CN115078419A - Source linear scanning local CT imaging method, storage medium and computer equipment for detecting defects of water-blocking buffer layer of high-voltage cable - Google Patents

Source linear scanning local CT imaging method, storage medium and computer equipment for detecting defects of water-blocking buffer layer of high-voltage cable Download PDF

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CN115078419A
CN115078419A CN202210533349.6A CN202210533349A CN115078419A CN 115078419 A CN115078419 A CN 115078419A CN 202210533349 A CN202210533349 A CN 202210533349A CN 115078419 A CN115078419 A CN 115078419A
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cable
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刘丰林
段晓礁
廖明娟
李雷
余海军
陈杰
倪松
陈大兵
刘建军
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Chongqing Zhence Science And Technology Co ltd
Electric Power Research Institute of State Grid Jiangsu Electric Power Co Ltd
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Abstract

The invention relates to the field of scanning detection analysis, in particular to a source linear scanning local CT imaging method for detecting defects of a water blocking buffer layer of a high-voltage cable; based on an X-ray source, performing single-side scanning on the cable along a direction vertical to the radial direction of the cable to obtain scanned projection data; and reconstructing the projection data by using an image reconstruction algorithm to obtain complete projection information of the detected region so as to detect the defect condition in the cable. Furthermore, the center of the cable part to be detected is placed at an intersection point M point of cross connecting lines of two ends of the scanning path of the X-ray source and two ends of the flat panel detector, so that the projection coverage angle of the X-ray source for scanning the cable part to be detected is the largest; the imaging method has simple movement mode and high imaging speed, can realize the online monitoring of the hidden defects by locally scanning and reconstructing the water-blocking buffer layer of the high-voltage cable, can realize the acquisition of projection data even under the condition of smaller space, and provides a new idea for the detection of the internal defects of the high-voltage cable.

Description

Source linear scanning local CT imaging method, storage medium and computer equipment for defect detection of water-blocking buffer layer of high-voltage cable
Technical Field
The invention relates to the field of scanning detection analysis, in particular to a source linear scanning local CT imaging method, a computer readable storage medium and computer equipment for detecting defects of a water blocking buffer layer of a high-voltage cable.
Background
Crosslinked polyethylene (XLPE) high-voltage cables play an important role in urban power transmission due to the advantages of excellent mechanical properties, good heat resistance, convenience in installation and maintenance and the like. The cable consists of a conductor, a conductor shielding layer, an XLPE insulating layer, an insulating shielding layer, a semiconductor water-blocking buffer layer, an aluminum sheath and an outer protective layer from inside to outside, and the structure of the cable is shown in figure 1; the cable is long-time electrified operation, and underground work environment humidity is big, and partial cable pit or tunnel ponding are serious, and the buffer layer that blocks water of high tension cable bottom is damped easily, separates out white powder for the contact resistance increase between insulation shield and the aluminium sheath, thereby radially produce certain voltage difference. When the voltage difference is larger than a certain value, the air gap is punctured, the discharge between the aluminum sheath and the buffer layer is caused, the buffer layer is ablated under the action of a long time, and a great potential safety hazard is generated;
at present, an X-ray digital imaging (DR) technology is one of the main methods for nondestructive testing of in-service cable defects, and DR images display the difference of the absorption degree of materials of all parts of a cable to X-rays by different gray values, so that the position and the size of the cable defect can be visually detected when the cable is in live operation. However, since the DR presents the superimposed information of all structures of the object in one direction and is interfered by the irregular gap shadow between the corrugated aluminum sheath and the outer sheath of the cable, the DR can only detect the region with obvious internal defects of the cable, and can not distinguish hidden defects from the superimposed information. The Computed Tomography (CT) technology can clearly present the three-dimensional internal structure of an object by acquiring projection information of a detection object from different angles, and obtain spatial position, shape and size information of a defect. Circular scanning is a common scanning mode in CT imaging, and complete projection data are acquired by a ray source and a detector which do circular rotation motion relative to a detection object, so that accurate reconstruction of an object is realized. But because underground tunnel cable detects on-the-spot space narrowly, mostly be a word or article word arrangement between the cable, it is big to use traditional circumference CT to scan the cable degree of difficulty of detecting in service. Therefore, the research on the novel CT imaging method for realizing in-service cable detection has important practical application value;
through looking up a large amount of existing detection reports, XLPE high tension cable buffer layer defect that blocks water appears in the cable joint bottom mostly, and the defect is distributed along cable circumference tangential. When the defect of the high-voltage cable water-blocking buffer layer is detected, the defect is close to the buffer layer density and is reflected in that the contrast ratio on a CT image is low, so that the X-ray with lower energy is needed to be adopted to improve the image contrast ratio, the density of a cable core is high, low-energy rays cannot penetrate through the cable core, the circumferential tangential defect at the bottom of the cable water-blocking buffer layer can be considered as a main target, and only the local part of the bottom of the cable is subjected to CT scanning imaging. In addition, in order to meet the requirement of in-service detection, the corresponding CT scanning imaging equipment has the characteristics of simple structure, simple scanning movement, mobility, portability and the like.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a source line scanning local CT imaging method (L-STCT imaging method for short) for detecting the defects of a water blocking buffer layer of a high-voltage cable, the bottom of the water blocking buffer layer of the high-voltage cable in service is scanned and detected, an iterative reconstruction algorithm is used for reconstructing the bottom of the water blocking buffer layer of the high-voltage cable, and the feasibility of the L-STCT imaging method is verified through simulation experiments and actual experiments.
The embodiment of the invention provides a source linear scanning local CT imaging method for detecting the defects of a water blocking buffer layer of a high-voltage cable, which comprises the following steps:
based on an X-ray source, performing single-side scanning on the cable along a direction vertical to the radial direction of the cable to obtain scanned projection data;
and reconstructing the projection data by using an image reconstruction algorithm to obtain complete projection information of the detected region so as to detect the defect condition in the cable.
Furthermore, the center of the cable part to be detected is placed at the point M of the intersection point of the cross connecting lines of the two ends of the scanning path of the X-ray source and the two ends of the flat panel detector, so that the projection coverage angle of the X-ray source for scanning the cable part to be detected is the largest.
Further, the specific method comprises the following steps:
intercepting a radial scanning section of the cable, and constructing a coordinate system by taking the center of an imaging area of a to-be-detected part of the cable in the radial scanning section as an original point o;
in a coordinate system, connecting two ends of a scanning path of an X-ray source with two ends of a flat panel detector in a crossed manner to obtain an intersection point M, and coinciding an original point o with the M, wherein the coordinate system is divided into four areas taking the M as a center;
calculating the maximum projection coverage angle of each data point in four areas of the coordinate system
Figure BDA0003646860410000021
Results at M Point
Figure BDA0003646860410000022
Obtaining the maximum projection coverage angle of the maximum M point
Figure BDA0003646860410000023
And placing the center of the part to be detected of the cable at the M point for scanning and imaging.
Further, the specific method for constructing the coordinate system is as follows:
constructing an o-xyz coordinate system by taking the center of an imaging area of a to-be-detected part of the cable as an original point o, the vertical direction as an x axis, the horizontal direction as a y axis and the axial direction of the cable as a z axis, and limiting the vertical upward direction as the positive direction of the x axis;
in an o-xyz coordinate system, intercepting a cone beam central horizontal plane along the emission direction of an X-ray source to obtain a radial scanning section of the cable, namely an xoy coordinate plane; in the xoy coordinate plane, scanning the two end values s of the track by the X-ray source 1 And s n And the two-end value d of the flat panel detector 1 And d m Cross-connecting to obtain an intersection point M; and recording the M point as a system central point, and coinciding an origin o point in the xoy coordinate plane with the M point.
Further, the maximum projection coverage angle of each data point in the four areas is calculated
Figure BDA0003646860410000024
The specific method comprises the following steps:
the horizontal width of the flat panel detector is d, the distance between the part to be detected of the cable and the motion trail of the X-ray source is h, and the distance between the part to be detected of the cable and the flat panel detector is l; setting any ray u emitted by X-ray source ij At an angle to the x-axis of
Figure BDA0003646860410000031
The included angle between the connecting line of the X-ray source focus and the o point and the positive X half axis is beta, and the o point to the ray u is calculated ij R; according to the angle of each ray to the x-axis
Figure BDA0003646860410000032
And the distance r from the origin o to the ray, and making a Radon space distribution diagram of projection data in the system; obtaining the maximum projection coverage angle at the o point according to the Radon space distribution diagram
Figure BDA0003646860410000033
Determining the scanning track s of the X-ray source, the horizontal width d of the flat panel detector, the X-ray source and the flat panel detectorThe distance between the panel detectors is l + h; scanning X-ray source to two ends of track s 1 And s n Two end values d of horizontal width of flat panel detector 1 And d m Cross-connecting, dividing the xoy coordinate plane into four regions with M point as center, calculating the maximum projection coverage angle of each data point in the four regions
Figure BDA0003646860410000034
Is obtained at the point M of the system center point
Figure BDA0003646860410000035
Obtaining a maximum value; and placing the center of the part to be detected of the cable at the M point for scanning and imaging.
Further, the included angle
Figure BDA0003646860410000036
The calculation formula of (2) is as follows:
Figure BDA0003646860410000037
in formula (1): l is the distance between the part to be detected of the cable and the flat panel detector;
h is the distance between the part to be detected of the cable and the motion track of the X-ray source;
x D in the xoy coordinate plane, ray u ij Abscissa, x, of intersection with flat-panel detector D ∈[-d/2,d/2]；
x S In the xoy coordinate plane, ray u ij Abscissa, X, of intersection with the X-ray source scanning trajectory S ∈[-s/2,s/2]；
The distance r is calculated as:
Figure BDA0003646860410000038
in formula (2): beta is the angle between the line from X ray source to M point and positive half axis of X, beta is arctan (-h/X) S )，β∈(0,180°) (ii) a Angular range of projection coverage
Figure BDA0003646860410000039
The calculation formula of (2) is as follows:
Figure BDA00036468604100000310
in formula (3):
Figure BDA00036468604100000311
when the focal point of the X-ray source is at s 1 When the distance between the emitted ray and the point o of the origin of the xoy coordinate plane is r, the ray forms an included angle with the x axis;
Figure BDA00036468604100000312
when detector unit d 1 When the distance between the received ray and the origin o point of the xoy coordinate plane is r, the ray forms an included angle with the x axis;
in the formula (3), the reaction mixture is,
Figure BDA00036468604100000313
and
Figure BDA00036468604100000314
the calculation formula of (2) is as follows:
Figure BDA0003646860410000041
Figure BDA0003646860410000042
in formula (5): s-X-ray source scanning trajectory; d-horizontal width of the flat panel detector.
Further, when the origin o of the coordinate system in the xoy coordinate plane is located at the point M, the maximum is obtained
Figure BDA0003646860410000043
The linear distance from the M point to the scanning path of the X-ray source is
Figure BDA0003646860410000044
The xoy coordinate plane is divided into four areas with M points as centers, and the four areas are named as: area1, Area2, Area3, Area 4;
in Area1, the maximum projection coverage angle of any data point P (x, y)
Figure BDA0003646860410000045
Is a ray d 1 P and ray s 1 The included angle of P; recording ray d 1 The angle between P and x-axis is
Figure BDA0003646860410000046
Ray s 1 P forms an angle with the x-axis
Figure BDA0003646860410000047
In Area2, the maximum projection coverage angle of any data point P (x, y)
Figure BDA0003646860410000048
Is a ray s n P and ray s 1 The included angle of P; recording ray s n The angle between P and x-axis is
Figure BDA0003646860410000049
In Area3, the maximum projection coverage angle of any data point P (x, y)
Figure BDA00036468604100000410
Is a ray d 1 P and ray d m The included angle of P; recording ray d m The angle between P and x-axis is
Figure BDA00036468604100000411
In Area4, the maximum projection coverage angle of any data point P (x, y)
Figure BDA00036468604100000412
Is a ray s n P and ray d m The included angle of P; the maximum projection coverage angle of the data point in each region
Figure BDA00036468604100000413
The calculation formula of (2) is as follows:
Figure BDA00036468604100000414
in formula (6):
Figure BDA00036468604100000415
in the above formula: x is the abscissa of the P point in the xoy coordinate plane;
y-the ordinate of the P point in the xoy coordinate plane.
Further, the image reconstruction algorithm is an iterative reconstruction algorithm;
the mathematical model of the iterative reconstruction algorithm is:
Af＝P， (7)
in formula (7): a ═ a ij )∈R I×J -the system projects a matrix;
i is the number of projections;
j-the number of pixels of the reconstructed image;
P＝[p 1 ,p 2 ,…,p I ] T -projecting the vector;
when the projection matrix A of the system is large, the reconstructed image f can not be obtained by direct inversion j Therefore, the SIRT algorithm is adopted to solve the reconstructed image f j The formula is as follows:
Figure BDA0003646860410000051
in formula (8): t-current iteration number of SIRT;
Figure BDA0003646860410000052
λ -relaxation factor.
A second aspect of embodiments of the present invention provides a computer-readable storage medium storing at least one instruction for execution by a processor to implement the method for source line scan local CT imaging for defect detection of an in-service high voltage cable water-blocking buffer layer according to the first aspect of the present invention.
A third aspect of embodiments of the present invention provides a computer device, including a processor and a memory; the memory stores at least one instruction for execution by the processor to implement a source line scan local CT imaging method for in-service high voltage cable water-blocking buffer layer defect detection according to a first aspect of the present invention.
Compared with the prior art, the invention has the following beneficial effects:
the L-STCT scanning imaging method has simple movement mode and high imaging speed, can realize the online monitoring of defect hidden dangers by locally scanning and reconstructing the water blocking buffer layer of the high-voltage cable, can realize the acquisition of projection data even under the conditions of crowded detection site and small cable distance, and provides a new idea and solution for the detection of the internal defects of the high-voltage cable; maximum projection coverage angle of each data point in imaging system by establishing geometric model
Figure BDA0003646860410000053
And the scanning parameters are analyzed to find the point M
Figure BDA0003646860410000054
And max. With increasing s and d, of the corresponding subregion data point within Area1-4
Figure BDA0003646860410000055
Increasing, increasing the collected projection information; the increase of the linear distance h from the cable to be measured to the motion trail of the X-ray source also leads to the data in the corresponding sub-area in the scanning systemOf dots
Figure BDA0003646860410000056
Increasing; the SIRT image reconstruction algorithm is used for reconstruction, and simulation experiments and actual experiment results show that estimated defect positions are placed in a rectangular region with a point M as the center, so that a defect structure in an imaging region is well reconstructed, and the defect detection of the high-voltage cable water-blocking buffer layer in the circumferential tangential direction can be realized; the reconstructed image quality can be improved by increasing d, increasing s or decreasing h.
The invention applies the CT technology to the defect detection of the cable in service, and solves the problem that the conventional portable DR technology and other traditional methods can not meet the requirement of in-service detection. The L-STCT imaging method does not image the conductor of the cable core, has lower requirement on the power of an X-ray source and simple scanning movement, realizes in-service detection of the hidden defect trouble by locally scanning and reconstructing the water blocking buffer layer of the high-voltage cable, can realize accurate detection of the hidden defect trouble even if the detection site is crowded and the cable distance is small, and provides a new solution for detecting the internal defect of the high-voltage cable. In addition, the method can be popularized to in-service CT detection of the same type of pipelines or cables, and the CT application field is enriched.
Drawings
Fig. 1 is a schematic structural view of a high voltage cable;
FIG. 2 is a schematic diagram of a geometric model of an o-xyz coordinate system of the L-STCT scanning system of the present invention:
FIG. 3 is a schematic view of a geometric model of the xoy coordinate plane of the present invention;
FIG. 4 is a projection data distribution diagram of L-STCT single segment scanning in Radon space in accordance with the present invention;
FIG. 5 is a schematic diagram of the division of the xoy coordinate plane into four regions centered around the M point in the present invention;
FIG. 6 is a schematic diagram of a solution to the maximum projection coverage angle for each data point in Area1-4 according to the present invention;
FIG. 7 is a graph of the maximum projection coverage angle distribution for each data point in the L-STCT scanning system of the present invention;
FIG. 8 is a horizontal sectional view and a vertical sectional view of the passing point M in FIG. 7;
FIG. 9 is a schematic structural diagram of a simulation model in a simulation experiment according to an embodiment of the present invention;
FIG. 10 is a schematic diagram of an image reconstruction result of changing a scanning trajectory s of an X-ray source and a horizontal width d of a flat panel detector in a simulation experiment according to an embodiment of the present invention;
FIG. 11 is an enlarged view of the ROI of FIG. 10;
FIG. 12 is a schematic diagram of an image reconstruction result of changing a distance h from an X-ray source to a cable to be measured in a simulation experiment according to an embodiment of the present invention;
FIG. 13 is an enlarged view of the ROI of FIG. 12;
FIG. 14 is a schematic structural diagram of an L-STCT experimental system in an actual experiment according to an embodiment of the present invention;
fig. 15 is a schematic diagram of an image reconstruction result obtained by changing the scanning trajectory s of the X-ray source and changing the cable immersion condition in an actual experiment according to an embodiment of the present invention, (a) s is 120mm, (b) s is 250mm, (c) is not immersed in water, and (d) is immersed in water);
FIG. 17 is a schematic view of a scanning mode of the STCT scanning system;
FIG. 18 is a schematic view of a scanning mode of the L-STCT scanning system;
FIG. 19 is a diagram of a computer device according to an embodiment of the present invention.
Detailed Description
The technical solution of the present invention is further explained with reference to the drawings and the embodiments.
The first embodiment is as follows:
a source linear scanning local CT imaging method for detecting defects of a water blocking buffer layer of a high-voltage cable comprises the following steps:
s1: an L-STCT scanning imaging system is built: the X-ray source and the flat panel detector are erected at intervals and are respectively placed on two sides of a cable to be detected, the flat panel detector is close to the cable to be detected, and the center of the flat panel detector is aligned with the bottom of the cable to be detected;
s2: constructing an o-xyz coordinate system by taking the center of an imaging area of a to-be-detected part of the cable as an original point o, the vertical direction as an x axis, the horizontal direction as a y axis and the axial direction of the cable as a z axis, and limiting the vertical upward direction as the positive direction of the x axis; the flat panel detector and the cable to be detected are kept still, the X-ray source translates at equal intervals along the direction of the X axis, and the part to be detected of the cable is scanned;
s3: in an o-xyz coordinate system, intercepting a cone beam central horizontal plane along the emission direction of an X-ray source to obtain a radial scanning section of the cable, namely an xoy coordinate plane; in the xoy coordinate plane, scanning the two end values s of the track by the X-ray source 1 And s n And the two-end value d of the flat panel detector 1 And d m Cross-connecting to obtain an intersection point M; recording the M point as a system central point, and overlapping an origin point o in the xoy coordinate plane with the M point;
s4: the horizontal width of the flat panel detector is d, the distance between the part to be detected of the cable and the motion trail of the X-ray source is h, and the distance between the part to be detected of the cable and the flat panel detector is l; setting any ray u emitted by X-ray source ij At an angle to the x-axis of
Figure BDA0003646860410000071
The included angle between the connecting line of the X-ray source focus and the o point and the positive X half axis is beta, and the o point to the ray u is calculated ij R; for a cable with radius R, the projection covers the angular range
Figure BDA0003646860410000072
Is defined as: through d 1 And the ray tangent to the cable and the pass s 1 And the included angle between the rays tangent to the cable; according to each ray and the x-axis
Figure BDA0003646860410000073
And the distance r from the origin o to the ray can obtain a Radon space distribution diagram of projection data collected in the L-STCT scanning imaging system; from the Radon spatial profile, at point o,
Figure BDA0003646860410000074
having a maximum value, denoted as maximum projection coverage angle
Figure BDA0003646860410000075
S5: in order to prove the properties of the M points, the scanning track s of the X-ray source, the horizontal width d of the flat panel detector and the distance l + h between the X-ray source and the flat panel detector are determined, a unique M point can be obtained at the moment, and two end values s of the scanning track of the X-ray source are used 1 And s n Two end values d of horizontal width of flat panel detector 1 And d m Cross-connecting, dividing the xoy coordinate plane into four regions with M point as center, calculating the maximum projection coverage angle of each data point in the four regions
Figure BDA0003646860410000076
Is obtained at the point M of the system center point
Figure BDA0003646860410000077
Obtaining a maximum value; defining the FOV of a system imaging area as a rectangular area taking the M point as the center; placing the center of the to-be-detected part of the cable at an M point for scanning imaging;
s6: and reconstructing projection data of the part to be detected of the cable scanned by the X-ray source through an iterative reconstruction algorithm.
In step S4, the included angle
Figure BDA0003646860410000078
The calculation formula of (2) is as follows:
Figure BDA0003646860410000079
in formula (1): l is the distance between the part to be detected of the cable and the flat panel detector;
h is the distance between the part to be detected of the cable and the motion track of the X-ray source;
x D in the xoy coordinate plane, ray u ij Abscissa, x, of intersection with flat-panel detector D ∈[-d/2,d/2]；
x S In the xoy coordinate plane, ray u ij The abscissa of the intersection point with the scanning trajectory of the X-ray source,x S ∈[-s/2,s/2]；
the distance r is calculated as:
Figure BDA0003646860410000081
in formula (2): beta is the angle between the line from X ray source to M point and positive half axis of X, beta is arctan (-h/X) S ) β ∈ (0,180 °); angular range of projection coverage
Figure BDA0003646860410000082
The calculation formula of (2) is as follows:
Figure BDA0003646860410000083
in formula (3):
Figure BDA0003646860410000084
when the focal point of the X-ray source is at s 1 When the distance between the emitted ray and the point o of the origin of the xoy coordinate plane is r, the ray forms an included angle with the x axis;
Figure BDA0003646860410000085
when detector unit d 1 When the distance between the received ray and the original point o of the xoy coordinate plane is r, the ray forms an included angle with the x axis;
in the formula (3), the reaction mixture is,
Figure BDA0003646860410000086
and
Figure BDA0003646860410000087
the calculation formula of (2) is as follows:
Figure BDA0003646860410000088
Figure BDA0003646860410000089
in formula (5): s-X-ray source scanning trajectory; d-horizontal width of the flat panel detector.
Is introduced to
Figure BDA00036468604100000810
Projection data are described for a Radon transformation space of a coordinate system, each point in the Radon space represents projection data obtained by each ray under different projection angles and positions, and projection data distribution of L-STCT single-segment scanning in the Radon space can be obtained through formulas (1) to (3), as shown in FIG. 4; it can be found in fig. 4 that when r is 0, i.e. at point M (also the origin of coordinates o),
Figure BDA00036468604100000811
obtaining the maximum value, and recording as the maximum projection coverage angle
Figure BDA00036468604100000812
In step S5, when the coordinate system origin o in the xoy coordinate plane is located at the point M, the maximum can be obtained
Figure BDA00036468604100000813
At the moment, the system parameters meet
Figure BDA00036468604100000814
The linear distance from the M point to the scanning path of the X-ray source is
Figure BDA00036468604100000815
The xoy coordinate plane is divided into four areas with M points as centers, and the four areas are named as: area1, Area2, Area3, Area 4;
in Area1, the maximum projection coverage angle of any data point P (x, y)
Figure BDA00036468604100000816
Is a ray d 1 P and ray s 1 The included angle of P; recording ray d 1 The angle between P and x-axis is
Figure BDA00036468604100000817
Ray s 1 P forms an angle with the x-axis
Figure BDA00036468604100000818
In Area2, the maximum projection coverage angle of any data point P (x, y)
Figure BDA00036468604100000819
Is a ray s n P and ray s 1 The included angle of P; recording ray s n The angle between the P and x axes is
Figure BDA00036468604100000820
In Area3, the maximum projection coverage angle of any data point P (x, y)
Figure BDA0003646860410000091
Is a ray d 1 P and ray d m The included angle of P; recording ray d m The angle between P and x-axis is
Figure BDA0003646860410000092
In Area4, the maximum projection coverage angle of any data point P (x, y)
Figure BDA0003646860410000093
Is a ray s n P and ray d m The included angle of P; as shown in fig. 6: (a) area1, (b) Area2, (c) Area3, (d) Area 4;
the maximum projection coverage angle of the data point in each region
Figure BDA0003646860410000094
The calculation formula of (2) is as follows:
Figure BDA0003646860410000095
in formula (6):
Figure BDA0003646860410000096
in the above formula: x is the abscissa of the P point in the xoy coordinate plane;
y-the ordinate of the P point in the xoy coordinate plane;
as can be seen in fig. 6: maximum projection coverage angle for data points within Area1, Area2, and Area4 with the remaining parameter conditions unchanged
Figure BDA0003646860410000097
Will increase with the increase of the scanning track s of the X-ray source; the maximum projection coverage angles of Area1, Area2, and Area4 when selecting a larger size flat panel detector
Figure BDA0003646860410000098
Will increase; the maximum projection coverage angles of Area1, Area2, and Area4 when the distance l + h between the X-ray source and the flat panel detector is reduced
Figure BDA0003646860410000099
And correspondingly increased, and conversely, decreased.
The maximum projection coverage angle of each data point in Area1, Area2, Area3 and Area4 can be obtained according to equation (6)
Figure BDA00036468604100000910
Distribution plot, as shown in FIG. 7, the abscissa and ordinate determine the geometric position of the data point in the xoy coordinate plane, with the corresponding value representing the maximum projection coverage angle
Figure BDA00036468604100000911
As can be seen in fig. 7: maximum projection coverage angle at M point
Figure BDA00036468604100000912
At maximum, the nature of the M point is demonstrated. At this point it is possible to obtain:
Figure BDA00036468604100000913
FIG. 8 is a cross-sectional view taken along the line M of FIG. 7 (FIG. 8(a)) and a cross-sectional view taken along the line M (FIG. 8 (b));
as shown in fig. 8 (a): in the areas around point M, namely Area1 and Area4, the maximum projection coverage angle
Figure BDA00036468604100000914
Symmetrically distributed and gradually reduced towards the left side and the right side of the y axis of the xoy coordinate plane;
as shown in fig. 8 (b): in the areas above and below point M, namely Area2 and Area3, the maximum projection coverage angle
Figure BDA00036468604100000915
The x-axis of the xoy coordinate plane is gradually reduced towards the upper side and the lower side, and the reduction speed is high in the direction close to the ray source.
The analysis shows that due to the limitation of the space environment of the scanning system and the imaging object, the projection angle is limited, the L-STCT scanning can not obtain the complete data required by image reconstruction, and the data at the M point
Figure BDA00036468604100000916
Maximum but less than 180 degrees, and the angles decrease in sequence towards the left and right sides of the y axis and the left and right sides of the x axis;
when reconstructing an image from finite angle projection data, a boundary of a feature of an object under examination is easily reconstructed from the finite data if the boundary is tangent to a ray in the finite data set, and is otherwise not easily reconstructed. For a single data point P (x, y), the projection covers an angular range
Figure BDA0003646860410000101
The larger the image, the better the reconstructed image result; in an L-STCT imaging system, the projections of the data points for Area1, Area3, and Area4 cover an angular range while other parameters remain unchanged
Figure BDA0003646860410000102
Is positively correlated with the horizontal width d of the flat panel detector, the larger d is,
Figure BDA0003646860410000103
the larger the projection data, the more projection data is acquired; therefore, in practical use, a flat panel detector with a larger size can be selected as much as possible; the longer the X-ray source scan trajectory s, the data points in Area1, Area2, and Area4
Figure BDA0003646860410000104
The larger, the more rays at different angles, the option is to increase the reconstructed image quality by increasing s. In addition, decreasing the distance h between the X-ray source motion trajectory and the object being measured will also cause data points in Area1, Area2, and Area4
Figure BDA0003646860410000105
The value of (a) increases.
In a conventional circular CT scan, the radiation beam is rotated at least 180 plus a fan angle around the object to be examined to acquire complete projection data for image reconstruction, and thus the field of view (FOV) is defined as the area through which all radiation passes at all angles. The FOV area is a circular area whose radius is related to the distance from the source to the center of rotation, the distance from the center of rotation to the detector and the effective width of the detector. And each point in the area has at least 180 degrees of rays passing through, so that each point in the area can be accurately reconstructed; when the ray angle is less than 180 degrees, the problem of limited angle in the CT system is solved.
The above analysis reveals that the L-STCT scanning system is not sufficient to cover 180 deg., so that the imaging area of the L-STCT cannot be described by a complete circular area. But in the area that the ray passes through, a part of the area has relatively more data volume, the area is mainly concentrated near M point, and the maximum projection coverage angle of the data point passing through the area
Figure BDA0003646860410000106
Relatively large, results in a relatively good quality of the reconstructed image. Therefore, for the purpose of improving the imaging quality, the FOV of the L-STCT imaging area is defined as a rectangular area taking the M point as the center. When the defects of the water blocking buffer layer of the high-voltage cable are detected, the estimated defect position (the bottom of the high-voltage cable buffer layer) is placed in an FOV (field of view), the maximum projection coverage angle of each data point in a rectangular area is the largest, the image reconstruction result is the best, and the size of the FOV area is determined according to the actual detection requirement;
the L-STCT imaging is essentially the problem of limited angle in CT imaging, and the tomography detection of the internal structure form and defects of the object to be detected is realized through incomplete scanning of the object to be detected. During the scanning process, projection data of an angle can be obtained for each focal spot position of the X-ray source. In actual cable detection, the distance between an X-ray source and a flat panel detector is limited, the cable is large in size, rays emitted by the X-ray source can only irradiate one part of the cable, projection data of each angle is truncated and only comprises projections of a part of the cable, and a traditional analytic reconstruction algorithm (such as an FBP algorithm) is adopted to generate serious truncation artifacts. In order to obtain a reconstructed image with higher quality, the invention adopts an iterative reconstruction algorithm to reconstruct a scanned image; compared with an analytic reconstruction algorithm, the iterative reconstruction algorithm has lower requirement on data consistency and stronger noise resistance;
the mathematical model of the iterative reconstruction algorithm is:
Af＝P， (7)
in formula (7): a ═ a (a) ij )∈R I×J -the system projects a matrix;
i is the number of projections;
j-the number of pixels of the reconstructed image;
P＝[p 1 ,p 2 ,…,p I ] T -projecting the vector;
when the projection matrix A of the system is large, the reconstructed image f can not be obtained by direct inversion j Therefore, the SIRT algorithm (namely the joint iterative reconstruction algorithm) is adopted to solve the reconstructed image f j The formula is as follows:
Figure BDA0003646860410000111
in formula (8): t-current iteration number of SIRT;
Figure BDA0003646860410000112
lambda is a relaxation factor, the relaxation factor lambda influences the convergence speed in the iterative process, when the lambda value is too large, the convergence speed of the algorithm is high, but the introduction of noise components into the reconstructed image is increased; when the value of λ is too small, the reconstructed image becomes smooth, but the algorithm also tends to converge slowly.
Simulation experiment:
in order to verify the source linear scanning local CT imaging method for detecting the defects of the water blocking buffer layer of the high-voltage cable provided in the first embodiment, the simulation model shown in fig. 9 is subjected to simulation scanning and image reconstruction;
the simulation model simulates the structure of a high-voltage cable and is composed of a plurality of layers of concentric circle structures, and the middle part of the simulation model is a metal conductor. The water-blocking buffer layer is spirally overlapped and wrapped outside the XLPE insulating layer, absorbs water and expands after being damped in the operation process, generates more white powder through chemical reaction under the action of the pressure of the aluminum protective sleeve and is accumulated at the bottom of the cable, and the water-blocking buffer layer can be visually displayed to be thickened or overlapped. With the increase of white powder, the potential difference between the water-blocking tape and the aluminum protective sleeve rises, and when the potential difference exceeds a certain range, current breakdown is caused, so that the ablation of the insulating shielding layer is caused, ablation holes appear, and even the insulating shielding layer is penetrated. Therefore, in the simulation experiment, different simulation defects shown in fig. 10, ablation defects caused by circular and elliptical simulation current breakdown, strip-shaped simulation cracks or other defects are arranged at the bottom of the water blocking buffer layer of the simulation model. The change of the ring structure of the simulation model can observe whether the cable leaks water, so that white powder accumulation is generated;
placing a simulation model between an X-ray source and a flat panel detector, constructing an o-xyz coordinate system and intercepting an xoy coordinate plane according to the method, wherein the estimated defect position (namely the bottom of the model) of the simulation model is placed at the coordinate origin o of the xoy coordinate plane according to the method as described above because the M point is overlapped with the coordinate origin o of the xoy coordinate plane; scanning the simulation model with various defects, and reconstructing the FOV of the imaging area by using the SIRT algorithm, wherein the size of the reconstructed image is 308 multiplied by 128 pixels. The relaxation factor λ of SIRT was set to 0.8 and the number of iterations was set to 500. The programming environment is Matlab R2017a, Windows 1064-bit system, 8.0GB memory, 3.4GHz CPU, NVIDIA GeForce GT 720; specific scan parameters are shown in table 1.
TABLE 1 simulation experiment Scan parameters
Table 1 Scanning paraMeters of siMulation experiMents
Figure BDA0003646860410000121
Fig. 10(a) shows the reconstruction results when the X-ray source scanning trajectory s is changed, and the X-ray source scanning trajectories s are 150mm, 250mm, and 350mm respectively from left to right with other parameters unchanged. It can be seen that due to the incomplete projection data obtained by the L-STCT scan and the truncated projection data, some white streak artifacts indicated by arrow 1 appear in the reconstructed image. Because rays tangential to the direction parallel to the x axis are fewer, the upper and lower parts of the annular structure and the circular simulation defect have obvious artifacts, but the bottom structure of the cable is completely reconstructed, and the elliptical defect and the strip defect are clearly visible and have complete structures. As s increases, the system Area Area1, Area2, and Area4 are scanned for each data point
Figure BDA0003646860410000122
The relative enlargement and the increase of projection rays tangent to the cable make the upper structure of the image reconstruction result more complete (as shown by an arrow 2 in fig. 10 (a)); the streak artifact caused by missing projection information is reduced (as shown by an arrow 1 in fig. 10 (a)), the streak artifact on the annular structure and the circular defect is reduced, the structure is complete, the image details are clear, and the ROI shown in fig. 11 is enlarged and thinnedThe above features can also be observed in section drawings;
FIG. 10(b) is a reconstructed result of a scanned image when the horizontal width d of the flat panel detector is changed, where d is equal to the product of the number m of detector elements and the size of the detector elements, and the size of d is changed by changing m in a simulation experiment; each row in fig. 10(b) is a reconstructed image of a different defect simulation phantom, and each column is a reconstructed image with 1536, 2536, and 3536 probe elements. As d increases, the system scans each data point within the areas Area1, Area3, and Area4
Figure BDA0003646860410000123
The effective projection data received by the flat panel detector is increased, the rays tangent to the cable edge structure are increased, the lower structure of the image reconstruction result is complete (as shown by an arrow 3), the lower structures of the annular structure and the circular defect become clear, and the reconstructed image quality is improved;
in the actual detection process, it is important to determine the distance (i.e. l and h) from the cable to be detected to the X-ray source motion track and the flat panel detector. When the distance l from the cable to be detected to the flat panel detector is unchanged, the smaller the linear distance h from the cable to be detected to the motion track of the X-ray source is, the more rays tangent to the upper structure of the FOV Area under the same scanning track s of the X-ray source are, and the more rays are distributed in the scanning system, namely the Area1, the Area2 and the Area4 at each data point
Figure BDA0003646860410000131
Becomes larger. FIG. 12 is a reconstructed image when other parameter conditions are not changed, h is 70mm, 120mm and 150mm respectively, as h increases, the upper structure of the FOV area is blurred as indicated by arrow 4 and arrow 5, the stripe artifact in the image is increased, and the quality of the reconstructed image is deteriorated, and FIG. 13 is a detailed enlarged view of the reconstructed ROI;
in conclusion, for the L-STCT scanning imaging system, a better reconstructed image can be obtained at the bottom of the cable, and the defects of the cable water blocking buffer layer can be obviously observed, so that the effectiveness of the scheme is proved. Increasing s or decreasing h increases the maximum projection coverage angle in the corresponding sub-region, increasing the visible structures above the FOV region; as d increases, the maximum projection coverage angle within the corresponding sub-region increases and the visible structures below the FOV area increase.
And (3) actual test:
in order to further verify the source linear scanning local CT imaging method for detecting the defects of the water blocking buffer layer of the high-voltage cable provided by the first embodiment, the method adopts an actual test means to perform verification again;
in the experiment, an L-STCT scanning imaging system is built, as shown in fig. 14, and the experiment is carried out, wherein the system consists of an X-ray source, a flat panel detector, two linear sliding tables and a computer, the two linear sliding tables are used for controlling the movement of the X-ray source and the flat panel detector and changing the translation distance of the X-ray source, and the computer is used for coordinating the work among subsystems.
Based on the above experimental system, the high-voltage cable is subjected to L-STCT scanning, the radius R of the cable to be detected is 50mm, and the cable to be detected consists of a plurality of annular structures. Under the experimental system, the X-ray source moves in the horizontal direction, the cable is placed in the vertical direction, the distance a from the center position of the cable to the origin of coordinates is 35mm, and local imaging is performed on the left side of the cable. The distance from a ray source to a detector is 150mm, the distance h between the motion track of the X-ray source and the part to be detected of the cable is 98mm, the distance l between a flat panel detector and the part to be detected of the cable is 52mm, the scanning track s of the X-ray source is 250mm, and the center M point of the system is determined to be coincident with the origin o of coordinates. The FOV area is set to be 30X 80mm with the bottom of the cable centered at M point 2 A rectangular area of (a). Other scan parameters as shown in table 1 in the simulation experiment, the scan image is reconstructed by using the algorithms shown in equations (7) and (8), and the relaxation factor λ of equation (8) is set to 0.8, and the iteration is performed 500 times.
Fig. 15 (a) (b) shows the slice reconstruction results of the 900 th slice of the cable with the X-ray source scanning trajectory s of 120mm and 250mm respectively, under the condition that other parameters are unchanged: because projection data are truncated and incomplete, partial strip artifacts still exist in the reconstructed image, but the fine-grained strip structures in the water blocking buffer layer are clear and visible, along with the increase of s, the FOV area structure is more complete, the strip artifacts are reduced, the image details become clear, and the quality of the reconstructed image becomes good. The fine bright spots in the figure are metal shavings (copper or aluminum) that fall inside the cable segment during cutting. And simulating actual detection conditions, and scanning and reconstructing the cable before and after immersion. Fig. 15 (c) and (d) show the reconstruction results of the 900 th layer after the cable is not immersed in water and is immersed in water for 10 hours, the line structure of the buffer layer which is not immersed in water is thin and neat, the line structure of the buffer layer which is immersed in water is thick, the buffer layer is completely penetrated by water molecules, and the structure of the buffer layer is changed obviously. As shown in fig. 15, the loop structure of the cable was completely restored, and it was found that no serious current breakdown occurred and the cable was damaged by ablation.
Fig. 16 is a control experimental group, which is the image reconstruction result of another cable with the same size: the s is 120mm, and the cable immersed in water for 2 hours is left to stand for 25Min (FIG. 16(a)) and 4.5 hours (FIG. 16(b)), respectively, while the other parameters are kept unchanged. After the cable is soaked in water, water molecules enter the material of the buffer layer, the overall density of the material of the buffer layer is increased, the longer the diffusion time of the water molecules is, the further chemical reaction of the cable aluminum sheath generates white powder which is accumulated on the water-blocking buffer layer, the line structure of the buffer layer is further thickened, the structural change effect is enhanced, and the water leakage range and the actual condition of the cable can be obviously observed;
in an actual experiment, due to the limited CT projection angle and the truncation of projection information, obvious artifacts exist in the reconstruction results of fig. 15 and 16, but structural changes caused by water leakage are clearly visible, the FOV region is completely reconstructed, and the effectiveness of the imaging mode in the defect detection of the high-voltage cable is verified.
As shown in fig. 17 and 18, the L-STCT is similar to the STCT in the scanning motion mode, and the main differences are: in an STCT scanning system, an object to be detected is placed close to an X-ray source, and complete projection data of the object are scanned and acquired through a multi-segment STCT (mSTCT); in the L-STCT scanning system, the object to be scanned is closer to the flat panel detector, and the maximum projection coverage angle of each data point in the imaging area is determined
Figure BDA0003646860410000141
Distributing, enabling a local imaging center of the object to be detected to be close to the M point, and carrying out CT imaging on the local part;
the invention is used for resisting the in-service high-voltage cableThe defect detection requirement of the water buffer layer, the L-STCT imaging method is provided, and the maximum projection coverage angle of each data point in the imaging system is established by establishing a geometric model
Figure BDA0003646860410000142
And the scanning parameters are analyzed to find the point M
Figure BDA0003646860410000143
And max. As s and d increase, the data points in the corresponding sub-region within Area1-4
Figure BDA0003646860410000144
Increasing, increasing the collected projection information; the linear distance h from the tested cable to the X-ray source is increased, so that the data points of the corresponding sub-area in the scanning system are also obtained
Figure BDA0003646860410000145
Increasing; the SIRT image reconstruction algorithm is used for scanning reconstruction, and simulation experiments and actual experiment results show that estimated defect positions are placed in a rectangular region with a point M as the center, the defect structure in an imaging region is well reconstructed, the defect detection in the circumferential tangential direction of the high-voltage cable water-blocking buffer layer can be realized, and the quality of reconstructed images can be improved by increasing d, increasing s or decreasing h.
Example two:
the second embodiment of the present invention further provides a computer-readable storage medium, where a computer program is stored on the computer-readable storage medium, and when the computer program is executed by a processor, the source linear scanning local CT imaging method for detecting defects of a water-blocking buffer layer of an in-service high-voltage cable described in the second embodiment of the present invention is executed. The storage medium may be a volatile or non-volatile computer-readable storage medium.
Example three:
based on the same technical concept, the third embodiment of the invention also provides computer equipment. Referring to fig. 19, a schematic diagram of a computer device 800 according to an embodiment of the present invention includes a processor 801, a memory 802, and a bus 803. The memory 802 is used for storing execution instructions, and includes a memory 8021 and an external memory 8022; the memory 8021 is also referred to as an internal memory and is used to temporarily store operation data in the processor 801 and data exchanged with the external memory 8022 such as a hard disk, and the processor 801 exchanges data with the external memory 8022 via the internal memory 8021.
In the third embodiment, the memory 802 is specifically configured to store program logic codes corresponding to the execution of the scan control method and/or the image reconstruction algorithm of the X-ray source in the first embodiment of the present invention, and is controlled by the processor 801 to execute the program logic codes. That is, when the computer device 800 is running, the processor 801 communicates with the memory 802 via the bus 803, so that the processor 801 executes the application program codes stored in the memory 802, thereby controlling the scanning action of the X-ray source and/or the complete reconstruction of the scanned image in the first embodiment.
The processor 801 may be an integrated circuit chip having signal processing capabilities. The processor may be a general-purpose processor, including a Central Processing Unit (CPU), a Network Processor (NP), and the like; but may also be a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic device, discrete hardware components. The various methods, steps and logic blocks disclosed in the embodiments of the present invention may be implemented or performed. A general purpose processor may be a microprocessor or the processor may be any conventional processor or the like.
The Memory 802 may be, but is not limited to, a Random Access Memory (RAM), a Read Only Memory (ROM), a Programmable Read Only Memory (PROM), an Erasable Read Only Memory (EPROM), an electrically Erasable Read Only Memory (EEPROM), and the like.
It is to be understood that the third embodiment and the structure illustrated in fig. 19 do not specifically limit the computer apparatus 800. In actual use, computer device 800 may include more or fewer components than illustrated, or combine certain components, or split certain components, or a different arrangement of components. The illustrated components may be implemented in hardware, software, or a combination of software and hardware.
In addition, the present invention further provides a computer program product, where the computer program product carries a program code, and instructions included in the program code may be used to execute the source linear scanning local CT imaging method for detecting defects of a water blocking buffer layer of an in-service high-voltage cable described in the foregoing method embodiments.
The computer program product may be implemented by hardware, software or a combination thereof. In an alternative embodiment, the computer program product is embodied in a computer storage medium, and in another alternative embodiment, the computer program product is embodied in a Software product, such as a Software Development Kit (SDK), or the like.
Finally, as will be appreciated by one of skill in the art, embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein. The scheme in the embodiment of the invention can be realized by adopting various computer languages, such as object-oriented programming language Java and transliterated scripting language JavaScript.
The present invention is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all such alterations and modifications as fall within the scope of the invention.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.

Claims (10)

1. The source linear scanning local CT imaging method for detecting the defects of the water blocking buffer layer of the high-voltage cable is characterized by comprising the following steps of:
based on an X-ray source, performing single-side scanning on the cable along a direction vertical to the radial direction of the cable to obtain scanned projection data;
and reconstructing the projection data by using an image reconstruction algorithm to obtain complete projection information of the detected region so as to detect the defect condition in the cable.
2. The source line scanning local CT imaging method for defect detection of water-blocking buffer layers of high-voltage cables as claimed in claim 1,
the center of the cable part to be detected is placed at the point M of the intersection point of the cross connecting lines of the two ends of the X-ray source scanning path and the two ends of the flat panel detector, so that the projection coverage angle of the X-ray source scanning the cable part to be detected is the largest.
3. The source line scanning local CT imaging method for detecting the defects of the water blocking buffer layer of the high-voltage cable as claimed in claim 2, wherein the specific method comprises the following steps:
intercepting a radial scanning section of the cable, and constructing a coordinate system by taking the center of an imaging area of a to-be-detected part of the cable in the radial scanning section as an original point o;
in a coordinate system, connecting two ends of a scanning path of an X-ray source with two ends of a flat panel detector in a crossed manner to obtain an intersection point M, and coinciding an original point o with the M, wherein the coordinate system is divided into four areas taking the M as a center;
calculating the maximum projection coverage angle of each data point in four areas of the coordinate system
Figure FDA0003646860400000011
Results at M Point
Figure FDA0003646860400000012
Obtaining the maximum projection coverage angle of the maximum M point
Figure FDA0003646860400000013
In the part to be inspected of the cableThe heart is placed at the M point for scanning imaging.
4. The source line scanning local CT imaging method for the defect detection of the water-blocking buffer layer of the high-voltage cable according to claim 3, wherein the specific method for constructing the coordinate system is as follows:
constructing an o-xyz coordinate system by taking the center of an imaging area of a to-be-detected part of the cable as an original point o, the vertical direction as an x axis, the horizontal direction as a y axis and the axial direction of the cable as a z axis, and limiting the vertical upward direction as the positive direction of the x axis;
in an o-xyz coordinate system, intercepting a cone beam central horizontal plane along the emission direction of an X-ray source to obtain a radial scanning section of the cable, namely an xoy coordinate plane; in the xoy coordinate plane, scanning the two end values s of the track by the X-ray source 1 And s n And the two-end value d of the flat panel detector 1 And d m Cross-connecting to obtain an intersection point M; and recording the M point as a system central point, and coinciding an origin o point in the xoy coordinate plane with the M point.
5. The method of claim 4, wherein the maximum projection coverage angle of each data point in four regions is calculated for the source line scan local CT imaging for high voltage cable water blocking buffer defect detection
Figure FDA0003646860400000014
The specific method comprises the following steps:
the horizontal width of the flat panel detector is d, the distance between the part to be detected of the cable and the motion trail of the X-ray source is h, and the distance between the part to be detected of the cable and the flat panel detector is l; setting any ray u emitted by X-ray source ij At an angle to the x-axis of
Figure FDA0003646860400000021
The included angle between the connecting line of the X-ray source focus and the o point and the positive X half axis is beta, and the o point to the ray u is calculated ij R; according to the angle of each ray to the x-axis
Figure FDA0003646860400000022
And the distance r from the origin o to the ray, and making a Radon space distribution diagram of projection data in the system; according to the Radon space distribution diagram, the maximum projection coverage angle at the o point is obtained
Figure FDA0003646860400000023
Determining a scanning track s of an X-ray source, the horizontal width d of a flat panel detector and the distance l + h between the X-ray source and the flat panel detector; scanning the X-ray source to two ends of the track s 1 And s n Two end values d of horizontal width of flat panel detector 1 And d m Cross-connecting, dividing the xoy coordinate plane into four regions with M point as center, calculating the maximum projection coverage angle of each data point in the four regions
Figure FDA0003646860400000024
Is obtained at the point M of the system center point
Figure FDA0003646860400000025
Obtaining a maximum value; and (4) placing the center of the part to be detected of the cable at the M point for scanning and imaging.
6. The source line scan local CT imaging method for high voltage cable water blocking buffer layer defect detection according to claim 5,
included angle
Figure FDA0003646860400000026
The calculation formula of (2) is as follows:
Figure FDA0003646860400000027
in formula (1): l is the distance between the part to be detected of the cable and the flat panel detector;
h is the distance between the part to be detected of the cable and the motion track of the X-ray source;
x D in the xoy coordinate plane, ray u ij Abscissa, x, of intersection with flat-panel detector D ∈[-d/2,d/2]；
x S In the xoy coordinate plane, ray u ij Abscissa, X, of intersection with the X-ray source scanning trajectory S ∈[-s/2,s/2]；
The distance r is calculated as:
Figure FDA0003646860400000028
in formula (2): beta is the angle between the line from X ray source to M point and positive half axis of X, beta is arctan (-h/X) S )，β∈(0,180°)；
Angular range of projection coverage
Figure FDA0003646860400000029
The calculation formula of (c) is:
Figure FDA00036468604000000210
in formula (3):
Figure FDA00036468604000000211
when the focal point of the X-ray source is located at s 1 When the distance between the emitted ray and the point o of the origin of the xoy coordinate plane is r, the ray forms an included angle with the x axis;
Figure FDA00036468604000000212
when detector unit d 1 When the distance between the received ray and the origin o point of the xoy coordinate plane is r, the ray forms an included angle with the x axis;
in the formula (3), the reaction mixture is,
Figure FDA00036468604000000213
and
Figure FDA00036468604000000214
the calculation formula of (2) is as follows:
Figure FDA0003646860400000031
Figure FDA0003646860400000032
in formula (5): s-X-ray source scanning trajectory; d-horizontal width of the flat panel detector.
7. The source line scan local CT imaging method for high voltage cable water blocking buffer layer defect detection according to claim 6,
when the origin o of the coordinate system in the xoy coordinate plane is located at the point M, the maximum is obtained
Figure FDA0003646860400000033
The linear distance from the M point to the scanning path of the X-ray source is
Figure FDA0003646860400000034
The xoy coordinate plane is divided into four areas with M points as centers, and the four areas are named as: area1, Area2, Area3, Area 4;
in Area1, the maximum projection coverage angle of any data point P (x, y)
Figure FDA0003646860400000035
Is a ray d 1 P and ray s 1 The included angle of P; recording ray d 1 The angle between P and x-axis is
Figure FDA0003646860400000036
Ray s 1 P forms an angle with the x-axis
Figure FDA0003646860400000037
In Area2, the maximum projection coverage angle of any data point P (x, y)
Figure FDA0003646860400000038
Is a ray s n P and ray s 1 The included angle of P; recording ray s n The angle between P and x-axis is
Figure FDA0003646860400000039
In Area3, the maximum projection coverage angle of any data point P (x, y)
Figure FDA00036468604000000310
Is a ray d 1 P and ray d m The included angle of P; recording ray d m The angle between P and x-axis is
Figure FDA00036468604000000311
In Area4, the maximum projection coverage angle of any data point P (x, y)
Figure FDA00036468604000000312
Is a ray s n P and ray d m The included angle of P;
the maximum projection coverage angle of the data points in each region
Figure FDA00036468604000000313
The calculation formula of (2) is as follows:
Figure FDA00036468604000000314
in formula (6):
Figure FDA00036468604000000315
in the above formula: x is the abscissa of the P point in the xoy coordinate plane;
y-the ordinate of the P point in the xoy coordinate plane.
8. The source line scan local CT imaging method for high voltage cable water-blocking buffer layer defect detection according to claim 1, wherein said image reconstruction algorithm is an iterative reconstruction algorithm;
the mathematical model of the iterative reconstruction algorithm is:
Af＝P，(7)
in formula (7): a ═ a ij )∈R I×J -the system projects a matrix;
i is the number of projections;
j-the number of pixels of the reconstructed image;
P＝[p 1 ,p 2 ,…,p I ] T -projecting the vector;
when the projection matrix A of the system is large, the reconstructed image f can not be obtained by direct inversion j Therefore, the SIRT algorithm is adopted to solve the reconstructed image f j The formula is as follows:
Figure FDA0003646860400000041
in formula (8): t-current iteration number of SIRT;
Figure FDA0003646860400000042
λ -relaxation factor.
9. A computer-readable storage medium storing at least one instruction for execution by a processor to implement the method for source line scan local CT imaging for defect detection of a water-blocking buffer layer of an in-service high-voltage cable according to any one of claims 1 to 8.
10. A computer device comprising a processor and a memory; the memory stores at least one instruction for execution by the processor to implement the method of any one of claims 1-8 for source line scan local CT imaging for in-service high voltage cable water-blocking buffer defect detection.
CN202210533349.6A 2022-05-17 2022-05-17 Source linear scanning local CT imaging method, storage medium and computer equipment for detecting defects of water-blocking buffer layer of high-voltage cable Pending CN115078419A (en)

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Publication number Priority date Publication date Assignee Title
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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117152077A (en) * 2023-08-30 2023-12-01 苏州谱睿源电子有限公司 Nondestructive detection method and device based on chromatographic fusion technology and storage medium

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