WO2011070702A1

WO2011070702A1 - Plate thickness control method and plate thickness control state judgment device

Info

Publication number: WO2011070702A1
Application number: PCT/JP2010/006093
Authority: WO
Inventors: 直谷本
Original assignee: Tanimoto Sunao
Priority date: 2009-12-08
Filing date: 2010-10-13
Publication date: 2011-06-16
Also published as: JP4565246B1; JP2011121071A

Abstract

Provided is a plate thickness control method for controlling, in a rolling mill for rolling a plate to obtain a target plate thickness, a plate thickness by determining an estimated plate thickness deviation from the following expression (1): ∆h_e(t) = ∆S(t)+G×∆P(t)/Kc (1), in which Kc, t, ∆P(t), ∆S(t), and ∆h_e(t) (A) represent the rigidity of the rolling mill used for the control, a period of time, and the deviation of a rolling weight, the deviation of a roll gap of the rolling mill, and the estimated plate thickness deviation from a standard state, respectively, and G represents a constant value that satisfies 0<G≤1 (B). In this method, during the control, whether the state of the control is stable or not is judged from the relationship between the value of |∆S(t)| (C) and the value of |G×∆P(t)/Kc| (D), and when it is judged that the state of the control is not stable, at least one of the lowering of the value of G in the expression (1) and the generation of an alarm is carried out.

Description

Plate thickness control method and plate thickness control state determination device

The present invention provides a rolling mill that rolls a sheet to a desired sheet thickness, and controls the sheet thickness by obtaining an estimated sheet thickness deviation based on a deviation of a rolling load from a reference state and a deviation of a rolling position of a roll of the rolling mill. The present invention relates to a so-called BISRA type plate thickness control method and a plate thickness control state determination device used in the control method.

The BISRA type plate thickness control system is widely used in the field of metal rolling and is also called a BISRA-AGC (Automatic Gauge Control) system (for example, Patent Document 1). The BISRA-AGC will be described in detail later. The reason why BISRA-AGC is widely used is that it is possible to quickly obtain an estimated thickness deviation during rolling by using information on a rolling load during rolling and a rolling position of a roll of a rolling mill. On the other hand, in order to control the sheet thickness based on the estimated sheet thickness deviation obtained in this way, the roll reduction position of the roll of the rolling mill is operated. Therefore, in the BISRA-AGC, a feedback loop including a reduction position is formed. Generally, in the feedback loop, the stability of control and the performance of control are in a so-called trade-off relationship in which priority is given to one and the other is sacrificed. In a rolling mill using BISRA-AGC, if the control becomes unstable, there is a high possibility that a large-scale rolling failure will occur. Therefore, conventionally, in a rolling mill using BISRA-AGC, priority is given to stability of control at the expense of control performance to some extent. In other words, the control performance of the BISRA-AGC is not sufficiently exhibited in order to ensure control stability.

Thus, conventionally, in the rolling mill using BISRA-AGC, a plate thickness control method for improving the control performance while ensuring the stability of control has not been developed.

JP 2001-179317 A

Therefore, there is a need for a plate thickness control method in BISRA-AGC that enhances control performance while ensuring control stability.

The sheet thickness control method according to the present invention is a rolling mill for rolling a sheet to a target sheet thickness, the rigidity of the rolling mill used for control, time, deviation of rolling load from the reference state, deviation of the rolling position of the rolling mill, Estimated thickness deviations, respectively,

And G is

As a constant that satisfies

To obtain the estimated thickness deviation and control the thickness. In this method, during control

Value and

It is determined whether the control state is stable from the relationship between the values of the values, and when it is determined that the control state is not stable, at least one of reducing G in Formula (1) and generating an alarm To implement.

According to the method according to the invention, during control

Value and

Whether or not the control state is stable can be determined from the relationship of the values of. Therefore, in BISRA-AGC, in a state where it is determined that the control state is stable, an estimated plate thickness deviation is obtained with G in Formula (1) being 1 or a value close to 1, and the plate thickness control residual is minimized. It can be. In other words, in BISRA-AGC, considering the case where the control state becomes unstable, it is not necessary to set G in Equation (1) to a lower fixed value.

According to an embodiment of the present invention, β is

As a constant that satisfies

When is established, it is determined that the control state is not stable.

According to the method according to the present embodiment, it is possible to easily determine whether or not the control state is stable by using Expression (2).

According to the embodiment of the present invention, when it is determined that the state of control is not stable, γ is
0 <γ <1
As a constant satisfying

As a result, the estimated thickness deviation is obtained by the equation (1) to control the thickness.

According to the method according to the present embodiment, when it is determined that the control state is not stable, the control stability can be obtained by underestimating the magnitude (absolute value) of the second term on the right side of Equation (1) using γ. Is improved.

According to the embodiment of the present invention, when the determination according to the expression (2) is repeatedly performed and it is determined that the control state is not stable, δ is 0 <δ <1
As a constant satisfying

As described above, the plate thickness is controlled by obtaining the estimated plate thickness deviation according to the equation (1) so that G decreases with the lapse of time that the state in which it is determined that the control state is not stable.

According to the method according to the present embodiment, G decreases with the lapse of time of the state in which the state of control is determined to be unstable, so that the case where the stability of control deteriorates with the lapse of time is also supported. can do. On the other hand, the plate thickness control residual is not rapidly increased.

The control state determination device according to the present invention is a rolling mill that rolls a plate to a target thickness, the rigidity of the rolling mill, time, deviation of rolling load from the reference state, deviation of the rolling position of the rolling mill, estimated thickness deviation Respectively

And G is

As a constant that satisfies

Is used in a plate thickness control system for calculating the estimated plate thickness deviation and controlling the plate thickness. The control state determination apparatus according to the present invention receives a deviation of the rolling load from the reference state and a deviation of the rolling position of the rolling mill,

Value and

Whether or not the control state is stable is determined from the relationship between the values, and a signal is output when it is determined that the control state is not stable.

According to the control state determination apparatus of the present invention,

Value and

Whether or not the control state is stable can be determined from the relationship of the values of. Therefore, in BISRA-AGC, in a state where it is determined that the control state is stable, an estimated plate thickness deviation is obtained by setting G in formula (1) to 1 or a value close to 1, and the plate thickness control residual is minimized. can do. In other words, in BISRA-AGC, considering the case where the control state becomes unstable, it is not necessary to set G in Equation (1) to a lower fixed value.

It is a figure which shows the structure of a BISRA-AGC system. It is a figure which shows the relationship between plate | board thickness, a reduction position, and a rolling load. It is the figure which expanded the area | region containing the point A and the point B of FIG. It is a figure which shows the structure of BISRA-AGC. It is a block diagram which shows the relationship between disturbance of rolling load, and plate | board thickness. It is a figure which shows the structure of the BISRA-AGC system containing the control state determination apparatus by this invention. 6 is a flowchart for explaining a control method according to the second embodiment.

FIG. 1 is a diagram showing the configuration of the BISRA-AGC system. The plate 301 is rolled to a desired plate thickness by a rolling mill (hereinafter also referred to as a mill). The rolling mill includes work roll pairs 201 and 203 and backup roll pairs 205 and 207. The reduction positions of these roll pairs are operated by a reduction cylinder 113. The reduction position is set in advance to a reduction position target value by the reduction control device 103 before the start of rolling. The plate 301 is rolled by passing between a pair of work rolls 201 and 203 set at a predetermined reduction position. A load cell 111 for detecting a rolling load is installed in the mill. The rolling load detected by the load cell 111 is sent to the AGC 101. Further, the roll-down position of the roll pair is detected by the position detector 115 of the roll-down cylinder 113, and the detected roll-down position is sent to the roll-down control device 103 and the AGC 101. The AGC 101 obtains an estimated plate thickness deviation based on the detected rolling load and the reduction position, as described in detail later, and obtains a reduction position change amount based on the estimated plate thickness deviation and the target plate thickness deviation. The change amount is sent to the reduction control device 103. The reduction control device 103 controls the plate thickness by operating the reduction position based on the change amount.

BISRA-AGC calculates the estimated thickness deviation Δhe during rolling by the following BISRA equation.

Here, S is a reduction position, P is a rolling load, and Kc is a mill rigidity used for control, that is, a rolling load that causes elongation of a mill having a unit length. Equation (3) shows that the change in sheet thickness is the sum of the change in the reduction position and the change in the elongation of the mill due to the rolling load. Formula (3) is demonstrated using FIG.2 and FIG.3.

FIG. 2 is a diagram showing the relationship between the plate thickness, the reduction position, and the rolling load. The horizontal axis in FIG. 2 indicates the plate thickness and the reduction position. The vertical axis | shaft of FIG. 2 shows a rolling load.

Curves

311 and 313 in FIG. 2 are curves showing the rigidity of the mill. Pressing position of the curve 311 is _{S 1,} pressing position of the curve 313 is _{S 2.} A curve 315 in FIG. 2 is a plastic curve of a plate having a plate thickness H before rolling. The intersection of the curve 311 and the curve 315 is a point A. The value on the horizontal axis of the point A is h ₁ and indicates the thickness after rolling. The value on the vertical axis of the point A is P _1, showing the rolling load. In this case, the rolling load P _1, the thickness is reduced from H to h _1, pressing position of the mill, by milling extend by rolling load P _1, it is increased from S ₁ to h _1. Similarly, the intersection of the curve 313 and the curve 315 is a point B. The value on the horizontal axis of the point B is h _2, showing the plate thickness after rolling. The value on the vertical axis of the point B is P _2, showing a rolling load. In this case, the rolling load P _2, the thickness is reduced from H to h _2, pressing position of the mill, by milling extend by rolling load P _1, it is increased from S ₂ to h _2.

FIG. 3 is an enlarged view of a region including the points A and B in FIG. In FIG. 3, an intersection of a straight line passing through the point A and parallel to the horizontal axis and the curve 313 is defined as a point C. In FIG. 3, curves 313 and 315 are regarded as straight lines, and their slopes are K and −M, respectively. Here, K is the mill rigidity, that is, the rolling load that causes the elongation of the mill of a unit length, and M is the plastic gradient, that is, the rate of change of the rolling load with respect to the plate thickness change after rolling. Considering the sign, the following equation holds.

When deformed,

This equation corresponds to equation (3). When the rolling position is decreased by ΔS, the rolling load increases, so the mill elongation increases. Therefore, the sum of the decrease in the reduction position and the increase in the mill elongation is the decrease in the plate thickness.

Next, changes in rolling load are considered. In FIG. 3, considering the sign,

Transform this formula

Is obtained.

FIG. 4 is a diagram showing the configuration of BISRA-AGC. The symbols in FIG. 4 are as follows, including those already described.

As is apparent from FIG. 4, the following equation including the tuning rate α is used as the BISRA equation instead of the equation (3).

Here, the tuning rate α is a positive value smaller than 1.

From FIG. 4, the number of transmissions from the target plate thickness deviation to the deviation from the reference reduction position of the actual reduction position can be expressed by the following equation. Here, k / A is g.

Therefore, the characteristic root is

It becomes. According to the control theory, if the real part of the characteristic root is negative, the control system is stable. The condition that the real part of the characteristic root is negative is that g is positive.

It is.

From equation (8), the smaller the tuning rate α, the more stable the control system. For example, when the mill stiffness K is larger than the mill stiffness Kc used for control, such as when the plate thickness is thin and the plate width is wide, the stability of the control system decreases. Therefore, in such a case, the tuning rate α is set to a value smaller than 1 in order to ensure the stability of the control system.

Next, in BISRA-AGC using Equation (5), the control residual when a step-like disturbance enters the rolling load will be described.

FIG. 5 is a block diagram showing the relationship between the disturbance of the rolling load and the plate thickness. The symbols in FIG. 5 are as follows. However, the description of the same reference numerals as those in FIG. 4 is omitted.

From FIG. 5, the number of transmissions from the disturbance of the rolling load to the deviation of the actual sheet thickness can be expressed by the following equation.

Applying the final value theorem to (9), the control residual for unit step disturbance is

Here, as an example, with a rolling mill after hot strip mill finishing of a steel plate using BISRA-AGC, the mill rigidity (K, Kc) is 5 [MN / mm] and the rolling load is 1 [MN] during rolling. Consider the case of a disturbance. If there is no AGC,
1 [MN] / 5 [MN / mm] = 200μm
Sheet thickness control residual

Should result.

Table 1 shows the plate thickness control residual [unit: μm] of a single stand generated by BISRA-AGC when the tuning rate α and the plastic gradient of the plate are changed.

Thus, it can be seen that when α = 1.0, the disturbance can be completely absorbed, but when α is reduced, the automatic plate thickness control performance is deteriorated particularly by a material having a large M (such as a thin wide material).

BISRA-AGC falls into an unstable region of control, which means that in the worst case, a very dangerous situation involving the destruction of the rolling mill occurs. However, conventionally, it has not been possible to predict the stability of BISRA-AGC control in advance. As a result, while equipped with high-performance actuators such as a hydraulic reduction device, the tuning rate α is set to about 0.8 for thin and wide materials with large M regardless of the state of the rolling mill. Currently. As can be seen from Table 1, in this case, it is no exaggeration to say that the plate thickness control by BISRA-AGC is hardly performed. That is, conventionally, a low tuning rate is used even when the rolling mill is in a normal state (a state where the control is stable) in consideration of a rolling mill failure caused by an unstable state of control unknown when it occurs. As a result, the function of BISRA-AGC is lowered. In other words, BISRA-AGC is currently effective only for rolling a material having a small M, that is, a thick material or a narrow material.

Further, the control of the plate thickness by reducing the tuning rate α corresponds to the fact that the so-called absolute value AGC function for controlling by setting the product plate thickness to the target plate thickness cannot be used. This is a large loss in yield.

As a result of examining the configuration of the BISRA-AGC shown in FIG. 4, the inventor determines the stability of the control by considering the deviation of the actual reduction position from the reference reduction position and the thickness change due to the mill elongation. I got new knowledge that I could do it.

Here, as shown in FIG. 3, the reduction in the rolling position (ΔS, where ΔS <0) is the increase in rolling load (ΔP, where ΔP> 0), that is, the increase in mill elongation change (ΔP / Kc). ). Therefore, we compared the absolute value of the rolling position change used in BISRA-AGC with the absolute value of the mill elongation change,

Then it ’s stable,

If so, it is determined to be unstable. Expression (12) is the same as Expression (2). Where G is the tuning rate,

It is a constant that satisfies Here, the tuning rate according to the present invention is defined as G, and is distinguished from the tuning rate α according to the prior art. β is a constant related to the position of the characteristic root, and the position of the characteristic root is determined by Expressions (11) and (12). Specifically, β is

Is a constant satisfying

Corresponds to the position of the characteristic root. That is, as the value of β is larger, the characteristic root is located on the negative side (control stable side). According to the equations (11) and (12), the characteristic root is

It is determined whether it is on the negative side or the positive side from the position of.

In order to shift the unstable or nearly unstable state to the stable state, it is only necessary to underestimate the mill elongation change and obtain the estimated plate thickness deviation. This is equivalent to reducing the tuning rate.

∙ Control instability cannot be prevented by changing the forward function of feedback control, that is, the transfer function of the controller.

FIG. 6 is a diagram showing a configuration of a BISRA-AGC system including the control state determination device 105 according to the present invention. The portion of the AGC system of FIG. 6 excluding the control state determination device 105 is the same as the AGC system described with reference to FIG. The control state determination device 105 is connected to the AGC 101, and the deviation from the reference reduction position of the actual reduction position from the AGC 101.

And actual rolling load deviation from standard rolling load

Receive. The control state determination apparatus 105 determines the stability of control using these values. If the control state determination device 105 determines that the control state is unstable, the control state determination device 105 changes the control parameter of the AGC 101. If the control state determination device 105 determines that the control state is unstable, it sends an alarm output command to the alarm output device 107 to output an alarm.

Embodiments of the control method according to the present invention will be described below.

Example 1
AGC101 is

The estimated plate thickness deviation is obtained by the feedback plate thickness control. Equation (13) corresponds to the equation (1) with G = 1.0. During the feedback plate thickness control, the control state determination device 105 has the formula

Monitor whether or not here,

Is a positive constant of 1 or more, and is 1.05 as an example. If Expression (14) does not hold, the control state determination device 105 determines that the control is in a stable state, and continues control using Expression (13). If Expression (14) is satisfied, the control state determination device 105 determines that the control is in an unstable state, and changes the expression for obtaining the estimated thickness deviation as follows.

here,
γ
Is a positive constant less than 1, for example 0.8. By changing the equation for obtaining the estimated thickness deviation from Equation (13) to Equation (15), the position of the characteristic root according to Equation (7) moves to the stable side, and feedback control can escape from the unstable state. On the other hand, in this state, a control residual of the plate thickness as shown in Table 1 occurs with respect to the disturbance of the rolling load. In other words, according to the present embodiment, the control stability is ensured at the expense of the control performance only when the control becomes unstable while monitoring the control stability. When the control is stable, the use of Equation (11) is different from the conventional control method in that the control performance is sufficiently exhibited.

Example 2
AGC101

The estimated plate thickness deviation is obtained by the feedback plate thickness control. Expression (16) is the same as Expression (1). During the feedback plate thickness control, the control state determination device 105 has the formula

It is determined whether or not here,

The initial value of is 1.0

Is a positive constant of 1 or more, and is 1.05 as an example.

FIG. 7 is a flowchart for explaining the control method of the second embodiment.

In step S110 in FIG. 7, the control state determination device 105 determines the deviation from the reference reduction position of the actual reduction position from the AGC 101.

And actual rolling load deviation from standard rolling load

Receive. The AGC 101 takes in the actual plate thickness, the actual rolling load, and the actual reduction position as reference values when the plates are bitten (lock-on process), and a deviation is obtained from these reference values.

Although not shown in the flowchart of FIG. 7, in order to prevent erroneous determination due to noise, the absolute value of the deviation of the actual reduction position from the reference reduction position.

Absolute value of mill elongation due to deviation from standard rolling load and actual rolling load

If is less than a predetermined value, the process may be terminated without performing the determination process. The predetermined value may be, for example, 0.1 mm or 3% of the target plate thickness.

In step S120 of FIG.

It is determined whether or not If Formula (17) is materialized, it will progress to Step S130. If Expression (17) does not hold, the process proceeds to step S140.

In step S130 in FIG. 7, it is determined that the control is in an unstable state.

And here,
δ
Is a constant less than 1, for example 0.9. By changing G in Expression (16) according to Expression (18), the position of the characteristic root according to Expression (7) moves to the stable side. Until the stability of control is ensured by repeating the process of step S130 at regular intervals.

The value of is decreased. On the other hand, if expression (17) does not hold, it is determined that the control is in a stable state.

As is, control using the equation (16) is continued.

7, the control state determination device 105 determines whether or not AGC control is being performed. If AGC control is being performed, the process returns to step S110. If AGC control is not in progress, the process is terminated.

According to this embodiment, while monitoring the control stability, the control stability is ensured at the expense of the control performance only when the control becomes unstable. If the control is stable, in equation (16)

Thus, the point that the control performance is sufficiently exhibited is different from the conventional control method.

For example, in a hot strip mill rolling of a steel plate (M = 30 [MN / mm]) having a thickness of 1.6 mm and a width of 1200 mm, a rolling load disturbance of 0.5 MN occurs due to a skid mark generated in a heating furnace before rolling. And Assuming that the tuning coefficient α is 0.8, from Table 1, the plate thickness variation caused by the rolling load disturbance is

It is. According to the present invention, if the tuning coefficient α can be set to 1.0 by ensuring the stability of the control,

The yield can be improved.

Although the present invention has been described using a hot strip mill as an example, the present invention can be applied to other rolling mills such as a cold strip mill and a thick plate mill as long as the mill uses a BISRA-AGC.

Claims

In the rolling mill that rolls the plate to the target plate thickness, the rigidity of the rolling mill used for control, the time, the deviation of the rolling load from the reference state, the deviation of the rolling position of the rolling mill, the estimated thickness deviation,

And G is

As a constant that satisfies

Is a plate thickness control method for calculating the estimated plate thickness deviation and controlling the plate thickness,
During control

Value and

It is determined whether the control state is stable from the relationship between the values of the values, and when it is determined that the control state is not stable, at least one of reducing G in Formula (1) and generating an alarm The thickness control method which implements.
β is

As a constant that satisfies

The plate | board thickness control method of Claim 1 which determines with the state of control not being stable when is materialized.
When it is determined that the control state is not stable, γ is
0 <γ <1
As a constant satisfying

The plate | board thickness control method of Claim 1 or 2 which calculates | requires an estimated plate | board thickness deviation by Formula (1) as follows, and controls plate | board thickness.
When the determination by the expression (2) is repeated and it is determined that the control state is not stable, δ is 0 <δ <1
As a constant satisfying

The sheet thickness is controlled by obtaining an estimated sheet thickness deviation according to equation (1) such that G decreases with the lapse of time for which it is determined that the control state is not stable. Or the thickness control method according to 2.
In the rolling mill that rolls the plate to the target plate thickness, the rolling mill stiffness, time, deviation of the rolling load from the reference state, deviation of the rolling mill reduction position, estimated plate thickness deviation,

And G is

As a constant that satisfies

Is a control state determination device in a plate thickness control system that controls the plate thickness by obtaining an estimated plate thickness deviation, and receives a rolling load deviation from a reference state and a rolling mill deviation,
During control

Value and

A control state determination device that determines whether or not the control state is stable based on the relationship between the values of the values and outputs a signal when it is determined that the control state is not stable.