JP6597565B2 - Thickness control method in cold rolling - Google Patents

Description

  The present invention relates to a sheet thickness control method in cold rolling for controlling the sheet thickness of a metal strip in cold rolling.

  Conventionally, in cold rolling, a metal strip is manufactured by a continuous rolling mill having a plurality of rolling stands. It is important to improve the plate thickness accuracy of the metal strip rolled by this continuous rolling mill. As one of the methods, for example, automatic plate thickness control called AGC (Automatic Gauge Control) disclosed in Patent Document 1 The method is widely used.

  Patent Document 1 discloses a technique for expressing the dispersion of the plastic coefficient Q for each metal band by a probability density function and obtaining an optimal solution of the control gain of the screw AGC and the monitor AGC using the technique of the optimization problem. Yes.

JP 2011-143447 A

  However, although the technique disclosed in Patent Document 1 considers variations in the plastic coefficient Q for each metal band, the control gain is not necessarily optimal because the plastic coefficient Q is constant in the same metal band. . That is, since the plastic coefficient (corresponding to deformation resistance) of an actual metal band is not uniform in the longitudinal direction, the control gain determination method disclosed in Patent Document 1 can set an optimum gain in the longitudinal direction of the metal band. There is no problem. For this reason, especially in a high strength metal band such as high-strength steel, the deformation resistance may fluctuate greatly, which may cause a problem of fracture due to large plate thickness fluctuation or excessive thinness during cold rolling. .

  Accordingly, an object of the present invention is to provide a sheet thickness control method in cold rolling, which can reduce a variation in sheet thickness in cold rolling and obtain a metal strip having good sheet thickness accuracy.

  In order to solve the above problems, the present invention provides the following [1] to [3].

[1] In cold rolling after hot rolling, or cold rolling after hot rolling and pickling, cold is performed by using a monitor AGC so that the metal strip at the time of cold rolling has a predetermined target thickness. A sheet thickness control method in rolling,
The first step of calculating the upper limit value of each gain of P control and I control in PI control immediately before the control system does not diverge and deviates from the tolerance of the target plate thickness while keeping the winding temperature of the metal plate after hot rolling constant When,
A second step of classifying fluctuations in the winding temperature into a plurality of specific patterns according to the change and variance of the moving average calculated from the winding temperature;
A third step of setting a maximum value and a minimum value of each gain of P control and I control for each specific pattern based on the calculated gain upper limit value;
A fourth step of measuring the winding temperature of the metal plate after hot rolling in the longitudinal direction;
A fifth step of calculating the moving average change and variance of the measured coiling temperature;
Based on the calculated moving average change and variance, a sixth step of determining whether the measured variation in the longitudinal direction of the winding temperature corresponds to the specific pattern, and applying to the specific pattern;
For the corresponding specific pattern, within the range of the maximum value and the minimum value of the P control and I control obtained in the third step, each gain is changed to execute a plate thickness control simulation, and the optimal range of the PI control gain A seventh step of setting
A sheet thickness control method in cold rolling characterized by comprising:

  [2] The optimum range of the PI control gain is set at the leading end of the metal strip during cold rolling corresponding to the leading end of the metal plate during hot rolling. Thickness control method in cold rolling.

  [3] The plate thickness control method in cold rolling according to [1] or [2], wherein an optimum range of PI control gain is set for the first stand of cold rolling.

  According to the present invention, when the coiling temperature of the metal plate in hot rolling varies in the longitudinal direction, the deformation resistance of the metal strip during cold rolling takes into account the characteristic that changes in the longitudinal direction. Since the optimum control gain in the thickness control is set, fluctuations in the plate thickness of the metal strip after cold rolling can be reduced. As a result, it is possible to obtain an effect of reducing the off-gauge length of the metal band and suppressing the breakage due to the thinness.

It is a schematic diagram which shows the structural example of the apparatus used for implementation of the board thickness control method of this invention. It is a control block diagram which shows the controlled object and control system of monitor AGC. It is a figure which shows plate | board thickness fluctuation | variation and the length of the off gauge by this. It is a figure which shows an example of the flow of the plate | board thickness control method in the cold rolling which concerns on this invention. It is the figure which classified and illustrated the coiling temperature fluctuation pattern in hot rolling into four. It is a figure which shows the board thickness control simulation result which is an Example of this invention, and is a figure which shows the case of the pattern A shown by (a) of FIG. It is a figure which shows the plate | board thickness control simulation result which is an Example of this invention, and is a figure which shows the case of the pattern B shown by (b) of FIG. It is a figure which shows the board thickness control simulation result which is an Example of this invention, and is a figure which shows the case of the pattern C shown by (c) of FIG. It is a figure which shows the board thickness control simulation result which is an Example of this invention, and is a figure which shows the case of the pattern D shown by (d) of FIG.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic diagram showing a configuration example of an apparatus used for carrying out the plate thickness control method of the present invention. Here, a part of a stand of a rolling mill and a plate thickness control device for cold rolling a metal strip after hot rolling or a metal strip after hot rolling and pickling are shown. In the figure, 1 is a rolling stand, 2a and 2b are work rolls, 3a and 3b are backup rolls, 4 is a reduction device, 5 is a thickness gauge, 6 is a control unit, and 7 is a metal strip.

  The rolling stand 1 includes a pair of upper and lower work rolls 2a and 2b for rolling the metal strip 7, and a pair of upper and lower backup rolls 3a and 3b that support the upper and lower work rolls 2a and 2b. Furthermore, the rolling stand 1 includes a reduction device 4 that can change the gap between the pair of work rolls 2a and 2b. The reduction device 4 moves the backup roll (upper backup roll 3a in the figure) up and down to manipulate the roll gap between the work rolls 2a and 2b, thereby changing the thickness of the exit side of the rolling stand 1. Furthermore, a plate thickness gauge 5 for measuring the plate thickness of the metal strip 7 after rolling is provided on the exit side of the rolling stand 1.

  The metal strip 7 transferred from the upstream side is sandwiched between the pair of work rolls 2a and 2b and is pressed down to become a metal strip 7 having a predetermined plate thickness, which is then transferred downstream, and rolled by a plurality of rolling stands. Applied.

  The rolling stand 1 of the present embodiment is provided with a control unit 6 that controls the roll gap in order to control the thickness of the metal strip 7 with high accuracy. The control unit 6 has a function of executing a monitor AGC that issues a command to the reduction device 4 based on the actual thickness value of the metal strip 7 measured by the thickness gauge 5.

  Hereinafter, the monitor AGC will be described. In the following description, PI control refers to proportional-integral control, and is obtained by adding integral (I) control to proportional (P) control.

FIG. 2 is a control block diagram showing the control target and control system of the monitor AGC. In the figure, T is a time constant of the rolling device 4, Q is a plastic coefficient indicating the difficulty of deformation of the metal strip 7, L is a dead time in the plate thickness measurement by the plate thickness meter 5, and K _p is a proportionality of the monitor AGC ( P) gain, K _I is the integral of the monitor AGC (I) gain, M is the nominal value of the mill modulus, e is Napier constant, s is a Laplace operator defined by the Laplace transform.

  Since the thickness gauge 5 can be installed only at a location away from the roll due to restrictions on equipment installation, there is always a dead time L in the thickness measurement. Therefore, in the block diagram of FIG. 2, dead time is put in the feedback loop.

ここで、Ｇはロールギャップ、Ｍはミル定数、Ｑは金属帯７の塑性係数、ｈは圧延スタンド出側板厚の実測値である。 The monitor AGC is a controller that removes the thickness deviation based on the result measured by the thickness gauge 5 based on the following equation (1).

Here, G is a roll gap, M is a mill constant, Q is a plastic coefficient of the metal strip 7, and h is an actual measurement value of the rolling stand outlet side plate thickness.

  FIG. 3 is a diagram showing the plate thickness variation and the length of the off-gauge caused thereby. When the steel strip is cold-rolled as a metal strip and the plate thickness is controlled, the fluctuation of the thickness of the metal strip on the first stand exit side of the cold rolling mill at the joint between the preceding and succeeding members of the metal strip Show. The plate thickness of the metal strip is out of the target plate thickness tolerance at the start of the subsequent material rolling, and enters the tolerance after rolling for a while. The plate thickness variation at the leading end of the following material is due to a change in the plastic coefficient Q of the metal strip, that is, a change in the deformation resistance of the metal strip. The length until the plate thickness falls within the tolerance is called an off gauge, and it is necessary to improve the convergence to the plate thickness target value to suppress the plate thickness variation and to shorten the off gauge.

  However, in the plate thickness control by the conventional monitor AGC, the gain of PI control was set uniformly, and after rolling for a while, the plate thickness accuracy was monitored and readjusted when the plate thickness accuracy dropped significantly. It was difficult to control the thickness to achieve the target thickness range. Further, as a result of adjustment over a long period of time, the gain of P control or I control may approach zero or diverge to ∞, which is a problem.

  Therefore, the present inventors examined a method for optimally adjusting the control gain of the monitor AGC according to the deformation resistance that changes in the longitudinal direction of the metal strip.

The control gain determination method in the plate thickness control method of the present invention will be described below.
First, the inventors paid attention to a change in a coiling temperature (hereinafter abbreviated as CT) in a hot rolling process as a factor of deformation resistance fluctuation. In particular, in a high-strength metal band such as high-strength steel, CT fluctuations in one metal band may become large.

  When CT varies, the metal structure changes, and the deformation resistance changes as the metal structure changes. When the deformation resistance changes, the gap between the work rolls cannot be kept constant without controlling the sheet thickness, so that the sheet thickness during cold rolling varies.

  Thus, there is a close relationship between CT and deformation resistance during cold rolling, and it is possible to predict a change in deformation resistance within one metal strip using CT as an index. Therefore, CT fluctuations were classified into specific patterns, CT fluctuations were regarded as changes in deformation resistance of the metal strip, and the influence of the monitor AGC gain on the board thickness accuracy was analyzed using a board thickness control simulation. As a result of this analysis, CT fluctuations can be classified into, for example, four specific patterns to be described later, and if the control gain of PI control is set for each of these specific patterns, the control gain approaches zero or becomes ∞. The present invention has been made by obtaining the knowledge that the plate thickness can be controlled with high accuracy without any divergence.

  FIG. 4 is a diagram showing an example of a flow of a sheet thickness control method in cold rolling according to the present invention. First, at Step 01, each of the P (proportional) control and I (integral) control in PI control (proportional / integral control) in which the control system does not diverge with the coiling temperature (CT) of the metal plate after hot rolling constant. An upper limit value of gain (value of each gain immediately before the plate thickness deviates from the target tolerance) is calculated.

  Next, at Step 02, the winding temperature is classified into a specific pattern based on the change and dispersion of the moving average calculated from the winding temperature.

  Next, in Step 03, for each gain of P (proportional) control and I (integral) control for each specific pattern, a maximum value and a minimum value multiplied by a predetermined ratio based on the calculated gain upper limit value are set. deep.

  Further, in Step 04, the winding temperature of the corresponding metal plate in the hot rolling process is measured in the longitudinal direction. In Step 05, the moving average and dispersion in the longitudinal direction are calculated for the measured winding temperature of the metal plate.

  Next, in Step 06, based on the moving average change and variance calculated in Step 02, it is determined to which specific pattern the longitudinal variation of the measured winding temperature corresponds, and the specific pattern is applied.

  FIG. 5 is a diagram illustrating a coiling temperature (CT) variation pattern in hot rolling classified into four. In the figure, the inside of the round frame shown with a dotted line shows each characteristic part of (a)-(d). That is, in the four specific patterns, the pattern A (FIG. 5A) is characterized in that the variation of the moving average of CT is small but the variance is large (the variation is large). Further, the pattern B (FIG. 5B) is characterized in that the variation of the moving average of CT is large but the variance is small. The pattern C (FIG. 5C) is characterized in that both the change and variance of the moving average of CT are small and the CT is stable. Furthermore, the pattern D (FIG. 5 (d)) is characterized in that the moving average of CT changes greatly with a slope and the variance is large. In FIG. 5, the specific patterns are exemplified as the four patterns A to D, but the present invention is not limited to this, and the patterns may be classified into more than four specific patterns.

  In Step 07, an optimum value of the PI control gain (hereinafter also referred to as PI gain) is set. In setting the optimum value, the PI gain is changed to execute a plate thickness control simulation, and the PI gain is changed based on the specific pattern applied in Step 06. At this time, referring to the maximum and minimum values of P gain and I gain obtained in Step 03, the PI gain is changed within the range, and a plate thickness control simulation is executed. The optimal PI gain is set based on the degree of fluctuation (increase / decrease)) and the convergence.

  When changing the PI gain, the maximum value and the minimum value of each of the P (proportional) gain and the I (integral) gain may be determined as follows, for example.

  First, for the reference PI gain, a plate thickness control simulation is performed based on the Ziegler-Nichols limit sensitivity method under the condition that the deformation resistance is constant in the metal band, and the optimal control gain is, for example, P: 0.8 and I: 0.5, respectively. The condition for making the deformation resistance constant in the metal strip may be obtained from the average value of CT of the metal plate during hot rolling, or the CT at a specific position of the metal plate may be obtained as a representative value.

  Regarding the method for obtaining the optimum control gain, assuming that the deformation resistance is constant in the metal band, for example, in the plate thickness control simulation, the I gain is set to 0 (zero), and the P gain is gradually increased to increase the plate thickness. Pm, which is the upper limit value of P gain immediately before diverging (out of the target thickness tolerance), is obtained, and an optimum P gain is obtained by multiplying Pm by a certain ratio. In this example, Pm immediately before the plate thickness diverges is 1.78, and the fixed ratio is 0.45, so the P gain is 0.8. Similarly, for the I gain, the P gain is set to 0 (zero), the upper limit value Im of the I gain immediately before the plate thickness diverges is obtained, and the optimum I gain is set to 0.5 by multiplying Im by a certain ratio.

  The maximum and minimum values of the P gain and I gain in the plate thickness control simulation are determined as follows based on the gain obtained by the Ziegler-Nichols limit sensitivity method.

  First, with respect to the P gain, the plate thickness control simulation does not diverge, and the upper limit value Pm of the P gain by the above-mentioned limit sensitivity method is set to a maximum value of 0.01, which is substantially zero. Set to the minimum value.

  Similarly, with respect to the I gain, the maximum value of β times the upper limit value Im of the I gain according to the above-described limit sensitivity method, which is a range in which the plate thickness of the plate thickness control simulation does not diverge, is approximately zero. Is the minimum value.

  A plate thickness control simulation is performed between the maximum value and the minimum value of the P gain and I gain described above, and an optimal control gain corresponding to the CT variation pattern is derived.

  Once the optimal PI gain has been derived, the metal plate position where the CT during hot rolling is measured is tracked, and the thickness of the corresponding metal strip position during cold rolling is controlled using the derived optimal PI gain. .

  In this embodiment, CT temperature fluctuations are classified into specific patterns, and an optimal control gain is set for each specific pattern, so that the plate thickness fluctuations during cold rolling can be reduced as compared with the conventional case. As a result, it is possible to obtain an effect of reducing the off-gauge length of the metal band and suppressing the breakage due to the thinness.

Examples of the present invention will be described below.
Here, an example in which the sheet thickness is controlled using the above-described method for deriving the optimum control gain (result of sheet thickness control simulation) will be described taking as an example the case of cold rolling a steel strip.

  A plurality of hot-rolled steel sheets having different CTs were collected in advance, the deformation resistance was measured by a tensile test, the relationship between CT and the deformation resistance was determined, and the reduction ratio of the deformation resistance corresponding to the increase in CT was determined.

  In order to set the optimum range of PI control gain at the leading end of the metal strip at the time of the first stand rolling of the cold rolling corresponding to the leading end of the metal plate at the time of hot rolling, the preceding material and the following material The point of the preceding material before the rolling direction from the joint of the sheet is set as the plate thickness control simulation start point, the preceding material has a constant deformation resistance in the longitudinal direction of the steel strip, and the following material corresponds to the change in the measured CT chart. The deformation resistance decrease ratio corresponding to the above-described increase in CT was obtained, and the deformation resistance was changed in the longitudinal direction of the steel strip.

  FIG. 6 to FIG. 9 show the plate thickness control simulation results according to the embodiment of the present invention. In addition, the scale of the vertical axis | shaft which shows the rolling stand delivery side plate | board thickness of FIGS. 6-9 is the same value in each figure.

  FIG. 6 is a diagram showing a plate thickness control simulation result of the pattern A shown in FIG. 5A, that is, “(a) when the moving average change of CT is small but the variance is large”.

The upper left figure in FIG. 6 shows the state of CT fluctuation in the longitudinal direction of the steel strip shown in FIG. The lower left figure in FIG. 6 uses the control gain (proportional gain K _p : 0.8, integral gain K _I : 0.5) obtained by the Ziegler-Nichols limit sensitivity method, which is obtained based on the conventional constant deformation resistance. The fluctuation of the plate thickness in the longitudinal direction of the steel strip is shown. From the figure on the lower left, it can be seen that the deviation of the sheet thickness tolerance of the succeeding material is caused by the variation of the coiling temperature (CT) in the hot rolling process.

Incidentally, the upper limit of the upper limit value and the integral gain K _I of the proportional gain K _p of CT after hot rolling is immediately before deviates from target thickness tolerances in PI control when considered to be constant, the proportional gain K is multiplied by a predetermined ratio 1.2 the maximum value of _p, the minimum value is 0.01, and the maximum value of the integral gain _{K I} 1.0, the minimum value was 0.01.

Center on Fig. (1) is a PI gain _{[K p 1.2, K I 0.01} ] in FIG. 6, the top right of FIG. (2) in FIG. 6 is PI gain _[K p 1.2, K _I 1.0], (3) in the lower center of FIG. 6 shows the PI gain [K _p 0.01, K _I 0.01], and (4) in the lower right of FIG. 6 shows the PI gain. Are set to [K _p 0.01, K _I 1.0], respectively, and the results of simulating the variation of the plate thickness in the longitudinal direction of the steel strip on the first stand exit side are shown.

When comparing (1) to (4) in FIG. 6 and the lower left diagram in FIG. 6 showing the variation of the plate thickness with the conventional control gain, the case of K _p 1.2 (upper center in FIG. 6). In (1) and the upper right diagram (2) in FIG. 6, the plate thickness fluctuates greatly. On the other hand, when K _p 0.01 is set (lower center diagram (3) in FIG. 6 and lower right diagram (4) in FIG. 6). ) Shows less variation in plate thickness. That is, the change of the moving average of the CT is small in case the variance is large (pattern A), it is possible to reduce the thickness variation by suppressing the P gain K _p.

Therefore, when it changes the moving average of the CT is small is large dispersion, to reduce the P gain K _p and the minimum value (0.01), by changing the I gain K _I between the minimum value from the maximum value perform gauge control simulation, it is understood that it is preferable to set the optimum I gain K _I from a thickness of convergence.

  FIG. 7 is a diagram showing a plate thickness control simulation result of the pattern B shown in FIG. 5B, that is, “(b) When the moving average change of CT is large but the variance is small”.

  As in FIG. 6, the upper left diagram in FIG. 7 shows the state of CT variation in the longitudinal direction of the steel strip (FIG. 5B), and the lower left diagram in FIG. 7 shows the variation of the plate thickness in the longitudinal direction of the steel strip in the case of using the control gain by the Ziegler-Nichols limit sensitivity method obtained in step (1) to (4) in FIG. The variation of the plate thickness in the longitudinal direction of the steel strip when the combination of the maximum value and the minimum value of the PI gain is the same as (4 cases) is shown.

When comparing (1) to (4) in FIG. 7 with the lower left diagram in FIG. 7 showing the variation of the plate thickness with the conventional control gain, when K _{I is} 0.01 (upper center in FIG. 7). in Figure (1) and the center of the figure (3) in FIG. 7), the overshoot (notably thickness than the target thickness variation (increase or decrease) to) faster convergence to small becomes within the tolerance, K _I on the opposite In the case of 1.0 (upper right diagram (2) in FIG. 7 and lower right diagram (4) in FIG. 7), the overshoot is greatly out of tolerance. That is, the change of the moving average of the CT is large when it dispersion is small, it is possible to suppress the overshoot by suppressing I gain K _I.

Therefore, when the change of the moving average of CT is large but the variance is small, the I gain K _I is reduced to the minimum value (0.01), and the P gain K _p is changed between the maximum value and the minimum value. It can be seen that an optimal P gain _Kp should be set from the plate thickness control simulation by performing plate thickness control simulation.

  FIG. 8 is a diagram showing a plate thickness control simulation result of the pattern C shown in FIG. 5C, that is, “(c) when the moving average change and dispersion of CT are both small and stable”.

  Similar to FIG. 6, the upper left figure in FIG. 8 shows the state of CT fluctuation in the longitudinal direction of the steel strip (FIG. 5 (c)), and the lower left figure in FIG. 8 shows the variation of the plate thickness in the longitudinal direction of the steel strip when the control gain is determined by the Ziegler-Nichols limit sensitivity method obtained in step (1) to (4) in FIG. The variation of the plate thickness in the longitudinal direction of the steel strip when the combination of the maximum value and the minimum value of the PI gain is the same as (4 cases) is shown.

  Comparing (1) to (4) in FIG. 8 with the lower left diagram in FIG. 8 showing the variation of the plate thickness with the conventional control gain, in (1) to (4) and the lower left diagram in FIG. There are no major differences. Therefore, when the CT fluctuation is small and stable, the PI gain can be changed to the optimum value within the range from the maximum value to the minimum value of the P gain and the I gain.

  FIG. 9 is a diagram showing a plate thickness control simulation result in the pattern D shown in FIG. 5D, that is, “(d) when the moving average change and dispersion of CT greatly vary”.

  Similar to FIG. 6, the upper left diagram in FIG. 9 shows the state of CT variation (FIG. 5 (d)) in the longitudinal direction of the steel strip, and the lower left diagram in FIG. 9 shows the conventional constant deformation resistance. FIG. 9 (1) to (4) shows the variation of the sheet thickness in the longitudinal direction of the steel strip when the control gain is obtained by the Ziegler-Nichols limit sensitivity method obtained in the original. The variation of the plate thickness in the longitudinal direction of the steel strip when the combination of the maximum value and the minimum value of the PI gain is the same as (4) is shown.

When comparing (1) to (4) in FIG. 9 with the lower left diagram in FIG. 9 showing the variation of the plate thickness with the conventional control gain, when K _{I is} 0.01 (on the center in FIG. 9). In the figure (1) and the figure (3) in the lower center of FIG. 9, the variation of the plate thickness is slightly reduced. In addition, when K _{I is} 1.0 (the upper right diagram (2) in FIG. 9 and the lower right diagram (4) in FIG. 9), the slope of the change in the CT moving average can be suppressed.

Further, when K _{p is} 1.2 (FIG. 9 (1) in the upper center of FIG. 9 and (2) in the upper right of FIG. 9), when K _{p is} 0.01 (FIG. 3) and the lower right figure (4) in FIG. 9 are not clearly different from the conventional case (lower left figure in FIG. 9).

Therefore, if even distributed large slope of change in CT moving average large performs plate thickness control simulating I gain K _I as minimum or maximum value, change the inclination or the thickness of the plate thickness moving average change It can be seen that there is no choice but to set the better one of the convergence properties.

  Note that the present invention is not limited to the front end of the cold rolled metal strip corresponding to the front end of the metal plate during hot rolling, and the CT is measured over the entire length of the hot rolled metal plate. You may use for selection of the optimal setting value of PI gain set over the whole metal strip of rolling. The rolling stand to which the present invention is applied is preferably the first cold rolling stand, but is not particular to this, and may be applied to rolling stands subsequent to the second stand, enabling accurate plate thickness control. It is.

DESCRIPTION OF SYMBOLS 1 Rolling stand 2a, 2b Work roll 3a, 3b Backup roll 4 Reduction device 5 Sheet thickness meter 6 Sheet thickness control part 7 Metal strip

Claims (3)

In cold rolling after hot rolling, or cold rolling after hot rolling and pickling, a plate in cold rolling in which a metal strip at the time of cold rolling is set to a predetermined target thickness by monitor AGC A thickness control method,
A first step of calculating an upper limit value of each gain of P control and I control in PI control immediately before the control system does not diverge and deviates from the target plate thickness tolerance, with the coiling temperature of the metal plate after hot rolling kept constant; ,
A second step of classifying fluctuations in the winding temperature into a plurality of specific patterns according to the change and variance of the moving average calculated from the winding temperature;
A third step of setting a maximum value and a minimum value of each gain of P control and I control for each specific pattern based on the calculated gain upper limit value;
A fourth step of measuring the winding temperature of the metal plate after hot rolling in the longitudinal direction;
A fifth step of calculating the moving average change and variance of the measured coiling temperature;
Based on the calculated moving average change and variance, a sixth step of determining whether the measured variation in the longitudinal direction of the winding temperature corresponds to the specific pattern, and applying to the specific pattern;
For the corresponding specific pattern, within the range of the maximum value and the minimum value of the P control and I control obtained in the third step, each gain is changed to execute a plate thickness control simulation, and the optimal range of the PI control gain A seventh step of setting
A sheet thickness control method in cold rolling characterized by comprising:   The cold range according to claim 1, wherein an optimum range of PI control gain is set at the leading end of the metal strip during cold rolling corresponding to the leading end of the metal plate during hot rolling. Thickness control method in rolling.   3. The sheet thickness control method in cold rolling according to claim 1 or 2, wherein an optimum range of PI control gain is set for the first stand of cold rolling.

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