Plate-shaped object shape measuring method, plate-shaped object manufacturing method, plate-shaped object quality control method, plate-shaped object shape measuring device, and plate-shaped object manufacturing facility

Abstract

To provide a shape measuring method of a plate-like object, a manufacturing method of the plate-like object, a quality control method of the plate-like object, a shape measuring device of the plate-like object, and a manufacturing facility of the plate-like object, capable of measuring accurately the shape of the plate-like object by an inexpensive and simple constitution.SOLUTION: The shape measurement method of the plate-like object includes a luminance acquisition step of imaging an image of thermal radiation light of the plate-like object during conveyance and acquiring a luminance value of the thermal radiation light at a plurality of measurement points on a surface of the plate-like object from the image of the thermal radiation light, an angle acquisition step of imaging an image of a side surface of the plate-like object during conveyance in synchronization with imaging of the image of the thermal radiation light and acquiring an inclination angle of the surface of the plate-like object at a measurement point of the side surface of the plate-like object from the image of the side surface, and a correction step of calculating a correction coefficient for converting the luminance value at the measurement point to the inclination angle using the luminance value acquired in the luminance acquisition step and the inclination angle acquired in the angle acquisition step, and converting the luminance value at other measurement points to the inclination angle.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a method for measuring the shape of a plate-like object, a method for manufacturing a plate-like object, a quality control method for a plate-like object, an apparatus for measuring the shape of a plate-like object, and a manufacturing facility for a plate-like object. [Background technology]

[0002] Shape control of plate-shaped materials is important in the materials industry. For example, in the steelmaking process, shape distortion occurs during the steel plate manufacturing process on the production line for thick and thin plates. In this case, an appropriate rolling process or straightening process can be carried out depending on the degree of shape distortion to produce an appropriate final product.

[0003] Shape distortion occurs when the reduction in the width direction of a steel sheet becomes uneven during rolling, causing the steel sheet to be partially elongated. Therefore, it is desirable to quantitatively measure shape distortion over the entire surface of the steel sheet.

[0004] There are various methods for measuring shape distortion. For example, Patent Document 1 discloses a method for stably measuring shape regardless of specularity or the tilt of the object by using a powerful LED light source to project a stripe pattern consisting of multiple lines onto the object surface. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-65863 [Non-patent literature]

[0006] [Non-Patent Document 1] Kaneshige, "Heat Measurement Using a Radiation Thermometer", Molding and Processing, Society of Plastics Processing, 2020, Vol. 32, No. 4, pp. 121-124 Summary of the Invention [Problem to be solved by the invention]

[0007] In the method disclosed in Patent Document 1, a light source is used to irradiate light onto a hot-rolled steel plate, and the reflected light is captured by a camera to measure the shape of the target. However, considering the effects of high temperatures due to radiant heat, and the adhesion of steam, dust, oil, etc. to the steel plate, advanced technology is required to perform stable measurements over a long period of time with a light source and sensor placed close to the steel plate during transportation, and maintenance costs are also high.

[0008] The present invention has been made in consideration of the above, and aims to provide a method for measuring the shape of a plate-like object, a method for manufacturing a plate-like object, a quality control method for a plate-like object, an apparatus for measuring the shape of a plate-like object, and a manufacturing facility for a plate-like object, which are capable of accurately measuring the shape of a plate-like object with a low-cost and simple configuration. [Means for solving the problem]

[0009] (1) A method for measuring the shape of a plate-like object according to the present invention includes: a brightness acquisition step of capturing an image of thermal radiation light of the plate-like object being transported and acquiring brightness values ​​of the thermal radiation light at a plurality of measurement points on the surface of the plate-like object from the image of the thermal radiation light; an angle acquisition step of acquiring an image of a side surface of the plate-like object during transportation in synchronization with the acquisition of the image of the thermal radiation light, and acquiring an inclination angle of the surface of the plate-like object at a measurement point on the side surface of the plate-like object from the image of the side surface; a correction step of calculating a correction coefficient for converting the luminance value into the tilt angle using the luminance value acquired in the luminance acquisition step and the tilt angle acquired in the angle acquisition step, and converting the luminance values ​​at other measurement points acquired in the luminance acquisition step into the tilt angle; Includes:

[0010] (2) The method for measuring the shape of a plate-like object according to the present invention is the method for measuring the shape of a plate-like object described in (1) above, wherein in the brightness acquisition step, the angle formed between the optical axis of the imaging unit that captures the image of the thermal radiation light and the surface of the plate-like object is 20° or less.

[0011] (3) The method for manufacturing a plate-like object according to the present invention measures the shape of the plate-like object using the method for measuring the shape of a plate-like object described in (1) or (2) above, and manufactures the plate-like object based on the measurement results.

[0012] (4) The quality control method for plate-like objects according to the present invention measures the shape of the plate-like object using the shape measurement method for plate-like objects described in (1) or (2) above, and controls the quality of the plate-like object based on the measurement results.

[0013] (5) The shape measuring device for a plate-like object according to the present invention is a first image capturing unit configured to capture an image of thermal radiation light of the plate-like object being transported; a brightness acquisition unit that acquires brightness values ​​of the thermal radiation light at a plurality of measurement points on the surface of the plate-like object from the image captured by the first imaging unit; a second imaging unit that captures an image of a side surface of the plate-like object being transported in synchronization with the capture of the image of the thermal radiation light; an angle acquisition unit that acquires an inclination angle of the surface of the plate-like object at a measurement point on a side surface of the plate-like object among the plurality of measurement points from the image captured by the second imaging unit; a correction unit that calculates a correction coefficient for converting the luminance value acquired by the luminance acquisition unit into the tilt angle using the luminance value acquired by the luminance acquisition unit and the tilt angle acquired by the angle acquisition unit, and converts the luminance values ​​at other measurement points acquired by the luminance acquisition unit into the tilt angle; Equipped with.

[0014] (6) A manufacturing facility for a plate-like object according to the present invention includes the shape measuring device for a plate-like object described in (5) above. [Effects of the Invention]

[0015] The shape measurement method, manufacturing method, quality control method, and manufacturing equipment for plate-like objects according to the present invention can quantify the actual amount of shape distortion from the luminance value of thermal radiation light emitted from the plate-like object, thereby enabling accurate measurement of the shape of the plate-like object with a low-cost and simple configuration. [Brief explanation of the drawings]

[0016] [Figure 1] Figure 1 shows an image of a steel plate emitting thermal radiation at high temperatures, taken with an industrial camera with imaging sensitivity up to near-infrared light. [Figure 2] FIG. 2 is a diagram showing a schematic configuration of an apparatus for measuring the shape of a plate-like object according to an embodiment of the present invention, and is a diagram showing a steel plate being hot rolled as viewed from the upstream side of a transfer line. [Figure 3] FIG. 3 is a schematic diagram showing an example of the field of view of the first imaging unit and an example of measurement points for the brightness of thermal radiation light emitted from the surface of a steel plate. [Figure 4] FIG. 4 is a diagram showing a schematic configuration of an apparatus for measuring the shape of a plate-like object according to an embodiment of the present invention, and is a diagram showing the second imaging unit that images the side surface (edge ​​portion) of the steel plate as seen from behind. [Figure 5] FIG. 5 is a flowchart showing a specific process flow of the method for measuring the shape of a plate-like object according to the embodiment of the present invention. [Figure 6] FIG. 6 is a graph showing an example in which the brightness value of point A in FIG. 3 is acquired for each of a plurality of images captured by the first imaging unit and plotted against the distance in the longitudinal direction of the steel plate. [Figure 7] FIG. 7 is a diagram showing an example of an image of the side surface of a steel plate captured by the second imaging unit. [Figure 8] FIG. 8 is a diagram showing an example of an image (binarized image) obtained by performing binarization processing on the image of FIG. [Figure 9] FIG. 9 is a diagram showing an example of coordinates of the contour of the surface (upper surface) of the steel plate, obtained by performing labeling processing on the image of FIG. [Figure 10]FIG. 10 is a schematic diagram for explaining how to determine the inclination angle θ of the steel sheet surface. [Figure 11] FIG. 11 is a graph showing an example in which the inclination angle θ of the steel plate surface at the same point as point A in FIG. 3 is obtained for each of multiple images captured by the second imaging unit and plotted against the distance in the longitudinal direction of the steel plate. [Figure 12] FIG. 12 shows FIGS. 6 and 11 on the same graph. [Figure 13] FIG. 13 is a graph showing the correlation between the brightness value obtained in FIG. 12 and the inclination angle θ of the steel sheet surface. [Figure 14] FIG. 14 is a schematic diagram for explaining a method for calculating the actual shape of a steel plate from the relationship between the inclination angle θ of the steel plate surface and the distance in the longitudinal direction of the steel plate. [Figure 15] FIG. 15 is a graph showing an example of the relationship between the luminance value of the steel sheet surface and the light-receiving angle φ. [Figure 16] FIG. 16 shows an example of an image of a steel plate captured in the brightness value extraction step and a set region, where (a) is a diagram showing the reference image, and (b) is a diagram showing an image five frames after the reference image. [Figure 17] FIG. 17 is a graph showing the transition of the moving distance of the steel plate, where the vertical axis represents the moving distance [pix] of the steel plate every five frames, and the horizontal axis represents the number of images in chronological order. [Figure 18] FIG. 18 is a graph showing the results of using a median filter on FIG. [Figure 19] FIG. 19 is a graph showing the transition of the moving distance of the steel plate, where the vertical axis represents the moving distance [mm] of the steel plate per frame and the horizontal axis represents the number of images in chronological order. [Figure 20] FIG. 20 is a graph showing the trend of brightness when the vertical axis represents brightness values ​​and the horizontal axis represents the number of images in chronological order. [Figure 21] FIG. 21 is a graph in which the number of images in chronological order on the horizontal axis of FIG. 20 is converted into the longitudinal distance of the steel plate S using the movement distance of the steel plate S for each frame obtained in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0017] A method for measuring the shape of a plate-like object, a manufacturing method for a plate-like object, a quality control method for a plate-like object, a shape measuring device for a plate-like object, and a manufacturing facility for a plate-like object according to embodiments of the present invention will be described with reference to the drawings. Note that the components in the following embodiments include those that are easily replaceable by a person skilled in the art, or those that are substantially identical.

[0018] Existing technology for measuring the shape distortion of high-temperature plate-like objects (e.g., steel plates) involves irradiating the object with light from a light source and capturing the reflected light with an imaging device. However, considering the effects of high temperatures due to radiant heat, and the fact that steam, dust, oil, etc. may adhere to the steel plate, advanced technology is required to perform stable, long-term measurements with a light source or sensor placed close to the steel plate during transportation, which also results in high maintenance costs.

[0019] Therefore, the inventors focused on thermal radiation light emitted from a high-temperature steel sheet. The steel sheet to be measured is undergoing hot rolling, and is therefore heated to a high temperature (for example, 600°C or higher). Therefore, electromagnetic waves including visible light (called "thermal radiation light" in this embodiment) are emitted due to high-temperature light emission, and the luminance of the steel sheet surface can be captured with an imaging device without a light source.

[0020] For example, an imaging device equipped with an inexpensive Si imaging element has an infrared imaging sensitivity of 0.8 to 1.0 μm. Furthermore, thermal radiation light can be effectively obtained at this sensitivity in a temperature range of approximately 600°C or higher, regardless of the material. In this embodiment, when measuring the shape of a steel material such as a steel plate, the temperature of the steel plate is preferably 600°C or higher.

[0021] Here, when the steel sheet S was imaged using an industrial camera with imaging sensitivity up to near-infrared light, the image shown in Figure 1 was obtained. As shown in Figure 1, it can be seen that the shape distortion of the steel sheet S was observed as a striped brightness pattern. The inventors believed that this change in surface brightness was dependent on the angle of the high-temperature steel sheet surface relative to the camera, and developed a method for quantifying the shape distortion of the steel sheet S using this phenomenon. Details are described below.

[0022] (shape measuring device) The configuration of the shape measuring device for a plate-like object according to the embodiment will be described with reference to Fig. 2 to Fig. 4. Fig. 2 and Fig. 3 are views of a steel sheet S undergoing hot rolling as viewed from the upstream side of a conveying line. Fig. 4 is a view of a second imaging unit that images the side surface (edge ​​portion) of the steel sheet S as viewed from behind.

[0023] The shape measuring device according to the embodiment is a device for measuring the shape (shape distortion) of a plate-like object. The following describes a case where the shape measuring device is applied to hot finish rolling. The following also describes a case where the plate-like object to be measured is a steel sheet S. The plate-like object includes not only plate-like objects such as the steel sheet S, but also strip-like objects. The shape measuring device according to the embodiment includes a first imaging unit 1, a second imaging unit 2, and a calculation unit 3, as shown in FIGS. 2 and 3 .

[0024] The first imaging unit 1 captures an image of thermal radiation light of the steel sheet S being transported in the hot rolling process. That is, the first imaging unit 1 captures an image of the brightness of the surface of the steel sheet S (hereinafter referred to as "steel sheet surface") during hot rolling. Furthermore, in order to obtain a sufficient amount of thermal radiation light, it is preferable to select an industrial camera or the like that can capture near-infrared light (wavelength 0.8 μm or more) as the first imaging unit 1. In this embodiment, the "steel sheet surface" refers to the top surface of the steel sheet S.

[0025] As will be described later, the first imaging unit 1 is preferably installed so that the angle formed between the optical axis of the first imaging unit 1 and the surface of the steel plate S is 20° or less. Details of the installation position of the first imaging unit 1 will be described later.

[0026] The field of view (imaging field of view) of the first imaging unit 1 is preferably set to a field of view that includes the entire width of the steel sheet S, as shown in Fig. 2, for example. This makes it possible to obtain the distribution of shape distortion across the entire width of the steel sheet S using a single first imaging unit 1. Furthermore, the field of view of the first imaging unit 1 is set to a field of view that always includes a measurement point (point A) on the side surface (edge ​​portion) of the steel sheet S, and also includes one or more measurement points other than point A (points B and C), as shown in Fig. 3, for example.

[0027] The second imaging unit 2 captures an image of the side surface (edge ​​portion) of the steel sheet S during transportation in synchronization with the capturing of an image of thermal radiation light of the steel sheet S by the first imaging unit 1. That is, the second imaging unit 2 captures an image of the brightness of the side surface of the steel sheet S during hot rolling. Like the first imaging unit 1, the second imaging unit 2 is configured by an industrial camera or the like capable of capturing near-infrared light (wavelength 0.8 μm or more).

[0028] As shown in Figure 4, the second imaging unit 2 is installed at an angle that is both vertical and horizontal to the side of the steel plate S. In other words, the second imaging unit 2 is placed almost directly to the side of the steel plate S during transportation. Furthermore, the imaging by the second imaging unit 2 is performed in synchronization with the imaging by the first imaging unit 1. The imaging synchronization only requires that the imaging be performed at substantially the same time. "Substantially the same time" means that slight deviations that occur due to differences in the operating characteristics of the first imaging unit 1 and the second imaging unit 2 are allowed.

[0029] The field of view of the second imaging unit 2 is set to include a measurement point (point A) on the side surface of the steel sheet S, as shown in Fig. 4, for example. That is, the field of view of the second imaging unit 2 is set to always include the measurement point (point A) on the side surface of the steel sheet S included in the field of view of the first imaging unit 1. In this way, by including the same measurement point in the field of view of the second imaging unit 2 and the field of view of the first imaging unit 1, it becomes possible to associate the respective images captured at the same time.

[0030] The calculation unit 3 is realized by, for example, a general-purpose computer such as a workstation or a personal computer, or a server located on the cloud. The calculation unit 3 may be installed near the first imaging unit 1 and the second imaging unit 2, or may be installed at a base such as a driver's cab. Furthermore, by being connected to the first imaging unit 1 and the second imaging unit 2, the calculation unit 3 functions as a controller and can issue an image capture trigger to the first imaging unit 1 and the second imaging unit 2.

[0031] Specifically, the calculation unit 3 functions as a luminance acquisition unit, an angle acquisition unit, and a correction unit. The luminance acquisition unit acquires luminance values ​​of thermal radiation light at multiple measurement points (e.g., points A, B, and C in FIG. 3) on the surface of the steel sheet S from the image captured by the first imaging unit 1. The angle acquisition unit acquires, from the image captured by the second imaging unit 2, the tilt angle θ of the surface of the steel sheet S at a measurement point (e.g., point A) on the side of the steel sheet S among the multiple measurement points (e.g., points A, B, and C).

[0032] The correction unit uses the luminance value acquired by the luminance acquisition unit and the tilt angle θ acquired by the angle acquisition unit to calculate a correction coefficient (e.g., a calibration curve) that converts the luminance value into the tilt angle θ. Then, the correction unit converts the luminance values ​​at other measurement points (e.g., points B and C) acquired by the luminance acquisition unit into the tilt angle θ.

[0033] (Plate-shaped object manufacturing equipment) The shape measurement device for plate-like objects according to the embodiment can also be applied to a manufacturing facility for plate-like objects. In this case, the manufacturing facility for plate-like objects is configured to include a shape measurement device for plate-like objects. In the manufacturing facility for plate-like objects according to the embodiment, the shape measurement device can quantify the actual amount of shape distortion from the luminance value of the thermal radiation light of the plate-like object, thereby enabling the manufacturing of plate-like objects with a low-cost and simple configuration.

[0034] (Shape measurement method) The flow of the method for measuring the shape of a plate-like object according to the embodiment will be described with reference to FIGS. 5 to 14. The method for measuring the shape of a plate-like object according to the embodiment includes a brightness value acquisition step (steps S1 to S3), an angle acquisition step (steps S4 to S7), a correction step (steps S8 and S9), and a quantification step (step S10). The brightness value acquisition step and the angle acquisition step may be performed in parallel. Alternatively, the angle acquisition step may be performed first, followed by the brightness value acquisition step.

[0035] <Brightness value acquisition step> In this step, the surface of the steel sheet S being transported is first imaged at a predetermined frame rate by the first imaging unit 1, thereby capturing images corresponding to changes in the longitudinal distance of the steel sheet S (step S1). The acquired images are stored and accumulated in a predetermined memory area (not shown). The frame rate (time interval between images) when capturing images by the first imaging unit 1 is preferably determined taking into consideration, for example, the pitch of the expected shape distortion of the steel sheet S and the transport speed of the steel sheet S. Furthermore, the frame rate is preferably set so as to include at least the darkest and brightest parts for one shape distortion.

[0036] The section of the steel plate surface imaged in step S1 may be the entire length of the steel plate S, or may be limited to a specific section on the steel plate surface. The images captured in step S1 are stored in a memory area of ​​the calculation unit 3, for example.

[0037] Next, the calculation unit 3 sets a plurality of measurement points in the image acquired in step S1, including a measurement point (point A) on the side surface of the steel plate S (step S2). In step S2, a plurality of measurement points are set, such as points A, B, and C shown in FIG. 3. In step S2, a measurement point is always set at the same location as the measurement point (point A) corresponding to the side surface of the steel plate S imaged by the second imaging unit 2 in step S4, which will be described later. This is because the brightness value acquired at point A will be used to perform correction processing on points B and C in the correction steps (steps S8 and S9), which will be described later.

[0038] Point A, which is always set as a measurement point in step S2, may be a fixed coordinate, for example, as long as the side surface of the steel sheet S always passes through the same point in the width direction of the steel sheet S. Furthermore, if the side surface of the steel sheet S varies in the width direction, the coordinates of the side surface of the steel sheet S may be detected and point A may be determined based on those coordinates. Furthermore, it is preferable to set multiple other measurement points in the width direction, such as points B and C shown in Figure 3, by adjusting the distance between point A and the steel sheet S in the longitudinal direction. In other words, it is preferable to set the multiple measurement points set in step S2 so that they are aligned in the width direction of the steel sheet S. Note that the number of measurement points is not limited to three, points A, B, and C, and four or more points may be set.

[0039] Next, the calculation unit 3 acquires a brightness value for each measurement point for each image captured by the first imaging unit 1, and creates a graph showing the change in brightness value (brightness distribution) with respect to the distance of the steel sheet S based on the frame rate of the first imaging unit 1 and the conveying speed of the steel sheet S (step S3). The graph created in step S3 for point A on the steel sheet S (see FIG. 3) is shown in FIG. 6.

[0040] In Fig. 6, the vertical axis represents the brightness value, and the horizontal axis represents the distance in the longitudinal direction of the steel sheet S. The graph in Fig. 6 was created from images of the steel sheet S being transported at a speed of approximately 3.6 m / sec, captured at a frame rate of 20 Hz. Therefore, brightness values ​​were acquired at 180 mm intervals in the transport direction of the steel sheet S.

[0041] Furthermore, Figure 6 confirms that the brightness value changes like a wave in response to changes in the longitudinal distance of the steel plate S. This brightness change is thought to indicate the distortion shape of the steel plate S, but since it is extremely difficult to quantify the shape distortion using only this value, it is compared with the true value. Therefore, as will be described later, we investigated a method for determining a correction coefficient for converting the brightness value into the inclination angle θ of the steel plate surface by obtaining the true value of the inclination angle θ of the steel plate surface at point A based on the image captured by the second imaging unit 2.

[0042] <Angle acquisition step> In this step, first, the side surface of the steel sheet S being transported is imaged at a predetermined frame rate by the second imaging unit 2, thereby capturing images corresponding to changes in the longitudinal distance of the steel sheet S (step S4). The captured images are stored and accumulated in a predetermined storage area (not shown). The frame rate and imaging timing when capturing images by the second imaging unit 2 are synchronized with those of the first imaging unit 1. This makes it possible to capture images corresponding to the same longitudinal distance of the steel sheet S.

[0043] The section of the side surface of the steel sheet S imaged in step S4 may be the entire length of the steel sheet S, or may be limited to a specific section of the side surface of the steel sheet S. The images captured in step S4 are stored, for example, in a memory area of ​​the calculation unit 3. An example of an image acquired in step S4 is shown in FIG. 7. In FIG. 7, the side surface of the steel sheet S can be seen, but because the steel sheet S is distorted downward, the brightness of the thermal radiation light emitted from the surface of the steel sheet is also captured. Note that in FIG. 7, the conveying rolls are visible below the steel sheet S.

[0044] Next, the calculation unit 3 binarizes the image acquired in step S4 (step S5). In step S5, focusing on the fact that the surface of the steel sheet is imaged brighter than the side surface, a threshold value is determined from the brightness value of the side surface of the steel sheet S, and binarization is performed. Figure 8 shows an image (binarized image) obtained by binarizing the image of Figure 7 in step S5. In the binarized image shown in Figure 8, it can be seen that the portion corresponding to the steel sheet surface has been removed and the upper contour of the side surface of the steel sheet S has been clearly extracted, compared to the image of Figure 7 before binarization processing. This binarization processing in step S5 is performed on all images captured in step S4.

[0045] Next, the calculation unit 3 performs a labeling process on the binarized image created in step S5 to extract the contour shape of the steel plate surface (step S6). The contour shape of the steel plate surface (top surface of the steel plate S) extracted in step S6 from the binarized image of Fig. 8 is shown in Fig. 9. In Fig. 9, the vertical axis represents height, and the horizontal axis represents the distance in the longitudinal direction of the steel plate S. This contour shape extraction process in step S6 is performed on all images captured in step S4.

[0046] Next, the calculation unit 3 calculates the angle θ (hereinafter referred to as the "inclination angle") between the tangent at point A and the horizontal plane in the contour shape of the steel plate surface, and creates a graph showing the change in the inclination angle θ against the distance of the steel plate S (step S7).

[0047] The inclination angle θ of the steel plate surface is the angle between the horizontal plane and a tangent corresponding to the inclination of the steel plate surface at the same point as point A imaged by the first imaging unit 1, as shown in Fig. 10. Also, as shown in Fig. 10, the inclination angle θ of the steel plate surface is always the angle on the tail end side of the steel plate S, with point A as the reference, when viewed perpendicularly to the conveyance direction of the steel plate S. In this case, the inclination angle θ of the steel plate surface takes a positive value when it is inclined above the horizontal plane, and takes a negative value when it is inclined below the horizontal plane.

[0048] The calculation unit 3 creates a graph in which the vertical axis represents the inclination angle θ of the steel sheet surface at point A and the horizontal axis represents the longitudinal distance of the steel sheet S, based on the order in which the images are captured, the frame rate of the second imaging unit 2, and the conveying speed of the steel sheet S. An example of the graph created in step S7 is shown in Fig. 11.

[0049] Since the second imaging unit 2 has the same imaging timing as the first imaging unit 1, the horizontal axis in Fig. 11 is the same as the horizontal axis in Fig. 6. In Fig. 11, the positive and negative expressions for the tilt angle θ of the steel plate S are expressed as positive on the side where the steel plate S is raised toward the first imaging unit 1 and negative on the side where the steel plate S is laid backward.

[0050] 6 and 11 are plotted on a two-axis graph in Fig. 12. As shown in Fig. 12, it can be seen that the brightness value obtained by the first imaging unit 1 and the inclination angle θ of the steel plate surface obtained by the second imaging unit 2 show the same trend over time. Therefore, when the relationship between the brightness value and the inclination angle θ was plotted as a correlation diagram, Fig. 13 was obtained.

[0051] The correlation coefficient between the brightness value obtained at point A in Figure 13 and the inclination angle θ of the steel plate surface is 0.9, indicating a strong positive correlation. Therefore, in the subsequent correction step, the brightness value of the measurement point obtained by the first imaging unit 1 is corrected as the inclination angle θ of the steel plate surface.

[0052] <Correction step> In the correction step, first, the calculation unit 3 creates a calibration curve for converting the brightness value to the tilt angle θ from the relationship between the brightness value at point A obtained in Figure 13 and the tilt angle θ, using, for example, the least squares method (step S8).

[0053] In step S8, when creating the calibration curve, the reliability of the calibration curve can be taken into consideration by, for example, calculating a correlation coefficient and setting a threshold value. If the value falls below the specified threshold value, the data may be regarded as unreliable, or by outputting the data externally, it is possible to detect that there is a defect in the acquisition of the brightness value at point A, the tilt angle θ of the steel sheet surface, or both.

[0054] Next, the calculation unit 3 converts the brightness values ​​into tilt angle θ by applying the calibration curve as a correction coefficient to measurement points other than point A (for example, points B and C) (step S9). This corrects the graph for measurement points other than point A created in step S3 and makes it possible to convert it into a graph of the tilt angle θ of the steel sheet surface versus the longitudinal distance of the steel sheet S, as shown in Fig. 11. As a result, it becomes possible to quantify the shape distortion of the steel sheet S based on the relationship between the longitudinal distance of the steel sheet S and the tilt angle θ of the steel sheet surface.

[0055] <Quantification step> In this step, the calculation unit 3 calculates and quantifies the wave (distortion) height and steepness of the shape of the steel sheet S based on the relationship of the inclination angle θ to the distance of the steel sheet S (step S10). In step S10, for example, a new graph is created using the inclination angle θ of the steel sheet surface on the vertical axis, which is further converted to tan θ, as the new vertical axis, as shown in FIG. 11. An example of the created new graph is shown in FIG. 14(b). Then, for the graph of FIG. 14(b), the tan θ on the vertical axis is integrated with the distance in the longitudinal direction of the steel sheet S on the horizontal axis, and the result is used as the new vertical axis. As a result, the graph of FIG. 14(a) can be calculated. In other words, the wave height of the actual shape of the steel sheet S can be calculated as shown in FIG. 14(a).

[0056] In step S10, it is also possible to obtain an index called "steepness" by dividing the wave height by the wave pitch. By carrying out the above-mentioned processing, it is possible to quantify the overall shape distortion of the steel sheet surface at any point, and by utilizing this information in setting up the rolling mill and straightening machine, it is possible to manufacture an appropriate final product.

[0057] (Variation 1) In the brightness acquisition step, it is preferable that the angle between the optical axis of the first imaging unit 1 that captures the image of thermal radiation light and the surface of the steel plate is 20° or less. In other words, it is preferable that the first imaging unit 1 is installed at as low an angle as possible so that the angle between the optical axis of the first imaging unit 1 and the surface of the steel plate is 20° or less.

[0058] The inventors conducted an experiment on the angle dependency of thermal radiation light from steel sheet S in relation to the installation position of the first imaging unit 1. In this experiment, a sample of steel sheet S was heated by a heater to stabilize the temperature, and the surface of the steel sheet was imaged by the first imaging unit 1 to measure the luminance. The angle φ formed between the optical axis of the first imaging unit 1 and the surface of the steel sheet (hereinafter referred to as the "light-receiving angle") was changed in the range of 0 to 90° to acquire luminance values, and the relationship between the light-receiving angle φ and the luminance value is shown in FIG. 15 .

[0059] In Fig. 15, the vertical axis represents the luminance value normalized with the maximum value set to 100, and the horizontal axis represents the light-receiving angle φ. Fig. 15 shows that the luminance value hardly changes when the light-receiving angle φ is in the range of 20 to 90°, but drops sharply when the light-receiving angle φ is 20° or less. This shows that when the light-receiving angle φ is in the range of 0 to 20°, a small change in angle causes a large change in the luminance value.

[0060] In other words, by positioning the first imaging unit 1 so that the light-receiving angle φ is 0 to 20°, if the tilt angle θ of the steel plate surface changes, for example, and the apparent light-receiving angle φ changes, even a slight change in the angle of the steel plate surface will result in a large change in the brightness value.For the above reasons, it is preferable to install the first imaging unit 1 at as low an angle as possible so that the light-receiving angle φ is 20° or less.

[0061] (Variation 2) In the explanation in paragraph 0040, the longitudinal distance (movement distance) of a plate-like object (e.g., steel plate S) is calculated using a known conveying speed and frame rate (image capture frame rate). Below, we will explain a method for calculating the longitudinal distance of a plate-like object from images when the conveying speed of the plate-like object is unknown, and a method for calculating the longitudinal distance of a plate-like object from the chronological order of images when the movement distance per frame rate changes.

[0062] For example, if the moving distance of a plate-like object per frame is constant, the longitudinal distance of the plate-like object at any point can be calculated by multiplying the distance the plate-like object moved between each captured image (movement distance per image) by the number of images at that point.

[0063] If the conveying speed of the plate-like object while acquiring images is constant and known, the moving distance of the plate-like object between frames can be calculated from the conveying speed of the plate-like object and the frame rate, for example, as shown in the following equation (1).

[0064] Distance traveled by the plate-shaped object between frames [mm] = Transport speed [mm / sec] ÷ Frame rate [1 / sec] (1)

[0065] On the other hand, it is also possible that the conveying speed of the plate-like object fluctuates while the images are being acquired. In this case, the command value for the rotation speed of the conveying roll of the conveying device that conveys the plate-like object, or the actual measured value of the rotation speed of the conveying roll, is acquired. The actual measured value of the rotation speed can be acquired, for example, from a rotation measurement unit installed on the conveying roll. Then, as shown in the following equation (2), for example, the conveying speed of the plate-like object can be calculated from the acquired rotation speed. Furthermore, the movement distance of the plate-like object between frames can be calculated using the following equation (3) obtained by substituting the following equation (2) into the above equation (1).

[0066] Conveying speed [mm / sec] = total circumference of conveying roll [mm] x rotation speed [1 / sec] ···(2)

[0067] Distance traveled by the plate-like object between frames [mm] = total circumference of the transport roll [mm] × rotation speed [1 / sec] ÷ frame rate [1 / sec] (3)

[0068] However, if a rotation measurement unit or the like is not installed on the transport roll, the rotation speed of the transport roll cannot be measured, making it difficult to calculate the travel distance of the plate-like object. Therefore, the following describes a method for determining the travel distance of the plate-like object between frames using images of the plate-like object's surface captured in the brightness value extraction step when the transport speed of the plate-like object changes or when the rotation speed of the transport roll cannot be measured. Furthermore, the following describes a steel plate S that emits thermal radiation at a high temperature as an example of a plate-like object.

[0069] (1) First, the image of the steel plate surface captured in the brightness value extraction step is projectively transformed to convert it into an image viewed from directly above, perpendicular to the conveyance direction of the steel plate S. This makes it possible to capture the movement of the steel plate S on a two-dimensional plane.

[0070] (2) Next, a predetermined area (e.g., a rectangular area) is set on the steel plate surface in the projectively transformed image, and the difference is calculated using the brightness values ​​of the pixels in that area (hereinafter referred to as the "set area"). Specifically, using the brightness value data for each pixel of the set area set in the reference image (hereinafter referred to as the "reference image"), a search is performed while taking the difference from an image captured after the reference image, and the coordinates of the area whose brightness value is most similar to that of the set area are found. Here, the frame rate was set to 50 Hz, and the search target image was assumed to be 5 frames later (100 msec later). Note that because searching in an image one frame after the reference image resulted in high noise and instability, the search target was set to the image 5 frames after the reference image.

[0071] FIG. 16 shows an example of an image of the steel sheet S captured in the brightness value extraction step and a set area set in the image. In FIG. 16, (a) shows the reference image, and (b) shows an image five frames after the reference image. As shown in FIG. 16, a search is performed in image (b) to find an area whose brightness value is most similar to that of the set area set in the reference image (a). Then, by comparing the coordinates of the area identified by the search with those of the set area, the movement distance of the steel sheet S over the five frames is obtained as a pixel value [pix].

[0072] (3) Next, the captured images of the steel sheet surface are arranged in chronological order, and starting from the first image, differences are calculated between the previous and next images at a predetermined image interval, and the travel distance [pix] of the steel sheet S in the transport direction is calculated and plotted as shown in Figure 17. In Figure 17, the predetermined image interval is set to every five frames in accordance with the above assumption. Note that when there is a lot of noise, it is preferable to use a moving average filter or median filter. Figure 18 shows the results of using a median filter on the data in Figure 17.

[0073] (4) Next, the movement distance [pix] of the steel sheet S for every five frames (see Figure 18) is converted into the movement distance [mm] of the steel sheet S for every frame (see Figure 19) using the obtained data and the weight of the distance of one pixel in the conveyance direction of the steel sheet S relative to the projectively transformed image of the steel sheet surface. In this example, assuming that the above weight is 5 mm / pix, the vertical axis [pix] of Figure 18 is divided by 5 frames to make 5 frames into 1 frame, and then multiplied by the weight of 5 mm / pix. This results in Figure 19, in which the vertical axis is converted into the movement distance [mm] for every frame of the image.

[0074] 19, it can be seen that the movement distance per frame decreases until approximately the 80th sheet, then increases until approximately the 350th sheet, and becomes approximately constant from the 400th sheet onwards. If this is substituted for the transport speed of the steel sheet S, it is shown that the speed first decelerates, then accelerates, and then becomes constant.

[0075] (5) Here, the brightness trend obtained from the same images as those used in (1) above is shown in Figure 20, with the vertical axis representing brightness and the horizontal axis representing the number of images in chronological order. In the brightness trend shown in Figure 20, the pitch of the wave-like changes is wide in range α (approximately from the 50th image to the 330th image), and the pitch becomes narrower in the subsequent range β (from the 350th image onwards).

[0076] 19, it can be seen that the movement distance of the steel plate S per frame in range α is shorter than that in range β. In other words, it is thought that the pitch of the brightness change is wider because the transport speed of the steel plate S is slower.

[0077] (6) Next, using the movement distance of the steel plate S for each frame obtained in Figure 19, the number of images in chronological order on the horizontal axis of Figure 20 is converted into the longitudinal distance of the steel plate S and plotted. As a result, Figure 21 can be obtained, in which the longitudinal distance of the steel plate S is shown on the horizontal axis and the brightness value obtained in each frame is shown on the vertical axis. In Figure 21, the pitch of the waves corresponding to the range α in Figure 20 has been improved, and the actual movement distance of the steel plate S has been reflected.

[0078] A specific method for converting the number of images in chronological order on the horizontal axis of FIG. 20 into the longitudinal distance of the steel plate S in FIG. 21 is, for example, as follows. First, the movement distance for each frame calculated in FIG. 19 is accumulated starting from the first image. The longitudinal distance of the steel plate S in that frame is the movement distance for each frame accumulated from the first image to that frame. This makes it possible to obtain FIG. 21, in which the brightness value of that frame is represented on the vertical axis and the longitudinal distance of the steel plate S is represented on the horizontal axis. The obtained FIG. 21 corresponds to a plot of the brightness values ​​in FIG. 12 (the dashed line in the figure).

[0079] By using the method described above, it is possible to determine the longitudinal distance of the steel sheet S even when the conveying speed of the plate-like object changes or when the rotation speed of the conveying rolls cannot be measured. With this method, the data acquired in the brightness value acquisition step can be used as is, so there is no need to place a rotation measurement unit on the conveying rolls of the conveying device, and there is no need to acquire data related to the conveying speed from the conveying device. This makes it possible to complete the processing within the system.

[0080] (Method of manufacturing a plate-shaped object) The method for measuring the shape of a plate-like object according to the embodiment can also be applied to a method for manufacturing a plate-like object. In this case, the method for manufacturing a plate-like object includes measuring the shape of the plate-like object using the method for measuring the shape of the plate-like object and manufacturing the plate-like object based on the measurement results. In the method for manufacturing a plate-like object according to the embodiment, the shape measurement method can quantify the actual amount of shape distortion from the luminance value of the thermal radiation light of the plate-like object, so that the plate-like object can be manufactured at low cost and with a simple configuration.

[0081] (Quality control method for plate-shaped objects) The shape measurement method for a plate-like object according to the embodiment can also be applied to a quality control method for a plate-like object. In this case, the quality control method for a plate-like object includes measuring the shape of the plate-like object using the shape measurement method for a plate-like object and controlling the quality of the plate-like object based on the measurement results. In the quality control method for a plate-like object according to the embodiment, the shape measurement method can quantify the actual amount of shape distortion from the luminance value of the thermal radiation light of the plate-like object, thereby enabling quality control of the plate-like object with a low-cost and simple configuration.

[0082] According to the above-described embodiments of the method for measuring the shape of a plate-like object, the method for manufacturing a plate-like object, the method for quality control of a plate-like object, the shape measuring device for a plate-like object, and the manufacturing equipment for a plate-like object, the actual amount of shape distortion can be reflected and quantified from the luminance value of the thermal radiation light emitted from the plate-like object. As a result, the shape of the plate-like object can be accurately measured with a low-cost and simple configuration.

[0083] The method for measuring the shape of a plate-like object, the method for manufacturing a plate-like object, the method for quality control of a plate-like object, the shape measuring device for a plate-like object, and the manufacturing equipment for a plate-like object according to the present invention have been specifically described above using the preferred embodiments of the invention, but the scope of the present invention is not limited to these descriptions and should be broadly interpreted based on the claims. Furthermore, it goes without saying that various changes and modifications based on these descriptions are also included in the scope of the present invention. [Explanation of symbols]

[0084] 1 First imaging unit 2 Second imaging unit 3 Arithmetic section S steel plate

Claims

1. a brightness acquisition step of capturing an image of thermal radiation light of the plate-like object being transported and acquiring brightness values ​​of the thermal radiation light at a plurality of measurement points on the surface of the plate-like object from the image of the thermal radiation light; an angle acquisition step of acquiring an image of a side surface of the plate-like object during transportation in synchronization with the acquisition of the image of the thermal radiation light, and acquiring an inclination angle of the surface of the plate-like object at a measurement point on the side surface of the plate-like object from the image of the side surface; a correction step of calculating a correction coefficient for converting the luminance value into the tilt angle using the luminance value acquired in the luminance acquisition step and the tilt angle acquired in the angle acquisition step, and converting the luminance values ​​at other measurement points acquired in the luminance acquisition step into the tilt angle; A method for measuring the shape of a plate-like object, comprising:

2. 2. The method for measuring the shape of a plate-like object according to claim 1, wherein in the brightness acquisition step, an angle formed between an optical axis of an imaging unit that captures an image of the thermal radiation light and the surface of the plate-like object is 20 degrees or less.

3. 3. A method for manufacturing a plate-like object, comprising measuring the shape of the plate-like object by the method for measuring the shape of the plate-like object according to claim 1 or 2, and manufacturing the plate-like object based on the measurement results.

4. 3. A quality control method for a plate-like object, comprising measuring the shape of the plate-like object by the method for measuring the shape of the plate-like object according to claim 1 or 2, and controlling the quality of the plate-like object based on the measurement results.

5. a first image capturing unit configured to capture an image of thermal radiation light of the plate-like object being transported; a brightness acquisition unit that acquires brightness values ​​of the thermal radiation light at a plurality of measurement points on the surface of the plate-like object from the image captured by the first imaging unit; a second imaging unit that captures an image of a side surface of the plate-like object being transported in synchronization with the capture of the image of the thermal radiation light; an angle acquisition unit that acquires an inclination angle of the surface of the plate-like object at a measurement point on a side surface of the plate-like object among the plurality of measurement points from the image captured by the second imaging unit; a correction unit that calculates a correction coefficient for converting the luminance value acquired by the luminance acquisition unit into the tilt angle using the luminance value acquired by the luminance acquisition unit and the tilt angle acquired by the angle acquisition unit, and converts the luminance values ​​at other measurement points acquired by the luminance acquisition unit into the tilt angle; A shape measuring device for a plate-like object comprising:

6. A manufacturing facility for plate-like objects, comprising the plate-like object shape measuring device according to claim 5.

Images