A method for controlling the roll gap position of the strip threading head in a hot strip mill

Abstract

This invention discloses a method for controlling the roll gap position of the strip threading head in a hot strip mill, comprising the following steps: S1, determining whether there is a steel biting signal on the stand; if so, proceeding to step S2; S2, starting stand deviation calculation; S3, selecting the subsequent stand roll gap control mode based on the calculation result of step S2. This invention improves roll gap fluctuations caused by abnormal sensor position detection after strip threading by combining strip head tracking with the current roll gap position of the target stand and employing locked position control.

Description

Technical Field

[0001] This invention relates to finishing mill reduction thickness control technology in the field of hot rolling finishing mill, and more specifically, to a method for controlling the roll gap position of the strip threading head in a hot continuous rolling mill. Background Technology

[0002] In the hot rolling production process, the thickness detection and closed-loop control of the finishing mill AGC are mainly achieved by the feedback of the AGC position sensor. Due to the impact of the head biting the steel during the strip threading process, once the position of the AGC position sensor fluctuates, it will cause the stand AGC locking position control to malfunction. In severe cases, it will lead to subsequent crushing and scrap steel accidents.

[0003] The hot strip mill AGC system has two control modes: absolute value AGC (ABS-GM-AGC) and thickness-locked AGC (LKON-GM-AGC). Its main control functions include: 1. Calculating the absolute thickness of the strip at the exit of each stand using the thickness gauge formula; 2. Using the absolute thickness at the exit of each stand as feedback to control the roll gap value; 3. The target absolute thickness at the exit of each stand is calculated using the finishing mill setting model; 4. Early AGC start time results in a small deviation between the strip head thickness and the target thickness; 5. High accuracy is required for the finishing mill setting model calculation, otherwise a large thickness gradient will appear on the thickness curve.

[0004] The aforementioned control process places high demands on the detection of the roll gap position of the current frame. Any abnormality in this detection will directly lead to AGC control malfunction, resulting in head crushing and scrap steel accidents, severely impacting the stable production of the line. Previously, during production, abnormal fluctuations in the AGC sensor data caused the frame AGC to lock onto the current roll gap, leading to a scrap steel accident.

[0005] In existing patent applications, such as Chinese Patent Application No. 02132974.5, a method for controlling the roll gap of a strip mill is disclosed. This method mainly involves a computer sequentially calculating the entry temperature of the finishing mill, the temperature values ​​of each stand, the rolling force values ​​of each stand, and the roll gap values ​​of each stand. These calculations are then set to a primary computer, which controls a PLC to adjust the roll gap via the pressing motor and hydraulic device. The mathematical model for the entry temperature is: FET = RDT - αH - βGD - γL + δ. By accurately calculating the entry temperature (i.e., the temperature of the intermediate billet head), the method solves the problem of low head hit rate in the process control model during the production of intermediate billets using a hot-rolling box, increasing it from 72% to 96%. This effectively controls the accuracy of the finishing mill roll gap and the width accuracy of the hot-rolled strip, ultimately improving the thickness accuracy and yield of the finished strip. This patented technology compensates for the roll gap by detecting the strip head temperature, improving the head thickness and width hit rate.

[0006] For example, Chinese Patent Application No. 201710172208.5 discloses a method for controlling the roll gap of a rolling mill, including the following steps: (1) During the rolling process, the detected upper roll plunger pressure value and lower roll plunger pressure value are summed, compared, and averaged; (2) During the rolling process, the detected upper roll stand pressure value and lower roll stand pressure value are summed, compared, and averaged; (3) The values ​​obtained in steps (1) and (2) are summed, compared, and averaged to obtain the rolling force P; (4) The rolling force P is substituted into the bounce equation to calculate the real-time deformation of the stand. This invention obtains a more realistic rolling force by averaging the plunger cavity pressure and stand pressure, which can reduce the error caused by detecting the pressure of the plunger cavity or the pressure of the stand alone, thereby accurately controlling the mill accuracy. This patented technology improves the stability of roll gap control by detecting the fluctuation of the hydraulic system pressure value and through a series of calculations and adjustments.

[0007] Neither of the two patented technologies mentioned above can solve the abnormal fluctuations in the AGC position sensor caused by the impact of the strip head. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the present invention aims to provide a method for controlling the roll gap position of the strip threading head in a hot strip mill. By tracking the strip head and combining it with the current roll gap position of the target stand, a locking position control is adopted to improve the roll gap fluctuation caused by abnormal sensor position detection after strip threading.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A method for controlling the roll gap position of the strip threading head in a hot strip mill includes the following steps:

[0011] S1. Determine if the frame has a steel biting signal. If so, proceed to step S2.

[0012] S2. Begin calculating the frame deviation;

[0013] S3. Select the rear frame roll gap control mode based on the calculation results of step S2.

[0014] Preferably, step S1 further includes:

[0015] The first stand on the hot strip mill is used as the head roll gap fluctuation detection stand. When the rolling force F of the first stand... LC When the temperature reaches ≥400t, it is determined that a steel biting signal has been generated.

[0016] Preferably, the frame deviation calculation in step S2 includes frame single-side deviation calculation, frame two-side deviation calculation, and strip head dynamic oil column position deviation calculation.

[0017] Preferably, the calculation of the single-sided deviation of the frame is as follows:

[0018] Q 工 =x1-x2

[0019] Q 传 =x3-x4

[0020] Among them, Q 工 For the working side deviation of the frame; Q 传 x1 represents the deviation on the frame drive side; x2 represents the feedback data of the AGC hydraulic cylinder inlet position sensor on the frame working side, in mm; x3 represents the feedback data of the AGC hydraulic cylinder outlet position sensor on the frame working side, in mm; x4 represents the feedback data of the AGC hydraulic cylinder outlet position sensor on the frame drive side, in mm.

[0021] And set the deviation limit value A, A≤5mm, when |Q 工 |>A, or |Q 传 If |>A, it indicates that there is an abnormal deviation in the hot continuous rolling mill.

[0022] Preferably, the deviation on both sides of the frame is calculated as follows:

[0023]

[0024] Where Q represents the deviation value between the two sides of the frame; x1 is the feedback data of the AGC hydraulic cylinder inlet position sensor on the working side of the frame, in mm; x2 is the feedback data of the AGC hydraulic cylinder outlet position sensor on the drive side of the frame, in mm; x3 is the feedback data of the AGC hydraulic cylinder inlet position sensor on the drive side of the frame, in mm; and x4 is the feedback data of the AGC hydraulic cylinder outlet position sensor on the drive side of the frame, in mm.

[0025] A deviation limit value B is set, B≤5mm. When |Q|>B, it indicates that there is an abnormal deviation in the hot strip mill.

[0026] Preferably, the calculation of the dynamic oil column position deviation at the strip head is as follows:

[0027]

[0028] Among them, s 2 λ represents the variance of the oil column position change of the two AGC cylinders; λ is the variance coefficient, ranging from 0.6 to 1; n is the number of scans per second; θ is the sampled data of the oil column position in each scan cycle.

[0029] And set a jitter detection threshold α, α = 0.01 mm, when s 2 If the value is greater than α, it indicates that there is abnormal vibration in the hot strip mill.

[0030] Preferably, step S3 further includes:

[0031] When |Q 工 |>A,|Q 传 If |>A or |Q|>B, an alarm will be issued and the AGC hydraulic cylinder roller gap control will be locked;

[0032] When s 2 When ≤α, then conventional AGC hydraulic cylinder roll gap control is executed;

[0033] When s 2 When the value is greater than α, the calculation of the roller gap fluctuation compensation output at the head of the rear frame is performed.

[0034] Preferably, the calculation of the head roll gap fluctuation compensation output of the rear stand includes calculating the target rolling force to press down the roll gap and calculating the given limit value of the oil column of the AGC hydraulic cylinder.

[0035] Preferably, the calculated target rolling force should reduce the roll gap as follows:

[0036] S gap_t =(F fbk -F tar ) / M

[0037] Among them, S gap_tThe roll gap to be reduced by the target rolling force; F fbk For rolling force feedback in hot strip mills; F tar M represents the target rolling force of the hot strip mill; M represents the mill stiffness of the corresponding stand.

[0038] Preferably, the given limit value for the oil column of the AGC hydraulic cylinder is as follows:

[0039] S cyl_i =∑{limit[(S gap_t -S cyl_i-1 ),spd]}

[0040] Among them, S cyl_i The oil column of the AGC hydraulic cylinder is given for the current cycle; S cyl_i-1 The oil column of the AGC hydraulic cylinder in the previous scan is given; S gap_t The roll gap should be reduced by the target rolling force; spd is the given limit value of the oil column in the AGC hydraulic cylinder during one scanning cycle;

[0041] The given limit is obtained based on the difference between the rolling force feedback from the rolling mill and the target rolling force, with the rolling force deviation value C as the boundary:

[0042]

[0043] When the rolling force deviation is greater than C, the AGC hydraulic cylinder slowly supplies oil to reduce fluctuations; when the rolling force deviation reaches C, the hot strip mill has become stable and adjustable, and outputs the final given rolling force to the hot strip mill.

[0044] The method for controlling the roll gap position of the strip threading head in a hot strip mill provided by this invention has the following beneficial effects:

[0045] 1) The F1 head roll gap fluctuation detection is adopted, and the fluctuation deviation of the frame is used as the feedforward prediction control of the rear frame.

[0046] 2) Depending on the situation, lock or limit the width of the rear frame to minimize the thickness deviation of the strip head while avoiding excessive adjustment that could lead to scrap steel. Attached Figure Description

[0047] Figure 1 This is a flowchart illustrating the method for controlling the roll gap position of the strip-threading head in a hot strip mill according to the present invention. Detailed Implementation

[0048] To better understand the above-mentioned technical solutions of the present invention, the technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0049] Combination Figure 1As shown, the present invention provides a method for controlling the head roll gap position of a hot strip mill. Because the mill speed of the F1 stand is slow, the roll gap fluctuation error is small. Therefore, the F1 stand is used as the head roll gap fluctuation detection stand, and the fluctuation deviation detected by the F1 stand is used as the feedforward prediction control of the subsequent stands. In short, the F1 stand is used as the roll gap fluctuation detection stand to achieve dynamic adaptive adjustment of the roll gap in the subsequent stands.

[0050] Define the head length of the hot-rolled coil as L HEAD Due to the impact during strip threading, the AGC hydraulic cylinder adjustment response is delayed, resulting in poor threading stability and fluctuations in the longitudinal and transverse thickness of the strip head, sometimes even exceeding tolerances. This is a common phenomenon observed in finished coils from all hot-rolled mills in the industry. The only difference lies in the extent of the thickness fluctuation at the strip head, determined by the different mill characteristics and equipment control functions. However, when poor head stability occurs, it can easily lead to strip instability throughout the strip. The lack of regularity in head fluctuations causes significant target deviations in the adaptive adjustments of the AGC hydraulic cylinder, inter-stand tension, and threading speed, potentially leading to serious scrap accidents. Therefore, this invention primarily addresses this issue by using strip head tracking combined with the current roll gap position of the target stand, employing locked position control to improve roll gap fluctuations caused by abnormal sensor position detection after strip threading.

[0051] This invention uses head tracking and stand rolling force status to identify the head position. When the tracking system detects that the head is in the stand biting area and the rolling force feedback generates a biting signal, the strip head position is locked and the strip head tracking position is corrected.

[0052] Strip head tracking is used to determine the data before the target mill bites the strip, which is then used as the holding data. A delayed locking function is activated when the target mill completes the bite signal. That is, based on the sensor data read within one scan cycle at the moment of bite, a self-cyclic holding function is performed for two scan cycles to ensure steady-state position control of the strip when the head bites, thereby avoiding incorrect adjustment of the AGC hydraulic cylinder due to data fluctuations.

[0053] The method for controlling the position of the threading head roller gap in this invention specifically includes the following steps:

[0054] S1. Determine if there is a bite signal on stand F1. If so, proceed to step S2. Apply rolling force F to stand F1. LC A value exceeding 400 tons serves as the threshold for judgment and correction. When the stand rolling force F... LC When the load is ≥400t, it is determined to be in a state of steel biting, and step S2, frame deviation calculation, begins.

[0055] S2. Begin calculating the frame deviation, including the single-sided deviation of the frame, the deviation of both sides of the frame, and the dynamic oil column position deviation of the strip head.

[0056] The specific calculation of the frame one-sided deviation is as follows:

[0057] Q 工 =x1-x2

[0058] Q 传 =x1-x2

[0059] Among them, Q 工 For the working side deviation of the frame; Q 传 x1 represents the deviation on the frame drive side; x2 represents the feedback data of the AGC hydraulic cylinder inlet position sensor on the frame working side, in mm; x3 represents the feedback data of the AGC hydraulic cylinder outlet position sensor on the frame working side, in mm; x4 represents the feedback data of the AGC hydraulic cylinder outlet position sensor on the frame drive side, in mm.

[0060] And set the deviation limit value A, based on the maximum allowable deviation of the equipment and the accuracy of the sensor. When |Q 工 |>A, or |Q 传 If |>A, it indicates that there is an abnormal deviation in the hot strip mill, which may be caused by sensor malfunction or impact fluctuations when the strip bites into the steel.

[0061] The specific calculation of the deviation on both sides of the frame is as follows:

[0062]

[0063] Where Q represents the deviation value between the two sides of the frame; x1 is the feedback data of the AGC hydraulic cylinder inlet position sensor on the working side of the frame, in mm; x2 is the feedback data of the AGC hydraulic cylinder outlet position sensor on the working side of the frame, in mm; x3 is the feedback data of the AGC hydraulic cylinder inlet position sensor on the drive side of the frame, in mm; and x4 is the feedback data of the AGC hydraulic cylinder outlet position sensor on the drive side of the frame, in mm.

[0064] A deviation limit value B is set. When |Q|>B, it indicates that there is an abnormal deviation in the hot strip mill, which may be caused by abnormal plate shape or impact fluctuations when the strip bites.

[0065] The specific calculation of the dynamic oil column position deviation at the strip head is as follows:

[0066]

[0067] Among them, s 2λ represents the variance of the oil column position change between the two AGC cylinders; λ is the variance coefficient, ranging from 0.6 to 1. The larger the value, the higher the detection sensitivity, and it should be set according to the actual working conditions and detector accuracy; n is the number of scans per second; θ is the data sampled for each scan cycle of the oil column position.

[0068] And set a vibration judgment threshold α (an empirical value, determined based on mill stability and cylinder performance), when s 2 When the value is greater than α, it indicates that the mean variance of the hydraulic system within n detection cycles has reached the threshold α. It is considered that the position sensor deviation of the oil column has changed too much, and there is abnormal vibration in the hydraulic system. The system then enters the back frame roll gap fluctuation compensation control.

[0069] S3. Based on the calculation results of step S2, select the rear frame roll gap control mode, specifically including:

[0070] When |Q 工 |>A,|Q 传 When |>A or |Q|>B, abnormal deviation may be due to sensor erroneous signals or large material deviation. In this case, adjusting the roll gap may cause strip misalignment or scrapping. Therefore, an alarm is issued and the ABS and MMC control modes of the AGC are interrupted, the operator's leveling command is blocked, and the roll gap control of the AGC hydraulic cylinder is locked, with the sole objective of maintaining the current rolling stability.

[0071] When s 2 When the value is ≤α, it indicates that the impact vibration is small, so conventional AGC hydraulic cylinder roller gap control is performed;

[0072] When s 2 When the value is greater than α, it indicates that the system is shaking significantly. The control of the frame pressing system working mode is locked, the single-sided leveling control signal of the frame pressing is blocked, and the calculation of the roller gap fluctuation compensation output at the head of the rear frame is performed again.

[0073] The calculation of the head roll gap fluctuation compensation output of the rear stand includes calculating the roll gap that the target rolling force should press down and calculating the given limit value of the oil column of the AGC hydraulic cylinder.

[0074] The target rolling force should reduce the roll gap as follows:

[0075] S gap_t =(F fbk -F tar ) / M

[0076] Among them, S gap_t The roll gap to be reduced by the target rolling force; F fbk For rolling force feedback in hot strip mills; F tar M represents the target rolling force of the hot strip mill; M represents the mill stiffness of the corresponding stand.

[0077] When controlling the AGC hydraulic cylinder to press down, the calculated rolling force to be pressed down at the roll gap is not directly used as the oil column input. Instead, it needs to be limited to ensure safety. The calculated oil column input limit value for the AGC hydraulic cylinder is as follows:

[0078] S cyl_i =∑{limit[(S gap_t -S cyl_i-1 ),spd]}

[0079] Among them, S cyl_i The oil column of the AGC hydraulic cylinder is given for the current cycle; S cyl_i-1 The oil column of the AGC hydraulic cylinder in the previous scan is given; S gap_t The roll gap should be reduced by the target rolling force; spd is the given limit value of the oil column in the AGC hydraulic cylinder during one scanning cycle;

[0080] The given limit is obtained based on the difference between the rolling force feedback from the rolling mill and the target rolling force, with the rolling force deviation value C as the boundary:

[0081]

[0082] When the rolling force deviation is greater than C, the AGC hydraulic cylinder slowly supplies oil to reduce fluctuations; when the rolling force deviation reaches C, the hot strip mill has become stable and adjustable, and outputs the final given rolling force to the hot strip mill.

[0083] Example 1

[0084] This embodiment 1 uses the F5 rack of a certain production line as an example:

[0085] Determining the static state of the rack

[0086] When the F5 stand detects a rolling force threshold of 400 tons using the pressure probe, it is determined whether the stand has engaged steel. In other words, if the detected rolling force is greater than or equal to 400 tons, the program determines that F1 has engaged steel. This signal serves as the core basis for judging the stand's status. When the detected rolling force is less than 400 tons, it is judged to be in a static state.

[0087] Calculation of single-sided deviation of frame

[0088] Q 工 =x1-x2

[0089] Q 传 =x3-x4

[0090] x1: Feedback data from the AGC cylinder position sensor on the working side inlet side: 70.97mm

[0091] x2: Feedback data from the AGC cylinder position sensor on the working side outlet side: 66.48mm

[0092] x3: The AGC cylinder position sensor feedback data on the inlet side of the transmission side is 69.78mm.

[0093] x4: The AGC cylinder position sensor feedback data on the output side of the transmission is 67.46mm.

[0094] Frame unilateral deviation

[0095] Q 工 =x1-x2=70.97-66.48=4.49mm

[0096] Q 传 =x3-x4=69.78-67.46=2.32mm

[0097] Combining the deviations on both sides

[0098] Bilateral deviation

[0099] Calculation of dynamic oil column position deviation at the strip head: (λ is taken as 0.9)

[0100]

[0101] Right now

[0102]

[0103] Considering that the PLC's scanning cycle is 50ms, n is tentatively set to 20 in this embodiment 1, which means calculating the variance within 1 second.

[0104] The control principle is as follows:

[0105] When |Q 工 |>A,|Q 传 If |>A or |Q|>B, an alarm will be issued and the AGC hydraulic cylinder roller gap control will be locked;

[0106] When s 2 When ≤α, then conventional AGC hydraulic cylinder roll gap control is executed;

[0107] When s 2 When the value is greater than α, the calculation of the roller gap fluctuation compensation output at the head of the rear frame is performed.

[0108] In this embodiment 1, S 2 When the deviation on both sides is >0.01 (value range) and the deviation is 0≤Q≤5, the calculation of the roller gap fluctuation compensation output at the head of the rear frame will be performed.

[0109] Example 2

[0110] This embodiment 2 uses frame F1 of a certain production line as an example:

[0111] When the F1 stand detects a rolling force of 2500 tons by the pressure measuring head, which is greater than the threshold value of 400 tons, it is determined that the stand is biting steel.

[0112] at this time

[0113] x1: 82.45, unit: mm

[0114] x2: 68.52, unit: mm

[0115] x3: 76.51, unit: mm

[0116] x4: 73.52, unit: mm

[0117] Frame one-sided deviation:

[0118] Q 工 =x1-x2=82.45-68.52=13.93mm

[0119] Q 传 =x3-x4=76.51-73.52=2.99mm

[0120] At this time, the deviation on both sides

[0121] Right now

[0122] Calculation of dynamic oil column position deviation at the strip head: (λ is taken as 0.9)

[0123]

[0124] Right now

[0125]

[0126] When |Q 工 |>A,|Q 传 When |>A or |Q|>B (standard requirement: deviation limits A and B ≤ 5mm), an alarm is issued and the AGC hydraulic cylinder roll gap control is locked; in the example, |Q 工 |=13.93mm>A Therefore, an alarm is triggered and the control of the rack pressing system's working mode is locked. At the same time, the single-sided leveling control signal of the rack pressing system is blocked on site.

[0127] Those skilled in the art should recognize that the above embodiments are merely illustrative of the present invention and are not intended to limit the present invention. Any variations or modifications to the above embodiments that are within the spirit and essence of the present invention will fall within the scope of the claims of the present invention.

Claims

1. A method for controlling the roll gap position of the strip threading head in a hot continuous rolling mill, characterized in that, Includes the following steps: S1. Determine if the frame has a steel biting signal. If so, proceed to step S2. S2. Begin calculating the frame deviation; The frame deviation calculation includes the calculation of single-sided frame deviation, the calculation of two-sided frame deviation, and the calculation of dynamic oil column position deviation at the strip head; The specific calculation of the deviation on both sides of the frame is as follows: Where Q represents the deviation value between the two sides of the frame; x1 is the feedback data of the AGC hydraulic cylinder inlet position sensor on the working side of the frame, in mm; x2 is the feedback data of the AGC hydraulic cylinder outlet position sensor on the working side of the frame, in mm; x3 is the feedback data of the AGC hydraulic cylinder inlet position sensor on the drive side of the frame, in mm; and x4 is the feedback data of the AGC hydraulic cylinder outlet position sensor on the drive side of the frame, in mm. A deviation limit value B is set, B≤5mm. When |Q|>B, it indicates that there is an abnormal deviation in the hot strip mill. The calculation of the dynamic oil column position deviation at the strip head is as follows: Among them, s 2 λ represents the variance of the oil column position change of the two AGC cylinders; λ is the variance coefficient, ranging from 0.6 to 1; n is the number of scans per second; θ is the sampled data of the oil column position in each scan cycle. And set a jitter detection threshold α, α = 0.01 mm, when s 2 If the value is greater than α, it indicates that there is abnormal vibration in the hot strip mill; S3. Select the rear frame roll gap control mode based on the calculation results of step S2; When |Q|>B, an alarm is issued and the AGC hydraulic cylinder gap control is locked; When s 2 When ≤α, then conventional AGC hydraulic cylinder roll gap control is executed; When s 2 When the value is greater than α, the calculation of the roller gap fluctuation compensation output at the head of the rear frame is performed. The calculation of the roll gap fluctuation compensation output of the rear stand head includes calculating the roll gap that the target rolling force should press down and calculating the given limit value of the oil column of the AGC hydraulic cylinder; The calculated target rolling force should reduce the roll gap as follows: S gap_t =(F fbk -F tar ) / M Among them, S gap_t The roll gap to be reduced by the target rolling force; F fbk For rolling force feedback in hot strip mills; F tar M represents the target rolling force of the hot strip mill; M represents the mill stiffness of the corresponding stand.

2. The method for controlling the roll gap position of the strip-threading head in a hot strip mill according to claim 1, characterized in that, Step S1 further includes: The first stand on the hot strip mill is used as the head roll gap fluctuation detection stand. When the rolling force F of the first stand... LC When the value is ≥400t, it is determined that a steel biting signal has been generated.

3. The method for controlling the roll gap position of the strip-threading head in a hot strip mill according to claim 1, characterized in that, The calculation of the single-sided deviation of the frame is as follows: Q 工 =x1-x2 Q 传 =x3-x4 Among them, Q 工 For the working side deviation of the frame; Q 传 x1 represents the deviation on the frame drive side; x2 represents the feedback data of the AGC hydraulic cylinder inlet position sensor on the frame working side, in mm; x3 represents the feedback data of the AGC hydraulic cylinder outlet position sensor on the frame working side, in mm; x4 represents the feedback data of the AGC hydraulic cylinder outlet position sensor on the frame drive side, in mm. And set the deviation limit value A, A≤5mm, when |Q 工 |>A, or |Q 传 If |>A, it indicates that there is an abnormal deviation in the hot continuous rolling mill.

4. The method for controlling the roll gap position of the strip-threading head in a hot strip mill according to claim 3, characterized in that, Step S3 further includes: When |Q 工 |>A or|Q 传 When |>A, an alarm is issued and the AGC hydraulic cylinder roller gap control is locked; When s 2 When ≤α, then conventional AGC hydraulic cylinder roll gap control is executed; When s 2 When the value is greater than α, the calculation of the roller gap fluctuation compensation output at the head of the rear frame is performed.

5. The method for controlling the roll gap position of the strip-threading head in a hot continuous rolling mill according to claim 1 or 4, characterized in that, The given limit value for the oil column of the AGC hydraulic cylinder is calculated as follows: S cyl_i =∑{limit[(S gap_t -S cyl_i-1 ),spd]} Among them, S cyl_i The oil column of the AGC hydraulic cylinder is given for the current cycle; S cyl_i-1 The oil column of the AGC hydraulic cylinder in the previous scan is given; S gap_t The roll gap should be reduced by the target rolling force; spd is the given limit value of the oil column in the AGC hydraulic cylinder during one scanning cycle; The given limit is obtained based on the difference between the rolling force feedback from the rolling mill and the target rolling force, with the rolling force deviation value C as the boundary: When the rolling force deviation is greater than C, the AGC hydraulic cylinder slowly supplies oil to reduce fluctuations; when the rolling force deviation reaches C, the hot strip mill has become stable and adjustable, and outputs the final given rolling force to the hot strip mill.

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