JPH0587351B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a molten metal level control device for appropriately controlling the molten metal level in a continuous casting process. [Prior art] In continuous casting of steel, aluminum alloys, etc., hot water made of molten metal is poured from above into a mold that is open at the top and bottom, cooled from the side of the mold to solidify part of the surface, and then poured into a mold from below. Casting is performed continuously by cooling the material while drawing it between rolls. In this continuous casting process, it is well known that the control state of the level of the molten metal in the mold is an important factor that affects the quality of the slab, and in particular, it is important to keep the amount and rate of fluctuation of the molten metal level low. is essential (see, for example, Japanese Patent Publication No. 16218/1983). The control method is generally fixed value control using PID calculation, and in particular, control based on proportional action (P) and integral action (I) is performed. [Problems to be Solved by the Invention] Requirements for product quality and yield are becoming stricter year by year, and recently, fine sustained vibrations that occur during stable conditions have become a problem. In addition, a sudden rise in the level of the hot water often occurs, but this phenomenon is said to be caused by the alumina adhering to the nozzle being peeled off and the opening area expanding, resulting in a sudden rise in the amount of inflow. Conventional control devices are designed with the main focus on matching the hot water level to the target level without any deviation.
As described above, since the control is mainly based on the P operation and the I operation, the hot water level rapidly rises and falls every time a disturbance occurs, which is not a desirable control from the viewpoint of the hot water level fluctuation speed. Therefore, an object of the present invention is to propose a hot water level control device that does not cause sustained vibration when stable, and minimizes the amount and speed of fluctuation in the hot water level against disturbances caused by alumina peeling, etc. There is a particular thing. [Means for Solving the Problems] FIG. 1 is a diagram showing the principle configuration of a hot water level control device according to the present invention. In the figure, the molten metal level control device for the continuous casting process of the present invention includes a molten metal level detection means 10 for detecting the molten metal level in a continuous casting mold 50, and a molten metal level detection means 10 for detecting the molten metal level in a continuous casting mold 50, and a molten metal level detection means 10 for detecting the molten metal level in a continuous casting mold 50, and PID calculation means 12 that performs PID calculation based on a PID constant and outputs the calculation result as a manipulated variable;
A continuous casting process hot water level control device comprising injection amount increasing/decreasing means 14 for increasing/decreasing the amount of hot water injected into the mold 50, the hot water level detecting means 10, the PID calculating means 12, and The characteristic value of the linear element in the control loop including the injection amount increase/decrease means 14 and the arbitrarily determined PID
a function L calculation means 20 that calculates a function L that expresses the characteristics of the linear element from a constant; and a function N that expresses the characteristics of the nonlinear element in the control loop with a descriptive function.
The function N calculation means 22 that calculates the function L and the function N do not always satisfy the condition NL+1=0.
region determining means 24 for finding the region of the PID constant;
A constant determining means for performing a simulation calculation of the change in the hot water level when a predetermined disturbance is applied to each set of values in the region of the PID constant, and finding a set of PID constants with the smallest hot water level fluctuation speed and the smallest hot water level fluctuation width. 2
6. [Effect] As will be detailed later, the present inventors estimated that the sustained vibration during stability is caused by a nonlinear element in the control loop, and found that this phenomenon could be explained using the descriptive function method. Ta. According to this method, the characteristics of a nonlinear element are approximated by a descriptive function N, while if the characteristics of other linear elements are a function L, the condition for sustained vibration is given by NL+1=0 (1). In other words, the frequency and amplitude that satisfy equation (1) are the frequency and amplitude of sustained vibration. Conversely, the region of the set of PID constants determined by the region determining means 24 becomes the region of the set of PID constants that does not cause sustained vibration. The constant determining means 26 further finds a set of PID constants that minimize the rate of fluctuation in the hot water level and the width of the fluctuation in the hot water level in response to disturbances, so that the constant vibration does not occur and the rate of fluctuation in the hot water level and the width of the hot water level change in response to disturbances are minimized. The PID constant with the minimum width is found. [Embodiment] FIG. 2 is a diagram schematically showing an apparatus to which the present invention is applied. A tandem tray 502 is provided above the mold 500 and supported by a TD car 504.
Molten steel in the tundish 502 is supplied to the mold 500 through a submerged nozzle 508 provided at the bottom thereof. Opening 50 above immersion nozzle 508
6 is closed by a stopper 140, and by moving the stopper 140 up and down, the amount of water flowing into the mold 500 can be increased or decreased. The stopper 140 is connected to a piston 144 of the stepping cylinder 142 via a connecting portion 146, and as the piston 144 moves up and down based on a control signal from the controller 120, the stopper 140 moves up and down, and the inflow amount is adjusted. . A hot water level sensor 100 that detects the hot water level using electromagnetic induction is provided above the hot water level in the mold 500, and a signal of the detected hot water level is input to the controller 120. Controller 120 is a well-known PID controller. The computer 200 is a well-known process control computer, and is
Calculate the PID value and use the controller 12 online
0 or the calculated result is provided offline to the controller 120. FIG. 3 is a block diagram representing the control system of FIG. 2. Block 1200, 1202,
1204 shows the transfer functions of the integral action, proportional action, and differential action of the controller 120, respectively. Block 1400 shows the first-order lag transfer function of time constant Ts in stepping cylinder 142, and block 1402 represents hysteretic play in connection 146. K in block 5000 is stopper 1
This is the differential coefficient of the curve representing the inflow amount with respect to the position 40, that is, the flow rate coefficient, and the block 5002 is the transfer function of the mold 500 when the effective cross-sectional area of the mold 500 is set to A. block 100
0 indicates the transfer function of the level meter 1000. Therefore, the mold 500 and the hot water level sensor 10
0, the loop transfer function L(s) of the linear element in the control loop including the controller 120, stepping cylinder 142, and stopper 140 is L(s)=Kp(1+1/T _I s+T _D s)・1 /1+T _S s・
It is given by K・1/As・1/1+T _L s(2). Therefore, the function L(w) of w obtained by substituting s=jw into this equation becomes a complex function representing the frequency characteristic of the linear element. According to the descriptive function method, the descriptive function for the friction load with hysteresis represented by block 1402 is

[ ] (“Automatic Control” (Maruzen) by Masami Ito p205~
209). However, X is the amplitude of the input signal,
2β is the width of the play. If L(w) and -1/N(X) for the device shown in FIG. 2 are expressed on a complex plane according to the Nyquist diagram method in the descriptive function method, the result will be as shown in FIG. 4. w and X at the intersection of these two curves
The values correspond to the frequency and amplitude of sustained vibration, respectively. The following table shows the values obtained from such analysis and the periods and amplitudes of sustained vibrations actually observed.

〔Effect of the invention〕

As described above, according to the present invention, the problem of sustained vibration caused by nonlinear elements is solved, and the speed and range of fluctuations in the melt level can be minimized in response to disturbances caused by alumina peeling, etc. This makes it possible to improve product quality and yield.

[Brief explanation of drawings]

Figure 1 is a diagram representing the principle configuration of the present invention, Figure 2 is a diagram representing an embodiment of the present invention, Figure 3 is a block diagram of the control system in Figure 2, and Figure 4 is based on the descriptive function method. A diagram showing the analysis, FIG. 5 is a diagram showing the region of the PID constant that does not cause sustained oscillation, and FIG. 6 is a diagram for explaining the evaluation function E. In the figure, 100... hot water level sensor, 140...
... Stopper, 142 ... Stepping cylinder, 146 ... Connection section, 500 ... Mold, 5
02...Tandaitsuyu, 508...Immersion nozzle.

Claims (1)

[Scope of Claims] 1. A liquid level detection means 10 for detecting the liquid level in the continuous casting mold 50, and a deviation between the liquid liquid level and a target level 16 based on a PID constant.
A continuous system comprising a PID calculation means 12 that performs PID calculation and outputs the calculation result as a manipulated variable, and an injection amount increase/decrease means 14 that increases or decreases the amount of hot water injected into the mold 50 according to the manipulated variable. In a mold level control device for a casting process, the mold 50, the level detection means 10,
The PID calculation means 12 and the injection amount increase/decrease means 1
4, a function L calculation means 20 for calculating a function L expressing the characteristics of the linear element from the characteristic value of the linear element in the control loop and an arbitrarily determined PID constant; function N calculation means 22 for calculating a function N that expresses the characteristics of the nonlinear element of by a descriptive function;
and a region determining means 24 for finding a region of the PID constant that does not always satisfy the condition NL+1=0 from the function L and the function N; and when a predetermined disturbance is applied to each value set within the region of the PID constant. a constant determining means 26 for performing simulation calculations of changes in the melt level and finding a set of PID constants with the smallest melt level fluctuation rate and the smallest melt level fluctuation width. .