JPH02165807A - Method for controlling sheet thickness in rolling mill for steel strip - Google Patents

Abstract

PURPOSE:To perform sheet thickness control with quick response and stability by performing the Smith method of control in the time when a sheet thickness deviation exceeds preset range of a high or a low limit values and performing proportional-plus-integral control in the time when the deviation is within the range between the two limits. CONSTITUTION:For a sheet thickness deviation h, a high and a low limit values are previously set. A controller is constituded so that quick sheet thickness correction is performed by the Smith compensation method of control when a measured sheet thickness deviation h exceeds the range of the high and low limit values and when the deviation is within the range of the two limit values, proportional-plus-integral control is performed to do stable sheet thickness control. Hence, sheet thickness control having quick response and stability is performance in rolling a steel strip 10 by use of a rolling mill.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a method for controlling the thickness of a steel strip in a rolling mill.
More specifically, when rolling a strip using a rolling mill, the thickness of the steel strip is measured by operating a rolling device based on a thickness deviation signal sent from a thickness gauge that measures the thickness of the steel strip. This invention relates to a plate thickness control method using feedback control.

[Conventional technology]

Conventionally, thickness control in a steel strip rolling mill has been carried out by a method as shown in FIG. That is, in FIG.
The thickness of the steel strip 10 is measured by a plate thickness gauge 12 installed on the outlet side of the steel strip 10, and the proportional/integral control circuit 14 measures the thickness of the steel strip 10 based on the plate thickness deviation signal Δh sent from the plate thickness gauge 12. A command signal ΔS that performs integral control and is sent out from the control circuit 14
The rolling down device 16 was operated to change the positions of the rolling rolls 18a and 18b, and ultimately the thickness of the steel strip 10 was controlled by feedback. However, in the conventional example shown in FIG. 7, there is a certain distance from just below the rolling roll 18c (that is, the neutral point of the part where the rolling rolls 18b, 18c press the steel strip 10) to the plate thickness gauge 12. The 11% F transfer time during that time was wasted time. Also, because of this wasted time,
It takes a certain amount of time from the start of the proportional/integral control until the steel strip 10 reaches the target thickness, and during this time the thickness of the steel strip 10 being rolled becomes off-gauge (out of thickness). There was a problem. Moreover, the above-mentioned bad influence of the dead time on the response of the control system was particularly noticeable when the steel strip 10 was rolled at low speed. On the other hand, in order to avoid the above-mentioned influence of dead time on the control system and improve the responsiveness of the control system, control using the Smith compensation method as shown in FIG. 8 has also been attempted. That is, the gain of control using the Smith compensation method is C, BI 5RA-AGC
(Automatic thickness control) tuning rate is α, mill constant is M
, the plastic constant of the rolled material (#!J strip 10) is Q, and the steel strip transfer time between the rolling rolls 18b, 18C and the plate thickness gauge 12 is TL.
, the proportional control gain is KP, the integral control gain is Xt,
When the first-order delay time constant of the proportional term is T, the rolling load detected by the load cell 20 is P, the rolling load setting value is Po, and the gap setting value between the rolling rolls 18b and 18C is So, the control by the Smith compensation method is The configuration is as shown in FIG. 8, and a certain amount of correction is made in anticipation of the delay from when the plate thickness deviation Δh of the steel strip 10 is detected by the plate thickness gauge 12 until the command signal ΔS controls the rolling down device 16. This enables real-time sheet thickness control. However, the control using the Smith compensation method has the following problems. That is, first, the Mill constant M used in the Smith compensation method can be measured, but the plastic constant Q of the rolled material cannot be measured at the time of rolling, although it varies depending on the material. However, if this estimated value does not necessarily match the actual value of the plastic constant Q, and there is a difference between the two (i.e., an error in the plastic constant Q), the control using the Smith compensation method will be difficult. There is a problem in that this method causes errors and causes a larger error in plate thickness accuracy than in the case of proportional and integral control. Second, the steel strip transfer time TL from directly below the rolling rolls 18b and 18c to the plate thickness gauge 12 in FIG. 8 is calculated using the following formula (1).
However, unless the transfer speed (collection speed) of the steel strip 10 is actually measured, it is impossible to actually measure the advance rate f, and an estimated value must be used. TL=L/V (1+f) - (1) Here, L is the distance between the rolling rolls 18b, 18c and the plate thickness gauge 12,
is the circumferential speed of the rolling roll, and is the advance rate. However, as the rolling speed changes, the friction coefficient between the steel strip 10 and the rolling rolls 18b, 18c changes, and the advance rate changes accordingly. For this reason, there is a problem in that the estimated value of the advance rate f does not necessarily match the actual value, and the difference between the two (that is, the error in the advance rate f) directly causes a control error.

[Problem to be achieved by the invention]

The present invention has been made in view of the gaps in the conventional methods, and its object is to provide a method that can quickly respond and stably control the thickness of a steel strip when rolling a steel strip using a rolling mill. The object of the present invention is to provide a method for controlling plate thickness.

[Means to solve the problem]

In the present invention, when rolling a steel strip using a rolling mill, the thickness of the steel strip is measured by operating a rolling device based on a plate thickness difference signal sent from a plate thickness gauge that measures the thickness of the steel strip. In a plate thickness control method that performs feedback control, when the plate thickness deviation exceeds preset upper and lower limits, control is performed using the Smith compensation method, and the plate thickness deviation is between the upper and lower limits. In some cases, the above problem is solved by performing proportional/integral control.

[Effect]

In the present invention, the upper and lower limits of the plate thickness deviation are set in advance when rolling a steel strip, and when the plate thickness deviation becomes a value larger than the upper limit value or smaller than the lower limit value, the Smith compensation method is applied. control is carried out to quickly correct the plate thickness to within the above upper and lower limit values, and when the plate thickness deviation becomes a value within the above upper and lower limit values, proportional/integral H'lIJ is performed to adjust the plate thickness. This provides stable control. In other words, in the thickness control method for steel strip rolling mills, we focused on the fact that control using the Smith compensation method has a faster response than proportional/integral control. If the thickness deviation exceeds the upper or lower limits set in advance, control is performed using the Smith compensation method, and if the plate thickness deviation is within the upper or lower limits, proportional/integral control is performed to ensure a fast and stable response. The plate thickness is controlled accordingly.

【Example】

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a configuration explanatory diagram for explaining the present invention in detail. In this figure, a sensor including a plate thickness gauge 12 as a sensor, for example, a DDC (Direct Digital Conn.
A proportional/integral control circuit 14 and a Smith compensation method control circuit 20 are provided in parallel in a thickness control device (the external shape of the device is not shown) such as a thickness control device such as trol, and the thickness is sent from the thickness meter 12. A determination circuit 22 is provided which receives the thickness deviation signal Δh and determines the thickness deviation. The output of the determination circuit 22 causes the switch circuits 24a, 2
4b is turned on, the output ΔS of the proportional/integral control circuit 14 or the Smith compensation method i9J control circuit 20
is sent to the reduction device 16. FIGS. 2 and 3 are logic circuit diagrams showing the logic of the determination circuit 22 and explanatory diagrams of its operation. In this figure, if the value of the plate thickness deviation Δh sent out from the plate thickness meter 12 of FIG. 1 is between the preset upper limit value Δhu1 and lower limit value ΔhL1, One side of the AND circuit 100 (upper part of the figure) due to thick and thin clothing Δh
The logic signal input to becomes a high level, and the output of the AND circuit 106 (to be described later) is ANDed with the inverted signal, and then the circuit 108 for proportional/integral control is operated.
(More specifically, the signal is sent to the switch circuit 24a in FIG. 1) to perform proportional/integral control. Here, the reason for performing the logical product with the negation of the output of the logical product circuit 106 to perform control using the Smith compensation method is that the plate thickness deviation Δh is the upper limit value Δhul, as shown in FIG. Lower limit value ΔhL
Even if the value is between 1, if control based on the Smith compensation method is being executed, hysteresis is given priority to this to prevent control switching from being performed too frequently. On the other hand, if the value of the plate thickness deviation Δh is larger than the upper limit value ΔhU1 or smaller than the lower limit value ΔhL1, the plate thickness deviation Δh causes the OR circuit 102 to One of the logic signals input to the logic circuit becomes high level, the output of the logic sum circuit 102 is input to the logic sum circuit 104, and the output of the logic product circuit 106 (described later) is logically connected to the inverted signal. S is calculated. This determines whether the plate thickness deviation Δh is greater than the upper limit value ΔhU1 or not.
If it is smaller than the value ΔhL1, switching to control using the Smith compensation method is performed regardless of whether proportional/integral control is being executed. Furthermore, the value of the plate thickness deviation Δh is the upper limit value hu2 and the lower limit value hL2.
If the value is between, the theoretical signal that is inverted and input to one side of the AND circuit 106 (lower part of the figure) becomes low level due to the plate thickness deviation Δh, and the difference between the output of the AND circuit 104 and the output of the OR circuit 104 becomes low. The logical AND operation is performed. The output of the AND circuit 106 is input to the OR circuit 104, and is also inverted and input to the AND circuit 100, and a circuit 110 for controlling according to the Smith compensation method (more specifically, the switch shown in FIG. The signal is sent to circuit 24b) to perform control using the Smith compensation method. That is, the determination circuit 22 shown in FIG. 1, which was explained in detail using FIG. Δ
When the value becomes larger than hu1 or smaller than the lower limit value ΔhLi, the Smith compensation method control circuit 110 is switched to perform Smith compensation method control. Further, when the thickness deviation Δh of the steel strip 10 falls between the upper limit value Δhu2 and the lower limit value ΔhL2 by such Smith compensation method control, the proportional/integral control circuit 108 is switched again to perform proportional/integral control. In the embodiment described above, when a step-like disturbance is applied to the plate thickness deviation Δh sent from the plate thickness gauge 12 in FIG. 1, the step response of the proportional/integral control by the proportional/integral control circuit 14 is, for example, The response is as shown in FIG. 4, and the step response of the Smith compensation method control by the Smith compensation method control circuit 20 is as shown in FIG. 5, for example. As is clear from a comparison between FIG. 4 and FIG. 5, control based on the Smith compensation method has a faster response than proportional/integral control. Therefore,
As in this embodiment, the plate thickness deviation Δh of the steel strip 10 is the upper limit value Δ
When the value becomes larger than hu2 (Δhu1) (or when the value becomes smaller than the lower limit value ΔhL2 (ΔhL1)), if you switch from proportional/integral control to Smith compensation method control, the case of proportional/integral control alone It can be seen that the responsiveness is improved, and as shown in FIG. 6, the responsiveness of the control is quick and stable throughout.

【Effect of the invention】

According to the present invention as explained in detail above, the upper and lower limits are set in advance for the plate thickness deviation, and when the actually measured plate thickness layer difference is outside the range of the upper and lower limits, the Smith compensation method is used. *
The rolling mill is configured to perform 1flJ to quickly correct the plate thickness, and when the plate thickness difference falls within the upper and lower limit values, proportional/integral control is performed to achieve stable plate thickness control. When rolling a steel strip using this method, the thickness can be controlled stably and with a quick response. By the way, when the present invention was applied to the first stand of a fully continuous cold tandem rolling mill, it became possible to change the on-gauge quickly after changing the running plate thickness, and it was possible to achieve an off-gauge reduction of approximately Δ5i/coil. . Furthermore, when the present invention is applied to the first stand of a batch-type cold tandem rolling mill, it is possible to achieve a reduction in off-gauge of about Δ1311/coil by preventing the occurrence of off-gauge in the low-speed rolling section at the front and rear ends of the coil. Ta.

[Brief explanation of the drawing]

Fig. 1 is a configuration explanatory diagram for explaining the actual/male side of the present invention, and Fig. 2 is a logic circuit showing the logic of a judgment circuit that judges a plate thickness error signal sent from a plate thickness gauge. Figure 3 is
4 is a diagram showing an example of a step response of conventional proportional/integral control; FIG. 5 is a line diagram showing an example of a step response of control using the Smith compensation method; Fig. 6 is a diagram showing an example of step response of plate thickness control according to an embodiment of the present invention, Fig. 7 is a configuration explanatory diagram for explaining a conventional example of plate thickness control, and Fig. 8 is Smith compensation. FIG. 2 is a configuration explanatory diagram for explaining control based on the law. Fig. 7 10... Steel strip, 12... Plate thickness gauge, 14.
. . . Proportional/integral control circuit, 16 .

Claims (1)

[Claims] (1) When rolling a steel strip using a rolling mill, the thickness of the steel strip is fed back by operating a rolling device based on a thickness deviation signal sent from a thickness gauge that measures the thickness of the steel strip. In the plate thickness control method, when the plate thickness deviation exceeds preset upper and lower limit values, control is performed using the Smith compensation method, and when the plate thickness deviation is between the upper and lower limit values, control is performed. A method for controlling plate thickness in a steel strip rolling mill, which is characterized by carrying out proportional/integral control.