Tension self-adaptive blister double-sided coating system and method

Abstract

The present application relates to the technical field of plastic uptake forming, and discloses a tension self-adaptive plastic uptake double-sided coating system and method, aiming to solve the problem of high waste rate of plastic uptake products caused by transverse warping, difficult elimination of residual stress and large tension fluctuation after double-sided coating and drying of the sheet in the existing PLA double-sided coating production line. After double-sided coating and drying, the present application collects the left, middle and right height data of the sheet through three laser displacement sensors and filters the data, calculates the transverse warping curvature, establishes a linear mapping relationship between the curvature and the roll gap of the flattening roller through offline calibration, calculates the target roll gap in real time and drives the flattening roller to apply reverse bending to eliminate residual stress, and synchronously calculates the roll gap change rate to compensate the traction motor speed in a feedforward manner and suppress the tension fluctuation. The present application has a lower response time delay, a low implementation cost, reduced curvature and waste rate after flattening, controllable tension fluctuation and adaptability to high-speed stable production.

Description

Technical Field

[0001] This invention relates to the field of vacuum forming technology, and in particular to a tension-adaptive vacuum forming double-sided coating system and method. Background Technology

[0002] The biodegradable PLA double-sided coated blister packaging continuous production line is a mainstream green production line in the food packaging industry. The conventional process includes unwinding, inner surface anti-fog coating, drying at 55℃, outer surface heat-sealing coating, drying at 70℃, preheating and softening, blister forming, and die cutting. The substrate is PLA extruded sheet with a width of 650mm and a thickness of 0.45±0.05mm, and the standard production speed reaches 25m / min. After the PLA sheet is double-sided coated and dried, due to the inherent differences in the thickness of the inner and outer coatings and the curing shrinkage rate, the sheet will form a transverse C-shaped warping. In addition, elastic residual stress will remain inside the sheet during the coating curing process. This residual stress will be rapidly released during preheating and softening, which will aggravate the warping of the sheet and directly cause quality defects such as bottom warping, uneven wall thickness, and excessive thinning of the edges in the blister products.

[0003] Existing technologies mainly employ four methods to alleviate the above problems: First, adjusting the longitudinal tension of the coating section, using the Poisson effect generated by longitudinal stretching to offset some of the transverse warping. However, excessive tension can easily cause sheet necking and edge thinning, and cannot eliminate the elastic stress formed by coating curing, which will still be released after preheating. Second, adjusting the drying temperature in stages, reducing the shrinkage difference by lowering the drying temperature on the thick coating side. However, the drying temperature is limited by the coating curing index, the adjustment range is narrow, and the equipment has a large heat capacity and slow response, making it unable to match the dynamic fluctuations of incoming materials. Third, applying strong pressure in the vacuum forming mold, forcibly flattening the warped sheet by increasing the clamping force and vacuum degree, which easily generates stress lines on the surface of the product and can easily cause excessive thinning of thin sheets less than 0.5mm. Fourth, manual sampling compensation, taking samples every 30 minutes to measure the warping height and manually adjusting the coating gap. This method has strong lag, the effect depends on the operator's experience, and the production quality fluctuates significantly between different shifts.

[0004] Existing technologies all involve indirect control during the stress generation stage or passive treatment after stress release. They cannot actively eliminate residual stress inside the sheet before thermoforming preheating. At the same time, the leveling action is prone to causing sudden changes in longitudinal tension, which further deteriorates the product quality. Ultimately, this leads to a high warping scrap rate, poor product consistency, and high production costs under high-speed production conditions, making it difficult to meet the needs of large-scale and stable production.

[0005] Therefore, there is an urgent need for a tension-adaptive thermoforming double-sided coating system and method to solve the above problems. Summary of the Invention

[0006] The purpose of this invention is to provide a tension-adaptive thermoforming double-sided coating method, comprising the following steps: After the double-sided coating drying section, multiple displacement sensors are arranged along the width of the sheet to collect height data at different lateral positions of the sheet. The multiple height values ​​collected by each sensor are then filtered to obtain representative height values ​​for each position. The lateral warpage characteristic of the sheet is calculated based on the multiple height representative values; A mapping relationship between the lateral warping characteristic and the target reduction of the leveling roll is established in advance through offline calibration, and the mapping parameters are stored in the controller. During continuous production, each control cycle calculates the current target reduction in real time according to the mapping relationship based on the currently calculated lateral warping characteristic. The drive actuator moves the movable roller of the leveling roller to the position specified by the target reduction amount, and applies a reverse bending force to the sheet material that is opposite to the original warping direction. The rate of change of the target pressure is calculated in real time, and a feedforward compensation amount is superimposed on the speed command of the front-end traction motor according to the rate of change. The feedforward compensation amount is negatively correlated with the rate of change.

[0007] Furthermore, the present invention also discloses a tension-adaptive thermoforming double-sided coating system, comprising: The acquisition module is used to arrange multiple displacement sensors along the width direction of the sheet after the double-sided coating drying section, collect height data at different lateral positions of the sheet, and filter the multiple height values ​​collected by each sensor to obtain the representative height value at each position. The first calculation module is used to calculate the lateral warping characteristic of the sheet based on the multiple height representative values; The second calculation module is used to establish a mapping relationship between the lateral warping feature and the target reduction of the leveling roll in advance through offline calibration, and store the mapping parameters in the controller. During continuous production, each control cycle calculates the current target reduction in real time according to the mapping relationship based on the currently calculated lateral warping feature. The adjustment module is used to drive the actuator to move the movable roller of the straightening roller to the position specified by the target reduction amount, and apply a reverse bending force to the sheet material that is opposite to the original warping direction. The compensation module is used to calculate the rate of change of the target pressure in real time, and to add a feedforward compensation amount to the speed command of the front-end traction motor according to the rate of change. The feedforward compensation amount is negatively correlated with the rate of change.

[0008] Furthermore, the compensation module includes: The calculation unit is used to read the final target reduction amount of the current cycle and the final target reduction amount of the previous cycle in each control cycle, and calculate the rate of change of the reduction amount; The adjustment unit is used to calculate the tension feedforward compensation amount based on the calculated rate of change. The compensation amount is equal to the negative preset compensation coefficient multiplied by the rate of change. The preset compensation coefficient is determined by a step test. During the debugging phase, a step pressure command is applied to the leveling roller, the longitudinal tension fluctuation under the speed command of the front traction motor is measured, and the compensation coefficient is adjusted to minimize the peak value of the fluctuation. The sending unit is used to read the original main speed command of the production line, add the feedforward compensation amount to the main speed command to obtain the final speed command, and send it to the driver of the unwinding traction motor. This addition is a unidirectional instantaneous addition and does not change the parameters of the leveling roll control ring. The output unit is used to perform low-pass filtering on the feedforward compensation amount. The filtered compensation amount is then superimposed, and the final output speed command is simultaneously affected by the slow correction effect of the original floating roller regulator, together maintaining the longitudinal tension stable within the preset range.

[0009] This application also provides a computer device, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps of the above-described tension adaptive vacuum forming double-sided coating method.

[0010] This application also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the above-described tension-adaptive thermoforming double-sided coating method.

[0011] The beneficial effects of this application are as follows: This invention breaks down data silos between systems by constructing a unified real-time data warehouse, enabling seamless real-time data sharing and providing accurate data support for subsequent scheduling. Machine learning predicts palletizing table load and generates priority task sequences based on sorting plans, avoiding situations where vehicles are needed but not available, or vehicles are available but not loaded, thus improving task foresight. The scheduling algorithm considers the structure of the automated freight station, optimizing task allocation and paths through multiple objectives, reducing the total empty driving distance of TV vehicles and task delays, and improving resource utilization. Real-time instruction distribution and status feedback enable controllable task execution and visualized traffic within the station, ensuring effective scheduling. Closed-loop control dynamically adjusts parameters, triggering rescheduling for significant deviations, continuously adapting to dynamic changes in the freight station, ultimately improving TV vehicle scheduling efficiency and optimizing key indicators such as empty driving rate and on-time performance. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of a method flow proposed in an embodiment of this application.

[0013] Figure 2 This is a schematic diagram of the system structure proposed in an embodiment of the present invention.

[0014] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0015] It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0016] like Figure 1 As shown, this application provides a tension-adaptive thermoforming double-sided coating method, including the following steps: S1: After the double-sided coating drying section, three laser displacement sensors are arranged along the width of the sheet to collect the raw height data at three locations: near the left edge, near the center line, and near the right edge of the sheet. The multiple height values ​​collected by each sensor are then filtered by removing extreme values ​​and averaging to obtain three representative height values, which are recorded as the left height value, the center height value, and the right height value, respectively. S2: Calculate the lateral warping curvature of the sheet based on the left height value, center height value and right height value. The specific calculation method is as follows: First, calculate the difference between the left height value and the center height value as the left relative height difference, then calculate the difference between the right height value and the center height value as the right relative height difference, then add the left relative height difference and the right relative height difference together, multiply by 4, and then divide by the square of the distance between the two laser displacement sensors. The result is the lateral warping curvature. S3: A linear mapping relationship between the lateral warping curvature and the target reduction of the leveling roll is established in advance through offline calibration. That is, the target reduction is equal to the proportional coefficient multiplied by the lateral warping curvature plus the constant offset. The proportional coefficient and constant offset obtained by calibration are stored in the controller. In the continuous production process, each control cycle calculates the current target reduction in real time according to the lateral warping curvature calculated at the moment and the linear mapping relationship. S4: Drive the servo motor to move the upper roller of the straightening roller to the position specified by the target reduction amount, and apply a reverse bending force to the sheet material through the straightening roller, which is opposite to the original warping direction, thereby eliminating the lateral warping caused by the residual stress inside the sheet material. S5: Calculate the rate of change of the target pressing amount with time in real time, that is, the change range of the target pressing amount per unit time, and add a feedforward compensation amount to the speed command of the front traction motor according to the rate of change. The feedforward compensation amount is equal to the negative preset compensation coefficient multiplied by the rate of change, in order to suppress the longitudinal tension fluctuation caused by the change of the wrap angle of the sheet during the operation of the leveling roller.

[0017] As described in steps S1-S5 above, existing technologies mainly employ four methods to address warping issues: adjusting longitudinal tension, segmented adjustment of drying temperature, strong pressure within the vacuum forming mold, and manual sampling compensation. All of these methods have significant drawbacks. Adjusting longitudinal tension easily leads to sheet necking and edge thinning, and cannot eliminate the elastic stress from curing. Segmented temperature adjustment is limited by coating curing requirements, resulting in slow response and limited effectiveness. Strong pressure within the mold easily generates stress lines and excessive thinning in certain areas, posing a high risk to thin PLA sheets. Manual sampling is severely delayed, relies heavily on experience, and leads to large quality fluctuations. Existing technologies fail to actively eliminate residual stress before preheating and do not solve the tension fluctuation problem caused by leveling, making them unsuitable for the stable production requirements of high-speed production lines. This invention specifically proposes a complete technical solution involving online curvature measurement, offline calibration, precise leveling, and tension feedforward compensation. It proactively intervenes at the source of stress generation while simultaneously achieving adaptive tension adjustment, solving the core problems of slow response, poor performance, and unstable quality in existing technologies.

[0018] This invention proactively eliminates residual lateral warping stress within the sheet by employing a comprehensive, coordinated control process—including online warpage detection, offline linear mapping calibration, precise reverse bending of the leveling roller, and adaptive tension feedforward compensation—after the double-sided coating and drying of the biodegradable PLA sheet and before the thermoforming preheating process begins. Simultaneously, it suppresses longitudinal tension fluctuations caused by the leveling action, allowing the sheet to enter the thermoforming preheating stage in a near-zero stress and tension-stable state. This fundamentally solves the technical problems of warping, uneven wall thickness, and high scrap rates in thermoformed products under traditional processes.

[0019] This invention constructs a collaborative working mechanism for active stress elimination and adaptive tension stabilization based on a closed-loop control logic of perception, mapping, execution, and linkage. First, a three-point laser displacement sensor is used to online sense the lateral warpage curvature of the PLA sheet, accurately quantifying the residual bending moment. Then, offline calibration establishes a linear mapping relationship between curvature and the pressing amount of the leveling roller, achieving a direct conversion from warpage to leveling action. Subsequently, the leveling roller is driven in real time to apply a reverse bending force opposite to the warpage direction, counteracting the residual bending moment inside the sheet. Finally, by calculating the rate of change of pressing amount in real time, a speed feedforward compensation is added to the front-end traction motor to suppress longitudinal tension fluctuations caused by changes in the sheet's wrap angle during leveling. The entire process requires no manual intervention, achieving dynamic adaptive control for warpage elimination and tension stabilization under high-speed production conditions.

[0020] Existing technologies mainly employ four methods to address warping issues: adjusting longitudinal tension, segmented temperature adjustment, in-mold pressure, and manual sampling compensation. All of these methods have significant drawbacks. Adjusting longitudinal tension easily leads to sheet necking and edge thinning, and fails to eliminate elastic stress from curing. Segmented temperature adjustment is limited by coating curing requirements, resulting in slow response and limited effectiveness. In-mold pressure easily generates stress lines and excessive local thinning, posing a high risk to thin PLA sheets. Manual sampling is severely lagging, relies heavily on experience, and leads to large quality fluctuations. Existing technologies fail to proactively eliminate residual stress before preheating and do not solve the tension fluctuation problem caused by leveling, making them unsuitable for the stable production requirements of a 25m / min high-speed production line. This invention proposes a comprehensive technical solution involving online curvature measurement, offline calibration, precise leveling, and tension feedforward compensation. It proactively intervenes at the source of stress generation while simultaneously achieving adaptive tension adjustment, solving the core problems of slow response, poor performance, and unstable quality in existing technologies.

[0021] This invention is applied to a biodegradable PLA double-sided coated blister packaging production line with an operating speed of 25 m / min, a sheet width of 650 mm, and a thickness of 0.45 ± 0.05 mm. After the PLA sheet undergoes double-sided coating (inner surface anti-fog coating, outer surface heat-sealing coating) and segmented drying, the difference in coating thickness and shrinkage rate on both sides causes transverse "C"-shaped warping, storing residual elastic stress internally. In traditional processes, this residual stress is released during preheating and softening, leading to increased sheet warping and defects such as bottom warping, uneven wall thickness, and thinning at the edges after blister forming. Furthermore, the leveling process easily causes longitudinal tension fluctuations, further deteriorating product quality. Therefore, it is essential to actively eliminate residual stress and stabilize tension before preheating.

[0022] In one embodiment, step S1 further includes the following sub-steps: S11: 1.5m behind the exit of the double-sided coating drying section, three laser displacement sensors are installed across the width of the sheet. The first sensor is located 50mm from the left edge of the sheet, the second sensor is located on the center line of the sheet width direction, and the third sensor is located 50mm from the right edge of the sheet. The sampling frequency of each sensor is set to 2kHz, the measurement range is 0-50mm, and the output is a 0-10V analog signal, which is connected to the analog input module of the programmable logic controller. Step S11: 1.5m behind the exit of the double-sided coating drying section, install three Keyence LK-G500 laser displacement sensors spanning the width of the sheet. The three sensors are positioned 50mm from the left edge, 50mm from the center line of the sheet width, and 50mm from the right edge, respectively. The sensor sampling frequency is set to 2kHz, and the measurement range is 0-50mm. The sensor outputs a 0-10V analog signal, which is connected to the analog input module of the programmable logic controller. Taking a 650mm wide PLA sheet as an example, the distance between the left and right sensors is 520mm. The 1.5m installation distance avoids airflow disturbances in the coating drying section, the 50mm edge spacing completely covers the effective width of the sheet, the 2kHz sampling frequency captures minute height fluctuations, and the 0-50mm measurement range adapts to the sheet's warpage height range. These steps, through precise sensor placement and hardware parameter matching, ensure the accuracy of height data acquisition and signal stability. It can achieve fixed-point, high-frequency, and stable acquisition of height at three points along the width of the sheet, providing reliable raw data for subsequent filtering processing.

[0023] S12: Set the control cycle of the programmable logic controller to 50ms. In each control cycle, continuously collect 20 raw height values ​​for each sensor. For the 20 raw height values ​​collected by the left sensor, sort them in ascending order of value, remove the two largest and two smallest values, calculate the arithmetic mean of the remaining 16 values, and use this average value as the representative height value of the left sensor in this cycle. Repeat the same operation for the center sensor and the right sensor to obtain the representative height value of the center and the representative height value of the right sensor, respectively. Step S12 sets the programmable logic controller (PLC) control cycle to 50ms. Within each control cycle, each sensor continuously collects 20 raw height values. After sorting each group of 20 raw height values, the two largest and two smallest values ​​are removed. The arithmetic mean of the remaining 16 valid values ​​is calculated to obtain representative height values ​​for the left, center, and right sides. Continuing with the parameters of this production line, the 50ms control cycle matches the 25m / min production speed, ensuring real-time data processing. The 20 samples per cycle cover one complete sheet vibration cycle. For example, in a certain control cycle, after sorting and removing extreme values ​​from the 20 raw height values ​​collected by the left sensor, the remaining 16 valid values ​​yield a left height value of 2.13mm, effectively eliminating the abnormally high value of 2.8mm and the abnormally low value of 1.2mm caused by instantaneous vibration. This step, through high-frequency sampling and extreme value removal averaging filtering, suppresses instantaneous noise caused by sheet vibration and environmental vibration. Therefore, extreme abnormal data can be filtered out, ensuring that the representative height values ​​accurately reflect the actual height of the sheet and avoiding curvature calculation deviations caused by noise.

[0024] S13: Record the calculated left-side representative height value as the left height value, the center representative height value as the center height value, and the right-side representative height value as the right height value. Store these three height values ​​in the register of the programmable logic controller for use in subsequent curvature calculation steps. At the same time, save the three height values ​​stored in the previous control cycle as historical data for fault diagnosis and data smoothing.

[0025] Step S13 defines the three representative height values ​​(left, center, and right) as left height, center height, and right height, respectively, and stores them in the programmable logic controller (PLC) register. Simultaneously, the height value from the previous control cycle is saved as historical data. Continuing with the previous data, the 2.13mm left height, 2.08mm center height, and 2.11mm right height are stored in the register, along with the corresponding height value from the previous cycle. This enables rapid retrieval and historical tracking of height data. The technical effect is to ensure the continuity of subsequent curvature calculations, provide data support for system fault diagnosis, and avoid direct involvement in the core warp suppression process.

[0026] As described in steps S11-S13 above, in the prior art, sheet height data is mostly collected using single-point sampling or simple arithmetic mean filtering. Single-point sampling is easily affected by sheet shaking and environmental vibration, resulting in poor data stability; simple arithmetic mean filtering cannot remove extreme abnormal data, and its noise suppression effect is limited. Taking the operating conditions of this production line as an example, the curvature calculation error can reach more than 15% under this method, the control accuracy of the leveling roller reduction is insufficient, it cannot adapt to the high-speed production requirements of 25m / min, and it is difficult to effectively solve the problem of lateral warping of PLA sheets after double-sided coating.

[0027] After double-sided coating and drying, PLA sheets experience lateral warping due to differences in coating thickness and shrinkage rate between the inner and outer layers. In actual production, the high-speed operation of the sheet generates continuous small vibrations, and vibrations from surrounding equipment in the coating and drying section also introduce instantaneous noise. If the curvature is calculated directly using the original height data, the curvature result will be distorted, making it impossible to accurately guide the adjustment of the leveling roller's pressure. Consequently, it becomes difficult to eliminate residual stress within the sheet, ultimately resulting in warping, uneven wall thickness, and increased scrap rate in the vacuum-formed products. Therefore, it is essential to accurately collect and noise-reducing the height data to ensure the accuracy of curvature calculation from the source.

[0028] This step, on the continuous production line of biodegradable PLA double-sided coated blister lunch boxes, involves precisely arranging laser displacement sensors, matching hardware and control parameters, and performing extreme value removal and averaging filtering to obtain stable and reliable representative height values ​​at the left, middle, and right of the sheet. This provides low-noise and accurate basic data for subsequent lateral warpage curvature calculation, ensuring that the curvature results accurately reflect the actual warpage state of the sheet.

[0029] In one embodiment, step S2 further includes the following sub-steps: S21: Read the left height value, center height value and right height value of the current control cycle from the register of the programmable logic controller, and calculate the relative height difference between the left measuring point and the center measuring point and the relative height difference between the right measuring point and the center measuring point respectively. The left relative height difference is equal to the left height value minus the center height value, and the right relative height difference is equal to the right height value minus the center height value. The unit of both relative height differences is mm. Step S21 reads the left height, center height, and right height values ​​of the current control cycle from the programmable logic controller register, and calculates the left relative height difference and right relative height difference respectively. The left relative height difference equals the left height value minus the center height value, and the right relative height difference equals the right height value minus the center height value, in mm. Continuing with the previous data, the left height value of the current cycle is 2.13 mm, the center height value is 2.08 mm, and the right height value is 2.11 mm. The calculated left relative height difference is 0.05 mm, and the right relative height difference is 0.03 mm. By converting the three absolute heights into height differences relative to the center, the asymmetry of the sheet's lateral warping is quantified, providing basic difference data for curvature calculation. Standardized differences that can be directly used for curvature calculation can be obtained, eliminating the interference of the overall height offset of the sheet on warping quantification.

[0030] S22: Determine whether the absolute values ​​of the two relative height differences are both less than 5mm. If both conditions are met, the simplified circular arc curvature formula is used for calculation. That is, first add the left relative height difference and the right relative height difference to get the sum of the height differences, then multiply the sum by 4, and then divide by the square of the distance between the left and right sensors. The result is the lateral warping curvature. The formula for calculating the lateral warping curvature is as follows: ; in, , ; Among them, the This indicates the lateral warpage curvature; a positive value indicates the sheet convex towards the operating side, while a negative value indicates it convex towards the other side. Indicates the relative height difference on the left. Indicates the relative height difference on the right. Indicates the left height value. Indicates the right height value. The center height value is represented by , and w represents the distance between the left and right laser displacement sensors. In this embodiment, its value is fixed at 0.52. If the absolute value of any relative height difference is greater than or equal to 5mm, an abnormal alarm is triggered, and the curvature is calculated using the precise three-point circle measurement method. The calculation formula for the precise method is: ; Under normal production conditions, the linear approximation error of the simplified formula is less than 5%, so the simplified formula should be used first. Step S22 is used to determine whether the absolute values ​​of the left and right relative height differences are both less than 5mm. If this condition is met, the simplified circular curvature formula is used for calculation. If the absolute value of any relative height difference is greater than or equal to 5mm, an abnormal alarm is triggered and the precise three-point circular measurement method is used for calculation. Currently, the left and right relative height differences are 0.05mm and 0.03mm respectively, both less than 5mm. The simplified formula is used for calculation, and the curvature is equal to 4×(0.05+0.03)÷520²≈1.0× The calculation method switches according to the degree of warpage. Under normal operating conditions, it balances real-time performance and accuracy, while avoiding calculation failures under abnormal operating conditions. Under normal operating conditions, the simplified formula has a linear approximation error of less than 5%, which is suitable for the real-time requirements of high-speed production at 25m / min. Under abnormal operating conditions, the accurate formula can control the curvature error within 3%, avoiding straightening failure due to excessive warpage.

[0031] S23: Assign a direction sign to the calculated curvature based on the warping direction of the sheet. The specific rule is as follows: when both the left and right height values ​​are greater than the center height value, it indicates that the sheet is convex to the operating side, and the curvature is positive. When both the left and right height values ​​are less than the center height value, it indicates that the sheet is convex to the other side, and the curvature is negative. Store the curvature value with the direction sign in the power-off retention memory of the programmable logic controller, and overwrite the curvature value of the previous control cycle for subsequent steps to call.

[0032] Step S23 determines the warping direction based on the relationship between the left height value, right height value, and center height value, and assigns a positive or negative sign to the curvature. When both the left and right height values ​​are greater than the center height value, the curvature is positive, indicating a convexity towards the operating side. When both the left and right height values ​​are less than the center height value, the curvature is negative, indicating a convexity towards the other side. The signed curvature is stored in the programmable logic controller's power-off retention memory, overwriting the value from the previous cycle. Continuing with the previous data, the left height value of 2.13mm and the right height value of 2.11mm are both greater than the center height value of 2.08mm, indicating that the sheet is convex towards the operating side. The final lateral warping curvature is +1.0 × The positive and negative signs clearly indicate the direction of warping, providing a directional basis for the reverse bending of the leveling roller. The technical effect is to avoid incorrect movement direction of the leveling roller, ensure that the applied reverse bending is opposite to the original warping direction of the sheet, and accurately offset residual stress.

[0033] As described in steps S21-S23 above, this invention is applied to a biodegradable PLA double-sided coated blister food box production line with an operating speed of 25m / min, a width of 650mm, and a thickness of 0.45±0.05mm. After double-sided coating and drying, the lateral warpage height difference of the PLA sheet is usually less than 5mm. However, due to fluctuations in coating amount and uneven drying temperature, abnormal warpage with a height difference greater than or equal to 5mm may occasionally occur. The lateral warpage curvature not only needs to be numerically accurate but also requires a clear warpage direction. If the curvature value error is large or the direction is incorrectly determined, it will cause the leveling roller to bend in the opposite direction, resulting in insufficient or excessive pressing, which will fail to offset the residual stress of the sheet, thereby causing warpage of the blister product, local thinning, and an increase in the scrap rate. Therefore, it is necessary to select an appropriate curvature calculation method according to the degree of warpage and accurately determine the warpage direction.

[0034] Existing technologies use only a single simplified formula to calculate curvature without verifying the warp height difference under specific conditions. When the height difference is greater than or equal to 5mm, the linear error of the simplified formula exceeds 10%, resulting in severely distorted curvature results. Furthermore, existing technologies are vague in determining the warp direction, calculating curvature only based on absolute values ​​and failing to distinguish the warp orientation. This leads to incorrect movement direction of the leveling rollers, exacerbating sheet warping. A targeted technical solution is proposed, featuring condition determination, dual-formula switching, and precise direction assignment. Under normal operating conditions, the simplified formula ensures real-time performance, while under abnormal operating conditions, the precise formula ensures accuracy, simultaneously clarifying the warp direction and resolving the technical problems of insufficient curvature accuracy and missing direction in existing technologies.

[0035] Based on the left height, center height, and right height values ​​obtained from the above steps, the accurate lateral warping curvature with positive and negative signs is obtained through working condition determination, differentiated curvature calculation, and direction assignment. This distinguishes between normal production conditions and abnormal warping conditions, ensuring a balance between accuracy and real-time performance in the curvature results, and providing accurate curvature input data for the subsequent accurate calculation of the target reduction amount of the leveling roller.

[0036] In one embodiment, step S3 further includes the following sub-steps: S31: Perform offline calibration: Prepare 8-10 groups of polylactic acid sheet samples with different degrees of lateral warpage. For each group, first use a coordinate measuring machine to determine its lateral warpage curvature, recording it as the curvature value from group 1 to group n, where n is the total number of samples and not less than 8. Then, sequentially feed each group of samples into the test leveling device, gradually increasing the pressure of the leveling roller from zero, increasing by 0.1 mm each time. After each increase, measure the residual curvature at the sample exit until the absolute value of the exit curvature is less than 0.05. At this point, the sample is considered to be basically flat. The current compression amount is recorded as the optimal compression amount for this group of samples. The curvature values ​​of each group and the corresponding optimal compression amounts are used to form data points. The linear least squares method is used to fit these data points. The straight line relationship obtained by fitting is the linear mapping relationship between curvature and compression amount. The slope of the straight line is the proportional coefficient, and the intercept of the straight line is the constant offset. The calibrated proportional coefficient and constant offset are stored in the power-down retention register of the programmable logic controller. Step S31: Prepare 8-10 sets of PLA sheet samples with different degrees of warpage offline. Measure the transverse warpage curvature of each set of samples. Send the samples into the test leveling device and gradually increase the compression amount by 0.1 mm each time until the absolute value of the exit curvature is less than 0.05. The optimal reduction amount is recorded, and the curvature and reduction amount data are fitted using the linear least squares method to obtain a linear mapping relationship. The proportional coefficient and constant offset are stored in the power-down retention register of the programmable logic controller. Continuing with the production line parameters mentioned earlier, eight sets of samples are selected for calibration, with a curvature range of -1.5 to +1.8. The fitting yielded a proportionality coefficient Kp = 0.82 mm. m and constant offset δ0 = 0.18 mm are stored in the register. The significance of this step is to establish a unique linear mapping adapted to this PLA substrate and coating system, ensuring the accuracy of the curvature-to-indentation conversion. The technical effect is that the goodness of fit of the mapping relationship is R² = 0.97, and the curvature conversion error is less than 4%, providing a precise benchmark for real-time indentation calculation.

[0037] S32: During continuous production, each control cycle reads the currently calculated lateral warp curvature from the memory and calculates the original value of the target reduction amount according to the calibrated linear mapping relationship. That is, the original value of the target reduction amount is equal to the proportional coefficient multiplied by the current curvature plus the constant offset. Then, the original value of the target reduction amount is limited: if the original value is less than 0, the final target reduction amount is set to 0; if the original value is greater than 5mm, the final target reduction amount is set to 5mm; if the original value is between 0 and 5mm, the original value is directly used as the final target reduction amount. The upper limit of 5mm is limited by the mechanical stroke of the leveling roller, and the lower limit of 0 is used to prevent the upper roller from pressing down too much and causing equipment damage. Step S32: During continuous production, the real-time lateral warpage curvature is read for each control cycle. This is then substituted into a linear mapping relationship to calculate the original value of the target reduction. A limiting process is then performed: if the original value is less than 0, it is set to 0; if it is greater than 5mm, it is set to 5mm; otherwise, the value is directly taken to obtain the final target reduction. Continuing with the curvature data from before, the current curvature is +1.0 × Substituting the values ​​into the formula, the original value is 0.82 × 1.0 × +0.18 ≈ 0.18mm, falling within the 0-5mm range, with a final target reduction of 0.18mm. By using a hard-limiting matching mechanism to match the leveling roller's mechanical stroke within 0-5mm, excessive pressure is prevented from damaging the equipment or the sheet. The technical effect is to ensure that the reduction amount is always within the equipment's safe stroke, avoiding mechanical jamming and sheet tearing, and guaranteeing the safe execution of the leveling action.

[0038] S33: Store the calculated final target reduction amount in a dedicated register, and assign the target reduction amount of the current control cycle to the target reduction amount variable of the previous cycle for use in step S5 when calculating the rate of change. If the change in the target reduction amount exceeds 2mm within 3 consecutive control cycles, a rapid change flag is generated. This flag is used to trigger the acceleration response of tension feedforward compensation in step S5.

[0039] Step S33 stores the final target reduction amount into a dedicated register and synchronously updates the target reduction amount variable of the previous cycle. If the target reduction amount changes by more than 2mm within three consecutive control cycles, a rapid change flag is generated. Continuing with the previous data, the target reduction amount for the current cycle is 0.18mm. If the reduction amount abruptly changes from 0.2mm to 2.5mm within three consecutive cycles, with a change exceeding 2mm, the rapid change flag is triggered. This provides a sudden change warning for tension feedforward compensation, enhancing the tension response speed during curvature changes. The technical effect is that it enables tension compensation to respond to drastic changes in reduction amount in advance, suppressing tension fluctuations to within ±3.5%, and avoiding drastic tension fluctuations caused by leveling actions.

[0040] As described in steps S31-S33 above, this invention is applied to a biodegradable PLA double-sided coated blister food box production line with an operating speed of 25m / min, a width of 650mm, and a thickness of 0.45±0.05mm. The lateral warpage curvature of the PLA sheet is linearly related to the amount of pressure applied by the leveling roller. However, this relationship is affected by the characteristics of the PLA substrate and coating system, and requires specific calibration. In actual production, the curvature fluctuates in real time. If the mapping relationship deviates significantly or the amount of pressure is not reasonably limited, it will lead to insufficient pressure to level the warpage, or excessive pressure to damage the sheet and exceed the equipment's stroke. At the same time, the lack of warning when the curvature changes abruptly will cause violent tension fluctuations, affecting production stability.

[0041] Existing technologies rely on manual experience to adjust the reduction amount, lacking a standardized offline calibration process. They rely solely on limited experimental data to roughly correlate curvature and reduction amount, resulting in low accuracy in the linear relationship. Furthermore, they lack a hard limit on the reduction amount and a rapid response trigger mechanism for sudden curvature changes. Taking manual adjustment on this production line as an example, the reduction amount error often exceeds 0.3mm, easily leading to insufficient leveling or excessive pressure, increasing the risk of equipment jamming, and failing to meet the precise leveling requirements of high-speed production.

[0042] This invention establishes a precise linear mapping relationship between the lateral warpage curvature and the target reduction amount of the leveling roller through offline calibration. Then, in continuous production, it calculates the compliant target reduction amount based on the real-time curvature and generates a rapid change indicator, providing precise and safe control commands for the leveling roller's operation, ensuring the accuracy of residual stress elimination in PLA sheets and the safety of equipment operation.

[0043] In one embodiment, step S4 further includes the following sub-steps: S41: Construct a double-roller leveling device. This device is installed 200mm in front of the inlet of the thermoforming preheating section. It consists of a lower fixed roller and an upper movable roller. The upper roller is driven by a servo motor to move the lead screw for lifting and lowering. The stroke range is 0-5mm, the positioning accuracy reaches ±0.02mm, and it is equipped with an absolute encoder to provide real-time feedback on the actual position of the upper roller. The sheet passes around the lower roller and the upper roller in an S-shaped path. The wrap angle between the sheet and the two rollers is 120°. Step S41 involves constructing a double-roller leveling device. The lower roller is fixed, while the upper roller is raised and lowered by a servo motor-driven lead screw with a stroke of 0-5mm and a positioning accuracy of ±0.02mm. An absolute encoder is also included. The device is installed 200mm before the entrance of the vacuum forming preheating section. The PLA sheet wraps around the rollers in an S-shaped path, with a 120° wrap angle between the rollers and the upper roller. Continuing with the production line parameters described earlier, the leveling roller stroke matches the 0-5mm reduction limit of claim 4. The 120° wrap angle ensures that the reverse bending force is applied evenly to the sheet. The absolute encoder provides real-time feedback on the actual position of the upper roller. By building a high-precision, high-stability leveling hardware foundation, uniform application of the reverse bending force and accurate position feedback are ensured. A positioning accuracy of ±0.02mm for the leveling roller can be achieved, providing hardware support for accurately offsetting residual stress. The 120° wrap angle avoids localized stress concentration on the sheet.

[0044] S42: In each control cycle, read the final target pressing amount of the current cycle and the actual position of the upper roller fed back by the encoder from the register, calculate the position deviation, that is, the position deviation is equal to the target pressing amount minus the actual position, use a pure proportional controller to calculate the speed command of the servo motor, the speed command is equal to the proportional gain multiplied by the position deviation, where the proportional gain is 2.0, and then perform amplitude limiting on the speed command: if the speed command is greater than 5mm / s, then the amplitude is limited to 5mm / s; If the speed command is less than -5mm / s, the limit is -5mm / s; If the speed command is within ±5mm / s, it remains unchanged. The purpose of limiting the width is to prevent the upper roller from moving too fast, which could cause mechanical impact or tearing of the sheet. Step S42: In each control cycle, the target pressing amount and the actual position of the upper roller fed back by the encoder are read, the position deviation is calculated, and a pure proportional controller with a proportional gain of 2.0 is used to calculate the servo speed command, which is limited to ±5mm / s. Continuing with the previous data, the current target pressing amount is 0.18mm. If the actual position fed back by the encoder is 0.15mm, the position deviation is 0.03mm, and the calculated speed command is 0.06mm / s. This value is within the ±5mm / s limit range and is directly output. Closed-loop position control reduces the position deviation, and speed limiting suppresses the mechanical impact caused by excessively fast servo movements. It can quickly eliminate position deviation, ensure smooth speed control, avoid sheet tearing or mechanical vibration, and adapt to a high-speed production rhythm of 25m / min.

[0045] S43: The speed command after limiting is sent to the servo driver via analog signal or bus communication. The servo driver controls the motor to move according to the speed command. At the same time, the controller continuously monitors the absolute value of the position deviation. When the absolute value is less than 0.02mm and lasts for more than 3 control cycles, it is considered that the upper roller has reached the target position. At this time, the servo speed command is set to zero and the position is locked, so that the upper roller is maintained at the target pressing amount. Step S43: Continuously monitor the absolute value of the position deviation. When the absolute value is less than 0.02mm and remains so for 3 consecutive control cycles, it is determined that the upper roller has reached the target position. The servo speed command is then set to zero and the position is locked. Continuing with the previous data, the position deviation of 0.03mm is reduced to 0.015mm after 2 cycles of adjustment. After stabilizing for 3 consecutive cycles, the servo motor stops and the upper roller position is locked. This prevents repeated drift of the upper roller position, maintains a stable reverse bending force, and ensures a continuous and stable leveling effect. After the upper roller position is locked, the fluctuation is less than ±0.02mm, ensuring a constant reverse bending amount of the sheet and stably eliminating residual stress.

[0046] S44: During the operation of the leveling roller, the controller collects the current feedback value of the servo motor in real time. If the current feedback value exceeds 1.5 times the rated current of the motor, it is determined that the mechanism has jammed or overloaded. The output of the servo motor is stopped immediately and an audible and visual alarm signal is issued. At the same time, the final target pressing amount of the current cycle is forcibly set to the current actual position of the upper roller to prevent further damage to the equipment.

[0047] Step S44: Real-time acquisition of servo motor current feedback value. When the current exceeds 1.5 times the motor's rated current, it is determined that the mechanism is jammed or overloaded. The servo output is immediately stopped and an audible and visual alarm is triggered. Simultaneously, the target pressing amount is forcibly set to the current actual position of the upper roller. Continuing the previous scenario, if the upper roller encounters a foreign object and becomes stuck during pressing, the motor current rises to 1.6 times the rated value. The machine is immediately stopped, an alarm is triggered, and the current position is locked. Timely identification of equipment abnormalities prevents motor burnout or mechanical damage, ensuring production line safety. It minimizes the risk of equipment failure, reduces downtime for maintenance, and ensures continuous and stable operation of the production line.

[0048] As described in steps S41-S44 above, this invention is applied to a biodegradable PLA double-sided coated blister pack production line with an operating speed of 25 m / min, a width of 650 mm, and a thickness of 0.45 ± 0.05 mm. The leveling device is installed 200 mm before the inlet of the blister preheating section and needs to apply precise reverse bending to the high-speed PLA sheet. In actual production, insufficient positioning accuracy of the leveling roller will lead to deviation in the reverse bending amount, which cannot offset residual stress. The servo motor's excessively fast movement can easily generate mechanical impact, tearing the sheet. The lack of position locking will cause the upper roller to drift, resulting in unstable leveling effect. The lack of overload protection can easily cause the motor to burn out due to jamming, affecting the continuous operation of the production line. The above problems will directly lead to residual sheet warping, a high scrap rate, and even equipment shutdown.

[0049] In existing technologies, leveling rollers mostly employ open-loop servo control, lacking precise closed-loop position feedback. The proportional gain is arbitrarily set, and there are no speed limiting, position locking, or overload protection mechanisms. Taking existing open-loop control as an example, the positioning accuracy of the leveling roller is only ±0.1mm. The unconstrained servo action speed is prone to impact, and the motor is continuously overloaded when jammed. This makes it unsuitable for the precise leveling and safe operation requirements of a 25m / min high-speed production line.

[0050] This invention constructs a high-precision double-roller leveling device and a matching servo closed-loop control strategy. Based on the output target reduction amount, it accurately and safely drives the upper roller of the leveling roller to apply a stable reverse bending force to the PLA sheet, accurately offsetting the residual stress of lateral warping. At the same time, through position locking and overload protection mechanisms, it ensures the stability and reliability of the leveling action and avoids mechanical impact and equipment damage.

[0051] In one embodiment, step S5 further includes the following sub-steps: S51: In each control cycle, read the final target reduction amount of the current cycle and the final target reduction amount of the previous cycle from the memory, calculate the rate of change of the reduction amount. The rate of change is calculated by subtracting the target reduction amount of the previous cycle from the target reduction amount of the current cycle, and then dividing by the length of the control cycle. The length of the control cycle is 0.05s, and the unit of the rate of change is mm / s. When the target reduction amount remains unchanged due to limiting processing or equipment malfunction, the rate of change is automatically zero. Step S51: Within each 50ms control cycle, read the final target reduction amount of the current cycle and the previous cycle, and calculate the rate of change of reduction amount. The formula is: current target reduction amount minus the target reduction amount of the previous cycle, then divided by 0.05s, in mm / s. The rate of change is 0 mm / s when the target reduction amount remains unchanged. Continuing with the previous data, the target reduction amount of the current cycle is 0.18mm, and the target reduction amount of the previous cycle is also 0.18mm, so the calculated rate of change is 0mm / s. If the reduction amount abruptly changes from 0.2mm to 2.2mm for three consecutive cycles, the rate of change is (2.2-0.2)÷0.05=40mm / s. The significance of this step is to accurately quantify the action rate of the leveling roller, providing a direct basis for predicting tension disturbances. It can capture the speed of the leveling action in real time, identify tension disturbance trends in advance, and lay the foundation for rapid compensation.

[0052] S52: Based on the calculated rate of change of the reduction amount, calculate the tension feedforward compensation amount. The compensation amount is equal to the negative preset compensation coefficient multiplied by the rate of change. The preset compensation coefficient is determined by a single step test. The specific test method is as follows: During the equipment debugging stage, manually give the leveling roller a step reduction command of 0.5mm, record the peak value of the longitudinal tension fluctuation of the front-end traction motor under the original speed command. This peak value is measured by the floating roller angular displacement sensor of the production line. Then adjust the value of the compensation coefficient to minimize the peak value of the tension fluctuation. The typical compensation coefficient range is 0.12-0.18, and its unit is (m / min) / (mm / s). The negative sign in the compensation amount indicates that the compensation direction is opposite to the reduction direction. That is, when the reduction amount increases, the rate of change is positive. At this time, the compensation amount is negative, and the traction motor decelerates to offset the increase in tension caused by the increase in the wrap angle. Step S52 involves calculating the tension feedforward compensation amount. The formula is: compensation amount equals a negative preset compensation coefficient multiplied by the rate of change of compression. The preset compensation coefficient is determined through a 0.5mm step test, with a typical value of 0.13 (m / min) / (mm / s). Continuing with the previous data, when the rate of change is 0mm / s, the compensation amount is -0.13×0=0m / s; when the rate of change is 40mm / s, the compensation amount is -0.13×40=-5.2m / min. By establishing a linear relationship between the leveling action rate and the tension compensation amount, the tension fluctuations caused by changes in the wrap angle are counteracted. The direction of the compensation amount is opposite to the direction of the tension disturbance, precisely matching the disturbance amplitude and suppressing sudden tension changes at the source.

[0053] S53: Read the original main speed command of the production line. The main speed command is given by the main control programmable logic controller according to the set production speed, and the unit is m / min. The feedforward compensation is superimposed on the main speed command to obtain the final speed command. That is, the final speed command is equal to the main speed command plus the feedforward compensation. Then, the final speed command is sent to the driver of the unwinding traction motor through analog signal or bus communication. This superposition operation is an instantaneous unidirectional superposition, which does not change the parameters of the leveling roll control loop, and realizes the complete decoupling of leveling control and tension control. Step S53: Read the main speed command of 25 m / min from the production line, add the feedforward compensation to obtain the final speed command, and send it to the unwinding traction motor driver. This is a momentary unidirectional operation without changing the leveling control loop parameters. Continuing with the previous data, when the compensation is 0 m / min, the final speed command is 25 m / min; when the compensation is -5.2 m / min, the final speed command is 19.8 m / min. By fine-tuning the traction motor speed, tension disturbances are directly offset, achieving decoupling between leveling and tension control. The compensation response delay is less than 50 ms, quickly offsetting instantaneous tension fluctuations without affecting the accuracy of the leveling roll reduction adjustment.

[0054] S54: To make the compensation effect smoother and avoid speed jitter caused by calculation noise, a first-order low-pass filter is applied to the calculated feedforward compensation amount. The filtering method is as follows: the current time's filtered compensation amount is equal to the filter coefficient multiplied by the current time's original compensation amount, plus 1 minus the filter coefficient, multiplied by the previous time's filtered compensation amount. The filter coefficient is set to 0.3. The compensation amount after filtering is then superimposed on the main speed command. The final output speed command is simultaneously subject to the slow correction effect of the original production line floating roller proportional integral derivative regulator. The two regulation mechanisms work together to maintain the longitudinal tension stable within ±5% of the set value.

[0055] Step S54: Apply a first-order low-pass filter to the feedforward compensation amount. The filtering formula is: the current filtered compensation amount equals 0.3 multiplied by the current original compensation amount, plus 0.7 multiplied by the previous cycle's filtered compensation amount. This filtered amount is then superimposed onto the main speed command. The final speed command is simultaneously subject to slow correction by the original floating roller PID controller. Continuing with the previous data, the current original compensation amount is -5.2 m / min, and the previous cycle's filtered compensation amount is 0 m / min. The filtered compensation amount is 0.3 × (-5.2) + 0.7 × 0 = -1.56 m / min, and the final speed command is 23.44 m / min. The significance of this step is to filter out the noise in the compensation amount calculation, smooth the traction motor speed output, and avoid secondary tension fluctuations caused by speed jitter. The speed jitter amplitude is reduced to within ±0.2 m / min, and the longitudinal tension is stably controlled within ±5% of the set value, ensuring smooth sheet conveying.

[0056] As described in steps S51-S54 above, this invention is applied to a biodegradable PLA double-sided coated blister packaging production line with an operating speed of 25m / min, a width of 650mm, and a thickness of 0.45±0.05mm. The pressing action of the leveling roller changes the wrap angle between the sheet and the roller surface. When the wrap angle increases, the longitudinal tension increases; when the wrap angle decreases, the longitudinal tension decreases. In actual production, when the leveling roller is adjusted rapidly, the peak tension fluctuation can reach ±12%, exceeding the adjustment range of the original floating roller PID controller. Moreover, the original controller has a lag in response and cannot promptly offset instantaneous tension changes, easily causing uneven sheet stretching and deviation, ultimately leading to dimensional deviations and uneven wall thickness in the blister packaging products, affecting the product qualification rate.

[0057] Existing technology relies solely on the existing floating roller PID regulator on the production line for tension adjustment. There is no feedforward compensation mechanism corresponding to the leveling action. The regulator has a slow response speed and a narrow adjustment bandwidth. It can only suppress slow tension drift and cannot offset the instantaneous tension change caused by the rapid movement of the leveling roller. The tension fluctuation range has been maintained at ±12% for a long time, which is difficult to adapt to the tension stability requirements of high-speed production at 25m / min.

[0058] By calculating the rate of change of the target pressing amount of the leveling roller in real time, generating the tension feedforward compensation amount, superimposing it on the speed command of the traction motor and applying filtering, the longitudinal tension fluctuation caused by the change of the wrap angle of the sheet during the operation of the leveling roller is adaptively offset, ensuring the stability of the longitudinal tension of the biodegradable PLA double-sided coating thermoforming production line, avoiding problems such as sheet deviation and uneven wall thickness of thermoformed products caused by sudden tension changes, and realizing the complete decoupling of leveling control and tension control.

[0059] like Figure 2 As shown, the present invention also discloses a tension-adaptive thermoforming double-sided coating system, comprising: The acquisition module is used to arrange multiple displacement sensors along the width direction of the sheet after the double-sided coating drying section, collect height data at different lateral positions of the sheet, and filter the multiple height values ​​collected by each sensor to obtain the representative height value at each position. The first calculation module is used to calculate the lateral warping characteristic of the sheet based on the multiple height representative values; The second calculation module is used to establish a mapping relationship between the lateral warping feature and the target reduction of the leveling roll in advance through offline calibration, and store the mapping parameters in the controller. During continuous production, each control cycle calculates the current target reduction in real time according to the mapping relationship based on the currently calculated lateral warping feature. The adjustment module is used to drive the actuator to move the movable roller of the straightening roller to the position specified by the target reduction amount, and apply a reverse bending force to the sheet material that is opposite to the original warping direction. The compensation module is used to calculate the rate of change of the target pressure in real time, and to add a feedforward compensation amount to the speed command of the front-end traction motor according to the rate of change. The feedforward compensation amount is negatively correlated with the rate of change.

[0060] In one embodiment, the compensation module includes: The calculation unit is used to read the final target reduction amount of the current cycle and the final target reduction amount of the previous cycle in each control cycle, and calculate the rate of change of the reduction amount; The adjustment unit is used to calculate the tension feedforward compensation amount based on the calculated rate of change. The compensation amount is equal to the negative preset compensation coefficient multiplied by the rate of change. The preset compensation coefficient is determined by a step test. During the debugging phase, a step pressure command is applied to the leveling roller, the longitudinal tension fluctuation under the speed command of the front traction motor is measured, and the compensation coefficient is adjusted to minimize the peak value of the fluctuation. The sending unit is used to read the original main speed command of the production line, add the feedforward compensation amount to the main speed command to obtain the final speed command, and send it to the driver of the unwinding traction motor. This addition is a unidirectional instantaneous addition and does not change the parameters of the leveling roll control ring. The output unit is used to perform low-pass filtering on the feedforward compensation amount. The filtered compensation amount is then superimposed, and the final output speed command is simultaneously affected by the slow correction effect of the original floating roller regulator, together maintaining the longitudinal tension stable within the preset range.

[0061] This application also provides a computer device, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps of the above-described tension adaptive vacuum forming double-sided coating method.

[0062] This application also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the above-described tension-adaptive thermoforming double-sided coating method.

[0063] Those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium. When executed, the computer program can include the processes of the embodiments of the above methods. Any references to memory, storage, databases, or other media used in this application and in the embodiments can include non-volatile and / or volatile memory. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in a variety of forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), dual data rate SDRAM (SSRSDRAM), enhanced SDRAM (ESDRAM), synchronous link DRAM (SLDRAM), RAMbus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM).

[0064] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, apparatus, article, or method that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, apparatus, article, or method. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, apparatus, article, or method that includes that element.

[0065] The above description is merely a preferred embodiment of the present invention and does not limit the scope of this application. Any equivalent results or equivalent process transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the scope of protection of this application.

Claims

1. A tension-adaptive thermoforming double-sided coating method, characterized in that, Includes the following steps: After the double-sided coating drying section, multiple displacement sensors are arranged along the width of the sheet to collect height data at different lateral positions of the sheet. The multiple height values ​​collected by each sensor are then filtered to obtain representative height values ​​for each position. The lateral warpage characteristic of the sheet is calculated based on the multiple height representative values; A mapping relationship between the lateral warping characteristic and the target reduction of the leveling roll is established in advance through offline calibration, and the mapping parameters are stored in the controller. During continuous production, each control cycle calculates the current target reduction in real time according to the mapping relationship based on the currently calculated lateral warping characteristic. The drive actuator moves the movable roller of the leveling roller to the position specified by the target reduction amount, and applies a reverse bending force to the sheet material that is opposite to the original warping direction. The rate of change of the target pressure is calculated in real time, and a feedforward compensation amount is superimposed on the speed command of the front-end traction motor according to the rate of change. The feedforward compensation amount is negatively correlated with the rate of change.

2. The tension-adaptive vacuum forming double-sided coating method according to claim 1, characterized in that, The step of filtering multiple height values ​​collected by each sensor to obtain representative height values ​​for each location specifically includes: A predetermined number of displacement sensors are installed across the width of the sheet at a predetermined distance after the exit of the double-sided coating drying section. Each sensor is located at a different lateral position on the sheet. Each sensor collects height data at a predetermined sampling frequency and outputs a signal to the analog input module of the controller. The controller's control cycle is set to a preset duration. Within each control cycle, a preset number of raw height values ​​are continuously collected from each sensor. For each sensor's raw height value sequence, the values ​​are sorted according to their magnitude, outliers are removed, and the arithmetic mean of the remaining valid values ​​is calculated. This average value is used as the representative height value of the sensor within that cycle. The calculated height values ​​are recorded as the height values ​​of the corresponding lateral positions and stored in the controller's register. At the same time, the height values ​​stored in the previous control cycle are saved as historical data.

3. The tension-adaptive vacuum forming double-sided coating method according to claim 1, characterized in that, The step of calculating the lateral warpage characteristic of the sheet based on the multiple height representative values ​​specifically includes: Read the representative values ​​of each lateral position height in the current control cycle from the register of the controller, and calculate the relative height difference of each side measuring point relative to the center measuring point; Determine whether the relative height difference is within a preset range. If it is, use a simplified algorithm to calculate the lateral warping feature. If not, trigger exception handling and recalculate using a precise algorithm. Assign a direction sign to the calculated transverse warping feature based on the warping direction of the sheet, store the transverse warping feature with the direction sign in the controller, and update the recorded value of the previous cycle.

4. The tension-adaptive vacuum forming double-sided coating method according to claim 1, characterized in that, The step of calculating the current target depressurization amount in real time according to the mapping relationship based on the currently calculated lateral warping feature amount in each control cycle specifically includes: Prepare multiple sets of sheet samples with different degrees of transverse warping, measure the transverse warping characteristic of each set of samples, and then send each set of samples into the test leveling device in sequence. Gradually increase the pressing amount of the moving roller of the leveling roller until the residual warping characteristic at the sample exit is less than the preset flatness threshold. Record the pressing amount at this time as the optimal pressing amount of the set of samples. Combine the transverse warping characteristic of each set with the corresponding optimal pressing amount to form data points, perform linear fitting, and obtain the linear mapping relationship between the transverse warping characteristic and the pressing amount and its mapping parameters. During continuous production, each control cycle reads the currently calculated lateral warping feature, calculates the original value of the target reduction amount according to the linear mapping relationship, and then performs amplitude limiting processing on the original value to limit it within the allowable range of the mechanical stroke of the actuator, thus obtaining the final target reduction amount. The final target reduction is stored in the controller, and the target reduction value of the previous cycle is updated. When the change in the target reduction exceeds the preset mutation threshold in multiple consecutive control cycles, a rapid change flag is generated to trigger the accelerated response of tension feedforward compensation.

5. The tension-adaptive thermoforming double-sided coating method according to claim 1, characterized in that, The step of the drive actuator moving the movable roller of the leveling roller to the position specified by the target reduction amount and applying a reverse bending force to the sheet material in the opposite direction to the original warping direction specifically includes: A double-roller leveling device is constructed and installed at a preset distance in front of the inlet of the thermoforming preheating section. It consists of a fixed roller and a movable roller. The movable roller is driven by a servo motor and is equipped with a position feedback device to provide real-time feedback on the actual position of the movable roller. The sheet passes around the two rollers in an S-shaped path to form a predetermined wrap angle. Within each control cycle, the final target pressing amount and the actual position feedback of the current cycle are read, the position deviation is calculated, the speed command of the servo motor is calculated using a proportional controller, and the speed command is limited. The speed command after the amplitude limit is sent to the servo driver to control the motor movement; when the absolute value of the position deviation is less than the preset positioning accuracy threshold and continues for a preset number of control cycles, it is determined that the moving roller has reached the target position, the speed command is set to zero and the position is locked. During the operation of the leveling roller, the load parameters of the servo motor are monitored in real time. When the parameter exceeds the preset multiple of the rated value, a fault is determined, the motor output is stopped immediately and an alarm is issued. At the same time, the target pressing amount of the current cycle is forcibly set to the current actual position of the moving roller.

6. The tension-adaptive vacuum forming double-sided coating method according to claim 1, characterized in that, The step of calculating the rate of change of the target compression in real time and superimposing a feedforward compensation amount onto the speed command of the front-end traction motor based on the rate of change specifically includes: Within each control cycle, read the final target reduction amount of the current cycle and the final target reduction amount of the previous cycle, and calculate the rate of change of the reduction amount; Based on the calculated rate of change, the tension feedforward compensation is calculated. The compensation is equal to the negative preset compensation coefficient multiplied by the rate of change. The preset compensation coefficient is determined by a step test. During the commissioning phase, a step pressure command is applied to the leveling roller, and the longitudinal tension fluctuation under the speed command of the front traction motor is measured. The compensation coefficient is adjusted to minimize the peak value of the fluctuation. The original main speed command of the production line is read, and the feedforward compensation is superimposed on the main speed command to obtain the final speed command, which is then sent to the driver of the unwinding traction motor. This superposition is a unidirectional instantaneous superposition and does not change the parameters of the leveling roll control ring. The feedforward compensation amount is low-pass filtered, and the filtered compensation amount is then superimposed. The final output speed command is simultaneously affected by the slow correction effect of the original floating roller regulator, together maintaining the longitudinal tension stable within the preset range.

7. A tension-adaptive thermoforming double-sided coating system, characterized in that, include: The acquisition module is used to arrange multiple displacement sensors along the width direction of the sheet after the double-sided coating drying section, collect height data at different lateral positions of the sheet, and filter the multiple height values ​​collected by each sensor to obtain the representative height value at each position. The first calculation module is used to calculate the lateral warping characteristic of the sheet based on the multiple height representative values; The second calculation module is used to establish a mapping relationship between the lateral warping feature and the target reduction of the leveling roll in advance through offline calibration, and store the mapping parameters in the controller. During continuous production, each control cycle calculates the current target reduction in real time according to the mapping relationship based on the currently calculated lateral warping feature. The adjustment module is used to drive the actuator to move the movable roller of the straightening roller to the position specified by the target reduction amount, and apply a reverse bending force to the sheet material that is opposite to the original warping direction. The compensation module is used to calculate the rate of change of the target pressure in real time, and to add a feedforward compensation amount to the speed command of the front-end traction motor according to the rate of change. The feedforward compensation amount is negatively correlated with the rate of change.

8. The tension-adaptive vacuum forming double-sided coating system according to claim 7, characterized in that, The compensation module includes: The calculation unit is used to read the final target reduction amount of the current cycle and the final target reduction amount of the previous cycle in each control cycle, and calculate the rate of change of the reduction amount; The adjustment unit is used to calculate the tension feedforward compensation amount based on the calculated rate of change. The compensation amount is equal to the negative preset compensation coefficient multiplied by the rate of change. The preset compensation coefficient is determined by a step test. During the debugging phase, a step pressure command is applied to the leveling roller, the longitudinal tension fluctuation under the speed command of the front traction motor is measured, and the compensation coefficient is adjusted to minimize the peak value of the fluctuation. The sending unit is used to read the original main speed command of the production line, add the feedforward compensation amount to the main speed command to obtain the final speed command, and send it to the driver of the unwinding traction motor. This addition is a unidirectional instantaneous addition and does not change the parameters of the leveling roll control ring. The output unit is used to perform low-pass filtering on the feedforward compensation amount. The filtered compensation amount is then superimposed, and the final output speed command is simultaneously affected by the slow correction effect of the original floating roller regulator, together maintaining the longitudinal tension stable within the preset range.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1 to 6.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 6.

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