CN113183470A - 3D printing self-adaptive layering method capable of reserving irregular features of model - Google Patents
3D printing self-adaptive layering method capable of reserving irregular features of model Download PDFInfo
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- CN113183470A CN113183470A CN202110515918.XA CN202110515918A CN113183470A CN 113183470 A CN113183470 A CN 113183470A CN 202110515918 A CN202110515918 A CN 202110515918A CN 113183470 A CN113183470 A CN 113183470A
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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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- 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 3D printing self-adaptive layering method for reserving unconventional characteristics of a model, which comprises the following steps of: s1, defining and identifying the conventional features of the model, adjusting the feature height interval, and setting a layering plane at each conventional feature height after adjustment; s2, subdividing the model by controlling the layer thickness between every two adjacent conventional feature heights through the volume error rate, and keeping the unconventional features; and S3, adjusting the layering height according to the actual printing layer thickness limit. The method not only defines and identifies the common conventional characteristic points, characteristic lines and characteristic surfaces of most models, but also ensures that the characteristics are not lost or shifted in the printing process; and the model is subdivided at the detail features which do not meet the conventional definition by adopting a method for calculating the volume error rate, so that the unconventional features of the model are effectively reserved, the printing error is further reduced, and the model forming precision is improved.
Description
Technical Field
The invention belongs to the technical field of 3D printing data processing, and particularly relates to a 3D printing self-adaptive layering method for reserving unconventional features of a model.
Background
The 3D printing technology is additive manufacturing technology for processing a three-dimensional CAD model into an entity in a mode of accumulating materials layer by layer, and the basic principle of the additive manufacturing technology is 'layered manufacturing and layer by layer superposition', a series of data processing processes are carried out on a part model to be processed through data processing software, the three-dimensional CAD model is dispersed into two-dimensional layers, and then a processing path of a layer file is converted into a machine code which can be recognized by a printer to complete the entity printing of the part. Therefore, the data processing process, particularly the layered slicing link, is the core content of 3D printing, and has a crucial influence on the accuracy and efficiency of entity printing.
The current research on hierarchical algorithms is mainly divided into two categories: equal thickness layering and adaptive layering. The uniform-thickness layering algorithm is used for uniformly layering the whole model according to the thickness of a fixed layer, is simple to implement, and easily causes the loss of the dense characteristics of the outer surface of the model; the self-adaptive layering algorithm automatically corrects the printing thickness according to the curvature change of the outer surface of the model, and reduces the printing error by the number of layers as few as possible. However, in terms of processing the detailed features of the outer surface of the model, most of the current adaptive layering algorithms only summarize and define conventional features such as steps, holes and the like, and irregular features which do not meet the conventional definition, such as chutes, cannot be identified and processed, and are easily lost in the layering process, so that the situations of loss and deviation of the irregular features of the model in the adaptive layering process need to be considered, and the printing error is further reduced.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a 3D printing self-adaptive layering method which can identify the conventional features of a model in the layering process, ensure that the features are not lost or deviated, subdivide the irregular features and effectively reserve the irregular features of the model.
The purpose of the invention is realized by the following technical scheme: A3D printing self-adaptive layering method for preserving irregular features of a model comprises the following steps:
s1, defining and identifying the conventional features of the model, adjusting the feature height interval, and setting a layering plane at each conventional feature height after adjustment;
s2, subdividing the model by controlling the layer thickness between every two adjacent feature heights through the volume error rate, and keeping the unconventional features;
and S3, adjusting the layering height according to the actual printing layer thickness limit.
Further, the step S1 specifically includes the following sub-steps:
s11, summarizing the conventional features into three types of feature points, feature lines and feature surfaces, and then respectively identifying the feature points, the feature lines and the feature surfaces according to the topological structure data;
s12, adjusting the feature height interval:
s121, storing the lowest point height and the highest point height of the model into a characteristic height sequence, and reordering the whole sequence from low to high;
s122, calculating the height difference between every two feature heights from the lowest point of the model from low to high, and setting the height difference of the two feature heights from low to high as hc1And hc2If h isc2-hc1If min _ Δ h is less than m, h is calculatedc2Next characteristic height hc3And hc1The height difference of (a); if hc3-hc1If h is 2 min _ Δ h, then h is addedc2Is adjusted to a height of hc1+ min _ Δ h; if hc3-hc1< 2 × min _ Δ h and hc3-hc1If min _ Δ h, then h is directly discardedc2(ii) a If hc3-hc1If min _ Δ h is less than the threshold, then h is discardedc2Continue to judge hc3Next characteristic height hc4And hc1The height difference of (a); repeating the above operations until hc1The height difference with the next characteristic height is greater than or equal to min _ Δ h; then h is putc1Is set to a new hc1Adjusting the height difference until hc2Is the highest point height of the model; if when h is presentc2Is the highest point height h of the modelc2-hc1If min _ Δ h is less than the threshold, then h is discardedc1(ii) a Where min _ Δ h represents the minimum printable thickness.
Further, the feature points, the feature lines, and the feature planes are defined as follows:
the characteristic points are as follows: a locally highest or lowest dot in the printing direction; the point is a common intersection point of a plurality of triangular patches, and the coordinate value along the printing direction is the minimum value or the maximum value of the coordinate values along the printing direction in all vertexes of the triangular patch;
characteristic line: a line segment perpendicular to the printing direction, wherein two adjacent triangular surface patches of the line segment are not parallel to the layering plane, and the included angle of the normal vectors of the two triangular surface patches is larger than a set threshold;
the characteristic surface is as follows: a plane perpendicular to the printing direction.
Further, the method for identifying the feature points, the feature lines and the feature surfaces comprises the following steps:
the characteristic points are as follows: traversing all vertexes of the STL model, searching all vertexes of all triangular patches where the point is located, if the Z coordinate value of the point is the maximum value or the minimum value in the Z coordinate values of all vertexes, determining the point as a feature point, and determining the feature height as the Z coordinate value of the point;
characteristic line: traversing all edges of the STL model, if the Z coordinate values of the starting point and the ending point of the edge are equal, then judging whether two adjacent triangular patches of the line segment are feature planes, if not, calculating the normal vector included angle of the two triangular patches, if the normal vector included angle of the two triangular patches exceeds a set threshold value, determining the line segment as a feature line, and if the normal vector included angle of the two triangular patches exceeds the set threshold value, determining the feature height as the Z coordinate value of the starting point or the ending point of the line segment;
the characteristic surface is as follows: and traversing all the triangular patches of the STL model, if the Z coordinate values of three vertexes of the triangular patches are equal, determining that the plane where the triangular patch is located is a characteristic plane, and the characteristic height is the Z coordinate value of any vertex.
Further, the step S2 specifically includes the following steps:
s21, setting the layering plane where the lowest conventional feature height is located as a reference layering plane, and presetting the next layering height as the current height plus the maximum printable thickness along the layering direction;
s22, calculating the volume error rate between two layered planes:
where η is the volume error rate, VmAnd VpActual volume and printing volume, V, of the current two-layer modeleIs the printing error volume; the calculation method is as follows:
(1) model printing volume VpThe calculation method comprises the following steps: the height of the two sub-layers is respectively h from low to high1And h2The forming principle of 3D printing is that the cylinders with layered cross section as bottom and high layer thickness are piled up layer by layer to form a solid body, so h1And h2The inter-model print volume is actually h1The cross section is a bottom surface h2-h1High column volume;
thus, h is first obtained1Cross-sectional profile data at height: firstly, the triangular patches are sorted and preprocessed, and then the triangular patches are found out1Calculating to obtain all intersecting line segments by using the highly-intersected triangular patches, sequentially connecting the intersecting line segments end to obtain a closed contour line, and finally judging the inner contour and the outer contour line and storing the contour lines;
after all closed contour lines of the current layer are obtained, calculating the polygonal area of the section of the current layer by a triangle segmentation method; if the layering direction is along the Z-axis positive direction, the plane polygon area calculation formula is as follows:
wherein n is the number of polygon vertexes (x)a,ya)、(xb,yb) The coordinates of the other two vertexes of the triangle except the origin point;
from equation (2), h1Layered cross-sectional area S at heighth1Further obtaining the printing volume V of the current partial modelp＝Sh1·(h2-h1)；
(2) Printing error volume VeThe printing error volume between two layered planes is composed of the sum of volume errors generated between the two planes by all triangular surface patches; let SiIs a triangular surfaceSlice ACD at h1And h2Area between two layered planes, thetaiIs the sum of the normal vectors h of the triangular patches1The included angle of the layering plane at the height part is that the triangular patch ACD is at h1And h2The calculation method of the volume error between the two layers comprises the following steps:
traversing the triangular patch to find h1And h2And (3) calculating printing errors between two layers by using all triangular patches between two layering heights according to a formula (4):
then, according to the formula (1), the volume error rate eta of printing between two layers under the current layer thickness is obtainedcEta is tocWith print-enabled volume error rate threshold η0Make a comparison if ηc＞η0Then, the layer thickness is adjusted according to equation (5):
adjusting layer height to current layer height and Δ hnewRepeating the steps to calculate a new volume error rate until the volume error rate is within a given threshold range;
and S23, taking the layering plane where the obtained layer height is located as a new reference layering plane, and repeating S21 and S23 until the model layering between the two feature heights is completed.
Further, the step S3 is performed as follows: let the minimum printable thickness be min _ Δ h, and the current regular feature height be hcThe heights of the two adjacent layers are h1、h2If h isc-h2< min _ Δ h and hc-h1If h is 2 min _ Δ h, then h is added2Is adjusted to a height of hc-min_Δh；
If hc-h1If < 2 min _ Δ h, then h is discarded2。
The invention has the beneficial effects that: in the process of carrying out self-adaptive layering on the three-dimensional model, the method firstly defines and identifies the common conventional characteristic points, characteristic lines and characteristic surfaces of most models, and ensures that the characteristics are not lost or deviated in the printing process; and then, the model is subdivided at the position of the detail feature which does not meet the conventional definition by adopting a method for calculating the volume error rate, so that the unconventional feature of the model is effectively reserved, the printing error is further reduced, and the model forming precision is improved.
Drawings
FIG. 1 is a flow chart of a 3D printing adaptive layering method of the present invention;
FIG. 2 is a schematic diagram of the topology of an STL file;
FIG. 3 is a schematic diagram of polygon area calculation;
FIG. 4 is a schematic diagram of conventional features;
FIG. 5 is a schematic illustration of the layering of conventional features by the method of the present invention;
FIG. 6 is a schematic of tip height method vs. layering of conventional features;
FIG. 7 is a schematic view of an unconventional feature;
FIG. 8 is a schematic of the layering of the unconventional features by the method of the present invention;
fig. 9 is a schematic of the tip height method versus layering of unconventional features.
Detailed Description
The technical scheme of the invention is further explained by combining the attached drawings.
As shown in FIG. 1, the invention relates to a 3D printing self-adaptive layering method for preserving the unconventional characteristics of a model based on volume error rate, which comprises the following steps:
s1, defining and identifying the conventional features of the model, adjusting the feature height interval, and setting a layering plane at each conventional feature height after adjustment;
the method specifically comprises the following substeps:
s11, summarizing the conventional features into three types of feature points, feature lines and feature surfaces, and then respectively identifying the feature points, the feature lines and the feature surfaces according to the topological structure data;
the characteristic points, the characteristic lines and the characteristic surfaces are defined as follows:
the characteristic points are as follows: a locally highest or lowest dot in the printing direction; the point is a common intersection point of a plurality of triangular patches, and the coordinate value along the printing direction is the minimum value or the maximum value of the coordinate values along the printing direction in all vertexes of the triangular patch;
characteristic line: a line segment perpendicular to the printing direction, wherein two adjacent triangular surface patches of the line segment are not parallel to the layering plane, and the included angle of the normal vectors of the two triangular surface patches is larger than a set threshold;
the characteristic surface is as follows: a plane perpendicular to the printing direction.
To facilitate the identification of the conventional features, the STL model data topology shown in fig. 2 is first established, and the data structure for storing points, lines, and planes is as follows:
the method for identifying the feature points, the feature lines and the feature surfaces comprises the following steps:
the characteristic points are as follows: traversing all vertexes of the STL model, searching all vertexes of all triangular patches where the point is located, if the Z coordinate value of the point is the maximum value or the minimum value in the Z coordinate values of all vertexes, determining the point as a feature point, and determining the feature height as the Z coordinate value of the point;
characteristic line: traversing all edges of the STL model, if the Z coordinate values of the starting point and the ending point of the edge are equal, then judging whether two adjacent triangular patches of the line segment are feature planes, if not, calculating the normal vector included angle of the two triangular patches, if the normal vector included angle of the two triangular patches exceeds a set threshold value, determining the line segment as a feature line, and if the normal vector included angle of the two triangular patches exceeds the set threshold value, determining the feature height as the Z coordinate value of the starting point or the ending point of the line segment;
the characteristic surface is as follows: and traversing all the triangular patches of the STL model, if the Z coordinate values of three vertexes of the triangular patches are equal, determining that the plane where the triangular patch is located is a characteristic plane, and the characteristic height is the Z coordinate value of any vertex.
S12, adjusting the feature height interval:
s121, storing the lowest point height and the highest point height of the model into a characteristic height sequence, and reordering the whole sequence from low to high;
s122, calculating the height difference between every two feature heights from the lowest point of the model from low to high, and setting the height difference of the two feature heights from low to high as hc1And hc2If h isc2-hc1If min _ Δ h is less than m, h is calculatedc2Next characteristic height hc3And hc1The height difference of (a); if hc3-hc1If h is 2 min _ Δ h, then h is addedc2Is adjusted to a height of hc1+ min _ Δ h; if hc3-hc1< 2 × min _ Δ h and hc3-hc1If min _ Δ h, then h is directly discardedc2(ii) a If hc3-hc1If min _ Δ h is less than the threshold, then h is discardedc2Continue to judge hc3Next characteristic height hc4And hc1The height difference of (a); repeating the above operations until hc1The height difference with the next characteristic height is greater than or equal to min _ Δ h; then h is putc1Is set to a new hc1Adjusting the height difference until hc2Is the highest point height of the model; if when h is presentc2Is the highest point height h of the modelc2-hc1If min _ Δ h is less than the threshold, then h is discardedc1(ii) a Where min _ Δ h represents the minimum printable thickness.
S2, subdividing the model by controlling the layer thickness between every two adjacent feature heights through the volume error rate, and keeping the unconventional features;
the method specifically comprises the following steps:
s21, setting the layering plane where the lowest conventional feature height is located as a reference layering plane, and presetting the next layering height as the current height plus the maximum printable thickness along the layering direction;
s22, calculating the volume error rate between two layered planes:
where η is the volume error rate, VmAnd VpActual volume and printing volume, V, of the current two-layer modeleIs the printing error volume; the calculation method is as follows:
(1) model printing volume VpThe calculation method comprises the following steps: the height of the two sub-layers is respectively h from low to high1And h2The forming principle of 3D printing is that the cylinders with layered cross section as bottom and high layer thickness are piled up layer by layer to form a solid body, so h1And h2The inter-model print volume is actually h1The cross section is a bottom surface h2-h1High column volume;
thus, h is first obtained1Cross-sectional profile data at height: firstly, the triangular patches are sorted and preprocessed, and then the triangular patches are found out1Calculating to obtain all intersecting line segments by using the highly-intersected triangular patches, sequentially connecting the intersecting line segments end to obtain a closed contour line, and finally judging the inner contour and the outer contour line and storing the contour lines;
after all closed contour lines of the current layer are obtained, calculating the polygonal area of the section of the current layer by a triangle segmentation method; if the layering direction is along the Z-axis positive direction, the plane polygon area calculation formula is as follows:
wherein n is the number of polygon vertexes (x)a,ya)、(xb,yb) The coordinates of the other two vertexes of the triangle except the origin point;
from equation (2), h1Layered cross-sectional area S at heighth1Further obtaining the printing volume V of the current partial modelp＝Sh1·(h2-h1)；
(2) Printing error volume VeThe printing error volume between two layered planes is composed of the sum of volume errors generated between the two planes by all triangular surface patches; as shown in FIG. 3, let SiFor a triangular patch ACD at h1And h2Area between two layered planes, thetaiIs the sum of the normal vectors h of the triangular patches1The included angle of the layering plane at the height part is that the triangular patch ACD is at h1And h2The calculation method of the volume error between the two layers comprises the following steps:
traversing the triangular patch to find h1And h2And (3) calculating printing errors between two layers by using all triangular patches between two layering heights according to a formula (4):
then, according to the formula (1), the volume error rate eta of printing between two layers under the current layer thickness is obtainedcEta is tocWith print-enabled volume error rate threshold η0Make a comparison if ηc＞η0Then, the layer thickness is adjusted according to equation (5):
adjusting layer height to current layer height and Δ hnewRepeating the steps to calculate a new volume error rate until the volume error rate is within a given threshold range;
and S23, taking the layering plane where the obtained layer height is located as a new reference layering plane, and repeating S21 and S23 until the model layering between the two feature heights is completed.
S3, adjusting the layering height according to the practical printing layer thickness limit; the invention adopts the layering idea of the method to be composed of the current layerThe height is used to obtain the next layering height, so that the distance between some conventional feature heights and the previous layering height is less than the minimum printable thickness, and the layering height needs to be adjusted as follows: let the minimum printable thickness be min _ Δ h, and the current regular feature height be hcThe heights of the two adjacent layers are h1、h2If h isc-h2< min _ Δ h and hc-h1If h is 2 min _ Δ h, then h is added2Is adjusted to a height of hc-min_Δh；
If hc-h1If < 2 min _ Δ h, then h is discarded2。
In this embodiment, the trophy model shown in fig. 4 and the chute model shown in fig. 7 are used to test the improvement effect of the method of the present invention on the situations of loss and deviation of the conventional features and the non-conventional features, and based on C + + programming, the method specifically includes the following steps:
the trophy model:
s1: identifying the conventional features of the model, selecting h as shown in FIG. 40、h1、h2、h3Three feature heights are used to measure the shift and loss of the conventional feature.
S2: according to the actual printing requirement, the minimum printable thickness is set to be 1mm, and the maximum printable thickness is set to be 4 mm. For the method of the invention, a volume error rate threshold of 0.1 is set.
S3: and importing the model into a program, and operating to obtain a layering result.
S4: in order to conveniently compare the effects, under the same printing condition, the center height value of 1mm is adopted to layer the model by using a center height method, and a layering result is obtained.
The results of the layering of the present invention and the tip height method on the trophy model are shown in fig. 5 and 6, respectively, the number of layering and the volume error rate for both methods are shown in table 1, and the deviation of the model characteristics is shown in table 2. By comparison, the tip height method has 148 layering and 153 layering, and both methods produce a volume error rate of about 0.2, but the tip height method results in h in dealing with loss and offset of conventional features0Loss of features at height (see FIG. 6) and h1、h2、h3The characteristic at the height is deviated to different degrees (see table 2), and the method of the invention not only retains h0Features at height (see fig. 6) while ensuring h1、h2、h3The features did not shift at height (see table 2). Thus demonstrating the effectiveness of the method of the present invention in dealing with conventional feature loss and offset situations.
TABLE 1
TABLE 2
Chute model:
s1: according to actual printing requirements, the minimum printable thickness is set to be 0.5mm, and the maximum printable thickness is set to be 10 mm. For the method of the invention, a volume error rate threshold of 0.1 is set.
S2: and importing the model into a program, and operating to obtain a layering result.
S3: in order to conveniently compare the effects, the tip height method is adopted to layer the model by adopting the tip height value of 0.5mm under the same printing condition, and a layering result is obtained.
The results of the layering of the chute models by the inventive method and tip height method are shown in fig. 8 and 9, respectively, and the number of layering and the volume error rate for both methods are shown in table 3. As can be seen from the graph, when the curvature change of the outer surface of the model cannot be identified as a conventional feature point, a feature line and a feature surface, the feature of the model cannot be effectively retained by the apex height method, so that a large volume error is generated, for example, as shown in fig. 9, according to the algorithm, the model after being printed and formed is a quadrangular prism, and all the inclined grooves are lost; the method of the invention subdivides the height of each chute, effectively retains the detail characteristics and reduces the volume error to the maximum extent. Thus demonstrating the effectiveness of the method of the present invention in dealing with the loss of unconventional features.
The invention provides a 3D printing self-adaptive layering method for reserving model unconventional features, which effectively prevents the conventional features from being lost and offset in the layering process by defining and identifying feature points, feature lines and feature surfaces, and meanwhile, controls a layer thickness subdivision model by adopting a method for calculating a volume error rate, effectively reserves the unconventional features that the model does not meet the conventional definition, further reduces printing errors and improves the model forming precision.
TABLE 3
It will be appreciated by those of ordinary skill in the art that the embodiments described herein are intended to assist the reader in understanding the principles of the invention and are to be construed as being without limitation to such specifically recited embodiments and examples. Those skilled in the art can make various other specific changes and combinations based on the teachings of the present invention without departing from the spirit of the invention, and these changes and combinations are within the scope of the invention.
Claims (6)
1. A3D printing self-adaptive layering method for preserving unconventional features of a model is characterized by comprising the following steps:
s1, defining and identifying the conventional features of the model, adjusting the feature height interval, and setting a layering plane at each conventional feature height after adjustment;
s2, subdividing the model by controlling the layer thickness between every two adjacent feature heights through the volume error rate, and keeping the unconventional features;
and S3, adjusting the layering height according to the actual printing layer thickness limit.
2. The 3D printing adaptive layering method for preserving model unconventional features according to claim 1, wherein the step S1 specifically comprises the following sub-steps:
s11, summarizing the conventional features into three types of feature points, feature lines and feature surfaces, and then respectively identifying the feature points, the feature lines and the feature surfaces according to the topological structure data;
s12, adjusting the feature height interval:
s121, storing the lowest point height and the highest point height of the model into a characteristic height sequence, and reordering the whole sequence from low to high;
s122, calculating the height difference between every two feature heights from the lowest point of the model from low to high, and setting the height difference of the two feature heights from low to high as hc1And hc2If h isc2-hc1If min _ Δ h is less than m, h is calculatedc2Next characteristic height hc3And hc1The height difference of (a); if hc3-hc1If h is 2 min _ Δ h, then h is addedc2Is adjusted to a height of hc1+ min _ Δ h; if hc3-hc1< 2 × min _ Δ h and hc3-hc1If min _ Δ h, then h is directly discardedc2(ii) a If hc3-hc1If min _ Δ h is less than the threshold, then h is discardedc2Continue to judge hc3Next characteristic height hc4And hc1The height difference of (a); repeating the above operations until hc1The height difference with the next characteristic height is greater than or equal to min _ Δ h; then h is putc1Is set to a new hc1Adjusting the height difference until hc2Is the highest point height of the model; if when h is presentc2Is the highest point height h of the modelc2-hc1If min _ Δ h is less than the threshold, then h is discardedc1(ii) a Where min _ Δ h represents the minimum printable thickness.
3. The 3D printing adaptive layering method for preserving model unconventional features according to claim 2, wherein the feature points, feature lines and feature planes are defined as follows:
the characteristic points are as follows: a locally highest or lowest dot in the printing direction; the point is a common intersection point of a plurality of triangular patches, and the coordinate value along the printing direction is the minimum value or the maximum value of the coordinate values along the printing direction in all vertexes of the triangular patch;
characteristic line: a line segment perpendicular to the printing direction, wherein two adjacent triangular surface patches of the line segment are not parallel to the layering plane, and the included angle of the normal vectors of the two triangular surface patches is larger than a set threshold;
the characteristic surface is as follows: a plane perpendicular to the printing direction.
4. The 3D printing adaptive layering method for preserving the unconventional features of the model according to claim 2, wherein the method for identifying the feature points, the feature lines and the feature planes comprises the following steps:
the characteristic points are as follows: traversing all vertexes of the STL model, searching all vertexes of all triangular patches where the point is located, if the Z coordinate value of the point is the maximum value or the minimum value in the Z coordinate values of all vertexes, determining the point as a feature point, and determining the feature height as the Z coordinate value of the point;
characteristic line: traversing all edges of the STL model, if the Z coordinate values of the starting point and the ending point of the edge are equal, then judging whether two adjacent triangular patches of the line segment are feature planes, if not, calculating the normal vector included angle of the two triangular patches, if the normal vector included angle of the two triangular patches exceeds a set threshold value, determining the line segment as a feature line, and if the normal vector included angle of the two triangular patches exceeds the set threshold value, determining the feature height as the Z coordinate value of the starting point or the ending point of the line segment;
the characteristic surface is as follows: and traversing all the triangular patches of the STL model, if the Z coordinate values of three vertexes of the triangular patches are equal, determining that the plane where the triangular patch is located is a characteristic plane, and the characteristic height is the Z coordinate value of any vertex.
5. The 3D printing adaptive layering method for preserving model unconventional features according to claim 1, wherein the step S2 specifically comprises the following steps:
s21, setting the layering plane where the lowest conventional feature height is located as a reference layering plane, and presetting the next layering height as the current height plus the maximum printable thickness along the layering direction;
s22, calculating the volume error rate between two layered planes:
where η is the volume error rate, VmAnd VpActual volume and printing volume, V, of the current two-layer modeleIs the printing error volume; the calculation method is as follows:
(1) model printing volume VpThe calculation method comprises the following steps: the height of the two sub-layers is respectively h from low to high1And h2The forming principle of 3D printing is that the cylinders with layered cross section as bottom and high layer thickness are piled up layer by layer to form a solid body, so h1And h2The inter-model print volume is actually h1The cross section is a bottom surface h2-h1High column volume;
thus, h is first obtained1Cross-sectional profile data at height: firstly, the triangular patches are sorted and preprocessed, and then the triangular patches are found out1Calculating to obtain all intersecting line segments by using the highly-intersected triangular patches, sequentially connecting the intersecting line segments end to obtain a closed contour line, and finally judging the inner contour and the outer contour line and storing the contour lines;
after all closed contour lines of the current layer are obtained, calculating the polygonal area of the section of the current layer by a triangle segmentation method; if the layering direction is along the Z-axis positive direction, the plane polygon area calculation formula is as follows:
wherein n is the number of polygon vertexes (x)a,ya)、(xb,yb) The coordinates of the other two vertexes of the triangle except the origin point;
from equation (2), h1Layered cross-sectional area S at heighth1Further obtaining the printing volume V of the current partial modelp＝Sh1·(h2-h1)；
(2) Printing error volume VeThe printing error volume between two layered planes is composed of the sum of volume errors generated between the two planes by all triangular surface patches; let SiFor a triangular patch ACD at h1And h2Area between two layered planes, thetaiIs the sum of the normal vectors h of the triangular patches1The included angle of the layering plane at the height part is that the triangular patch ACD is at h1And h2The calculation method of the volume error between the two layers comprises the following steps:
traversing the triangular patch to find h1And h2And (3) calculating printing errors between two layers by using all triangular patches between two layering heights according to a formula (4):
then, according to the formula (1), the volume error rate eta of printing between two layers under the current layer thickness is obtainedcEta is tocWith print-enabled volume error rate threshold η0Make a comparison if ηc＞η0Then, the layer thickness is adjusted according to equation (5):
adjusting layer height to current layer height and Δ hnewRepeating the steps to calculate a new volume error rate until the volume error rate is within a given threshold range;
and S23, taking the layering plane where the obtained layer height is located as a new reference layering plane, and repeating S21 and S23 until the model layering between the two feature heights is completed.
6. The 3D printing adaptive layering method for preserving model unconventional features as claimed in claim 1, wherein the method comprisesThe step S3 adjustment method is as follows: let the minimum printable thickness be min _ Δ h, and the current regular feature height be hcThe heights of the two adjacent layers are h1、h2If h isc-h2< min _ Δ h and hc-h1If h is 2 min _ Δ h, then h is added2Is adjusted to a height of hc-min _ Δ h; if hc-h1If < 2 min _ Δ h, then h is discarded2。
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