Rolling taking frequency behavior into account

Abstract

A metal strip (1) is fed to a rolling stand (2) of a rolling mill at a feed rate (v) by an upstream feeding device (3), and the metal strip is rolled in the rolling stand (2). A measuring device (4) between the feeding device (3) and the rolling stand (2) detects thickness values ​​(d) of the metal strip (1) for successive portions (9) of the metal strip (1) and supplies the values ​​to a control device (6) of the rolling mill. The control device (6) determines respective preliminary thickness deviations based on the deviations of the respective thickness values ​​(d) from the target thickness for each portion (9) of the metal strip (1), and a final thickness deviation based on the preliminary thickness deviations. The control device (6) determines respective control values ​​(A2, A3) for the rolling stand (2) and / or the feeding device (3) for the portions (9) of the metal strip (1) based on the final wall thickness deviation of each portion (9) of the metal strip (1) and the final wall thickness deviations of a plurality of preceding and / or succeeding portions (9) of the metal strip (1), taking into account the description of the inverse frequency behavior of the rolling stand (2) and / or the feeding device (3) and / or the measuring device (4). It then outputs the respective control values ​​(A2, A3) to the rolling stand (2) and / or the feeding device (3) at the appropriate time.

Description

[Technical field]

[0001] The invention is based on an operating method for a rolling mill, comprising: - a feeding device arranged upstream of the rolling stand of the rolling mill feeds the metal strip into the rolling stand at an inlet speed; - the metal strip is rolled in a rolling stand, - a thickness value for the thickness of the metal strip is determined for each successive section of the metal strip by means of a measuring device arranged between the feed device and the rolling stand, - The thickness value is sent to the control unit of the rolling mill. - the control device determines respective interim thickness deviations based on deviations of respective thickness values ​​from a set thickness for respective portions of the metal strip; - The control device determines the final thickness deviation based on the provisional thickness deviation, the control device determines control values ​​for the rolling stands and / or the feed devices in each case for the portion of metal strip and outputs the respective control values ​​to the rolling stands and / or the feed devices at the appropriate times;

[0002] The invention is also based on a control program comprising machine code executable by a control device for a rolling mill, the execution of the machine code by the control device having the effect that the control device operates the rolling mill in accordance with such an operating method.

[0003] The invention is also based on a control device for a rolling mill, which is programmed with such a control program, so that the control device operates the rolling mill according to such an operating method.

[0004] The invention is also based on a rolling mill for rolling metal strip, - the rolling mill has at least one rolling stand, a feed device arranged upstream of the rolling stand, a measuring device arranged between the feed device and the rolling stand, and a control device, - The metal strip is fed by the feeder into the rolling stand at the inlet speed, - the metal strip is rolled in a rolling stand, - a thickness value for the thickness of the metal strip is determined for each successive section of the metal strip by the measuring device, - The detected thickness value is sent to the control device The control device operates the rolling mill according to the operating method itself.

[0005] When producing metal strip, after casting of the slab, the slab is first hot rolled, resulting in hot strip. The thickness of the hot strip is usually in the range of a few millimeters, sometimes more or less depending on the production process, for example between 1.0 mm and 20 mm for conventional hot rolling mills and between 0.6 mm and 6 mm for so-called ESP plants. In some cases, the hot strip is further processed without further thinning. In other cases, after hot rolling, the strip thickness is reduced even further in a cold rolling mill. The aim of cold rolling is the production of cold-rolled metal strip whose final thickness corresponds to the target thickness with the smallest possible deviations.

[0006] The finished hot strip - i.e. after hot rolling but before rolling in the cold rolling mill - generally has thickness deviations. The thickness deviations often have both periodic and stochastic components. Without compensation for these deviations, the metal strip will have such deviations after cold rolling. The absolute degree of deviations is less than in the case of hot strip, but the relative deviations remain. Thus - for example - if before cold rolling a metal strip has a thickness of 3.0 mm and a thickness deviation in the range of 30 μm, and after cold rolling the metal strip still has a thickness of 1.0 mm, then without compensation for the thickness deviations the metal strip will have a thickness deviation in the range of 10 μm after cold rolling. [Background technology]

[0007] Various procedures for compensating for such deviations are known in the prior art.

[0008] Thus, for example, it is known from EP 1 099 436 A1 to detect the thickness of the rolled metal strip at the exit side of the rolling stand and to carry out a thickness feedback control of the rolling stand. Since tension fluctuations also affect the thickness of the rolled metal strip, there is also a compensation for them. In order to achieve a relatively high degree of dynamic feedback control of the tension, on the one hand between the feeding device and the rolling stand, and on the other hand also between the rolling stand and the winding device arranged downstream of the rolling stand, there are rollers or similar elements which can deflect the metal strip before and / or after rolling in the rolling stand. The procedure of EP 1 099 436 A1 is based on the idea that feedback control by the feeding device itself and the winding device itself is very slow to react and that the dynamics of the feedback control can be increased by additional rollers. EP 1 099 436 A1 also contains a description of a procedure in which the thickness and speed of the metal strip are detected at the entrance side of the rolling stand and are used in the process of determining the adjustment of the rolling stand.

[0009] It is likewise known from DE 10 200 03 133 A1 to detect the thickness of the rolled metal strip at the exit side of the rolling stand and to carry out a feedback control of the thickness of the rolling stand. Periodic deviations are separated from probabilistic deviations. Periodic deviations are assumed to be caused by eccentricities of the rolls of the rolling stand. Corrections to the adjustment of the rolling stand occur accordingly.

[0010] In the case of US Pat. No. 5,999,136, the thickness of the stationary and unwound metal strip is detected at the inlet side of the rolling stand and averaged over a unit of length. The average is used to control the adjustment of the rolling stand. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] European Patent Application Publication No. 0435595 [Patent Document 2] European Patent Application Publication No. 3332883 European Patent Application Publication No. [Patent Document 3] Japanese Patent Application Publication No. 58-068414 [Non-patent literature]

[0012] [Non-Patent Document 1] “Stabile Neuronale Online Identifikation und Kompensation statischer Nichtlinearitaten” [Stable neural online identification and compensation of static nonlinearities], Thomas Frenz Summary of the Invention [Problem to be solved by the invention]

[0013] The inlet thickness deviations can already be compensated to a certain extent using prior art procedures, however, the prior art procedures can still be improved.

[0014] The object of the present invention is to provide the possibility of achieving excellent compensation of inlet wall thickness deviations of the metal strip. [Means for solving the problem]

[0015] This object is achieved by an operating method for a rolling mill having the features of claim 1. Advantageous configurations of this operating method are the subject of dependent claims 2 to 8.

[0016] According to the invention, an operating method of the type mentioned at the outset is configured in that the control device determines the respective control values ​​on the basis of the final wall thickness deviation of the respective portion of the metal strip and also on the final wall thickness deviation of a number of portions of the metal strip preceding and / or following the respective portion of the metal strip, taking into account a description of the inverse frequency response of the rolling stand and / or the feed device and / or the measuring device.

[0017] It has been recognized by the inventors that the extent to which the determined wall thickness deviations are corrected depends not only on the wall thickness deviation itself but also on the range of the wall thickness deviations. In particular, compensation for higher frequency wall thickness deviations is generally only provided to a lesser extent and with a greater phase offset than for lower frequency wall thickness deviations. In order that higher frequency wall thickness deviations can also be compensated to a full extent and without phase offset, consideration must therefore be given to the frequency response of the controlled device - this is generally the adjustment of the rolling stand with respect to the size of the rolling gap and of the feed device with respect to the size of the inlet speed and / or the inlet tension. The measurement acquisition may also have a frequency response, which can also be taken into account in this case. Consideration is given on the basis of a description of the inverse frequency response of the rolling stand and / or the feed device and / or the measuring device.

[0018] There are various possibilities for the manner in which this consideration may take place. The currently preferred way is: - a description of the inverse frequency response of the rolling stand and / or the feed device and / or the measuring device is specified for this control device by an inverse model, - the final thickness deviation of a portion of the metal strip is fed to the inverse model in each case; This control device, which uses the respective final thickness deviations by means of an inverse model, on the one hand correctively adjusts the internal state of the inverse model and, on the other hand, determines the respective control values.

[0019] This procedure is associated with the lowest computational complexity.

[0020] Alternatively, it is possible that a description of the inverse frequency response of the rolling stand and / or the feed device and / or the measuring device is specified to the control device as a frequency response characteristic, and the control device determines the respective control value by transforming the profile of the final wall thickness deviation into the frequency domain, then multiplying the transformed profile of the final wall thickness deviation by the frequency response characteristic and then transforming it back into the time domain. This procedure leads to particularly high quality results.

[0021] It is generally known that multiplication in the frequency domain corresponds to convolution in the time domain, so it is alternatively possible and generally equivalent that a description of the inverse frequency response of the rolling stand and / or the feed device and / or the measuring device is specified to the control device as a convolution kernel, and that the control device determines the respective control value by convolution of the final wall thickness deviation profile with the convolution kernel.

[0022] The detection of the frequency response characteristic and, on the basis of this, the determination or parameterization of the inverse model or the determination of the gains or the convolution kernels for the individual frequency ranges can take place automatically. In particular, predefined minor disturbances can be applied to the set roll gap values ​​of the rolling stands while the rolling mill is in operation. These disturbances are reflected at the exit side of the rolling stand with corresponding variations in the exit thickness of the metal strip. If a measuring device is arranged downstream of the rolling stand, by which this exit thickness is detected, the frequency response characteristic can be determined automatically by a combined evaluation of the applied disturbances on the one hand and the exit thickness variations on the other hand. This is in principle known to the person skilled in the art.

[0023] Preferably, for determining the respective control values, the control device uses both the final thickness deviations of the portions of the metal strip preceding the respective portions of the metal strip as well as the final thickness deviations of the portions of the metal strip following the respective portions of the metal strip. The determination of the respective control values ​​is consequently particularly reliable. This is particularly true if the number of portions of the metal strip preceding the respective portions of the metal strip, the final thickness deviations of which are used by the control device to determine the respective control values, is substantially equal to the number of portions of the metal strip following the respective portions of the metal strip, the final thickness deviations of which are used by the control device to determine the respective control values.

[0024] In the simplest case, the controller adopts the provisional wall thickness deviation 1:1 as the final wall thickness deviation. Preferably, however, the controller determines the final wall thickness deviation from the provisional wall thickness deviation using zero-phase filtering. This procedure leads to a more stable and more robust operation of the rolling stand and / or the feeder. This is especially true if a low-pass filtering of the provisional wall thickness deviation is performed using zero-phase filtering.

[0025] The above object is also achieved by a control program having the features of claim 9. According to the invention, execution of the control program has the effect that the control device operates the rolling mill according to the operating method according to the invention.

[0026] The above object is also achieved by a control device having the features of claim 10. According to the invention the control device is programmed with a control program according to the invention, so that the control device operates the rolling mill according to the operating method according to the invention.

[0027] The above object is also achieved by a rolling mill with the features of claim 11. According to the invention, a control device operates the rolling mill according to an operating method according to the invention.

[0028] The above-mentioned nature, features and advantages of the present invention and the manner in which they are accomplished will become more apparent and will be more clearly understood in connection with the following description of illustrative embodiments which are set forth in more detail in conjunction with the schematic drawings. [Brief description of the drawings]

[0029] [Figure 1] FIG. [Diagram 2] FIG. [Diagram 3] FIG. 2 shows a metal strip. [Figure 4] FIG. [Diagram 5] FIG. 2 is a diagram showing the structural configuration of a control device. [Figure 6]FIG. 4 shows a further structural configuration of the control device. [Figure 7] FIG. 4 is a diagram showing a frequency response characteristic. [Figure 8] FIG. 4 shows a further structural configuration of the control device. [Figure 9] FIG. 2 illustrates a convolution kernel. [Figure 10] FIG. 4 shows a further structural configuration of the control device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] According to FIG. 1, a rolling mill for rolling a metal strip 1 has a rolling stand 2. The metal strip 1 is rolled in the rolling stand 2. The rolling stand 2 may in particular be a cold rolling stand, in which the cold rolling of the metal strip 1 takes place. Only the working rollers of the rolling stand 2 are illustrated in FIG. 1. In general, the rolling stand 2 additionally comprises at least two backup rollers (four-high stand), in some cases even more rollers. For example, the rolling stand 2 may be formed as a six-high stand (two working rollers, two intermediate rollers, two backup rollers) or as a twelve-roller rolling stand or as a twenty-roller rolling stand. The metal strip 1 may consist of steel, of aluminum or of some other metal, for example of copper or of brass.

[0031] The rolling mill also has a feed device 3. The feed device 3 is arranged upstream of the rolling stand 2. The metal strip 1 is fed into the rolling stand 2 with an inlet speed v by the feed device 3. According to FIG. 1 the feed device 3 is formed as a coiler. It can however also be formed differently, for example as a driver or as a further rolling stand different from the rolling stand 2. The feed device 3 can also be formed as so-called S-rollers, i.e. as a number of rollers along which the metal strip 1 is eventually guided in an S-shape.

[0032] Strictly speaking, the speed at which the metal strip 1 enters the rolling stand 2 and the speed at which the metal strip 1 leaves (e.g. is unwound) from the feeder 3 must be distinguished from each other. The speed at which the metal strip 1 enters the rolling stand 2 is determined by the peripheral speed of the working rollers of the rolling stand 2 and the delay in the rolling stand 2. In the case of a coiler, for example, the speed at which the metal strip 1 leaves by the feeder 3 is determined by the rotational speed at which the coiler rotates the coil and by the current diameter of the coil, which diameter changes over time. A slight difference between these two speeds may exist momentarily. If such a momentary difference exists, the tension on the metal strip 1 between the feeder 3 and the rolling stand 2 changes. However, hereafter only the entrance speed v is referred to. Unless explicitly mentioned, hereafter, in case of uncertainty, the speed at which the metal strip 1 leaves by the feeder 3 is meant.

[0033] A measuring device 4 is arranged between the infeed device 3 and the rolling stand 2. A thickness value d for the thickness of the metal strip 1 is repeatedly determined by means of the measuring device 4. Furthermore, a further measuring device 5 may additionally be present, by means of which a measured value for the inlet velocity v is repeatedly determined.

[0034] The respectively detected thickness value d and optionally also the respectively detected value for the inlet velocity v are sent to a control device 6, which is also a component of the rolling mill. The control device 6 iteratively determines control values ​​A2, A3 for the rolling stand 2 and / or the feed device 3. The control device 6 generally determines both control values ​​A2, A3.

[0035] The control value A2 for the rolling stand 2 very generally influences at least the adjustment of the rolling stand 2, i.e. the setting of the rolling gap. By way of example, the respective control value A2 can be output to a so-called HGC (=hydraulic gap control). Alternatively, the control value A2 can influence the main drive of the rolling stand 2, i.e. vary the rolling torque or the rolling speed. The control value A2 frequently influences both the adjustment of the rolling stand 2 and its main drive. In this case, the control value A2 for the rolling stand 2 can be regarded as a vector quantity which in each case has a component for the adjustment of the rolling stand 2 and for the main drive of the rolling stand 2.

[0036] The control value A3 is fed to a rotational speed or torque feedback control for the feeder 3 and influences the inlet speed v and / or the tension on the metal strip 1 at the inlet side of the rolling stand 2. If necessary, further devices arranged upstream of the feeder 3 must also be concomitantly controlled in conjunction with the control of the feeder 3. Taking into account such further devices makes the calculation of the control value A3 more complicated, but it does not change anything with regard to the principle of the invention.

[0037] The controller 6 is programmed with a control program 7. The control program 7 comprises machine code 8 executable by the controller 6. The programming of the controller 6 with the control program 7 or the execution of the machine code 8 by the controller 6 has the effect that the controller 6 operates the mill in accordance with a method of operation which is described in more detail below, with reference first to Figure 2 and then to Figures 3 and 4.

[0038] According to Fig. 2, in step S1, the control device 6 receives the respectively detected thickness value d and optionally also the respectively detected value for the inlet velocity v. In step S2, the control device 6 determines a deviation δd of the detected thickness value d from the set thickness d*, hereafter referred to as thickness deviation δd for short.

[0039] The thickness deviation δd determined in step S2 is simply the provisional thickness deviation δd. In step S3, the control device 6 determines the final thickness deviation δd' based on the provisional thickness deviation δd. In the simplest case, step S3 is trivial. In this case, the control device 6 adopts the provisional thickness deviation δd 1:1 as the final thickness deviation δd'.

[0040] However, the true determination is preferably made such that the final wall thickness deviation δd' is determined from the provisional wall thickness deviation δd using a non-trivial determination specification. As an example, in order to determine the final wall thickness deviation δd', the control device 6 may perform zero-phase filtering in step S3. With zero-phase filtering, a filter profile of values ​​(here, the time profile of the final wall thickness deviation δd') is determined from an original profile of values ​​(here, the time profile of the provisional wall thickness deviation δd) such that no systematic phase offset occurs between the original profile and the filter profile. In general and also in the context of the present invention, zero-phase filtering is low-pass filtering, which results in that high-frequency fluctuations are removed. Low-pass filtering significantly improves the stability of the inverse modeling, in particular of the rolling stand 2, the feed device 3 and / or the measuring device 4.

[0041] For zero-phase filtering, it is also necessary to know the interim thickness deviation δd of the portion 9 following the portion 9 for which the final thickness deviation δd' is intended to be determined. In the case of zero-phase filtering, step S3 is therefore performed for another portion 9, but whose interim thickness deviation δd has already been detected.

[0042] Zero-phase filtering processes are generally known to those skilled in the art. The so-called IIR (=infinite impulse response) may be mentioned merely as an example. Another possibility for implementing zero-phase filtering is the convolution of the interim offset δd with the symmetrical impulse response of an FIR filter (FIR=finite impulse response).

[0043] In step S4, the controller 6 determines the control values ​​A2, A3 using the final wall thickness deviation δd'. In step S5, the controller 6 outputs the control values ​​A2, A3 to the rolling stand 2 and / or the feeder 3. The controller 6 then returns to step S1.

[0044] The procedure described above in conjunction with figure 2 is therefore repeatedly performed cyclically. Usually, it is performed strictly on a clock basis, i.e. even with a fixed cycle time T of, for example, 8 ms.

[0045] The procedure according to the invention is again explained in more detail below in conjunction with FIGS.

[0046] Figure 3 shows the metal strip 1 from above. The metal strip 1 is virtually divided into portions 9. In Figure 3, some of the portions 9 are supplemented by lowercase letters (e.g. a, b, etc.) in addition to the reference sign 9 in order to be able to refer to them individually.

[0047] During each cycle, i.e. during each execution of step S1, for a particular portion 9 - for example portion 9a - its thickness value d is detected and queried to the control device 6. The detected thickness value d, the associated provisional thickness deviation δd and the associated final thickness deviation δd' therefore relate to this portion 9a.

[0048] During the same cycle, another portion 9 - for example portion 9b - is rolled in the rolling stand 2. The geometrical distance between portions 9a and 9b on the metal strip 1 corresponds to the geometrical distance a between the measuring device 4 and the rolling stand 2.

[0049] A certain time T' is required to transport the portion 9a from the measuring device 4 to the rolling stand 2. This time T' is usually called the transport time. It is determined by the inlet speed v of the metal strip 1 and the distance a between the measuring device 4 and the rolling stand 2. Given a constant inlet speed v, the relationship T'=a / v holds true.

[0050] The time T' is very generally significantly greater than the cycle time T. Thus, between the portions 9a and 9b there are a number of further portions 9, for example portion 9c, for which the respective thickness value d has already been determined before the rolling of portion 9b. Furthermore, the metal strip 1 has portions 9, for example portion 9d, which have already been rolled in the rolling stand 2.

[0051] Due to the circumstance that a time T' is required for transporting each portion 9 from the measuring device 4 to the rolling stand 2, it is possible in a certain cycle to actually detect the thickness value d for the portion 9a in step S1 and to determine a provisional thickness deviation δd for this portion 9a, but to determine in step S4, for example, the control values ​​A2, A3 for the portion 9c, and to output the control values ​​A2, A3 determined in step S4 to the rolling stand 2 and / or the feed device 3 in step S5. Optionally, the control values ​​A2, A3 already determined in advance for the portion 9 between the portions 9c and 9b can also be output to the rolling stand 2 and / or the feed device 3. In the last-mentioned case, it is merely necessary that the thickness value d detected in the respective cycle, the thickness deviation δd, δd' determined in the respective cycle, and the control values ​​A2, A3 determined in the respective cycle are assigned to the respective portion 9, and that a path tracing of the portion 9 is performed. A corresponding procedure is shown in figure 4 by the fact that for steps S1 to S5, the respective parts 9a, 9b, 9c in which the respective steps S1 to S5 are performed are indicated as well. The reason why the control values ​​A2, A3 output by the control device 6 are not for part 9b, but rather for part 9c or for a part 9 between parts 9b and 9c, is that allowance must be made for certain dead times of the rolling stand 2 and / or the feed device 3.

[0052] The implementation of path tracing is generally known to the person skilled in the art. As a result, it is therefore possible to output the control values ​​A2, A3 to the rolling stand 2 and / or the feed device 3 in due time. In the context of the present invention, in due time means that the control values ​​A2, A3 output to the rolling stand 2 and / or the feed device 3 affect the metal strip 1 at the time when the respective portion 9 of the metal strip 1 is being rolled in the rolling stand 2. In this case, consideration can be given, if necessary, to the time T' and, if appropriate, to the reaction time (dead time) of the rolling stand 2 and / or the feed device 3. The reaction time is the time required by the rolling stand 2 and / or the feed device 3 to react to a control value A2, A3 newly sent to the rolling stand 2 and / or the feed device 3. Furthermore, consideration can be given to the dead times which occur in the communication between different devices or in the automation. The determination of the control values ​​A2, A3 must of course be completed before the output.

[0053] Due to the situation that the respective thickness values ​​d have already been determined for the portions 9 between the portions 9a and 9c and accordingly the respective provisional thickness deviations δd are already known and furthermore the final thickness deviations δd' are also known for the portions 9 adjacent to the portion 9c at least in the direction of the portion 9a, it is possible, for example, for the determination of the control values ​​A2, A3 for the portion 9c to take into account not only the final thickness deviation δd' of the portion 9c but also additionally any of the other final thickness deviations δd', provided that they have in fact already been determined. For example, in addition to the thickness deviation δd' of the portion 9c, the control device 6 can take into account the final thickness deviations δd' of the several adjacent portions 9 towards the portion 9a. Alternatively or additionally, in addition to the thickness deviation δd' of the portion 9c, the control device 6 can take into account the final thickness deviations δd' of the several adjacent portions 9 towards the portion 9b, optionally also beyond the portion 9b.

[0054] In the context of determining the respective control values ​​A2, A3, the control device 6 also takes into account a description of the inverse frequency response of the rolling stand 2 and / or the feed device 3 and / or the measuring device 4. A description is therefore specified for the control device 6, which directly characterizes the corresponding frequency response itself. In other words, the frequency response can be determined on the basis of the above-mentioned description. Possibilities for specifying the description of the frequency response are explained in more detail below. The control device 6 therefore does not only determine the respective control values ​​A2, A3 in such a way that consideration is given to the corresponding inverse frequency response. Rather, the control device 6 explicitly specifies the corresponding inverse frequency response itself. The characteristic variables defining the inverse frequency response are therefore known to the control device 6. This will be explained more specifically below in connection with the rolling stand 2. A similar description applies in each case to the feed device 3 and, if appropriate, to the measuring device 4 as well.

[0055] The rolling stand 2 can be modelled in different ways. In the simplest case, the rolling stand 2 is modelled as a PT1 element. Alternatively, higher order modelling comes into consideration. The modelling describes the rolling stand 2 itself, including its control if applicable. In contrast, the transport time, i.e. the time T', is not part of the modelling.

[0056] The frequency response of the rolling stand 2 can for example be described by a transfer function. If - in the generally conventional way - the transfer function itself is denoted by G and the Laplace operator is denoted by the letter s, then the transfer function G(s) can be written as follows:

[0057]

number

[0058] In this case, b i (where i=1,2...m) and c jwhere j=1,2...n are constant coefficients. The degree m of the numerator polynomial is at most equal to the degree n of the denominator polynomial. If the rolling stand 2 is modelled as a PT1 element, the transfer function G(s) can be obtained, for example, as follows:

[0059]

number

[0060] In the equation, T2 is the characteristic time constant of rolling stand 2.

[0061] The associated inverse transfer function G -1 For (s), the following applies in the general case:

[0062]

number

[0063] Inverse transfer response G -1 (s) is consequently clearly defined. If the rolling stand 2 is modelled as a PT1 element, the associated inverse transfer function G -1 (s) can be obtained precisely as follows:

[0064]

number

[0065] Inverse transfer function G -1 If (s) is modelled accurately, however, the modelled response of the rolling stand 2 is often unstable. In some cases even the response of a real rolling stand 2 can be unstable. For example, the inverse of the PT1 element gives the PD element. The PD element amplifies very high frequencies. Also, the theoretically determinable output signal of the PD element cannot be implemented in reality. The reason for this is that we are now setting limits for the actuators of the rolling stand 2. To guarantee stability and feasibility, the inverse transfer function G -1 The denominator polynomial of (s) is therefore the inverse transfer function G-1 The inverse modelling of the frequency response of the rolling stand 2 used in practice is consequently a modified inverse transfer function G -1 (s), which has the following format:

[0066]

number

[0067] TC is a small time, i.e. much smaller than the characteristic time constant T2 of the rolling stand 2. The smaller the time TC can be chosen, the better the modeling of the inverse frequency response of the rolling stand 2. In practice, the time TC will be chosen to be equal to the cycle time T or approximately equal to the cycle time T.

[0068] A similar statement applies to the feeder 3, as already mentioned. If, analogously to the rolling stand 2, the feeder 3 is modeled by PT1 elements, the resulting inverse transfer function G for the feeder 3 is -1 (s) is the modified inverse transfer function G -1 (s), which has the following format:

[0069]

number

[0070] In the formula, T3 is the characteristic time constant of the feeder 3.

[0071] Due to the above facts, it is possible to specify a corresponding inverse model 10 of the rolling stand 2 to the control device 6, in a manner corresponding to the representation in FIG. 5. As already explained, the inverse model 10 describes the inverse frequency response of the rolling stand 2, including, if applicable, the inverse frequency response of the measuring device 4. Within the differential operating time T2′, consideration can be given according to requirements for certain dead times etc. within or outside the inverse model 10. In a manner corresponding to the representation in FIG. 5, for example, the inverse model 10 may be given by an inverse transfer function G of the form -1 (s) can be implemented.

[0072]

number

[0073] The inverse model 10 is fed - on the basis of a clock with a cycle 10T - with the final wall thickness deviation δd' of the portion 9 of the metal strip 1 in each case. Using the inverse model 10, the control device 6 determines the respective control values ​​A2 for the rolling stand 2, additionally taking into account the internal states Z2 of the inverse model 10, and outputs the control values ​​A2 to the rolling stand 2. Furthermore, the control device 6 correctively adjusts the internal states Z2 by using the respective final wall thickness deviation δd' and the internal states Z2 immediately preceding the inverse model 10. The consideration of the internal states Z2 and the corrective adjustment of the internal states Z2 are necessary, since otherwise the inverse model 10 of the rolling stand 2 would not be able to store any knowledge of the history immediately preceding the final wall thickness deviation δd' and would always only be able to model a purely proportional response and not a frequency response.

[0074] A transport model 11 is arranged upstream of the inverse model 10. To the transport model 11 - on the basis of a clock with a cycle time T - the respective final wall thickness deviation δd' and the inlet velocity v are sent. The transport model 11 models the path tracing of the respective portion 9 to which the respective final wall thickness deviation δd' is assigned. Furthermore, a differential operating time T2' is sent to the transport model 11. The transport model 11 outputs the respective final wall thickness deviation δd' with a time delay with respect to the time at which the respective final wall thickness deviation δd' was sent to the transport model 11. As already mentioned, the time delay is chosen such that the control value A2 output for a particular portion 9 is valid at the time at which the corresponding portion 9 of the metal strip 1 is rolled in the rolling stand 2.

[0075] The modeling and implementation of route tracing is generally known to those skilled in the art, and therefore it need not be described in further detail.

[0076] Generally, moreover, the respective final wall thickness deviation δd' is not fed directly by the transport model 11 to the inverse model 10 of the roll stand 2, but is rather premultiplied by a static gain factor V2 in a multiplier 12. By means of the multiplier 12, the respective final wall thickness deviation δd' is converted, for example, into an additional setting value for the roll gap of the roll stand 2 or for the main drive of the roll stand 2. In principle, however, it is also possible to additionally incorporate the gain factor V2 into the inverse model 10 of the roll stand 2.

[0077] In a completely similar manner, as already mentioned, it is also possible to carry out modeling of the inverse frequency response of the feed device 3, optionally including the inverse frequency response of the measuring device 4. In a manner corresponding to the representation in FIG. 5, this leads to a completely similar arrangement including an inverse model 13, a transport model 14 and a multiplier 15. T3' is the differential operating time for the feed device and V3 is a gain factor. With the multiplier 15, the respective final wall thickness deviation δd' is converted into an additional setpoint for the inlet speed v of the metal strip 1. If the feed device 3 does not control the inlet speed v but rather the tension on the metal strip 1 at the inlet side of the rolling stand 2, it may additionally be necessary to take into account the moment of inertia of the feed device 3 as well.

[0078] The control value A2 is a vector quantity which in each case has a component for the adjustment of the roll stand 2 and for the main drive of the roll stand 2, and the modelling described above for the roll stand 2 has to be implemented separately for each component of the vector quantity. If applicable, there are therefore multiple inverse sub-models for the roll stand 2. However, this does not change anything in terms of the principle.

[0079] The corresponding control of the rolling stand 2 is performed with the control value A2 in such a way that there are only the smallest possible variations in the thickness of the metal strip 1 on the outlet side of the rolling stand 2. The corresponding control of the feeding device 3 is performed with the control value A3 in such a way that the inlet speed v and / or the inlet side tension in the metal strip 1 are kept as constant as possible. In particular, the tension influences the pass reduction in the rolling stand 2. In order that changes in the tension on the metal strip 1 do not have an undesired effect on the pass reduction, the inlet speed v must be adapted synchronously with respect to changes in the adjustment of the rolling stand 2 and changes in the circumferential speed of the working rollers of the rolling stand 2.

[0080] As already mentioned, the final thickness deviation δd' is determined using zero-phase filtering of the provisional thickness deviation δd. Therefore, the respective zero-phase filters 16, 17 can be placed upstream or downstream of the transport models 11, 14. It is also possible to incorporate zero-phase filtering into the respective transport models 11, 14.

[0081] The transport models 11, 14 are embodied such that they are of substantially the same kind. The structure of the control device 6 in FIG. 5 can therefore be modified according to the structure in FIG. 6. As a result, one of the transport models 11, 14 can be omitted in the configuration according to FIG. 6. Instead, a delay element 18 is present, with which the difference between the differential action times T2′ and T3′ is compensated. The differential action time T3′ will normally be greater than the differential action time T2′. In this case, as illustrated in FIG. 6, the transport model 14 is omitted and furthermore a delay element 18 is placed in the path for the control value A2.

[0082] The structures of the control device 6 described above in conjunction with Figures 5 and 6 are embodied as software blocks in the control device 6. They are therefore formed on the basis of the programming of the control program 7 and the execution of the machine code 8.

[0083] An alternative configuration of the invention consists in specifying a description of the inverse frequency response of the rolling stand 2 - optionally also as a combined description with the inverse frequency response of the measuring device 4 - as a frequency response characteristic FG. In a manner corresponding to the representation in Fig. 7, for various frequency ranges FBk (where k=1, 2...), the frequency response characteristic FG indicates the respective combined gains V with which time-varying wall thickness deviations having frequencies within the respective frequency ranges FB must be amplified in order to be fully compensated.

[0084] The frequency response characteristic FG is based on the following considerations: If a metal strip 1 of constant thickness is fed to the rolling stand 2 and, moreover, if the control value A2 fed to the rolling stand 2 varies with a certain amplitude and with a certain frequency, it is found that for the same amplitude of the control value A2 (=input variable), the extent to which the thickness change is imparted to the metal strip 1 by the rolling stand 2 with respect to the outlet side (=output variable) depends on the frequency. In particular, it is found that the amplitude as well as the phase angle of the outlet side changes to the thickness change. In particular, it is found that, in fact, as the frequency increases, the amplitude of the outlet side thickness deviation decreases and the phase lag increases. Depending on the frequency of the inlet side final thickness deviation δd', the "change in the position of the rolling stand 2" and / or the "change in the torque of the working rollers" or the "change in the rotational speed of the working rollers" by the correction variables must therefore be dynamically adapted with respect to the amplitude and phase angle in order to generate an optimal correction signal. In order to compensate for the final thickness deviation δd' occurring at the inlet side of the rolling stand 2 with higher frequencies, the rolling stand 2 must therefore be controlled to a greater extent.

[0085] The amplitude and the phase angle of the reaction of the roll stand 2 to the respective control value A2 can be combined into a complex factor for the respective frequency. For each frequency, the inverse of the respective complex factor corresponds to a complex gain factor V with which the wall thickness deviation at the respective frequency must be scaled in order for it to be fully compensated at the output of the roll stand 2. The sum of these gain factors V, i.e. the gain factors V for the different frequencies or frequency ranges FB, forms a frequency response characteristic FG that is specified for the control device 6.

[0086] If a frequency response description is specified for the control device 6 as such a frequency response characteristic FG, then a procedure corresponding to the representation in Figure 8 can be adopted for the determination of the respective control values ​​A2. The procedure in Figure 8 may need to be performed separately for each component of the respective control values ​​A2.

[0087] According to FIG. 8, for each portion 9 and for the further portions 9, a respective final thickness deviation δd' is specified to the control device 6. The final thickness deviation δd' forms a time profile. The control device 6 transforms the time profile into the frequency domain in a transformation block 19. By way of example, the control device 6 can perform a Fourier transform (FT), in particular an STFT (= Short Time Fourier Transform), in the transformation block 19. The Fourier transform can be continuous or discrete, as required. It can be analog or digital, also as required. Furthermore, other transformations, for example the discrete cosine transform, can also be considered as an alternative to the Fourier transform.

[0088] Regardless of the specific procedure, the control device 6 determines the frequency components FA of the above-mentioned profile by means of a transformation block 19. In a downstream decision block 20 - separately for each individual frequency range FB - the respective frequency components FA are multiplied by a gain factor V for the respective frequency range FB. The transformed profile is then multiplied by the frequency response characteristic FG. Due to the multiplication in the complex frequency domain, the amplitude is scaled and also the phase is shifted as a result. Through this multiplication, a correction spectrum of the final wall thickness deviation δd' in the frequency domain is generated, which spectrum optimally compensates for the frequency-dependent transfer response of the rolling stand 2.

[0089] In a further transformation block 21, the control device 6 transforms the output signal of the decision block 20 - i.e. the frequency-scaled frequency profile - back into the time domain. The transformation in the transformation block 21 is the inverse of the transformation in the transformation block 19. From the output signal of the transformation block 21, the control device 6 finally selects a decision for each portion 9.

[0090] The number of the final thickness deviations δd' used in connection with the procedure according to FIG. 8 can be determined as required. It is particularly appropriate to choose the number such that it is equal to a power of 2. The Fourier transform can then be implemented as a fast Fourier transform.

[0091] It is generally known to those skilled in the art that multiplication in the frequency domain corresponds to convolution in the time domain. As an alternative to specifying the frequency response characteristic FG, it is therefore possible to specify a convolution kernel FK to the control device 6 in a manner corresponding to the representation in Fig. 9. The convolution kernel FK can be determined, for example, through a separate transformation of the frequency response characteristic FG from Figs. 7 and 8 into the time domain.

[0092] If the description of the frequency response is specified as such a convolution kernel FK for the control device 6, then for the determination of the respective control values ​​A2 a procedure corresponding to the representation in FIG. 10 can be adopted as follows:

[0093] For each portion 9 and for the further portions 9 - as in the case of FIG. 8 - a respective final thickness deviation δd' is assigned to the control device 6. The final thickness deviation δd' - as in the case of FIG. 8 - forms a time profile. In a decision block 22, the control device 6 carries out a convolution of this profile with a convolution kernel FK. From the output signal of the decision block 22, the control device 6 selects as control value A2 the one determined for the respective portion 9.

[0094] 8 and 10, only a single final thickness deviation δd' is explicitly sent anew to the control device 6. The other required final thickness deviations δd' have already been sent to the control device 6 in the context of the implementation of the previous cycle. They are therefore only required to be buffered there and read out again for use.

[0095] The procedures in figures 8 and 10 have been described above in connection with the determination of the control values ​​A2 for the rolling stand 2. An entirely similar procedure is possible for the determination of the control values ​​A3 for the feed device 3. In both cases, in addition to the frequency response of the respective device 2, 3, the frequency response of the measuring device 4 can also be taken into account, if necessary.

[0096] The structures of the control device 6 described above in conjunction with Figures 8 and 10 - exactly like the structures of the control device 6 according to Figures 5 and 6 - are embodied as software blocks in the control device 6. They are therefore formed on the basis of the programming of the control program 7 and the execution of the machine code 8.

[0097] In each of the configurations of the invention, the further portion 9, whose final thickness deviation δd' is taken into account in connection with determining the respective control value A2, A3, can be exclusively the portion 9 preceding the respective portion 9 of the metal strip 1. Likewise, in the configurations in Fig. 8 and Fig. 10, the further portion 9 can be exclusively the portion 9 following the respective portion 9 of the metal strip 1. In general, however, in the case of the configurations in Fig. 8 and Fig. 10, better results are obtained if a mixed procedure is implemented, i.e. if a part of the further portion 9 precedes the respective portion 9 of the metal strip 1 and if a further part of the further portion 9 follows the respective portion 9 of the metal strip 1. As an example - for the portion 9 whose thickness d is detected in each cycle - it is always possible to use the portion 9 located in the area indicated by 23 in Fig. 3.

[0098] 3 also shows a further advantageous configuration, since if the control values ​​A2, A3 are determined in each case for the portion 9c, in a manner corresponding to the representation in FIG. 3, the number of portions 9 of the metal strip 1, the final wall thickness deviation δd' of which preceding the respective portion 9 of the metal strip 1 is used by the control device 6 to determine the respective control value A2, is substantially equal to the number of portions 9 of the metal strip 1, the final wall thickness deviation δd' of which following the respective portion 9 of the metal strip 1 is used by the control device 6 to determine the respective control value A2, A3. Slight deviations (for example up to two portions 9 more or less) are, however, generally not problematic. Furthermore, it is possible to determine a total of two n In this case, the number of portions 9 of the metal strip 1 preceding the respective portion 9 of the metal strip 1 is preferably strictly one more or one less than the number of portions 9 of the metal strip 1 following the respective portion 9 of the metal strip 1.

[0099] The invention has many advantages. In particular, an almost complete correction of the inlet wall thickness deviation δd is obtained in a simple manner. This is especially true if both the control values ​​A2 and A3 are determined in the manner according to the invention. Moreover, it is directly possible to retrofit existing rolling mills in the manner according to the invention, since the hardware itself, i.e. the rolling stands 2, the feed devices 3, the measuring devices 4, 5 and the control device 6, does not have to be modified. All that is required is that the control program 7 for the control device 6 be modified.

[0100] Although the present invention has been more particularly illustrated and described in detail using preferred exemplary embodiments, the invention is nevertheless not limited to the disclosed examples, from which other variants can be derived by those skilled in the art without departing from the scope of protection of the invention. [Explanation of symbols]

[0101] 1 metal strip 2 Rolling Stand 3 Feeder 4, 5 Measuring equipment 6. Control device 7 Control Program 8 Machine Code 9 parts 10, 13 Reverse model 11, 14 Transportation Model 12, 15 multiplier 16, 17 Zero Phase Filter 18 Delay elements 19, 21 Conversion block 20, 22 Decision Block 23 areas a Distance A2, A3 control values d thickness value d* Set thickness FA Frequency Component FB Frequency Range FG frequency response characteristics FK Convolution Kernel G transfer function s Laplace operator S1~S5 steps T cycle time T2, T3 characteristic time constants T2´, T3´ Differential action time v Inlet velocity V, V2, V3 gain factor Z2, Z3 internal state δd, δd´ Uneven thickness

Claims

1. 1. A method of operation for a rolling mill, comprising the steps of: - the metal strip (1) is fed to the rolling stand (2) of the rolling mill by a feed device (3) arranged upstream of said rolling stand (2) at an inlet speed (v), - said metal strip (1) is rolled in said rolling stand (2), - a thickness value (d) for the thickness of the metal strip (1) is determined for each successive portion (9) of the metal strip (1) by means of a measuring device (4) arranged between the feed device (3) and the rolling stand (2), the detected thickness value (d) is sent to the control device (6) of the rolling mill, the control device (6) determines a respective provisional thickness deviation (δd) on the basis of the deviation of each of the thickness values ​​(d) from a set thickness (d*) for each of the portions (9) of the metal strip (1); The control device (6) determines the final thickness deviation (δd') based on the provisional thickness deviation (δd), a method of operation in which the control device (6) determines a control value (A3) for the feed device (3) for each of the portions (9) of the metal strip (1) and outputs the respective control value (A3) to the feed device (3) at the appropriate time, the control device (6) determines the respective control value (A3) on the basis of the final wall thickness deviation (δd') of the respective portion (9) of the metal strip (1) and also on the final wall thickness deviation (δd') of a plurality of portions (9) of the metal strip (1) preceding and / or following the respective portion (9) of the metal strip (1), taking into account a description of the inverse frequency response of the rolling stand (2) and / or the feed device (3) and / or the measuring device (4), the description of the inverse frequency response of the rolling stand (2) and / or the feed device (3) and / or the measuring device (4) being assigned to the control device (6) as a convolution kernel (FK), and the control device (6) determining the respective control value (A3) by convolution of the profile of the final wall thickness deviation (δd') with the convolution kernel (FK), A method of operation comprising:

2. - said description of the inverse frequency response of said rolling stand (2) and / or said feed device (3) and / or said measuring device (4) is specified to said control device (6) by means of an inverse model (10, 13); the final thickness deviation (δd') of a portion of the metal strip (1) is fed in each case to the inverse model (10, 13); the control device (6), using the respective final thickness deviations (δd') by means of the inverse models (10, 13), correctively adjusts the internal states (Z2, Z3) of the inverse models (10, 13) on the one hand and determines the respective control values ​​(A3), The method of claim 1 , further comprising:

3. the description of the inverse frequency response of the rolling stand (2) and / or the feed device (3) and / or the measuring device (4) is specified to the control device (6) as a frequency response characteristic (FG), and the control device (6) determines the respective control value (A3) by transforming the profile of the final wall thickness deviation (δd') into the frequency domain, then multiplying the transformed profile of the final wall thickness deviation (δd') by the frequency response characteristic (FG) and then transforming it back into the time domain, The method of claim 1 , further comprising:

4. said control device (6) uses, for determining each of said control values ​​(A3), both the final thickness deviation (δd') of the portion (9) of the metal strip (1) preceding each of said portions (9) of the metal strip (1) and the final thickness deviation (δd') of the portion (9) of the metal strip (1) following each of said portions (9) of the metal strip (1); 4. A method according to claim 1 or 3, characterized in that

5. the number of portions (9) of the metal strip (1) whose final wall thickness deviation (δd') is used by the control device (6) to determine the respective control value (A3) prior to each of the portions (9) of the metal strip (1) is substantially equal to the number of portions (9) of the metal strip (1) whose final wall thickness deviation (δd') is used by the control device (6) to determine the respective control value (A3) subsequent to each of the portions (9) of the metal strip (1); The method of claim 4, characterized in that:

6. The control device (6) adopts the provisional thickness deviation (δd) 1:1 as a final thickness deviation (δd'), or the control device (6) determines the final thickness deviation (δd') from the provisional thickness deviation (δd) using zero-phase filtering; A method according to any one of claims 1 to 5, characterized in that

7. The low-pass filtering of the provisional thickness deviation (δd) is performed using the zero-phase filtering; The method of claim 6, characterized in that:

8. A control program comprising machine code (8) executable by a control device (6) for a rolling mill, the execution of the machine code (8) by the control device (6) having the effect that the control device (6) operates the rolling mill according to a method of operation as claimed in any one of claims 1 to 7.

9. A control device for a rolling mill, programmed with a control program (7) according to claim 8, thereby operating said rolling mill according to the operating method according to any one of claims 1 to 7.

10. A rolling mill for rolling a metal strip (1), comprising: the rolling mill comprises at least one rolling stand (2), a feed device (3) arranged upstream of the rolling stand (2), a measuring device (4) arranged between the feed device (3) and the rolling stand (2), and a control device (6), - said metal strip (1) is fed by said feed device (3) into said rolling stand (2) at an inlet speed (v); - said metal strip (1) is rolled in said rolling stand (2), - by means of the measuring device (4), a thickness value (d) for the thickness of the metal strip (1) is determined for each successive portion (9) of the metal strip (1), - said detected thickness value (d) is sent to said control device (6), A rolling mill, wherein said control device (6) operates said mill according to a method of operation as claimed in any one of claims 1 to 7.

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