A skeleton path generation method and system based on triangular net bidirectional search

Abstract

The disclosure provides a skeleton path generation method and system based on a triangulation network bidirectional search, relates to the technical field of additive manufacturing, and comprises the following steps: grouping and pairing a plurality of inner contours and outer contours obtained by slicing a three-dimensional model; constructing a constrained Delaunay triangulation network for each group of contours, dividing a connected domain into a plurality of grid triangles, and defining the midpoints of two internal edges in a triangle containing at least two internal edges as brother relationships; in each constructed triangulation network, taking a pair of points with a brother relationship as a search starting point, and adaptively generating a skeleton path according to the contour characteristics by using a path point bidirectional search algorithm. The present application solves the problems of low skeleton extraction efficiency and limited use conditions in the prior art by respectively generating a skeleton path for each connected domain based on the path point bidirectional search algorithm of the Delaunay triangulation network, and improves the additive manufacturability of complex and narrow features and thin-walled features by using the generated single-path skeleton path.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of additive manufacturing, in particular to a skeleton path generation method and system based on triangular mesh bidirectional search. BACKGROUND

[0002] Additive manufacturing technology, also known as 3D printing technology, is a layer-by-layer manufacturing technology for forming actual objects by stacking materials layer by layer. The printing path is the key to the additive manufacturing process. For the same model, different paths may produce completely different printing accuracy and efficiency. Whether the path is appropriate deeply affects the printing efficiency, forming effect, and even the manufacturability of some features of the part. Currently, the most commonly used paths in the field of additive manufacturing are zigzag path and contour offset path.

[0003] Narrow or thin-walled features are common structural features of components. Currently, additive manufacturing of such features, such as using a zigzag path, will generate a large number of short paths and frequent turning points, resulting in time-consuming manufacturing and poor quality. If a contour offset path is used, since the contour offset path is obtained by offsetting inward along the contour of the narrow feature, the path conforms to the shape and direction of the feature contour, and good forming quality can be obtained. However, the contour offset path also has its limitations, that is, the offset is based on the closed contour, so a closed path is inevitably obtained. This leads to the following situations: if a given offset distance is used, for particularly narrow features, offset failure may occur due to the self-intersection of the closed path after offsetting, and a reasonable offset path cannot be generated, so the feature cannot be manufactured; if the offset distance is reduced to eliminate self-intersection, the path may generate material accumulation in the region due to the requirement that the path must "walk around" the contour, thereby failing to ensure the dimensional accuracy of the narrow feature. Therefore, the single-path skeleton path planning method for additive manufacturing of narrow or thin-walled features is the key to solving the problem.

[0004] Skeleton is a simplified representation of the topological information of polygon shape. Commonly used methods for extracting polygon skeleton include Voronoi diagram method, angle bisector method, and Delaunay triangular mesh method. Among them, the Delaunay triangular mesh method is to construct a constrained Delaunay triangular mesh for the polygon, and the main skeleton is directly obtained by connecting the midpoints of the mesh edges (or the barycenter, incenter, etc.), without the need for cumbersome pruning operations. Only the parallel degree of the contour needs to be focused on. The more parallel the contour is, the better the skeleton extraction effect will be. Narrow features and thin-walled features generally have good contour parallelism, so the skeleton extraction effects of the above three methods are not much different for such features. However, compared with the cumbersome Voronoi diagram method and angle bisector method, the Delaunay triangular mesh method has the advantages of simple implementation and high efficiency, so it is favored by technical personnel.

[0005] The method for extracting the skeleton based on the Delaunay triangulation network mostly uses the binary tree structure to search and store the skeleton points, and the disadvantages of this kind of method are as follows: ① the end points of the skeleton line need to be specified as the search starting points before the search, and the number of the end points is less than that of other non-end points of the skeleton points, and the search needs to consume extra time; ② the search is carried out in a single direction, and the search efficiency is low; ② the structure features such as the circular ring and the closed thin curved surface are long and thin, and the skeleton is theoretically closed and does not have the end points, and it is difficult to specify the end points of the skeleton, and therefore the ability to generate the closed skeleton path is poor, and the method cannot be used for the additive manufacturing of the closed long and thin structure.

[0006] In summary, the existing Delaunay triangulation skeleton extraction method has low extraction efficiency and limited use conditions, which affects the additive manufacturability of the complex long and thin features and the thin wall features. SUMMARY

[0007] To solve the above problems, the present disclosure provides a skeleton path generation method and system based on triangulation bidirectional search, which generates a skeleton path for each connected domain by using a path point bidirectional search algorithm based on a Delaunay triangulation network, solves the problems of low skeleton extraction efficiency and limited use conditions in the prior art, and improves the additive manufacturability of complex long and thin features and thin wall features by using the generated single-pass skeleton path.

[0008] According to some embodiments, the present disclosure adopts the following technical solutions:

[0009] A skeleton path generation method based on triangulation bidirectional search, comprising:

[0010] Slicing a three-dimensional model to be printed to obtain a plurality of inner and outer contours, and grouping and pairing the inner and outer contours;

[0011] Constructing a constrained Delaunay triangulation network for each group of contours, dividing the connected domain formed by each group of contours into a plurality of grid triangles, classifying the triangles according to the number of internal edges, and defining the midpoints of the two internal edges in the triangle containing at least two internal edges as siblings;

[0012] In each constructed constrained Delaunay triangulation network, a pair of points with sibling relationship is randomly selected as a search starting point, and a path point bidirectional search algorithm is used to adaptively generate a skeleton path according to the contour characteristics;

[0013] Merging and outputting the skeleton paths generated by all the constrained Delaunay triangulation networks as the final printing path for additive manufacturing.

[0014] According to some embodiments, the present disclosure adopts the following technical solutions:

[0015] A skeleton path generation system based on a triangulation network bidirectional search, comprising:

[0016] A contour grouping module configured to slice a three-dimensional model to be printed to obtain a plurality of inner contours and outer contours, and group and pair the inner and outer contours;

[0017] A triangulation module configured to construct a constrained Delaunay triangulation network for each group of contours, divide a connected domain formed by each group of contours into a plurality of grid triangles, classify the triangles according to the number of internal edges, and define that the midpoints of two internal edges in a triangle containing at least two internal edges are in sibling relationship with each other;

[0018] A bidirectional search module configured to take a pair of points with sibling relationship in each constructed constrained Delaunay triangulation network as a search starting point, adopt a path point bidirectional search algorithm, and adaptively generate a skeleton path according to contour characteristics;

[0019] A path output module configured to combine and output the skeleton paths generated by all the constrained Delaunay triangulation networks as a final additive manufacturing printing path.

[0020] According to some embodiments, the present disclosure adopts the following technical solutions:

[0021] A computer program product comprising a computer program, which, when executed by a processor, implements the skeleton path generation method based on a triangulation network bidirectional search.

[0022] According to some embodiments, the present disclosure adopts the following technical solutions:

[0023] A non-transitory computer-readable storage medium for storing computer instructions, which, when executed by a processor, implements the skeleton path generation method based on a triangulation network bidirectional search.

[0024] According to some embodiments, the present disclosure adopts the following technical solutions:

[0025] An electronic device comprising a processor, a memory, and a computer program; wherein the processor is connected with the memory, and the computer program is stored in the memory; when the electronic device is running, the processor executes the computer program stored in the memory, so that the electronic device implements the skeleton path generation method based on a triangulation network bidirectional search.

[0026] Compared with the prior art, the present disclosure has the following beneficial effects:

[0027] 1) The present application groups and pairs the plurality of inner and outer contours obtained by slicing, constructs a network and generates a path for each connected domain respectively, and the skeleton search process of each connected domain does not interfere with each other, thereby improving the search efficiency of the path point.

[0028] 2) The present application improves the traditional skeleton line extraction algorithm based on Delaunay triangulation network, so that the end points of the skeleton line do not need to be found and specified before extracting the skeleton, but a pair of points with brother relationship is taken as the starting point of search, thereby reducing the limitation of the algorithm.

[0029] 3) The present application proposes a bidirectional search algorithm for path points, which is more efficient than the traditional one-way skeleton line extraction algorithm based on binary tree structure which needs to specify the end points, and can generate closed or non-closed skeleton path according to the contour characteristics, and has good adaptability. BRIEF DESCRIPTION OF DRAWINGS

[0030] The accompanying drawings, which form a part of this disclosure, are intended to provide further understanding of the disclosure and are incorporated herein in conjunction with the description of the disclosure. The illustrative embodiments of the disclosure, and their description, serve to explain the disclosure without limiting it.

[0031] Figure 1 The overall flowchart of the skeleton path generation method of embodiment 1.

[0032] Figure 2 The contrast diagram of the Delaunay triangulation network before and after refinement of embodiment 1.

[0033] Figure 3 The schematic diagram of the internal edge of the triangular mesh of embodiment 1.

[0034] Figure 4 The schematic diagram of the bidirectional search algorithm of embodiment 1.

[0035] Figure 5 And Figure 6 The generation effect example diagram of the skeleton path of embodiment 1. DETAILED DESCRIPTION

[0036] The disclosure will be further described below in conjunction with the drawings and embodiments.

[0037] It should be pointed out that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as generally understood by those skilled in the art to which the disclosure belongs.

[0038] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments in accordance with the present disclosure. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, steps, operations, elements, components, and / or groups thereof, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof.

[0039] Embodiment 1

[0040] In one embodiment of the present disclosure, a skeleton path generation method based on triangulation network bidirectional search is provided, comprising:

[0041] Step one: slice the three-dimensional model to be printed to obtain a plurality of inner and outer contours, and group and pair the inner and outer contours;

[0042] Step two: construct a constrained Delaunay triangulation network for each group of contours, divide the connected domain formed by each group of contours into a plurality of grid triangles, classify the triangles according to the number of internal edges, and define that the midpoints of the two internal edges in the triangle containing at least two internal edges are siblings of each other;

[0043] Step three: in each constructed constrained Delaunay triangulation network, take a pair of points with sibling relationship as the search starting point, and use the path point bidirectional search algorithm to adaptively generate a skeleton path according to the contour characteristics;

[0044] Step four: combine and output the skeleton paths generated by all constrained Delaunay triangulation networks as the final printing path for additive manufacturing.

[0045] As an embodiment, the skeleton path generation method based on triangulation network bidirectional search of the present disclosure solves the problems of low efficiency and limited use conditions of skeleton extraction in the prior art by using the path point bidirectional search algorithm based on the Delaunay triangulation network to generate a single skeleton path for each connected domain, thereby improving the additive manufacturability of complex and narrow features and thin-walled features, such as Figure 1 As shown in the figure, the specific implementation process is as follows:

[0046] S1, input the slice contour:

[0047] The slice contour can be a single or multiple two-dimensional closed polygon, which is obtained by slicing the three-dimensional model to be printed.

[0048] S2, simplify the slice contour:

[0049] Using polygon simplification algorithm, delete collinear redundant points, which on the one hand provides a good foundation for the subsequent steps to build triangular network, on the other hand, by reducing the number of contour points to enhance the network speed.

[0050] S3, pair the inner and outer contours, write.poly file, specifically:

[0051] S31, distinguish the inner and outer contours, and group and pair.

[0052] Each inner contour corresponds to a unique outer contour, and each outer contour may contain multiple inner contours. Each group of contours forms a connected domain, and each group of contours has and only has one outer contour. The number of inner contours is greater than or equal to 0.

[0053] S32, write each group of contours into a.poly file respectively.

[0054] The contents to be written include: contour point information, contour edge information, and hole characterization information. The.poly file is a file format specific to Triangle library for storing polygon data, and Triangle library is a geometric library specifically used for triangular mesh partitioning.

[0055] S4, build a refined constrained Delaunay triangular mesh:

[0056] For each.poly file written in S3, use the constrained meshing and refined meshing instructions of Triangle library to build a Delaunay triangular mesh.

[0057] The constrained meshing refers to giving certain boundary constraints so that the triangular mesh is generated only within the boundary; the refined meshing refers to encrypting and subdividing the mesh to generate more mesh triangles.

[0058] Appendix Figure 2 The effects of non-refined constrained meshing and refined constrained meshing are shown. The inverted "T" shape contour is the specified boundary constraint. As can be seen in the figure, the non-refined constrained meshing will have the probability of generating narrow triangles, making it impossible to accurately detect the nearest contour direction through the mesh, which will reduce the accuracy of the skeleton in representing the contour shape. Therefore, the refined meshing instruction needs to be used to build an encrypted mesh to provide support for more accurate skeleton extraction. As can be seen in the figure, the use of the refined meshing instruction has a good inhibitory effect on the appearance of narrow triangles.

[0059] S5, extract the internal edges of the triangular mesh:

[0060] For the Delaunay triangular mesh built in S4, define the mesh edges that are not on the contour as the internal edges of the current connected domain, otherwise as the contour edges, and store the internal edge information.

[0061] AppendixFigure 3 For example, the inner and outer contours constitute a rectangular frame shape connected domain, ABC and BDE are two triangles in the Delaunay triangulation, according to the definition of the internal edge, in the two triangles, the edges AB, AC, BD, BE are the internal edges of the current connected domain.

[0062] S6, the topological relationship of three types of triangles is constructed:

[0063] According to the number of internal edges contained, the triangles existing in the Delaunay triangulation are divided into three types, the characteristics of the path segments (i.e. internal path segments) contained in each type of triangle are specified, and the topological relationship of each type of triangle is constructed respectively, which specifically includes:

[0064] a) The first type (edge triangle): containing one internal edge and two contour edges.

[0065] The path segment characteristics are: the path segment will be connected from the midpoint of the internal edge to the contour edge, and the connection point is one of the midpoints of the two contour edges and the vertex corresponding to the internal edge. The specific selection method is: compare the included angle between the three connection directions and the last direction of the current path (i.e. the current path in the search process of step S7), and take the point corresponding to the smallest included angle as the final connection point.

[0066] The topological relationship is: define the midpoint of the unique internal edge as an isolated point, which cannot be queried from the isolated point to the midpoints of the other two edges of the same triangle.

[0067] b) The second type (path triangle): containing two internal edges and one contour edge.

[0068] The path segment characteristics are: taking the midline of the two internal edge midpoints as the path segment.

[0069] The topological relationship is: define the midpoints of the two internal edges as brother relationship, and the other point can be queried through any one of them;

[0070] c) The third type (branch triangle): containing three internal edges.

[0071] The path segment characteristics are: containing two path segments belonging to different paths, taking two internal edges, connecting the midpoint of one internal edge, the centroid of the triangle, and the midpoint of the other internal edge in sequence as one path segment, and connecting the remaining internal edge midpoint to the centroid of the triangle as another path segment.

[0072] The topological relationship is: define the midpoints of two internal edges as brother relationship, and the midpoint of the remaining internal edge is defined as an isolated point.

[0073] The triangular topological relationship further includes: no matter the triangular type, each internal edge actually belongs to two adjacent triangles, defining a pair of midpoints of two triangles on their common edge as an adjacency relationship, and any one of the pair can be used to query the other.

[0074] S7, bidirectional search path point, generate skeleton path, including the following steps:

[0075] For all connected domains after network construction (i.e., each group of contours forms a constrained Delaunay triangular network), the path generation is carried out according to the following steps:

[0076] S71, judge whether the Delaunay triangular network of the current connected domain contains only one triangle, if yes, do not consider generating a skeleton path for it, and jump to step S74; otherwise, continue to the next step.

[0077] S72, judge whether the Delaunay triangular network of the current connected domain contains only two triangles, if yes, in the two triangles, respectively compare the lengths of the two midlines passing through the midpoints of the common edge, select the longer two midlines to form the skeleton path, and jump to step S74; otherwise, continue to the next step.

[0078] S73, if the Delaunay triangular network of the current connected domain contains more than two triangles, a path point bidirectional search algorithm is used, as shown in Figure 4 , which specifically includes:

[0079] S731, when there is a "midpoint in unused state", a new empty path is created, an unused midpoint and its sibling point are selected to join the empty path as the starting point and the ending point of the current path respectively, and the point and its sibling point are marked as used state, and then jump to S732 to continue the search of the current path.

[0080] When there is no "midpoint in unused state", it means that the search of the Delaunay triangular network of the current connected domain is completed, and jump to S74 to output the skeleton path of the current connected domain.

[0081] S732, starting from the starting point and the ending point of the current path, search to both sides of the path respectively, and constantly update the current starting point and the ending point of the path: find the adjacent point of the current point through the adjacency relationship, and then query the sibling point of the adjacent point, and add the triangular internal path segment constructed according to the classification to the current path, until the search end condition is met.

[0082] The internal path segment of the triangle here is constructed by each triangle path segment mode in S6. The path segment is added to the current path, and two points searched in two search directions are added to the head and tail of the path respectively. The starting point and the ending point of the path are updated, and the two points are marked as used. If the triangle type of the searched point is the third type (branch triangle), the triangle centroid is added first, and then the point is added. If no point is searched in a certain direction, no operation is performed in this direction.

[0083] The search end condition includes three types of search end conditions. If any one of the conditions is met, the search is ended, and the ending work is performed in S733. Otherwise, S732 is iteratively executed.

[0084] S733, three types of search end conditions and ending work, specifically:

[0085] a) If the points searched in two search directions are in an adjacent relationship, the coordinates of the two points are the same, and the current path will be closed. At this time, the searched points are added to the head and tail of the path respectively, and the two points are marked as used. If the triangle type of one of the points is three (three internal edges), the triangle centroid is added first, and then the point is added, and finally a closed path is generated.

[0086] b) If the points searched in two search directions are brother points, the two points belong to the same triangle, and the current path will be closed. At this time, one of the points is selected and added to the end of the path in the corresponding search direction, and the two points are marked as used. If the selected point belongs to a triangle of type three, the triangle centroid is added first, and then the point is added, and finally a closed path is generated.

[0087] c) If no point can be searched in two search directions, the starting point and the ending point of the current path are: if the adjacent point belongs to a triangle of type one, the path at the current point is extended according to the characteristics of the first type of triangle path segment, and the points on the contour edge are added after the current point; if the adjacent point belongs to a triangle of type three, the path at the current point is extended according to the characteristics of the third type of triangle path segment, and the triangle centroid is added to the current point, and finally a non-closed path is generated.

[0088] After the ending work of the current path is processed, jump to S731 to determine whether to create an empty path.

[0089] S74, output the skeleton path of the current connected domain,

[0090] Among them, the skeleton path can be a single / multiple closed path, a single / multiple non-closed path, a closed / non-closed mixed path.

[0091] S8, merge redundant paths:

[0092] Simplify each path contained in the skeleton path, a path can be composed of multiple line segments, if there are multiple line segments in a row, the redundant path points need to be deleted, and the multiple line segments are combined into one segment, so as to reduce the code amount and storage size of the processing code generated from the path.

[0093] Specifically, multiple line segments in a path will generate multiple "G1" processing instructions, after simplification, the multiple line segments are combined into one segment, and only one "G1" instruction is used to represent it.

[0094] Figures 5 to 6 For the generation effect example of the skeleton path in the embodiment, in order to clearly show that the skeleton path of the complex contour is composed of multiple different paths, the path effect of not extending the path to the third type of triangular center of gravity is also provided in the dashed line box.

[0095] Embodiment 2

[0096] An embodiment of the present disclosure provides a skeleton path generation system based on bidirectional search of triangular mesh, comprising:

[0097] The contour grouping module is configured to slice the three-dimensional model to be printed to obtain multiple inner and outer contours, and group and pair the inner and outer contours;

[0098] The triangular division module is configured to construct a constrained Delaunay triangular mesh for each group of contours, divide the connected domain formed by each group of contours into multiple mesh triangles, classify the triangles according to the number of internal edges, and define that the midpoints of the two internal edges in a triangle containing at least two internal edges are brothers of each other;

[0099] The bidirectional search module is configured to take a pair of points with brother relationship in each constructed constrained Delaunay triangular mesh as a search starting point, adopt a path point bidirectional search algorithm, and adaptively generate a skeleton path according to the contour characteristics;

[0100] The path output module is configured to combine and output the skeleton paths generated by all the constrained Delaunay triangular meshes as the final printing path for additive manufacturing.

[0101] Embodiment 3

[0102] An embodiment of the present disclosure provides a computer program product, comprising a computer program, which, when executed by a processor, implements the skeleton path generation method based on bidirectional search of triangular mesh.

[0103] Embodiment 4

[0104] In an embodiment of the present disclosure, a non-transitory computer-readable storage medium is provided for storing computer instructions, which, when executed by a processor, implement the method for generating a skeleton path based on bidirectional search of a triangular mesh.

[0105] Embodiment 5

[0106] In an embodiment of the present disclosure, an electronic device is provided, comprising a processor, a memory, and a computer program; wherein the processor is connected with the memory, and the computer program is stored in the memory; when the electronic device is running, the processor executes the computer program stored in the memory, so that the electronic device implements the method for generating a skeleton path based on bidirectional search of a triangular mesh.

[0107] The present disclosure is described with reference to the flowcharts and / or block diagrams of the method, device (system) and computer program product according to embodiments of the present disclosure. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, and the combination of the flows and / or blocks in the flowcharts and / or block diagrams can be implemented by computer program instructions. These computer program instructions can be provided to a general-purpose computer, a special-purpose computer, an embedded processor or other programmable data processing devices to produce a machine, so that the instructions executed by the computer or other programmable data processing devices generate a means for implementing the functions specified in the flowcharts and / or block diagrams. Figure 1 The functions specified in one or more flows and / or blocks Figure 1 The means for implementing the functions specified in one or more flows and / or blocks.

[0108] These computer program instructions can also be loaded onto a computer or other programmable data processing device to cause a series of operational steps to be performed on the computer or other programmable data processing device to produce a computer-implemented process, so that the instructions executed by the computer or other programmable data processing device provide a means for implementing the functions specified in the flowcharts and / or block diagrams. Figure 1 The functions specified in one or more flows and / or blocks Figure 1 The steps for implementing the functions specified in one or more flows and / or blocks.

[0109] Although the specific embodiments of the present disclosure are described above with reference to the accompanying drawings, the present disclosure is not limited thereto, and various modifications or variations can be made by those skilled in the art without creative labor, which are still within the protection scope of the present disclosure.

Claims

1. A skeleton path generation method based on bidirectional search of a triangulated mesh, characterized by, The application relates to a method for generating a printing path for additive manufacturing, comprising the following steps: slicing a three-dimensional model to be printed to obtain a plurality of inner contours and outer contours, and grouping and pairing the inner and outer contours; constructing a constrained Delaunay triangular mesh for each group of contours, dividing a connected domain formed by each group of contours into a plurality of mesh triangles, defining mesh edges not on the contours as internal edges of a current connected domain and otherwise as contour edges, and storing internal edge information; classifying the triangles according to the number of internal edges, and defining the midpoints of two internal edges in a triangle containing at least two internal edges as siblings; the classification includes three types: an edge triangle containing one internal edge and two contour edges; a passage triangle containing two internal edges and one contour edge; and a branch triangle containing three internal edges; and defining two types of relationships between the centers of internal edges: sibling relationship and adjacency relationship; in each constructed constrained Delaunay triangular mesh, taking a pair of points with a sibling relationship as a search starting point, and adaptively generating a skeleton path according to contour characteristics by using a path point bidirectional search algorithm; merging and outputting the skeleton paths generated by all the constrained Delaunay triangular meshes as a final additive manufacturing printing path; the path point bidirectional search algorithm specifically comprises the following steps: newly creating an empty path, taking a pair of points with a sibling relationship as a search starting point, adding the found midpoint and its sibling point to the path, and marking the two points as the starting point and the ending point of the current path; starting from the starting point and the ending point of the current path, respectively searching to both sides of the path, and constantly updating the current starting point and the current ending point of the path: finding the adjacent point of the current point through the adjacency relationship, then querying the sibling point of the adjacent point, and adding the internal path segment of the triangle constructed according to the classification to the current path until a search end condition is met; the adjacency relationship is a pair of midpoints on a common edge of two adjacent triangles; when the search end condition is met, performing finishing work on the current path to obtain a skeleton path of a current connected domain; the internal path segment of the triangle constructed according to the classification specifically comprises the following steps: when the triangle is an edge triangle, selecting one point from three points composed of two contour edge midpoints and internal edge vertices, and connecting the selected point and the internal edge midpoint as an internal path segment; when the triangle is a passage triangle, taking the line connecting the midpoints of the two internal edges as an internal path segment; when the triangle is a branch triangle, sequentially connecting the midpoint of one internal edge, the triangle barycenter and the midpoint of the other internal edge as a first internal path segment, and connecting the remaining internal edge midpoint to the triangle barycenter as a second internal path segment; wherein the internal path segment of the edge triangle and the second internal path segment of the branch triangle are only used for finishing work.

2. The skeleton path generation method based on the two-way search of the triangulated net according to claim 1, wherein, the grouping and pairing specifically comprises the following steps: each inner contour corresponds to a unique outer contour, each outer contour contains a plurality of inner contours, and each outer contour and the contained inner contours are taken as a group of contours, and each group of contours forms a connected domain.

3. The skeleton path generation method based on the TIN bidirectional search of claim 1, wherein, the steps for constructing a constrained Delaunay triangular mesh specifically comprise the following steps: writing each group of contours into a.poly file; The poly file is used to build the constrained Delaunay triangulation network by using the constraint network and the refinement network instruction of the Triangle library. The constraint network is given a certain boundary constraint, so that the triangulation network is generated only in the boundary; the refinement network is a grid encryption subdivision, which will generate more grid triangles.

4. The skeleton path generation method based on the TIN bidirectional search of claim 1, wherein, The search end condition and the finishing work include: If the points searched by the two search directions are adjacent, according to the type of the triangle to which the searched points belong, the corresponding internal path segment is added to the head and tail of the path to generate a closed path.

5. The skeleton path generation method based on the TIN bidirectional search of claim 1, wherein, The search end condition and the finishing work also include: If the points searched by the two search directions are brothers, at this time, any point is selected, according to the type of the triangle to which the point belongs, the corresponding internal path segment is added to the tail of the path in the corresponding search direction of the point to generate a closed path.

6. The skeleton path generation method based on the TIN bidirectional search of claim 1, wherein, The search end condition and the finishing work also include: If the points searched by the two search directions are brothers, at this time, any point is selected, according to the type of the triangle to which the point belongs, the corresponding internal path segment is added to the tail of the path in the corresponding search direction of the point to generate a closed path.

7. A skeleton path generation system based on a triangulated mesh bidirectional search, employing a skeleton path generation method based on a triangulated mesh bidirectional search according to any one of claims 1 to 6, characterized by, It includes: The contour grouping module is configured to slice the three-dimensional model to be printed to obtain a plurality of inner contours and outer contours, and group and pair the inner and outer contours; The triangle division module is configured to construct a constrained Delaunay triangulation network for each group of contours, divide the connected domain formed by each group of contours into a plurality of grid triangles, classify the triangles according to the number of internal edges, and define that the midpoints of two internal edges in a triangle containing at least two internal edges are brothers; The bidirectional search module is configured to take a pair of points with brother relationship as the search starting point in each constructed constrained Delaunay triangulation network, and adaptively generate a skeleton path according to the contour characteristics by using a path point bidirectional search algorithm; The path output module is configured to combine and output the skeleton paths generated by all the constrained Delaunay triangulation networks as the final printing path for additive manufacturing.

Images