KR100406390B1 - Apparatus and method for measuring the slab width by using the mapping algorithm in two dimentinoal coordinates - Google Patents

Abstract

The present invention relates to a slab width measuring apparatus and method that can accurately measure the width of the slab produced in steel mills, and more specifically slab width by enabling accurate width measurement even for slabs bent in the longitudinal direction or inclined in the width direction The present invention relates to a slab width measuring apparatus and a measuring method using an improved two-dimensional coordinate mapping algorithm to reduce a measurement error of a.

The present invention, CCC camera located on the upper side of the slab; A light source positioned at a lower side of the slab to provide light to the CCC camera; A controller electrically connected to the CCC camera to calculate a slab width signal and calculate a slab width; And a slab width measuring device for continuously measuring the width of the slab, including: a CRT outputting the slab width value calculated by the controller to the outside, wherein the plurality of CCC cameras are provided on the both sides of the slab at a predetermined interval. And a slab width measuring device using a two-dimensional coordinate mapping algorithm, wherein the control unit has four A / D converters electrically connected to the CCD camera to convert analog signals into digital signals, and electrically connected to a calculation unit. , Shows a slab width measurement method using the same.

Description

Slab width measuring device and measuring method using 2D coordinate mapping algorithm {APPARATUS AND METHOD FOR MEASURING THE SLAB WIDTH BY USING THE MAPPING ALGORITHM IN TWO DIMENTINOAL COORDINATES}

The present invention relates to a slab width measuring apparatus and method that can accurately measure the width of the slab produced in steel mills, and more specifically slab width by enabling accurate width measurement even for slabs bent in the longitudinal direction or inclined in the width direction The present invention relates to a slab width measuring apparatus and a measuring method using an improved two-dimensional coordinate mapping algorithm to reduce a measurement error of a.

In general, slabs used as intermediate materials in the steelmaking process are produced in the form of cuboids (length: 5m-11m, width: 0.7m-2m, thickness: about 0.25m). These slabs are made of hot rolled coil through hot rolling process, where accurate control of the thickness, width and length of the coil is essential to produce the coil desired by the demander.

In order to control the slab width during the size control, the slab width is measured before rolling using a slab width measuring device. Using the width information measured in this way, by setting the edge roll of the rolling mill in advance, it is possible to accurately control the coil width to the desired size. In other words, accurate slab width measurement has a decisive influence on accurate coil width control.

Conventional slab width measuring apparatuses have been mainly developed as a laser (LASER) type or a CCD (Charge Coupled Device) camera type. As shown in FIG. 1, the dual CCD camera type includes two cameras, a lower light source 200, a controller 210, and a CRT 220. 1 and 2 are diagrams showing a conventional CCD camera type slab width measuring device for measuring a slab width of a normal shape (cuboid) from the side and the front, respectively.

Each camera is set to have the same measurement field of view. For accurate measurement, the lower left corner of the slab is positioned at the right field of view with respect to the center line of Camera 1, and the lower right corner is positioned at the left field of view of Camera 2. Position it. The reason for this is to eliminate the error in the slab thickness, and each camera measures the distance (M1, M2) from the camera centerline to both edges of the slab by detecting both edges in the slab width direction. At this time, the distance (M1, M2) between the camera center line and the edges of both sides of the slab is measured by the image formed on the pixels (Pixel) of each CCD camera.

In other words, the measurement distance is determined by the number of pixels brightly formed by the light of the lower light source 200. As shown in FIG. 2, the measurement reference position of the pixel is the upper surface of the roller table. do. On the other hand, the measured value of the CCD camera is a value obtained by multiplying the number of brightly formed pixels by the distance per pixel (d), and thus, the width (W) of the slab is equal to the measured value M1 at a predefined distance between cameras (D). Can be defined as minus M2. At this time, the width of the slab to be measured is the distance from the lower left corner of the slab to the lower right corner of the slab, which can be expressed as Equation 1 below.

Slab width (W) = distance between cameras (D)-measured values of both cameras (M1 + M2) --- Equation 1

The conventional slab width measuring step is shown in FIG. 3. This is followed by the step 252 of determining the slab entry after the initialization step 250, and the steps 254 and 256 of calculating the measured values of the CCD camera are performed, and the slab width is determined using Equation 1. A calculation step 258 is made. A step 260 of storing the calculated slab width in the storage device RAM is performed, and a step 262 of determining whether the slab is out of view of the camera is made, calculating the calculated slab width, and taking the next measurement. Performing steps 264 and 266 are performed.

However, the above-described conventional measuring method can accurately measure the width only when the slab of the normal shape (cuboid) without upper and lower warpage. In other words, an error is generated in the width measurement of the slab which is bent vertically in the longitudinal direction or inclined in the width direction.

Figure 4 is a side view showing a conventional CCD camera-type slab width measuring device for measuring the width of the slab is bent in the longitudinal direction. Such slab bending occurs in various forms depending on the playing process. In FIG. 4, it can be seen that the front part of the slab is lifted upward (upper bending) and the back part is bent down (lower bending). 5 is a view showing that the slab with the upper warp is measured by a conventional CCD camera-type slab width measuring device.

As shown in FIG. 5, the slab width at the portion where the upper bending occurs is shorter than the actual slab width when viewed from the reference position. It can be seen in FIG. 5 that errors Eu1 and Eu2 occur in each camera. This error is because the slab width of the portion where the upper warp is raised is not in contact with the roller and is raised so that the light of the CCD camera projected in the inclined state is incident as much as Eu1 and Eu2 into the lower part of the slab. To generate. In other words, the measured slab width is shorter than the actual slab width by the sum of the errors Eu1 and Eu2.

Error (Eu) = error (Eu1) of camera 1 + error (Eu2) of camera 2 ----- Equation 2

Actual slab width (W) = measured slab width (Weu) + and (Eu) ------- Equation 3

6 is a view showing that the slab in which the lower warp is generated is measured by a conventional CCD camera-type slab width measuring apparatus.

As shown in FIG. 6, the actual slab width and the measured slab width are different from each other when viewed from the reference position. As a result, the slab width portion of the portion where the lower deflection occurs is longer than the actual slab width. . This is because the slab width of the lower bending part is lowered to the lower side of the roller, so the light of the CCD camera projected in the inclined state does not enter the lower edges of both sides of the slab. It causes an error.

Error (Ed) = error of Camera 1 (Ed1) + error of Camera 2 (Ed2) ------- Equation 4

Actual slab width (W) = measured slab width (Wdu) -error (Ed) -------- Equation 5

On the other hand, Figure 7 is a view showing that the slab inclined laterally measured by a conventional CCD camera-type slab width measuring device. In the slab as described above, the error Et1 is generated by the camera of the tilted side. Further, it can be seen that the slab width W is inclined by the width W 'and the angle θ of the slab being projected, so that it is W' / (cosθ). The width W 'of the projected slab is the distance between when the slab edge is vertically extended on the roller.

Projected Slab Width (W ') = Measured Slab Width (Wet) + Error (Et1) ----- Equation 6

Actual slab width (W) = projected slab width (W ') / cosθ ------- Equation 7

As described above, the conventional slab width measuring apparatus using two CCD cameras can accurately measure only the normal slab without bending. In other words, accurate width measurement was not possible for slabs that were curved in the longitudinal direction or inclined in the width direction.

The present invention is to solve the conventional problems as described above, the object is

The present invention provides a slab width measuring device using an improved two-dimensional coordinate mapping algorithm to reduce the measurement error of slab width by enabling accurate width measurement even for slabs that are curved in the longitudinal direction or in the width direction.

1 is a side view showing a slab width measuring apparatus using two CCD cameras according to the prior art;

2 is a front view showing a slab width measuring apparatus using two CCD cameras according to the prior art;

3 is a flow chart showing a processing step of a slab width measuring apparatus using two CCD cameras according to the prior art in order;

Figure 4 is a side view showing the top, bottom bending of a typical slab;

5 is a front view showing the error of the slab width due to the upper bending of the slab in the slab width measuring apparatus using two CCD camera according to the prior art;

Figure 6 is a front view showing the error of the slab width due to the lower bending of the slab in the slab width measuring apparatus using two CCD camera according to the prior art;

7 is a front view showing the error of the slab width due to the lateral tilt of the slab in the slab width measuring apparatus using two CCD camera according to the prior art;

8 is a front view showing a state of measuring the width of the normal slab in the slab width measuring apparatus using four CCD camera according to the present invention;

FIG. 9 is an explanatory diagram illustrating a method of measuring slab width by a two-dimensional mapping method according to the present invention with respect to a normal slab as shown in FIG. 8; FIG.

10 is a front view showing a state of measuring the slab width in the case of the upper bending and inclination of the slab in the slab width measuring apparatus using four CCD camera according to the present invention;

FIG. 11 is an explanatory diagram illustrating a method of measuring slab width in a two-dimensional mapping method according to the present invention when the upper bending and the slant of the slab occur as shown in FIG. 8; FIG.

12 is a flow chart showing a processing step of a slab width measuring apparatus using four CCD cameras according to the present invention in basic steps;

13 is a flow chart showing in detail the processing steps of the slab width measuring apparatus using four CCD camera according to the present invention.

Explanation of symbols on the main parts of the drawings

11,12,21,22 .... CCD camera 200 ..... light source

210 ..... control unit 212 ..... A / D converter

220 ..... CRT

The present invention to achieve the above object,

A CCC camera located on the upper side of the slab; A light source positioned at a lower side of the slab to provide light to the CCC camera; A controller electrically connected to the CCC camera to calculate a slab width signal and calculate a slab width; In the slab width measuring apparatus for continuously measuring the width of the slab, including; CRT for outputting the slab width value calculated by the controller to the outside;

Four CCC cameras are mounted on both sides of the slab, each of which is provided in plurality at predetermined intervals, and the controller is equipped with four A / D converters electrically connected to the CCD camera to convert analog signals into digital signals. By providing a slab width measuring apparatus using a two-dimensional coordinate mapping algorithm characterized in that connected to.

In addition, the present invention provides a slab width measuring method that can accurately measure the slab width continuously produced using a CCC camera-type slab width measuring apparatus,

Determining whether the slab enters; Measuring both sides of the slab using a plurality of CCC cameras, respectively; Calculating coordinates of the left and right edges of the slab using the slab width measurements; Calculating a slab width using a trigonometric function through the left and right edges; Storing the calculated slab width in a memory; And determining whether the slab is out of the CCD camera by providing a slab width measuring method using a two-dimensional coordinate mapping algorithm.

Hereinafter, the present invention will be described in more detail with reference to the drawings.

As shown in FIG. 8, the slab width measuring apparatus 300 proposed in the present invention includes four CCD line cameras 11, 12, 21, and 22, a lower light source 200, a controller 210, and It consists of the CRT 220. Four CCC cameras are mounted on each side of the slab at a plurality of predetermined intervals, respectively, and the controller 210 is electrically connected to the CCD cameras 11, 12, 21, and 22 to convert analog signals into digital signals. Four A / D converters 212 are mounted and electrically connected to the calculation unit. The controller 210 converts analog signals from four cameras 11, 12, 21, and 22 into digital signals by four A / D converters 212 and is output through the A / D converters 212. The digital signal is processed by a program preconfigured in the calculator 215 to calculate and obtain a slab width value. The width calculated by the calculator 215 is displayed through the CRT 220.

Hereinafter, a method of operating the slab width measuring apparatus 300 using the two-dimensional coordinate mapping algorithm of the present invention will be described below.

In the slab width measuring apparatus using the two-dimensional coordinate mapping algorithm of the present invention, if the slab width is to be measured in a normal state, as shown in FIG. 8, two CCD cameras (cameras 11 and 12) are located at the lower left of the slab. The corner part is detected, and the remaining two cameras (cameras 21 and 22) detect the lower right corner part. In this case, one light source 200 is positioned at the lower side of the roller to supply light to the plurality of CCD cameras.

And, for accurate measurement, the lower left corner of the slab is positioned at the overlapping area of the right view of camera 11 and the right view of 12, and the lower right corner of the slab is located at the overlapping area of the left field of camera 21 and the left field of 22. Do it.

At this time, the distance between cameras 11 and 12 and the distance between 21 and 22 are set in advance as distance B, and the distance between cameras 11 and 22 is set as D2. Each camera is installed at height H. And, when the reference position for measuring the slab width is the upper end of the roller table, it can be seen that the measuring distances of the cameras 11, 12, 21, 22 are M11, M12, M21, M22, respectively. Here M11 is the sum of M12 and the camera interval B.

M11 = M12 + B

FIG. 9 illustrates mapping the structure of FIG. 8 to two-dimensional coordinates. At this time, the center line of the camera 11 is to be the y-axis of the first two-dimensional coordinates and the top of the roller table is set to the X-axis to detect the lower left corner of the slab. In order to detect the lower right corner of the slab, a second two-dimensional coordinate is set with the y-axis of the center line of the camera 22 and the X-axis of the upper end of the roller table. At this time, the X axis of the first coordinate for detecting the lower left corner is set to the plus direction, and the X axis of the second coordinate for detecting the lower right corner is set to the plus direction. . The reason for this is to be symmetrical with the first coordinate on the left.

The positions of the objects in FIG. 8 are mapped to respective coordinates in FIG. 9. First, the positions of cameras 11 and 12 are mapped to coordinate points 11 (O, H) and 12 (B, H), respectively. The measured values of cameras 11 and 12 at the reference position are mapped to coordinate points 11 '(M11,0) and 12' (B + M12,0), respectively. Also, map the position of the lower left corner of the slab to the coordinates (X1, Y1). At this time, the lower left corner of the slab that we want to know can be seen in Figure 8 where the measuring lines of the camera 11 and 12 intersect. 9, the coordinates at which the lines connecting the points 11 and 11 'and the lines connecting the points 22 and 22' intersect (X1, Y1), which are the coordinates of the lower left corner of the slab. . Equation 11 of the line connecting points 11 and 11 'and Equation 12 of the line connecting points 12 and 12' are as follows.

y =-(H / M11) x + H ------- Equation 11

y =-(H / M12) x + (H + HB / M12) -------- Equation 12

The coordinates of the points where the above two expressions intersect can be obtained through a two-dimensional system of equations.

X1 = BM11 / (M11-M12) ---------- Equation 13

Y1 =-(HB) / (M11-M12) + H --------- Equation 14

The lower right corner of the slab is measured in the same manner as the method of measuring the lower left corner of the slab. In this case, the coordinates of the cameras 21 and 22 are mapped to points 21 (B, H) and 22 (O, H), respectively. In addition, the coordinates of the values measured at the reference position are mapped to points 21 '(M21 + B, O) and points 22' (M22, 0), respectively. In addition, the position of the lower right corner of the slab is mapped to coordinates (X2, Y2). Equation 21 of the line connecting points 21 and 21 'is the equation 22 of the line connecting point 21 and point 22'.

y =-(H / M21) x + (H + HB / M21) ------- Equation 21

y =-(H / M22) x + H ------------- Equation 22

The coordinates of the above two expressions are as follows.

X2 = BM22 / (M22-M21) --------- Equation 23

Y2 =-(HB) / (M22-M21) + H -------- Equation 24

The width of the slab can be calculated using the coordinates of the lower left and right edges of the slab obtained above, that is, coordinates (X1, Y1) and coordinates (X2, Y2).

On the other hand, based on the measurement method as described above it is possible to accurately measure the width of the slab is bent in the longitudinal direction and tilted in the width direction as shown in Figures 10 and 11. In FIG. 10, two CCD cameras (cameras 11 and 12) detect the lower left corner of the slab, and the remaining two cameras (cameras 21 and 22) detect the lower right corner. Even in this case, one light source 200 is positioned at the lower side of the roller to supply light to the plurality of CCD cameras.

And, for accurate measurement, the lower left corner of the slab is positioned at the overlapping area of the right view of camera 11 and the right view of 12, and the lower right corner of the slab is located at the overlapping area of the left field of camera 21 and the left field of 22. Do it.

At this time, the distance between cameras 11 and 12 and the distance between 21 and 22 are set in advance as distance B, and the distance between cameras 11 and 22 is set as D2. Each camera is installed at height H. And, when the reference position for measuring the slab width is the upper end of the roller table, it can be seen that the measuring distances of the cameras 11, 12, 21, 22 are M11, M12, M21, M22, respectively. However, the M11 is not the sum of the M12 and the camera gap B, and becomes larger than that, because the slab portion is raised from the roller table.

FIG. 11 illustrates mapping the structure of FIG. 10 to two-dimensional coordinates. At this time, the center line of the camera 11 is to be the y-axis of the first two-dimensional coordinates and the top of the roller table is set to the X-axis to detect the lower left corner of the slab. In order to detect the lower right corner of the slab, a second two-dimensional coordinate is set with the y-axis of the center line of the camera 22 and the X-axis of the upper end of the roller table. At this time, the X axis of the first coordinate for detecting the lower left corner is set to the plus direction, and the X axis of the second coordinate for detecting the lower right corner is set to the plus direction. .

The positions of the objects in FIG. 10 are mapped to respective coordinates in FIG. 11.

8 and 9, coordinates (X1, X2) where Equation 11 and Equation 12 intersect with respect to both lower and lower edges of the slab inclined at a constant angle θ, that is, the lower left corner, are obtained. You can get it,

y =-(H / M11) x + H ------- Equation 11

y =-(H / M12) x + (H + HB / M12) -------- Equation 12

The coordinates of the points where the above two expressions intersect can be obtained through a two-dimensional system of equations.

X1 = BM11 / (M11-M12) ---------- Equation 13

Y1 =-(HB) / (M11-M12) + H --------- Equation 14

Then, the coordinates (X2, Y2) are obtained by using Equation 21 and Equation 22 with respect to the lower right corner of the slab.

y =-(H / M21) x + (H + HB / M21) ------- Equation 21

y =-(H / M22) x + H ------------- Equation 22

The coordinates of the above two expressions are as follows.

X2 = BM22 / (M22-M21) --------- Equation 23

Y2 =-(HB) / (M22-M21) + H -------- Equation 24

On the other hand, when calculating the slab width inclined by a certain angle (θ) by using the coordinates (X1, Y1), (X2, Y2) of the lower left and right edges of the slabs obtained above, in FIG. You can see the distance projected to the table.

In other words, the slab projection distance W ',

W '= D2- (X1 + X2) -------- Equation 25,

Understanding the Pythagorean Definition The actual slab width can be calculated as:

W (actual slab width) = SQRT {W SUP {prime 2} + (Y2-Y1) SUP {2}} --------- Equation 26

In this way, the width of the lower bending slab bent downward in the longitudinal direction can also be measured accurately.

The slab width measuring method of the present invention can accurately measure the slab width continuously produced using the CCC camera type slab width measuring apparatus of the present invention using the above-described method. In the slab width measuring method of the present invention, as shown in FIGS. 12 and 13, a step 400 of determining whether the slab enters is performed, which determines whether the slab enters the field of view of the CCD camera. In addition, a step 420 of measuring both edges of the slab by using a plurality of CCC cameras is performed, and the step 420 is performed by the A / D converter 212 of the control unit 210, respectively. Calculating the measured values of the CCD cameras 11, 12, 21, and 22 as the number of pixels brightly formed by the light of the lower light source 200, that is, the number of brightly lit pixels. It is to calculate the measured value of each CCD camera by using the value multiplied by the distance per pixel d.

In addition, a step 440 of calculating the coordinates of the left and right edges of the slab is performed using the slab width measurement values, and the step 440 is performed by mapping the CCD measurement value to two-dimensional coordinates (446). In operation 450, equations for each camera are calculated in two-dimensional coordinates using Equations 11, 12, 21, and 22. After the step 450, the step 452 of calculating the coordinates of the lower left corner of the slab is performed using Equations 11 and 12, and the next step 454 is the coordinates of the lower right corner of the slab. The operation of calculating is performed using Equation 21 and Equation 22.

In addition, after the step 454, a step 460 of calculating a slab width using a trigonometric function through the left and right edges is made, which is expressed by Equations 25 and 26.

W '= D2- (X1 + X2) -------- Equation 25

W (actual slab width) = SQRT {W SUP {prime 2} + (Y2-Y1) SUP {2}} --------- Equation 26

To calculate the actual slab width.

Then, after the step 460, a step 480 of storing the calculated slab width in the memory is performed, and then determining whether the slab has left the CCD camera.

In order to more specifically grasp the effect of the present invention as described above, the calculated slab width according to the method of the present invention and the slab width according to the conventional method were calculated and the result values were compared.

Example

10 and 11, the camera mounting height H = 1000 mm, the distance between the camera 11 and 12 B = 50 mm, the distance between the camera 11 and 22 D2 = 1800 mm, the measured value of the camera 11 M11 = 259 mm, the measured value of the camera 12 M12 = 203 mm, measured value M21 = 192 mm of camera 21, and measured value M22 = 252 mm of camera 22.

If you calculate the width of the slab by the conventional method,

W = D2-(M1 + M2) = 1800-(259 + 252) = 1289 mm.

However, according to the present invention,

The coordinates (X1, Y1) and (X2, Y2) of the lower left and right edges of the slab are expressed by Equations 13 and 14,

X1 = BM11 / (M11-M12) = 50259 / (259-203) = 231.25 mm

Y1 =-(HB) / (M11-M12) + H = -1000-50 / (259-203) = 107 mm

Then, using Equation 23 and Equation 24

X2 = BM22 / (M22-M21) = 50252 / (252-192) = 192 mm

Y2 =-(H.B) / (M22-M21) + H = -1000.50 / (252-192) = 167 mm.

In addition, using Equations 25 and 26,

W '= D2- (X1 + X2) = 1800-(231.25 + 210)

W (actual slab width) = SQRT {W SUP {prime 2} + (Y2-Y1) SUP {2}} = √ ((1800-(231.25 + 210)) ² + (167-107) ² ] = 1360 mm.

Therefore, it can be seen that the conventional method has an error of 71 mm compared to the present invention.

As described above, according to the present invention, an improved effect can be obtained to reduce the measurement error of the slab width by enabling accurate width measurement even for the slab in which the upper or lower bow is bent in the longitudinal direction or tilted in the width direction. will be.

Claims (6)

In the slab width measuring method that can accurately measure the slab width continuously produced using a CCD camera type slab width measuring device, Determining whether the slab enters 400; Each side edge of the slab is measured using a plurality of CCD cameras, and the measured value of each CCD camera is calculated using a value obtained by multiplying the number of brightly formed pixels of the lower light source 200 by the distance per pixel (d). Step 420; Calculating coordinates of the slab left and right edges using the slab width measurements (440); Calculating a slab width using a trigonometric function through the left and right edges (460); Storing the calculated slab width in the memory (480); And And a step (450) of determining whether the slab has left the CCD camera. The method of claim 1, wherein the step 440, Mapping 446 the CCD measurement to two-dimensional coordinates; Calculating 450 equations for each camera in two-dimensional coordinates; Calculating (452) the coordinates of the lower left corner of the slab; Computing coordinates of the lower right corner of the slab (454); Slab width measuring method using a two-dimensional coordinate mapping algorithm, characterized in that it comprises a. The method of claim 2, wherein step 450, y =-(H / M11) x + H ------- Equation 11 y =-(H / M12) x + (H + HB / M12) -------- Equation 12 y =-(H / M21) x + (H + HB / M21) ------- Equation 21 y =-(H / M22) x + H ------------- Equation 22 Compute the equations for each camera in two-dimensional coordinates B above, the distance between cameras 11 and 12 and the distance between 21 and 22, D2: distance between cameras 11 and 22, H: Each camera has a height, M11, M12, M21, M22: Slab width using two-dimensional coordinate mapping algorithm, characterized in that the respective measurement distance of the camera 11, 12, 21, 22 when the reference position for measuring the slab width is at the top of the roller table How to measure. The method of claim 2, wherein step 452, X1 = BM11 / (M11-M12) ---------- Equation 13 Y1 =-(HB) / (M11-M12) + H --------- Equation 14 Find the lower left corner coordinates (X1, Y1) of the slab through B above, the interval between cameras 11 and 12, H: Each camera has a height, M11, M12: Slab width measuring method using a two-dimensional coordinate mapping algorithm, characterized in that the measuring distance of each of the camera 11,12 when the reference position for measuring the slab width is at the top of the roller table. The method of claim 2, wherein the step 454, X2 = BM22 / (M22-M21) --------- Equation 23 Y2 =-(HB) / (M22-M21) + H -------- Equation 24 Find the lower right corner coordinates (X2, Y2) of the slab through B above, the distance between cameras 21 and 22, H: Each camera has a height, M21, M22: Slab width measuring method using a two-dimensional coordinate mapping algorithm, characterized in that the measuring distance of each of the cameras 21,22 when the reference position for measuring the slab width is at the top of the roller table. The method of claim 2, wherein step 460, W '= D2- (X1 + X2) -------- Equation 25 W (actual slab width) = SQRT {W SUP {prime 2} + (Y2-Y1) SUP {2}} --------- Equation 26 To calculate the actual slab width, W 'in the above: distance projected slab to roller table side, X1, X2, Y1, Y2: Slab width measurement method using a two-dimensional coordinate mapping algorithm, characterized in that the coordinates of the lower left and right lower edge.