Nondestructive testing method for internal structural defects of optical fiber cable package

Abstract

The present invention discloses a nondestructive detection method for internal structural defects of an optical fiber package, and the specific steps are as follows: Step 1, using industrial CT equipment to shoot the optical fiber package and then perform three-dimensional reconstruction to obtain a three-dimensional visualization image of the corresponding optical fiber package; Step 2, discretizing the three-dimensional visualization image into a two-dimensional cross-sectional image stack, and performing image enhancement processing and binarization processing on the two-dimensional cross-sectional image in sequence; Step 3, converting the centroid coordinates of each optical fiber core cross section in the binarized image into three-dimensional cylindrical coordinates and reconstructing the geometric reconstruction model of the optical fiber package; Step 4, defining various structural defects inside the optical fiber package, and determining the judgment method of various structural defects in the geometric reconstruction model; Step 5, identifying and detecting various structural defects inside the optical fiber package according to the abnormality of the relevant geometric parameters obtained in Step 4. The present invention solves the problem that the structural defects existing in the prior art can only be observed and judged artificially based on the three-dimensional visualization image.

Description

Technical Field

[0001] The invention belongs to the technical field of nondestructive testing methods and relates to a nondestructive testing method for internal structural defects of an optical fiber package. Background Art

[0002] The optical fiber package refers to a spindle-shaped entity formed by tightly winding the optical fiber on the surface of a truncated cone-shaped core tube. However, during the winding and forming process of the optical fiber package, factors such as fluctuations in the optical fiber diameter and hysteresis angle, uneven adhesive coating, and different thermal expansion coefficients of various materials will cause various structural defects inside it, which will greatly reduce the reliability of the optical fiber when it is released. Therefore, it is necessary to detect the internal structural defects of the optical fiber package.

[0003] Nondestructive testing refers to a method of inspecting and testing the structure, state, type, quantity, shape, position, size and changes of defects inside and on the surface of the test piece by using physical or chemical methods, with the help of modern technology and equipment, without damaging the performance of the object being tested or the internal organization of the object being tested, and by utilizing the changes in thermal, acoustic, optical, electrical, magnetic and other properties caused by abnormal internal structure, defects or inhomogeneity of the material, without damaging the internal structure of the object being tested. There are many commonly used nondestructive testing methods, such as visual inspection, X-ray inspection, ultrasonic inspection, etc.

[0004] Visual inspection refers to a method of observing or measuring the surface of industrial products with human eyes or with the help of optical instruments. Its advantages are simple principle, easy to master, and no need for complex equipment. Its disadvantages are that it cannot observe the internal defects of the object being tested and the effect is unstable. X-ray detection uses rays with a certain energy and intensity to irradiate the object, and then detects the attenuation law and distribution of the rays in the object, so as to complete the inspection of the object being tested. The advantage of X-ray detection is that it can accurately locate defects and can detect internal defects of objects with a large thickness, but it is not effective in detecting area defects and is easy to miss. Ultrasonic testing is a non-destructive testing method that uses the difference in acoustic properties of materials and their defects to reflect the ultrasonic propagation waveform and the energy change of penetration time to detect the internal defects of the object being tested. The advantages of ultrasonic testing are large detection thickness, high sensitivity, low cost, and the ability to locate and quantitatively analyze defects, but its display of defects is not intuitive enough, detection is difficult, and the test results are inconvenient to save.

[0005] Industrial CT, also known as industrial computer tomography, is based on X-ray detection. It performs multiple continuous end-face scans around the sample and reconstructs the scan results into a three-dimensional visual image through computer information processing and image reconstruction technology. Compared with other non-destructive testing methods, it has the advantages of fast detection speed, high resolution, intuitive detection results, and no restrictions on the geometric structure of the object being tested. It is widely used in non-destructive testing and quality assessment of industrial equipment and products. However, since it only reconstructs a three-dimensional visual image and lacks data information, the structural defects inside the sample can only be observed and determined by experienced staff. Summary of the invention

[0006] The purpose of the present invention is to provide a nondestructive detection method for internal structural defects of an optical fiber package, which solves the problem in the prior art that structural defects can only be observed and determined manually based on three-dimensional visual images.

[0007] The technical solution adopted by the present invention is a non-destructive detection method for internal structural defects of optical fiber package, and the specific steps are as follows:

[0008] Step 1: Use industrial CT equipment to photograph the optical fiber package and then perform three-dimensional reconstruction to obtain a three-dimensional visualization image of the corresponding optical fiber package;

[0009] Step 2, discretizing the three-dimensional visualization image into a two-dimensional cross-sectional image stack along the circumferential direction, and performing image enhancement processing and binarization processing on the two-dimensional cross-sectional image in sequence to obtain a corresponding binary image;

[0010] Step 3, converting the centroid coordinates of each optical fiber core cross section in the obtained binary image into three-dimensional cylindrical coordinates, and reconstructing the geometric reconstruction model of the optical fiber line package according to the three-dimensional cylindrical coordinates;

[0011] Step 4, defining various structural defects inside the optical fiber package and determining the determination method of various structural defects in the geometric reconstruction model;

[0012] Step 5, identifying and detecting various structural defects inside the optical fiber package based on the abnormalities of the relevant geometric parameters obtained in step 4.

[0013] The present invention is also characterized in that

[0014] Step 1 is implemented as follows:

[0015] Step 1.1, using industrial CT equipment to photograph the optical fiber package to obtain an image formed by geometric projection of the optical fiber package, and using an objective lens coupled detector to perform optical secondary amplification on the image formed by the geometric projection;

[0016] Step 1.2, using the FDK reconstruction algorithm to reconstruct the image formed by the geometric projection after optical secondary magnification obtained in step 1.1 to obtain reconstructed two-dimensional image information;

[0017] Step 1.3, using the 3D reconstruction software VoxelStudio Recon, reconstruct the 2D image information into 3D visualization data, and finally obtain a 3D visualization image of the optical fiber cable package.

[0018] In step 2, the three-dimensional visualization image is discretized into a two-dimensional cross-sectional image stack along the circumferential direction. Specifically, in the three-dimensional visualization image of the optical fiber package, n two-dimensional cross-sectional images of the optical fiber package are uniformly intercepted along the circumferential direction with a step length of g, where n is calculated by formula (1):

[0019] (1).

[0020] The image enhancement processing for the two-dimensional cross-sectional image in step 2 is specifically as follows:

[0021] Step 2.1, find the largest fiber core cross-sectional radius r in the two-dimensional cross-sectional image max Then, according to the cross-sectional shape of the optical fiber core, a disc-shaped structural element SE with a radius of R is created, where R is greater than r max ;

[0022] Step 2.2, using image opening operation to delete objects that cannot contain SE in the two-dimensional cross-sectional image of the optical fiber package, and obtain a background image that does not contain the cross-sectional area of ​​the optical fiber core;

[0023] Step 2.3, subtract the grayscale value of the corresponding pixel in the background image from the grayscale value of each pixel column in the original optical fiber package two-dimensional cross-sectional image, to obtain an intermediate image in which the background in the source image is replaced with a black background;

[0024] Step 2.4, draw a grayscale distribution histogram of the two-dimensional cross-sectional image of the optical fiber package after replacing the grayscale value in step 2.3, and confirm the interval [min, max] according to the grayscale distribution histogram to ensure that at least 95% of the pixel grayscale levels of the two-dimensional cross-sectional image of the optical fiber package are distributed within this interval;

[0025] Step 2.5, linearly expand the grayscale range [min, max] of the two-dimensional cross-sectional image of the optical fiber package to [0, 255], then the grayscale value of any point in the two-dimensional cross-sectional image of the optical fiber package is The grayscale transformation is performed by formula (2). The grayscale value of any point after transformation is , after transformation, the enhanced two-dimensional cross-sectional image is obtained;

[0026] (2)

[0027] Wherein, MAX is the maximum grayscale value of all pixels in the grayscale distribution histogram of the two-dimensional cross-sectional image of the optical fiber package.

[0028] The binarization process in step 2 is as follows:

[0029] The enhanced two-dimensional cross-sectional image is The binarization threshold of each pixel in the neighborhood , thus obtaining the binary image of the two-dimensional cross-section image of the optical fiber package:

[0030] (3)

[0031] in, Any pixel point on the enhanced two-dimensional cross-sectional image is The mean gray value in the neighborhood, Any pixel point on the enhanced two-dimensional cross-sectional image is The standard deviation within the neighborhood, is the denoising coefficient, which is pre-set by experience;

[0032] in and Calculate according to formula (4) and formula (5) respectively:

[0033] (4)

[0034] (5)

[0035] in, is any pixel point on the enhanced two-dimensional cross-sectional image ( x,y )exist Gray value in the neighborhood;

[0036] Neighborhood radius The determination method is as follows:

[0037] The number of connected domains in the same area when different neighborhood radii are selected , then according to The relative difference is calculated by comparing the actual fiber section number N in the enhanced two-dimensional cross-sectional image

[0038] (6)

[0039] Take relative difference The neighborhood radius corresponding to the minimum is the final determined neighborhood radius .

[0040] In step 3, the centroid coordinates of each optical fiber core cross section in the obtained binary image are converted into three-dimensional cylindrical coordinates as follows:

[0041] Get the centroid position and centroid coordinates of all connected domains in the binary image of the i-th two-dimensional cross-sectional image , i=1,2,…,n, and then the centroid coordinates Convert to cylindrical coordinates to get three-dimensional cylindrical coordinates, specifically:

[0042] (7).

[0043] The geometric reconstruction model of the optical fiber package reconstructed according to the three-dimensional cylindrical coordinates in step 3 is specifically:

[0044] Step 3.1, first set the fiber diameter to d, the core diameter to D, and manually select the starting point , whose coordinates are ), represents the centroid point of the optical fiber core on the qth section of the mth turn of the optical fiber in the lth layer, where l, m, and q are all positive integers, and q=1, 2, ..., n;

[0045] Step 3.2, find the starting point in the q+1th section The radius is Neighborhood of;

[0046] Step 3.3, the maximum distance between the associated centroids of two adjacent cross-sections when the optical fiber is unwound is calculated by formula (8): ;

[0047] (8);

[0048] Step 3.4: Calculate the value confirmed in step 3.2 according to formula (9): Each point in the neighborhood Distance ;

[0049] (9);

[0050] Step 3.5, if the minimum distance calculated in step 3.4 is , then the corresponding point of this distance is the associated centroid point in the q+1 section ,connect and ;

[0051] If the minimum distance calculated , then let the associated centroid point in the q+1 section The coordinates are ), connect p (l,m,q) and ;

[0052] Step 3.6, identifying and connecting the associated centroid points in sequence, until the core cross section of one turn of optical fiber is traversed according to steps 3.1-3.5, that is, the connection of one turn of optical fiber is completed;

[0053] Step 3.7, when When The three-dimensional coordinates are set as the starting point of the next turn of optical fiber connection The coordinates of the fiber are then traversed through all the cross sections to find the associated points on each cross section to complete the connection of the next turn of optical fiber;

[0054] Step 3.8, repeat steps 3.1-3.7 until the area of ​​the optical fiber package to be reconstructed is reconstructed to obtain a geometric reconstruction model.

[0055] The various structural defects inside the optical fiber package defined in step 4 are specifically:

[0056] Crack: A continuous gap with a width less than one wire diameter that penetrates multiple layers inside the wire package;

[0057] End face extrusion: The optical fiber that should be located at the end face of the optical fiber package is squeezed to the upper limit position of the end face of the package core tube by forces from multiple directions;

[0058] Cross-layer slippage: At the cross-layer unwinding point between the fiber optic cable sheath layers, due to the concentration of stress changes inside the fiber optic cable sheath and the special structure of the cross-layer unwinding section, the fiber optic cable slips from the current layer to the internal adjacent layer;

[0059] Bump: The surface of some optical fibers in the current layer is higher than that of other adjacent optical fibers in the same layer;

[0060] Collapse: The surface of some optical fibers in the current layer is significantly lower than other adjacent turns in the same layer;

[0061] Void: A cavity inside the optical fiber package that is wider than one optical fiber diameter and exists only in a single layer of optical fiber.

[0062] The specific method for determining various structural defects in the geometric reconstruction model in step 4 is:

[0063] With the center of the bottom end face of the optical fiber package as the origin and the axis perpendicular to the bottom end face of the optical fiber package as the Z axis, a semi-polar coordinate system is established. Defect determination is performed based on the relative axial distance and relative radial distance between the centroids of the two optical fiber cross sections of adjacent turns under the coordinate system;

[0064] The cracks are determined according to formula (10):

[0065] (10)

[0066] in, represents the axial coordinate of the qth fiber section of the mth turn of the lth layer, D max D is the maximum value of all optical fiber diameters in the optical fiber package. min is the minimum value of all optical fiber diameters in the optical fiber package. It is the taper of the optical fiber core tube;

[0067] End face extrusion is determined according to formula (11):

[0068] (11)

[0069] Among them, Zxt is the axial coordinate of the limit position of the optical fiber core tube;

[0070] The cross-layer slip is determined according to formula (12):

[0071] (12)

[0072] Among them, e is the number of unwinding turns in the cross-layer unwinding section, which ranges from 1.5 to 2.5. represents the radial coordinate of the qth fiber section of the mth turn in the lth layer;

[0073] The bulge is determined according to formula (13):

[0074] (13)

[0075] Collapse is determined according to formula (14):

[0076] (14)

[0077] The void is determined according to formula (15):

[0078] (15).

[0079] Step 5 is as follows:

[0080] According to the defect determination method determined in step 4, by calculating the maximum relative axial distance of each turn of optical fiber, the abnormal value is found, the location of the crack defect is determined, and the width at its widest point is obtained;

[0081] Calculate the maximum value of the axial coordinate of each turn of optical fiber, and determine the location of the end face extrusion defect through the abnormal value;

[0082] The abnormal value of the maximum relative radial distance of each turn of optical fiber is calculated to determine the position of the cross-layer slip and its approximate slip amount;

[0083] Calculate the relative radial distance of each turn of optical fiber and the maximum relative radial distance, determine the location of the convex defect and understand the degree of convexity at each convex position;

[0084] Calculate the relative radial distance of each turn of optical fiber and the maximum relative radial distance, determine the location of the collapse defect through the anomaly, and understand the collapse degree of each collapse point;

[0085] The location of the cavity defect and the maximum width of the cavity defect are determined by calculating the maximum relative axial distance of each turn of optical fiber.

[0086] The beneficial effects of the present invention are:

[0087] The advantage of the present invention over the prior art is that the high-resolution three-dimensional image obtained by industrial CT can be reconstructed into a fine optical fiber package geometry model by means of digital image processing technology, optical fiber connection reconstruction algorithm, etc., so that the fine winding structure inside large-scale complex optical fiber packages can be observed, and the geometric data required for automated non-destructive detection of defects can be obtained; the present invention defines the main geometric features of several common structural defects in optical fiber packages, and based on the optical fiber package geometry reconstruction model, calculates the relevant geometric parameters, and detects the structural defects in the optical fiber package by identifying the abnormalities of the geometric parameters, without the need for manual observation and judgment. BRIEF DESCRIPTION OF THE DRAWINGS

[0088] Figure 1 is a schematic diagram of a three-dimensional visualization image in Example 1 of the nondestructive detection method for internal structural defects of an optical fiber package of the present invention;

[0089] Figure 2 is a schematic diagram of a two-dimensional cross-sectional image in Example 1 of the nondestructive detection method for internal structural defects of an optical fiber package of the present invention;

[0090] Figure 3 It is a background image without a cross section of an optical fiber core in Embodiment 1 of the nondestructive detection method for internal structural defects of an optical fiber package of the present invention;

[0091] Figure 4 is a schematic diagram of an intermediate image in Embodiment 1 of the nondestructive detection method for internal structural defects of an optical fiber package of the present invention;

[0092] Figure 5 Schematic diagram of the enhanced image in Example 1 of the nondestructive detection method for internal structural defects of an optical fiber package of the present invention;

[0093] Figure 6 Schematic diagram of a binarized image in Embodiment 1 of the nondestructive detection method for internal structural defects of an optical fiber package of the present invention;

[0094] Figure 7 Schematic diagram of the centroid position in Embodiment 1 of the nondestructive detection method for internal structural defects of an optical fiber package of the present invention;

[0095] Figure 8It is a schematic diagram of the reconstruction completed in Example 1 of the nondestructive detection method for internal structural defects of an optical fiber package of the present invention;

[0096] Fig. 9 It is a schematic diagram of cracks in the nondestructive detection method of internal structural defects of optical fiber cable package of the present invention;

[0097] Fig.10 It is a schematic diagram of end face extrusion in the nondestructive detection method of internal structural defects of optical fiber package of the present invention;

[0098] Fig.11 It is a schematic diagram of the slippage at the cross-layer in the nondestructive detection method of the internal structural defects of the optical fiber package of the present invention;

[0099] Fig.12a It is a schematic diagram of a bulge caused by a sudden increase in the diameter of an optical fiber in the nondestructive detection method of the internal structural defects of an optical fiber package of the present invention;

[0100] Figure 12b It is a schematic diagram of protrusions caused by uneven adhesive coating on the surface of the optical fiber winding layer in the nondestructive detection method of the internal structural defects of the optical fiber package of the present invention;

[0101] Fig.13 It is a schematic diagram of collapse in the nondestructive detection method of the internal structural defects of the optical fiber package of the present invention;

[0102] Fig.14 It is a schematic diagram of a cavity in the nondestructive detection method of the internal structural defects of the optical fiber package of the present invention;

[0103] Fig.15 It is a schematic diagram of a semi-polar coordinate system in the nondestructive detection method of internal structural defects of an optical fiber package of the present invention;

[0104] Fig.16 A schematic diagram of determining defects in the nondestructive detection method for internal structural defects of an optical fiber package of the present invention. DETAILED DESCRIPTION

[0105] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0106] Example 1

[0107] The nondestructive detection method of the internal structural defects of the optical fiber package of the present invention comprises the following specific steps:

[0108] Step 1: Use industrial CT equipment to photograph the optical fiber package and perform three-dimensional reconstruction to obtain a three-dimensional visualization image of the corresponding optical fiber package; the specific implementation steps are as follows:

[0109] Step 1.1, using industrial CT equipment to photograph the optical fiber package. Since the sample optical fiber package is large in size, it is scanned multiple times from top to bottom using an offset scanning method to obtain an image formed by the geometric projection of the optical fiber package. The image formed by the geometric projection is optically amplified by a second stage using an objective lens coupled detector to improve the spatial resolution of the imaging;

[0110] Step 1.2, using the FDK reconstruction algorithm to reconstruct the image formed by the geometric projection after optical secondary magnification obtained in step 1.1, to obtain the reconstructed two-dimensional image information; the FDK algorithm is an approximate algorithm based on circular orbit cone beam reconstruction, and is also the most practical algorithm in circular orbit cone beam reconstruction;

[0111] Step 1.3, use the 3D reconstruction software VoxelStudio Recon to reconstruct the 2D image information into 3D visualization data, and finally obtain a 3D visualization image of the optical fiber package, such as Figure 1 As shown;

[0112] Step 2, discretizing the three-dimensional visualization image into a two-dimensional cross-sectional image stack along the circumferential direction, and performing image enhancement processing and binarization processing on the two-dimensional cross-sectional image in sequence to obtain a corresponding binary image;

[0113] The three-dimensional visualization image is discretized into a two-dimensional cross-sectional image stack along the circumferential direction as follows: in the three-dimensional visualization image of the optical fiber package, n two-dimensional cross-sectional images of the optical fiber package are uniformly intercepted along the circumferential direction with a step length of g, such as Figure 2 As shown, n is calculated by formula (1):

[0114] (1);

[0115] The image enhancement processing for the two-dimensional cross-sectional image is specifically as follows:

[0116] Step 2.1, find the largest fiber core cross-sectional radius r in the two-dimensional cross-sectional image max Then, according to the cross-sectional shape of the optical fiber core, a disc-shaped structural element SE with a radius of R is created, where R is greater than r max ;

[0117] Step 2.2, use image opening operation to delete the objects that cannot contain SE in the two-dimensional cross-sectional image of the optical fiber package, that is, the optical fiber core cross section, and obtain a background image without the optical fiber core cross section, such as Figure 3 As shown;

[0118] Step 2.3, subtract the grayscale value of the corresponding pixel in the background image from the grayscale value of each pixel in the original optical fiber package two-dimensional cross-section image to obtain an intermediate image in which the background in the source image is replaced with a black background, such as Figure 4 As shown;

[0119] Step 2.4: Since there are still interference elements with similar grayscale around the fiber core in the intermediate image after background replacement, the contrast of the intermediate image still needs to be improved. Draw the grayscale distribution histogram of the two-dimensional cross-sectional image of the optical fiber package after the grayscale value is replaced in step 2.3. According to the grayscale distribution histogram, confirm the interval [min, max] to ensure that at least 95% of the pixel grayscale levels of the two-dimensional cross-sectional image of the optical fiber package are distributed within this interval;

[0120] Step 2.5, linearly expand the grayscale range [min, max] of the two-dimensional cross-sectional image of the optical fiber package to [0, 255], then the grayscale value of any point in the two-dimensional cross-sectional image of the optical fiber package is The grayscale transformation is performed by formula (2). The grayscale value of any point after transformation is , after transformation, the enhanced two-dimensional cross-sectional image is obtained, such as Figure 5 As shown;

[0121] (2)

[0122] Wherein, MAX is the maximum grayscale value of all pixels in the grayscale distribution histogram of the two-dimensional cross-sectional image of the optical fiber package.

[0123] The specific binarization process is as follows:

[0124] The enhanced two-dimensional cross-sectional image is The binarization threshold of each pixel in the neighborhood , thus obtaining a binary image of the two-dimensional cross-sectional image of the optical fiber package, such as Figure 6 As shown:

[0125] (3)

[0126] in, Any pixel point on the enhanced two-dimensional cross-sectional image is The mean gray value in the neighborhood, Any pixel point on the enhanced two-dimensional cross-sectional image is The standard deviation within the neighborhood, is the denoising coefficient, which is pre-set by experience;

[0127] in and Calculate according to formula (4) and formula (5) respectively:

[0128] (4)

[0129] (5)

[0130] in, is any pixel point on the enhanced two-dimensional cross-sectional image ( x,y )exist Gray value in the neighborhood;

[0131] Neighborhood radius The determination method is as follows:

[0132] The number of connected domains in the same area when different neighborhood radii are selected , then according to The relative difference is calculated by comparing the actual fiber section number N in the enhanced two-dimensional cross-sectional image

[0133] (6)

[0134] Take relative difference The neighborhood radius corresponding to the minimum is the final determined neighborhood radius ;

[0135] Step 3, converting the centroid coordinates of each optical fiber core cross section in the obtained binary image into three-dimensional cylindrical coordinates, and reconstructing the geometric reconstruction model of the optical fiber line package according to the three-dimensional cylindrical coordinates;

[0136] The conversion of the centroid coordinates of each optical fiber core cross section in the obtained binary image into three-dimensional cylindrical coordinates is specifically as follows:

[0137] Get the centroid position and centroid coordinates of all connected domains in the binary image of the i-th two-dimensional cross-sectional image , i=1,2,…,n, such as Figure 7 As shown, then the centroid coordinates Convert to cylindrical coordinates to get three-dimensional cylindrical coordinates, specifically:

[0138] (7);

[0139] The geometric reconstruction model of the optical fiber package is reconstructed according to the three-dimensional cylindrical coordinates:

[0140] Step 3.1, first set the fiber diameter to d, the core diameter to D, and manually select the starting point , whose coordinates are ), represents the centroid point of the optical fiber core on the qth section of the mth turn of the optical fiber in the lth layer, where l, m, and q are all positive integers, and q=1, 2, ..., n;

[0141] Step 3.2, find the starting point in the q+1th section The radius is Neighborhood of;

[0142] Step 3.3, the maximum distance between the associated centroids of two adjacent cross-sections when the optical fiber is unwound is calculated by formula (8): ;

[0143] (8);

[0144] Step 3.4: Calculate the value confirmed in step 3.2 according to formula (9): Each point in the neighborhood Distance , unwinding refers to a section of cross-layer wound optical fiber that moves in the winding direction of the next layer of optical fiber when the winding of one layer of optical fiber is completed;

[0145] (9);

[0146] Step 3.5, if the minimum distance calculated in step 3.4 is , then the corresponding point of this distance is the associated centroid point in the q+1 section ,connect and ;

[0147] If the minimum distance calculated , then let the associated centroid point in the q+1 section The coordinates are ), connect p (l,m,q) and ;

[0148] Step 3.6, identifying and connecting the associated centroid points in sequence, until the core cross section of one turn of optical fiber is traversed according to steps 3.1-3.5, that is, the connection of one turn of optical fiber is completed;

[0149] Step 3.7, when When The three-dimensional coordinates are set as the starting point of the next turn of optical fiber connection The coordinates of the fiber are then traversed through all the cross sections to find the associated points on each cross section to complete the connection of the next turn of optical fiber;

[0150] Step 3.8, repeat steps 3.1-3.7 until the area of ​​the optical fiber package to be reconstructed is reconstructed and a geometric reconstruction model is obtained, such as Figure 8 As shown;

[0151] Step 4, defining various structural defects inside the optical fiber package and determining the determination method of various structural defects in the geometric reconstruction model;

[0152] Define various structural defects inside the optical fiber package, specifically:

[0153] Crack: A continuous gap with a width less than one wire diameter that penetrates multiple layers inside the wire package, such as Fig. 9 As shown, the main reason for the defect is that the thermal expansion coefficients of the various materials constituting the optical fiber are different;

[0154] End face extrusion: The optical fiber that should be located at the end face of the optical fiber package is squeezed out to the upper limit position of the end face of the package core tube by forces from multiple directions, such as Fig.10 As shown;

[0155] Cross-layer slippage: At the cross-layer unwinding point between the fiber optic cable sheath layers, due to the concentration of stress changes inside the fiber optic cable sheath and the special structure of the cross-layer unwinding section of the fiber, the fiber slips from the current layer to the internal adjacent layer, such as Fig.11 As shown;

[0156] Bump: The surface of some optical fibers in the current layer is higher than that of other adjacent optical fibers in the same layer. The causes include the sudden increase of the optical fiber diameter, such as Fig.12a ; The adhesive coating on the surface of the optical fiber winding layer is uneven, such as Figure 12b ;

[0157] Collapse: The surface of some optical fibers in the current layer is significantly lower than that of other adjacent turns in the same layer, such as Fig.13 As shown in the figure, the main reason for this is that the lag angle of the lower optical fiber is too small. The lag angle refers to the angle at which the optical fiber being wound is offset toward the direction of the already wound optical fiber in order to ensure tight winding during the winding process.

[0158] Void: A cavity inside the fiber package that is wider than one fiber diameter and exists only in a single layer of fiber, such as Fig.14 As shown, the main reasons for this are the small hysteresis angle of the optical fiber winding, the different thermal expansion coefficients of the various materials constituting the optical fiber, and the uneven coating of the adhesive.

[0159] The specific method for determining various structural defects in the geometric reconstruction model is as follows:

[0160] With the center of the bottom end face of the optical fiber package as the origin and the axis perpendicular to the bottom end face of the optical fiber package as the Z axis, a semi-polar coordinate system is established, such as Fig.15 As shown, using the same Defects are determined by the relative axial distance and relative radial distance between the centroids of the two corresponding optical fiber cross sections of adjacent turns under the coordinate system, such as Fig.16 As shown;

[0161] The main change in the location of the crack is that the relative axial distance of adjacent optical fibers in multiple layers is greater than the normal value. Therefore, the defect is determined by the relative axial distance of adjacent turns of optical fibers in two consecutive layers, and is distinguished by the upper limit value and the identification interval of the cavity. Therefore, the crack is determined according to formula (10):

[0162] (10)

[0163] in, represents the axial coordinate of the qth fiber section of the mth turn of the lth layer, D max D is the maximum value of all optical fiber diameters in the optical fiber package. min is the minimum value of all optical fiber diameters in the optical fiber package. It is the taper of the optical fiber core tube;

[0164] The relative axial distance and relative radial distance of the end-face extruded optical fiber vary significantly. However, since its axial and radial parameters are sometimes close to the cross-layer unwinding point, the end-face extruded optical fiber is identified by directly comparing its axial coordinate maximum value with the Z coordinate of the core tube limit point through formula (11). The end-face extrusion is determined according to formula (11):

[0165] (11)

[0166] Among them, Zxt is the axial coordinate of the limit position of the optical fiber core tube;

[0167] The optical fiber that slips at the cross-layer has obvious changes in both the axial and radial directions. In the axial direction, its relative axial distance exceeds the relative axial distance of the normal cross-layer unwinding section; in the radial direction, its relative radial distance also significantly exceeds the relative radial distance of the cross-layer unwinding section. Therefore, the relative axial distance and relative radial distance of the optical fiber are comprehensively considered to determine the slip at the cross-layer according to formula (12):

[0168] (12)

[0169] Among them, e is the number of unwinding turns in the cross-layer unwinding section, which ranges from 1.5 to 2.5. represents the radial coordinate of the qth fiber section of the mth turn in the lth layer;

[0170] Regardless of whether it is due to an increase in wire diameter or uneven adhesive coating, the most important geometric feature of a bulged optical fiber is the increase in relative radial distance. Therefore, the judgment is made based on its relative radial distance. In order to distinguish between bulges and normal winding conditions, the lower limit for judging optical fiber bulges is set as: , the upper limit is: , we can get the bulge according to formula (13):

[0171] (13)

[0172] The intuitive manifestation of collapse is that the relative radial distance of the collapsed part of the optical fiber is significantly reduced compared with other turns in the layer. Therefore, collapse is determined according to formula (14):

[0173] (14)

[0174] The void is similar to the crack type, but the difference is that the gap is larger and does not penetrate multiple layers, so it is still judged by the relative axial distance. In order to distinguish it from the axial characteristics of the optical fiber slipping across the layer, the upper limit is set to 1.5D max , the void is determined according to formula (15):

[0175] (15).

[0176] Step 5, identifying and detecting various structural defects inside the optical fiber package according to the abnormalities of the relevant geometric parameters obtained in step 4, specifically:

[0177] According to the defect determination method determined in step 4, by calculating the maximum relative axial distance of each turn of optical fiber, the abnormal value is found, the location of the crack defect is determined, and the width at its widest point is obtained;

[0178] Calculate the maximum value of the axial coordinate of each turn of optical fiber, and determine the location of the end face extrusion defect through the abnormal value;

[0179] The abnormal value of the maximum relative radial distance of each turn of optical fiber is calculated to determine the position of the cross-layer slip and its approximate slip amount;

[0180] Calculate the relative radial distance of each turn of optical fiber and the maximum relative radial distance, determine the location of the convex defect and understand the degree of convexity at each convex position;

[0181] Calculate the relative radial distance of each turn of optical fiber and the maximum relative radial distance, determine the location of the collapse defect through the anomaly, and understand the collapse degree of each collapse point;

[0182] The location of the cavity defect and the maximum width of the cavity defect are determined by calculating the maximum relative axial distance of each turn of optical fiber.

[0183] Example 2

[0184] Based on Example 1, in step 2.1, find the largest fiber core cross-sectional radius r in the two-dimensional cross-sectional image. max Use the image measurement tool imdistline in MATLAB for measurement.

[0185] Example 3

[0186] Based on Example 1, in the binarization process of step 2, when determining the neighborhood radius When: measure the average distance D between the centroids of adjacent optical fiber sections m , then the selection range of the neighborhood radius of the local adaptive binarization algorithm is determined to be [D m ,2D m ], by D mAt the beginning, the step size is 1, and the number of connected domains n in the same area is calculated in turn when different neighborhood radii are selected r The relative difference Δ with the actual fiber cross-section number N, and then take the relative difference The neighborhood radius corresponding to the minimum is the final determined neighborhood radius .

[0187] In step 3, the centroid positions and centroid coordinates of all connected domains in the binary image are obtained. Use the centroid calculation tool regionprops in MATLAB.

Claims

1. A nondestructive detection method for internal structural defects of an optical fiber package, characterized in that: The specific steps are as follows: Step 1: Use industrial CT equipment to photograph the optical fiber package and perform three-dimensional reconstruction to obtain a three-dimensional visualization image of the corresponding optical fiber package. The specific steps are as follows: Step 1.1, using industrial CT equipment to photograph the optical fiber package to obtain an image formed by geometric projection of the optical fiber package, and using an objective lens coupled detector to perform optical secondary amplification on the image formed by the geometric projection; Step 1.2, using the FDK reconstruction algorithm to reconstruct the image formed by the geometric projection after optical secondary magnification obtained in step 1.1 to obtain reconstructed two-dimensional image information; Step 1.3, using the 3D reconstruction software VoxelStudio Recon, reconstruct the 2D image information into 3D visualization data, and finally obtain a 3D visualization image of the optical fiber cable package; Step 2: discretize the three-dimensional visualization image into a two-dimensional cross-sectional image stack along the circumferential direction, and perform image enhancement processing and binarization processing on the two-dimensional cross-sectional image in sequence to obtain a corresponding binary image; wherein the image enhancement processing of the two-dimensional cross-sectional image is specifically as follows: Step 2.1, find the largest fiber core cross-sectional radius r in the two-dimensional cross-sectional image max Then, according to the cross-sectional shape of the optical fiber core, a disc-shaped structural element SE with a radius of R is created, where R is greater than r max ; Step 2.2, using image opening operation to delete objects that cannot contain SE in the two-dimensional cross-sectional image of the optical fiber package, and obtain a background image that does not contain the cross-sectional area of ​​the optical fiber core; Step 2.3, subtract the grayscale value of the corresponding pixel in the background image from the grayscale value of each pixel column in the original optical fiber package two-dimensional cross-sectional image, to obtain an intermediate image in which the background in the source image is replaced with a black background; Step 2.4, draw a grayscale distribution histogram of the two-dimensional cross-sectional image of the optical fiber package after replacing the grayscale value in step 2.3, and confirm the interval [min, max] according to the grayscale distribution histogram to ensure that at least 95% of the pixel grayscale levels of the two-dimensional cross-sectional image of the optical fiber package are distributed within this interval; Step 2.5, linearly expand the grayscale range [min, max] of the two-dimensional cross-sectional image of the optical fiber package to [0, 255], then the grayscale value of any point in the two-dimensional cross-sectional image of the optical fiber package is The grayscale transformation is performed by formula (2). The grayscale value of any point after transformation is , after transformation, the enhanced two-dimensional cross-sectional image is obtained; （2） Among them, MAX is the maximum grayscale value of all pixels in the grayscale distribution histogram of the two-dimensional cross-sectional image of the optical fiber package; Step 3, converting the centroid coordinates of each optical fiber core cross section in the obtained binary image into three-dimensional cylindrical coordinates, and reconstructing the geometric reconstruction model of the optical fiber package according to the three-dimensional cylindrical coordinates; wherein the geometric reconstruction model of the optical fiber package reconstructed according to the three-dimensional cylindrical coordinates is specifically: Step 3.1, first set the fiber diameter to d, the core diameter to D, and manually select the starting point , whose coordinates are ), Indicates l Tier m Optical fiber turn q The optical fiber core centroid point on the cross section is l , m , q are all positive integers, q =1,2,……, n ; Step 3.2, in q +1 section to find the starting point The radius is Neighborhood of; Step 3.3, the maximum distance between the associated centroids of two adjacent cross-sections when the optical fiber is unwound is calculated by formula (8): ; （8）； Wherein, in the three-dimensional visualization image of the optical fiber package, g is used as the step length; Step 3.4: Calculate the value confirmed in step 3.2 according to formula (9): Each point in the neighborhood Distance ; （9）； is the radial distance of the three-dimensional cylindrical coordinates, and Z is the height of the three-dimensional cylindrical coordinates; Step 3.5, if the minimum distance calculated in step 3.4 is , then the corresponding point of this distance is the associated centroid point in the q+1 section ,connect and ; If the minimum distance calculated , then suppose q +1 Associated centroid point in cross section The coordinates are ),connect p (l,m,q) and ; Step 3.6, identifying and connecting the associated centroid points in sequence, until the core cross section of one turn of optical fiber is traversed according to steps 3.1-3.5, that is, the connection of one turn of optical fiber is completed; Step 3.7, when When The three-dimensional coordinates are set as the starting point of the next turn of optical fiber connection The coordinates of the fiber are then traversed through all the cross sections to find the associated points on each cross section to complete the connection of the next turn of optical fiber; Step 3.8, repeating steps 3.1-3.7 until the region of the optical fiber package to be reconstructed is reconstructed to obtain a geometric reconstruction model; Step 4, defining various structural defects inside the optical fiber package and determining the determination method of various structural defects in the geometric reconstruction model; Step 5, identifying and detecting various structural defects inside the optical fiber package based on the abnormalities of the relevant geometric parameters obtained in step 4.

2. The nondestructive detection method for internal structural defects of optical fiber package according to claim 1, characterized in that: In step 2, the three-dimensional visualization image is discretized into a two-dimensional cross-sectional image stack along the circumferential direction as follows: in the three-dimensional visualization image of the optical fiber package, n two-dimensional cross-sectional images of the optical fiber package are uniformly intercepted along the circumferential direction with a step length of g, where n is calculated by formula (1): （1）。 3. The nondestructive detection method for internal structural defects of optical fiber package according to claim 1, characterized in that: The binarization process in step 2 is as follows: The enhanced two-dimensional cross-sectional image is The binarization threshold of each pixel in the neighborhood , thus obtaining the binary image of the two-dimensional cross-section image of the optical fiber package: （3） in, Any pixel point on the enhanced two-dimensional cross-sectional image is The mean gray value in the neighborhood, Any pixel point on the enhanced two-dimensional cross-sectional image is The standard deviation within the neighborhood, is the denoising coefficient, which is pre-set by experience; in and Calculate according to formula (4) and formula (5) respectively: （4） （5） in, is any pixel point on the enhanced two-dimensional cross-sectional image ( x,y )exist Gray value in the neighborhood; The neighborhood radius The determination method is as follows: The number of connected domains in the same area when different neighborhood radii are selected , then according to The relative difference is calculated by comparing the actual fiber section number N in the enhanced two-dimensional cross-sectional image （6） Take relative difference The neighborhood radius corresponding to the minimum is the final determined neighborhood radius .

4. The nondestructive detection method for internal structural defects of optical fiber package according to claim 1, characterized in that: In step 3, the centroid coordinates of each optical fiber core cross section in the obtained binary image are converted into three-dimensional cylindrical coordinates as follows: Get the centroid position and centroid coordinates of all connected domains in the binary image of the i-th two-dimensional cross-sectional image , where i = 1, 2…n, and then the centroid coordinates Convert to cylindrical coordinates to get three-dimensional cylindrical coordinates, specifically: （7）。 5. The nondestructive detection method for internal structural defects of optical fiber package according to claim 1, characterized in that: The various structural defects inside the optical fiber package defined in step 4 are specifically: Crack: A continuous gap with a width less than one wire diameter that penetrates multiple layers inside the wire package; End face extrusion: The optical fiber that should be located at the end face of the optical fiber package is squeezed to the upper limit position of the end face of the package core tube by forces from multiple directions; Cross-layer slippage: At the cross-layer unwinding point between the fiber optic cable sheath layers, due to the concentration of stress changes inside the fiber optic cable sheath and the special structure of the cross-layer unwinding section, the fiber optic cable slips from the current layer to the internal adjacent layer; Bump: The surface of some optical fibers in the current layer is higher than that of other adjacent optical fibers in the same layer; Collapse: The surface of some optical fibers in the current layer is significantly lower than other adjacent turns in the same layer; Void: A cavity inside the optical fiber package that is wider than one optical fiber diameter and exists only in a single layer of optical fiber.

6. The nondestructive detection method for internal structural defects of optical fiber package according to claim 5, characterized in that: The determination method of various structural defects in the geometric reconstruction model in step 4 is specifically as follows: With the center of the bottom end face of the optical fiber package as the origin and the axis perpendicular to the bottom end face of the optical fiber package as the Z axis, a semi-polar coordinate system is established. Defect determination is performed based on the relative axial distance and relative radial distance between the centroids of the two optical fiber cross sections of adjacent turns under the coordinate system; The cracks are determined according to formula (10): （10） in, Indicates l The axial coordinate of the qth fiber section of the mth turn in the layer, D max D is the maximum value of all optical fiber diameters in the optical fiber package. min is the minimum value of all optical fiber diameters in the optical fiber package. It is the taper of the fiber optic cable core tube; End face extrusion is determined according to formula (11): （11） Among them, Zxt is the axial coordinate of the limit position of the optical fiber core tube; The cross-layer slip is determined according to formula (12): （12） Among them, e is the number of unwinding turns in the cross-layer unwinding section, which ranges from 1.5 to 2.

5. Indicates l Tier m Zadi q The radial coordinates of the fiber cross section; The bulge is determined according to formula (13): （13） Collapse is determined according to formula (14): （14） The void is determined according to formula (15): （15）。 7. The nondestructive detection method for internal structural defects of optical fiber package according to claim 6, characterized in that: The step 5 is specifically as follows: According to the defect determination method determined in step 4, by calculating the maximum relative axial distance of each turn of optical fiber, the abnormal value is found, the location of the crack defect is determined, and the width at its widest point is obtained; Calculate the maximum value of the axial coordinate of each turn of optical fiber, and determine the location of the end face extrusion defect through the abnormal value; The abnormal value of the maximum relative radial distance of each turn of optical fiber is calculated to determine the position of the cross-layer slip and its approximate slip amount; Calculate the relative radial distance of each turn of optical fiber and the maximum relative radial distance, determine the location of the convex defect and understand the degree of convexity at each convex position; Calculate the relative radial distance of each turn of optical fiber and the maximum relative radial distance, determine the location of the collapse defect through the anomaly, and understand the collapse degree of each collapse point; The location of the cavity defect and the maximum width of the cavity defect are determined by calculating the maximum relative axial distance of each turn of optical fiber.

Images