Inspection method for steel end shape defects

Abstract

To provide an automatic inspection method for steel materials that suppresses missed detection of defective chamfer formation.SOLUTION: The inspection method for steel material 4 according to this embodiment includes the processes of (A) obtaining image data of the end face 10 of the steel material 4, (B) setting a plurality of determination areas 30 and detecting level differences based on the image data, (C) identifying a chamfered portion 16 for each determination area 30 based on the level differences, and (D) determining pass / fail based on information about the chamfered portion 16 for each determination area 30.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. Visual inspections are particularly performed on the shape of steel product edges, but 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 steel product surface and analyzing the images is disclosed in JP 2016-070875 A. Furthermore, a method for inspecting the shape of angle iron edges 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] At the ends of steel materials, the corners between the end face and the side are usually chamfered. It is not easy to visually check whether the chamfers are correctly formed for all of the steel materials being inspected, and there is a problem of improper chamfer formation being overlooked.

[0005] The present inventors have an intention to provide a method for automatically inspecting chamfered portions of steel products for formation defects. [Means for solving the problem]

[0006] A steel material inspection method according to one embodiment includes: (A) obtaining image data of an end surface of a steel material; (B) setting a plurality of determination areas and detecting steps based on the image data; (C) identifying a chamfered portion for each of the determination regions based on the step; and (D) a step of determining pass / fail based on the information of the chamfered portion for each of the determination areas. Includes:

[0007] Preferably, in the step (B), the step is detected based on the gradation of the image data.

[0008] Preferably, the number of judgment regions set in step (B) is 8 or more and 18 or less.

[0009] Preferably, in the step (C), a region between two steps larger than a predetermined threshold value Th is identified as a chamfered portion.

[0010] Preferably, in step (D), pass / fail is determined based on the number of determination regions having the identified chamfered portion and the width of the chamfered portion in each determination region. [Effects of the Invention]

[0011] This inspection method sets multiple judgment areas and detects steps from image data of the steel end face, and identifies the chamfer for each judgment area. By determining whether the chamfer is formed correctly based on the chamfer information obtained for each small judgment area, excellent defect detection accuracy can be achieved. This detection method reduces the chance of missing a chamfer due to improper chamfer formation. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram showing the flow of inspection of a steel material, including a steel material inspection system according to one embodiment. [Figure 2]FIG. 2(a) is a front view of the steel material to be inspected, and FIG. 2(b) is a side view of the steel material in FIG. 2(a). [Figure 3] FIG. 3 is a flowchart showing an inspection method according to one embodiment, which is performed in the inspection system of FIG. [Figure 4] FIG. 4(a) is a diagram showing the end face of the steel material photographed by a camera, and FIG. 4(b) is a schematic diagram showing the step data obtained from FIG. 4(a). [Figure 5] FIG. 5 is a diagram showing an example of a determination region set on the end face of FIG. 4(a). [Figure 6] FIG. 6 is an enlarged view of one of the decision regions in FIG. [Figure 7] FIG. 7 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 the flow of inspection of steel materials 4, including a steel material inspection system 2 according to one embodiment. As shown in FIG. 1, steel materials 4 are sent to the inspection system 2 from a storage facility 6 in which a plurality of steel materials 4 are stored. In the inspection system 2, the steel materials 4 are inspected one by one. After inspection, the steel materials 4 are sent to the next process or to the storage facility by a conveyor 8.

[0015] FIG. 2(a) is a front view of an example of a steel material 4 to be inspected. This figure shows the end face 10 of the steel material 4. FIG. 2(b) is a side view of the end portion of the steel material 4. When viewed from the front, this steel material 4 has a rod-like shape with a circular outer circumferential surface 12. The corners of this steel material 4 between the end face 10 and the outer circumferential surface 12 are chamfered. The non-chamfered portion of the end face 10 is referred to as the "center portion 14." The surface formed by the chamfering and inclined relative to the center portion 14 is referred to as the "chamfered portion 16." As shown in FIG. 2(a), when viewed from the front, the width of the chamfered portion 16 of this steel material 4 is not constant. Ideally, the width of the chamfered portion 16 should be constant. FIGS. 2(a) and (b) show an example of a poorly formed chamfered portion 16.

[0016] 1, an inspection system 2 according to one embodiment includes a light 18, a camera 20, a determiner 22, and a notifier 24. In this embodiment, the light 18 and the camera 20 are integrated together. Alternatively, the light 18 and the camera 20 may be separate.

[0017] The light 18 illuminates the end face 10 of the steel material 4. In this embodiment, the multiple lights 18 can illuminate the end face 10 of the steel material 4 from different directions.

[0018] The camera 20 photographs the end face 10 to acquire image data. The camera 20 is an area camera that can photograph the entire end face 10 at once. The camera 20 takes a predetermined time (for example, one second) to photograph the end face 10. In the image obtained, the central portion 14, which is illuminated by the light 18 from the front, appears bright, the chamfered portion 16 is darker than the central portion 14, and the area other than the steel material 4 appears even darker.

[0019] The determiner 22 determines whether the chamfered portion 16 is correctly formed based on image data of the end face 10 of the steel material 4 photographed by the camera 20. The determiner 22 is connected to the camera 20. The determiner 22 may be integrated with the camera 20, or may be connected to the camera 20 via a network. Although not shown, in this embodiment, the determiner 22 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 22 may be configured as a dedicated circuit.

[0020] The notifier 24 notifies the user of the determination result of the determiner 22. In this embodiment, the notifier 24 displays the result on a display. The notifier 24 may be integrated with the determiner 22, or may be connected to the determiner 22 via a network. In this embodiment, the notifier 24 is a personal computer.

[0021] Fig. 3 is a flowchart showing a method for inspecting steel materials 4, which is carried out by the inspection system 2 of Fig. 1. This method includes steps S1 to S8. In this embodiment, step S1 is performed by the camera 20, and steps S2 to S8 are performed by the determiner 22.

[0022] In step S1, as described above, the camera 20 acquires image data of the end face 10 of the steel material 4. An example of the acquired image is shown in FIG. 4(a). As described above, the central portion 14 is bright, the chamfered portion 16 is darker than the central portion 14, and the area other than the steel material 4 is even darker. The brightness is approximately constant within each of the chamfered portion 16, the central portion 14, and the area other than the steel material 4. In other words, the brightness is approximately constant in areas with a constant height gradient. The image data is, for example, a collection of data on the position of each pixel and its gradation. In this step, the image data may be modified to emphasize differences in gradation within the image. For example, the gradation of the pixel in the darkest position may be set to 0, the gradation of the pixel in the brightest location in the central portion 14 may be set to 255, and the gradation values ​​of the other pixels may be normalized.

[0023] In step S2, locations where the gradient of the height changes (gradation steps) are detected from the image data. The locations where the gradient of the height changes can be detected by calculating the difference in gradation between adjacent pixels across the entire image data. A location where the difference in gradation between adjacent pixels is equal to or greater than a predetermined value is a "step," and this difference is defined as the "step height." Figure 4(b) shows an example of a portion of a graph showing the detected steps. In this graph, the horizontal axis corresponds to the horizontal position in Figure 4(a), and the vertical axis corresponds to the step height. In this graph, two peaks correspond to the steps. In the example of Figure 4(b), steps are detected at the inner edge 26 of the chamfered portion 16 (the boundary between the central portion 14 and the chamfered portion 16) and the outer edge 28 of the chamfered portion 16 (the boundary between the chamfered portion 16 and the outer peripheral surface 12). Consecutive "steps" are detected as a single step. In the example of FIG. 4(b), two steps corresponding to the inner edge 26 and the outer edge 28 of the chamfered portion 16 are detected.

[0024] In detecting a step, a predetermined number of adjacent pixels may be grouped together to form a single "pixel." The gradation of this grouped pixel may be, for example, the average of the gradations of the original pixels. In this case, a step is detected by calculating the difference in gradation between the adjacent "grouped pixels."

[0025] In step S3, multiple regions (judgment regions) are set. Each judgment region includes a portion of the end face 10. FIG. 5 shows an example of a judgment region 30 together with the steel material 4. For clarity, hatching of regions other than the steel material 4 has been omitted. In this embodiment, multiple judgment regions 30 are set by an outer circle 32, an inner circle 34 located inside the outer circle 32, and multiple radial lines 36 connecting the inner circle 34 and the outer circle 32. In this embodiment, 12 judgment regions 30 are set. The centers of the inner circle 34 and the outer circle 32 are both coincident with the center of the outer circumference of the steel material 4. Lines extending from each radial line 36 pass through the center of the outer circle 32. Each judgment region 30 has an "annular sector" shape, with the annulus formed by the inner circle 34 and the outer circle 32 divided by the radial lines 36. In this embodiment, the central angle of the annular sector is 30°.

[0026] As shown in FIG. 5 , the outer circle 32 is set to include the outer peripheral surface 12 of the steel material 4. That is, each judgment region 30 includes a portion of the outer edge 28 of the chamfered portion 16. The inner circle 34 is set to be included within the central portion 14 when the chamfered portion 16 is formed in a range that is judged to be a pass-quality product. That is, when the chamfered portion 16 is formed in a range that is judged to be a pass-quality product, each judgment region 30 includes a portion of the inner edge 26 of the chamfered portion 16. When the chamfered portion 16 is formed in a range that is judged to be a pass-quality product, the combined area of ​​all judgment regions 30 includes the entire chamfered portion 16.

[0027] The shape of the determination area 30 does not have to be an annular sector. For example, it may be a "sector" without an inner circle 34. The shape of the determination area 30 may be any other shape as long as it is set to include a part of the inner edge 26 and a part of the outer edge 28 within the area when the chamfered portion 16 is formed within a range that is determined to be a non-defective product.

[0028] In step S4, within each judgment region 30, a chamfered portion 16 is identified from the detected steps that exist within this judgment region 30. For this purpose, within each judgment region 30, steps whose height is greater than a predetermined threshold Th are selected from the detected steps. In the example of FIG. 4(b), steps corresponding to two peaks are selected. If two steps are selected, the space between these steps is identified as the chamfered portion 16 within this judgment region 30. If one step is selected, it is determined that no chamfered portion 16 has been identified. If three or more steps are selected, it is determined that a chip or scratch exists, and the process proceeds to step S9.

[0029] In step S5, the width of the detected chamfered portion 16 is calculated in each determination region 30. FIG. 6 shows an enlarged view of one of the determination regions 30. The width of the chamfered portion 16 is measured in the radial direction. FIG. 5 shows the width Wi measured at a point Pi on the inner circle 34. In this step, the average width W within the determination region 30 is calculated. For example, the average width W can be obtained by adding up the width Wi at each position when the point Pi is moved from one end of the inner circle 34 to the other end within the determination region 30 and dividing this sum by the arc length of the inner circle 34 within the determination region 30. The width W may also be calculated by averaging the width Wi at each position for a predetermined number of points Pi arranged at equal intervals on the inner circle 34.

[0030] In step S6, the pass / fail of the steel material 4 is determined based on the presence or absence of the identified chamfered portion 16 and the width of the chamfered portion 16. In this embodiment, it is determined whether or not the following judgment formula is satisfied for the smallest width Wm among the widths W of the judgment regions 30 and the number N of judgment regions 30 in which the chamfered portion 16 is identified. Wm≧Tw and N≧Tn In this formula, Tw and Tn are predetermined thresholds. Tn is set to be equal to or less than the number of judgment areas 30. If the above judgment formula is satisfied, the process proceeds to step S7, and the result is output as a pass for the inspection. If the above judgment formula is not satisfied, the process proceeds to step 8, and the result is output as a fail for the inspection.

[0031] In step S6, pass / fail may be determined based only on whether "Wm≧Tw" is satisfied. Although a determination is not made based on "N≧Tn," for example, by setting the width of chamfered portion 16 in an area where chamfered portion 16 could not be identified to 0 and setting Tw to a number greater than 0, if there is even one area where chamfered portion 16 could not be identified, the result can be determined as failing based on the formula "Wm≧Tw."

[0032] The effects of this embodiment will be described below.

[0033] In the inspection method for steel materials 4 of this embodiment, multiple judgment areas 30 are set, each including a portion of the end face 10. For each judgment area 30, the chamfered portion 16 is identified based on the step obtained from the image data of the end face 10 of the steel material 4. By determining whether the chamfered portion 16 is correctly formed based on the information about the chamfered portion 16 obtained for each small area, excellent defect detection accuracy can be achieved. This detection method reduces the chance of missing a chamfered portion 16 due to poor formation.

[0034] The number of determination regions 30 to be set is preferably 8 or more. By setting the number of determination regions 30 to 8 or more, excellent defect detection accuracy can be achieved. This detection method reduces the risk of missing detection of defects in the formation of the chamfered portion 16. From this perspective, the number of determination regions 30 is more preferably 10 or more. The number of determination regions 30 is preferably 18 or less. By setting the number of determination regions 30 to 18 or less, efficient inspection is possible. From this perspective, the number of determination regions 30 is more preferably 16 or less.

[0035] In this embodiment, among the detected steps in each determination region 30, steps whose height is greater than a predetermined threshold Th are selected, and the selected steps are used to identify the chamfered portion 16. Images of the end face 10 may contain noise. By using steps greater than the threshold Th to identify the chamfered portion 16, the influence of noise can be suppressed. This detection method allows the chamfered portion 16 to be identified with high accuracy.

[0036] In this embodiment, pass / fail is determined based on the number of regions having chamfered portions 16 and the minimum width of the chamfered portions 16. By using both of these as judgment criteria, excellent defect detection accuracy can be achieved. This detection method reduces the chance of missing detection of defective chamfered portions 16.

[0037] Fig. 7 is a flowchart showing an inspection method for a steel material 4 according to another embodiment. In this method, unlike the method of Fig. 3, the determination area 30 is set in step S3 before the step detection. In this method, steps from step S4 onwards are the same as in the method of Fig. 3.

[0038] In this embodiment, after step S1, a determination area 30 is set in step S3, and then steps are detected in step S2'. This step detection is performed for each determination area 30. Within each determination area 30, the difference in gradation between adjacent pixels is calculated. A location where this difference in gradation is equal to or greater than a predetermined value is determined to be a "step," and this difference is determined to be the "height of the step."

[0039] In this embodiment, step detection is not performed at positions outside the determination area 30. This allows the steps required for detecting the chamfered portion 16 to be detected efficiently.

[0040] As described above, in this embodiment, automatic inspection of the chamfered portion of a steel material can be performed with high accuracy. This clearly shows the superiority of this embodiment. [Industrial Applicability]

[0041] The steel inspection method described above can be applied to the inspection of various steel products. [Explanation of symbols]

[0042] 2. Inspection system 4...Steel material 6... Storage 8. Conveyor 10...End face 12...Outer surface 14...Central part 16. Chamfered part 18...Light 20. Camera 22...Judgment device 24...Notifier 26... Common-law marriage 28...Outer edge 30...Judgment area 32 Outer circle 34...inner circle 36... diameter

Claims

1. (A) obtaining image data of an end face of a steel material; (B) setting a plurality of determination areas and detecting steps based on the image data; (C) identifying a chamfered portion for each of the determination regions based on the step; and (D) determining pass / fail based on the information on the chamfered portion for each of the determination areas; A method for inspecting steel materials, including:

2. 2. The steel inspection method according to claim 1, wherein in step (B), the step is detected based on gradation of the image data.

3. 3. The steel material inspection method according to claim 1, wherein the number of judgment regions set in step (B) is 8 or more and 18 or less.

4. 3. The steel product inspection method according to claim 1, wherein in step (C), a region between two steps having a magnitude greater than a predetermined threshold value Th is identified as a chamfered portion.

5. 3. The steel product inspection method according to claim 1, wherein in step (D), pass / fail is determined based on the number of judgment areas having the identified chamfered portion and the width of the chamfered portion in each judgment area.

Images