Defect measurement device, defect measurement method, zinc-based coated steel sheet manufacturing equipment, zinc-based coated steel sheet manufacturing method, and zinc-based coated steel sheet quality control method

Abstract

To provide a defect measuring device and a defect measuring method capable of directly and quickly measuring the appearance characteristics of the surface of a galvanized steel sheet caused by a stripe defect in a simple optical system.SOLUTION: Disclosed is a defect measurement device according to the present invention which measures a stripe defect on the surface of a galvanized steel sheet. This measurement device includes: irradiation means for irradiating the surface of the galvanized steel sheet with line illumination light; and imaging means for photographing a surface image of the galvanized steel sheet by receiving the line illumination light reflected on the surface of the galvanized steel sheet. The irradiation means and the imaging means are arranged so that the difference between an irradiation angle and a light receiving angle of the line illumination light falls within a range of 20° or more and 40° or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a defect measuring device, a defect measuring method, a manufacturing facility for zinc-based plated steel sheets, a manufacturing method for zinc-based plated steel sheets, and a quality control method for zinc-based plated steel sheets. [Background technology]

[0002] The surface quality of steel products is an important factor in the appearance of steel products, and surface quality that impairs the appearance of steel products significantly reduces their value. Changes in appearance characteristics due to surface quality are often caused by minute shapes such as the surface roughness of the steel product surface, chemical composition, and unevenness in coating thickness. For example, in zinc-plated steel sheets, minute (several hundred nm to several μm) irregularities in the form of line defects may occur on the surface, and the irregularities may become apparent during the subsequent painting process, impairing the appearance. These irregularities occur when slight segregation of surface components occurs during the manufacturing process of zinc-plated steel sheets, causing an unevenness in the ease of alloying between iron and zinc. In addition, the unevenness in the ease of alloying is stretched in the rolling direction of the steel sheet during the rolling process, and the unevenness often occurs as lines several hundred μm to several tens of mm wide in the rolling direction of the steel sheet.

[0003] However, the change in the appearance characteristics of a zinc-based coated steel sheet caused by minute irregularities in the form of line defects (hereinafter referred to as line defects) is only a faint line-like pattern when observed visually. In addition, since the amount of irregularities is small and the ratio of minute irregularities to the surface on which they occur is small, it is difficult to directly measure and quantify the irregularities. In light of this background, past research and development focused on how to improve the appearance, and the evaluation of the appearance relied exclusively on visual inspection. Specifically, Patent Documents 1 and 2 describe methods for visually judging the appearance of a hot-dip galvanized steel sheet. On the other hand, for quantifying such appearance characteristics, a method has been proposed in which a pulsed laser beam is irradiated onto the plated surface and the emission spectrum is spectroscopically analyzed for each pulse for each analysis point (see Patent Document 3), and a method has been proposed in which a pattern called spangle is inspected from the areas of light and dark areas in an image obtained by irradiating light onto the plated surface (see Patent Document 4). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-153004 A [Patent Document 2] JP 2018-44190 A [Patent Document 3] JP 2006-317379 A [Patent Document 4] Japanese Patent Application Publication No. 11-72317 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the methods described in Patent Documents 1 and 2 not only cause variation in judgments of the appearance characteristics of zinc-based plated steel sheets based on personal factors, but also make the standards for appearance characteristics vague, making it difficult to provide a convincing conclusion as to whether the appearance has truly been improved. On the other hand, the method described in Patent Document 3 is a method for analyzing the plating structure rather than a method for quantifying the appearance characteristics of zinc-based plated steel sheets, and the influence of the analysis results on the appearance must be further evaluated, so it is indirect from the viewpoint of judging the appearance characteristics. In addition, since only the irradiation points of the pulsed laser light are evaluated, it is necessary to scan the pulsed laser light in order to evaluate the appearance in a planar manner, which requires a large-scale device. In addition, it is difficult to measure a line-like defect with a width smaller than the spot diameter of the pulsed laser light. In addition, the method described in Patent Document 4 uses an area sensor, so the optical system may vary within the field of view. In addition, only spangles are evaluated, and it is unclear whether it is possible to evaluate even minute unevenness of line-like defects.

[0006] The present invention has been made in view of the above problems, and an object of the present invention is to provide a defect measuring device and a defect measuring method capable of directly measuring the appearance characteristics of the surface of a zinc-based plated steel sheet caused by minute irregularities in the form of a line defect (hereinafter referred to as a line defect) in a short time using a simple optical system. Another object of the present invention is to provide a zinc-based plated steel sheet manufacturing facility and manufacturing method capable of manufacturing zinc-based plated steel sheets with a high yield. Another object of the present invention is to provide a zinc-based plated steel sheet quality control method capable of providing a high-quality zinc-based plated steel sheet. [Means for solving the problem]

[0007] The defect measuring device of the present invention is a defect measuring device that measures line-like defects on the surface of a zinc-based plated steel sheet, and comprises an illumination means that irradiates line illumination light onto the surface of the zinc-based plated steel sheet, and an imaging means that captures a surface image of the zinc-based plated steel sheet by receiving the line illumination light reflected from the surface of the zinc-based plated steel sheet, and the illumination means and the imaging means are positioned so that the difference between the illumination angle and reception angle of the line illumination light is within the range of 20 degrees or more and 40 degrees or less.

[0008] The present invention preferably includes a calculation means for calculating, from a surface image of the zinc-based plated steel sheet, a feature amount of the line defect in a direction parallel to the rolling direction of the zinc-based plated steel sheet as an index of the line defect, and the irradiation means is arranged so that the extension direction of the line illumination light is perpendicular to the rolling direction of the zinc-based plated steel sheet.

[0009] The calculation means may generate a corrected image from a surface image of the zinc-based plated steel sheet by correcting brightness unevenness in the vertical direction, select an image of an area including a line defect from the corrected image, and calculate the index from the selected image of the line defect.

[0010] The defect measurement method of the present invention is a defect measurement method for measuring line defects on the surface of a zinc-based plated steel sheet, and includes an illumination step in which an illumination means illuminates the surface of the zinc-based plated steel sheet with line illumination light, and an imaging step in which an imaging means receives the line illumination light reflected from the surface of the zinc-based plated steel sheet, thereby capturing a surface image of the zinc-based plated steel sheet, wherein the illumination means and the imaging means are positioned so that the difference between the illumination angle and the reception angle of the line illumination light is within a range of 20 degrees or more and 40 degrees or less.

[0011] A manufacturing facility for zinc-based plated steel sheet according to the present invention includes manufacturing facility for manufacturing zinc-based plated steel sheet, and a defect measurement device according to the present invention for measuring the surface of the zinc-based plated steel sheet manufactured by the manufacturing facility.

[0012] The manufacturing method of the zinc-based plated steel sheet according to the present invention includes a manufacturing step of manufacturing a zinc-based plated steel sheet, and a measurement step of measuring a surface of the zinc-based plated steel sheet manufactured in the manufacturing step using the defect measurement method according to the present invention.

[0013] The quality control method for a zinc-based plated steel sheet according to the present invention includes a measurement step of measuring a surface of a zinc-based plated steel sheet using the defect measurement method according to the present invention, and a quality control step of performing quality control of the zinc-based plated steel sheet based on the measurement results of line defects in the measurement step. Effect of the Invention

[0014] The defect measuring device and defect measuring method according to the present invention can directly measure the appearance characteristics of the surface of a zinc-based plated steel sheet caused by a line defect in a short time using a simple optical system. Also, the zinc-based plated steel sheet manufacturing equipment and manufacturing method according to the present invention can manufacture zinc-based plated steel sheets with a high yield. Also, the zinc-based plated steel sheet quality control method according to the present invention can provide a high-quality zinc-based plated steel sheet. [Brief description of the drawings]

[0015] [Figure 1]FIG. 1 is a side view and a front view showing the configuration of a defect measuring device according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing the definitions of the illumination angle of a line light source and the light receiving angle of a line sensor. [Diagram 3] FIG. 3 is a flowchart showing the flow of the quantification process according to one embodiment of the present invention. [Figure 4] FIG. 4 is a diagram showing an example of a surface image of a hot-dip galvanized steel sheet. [Diagram 5] FIG. 5 is a diagram showing a corrected image of the surface image shown in FIG. [Figure 6] FIG. 6 is a diagram showing an example of a line defect image and a profile. [Figure 7] FIG. 7 is a diagram showing an example of a line defect image and a profile when a line defect is present and when a line defect is not present. [Figure 8] FIG. 8 is a diagram showing an example of the transition of the index when there is a line defect and when there is no line defect. [Figure 9] FIG. 9 is a side view and a front view showing the configuration of a modified example of a defect measuring device according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, with reference to the drawings, a defect measurement device, a defect measurement method, a manufacturing facility for zinc-based plated steel sheets, a manufacturing method for zinc-based plated steel sheets, and a quality control method for zinc-based plated steel sheets, which are embodiments of the present invention, will be described.

[0017] In this specification, the term "zinc-based plated steel sheet" refers to a plated steel sheet containing zinc in the plated layer. Specifically, examples of zinc-based plated steel sheets include hot-dip galvanized steel sheets (GI), alloyed hot-dip galvanized steel sheets (GA) obtained by alloying hot-dip galvanized steel sheets, electrogalvanized steel sheets (EG), Zn-Ni plated steel sheets, Zn-Mg plated steel sheets, Zn-Al-Mg plated steel sheets (e.g., Zn-6% by mass Al-3% by mass Mg alloy plated steel sheets, Zn-11% by mass Al-3% by mass Mg alloy plated steel sheets, etc.), and Zn-Al plated steel sheets (e.g., Zn-5% by mass Al alloy plated steel sheets, Zn-55% by mass Al alloy plated steel sheets, etc.). In addition, the plated layer may contain a small amount of one or more of nickel, cobalt, manganese, iron, molybdenum, tungsten, titanium, chromium, aluminum, magnesium, lead, antimony, tin, copper, and silicon as a different metal element or impurity. The plating layer may be formed by forming two or more plating layers of the same type or different types.

[0018] In addition, an example of a steel type for the steel sheet that serves as the base for the zinc-based plated steel sheet is a steel type having a steel composition, in mass %, of C: 0.0001% or more and 0.25% or less, Si: 0.001% or more and 2.0% or less, Mn: 0.01% or more and 3.0% or less, P: 0.001% or more and 0.02% or less, S: 0.0001% or more and 0.02% or less, Al: 0.001% or more and 0.10% or less, N: 0.0001% or more and 0.007% or less, with the balance being Fe and unavoidable impurities. In addition to the above essential elements, the steel sheet may contain one or more optional elements selected from the following: Cr: more than 0% and up to 2.0%, Nb: 0.001% or more and up to 1.0%, V: 0.001% or more and up to 1.0%, W: more than 0% and up to 0.3%, Ni: more than 0% and up to 2.0%, Cu: more than 0% and up to 2.0%, Mo: more than 0% and up to 1.0%, B: more than 0% and up to 0.01%, Ti: 0.001% or more and up to 0.1%, Ca: more than 0% and up to 0.03%, and Mg: more than 0% and up to 0.03%. Furthermore, the present invention works more effectively if the steel sheet is cold-rolled in addition to the above steel types.

[0019] [Configuration of defect measurement device] First, the configuration of a defect measuring device according to an embodiment of the present invention will be described with reference to FIGS.

[0020] 1(a) and (b) are a side view and a front view showing the configuration of a defect measurement device according to one embodiment of the present invention. As shown in Figs. 1(a) and (b), the defect measurement device 1 according to one embodiment of the present invention is an offline defect measurement device that quantifies the appearance characteristics of a cut sheet sample S partially cut out from a zinc-based plated steel sheet (hereinafter abbreviated as steel sheet) as an index of a line defect on the surface of the cut sheet sample S. The defect measurement device 1 includes a linear stage 2, a line light source 3, a line sensor 4, and a calculation device 5. It is preferable that the cut sheet sample S is as flat as possible.

[0021] The linear stage 2 is a conveying device that carries a cut sheet sample S on its upper portion and conveys the cut sheet sample S along the rolling direction of the steel sheet.

[0022] The line light source 3 irradiates the surface of the cut sheet sample S with line illumination light extending in a direction perpendicular to the rolling direction of the steel sheet. It is preferable that the irradiation direction of the line illumination light and the conveying direction of the cut sheet sample S are parallel to the rolling direction of the steel sheet, but the line illumination light may be irradiated in a direction perpendicular or oblique to the rolling direction of the steel sheet. In this embodiment, the extension direction of the line defect often coincides with the rolling direction of the steel sheet, so the line illumination light is irradiated in a direction parallel to the rolling direction of the steel sheet. On the other hand, when the extension direction of the line defect does not coincide with the rolling direction of the steel sheet, it is preferable to irradiate the line illumination light in a direction parallel to the extension direction of the line defect. The line light source 3 functions as an irradiation means according to the present invention.

[0023] The line sensor 4 is composed of an imaging device having one or more lines of imaging elements arranged in a direction perpendicular to the rolling direction of the steel plate. The line sensor 4 receives the line illumination light reflected from the surface of the cut sheet sample S, thereby continuously capturing images of the cut sheet sample S conveyed by the linear stage 2, and outputs the captured image data to the calculation device 5. When an image of the cut sheet sample S is captured using a general digital camera and a spot light source, the illumination angle and reception angle of the illumination light differ depending on the imaging position, so that the appearance of the line defect changes. Therefore, in the defect measurement device 1 of this embodiment, the illumination direction and imaging direction of the illumination light are limited to a direction parallel to the rolling direction of the steel plate, and the cut sheet sample S is scanned using the linear stage 2. In such an embodiment, the entire cut sheet sample S can be captured under uniform optical conditions, which is very preferable. The line sensor 4 functions as an imaging means according to the present invention.

[0024] In addition, when the illumination angle of the line light source 3 and the light receiving angle of the line sensor 4 are equal to the surface normal direction of the cut sheet sample S shown in FIG. 2, the optical condition is the specular reflection condition, and an image of the specular reflection component of the cut sheet sample S can be obtained. The specular reflection component decreases as the difference between the illumination angle of the line light source 3 and the light receiving angle of the line sensor 4 increases, and conversely, the diffuse reflection component increases. As a result of detailed observation of the surface of the cut sheet sample S, the inventors of the present invention found that when the optical condition approaches the specular reflection condition, the specular reflection component becomes noise, while when the optical condition deviates too far from the specular reflection condition, the surface roughness of the texture of the cut sheet sample S itself is emphasized, and the signal of the line defect is buried. For this reason, the difference between the illumination angle of the line light source 3 and the light receiving angle of the line sensor 4 is set to a range of 20 degrees or more and 40 degrees or less. In addition, this angle range can be obtained by learning, for example, by a machine learning method, the angle range in which the difference in the index of the line defect, which will be described later, is the largest depending on the presence or absence of the line defect.

[0025] In addition, it is preferable that the light receiving luminance of the line sensor 4 is not too dark and not saturated. In addition, it is preferable that the resolution in the width direction (direction perpendicular to the rolling direction of the steel plate) of the image of the cut sheet sample S is sufficiently small compared to the width direction pitch of the line defect to be evaluated. For example, when evaluating a line defect with a minimum width of 0.5 mm, the resolution in the width direction is preferably 0.25 mm or less. On the other hand, the resolution in the longitudinal direction (rolling direction of the steel plate) of the image of the cut sheet sample S is not particularly limited, but it is preferable that it does not change when the cut sheet sample S is transported. To achieve this, it is preferable to transport the cut sheet sample S at a constant speed using the linear stage 2, or to capture an image of the cut sheet sample S using a pulse signal according to the transport amount of the cut sheet sample S as a trigger signal.

[0026] In addition, it is preferable to use wavelengths in the visible light region for the wavelength of the line illumination light and the wavelength of light received by the line sensor 4, since the object of this embodiment is to quantify the visual judgment of the appearance characteristics of the zinc-based plated steel sheet as an index of line defects. In addition, since the sensitivity characteristics of Si elements usually used in visible light cameras include near-infrared light, it is preferable to remove wavelengths in the infrared region by inserting an infrared light cut filter. Furthermore, it is preferable that the wavelength of the line illumination light is broad to match the visual observation, and in this case, it is preferable to use a xenon light source, a halogen light source, a metal halide light source, or the like as the line light source 3.

[0027] The calculation device 5 is configured with an information processing device. The calculation device 5 generates a surface image of the cut sheet sample S by connecting in the longitudinal direction the data of the images in the width direction continuously captured by the line sensor 4. The calculation device 5 then quantifies the index of the line defect by performing a quantification process described later on the generated surface image of the cut sheet sample S. The calculation device 5 functions as a calculation means according to the present invention.

[0028] [Quantification Processing] Next, the quantification process according to one embodiment of the present invention will be described with reference to FIG.

[0029] 3 is a flowchart showing the flow of the quantification process according to one embodiment of the present invention. The flowchart shown in Fig. 3 starts when the calculation device 5 generates a surface image of the cut sheet sample S, and the quantification process proceeds to step S1.

[0030] In the process of step S1, the calculation device 5 corrects (removes) the brightness unevenness in the width direction (direction perpendicular to the rolling direction of the steel sheet) of the surface image of the cut sheet sample S, so that the same measurement value can be obtained regardless of where the line defect occurs in the surface image. Specifically, the optical system is designed to obtain uniform brightness in the width direction, but brightness unevenness occurs in the width direction due to the influence of the gradual change in the reflection characteristics of the steel sheet itself. Therefore, the calculation device 5 first removes low-frequency components contained in the surface image of the cut sheet sample S. Then, the calculation device 5 generates a corrected image by taking the ratio between the brightness of the surface image from which only the low-frequency components have been extracted and the brightness of the image from which the low-frequency components have been removed.

[0031] If the low-frequency components are simply removed, the contrast of the same line defect will be strong if the brightness value of the peripheral area is high, and weak if the brightness value is low, so the measurement value of the line defect in the subsequent process will depend on the position in the surface image. In contrast, by generating a correction image that is the brightness ratio between a surface image in which only low-frequency components are extracted and an image in which the low-frequency components are removed, the contrast difference of the line defect occurring in the peripheral areas with high and low brightness values ​​can be averaged. Figure 4 shows an image of the surface of a hot-dip galvanized steel sheet in which a line defect has occurred, taken with the irradiation angle of the line light source 3 set to 10 degrees, the receiving angle of the line sensor 4 set to 40 degrees, the width resolution set to 0.11 mm, and the length resolution set to 0.08 mm. Also, a corrected image of the surface image shown in Figure 4 is shown in Figure 5. With this, the process of step S1 is completed, and the quantification process proceeds to the process of step S2.

[0032] In the process of step S2, the calculation device 5 selects an image of a certain range of an area including a line defect from the corrected image generated by the process of step S1, and generates a line defect image by setting the image of the selected area including the line defect as a line defect image. An example of the selection of an area including a line defect is shown in FIG. 6(a). The image after the area selection is color-toned so that it is easy to understand. In this example, a sufficient length in the longitudinal direction is selected so as to include a stable area of ​​white and black lines that are vertical lines that cause appearance defects. Since the line defect may be faded in some places in the line defect image, it is preferable to select an area that occurs as stably as possible. In addition, if there is a foreign object other than the line defect, such as a stain or a defect, around the line defect, the image of the foreign object becomes a noise factor in the line defect image, so it is preferable to remove the image of the foreign object from the range of image selection. This completes the process of step S2, and the quantification process proceeds to the process of step S3.

[0033] In the process of step S3, the calculation device 5 performs a process of averaging brightness in the longitudinal direction on the line defect image generated by the process of step S2. Specifically, if the brightness of the line defect part and the brightness of the surrounding part in the line defect image generated by the process of step S2 are simply compared as they are, the variation becomes large depending on the surface properties such as the surface roughness of the steel sheet itself. Therefore, in consideration of the characteristic that the line defect extends in the longitudinal direction, the calculation device 5 performs a process of averaging brightness in the longitudinal direction on the line defect image. In other words, the calculation device 5 generates a one-dimensional (linear) profile in which the two-dimensional line defect image is compressed to zero dimensions in the longitudinal direction while keeping the width direction one-dimensional. In detail, the calculation device 5 performs a process in the longitudinal direction so as to obtain a representative value that reflects the longitudinal characteristics of the two-dimensional line defect image. For example, since the line defect image is a two-dimensional matrix, the line defect image can be expressed as I(p, q) (1≦p≦P, 1≦q≦Q, resolution of P×Q) (see FIG. 6(a)). Therefore, in the case of averaging processing, the one-dimensional profile L(p) (1≦p≦P) can be calculated by the following formula (1). The one-dimensional profile L(p) calculated from the line defect image shown in Fig. 6(a) is shown in Fig. 6(b).

[0034]

number

[0035] Examples of processing other than the averaging processing include maximum processing (processing in which the maximum value of the luminance in the longitudinal direction is used as the representative value), minimum processing (processing in which the minimum value of the luminance in the longitudinal direction is used as the representative value), median processing (processing in which the median value of the luminance in the longitudinal direction is used as the representative value), and percentile processing (processing in which the luminance value in the determined order after rearranging in descending order is adopted). However, any processing may be used as long as it can stably obtain a representative value of the line defect portion in the longitudinal direction. In addition, it is preferable that the longitudinal length of the line defect image is sufficiently long so that the variation due to the surface roughness can be reduced. For example, when the average processing is adopted, if it is assumed that the noise caused by the surface roughness occurs randomly and the noise is normally distributed, the noise is multiplied by √Q by averaging Q points. Therefore, assuming that the longitudinal length of the line defect image, i.e., the number of points to be averaged in the longitudinal direction, is Q, the signal of the representative point of the line defect is S, the noise of the healthy part is N, and the required SN ratio is ρ, it is preferable that ρ satisfies the following mathematical formula (2).

[0036]

number

[0037] In the process of step S4, the calculation device 5 extracts a numerical value at a position corresponding to the line defect from the one-dimensional profile obtained by the process of step S3, and uses the numerical value as an index of the line defect. Since the signal intensity is on the positive side when the line defect is brighter than the surrounding area, and on the negative side when the line defect is darker, the absolute value may be used as the index of the line defect, or the value obtained by subtracting the minimum value from the maximum value may be used as the index of the line defect. Here, FIG. 7(a) and (b) show line defect images and one-dimensional profiles when a line defect is present and when a line defect is not present. The black arrow and the white arrow in FIG. 7(a) indicate the position of the line defect confirmed by visual inspection, and the numerical values ​​-6.8 and +3, 4 indicate the numerical values ​​of the one-dimensional profile at the position of the line defect. It can be seen that the obtained numerical value is in good agreement with the intuitive judgment by visual inspection. FIG. 8 shows the transition of the index in a sample with a line defect and a sample without a line defect when the irradiation angle of the line light source 3 is fixed at 10 degrees and the light receiving angle of the line sensor 4 is changed. In the example shown in FIG. 8, the index is the difference between the maximum and minimum values ​​so that the extracted numerical value is an index for the line defect. This is because it is clear that the greater the difference between the maximum and minimum values ​​of the extracted numerical value, the more severe the line defect is and the worse the appearance characteristics of the zinc-based coated steel sheet are. In addition, the "difference between the index for the presence of a defect and the index for the absence of a defect" in FIG. 8 is the value obtained by subtracting the index for the absence of a line defect from the index for the presence of a line defect at each light receiving angle (unit: degree). The index for the absence of a line defect (in the case of FIG. 8, the difference between the maximum and minimum values ​​in the area without a line defect) is considered to correspond to an index that is inherent to the zinc-based coated steel sheet to be measured, for example, background noise. Therefore, if the index for the absence of a line defect, which corresponds to background noise, is further subtracted from the index for the presence of a line defect (in the case of FIG. 8, the difference between the maximum and minimum values ​​in the area with a line defect), the change in the index for the presence of a line defect can be further emphasized.

[0038] As shown in FIG. 8, when the light receiving angle of the line sensor 4 is near 10 degrees, which is close to the specular reflection region, microscopic specular reflections are present sparsely, and the index value increases regardless of the presence or absence of a line defect. In contrast, when the light receiving angle of the line sensor 4 is increased, the signal value of the line defect itself weakens, and the index value decreases regardless of the presence or absence of a line defect. Then, when the light receiving angle of the line sensor 4 is 40 degrees, which is 30 degrees away from the specular reflection direction (when the difference with the irradiation angle of the line light source 3 is 30 degrees), the difference in the index depending on the presence or absence of a line defect becomes the largest. In detail, when the light receiving angle of the line sensor 4 is increased from 10 degrees, which is the specular reflection direction, the index starts to increase at 30 degrees, reaches a peak at 40 degrees, and then decreases to 50 degrees. This confirmed that when the irradiation angle of the line light source 3 is 10 degrees, the difference in the above-mentioned index can be increased within the range of the light receiving angle of the line sensor 4 from 30 degrees to 50 degrees. Therefore, in this example, since the illumination angle of line light source 3 is fixed at 10 degrees, it is preferable to arrange line sensor 4 so that the light receiving angle of line sensor 4 differs from the specular reflection direction in the range of 20 degrees to 40 degrees, and it is best to have a difference of 30 degrees. Also, from this, it is preferable to set the difference between the illumination angle of line light source 3 and the light receiving angle of line sensor 4 in the range of 20 degrees to 40 degrees. This completes the process of step S4, and the series of quantification processes ends.

[0039] As is clear from the above description, the defect measuring device 1, which is one embodiment of the present invention, includes a line light source 3 that irradiates a line illumination light onto the surface of a zinc-based plated steel sheet, and a line sensor 4 that captures a surface image of the zinc-based plated steel sheet by receiving the line illumination light reflected by the surface of the zinc-based plated steel sheet, and the line light source 3 and the line sensor 4 are arranged so that the difference between the illumination angle and reception angle of the line illumination light is within a range of 20 degrees or more and 40 degrees or less. This makes it possible to directly measure a line defect in a short time using a simple optical system.

[0040] In addition, various effects can be obtained by using this index to grade the occurrence status of line defects for each product (for example, the degree of appearance, frequency of occurrence, and size of line defects, etc.), for example, using the index to judge the pass / fail of a product, feeding the index back into the operations of the product manufacturing process to suppress the occurrence of line defects, treating the index together with various other operational data as large-scale data and identifying the causes and conditions of occurrence of line defects through multivariate analysis, predicting the risk of line defect occurrence from other operational data, presenting the prediction results to the operation site, and using the prediction results to perform automatic operations.

[0041] The present invention may also be applied to a defect measurement device constituting a manufacturing facility for zinc-based plated steel sheets, and a zinc-based plated steel sheet manufactured by a known or existing manufacturing facility may be measured by the defect measurement device according to the present invention, and a line-like defect in the zinc-based plated steel sheet may be measured. The present invention may also be applied to a defect measurement method included in a manufacturing method for zinc-based plated steel sheets, and a measurement step of measuring a zinc-based plated steel sheet manufactured by known or existing manufacturing steps may be included, and a line-like defect may be measured in the zinc-based plated steel sheet. According to such manufacturing facility for zinc-based plated steel sheets and a manufacturing method for metal strip, zinc-based plated steel sheets can be manufactured with a high yield. Furthermore, the present invention may also be applied to a quality control method for zinc-based plated steel sheets, and a measurement step of measuring a zinc-based plated steel sheet may be included, and the quality control of the zinc-based plated steel sheet may be performed based on the measurement result of the line-like defect in the zinc-based plated steel sheet. According to such a quality control method for zinc-based plated steel sheets, a high-quality zinc-based plated steel sheet may be provided.

[0042] Although the embodiments to which the invention made by the present inventors is applied have been described above, the present invention is not limited to the descriptions and drawings which form a part of the disclosure of the present invention according to the present embodiments.

[0043] For example, the above embodiment is an example using a cut sheet sample, but by applying the present invention to a zinc-based plated steel sheet being transported online, it is also possible to perform online quantification of the index of a line defect occurring over the entire length and width of a product, i.e., the appearance characteristics of the zinc-based plated steel sheet. An example of the application of the present invention online is shown in FIG. 9. In the example shown in FIG. 9, a line light source 3 and a line sensor 4 are installed on a zinc-based plated steel sheet ST being transported in the same manner as the cut sheet sample S, a pulse signal is generated by an encoder 6 in accordance with the rotation of the roll R, and the pulse signal is used as a trigger to photograph a surface image of the zinc-based plated steel sheet ST. At this time, it is preferable to count the pulse value of the encoder 6 so that the position where the line defect occurs can be matched. Then, the calculation device 5 calculates the index of the line defect from the photographed surface image in real time. Also, the calculation device 5 obtains information on the zinc-based plated steel sheet ST from the upper PC 7, determines the harmfulness of the index, and manages the index of the line defect by transmitting the index to the upper PC 7. Also, the calculation device 5 calculates the index of the line defect over the entire length and width of the zinc-based plated steel sheet ST to create an index map. At this time, a threshold value may be set so that only images of the areas where the line defect actually occurs are saved, and then the characteristics of the line defect may be analyzed in more detail based on the intensity, width, occurrence range, etc. of the line defect, which may be useful for quality assurance and factor analysis. In this way, all other embodiments, examples, operational techniques, etc. made by those skilled in the art based on this embodiment are included in the scope of the present invention. [Explanation of symbols]

[0044] 1. Defect measurement equipment 2 Linear Stage 3 Line light source 4 Line Sensor 5 Computing device S Cutting plate sample ST Zinc-plated steel sheet

Claims

1. A defect measuring device for measuring a line-like defect on a surface of a zinc-based plated steel sheet, comprising: an illumination means for irradiating a surface of the zinc-based plated steel sheet with a line illumination light; an imaging means for capturing an image of a surface of the zinc-based plated steel sheet by receiving the line illumination light reflected by the surface of the zinc-based plated steel sheet; a calculation means for calculating an index of the line defect from a surface image of the zinc-based plated steel sheet, the computing means extracts maximum and minimum values ​​of a one-dimensional profile generated by compressing a two-dimensional image of a line defect into zero dimensions in a direction parallel to the rolling direction of the zinc-based plated steel sheet while keeping the image one-dimensional in a direction perpendicular to the rolling direction of the zinc-based plated steel sheet, and calculates a value obtained by subtracting the minimum value from the maximum value as an index of the line defect; the illumination means and the imaging means are arranged so that a difference between an illumination angle and a receiving angle of the line illumination light is within a range of 20 degrees to 40 degrees, which is an angle range in which a difference in the index of the line defect becomes relatively large depending on the presence or absence of the line defect. Defect measurement equipment.

2. A defect measuring device as described in Claim 1, wherein the irradiation means is arranged so that the extension direction of the line illumination light is perpendicular to the rolling direction of the zinc-based plated steel sheet.

3. 3. The defect measuring device according to claim 2, wherein the calculation means generates a corrected image by correcting brightness unevenness in the vertical direction from a surface image of the zinc-based plated steel sheet, selects an image of an area including a line defect from the corrected image, and calculates the index from the selected image of the line defect.

4. A defect measurement method for measuring a line-like defect on a surface of a zinc-based plated steel sheet, comprising: an illumination step in which an illumination means illuminates a surface of the zinc-based plated steel sheet with line illumination light; an imaging step of capturing an image of a surface of the zinc-based plated steel sheet by receiving the line illumination light reflected by the surface of the zinc-based plated steel sheet with an imaging means; A calculation step of calculating an index of the line defect from a surface image of the zinc-based plated steel sheet, the computing step extracts maximum and minimum values ​​of a one-dimensional profile generated by compressing a two-dimensional image of a line defect into zero dimensions in a direction parallel to the rolling direction of the zinc-based plated steel sheet while keeping the image one-dimensional in a direction perpendicular to the rolling direction of the zinc-based plated steel sheet, and calculates a value obtained by subtracting the minimum value from the maximum value as an index of the line defect; the illumination means and the imaging means are arranged so that a difference between an illumination angle and a receiving angle of the line illumination light is within a range of 20 degrees to 40 degrees, which is an angle range in which a difference in the index of the line defect becomes relatively large depending on the presence or absence of the line defect. Defect measurement methods.

5. A manufacturing facility for manufacturing zinc-based plated steel sheets; The defect measuring device according to any one of claims 1 to 3, which measures a surface of a zinc-based plated steel sheet manufactured by the manufacturing facility; A zinc-based plated steel sheet manufacturing facility equipped with the following:

6. A manufacturing step of manufacturing a zinc-based coated steel sheet; a measuring step of measuring a surface of the zinc-based plated steel sheet produced in the manufacturing step by using the defect measuring method according to claim 4; A method for producing a zinc-based plated steel sheet, comprising:

7. a measuring step of measuring a surface of a zinc-based plated steel sheet using the defect measuring method according to claim 4; a quality control step of performing quality control of the zinc-based plated steel sheet based on a measurement result of the line defect in the measurement step; A quality control method for zinc-based coated steel sheet, including:

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