阅读说明：本技术 喷墨位置调整方法以及立体打印设备 (Ink jet position adjusting method and three-dimensional printing apparatus ) 是由 施可葳 谢欣达 黄郁庭 袁国砚 于 2018-07-09 设计创作，主要内容包括：本发明提出一种喷墨位置调整方法以及立体打印设备。所述喷墨位置调整方法包括：获取立体数字模型,对立体数字模型进行切层处理而产生具有截面轮廓的切层物件；自立体数字模型获取切层物件所对应的物件表面的法线方向；当法线方向指向第一轴向的负方向时,获取切层物件所对应的物件表面的表面倾斜程度,并依据表面倾斜程度计算切层物件的喷墨位置的内缩量；依据内缩量与截面轮廓获取切层物件的喷墨范围；以及在控制打印模块打印切层物件之后,依据喷墨范围而控制喷墨模块朝切层物件。(The invention provides an ink jet position adjusting method and a three-dimensional printing device. The ink ejection position adjustment method includes: obtaining a three-dimensional digital model, and performing layer cutting processing on the three-dimensional digital model to generate a layer cutting object with a cross section outline; acquiring the normal direction of the surface of the object corresponding to the layer-cutting object by using the stereo digital model; when the normal direction points to the negative direction of the first axial direction, the surface inclination degree of the surface of the object corresponding to the layer cutting object is obtained, and the retraction amount of the ink jet position of the layer cutting object is calculated according to the surface inclination degree; acquiring the ink jet range of the layer cutting object according to the retraction amount and the section profile; and after controlling the printing module to print the layer cutting object, controlling the ink jet module to face the layer cutting object according to the ink jet range.)

1. An ink-jet position adjusting method is suitable for printing a color three-dimensional object, and is characterized by comprising the following steps:

obtaining a three-dimensional digital model, and carrying out layer cutting processing on the three-dimensional digital model to generate a layer cutting object with a cross section outline;

acquiring the normal direction of the surface of the object corresponding to the layer-cutting object from the three-dimensional digital model;

when the normal direction points to the negative direction of the first axial direction, obtaining the surface inclination degree of the surface of the object corresponding to the layer cutting object from the three-dimensional digital model, and calculating the retraction amount of the ink jet position of the layer cutting object according to the surface inclination degree corresponding to the layer cutting object;

acquiring the ink jet range of the layer cutting object according to the retraction amount and the section profile; and

and after the printing module is controlled to print the layer cutting object, controlling the ink jetting module to jet ink towards the layer cutting object and along the cross section outline according to the ink jetting range.

2. The inkjet position adjusting method according to claim 1, wherein the step of obtaining the normal direction of the surface of the object corresponding to the sliced object from the stereoscopic digital model comprises:

obtaining at least one polygonal mesh unit corresponding to the layer cutting object from the three-dimensional digital model; and

and acquiring a normal vector of the at least one polygon mesh unit, wherein the normal vector points to the outside of the stereoscopic digital model.

3. The ink ejection position adjustment method according to claim 2, further comprising:

and judging whether the normal direction points to the negative direction of the first axial direction, wherein the first axial direction is vertical to the horizontal plane.

4. The method according to claim 2, wherein when the normal direction points to a negative direction of the first axis, the step of obtaining the surface inclination degree of the object surface corresponding to the layer-cutting object from the three-dimensional digital model, and calculating the retraction amount of the ink ejection position of the layer-cutting object according to the surface inclination degree corresponding to the layer-cutting object comprises:

calculating at least one included angle between the at least one polygonal grid unit and the horizontal plane to represent the surface inclination degree; and

and calculating the retraction amount of the ink jet position of the layer cutting object according to the at least one included angle and the preset retraction amount.

5. The method according to claim 4, wherein the step of calculating the retraction amount of the ink ejection position of the layer cutting object according to the at least one included angle and the predetermined retraction amount comprises:

and calculating the product of the cosine value of the at least one included angle, the preset retraction amount and the adjustment parameter to obtain the retraction amount.

6. The method according to claim 5, wherein the predetermined setback corresponds to a reference angle, the adjustment parameter is a reciprocal of a cosine of the reference angle, and the reference angle is between 0 and 90 degrees.

7. The method according to claim 4, wherein the at least one polygon mesh unit comprises a first polygon mesh unit and a second polygon mesh unit, and the step of calculating the at least one angle between the at least one polygon mesh unit and the horizontal plane comprises:

and calculating a first included angle between the first polygonal grid unit and the horizontal plane, and calculating a second included angle between the second polygonal grid unit and the horizontal plane.

8. The method according to claim 7, wherein the step of calculating the retraction amount of the ink ejection position of the layer cutting object according to the at least one included angle and the predetermined retraction amount comprises:

calculating a first inner shrinkage amount in the inner shrinkage amount according to the first included angle and the preset inner shrinkage amount: and

and calculating a second inner shrinkage amount in the inner shrinkage amount according to the second included angle and the preset inner shrinkage amount.

9. The inkjet position adjusting method according to claim 1, wherein obtaining the inkjet range of the layer cutting object according to the retraction amount and the cross-sectional profile comprises:

generating an inkjet image according to the retraction amount, an inkjet width and the cross-sectional profile, wherein the inkjet image includes the inkjet range formed based on the retraction amount.

10. A stereoscopic printing apparatus adapted to print a stereoscopic object in color, comprising:

a printing module comprising a printhead;

an inkjet module including an inkjet head;

a storage device in which a plurality of modules are recorded; and

a processing device coupled to the storage device and configured to execute the plurality of modules to:

obtaining a three-dimensional digital model, and carrying out layer cutting processing on the three-dimensional digital model to generate a layer cutting object with a cross section outline;

acquiring the normal direction of the surface of the object corresponding to the layer-cutting object from the three-dimensional digital model;

when the normal direction points to the negative direction of the first axial direction, obtaining the surface inclination degree of the surface of the object corresponding to the layer cutting object from the three-dimensional digital model, and calculating the retraction amount of the ink jet position of the layer cutting object according to the surface inclination degree corresponding to the layer cutting object;

acquiring the ink jet range of the layer cutting object according to the retraction amount and the section profile; and

and after the printing module is controlled to print the layer cutting object, controlling the ink jetting module to jet ink towards the layer cutting object and along the cross section outline according to the ink jetting range.

11. The stereoscopic printing apparatus of claim 10, wherein the processing device is configured to: obtaining at least one polygonal mesh unit corresponding to the layer cutting object from the three-dimensional digital model; and acquiring a normal vector of the at least one polygon mesh unit, wherein the normal vector points to the outside of the stereoscopic digital model.

12. The stereoscopic printing apparatus of claim 11, wherein the processing device is configured to: and judging whether the normal direction points to the negative direction of the first axial direction, wherein the first axial direction is vertical to the horizontal plane.

13. The stereoscopic printing apparatus of claim 11, wherein the processing device is configured to: calculating at least one included angle between the at least one polygonal grid unit and the horizontal plane to represent the surface inclination degree; and calculating the inner shrinkage of the ink jet position of the layer cutting object according to the at least one included angle and a preset inner shrinkage.

14. The stereoscopic printing apparatus of claim 13, wherein the processing device is configured to: and calculating the product of the cosine value of the at least one included angle, the preset retraction amount and the adjustment parameter to obtain the retraction amount.

15. The stereoscopic printing apparatus according to claim 14, wherein the preset amount of retraction corresponds to a reference angle, the adjustment parameter is an inverse of a cosine value of the reference angle, and the reference angle is between 0 and 90 degrees.

16. The stereoscopic printing apparatus according to claim 13, wherein the at least one polygonal mesh unit comprises a first polygonal mesh unit and a second polygonal mesh unit, the processing device being configured to: and calculating a first included angle between the first polygonal grid unit and the horizontal plane, and calculating a second included angle between the second polygonal grid unit and the horizontal plane.

17. The stereoscopic printing apparatus of claim 16, wherein the processing device is configured to: calculating a first inner shrinkage amount in the inner shrinkage amount according to the first included angle and the preset inner shrinkage amount: and calculating a second inner shrinkage amount in the inner shrinkage amount according to the second included angle and the preset inner shrinkage amount.

18. The stereoscopic printing apparatus of claim 11, wherein the processing device is configured to: generating an inkjet image according to the retraction amount, an inkjet width and the cross-sectional profile, wherein the inkjet image includes the inkjet range formed based on the retraction amount.

Technical Field

The present disclosure relates to inkjet technologies for three-dimensional printing, and particularly to an inkjet position adjusting method and a three-dimensional printing apparatus.

Background

With the advancement of Computer-Aided Manufacturing (CAM), the Manufacturing industry has developed stereoscopic printing technology to quickly make the original design. The three-dimensional printing technology is a general name of a series of Rapid Prototyping (RP) technologies, and the basic principle thereof is to manufacture a plurality of layers of cut-layer objects in a stacked manner on a printing platform by a Rapid Prototyping machine, wherein the cut-layer objects are sequentially printed on the printing platform in a scanning manner in a horizontal plane, so that the cut-layer objects can be stacked to form a three-dimensional printed object. Taking Fused Deposition Modeling (FDM) technology as an example, a molding material is made into a wire, and the molding material is heated and fused and then stacked layer by layer on a molding platform according to a required shape/contour to form a three-dimensional object.

In response to the requirement of color three-dimensional printing, the current three-dimensional printing technology further includes performing an inkjet operation on the three-dimensional printed object under printing. That is, when the three-dimensional printing device prints the cut-layer objects, the three-dimensional printing device can color each layer of cut-layer object at the same time, so as to manufacture a colored three-dimensional object. In a color three-dimensional printing technique, a three-dimensional printing device colors the contour edge of each layer-cutting object according to a preset ink-jet width, so that the surface of the three-dimensional object is colored. Specifically, when the stereo printing device performs the ink-jet operation, the ink-jet head applies ink to the edge of the upper surface of the layer-cutting object.

Ideally, the ink ejected from the ink jet head will fall completely on the upper surface of the layer-cutting object. However, when the edge of a layer-cutting object is suspended, the lower unsupported edge will slightly collapse, resulting in a difference between the actual object edge and the ideal object edge. In this case, since the ink jetting range of the inkjet head is determined based on the predetermined ink jetting width and the cross-sectional profile of the layer cutting object, and the edge of the object is collapsed as an unexpected event of the processing software, the ink sprayed based on the ink jetting range without considering the collapse may not completely fall on the layer cutting object, and the ink may spill on the platform or the object below. Fig. 1 shows an example of ink-jet operation performed on an edge portion of a sliced piece. As shown in fig. 1, when the edge of the laminated object L1 is suspended, the edge 11 will slightly collapse, so that the formed edge E1 of the actual object is different from the edge E2 of the ideal object. Thus, the inkjet head 12 sprays ink based on the preset ink-jet width Wk and the ideal object edge E2 to contaminate the three-dimensional object or platform being printed. Therefore, how to design a better color three-dimensional printing method becomes one of the issues that the related technical personnel need to think about.

Disclosure of Invention

The invention provides an ink-jet position adjusting method and a three-dimensional printing device, which can adjust the ink-jet position according to the surface inclination degree corresponding to a layer cutting object so as to avoid the phenomenon of ink spilling.

The embodiment of the invention provides an ink-jet position adjusting method which is suitable for printing a color three-dimensional object. The ink ejection position adjustment method includes: obtaining a three-dimensional digital model, and performing layer cutting processing on the three-dimensional digital model to generate a layer cutting object with a cross section outline; acquiring the normal direction of the surface of the object corresponding to the layer-cutting object by using the stereo digital model; when the normal direction points to the negative direction of the first axial direction, the surface inclination degree of the surface of the object corresponding to the layer cutting object is obtained by the independent body digital model, and the retraction amount of the ink jet position of the layer cutting object is calculated according to the surface inclination degree corresponding to the layer cutting object; acquiring the ink jet range of the layer cutting object according to the retraction amount and the section profile; and after controlling the printing module to print the layer cutting object, controlling the ink jet module to jet ink towards the layer cutting object and along the cross section contour according to the ink jet range.

In an embodiment of the present invention, the step of obtaining the normal direction of the surface of the object corresponding to the sliced object by the stereo digital model includes: obtaining at least one polygonal grid unit corresponding to the layer-cutting object by a digital model of the independent body; and acquiring a normal vector of at least one polygon mesh unit, wherein the normal vector points to the outside of the stereoscopic digital model.

In an embodiment of the present invention, the method further includes: and judging whether the normal direction points to the negative direction of a first axial direction, wherein the first axial direction is vertical to the horizontal plane.

In an embodiment of the present invention, when the normal direction points to a negative direction of the first axial direction, the step of obtaining the surface inclination degree of the surface of the object corresponding to the layer-cutting object from the stereo digital model, and calculating the retraction amount of the ink-jetting position of the layer-cutting object according to the surface inclination degree corresponding to the layer-cutting object includes: calculating at least one included angle between at least one polygonal grid unit and the horizontal plane to represent the surface inclination degree; and calculating the retraction amount of the ink jet position of the layer cutting object according to the at least one included angle and the preset retraction amount.

In an embodiment of the present invention, the step of calculating the retraction amount of the ink-jetting position of the layer-cutting object according to the at least one included angle and the predetermined retraction amount includes: and calculating the product of the cosine value of at least one included angle, the preset retraction amount related to the reference angle and the adjustment parameter to obtain the retraction amount.

In an embodiment of the invention, the adjustment parameter is an inverse of a cosine value of a reference angle, and the reference angle is between 0 and 90 degrees.

In an embodiment of the present invention, the at least one polygon mesh unit includes a first polygon mesh unit and a second polygon mesh unit, and the step of calculating the at least one included angle between the at least one polygon mesh unit and the horizontal plane includes: and calculating a first included angle between the first polygonal grid unit and the horizontal plane, and calculating a second included angle between the second polygonal grid unit and the horizontal plane.

In an embodiment of the present invention, the step of calculating the retraction amount of the ink-jetting position of the layer-cutting object according to the at least one included angle and the predetermined retraction amount includes: calculating a first inner shrinkage amount in the inner shrinkage amount according to the first included angle and a preset inner shrinkage amount: and calculating a second inner shrinkage amount in the inner shrinkage amount according to the second included angle and the preset inner shrinkage amount.

In an embodiment of the present invention, the obtaining the ink jetting range of the sliced layer object according to the shrinkage and the cross-sectional profile includes: and generating an ink jet image according to the retraction amount, the ink jet width and the cross section profile, wherein the ink jet image comprises an ink jet range formed based on the retraction amount.

From another perspective, an embodiment of the present invention provides a stereoscopic printing apparatus suitable for manufacturing a color stereoscopic object, which includes a printing module, an inkjet module, a storage device, and a processing device. The print module includes a printhead and the inkjet module includes an inkjet head. The storage device records a plurality of modules, and the processing device is coupled to the storage device and configured to execute the modules to: obtaining a three-dimensional digital model, and performing layer cutting processing on the three-dimensional digital model to generate a layer cutting object with a cross section outline; acquiring the normal direction of the surface of the object corresponding to the layer-cutting object by using the stereo digital model; when the normal direction points to the negative direction of the first axial direction, the surface inclination degree of the surface of the object corresponding to the layer cutting object is obtained by the independent body digital model, and the retraction amount of the ink jet position of the layer cutting object is calculated according to the surface inclination degree corresponding to the layer cutting object; acquiring the ink jet range of the layer cutting object according to the retraction amount and the section profile; and after controlling the printing module to print the layer cutting object, controlling the ink jet module to jet ink towards the layer cutting object and along the cross section contour according to the ink jet range.

Based on the above, the inkjet position adjusting method and the three-dimensional printing apparatus according to the embodiments of the invention can determine the retraction amount of the inkjet position according to the surface inclination degree corresponding to the layer cutting object, and translate the original inkjet position according to the retraction amount to generate a new inkjet position. Therefore, after the printing head prints the layer cutting object, the three-dimensional printing equipment can control the ink jet module to jet ink towards the layer cutting object and along the cross section outline according to the adjusted ink jet range, and the condition that the ink is spilled on the three-dimensional object or the platform below the three-dimensional object due to the collapse of the edge of the layer cutting object can be avoided.

In order to make the aforementioned and other features and advantages of the invention more comprehensible, embodiments accompanied with figures are described in detail below.

Drawings

FIG. 1 illustrates an example of ink-jetting operation on an edge portion of a sliced layer article;

FIG. 2 is a block diagram of a stereoscopic printing apparatus according to an embodiment of the invention;

FIG. 3 is a schematic diagram of a stereoscopic printing apparatus according to the embodiment of FIG. 2;

FIG. 4 is a flowchart illustrating an ink ejection position adjustment method according to an embodiment of the invention;

FIGS. 5A and 5B are schematic diagrams illustrating the determination of an ideal ink ejection range according to an embodiment of the present invention;

FIG. 6 is a schematic diagram of an angle between a polygonal mesh unit and a horizontal plane according to an embodiment of the present invention;

FIG. 7 is a flowchart illustrating an inkjet width adjustment method according to an embodiment of the invention.

The reference numbers illustrate:

l1, 80a, 80c, 52(1), 52(2), 52(n-1), 52 (n): layer cutting article

E1: edge of physical object

E2: ideal article edge

11: edge part

12: ink jet head

20: three-dimensional printing equipment

210: printing module

220: ink jet module

230: storage device

240: processing apparatus

250: forming platform

210 a: printing head

220 a: ink jet head

220 b: ink cartridge

S1: bearing surface

80: three-dimensional object

F1: molding material

I1: ink for ink jet recording

S401 to S405, S701 to S708: step (ii) of

51: stereo digital model

T1, T2: degree of surface inclination

F1, F2: original ink jet range

F3, F4: novel ink jet range

Img1, Img 2: ink jet image

M1: triangular mesh unit

V1, V2, V3: endpoint

HP: horizontal plane

Ws1, Ws 2: internal shrinkage

Ln 1: straight line

LA, LB: vertical line

θ 1: included angle

Detailed Description

In order that the present invention may be more readily understood, the following detailed description is provided as an illustration of specific embodiments of the invention. Further, wherever possible, the same reference numbers will be used throughout the drawings and the description to refer to the same or like parts.

Fig. 2 shows a schematic diagram of a stereoscopic printing apparatus according to an embodiment of the present invention. Referring to fig. 2, the stereoscopic printing apparatus 20 includes a printing module 210, an inkjet module 220, a storage device 230, and a processing device 240. The processing device 240 is coupled to the printing module 210, the inkjet module 220, and the storage device 230. In the present embodiment, the processing device 240 is used for controlling the printing module 210 and the inkjet module 220 to perform a stereoscopic printing operation.

In the present embodiment, the storage device 230 may be used for storing data, and may be a buffer memory, an internal storage medium, an external storage medium, other types of storage devices, or a combination thereof. For example, the buffer memory may include random access memory, read only memory, or other similar devices. For example, the internal storage medium may include a Hard Disk (HDD), a Solid State Disk (Solid State Disk), a flash (flash) storage device, or other similar devices. For example, the external storage medium may include an external hard disk, a USB drive (USB drive), a cloud hard disk, or other similar devices. In one embodiment, the storage device 230 may further store a plurality of modules, which may be software programs, so that the processing device 240 can read or execute the modules to implement the ink jet position adjusting method according to the embodiments of the present invention.

In the embodiment, the Processing Device 240 may include a Processing chip, an image Processing chip, or a Central Processing Unit (CPU), or other Programmable general purpose or special purpose microprocessor (microprocessor), a Digital Signal Processor (DSP), a Programmable controller, an Application Specific Integrated Circuit (ASIC), a Programmable Logic Device (PLD), other similar Processing Circuits, or a combination thereof.

In the present embodiment, the processing device 240 may control the printing module 210 and the inkjet module 220 to perform the stereoscopic printing operation and the inkjet operation based on the stereoscopic digital model. For example, the three-dimensional printing operation includes feeding out the molding material on the molding platform through the printing module 210. Alternatively, the ink jet module 220 may perform ink jet operations on the cured or curing molding material on the molding platform. In addition, those skilled in the art should understand that the stereo printing apparatus 20 may further include other components (e.g., a forming platform, a material supply line, an ink jet line, a print head linkage mechanism, a driving motor, etc.) for performing the stereo printing operation and the ink jet operation together with the printing module 210 and the ink jet module 220.

It should be noted that, in an embodiment, the stereoscopic printing apparatus 20 may include a computer host and a stereoscopic printer having the printing module 210 and the inkjet module 220, and the processing device 240 may be implemented as a processor of the computer host and a processor and/or a controller of the stereoscopic printer. For example, the stereo printing apparatus 20 may be composed of a notebook computer or a desktop computer and a stereo printer, and the invention is not limited thereto. In another embodiment, the stereoscopic printing device 20 may also be a stereoscopic printer with the capability of processing the stereoscopic digital model, and the processing device 240 may be implemented as a processor and/or a controller of the stereoscopic printer, which is not limited herein.

Fig. 3 is a schematic view of a stereoscopic printing apparatus according to the embodiment of fig. 2. Referring to fig. 3, the printing module 210 may include a printing head 210a, and the inkjet module 220 may include an inkjet head 220a, and a rectangular coordinate system is provided to describe the related components and the motion states thereof. The forming platform 250 includes a carrying surface S1 for carrying the color three-dimensional object 80 during printing. The forming platform 250 is disposed below the print head 210a and the inkjet head 220 a.

In detail, in the present embodiment, the processing device 240 may obtain a three-dimensional digital model, wherein the three-dimensional digital model conforms to a three-dimensional File Format of a Polygon File (PLY), an STL File, an OBJ File, or the like. The three-dimensional model in the three-dimensional file format is composed of a plurality of polygon Mesh units (Mesh), and each polygon Mesh unit is composed of a plurality of endpoints, wherein the endpoints have different coordinates respectively. In this embodiment, the processing device 240 may be configured to perform layer cutting processing on the three-dimensional digital model to obtain a plurality of layer cutting objects, so as to obtain layer cutting information of each layer cutting object. The layer cutting information includes the cross-sectional profile and ink jetting range of the layer cutting object. The processing device 240 may control the stereoscopic printing apparatus 20 according to the above-mentioned layer cutting information, so that the stereoscopic printing apparatus 20 generates a plurality of layer cutting objects layer by layer and colors the layer cutting objects layer by layer.

In the present embodiment, the stereoscopic printing apparatus 20 prints the stereoscopic object 80 in a Fused Deposition Modeling (FDM) technique. That is, the print head 210a is configured to move along the XY plane and move along the normal direction (Z axis) of the XY plane, the molding material F1 enters the print head 210a through the supply line to be melted by heating, and is extruded by the print head 210a to be molded layer by layer on the carrying surface S1 of the molding platform 250 to form a plurality of layer-cutting objects (fig. 3 illustrates the layer-cutting objects 80a and 80 c). Thus, the layer-by-layer formed layer-by- layer cut pieces 80a and 80c are stacked on the carrying surface S1 to form the three-dimensional piece 80. Specifically, the molding material F1 may be a hot melt material suitable for use in a manufacturing method such as a Fused Fiber Fabric (FFF) method or a melt and pressure molding (Melted and extruded molding), but the present invention is not limited thereto.

In the present embodiment, the inkjet head 220a sprays the ink I1 on the contour edge of each layer-cutting object 80a, 80c layer by layer, so that the ink I1 overlaps the upper surface of the layer-cutting objects 80a, 80 c. Therefore, the inkjet head 220a may include an ink cartridge 220b, wherein the ink cartridge 220b is used to contain the ink I1, and the inkjet head 220a sprays the ink I1 in the ink cartridge 220b onto the layer cutting objects 80a, 80c according to the control of the processing device 240, so as to color the edge portions of the layer cutting objects 80a, 80 c. Although FIG. 3 shows only one ink cartridge 220b, the number of ink cartridges and the number of colors of ink are not limited in the present invention. For example, the inkjet module 220 may include 4 ink cartridges respectively holding different colors (e.g., yellow (Y), magenta (M), cyan (C), and black (K)), and 4 corresponding inkjet heads.

With this arrangement, after the printing head 210a prints the layer-cutting object 80a on the forming platform 250, the ink can be sprayed on the upper surface of the layer-cutting object 80a by the ink-jet head 220a to color the edge of the layer-cutting object 80 a. After the print head 210a prints another layer of the layered object 80c on the forming platform 250, the ink can be sprayed on the upper surface of the layered object 80c by the ink jet head 220a to color the edge of the layered object 80 c. It can be known that by repeatedly and alternately performing the three-dimensional printing operation and the ink-jet operation, a plurality of colored cut-layer objects are sequentially stacked to form a color three-dimensional object.

It should be noted that, in the embodiment of the present invention, the stereoscopic printing apparatus 20 may perform the inkjet operation on the contour edge of each layer-cutting object according to a preset inkjet width, so that the surface of the stereoscopic object is colored. In detail, when the inkjet module 220 colors the layered object, the inkjet module 220 moves on the XY plane along the cross-sectional profile of the layered object to apply the ink I1 to the outer edge of the cross-section of the layered object. The outer edge of the section of each cut layer object is colored, so that the outer surface of the finally formed colored three-dimensional object can present diversified colors. That is, the ink jetting range for each layer-cutting object is determined based on the cross-sectional profile and the ink jetting width of the layer-cutting object. In more detail, the processing device 240 may generate inkjet images corresponding to the respective layer-cutting objects in advance according to the cross-sectional profiles of the layer-cutting objects, so as to control the inkjet module 220 to perform inkjet operations on the XY plane according to the inkjet images. Specifically, in the embodiment of the present invention, the ink jetting position determined based on the cross-sectional profile of each layer cutting object can be translated according to the surface inclination degree corresponding to the layer cutting object, and the retraction amount for translating the ink jetting position is determined according to the surface inclination degree corresponding to the layer cutting object.

Fig. 4 is a flowchart of a method for stereoscopic color printing according to an embodiment of the invention. The method of the present embodiment is applied to the three-dimensional printing apparatus 20 of fig. 2 and 3, and the detailed steps of the inkjet position adjusting method of the present embodiment will be described below with reference to the components of the three-dimensional printing apparatus 20.

In step S401, the processing device 240 obtains the stereoscopic digital model, and performs a layer cutting process on the stereoscopic digital model to generate a layer-cut object with a cross-sectional profile. Specifically, the stereo digital model (e.g., STL file) is further compiled and computed to be converted into relevant information for performing the color stereo printing function. First, the processing device 240 performs a layer cutting process on the stereo digital model to generate a plurality of layer-cut objects. Generally, the stereoscopic digital model is cut with a plurality of cut-layer planes at regular intervals to extract the cross-sectional profiles of the cut-layer objects. Herein, the cutting interval for cutting the stereoscopic digital model may be regarded as a slice thickness of the slice object.

Next, in step S402, the processing device 240 obtains the normal direction of the object surface corresponding to the sliced object from the stereo digital model. In one embodiment, the processing device 240 may obtain the normal direction of the object surface according to the normal vector of the polygon mesh unit of the three-dimensional digital model. Furthermore, the processing device 240 may obtain at least one polygon cell corresponding to the layer-cut object from the stereo digital model, and obtain a normal vector of the at least one polygon cell passed by the layer-cut object. Based on the definition of the polygon mesh cells of the STL file, the normal vectors of the polygon mesh cells point outside the stereoscopic digital model, and the normal vectors of the polygon mesh cells are defined according to the right-hand rule.

Specifically, after the slicing process is performed to obtain a plurality of sliced objects, the processing device 240 may further obtain a plurality of polygonal mesh cells corresponding to the sliced object, that is, obtain polygonal mesh cells intersecting with the slicing plane of the sliced object, and then obtain normal vectors of the polygonal mesh cells corresponding to the sliced object. It can be known that when the normal direction of the surface of the object is downward (toward the negative Z-axis direction), it means that the surface of the object is downward, and the edge of the layer-cutting object is in a suspended state. In other words, to create a downward facing shape of the object, the edge of the upper layer of cut pieces will extend beyond the edge of the lower layer of cut pieces.

Therefore, in the embodiment of the present invention, the processing device 240 further determines whether the normal direction of the object surface points to a negative direction of a first axial direction (i.e. Z axis), wherein the first axial direction is perpendicular to the horizontal plane (i.e. XY plane). Specifically, the processing device 240 can determine whether the normal direction of the surface of the object is directed to the negative direction of the Z axis by determining whether the Z axis component of the normal vector of the polygonal mesh unit corresponding to the sliced object is positive or negative. If the Z-axis component of the normal vector of the polygon mesh unit corresponding to the layer-cut object is negative, the processing device 240 may determine that the normal direction of the surface of the object points to the negative direction of the Z-axis. Taking a triangular grid cell as an example, the coordinates of the endpoints of the three are (-10,10,10), (0,0,0), respectively, and the normal vector of the triangular grid cell is (0,1, -1). Since the Z-axis component with the normal vector of (0,1, -1) is negative, the processing device 240 can determine that the normal direction of the object surface corresponding to the triangular grid unit points to the negative direction of the Z-axis.

Next, in step S403, when the normal direction points to the negative direction of the first axis, the processing device 240 obtains the surface inclination degree of the surface of the object corresponding to the layer-cutting object from the stereo digital model, and calculates the retraction amount of the ink-jetting position of the layer-cutting object according to the surface inclination degree of the layer-cutting object. In step S404, the processing device 240 obtains the ink jetting range of the layer cutting object according to the retraction amount and the cross-sectional profile. Specifically, the processing device 240 generates an inkjet image according to the retraction amount, the inkjet width, and the cross-sectional profile, wherein the inkjet image includes an inkjet range formed based on the retraction amount. In detail, in the embodiment of the invention, the processing device 240 may determine an original ink jetting range according to the cross-sectional profile of the layer cutting object and the preset ink jetting width, wherein the original ink jetting range is to be matched with the cross-sectional profile of the layer cutting object generated by the layer cutting process. When the normal direction points to the negative direction of the first axis, after determining the retraction amount of the ink ejection position of the layer cutting object, the processing device 240 adjusts the original ink ejection range according to the retraction amount to generate a new original ink ejection range, wherein the new original ink ejection range does not conform to the cross-sectional profile of the layer cutting object generated by the layer cutting process.

For example, referring to fig. 5A and 5B together, fig. 5A and 5B are schematic diagrams illustrating the determination of an ideal ink jetting range according to an embodiment of the present invention. It is assumed that the processing device 240 obtains the stereoscopic digital model 51, and the stereoscopic digital model 51 is a sphere with a downward spherical surface. The processing device 240 may perform a slicing process on the three-dimensional digital model 51 according to the same slicing thickness to obtain a plurality of slicing objects 52(1), (52), (2), (…), (52 (n-1), and (52 (n), where n is an integer greater than 0. Thus, the processing device 240 can obtain the cross-sectional profiles of the sliced objects 52(1) to 52(n) by the slicing process. In this example, since the three-dimensional digital model 51 is a hemisphere, the cross-sectional profiles of the layered objects 52(1) to 52(n) are circular profiles with different radii, and the surface inclinations of the polygonal grid cells of the same layered object are uniform.

Take the layer cutting device 52(2) as an example. Since the normal direction of the surface of the object corresponding to the sliced layer object 52(2) points to the negative direction of the first axial direction (Z axis), the processing device 240 obtains the surface inclination degree T1 of the surface of the object corresponding to the sliced layer object 52(2) from the stereo digital model. Thereafter, as shown in fig. 5B, the processing device 240 may calculate the retraction amount Ws1 according to the surface inclination degree T1 corresponding to the object surface of the layer-cutting object 52 (2). The processing device 240 shifts the original ink ejection range F1 (which is composed of the original ink ejection segments corresponding to each polygon-shaped grid cell) inward according to the retraction amount Ws1 to generate a new ink ejection range F2.

Further, the layer-cutting object 52(n-1) is taken as an example. Since the normal direction of the surface of the object corresponding to the sliced object 52(n-1) points to the negative direction of the first axial direction (Z axis), the processing device 240 obtains the surface inclination degree T2 of the surface of the object corresponding to the sliced object 52(n-1) from the stereo digital model. Thereafter, as shown in FIG. 5B, the processing device 240 may calculate the retraction amount Ws2 according to the surface inclination degree T2 corresponding to the object surface of the layer-cutting object 52 (n-1). The processing device 240 shifts the original ink ejection range F3 (which is composed of the original ink ejection segments corresponding to each polygon-shaped grid cell) inward according to the retraction amount Ws2 to generate a new ink ejection range F4.

It should be noted that, since the surface inclination degree T1 corresponding to the object surface of the layer cutting object 52(2) and the surface inclination degree T2 corresponding to the object surface of the layer cutting object 52(n-1) are different from each other, the retraction amount Ws1 is different from the retraction amount Ws 2. Here, since the surface inclination degree T2 corresponding to the object surface of the layer-cutting object 52(n-1) is steeper than the surface inclination degree T1 corresponding to the object surface of the layer-cutting object 52(2), the retraction amount Ws2 is smaller than the retraction amount Ws 1. That is, in one embodiment, for each layer of the sliced object, whether the ink ejection position is retracted and the corresponding amount of retraction can be determined individually.

Then, in step S405, after controlling the printing module 210 to print the layer-cutting object, the processing device 240 controls the ink-jet module 220 to jet ink toward the layer-cutting object and along the cross-sectional profile according to the ink-jet range. Referring to fig. 5B, the processing device 240 generates the inkjet image Img1 according to the retraction amount Ws1, so that the inkjet module 220 can spray the ink I1 on the layer-cutting object 52(2) according to the pixel position and the color feature value of the inkjet range F2 recorded by the inkjet image Img 1. The processing device 240 generates the inkjet image Img2 according to the retraction amount Ws2, so that the inkjet module 220 can spray the ink I1 on the layer-cutting object 52(n-1) according to the pixel position and the color feature value of the inkjet range F4 recorded by the inkjet image Img 2.

However, fig. 5A and 5B are only exemplary and not intended to limit the present invention. Those skilled in the art will have sufficient teaching and suggestions to deduce how to perform similar processing for other shapes of solid digital models after the description with reference to fig. 5A and 5B.

The following examples are provided to illustrate how to obtain the surface inclination of the surface of the object corresponding to the sliced object. In one embodiment, the three-dimensional digital model is composed of a plurality of polygonal Mesh units (Mesh), and each polygonal Mesh unit has a plurality of endpoints, wherein the endpoints have different coordinates respectively. For example, the polygonal mesh cells are typically triangular mesh cells, which may be considered as triangular faces formed by three endpoints. When the layer cutting processing is executed, a certain layer cutting plane for performing the layer cutting processing passes through partial polygonal mesh units of the three-dimensional digital model, so that the section outline of the layer cutting object is extracted. Thus, in one embodiment, the processing device 240 may obtain at least one polygonal mesh unit corresponding to the layer-cut object from the stereo digital model. Then, the processing device 240 may calculate at least one included angle between the at least one polygon mesh unit and the horizontal plane to represent the degree of surface inclination corresponding to the layer-cutting object. Specifically, according to the coordinates of the end points of the polygon mesh unit, the processing device 240 may calculate the included angle between the polygon mesh unit and the horizontal plane.

Referring to fig. 6, fig. 6 is a schematic diagram illustrating an included angle between a polygonal mesh unit and a horizontal plane according to an embodiment of the present invention. Assuming that the sliced object corresponds to the triangular mesh cell M1 formed by the endpoints V1, V2, and V3, the processing device 240 calculates an angle between the triangular mesh cell M1 and the horizontal plane HP to obtain an angle representing the surface inclination degree of the object surface. The horizontal plane HP can be considered as XY plane. Further, when the slicing process is performed using the horizontal plane HP, the horizontal plane HP intersects the triangular mesh unit M1 at the intersection point V7 and the intersection point V8, and the straight line Ln1 between the intersection point V7 and the intersection point V8 may constitute a part of the cross-sectional profile. The included angle θ 1 between the triangular mesh unit M1 and the horizontal plane HP is the included angle between the triangular plane formed by the vertex V1 and the two intersection points V7 and V8 and the horizontal plane HP. The angle θ 1 between the triangular mesh cell M1 and the horizontal plane HP can be obtained as follows. The endpoint V1 is a perpendicular LA perpendicular to the line Ln1 (the line between the intersection V7 and the intersection V8), and the perpendicular LA intersects the line Ln1 at the foothold point V9. Then, another perpendicular line LB perpendicular to the straight line Ln1 and located on the horizontal plane HP is obtained from the foot passing point V9, and the included angle θ 1 can be obtained from the included angle between the perpendicular line LA and the perpendicular line LB. However, the included angle between the two perpendicular lines may include a first included angle between 0-90 degrees and a second included angle between 90-180 degrees, and in the embodiment of the present invention, the first included angle between 0-90 degrees is used as the included angle between the triangular mesh unit M1 and the horizontal plane HP. It should be noted that the processing device 240 may also calculate an angle between another triangular mesh unit and the horizontal plane HP for the same sliced object to obtain another angle representing the surface inclination degree of the object surface. That is, for the same layer-cutting object, the layer-cutting object can correspond to a plurality of different included angles. In other words, for the same sliced object, since the shape of the three-dimensional digital model is irregular, a single sliced object will likely correspond to a plurality of different degrees of surface inclination.

As described above, when the slicing process is performed using the horizontal plane HP, the horizontal plane HP intersects the triangular mesh unit M1 at the intersection point V7 and the intersection point V8, and the straight line Ln1 between the intersection point V7 and the intersection point V8 is a partial section of the cross-sectional profile. Based on this, the processing device 240 may calculate the retraction amount for the partial section corresponding to the cross-sectional profile of the triangular mesh unit M1. That is, since the same slice plane can pass through different triangular mesh units, the processing device 240 can calculate a plurality of retraction amounts corresponding to different contour segments of the cross-sectional contour for the same slice object.

In one embodiment, after obtaining at least one angle representing the degree of surface inclination, the processing device 240 may calculate the retraction amount of the ink ejection position of the slice object according to the at least one angle between the polygonal mesh unit and the horizontal plane and the predetermined retraction amount. In one embodiment, the processing device 240 can calculate the retraction amount of the ink ejection position of the layer cutting object according to the following formula (1).

Ws_iedalWud × cos θ xR1 formula (1)

Wherein, Ws_idealRepresents the amount of retraction, θ represents the angle between the polygonal mesh unit and the horizontal plane, Wd represents the preset amount of retraction, and R1 represents the adjustment parameter. Referring to the formula (1), the processing device 240 calculates a product of the cosine value of the at least one angle, the predetermined retraction amount and the adjustment parameter to obtain the retraction amount. The predetermined amount of retraction and the adjustment parameters can be designed according to the actual requirement. It will be appreciated that the amount of retraction will increase with decreasing included angle between the polygonal mesh cells and the horizontal plane, and the amount of retraction will decrease with increasing included angle between the polygonal mesh cells and the horizontal plane. In other words, the processing device 240 determines the corresponding retraction amount according to the angle between the polygon mesh unit and the horizontal plane.

In addition, in one embodiment, the predetermined setback may be configured to correspond to a reference angle, and the adjustment parameter may be an inverse of a cosine value of the reference angle, and the reference angle is between 0 and 90 degrees. For example, assuming that the reference angle is 45 degrees and the predetermined retraction amount is a reference amount corresponding to 45 degrees, such as 0.5 cm, the formula (1) can be further set as the formula (2).

Wherein, Ws_idealRepresents the amount of retraction, θ represents the angle between the polygonal mesh unit and the horizontal plane (e.g., the angle θ 1 shown in FIG. 6), Wd represents the predetermined amount of retraction, and θ represents the amount of retraction_rRepresenting a reference angle. In this case, as can be seen from the formula (2), when the angle θ between the polygon mesh unit and the horizontal plane is equal to the reference angle (45 degrees), the processing device 240 calculates the amount of retraction Ws_idealEqual to the preset retraction amount Wd.

The calculation method of the formula (1) and the formula (2) is only one embodiment of the present invention. In other embodiments, the processing device 240 may perform a table look-up operation by using a preset look-up table based on the included angle representing the degree of surface inclination, so as to obtain the corresponding retraction amount. For example, if the included angle representing the degree of surface inclination is within a first predetermined angle range, the processing device may directly obtain the amount of retraction corresponding to the first predetermined angle range according to the lookup table. If the included angle representing the surface inclination degree is within a second preset angle range, the processing device can directly obtain the retraction amount corresponding to the second preset angle range according to the lookup table. Herein, the first predetermined angle range is different from the second predetermined angle range.

In addition, based on the foregoing, for the three-dimensional digital model with irregular shape, the same sliced object may correspond to different surface inclinations. That is, the angles between the plurality of polygonal grid cells corresponding to the layer-cutting object and the horizontal plane are different. In this case, the polygon mesh units corresponding to the layer-cutting object may include a first polygon mesh unit and a second polygon mesh unit. In one embodiment, the processing device 240 calculates a first angle between the first polygon mesh unit and the horizontal plane, and calculates a second angle between the second polygon mesh unit and the horizontal plane. Then, the processing device 240 calculates a first inner shrinkage amount of the inner shrinkage amounts according to the first included angle and the preset inner shrinkage amount, and calculates a second inner shrinkage amount of the inner shrinkage amounts according to the second included angle and the preset inner shrinkage amount. That is, for the same sliced object, it may correspond to a plurality of different setbacks. Generally, two volumetric digital models of similar size are obtained, wherein a more complex or irregular model has more polygonal mesh cells with smaller area than the other model, which may correspond to more different shrinkage.

Fig. 7 is a flowchart illustrating an inkjet position adjustment method according to an embodiment of the invention, and details of the implementation of the method may refer to the description of the embodiment in fig. 2 to 6. Referring to fig. 7, in step S701, a stereo digital model is obtained, and a layer-cutting process is performed on the stereo digital model to generate a layer-cut object with a cross-sectional profile. In step S702, at least one polygonal mesh unit corresponding to the layer-cut object is obtained from the stereo digital model. In step S703, a normal vector of at least one polygon mesh unit is obtained. In step S704, it is determined whether the normal direction points to the negative direction of the first axis direction according to the normal vector of the at least one polygon mesh unit. In step S705, when the normal direction points to the negative direction of the first axis, at least one included angle between at least one polygon mesh unit and the horizontal plane is calculated to represent the surface inclination degree. In step S706, the inner shrinkage of the ink jetting position of the layer cutting object is calculated according to the at least one included angle and the predetermined inner shrinkage. In step S707, an inkjet image is generated according to the retraction amount, the inkjet width and the cross-sectional profile, wherein the inkjet image includes an inkjet range formed based on the retraction amount. In step S708, after the printing module is controlled to print the layer-cutting object, the ink-jet module is controlled to jet ink toward the layer-cutting object and along the cross-sectional profile according to the ink-jet range.

In summary, the ink-jetting position adjusting method and the three-dimensional printing apparatus according to the embodiments of the invention can determine the retraction amount of the ink-jetting position according to the surface inclination degree corresponding to the layer-cutting object, and translate the original ink-jetting position according to the retraction amount to generate a new ink-jetting position. Therefore, after the printing head prints the layer cutting object, the three-dimensional printing equipment can control the ink jet module to jet ink towards the layer cutting object and along the cross section outline according to the adjusted ink jet range, and the condition that the ink is spilled on the three-dimensional object or the platform below the three-dimensional object due to the collapse of the edge of the layer cutting object can be avoided. Therefore, the three-dimensional printing equipment can obviously improve the printing quality of color three-dimensional printing.

Although the present invention has been described with reference to the above embodiments, it should be understood that various changes and modifications can be made therein by those skilled in the art without departing from the spirit and scope of the invention.