A corona treatment device for packaging film composite and its use method

Abstract

The present application relates to the field of corona treatment technology for packaging films, and more particularly to a corona treatment device for packaging film composites and its use method, which includes a corona assembly, a conveying assembly, and a control module. The corona assembly detects the equivalent charge on the surface of the packaging film by detecting the adsorption of dust particles of different sizes within a test box. The image detection module calculates the charge and identifies abnormal features based on a preset strategy. The control module adjusts the discharge electrode voltage or conveying speed based on the charge and ensures detection reliability through an environmental interference elimination strategy. The present application can precisely control the corona treatment effect, avoid excessive or insufficient treatment, and improve the surface treatment quality and production efficiency of the packaging film.

Description

Technical Field

[0001] The present invention relates to the technical field of packaging material processing, in particular to a corona treatment device for packaging film composite and a control method thereof. Background Art

[0002] In the production and processing of modern packaging materials, corona treatment technology is widely used as an important surface modification method to enhance the surface properties of packaging films. This technology uses a high-voltage electric field generated by discharge electrodes to ionize gas molecules, generating plasma. This plasma adsorbs onto the surface of the packaging film, thereby changing its surface energy and enhancing adhesion during subsequent printing, lamination, or coating processes. However, in practical applications, accurately evaluating and controlling the effectiveness of corona treatment, particularly the detection and adjustment of surface charge uniformity, has been a technical challenge within the industry.

[0003] Existing corona treatment equipment primarily relies on impedance sensors to detect the charging capacity of packaging film surfaces. While this method can reflect variations in surface charge to a certain extent, it cannot fully assess the uniformity of charge distribution. Especially in high-speed continuous production scenarios, factors such as uneven electric field distribution, environmental interference, and differences in material properties can cause localized under- or over-charging of the packaging film surface, leading to unstable product quality or even scrap. Furthermore, traditional detection methods lack the ability to analyze surface microscopic properties, making it difficult to meet the stringent surface performance consistency requirements of high-end packaging materials. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a corona treatment device for packaging film composite and its use method, which is used to quantify the surface charge state through visualization means and realize dynamic adjustment of the corona treatment process based on this.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a corona treatment device for packaging film lamination, comprising a corona assembly, a conveyor assembly, and a control module disposed within a corona region. The corona assembly includes an inspection box, an image acquisition module, and an image detection module. The inspection box is disposed on the side of the packaging film away from the discharge electrode, containing a plurality of dust particles of varying sizes and specific colors. A transparent window is provided on the top of the inspection box. When the discharge electrode generates plasma, the dust particles within the inspection box are attracted to the surface of the isolation window due to the electric field force. The image acquisition module is configured to capture adsorption image information on the isolation window. The image detection module calculates the equivalent charge on the packaging film surface based on a preset image detection strategy. The conveyor assembly delivers the packaging film into the corona region at a set speed, and the control module adjusts the voltage of the discharge electrode or the speed of the conveyor assembly based on the equivalent charge.

[0006] Furthermore, the image detection strategy includes preprocessing the adsorption image information, and the preprocessing includes edge feature enhancement and temperature compensation. The edge feature enhancement extracts the boundary features of each color particle and optimizes its clarity. The temperature compensation eliminates the impact of temperature changes on the visual characteristics of the particles based on real-time temperature data; then, the color distribution characteristics and shape characteristics in the adsorption image information are analyzed, the area proportion and connected domain morphology of each color area are extracted, and the abnormal features are identified by combining the difference comparison of adjacent frames. If an abnormality is found, it is further determined whether it is a local defect or a global defect.

[0007] Furthermore, the abnormal feature judgment process includes: obtaining the position and parameter information of the abnormal area, extracting the color distribution characteristics and shape characteristics of the area, and comparing them with the characteristics of the corresponding areas in adjacent frames. If the similarity is lower than a preset similarity threshold and the position difference is less than a preset position difference threshold, it is judged as a local defect; if abnormal features appear in the same position in multiple consecutive frames and the feature similarity is higher than the preset similarity threshold, it is judged as a global defect.

[0008] Furthermore, the image detection module is configured with a target abnormal area delineation strategy, which draws several rectangular wireframes on the adsorbed image information to enclose the abnormal features in the abnormal area, selects the rectangular wireframe with the smallest area as the pending area, matches the scaling factor based on the size of the pending area, and enlarges the pending area with the center of the pending area as the base point as the target abnormal area, and extracts the color distribution characteristics and area ratio of the target abnormal area.

[0009] Furthermore, the corona treatment equipment is equipped with a calibration strategy, which includes performing no-load tests at different voltages through a controllable corona discharge device, recording the adsorption area ratio of red (10μm), blue (30μm), and green (50μm) particles on the isolation window surface, establishing a mathematical model of the adsorption amount of particles of each particle size and the electric field strength, and calibrating the temperature correction coefficient in combination with temperature sensor data to ensure that subsequent testing is not affected by ambient temperature changes.

[0010] Furthermore, the control module adjusts the voltage of the discharge electrode or the speed of the conveying component based on the equivalent charge amount. If the equivalent charge amount is lower than the target range, the voltage of the discharge electrode is increased; if the equivalent charge amount is higher than the target range, the voltage is reduced or the conveying speed is increased to shorten the residence time of the packaging film in the corona zone and avoid excessive processing; the adjustment process follows the voltage adjustment coefficient and speed adjustment curve determined in advance by experiments to ensure that the adjustment process is smooth and accurate.

[0011] Furthermore, the corona treatment equipment is equipped with an environmental interference elimination strategy, which includes determining whether there are ambient light fluctuations by monitoring the consistency of image brightness, identifying airflow interference by particle displacement, and triggering the constant temperature module to work through temperature sensor data; when it is detected that the interference exceeds the threshold, the system suspends processing and starts a compensation mechanism, such as activating the temperature control module to restore constant temperature, or recording the interference image for subsequent algorithm optimization.

[0012] Furthermore, the environmental interference elimination strategy also includes an interference elimination sub-strategy, which includes pre-storing a number of ambient light interference image information. The ambient light interference image information is specifically an image of ambient light projected on the surface of the isolation window captured by the image acquisition module during normal use of the system. When it is determined that ambient light interference occurs, a pending interference image is obtained. If the duration of the pending interference image exceeds the preset duration, the corresponding pending interference image is identified as ambient light interference image information and stored.

[0013] A method for using a corona treatment device for packaging film composites comprises the following steps: first, completing system initialization and basic calibration, inputting material parameters of the packaging film to be treated, and the system automatically calling a dielectric constant correction factor and weight coefficients of particles of different particle sizes; then, starting a calibration strategy, recording the adsorption area ratio of particles of each particle size under different voltages, establishing a mathematical model, and calibrating the temperature correction coefficient; then, operating the device, wherein a conveying component conveys the packaging film into a corona area at a set speed, a discharge electrode generates plasma to charge the surface of the packaging film, and an image acquisition module simultaneously collects adsorption image information on an isolation window; an image detection module calculates the equivalent charge of the packaging film surface based on a preset image detection strategy, and a control module adjusts the voltage of the discharge electrode or the speed of the conveying component according to the equivalent charge; finally, an environmental interference elimination strategy is used to monitor and eliminate external interference to ensure the reliability of the detection data.

[0014] Furthermore, the calculation method of the equivalent charge includes converting the adsorption area ratio of particles of different particle sizes into the equivalent charge based on the mathematical model established in the calibration stage. The specific formula is as follows:

[0015] ,

[0016] in, represents the equivalent charge, represents the adsorption area ratio of the i-th color particle, represents the weight coefficient of the i-th color particle, It represents the electric field strength correction coefficient of the i-th color particle, and i represents the total number of particle types.

[0017] Furthermore, the specific method of voltage regulation and speed regulation includes: if the equivalent charge is lower than the target range, then according to the formula ,

[0018] Adjust the discharge electrode voltage, where and Respectively represent the voltage values ​​before and after adjustment, Indicates the voltage increment; if the equivalent charge is higher than the target range, then according to the formula Adjust the conveying speed, where and Respectively represent the conveying speed before and after adjustment, represents the speed increment; the voltage increment and speed increment are both determined through experiments and stored in the system.

[0019] Furthermore, the specific implementation method of the environmental interference elimination strategy includes: judging the ambient light fluctuation by monitoring the consistency of image brightness. If the brightness deviation exceeds a preset threshold, pausing the processing and waiting for the ambient light to stabilize; identifying airflow interference through particle displacement. If the displacement exceeds a preset threshold, an airflow adjustment signal is generated; triggering the constant temperature module to work through temperature sensor data. If the temperature fluctuation exceeds ±2°C, a temperature adjustment signal is generated.

[0020] Beneficial effects of the present invention:

[0021] From the above, it can be seen that the present application provides a corona treatment device for packaging film composites and its use method, which uses built-in multi-color particles in the test box to adsorb to the surface of the isolation window, combines image analysis technology to calculate the equivalent charge in real time, and dynamically adjusts the corona treatment parameters, thereby solving the problem that traditional technology cannot evaluate the uniformity of charge, and has the advantages of real-time monitoring and automatic optimization of treatment effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The figure shows the overall structure of a corona treatment device for packaging film composite according to the present invention.

[0023] Figure 2 It is a schematic diagram of the internal structure of the test box and the adsorption state of the isolation window in the present invention.

[0024] Figure 3 These are the specific steps for determining brightness anomalies in the environmental interference elimination strategy.

[0025] Figure 4 These are the specific steps for judging abnormal fluctuations in particle displacement in the environmental interference elimination strategy.

[0026] Figure 5 These are the specific steps for determining abnormal temperature fluctuations in the environmental interference elimination strategy.

[0027] Figure numerals: 1. inspection box; 2. image acquisition module; 3. image detection module; 4. transparent window; 5. corona mechanism; 6. coating mechanism; 7. compounding mechanism; 8. drying mechanism; 9. winding mechanism. DETAILED DESCRIPTION

[0028] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0029] It should be noted that when a component is referred to as being "fixed to" another component, it may be directly on the other component or there may also be a central component. When a component is considered to be "connected to" another component, it may be directly connected to the other component or there may also be a central component. When a component is considered to be "set on" another component, it may be directly set on the other component or there may also be a central component. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one skilled in the art to which this invention pertains. The terms used in this specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0031] Existing technologies often use corona technology to enhance the surface energy of packaging film surface treatments. However, traditional equipment relies on impedance sensors to detect charging capacity, making it impossible to assess surface charging uniformity. During high-speed production, uneven electric field distribution, environmental interference, or differences in material properties can lead to localized under- or over-charging of the packaging film, resulting in unstable adhesion during the lamination process. Existing detection methods lack the ability to dynamically analyze microscopic charge distribution, making it difficult to meet the surface treatment consistency requirements of high-end packaging materials.

[0032] To address this issue, traditional methods use a single sensor to obtain overall charge parameters, which cannot reflect subtle differences in surface charge distribution. The inventors observed a correlation between the adsorption behavior of particles under the influence of an electric field during corona treatment and the surface charge state. They therefore proposed visually inspecting the distribution characteristics of adsorbed particles to indirectly assess charge distribution uniformity. Furthermore, by dynamically adjusting corona parameters and conveying speed, treatment results can be optimized in real time.

[0033] Therefore, the present application proposes a corona treatment device for packaging film composite, which includes a corona component, a conveying component and a control module. The corona component includes a test box, an image acquisition module and an image detection module. The test box has built-in dust particles of specific colors with different particle sizes, and a transparent window is set on the top. When the discharge electrode generates plasma, the dust particles are adsorbed to the surface of the isolation window due to the electric field force. The image acquisition module captures the adsorption image, and the image detection module calculates the equivalent charge based on a preset strategy. The conveying component conveys the packaging film at a set speed, and the control module adjusts the voltage or speed according to the equivalent charge. The present invention provides a corona treatment device for packaging film composite and a method of using the same, combined with the attached Figure 1 To the attached Figure 5 Specific embodiments of the present invention are described in detail.

[0034] Among them, the test box refers to a closed container used to hold dust particles of a specific color. It can be specifically implemented by a transparent polymer material, and its interior is filled with colored particles of different particle sizes. The transparent window on the top allows the electric field to penetrate and capture the particles. The image acquisition module refers to a device used to collect images of the distribution of particles on the surface of the isolation window. It can be specifically implemented by a high-resolution industrial camera, which captures the adsorption form of the particles through an optical lens. The image detection module refers to an arithmetic unit that processes image data and calculates the equivalent charge. It can be specifically implemented by an embedded processor with a built-in edge enhancement algorithm and temperature compensation mechanism. The conveying component refers to the transmission mechanism that drives the packaging film to continuously pass through the corona area. It can be specifically implemented by a roller system driven by a servo motor, and the adjustable speed range covers common production needs. The control module refers to a logic unit that dynamically adjusts the processing parameters according to the equivalent charge. It can be specifically implemented by a PLC controller with a built-in voltage regulation algorithm and speed control curve.

[0035] Specifically, the packaging film is fed into the corona area at a constant speed by the conveying assembly, and the plasma generated by the discharge electrode charges the surface of the film. The colored particles in the test box are adsorbed to the isolation window under the action of the electric field force, forming a pattern corresponding to the surface charge distribution. The image acquisition module captures the adsorption image in real time, and the image detection module processes the image data through edge feature enhancement and temperature compensation, analyzes the area ratio and morphological characteristics of each color area, and converts them into equivalent charge according to the mathematical model established in the calibration stage. The control module automatically adjusts the discharge voltage or conveying speed according to the deviation between the equivalent charge and the target value. For example, when the equivalent charge is detected to be low, the voltage is increased to enhance the electric field strength; when the charge is high, the voltage is reduced or the conveying speed is increased to maintain the stability of the treatment effect.

[0036] Compared to existing technologies, traditional impedance sensors can only measure the overall charge level and cannot identify localized charge distribution anomalies. This solution accurately reflects the surface charge uniformity by analyzing the spatial distribution characteristics of particle adsorption patterns. Combined with a dynamic adjustment mechanism, it effectively avoids localized under- or over-treatment. Compared to single-parameter feedback, multi-dimensional image data can identify the impact of environmental factors such as temperature fluctuations and airflow disturbances on treatment results, improving the detection system's anti-interference capabilities.

[0037] Through the above-mentioned technical solution, this application achieves dynamic monitoring and real-time control of the surface charge state of packaging film. Calculating the equivalent charge based on the adsorption characteristics of particles accurately assesses the uniformity of charge distribution, avoiding composite quality defects caused by local anomalies in traditional methods. A feedback control mechanism automatically optimizes processing parameters, ensuring consistent surface treatment results under different production conditions and significantly improving the yield rate of the packaging film composite process.

[0038] The present application further proposes an image detection strategy including preprocessing of adsorption image information, the preprocessing including edge feature enhancement and temperature compensation. Edge feature enhancement extracts the boundary features of each color particle and optimizes its clarity. Temperature compensation eliminates the impact of temperature changes on the visual characteristics of the particles based on real-time temperature data; then, the color distribution characteristics and shape characteristics in the adsorption image information are analyzed, and the area proportion and connected domain morphology of each color area are extracted. The connected domain morphology represents the geometric characteristics of the continuous area composed of adjacent pixels in the adsorption image information, including the area or perimeter distribution, and abnormal features are identified in combination with the difference comparison of adjacent frames.

[0039] Edge feature enhancement refers to sharpening the edge contours of particles in an image. This can be achieved using the Laplace operator or the Canny edge detection algorithm. This enhances the gradient values ​​of boundary pixels to improve feature extraction accuracy. Temperature compensation dynamically corrects image chromaticity and brightness based on real-time data collected by a temperature sensor. This can be achieved by establishing a temperature-color mapping table or applying a linear regression model to eliminate color deviation and reflective intensity fluctuations caused by temperature changes. Color distribution features refer to the coverage ratio of particles of different colors within the adsorption area. They can be extracted using HSV color space segmentation or the K-means clustering algorithm and are used to quantify the adsorption status of particles of different sizes. Shape features refer to the geometric parameters of the particle aggregation area, including metrics such as the area of ​​the connected domain, perimeter, and roundness. They can be calculated using morphological operations or contour analysis algorithms and used to assess adsorption uniformity. Frame difference comparison compares the current image with the previous image at the pixel level. Optical flow or inter-frame difference algorithms can be used to detect particle displacement or morphological changes to identify abnormal areas.

[0040] Specifically, the preprocessing stage first performs edge enhancement on the original adsorption image. For example, this involves using a Gaussian filter to remove noise and then overlaying the edge detection results to make the particle boundaries clearer. Next, based on real-time data from the temperature sensor, such as ambient temperature fluctuations between 20°C and 35°C, the hue and brightness of the particles in the image are compensated. For example, when rising temperature causes red particles to reflect more light, the true color information is restored by reducing the gain of the red channel. In the feature analysis stage, the preprocessed image is input into the color segmentation module. For example, a threshold-based region partitioning method is used to calculate the area percentage of each color region. Morphological parameters of connected domains are also extracted, such as calculating the minimum bounding rectangle aspect ratio to filter out abnormally shaped clusters. Finally, the particle distribution data of the current frame is compared with historical frames. For example, the particle distribution data of the same location is detected to detect sudden changes in area or morphological distortion, thereby determining the type of abnormal feature.

[0041] Compared with existing technologies, existing corona treatment equipment relies solely on impedance sensors to detect the total amount of surface charge, making it unable to distinguish between local and global defects. Traditional image processing methods do not consider the impact of temperature on color recognition. For example, when high temperatures cause image color cast, the amount of adsorbed particles may be misjudged. In addition, existing technologies do not use a multi-frame comparison mechanism, making it difficult to distinguish between transient interference and persistent defects. This solution addresses the problem of detection errors caused by environmental factors by introducing temperature compensation and edge enhancement algorithms; by combining color distribution and shape feature analysis, it achieves a refined assessment of the adsorption state; and by comparing the differences between adjacent frames, it effectively distinguishes between local and global defects.

[0042] Through the above technical solution, this application solves the problems of existing corona treatment equipment's inability to accurately detect surface charge uniformity and its susceptibility to environmental interference. A preprocessing mechanism improves the reliability of image feature extraction, ensuring consistent detection results under different temperature conditions. Multi-dimensional feature analysis accurately quantifies particle adsorption states, enabling the identification of subtle partial discharge anomalies. An inter-frame comparison mechanism effectively eliminates transient interference, preventing misjudgments caused by airflow or light fluctuations.

[0043] This application further proposes a process for judging abnormal features, including obtaining the position and parameter information of the abnormal area, extracting the color distribution characteristics and shape characteristics of the area, and comparing them with the characteristics of the corresponding areas in adjacent frames. If the similarity is lower than the preset similarity threshold and the position difference is less than the preset position difference threshold, it is judged as a local defect; if abnormal features appear in the same position in multiple consecutive frames and the feature similarity is higher than the preset similarity threshold, it is judged as a global defect.

[0044] Among them, the position and parameter information of the abnormal area refers to the coordinates of the abnormal area and its shape parameters extracted by the image processing algorithm. Specifically, it can be implemented by edge detection combined with morphological analysis to accurately locate the physical position of the abnormal area. The color distribution feature refers to the distribution pattern of pixels of different colors in the abnormal area. Specifically, it can be implemented by color histogram statistics to quantify the visual properties of the abnormal area. The shape feature refers to the geometric morphological feature of the abnormal area. Specifically, it can be implemented by contour extraction combined with Fourier descriptor analysis to characterize the structural characteristics of the abnormal area. The similarity threshold refers to the pre-set feature matching critical value, which can be determined by the machine learning training sample set to determine whether the feature difference exceeds the normal fluctuation range. The position difference threshold refers to the allowable coordinate offset range, which can be set according to the equipment operation accuracy to eliminate misjudgment caused by mechanical vibration.

[0045] Specifically, during the continuous conveying of the packaging film, the image detection system continuously collects images of particle adsorption on the surface of the isolation window. When an abnormal area is detected, the system immediately extracts the coordinate position, color distribution histogram and contour shape parameters of the area, and simultaneously retrieves the detection data of the same position in the adjacent time frame. By calculating the cosine similarity of the color histogram and the matching degree of the contour shape, combined with the statistical analysis of the position offset, it is possible to effectively distinguish between transient interference and substantial defects. For abnormal areas with sudden changes in color characteristics but stable positions, the system determines that there are local defects on the surface of the material, which may be caused by surface contamination of the packaging film, uneven thickness or abnormal local discharge electrodes; for similar abnormal features that appear stably in multiple consecutive frames, they are identified as global processing defects caused by equipment parameter imbalance, such as unstable corona effects that cause large-area charging differences in the packaging film.

[0046] Compared to existing technologies, traditional detection methods focus solely on changes in overall charge and are unable to effectively distinguish between local defects and systematic errors. This solution, through multi-dimensional feature extraction and dynamic comparative analysis, can accurately identify the type and cause of abnormal features. This enables intelligent identification of defect types during high-speed production, avoiding misadjustments caused by traditional methods that cannot distinguish defect properties.

[0047] Through the above technical solution, the present application can effectively identify transient interference and substantial defects that occur during the corona treatment process, accurately distinguish between two types of faults: insufficient local surface treatment of the material and improper equipment parameter settings, and provide precise adjustment basis for subsequent control modules, thereby avoiding over-adjustment or adjustment lag caused by misjudgment, and significantly improving the stability of corona treatment quality.

[0048] The present application further proposes that the image detection module is configured with a target abnormal area delineation strategy, and several rectangular wireframes are drawn on the adsorbed image information to enclose the abnormal features in the abnormal area, and the rectangular wireframe with the smallest area is selected as the pending area. The scaling factor is matched based on the size of the pending area, and the pending area is enlarged with the center of the pending area as the base point as the target abnormal area, and the color distribution characteristics and area ratio of the target abnormal area are extracted.

[0049] Among them, the target abnormal area delineation strategy refers to a technical method that focuses on key abnormal features by dynamically adjusting the image analysis range. Specifically, it can be achieved by using an edge detection algorithm combined with a minimum bounding box calculation. Its function is to exclude interference information in non-critical areas. A rectangular wireframe refers to a geometric marking box that covers abnormal features. Specifically, it can be generated by an image coordinate point set traversal algorithm and is used to preliminarily locate the boundaries of abnormal areas. The pending area refers to the minimum abnormal feature range that has been preliminarily screened out. Specifically, it can be determined by an area threshold comparison method. Its function is to avoid over-magnification of non-critical areas. The scaling factor refers to a magnification ratio parameter that is dynamically adjusted according to the size of the pending area. Specifically, it can be calculated based on a preset mapping relationship between pixel size and physical size to ensure that the magnified area completely covers the abnormal features.

[0050] Specifically, when abnormal features appear in the adsorption image information, the system first automatically generates multiple rectangular wireframes of different sizes on the image. By comparing the completeness of the abnormal features covered by each wireframe, the wireframe with the smallest area is selected as the area to be determined. Then, the corresponding scaling factor is matched according to the pixel size of the area to be determined. For example, when the side length of the area to be determined is less than the preset threshold, a 1.5x scaling factor can be selected to expand outward from this center point to generate the target abnormal area. After the area is locked, the system extracts its color distribution characteristics and area ratio through color channel separation and morphological analysis, providing accurate data input for subsequent equivalent charge calculation.

[0051] Compared with existing technologies, traditional methods typically use a fixed-size detection window for anomaly analysis, making it difficult to adapt to defect features of varying sizes. This solution dynamically delineates the target anomaly area and adaptively adjusts the detection range based on the actual feature size. This avoids the waste of computing resources caused by large-scale detection and solves the problem of missed detection of small features.

[0052] Through the above technical solution, this application realizes the precise positioning and analysis of abnormal features, effectively improves the sensitivity and accuracy of surface charge detection, and provides a reliable basis for the dynamic adjustment of subsequent corona treatment parameters, thereby ensuring that the surface charge uniformity of the packaging film meets the process requirements.

[0053] This application further proposes a calibration strategy, which includes performing no-load tests at different voltages through a controllable corona discharge device, recording the adsorption area ratio of particles of each particle size on the isolation window surface, establishing a mathematical model of the adsorption amount of particles of each particle size and the electric field strength, and calibrating the temperature correction coefficient in combination with the temperature sensor data.

[0054] Among them, the calibration strategy refers to eliminating parameter deviations in equipment operation through a preset test process. Specifically, it can be implemented using a programmed no-load test module, which triggers corona discharge according to a preset voltage gradient and simultaneously records adsorption data. No-load testing refers to starting corona discharge when no packaging film passes by to eliminate the interference of material properties on the test results. Specifically, it can be implemented using a closed calibration box to ensure that the test environment is consistent with the actual working conditions. The mathematical model refers to the functional relationship between the quantitative particle adsorption amount and the electric field strength. Specifically, it can be constructed using polynomial fitting or machine learning algorithms. For example, regression analysis is performed based on the corresponding data of the adsorption area ratio and the voltage value. The temperature correction coefficient refers to a compensation parameter that eliminates the influence of temperature changes on the adsorption behavior of particles. Specifically, real-time data can be collected through a temperature sensor, and a correction function can be established in combination with experimental data on the change of adsorption amount with temperature.

[0055] Specifically, during calibration, the corona treatment equipment is first operated in a state without packaging film, and different voltage values ​​are applied in sequence through a controllable corona discharge device, for example, increasing in steps of 5kV in the range of 10kV to 50kV. After each discharge, the image acquisition module collects the adsorption distribution image of particles of various sizes on the surface of the isolation window, calculates its area ratio and records the corresponding voltage value. Subsequently, based on the corresponding data of the adsorption area ratio and the voltage, the least squares method is used to fit the mathematical relationship between the adsorption amount and the electric field strength of particles of various sizes. At the same time, the temperature sensor monitors the ambient temperature in real time, and by comparing the adsorption data at different temperatures, a correction coefficient for the influence of temperature changes on the adsorption amount is established, such as calibrating the temperature compensation curve in the range of 20°C to 40°C.

[0056] Compared with existing technologies, traditional corona treatment equipment lacks a systematic calibration mechanism, making it unable to eliminate the impact of ambient temperature changes on test results, resulting in large errors in equivalent charge calculations. Existing technologies rely solely on empirical judgments to determine the relationship between particle adsorption and electric field strength, without a quantitative model. This makes it difficult to accurately reflect dynamic changes under actual operating conditions. This solution establishes a mathematical model through no-load testing and introduces temperature compensation, providing physical support for equivalent charge calculations and significantly improving test accuracy.

[0057] Through the above technical solution, this application solves the problem of inaccurate detection caused by ambient temperature fluctuations in traditional corona treatment equipment. The mathematical model established through no-load testing can accurately reflect the changing law of particle adsorption under different voltages. Combined with the temperature correction coefficient, it can effectively eliminate the influence of temperature drift and ensure the stability and reliability of the equivalent charge calculation results under different environmental conditions.

[0058] The present application further proposes that the control module adjusts the voltage of the discharge electrode or the speed of the conveying component based on the equivalent charge. If the equivalent charge is lower than the target range, the voltage of the discharge electrode is increased; if the equivalent charge is higher than the target range, the voltage is reduced or the conveying speed is increased to shorten the residence time of the packaging film in the corona zone; the adjustment process follows the voltage adjustment coefficient and speed adjustment curve determined in advance by experiments.

[0059] Among them, the equivalent charge refers to the conversion of the adsorption area ratio of particles of different particle sizes into a quantitative indicator through the mathematical model established in the calibration stage. Specifically, it can be achieved by the sum of the product of the color area ratio and the correction coefficient, which is used to reflect the comprehensive parameter of the charging ability of the packaging film surface.

[0060] The target range refers to the numerical range of the surface charge state of the packaging film determined through experiments within a reasonable range. Specifically, it can be achieved by using preset thresholds under different material or process conditions as the triggering benchmark for the adjustment action.

[0061] The voltage regulation coefficient and speed regulation curve refer to the correlation between voltage and charge, speed and processing effect established through no-load testing or actual operation data. Specifically, they can be implemented using linear or nonlinear function models to guide the incremental amplitude and change trend during the regulation process.

[0062] Specifically, during operation, the control module receives the equivalent charge value calculated by the image detection module in real time and compares it with the preset target range. When it is detected that the equivalent charge is lower than the target lower limit, the system gradually increases the operating voltage of the discharge electrode according to the stored voltage adjustment coefficient. For example, the voltage increment can be set to increase by 50V to 200V per adjustment step until the charge returns to the target range. When the charge exceeds the target upper limit, the system can choose to reduce the voltage or increase the operating speed of the conveying component. For example, the speed increment can be set to increase by 0.5 meters to 2 meters per minute, reducing the risk of over-processing by shortening the exposure time of the packaging film in the corona area. The incremental amplitude and change rate used in the adjustment process are based on the pre-established experimental data model to ensure the stability and response speed of the adjustment process.

[0063] Compared to existing technologies, traditional methods only monitor charging parameters at a single location through impedance sensors, making it impossible to identify differences in surface treatment uniformity. This solution utilizes a dual control mechanism that dynamically adjusts voltage and conveyor speed. This allows for coordinated adjustment of multiple parameters based on real-time equivalent charge levels. For example, if an abnormal charge level is detected in a local area, the system can adjust the conveyor speed to change the material's residence time in the corona zone, while also fine-tuning the voltage to achieve rapid correction.

[0064] Through the above technical solution, this application achieves closed-loop dynamic control of corona treatment parameters, effectively addressing the problem of treatment instability caused by uneven electric field distribution or fluctuating material properties during high-speed production. By matching preset adjustment coefficients and curves to different working conditions, the lag of manual intervention is avoided while maintaining treatment quality, while also reducing energy waste caused by excessive treatment.

[0065] The present application further proposes configuring an environmental interference elimination strategy. The environmental interference elimination strategy includes determining whether there are ambient light fluctuations by monitoring the consistency of image brightness, identifying airflow interference by particle displacement, and triggering the constant temperature module to work through temperature sensor data. When interference is detected to exceed a threshold, the system suspends processing and starts a compensation mechanism. The environmental interference elimination strategy also includes an interference elimination sub-strategy. The interference elimination sub-strategy includes pre-storing a number of ambient light interference image information. The ambient light interference image information is specifically an image of ambient light projected on the surface of the isolation window captured by the image acquisition module during normal use of the system. When it is determined that ambient light interference occurs, a pending interference image is obtained. If the duration of the pending interference image exceeds the preset duration, the corresponding pending interference image is identified as ambient light interference image information and stored.

[0066] Among them, ambient light fluctuation refers to the abnormal image brightness distribution caused by changes in the intensity of external light sources. Specifically, an image sensor can be used to capture the brightness distribution on the surface of the isolation window in real time, and the judgment can be made by calculating whether the regional brightness variance value exceeds the threshold.

[0067] Particle displacement refers to the abnormal movement distance of dust particles on the surface of the isolation window due to the action of airflow. It can be quantified by the statistical mean of the change in particle coordinates in consecutive frame images.

[0068] The constant temperature module refers to a device used to maintain a stable temperature inside the test box. Specifically, a semiconductor refrigeration chip can be used in conjunction with a temperature feedback control system to suppress temperature fluctuations.

[0069] The compensation mechanism means that when a disturbance is detected, the system automatically pauses the processing flow and initiates a repair operation. This can be achieved by disconnecting the power supply to the corona component, shutting down the conveyor component motor and triggering an alarm signal.

[0070] Specifically, during the operation of the equipment, the image sensor continuously collects adsorption images on the surface of the isolation window and identifies ambient light interference by analyzing the brightness consistency between consecutive frames. When it is detected that the image brightness variance value exceeds the preset threshold, the system determines that there is ambient light fluctuation, and the corona treatment process is suspended at this time to avoid data distortion. At the same time, by comparing the position offset of the particles in adjacent frame images, it is calculated whether the average displacement exceeds the allowable range. If it exceeds, it is determined that there is airflow interference. The temperature sensor monitors the internal temperature of the test box in real time. When the temperature fluctuation exceeds the allowable range, the constant temperature module is started to restore temperature stability. If any of the above interferences exceeds the preset threshold, the system will automatically enter a pause state and perform compensation operations, such as turning off the high-voltage power supply, stopping the conveyor belt and issuing a warning signal.

[0071] Compared to existing technologies, traditional corona treatment equipment typically relies on a single sensor to detect environmental interference, such as a temperature sensor to control a constant temperature module. This lacks comprehensive assessment of light fluctuations and airflow disturbances. This solution, by integrating a multi-dimensional detection mechanism that combines image brightness analysis, particle displacement monitoring, and temperature feedback, can more comprehensively identify and isolate multiple sources of environmental interference, avoiding misjudgments or missed detections caused by a single interference source.

[0072] Through the above technical solution, this application can effectively eliminate interference from ambient light fluctuations, airflow disturbances, and temperature changes on corona treatment effect detection in high-speed continuous production scenarios, ensuring the authenticity and stability of adsorption image data. By pausing the processing flow and linking the compensation mechanism, the impact of interfering factors on the system can be quickly eliminated, avoiding product quality fluctuations caused by environmental anomalies and improving the reliability and consistency of the corona treatment process.

[0073] The present application further proposes that the environmental interference elimination strategy also includes an interference elimination sub-strategy, and the interference elimination sub-strategy includes pre-storing a number of ambient light interference image information. The ambient light interference image information is specifically an image of ambient light projected on the surface of the isolation window captured by the image acquisition module during normal use of the system. When it is determined that ambient light interference occurs, a pending interference image is obtained. If the duration of the pending interference image exceeds the preset duration, the corresponding pending interference image is identified as ambient light interference image information and stored.

[0074] Among them, the ambient light interference image information refers to the optical characteristic data of ambient light reflected or projected on the surface of the isolation window captured by the system under normal working conditions. It can be specifically represented by the image grayscale distribution histogram and frequency domain transformation coefficient, and interference pattern recognition is achieved by establishing a baseline interference database.

[0075] Among them, the pending interference image refers to the adsorption image fragment that is suspected to be ambient light interference in real-time detection. Specifically, it can be extracted by using timestamp continuous interception and image similarity matching algorithm, and the interference type can be determined by comparing historical interference features.

[0076] Among them, the duration refers to the judgment time window for triggering the interference storage mechanism. Specifically, a dynamic threshold adjustment strategy can be adopted to adjust the duration setting value according to the frequency of changes in ambient light intensity to ensure the timeliness and accuracy of interference identification.

[0077] Specifically, during equipment operation, when the image detection module detects abnormal brightness fluctuations in the adsorption image, the system automatically captures the current frame and subsequent continuous image sequences as pending interference images. By matching the features of the pending interference image with pre-stored ambient light interference images, if the match exceeds a set threshold and persists for more than, for example, 30 seconds, the image features are added to the ambient light interference database. This creates a dynamically updated interference feature library, enabling the system to adapt to changing lighting conditions in diverse production environments.

[0078] Compared to existing technologies, traditional methods rely solely on fixed thresholds to detect ambient light interference, making them incapable of adapting to dynamically changing production environments. This solution, by establishing a scalable interference signature library and incorporating a time-based judgment mechanism, effectively distinguishes between transient interference and persistent ambient light changes, avoiding frequent equipment startups and shutdowns due to misjudgments.

[0079] Through the above technical solution, this application achieves autonomous learning and dynamic updating of ambient light interference characteristics, significantly improving the accuracy of interference elimination. During the continuous processing of packaging film, the system can quickly identify and filter known ambient light interference patterns, reducing the number of false alarms caused by external lighting changes and ensuring the stable operation of the corona treatment process.

[0080] This application further proposes a method for calculating the equivalent charge, which includes converting the adsorption area ratio of particles of various particle sizes into the equivalent charge based on a mathematical model established in the calibration phase. The specific formula is as follows:

[0081] ,

[0082] in, represents the equivalent charge, represents the adsorption area ratio of the i-th color particle, represents the weight coefficient of the i-th color particle, It represents the electric field strength correction coefficient of the i-th color particle, and i represents the total number of particle types.

[0083] Among them, the adsorption area ratio refers to the ratio of the coverage area of ​​particles of a specific color on the surface of the isolation window to the total adsorption area. It can be achieved by extracting color features and calculating pixel ratios through image segmentation algorithms, and is used to quantify the adsorption intensity of particles of different particle sizes; the weight coefficient refers to a proportional factor set according to the particle size, which can be determined by a pre-calibrated particle size-adsorption force relationship, and is used to reflect the difference in contribution of particles of different particle sizes to the charge; the electric field strength correction coefficient refers to the electric field strength deviation compensation parameter caused by temperature or environmental factors, which can be obtained by fitting experimental data, and is used to eliminate the influence of external interference on the calculation of equivalent charge.

[0084] Specifically, during the corona treatment process, particles of different sizes are adsorbed to the surface of the isolation window due to the electric field force, and the adsorption distribution is directly related to the surface charge intensity of the packaging film. The adsorption image of the color particles is collected through the image detection module, and the area ratio data of each color area is extracted. Then, combined with the mathematical model established in the calibration stage, the adsorption area ratio data is weightedly calculated with the weight coefficient and the electric field strength correction coefficient, and the equivalent charge value is finally output. For example, during the operation of the system, if the adsorption area ratio of red particles is detected to be 15%, the corresponding weight coefficient is 0.8, and the electric field strength correction coefficient is 1.2, then this type of particles is The contribution value is 15%×0.8×1.2=0.144, and the equivalent charge is obtained by adding up the contribution values ​​of all color particles.

[0085] Compared to existing technologies, traditional methods that rely on impedance sensors can only measure overall charge and are unable to distinguish differences in charge across different regions. This solution, however, analyzes the adsorption distribution of multi-colored particles and, combined with mathematical models, converts microscopic adsorption behavior into quantitative parameters, accurately reflecting the uniformity of charge on the packaging film surface. For example, when an abnormal adsorption area is detected in a local area, the system can quickly locate the defect through regional calculations, a capability unavailable to traditional sensors.

[0086] Through the above technical solution, this application can dynamically evaluate the surface charge state of packaging film based on multi-dimensional data, resolving the inability of traditional detection methods to quantify charge uniformity. Furthermore, by integrating temperature and environmental interference correction parameters into a mathematical model, it significantly improves detection accuracy and control stability. For example, in high-speed production scenarios, when ambient temperature fluctuations cause changes in electric field strength, the system can automatically adjust the correction factor to avoid misjudgments caused by distorted data from a single sensor.

[0087] This application further proposes a specific method of voltage regulation and speed regulation, including: if the equivalent charge is lower than the target range, according to the formula Adjust the discharge electrode voltage, where and Represent the voltage values ​​before and after adjustment respectively, ΔV represents the voltage increment; if the equivalent charge is higher than the target range, then according to the formula Adjust the conveying speed, where and Respectively represent the conveying speed before and after adjustment, Represents the speed increment; both the voltage increment and the speed increment are determined through experiments and stored in the system.

[0088] The voltage increment refers to the change in voltage required to restore the equivalent charge to the target range. This can be calculated using a linear or nonlinear function model, dynamically matching the increment requirements under different operating conditions through a preset voltage adjustment coefficient. The speed increment refers to the speed increase set to shorten the packaging film's residence time in the corona zone. This can be achieved using a segmented adjustment strategy, selecting the corresponding increment gradient based on the deviation in the equivalent charge detected in real time. The voltage adjustment coefficient and speed adjustment curve are determined experimentally, specifically by fitting multiple sets of test data under different materials and environmental conditions to ensure that the adjustment parameters are highly compatible with the equipment's operating conditions.

[0089] Specifically, when the equivalent charge is detected to deviate from the target range, a formulaic adjustment mechanism is used to make real-time corrections to the discharge electrode voltage or conveying speed. For example, if the packaging film's charge absorption is insufficient, the system automatically triggers a voltage increment superposition algorithm, gradually increasing the discharge intensity based on a preset adjustment factor. If the charge absorption exceeds the target, speed increment adjustment is prioritized to shorten processing time and avoid material damage caused by excessive corona discharge. The two adjustment modes are linked by establishing rules based on experimental data. For example, speed adjustment is prioritized in high-temperature environments to prevent arc breakdown, while voltage adjustment is prioritized to maintain processing stability when material thickness varies.

[0090] Compared with existing technologies, traditional corona treatment equipment relies solely on single-parameter adjustment and lacks quantitative formula support, which can easily lead to adjustment lag or overshoot. This solution, however, utilizes a dual-parameter collaborative adjustment mechanism, combined with an experimentally calibrated incremental model, to select the optimal adjustment path for different operating conditions. For example, it uses progressive voltage adjustment when slight deviations are detected, while initiating emergency speed adjustment for sudden deviations. This enables rapid response and precise control of fluctuations in equivalent charge quantity.

[0091] A method for using a corona treatment device for packaging film lamination includes the following steps:

[0092] Model building step: establishing a mathematical model based on the adsorption area ratio of particles of different particle sizes under different voltages;

[0093] The equipment operates as follows: the conveying assembly delivers the packaging film into the corona area at a set speed; the discharge electrode generates plasma to charge the surface of the packaging film; and the image acquisition module collects adsorption image information on the isolation window;

[0094] In the equivalent charge calculation step, the image detection module calculates the equivalent charge on the surface of the packaging film based on a preset image detection strategy, and the control module adjusts the voltage of the discharge electrode or the speed of the conveying component according to the equivalent charge.

[0095] The method includes an environmental interference elimination step, which includes: determining ambient light fluctuations by monitoring image brightness consistency. If the brightness deviation exceeds a preset threshold, processing is suspended and the ambient light stabilizes. Airflow disturbances are identified by particle displacement. If the displacement exceeds a preset threshold, an airflow adjustment signal is generated. It should be noted that although the test box is sealed, ambient airflow in the production workshop, such as from the ventilation system and equipment operation, may infiltrate through non-fully sealed areas such as gaps between the test box and the main body of the equipment, cable connectors, and other non-perfectly sealed areas. Furthermore, airflow disturbances generated by high-speed packaging film transport can affect the air flow field around the test box, indirectly causing particle displacement within the box. Two common methods for airflow adjustment are: 1. Replacing the test box's sealing ring; 2. Adding an air curtain device to form an airflow barrier around the test box to block external disturbances, or generating a reverse air curtain in the opposite direction of the packaging film transport to offset the airflow. The constant temperature module is triggered by temperature sensor data. If temperature fluctuations exceed a preset temperature fluctuation threshold, a temperature adjustment signal is generated, activating the workshop temperature control module to restore the constant temperature state and ensure a stable testing environment.

[0096] Through the above technical solution, this application effectively solves the problem of unstable treatment effect caused by the single adjustment method of traditional corona treatment equipment. Through the coordinated formula adjustment of voltage and speed, it not only avoids the risk of unstable discharge caused by over-reliance on voltage regulation, but also prevents insufficient treatment caused by simple speed increase, thereby maintaining the dynamic balance of the charge on the surface of the packaging film in high-speed continuous production scenarios, ensuring the uniformity and consistency of the corona treatment quality.

[0097] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions based on the principles of the present invention are within the scope of protection of the present invention. It should be noted that improvements and modifications that do not depart from the principles of the present invention are within the scope of protection of the present invention.

Claims

1. A corona treatment device for packaging film lamination, characterized in that: The invention comprises a corona assembly, a conveying assembly and a control module arranged in a corona area, wherein the corona assembly comprises a test box (1), an image acquisition module (2) and an image detection module (3), wherein the test box (1) is arranged on a side of the packaging film away from the discharge electrode, wherein a plurality of dust particles of different particle sizes are built into the test box, and dust particles of different particle size ranges are correspondingly provided with different colors, and a transparent window (4) is provided on the top of the test box, and when the discharge electrode generates plasma, the dust particles in the test box are adsorbed to the surface of the isolation window due to the action of the electric field force, the image acquisition module (2) is used to obtain adsorption image information on the isolation window, the image detection module (3) calculates the equivalent charge amount of the packaging film surface based on a preset image detection strategy, the conveying assembly conveys the packaging film into the corona area at a set speed, and the control module adjusts the voltage of the discharge electrode or the speed of the conveying assembly according to the equivalent charge amount.

2. The corona treatment equipment for packaging film lamination according to claim 1, characterized in that: The image detection strategy includes preprocessing the adsorption image information, which includes edge feature enhancement and temperature compensation. The edge feature enhancement extracts the boundary features of each color particle and optimizes its clarity. The temperature compensation eliminates the impact of temperature changes on the visual characteristics of the particles based on real-time temperature data. Subsequently, the color distribution characteristics and shape characteristics in the adsorption image information are analyzed to extract the area proportion and connected domain morphology of each color area. The connected domain morphology represents the geometric characteristics of the continuous area composed of adjacent pixels in the adsorption image information, and abnormal features are identified in combination with the difference comparison of adjacent frames.

3. The corona treatment equipment for packaging film lamination according to claim 2, characterized in that: The abnormal feature judgment process includes obtaining the position and parameter information of the abnormal area, extracting the color distribution characteristics and shape characteristics of the abnormal area, and comparing them with the characteristics of the corresponding areas in adjacent frames. If the similarity is lower than the preset similarity threshold and the position difference is less than the preset position difference threshold, it is judged as a local defect; if abnormal features appear in the same position in multiple consecutive frames and the feature similarity is higher than the preset similarity threshold, it is judged as a global defect.

4. The corona treatment equipment for packaging film lamination according to claim 2, characterized in that: The image detection module (3) is configured with a target abnormal area delineation strategy, wherein a plurality of rectangular wireframes are drawn on the adsorption image information to enclose abnormal features in the abnormal area, and the rectangular wireframe with the smallest area is selected as the pending area. A scaling factor is matched based on the size of the pending area, and the pending area is enlarged with the center of the pending area as the base point to serve as the target abnormal area, and the color distribution characteristics and area proportion of the target abnormal area are extracted.

5. The corona treatment equipment for packaging film lamination according to claim 1, characterized in that: The corona treatment equipment is equipped with a calibration strategy, which includes performing no-load tests at different voltages using a controllable corona discharge device, recording the adsorption area ratio of particles of various particle sizes on the isolation window surface, establishing a mathematical model of the adsorption amount of particles of various particle sizes and the electric field strength, and calibrating the temperature correction coefficient based on temperature sensor data.

6. The corona treatment equipment for packaging film lamination according to claim 1, characterized in that: The control module adjusts the voltage of the discharge electrode or the speed of the conveying assembly based on the equivalent charge amount. If the equivalent charge amount is lower than the target range, the voltage of the discharge electrode is increased; if the equivalent charge amount is higher than the target range, the voltage is reduced or the conveying speed is increased to shorten the residence time of the packaging film in the corona zone. The regulation process follows the voltage regulation coefficient and speed regulation curve determined in advance by experiments.

7. The corona treatment equipment for packaging film lamination according to claim 1, characterized in that: The corona treatment equipment is equipped with an environmental interference elimination strategy, which includes determining whether there are ambient light fluctuations by monitoring image brightness consistency, identifying airflow interference by particle displacement, and triggering the operation of the constant temperature module through temperature sensor data; when interference exceeding a threshold is detected, the system suspends processing and activates a compensation mechanism.

8. The corona treatment equipment for packaging film lamination according to claim 7, characterized in that: The environmental interference elimination strategy also includes an interference elimination sub-strategy, which includes pre-storing a number of ambient light interference image information. The ambient light interference image information is specifically an image of ambient light projected on the surface of the isolation window captured by the image acquisition module during normal use of the system. When it is determined that ambient light interference occurs, a pending interference image is obtained. If the duration of the pending interference image exceeds a preset duration, the corresponding pending interference image is identified as ambient light interference image information and stored.

9. A method for using a corona treatment device for packaging film composites, comprising providing the corona treatment device for packaging film composites according to any one of claims 1 to 8, characterized in that: The following steps are involved: Model building step: establishing a mathematical model based on the adsorption area ratio of particles of different particle sizes under different voltages; The equipment operates as follows: the conveying assembly delivers the packaging film into the corona area at a set speed; the discharge electrode generates plasma to charge the surface of the packaging film; and the image acquisition module collects adsorption image information on the isolation window; In the equivalent charge calculation step, the image detection module calculates the equivalent charge on the surface of the packaging film based on a preset image detection strategy, and the control module adjusts the voltage of the discharge electrode or the speed of the conveying component according to the equivalent charge.

10. The method for using the corona treatment equipment for packaging film lamination according to claim 9, characterized in that: The method of use includes an environmental interference elimination step, which includes: judging ambient light fluctuations by monitoring image brightness consistency, and pausing processing and waiting for the ambient light to stabilize if the brightness deviation exceeds a preset threshold; identifying airflow interference through particle displacement, and generating an airflow adjustment signal if the displacement exceeds a preset threshold; triggering the constant temperature module to work through temperature sensor data, and generating a temperature adjustment signal if the temperature fluctuation exceeds a preset temperature fluctuation threshold.

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