A high-precision fast-response thickness control method for hot continuous rolling equipment

Abstract

This invention relates to a high-precision, fast-response thickness control method for a hot strip rolling mill. The hot strip rolling mill includes N sets of roll mechanisms, a reduction system, a frequency conversion system, and a thickness control system. The thickness value of the strip after being rolled by the roll mechanisms is input to the thickness control system. The high-precision, fast-response thickness control method for the hot strip rolling mill includes the following steps performed by the thickness control system: receiving the thickness deviation through a feedforward predictive control regulator F, and calculating the intermediate value K. G And based on the intermediate quantity K G The thickness feedforward estimated adjustment amount is calculated and output. The thickness deviation is received by the thickness feedback proportional-integral controller M. The calculated thickness feedback proportional-integral adjustment amount is then output. The thickness feedforward estimated adjustment amount and the thickness feedback proportional-integral adjustment amount are superimposed by an overlay device to obtain the roll gap adjustment amount ΔG, which is input into the roll adjustment mechanism of the pressing system. This effectively solves the problem of thickness step fluctuation in strip steel caused by uncontrollable factors.

Description

Technical Field

[0001] This invention relates to a high-precision, fast-response thickness control method for hot continuous rolling mills in the field of metal rolling mill or its processed products control. Background Technology

[0002] Currently, there are two main control schemes for hot-rolled strip thickness control systems. The first is the monitoring-based AGC (Automatic Gain Control), a standard proportional-integral-derivative (PID) control system. This automatic control method adjusts the gain of the amplifier circuit automatically according to the signal strength, adjusting the roll gap in real time based on the strip thickness measured by the thickness gauge. The shorter the distance between the mill and the thickness gauge, the better the monitoring-based AGC control quality. However, due to the lag in the thickness measurement by the thickness gauge, this scheme cannot achieve accurate control of strip thickness. The second is the Smith AGC, based on the predictive compensation control scheme proposed by American professor Smith in 1957. Whether using a proportional or integral controller, as long as the system's amplification factor is appropriately selected, the controller's first step can completely eliminate the error, solving the product quality problem of a pure lag closed-loop system. This was later transformed into a classic control system for strip thickness control. However, due to the pure lag in the trend-based pre-processing system, it cannot quickly respond to and adjust for thickness fluctuations caused by uncontrollable factors. Summary of the Invention

[0003] To address the aforementioned problems, this invention relates to a high-precision, fast-response thickness control method for a hot strip rolling mill. The hot strip rolling mill includes N sets of roll mechanisms, a pressing system, a frequency conversion system, and a thickness control system. The thickness value of the strip after being rolled by the roll mechanisms is input to the thickness control system. The high-precision, fast-response thickness control method for the hot strip rolling mill includes the following steps performed by the thickness control system:

[0004] The feedforward predictive control regulator F receives the thickness deviation and calculates the intermediate amount. And based on the intermediate amount Calculate and output the thickness feedforward prediction adjustment amount. ;

[0005] The thickness deviation is received by the thickness feedback proportional-integral controller M, and the thickness feedback proportional-integral adjustment amount is calculated and output. ;

[0006] Adjust the thickness feedforward prediction amount The proportional-integral adjustment amount of the thickness feedback The roll gap adjustment amount ∆G is obtained by superimposing the values ​​through a superimposed device and then input into the roll adjustment mechanism of the pressing system.

[0007] The second aspect of the present invention relates to a high-precision, fast-response thickness control system for hot continuous rolling mills, comprising at least one processor; and a memory storing instructions which are executed by the at least one processor.

[0008] The beneficial effect of the present invention is that the high-precision and fast-response hot strip rolling mill thickness control method of the present invention effectively solves the problem of thickness step fluctuation of strip steel caused by uncontrollable factors. Attached Figure Description

[0009] Figure 1 Flowchart of the feedforward prediction monitoring AGC (FM-AGC) structure.

[0010] Figure 2 Schematic diagram of feedforward predictive monitoring AGC (FM-AGC). The meanings of the corresponding English names are as follows:

[0011] Cal means calculation;

[0012] LPF stands for low-pass filter;

[0013] ASR stands for Acceleration Anti-Slip Control System;

[0014] HPC stands for High Performance Computer Group;

[0015] NEG represents the complement instruction;

[0016] Smith predictor refers to the Smith predictor;

[0017] PI represents proportional-integral control;

[0018] Strip Speed ​​indicates a conveyor belt;

[0019] Tickness Gauge refers to a thickness gauge.

[0020] Figure 3 Feedforward prediction monitoring AGC (FM-AGC) monitoring and adjustment diagram. The meanings of the corresponding English names are as follows:

[0021] FM-AGC stands for Feedforward Prediction Monitoring AGC;

[0022] M represents the thickness feedback proportional controller;

[0023] F indicates the thickness feedforward regulator;

[0024] Thickness feedforward estimation adjustment;

[0025] hxi represents the strip thickness value;

[0026] Cal means calculation;

[0027] ∆G Roll gap adjustment amount;

[0028] ∆V frequency conversion adjustment amount.

[0029] Figure 4 A graph showing the output of the AGC eight-stand rolling mill regulator and thickness deviation. The meanings of the corresponding English names are as follows:

[0030] GM_Gauge_Dif represents real-time detection data of strip thickness deviation.

[0031] GM_Gauge represents real-time strip thickness monitoring data.

[0032] PLC32_Real_Spare23 indicates the real-time data output from the F-section of the eight-rack FM-AGC regulator.

[0033] F8_AGC_Gap_Adj indicates the real-time output data of the old eight-rack AGC regulator (not using FM-AGC).

[0034] F8_Auto_Total_Spd represents the real-time speed data for the eight racks.

[0035] Figure 5 Output and thickness deviation diagram of the regulator in an eight-stand rolling mill example using feedforward prediction monitoring AGC (FM-AGC). The meanings of the corresponding English names are as follows:

[0036] GM_Gauge_Dif represents real-time detection data of strip thickness deviation;

[0037] GM_Gauge represents real-time detection data of strip thickness;

[0038] Wide_M represents the real-time detection data of the strip width;

[0039] PLC32_Real_Spare23 indicates the real-time output data of the F section of the FM-AGC regulator in the eight-stand rolling mill.

[0040] F8_MAGC_Gap_Adj represents the real-time output data of the M section of the FM-AGC regulator in the eight-stand rolling mill.

[0041] F8_AGC_Gap_Adj indicates the real-time output data of the old AGC regulator (not using FM-AGC) in the eight-stand rolling mill;

[0042] F8_Auto_Total_Spd represents the real-time speed data of the eight-stand rolling mill.

[0043] Figure 6Example of feedforward prediction monitoring AGC (FM-AGC) for 1.15mm strip steel in a nine-strand rolling mill: regulator output and thickness deviation diagram. The English names and their corresponding meanings are as follows:

[0044] GM_Gauge_Dif represents real-time detection data of strip thickness deviation;

[0045] GM_Gauge represents real-time detection data of strip thickness;

[0046] SMITIH_OUT_F9 indicates the real-time output data of the F section of the FM-AGC regulator in the nine-strand rolling mill.

[0047] F9_MAGC_Gap_Adj represents the real-time output data of the M section of the FM-AGC regulator in the nine-strand rolling mill.

[0048] F9_Auto_Total_Spd represents the real-time speed data of the nine-strand rolling mill. Detailed Implementation

[0049] Existing thickness control systems, including monitoring AGC, suffer from delays in thickness measurement due to the lag between the thickness gauge and the roll, resulting in delayed feedback and hindering accurate control of strip thickness. Related technologies have also reported Smith AGC, which comprises a Smith controller and a monitoring AGC. While Smith AGC can address the theoretical time delay issue inherent in monitoring AGC, it relies on a purely delayed pre-regulation system, making it unable to quickly respond to abrupt thickness fluctuations in strip caused by uncontrollable factors.

[0050] Therefore, the known Smith AGC has at least the following problem: it cannot quickly respond to thickness step fluctuations caused by adjusting the strip.

[0051] Furthermore, existing processing methods cannot simultaneously guarantee the stability of strip threading and the stability of strip thickness in the production of products of different specifications; increasing the speed of finishing rolling may cause changes in the thickness of the strip along its entire length.

[0052] The specific embodiments provided by the present invention will be described in detail below with reference to the accompanying drawings.

[0053] In view of the technical problems in the prior art, some embodiments of the present invention, such as Figure 3As shown, the hot strip mill includes N sets of roll mechanisms (such as servo hydraulic vertical rolls), a reduction system (such as a servo reduction system), a frequency conversion system (such as a main motor frequency conversion control system), and a thickness control system. The (i-1)th set of frequency conversion systems adjusts the strip speed and outputs the strip. The i-th set of roll mechanisms receives the strip and uses the N-th set of reduction systems. The i+1th set of roll mechanisms receives the strip output from the i-th set of roll mechanisms and uses the i-th set of frequency conversion systems to adjust the strip speed and output the strip. This cycle repeats until i+1=N, adjusting the strip speed and outputting the strip. The strip thickness is adjusted using the reduction system of the N-th set of roll mechanisms. A feedforward prediction monitoring AGC is introduced into the thickness control system to improve thickness parameters. Since the known thickness control systems of hot strip mills are affected by thickness step fluctuations, some embodiments of this invention calculate the feedforward prediction value through the feedforward prediction monitoring AGC, and the feedforward prediction monitoring AGC then adjusts the thickness feedforward prediction amount. Proportional-integral adjustment amount with thickness feedback A 1:1 stacking method is used to reduce the impact of thickness step fluctuations.

[0054] Furthermore, some other effects of the present invention are as follows: (1) When the strip is threaded at a constant speed during finishing rolling, the thickness stability of the strip and the thickness of the strip head and tail are ensured by feedforward prediction monitoring AGC and thickness compensation of the pressure head and tail; (2) When the finishing rolling speed is increased, the uniformity of the strip thickness along the entire length is ensured by feedforward prediction monitoring AGC and acceleration / deceleration thickness compensation.

[0055] A high-precision, fast-response thickness control method for hot strip mills, in some embodiments, achieves complete, dead-zone-free control of the roll gap, guiding pre-adjustment correction of the roll gap fit to ensure that the measured actual thickness of the strip equals the target thickness set in the specification (zero deviation). This high-precision, fast-response thickness control method for hot strip mills can directly detect the redirected measured thickness and simultaneously uses an automatic locking function to avoid low-precision adjustments.

[0056] In some embodiments of the thickness control method for high-precision, fast-response hot rolling mills, the hot rolling mill includes N sets of roll mechanisms, a reduction system, a frequency conversion system, and a thickness control system, such as... Figure 3 As shown, the thickness control method of the high-precision, fast-response hot rolling mill includes the following steps performed by the thickness control system:

[0057] The feedforward predictive control regulator F receives the thickness deviation and calculates the intermediate amount. And based on the intermediate amount Calculate and output the thickness feedforward prediction adjustment amount. ;

[0058] The thickness feedback proportional-integral controller M receives the real-time thickness deviation, calculates it, and outputs the thickness feedback proportional-integral adjustment amount. ;

[0059] Adjust the thickness feedforward prediction amount The proportional-integral adjustment amount of the thickness feedback The roll gap adjustment amount ∆G is obtained by superimposing the values ​​through a superimposed device and then input into the roll adjustment mechanism of the pressing system.

[0060] Furthermore, in the thickness control method for a high-precision, fast-response hot rolling mill, the thickness feedforward prediction adjustment amount per unit scanning cycle... Proceed according to Equation I:

[0061] (I)

[0062] in: This represents the thickness feedforward estimation adjustment amount within the unit scanning cycle; This indicates the intermediate amount of roller gap adjustment for each unit of scanning cycle. express Fine-tuning amount within a unit scan cycle; This represents the adjustable integral time constant in memory; This represents the adjustable proportional time constant in memory; T represents the unit scan cycle.

[0063] In some embodiments, such as Figure 2 As shown, the thickness gauge measures the strip thickness value, obtains the thickness deviation in the control system, inputs it into the feedforward prediction monitoring AGC, calculates it through the thickness feedforward prediction control regulator F, and calculates it through the thickness feedback proportional integral regulator.

[0064] Thickness deviation refers to the fitted average value of the detected strip thickness deviation over a specific strip length. The strip length corresponds to the distance between the exit thickness gauge and the roll mechanism. The strip running time within this distance is used as the unit scanning cycle, and the calculated output value is used to adjust the roll mechanism.

[0065] Furthermore, the thickness feedforward prediction adjustment within a unit scanning cycle Intermediate quantities in the calculation process Proceed according to Equation II:

[0066] (II)

[0067] in: This represents the thickness feedforward prediction adjustment amount within the unit scan cycle. The intermediate value; QX represents the vertical plastic deformation coefficient of the strip, the rolling force required for the strip to be reduced by 1mm in the last stand; M represents the mill stiffness coefficient, the rolling force required for the roll mechanism to be reduced by 1mm. F represents the roll gap compensation amount controlled by the F-section; G represents the adjustable gain coefficient. Indicates thickness deviation; Indicates the strip speed of the rolling mill mechanism; This represents the speed value in memory; it is a constant in the example program. This indicates the time required for the thickness gauge, PLC, and hydraulic cylinder to calculate and execute.

[0068] A thickness control method for a high-precision, fast-response hot strip mill includes the thickness control system further performing the following steps:

[0069] The thickness deviation is received by a frequency converter, the frequency adjustment amount ∆V is calculated, and the frequency conversion system is input to adjust the roll mechanism.

[0070] Furthermore, a thickness control method for a high-precision, fast-response hot rolling mill includes some embodiments of the thickness control system, such as... Figure 3 As shown, the feedforward predictive monitoring AGC outputs a frequency conversion adjustment amount ∆V, which adjusts the roll speed and thus the strip speed. The product of strip thickness and strip speed is a relatively constant value, so the percentage of thickness deviation can be calculated from the basic calculations of the thickness control system to determine the percentage of strip speed deviation. Since the feedforward predictive monitoring AGC outputs a frequency conversion adjustment amount ∆V that adjusts the roll speed rather than the strip speed, the percentage of strip speed deviation also needs to be calculated corresponding to the percentage of roll speed deviation. During the calculation, the roll mechanism stiffness coefficient and the strip vertical plastic deformation coefficient are used to perform material equation calculations to obtain the frequency conversion adjustment amount ∆V of the roll mechanism. This logical operation is a fundamental formula in materials science and is directly applied by the computer program.

[0071] This invention does not specifically limit the method of overall strip speed adjustment. For example, it can be designed based on the following principles: The data transmission delay time is a fixed value, and the regulator gain is only limited by the strip transmission time between the adjusting roll mechanism and the measuring equipment. For the pressure roll mechanism, the strip transmission time is equal to the distance between the roll mechanism and the thickness gauge divided by the strip speed. When the strip transmission time increases, the regulator gain must decrease, and vice versa. Therefore, in the roll gap adjustment and speed adjustment programs, the strip speed can be designed as a positively correlated input variable, changing the overall adjustment rate of the control output in real time to adjust the strip thickness over its entire length.

[0072] In some embodiments of a high-precision, fast-response thickness control method for hot continuous rolling mills (corresponding to the actual program), such as... Figure 1 The steps shown are as follows:

[0073] Start running N sets of roll mechanisms and controllers; input raw data and read roll data; determine the controller's pressing regime; control the tension regime; control the strip speed; control the deformation resistance; determine the friction coefficient; determine the strip's forward slip; control the rolling force; control the motor torque; control the motor power; perform a motor power limit check; after the motor power limit check is passed, perform a motor balance check; after the motor balance check is passed, control the roll position; input the roll data into the thickness control system; the control process ends.

[0074] In the aforementioned hot rolling mill thickness control method, the N sets of roll mechanisms include 8 sets of roll mechanisms and 9 sets of roll mechanisms.

[0075] Furthermore, a thickness control method for a high-precision, fast-response hot rolling mill includes the following steps: Figure 1 It also includes the following steps:

[0076] During the motor power limit check, if the motor power does not reach the ideal state, the pressure reduction system is modified. If the motor power limit check passes, the motor power balance check is performed.

[0077] During the motor power balance check, if the result is not ideal, the strip speed is adjusted; if the motor power balance check result is satisfactory, the roll position is adjusted.

[0078] The roll position data is input into the thickness control system to adjust the roll position and the strip speed.

[0079] In some embodiments, process parameters such as finishing mill load, speed regime, looper tension, and looper height are set according to the steel grade and finished product thickness of the strip. Inappropriate load distribution can easily lead to overload and shutdown of a certain roll mechanism. The speed regime also needs to be optimized based on the model classification and equipment conditions. A low speed setting affects output and energy consumption, while a high speed setting can lead to motor overload and production instability. Based on the optimized finishing mill process parameters, which are crucial for stable production specifications, high-precision control of the strip thickness is achieved.

[0080] Furthermore, in some embodiments of a high-precision, fast-response hot strip mill thickness control method, the following measures are taken to ensure the consistency of the thickness of the finished strip throughout the entire length during the hot finishing mill rolling process: (1) When the strip is threaded at a constant speed during finishing milling, the thickness stability of the strip and the thickness index of the strip head and tail are ensured by feedforward prediction monitoring AGC and thickness compensation of the pressure head and pressure tail; (2) When the finishing mill is rolled at a higher speed, the uniformity of the thickness of the strip throughout the entire length is ensured by feedforward prediction monitoring AGC and acceleration / deceleration thickness compensation.

[0081] The technical solution of the present invention will be further described below with reference to Embodiment 1, such as... Figure 5As shown, the thickness control method of the hot continuous rolling mill of the present invention is applied to a hot continuous rolling production line, using a continuous rolling mill with N=8 rolls to test the products.

[0082] Under the premise of stable and reasonable finishing mill load distribution parameters, the finished strip steel specifications are (finished thickness 2.97mm, width 593mm). The existing system for monitoring and controlling the AGC system is used, such as... Figure 4 As shown, the strip thickness deviation detection value at the acceleration point is -0.03mm, the tail deviation detection value is 0.031mm, and the through strip thickness deviation detection value is ±0.031mm. A feedforward predictive monitoring AGC control system is adopted, such as... Figure 5 As shown, the strip thickness deviation detection value at the acceleration point is -0.005mm, the tail deviation detection value is 0.008mm, and the through strip thickness deviation detection value is ±0.008mm. The real-time data output from regulator F has the characteristics of gentle forward adjustment, while the real-time data output from regulator M has the characteristics of fast and stable adjustment. Together, they achieve a thickness control accuracy superior to the original system's measured results. Simultaneously, the real-time width detection data shows a width deviation accuracy of ±1mm, indicating that the feedforward predictive monitoring AGC ensures both thickness control accuracy and width accuracy. See Table 1 for detailed data comparison.

[0083] Table 1 Comparison of thickness control accuracy between the original AGC and FM-AGC systems in the eight-stand rolling mill

[0084]

[0085] The technical solution of the present invention will be further described below with reference to Embodiment 2. For example... Figure 6 As shown, the actual measurement was performed on the nine-strand rolling mill (without a comparison system).

[0086] For rolling 1.15mm thick strip steel, the thickness deviation measurement accuracy is ±0.012mm. Achieving the control accuracy described in this example is a prerequisite for continuous and stable rolling of hot-rolled strip steel. This example demonstrates that feedforward prediction monitoring AGC is a high-precision, fast-response thickness control method for hot continuous rolling mills. It can be widely applied to various types of strip steel control production lines and is superior to other single-category monitoring AGC control systems currently available.

[0087] The embodiments and functional operations of the subject matter described in this specification can be implemented in the following ways: digital electronic circuits, tangibly implemented computer software or firmware, computer hardware, including the structures disclosed in this specification and their equivalents, or combinations thereof. Embodiments of the subject matter described in this specification can be implemented as one or more computer programs, that is, one or more modules of computer program instructions encoded on one or more tangible non-transitory program carriers, for execution by a data processing unit or to control the operation of a data processing device.

[0088] Alternatively or additionally, program instructions may be encoded on artificially generated propagation signals, such as machine-generated electrical, optical, or electromagnetic signals, which are then generated as coded information to be transmitted to an appropriate receiver device executed by data processing equipment. The computer storage medium may be a machine-readable storage device, a machine-readable storage substrate, a random or serial access memory device, or one or more combinations of the above.

[0089] The term "data processing unit" encompasses all kinds of devices, apparatuses, and machines for processing data, including, for example, programmable processors, computers, or multiprocessor or multicomputer systems. Devices may include special-purpose logic circuitry, such as FPGAs (Field-Programmable Gate Arrays) or ASICs (Application-Specific Integrated Circuits). In addition to hardware, devices may also include code that creates the execution environment for related computer programs, such as processor firmware, protocol stacks, database management systems, operating systems, or combinations thereof.

Claims

1. A method for thickness control in a high-precision, fast-response hot strip rolling mill, wherein the hot strip rolling mill comprises N sets of roll mechanisms, a pressing system, a frequency conversion system, and a thickness control system, wherein the thickness value of the strip after being rolled by the roll mechanisms is input to the thickness control system, characterized in that... The thickness control method for the high-precision, fast-response hot rolling mill includes the following steps performed by the thickness control system: The feedforward predictive control regulator F receives the thickness deviation and calculates the intermediate value. And based on the intermediate amount Calculate and output the thickness feedforward prediction adjustment amount. ; The thickness deviation is received by the thickness feedback proportional-integral controller M, and the thickness feedback proportional-integral adjustment amount is calculated and output. ; Adjust the thickness feedforward prediction amount The proportional-integral adjustment amount of the thickness feedback The roll gap adjustment ∆G is obtained by superimposing the values ​​through a superimposed unit and then input into the roll adjustment mechanism of the pressing system to estimate the thickness feedforward adjustment within a unit scanning cycle. Proceed according to Equation I: （I） in: This represents the thickness feedforward estimation adjustment amount within the unit scanning cycle; This indicates the intermediate amount of roller gap adjustment for each unit of scanning cycle. express Fine-tuning amount within a unit scan cycle; This represents the adjustable integral time constant in memory; The variable proportional time constant in memory is represented by T; T represents the unit scan cycle, and the adjustment amount is estimated based on the thickness feedforward within the unit scan cycle. Calculate the intermediate quantity Proceed according to Formula II: (II) in: This represents the thickness feedforward prediction adjustment amount within the unit scan cycle. The intermediate value; QX represents the vertical plastic deformation coefficient of the strip; M represents the mill stiffness coefficient; F represents the roll gap compensation amount controlled by the F-section; G represents the adjustable gain coefficient. Indicates thickness deviation; Indicates the strip speed of the rolling mill mechanism; This represents the speed value in memory; This indicates the time required for the thickness gauge, PLC, and hydraulic cylinder to calculate and execute.

2. The thickness control method for a high-precision, fast-response hot rolling mill according to claim 1, characterized in that, The thickness control system also performs the following steps: The thickness deviation is received by the frequency converter and the frequency conversion adjustment amount ∆V is calculated. The frequency conversion adjustment amount ∆V is then input into the frequency conversion system to adjust the roll mechanism.

3. The thickness control method for a high-precision, fast-response hot rolling mill according to claim 2, characterized in that, The step of receiving the thickness deviation and calculating the frequency adjustment amount ∆V using a frequency converter includes: The frequency converter receives the thickness deviation, calculates the strip speed deviation, and uses the mill stiffness coefficient and the strip vertical plastic deformation coefficient to calculate the frequency conversion adjustment amount ∆V of the roll mechanism based on the strip speed deviation.

4. The thickness control method for a high-precision, fast-response hot rolling mill according to claim 1, characterized in that, The thickness control system also performs the following steps: Input the strip thickness value into the thickness deviation calculator, calculate and output the fitted average value of the strip thickness deviation value, which is the thickness deviation.

5. The thickness control method for a high-precision, fast-response hot rolling mill according to claim 1, characterized in that, The thickness control method further includes the following steps: Start running N sets of roll mechanisms and controllers; input raw data and read roll data; determine the controller's pressing regime; control the tension regime; control the strip speed; control the deformation resistance; determine the friction coefficient; determine the strip's forward slip; control the rolling force; control the motor torque; control the motor power; perform a motor power limit check; after the motor power limit check is passed, perform a motor balance check; after the motor balance check is passed, control the roll position; input the roll data into the thickness control system; the control process ends.

6. The thickness control method according to claim 5, characterized in that, It also includes the following steps: During the motor power limit check, if the motor power does not reach the ideal state, the pressure reduction system is modified. If the motor power limit check passes, the motor power balance check is performed. During the motor power balance check, if the result is not ideal, the strip speed is adjusted; if the motor power balance check result is satisfactory, the roll position is adjusted. The roll position data is input into the thickness control system to adjust the roll position and the strip speed.

7. The thickness control method for a high-precision, fast-response hot rolling mill according to claim 1, characterized in that, The N-group rolling mill mechanism includes 8-group rolling mill mechanisms and 9-group rolling mill mechanisms.

8. A high-precision, fast-response thickness control system for a hot continuous rolling mill, the system comprising at least one processor; and a memory storing instructions that, when executed by the at least one processor, implement the steps of the thickness control method according to any one of claims 1-7.

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