METHOD FOR PRINTING A THREE-DIMENSIONAL ARTICLE

Description

[0001] The invention relates to a method and a device for printing on a three-dimensional article.

[0002] Digital printing has long been widely used for printing on two-dimensional items, such as paper. It has now also become established for printing on items with more complex geometries, such as vehicle parts or packaging. The term "digital printing" generally refers to printing processes in which the print image is transferred directly from a file or data stream from a computer to a printing press, without the use of a static printing form. Therefore, with its dynamic image generation, digital printing offers the possibility of cost-effective, customized printing, even on larger three-dimensional items.

[0003] A widely used method in digital printing is inkjet printing. Inkjet printing allows for the high-speed printing of large-format items. For example, document EP 0 571 804 B1 describes a printing device with multiple printheads for printing large-area items. The printing of a three-dimensional item is described as an example in document EP 1 225 053 A2.

[0004] In prior art processes, a template print image based on known master data, such as known dimensions, of the three-dimensional article to be printed is often used as the print image. For example, such a printing process is described in DE 10 2017 215 429 A1. Other techniques for providing print images are also known from the prior art. For example, DE 10 2012 006 371 A1 describes the use of 3D measurement to generate path data for moving a print head to apply a template print image based on known master data to a surface to be printed. DE 10 2012 006371 A1 and DE 10 2014 108092 A1 also disclose the use of 3D measurement for printing on three-dimensional articles.

[0005] With known techniques, i.e., when a previously created print image is used based on known master data, or the print image is adapted to the actual dimensions of the item to be printed by scaling, deviations occur, especially when printing the entire surface of the item, to such an extent that the item cannot be printed precisely enough and therefore insufficient print quality is not achieved.

[0006] The object of the present invention is to provide an improved method for printing on a three-dimensional article.

[0007] This problem is solved by a method having the features of claim 1. According to claim 1, a method for printing on a three-dimensional article is provided.

[0008] The three-dimensional article can be essentially a cuboid or cube-shaped body bounded by rectangles, with its faces at right angles to each other. However, the three-dimensional article can also have a different three-dimensional geometry, for example, a prism or a cylinder, and be bounded by multiple surfaces. For instance, the three-dimensional article could be an electronic or electrical component.

[0009] The term "printable area" can be used here to refer to an area on the surface of the three-dimensional article that is to be printed completely or partially. In some examples, the printable area can be further subdivided into sub-areas that can be printed in the same or different ways.

[0010] The three-dimensional object can be spatially fixed during measurement and printing using a holding device, ensuring that the object is printed in the position in which it is measured. Three-dimensional imaging methods can include, for example, laser triangulation, structured light projection, time-of-flight, shape-from-shading, photometric stereo, white-light interferometry, or a combination thereof.

[0011] The survey data can then be electronically provided to a processing unit to generate the print image. Based on the generated print image, the area to be printed can be printed using digital printing, for example, with an inkjet printhead.

[0012] Advantageously, by measuring the area to be printed using a three-dimensional imaging method and subsequently generating a print image based on the measurement data obtained from this method, even deeper contours within the print area can be detected, resulting in an image that already incorporates all tolerances. For example, edges and openings that are not to be printed can also be precisely measured using this method.

[0013] Compared to measurement using a two-dimensional imaging method, edge extraction for determining article geometry is largely independent of the surface's reflective properties. This means that different colors or structures within the material have little to no influence on the measurement. Furthermore, with three-dimensional imaging, edges or transitions do not need to be approximated, as they exhibit a much stronger value difference in the image compared to a two-dimensional image and do not show a brightness gradient dependent on lighting conditions. Additionally, height differences within the article are measurable and can be addressed during print image generation if they would otherwise affect the print quality.

[0014] According to the invention, generating the printed image comprises: recognizing at least one sub-area in the area to be printed, and providing measurement data relating to the sub-area.

[0015] A sub-area can be defined as a section within the area to be printed that differs from the rest of the area to be printed. For example, the sub-area might differ in height or geometry, such as angled or curved surfaces, from the rest of the area to be printed, or the remaining sub-areas of the area to be printed.

[0016] In one example, the recognition of at least a sub-area shows: Identifying the sub-area using an image processing method, and / or comparing known geometric information regarding the sub-area with geometric information in the survey data.

[0017] For example, image processing techniques can be applied, such as color classifiers, Hough transforms, and contrast analysis for the detection of geometric objects, Gabor wavelets and Laplace filters for edge detection, etc. Alternatively or additionally, known geometries can be searched for by comparing known geometric information regarding the sub-area with geometric information in the survey data. In one example, the geometric information includes elevation and / or contour information.

[0018] According to the invention, the generation of the printed image is characterized by: Generating at least one partial print image based on the sub-area of ​​the area to be printed; and generating the print image based on the partial print image.

[0019] This allows for the advantageous processing of printed surfaces of varying heights and geometries, such as angled or curved surfaces. In conventional two-dimensional images, this information can only be extracted approximately, or not at all, through projection onto the image plane.

[0020] For example, by generating at least a partial print image, regions can be identified that should be colored on the three-dimensional article and those that should not be printed, such as the cable entry slots of an electronic or electrical component.

[0021] In one example, the creation of the printed image shows: Generating a multitude of partial print images, each based on a sub-area of ​​the area to be printed; and generating the print image based on the multitude of partial print images.

[0022] This allows different parts of the three-dimensional article to be colored independently of each other and combined into a final printed image.

[0023] Advantageously, with such a composite print image made up of various partial print images, the areas are aligned with the actual printable area of ​​the three-dimensional article and are not assembled from a pre-made template image based on known master data. With a template print image assembled from templates based on master data, any change in the length of the printable area—that is, the difference between the template and the actual three-dimensional article—would have to be compensated for by stretching the print image. This results in undesirable and visible distortions of individual parts of the image, which are then noticeable on the three-dimensional article. For example, round cable entry openings would no longer be round, but would become ovals due to stretching. A similar effect occurs with rectangular areas, such as those found on pushers.

[0024] The advantage of the described method is that no scaling of a predefined template print image or predefined print areas takes place; instead, the actual geometries of the three-dimensional article serve as precise specifications for the print image generation.

[0025] In another example, the generation of the printed image is based on known master data of the three-dimensional article.

[0026] For example, individual partial print images relating to sub-areas where the probability of deformation between a predefined template print image and the actual area of ​​the object is low can also include template print images as partial print images to make the generation of the print image more efficient. However, in examples of the invention, the use of template print images is completely dispensed with. In these examples, the print image is generated exclusively on the multitude of partial print images, each based on a sub-area of ​​the area to be printed, which were therefore previously measured using the imaging three-dimensional method.

[0027] In one example, the three-dimensional imaging method is a method or a combination of methods from the group: laser triangulation method, grazing light projection method, time-of-flight method, shape-from-shading method, photometric stereo method, and / or white light interferometry method.

[0028] One example of the measurement process is: three-dimensional measurement of the area to be printed using a robot-guided measuring head.

[0029] Here, for example, the measuring head can be guided relative to the three-dimensional article with the area to be printed. For this purpose, the three-dimensional article can be fixed in a stationary position, for example, in a holding device that keeps the three-dimensional article in a predetermined position during the measuring, printing, and intervening phases. This can advantageously enable precise printing.

[0030] One example of printing involves three-dimensional digital printing using a robot-guided printhead, in particular a piezoelectric inkjet printhead.

[0031] For example, the inkjet printhead can be used for a printing technique known as drop-on-demand, in which the printhead nozzles open for each individual ink droplet of the printed image. The advantage is that ink droplets are only ejected when they are actually needed. In one example, the precise opening of the nozzles can be achieved piezoelectrically.

[0032] In one example, the method includes the step of fixing the article during measurement and printing in a holding device, in particular a movable holding device adapted to move the three-dimensional article during measurement and printing.

[0033] For example, in addition to or as an alternative to moving the measuring head and / or the print head, the item can be moved to make printing on the item more efficient and faster.

[0034] The invention also relates to a device for printing on a three-dimensional article, in particular for printing using a method according to one of the preceding claims, according to claim 9.

[0035] In one example, the measuring device includes at least a robot-guided measuring head for three-dimensional measurement of the area to be printed.

[0036] In one example, the means for generating the printed image includes a computing unit.

[0037] In one example, the printing device has at least one robot-guided printhead, in particular a piezoelectric inkjet printhead.

[0038] In one example, the device includes at least one holding means for fixing the three-dimensional article during measuring and printing, in particular a movable holding means adapted to move the three-dimensional article during measuring and printing. The underlying concept of the invention will be explained in more detail below with reference to exemplary embodiments illustrated in the figures. The figures show: Fig. 1 a schematic view of a device for printing a three-dimensional article according to one embodiment; and Fig. 2 a schematic process flow of a method for printing a three-dimensional article according to one embodiment.

[0039] Figure 1 Figure 1 shows a schematic view of a device 1 for printing on a three-dimensional article 3 according to one embodiment.

[0040] The device 1 shown for printing on a three-dimensional article 3 comprises means 5 for measuring at least one area of ​​the three-dimensional article 3 to be printed by means of a three-dimensional imaging method. In the illustrated embodiment, the measuring means 5 comprises a robot-guided measuring head for three-dimensionally measuring the area to be printed. Three-dimensional imaging methods such as laser triangulation, structured light projection, time-of-flight, shape-from-shading, photometric stereo, white light interferometry, or a combination of these methods can be used in embodiments.

[0041] In the illustrated embodiment, the measuring means 5 can be guided relative to the three-dimensional article 3 with the area to be printed. For this purpose, the three-dimensional article 3 is fixed in a holding means 11, which holds the three-dimensional article 3 in a predetermined position during the measuring, printing, and intervening periods. The predetermined position can either be fixed or the holding means 11 can move the three-dimensional article 3 during the measuring and printing processes.

[0042] As in Figure 1 As shown, the measuring means 5 is connected to a means 7 for generating a printed image. In the illustrated embodiment, the means 7 for generating a printed image comprises a processing unit adapted to generate the printed image based on the measurement data from the measuring means 5.

[0043] Furthermore, in Figure 1The printing means 9 is shown, which is also connected to the means for generating the printed image 7. In the illustrated embodiment, the printing means 9 has a robot-guided printhead.

[0044] Figure 2 shows a schematic process flow of a method 100 for printing a three-dimensional article according to one embodiment.

[0045] Procedure 100 includes the following steps: 110 Measuring at least one area of ​​the three-dimensional article to be printed using a three-dimensional imaging method and providing measurement data relating to the area to be printed; 120 Generating a print image based on the measurement data; and 130 Printing the area to be printed using digital printing.

[0046] The in Figure 2The process steps shown with a dashed outline are merely optional and not essential for carrying out the invention.

[0047] Accordingly, the measurement 110 of the area to be printed can optionally include the step: Three-dimensional measurement 112 of the area to be printed using a robot-guided measuring head.

[0048] The step of generating a printed image based on the survey data can optionally include generating a multitude of partial printed images, each based on a sub-area of ​​the area to be printed, and generating the printed image based on these multiple partial printed images. This generation step can optionally include recognizing at least one sub-area within the area to be printed and providing survey data relating to that sub-area. This recognition can include recognizing the sub-area using an image processing method and / or comparing known geometric information relating to the sub-area with geometric information in the survey data.

[0049] The printing 130 of the area to be printed by means of digital printing can optionally include the step: Three-dimensional digital printing 132 by means of a robot-guided printhead, in particular a piezoelectric inkjet printhead.

[0050] The method may optionally also include: fixing the three-dimensional article during measurement and printing in a holding device, in particular a movable holding device which is adapted to move the three-dimensional article during measurement and printing. Reference symbol list

[0051] 1. Device for printing 3. Three-dimensional article 5. Measuring device 7. Producing device 9. Printing device 11. Holding device 100 Printing methods 110 Measuring 112 Three-dimensional measuring 120 Generating 122 Detecting a partial area 124 Detecting using image processing methods 126 Generating a multitude of partial print images 130 Printing 132 Three-dimensional printing 140 Fixing

Claims

1. Method for printing a three-dimensional article (3), comprising the steps: measuring (110) at least one region to be printed of the three-dimensional article (3) by means of a three-dimensional imaging method and providing measurement data relating to the region to be printed; generating (120) a printing image on the basis of the measurement data, comprising: detecting (122) at least one subregion in the region to be printed, providing measurement data relating to the subregion, generating (126) a multiplicity of partial printing images respectively on the basis of a subregion of the region to be printed, and generating the printing image on the basis of the multiplicity of partial printing images; and printing (130) the region to be printed by means of digital printing.

2. Method according to Claim 1, characterized in that the detection (122) of at least one subregion comprises: detecting (124) the subregion by means of an image processing method, and / or comparing known geometrical information relating to the subregion with geometrical information in the measurement data.

3. Method according to Claim 2, characterized in that the geometrical information comprises height information and / or contour information.

4. Method according to one of the preceding claims, characterized in that the generation of the printing image is based on known master data of the three-dimensional article (3).

5. Method according to one of the preceding claims, characterized in that the three-dimensional imaging method is a method or a combination of methods from the group: laser triangulation methods, structured light projection methods, time-of-flight methods, shape-from-shading methods, photometric stereo methods, and / or white light interferometry methods.

6. Method according to one of the preceding claims, characterized in that the measurement (110) comprises: three-dimensional measurement (112) of the region to be printed by means of a robot-guided measurement head.

7. Method according to one of the preceding claims, characterized in that the printing (130) comprises: three-dimensional digital printing (132) by means of a robot-guided printing head, in particular a piezoelectric inkjet printing head.

8. Method according to one of the preceding claims, characterized by: fixing the three-dimensional article (3) during the measurement (110) and the printing (130) in a holding means (11), in particular a movably arranged holding means (11), which is configured to move the three-dimensional article (3) during the measurement (110) and the printing (130).

9. Device for printing a three-dimensional article (3), in particular for printing with a method according to one of the preceding claims, comprising: means (5) for measuring at least one region to be printed of the three-dimensional article (3) by means of a three-dimensional imaging method and for providing measurement data relating to the region to be printed; means (7) for generating a printing image on the basis of the measurement data, wherein the generation of the printing image comprises: detecting (122) at least one subregion in the region to be printed, providing measurement data relating to the subregion, generating (126) a multiplicity of partial printing images respectively on the basis of a subregion of the region to be printed; and generating the printing image on the basis of the multiplicity of partial printing images; and means (9) for printing the region to be printed by means of digital printing.

10. Device according to Claim 9, characterized in that the measuring means (5) comprises at least one robot-guided measurement head for three-dimensional measurement of the region to be printed.

11. Device according to Claim 9 or 10, characterized in that the means (7) for generating the printing image comprises a computation unit.

12. Device according to one of Claims 9 to 11, characterized in that the printing means (9) comprises at least one robot-guided printing head, in particular a piezoelectric inkjet printing head.

13. Device according to one of Claims 9 to 12, characterized by at least one holding means (11) for fixing the three-dimensional article (3) during the measurement and the printing, in particular a movably arranged holding means (11), which is configured to move the three-dimensional article (3) during the measurement (110) and the printing (130).