A method and system for detecting bubble stability air pressure of a cast film

Abstract

The present application relates to the technical field of cast film detection, and particularly relates to a cast film stable bubble air pressure detection method and system. The method comprises obtaining a reference image with grating fringe characteristics, and each deformed grating image of optical collection of a to-be-detected molten film bubble; determining a local deformation amount in each deformed grating image based on the reference image with grating fringe characteristics and each deformed grating image; confirming a deformation distribution curve of all sectors divided in a circumferential direction on the molten film bubble within a period of time based on the local deformation amount in each deformed grating image; and obtaining a detection result of the cast film based on the deformation distribution curve, the pressure distribution state and the disturbance type of the molten film bubble. The present application aims to solve the problem that the existing detection method cannot capture the uneven distribution of local geometric deformation on the film bubble circumference induced by uneven air flow and the rapid change with time, and the detection accuracy is low.

Description

Technical Field

[0001] This invention relates to the field of cast film testing technology, specifically to a method and system for detecting the stable bubble pressure of cast film. Background Technology

[0002] Cast film is a type of non-stretched and non-oriented flat extrusion film produced by rapidly cooling a cast melt. There are two methods: single-layer casting and multi-layer co-extrusion. It features high production speed, high output, and excellent film transparency, gloss, and thickness uniformity. In the production of multi-layer co-extrusion films, especially in manufacturing high-end packaging materials with stringent gas barrier requirements, maintaining the geometric stability of the molten film bubble during the blow-forming process is crucial for ensuring the uniformity of the final product quality.

[0003] Current detection methods typically rely on a single pressure monitoring point in the gas supply line to maintain a constant overall gas pressure inside the membrane bubble. However, this single-point monitoring method only reflects changes in the average pressure inside the membrane bubble. It cannot effectively detect localized and high-frequency pressure inconsistencies at different locations within the membrane bubble caused by external environmental disturbances due to uneven cooling airflow. Localized pressure inconsistencies can lead to microscopic thickness variations or abnormal stretching and orientation of the membrane in the corresponding areas. For membranes containing functional materials such as gas barrier layers, these microscopic defects can become channels for gas molecule permeation, severely damaging the core performance of the product and reducing yield. Furthermore, single-point monitoring only provides information on overall pressure changes within the membrane bubble and cannot distinguish between a uniform pressure drop caused by insufficient gas supply and a localized pressure disturbance in a specific location due to uneven external cooling. When localized low-pressure ripples appear, the minute pressure drop recorded by a single monitoring point may be misinterpreted as insufficient overall pressure. This not only fails to compensate for the localized low pressure but may also exacerbate instability in other areas of the membrane bubble by increasing overall pressure, creating a vicious cycle. Existing detection methods cannot capture the local geometric deformations that are unevenly distributed on the circumference of the membrane bubble and change rapidly over time, induced by airflow imbalance. The detection accuracy is low, and it cannot provide a direct and reliable basis for judgment for subsequent precise adjustment schemes that require zoned control of the cooling system. Summary of the Invention

[0004] The purpose of this invention is to provide a method and system for detecting the stable air pressure of cast film, which solves the problem that existing detection methods cannot capture the local geometric deformation that is unevenly distributed on the circumference of the film bubble and changes rapidly over time due to airflow imbalance, resulting in low detection accuracy.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a method for detecting the stable air pressure of cast film, comprising:

[0006] Acquire a reference image with grating stripe features obtained by optically acquiring a sample molten film bubble of a cast film over a period of time, and an image of each deformed grating obtained by optically acquiring a sample molten film bubble under test;

[0007] Based on the reference image with grating stripe features and each deformed grating image, the local deformation amount within each deformed grating image is determined;

[0008] Based on the local deformation amount within each deformed grating image, the deformation distribution curve of all sectors divided along the circumferential direction on the molten film bubble is confirmed over a period of time.

[0009] Based on the deformation distribution curve, the pressure distribution state and disturbance type inside the molten film bubble are determined, and the detection result of the cast film is obtained.

[0010] Furthermore, this application also proposes a step for obtaining the detection result of the cast film after determining the pressure distribution state and disturbance type inside the molten film bubble based on the deformation distribution curve, including:

[0011] Using the deformation distribution curve, determine the deformation amount of all local deformations distributed in each sector and the global deformation component of all local deformations in all sectors.

[0012] The deformation amount of each sector is compared with the global deformation component to obtain a local deformation amount sequence;

[0013] Based on the global deformation components and local deformation sequence, the pressure distribution and disturbance type inside the molten film bubble are determined, and the detection results of the cast film are obtained.

[0014] Furthermore, this application also proposes a step for determining the local deformation amount within each deformed grating image based on the reference image having grating fringe features and each deformed grating image, including:

[0015] Based on the reference image with grating stripe features and each deformed grating image, the signal sequence of each sector characterizing each deformed grating image over time is confirmed;

[0016] Based on the signal sequence of each sector, after identifying the signal components of each sector signal sequence that are consistent with the direction of movement of the molten film bubble between adjacent sectors, an apparent deformation signal is generated.

[0017] Remove the apparent deformation signal from the signal sequence of each sector to confirm the geometric deformation signal;

[0018] Based on the geometric deformation signal, the local deformation amount within each deformed grating image is determined.

[0019] Furthermore, this application also proposes a step of generating an apparent deformation signal based on each sector signal sequence, after identifying the signal components of each sector signal sequence that are consistent with the direction of movement of the molten film bubble between adjacent sectors:

[0020] Based on the signal sequence of each sector, the artifact signal characterizing the fixed optical artifact of the detection device is obtained;

[0021] Remove artifact signals from each of the sector signal sequences to determine each corrected sector signal sequence;

[0022] Based on each corrected sector signal sequence, after identifying the signal components in each sector signal sequence that are consistent with the direction of movement of the molten film bubble between adjacent sectors, an apparent deformation signal is generated.

[0023] Furthermore, this application also proposes a step of generating an apparent deformation signal based on each corrected sector signal sequence, after identifying the signal components of each sector signal sequence that are consistent with the direction of movement of the molten film bubble between adjacent sectors:

[0024] Based on the corrected sector signal sequence, the current process parameters associated with the moving speed of the molten film bubble are identified, as well as the propagation interval time of each sector signal to its adjacent sector is identified.

[0025] Based on the current process parameters, determine the expected delay time for each sector to propagate between its adjacent sectors;

[0026] After comparing each propagation interval with the corresponding expected delay time, the expected delay time extracts the signal component in the sector signal sequence corresponding to the actual time interval and the expected delay time.

[0027] An apparent deformation signal is generated based on the signal components.

[0028] Furthermore, this application also proposes the steps of acquiring a reference image with grating stripe features obtained by optically acquiring a sample molten film bubble of a cast film over a period of time, and acquiring each deformed grating image of the molten film bubble under test by optical acquisition, including:

[0029] Acquire a reference initial image with grating stripe features obtained by optically acquiring a sample molten film bubble of a cast film over a period of time, and an initial image of each deformed grating obtained by optically acquiring a molten film bubble under test;

[0030] The reference initial image and each deformed grating initial image are subjected to noise reduction and contrast enhancement processing respectively to obtain the reference image and each deformed grating image.

[0031] Furthermore, this application also proposes a step for acquiring a reference image with grating stripe features obtained by optically acquiring a sample molten film bubble of a cast film over a period of time, including:

[0032] The intensity and range of the light source output by the modulation light source projection device are adjusted so that the light source is projected onto the circumferential area of ​​the molten film bubble;

[0033] For a period of time, the driving light source outputs light to the circumferential area of ​​the molten film bubble of the casting film, so that the surface of the molten film bubble of the casting film produces specular reflection light;

[0034] The image acquisition unit is driven to acquire images of specularly reflected light, thereby obtaining a reference image with grating stripe features.

[0035] Furthermore, this application also proposes a step for the driving image acquisition unit to acquire images of specularly reflected light and obtain a reference image with grating stripe features, including:

[0036] The image acquisition unit is driven to acquire images of specularly reflected light, resulting in an image sequence;

[0037] After confirming the position of each pixel in the image sequence, the reference signal and the orthogonal signal orthogonal to the reference signal are confirmed respectively.

[0038] Based on the reference signal and the orthogonal signal, two product sequences are obtained;

[0039] The two product sequences are filtered in the time dimension to extract two low-frequency components;

[0040] Based on the two low-frequency components, after confirming the signal amplitude at all pixel positions in the image sequence, a reference pattern is generated.

[0041] Furthermore, this application also proposes a step for obtaining the detection result of the cast film after determining the pressure distribution state and disturbance type inside the molten film bubble based on the global deformation component and local deformation sequence:

[0042] Based on the local deformation sequence, determine the pressure distribution state inside the molten film bubble;

[0043] Determine the type of disturbance based on global deformation components;

[0044] The detection results of the cast film are obtained by considering the overall pressure distribution and disturbance type.

[0045] The present invention also provides a casting film bubble stabilization pressure detection system for performing the casting film bubble stabilization pressure detection method described in any of the above claims, the system comprising:

[0046] The image acquisition module is used to acquire a reference image with grating stripe features that is optically acquired from a sample molten film bubble of a cast film over a period of time, as well as each deformed grating image that is optically acquired from the molten film bubble to be tested.

[0047] The first determining module is used to determine the local deformation amount in each deformed grating image based on the reference image with grating stripe features and each deformed grating image;

[0048] The second determining module is used to determine the deformation distribution curve of all sectors divided along the circumferential direction on the molten film bubble over a period of time, based on the local deformation amount in each of the deformed grating images.

[0049] The judgment module is used to determine the pressure distribution state and disturbance type inside the molten film bubble based on the deformation distribution curve, and then obtain the detection result of the cast film.

[0050] Compared with the prior art, the casting film bubble pressure detection method and system of the present invention have the following advantages:

[0051] This invention optically acquires a reference image with grating stripe features from a sample molten film bubble of a cast film, while simultaneously optically acquiring the molten film bubble under test to obtain each deformed grating image. Optical methods are used to avoid interference that might occur due to physical contact with the film bubble. Based on the reference image and the deformed grating image, the local deformation amount within each deformed grating image is determined. By comparing the changes in the grating stripes before and after deformation, the microscopic deformation at each point on the bubble surface is precisely quantified. The local deformation amounts are spatially mapped and integrated along the circumference of the molten film bubble, confirming the deformation distribution curves of all sectors divided along the circumference on the molten film bubble over a period of time. Based on the deformation distribution curves, the pressure distribution state inside the molten film bubble and the type of disturbance causing deformation can be determined, and the detection results of the cast film can be output. This allows for the differentiation between overall pressure fluctuations and localized airflow impacts or uneven cooling, thus providing clear detection information and improving detection accuracy. Attached Figure Description

[0052] To more clearly illustrate the specific embodiments of the present invention, the accompanying drawings used in the specific embodiments will be briefly described below. In all the drawings, the elements or parts are not necessarily drawn to scale.

[0053] Figure 1 This is a flowchart of a method for detecting the stable air pressure of a cast film according to the present invention.

[0054] Figure 2 This is a structural block diagram of a cast film bubble stabilization pressure detection system according to the present invention.

[0055] In the diagram: 210, image acquisition module; 220, first determination module; 230, second determination module; 240, judgment module.

[0056] The implementation and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0057] The following drawings disclose several embodiments of the present invention. For clarity, many practical details will be described in the following description. However, it should be understood that these practical details are not intended to limit the invention. That is, in some embodiments of the invention, these practical details are not essential. Furthermore, for the sake of simplicity, some conventional structures and components will be shown in the drawings in a simple schematic manner.

[0058] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0059] Furthermore, in this invention, the use of terms such as "first" and "second" is for descriptive purposes only and does not specifically refer to any order or sequence, nor is it intended to limit the invention. They are merely used to distinguish components or operations described using the same technical terms, and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of various embodiments can be combined with each other, but only if they are feasible for those skilled in the art. If a combination of technical solutions is contradictory or impossible to implement, such a combination should be considered nonexistent and not within the scope of protection claimed by this invention.

[0060] In traditional multilayer co-extruded film production, maintaining the geometric stability of the molten film bubble typically relies on a single pressure monitoring point in the gas supply line to keep the overall internal gas pressure of the bubble constant. However, monitoring at this point only reflects changes in the average pressure inside the bubble. It cannot effectively detect localized and high-frequency pressure inconsistencies at different locations within the bubble caused by external environmental disturbances, resulting in low detection accuracy. These localized pressure inconsistencies can lead to microscopic thickness unevenness or abnormal stretching orientation in the corresponding areas of the film. For films containing functional materials such as gas barrier layers, these microscopic defects can become channels for gas molecule permeation, impairing product performance and reducing yield.

[0061] To further understand the content, features, and effects of this invention, the following embodiments are provided, and detailed descriptions are given below in conjunction with the accompanying drawings:

[0062] Please see Figure 1 This invention provides a method for detecting the stable air pressure of cast film, comprising the following steps:

[0063] S100: Acquire a reference image with grating stripe features obtained by optically acquiring a sample molten film bubble of the cast film over a period of time, and an image of each deformed grating pattern obtained by optically acquiring the molten film bubble under test. The grating stripe features are patterns with periodic brightness or phase changes projected onto the surface of the molten film bubble by a specific optical device, which are captured by the image acquisition unit after reflection or transmission on the bubble surface. This provides a recognizable, high-contrast reference pattern for subsequent quantification of minute deformations on the bubble surface using digital image processing technology.

[0064] S200. Based on the reference image with grating fringe features and each deformed grating image, determine the local deformation amount within each deformed grating image. The local deformation amount is a quantified value of the degree of geometric deformation of the molten film bubble surface in a specific region relative to its undeformed state or reference state. It can be calculated based on the local displacement, distortion, or density changes of the grating fringe features in the deformed grating image, for example, through Fourier transform, phase unwrapping, or digital image correlation methods. This accurately reflects the local stress or pressure changes experienced by the molten film bubble at different locations.

[0065] S300. Based on the local deformation amount within each of the deformed grating images, confirm the deformation distribution curves of all sectors divided circumferentially on the molten film bubble over a period of time. The deformation distribution curves are trend diagrams or data sequences showing the change in local deformation amount of each sector with its circumferential position across multiple sectors divided circumferentially on the molten film bubble. These curves can be obtained by spatial mapping and temporal averaging or statistical analysis of the local deformation amounts of multiple deformed grating images acquired over a period of time. The purpose is to visually demonstrate the uniformity or non-uniformity of deformation of the molten film bubble in the circumferential direction, thereby revealing the spatial distribution characteristics of the internal pressure field.

[0066] S400. Based on the deformation distribution curve, the pressure distribution state and disturbance type inside the molten film bubble are determined to obtain the detection result of the cast film. The pressure distribution state and disturbance type are diagnostic judgments made based on the deformation characteristics of the molten film bubble surface revealed by the deformation distribution curve, assessing the uniformity and stability of the internal pressure of the bubble and identifying external or internal factors causing deformation fluctuations. The pressure distribution state can refer to whether the internal pressure of the bubble is uniform overall, locally high, or locally low; the disturbance type can refer to overall pressure fluctuations, local airflow impacts, or uneven cooling. This provides a clear basis for identifying the root cause of bubble instability and guiding subsequent process adjustments.

[0067] Specifically, an industrial camera is used as the image acquisition module. This camera is equipped with a suitable lens and works in conjunction with a light source projection device capable of projecting a specific grating pattern. The light source projection device can be an LED array or a laser projection module, and the projected grating pattern has a preset period and contrast. When acquiring a reference image, the light source projection device projects the grating pattern onto the surface of a molten film bubble in a known stable state, while the industrial camera simultaneously acquires an image sequence formed by specular reflection. Image processing is then used to obtain a reference image with grating fringe characteristics. When inspecting the molten film bubble under test, the same light source projection device projects the grating pattern onto its surface, and the industrial camera acquires the deformed grating image in real time. Subsequently, a preset image processing algorithm is run on a computer equipped with a high-performance GPU. This algorithm can employ a phase analysis method based on Fourier transform or a digital image correlation (DIC) algorithm. By comparing the local displacement or deformation of the grating fringes in the reference image and each deformed grating image, the local deformation amount within each deformed grating image is accurately calculated. Next, the circumferential region of the molten membrane bubble is logically divided into multiple sectors, for example, uniformly divided into 360 sectors. The local deformation within each sector is statistically analyzed and integrated to generate a deformation distribution curve over a period of time. This curve can be presented as a two-dimensional chart, with the horizontal axis representing the circumferential position and the vertical axis representing the local deformation. An expert system or machine learning model is used to make judgments based on the morphological characteristics of the deformation distribution curve. For example, if the curve exhibits obvious periodic fluctuations and large differences between peaks and troughs, it may be judged as local airflow disturbance; if the curve rises or falls overall, it may be judged as overall pressure fluctuation. Finally, this module outputs the detection results regarding the stable pressure of the cast membrane bubble, such as the presence of local low-pressure disturbances on the eastern side of the bubble or the overall low pressure of the bubble, providing intuitive diagnostic information.

[0068] In this embodiment, optical acquisition is performed on the molten film bubble of the cast film sample to obtain a reference image with grating stripe features. Simultaneously, optical acquisition is performed on the molten film bubble under test to obtain each deformed grating image. This establishes a benchmark and test object for subsequent deformation analysis, avoiding potential interference from physical contact with the film bubble using optical methods. Based on the reference image and the deformed grating image, the local deformation amount within each deformed grating image is determined. By comparing the changes in the grating stripes before and after deformation, the microscopic deformation at each point on the film bubble surface is accurately quantified, extracting the key transformation of the microscopic physical state from macroscopic image information. The local deformation amount is spatially mapped and integrated along the circumference of the molten film bubble, confirming the deformation distribution curve of all sectors divided along the circumference on the molten film bubble over a period of time. This visually demonstrates the deformation differences and dynamic changes of the film bubble at different circumferential positions, thus transforming discrete local deformation data into spatially continuous pressure distribution features. Based on this deformation distribution curve, the pressure distribution state inside the molten film bubble and the type of disturbance causing deformation can be determined, and the detection results of the cast film can be output. The test results can distinguish between overall pressure fluctuations and localized airflow impacts or uneven cooling, providing more accurate diagnostic information and enabling targeted adjustments to process parameters.

[0069] In some embodiments described above, this application also proposes a step for obtaining the detection result of the cast film after determining the pressure distribution state and disturbance type inside the molten film bubble based on the deformation distribution curve, including:

[0070] Using the aforementioned deformation distribution curve, the deformation amounts distributed across each sector and the global deformation components of all local deformations across all sectors are determined. Specifically, the deformation amounts distributed across each sector represent the set of all local deformations within the circumferentially divided sectors of the molten bubble, or their statistical characteristics, such as average, maximum, or integral values. This can be achieved by summing or averaging the local deformations within each sector to quantify the deformation degree of each local region. The global deformation components of all local deformations across all sectors represent the overall deformation trend or average deformation level of the molten bubble. This can be achieved by averaging or weighted averaging all local deformations across all sectors, providing an overall deformation benchmark.

[0071] The deformation amount of each sector is compared with the global deformation component to obtain a local deformation amount sequence. This local deformation amount sequence is an ordered set of data reflecting the difference between the deformation of each sector and the overall deformation, obtained by comparing the deformation amount of each sector with the global deformation component. It can be achieved by subtracting or dividing the deformation amount of each sector by the global deformation component and arranging the data in sector order, thus highlighting the local deformation situation.

[0072] Based on the global deformation components and local deformation sequence, the pressure distribution and disturbance type inside the molten film bubble are determined to obtain the detection result of the cast film. The detection result of the cast film is an assessment conclusion of the quality or production status of the cast film, such as qualified, unqualified, or requiring adjustment. This can be achieved by making a decision based on a comprehensive assessment of the pressure distribution and disturbance type, guiding adjustments to the production process and controlling product quality.

[0073] Specifically, after obtaining the deformation distribution curves of all sectors along the circumferential direction on the molten membrane bubble over a period of time, the data processing unit can analyze these curves. By determining the deformation amount of all local deformations distributed in each sector, the local deformation amounts within each sector can be integrated or averaged to obtain the representative deformation amount of each sector at the current moment. For example, if a sector contains local deformation data points, the arithmetic mean of these data points can be calculated as the deformation amount of that sector. Simultaneously, to determine the global deformation component of all local deformations across all sectors, the local deformation amounts of all sectors can be averaged overall, or a weighted average can be calculated to obtain a benchmark value reflecting the overall deformation trend of the membrane bubble. Next, the deformation amount of each sector is compared with the calculated global deformation component. This can be done using difference calculation (deformation amount of each sector minus the global deformation component) or ratio calculation (deformation amount of each sector divided by the global deformation component). Arranging these comparison results in sector order yields the local deformation amount sequence. For example, if the deformation of a certain sector is higher than the global deformation component, it will show a positive deviation in the local deformation sequence, indicating that there may be local high pressure or external impact in that area. Based on the global deformation component and the local deformation sequence, the pressure distribution state and disturbance type inside the molten film bubble are comprehensively judged, and the detection result of the cast film is output. For example, if the global deformation component continuously deviates from the normal range for a period of time, and the local deformation sequence shows that the deviation of each sector is not large, it can be judged that the uniform pressure distribution state is abnormal due to the fluctuation of the overall gas supply pressure. If the global deformation component remains stable, but one or several sectors in the local deformation sequence show periodic deviations, it can be judged that the non-uniform pressure distribution state is caused by uneven local cooling air or external mechanical disturbance. By pre-setting a series of judgment rules or using machine learning models, the specific pressure distribution state and disturbance type can be automatically identified based on these feature combinations, and the detection result can be given as to whether the cast film is qualified or not or what process adjustments are needed.

[0074] In this embodiment, the deformation distribution curve is used to determine the deformation amount of all local deformations distributed in each sector and the global deformation component of all local deformations across all sectors. These are then compared to obtain a local deformation sequence, which allows for a more detailed capture of the deformation characteristics of the molten film bubble and a distinction between overall and local deformation. The assessment of the pressure distribution and disturbance type within the molten film bubble is no longer a rough overall evaluation, but rather the identification of localized pressure anomalies and specific sources of disturbance. Therefore, more accurate casting film detection results can be obtained, providing a reliable basis for precise control and quality improvement in the production process.

[0075] In some embodiments described above, this application also proposes a step of determining the local deformation amount within each deformed grating image based on the reference image having grating stripe features and each deformed grating image, including:

[0076] Based on the reference image with grating fringe features and each deformed grating image, a signal sequence characterizing the temporal variation of each deformed grating image is identified. The sector signal sequence is a set of signals formed by processing each deformed grating image to extract the grating fringe variation information of each sector along the circumferential direction of the molten film bubble at different time points, and arranging them in chronological order. This characterizes the deformation or displacement of each sector in continuous time frames, decomposing the complex deformation of the entire film bubble into analyzable local time sequences, providing fundamental data for subsequent signal separation and accurate deformation calculation.

[0077] Based on each sector signal sequence, after identifying the signal components in each sector signal sequence that exhibit the same direction of movement as the molten bubble between adjacent sectors, an apparent deformation signal is generated. This apparent deformation signal is a signal component in the sector signal sequence caused by the overall movement of the molten bubble or optical artifacts of the detection device, and not by the actual geometric deformation of the bubble. It manifests as a global or local shift in the grating fringes, but this shift does not reflect the expansion or contraction of the bubble itself. The goal is to identify and separate these interfering signals from the total deformation signal to avoid interfering with the calculation of the true deformation.

[0078] The apparent deformation signal in each sector signal sequence is removed to confirm the geometric deformation signal. The geometric deformation signal is the signal component that reflects only the actual geometric deformation of the molten bubble, obtained after removing the apparent deformation signal from the sector signal sequence. It eliminates interference from bubble movement or optical artifacts, aiming to provide pure and accurate information on the local deformation of the bubble, laying the foundation for subsequent precise determination of the local deformation amount.

[0079] Based on the geometric deformation signal, the local deformation amount within each deformed grating image is determined.

[0080] Specifically, this involves continuously acquiring a reference image with grating fringe features and a series of time-varying deformed grating images. Each deformed grating image is then uniformly divided into multiple sectors along its circumference, such as 360 sectors, each corresponding to one degree of the circumference of the molten bubble. For each sector, the displacement or phase change of the grating fringes within it is analyzed, and combined with the time series, to identify the signal sequence of each sector representing the time-varying changes of each deformed grating image. For example, Fourier transform profilometry or digital image correlation methods can be used to extract the phase information of the grating fringes within each sector and record its changes over time, forming a time-series signal. To identify and generate the apparent deformed signal, the signal propagation characteristics of each sector signal sequence between adjacent sectors can be analyzed. If the molten bubble exhibits overall vertical movement, similar signal patterns will appear sequentially with a certain time delay in the adjacent sector signal sequences. By calculating the cross-correlation function or phase difference between adjacent sector signals, this signal component consistent with the direction of molten bubble movement can be identified. A threshold can be set so that when the propagation interval of signals from adjacent sectors matches the expected delay time predicted based on the overall movement speed of the bubble, the signal component is considered an apparent deformation signal. The identified apparent deformation signals are then removed from the original signal sequence of each sector. This is achieved through signal filtering techniques; if the apparent deformation signal exhibits a specific frequency or time pattern, a corresponding filter can be designed to remove it. After removing the apparent deformation signals, the remaining signals are confirmed as geometric deformation signals, reflecting only the actual geometric deformation of the molten bubble itself. Based on these pure geometric deformation signals, a pre-established deformation-signal conversion model can be used, such as utilizing the physical relationship between grating fringe displacement and the curvature change of the bubble surface, to accurately determine the local deformation amount within each deformed grating image.

[0081] In this embodiment, the apparent deformation signal caused by the movement of the molten film bubble or optical artifacts of the detection device is effectively identified and separated. This allows the interference of these non-real deformation factors to be eliminated when determining the local deformation amount, thereby obtaining a geometric deformation signal that only reflects the actual geometric deformation of the molten film bubble. This results in higher accuracy of the local deformation amount within each deformation grating image, which can truly reflect the deformation of the molten film bubble and provide a reliable data foundation for subsequent pressure distribution judgment.

[0082] In some embodiments described above, this application further proposes a step of generating an apparent deformation signal based on each sector signal sequence, after identifying signal components in each sector signal sequence that are consistent with the direction of movement of the molten film bubble between adjacent sectors:

[0083] Based on the signal sequence of each sector, artifact signals characterizing the fixed optical artifacts of the detection device are obtained. These artifact signals are fixed, recurring interference signals generated in the image by the optical system of the detection device during image acquisition due to inherent defects, dust, scratches, or non-uniformity of optical elements. They can be obtained through statistical analysis or pre-calibration of image data acquired without a molten film bubble or under known stable conditions. The goal is to characterize and quantify the interference of the detection device itself on the original sector signal sequence.

[0084] Artifact signals in each sector signal sequence are removed to determine each corrected sector signal sequence. The corrected sector signal sequence refers to the signal sequence that more accurately reflects the state of the molten film bubble after removing artifact signals from the original sector signal sequence. This can be achieved through signal subtraction, filtering, or model fitting. The aim is to eliminate noise and bias introduced by the detection device itself, providing a clean data foundation for subsequent signal analysis.

[0085] Based on each corrected sector signal sequence, after identifying the signal components in each sector signal sequence that are consistent with the direction of molten bubble movement between adjacent sectors, an apparent deformation signal is generated. Specifically, identifying the signal components in each sector signal sequence that are consistent with the direction of molten bubble movement between adjacent sectors is achieved by analyzing the propagation characteristics of the sector signal sequence between different sectors and extracting the signal components related to the overall or local movement of the molten bubble. This can be achieved using methods such as signal correlation analysis, pattern matching, or signal propagation delay calculation based on a physical model. The goal is to separate the signal caused by the movement of the molten bubble from the complex sector signals in order to subsequently generate an accurate apparent deformation signal.

[0086] Specifically, when acquiring artifact signals of the fixed optical artifacts characterizing the detection device, this application can acquire multiple grating images of the film without molten film bubbles or in a stable state via an image acquisition unit before the casting film production line starts up or during production when the molten film bubble is in a stable state. These acquired images are then averaged, or specific regions in the images are statistically analyzed, such as calculating the average gray value or signal intensity of each pixel location, to obtain an artifact image or artifact signal sequence representing the fixed optical artifacts. The artifact signal can be stored in the system's storage unit as a reference for subsequent correction. When removing artifact signals from each sector signal sequence, signal subtraction can be used. For example, for each newly acquired sector signal sequence, it is subtracted from the pre-acquired artifact signal point-by-point or frame-by-frame. If the artifact signal is in image form, the pixel values ​​of the original sector signal sequence are subtracted from the pixel values ​​of the corresponding artifact image. If the artifact signal is in sequence form, the signal value of each time point or spatial point in the original sector signal sequence is subtracted from the corresponding artifact signal value. This subtraction operation effectively eliminates the superposition effect of artifacts on the original signal, resulting in a purer corrected sector signal sequence. Based on this, and using the corrected sector signal sequence, the apparent deformation signal is generated by identifying the signal components in each sector that exhibit the same direction of molten bubble movement as the adjacent sectors. For example, time-domain or frequency-domain analysis can be performed on the corrected sector signal sequence to determine the signal propagation delay by calculating the cross-correlation function or phase difference between adjacent sector signals. If this delay matches the actual or expected propagation speed of the molten bubble, the corresponding signal component can be considered to be in the same direction as the molten bubble's movement. These identified signal components can be extracted and combined to form the apparent deformation signal. For example, digital signal processing techniques, such as bandpass filtering or pattern recognition algorithms, can be used to extract signal components with specific propagation characteristics from the corrected sector signal sequence; these components represent the apparent deformation of the molten bubble.

[0087] In this embodiment, before identifying the apparent deformation signal, fixed artifact interference introduced by the detection device's own optical system is effectively identified and removed. This makes the sector signal sequence used to identify the apparent deformation signal cleaner, thereby improving the accuracy of apparent deformation signal identification. Since the accuracy of the apparent deformation signal directly affects the confirmation of subsequent geometric deformation signals and the calculation of local deformation, it ensures the accuracy of the entire data chain from the original image to the final pressure distribution judgment, thus improving the overall accuracy and reliability of cast film bubble pressure detection.

[0088] In some embodiments described above, this application also proposes a step of generating an apparent deformation signal based on each corrected sector signal sequence, after identifying signal components in each sector signal sequence that are consistent with the direction of movement of the molten film bubble between adjacent sectors:

[0089] Based on each corrected sector signal sequence, the current process parameters associated with the moving speed of the molten film bubble are identified, as well as the propagation interval time for each sector signal to propagate to its adjacent sectors. The current process parameters are production process parameters directly related to the overall moving speed of the molten film bubble, which can be obtained using data such as bubble traction speed, extrusion speed, or blow-up ratio provided by the production line control system. This provides a basis for subsequent calculations of the theoretical signal propagation time. The propagation interval time is the time required for a signal feature within one sector to propagate to its adjacent sectors in the corrected sector signal sequence. It can be measured using signal processing techniques, such as cross-correlation analysis, peak detection, or feature point tracking, to measure the time delay between adjacent sector signals. This reflects the actual motion state of local areas of the molten film bubble.

[0090] Based on the current process parameters, the expected delay time for each sector to propagate between its adjacent sectors is determined. The expected delay time is the theoretically calculated time required for a signal to propagate from one sector to its adjacent sector, based on the current process parameters of the molten film bubble and the geometric distance between sectors. It can be calculated using a preset physical model or empirical formula. The aim is to establish a benchmark to determine whether the actual signal propagation conforms to the normal movement pattern of the molten film bubble.

[0091] After comparing each propagation interval with the corresponding expected delay time, the expected delay time extracts the signal component from the sector signal sequence corresponding to the actual time interval matching the expected delay time. Here, the signal component is a signal component in the sector signal sequence that has specific spatiotemporal characteristics caused by the actual movement and deformation of the molten film bubble, and it can be separated from the original signal using methods such as filtering, pattern recognition, or threshold screening. This serves as an effective data source for generating apparent deformation signals.

[0092] An apparent deformation signal is generated based on the signal components.

[0093] In this embodiment, by introducing the molten bubble's moving speed and comparing the actual signal propagation time with the theoretically expected time, accurate extraction of apparent deformation signals is achieved. Specifically, after obtaining the signal sequence of each corrected sector, the current process parameters associated with the molten bubble's moving speed, such as the bubble's traction speed or extrusion speed, are first identified. Simultaneously, each propagation interval time from one sector to its adjacent sectors is identified. The current process parameters provide macroscopic information about the overall movement of the molten bubble, while the propagation interval time reflects the actual transmission speed of the local signal between sectors. Based on this, and using the identified current process parameters, each expected delay time for the propagation of each sector between its adjacent sectors is confirmed. The expected delay time is a theoretical value calculated based on the overall moving speed of the molten bubble and the fixed geometric relationship between sectors, representing the normal time delay caused by the overall movement of the bubble. Each actually measured propagation interval time is compared with the corresponding expected delay time. This comparison mechanism is the core of this scheme; it effectively distinguishes signal components caused by the molten bubble's own movement and deformation from those that may be caused by residual fixed optical artifacts or other non-bubble movement factors. Only when the actual propagation interval is highly consistent with the expected delay time is the signal component considered to be indeed caused by the movement of the molten film bubble, and it is extracted from the sector signal sequence. Based on these rigorously screened and extracted signal components, an apparent deformation signal is generated. Building upon the previous artifact removal, a secondary screening is performed using the kinematic properties of the molten film bubble, ensuring that the generated apparent deformation signal is purer and more accurate. This allows subsequent calculations of local deformation and judgments of the internal pressure distribution of the molten film bubble to be based on more reliable data, thereby significantly improving the accuracy of cast film bubble pressure detection.

[0094] In some embodiments described above, this application also proposes the steps of acquiring a reference image with grating stripe features obtained by optically acquiring a sample molten film bubble of a cast film over a period of time, and acquiring each deformed grating image of the molten film bubble under test by optical acquisition, including:

[0095] Acquire a reference initial image with grating stripe features obtained by optically acquiring a sample molten film bubble of the cast film over a period of time, and an initial image of each deformed grating obtained by optically acquiring a molten film bubble under test.

[0096] The reference initial image and each deformed grating initial image are subjected to denoising and contrast enhancement processing, respectively, to obtain the reference image and each deformed grating image. The denoising process removes unnecessary random interference or artifacts from the image using algorithms, specifically employing techniques such as median filtering, Gaussian filtering, non-local mean filtering, or wavelet denoising, aiming to improve the signal-to-noise ratio and reduce noise interference in subsequent image analysis. The contrast enhancement process adjusts the brightness, color, or grayscale range of the image to make the visual differences between different regions of the image more pronounced. This can be achieved using techniques such as histogram equalization, gamma correction, Laplacian sharpening, or contrast-limited adaptive histogram equalization, highlighting the grating stripe features in the image and making deformation information easier to identify and quantify.

[0097] In this embodiment, a reference initial image with grating stripe features, obtained through optical acquisition of a sample molten film bubble of a cast film over a period of time, and initial images of each deformed grating, obtained through optical acquisition of the molten film bubble under test, provide the raw data foundation for subsequent image processing. Given the potential noise and insufficient contrast in the initial images, this scheme further performs noise reduction and contrast enhancement processing on the reference initial image and each deformed grating initial image, respectively. Noise reduction effectively filters out random noise introduced during image acquisition, ensuring the purity of image information and avoiding interference from noise in subsequent calculations of local deformation. Simultaneously, contrast enhancement significantly improves the clarity and recognizability of the grating stripes in the image, making the changes in grating stripes caused by minute deformations on the surface of the molten film bubble more prominent and easier to capture accurately. Due to the high-quality preprocessing of the original images, more accurate and reliable deformation data can be obtained when determining the local deformation within each deformed grating image based on the reference image and each deformed grating image. The close integration of image preprocessing and subsequent deformation determination enables the entire cast film bubble pressure detection method to more accurately reflect the actual deformation state of the molten film bubble, thereby improving the accuracy of judging the internal pressure distribution and disturbance type of the molten film bubble, and ultimately improving the reliability of the cast film detection results.

[0098] In some embodiments described above, this application also proposes a step of acquiring a reference image with grating stripe features obtained by optically acquiring a sample molten film bubble of a cast film over a period of time, including:

[0099] The intensity and range of the light source output by the modulated light source projection device are adjusted so that the light source is projected onto the circumferential area of ​​the molten film bubble. The light source projection device is a device capable of emitting and guiding light to illuminate a specific area. It can be implemented using various methods such as lasers, LED arrays, halogen lamps combined with optical lens groups, etc., to provide stable and controllable illumination conditions for the surface of the molten film bubble.

[0100] For a period of time, the driving light source outputs light to the circumferential area of ​​the molten film bubble of the casting film, so that the surface of the molten film bubble of the casting film produces specular reflection light.

[0101] The image acquisition unit is driven to acquire images of specularly reflected light, obtaining a reference image with grating stripe characteristics. The image acquisition unit is a device capable of capturing light and converting it into digital image signals; it can be implemented using various methods such as a CCD camera, CMOS camera, or high-speed camera, and its purpose is to acquire optical image information of the molten film bubble surface.

[0102] Specifically, a ring-shaped light source array composed of multiple high-brightness LED beads is used as the light source projection device, which can surround the outside of the molten film bubble. By controlling the driving current and on / off mode of the LED beads, the intensity of the light source can be precisely modulated, and the projection range can be controlled by adjusting the physical position of the array or using a variable aperture, ensuring that the light can be concentrated and uniformly projected onto the circumferential area of ​​the molten film bubble. For a period of time, such as several seconds, the ring-shaped LED light source array can be driven to continuously output light to the circumferential area of ​​the molten film bubble of the casting film sample. Due to the certain smoothness of the molten film bubble surface, the projected light will produce specular reflection on its surface. The reflected light carries the grating stripe information of the molten film bubble surface, and due to the specular reflection characteristics, the stripes will appear clearer and brighter. At the same time, a high-resolution industrial camera is configured as an image acquisition unit. This camera can be installed opposite the light source projection device or at a specific angle to capture the specular reflection light reflected back from the surface of the molten film bubble. When a light source continuously projects and generates specularly reflected light, the industrial camera can be driven to continuously acquire images at a preset frame rate, thereby obtaining a series of reference images containing clear grating stripe features. These images can be directly used for subsequent analysis, allowing for the identification of grating stripes without complex preprocessing.

[0103] In this embodiment, by precisely controlling the projection method and range of the light source and utilizing the specular reflection characteristics of the molten film bubble, the clarity and contrast of the grating fringes in the acquired reference image can be enhanced. This makes the grating fringes more prominent, thus providing a more reliable and high-quality image basis for accurately determining the local deformation of the molten film bubble.

[0104] In some embodiments described above, this application also proposes a step for the driving image acquisition unit to acquire images of specularly reflected light and obtain a reference image with grating stripe features, including:

[0105] The image acquisition unit is driven to acquire images of specularly reflected light, resulting in an image sequence.

[0106] After confirming the position of each pixel in the image sequence, a reference signal and an orthogonal signal orthogonal to the reference signal are identified. The reference signal and the orthogonal signal orthogonal to the reference signal are two mutually orthogonal reference signals used for demodulating or analyzing the original image signal; for example, they can be a pair of sine and cosine signals with a 90-degree phase difference. This decomposes the complex image signal into independent components that are easy to process and analyze, laying the foundation for subsequent signal extraction and noise suppression.

[0107] Two product sequences are obtained based on the reference signal and the orthogonal signal.

[0108] The two product sequences are filtered in the time dimension to extract two low-frequency components. This time-dimensional filtering processes the signal of each pixel in the image sequence as it changes over time to remove noise or extract specific frequency components. For example, a low-pass filter can be used to process the signal values ​​of the same pixel at different time frames in the image sequence, smoothing signal fluctuations, removing high-frequency noise and transient interference, and preserving stable low-frequency information in the image signal. Low-frequency components are slowly changing and low-frequency components in the signal, typically representing the main trend or stability information of the signal. They are crucial for separating the effective information of the image from noise and high-frequency interference. This effective information usually carries the stability characteristics of the grating fringes and is key to generating high-quality reference patterns.

[0109] Based on the two low-frequency components, after confirming the signal amplitude at all pixel positions in the image sequence, a reference pattern is generated.

[0110] Specifically, when acquiring specular reflection images of the molten film bubble, the image acquisition unit can be a high-speed industrial camera, such as a CMOS camera with a frame rate of hundreds of frames per second. This camera is configured to continuously capture images of the molten film bubble surface at a fixed frequency, resulting in a series of consecutive image frames, i.e., an image sequence. When processing each pixel position in the image sequence, the grayscale value change of each pixel along the time axis can be analyzed. The reference signal and orthogonal signals can be sine and cosine wave signals generated by software algorithms and synchronized with the camera's acquisition frequency. For example, if the camera acquires images at a frequency of 100Hz, 100Hz sine and cosine signals can be generated as references. Multiplying the original grayscale value sequence of each pixel with these two reference signals yields two product sequences. To remove high-frequency noise from these product sequences, a digital low-pass filter can be used for time-dimensional filtering. For example, a moving average filter or Butterworth filter with a cutoff frequency lower than the image acquisition frequency can be used to smooth the product sequence of each pixel, thereby extracting two stable low-frequency components. Finally, based on these two filtered low-frequency components, the signal amplitude or phase information at each pixel location can be calculated using the arctangent function or other phase demodulation algorithms, and reconstructed into a sharp, noise-free reference pattern that clearly displays the grating fringes on the surface of the molten film bubble.

[0111] In this embodiment, by performing signal decomposition, temporal filtering, and low-frequency component extraction on the image sequence, artifacts caused by ambient light fluctuations, camera sensor noise, and minute vibrations on the surface of the molten film bubble can be significantly suppressed, thereby obtaining a reference pattern with a higher signal-to-noise ratio, greater clarity, and higher accuracy. The high-quality reference pattern can more realistically reflect the grating stripe characteristics of the molten film bubble surface, providing a precise benchmark for subsequent calculations of local deformation, thus improving the overall accuracy and reliability of the molten film bubble pressure detection and ensuring higher accuracy in judging the internal pressure distribution and disturbance type of the molten film bubble.

[0112] In some embodiments described above, this application also proposes a step for obtaining the detection result of the cast film after determining the pressure distribution state and disturbance type inside the molten film bubble based on global deformation components and local deformation sequence:

[0113] Based on the local deformation sequence, the pressure distribution inside the molten film bubble is determined.

[0114] The type of disturbance is determined based on the global deformation components.

[0115] The detection results of the cast film are obtained by considering the overall pressure distribution and disturbance type.

[0116] In this embodiment, by performing refined analysis of the deformation information of the molten film bubble, the accurate determination of the internal pressure distribution and disturbance type of the bubble is achieved. Specifically, after obtaining the local deformation sequence characterizing the local deformation of the bubble and the global deformation component characterizing the overall deformation of the bubble, this scheme first determines the internal pressure distribution of the molten film bubble based on the local deformation sequence. This is because the local deformation sequence directly reflects the deformation details of the bubble surface in different sectors, and these details are directly related to the local non-uniformity of the internal gas pressure. For example, a significant deviation in a certain sector of the local deformation sequence may indicate the presence of local high or low pressure in that area. Simultaneously, this scheme independently determines the disturbance type based on the global deformation component. The global deformation component reflects the overall expansion or contraction trend of the bubble and is closely related to disturbance factors that cause overall instability, such as gas supply fluctuations and overall displacement of the cooling air ring. By separating the local deformation sequence and the global deformation component for judgment, the interference of global changes on local pressure judgment and the confusion of local details on the overall disturbance type judgment can be avoided. By comprehensively considering the independently determined pressure distribution and disturbance types, the detection results of the cast film are obtained. This step-by-step judgment and comprehensive analysis strategy makes the identification of complex internal states of the film bubble more accurate, effectively distinguishing between overall pressure fluctuations and local pressure disturbances, providing a more precise basis for subsequent process adjustments. By combining the refined judgment process with the previous steps of determining the local deformation sequence and global deformation components through deformation distribution curves, the entire chain from raw image data to the final detection results is more complete and accurate, thus more effectively solving film quality problems caused by uneven local pressure.

[0117] Based on the method for detecting the stable air pressure of cast film described in any of the above embodiments, please refer to... Figure 2 The present invention also provides a casting film bubble pressure detection system, which includes an image acquisition module 210, a first determination module 220, a second determination module 230 and a judgment module 240.

[0118] The image acquisition module 210 is used to acquire a reference image with grating stripe features obtained by optically acquiring a sample molten film bubble of the cast film over a period of time, as well as each deformed grating image obtained by optically acquiring the molten film bubble to be tested.

[0119] The first determining module 220 is used to determine the local deformation amount within each deformed grating image based on the reference image with grating stripe features and each deformed grating image.

[0120] The second determining module 230 is used to determine the deformation distribution curve of all sectors divided along the circumferential direction on the molten film bubble over a period of time based on the local deformation amount in each of the deformed grating images.

[0121] The judgment module 240 is used to determine the pressure distribution state and disturbance type inside the molten film bubble based on the deformation distribution curve, and then obtain the detection result of the cast film.

[0122] In this embodiment, the image acquisition module 210 first acquires optical images of the molten film bubble, including a reference image with grating stripe features and each deformed grating image. These images form the basis for all subsequent analyses, ensuring the accuracy and real-time nature of the data source. The first determination module 220 receives these image data and calculates the local deformation amount within each deformed grating image based on the difference between the reference image and the deformed grating image. This process is a crucial step in quantifying the film bubble deformation, laying the foundation for subsequent analysis. The second determination module 230 integrates and processes the discrete local deformation amounts to confirm the deformation distribution curves of all sectors divided circumferentially on the molten film bubble over a period of time. By constructing the deformation distribution curves, the system can grasp the overall deformation trend and spatial distribution of the film bubble. The judgment module 240 receives and analyzes the deformation distribution curves to determine the pressure distribution state and disturbance type inside the molten film bubble, and outputs the detection results of the cast film, thereby improving the detection accuracy.

[0123] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the present invention specification.

Claims

1. A method for detecting the stable air pressure of cast film, characterized in that, include: Acquire a reference image with grating stripe features obtained by optically acquiring a sample molten film bubble of a cast film over a period of time, and an image of each deformed grating obtained by optically acquiring a sample molten film bubble under test; Based on the reference image with grating stripe features and each deformed grating image, the local deformation amount within each deformed grating image is determined; Based on the local deformation amount within each deformed grating image, the deformation distribution curve of all sectors divided along the circumferential direction on the molten film bubble is confirmed over a period of time. Based on the deformation distribution curve, the pressure distribution state and disturbance type inside the molten film bubble are determined, and the detection result of the cast film is obtained. Based on the deformation distribution curve, the steps for determining the pressure distribution state and disturbance type inside the molten film bubble, and then obtaining the detection result of the cast film, include: Using the deformation distribution curve, determine the deformation amount of all local deformations distributed in each sector and the global deformation component of all local deformations in all sectors. The deformation amount of each sector is compared with the global deformation component to obtain a local deformation amount sequence; Based on the global deformation components and local deformation sequence, the pressure distribution and disturbance type inside the molten film bubble are determined, and the detection results of the cast film are obtained.

2. The method for detecting the stable air pressure of cast film according to claim 1, characterized in that, The step of determining the local deformation amount within each deformed grating image based on the reference image with grating fringe features and each deformed grating image includes: Based on the reference image with grating stripe features and each deformed grating image, the signal sequence of each sector characterizing each deformed grating image over time is confirmed; Based on the signal sequence of each sector, after identifying the signal components of each sector signal sequence that are consistent with the direction of movement of the molten film bubble between adjacent sectors, an apparent deformation signal is generated. Remove the apparent deformation signal from the signal sequence of each sector to confirm the geometric deformation signal; Based on the geometric deformation signal, the local deformation amount within each deformed grating image is determined.

3. The method for detecting the stable air pressure of cast film according to claim 2, characterized in that, The step of generating an apparent deformation signal based on each sector signal sequence, after identifying the signal components of each sector signal sequence that are consistent with the direction of movement of the molten film bubble between adjacent sectors, includes: Based on the signal sequence of each sector, the artifact signal characterizing the fixed optical artifact of the detection device is obtained; Remove artifact signals from each of the sector signal sequences to determine each corrected sector signal sequence; Based on each corrected sector signal sequence, after identifying the signal components in each sector signal sequence that are consistent with the direction of movement of the molten film bubble between adjacent sectors, an apparent deformation signal is generated.

4. The method for detecting the stable air pressure of cast film according to claim 3, characterized in that, Based on each corrected sector signal sequence, the step of generating an apparent deformation signal after identifying the signal component in each sector signal sequence that is consistent with the direction of movement of the molten film bubble between adjacent sectors includes: Based on the corrected sector signal sequence, the current process parameters associated with the moving speed of the molten film bubble are identified, as well as the propagation interval time of each sector signal to its adjacent sector is identified. Based on the current process parameters, determine the expected delay time for each sector to propagate between its adjacent sectors; After comparing each propagation interval with the corresponding expected delay time, the signal components in the sector signal sequence corresponding to the actual time interval and the expected delay time are extracted. An apparent deformation signal is generated based on the signal components.

5. The method for detecting the stable air pressure of cast film according to claim 1, characterized in that, The steps of acquiring a reference image with grating stripe features obtained by optically acquiring a sample molten film bubble of the cast film over a period of time, and each deformed grating image obtained by optically acquiring a molten film bubble under test, include: Acquire a reference initial image with grating stripe features obtained by optically acquiring a sample molten film bubble of a cast film over a period of time, and an initial image of each deformed grating obtained by optically acquiring a molten film bubble under test; The reference initial image and each deformed grating initial image are subjected to noise reduction and contrast enhancement processing respectively to obtain the reference image and each deformed grating image.

6. The method for detecting the stable air pressure of cast film according to claim 5, characterized in that, The steps for acquiring a reference image with grating stripe characteristics obtained by optically acquiring a sample molten film bubble of a cast film over a period of time include: The intensity and range of the light source output by the modulation light source projection device are adjusted so that the light source is projected onto the circumferential area of ​​the molten film bubble; For a period of time, the driving light source outputs light to the circumferential area of ​​the molten film bubble of the casting film, so that the surface of the molten film bubble of the casting film produces specular reflection light; The image acquisition unit is driven to acquire images of specularly reflected light, thereby obtaining a reference image with grating stripe features.

7. The method for detecting the stable air pressure of cast film according to claim 6, characterized in that, The steps of the driving image acquisition unit to acquire images of specularly reflected light and obtain a reference image with grating stripe features include: The image acquisition unit is driven to acquire images of specularly reflected light, resulting in an image sequence; After confirming the position of each pixel in the image sequence, the reference signal and the orthogonal signal orthogonal to the reference signal are confirmed respectively. Based on the reference signal and the orthogonal signal, two product sequences are obtained; The two product sequences are filtered in the time dimension to extract two low-frequency components; Based on the two low-frequency components, after confirming the signal amplitude at all pixel positions in the image sequence, a reference pattern is generated.

8. The method for detecting the stable air pressure of cast film according to claim 1, characterized in that, The steps for determining the pressure distribution and disturbance type inside the molten film bubble based on global deformation components and local deformation sequence, and then obtaining the detection result of the cast film, include: Based on the local deformation sequence, determine the pressure distribution state inside the molten film bubble; Determine the type of disturbance based on global deformation components; The detection results of the cast film are obtained by considering the overall pressure distribution and disturbance type.

9. A casting film bubble stabilization pressure detection system, used to execute the casting film bubble stabilization pressure detection method according to any one of claims 1-8, characterized in that, The system includes: The image acquisition module is used to acquire a reference image with grating stripe features that is optically acquired from a sample molten film bubble of a cast film over a period of time, as well as each deformed grating image that is optically acquired from the molten film bubble to be tested. The first determining module is used to determine the local deformation amount in each deformed grating image based on the reference image with grating stripe features and each deformed grating image; The second determining module is used to determine the deformation distribution curve of all sectors divided along the circumferential direction on the molten film bubble over a period of time, based on the local deformation amount in each of the deformed grating images. The judgment module is used to determine the pressure distribution state and disturbance type inside the molten film bubble based on the deformation distribution curve, and then obtain the detection result of the cast film. Based on the deformation distribution curve, after determining the pressure distribution state and disturbance type inside the molten film bubble, the detection results of the cast film are obtained, including: Using the deformation distribution curve, determine the deformation amount of all local deformations distributed in each sector and the global deformation component of all local deformations in all sectors. The deformation amount of each sector is compared with the global deformation component to obtain a local deformation amount sequence; Based on the global deformation components and local deformation sequence, the pressure distribution and disturbance type inside the molten film bubble are determined, and the detection results of the cast film are obtained.

Images