DE2440166C2 - Device for regulating the thickness of rolled strip - Google Patents

Description

ΦΛ, <P> h '

an eccentricity calculating element (25) for determining the roller eccentricity (e) from this coherence function (γ ² ), and calculating elements (41, 42) for calculating the phase of the roller eccentricity relative to the rotational movement of the rollers (2, 2 ', 3) from the Correlation between a reference signal of the drive system of the rolls (2, 2 ', 3) and the modified rolling force signal; and that a device for feedback of the input-side thickness component of the input-side thickness component and a roll eccentricity component containing the modified rolling force signal to the control member contains the following components:
a filter (29) for the modified rolling force signal, which only lets through output signals matched to a roll eccentricity frequency (fe),

a coefficient multiplier (30) which determines the roller eccentricity component from the filtered signal by multiplying it by a coefficient β = 1- γ ^{2, and}
The invention relates to a device for regulating the thickness of rolled strip for a roll stand with a hydraulic adjusting device and an associated control element of the type specified in the preamble of claim 1.

The production-related or structural changes as well as temperature changes of the roll barrel The resulting roll eccentricities lead to cyclical changes in the thickness of the rolled strip and thus to its deterioration in quality. Conventional regulating devices to achieve tightest Strip thickness tolerances, consisting of a strip thickness meter, a setpoint generator, a controller and a hydraulic dividing device, are due to their inertia to compensate for roller eccentricities Not suitable especially for high-speed conveyor belts. Also newer control devices with indirect strip thickness measurement in the roll gap using load cells or direct strip thickness measurement in the roll gap did not lead to the desired goal of as complete a compensation as possible the strip thickness changes caused by the roll eccentricities.

From DE-OS 18 09 639 a device is already known for the thickness control of rolled strip of the specified type, in which rolling force changes and changes in the thickness of the strip entering the roll gap measured by separate sensors and in electrical signals are converted. A ratio signal is obtained from the two signals by comparing them generated, which together with the signal characterizing the rolling stock thickness by multiplying in a modified Signa! is converted. From this modified signal and your first, i. H. to the Rolling force signal is obtained by subtracting a control signal, which predominantly those changes the initial thickness of the rolling stock, which has been caused by roll eccentricity. This control signal is fed to the control element of the adjusting device. Due to only simple conversion processes however, these control signals do not exactly correspond to the respective roller eccentricities and the adjustment of the adjusting devices takes place with a time delay, so that only an incomplete Compensation for the cyclic strip thickness changes caused by roll eccentricities is achieved can be.

The object of the invention is to precisely adjust the roll eccentricity component using simple means determine and their disadvantageous influence on the thickness control of the rolled strip practically without delay to eliminate.

This object is achieved by the characterizing features of the patent claim.

According to the invention, a statistical technique is used to detect the roll eccentricity, to remove this disturbance from the thickness control loop. The principle of the regulation according to the invention is explained below.

In general, there are cyclical ones on the input side

Changes in the thickness of the rolled strip rarely occur and can be regarded as random statistical values. In contrast, the roll eccentricity causes cyclical changes in thickness. On the other hand, the output-side thickness changes are a function of the input-side thickness changes and the roll eccentricity change and also represent random values. Since the measurable values, i.e. the input-side thickness or a fictional output-side thickness of the rolled strip 1 are random values, it is necessary to use the data as statistical values to be processed in order to obtain the roller eccentricity e. For data processing according to the invention, the autocorrelation functions and the cross-correlation function of the input-side rolled strip thickness Ai and a fictitious rolled strip thickness A _{2 are first obtained} in a correlator. The Fourier integral is then formed using the correlation functions in order to determine the corresponding power spectra, from which the coherence is then calculated in order to separate the input-side thickness Ai and the roller eccentricity e from one another.

The autocorrelation function is defined for the input-side thickness Aiftj as follows:

AA ₁ = lim 4:

(D

The autocorrelation function Rhi for the fictitious thickness Λ ^ ζ / is defined accordingly.

Furthermore, the cross-correlation function ΛΛ1Λ2 for the input-side thickness h \ (t) and the fictitious thickness hi (t) is defined as follows:

ΛΛι A ₂ = lim -

AOh ₂ (I + τ) dl.

(2)

The mentioned correlation function primarily reflects the statistical characteristic of a signal. However, this characteristic becomes even more apparent by determining a range of services. This power spectrum corresponds to the square of the Fourier component, which results from the Fourier transformation of the correlation function. Consequently e ^r to enter the auto power spectra ΦΛ | and ΦΙη for the input-side thickness h \ (t) \ ma the fictitious thickness hi (t) z \ i:

1 = y ÄÄ,

2 = \ Rh ₁

exp (- jlnft) dr,

(3)

exp (-j

dr.

while the cross-power spectrum Φ H _x Ii ₁ for /), (/) and I) ₂ (I) results in:

= j

exp (-j2n / r) dr. (4)

The autocorrelation function is symmetric about r = 0, while the cross-correlation function is asymmetric about T = O. As a result, the auto power spectra contain ΦΛι and Φ / ;? the input-side thickness h \ (t) and the fictitious thickness h (t) are only real numbers, while the cross-power spectrum Φ Ai A _{2 has} a real part and an imaginary part.
The coherence is a factor that reflects the relationship between each input signal and the output signal when there are several input signals in the control loop.Thus, by measuring the coherence of the input-side thickness Ai and the fictitious thickness Aj, it can be determined numerically whether the cyclical change in the fictitious thickness Aj comes from the input-side thickness Ai or from the roll eccentricity e. This coherence γ ¹ is defined as follows:

ΦΑ, ΦΛ ₂ '

where the product y ² Ai of the coherence γ ⁷ and the input-side thickness A | the percentage of change in

input-side thickness Ai on the change of the fictitious thickness A ₂ represents In a rolling. * centricity. e = 0 there is thus y = ² i, thereby determining the notional thickness Λ2 only by the input-side thickness Ai. On the other hand, if y ² <1, then (1-y ² ) Ai is the component of the roll eccentricity e at its frequency? That is, according to the controller according to the invention with a thickness meter, the total output of the roller eccentricity cycle fe and the output of the pure roller eccentricity part are determined first,

JO then determines its ratio JS = IJ " ² , after which the roller eccentricity component is fed as an input signal to the automatic thickness control circuit with a thickness meter, whereby its influence is eliminated.

In the following, exemplary embodiments of the invention are described in detail with reference to the drawing. It shows

Fig. I a thickness control circuit with sensors and actuators on a four-high roll stand,

FIG. 2 shows a block diagram of a device for detecting an eccentricity characterizing the roll Control signal for a duo roll stand,

3 shows the coherence obtained according to FIG. 2 as a function of the frequency,
FIG. 4 shows a block diagram of the control device, FIG. 5 shows a block diagram of a device for detecting phase information on the basis of the angle of rotation of a roller.

The in Fig. 1, the roll stand shown schematically has work rolls 2 and backup rolls 3 for rolling a strip 1. The rolls are adjusted by means of a hydraulic adjusting device, which consists of a hydraulic cylinder 5, an adjusting element 6 and an adjusting valve 4 for adjusting the roll gap ^{by means of the} amount of oil to be supplied. For the purpose of regulating the thickness of the rolled strip during the rolling operation, the displacements S del adjusting member 6 are detected by a measuring sensor 7 and the measured values returned are compared with a nominal thickness value ha . At the same time, the rolling force Z ^{7 is} measured by means of a pressure sensor 8.

The rolling force measurement values are divided in a coefficient multiplier 9 by a stand constant km and added to the values of the measuring sensor 7 in a summing element 10 in order to be fed back negatively to the pre-comparison with the nominal value Ad. With this

f> 5 establishment becomes the relationship

h _d = (S + P / km)
fulfilled, so that the thickness of the rolled strip remains constant.

F i g. 2 shows a block diagram of a coherence computer with the measuring sensors and other components of the control loop. The rolled strip thickness h \ on the inlet side is measured by means of a sensor designed as an X-ray thickness meter 13, 13 '. The thickness meter 13, 13 'is arranged at a distance from / in front of the roll gap, so that the current input-side rolled strip thickness h \ can be obtained by providing a delay circuit 14 which delays the measurement signal by l / v , where ν is the entry speed of the rolled strip 11. The rolling force measured values detected by the pressure sensor 8 are input to a coefficient multiplier 16 and multiplied by 1 / ^ r, where / er is the gradient of the change in shape of the rolling stock. The product is subtracted from the rolled strip thickness h \ on the input side in a summing element 17 in order to obtain the fictitious rolled strip thickness h ₂ . These thickness values h 1 and 2 correlators 18 to 20 are then carried out. in order to obtain the autocorrelation functions Rh: and Rh: as well as the cross-correlation function Rh \ hi , which are then Fourier-transformed in power spectrum arithmetic units 21 to 23 in order to obtain the power spectra ^r Ph \. 'Ph ₂ . ^< Ph \ h ₂ to get. These values are input to a coherence calculator 24 in order to obtain the

'Φ / ΐ; ■ <Ph _:

to obtain a defined coherence, from which the roller eccentricity component e can be calculated by means of an eccentricity calculating element 25.

As described, the coherence y ² reflects the relationship between the input-side rolled strip thickness h \ and the fictitious rolled strip thickness / j>. If the factor determining the change in the fictitious rolled strip thickness /? 2 is only the incoming rolled strip thickness h \ . results for the coherence; · ² = Ι. However, if the fictitious rolled strip thickness hi is also influenced by other factors, such as the roll eccentricity c. is influenced, the coherence / ² <1 at a frequency fe. As in Fig. 3, the coherence is reduced at different frequencies compared to the value 1, which is due to the mutual influence of the backup roll eccentricity and work roll eccentricity. It is assumed that / ti and 4j are the first and third frequencies of the backup roll and / »ι and /» 3 are the first and third frequencies of the work roll.

The correction of the roll eccentricity component can be determined depending on the desired thickness accuracy. The area in which the roll eccentricity the output-side thickness /? ₂ , was determined as coherence y ² (f) , so that the admissibility limit (tolerance limit) ya ² of y ² (f) can be set according to the thickness accuracy to be guaranteed. Accordingly, only a small influence due to the "roll eccentricity According to the results in g F i for ⁱ va <y ¹ (f) ^ \. 3 must example shown the third frequency /».3 of the work roll can not be corrected, while only f- _o 1, / »1 and fb 3 need to be corrected.

To correct this, the size of the eccentricity (gain factor) at the frequency fe and also the phase must be determined. The phase information can be obtained from a reference signal based on the rotation angle of the backup roll or the work roll. If z. If, for example, the size of the roll eccentricity in the back-up roll system at f = fb \ is large and needs to be corrected, then the phase can be determined together with the gain factor by the correlation between the rolling force and the back-up roll speed. F i g. 5 shows a block diagram in which this phase information is used as the output signal

- Thickness control loop is fed. The phase information is obtained by calculating the correlation between the rolling force detected by the pressure sensor 8 and that of a Impulsgenei .itor 40 detected angle of rotation by means of a computer 41 and as the output signal of a circuit 42 for compensating the phase delay of the thickness control loop.

4 shows a block diagram of a typical embodiment of the thickness control device. The figure shows a transfer function C of a servo actuator for the nominal thickness value ha . The transfer function G is instantaneous in the low frequency range and has a gain factor of one. A coefficient which is generally one is denoted by λ. The roll eccentricity influences the fictitious output-side thickness h ₂ as a disturbance variable. It is detected as the rolling force and fed to the feedback path 26 via the steps already mentioned. For this purpose, the feedback path 26 is branched into a feedback branch 27 and a feedback branch 28, whereby the signal containing the input-side thickness component and the roller eccentricity component is on the one hand a link 32, on the other hand a filter 29, the damping of which is only zero at a roller eccentricity frequency fe and which does not cause phase lag, and then a coefficient multiplier 30 with /? = 1 - y ^{2 is} supplied. As a result, the roller eccentricity component only reaches the logic element 32 via the feedback value 31 as a negative output signal at the roller eccentricity frequency fe. In addition, the size of the roll eccentricity component e can be determined according to the method shown in FIG. 2 and the phase according to the block diagram shown in FIG. 5 can be obtained. Since the transfer function C is delayed at a higher frequency fe , a phase compensation of the roller eccentricity e corresponding to this time delay is necessary. An addition point 35 is fed via the V "; g 34 an eccentricity signal (-e ^ in antiphase, in order to automatically compensate for the influence of the roller eccentricity, whereby an automatic thickness control loop with thickness measurement is formed.

However, if the eccentricity of the work roll system is large and needs to be corrected, the Correlation between the angle of rotation of the work roll and the roll pressure obtained to determine the roll eccentricity component to determine in the manner already described and to use it as an output signal in the Introduce thickness control loop in the manner already described.

For this purpose 3 sheets of drawings

Claims (1)

Claim: Device for regulating the thickness of rolled strip for a roll stand with a hydraulic adjusting device and an associated control element, with a setpoint generator for the control element, with a sensor for detecting changes in the roll gap and the rolling force and for feeding back the detected values to the control element a sensor for detecting the thickness of the rolling stock on the input side, with a computer with arithmetic elements to obtain the correlation function from a signal proportional to the thickness of the rolling stock on the input side and a modified rolling force signal and ι> for obtaining an output signal based only on the roll eccentricity and having the amplitude and phase of the roll eccentricity and is supplied to the control element as a reference variable, characterized in that a summing element (17) is provided which subtracts the modified rolling force signal from the input-side rolling stock thickness (Λι) to generate a fictitious rolling stock thickness [H ₂ );
that the calculator contains: a first autocorrelator (18) for determining the autocorrelation function (RJ.'t) of the rolling stock thickness (Λι) on the input side, a second autocorrelator (20) for determining the autocorrelation function (Rh ₂ ) of the fictitious rolling stock thickness (A ₂ ), a Kreuzi.orrelator (19) for determining the cross-correlation function ( ⁰ Mh ₂ ) of the input-side rolling stock thickness (A ₁ ) and the fictitious rolling stock thickness (A ₂ ), power spectrum computing elements (21, 22, 23) for generating the individual power spectra (ΦΛι, Φ / 72, ΦΛ1Λ2) from the correlation functions (Rh \, Rh ₂ , RfHh ₂ ), a coherence calculator (24) for generating the coherence function (γ ² ) from the power spectra, ΦΛ ₂ , ΦΛ1Λ2) according to the modified rolling force signal and the output signal the coefficient multiplier (30) and detect in the form of deviation signals the Feed control organ.