KR102300473B1 - Adaptive Slicing Method by Merging Vertical Layer Polylines for Reducing 3D Printing Time - Google Patents

Abstract

A variable slicing method based on merging top and bottom layers polyline for reducing 3D printing time is provided. This slicing method includes the steps of receiving a 3D model; and classifying the input 3D model into different output thicknesses for each group.
Thereby, through variable slicing based on the merging of upper and lower layers polyline, the entire shape is grouped into regions in which a vertical connection relationship is established, and the output time can be shortened by independently performing variable slicing for each group, especially support Since it is sliced to the maximum thickness, printing time can be greatly reduced in the case of a shape that requires a lot of support.

Description

Adaptive Slicing Method by Merging Vertical Layer Polylines for Reducing 3D Printing Time

The present invention relates to 3D printing-related technology, and more particularly, to a variable slicing method for reducing 3D printing time.

Currently, most 3D printers used by non-professional users operate based on the Fused Filament Fabrication (FFF) method. In the FFF method, a high-temperature nozzle flows out a plastic filament and moves along a specific path at the same time to build up the cross section of the shape layer by layer to complete the final 3D print. After cutting the model to a thin thickness to determine the movement path of the nozzle, a slicing operation is performed to extract the outline of each cross-sectional area. That is, a build plate of the printer having the +Z axis as the normal direction is defined at the origin in the three-dimensional space, and the polygon model is placed thereon. The slicing plane intersects the polygon model while moving from the build plate to the highest point of the model in the +Z direction by a certain thickness, and creates a polyline for the cross-sectional area caused by the intersection.

Uniform slicing using a single layer thickness requires more layers if high surface quality of the print is intended, and therefore requires a longer print time. Accordingly, research on adaptive slicing, which reduces the output time by varying the layer thickness in consideration of the model surface characteristics, has been actively conducted. The existing global variable slicing determines the layer thickness by examining all triangle normals intersecting the slicing plane. In other words, the thicker the layer thickness is determined as the normal direction of the triangle is perpendicular to the Z-axis. Accordingly, when a highly curved shape and a vertical shape such as a cylinder exist at the same time on the same height, the vertical shape unnecessarily generates many layers. This phenomenon intensifies as more support structures are created in the form of vertical bars to support the overhang region of the model.

The present invention has been devised to solve the above problems, and an object of the present invention is to provide a variable slicing method based on merging upper and lower layers polyline as a method for reducing 3D printing time.

According to an embodiment of the present invention for achieving the above object, a slicing method includes: receiving a 3D model; and classifying the input 3D model into different output thicknesses for each group.

The dividing step may include uniformly slicing the input 3D model; generating polylines for boundaries of each sliced cross-sectional area of each layer; grouping polylines; and merging layers by deleting some polylines in each group.

The slicing step may be slicing to a minimum layer thickness supported by the 3D printer.

The thickness of the polylines may be expressed as a multiple of the minimum layer thickness.

The grouping step may be to group polylines based on top and bottom connectivity.

The deleting step may include: determining a layer thickness based on a cusp height; and deleting polylines based on the determined layer thickness.

The output thickness of the support may be the thickest.

On the other hand, according to another embodiment of the present invention, a computer-readable recording medium in which a program capable of performing a slicing method is recorded includes the steps of: receiving a 3D model; and classifying the input 3D model into output thicknesses that may be different for each group.

As described above, according to embodiments of the present invention, through variable slicing based on merging upper and lower polylines, the entire shape is grouped into regions in which a vertical connection relationship is established, and variable slicing is performed independently for each group. , the printing time can be shortened, and especially in the case of supports, since they are sliced to the maximum thickness, the printing time can be greatly reduced in the case of shapes that require many supports.

1 is an operation pipeline of a variable slicing method based on merging upper and lower polylines according to an embodiment of the present invention;
2 is Algorithm 1,
3 to 6 are diagrams provided for a further explanation of a variable slicing method according to an embodiment of the present invention;
7 is Algorithm 2,
8 is Algorithm 3,
9 is Algorithm 4,
10 shows the cusp height;
11 is Algorithm 5,
12 is a polygon model;
13 and 14 show a variable slicing result and a globally variable slicing result according to an embodiment of the present invention;
15 is a block diagram of a computing system to which a variable slicing method according to an embodiment of the present invention is applicable.

Hereinafter, the present invention will be described in more detail with reference to the drawings.

1. Layer Merge-based Variable Slicing Method

In the adaptive slicing method according to an embodiment of the present invention, adaptive slicing based on merging of upper and lower layer polylines is proposed. First, the input 3D polygon model is uniformly sliced using the minimum outputable thickness value, and polylines are generated for the boundary of the cross-sectional area of each layer. Next, after grouping polylines with high top-down connectivity, unnecessary polylines are deleted from within each group. To determine the layer to be deleted, the cusp height, which is a geometric error measure, is calculated and an appropriate layer thickness is determined based on this. Finally, by deleting polylines within the layer thickness range, they are merged into one layer.

1 is an operation pipeline of a variable slicing method based on merging upper and lower polylines according to an embodiment of the present invention. The detailed algorithm is as described in Algorithm 1 of FIG. A brief description of the three main stages of the variable slicing pipeline is given below.

1.1 Uniform Slicing

It receives a 3D polygon model and slices the model using the minimum layer thickness T _MIN supported by the printer. This step corresponds to line 1 of Algorithm 1 of FIG. 2, and the uniform slicing result for the bunny model of FIG. 3 is shown in FIG. The red rectangle is an enlarged view of a partial area as a result of uniform slicing, and it can be seen that the distance between the layers is constant.

1.2 Grouping polylines

When the shape of the upper and lower polylines changes rapidly, the polylines of the corresponding layer should be excluded from merging as the main feature area of the input model. In this step, polylines are grouped by evaluating vertical connectivity based on the similarity of upper and lower layer polylines, and each group is defined as a subpart structure. The highest/lowest layer polylines of each subpart are considered feature regions of the model shape and are excluded from layer merging. This step corresponds to line 2 of Algorithm 1 of FIG. 2 and the result is shown in FIG. 5 . In the figure, subparts are indicated in different colors.

1.3 Merge Layers

Layer merging is performed on polylines in each subpart. Calculates the cusp height, which represents the error between the polygon model and the layer model, to determine how many layer polylines should be merged from the current layer. Polylines selected for merging are deleted. After merging, the thickness of the top polyline increases as much as the number of merged polylines. As a result, the thickness of all polylines is expressed as multiples _{of T MIN .} This step corresponds to lines 3 to 35 of Algorithm 1 of FIG. 2, and the result is as shown in FIG.

2. Uniform slicing

Uniform slicing corresponds to the first line of Algorithm 1 of FIG. 2 as the first step of variable slicing. All 3D printers have a range of printable layer thicknesses.

First, the input polygon model is evenly sliced using the _{minimum layer thickness T MIN .} That is, after defining the center of the printer build plate as the origin and locating the model on the plane, the slicing planes are arranged at _{T MIN} intervals to the top point of the model in the +Z direction, which is the output direction and the normal direction of the printer build plate. Place it parallel to and calculate the intersection. For a set of vertices that exist on the cross section of the slicing plane and the model, all vertices are sequentially aligned by searching for the closest vertex from any starting point. Since one polyline is created for each separated region, each layer is composed of several polylines. The result of uniform slicing is L, which is a set of the height (z) values of all layers and the layer polylines belonging to it, and each polyline is stored with a linked list of vertices specifying whether it belongs to the support or the model.

3. Polyline grouping

The second step receives L, which is the result of uniform slicing, and groups polylines in a vertical connection relationship into subparts, and finally generates S, which is a set of subparts. A subpart is defined in the following structure, sid indicates a subpart unique number, and zmax and zmin indicate the maximum and minimum layer height of the subpart, respectively. Finally, z is a temporary variable used in the layer merging step, which will be described in detail later.

struct Subpart {

uint sid;

uint zmax;

uint zmin;

uint z;

};

Polyline grouping is performed sequentially for each polyline present in each layer, starting with the first layer and ending with the last layer. In the case of a nested polyline having an independent polyline such as a hole, it is performed only on the outermost polyline, and the same result is applied to the inner polylines. That is, the layer thickness determined by the outermost polyline becomes the thickness of the inner polyline. In addition, each polyline has a unique number sid of the subpart to which it belongs.

In the embodiment of the present invention, it is assumed that the higher the degree of similarity between the upper and lower polylines, the higher the upper and lower connection relationships are established. Referring to Algorithm 2 of FIG. 7 , the similarity with the polyline pline of the i-th layer L[i] and all polylines of the layer L[i-1] immediately below it is checked. If p, one of the polylines of L[i-1], has a high similarity to pline, set the sid of the pline to the sid of p, and set the zmax of the subpart[sid] to the height value of the current layer L[i].z Reset. If a polyline with high similarity is not found in L[i-1], a new subpart is created.

The similarity check is performed by the isSimilarTwoPolylines function, and after performing a set operation on the upper and lower two polylines (pline1, pline2), it is performed through the size of the result area (Algorithm 3 in FIG. 8). That is, after projecting polyline pline1 to pline2 while the coordinates of the polylines are fixed, the size of the union result area (areaUnion) and the intersection result area size (areaIntersection) of the two polylines are calculated, and then areaIntersection becomes areaUnion If it is larger than the contrast threshold areaThreashold, the two polylines are judged to have high similarity. 5 shows the polyline grouping results for the bunny model. In the area from bunny's head to the ears, you can see that two new subparts have been created for the ears.

4. Merge Layers

Layer merging is performed by selecting unnecessary polylines by examining each layer from the lowest first layer to the highest layer, and then deleting the selected polylines all at once. For this, a boolean type variable called merged is given to all polylines and initialized to false (6-8 of Algorithm 1 in FIG. 2).

When the variable thickness calculation for all layers and the selection of polylines to be deleted (9 to 28 in Algorithm 1 in Fig. 2) are finished, all polylines for which merged is true in L are deleted (29 to 35 in Algorithm 1 in Fig. 2). As a result, only polylines that have not been deleted remain in L.

From line 9 of Algorithm 1 of FIG. 2 , an appropriate layer thickness is calculated at a corresponding height for a polyline in which merged is false from the first layer. t is a real value representing the layer thickness and has the range _{[T MIN} , T _{MAX ].} How t is calculated depends on whether the polyline corresponds to a support or a model. For a support polyline, t is _{set to the maximum printable thickness (T MAX} ), and for a model polyline, it is calculated separately in the CalcThickness function. As described in Algorithm 4 of Fig. 9, the CalcThickness function calculates the layer thickness using the cusp height. The cusp height means the distance between the polygon model and the layer model as shown in FIG. 10 . As the cusp height increases, the layer thickness becomes thicker. The method of calculating the layer thickness according to the maximum cusp height is as Equation (1) below.

t = min{C _MAX /n _(i,z) },(i = 0, ... ,N) (1)

In the above equation, N means the total number of triangles intersecting the corresponding polyline among the triangles of the polygon model. n _{( i,z )} represents the Z component of the triangle normal vector. The maximum cusp height C _MAX is calculated using the maximum layer thickness T _MAX and the angle θ input by the user as shown in the following equation.

C _MAX = T _MAX cos θ (2)

_{Next, MergePolylines is calculated using T MIN} how many layers the thickness t corresponds to (Algorithm 5 in FIG. 11). Finally, merged of polylines belonging to an upper layer within the range of numLayers, the number of layers to be merged calculated through the MergePolylines function, is set to true (20 to 26 of Algorithm 1 in FIG. 2).

5. Experimental results

Hereinafter, an implementation and performance experiment of a variable slicing method based on merging upper and lower polylines according to an embodiment of the present invention will be described.

5.1 Implementation and Environment

The Clipper library was used for polyline alignment, union, and intersection operations required for variable slicing implementation according to an embodiment of the present invention, and the Libigl library was used for basic geometric model processing and rendering implementation. The development tool is MS Visual Studio 2013, and the operating system is Windows 7 Professional 64bit.

Uniform slicing (US), globally variable slicing (Global AS), and variable slicing according to an embodiment of the present invention were applied to a total of 10 polygon models ( FIGS. 3 and 12 ), and the results were compared. As parameters for this experiment, the minimum and maximum layer thicknesses T _MIN and T _MAX were set to 0.02mm and 0.2mm, respectively. The area threshold areaThreashold required in Algorithm 3 of FIG. 8 was set to 0.8, and θ required to calculate the maximum cusp height in Equation (2) was set to 60.

5.2 Results

13 shows a variable slicing result and a globally variable slicing result according to an embodiment of the present invention for a total of 10 models. Polylines are rendered with different colors for each subpart. 14 shows slicing results of three slicing methods, namely, uniform slicing (US), globally variable slicing (Global AS), and variable slicing methods (Our AS) according to an embodiment of the present invention. Shows the total number of layers created by applying each method, the total length of all polylines, the total length of polylines belonging to the model, and the total length (m) of polylines belonging to the support. In addition, compared to the uniform slicing result, it also shows how many times the number of three items has been reduced.

Of the total 10 models, except for the skull model, the variable slicing method according to the embodiment of the present invention generated more layers than the global method for the remaining 9 models. This is because several subparts are generated because the similarity between upper and lower polylines is low in a feature region of a highly curved shape, and the uppermost and lowermost layers of the subpart are excluded from merging. As a result, this method is effective in reproducing the features of the shape more accurately. In fact, if you look at the toe part of the frog model of FIG. 12, it can be seen that the proposed method has more layers than global slicing, and thus the surface curvature is more accurately reproduced. Although the number of layers is larger, the total length of the actually generated polylines is shorter in the proposed method for 10 models. On average, in the variable slicing method according to the embodiment of the present invention, the length of the polyline is reduced by more than 8 times compared to the uniform slicing, and in particular, it can be seen that the total length of the support polyline is greatly shortened. The reduction in polyline length was relatively small in the frog, which does not need support, and the bunny, lion, fertility, mask, and skull models with a small amount of support. As a result of comparing the variable slicing method according to the embodiment of the present invention and the globally variable slicing method, the variable slicing method according to the embodiment of the present invention produced a polyline shortened by an average of 20.8%. The model with the smallest reduction was frog (10.3%) and the model with the largest reduction was javelin (40.8%).

6. Computing system

15 is a block diagram of a computing system to which a variable slicing method according to an embodiment of the present invention is applicable. As shown in FIG. 15 , the computing system includes a communication unit 110 , an output unit 120 , a processor 130 , an input unit 140 , and a storage unit 150 .

The communication unit 110 is a communication means for connecting to the 3D printer locally or through a network, and also directly or through a network with other devices.

The processor 130 processes a user command input through the input unit 140 and outputs it through the output unit 120 , and in this process, the storage space of the storage unit 150 is utilized. In particular, the processor 130 executes a variable slicing method according to an embodiment of the present invention.

7. Variations

On the other hand, it goes without saying that the technical idea of the present invention can also be applied to a computer-readable recording medium containing a computer program for performing the functions of the apparatus and method according to the present embodiment. In addition, the technical ideas according to various embodiments of the present invention may be implemented in the form of computer-readable codes recorded on a computer-readable recording medium. The computer-readable recording medium may be any data storage device readable by the computer and capable of storing data. For example, the computer-readable recording medium may be a ROM, RAM, CD-ROM, magnetic tape, floppy disk, optical disk, hard disk drive, or the like. In addition, the computer-readable code or program stored in the computer-readable recording medium may be transmitted through a network connected between computers.

In addition, although preferred embodiments of the present invention have been illustrated and described above, the present invention is not limited to the specific embodiments described above, and the technical field to which the present invention belongs without departing from the gist of the present invention as claimed in the claims Various modifications are possible by those of ordinary skill in the art, and these modifications should not be individually understood from the technical spirit or prospect of the present invention.

110: communication department
120: output unit
130: processor
140: input unit
150: storage

Claims (8)

receiving a 3D model as an input;
uniformly slicing the input 3D model;
generating polylines for boundaries of each sliced cross-sectional area of each layer;
grouping polylines;
merging layers by deleting some polylines in each group;
The merging step is
determining a layer thickness based on the cusp height;
A slicing method comprising: deleting polylines based on the determined layer thickness.
delete The method according to claim 1,
The slicing step is
A slicing method characterized by slicing to the minimum layer thickness supported by the 3D printer.
4. The method according to claim 3,
The thickness of the polylines is
A slicing method, characterized in that it is expressed as a multiple of the minimum layer thickness.
The method according to claim 1,
The grouping step is
A slicing method comprising grouping polylines based on top-down connectivity.
delete The method according to claim 1,
A slicing method, characterized in that the thickness of the output of the support is the thickest.
receiving a 3D model as an input;
uniformly slicing the input 3D model;
generating polylines for boundaries of each sliced cross-sectional area of each layer;
grouping polylines;
merging layers by deleting some polylines in each group;
The merging step is
determining a layer thickness based on the cusp height;
A computer-readable recording medium in which a program capable of performing a slicing method is recorded, comprising: deleting polylines based on the determined layer thickness.

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