Apparatus and method for contactless measurement of the flatness of a moving material strip

Abstract

The invention relates to an apparatus for the contactless measurement of the flatness of a moving material strip, in particular a moving metal strip (4), comprising: a positioning device (8) which determines a material strip spatial region (6); an electromagnetic deflection device (10) for generating a magnetic force for deflecting the material strip; and an optical measurement system (12) for measuring the deflection of the material strip, wherein the electromagnetic deflection device (10) and the optical measurement system (12) are arranged on opposite sides of the material strip spatial region (6). The invention also relates to a method for the contactless measurement of the flatness of a moving material strip. The invention addresses the problem of how to measure the flatness on strips in a contactless manner with high and low strip tension.

Description

[0001] Device and method for contactless measurement of the flatness of a moving material strip

[0002] The invention relates to a device and a method for the contactless measurement of the flatness of moving material webs, in particular a moving metal strip.

[0003] Flatness is an important property in the production of web-like products such as flat-rolled metal strips. This is measured in the production lines during the process to control the process or to demonstrate compliance with tolerances.

[0004] Without the influence of strip tension, flatness deviations typically appear in the form of bulges, edge waves, or center waves and are caused by uneven elongation of the strip. These shape deviations can be determined optically using light section methods.

[0005] Under the influence of strip tension, the forces in the uneven strip are distributed in such a way that the shorter fibers, defined as thin sections aligned longitudinally along the strip, are elastically stretched more strongly until all fibers are of equal length. Different fiber lengths no longer manifest themselves as height differences, so there are no longer any height differences remaining in the strip, and thus, flatness can no longer be measured optically. Here, the varying tensile stress distribution in the strip can be measured by contact using force sensors. These are typically installed in flatness measuring rollers.

[0006] Another method uses air pressure differences, such as compressed air or vacuum, to cause the strip to vibrate while under tension. Eddy current sensors measure the deflection, which is used to determine the flatness.

[0007] During the hot rolling of metal strip, flatness measurement with a contacting flatness measuring roll is generally not possible due to the high temperatures involved. Firstly, the sensors in the roll require complex protection from the heat. Secondly, the introduced heat causes stresses in the roll, which distorts the measurement results.

[0008] Therefore, optical systems are typically used here. These can measure the flatness at the beginning or end of the strip, when strip tension cannot yet be applied. No measurement values ​​are available in the middle of the strip, i.e., when the strip is clamped between the rolling mill and the coiler. The situation is particularly unfavorable in the production of endless hot strip, for example, in casting-rolling lines. In this case, flatness measurement is not possible over a long period of time. In lines with an endless strip, strip tension is present almost continuously, and necessary phases without strip tension are much rarer.

[0009] In certain process lines, flatness can also be measured optically due to the low strip tension. Depending on the production spectrum (e.g., thick or thin strips, high or low strength), non-flatness may or may not be visible. Therefore, there are many material strips where the non-flatness is no longer visible and cannot be directly measured optically. Measurement with a flatness measuring roller is still not possible with low strip tension. Therefore, a measuring system that can measure flatness is desired.

[0010] Therefore, a measuring system is needed that can measure the flatness of strips without contact under strip tension, regardless of their temperature or the strength of the strip tension. Therefore, the present invention is based on the technical problem of being able to measure the flatness of strips without contact under high and low strip tension.

[0011] The above-mentioned technical problem is solved according to the invention by a device having the features of claim 1.

[0012] The device for contactless measurement of the flatness of a moving material strip, in particular a moving metal strip, comprises a positioning device determining a material strip space area, an electromagnetic deflection device for generating a magnetic attractive or repulsive force for deflecting the material strip and an optical measuring system for measuring the deflection of the material strip, wherein the electromagnetic deflection device and the optical measuring system are arranged on opposite sides of the material strip space area.

[0013] According to the invention, non-flatness in the material strip can be made electromagnetically visible so that it can be measured using the known optical method. The deflection of the strip is generated by applying a force, particularly a homogeneous force, to the strip. Due to the different tensile stress distribution caused by non-flatness, this force leads to deflections of the strip of varying strengths. These deflections are measured via an optical system above the strip. By taking into account the generated magnetic force and the measured deflection of the material strip, conclusions can be drawn about the different tensile stress distribution and the flatness. A cyclic reference measurement can be performed during a time without magnetic force.

[0014] The force acting on the belt is generated by an electromagnetic deflection device. This generates a magnetic field whose field lines run through the preferably ferromagnetic material belt, generating an attractive or repulsive force. The optical measuring system measures the deflection of the belt in the section where the electromagnetic field is applied, preferably using laser triangulation to determine the deflection. Detection can be performed using point or line sensors, generating a line or point pattern projected onto the belt. The use of camera clusters consisting of a large number of cameras is advantageous. This allows reliable measurements to be taken even on changing surfaces. The cameras in the camera cluster each monitor only a small field of view and are therefore all aligned almost perpendicular to the laser line.The influence of matte or glossy surfaces is thus significantly reduced.

[0015] An advantage of the invention is that the device can be equipped with a conventional laser triangulation system for flatness measurement. Applications of this device with the projection of only one laser line are known. Alternatively, for example, two laser lines are projected onto the material web, which, with little or no web tension, measure the visible non-flatness by determining the longitudinal angle of the web. This allows strips to be measured without web tension using the same device as when using electromagnetic force application with web tension.

[0016] The device according to the invention therefore enables the contactless measurement of the flatness of the material strip with and without strip tension. The optical sensors for detecting the deflection can be arranged at a relatively large distance from the strip and easily protected from damage and temperatures. The distance to the surface of the material strip can, for example, be more than twice, or in particular a multiple of, the distance of the electromagnetic deflection device.

[0017] In a preferred embodiment of the device, the

[0018] The positioning device has two rollers, and the deflection device is arranged, particularly symmetrically, in the space between the rollers and at a distance from the material space. The electromagnetic deflection device is adequately protected by its arrangement between two rollers, despite the short distance to the potentially warm material web.

[0019] The rollers and the section of force applied to the material web by the electromagnetic deflection device form a variable triangle, the height of which depends on the belt's elongation. In areas with greater elongation, such as those caused by center waves, a larger deflection or a triangle with a greater height results.

[0020] A further preferred embodiment of the device is that the electromagnetic deflection device has at least one coil and a core with at least three poles for generating a deflecting magnetic field. A preferably symmetrical arrangement of the core's poles generates a homogeneous magnetic field that causes uniform and reliable deflection of the material strip. A homogeneous formation of the magnetic field in the direction of movement or transport of the material strip is advantageous. The design with three poles is advantageous for generating and introducing the magnetic field in a central section of the material web. The shape of the core can also be referred to as an "E" and has the described advantage of a defined point of attraction relative to the material strip.The deflection device preferably extends over at least the entire width of the material strip in order to apply the deflecting magnetic force to the material strip over this width.

[0021] The device described above is suitable for measuring magnetizable metal strips. If, however, the metal strips are not magnetizable, an electromagnetic eddy current device can be provided to induce an eddy current in the material strip. Thus, an eddy current is generated in a non-magnetic metal strip, for example, made of austenitic steel or aluminum, via the additional alternating field. This eddy current, in turn, generates a magnetic field in the metal strip, which interacts with the magnetic field of the electromagnetic deflection device and thus generates the force for deflecting the strip.

[0022] The technical problem outlined above is also solved according to the invention by a method for the contactless measurement of the flatness of a moving material strip, in particular a moving metal strip, in which the material strip is deflected using an electromagnetic force, in which the deflection of the material strip is measured optically, in which a variable magnetic force is generated using a time-varying current profile, and in which a height difference is determined from the deflection measured by the optical measuring system during a high magnetic field strength and the measured deflection during a low magnetic field strength. Preferably, the high magnetic field strength is in the region of the maximum of the variable current profile, and the low magnetic field strength is zero.

[0023] The described method can be carried out in particular with a previously described device.

[0024] The magnetic field is switched on and off, preferably cyclically. The optical system measures the strip contour with and without the application of force. The difference in deflections then represents the measure of the strip tension in the material strip. The differences in strip tension across the strip width are then converted into strip flatness.

[0025] To determine the height difference, a height profile is preferably first created over at least part of the strip width from the measured values ​​of the deflection device. From this profile, the height difference at a plurality of strip positions is then determined by comparing the height profiles during the magnetic pulse and between two magnetic pulses. In a preferred embodiment of the method, the variable magnetic force is generated with a pulsed current profile with rising ramps and / or with falling ramps, and the deflection of the material strip is measured during the duration of one of the ramps. This prevents vibrations in the material web because the magnetic field is continuously built up and broken down over the at least one ramp, and no jumps occur in the magnetic field profile. The ramps can be linear or curved. Ramps with a steep rise and then asymptotically approaching a maximum current value are preferred.The progression can also be exponential.

[0026] The described method can be further developed by determining the magnetic force along one of the current curve ramps at the time of a predetermined target deflection of the material strip. Through inline evaluation, the deflection and thus the time of a predetermined target deflection can be determined simultaneously, so that the magnetic field strength at this time can be determined as a key factor for the target deflection.

[0027] Furthermore, the same setup can be used to ensure that if the maximum deflection of the material web, determined by the optical measuring system, is exceeded during one of the current ramps, the current intensity is limited. This prevents excessive deflection of the material web and any resulting damage to the material web caused by contact with the magnet or other deformations.

[0028] Previously, the device for the application of a ferromagnetic metal strip has been described, which can be deflected by means of the electromagnetically induced magnetic field.

[0029] For a non-ferromagnetic material strip, the method can be implemented by using an induced eddy current to generate magnetization that interacts with the deflecting electromagnetic force. For this purpose, the device comprises a magnetic field generating device for generating an eddy current in the material strip. Thus, an eddy current can be generated in a non-ferromagnetic strip, for example, made of austenitic steel or aluminum, via an additional alternating field. This eddy current, in turn, generates a magnetic field in the material strip and thus the force for deflecting the material strip.

[0030] In the following, the invention is explained using exemplary embodiments with reference to the drawing. In the drawing,

[0031] Fig. 1 shows an embodiment of a device for contactless measurement of the flatness of a moving material strip,

[0032] Fig. 2 is a schematic representation of an electromagnetic deflection device,

[0033] Fig. 3 shows the various parameters for determining strip flatness,

[0034] Fig. 4 is a schematic representation of the time course of a magnet power and

[0035] Fig. 5 is a schematic representation of an electromagnetic deflection device with an eddy current.

[0036] In the following description of the various embodiments of the invention, components and elements with the same function and mode of operation are provided with the same reference numerals, even if the components and elements may differ in their dimensions or shape in the various embodiments. Fig. 1 shows a device 2 for the non-contact measurement of the flatness of a moving material strip, which in this case is designed as a moving metal strip 4.

[0037] The device 2 is defined per se without the presence of the metal strip 4; therefore, a positioning device 8 is initially provided that defines a material strip space area 6. The material strip space area 6 is the space in which the metal strip 4 is guided and moved within the device 2 for measurement. The approximate dimensions of the material space area 6 are shown with two dashed lines, with an upper dashed line indicating the upper surface of a non-deflected metal strip 4 and the lower dashed line indicating the lower surface of a maximally deflected metal strip 4.

[0038] The device 2 further comprises an electromagnetic deflection device 10 for generating a magnetic attraction force for deflecting the material strip 4. The deflection device 10 generates a variable magnetic field as a function of an induction current, which acts on the metal strip 4 and deflects the metal strip 4—downward in Fig. 1. The deflection device 10 extends over at least the entire width of the material strip 4 to be measured in order to generate the deflecting magnetic field across the entire width. It is also possible to provide multiple deflection devices that cover sections of the width of the material strip.

[0039] To measure the deflection of the metal strip 4, the device further comprises an optical measuring system 12 with a laser 14 for projecting a light pattern onto the surface of the metal strip 4 and with a camera 16 for detecting the light pattern. The data from the camera 16 are evaluated in an integrated evaluation unit. As shown in Fig. 1, the electromagnetic deflection device 10 and the optical measuring system 12 are arranged on opposite sides of the material strip space area 6. Thus, the measuring system 12 can be positioned at a greater distance from the material strip 4 and is thus better protected against contamination, damage, and thermal radiation.

[0040] The positioning device 8 further comprises two rollers 18 and 20, and the deflection device 10 is symmetrically spaced in the space between the rollers 18 and 20 and arranged below the material space 6. The vertical distance in Fig. 1 is sufficiently large to prevent contact with the material strip 4 even during the greatest possible deflections of the material strip 4.

[0041] The electromagnetic deflection device 10 has a coil 22 and a core 24 with a central pole 26 and two outer poles 28 and 30 arranged laterally thereto, in this case symmetrically, for generating a deflecting magnetic field. The coil 22 and the core 24 extend perpendicular to the plane of the figure across the entire width of the material strip 4 in order to apply a magnetic force that is distributed as evenly as possible to the entire material strip 4 when generating an electromagnetic field. The magnetic field should be homogeneous transversely to the transport direction of the material strip 4, i.e., generate an equal magnetic force at all points on the metal strip 4. In the transport direction of the material strip 4, the magnetic force should be as symmetrical as possible on both sides of the action zone in the material strip 4.

[0042] The electromagnetic deflection device 10 is shown in more detail in Fig. 2. The magnetic field lines are marked with the letter "B" and run symmetrically centrally through the section of the metal strip 4 to be deflected. The magnetic force is introduced into the metal strip 4 at a central section and acts homogeneously across the width of the metal strip 4. The optical measuring system 12 shown in Fig. 1 measures the deflection of the material strip 4 in the region of the maximum magnetic force introduction by the deflection device 10. For this purpose, a light line is projected onto the surface of the metal strip 4 in the region of the greatest expected deflection of the metal strip 4 using the laser 14 and a suitable scanning device. The camera 16, or a plurality of cameras arranged in parallel, monitors the area of ​​the laser line, and an evaluation unit (not shown) determines the vertical position of the laser line across the width of the metal strip 4.Instead of one line of light, at least two lines of light or even a multitude of light points can be projected onto the surface.

[0043] In the case of a laser line projection, the camera 16, for example a CCD or CMOS camera, captures the lines running across the strip surface in the recorded image with a resolution of several pixels per width of the laser line. Absolute strip flatness results in a uniform pattern of straight lines with equal line spacing. Deviations of the strip surface from the ideal plane due to unevenness or irregularities cause a change in the line spacing in the area of ​​the irregularity. The camera captures this change. The changes in the line pattern can be easily converted into height differences mathematically by comparing them with an ideal pattern.

[0044] For the operation of the device 2, a control unit 40 is provided for variably controlling the electromagnetic deflection device 10 and for controlling the optical measuring system 12. Thus, the deflection device 10 and the measuring system 12 can be coordinated and synchronized with one another. A measurement of the deflection with and without the application of electromagnetic force or further method steps described below can be implemented with the control unit 40. The described device 2 can be used to perform the method described below for the contactless measurement of the flatness of a moving metal strip 4. A time-varying current flow in the coil 22 generates a time-varying magnetic force with the deflection device 10.A height difference is determined from the deflection measured by the optical measuring system 12 during a magnetic pulse and the deflection between two magnetic pulses, i.e., without magnetic force. In particular, to determine the height difference, a height profile can first be created over at least part of the strip width from the measured values ​​of the deflection device. From this profile, the height difference at a plurality of strip positions can then be determined by comparing the height profiles during the magnetic pulse and between two magnetic pulses.

[0045] The following describes an example of an algorithm that shows how the measured data can be evaluated and how the strip flatness can be determined from it.

[0046] For this purpose, the metal strip is divided in sections in its width into a plurality of N so-called fibers (indexed with n = 1 ... N), whereby the fibers form finitely long longitudinal sections of the metal strip and can each have widths of less than 5 mm, in particular less than 1 mm or even less than 0.1 mm.

[0047] With optimal flatness of the metal strip, all N fibers are ideally the same length, regardless of whether the metal strip is under mechanical longitudinal tension, also called strip tension, or not. In the real world, the fiber lengths vary and are stretched to the same length when strip tension is applied.

[0048] This is achieved by the magnetic field of the electromagnetic deflection device, which acts on the metal strip across its width – from below in Fig. 1. Assuming that the magnetic force is uniform across the entire width, the resulting deflection Ahn of the individual fibers can be used to determine the flatness of the metal strip.

[0049] Fig. 3 shows the relevant quantities for the described device 2, with the illustration being understood as a section through a fiber n. The force FM of the electromagnet 22 and 24 acts vertically downward and deflects the metal strip 4 downward. The force FMÜ then acts on the fiber n, with Fwn = FM / N. The magnitude of the deflection is indicated by Ahn and is measured by the optical measuring system 12 from a dashed zero line.

[0050] From the fiber deflection Ahn and from the portion Fwn = FM / N of the total magnetic force FM acting on the fiber n, the forces Fßn acting in the band direction in the fibers n are determined: with

[0051] For a constant magnetic force FMn on the fiber n, the mean value of the forces acting in the direction of the band with summation over n=l to N is as follows:

[0052] This results in the relative force distribution F'ßn, which is independent of the magnetic force FM.

[0053] The flatness can be determined in 1 unit from the relative force deviation F'BN, the specific strip tension, and the elastic modulus. This describes the length deviation of the fibers without the influence of the strip tension:

[0054] -1 - 10 5

[0055] Flatness IUnits] = F R ■ specific bandzuq ■ — - —

[0056] L J 7 a Elastic modulus

[0057] Fig. 4 shows a typical curve of the variable current flow through coil 22. The time-varying magnetic force, designated as magnetic power in Fig. 4, is generated with a current curve with rising ramps and falling ramps, and the deflection of the material strip 4 is measured during the duration of each of the ramps. The frequency of the sequence of current pulses is, for example, in the range of 1 to 10 Hz.

[0058] With such a magnetic power curve, the magnetic force can be determined along one of the current curve ramps at the time of a specified target deflection of the material strip. The target deflection and the associated current flow can be used to determine the deflection of the material strip.

[0059] In addition, if a maximum deflection of the material strip is exceeded during one of the current ramps, the current intensity can be limited. In Fig. 5, an electromagnetic eddy current device is also provided for inducing a magnetic field (not shown in detail), whose magnetic field lines are labeled WB. The induced magnetic field WB generates an eddy current WS in the material strip 4. The magnetic field generated by the eddy current WS then interacts with the magnetic field B of the electromagnetic deflection device 10, so that a deflection of the material strip 4 can be generated without the material strip itself having to be magnetic.

Claims

Patent claims 1. Device for the contactless measurement of the flatness of a moving material strip, in particular a moving metal strip, with a positioning device (8) determining a material strip space area (6), with an electromagnetic deflection device (10) for generating a magnetic force for deflecting the material strip and with an optical measuring system (12) for measuring the deflection of the material strip, wherein the electromagnetic deflection device (10) and the optical measuring system (12) are arranged on opposite sides of the material strip space area (6).

2. Device according to claim 1, characterized in that the positioning device (8) has two rollers (18, 20) and that the deflection device (10) is arranged in the space area between the rollers (18, 20) and at a distance from the material space area (6).

3. Device according to claim 1 or 2, characterized in that the electromagnetic deflection device (10) has at least one coil (22) and a core (24) with at least three poles (26, 28, 30) for generating a deflecting magnetic field.

4. Device according to one of claims 1 to 3, characterized in that a controller (40) is provided for variably controlling the electromagnetic deflection device (10) and for controlling the optical measuring system (12).

5. Device according to one of claims 1 to 4, characterized in that an electromagnetic eddy current device is provided for inducing an eddy current in the material strip.

6. Method for the contactless measurement of the flatness of a moving material strip, in particular a moving metal strip, in which the material strip is deflected by an electromagnetic force, in which the deflection of the material strip is measured optically, in which a variable magnetic force is generated by a time-varying current profile and in which a height difference is determined from the deflection measured by the optical measuring system during a high magnetic field strength and the measured deflection during a low magnetic field strength.

7. Method according to claim 6, in which the variable magnetic force is generated with a pulsed current waveform with rising ramps and / or with falling ramps and in which the deflection of the material strip is measured during the duration of one of the ramps.

8. Method according to claim 6 or 7, wherein the magnetic force along one of the ramps of the current curve is determined at the time of a predetermined desired deflection of the material strip.

9. Method according to one of claims 6 to 8, wherein the current intensity is limited if a maximum deflection of the material strip is exceeded during one of the ramps of the current curve.

10. Method according to one of claims 6 to 9, in which a magnetization for interaction with the deflecting electromagnetic force is generated in a non-ferromagnetic material strip with an induced eddy current.

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