A ship weld seam feature parameter extraction method

Abstract

The application discloses a kind of extraction methods of ship weld characteristic parameters.First, according to joint space position and minimum contour line distance, weld feature recognition is completed;Then based on the recognition result, the corresponding contour line group and all distances between the two endpoints of contour line are stored;Then, by the total number of contour line and the two endpoints of minimum contour line distance, the characteristic points and lines at the weld bevel are identified;Finally, based on the mathematical model established for the three types of welding joints, the weld characteristic parameters related to welding process are extracted.The extraction method of ship weld characteristic parameters of the application helps to realize the accurate extraction of weld characteristic parameters in the digital model of ship welding parts, and further improves the database system to quickly and adaptively select the welding process parameters of welding robot, so as to optimize the weld forming quality, improve the production efficiency and realize the purpose of full-automatic welding.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of pattern recognition, and relates to a welding seam feature parameter extraction technology based on a welding piece digital model, in particular to a ship welding seam feature parameter extraction method. BACKGROUND

[0002] Welding seam robot automatic welding is a development trend of the shipbuilding industry. Using welding robots for automatic welding can not only improve the consistency of welding quality, but also improve production efficiency and reduce costs.

[0003] However, the premise of high quality and high efficiency brought by robots is the effective and reasonable setting of welding process parameters. Using a database system to recommend welding process parameters can adaptively obtain optimal process parameters, thereby improving welding efficiency and quality. The parameter recommendation is directly dependent on the welding seam structure, which requires welding seam feature recognition and parameter extraction on the welding piece digital model. Research on welding seam structure and feature parameter extraction is an important link to realize automatic welding. At present, the research mainly focuses on processing welding seam images or digital point cloud models. A visual system is built through a sensor, and the collected information is processed, and then the welding seam feature lines and points are obtained based on the extraction algorithm, and the feature parameters are extracted. Although this method can realize real-time extraction of the groove feature parameters, it is limited by the scanning range of the sensor, and it takes a long time to scan the welding seam to extract the feature parameters. In addition, the secondary development of the welding seam model is carried out through the API interface of the modeling software, or the attribute features of the welding piece are obtained through feature modeling design, and the welding seam feature parameter information can also be extracted. However, the joint or groove targeted by the welding seam feature parameter extraction is relatively single, the application range is narrow, or part of the welding seam feature parameters are extracted, the feature information obtained is limited, and it cannot fully provide the basis for the selection of welding process parameters. Therefore, the research on ship welding seam feature parameter extraction helps to realize the accurate extraction of the welding seam feature parameters in the ship welding piece digital model, and then improve the rapid adaptive selection of the welding process parameters of the welding robot by the database system, and finally achieve the purpose of optimizing the welding seam forming quality and improving the production efficiency. SUMMARY

[0004] The purpose of the present application is to extract the welding seam feature parameters of the welding piece digital model, and provide a ship welding seam feature parameter extraction method.

[0005] In order to achieve the above purpose, the present application adopts the following technical solutions:

[0006] A ship welding seam feature parameter extraction method, first, the welding seam feature recognition of the joint form and the groove type is completed based on the spatial position of the joint; then, the feature parameter extraction is carried out according to the three mathematical models that have been built, and then the information such as the welding seam gap, the included angle and the plate thickness at the groove is obtained. The specific content and method steps are as follows:

[0007] Step 1. Weld feature recognition based on joint spatial position and minimum profile line distance, including joint spatial position discrimination and minimum profile line distance judgment;

[0008] Step 2. Store joint profile line group and distance between joint profile line endpoints;

[0009] Step 3. Joint feature point and line extraction;

[0010] The joint feature point and line extraction includes flat joint feature point and line extraction, corner joint feature point and line extraction, and T-shaped joint feature point and line extraction.

[0011] Step 4. Joint weld feature parameter extraction.

[0012] The joint weld feature parameter extraction includes flat joint weld feature parameter extraction, corner joint weld feature parameter extraction, and T-shaped joint weld feature parameter extraction.

[0013] Further, the weld feature recognition based on joint spatial position and minimum profile line distance in step 1 includes joint spatial position discrimination and minimum profile line distance judgment, the joint spatial position discrimination is according to the parallel or perpendicular relationship of the normal vector (dashed line) at each face to be determined, when the number of parallel normal vectors is 6 and the number of opposite directions is 4, the two joints are in parallel state; when the number of perpendicular normal vectors is 4 and the number of opposite directions is 2, the two joints are in perpendicular state.

[0014] The minimum profile line distance judgment includes profile line group selection and profile line distance comparison, the profile line group selection is according to the total number of profile lines to divide 10 kinds of welding grooves into three categories of 24, 27 and 30 profile lines, the 24 profile lines include I and V type grooves of flat joints, no opening and single side grooves of corner joints, T-shaped and lap joints, the first 8 groups of profile lines with the shortest length are taken; the 27 profile lines include double side grooves of corner joints and single side grooves of T-shaped joints, the first 10 groups of profile lines with the shortest length are taken; the 30 profile lines include Y type grooves of flat joints and double side grooves of T-shaped joints, the first 12 groups of profile lines with the shortest length are taken. The profile line distance comparison is to calculate all the distances between the endpoints of the profile lines obtained above, remove the length of the profile line itself, compare the minimum distance with the second shortest length of the profile line, when greater than the second shortest profile line, it is called large interval; otherwise, it is called small interval.

[0015] The weld seam feature recognition includes joint form and groove type recognition; the joint form recognition is that when the joint is in parallel state and the profile line distance is small interval, it is a flat joint, when the joint is in parallel state and the profile line distance is large interval, it is a lap joint; when the joint is vertical and the distance is small interval, it is a corner joint, when the joint is vertical and the distance is large interval, it is a T joint.

[0016] The groove type recognition is that when the profile line is 24, the lap and T joints only have one type without groove, the groove of the flat and corner joints is determined by the angle α of the two smallest distance profile lines, when the joint form is flat and α=0, it is I type groove, when the joint form is flat and α≠0, it is V type groove; when the joint form is corner and α=90°, it is no groove; when the joint form is corner and α≠90°, it is single side groove. When the profile line is 27 and the profile line distance is small interval, it is the double side groove of the corner joint; when the profile line is 27 and the profile line distance is large interval, it is the single side groove of the T joint. When the profile line is 30 and the joint is in parallel state and small interval, it is Y type groove of the flat joint; when the profile line is 30 and the joint is in vertical state and large interval, it is the double side groove of the T joint.

[0017] Further, the method for storing the joint profile line group and the distance between the joint profile line endpoints in step 2 specifically adopts the following steps:

[0018] A) Different forms of processing are carried out according to the weld seam feature recognition identified in step (1); when the joint profile line is 24, the first 8 groups of the shortest profile lines are taken; when the joint profile line is 27, the first 10 groups of the shortest profile lines are taken; when the joint profile line is 30, the first 12 groups of the shortest profile lines are taken.

[0019] B) The shortest profile line groups taken in the above step A) are stored in the array space P, all distances between the endpoints of the profile lines are calculated and the lengths of the profile lines are removed; when the profile line is 24, the distance calculation results (with the distance between the two endpoints) are stored in the array space Q; when the profile line is 27 or 30, the distance calculation results of the four endpoints of the two parallel profile lines and the profile lines where the four endpoints are located are removed, and the remaining distance calculation results are stored in the array space Q.

[0020] Further, the joint feature point and line extraction in step 3 includes flat joint feature point and line extraction, corner joint feature point and line extraction and T joint feature point and line extraction, the specific content and method of the flat joint feature point and line extraction adopts the following steps:

[0021] (I) according to the total number of contour lines of the butt joint to determine three types of groove; when the total number of contour lines is 24, that is, the butt joint is I type or V type groove, turn to step (II); when the total number of contour lines is 30, that is, the butt joint is Y type groove, turn to step (III).

[0022] (II) Take the two endpoints corresponding to the minimum distance in the array space Q, that is, the first feature point A1 and the second feature point A2. Traverse the array space P to obtain the other endpoint of the contour line where the feature points are located.

[0023] (III) Traverse all the two endpoints of the contour lines in the array space P, and calculate the distance between the repeated points two by two. The two points corresponding to the minimum distance are the third feature point B1 and the fourth feature point B2. Calculate the distance between the remaining endpoints of the contour lines composed of points B1 and B2 two by two, and the two points corresponding to the minimum distance result are the first feature point A1 and the second feature point A2. The remaining two endpoints are the fifth feature point C1 and the sixth feature point C2.

[0024] Further, the method for extracting the feature points and lines of the corner joint in step 3, specifically adopts the following steps:

[0025] (a) According to the total number of contour lines of the corner joint to determine three types of groove; when the total number of contour lines is 24, that is, the corner joint is not opened or single-sided groove, turn to step (b); when the total number of contour lines is 27, that is, the corner joint is double-sided groove, turn to step (f).

[0026] (b) Traverse the array space P with the two endpoints of the minimum contour line distance in the array space Q, output the contour line where the repeated points are located, obtain two contour lines and calculate the included angle θ5.

[0027] (c) According to the included angle θ5 to determine the groove type of the corner joint; when θ5=90°, it is not opened, turn to step (d); otherwise, it is a single-sided groove, and take the two endpoints of the minimum distance as the starting point, and the included angle of the two vectors with the length and direction away from the respective starting point is β, turn to step (e).

[0028] (d) According to the two included angles to extract the feature points; take the two endpoints of the minimum contour line distance in the array space Q, and the two included angles formed by the intersecting line segment composed of the two endpoints, the one greater than 90 degrees is α, and the one less than 90 degrees is θ3. According to the two line segments constituting α, the seventh feature point A and the eighth feature point E can be obtained, and according to the two line segments constituting θ3, the first feature line BC can be obtained.

[0029] (e) According to the included angle β, two cases of the single-bevel groove are determined; when β > 90°, the two end points of the minimum distance in the array space Q are the seventh feature point A and the ninth feature point B. The other end point of the contour line where the feature point is located can be obtained by traversing the array space P. When β < 90°, the two end points of the minimum distance in the array space Q are the seventh feature point A and the tenth feature point C. Similarly, the eighth feature point E and the ninth feature point B can be obtained.

[0030] (f) The two end points of the minimum distance in the array space Q are the seventh feature point A and the ninth feature point B. By traversing all the end points of the contour lines in the array space P, if the other end point of the contour line where the repeated point is located is the seventh feature point A, then the repeated point is the eleventh feature point D, and the other end point in the array space P, which is not equal to the eleventh feature point D and not equal to the seventh feature point A, is the eighth feature point E. Similarly, by traversing the array space P, the other end point of the contour line where the ninth feature point B is located is the tenth feature point C.

[0031] Further, the method for extracting the T-shaped joint feature points and lines in the joint feature point and line extraction of step 3 specifically adopts the following steps:

[0032] Firstly, three types of bevels are determined according to the total number of contour lines of the T-shaped joint; when the total number of contour lines is 24, that is, the T-shaped joint is not beveled, the two end points of the minimum distance in the array space Q are the twelfth feature point B and the thirteenth feature point E. The other end point of the contour line where the feature point is located can be obtained by traversing the array space P.

[0033] When the total number of contour lines is 27, that is, the T-shaped joint is a single-bevel, the following steps are performed:

[0034] (A) By traversing all the end points of the contour lines in the array space P, two repeated points are obtained. If the two repeated points are not the same as the two end points of the minimum distance in the array space Q, then the two end points are traversed in the array space P to obtain the first contour line BC and the second contour line EF, and the positional relationship between the two contour lines is determined, and step (B) is performed.

[0035] (B) When the two contour lines are perpendicular, the two end points of the minimum distance are the twelfth feature point B and the thirteenth feature point E, and the other point of the contour line where the twelfth feature point B is located is the fourteenth feature point C. When the two contour lines are not perpendicular, or the two repeated points are the same as the two end points of the minimum distance, then the two repeated points and the points in the two end points of the minimum distance, which are not equal to the two end points of the contour line containing the repeated points, are pairwise distance calculated. The two end points of the minimum distance, which are not equal to the two repeated points, are the thirteenth feature point E, and the other point is the fourteenth feature point C.

[0036] (C) traversing the array space P, the other end point of the contour line where the thirteenth feature point E is located is the fifteenth feature point F, the contour line contains the fourteenth feature point C and the other end point perpendicular to the second contour line EF is the twelfth feature point B, and the other end point not perpendicular to the second contour line EF is the sixteenth feature point D.

[0037] When the total number of contour lines is 30, that is, the T-shaped joint is double-bevel groove, the following steps are taken for processing:

[0038] 1) traversing the two end points of all contour lines in the array space P, there are four repeated points, and the minimum distance of the two end points after removing the length of the contour line itself is the twelfth feature point B and the fourteenth feature point C. Traversing the array space P, the contour line whose two end points contain the twelfth feature point B and are not equal to the fourteenth feature point C is the seventeenth feature point A, and the contour line whose two end points contain the fourteenth feature point C and are not equal to the twelfth feature point B is the sixteenth feature point D.

[0039] 2) the twelfth feature point B and the fourteenth feature point C are respectively calculated with the minimum distance of the two end points in the array space Q, which are not equal to the feature points A, B, C and D, and the two points with the minimum distance result not equal to the feature points B and C are the thirteenth feature point E.

[0040] 3) the three contour lines with the twelfth feature point B as the intersection point and the three contour lines with the thirteenth feature point E as the intersection point are used to form six vectors with the direction away from the intersection point B, and the minimum included angle with the ninth vector EB is θ3.

[0041] Further, the joint weld feature parameter extraction of step 4 includes flat joint weld feature parameter extraction, corner joint weld feature parameter extraction and T-shaped joint weld feature parameter extraction, and the joint weld feature parameter extraction is based on the extraction of joint feature points and lines. The flat joint weld feature parameter extraction includes the extraction of the groove included angle θ, the groove bottom vertical gap l1, the groove top vertical gap l2 and the plate thickness h1 and h2, and the groove included angle θ is calculated as follows:

[0042] θ = θ1 + θ2

[0043] In the formula, θ1 is the left bevel angle; and θ2 is the right bevel angle.

[0044] When the total number of contour lines is 24, the first vector B1C1 is equivalent to the second vector A1C1, and the third vector A2B2 is equivalent to the fourth vector A2C2, and at this time, θ1 and θ2 are both 0.

[0045] The groove bottom vertical gap l1 is calculated as follows:

[0046] When it is a flat joint I-shaped or V-shaped groove, then:

[0047]

[0048] wherein α is the acute angle between the seventh vector A1B2 and the eighth vector A2B1; S A1A2C2C1 is the area of the quadrilateral A1A2B2B1; l A1C1 , l A1C2 and l A2C1 are the lengths of the line segments A1B1, A1B2 and A2B1, respectively.

[0049] When it is a flat joint Y-type groove, then:

[0050]

[0051] wherein α is the acute angle between the seventh vector A1B2 and the eighth vector A2B1; S A1A2B2B1 is the area of the quadrilateral A1A2B2B1; l A1B1 , l A1B2 and l A2B1 are the lengths of the line segments A1B1, A1B2 and A2B1, respectively.

[0052] The groove top vertical gap l2 is calculated as follows:

[0053]

[0054] wherein l C1B1 , l C2B2 are the lengths of the line segments C1B1, C2B2, respectively.

[0055] The plate thickness h1, h2 is calculated as follows:

[0056]

[0057]

[0058] Further, the corner joint weld feature parameter extraction in the joint weld feature parameter extraction of step 4 includes the extraction of the groove included angle θ, the groove bottom vertical gap l1, the groove top vertical gap l2 and the plate thickness h1, h2, wherein the groove included angle θ is calculated as follows:

[0059]

[0060] The groove bottom vertical gap l1 is calculated as follows:

[0061]

[0062] wherein l AB is the length of the line segment AB.

[0063] The vertical gap l2 at the top of the groove is calculated as follows:

[0064]

[0065] In the formula, l BC , l AD are the lengths of line segments BC and AD, respectively.

[0066] The plate thicknesses h1 and h2 are calculated as follows:

[0067] h1 = l ED + l3

[0068] h2 = l BC cos θ2

[0069] In the formula, l ED is the length of line segment ED; when the total number of contour lines is 24, l ED = l EA .

[0070] Further, the T-joint weld feature parameter extraction in step 4 includes the extraction of the groove included angle θ, the vertical gap l1 at the bottom of the groove, the vertical gap l2 at the top of the groove, l3, and the plate thicknesses h1 and h2, wherein the groove included angle θ includes the left groove angle θ1 and the right groove angle θ2, and is calculated as follows:

[0071]

[0072] The vertical gap l1 at the bottom of the groove is calculated as follows:

[0073] l1 = l EB sin θ3

[0074] In the formula, l EB is the length of line segment EB.

[0075] The vertical gap l2 at the top of the groove, l3 is calculated as follows:

[0076] l2 = l1 + l AB sin θ1

[0077] l3 = l1 + l CD sin θ2

[0078] In the formula, l AB , l CD are the lengths of line segments AB and CD, respectively.

[0079] The plate thicknesses h1 and h2 are calculated as follows:

[0080] h1 = l BC + l ABcosθ1+l CD cosθ2

[0081]

[0082] In the formula, l BC is the length of the line segment BC;(x E ,y E ,z E ) are the coordinates of point E;(x F ,y F ,z F ) are the coordinates of point F.

[0083] The present application has the following advantages and beneficial effects:

[0084] (1) The weld feature recognition algorithm based on the total number of contour lines and the minimum contour line distance can accurately identify four types of joint forms and ten types of groove types, has many types of recognition, less time consumption, high accuracy, and greatly improves the practicality and universality of the algorithm.

[0085] (2) Based on the total number of model contour lines, the present application can quickly identify the groove types of the three types of joints, i.e., flat joints, corner joints and T-shaped joints, so that the joint form and the groove type of the weld are quickly confirmed; according to the two endpoints of the minimum contour line distance, the feature points, lines and key angles required by the mathematical model can be quickly extracted, which is beneficial to the extraction of the weld feature parameters and facilitates the quick selection of the mathematical model of the three types of joints, thereby saving the extraction time of the weld feature parameters.

[0086] (3) The three types of weld feature parameter mathematical models established based on the three types of joint forms can be adapted to the commonly used groove types, such as I type, V type and Y type, no opening, single side and double side, etc., and can obtain the information of the thickness of the two welded pieces, the bottom groove gap, the top groove gap and the groove angle, etc., so that the extracted feature parameters are more complete, which provides a sufficient basis for the selection of the welding process parameters, and provides a guarantee for the quick and accurate selection of the process parameters by the ship welding robot, and improves the welding quality and efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0087] Figure 1 The total flow chart of the ship weld feature parameter extraction method of the present application;

[0088] Figure 2 is a schematic diagram with a judging surface, figure (a) shows a flat joint schematic diagram, figure (b) shows a corner joint schematic diagram, and figure (c) shows a T-shaped joint schematic diagram;

[0089] Figure 3 is a schematic diagram of contour line selection, figure (a) shows a schematic diagram of the first 8 groups of contour lines, figure (b) shows a schematic diagram of the first 10 groups of contour lines, and figure (c) shows a schematic diagram of the first 12 groups of contour lines;

[0090] Figure 4 butt joint size diagram;

[0091] Figure 5 corner joint size diagram;

[0092] Figure 6 two cases of corner joint without beveling, figure (a) shows the minimum distance is located at the left end, figure (b) shows the minimum distance is located at the right end;

[0093] Figure 7 two cases of corner joint with single side beveling, figure (a) shows the minimum distance is located at the left end, figure (b) shows the minimum distance is located at the right end;

[0094] Figure 8 T joint size diagram;

[0095] Figure 9 two cases of T joint with single side beveling, figure (a) shows the minimum distance is located at the left end, figure (b) shows the minimum distance is located at the right end;

[0096] Figure 10 two cases of T joint with double side beveling, figure (a) shows the minimum distance is located at the left end, figure (b) shows the minimum distance is located at the right end;

[0097] Figure 11 cabin section weld test model, figure (a) shows the ship cabin section weld test, figure (b) shows the cargo cabin assembly section weld test. DETAILED DESCRIPTION

[0098] In order to make the purpose and technical scheme of the present application clearer, the technical scheme of the present application will be described clearly and completely below in combination with the drawings of the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the described embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0099] As shown in the drawings, a ship weld feature parameter extraction method of the present application first completes weld feature identification of joint form and bevel type based on joint spatial position; then carries out feature parameter extraction according to the three mathematical models built, and further obtains information such as weld gap, included angle and plate thickness at the bevel. The following steps are specifically adopted: Figure 1 (1) weld feature identification based on joint spatial position and minimum contour line distance;

[0100] (2) store joint contour line group and distance between joint contour line endpoints;

[0101] (3) joint feature point and line extraction;

[0102]

[0103] ​(4) Joint weld seam characteristic parameter extraction.

[0104] As shown in Fig. 2, the joint space position and minimum contour line distance based weld seam characteristic recognition includes joint space position discrimination and minimum contour line distance judgment. The joint space position discrimination is based on parallel or perpendicular relationship of normal vector (dotted line) at each face to be determined. If the number of parallel normal vectors is 6 and the number of opposite direction normal vectors is 4, the two joints are in parallel state. If the number of perpendicular normal vectors is 4 and the number of opposite direction normal vectors is 2, the two joints are in perpendicular state.

[0105] As shown in Fig. 3, the minimum contour line distance judgment includes contour line group selection and contour line distance comparison. The contour line group selection is based on total number of contour lines to divide 10 kinds of welding grooves into three categories of 24, 27 and 30 contour lines. The 24 contour lines include I and V type grooves of flat joint, no opening and single side groove of corner joint, no opening groove of T and lap joint, and the first 8 groups of contour lines with the shortest length are taken. The 27 contour lines include double side groove of corner joint and single side groove of T joint, and the first 10 groups of contour lines with the shortest length are taken. The 30 contour lines include Y type groove of flat joint and double side groove of T joint, and the first 12 groups of contour lines with the shortest length are taken. The contour line distance comparison is to calculate all distances between end points of each two contour lines, remove the length of the contour line itself, compare the minimum distance with the second shortest length of the contour line, and if the minimum distance is greater than the second shortest length, the contour line distance is large interval, otherwise, it is small interval.

[0106] The weld seam characteristic recognition includes joint form and groove type recognition. The joint form recognition is that if the joint is parallel, when the distance is small interval, it is flat joint, otherwise, it is lap joint; if the joint is perpendicular, when the distance is small interval, it is corner joint, otherwise, it is T joint.

[0107] The groove type recognition is that when the contour line is 24, the lap and T joint only has no opening groove type, and the groove of flat and corner joint is determined by the included angle α of the two minimum distance contour lines. If the joint form is flat joint, when α = 0, it is I type groove, otherwise, it is V type groove. If the joint form is corner joint, when α = 90°, it is no opening groove, otherwise, it is single side groove. When the contour line is 27, if the distance is small interval, it is double side groove of corner joint, otherwise, it is single side groove of T joint. When the contour line is 30, if the joint is parallel and small interval, it is Y type groove of flat joint, if the joint is perpendicular and large interval, it is double side groove of T joint.

[0108] The storage of the connector contour line group and the distance between the endpoints of the connector contour lines includes different processing methods for the total number of the three types of contour lines of the sub-connectors, as shown in Figure 3. If there are 24 contour lines, the first 8 groups with the shortest length are selected; if there are 27 contour lines, the first 10 groups with the shortest length are selected; if there are 30 contour lines, the first 12 groups with the shortest length are selected. The selected shortest contour line groups are stored in the array space P. All distances between the endpoints of each pair of contour lines are calculated and the length of the contour line itself is removed. If there are 24 contour lines, the distance calculation results (with the coordinate values ​​of the two endpoints) are stored in the array space Q; if there are 27 or 30 contour lines, the distance calculation results of the four endpoints of the two contour lines and the contour lines containing the four endpoints when the two contour lines are parallel are removed, and the remaining distance calculation results (with the coordinate values ​​of the two endpoints) are stored in the array space Q.

[0109] The extraction of joint feature points and lines includes the extraction of feature points and lines for flat joints, corner joints, and T-joints.

[0110] like Figure 4 The diagram shows the dimensions of a butt joint. θ1 is the angle between vectors A1B1 and B1C1; θ2 is the angle between vectors A2B2 and B2C2. There are three types of bevels for butt joints. For a type I bevel, points B1 and C1 coincide, and points B2 and C2 coincide, i.e., l C1B1 =0,l C2B2 =0, only the coordinates of four points A1, A2, C1, and C2 need to be determined; if it is a V-shaped bevel, then points B1 and A1 coincide, and points B2 and A2 coincide, i.e., l A1B1 =0,l A2B2 =0, only the coordinates of four points A1, A2, C1, and C2 need to be determined; if it is a Y-shaped bevel, then the coordinates of six points A1, A2, B1, B2, C1, and C2 need to be determined. The method for extracting the feature points and lines of the flat joint adopts the following steps:

[0111] (1) Determine the three bevel types based on the total number of outlines of the butt joint. If the total number of outlines is 24, the butt joint is a type I or V bevel, proceed to step (2); if it is 30, the butt joint is a type Y bevel, proceed to step (3).

[0112] (2) Take the two endpoints corresponding to the minimum distance in the array space Q, which are A1 and A2. Traverse the array space P, and the other endpoint of the contour line where point A1 is located is C1, and the other endpoint of the contour line where point A2 is located is C2.

[0113] (3) Traverse the two endpoints of all contour lines in the array space P, calculate the distance between each pair of overlapping points, and the two points corresponding to the minimum distance are B1 and B2. Calculate the distance between each pair of the remaining endpoints of the contour lines that form the intersection points B1 and B2, and the two points corresponding to the minimum distance are A1 and A2. The remaining two endpoints are C1 and C2.

[0114] like Figure 5 As shown in Figures 6 and 7, θ1 is the angle between vector AD and the horizontal vector to the right passing through point A; θ2 is the angle between vector BC and the horizontal vector to the right passing through point B; θ3 is the angle between vector BA and vector BC; θ4 is the angle between vector BA and the horizontal vector to the right passing through point B; θ5 is the angle between vector BC and vector ED; and θ6 is the angle between vector AD and vector BC. There are three types of bevels for angle joints. If there is no bevel, points A and D coincide, and points B and C coincide horizontally, i.e., l3 = 0, l ED =l EA Given θ1 = 0, θ2 = 0, θ6 = 0, θ3 = θ4, we only need to determine the coordinates of points A, B, C, and E. If it is a single-sided bevel, then points A and D coincide, i.e., l3 = 0, l ED =l EA If θ1 = 0, only the coordinates of points A, B, C, and E need to be determined; if it is a double-sided bevel, then the coordinates of points A, B, C, D, and E need to be determined. The method for extracting the feature points and lines of the corner joint adopts the following steps:

[0115] (1) Determine the three bevel types based on the total number of outline lines of the corner joint. If there are 24 lines, the corner joint is either without bevel or with a single-sided bevel, proceed to step (2); if there are 27 lines, the corner joint is either with a double-sided bevel, proceed to step (6).

[0116] (2) Traverse the array space P through the two endpoints with the minimum distance in array space Q, and output the contour lines where the repeated points are located. The two contour lines obtained are AE (i.e. DE) and BC. The included angle θ5 is calculated as follows:

[0117]

[0118] (3) Determine the bevel type of the corner joint based on the included angle θ5. If θ5 = 90°, then no bevel is required, proceed to step (4); otherwise, it is a single-sided bevel, and the two endpoints with the minimum contour line distance are taken as the starting points, and the included angle between the two vectors whose length is the contour line and whose direction is away from their respective starting points is denoted as β, proceed to step (5).

[0119] (4) Extract feature points based on the two included angles. For example... Figure 5As shown in (a) and (b), there are two cases: one of the two endpoints with the minimum contour line distance is the left endpoint, or the other is the right endpoint. In this case, take the two endpoints with the minimum contour line distance in the array space Q (corresponding to A and B in Figure 6(a) and A and C in Figure 6(b). Among the two included angles formed by the intersecting line segments AE, AB (AC), and BC that make up the two points, the one greater than 90 degrees is the included angle α, and the one less than 90 degrees is the included angle θ3. Points A and E can be obtained from the two line segments AE and AB (AC) that make up the included angle α, and the contour line BC can be obtained from the two line segments AB (AC) and BC that make up the included angle θ3.

[0120] (5) Two scenarios for determining the single-sided bevel based on the included angle β. If β > 90°, as shown in Figure 7(a), the two endpoints of the minimum distance between the contour lines in array space Q are A and B. Traversing array space P, the other endpoint of the contour line containing point A is E; the other endpoint of the contour line containing point B is C. If β < 90°, as shown in Figure 7(b), the two endpoints of the minimum distance between the contour lines in array space Q are A and C. Similarly, points E and B can be obtained.

[0121] (6) Take the two endpoints with the smallest distance in array space Q as A and B. Traverse the endpoints of all contour lines in array space P. If the other endpoint of the contour line containing a duplicate point is A, then the duplicate point is D. Output the other endpoints of the contour lines containing this point in array space P. The other endpoints that are not equal to points D and A are E. Similarly, traverse array space P, and the other endpoint of the contour line containing point B is C.

[0122] like Figure 8 As shown in Figures 9 and 10, θ1 is the angle between vectors BA and CB; θ2 is the angle between vectors CD and BC; and θ3 is the angle between vector EB and the horizontal vector passing through point E to the right. There are three types of bevels for T-joints. If there is no bevel, points A and B coincide, and points C and D coincide, i.e., l AB =0,l CD =0,l AD =l BC If θ1 = 0 and θ2 = 0, then only the coordinates of points B, C, E, and F need to be determined. If it is a single-sided bevel, then points A and B coincide (points C and D coincide), i.e., l AB =0,l AC =l BC (l BD =l BC If θ1 = 0 (θ2 = 0), only the coordinates of five points B, C, D (A), E, ​​and F need to be determined; if it is a double-sided bevel, then the coordinates of six points A, B, C, D, E, and F need to be determined. The method for extracting the feature points and lines of the T-joint specifically adopts the following steps:

[0123] Firstly, three types of groove are determined according to the total number of profile lines of the T joint. If the total number of profile lines is 24, i.e. the T joint is not grooved, the two end points of the minimum profile line distance in the array space Q are points B and E. The other end point of the profile line where point B is located in the array space P is point C; the other end point of the profile line where point E is located in the array space P is point F.

[0124] If the total number of profile lines is 27, i.e. the T joint is single-side grooved, the following steps are taken for processing:

[0125] (1) All the two end points of the profile lines in the array space P are traversed, and there are two repeated points. If the two repeated points are not the same as the two end points of the minimum profile line distance in the array space Q, the two end points are traversed in the array space P to obtain the profile lines BC (CD) and EF, and the positional relationship of the two profile lines is judged, and step (2) is turned.

[0126] (2) If the two profile lines are perpendicular, one of the two end points of the minimum profile line distance is the left end point, as shown in Fig. 9(a). At this time, the two end points are points B and E, and the other point of the profile line where point B is located is point C. If the two profile lines are not perpendicular, or as shown in Fig. 9(b), the two repeated points are the same as the two end points of the minimum profile line distance, then the two repeated points and the points which are not equal to the two repeated points among the two end points of the minimum profile line distance are taken two by two to obtain the distance, and the two end points of the minimum distance which are not equal to the two repeated points are points E and C.

[0127] (3) The other end point of the profile line where point E is located in the array space P is F, the other end point of the profile line which contains point C and is perpendicular to EF is point B, and the other end point of the profile line which does not perpendicular to EF is point D.

[0128] If the total number of profile lines is 30, i.e. the T joint is double-side grooved, the following steps are taken for processing:

[0129] (1) All the two end points of the profile lines in the array space P are traversed, and there are four repeated points. The two end points of the minimum distance after removing the length of the profile line itself are points B and C. As shown in Fig. 10, there are two cases, one of which is that one of the two end points of the minimum profile line distance is the left end point, and the other of which is that one of the two end points of the minimum profile line distance is the right end point. The point A is the point which contains point B and is not equal to point C, and the point D is the point which contains point C and is not equal to point B.

[0130] (2) The distances between points B and C and the end points which are not equal to points A, B, C and D in the two end points of the minimum distance in the array space Q are calculated, and the two points which are not equal to points B and C in the minimum distance result are points E and B.

[0131] (3) the three contour lines constituting intersection point B and the three contour lines constituting intersection point E are used to form six vectors which are away from intersection point B (E), wherein the minimum included angle with vector EB is θ3.

[0132] The joint weld characteristic parameter extraction includes flat joint weld characteristic parameter extraction, corner joint weld characteristic parameter extraction and T joint weld characteristic parameter extraction, and the joint weld characteristic parameter extraction is performed on the basis of the extracted joint characteristic points and lines.

[0133] The flat joint weld characteristic parameter extraction includes the extraction of bevel included angle θ, bevel bottom vertical gap l1, bevel top vertical gap l2 and plate thickness h1 and h2, and the bevel included angle θ is calculated as follows:

[0134] θ = θ1 + θ2

[0135] In the formula, θ1 is the left bevel angle, and θ2 is the right bevel angle.

[0136] If the total number of contour lines is 24, then vector B1C1 is equivalent to vector A1C1, and vector A2B2 is equivalent to vector A2C2, and θ1 and θ2 are both 0.

[0137] The bevel bottom vertical gap l1 is calculated as follows:

[0138] When it is a flat joint I type or V type bevel, then:

[0139]

[0140] In the formula, α is the acute included angle of the fifth vector A1C2 and the sixth vector A2C1; S A1A2C2C1 is the area of quadrilateral A1A2C2C1; l A1C1 , l A1C2 and l A2C1 are the lengths of line segments A1C1, A1C2 and A2C1 respectively.

[0141] When it is a flat joint Y type bevel, then:

[0142]

[0143] In the formula, α is the acute included angle of the seventh vector A1B2 and the eighth vector A2B1; S A1A2B2B1 is the area of quadrilateral A1A2B2B1; l A1B1 , l A1B2 and l A2B1 are the lengths of line segments A1B1, A1B2 and A2B1 respectively.

[0144] The bevel top vertical gap l2 is calculated as follows:

[0145]

[0146] In the formula, l C1B1 , l C2B2 are lengths of line segments C1B1 and C2B2 respectively.

[0147] The plate thicknesses h1 and h2 are calculated as follows:

[0148]

[0149]

[0150] The corner joint weld feature parameter extraction includes extraction of the groove included angle θ, the groove bottom vertical gap l1, the groove top vertical gap l2, and the plate thicknesses h1 and h2, and the groove included angle θ is calculated as follows:

[0151]

[0152] The groove bottom vertical gap l1 is calculated as follows:

[0153]

[0154] In the formula, l AB is a length of line segment AB.

[0155] The groove top vertical gap l2 is calculated as follows:

[0156]

[0157] In the formula, l BC , l AD are lengths of line segments BC and AD respectively.

[0158] The plate thicknesses h1 and h2 are calculated as follows:

[0159] h1 = l ED +l3

[0160] h2 = l BC cosθ2

[0161] In the formula, l ED is a length of line segment ED; if the total number of contour lines is 24, then l ED =l EA .

[0162] The T joint weld feature parameter extraction includes extraction of the groove included angle θ, the groove bottom vertical gap l1, the groove top vertical gap l2, l3, and the plate thicknesses h1 and h2, and the groove included angle θ includes a left groove angle θ1 and a right groove angle θ2, and is calculated as follows:

[0163]

[0164] The bottom vertical gap of the groove l1 is calculated as follows:

[0165] l1 = l EB sinθ3

[0166] In the formula, l EB is the length of the line segment EB.

[0167] The top vertical gap of the groove l2, l3 is calculated as follows:

[0168] l2 = l1 + l AB sinθ1

[0169] l3 = l1 + l CD sinθ2

[0170] In the formula, l AB , l CD are the lengths of the line segments AB, CD, respectively.

[0171] The plate thickness h1, h2 is calculated as follows:

[0172] h1 = l BC + l AB cosθ1 + l CD cosθ2

[0173]

[0174] In the formula, l BC is the length of the line segment BC; (x E , y E , z E ) are the coordinates of point E; (x F , y F , z F ) are the coordinates of point F.

[0175] In order to verify the effectiveness and stability of the ship weld feature parameter extraction method of the application, the feature recognition test was carried out on 12 welds on the two cabin sections of Fig. 11 (a) and Fig. 11 (b). And compared with the welding feature based welding workpiece library modeling (feature library design method) [1] and the traversal feature tree technology based on SolidWorks (traversal feature method) [2] The comparison test results of the three methods are shown in Table 1.

[0176] The comparison literature is as follows:

[0177] [1] Ying Can. Trajectory optimization research of welding robot workstation cooperative motion [D]. Guangzhou: South China University of Technology, 2013.

[0178] [2]Zhang Z N, Zhong Liang W. Secondary development of automatic weld marking based on SolidWorks[J]. Software Engineering, 2020, 23(5): 17-20.

[0179] As can be seen from Table 1, the traversal feature method can only identify two forms of flat joint and T joint, and cannot identify the type of bevel, the recognition effect is poor, and is limited by the modeling platform, and the application range is limited. Although the feature library design method can accurately identify six weld features as the method of the present application, the average running time of joint and bevel identification is higher than that of the method of the present application, the execution efficiency is low, in addition, the feature library design method needs to design the feature modeling of all welds on the cabin section and establish a database, which greatly increases the development workload, and when the database size is large, it may take a long time to match the weld features. The bevel recognition accuracy of the weld feature recognition method based on STL of the present application is 100%, the time consumption is improved by 16.65% compared with the feature library design method, the average running time is shorter, the execution efficiency is higher, and only the STL file of the model weld is needed, the pre-processing amount is smaller, the joint form and bevel type of the recognition are more, the accuracy is high.

[0180] Table 1:

[0181]

[0182] In order to further verify the effectiveness of the method of the present application, the feature parameter extraction test was carried out on the 12 welds on the two cabin sections of Figures 11(a) and 11(b), and compared with the feature points of the contour line based on the slope analysis (slope analysis method) [3] and the traversal feature method. The comparison test results of the three methods are shown in Table 2.

[0183] Comparative literature:

[0184] [3] Zhang Pengxian, Liu Zhihui, Yu Tong. Welding digital contour visual measurement based on laser grating[J]. Welding Machine, 2018, 48(7): 8-12.

[0185] As can be seen from Table 2, the traversal feature method can only extract parameters for butt joints and T joints, the joint forms are limited, the practicability is low, and only the plate thickness and the weld length of the two welded pieces at the groove can be extracted, the weld gap and the groove angle which are closely related to the welding process parameters cannot be obtained, the parameter extraction effect is poor, and the method is not conducive to the rapid and accurate selection of the welding process parameters. Compared with the traversal feature method, the slope method can extract more joint forms and groove types and obtain more weld feature parameter information, but when extracting the corner joint and the T joint, the plate thickness information of part of the welded pieces cannot be obtained, and the weld feature parameters of the double-sided groove of the T joint cannot be extracted, and the extraction effect is poor. The method of the present application can extract not only the butt joint, the corner joint and the T joint and nine kinds of grooves, but also more complete weld feature parameters, including the plate thickness of the two welded pieces, the bottom and top groove gap and the groove angle, which provides sufficient reference information for the rapid and accurate selection of the welding process parameters. This is mainly due to the weld feature recognition based on STL, which can identify the joint form and the groove type in the STL file of the weld model, has high execution efficiency, can identify multiple types accurately, and can quickly extract the feature parameters of the specific groove according to the three mathematical models built, which verifies the effectiveness of the method of the present application.

[0186] Table 2:

[0187]

[0188] The above examples are only used to illustrate the technical solutions of the present application and not to limit it, and although the present application has been described in detail with reference to the above examples, those skilled in the art should understand that the specific embodiments of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the present application, and any modification or equivalent replacement without departing from the spirit and scope of the present application should be covered in the protection scope of the claims of the present application.

Claims

1. A method of extracting a weld feature parameter of a ship, characterized by, It comprises the following steps: (1) weld feature recognition based on joint spatial position and minimum profile line distance, including joint spatial position discrimination and minimum profile line distance judgment; (2) storing joint profile line groups and distances between joint profile line endpoints, specific contents and methods, using the following steps: (A) different forms of processing according to the weld feature recognition identified in step (1); when the joint profile line is 24, take the first 8 groups of the shortest profile line; when the joint profile line is 27, take the first 10 groups of the shortest profile line; when the joint profile line is 30, take the first 12 groups of the shortest profile line; (B) store the shortest profile line group taken out in step (A) above into array space P, calculate all distances between the endpoints of each two profile lines and remove the profile line length itself; when the profile line is 24, store the result into array space Q; when the profile line is 27 or 30, remove the four endpoints of two profile lines parallel and the distance calculation result of the profile line where the four endpoints are located, and store the remaining result into array space Q; (3) joint feature point and line extraction, including flat joint feature point and line extraction, corner joint feature point and line extraction, and T-shaped joint feature point and line extraction; (4) joint weld feature parameter extraction, including flat joint weld feature parameter extraction, corner joint weld feature parameter extraction, and T-shaped joint weld feature parameter extraction; groove included angle θ, groove bottom vertical gap l1, groove top vertical gap l2, and plate thickness h1, h2 extraction; wherein, the groove included angle θ is calculated as follows: θ = θ1 + θ2 In the formula, θ1 is the left slope angle; θ2 is the right slope angle; When the total number of profile lines is 24, the first vector B1C1 is equivalent to the second vector A1C1, and the third vector A2B2 is equivalent to the fourth vector A2C2, at this time θ1 and θ2 are both 0; The groove bottom vertical gap l1 is calculated as follows: When it is a flat joint I or V type groove, then: wherein a is the acute angle between the fifth vector A1C2 and the sixth vector A2C1; S A1A2C2C1 is the area of the quadrangle A1A2C2C1; l A1C1 , l A1C2 and l A2C1 are the lengths of the line segments A1C1, A1C2 and A2C1, respectively. When it is a flat joint Y type groove, then: wherein a is the acute angle of the seventh vector A1B2 and the eighth vector A2B1; S A1A2B2B1 is the area of the quadrangle A1A2B2B1; l A1B1 , l A1B2 and l A2B1 are the lengths of the line segments A1B1, A1B2 and A2B1, respectively; The groove top vertical gap l2 is calculated as follows: wherein l C1B1 , l C2B2 are the lengths of the line segments C1B1, C2B2, respectively. The plate thickness h1, h2 is calculated as follows:

2. The method for extracting a shipweld feature parameter according to claim 1, characterized in that, The specific content and method of the flat joint feature point and line extraction in step (3) are as follows: 1) determine three types of grooves according to the total number of profile lines of the flat joint; when the total number of profile lines is 24, i.e. the flat joint is I or V type groove, go to step 2); when the total number of profile lines is 30, i.e. the flat joint is Y type groove, go to step 3); 2) take the two endpoints corresponding to the minimum distance in array space Q, i.e. the first feature point A1 and the second feature point A2; traverse array space P to obtain the other endpoint of the feature point on the profile line; 3) traverse all endpoints of the profile lines in array space P, calculate the distance between each two repeated points, and the two points corresponding to the minimum distance are the third feature point B1 and the fourth feature point B2; calculate the distance between the remaining endpoints of the profile lines composed of points B1 and B2, and the two points corresponding to the minimum distance are the first feature point A1 and the second feature point A2, and the remaining two endpoints are the fifth feature point C1 and the sixth feature point C2.

3. The method of claim 1, wherein, The specific content and method of the corner joint feature point and line extraction in step (3) are as follows: (a) determining three types of bevels according to the total number of profile lines of the corner joint; when the total number of profile lines is 24, i.e., the corner joint is not beveled or is single-beveled, step (b) is performed; when the total number of profile lines is 27, i.e., the corner joint is double-beveled, step (f) is performed; (b) traversing the array space P with the two end points of the minimum profile line distance in the array space Q to output the profile line where the repeated point is located, obtaining two profile lines and calculating the included angle θ5 therebetween; (c) determining the bevel type of the corner joint according to the included angle θ5; when θ5=90°, the corner joint is not beveled, and step (d) is performed; otherwise, the corner joint is single-beveled, and the included angle between the two vectors with the same length and opposite directions is denoted as β, and step (e) is performed; (d) extracting feature points according to the two included angles; taking the two end points of the minimum profile line distance in the array space Q, the two included angles formed by the intersecting line segments of the two end points are greater than 90 degrees and less than 90 degrees, respectively, and denoted as α and θ3; the seventh feature point A and the eighth feature point E are obtained according to the two line segments forming α, and the first feature line BC is obtained according to the two line segments forming θ3; (e) determining two situations of the single-beveled corner joint according to the included angle β; when β>90°, the two end points of the minimum distance in the array space Q are the seventh feature point A and the ninth feature point B; the other end point of the profile line where the feature point is located is obtained by traversing the array space P; when β<90°, the two end points of the minimum distance in the array space Q are the seventh feature point A and the tenth feature point C, and the other end points of the profile lines where the two feature points are located are the eighth feature point E and the ninth feature point B, respectively; (f) taking the two end points of the minimum distance in the array space Q as the seventh feature point A and the ninth feature point B; traversing all the end points of the profile lines in the array space P, if the other end point of the profile line where the repeated point is located is the seventh feature point A, the repeated point is the eleventh feature point D, and the other two end points of the profile line where the repeated point is located in the array space P are output, wherein the other end point which is not equal to the eleventh feature point D and not equal to the seventh feature point A is the eighth feature point E; similarly, by traversing the array space P, the other end point of the profile line where the ninth feature point B is located is the tenth feature point C.

4. The method of claim 1, wherein, The specific content and steps of the T-shaped joint feature point and line extraction in step (3) are as follows: First, three types of bevels are determined according to the total number of profile lines of the T-shaped joint; when the total number of profile lines is 24, i.e., the T-shaped joint is not beveled, the two end points of the minimum distance in the array space Q are the twelfth feature point B and the thirteenth feature point E; the other end point of the profile line where the feature point is located is obtained by traversing the array space P; when the total number of profile lines is 27, i.e., the T-shaped joint is single-beveled, the following steps are performed: (g) traversing two end points of all contour lines in the array space P, there are two repeated points, if two repeated points are not the same as two end points of the minimum distance in the array space Q, then traverse two end points in the array space P, to obtain a first contour line BC and a second contour line EF, and judge the positional relationship of the two contour lines, and turn to step (h); (h) when the two contour lines are perpendicular, the two end points of the minimum distance are the twelfth feature point B and the thirteenth feature point E, and the other point of the contour line where the twelfth feature point B is located is the fourteenth feature point C; when the two contour lines are not perpendicular, or the two repeated points are the same as the two end points of the minimum distance, then the two repeated points and the two end points of the minimum distance which are not equal to the two end points of the contour line containing the repeated points are pairwise distance, and the two end points of the minimum distance which are not equal to the two repeated points are the thirteenth feature point E, and the other point is the fourteenth feature point C; (i) traversing the array space P, the other end point of the contour line where the thirteenth feature point E is located is the fifteenth feature point F, the other end point of the contour line containing the fourteenth feature point C and perpendicular to the second contour line EF is the twelfth feature point B, and the other end point of the contour line not perpendicular to the second contour line EF is the sixteenth feature point D; When the total number of contour lines is 30, that is, the T joint is double bevel groove, the following steps are taken: (j) traversing two end points of all contour lines in the array space P, there are four repeated points, pairwise distance is taken, and the two end points of the minimum distance after removing the length of the contour line itself are the twelfth feature point B and the fourteenth feature point C; traversing the array space P, the contour line two end points containing the twelfth feature point B and not equal to the fourteenth feature point C are the seventeenth feature point A, and the contour line two end points containing the fourteenth feature point C and not equal to the twelfth feature point B are the sixteenth feature point D; (k) the twelfth feature point B and the fourteenth feature point C are respectively distance from the two end points of the minimum distance in the array space Q which are not equal to the feature points A, B, C and D, and the two points of the minimum distance result which are not equal to the feature points B and C are the thirteenth feature point E; (m) the three contour lines forming the twelfth feature point B as the intersection point and the three contour lines forming the thirteenth feature point E as the intersection point form six vectors away from the intersection point B, and the minimum included angle of the ninth vector EB is θ3.

5. The method of claim 1, wherein, The corner joint weld feature parameter extraction in step (4) includes the extraction of the groove included angle θ, the groove bottom vertical gap l1, the groove top vertical gap l2 and the plate thickness h1 and h2; the groove included angle θ is calculated according to the following formula respectively: The groove bottom vertical gap l1 is calculated according to the following formula respectively: wherein l AB is the length of the line segment AB; The groove top vertical gap l2 is calculated according to the following formula: wherein l BC , l AD are the lengths of the line segments BC, AD, respectively; The plate thickness h1 and h2 are calculated according to the following formula respectively: h1＝l ED +l3 h2 = l BC cosθ2 In the formula, l ED is the length of the line segment ED; when the total number of profile lines is 24, then l ED = l EA .

6. The method of claim 1, wherein, The T joint weld feature parameter extraction in step (4) includes the extraction of the groove included angle θ, the groove bottom vertical gap l1, the groove top vertical gap l2 and l3 and the plate thickness h1 and h2; the groove included angle θ includes the left groove angle θ1 and the right groove angle θ2, and is calculated according to the following formula respectively: The groove bottom vertical gap l1 is calculated according to the following formula: l1 = l EB sin θ3 wherein l EB is the length of the line segment EB; The groove top vertical gap l2 and l3 are calculated according to the following formula respectively: l2 = l1 + l AB sin θ1 l3 = l1 + l CD sin θ2 wherein l AB , l CD are the lengths of the line segments AB, CD, respectively; The plate thickness h1, h2 is respectively calculated as follows: h1 = l BC + l AB cosθ1 + l CD cosθ2 where l BC is the length of the line segment BC;(x E ,y E ,z E ) are the coordinates of point E;(x F ,y F ,z F ) are the coordinates of point F.

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