Method For Printing An Optical Component Utilizing Layer Compensation

Abstract

The present invention refers to a Method for printing a three-dimensional optical structure (1), wherein the three-dimensional optical structure (1) is built up from layers (L) of printing ink deposited through targeted placement of droplets of printing ink at least partially side by side in consecutive printing steps, wherein in order to at least partially compensate for deviations of a thickness from a nominal thickness of at least one layer (2), possible deviations are determined prior to printing said layer (2) and depositing the printing ink is controlled dependent on the determined possible deviations during printing of said layer (2).

Claims

1. A method for printing a three-dimensional optical structure comprising: building the three-dimensional optical structure from layers of printing ink deposited through targeted placement of droplets of printing ink at least partially side by side in consecutive printing steps; at least partially compensating for deviations of a thickness from a nominal thickness of at least one layer by determining possible deviations prior to printing the layer, wherein depositing the printing ink is controlled dependent on the determined possible deviations during printing of said layer; wherein during printing the layer, at least on a part of the layer, the droplets are placed according to a dither pattern, such that a number of droplets placed on the part is reduced; wherein the number of droplets is reduced by leaving blank spaces when placing the droplets, wherein no droplets are placed on said blank spaces; wherein the part of the layer is arranged parallel to a circumference of the layer; wherein the part of the layer is formed as a loop or ring; wherein the part of the layer is arranged a distance away from the circumference, or wherein the part of the layer adjoins the circumference.

2. (canceled)

3. The method according to claim 1, wherein the blank spaces are distributed over the entire layer if a diameter of the layer is below a minimum diameter.

4. (canceled)

5. The method according to claim 1, wherein the loop or the ring has a width, wherein the width is between 0.1 and 5 mm.

6. The method according to claim 1, wherein the blank spaces are arranged randomized or at least partially randomized on the part of the layer.

7. The method according to claim 1, wherein during printing the layer, at least on a further part of the layer, the volume of each droplet is reduced.

8. The method according to claim 7, wherein the further part of the layer covers the entire layer if a diameter of the layer is below a further minimum diameter.

9. The method according to claim 7, wherein the further part of the layer is arranged parallel to a circumference of the layer, wherein the further part of the layer is arranged a further distance away from the circumference, wherein the further distance is between 0.1 and 2 mm, or wherein the part of the layer adjoins the circumference.

10. The method according to claim 9, wherein the further part of the layer is formed as a loop or ring, wherein the loop or the ring has a further width, wherein the further width is between 0.1 and 5 mm.

11. The method according to claim 1, wherein in order to at least partially compensate for further deviations of a further thickness from a further nominal thickness of a further layer printed in a preceding printing step, depositing the printing ink is controlled dependent on the further deviations during printing of the layer.

12. (canceled)

13. The method according to claim 11, wherein the further blank spaces are arranged randomized or at least partially randomized on the second further part of the layer.

14. The method according to claim 11, wherein during printing the layer, at least on a third further part of the layer, the volume of each droplet is reduced.

15. The method according to claim 11, wherein the further deviations are determined by measuring the shape and/or volume of a surface of the further layer by confocal scanning.

16. The method according to claim 11, wherein the further deviations comprise deviations of thicknesses from further nominal thicknesses of all layers printed in preceding printing steps.

17. The method according to claim 1, wherein the deviations are determined by simulating a contraction of the printed layers.

18. The method according claim 17, wherein the deviations of all layers to be printed are determined before printing using a simulation, wherein the deviations are compensated during printing one or more layers.

19. The method according to claim 1, wherein the distance away from the circumference is between about 0.1 and about 2 mm.

20. The method according to claim 3, wherein the minimum diameter is about 5 mm.

21. The method according to claim 8, wherein the further minimum diameter is about 5 mm.

22. The method according to claim 11, wherein the deviations and/or the further deviations are determined by simulating a contraction of the printed layers.

23. The method according to claim 22, wherein the deviations and/or the further deviations of all layers to be printed are determined before printing using a simulation, wherein the deviations and/or further deviations are compensated during printing one or more layers.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 schematically illustrates a printing method according to an exemplary embodiment of the present invention.

[0026] FIG. 2 schematically illustrates a plot of the relative layer height over the layer length.

[0027] FIG. 3 schematically illustrates dither patterns used in a printing method according to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION

[0028] The present invention will be described with respect to particular embodiments and with target to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and for illustrative purposes may not be drawn to scale.

[0029] Where an indefinite or definite article is used when referring to a singular noun, e.g. “a”, “an”, “the”, this includes a plural of that noun unless something else is specifically stated.

[0030] Furthermore, the terms first, second, third and the like in the description and in the claims are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

[0031] In FIG. 1, a printing method according to an exemplary embodiment of the present invention is schematically illustrated. The three dimensional optical component 1 is printed by building up a number of layers L. From subFIGS. 1 (a)-(c) it is apparent, how the optical component 1 is constructed by consecutive steps of layer printing. For printing each layer L, droplets of printing ink are ejected from the nozzles of a print head (not shown). The droplets are targeted placed at least partially side by side such, that the droplets merge forming a thin film. Due to surface effects of the thin film, the layers L are contracted at the edges, leading to excesses of the thickness of the layer L (see FIG. 2). If the diameter d of the layer L is below a certain limit, typically below 5 mm, the excesses at the edges of the layer L merge and lead to an increase of thickness in the total layer L. These excesses in thickness are quite small but, however, sum up over a multitude of layers L and lead to an unwanted geometry of the optical component 1 and with this to optical distortions.

[0032] SubFIG. 1 (c) shows the optical component 1 comprising a number of slices, each consisting of one layer printed by placing droplets of printing ink such, that the droplets merge to a thin film. To maintain an optimal geometry of the optical component 1, the dimensions, i. e. thickness and lateral dimensions, such as diameter d, of each slice are calculated. Printing the layers, the calculated dimensions have to be matched. To match the calculated thickness, i.e. a nominal thickness, possible deviations of thickness of a layer 2 are determined by a calculation. During printing of the layer 2, depositing the printing ink is controlled such, that the possible deviations are compensated and the printed thickness matches the nominal thickness. To achieve this, the droplets are placed according to a dither pattern (see FIG. 3). A dither pattern is a two-dimensional template that contains the location of blank spaces, where no droplets are placed. Leaving out droplets at the blank spaces locally reduces the printed volume and therewith the thickness of the layer 2. To locally compensate for larger excesses of thickness, the dither pattern locally schedules more blank spaces, i.e. the density of blank spaces is higher. To locally compensate for lower excesses of thickness, the dither pattern locally schedules less blank spaces, i.e. the density of blank spaces is lower. To avoid diffraction, the positions of the blank spaces are randomized in a certain range. Therewith it is provided, that the blank spaces do not act as an optical grating.

[0033] In addition to using the dither pattern to compensate for the deviations, it is also foreseen that the deviations of thickness are compensated by applying less ink locally when printing the layer 2, thus reducing the thickness of the layer 2 locally. The printed volumes follow a volume pattern, which is a two-dimensional template that contains information about the volume of printing ink that is to be placed depending on the position.

[0034] Printing the layer 2, further deviations, i. e. deviations of a further thickness from a further nominal thickness of a further layer 3 printed in a preceding printing step, are compensated. The further deviations arise from droplet volume variations or droplet misplacements while printing the further layer 3 and cannot be simulated or calculated accurately. Hence, the further deviations are determined by confocal scanning of a surface of the further layer 3 and compensated by leaving further blank spaces following a further dither pattern during printing the layer 2 and/or locally reducing the droplet volume following a further volume pattern during printing the layer 2.

[0035] It is possible to compensate for deviations and further deviations during each printing step, as well as to compensate for deviations and further deviations only during a part of the printing steps. In particular, it is advantageous to compensate for the deviations and/or further deviations during the printing of the last and outermost, i.e. the curved layers and to compensate for the deviations and/or further deviations of the layers printed in the previous printing steps. Therefore, the sum of the deviations and/or further deviations can be determined to that point, where compensating starts.

[0036] In FIG. 2, a plot of the relative layer height, i. e. the layer thickness, over the layer length is schematically illustrated. The shown layer height is not compensated for deviations. At the edge of the layer, a clear excess of height is recognizable. This excess is caused by a contraction of the printing ink of the layer at the edges of the layer, which is caused by surface effects, such as surface tension, of the printing ink. As the diameter of the layer decreases, the excesses at the edges move closer together until they merge with each other at diameters of less than about 5 mm and become an excess of the entire layer.

[0037] In FIG. 3, dither patterns 4 used in a printing method according to an exemplary embodiment of the present invention are schematically illustrated. SubFIG. 3 (a) shows a dither pattern 4 for a round layer. The white spots mark positions where blank spaces, i. e. positions where no printing ink is to be placed, are provided. The distribution of blank spaces in inhomogeneous. More blank spaces are provided at the edges of the layer than in the center, which results in slightly rising flanks of the layer. SubFIG. 3 (b) shows a detail of subFIG. 3 (a). The progression of the distribution of blank spaces from more at the edge of the layer to less at the center of the layer can be clearly seen. The blank spaces are not evenly spaced. The positions of the blank spaces are rather shifted by hardly recognizable random offsets against each other. This prevents unwanted optical grid effects. SubFIG. 3 (c) shows a detail of a dither pattern 4. To compensate for an excess of thickness resulting from a contraction of the layer at the edges, the dither pattern 4 provides blank spaces arranged in a strip parallel to the circumference of the layer. The strip corresponds to the part of the layer described above and in the claims. The strip is provided as a closed ring with a width of approximately 0.5 mm and a distance of approximately 0.5 mm from the circumference.

KEY TO FIGURES

[0038] 1 Optical structure [0039] 2 Layer [0040] 3 Further layer [0041] 4 Dither pattern [0042] d Diameter [0043] L Layers