JP4429640B2 - Appearance inspection method for weld marks - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention, for example, inspects the appearance of the weld mark on the surface of a metal plate (including metal foil) that is overlapped with each other and welded at a plurality of locations to integrate the two, and inspects the appearance of the weld mark on the surface. It is about the method.
[0002]
[Prior art]
A method in which two metal plates (hereinafter, including metal foil) are overlapped and welded by laser, ultrasonic waves, or the like is used in various fields. Specifically, when electrically connecting conductors made of metal foil, the terminals of the conductors (metal foil) to be connected are partially overlapped, and a plurality of points are connected to this by a laser welding machine, an ultrasonic welding machine, or the like. Welding and connecting both. Normally, this welding is performed simultaneously at a plurality of locations in a grid pattern.
When inspecting the welded state of the surface of the metal plate thus obtained, the interval between the welding marks is extremely narrow, so that it is impossible to visually inspect. Therefore, various methods have been studied in the past in which these welding states, that is, the entire welding mark is photographed by an imaging means such as a camera, and the quality is judged by image processing using a computer.
[0003]
By the way, in image processing, where this kind of welding mark comes in the field of view of the camera is not always constant, it is necessary to first find the position of the welding mark.
[0004]
Thus, for example, there is Patent Document 1 as a proposal of a method for finding this position. The one described in Patent Document 1 performs a ternarization process on a grayscale image accumulated in a storage device by an input device that captures a welding mark, and generates a welding mark generated at the time of welding in a vertical direction. This is a method of finding a position (range) where a certain frequency or more is obtained by performing luminance frequency projection on the axis and luminance frequency projection on the horizontal axis.
[0005]
Patent Document 1: Japanese Patent Application Laid-Open No. 11-10373
However, in this method, since the shape of the weld mark is not constant, it is difficult to accurately align the position of the pattern. Further, when there are a plurality of welding traces, projection data is accumulated, and there is a problem that accurate pattern position information of the welding traces cannot be obtained.
[0007]
In view of the foregoing problems, the object of the present invention is to eliminate the need to align the position of the welding mark within the field of view of the imaging means, that is, the welding mark that can be inspected in a short time and can accurately inspect the appearance of the welding mark. It is to provide a visual inspection method.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides an image of visual inspection of a welding mark on a surface of a metal plate in which a plurality of welding marks are formed in a grid pattern at constant pitches in the vertical and horizontal directions. in appearance inspection method of welding mark performed using processing, the image of the read surface of the metal plate, triangular or rectangular region formed by connecting the centers of each of the plurality of welding marks adjacent to the unit block, said a unit block subjected to continuous unit block division processing for all the welding marks of the metal plate surface by dividing the surface of the metal plate into a plurality of blocks, of the divided pixel intensity values in said each block the average value and the integral value, the average value and the integral value as a sequence of numbers arranged in order of each block of the metal plate surface, to extract the change of said numerical sequence as a feature of the metal plate surface extraction Comprises sequentially using the extraction procedure to extract the feature quantity of the metal sheet surface with a plurality of metal plates welded state of the previously prepared surface of the metal plate is good, a good extracted the welded state set the Mahalanobis space using a set of the feature amount of the metal plate, by using the extraction procedure to extract the feature quantity of the metal plate surface to be inspected, the characteristic amount for each of the inspected products the Mahalanobis distance between the Mahalanobis space is calculated using, by comparing the Mahalanobis distances said calculated with a predetermined threshold, and wherein determining the quality of the weld marks of the metal plate surface is said object This is a method for determining the appearance of weld marks .
[0009]
According to the present invention thus configured, a region formed by connecting the centers of each of the plurality of welding marks is defined as a unit block, and the unit block continuously applies to all the welding marks on the surface of the metal plate. Since the unit block division processing is performed to divide the block into multiple blocks, there is a certain number of welding marks in each block, so the background (the part other than the welding marks in the block) shows certain characteristics. Assuming that it is possible to grasp the characteristics of the welding marks by grasping the characteristics of the entire block, the influence of pixel displacement of the welding marks can be absorbed by the block size, as in the conventional method Accurate alignment of welding marks is not necessary.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
The welding mark appearance inspection method of the present invention will be described below in detail with reference to the drawings. In addition, each figure has shown the example which piled up the metal plate 1 and the metal plate 2, and performed the welding of several places to this, but all are that the metal plate 2 is down and the metal plate 1 is up. Show.
[0012]
FIG. 1A shows the shape and size of a unit block that is the basis of the present invention. A plurality of weld marks 3 exist in a grid pattern with respect to the two metal plates 1 and 2 stacked. Here, the presence of a plurality of welding marks in the grid pattern means that there are welding marks at a predetermined pitch in the horizontal and vertical directions, and the horizontal pitch and the vertical pitch are the same. It may be a different pitch.
Let us say that the welding marks 3 are a, b, c, d, e, f, g,. Two welding marks e and f which are adjacent to each other on the surface of the metal plate 1 in the lateral direction among these welding marks 3 and one of the two welding marks e and f, which is now called a welding mark e Then, a right triangle formed by connecting the centers of three welding marks e, f, and g, each consisting of two adjacent welding marks e and g in the vertical direction including the welding mark e, or adjacent in the horizontal direction. The center of each of the four welding marks a, b, c, d, which is composed of the two welding marks a, b and the two welding marks c, d in the longitudinal direction adjacent to the two welding marks a, b, is connected. One of the formed rectangles (in this case, a rectangle) is defined as a unit block 4.
[0013]
Either the right triangle or the rectangle may be used as the unit block 4, but in the following embodiments, the surface of the metal plate 1 is formed by using the rectangle formed by connecting the centers of the welding marks a, b, c and d as the unit block 4. The unit block division processing was continuously performed on all the welding marks 3 of the above and divided into a plurality of blocks. This is shown in FIG.
[0014]
Here, the reason why it is not necessary to accurately align the welding marks 3 in the present invention will be described with reference to FIG.
As shown in FIG. 2, it is assumed that the number of pixels of the welding mark 3 is nine in the unit block 4A. The number of pixels of the welding mark 3 in the unit block 4B that is several pixels away from the unit block 4A in the direction of the arrow is also nine. In other words, the unit block 4 </ b> A and the unit block 4 </ b> B are not affected by the pixel shift of the welding mark 3 with respect to the welding mark 3 (here, the welding mark T). That is, the pixel shift of the welding mark 3 is absorbed by the block size. In FIG. 2, a small cell (a cell 5 on the left side of FIG. 2) indicates one pixel.
[0015]
In the present invention, using such a principle, a feature quantity that is strong against the influence of the pixel and shape deviation is extracted from the image of the weld mark 3, and the weld mark 3 is preliminarily based on a good weld state. A judgment criterion for the quality of the appearance of the product is created, and the quality of the welded state of the product to be inspected is judged by comparing this criterion with the feature quantity of the product to be inspected.
[0016]
FIG. 3 shows a model image of the welding mark 3 for determining the welding state. As described above, a plurality of welding marks 3 formed when the metal plate 1 and the metal plate 2 are overlapped and welded exist on the surface of the metal plate 1 in a grid pattern. A rectangular unit as shown in FIG. 1 (a) is used as a unit block 4, and unit blocks 4 are continuously subjected to unit block division processing for all welding marks 3 on the surface of the metal plate 1 by the unit block 4. Divided into blocks.
[0017]
Thereafter, an average value and an integral value of the pixel luminance values were obtained for each unit block 4. The obtained average value and integrated value were combined in an arbitrary order to form a number sequence, and the shape of this number sequence was used as the feature amount on the surface of the metal plate 1 of the product to be inspected. The flow of this feature amount extraction work is shown in the flowchart of FIG.
[0018]
On the other hand, when determining the welding state of the surface of the metal plate 1, a plurality of metal plates 1 having a good welding state are prepared in advance, and the product having a good welding state in accordance with the procedure shown in the flowchart of FIG. A set of feature quantities is formed.
As shown in FIG. 5A, the surface images of the plurality of non-defective metal plates 1 are taken with a camera and the images are taken in, and the rectangular unit block 4 is formed in the same manner as the procedure of FIG. The unit block division process was continuously performed on all the welding marks 3 on the surface of the metal plate 1 to obtain an average value and an integral value of pixel luminance values for each block. These values thus obtained are combined in the order shown in FIG. 3 to form a number sequence, and the shape of the number sequence is used as an aggregate of feature amounts on the surface of the metal plate 1 in a good welded state.
[0019]
Then, a Mahalanobis space was set by using an assembly of feature quantities of products having a good welded state.
Thereafter, as shown in the flowchart of FIG. 5 (b), the feature amount created from the image read from the surface of the metal plate 1 of the inspection target product, that is, each inspection target product obtained according to the flowchart shown in FIG. The Mahalanobis distance from the Mahalanobis space is calculated using the feature quantity. The quality of the welded state of the surface of the metal plate 1 is determined by comparing the calculated Mahalanobis distance with a predetermined threshold value.
[0020]
Specifically, when the Mahalanobis distance obtained from the surface image of a certain metal plate 1 to be inspected is larger than a set threshold value, it is determined that the welding is defective. Is determined.
[0021]
Specific examples of applying the method of the present invention to various welding defects and confirming the accuracy will be described with reference to FIGS.
First, a plurality of products with good welding conditions were prepared, and an assembly of feature quantities of products with good welding conditions was formed according to the flowchart of FIG. 5 (a) to create a Mahalanobis space. On the other hand, as shown in FIGS. 6 to 11, 8 products each having a product that seems to be in a good welding state and products that consciously created various welding failure states were prepared.
[0022]
Specifically, FIG. 6 shows a product with good welding (case 1), and FIGS. 7 to 11 show products with poor welding.
Incidentally, FIG. 7 shows a product (case 2) in which the metal plate 1 lacked a part 10 and caused poor welding, and FIG. 8 shows a defect because the foreign material 11 is attached below the surface of the metal plate 1. The product (example 3) that caused the problem is shown. FIG. 9 shows the state of a product (case 4) in which a welding leak 12 has occurred in the upper right portion of the metal plate 1, and FIG. 10 shows the product (case 5) in which an overall poor weld state has occurred. .
FIG. 11 shows a state where the entire metal plate 1 does not exist completely (case 6), that is, a state where the metal plate 1 is not on the metal plate 2 for some reason and is welded onto the metal plate 2. ing.
[0023]
A pass / fail judgment was made on each of the eight products showing each case according to the flowchart of FIG. The result is shown in FIG. As shown in FIG. 12, Case 1 showing a product with a good welded state has a Mahalanobis distance smaller than a threshold value, but each of Examples 2 to 6 in FIGS. The Mahalanobis distance was much larger than the threshold. Thus, according to the present invention, it was confirmed that various poorly welded products can be reliably determined as defective.
[0024]
In the above embodiment, whether or not the surface of the metal plate 1 is welded is determined by setting the Mahalanobis space, calculating the Mahalanobis distance in each inspection target product, and determining whether the value is larger or smaller than the threshold. For example, the quality of the welded state may be determined by calculating the degree of correlation with the non-defective product using the feature amount obtained in accordance with the flowchart of FIG. 4, or by calculating the Mahalanobis distance for each product. The quality of the welding state can also be determined by comparing the obtained value with a threshold value.
[0025]
Note that the method used in the above embodiment, that is, the method of calculating the Mahalanobis distance is usually called the MTS method (Taguchi method).
[0026]
In the above embodiment, the unit block is a right triangle or rectangle formed by connecting the centers of the adjacent three or four welding marks, but for example, the centers of the six adjacent welding marks 3 are defined as the unit block. A rectangular block formed by tying, or a region formed by linking the centers of more than one welding mark, can be used as a unit block.
[0027]
【The invention's effect】
As described above, according to the welding mark appearance inspection method of the present invention, it is not necessary to align the position of the welding mark in the imaging means. Therefore, the appearance inspection of the welding mark can be performed in a short time, and the appearance inspection of the welding mark can be accurately performed, that is, the quality of the welding state can be determined.
[Brief description of the drawings]
FIG. 1 shows one embodiment of a unit block shape and a unit block dividing method used in the welding mark appearance inspection method of the present invention, where (a) shows the unit block shape and (b) shows the unit block. It is a figure which shows the division | segmentation method by a block.
FIG. 2 is a diagram for explaining the reason why alignment of welding marks is unnecessary in the present invention.
FIG. 3 is a model image of a welding mark for determining a welding state according to the present invention.
FIG. 4 is a flowchart showing a flow of work for extracting feature quantities of a product to be inspected used in the present invention.
FIG. 5 is a flowchart showing a procedure for determining the quality of a welding state according to the present invention, wherein (a) is a flowchart for forming a set of feature quantities of products having a good welding state as a reference; It is a flowchart which shows the procedure which determines by comparing the welding state of a test object product with what was formed by (a).
FIG. 6 is a plan view of a product having a good welding state used for confirming the determination accuracy of the present invention.
FIG. 7 is a plan view showing an example of a product with a poor welding state used for confirming the determination accuracy of the present invention.
FIG. 8 is a plan view showing an example of a product with a poor welding state used for confirming the determination accuracy of the present invention.
FIG. 9 is a plan view showing an example of a product with a poor weld state used to confirm the determination accuracy of the present invention.
FIG. 10 is a plan view showing an example of a product with a poor welding state used for confirming the determination accuracy of the present invention.
FIG. 11 is a plan view showing an example of a product with a poor weld state used for confirming the determination accuracy of the present invention.
12 is a graph showing the result of calculating the Mahalanobis distance for each product of FIGS. 6 to 11; FIG.
[Explanation of symbols]
1 Metal plate 2 Metal plate 3 Weld mark 4 Unit block 11 Foreign material 12 Weld leakage

Claims (1)

Visual inspection of weld marks on the surface of a metal plate in which a plurality of weld marks are formed in a grid pattern at constant pitches in the vertical direction and the horizontal direction, and visual inspection of the weld marks is performed using image processing In the method
In the read image of the surface of the metal plate , a unit block is a triangular or rectangular area formed by connecting the centers of the plurality of adjacent welding marks,
Subjected to continuous unit block division processing for all the welding marks of the metal plate surface in the unit blocks by dividing the metal plate surface into a plurality of blocks,
The average value and the integral value of the divided pixel intensity values in said each block, the mean value and the integral value as a sequence of numbers arranged in order of each block of the metal plate surface, the metal changes in said numerical sequence Including an extraction procedure for extracting as a feature quantity of the plate surface
Using the extraction procedure to extract the feature quantity of previously prepared weld state of the metal plate surface with a plurality of metal plates is good metal plate surface,
It extracted the welding condition to set the Mahalanobis space using a set of the feature amount of good metal plate,
Using the extraction procedure, extract the feature quantity of the surface of the metal plate to be inspected,
Using the feature value for each of the test products to calculate the Mahalanobis distance between the Mahalanobis space, by comparing the Mahalanobis distances said calculated with a predetermined threshold value, weld marks of the metal plate surface is said object A method for determining the appearance of a weld mark for determining the quality of a weld.

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