Hot continuous rolling unit thickness detection and optimization method based on double closed-loop feedback control

Abstract

The invention discloses a hot continuous rolling unit thickness detection and optimization method based on double closed-loop feedback control. In order to improve the problems of thickness control precision, response speed, a multi-rolling-mill cooperative operation mechanism and the like of an existing hot continuous rolling process, the comprehensive regulation and control method combining driving motor double-closed-loop speed regulation control, hydraulic cylinder pressing closed-loop control and thickness delay correction is provided. A multi-rolling-mill interconnection control system is constructed by coupling the rolling mills, the loops, the driving motors and the hydraulic cylinders, and high-precision dynamic adjustment of the tapping thickness is achieved. A double-closed-loop feedback control method is adopted, the rotating speed of a driving motor is adjusted by combining a rotating speed loop and a current loop, rolling force is dynamically adjusted through a hydraulic cylinder, and a thickness delay correction system is introduced to compensate thickness transmission errors between racks. According to the method, the thickness response time and overshoot of the hot rolling mill can be reduced, the thickness control precision and the system stability are improved, and the method has important guiding significance and engineering application value for high-precision hot continuous rolling production.

Description

Technical Field

[0001] The present invention relates to the technical field of automatic control in the rolling process of steel, and particularly relates to a thickness detection and optimization method for a hot continuous rolling mill based on double closed-loop feedback control. Background Art

[0002] Hot strip continuous rolling, as a key process in steel production, is of great significance for improving steel quality, production efficiency, and reducing energy consumption. The rolling process involves various changing processes such as thermodynamics and mechanics. The control methods for different parameters such as thickness, speed, and temperature during the rolling process, as well as the combined operation mode between multiple rolling mills, are relatively complex. In order to meet the requirements of the rolling process and improve the quality of steel production, it is urgent to clarify the collaborative operation characteristics of the hot continuous rolling mill, and realize the interconnection between multiple rolling mills and the comprehensive regulation of parameters such as the thickness of the discharged steel and the driving speed.

[0003] Regarding the optimization control methods for parameters such as the thickness of the discharged steel and the final rolling temperature of the hot continuous rolling mill, existing research mainly improves the control accuracy of the thickness of the discharged steel and the final rolling temperature in the hot continuous rolling process through various prediction and control methods. However, there are still problems such as the unclear influence law of rolling operation parameters on temperature drop, the unclear coupling mechanism between multiple rolling mills, and the low thickness control accuracy in the hot continuous rolling process. At present, there is no systematic method to solve the problems of unclear influence law of rolling operation parameters on temperature drop, unclear coupling mechanism between multiple rolling mills, and delay correction of thickness transfer error between stands, resulting in the difficulty of the existing technology to achieve high-precision and low overshoot dynamic control of the thickness in the hot continuous rolling process. Summary of the Invention

[0004] The purpose of the present invention is to provide a thickness detection and optimization method for a hot continuous rolling mill based on double closed-loop feedback control, which solves the problems of low thickness control accuracy and slow response speed in the existing technology through multi-model coupling and double closed-loop collaborative regulation.

[0005] In order to achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A thickness detection and optimization method for a hot continuous rolling mill based on double closed-loop feedback control, comprising the following steps:

[0007] Step 1), establish a multi-stand collaborative operation control system for the hot continuous rolling mill, including a rolling mill, a loop, a driving motor, and a hydraulic cylinder;

[0008] Step 2), establish a double closed-loop speed regulation control system for the driving motor, and dynamically control the rolling transmission speed by jointly regulating the output speed of the motor through the speed loop and the current loop;

[0009] Step 3), establish a closed-loop control system for the hydraulic cylinder to adjust the rolling force according to the deviation between the thickness command and the measured thickness, and correct the thickness transfer error between stands in combination with the thickness delay correction system;

[0010] Step 4), analyze the influence law of strip thickness change on radiation temperature drop through radiation temperature drop calculation, so as to provide reference for the selection of parameters such as rolling speed and final rolling thickness;

[0011] Step 5), design a multi-rolling mill interconnection control algorithm to realize the coordinated regulation of tension, speed and thickness between stands, and ensure the high-precision following characteristics of the final rolling thickness.

[0012] In one embodiment, in the said Step 1), the rolling mill calculates the rolling thickness by using a mechanical model, and the calculation objects include the rolling force and the bounce equation, which are respectively expressed as follows:

[0013]

[0014] In the formula, P is the rolling force; F is the rolling area; p c is the average unit pressure; σ is the deformation resistance; n σ is the stress state influence coefficient; ε is the deformation rate; R is the work roll diameter; H is the thickness of the steel plate before rolling; m is the strain rate sensitivity index; σ f is the flow stress; f is the dimensionless factor of ε; c is the fitting coefficient, reflecting n σ 's sensitivity to the thickness-diameter ratio R / H.

[0015] The said bounce equation is used as the basis for setting the roll gap and calculating the exit thickness of the rolled piece during the rolling simulation, and is expressed as follows:

[0016]

[0017] In the formula, h is the exit thickness of the rolled piece; S0 is the measurement result of the roll gap gauge; K is the effective stiffness of the rolling mill; o v is the oil film thickness related to the rotational speed; f l is the wear amount related to the rolling volume;

[0018] The loop uses an elastic tensile tension formula to calculate the tension acting on the strip between every two rolling mills, and is expressed as follows:

[0019]

[0020] In the formula, q is the tension; E is the elastic modulus; L is the strip length; v1 and v2 are the driving speeds of the front and rear rolling mills respectively;

[0021] The drive motor adopts a single-axis drive system with a DC motor as the main body, and the dynamic balance differential equation of the motor torque M D acting on the shaft and the load torque M fz is expressed as follows:

[0022]

[0023] where ω is the angular velocity of the motor rotation; J is the moment of inertia of the motor, expressed as follows:

[0024]

[0025] where m is the mass of the rotating body; ρ is the radius of gyration; D is the diameter of gyration, or the inertia diameter; G is the weight of the rotating body; g is the acceleration due to gravity.

[0026] The hydraulic cylinder adopts a non-linear system, where the equation describing the hydrodynamic of the hydraulic fluid is expressed as follows:

[0027] Q = A·x + C t (P1 - P2)

[0028] where Q is the flow rate into the hydraulic cylinder; A is the piston area; x is the piston displacement; C t is the leakage coefficient; P1 and P2 are the input and output pressures of the hydraulic cylinder respectively.

[0029] The flow equation of the servo valve is expressed as follows:

[0030]

[0031] where K q is the flow amplification coefficient; u is the control voltage; P s is the supply pressure.

[0032] In order to more accurately express the dynamic response of the hydraulic cylinder, the piston motion equation is used and expressed as follows:

[0033]

[0034] where x is the piston displacement; m is the load mass; b is the damping coefficient; k is the equivalent stiffness; A·P1 is the driving force provided by the hydraulic cylinder.

[0035] In one embodiment, in step 2), the double closed-loop speed control system of the drive motor includes a speed feedback loop and a current feedback loop, and its transfer function is a second-order differential equation, and the dynamic regulation of the speed is realized through a PID controller, expressed as follows:

[0036]

[0037] where R S is the armature circuit resistance; L is the armature circuit inductance; C e is the electromotive force coefficient; C m represents the electromagnetic torque generated by unit current; M fz is the load torque; M D is the motor torque; n(t) is the speed.

[0038] In one embodiment, in step 3), the hydraulic cylinder is a device with the ability to quickly adjust the press-down. With the help of the hydraulic cylinder press-down closed-loop control system, and according to the changes in the actual production situation, the rolling mill stiffness is controlled accordingly to obtain the required rolled thickness. The hydraulic cylinder press-down closed-loop control system is controlled by an electro-hydraulic servo valve. The hydraulic cylinder press-down closed-loop control system includes a regulator, a servo valve amplifier, a servo valve coil, connecting pipes, a hydraulic cylinder body, etc. To simplify the system and simulation calculation, only its transfer function is calculated to represent its input-output characteristics. Specifically, the open-loop transfer function of the hydraulic cylinder press-down closed-loop control system is expressed as follows:

[0039]

[0040] In the formula, K p is the regulator proportionality coefficient; G a (s) is the lead-lag link; K2 is the servo valve amplifier coefficient; G sv (s) is the electro-hydraulic servo valve transfer function; G r (s) is the transfer function of the hydraulic cylinder body, K5 is the displacement sensor coefficient; K τ is the integral constant; K2 is the servo amplifier coefficient; K V is the servo valve flow gain; ξ V is the servo damping coefficient; ω V is the undamped natural oscillation frequency of the servo valve; ξ h is the damping ratio of the hydraulic cylinder; ω h is the natural frequency of the hydraulic cylinder; A P is the effective area of the hydraulic cylinder piston; K ce is the flow-pressure coefficient; K is the combined spring stiffness of the load; K5 is the displacement sensor conversion coefficient; s is the complex variable.

[0041] In one embodiment, the hydraulic cylinder press-down closed-loop control system is controlled by an electro-hydraulic servo valve. Its transfer function includes parameters such as the proportionality coefficient, the servo valve flow gain, and the natural frequency of the hydraulic cylinder. When a step signal input for simulating the rolling mill press-down is input, after the feedback of the output press-down height and signal amplification, through the electro-hydraulic servo valve, subtracting the loss of the hydraulic pipe transmission, the command is sent to the hydraulic cylinder and its position sensor, and then the press-down height of the hydraulic cylinder is output, realizing the change of the rolling pressure, and further changing the thickness of the passing strip steel.

[0042] In one embodiment, in step 3), the thickness delay correction system is combined to correct the thickness transfer error between rolling mill stands. Among them, when changing the roll gap or speed of any rolling mill during continuous rolling, it will change the exit thickness and the rolling piece speed of this stand. The speed change will immediately cause the tension change to be transmitted to the upstream and downstream rolling mills, but the rolling piece with the thickness change will be delayed in being transmitted to the next stand. The specific thickness change delay t0 is expressed as follows:

[0043]

[0044] In the formula, l0 is the distance between rolling mill stands; v0 is the strip driving speed.

[0045] In one embodiment, the strip thickness is further corrected. By comparing the theoretical calculated value of the steel plate outlet thickness with the strip initial thickness and the thickness change delay, the true value of the strip thickness is calculated. The specific process is as follows:

[0046] h2 = h1 - (h0 - t0)

[0047] In the formula, h0 is the initial thickness of the steel plate; h1 is the theoretical calculated value of the steel plate outlet thickness; h2 is the true value of the steel plate thickness; t0 is the thickness change delay.

[0048] In one embodiment, in step 4), the radiative temperature drop is the main temperature drop in the hot strip rolling process, and the calculation error mainly comes from the calculation error of this part of the temperature drop. The temperature drop coefficient K T is used to correct the radiative temperature drop, and the corrected formula is as follows:

[0049]

[0050] In the formula, σ is the Boltzmann constant; ε is the emissivity; γ is the density of the rolled piece; T is the absolute temperature of the rolled piece; C p is the specific heat capacity of the rolled piece; T0 is the initial temperature; h is the thickness of the rolled piece; ΔL is the stand distance; v is the steel plate driving speed.

[0051] In one embodiment, the influence law of the strip thickness change on the radiative temperature drop is calculated and analyzed through the radiative temperature drop, specifically: when the steel plate thickness decreases, the required rolling force increases, and the steel plate driving speed decreases, which in turn causes the radiative temperature drop during the steel plate driving to increase, thereby providing a reference for the selection of parameters such as the rolling speed and the final rolling thickness.

[0052] In one embodiment, in step 5), the rolling mill is coupled with the hydraulic cylinder down-acting closed-loop control system, the drive motor double closed-loop speed regulation control system, and the thickness delay correction system to obtain the comprehensive control system for the final rolling thickness and speed of the rolling mill. The control algorithm adjusts the speed difference between adjacent stands through the loop tension feedback and dynamically distributes the rolling force of each stand in combination with the thickness command, specifically as follows:

[0053] Under a given steel output thickness command, read the steel output thickness and drive speed values of the rolling mill at the previous moment, calculate the measured value of the steel plate thickness, and calculate the error by subtracting the thickness command; input the error signal into the electro-hydraulic servo valve to control the valve opening, change the rolling force of the hydraulic cylinder, and then change the steel output thickness; perform speed control on the drive motor, transfer the motor speed and the rolling force of the hydraulic cylinder to the rolling mill together, and calculate and output the new steel output thickness and the steel plate conveying speed; during rolling, change the steel output thickness command, and the thickness change signal shows a delay transmission characteristic. The steel output thickness cannot immediately become the current thickness command value, so a thickness delay correction system is used to simulate this process. That is, the steel output thickness command is corrected by the thickness delay correction system during the process.

[0054] Compared with the prior art, the beneficial effects of the present invention are:

[0055] (1) The present invention provides a thickness detection and optimization method for a hot continuous rolling mill based on double closed-loop feedback control. The strip drive speed is controlled through the double closed-loop speed regulation of the DC drive motor, the strip thickness is adjusted through the closed-loop control system of the hydraulic cylinder pressing down, and the strip thickness is detected and corrected. The prior art fails to systematically solve the problem of delay correction of the thickness transfer error between stands, resulting in hysteresis and overshoot in thickness control. The present invention effectively compensates for the thickness transfer error between stands by introducing thickness delay correction, significantly improving the control accuracy.

[0056] (2) The present invention improves the thickness control accuracy and dynamic response ability of the hot continuous rolling mill through the double closed-loop feedback control strategy and multi-model collaborative optimization. In the control link of the drive motor, a speed-current double closed-loop speed regulation system is adopted. The speed loop realizes the rapid tracking of the speed command, and the current loop suppresses the influence of load disturbance on the speed. At the same time, the hydraulic cylinder pressing down system accurately adjusts the rolling force through the electro-hydraulic servo valve, and combines the thickness delay correction model to compensate the transfer error between stands in real time, effectively solving the overshoot problem caused by detection hysteresis in the traditional method. Compared with the traditional rolling steel thickness optimization control method, the present invention can effectively improve the thickness detection ability, thickness control accuracy and dynamic response ability of the hot continuous rolling mill, and has important guiding significance and engineering application value for the design and optimization of the hot continuous rolling mill controller. Description of the Drawings

[0057] Figure 1 It is the overall block diagram of the rolling steel control system.

[0058] Figure 2 It is the schematic diagram of the finishing mill of the hot continuous rolling mill.

[0059] Figure 3 It is the DC motor model

[0060] Figure 4 It is the block diagram of the double closed-loop speed regulation system of the drive motor.

[0061] Figure 5 For the model verification of the DC motor speed regulation system.

[0062] Figure 6 For the control simulation block diagram of the hydraulic cylinder system.

[0063] Figure 7 For the model verification of the hydraulic cylinder lowering system.

[0064] Figure 8 For the curve of the change in the lowering height of the hydraulic cylinder under transient conditions.

[0065] Figure 9 For the strip thickness correction model.

[0066] Figure 10 For the input thickness command of the rolling mill.

[0067] Figure 11 For the strip temperature drop curve of Rolling Mill 1.

[0068] Figure 12 For the strip temperature drop curve of the three-stand rolling mill.

[0069] Figure 13 For the curve of the change in the final rolling thickness.

[0070] Figure 14 For the curve of the change in the drive speed. Specific implementation manner

[0071] See Figure 1 and Figure 2 and describe in detail the implementation manner of the present invention in conjunction with the accompanying drawings.

[0072] A thickness detection and optimization method for a hot strip mill based on double-closed-loop feedback control according to the present invention includes the following steps:

[0073] 1. Establish a multi-stand coordinated operation control system for the hot strip mill.

[0074] The control system of the present invention mainly includes a rolling mill, a loop, a drive motor, and a hydraulic cylinder, etc. Among them, for the rolling mill, a mechanical model is used to calculate the rolling thickness, and the calculation objects include the rolling force and the bounce equation, etc. The calculated rolling force is used to predict the unit pressure and the change in the thickness of the rolled piece during the rolling process, and is used as the basis for setting control parameters and adjusting the exit thickness. The bounce equation is used as the basis for setting the roll gap and calculating the exit thickness of the rolled piece during the rolling simulation.

[0075] For the loop, an elastic tensile tension formula is used to calculate the tension acting on the strip between every two rolling mills, which is used to balance the tension of the steel plate transmitted between the two rolling mills and avoid the breakage or accumulation of the steel plate due to different drive speeds of different rolling mills.

[0076] For the drive motor, a single-axis drive system with a DC motor as the main body is adopted, which has the characteristics of excellent speed regulation performance, fast response, high control precision, simple structure, and strong adaptability.

[0077] For the hydraulic cylinder, a non-linear system is adopted, which can truly reflect the dynamic response behavior of the hydraulic cylinder under the influence of factors such as load, oil compressibility, and throttling characteristics during the rolling process, and is used to accurately adjust the roll gap to achieve high-precision control of the strip thickness.

[0078] II. Establishment of the double closed-loop speed control system for the drive motor and verification of the control effect.

[0079] From Figure 3 the voltage equation of the DC motor can be obtained as shown in Equation (1).

[0080]

[0081] In the formula, R S is the armature circuit resistance, L is the armature circuit inductance, and C e is the electromotive force coefficient.

[0082] Substituting the moment of inertia J and the electromagnetic torque M D = C m i(t) into Equation (1), Equation (2) can be calculated as shown below.

[0083]

[0084] In the formula, C m represents the electromagnetic torque generated by unit current.

[0085] Considering the simplicity of the derivation, first let the load torque M fz = 0, and take the derivative of Equation (2) to obtain the relational expression for the current derivative of the DC motor as shown in Equation (3).

[0086]

[0087] Substituting Equation (2) and Equation (3) into Equation (1), the second-order differential equation of the DC motor with the armature voltage u(t) as the input quantity and the speed n(t) as the output quantity can be calculated as shown in Equation (4).

[0088]

[0089] In this equation, due to the presence of both electromagnetic inertia and mechanical inertia, there are two time constants, namely the electromagnetic time constant the mechanical and electrical time constant

[0090] At this time, the motor load torque M is added. fz , Equation (4) can be deduced as shown in Equation (5).

[0091]

[0092] Based on the second-order transfer function of the DC motor in Equation (5), a double-closed-loop speed regulation system for the drive motor is constructed as Figure 4 shown. As can be seen from Figure 4 , the constructed speed regulation model consists of a speed feedback loop and a double-closed-loop structure of current feedback. When the input given voltage is applied, after the adjustment of speed and current feedback, it is given to the DC motor, and then the motor speed is output. During this period, through the motor inertia integration link and PID control, the current and speed of the motor are comprehensively feedback-controlled to achieve the purpose of dynamically adjusting the output speed of the motor.

[0093] The double-closed-loop speed regulation system of the drive motor is simulated. Its rated speed is set to 615 r / min, and the simulation condition is to suddenly apply a load at 2.5 s to simulate the situation of passing steel. The comparison result of the simulated value of the output motor speed with the literature is as Figure 5 shown. As can be seen from Figure 5 , the speed error after stabilization is less than 10%. Through the double-closed-loop regulation of current and speed, the load mutation during passing steel is suppressed within 0.25 s, and the overshoot of the motor speed is 5.5%, reflecting its good speed regulation ability.

[0094] III. Establishment of the hydraulic height control system of the hydraulic cylinder down system and verification of the control effect

[0095] Figure 6 is the simulation block diagram of the hydraulic cylinder control system. It can be seen that when the step signal simulating the rolling mill down is input, after the feedback of the output down height and signal amplification, through the electro-hydraulic servo valve, subtracting the loss transmitted by the hydraulic pipe first, the instruction is sent to the hydraulic cylinder and its position sensor, and then the hydraulic cylinder down height is output, realizing the change of the rolling pressure, and then making the thickness of the passing strip steel change.

[0096] The hydraulic cylinder control system is simulated. The comparison result of the simulated value of the hydraulic cylinder down height with the literature is as Figure 7 shown. It can be seen that the down height error after stabilization is less than 10%. At the same time, the transient condition is set: a step signal is input at 5 s to simulate the thickness adjustment signal during rolling. The hydraulic cylinder control system adjusts the valve opening and hydraulic height. The obtained hydraulic cylinder down height is as Figure 8 shown. It can be seen that the response time of the step signal of the hydraulic cylinder control system is about 0.26 s, and the overshoot is 13.68%, indicating its good down height regulation ability and response speed.

[0097] IV. Thickness delay correction

[0098] When changing the roll gap or speed of any rolling mill during tandem rolling, it will change the thickness at the outlet of this mill and the speed of the rolled piece. The speed change will immediately cause a change in tension and be transmitted to the upstream and downstream rolling mills, but the rolled piece with a thickness change will be delayed in being transmitted to the next mill. The specific thickness change delay t0 is shown in Equation (6).

[0099]

[0100] In the formula, l0 is the distance between rolling mill stands; v0 is the driving speed of the strip steel.

[0101] Therefore, the thickness of the strip steel is corrected. By comparing the theoretical calculated value with the initial thickness of the strip steel and the thickness change delay, the true value of the strip steel thickness is calculated. The specific strip steel thickness correction model is as Figure 9 shown.

[0102] Coupling models such as hydraulic cylinders, DC drive motors, rolling mills, and thickness delay, a comprehensive rolling mill control system is obtained. Under the condition of a given outgoing steel thickness command, the outgoing steel thickness and driving speed values of the rolling mill at the previous moment are read, the measured value of the steel plate thickness is calculated, and the difference from the thickness command is obtained as the error. The error signal is input to the electro-hydraulic servo valve to control the valve opening, and then the hydraulic cylinder is controlled to change the rolling force. At the same time, the rotational speed of the drive motor is controlled. The motor rotational speed and the rolling force of the hydraulic cylinder are jointly transmitted to the rolling mill model, and the new outgoing steel thickness and the steel plate conveying speed are calculated and output. During rolling, when changing the outgoing steel thickness command, the thickness change signal shows a delay transmission characteristic, and the outgoing steel thickness cannot immediately become the current thickness command value. Therefore, a delay model is used to simulate this process. The specific rolling mill control system is as Figure 1 shown.

[0103] The application effect of the present invention will be described in detail below in combination with simulations.

[0104] Three rolling mills are connected in series through a loop to construct an interconnected control system for three rolling mills as Figure 2 shown. The initial thickness of the steel plate is selected as 10 mm, the initial temperature is 950 °C, and the initial rolling speed is set as 1 m / s. The input thickness command for each rolling mill is as Figure 10 shown. Furthermore, the influence law of the initial thickness of the strip steel on the temperature drop and the coordinated operation simulation analysis of the three-rolling mill system under different thickness input commands are respectively carried out.

[0105] (1) Analysis of the influence law of strip steel thickness on temperature drop.

[0106] The simulation conditions are as Figure 10 shown, and the strip steel temperature drop curves of the three rolling mills obtained by simulation are as shown. Among them, taking rolling mill 1 as an example for specific analysis. From Figure 11It can be seen that from 0 to 100 s, the thickness of the steel plate was set at 9 mm and the temperature dropped by 12.60 °C; from 100 to 200 s, the thickness of the steel plate was set at 8 mm and the temperature dropped by 13.45 °C; from 200 to 300 s, the thickness of the steel plate was set at 7 mm and the temperature dropped by 32.01 °C. As can be seen from the figure, the decrease in the thickness of the steel plate leads to an increase in the required rolling force and a decrease in the transmission speed of the steel plate, thereby increasing the radiative temperature drop during the transmission of the steel plate.

[0107] It can be seen from Figure 12 that while the change in the thickness of the single rolling mill affects the temperature change of the strip steel, there is also a corresponding temperature drop when rotating from one rolling mill to another. Among them, when the strip steel is transferred from rolling mill 1 to rolling mill 2 through the loop, the temperature drops by 44.32 °C during this period, and when the strip steel is transferred from rolling mill 2 to rolling mill 3 through the loop, the temperature drops by 66.39 °C during this period.

[0108] (2) Analysis of the final rolling thickness control effect.

[0109] The final rolling thickness of the strip steel of the three rolling mills is as Figure 13 shown, and the steel discharging instruction is as Figure 10 shown. The final rolling thickness of each rolling mill shows good following characteristics for the thickness instruction. The average thickness response time does not exceed 24.36 s, and the overshoot during the thickness adjustment period does not exceed 3.63%. It can be seen from Figure 14 that the transmission speed of each rolling mill also changes accordingly following the thickness instruction. At 100 s and 200 s, the transmission changes suddenly due to the change in the thickness instruction and shows a stepped decreasing trend. Moreover, the greater the difference between the current thickness and the thickness instruction, the greater the change amplitude of the speed and the smaller the stable value. Comparing the three rolling mills, when the strip steel is transferred from one rolling mill to another, for every 0.5 mm decrease in its thickness, the maximum decrease in the transmission speed is about 7.13%.

[0110] In summary, starting from the perspective of improving the low precision of hot continuous rolling thickness control, the unclear coupling mechanism between multiple rolling mills, and the unclear influence law of rolling operation parameters on temperature drop, the present invention establishes a simulation model of the interconnected system of three rolling mills considering the mechanics, speed, and temperature drop characteristics during the rolling process. Combining the drive motor, hydraulic cylinder model, and its control system, a thickness detection and optimization method for hot continuous rolling mills based on double closed-loop feedback control is proposed, and the output parameters of the rolling mill are corrected based on the delay model. The influence law of the discharged steel thickness on temperature drop is obtained, and the purpose of flexible control of the discharged steel thickness under the condition of thickness instruction change is achieved. Compared with the traditional rolling thickness optimization control method, the present invention can effectively improve the thickness detection ability, thickness control precision, and dynamic response ability of the hot continuous rolling mill, and has important guiding significance and engineering application value for the design and optimization of the hot continuous rolling mill controller.

[0111] The above are only the preferred examples of the present invention, and are not intended to limit the present invention. Moreover, it is not limited to the applications listed in the specification and embodiments, and can be applied to various fields suitable for the present invention. All other application examples obtained without any creative labor within the spirit and principles of the present invention belong to the protection scope of the present invention.

Claims

1. A thickness detection and optimization method for a hot strip rolling mill based on double closed-loop feedback control, characterized in that It includes the following steps: Step 1), establish a multi-stand coordinated operation control system for the hot strip mill, including a rolling mill, a loop, a drive motor, and a hydraulic cylinder; Step 2), establish a double-closed-loop speed control system for the drive motor, and dynamically control the rolling transmission speed by coordinately adjusting the motor output speed through the speed loop and the current loop; Step 3), establish a hydraulic cylinder position closed-loop control system, adjust the rolling force according to the deviation between the thickness command and the measured thickness, and correct the thickness transfer error between stands in combination with the thickness delay correction system; Step 4), calculate and analyze the influence law of strip thickness change on radiative temperature drop through radiative temperature drop calculation, and provide a reference for the selection of rolling speed and final rolling thickness; Step 5), design an interconnected control algorithm for multiple rolling mills to realize the coordinated control of tension, speed, and thickness between stands, and ensure the high-precision following characteristics of the final rolling thickness.

2. The thickness detection and optimization method for a hot strip mill based on double closed-loop feedback control according to claim 1, characterized in that In the said Step 1), the rolling mill uses a mechanical model to calculate the rolling thickness, and the calculation objects include the rolling force and the bounce equation, which are respectively expressed as follows: Wherein, P is the rolling force; F is the rolling area; p c is the average unit pressure; σ is the deformation resistance; n σ is the stress state influence coefficient; ε is the deformation rate; R is the diameter of the work roll; H is the thickness of the steel plate before rolling; m is the strain rate sensitivity index; σ f is the flow stress; f is the dimensionless factor of ε; c is the fitting coefficient, reflecting n σ 's sensitivity to the thickness-diameter ratio R / H; The said bounce equation is used as the basis for setting the roll gap and calculating the exit thickness of the rolled piece during the rolling simulation, and is expressed as follows: Where h is the exit thickness of the rolled piece; S0 is the measurement result of the roll gap gauge; K is the effective stiffness of the rolling mill; o v is the oil film thickness related to the rotational speed; f l is the wear amount related to the rolling volume; The loop uses the elastic tensile tension formula to calculate the tension acting on the strip between every two rolling mills, and is expressed as follows: In the formula, q is the tension; E is the elastic modulus; L is the strip length; v1 and v2 are the transmission speeds of the front and rear rolling mills respectively; The drive motor adopts a single-axis drive system with a DC motor as the main body, and the motor torque M acting on the shaft D and the load torque M fz The dynamic balance differential equation is expressed as follows: In the formula, ω is the motor rotation angular velocity; J is the motor moment of inertia, and is expressed as follows: In the formula, m is the mass of the rotating body; ρ is the radius of gyration; D is the diameter of gyration, or the inertia diameter; G is the weight of the rotating body; g is the acceleration due to gravity; The hydraulic cylinder adopts a nonlinear system, and the equation describing the hydrodynamics of the hydraulic fluid is expressed as follows: Q = A·x + C t (P1 - P2) Where Q is the flow rate into the hydraulic cylinder; A is the piston area; x is the piston displacement; C t is the leakage coefficient; P1 and P2 are the pressures at the input and output of the hydraulic cylinder, respectively; The servo valve flow equation is expressed as follows: where K q is the flow magnification factor; u is the control voltage; P s is the oil supply pressure; The piston motion equation is expressed as follows: In the formula, x is the piston displacement; m is the load mass; b is the damping coefficient; k is the equivalent stiffness; A·P1 is the driving force provided by the hydraulic cylinder.

3. The thickness detection and optimization method for a hot tandem rolling mill based on double closed-loop feedback control according to claim 1, characterized in that, In the said Step 2), the transfer function of the double-closed-loop speed control system of the drive motor is a second-order differential equation, and the dynamic regulation of the speed is realized through a PID controller, and is expressed as follows: where R S is the armature circuit resistance; L is the armature circuit inductance; C e is the electromotive force coefficient; C m represents the electromagnetic torque generated by unit current; M fz is the load torque; M D is the motor torque; n(t) is the rotational speed.

4. The thickness detection and optimization method for a hot strip mill based on double closed-loop feedback control according to claim 1, characterized in that, In the said Step 3), the hydraulic cylinder position closed-loop control system uses an electro-hydraulic servo valve for control, and its open-loop transfer function is expressed as follows: Where, K p is the regulator proportionality coefficient; G a (s) is the lead-lag link; K2 is the servo valve amplifier coefficient; G sv (s) is the electro-hydraulic servo valve transfer function; G r (s) is the transfer function of the hydraulic cylinder body, K5 is the displacement sensor coefficient; K τ is the integral constant; K2 is the servo amplifier coefficient; K V is the servo valve flow gain; ξ V is the servo damping coefficient; ω V is the undamped natural oscillation frequency of the servo valve; ξ h is the damping ratio of the hydraulic cylinder; ω h is the natural frequency of the hydraulic cylinder; A P is the effective area of the hydraulic cylinder piston; K ce is the flow-pressure coefficient; K is the combined spring stiffness of the load; K5 is the displacement sensor conversion coefficient; s is the complex variable.

5. The thickness detection and optimization method for hot tandem rolling mill based on double closed-loop feedback control according to claim 1, characterized in that In the said hydraulic cylinder position closed-loop control system, when a step signal simulating the rolling position is input, after the feedback of the output position height and signal amplification, through the electro-hydraulic servo valve, subtracting the loss transmitted by the hydraulic pipe, the command is sent to the hydraulic cylinder and its position sensor, and then the hydraulic cylinder position height is output to realize the change of the rolling pressure, and then the thickness of the passing strip is changed.

6. The thickness detection and optimization method for a hot strip mill based on double closed-loop feedback control according to claim 1 or 4 or 5, characterized in that, In the said Step 3), the thickness transfer error between rolling stands is corrected in combination with the thickness delay correction system, and the thickness change delay t0 is expressed as follows: In the formula, l0 is the distance between rolling stands; v0 is the strip transmission speed.

7. According to claim 1 or the thickness detection and optimization method of the hot continuous rolling mill based on double closed-loop feedback control, characterized in that, The strip thickness is corrected by comparing the theoretical calculated value of the strip exit thickness with the initial strip thickness and the thickness change delay, and then the true value of the strip thickness is calculated. The specific process is expressed as follows: h2 = h1 - (h0 - t0) Wherein, h0 is the initial thickness of the steel plate; h1 is the theoretically calculated value of the outlet thickness of the steel plate; h2 is the actual value of the steel plate thickness; and t0 is the time delay of thickness change.

8. According to claim 1 or the hot tandem rolling mill thickness detection and optimization method based on double closed-loop feedback control, characterized in that, In step 4), the temperature drop coefficient K is used T to correct the radiative temperature drop, and the corrected formula is expressed as follows: where σ is the Boltzmann constant; ε is the emissivity; γ is the density of the rolled piece; T is the absolute temperature of the rolled piece; C p is the specific heat capacity of the rolled piece; T0 is the initial temperature; h is the thickness of the rolled piece; ΔL is the stand spacing; v is the transmission speed of the steel plate.

9. According to claim 1 or 8 or the thickness detection and optimization method of the hot continuous rolling mill based on double closed-loop feedback control, characterized in that, By calculating the radiation temperature drop, the influence law of strip thickness change on the radiation temperature drop is analyzed as follows: when the steel plate thickness decreases, the required rolling force increases, and the driving speed of the steel plate decreases, which in turn increases the radiation temperature drop during the transmission of the steel plate, thereby providing a reference for the selection of parameters such as rolling speed and final rolling thickness.

10. The method according to claim 1, characterized in that, For the step 5), the control algorithm is as follows: Under the given steel plate outlet thickness command, read the steel plate outlet thickness and driving speed values at the previous moment, calculate the measured value of the steel plate thickness, and obtain the error by subtracting the thickness command; input the error signal into the electro-hydraulic servo valve to control the valve opening, change the rolling force of the hydraulic cylinder, and then change the outlet thickness; perform speed control on the drive motor, and jointly transmit the motor speed and the rolling force of the hydraulic cylinder to the rolling mill, and calculate and output the new outlet thickness and the steel plate transmission speed; wherein, the steel plate outlet thickness command is corrected by the thickness delay correction system.

Images