A method for monitoring the thickness of hot melt adhesive coating

Abstract

This application provides a method for monitoring the thickness of hot melt adhesive coating, comprising: constructing a usage scenario stress model based on stress distribution data, inputting the adhesive layer thickness into the usage scenario stress model, outputting the thickness allowance after curing, and generating a thickness allowance adjustment instruction; if the actual thickness of the crease stress concentration area is lower than a preset thickness threshold, dynamically adjusting the spraying parameters according to the thickness difference, spraying the crease stress concentration area with the adjusted spraying parameters to obtain the target adhesive layer thickness distribution; obtaining the adhesive layer cracking risk value corresponding to the target adhesive layer thickness distribution through a preset cracking risk assessment model, if the adhesive layer cracking risk value is lower than a preset risk threshold, generating a target production line parameter adjustment scheme based on the risk assessment result; executing the parameter adjustment scheme, updating the glue gun spraying and curing equipment parameters in real time, and obtaining stable brochure packaging quality.

Description

Technical Field

[0001] This invention relates to the field of information technology, and in particular to a method for monitoring the thickness of hot melt adhesive coating. Background Technology

[0002] The brochure packaging production line is a crucial link in the modern printing and packaging industry. Its core task is to ensure the structural stability and durability of brochures during folding, bonding, and long-term use. The hot melt adhesive application process, as a key step, directly affects the quality of the brochure, especially when users repeatedly flip through it. The adhesive layer must withstand stress changes caused by different opening angles to prevent cracking or delamination. However, existing methods often struggle to accurately adapt to changes in the brochure's folding angle when dynamically adjusting production line parameters, leading to uneven adhesive layer thickness distribution, affecting the reliability of the finished product and the user experience. Particularly when the brochure design adjusts the folding angle, the adhesive layer thickness cannot be dynamically compensated according to the expected stress areas, easily creating weak areas at stress concentration points along the creases. For example, some brochures crack at the creases due to stress concentration when users open them sharply, affecting both aesthetics and functionality. Furthermore, the allowance for the cured adhesive layer thickness is usually based on static experience, lacking accurate prediction of dynamic stress in the usage scenario, resulting in adhesive layers that are too thick or too thin in some areas, increasing material costs or reducing adhesion. If the application amount cannot be accurately predicted and adjusted, the adhesive layer may be too thin in high-stress areas, leading to cracking. For example, when a brochure is folded from 60 degrees to 120 degrees, the adhesive layer thickness at the stress concentration point of the crease needs to be increased, but existing equipment struggles to calculate and implement this change in real time. If the allowance cannot be dynamically optimized based on actual usage scenarios, the adhesive layer may not be able to adapt to stress changes when users repeatedly open the brochure, resulting in quality issues. Therefore, dynamically optimizing the compensating application amount of the adhesive layer in the expected stress area during folding angle adjustments on the production line, and precisely controlling the allowance for thickness at stress concentration points of the crease after curing, becomes a key issue in improving the packaging quality of brochures. Summary of the Invention

[0003] This invention provides a method for monitoring the thickness of hot melt adhesive coating, mainly including:

[0004] Obtain the stress magnitude corresponding to different folding angles of the brochure, and obtain a stress distribution map. Analyze the stress distribution map to determine the stress area, identify the stress magnitude in the stress area, and obtain the location and stress intensity of the stress concentration area of ​​the crease.

[0005] The stress magnitude of the adhesive layer in the target stress area is determined based on the location and stress intensity of the stress concentration area of ​​the crease. The load-bearing capacity of the adhesive layer in the target stress area is analyzed to obtain the stress distribution data of the adhesive layer. The amount of hot melt adhesive compensation is determined based on the obtained stress distribution data of the adhesive layer. The thickness of the adhesive layer is determined based on the amount of hot melt adhesive compensation.

[0006] Based on the stress distribution data, construct a stress model for the application scenario, input the adhesive layer thickness into the stress model for the application scenario, output the thickness allowance after curing, and generate a thickness allowance adjustment instruction.

[0007] The curing time and temperature are adjusted by the thickness reservation adjustment command. At the same time, the surface image of the adhesive layer in the crease area is acquired. The surface image of the adhesive layer in the crease area is processed to obtain the thickness distribution measurement data. The crease stress concentration area is determined based on the thickness distribution measurement data, and the actual thickness of the crease stress concentration area is obtained.

[0008] If the actual thickness of the stress concentration area of ​​the crease is lower than the preset thickness threshold, the spraying parameters are dynamically adjusted according to the thickness difference. The adjusted spraying parameters are then used to spray the stress concentration area of ​​the crease to obtain the target adhesive layer thickness distribution.

[0009] The cracking risk value of the adhesive layer corresponding to the target adhesive layer thickness distribution is obtained through a preset cracking risk assessment model. If the cracking risk value of the adhesive layer is lower than the preset risk threshold, an adjustment plan for the target production line parameters is generated based on the risk assessment results.

[0010] By implementing the parameter adjustment scheme, the parameters of the glue gun spraying and curing equipment are updated in real time to obtain stable brochure packaging quality.

[0011] Furthermore, the process of obtaining the stress magnitude corresponding to different folding angles of the brochure, generating a stress distribution map, analyzing the stress distribution map to determine the stress-bearing areas, identifying the stress magnitude in the stress-bearing areas, and obtaining the location and stress intensity of the stress concentration areas at the creases includes:

[0012] Stress sensors are placed at key folding locations in the brochure to collect stress data within the folding angle range. The stress data is converted into stress values, and the stress values ​​corresponding to each angle are recorded. A two-dimensional stress distribution map is generated based on the stress values, with the horizontal axis representing the folding angle and the vertical axis representing the stress magnitude. A continuous stress variation curve is generated through interpolation. The stress gradient is calculated based on the continuous stress variation curve, and the region where the stress gradient exceeds a threshold is identified as a stress concentration region. For the stress concentration region, the corresponding folding angle range and maximum stress value in the stress distribution map are extracted to determine the location range and stress intensity of the crease stress concentration region.

[0013] Furthermore, the step of determining the magnitude of the adhesive layer stress in the target stress area based on the location and stress intensity of the stress concentration area of ​​the crease, performing load-bearing capacity analysis on the magnitude of the adhesive layer stress in the target stress area to obtain adhesive layer stress distribution data, determining the hot melt adhesive compensation application amount based on the obtained adhesive layer stress distribution data, and determining the adhesive layer thickness based on the hot melt adhesive compensation application amount includes:

[0014] Based on the location and stress intensity of the stress concentration area of ​​the crease, a stress transfer coefficient is calculated, and a stress value of the adhesive layer is generated based on the stress transfer coefficient and the stress intensity. The load-bearing capacity is determined based on the stress value of the adhesive layer, and high-load areas are divided. Mesh cells are generated based on the high-load areas, and the stress balance of each cell is calculated to generate the stress distribution data of the adhesive layer. Based on the maximum stress value in the stress distribution data of the adhesive layer, the hot melt adhesive compensation application amount is calculated. Based on the hot melt adhesive compensation application amount and the area, the application amount per unit area is generated, and the adhesive layer thickness is generated based on the application amount per unit area and the curing shrinkage rate.

[0015] Furthermore, the step of constructing a usage scenario stress model based on stress distribution data, inputting the adhesive layer thickness into the usage scenario stress model, outputting the thickness allowance after curing, and generating a thickness allowance adjustment instruction includes:

[0016] Based on the stress distribution data, fit the stress change data to generate the stress model for the application scenario; based on the stress model for the application scenario, calculate the stress response value under different adhesive layer thicknesses to generate the thickness allowance after curing; based on the thickness allowance after curing, generate the thickness allowance adjustment instruction.

[0017] Furthermore, the process of adjusting the curing time and temperature via a thickness reservation adjustment command, simultaneously acquiring images of the adhesive layer surface in the crease area, performing image processing on the adhesive layer surface images in the crease area to obtain thickness distribution measurement data, determining the crease stress concentration area based on the thickness distribution measurement data, and obtaining the actual thickness of the crease stress concentration area includes:

[0018] Based on the thickness reservation adjustment instruction, the curing parameter table is queried to generate the adjusted curing process parameters; the adhesive layer is cured based on the adjusted curing process parameters, and the surface image of the adhesive layer in the crease area is acquired. The surface image of the adhesive layer in the crease area is processed to generate the thickness distribution measurement data; the thickness change rate is calculated based on the thickness distribution measurement data to determine the crease stress concentration area; the actual thickness of the crease stress concentration area is measured using laser ranging technology.

[0019] Furthermore, the step of processing the surface image of the adhesive layer in the crease area to generate the thickness distribution measurement data includes:

[0020] The surface image of the adhesive layer in the crease area is segmented, the thickness change gradient between adjacent measurement points is calculated, and the boundary of the region where the thickness change gradient exceeds a threshold is identified. Based on the thickness data within the boundary of the region, the location of the depression is identified, and the depression locations are connected to generate a depression region. Based on the characteristics of the depression region, weak zones are identified, and the thickness distribution measurement data is generated based on the thickness data within the weak zones. Dangerous areas are determined, and a list of target areas is generated.

[0021] Furthermore, if the actual thickness of the stress concentration area of ​​the crease is lower than a preset thickness threshold, the spraying parameters are dynamically adjusted based on the thickness difference. The adjusted spraying parameters are then used to spray the stress concentration area of ​​the crease to obtain the target adhesive layer thickness distribution, including:

[0022] The actual thickness of the stress concentration area of ​​the crease is compared with a preset thickness threshold to generate a thickness compensation amount; the parameter table is queried based on the thickness compensation amount to generate adjusted spraying parameters; the spraying equipment is controlled based on the adjusted spraying parameters to monitor the spraying thickness in real time and generate the target adhesive layer thickness distribution.

[0023] Furthermore, the step of spraying the crease stress concentration area with the adjusted spraying parameters to obtain the target adhesive layer thickness distribution includes:

[0024] The glue gun movement trajectory is generated based on the spatial distribution of the stress concentration area of ​​the crease; differentiated spraying parameters are set for the glue gun movement trajectory; the glue gun is controlled to perform spraying based on the differentiated spraying parameters, the thickness of each area is monitored in real time, the spraying parameters are adjusted based on the thickness deviation, and the target adhesive layer thickness distribution is generated.

[0025] Furthermore, the cracking risk value of the adhesive layer corresponding to the target adhesive layer thickness distribution is obtained through a preset cracking risk assessment model. If the cracking risk value of the adhesive layer is lower than a preset risk threshold, a target production line parameter adjustment plan is generated based on the risk assessment results, including:

[0026] Input the target adhesive layer thickness distribution into the cracking risk assessment model to generate the adhesive layer cracking risk value; compare the adhesive layer cracking risk value with a preset risk threshold to generate a safety margin coefficient; query the parameter adjustment mapping table based on the safety margin coefficient to generate the target production line parameter adjustment plan.

[0027] Furthermore, the execution of the parameter adjustment scheme, which updates the parameters of the glue gun spraying and curing equipment in real time to obtain stable brochure packaging quality, includes:

[0028] The production line dynamic control system receives the parameter adjustment scheme, converts the spraying speed into a pressure control value, generates a motor speed control command, sets the target temperature value of the heating controller, and adjusts the conveyor belt running cycle; it adjusts the spraying and curing equipment based on the converted parameters; and it monitors the adhesive layer thickness deviation and bonding force to obtain stable brochure packaging quality.

[0029] The technical solutions provided by the embodiments of the present invention may include the following beneficial effects:

[0030] This invention discloses a method for monitoring the thickness of hot melt adhesive application, addressing the core problem of weak adhesive layers and easy cracking in stress concentration areas of creases. By acquiring folding angle and stress distribution data through stress sensors, a stress model is constructed to accurately locate stress concentration areas and their stress intensity, determining the magnitude of stress on the target adhesive layer. Based on this, the invention dynamically optimizes the adhesive layer thickness distribution through hot melt adhesive compensation application and thickness allowance adjustment. Utilizing image processing and laser ranging technology, weak zones and micro-crack areas in the adhesive layer are identified, and spraying parameters and glue gun trajectory are adjusted to implement segmented differentiated spraying, ensuring uniform and stable adhesive layers in crease areas. A cracking risk assessment model further outputs adhesive layer cracking risk values, guiding dynamic adjustments to production line parameters, including spraying speed, adhesive temperature, and curing time, ultimately achieving stable brochure packaging quality. This invention significantly improves adhesive layer durability and packaging reliability, reduces the risk of folding cracking, and optimizes production efficiency. Attached Figure Description

[0031] Figure 1 This is a flowchart of a method for monitoring the thickness of hot melt adhesive application according to the present invention.

[0032] Figure 2 This is a schematic diagram of a hot melt adhesive coating thickness monitoring method according to the present invention. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and thoroughly described below with reference to the accompanying drawings. The described embodiments are merely some embodiments of the present invention.

[0034] like Figure 1-2 This embodiment of a method for monitoring the thickness of hot melt adhesive application may specifically include:

[0035] Step S101: Obtain the stress magnitude corresponding to different folding angles of the brochure, obtain the stress distribution map, determine the stress area through stress distribution map analysis, identify the stress magnitude of the stress area, and obtain the location and stress intensity of the stress concentration area of ​​the crease.

[0036] Multiple stress sensors are placed at key folding points in the brochure to acquire continuous stress data within the folding angle range of 0 to 180 degrees. The electrical signals collected by the sensors are converted into stress values, and the stress value corresponding to each angle is recorded. A two-dimensional stress distribution map is constructed based on the collected stress values, with the horizontal axis representing the folding angle and the vertical axis representing the stress magnitude. The discrete data points are smoothed using cubic spline interpolation to obtain a continuous stress variation curve. The first derivative of the stress variation curve is used to calculate the stress gradient. Regions with stress gradients exceeding a preset gradient threshold are identified as stress concentration areas. If the stress value in a certain region is greater than the average of all collected stress values ​​multiplied by a preset multiple threshold, the region is determined to be a high-risk area for crease formation. For the identified high-risk areas, the corresponding folding angle range and maximum stress value are extracted from the stress distribution map to determine the location range and corresponding stress intensity value of the crease stress concentration area in the folding angle coordinate system.

[0037] In one possible implementation, the placement of stress sensors needs to consider the material properties and folding method of the brochure. For common coated paper brochures, sensors are typically placed 5 mm on each side of the fold line, forming a symmetrical distribution. The sensors are thin-film piezoresistive sensors, only 0.2 mm thick, which will not affect the normal folding of the brochure. As the brochure is gradually folded from a flat state, the pressure on the sensor will cause a change in resistance. This change in resistance is converted into a voltage signal by a Wheatstone bridge circuit, and then converted into a digital stress value through analog-to-digital conversion.

[0038] Specifically, the folding angle is measured by installing an angle encoder on the folding shaft, triggering a stress data acquisition every time the angle changes by 1 degree. This synchronous acquisition method ensures the accuracy of the correspondence between angle and stress. The acquired discrete data points need to be processed to form a continuous analytical basis.

[0039] It should be noted that cubic spline interpolation has unique advantages in processing stress data. This method ensures the second-order continuity of the curve by constructing a cubic polynomial between adjacent data points. During the folding process of the brochure, stress changes exhibit continuous characteristics, and cubic spline interpolation can accurately reflect this smooth transition. The interpolated stress change curve shows obvious peak characteristics, with stress concentration typically occurring within the folding angle range of 60 to 120 degrees.

[0040] In one embodiment, the stress gradient is calculated using the central difference method. For any point on the curve, the gradient value at that point is obtained by dividing the stress difference between adjacent points by the angle difference. When the gradient value exceeds a preset threshold, it indicates that the stress in that area is changing drastically. Simultaneously, the average stress value at all collected points is calculated and multiplied by a preset threshold as a judgment criterion. This dual judgment mechanism improves the accuracy of identification.

[0041] For example, when a brochure is folded at a 90-degree angle, the stress value reaches its peak, which is 2.3 times the average stress, and the stress gradient value at this point is significantly higher than in other areas. By marking this on a stress distribution map, it can be clearly seen that a distinct stress concentration zone is formed within this angle range. This visual representation helps designers optimize the crease location. By adjusting the paper thickness or adding pre-crease treatment, the degree of stress concentration can be effectively reduced, extending the lifespan of the brochure.

[0042] Step S102: Determine the stress magnitude of the adhesive layer in the target stress area based on the location and stress intensity of the stress concentration area of ​​the crease. Perform load-bearing capacity analysis on the stress magnitude of the adhesive layer in the target stress area to obtain adhesive layer stress distribution data. Determine the hot melt adhesive compensation application amount based on the obtained adhesive layer stress distribution data. Determine the adhesive layer thickness based on the hot melt adhesive compensation application amount.

[0043] Based on the location and stress intensity of the stress concentration area at the crease, the stress transfer coefficient is calculated by multiplying the ratio of the material's elastic modulus to the adhesive layer's elastic modulus by the ratio of the crease area's area to the adhesive layer's contact area. The stress intensity is then multiplied by the stress transfer coefficient to obtain the adhesive layer's stress value in the target stress area. The load-bearing capacity of the adhesive layer is determined based on its stress value. If the stress value exceeds a preset load-bearing threshold, it is marked as a high-load area. By establishing mesh elements in the high-load area and solving the stress balance equations for each element, the adhesive layer stress distribution data is obtained. The difference between the maximum stress value and the adhesive layer material's yield stress is multiplied by the ratio of the adhesive layer material's bulk modulus to its density to determine the hot melt adhesive compensation application amount. The hot melt adhesive compensation application amount is divided by the area of ​​the high-load area to obtain the application amount per unit area. The adhesive layer thickness is determined by multiplying the application amount per unit area by the hot melt adhesive's curing shrinkage rate.

[0044] In one possible implementation, the stress transfer coefficient is calculated based on the stress transfer principle in materials mechanics. When stress concentration occurs at the crease of a brochure, this stress is transferred through the paper material to the adhesive layer. The elastic modulus of a material reflects its ability to resist deformation; the elastic modulus of paper is typically 3 to 5 GPa, while the elastic modulus of hot melt adhesive is approximately 0.1 to 0.3 GPa. The ratio of these two values ​​indicates the degree of stress attenuation during transmission between different materials. The ratio of the crease area to the adhesive layer contact area reflects the stress dispersion effect; the larger the contact area, the smaller the stress per unit area.

[0045] Specifically, when the crease stress intensity is 100 MPa, the stress transfer coefficient is calculated to be 12 using an elastic modulus ratio of 15 and an area ratio of 0.8, resulting in a stress value of 1200 MPa for the adhesive layer. This value directly affects the subsequent determination of the load-bearing capacity.

[0046] It should be noted that the load-bearing capacity determination adopts the material's yield criterion. The preset load-bearing threshold is usually set to 0.7 times the yield strength of the adhesive layer material, thus retaining a certain safety margin. When the stress on the adhesive layer exceeds this threshold, it indicates that there is a risk of failure in that area. The mesh generation process involves dividing the high-load area into multiple tiny elements, each approximately 0.5 mm square. By solving the force balance equations for each element, the stress distribution within the adhesive layer can be obtained.

[0047] In one embodiment, the stress distribution data of the adhesive layer exhibits a characteristic of gradually decreasing from the contact surface inwards. Maximum stress values ​​typically occur on the surface in direct contact with the paper, while the stress within the adhesive layer decreases with increasing depth. The yield stress of the adhesive layer material is the critical value at which it begins to undergo permanent deformation; for commonly used EVA hot melt adhesives, this value is approximately 8 to 12 MPa.

[0048] For example, when the maximum stress is 15 MPa and the yield stress is 10 MPa, the difference is 5 MPa. The ratio of bulk modulus to density reflects the compressibility of a material; for hot melt adhesives, this ratio is approximately 1000 cubic meters per kilogram. The compensation amount obtained through multiplication is 5000 cubic meters per square meter, a value that guides the actual application process.

[0049] It is understandable that hot melt adhesives undergo volume shrinkage during curing, typically between 5% and 15%. By dividing the amount applied per unit area by the area of ​​the high-load zone, and then considering the effect of curing shrinkage, the final adhesive layer thickness can compensate for the impact of stress concentration. This thickness calculation method ensures that the adhesive layer has sufficient buffering capacity when subjected to crease stress, effectively extending the service life of the brochure and preventing cracking or peeling of the adhesive layer due to repeated folding.

[0050] Step S103: Construct a stress model for the application scenario based on the stress distribution data, input the adhesive layer thickness into the stress model for the application scenario, output the thickness allowance after curing, and generate a thickness allowance adjustment command.

[0051] Based on the maximum stress value and the location of stress concentration areas in the stress distribution data, the stress change data under different folding times are fitted using the least squares method to construct a functional relationship between stress value and folding times as a stress model for the application scenario, thus obtaining model parameters. The stress response values ​​under different adhesive layer thicknesses are calculated using these model parameters. A safety factor is defined as the ratio of the yield strength of the adhesive material to the current stress value. When the safety factor is lower than a preset threshold, a cracking risk is identified, establishing a correspondence between adhesive layer thickness and cracking risk. The initial adhesive layer thickness is input into the correspondence between adhesive layer thickness and cracking risk to obtain the corresponding cracking risk value. If the risk value exceeds the preset risk threshold, the adhesive layer thickness is gradually increased until the risk value decreases below the threshold, outputting the required post-curing thickness allowance. Based on the difference between the post-curing thickness allowance and the initial adhesive layer thickness, a thickness allowance adjustment instruction containing the allowance value and an increase or decrease indicator is generated.

[0052] In one possible implementation, the least squares fitting process is based on actual measured stress data points. As the brochure undergoes different numbers of folds, the stress values ​​exhibit a regular change. The stress value is low at the initial folds, and gradually increases with the number of folds due to material fatigue accumulation. A discrete dataset is formed by collecting stress data at multiple nodes, such as 100, 500, and 1000 folds. The least squares method determines the optimal function parameters by minimizing the sum of squared errors between the measured values ​​and the fitted curve. A common form of the fitting function is a power function, where the number of folds is the independent variable and the stress value is the dependent variable.

[0053] Specifically, the construction of the stress model for the usage scenario needs to consider the actual usage environment. In daily use, the brochure is folded an average of 10 to 20 times per day, accumulating to approximately 5000 folds per year. Model parameters include the initial stress coefficient, stress growth rate, and material degradation coefficient. These parameters are automatically determined through a fitting process, reflecting the stress evolution under specific materials and structures.

[0054] It is important to note that the definition of the safety factor is crucial for crack risk assessment. The yield strength of the adhesive layer material is the critical stress value at which the material begins to undergo irreversible deformation. The current stress value is calculated through a model and represents the actual stress at a specific thickness and number of folds. The safety factor equals the yield strength divided by the current stress value; this ratio directly reflects the safety margin of the adhesive layer. When the safety factor drops below 1.5, it indicates that the adhesive layer is approaching a dangerous state.

[0055] In one embodiment, the relationship between adhesive layer thickness and cracking risk exhibits a non-linear characteristic. Increasing the thickness from 0.1 mm to 0.2 mm may reduce the cracking risk by 50%, but increasing it from 0.2 mm to 0.3 mm only reduces the risk by 20%. This diminishing marginal effect indicates the existence of an optimal thickness range. By establishing this relationship, the service life at different thicknesses can be accurately predicted.

[0056] For example, if the initial adhesive layer thickness is designed to be 0.15 mm, the calculated cracking risk value after inputting this value is 0.7. The preset risk threshold is usually set to 0.3, indicating that a 30% failure probability is the acceptable upper limit. Since 0.7 exceeds 0.3, the system automatically increases the thickness by 0.02 mm each time. When the thickness reaches 0.21 mm, the risk value drops to 0.28, meeting the requirements. The thickness allowance after curing is 0.21 mm.

[0057] Understandably, the thickness adjustment instruction was generated with the actual production process in mind. The difference calculation showed a need to increase the thickness by 0.06 mm. The "increase" indicator in the instruction guides the production line to adjust the adhesive application parameters to ensure the product reaches the target thickness.

[0058] Step S104: Adjust the curing time and temperature using the thickness reservation adjustment command, and simultaneously acquire an image of the adhesive layer surface in the crease area. Perform image processing on the adhesive layer surface image in the crease area to obtain thickness distribution measurement data. Determine the stress concentration area of ​​the crease based on the thickness distribution measurement data, and obtain the actual thickness of the stress concentration area of ​​the crease.

[0059] By consulting the corresponding relationship table between curing time and thickness using the values ​​in the thickness adjustment instruction, the corresponding curing time extension is obtained. Simultaneously, the temperature reduction is calculated based on the thickness increase, resulting in the adjusted curing process parameters. After curing the adhesive layer using the adjusted parameters, an industrial camera is used to capture images of the adhesive layer surface in the crease area. Noise is removed through contrast enhancement and Gaussian filtering to obtain a pre-processed surface image. Gradient calculation is performed on the pre-processed surface image, extracting pixels whose grayscale values ​​exceed a preset threshold. Thickness variation areas are identified based on pixel distribution density, and thickness distribution measurement data is obtained through the conversion between pixel coordinates and actual coordinates. The thickness change rate is calculated based on the thickness difference between adjacent measurement points in the thickness distribution measurement data. Continuous areas with change rates exceeding a preset threshold are identified as crease stress concentration areas. These areas are scanned point-by-point using a laser rangefinder sensor, measuring the vertical distance from the adhesive layer surface to the brochure paper substrate to obtain the actual thickness of the crease stress concentration area.

[0060] In one possible implementation, the relationship between curing time and thickness is established based on extensive experimental data. The curing process of hot melt adhesive involves cross-linking reactions of molecular chain segments; increasing thickness means a decrease in the rate of internal heat dissipation. When the adhesive layer thickness increases from 0.2 mm to 0.3 mm, the curing time needs to be extended from 30 seconds to 45 seconds. This relationship exhibits a non-linear characteristic, and accurate parameter adjustment values ​​can be quickly obtained by looking up a table. The temperature reduction is calculated based on the principle of heat conduction; for every 0.1 mm increase in thickness, the temperature decreases by 2 to 3 degrees Celsius, preventing the surface layer from curing too quickly while the interior remains in a fluid state.

[0061] Specifically, the adjusted curing process parameters directly affect the final performance of the adhesive layer. After curing, the adhesive layer possesses stable physical properties, allowing for accurate thickness distribution information to be obtained through image acquisition. An industrial camera with a resolution of 2048×1536 pixels is selected, coupled with a ring LED light source to provide uniform illumination. Contrast enhancement processing adjusts the brightness distribution range of the image, making the grayscale differences in areas of thickness variation more apparent. Gaussian filtering employs a 5×5 filter kernel to effectively remove random noise during image acquisition.

[0062] It's important to note that gradient calculation is a crucial step in identifying thickness variations. In digital images, grayscale values ​​reflect the height information of the adhesive layer surface. The gradient value is the difference in grayscale between adjacent pixels divided by the pixel spacing. When the adhesive layer thickness changes, the surface forms a slope or step structure, which manifests as a gradual or abrupt change in grayscale values ​​in the image. A gradient threshold of 10 grayscale levels per pixel is set; areas exceeding this value are marked as regions of thickness variation.

[0063] In one embodiment, the conversion between pixel coordinates and actual coordinates needs to be pre-calibrated. A mapping between pixel distance and actual distance is established by placing a standard scale on the imaging plane. Assuming the camera's field of view covers an area of ​​50 × 40 mm, each pixel corresponds to an actual size of approximately 0.024 mm. Thickness distribution measurement data is stored in matrix form, with each element representing the relative thickness value at the corresponding location.

[0064] For example, in the crease area, a thickness variation rate exceeding 15% was found at 20 consecutive measurement points, forming a strip area approximately 5 mm in length. The laser rangefinder sensor employs the triangulation principle; a laser beam is irradiated onto the adhesive surface at a fixed angle, and the reflected light is received by a position-sensitive detector. The precise distance value is calculated based on the offset of the laser spot position. The sensor scans the entire stress concentration area in 0.1 mm increments, and the data for each measurement point includes the horizontal and vertical coordinates and the thickness value. The accuracy of the obtained actual thickness data can reach 0.01 mm.

[0065] After image processing of the adhesive layer surface in the crease area, the thickness distribution measurement data obtained is used to segment the region, identify the boundary of the region with the largest thickness change gradient, mark the depression position where the adhesive layer thickness is significantly lower than the surrounding area, locate the weak zone formed by repeated bending during the folding of the brochure, confirm the dangerous area where the adhesive layer has microcracks or gaps, establish a spatial distribution map of the crease stress concentration area, and form a list of target areas that need to be reinforced.

[0066] The thickness distribution measurement data is processed by region segmentation. The thickness variation gradient is obtained by calculating the thickness difference between adjacent measurement points. A set of consecutive points with gradient values ​​exceeding a preset threshold is identified, and the boundary of the region with the largest thickness variation gradient is determined. Based on the thickness data within the region boundary, the average thickness of each measurement point and its eight surrounding adjacent measurement points arranged in a grid are calculated. If the thickness of a point is lower than a preset ratio threshold of this average, the point is marked as a depression, and adjacent depressions are connected to form a depression region. By analyzing the aspect ratio and continuity characteristics of the depression regions, depression regions distributed in a band along the fold line direction with an aspect ratio exceeding a preset value are identified as weak zones. The ratio of the minimum thickness within the weak zone to the thickness of the normal area is calculated. If the ratio is lower than a preset safety threshold, it is confirmed as a dangerous area where the adhesive layer has microcracks or voids. The center coordinates, coverage area, and thickness ratio data of the dangerous areas are recorded in a spatial distribution map. The risk level is determined from low to high based on the thickness ratio, and a list of target areas requiring key reinforcement is formed according to the risk level.

[0067] In one possible implementation, the region segmentation process employs a gradient-based segmentation method. Thickness distribution measurement data is stored in matrix form, with each element representing the thickness value of a measurement point. The distance between adjacent measurement points is typically 0.5 mm, forming a regular grid structure. The thickness variation gradient is obtained by calculating the thickness difference in the horizontal and vertical directions. When the gradient value in a certain direction exceeds a threshold of 0.02 mm per millimeter, it indicates a significant thickness variation at that location. These points exceeding the threshold are connected to form the region boundary, outlining the contours of the thickness anomaly region.

[0068] Specifically, the eight adjacent measurement points arranged in a grid include four positively adjacent points (top, bottom, left, and right) and four diagonally adjacent points. This neighborhood definition originates from the concept of 8-connectivity in image processing, which can comprehensively reflect the thickness distribution around the measurement point. When calculating the average value, each adjacent point has the same weight. The preset proportional threshold is usually set to 0.85, meaning that a point is identified as a depression when its thickness is less than 85% of the surrounding average. This relative determination method can adapt to the differences in basic thickness in different regions.

[0069] It's important to note that the aspect ratio is a key indicator for identifying weak points. During repeated folding of brochures, stress concentration causes the adhesive layer to form elongated damaged areas along the fold lines. When the length-to-width ratio of the recessed area exceeds 5:1, it can be generally determined that this is a weak point caused by folding rather than a random defect. Calculating the thickness ratio requires first determining the reference thickness of the normal area, typically choosing a location far from the fold area with a uniform thickness distribution.

[0070] In one embodiment, the identification of hazardous areas is based on the principles of materials mechanics. When the adhesive layer thickness decreases to below 60% of its normal value, its load-bearing capacity drops sharply. The preset safety threshold of 0.6 is based on this critical point. Areas below this threshold are highly susceptible to crack propagation during subsequent use. The spatial distribution map uses a two-dimensional coordinate system, with the lower left corner of the brochure as the origin, the horizontal axis representing the width direction, and the vertical axis representing the height direction.

[0071] For example, a hazardous area might have its center coordinates at 25 mm x 80 mm y, covering an area of ​​15 square millimeters with a thickness ratio of 0.55. This data comprehensively describes the area's location, size, and severity. Risk levels are categorized into three levels based on the thickness ratio: below 0.5 is high risk, 0.5 to 0.6 is medium risk, and 0.6 to 0.7 is low risk. The target area list is sorted according to this level, prioritizing high-risk areas. This quantitative assessment method provides clear priorities and targets for subsequent reinforcement treatments, avoiding material waste caused by indiscriminate reinforcement while ensuring adequate protection for critical areas.

[0072] Step S105: If the actual thickness of the stress concentration area of ​​the crease is lower than the preset thickness threshold, the spraying parameters are dynamically adjusted according to the thickness difference. The adjusted spraying parameters are then used to spray the stress concentration area of ​​the crease to obtain the target adhesive layer thickness distribution.

[0073] The actual thickness of the stress concentration area of ​​the crease is compared with a preset thickness threshold. If the actual thickness is lower than the preset thickness threshold, the difference between the preset thickness threshold and the actual thickness is calculated to obtain the thickness compensation amount. Based on the thickness compensation amount, a preset thickness-parameter correspondence table is consulted to obtain the spraying flow rate coefficient and speed coefficient corresponding to each millimeter of thickness. The thickness compensation amount is multiplied by the corresponding coefficients to obtain the increase in spraying flow rate and the decrease in spraying speed. The standard spraying flow rate is then added to the increase in flow rate, and the standard spraying speed is multiplied by the decrease in speed to obtain the adjusted spraying parameters. The adjusted spraying parameters are used to control the spraying equipment to spray layer by layer onto the stress concentration area of ​​the crease. The current spraying thickness is monitored in real time by a laser thickness sensor. The difference between the current thickness and the initial thickness is used as the cumulative amount. Spraying stops when the cumulative amount reaches the thickness compensation amount, thus obtaining the target adhesive layer thickness distribution.

[0074] In one possible implementation, the preset thickness threshold is determined based on the material's mechanical properties and usage requirements. For the adhesive layer of a brochure, the thickness threshold is typically set as the minimum thickness that can withstand the expected number of folds without cracking. When the actual measured thickness is 0.18 mm, and the preset threshold is 0.25 mm, the thickness compensation is 0.07 mm. This difference directly reflects the required increase in adhesive layer thickness to ensure sufficient strength in the crease area.

[0075] Specifically, the thickness-parameter correspondence table is an empirical table established based on extensive experimental data. This table records the spraying parameter adjustments required for different thickness increments. The spray flow rate coefficient indicates the increase in adhesive flow rate needed for every 1 mm increase in thickness, typically 15 to 20 ml per minute. The speed coefficient reflects the adjustment ratio of the spraying movement speed; the greater the required thickness, the slower the spraying speed to ensure sufficient adhesive deposition. When a 0.07 mm thickness compensation is needed, the table shows an increase in flow rate of 1.4 ml per minute and a reduction in speed to 0.8 times the original speed.

[0076] It should be noted that the standard spraying parameters are baseline values ​​under normal production conditions. The standard spraying flow rate is typically 50 ml per minute, and the standard spraying speed is 100 mm per second. After adjustment, the new spraying flow rate becomes 51.4 ml per minute, and the spraying speed becomes 80 mm per second. This combination of parameters allows for the deposition of more adhesive per unit area, achieving precise thickness compensation.

[0077] In one embodiment, the target area is covered layer by layer using a spiral or parallel path. Each layer is approximately 0.02 mm thick, and the target thickness is achieved through multiple layers. A laser thickness sensor is vertically mounted next to the nozzle, maintaining a fixed distance. The laser beam emitted by the sensor illuminates the adhesive layer surface, and the thickness at the current location is calculated by measuring the time difference of the reflected light. This non-contact measurement method does not interfere with the uncured adhesive layer.

[0078] For example, in an area with an initial thickness of 0.18 mm, the laser thickness sensor collects data every 0.5 seconds during the spraying process. After the first layer is sprayed, the thickness is measured to be 0.20 mm, with a cumulative amount of 0.02 mm. The second layer is then sprayed, reaching a thickness of 0.22 mm, with a cumulative amount of 0.04 mm. When the fourth layer is completed, the thickness is measured to be 0.25 mm, and the cumulative amount reaches the compensation target of 0.07 mm, at which point the control system immediately stops spraying.

[0079] Understandably, this real-time monitoring and dynamic control method avoids material waste and uneven thickness caused by over-spraying. The target adhesive layer thickness distribution exhibits a smooth transition, with no abrupt changes from the normal area to the reinforced area, ensuring uniform stress transmission.

[0080] Adjust the movement trajectory of the glue gun according to the spatial distribution of the stress concentration area of ​​the crease, increase the spraying dwell time in the weak glue layer area, perform multi-layer superimposed spraying treatment on the micro-crack location, control the filling depth of the glue in the recessed area, ensure that the dangerous area obtains sufficient glue layer coverage thickness, and achieve differentiated reinforcement of different areas through segmented spraying method, forming a uniform and stable glue layer thickness distribution in the stress concentration area of ​​the crease.

[0081] Based on the spatial distribution coordinates of the stress concentration areas in the creases, the center point of the weak area, the initiation and termination points of microcracks, and the boundary points of the depressions are designated as key control points. These control points are sequentially connected using a shortest path algorithm to generate the glue gun's movement trajectory. For the generated glue gun trajectory, the dwell time in the weak area is set to a preset multiple of the standard time. For microcrack locations, the number of stacking operations is determined based on the crack length. The maximum depth of the depression is multiplied by the area to obtain the required glue filling volume, forming a differentiated spraying parameter set for each region. This differentiated spraying parameter set controls the glue gun to perform segmented spraying. Spraying is maintained in each region according to the corresponding dwell time, repeated according to the number of stacking operations, and the flow rate is adjusted according to the filling volume to complete targeted reinforcement of the hazardous areas. A laser thickness sensor monitors the glue layer thickness in each region. The measured thickness is compared with the target thickness, and the spraying speed and flow rate are adjusted based on the difference until the thickness deviation at each point in the stress concentration area of ​​the crease is within a preset range, resulting in a uniform and stable glue layer thickness distribution.

[0082] In one possible implementation, the shortest path connection algorithm is based on the solution approach of the Traveling Salesman Problem in graph theory. The selection of key control points reflects the characteristics of different types of defects: weak areas are usually distributed in a sheet-like pattern, and their geometric centers are selected as representative points; microcracks extend in a line, and the start and end points mark the complete range of the crack; the boundary points of the concave region delineate the contours that need to be filled. The algorithm constructs a distance matrix by calculating the Euclidean distances between each point, and then uses a greedy strategy to start from the starting point, selecting the unvisited point closest to the current point as the next target, until all control points are traversed.

[0083] Specifically, the dwell time is set based on the flow and penetration characteristics of the adhesive. The standard dwell time is typically 0.5 seconds. In weak areas, where more adhesive needs to penetrate the material, the dwell time is set to 1.5 to 2 times the standard time. The number of coats is determined by considering the depth and width of the crack; one coat is applied for every millimeter of crack length to ensure thorough filling. The volume calculation for recessed areas uses the trapezoidal rule, approximating irregular recesses as a combination of multiple trapezoidal prisms. The relationship between the maximum depth and the average depth determines the actual amount of filling required.

[0084] It should be noted that the formation process of the differentiated spraying parameter set embodies the concept of precise control. Each parameter is related to a specific physical process: residence time affects the amount of adhesive deposited per unit area, the number of stacks determines the cumulative thickness in the vertical direction, and the filling volume ensures the complete filling of the recessed area. These parameters work together to achieve targeted treatment of different defect types.

[0085] In one embodiment, the segmented spraying process is similar to the layered manufacturing of 3D printing. The glue gun moves along a predetermined trajectory, automatically reducing its speed and maintaining spraying when it reaches weak areas, allowing the glue to spread evenly under the influence of gravity and surface tension. For microcrack locations, the glue gun moves back and forth along the same path, forming a coverage layer of approximately 0.03 mm with each spray; after multiple layers are accumulated, the crack is completely sealed. Recessed areas are filled using a spiral path from the outside in, ensuring the glue flows gradually from the edges to the center, avoiding the formation of air bubbles.

[0086] For example, real-time monitoring by a laser thickness sensor provides feedback for dynamic adjustments. The sensor acquires thickness data at a frequency of 10 Hz, comparing the thickness value at each measurement point with the target thickness at that location. When the measured thickness is 0.22 mm and the target thickness is 0.25 mm, a thickness difference of 0.03 mm is calculated. Based on this, the current spray flow rate is increased by 12%, while the moving speed is reduced by 8%. This closed-loop control ensures the uniformity of the final thickness distribution, with the thickness deviation at each measurement point controlled within ±5% of the target value, achieving reliable reinforcement of the crease area.

[0087] Step S106: Obtain the adhesive layer cracking risk value corresponding to the target adhesive layer thickness distribution through the preset cracking risk assessment model. If the adhesive layer cracking risk value is lower than the preset risk threshold, generate a target production line parameter adjustment plan based on the risk assessment results.

[0088] The target adhesive layer thickness distribution data is input into the cracking risk assessment model. The ratio of the minimum value in the thickness distribution to the preset benchmark thickness value is extracted as the thickness attenuation rate. The thickness attenuation rate is multiplied by the fatigue limit coefficient of the adhesive layer material to obtain the adhesive layer cracking risk value. If the adhesive layer cracking risk value is lower than the preset risk threshold, the difference between the preset risk threshold and the cracking risk value is calculated as a safety margin coefficient. Based on the safety margin coefficient, the corresponding spraying speed reduction ratio, adhesive temperature increase value, and curing time increase ratio are found in the pre-established parameter adjustment mapping table. The new spraying speed parameter is obtained by multiplying the found spraying speed reduction ratio by the current spraying speed, the new adhesive temperature parameter is obtained by adding the adhesive temperature increase value to the current temperature, and the new curing time parameter is obtained by multiplying the curing time increase ratio by the current curing time. The three new parameters are integrated to generate the target production line parameter adjustment plan.

[0089] In one possible implementation, the core of the crack risk assessment model lies in quantifying the stress-bearing capacity of the adhesive layer. A preset baseline thickness is typically set at 0.3 mm, which is the optimal thickness derived from extensive experimentation. When the target adhesive layer thickness distribution data shows a minimum thickness of 0.21 mm in a certain area, the thickness attenuation rate is 0.21 divided by 0.3, yielding 0.7. The fatigue limit coefficient of the adhesive layer material reflects its durability under cyclic stress; for hot melt adhesives, this coefficient is typically between 0.6 and 0.8. Multiplying the thickness attenuation rate of 0.7 by the fatigue limit coefficient of 0.7 yields a crack risk value of 0.49.

[0090] Specifically, the calculation of the safety margin coefficient reflects the principle of conservative design. The preset risk threshold is generally set at 0.3, indicating that a 30% failure probability is the acceptable upper limit. When the actual risk value is 0.49, exceeding the threshold, it indicates that production parameters need to be adjusted. If the risk value is 0.25, below the threshold, the safety margin coefficient is 0.3 minus 0.25, resulting in 0.05. The larger this coefficient, the more sufficient the safety margin, allowing for appropriate optimization of production efficiency.

[0091] It should be noted that the parameter adjustment mapping table is an empirical database established through orthogonal experiments. This table divides the safety margin coefficient into multiple intervals, each corresponding to a set of optimized parameters. When the safety margin coefficient is 0.05, the table shows that: the spraying speed can be increased to 1.1 times the original speed to improve production efficiency; the adhesive temperature can be reduced by 3 degrees Celsius to save energy; and the curing time can be shortened to 0.95 times the original time to accelerate the production pace. This mapping relationship ensures that efficiency is improved while maintaining quality.

[0092] In one embodiment, the parameter adjustment process takes into account the equipment's response characteristics. The current spraying speed is 80 mm / s; multiplied by a reduction ratio of 1.1, the new speed is 88 mm / s. The adhesive temperature is reduced by 3 degrees Celsius from 165 degrees Celsius to 162 degrees Celsius, a temperature still within the adhesive's optimal flow range. The curing time is shortened from 60 seconds to 57 seconds by adjusting the conveyor belt speed.

[0093] For example, after implementing parameter adjustments, a production line increased its daily output from 8,000 brochures to 8,800, while reducing energy consumption by 5%. More importantly, through precise risk assessment and parameter optimization, the product qualification rate remained above 99.5%. This dynamic parameter adjustment method based on risk assessment achieves a balance between quality control and production efficiency. The generated target production line parameter adjustment plan includes a complete combination of process parameters, which can be directly input into the production control system for execution, avoiding errors and delays caused by manual adjustments.

[0094] Step S107: Execute the parameter adjustment scheme to update the parameters of the glue gun spraying and curing equipment in real time, thereby obtaining stable brochure packaging quality.

[0095] The production line dynamic control system receives parameter adjustment plans, converts spraying speed parameters into corresponding pressure control values ​​based on the linear relationship between spraying flow and pressure, directly generates motor speed control commands based on speed parameters, uses adhesive temperature parameters as the target temperature value for the heating controller, and converts curing time parameters into conveyor belt operating cycles. The spraying pressure is adjusted to the corresponding value based on the converted pressure control values, the glue gun movement speed is set via motor speed control commands, the heating power is adjusted by inputting the target temperature value into the heating controller, and the conveyor speed is adjusted according to the conveyor belt operating cycle, ensuring that all equipment operates collaboratively according to the new parameters. Continuous production is carried out using the updated equipment parameters. Thickness measurement devices and tensile testing devices monitor the adhesive layer thickness deviation and the adhesion between the adhesive layer and paper for each batch of brochures. When the thickness deviation of consecutive preset batches is within a preset range and the adhesion exceeds a preset strength threshold, stable brochure packaging quality is achieved.

[0096] In one possible implementation, the production line dynamic control system acts as the central hub of the entire production process, responsible for accurately converting optimized parameters into control signals that each piece of equipment can recognize. The linear relationship between spray flow rate and pressure is based on fluid mechanics principles. When a 20% increase in spray flow rate is required, according to Bernoulli's equation, the pressure needs to be increased by approximately 44%. The system's built-in conversion table records the pressure values ​​corresponding to different flow rates. When a target flow rate parameter of 60 ml / min is received, the system automatically looks up the table to determine the required pressure to be set at 0.8 MPa.

[0097] Specifically, the generation of motor speed control commands involves kinematic calculations. The linear movement speed of the glue gun is related to the speed of the drive motor through the transmission ratio. If the pitch of the transmission mechanism is 5 mm, the motor speed should be set to 1200 rpm to achieve a movement speed of 100 mm per second. The heating controller uses a PID control algorithm to compare the target temperature value with the real-time temperature and adjust the heating power to stabilize the temperature within ±1 degree Celsius of the set value.

[0098] It's important to note that the key to successful equipment coordination lies in timing synchronization. The conveyor belt's cycle time determines the dwell time of each brochure at each workstation. When the curing time parameter is 45 seconds, considering the curing chamber length is 3 meters, the conveyor belt speed should be adjusted to 4 meters per minute. This ensures that each brochure remains in the curing area for exactly 45 seconds. All equipment maintains synchronization through a unified clock signal to avoid quality issues caused by timing misalignment.

[0099] In one embodiment, the thickness measuring device employs the principle of laser triangulation, setting a measuring point every 50 millimeters to cover the entire crease area. The measurement accuracy reaches 0.01 millimeters, enabling accurate detection of minute changes in adhesive layer thickness. Thickness deviation is calculated by the difference between the measured value and the target value, with a preset range typically ±0.02 millimeters. The tensile testing device simulates the peeling force in actual use, measuring the adhesion between the adhesive layer and the paper by vertically stretching the adhesive layer.

[0100] For example, in actual production, the test data of the first batch of 100 brochures showed that the average thickness of the adhesive layer was 0.251 mm, the standard deviation was 0.015 mm, and the thickness deviation at all measurement points was within ±0.02 mm. Tensile testing showed an average bonding force of 3.2 N / cm, exceeding the preset strength threshold of 2.5 N / cm. Data from five consecutive batches met the requirements, indicating that the production process has stabilized.

[0101] Understandably, this real-time monitoring and feedback mechanism ensures consistent production quality. By translating abstract parameters into specific equipment control commands and then verifying the effects through online testing, a complete quality control closed loop is formed. Stable packaging quality is not only reflected in numerical indicators, but more importantly, it ensures that each brochure can withstand repeated folding in actual use, extending the product's lifespan.

[0102] It should be noted that the above examples are merely some specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments and many variations are possible. All variations that can be directly derived or conceived by those skilled in the art from the content disclosed in this invention should be considered within the scope of protection of this invention.

Claims

1. A method for monitoring the thickness of hot melt adhesive coating, characterized in that, The method includes: Obtain the stress magnitude corresponding to different folding angles of the brochure, and obtain a stress distribution map. Analyze the stress distribution map to determine the stress area, identify the stress magnitude in the stress area, and obtain the location and stress intensity of the stress concentration area of ​​the crease. The stress magnitude of the adhesive layer in the target stress area is determined based on the location and stress intensity of the stress concentration area of ​​the crease. The load-bearing capacity of the adhesive layer in the target stress area is analyzed to obtain the stress distribution data of the adhesive layer. The amount of hot melt adhesive compensation is determined based on the obtained stress distribution data of the adhesive layer. The thickness of the adhesive layer is determined based on the amount of hot melt adhesive compensation. Based on stress distribution data, a usage scenario stress model is constructed. The adhesive layer thickness is input into the usage scenario stress model, and the output is the thickness allowance after curing. A thickness allowance adjustment instruction is generated, including: based on the maximum stress value and the location of stress concentration areas in the stress distribution data, the stress change data under different folding times is fitted using the least squares method to construct a functional relationship between stress value and folding times as the usage scenario stress model, and model parameters are obtained; the stress response value under different adhesive layer thicknesses is calculated using the model parameters, and the ratio of the yield strength of the adhesive layer material to the current stress value is defined as a safety factor. When the safety factor is lower than a preset threshold, it is determined that there is a risk of cracking, and a correspondence between adhesive layer thickness and cracking risk is established; the initial adhesive layer thickness is input into the correspondence between adhesive layer thickness and cracking risk to obtain the corresponding cracking risk value. If the risk value exceeds the preset risk threshold, the adhesive layer thickness is gradually increased until the risk value is reduced to below the threshold, and the required thickness allowance after curing is output. The curing time and temperature are adjusted by the thickness reservation adjustment command. At the same time, the surface image of the adhesive layer in the crease area is acquired. The surface image of the adhesive layer in the crease area is processed to obtain the thickness distribution measurement data. The crease stress concentration area is determined based on the thickness distribution measurement data, and the actual thickness of the crease stress concentration area is obtained. If the actual thickness of the stress concentration area of ​​the crease is lower than the preset thickness threshold, the spraying parameters are dynamically adjusted according to the thickness difference. The adjusted spraying parameters are then used to spray the stress concentration area of ​​the crease to obtain the target adhesive layer thickness distribution. The cracking risk value of the adhesive layer corresponding to the target adhesive layer thickness distribution is obtained through a preset cracking risk assessment model. If the cracking risk value of the adhesive layer is lower than the preset risk threshold, an adjustment plan for the target production line parameters is generated based on the risk assessment results. By implementing the parameter adjustment scheme, the parameters of the glue gun spraying and curing equipment are updated in real time to obtain stable brochure packaging quality.

2. The method for monitoring the thickness of hot melt adhesive coating according to claim 1, characterized in that, The process involves obtaining stress magnitudes corresponding to different folding angles of the brochure, generating a stress distribution map, analyzing the stress distribution map to determine the stress-bearing areas, identifying the stress magnitudes in these areas, and determining the location and intensity of stress concentration areas at the creases. Stress sensors are placed at key folding locations in the brochure to collect stress data within the folding angle range. The stress data is converted into stress values, and the stress values ​​corresponding to each angle are recorded. A two-dimensional stress distribution map is generated based on the stress values, with the horizontal axis representing the folding angle and the vertical axis representing the stress magnitude. A continuous stress variation curve is generated through interpolation. The stress gradient is calculated based on the continuous stress variation curve, and the region where the stress gradient exceeds a threshold is identified as a stress concentration region. For the stress concentration region, the corresponding folding angle range and maximum stress value in the stress distribution map are extracted to determine the location range and stress intensity of the crease stress concentration region.

3. The method for monitoring the thickness of hot melt adhesive coating according to claim 1, characterized in that, The process of determining the stress magnitude of the adhesive layer in the target stress area based on the location and stress intensity of the stress concentration area of ​​the crease, performing load-bearing capacity analysis on the stress magnitude of the adhesive layer in the target stress area to obtain adhesive layer stress distribution data, determining the hot melt adhesive compensation application amount based on the obtained adhesive layer stress distribution data, and determining the adhesive layer thickness based on the hot melt adhesive compensation application amount includes: Based on the location and stress intensity of the stress concentration area of ​​the crease, a stress transfer coefficient is calculated, and a stress value of the adhesive layer is generated based on the stress transfer coefficient and the stress intensity. The load-bearing capacity is determined based on the stress value of the adhesive layer, and high-load areas are divided. Mesh cells are generated based on the high-load areas, and the stress balance of each cell is calculated to generate the stress distribution data of the adhesive layer. Based on the maximum stress value in the stress distribution data of the adhesive layer, the hot melt adhesive compensation application amount is calculated. Based on the hot melt adhesive compensation application amount and the area, the application amount per unit area is generated, and the adhesive layer thickness is generated based on the application amount per unit area and the curing shrinkage rate.

4. The method for monitoring the thickness of hot melt adhesive coating according to claim 1, characterized in that, The process involves adjusting the curing time and temperature using a thickness pre-set adjustment command, simultaneously acquiring images of the adhesive layer surface in the crease area, processing these images to obtain thickness distribution measurement data, determining the crease stress concentration area based on the thickness distribution measurement data, and obtaining the actual thickness of the crease stress concentration area. This includes: Based on the thickness reservation adjustment instruction, the curing parameter table is queried to generate the adjusted curing process parameters; the adhesive layer is cured based on the adjusted curing process parameters, and the surface image of the adhesive layer in the crease area is acquired. The surface image of the adhesive layer in the crease area is processed to generate the thickness distribution measurement data; the thickness change rate is calculated based on the thickness distribution measurement data to determine the crease stress concentration area; the actual thickness of the crease stress concentration area is measured using laser ranging technology.

5. The method for monitoring the thickness of hot melt adhesive coating according to claim 4, characterized in that, The process of processing the surface image of the adhesive layer in the crease area to generate the thickness distribution measurement data includes: The surface image of the adhesive layer in the crease area is segmented, the thickness change gradient between adjacent measurement points is calculated, and the boundary of the region where the thickness change gradient exceeds a threshold is identified. Based on the thickness data within the boundary of the region, the location of the depression is identified, and the depression locations are connected to generate a depression region. Based on the characteristics of the depression region, weak zones are identified, and the thickness distribution measurement data is generated based on the thickness data within the weak zones. Dangerous areas are determined, and a list of target areas is generated.

6. The method for monitoring the thickness of hot melt adhesive coating according to claim 1, characterized in that, If the actual thickness of the stress concentration area of ​​the crease is lower than a preset thickness threshold, the spraying parameters are dynamically adjusted based on the thickness difference. The adjusted spraying parameters are then used to spray the stress concentration area of ​​the crease to obtain the target adhesive layer thickness distribution, including: The actual thickness of the stress concentration area of ​​the crease is compared with a preset thickness threshold to generate a thickness compensation amount; the parameter table is queried based on the thickness compensation amount to generate adjusted spraying parameters; the spraying equipment is controlled based on the adjusted spraying parameters to monitor the spraying thickness in real time and generate the target adhesive layer thickness distribution.

7. The method for monitoring the thickness of hot melt adhesive coating according to claim 1, characterized in that, The step of spraying the stress concentration area of ​​the crease with adjusted spraying parameters to obtain the target adhesive layer thickness distribution includes: The glue gun movement trajectory is generated based on the spatial distribution of the stress concentration area of ​​the crease; differentiated spraying parameters are set for the glue gun movement trajectory; the glue gun is controlled to perform spraying based on the differentiated spraying parameters, the thickness of each area is monitored in real time, the spraying parameters are adjusted based on the thickness deviation, and the target adhesive layer thickness distribution is generated.

8. The method for monitoring the thickness of hot melt adhesive coating according to claim 1, characterized in that, The cracking risk value of the adhesive layer corresponding to the target adhesive layer thickness distribution is obtained through a preset cracking risk assessment model. If the cracking risk value of the adhesive layer is lower than a preset risk threshold, a target production line parameter adjustment plan is generated based on the risk assessment results, including: Input the target adhesive layer thickness distribution into the cracking risk assessment model to generate the adhesive layer cracking risk value; compare the adhesive layer cracking risk value with a preset risk threshold to generate a safety margin coefficient; query the parameter adjustment mapping table based on the safety margin coefficient to generate the target production line parameter adjustment plan.

9. The method for monitoring the thickness of hot melt adhesive coating according to claim 1, characterized in that, The execution of the parameter adjustment scheme involves real-time updates to the parameters of the glue gun spraying and curing equipment to achieve stable brochure packaging quality, including: The production line dynamic control system receives the parameter adjustment scheme, converts the spraying speed into a pressure control value, generates a motor speed control command, sets the target temperature value of the heating controller, and adjusts the conveyor belt running cycle; it adjusts the spraying and curing equipment based on the converted parameters; and it monitors the adhesive layer thickness deviation and bonding force to obtain stable brochure packaging quality.

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