Electrode length measurement method

Abstract

This invention provides an electrode length measurement method that can accurately measure the length of an electrode while avoiding the risk of electrode breakage. [Solution] The present invention relates to an electrode length measurement method for measuring the length of an arc generating electrode 3 extending vertically, provided in an electric furnace 100 that utilizes an arc, comprising: an imaging step ST1 in which an imaging means 10 is set up so that at least the lower end of the electrode, when it is pulled up from the furnace lid of the electric furnace, is within the imaging field of view, and an imaging step ST2 in which an imaging means is used to image the electrode from the side to generate an image; an image processing step ST2 in which image processing is applied to the image to detect vertical edges to detect the lower end position of the electrode; and a length calculation step ST3 in which the length of the electrode is calculated based on the lower end position of the electrode.

Description

[Technical Field]

[0001] This invention relates to an electrode length measurement method for measuring the length of an electrode used for generating an arc in an electric furnace that utilizes an arc, such as an arc furnace (arc-type electric melting furnace) or a ladle refining furnace. In particular, this invention relates to an electrode length measurement method that can accurately measure the length of an electrode while avoiding the risk of electrode breakage. [Background technology]

[0002] Known electric furnaces that utilize an arc include arc furnaces and ladle smelting furnaces. Arc furnaces operate by supplying electricity received from commercial power distribution facilities to electrodes for arc generation via transformers, etc., and using the arc generated from these electrodes to heat and melt raw materials such as scrap. Ladle smelting furnaces operate by refining molten steel while it is heated by the arc generated from the electrodes for arc generation.

[0003] Controlling the length of the arc-generating electrodes in electric furnaces like the one described above is extremely important. If the electrode length is too long or too short compared to the intended length, it can lead to problems such as interference with other equipment in the electric furnace or a decrease in the heat transfer efficiency of the power supplied to the electrodes. For this reason, it is necessary to measure the electrode length periodically.

[0004] Conventionally, a method for measuring the length of an electrode has been used in which, for example, after moving the electrode outside the electric furnace, the gripping part that holds the upper end of the electrode is lowered until the lower end of the electrode contacts a pressure sensor placed on the floor, and the length of the electrode is calculated based on the vertical position of the gripping part at the moment the lower end of the electrode contacts the pressure sensor.

[0005] However, with the method described above, there is a risk of the electrode breaking when the lower end of the electrode comes into contact with the pressure sensor. In particular, the risk of breakage increases if metal deposits are present on the pressure sensor due to the operation of the electric furnace, or if the electrode is lowered manually.

[0006] Furthermore, methods described in Patent Documents 1 and 2 have been proposed as ways to measure the length of electrodes.

[0007] However, the method described in Patent Document 1 involves measuring the length of the electrode by bringing the lower end of the electrode into contact with the electrode contact area, and therefore, like the conventional method described above, there is a risk of the electrode breaking. Furthermore, the method described in Patent Document 2 measures the length of an electrode based on the temperature at two points on the electrode measured by a temperature sensor. However, since it is not a method for directly measuring the length, there is a risk that the length of the electrode cannot be measured with sufficient accuracy. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2016-148465 [Patent Document 2] Special table 2019-504286 publication [Overview of the project] [Problems that the invention aims to solve]

[0009] This invention has been made in view of the problems of the prior art described above, and aims to provide an electrode length measuring method that can accurately measure the length of an electrode while avoiding the risk of electrode breakage. [Means for solving the problem]

[0010] To solve the aforementioned problems, the present invention provides an electrode length measurement method for measuring the length of an arc generating electrode extending vertically in an electric furnace that utilizes an arc, comprising: an imaging step of generating an image by setting up an imaging means such that at least the lower end of the electrode, when it is pulled up from the furnace lid of the electric furnace, is within the imaging field of view, and imaging the electrode from the side using the imaging means; an image processing step of detecting the lower end position of the electrode by performing image processing on the imaged image to detect vertical edges; and a length calculation step of calculating the length of the electrode based on the lower end position of the electrode.

[0011] In this invention, "a state in which the electrode is lifted from the furnace lid of the electric furnace" means a state in which the lower end of the electrode is located above the furnace lid of the electric furnace. According to the present invention, in the imaging step, an image is generated by imaging the electrode from the side using imaging means installed so that at least the lower end of the electrode, when it is lifted from the furnace lid of the electric furnace, is within the imaging field of view. Since the lower end of the electrode, when it is lifted from the furnace lid of the electric furnace, is red-hot at certain times, the pixel value (luminance value) of the pixel area corresponding to the lower end of the electrode in the image generated in this state is larger than the pixel values ​​of other pixel areas. Therefore, in the image processing step, by applying image processing (e.g., differential processing) to detect vertical edges on the image, the boundary position where the pixel value changes significantly can be accurately detected as the lower end position of the electrode (vertical position of the lower end of the electrode). For this reason, in the length calculation step, the length of the electrode can be accurately calculated based on the lower end position of the electrode. Specifically, for example, the "length of the electrode" measured in the present invention is the vertical distance between the gripping part that grips the upper end of the electrode and the lower end of the electrode. Therefore, if the vertical position of the gripping part when generating the captured image is a known fixed position, the length of the electrode can be calculated accurately based on the position of this gripping part and the lower end position of the electrode. Furthermore, since the length of the electrode is calculated using the captured image, there is no need to bring the electrode into contact with a pressure sensor or the like, thus avoiding the risk of electrode breakage.

[0012] Preferably, in the imaging step, the image is generated by imaging the electrode within 10 minutes after stopping the application of the voltage to the electrode.

[0013] According to the preferred method described above, since the image is generated by imaging the electrode within 10 minutes after stopping the application of the voltage to the electrode, the image is generated at the timing when the lower end of the electrode is reliably red-hot. Therefore, the position of the lower end of the electrode can be detected with even greater accuracy in the image processing step.

[0014] Preferably, in the imaging step, multiple images are generated, and in the image processing step, image processing is performed on each of the multiple images to detect the vertical edge, thereby detecting the lower end position of the electrode for each of the multiple images, and in the length calculation step, the length of the electrode is calculated based on the average value of the lower end positions of the electrode detected for each of the multiple images.

[0015] According to the preferred method described above, multiple captured images are generated, the lower end position of the electrode is detected for each of the multiple captured images, and the length of the electrode is calculated based on the average value of the lower end positions of the electrode detected for each of the multiple captured images. Therefore, even if there is variation in the lower end position of the electrode detected in a single captured image due to the effect of light fluctuations during imaging, the calculated electrode length can be stabilized by using the average value obtained by averaging these variations.

[0016] Preferably, the imaging means includes an electronic shutter and / or an ND filter.

[0017] The lid of an electric furnace has an opening through which electrodes pass and move up and down, and white smoke rising from inside the furnace body may be captured in images through this opening. In this case, the pixel value of the pixel area corresponding to the white smoke in the captured image will be larger than the pixel values ​​of other pixel areas, similar to the lower end of the red-hot electrode. Therefore, there is a risk of misdetecting the boundary position of the pixel area corresponding to the white smoke as the lower end position of the electrode. According to the findings of the present inventors, by adjusting the exposure of the imaging means, imaging can be performed such that the pixel values increase in the order of the pixel region corresponding to the lower end portion of the red-hot electrode > the pixel region corresponding to white smoke > other pixel regions. With such imaging, even if the pixel value of the pixel region corresponding to white smoke increases, the pixel value of the pixel region corresponding to the lower end portion of the red-hot electrode is sufficiently larger, so by adjusting the parameters for detecting vertical edges in the image processing step, the lower end position of the electrode can be detected with high accuracy. According to the preferred method described above, since the imaging means includes an electronic shutter and / or an ND filter, the exposure of the imaging means can be adjusted. Therefore, imaging can be performed such that the pixel value of the pixel region corresponding to the lower end portion of the red-hot electrode is sufficiently larger than the pixel value of the pixel region corresponding to white smoke, and the lower end position of the electrode can be detected with high accuracy without being affected by white smoke.

[0018] Preferably, in the image processing step, image processing for detecting vertical edges is performed on the captured image to detect a lower end position candidate of the electrode, it is determined whether or not the length of the pixel region having pixel values equal to or greater than a predetermined threshold upward from the detected lower end position candidate of the electrode is equal to or greater than a preset reference length, if the length is equal to or greater than the reference length, the lower end position candidate is determined as the lower end position of the electrode, and in the length calculation step, the length of the electrode is calculated based on the determined lower end position of the electrode.

[0019] At the opening of the furnace lid of the electric furnace, there is a possibility that molten steel scattered from the inside of the furnace body adheres as base metal, or molten steel adhering to the electrode is transferred and adheres as base metal. Then, in the imaging step, imaging may be performed at the timing when this base metal is in a red-hot state. In this case, the pixel value of the pixel region corresponding to the base metal in the captured image is also larger than the pixel values of other pixel regions, similar to the lower end portion of the red-hot electrode, so there is a risk that the lower end position of the pixel region corresponding to the base metal is erroneously detected as the lower end position of the electrode. On the other hand, the length (vertical dimension) of the pixel region corresponding to the lower end portion of the red-hot electrode in the captured image is generally sufficiently longer than the length (vertical dimension) of the pixel region corresponding to the opening of the furnace lid in the captured image. The approximate values of the lengths of both pixel regions can be grasped in advance. According to the above preferred method, in the image processing step, first, image processing for detecting edges in the vertical direction is performed on the captured image to detect lower end position candidates of the electrode. These lower end position candidates include the lower end position of the electrode, but may also include the lower end position of base metal adhering to the opening of the furnace lid. Next, according to the above preferred method, it is determined whether or not the length of a pixel region having a pixel value equal to or greater than a predetermined threshold value upward from the detected lower end position candidate of the electrode is equal to or greater than a preset reference length. The reference length may be set, for example, to an intermediate value between the length of the pixel region corresponding to the lower end portion of the red-hot electrode in the captured image and the length of the pixel region corresponding to the opening of the furnace lid in the captured image. Thereby, if the length is less than the reference length, the lower end position candidate can be excluded as being considered the lower end position of the base metal adhering to the opening of the furnace lid, while if the length is equal to or greater than the reference length, the lower end position candidate can be determined as the lower end position of the electrode. As described above, according to the above preferred method, in the image processing step, the lower end position of the electrode can be accurately detected without being affected by the base metal adhering to the opening of the furnace lid, and in the length calculation step, the length of the electrode can be accurately calculated based on the determined lower end position of the electrode.

Effects of the Invention

[0020] According to the present invention, the length of the electrode can be accurately measured while avoiding the risk of electrode breakage.

Brief Description of the Drawings

[0021] [Figure 1] It is a schematic diagram schematically showing the configuration of an electric furnace and a measuring device. [Figure 2] It is a flow diagram schematically showing the steps of an electrode length measurement method according to an embodiment of the present invention. [Figure 3]This figure schematically illustrates the edge detection process performed by the image processing device 20 shown in Figure 1. [Figure 4] This figure schematically illustrates the edge detection process performed by the image processing device 20 when metal is attached to the opening 21 of the furnace lid 2 shown in Figure 1. [Figure 5] This example shows a comparison of the length of electrode 3 measured by the electrode length measurement method according to one embodiment of the present invention with the length of electrode 3 measured by a conventional method in which the lower end of electrode 3 is in contact with a pressure sensor. [Modes for carrying out the invention]

[0022] The electrode length measurement method according to one embodiment of the present invention will be described below with reference to the attached drawings as appropriate. The electrode length measurement method according to this embodiment is a method for measuring the length of an arc generating electrode that extends vertically and is provided in an electric furnace that utilizes an arc.

[0023] <Configuration of electric furnace and measuring device> First, the configuration of the electric furnace to which the electrode length measurement method according to this embodiment is applied, and the configuration of the measuring device for performing the electrode length measurement method according to this embodiment will be described. Figure 1 is a schematic diagram illustrating the configuration of the electric furnace and measuring device. Figure 1(a) is a side view showing the configuration of the electric furnace and measuring device, Figure 1(b) is a plan view taken along arrow AA in Figure 1(a), and Figure 1(c) is a plan view taken along arrow BB in Figure 1(a). Figure 1(a) shows a cross-section of the area below the furnace lid 2. As shown in Figure 1, the electric furnace 100 comprises a furnace body 1 for containing molten steel M obtained by heating and melting a raw material, a furnace lid 2 covering the upper end of the furnace body 1, an electrode 3 that generates an arc when power is supplied and heats and melts the raw material with the arc, and a lifting device 4 that grips and raises the electrode 3. In addition, the electric furnace 100 of this embodiment is equipped with a lance 5 for blowing oxygen and carbon for the purpose of refining the molten steel M.

[0024] The furnace lid 2 is provided with openings 21 through which the electrodes 3 pass and move up and down. The electric furnace 100 in this embodiment is a three-phase AC electric furnace and has three electrodes 3 (3a, 3b, 3c), so three openings 21 are provided. The diameter of the openings 21 is set to be slightly larger than the diameter (maximum diameter) of the electrodes 3.

[0025] The lifting device 4 comprises an arm portion 41 extending horizontally and a support column portion 42 extending vertically, and is configured so that the arm portion 41 can move up and down along the support column portion 42 by a drive source (not shown). The tip of the arm portion 41 is provided with a gripping portion 41a configured to grip the electrode 3. When the arm portion 41 moves up and down along the support column portion 42 with the electrode 3 gripped by the gripping portion 41a, the electrode 3 also moves up and down. Since the electric furnace 100 of this embodiment has three electrodes 3, there are also three arm portions 41 and three support column portions 42, and it is possible to move the three electrodes 3 up and down individually. The state shown in Figure 1(a) illustrates the state in which each electrode 3 is lifted up from the furnace lid 2 (the state in which the lower end of the electrode 3 is located above the furnace lid 2).

[0026] The measuring device 200 is set up so that at least the lower end of the electrode 3, when it is lifted from the furnace lid 2 of the electric furnace 100, is within the imaging field of view, and includes an imaging means 10 that generates an image by imaging the electrode 3 from the side, and an image processing device 20 that is electrically connected to the imaging means 10 and detects the position of the lower end of the electrode 3 by performing image processing to detect vertical edges on the image. As the imaging means 10, an area sensor camera equipped with an image sensor such as a CCD or CMOS can be used. In this embodiment, the imaging means 10 is preferably equipped with an electronic shutter. Since the electric furnace 100 in this embodiment is equipped with three electrodes 3, the imaging field of view of the imaging means 10 is set so that at least the lower ends of all three electrodes 3 are within the imaging field of view. It is preferable to use a PoE-powered imaging means as the imaging means 10. The image processing device 20 can, for example, be a general-purpose computer with programs installed for performing the image processing and arithmetic processing described later, but it is not limited to this, and can also be configured with dedicated hardware such as an ASIC.

[0027] <Electrode length measurement method> The electrode length measurement method according to this embodiment, that is, a method for measuring the length of an electrode 3 provided in an electric furnace 100 having the above configuration using a measuring device 200 having the above configuration, will be described below. The length of the electrode 3 measured by the electrode length measurement method according to this embodiment is the vertical distance between the gripping portion 41a and the lower end of the electrode 3 (distance L shown in Figure 1(a)).

[0028] Figure 2 is a schematic flowchart showing the steps of the electrode length measurement method according to this embodiment. As shown in Figure 2, the electrode length measurement method according to this embodiment includes an imaging step ST1, an image processing step ST2, and a length calculation step ST3. Each step ST1 to ST3 will be described below.

[0029] [Imaging Process ST1] In the imaging process ST1, the imaging means 10 is positioned so that at least the lower ends of the electrodes 3 (the lower ends of all three electrodes 3) are within the imaging field of view when they are lifted from the furnace lid 2 of the electric furnace 100, and an image is generated by imaging the electrodes 3 from the side (approximately horizontally) using the imaging means 10. Specifically, in this embodiment, an image is generated by imaging the electrodes from the side when the gripping portion 41 is raised to its upper limit by the lifting device 4 (i.e., when the electrodes 3 are pulled up to their highest position). The generated image is input to the image processing device 20. The imaging step ST1 is performed when the lower end of electrode 3 is red-hot. Specifically, it is preferable to perform the imaging step ST1 within 10 minutes after stopping the application of voltage to electrode 3. This ensures that the image is generated at the precise moment when the lower end of electrode 3 is red-hot.

[0030] The imaging means 10 is configured, for example, with a frame rate of 10fps and generates captured images continuously for 15 seconds during the imaging process ST1. This results in the generation of multiple (150) captured images. The imaging means 10 is also configured, for example, with an electronic shutter set to a shutter speed of 1 / 250sec. According to the inventors' findings, by setting the shutter speed of the electronic shutter to 1 / 250sec, the exposure amount of the imaging means 10 is appropriately adjusted, and even if white smoke rising from inside the furnace body 1 through the opening 21 of the furnace lid 2 is captured, the lower end position of the electrode 3 can be accurately detected without being affected by the white smoke. In this embodiment, the imaging means 10 is configured to include an electronic shutter, but is not limited to this configuration. It is also possible to adopt a configuration that includes an ND filter to allow adjustment of the exposure amount of the imaging means 10, or a configuration that includes an ND filter in addition to the electronic shutter.

[0031] [Image processing step ST2] In the image processing step ST2, the image processing device 20 detects the lower end position of the electrode 3 by performing image processing to detect vertical edges on the captured image input from the imaging means 10. As described above, the captured image in this embodiment is generated in the imaging step ST1 by imaging so that the lower ends of the three electrodes 3 are within the imaging field of view, and the captured image includes pixel regions corresponding to the lower ends of the three electrodes 3, so the image processing device 20 detects the lower end position for each of the three electrodes 3. Also, as described above, multiple captured images are generated in the imaging step ST1 and multiple captured images are input to the image processing device 20, so the image processing device 20 detects the lower end position of the three electrodes 3 for each of the multiple captured images by performing image processing to detect vertical edges for each of the multiple captured images.

[0032] The following describes in detail the image processing performed by the image processing apparatus 20 of this embodiment to detect vertical edges (hereinafter referred to as "edge detection processing" as appropriate). Figure 3 schematically illustrates the edge detection process performed by the image processing device 20. Figure 3(a) schematically shows an example of an captured image, and Figures 3(b) to 3(d) schematically show the edge detection process for the electrode 3c shown in Figure 3(a). In Figure 3, the Y direction is the vertical direction, and the X direction is the horizontal direction perpendicular to both the Y direction and the line of sight of the imaging means 10. The same applies to Figure 4, which will be described later. Since the lower end of electrode 3 is in a red-hot state, as shown in Figure 3(a), the lower end of electrode 3 is imaged brighter than other areas. That is, for example, if an 8-bit grayscale image is generated, the pixel value of each pixel will be a value between 0 and 255 (the pixel value of the brightest white pixel will be 255, and the pixel value of the darkest black pixel will be 0), but the pixel value of the pixel region corresponding to the lower end of electrode 3 will be a larger value than the pixel values ​​of other pixel regions.

[0033] To explain the edge detection process of this embodiment using the electrode 3c shown in Figure 3(a) as an example, as shown in Figure 3(b), the edge detection process first calculates the average value in the X direction of the pixel values ​​of the pixels located between coordinates X1 and X2 in the X direction, along the Y direction of the captured image. Since the approximate position of the electrode 3c in the X direction within the imaging field of view of the imaging means 10 can be known in advance, it is possible to set coordinates X1 and X2 in advance so that the pixel area corresponding to the electrode 3c is always included between coordinates X1 and X2. Figure 3(c) is a pixel value profile showing the average value in the X direction of the pixel values ​​along the Y direction (Y-direction distribution of the average value in the X direction) calculated as described above.

[0034] Next, in the edge detection process, the differential profile shown in Figure 3(d) is calculated by applying differential processing to the pixel value profile. In this embodiment, since the differential processing is applied from the bottom to the top in the Y direction, the position corresponding to the lower end position of electrode 3c where the pixel value (average value of pixel values) changes from a small value to a large value (Y=Y E1), the differential value in the differential profile is a positive value. On the other hand, at the position corresponding to the upper end position of the red-hot state at the lower end of the electrode 3c, the pixel value changes from a large value to a small value in the pixel value profile, so the differential value in the differential profile is a negative value. In the edge detection processing, since it is desired to detect only the lower end position of the electrode 3c (the upper end position of the red-hot state is not desired to be detected), the position in the Y direction where the differential value is equal to or greater than a predetermined threshold value Th1 (Th1>0) (Y=Y E1 ) is detected as the lower end position of the electrode 3c.

[0035] The image processing device 20 of the present embodiment executes the processing described above, but as a preferred aspect, the position in the Y direction where the differential value is equal to or greater than the predetermined threshold Th1 is not immediately determined as the lower end position of the electrode 3c, but is first detected as a lower end position candidate. Next, as shown in FIG. 3(c), the image processing device 20 detects the lower end position candidate (Y=Y E1 ), and determines whether the length L1 of the pixel region having a pixel value equal to or greater than a predetermined threshold Th2 (0<Th2<255) upward therefrom (the length of the pixel region having a pixel value (average pixel value) equal to or greater than the threshold Th2 in the pixel value profile) is equal to or greater than a preset reference length L0. The reference length L0 may be set, for example, to an intermediate value between the length of the pixel region corresponding to the lower end portion of the red-hot electrode 3c in the captured image and the length of the pixel region corresponding to the opening 21 of the furnace lid 2 in the captured image. Then, as shown in FIG. 3(c), if the length L1 of the pixel region having a pixel value equal to or greater than the threshold Th2 is equal to or greater than the reference length L0, the image processing device 20 sets the lower end position candidate (Y=Y E1 ) as the lower end position of the electrode 3c.

[0036] The image processing device 20 of the present embodiment also executes the same edge detection processing as described above for the electrode 3c for the other electrodes 3a and 3b, and detects (determines) the lower end positions of the electrodes 3a and 3b. Furthermore, the image processing device 20 of the present embodiment executes the same edge detection processing on a plurality of captured images, and detects the lower end position of the electrode 3 (3a to 3c) for each of the plurality of captured images.

[0037] Furthermore, molten steel scattered from inside the furnace body 1 may adhere to the opening 21 of the furnace lid 2 of the electric furnace 100 as base metal, or molten steel adhering to the electrode 3 may be transferred and adhere to the opening 21 as base metal. In the imaging process ST1, this base metal may be imaged when it is red-hot. In this case, the pixel value of the pixel area corresponding to the base metal in the captured image will be larger than the pixel values ​​of other pixel areas, similar to the lower end of the red-hot electrode 3, so there is a risk of misdetecting the lower end position of the pixel area corresponding to the base metal as the lower end position of the electrode 3. However, this misdetection can be avoided by the edge detection process of the preferred embodiment described above.

[0038] Figure 4 schematically illustrates the edge detection process performed by the image processing device 20 when metal is attached to the opening 21 of the furnace lid 2. Specifically, Figure 4 schematically shows the edge detection process for the electrode 3c as an example. As shown in Figure 4(a), in the edge detection process, as described above, first, the average value in the X direction of the pixel values ​​of pixels located from coordinate X1 to coordinate X2 in the X direction along the Y direction of the captured image is calculated. Figure 4(b) is a pixel value profile showing the average value in the X direction of the pixel values ​​along the Y direction calculated as described above (Y-direction distribution of the average value in the X direction).

[0039] Next, in the edge detection process, the differential profile shown in Figure 4(c) is calculated by applying differential processing to the pixel value profile. In this embodiment, since the differential processing is applied from bottom to top in the Y direction, in the pixel value profile, the position corresponding to the lower end position of the metal attached to the opening 21 of the furnace lid 2 where the pixel value (average value of the pixel values) changes from a small value to a large value (Y=Y E2 ) and the position corresponding to the lower end of electrode 3c (Y=Y E1 ) In this case, the derivative value in the differential profile is a positive value. Therefore, the image processing device 20 determines the position in the Y direction (Y=Y) where the derivative value is greater than or equal to a predetermined threshold Th1 (Th1>0). E2 and Y=Y E1) is detected as a lower end position candidate of the electrode 3c. Next, as shown in FIG. 4(b), the image processing device 20 uses the detected first lower end position candidate (Y=Y E2 ) to determine upward whether the length L2 of the pixel region having a pixel value equal to or greater than a predetermined threshold Th2 (the length of the pixel region having a pixel value (average pixel value) equal to or greater than the threshold Th2 in the pixel value profile) is equal to or greater than a preset reference length L0. Then, as shown in FIG. 4(b), if the length L2 of the pixel region having a pixel value equal to or greater than the threshold Th2 is less than the reference length L0, the image processing device 20 determines that the first lower end position candidate (Y=Y E2 ) is excluded. On the other hand, as shown in FIG. 4(b), the detected second lower end position candidate (Y=Y E1 ) is used to determine upward whether the length L1 of the pixel region having a pixel value equal to or greater than a predetermined threshold Th2 (the length of the pixel region having a pixel value (average pixel value) equal to or greater than the threshold Th2 in the pixel value profile) is equal to or greater than a preset reference length L0. Then, as shown in FIG. 4(b), if the length L1 of the pixel region having a pixel value equal to or greater than the threshold Th2 is equal to or greater than the reference length L0, the image processing device 20 determines that the second lower end position candidate (Y=Y E1 ) is determined as the lower end position of the electrode 3c. The same applies to the other electrodes 3a and 3b. As described above, according to the edge detection processing of the preferred embodiment executed by the image processing device 20 of the present embodiment, in the image processing step ST2, the lower end position of the electrode 3 can be accurately detected without being affected by the base metal adhering to the opening 21 of the furnace lid 2.

[0040] [Length calculation step ST3] In the length calculation step ST3, the image processing device 20 calculates the length L of the electrode 3 based on the detected lower end position of the electrode 3. Specifically, in this embodiment, multiple captured images are generated in the imaging step ST1, and the lower end position of the electrode 3 is detected for each of the multiple captured images in the image processing step ST2. Therefore, in the length calculation step ST3, the length L of the electrode 3 is calculated based on the average value of the lower end positions of the electrode 3 detected for each of the multiple captured images. As a result, even if there is variation in the detected lower end position of the electrode 3 due to the influence of light fluctuations during imaging for a single captured image, the calculated length of the electrode 3 can be stabilized by using the average value obtained by averaging these variations. The length L of the electrode 3 is the vertical distance between the gripping portion 41a, which grips the upper end of the electrode 3, and the lower end of the electrode 3. As described above, when the electrode 3 is imaged in the imaging step ST1, the gripping portion 41a is raised to its upper limit, and its vertical position is a known fixed position. The vertical position of the imaging means 10 is also a known fixed position. Therefore, by inputting these fixed positions into the image processing device 20 in advance, the image processing device 20 can accurately calculate the length L of the electrode 3 by geometric calculations using the fixed position of the gripping portion 41a, the fixed position of the imaging means 10, the position of the lower end of the electrode 3 in the image detected in the image processing step ST2, and the set resolution (mm / pixel) of the imaging field of view of the imaging means 10. Furthermore, if the imaging field of the imaging means 10 is set to be wide enough to also image the gripping portion 41a, the vertical position of the pixel region corresponding to the gripping portion 41a in the captured image can be determined in advance. By using this vertical position, the lower end position of the electrode 3 in the detected captured image, and the resolution of the set imaging field of the imaging means 10, the length L of the electrode 3 can be calculated with high accuracy.

[0041] Figure 5 shows an example of a comparison between the length of electrode 3 measured by the electrode length measurement method according to this embodiment and the length of electrode 3 measured by a conventional method in which the lower end of electrode 3 is in contact with a pressure sensor. In Figure 5, the vertical axis, "Measured value of the present invention," shows the length of electrode 3 measured by the electrode length measurement method according to this embodiment, and the horizontal axis, "Conventional measured value," shows the length of electrode 3 measured by a conventional method. As can be seen from Figure 5, the electrode length measurement method according to this embodiment allows for the measurement of the electrode 3 with the same accuracy as the conventional method. Furthermore, since the electrode length measurement method according to this embodiment calculates the length of the electrode 3 using an captured image, there is no need to bring the electrode 3 into contact with a pressure sensor or the like, as in the conventional method, thus avoiding the risk of the electrode 3 breaking. [Explanation of Symbols]

[0042] 1...Furnace body 2...Heart cover 3,3a,3b,3c...electrode 4. Lifting device 10. Imaging means 20. Image processing equipment 21...Opening 41a...Gripping part 100... Electric furnace 200... Measuring device ST1...Imaging Process ST2...Image processing process ST3...Length calculation process

Claims

1. An electrode length measurement method for measuring the length of an arc generating electrode that extends vertically in an electric furnace that utilizes an arc, The imaging step involves setting up an imaging means so that at least the lower end of the electrode, when it is lifted from the furnace lid of the electric furnace, is within the imaging field of view, and generating an image by imaging the electrode from the side using the imaging means; An image processing step to detect the lower end position of the electrode by applying image processing to the captured image to detect vertical edges, The system includes a length calculation step for calculating the length of the electrode based on the lower end position of the electrode. Electrode length measurement method.

2. In the imaging step, after stopping the application of the voltage to the electrode, the electrode is imaged within 10 minutes to generate the imaged image. The electrode length measurement method according to claim 1.

3. In the imaging step, multiple images are generated, In the image processing step described above, by performing image processing to detect vertical edges on each of the multiple captured images, the lower end position of the electrode is detected for each of the multiple captured images. In the length calculation step, the length of the electrode is calculated based on the average value of the lower end position of the electrode detected for each of the multiple captured images. The electrode length measurement method according to claim 1 or 2.

4. The imaging means comprises an electronic shutter and / or an ND filter. The electrode length measurement method according to claim 1 or 2.

5. In the image processing step, image processing is performed on the captured image to detect vertical edges, thereby detecting a candidate for the lower end position of the electrode. It is determined whether the length of the pixel region having a pixel value equal to or greater than a predetermined threshold, extending upward from the detected candidate for the lower end position of the electrode, is equal to or greater than a preset reference length. If it is equal to or greater than the reference length, the candidate for the lower end position is determined as the lower end position of the electrode. In the length calculation step, the length of the electrode is calculated based on the determined lower end position of the electrode. The electrode length measurement method according to claim 1 or 2.

Images