CN109522585B - Self-adaptive layering method for preventing feature migration of 3D printing model - Google Patents
Self-adaptive layering method for preventing feature migration of 3D printing model Download PDFInfo
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Abstract
The invention discloses a self-adaptive layering method for preventing characteristic deviation of a 3D printing model, which comprises the steps of establishing a three-dimensional model, carrying out gridding processing on the three-dimensional model to generate an STL file, reading the STL file, carrying out preprocessing operation on data read from the STL file to obtain preprocessed data, identifying characteristic height on the three-dimensional model after the gridding processing, and obtaining a group of height data
Adjusting the spacing between adjacent feature heights, i.e. for said height data
And adjusting, slicing in a layering mode at the position of the feature height, carrying out self-adaptive layering between adjacent feature heights, obtaining slice outline information, generating a printing file, and printing the 3D model. The invention ensures that the layered plane passes through the position of the model feature, thereby retaining the three-dimensional model feature, effectively preventing the feature deviation and loss caused by the layer-by-layer accumulation of materials in the 3D printing model printing process, and reducing the step error.
Description
Technical Field
The invention belongs to the technical field of 3D printing, and particularly relates to a self-adaptive layering method for preventing characteristic deviation of a 3D printing model.
Background
The 3D Printing (3D Printing) technology is also called Rapid Prototyping (RP) or Additive Manufacturing (AM), and is a technology for manufacturing a three-dimensional solid part by designing a CAD and accumulating materials layer by layer. The specific implementation steps are that firstly, a three-dimensional model is obtained by CAD design or reverse engineering, and is converted into an STL (stereolithography) format or other operable format files with simple format and good universality for processing; then intersecting planes with different heights with the model in the selected layering direction to obtain a series of contour information; and determining a printing path and other process parameters according to the contour information, controlling a printer to stack and bond the materials layer by layer from low to high, and finally forming a three-dimensional entity. The accumulation of the materials layer by layer can cause obvious step errors (or step-wise effects) of workpiece surface components and the loss and deviation of model characteristics when the inclined surfaces are printed, the surface quality of the machined part is directly influenced, and the determination of the layering position and the layer number can directly influence the surface precision and the machining efficiency of the machined part. However, whether the three-dimensional model of the workpiece is designed by CAD software or acquired by reverse engineering, the dividing direction and the dividing height must be selected first, and the workpiece is sent to the printing device for processing after the dividing process.
At present, the layering method based on the STL format mainly comprises an equal-thickness layering method and an adaptive layering method. The equal-thickness layering method has the advantages of fixed layer thickness, simple realization, high processing speed and obvious step effect, but is more applied to manufacturing workpieces with larger volume and low precision requirement; although a smaller layer thickness can result in higher surface quality, the increased number of layers increases the memory footprint, processing time, and model printing time, thereby reducing processing efficiency. The slice thickness of the self-adaptive layering is not constant, but is determined by the geometric shape of the model and the machining precision of the machine, and the layering thickness can be automatically adjusted according to the surface complexity of the workpiece model to be machined, so that the large-curvature model with a complex surface and serious inclination has smaller layering thickness, more layering layers and correspondingly fewer layering layers of the model with a simple surface. The self-adaptive layering algorithm adopts the changed layer thickness, so that the step error is reduced to a certain extent, the contradiction between the processing precision and the processing efficiency is solved, but no matter how small the layer thickness is, the step effect cannot be completely eliminated, and the layering plane cannot be ensured to pass through all model characteristics, so that the model characteristics are not printed or the positions of the characteristics are shifted, and the problems of loss and shift of the characteristics cannot be solved. Therefore, under the same surface quality, the number of layers obtained by the self-adaptive layering is less than that obtained by the equal-thickness layering, and the processing efficiency is higher. However, most of the current adaptive hierarchical algorithms mainly study the relation between the layer height and the step error, and the solution to the problem of model feature shift and loss is still less. Therefore, there is an urgent need to provide an improved adaptive hierarchical method for effectively solving the problem of model feature shift, so as to further reduce the step effect and solve the problems of feature shift and loss.
Disclosure of Invention
In view of the above-mentioned shortcomings of the prior art, the present invention aims to provide an adaptive hierarchical method for preventing feature shift of a 3D printing model, which is used to solve the problems of step effect, feature shift and loss in the prior art.
To achieve the above and other related objects, the present invention provides an adaptive layering method for preventing feature shift of a 3D printing model, the adaptive layering method for preventing feature shift of a 3D printing model, comprising: establishing a three-dimensional model, and carrying out gridding processing on the three-dimensional model to generate an STL file; reading the STL file, and carrying out preprocessing operation on the data read from the STL file to obtain preprocessed data; identifying the characteristic height on the three-dimensional model after gridding processing by using the preprocessed data to obtain a group of height data h; adjusting the distance between adjacent feature heights, namely adjusting the height data h; carrying out layered slicing at the positions of the feature heights, and carrying out self-adaptive layering between adjacent feature heights by adopting a tip height method to obtain slice profile information; and generating a printing file according to the slice outline information and the G code format, and printing the 3D model.
In an embodiment of the present invention, the files stored in the three-dimensional model include an STL file, an AMF file, an OBJ file, a STEP file, a 3MF file, an IGES file, a LEAF file, an RPI file, and an RP file.
In an embodiment of the present invention, the identifying the feature height on the three-dimensional model to obtain a set of height data includes:
the basic features of the three-dimensional model comprise feature points, feature lines and feature surfaces;
the characteristic surface is a triangular surface patch parallel to the layering plane, and when the Z coordinates of three vertexes of the triangular surface patch are the same, the triangular surface patch is judged to be the characteristic surface, and the characteristic height is the Z coordinate of one of the three vertexes of the triangular surface patch;
the characteristic line, two adjacent triangular patches have and only have the same Z coordinate of two common vertexes, and the dihedral angle of these two triangular patches is greater than the threshold value, the connecting line between two vertexes is the characteristic edge, the characteristic height is the Z coordinate of a certain vertex on the characteristic edge, the dihedral angle is calculated and obtained through the normal vector of two adjacent triangular patches, the threshold value is confirmed through the formula (1):
wherein the content of the first and second substances,
the method comprises the following steps that a characteristic edge threshold value is adopted, beta is the mean value of dihedral angles corresponding to all grid edges in an STL file, lambda = log (facetress), and the facetress is a control parameter for the accuracy of a generated STL grid model in a CAD model;
and if the Z coordinate of one vertex P of one triangular patch is higher or lower than the Z coordinates of the other two vertexes of all triangular patches taking the vertex P as the vertex, the vertex P is taken as the characteristic point, and the characteristic height is taken as the Z coordinate of the vertex P.
In an embodiment of the present invention, adjusting the distance between adjacent feature heights, that is, adjusting the height data h, includes:
preprocessing a group of height data h, respectively inserting layer height data with the height of 0 and layer height data with the maximum height of the three-dimensional model into the head and the tail of the height data h, respectively detecting whether the distance between the two boundary layer heights and the adjacent layer height is smaller than the minimum layer thickness, if so, adjusting the adjacent layer height to enable the distance between the boundary layer height and the adjacent layer height to be equal to the minimum layer thickness, sequencing the height data h in an ascending order again, detecting whether the layer height exists between the adjusted layer height and the corresponding boundary layer height, and if so, deleting the existing layer height;
given the maximum layer thickness h of a 3D printer max And minimum delamination thickness h min Checking the feature heights between the boundary layer heights by adopting a one-by-one traversal method, searching whether the distance between two adjacent feature heights is smaller than the minimum layer thickness, if so, adjusting the two adjacent feature heights to obtain a feature height adjusting result, wherein the feature height adjusting method specifically comprises the following steps:
the height difference between two adjacent feature heights is d;
inward merging: if d is less than or equal to h min 2, shifting the two sliced layers inwards by d/2, namely combining the two layers;
outward expansion: if d > h min And/2, respectively shifting the two sliced layers outwards by | d-h min |/2；
According to the characteristic height adjusting result, four adjacent layer heights, namely two adjacent characteristic heights b and c for adjustment and the maximum height difference d of two layer heights a and f respectively adjacent to the two adjacent characteristic heights b and c for adjustment max Judging whether two adjacent feature heights b and c have influence on two layer heights a and f adjacent to the two adjacent feature heights b and c after the height adjustment of inward deviation or outward deviation is carried out, if so, carrying out height adjustment aiming at different situations of inward merging, outward expansion and feature density, wherein the height adjustment method comprises the following steps:
inward combination for height adjustment;
two adjacent characteristic heights b and c in the middle are merged inwards, and the layer height difference between the merged layer height e and the two adjacent layer heights is d 1 And d 2 In (b), at least one is still less than the minimum delamination thickness h min ；
1) If h min ≤d max ＜2·h min Then d is 1 And d 2 Are all less than h min If yes, deleting the merged layer height e;
2) If d max ≥2·h min Then d is 1 And d 2 In is only one less than h min If is d 1 Adjusting the combined layer height e so that d 1 ＝h min (ii) a If is d 2 Adjust the combined layer height e so that d 2 ＝h min ；
Expanding outwards to adjust the height;
two adjacent characteristic heights b and c in the middle are expanded outwards, and the layer height difference d between the two shifted layer heights and the layer heights of the adjacent layer 1 And d 2 In (e), at least one remains less than the minimum delamination thickness h min ；
1) If d max ＜3·h min Then d is a 1 And d 2 Are all less than h min Outward expansion is changed into inward combination, and height adjustment treatment is carried out according to the inward combination;
2) If d max ≥3·h min Then d is 1 And d 2 Only one of which is less than h min If it is d 1 Adjusting the height of the expanded layer to keep the distance between the layers as h min While d is being caused 1 ＝h min (ii) a If it is d 2 Adjusting the height of the expanded layer to keep the distance between the layers as h min While d is being caused 2 ＝h min ；
Carrying out height adjustment on the dense features;
the height difference d between the highest layer height and the lowest layer height in four continuous adjacent layer heights is less than the minimum layered thickness h min Deleting the middle layer height, respectively searching the adjacent layer heights of the highest layer height and the lowest layer height in the four layer heights, judging the four layer heights again, and if the problems of inward combination, outward expansion and dense features still exist, using corresponding height adjustment to process; and if the problems of inward combination, outward expansion and dense features do not exist, ending the height adjustment and searching the subsequent layer height.
In an embodiment of the present invention, adjusting the distance between adjacent feature heights, that is, adjusting the height data h, includes: the feature density is that in a group of height data h, three existAnd (c) continuous feature heights, the height difference between the highest layer height and the lowest layer height being less than the minimum layer thickness h min 。
In an embodiment of the present invention, the slicing at the feature heights in a hierarchical manner, and the adaptively layering between adjacent feature heights by using a tip height method, wherein the obtaining of the slice profile information includes:
sequentially taking out two adjacent heights from the adjusted height data h, and carrying out self-adaptive layering on the model between the two adjacent heights by adopting a tip height method, wherein the tip height method is the maximum distance between the surface of the actually manufactured part and the surface of the CAD model, a triangular surface patch of the STL grid model is the inclined side of a right-angled triangle, and the height on the inclined side is the tip height d;
the calculation method of the vertical upward right-angle side of the right-angle triangle is as follows:
wherein h is the layering thickness of the current layer,
is the normal vector of the triangular patch,
in the layering direction, vertically upwards, theta is
And
the included angle of (3) is in the range of 0-pi;
traversing all the triangular patches of the STL mesh model as hierarchical planes, and finding out the minimum hierarchical thickness h min If the minimum layer thickness h min Below or above the printing range of the 3D printer, the minimum lamination thickness h will be min A minimum layer thickness or a maximum layer thickness instead; will minimum lamination thickness h min Adding the height l of the layering plane, namely the height on the hypotenuse of the right triangle, to obtain the height l' = h + l of the current layering plane until a series of layer heights for self-adaptive layering of the STL mesh model are obtained;
when adaptive layering is performed between two adjacent feature heights a and b, when d is less than 2 · h min When the distance is too small, the self-adaptive layering cannot be carried out, and the self-adaptive layering between the a and the b is finished; d represents the height difference between two adjacent feature heights; when d is more than or equal to 2. H min When the height of the layered plane is determined, the distance d 'between the current layered plane and the b is calculated, and if the distance d' is smaller than the minimum layered thickness h min Then, the layer height of the layered plane is adjusted so that d' = h min (ii) a The distance between the layered plane and the adjacent layered plane is less than the minimum layered thickness h min Then the hierarchical plane is deleted.
As described above, the adaptive layering method for preventing feature shift of a 3D printing model according to the present invention has the following advantages:
the self-adaptive layering method for preventing the 3D printing model characteristic offset ensures that the layering plane passes through the position of the model characteristic, thereby retaining the three-dimensional model characteristic, effectively preventing the characteristic offset and loss caused by the layer-by-layer accumulation of materials in the 3D printing model printing process, and reducing the step error.
The invention gives consideration to the surface precision and the printing efficiency of the printed matter, and reduces the layering number as much as possible by the top height self-adaptive layering method on the premise of ensuring the printing precision, thereby reducing the memory occupation and the processing time and improving the printing processing efficiency.
The invention provides a characteristic height identification method and a characteristic height interval adjustment method, which can reduce the step effect of a machined part as much as possible and improve the machining quality.
The method is simple and efficient, and has strong universality and practicability and wide application range.
Drawings
Fig. 1 is a schematic flowchart of an adaptive layering method for preventing feature shifting of a 3D printing model according to an embodiment of the present application;
FIG. 2 is a three-dimensional model provided in an embodiment of the present application, where 1, 2, and 3 are corresponding features;
FIG. 3 is a diagram of model features provided in an embodiment of the present application, including feature planes, feature lines, and feature points;
FIG. 4 is an inward-merge schematic diagram of a feature height adjustment method provided by an embodiment of the present application;
FIG. 5 is an outward expansion schematic view of a feature height adjustment method provided in an embodiment of the present application;
FIG. 6 is a schematic diagram illustrating the inward merge problem after feature height adjustment provided by an embodiment of the present application;
FIG. 7 is a schematic diagram illustrating the outward expansion problem after feature height adjustment provided by an embodiment of the present application;
FIG. 8 is a schematic diagram illustrating a feature crowding problem after feature height adjustment according to an embodiment of the present application;
FIG. 9 is a schematic diagram of a solution to the inward merge problem after adjustment provided by an embodiment of the present application;
FIG. 10 is a schematic illustration of a solution to the problem of outward flare after adjustment provided by an embodiment of the present application;
FIG. 11 is a schematic diagram of a solution to the feature crowding problem after adjustment provided by an embodiment of the present application;
fig. 12 is a schematic view of the height of the tip provided by an embodiment of the present application;
FIG. 13 is a graph of the layering results of the uniform-thickness layering method provided in the embodiment of the present application at a feature corresponding to 1 of the three-dimensional model in FIG. 2;
FIG. 14 is a diagram of a layering result of an adaptive layering method provided in an embodiment of the present application at a feature corresponding to 1 of the three-dimensional model in FIG. 2;
FIG. 15 is a diagram of a layering result of an adaptive layering method for preventing feature shift of a 3D printing model at a feature corresponding to 1 of the three-dimensional model in FIG. 2 according to an embodiment of the present application;
FIG. 16 is a graph of the layering results of the uniform-thickness layering method provided in the embodiment of the present application at a feature corresponding to 2 of the three-dimensional model in FIG. 2;
fig. 17 is a diagram of a layering result of an adaptive layering method provided in an embodiment of the present application at a feature corresponding to 2 of the three-dimensional model in fig. 2;
FIG. 18 is a graph of the layering result of the adaptive layering method for preventing feature shift of a 3D printing model at 2 corresponding features of the three-dimensional model in FIG. 2 according to the embodiment of the present application;
FIG. 19 is a graph of the layering results of the uniform-thickness layering method provided in the embodiment of the present application at the feature position corresponding to 3 of the three-dimensional model in FIG. 2;
FIG. 20 is a graph of the layering results of the adaptive layering method provided in the embodiment of the present application at feature 3 of the three-dimensional model in FIG. 2;
fig. 21 is a diagram of a layering result of the adaptive layering method for preventing feature shift of a 3D printing model at a feature corresponding to 3 of the three-dimensional model in fig. 2 according to the embodiment of the present application.
Description of the element reference numerals
S1 to S6
Detailed Description
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention. It is to be noted that the features in the following embodiments and examples may be combined with each other without conflict.
It should be noted that the drawings provided in the following embodiments are only for illustrating the basic idea of the present invention, and the components related to the present invention are only shown in the drawings rather than drawn according to the number, shape and size of the components in actual implementation, and the type, quantity and proportion of the components in actual implementation may be changed freely, and the layout of the components may be more complicated.
The method is realized in a Visual Studio2017 development environment by using a C + + language, the maximum and minimum layering thicknesses are set to be 0.1mm and 0.3mm according to the precision of an actual machine, and the center height is set to be 0.1mm according to the required precision. The flow chart of the improved adaptive hierarchical algorithm of the invention is shown in fig. 1 in combination with the top adaptive hierarchical method. In order to further explain the superiority of the method, the number of layering layers and characteristic offset obtained by comparing and analyzing the equal-thickness layering and the self-adaptive layering with the improved self-adaptive layering method are compared, and the layering method provided by the invention can verify the height of the characteristic, can effectively prevent the characteristic offset and loss of the model, reduce the step error, and can carry out self-adaptive layering at the position except the height of the characteristic, thereby reducing the number of layering while ensuring the surface quality of a printed product, improving the processing efficiency and providing the self-adaptive layering method for preventing the characteristic offset of the 3D printing model for the practical application of 3D printing. The default layering direction of the invention is the same as the positive direction of the Z axis of the rectangular coordinate system where the vertexes of the model triangular patch are located. If the layering direction is different from the default direction, the method provided by the invention can be used only by converting the three-dimensional coordinates of the vertexes of all the triangular patches of the model into a rectangular coordinate system taking the layering direction as the positive direction of the Z axis.
According to actual requirements, generating a three-dimensional model by using three-dimensional computer aided design software, wherein circled 1, 2 and 3 are characteristic positions corresponding to the three-dimensional model, and gridding the three-dimensional model to generate specific STL format file data, as shown in figure 2.
Reading the STL file, adjusting the Z coordinate of the vertex, sequencing the triangular patches, calculating the dihedral angle threshold of the characteristic line, and performing a series of preprocessing operations, wherein the preprocessing operations comprise the following steps:
reading STL files
And reading in model data according to the STL format, and removing redundant data by adopting a hash table. The vertices of the triangular patch are stored in the Point class, containing the three-dimensional coordinates of the vertices. The triangular patch is stored in the Face class and contains information of a vertex and an adjacent triangular surface. In order to complete the discrimination of all the characteristics through one traversal, a decision variable is added into a Point class and three decision variables are added into a Face class, the decision variables respectively correspond to three edges of a triangular surface, and the decision variables represent whether the vertex or the edge of the triangular surface is judged. An STL model is represented by Mesh class, and includes all vertex information (vector < Point > points) and triangular surface information (vector < Face > faces).
Adjusting vertex Z coordinate
Because of the minimum Z in all vertex Z coordinates on the three-dimensional model min May not be 0 and the method of the invention is used with the proviso that Z min Is 0, all the vertices of the three-dimensional model need to be traversed to ensure the correctness of the method, if Z is min If not 0, the adjustment is made. The adjusting method comprises the following steps: finding Z of model min Calculating the offset delta =0-Z min Then Δ is added to the Z coordinates of all vertices of the model.
Triangular patch sorting
Because the apex height method needs to traverse all the triangular planes intersected with the last hierarchical plane, in order to reduce the time for searching the triangular surface patch, the faces in the Mesh are sorted, and the faces are arranged in an ascending order according to the minimum Z coordinate value in the vertex of the triangular surface. At the moment, only the corner mark a of the triangular surface, in which the minimum Z coordinate value of the first vertex in the faces is less than or equal to the given height and the maximum Z coordinate value is greater than or equal to the given height, is needed to be found; and finding the corner mark b of the triangular surface with the first vertex minimum Z coordinate value larger than the given height, wherein the triangular surface to be found is the triangular surface in the range of the corner mark [ a, b) in the faces.
Calculating dihedral angle thresholds for feature lines
When calculating the threshold of the feature line, it is necessary to obtain the mean β of the dihedral angles corresponding to all the mesh edges in the STL model. In order to calculate the β value, it is necessary to traverse the dihedral angles corresponding to the three edges of all the triangular surfaces, and then obtain the sum of all the dihedral angles and divide the sum by the number of total edges to obtain β. However, since one side is shared by two triangular surfaces, the calculation may be repeated, and therefore, after one side is calculated, the determination variable corresponding to the side of each of the three determination variables of the two triangular surfaces related to the side needs to be set to be true. After the value of β is calculated, all the decision variables in all the triangular surfaces are set to false so as not to affect the subsequent decision of the feature edge.
Judging the characteristics of a triangular surface, an edge, a vertex and the like on the model, identifying the height of the characteristics to obtain a group of ordered height data, and determining the height of the characteristics specifically comprises the following steps:
(1) And finishing the judgment of all the characteristics of the triangular surface, the edge, the vertex and the like in the model by traversing the faces in the Mesh once. The model features refer to the parts of the three-dimensional model which can represent the shape characteristics of the model and have non-smooth transition. The model shown in fig. 3 includes basic features including feature points, feature lines, and feature planes. When a certain triangular surface is traversed, judging the characteristic surface, the characteristic line and the characteristic point of the triangular surface, the edge and the vertex in sequence, and if one of the characteristic surfaces is judged to be true, not carrying out subsequent judgment; and if the feature height obtained later is not in the feature height sequence h, storing the feature height into h. The specific method for identifying the characteristic surface, the characteristic line and the characteristic point is as follows:
the characteristic surface is as follows: the triangular patches parallel to the layering plane are feature planes, such as 3 and 4 in fig. 3. Then when the three vertex Z coordinates of the triangular patch are the same, the triangular patch is determined to be a feature plane, and the feature height is the Z coordinate of one vertex.
Characteristic line: two surface intersecting lines with included angles larger than a specified threshold value and not being characteristic surfaces are characteristic lines, and the intersecting lines are perpendicular to the layering direction, as shown in fig. 3 1, 2, 5 and 6. Two adjacent triangular patches have the same Z coordinate of only two common vertexes, the dihedral angles of the two triangular patches are larger than a certain threshold value, and the characteristic height is the Z coordinate of a certain vertex on the characteristic edge. The dihedral angle can be obtained by calculating the normal vector of two triangular surfaces, the characteristic edge threshold value is determined by the following formula,
wherein the content of the first and second substances,
the method comprises the following steps that a characteristic edge threshold value is adopted, beta is the mean value of dihedral angles corresponding to all grid edges in an STL file, lambda = log (facetress), and the facetress is a control parameter for the accuracy of a generated STL grid model in a CAD model;
the characteristic points are as follows: in the layering direction, the local highest or lowest point is a feature point, such as 7 in fig. 3. When the Z coordinate of the vertex P is higher or lower than the Z coordinates of the other two vertexes of the triangular surface taking the vertex P as the vertex, the vertex P is a characteristic point, and the characteristic height is the Z coordinate of the vertex P.
(2) After the characteristic judgment is finished, setting the judgment variables in the three vertex points of the triangular surface as true; setting three judgment variables in the triangular surface to be true; and setting the decision variable corresponding to the corresponding edge in the other three triangular surfaces respectively related to the three edges as true. Meanwhile, in the determination process, if the determination variable in the vertex Point is true or the determination variable corresponding to a certain side in the triangular surface is true, the vertex or the side is not determined and the subsequent operation is performed.
(3) And circulating the characteristic judgment process until the traversal is finished. And finally, sequencing the characteristic height sequence h in an ascending order.
And (4) adjusting the distance between adjacent feature heights, namely adjusting the feature height sequence h in the step (3) to avoid feature deviation and loss, and specifically comprising the following steps:
(1) Firstly, the ordered characteristic height sequence h is preprocessed. The 3D printer has maximum and minimum printable thicknesses, also called maximum layered thickness h max And minimum delamination thickness h min . If the model has more dense features in a certain height intervalThen, in an ordered set of height data obtained after identifying and positioning the features, it may happen that the height difference d between two adjacent heights is smaller than the minimum layering thickness h min . Since the printing is stacked from low to high, the contour information on the higher level of the hierarchy cannot be printed, so that both heights need to be adjusted. In order to ensure that the printed model height is unchanged and the first and last layers can be printed, the ordered feature height sequence h needs to be preprocessed. The pretreatment method comprises the following steps: first, layer height data with height 0 and maximum model height are inserted into the head and tail of the sequence h (these two layer heights are called boundary layer heights). And then respectively detecting whether the distance between the height of the two boundary layers and the height of the adjacent layer is smaller than the minimum layer thickness, if so, adjusting the height of the adjacent layer to enable the distance to be equal to the minimum layer thickness. And re-ascending the sequence h, detecting whether layer heights exist between the adjusted layer heights and the corresponding boundary layer heights, and if so, deleting the layer heights.
(2) After the pretreatment is finished, the ordered characteristic height sequence h is checked by adopting a one-by-one traversal method, whether two adjacent heights with the distance smaller than the minimum layer thickness and the other two adjacent heights exist or not is searched, and the maximum height difference d of the four adjacent layer heights (the two layer heights with the height difference smaller than the minimum layer thickness and the other adjacent layer height of the two layer heights) is calculated max And determines whether it needs to perform an inward merge or outward flare operation, adjusting both heights. The adjustment method is shown in fig. 4 and 5, and the specific operation process is as follows:
inward merging: if the height difference d is less than or equal to h min And/2, shifting both slicing layers inwards by d/2, namely combining the two layers.
Outward expansion: if the height difference d is greater than h min And/2, respectively shifting the two sliced layers outwards min |/2。
(3) Then, the height adjustment result and the height difference d are determined according to the determined height max And judging whether the two adjacent feature heights have influence on the respective adjacent heights after the height adjustment of inward combination or outward expansion is carried out. Wherein two adjusted heights up and down may still be possibleWith other adjacent feature heights, the adjusted height may affect the adjacent upper and lower feature heights, and the effect is shown in fig. 6, 7, and 8:
after inward combination, the layer height difference d between the combined layer height a and the two adjacent layer heights b and c 1 、d 2 At least one is still less than the minimum delamination thickness.
After outward expansion, the layer height difference d of the two layer heights a and b after deviation and the layer heights c and d of the adjacent layers respectively 1 、d 2 At least one is still less than the minimum delamination thickness.
The feature heights are too dense, and the difference d between the highest layer height and the lowest layer height in three or four consecutive adjacent heights is still less than the minimum delamination thickness.
(4) And finally, performing corresponding adjustment according to the height adjustment result judged in the step (2) and the judgment of the influence of the step (3) on the respective adjacent heights. If there is an effect, then adjustments are made for different situations where inward merging, outward dilation, and features are too dense. Four adjacent layer heights (two layer heights with a height difference smaller than the minimum layer thickness and the other adjacent layer height of each of the two layer heights) having the above three problems are taken out as shown in fig. 9, 10 and 11, and then adjusted accordingly according to the different problems. The specific influence expression and the corresponding processing method are as follows:
inward merging problems and processing methods:
a. if h min ≤d max ＜2·h min D after merging the two middle layer heights b and c 1 And d 2 Are all less than h min In order not to affect other feature heights, directly deleting the combined layer height e;
b. if d is max ≥2·h min D after merging the two middle layer heights b and c 1 And d 2 Only one of which is less than h min Let us assume d 1 Adjusting the combined layer height e so that d 1 ＝h min 。
Outward expansion problem and processing method:
a. if d is max ＜3·h min Then the two layer heights b and c, d after outward expansion 1 And d 2 Are all less than h min In order to not influence other feature heights, the layer heights needing to be adjusted can only be combined, at the moment, the outward expansion problem is converted into the inward combination problem, and the inward combination problem is processed according to an inward combination problem processing method;
b. if d is max ≥3·h min After expanding the two layer heights b and c outward, d 1 And d 2 Only one of which is less than h min Assume to be d 1 Adjusting the height b of the expanded layer while keeping the distance h between the layers min While d is being caused 1 ＝h min 。
The problem of excessively dense feature height and a processing method are as follows:
the feature heights are too dense, and the difference d between the highest layer height and the lowest layer height in three or four consecutive adjacent heights is still less than the minimum delamination thickness. d max ＜h min In order to not affect other feature heights, directly deleting the middle layer height, then respectively searching the adjacent layer heights of the original four layer heights, namely the highest layer height and the lowest layer height, judging the four layer heights again, and if the three problems still exist, processing by using a corresponding solution method; if not, the adjustment is ended, and the subsequent layer height is continuously searched.
After slicing is carried out on the feature heights in a layering mode, self-adaptive layering is carried out between every two adjacent feature heights by adopting a tip height method, and slice outline information is obtained. Wherein, the tip height method is described as follows:
the feature height refers to a series of values obtained after the steps S3 and S4, and these values represent the height from the bottom of the model, that is, the height of the model feature relative to the bottom of the model. It is a constant value, not an interval.
Layering or slicing means that an infinite plane (called a layering plane) is intersected with a model at a certain position of the model to obtain required contour information of the model, namely, a knife is used for cutting the model to obtain a very flat cross section, and the contour of the cross section is the information required by the user. This plane is perpendicular to the layering direction, but is generally vertical up by default, so this plane is generally horizontal. If the layering direction is not vertical, the model can be rotated to make the layering method vertical, and the method of the invention can also be used.
Layering at the characteristic height, namely intersecting a horizontal plane with the characteristic height, which is the vertical distance from the horizontal plane at the bottom of the model, with the model to obtain the contour information at the position.
In order to take account of the surface precision and the processing efficiency of the machined part and ensure that the model between the feature heights does not need to consider the feature problem, the model of the part is directly subjected to self-adaptive layering by adopting a tip height method. The tip height refers to the maximum distance between the surface of the actual manufactured part and the surface of the CAD model, as shown in fig. 12. BC is a triangular patch of the STL model, AB and AC are surfaces of the printed matter, AC is also a last layering plane, h is the layering thickness of the current layer,
is a normal vector of the triangular patch,
in the direction of the stratification, theta is
And
the included angle of (d) is 0-pi, and d is the height of the center. The corresponding layer height calculation method is shown in the following formula. All triangular patches intersected by the hierarchical plane BC are traversed to find the minimum h, which is changed to the minimum or maximum layer thickness if h is below or above the printable range. Then, the height l of the layering plane BC is added to h to obtain the height l' = h + l of the current layering plane. Looping through this step results in a series of layer heights for the model adaptation layering.
Note that the pitch problem of a and b is also noted when adaptive layering is performed between two adjacent feature heights a and b (let b be higher than a).
(1) When d is less than 2. H min When the distance is too small, layering cannot be carried out, and self-adaptive layering between a and b is finished;
(2) When d is more than or equal to 2. H min During the process, adaptive layering can be performed between a and b, but each time the height of the layered plane is determined, the distance d ' from the current layered plane to b needs to be calculated, and if the distance d ' is smaller than the minimum layered thickness, the height of the layered plane is adjusted, so that d ' = h min (ii) a And if the distance between the layered plane and the adjacent layered plane after adjustment is less than the minimum layered thickness, deleting the layered plane.
And generating a corresponding printing file according to the slicing format, and printing the 3D model. Selecting 5 models, and layering by respectively using an equal-thickness layering method, a self-adaptive layering by a tip height method and an improved self-adaptive layering method, wherein the maximum and minimum layering thicknesses are respectively set to be 0.1mm and 0.3mm, the tip height is set to be 0.1mm, and in order to minimize the characteristic offset of the model generated by the equal-thickness layering, the thickness of the equal-thickness layering is 0.1mm, the results shown in table 1 are obtained, and the table 1 is the layering number result of three layering methods.
TABLE 2
As can be seen from the layering results of the 5 models in Table 1, the number of layers obtained by the self-adaptive layering and the method of the invention is less than that of the equal-thickness layering. A great deal of research proves that the self-adaptive layering method can effectively improve the processing efficiency, and the improved self-adaptive method is similar to the traditional self-adaptive method in the layering number, so that the self-adaptive layering method can effectively reduce the layering number between two characteristic heights, and can improve the processing efficiency to a certain extent on the premise of ensuring the surface precision. In addition, when the number of feature heights is small, the method of the invention is similar to the result of self-adaptive layering, such as the layering result of models 1-3 in table 1; with the increase of the feature height, the number of layers obtained by the method is less than that obtained by self-adaptive layering, and the processing efficiency is further improved. This is because the method of the present invention, in order to ensure that the contours at feature heights can be printed, employs tip height method adaptive layering in the portions between feature heights, which may cause the spacing of the layering planes adjacent to and below the plane in which the feature height lies to be close to twice the minimum layering thickness, and thus one less layering plane compared to adaptive layering. As the number of feature heights increases, the number of occurrences of this situation increases, and thus the number of layers obtained by the method of the present invention is significantly less than the number of layers obtained by adaptive layering. The reduction of the layering number can save the occupied space of the memory and the processing time for subsequent software processing and design processing, and improve the processing efficiency. The height adjusting method ensures that the layering position passes through the characteristic height, can effectively prevent the characteristic from deviating and losing, and improves the processing quality.
In addition, taking the three-dimensional model in fig. 2 as an example, three features are selected for comparison, and the detailed results are shown in fig. 13 to fig. 21, the feature offset is shown in table 2, table 2 is the offset of the three layering methods, and the minimum maximum value of the given Z coordinate in the experiment is 0mm and 54mm respectively. Three layering methods were separately: the contour information obtained by the method is stored in SLC format files, and then the three files and the STL file of the original model are respectively led into Materialise Magics software together, so that the coordinate system of the model is completely superposed with the coordinate system of the contour, and the offset of the model characteristic is obtained by measurement.
TABLE 2
From the feature offset details of features 1-3 shown in fig. 13-21, it is evident that the method of the present invention produces no offset and, in addition, because the slice plane passes through the feature height position, there is no feature loss problem. The results in Table 2 show that the characteristic offsets processed by the method are all 0mm, and the equal-thickness layering and the self-adaptive layering have different degrees of offset, so that the method is further explained to be superior to other methods, and the improved self-adaptive layering method can effectively prevent the offset and loss of the model characteristics and reduce the step error.
In conclusion, the self-adaptive layering method for preventing the characteristic offset of the 3D printing model ensures that the layering plane passes through the position of the model characteristic, thereby retaining the three-dimensional model characteristic, effectively preventing the characteristic offset and loss caused by the layer-by-layer accumulation of materials in the 3D printing model printing process, and reducing the step error.
The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Those skilled in the art can modify or change the above-described embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which may be made by those skilled in the art without departing from the spirit and scope of the present invention as defined in the appended claims.
Claims (5)
1. An adaptive layering method for preventing feature migration of a 3D printing model, which is characterized by comprising the following steps:
establishing a three-dimensional model, and carrying out gridding processing on the three-dimensional model to generate an STL file;
reading the STL file, and carrying out preprocessing operation on the data read from the STL file to obtain preprocessed data;
identifying the characteristic height on the three-dimensional model after gridding treatment by using the preprocessed data to obtain a group of height data h;
adjusting the distance between adjacent characteristic heights, namely adjusting the height data h;
carrying out layered slicing at the positions of the feature heights, and carrying out self-adaptive layering between adjacent feature heights by adopting a tip height method to obtain slice profile information;
generating a printing file according to the slice outline information and the G code format, and printing a 3D model;
wherein the identifying the feature height on the three-dimensional model to obtain a set of height data comprises:
the basic features of the three-dimensional model comprise feature points, feature lines and feature surfaces;
the characteristic surface is a triangular surface patch parallel to the layering plane, and when the Z coordinates of three vertexes of the triangular surface patch are the same, the triangular surface patch is judged to be the characteristic surface, and the characteristic height is the Z coordinate of one vertex of the three vertexes of the triangular surface patch;
the characteristic line, two adjacent triangular patches have and only have the same Z coordinate of their two common vertexes, and the dihedral angle of these two triangular patches is greater than the threshold value, the line between two vertexes is the characteristic edge, the characteristic height is the Z coordinate of a certain vertex on the characteristic edge, the dihedral angle is calculated and obtained through the normal vector of two adjacent triangular patches, the threshold value is confirmed through the formula (1):
wherein, the first and the second end of the pipe are connected with each other,
the method comprises the steps that a characteristic edge threshold value is adopted, beta is the mean value of dihedral angles corresponding to all grid edges in an STL file, lambda = log (Facetres) is adopted, and the Facetres is a control parameter for the accuracy of a generated STL grid model in a CAD model;
and if the Z coordinate of one vertex P of one of the triangular patches is higher or lower than the Z coordinates of the other two vertexes of all the triangular patches taking the vertex P as the vertex, the vertex P is taken as the characteristic point, and the characteristic height is taken as the Z coordinate of the vertex P.
2. The adaptive hierarchical method for preventing feature shift of 3D printing model according to claim 1, characterized in that: the files stored in the three-dimensional model comprise an STL file, an AMF file, an OBJ file, a STEP file, a 3MF file, an IGES file, a LEAF file, an RPI file and an RP file.
3. The adaptive layering method for preventing feature shift of a 3D printing model according to claim 1, wherein adjusting the distance between adjacent feature heights, namely adjusting the height data h, comprises:
preprocessing a group of height data h, respectively inserting layer height data with the height of 0 and layer height data with the maximum height of a three-dimensional model into the head and the tail of the height data h, respectively detecting whether the distance between the two boundary layer heights and the adjacent layer height is less than the minimum layer thickness, if so, adjusting the adjacent layer height to enable the distance between the boundary layer height and the adjacent layer height to be equal to the minimum layer thickness, sequencing the height data h in an ascending order again, detecting whether the layer height exists between the adjusted layer height and the corresponding boundary layer height, and if so, deleting the existing layer height;
given the maximum layer thickness h of the 3D printer max And a minimum delamination thickness h min Checking the feature heights between the boundary layer heights by adopting a one-by-one traversal method, searching whether the distance between two adjacent feature heights is smaller than the minimum layer thickness, if so, adjusting the two adjacent feature heights to obtain a feature height adjusting result, wherein the feature height adjusting method specifically comprises the following steps:
the height difference between two adjacent feature heights is d;
inward merging: if d is less than or equal to h min 2, shifting the two slicing layers inwards by d/2, namely combining the two layers;
outward expansion: if d > h min And/2, respectively shifting the two sliced layers outwards min |/2；
According to the characteristic height adjusting result, four adjacent layer heights, namely two adjacent characteristic heights b and c for adjustment and the maximum height difference d of two layer heights a and f respectively adjacent to the two adjacent characteristic heights b and c for adjustment max Judging whether two adjacent feature heights b and c have influence on two layer heights a and f adjacent to the two adjacent feature heights b and c after the height adjustment of inward deviation or outward deviation is carried out, if so, carrying out height adjustment aiming at different situations of inward merging, outward expansion and feature density, wherein the height adjustment method comprises the following steps:
inward combination for height adjustment;
inwardly merging two adjacent characteristic heights b and c in the middle, wherein the layer height difference between the merged layer height e and the two adjacent layer heights is d 1 And d 2 In (e), at least one remains less than the minimum delamination thickness h min ；
1) If h min ≤d max ＜2·h min Then d is 1 And d 2 Are all less than h min If yes, deleting the merged layer height e;
2) If d max ≥2·h min Then d is a 1 And d 2 In is only one less than h min If is d 1 Adjusting the combined layer height e so that d 1 ＝h min (ii) a If it is d 2 Adjust the combined layer height e so that d 2 ＝h min ；
Expanding outwards to adjust the height;
two adjacent characteristic heights b and c in the middle are expanded outwards, and the layer height difference d between the two layer heights after the displacement and the layer height of the adjacent layer 1 And d 2 In (e), at least one remains less than the minimum delamination thickness h min ；
1) If d max ＜3·h min Then d is a 1 And d 2 Are all less than h min Outwardly expanding the rotorChanging into inward combination, and performing height adjustment processing according to the inward combination;
2) If d max ≥3·h min Then d is 1 And d 2 In is only one less than h min If it is d 1 Adjusting the height of the expanded layer to keep the distance between the layers as h min While d is being caused 1 ＝h min (ii) a If is d 2 Adjusting the height of the expanded layer to keep the distance between the layers as h min At the same time, make d 2 ＝h min ；
Carrying out height adjustment on the dense features;
the height difference d between the highest layer height and the lowest layer height of four continuously adjacent layer heights is less than the minimum layered thickness h min Deleting the middle layer height, respectively searching the adjacent layer heights of the highest layer height and the lowest layer height in the four layer heights, judging the four layer heights again, and if the problems of inward combination, outward expansion and dense features still exist, using corresponding height adjustment to process; and if the problems of inward combination, outward expansion and dense features do not exist, finishing the height adjustment and searching the subsequent layer height.
4. The adaptive layering method for preventing feature shift of a 3D printing model according to claim 3, wherein the adjusting the distance between adjacent feature heights, namely adjusting the height data h, comprises: the feature density is that in a group of height data h, three or more continuous feature heights exist, and the height difference between the highest layer height and the lowest layer height is smaller than the minimum layering thickness h min 。
5. The adaptive layering method for preventing feature shift of a 3D printing model according to claim 3 or 4, wherein layered slicing is performed at the feature heights, adaptive layering is performed between adjacent feature heights by using a tip height method, and obtaining slice profile information comprises:
sequentially taking out two adjacent heights from the adjusted height data h', and carrying out self-adaptive layering on a model between the two adjacent heights by adopting a centre height method, wherein the centre height method is the maximum distance between the surface of the actually manufactured part and the surface of the CAD model, a triangular surface patch of the STL grid model is the inclined edge of a right-angled triangle, and the height on the inclined edge is the centre height d;
the calculation method of the vertical upward right-angle side of the right-angle triangle is as follows:
wherein h is the layering thickness of the current layer,
is the normal vector of the triangular patch,
in the layered direction, vertically upwards, theta is
And
the included angle of (3) is in the range of 0-pi;
traversing all the triangular patches of the STL mesh model as hierarchical planes, and finding out the minimum hierarchical thickness h min If the minimum lamination thickness h min Below or above the printing range of the 3D printer, the minimum lamination thickness h will be min A minimum layer thickness or a maximum layer thickness instead; will minimum lamination thickness h min Adding the height l of the layering plane, namely the height on the hypotenuse of the right triangle, to obtain the height l' = h + l of the current layering plane until a series of layer heights for self-adaptive layering of the STL mesh model are obtained;
when adaptive layering is performed between two adjacent feature heights a and b, when d is less than 2 · h min When the distance is too small, the self-adaptive layering cannot be carried out, and the self-adaptive layering between the a and the b is finished; d represents the height difference between two adjacent feature heights; when d is more than or equal to 2. H min When the height of the layering plane is determined, the distance d 'from the current layering plane to the b is calculated, and if the distance d' is smaller than the minimum layering thickness h min Then, the layer height of the layered plane is adjusted so that d' = h min (ii) a The distance between the layered plane and the adjacent layered plane is less than the minimum layered thickness h min Then the hierarchical plane is deleted.
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| CN111730057A (en) * | 2020-06-01 | 2020-10-02 | 成都飞机工业（集团）有限责任公司 | Powder feeding type 3D printing layered modeling method |
| CN112182677A (en) * | 2020-09-17 | 2021-01-05 | 上海漫格科技有限公司 | Interactive variable-layer thickness slicing method in three-dimensional printing |
| CN113158270A (en) * | 2021-03-15 | 2021-07-23 | 电子科技大学 | Additive manufacturing self-adaptive composite layered slicing method |
| CN113276420B (en) * | 2021-04-29 | 2021-11-26 | 广东海洋大学 | 3D printing method and system based on machine vision |
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| CN114454487B (en) * | 2022-02-14 | 2023-06-23 | 佛山科学技术学院 | Additive manufacturing layering slicing method capable of adaptively generating supporting structure |
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