Steel material end shape defect inspection method

Abstract

To provide a steel material end face inspection method which reduces missed detection.SOLUTION: A steel material inspection method disclosed herein comprises (A) acquiring end face irregularity data from an image of the end face of a steel material, (B) obtaining a maximum step height in each of predetermined areas from the irregularity data, (C) detecting scratches on the basis of the maximum step heights, and (D) determining pass or fail according to the detected scratches.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a method for inspecting steel products. [Background technology]

[0002] Visual inspections of steel products are performed to detect surface defects such as scratches, cracks, and chips. While visual inspections are performed to detect cracks and chips at the ends of steel products, overlooking defects in areas that are difficult to see can be problematic. Furthermore, because visual inspections depend on the skill of the inspector, there is a need for an inspection method that can reduce the risk of overlooking defects through quantitative judgment and automate the inspection. In order to prevent overlooking surface defects, a method for detecting defects by photographing the surface of steel products and analyzing the images is disclosed in JP 2016-070875 A. Furthermore, a method for inspecting the shape of angle iron ends by photographing and analyzing the images is disclosed in JP 2013-134198 A. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-070875 A [Patent Document 2] JP 2013-134198 A Summary of the Invention [Problem to be solved by the invention]

[0004] Images of steel materials contain noise caused by light reflection and by the inherent irregularities on the steel material end surface. This noise can cause cracks on the steel material end surface to be missed, especially tightly packed cracks that do not appear clearly on the photograph.

[0005] The present inventors intend to provide a method for inspecting the end faces of steel materials in which detection omissions are reduced. [Means for solving the problem]

[0006] A steel material inspection method according to one embodiment includes: (A) obtaining unevenness data of the end surface from an image of the end surface of the steel material; (B) obtaining the maximum step height for each predetermined region from the unevenness data; (C) detecting a flaw based on the maximum step; and (D) a step of determining pass / fail based on the detected flaws. Includes:

[0007] Preferably, the step (B) is (B-1) A step of assigning a value corresponding to the height of each unit area of the end face based on the unevenness data. and (B-2) A step of determining, for a group of a predetermined number of adjacent unit areas, the difference between the maximum value and the minimum value of the assigned values as the maximum step of the group. Includes:

[0008] Preferably, after the step (B-1), (B-1') Further provided is a pass / fail judgment process based on the step difference between the unit areas, and if the step (B-1') is passed, the steps (B-2) to (D) are executed.

[0009] Preferably, in the step (C), a region in which the maximum step difference is greater than a predetermined threshold is detected as a flaw.

[0010] Preferably, the step (D) is (D-1) calculating the size of each of the detected flaws on the surface of the end face; (D-2) comparing the size of the largest flaw with a predetermined threshold value. [Effects of the Invention]

[0011] In this inspection method, the maximum step height is calculated for each specified area from the unevenness data obtained from the image of the steel end face, and flaws are detected based on this maximum step height. This makes it possible to detect flaws with reduced noise effects. This detection method reduces the chance of missing flaws on the steel end face. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram showing a steel product inspection system according to one embodiment. [Figure 2] FIG. 2 is a diagram showing unevenness data of the end face of the steel material photographed by the camera in FIG. [Figure 3] FIG. 3 is a flowchart illustrating an inspection method according to an embodiment. [Figure 4] FIG. 4(a) is a diagram showing values corresponding to the height of each unit area of the end face created by the determiner in FIG. 1, and FIG. 4(b) is a diagram showing the maximum step height for each specified area in FIG. 4(a). [Figure 5] FIG. 5(a) shows an example of a flaw detected based on the maximum step in FIG. 4(b), and FIG. 5(b) shows an image of the detected flaw. [Figure 6] FIG. 6 is a flowchart showing an inspection method according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, the present invention will be described in detail based on preferred embodiments, with appropriate reference to the drawings.

[0014] FIG. 1 is a schematic diagram showing an example of an inspection system 2 for carrying out an inspection method according to one embodiment. The system 2 includes a light 4, a camera 6, a determiner 8, and a notifier 10. In this embodiment, the light 4 and the camera 6 are integrated. FIG. 1 also shows a steel material 12 to be inspected. In this figure, the light 4, the camera 6, and the steel material 12 are shown as viewed from diagonally below.

[0015] The light 4 illuminates the end surface 14 of the steel material 12. In this embodiment, the multiple lights 4 can illuminate the end surface 14 of the steel material 12 from different directions.

[0016] The camera 6 photographs the end face 14 to acquire image data. In this embodiment, the aforementioned multiple lights 4 illuminate the end face 14 of the steel material 12 in turn, and the camera 6 acquires image data when each light 4 is illuminating. In this embodiment, the camera 6 combines the multiple image data acquired in this way to acquire unevenness data of the end face 14. Figure 2 shows an example of unevenness data acquired by the camera 6. This is an image display of the acquired unevenness data. In this image, areas within the circle of the specified judgment range 15 that are different in height from the surrounding area are displayed darker. In the example of Figure 2, there is a line 16 that passes through the vicinity of the center of the end face 14 and vertically crosses the judgment range 15, as well as multiple other areas that are different in height from the surrounding area.

[0017] The determiner 8 detects flaws on the end face 14 from the unevenness data and determines whether the steel material 12 is acceptable or not. The determiner 8 is connected to the camera 6. The determiner 8 may be integrated with the camera 6, or may be connected to the camera 6 via a network. Although not shown, in this embodiment, the determiner 8 includes a controller and a memory. A typical controller is a CPU. The memory is typically a semiconductor memory or a hard disk. The determiner 8 may be configured as a dedicated circuit.

[0018] The notifier 10 notifies the user of the flaw data detected by the determiner 8 and the pass / fail determination result. In this embodiment, the notifier 10 displays these on a display. The notifier 10 may be integrated with the determiner 8 or may be connected to the determiner 8 via a network. In this embodiment, the notifier 10 is a personal computer.

[0019] Fig. 3 is a flowchart showing a method for inspecting steel materials 12, which is carried out by the inspection system 2 of Fig. 1. This method includes six steps, from step S1 to S6. In this embodiment, step S1 is performed by the camera 6, and steps S2 to S6 are performed by the determiner 8.

[0020] As described above, in step 1, the camera 6 acquires multiple image data of the end face 14 of the steel material 12, and by combining these, the unevenness data of the end face 14 shown in Fig. 2 is obtained as image data. In this image, areas that are different in height from the surrounding area are displayed darker.

[0021] In step 2, the maximum step height for each predetermined region is obtained. Step 2 includes steps 2-1 and 2-2. In step 2-1, a value (height value) corresponding to the height of each unit region of the end face 14 is assigned based on the unevenness data. FIG. 4(a) shows an example of unit regions and height values assigned to each unit region for a portion of the end face 14. In this example, the lower the unit region, the larger the height value assigned. A unit region corresponds to, for example, one pixel in an image representing the unevenness data. The height value corresponds to, for example, the gradation value of the pixel (for example, the gradation value when the lowest position is set to 0, which is black, and the lowest position is set to 255, which is white). A unit region may also correspond to multiple adjacent pixels. The height value may also correspond to the average gradation value of these multiple pixels.

[0022] In step 2-2, the difference between the maximum height value and the minimum height value is calculated for a group of a predetermined number of adjacent unit areas, and this value is defined as the maximum step height for that group. In this embodiment, four unit areas adjacent to each other vertically and horizontally are defined as one group. The symbols R1, R2, and R3 in FIG. 4(a) are examples of groups. Group R2 is a group obtained by shifting group R1 to the right by one unit area. Therefore, groups R1 and R2 share two unit areas. Similarly, groups are defined in order to the right of group R2. Group R3 is a group obtained by shifting group R1 downward by one unit area. Therefore, groups R1 and R3 share two unit areas. Similarly, groups are defined in order below group R3. In a similar manner, a group matrix corresponding to the entire end face 14 is defined.

[0023] In step 2-2, the difference between the maximum height value and the minimum height value is calculated for each group, and this value is set as the maximum step for that group. FIG. 4(b) shows an example of calculating the maximum step. In FIG. 4(b), symbols R1, R2, and R3 represent the maximum steps for groups R1, R2, and R3 in FIG. 4(a), respectively. For example, in group R1, the difference between the maximum height value of 180 and the minimum height value of 20 is set as the maximum step of 160 for group R1 in FIG. 4(b). As shown in FIG. 4(b), the maximum steps are also calculated for the other groups.

[0024] In step 3, groups whose maximum step difference is equal to or greater than a predetermined threshold value Ts are detected as scratches. In this embodiment, groups whose maximum step difference is equal to or greater than 50 are detected as scratches. In FIG. 5(a), groups detected as scratches are indicated by hatching. In FIG. 5(b), positions on the end surface 14 corresponding to the groups detected as scratches are shown as images. As can be seen by comparing FIG. 5(b) with FIG. 2, only some of the locations in FIG. 2 that are at a different height from the surrounding areas are detected as scratches.

[0025] In step 4, the pass / fail of the steel material 12 is judged. Step 4 includes step 4-1 and step 4-2. In step 4-1, the size of each detected flaw on the surface of the end face 14 is calculated. Adjacent flaws are grouped together as a single flaw, and the size is calculated. In the example of FIG. 5(b), the detected flaws are grouped into three flaws, G1, G2, and G3. The number of groups included in the grouped flaw is determined to be the size of the flaw.

[0026] In step 4-2, the size A of the largest flaw among the grouped flaws is compared with a predetermined threshold value Ta. In the example of FIG. 5(a), the size of flaw G3 is size A. If size A is equal to or smaller than threshold value Ta, the process proceeds to step 5, and the result is output as a pass for the inspection. If size A is greater than threshold value Ta, the process proceeds to step 6, and the result is output as a fail for the inspection.

[0027] The effects of this embodiment will be described below.

[0028] In the inspection method for steel material 12 of this embodiment, the maximum step is calculated for each predetermined area based on unevenness data obtained from an image of the end face 14 of the steel material 12. In this embodiment, four unit areas are grouped together, and the difference between the maximum height value and the minimum height value in this group is taken as the maximum step. Flaws are detected based on this maximum step. By detecting flaws based on the maximum step in a group including multiple unit areas, it is possible to detect flaws with reduced influence of noise. This inspection method reduces the chance of missing flaws.

[0029] In this embodiment, a group whose maximum step is equal to or greater than a predetermined threshold value Ts is detected as a flaw. This further reduces the influence of noise. Also, irregularities that do not affect the quality of the steel product 12 can be excluded from the inspection. This contributes to the realization of efficient inspection.

[0030] In this embodiment, the size of each detected flaw on the surface of the end face 14 is calculated, and if the size of the largest flaw is larger than a predetermined threshold, the product is judged as unacceptable. This further reduces the influence of noise. Also, it prevents the steel product 12 from being rejected based on unevenness that does not affect the quality of the product.

[0031] Fig. 6 is a flowchart showing a method for inspecting a steel material 12 according to another embodiment. This method is different from the method of Fig. 3 in that step S2-1' is added after step S2-1. Other than the addition of step S2-1', this method is the same as the method of Fig. 3.

[0032] In step S2-1', a pass / fail judgment is made based on the step difference between unit areas. In step S2-1', the step difference between unit areas is calculated from the height values assigned to the unit areas. This is found by taking the difference in height values between adjacent unit areas. The step difference between each pair of adjacent unit areas is found, and these step differences are compared with a predetermined threshold Tb. This threshold Tb is set to a value greater than the threshold Ts in step 3. If a step greater than threshold Tb exists, the inspection is deemed a failure and the process proceeds to step S6. If a step greater than threshold Tb does not exist, the process proceeds to step S2-2. From this point on, the same process as the method in Figure 3 is performed.

[0033] In this embodiment, the step between unit areas is compared with a threshold value Tb, and if there is a step greater than the threshold value Tb, the inspection is rejected. Among defects on the end face 14, chips on the end face appear as large steps, and therefore can be detected regardless of whether noise is present. By performing detection processing for more noticeable defects such as chips at an early stage, the inspection of the steel material 12 can be made more efficient.

[0034] As described above, in this embodiment, the end face 14 of the steel material 12 can be inspected with high precision. This clearly shows the superiority of this embodiment. [Industrial Applicability]

[0035] The steel inspection method described above can be applied to the inspection of various steel products. [Explanation of symbols]

[0036] 2. Inspection system 4. Light 6. Camera 8...Judgment device 10...Notifier 12...Steel 14...end face 16...line

Claims

1. (A) obtaining unevenness data of the end surface from an image of the end surface of the steel material; (B) obtaining a maximum step difference for each predetermined region from the unevenness data; (C) detecting a flaw based on the maximum step; and (D) a step of determining whether the product passes or fails based on the detected flaws. A method for inspecting steel materials, including:

2. The step (B) (B-1) A step of assigning a value corresponding to the height of each unit area of the end face based on the unevenness data. and (B-2) A step of determining, for a group of a predetermined number of adjacent unit areas, the difference between the maximum value and the minimum value of the assigned values as the maximum step of the group. The method for inspecting a steel product according to claim 1 , comprising:

3. After the step (B-1), (B-1') A steel inspection method as described in claim 2, further comprising a pass / fail judgment process based on the step between the unit areas, and if the step (B-1') is passed, the steps (B-2) to (D) are executed.

4. 4. The steel product inspection method according to claim 1, wherein in step (C), an area in which the maximum step difference is greater than a predetermined threshold is detected as a flaw.

5. The step (D) (D-1) calculating the size of each of the detected scratches on the surface of the end face; (D-2) comparing the size of the largest flaw with a predetermined threshold; The steel material inspection method according to claim 1 , further comprising:

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