EP0170016B1 - Method to compensate the influence of roll excentricities - Google Patents

Abstract

A process and device for compensation of the effect of roll eccentricities upon thickness regulation of material being rolled in a roll stand (1), wherein eccentricity oscillations are simulated by a model (6) based on measured values of roll adjustment position (s), roll force (FW) and mean support roll speed (n), together with spring constants (CG, CM) for the roll stand and the material. An output signal ( DELTA R) of the model (6) is used to modify the thickness value (ha+ DELTA R) used for regulation, so as to compensate for the effect of roll eccentricity. The model may be implemented by a device (RECO) comprising pairs of oscillators (7), the phase and amplitude relationships of which are adjusted according to the observer principle.

Description

The invention relates to a method for determining and compensating for the influence of roll eccentricities during the ongoing rolling operation in the position or thickness control of roll stands, in particular with indirect actual value formation which takes place by determining the roll stand stretch.

According to US Pat. No. 3,928,994, it is known to use the method of autocorrelation to eliminate the influence of the roll eccentricities on the signal used for the stand expansion in the actual value channel. The other component of the indirectly formed actual value signal, namely the roll adjustment, is not affected by this, so that this known method only partially compensates for the influence of the roll eccentricities. Furthermore, because of the averaging used, auto-correlation methods are always associated with a time that is detrimental to a rapid reaction of the thickness control.

US-A 3543549 describes a method of the type mentioned at the outset which requires the sine and cosine signals from sensors additionally to be attached to the support rollers. The invention has for its object to provide a method for compensating the roll eccentricities in thickness controls of the type mentioned, which works both more accurately and faster and manages with the sensors usually present on roll stands. According to the invention, this object is achieved by the features specified in the characterizing part of the main claim.

• Fig. 1 die Anordnung eines erfindungsgemäss arbeitenden Walzenexzentrizitäts-Kompensators (RECO) bei der Dickenregelung eines Walzgerüsts,
• Fig. die grundsätzliche Struktur des Walzenexzentrizitäts-Kompensators,
• Fig. 3 ein Ausführungsbeispiel für die innerhalb des Walzenexzentrizitäts-Kompensators erfolgende modellmässige Nachbildung eines Walzenexzentrizitätsschwingungspaares,
• Fig.4 die Signalverarbeitung bei mehreren nachgebildeten Exzentrizitätsschwingungspaaren,
• Fig.5 den Aufbau des Walzenexzentrizitäts-Kompensators bei digitaler Signalverarbeitung.

The invention will be explained in more detail below with reference to the figures, in which:

• 1 shows the arrangement of a roll eccentricity compensator (RECO) according to the invention in the thickness control of a roll stand,
• FIG. 1 shows the basic structure of the roller eccentricity compensator,
• 3 shows an exemplary embodiment for the model-like simulation of a pair of roller eccentricity oscillations which takes place within the roller eccentricity compensator,
• 4 shows the signal processing in the case of several simulated eccentricity oscillation pairs,
• 5 shows the structure of the roller eccentricity compensator in digital signal processing.

wobei mit ΔR die sich überlagernden Einflüsse der beiden Stützwalzenexzentrizitäten △R_o und △R_u zusammengefasst sind.In Fig. 1 a roll stand 1 is shown schematically. It consists of the upper back-up roll with the radius R _o , the lower back-up roll with the radius R _u , the two smaller-diameter work rolls, a hydraulic piston that adjusts the upper back-up roll, and an associated hydraulic cylinder, which is supported on the scaffold frame. The elastic frame is symbolically represented by a spring with the spring constant C _G. The rolling stock, to which an equivalent material spring with the spring constant C _{m is} assigned in the roll gap, is rolled down from the inlet thickness h _e to the outlet thickness h _a by means of the two work rolls. The roll eccentricities of the upper and lower backup rolls are caused by uneven roll wear, deformations due to thermal stresses and by deviations of the geometrical cylinder axes of the rolls from the operationally occurring rotation axes. They are denoted by △ R _o and △ R _u , that is, as deviations from the ideal supporting roller half-diameters R _e and R _u . Furthermore, there are provided sensors for the support roller speed n, usually in the form of a tachodynamo coupled to the drive motor, for the rolling force F _w exerted by the hydraulic piston and for the roller position, which corresponds to the relative position s of the piston in the hydraulic cylinder that adjusts the upper support roller. With 2 a control element is designated, by means of which the hydraulic piston is acted upon by a valve with pressure oil. The control signal for the control element 2 consists in the output signal of a controller 3, which has the task of bringing the thickness h _{a of} the rolling stock to be brought out in accordance with the thickness target value h * _a supplied to it. The actual value of the controlled variable h _a is not measured directly at the point of its creation, ie in the roll gap, but is determined from the roll stand expansion and the roll position. For this purpose, the device designated by GM in FIG. 1, which essentially contains a multiplier, which multiplies the rolling force F _w by the reciprocal of the frame spring constant C _G and adds the measured value signal s of the relative hydraulic piston position to this product. The relationship between the input signals and the output signal of the device GM, also known as a gauge, is therefore:

with ΔR the overlapping influences of the two support roller eccentricities △ R _o and △ R _{u are} summarized.

- △R, so dass die Dickenregelung fehlerhafterweise bewirken würde, dass dem Band mit der Auslaufdicke h_a die Exzentrizität △R um 180° phasenverschoben eingewalzt würde. Dabei können die Grösstwerte der Exzentrizitäten mehrere zehn Mikrometer betragen, was mit den heutigen Toleranzforderungen bei kaltgewalztem Band nicht verträglich ist.The arrangement described so far essentially corresponds to the known strip thickness control with the gage meter principle determining the actual value of the strip thickness h _a . If roll eccentricities ΔR are present, however, the gauge GM does not supply the strip thickness h _a alone but the sum of the strip thickness and roll eccentricity. A strip thickness control built up with the gauge meter signal (h _a + ΔR) as the actual value would compensate for changes in the strip inlet thickness into the roll stand, but would behave incorrectly with respect to roll eccentricities, because a thickness regulation with the output signal h _a + ΔR of the gauge meter GM as the actual value behaves exactly like a thickness control with h _a as the actual value and a setpoint h

- △ R, so the thick rain would incorrectly cause the strip with the outlet thickness h _{a to have} the eccentricity △ R rolled out of phase by 180 °. The maximum values of the eccentricities can be several tens of micrometers, which is not compatible with today's tolerance requirements for cold-rolled strip.

A compensation device called RECO (Roll Eccentricity Compensator) is therefore used, which has the task of using the sensor signals s, n and F _w supplied to it and the setting parameters R _° , R _u , C _G and C _m to add the roll eccentricity ΔR identify or emulate, and the signal R simulated by it is used to correct the falsified actual value of the strip outlet thickness supplied by the gauge GM, so that the actual thickness value h _a occurring in the roll gap can be fed to the controller 3 as an actual value, with which the influence of the roll eccentricities △ R is exactly compensated for. The framework spring constant C _G is determined once by a test before the start of rolling and C _m by running online calculations. It was essential for the RECO device, which works according to the compensation method according to the invention, to recognize that, in order to accurately reproduce the roll eccentricities, not only the mill stretch, but also the elastic deformation of the material during the rolling process should be taken into account.

The compensation device according to the invention can also be used for pure position control with the same advantages. Here, the gage meter GM is eliminated and the output signal of the compensation device RECO is subtracted from the measured value signal s and the result is used as the actual position value. Instead of the setpoint h * _{a of} the outlet thickness, a position setpoint is then fed to the controller 3.

Figure 2 shows the basic structure of the roll eccentricity compensator RECO. It contains a multiplier 4 to which the rolling force measurement signal F _w and the sum of the reciprocal values of the frame spring constant C _G and the material spring constant C _{m are} fed on the input side. This reciprocal value corresponds to the reciprocal of a spring constant, which results from the series arrangement of the spring of the roll stand and the spring of the rolling stock. The position measurement value s of the hydraulic piston adjusting the upper support roller is added to the output signal of the multiplier 4 in a mixer element 5, and it can be shown that the output signal of the mixer element 5 is then in the eccentricity signal ΔR caused by the eccentricities ΔR _° and ΔR _u and the strip inlet thickness h _e consists, the latter consisting of a constant component H _e and a superimposed, statistically fluctuating alternating component h _e . So h _e = H _e + h _e . The DC component h _{e of} the inlet thickness h _{e is} extracted from the output signal of the mixing element 5 by means of a high-pass filter HF, so that the signal ΔR + h _e results at the output of the high-pass filter HF, which has its corner frequency with the speed measurement value n. From this signal, a signal ΔR corresponding to the roll eccentricity is then modeled in an arrangement 6 designed according to the observer principle. The arrangement 6, which represents a feedback model for the eccentricity disturbances △ R, contains at least two oscillators for the paired fundamental vibrations of the eccentricities △ R _o and △ R _{u of} the upper and the lower backup roller and is used in the event that relevant harmonic pairs occur, appropriately supplemented by appropriate pairs of oscillators. The frequencies of the oscillators are tuned by entering the support roller radius R _e and R _u and the average support roller speed n. The outputs of the individual oscillators are combined to form a sum signal △ R and are compared with the output signal of the high-pass filter HF in a mixer 8, the resulting deviation e adjusting the oscillations in their phase positions and amplitudes generated by the oscillators until the signal △ R is an image of the eccentricity vibration △ R, which is the case when the deviation e becomes a minimum and only corresponds to the statistically fluctuating portion h _{e of} the inlet thickness h _e . The frequency is adjusted as a function of the backup roller speed n continuously during the rolling operation, and the corner frequency of the high-pass filter HF is also carried accordingly.

FIG. 3 shows an implementation example for a model 6 emulating the roll eccentricity △ R with an oscillator pair for emulating the basic eccentricity oscillation. Each oscillator consists of two integrators 9, 10 and 11, 12 arranged one behind the other, the output signal of the integrators 10 and 12 being fed back to the input of the integrators 9 and 11. Multipliers 13 to 16 are arranged in the input circuit of each of the integrators and are used to determine the frequencies of the oscillators. The second inputs of these multipliers are acted upon by a signal n corresponding to the average backup roller speed. The components which determine the time behavior of the integrators are designed to be adjustable, for example as rotary potentiometers or rotary capacitors, and are adjusted in accordance with the determined values of the radius R _e or R _{u of} the support rollers. In this way, the frequency of the oscillators is preset as a function of the radii R _o or R _{u of} the support rollers and is adjusted as a function of the support roller speed n. The outputs of the integrators 10 and 12 are added in a mixer 17 and its output signal is subtracted from the output signal △ R + h _{e of} the high-pass filter in a further mixer 18. With the resulting deviation e, the oscillations generated by the oscillators 9, 10 and 11, 12, respectively, are made via proportional elements a to d conditions in their phase positions and amplitudes until the sum signal AR of the integrators 10 and 12 coincides with the portion ΔR of the input signal fed to the interference model 6 (ΔR + h _e ) resulting from the roll eccentricity. The parallel arrangement of two oscillator pairs shown in FIG. 3 can be converted into a functionally equivalent series circuit using known transformation rules. Such a 4th order filter can be recommended for some applications.

in Überlagerung die Nachbildung der Gesamtexzentrizität ΔR ergeben. Die Phasen- und Amplitudennachstellung erfolgt abhängig von den Einzelfehlern e_o, e₁, e2, e3. Je Oszillator sind dabei zwei Nachstellverstärkungen a_o, b_o bzw. c_o, d_o erforderlich, wie für das Grundschwingungspaar des Modellteils 60 gezeigt ist.FIG. 4 shows the structure of the disturbance model 6 in the roller eccentricity compensator RECO in the event that in addition to the fundamental vibration of the roller eccentricity, three further harmonics have to be considered as relevant. The parts of this model which are designated by 60, 61, 62 and 63 and have the same structure are designed in accordance with FIG. 3 and contain oscillator pairs for the basic oscillation pair and for the 1st, 2nd and 3rd harmonic pair, their individual eccentricity replicas

overlay the simulation of the total eccentricity ΔR. The phase and amplitude are adjusted depending on the individual errors e _o , e ₁ , e2, e3. Two adjustment amplifications a _o , b _o and c _o , d _{o are} required for each oscillator, as shown for the basic oscillation pair of the model part 60.

FIG. 5 shows the structure of the roller eccentricity compensator RECO using a digitally operating microcomputer 19, in which the signal processing takes place by supplying the input signals via two analog / digital converters 20 and 21 and the signal removal via a digital / analog converter 22. The microcomputer 19 is divided into three function blocks 191 to 193. In block 191, the presetting of the two backup roll radii R _e and R _u and assuming a nominal average backup roll speed takes place offline the calculation of the oscillator frequencies to be preset. In block 192, which contains a signal processor, the signal processing for emulating the roll eccentricity ΔR takes place by means of oscillators in accordance with the arrangements according to FIGS. 3 and 4, but implemented in functionally equivalent digital technology. The signal processing takes place in a known manner in each case with the values of the input signals sampled at discrete points in time, and a result is output in each case at sampling points in time, a reconstruction filter downstream of the digital-to-analog converter being provided in a manner known per se in order to obtain the analog result sequence obtained in a discrete-time manner to convert a continuous-time signal. Since block 192 practically represents a digital filter, a so-called anti-aliasing filter AF is arranged after high-pass filter HF in order to suppress the occurrence of interfering external frequencies caused by the scanning process. Antialiasing filters, as described, for example, in the “2920 Analog Signal Processor Design Handbook” published by the Intel Corporation in 1980, pp. 2-1 to 2-5, are low-pass filters which, at half the sampling frequency, have a noteworthy attenuation, for example 60 dB exhibit. The filters HF, AF and RF, which consist of a combination of integrators and summing amplifiers, are in turn tracked in their corner frequencies as a function of the backup roller speed n, which is done by means of multipliers arranged in the input of the integrators, corresponding to the arrangement in FIG. 3 can. Block 193 contains a timer which adjusts the frequency of the oscillators implemented in block 192 in digital technology as a function of the current backup roller speed n. The timer can consist, for example, of a counter which can be preset to the output value of the analog-digital converter 20 and which is continuously counted down at a constant clock rate, in each case emits a pulse to the signal processor 192 when the counter reading reaches zero.

Claims (3)

1. A method for determining and compensating the influence of roll eccentricities during running rolling-mill operation in the case of the position or thickness control of roll stands, more particularly with an indirect actual value formation effected by determining the roll stand elasticity, characterised by the following process steps:

a) A sum signal is formed from the test value signal of the rolling force (F_w), which is multiplied by the reciprocal value sum of stand elasticity constants (C_G) and material elasticity constants (C_M), and the test value signal of the roll setting position (s);

b) the sum signal is fed through a high-pass filter (HF), which is altered in its angular frequency proportional to the backing roll velocity (n);

c) the output signal of the high-pass filter is compared with the sum output signal of at least one oscillator pair, which is used as an eccentricity disturbance model and the frequencies of which are preset as a function of the radius of the upper or lower backing roll and are reset as a function of the backing roll velocity;

d) with the deviation (e) between the output signal of the highpass filter and the sum output signal of the oscillator pair, the oscillators are readjusted in amplitude and phase position according to the principle of observation so that said deviation becomes a minimum; ,

e) the sum output signal (ΔR) of the oscillators is subtracted from the actual value signal.

2. A method according to claim 1, characterised in that for reproducing the substantial harmonic oscillations, corresponding back-coupled oscillator pairs are additionally provided, the sum output signals of which are subtracted from the actual value signal.

3. A method according to claim 1 or 2, characterised in that a signal processor (192) is used for the eccentricity modelling, which signal processor is arranged between an analogue-digital converter (21) and a digital-analogue converter (22), operates as a digital filter, and is acted upon by the output signal of the high-pass filter, a timer (193), which is influenced via an analogue-digital converter by the mean backing roll velocity (n), being associated with the signal processor (192).

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