Melt level detection method and melt level detection apparatus

Abstract

To provide a molten metal surface height detection method and a molten metal surface height detection device capable of continuously detecting the height of the molten metal surface without bringing a measuring device into contact with the molten metal.SOLUTION: A preparation step of providing a plurality of scale lines 42 on an inner wall surface 41 of a molten metal container 4, associating the scale lines 42 with a height position of a molten metal surface of molten metal, and fixing an imaging device 2 capable of capturing a moving image to a position where the imaging device 2 can capture an image of an inside of the molten metal container; A molten metal surface height detection method includes a scale detection step of detecting a position of a scale line, an object image acquisition step of extracting an object image from a captured image obtained as a moving image with respect to a molten metal container storing molten metal, a molten metal surface detection step of extracting a continuous line corresponding to an arrival position of a molten metal surface in the object image and setting the continuous line as a molten metal surface line, and a height determination step of determining a height position of the molten metal surface by associating the position of the molten metal surface line in the object image with the position of the scale line detected in the scale detection step.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a molten metal surface height detection method and device, and more particularly to a detection method and device capable of detecting the molten metal surface height of molten metal stored in a molten metal container. [Background technology]

[0002] A molten metal vessel, such as a tundish in a continuous casting machine, is used to store molten metal in a manner that allows access. There is a great demand for detecting the level of the molten metal in the vessel, for example, to control the amount of molten metal stored in the vessel. Patent Document 1, for example, discloses a method for detecting the level of the molten metal, in which a level detection rod with a conductor fixed inside a protective tube is immersed in the molten metal and the position of the molten metal is detected based on the presence or absence of electrical continuity with the molten metal. Patent Document 2 also discloses a molten metal level measurement method, in which an image processing camera installed in the hood of a hot metal desulfurization system detects a splash that occurs when the tip of an impeller refractory touches the molten metal surface during descent, and the molten metal level is measured based on the vertical position of the impeller at the time the splash is detected. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 6-281490 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-301362 Summary of the Invention [Problem to be solved by the invention]

[0004] When detecting the molten metal level by contacting a sensor with the molten metal, as in the case disclosed in Patent Document 1, direct contact with the high-temperature molten metal reduces the durability and maintainability of the sensor. Contact can also introduce impurities into the molten metal. The same problem can occur with the impeller refractory material that comes into contact with the molten metal in the case disclosed in Patent Document 2. Although the camera is not intentionally brought into contact with the molten metal, it uses the generation of splashes to detect them, so splashes may adhere to the camera. Furthermore, in both methods, the molten metal level is detected only when the sensor or impeller refractory material comes into contact with the molten metal, making it difficult to continuously monitor changes in the molten metal level.

[0005] The problem to be solved by the present invention is to provide a method and device for detecting the level of a molten metal surface that can continuously detect the level of the molten metal surface without bringing the measuring device into contact with the molten metal. [Means for solving the problem]

[0006] In order to solve the above problems, a molten metal level detection method and a molten metal level detection device according to the present invention have the following configuration.

[0007] [1] The method for detecting a molten metal level in a molten metal container that stores molten metal in a manner that allows the molten metal to be taken in and out includes the steps of: providing a plurality of scale lines on an inner wall surface of the molten metal container at positions of different heights from a bottom surface of the molten metal container; corresponding each of the scale lines to a height position of the molten metal level in the molten metal container; and fixing a video camera capable of taking video from outside the molten metal container at a position where the inside of the molten metal container, including the plurality of scale lines, can be photographed; and photographing the molten metal container when the molten metal is not stored therein with the video camera. The method includes a scale detection step of detecting the position of the scale line in the captured image; an object image acquisition step of taking an image of the molten metal container storing the molten metal using the camera and extracting an object image to be analyzed from the captured image obtained as a video; a molten metal level detection step of extracting a continuous line in the object image that corresponds to the position to which the molten metal surface has reached on the inner wall surface and setting it as a molten metal level line; and a height determination step of determining the height position of the molten metal surface stored in the molten metal container by correlating the position of the molten metal level line in the object image with the position of the scale line detected in the scale detection step.

[0008] [2] In the above aspect [1], the molten metal container may be contained in a storage chamber having a transparent window, and the photographing device may be installed outside the storage chamber and photograph the inside of the molten metal container through the window.

[0009] [3] In the above aspect [1] or [2], in the target image acquisition step, a plurality of images taken at consecutive times may be extracted from the images taken as a video, and averaged to obtain the target image.

[0010] [4] In any of the above aspects [1] to [3], in the molten metal level detection step, the extracted molten metal level line is divided into a plurality of sections passing through a plurality of divided regions, and among the plurality of divided regions, a region in which the molten metal level line deviates from the molten metal level lines in other regions by more than a predetermined standard is detected as a deviation region, and when the deviation region is detected, the section passing through the deviation region is excluded from the molten metal level line.

[0011] [5] In the above aspect [4], the center of the molten metal surface line when the entire molten metal surface line is approximated to an arc is taken as the overall center, and the center of the molten metal surface line when the entire molten metal surface line is approximated to an arc in each of the plurality of divided regions is taken as the division center. When the distance between the overall center and the division center is equal to or greater than a threshold value, the divided region corresponding to the division center is detected as the deviation region.

[0012] [6] The molten metal level detection device of the present invention is provided together with the molten metal vessel having the scale lines, and comprises the photographing device fixed in a position where the interior of the molten metal vessel including the plurality of scale lines can be photographed from outside the molten metal vessel, and an analyzing device that can perform image analysis on the photographed image obtained by the photographing device, and the photographing device and the analyzing device can carry out the scale detection process, the target image acquisition process, the molten metal level detection process, and the height determination process in any of the molten metal level detection methods [1] to [5] above. [Effects of the Invention]

[0013] In the method for detecting a molten metal level according to the present invention having the configuration described in [1] above, a scale line is provided on the inner wall surface of a container for molten metal in a preparation step, and a video camera is installed in a position where the interior of the container for molten metal, including the scale line, can be photographed from the outside. In a scale detection step, an image of the container for molten metal that does not contain molten metal is taken, and the position of the scale line in the photographed image is detected. Then, in an object image acquisition step, an image is taken of the container for molten metal that contains molten metal, and in a molten metal level detection step, the position of the molten metal level on the inner wall surface of the container for molten metal is detected as the molten metal level line for the object image. A height determination step is then performed, and the position of the previously detected scale line is associated with the position of the molten metal level line in the object image. This makes it possible to detect the height of the molten metal level at the time the object image was acquired, even if the scale line is not visible in the object image.

[0014] As described above, the molten metal level detection method of the present invention detects the molten metal level based on images captured by a camera fixed outside the molten metal vessel, and does not require contact between the camera and other devices used for detection and the molten metal. Therefore, the molten metal level can be detected without affecting the durability or maintainability of the device due to contact with the molten metal. Furthermore, since the camera captures video and extracts target images from the video to detect the molten metal level, the molten metal level can be detected continuously. Therefore, the molten metal level detection method of the present invention can be suitably used for continuous monitoring of the molten metal level, even when the molten metal level changes.

[0015] In the above-mentioned aspect [2], the photographing device is installed outside the containing chamber that contains the molten metal vessel, and photographs the inside of the molten metal vessel through a transparent window installed in the containing chamber. By placing the photographing device outside the containing chamber, the photographing device is less susceptible to the environment inside the containing chamber, further improving the durability and maintainability of the device. In addition, the photographing conditions by the photographing device are stable, and the reliability of the detection of the molten metal level can be improved.

[0016] In the above aspect [3], in the object image acquisition step, a plurality of consecutive images acquired as a video are averaged to obtain the object image. Averaging can mitigate the influence of time-varying, flowing disturbances, such as smoke generated from the surface of the molten metal, on the object image. This can prevent a decrease in the accuracy of detecting the molten metal level due to the influence of disturbances.

[0017] In the above-described embodiment [4], in the molten metal level detection step, the extracted molten metal level line is divided into multiple divided regions, and a region among the multiple divided regions where the molten metal level line significantly deviates from the molten metal level lines in the other regions is detected as a deviation region. When a deviation region is detected, the section within the deviation region is excluded from the molten metal level line. In a molten metal container such as a tundish, deposits are likely to form on the inner wall surface, and in the target image, the position of the molten metal level line at the location where the deposits occur may significantly deviate from the other locations. If the molten metal level is detected by comparing the position of the scale line based on the molten metal level line that is affected by the deposits, the detection of the molten metal level may be inaccurate. Therefore, by detecting a region among the multiple divided regions where the molten metal level line significantly deviates from the molten metal level lines in the other regions and excluding it from the analysis, the influence of the deposits can be reduced and the molten metal level can be detected.

[0018] In the above-described embodiment [5], when detecting a deviation region, the distance between the overall center when the entire molten metal level line is approximated as an arc and the division center when the molten metal level line in each divided region is approximated as an arc is considered. If the distance is equal to or greater than a predetermined threshold, the divided region corresponding to the division center is deemed to be a deviation region. Even if the position of the molten metal level line is affected by deposits in some of the divided regions, the arc approximating the entire molten metal level line will even out the local effects of deposits. In many cases, in divided regions not affected by deposits, the position of the molten metal level line is not significantly different from the overall approximated arc, resulting in a small distance between the overall center and the division center. On the other hand, in regions affected by deposits, the position of the molten metal level line deviates significantly from the overall approximated arc, resulting in a large distance between the overall center and the division center. Therefore, deviation regions can be detected by identifying divided regions where the distance between the overall center and the division center is large using a threshold. In this way, using the approximation to an arc and determining the distance between the arc centers makes it possible to easily detect deviation regions.

[0019] The molten metal level detection device of the present invention having the configuration [6] above is provided with a molten metal container provided with a scale line, and has a photographing device and an analyzing device, and the molten metal level detection method can be carried out using these devices. Therefore, the molten metal level can be continuously detected without the measuring device coming into contact with the molten metal. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a diagram showing a schematic diagram of a molten metal level detection device according to an embodiment of the present invention, together with equipment provided together with the molten metal level detection device. [Figure 2] FIG. 1 is a flow chart showing a method for detecting a molten metal surface height according to an embodiment of the present invention. [Figure 3] 1 is a schematic diagram showing a scale image obtained in the scale detection step, in which (a) shows the scale image itself, and (b) shows the detection results of the scale lines displayed on the scale image. [Figure 4] Schematic diagrams showing the target images obtained in the target image acquisition step, where (a) corresponds to a case where no deposits exist on the inner wall surface of the molten metal container, and (b) corresponds to a case where deposits exist on the inner wall surface of the molten metal container. [Figure 5] The molten metal level lines detected in the molten metal level detection process are displayed on the target images in Figure 4. Figures 5(a) and (b) correspond to Figures 4(a) and (b), respectively. [Figure 6] 10A and 10B are diagrams illustrating the exclusion of deviation regions in the molten metal level detection process, in which (a) shows the state in which the overall center and division centers are set, and (b) shows the state after the deviation regions have been excluded. [Figure 7] FIG. 10 is a diagram for explaining the height determination process, showing a state in which a scale line is superimposed on an object image showing a molten metal surface line. [Figure 8] This shows the scale image actually obtained in the scale detection process. (a) is the scale image itself, and (b) shows the detected scale lines. [Figure 9] The images shown are those actually taken in the target image acquisition process. (a) is the image taken before averaging when the molten metal was stored, (b) is the target image after averaging, and (c) is the target image showing the molten metal surface line. All of these images correspond to cases where there is no adhesion on the inner wall surface of the molten metal container. [Figure 10] In the case where there is adhesion on the inner wall surface of a molten metal container, (a) shows the target image together with the molten metal surface line and the center of each arc when the divided area is set to three equal parts. (b) shows the state when the divided area is set to nine parts, excluding the area that deviates from the molten metal surface line. [Figure 11] In response to the height determination process, the stored scale lines are superimposed on the object image in which the molten metal surface line is set in FIG. 10(b). [Figure 12] 10 is a graph recording the change over time in the detected molten metal surface height. DETAILED DESCRIPTION OF THE INVENTION

[0021] A method and device for detecting a molten metal level according to an embodiment of the present invention will be described below. The method and device for detecting a molten metal level according to the present embodiment detect the level of the molten metal stored in a molten metal container.

[0022] [Outline of the melt level detection device] First, a molten metal level detecting device according to one embodiment of the present invention will be described. Fig. 1 shows a molten metal level detecting device 1 according to this embodiment, together with related equipment such as a molten metal container 4. The longitudinal direction in Fig. 1 corresponds to the vertical direction, and the lateral direction corresponds to the horizontal direction.

[0023] The molten metal level detection device 1 according to this embodiment has a photographing device 2 and an analyzing device 3. The photographing device 2 is a device capable of taking moving pictures and can be suitably configured as a video camera capable of taking pictures in the visible range. The analyzing device 3 is a device that can perform image analysis on the photographed image acquired by the photographing device 2 and can be suitably configured as a computer.

[0024] The molten metal level detection device 1 is installed along with a molten metal vessel 4, which constitutes the detection target, and other related equipment. The molten metal vessel 4 is a vessel that stores molten metal in a manner that allows it to be taken in and out. While the type and use of the molten metal vessel 4 are not particularly limited, here, it is assumed that the molten metal vessel 4 is a tundish included in a continuous casting machine or the like. The molten metal is supplied to the molten metal vessel 4 from a furnace 6 via a ladle 5. Specifically, the molten metal is poured from a tapping hole 51 at the bottom of the ladle 5 into an opening 43 at the top of the molten metal vessel 4. A tapping hole 44 is provided at the bottom of the molten metal vessel 4, and the molten metal can be supplied to the outside through the tapping hole 44. For example, the molten metal that flows out of the tapping hole 44 is supplied to the casting section of the continuous casting machine. The opening 43 of the molten metal vessel 4 is provided with a sufficient width to allow the imaging device 2 to capture images of the interior of the molten metal vessel 4. The molten metal vessel 4, along with the ladle 5 and the furnace 6, is housed in a housing chamber 7.

[0025] The containing chamber 7 is provided with a transparent window 71, i.e., a window that transmits visible light. The camera 2 is installed outside the containing chamber 7, and can photograph the interior of the molten metal container 4 in the containing chamber 7 from the opening 43 through the window 71. The window 71 is disposed at a position and angle that allows the camera 2 to photograph the interior of the molten metal container 4, including the inner wall surface 41. For example, as shown in the figure, the window 71 is provided in the containing chamber 7 diagonally above the opening 43 of the molten metal container 4, and the camera 2 is disposed with its optical axis perpendicular to the window 71.

[0026] The analysis device 3 receives the photographed image acquired by the photographing device 2 and analyzes the photographed image. Among the steps of the molten metal level detection method described below, the analysis device 3 performs the scale detection step and the target image acquisition step together with the photographing device 2. Furthermore, the analysis device 3 performs the subsequent molten metal level detection step and height determination step. The analysis device 3 may also function as a control device that controls the photographing device 2.

[0027] [Method for detecting the melt level] Next, a molten metal level detection method according to one embodiment of the present invention will be described. As shown in FIG. 2, the molten metal level detection method according to this embodiment involves the following steps in this order: (1) preparation step, (2) scale detection step, (3) object image acquisition step, (4) molten metal level detection step, and (5) height determination step. Of these steps, the preparation step and scale detection step only need to be performed once, unless changes are made to the components and related members of the molten metal level detection device 1, and do not need to be performed each time molten metal is stored in the molten metal container 4. The object image acquisition step, molten metal level detection step, and height determination step are performed while molten metal is stored in the molten metal container 4. It is preferable that each of these steps be performed continuously, that is, continuously or intermittently. Each step will be described below.

[0028] (1) Preparation process In the preparation process, a scale is applied to the molten metal container 4 and the photographing device 2 is fixed. The scale serves as a reference for the height of the surface of the molten metal stored in the molten metal container 4, and is composed of a collection of multiple scale lines 42.

[0029] The scale lines 42 are lines displayed on the inner wall surface 41 of the molten metal container 4. The scale lines 42 are preferably arranged parallel to the bottom surface of the molten metal container 4. Multiple scale lines 42 are arranged at different heights from the bottom surface, and each scale line 42 corresponds to the height of the molten metal in the molten metal container 4. In other words, the height of the molten metal surface when the molten metal surface reaches each of the multiple scale lines 42 corresponds to the height of the molten metal surface. The height of the molten metal surface may be set as the height position from the bottom surface itself, i.e., a quantity having a length dimension such as "mm," or may be set as the amount of stored molten metal, i.e., a quantity having a mass dimension such as "kg." The scale lines 42 may be arranged at equal intervals or at uneven intervals, for example, by spacing the molten metal surface at smaller intervals in areas where precise detection of the molten metal surface is required than in other areas. When the molten metal container 4 has a cylindrical inner wall surface 41, the scale lines 42 are displayed as circles. The means for applying the scale lines 42 to the inner wall surface 41 of the molten metal container 4 is not particularly limited, and examples thereof include lines drawn with paint or the like, and engraved lines formed by scratching or the like.

[0030] The photographing device 2 is fixed in a position where it can photograph the interior of the molten metal container 4, including the multiple scale lines 42, from outside the molten metal container 4. When a window 71 is provided diagonally above the opening 43 of the molten metal container 4 in the storage chamber 7 that houses the molten metal container 4, as shown in FIG. 1 , the photographing device 2 is fixed so that the interior of the molten metal container 4, including the inner wall surface 41 on which the scale lines 42 are provided, can be viewed through the window 71, and the photographing range 2a of the photographing device 2 can be set. The photographing range 2a of the photographing device 2 may be set so that all of the scale lines 42 provided on the inner wall surface 41 of the molten metal container 4 are captured, or it may be set so that only some of the scale lines 42 are captured, including the scale lines 42 corresponding to the height position at which the molten metal level is to be detected. The photographing device 2 is fixed so that the installation position or installation angle of the photographing device 2 does not change between the subsequent scale detection process and the target image acquisition process, thereby preventing the position of the molten metal container 4 in the photographed image from changing. Additionally, the photographing conditions of the photographing device 2, such as the magnification, are fixed so that the position of the molten metal container 4 in the photographed image does not change during these processes.

[0031] (2) Scale detection process In the scale detection process, the molten metal container 4, which does not contain molten metal, is photographed by the photographing device 2, and the positions of the scale lines 42 are detected from the photographed image. At this time, the photographed image acquired by the photographing device 2 is used as a scale image Is and is subjected to analysis by the analyzing device 3. The scale image Is may be acquired as a still image. As shown in FIG. 3(a), the scale image Is shows the interior of the molten metal container 4, including the upper end surface 41a of the wall and the inner wall surface 41 on which the multiple scale lines 42 are provided.

[0032] An analysis is performed on this scale image Is. In the analysis, the position of each of the multiple scale lines 42 is detected and the detected positions are stored in the analysis device 3. In this case, for example, the scale image Is is binarized and the multiple scale lines 42 are identified in the binarized image. The identified scale lines 42 are then approximated by continuous lines and the positions of the approximated lines are stored. Typically, the multiple scale lines 42 can be approximated by circular arcs. The position of each scale line 42 can be stored as coordinates within the scale image Is. In FIG. 3(b), the multiple approximated scale lines 42a detected by analysis are displayed in bold on the scale image Is.

[0033] (3) Object image acquisition process The steps up to this point have been carried out without storing any metal in the molten metal container 4, but the steps that follow are carried out with the molten metal stored in the molten metal container 4, with the molten metal being taken in and out. First, the target image acquisition step is carried out.

[0034] In the object image acquisition step, the molten metal container 4 containing the molten metal is photographed by the photographing device 2. At this time, the scale image Is and the molten metal container 4 are photographed at the same position within the photographed image without changing the position or magnification of the photographing device 2 from the point at which the scale image Is was acquired in the scale detection step. The photographed image obtained as a video is sent to the analysis device 3 in real time.

[0035] The analysis device 3 extracts a target image to be analyzed from the captured images obtained as a video. The target image It is shown schematically in FIGS. 4(a) and 4(b). These target images It show the surface (melt surface) of the molten metal M stored inside the molten metal container 4. The distribution of the molten metal M shown in the target image It differs between FIGS. 4(a) and 4(b). As shown in these figures, the inner wall surface 41 of the molten metal container 4 is also shown along with the molten metal M. However, the scale lines 42 on the inner wall surface 41 are often not visible in the captured images because they are hidden by the stored molten metal M and because of the contrast between the molten metal M, which shines brightly due to thermal radiation, and the dark inner wall surface 41 (see FIG. 9, etc.). As the target image It, a single captured image (one frame) extracted from a video may be used as is, but it is preferable to extract and average multiple captured images, that is, multiple images captured at consecutive times, and use the averaged image as the target image It for subsequent analysis. Averaging reduces the influence of temporary disturbances, such as smoke emerging from the surface of the molten metal M, on the target image It, thereby improving the accuracy of subsequent analysis.

[0036] (4) Molten metal level detection process Next, a molten metal level detection step is performed, in which a molten metal level line is extracted from the target image It acquired in the target image acquisition step. The molten metal level line is a continuous line corresponding to the position of the molten metal M's surface, and refers to the position on the inner wall surface 41 of the molten metal container 4 where the molten metal M's surface reaches, i.e., the position where the molten metal M's surface meets the inner wall surface 41 of the molten metal container 4. As shown by the symbol M1 in Figures 4(a) and (b), the boundary where the molten metal M meets the inner wall surface 41 of the molten metal container 4 in the target image It corresponds to the position of the molten metal level line. In order to detect the molten metal level line through image analysis by the computer-based analysis device 3, a target area Rt to be analyzed is set in the target image It, as shown in Figures 5(a) and (b), which correspond to Figures 4(a) and (b), respectively, and the molten metal level line is extracted within the target area Rt. To extract the molten metal surface line, for example, the target image It is binarized, and in the binarized target image It, the boundary between the low-brightness area corresponding to the inner wall surface 41 of the molten metal container 4 and the high-brightness area corresponding to the surface of the molten metal M is extracted as a continuous line, and this is used as the molten metal surface line. In Figures 5(a) and (b), the extracted molten metal surface line L is shown by a thick line.

[0037] The molten metal level line L thus obtained as the boundary between the low-brightness area and the high-brightness area may be used as is in the next height determination step. However, it is preferable to subject the molten metal level line L to processing for detecting and excluding deviation areas before subjecting it to the height determination step. These processing steps will now be explained.

[0038] In a target image It captured inside a molten metal container 4 storing molten metal M, as shown in FIG. 5(b), the molten metal level line L may be located in some places (indicated by the symbol M2 in the figure; hereinafter, referred to as the abnormal area) that are further inward than other places in the molten metal container 4. These abnormal areas M2 are often caused by deposits on the inner wall surface 41 of the molten metal container 4. The deposits are components that were not dissolved in the molten metal M or precipitated components. While the molten metal M is captured in an image with high brightness, the deposits, like the inner wall surface 41 of the molten metal container 4, are captured in an image with low brightness. Therefore, it is difficult to distinguish the deposits from the inner wall surface 41 of the molten metal container 4 in the target image It. Therefore, in the target image It, the molten metal level line L is easily extracted as a line passing through the surface of the deposit at the location of the deposit. In such cases, the area corresponding to the deposit is identified as the abnormal area M2. The abnormal portion M2 does not accurately reflect the position of the molten metal M surface in the target image It, and in the target image It, it passes locally inside (below) the inner wall surface 41 rather than the actual position of the molten metal M surface. Therefore, if the subsequent height determination step is performed using the molten metal level line L including the abnormal portion M2, there is a possibility that the molten metal level will not be determined correctly. Therefore, in this molten metal level detection step, it is preferable to remove the area including the abnormal portion M2 from the molten metal level line L.

[0039] To remove the abnormal portion M2, first, as shown in FIG. 6(a), the target image It corresponding to FIG. 5(b) is divided into multiple parts along the direction of extension of the molten metal level line L, which has already been extracted through binarization. In this case, multiple divided regions are set in the region through which the molten metal level line L passes, and the molten metal level line L is divided into multiple sections passing through these multiple divided regions. For example, multiple divided regions can be set by equally dividing the central angle of the target region Rt, which is set in a sector shape. In FIG. 6(a), three divided regions r1 to r3 are set in this way. Of the multiple divided regions r1 to r3 that have been set, a divided region in which the molten metal level line L deviates from the molten metal level lines L of the other divided regions by more than a predetermined standard is set as a deviation region. For example, if the molten metal level line L of a certain divided region deviates from the molten metal level line L of another divided region or a line obtained by extrapolating that approximation line by more than a predetermined reference amount, it is considered that the molten metal level line L of that divided region deviates from the molten metal level lines L of the other divided regions, and that divided region can be recognized as a deviation region. When a deviation region is detected, the section passing through that deviation region can be excluded from the molten metal level line L, and the section can be used as the target of analysis in the next height determination step.

[0040] As an example of a specific method for determining whether a certain divided region is a deviation region, there is a method of comparing the positions of the centers when the molten metal level line L is approximated to a circular arc. First, the center when the entire molten metal level line L is approximated to a circular arc over the entire target region Rt is taken as the overall center Ot. Furthermore, in each of the multiple divided regions r1 to r3 that have been set, the center when the molten metal level line L included in each divided region is approximated to a circular arc is taken as the divided centers o1 to o3. Even if a region that is affected by the abnormal portion M2 exists in part of the molten metal level line L, as long as the molten metal level line L is sufficiently long overall relative to the abnormal portion M2, the circular arc that approximates the entire molten metal level line L will smooth out that influence. Therefore, among the divided regions r1 to r3, for the divided regions r2 and r3 that do not include the abnormal portion M2, the arc that approximates the molten metal level line L within each divided region is close to the arc that approximates the entire molten metal level line L, but for the divided region r1 that includes the abnormal portion M2, the arc that approximates the molten metal level line L within the divided region deviates significantly from the arc that approximates the entire molten metal level line L. The degree of proximity between these arcs can be evaluated based on the positional relationship of the centers of the arcs.

[0041] Specifically, the distance between the obtained overall center Ot and each of the division centers o1 to o3 is measured and defined as the center-to-center distance. If the center-to-center distance is equal to or greater than a predetermined threshold, the division area corresponding to that division center is detected as a deviation area. A division area whose center-to-center distance is less than the threshold is not recognized as a deviation area. In FIG. 6(a), the center-to-center distance between each of the division centers o1 to o3 corresponding to the division areas r1 to r3 and the overall center Ot is indicated by a dotted line. However, the center-to-center distance (o1-Ot) corresponding to the division area r1 including the abnormal area M2 is larger than the center-to-center distances (o2-Ot and o3-Ot) corresponding to the other division areas r2 and r3. Therefore, by setting a threshold value that is smaller than the center-to-center distance corresponding to the division area r1 and larger than the center-to-center distances corresponding to the other division areas r2 and r3, the division area r1 whose center-to-center distance is equal to or greater than the threshold can be detected as a deviation area. Then, the section of the molten metal level line L that passes through the deviation region can be removed. This makes it possible to remove the influence of the abnormal portion M2 from the molten metal level line L. The molten metal level line L from which the portion passing through the deviation region has been removed may be used as is in the next height determination step, but it is preferable to further approximate the molten metal level line L as a circular arc and use it in the next height determination step. As described here, by using the molten metal level line L from which the influence of the deviation region has been removed in the subsequent height determination step, the influence of factors other than the molten metal surface, such as deposits, can be reduced, making it possible to accurately determine the molten metal level. Even if multiple anomalous portions M2 are present, the multiple deviation regions detected as regions containing the anomalous portions M2 can be processed in the same way. If no deviation region is detected, the entire molten metal level line L extracted initially, or an approximation of it as a circular arc, i.e., an arc centered at the overall center Ot, can be used as the molten metal level line L in the next height determination step. The threshold value may be determined by a preliminary test or the like as a center distance at which divided regions including abnormal locations can be detected without excess or deficiency.

[0042] In the above-described deviation region detection process, if a certain divided region is detected as a deviation region, the deviation region can be further narrowed down. For example, the divided region detected as a deviation region is further subdivided into smaller divided regions to set subdivided regions. Then, the position of the molten metal level line L in the divided region first detected as a deviation region (divided region r1 in the illustrated embodiment) is compared with the position of an arc approximating the entire molten metal level line L (an arc with an overall center Ot). A subdivided region containing a point where the deviation between the two is large is reset as a deviation region, and a section passing through the reset deviation region is removed from the molten metal level line L. In this way, by detecting and subdividing the deviation region on the molten metal level line L and narrowing down the region containing the abnormal point M2, the section to be removed from the molten metal level line L can be kept small. This increases the length of the molten metal level line L available for the subsequent height determination process, thereby improving the accuracy of determining the molten metal level.

[0043] (5) Height determination process In the height determination step, the height of the molten metal M stored in the molten metal vessel 4 is determined based on the molten metal level line L obtained in the molten metal level detection step. At this time, the molten metal level is quantitatively determined by correlating the position of the molten metal level line L in the object image It with the position of the scale lines 42a detected in the scale image Is. In Fig. 7, the scale lines 42a detected from the scale image Is in Fig. 3(b) and stored in the analysis device 3 are superimposed on the object image It showing the molten metal level line L obtained in Fig. 6(b). The scale lines 42a are shown as dotted lines.

[0044] The height of the molten metal surface is determined, for example, by determining whether the position of the molten metal surface line L in the target image It coincides with any of the multiple scale lines 42a in the scale image Is based on coordinate information within the image. Each scale line 42a in the scale image Is is associated with the height position of the molten metal surface of the molten metal M, and the height position corresponding to the scale line 42a determined to coincide with the position of the molten metal surface line L is the height position of the molten metal surface of the molten metal M in the molten metal container 4 at the time that the target image It was acquired. When the molten metal surface line L is located between two adjacent scale lines 42a, the height position of the molten metal surface of the molten metal M corresponding to the position of the molten metal surface line L can be calculated, as appropriate, by linear interpolation or the like, based on the molten metal surface heights corresponding to those two scale lines 42a. 7, the molten metal level line L is located outside the image, that is, between the first and second scale lines 42a from above the molten metal container 4, and linear interpolation can be performed between the height position corresponding to the first scale line 42a and the height position corresponding to the second scale line 42a to calculate the height position of the molten metal M corresponding to the position of the molten metal level line L. In this way, the height of the molten metal M in the target image It can be determined based on a comparison between the scale image Is and the target image It.

[0045] (6) Use of the molten metal surface height detection method In the method for detecting a level of the molten metal M stored in the melt container 4, the level of the molten metal M can be quantitatively detected by performing the steps described above. When the molten metal M is poured into the melt container 4 and then poured out of the melt container 4, the object image acquisition step, the melt level detection step, and the level determination step are repeatedly performed to monitor changes in the amount of the molten metal M stored in the melt container 4. The results of this monitoring can be used, for example, to measure the pouring speed of the molten metal M from the melt container 4, to determine the timing for adding more molten metal M to the melt container 4, and to provide feedback to operational conditions such as the conditions for producing the molten metal M in the furnace 6. The object image acquisition step, the melt level detection step, and the level determination step can be automatically performed by the analysis device 3, so that continuous monitoring of the level of the molten metal M and control based on the monitoring results can be performed (semi-)automatically.

[0046] In the method for detecting the molten metal level according to this embodiment, a camera 2 installed away from the molten metal container 4 is used to detect the molten metal level of the molten metal M. Because detecting the molten metal level does not require contact between any components or devices and the molten metal M, the durability and maintainability of the components and devices required for detecting the molten metal level can be maintained. As a result, the molten metal level can be detected under stable conditions for a long period of time. Furthermore, by placing the camera 2 outside the storage chamber 7, which houses the various facilities that handle the high-temperature molten metal M, such as the molten metal container 4, and taking photographs through a window 71 provided in the storage chamber 7, the molten metal M does not adhere to the camera 2 and the effects of heat are suppressed. This significantly improves the durability and maintainability of the camera 2 and the stability of the molten metal level detection. When the molten metal M is stored in the molten metal container 4, the brightness difference in the target image It becomes large, and the scale lines 42 displayed on the inner wall surface 41 of the molten metal container 4, which is photographed at low brightness, cannot be seen in the target image It. However, if the position of the photographing device 2 is fixed so as not to move, the height position of the molten metal M can be determined based on the scale lines 42a by comparing the scale image Is when the molten metal M is not stored with the target image It when the molten metal M is stored, that is, by comparing the position of the detected scale lines 42a with the position of the molten metal surface line L. Furthermore, once the preparation step and the scale detection step have been performed, the molten metal level height can be determined over a long period of time by comparing the scale image Is with the target image It using the detection results of the same scale lines 42a.

[0047] In addition to the use of a photographing device 2 such as a camera, there are non-contact liquid level detection methods based on laser measurement, etc., but the photographing device 2 is not a precision device like a laser measurement device and does not require the same level of precision adjustment and condition setting as such precision devices, which also contributes to improving the durability and maintainability of the device and improving the stability of detection. Compared to precision devices such as laser measurement devices, the photographing device 2 is less susceptible to the effects of heat, dust, etc., and even when the liquid level is detected through the window 71, reflection or refraction on the surface of the window 71 is less likely to affect the detection results.

[0048] Furthermore, in the method for detecting the level of the molten metal M in this embodiment, video recording by the camera 2 is used to detect the level of the molten metal M, so that the detection of the level of the molten metal M can be continuously and repeatedly performed. This allows for easy and continuous monitoring of the level of the molten metal M, as described above. As explained above regarding the target image acquisition step, averaging multiple captured images extracted from the video as the target image It reduces the influence of transient disturbances such as smoke, thereby improving the accuracy of the detection of the level of the molten metal M. Normally, the rate of change in the level of the molten metal M is slower than changes in disturbance factors such as smoke, so averaging can be performed within a time range in which the change in the level of the molten metal M can be identified.

[0049] Furthermore, in the mold level detection method according to this embodiment, the mold level is detected as a continuous line in the mold level detection step. Therefore, unlike detection of the mold level at only one point or multiple discontinuous points, the mold level can be detected with high accuracy and stability. Because the mold level line L is a continuous line, even if an abnormality M2 that does not reflect the actual position of the mold level of the molten metal M occurs in the mold level line L due to adhesions on the inner wall surface 41 of the molten metal container 4, the influence of the abnormality M2 can be reduced by detecting a deviation area and removing the section passing through the deviation area from the mold level line L, as described above in the mold level detection step. Furthermore, in the mold level detection method according to this embodiment, the mold level is detected based on a comparison between the position of the scale line 42 photographed by the photographing device 2 fixed in a fixed position and the position of the mold level line L in the target image It. Therefore, there is no need to detect or set any height reference in the target image It itself. Therefore, as long as the molten metal level is within the range in which the scale lines 42 are provided, detection of the molten metal level can be easily performed over a wide range of molten metal level heights, even if there are large changes in the molten metal level height. [Example]

[0050] Examples of the present invention are shown below. However, the present invention is not limited to these examples. In these examples, the molten metal surface height detection method according to the embodiment of the present invention described above is actually carried out.

[0051] [Test method] As shown in Figure 1, a facility including a molten metal vessel configured as a tundish was installed, along with a molten metal level detection device according to the above embodiment, including a photography device and an analysis device. Then, before pouring molten metal into the molten metal vessel, the above-mentioned (1) preparation step was carried out. Scale lines were provided at uneven intervals on the inner wall surface of the molten metal vessel, with the intervals narrowed in areas where precise detection of the molten metal level was required.

[0052] Next, the scale detection step (2) was carried out. At this time, the detected scale lines were approximated as arcs and stored in the analysis device. Each scale line was associated with the surface height of the molten metal based on the mass (unit: kg) of the molten metal.

[0053] While the molten metal was being poured into the molten metal container through the opening and discharged from the tap hole, the above-mentioned (3) target image acquisition process, (4) molten metal level detection process, and (5) height determination process were repeatedly carried out to monitor changes in the molten metal level. In the (3) target image acquisition process, video images were taken at a shooting speed of 300 ms per frame, and the target image was the average of 10 consecutive images. In the (4) molten metal level detection process, the target area was divided into three equal parts to detect deviation areas. If a deviation area was detected, the detected deviation area was further subdivided into three equal parts (equivalent to nine equal parts for the entire target area) to narrow the deviation area. The molten metal level line was approximated using an arc shape.

[0054] [Test Results] Figure 8(a) shows the scale image obtained in the scale detection process. The scale image shows the inner wall surface as well as the top surface of the molten metal container, and as shown by the arrows, although they are thin, several scale lines on the inner wall surface can be seen. The scale image was then binarized to detect each scale line, which were then approximated as an arc and superimposed on the scale image, as shown in Figure 8(b). Figure 8(b) shows arc-shaped scale lines that closely replicate the actual scale lines.

[0055] Figure 9 shows images taken during the image acquisition process with molten metal stored in a molten metal container. Figure 9(a) shows a single image extracted from a video. In this image, smoke emanating from the molten metal appears as a hazy, dark haze over a wide area near the location indicated by the arrow. Figure 9(b) shows an image obtained by averaging 10 consecutive images, including the image in Figure 9(a). The hazy smoke-induced haze seen in the image in Figure 9(a) is almost completely absent in this image. Thus, averaging the images reduces the effects of external disturbances. The fan-shaped frame around the image in Figure 9(b) indicates the target area for subsequent analysis.

[0056] Furthermore, the target image in Figure 9(b) was subjected to a molten metal level detection process. Figure 9(c) shows the results of detecting the molten metal level line within the target area. In this process, the captured image was binarized, and the molten metal level was detected as the boundary between the low-brightness and high-brightness regions. The detected molten metal level was then approximated as an arc to create the molten metal level line. In Figure 9(c), this molten metal level line is displayed as a thick, dark line (indicated by a solid arrow). Figure 9(c) confirms that the molten metal level recognized visually in the target image in Figure 9(b), i.e., the position on the inner wall of the molten metal container where the molten metal level reaches, was correctly detected and the molten metal level line was set. Note that, as indicated by the dashed arrow in Figure 9(c), there is a change in brightness inside the molten metal level line (to the lower right of the image). This is due to the temperature distribution of the molten metal and does not correspond to the molten metal level.

[0057] Figure 9 deals with the case where there is no adhesion on the inner wall of the molten metal container, and a smooth molten metal level line that is well approximated by a circular arc is obtained, but Figure 10(a) shows an image of a case where there is adhesion on the inner wall of the molten metal container, and it is affecting the detected molten metal level line. Here too, the molten metal level line detected after binarization is displayed as a thick, dark line. The adhesion is located at the position indicated by the arrow, and as a result, the molten metal level line passes locally inside the molten metal container.

[0058] FIG. 10(a) also shows the overall center Ot and three division centers o1 to o3. The overall center Ot is the center of the arc when the molten metal surface line is approximated as an arc throughout the entire target area. Note that this overall center Ot also roughly coincides with the center of the scale line in FIG. 8(b) when it is approximated as an arc. The division centers o1 to o3 are the centers of the arcs when the molten metal surface line is approximated as an arc for each of the divided regions r1 to r3, which are obtained by dividing the central angle of the target area into three equal parts. Of the three division centers o1 to o3, the division centers o2 and o3 corresponding to the two right-hand divided regions r2 and r3 are located close to the overall center Ot. On the other hand, the division center o1 corresponding to the left-hand divided region r1 is located farther from the overall center Ot. The large distance between the division center o1 and the overall center Ot indicates that the divided region r1 is a deviation region containing an abnormality corresponding to an attachment.

[0059] Figure 10(b) shows the state in which the divided region r1, which was determined to be a deviation region above, has been further subdivided into three equal parts. In Figure 10(b), not only the divided region r1 but also the entire target area is divided into nine equal parts. For each of the subdivided regions r1a, r1b, and r1c, which are obtained by subdividing the divided region r1, the actual position of the mold surface line is compared with the position of an arc approximating the entire mold surface line, i.e., the position of an arc centered on the overall center Ot. The two subdivided regions r1a and r1b on the left are determined to be deviation regions, where the positions of the two are significantly different. Therefore, the sections passing through these two subdivided regions r1a and r1b are excluded from the initially extracted mold surface line that includes the contribution of the deposits, and the entire mold surface line after excluding them is approximated by an arc, which is then set as a new mold surface line. This newly set mold surface line is shown by a thick, dark line in Figure 10(b).

[0060] Next, in relation to the height determination process, Figure 11 shows the molten metal level line set in Figure 10(b) superimposed with the scale lines shown in Figure 8(b). From this, it can be seen that the molten metal level line (indicated by an arrow), displayed as a series of white dots, is located between the second and third scale lines from the outside. By converting the position of the molten metal level line to the molten metal level using linear interpolation from the molten metal level corresponding to these two scale lines, the mass of the molten metal can be determined to be "162.9 kg."

[0061] The results of repeated detection of the molten metal surface height are shown in Figure 12. The horizontal axis is time, and the vertical axis is the molten metal surface height, expressed in terms of mass. In Figure 12, changes in the molten metal surface height were detected in real time. The sudden increases in the molten metal surface height (increases in the amount of molten metal) indicated by the arrows in the figure are due to the addition of molten metal to the molten metal container. Meanwhile, the gradual declines in the molten metal surface height (decrease in the amount of molten metal) occurring between these multiple additions of molten metal correspond to the pouring of the molten metal from the molten metal container.

[0062] Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments and various modifications can be made. [Explanation of symbols]

[0063] 1. Molten metal level detection device 2. Imaging equipment 2a Shooting range 3 Analysis device 4 Molten metal container 41 Inner wall surface 41a Upper end of wall 42 Scale lines 42a Detected scale line 43 Aperture 44 Tap 7 Containment Room 71 Window Is scale image It object image L hot water surface line M Molten metal M1 Position of the melt level line M2 Abnormal location Ot whole center o1~o3 Center of division Rt target area r1~r3 divided area

Claims

1. A method for detecting the height of a surface of a molten metal stored in a molten metal container that stores the molten metal in an accessible manner, comprising: a preparation step of providing a plurality of scale lines on the inner wall surface of the molten metal container at positions of different heights from the bottom surface of the molten metal container, each of the scale lines corresponding to a height position of the surface of the molten metal in the molten metal container, and fixing a video camera capable of taking videos at a position where the inside of the molten metal container, including the plurality of scale lines, can be photographed from outside the molten metal container; a scale detection step of photographing the molten metal container in a state where the molten metal is not stored therein by the photographing device and detecting the position of the scale line in the photographed image; an object image acquisition step of photographing the molten metal container storing the molten metal with the photographing device and extracting an object image to be analyzed from the photographed image obtained as a video; a molten metal level detection step of extracting a continuous line corresponding to a position where the molten metal level reaches on the inner wall surface from the target image, and setting the line as a molten metal level line; a height determination step of determining the height position of the molten metal surface stored in the molten metal container by correlating the position of the molten metal surface line in the target image with the position of the scale line detected in the scale detection step.

2. The molten metal container is accommodated in a chamber having a transparent window, 2. The method for detecting a molten metal surface level according to claim 1, wherein the photographing device is installed outside the containing chamber and photographs the inside of the molten metal container through the window.

3. 2. The method for detecting a molten metal surface height according to claim 1, wherein in the object image obtaining step, a plurality of images obtained at successive times are extracted from the images taken as a moving image, and the extracted images are averaged to obtain the object image.

4. In the molten metal level detection step, the extracted molten metal level line is divided into a plurality of sections passing through a plurality of divided regions; a region among the plurality of divided regions in which the molten metal level line deviates from the molten metal level lines in other regions by more than a predetermined standard is detected as a deviation region; 2. The method for detecting a molten metal level according to claim 1, further comprising the step of: excluding, from the molten metal level line, a section passing through the deviation region when the deviation region is detected.

5. the center of the molten metal level line when the entire molten metal level line is approximated to an arc is defined as an overall center, and the center of the molten metal level line when the molten metal level line is approximated to an arc in each of the plurality of divided regions is defined as a divided center, 5. The method for detecting a molten metal surface height according to claim 4, wherein, when a distance between the overall center and the division center is equal to or greater than a threshold value, the division region corresponding to the division center is detected as the deviation region.

6. The scale line is provided in the molten metal container. the photographing device is fixed at a position where it can photograph the inside of the molten metal vessel, including the plurality of scale lines, from outside the molten metal vessel; and and an analysis device capable of performing image analysis on the photographed image obtained by the photographing device, A molded body level detection device that can perform the scale detection step, the object image acquisition step, the molded body level detection step, and the height determination step in the molded body level detection method according to any one of claims 1 to 5 by using the photographing device and the analyzing device.

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