Method and device for measuring loop state of plate material, and rolling method of plate material

Abstract

To provide a plate material loop state measurement apparatus and the like which can accurately and stably measure the loop state of a plate material.SOLUTION: A loop state measurement apparatus 100 according to the present invention comprises: 2 two-dimensional imaging devices 1, 2 which are provided along the width direction of a plate material S and generate photographed images by performing imaging such that an edge of the plate material is included within an imaging visual field from above a pass line PL of a hot-rolling line; and a calculation device 3 which calculates coordinates of the edge of the plate material at a plurality of positions in the rolling direction of the plate material by using a method of stereo three-dimensional view on the basis of the photographed images and calculates the length of the edge of the plate material S between 2 pairs of roll pairs WRa, WRb adjacent to each other on the basis of the calculated coordinates of the edge of the plate material at the plurality of positions.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a method and device for measuring the loop state of a plate material (presence or absence of a loop and the degree of the loop) in a hot rolling line for the plate material such as a hot-rolled steel plate, and a rolling method for the plate material using the same. [Background technology]

[0002] FIG. 1 is a diagram showing a schematic diagram of an example of the equipment configuration of a hot rolling line for hot-rolled steel sheets. FIG. 1(a) is an overall diagram, and FIG. 1(b) is an enlarged diagram of the periphery of the sixth and seventh rolling stands shown surrounded by a dashed line in FIG. 1(a). The finishing mill in the hot rolling line for hot-rolled steel sheets is composed of 6 to 7 rolling mills (hereinafter referred to as "rolling stands") arranged horizontally at intervals of, for example, about 5.5 m. Each rolling stand is numbered, such as the first rolling stand and the second rolling stand, in order from the upstream side in the rolling direction (transport direction) of the plate material S. As shown in FIG. 1(b), each rolling stand is provided with work rolls WRa and WRb arranged opposite each other above and below, which press and roll the plate material S sandwiched therebetween, and backup rolls BRa and BRb which support them. Then, the plate material S, called a rough bar, having dimensions of 30-60 mm in thickness, 700-2100 mm in width, and about 70 m in length at the entrance of the finishing mill, is successively rolled in each rolling stand of the finishing mill at a high temperature of about 1000°C, and thinned to a predetermined product thickness of 1.2 to several mm at the final rolling stand (the seventh rolling stand in the example shown in Fig. 1). The temperature of the plate material S at the exit of the final rolling stand is 850-950°C, and the speed of the plate material S is accelerated from the front end to the rear end in order to suppress a drop in temperature of the plate material S, with the maximum speed being 1600 mpm.

[0003] As shown in FIG. 1(b) by way of example focusing on the sixth rolling stand F6 and the seventh rolling stand F7, a looper LP is provided between each rolling stand of the finishing rolling mill to apply tension to the plate material S and stabilize the passing of the plate. The looper LP comprises a looper roll LR and a looper arm LA. The looper roll LR is held at the tip of the looper arm LA, and by raising and lowering the looper roll LR by rotating the looper arm LA, the plate material S in contact with it is raised and lowered, absorbing the slack of the plate material S between the rolling stands and applying an appropriate tension. Usually, the tension applied to the plate material S during rolling in the finishing rolling mill is about 1 kg / mm 2 It is considered desirable. If the tension applied to the plate material S becomes smaller than this tension, the plate material S will meander and the threading will become unstable, and if the tension becomes larger, the width of the plate material S will shrink, causing defects in the width dimensions and reducing the product yield. In particular, when the leading edge of the plate material S is passed through each rolling stand of the finishing rolling mill, the plate material S is in an untensioned state, so it is the most difficult part of the rolling process to ensure the product dimensions while stably threading the plate material S. An electric motor or hydraulic motor is used as the drive device for the looper LP (the device that rotates the looper arm LA).

[0004] A conventional method for rolling a plate material S in a finishing mill will be described below. In the conventional rolling method, the setup control of the finishing mill, the looper control during threading of the leading edge of the strip material, and the tension control mode are executed in this order. These will be described in order below.

[0005] <Finishing mill setup control> In the setup control of the finishing rolling mill, when the leading end of the sheet material S is rolled by being bitten into each rolling stand in order, the opening (roll gap amount) and circumferential speed of the work rolls WRa and WRb of each rolling stand are set in advance by a process computer based on the predicted values ​​of the deformation resistance and temperature of the sheet material S. In the setup control, the target thickness of each rolling stand (first to seventh rolling stands in the example shown in FIG. 1) is first determined, and the opening of the work rolls WRa and WRb of each rolling stand is determined based on the predicted values ​​of the deformation resistance and temperature of the sheet material S in each rolling stand. Next, the speed V7 of the sheet material S on the exit side of the final rolling stand (seventh rolling stand F7 in the example shown in FIG. 1) is determined taking into consideration the temperature drop of the sheet material S during finish rolling, and the circumferential speed (roll circumferential speed) of the work rolls WRa and WRb of each rolling stand is determined so that the speed of the sheet material S on the exit side of each rolling stand is balanced.

[0006] If an arbitrary i-th rolling stand is the i-th rolling stand, the speed V of the strip S at the exit of the i-th rolling stand is i is the roll peripheral speed V of the i-th rolling stand Ri and the forward advance rate f i Using the above, it can be expressed as the following equation (1): i is a constant that expresses the ratio of slip between the work rolls WRa, WRb and the sheet material S, and a predicted value based on rolling theory or experimental values ​​is used. V i =V Ri (1+f i ) · · · (1) Therefore, the volume velocity Q of the strip S at the exit of the i-th rolling stand i is the thickness (thickness) of the plate material S at the exit of the i-th stand i and width (board width) W i Using this, it can be expressed as the following equation (2). Q i =W i t i ·V i =W i t i ·V Ri (1+f i ) · · · (2)

[0007] For example, if there are seven rolling stands, the volume velocity Q of the strip material S at the exit of the seventh rolling stand F7, which is the final rolling stand, is i can be expressed as the following equation (3) by substituting i=7 into the above equation (2). Q7=W7·t7·V R7 (1+f7) (3)

[0008] In order to balance the speed of the strip material S at the exit of each rolling stand and to prevent excessive loops or excessive tension between each rolling stand, the volume speed Q7 of the strip material S at the exit of the seventh rolling stand F7, which is the final rolling stand, and the volume speed Q of the strip material S at the exit of each rolling stand i In other words, the following formula (4) must be satisfied. W i t i ·V Ri (1+f i )=W7 t7 V R7 (1+f7) (4)

[0009] In the above formula (4), the plate width W i does not change at the exit of each rolling stand (the amount of change is negligible), so W i = W7. Substituting this into the above equation (4) and rearranging it, we get the roll peripheral speed V of the i-th rolling stand. Ri is expressed by the following equation (5). V Ri =t7 V R7 (1+f7) / {t i (1+f i )}···(5) V on the right side of the above equation (5) R7 As described above, is calculated by formula (1) using the speed V7 of the strip material S on the outlet side of the seventh rolling stand F7, which is the final rolling stand, determined taking into account the temperature drop of the strip material S during finish rolling. In setup control, V calculated by this formula (5) Ri The roll peripheral speed of each rolling stand is set using

[0010] <Looper control when threading the leading edge of a plate> Fig. 2 is a schematic diagram of a rolling control device in a state where control is executed when the leading end of a sheet material S passes through the i-th rolling stand and the i+1-th rolling stand. Specifically, Fig. 2 shows a state where the leading end of the sheet material S passes between the i-th rolling stand and the i+1-th rolling stand, and the leading end of the sheet material S is engaged in the i+1-th rolling stand to control the looper LP. Note that the pass line PL shown in Fig. 2 means a straight line connecting the apex (top in the vertical direction) of the roll (work roll Wb of the i-th rolling stand) located below the roll pair (work rolls Wa, Wb of the i-th rolling stand) located upstream in the rolling direction of the sheet material S, and the apex (top in the vertical direction) of the roll (work roll Wb of the i+1-th rolling stand) located below the roll pair (work rolls Wa, Wb of the i+1-th rolling stand) located downstream in the rolling direction of the sheet material S. As shown in FIG. 2, the speed controller controls the peripheral speeds of the work rolls WRa and WRb of the i-th rolling stand. The roll peripheral speed (set peripheral speed) V Ri By transmitting this, the speed control device detects the work rolls WRa and WRb at the roll peripheral speed V Ri Similarly, the process computer controls the speed controller that controls the peripheral speed of the work rolls WRa and WRb of the (i+1)th rolling stand to control the roll peripheral speed (set peripheral speed) V of the (i+1)th rolling stand calculated by the setup control. Ri+1 By transmitting this, the speed control device detects the work rolls WRa and WRb at the roll peripheral speed V Ri+1 The drive device M of the work rolls WRa and WRb is controlled so that the work rolls WRa and WRb of the i-th rolling stand rotate at a peripheral speed V Ri The work rolls WRa and WRb of the (i+1)th rolling stand rotate at a peripheral speed of V Ri+1 Rotate in advance with .

[0011] The leading edge of the plate material S that has passed through the i-th rolling stand advances while being supported by the upper side (left side in Figure 2) of the looper arm LA of the looper LP waiting at the lower limit position, passes through the looper roll LR, and enters the roll gap (the gap between the work rolls WRa and WRb) of the i+1th rolling stand while being supported by a side guide (not shown) on the entry side of the i+1th rolling stand. When a load cell (not shown) detects that a rolling load has been generated in the (i+1) rolling stand as a result of the leading edge of the plate material S entering the roll gap of the (i+1) rolling stand, the torque control device connected to the looper LP transmits a start-up command (raise command) to the drive device M of the looper LP. At this time, the torque control device also transmits the value of the start-up torque Ts transmitted from the process computer to the drive device M. As a result, the drive device M of the looper LP raises the looper roll LR with a constant torque Ts (raises at a constant speed), and after a predetermined time has elapsed, transitions to tension control mode.

[0012] <Tension control mode> FIG. 3 is a diagram showing a schematic diagram of the rolling control device in a state in which the tension control mode is executed. As shown in FIG. 3, in the tension control mode, the torque control device connected to the looper LP converts the actual tension T of the plate material S (the tension of the plate material S actually measured by the tension meter TM) into the target tension T transmitted from the process computer. aim Specifically, the torque control device controls the torque acting on the looper roll LR so that the actual tension T approaches the target tension T. aim The torque value approaching the torque (hereinafter referred to as "control torque") is calculated and transmitted to the drive device M of the looper LP. As a result, the drive device M of the looper LP applies the control torque to the looper roll LR. As the tension meter TM, for example, a configuration in which the tension is calculated using a load meter attached to the looper arm LA, or a configuration in which the tension is calculated from the torque record of the drive device M of the looper LP can be used. In the tension control mode, the speed control device that controls the peripheral speeds of the work rolls WRa and WRb of the i-th rolling stand adjusts the actual angle θ of the looper roll LR (the angle of the looper roll LR from the horizontal direction measured by the angle meter AM) to the target angle θ transmitted from the process computer. aim Set the peripheral speed V Ri Specifically, the speed control device controls the peripheral speeds of the work rolls WRa and WRb of the i-th rolling stand by correcting the actual angle θ to the target angle θ aim The value of the peripheral speed of the work rolls WRa, WRb that approaches the target angle θ (hereinafter, this will be referred to as the "controlled peripheral speed") is calculated and transmitted to the drive device M of the work rolls WRa, WRb. As a result, the drive device M of the work rolls WRa, WRb rotates the work rolls WRa, WRb at the controlled peripheral speed. Note that the actual angle θ of the looper roll LR is equal to the target angle θ aim When the actual angle θ is greater than the target angle θ, the speed control device reduces the peripheral speed of the work rolls WRa and WRb. aim When the target angle θ is smaller than the target angle θ, the peripheral speed of the work rolls WRa and WRb is accelerated. aim is generally in the range of 15 to 20° and is empirically set in consideration of the stability of the sheet material S passing between the rolling stands, tension controllability, etc. As the angle meter AM, for example, a rotary encoder attached to the rotating shaft of the driving device M of the looper LP can be used.

[0013] In the rolling method of the plate material S in the conventional finishing rolling mill described above, the forward slip rate predicted based on rolling theory and experimental values ​​contains an error, so when the leading edge of the plate material S passes through each rolling stand, the speed balance of the plate material S at the exit of each rolling stand calculated based on the forward slip rate is lost, and a loop or excessive tension may occur. The occurrence of a loop is a state in which the plate material S is not in contact with the looper roll LR even after the looper roll LR has completed starting up (rising) and the system has transitioned to tension control mode, and if an excessive loop occurs, tension control becomes impossible, causing rolling trouble. Excessive tension occurs when the target angle θ immediately after the looper roll LR starts to start up (rising) aimBelow this point, the looper roll LR comes into contact with the strip S, and the looper roll LR continues to rise, causing excessive tension on the strip S, which causes the strip S to shrink in width and reduces the yield. For this reason, the operator of the finishing rolling mill visually monitors the state of the strip S between the rolling stands, and, if necessary, manually operates and corrects (ΔV shown in Fig. 2) the peripheral speeds of the work rolls WRa and WRb of the rolling stand (i-th rolling stand) located upstream. However, such operation by the operator can cause rolling troubles or a decrease in yield due to the strip width shrinkage due to delays in operation or an inappropriate correction amount of the peripheral speed. In addition, the volume speed of the strip S is empirically corrected and set, taking into account prediction errors of the forward rate based on rolling performance, but since such predictions are not perfect, various strip rolling technologies have been proposed in the past.

[0014] Conventionally proposed rolling technologies for plate materials can be roughly divided into two types: a technology that estimates the tension of the plate material by a torque meter or a load meter provided on the looper, and a technology that directly measures the loop state of the plate material by a sensor. As the former technology, for example, the technologies described in Patent Documents 1 and 2 have been proposed, and as the latter technology, for example, the technologies described in Patent Documents 3 and 4 have been proposed.

[0015] Patent Document 1 proposes a looper control device for a continuous hot rolling mill, which is provided with a looper height control system for controlling the speed of a looper drive motor so that a looper height detection value obtained by detecting the height of an electric looper installed between the stands follows a looper height target value, and a tension control system for controlling the speed of a main machine drive motor so that a tension detection value between the stands calculated based on the output of a load meter installed on the underside of the looper roll follows a tension target value, characterized in that the looper control device for a continuous hot rolling mill is provided with a strip separation detection means for detecting strip separation from the looper roll of the material between the stands, and a main machine speed correction means for adding a speed correction signal or a gain correction signal to the tension control system so as to reduce the loop of the material between the stands when the strip separation detection means detects strip separation" (Claims, etc. of Patent Document 1).

[0016] Patent Document 2 proposes a method for controlling the tension of the inter-stand louvers of a hot tandem rolling mill equipped with a device for detecting the driving torque of the looper and a device for converting the torque detected by the detection device into an inter-stand tension value as a function of the height of the looper roll, the method being characterized in that the looper roll is raised at a preset high speed in response to a command to raise the looper, and the torque for driving the looper is controlled after the inter-stand tension value falls within an allowable range of a preset target tension value until the inter-stand tension value coincides with the target tension value (Claims, etc. of Patent Document 2).

[0017] Patent Document 3 proposes "a speed setting device for a continuous rolling mill having multiple rolling stands for rolling the rolled material, the speed setting device comprising a means for detecting the amount of speed unbalance between the rolling stands and a speed correction means for correcting the rolling speed setting value for the next rolled material based on the amount of speed unbalance" (Claim 1 of Patent Document 3, etc.).

[0018] Patent Document 4 proposes a rolling control system comprising: "an imaging unit that is installed on the side between two adjacent stands among a plurality of stands that constitute a finishing rolling mill that rolls the rolled material to a predetermined product thickness, and images the side of the rolled material; an image processing unit that determines a loop amount of the rolled material between the two stands based on image data obtained by the imaging unit and compares the loop amount with a reference value; a rolling speed calculation unit that calculates an amount of change in rolling speed based on the distance between the two stands and the loop amount if the loop amount is greater than the reference value; and a rolling speed control unit that controls the rolling speed of the stand that is upstream of the two stands in the transport direction of the rolled material in accordance with the amount of change in speed" (Claim 1 of Patent Document 4, etc.). [Prior art documents] [Patent documents]

[0019] [Patent Document 1] Japanese Patent Application Publication No. 1-48616 [Patent Document 2] Japanese Patent Application Publication No. 54-117358 [Patent Document 3] Japanese Patent Application Publication No. 9-52107 [Patent Document 4] JP 2004-243365 A Summary of the Invention [Problem to be solved by the invention]

[0020] The technology disclosed in Patent Document 1 has a feature of being able to suppress strip separation, i.e., the occurrence of loops. However, according to the technology disclosed in Patent Document 1, the tension detection value between the rolling stands is calculated based on the output of a load meter installed on the underside of the looper roll, but the environment in which the looper roll is used is a high-temperature and high-vibration environment, and the load meter is prone to failure. For this reason, the technology disclosed in Patent Document 1 has a problem that maintenance is difficult. In addition, the technology disclosed in Patent Document 1 only assumes strip separation during rolling (after the strip is bitten by all the rolling stands). For this reason, the technology disclosed in Patent Document 1 also has a problem that it cannot handle a situation in which the leading end of the strip is bitten by the rolling stand.

[0021] According to the technology disclosed in Patent Document 2, if the tension value between the rolling stands can be accurately predicted, it is possible to appropriately stop the ascent of the looper roll without generating loops or excessive tension in the strip material, and it is considered possible to suppress rolling troubles. However, the calculation formula for the tension value disclosed in Patent Document 2 includes uncertain factors such as the weight of the strip material, and is derived on the premise that the strip material and the looper roll are in stable contact with each other, so there is a problem that it is not possible to detect strip separation when the strip material enters the rolling stand while overlapping. As described above, the technology of estimating the tension of the plate material by using a torque meter or a load meter provided on the looper does not directly measure the loop state of the plate material between the rolling stands, and therefore has a problem in that it is not possible to accurately determine the contact state between the plate material and the looper roll.

[0022] Patent Document 3 describes a configuration for detecting the speed unbalance between rolling stands, in which a plate speed sensor is used to measure the plate speed at the exit side of a rolling stand located on the upstream side and the plate speed at the entry side of a rolling stand located on the downstream side, and the amount of speed unbalance is calculated based on the measurement results. In order to measure the plate speed before the looper roll contacts the plate material, a non-contact plate speed sensor must be used, and a laser Doppler velocimeter is generally used. However, the space between the rolling stands of a finishing rolling mill is a poor environment filled with dust and steam, and a large amount of water droplets are scattered, so there is a problem that it is not easy to stably measure the speed of the steel plate using a laser Doppler velocimeter.

[0023] Patent Document 4 describes that the edge shape of a plate material is imaged from the side between the rolling stands of a finishing rolling mill using a two-dimensional camera as an imaging unit, the loop height is calculated from the image, and the length of the broken line connecting the apex of the lower work roll of the rolling stand located on the upstream side, the loop apex, and the apex of the lower work roll of the rolling stand located on the downstream side is calculated as the edge length of the plate material (plate length K in Patent Document 4). However, in a tensionless state, it is clear that the edge length of the plate material calculated (approximated) by the broken line connecting the apex of the lower work roll and the loop apex is shorter in principle than the actual edge length, and there is a large error. In addition, when imaging a plate material from the side between the rolling stands, it is difficult to actually image the plate material because of interference from a crane used in the operation and the limited field of view due to the housing and side guides of the rolling stands. As described above, the technique of measuring the loop state of a plate material using a plate speed sensor or an imaging means installed to the side of a hot rolling line has the problem that it is not possible to measure the loop state stably and with high accuracy.

[0024] The present invention has been made to solve the problems of the conventional technology as described above, and has an object to provide a method and device for measuring the loop state of a plate material, which are capable of measuring the loop state of the plate material stably with high accuracy, and a rolling method for plate material, which is capable of rolling the plate material stably by using the same. [Means for solving the problem]

[0025] In order to solve the above-mentioned problems, the inventors of the present invention conducted intensive research and found that, from the perspective of equipment maintenance between the rolling stands, space is secured above the rolling stands of a finishing rolling mill, and that if the plate material is imaged from above between the rolling stands using a two-dimensional imaging device, the inside of the side guide can also be imaged, thereby providing a wide measurement field of view in the rolling direction as well, and that if two two-dimensional imaging devices are used for stereoscopic viewing, the shape of the edge of the plate material, and ultimately the length of the edge of the plate material, can be measured accurately and stably. The present invention has been completed based on the above findings of the present inventors.

[0026] That is, in order to solve the above-mentioned problems, the present invention provides a method for measuring a loop state of a plate material in a hot rolling line in which a plurality of roll pairs, each consisting of rolls arranged opposite to one another above and below, are installed in the horizontal direction, the method comprising the steps of: capturing an image of the plate material from above a pass line of the hot rolling line using two two-dimensional imaging devices installed along the width direction of the plate material between two adjacent pairs of rolls among the plurality of roll pairs, so that an edge of the plate material is included within an imaging field of view to generate an image; calculating coordinates of the edge of the plate material at a plurality of points in the rolling direction of the plate material based on the captured image, and calculating the coordinates of the calculated edge of the plate material at the plurality of points. and a calculation step of calculating a length of the edge of the plate material between the two adjacent roll pairs based on coordinates of the image of the edge of the plate material between the two adjacent roll pairs, the two two-dimensional imaging devices being provided such that the directions of the optical axes when viewed from the rolling direction of the plate material are different from each other, and the calculation step includes detecting a position of the edge of the plate material in the image captured by the two two-dimensional imaging devices, calculating distances from the two two-dimensional imaging devices to the edge of the plate material at the multiple locations based on the position of the edge of the plate material in the detected captured image, and calculating coordinates of the edge of the plate material at the multiple locations in the rolling direction of the plate material based on the calculated distances and a geometric arrangement condition of the two two-dimensional imaging devices. and as the length of the edge of the plate material between the two adjacent sets of roll pairs, a length of a broken line connecting a vertex of a roll located on the lower side of the roll pair located on the upstream side in the rolling direction of the plate material among the two adjacent sets of roll pairs, the calculated coordinates of the edge at the multiple locations, and a vertex of a roll located on the lower side of the roll pair located on the downstream side in the rolling direction of the plate material among the two adjacent sets of roll pairs is calculated. A method for measuring the loop state of a plate material is provided.

[0027] In the method for measuring the loop state of a plate material according to the present invention, the term "roll pair" is not limited to rolling rolls (work rolls) that press and roll the plate material sandwiched therebetween, but also includes a concept of a restraining roll (a roll capable of applying tension to the plate material by controlling the peripheral speed of the roll, such as a pinch roll or a bridle roll) that applies tension to the plate material sandwiched therebetween (but does not roll it). In addition, the term "pass line" refers to a straight line connecting the apex (topmost part in the vertical direction) of the roll located below the roll pair located upstream in the rolling direction of the plate material, among two adjacent roll pairs, with the apex (topmost part in the vertical direction) of the roll located below the roll pair located downstream in the rolling direction of the plate material. In addition, the term "edge" refers to an edge (widthwise end part of the plate material) in the width direction (direction perpendicular to the rolling direction) of the plate material. The edges of the plate material imaged in the imaging step of the plate material loop state measuring method according to the present invention do not necessarily have to be both edges forming both ends in the width direction of the plate material, but may be either one of the edges. However, when either one of the edges is imaged, the edge imaged by the two two-dimensional imaging devices is the edge on the same side. According to the method for measuring the loop state of a plate material according to the present invention, in the imaging step, two two-dimensional imaging devices are provided along the width direction of the plate material and have different optical axis (visual axis) directions when viewed from the rolling direction of the plate material, and images are taken from above the pass line of the hot rolling line so that the edge of the plate material is included in the imaging field of view. Then, in the calculation step, coordinates of the edge of the plate material at multiple points in the rolling direction of the plate material are calculated by a so-called stereoscopic vision method using the images of the plate material captured from different directions by the two two-dimensional imaging devices, and the length of the edge of the plate material between two adjacent roll pairs is calculated based on the coordinates of the edge of the plate material at multiple points. Specifically, the stereoscopic vision technique in the plate material loop state measuring method of the present invention detects the position of the edge of the plate material in an image of the plate material captured by two two-dimensional imaging devices, calculates the distances from the two two-dimensional imaging devices to the edge of the plate material at multiple locations based on the position of the edge of the plate material in the detected image, and calculates the coordinates of the edge of the plate material at multiple locations in the rolling direction of the plate material based on the calculated distances and the geometric arrangement conditions of the two two-dimensional imaging devices. According to the method for measuring the loop state of a plate material according to the present invention, there is no need to install a two-dimensional imaging device in a location with a poor environment, as in the case of the plate speed sensor described in Patent Document 3, and interference from cranes caused by imaging from the side between the rolling stands, as in the case of the camera described in Patent Document 4, can be avoided, and the loop state of the plate material (the length of the edge of the plate material related to the loop state) can be measured with high accuracy and stability. Furthermore, since the loop of the plate material also occurs when the deformation resistance of the plate material changes due to a change in the temperature of the plate material, etc., by applying the measuring method according to the present invention not only when the tip of the plate material is bitten by the roll pair, but also in the steady part of rolling, it is possible to detect abnormalities in rolling and prevent troubles even in the steady part of rolling.

[0028] In addition, according to the method for measuring the loop state of a plate material according to the present invention, In the calculation process, the length of the edge of the plate material between the two adjacent roll pairs is calculated as the length of a broken line connecting the vertex of the roll located below the pair of rolls located upstream in the rolling direction of the plate material, of the two adjacent roll pairs, the calculated coordinates of the edge at the multiple locations, and the vertex of the roll located below the pair of rolls located downstream in the rolling direction of the plate material, of the two adjacent roll pairs.

[0029] The above direction According to this method, it is possible to calculate a value closer to the actual length of the edge of the plate material than when the length of the edge of the plate material is calculated from the length of a broken line connecting three points (the apex of the lower work roll of the rolling stand located on the upstream side, the apex of the loop, and the apex of the lower work roll of the rolling stand located on the downstream side) as described in Patent Document 4. In addition, direction In this method, the coordinates of the apex of the lower roll of the pair of rolls located on the upstream side and the coordinates of the apex of the lower roll of the pair of rolls located on the downstream side can be obtained in advance based on the design specifications of the hot rolling line, etc.

[0030] Preferably, in the calculation step, the length of a line segment connecting an apex of a roll located below a pair of rolls located upstream in the rolling direction of the plate material and an apex of a roll located below a pair of rolls located downstream in the rolling direction of the plate material is calculated as the length of the roll pair between the two adjacent pairs of rolls, and the loop length of the plate material between the two adjacent pairs of rolls is calculated by subtracting the length of the roll pair between the two adjacent pairs of rolls from the length of the edge of the plate material between the two adjacent pairs of rolls.

[0031] As in the above-mentioned preferred method, by calculating the loop length as an index showing the loop state of the strip material, it is possible to perform appropriate rolling of the strip material according to the loop state of the strip material. In the above-mentioned preferred method, the length between the pair of rolls can be determined in advance based on the design specifications of the hot rolling line, etc.

[0032] Preferably, the hot rolling line has a looper roll between the two adjacent sets of roll pairs, the two two-dimensional imaging devices include the looper roll within an imaging field of view, and in the calculation step, a shortest plate length that is the shortest length that the plate can have between the two adjacent sets of roll pairs is calculated based on an actual angle or height of the looper roll, and a shortest loop length of the plate between the two adjacent sets of roll pairs is calculated by subtracting the length between the roll pairs from the shortest plate length, and a difference between the loop length of the plate and the shortest loop length of the plate is calculated. The hot rolling line includes a looper roll between the two adjacent sets of roll pairs, and the two two-dimensional imaging devices used in the imaging process include the looper roll within an imaging field of view. In the calculation process, a shortest plate length, which is the shortest length that the plate can have between the two adjacent sets of roll pairs, is calculated based on an actual angle or height of the looper roll, and the shortest loop length of the plate material between the two adjacent sets of roll pairs is calculated by subtracting the length between the roll pairs from the shortest plate length, and a difference between the loop length of the plate material and the shortest loop length of the plate material is calculated.

[0033] The difference between the loop length of the plate material calculated by the above-mentioned preferred method and the shortest loop length of the plate material varies depending on whether the plate material comes into contact with the looper roll and tension is applied to the plate material. Since the two two-dimensional imaging devices have the looper roll within the imaging field of view, the points in the rolling direction of the plate material where the coordinates of the edge of the plate material are calculated in the calculation process can include points that may come into contact with the looper roll, and the length of the edge of the plate material and therefore the loop length of the plate material can be calculated with high accuracy. Therefore, if the absolute value of the difference between the loop length of the plate material and the shortest loop length of the plate material exceeds a predetermined threshold value, it can be determined that the plate material is not in contact with the looper roll, i.e., that a loop has occurred, and if the absolute value of the difference between the loop length of the plate material and the shortest loop length of the plate material is equal to or less than a predetermined threshold value, it can be determined that the plate material is in contact with the looper roll. Therefore, as in the above-mentioned preferred method, by calculating the difference between the loop length of the strip material and the shortest loop length of the strip material as an index indicating the loop state of the strip material, it is possible to perform more appropriate rolling of the strip material in accordance with the loop state of the strip material.

[0034] Preferably, the temperature of the plate material is measured upstream of the two adjacent roll pairs in the rolling direction of the plate material, and the exposure times of the two two-dimensional imaging devices used in the imaging process are set based on the measured temperature.

[0035] In a hot rolling line, since the plate material is at a high temperature, the plate material's strong self-luminescence is superimposed on the captured image (brightness image). Therefore, if the sensitivity of the two-dimensional imaging device is not appropriate for the plate material's temperature, the position of the plate material's edge in the captured image may not be accurately detected due to halation, or the image may be too dark to recognize the edge of the plate material. In the steady state of plate material rolling, it is possible to automatically adjust the exposure time and sensitivity of the two-dimensional imaging device, but this is difficult when it is desired to detect the position of the edge from the leading edge of the plate material. According to the above-mentioned preferred method, the temperature of the plate material is measured upstream of two adjacent sets of roll pairs in the rolling direction of the plate material, and the exposure time of the two-dimensional imaging device is set based on the measured temperature. Therefore, it is possible to detect the position of the edge from the tip of the plate material and, ultimately, to calculate the length of the edge of the plate material.

[0036] In order to solve the above-mentioned problems, the present invention provides a first rolling method for a strip material, which uses the above-mentioned method for measuring a loop state of a strip material, and sequentially calculates a difference between a loop length of the strip material and a shortest loop length of the strip material in a process of raising the looper roll after a leading end of the strip material is bitten by a roll pair located downstream in a rolling direction of the strip material out of the two adjacent roll pairs, and when a state in which the absolute value of the calculated difference is equal to or smaller than a predetermined threshold value continues for a predetermined set time or longer, it is determined that tension has been applied to the strip material by the looper roll, and transitions to a tension control mode in which a torque acting on the looper roll is controlled so that an actual tension of the strip material approaches a target tension, and a peripheral speed of a roll pair located at least on either the upstream side or the downstream side in the rolling direction of the strip material is controlled so that an actual angle of the looper roll approaches a target angle.

[0037] As described above, in the conventional rolling method for a plate material, after the leading edge of the plate material is caught in the pair of rolls located downstream in the rolling direction of the plate material, the looper roll is raised, and after a predetermined time has elapsed since the raising, the mode is switched to the tension control mode. However, if the speed balance of the plate material on the outlet side of each pair of rolls is not proper and the loop length is shorter than expected, the looper roll comes into contact with the plate material immediately after the looper roll starts to rise, and excessive tension is applied to the plate material for a long time, which causes the width of the plate material to shrink. According to the first strip rolling method of the present invention, by calculating the difference between the loop length of the strip and the shortest loop length of the strip, it is possible to determine whether or not the strip has come into contact with the looper roll and tension has been applied to the strip. If the loop length of the strip can be calculated without error (the length of the strip edge can be calculated without error), it can be determined that the strip is not in contact with the looper roll when the difference between the loop length of the strip and the shortest loop length of the strip is a positive value, and that the strip has come into contact with the looper roll and tension has been applied to the strip when the difference between the loop length of the strip and the shortest loop length of the strip is zero. However, since the calculated loop length may contain an error, in the first rolling method for a plate material according to the present invention, it is determined that tension has been applied to the plate material only when the absolute value of the difference between the loop length of the plate material and the shortest loop length of the plate material remains below a predetermined threshold value for a predetermined set time or more, and regardless of whether a predetermined time has passed since the looper roll was raised, the method transitions to a tension control mode, thereby preventing excessive tension from being applied to the plate material and enabling stable rolling of the plate material. In the tension control mode of the conventional rolling method for a strip material, the peripheral speed of the roll pair located on the upstream side in the rolling direction of the strip material is controlled so that the actual angle of the looper roll approaches the target angle, but this is not limited to this, and the same effect can be obtained even if the peripheral speed of the roll pair located on at least one of the upstream side and downstream side in the rolling direction of the strip material is controlled so that the actual angle of the looper roll approaches the target angle, as in the tension control mode of the first rolling method for a strip material according to the present invention. This point is also true for the second rolling method for a strip material described later. The tension record used in the tension control mode of the first plate rolling method according to the present invention can be, for example, a tension calculated using a load meter attached to a looper arm that holds a looper roll, a tension calculated from the torque record of a drive device of a looper (looper roll and looper arm), or a tension calculated from the torque record of a drive device of a roll pair located on the upstream or downstream side. Also, the angle record used in the tension control mode of the first plate rolling method according to the present invention can be, for example, an angle measured by a rotary encoder attached to the rotation shaft of the drive device of the looper. This point is the same for the second plate rolling method described later.

[0038] In addition, in order to solve the above-mentioned problems, the present invention provides a second rolling method for a strip material, which uses the above-mentioned loop state measuring method to sequentially calculate a difference between the loop length of the strip material and the shortest loop length of the strip material in a process of raising the looper roll after a leading end of the strip material is bitten by one of the two adjacent roll pairs that is located downstream in the rolling direction of the strip material, and controls a torque acting on the looper roll so that the actual tension of the strip material approaches a target tension when a predetermined time has elapsed since the looper roll was raised, and controls a torque acting on the looper roll so that the actual tension of the strip material approaches a target tension when the actual angle of the looper roll approaches a target angle. and in the tension control mode, an amount of increase or decrease in the circumferential speed of the roll pair located at least on the upstream side or downstream side in the rolling direction of the plate material is determined based on a difference between a loop length of the plate material calculated at the time of transition to the tension control mode and a shortest loop length of the plate material, and the circumferential speed of the roll pair located at least on the upstream side or downstream side in the rolling direction of the plate material is increased or decreased in accordance with the determined amount of increase or decrease.

[0039] The second rolling method for a strip material according to the present invention is similar to the conventional rolling method for a strip material in that after the leading edge of the strip material is caught in the pair of rolls located downstream in the rolling direction of the strip material, the looper roll is raised, and after a predetermined time has elapsed since the raising, the mode is switched to the tension control mode. Here, since the upper limit of the lift amount of the looper roll (upper angle limit of the looper roll) is mechanically determined, it is necessary to switch to the tension control mode before the upper limit is reached. Therefore, the predetermined time to switch to the tension control mode is set before the time when the upper limit is reached, which is estimated from the lift speed of the looper roll. However, if the speed balance of the strip material on the exit side of each roll pair is not appropriate and the loop length is longer than expected, the looper roll does not come into contact with the strip material even after a predetermined time has elapsed since the looper roll started to rise, and the system may transition to the tension control mode in a state where no tension is applied to the strip material. In this case, the tension control mode controls the peripheral speed of the roll pair located at least on the upstream side or downstream side in the rolling direction of the strip material so as to shorten the loop length, but the conventional strip material control method does not know how much loop length has been generated, so the peripheral speed of the roll pair is not controlled appropriately, and the strip material remains out of contact with the looper roll, which may cause a rolling trouble. According to the second strip rolling method of the present invention, the amount of increase or decrease in the peripheral speed of the roll pair located at least on the upstream side or downstream side in the rolling direction of the strip is determined based on the difference between the loop length of the strip calculated at the time of transition to the tension control mode and the shortest loop length of the strip (in other words, depending on how much loop length has occurred), and the peripheral speed of the roll pair located at least on the upstream side or downstream side in the rolling direction of the strip is increased or decreased according to the determined amount of increase or decrease, so that the strip comes into contact with the looper rolls stably early and can be controlled to approach the target tension and target angle. As in the above-mentioned conventional strip control method, in the tension control mode, the looper angle actual value θ is adjusted to the target angle θ aim It is possible to calculate the circumferential speed of the roll pair (work rolls WRa, WRb) by correcting the set circumferential speed VRi so as to approach the set circumferential speed VRi. In the second strip rolling method according to the present invention, the increase or decrease in the circumferential speed of the roll pair based on the difference between the strip loop length calculated at the time of transition to the tension control mode and the shortest loop length of the strip may be performed on the circumferential speed calculated in this tension control mode.

[0040] In addition, in order to solve the above-mentioned problems, the present invention provides a third rolling method for a plate material, which uses the plate material loop state measuring method to calculate the length of the edge of the plate material at both edges of the plate material between the two adjacent sets of roll pairs, and controls leveling of the roll pair located on at least one of the upstream and downstream sides in the rolling direction of the plate material, of the two adjacent sets of roll pairs, based on the difference in the calculated lengths of the edge of the plate material at both edges.

[0041] The lengths of the edges of the plate material at both ends may not necessarily be the same. This is due to differences in the reduction rate in the width direction during rolling, which causes unevenness in the speed of the plate material in the width direction, etc. According to the third method for rolling plate material of the present invention, the leveling of the roll pair located on at least one of the upstream and downstream sides in the rolling direction of the plate material out of two adjacent roll pairs is controlled (the widthwise distribution of the roll gap amount of the roll pair is adjusted) based on the difference in the length of the plate material edges at both edges, thereby realizing a uniform rolling speed across the width direction of the plate material and preventing rolling problems due to defective shapes such as meandering and ear waves of the plate material.

[0042] Furthermore, in order to solve the above-mentioned problems, the present invention provides a plate material loop state measuring device for measuring a loop state of a plate material being rolled in a hot rolling line in which a plurality of roll pairs, each consisting of rolls arranged opposite to one another above and below, are installed in the horizontal direction, the plate material being rolled comprising: two two-dimensional imaging devices that are provided along the width direction of the plate material between two adjacent roll pairs among the plurality of roll pairs, and capture images of the plate material from above a pass line of the hot rolling line so that an edge of the plate material is included within an imaging field of view to generate captured images; and a two-dimensional imaging device that calculates coordinates of the edge of the plate material at a plurality of points in the rolling direction of the plate material based on the captured images, and calculates the calculated coordinates of the edge of the plate material at the plurality of points. and a calculation device that calculates a length of the edge of the plate material between the two adjacent roll pairs based on the calculated distance and a geometric arrangement condition of the two two-dimensional imaging devices, the two two-dimensional imaging devices being arranged so that the directions of the optical axes when viewed from the rolling direction of the plate material are different from each other, and the calculation device detects a position of the edge of the plate material in the image captured by the two two-dimensional imaging devices, calculates distances from the two two-dimensional imaging devices to the edge of the plate material at the multiple locations based on the position of the edge of the plate material in the detected image, and calculates coordinates of the edge of the plate material at the multiple locations in the rolling direction of the plate material based on the calculated distance and a geometric arrangement condition of the two two-dimensional imaging devices. and as the length of the edge of the plate material between the two adjacent sets of roll pairs, a length of a broken line connecting a vertex of a roll located on the lower side of the roll pair located on the upstream side in the rolling direction of the plate material among the two adjacent sets of roll pairs, the calculated coordinates of the edge at the multiple locations, and a vertex of a roll located on the lower side of the roll pair located on the downstream side in the rolling direction of the plate material among the two adjacent sets of roll pairs is calculated. It can also be used as a plate loop condition measuring device. Effect of the Invention

[0043] According to the method and device for measuring the loop state of a plate material of the present invention, the loop state of the plate material can be measured stably with high accuracy. Also, according to the method for rolling a plate material of the present invention, the plate material can be rolled stably. [Brief description of the drawings]

[0044] [Figure 1] FIG. 1 is a diagram illustrating an example of the equipment configuration of a hot rolling line for hot-rolled steel sheets. [Diagram 2]FIG. 1 is a schematic diagram showing a rolling control device in a state where control is executed when a leading edge of a strip material passes through an ith rolling stand and an (i+1)th rolling stand in a conventional strip material rolling method. [Diagram 3] FIG. 1 is a diagram showing a schematic diagram of a rolling control device in a state where a tension control mode is executed in a conventional rolling method for a plate material. [Figure 4] 1 is a diagram showing a schematic configuration of a plate material loop state measuring device according to an embodiment of the present invention; [Diagram 5] An example of captured images captured by the two-dimensional imaging devices 1 and 2 shown in FIG. 4 is shown. [Figure 6] 5 is an explanatory diagram for explaining the calculation content (calculation of edge coordinates) in the calculation device shown in FIG. 4. FIG. [Figure 7] 7 is an explanatory diagram seen from a direction perpendicular to the CC' plane in FIG. 6. FIG. [Figure 8] 5 is an explanatory diagram for explaining the calculation content (calculation of edge length) in the calculation device shown in FIG. 4. FIG. [Figure 9] FIG. 13 is a diagram showing the results of an accuracy evaluation test using the plate material loop state measuring device according to one embodiment of the present invention. [Figure 10] 1 shows an example of the results of measuring the shape of the edge of a plate material using the plate material loop state measuring device according to one embodiment of the present invention. [Figure 11] FIG. 11 is a diagram showing the results of measuring the loop height, loop length, and difference between the loop length and the shortest loop length for the same plate material as in FIG. 10 using a plate material loop state measuring device according to one embodiment of the present invention. [Figure 12] 13 shows another example of the results of measuring the shape of the edge of a plate material using the plate material loop state measuring device according to one embodiment of the present invention. [Figure 13] FIG. 13 is a diagram showing the results of measuring the loop height, loop length, and the difference between the loop length and the shortest loop length for the same plate material as in FIG. 12 using a plate material loop state measuring device according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] Hereinafter, with reference to the attached drawings as appropriate, one embodiment of the present invention will be described by taking as an example a case in which the plate material is a hot-rolled steel plate, and two adjacent pairs of rolls that measure the loop state of the plate material therebetween are work rolls of the sixth and seventh rolling stands of a finishing mill that is composed of seven rolling stands in a hot rolling line for hot-rolled steel plate.

[0046] Fig. 4 is a diagram showing a schematic configuration of a loop state measuring device for a sheet material according to one embodiment of the present invention (hereinafter, simply referred to as "loop state measuring device" where appropriate). Fig. 4(a) is a side view seen from a horizontal direction perpendicular to the rolling direction (conveyance direction) of the sheet material. Fig. 4(b) is a front view of the sixth rolling stand seen from the rolling direction of the sheet material. Work rolls and backup rolls are not shown in Fig. 4(b). 4, the loop state measuring device 100 is a device for measuring the loop state of a plate material S being rolled in a hot rolling line in which a plurality of roll pairs, each consisting of work rolls WRa and WRb arranged opposite each other above and below, are installed horizontally. In this embodiment, as an example, the loop state of the plate material S between the sixth rolling stand F6 and the seventh rolling stand F7 of a finishing rolling mill is measured. The loop state measuring device 100 includes two two-dimensional imaging devices 1 and 2 and a calculation device 3. Between the sixth rolling stand F6 and the seventh rolling stand F7, a looper LP having a looper roll LR and a looper arm LA is provided to apply tension to the sheet material S and stabilize the sheet threading. Also, while Fig. 4 shows only the backup roll BRa that supports the work roll WRa located on the upper side, in reality, a backup roll that supports the work roll WRb located on the lower side is also provided.

[0047] The two two-dimensional imaging devices 1, 2 are arranged side by side along the width direction of the sheet material S between the work rolls WRa, WRb of the sixth rolling stand F6 and the work rolls WRa, WRb of the seventh rolling stand F7. The two two-dimensional imaging devices 1, 2 are also arranged such that the directions of their optical axes (visual axes) 11, 21 are different from each other when viewed from the rolling direction of the sheet material S. In this embodiment, the two-dimensional imaging devices 1, 2 are attached to the upper part of a housing on the exit side of the sixth rolling stand F6. The dashed lines shown in Fig. 4 are boundaries between the imaging fields of the two-dimensional imaging devices 1 and 2. As can be seen from the positions of the dashed lines shown in Fig. 4, the two-dimensional imaging devices 1 and 2 image the sheet material S transported between the sixth rolling stand F6 and the seventh rolling stand F7 from above the pass line PL so that the edges (both edges in this embodiment) of the sheet material S are included in the imaging field of view. In addition, the two-dimensional imaging devices 1 and 2 include the looper roll LR in their imaging field of view.

[0048] As the two-dimensional imaging devices 1 and 2, for example, a CMOS camera with an electronic shutter having an effective pixel count of 720×500 can be used. For example, an external trigger may be used to drive the electronic shutters of two devices at the same time to capture images at the same timing, thereby generating a captured image. Since the temperature of the plate material S rolled by the finishing rolling mill is as high as 850 to 950° C., in order to capture an image of the leading end of the plate material S without halation, in this embodiment, the temperature of the plate material S is measured between the rolling stands upstream of the sixth rolling stand F6 using a radiation thermometer (not shown), and the exposure time of the two-dimensional imaging devices 1 and 2 is set based on the measured temperature. Furthermore, in order to capture an image of the plate material S with appropriate brightness even if the temperature of the plate material S changes during rolling of the plate material S, the two-dimensional imaging devices 1 and 2 are configured to switch to an automatic brightness adjustment mode (a mode in which the exposure time is automatically changed so that the brightness value of the pixel area corresponding to the plate material S becomes the same as the set value) after a predetermined time has elapsed after the leading end of the plate material S passes through the imaging field of view of the two-dimensional imaging devices 1 and 2.

[0049] Fig. 5 shows examples of captured images captured by two-dimensional imaging devices 1 and 2. Fig. 5(a) is an example of an image captured by two-dimensional imaging device 1, and Fig. 5(b) is an example of an image captured by two-dimensional imaging device 2 at the same timing as that of two-dimensional imaging device 1. As described later, the calculation device 3 calculates the positions of edges (for convenience, both edges E at L0 in FIG. 5) at a plurality of positions (in this embodiment, eight positions L0 to L7 shown by dashed lines in FIG. 5) in the rolling direction of the plate material S in the captured image shown in FIG. WS and E DS Based on the position of the detected edge, a predetermined calculation is performed to calculate the coordinates of the edge, and the length of the edge of the plate material S, etc. The specific calculation content will be described later.

[0050] The arithmetic device 3 is connected to the two two-dimensional imaging devices 1 and 2, and is configured as a computer in which a program is installed that performs a predetermined calculation on the captured images captured by the two two-dimensional imaging devices 1 and 2. The arithmetic device 3 calculates the coordinates of the edges of the plate material S at multiple points in the rolling direction of the plate material S by a stereoscopic vision method based on the captured images of the plate material S captured by the two two-dimensional imaging devices 1 and 2, respectively. Specifically, as shown in FIG. 5, the arithmetic device 3 detects the positions of the edges of the plate material S at multiple points in the rolling direction of the plate material S in the captured images of the plate material S captured by the two two-dimensional imaging devices 1 and 2, respectively, calculates the distances from the two two-dimensional imaging devices 1 and 2 to the edges of the plate material S at the multiple points based on the positions of the edges of the plate material S in the detected captured images, and calculates the coordinates of the edges of the plate material S at multiple points in the rolling direction of the plate material S based on the calculated distances and the geometric arrangement conditions of the two two-dimensional imaging devices 1 and 2. Then, the calculation device 3 calculates the length of the edge of the plate material S between the sixth rolling stand F6 and the seventh rolling stand F7 based on the calculated coordinates of the edge of the plate material S at the multiple points. Note that the positions of the edges of the plate material S at multiple points in the rolling direction in the captured image of the plate material S (for example, both edges E shown in FIG. 5) are calculated based on the calculated coordinates of the edges of the plate material S at the multiple points in the rolling direction in the captured image of the plate material S. WS and E DSThe position of the edge of the board material S can be detected using a known method that uses the difference between the luminance value of a pixel area corresponding to the board material S and the luminance value of a pixel area corresponding to the background, as described in, for example, JP 2004-141956 A and JP 2012-26767 A, and therefore a detailed description of the method will be omitted here.

[0051] The calculation contents in the calculation device 3 will be specifically described below.

[0052] <Edge P of plate S i Coordinates (X i ,Y i ) calculation> FIG. 6 is an explanatory diagram for explaining the calculation contents (calculation of edge coordinates) in the calculation device 3, and is a schematic side view of the area between the sixth rolling stand F6 and the seventh rolling stand F7 as seen from a horizontal direction perpendicular to the rolling direction of the plate material S (X-axis direction in FIG. 6). The Y-axis direction in FIG. 6 indicates the up-down direction. The origin of the X-axis coincides with the center of the work rolls WRa, WRb arranged in the sixth rolling stand F6, and the origin of the Y-axis is a predetermined position that has been determined in advance. The CC' plane in FIG. 6 is a plane that includes the optical axes of the two two-dimensional imaging devices 1, 2 (optical axes 11, 21 shown in FIG. 2(b)). Note that the loopers are not shown in FIG. 6. As shown in FIG. 6, the calculation device 3 calculates the distances from the two-dimensional imaging devices 1 and 2 to the edges of the plate material S at multiple points (eight points circled in FIG. 6) based on the captured images generated using the two-dimensional imaging devices 1 and 2, and calculates the distances from the two-dimensional imaging devices 1 and 2 to the edges of the plate material S at eight points in the rolling direction of the plate material S. i Point P projected onto the CC' plane (i=0~7) i Distance to h i Then, the calculation device 3 calculates the distance h i Based on the geometric arrangement conditions of the two two-dimensional imaging devices 1 and 2, the edge P of the plate material S at eight points in the rolling direction of the plate material S is i Coordinates (X i ,Y i As shown in FIG. 6, the coordinates of the two-dimensional imaging devices 1 and 2 are calculated as (L C ,H C), and the inclination angle of the optical axes of the two-dimensional imaging devices 1 and 2 with respect to the vertical direction (the inclination angle with respect to the X-axis direction) is θ C Let edge P i is at an angle φ i If we make the edge P i Coordinates (X i ,Y i ) is calculated geometrically using the following equations (6) and (7). X i =L C +h i sin(θ C -φ i ) / cosφ i (6) Y i =H C -h i cos(θ C -φ i ) / cosφ i (7)

[0053] Due to differences in the reduction rate in the width direction during rolling and uneven speed of the sheet material S in the width direction, the lengths of the edges of the sheet material S at both edges of the sheet material S between the sixth rolling stand F6 and the seventh rolling stand F7 may not necessarily be the same. For this reason, the calculation device 3 of this embodiment, as described below, calculates the length of the edges of the sheet material S by distinguishing between the DS (Drive Side) side on which the drive devices (not shown) of the work rolls WRa and WRb are arranged and the WS (Work Side) side on the opposite side of the DS side, of both sides of the sheet material S in the width direction. For this reason, the distance h i Or Edge P i Coordinates (X i ,Y i ), the WS side and the DS side are distinguished and calculated for each side. i Regarding the distance h on the WS side calculated as described below, WSi h in the above equations (6) and (7) i By substituting into, the coordinate (X i ,Y i ) and calculate the edge P iRegarding the distance h on the DS side calculated as described below, DSi h in the above equations (6) and (7) i By substituting into, the coordinate (X i ,Y i ) is calculated.

[0054] <Distance h from the 2D imaging devices 1 and 2 to the edge of the plate material S i (h DSi , h WSi ) calculation> Fig. 7 is an explanatory diagram viewed from a direction perpendicular to the CC' plane in Fig. 6. For convenience of explanation, in Fig. 7, the optical axis 11 of the two-dimensional imaging device 1 is inclined at an inclination angle θ a The figure shows a state in which the inclination angle is θ a As shown in Fig. 4(b), a = 0°, and the inclination angle θ b It can be set at any angle different from the above. The two two-dimensional imaging devices 1 and 2 are disposed at a distance H from the origin of the Y axis (Y=0). Therefore, the position of the edge of the plate material S in the images captured by the two-dimensional imaging devices 1 and 2 detected by the computing device 3 is a point P projected onto the CC' plane shown in FIG. i '(In Fig. 7, the edge P on the WS side i The projected point is P WSi ', and the edge P on the DS side i The projected point is P DSi 7, the position of the edge on the WS side in the image captured by the two-dimensional imaging device 1 is detected as the coordinates of a point projected from the center line of the sixth rolling stand F6 (the center line of the sixth rolling stand F6 in the strip width direction) CL to the center line of the sixth rolling stand F6. aWSi The position of the edge on the DS side in the image captured by the two-dimensional imaging device 1 is detected as a distance W from the center line CL. aDSi Similarly, the position of the edge on the WS side in the image captured by the two-dimensional imaging device 2 is detected as a distance W bWSiThe position of the edge on the DS side in the image captured by the two-dimensional imaging device 1 is detected as a distance W from the center line CL. bDSi is detected as

[0055] The inclination angles of the optical axes 11 and 21 of the two-dimensional imaging devices 1 and 2 in the width direction of the plate material S with respect to the vertical direction are respectively represented as θ a , θ b Then, the projection point P WSi ', P DSi ' to h WSi , h DSi Then, the distances detected as above and the actual projected point P WSi ', P DSi Distance from center line CL of W WSi , W DSi The relationship between them is expressed by the following formulas (8) to (11). W WSi =h WSi / H.W. aWSi -(Hh WSi )·tanθ a (8) W DSi =h DSi / H.W. aDSi -(Hh DSi )·tanθ a (9) W WSi =h WSi / H.W. bWSi -(Hh WSi )·tanθ b (10) W DSi =h DSi / H.W. bDSi -(Hh DSi )·tanθ b (11)

[0056] The following equation (12) holds from the above equations (8) and (10), and the following equation (13) holds from the above equations (9) and (11). W bWSi -W aWSi =H / h WSi ·(Hh WSi )(tanθb -tan θ a ) · · · (12) W aDSi -W bDSi =H / h DSi ·(Hh DSi )(tanθ b -tan θ a ) · · · (13) Here, C pass =H(tanθ b -tan θ a ), then the following equations (14) and (15) hold from the above equations (12) and (13). W bWSi -W aWSi =C pass (H / h WSi -1) (14) W aDSi -W bDSi =C pass (H / h DSi -1) · · · (15) C pass is a fixed value determined by the arrangement of the two two-dimensional imaging devices 1 and 2. Therefore, the difference between the position of the edge on the WS side detected in the image captured by one two-dimensional imaging device 1 and the position of the edge on the WS side detected in the image captured by the other two-dimensional imaging device 2, that is, the parallax on the WS side (W aWSi -W bWSi ) and the distance h WSi Similarly, the disparity on the DS side (W aDSi -W bDSi ) and the distance h DSi can be calculated. In this manner, the calculation device 3 calculates the distance h WSi , h DSi Calculate the distance h as described above. WSi , h DSi h in Eqs. (6) and (7) i By substituting into, the edge P on the WS side i Coordinates (X i ,Y i ) and the edge P on the DS side i Coordinates (X i ,Y i) can be calculated.

[0057] The calculated distance h WSi , h DSi By substituting these into equations (8) and (9), the actual projected point P WSi ', P DSi Distance from center line CL of W WSi , W DSi It is also possible to calculate the distance W WSi , W DSi By calculating the width and meandering amount of the sheet material S, it is possible to calculate the width and the amount of bending of the tip, and it is also possible to detect the change in width and bending of the tip. In addition, by comparing the widths of the sheet material S calculated at multiple points in the rolling direction, it is also possible to determine whether there is an abnormality in the calculation result of the edge length of the sheet material S, which will be described later (for example, if there is a large difference in the widths of the sheet material S calculated at multiple points, it is determined that there is an abnormality in the calculation result of the edge length of the sheet material S).

[0058] <Calculating the edge length of plate material S> Fig. 8 is an explanatory diagram for explaining the calculation contents (calculation of edge length) in the calculation device 3, and is a schematic side view of the area between the sixth rolling stand F6 and the seventh rolling stand F7 as viewed from a horizontal direction perpendicular to the rolling direction of the sheet material S (X-axis direction in Fig. 8). The X-axis and Y-axis shown in Fig. 8 are the same as the X-axis and Y-axis shown in Fig. 6. Note that Fig. 8 is an explanatory diagram illustrating an example of calculation of the edge length on the WS side, but the edge length on the DS side can also be calculated in a similar manner. As shown in FIG. 8, the calculation device 3 calculates the length of the WS-side edge of the sheet material S between the sixth rolling stand F6 and the seventh rolling stand F7 by calculating the apex P of the work roll WRb located below the sixth rolling stand F6. F6 (0,Y F6 ) and the edge P on the WS side at multiple locations calculated as described above WSi The coordinates of (i = 0 to 7) and the apex P of the work roll WRb located below the seventh rolling stand F7 F7 (L STD ,Y F7 ) is calculated. In other words, the length of the edge on the WS side of the plate material S is calculated as LWS Then, the length of the edge on the WS side, L, is calculated by the following equation (16). WS Calculate.

number

number

[0059] As described above, according to the loop state measuring device 100 of this embodiment, it is not necessary to install the two-dimensional imaging devices 1 and 2 in a location with a poor environment, and it is possible to avoid interference with cranes caused by imaging from the side between the rolling stands, and it is possible to measure the loop state of the plate material S (the length L of the edge of the plate material S related to the loop state) WS , L DS This can be measured stably and accurately using stereoscopic techniques.

[0060] In addition, the calculation device 3 of the loop state measurement device 100 according to this embodiment calculates the length L of the edge of the plate material S. WS , L DS In addition, the loop length of the strip S between the sixth rolling stand F6 and the seventh rolling stand F7 (the loop length L PWS , DS side loop length L PDSThe loop length of the plate material S is calculated by multiplying the length of the edge of the plate material S (the length of the edge on the WS side L WS , the length of the edge on the DS side L DS ), the roll pair distance (the apex P of the work roll WRb located below the sixth rolling stand F6) expressed by the following formula (18) is obtained. F6 and the apex P of the work roll WRb located below the seventh rolling stand F7 F7 (The length of the line segment connecting R It is defined as the value obtained by subtracting

number

[0061] In addition, the calculation device 3 of this embodiment calculates the shortest length L of the strip S between the sixth rolling stand F6 and the seventh rolling stand F7. min The length of the plate material S is shortest when the plate material S is in the state shown by the broken line S' in FIG. 8 (i.e., when the looper roll LR is in contact with the plate material S and tension is applied to the plate material S), so the shortest plate material length L min is calculated geometrically by the following equation (21). L min ={(x L +l L cosθ) 2 +(l L sinθ-y L -Y F6 +r L ) 2} 1 / 2 +{(L STD -x L -l L cosθ) 2+(l L sinθ-y L -Y F7 +r L ) 2} 1 / 2 ···(twenty one) In the above formula (21), (X L , Y L ) is the coordinate of the rotation center of the looper arm LA, and l L is the distance between the rotation center of the looper arm LA and the center of the looper roll LR, θ is the actual angle of the looper roll LR, and r L is the radius of the looper roll LR. Although not shown in Fig. 4, the calculation device 3 is connected to a goniometer that measures the actual angle θ of the looper roll LR, and is capable of performing the calculation expressed by the above formula (21) by sequentially inputting the actual angle θ from the goniometer. Then, the calculation device 3 calculates the shortest plate length L min From the roll pair length L R By subtracting the above, the shortest loop length L of the strip S between the sixth rolling stand F6 and the seventh rolling stand F7 is obtained. pmin That is, the shortest loop length L of the plate material S is calculated by the following formula (22). pmin Calculate. L Pmin =L min -L R ···(twenty two) Furthermore, the calculation device 3 calculates the loop length of the plate material S (the loop length L PWS , DS side loop length L PDS ) and the shortest loop length L of the plate S pmin Calculate the difference between the loop length L on the WS side. PWS and the shortest loop length L pmin Difference ΔL WS , and the loop length L on the DS side PDS and the shortest loop length L pmin Difference ΔL DS Calculate.

[0062] In addition, the calculation device 3 of the present embodiment calculates the loop height. The loop height is calculated based on the calculated edge P i Coordinates (Xi ,Y i ) means the largest Y coordinate, and the calculation device 3 calculates the loop height for both the WS side and the DS side. PWS The loop height on the DS side is h PDS The same applies to. Furthermore, the calculation device 3 of this embodiment calculates the looper roll height h L Calculate the looper roll height h L is calculated by the following formula (23) using the actual angle θ of the looper roll LR. h L =l L sinθ-y L +r L ···(twenty three)

[0063] Hereinafter, an example of a rolling method for a plate material S using the loop state measuring device 100 according to this embodiment (hereinafter, simply referred to as a "rolling method" as appropriate) will be described. As described above, the loop state measuring device 100 (the calculation device 3) according to this embodiment measures the edge length (L WS , L DS ) and the loop length of the plate material S (WS side loop length L PWS , DS side loop length L PDS ) and the shortest loop length L of the plate S pmin Difference from (ΔL WS , ΔL DS ) can be calculated, and by utilizing these, it is possible to roll the plate material S in a manner that has not been possible before. Specific examples of the rolling method (first to third rolling methods) will be described below.

[0064] <First rolling method> In the first rolling method, after the leading end of the plate material S is bitten by the work rolls WRa and WRb of the seventh rolling stand F7, in the process of raising the looper roll LR, the loop length (L PWS , L PDS ) and the shortest loop length L of the plate S pmin Difference from (ΔL WS , ΔL DS) is calculated successively. When the absolute value of the calculated difference is equal to or smaller than a predetermined threshold value for a predetermined set time or longer, it is determined that tension is applied to the plate material S by the looper roll LR, and the system transitions to a tension control mode. In the tension control mode, the tension actual value T of the plate material S is calculated based on the target tension T aim The torque acting on the looper roll LR is controlled so that the actual angle θ of the looper roll LR approaches the target angle θ aim The peripheral speed of the work rolls WRa, WRb in at least one of the sixth rolling stand F6 and the seventh rolling stand F7 is controlled so as to approach

[0065] The first rolling method can be performed by connecting the loop state measuring device 100 according to this embodiment to a rolling control device used in the conventional rolling method shown in Fig. 3. For example, a mode can be considered in which the loop state measuring device 100 is connected to a process computer shown in Fig. 3, and the process computer judges whether or not a state in which the absolute value of the difference input from the loop state measuring device 100 is equal to or smaller than a predetermined threshold value continues for a predetermined set time or more, and if this state continues, the torque control device and the speed control device are operated in a tension control mode. According to the first rolling method, the loop length (L PWS , L PDS ) and the shortest loop length L of the plate S pmin Difference from (ΔL WS , ΔL DS The system determines that tension is being applied to the plate material S only when the absolute value of (a) is below a predetermined threshold value for a predetermined set time or longer, and switches to tension control mode regardless of whether a predetermined time has elapsed since the looper roll LR was raised. This prevents excessive tension from being applied to the plate material S, making it possible to roll the plate material S stably.

[0066] <Second rolling method> In the second rolling method, as in the conventional rolling method, the mode is switched to the tension control mode after a predetermined time has elapsed since the looper roll LR was raised. However, in the tension control mode of the second rolling method, the loop length (L PWS , L PDS) and the shortest loop length L of the plate S pmin Difference from (ΔL WS , ΔL DS This method differs from conventional rolling methods in that the amount of increase or decrease in the peripheral speed of the work rolls WRa, WRb in at least one of the sixth rolling stand F6 and the seventh rolling stand F7 is determined based on the above-mentioned rolling speed information, and the peripheral speed of the work rolls WRa, WRb in at least one of the sixth rolling stand F6 and the seventh rolling stand F7 is increased or decreased in accordance with the determined amount of increase or decrease.

[0067] The second rolling method can also be performed by connecting the loop state measuring device 100 according to this embodiment to a rolling control device used in the conventional rolling method shown in Fig. 3. For example, a mode can be considered in which the loop state measuring device 100 is connected to the process computer shown in Fig. 3, and the process computer determines the amount of increase or decrease in the peripheral speed of the work rolls WRa, WRb in at least one of the sixth rolling stand F6 and the seventh rolling stand F7 based on the difference input from the loop state measuring device 100, and transmits this amount of increase or decrease to the speed control device to reflect it in the operation in the tension control mode. According to the second rolling method, the loop length (L PWS , L PDS ) and the shortest loop length L of the plate S pmin Difference from (ΔL WS , ΔL DS ) (in other words, depending on how much loop length has been generated), the amount of increase or decrease in the circumferential speed of the work rolls WRa, WRb in at least one of the sixth rolling stand F6 and the seventh rolling stand F7 is determined, and the circumferential speed of the work rolls WRa, WRb in at least one of the sixth rolling stand F6 and the seventh rolling stand F7 is increased or decreased according to the determined amount of increase or decrease, so that the plate material S is brought into contact with the looper roll LR early and stably, and control can be performed to approach the target tension and target angle.

[0068] <Third rolling method> In the third rolling method, the calculated edge lengths (L WS , L DSBased on the difference between the rolling speeds of the work rolls WRa and WRb in at least one of the sixth rolling stand F6 and the seventh rolling stand F7, the leveling of the work rolls WRa and WRb in at least one of the sixth rolling stand F6 and the seventh rolling stand F7 is controlled.

[0069] The third rolling method can be carried out by connecting the loop state measuring device 100 according to the present embodiment to a leveling adjustment device for work rolls WRa and WRb that are generally provided in a hot rolling line for hot-rolled steel sheets. For example, the leveling adjustment device may measure the edge lengths (L WS , L DS In accordance with the difference between the rolling speeds of the work rolls WRa, WRb in at least one of the sixth rolling stand F6 and the seventh rolling stand F7, the leveling of the work rolls WRa, WRb in the sixth rolling stand F6 and the seventh rolling stand F7 may be adjusted. According to the third rolling method, leveling is controlled based on the difference in edge length between the two edges, thereby achieving a uniform speed across the width of the sheet material S and preventing rolling problems caused by defective shapes such as meandering and edge waves of the sheet material S.

[0070] An example of the measurement result by the loop state measuring device 100 according to this embodiment will be described below.

[0071] <Evaluation of measurement accuracy> In order to evaluate the measurement accuracy of the loop state measuring device 100, a flat plate material is placed at a predetermined height (set height) on the hot rolling line of the hot rolled steel plate and within the imaging field of the two-dimensional imaging devices 1 and 2, and the height of the edge of the plate material (the above-mentioned loop height h PWS , h PDS In this test, the set height at which the plate material was placed was changed, and the height of the edge of the plate material (measurement height) was measured by the loop state measuring device 100 for each set height. Figure 9 shows the results of the above evaluation test. Figure 9(a) shows the measurement results for the WS side, and Figure 9(b) shows the measurement results for the DS side. As shown in Figure 9, the error in the measurement height on both the WS side and the DS side was 3 mm or less in σ (standard deviation), confirming that it is possible to measure the edge height of the plate material (i.e., the loop height) with high accuracy.

[0072] <Online measurement example when tension is slightly excessive> A measurement example will be described in which the leading end of the plate material S passes between the sixth rolling stand F6 and the seventh rolling stand F7 without generating a loop. After the leading end of the plate material S is bitten by the sixth rolling stand F6, the loop state measuring device 100 detects the plate material S between the sixth rolling stand F6 and the seventh rolling stand F7 and starts measuring. After that, the leading end of the plate material S is bitten by the seventh rolling stand F7 and the looper roll LR starts rising. FIG. 10 shows an example of the results of measuring the shape of the edge of the plate material S between the sixth rolling stand F6 and the seventh rolling stand F7 (specifically, the coordinates of the edge of the plate material S at eight points in the rolling direction of the plate material S) every 0.1 seconds after the loop state measuring device 100 detects the plate material S. FIG. 10(a) shows the measurement results on the DS side, and FIG. 10(b) shows the measurement results on the WS side. FIG. 10 also shows the shortest loop length L calculated every 0.1 seconds based on the actual angle θ of the looper roll LR. pmin The shape of the edge of the plate material S when this is obtained (hereinafter, appropriately referred to as the "shortest edge shape") is shown by a dashed line. As can be seen from Fig. 10(a), the shape of the edge on the DS side measured at 0.5 seconds almost coincides with the shape of the shortest edge. On the other hand, as can be seen from Fig. 10(b), the shape of the edge on the WS side measured at 0.6 seconds almost coincides with the shape of the shortest edge. From these conditions, it can be seen that on the DS side, the looper roll LR comes into contact with the sheet material S at 0.5 seconds and tension is applied, and on the WS side, the looper roll LR comes into contact with the sheet material S at 0.6 seconds and tension is applied.

[0073] FIG. 11 shows the loop height (h PDS , h PWS ), Loop Length (L PDS , L PWS ), and the difference between the loop length and the shortest loop length (ΔL WS , ΔL DS11(a) shows the results of measuring the loop height, FIG. 11(b) shows the results of measuring the loop length, and FIG. 11(c) shows the results of measuring the difference between the loop length and the shortest loop length. The horizontal axes of FIG. 11(a) to FIG. 11(c) all represent the same time, so they are only shown in FIG. 11(c). FIG. 11(a) shows the results of measuring the loop height, h L The shortest loop length L pmin is also illustrated. As shown in FIG. 11, at 0.32 seconds, the leading edge of the plate material S is engaged with the seventh rolling stand F7, the looper roll LR starts to rise, and after a predetermined time (0.5 seconds in the example shown in FIG. 11) has elapsed, at 0.82 seconds, the mode switches to tension control mode. As shown in FIG. 11(a), after 0.5 seconds when tension is applied to the plate material S (the DS side of the plate material S), the loop height almost coincides with the looper roll height, and the loop height can be measured with high accuracy. Also, as shown in Figure 11(b), 0.5 seconds after tension was applied to the plate material S, the loop length was almost equal to the shortest loop length, and it can be seen that the plate material S passed without slack. Also, the loop length was extended by about 30 mm due to the rise of the looper roll LR, and it is possible that the width of the plate material S was reduced by that amount. Furthermore, as shown in FIG. 11(c), the absolute value of the difference between the loop length and the shortest loop length is almost 0 mm (within ±2 mm) after 0.5 seconds, and it can be determined that tension is applied to the sheet material S at this timing. If the tension control mode had been entered at 0.5 seconds determined based on the absolute value of the difference between the loop length and the shortest loop length, it is estimated from FIG. 11(b) that the increase in loop length would have been limited to about 5 mm, and the decrease in width of the sheet material S would have been minimized. In addition, in application to an actual finishing rolling mill, in order to prevent malfunction due to measurement errors, it is also possible to enter the tension control mode when a state in which the absolute value of the difference between the loop length and the shortest loop length is equal to or less than a predetermined threshold value continues for a predetermined set time or more. In this example, it is desirable to forcibly enter the tension control mode when a state in which the absolute value is equal to or less than the threshold value of 2 mm continues for 0.1 seconds.

[0074] As described above, the loop state measuring device 100 according to this embodiment can measure the difference between the loop length and the shortest loop length, and accurately detect the timing of tension application to the strip material S during the ascending process of the looper roll LR. Therefore, by executing the above-mentioned first rolling method and switching to the tension control mode at the detected timing of tension application to the strip material S, it is possible to prevent excessive tension on the strip material S and prevent a decrease in yield due to a reduction in the width of the strip material S.

[0075] <Example of online measurement when a loop occurs> A measurement example in which a loop of the plate material S occurs between the sixth rolling stand F6 and the seventh rolling stand F7 will be described. After the leading edge of the plate material S is bitten by the sixth rolling stand F6, the loop state measuring device 100 detects the plate material S between the sixth rolling stand F6 and the seventh rolling stand F7 and starts measuring. After that, the leading edge of the plate material S is bitten by the seventh rolling stand F7 and the looper roll LR starts rising. FIG. 12 shows an example of the result of measuring the shape of the edge of the plate material S between the sixth rolling stand F6 and the seventh rolling stand F7 every 0.2 seconds after the loop state measuring device 100 detects the plate material S (specifically, the coordinates of the edge of the plate material S at eight points in the rolling direction of the plate material S). FIG. 12(a) shows the measurement result on the DS side, and FIG. 12(b) shows the measurement result on the WS side. In FIG. 12, the shortest edge shape of the plate material S calculated every 0.2 seconds is shown by a broken line, as in FIG. 10. As can be seen from Fig. 12(a), the shape of the edge on the DS side measured at 1.8 seconds almost coincides with the shape of the shortest edge. On the other hand, as can be seen from Fig. 12(b), the shape of the edge on the WS side measured at 1.0 seconds almost coincides with the shape of the shortest edge. From these conditions, it can be seen that tension is being applied to the sheet material S on the WS side at 1.0 seconds, but there is a large sag in the sheet material S on the DS side, and tension is finally being applied to the sheet material S at 1.8 seconds.

[0076] FIG. 13 shows the loop height (h PDS , h PWS), Loop Length (L PDS , L PWS ), and the difference between the loop length and the shortest loop length (ΔL WS , ΔL DS 13(a) shows the results of measuring the loop height, FIG. 13(b) shows the results of measuring the loop length, and FIG. 13(c) shows the results of measuring the difference between the loop length and the shortest loop length. The horizontal axes of FIG. 13(a) to FIG. 13(c) all represent the same time, so they are only shown in FIG. 13(c). FIG. 13(a) shows the results of measuring the loop height, h L The shortest loop length L pmin is also illustrated. As shown in FIG. 13, at 0.4 seconds, the leading edge of the plate material S is engaged with the seventh rolling stand F7, the looper roll LR starts to rise, and at 0.9 seconds after a predetermined time has elapsed (0.5 seconds in the example shown in FIG. 13), the mode switches to tension control mode. The difference between the loop height shown in FIG. 13(a) and the looper roll height after 1.0 second on both the DS and WS sides is small compared to the looper roll height, making it difficult to determine the timing of tension application. For example, the loop height almost matches the looper roll height at 1.2 seconds when tension is not yet applied. On the other hand, the loop length shown in FIG. 13(b) clearly differs from the shortest loop length up to 1.0 second on the WS side and up to 1.8 seconds on the DS side, which are the tension application timings as can be seen from FIG. 12, and after that it almost matches the shortest loop length. Furthermore, the absolute value of the difference between the loop length and the shortest loop length shown in FIG. 13(c) is almost 0 mm (within ±2 mm) on both the DS and WS sides after 1.8 seconds, making it possible to accurately and easily determine the timing when tension is applied.

[0077] In this measurement example, the mode was switched to tension control mode at 0.9 seconds, but the DS side was unable to apply tension to the plate material S due to the loop. The mode was switched to tension control mode, and the actual angle θ of the looper roll LR became equal to the target angle θ aimBy reducing the peripheral speed of the work rolls WRa and WRb of the sixth rolling stand F6 to correct this, tension could be applied across the entire strip width at 1.8 seconds, and the strip was threaded stably. As shown in Fig. 13(c), when the mode was switched to tension control mode, the difference between the loop length on the DS side and the shortest loop length was 10 mm, so if the amount of deceleration had been corrected according to this difference, it is estimated that the loop could have been eliminated at an earlier timing. As described above, according to the loop state measuring device 100 of this embodiment, by measuring the difference between the loop length and the shortest loop length, it is possible to quantitatively grasp the sag (difference between the loop length and the shortest loop length) of the sheet material S at the time of transition to the tension control mode (at the end of the ascending process of the looper roll LR). Therefore, by executing the above-mentioned second rolling method and determining the amount of increase or decrease in the peripheral speed of the work rolls WRa, WRb according to the difference between the loop length and the shortest loop length at the time of transition to the tension control mode, and increasing or decreasing the peripheral speed of the work rolls WRa, WRb according to the determined amount of increase or decrease, it is possible to eliminate the loop early and prevent rolling troubles due to excessive loops.

[0078] Moreover, the reason why the difference in the loop lengths of both edges occurs as in this measurement example is because the speed of the sheet material varies in the width direction during rolling. According to the loop condition measuring device 100 of this embodiment, the loop lengths of both edges can be measured, so that by carrying out the third rolling method described above and adjusting the leveling of the work rolls WRa and WRb based on the difference in edge length between both edges, rolling troubles due to meandering and shape defects can be prevented. [Explanation of symbols]

[0079] 1, 2...2D imaging device 3...Arithmetic unit 100 Loop status measuring device S...Plate material LR···Looper Roll WRa, WRb... Work roll (roll pair)

Claims

1. A method for measuring a loop state of a plate material in a hot rolling line in which a plurality of roll pairs, each consisting of rolls arranged opposite to each other above and below, are installed in a horizontal direction, the method comprising: an imaging step of imaging the plate material from above a pass line of the hot rolling line using two two-dimensional imaging devices provided along a width direction of the plate material between two adjacent pairs of rolls among the plurality of roll pairs, so that an edge of the plate material is included in an imaging field of view to generate an image; A calculation step of calculating coordinates of an edge of the plate material at a plurality of points in the rolling direction of the plate material based on the captured image, and calculating a length of the edge of the plate material between the two adjacent roll pairs based on the calculated coordinates of the edge of the plate material at the plurality of points; having The two two-dimensional imaging devices are provided such that the directions of their optical axes when viewed from the rolling direction of the plate material are different from each other, In the calculation step, detecting a position of an edge of the plate material in the captured image captured by the two two-dimensional imaging devices, calculating distances from the two two-dimensional imaging devices to the edges of the plate material at the multiple locations based on the detected positions of the edges of the plate material in the captured image, and calculating coordinates of the edges of the plate material at the multiple locations in the rolling direction of the plate material based on the calculated distances and a geometric arrangement condition of the two two-dimensional imaging devices; The method for measuring the loop state of a plate material calculates, as the length of the edge of the plate material between the two adjacent sets of roll pairs, the length of a broken line connecting the apex of the roll located on the lower side of the roll pair located on the upstream side of the rolling direction of the plate material among the two adjacent sets of roll pairs, the calculated coordinates of the edge at the multiple locations, and the apex of the roll located on the lower side of the roll pair located on the downstream side of the rolling direction of the plate material among the two adjacent sets of roll pairs.

2. In the calculation step, As the length between the two adjacent roll pairs, the length of a line segment connecting an apex of a roll located on the lower side of the roll pair located on the upstream side in the rolling direction of the plate material and an apex of a roll located on the lower side of the roll pair located on the downstream side in the rolling direction of the plate material is calculated; 2. The method for measuring the loop state of a plate material according to claim 1, further comprising the step of subtracting a roll pair length between the two adjacent roll pairs from a length of an edge of the plate material between the two adjacent roll pairs to calculate a loop length of the plate material between the two adjacent roll pairs.

3. the hot rolling line has a looper roll between the two adjacent sets of roll pairs, The two two-dimensional imaging devices each include the looper roll within an imaging field of view, In the calculation step, Calculating a minimum strip length, which is the shortest length that the strip can have between the two adjacent roll pairs, based on the actual angle or height of the looper roll; Calculating the shortest loop length of the plate material between the two adjacent roll pairs by subtracting the length between the roll pairs from the shortest plate material length; The method for measuring the loop state of a plate material according to claim 2 , further comprising the step of calculating a difference between the loop length of the plate material and the shortest loop length of the plate material.

4. 4. The method for measuring the loop state of a plate material according to claim 1, further comprising: measuring a temperature of the plate material upstream of the two adjacent roll pairs in the rolling direction of the plate material; and setting an exposure time of the two two-dimensional imaging devices used in the imaging process based on the measured temperature.

5. Using the method for measuring the loop state of a plate material according to claim 3, a difference between a loop length of the plate material and a shortest loop length of the plate material is sequentially calculated in a process of raising the looper roll after a leading end of the plate material is bitten into a roll pair located downstream in a rolling direction of the plate material out of the two adjacent roll pairs, When the calculated absolute value of the difference is equal to or smaller than a predetermined threshold value for a predetermined set time or longer, the rolling method for a plate material, determining that tension has been applied to the plate material by the looper roll, and transitioning to a tension control mode in which a torque acting on the looper roll is controlled so that an actual tension of the plate material approaches a target tension, and a peripheral speed of a pair of rolls located on at least one of the upstream side and the downstream side in the rolling direction of the plate material is controlled so that an actual angle of the looper roll approaches a target angle.

6. Using the method for measuring the loop state of a plate material according to claim 3, a difference between a loop length of the plate material and a shortest loop length of the plate material is sequentially calculated in a process of raising the looper roll after a leading end of the plate material is bitten into a roll pair located downstream in a rolling direction of the plate material out of the two adjacent roll pairs, When a predetermined time has elapsed since the looper roll was raised, transitioning to a tension control mode in which a torque acting on the looper roll is controlled so that the tension performance of the plate material approaches a target tension, and a peripheral speed of a roll pair located at least on either the upstream side or the downstream side in the rolling direction of the plate material is controlled so that the angle performance of the looper roll approaches a target angle; In the tension control mode, an amount of increase or decrease in a peripheral speed of a pair of rolls located on at least one of the upstream side and the downstream side in the rolling direction of the plate material is determined based on a difference between a loop length of the plate material calculated at the time of transition to the tension control mode and a shortest loop length of the plate material, and the peripheral speed of the pair of rolls located on at least one of the upstream side and the downstream side in the rolling direction of the plate material is increased or decreased in accordance with the determined amount of increase or decrease.

7. 5. The method for measuring the loop state of a plate material according to claim 1, wherein the length of the edge of the plate material at both edges of the plate material between the two adjacent pairs of rolls is calculated; A method for rolling a plate material, comprising controlling leveling of a roll pair located on at least one of the upstream and downstream sides in the rolling direction of the plate material, of the two adjacent roll pairs, based on the calculated difference in edge length of the plate material at both edges.

8. A plate loop state measuring device for measuring a loop state of a plate material being rolled in a hot rolling line in which a plurality of roll pairs each consisting of rolls arranged opposite to each other above and below are installed in a horizontal direction, two two-dimensional imaging devices that are provided between two adjacent roll pairs among the plurality of roll pairs along a width direction of the plate material, and capture an image of the plate material from above a pass line of the hot rolling line so that an edge of the plate material is included in an imaging field of view to generate an image; A calculation device that calculates coordinates of an edge of the plate material at a plurality of points in the rolling direction of the plate material based on the captured image, and calculates a length of the edge of the plate material between the two adjacent roll pairs based on the calculated coordinates of the edge of the plate material at the plurality of points; having The two two-dimensional imaging devices are provided such that the directions of their optical axes when viewed from the rolling direction of the plate material are different from each other, The computing device includes: detecting a position of an edge of the plate material in the captured image captured by the two two-dimensional imaging devices, calculating distances from the two two-dimensional imaging devices to the edges of the plate material at the multiple locations based on the detected positions of the edges of the plate material in the captured image, and calculating coordinates of the edges of the plate material at the multiple locations in the rolling direction of the plate material based on the calculated distances and a geometric arrangement condition of the two two-dimensional imaging devices; The plate material loop state measuring device calculates, as the length of the edge of the plate material between the two adjacent sets of roll pairs, the length of a broken line connecting the apex of the roll located on the lower side of the roll pair located on the upstream side of the rolling direction of the plate material among the two adjacent sets of roll pairs, the calculated coordinates of the edge at the multiple locations, and the apex of the roll located on the lower side of the roll pair located on the downstream side of the rolling direction of the plate material among the two adjacent sets of roll pairs.

Images