Measuring system and method for detecting flatness defects on metal strips

Abstract

The invention relates to a measuring system for detecting flatness defects on a rolled metal strip, having a linear light source which is arranged laterally adjacent to the metal strip and is positioned such that the light source projects a light strip onto one surface of the metal strip. The measuring system additionally has a camera which is arranged laterally adjacent to the metal strip and is positioned such that light of the light strip reflected by the surface of the metal strip is detected. The light source and the camera face opposite faces of the metal strip. In a coordinate system in which the Z coordinate axis describes the normal direction that runs perpendicularly to the surface of the metal strip, the X coordinate axis points in the metal strip running direction, the Y coordinate axis points in the transverse direction of the metal strip, and the linear light source has a lower end point with the coordinates (x1,y1,z1) and an upper end point with the coordinates (x2,y2,z2), wherein the light source is oriented such that x1 ≠ x2.

Description

[0001] MEASURING SYSTEM AND METHOD FOR DETECTING FLATNESS DEFECTS ON METAL STRIPS

[0002] The invention relates to the detection of flatness defects on a rolled metal strip.

[0003] During the production of metal strips, flatness defects such as longitudinal wrinkles can occur, which can make further processing of the metal strip considerably more difficult or lead to rejects (metal scrap).

[0004] The problem is that the occurrence of flatness defects in the metal strip manufacturing process is subject to strong and sometimes unpredictable fluctuations depending on the process parameters. For example, a slight change in process parameters can result in a sudden increase in flatness defects. In general, the risk of flatness defects increases with increasing strip speed.

[0005] Since metal strips should be produced at the highest possible strip running speed for cost reasons, the metrological detection of flatness defects during the manufacturing process is of great importance in practice.

[0006] It is desirable to provide a suitable (quantitative) measure for the severity of flatness defects in order to be able to intervene in them early and in a targeted manner (i.e., preferably inline) during the manufacturing process.

[0007] A measuring system for detecting flatness defects in the production process is exposed to adverse environmental conditions (e.g., vibrations, etc.). Furthermore, damage to the measuring system can occur in the event of disturbances (e.g., strip breaks near the measurement point). It is therefore desirable to create a robust measuring system whose risk of damage is as low as possible.

[0008] JP 2010-117322 A describes a surface defect detection on a steel strip, in which a light strip is projected onto the steel strip and an image of the light strip is detected by means of a camera arranged obliquely above the steel strip.

[0009] JP 2004354235 A describes a camera system for detecting folds in a stainless steel band, whereby the camera system is located almost vertically above the stainless steel band.

[0010] JP 2000121574 A describes a surface defect detection on steel strips which uses a linear light source arranged obliquely to the strip path.

[0011] One object underlying the invention can be seen in the creation of a measuring system for detecting flatness defects on a rolled metal strip, which can withstand adverse environmental conditions in the production process and in which the risk of damage to the measuring system, e.g. in the event of disruptions in the production process, is as low as possible.

[0012] A further object of the invention may be to provide a meaningful measure for the severity of flatness defects on a rolled metal strip.

[0013] Furthermore, the invention aims to provide a method for detecting flatness defects on a rolled metal strip, which method has one or more of the aforementioned properties. The object underlying the invention is achieved by the features of the independent claims. Examples and further developments are the subject of the dependent claims.

[0014] Accordingly, a measuring system for detecting flatness defects on a rolled metal strip comprises a linear illumination source arranged laterally next to the metal strip and positioned to project a light strip onto a surface of the metal strip. The measuring system further comprises a camera arranged laterally next to the metal strip and positioned to capture the reflected light of the light strip from the surface of the metal strip. The illumination source and the camera face opposite sides of the metal strip.In a coordinate system in which the Z-coordinate axis denotes a normal direction which is perpendicular to the surface of the metal strip, the X-coordinate axis points in the direction of travel of the metal strip and the Y-coordinate axis points in the transverse direction of the metal strip, the linear illumination source has a lower end point with the coordinates (x^ y^ Z! ) and an upper end point with the coordinates (x2, y2, z2), whereby the illumination source is oriented such that x2. x2is .

[0015] By positioning the illumination source and camera to the side of the metal strip, the measuring system is effectively protected from damage that could occur in the event of a disruption in the production process (metal strip manufacturing process). In particular, if a strip break occurs, the areas to the side of the metal strip are significantly safer than areas above or below the metal strip. Furthermore, it has been shown that the sensitivity of the measurement can be significantly influenced, and in particular increased, by tilting the linear illumination source according to Xi x2.

[0016] 180° Ax

[0017] The angle of inclination can be determined by the angle ß x = arctan(— ), where Ax = | x2- x21 and Az = z2- z2. For example, it has been shown that the sensitivity of the measurement is particularly high when the angle ß x between 5 ° and 25 ° , in particular 8 ° and 15 ° .

[0018] In order to provide the best possible protection against damage to the measuring system, a distance between the illumination source and the side of the metal strip facing the illumination source in a transverse direction of the metal strip can be at least 0.3 m, in particular at least 0.5 m or at least 1 m.

[0019] For the same reasons, a distance between the camera and the side of the metal strip facing the camera in a transverse direction of the metal strip may be at least 0.3 m, in particular at least 0.5 m or at least 1 m.

[0020] It has also been shown that positioning the illumination source and the camera on opposite sides of the metal strip enables sensitive detection of flatness defects, providing a meaningful measure of the severity of flatness defects. In particular, the measuring system enables continuous monitoring of the production process with the option of rapid intervention as soon as flatness defects occur that grow into the critical range. This can significantly reduce the production of rejects (metal scrap). The illumination source can be oriented towards the metal strip so that the light strip runs at an angle to a transverse direction of the metal strip. This arrangement has proven advantageous with regard to the measurement data acquisition and the quality of the measure derived from the measurement data for evaluating the severity of flatness defects.

[0021] An oblique illumination of the metal strip is advantageous , in which the light strip runs at an angle a with respect to the transverse direction of the metal strip which is between 30 ° and 60 ° , in particular 40 ° and 50 ° .

[0022] The illumination source can be arranged in front of the camera in the direction of travel of the strip. With such an arrangement the light stripe, starting from the illumination source, runs diagonally in the direction of travel of the strip. Since the sensitivity of the measurement is greater in the strip area close to the illumination source than in the strip area remote from the illumination source, this can be achieved by positioning the illumination source closer to a roll (e.g. a stabilizing roll) in the production process than the camera. Since the height of the strip is well known and relatively stable near a stabilizing roll, this measure often creates a metrologically advantageous arrangement of the illumination source and the camera.

[0023] The camera can, for example, output a signal that assigns brightness values ​​of the reflected light to an image of the surface of the metal strip. In such a deflectometry-based measuring system, the flatness defects are detected based on the reflected light. The measuring system can have an evaluation device designed to calculate a measure of the flatness defect. An input of the evaluation device can be coupled to a signal output by the camera.

[0024] For example, the evaluation device can have a first calculation means designed to calculate a line path of the reflected light depending on the signal output by the camera. This results in data reduction and generates a signal suitable for the subsequent calculation steps.

[0025] The evaluation device can further comprise a second calculation means which is designed to calculate a height profile of the surface of the metal strip along a transverse direction of the metal strip as a function of the line path of the reflected light.

[0026] Furthermore, the evaluation device can comprise a third calculation means designed to calculate the measure of the flatness defect depending on the height profile of the surface of the metal strip. For this purpose, calculation steps such as signal limitation, weighting of the height profile data, and / or a maximum evaluation of a signal calculated from the height profile data can be performed.

[0027] A method for detecting flatness defects on a rolled metal strip comprises illuminating a surface of the metal strip with an illumination source that is arranged laterally next to the metal strip and positioned such that it projects a light strip onto the surface of the metal strip. The method further comprises detecting reflected light of the light strip from the surface of the metal strip by means of a camera that is arranged laterally next to the metal strip. The illumination source and the camera face opposite sides of the metal strip. This means that a light beam running from the illumination source to the camera can, for example, cross the metal strip over its entire width.

[0028] The method may further comprise, for example, evaluating a signal output by the camera to calculate a measure of the flatness defect.

[0029] Depending on the signal output by the camera, a line path of the reflected light can be calculated, for example.

[0030] Depending on the line path of the reflected light, for example, a height profile of the surface of the metal strip can be calculated along a transverse direction of the metal strip.

[0031] For example, a measure of the flatness defect can be calculated depending on the height profile of the surface of the metal strip.

[0032] The method can, for example, be carried out in a production process of the metal strip in the strip running direction after a cold rolling and before or after an annealing of the metal strip.

[0033] It is also possible to perform the measurement procedure in a later step of the production process. For example, after cold rolling, the metal strip can be wound into a coil, annealed, and then unwound from the coil after cooling. The process can be performed in the strip travel direction after the metal strip has been unwound from the coil.

[0034] Examples and possible embodiments of the invention are explained in more detail below with reference to the drawings. The elements in the drawings are not necessarily to scale. Like reference numerals designate correspondingly similar parts. The features of the various illustrated embodiments may be selectively combined, provided they are not mutually exclusive, and / or they may be selectively omitted unless described as absolutely necessary.

[0035] Figure 1 shows a schematic cross-sectional view of a section of a metal strip.

[0036] Figure 2 shows a schematic perspective view of an example of a measuring system for detecting flatness defects on a rolled metal strip.

[0037] Figure 3A shows a schematic partial sectional view of the measuring system and the metal strip of Figure 2 with a measuring system shown in side view (viewing direction in the -X coordinate axis direction).

[0038] Figure 3B shows a schematic side view (viewing direction in -Y coordinate axis direction) of the linear illumination source to illustrate an inclination angle ß x the illumination source relative to the Z coordinate axis.

[0039] Figure 4A shows an example of an image of the illumination source and the metal strip as captured by a camera. Figures 4B to 4F show the line path of the reflected light according to Figure 4A for the angles ß x = 0 ° , 5 ° , 10 ° , 15 ° and 20-30 ° .

[0040] Figure 5 shows a schematic block diagram of an example of an evaluation device.

[0041] Figure 6 illustrates a signal indicating a line pattern of the reflected light.

[0042] Figure 7 shows the image of Figure 4A, to which the line pattern of the reflected light from Figure 6 is added.

[0043] Figure 8 illustrates a signal indicating a height profile of the metal strip surface.

[0044] Figure 9 illustrates an example of signal processing which includes further processing of the signal of Figure 8.

[0045] Figure 10 illustrates a signal obtained by the signal processing of Figure 9 .

[0046] Figure 11 illustrates an example of signal processing that includes edge clipping of the signal of Figure 10.

[0047] Figure 12 illustrates an example of a time course of a signal which indicates a measure of flatness defects of the metal strip.

[0048] Figure 13 shows a flow chart illustrating an example of a method for detecting flatness defects on a rolled metal strip. The term "over," used in reference to an element formed or mounted "over" a surface or other element, may be used herein to mean that the element is mounted "indirectly on" the surface or element, with intervening further elements being present between the surface or other element. However, the term "over" may also have the specific meaning that the element mounted "over" a surface or other element is located "directly on," e.g., in direct contact with the surface or other element in question. The same applies analogously to similar terms such as "overlying," "underlying," "underlying," etc.

[0049] Terms used in the description such as (electrically) "connected" or "coupled" or similar terms are not to be understood as meaning that the elements are in direct electrical contact with each other; intermediate electrical elements may be provided between the "connected" or "coupled" elements. However, according to the disclosure, the above and similar terms may optionally also have the specific meaning that the elements are in direct electrical contact with each other, i.e., that no intermediate elements are provided between the "connected" or "coupled" elements.

[0050] Figure 1 shows a section of a metal strip 100. As can be seen in Figures 2 and 3, X denotes a coordinate axis in the longitudinal direction of the metal strip 100, Y a coordinate axis in the transverse direction of the metal strip 100 and Z a coordinate axis in a direction perpendicular to X and to Y (i.e. in the normal direction to a surface (flat side) 100A of the metal strip 100). The metal strip 100 can, for example, be a steel strip. For example, the metal strip 100 is a so-called electrical strip. Electrical strips are used in the electrical industry where they form the starting material for the construction of electrical cores that are used in generators, electric motors, transformers or other electrical devices.

[0051] The thickness D of the metal strip 100 can, for example, be between 0.15 mm and 0.7 mm. In particular, strip thicknesses D equal to or greater than or less than 0.25 mm, 0.3 mm, 0.35 mm, 0.4 mm, or 0.5 mm are possible.

[0052] During the production of rolled metal strips 100, for example, using a continuous annealing process, flatness defects can occur. The risk of such flatness defects occurring is particularly high with thin metal strips 100 (e.g., thin electrical strips). The flatness defects can occur suddenly during strip travel or, for example, upon a slight change in production process parameters (such as strip travel speed). The flatness defects are not thickness variations, but rather the occurrence of bulges or folds on the metal strip 100.

[0053] Figure 1 shows, by way of example, two longitudinal folds 110 that form typical flatness defects. Longitudinal folds 110 result in a corrugated surface 100A of the metal strip 100, wherein the wave troughs extend essentially in the longitudinal direction of the strip (coordinate axis X). The wavelength X1, X2 of the longitudinal folds 110 can, for example, be in the range from 1 to 5 cm. The longitudinal folds 110 can, for example, have a height H between 30 pm and 100 pm.

[0054] The tolerable height H of longitudinal folds 110 depends on the intended further processing and desired use of the products to be manufactured from the metal strip 100. If the metal strip 100 is, for example, an electrical strip from which circuit boards are to be punched, stacked, and glued, problems can arise during the further processing of the metal strip 100, for example, from a height H of 30 μm. For example, longitudinal folds 110 can limit the stacking height of circuit boards or reduce the strength of adhesive bonds (with so-called baked varnishes) of the circuit boards.

[0055] In some cases, longitudinal fold heights H between 30 pm and 50 pm can still be tolerated. A longitudinal fold height H above 50 pm is critical in most cases, i.e., such metal strips 100 are often rejected (metal scrap).

[0056] Depending on the stage of the manufacturing process at which the longitudinal folds 110 occur, the rejects may also include qualitatively perfect metal strip 100. For example, a coil of a metal strip 100 may be rejects if only a short section of the metal strip 100 in the coil has longitudinal folds 110 with a height H that exceeds the tolerance range.

[0057] The problem is that longitudinal wrinkles can occur suddenly during the manufacturing process, i.e., within a relatively short period of time. In this case, it is necessary to be able to react quickly by intervening in the manufacturing process in order to prevent further production of metal strip 100 with longitudinal wrinkles 110. For example, this can be achieved by changing manufacturing parameters (as quickly as possible). For example, it is known that the formation of longitudinal wrinkles 110 can be stopped by reducing the strip running speed. There are also other manufacturing parameters available that influence the formation of longitudinal wrinkles and / or their prevention.

[0058] This means that the higher the (desired) belt speed, the greater the risk of longitudinal wrinkles forming. The goal of the manufacturing process is to produce a 100 mm metal belt free of longitudinal wrinkles at high belt speeds.

[0059] Flatness defects, such as longitudinal wrinkles, are typically first detectable in the manufacturing process after cold rolling. They can also occur downstream in the production chain. For example, flatness defects can also occur after the metal strip 100 is wound into a coil, the coil is annealed, and the metal strip is unwound from the coil. Therefore, a method for detecting flatness defects can be carried out at different, and in particular, at multiple, locations in the process chain.

[0060] Figure 2 shows a schematic, perspective view of an example of a measuring system 200 for detecting flatness defects on the rolled metal strip 100. The measuring system 200 has an illumination source 220 and a camera 240.

[0061] The illumination source 220 is rod-shaped (i.e., ideally linear) and has a lower end point P1 with the coordinates (x^y^Z!) and an upper end point P2 with the coordinates (x2,y2,z2). The line on which the end points P1, P2 lie can be, for example, the central longitudinal axis of a luminous strip that represents the light-emitting surface of the illumination source 220. The distance between the points P1, P2 can thus represent the length of the linear illumination source 220, i.e., the length of the light-emitting luminous strip of the illumination source 220.

[0062] Figure 3A shows the metal strip 100 in a sectional view and the illumination source 220 and the camera 240 in a side view from the opposite direction of strip travel (-X coordinate axis). As shown by way of example in Figure 3A, the illumination source 220 is arranged laterally (i.e., in the direction of the negative Y coordinate axis) next to the metal strip 100. The camera 240 is arranged on the opposite side of the metal strip 100, laterally (in the direction of the positive Y coordinate axis) next to the metal strip 100.

[0063] The position of the illumination source 220 and the position of the camera 240 are selected such that the illumination source 220 projects a light stripe 260 onto the surface 100A of the metal strip 100, and that the camera 240 captures reflected light of the light stripe 260 from the surface 100A of the metal strip 100. Furthermore, the illumination source 220 and the camera 240 can be positioned such that a light beam 250 extending from the illumination source 220 to the camera 240 traverses the metal strip 100 across its entire width (i.e., from one edge 100B of the metal strip to an opposite edge 100C of the metal strip 100).

[0064] For example, it can be provided that all light rays 250 of the illumination source 220 impinging on the surface 100A of the metal strip 100 cross the metal strip 100 across its entire width. The illumination source 220 and / or the camera 240 can, for example, be arranged at a certain distance from the sides of the metal strip (edge ​​100B or edge 100C) facing the illumination source 220 or the camera 240. For example, this distance A1 or A2 in the transverse direction (coordinate axis Y) of the metal strip 100 can be at least 0.3 m, 0.5 m, 0.8 m, or 1 m. The distance Al between the illumination source 220 and the side of the metal strip 100 facing the illumination source 220 is determined, for example, as the minimum of the distances between the edge 100B and the Y coordinate of a point P of the illumination source 220 that contributes to the projection of the light strip 260 on the surface 100A of the metal strip 100.The distance A2 between the camera 240 and the side of the metal strip (edge ​​100C) facing the camera 240 is determined, for example, by the distance between the edge 100C and the Y coordinate of the main optical plane of the camera lens (not shown).

[0065] The illumination source 220 is a linear or rod-shaped illumination source. For example, the illumination source 220 can be an LED illumination source comprising a row of LEDs arranged along the line P1-P2. The line can be rectilinear and / or the illumination source 220 can also contain multiple adjacent rows (lines) of LEDs.

[0066] The illumination source 220 projects the light strip 260 onto the surface 100A of the metal strip 100. The light strip 260 can run obliquely to the transverse direction (Y-coordinate axis) of the metal strip 100. For example, the angle a at which the light strip 260 runs relative to the transverse direction of the metal strip can be between 30° and 60°, in particular 40° and 50°. For example, an angle a = 45° can be set. An angle a between 30° and 60° has proven to be preferred for the detection of flatness defects. For a = 0°, the sensitivity with respect to the flatness defect to be measured is 0, while for a close to 90°, no longitudinal wrinkles can be measured.

[0067] The linear illumination source 220 is inclined at an angle ß relative to the Z-coordinate axis, which in Figures 3A and 3B is represented by its angular components ß y and ß xin the planes ZY and ZX, respectively. The Z coordinate axis is the normal direction, which is perpendicular to the surface 100A of the metal strip 100.

[0068] Figure 3A shows the illumination source 220 from the viewing direction -X . The angle ß y is the tilt angle component of the illumination source 220 in the ZY plane relative to the Z-axis, i.e. the inclination of the illumination source 220 in the direction of 180° Av

[0069] Metal band 100. The angle ß y can be replaced by ß y = — arctan(— ) with

[0070] Ay = y2- yi, Az = z2- z2.

[0071] This angle ß y can be 0°. It is also possible that a slight "band tilt" (ie ß y > 0), whereby the light intensity of the light strip 260 on the metal strip 100 can be increased. For example, ß y between 0° or 1° and 10°, in particular between 2° and 7°.

[0072] Figure 3B shows the illumination source 220 from the viewing direction -Y. The angle ß x is the tilt angle component of the illumination source 220 in the ZX plane relative to the Z-axis, i.e. the inclination of the illumination source 220 in the tape travel direction X or (as shown here) in the opposite tape travel direction -X. The angle ß x can be replaced by ß x arctan(— ) with Ax = | x2- x21 , Az z2- z 2expressed.

[0073] This angle ß x must be > 0° to enable a sensitive longitudinal wrinkle measurement. This means that the line Pl - P2 in Figure 3B must not run in the Z direction, but must be in the X direction or -X direction by the angle ß x be tilted to the Z direction.

[0074] In other words, the inclination plane in which the illumination source 220 is inclined relative to the Z-coordinate axis can extend in all planes oriented in the Z-direction, but always with an inclination component ß x > 0° in the ZX plane must be present either in the direction of tape travel or against the direction of tape travel.

[0075] The inclination ß x is used to adjust the sensitivity of the measurement. A slope of ß is preferred. x between 5° and 25°. In particular, an inclination ß x equal to, less than, or greater than 8°, 10°, or 15°.

[0076] The camera 240 creates an image of the surface 100A of the metal strip 100, which contains the reflected light of the light strip 260. The camera 240 can, for example, be a 2D camera.

[0077] Preferably, the camera 240 can be equipped with a tilt-shift lens 242. Due to the shallow angle between the camera 240 and the metal strip 100, it is difficult to image a sufficiently sharp reflection across the entire width of the metal strip 100. It has been shown that by means of a

[0078] Tilt-shift lens 242, by means of which the axis of the lens 242 of the camera 240 can be tilted and shifted relative to the camera axis, the object plane (belt surface 100A) remains parallel to the image plane of the camera 240 and can thus be imaged undistorted. This means that the reflection (light stripe 260) can be sharply imaged across the entire width of the metal strip 100 by means of a tilt-shift lens 242 (also referred to in technology as a tilt-shift adapter), whereby sensitivity fluctuations of the longitudinal wrinkle measurement along the Y-coordinate axis can be minimized.

[0079] The optical measuring system 200 is based on deflectometry. In deflectometry, a pattern (here: the light stripe 260) is projected onto a surface (surface 100A) by a pattern generator (here: illumination source 240), and the mirror image is observed and, in particular, recorded with a camera (here: camera 240). A measuring system 200 based on the principle of deflectometry is very sensitive to local changes in the surface slope. Therefore, flatness defects can be detected with high sensitivity using a measuring system based on deflectometry.

[0080] The illumination source 220 can be arranged in front of the camera 240 in the strip travel direction (coordinate axis X). This is particularly advantageous when the illumination source 220 is located near a roller 270 over which the metal strip 100 is guided. The roller 270 has the effect of steadying the metal strip 100, i.e., its surface height near the roller 270 is relatively well known and stable over time. In the area further away from the roller 270, the height of the metal strip 100 is less precisely known and the metal strip 100 has a greater tendency to flutter (i.e., the height is less stable over time). Since the measuring system 200 has decreasing accuracy with increasing distance of the light strip 260 from the illumination source 220, such an arrangement can result in lower measurement sensitivity in areas with less mechanical control of the metal strip 100.

[0081] Figure 4A shows an image 400 of the illumination source 220 and the surface 100A of the metal strip 100 with the light strip 260 projected thereon in the camera 240. The light strip 260 shows a fluctuating profile which represents height variations H of the surface 100A.

[0082] In the example shown here, the light strip 260 extends, for example, from one edge 100B of the metal strip 100 to the opposite edge 100C. However, it is also possible for the light strip 260 to extend only over a partial region of the metal strip 100. For example, the light strip 260 can extend only over a central region of the metal strip 100, so that edge regions remain unilluminated (see also Figure 11, which shows signal processing that cuts off the edge regions).

[0083] The camera 240 outputs a signal S 1 at an output 241, which, for example, assigns brightness values ​​of the reflected light to the image of the surface 100A of the metal strip 100. By way of example, Figure 4A shows pixels (image points) in an image plane of the camera 240, to which the brightness values ​​are assigned in the signal S 1. For example, the camera 240 outputs a signal S 1, which assigns a brightness value of the reflected light to each pixel that captures an image of the surface 100A of the metal strip 100 in the longitudinal and transverse directions (X-coordinate axis and Y-coordinate axis).

[0084] Figures 4B to 4F show that the light stripe profile for a given surface 100A of the metal strip 100 depends significantly on the angle of inclination ß x depends. At small inclination angles ß x = 0° and 5° (Figures 4B-4C), the light stripe pattern has little evaluable structure, making the measurement impossible (ßx = 0°) or the measurement accuracy is impaired (ß x = 5°). For larger inclination angles ß x = 10°, 15°, 20° (Figures 4D-4E), the structure of the light strip 260 caused by the longitudinal folds increases, and thus the measurement accuracy. At inclination angles ß x > 25° (Figure 4F), the light strip 260 is so "washed out" or blurred that evaluation is made difficult and / or inaccurate. It should be taken into account that the surface 100A of the metal strip 100 shown in Figures 4B to 4F had comparatively small longitudinal wrinkles, so that with larger longitudinal wrinkles of, for example, 100 pm in height, the signal width of the light strip 260 in Figure 4F increases to such an extent that evaluation is practically no longer possible.

[0085] Figure 5 shows a schematic block diagram of an exemplary evaluation device 500. An input 501 of the evaluation device 500 can be connected to the output 241 of the camera 240 and receive, for example, the signal S1.

[0086] The evaluation device 500 can, for example, have a first calculation means 510 which is connected to the output 241 of the camera 240 and receives, for example, the output signal S1.

[0087] The evaluation device 500 may further comprise a second calculation means 520, which is connected to an output of the first calculation means 510. An output of the second calculation means 520 may be connected to an input of a third calculation means 530. The third calculation means 530 may provide an output signal S2 of the evaluation device 500. The output signal S2 may indicate a measure of the flatness defect.

[0088] According to an example of the evaluation device 500, the first calculation means 510 can perform a signal processing of the output signal S 1 , which converts the two-dimensional output signal S 1 into a signal Sa , which represents a line in the image plane of the camera 240 .

[0089] Figure 6 shows a line 600 calculated from the brightness distribution of the output signal S 1 in the image plane of the camera 240. To calculate the line 600, the first calculation means 510 can perform a statistical evaluation of the output signal S 1, which includes, for example, statistical operations on the brightness values ​​of the signal S 1.

[0090] For example, the first calculation means 510 can comprise a spatial averaging weighted with the brightness values ​​of the signal S 1 . The line 600 can, for example, represent a "center of gravity" of the brightness values ​​of the image of the light strip 260 . The calculation of the "center of gravity" 600 of the light strip 260 corresponds to the calculation of the center of gravity of a body , wherein instead of the mass distribution in the body, the brightness distribution of the light strip 260 measured pixel by pixel in the camera 240 , for example, is used as the basis for the calculation.

[0091] The calculation of line 600 results in a reduction of the measured data, since instead of the brightness distribution in the light strip 260, the line profile of the center of gravity of the brightness distribution is calculated and output, for example, as an output signal Sa of the first calculation means 510. Figure 7 shows the illustration of Figure 4A, to which the (calculated) line profile 600 of Figure 6 is graphically added.

[0092] The second calculation means 520 calculates, for example, as a function of the line profile 600 (output signal Sa of the first calculation means 510), a height profile H of the surface 100A of the metal strip 100 along the transverse direction (coordinate axis Y) of the metal strip 100. An example of an output signal Sb of the second calculation means 520 is shown in Figure 8. In Figure 8, the signal Sb is shown as a height profile (H in pm) against the width (Y coordinate axis) in m (meters). The calculation of the height profile H from the signal Sa (corresponds, for example, to the line 600 in Figure 6) can be carried out easily using a geometric model of the measuring system 200. The geometric model can use various approximations. For example, the lens of the camera 240 can be idealized as a point-shaped hole (keyhole camera).

[0093] For the calculation of the height profile H, a long-wave band curvature can be suppressed by high-pass filtering of the signal Sa, which is evident in Figure 6 as a curvature (i.e. deviation from an essentially straight line) of the line 600. Subsequently, depending on the short-wave fluctuations of the line 600, the height profile H of Figure 8 can be calculated taking into account geometric parameters (e.g. angles α and β x as well as the height of the illumination source 220 and the camera 240 above the strip surface 100A and the distances A1 and A2) of the measuring system 200 are calculated.

[0094] For example, based on the signal Sb, the third calculation means 530 can calculate a measure S2 for the flatness defect. The third calculation means 530 can have calculation means 530_l, 530_2 and / or 530_3, which, for example, perform a signal limitation (at 530_l) and / or an edge region clipping operation (at 530_2) and / or a maximum operation (at 530_3).

[0095] The output signal S2 can, for example, indicate a measure (key figure) for the measured flatness defect, which is determined from the signal Sb (e.g., height profile of Figure 8). In other words, the third calculation means 530 can perform a further data reduction, which makes it possible to convert the signal Sb into a form suitable for the plant operator, allowing him to continuously and promptly monitor the flatness of the metal strip 100 during operation.

[0096] Figure 9 illustrates, by way of example, signal processing for signal limitation (at 530_l). The signal processing can use a sliding window technique for signal limitation. For example, a sliding window 910 is shifted along the Y coordinate axis, e.g., from left to right, across the height profile H (Figure 8), and the value 920 of the difference between maximum and minimum within the sliding window 910 is continuously calculated. In the example shown, this value 920 is, for example, 80 pm at the position of the sliding window 910 shown.

[0097] Figure 10 illustrates an exemplary output signal Sc of the signal processing at 530_1. The output signal Sc can, for example, indicate the value 920 as a function of the width (coordinate axis Y) of the metal strip 100. Figure 10 illustrates that zones of varying intensity of longitudinal fold formation can occur across the width of the metal strip 100. The third calculation means 530 can, for example, further carry out an edge region clipping operation (at 530_2). The functioning of the edge region clipping operation is illustrated in Figure 11. For example, edge regions can be clipped off using selectable range limits RI, R2 of the signal Sc. In the example shown in Figure 11, for example, only those values ​​of the signal Sc that lie within an inner bandwidth range between the limits RI and R2 are taken into account for further signal evaluation.In the example shown in Figure 11, this range may, for example, cover 90% of the (total) bandwidth.

[0098] An output signal Sd of the edge clipping operation (at 530_2) can only contain the values ​​of the signal Sc that lie within this inner bandwidth range [RI, R2 ].

[0099] Furthermore, the third calculation means 530 can comprise a maximum operation (at 530_3) which converts the signal Sd (or another signal representing, for example, a machined height profile H of the metal strip 100) into a measure (key figure) for the flatness of the surface 100A of the metal strip 100 with respect to the longitudinal direction of the strip (e.g. with respect to an X coordinate or a region along the X coordinate axis). For example, this measure can be represented by the output signal S2. The measure can be calculated, for example, as the maximum of the signal Sd (i.e., the curve in Figure 11 within the inner edge region [RI, R2]). In the example shown in Figure 11, the key figure (signal S2) results in the value 80 pm, for example. Based on this value, the operator can immediately recognize whether flatness defects have occurred in a critical region (which would be the case with S2 = 80 pm). The operation(s) represented in the third calculation means 530 can or .may further include an averaging along the X-coordinate axis (i.e., in the direction of tape travel). For example, the characteristic (signal S2) may have been averaged over a specific range along the X-axis.

[0100] The calculations performed by the evaluation device 500 can be carried out at a repetition rate ( e.g. , greater than 10, 100 or 1000 Hz ) that enables real-time detection of flatness defects.

[0101] All calculation means and operations of the evaluation circuit 500 can be implemented in software or hardware. In particular, the disclosure includes a data processing device (e.g., a computer) with means for implementing the evaluation method described by way of example with reference to the evaluation device 500.

[0102] Furthermore, the disclosure includes a computer program having instructions which, when the computer program is executed by a computer, cause the computer to carry out the evaluation method.

[0103] The disclosure further includes a computer-readable storage medium with instructions that, when executed by a computer, cause the computer to perform the evaluation method. The storage medium is, in particular, a non-volatile storage medium, for example, a solid-state memory.

[0104] Figure 12 shows a diagram in which an example of a signal S2 (key figure) is plotted against time t. At t1, during the manufacturing process of the metal strip 100, there is a rapid increase in the key figure to the range in which scrap is produced. The operator intervention E1 at t2 typically includes reducing the strip running speed and, if necessary, changing other manufacturing parameters that influence the flatness of the metal strip 100.

[0105] At t3, the strip speed is increased again. The key figure shows that longitudinal wrinkles occur again, although they are less pronounced than at t2. At t4, therefore, another user intervention E2 takes place, e.g. by reducing the strip speed and changing other production parameters. At ts, the strip speed is increased again, and the key figure shows that excessive flatness defects no longer occur. The production process can be continued at a high strip speed using the settings found.

[0106] The output of the evaluation device 500 can be visualized, for example, on a monitor. Figure 12 shows an example of such a visualization.

[0107] Figure 13 shows a flowchart illustrating stages of a method for detecting flatness defects on a rolled metal strip. At 1310, a surface of the metal strip is illuminated with a linear illumination source arranged laterally adjacent to the metal strip and positioned to project a strip of light onto the surface of the metal strip.

[0108] At 1320, reflected light from the light stripe is reflected from the

[0109] The surface of the metal strip is captured by a camera which is arranged laterally next to the metal strip. The linear illumination source and the camera are facing opposite sides of the metal strip, such that a light beam running from the linear illumination source to the camera crosses the metal strip over its entire width. As already described, an inclination of the illumination source ß x > 0 used .

[0110] The method may further comprise the evaluation calculations explained, for example, with reference to Figures 5 to 12.

[0111] The method can be carried out, for example, on a bare (uncoated) metal strip 100. The surface 100A of an uncoated metal strip 100 is particularly suitable for a measurement method based on the principle of deflectometry.

[0112] The method can be carried out at various stages in the production process, for example after cold rolling of the metal strip and before / after annealing the metal strip. It is also possible, alternatively or additionally, to carry out the method in the strip travel direction after winding the cold-rolled metal strip into a coil, annealing the coil, cooling, and unwinding the metal strip from the coil. In this respect, the disclosure also encompasses a method for producing a rolled metal strip with one or more of the aforementioned steps, which method comprises a method for detecting flatness defects on metal strips according to the above description.

Claims

Patent claims 1. A measuring system for detecting flatness defects on a rolled metal strip, the measuring system comprising: a linear illumination source arranged laterally next to the metal strip and positioned to project a light strip onto a surface of the metal strip;and a camera arranged laterally next to the metal strip and positioned to capture reflected light of the light strip from the surface of the metal strip, wherein the illumination source and the camera face opposite sides of the metal strip such that a light beam traveling from the illumination source to the camera crosses the metal strip over its entire width, wherein in a coordinate system in which the Z coordinate axis denotes a normal direction perpendicular to the surface of the metal strip, the X coordinate axis points in the metal strip travel direction and the Y coordinate axis points in the transverse direction of the metal strip, the linear illumination source has a lower end point with the coordinates; z2) and an upper endpoint with the coordinates (x2,y2,z2) and is oriented so that x2 x2ist.

2. Measuring system according to claim 1, wherein the linear illumination source is oriented to the metal strip such that the light strip runs obliquely to the transverse direction of the metal strip.

3. Measuring system according to claim 2, wherein the light strip runs at an angle a relative to the transverse direction of the metal strip, which is between 30° and 60°, in particular 40° and 50°.

4. Measuring system according to one of the preceding claims, wherein 180° Ax Ax = | x2- x21 , Az = z2- z2 and an angle ß x = — arctan(— ) is between 5° and 25°, in particular 8° and 15°.

5. Measuring system according to one of the preceding claims, wherein 180° Ay Ay = y2- yi, Az = z2- z2 and an angle ß y = - arctan(— ) is greater than 0°.

6. Measuring system according to claim 5, wherein the angle ß y between 1° and 10°, in particular 2° and 6°.

7. Measuring system according to one of the preceding claims, which is designed to detect longitudinal folds of the metal strip inline during a manufacturing process of the metal strip.

8. Measuring system according to one of the preceding claims, wherein the camera outputs a signal which assigns brightness values ​​of the reflected light to an image of the surface of the metal strip.

9. Measuring system according to one of the preceding claims, wherein a distance between the illumination source and the side of the metal strip facing the illumination source in a transverse direction of the metal strip is at least 0.3 m, in particular 0.5 m or 1 m.

10. Measuring system according to one of the preceding claims, wherein a distance between the camera and the side of the metal strip facing the camera in a transverse direction of the metal strip is at least 0.3 m, in particular 0.5 m or 1 m.

11. Measuring system according to one of the preceding claims, wherein the camera is equipped with a tilt-shift lens.

12. Measuring system according to one of the preceding claims, further comprising: an evaluation device having an input that can be coupled to a signal output by the camera, wherein the evaluation device is designed to calculate a measure of the flatness defect.

13. Measuring system according to claim 12, wherein the signal output by the camera assigns brightness values ​​of the reflected light to an image of the surface of the metal strip, and the evaluation device comprises: a first calculation means which is designed to calculate a line profile of the reflected light as a function of the signal output by the camera.

14. Measuring system according to claim 13, wherein the evaluation device further comprises: a second calculation means which is designed to calculate a height profile of the surface of the metal strip along a transverse direction of the metal strip as a function of the line path of the reflected light.

15. Measuring system according to claim 14, wherein the evaluation device further comprises: a third calculation means which is designed to calculate the measure of the flatness defect as a function of the height profile of the surface of the metal strip.

16. A method for detecting flatness defects on a rolled metal strip, the method comprising: Illuminating a surface of the metal strip with a line-shaped illumination source which is arranged laterally next to the metal strip and positioned such that it projects a light strip onto the surface of the metal strip; and capturing reflected light of the light strip from the surface of the metal strip by means of a camera which is arranged laterally next to the metal strip; wherein the illumination source and the camera face opposite sides of the metal strip, wherein in a coordinate system in which the Z-coordinate axis denotes a normal direction which is perpendicular to the surface of the metal strip, the X-coordinate axis points in the metal strip running direction and the Y-coordinate axis points in the transverse direction of the metal strip, the line-shaped illumination source has a lower end point with the coordinates z2) and an upper endpoint with the coordinates (x2, y2 , z2) and is oriented such that x2V x2ist .

17. The method of claim 16, further comprising: Evaluating a signal output by the camera to calculate a measure of the flatness defect.

18. A method according to claim 17, wherein the signal output by the camera assigns brightness values ​​of the reflected light to an image of the surface of the metal strip, the method further comprising: Calculate a line path of the reflected light depending on the signal output by the camera. 19 . The method of claim 18 , further comprising : Calculating a height profile of the surface of the metal strip along a transverse direction of the metal strip as a function of the line path of the reflected light.

20. The method of claim 19, further comprising: Calculating the degree of flatness defect as a function of the height profile of the surface of the metal strip.

21. Method according to one of claims 16 to 20, wherein the method is carried out inline during a production process of the metal strip in the strip running direction after cold rolling of the metal strip and before annealing of the metal strip.

22. Method according to one of claims 16 to 21, wherein the method is carried out inline during a production process of the metal strip in the strip running direction after winding the metal strip into a coil, annealing the coil and unwinding the metal strip from the coil.

23. Method according to one of claims 16 to 21, wherein the method is carried out inline during a production process of the metal strip in the strip running direction before coating the metal strip with a layer of lacquer, in particular baking varnish. 24 . Method according to one of claims 16 to 23 , wherein the Metal strip is an electrical strip.

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