TWI886681B - Method for controlling steel strip thickness - Google Patents

Abstract

A method for controlling steel strip thickness which is suitable for a hot rolling system is provided. The hot rolling system includes N rolling mill stands sequentially arranged on the conveying line to roll and extend a steel strip traveling on the conveying line. The method includes: obtaining the final outlet thickness of the steel strip by a thickness measuring machine arranged on the outlet end of the conveying line after being rolled and extended by the final stand; obtaining the speed at which the steel strip passes through each stand to obtain the required time for the steel strip to travel from the xth stand to the thickness measuring machine; correcting the thickness to be rolled by each stand based on a difference between the target thickness and the final outlet thickness of the steel strip.

Description

Steel Strip Thickness Control Method

The present invention relates to a steel strip thickness control method, and in particular to a steel strip thickness control method applicable to a hot rolling system.

In the hot rolling process, the thickness of the steel strip is an important indicator for evaluating the quality of the steel strip product. During the hot rolling process, the steel strip usually passes through multiple rolling mills for rolling. Each rolling mill has pre-set parameters to roll the steel strip to the set thickness, and the outlet thickness obtained after passing through the last rolling mill can meet the thickness specified by the product specifications. However, due to multiple factors such as the ambient temperature and material of each steel strip during the production process, the rolling mill with set parameters cannot roll the steel strip to the preset thickness, resulting in the thickness of the final product not meeting the product specifications, and additional repair work must be performed.

To avoid this situation, the traditional thickness control strategy for rolled steel strips is to use the Monitor Automatic Gauge Control (M-AGC) technology to perform feedback control based on the error between the outlet thickness of the rolled steel strip at the last rolling mill and the target thickness, so as to synchronously adjust the roll gap of all rolling mills on the entire conveyor line, thereby adjusting the outlet thickness of each rolling mill to meet the set thickness. However, due to the control delay characteristics, if the feedback control responds too quickly, it is easy to over-correct, causing the outlet thickness error to oscillate back and forth. That is, if the steel strip is too thick, the opening of all rolling mills is controlled to decrease, but if the opening is too small and the steel strip is too thin, the opening of all rolling mills needs to be increased, causing oscillation back and forth. If the response is too slow, when the error occurs, it takes too long to adjust the opening of the previous rolling mill to reach the expected time, that is, the convergence speed is too slow, causing the excess steel strip to be cut off because the thickness does not meet the specifications, resulting in excessive losses.

In order to improve the feedback delay of the known automatic thickness control method, which causes the inability to respond in time to adjust the thickness of the rolling mill, one of the purposes of the present invention is to provide a steel strip thickness control method to improve the situation of vibration or slow convergence.

To achieve the above-mentioned object, one aspect of the present invention is to provide a steel strip thickness control method applicable to a hot rolling system, wherein the hot rolling system comprises a first rolling mill, a second rolling mill, ..., an (N-1)th rolling mill and an Nth rolling mill arranged in sequence on a conveyor line to roll the steel strip traveling on the conveyor line, wherein the Nth rolling mill is the last rolling mill on the conveyor line, and the steel strip thickness control method comprises: (a) The final exit thickness of the steel strip after rolling at the Nth rolling mill is obtained by a thickness gauge installed at the exit end of the conveyor line; (b) The speed of the steel strip passing through each rolling mill is obtained to obtain the time required for the steel strip to go from the xth rolling mill to the thickness gauge; (c) According to the error value Dev between the target thickness of the steel strip and the final exit thickness, the thickness to be rolled at each rolling mill is corrected using equations (1) and (2), where

其中M_x’為第x軋延機的軋延厚度的修正量、M_x為第x軋延機利用M-AGC控制所得到的軋延厚度的修正量、△T_x為第x軋延機到測厚機所需的時間、k_p為M-AGC 控制的比例控制增益、k_i為M-AGC控制的積分控制增益、α_x為第x軋延機的同步率、k_x為第x軋延機的調機係數、s則是拉普拉斯轉換符號，1

x

N。

Where _Mx ' is the correction value of the rolling thickness of the x-th rolling mill, _Mx is the correction value of the rolling thickness obtained by the x-th rolling mill using M-AGC control, △ _Tx is the time required for the x-th rolling mill to reach the thickness gauge, _kp is the proportional control gain of M-AGC control, k _i is the integral control gain of M-AGC control, _αx is the synchronization rate of the x-th rolling mill, _kx is the adjustment coefficient of the x-th rolling mill, s is the Laplace transform symbol, 1

x

N.

According to some embodiments of the present invention, when the absolute value of the error value Dev is greater than or equal to the upper limit value UV, α _x =1.

According to some embodiments of the present invention, when the absolute value of the error value Dev is less than or equal to the lower limit value LV, α _x =0.

According to some embodiments of the present invention, when the absolute value of the error value Dev is less than the upper limit value UV and greater than the lower limit value LV, _αx is obtained by formula (3).

According to some embodiments of the present invention, before step (a), the steel strip thickness control method further includes: (d) setting the upper limit value UV and the lower limit value LV of the xth rolling mill according to the target thickness of the steel strip.

According to some embodiments of the present invention, after step (b) and before step (c), the steel strip thickness control method further comprises: (e) setting the synchronization rate α _x of the xth rolling mill according to the error value Dev, the upper limit value UV and the lower limit value LV of the xth rolling mill.

According to some embodiments of the present invention, N=7, when x=4, the upper limit value UV is 0.08 mm, and the lower limit value LV is 0.02 mm.

According to some embodiments of the present invention, N=7, when x=5, the upper limit value UV is 0.06 mm, and the lower limit value LV is 0.02 mm.

According to some embodiments of the present invention, N=7, when x=6, the upper limit value UV is 0.05 mm, and the lower limit value LV is 0.02 mm.

According to some embodiments of the present invention, k _x =1.

In summary, the steel strip thickness control method of the present invention is used to control the synchronization rate and thickness correction of the rolling mill. In addition to increasing the convergence speed of the feedback control when the error value is large, it can also avoid vibration.

100:Hot rolling system

110:Conveyor line

110A: Input terminal

110B: Output terminal

130: Rolling machine

130_1: The first rolling mill

130_2: The second rolling mill

130_3: The third rolling mill

130_4: The fourth rolling mill

130_5: The fifth rolling mill

130_6: The sixth rolling mill

130_7: The seventh rolling mill

150:Thickness gauge

170:Steel belt

200: Steel strip thickness control method

S210, S230, S250, S270, S290: Steps

D1: First direction

L1, L2, L3, L4, L5, L6: curves

T1, T2, T3: time

Figure 1 is a schematic diagram of a hot rolling system according to an embodiment of the present invention.

Figure 2 is a schematic diagram of the process of a steel strip thickness control method according to an embodiment of the present invention.

Figure 3 is a graph showing thickness correction using M-AGC and a steel strip thickness control method according to an embodiment of the present invention.

Figure 4 is a graph showing thickness correction using a steel strip thickness control method according to an embodiment of the present invention.

Figure 5 is a graph showing thickness correction using M-AGC and a steel strip thickness control method according to another embodiment of the present invention.

In order to make the above and other purposes, features and advantages of the present invention more clearly understood, the following will specifically cite the preferred embodiments of the present invention and provide a detailed description with reference to the attached drawings.

Please refer to FIG. 1, which is a schematic diagram of a hot rolling system 100 according to an embodiment of the present invention. The hot rolling system 100 may include a conveyor line 110, N rolling mills 130, and a thickness gauge 150. The conveyor line 110 may have an input end 110A and an output end 110B, and is configured to convey a steel strip 170 from the input end 110A to the output end 110B along a first direction D1. The N rolling mills 130 are disposed between the input end 110A and the output end 110B of the conveyor line 110, and are configured to roll the steel strip 170 traveling on the conveyor line 110. The thickness gauge 150 is disposed near the output end 110B of the conveyor line 110 and is configured to measure the thickness of the steel strip 170 passing through the output end 110B, which thickness may also be referred to as the final outlet thickness. In one embodiment, the thickness gauge 150 may be an X-ray thickness gauge.

In one embodiment, after obtaining the final outlet thickness of the steel strip 170, it will be compared with the target thickness of the steel strip 170 (i.e., the thickness required by the product specification) and the error value will be obtained. When the error value exceeds the tolerance range, that is, the error value exceeds the allowable error range of the thickness required by the product specification, the opening of the rolling mill 130 must be adjusted to adjust the thickness of the steel strip passing through the rolling mill 130 so that the final outlet thickness after rolling through the last rolling mill 130 (i.e., the rolling mill 130 closest to the output end 110B) can meet the thickness required by the product specification.

其中，M_x為第x軋延機利用M-AGC控制所得到的軋延厚度的修正量、Dev為鋼帶的最後出口厚度與目標厚度的誤差值、△T_x為第x軋延機到測厚機150所需的時間、s則是拉普拉斯轉換符號，1

x

N、k_p與k_i分別為PI控制器的比例控制增益以及積分控制增益，也就是M-AGC控制的比例控制增益以及積分控制增益。 As mentioned above, the conventional practice is to use the Monitor Automatic Gauge Control (M-AGC) technology to perform feedback control using a PI controller to synchronously control the opening of all N rolling mills 130 on the conveyor line 110. The formula currently used by M-AGC is shown in the following formula (1):

Wherein, _Mx is the correction value of the rolling thickness obtained by the M-AGC control of the x-th rolling mill, Dev is the error value between the final outlet thickness of the steel strip and the target thickness, △ _Tx is the time required from the x-th rolling mill to the thickness gauge 150, s is the Laplace transform symbol, 1

x

N, _kp and _ki are the proportional control gain and integral control gain of the PI controller, that is, the proportional control gain and integral control gain of the M-AGC control.

However, the above approach still has some defects. For example, the feedback control of M-AGC synchronously adjusts the opening of all N rolling mills 130 on the conveyor line 110, which can easily cause vibration. That is, if the steel strip is too thick, the opening of the rolling mill is controlled to decrease, but if the opening is too small and the steel strip is too thin, it is necessary to control the opening of all rolling mills to increase, and this situation occurs repeatedly. When the error value is too large, it will cause the opening of the front rolling mill to reach the expected time too slowly, that is, the convergence speed is too slow, causing the excess steel strip to be cut off because the thickness does not meet the specifications, resulting in excessive losses.

In order to improve the defects of the conventional M-AGC control, the present invention proposes a steel strip thickness control method based on this, which is a feedback control method of the improved M-AGC control. Please refer to FIG. 2, which is a schematic flow chart of a steel strip thickness control method 200 according to an embodiment of the present invention. The steel strip thickness control method 200 can be applied to the hot rolling system 100 shown in FIG. 1. For the sake of convenience, the number of rolling mills in the hot rolling system 100 is N=7, that is, between the input end 110A and the output end 110B of the conveyor line 110, the first rolling mill 130_1, the second rolling mill 130_2, the third rolling mill 130_3, the fourth rolling mill 130_4, the fifth rolling mill 130_5, the sixth rolling mill 130_6 and the seventh rolling mill 130_7 are arranged in sequence.

First, in step S210, the upper limit value UV and the lower limit value LV of the xth rolling mill are set according to the target thickness of the steel strip 170. These two threshold values will be used for the subsequent synchronization rate and thickness correction, but they can be initially set according to the expected thickness of the steel strip 170. In some embodiments, the lower limit value LV of the fourth rolling mill 130_4 can be set to 0.08 mm, and its upper limit value UV can be set to 0.02 mm. The lower limit value LV of the fifth rolling mill 130_5 can be set to 0.06 mm, and its upper limit value UV can be set to 0.02 mm. The lower limit value LV of the sixth rolling mill 130_6 can be set to 0.05 mm, and its upper limit value UV can be set to 0.02 mm.

Next, in step S230, the thickness gauge 150 is used to obtain the final exit thickness of the steel strip 170 after it passes through the seventh rolling mill 130_7 (i.e., the rolling mill closest to the output end 110B).

Next, in step S250, the speed of the steel strip 170 passing through each rolling mill is obtained to obtain the time required for the steel strip to pass from the xth rolling mill to the thickness gauge 150. For example, the time can be estimated by multiplying the linear speed of the rolling mill roller by the slip coefficient estimated by the L-2 model, that is, steel strip speed = linear speed of the rolling mill roller _× (1 + slip coefficient). The L-2 model is one of the fine rolling setting models in an automation system, which can be used to set the initial settings of the rolling mill, such as thickness reduction, roller opening, speed, etc.

Next, in step S270, the synchronization rate α _x of the xth rolling mill is set according to the error value Dev between the target thickness of the steel strip 170 and the final exit thickness, the upper limit value UV and the lower limit value LV of the xth rolling mill. In the present invention, each rolling mill (for example, the fourth rolling mill 130_4 to the sixth rolling mill 130_6) is not the same, thereby avoiding the occurrence of vibration. In one embodiment, the opening of the rolling mills arranged along the first direction D1 increases in sequence. That is, from the input end 110A to the output end 110B, the opening of the rolling mill 130 is designed to be: the first rolling mill 130_1 < the second rolling mill 130_2 < the third rolling mill 130_3 < the fourth rolling mill 130_4 < the fifth rolling mill 130_5 < the sixth rolling mill 130_6 < the seventh rolling mill 130_7. Therefore, it can be seen that the influence on the thickness of the steel strip is: the first rolling mill 130_1 < the second rolling mill 130_2 < the third rolling mill 130_3 < the fourth rolling mill 130_4 < the fifth rolling mill 130_5 < the sixth rolling mill 130_6 < the seventh rolling mill 130_7. In some embodiments, the openings of the first rolling mill 130_1, the second rolling mill 130_2 and the third rolling mill 130_3 (i.e., the three rolling mills closest to the input end 110A) are not set too large, so there is no need to calibrate or correct their rolling thicknesses, but the focus is on the fourth rolling mill 130_4, the fifth rolling mill 130_5 and the sixth rolling mill 130_6.

其中，M_x’為該第x軋延機的軋延厚度的修正量、M_x為第x軋延機利用M-AGC控制所得到的軋延厚度的修正量、△T_x為第x軋延機到該測厚機所需的時間、α_x為第x軋延機的同步率、k_x為第x軋延機的調機係數、s則是拉普拉斯轉換符號，1

x

N。第x軋延機的調機係數k_x可根據鋼種的特性或是品質進行調整，進而影響同步率α_x的影響程度，k_x的範圍介於0.8~1.2之間，一般初始值是設定為1。 Next, in step S290, the thickness correction amount to be rolled by the xth rolling mill is corrected using equations (1) and (2) according to the error value Dev between the target thickness of the steel strip 170 and the final exit thickness. Equation (1) is as described above, and equation (2) can be expressed as follows:

Among them, M _x 'is the correction amount of the rolling thickness of the x-th rolling mill, M _x is the correction amount of the rolling thickness obtained by the x-th rolling mill using M-AGC control, △T _x is the time required for the x-th rolling mill to reach the thickness gauge, α _x is the synchronization rate of the x-th rolling mill, k _x is the adjustment coefficient of the x-th rolling mill, s is the Laplace transform symbol, 1

x

N. The adjustment coefficient _kx of the xth rolling mill can be adjusted according to the characteristics or quality of the steel type, thereby affecting the degree of influence of the synchronization rate _αx . The range of _kx is between 0.8 and 1.2, and the initial value is generally set to 1.

In some embodiments, when the absolute value of the error value Dev is greater than or equal to the upper limit value UV, the synchronization rate α _x of the xth rolling mill is 1. Specifically, when the absolute value of the error value Dev is greater than or equal to the upper limit value UV, it means that the error value of the steel strip 170 is large, so the rolling mill must be adjusted quickly to avoid the situation of too slow convergence, so the synchronization rate will be equal to 1.

In some embodiments, when the absolute value of the error value Dev is less than or equal to the lower limit value LV, the synchronization rate α _x of the xth rolling mill is 0. Specifically, when the absolute value of the error value Dev is less than or equal to the lower limit value LV, it means that the error value of the steel strip 170 is very small, so it is not necessary to adjust each rolling mill, so the synchronization rate will be equal to 0 to avoid vibration.

According to some embodiments of the present invention, when the absolute value of the error value Dev is less than the upper limit value UV and greater than the lower limit value LV, α _x can be obtained using formula (3).

具體來說，在誤差值Dev的絕對值介於上限值UV和下限值LV之間的情況下，則根據誤差值Dev的絕對值的大小正比例調整便提高。換句話說，也是按照誤差值Dev越大便提高同步率的原則下進行調整，以加快收斂的速度且盡量避免震盪的情況發生。

Specifically, when the absolute value of the error value Dev is between the upper limit value UV and the lower limit value LV, the error value Dev is adjusted in proportion to the absolute value of the error value Dev. In other words, the error value Dev is adjusted to increase the synchronization rate, so as to speed up the convergence and avoid vibration as much as possible.

Please refer to FIG. 3, which is a graph of thickness correction using M-AGC and the steel strip thickness control method 200 according to an embodiment of the present invention. FIG. 3 (a) shows a curve of the error value between the final exit thickness of the steel strip 170 and the target thickness. FIG. 3 (b) to (e) show the thickness correction curves of the seventh rolling mill 130_7, the sixth rolling mill 130_6, the fifth rolling mill 130_5 and the fourth rolling mill 130_4 using M- AGC and the steel strip thickness control method 200, wherein the dotted line represents the curve obtained by the steel strip thickness control method 200, and the solid line represents the curve obtained by M-AGC.

As can be seen from FIG. 3, at time T1, the absolute value of the error value is greater than the tolerance range allowed by the product, and the openings of the seventh rolling mill 130_7, the sixth rolling mill 130_6, the fifth rolling mill 130_5 and the fourth rolling mill 130_4 are adjusted to adjust the thickness of the steel strip. At this time, due to the large error value, it is obvious in FIG. 3 (b) to (e) that the synchronization rate of the curve obtained by the steel strip thickness control method 200 is higher than the synchronization rate of the curve obtained by M-AGC, so the convergence speed can be increased to quickly correct the rolled thickness to the expected thickness. In the later stage, when the error value is smaller, the synchronization rate gradually decreases, and the opening increase or decrease time of the seventh rolling mill 130_7, the sixth rolling mill 130_6, the fifth rolling mill 130_5 and the fourth rolling mill 130_4 begins to be different.

Please refer to FIG. 4 , which is a graph showing thickness correction using a steel strip thickness control method 200 according to an embodiment of the present invention, wherein curves L1, L2, L3 and L4 represent thickness correction curves of the fourth rolling mill 130_4, the fifth rolling mill 130_5, the sixth rolling mill 130_6 and the seventh rolling mill 130_7, respectively. It can be clearly seen from Figure 4 that initially, at time T2, the openings of the fourth rolling mill 130_4, the fifth rolling mill 130_5, the sixth rolling mill 130_6 and the seventh rolling mill 130_7 are increased almost synchronously, and at time T3, when the error value becomes smaller due to correction, the phase of the openings of the fourth rolling mill 130_4, the fifth rolling mill 130_5, the sixth rolling mill 130_6 and the seventh rolling mill 130_7 is delayed (i.e., the time of increasing or decreasing the openings is delayed).

Please refer to FIG. 5, which is a curve diagram of thickness correction using M-AGC and steel strip thickness control method 200 according to another embodiment of the present invention, wherein curve L5 represents the curve of thickness correction using M-AGC, and curve L6 represents the curve of thickness correction using steel strip thickness control method 200. It can be clearly seen from FIG. 5 that when the error value is large at the beginning, the convergence speed of curves L5 and L6 is very fast, and when the error value enters the range proposed by the present invention, the correction rate of curve L6 becomes slower, reducing the occurrence of vibration, thereby reducing the loss of cutting thickness that does not meet the specifications.

In summary, by controlling the synchronization rate and thickness correction amount of the rolling mill 130 through the steel strip thickness control method 200 of the present invention, not only can the convergence speed of the feedback control be increased when the error value is large, but also vibration can be avoided.

Although the present invention has been disclosed with preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of the patent application attached hereto.

200: Steel strip thickness control method

S210, S230, S250, S270, S290: Steps

Claims (10)

A method for controlling the thickness of a steel strip is applicable to a hot rolling system. The hot rolling system comprises a first rolling mill to an Nth rolling mill arranged in sequence on a conveyor line to roll a steel strip traveling on the conveyor line, wherein the Nth rolling mill is the last rolling mill on the conveyor line, and N is a positive integer greater than 1. The method for controlling the thickness of the steel strip comprises: (a) obtaining a final exit thickness of the steel strip after being rolled by the Nth rolling mill through a thickness gauge arranged at an exit end of the conveyor line; (b) obtaining the speed of the steel strip passing through each rolling mill to obtain the time required for the steel strip to travel from an xth rolling mill to the thickness gauge; (c) According to an error value Dev between a target thickness of the steel strip and the final outlet thickness, the thickness correction amount of each rolling mill to be rolled is corrected using equations (1) and (2), where …(1) …(2) Where M _x ' is the correction value of the rolled thickness of the x-th rolling mill, M _x is the correction value of the rolled thickness of the x-th rolling mill obtained by M-AGC control, △T _x is the time required for the x-th rolling mill to reach the thickness gauge, k _p is the proportional control gain of M-AGC control, k _i is the integral control gain of M-AGC control, α _x is the synchronization rate of the x-th rolling mill, k _x is the machine adjustment coefficient of the x-th rolling mill, and s is the Laplace transform symbol, 1 ≤ x ≤ N. A steel strip thickness control method as described in claim 1, wherein when the absolute value of the error value Dev is greater than or equal to an upper limit value UV, α _x = 1. A steel strip thickness control method as described in claim 2, wherein when the absolute value of the error value Dev is less than or equal to a lower limit value LV, α _x = 0. The steel strip thickness control method as described in claim 3, wherein when the absolute value of the error value Dev is less than the upper limit value UV and greater than the lower limit value LV, α _x is obtained by formula (3): …(3). The steel strip thickness control method as described in claim 4, wherein before step (a), the method further comprises: (d) setting the upper limit value UV and the lower limit value LV of the xth rolling mill according to the target thickness of the steel strip. The steel strip thickness control method as described in claim 5, wherein after step (b) and before step (c), the method further comprises: (e) setting the synchronization rate α _x of the xth rolling mill according to the error value Dev, the upper limit value UV and the lower limit value LV of the xth rolling mill. A steel strip thickness control method as described in claim 4, wherein N = 7, when x = 4, the upper limit value UV is 0.08 mm, and the lower limit value LV is 0.02 mm. A steel strip thickness control method as described in claim 4, wherein N = 7, when x = 5, the upper limit value UV is 0.06 mm, and the lower limit value LV is 0.02 mm. A steel strip thickness control method as described in claim 4, wherein N = 7, when x = 6, the upper limit value UV is 0.05 mm, and the lower limit value LV is 0.02 mm. A steel strip thickness control method as described in claim 1, wherein k _x = 1.