JPH08147044A - Molten metal level control method for continuous casting machine - Google Patents

Abstract

PURPOSE: To stabilize the level of molten metal by performing estimation and correction by using a model generated by representing flow rate disturbance due to nonstationary bulging, etc., as the sum of plural frequencies. CONSTITUTION: The flow rate disturbance d(t) of the molten metal is assumed as the sum of sine waves of plural frequencies and this is assumed as the control model; and a control command u(t) and a molten metal surface level measured value by a molten metal level sensor are inputted to a filter 21 to obtain functions Z1 (t) and Z2 (t), which are supplied to a filter 22 and a disturbance estimation arithmetic part 23. The filter 22 finds and supplies a function Φ(t) to the disturbance estimation arithmetic part 23, which finds a disturbance estimated value d(t) hat; and this is multiplied by a correction gain Ko and the product is supplied to an adder 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molten metal level control method in a continuous casting machine in which the amount of molten metal flowing into a mold is controlled by operating a stopper or a sliding gate with an actuator.

[0002]

2. Description of the Related Art In a continuous casting machine, a slab in a mold has a shell formed on its outer periphery, and the inside remains unsolidified.
It is pulled down by a pinch roll. For this reason, when the pulling action by the pinch roll acts on the slab, an unsteady phenomenon called so-called bulging occurs in the slab with a liquid inside, where the shell repeatedly expands and contracts cyclically, causing the molten metal in the slab to rise upward. ， It vibrates downward, and this appears as the fluctuation of the molten metal level in the mold. Conventionally, as a countermeasure against this, a method of suppressing the periodic fluctuation of the bulging by making the installation intervals of the pinch rolls uneven, or estimating the bulging as a periodic disturbance and correcting it, There has been proposed a method (Japanese Patent Laid-Open No. Hei 5-23511) for controlling fluctuations in the molten metal surface level.

FIG. 4 is a block diagram showing the control contents of the conventional control system disclosed in the above-mentioned publication, which shows a molten metal level target value Lref and a molten metal level measured value L detected by a molten metal level sensor. The comparison is made by the comparator 31, and the deviation e is given to the PI controller 32. The PI controller 32 calculates a position command value U ₀ of the stopper for molten metal control necessary to set the deviation e to zero based on a predetermined control parameter (K _p : proportional gain, T ₁ : integration time), This is given to the adder 33.

The adder 33 adds the position command value U ₀ and a stopper correction signal U _c described later, and controls the stopper position as a corrected position command value u for the stopper. As a result, the molten metal flow rate proportional to the stopper position is determined from the stopper dynamic characteristic 34, the immersion nozzle flow rate characteristic 35, and the like, and the flow disturbance Q _w and the in-mold phenomenon 36 are added to determine the molten metal level L.

The molten metal level L is measured by a molten metal level sensor and fed back to the comparator 31 as a molten metal level measured value L, and is also given to the correction signal calculator 37. Correction signal calculator 37 calculates a stopper correction signal U _c for worth estimating the flow disturbance on the basis of the control model from the stopper position actual value and a molten metal surface level measurement, counteract this, adding multiplied by the gain K _G Feedback to the container 33. The control model used in the correction signal calculator 37 is created such that the flow rate disturbance changes into one kind of sine wave shape or ramp shape determined by the pinch roll and the casting speed.

[0006]

By the way, in the former method of making the installation intervals of the pinch rolls uneven, the pitch of the pinch rolls is basically set to R ₀ , and this is dealt with by changing it within the range of ΔR. Therefore, although there is an effect of suppressing the level fluctuation of the molten metal, bulging that occurs corresponding to the interval R ₀ cannot be avoided. In order to suppress this, there is no choice but to reduce the basic distance R ₀ of the pinch roll interval, but this is not realistic because the equipment cost rises, and the change width ΔR
Since the fluctuation due to is not negligible, the vibration becomes a multi-frequency disturbance and it is difficult to suppress it. In the latter method, the periodic disturbance is assumed to be one kind of sinusoidal or ramp-like fluctuation determined by the pinch roll and casting speed, but in reality it contains multifrequency components such as high frequency and fractional frequency. , I can't correct it accurately.

FIG. 5 is an explanatory view showing a general disturbance waveform. The disturbance is W, 3W, 5W, 1/3 as shown by a solid line.
W and 1 / 5W include high frequency and fractional frequency components and have a waveform as shown by the solid line, while the control is performed assuming that it is a sine wave with a period W and an amplitude of 2A, as shown by the broken line. The part indicated by is left as a level change.

The present invention has been made in view of such circumstances, and an object of the present invention is to assume that the disturbance due to bulging is a multi-frequency disturbance, estimate it, and create a model for correcting it. It is another object of the present invention to provide a molten metal level control method for a continuous casting machine which performs control based on this.

[0009]

SUMMARY OF THE INVENTION A molten metal level control method for a continuous casting machine according to the present invention obtains a control command to eliminate a deviation between a molten metal level target value and a molten metal level measured value, and executes this control. In the molten metal level control method of the continuous casting machine, which gives the command to the actuator that adjusts the inflow amount of the molten metal into the mold, the disturbance that changes the molten metal level in the mold is the sum of multi-frequency sine waves, A control command for the actuator or an actual operation value of the actuator,
It is characterized in that it is estimated using the molten metal level measurement value, a correction signal for canceling the disturbance is obtained using this disturbance estimation value, and this correction signal is given to the actuator as a correction amount for the control command. .

[0010]

According to the present invention, it becomes possible to obtain a correction signal capable of canceling out the disturbance consisting of the sum of multi-frequency sinusoidal waves by individually dealing with the disturbance of each frequency. .

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments. FIG. 1 is a schematic cross-sectional view of a continuous casting facility to which the molten metal level control method of a continuous casting machine is applied. In the figure, 1 is a tundish for storing the molten metal, 2 is a mold, 3 is the molten metal from the tundish 1 to the mold. Dipping nozzle 4 leading to 2
It shows a sliding gate for cutting off the molten metal attached to the.

A rod of a stepping cylinder 5 is connected to the sliding gate 3, and the opening degree of the sliding gate 3 is adjusted by driving the stepping cylinder 5. The stepping cylinder 5 is provided with a pulse motor 6 as a drive source and a spool which is moved and positioned by the pulse motor 6, and is driven according to the rotation of the pulse motor 6 under the control of the controller 7. SE is a molten metal level sensor installed above the mold 2.

FIG. 2 is a block diagram showing the contents of molten metal level control of the continuous casting machine according to the present invention. The molten metal level target value Lref and the molten metal level measured by the molten metal level sensor and fed back are subtracted by the subtracter 11 and the deviation Δ is input to the PID controller 12. PI
The D controller 12 calculates a position command U ₀ for the sliding gate 3 required to set the deviation Δ to zero based on a predetermined control parameter, and outputs this to the adder 13.

An adder 13 adds a position command U ₀ and a correction signal U _C for an estimated disturbance described later, drives a pulse motor 6 as a control command u (t) for the sliding gate 3, and includes a stepping cylinder 5. The level control system 14 is operated. The stepping cylinder 5 operates based on the control command u (t), and the immersion nozzle 4 is set to the opening degree. The molten metal is supplied to the immersion nozzle (flow rate characteristic K _Q , cross-sectional area A, molten metal flow velocity V _C ) with the molten metal inflow amount Q _IN , and the molten metal discharge amount Q _{OUT is} passed through the immersion nozzle 4 with disturbance d (t). Is supplied to the mold M. The cross-sectional area A
Is known, and the molten metal flow velocity V _C is measured.

In the mold M, a phenomenon in the mold (A: mold cross-sectional area, S: Laplace operator) is added to the total inflow amount of the molten metal to determine the molten metal level L. The molten metal level L is detected by a molten metal level sensor SE {sensor characteristic: 1 / (1 + ST)} and fed back to the subtractor 11 as the molten metal level measured value L as described above.
Given to. The disturbance estimation calculation device 15 estimates and calculates the disturbance according to a predetermined control model based on the level measurement value L measured by the level sensor SE and the control command u (t) described above.

The disturbance estimation calculation device 15 includes a filter 21,
A filter 22 and a disturbance estimation calculation unit 23 are provided, and the above-mentioned molten metal level measurement value L and control command u (t) are first taken into the filter 21 and subjected to filter processing to output Z ₁ (t), Z ₂ (t) is output to the filter 22 and the disturbance estimation calculation unit 23. Where Z ₁ (t), Z
₂ (t) is given by the following equations (1) and (2).

[0017]

[Equation 1]

The filter 22 filters this and outputs the output Φ (t) to the disturbance estimation calculation unit 23.
Here, Φ (t) is a vector composed of Φi (t), and is given by the following equation (3).

[0019]

[Equation 2]

In the equation (3), ap and bp are coefficients of the equation (4), which is the following state equation.

[0021]

(Equation 3)

The disturbance estimation calculation unit 23 is set with a control model assuming that the disturbance d (t) is composed of the sum of multi-frequency (m) sine waves as shown in the following equation (5). d (t) = h ₁ sin (w _i t + α ₁ ) + h ₂ sin (w ₂ t + α ₂ ) + ... + h _m sin (w _i t + α _m ) = Σh _i sin (w _i t + α _i ) ... (5) However, h _i : amplitude α _i : phase (i = 1 ... m) w _i : frequency initial value η _2i-1 (0) = h _i sin α _i η _2i (0) = h _i cos α _{i The} disturbance d (t) is It is a state equation defined by the following equation (6).

[0023]

[Equation 4]

W _i in the equation (6) is an unknown parameter, η
(T) is the state vector of equation (6). On the other hand, the estimated disturbance value d (t) hat is expressed by the following equation (7).

[0025]

(Equation 5)

The x (t) hat in the equation (7) is the following (8)
It is an estimated value of the state space X (t) defined by the formula.

[0027]

(Equation 6)

Therefore, the estimated value x of X (t) in the equation (8) is
If the (t) hat is obtained, d according to the above equation (7)
(T) The hat can be calculated. The x (t) hat can be calculated by the following equation (9).

[0029]

(Equation 7)

There is the following relationship between q ₂ , q ₄ ... q _2m in the equation (9) and the frequencies w ₁ , w ₂ ... w _m which are unknowns in the equation (6). A description will be given according to the flowchart shown in FIG. That is, based on the Φ given from the filter 22 (t) (10) estimates a disturbance frequency according to equation (step S1), and then q = seeking [q ₂ ... q _2m] (step S2), the disturbance frequency the w _i (11) is calculated according to equation (step S3).

[0031]

(Equation 8)

[0032]

[Equation 9]

The estimated disturbance value d (t) thus obtained
The hat is multiplied by the correction gain K _G in the gain setting device as shown in FIG. 2, and the correction output K _G · d (t) hat is added to the adder 1
Give to 3. As a result, the correction gain corresponding to the disturbance d (t) added later is added to the position command U _0, and the influence of the disturbance can be reliably removed by the control command u (t) that compensates for the disturbance. In the above-described embodiment, the disturbance is estimated based on the control command for the pulse motor 6 and the measured level of the molten metal surface. However, the actual opening value of the sliding gate 4 or the spool position and the molten metal of the stepping cylinder 5 are used. It may be estimated based on the surface level measurement value.

[0034]

As described above, in the present invention, it is possible to stably maintain the molten metal level by estimating and correcting the molten metal flow rate disturbance caused by unsteady bulging.
The slab quality can be improved, the occurrence of defects can be controlled, the yield can be greatly improved, the casting speed can be improved, and the excellent effect of improving productivity can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of continuous casting equipment to which a molten metal level control method for a continuous casting machine according to the present invention is applied.

FIG. 2 is a block diagram showing the control contents of the present invention.

FIG. 3 is a flowchart showing a conventional disturbance frequency estimation process.

FIG. 4 is a block diagram showing a conventional control mode.

FIG. 5 is an explanatory diagram showing a conventional control result.

[Explanation of symbols]

 1 Tundish 2 Mold 3 Sliding Gate 4 Immersion Nozzle 5 Stepping Cylinder 6 Pulse Motor 7 Controller 11 Subtractor 12 PID Controller 13 Adder 14 Level Control System 15 Disturbance Estimator

Claims (1)

[Claims] 1. A control command is obtained to eliminate the deviation between the molten metal level target value and the molten metal level measured value, and this control command is given to an actuator for adjusting the inflow amount of molten metal into the mold. In the molten metal level control method of the continuous casting machine, the disturbance that changes the molten metal level in the mold is defined as the sum of multi-frequency sine waves, and this is the control command to the actuator or the actual operation value of the actuator and the molten metal level measured value. And using the estimated disturbance value, a correction signal for canceling the disturbance is obtained, and the correction signal is given to the actuator as a correction amount for the control command. Surface level control method.