CN112749423A - Quick analysis method for removability of supporting structure in any direction - Google Patents
Quick analysis method for removability of supporting structure in any direction Download PDFInfo
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- CN112749423A CN112749423A CN202011430629.1A CN202011430629A CN112749423A CN 112749423 A CN112749423 A CN 112749423A CN 202011430629 A CN202011430629 A CN 202011430629A CN 112749423 A CN112749423 A CN 112749423A
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F30/00—Computer-aided design [CAD]
- G06F30/10—Geometric CAD
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C64/00—Additive manufacturing, i.e. manufacturing of three-dimensional [3D] objects by additive deposition, additive agglomeration or additive layering, e.g. by 3D printing, stereolithography or selective laser sintering
- B29C64/30—Auxiliary operations or equipment
- B29C64/386—Data acquisition or data processing for additive manufacturing
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B33—ADDITIVE MANUFACTURING TECHNOLOGY
- B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
- B33Y50/00—Data acquisition or data processing for additive manufacturing
Abstract
The invention discloses a quick analysis method for removability of a supporting structure in any direction. The method comprises the following steps: step 1, carrying out voxelization on a three-dimensional model facing the accessibility of a rapid judgment separation point; step 2, quickly generating a voxel path II which approaches to a straight-line segment based on a three-dimensional Bresenham algorithm; and 3, parallelly and efficiently detecting the accessibility of all the separation points of the three-dimensional model. The method solves the problems of limited clearing direction and time consumption of the supporting structure in the 3D printing product, and supports quick analysis of the removability of the supporting structure along any direction and optimization of printing direction calculation. According to the method, the Bresenham algorithm is expanded into a three-dimensional space, the voxel path approaching a straight-line segment in any direction can be generated, the three-dimensional Bresenham algorithm is an integer traversal algorithm, the judgment formula is refined, the calculated amount is small, no accumulated error exists, and the searching efficiency of the voxel path in the step 1 is accelerated. Therefore, the removability analysis of the support structure at any angle can be rapidly supported.
Description
Technical Field
The invention relates to the field of 3D printing, in particular to a quick analysis method for the removability of a supporting structure in any direction.
Background
3D printing has attracted extensive attention in the industry and academia with its unique advantages of supporting free design, personalized customization, energy saving, etc. When manufacturing complex geometric models, 3D printing often requires the addition of support structures to prevent local collapse, curling, etc. of the printed results. Also, to ensure that the product can be manufactured efficiently, the 3D printed results often require a support structure. Considering that the support structure is generally difficult to dissolve directly and needs to be removed by manual operation, in order to avoid that the printed result fails because the support structure cannot be removed, thereby affecting the iterative design cycle of the product and wasting resources, the support structure removability analysis needs to be performed on the three-dimensional digital model before printing. However, the difficulty of manually judging whether the support structure can be removed after the three-dimensional digital model is manufactured is increased along with the increase of the geometric complexity of the three-dimensional model, and the effectiveness is difficult to guarantee.
Currently, a typical automated method for conducting support structure removability analysis prior to three-dimensional model printing has the following work: (1) the octree neighbor searching method is characterized in that an octree method is adopted to divide a three-dimensional model bounding box, and accessibility of a supporting structure is determined by judging an accessible boundary of a small cube containing the supporting structure in the axial direction; (2) calculating all the clearable directions for each support structure in C-Space requires a significant amount of preprocessing calculations to arrive at the lowest cost support structure removal order by solving the TSP problem on the search map. The existing method is time-consuming, difficult to support the removability analysis of the support structure at any angle and narrow in application range.
In view of the above situation, the invention provides a quick analysis method for the removability of a support structure in any direction, which can quickly support the removability analysis of the support structure in any angle, and further effectively support the optimized calculation of the printing direction.
Disclosure of Invention
The invention mainly aims to provide a method for rapidly analyzing the removability of a supporting structure in any direction, so as to solve the problem that the removability of the supporting structure is difficult to rapidly analyze along any angle in the background technology.
The relevant work to analyze the removability of the support structure shows: (1) the contact part of the support structure and the surface of the three-dimensional model is called a separation point, and the support structure can be separated from the three-dimensional model by breaking the separation point; (2) by default, a separation point accessible (visible) from the outside in the viewing direction can be disconnected. I.e. the support structure associated with the separation point that can be accessed from the outside in a certain direction, is considered to be removable.
The technical scheme adopted by the invention mainly comprises the following steps:
step 1, carrying out voxelization on a three-dimensional model by facing the accessibility of a rapid judgment separation point;
to avoid time consuming intersection calculations with straight lines and three-dimensional models, it can be quickly determined whether a separation point can be accessed along a given viewing direction v. Firstly, the three-dimensional model is voxelized; then, in a discrete space after voxelization, searching a voxel path I approaching to the v direction, wherein voxels in the voxel path I are adjacent to each other; finally, whether the separation point along the v direction can be accessed is determined by judging whether the voxel path I contains the voxel inside the model;
step 2, quickly generating a voxel path II which approaches to a straight-line segment based on a three-dimensional Bresenham algorithm;
introducing a Bresenham algorithm into a three-dimensional model voxel set for searching a three-dimensional voxel path II approaching the v direction, avoiding floating point number calculation, and accelerating path searching efficiency, namely accelerating analysis efficiency of accessibility of separation points; the Bresenham algorithm is used for searching an approximating straight-line segment pixel set in a two-dimensional pixel space;
step 3, the accessibility of all the separation points of the three-dimensional model is detected in parallel and efficiently
Considering that the accessibility analyses of the separation points are independent, the accessibility analyses are simultaneously carried out on the separation points related to all the support structures on the surface of the three-dimensional model in a parallel mode, and therefore the accessibility analysis efficiency of the support structures of the three-dimensional model is further improved. And if a certain separation point still cannot be accessed after traversing all the bounding box surface voxels, judging that the support structure associated with the separation point which cannot be accessed is not capable of being cleaned.
The invention has the following beneficial effects:
according to the method, a Bresenham algorithm (an algorithm for approximating a straight-line segment through a pixel point in a two-dimensional plane) is expanded into a three-dimensional space, a voxel path approximating the straight-line segment in any direction can be generated, the three-dimensional Bresenham algorithm is an integer traversal algorithm, the judgment formula is refined, the calculated amount is small, no accumulated error exists, and the searching efficiency of the voxel path in the step 1 is accelerated. Therefore, the removability analysis of the support structure at any angle can be rapidly supported.
By performing accessible analysis on all separated points on the surface of the three-dimensional model, the optimal calculation of the printing direction can be effectively supported. The method solves the problems of limited clearing direction and time consumption of the supporting structure in the 3D printing product, and supports quick analysis of the removability of the supporting structure along any direction and optimization of printing direction calculation.
Drawings
FIG. 1 is a flow chart of the present invention.
FIG. 2 is a diagram of an input STL three-dimensional model.
Fig. 3 is a three-dimensional model voxelization effect graph.
Fig. 4 is a three-dimensional model voxelization classification effect graph.
FIG. 5 is a three-dimensional model surface separation point display.
Fig. 6 is a voxel accessibility direction display of a separation point.
Fig. 7 shows voxel accessibility directions for a plurality of separation points.
Detailed Description
The invention will be further explained with reference to the drawings and examples
As shown in fig. 1, the method for rapidly analyzing the removability of a support structure in any direction mainly comprises the following steps:
step 1 developing three-dimensional model voxelization oriented to rapid judgment of accessibility of separation points
1-1. voxelization of the three-dimensional model in STL format, as shown in FIG. 2, calculating an AABB (i.e. axial) bounding box of the three-dimensional model relative to a world coordinate system, and dividing the bounding box into cube voxel sets with the same size according to the required resolution. As shown in fig. 3, voxels of the entire bounding box are obtained, the higher the resolution the smaller the voxels obtained, and the side length of the voxels is set to the diameter of the clear tool. The three-dimensional model of this example has a bounding box size of 75 x 28 (units: mm) with a voxel side length set to 1 mm. According to the position relation of eight vertexes of the voxel relative to the three-dimensional model, all the voxels in the voxel set can be classified into four types:
(1.1) three-dimensional model interior voxels: the eight vertices of the voxel are completely inside the three-dimensional model, as indicated by the light gray voxels in fig. 4.
(1.2) three-dimensional model boundary voxels: the eight vertices of a voxel are some inside (no more than 2) and others outside the three-dimensional model, as represented by the dark gray voxels in fig. 4.
(1.3) bounding box boundary voxels: four of the eight vertices of the voxel coincide with the bounding box, as indicated by the black voxel in fig. 4.
(1.4) empty voxels: voxels other than the three-dimensional model interior voxels, the three-dimensional model boundary voxels, and the bounding box boundary voxels are represented as white voxels in fig. 4.
1-2, obtaining the positions of separation points associated with all support structures of the three-dimensional model according to the existing support structure generation method, and calling voxels containing the separation points as separation point voxels. If the angle between the normal vector of the triangular surface of the three-dimensional model and the printing direction is larger than 135 degrees, the surface needs a support structure. The standard is applied to all triangular surfaces of the three-dimensional model, and all areas needing the supporting structure can be identified. Given the printing direction, the positions of the separation points associated with all the support structures of the three-dimensional model can be calculated before printing. As shown in fig. 5, assuming that the printing direction is the Z axis, the red dots represent the separation dots. In particular, when a three-dimensional model surface voxel contains a separation point, the voxel is referred to as a separation point voxel.
1-3, starting from the voxel center of the separation point, connecting the voxel center of any bounding box with the voxel center of the bounding box to form a straight line segment, and if only one straight line segment can be found, so that the voxel path approaching the straight line segment does not contain the voxel inside the three-dimensional model, considering that the voxel of the separation point can be accessed from the outside, namely, the voxel is accessed along the straight line of the straight line segment.
Step 2, quickly generating a voxel path approximating a straight-line segment based on a three-dimensional Bresenham algorithm
In order to more quickly judge that the voxel at the separation point is accessed from the outside along the straight line segment connected with the voxel at the boundary of the bounding box, the invention adopts a three-dimensional Bresenham algorithm along the direction of XYZ axes to carry out axial accumulation from the voxel at the separation point to the voxel at the boundary of the bounding box (the side length of the voxel is an accumulation unit) so as to efficiently and quickly find a voxel path which is as close to a given straight line segment as possible. Specifically, the method comprises the following steps:
2-1. voxel D of the separation point to be detected before hypothesisvoxHas central coordinates of (x1, y1, z1), i.e. the distance of the voxel center from the world coordinate system origin is x1, y1 and z1 voxel side length, respectively. At the same time, assume DvoxCentral current and bounding box boundary voxel BvoxCenter-connected bounding box boundary voxels BvoxThe central coordinates of (x2, y2, z2) are given by dx ═ x2-x1|, dy ═ y2-y1|, dz ═ z2-z1 |; when dx is greater than dy and dz at the same time, the traversal is accumulated along the X axis; when dy is greater than dx and dz at the same time, cumulatively traversing along the Y axis; when dz is larger than dy and dx simultaneously, the traversal is accumulated along the Z axis; separation point voxel DvoxThe cumulative traversal along the X, Y and Z axes is the same;
2-2. the voxel accumulation traversal can be carried out along three axes (X-axis, Y-axis, Z-axis), separating point voxel D when dx is greater than dy, dz simultaneouslyvoxCumulative traversal along the X-axis, separating point voxel DvoxAccumulating the side lengths of 1 unit of voxels along the X axial direction to obtain new voxels; judging the new voxel Y coordinate relative to the separation point voxel D by formula (1)voxWhether the Y coordinate changes; substituting the result obtained by the formula (1) into the formula (2), continuously recurrently deducing to deduce a voxel D at a separation pointvoxWhether the Y coordinate of the subsequent n +1 new voxels changes relative to the Y coordinate of the nth new voxel or not; the recurrence formula is as follows:
Pxy(1)＝y1-Vl+(Vl-x1)*kxy (1)
if the current voxel increases one unit voxel side length along the X-axis direction to obtain a new voxel PxyIndicating whether the new voxel Y coordinate changes relative to the current voxel Y coordinate; pxyMore than or equal to 0 represents Y coordinate plus one unit voxel side length, Pxy< 0 means that the Y coordinate is unchanged;
n represents the number of voxels increasing along the X-axis; vlDefault to 1 for voxel increasing length;
similarly, whether the Z coordinate of the current voxel changes is judged as follows:
Pxz(1)＝z1-Vl+(Vl-x1)*kxz (3)
if the current voxel increases one unit voxel side length along the X-axis direction to obtain a new voxel PxzIndicating whether the Z coordinate of the new voxel changes relative to the Z coordinate of the current voxel; pxzMore than or equal to 0 represents Z coordinate plus one unit voxel side length, Pxz< 0 indicates that the Z coordinate is unchanged;
n represents the number of voxels increasing along the X-axis.
The process of the cumulative traversal method in three axial directions (X-axis, Y-axis, Z-axis) is similar, and the cumulative traversal along the X-axis direction is taken as an example here.
From the above recursion, if the current voxel is V (Xi, Yi, Zi), the next voxel coordinate may be one of four coordinates of V1(Xi +1, Yi +1, Zi), V2(Xi +1, Yi, Zi), V3(Xi +1, Yi +1, Zi +1), and V4(Xi +1, Yi, Zi + 1).
(3) As shown in FIG. 6, the plan view is threeThe dimension model XY plane is a layered graph, and the gray straight line segment represents DvoxCenter coordinates (x1, y1, z1) and BvoxStraight line with center coordinates (x2, y2, z2), middle gray voxel representation approximating gray straight line segment from DvoxStarting to accumulate and traverse along the X axis, obtaining the voxel by recursion according to the formulas (2) and (4), wherein the voxel is not the internal voxel of the three-dimensional model and is used for representing the voxel DvoxThe direction of accessibility.
Step 3, the accessibility of all the separation points of the three-dimensional model is detected in parallel and efficiently
As shown in fig. 7, the operations of steps 1-3 are performed simultaneously for all the voxels of the separation point on the surface of the three-dimensional model based on the method of step 2 in a multi-thread manner. Specifically, the method comprises the following steps:
3-1, sequentially traversing each bounding box voxel by taking the current separation point voxel as a center, and testing a line segment formed between the current separation point voxel and each bounding box voxel to determine whether a corresponding voxel path meets the requirement that the separation point is accessible;
3-2, if a certain separation point voxel is traversing the bounding box boundary voxel, once the separation point voxel is judged to be accessible, immediately excluding the separation point voxel from a subsequent row and column needing retesting;
and 3-3, if a certain separation point still cannot be accessed after traversing all bounding box boundary voxel voxels, judging the support structure associated with the separation point which cannot be accessed as unable to be cleaned.
Claims (6)
1. The method for rapidly analyzing the removability of the supporting structure in any direction is characterized by comprising the following steps of:
step 1, carrying out voxelization on a three-dimensional model facing the accessibility of a rapid judgment separation point;
firstly, the three-dimensional model is voxelized;
then, in a discrete space after voxelization, searching a voxel path I approaching to the v direction, wherein voxels in the voxel path I are adjacent to each other;
finally, whether the separation point along the v direction can be accessed is determined by judging whether the voxel path I contains the voxel inside the model;
step 2, quickly generating a voxel path II which approaches to a straight-line segment based on a three-dimensional Bresenham algorithm;
introducing a Bresenham algorithm into a three-dimensional model voxel set for searching a three-dimensional voxel path II approaching the v direction, avoiding floating point number calculation, and accelerating path searching efficiency, namely accelerating analysis efficiency of accessibility of separation points;
the Bresenham algorithm is used for searching an approximating straight-line segment pixel set in a two-dimensional pixel space;
step 3, parallelly and efficiently detecting the accessibility of all separation points of the three-dimensional model
And simultaneously carrying out accessibility analysis on the separation points associated with all the support structures on the surface of the three-dimensional model in a parallel mode, and judging that the support structures associated with the inaccessible separation points cannot be cleaned if a certain separation point still cannot be accessed after traversing all the voxels on the surface of the bounding box.
2. The method for rapidly analyzing the removability of a supporting structure according to claim 1, wherein in step 1, a voxel path i approaching to the v direction is found to avoid the time-consuming intersection calculation between the straight line and the three-dimensional model, and the specific steps are as follows:
1-1, voxelizing the three-dimensional model in the STL format, and calculating an AABB (axial direction) bounding box of the three-dimensional model relative to a world coordinate system; then, dividing the bounding box into a cubic voxel set with the same size according to the required spatial resolution, and dividing the voxels in the voxel set into four types: bounding box boundary voxels, three-dimensional model internal voxels, and empty voxels;
1-2, obtaining the positions of separation points associated with all support structures of the three-dimensional model according to the existing support structure generation method, and calling voxels containing the separation points as separation point voxels;
1-3, starting from the voxel center of the separation point, connecting the voxel center of any bounding box with the voxel center of the bounding box to form a straight line segment, and if only one straight line segment can be found, so that the voxel path approaching the straight line segment does not contain the voxel inside the three-dimensional model, considering that the voxel of the separation point can be accessed from the outside, namely, the voxel is accessed along the straight line of the straight line segment.
3. Method for the rapid analysis of the removability of a support structure in any direction according to claim 2, characterised in that the determination of the removability of the support structure is made by determining the accessibility of all the associated detachment points of the support structure.
4. The method for rapidly analyzing the removability of the supporting structure in any direction according to claim 1, 2 or 3, wherein the voxel path II approximating the straight line segment is rapidly generated by adopting a three-dimensional Bresenham algorithm in the step 2, and the specific steps are as follows:
2-1. voxel D of the assumed separation pointvoxHas a central coordinate of (x1, y1, z1) and encloses a box boundary voxel BvoxThe central coordinates of (x2, y2, z2) are given by dx ═ x2-x1|, dy ═ y2-y1|, dz ═ z2-z1 |; when dx is greater than dy and dz at the same time, the traversal is accumulated along the X axis; when dy is greater than dx and dz at the same time, cumulatively traversing along the Y axis; when dz is larger than dy and dx simultaneously, the traversal is accumulated along the Z axis; separation point voxel DvoxThe cumulative traversal along the X, Y and Z axes is the same;
2-2. when dx is greater than dy, dz simultaneously, the voxel D at the separation pointvoxCumulative traversal along the X-axis, separating point voxel DvoxAccumulating the side lengths of 1 unit of voxels along the X axial direction to obtain new voxels; judging the new voxel Y coordinate relative to the separation point voxel D by formula (1)voxWhether the Y coordinate changes; substituting the result obtained by the formula (1) into the formula (2), continuously recurrently deducing to deduce a voxel D at a separation pointvoxWhether the Y coordinate of the subsequent n +1 new voxels changes relative to the Y coordinate of the nth new voxel or not; the recurrence formula is as follows:
Pxy(1)＝y1-Vl+(Vl-x1)*kxy (1)
if the current voxel increases one unit voxel side length along the X-axis direction to obtain a new voxel PxyIndicating whether the new voxel Y coordinate changes relative to the current voxel Y coordinate; pxyMore than or equal to 0 represents Y coordinate plus one unit voxel side length, Pxy< 0 means that the Y coordinate is unchanged;
n represents the number of voxels increasing along the X-axis; vlDefault to 1 for voxel increasing length;
similarly, whether the Z coordinate of the current voxel changes is judged as follows:
Pxz(1)＝z1-Vl+(Vl-x1)*kxz (3)
if the current voxel increases one unit voxel side length along the X-axis direction to obtain a new voxel PxzIndicating whether the Z coordinate of the new voxel changes relative to the Z coordinate of the current voxel; pxzMore than or equal to 0 represents Z coordinate plus one unit voxel side length, Pxz< 0 indicates that the Z coordinate is unchanged;
n represents the number of voxels increasing along the X-axis.
5. The method for rapidly analyzing the removability of a supporting structure according to claim 4, wherein the operations of steps 1-3 are implemented in a multithreading manner for all the voxels of the separation points on the surface of the three-dimensional model, and are implemented as follows:
1-3-1, sequentially traversing each bounding box voxel by taking the current separation point voxel as a center, and testing a line segment formed between the current separation point voxel and each bounding box voxel to determine whether a corresponding voxel path meets the requirement that the separation point is accessible;
1-3-2, when a certain separation point voxel traverses the bounding box boundary voxel, once the separation point voxel is judged to be accessible, immediately excluding the separation point voxel from a subsequent row and column which need retesting;
1-3-3, if a certain separation point still cannot be accessed after traversing all bounding box boundary voxel voxels, judging that a supporting structure associated with the separation point which cannot be accessed cannot be cleaned.
6. The method for rapidly analyzing the removability of a supporting structure in any direction according to claim 5, wherein the rapid analysis of the removability of the supporting structure in any printing direction is realized by efficiently detecting the accessibility of all the separation points of the three-dimensional model in parallel.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114274505A (en) * | 2021-12-23 | 2022-04-05 | 山东大学 | Sandwich plate fused deposition printing support structure generation method and system |
| CN114834043A (en) * | 2022-05-09 | 2022-08-02 | 华中科技大学鄂州工业技术研究院 | Laser three-dimensional processing model slice data processing method |
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114274505A (en) * | 2021-12-23 | 2022-04-05 | 山东大学 | Sandwich plate fused deposition printing support structure generation method and system |
| CN114274505B (en) * | 2021-12-23 | 2022-08-30 | 山东大学 | Sandwich plate fused deposition printing support structure generation method and system |
| CN114834043A (en) * | 2022-05-09 | 2022-08-02 | 华中科技大学鄂州工业技术研究院 | Laser three-dimensional processing model slice data processing method |
| CN114834043B (en) * | 2022-05-09 | 2023-09-05 | 华中科技大学鄂州工业技术研究院 | Laser three-dimensional processing model slice data processing method |
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