A hot-rolled strip crown feedback control method based on double-target convexity

Abstract

The application provides a hot-rolled strip steel convexity feedback control method based on double-target convexity, which comprises the following control steps: S1, calculating the deviation AC of the actual convexity value of the strip steel and the target convexity value; S2, based on the obtained deviation of the actual convexity value of the strip steel and the target convexity value, distributing the calculation result to F1-F4 racks; S3, based on the proportional convexity consistency principle, converting the convexity deviation distributed to the F1-F4 racks into F1-F4 outlet convexity correction values; S4, on the basis of the F1-F4 outlet convexity correction values, converting the convexity deviation into the correction amount of the F1-F4 rack bending roller force; and S5, applying the correction amount of the F1-F4 bending roller force to the first four racks.

Description

Technical Field

[0001] This invention belongs to the field of hot-rolled strip steel production technology, and particularly relates to a feedback control method for the crown of hot-rolled strip steel based on dual-target crown. Background Technology

[0002] The quality of hot-rolled strip steel is heavily influenced by its shape characteristics, with key shape indicators including crown and straightness. Crown, also known as transverse thickness difference, refers to the thickness difference along the width of the strip. Given the varying performance requirements of hot-rolled strip steel across different applications, the standards for crown control also differ. To meet the diverse needs of users, hot continuous rolling mills, while ensuring the straightness of the strip at the finishing mill exit, need to control the crown within a target range. In the actual production process of hot-rolled strip steel, the predetermined target crown is achieved primarily through pre-setting and dynamic feedback control of the strip shape.

[0003] The strip shape is pre-set based on product specifications, customer requirements, and quality standards, with an ideal crown target value pre-defined. Taking into account key process parameters such as roll profile, rolling force, and bending force, the initial setpoints required to achieve the target crown are calculated based on a precise mathematical model and extensive production experience. Hot strip forming control is complex and variable, involving multivariable, time-varying, strongly coupled, and nonlinear characteristics. In actual rolling processes, due to the interdependent influence of rolling force, bending force, roll wear, and thermal crown, existing mathematical models, mostly based on simplifications and assumptions, are insufficient to meet high-precision requirements. Some hot rolling lines have introduced adaptive control mechanisms to optimize subsequent strip division of the same category; however, adaptive control lacks the ability to immediately correct current strip deviations, potentially leading to overall crown deviations.

[0004] Dynamic feedback control mainly includes rolling force compensation and crown feedback. Rolling force compensation locks the initial rolling force and adjusts the bending roll force of each stand in real time to correct the deviation between the actual rolling force and the set value, ensuring a constant exit crown. Crown feedback, on the other hand, compares the measured value of the crown detection instrument at the last stand with the target value, converting the deviation into a bending roll force adjustment. Crown feedback generally only adjusts the bending roll force of the front stand. Due to the large strip width-to-thickness ratio at the rear stand, to maintain proportional crown rolling and avoid waviness defects, the bending roll force at the rear stand is generally not corrected.

[0005] Chinese patent document with application number 202110715193.9 provides a method for controlling the edge waviness of hot-rolled thin-gauge SPA-H steel for containers. This invention uses a two-level control model to calculate the crown value and compare it with the PDI crown target value to dynamically adjust the APC control target and optimize the rolling model to improve the edge waviness of thin-gauge SPA-H steel.

[0006] Chinese patent document with application number 201410030077.3 provides a "Feedback Control Method for Crown of Hot-Rolled Strip Steel Based on Moving Average Filtering". This invention relates to a feedback control method for crown of hot-rolled strip steel based on moving average filtering. By analyzing the deviation between the actual crown and the target crown after moving average filtering, the trend change of crown is extracted, which solves the problem that traditional crown control methods are prone to misadjustment or overadjustment and have low overall crown control accuracy.

[0007] Chinese patent document with application number 201310011313.2 provides a "Method for Controlling the Crown of Hot-Rolled Strip". This invention relates to a method for controlling the crown of hot-rolled strip. By distributing the crown deviation of the strip output from the finishing mill within the current control cycle to the first six finishing mill stands, and adjusting the bending roll force based on this, the crown of the hot-rolled strip can be dynamically controlled in real time.

[0008] Chinese patent document with application number 201410297832.4 provides "An Online Closed-Loop Control Method for Hot-Rolled Strip Crown". This invention relates to an online closed-loop control method for hot-rolled strip crown. By using the deviation between the feedback value of strip crown and the set value detected in real time by the crown meter at the finishing mill exit, and relying on an algorithm for converting crown into bending roll force, the adjustment value of the bending roll force required for each stand is calculated, and the bending roll force of each stand of the finishing mill is adjusted in real time to achieve closed-loop control of strip crown.

[0009] Chinese patent document with application number 201410030077.3 provides a "Coverage Control Method for Single-Stand Double-Coil Aluminum Hot Rolling Mill". This patent is a crownage control method for aluminum hot rolling mills, which differs from the crownage control method for steel hot rolling mills. In the third to last pass or the last pass for crownage measurement, closed-loop control of the bending roll force is performed based on the alloy characteristics to ensure the crownage and plate shape along the entire length.

[0010] The above methods mainly aim to improve the accuracy of convexity control through feedback control by reducing the difference between the measured convexity and the target set convexity measured by the measuring instrument. Summary of the Invention

[0011] The technical problem to be solved by this invention is to address the issue of inconsistent crown at the head and tail of strip steel during the rolling process. This invention provides a crown feedback control method for hot-rolled strip steel based on dual-target crown to ensure that the strip steel maintains a relatively stable crown distribution at different rolling stages, thereby improving the overall quality of the product and the crown accuracy of the entire strip steel length.

[0012] The technical problem it aims to solve can be addressed through the following technical solutions.

[0013] A feedback control method for the crown of hot-rolled strip steel based on dual-target crown, characterized by the following control steps:

[0014] S1. Calculate the deviation ΔC between the actual crown value and the target crown value of the strip;

[0015] S2. Based on the deviation between the actual convexity value and the target convexity value of the strip, the calculation results are allocated to frames F1-F4 according to the following formula:

[0016] ΔCm i =cpe i ·ΔC

[0017] In the formula, cpe i ΔCm is the convexity allocation coefficient assigned to the i-th rack. i The convexity deviation is assigned to the i-th rack, where i = 1 to 4, corresponding to racks F1 to F4;

[0018] S3. Based on the principle of consistent proportional convexity, the convexity deviation allocated to F1-F4 racks is converted into the F1-F4 outlet convexity correction value.

[0019] S4. Based on the F1-F4 outlet crown correction value, convert the crown deviation into the correction amount of the F1-F4 frame bending roll force;

[0020] S5. Apply the correction amount of the bending roller force of F1-F4 to the first four frames.

[0021] Furthermore, in step S1,

[0022] Based on the type of incoming strip steel and the strip steel production process, it was determined that the problem of inconsistent head and tail crown of the strip steel is prone to occur during the rolling process.

[0023] When determining that a strip steel product has consistent head and tail convexity, the formula is ΔC = C. j -C T Calculate the deviation ΔC between the actual convexity value and the target convexity value; where C j For the crown measurement instrument to measure the crown value in the j-th cycle, j depends on the strip speed at the finishing mill exit, the strip length, and the sampling cycle of the finishing mill and the crown measurement instrument; C T The target convexity issued by the L3 level area control unit;

[0024] When a strip grade is identified as prone to inconsistent head and tail crown during the rolling process, a secondary correction is made to the target crown. In this case, ΔC = C j -C T +C correct Calculate the deviation ΔC between the actual convexity value and the target convexity value; where C correctThe secondary correction value for the target convexity is a constant related to the strip steel type, strip steel specifications, and production process.

[0025] Further, in step S3, the convexity deviations allocated to frames F1-F4 are converted into F1-F4 outlet convexity correction values ​​using the following formula:

[0026]

[0027] In the formula,

[0028] ΔCout i : The exit convexity correction value of the i-th frame, where i = 1 to 4, corresponding to frames F1 to F4;

[0029] Gcm i : Gain coefficient of the exit convexity correction value of the i-th rack, a constant related to the rack, where i = 1 to 4, corresponding to racks F1 to F4;

[0030] h i : The thickness of the strip at the exit of the i-th frame, where i = 1 to 4, corresponding to frames F1 to F4;

[0031] h7: Thickness of the strip at the exit of the 7th frame.

[0032] Furthermore, in step S4, the convexity deviation is converted into a correction amount for the bending roll force of the F1-F4 frame using the following formula.

[0033]

[0034] In the formula:

[0035] Δbf i : The total correction amount of the bending roller force of the i-th frame, where i = 1 to 4, corresponding to frames F1 to F4;

[0036] ΔCout i : The exit convexity correction value of the i-th frame, where i = 1 to 4, corresponding to frames F1 to F4;

[0037] Ebc i The influence coefficient of the bending roll force on the crown of the i-th frame is related to factors such as the frame, processing technology, and type of strip steel product. It is calculated by the L2 process control model, where i = 1 to 4, corresponding to frames F1 to F4.

[0038] Furthermore, in step S5, the proportional control gain and integral control gain of the strip that are prone to inconsistent head and tail crown during the rolling process are corrected. The specific algorithm is as follows:

[0039] ΔBF_P (i,j) =Δbf i ·GP i·E GP

[0040] ΔBF_I (i,j) =Δbf i ·GI i ·E GI ·T c +ΔBF_I (i,j-1)

[0041] ΔBF (i,j) =ΔBF_P (i,j) +ΔBF_I (i,j)

[0042] In the formula:

[0043] ΔBF_P (i,j) : The proportional correction part of the bending roll force correction amount for the i-th stand in the j-th cycle, where i = 1 to 4, corresponding to stands F1 to F4, and j depends on the strip speed at the finishing mill exit, strip length, and sampling cycle of the finishing mill and crown detection instruments;

[0044] Δbf i : The total correction amount of the bending roller force of the i-th frame, where i = 1 to 4, corresponding to frames F1 to F4;

[0045] GP i : The proportional control gain of the i-th rack;

[0046] E GP : Proportional control gain correction factor;

[0047] ΔBF_I (i,j) The integral correction part of the bending roll force correction for the i-th frame in the j-th cycle;

[0048] GI i : Integral control gain of the i-th rack;

[0049] E GI Integral control gain correction factor;

[0050] T c : Control cycle for convexity control;

[0051] ΔBF_I (i,j-1) The integral correction part of the bending roll force correction for the i-th frame in the j-1th cycle;

[0052] ΔBF (i,j) The total correction amount of the bending roll force for the i-th frame in the j-th cycle;

[0053] At this point, the set value of the bending roller force after convexity feedback correction is: BF (i,j)＝ BF0+ΔBF (i,j) Among them, BF(i,j) : The set value of the bending roll force after correction for the i-th frame in the j-th cycle; BF0: The initial set value of the bending roll force calculated by the plate shape preset model.

[0054] Furthermore, considering the equipment control limits, the correction amount of the bending roller force of each frame in each control cycle and the set value of the corrected bending roller force need to be limited.

[0055] Furthermore, when the correction amount or the set value of the correction roller force of a certain frame is greater than the corresponding upper limit of amplitude, the correction amount or the set value of the correction roller force is equal to the corresponding upper limit of assignment; when the correction amount or the set value of the correction roller force of a certain frame is less than the corresponding lower limit of amplitude, the correction amount or the set value of the correction roller force is equal to the corresponding lower limit of assignment.

[0056] Compared with the prior art, the main difference of the present invention is that, for strip steel that is prone to inconsistent crown at the head and tail during the rolling process, a dual-target crown feedback control method is adopted to ensure that the strip steel can maintain a stable crown distribution at different rolling stages, thereby improving the overall quality of the product and improving the crown accuracy of the entire strip steel. Attached Figure Description

[0057] Figure 1 This is a schematic diagram of the feedback control principle for crown of hot continuous rolling mill.

[0058] Figure 2 This is a flowchart of the hot continuous rolling mill crown feedback process.

[0059] Figure 3 This is a graph showing the change of strip bending roll force over time in an embodiment of the present invention;

[0060] Figure 4 This is a graph showing the variation of the measured strip crown over time in an embodiment of the present invention. Detailed Implementation

[0061] This invention relates to a control method for improving the overall crown accuracy of hot-rolled strip. It aims to address the issue of inconsistent crown at the beginning and end of the strip during certain rolling processes by employing a dual-target crown feedback control method. This method eliminates overshoot and instability in the crown control of the later section of the strip caused by special rolling processes in some strip varieties, thereby improving the overall crown accuracy of the strip. Specifically, for strip varieties prone to inconsistent crown at the beginning and end during certain rolling processes, in the first four stands of a seven-stand hot-rolled finishing mill, the bending roll force of stands F1-F4 is dynamically adjusted based on the deviation between the actual crown measured by the instrument at the exit position of the last stand and the secondary set target crown, thus eliminating crown deviation. Its main feature is that for strip steel varieties that are prone to inconsistent convexity at the head and tail of the strip during the rolling process, the strip steel after special rolling process is re-corrected according to the strip steel exit mark, and the convexity feedback control is optimized; at the same time, the relevant parameters of the feedback controller are set a second time to avoid convexity fluctuations caused by changes in the target convexity and overshoot and instability of the convexity feedback control.

[0062] like Figure 1 As shown, based on the rolling plan issued by the L3-level area control machine, and addressing the issue of inconsistent strip head and tail crown during some strip rolling processes, a special rolling process is implemented. After the strip is threaded and the strip head reaches the crown detection instrument via the last stand exit, the crown detection instrument measures the actual crown value and transmits it to the crown feedback controller. The crown feedback controller, based on the strip production process and strip type, determines whether to adopt dual-target crown feedback control. For a specified steel type and process, the crown feedback controller, based on the difference between the secondary set target crown and the actual crown, calculates the required bending roll force correction value to eliminate the crown difference through a series of related control models in the L2-level process control machine. This correction value is then added to the current bending roll force calculation value and allocated to the first four stands (F1 to F4) for execution of the new setting. This eliminates the deviation between the set target crown and the actual crown, thereby improving crown control accuracy and reducing the product quality defect blocking rate.

[0063] The hot-rolled strip crown feedback control method based on dual-target crown has a certain delay in feedback control due to the distance between the feedback control area and the crown detection instrument. This type of dual-target crown feedback control technology mainly adjusts the overall crown change trend of the hot-rolled strip to reduce the overall crown deviation. Crown feedback control is mainly for the strip in the first four stands, and generally does not adjust the bending roll force of the rear stands (such as F5 to F7 stands of a seven-stand continuous rolling mill) to adjust the crown, to prevent the thinner strip at the exit of the rear stands from developing other waviness defects due to changes in bending roll force.

[0064] like Figure 2 As shown, the specific steps are as follows:

[0065] (1) Calculate the deviation between the actual crown value and the target crown value of the strip. Dual-target crown feedback for hot-rolled strip is only applicable to strip varieties prone to inconsistent crown at the head and tail during the rolling process. First, it is necessary to determine the type of incoming strip and the strip production process. For strip varieties with consistent crown at both the head and tail:

[0066] ΔC=C j -C T

[0067] In the formula:

[0068] ΔC: The deviation between the actual convexity value and the target convexity value;

[0069] C j The crown measurement instrument measures the crown value in the j-th cycle, where j depends on the strip speed at the finishing mill exit, the strip length, and the sampling cycle of the finishing mill and the crown measurement instrument.

[0070] C T Target convexity issued by the L3 level area control unit;

[0071] (2) For strip grades that are prone to inconsistent convexity at the head and tail of the strip during the rolling process, after the strip is threaded and the head of the strip reaches the convexity detection instrument through the last stand exit, the target convexity is corrected a second time:

[0072] ΔC=C j -C T +C correct

[0073] In the formula:

[0074] C correct The target convexity is corrected for a second time; this is a constant related to the strip steel type, strip steel specifications, and production process.

[0075] (3) Based on the deviation between the actual crown value and the target crown value of the strip, the calculation results are allocated to frames F1-F4:

[0076] ΔCm i =cpe i ·ΔC

[0077] In the formula:

[0078] ΔCm i : The convexity deviation assigned to the i-th frame, where i = 1 to 4, corresponding to frames F1 to F4;

[0079] cpe i : Assign the convexity allocation coefficient to the i-th rack;

[0080] (4) Based on the principle of consistent proportional convexity, the convexity deviations allocated to F1-F4 racks are converted into F1-F4 outlet convexity correction values:

[0081]

[0082] In the formula:

[0083] ΔCout i : The exit convexity correction value of the i-th frame, where i = 1 to 4, corresponding to frames F1 to F4;

[0084] Gcm i : Gain coefficient of the exit convexity correction value of the i-th rack, a constant related to the rack, where i = 1 to 4, corresponding to racks F1 to F4;

[0085] h i : The thickness of the strip at the exit of the i-th frame, where i = 1 to 4, corresponding to frames F1 to F4;

[0086] h7: Thickness of the strip steel at the exit of the 7th frame;

[0087] (5) Based on the F1-F4 outlet crown correction value, the crown deviation is converted into the correction amount of the F1-F4 frame bending roll force.

[0088]

[0089] In the formula:

[0090] Δbf i : The total correction amount of the bending roller force of the i-th frame, where i = 1 to 4, corresponding to frames F1 to F4;

[0091] Ebc i The influence coefficient of the bending roll force on the crown of the i-th frame is related to factors such as frame, processing technology, and strip product type. It is calculated by the L2 process control model, where i = 1 to 4, corresponding to frames F1 to F4.

[0092] (6) Apply the correction amount of the bending roll force F1-F4 to the first four stands. To prevent system instability caused by sudden changes in bending roll force, which could affect the control of hot-rolled strip crown, a PI controller is used to reduce system fluctuations and improve the strip shape control accuracy. The proportional control gain and integral control gain in the PI controller are used to correct strips that are prone to inconsistent crown at the head and tail during rolling. The specific algorithm is as follows:

[0093] ΔBF_P (i,j) =Δbf i ·GP i ·E GP

[0094] ΔBF_I(i,j) =Δbf i ·GI i ·E GI ·T c +ΔBF_I (i,j-1)

[0095] ΔBF (i,j) =ΔBF_P (i,j) +ΔBF_I (i,j)

[0096] In the formula:

[0097] ΔBF_P (i,j) : The proportional correction part of the bending roll force correction amount for the i-th stand in the j-th cycle, where i = 1 to 4, corresponding to stands F1 to F4, and j depends on the strip speed at the finishing mill exit, strip length, and sampling cycle of the finishing mill and crown detection instruments;

[0098] ΔBF_I (i,j) The integral correction part of the bending roll force correction for the i-th frame in the j-th cycle;

[0099] ΔBF_I (i,j-1) The integral correction part of the bending roll force correction for the i-th frame in the j-1th cycle;

[0100] ΔBF (i,j) The total correction amount of the bending roll force for the i-th frame in the j-th cycle;

[0101] Δbf i : Total correction amount for the bending roll force of the i-th frame;

[0102] GP i : The proportional control gain of the i-th rack;

[0103] GI i : Integral control gain of the i-th rack;

[0104] E GP : Proportional control gain correction factor;

[0105] E GI Integral control gain correction factor;

[0106] T c : Control cycle for convexity control;

[0107] At this point, the set value of the bending roller force after crown feedback correction is:

[0108] BF (i,j)＝ BF0+ΔBF (i,j)

[0109] Bf (i,j): The set value of the bending roller force is corrected for the i-th frame in the j-th cycle;

[0110] BF0: Initial setting value of bending roll force calculated by the plate shape preset model;

[0111] (7) Considering the equipment control limits, the correction amount and the set value of the corrected bending roller force for each frame in each control cycle should be limited. When the correction amount or the set value of the corrected bending roller force for a certain frame is greater than the corresponding upper limit, the correction amount or the set value of the corrected bending roller force is equal to the corresponding upper limit. Similarly, when the correction amount or the set value of the corrected bending roller force for a certain frame is less than the corresponding lower limit, the correction amount or the set value of the corrected bending roller force is equal to the corresponding lower limit.

[0112] The following are specific examples.

[0113] Example

[0114] Calculate the deviation between the actual and target crown values ​​of the strip. In a certain special rolling process, inconsistency in the crown of the strip's head and tail is prone to occur. The initial target crown of the strip is 30 μm. After the strip is threaded and the head reaches the crown detection instrument via the last stand exit, the measured crown of the strip at a certain moment is 31 μm. What is the deviation between the actual and target crown values ​​at this point?

[0115] ΔC=C1-C T =1μm

[0116] A second correction is made to the target convexity. The deviation between the actual convexity value and the target convexity value at this point is:

[0117] ΔC 修正 =ΔC+C correct =9μm

[0118] Based on the deviation between the actual crown value and the target crown value of the strip, the calculation results are distributed to frames F1-F4.

[0119] ΔCm1=cpe1·ΔC=2.5μm

[0120] ΔCm2=cpe2·ΔC=2.25μm

[0121] ΔCm3=cpe3·ΔC=2μm

[0122] ΔCm4=cpe4·ΔC=1.75μm

[0123] Based on the principle of consistent proportional convexity, the convexity deviation allocated to F1-F4 racks is converted into the F1-F4 outlet convexity correction value.

[0124]

[0125] By utilizing the influence coefficient of bending roller force on crown, the crown deviation is converted into the correction amount of bending roller force for frames F1-F4, and it is determined whether the correction amount of bending roller force exceeds the limit value of bending roller force correction.

[0126]

[0127] Based on this, the set value of the bending roller force is calculated, and it is determined whether the set value of the bending roller force exceeds the limit value of the bending roller force setting. A PI controller is used to reduce system fluctuations, and the set values ​​of the bending roller force F1-F4 are applied to the first four frames.

[0128] ΔBF (1,1) =677kN

[0129] ΔBF (2,1) =796kN

[0130] ΔBF (3,1) =1037kN

[0131] ΔBF (4,1) =1064kN

[0132] Once this cycle calculation is complete, the next cycle calculation begins, continuing until the rolling process is finished.

[0133] The final implementation result is as follows Figure 3 The graph shows the change of strip bending roll force over time, and... Figure 4 The graph shows the variation of the measured crown value over time. The crown at the head of the strip is too small; the dynamic control program reduces the downward adjustment bending roll force, increasing the crown at the tail of the strip. This application example demonstrates that the dual-target crown feedback control method for hot-rolled strip can effectively address the issue of inconsistent crown at the head and tail of the strip during rolling. It ensures a stable crown distribution across different rolling stages, thereby improving overall product quality and the crown accuracy along the entire strip length.

[0134] Crown is a crucial quality indicator for hot strip rolling mills. This invention provides a dual-objective crown feedback control method to ensure a stable exit crown distribution for the strip at different rolling stages. Compared to traditional crown feedback techniques, this invention offers smoother control and higher precision, making it widely applicable in the hot strip rolling industry.

Claims

1. A method for feedback control of crown of hot-rolled strip steel based on dual-target crown, characterized in that, The following control steps are included: S1. Calculate the deviation ΔC between the actual crown value and the target crown value of the strip; S2. Based on the deviation between the actual convexity value and the target convexity value of the strip, the calculation results are allocated to frames F1-F4 according to the following formula: ΔCm i =cpe i ·ΔC In the formula, cpe i ΔCm is the convexity allocation coefficient assigned to the i-th rack. i The convexity deviation is assigned to the i-th rack, where i = 1 to 4, corresponding to racks F1 to F4; S3. Based on the principle of consistent proportional convexity, the convexity deviation allocated to F1-F4 racks is converted into the F1-F4 outlet convexity correction value. S4. Based on the F1-F4 outlet crown correction value, convert the crown deviation into the correction amount of the F1-F4 frame bending roll force; S5. Apply the correction amount of the bending roller force of F1-F4 to the first four frames.

2. The hot-rolled strip crown feedback control method based on dual-target crown as described in claim 1, characterized in that, In step S1, Based on the type of incoming strip steel and the strip steel production process, it was determined that the problem of inconsistent head and tail crown of the strip steel is prone to occur during the rolling process. When determining that a strip steel product has consistent head and tail convexity, the formula is ΔC = C. j -C T Calculate the deviation ΔC between the actual convexity value and the target convexity value; where C j For the crown measurement instrument to measure the crown value in the j-th cycle, j depends on the strip speed at the finishing mill exit, the strip length, and the sampling cycle of the finishing mill and the crown measurement instrument; C T The target convexity issued by the L3 level area control unit; When a strip grade is identified as prone to inconsistent head and tail crown during the rolling process, a secondary correction is made to the target crown. In this case, ΔC = C j -C T +C correct Calculate the deviation ΔC between the actual convexity value and the target convexity value; where C correct The secondary correction value for the target convexity is a constant related to the strip steel type, strip steel specifications, and production process.

3. The hot-rolled strip crown feedback control method based on dual-target crown as described in claim 1, characterized in that, In step S3, the convexity deviations allocated to frames F1-F4 are converted into F1-F4 outlet convexity correction values ​​using the following formula: In the formula, ΔCout i : The exit convexity correction value of the i-th frame, where i = 1 to 4, corresponding to frames F1 to F4; Gcm i : Gain coefficient of the exit convexity correction value of the i-th rack, a constant related to the rack, where i = 1 to 4, corresponding to racks F1 to F4; h i : The thickness of the strip at the exit of the i-th frame, where i = 1 to 4, corresponding to frames F1 to F4; h7: Thickness of the strip at the exit of the 7th frame.

4. The hot-rolled strip crown feedback control method based on dual-target crown as described in claim 1, characterized in that, In step S4, the convexity deviation is converted into a correction amount for the bending roll force of the F1-F4 frame using the following formula. In the formula: Δbf i : The total correction amount of the bending roller force of the i-th frame, where i = 1 to 4, corresponding to frames F1 to F4; ΔCout i : The exit convexity correction value of the i-th frame, where i = 1 to 4, corresponding to frames F1 to F4; Ebc i The influence coefficient of the bending roll force on the crown of the i-th frame is related to factors such as the frame, processing technology, and type of strip steel product. It is calculated by the L2 process control model, where i = 1 to 4, corresponding to frames F1 to F4.

5. The hot-rolled strip crown feedback control method based on dual-target crown as described in claim 1, characterized in that, In step S5, the proportional control gain and integral control gain of the strip that are prone to inconsistent head and tail crown during the rolling process are corrected. The specific algorithm is as follows: ΔBF_P (i,j) =Δbf i ·GP i ·E GP ΔBF_I (i,j) =Δbf i ·GI i ·E GI ·T c +ΔBF_I (i,j-1) ΔBF (i,j) =ΔBF_P (i,j) +ΔBF_I (i,j) In the formula: ΔBF_P (i,j) : The proportional correction part of the bending roll force correction amount for the i-th stand in the j-th cycle, where i = 1 to 4, corresponding to stands F1 to F4, and j depends on the strip speed at the finishing mill exit, strip length, and sampling cycle of the finishing mill and crown detection instruments; Δbf i : The total correction amount of the bending roller force of the i-th frame, where i = 1 to 4, corresponding to frames F1 to F4; GP i : The proportional control gain of the i-th rack; E GP : Proportional control gain correction factor; ΔBF_I (i,j) The integral correction part of the bending roll force correction for the i-th frame in the j-th cycle; GI i : Integral control gain of the i-th rack; E GI Integral control gain correction factor; T c : Control cycle for convexity control; ΔBF_I (i,j-1) The integral correction part of the bending roll force correction for the i-th frame in the j-1th cycle; ΔBF (i,j) The total correction amount of the bending roll force for the i-th frame in the j-th cycle; At this point, the set value of the bending roller force after convexity feedback correction is: BF (i,j)＝ BF0+ΔBF (i,j) ; Among them, BF (i,j) : The set value of the bending roll force after correction for the i-th frame in the j-th cycle; BF0: The initial set value of the bending roll force calculated by the plate shape preset model.

6. The hot-rolled strip crown feedback control method based on dual-target crown according to claim 1, characterized in that, Considering the equipment control limits, the correction amount of the bending roller force of each frame in each control cycle and the set value of the corrected bending roller force need to be limited.

7. The hot-rolled strip crown feedback control method based on dual-target crown as described in claim 6, characterized in that, When the correction amount or the set value of the bent roller force of a certain frame is greater than the corresponding upper limit of amplitude, the correction amount or the set value of the bent roller force is equal to the corresponding upper limit of assignment. When the correction amount or the set value of the bent roller force of a certain frame is less than the corresponding lower limit of amplitude, the correction amount or the set value of the bent roller force is equal to the corresponding lower limit of assignment.

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