EP2445667B1 - Regulation method for the casting mirror of a continuous casting mould - Google Patents

Description

• wobei der Zufluss flüssigen Metalls in die Stranggießkokille mittels einer Verschlusseinrichtung eingestellt und der teilerstarrte Metallstrang mittels einer Abzugseinrichtung aus der Stranggießkokille abgezogen wird,
• wobei ein gemessener Istwert des Gießspiegels einem Gießspiegelregler zugeführt wird, der anhand des Istwerts und eines korrespondierenden Sollwerts eine Sollstellung für die Verschlusseinrichtung ermittelt,
• wobei der gemessene Istwert des Gießspiegels einem Störgrößenkompensator zugeführt wird,
• wobei dem Störgrößenkompensator weiterhin die Sollstellung für die Verschlusseinrichtung, eine um einen Störgrößenkompensationswert korrigierte Sollstellung für die Verschlusseinrichtung, eine Iststellung der Verschlusseinrichtung oder eine um den Störgrößenkompensationswert korrigierte Iststellung der Verschlusseinrichtung zugeführt wird,
• wobei der Störgrößenkompensator anhand der ihm zugeführten Werte den Störgrößenkompensationswert ermittelt,
• wobei der Verschlusseinrichtung die um den Störgrößenkompensationswert korrigierte Sollstellung zugeführt wird,
• wobei der Störgrößenkompensator ein Modell der Stranggießkokille umfasst, mittels dessen der Störgrößenkompensator anhand eines Modelleingangswertes einen Erwartungswert für den Gießspiegel ermittelt,
• wobei der Störgrößenkompensator eine Anzahl von Schwingungskompensatoren umfasst, mittels derer der Störgrößenkompensator anhand der Differenz von Istwert und Erwartungswert jeweils einen auf eine jeweilige Störfrequenz bezogenen Frequenzstöranteil ermittelt,
• wobei die Summe der Frequenzstöranteile dem Störgrößenkompensationswert entspricht.

The present invention relates to a control method for the casting level of a continuous casting mold,

• wherein the inflow of liquid metal is adjusted in the continuous casting mold by means of a closure device and the partially solidified metal strand is withdrawn by means of a take-off device from the continuous casting mold,
• wherein a measured actual value of the casting level is fed to a pouring-mirror regulator which determines a setpoint position for the closure device on the basis of the actual value and a corresponding setpoint value,
• wherein the measured actual value of the casting level is fed to a disturbance variable compensator,
• the setpoint position for the closure device, a set position for the closure device corrected by a disturbance compensation value, an actual position of the closure device or an actual position of the closure device corrected by the disturbance compensation value, are supplied to the disturbance variable compensator;
• wherein the disturbance variable compensator determines the disturbance compensation value on the basis of the values supplied to it,
• wherein the closure device is supplied with the nominal position corrected by the disturbance compensation value,
• wherein the disturbance variable compensator comprises a model of the continuous casting mold, by means of which the disturbance variable compensator determines an expectation value for the pouring level on the basis of a model input value,
• wherein the disturbance variable compensator comprises a number of oscillation compensators, by means of which the disturbance variable compensator uses the difference between the actual value and the expected value to determine a respective frequency disturbance component related to a respective disturbance frequency,
• wherein the sum of the frequency noise components corresponds to the Störgrößenkompensationswert.

Such a control method is for example from the US 5,921,313 A known. In the known control method, only a single vibration compensator is present. In this case, the sum of the frequency noise components is identical to the only determined frequency interference component.

The present invention further relates to a computer program comprising machine code which is directly executable by a control device for a continuous casting plant and whose execution by the control device causes the control device to regulate the casting level of a continuous casting mold of the continuous casting plant according to such a control method.

The present invention further relates to a control device for a continuous casting plant, which is designed such that it performs such a control method during operation.

Finally, the present invention relates to a continuous casting plant, which is controlled by such a control device.

In continuous casting, the cast strand is withdrawn from the continuous casting mold, while the core of the strand is still liquid. After the strand has emerged from the continuous casting mold, the strand for supporting the strand shell is guided and supported against the metallostatic pressure of the core via roller pairs. The support prevents, inter alia, a bulging of the cast strand on the broad side of the strand. The distance between the rollers that support the strand at the same point on both sides must correspond to the desired strand thickness.

The cast strand is actively and / or passively cooled after it leaves the continuous casting mold. Due to the cooling shrinks the strand thickness. For this reason, the distances of the rollers, which cast the strand at the same Support point on both sides, have the correct distance from each other. Until the solidification point, also called marsh point, the cast strand is not completely solidified. So it's a liquid core. Uneven exposure to the strand as it passes through the roller pairs therefore affects the casting level. Gießspiegelschwankungen but are for various reasons, for example, because of the risk of Gießpulvereinzugs in the strand surface, if possible to avoid.

As a result of fluctuations in the shell thickness occurring in the continuous casting mold, a so-called "transient bulging" can occur when the pairs of rolls pass through. The cause of the "bulging" is that a point with disturbed shell thickness passes successively different pairs of rolls and therefore changes cyclically the casting level. Since the pairs of rollers seen in the transport direction of the strand usually have a constant distance from each other and the withdrawal speed at which the strand is withdrawn from the continuous casting mold is constant, the "unsteady bulging" leads to periodic Gießspiegeländerungen. Thus, vibrations of constant frequency are formed in the casting mirror.

That from the US 5,921,313 A Known control method serves the purpose of eliminating such Gießspiegelschwankungen. The known control method is already working quite well. In particular, the pouring mirror can be regulated to within a few millimeters.

From the technical paper " Suppression of Periodic Disturbances in Continuous Casting using an Internal Model Predictor "by C. Furtmueller and E. Gruenbacher, IEEE International Conference on Control Applications, Munich, Germany, Oct. 4-6, 2006, pp. 1764-1769 , a control method for the casting level of a continuous casting mold is known in which the inflow of liquid metal into the continuous casting mold set by means of a closure device and the partially solidified metal strand is withdrawn by means of a take-off device from the continuous casting mold. A measured actual value of the pouring level is fed to a pouring-mirror regulator, which determines a set position for the closing device on the basis of the actual value and a corresponding desired value. The motor currents of drives of the discharge device are subjected to a frequency analysis. Based on the proportions of a fundamental frequency and its harmonic frequencies, a disturbance compensation value is determined, which is applied to the output signal of the Gießspiegelreglers. The shutter is controlled in accordance with the thus corrected output of the Gießspiegelreglers.

The object of the present invention is to provide opportunities to achieve even more accurate control.

The object is achieved by a control method having the features of claim 1. Advantageous embodiments of the control method according to the invention are the subject of the dependent claims 2 to 9.

• dass der Modelleingangswert durch die Beziehung $$i=p\prime +z\prime$$
  
  bestimmt ist, wobei p' die unkorrigierte Soll- oder Iststellung der Verschlusseinrichtung und z' ein Sprungkompensationswert sind, und
• dass der Störgrößenkompensator einen Sprungermittler umfasst, mittels dessen der Störgrößenkompensator durch Integrieren der Differenz von Istwert und Erwartungswert den Sprungkompensationswert ermittelt.

According to the invention, it is intended to design a control method of the type mentioned in the introduction,

• that the model input value through the relationship $$i=p\text{'}+z\text{'}$$
  
  where p 'is the uncorrected set or actual position of the shutter and z' is a jump compensation value, and
• in that the disturbance compensator comprises a step determiner by means of which the disturbance variable compensator determines the jump compensation value by integrating the difference between the actual value and the expected value.

• dass das Modell der Stranggießkokille aus einer Reihenschaltung eines Modellintegrators mit einem Modellverzögerungsglied besteht, jeder Schwingungskompensator aus einer Reihenschaltung zweier Schwingungsintegratoren besteht und der Sprungermittler aus einem Sprungintegrator besteht,
• dass als jeweilige Eingangsgröße
  • -- dem Modellintegrator ein Wert m = Vi + h1e,
  • -- dem Modellverzögerungsglied ein Wert m'= I + h2e,
  • -- dem vorderen Schwingungsintegrator eines jeweiligen Schwingungskompensators ein Wert s1 = h3e - S2,
  • -- dem hinteren Schwingungsintegrator eines jeweiligen Schwingungskompensators ein Wert s2 = h4e + S1 und
  • -- dem Sprungintegrator ein Wert s3 = h5e
    zugeführt werden, wobei
  • -- V ein Verstärkungsfaktor ist,
  • -- i der Modelleingangswert ist,
  • -- e die Differenz von Istwert und Erwartungswert ist,
  • -- I das Ausgangssignal des Modellintegrators ist,
  • -- S1 das Ausgangssignal des jeweiligen vorderen Schwingungsintegrators ist,
  • -- S2 das Ausgangssignal des jeweiligen hinteren Schwingungsintegrators ist,
  • -- h1 und h2 Modellanpassungsfaktoren sind,
  • -- h3 und h4 für den jeweiligen Schwingungskompensator spezifische Schwingungsanpassungsfaktoren sind und
  • -- h5 ein Sprunganpassungsfaktor ist.

In a preferred embodiment of the present invention is provided

• the model of the continuous casting mold consists of a series connection of a model integrator with a model delay element, each oscillation compensator consists of a series connection of two oscillation integrators and the step determinator consists of a jump integrator,
• that as respective input quantity
  • the model integrator has a value m = Vi + h 1 e,
  • the model delay element has a value m ' = I + h 2 e,
  • a value s 1 = h 3 e - S 2 for the front vibration integrator of a respective vibration compensator,
  • - The rear vibration integrator of each vibration compensator a value s 2 = h 4 e + S 1 and
  • - the value of the jump integrator is s 3 = h 5 e
    be fed, wherein
  • V is an amplification factor,
  • i is the model input value,
  • - e is the difference between the actual value and the expected value,
  • I is the output of the model integrator,
  • S1 is the output signal of the respective front vibration integrator,
  • S2 is the output signal of the respective rear vibration integrator,
  • h1 and h2 are model adaptation factors,
  • - h3 and h4 are specific vibration adjustment factors for the respective vibration compensator and
  • - h5 is a jump adjustment factor.

• Pro Störfrequenz ergibt sich je ein Paar konjugiert komplexer Pole, deren Realteile kleiner als Null sind und deren Imagimärteile gleich einer durch die jeweilige Störfrequenz definierten Kreisstörfrequenz sind,
• es ergeben sich drei reelle Pole, die alle kleiner als Null sind.

The various adjustment factors can be determined as needed. In tests, good results could be achieved by determining the adaptation factors such that the poles of the transfer function determined by the model of the continuous casting mold fulfill the following conditions:

• Per each interference frequency results in a pair of conjugate complex poles whose real parts are smaller than zero and their imaginary parts are equal to a defined by the respective noise frequency Kreisstörfrequenz,
• There are three real poles, all smaller than zero.

In a preferred embodiment, it is further provided that the adaptation factors are determined such that the real parts of the complex conjugate poles, with respect to the respective circuit interference frequency, are between -0.3 and -0.1. In particular, a value of about -0.2 is desirable. With such values, good damping properties could be achieved in tests.

Preferably, the adjustment factors are determined such that the real poles are all less than -2.0. In this case, the control method works reliably and stably even if the model of the continuous casting mold modeled the real casting mold only very inaccurate.

Particularly good results could still be achieved if the adaptation factors are determined in such a way that the real poles are pairwise different from one another.

The latter two measures (real poles less than -2.0 and in pairs different from each other) can of course be combined. Optimal results were achieved when the real poles are -3.0, -4.0 and -5.0, +/- 0.5 each.

Preferably, the number of vibration compensators is greater than one. This makes it possible to compensate for more than one "bulging oscillation".

Furthermore, it is preferable for the disturbance variable compensator to be supplied with the setpoint position for the closure device or the nominal position corrected for the disturbance compensation value for the closure device, but not the actual position of the closure device or the actual position of the closure device corrected by the disturbance compensation value. This leads to better results.

The present invention is further achieved by a computer program of the aforementioned type, wherein the execution of the computer program causes the control device controls the pouring level of the continuous casting mold according to a control method according to the invention. The computer program can for example be stored on a data carrier in machine-readable form. The data carrier may in particular be part of the control device.

The object is further achieved by a control device for a continuous casting plant, which is designed such that it carries out an inventive control method during operation. Finally, the object is achieved by a continuous casting plant, which is controlled by a control device according to the invention.

FIG 1

schematisch eine Stranggießanlage,

FIG 2

ein regelungstechnisches Blockschaltbild einer Regelanordnung,

FIG 3

schematisch die interne Struktur eines Störgrößenkompensators,

FIG 4

eine mögliche Ausgestaltung des Störgrößenkompensators von FIG 3,

FIG 5

zeitliche Verläufe eines Gießspiegelistwerts und einer Verschlussstellung bei Anwendung eines erfindungsgemäßen Regelverfahrens und

FIG 6

die korrespondierenden Größen bei Anwendung eines Regelverfahrens des Standes der Technik.

Further advantages and details will become apparent from the following description of exemplary embodiments in conjunction with the drawings. In a schematic representation:

FIG. 1

schematically a continuous casting plant,

FIG. 2

a control block diagram of a control arrangement,

FIG. 3

schematically the internal structure of a disturbance compensator,

FIG. 4

a possible embodiment of Störgrößenkompensators of FIG. 3 .

FIG. 5

time profiles of a Gießspiegelistwerts and a closed position when using a control method according to the invention and

FIG. 6

the corresponding sizes using a control method of the prior art.

According to FIG. 1 a continuous casting plant has a continuous casting mold 1. In the continuous casting mold 1 2 liquid metal 3 is poured over a dip tube, for example steel or aluminum. The inflow of the liquid metal 3 into the continuous casting mold 1 is adjusted via a closure device 4. Is shown in FIG. 1 an embodiment of the closure device 4 as a sealing plug. In this case, a position of the closure device 4 corresponds to a stroke position of the sealing plug. Alternatively, the closure device 4 may be designed as a slide. In this case, the closed position corresponds to the slider position.

The liquid metal 3 contained in the continuous casting mold 1 is cooled by means of cooling devices, so that a strand shell 5 is formed. However, the core 6 of the metal strand 7 is still liquid. He freezes later. The cooling facilities are in FIG. 1 not shown. The partially solidified metal strand 7 (solidified strand shell 5, liquid core 6) is withdrawn by means of a discharge device 8 from the continuous casting mold 1.

The pouring mirror 9 of the liquid metal 3 in the continuous casting mold 1 should be kept as constant as possible. A withdrawal speed v at which the partially solidified metal strand 7 is withdrawn from the continuous casting mold 1 is generally constant. Therefore, both in the prior art and in the present invention, the position of the closure device 4 is tracked to adjust the inflow of the liquid metal 3 in the continuous casting mold 1 so that the mold level 9 is kept as constant as possible.

By means of a corresponding measuring device 10 (known as such), an actual value hG of the pouring mirror 9 is detected. The actual value hG is fed to a control device 11 for the continuous casting plant. The control device 11 determines, according to a control method, which is explained in more detail below, a desired position p * to be assumed by the closure device 4. The closure device 4 is then controlled accordingly by the control device 11. As a rule, the control device 11 outputs a corresponding actuating signal to an adjusting device 12 for the closure device 4. The adjusting device 12 may be, for example, a hydraulic cylinder unit.

In general, an actual position p of the closure device 4 is further detected by means of a corresponding measuring device 13 (known as such) and fed to the control device 11. Usually, therefore, a closed-loop control of the closure position takes place. Alternatively, a pure control (open loop control) would be possible.

The control device 11 is designed such that it carries out an inventive control method during operation. In general, the operation of the control device 11 is determined by a computer program 14, with which the control device 11 is programmed. For this purpose, the computer program 14 is stored within the control device 11 in a data carrier 15, for example a flash EPROM. The storage is of course in machine-readable form.

The computer program 14 may have been supplied to the control device 11 via a mobile data carrier 16, for example a USB memory stick (shown) or an SD memory card (not shown). Also on the mobile data carrier 16, the computer program 14 is of course stored in machine-readable form. Alternatively, it is possible to supply the computer program 14 to the control device 11 via a computer network connection or a programming device.

The computer program 14 comprises machine code 17, which is directly executable by the control device 11. The execution of the machine code 17 by the control device 11 causes the control device 11 to control the pouring level 9 of the continuous casting mold 1 according to a control method according to the invention. This control method will be described below in connection with the FIGS. 2 and 3 explained in more detail.

FIG. 2 shows a control arrangement implemented by the control device 11. The operation of the control arrangement of FIG. 2 allows a control method according to the invention for the pouring mirror 9 of the continuous casting mold 1.

According to FIG. 2 the regulating arrangement has a pouring-mirror regulator 18. Based on a setpoint value hG * for the pouring mirror 9 and the actual value hG for the pouring mirror 9 detected by the measuring device 10, the pouring-mirror regulator 18 determines the setpoint position p * for the closure device 4 according to a controller characteristic. The regulator characteristic of the pouring-glass regulator 18 is shown in FIG FIG. 2 proportional-integral. However, other control characteristics are alternatively possible, for example PID, PT1, PT2, etc ..

The desired position p * for the closure device 4 is supplied to the closure device 4. Beforehand, however, the setpoint position p * is corrected by a disturbance compensation value z.

einem Positionsregler 19 zugeführt, dem weiterhin auch die Iststellung p der Verschlusseinrichtung 4 zugeführt wird. Der Positionsregler 19 kann beispielsweise als P-Regler ausgebildet sein.As already mentioned, the setting of the closure device 4 is usually regulated. In this case, the in FIG. 2 is shown, the corrected nominal position, ie the value $$p*-z$$

supplied to a position controller 19, which is also the actual position p of the closure device 4 is supplied. The position controller 19 may be formed, for example, as a P controller.

The actual position h of the pouring mirror 9 is detected and, as already mentioned, fed to the pouring-mirror regulator 18.

On the continuous casting mold 1 disturbances can act, which influence the pouring mirror 9. For compensation of the disturbance variables a disturbance compensator 20 is provided. The Störgrößenkompensator 20, the measured actual value hG of the casting mirror 9 and another size are supplied.

According to FIG. 2 is the Störgrößenkompensator 20 as a further size to the Störgrößenkompensationswert z corrected target position p * of the closure device 4 is supplied. Alternatively, the uncorrected setpoint position p * could be fed to the disturbance variable compensator 20. This alternative is in FIG. 2 indicated by dashed lines. Their equivalence to the realized solution is readily apparent. Because the Störgrößenkompensationswert z is in accordance with FIG. 2 determined by the Störgrößenkompensator 20 based on the values supplied to it. The corrected nominal position, that is to say the value p * -z, can therefore also be determined within the disturbance variable compensator 20 without further ado.

The determination of the disturbance compensation value z using (among other things) the corrected or uncorrected nominal position p * -z or p * of the shutter 4 is preferred within the scope of the present invention. Alternatively, the actual position p or the actual position pz corrected by the disturbance compensation value z could be supplied to the disturbance variable compensator 20 of the closure device 4. Also these alternatives are in FIG. 2 dashed lines.

The structure and operation of the Störgrößenkompensators 20 are described below in conjunction with FIG. 3 explained in more detail.

bestimmt ist. p' ist in obiger Beziehung die unkorrigierte Sollstellung p* der Verschlusseinrichtung 4, also das Ausgangssignal des Gießspiegelreglers 18. Falls dem Störgrößenkompensator 20 an Stelle der Sollstellung p* die Iststellung p der Verschlusseinrichtung 4 zugeführt würde, müsste in obiger Beziehung an Stelle des Wertes p* der Wert p verwendet werden. z' ist ein Sprungkompensationswert.According to FIG. 3 Among other things, the disturbance compensator 20 comprises a model 21 of the continuous casting mold 1. By means of the model 21, the disturbance compensator 20 determines an expectation hE for the pouring mirror 9. For this purpose, a model input value i is fed to the model 21, which is given by the relationship $$i=p\text{'}+z\text{'}$$

is determined. p 'is in the above relationship the uncorrected desired position p * of the closure device 4, ie the output signal of the Gießspiegelreglers 18. If the Störgrößenkompensator 20 instead of the desired position p * the actual position p of the closure device 4 would be supplied, instead of the value p in the above relationship * the value p can be used. z 'is a jump compensation value.

The jump compensation value z 'is determined by the disturbance variable compensator 20 by means of a jump determiner 22, which is likewise part of the disturbance variable compensator 20. The determination of the jump compensation value z 'takes place according to FIG. 3 on the basis of the difference e of the actual value hG and the expected value hE of the pouring mirror 9, in the following explanations FIG. 3 only briefly referred to as "difference e".

According to FIG. 3 The disturbance compensator 20 furthermore comprises a number of oscillation compensators 23. By means of the oscillation compensators 23, the disturbance variable compensator 20 determines a disturbance component zS referred to a respective disturbance frequency fS, hereinafter referred to as the disturbance frequency component zS. The determination is based on the difference e.

At a minimum, the number of vibration compensators 23 is one. In this case only a single interference frequency component zS is compensated. Alternatively, the number of vibration compensators 23 may be greater than one. In this case, the corresponding frequency interference component zS is determined per oscillation compensator 23 at its own interference frequency fs. Shown in FIG. 3 However, embodiments with three, four, five, ... vibration compensators 23 are also conceivable.

The output signals zS of the oscillation compensators 23 are summed in a node 24 whose result corresponds to the disturbance compensation value z. In the case of only a single vibration compensator 23 is of course no Summation required, since in this case the sum is identical to the single summand.

In a preferred embodiment of Störgrößenkompensators 20 - see FIG. 4 - Is the model 21 of the continuous casting mold 1 from an integrator 25 and a delay element 26, which corresponds to the representation of FIG. 4 are connected in series. Since the integrator 25 and the delay element 26 are components of the model 21 of the continuous casting mold 1, they are subsequently supplemented by the addition "model". They are thus referred to as model integrator 25 and model delay 26. However, the addition "model" only serves to identify this affiliation. A further meaning does not apply to the addition "model".

The model integrator 25 has an integration time constant T1, the model delay 26 a delay time constant T2. The time constants T1, T2 are determined in such a way that they describe the real continuous casting mold 1 as realistically as possible.

zugeführt. V ist ein Verstärkungsfaktor. i ist der bereits erwähnte Modelleingangswert. e ist die ebenfalls bereits erwähnte Differenz. h1 ist ein Anpassungsfaktor.The model integrator 25 becomes a value as an input signal m $$m=V\cdot i+H1\cdot e$$

fed. V is a gain factor. i is the already mentioned model input value. e is the difference already mentioned. h1 is an adjustment factor.

korrigiert und sodann dem Modellverzögerungsglied 27 als dessen Eingangssignal zugeführt. h2 ist ein weiterer Anpassungsfaktor.The model integrator 25 provides an output signal I. The output signal I is at a node 27 by a value $$H$$$$2\cdot e$$

corrected and then supplied to the model delay 27 as its input. h2 is another adjustment factor.

The quantities I, h 2 · e supplied to the node 27 are added in the node 27. This results from the fact that the two input signals I, h 2 · e of the node 27 on the input side of the node 27 are not provided with negative signs.

The adaptation factors h1 and h2 are related to the model 21 of the continuous casting mold 1. They are therefore referred to below as model adaptation factors h1, h2.

The Schwingungskompensatoren 23 are constructed similarly from the approach. Hereinafter, therefore, only one of the vibration compensators 23 will be described in detail, namely, the in FIG. 4 upper vibration compensator 23. However, the embodiments are valid analogously for the other vibration compensators 23.

According to FIG. 4 is the in FIG. 4 upper vibration compensator 23 of two integrators 28, 29 which are connected in series. The two integrators 28, 29 are hereinafter referred to as vibration integrators 28, 29, since they are components of the corresponding Schwingungskompensators 23. The addition "vibration" serves only to express the affiliation of these two integrators 28, 29 to the respective vibration compensator 23. A further meaning does not apply to the addition "vibration".

fS ist die jeweilige zu kompensierende Störfrequenz. Die Störfrequenz fS muss vorab bekannt sein.The vibration integrators 28, 29 have an integration time constant a. The integration time constant a is given by $$a=\frac{1}{2\mathit{\pi fS}}$$

fS is the respective interference frequency to be compensated. The interference frequency fS must be known in advance.

zugeführt. Dem hinteren Schwingungsintegrator 29 wird als Eingangsgröße s2 der Wert $$s2=h4\cdot e+s1$$

zugeführt. S1 und S2 sind die Ausgangssignale des vorderen und des hinteren Schwingungsintegrators 28, 29. h3 und h4 sind Anpassungsfaktoren. Sie werden nachfolgend auf Grund ihrer Zugehörigkeit zum jeweiligen Schwingungskompensator 23 als Schwingungsanpassungsfaktoren h3, h4 bezeichnet.The front vibration integrator 28 is according to FIG. 4 as input s1 the value $$s1=\mathrm{<figure-callout\; id="3"\; label="H"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">H</figure-callout>}3\cdot e-\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="imgf0003.png"\; state="\{\{state\}\}">S</figure-callout>}2$$

fed. The rear vibration integrator 29 is the input s2, the value $$s2=\mathrm{<figure-callout\; id="4"\; label="H"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">H</figure-callout>}4\cdot e+s1$$

fed. S1 and S2 are the output signals of the front and rear vibration integrators 28, 29. h3 and h4 are adjustment factors. They are referred to below as belonging to the respective vibration compensator 23 as vibration adjustment factors h3, h4.

zugeführt, wobei h5 ein Anpassungsfaktor ist, nachfolgend als Sprunganpassungsfaktor bezeichnet.The jump determiner 22 consists of a single integrator 30, hereinafter referred to as jump integrator 30 on the basis of its membership in the skip determiner 22. He becomes a value $$s3=H5\cdot e$$

supplied, wherein h5 is an adjustment factor, hereinafter referred to as a jump adjustment factor.

As already mentioned, several vibration compensators 23 may be present. In this case, the vibration adjustment factors h3, h4 of the individual vibration compensators 23 are independent of each other. Furthermore, the integration time constants a of all the vibration compensators 23 are different from each other.

For determining the adaptation factors h1 to h5, that is to say the model adaptation factors h1, h2, the jump adaptation factor h5 and per vibration compensator 23 of the two respective vibration adjustment factors h3, h4, the transmission function of the in FIG. 4 shown Systems determined. The transfer function is a fractional rational function of the Laplace operator, that is, a function that can be represented as the quotient of a numerator and a denominator, where both the numerator and the denominator are polynomials of the Laplace operator. Both the numerator polynomial and the denominator polynomial include in their coefficients the adaptation factors h1 to h5.

Now the desired zeros are specified for the denominator polynomial, ie the desired poles of the transfer function. This results in a system of equations in which only the adaptation factors h1 to h5 are unknown. The equations of the equation system are independent of each other. Their number coincides with the number of adjustment factors h1 to h5. The adaptation factors h1 to h5 can therefore be unambiguously determined on the basis of the equation system.

Preferably, the desired poles are given as follows:
For each interfering frequency fS to be compensated, a pair of conjugate complex poles are given. The imaginary parts of the respective pole pair are equal to +/- 2πfS. fS is, as already mentioned, the interference frequency fS to be compensated. The imaginary parts are thus (in terms of their amount) equal to the corresponding circular noise frequency ωS. The real parts of the respective pole pair are smaller than zero.

The three further poles are preferably all real and less than zero, that is negative.

If the model time constants T1, T2 model the real continuous casting mold 1 well, the real parts of the complex conjugate poles and the real poles can be varied within wide limits, without sacrificing the quality of the control method. Often, however, the correct model time constants T1, T2 can only be roughly estimated. Nevertheless, there is one good control quality, if the real parts of the complex conjugate poles and the real poles meet certain criteria.

The stability of the control method can be increased, for example, by the fact that the real parts of the complex conjugate poles are between -0.1 times and -0.3 times the corresponding circuit interference frequency ωs. It has proven to be particularly advantageous in experiments when the real parts are approximately equal to -0.2 times the corresponding circular interference frequency ωS.

Furthermore, it has proven to be advantageous if the real poles are all smaller than -2.0 or in pairs are different from each other. It is even better if both criteria are met. Particularly good results were achieved if one of the real poles was -3.0, -4.0 and -5.0 (+/- 0.5 each, preferably +/- 0.2).

FIG. 5 shows a curve of the measured actual value hG of the casting mirror 9 and a corresponding course of the actual position p of the closure device 4 a real continuous casting mold 1 as a function of time. In the course of FIG. 5 For example, the pouring mirror 9 was controlled in the manner of the present invention, compensating for two spurious frequencies f S and adjusting the adjustment factors h 1 to h 5 to the optimum values explained above. Obviously, considerable variations of the actual position p of the closure device 4 are required. However, it is achieved that the pouring mirror 9 remains very stable. The fluctuation is only about +/- three millimeters.

Opposite shows FIG. 6 the corresponding courses of a Gießspiegelregelung of the prior art. Obviously, the pouring level 9 fluctuates considerably more. For a short time, namely at points 31 and 32, it even leaves the drawn tolerance band of +/- ten millimeters.

It has been mentioned above that the interference frequencies fS to be compensated must be known in advance. The determination of the interference frequencies fs can, for example, by evaluating the time course of the actual value p of the casting mirror 9 of FIG. 6 respectively. Then the corresponding interference frequencies fs and thus also the integration time constants a can be determined.

The above description is only for explanation of the present invention. The scope of the present invention, however, is intended to be determined solely by the appended claims.

Claims (14)

1. Control method for the casting level (9) of a continuous casting mold (1),

   - wherein the inlet flow of liquid metal (3) into the continuous casting mold (1) is adjusted by means of a closure device (4), and the partially solidified metal strand (7) is withdrawn from the continuous casting mold (1) by means of a withdrawal device (8),

   - wherein a measured actual value (hG) of the casting level (9) is supplied to a casting level regulator (18), which uses the actual value (hG) and a corresponding nominal value (hG*) to determine a nominal position (p*) of the closure device (4),

   - wherein the measured actual value (hG) of the casting level (9) is supplied to a disturbance variable compensator (20),

   - wherein the disturbance variable compensator (20) is also supplied with the nominal position (p*) of the closure device (4), a nominal position for the closure device (4), corrected by a disturbance variable compensation value (z), an actual position (p) of the closure device (4) or an actual position of the closure device (4), corrected by the disturbance variable compensation value (z),

   - wherein the disturbance variable compensator (20) uses the values (hG, p*, p) supplied to it to determine the disturbance variable compensation value (z),

   - wherein the closure device (4) is supplied with the nominal position corrected by the disturbance variable compensation value (z),

   - wherein the disturbance variable compensator (20) comprises a model (21) of the continuous casting mold (1), by means of which the disturbance variable compensator (20) determines an expected value (hE) for the casting level (9) on the basis of a model input value (i),

   - wherein the disturbance variable compensator (20) comprises a number of oscillation compensators (23), by means of which the disturbance variable compensator (20) in each case determines a frequency disturbance component (zS), which is related to a respective disturbance frequency (fS)on the basis of the difference (e) between the actual value (hG) and expected value (hE),

   - wherein the sum of the frequency disturbance components (zS) corresponds to the disturbance variable compensation value (z),

   - wherein the model input value (i) is defined by the relationship $$\mathrm{i}=\mathrm{p}\prime +\mathrm{z}\prime ,$$

   

   where p' is the uncorrected nominal or actual position (p*, p) of the closure device (4) and z' is a step-function compensation value,

   - wherein the disturbance variable compensator (20) comprises a step-function determining means (22), by means of which the disturbance variable compensator (20) determines the step-function compensation value (z') by integration of the difference (e) between the actual value (hG) and the expected value (hE).
2. Control method according to Claim 1,
   characterized

   - in that the model (21) of the continuous casting mold (1) consists of a model integrator (25) connected in series with a model delay element (26), each oscillation compensator (23) consists of two oscillation integrators (28, 29) connected in series, and the step-function determining means (22) consists of a single step-function integrator (30),

   - in that, as respective input variables,

   -- a value m = Vi + h1e is supplied to the model integrator (25),

   -- a value m' = I + h2e is supplied to the model delay element (26),

   -- a value s1 = h3e-S2 is supplied to the front oscillation integrator (28) of a respective oscillation compensator (23),

   -- a value s2 = h4e + S1 is supplied to the rear oscillation integrator (29) of a respective oscillation compensator (23), and

   -- a value s3 = h5e is supplied to the step-function integrator (30),
   wherein

   -- V is a gain factor,

   -- i is the model input value,

   -- e is the difference between the actual value (hG) and the expected value (hE)

   -- I is the output signal from the model integrator (25),

   -- S1 is the output signal from the respective front oscillation integrator (28),

   -- S2 is the output signal from the respective rear oscillation integrator (29),

   -- h1 and h2 are model matching factors,

   -- h3 and h4 are oscillation matching factors which are specific for the respective oscillation compensator (23), and

   -- h5 is a step-function matching factor.
3. Control method according to Claim 2, characterized in that the matching factors (h1 to h5) are defined such that the poles of the transfer function which is defined by the model (21) of the continuous casting mold (1) satisfy the following conditions:

   - there are in each case one pair of complex conjugate poles for each disturbance frequency (fS), the real parts of which poles are less than zero and the imaginary parts of which poles are equal to a circular disturbance frequency (ωS) which is defined by the respective disturbance frequency (fS),

   - there are three real poles, which are all less than zero.
4. Control method according to Claim 3, characterized in that the matching factors (h1 to h5) are defined such that the real parts of the complex conjugate poles are between -0.3 and -0.1 with respect to the respective circular disturbance frequency (ωS).
5. Control method according to Claim 3 or 4, characterized in that the matching factors (h1 to h5) are defined such that the real poles are all less than -2.0.
6. Control method according to Claim 3, 4 or 5, characterized in that the matching factors (h1 to h5) are defined such that the real poles differ from one another in pairs.
7. Control method according to Claim 3 or 4, characterized in that the matching factors (h1 to h5) are defined such that in each case one of the real poles is between -2.5 and -3.5, between -3.5 and -4.5, and between -4.5 and -5.5.
8. Control method according to one of the above claims, characterized in that the number of oscillation compensators (23) is greater than one.
9. Control method according to one of the above claims, characterized in that the disturbance variable compensator (20) is supplied with the nominal position (p*) for the closure device (4) or with the nominal position for the closure device (4), corrected by the disturbance variable compensation value (z), but not with the actual position (p) of the closure device (4) or with the actual position of the closure device (4), corrected by the disturbance variable compensation value (z).
10. Computer program which comprises machine code (17) which can be run directly by a control device (11) for a continuous casting installation, and the running thereof by the control device (11) results in the control device (11) controlling the casting level (9) of a continuous casting mold (9) in the continuous casting installation using a control method according to one of the above claims.
11. Computer program according to Claim 10, characterized in that the computer program is stored in machine-legible form on a data storage medium (15, 16).
12. Computer program according to Claim 11, characterized in that the data storage medium (15) is a component of the control device (11).
13. Control device for a continuous casting installation, characterized in that the control device is designed such that it carries out a control method according to one of Claims 1 to 9 during operation.
14. Continuous casting installation, characterized in that the continuous casting installation is controlled by a control device (11) according to Claim 13.

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