A dynamic PID sheet straightening method based on the change of yield strength

Abstract

The present invention discloses a dynamic PID sheet straightening method based on the change of yield strength. The method includes: determining the yield strength of the sheet at the initial temperature; calculating the predicted straightening force of each straightening roll according to the yield strength; obtaining the measured straightening force of each straightening roll; using the numerical approximation method to determine the yield strength error value Δσbefore, the yield strength error value Δσmiddle, and the yield strength error value Δσafter; determining the parameters of the PID controller based on the yield strength error value Δσbefore, the yield strength error value Δσmiddle, and the yield strength error value Δσafter; calculating the target reduction amount of the corresponding straightening roll based on the yield strength error value Δσmiddle and the yield strength at the initial temperature; and adjusting the measured reduction amount of the current straightening roll by using the PID controller with the determined parameters based on the target reduction amount. The present invention can dynamically adjust the straightening reduction amount of each straightening roll by using the PID method according to the change of yield strength during the straightening process.

Description

Technical Field

[0001] The present invention relates to the technical field of plate straightening, and particularly to a dynamic PID plate straightening method based on the change of yield strength. Background Art

[0002] For plates at a relatively high temperature, due to various reasons during processing, transportation, and cooling, heat loss will occur, resulting in temperature changes in different parts of the plate, which causes changes in key parameters of the plate such as yield strength, and further leads to changes in straightening force. Usually, when calculating the straightening force, the plate is regarded as a whole, and a unified yield strength value is used as the yield strength value of the whole plate for calculation to obtain the straightening setting process and predict key force energy parameters such as the straightening force. However, in actual high-temperature plates, there are large temperature changes in parts such as the head and tail, the surface of the plate, and the edge of the plate, resulting in uneven temperature distribution throughout the plate. The above reasons make the yield strength of the plate not a constant value. Especially for the head and tail of high-temperature and thin plates, in addition, there are also large temperature changes during the straightening process of the plate, which all make the yield strength values of each part of the plate change greatly due to temperature changes. If processed at the same temperature, it often causes large calculation errors in the straightening process of the head and tail of the plate and cannot perform targeted straightening on the corresponding parts well. Optimizing the calculation of straightening process parameters for different parts of the plate, calculating the straightening process and straightening force using different yield strength values, and considering the constantly changing position of the plate during the straightening process, and further considering the past, current, and future trends of the change of its key parameters, can make the adjustment of the plate straightening process more accurate and with higher precision. Summary of the Invention

[0003] Based on this, the purpose of the present invention is to provide a dynamic PID plate straightening method based on the change of yield strength, which dynamically adjusts the straightening reduction amount of each straightening roll by using the PID method according to the change of yield strength during the straightening process.

[0004] To achieve the above purpose, the present invention provides the following solution:

[0005] A dynamic PID plate straightening method based on the change of yield strength, comprising:

[0006] Determine the yield strength of the plate at the initial temperature;

[0007] Calculate the predicted straightening force of each straightening roll according to the yield strength at the initial temperature;

[0008] Obtain the measured straightening force of each straightening roll;

[0009] According to the error between the predicted straightening force and the measured straightening force of the previous straightening roll, use the numerical approximation method to determine the yield strength error value Δσ 前 ;

[0010] According to the error between the predicted straightening force and the measured straightening force of the current straightening roll, the yield strength error value Δσ is determined by the numerical approximation method 中 ;

[0011] According to the error between the predicted straightening force and the measured straightening force of the subsequent straightening roll, the yield strength error value Δσ is determined by the numerical approximation method 后 ;

[0012] Based on the yield strength error value Δσ 前 、yield strength error value Δσ 中 and yield strength error value Δσ 后 , determine the parameters of the PID controller;

[0013] Based on the yield strength error value Δσ 中 and the yield strength at the initial temperature, calculate the target reduction of the corresponding straightening roll;

[0014] Based on the target reduction, use the PID controller with determined parameters to adjust the measured reduction of the current straightening roll.

[0015] Optionally, the calculation of the predicted straightening force of each straightening roll according to the yield strength at the initial temperature specifically includes:

[0016] Calculate the reduction of each straightening roll according to the yield strength at the initial temperature;

[0017] Calculate the change amount of the curvature ratio of each straightening roll according to the reduction;

[0018] Calculate the elastic bending moment of each straightening roll according to the change amount of the curvature ratio;

[0019] Calculate the predicted straightening force of each straightening roll according to the elastic bending moment.

[0020] Optionally, the determination of the parameters of the PID controller based on the yield strength error value Δσ 前 、yield strength error value Δσ 中 and yield strength error value Δσ 后 specifically includes:

[0021] The parameter D of the PID controller = Δσ 前 / σ0, P = Δσ 中 / σ0, I = Δσ 后 / σ0; where σ0 represents the yield strength of the sheet at the initial temperature.

[0022] Optionally, the calculation of the target reduction of the corresponding straightening roll based on the yield strength error value Δσ 中 and the yield strength at the initial temperature specifically includes:

[0023] Based on the yield strength error value Δσ 中 and the yield strength at the initial temperature to determine the actual yield strength;

[0024] Calculate the target reduction of the current straightening roll based on the actual yield strength.

[0025] According to the specific embodiments provided by the present invention, the following technical effects are disclosed:

[0026] The present invention observes the change of the actual yield strength of the plate to be straightened according to the measured straightening force of each roll during the straightening process, uses a PID controller to continuously reduce the error value between the original yield strength and the actual yield strength, and updates the reduction of each straightening roll according to the found actual yield strength value, so as to realize the dynamic adjustment of the straightening reduction of each straightening roll according to the change of the yield strength during the straightening process by using the PID method. Brief Description of the Drawings

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0028] Figure 1 It is a flowchart of the dynamic PID plate straightening method based on the change of yield strength provided by the present invention;

[0029] Figure 2 It is a process diagram of the plate straightening provided by the present invention;

[0030] Figure 3 It is a schematic diagram of the reduction adjustment using a PID controller provided by the present invention. Detailed Embodiments

[0031] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the protection scope of the present invention.

[0032] The purpose of the present invention is to provide a dynamic PID plate straightening method based on the change of yield strength, which can dynamically adjust the dynamic high-precision straightening of the straightening process of each straightening roll according to the change of yield strength.

[0033] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] As Figure 1 shown, the dynamic PID plate straightening method based on the change of yield strength provided by the present invention includes the following steps:

[0035] Step 101: Determine the yield strength of the plate at the initial temperature.

[0036] Use a sensor to transmit the current temperature value of the plate back, and determine the yield strength value in the knowledge base according to the transmitted temperature.

[0037] Step 102: Calculate the predicted straightening force of each straightening roll according to the yield strength at the initial temperature.

[0038] (1) Calculate the reduction

[0039] Divide the plate evenly into multiple segments. In this embodiment, it is divided into 11 segments. Due to reasons such as temperature, the distribution of the plate is uneven, resulting in different yield strength values for each segment. During the straightening process, first calculate according to the yield strength value of the first segment to obtain the reduction of the first straightening roll. During the straightening of the plate, the reduction decreases linearly. When reaching the exit roll, the reduction is the normal value. The reduction of the remaining straightening rolls is calculated according to the reduction of the second straightening roll.

[0040] Elastic limit curvature: where T represents the roll pitch, ρ t represents the elastic limit curvature, σ s represents the yield strength, h represents the plate thickness, and E represents the elastic modulus.

[0041] Calculate the reduction of the second straightening roll according to this formula: During the straightening of the plate, the reduction decreases linearly. When reaching the exit roll, the reduction is the normal value. The calculation formula for the reduction of the remaining straightening rolls:

[0042] Upper roll system:

[0043] Lower roll system:

[0044] (2) Calculate the change amount of the curvature ratio of

[0045] Calculate the reverse bending curvature of the first straightening roll according to the reduction. Calculate the value of the original curvature according to the reverse bending curvature of the first roll straightening. Calculate the change amount of the curvature ratio according to the value of the original curvature. The calculation formula is as follows:

[0046] Anti-bending rate at the i-th straightening roll: where T represents the roll pitch;

[0047] Original residual curvature at the i-th straightening roll:

[0048]

[0049] Change in curvature ratio of the second roll:

[0050] Change in curvature ratio of the remaining straightening rolls:

[0051]

[0052] where ρ t represents the elastic limit curvature, σ s represents the yield strength, h represents the plate thickness, E represents the elastic modulus, S i represents the reduction of the i-th straightening roll, and T represents the roll pitch.

[0053] (3) Calculate the elastic bending moment M i .

[0054] Calculate according to the value of the change in curvature ratio to obtain the elastic bending moment of the first roll. The calculation formula is as follows:

[0055]

[0056] where Mt represents the limit value of the elastic bending moment, w represents the plate width, h represents the plate thickness, and σ s represents the yield strength.

[0057]

[0058] where M i represents the bending moment of the i-th roll, represents the change in curvature ratio of the i-th roll.

[0059] (4) Calculate the predicted straightening force of the straightening roll

[0060]

[0061]

[0062]

[0063] ......

[0065]

[0066]

[0067] Among them, M i represents the bending moment of the i-th straightening roll, and F i represents the predicted straightening force of the i-th straightening roll.

[0068] Step 103: Obtain the measured straightening force of each straightening roll.

[0069] Step 104: According to the error between the predicted straightening force and the measured straightening force of the previous straightening roll, use the numerical approximation method to determine the yield strength error value Δσ 前 .

[0070] Step 105: According to the error between the predicted straightening force and the measured straightening force of the current straightening roll, use the numerical approximation method to determine the yield strength error value Δσ 中 .

[0071] Step 106: According to the error between the predicted straightening force and the measured straightening force of the next straightening roll, use the numerical approximation method to determine the yield strength error value Δσ 后 .

[0072] The specific processes of Steps 104 - 106 are as follows:

[0073] Compare the calculated predicted straightening force F i with the measured straightening force F i ' to obtain an error value, ΔF = F i ' - F i . If ΔF > 0, it indicates that the value of the measured straightening force is larger than the value of the predicted straightening force, then the value of the yield strength is larger than the original yield strength value, and adjustment is required. Based on this error value, perform backward deduction. Using the numerical approximation method, the yield strength is incremented by 0.00001 MPa each time. Each time an adjustment is made, a value of the yield strength is obtained, and a value of the straightening force is calculated and compared with the measured straightening force F i ' until the error between the calculated straightening force value continuously adjusted according to the change of the yield strength and the measured straightening force value is less than 1%, thereby obtaining the true value σ' of the yield strength, and the predicted yield strength error value Δσ = σ' - σ. If ΔF < 0, it indicates that the value of the measured straightening force is smaller than the value of the predicted straightening force, then the value of the yield strength is smaller than the original yield strength value. Using the numerical approximation method, the yield strength is decremented by 0.00001 MPa each time. For each value of the yield strength, a value of the straightening force is calculated until the error between the predicted value and the measured value of the straightening force is less than 1%. Obtain the true true value σ' of the yield strength and the error value Δσ.

[0074] Step 107: Based on the yield strength error value Δσ 前 , the yield strength error value Δσ 中 and the yield strength error value Δσ 后, determine the parameters of the PID controller.

[0075] It is assumed that the roller straightening machine has n rollers. If the current roller is not the 1st roller and the Nth roller, then there must be front and rear rollers for any roller. According to the yield strength error value Δσ 前 , Δσ 中 , Δσ 后 , determine the PID controller parameters, D = Δσ 前 / σ0, P = Δσ 中 / σ0, I = Δσ 后 / σ0, where σ0 represents the yield strength of the sheet at the initial temperature.

[0076] Step 108: Calculate the target reduction of the corresponding straightening roller based on the yield strength error value Δσ 中 and the yield strength at the initial temperature. Specifically, it includes: determining the actual yield strength based on the yield strength error value Δσ 中 and the yield strength at the initial temperature; calculating the target reduction of the current straightening roller based on the actual yield strength.

[0077] Step 109: Based on the target reduction, use the PID controller with determined parameters to adjust the measured reduction of the current straightening roller.

[0078] As Figure 3 shown, according to the constructed PID controller, with the set parameter K Pi , default value = 1, control the reduction of the current roller, and realize the closed-loop control of the reduction amount by dynamically adjusting the PID parameters according to the change of the yield strength. The input of the closed-loop control is the target reduction amount S 0i , and the output is the measured reduction amount S 1i , and the feedback error ΔS i = S 0i -S 1i .

[0079] Since there is no straightening force on the 1st roller and the nth roller, the default straightening force is equal to 0, and the change amount of the straightening force is equal to 0. Repeat the above steps for the straightening rollers except the 1st roller and the nth roller until the sheet is straightened. Figure 2 This is the process diagram of sheet straightening provided by the present invention. F2, F3, and F4 are the predicted straightening forces of the second, third, and fourth straightening rollers, F2', F3', and F4' are the measured straightening forces of the second, third, and fourth straightening rollers, and ΔF is the error between the predicted straightening force and the measured straightening force.

[0080] The present invention observes the change in the actual yield strength of the sheet to be straightened based on the measured straightening force of each roll during the straightening process, and sets the parameters of the PID controller according to the yield strength change rates at the front, middle, and rear, thereby considering the influence of the current, past, and future changes in the yield strength on the straightening process, continuously reducing the reduction error caused by the error value between the original yield strength and the actual yield strength, updating the reduction process of each roll based on the found yield strength value, and achieving dynamic high-precision straightening by dynamically adjusting the straightening process of each straightening roll according to the change in the yield strength.

[0081] The various embodiments in this specification are described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. For the same and similar parts among the various embodiments, reference can be made to each other. For the system disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and reference can be made to the description in the method part for the relevant parts.

[0082] Specific examples are used in this article to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea; at the same time, for those of ordinary skill in the art, based on the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A dynamic PID sheet straightening method based on the change of yield strength, characterized in that, Including: Determine the yield strength of the sheet at the initial temperature; Calculate the predicted straightening force of each straightening roll according to the yield strength at the initial temperature; Obtain the measured straightening force of each straightening roll; According to the error between the predicted straightening force and the measured straightening force of the previous straightening roll, the yield strength error value Δσ is determined by the numerical approximation method 前 ; According to the error between the predicted straightening force and the measured straightening force of the current straightening roll, the yield strength error value Δσ is determined by the numerical approximation method 中 ; According to the error between the predicted straightening force and the measured straightening force of the subsequent straightening roll, the yield strength error value Δσ is determined by the numerical approximation method 后 ; Based on the yield strength error value Δσ 前 , the yield strength error value Δσ 中 and the yield strength error value Δσ 后 , determine the parameters of the PID controller; Based on the yield strength error value Δσ 中 and calculate the target reduction of the corresponding straightening roll based on the yield strength at the initial temperature; Based on the target reduction, use the PID controller after determining the parameters to adjust the measured reduction of the current straightening roll.

2. The dynamic PID plate straightening method based on the change of yield strength according to claim 1, wherein, The calculating the predicted straightening force of each straightening roll according to the yield strength at the initial temperature specifically includes: Calculate the reduction of each straightening roll according to the yield strength at the initial temperature; Calculate the change amount of the curvature ratio of each straightening roll according to the reduction; Calculate the elastic bending moment of each straightening roll according to the change amount of the curvature ratio; Calculate the predicted straightening force of each straightening roll according to the elastic bending moment.

3. The dynamic PID sheet straightening method based on the change of yield strength according to claim 1, characterized in that Based on the yield strength error value Δσ 前 , the yield strength error value Δσ 中 and the yield strength error value Δσ 后 , determine the parameters of the PID controller, specifically including: The parameters of the PID controller are D = Δσ 前 / σ0, P = Δσ 中 / σ0, I = Δσ 后 / σ0; where σ0 represents the yield strength of the sheet at the initial temperature.

4. The dynamic PID sheet straightening method based on the change of yield strength according to claim 1, wherein Based on the yield strength error value Δσ 中 Calculating the target reduction of the straightening roll corresponding to the yield strength at the initial temperature, specifically including: Determine the actual yield strength based on the yield strength error value Δσ 中 and the yield strength at the initial temperature; Calculate the target reduction of the current straightening roll based on the actual yield strength.

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