Weight measuring device, hot rolling line, and weight measuring method

Abstract

To enable accurate acquisition of slab weight information without the need to measure the slab's weight using a weighing machine. [Solution] A weight measuring device 60 for measuring the weight of a slab while it is being transported, comprising: an imaging device 54 for imaging the slab as it is being transported; an image processing unit 62 for performing a projection transformation on the image of the slab obtained by imaging; and a calculation unit 64 for calculating the weight of the slab from the projection transformed image. The slab is produced in a continuous casting machine that generates a continuous cast slab by drawing out molten steel while cooling it, and also cuts the continuous cast slab to a predetermined size. Preferably, the imaging device 54 images the slab as it is being transported from the continuous casting machine toward a heating furnace that heats the slab.

Description

Technical Field

[0001] The present invention relates to an apparatus for measuring the weight of a slab generated in a continuous casting machine, a hot rolling line equipped with the apparatus, and a method for measuring the weight of a slab.

Background Art

[0002] A continuous casting machine is an apparatus that continuously generates a plurality of slabs by cutting a strip of steel drawn from a mold at predetermined length intervals using a torch. The plurality of slabs generated by the continuous casting machine are conveyed to a hot rolling facility (hot rolling line) and subjected to a hot rolling process. By performing the hot rolling process, each slab becomes a steel plate rolled to a desired thickness. Hereinafter, the steel plate generated by rolling a slab is referred to as a rolled steel plate. In the hot rolling process, predictive calculations are performed on each slab, and each part of the hot rolling line is controlled according to the result of the calculation. Hereinafter, the control in the hot rolling process is referred to as mill pacing control.

[0003] Mill pacing control is executed based on, for example, the weight of a slab measured by a weighing machine provided in any one of a continuous casting machine, the conveyance process from the continuous casting machine to the hot rolling line, or the hot rolling line. By the way, it has been found that the weight of a slab generated by a continuous casting machine varies depending on the amount of thermal contraction of the casting strand at the time of cutting by a torch. As a method for suppressing the variation in the weight of a slab, for example, it has been proposed to calculate the average unit weight of the casting strand at the torch position and divide the target slab weight by the calculated average unit weight to correct the cutting length of the slab (see Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Incidentally, in manufacturing plants that produce rolled steel sheets, weighing machines are sometimes not installed in the continuous casting machine, the transport route from the continuous casting machine to the hot rolling line, or the hot rolling line itself. For example, if a weighing machine is not available, mill pacing control is performed using the planned weight of the rolled steel sheet being manufactured. However, the resulting slabs not only vary in weight from slab to slab, but also have errors in the weight of the slabs calculated from the planned weight of the rolled steel sheet. As a result, the quality of the rolled steel sheet and its productivity will differ depending on whether the mill pacing control for each slab uses the weight of the slab calculated from the planned weight of the rolled steel sheet or the actual measured weight of the slab. Therefore, in order to avoid problems such as a decrease in the quality of rolled steel sheets produced by the hot rolling process and a decrease in its productivity, a technology is needed that can accurately measure the weight of the slab even without a weighing machine.

[0006] The present invention has been made in view of the above, and aims to provide a technology that enables the appropriate acquisition of information on the weight of a slab without having to measure the weight of the slab using a weighing machine. [Means for solving the problem]

[0007] From one perspective, the weight measuring device of the present invention is a device for measuring the weight of a slab while it is being transported, and is characterized by comprising: an imaging unit for imaging the slab being transported; an image processing unit for performing a projection transformation on the image of the slab obtained by imaging; and a calculation unit for calculating the weight of the slab from the projection transformed image.

[0008] From another perspective, the hot rolling line of the present invention comprises the weight measuring device described above, a heating furnace for heating a slab, a plurality of rolling mills for rolling the slab heated by the heating furnace, and a control unit for controlling the driving of the heating furnace and the plurality of rolling mills, wherein the control unit controls the heating time of the slab in the heating furnace or the rolling load in the plurality of rolling mills based on the weight of the slab measured by the weight measuring device.

[0009] Furthermore, from another perspective, the present invention is a method for measuring the weight of a slab while it is being transported, and is characterized by comprising: an imaging step of capturing an image of the entire slab being transported; an image processing step of performing a projection transformation on the image of the entire slab obtained by imaging; and a calculation step of calculating the weight of the slab from the projection transformed image. [Effects of the Invention]

[0010] According to this disclosure, it is possible to appropriately obtain information on the weight of the slab without having to measure the weight of the slab using a weighing machine. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a schematic diagram illustrating the flow of the process for manufacturing steel sheets. [Figure 2] Figure 2 is a schematic diagram illustrating an example of a continuous casting machine. [Figure 3] Figure 3 is a schematic diagram illustrating an example of a hot rolling line. [Figure 4] Figure 4 is a schematic diagram showing an example of a conveyor system installed between a continuous casting machine and a heating furnace in a hot rolling line. [Figure 5] Figure 5 is a schematic side view showing the positional relationship between the conveying surface of the conveyor and the imaging device. [Figure 6] Figure 6 is a schematic block diagram illustrating an example of the configuration of a weight measuring device. [Figure 7] Figure 7 is a schematic flowchart showing an example of the process for measuring the weight of a slab. [Figure 8] Figure 8(a) shows an example of an image of a transport table captured by an imaging device, and Figure 8(b) shows an example of an image obtained by performing aberration correction processing and projection transformation processing on the image shown in Figure 8(a). [Figure 9] Figure 9(a) shows an example of an image of a transport table and slab captured by an imaging device, and Figure 9(b) shows an example of an image obtained by performing aberration correction processing and projection transformation processing on the image shown in Figure 9(a). [Figure 10] Figure 10(a) shows the error between the calculated value and the measured value of the slab's weight, Figure 10(b) shows the error between the calculated value and the measured value of the volume of each of the two slabs, and Figure 10(c) shows the error between the calculated value and the measured value of the length of each of the five slabs. [Modes for carrying out the invention]

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. As shown in Figure 1, the steel sheet is produced through processes such as a continuous casting process and a hot rolling process. The continuous casting process is a process in which molten steel 31 (see Figure 2), which has had impurities removed and its composition adjusted, is drawn out of a mold 13 (see Figure 2), and the continuously cast slab produced by cooling the molten steel 31 during the process of drawing it out of the mold 13 is cut to a predetermined size to produce, for example, a steel billet (hereinafter referred to as a slab). The hot rolling process is a process in which the slab heated in a heating furnace 41 (see Figure 3) is rolled to a predetermined plate thickness, and then cooled to produce a steel material of the desired plate thickness. The steel sheet produced by the hot rolling process is wound into a coil.

[0013] Figure 2 is a schematic diagram illustrating an example of a continuous casting machine 10. The continuous casting machine 10 is a device used in the continuous casting process described above. As shown in Figure 2, the continuous casting machine 10 is, for example, a vertical bending type continuous casting machine. The continuous casting machine 10 includes a ladle 11, a tundish 12, a mold 13, a plurality of support rolls 14, a cooling device 15, and a gas cutting machine (torch) 16.

[0014] In the continuous casting machine 10 having the above-described configuration, the molten steel 31 supplied to the ladle 11 is fed to the tundish 12 through the refractory nozzle 11a, and the molten steel 31 supplied to the tundish 12 is fed to the mold 13 through a refractory nozzle 12a called an immersion nozzle. The mold 13 is vibrated by a vibration device (not shown) so as not to stick. Further, an electromagnetic stirring device (not shown) is provided in the mold 13. The electromagnetic stirring device is provided to improve the central segregation of the continuously cast slab 32 by stirring (electromagnetic stirring) the molten steel fed into the mold 13.

[0015] A cooling zone 21 is provided below the mold 13. In the cooling zone 21, the above-described support rolls 14 and the cooling device 15 are arranged. The cooling device 15 cools the molten steel 31 from the outside by spraying cooling water in a mist form from a spray nozzle. By the cooling by the cooling device 15, the molten steel 31 supported by the plurality of support rolls 14 is guided in the horizontal direction while promoting the growth of the solidified shell, and then becomes the continuously cast slab 32 whose bending is corrected.

[0016] The gas cutting machine (torch) 16 is a device for cutting the continuously cast slab 32. The gas cutting machine 16 moves along the continuously cast slab 32 according to the casting speed in the continuous casting machine 10, and cuts the continuously cast slab 32 into a predetermined length, thereby generating a slab 33.

[0017] FIG. 3 is a schematic diagram showing an example of the hot rolling line 40. The hot rolling line 40 performs the above-described hot rolling process. As shown in FIG. 3, the hot rolling line 40 includes a heating furnace 41, a descaling device 42, a width reduction press device 43, a rough rolling mill 44, a finishing rolling mill 45, a cooling facility 46, a coiler 47, a control device 48, and an imaging device 54.

[0018] The slab 33 produced by the continuous casting machine 10 is conveyed toward the heating furnace 41 by the conveying conveyors 51 and 52 described later and charged into the heating furnace 41. The slab 33 charged into the heating furnace 41 is heated to a predetermined set temperature and extracted from the heating furnace 41 as a heated slab (hot slab). The heated slab is conveyed to the descaling device 42. In the descaling device 42, the scale formed on the surface of the heated slab is removed. The heated slab from which the scale has been removed is width-reduced to a predetermined set width in the width reduction press device 43. Thereafter, the heated slab is rolled to a predetermined thickness by the rough rolling mill 44 and then conveyed to the finishing rolling mill 45 as a rough bar. The rough bar conveyed to the finishing rolling mill 45 is rolled to the product thickness by, for example, a 7-stand continuous rolling mill. A cooling facility 46 is provided on the downstream side of the finishing rolling mill 45. The cooling facility 46 cools the hot rolled steel sheet produced by rolling in the finishing rolling mill 45 to a predetermined temperature. The coiler 47 winds up the hot rolled steel sheet into a coil shape. Hereinafter, the hot rolled steel sheet may be referred to as a rolled steel sheet.

[0019] The control device 48 calculates the weight of the slab 33 charged into the heating furnace 41 from the image captured by the imaging device 54 and controls each part of the hot rolling line (mill pacing control) based on the calculated weight of the slab 33. Specifically, the control device 48 obtains, by calculation (prediction calculation), the positions of the front end and the rear end of the slab 33 and the time when the front end of the slab 33 reaches the target position from the calculated weight of the slab 33. Further, the control device 48 obtains, by calculation, the heating time of the slab 33 in the heating furnace 41, the pressure during width reduction of the heated slab in the width reduction press device 43, and the rolling load in the rough rolling mill 44 and the finishing rolling mill 45. Then, the control device 48 controls each part of the hot rolling line 40 based on the various values obtained.

[0020] As shown in Figure 4, the slab 33 described above is transported to the heating furnace 41 by a conveyor 51 and a conveying table 52, which are provided between the continuous casting machine 10 and the hot rolling line 40. The imaging device 54 images the slab 33 being transported toward the heating furnace 41 by the conveying table 52 from above the conveying table 52. The conveying table 52 corresponds to the conveying means described in the claim.

[0021] As shown in Figure 5, the imaging device 54 is positioned at a height H from the transport surface 52a of the transport table 52, and captures an image of the entire slab 33 being transported toward the heating furnace 41 from an oblique upward position upstream of the transport table 52. Here, the height H is, for example, 2.3m. The imaging device 54 performs imaging when the distance D1 from the intersection point P1 of the vertical line L1 passing through the center P0 of the imaging device 54 and the transport surface 52a of the transport table 52 to the center P2 of the lower surface of the slab 33 is 2 to 5m. At this time, the distance D2 from the center P0 of the imaging device 54 to the center P2 of the lower surface of the slab 33 is, for example, 3 to 5m. Since it is sufficient for the imaging device 54 to capture an image of the entire slab 33, the distance D2 from the center P0 of the imaging device 54 to the center P2 of the lower surface of the slab 33 is preferably 10.5m or less. The imaging device 54 transmits the captured image to the control device 48.

[0022] As shown in Figure 6, the control device 48 and the imaging device 54 described above constitute the weight measuring device 60 in this embodiment. The weight measuring device 60 is a device that measures the weight of the slab 33 from the image of the entire slab 33 acquired by the imaging device 54.

[0023] The control device 48, which constitutes the weight measuring device 60, has the functions of a main control unit 61, an image processing unit 62, an image identification unit 63, and a calculation unit 64. In Figure 5, only the part that calculates the weight of the slab is shown, and the other parts are omitted. The main control unit 61 controls the drive of the imaging device 54, as well as the operation of the image processing unit 62, the image identification unit 63, and the calculation unit 64.

[0024] The image processing unit 62 performs aberration correction processing and projection transformation processing on the image acquired by the imaging device 54. The aberration correction processing corrects lens aberrations and other distortions contained in the image captured by the imaging device 54. The projection transformation processing transforms the image of the slab 33 contained in the image captured by the imaging device 54 so that it matches or is similar to the planar shape of the slab 33 in real space.

[0025] The image identification unit 63 performs feature extraction on the image that has undergone projection transformation processing to identify the region of the slab 33.

[0026] The calculation unit 64 calculates the length, width, and height of the slab 33 from the region of the slab 33 identified by the image identification unit 63. Here, the length, outer diameter, and spacing of the transport rollers 52c of the transport table 52 are set in advance. Therefore, the length per pixel can be calculated from the number of pixels of the transport rollers 52c included in the captured image. Accordingly, the calculation unit 64 determines the length, width, and height of the slab 33 from the number of pixels included in the identified region of the slab 33 and the length per pixel.

[0027] Furthermore, the calculation unit 64 calculates the weight of the slab 33, as captured by the imaging device 54, from the calculated length, width, and height values ​​of the slab 33 and the weight per unit volume of the steel material obtained in advance. The calculated weight of the slab 33 is output to the main control unit 61. In addition to performing the prediction calculations described above, the main control unit 61 determines the heating time of the slab 33 in the heating furnace 41, the pressure during width reduction of the slab 33 in the width reduction press device 43, and the rolling load in the roughing mill 44 and the finishing mill 45. The main control unit 61 then controls each part of the hot rolling line 40 based on the various values ​​obtained.

[0028] Next, the control of the hot rolling line 40 will be explained using the flowchart in Figure 7.

[0029] In step S101, the main control unit 61 determines whether or not the entire slab 33 has been imaged. This process is performed depending on whether or not an image of the entire slab 33 has been transmitted from the imaging device 54. Here, the timing for the imaging device 54 to image the entire slab 33 can be, for example, a predetermined time after the slab 33 is detected by a detection sensor (not shown). Alternatively, the main control unit 61 of the control device 48 may detect the entire slab 33 from the moving image captured by the imaging device 54.

[0030] When the control device 48 receives an image from the imaging device 54, the main control unit 61 of the control device 48 determines that the entire slab 33 has been imaged (determination process in step S101: Yes). In this case, the process proceeds to step S102. On the other hand, if the control device 48 has not received an image from the imaging device 54, the main control unit 61 determines that the entire slab 33 has not been imaged (determination process in step S101: No). In this case, the process in step S101 is repeatedly executed until the main control unit 61 determines that the entire slab 33 has been imaged.

[0031] In step S102, the image processing unit 62 of the control device 48 performs aberration correction processing and projection transformation processing on the image. As shown in Figures 8(a) and 8(b), image P1' is an image obtained by applying aberration correction processing and projection transformation processing to image P1 captured by the imaging device 54. Also, as shown in Figures 9(a) and 9(b), image P2' is an image obtained by applying aberration correction processing and projection transformation processing to image P2 captured by the imaging device 54. That is, in the projection transformation processing in the image processing unit 62, the transformation parameters in the projection transformation processing are set in advance so that the lengths of each transport roller 52c of the transport table 52 become the same length. Therefore, as shown in Figures 9(a) and 9(b), by performing aberration correction processing and projection transformation processing on image P2, an image P2' is obtained in which the shape of the slab 33 in plan view matches the planar shape of the slab 33 in real space.

[0032] In step S103, the image identification unit 63 of the control device 48 identifies the region of the slab 33 from the image that has undergone projection transformation processing. Then, the calculation unit 64 of the control device 48 calculates the length, width, and height of the slab 33 from the identified region of the slab 33.

[0033] In step S104, the calculation unit 64 calculates the weight of the slab 33 using the length, width, and height of the slab and the weight per unit volume obtained in step S103. The calculation unit 64 outputs the calculated weight of the slab 33 to the main control unit 61.

[0034] In step S105, the main control unit 61 performs the prediction calculations described above, and also calculates the heating time of the slab 33, the pressure when the width of the heated slab is reduced in the width reduction press device 43, and the rolling load in the roughing mill 44 and the finishing mill 45. Based on the various values ​​obtained by the calculations, the main control unit 61 sets the processing content (processing content in the hot rolling process) for each device in the hot rolling line 40.

[0035] In step S106, the main control unit 61 drives and controls each device of the hot rolling line 40 based on the processing content set in step S105.

[0036] According to this, in the hot rolling line 40, processing in each part of the hot rolling line 40 is performed based on the weight of the slabs 33 being transported. For example, if the weight of the slabs 33 varies, the line operators would need to manually make adjustments to compensate for the variation. However, in this embodiment, the weight of the slabs 33 can be accurately determined from the image, so there is no need for the line operators to make adjustments to compensate for the variation. Furthermore, when mill pacing control is used, not only is control associated with the movement of each slab 33 accurately performed, but control in each device of the hot rolling line 40 (for example, control from the time the slabs 33 are loaded into the heating furnace 41 until the heated slabs 33 are removed from the heating furnace 41) can also be accurately performed. As a result, it is possible to suppress the deterioration of the quality of rolled steel sheets produced by the hot rolling line and the decrease in its productivity.

[0037] Finally, the measurement error results for the slab 33 produced in the continuous casting machine 10 will be explained. Figure 10(a) shows the error between the calculated value obtained by the above calculation and the measured weight of the slab 33 (Example 1). The range of error for the measured value that is valid for the slab 33 was set to be within three times the standard deviation σ1 of the error between the measured value and the planned value of the weight of the slab 33 (±3σ1). As shown in Figure 10(a), the error between the measured value and the measured weight of the slab 33 was approximately -0.2%, which was found to be within the error range (±3σ1).

[0038] Figure 10(b) shows the error between the calculated values ​​obtained by the above calculation and the measured volumes of the two slabs 33 (Examples 2 and 3). The range of error in the measured values ​​that is valid for the slab 33 was set to be within three times the standard deviation σ² of the error between the measured value and the planned value of the slab 33 volume (±3σ²).

[0039] As shown in Figure 10(b), in Example 1, the error between the calculated value and the measured value of the slab 33 volume was approximately 1.5%. In Example 2, the error between the calculated value and the measured value of the slab 33 volume was approximately 1.2%. In other words, in both Example 1 and Example 2, the error between the calculated value and the measured value of the slab 33 volume was found to be within a range of three times the standard deviation σ² of the error between the measured value and the planned value of the slab 33 volume (±3σ²).

[0040] Figure 10(c) shows the error between the calculated values ​​obtained by the above calculation and the measured lengths of the five slabs 33 (Examples 4 to 7). The range of error in the measured values ​​that is valid for the slab 33 was set to within three times the standard deviation σ3 of the error between the measured value and the planned value of the slab length (±3σ3).

[0041] As shown in Figure 10(c), in Example 3, the error between the calculated value and the measured value of the slab 33 length was approximately 0.6%. In Example 4, the error between the calculated value and the measured value of the slab 33 length was approximately -0.7%. In Example 5, the error between the calculated value and the measured value of the slab 33 length was approximately 0.9%. In Example 6, the error between the calculated value and the measured value of the slab 33 length was 0.0%. In Example 7, the error between the calculated value and the measured value of the slab 33 length was approximately 0.1%. In other words, in each of Examples 3 to 7, the error between the calculated value and the measured value of the slab 33 length was found to fall within a range of three times the standard deviation σ3 of the error between the measured value and the planned value of the slab 33 length ((±3σ3)).

[0042] In other words, using the method shown in this embodiment, it becomes possible to accurately calculate the weight, volume, or length of a slab. Therefore, even if there is no weighing machine in the continuous casting machine, on the transfer path from the continuous casting machine to the hot rolling line, or in any of the rolling equipment, it becomes possible to control the hot rolling process according to the slab.

[0043] Furthermore, when mill pacing control is implemented, it becomes possible to accurately predict and calculate the positions of the preceding slab and the following slab, thereby enabling effective transport of both slabs. As a result, it becomes possible to manufacture rolled steel sheets efficiently.

[0044] In this embodiment, a hot rolling line that produces a strip-shaped rolled steel sheet from a single slab is illustrated. However, a hot rolling line that produces a strip-shaped rolled steel sheet by joining steel sheets produced from two slabs as they travel from the roughing mill to the finishing mill is also possible. In this case, it is necessary to wind the steel sheet rolled in the roughing mill into a coil. In this case, the processing time of the slab that produces the steel sheet first and the processing time of the slab that produces the replacement sheet later must be accurately determined. By accurately determining the weight of the two slabs, it becomes possible to join the two steel sheets without waste.

[0045] In this embodiment, the imaging device 54 captures an image that covers the entire slab 33, but it is also possible to obtain an image of the entire slab 33 by taking multiple images with the imaging device 54.

[0046] In this embodiment, the images acquired by the imaging device 54 are not specifically mentioned, but they may be still images or moving images.

[0047] <Summary of effects> The weight measuring device 60 of this embodiment is a device for measuring the weight of a slab 33 while it is being transported, and is characterized by comprising an imaging device 54 for imaging the slab 33 being transported, an image processing unit 62 for performing a projection transformation on the image of the slab 33 obtained by imaging, and a calculation unit 64 for calculating the weight of the slab 33 from the projection transformed image.

[0048] According to this method, it becomes possible to appropriately obtain information about the weight of the slab 33 from an image of the slab 33 without actually weighing the slab 33 with a weighing machine.

[0049] Furthermore, the slab 33 is produced in a continuous casting machine 10 that generates a continuous cast piece 32 by drawing out the molten steel 31 while cooling it, and also cuts the continuous cast piece 32 to a predetermined size. The imaging device 54 preferably captures an image of the slab 33 as it is transported from the continuous casting machine 10 toward the heating furnace 41 that heats the slab 33.

[0050] According to this, it is only necessary to install the imaging device 54 on the existing transport path between the continuous casting machine 10 and the heating furnace 41, thus eliminating the need to install a new weighing machine.

[0051] Furthermore, it is preferable that the heating furnace 41 is the heating furnace 41 of a hot rolling line 40 that produces a steel plate of a predetermined thickness by rolling the slab 33.

[0052] According to this, it is not necessary to shut down the continuous casting machine 10 and the hot rolling line 40 for a certain period of time in order to install a new weighing machine between them.

[0053] Furthermore, it is preferable that the imaging device 54 is positioned at a predetermined height above the transport surface 52a of the transport table 52 that transports the slab 33, and that the imaging device 54 captures an image of the entire slab 33 from diagonally above the slab 33 being transported by the transport table 52.

[0054] According to this method, an image of the entire slab 33 can be captured in a single scan, allowing for an accurate calculation of the slab 33's weight.

[0055] Furthermore, the transport table 52 has a plurality of transport rollers 52c, and it is preferable that the image processing unit 62 sets the transformation parameters for the projection transformation of the slab 33 to the overall image of the slab 33 such that the length of each of the plurality of transport rollers 52c included in the image of the transport table 52 obtained by the imaging device 54 is constant.

[0056] According to this method, by setting the transformation parameters for the projection transformation based on the transport table 52 included in the image, it becomes possible to accurately calculate the size (length, width, and thickness) of the slab 33 included in the image after the projection transformation. [Explanation of Symbols]

[0057] 10 Continuous casting machines 31 Molten steel 32 continuous cast slabs 33 Slabs 40 Hot Rolling Line 41 Heating furnace 44 Roughing mill 45 Finishing Rolling Mill 48 Control device 52 Transport Table 52c Conveyor Roller 54 Imaging device 60 Weight measuring device 61 Main Control Unit 62 Image Processing Unit 64 Arithmetic section

Claims

1. A device for measuring the weight of a slab during its transport, An imaging unit for imaging the slab being transported, An image processing unit that performs a projection transformation on the image of the slab obtained by the aforementioned imaging, A calculation unit that calculates the weight of the slab from the projected image, A weight measuring device characterized by having the following features.

2. The slab is produced by a continuous casting machine that generates a continuous cast slab by drawing out molten steel while cooling it, and also cuts the continuous cast slab to a predetermined size. The imaging unit captures an image of the slab as it is transported from the continuous casting machine toward the heating furnace that heats the slab. The weight measuring device according to feature 1.

3. The heating furnace is a heating furnace in a hot rolling line that produces steel plates of a predetermined thickness by rolling the slab. The weight measuring device according to feature 2.

4. The imaging unit is positioned at a predetermined height from the transport surface of the transport means that transports the slab. The imaging unit captures an image of the entire slab from diagonally above the slab being transported by the transport means. The weight measuring device according to feature 2.

5. The imaging distance of the slab in the imaging unit is within 10.5 m. The weight measuring device according to feature 4.

6. The conveying means has a plurality of conveying rollers, The image processing unit sets the transformation parameters for the projection transformation applied to the image of the entire slab so that the length of each of the multiple transport rollers included in the image of the transport means obtained by the imaging unit becomes constant. The weight measuring device according to feature 4.

7. A weight measuring device according to any one of claims 1 to 6, A heating furnace for heating the slab, Multiple rolling mills for rolling the slab heated by the aforementioned heating furnace, A control unit that controls the drive of the heating furnace and the plurality of rolling mills, It has, The hot rolling line is characterized in that the control unit controls the heating time of the slab in the heating furnace or the rolling load in the plurality of rolling mills based on the weight of the slab measured by the weight measuring device.

8. A method for measuring the weight of a slab during its transport, An imaging step to capture an image of the entire slab being transported, An image processing step is performed on the image of the entire slab obtained by the aforementioned imaging, and A calculation step of calculating the weight of the slab from the projected image, A method for measuring weight characterized by having the following features.

9. The slab is produced in a continuous casting machine that generates a continuous cast slab by drawing out molten steel while cooling it, and then cuts the continuous cast slab to a predetermined size. The imaging step involves capturing an image of the entire slab as it is being transported from the continuous casting machine towards a heating furnace for heating the slab. The weight measurement method according to feature 8.

10. A conveying means for conveying the slab from the continuous casting machine to the heating furnace, An imaging unit positioned at a predetermined height from the transport surface of the transport means, It has, The imaging step involves the imaging unit capturing an image of the entire slab being transported from the continuous casting machine toward the heating furnace, from diagonally above the transport conveyor. The weight measurement method according to feature 9.

11. The imaging distance of the slab in the imaging unit is within 10.5 m. The weight measurement method according to feature 10.

12. The conveying means has a plurality of conveying rollers, The image processing unit sets the transformation parameters for the projection transformation applied to the image of the entire slab so that the length of each of the multiple transport rollers included in the image of the transport means obtained by the imaging unit becomes constant. The weight measurement method according to feature 10.

Images