JPH0229420B2 - RENCHUKINIOKERUIGATANAIYUMENREBERUSEIGYOHOHO - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an improvement in a method for controlling the level of molten metal in a mold in a continuous casting machine.

(Prior art and its problems) As a method of controlling the level of molten metal in the mold, the 11th
As shown in the figure, the molten metal level in the mold is controlled using a vortex method.
The control signal from the controller is sent to the servo amplifier so as to eliminate the deviation e between the set value SV, which is detected using a gamma ray type or electrode type level meter, and the actual value PV set in advance by the setting device. A method of controlling the slide nozzle or stopper nozzle via a hydraulic unit while detecting the opening with an opening detector to adjust the amount of molten metal injected from the tundish into the mold, by driving a servo motor. A method of controlling the slab drawing speed and a cooperative control method that combines the two have been adopted, but since the control signal is based on the deviation e between the actual value from the level meter and the set value, the control system is complicated. If there is mutual interference or disturbance inside the tank, the control system will become unstable and the hot water level will fluctuate.
In particular, in a device where the cross-sectional area of the mold is small and the drawing speed is high, even a slight disturbance will cause level fluctuations, which will adversely affect the surface quality of the slab. Therefore, rapid level fluctuations must be avoided. However, if it is stabilized against external disturbances, tracking performance deteriorates, so in order to achieve control that satisfies both conditions, at present, as shown in Figure 12, actual measured values from detectors such as level meters are used.
Based on the deviation e between PV and set value SV, the actual process is compared with the process model when outputting the control output from the regulator, and the so-called model reference type control is controlled to match the actual process using corrective logic. There is no choice but to use a two-degree-of-freedom PID control method that uses two types of PID elements depending on the situation by inserting a target value filter at the front stage of the PID control system. However, although the former requires a large-capacity computer and a complicated program, it has the problem that responsiveness does not improve much. On the other hand, the latter satisfies both stability and followability, but in reality, the optimal parameters (α,
There is a difficulty in that it is impossible to select β, γ).

(Problem of the Invention) An object of the present invention is to provide an excellent control method that satisfies both stability and followability as an alternative to the conventional model-based control method and two-degree-of-freedom PID control method.

(Means for Solving Problems) The present invention detects the level of hot water in the mold with a level meter, calculates the deviation e between the actual hot water level PV and the target hot water level SV, and calculates based on the deviation. When adjusting the nozzle opening degree and/or slab withdrawal speed using the control output signal MV to control the mold level, if the set value or process value suddenly changes, the deviation e will change as shown in Figure 7. Therefore, if the followability of the control device is poor, the integral value in a certain section will become large as shown in Figure 8a, and on the other hand, if the stability is poor,
As shown in Fig. 8b, the integral value in a certain section is small and becomes oscillatory, but as shown in Fig. 9a, when the deviation e suddenly changes, a larger correction control is performed at the beginning of the sudden change in the deviation. If the correction operation is braked when the deviation e starts to become small, but if the correction control is not applied when the deviation e is small until it becomes large to a certain extent, as shown in FIG.
This was done with a focus on the ability to achieve the ideal response shown in the figure, and its gist is to detect and integrate the amount of change in the actual hot water level measured every unit time. The integral value is input to a non-linear hysteresis characteristic circuit, and when the amount of change in the above-mentioned actually measured hot water level is greater than a predetermined value, a correction output y is outputted, and the above-mentioned control output MV is corrected by the correction output y, as shown in Fig. 8 above. Based on the ideal response shown in
The purpose of this method is to improve the surface quality of slabs by controlling the mold level and eliminating sudden changes in the level.

Note that the above control method usually uses the difference PVn-PVn- ₁ between the current and previous measured hot water level as the amount of change in the measured hot water level measured every unit time. This amount of change is particularly effective when the deviation e between the measured hot water level PV and the target hot water level SV changes suddenly, but in fixed value control where the target hot water level does not change much, changes in the above PVn itself,
That is, PVn-SV is periodically sampled and integrated, the integrated value is input to a nonlinear hysteresis characteristic circuit, and when the above-mentioned amount of change is greater than a predetermined value, a correction output y is output, and the correction output y is used to adjust the above-mentioned control output.
The control additional circuit configuration may be simplified by modifying the MV.

It is desirable to use the control method of this invention as an auxiliary output y for the control output MV in the normal PID control method, and what kind of correction output y to calculate and output should be determined by taking into account the influence of disturbance on the control output MV. The decision should be made based on the Normal disturbances include: (1) dead zone or tracking error of the hydraulic servo valve (2) malfunction due to hydraulic cylinder leakage (3) dead zone or malfunction due to air intrusion into the hydraulic piping (4) mechanical play in the opening detection mechanism (5) Electrical noise (6) Changes in the diameter of the valve part due to erosion of the slide valve part or adhesion of inclusions such as aluminum, etc. Therefore, the nonlinear hysteresis circuit characteristics are determined in consideration of such disturbance effects, and a correction output is calculated so as to obtain an ideal response.

Hereinafter, the control method of the present invention will be explained in detail based on specific examples.

(Example) Fig. 1 is a control block diagram for implementing the method of the present invention, Fig. 2 is a block diagram showing details of the additional circuit configuration, Fig. 3 is an explanatory diagram of the operation of the switch mechanism in Fig. 2, 4a to 4d are graphs showing how the additional circuit shown in FIG. 2 outputs a corrected output.

In the drawing, the control circuit is configured to perform normal PID control, and detects the hot water level in the mold with a detector 1 such as a level meter, and calculates the actual hot water level PV and target hot water level SV. When adjusting the opening degree of the nozzle and/or the slab withdrawal speed via the process control device 3 using the control output signal MV calculated by the regulator 2 based on the deviation e, the above-mentioned detector The measured hot water level signal PV from 1 is also input to the additional circuit 4, and the above control output MV is corrected as necessary by the correction output y output from the additional circuit 4, and the ideal response output is used to adjust the level of the hot water in the mold. It's starting to control the level.

Specifically, the additional circuit 4 has holding circuits 42 and 43 connected in parallel that store and hold the measured hot water level signal PV via a switch mechanism 41 that performs the operation shown in FIG. ,43
The measured hot water level signal PV is input to (in the illustrated state, it is input to the holding circuit 42),
It is designed to hold the final value for each unit of time. Therefore, the holding circuit 43 in which the switch is not turned on holds the previous final value PVn- ₁ . On the other hand, the above measured hot water level signal PV is the fourth
As shown in Figure a, the difference detection circuit 4
4, the difference detection circuit 44 detects the change in the actual hot water level measured every unit time between the previous final value PVn- ₁ and the above-mentioned actual hot water level signal PVn that changes every moment. Quantity PVn−PVn− ₁
is output (see FIG. 4b), integrated by an integrator 45, and the integrated value (see FIG. 4c) is sent to a nonlinear hysteresis characteristic circuit 47 via a switch mechanism 46 that performs the operation shown in FIG. 3b. is input, and if the amount of change in the above-mentioned actually measured hot water level is more than a predetermined value, the correction output y
(see FIG. 4d), and the control output MV is corrected by the correction output y.

In fixed value control in which the target hot water level SV does not change much, the additional circuit 4 is configured as shown in FIG.
transformed. In other words, the actual hot water level is determined by detecting the hot water level in the mold with a detector 1 such as a level meter.
The deviation e between PV and the target melt level SV is calculated, and the control output signal MV is calculated by the regulator 2 based on the deviation, and the nozzle opening and/or slab withdrawal speed is controlled via the process control device 3. To adjust the control output signal MV, the additional circuit 5 inputs the deviation signal e to the integrator 52 via the switch mechanism 51 that operates as shown in FIG. Characteristic circuit 53
and a switch mechanism 54 that performs the same operation as the switch mechanism 51 that performs the operation shown in FIG. 6a above.
While outputting the corrected output y′ via
A switch mechanism 55 that performs the operation shown in FIG. 6b is connected in parallel with the integrator 52, and when the amount of change in the deviation e sampled at fixed time intervals is greater than a predetermined value, the correction output y' is used to output the control output MV. may be modified.

(Operations and Effects of the Invention) As is clear from the above explanation, according to the present invention, the molten metal level in the mold is detected by a level meter, and the deviation e between the measured molten metal level PV and the target molten metal level SV is
The control output signal MV calculated based on the deviation is used to adjust the opening degree of the nozzle and/or the slab withdrawal speed to control the level of the molten metal in the mold. The amount of change in the hot water level is detected and its integral value is input to a nonlinear hysteresis characteristic circuit, and when the amount of change in the measured hot water level is greater than a predetermined value, a correction output y is output, and the correction output y is used to perform the above control. Since the output MV is corrected, it responds quickly and non-oscillatingly to sudden changes in the deviation e, while providing slow control to gradual changes in the deviation e, ensuring stability against disturbances. As a result, it is possible to achieve both stability and followability, and stable control of the molten metal level, that is, control with less hunting, and as a result, the quality of the slab can be improved.

[Brief explanation of drawings]

Fig. 1 is a control block diagram for implementing the method of the present invention, Fig. 2 is a block diagram showing details of the additional circuit configuration, Fig. 3 is an explanatory diagram of the operation of the switch mechanism shown in Fig. 2, and Figs. d is a graph showing how the additional circuit shown in FIG. 2 outputs a corrected output. Fig. 5 is a control block diagram of a second embodiment of the method of the present invention, Figs. 6 a to d are graphs explaining the operating state of the control device shown in Fig. 5, and Fig. 7 shows the measured hot water level and the set hot water level. Graphs showing changes in deviation from the level; Figures 8a and b are graphs showing changes in response in cases a when tracking is poor and b when stability is poor; Figures 9a and b are graphs showing deviations according to the present invention. Graphs illustrating the response states to changes in , where a shows a case where a large corrective control action is applied, and b shows a case where a corrective control action is not applied until the deviation becomes large to a certain extent. 10th
Figure 1 is a graph showing the ideal response to deviation.
FIG. 1 is a block diagram showing a conventional hot water level control method, and FIG. 12 is a block diagram showing a model reference type control method. 1...Level detector, 2...Adjuster, 3...Process control device, 4, 5...Additional circuit.

Claims (1)

[Claims] 1. Detecting the level of hot water in the mold with a level meter and determining the deviation e between the actual hot water level PV and the target hot water level SV.
In this method, the nozzle opening degree and/or slab withdrawal speed are adjusted using a control output signal MV calculated based on the deviation to control the level of the molten metal in the mold, which is measured every unit time. The amount of change in the measured hot water level is detected and its integral value is input to a nonlinear hysteresis characteristic circuit, and when the amount of change in the measured hot water level is greater than a predetermined value, a correction force y is output, and the correction force y is used to A method for controlling the level of molten metal in a mold, characterized by modifying the control output MV. 2. The mold level control method according to item 1 above, in which the difference between the current and previous measured melt level (PVn-PVn- ₁ ) is used as the amount of change in the melt level in the mold. 3. The mold level control method according to item 1 above, which uses the difference between the actual measured level and the target level (PVn-SV) as the amount of change in the level of the level within the mold.