A method for detecting the size of cross-linked polyethylene cable joints

Abstract

The present invention discloses a method for detecting the size of a cross-linked polyethylene (XLPE) cable joint, which comprises: firstly obtaining the three-dimensional point cloud data of the cross-linked polyethylene cable joint, secondly pre-processing the three-dimensional point cloud data of the cross-linked polyethylene cable joint, including filtering and coordinate conversion to obtain the three-dimensional point cloud of the cross-linked polyethylene cable joint in a cylindrical coordinate system, then segmenting it, and finally obtaining the size of each part of the cross-linked polyethylene cable joint. The method can realize the accurate segmentation of each part of the cross-linked polyethylene cable joint point cloud, and complete the automatic detection and determination of the size.

Description

Technical Field

[0001] The invention belongs to a method for detecting the size of a cross-linked polyethylene cable joint and relates to the field of non-destructive testing. Background Art

[0002] With the continuous advancement of urbanization in my country, the demand for electricity in urbanization is also expanding, which means that more power supply lines need to be provided. Most of the traditional transmission lines are erected in the air through poles, which not only occupies urban land and air resources, but also poses a great safety hazard to the suspended high-voltage wires. Therefore, traditional overhead transmission lines have been difficult to meet the needs of urban power supply and distribution. By burying cross-linked polyethylene cables underground, the construction of underground power supply and distribution networks has become a new development trend. In addition, the cross-linked polyethylene cables used in underground power supply and distribution networks support the transmission of 110kV and 220kV voltage levels of electricity, providing efficient power supply to meet the needs of urbanization construction. However, at present, there are still many technical difficulties in the construction of underground cables in my country's power sector. Usually, a single cable is difficult to meet the complex power supply needs of cities, so different cables need to be connected. The connecting parts of the cable connector are mostly pre-formed products, and the cable connector needs to be manually stripped to adapt to the connecting parts of the cable connector. Therefore, the stripping quality of the cable connector has become one of the key factors affecting the safe and stable operation of the power supply and distribution network.

[0003] At present, the size of cable joints after stripping is completely measured manually using a tape measure. The efficiency and accuracy of obtaining the size data of each part of the cable joint have certain limitations, which may easily pose a safety hazard to the project. Summary of the invention

[0004] In response to the above problem, the present invention provides a method for detecting the size of a cross-linked polyethylene cable joint, comprising four modules: three-dimensional point cloud acquisition (1), point cloud preprocessing (2), point cloud segmentation (3), and size detection and determination (4). The method can accurately segment the point cloud of a cross-linked polyethylene cable joint after manual polishing, and complete the automatic detection and determination of the size.

[0005] The functions of each module in the technical solution adopted by the present invention to solve the above technical problems are as follows:

[0006] The steps of the point cloud preprocessing module are as follows:

[0007] S21, filtering the three-dimensional point cloud data of the cross-linked polyethylene cable joint according to a certain radius range and a certain number of adjacent points;

[0008] S22, using a random sample consensus (RANSAC) algorithm to fit the cylindrical features of the three-dimensional point cloud data processed in step S21, and obtaining a direction vector of the central axis of the fitted cylindrical model;

[0009] S23, performing a rigid body transformation on the three-dimensional point cloud data processed in step S21, so that the direction vector of the central axis of the cylinder extracted in step S22 coincides with the Z axis of the Cartesian coordinate system;

[0010] S24, converting the three-dimensional point cloud data processed in step S23 from a three-dimensional Cartesian coordinate system to a cylindrical coordinate system.

[0011] The steps of the point cloud segmentation module are as follows:

[0012] S31. Segment the six regions (conductor, inner semi-conductive, reaction cone, XLPE insulation layer, outer semi-conductive transition zone, outer semi-conductive) in the standard size of cross-linked polyethylene cable joints;

[0013] S32, for the conductor, the inner semi-conductive region point cloud uses segmentation method 1 shown in the following formula to extract the height coordinates of the intersection point between region 1 and region 2 in the cylindrical coordinate system;

[0014]

[0015]

[0016]

[0017]

[0018] Among them, r i is the outer diameter of a point in the point cloud of the area to be segmented, N is the total number of point clouds in the area to be segmented, l1 is the number of point clouds in area 1, m1 is the average outer diameter of the point cloud in area 1, m2 is the average outer diameter of the point cloud in area 2, and m g is the mean value of the outer diameter of the point cloud in the area to be segmented, and σ is the variance of the outer diameter of the point cloud in the area to be segmented. By changing the number of point clouds in area 1, when σ takes the maximum value, the height coordinate h corresponding to the best segmentation point i in the area to be segmented can be obtained. i .

[0019] S33. For the reaction force cone, XLPE insulation layer, outer semi-conductive transition zone, and outer semi-conductive region point cloud, segmentation method 2 as shown in the following formula is used to extract the height coordinates of the junction point between region 3 and region 4 in the cylindrical coordinate system.

[0020]

[0021]

[0022]

[0023] Among them, r i is the outer diameter of a point in the point cloud of the area to be segmented, N is the total number of point clouds in the segmented area, l2 is the number of point clouds in area 3, m3 is the mean of the outer diameter of the point clouds in area 3, m4 is the mean of the outer diameter of the point clouds in area 4, and σ1 is the variance of the outer diameter of the point clouds in area 3. By changing the number of point clouds in area 3, when σ2 takes a larger value and σ1 takes a smaller value, the height coordinate h corresponding to the best segmentation point i in the segmented area can be obtained. i .

[0024] The steps of the size detection and determination module are as follows:

[0025] S41, calculating the distance between the intersection points of adjacent point clouds in each area according to the height coordinates of the best segmentation points obtained after segmentation by the point cloud segmentation module, and obtaining the sizes of different areas of the cross-linked polyethylene cable joint;

[0026] S42, calculating the deviation between the cable dimensions in different regions obtained in step S41 and the standard dimensions of the cable connector;

[0027] S43, determining whether the size parameters of each area are qualified.

[0028] Optionally, in the three-dimensional point cloud acquisition module, the three-dimensional point cloud data acquisition device for the cross-linked polyethylene cable joint can be a non-contact measurement device such as a laser scanner, a depth camera, a structured light scanner, etc. The resolution range of the collected point cloud is set to 0.2 mm to 0.5 mm, and the number of point clouds is at least 500,000.

[0029] Optionally, in the point cloud preprocessing module, the radius of the filter ranges from 1 mm to 3 mm, and the neighboring point threshold is set to 3 to 5 points.

[0030] The beneficial effects of this application are:

[0031] The cross-linked polyethylene cable joint size detection method provided in the embodiment of the present application first obtains the three-dimensional point cloud data of the cross-linked polyethylene cable joint, and then pre-processes the three-dimensional point cloud data of the cross-linked polyethylene cable joint, including filtering and coordinate conversion to obtain the three-dimensional point cloud of the cross-linked polyethylene cable joint in the cylindrical coordinate system, and then segment it, and finally obtain the size of each part of the cross-linked polyethylene cable joint. The method can realize the accurate segmentation of each part of the cross-linked polyethylene cable joint point cloud, and complete the automatic detection and determination of the size.

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a flow chart of the detection method of the present invention;

[0034] Figure 2 It is a schematic diagram of the rotation of the point cloud model;

[0035] Figure 3 This is a schematic diagram of the dimensions of each area of ​​a standard cross-linked polyethylene cable connector;

[0036] Figure 4 This is a schematic diagram of the preset dimensions of each area of ​​the standard cross-linked polyethylene cable joint for the algorithm in this paper;

[0037] Figure 5 Schematic diagram of segmentation effect of segmentation method 1;

[0038] Figure 6 Schematic diagram of segmentation effect of segmentation method 2;

[0039] Figure 7 Diagram showing the division of different areas of a standard cross-linked polyethylene cable connector. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0041] In one embodiment, the present invention provides a method for detecting the size of a cross-linked polyethylene cable joint based on high-precision point cloud data with high calculation accuracy and high calculation efficiency. Figure 1 As shown, the method includes four modules: 3D point cloud acquisition (1), point cloud preprocessing (2), point cloud segmentation (3), and size detection and determination (4).

[0042] The 3D point cloud acquisition module uses laser scanners, depth cameras, and structured light scanners to perform 3D point cloud acquisition on cross-linked polyethylene cable connectors;

[0043] The specific implementation steps of the point cloud preprocessing module are as follows:

[0044] S21, filtering the three-dimensional point cloud data according to a certain radius range (1 mm to 3 mm, 1 mm is used in this embodiment) and a certain number of neighboring points (3 to 5, 3 is used in this embodiment);

[0045] S22, using a random sample consensus (RANSAC) algorithm to fit the cylindrical features of the three-dimensional point cloud data processed in step S21, and obtaining a central axis direction vector of the fitted cylindrical model;

[0046] S23, perform rigid body transformation on the three-dimensional point cloud data processed in step S21, so that the direction vector of the central axis of the cylinder extracted in step S22 coincides with the Z axis of the Cartesian coordinate system. The specific principle is as follows: Figure 2 As shown,

[0047]

[0048]

[0049] Where n1 is the direction vector of the central axis of the fitted cylinder, and its rotated vector coincides with the z-axis as n2. The following formula can be used to calculate the normal vector n3 of the plane formed by these two vectors. The normal vector n3 is perpendicular to both vectors n1 and n2, and passes through the intersection of vectors n1 and n2.

[0050] Then calculate the angle θ between vectors n1 and n2, and use n3 as the rotation axis. Finally, substitute the Rodriguez rotation formula to obtain the coordinates of the rotated point cloud.

[0051]

[0052] Among them, p j is the rotated point cloud coordinate vector, p i is the point cloud coordinate vector before rotation.

[0053] S24, converting the three-dimensional point cloud data processed in step S23 from a three-dimensional Cartesian coordinate system to a cylindrical coordinate system, specifically including:

[0054] Assume point p n For a point in the transformed point cloud, the point cloud coordinate system is transformed into the cylindrical coordinate system using the following formula

[0055]

[0056]

[0057]

[0058] where x n ,yn ,z n , is point p n The Cartesian coordinates of n Radial distance, ψ n is the azimuth, h n Height. These three coordinate parameters form a cylindrical coordinate system.

[0059] The steps of the point cloud segmentation module are as follows:

[0060] S31, according to Figure 3 The standard cross-linked polyethylene cable joint shown is divided into 6 areas: 1. Conductor (height 30mm), 2. Inner semi-conductive layer (height 10mm), 3. Reaction force cone (height 55mm), 4. XLPE insulation layer (height 165mm), 5. Outer semi-conductive transition zone (height 40mm), 6. Outer semi-conductive (height not included). Specifically including:

[0061] First, the point cloud is divided into 72 strip point clouds according to the azimuth angle of every 5 degrees, and then according to Figure 4 The schematic diagram of preset dimensions of each area of ​​a standard cross-linked polyethylene cable joint is shown, and the strip point cloud is divided into conductor, inner semi-conductive, reaction force cone, XLPE insulation layer, outer semi-conductive transition zone, and outer semi-conductive predefined areas according to height.

[0062] S32, for the conductor, the inner semi-conductive region point cloud uses segmentation method 1 to extract the height coordinates of the intersection points of the to-be-segmented regions in a cylindrical coordinate system; specifically including:

[0063] First, the segmented area point cloud is divided into Figure 5 Region 1 and Region 2 are shown.

[0064]

[0065]

[0066]

[0067]

[0068] Among them, r i is the outer diameter of a point in the point cloud of the area to be segmented, N is the total number of point clouds in the area to be segmented, l1 is the number of point clouds in area 1, m1 is the average outer diameter of the point cloud in area 1, m2 is the average outer diameter of the point cloud in area 2, and m g is the mean value of the outer diameter of the point cloud in the area to be segmented, and σ is the variance of the outer diameter of the point cloud in the area to be segmented. By changing the number of point clouds in area 1, when σ takes the maximum value, the height coordinate h corresponding to the best segmentation point i in the area to be segmented can be obtained. i .

[0069] Take the point cloud processing of the conductor predefined area as an example. First, follow Figure 4 As shown, the conductor predefined area point cloud (A) is selected, and then the height coordinates of the best segmentation point in the conductor predefined area are calculated using segmentation method 1. The conductor predefined area point cloud is composed of the conductor actual area point cloud and part of the inner semi-conductive transition zone area point cloud. The best segmentation point obtained by segmentation method 1 is actually the junction point between the conductor area and the inner semi-conductive transition zone area. Repeat the above steps to obtain the junction point between the insulating layer and the outer semi-conductive transition zone, and the junction point between the outer semi-conductive transition zone and the outer semi-conductive transition zone.

[0070] S33, extracting the height coordinates of the intersection points of the to-be-segmented regions in the cylindrical coordinate system using segmentation method 2 for the reaction force cone, XLPE insulation layer, outer semi-conductive transition zone, and outer semi-conductive region point cloud. Specifically including:

[0071] First, the selected predefined area point cloud is divided into Figure 6 Region 3 and Region 4 shown.

[0072]

[0073]

[0074]

[0075] Among them, r i is the outer diameter of a point in the point cloud of the area to be segmented, N is the total number of point clouds in the segmented area, l2 is the number of point clouds in area 3, m3 is the mean of the outer diameter of the point clouds in area 3, m4 is the mean of the outer diameter of the point clouds in area 4, and σ1 is the variance of the outer diameter of the point clouds in area 3. By changing the number of point clouds in area 3, when σ2 takes a larger value and σ1 takes a smaller value, the height coordinate h corresponding to the best segmentation point i in the segmented area can be obtained. i .

[0076] Take the predefined area point cloud processing of XLPE insulation layer as an example. First, follow Figure 4 As shown in the figure, the predefined area point cloud of the reaction force cone is selected, and then segmentation method 2 is used to calculate the best segmentation point in the predefined area of ​​the reaction force cone. The point cloud of the predefined area of ​​the reaction force cone is composed of the actual area point cloud of the reaction force cone and part of the XLPE insulation layer area point cloud. The best segmentation point obtained by segmentation method 2 is actually the intersection point of the reaction force cone area and the XLPE insulation layer area. Repeat the above steps to get the intersection point of the inner semi-conductive and XLPE insulation layer areas. The specific segmentation effect is as follows Figure 7 shown.

[0077] The size detection and determination module performs size measurement and determination on the manually polished cross-linked polyethylene cable joint point cloud according to different regions based on the information of the segmentation points. The specific steps are as follows:

[0078] Step S41, through the above segmentation point extraction algorithm, the intersection point between the conductor and the inner semi-conductive, the intersection point between the inner semi-conductive and the reaction force cone, the intersection point between the reaction force cone and the XLPE insulation layer, the intersection point between the XLPE insulation layer and the outer semi-conductive transition zone, and the outer semi-conductive transition zone and the outer semi-conductive intersection point are obtained, a total of 7 intersection points. Since the regional point cloud is divided into 72 strip point clouds according to the azimuth angle of every 5 degrees. Therefore, for each intersection point, there are 72 measurement values. The adjacent regional intersection points are subtracted in pairs to obtain the actual measurement length range of the conductor, inner semi-conductive, reaction force cone, XLPE insulation layer, outer semi-conductive transition zone, and outer semi-conductive layer.

[0079] Step S42, respectively calculate the mean, maximum, minimum and Figure 3 Deviations in dimensions of various areas of standard cross-linked polyethylene cable connectors are shown.

[0080] Step S43: determine whether the parameters of each area are qualified.

Claims

1. A method for detecting the size of a cross-linked polyethylene cable joint, comprising four modules: three-dimensional point cloud acquisition (1), point cloud preprocessing (2), point cloud segmentation (3), and size detection and determination (4); The steps of the point cloud preprocessing module are as follows: S21, filtering the Lanwei point cloud data of the cross-linked polyethylene cable joint according to the radius range of 1 mm to 3 mm and the number of neighboring points of 3 to 5; S22, using a random sample consensus (RANSAC) algorithm to fit the cylindrical features of the three-dimensional point cloud data processed in step S21, and obtaining a direction vector of the central axis of the fitted cylindrical model; S23, performing a rigid body transformation on the three-dimensional point cloud data processed in step S21, so that the direction vector of the central axis of the cylinder extracted in step S22 coincides with the Z axis of the Cartesian coordinate system; S24, converting the three-dimensional point cloud data processed in step S23 from a three-dimensional Cartesian coordinate system to a cylindrical coordinate system; the point cloud segmentation module steps are as follows: S31, dividing the conductor, inner semi-conductive layer, reaction cone, XLPE insulation layer, outer semi-conductive transition zone, and outer semi-conductive area in the standard size of the cross-linked polyethylene cable joint; S32, for the conductor, the inner semi-conductive region point cloud uses segmentation method 1 shown in the following formula to extract the height coordinates of the intersection point between region 1 and region 2 in the cylindrical coordinate system; in, r i is the outer diameter of a point in the point cloud of the area to be segmented, N is the total number of point clouds in the area to be segmented, l1 is the number of point clouds in area 1, m1 is the average outer diameter of the point cloud in area 1, m2 is the average outer diameter of the point cloud in area 2, and m g is the mean value of the outer diameter of the point cloud in the area to be segmented, and σ is the variance of the outer diameter of the point cloud in the area to be segmented; by changing the number of point clouds in area l, when σ takes the maximum value, the height coordinate h corresponding to the best segmentation point i in the area to be segmented can be obtained i ; S33, extracting the height coordinates of the junction point between region 3 and region 4 in the cylindrical coordinate system by using segmentation method 2 shown in the following formula for the reaction force cone, XLPE insulation layer, outer semi-conductive transition zone, and outer semi-conductive region point cloud; Among them, r i is the outer diameter of a point in the point cloud of the area to be segmented, N is the total number of point clouds in the segmented area, l2 is the number of point clouds in area 3, m3 is the mean of the outer diameter of the point cloud in area 3, m4 is the mean of the outer diameter of the point cloud in area 4, and σ1 is the variance of the outer diameter of the point cloud in area 3; by changing the number of point clouds in area 3, when σ2 takes a larger value and σ1 takes a smaller value, the height coordinate h corresponding to the best segmentation point i in the segmented area can be obtained i ; The steps of the size detection and determination module are as follows: S41, calculating the distance between the intersection points of adjacent point clouds in each area according to the height coordinates of the best segmentation points obtained after segmentation by the point cloud segmentation module, and obtaining the sizes of different areas of the cross-linked polyethylene cable joint; S42, calculating the deviation between the cable dimensions in different regions obtained in step S41 and the standard dimensions of the cable connector; S43, determining whether the size parameters of each area are qualified.

2. A method for detecting the size of a cross-linked polyethylene cable joint according to claim 1, characterized in that: The three-dimensional point cloud acquisition module performs three-dimensional point cloud data acquisition on the cross-linked polyethylene cable connector, and its acquisition device can be a laser scanner, a depth camera, or a structured light scanner.

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