JP7622667B2 - 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 - Google Patents

Description

The present invention relates to 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.

The surface quality of steel products is an important factor in the appearance of steel products, and surface quality that impairs the appearance significantly reduces the value of the steel product. 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 unevenness 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 these irregularities often occur as lines several hundred μm to several tens of mm wide in the rolling direction of the steel sheet.

However, the change in the appearance characteristics of zinc-based plated steel sheets 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 hot-dip galvanized steel sheets. 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 area of light and dark areas in an image obtained by irradiating light onto the plated surface (see Patent Document 4).

JP 2020-153004 A JP 2018-44190 A JP 2006-317379 A Japanese Patent Application Publication No. 11-72317

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 it difficult to persuade people that the appearance has truly been improved because the standards for the appearance characteristics are unclear. 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 impact of the analysis results on the appearance must be further evaluated, so it is indirect from the perspective of judging the appearance characteristics. In addition, since the evaluation is only performed on the irradiation points of the pulsed laser light, it is necessary to scan the pulsed laser light to evaluate the appearance in a planar manner, which requires a large-scale device. In addition, it is difficult to measure line defects 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 irregularities in line defects.

The present invention has been made in consideration of the above problems, and its object is to provide a defect measurement device and defect measurement method that can directly measure the appearance characteristics of the surface of a zinc-based plated steel sheet caused by minute irregularities in the form of line defects (hereinafter referred to as line defects) 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 that can manufacture zinc-based plated steel sheets with a high yield. Another object of the present invention is to provide a quality control method for zinc-based plated steel sheets that can provide high-quality zinc-based plated steel sheets.

The defect measuring device according to the present invention is a defect measuring device for measuring line defects on the surface of a zinc-based plated steel sheet, and includes an illumination means for illuminating the surface of the zinc-based plated steel sheet with line illumination light, and an imaging means for capturing an image of the 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, and the illumination means and the imaging means 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.

The apparatus 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 preferably arranged so that the extension direction of the line illumination light is perpendicular to the rolling direction of the zinc-based plated steel sheet.

The calculation means may generate a corrected image by correcting the brightness unevenness in the vertical direction from the surface image of the zinc-based plated steel sheet, 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.

The defect measurement method according to 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 irradiation step in which an irradiation means irradiates 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 by the surface of the zinc-based plated steel sheet to capture a surface image of the zinc-based plated steel sheet, and the irradiation means and the imaging means are arranged so that the difference between the irradiation angle and the reception angle of the line illumination light is within a range of 20 degrees to 40 degrees.

The manufacturing equipment for zinc-based plated steel sheets according to the present invention includes manufacturing equipment for manufacturing zinc-based plated steel sheets, and a defect measurement device according to the present invention for measuring the surface of the zinc-based plated steel sheets manufactured by the manufacturing equipment.

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 the surface of the zinc-based plated steel sheet manufactured in the manufacturing step using the defect measurement method according to the present invention.

The quality control method for zinc-based plated steel sheet according to the present invention includes a measurement step of measuring the surface of the 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 the line defects in the measurement step.

The defect measurement device and defect measurement 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. Furthermore, 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. Furthermore, the quality control method for zinc-based plated steel sheets according to the present invention can provide high-quality zinc-based plated steel sheets.

FIG. 1 is a side view and a front view showing the configuration of a defect measuring device according to an embodiment of the present invention. 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. FIG. 3 is a flowchart showing the flow of the quantification process according to an embodiment of the present invention. FIG. 4 is a diagram showing an example of a surface image of a hot-dip galvanized steel sheet. FIG. 5 is a diagram showing a corrected image of the surface image shown in FIG. FIG. 6 is a diagram showing an example of a line defect image and a profile. FIG. 7 is a diagram showing an example of a line defect image and a profile when a line defect is present and when no line defect is present. 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. FIG. 9 is a side view and a front view showing the configuration of a modified example of a defect measuring device according to an embodiment of the present invention.

Below, an embodiment of the present invention, 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, will be described with reference to the drawings.

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, electrolytic galvanized 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 also be formed by forming two or more plating layers of the same or different types.

In addition, examples of the steel type of the steel sheet that serves as the base for the zinc-based plated steel sheet include steel types whose steel composition contains, in mass %, 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% to 1.0%, V: 0.001% to 1.0%, W: more than 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% to 0.1%, Ca: more than 0% and up to 0.03%, Mg: more than 0% and up to 0.03%. Furthermore, in addition to the above steel types, the steel sheet may be cold-rolled, and the present invention will function more effectively.

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

Figures 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 Figures 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 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.

The linear stage 2 is a transport device that places a cut sheet sample S on its upper portion and transports the cut sheet sample S along the rolling direction of the steel sheet.

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.

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, and continuously captures images of the cut sheet sample S transported 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 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 this embodiment, the entire cut sheet sample S can be imaged under uniform optical conditions, which is very preferable. The line sensor 4 functions as an imaging means according to the present invention.

When the illumination angle of the line light source 3 relative to the surface perpendicular direction of the cut sheet sample S shown in FIG. 2 is equal to the light receiving angle of the line sensor 4, the optical condition becomes a regular 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 conditions approach the regular reflection condition, the specular reflection component becomes noise, while when the optical conditions are too far from the regular 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. 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.

It is also preferable that the light receiving brightness of the line sensor 4 is not too dark and not saturated. It is also preferable that the resolution in the width 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, if a line defect with a minimum width of 0.5 mm is to be evaluated, the resolution in the width direction is preferably 0.25 mm or less. On the other hand, there is no particular limit to the resolution in the length direction (rolling direction of the steel plate) of the image of the cut sheet sample S, 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 corresponding to the transport amount of the cut sheet sample S as a trigger signal.

In addition, since the purpose of this embodiment is to quantify the visual judgment of the appearance characteristics of zinc-based plated steel sheet as an index of line defects, it is preferable to use wavelengths in the visible light range for the wavelength of the line illumination light and the receiving wavelength of the line sensor 4. In addition, since the sensitivity characteristics of Si elements normally used in visible light cameras include near-infrared light, it is preferable to remove wavelengths in the infrared range 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, halogen light source, metal halide light source, etc. as the line light source 3.

The calculation device 5 is composed of an information processing device. The calculation device 5 generates a surface image of the cut sheet sample S by stitching together 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 indicator 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.

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

Figure 3 is a flowchart showing the flow of the quantification process according to one embodiment of the present invention. The flowchart shown in Figure 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.

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 plate) 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 in the width direction still occurs due to the influence of the gradual change in the reflection characteristics of the steel plate itself. Therefore, the calculation device 5 first removes the low-frequency components contained in the surface image of the cut sheet sample S. The calculation device 5 then 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.

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 performed 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 the surface image in which only the low-frequency components are extracted and the image in which the low-frequency components are removed, the contrast difference of the line defect occurring in the high brightness area and the low brightness area of the peripheral area 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, 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 correction image of the surface image shown in Figure 4 is shown in Figure 5. With this, the processing of step S1 is completed, and the quantification processing proceeds to the processing of step S2.

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 a selected area including a line defect is shown in FIG. 6(a). The image after the area selection is color-toned for easy understanding. In this example, a sufficient longitudinal length is selected to include a stable area of white and black lines, which are vertical lines that cause appearance defects. Since the line defect may be faint 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.

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 will be large depending on the surface properties such as the surface roughness of the steel plate itself. Therefore, taking into account 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 remains one-dimensional in the width direction and is compressed to zero dimensions in the longitudinal direction. In detail, the calculation device 5 performs a process in the longitudinal direction so that a representative value that reflects the longitudinal characteristics of the two-dimensional line defect image is obtained. 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, P×Q resolution) (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).

Examples of processing other than the averaging process include maximum processing (processing in which the maximum value of the luminance in the longitudinal direction is the representative value), minimum processing (processing in which the minimum value of the luminance in the longitudinal direction is the representative value), median processing (processing in which the median value of the luminance in the longitudinal direction is 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, if 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 S/N ratio is ρ, then ρ should satisfy the following formula (2).

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. In addition, since the signal intensity appears 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 of the visual inspection. FIG. 8 also shows the change in the index in the sample with a line defect and the 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 of 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 plated steel sheet are. In addition, the "difference between the index with defect and the index without defect" in FIG. 8 is the value obtained by subtracting the index without the line defect from the index with the line defect at each light receiving angle (unit: degree). The index without the line defect (in the case of FIG. 8, the difference between the maximum and minimum values in the area without the line defect) is considered to correspond to an index that the zinc-based plated steel sheet to be measured originally has, for example, background noise. Therefore, if the index without the line defect, which corresponds to background noise, is further subtracted from the index with the line defect (in the case of FIG. 8, the difference between the maximum and minimum values in the area with the line defect), the change in the index when the line defect is present can be further emphasized.

As shown in FIG. 8, when the light receiving angle of the line sensor 4 is close to 10 degrees, which is close to the regular 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 regular reflection direction (when the difference with the illumination angle of the line light source 3 becomes 30 degrees), the difference in the index due to 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 regular reflection direction, the index starts to increase at 30 degrees, peaks at 40 degrees, and then decreases to 50 degrees. This confirmed that when the illumination angle of the line light source 3 is 10 degrees, the difference in the above-mentioned index can be increased within the range of 30 degrees to 50 degrees for the light receiving angle of the line sensor 4. Therefore, in this example, since the illumination angle of the line light source 3 is fixed at 10 degrees, it is preferable to position the line sensor 4 so that the light receiving angle of the line sensor 4 varies from the specular reflection direction in a range of 20 degrees to 40 degrees, and it is best to have a difference of 30 degrees. For this reason, it is preferable to set the difference between the illumination angle of the line light source 3 and the light receiving angle of the line sensor 4 in a range of 20 degrees to 40 degrees. This completes the processing of step S4, and the series of quantification processes ends.

As is clear from the above description, the defect measurement device 1, which is one embodiment of the present invention, comprises 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 line defects in a short time using a simple optical system.

In addition, various effects can be obtained by using this index to grade the occurrence of line defects for each product (e.g., the degree of appearance, frequency of occurrence, and size of line defects). For example, the index can be used to judge the pass/fail of a product, the index can be fed back into the operations of the product manufacturing process to suppress the occurrence of line defects, the index can be treated as large-scale data in combination with various other operational data and the causes and conditions of occurrence of line defects can be identified through multivariate analysis, the risk of line defects occurring can be predicted from other operational data, the predicted results can be presented at the operation site, and the predicted results can be used to perform automatic operations.

The present invention may also be applied to a defect measurement device constituting a manufacturing facility for zinc-based plated steel sheets, and the defect measurement device according to the present invention may be used to measure a zinc-based plated steel sheet manufactured by known or existing manufacturing facilities, and measure line-shaped defects in the zinc-based plated steel sheet. 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 may be included to measure a zinc-based plated steel sheet manufactured by known or existing manufacturing steps, thereby measuring line-shaped defects in the zinc-based plated steel sheet. According to such manufacturing facility for zinc-based plated steel sheets and a manufacturing method for metal strips, 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 may be included to measure the zinc-based plated steel sheet, thereby performing quality control of the zinc-based plated steel sheet based on the measurement results of line-shaped defects 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 can be provided.

The above describes an embodiment of the invention made by the inventors, but the present invention is not limited to the description and drawings that form part of the disclosure of the present invention according to this embodiment.

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 line defects occurring over the entire length and width of the 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 the zinc-based plated steel sheet ST being transported in the same manner as the cut sheet sample S, a pulse signal is generated by the encoder 6 in accordance with the rotation of the roll R, and the pulse signal is used as a trigger to photograph the 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 line defects in real time from the photographed surface image. In addition, 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 line defects by transmitting the index to the upper PC 7. In addition, the calculation device 5 calculates the index of line defects 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 to store only images of areas where line defects have actually occurred, and then the characteristics of the line defects may be analyzed in more detail based on the strength, width, and occurrence range of the line defects, which may be useful for quality assurance and causal analysis. In this manner, all other embodiments, examples, and operational techniques made by those skilled in the art based on this embodiment are included in the scope of the present invention.

REFERENCE SIGNS LIST 1 Defect measurement device 2 Linear stage 3 Line light source 4 Line sensor 5 Calculation device S Cut sheet sample ST Zinc-based plated steel sheet

Claims (7)

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. The defect measuring device according to claim 1, wherein the irradiating means is disposed so that an extension direction of the line illumination light is perpendicular to a rolling direction of the zinc-based plated steel sheet. The defect measurement device according to claim 2, wherein the calculation means generates a corrected image by correcting the brightness unevenness in the vertical direction from the 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. 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. 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: 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: 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:

Images