JPH0798208B2 - Optimal control device for rolling mill - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control system including a variable time delay element, and more particularly to an optimum controller for a rolling mill.

[Background explanation]

The phase characteristic of the control system including the dead time changes remarkably depending on the frequency band, which is a major factor in destabilizing the control system. Therefore, the loop gain of the control system is often set to a small value so as to secure a sufficient gain margin and phase margin in any conceivable frequency band.

As an example of this, using a thickness gauge provided on the roll stand exit side of an automatic plate thickness control device (hereinafter referred to as AGC) for controlling the thickness of the material to be rolled in the rolling roll stand to be constant after rolling. The feed back control (normally called monitor AGC; hereinafter referred to as monitor) aiming at zero offset control is a specific example.

FIG. 2 shows a control configuration explanatory diagram (a) and a block diagram (b) as an example of this monitor control system. In FIG. 2 (a), the material to be rolled 1 is rolled by the roll stand 2 and then sent to the right in the figure at a rolling speed V.
The actual thickness deviation (difference between the actual thickness and the target thickness) is measured with a thickness gauge installed at a distance L from the roll stand 2. The measurement signal is input to the monitor AGC,
The control output signal is compared with a target thickness deviation (generally zero), and then the deviation from the target value is given to the reduction control device 5. A block diagram of this series of closed loop control is shown in FIG. 2 (b). In the figure, block 11
Is a roll-down controller, block 14 is a thickness gauge, block 15 and addition point 16 are monitors AGC. The rate of change in the thickness h of the material to be rolled due to the amount of reduction movement S of the reduction control device 11 is given by (Δh / ΔS) as a relative ratio of the two. Generally, the rolling movement amount S is represented by the following equation when the control amount for controlling the rolling control device 11 is Sc and the friction coefficient between the processing machine (rolling roll) and the material to be rolled in the rolling state is μ. Given. That is, S = f (Sc, μ, ...) And the thickness h of the rolled material is given by h = f (P, S, M, ...). (However, P: rolling load, M: the elastic deformation constant of the material to be rolled in rolling.) As described above, since the rolling state constitutes a complicated other variable control system, the relative relationship of any two variables can be expressed. It is customary to use a partial differential form for evaluation, and the above (Δh / ΔS) is also represented by (∂h / ∂S).

Therefore, the coefficient of influence of the reduction movement amount S of the reduction control device 11 on the thickness h of the rolled material is a partial differential type (∂h / ∂S) as indicated by 12 in FIG. 2 (b). Given. The block 13 shows the process in which the material to be rolled from the roll stand 2 to the thickness gauge 3 is transferred in FIG. 2, that is, the dead time element, and the time constant T ₂ shown in the block 13 is T ₂ = L It is given by / V and has the property of becoming smaller as the rolling speed V increases. Therefore, in this closed loop control system, the dead time changes depending on the rolling speed, and generally, even at the minimum value of the rolling speed section where the control is practically used, the monitor AGC15 which makes the closed loop stable. A gain of K ₄ was selected.

FIG. 3 shows an example in which the open-loop transfer function of the loop control system shown in FIG. 2 (b) is shown in a Bode diagram. In the figure, G indicates the gain characteristic of the open-loop open-loop transfer function, and φ ₁ and φ _{2 respectively} indicate the phase characteristic at the maximum value and the minimum value in the practical speed region. As is clear from FIG. 3, the gain margin g ₂ determined by the phase characteristic φ _{2 of the} minimum speed is selected so that a specified value can be secured (generally, about 10 dB is selected in this type of control system). To be done. That is, if this value is maintained, a gain margin of g ₁ is secured even at the maximum speed, and the control system does not become unstable. But, conversely, because of the unwanted gain given by (g ₁ −g ₂ ),
It was impossible to improve the responsiveness of the monitor AGC at high speed.

The Sigurani-Kors method and the chain method are known as methods for giving an indication of the optimum setting method for this type of system (for example, Control Engineering Handler, p.184, Optimum Adjustment Theory, published by Asakura Shoten). Even in the guidance, the transfer delay waste time T ₂ as shown in FIG. 2 (b) is shown only on the premise that it is treated as a fixed value (constant). From this point of view, an automatic gain correction device (Japanese Patent Publication No. 53-2144) is known as an analog method for giving a monitor gain proportional to the rolling speed. This device exerts its effect by continuously and proportionally changing the control gain of the monitor AGC by increasing or decreasing the detection gain from the thickness gauge signal by multiplying the rolling speed using an analog multiplier. I've been However, in the entire rolling, the dead time T ₂ of the dead time element in FIG. 2 (b) is given by T ₂ = L / V (that is, the rolling speed V is T ₂ inversely proportional to, in the large area and V, the change in T ₂ are small, since T ₂ are rapidly increased in a small area of V) linearly proportional to the speed (proportional)
However, the appropriate control range of the gain is still often restricted by the method of giving the reference speed of the multiplication process, and it is possible to construct the optimum control system in any area of the rolling speed. I never happened.

This fact, regardless of the case shown in the monitor AGC mentioned above,
This is a universal fact in a control system that includes variable waste time control elements, and a perfect compensation method for optimum control in the variable waste time region (the practical rolling speed range in monitor AGC) has been established technology. Is not.

[Object of the Invention]

An object of the present invention is to provide a control device for a rolling mill that gives an optimum gain that always maintains a stability limit in a control system including a dead time element that changes depending on the rolling speed as described above.

[Outline of Invention]

The present invention provides a thickness gauge for detecting the thickness of a material to be rolled, which is provided on the exit side of a roll stand, and a plate thickness control device for feeding back an output signal of the thickness gauge to control the thickness of the material to be rolled to a predetermined value. And a speed detection means for detecting rolling of the material to be rolled, an output signal of the existing degree detection means, and a distance from the roll stand to the speed detection means. Using the delay time calculating means for calculating the transfer delay time of the rolled material and the delay time calculated by the delay time calculating means, each frequency at the point where the phase characteristic of the plate thickness controller falls below about -180 ° A loop gain of the plate thickness control device is calculated by using a first calculation means for performing calculation, each frequency obtained by the first calculation device, and a predetermined target gain margin of the plate thickness control device. Second performance to adjust by And a device, in response to the behavior of varying dead time element, it is characterized always ensure loop gain increased to near the stability limit to maximize the capacity exhibited in the control system.

Example of Invention

 First, the basic items are described.

The open-loop open-loop transfer function G _C1 of the control system including the dead time is
When the loop gain is K _L and the dead time is T _d , if the time constants included in the loop are T ₁ , T ₂ , ... Given in.

More specifically, the closed-loop open-loop transfer function G _C2 in the monitor AGC system shown in FIG. Given in. However, T ₂ = L / V.

In the equation (2), the gain G with respect to the angular frequency and the phase φ are given by the equations (3A) and (3B) by a known method.

However, in the formula (3B), π [rad] = 180 °.

Now, in the present invention, in order to execute the optimum control, the gain margin must always maintain the specified gain g ₀ (for example, about 10 [dB] in the monitor AGC) over the entire rolling speed. From equation (3B), find the angular frequency ω at which the phase φ is below -180 °. If φ = −π is given and Eq. (3B) is solved, T ₁ and T ₂ are peculiar time constants in the control system, that is, ω can be calculated because they are known. Now, the angular frequency obtained by the above means is ω _0, and this is substituted into the equation (3A). However, since G in equation (3A) needs to maintain the specified gain g ₀ as described above, set G = g ₀ and ω = ω ₀ and solve equation (3A) to determine the value of K _M. For example, the monitor AGC gain K _M ensures the optimum gain at the rolling speed, in other words, at the angular frequency ω ₀ . That is, if this arithmetic processing is executed continuously or at a constant time interval in the sample value system, the optimum monitor AGC gain corresponding to the rolling speed, in other words, the waste time can be determined at all times. .

This method can be similarly processed using the general formula (1) as follows. That is, the gain G _C of the open-loop open-loop transfer function given by equation (1)
And the phase φ _C is Therefore, ω can be obtained from the equation (4B) under the condition of φ _C = −180 °, and the optimum value of K _L can be calculated by adding the ω and the specified gain g _C by the equation (4A). It is possible.

As a specific embodiment, FIG. 1 shows an application example of the invention of the monitor AGC shown in FIGS. 2 (a) and 2 (b).

The part numbers 1 to 5 in FIG. 1 are the same as those in FIG. 2 (a).

The material to be rolled 1 delivered from the roll stand 2 is measured for its actual thickness by the output side thickness gauge 3, and then the output signal is given to the multiplier 44 of the monitor AGC4. The multiplier 44 is given a multiplicand calculated by the following procedure.

That is, the rolling speed detected by the speed generator (pulse generator) 20 coupled to the work roll of the roll stand 2 (substantially the same as the transfer speed of the material 1 to be rolled,
There is no difference between this value and the speed of the material to be rolled. (Strictly speaking, it is necessary to consider a correction coefficient called an advanced rate.) A signal is given to the divider 41 in the monitor AGC as a denominator, and the distance L between the roll stand and the thickness gauge given to the constant setter 40a is given.
Is performed as a numerator to calculate the required transfer delay waste time at that timing. This dead time is equivalent to T ₂ shown in the block diagram of FIG. 2 (b). The constant setter 4 which gives the calculated waste time and the constant value −180 °
The first computing unit 42 for calculating the angular frequency ω that meets the above condition from the preset phase characteristics of the open loop open loop transfer function of the control system using the setting signal of 0c as an input condition.
Then, ω obtained by the calculation is output to the second calculator 43. In this process, ω is calculated by using a linear approximation formula or a convergence calculation method for convenience of trigonometric calculation.
This calculation method does not limit the embodiments of the present invention.

The second computing unit 43 further receives the specified gain margin g _C given by the constant setting unit 40b, and determines the desired monitor gain K _M (FIG. 2) from the gain characteristic of the open-loop open-loop transfer function of the control system. (Equivalent to K _{4 in} the block diagram of (b)) is calculated and output to the multiplier 44.

In this way, the monitor AGC 4 can always give the optimum gain adapted to the stable operation state to the loop via the multiplier 44.

In the present embodiment, the monitor AGC4 is shown on the premise of the arithmetic operation based on the application of the microprocessor, but the function concerned can also be realized by the device configuration without the intervention of the software depending on the combination of the arithmetic unit and the register. It is self-evident and does not impose any restrictions on the specific device. In addition, although the present embodiment shows an application example in AGC, the present invention is not limited to this, and a control system including a variable waste time element can be applied in exactly the same manner. This is also shown.

In this way, the dead time of the variable waste time element in the open-loop open-loop transfer function is constantly monitored, and the phase characteristic of the control system stabilizes from an angular frequency below -180 ° as the value changes. By determining the loop gain that secures the marginal gain, the control system does not become unstable in any variable waste time domain, and the capability of the control system is maximized. Therefore, ideal optimum control can be executed over the entire range of application conditions.

Especially, in the above-mentioned monitor AGC, during high-speed rolling, monitor A
In addition to increasing the GC gain to obtain quick response of control, an appropriate gain conforming to the rolling speed is selected in the low speed range, and as a result, the thickness control performance is remarkably improved. The control, which showed a stable tendency, became a completely stable system, avoiding barriers in rolling operation and contributing to improvement of operation efficiency.

〔The invention's effect〕

According to the present invention, the dead time is obtained and controlled in real time based on the rolling speed of the rolling mill, so that stable control can be performed even if the dead time changes depending on the rolling speed.

[Brief description of drawings]

FIG. 1 shows a specific embodiment of the present invention, FIGS. 2 (a) and 2 (b) show a control configuration and a block diagram for explaining a conventional technique, and FIG. 3 shows an outline of the present invention. Bode diagrams for doing so are shown respectively. 1 ... Rolled material, 2 ... Roll stand, 3 ... Thickness gauge, 4 ... Monitor AGC, 5 ... Roll-down control device, 40a, 40b, 4
0c …… Constant setter, 41 …… Divider, 42 …… First calculator, 43 …… Second calculator, 44 …… Multiplier

Claims (1)

[Claims] 1. A thickness gauge for detecting the thickness of a material to be rolled, which is provided on the exit side of a roll stand, and a plate thickness control for feeding back an output signal of the thickness gauge to control the thickness of the material to be rolled to a predetermined value. A speed controller for detecting a rolling speed of the material to be rolled, an output signal of the speed detector and a distance from the roll stand to the speed detector, Using the delay time calculating means for calculating the transfer delay time of the material to be rolled and the delay time calculated by the delay time calculating means, each frequency at the point where the phase characteristic of the plate thickness control device falls below about -180 ° The loop gain of the strip thickness control device is calculated by using the first computing means for computing the above, each frequency obtained by the first computing means, and a predetermined target gain margin of the strip thickness control device. Calculate and adjust An optimum control device for a rolling mill, comprising: a second arithmetic device.