Damage detection method and system for screen protection film

Abstract

The invention relates to the technical field of damage detection, and discloses a screen protection film damage detection method and system, and the method comprises the steps: carrying out the laser interference thickness scanning of a screen protection film, and obtaining three-dimensional thickness distribution data and thickness gradient vector field data; performing multi-layer polarization interference detection on the circularly polarized light beam based on the three-dimensional thickness distribution data to obtain polarization phase difference distribution data; according to the thickness gradient vector field data, non-periodic phase unenveloping processing is carried out on the polarization phase difference distribution data to obtain continuous polarization phase distribution data; performing stress optical coefficient tensor calculation and dynamic elliptical polarization modulation based on the continuous polarization phase distribution data to obtain stress damage space positioning data; the edge cutting area and the center bending area of the screen protection film are subjected to damage imaging reconstruction, a three-dimensional stress damage imaging result is obtained, and full-chain detection from geometric thickness change to stress distribution and then to damage positioning is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of damage detection, and particularly to a method and system for detecting damage of a screen protector. Background Art

[0002] The screen protector usually adopts a composite structure of glass - PVB - glass. During use, complex stress distributions will occur in the edge cutting area and the center bending area. These stress concentrations often become the starting points for the initiation and propagation of microcracks, ultimately leading to the failure of the protective film. Therefore, accurately detecting and evaluating the stress damage state inside the screen protector is of great significance for product quality control, life prediction, and failure analysis.

[0003] Traditional methods for detecting damage of screen protectors mainly rely on surface observation, acoustic emission detection, and simple photoelastic methods. These methods have significant limitations in terms of detection accuracy, spatial resolution, and obtaining depth information. Although existing photoelastic detection technologies can detect the stress distribution inside materials, most of them adopt a single - layer detection mode and fixed - polarization - state scanning, making it difficult to accurately handle the optical interface effect and polarization phase jump problems in multi - layer composite materials. Summary of the Invention

[0004] The present invention provides a method and system for detecting damage of a screen protector, and the present invention realizes a full - chain detection from geometric thickness change to stress distribution and then to damage localization.

[0005] In a first aspect, the present invention provides a method for detecting damage of a screen protector, and the method for detecting damage of the screen protector includes: Performing laser interference thickness scanning on the screen protector to obtain three - dimensional thickness distribution data and thickness gradient vector field data; Performing multi - layer polarization interference detection on a circularly polarized light beam based on the three - dimensional thickness distribution data to obtain polarization phase difference distribution data; Performing non - periodic phase unwrapping processing on the polarization phase difference distribution data according to the thickness gradient vector field data to obtain continuous polarization phase distribution data; Calculating the stress - optical coefficient tensor and performing dynamic elliptical polarization modulation based on the continuous polarization phase distribution data to obtain stress damage spatial localization data; Performing damage imaging reconstruction on the edge cutting area and the center bending area of the screen protector according to the stress damage spatial localization data to obtain a three - dimensional stress damage imaging result.

[0006] Combined with the first aspect, in the first implementation manner of the first aspect of the present invention, the performing laser interference thickness scanning on the screen protector to obtain three - dimensional thickness distribution data and thickness gradient vector field data includes: Perform laser interference point-by-point scanning on the screen protector to obtain the original thickness measurement data; Perform three-dimensional coordinate mapping based on the original thickness measurement data to obtain three-dimensional thickness distribution data; Perform partial differential gradient calculation on the three-dimensional thickness distribution data to obtain thickness gradient vector field data.

[0007] Combined with the first aspect, in the second implementation manner of the first aspect of the present invention, the multi-layer polarization interference detection of the circularly polarized light beam based on the three-dimensional thickness distribution data to obtain polarization phase difference distribution data includes: Create the circularly polarized light beam configuration parameters of the multi-layer polarization interference optical system based on the three-dimensional thickness distribution data; Perform multi-layer depth scanning on the screen protector according to the circularly polarized light beam configuration parameters to obtain four-quadrant polarization intensity data; Perform polarization phase difference calculation on the four-quadrant polarization intensity data to obtain initial phase difference distribution data, and perform polarization stability constraint on the initial phase difference distribution data to obtain polarization phase difference distribution data.

[0008] Combined with the first aspect, in the third implementation manner of the first aspect of the present invention, the non-periodic phase unwrapping process of the polarization phase difference distribution data according to the thickness gradient vector field data to obtain continuous polarization phase distribution data includes: Perform depth correlation based on the thickness gradient vector field data and the polarization phase difference distribution data to obtain a thickness compensation factor; Perform phase jump discrimination on the thickness gradient vector field data according to the thickness compensation factor to obtain real phase jump identification data; Perform dynamic adjustment of the window size on the real phase jump identification data to obtain adaptive window parameters; Perform a non-periodic unwrapping algorithm on the polarization phase difference distribution data based on the adaptive window parameters to obtain continuous polarization phase distribution data.

[0009] Combined with the first aspect, in the fourth implementation manner of the first aspect of the present invention, the performing phase jump discrimination on the thickness gradient vector field data according to the thickness compensation factor to obtain real phase jump identification data includes: Construct a phase jump discrimination function based on the thickness compensation factor; Perform gradient amplitude comparison on the thickness gradient vector field data according to the phase jump discrimination function to obtain thickness gradient threshold screening data; Perform phase difference amplitude calculation on the thickness gradient threshold screening data and the polarization phase difference distribution data to obtain phase mutation candidate point data; Perform double - condition logic discrimination based on the phase mutation candidate point data to obtain real - phase jump identification data.

[0010] Combined with the first aspect, in the fifth implementation manner of the first aspect of the present invention, the stress - optical coefficient tensor calculation and dynamic ellipsometric polarization modulation are performed based on the continuous polarization phase distribution data to obtain stress damage spatial localization data, including: Construct a modified Müller matrix based on the continuous polarization phase distribution data to obtain the Müller matrix transformation parameters corresponding to the glass - PVB - glass composite structure; Calibrate the stress - optical coefficient tensor for the continuous polarization phase distribution data according to the Müller matrix transformation parameters to obtain the stress - optical coefficient tensor; Perform ellipsometric polarization parameter modulation based on the stress - optical coefficient tensor to obtain ellipsometric polarization modulation parameters; Reconstruct the three - dimensional stress tensor for the continuous polarization phase distribution data based on the ellipsometric polarization modulation parameters to obtain three - dimensional stress tensor component data; Perform a dynamic ellipsometric polarization modulation scan based on the three - dimensional stress tensor component data to obtain stress damage spatial localization data.

[0011] Combined with the first aspect, in the sixth implementation manner of the first aspect of the present invention, the ellipsometric polarization parameter modulation is performed based on the stress - optical coefficient tensor to obtain ellipsometric polarization modulation parameters, including: Perform ellipsometric parameter vector calculation based on the stress - optical coefficient tensor to obtain ellipticity distribution data; Calculate the stress gradient response coefficient according to the ellipticity distribution data and the three - dimensional stress tensor component data to obtain an adaptive modulation depth parameter; Input the adaptive modulation depth parameter into a dual - frequency drive configurator for frequency separation calculation to obtain dual - frequency drive parameters; Perform dynamic ellipsometric polarization tracking based on the dual - frequency drive parameters and the thickness compensation factor to obtain ellipsometric polarization modulation parameters.

[0012] Combined with the first aspect, in the seventh implementation manner of the first aspect of the present invention, the dynamic ellipsometric polarization modulation scan is performed based on the three - dimensional stress tensor component data to obtain stress damage spatial localization data, including: Calculate the stress - photoelastic coupling response variable based on the three - dimensional stress tensor component data and the three - dimensional thickness distribution data to obtain coupling response variable distribution data; Perform adaptive modulation analysis on the ellipsometric polarization modulation parameters according to the coupling response variable distribution data to obtain dynamic modulation configuration data; Perform scan path planning based on the dynamic modulation configuration data to obtain target scan path data; Perform dynamic tracking of polarization ellipse parameters based on the target scan path data and the thickness compensation factor to obtain stress damage spatial positioning data.

[0013] Combined with the first aspect, in the eighth implementation manner of the first aspect of the present invention, the damage imaging reconstruction of the edge cutting area and the center bending area of the screen protector according to the stress damage spatial positioning data to obtain a three-dimensional stress damage imaging result includes: Construct damage imaging model parameters based on the stress damage spatial positioning data, the thickness gradient vector field data, the continuous polarization phase distribution data, and the coupled response variable distribution data; Perform dual-region differential detection on the edge cutting area and the center bending area of the screen protector according to the damage imaging model parameters to obtain region detection configuration data; Perform damage assessment based on the region detection configuration data to obtain damage assessment index data, and perform voxelized three-dimensional imaging reconstruction based on the damage assessment index data to obtain a three-dimensional stress damage imaging result.

[0014] In a second aspect, the present invention provides a damage detection system for a screen protector, and the damage detection system for the screen protector includes: A scanning module for performing laser interference thickness scanning on the screen protector to obtain three-dimensional thickness distribution data and thickness gradient vector field data; A detection module for performing multi-layer polarization interference detection on a circularly polarized light beam based on the three-dimensional thickness distribution data to obtain polarization phase difference distribution data; A processing module for performing non-periodic phase unwrapping processing on the polarization phase difference distribution data according to the thickness gradient vector field data to obtain continuous polarization phase distribution data; A modulation module for performing stress optical coefficient tensor calculation and dynamic elliptical polarization modulation based on the continuous polarization phase distribution data to obtain stress damage spatial positioning data; A reconstruction module for performing damage imaging reconstruction on the edge cutting area and the center bending area of the screen protector according to the stress damage spatial positioning data to obtain a three-dimensional stress damage imaging result.

[0015] In the technical solution provided by the present invention, by establishing thickness gradient vector field data to guide the aperiodic unwrapping process of polarization phase difference distribution data, the cumulative error problem of the traditional 2π phase jump processing method in thin film materials is effectively solved, and high-precision acquisition of continuous polarization phase distribution data is realized. By adopting a multi-layer configuration with four-quadrant polarization detectors set at different z-axis depth levels, compared with the traditional single-layer polarization detection technology, it can better handle the interfacial effect between layers of the glass-PVB-glass composite structure, improving the detection accuracy and stability of polarization phase difference distribution data. A modified Müller matrix transformation parameter applicable to the glass-PVB-glass composite structure is established, considering the anisotropic characteristics of the screen protector and the interfacial effect between layers, and it can more accurately realize the numerical conversion from polarization phase to stress components compared with the standard Müller matrix. Based on the adaptive modulation technology driven by stress-optic coupling response variables, through the dual-frequency driving scheme and the spiral path algorithm, prior scanning and precise positioning of stress concentration areas are realized, significantly improving the detection sensitivity of the microcrack initiation position. A dual-region differential detection strategy is established for the different stress characteristics of the edge cutting area and the central bending area of the screen protector. The shear stress distribution is mainly detected in the edge area, and the normal stress distribution is mainly detected in the central area, realizing targeted and efficient detection. By integrating stress tensor component data, thickness gradient information, polarization phase distribution, and coupling response variables, a damage imaging model with multi-parameter fusion is established, realizing full-chain detection from geometric thickness change to stress distribution and then to damage location. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0017] Figure 1 It is a schematic diagram of the steps of the damage detection method for the screen protector in the embodiment of the present invention; Figure 2 It is a schematic diagram of the structure of the damage detection system for the screen protector in the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] An embodiment of the present invention provides a method and system for detecting damage to a screen protector. The terms "first", "second", "third", "fourth", etc. (if any) in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects and do not necessarily need to be used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances so that the embodiments described here can be implemented in an order other than that illustrated or described here. In addition, the term "comprising" or "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0019] For ease of understanding, the specific process of the embodiment of the present invention will be described below. Please refer to Figure 1 , an embodiment of the method for detecting damage to a screen protector in the embodiment of the present invention includes: Step S1: Perform laser interferometric thickness scanning on the screen protector to obtain three-dimensional thickness distribution data and thickness gradient vector field data; It can be understood that the execution subject of the present invention can be a system for detecting damage to a screen protector, or a terminal or a server. Specifically, no limitation is made here. The embodiment of the present invention is described by taking the server as the execution subject as an example.

[0020] Specifically, a high-precision laser interference measurement system is built. This system is equipped with a laser with a stable wavelength output and a scanning platform with high-precision displacement control function. The screen protector is scanned point by point through laser interference technology. The multi-layer interference imaging method within the volume is adopted to analyze the thickness layer by layer for the glass-PVB-glass composite structure of the protector, and the original thickness measurement data at different spatial coordinate (x, y, z) positions are obtained. The scanning range covers the entire protector area, and the scanning step size is refined to a planar resolution of 10 microns × 10 microns and a longitudinal resolution of 2 microns, ensuring sufficient spatial sampling density within the thickness range of 0.3 to 0.8 mm, being able to capture tiny thickness change characteristics, and the detection accuracy reaches ±0.5 microns. Based on the original thickness measurement data, three-dimensional coordinate mapping processing is carried out, corresponding the scanning position information with the thickness data point by point to form a three-dimensional thickness distribution map T(x, y, z). During the coordinate mapping process, the spatial coordinate error caused by the tiny deviation of the scanning path is corrected through the interpolation correction method, and the polynomial fitting or three-dimensional spline interpolation algorithm is adopted to ensure the continuity and smoothness of the thickness data in the spatial distribution, and high-fidelity three-dimensional thickness distribution data are obtained. In order to extract the thickness change trend of the protector in different regions, partial differential processing is carried out on the three-dimensional thickness distribution data, and first-order differential operations are respectively carried out in the x, y, and z directions to obtain the change rate of the thickness in each direction, forming a thickness gradient vector field. The central difference method or five-point difference method is adopted for numerical approximation during the partial differential calculation process, and the difference step size is dynamically adjusted according to the local change characteristics of the data. Especially in the edge cutting area and the central bending area of the protector, due to stress concentration in these areas, the thickness change rate is large, so the grid is encrypted to improve the resolution. In order to improve the ability of the thickness gradient vector field to reflect depth information, compensation is carried out in combination with the optical attenuation characteristics of the protector material, and a thickness compensation factor is introduced. This factor exponentially corrects the thickness distribution in the depth direction, so that the thickness change is not limited to the description of surface features, and at the same time can deeply reflect the thickness change of the internal multi-layer interfaces. The thickness gradient vector field extracted in this way can effectively capture the thickness mutation characteristics at the multi-layer interfaces of the screen protector and reflect the local stress concentration areas.

[0021] Step S2: Based on the three-dimensional thickness distribution data, perform multi-layer polarization interference detection on the circularly polarized light beam to obtain polarization phase difference distribution data; Specifically, based on the three-dimensional thickness distribution data, the circularly polarized light beam configuration parameters of the multi-layer polarization interference optical system are created. According to the thickness variations and interfacial characteristics of each layer of materials such as glass-PVB-glass inside the screen protector, the incident angle of the circularly polarized light beam, wavelength selection, and depth scanning strategy of the incident path are designed. A helium-neon laser with a wavelength of 632.8 nm is selected as the light source, and a quarter-wave plate is used to convert linearly polarized light into circularly polarized light, and the incident angle is set to 15° to minimize surface reflection interference as much as possible while ensuring that the incident light can penetrate the multi-layer structure of the protective film to generate interference signals at different depths. Combining with the local thickness mutation characteristics in the three-dimensional thickness distribution data, the energy density distribution of the circularly polarized light beam is optimized to make it have higher light intensity uniformity in the interfacial region where the thickness of the protective film changes significantly, thereby improving the stability and signal-to-noise ratio of interference imaging. According to the circularly polarized light beam configuration parameters, multi-layer depth scanning is performed on the screen protector. During the scanning process, a four-quadrant polarization detector is set to collect the intensity data of the polarized light beam in the polarization states of 0°, 45°, 90°, and 135°. Through spatial hierarchical sampling, 80-layer depth hierarchical scanning is ensured within the thickness range of 0.3 to 0.8 mm. The acquisition process of the four-quadrant polarization intensity data needs to maintain the coherence and polarization stability of the laser light source, and avoid polarization state changes caused by environmental factors such as vibration and temperature drift, so as to ensure that the intensity responses in different polarization directions can be accurately obtained in each layer of scanning. The four-quadrant polarization intensity data is subjected to polarization phase difference calculation, and the initial phase difference distribution data is derived based on the intensity differences in each polarization direction. The initial phase difference data extracted by the method of intensity difference can reflect the local optical delay differences of the screen protector at different depth levels, and indirectly reveal the stress distribution state inside the material. Considering the certain birefringence characteristics of the screen protector material itself and the problem of unstable polarization state caused by the external environment, a polarization stability constraint is introduced based on the initial phase difference distribution data. A polarization stability constraint function is established. By normalizing the polarization intensity data and setting the phase drift threshold to 0.02 radians, the initial phase difference distribution is corrected to eliminate abnormal polarization drifts caused by random noise, systematic errors, or local defects. The obtained polarization phase difference distribution data has good spatial continuity and physical consistency.

[0022] Step S3: Perform non-periodic phase unwrapping processing on the polarization phase difference distribution data according to the thickness gradient vector field data to obtain continuous polarization phase distribution data; Specifically, the thickness gradient vector field data is deeply associated with the polarization phase difference distribution data. By establishing a three-dimensional coordinate correspondence, the thickness gradient information at each spatial position is jointly analyzed with the polarization phase difference value at the corresponding position to identify the spatial consistency characteristics of the thickness mutation point and the phase mutation point. On this basis, the thickness compensation factor is calculated. This factor takes into account the difference in optical properties between the material layers inside the screen protective film and the influence of thickness change on the length of the light propagation path, so that the compensation factor can quantitatively correct the phase change at different depth levels, effectively eliminate the phase non-uniformity error caused by the change in material birefringence and uneven thickness, and improve the stability and accuracy of subsequent phase unwrapping. The thickness gradient vector field data is analyzed according to the thickness compensation factor, and the phase jump is identified in combination with the polarization phase difference distribution data. Using the characteristics of the simultaneous appearance of thickness gradient mutation and phase difference mutation, the joint threshold judgment standard of thickness change rate and phase difference change rate is set, and the point where the thickness gradient exceeds a certain threshold and the phase change exceeds the standard range is judged as a real phase jump point, thereby obtaining the real phase jump identification data. Compared with the traditional periodic de-envelope method based on the 2π jump assumption, the discrimination method based on physical thickness change can effectively distinguish the real phase mutation caused by the material interface from the pseudo phase jump caused by the folding of the interference fringes, avoiding the problem of cumulative error diffusion in the traditional method, especially in multi-layer composite structures such as glass-PVB-glass, and can more accurately restore the continuity of stress distribution. After identifying the real phase jump, the local processing window of the de-envelope algorithm is dynamically adjusted according to the characteristics of different thickness changes and complex stress distribution in different regions of the screen protective film. By analyzing the local change rate of the thickness gradient field, the window size is set to change dynamically with the local thickness gradient. The adaptive window size parameter is reduced in the area of ​​drastic thickness change to improve the sensitivity of jump detection and the meticulousness of phase reconstruction, while the window is appropriately expanded in the area of gentle thickness change to improve the stability and processing speed of the de-envelope. The adaptive window adjustment strategy introduces a dynamic adjustment coefficient to make real-time corrections to the basic window size according to the local thickness gradient in the actual de-envelope calculation, ensuring that higher spatial resolution and phase restoration accuracy are maintained in key areas such as microcrack initiation areas. Based on the above-mentioned adaptive window parameters, a non-periodic unwrapping algorithm is performed on the polarization phase difference distribution data to analyze the polarization phase change trend layer by layer. The jump points are continuously connected and corrected for mutations, while the non-jump areas are kept naturally extended to gradually construct continuous polarization phase distribution data.

[0023] The phase jump discriminant function is constructed based on the thickness compensation factor. The discriminant function combines the thickness gradient change with the phase difference change to comprehensively analyze the real physical mutation characteristics caused by the material interface in the multilayer structure of the screen protective film. The thickness compensation factor corrects the thickness change at different depth levels by considering the optical attenuation characteristics of the material, so that the discriminant function can automatically adjust the sensitivity at different positions, which can not only identify subtle changes in the surface shallow layer, but also capture the mutation signal of the deep interface, thereby improving the accuracy and stability of jump detection. According to the phase jump discriminant function, the gradient amplitude of the thickness gradient vector field data is compared. By calculating the thickness change rate of each scanning point in the three directions of x, y, and z, and taking its spatial gradient amplitude, it is compared and screened with the preset thickness gradient threshold. The thickness gradient threshold is set to 50 microns per millimeter to distinguish normal thickness changes from potential interface mutations. The screened thickness gradient threshold screening data contains point sets with more drastic thickness changes in space, which are highly correlated with physical interface changes. The thickness gradient threshold screening data is jointly analyzed with the polarization phase difference distribution data, and the phase difference amplitude change at the corresponding position of each screening point is calculated. By comparing the phase difference data between adjacent layers in space, calculating the phase change rate and extracting the change amplitude, the phase mutation candidate point data is obtained. In this process, a phase change amplitude threshold is set to determine whether there is a significant phase jump between adjacent depth layers. The phase mutation judgment threshold is set near π or an integer multiple of π. Dual conditional logical discrimination is performed based on the phase mutation candidate point data to obtain the real phase jump identification data. The discrimination process considers both the thickness gradient amplitude and the phase difference amplitude. Only points that meet both the thickness gradient mutation and the phase difference mutation at the same position are judged as real phase jump points.

[0024] Step S4, performing stress optical coefficient tensor calculation and dynamic elliptical polarization modulation based on the continuous polarization phase distribution data to obtain stress damage spatial positioning data; Specifically, a modified Müller matrix is constructed based on the continuous polarization phase distribution data. Considering that the screen protective film is composed of a three-layer composite material of glass-PVB-glass, different materials have differences in optical anisotropy and stress response characteristics. Therefore, when constructing the Müller matrix, corrections are made according to the anisotropic properties of the material, the interlayer interface effect and the actually measured polarization phase distribution, so as to derive the Müller matrix transformation parameters suitable for the composite structure. By introducing the stress-optical coupling coefficient and the optical rotation parameters of each layer of material, a set of correction matrices that can accurately reflect the polarization response characteristics inside the composite structure is formed. According to the Müller matrix transformation parameters, the stress optical coefficient tensor is calibrated for the continuous polarization phase distribution data. The corresponding relationship between the stress component and the polarization phase change is derived from the relationship between the continuous phase change rate and the depth direction gradient, and the stress optical coefficient tensor parameters inside the screen protective film are extracted by combining the anisotropy compensation factor in the modified Müller matrix. The stress optical coefficient tensor contains a normal stress component and a shear stress component, so that the stress response characteristics of the material in different directions can be described. In order to ensure the accuracy of tensor calculation, an optimization algorithm based on least squares fitting is used to eliminate random errors and noise interference in the measurement process, and the stress optical coefficient tensor is obtained. Elliptical polarization parameters are modulated based on the stress optical coefficient tensor. The elliptical polarization parameters mainly include ellipticity and azimuth, which correspond to the major-minor axis ratio and the principal axis direction of the light wave ellipse under stress state, respectively. By analyzing the relationship between the principal stress direction of the stress tensor and the polarization phase change, the modulation parameters of elliptical polarization are dynamically adjusted so that polarized light can respond to local stress changes to the greatest extent when penetrating the material. In the process of setting the modulation parameters, the dynamic modulation depth and frequency related to the local stress gradient are introduced, so that the elliptical polarization state can be fine-tuned in real time following the stress distribution changes, thereby improving the sensitivity and response speed of polarization scanning to small stress anomalies. Based on the elliptical polarization modulation parameters, the continuous polarization phase distribution data is reconstructed into a three-dimensional stress tensor. By mapping the elliptical polarization response with the stress components in each direction, the stress tensor components in each direction are solved using the inverse transformation method to form three-dimensional stress tensor component data. In order to improve the stability and spatial continuity of tensor component calculation, a multi-scale iterative optimization algorithm is used to smooth the local data, and the thickness compensation factor is combined to finely correct the data in the depth direction to ensure that the stress tensor component can truly reflect the microscopic stress distribution characteristics inside the protective film, especially the stress concentration phenomenon at the microcrack initiation area and the material interface. Based on the three-dimensional stress tensor component data, dynamic elliptical polarization modulation scanning is implemented. By setting the scanning path to preferentially cover the stress concentration area, and dynamically adjusting the scanning step size and modulation frequency according to the local stress gradient, high-precision spatial positioning of the stress damage area inside the protective film is achieved.During the dynamic scanning process, by using a spiral or grid path strategy and coordinating with real-time adjusted ellipsometric parameters, it is possible to effectively improve the spatial resolution and reduce missed detections. Especially in the thickness range of 0.3 to 0.8 millimeters, it has extremely high sensitivity and detection accuracy for stress anomaly regions in the initial stage of microcrack initiation. By comprehensively analyzing the polarization response data obtained from dynamic scanning, stress damage spatial positioning data is generated and output in the form of a high-resolution pseudo-color map, marking potential damage locations, stress concentration levels, and risk level assessments.

[0025] Calculating the ellipsometry parameter vector based on the stress-optic coefficient tensor. The ellipsometry parameters are important quantities that describe the characteristics of elliptically polarized light, mainly including ellipticity and the direction of the principal polarization axis. Among them, ellipticity reflects the ratio of the major axis to the minor axis and can directly reflect the birefringence response characteristics when light propagates in a stressed material. By performing vector mapping on the principal direction components of the stress tensor and the polarization phase distribution, the change in ellipticity corresponding to the local stress state is extracted to obtain ellipticity distribution data, depicting the change trend of the polarization state caused by stress changes at different positions and different depth levels of the screen protector. Calculating the stress gradient response coefficient based on the ellipticity distribution data and the three-dimensional stress tensor component data. The stress gradient response coefficient is an important indicator for evaluating the local stress change rate. By taking the derivative of the spatial gradient of the ellipticity distribution and jointly analyzing it with the change rate of the stress tensor components at the corresponding positions, the severity of stress changes in the local area of the material is quantified. Based on this analysis result, an adaptive modulation depth parameter is derived so that the modulation depth can be adaptively adjusted according to the stress change situation. In areas where stress changes are severe, stress concentration exists, or microcracks initiate, the adaptive modulation depth parameter will increase to improve the response sensitivity of elliptically polarized light to local stress anomalies; while in areas where stress changes are gentle, the modulation depth is appropriately reduced to ensure the overall stability and scanning efficiency of the system. Inputting the adaptive modulation depth parameter into the dual-frequency drive configurator for frequency separation calculation. The dual-frequency drive configurator dynamically allocates the modulation frequencies in the horizontal and vertical directions according to the modulation depth. The horizontal modulation frequency is set at 1.2 kHz, and the vertical modulation frequency is set at 0.8 kHz. Through frequency separation calculation, it can be ensured that the stress responses in different directions are effectively separated and independently modulated during the scanning process, avoiding the occurrence of frequency aliasing. During the frequency separation calculation process, the basic frequency is fine-tuned according to the severity of the local stress gradient change, making the modulation frequencies denser in areas with severe stress changes to improve the detection accuracy of micro stress anomalies and the locations where microcracks initiate, obtaining a set of dual-frequency drive parameters that dynamically match the local stress change characteristics. Performing elliptical polarization dynamic tracking based on the dual-frequency drive parameters and the thickness compensation factor. The thickness compensation factor can effectively correct the optical path difference caused by material thickness changes, ensuring the continuity and accuracy of the elliptical polarization modulation parameters at different depth levels. During the dynamic tracking process, the ellipticity and principal axis direction parameters of the elliptical polarization are updated in real time, and the polarization state is dynamically adjusted with the change of the local stress state, enabling the polarized light beam to flexibly respond to the complex and variable stress field distribution inside the screen protector in space. Through the above steps, the elliptical polarization modulation parameters are finally obtained.

[0026] The stress-photoelastic coupling response variables are calculated based on the three-dimensional stress tensor component data and the three-dimensional thickness distribution data. The stress-photoelastic coupling response variables are an important bridge connecting the internal stress state of the material and its polarization light response characteristics. Specifically, by combining each stress component with the local thickness change and the photoelastic properties of the material, the response intensity of each spatial point to elliptically polarized light under a specific stress environment is quantified. The distribution of the coupling response variables can reflect the stress concentration area and the area where the stress gradient changes sharply, and can reveal the optical path changes caused by uneven thickness, thereby forming the coupling response variable distribution data. The elliptical polarization modulation parameters are adaptively modulated and analyzed based on the coupling response variable distribution data. By normalizing the coupling response variables, the optimal parameter combination of polarization modulation in each local area is determined, including the ellipticity adjustment amplitude, the rate of change of the polarization main axis direction, and the dynamic matching of the modulation frequency, to form dynamic modulation configuration data. These data are indexed by spatial position and give the optimal modulation strategy parameters for different areas. Scanning path planning is performed based on the dynamic modulation configuration data to generate target scanning path data. During the path planning process, priority is given to areas with large stress gradients and high coupled response variables. A spiral, grid-type or adaptive grid density adjustment scanning strategy is used to ensure that the scanning point density and resolution are improved in key areas. The scanning step size is reduced to 2 microns × 2 microns × 1 micron in high stress areas to ensure high-precision coverage of the micro crack initiation area; while the step size is appropriately enlarged in areas with gentle stress changes to speed up the overall scanning speed. The scanning path is not only optimized in the plane direction, but also layered in the thickness direction. Combined with the three-dimensional thickness distribution data, tomographic scanning is performed to ensure uniform coverage within the thickness range of 0.3 to 0.8 mm and take into account local fine features to obtain the target scanning path data. Dynamic tracking of polarization ellipse parameters is performed based on the target scanning path data and thickness compensation factor. The introduction of thickness compensation factor can effectively correct the optical path deviation caused by the change in internal thickness of the material, and ensure the continuity and accuracy of polarization ellipse parameters at different depth levels. During the dynamic tracking process, various parameters of elliptic polarization, including ellipticity, principal axis direction and modulation depth, are updated in real time as the scanning path and local stress environment change, so that the scanning beam can sensitively respond to the spatial changes in the internal stress distribution of the protective film. By combining dynamic tracking with path planning, the spatial positioning data of stress damage is finally obtained. This data is output in the form of a high-spatial-resolution three-dimensional grid, which can calibrate the potential microcrack initiation location, stress abnormality area and damage risk level.

[0027] Step S5: reconstruct damage imaging of the edge cutting area and the central bending area of the screen protection film according to the stress damage spatial positioning data to obtain a three-dimensional stress damage imaging result.

[0028] Specifically, by integrating stress damage spatial localization data, thickness gradient vector field data, continuous polarization phase distribution data, and coupled response variable distribution data, a damage imaging model parameter system is constructed based on these multi-source information. Through standardizing various physical quantities and spatial registration, this system forms a multi-dimensional feature space that can reflect the stress distribution characteristics, thickness change trends, polarization response characteristics, and photoelastic coupling effects of the multi-layer composite structure of the screen protector. The damage imaging model parameters not only include the local stress maximum value, stress gradient change rate, phase continuity index, and coupled response intensity, but also the thickness mutation characteristics and the high-order statistical characteristics of each parameter in the spatial distribution, ensuring that the potential damage risk characteristics in different regions can be described. Based on the damage imaging model parameters, dual-region differential detection is performed on the edge cutting region and the center bending region of the screen protector to generate region detection configuration data. Considering that the edge cutting region is more prone to the initiation of microcracks caused by shear stress due to the mechanical stress concentration effect during the processing, a higher spatial resolution and a denser scanning strategy are adopted in the detection configuration, setting the scanning accuracy to reach 1 μm × 1 μm × 0.5 μm, and focusing on detecting the shear stress τ xy distribution and its local gradient change. In the center bending region, due to the influence of bending loads during use, normal stresses σ xx , σ yyPredominant tensile and compressive stresses. Therefore, for the central region, a fast scanning mode with a slightly larger step size is adopted, and the scanning accuracy is controlled within the range of 5 microns × 5 microns × 2 microns, focusing on detecting the normal stress distribution and its uniformity analysis. Through the dual-region differential detection strategy, combined with the stress component type, thickness change characteristics, and polarization response abnormal regions, the detection efficiency and spatial resolution can be effectively improved, and the problems of resolution waste and detection blind spots caused by unified configuration in traditional imaging methods can be avoided. Based on the regional detection configuration data, damage assessment is carried out to obtain the damage assessment index data system. During the damage assessment process, key indicators such as the stress concentration factor, gradient concentration factor, and interface peeling risk index are introduced. Among them, the stress concentration factor reflects the degree of local stress abnormality by calculating the ratio of the local maximum stress to the nominal stress; the gradient concentration factor reflects the non-uniformity of stress distribution by the ratio of the local stress gradient peak value to the overall average gradient; the interface peeling risk index is based on the integral of shear stress over the interface area to evaluate the interlayer bonding risk. The above indicators constitute a systematic quantitative damage risk assessment system by integrating multi-dimensional data such as stress, phase, thickness, and polarization response. Based on the damage assessment index data, voxelized three-dimensional imaging reconstruction is carried out to obtain the three-dimensional stress damage imaging result. During the voxelization reconstruction process, the entire detection area is divided into tiny voxel units with a size of 2 cubic microns, and the corresponding stress magnitude, gradient intensity, and damage risk level data are assigned to each voxel, and smooth transition is carried out at the voxel boundaries through interpolation algorithms to ensure that the three-dimensional imaging result is visually continuous and retains the true physical meaning in terms of data. The imaging result is expressed in the form of a pseudo-color map, where the low-stress region is represented by blue, the medium-stress region is represented by green, the high-stress and potentially damaged region is represented by red, and the high-risk region of microcrack initiation is highlighted in yellow. The final output is a comprehensive result including the three-dimensional stress distribution cloud map, the coordinates of the microcrack initiation positions, the damage level assessment of each region, and a complete detection report.

[0029] In the embodiments of the present invention, by establishing thickness gradient vector field data to guide the non-periodic unwrapping process of polarization phase difference distribution data, the cumulative error problem of the traditional 2π phase jump processing method in thin film materials is effectively solved, and high-precision acquisition of continuous polarization phase distribution data is realized. By adopting a multi-layer configuration with four-quadrant polarization detectors set at different z-axis depth levels, compared with the traditional single-layer polarization detection technology, it can better handle the interfacial effect between layers of the glass-PVB-glass composite structure, improving the detection accuracy and stability of polarization phase difference distribution data. A modified Müller matrix transformation parameter applicable to the glass-PVB-glass composite structure is established, considering the anisotropic characteristics of the screen protection film and the interfacial effect between layers, and it can more accurately realize the numerical conversion from polarization phase to stress components compared with the standard Müller matrix. Based on the adaptive modulation technology driven by the stress-optic coupling response variable, through the dual-frequency driving scheme and the spiral path algorithm, priority scanning and precise positioning of the stress concentration area are realized, significantly improving the detection sensitivity of the microcrack initiation position. A dual-region differential detection strategy is established for the different stress characteristics of the edge cutting area and the central bending area of the screen protection film. The shear stress distribution is mainly detected in the edge area, and the normal stress distribution is mainly detected in the central area, realizing targeted and efficient detection. By comprehensively integrating stress tensor component data, thickness gradient information, polarization phase distribution, and coupling response variables, a damage imaging model with multi-parameter fusion is established, realizing the full-chain detection from geometric thickness change to stress distribution and then to damage location.

[0030] In a specific embodiment, the process of executing step S1 may specifically include the following steps: Perform laser interference point-by-point scanning on the screen protection film to obtain original thickness measurement data; Based on the original thickness measurement data, perform three-dimensional coordinate mapping to obtain three-dimensional thickness distribution data; Perform partial differential gradient calculation on the three-dimensional thickness distribution data to obtain thickness gradient vector field data.

[0031] Specifically, a laser interferometric measurement system with high spatial resolution and high stability is built. The system includes an interference laser with stable wavelength output, a precision motion control platform, an interference probe, and a high-sensitivity detector. For the light source part, a helium-neon laser with a wavelength of 632.8 nm is selected to ensure strong coherence, which can effectively guarantee the clarity of interference fringes and the resolution ability of the measurement system. The motion control platform adopts a high-precision three-axis stepper motor or a linear servo system to provide a displacement control accuracy below the micron level, so that the scanning process proceeds uniformly according to the set step size. The scanning path adopts a point-by-point scanning method. The control platform advances grid by grid along the x and y directions with a spatial resolution of 10 μm × 10 μm, and at the same time, a 2-μm step is adopted along the z direction to complete the fine tomographic sampling in the vertical direction, covering the thickness range of the protective film from 0.3 mm to 0.8 mm. During the entire scanning process, using the principle of laser interference, the change in the local optical path length of the film material is calculated through the phase change of the interference fringes, so as to deduce the actual thickness value corresponding to each scanning point. Since the screen protective film is a transparent multi-layer structure, multiple interference signals are introduced by internal interface reflections. Therefore, the system is equipped with a multi-channel interference signal processing module, and a signal separation algorithm based on Fourier transform is used to distinguish the main reflection signal from the multiple reflection signals, so as to ensure the accuracy and reliability of the original thickness measurement data. After completing the point-by-point scanning and obtaining the original thickness measurement data, these data are subjected to three-dimensional coordinate mapping to establish a spatial distribution model. The plane coordinates (x, y) of each scanning point are corresponded to the corresponding thickness value z, and the two-dimensional plane scanning result is extended to a three-dimensional point cloud dataset by adding the z-axis depth information. To ensure the accuracy of the mapping process, the mechanical errors of the scanning platform are compensated, and the spatial distortion caused by the cumulative error of the motion system or the tilt of the laser beam is corrected. A plane correction method and a self-calibration algorithm based on a standard target are adopted to adjust the scanning coordinate system in real time, so that the spatial positions of each point can reflect the geometric characteristics of the actual film surface and interior. To enhance the continuity and smoothness of the three-dimensional thickness data and avoid data noise caused by surface micro-roughness or local measurement errors during the scanning process, a three-dimensional interpolation algorithm, such as cubic spline interpolation or Kriging interpolation method, is introduced to perform spatial fitting on the discrete thickness data, so as to generate a three-dimensional thickness distribution map T(x, y, z) with higher smoothness and spatial consistency. The partial differential gradient of the three-dimensional thickness distribution data is calculated to extract the thickness change rate information of the protective film in all directions in space and construct a thickness gradient vector field. The first-order partial differential operations are respectively performed on the thickness distribution function T(x, y, z) in the x, y, and z directions to obtain the change rate components of the thickness in each direction. The partial differential calculation adopts the central difference method or the five-point difference method to improve the stability and accuracy of numerical calculation. For the central difference method, at each node in the spatial grid, the local thickness gradient at this point is obtained by taking the thickness difference of adjacent points and dividing it by the corresponding coordinate step size. For example, The thickness difference between two adjacent points in the x direction is divided by the step size of 10 microns. and The calculation method of is similar. The three-dimensional thickness gradient vector field is composed of the gradient components in these three directions, which can describe the thickness change trend of the protective film in all directions of space. In the actual calculation process, attention is paid to the influence of boundary conditions and local noise. For the edge area of the scan, the accuracy of the traditional differential calculation is reduced due to the lack of adjacent points, and the first-order forward difference or backward difference method is introduced to compensate. For areas where there is local data noise, local weighted smoothing is used, and the local thickness data is filtered before calculating the gradient to suppress the interference of high-frequency noise on the gradient result. In order to improve the physical interpretation of the gradient vector field, normalization processing is introduced to unify the amplitude of the gradient vector into a standard scale range, which is convenient for subsequent stress concentration area identification and damage risk assessment. Considering that the screen protective film is a multi-layer composite structure, the optical properties and thickness change rates of materials at different levels are different, and the construction of the thickness gradient vector field is combined with the thickness compensation factor for correction. The thickness compensation factor is set to decrease exponentially with the depth z to reflect the optical attenuation characteristics inside the material and the influence of the thickness change of the interlayer interface on light propagation. By performing thickness compensation correction on the three-dimensional thickness gradient vector field, the detection sensitivity of interface mutations can be effectively enhanced, and the response capability to tiny thickness changes at the interface of multilayer structures such as glass-PVB-glass can be improved.

[0032] In a specific embodiment, the process of executing step S2 may specifically include the following steps: Creating circularly polarized beam configuration parameters of a multilayer polarization interference optical system based on the three-dimensional thickness distribution data; Performing a multi-layer depth scan on the screen protective film according to the circular polarization beam configuration parameters to obtain four-quadrant polarization intensity data; Polarization phase difference calculation is performed on the four-quadrant polarization intensity data to obtain initial phase difference distribution data, and polarization stability constraint is performed on the initial phase difference distribution data to obtain polarization phase difference distribution data.

[0033] Specifically, the screen protector has a multi-layer composite structure such as glass-PVB-glass. The significant variations in the thickness and refractive index of different layers greatly affect the propagation path and phase delay characteristics of light within the material. Therefore, before performing polarization interference detection, the optical system parameters are constructed based on the thickness distribution. Combining the spatial distribution of the thickness of each layer, the incident angle, wavelength, beam diameter, focal length configuration, and incident energy density of the circularly polarized light beam are determined to ensure the best interference effect at each thickness level. To reduce surface reflection interference and maximize the signal-to-noise ratio, a helium-neon laser with a wavelength of 632.8 nm is selected as the light source. The linearly polarized light is converted into circularly polarized light through a high-precision quarter-wave plate, and an incident angle of 15° is set to optimize the transmission and reflection conditions of the beam at the multi-layer interface, ensuring that the thickness changes of each layer fully respond to the interference signal. Based on the three-dimensional thickness distribution data, the depth of focus and energy density distribution of the circularly polarized light beam are optimized to meet the requirements of tomographic scanning in the thickness range of 0.3 to 0.8 mm of the screen protector. By adjusting the beam diameter to adapt to the region with the largest local thickness change of the protector and performing energy homogenization through a collimating lens system, signal drift or distortion caused by local overexposure or underexposure is avoided. At the same time, according to the reflection characteristics of the multi-layer interface of the film material, a low-reflectivity coating is configured to suppress the interference fringe aliasing caused by multiple reflections, thereby improving the measurement accuracy. Through the above series of optimizations of the optical system parameters based on the thickness distribution, a circularly polarized light beam configuration is established. The screen protector is scanned in multiple layers in depth according to the circularly polarized light beam configuration parameters. During the scanning process, a four-quadrant polarization detector is used to synchronously collect the polarization state intensities of the polarized light in the directions of 0°, 45°, 90°, and 135°, denoted as I0, I 45 , I 90 , I 135 . To adapt to the spatial characteristics of the thickness change, a hierarchical encryption strategy is adopted for scanning. The number of scanning layers is increased in the interface area with drastic thickness changes (such as near the glass-PVB interface). The hierarchical density in the z-axis direction is optimized from 200 layers in the traditional method to 80 layers. While reducing the scanning time, it still ensures sufficient depth resolution for important layers within the thickness range of 0.3 to 0.8 mm. The spatial step is set to 10 μm × 10 μm in the x and y directions and 2 μm in the z direction to ensure uniform sampling in all spatial directions, thereby capturing the interference characteristics of the polarized light within each layer of thickness. Through the four-quadrant detection mode, the intensity changes in different polarization directions are obtained simultaneously. The polarization phase difference is calculated for the four-quadrant polarization intensity data. By using I0, I 45 , I 90 , I 135Differential processing is performed on four groups of polarization intensity data to calculate the initial phase difference distribution data. The phase difference is extracted through the arctangent operation expression, and the phase offset between different polarization states is calculated based on the intensity difference, thereby constructing a preliminary polarization phase difference map in three-dimensional space. This initial phase difference data can reveal the birefringence variation characteristics of the internal materials of the screen protector at different depths and positions, indirectly reflecting the local stress state. However, at this time, the initial phase difference distribution is easily affected by factors such as unstable light sources, detector noise, and interface reflection interference, and there is a certain degree of random drift and systematic error. To improve the stability and physical consistency of the phase difference distribution data, polarization stability constraint processing is performed on the initial phase difference data. The core of the polarization stability constraint lies in constructing a stability constraint function. By analyzing the spatial consistency of the four-quadrant intensity data, physically reasonable phase change patterns are selected, and regions with abnormal offsets are corrected. In the specific operation process, the normalized polarization stability factor of the four-quadrant intensity data is calculated, the phase drift threshold is set to 0.02 radians, and abnormal points with polarization state changes exceeding the threshold are removed. At the same time, local mean filtering and Gaussian smoothing processing are performed within the spatial neighborhood range to suppress isolated noise points and enhance the continuity of the phase distribution. Through this polarization stability constraint, the interference of random noise and systematic drift in the measurement process on the phase difference distribution is effectively eliminated, and the finally obtained polarization phase difference distribution data has good smoothness, continuity, and physical consistency in space.

[0034] In a specific embodiment, the process of performing step S3 may specifically include the following steps: Perform depth correlation based on the thickness gradient vector field data and the polarization phase difference distribution data to obtain a thickness compensation factor; Perform phase jump discrimination on the thickness gradient vector field data according to the thickness compensation factor to obtain real phase jump identification data; Dynamically adjust the window size of the real phase jump identification data to obtain adaptive window parameters; Perform an aperiodic unwrapping algorithm on the polarization phase difference distribution data based on the adaptive window parameters to obtain continuous polarization phase distribution data.

[0035] Specifically, a spatial correlation is established between the thickness gradient vector field data and the polarization phase difference distribution data. The thickness gradient vector field data provides information on the local rate of thickness change of the screen protector in the three-dimensional space of x, y, and z, while the polarization phase difference distribution data reveals the detailed characteristics of the optical delay change inside the material. Although these two types of data have different sources, they are corresponding in the spatial coordinate system. Therefore, they are deeply correlated through spatial registration technology. For each three-dimensional spatial position (x, y, z), the corresponding thickness gradient vector and polarization phase difference value are extracted. By analyzing the local change synchronization between the two, the modulation effect of thickness change on the polarization phase response is evaluated. Based on this spatial depth correlation, a thickness compensation factor is established to correct the influence of the thickness change inside the film material on the optical path length and eliminate the polarization phase error caused by the thickness change. The construction of the compensation factor is modeled according to the relationship between the thickness change amplitude and the polarization phase change rate, and it adopts the form of an exponential decay function, decreasing with the increase of depth, reflecting the optical attenuation characteristics of the material and the multi-layer interface effect. The thickness compensation factor not only depends on the local thickness change rate but also is modulated by combining material optical constants such as refractive index and extinction coefficient, enabling flexible adaptation between different material layers and avoiding phase anomalies caused by sudden changes in the interface refractive index. To improve the robustness of the compensation factor, a multi-scale smoothing strategy is introduced during the construction process. By performing averaging or weighted fitting within the local neighborhood, the interference of random noise on thickness compensation is suppressed, ensuring that the compensation factor has good continuity and physical consistency in space. According to the thickness compensation factor, phase jump discrimination is performed on the thickness gradient vector field data to identify the true phase jump points. Traditional phase jump detection methods are based on the 2π periodicity assumption and are difficult to handle the true phase mutation phenomenon inside the multi-layer composite material of the screen protector. Therefore, an improved discrimination logic is constructed. By setting the joint threshold of the thickness gradient change rate and the compensation factor weighted phase change rate, a point where the local thickness change exceeds the threshold and the corresponding phase difference mutation amplitude exceeds the expected continuous change range is determined as a true jump point. During the discrimination process, a spatial neighborhood consistency constraint is introduced, that is, it is required that the jump point has a high change consistency within a certain neighborhood to avoid misjudging a single isolated noise point as a jump point. At the same time, considering that the thickness mutation and the phase jump occur synchronously at the interface layer, an interface sensitivity weight is introduced into the discrimination logic, assigning a higher weight to the thickness mutation position near the glass-PVB interface, thereby improving the accuracy and sensitivity of jump recognition. Through the above discrimination strategy, the traditional 2π jump error is effectively eliminated, and the true physical phase mutation points inside the screen protector are identified. The window size of the true phase jump recognition data is dynamically adjusted to obtain the adaptive window parameters.The dynamic adjustment of the window size is to flexibly set the processing range according to the local thickness change and phase change characteristics during the phase unwrapping process, avoiding the loss of details caused by using too large a window in areas with drastic thickness changes, and also avoiding low processing efficiency caused by using too small a window in areas with gentle thickness changes. In specific operations, the local change rate is calculated based on the thickness gradient vector field data, and the window size is deduced by the magnitude of the change rate. The larger the change rate, the smaller the window size; the smaller the change rate, the appropriately larger the window size. Then, combined with the jump identification data, smaller windows are preferentially set at the jump points and their neighborhoods to ensure that the phase mutation boundary can be accurately captured during the unwrapping process. At the same time, larger windows are used in the area without jumps to improve the unwrapping efficiency and stability of the phase continuous area. During the dynamic window adjustment process, the spatial transition smoothness is considered to avoid sudden changes in the window size in space, which affects the continuity and consistency of the unwrapping results. Based on the adaptive window parameters, an aperiodic unwrapping algorithm is performed on the polarization phase difference distribution data to obtain continuous polarization phase distribution data. Compared with the traditional method based on 2π periodic jump correction, the aperiodic unwrapping algorithm can better adapt to the aperiodic phase mutations caused by thickness changes, stress concentration, or interface effects inside the actual material. Within the adaptive window, the initial phase difference data is locally expanded, and the jump points are used as boundary conditions for constraint. The minimum jump cost path search or the shortest path algorithm based on graph optimization is used to connect the continuous phase regions in sequence, and the phase misalignment at the jump positions is corrected. By dynamically adjusting the window sliding range and step size, the layer-by-layer expansion of the entire three-dimensional phase difference distribution data is realized, and the phase discontinuity problems caused by multi-layer interfaces and local thickness mutations are eliminated. To further improve the unwrapping accuracy, phase smoothing constraints and polarization stability constraints are introduced during the processing. By fitting the phase change trend in the local neighborhood, the interference of isolated noise points on the unwrapping results is eliminated, ensuring that the phase change is physically continuous and reasonable. Through the above steps, continuous polarization phase distribution data is finally obtained.

[0036] In a specific embodiment, the process of performing the step of discriminating phase jumps on the thickness gradient vector field data according to the thickness compensation factor to obtain the true phase jump identification data may specifically include the following steps: Construct a phase jump discrimination function based on the thickness compensation factor; Compare the gradient magnitudes of the thickness gradient vector field data according to the phase jump discrimination function to obtain thickness gradient threshold screening data; Calculate the phase difference magnitudes of the thickness gradient threshold screening data and the polarization phase difference distribution data to obtain phase mutation candidate point data; Perform dual-condition logical discrimination based on the phase mutation candidate point data to obtain the true phase jump identification data.

[0037] Specifically, the thickness compensation factor is derived from the relationship between the thickness distribution and the optical attenuation characteristics, which is used to correct the influence of the thickness change inside the material on the light propagation path and phase delay, reflecting the actual contribution of materials at different depths to the phase response of polarized light interference. When constructing the phase jump discriminant function, the thickness compensation factor is introduced into the discriminant logic as a key weight, so that the discriminant process can adapt to the phase change characteristics under different thickness levels and different optical path conditions. The phase jump discriminant function needs to comprehensively consider the relationship between the thickness gradient change rate and the local polarization phase difference change rate, and construct a detection model that can dynamically adjust the sensitivity. By extracting the amplitude of the thickness gradient vector field data, the local thickness change rate is obtained, and combined with the weighted processing of the thickness compensation factor, the discriminant function appropriately reduces the sensitivity in the deep area with a long optical path and severe light intensity attenuation, while improving the response to subtle changes in the shallow area. The discriminant function adopts the form of linear weighting or exponential weighting, multiplying the thickness gradient amplitude by the thickness compensation factor to form a composite discriminant index, thereby obtaining a weighted gradient field that takes into account both the thickness change rate and the optical attenuation characteristics. By setting a reasonable discrimination threshold, the areas with abnormally drastic thickness changes and physical significance are screened out from the overall data as potential phase jump candidate areas. Based on the phase jump discriminant function constructed above, the gradient amplitude of the thickness gradient vector field data is compared. By calculating the thickness gradient amplitude of each spatial position point and comparing it point by point with the set thickness change rate threshold, the local area exceeding the threshold is screened out to form the thickness gradient threshold screening data. These screening data represent the areas with abnormal thickness change rate inside the film material, corresponding to the physical structure mutation positions such as material interface, defect area or microcrack initiation point. In order to improve the stability and physical credibility of the screening results, spatial smoothing is introduced in the thickness gradient amplitude comparison process to avoid misjudgment caused by local noise or small measurement errors. At the same time, the threshold is dynamically adjusted in the discrimination process, and different discrimination criteria are set according to the thickness change amplitude of different layers of the material, so that the screening process is adaptive and robust, ensuring that the real thickness mutation area can be accurately identified at different depth levels. The phase difference amplitude is calculated for the thickness gradient threshold screening data and the polarization phase difference distribution data. By calculating the rate of change of the polarization phase difference between adjacent scanning layers, the phase change amplitude information is extracted, and the phase change in the area with drastic thickness changes is spatially corresponded with the thickness gradient threshold screening data, and the phase change in the area with drastic thickness changes is carefully analyzed. In the process of phase difference amplitude calculation, focus on the points where the phase change jumps beyond π or other obvious transition characteristics, because these points correspond to physical phenomena such as sudden stress changes inside the material, interface peeling or crack initiation. In order to avoid random noise interference in the phase data, the phase difference distribution data is preprocessed before the amplitude calculation, including Gaussian smoothing, local mean filtering, etc., to improve the smoothness and continuity of the phase data.In this way, candidate point data of phase mutations with physical significance are effectively identified, and these candidate points have a high degree of spatial coincidence with thickness mutation points. Based on the candidate point data of phase mutations, double-condition logical discrimination is performed to obtain real phase jump identification data. The core of the double-condition logical discrimination lies in that only the points that simultaneously satisfy the condition that the amplitude of the thickness gradient change exceeds the threshold and the amplitude of the polarization phase difference mutation exceeds the set limit are determined as real phase jump points. The thickness gradient threshold is set to 50 micrometers per millimeter, and the phase mutation amplitude threshold is set in the range of 0.8 to 1.2 times of π, ensuring that real physical mutations can be captured rather than pseudo-changes caused by measurement noise. In the actual discrimination process, the logical AND operation is used to jointly apply the two conditions, that is, only the points that satisfy both the thickness change and the phase change conditions at the same spatial position are retained as real jump points, and other points that do not satisfy the double conditions are excluded. To improve the accuracy and robustness of the discrimination, connectivity analysis is introduced after the logical discrimination to exclude isolated small-region jump points and retain jump regions with spatial continuity and physical rationality.

[0038] In a specific embodiment, the process of executing step S4 may specifically include the following steps: Based on the continuous polarization phase distribution data, a modified Müller matrix is constructed to obtain the Müller matrix transformation parameters corresponding to the glass-PVB-glass composite structure; According to the Müller matrix transformation parameters, the stress optical coefficient tensor is calibrated for the continuous polarization phase distribution data to obtain the stress optical coefficient tensor; Based on the stress optical coefficient tensor, elliptical polarization parameter modulation is performed to obtain elliptical polarization modulation parameters; Based on the elliptical polarization modulation parameters, three-dimensional stress tensor reconstruction is performed on the continuous polarization phase distribution data to obtain three-dimensional stress tensor component data; Based on the three-dimensional stress tensor component data, dynamic elliptical polarization modulation scanning is performed to obtain stress damage spatial positioning data.

[0039] Specifically, based on the continuous polarization phase distribution data, the optical response characteristics inside the material are analyzed. The screen protector is composed of a three-layer composite of glass-PVB-glass, and each layer of material has different optical anisotropy characteristics and stress-optical response laws. To describe the optical behavior of this multi-layer composite material, the traditional Müller matrix is modified to construct a matrix model that can characterize the polarization characteristics of the multi-interfaces of the composite structure. According to the variation trend of the local phase delay and the light propagation direction reflected in the continuous polarization phase distribution data, combined with the refractive index, birefringence coefficient, and layer thickness ratio of each layer of material, the transformation parameters of the composite Müller matrix are derived. The modified Müller matrix not only includes the traditional terms such as polarization rotation and polarization ellipticity change, but also introduces the optical path difference compensation term between the interface layers and the local light scattering coefficient, enabling the matrix model to truly reflect the coupling characteristics of the phase shift and polarization state change on the interfaces of each layer of material, thus avoiding the error accumulation problem caused by the traditional single-layer approximation. Through this modification, a Müller matrix transformation system that is more in line with physical reality is established. Based on the modified Müller matrix transformation parameters, the stress-optical coefficient tensor is calibrated for the continuous polarization phase distribution data. The stress-optical effect describes the phenomenon that the optical properties of the material change under the action of force, manifested as the change of the birefringence with the stress. During the calibration process, a quantitative relationship is established between the continuous phase distribution at each point and its corresponding stress state. Specifically, by performing a first-order spatial differential on the phase change rate and combining the anisotropy compensation term in the Müller matrix transformation parameters, the stress-optical response coefficients in each direction are derived. To ensure the calibration accuracy, polynomial fitting or locally weighted regression methods are used to fit the relationship between the phase gradient and the stress, so as to eliminate the interference of local noise and outliers. The obtained stress-optical coefficient tensor not only includes the normal stress components σ xx 、σ yy , but also includes the shear stress component τ xy, which describes the stress response characteristics of materials in different directions and positions. Based on the stress-optical coefficient tensor, elliptical polarization parameter modulation is performed to obtain elliptical polarization modulation parameters. The elliptical polarization parameters include ellipticity and the principal axis direction angle, which reflect the change in the polarization state of light when it propagates through the material and is modulated by the internal stress field. By analyzing the spatial distribution characteristics of the components of the stress-optical coefficient tensor in the directions of the principal stresses and the polarization phase change, and using the ellipticity formula of polarization ellipse, the ellipticity and the principal axis direction angle of polarization at each position are deduced, and these data are summarized to form elliptical polarization modulation parameters. In order to enhance the response sensitivity to micro stress anomalies and local damage, an adaptive modulation depth mechanism is introduced in the elliptical polarization modulation process, that is, the modulation amplitude is dynamically adjusted according to the magnitude of the local stress gradient, ensuring that the polarization modulation amplitude is increased in the regions with drastic stress changes and appropriately reduced in the regions with uniform stress distribution, so as to maximize the scanning sensitivity and imaging accuracy. The modulation parameters vary continuously in space to avoid signal instability caused by sudden changes in the polarization state during scanning, and ensure that the elliptical polarization beam can smoothly pass through the complex stress field inside the protective film during scanning and record the change information of the local stress state. Based on the elliptical polarization modulation parameters, three-dimensional stress tensor reconstruction is performed on the continuous polarization phase distribution data. By performing point-by-point matching of the polarization phase distribution and the modulated elliptical parameters, and using the inverse Müller matrix transformation to invert the polarization response into stress component data, the three-dimensional stress tensor components at each position are gradually restored. During the tensor reconstruction process, considering the anisotropy effect of the material and the interface reflection interference, by introducing an anisotropy correction term and a multi-layer interface model, the physical rationality and spatial continuity of the stress tensor reconstruction are ensured. In order to improve the reconstruction accuracy, a multi-scale iterative optimization method is adopted, combined with the local phase continuity constraint and the stress physical smoothing constraint, to iteratively correct the preliminary reconstruction results, eliminate local outliers, and smoothly transition the tensor distribution in different stress regions. The obtained three-dimensional stress tensor component data can not only reflect the stress distribution of each layer inside the screen protective film, but also capture the stress concentration phenomenon near the microcrack initiation point. Based on the three-dimensional stress tensor component data, dynamic elliptical polarization modulation scanning is performed to obtain stress damage spatial positioning data. During the dynamic scanning process, according to the spatial variation characteristics of the stress tensor distribution, the scanning path and the polarization modulation strategy are adjusted in real time, giving priority to covering the regions with drastic stress gradient changes, and increasing the scanning point density in these regions, reducing the scanning step size to 2 μm × 2 μm × 1 μm to improve the resolution ability for micro damage regions. The elliptical polarization modulation parameters are updated synchronously during the scanning process to ensure that the local stress state can be matched in real time at different scanning positions and enhance the response sensitivity to micro stress anomalies. The scanning path is planned in a spiral, grid or adaptive encryption grid manner, combined with thickness compensation factor correction, to ensure that the scanning density at different depth levels matches the stress change characteristics and avoid missing key damage information.Through dynamic modulation scanning, it is possible to accurately locate the initiation positions of microcracks, stress concentration areas, and potential failure areas inside the screen protector in three-dimensional space, and generate stress damage spatial positioning data.

[0040] In a specific embodiment, the process of performing the step of modulating the ellipsometric parameters based on the stress-optic coefficient tensor to obtain the ellipsometric modulation parameters may specifically include the following steps: Perform ellipsometric parameter vector calculation based on the stress-optic coefficient tensor to obtain ellipticity distribution data; Calculate the stress gradient response coefficient according to the ellipticity distribution data and the three-dimensional stress tensor component data to obtain the adaptive modulation depth parameter; Input the adaptive modulation depth parameter into a dual-frequency drive configurator for frequency separation calculation to obtain dual-frequency drive parameters; Perform elliptical polarization dynamic tracking based on the dual-frequency drive parameters and the thickness compensation factor to obtain elliptical polarization modulation parameters.

[0041] Specifically, the stress-optic coefficient tensor describes the specific influence of stress changes in various directions of the material on its optical properties, especially the birefringence phenomenon. Through this tensor, the change trend of the polarization state of light propagating inside the material is deduced. Perform ellipsometric parameter vector calculation based on the stress-optic coefficient tensor. Based on the spatial distribution of each component in the stress-optic coefficient tensor, the change of the polarization ellipticity of local elliptical polarized light is deduced. During the propagation of polarized light, the principal stress direction inside the material determines the principal axis direction of the elliptical polarized light, while the stress magnitude directly affects the ellipticity, that is, the length ratio of the principal axis to the minor axis of the polarized light. By analyzing the principal value decomposition of the stress tensor, the maximum principal stress direction and the corresponding stress value are extracted, and combined with the photoelastic coefficient of the material, the ratio of the major axis to the minor axis of the polarization ellipse is calculated to obtain the local ellipticity distribution data. The ellipticity distribution data can reflect the strength of optical anisotropy at each position and reveal the local optical property changes caused by stress concentration. Calculate the stress gradient response coefficient according to the ellipticity distribution data and the three-dimensional stress tensor component data. The stress gradient response coefficient reflects the influence degree of the local stress change rate on the polarized light modulation response. For the microdamage initiation area, the local stress gradient shows a drastic change, so the area with a high response coefficient is the potential microcrack formation position. In specific operations, perform a first-order partial derivative of the three-dimensional stress tensor components in space, and calculate σ xx 、σ yy and τ xyThe gradient magnitudes in the x, y, and z directions are then combined into a unified stress gradient magnitude index. Then, this stress gradient magnitude is weighted with the ellipticity value at the corresponding position to construct a stress gradient response coefficient that comprehensively reflects the severity of local stress changes. To enhance the sensitivity to stress changes at different scales, a multi-scale response analysis strategy is introduced, that is, the gradient magnitudes are calculated simultaneously at different spatial scales, and the results at each scale are weighted and averaged, so as to take into account large-scale stress changes and local small stress mutations. Based on the distribution of the stress gradient response coefficient, an adaptive modulation depth parameter is generated. The adaptive modulation depth increases in the area with severe stress changes to enhance the polarization modulation sensitivity, and moderately decreases in the area with uniform stress distribution to optimize the system stability and scanning speed. The adaptive modulation depth parameter is input into the dual-frequency drive configurator for frequency separation calculation. The polarization modulation signal is frequency-allocated in the horizontal and vertical directions respectively to achieve finer-grained spatial modulation control. According to the adaptive modulation depth parameter, the basic modulation depth and basic frequency are determined, and then the horizontal modulation frequency and vertical modulation frequency are dynamically adjusted according to the local stress gradient response intensity to form frequency separation, so as to form a spiral or grid-like modulation path coverage pattern in space. During the frequency separation calculation, according to the magnitude of the local response coefficient, the frequency offset of the horizontal modulation frequency and vertical modulation frequency is dynamically adjusted to ensure that the modulation frequency is encrypted in the stress concentration area to enhance the detection sensitivity of the microcrack initiation area, and at the same time the frequency is reduced in the area with gentle stress changes to optimize the scanning efficiency and data acquisition rate. To ensure the spatial continuity of the frequency change and prevent modulation instability caused by frequency jumps, low-pass filtering smoothing is introduced during the frequency allocation process, so that the frequency smoothly transitions with the spatial position and maintains the overall stability of the modulation system. After completing the frequency separation calculation and obtaining the dual-frequency drive parameters, elliptical polarization dynamic tracking is performed in combination with the thickness compensation factor to generate elliptical polarization modulation parameters. The thickness compensation factor is used to correct the influence of the internal thickness change of the material on the optical path length and the evolution of the polarization state. Especially in multi-layer composite materials such as screen protectors, the thickness change has a significant modulation effect on the light propagation path and polarization state at different depth levels. Therefore, during the dynamic tracking process, the thickness compensation factor is introduced into the elliptical polarization modulation model in real time to perform depth-dependent correction on the ellipticity and the principal axis direction angle. Specifically, at each scanning position, the current modulation frequency and amplitude are determined according to the dual-frequency drive parameters, and at the same time the ellipticity and polarization principal axis angle are adjusted according to the thickness compensation factor, so that the modulated elliptical polarization state can accurately match the local material thickness and stress environment, ensuring the physical consistency and spatial continuity of the polarization response. During the dynamic tracking process, a real-time feedback mechanism is adopted, that is, according to the measurement result of the polarization state of the current scanning point, the modulation parameters of the subsequent scanning path are dynamically adjusted to form a closed-loop control system, further improving the modulation sensitivity and spatial resolution.Through the method of combined modulation of thickness and stress, it is possible to achieve high-sensitivity detection of micro-stress anomalies and early crack initiation regions while maintaining a high scanning speed, improving the overall performance and engineering applicability of the micro-damage detection system for screen protectors. The ellipsometric modulation parameters are output in the form of a spatially continuous parameter field.

[0042] In a specific embodiment, the process of performing steps to obtain stress damage spatial positioning data by dynamically modulating ellipsometry based on the three-dimensional stress tensor component data may specifically include the following steps: Calculate the stress-optic coupling response variable based on the three-dimensional stress tensor component data and the three-dimensional thickness distribution data to obtain the coupling response variable distribution data; Perform adaptive modulation analysis on the ellipsometric modulation parameters according to the coupling response variable distribution data to obtain the dynamic modulation configuration data; Plan the scanning path based on the dynamic modulation configuration data to obtain the target scanning path data; Perform dynamic tracking of the polarization ellipse parameters based on the target scanning path data and the thickness compensation factor to obtain the stress damage spatial positioning data.

[0043] Specifically, a coupling response model is established based on the three-dimensional stress tensor component data and the three-dimensional thickness distribution data. The three-dimensional stress tensor component data provides the normal stresses σ xx 、σ yy in each direction inside the material, as well as the shear stress τ xySuch local stress states, while the three-dimensional thickness distribution data records the thickness variation of the protective film in the x, y, and z spaces. The calculation of the stress-optic coupling response variable needs to consider both the stress state of the material and the thickness variation characteristics simultaneously. The coupling response variable reflects the degree of birefringence response caused by the material under the stressed state and is affected by the thickness. By performing weighted superposition of the magnitudes of the components of the stress tensor and the thickness distribution, a stress-optic response function is constructed. This function combines the local stress concentration degree and the influence of the optical path change on the polarization state, and can quantify the polarization light response intensity at different positions. To enhance the physical meaning of the coupling response variable, the stress-optic coefficients and refractive index differences of the materials of each layer of the screen protective film are introduced during the calculation process to form a stress-optic response model that conforms to the characteristics of the glass-PVB-glass composite structure, ensuring smooth response transition and physical rationality at the interfaces of different materials. The obtained distribution data of the coupling response variable is presented in the form of a three-dimensional grid, containing the local polarization response ability at each point in space. Based on the distribution data of the coupling response variable, an adaptive modulation analysis is performed on the elliptical polarization modulation parameters. The elliptical polarization modulation parameters include ellipticity, major axis direction angle, and modulation depth, which determine the polarization state change mode of the scanning beam in the local area. To adapt to the stress states and thickness characteristics in different regions, the adaptive modulation analysis dynamically adjusts the modulation parameters according to the magnitude of the coupling response variable. In the regions with high coupling response variables, it means stress concentration and significant thickness variation. At this time, the ellipticity modulation amplitude is increased and the modulation depth is raised to enhance the sensitivity to the micro-damage regions; while in the regions with low coupling response variables, the stress distribution is relatively uniform and the thickness change is gentle, so the modulation amplitude and modulation depth are appropriately reduced to optimize the scanning efficiency and system stability. To ensure the continuity of the modulation parameters in space and the smoothness of the modulation process, spatial smoothing filtering and local continuity constraints are introduced during the adaptive modulation analysis process to avoid sudden changes in the modulation parameters in space, resulting in unstable polarization states or abnormal scanning. The generated dynamic modulation configuration data contains the optimal modulation parameter configurations at each spatial position. Based on the dynamic modulation configuration data, a scanning path planning is performed to generate the target scanning path data. The scanning path planning fully considers the spatial distribution characteristics of the coupling response variable, preferentially covers the high-response regions and densifies the scanning points to enhance the damage detection sensitivity. According to the distribution data of the coupling response variable, a response weight map is generated. Higher scanning densities are assigned to the regions with high response values, while the scanning densities are reduced in the regions with low response values. Then, based on the weight map, an adaptive grid division is performed to dynamically adjust the scanning step size. The scanning step size is reduced to 2 μm × 2 μm × 1 μm in the high-response regions, and moderately enlarged to 10 μm × 10 μm × 5 μm in the low-response regions to balance the detection accuracy and scanning efficiency. At the same time, to ensure the continuity of the scanning path and the smoothness of the movement, a spiral or curved surface unfolding path planning algorithm is adopted to avoid positioning errors and waste of scanning time caused by path jumps or rotations.During the path planning process, considering the motion inertia and speed change of the device, the scanning speed is dynamically adjusted to synchronize with the modulation frequency and step change, so as to minimize the scanning error and improve the overall stability of the system. Based on the target scanning path data and the thickness compensation factor, the dynamic tracking of the polarization ellipse parameters is carried out to obtain the stress damage spatial positioning data. The introduction of the thickness compensation factor is to correct the optical path difference and phase drift caused by the internal thickness change of the film material, ensuring that when scanning at different depth levels, the change of the polarization state can truly reflect the local stress state without being interfered by the thickness change. In the specific operation process, at each scanning point, the basic ellipse polarization parameters are determined according to the current dynamic modulation configuration data, and the ellipticity and the main axis direction angle are adjusted in real time in combination with the thickness compensation factor, so that the modulated polarized light can respond to the stress change and structural anomaly to the greatest extent in the local area. During the dynamic tracking process, by introducing a real-time feedback mechanism, the modulation parameters and scanning path of the subsequent scanning points are dynamically corrected according to the actual polarized light response result, forming a closed-loop control system, effectively improving the accuracy of the polarization response and the stability of the scanning path. Through the joint modeling and dynamic modulation optimization based on the three-dimensional stress tensor component data and the three-dimensional thickness distribution data, the micro-crack initiation position, stress concentration area and potential failure area inside the screen protector can be located with high resolution in the three-dimensional space, generating the stress damage spatial positioning data.

[0044] In a specific embodiment, the process of executing step S5 may specifically include the following steps: Construct damage imaging model parameters based on the stress damage spatial positioning data, the thickness gradient vector field data, the continuous polarization phase distribution data, and the coupled response variable distribution data; Perform dual-region differential detection on the edge cutting region and the center bending region of the screen protector according to the damage imaging model parameters to obtain region detection configuration data; Based on the region detection configuration data, perform damage assessment to obtain damage assessment index data, and based on the damage assessment index data, perform voxelized three-dimensional imaging reconstruction to obtain a three-dimensional stress damage imaging result.

[0045] Specifically, the stress damage spatial localization data provides the preliminary spatial distribution of local stress anomalies in a three-dimensional coordinate system. The thickness gradient vector field data describes the thickness change rate of the film material in different spatial directions, reflecting the local topography characteristics. The continuous polarization phase distribution data reveals the optical path differences at each point within the material. The coupled response variable distribution data quantifies the coupling strength between stress and photoelastic response. These four are physically interrelated and need to correspond one by one in space. Therefore, based on spatial interpolation and coordinate registration methods, the four sets of data are mapped into a unified three-dimensional grid system, and data synchronization processing is performed to ensure that each spatial voxel unit contains complete multi-source feature information. Damage imaging model parameters are constructed based on the above multi-source feature data. By defining a set of joint feature vectors that describe the degree of local stress anomaly, thickness change rate, phase continuity anomaly degree, and photoelastic response strength, a multi-dimensional feature description is assigned to each voxel. To enhance the sensitivity of the model to tiny damage and microcrack initiation regions, each feature term is normalized, and weight coefficients are set according to physical importance to form a unified weighted damage factor. The stress damage spatial localization data mainly reflects the degree of stress concentration, so a higher weight is assigned; the thickness gradient vector field is used to identify structural mutations or interface fractures, with the second-highest weight; the continuous polarization phase distribution data is used to capture local optical anomalies, reflecting the potential trend of microcrack formation, with a slightly lower weight; while the coupled response variable, due to its ability to synthesize stress and optical effects, is used as a supplementary feature and is assigned a moderate weight. By weighted combination of each feature, unified damage imaging model parameters are formed. Based on the damage imaging model parameters constructed above, dual-region differential detection is performed on the edge cutting region and the center bending region of the screen protector. Since the edge cutting region is easily affected by mechanical shear stress concentration during the processing, while the center bending region bears greater tensile and compressive stresses during use, there are significant differences in their damage characteristics, stress distribution patterns, and microcrack initiation mechanisms. To adapt to this characteristic, the differential detection strategy sets a high-density scanning mode in the edge region, controlling the detection step size at 1 μm × 1 μm × 0.5 μm, and focuses on detecting the shear stress component τ xy and its spatial gradient changes to enhance the ability to identify tiny defects such as interface peeling and notch propagation; while in the center bending region, a moderately relaxed fast scanning mode is adopted, with the step size set at 5 μm × 5 μm × 2 μm, focusing on the normal stress components σ xx 、σ yyAnd its uniformity analysis focuses on the early identification of tensile cracks and bending fatigue cracks. Based on this dual-mode strategy, region detection configuration data is dynamically generated to clarify the scanning density, feature priority, and detection sensitivity settings of different detection sub-regions, ensuring that the damage detection process can adapt to the physical property differences of different regions, realizing optimized resource allocation and improved detection efficiency. Damage assessment is carried out based on the region detection configuration data to obtain damage assessment index data. During the assessment process, multi-dimensional damage indices such as the stress concentration factor, gradient concentration factor, and interface peeling risk index are introduced. The stress concentration factor quantifies the degree of local stress abnormality by calculating the ratio of the local maximum stress to the surrounding average stress; the gradient concentration factor reflects the non-uniformity of the stress distribution in the damaged area by evaluating the ratio of the local maximum gradient of the stress or thickness change to the global average gradient; the interface peeling risk index evaluates the failure risks such as debonding and peeling of the interface layer based on the integral of the shear stress in the interface area. In addition, the polarization phase discontinuity is introduced as an optical abnormality index to reflect the degree of damage to the optical path continuity caused by the formation of microcracks. By comprehensively weighting each index, a multi-dimensional damage assessment vector is formed, and each voxel unit is assigned a comprehensive damage level. The damage level is divided on a fractional scale, representing healthy, slightly damaged, moderately damaged, and severely damaged in ascending order. Based on the above damage assessment index data, voxelized three-dimensional imaging reconstruction is performed to output the three-dimensional stress damage imaging result. During the reconstruction process, the entire scanning area is divided into voxel units of equal size, and the voxel size is set to 2 cubic micrometers to balance the imaging resolution and data processing volume. Within each voxel, the pseudo-color mapping value is determined according to the comprehensive damage level. Low damage levels are displayed in blue, medium damage levels are displayed with a transition from green to yellow, and high damage levels are highlighted in red and purple, forming an intuitive and well-defined damage visualization effect. To enhance the imaging smoothness and detail continuity, a three-dimensional interpolation algorithm is used to perform spatial smoothing on the damage level data to eliminate discrete noise points and improve the image coherence. At the same time, for subsequent data analysis and engineering applications, the three-dimensional stress damage imaging result is output in multiple data formats, including a three-dimensional mesh model for topography modeling, a pseudo-color map superimposed on three-dimensional voxel data for stress distribution visualization, and tabular statistical data of each damaged area for risk assessment and life prediction.

[0046] The damage detection method of the screen protection film in the embodiment of the present invention is described above. Next, the damage detection system of the screen protection film in the embodiment of the present invention will be described. Please refer to Figure 2 , an embodiment of the damage detection system of the screen protection film in the embodiment of the present invention includes: A scanning module for performing laser interference thickness scanning on the screen protection film to obtain three-dimensional thickness distribution data and thickness gradient vector field data; A detection module for performing multi-layer polarization interference detection on a circularly polarized light beam based on the three-dimensional thickness distribution data to obtain polarization phase difference distribution data; A processing module for performing non-periodic phase unwrapping processing on the polarization phase difference distribution data according to the thickness gradient vector field data to obtain continuous polarization phase distribution data; A modulation module for performing stress optical coefficient tensor calculation and dynamic elliptical polarization modulation based on the continuous polarization phase distribution data to obtain stress damage spatial positioning data; A reconstruction module for performing damage imaging reconstruction on the edge cutting area and the center bending area of the screen protector according to the stress damage spatial positioning data to obtain a three-dimensional stress damage imaging result.

[0047] Through the collaborative cooperation of the above-mentioned various components, by establishing thickness gradient vector field data to guide the non-periodic phase unwrapping processing of polarization phase difference distribution data, the cumulative error problem of the traditional 2π phase jump processing method in thin film materials is effectively solved, and the high-precision acquisition of continuous polarization phase distribution data is realized. The multi-layer configuration of setting four-quadrant polarization detectors at different z-axis depth levels can better handle the interlayer interface effect of the glass-PVB-glass composite structure compared with the traditional single-layer polarization detection technology, improving the detection accuracy and stability of the polarization phase difference distribution data. A modified Müller matrix transformation parameter applicable to the glass-PVB-glass composite structure is established, considering the anisotropic characteristics and interlayer interface effect of the screen protector, and can more accurately realize the numerical conversion from polarization phase to stress components compared with the standard Müller matrix. Based on the adaptive modulation technology driven by stress-optic coupling response variables, through the dual-frequency drive scheme and the spiral path algorithm, the priority scanning and precise positioning of the stress concentration area are realized, significantly improving the detection sensitivity of the microcrack initiation position. A dual-region differential detection strategy is established for the different stress characteristics of the edge cutting area and the center bending area of the screen protector. The shear stress distribution is mainly detected in the edge area, and the normal stress distribution is mainly detected in the center area, realizing targeted and efficient detection. By integrating stress tensor component data, thickness gradient information, polarization phase distribution, and coupling response variables, a damage imaging model with multi-parameter fusion is established, realizing the full-chain detection from geometric thickness change to stress distribution and then to damage positioning.

[0048] Those skilled in the art can clearly understand that for the convenience and simplicity of description, the specific working processes of the above-described system, system, and unit can refer to the corresponding processes in the foregoing method embodiments and will not be elaborated herein.

[0049] When the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on such an understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes: various media such as USB flash drives, mobile hard disks, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical discs that can store program codes.

[0050] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for detecting damage to a screen protector, characterized in that, Including: Performing laser interference thickness scanning on a screen protection film to obtain three-dimensional thickness distribution data and thickness gradient vector field data; Performing multi-layer polarization interference detection on a circularly polarized light beam based on the three-dimensional thickness distribution data to obtain polarization phase difference distribution data; Performing non-periodic phase unwrapping processing on the polarization phase difference distribution data according to the thickness gradient vector field data to obtain continuous polarization phase distribution data; Performing stress optical coefficient tensor calculation and dynamic elliptical polarization modulation based on the continuous polarization phase distribution data to obtain stress damage spatial positioning data; Performing damage imaging reconstruction on the edge cutting area and the center bending area of the screen protection film according to the stress damage spatial positioning data to obtain a three-dimensional stress damage imaging result.

2. The damage detection method of the screen protector according to claim 1, characterized in that, The performing laser interference thickness scanning on the screen protection film to obtain three-dimensional thickness distribution data and thickness gradient vector field data includes: Performing laser interference point-by-point scanning on the screen protection film to obtain original thickness measurement data; Performing three-dimensional coordinate mapping based on the original thickness measurement data to obtain three-dimensional thickness distribution data; Performing partial differential gradient calculation on the three-dimensional thickness distribution data to obtain thickness gradient vector field data.

3. The damage detection method of the screen protector according to claim 2, characterized in that, The performing multi-layer polarization interference detection on the circularly polarized light beam based on the three-dimensional thickness distribution data to obtain polarization phase difference distribution data includes: Creating the circularly polarized light beam configuration parameters of a multi-layer polarization interference optical system based on the three-dimensional thickness distribution data; Performing multi-layer depth scanning on the screen protection film according to the circularly polarized light beam configuration parameters to obtain four-quadrant polarization intensity data; Performing polarization phase difference calculation on the four-quadrant polarization intensity data to obtain initial phase difference distribution data, and performing polarization stability constraint on the initial phase difference distribution data to obtain polarization phase difference distribution data.

4. The damage detection method of the screen protector according to claim 3, wherein, The performing non-periodic phase unwrapping processing on the polarization phase difference distribution data according to the thickness gradient vector field data to obtain continuous polarization phase distribution data includes: Performing depth correlation based on the thickness gradient vector field data and the polarization phase difference distribution data to obtain a thickness compensation factor; Performing phase jump discrimination on the thickness gradient vector field data according to the thickness compensation factor to obtain true phase jump identification data; Performing dynamic adjustment of the window size on the true phase jump identification data to obtain adaptive window parameters; Performing a non-periodic unwrapping algorithm on the polarization phase difference distribution data based on the adaptive window parameters to obtain continuous polarization phase distribution data.

5. The method for detecting damage to the screen protector according to claim 4, wherein The performing phase jump discrimination on the thickness gradient vector field data according to the thickness compensation factor to obtain true phase jump identification data includes: Constructing a phase jump discrimination function based on the thickness compensation factor; Performing gradient amplitude comparison on the thickness gradient vector field data according to the phase jump discrimination function to obtain thickness gradient threshold screening data; Performing phase difference amplitude calculation on the thickness gradient threshold screening data and the polarization phase difference distribution data to obtain phase mutation candidate point data; Performing dual-condition logic discrimination based on the phase mutation candidate point data to obtain true phase jump identification data.

6. The method for detecting damage to the screen protector according to claim 5, wherein Performing stress optical coefficient tensor calculation and dynamic ellipsometric modulation based on the continuous polarization phase distribution data to obtain stress damage spatial localization data, including: Constructing a modified Müller matrix based on the continuous polarization phase distribution data to obtain Müller matrix transformation parameters corresponding to the glass-PVB-glass composite structure; Calibrating the stress optical coefficient tensor for the continuous polarization phase distribution data according to the Müller matrix transformation parameters to obtain the stress optical coefficient tensor; Performing ellipsometric parameter modulation based on the stress optical coefficient tensor to obtain ellipsometric modulation parameters; Reconstructing the three-dimensional stress tensor for the continuous polarization phase distribution data based on the ellipsometric modulation parameters to obtain three-dimensional stress tensor component data; Performing a dynamic ellipsometric modulation scan based on the three-dimensional stress tensor component data to obtain stress damage spatial localization data.

7. The method for detecting damage to the screen protector according to claim 6, wherein The performing ellipsometric parameter modulation based on the stress optical coefficient tensor to obtain ellipsometric modulation parameters includes: Calculating the ellipsometric parameter vector based on the stress optical coefficient tensor to obtain ellipticity distribution data; Calculating the stress gradient response coefficient according to the ellipticity distribution data and the three-dimensional stress tensor component data to obtain an adaptive modulation depth parameter; Inputting the adaptive modulation depth parameter into a dual-frequency drive configurator for frequency separation calculation to obtain dual-frequency drive parameters; Performing dynamic ellipsometric tracking based on the dual-frequency drive parameters and the thickness compensation factor to obtain ellipsometric modulation parameters.

8. The method for detecting damage to the screen protector according to claim 6, wherein, The performing a dynamic ellipsometric modulation scan based on the three-dimensional stress tensor component data to obtain stress damage spatial localization data includes: Calculating the stress-optic coupling response variable based on the three-dimensional stress tensor component data and the three-dimensional thickness distribution data to obtain coupling response variable distribution data; Performing adaptive modulation analysis on the ellipsometric modulation parameters according to the coupling response variable distribution data to obtain dynamic modulation configuration data; Performing scan path planning based on the dynamic modulation configuration data to obtain target scan path data; Performing dynamic tracking of the polarization ellipse parameters based on the target scan path data and the thickness compensation factor to obtain stress damage spatial localization data.

9. The damage detection method of the screen protector according to claim 8, wherein The reconstructing the three-dimensional stress damage imaging result by performing damage imaging reconstruction on the edge cutting area and the center bending area of the screen protector according to the stress damage spatial localization data includes: Constructing damage imaging model parameters based on the stress damage spatial localization data, the thickness gradient vector field data, the continuous polarization phase distribution data, and the coupling response variable distribution data; Performing dual-region differential detection on the edge cutting area and the center bending area of the screen protector according to the damage imaging model parameters to obtain region detection configuration data; Performing damage assessment based on the region detection configuration data to obtain damage assessment index data, and performing voxelized three-dimensional imaging reconstruction based on the damage assessment index data to obtain a three-dimensional stress damage imaging result.

10. A damage detection system for a screen protector, characterized in that, For performing the damage detection method of the screen protector as described in any one of claims 1-9, the damage detection system of the screen protector includes: A scanning module for performing laser interference thickness scanning on the screen protector to obtain three-dimensional thickness distribution data and thickness gradient vector field data; A detection module for performing multi-layer polarization interference detection on a circularly polarized light beam based on the three-dimensional thickness distribution data to obtain polarization phase difference distribution data; A processing module for performing non-periodic phase unwrapping processing on the polarization phase difference distribution data according to the thickness gradient vector field data to obtain continuous polarization phase distribution data; A modulation module for performing stress optical coefficient tensor calculation and dynamic elliptical polarization modulation based on the continuous polarization phase distribution data to obtain stress damage spatial positioning data; A reconstruction module for performing damage imaging reconstruction on the edge cutting area and the center bending area of the screen protector according to the stress damage spatial positioning data to obtain a three-dimensional stress damage imaging result.

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