An artificial joint coating structure and a 3D printing data model generation method thereof

Abstract

The present invention relates to the field of 3D printing technology, and in particular to an artificial joint coating structure. It includes a coating body in a three-dimensional mesh structure, the three-dimensional mesh structure includes a plurality of interconnected units, the unit includes external nodes, internal nodes and mesh wires, the mesh wires are connecting lines between the external nodes and internal nodes of each unit, and the external nodes of the corresponding surfaces of adjacent units overlap. The position of the external node or the internal node is determined by the offset obtained by random function calculation. The present invention also discloses a data model generation method, including 1) establishing a model, 2) making an external rectangular frame, 3) voxelization, 4) cutting mesh wires and nodes outside the model, and 5) forming coordinate data. The beneficial effects of the present invention are: the obtained coating structure has a uniform structure at the macro level, a structural difference at the micro level, a porosity similar to that of real human bones, high strength, and good fusion with human tissue; it is easy to form using laser 3D printing.

Description

Technical Field

[0001] The present invention relates to the technical field of 3D printing, and in particular to an artificial joint coating structure and a 3D printing data model generation method thereof. Background Art

[0002] Currently, artificial joint replacement has been widely used in clinical practice to treat osteoarthritis of the shoulder, hip and other joints, fractures, bone injuries, ischemic necrosis of bones and other diseases. Existing artificial joint prostheses have various structural designs, and the porous coating on the surface of the artificial joint is crucial to the effect of prosthesis replacement, which determines the biocompatibility and durability between the prosthesis and human tissue.

[0003] At present, the technologies used to manufacture porous surface coatings in artificial joints are mostly metal microbead sintering, metal filament weaving, and plasma spraying. More advanced technologies such as chemical vapor deposition and arc ion plating low-temperature deposition are also used to manufacture surface coatings for artificial joints. These technologies are limited by their manufacturing principles and low resolution. It is difficult to accurately control the geometric shape of the pore structure in the coating during the manufacturing process, and it is difficult to meet the requirements of good growth of human bone tissue into the coating structure. This directly leads to the low compatibility of artificial joint implants with the human body's own bones and poor durability. Generally speaking, every ten years or even several years, due to the decline in the performance of joint implants, artificial joint replacement surgery that causes great pain to the patient's body and mind needs to be performed again. Therefore, for younger patients, the compatibility and long-term stability of implants with the human body are particularly important.

[0004] Laser metal 3D printing technology has developed rapidly in recent years. It has the characteristics of high resolution and precise control of printed component structure, and can form parts with extremely complex shapes. It has been increasingly widely used in industrial manufacturing, scientific research and medical fields. This brings greater structural design freedom to the manufacturing process of artificial prosthesis coatings, making it possible to achieve a more ideal artificial prosthesis structure.

[0005] However, 3D printing technology is highly dependent on computer-aided design, especially in the computer algorithms for designing porous structures and the preparation of printer data. Therefore, how to design an artificial joint coating structure that is biocompatible and durable with human bone tissue is a key issue in the successful application of laser metal 3D printing in the manufacture of high-performance artificial joint coatings.

[0006] In terms of the printing model generation algorithm, the algorithm needs to have the following requirements: (1) a wealth of setting options to change the final generated structure; (2) a high degree of stability to ensure that the structures generated multiple times with the same parameters have extremely similar physical structures and properties; (3) the generated data format can be converted into the input format of the laser 3D printer. Summary of the invention

[0007] The present invention aims at the above-mentioned deficiencies of the existing artificial joint porous coating manufacturing technology and provides an artificial joint coating structure which can significantly improve the quality of the prosthesis.

[0008] The technical solution of the present invention to solve the above technical problems is as follows:

[0009] An artificial joint coating structure comprises a coating body, characterized in that the coating body is a three-dimensional mesh structure comprising nodes and mesh wires connected between adjacent nodes.

[0010] The beneficial effects of the present invention are: the use of a three-dimensional mesh structure can be based on the specific requirements of the implant to be made, by flexibly setting the mesh thickness and the distance between the mesh connection nodes, it can better ensure that the implant has a microstructure similar to the real bone structure, and the high porosity can allow the bone tissue to grow deeper into the artificial coating compared to the traditional bone growth coating structure, thereby providing a higher bonding strength. At the same time, different microstructures generated by different parameters provide the possibility of customization for different individuals.

[0011] Based on the above technical solution, the present invention can also be improved as follows.

[0012] Furthermore, the three-dimensional network structure includes a plurality of interconnected unit bodies, the outer contour of the unit body is a hexagonal frame structure, the nodes include external nodes and internal nodes, the eight vertices of the hexagonal frame structure are the external nodes, and one internal node is provided in the hexagonal frame; the mesh wire is a line connecting the external nodes and the internal nodes of the unit body, and the external nodes of corresponding faces of adjacent unit bodies overlap.

[0013] The beneficial effect of adopting the above further scheme is that the external nodes of the six-sided frame structure are connected to a point inside the six-sided frame, namely the internal node, which further improves the support strength of the coating while ensuring a low relative density. Due to the connection between the internal node and the external node, all mesh wires can be summarized to one side of a certain triangle, so that the three-dimensional mesh structure of the present invention has the stability of a triangle, that is, high support strength.

[0014] Furthermore, the position of the inner node is determined by an offset obtained through a random function operation.

[0015] The beneficial effect of adopting the above further scheme is that the position of the internal nodes is randomly moved, and its movement range is inside or outside the six-sided frame, so that the overall structure of the coating is uniform, while the unit body structure has relative differences, which is closer to the characteristics of human bones, thereby promoting biocompatibility.

[0016] Furthermore, the outer contour of the unit body is a parallelepiped frame structure or a non-parallelepiped frame structure. The non-parallelepiped frame structure is formed by calculating one or more external nodes of the parallelepiped frame structure through a random function to obtain an offset and then moving the position.

[0017] The beneficial effect of adopting the above further scheme is that a non-parallel six-sided frame structure can also be formed by randomly moving the external nodes of the parallel six-sided frame structure. This structure not only retains the uniformity of the overall coating structure, but also has the relative difference of the unit body's own shape, which is more compatible with the characteristics of the irregular structure of the human skeleton, thereby promoting biocompatibility.

[0018] Furthermore, the parallelepiped frame structure includes a regular hexahedral frame structure.

[0019] The beneficial effect of adopting the above further solution is that the regular hexagonal frame structure is easy to represent when constructing the model, which reduces the amount of calculation for the subsequent randomization process.

[0020] The present invention also discloses a method for generating a 3D printing data model of an artificial joint coating, comprising a coating body, wherein the steps for generating the 3D printing data model of the coating body are as follows;

[0021] 1) Establishing a three-dimensional model S according to the coating body structure;

[0022] 2) Calculate the circumscribed rectangular box SBB (S Bounding Box) of the three-dimensional model S;

[0023] 3) voxelizing the circumscribed rectangular frame SBB of the three-dimensional model S; that is, dividing the circumscribed rectangular frame SBB into a plurality of parallelepiped frames in three-dimensional distribution to form the unit body, each of which includes 8 external nodes and 1 internal node; the edges of each unit body and the lines connecting the external nodes and the internal nodes form the mesh, and the three-dimensional mesh structure includes the external nodes, internal nodes and mesh of each unit body; the unit body is a hollow structure composed of the external nodes, internal nodes and mesh; here, the internal node is the center point of the unit body;

[0024] 4) Trimming: trimming the circumscribed rectangular frame SBB, i.e. removing the nodes and mesh outside the three-dimensional model S to form a three-dimensional structure that matches the outline of the three-dimensional model S;

[0025] 5) The position coordinates of each of the cut external nodes, internal nodes and mesh wires are stored and form modeling data, thus completing the construction of the 3D printing data model.

[0026] The beneficial effect of the data model generation method of the present invention is that the 3D printing data model formed by the above method can realize the prosthetic bone coating of the three-dimensional grid structure through 3D printing after data layering processing. The prosthetic bone coating obtained by this method can be more suitable for integration with human tissue, and is more convenient for artificial design in terms of performance than the currently selected natural porous materials or sintered porous materials, so as to obtain better prosthetic performance.

[0027] Based on the above technical solution, the present invention can also be improved as follows.

[0028] Furthermore, the method also includes randomly transforming the coordinates of the external nodes and / or internal nodes of each unit body after step 3), and using the edge lines of the unit body and the connecting lines of each external node and internal node formed after the transformation as mesh wires.

[0029] The beneficial effect of adopting the above further solution is that the coordinates of the external nodes and / or internal nodes of each unit body are randomly transformed, so that the generated coating structure is closer to the human skeleton structure, because the fine tissue of the human body structure is not the same everywhere.

[0030] Furthermore, the step 3) further includes dividing the circumscribed rectangular frame SBB into a plurality of parallelepiped frames, that is, determining the number of the unit bodies:

[0031] Assume that the length of the circumscribed rectangular frame SBB is L, the width is W, and the height is H; the length of each unit body is l, the width is w, and the height is h, then:

[0032] Number of units in the X direction

[0033] Number of units in the Y direction

[0034] The number of units in the Z direction

[0035] The above calculation results are rounded off to the next integer, that is, the number of unit bodies in the X, Y, and Z directions and the total number of unit bodies are obtained respectively.

[0036] The beneficial effect of adopting the above further solution is that the number of unit bodies in the circumscribed rectangular frame SBB can be determined through the above calculation, and then the size of the unit body can be determined. Determining the number of unit bodies also facilitates the formation of a digitized circumscribed rectangular frame SBB.

[0037] Furthermore, after determining the number of unit bodies, the number of the unit bodies in the X, Y and Z directions is adjusted to ensure that the coordinates of the vertices do not shrink into the outer contour of the three-dimensional model S after the coordinates of the vertices change randomly.

[0038] The beneficial effect of adopting the above further solution is that, after the random transformation of the external nodes of the unit body, some unit bodies or external nodes may potentially completely enter the interior of the original three-dimensional model S, thus causing the surface of the final structure to be incomplete and non-uniform. Determining and adjusting the reasonable number of unit bodies can avoid this problem.

[0039] Furthermore, the method further includes offsetting a starting point R of the circumscribed rectangular frame SBB to ensure uniformity of the surface of the coating body.

[0040] The beneficial effect of adopting the above further solution is: this step ensures that the three-dimensional model S can be completely covered by the voxelized circumscribed rectangular frame SBB, thereby further ensuring the uniformity of the surface of the porous structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a schematic diagram of the structure of an artificial joint coating of the present invention;

[0042] Figure 2 It is a schematic diagram of the parallelepiped frame structure of the present invention;

[0043] Figure 3 for Figure 2 Schematic diagram of the structure after the positions of the Chinese and foreign nodes are transformed;

[0044] Figure 4 It is a schematic diagram of the unit structure with mesh wire of the present invention;

[0045] Figure 5 for Figure 4 Schematic diagram of the unit body structure after the position of the internal nodes is transformed;

[0046] Figure 6 for Figure 5 Schematic diagram of the unit structure after the position of the external nodes is transformed;

[0047] Figure 7 Schematic diagram (plane) of the circumscribed rectangular frame SBB structure of the three-dimensional model S in the present method invention;

[0048] Figure 8 It is a schematic diagram of the structure after the reference point is adjusted in the present method invention;

[0049] Fig. 9 Schematic diagram of the plane outline of the three-dimensional model S after trimming in the present invention (without removing the edges);

[0050] Fig.10 A flowchart of the steps for forming a 3D printing data model in the present invention;

[0051] Fig.11 This is a schematic diagram of the unit structure without edges in the present invention;

[0052] Fig.12 A schematic diagram of the organizational structure of a cubic three-dimensional model formed by the method of the present invention;

[0053] Fig.13 for Fig.11 A partial enlarged view of .

[0054] In the figure, 1, three-dimensional model S; 2, circumscribed rectangular frame SBB; 3, unit body; 3-1, edge line; 3-2, mesh; 3-3, external node; 3-4, internal node. DETAILED DESCRIPTION

[0055] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0056] like Figure 1-Figure 6 As shown, an artificial joint coating structure includes a coating body, characterized in that the coating body is a three-dimensional network structure, and the three-dimensional network structure includes nodes and mesh wires connected between adjacent nodes.

[0057] The three-dimensional network structure includes a plurality of interconnected unit bodies 3, the outer contour of the unit body 3 is a six-sided frame structure, the nodes include external nodes 3-3 and internal nodes 3-4, the eight vertices of the six-sided frame structure are the external nodes 3-3, and one internal node 3-4 is provided in the six-sided frame; the mesh 3-2 is a line connecting the external nodes 3-3 and the internal nodes 3-4 of each unit body, and the external nodes 3-3 of the corresponding faces of adjacent unit bodies 3 overlap.

[0058] For ease of expression, the six-sided frame structure in the figure also has an edge line (dashed line) 3-1 drawn. The solid line is the mesh 3-2. Figure 1 As shown, it can be seen that the three-dimensional network structure includes Figure 4 Among the multiple unit bodies shown, the edge line (dashed line) 3 - 1 is only used to express the outline of the unit body.

[0059] The position of the inner node 3-4 is determined by the offset obtained by random function operation.

[0060] The outer contour of the unit body 3 is a parallelepiped frame structure or a non-parallelepiped frame structure. The non-parallelepiped frame structure is formed by applying a random function to one or more external nodes 3-3 of the parallelepiped frame structure to obtain an offset and moving the position according to the offset. When the coordinates of the external nodes 3-3 change, the corresponding mesh wire changes accordingly, thereby forming a non-parallelepiped frame structure.

[0061] The parallelepiped frame structure includes a regular hexahedral frame structure.

[0062] When a specific random function is operated, a limit is given to the offset percentage, which can be -60% to +60%. For example, the maximum offset is plus or minus 60% of the unit body side length, that is, the increase or decrease of the coordinate value of each dimension of each vertex is at most 60% of the unit body side length.

[0063] like Figure 7-Figure 9 As shown, it is used to assist in explaining the method invention. For ease of understanding, it is assumed that the coating body is spherical, and a plane view is used for clear observation.

[0064] The present invention also discloses a method for generating a 3D printing data model of an artificial joint coating, comprising a coating body, wherein the steps for generating a 3D printing data model of the coating body are as follows;

[0065] 1) A three-dimensional model S1 is established in a computer according to the coating body structure; the contour of the three-dimensional model is the contour of the coating to be formed.

[0066] 2) Calculate the circumscribed rectangular frame SBB2 of the three-dimensional model S;

[0067] Assume that the minimum X coordinate, Y coordinate, and Z coordinate of the three-dimensional model S are Xmin, Ymin, and Zmin; the maximum X coordinate, Y coordinate, and Z coordinate of the three-dimensional model S are Xmax, Ymax, and Zmax; then the eight vertices (s1-s8) of the circumscribed rectangular box SBB of the three-dimensional model S are defined as follows:

[0068] s1(Xmin,Ymin,Zmin)

[0069] s2(Xmin,Ymax,Zmin)

[0070] s3(Xmax,Ymax,Zmin)

[0071] s4(Xmax,Ymin,Zmin)

[0072] s5(Xmin,Ymin,Zmax)

[0073] s6(Xmin,Ymax,Zmax)

[0074] s7(Xmax,Ymax,Zmax)

[0075] s8(Xmax,Ymin,Zmax)

[0076] The circumscribed rectangular box SBB is determined by the coordinates of the above 8 vertices.

[0077] 3) voxelizing the circumscribed rectangular frame SBB of the three-dimensional model S; the voxelization is to divide the circumscribed rectangular frame SBB into a plurality of parallelepiped frames in three-dimensional distribution, each of which is a unit body 3, each of which includes 12 edges, 8 external nodes 3-3 and 1 internal node 3-4, and the lines connecting the external nodes and the internal nodes of each unit body 3 form the mesh, and the interior of the circumscribed rectangular frame SBB presents the three-dimensional mesh structure;

[0078] The circumscribed rectangular frame SBB is divided into several parallelepiped frames, and the following algorithm can be used:

[0079] Assume that the length of the circumscribed rectangular frame SBB is L, the width is W, and the height is H; the length of each unit body is l, the width is w, and the height is h, then:

[0080] Number of units in the X direction

[0081] Number of units in the Y direction

[0082] The number of units in the Z direction

[0083] The above calculation results are rounded off to the next integer, that is, the number of unit bodies in the X, Y, and Z directions and the total number of unit bodies are obtained respectively.

[0084] According to the above calculation, the circumscribed rectangular frame SBB can be easily divided into a number of parallelepiped frames distributed in three dimensions, that is, voxelization is achieved.

[0085] 4) Clipping: trimming the circumscribed rectangular frame SBB, i.e. removing the nodes and meshes outside the three-dimensional model S to form a three-dimensional structure that matches the outline of the three-dimensional model S; that is, the circumscribed rectangular frame SBB after voxelization presents a three-dimensional mesh structure as a whole, and the three-dimensional model S is contained therein. All meshes and nodes outside the three-dimensional model S are clipped, and the remaining three-dimensional mesh structure is the three-dimensional mesh three-dimensional model to be formed;

[0086] 5) The position coordinates of each of the cut external nodes, internal nodes and mesh wires are stored and form modeling data, thus completing the construction of the 3D printing data model.

[0087] The modeling process is equivalent to making the artificial joint coating tissue structure three-dimensional. The three-dimensional mesh structure can be used to set the mesh thickness and the distance between the mesh connection nodes according to the specific requirements of the prosthesis to ensure that the prosthesis has the characteristics of low relative density, high specific strength, high specific surface area, light weight, good permeability, etc. Compared with the void structure produced by traditional methods, its uniformity and bio-integration are better.

[0088] When 3D printing artificial joint coatings, the modeling data only needs to be treated as a three-dimensional model and processed in layers according to the plane. The 3D printer can then print in layers to form a prosthetic coating with a three-dimensional mesh structure.

[0089] Based on the above technical solution, the present invention can also be improved as follows.

[0090] Furthermore, the method also includes randomly transforming the coordinates of the external nodes and / or internal nodes of each unit body after step 3), and using the edge lines of the unit body and the connecting lines of each external node and internal node formed after the transformation as mesh wires.

[0091] The following steps can be used to perform random transformation of coordinates, assuming:

[0092] The coordinates of a vertex (external node) v are (x, y, z), and the coordinates after random transformation are (x′, y′, z′). Direction variable d. d has only two values, 1 and -1, and the probability of taking 1 and -1 is the same.

[0093] Assume an offset variable a. The value of a can be arbitrarily selected from the interval [-1, 1], and the distribution of a values ​​follows the continuous uniform distribution generated by the Mersenne Twister algorithm initialized with the same value. This ensures the similarity between multiple operations.

[0094] Minimum offset percentage in X direction

[0095] Maximum offset percentage in X direction

[0096] Minimum offset percentage in Y direction

[0097] Maximum offset percentage in Y direction

[0098] Minimum offset percentage in Z direction

[0099] Maximum offset percentage in Z direction

[0100] X-direction offset percentage Mx = perXmax-(perXmax-perXmin)×a

[0101] Y-direction offset percentage My=perYmax-(perYmax-perYmin)×a

[0102] Z-direction offset percentage Mz=perZmax-(perZmax-perZmin)×a

[0103] The final randomly transformed coordinates (x′, y′, z′) are:

[0104] x′=x+Mx×d×l

[0105] y′=y+My×d×w

[0106] z′=z+Mz×d×h

[0107] For each unit body, the eight vertices and / or one internal node are transformed according to the above random transformation rules, and then the transformed internal nodes are connected with the eight transformed vertices to form eight lines. After each unit body is processed, calculated and connected, a linear random three-dimensional mesh structure within the scope of the external rectangular frame SBB of the three-dimensional model S is generated.

[0108] The above transformation randomly transforms the coordinates of the external nodes and / or internal nodes of each unit body, so that the generated coating structure is more similar to the human skeleton structure, because the fine organization of the human body structure is not the same everywhere.

[0109] Furthermore, after determining the number of unit bodies, the number of the unit bodies in the X, Y and Z directions is adjusted to ensure that the coordinates of the vertices do not shrink into the outer contour of the three-dimensional model S after the coordinates of the vertices change randomly.

[0110] When the coordinates of the external nodes of the unit body are randomly transformed, the external nodes of the unit body on the contour of the three-dimensional model S may be completely offset into the contour of the three-dimensional model S, resulting in the contour of the final data model being incomplete and uneven compared with the actual contour of the three-dimensional model S. In order to solve this problem, the number of unit bodies in the X, Y and Z directions needs to be adjusted as follows:

[0111] Assume that the maximum movement in the X direction in the random coordinate transformation is Mxmax, the maximum movement in the Y direction is Mymax, and the maximum movement in the Z direction is Mzmax. Then the final number of unit bodies Nx, Ny, and Nz in the X, Y, and Z directions are defined as follows:

[0112] (Round to the next integer)

[0113] (Round to the next integer)

[0114] (Round to the next integer)

[0115] Furthermore, the method further includes offsetting a starting point R of the circumscribed rectangular frame SBB to ensure uniformity of the surface of the coating body.

[0116] In order to ensure that the three-dimensional model S can be symmetrically covered by the voxelized bounding rectangle SBB, and thus further ensure the uniformity of the porous structure surface, the bounding rectangle is appropriately extended outward a little, that is, offset outward in the three coordinate directions of X, Y and Z, and the coordinates of the offset reference point, that is, the reference point R of the bounding rectangle, are defined as follows:

[0117]

[0118]

[0119]

[0120] The variable definitions on the right side of the above equation are the same as the corresponding variable definitions above.

[0121] like Fig.10 , 11 , which is a schematic diagram of a model structure formed by using the 3D printing data model generation method of the present invention. It can be seen from the figure that a three-dimensional mesh structure is formed.

[0122] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An artificial joint coating structure, comprising a coating body, It is characterized in that The coating body is in a three-dimensional mesh structure, and the three-dimensional mesh structure includes nodes and mesh wires connected between adjacent nodes. The three-dimensional mesh structure includes a plurality of interconnected unit bodies, the outer contour of the unit body is a six-sided frame structure, the nodes include external nodes and internal nodes, the eight vertices of the six-sided frame structure are the external nodes, and one internal node is provided in the six-sided frame; the mesh wire is a line connecting the external nodes and the internal nodes of each unit body, and the external nodes of the corresponding faces of adjacent unit bodies overlap, The position of the inner node is determined by the offset obtained by random function operation. The outer contour of the unit body is a parallelepiped frame structure or a non-parallelepiped frame structure; the non-parallelepiped frame structure is formed by calculating one or more external nodes of the parallelepiped frame structure through a random function to obtain an offset and move the position.

2. A method for generating a 3D printing data model for an artificial joint coating, comprising a coating body, It is characterized in that The steps for generating the 3D printing data model of the coating body are as follows; 1) Establishing a three-dimensional model S in a computer according to the coating body structure; 2) Calculate the circumscribed rectangular frame SBB of the three-dimensional model S; 3) voxelizing the circumscribed rectangular frame SBB of the three-dimensional model S; that is, dividing the circumscribed rectangular frame SBB into a plurality of parallelepiped frames distributed in three dimensions to form unit bodies, each of which includes 8 external nodes and 1 internal node, and the lines connecting the external nodes and the internal nodes of each unit body form a mesh; 4) Trimming: trimming the circumscribed rectangular frame SBB to form a three-dimensional structure that matches the outline of the three-dimensional model S; 5) The position coordinates of each of the cut external nodes, internal nodes and mesh wires are stored and formed into modeling data, that is, the construction of the 3D printing data model is completed; Also includes a starting point R of the offset circumscribed rectangular frame SBB to ensure uniformity of the surface of the coating body; The method further includes randomly transforming the coordinates of the external nodes and / or internal nodes of each unit body after step 3), and using the connecting lines of the external nodes and internal nodes of the unit body formed after the transformation as mesh threads.

3. The method for generating a 3D printing data model for an artificial joint coating according to claim 2, It is characterized in that In step 3), the circumscribed rectangular frame SBB is divided into a number of parallelepiped frames, that is, the number of the unit bodies is determined: Assume the length of the circumscribed rectangular frame SBB is , width is , Gao Wei ; The length of each unit body is , width , Gao Wei ,but: The number of unit bodies in the X direction Nx= The number of unit bodies in the Y direction Ny= The number of unit bodies in the Z direction Nz= The above calculation results are rounded off to the nearest integer, and the number of unit bodies in the X, Y, and Z directions and the total number of unit bodies are obtained respectively.

4. The method for generating a 3D printing data model for an artificial joint coating according to claim 3, It is characterized in that After determining the number of unit bodies, the number of the unit bodies in the X, Y and Z directions is adjusted to ensure that the coordinates of the external nodes do not shrink into the outer contour of the three-dimensional model S after the coordinates of the external nodes change randomly.

Images