12  is realized by the configuration of the rear surface holding surface  14  of the second holding portion  5 . The rear surface holding surface  14  is not parallel to the front surface holding surface  13  of the first holding portion  4 , and a normal line thereof is configured to have not only the component of the first direction  25  but also the component of the second direction  26 . 
     Accordingly, as the second holding portion  5  moves toward the first direction  25  with respect to the first holding portion  4  and comes into contact with the subject  20 , it is possible to apply the load in the second direction  26  to the subject  20 . By the above-described configuration, even when eliminating the load applying mechanism  12  which is provided in the welding monitoring system  1  according to the first embodiment, it is possible to obtain similar effects. 
     Action and Effect 
     In this manner, in the welding monitoring system  1  according to the third embodiment, not only the effects similar to those of the welding monitoring system according to the first embodiment can be obtained, but also it is possible to eliminate the configuration member of the welding monitoring system  1  by the configuration in which the second holding portion  5  also plays a role of the load applying mechanism  12 . 
     Example 4 
     A welding monitoring system according to a fourth embodiment of the present invention will be described with reference to  FIG. 6 .  FIG. 6  is a schematic view of the welding monitoring system  1  according to the embodiment. 
     The welding monitoring system  1  according to the embodiment is different from the configuration of the welding monitoring system  1  according to the first embodiment in that a magnifying lens  30  and a condensing mirror  31  are provided in front of the light receiving surface  6 . Since other configurations of the welding monitoring system  1  according to the embodiment are the same as those of the welding monitoring system  1  according to the first embodiment, the description thereof will be omitted. 
     In the welding monitoring system  1  according to the embodiment, in front of the light receiving surface  6  in the middle of the optical paths  27 A to  27 D, the magnifying lens  30  and the condensing mirror  31  are installed. Accordingly, the light generated from each of the side surfaces (the subject front surface  21 , the subject first side surface  22 , the subject second side surface  23 , and the subject rear surface  24 ) of the subject  20  is condensed to be densely focused on the light receiving surface  6 . By the above-described configuration, it is possible to perform the imaging by improving resolution of the subject  20 . 
     Action and Effect 
     In this manner, in the welding monitoring system  1  according to the fourth embodiment, not only the effects similar to those of the welding monitoring system  1  according to the first embodiment can be obtained, but also it is possible to perform the imaging by improving the resolution of the subject  20  by providing the magnifying lens  30  and the condensing mirror  31  of the light receiving surface  6 . 
     Example 5 
     A welding monitoring system according to a fifth embodiment of the present invention will be described with reference to  FIG. 7 .  FIG. 7  is a schematic view of the periphery of the subject  20  according to the embodiment. 
     The welding monitoring system  1  according to the embodiment is different from the configuration of the welding monitoring system  1  according to the first embodiment in that a slit  32  is installed on the periphery of the subject  20 . Since other configurations of the welding monitoring system  1  according to the embodiment are the same as those of the welding monitoring system  1  according to the first embodiment, the description thereof will be omitted. 
     In the welding monitoring system  1  according to the embodiment, a plurality of the radial slits  32  around the subject  20  are provided on the periphery of the subject  20 . By the slit  32 , it is possible to perform the imaging by extracting a ray of light which is substantially perpendicular to a curved surface (surface of the subject  20 ) from the generated light of the subject  20 . Therefore, it is possible to narrow a point on the subject  20  which is a starting point of the ray of light that has reached each point on the light receiving surface  6 , and to suppress widening (blur) of the image. 
     Action and Effect 
     In this manner, in the welding monitoring system  1  according to the fifth embodiment, not only the effects similar to those of the welding monitoring system  1  according to the first embodiment can be obtained, but also it is possible to suppress blur during the imaging by providing the slit  32  on the periphery of the subject  20 . 
     Example 6 
     A welding monitoring system and a welding monitoring method according to a sixth embodiment of the present invention will be described with reference to  FIGS. 8 and 9 .  FIG. 8  is a schematic view of a system configuration of the welding monitoring system  1  according to the embodiment.  FIG. 9  is a flowchart illustrating a welding monitoring method according to the embodiment. 
     The embodiment is different from the configuration of the welding monitoring system  1  according to the first embodiment in that a series of information processing and control systems is provided. Since other configurations of the welding monitoring system  1  according to the embodiment are the same as those of the welding monitoring system  1  according to the first embodiment, the description thereof will be omitted. 
     The welding monitoring system  1  according to the embodiment is configured of the mechanical portion which transports the subject  20  for the welding at a predetermined position, and the imaging portion which determines the quality by imaging the subject  20  and analyzing the image data. The mechanical portion includes, for example, the transport arm, the subject holding portion, and the energizing device. The imaging portion includes, for example, a data recording portion, an analyzing portion, a comparison determination portion, and a determination result display portion (determination result output portion). 
     The imaging portion images a subject in each process of the operation of the mechanical portion. Specifically, for example, the imaging is performed in a process in which the transport arm transports the subject to the subject holding portion (imaging  1 ), a subject after the holding by the subject holding portion (imaging  2 ), a process of operating the energizing device and performing the welding (imaging  3 ), a subject after the welding (imaging  4 ), and a process in which the subject is transported by the transport arm again for performing the process after the welding (imaging  5 ). 
     The imaging data of the subject  20  obtained in this manner is transported to the data recording portion, and characteristics which are required in determination of the quality in the analyzing portion are extracted. The analysis result is input to the comparison determination portion, and is recorded in an analysis result accumulation portion. In the comparison determination portion, for example, compared to the previous data recorded in the analysis result accumulation portion or subject shape data, the presence or absence of abnormality is output. The abnormality is notified with respect to a field supervisor by abnormality informing means, and is informed with respect to a manufacturing execution system (MES) which controls the entire production system or a portable terminal via a programmable logic controller (PLC), and thus, necessary controls are performed. 
     A specific example of abnormality to be sensed will be described. From the picture of the process in which the transport arm transports the subject to the subject holding portion (imaging  1 ), it is possible to investigate necessity of maintenance of a driving portion of the arm by calculating an operation speed of the transport arm and by sensing the presence or absence of the abnormality of the arm. From the picture of the subject (imaging  2 ) after the holding performed by the subject holding portion, it is possible to sense whether or not the subject is held at a predetermined position, and to investigate whether or not the welding is performed at a predetermined positional relationship. From the picture of the process of operating the energizing device and performing the welding (imaging  3 ), it is possible to investigate the possibility of a welding defect by analyzing the light generation of the subject. From the picture of the subject after the welding (imaging  4 ), it is possible to sense the presence or absence of damage or dirt of the subject, and to investigate whether or not the predetermined quality of external appearance is satisfied. From the picture of the process of operating the transport arm again for performing the process after the welding (imaging  5 ), it is possible to investigate the presence or absence of abnormality of the arm again. 
     The welding monitoring method of the embodiment described above is illustrated in the flowchart of  FIG. 9 . First, the subject (welding member) is transported to the subject holding portion by the transport arm (step S 1 ). The subject (welding member) during the transport is captured, and the imaging data is recorded in the data recording portion (step S 2 ). 
     Next, the subject (welding member) is fixed and held to the subject holding portion by the load applying mechanism (step S 3 ). In a state where the subject (welding member) is held by the subject holding portion, the subject (welding member) before the welding is captured, and the imaging data is recorded in the data recording portion (step S 4 ). 
     Then, the subject (welding member) is welded by the energizing device (welding machine) (step S 5 ). The subject (welding member) during the welding is captured, and the imaging data is recorded in the data recording portion (step S 6 ). Furthermore, in a state where the subject (welding member) is held by the subject holding portion, the subject (welding member) after the welding is captured, and the imaging data is recorded in the data recording portion (step S 7 ). 
     Then, the subject (welding member) after the welding is carried out by the transport arm (step S 8 ). The subject (welding member) during the transport is captured, the imaging data is recorded in the data recording portion (step S 9 ). 
     Then, the predetermined characteristics are extracted from the imaging data obtained in each of the steps (step S 10 ). 
     After this, normal characteristics are read from a subject shape data base (step S 11 ). The predetermined characteristics of the imaging data extracted in step S 10  and the normal characteristics of the subject read in step S 11  are compared to each other, and the presence or absence of abnormality is determined (step S 12 ). In a case where it is determined that the abnormality is absent, the process moves to step S 13 , the content that the state is normal is notified with respect to the managing system or the manager, and the operation of the welding machine continues. Meanwhile, in a case where it is determined that the abnormality is present, generation of the abnormality is notified with respect to the managing system or the manager (step S 14 ). 
     Action and Effect 
     In this manner, in the welding monitoring system  1  according to the sixth embodiment, not only the effects similar to those of the welding monitoring system  1  according to the first embodiment can be obtained, but also it is possible to sense the abnormality in the welding process, and to control the operation situation of a production line, by analyzing the image data obtained by the imaging portion. 
     In addition, the present invention is not limited to the above-described examples, and various modification examples are included. For example, the above-described examples are described in detail for making it easy to understand the present invention, and are not limited to the example in which all of the described configurations are necessarily provided. In addition, it is possible to replace apart of the configuration of a certain example with a configuration of other examples, and it is also possible to add a configuration of other examples to the configuration of a certain configuration. In addition, it is possible to add, eliminate, and replace other configurations with respect to a part of the configuration of each of the examples. 
     REFERENCE SIGNS LIST 
     
         
           1  . . . WELDING MONITORING SYSTEM 
           2  . . . WELDING MACHINE 
           3  . . . IMAGING PORTION 
           4  . . . FIRST HOLDING PORTION 
           5  . . . SECOND HOLDING PORTION 
           6  . . . LIGHT RECEIVING SURFACE 
           7  . . . OPTICAL PATH LENGTH ADJUSTMENT PORTION 
           8  . . . FIRST MIRROR 
           9  . . . SECOND MIRROR 
           10  . . . THIRD MIRROR 
           11  . . . FOURTH MIRROR 
           12  . . . LOAD APPLYING MECHANISM 
           13  . . . FRONT SURFACE HOLDING SURFACE 
           14  . . . REAR SURFACE HOLDING SURFACE 
           15  . . . SIDE SURFACE HOLDING SURFACE 
           20  . . . SUBJECT 
           21  . . . SUBJECT FRONT SURFACE 
           22  . . . SUBJECT FIRST SIDE SURFACE 
           23  . . . SUBJECT SECOND SIDE SURFACE 
           24  . . . SUBJECT REAR SURFACE 
           25  . . . FIRST DIRECTION 
           26  . . . SECOND DIRECTION 
           27 ,  27 A,  27 B,  27 C,  27 D . . . OPTICAL PATH 
           28 ,  28 A,  28 B,  28 C,  28 D . . . OPTICAL PATH LENGTH ADJUSTMENT PORTION 
           29  . . . OPTICAL PATH LENGTH EXTENDING MIRROR 
           30  . . . MAGNIFYING LENS 
           31  . . . CONDENSING MIRROR 
           32  . . . SLIT