METHOD FOR PRINTING AN OPTICAL COMPONENT WITH TRUE LAYER SLICING

Abstract

A method for printing a three-dimensional optical structure, in particular an ophthalmic lens, wherein the three-dimensional optical structure is built up from layers of printing ink deposited through targeted placement of droplets of printing ink at least partially side by side in consecutive printing steps, wherein a slicing (3) of the three-dimensional structure to be printed is adapted depending on a predefined true layer shape (2) so that during at least one printing step at least one layer is printed depending on the predefined true layer shape (2), wherein the predefined true layer shape (2) comprises the shape and/or volume characteristics of a typical printed layer.

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; and adapting a slicing of the three-dimensional optical structure to be printed depending on a predefined true layer shape so that during at least one printing step n at least one layer is printed depending on the predefined true layer shape; wherein the predefined true layer shape comprises shape and/or volume characteristics of a typical printed layer. wherein the typical printed layer is an average layer deposited by a specific printer, depending on a print head and printing ink used; wherein the predefined true layer shape is determined in a calibration step prior to the at least one printing step n; wherein determining the predefined true layer shape comprises printing at least one calibration layer and measuring a shape and/or volume of the at least one calibration layer at least once during the calibration step; wherein multiple calibration layers are deposited and their volume and/or shape are measured and averaged, respectively.

2. (canceled)

3. (canceled)

4. (canceled)

5. The method according to claim 1, wherein the shape and/or volume of the at least one calibration layer are determined through an area measurement during the calibration step.

6. The method according to claim 1, wherein the shape and/or volume of the at least one calibration layer are determined through a line measurement during the calibration step.

7. The method according to claim 1, wherein the at least one layer is printed during the at least one printing step n depending on a feedforward of the predefined true layer shape.

8. The method according to claim 1, wherein the at least one layer is printed during the at least one printing step n depending on a feedback of the predefined true layer shape.

9. The method according to claim 1, wherein a height and/or shape of a slice corresponding to the at least one layer is adapted depending on the predefined true layer shape.

10. The method according to claim 9, wherein the height and/or shape of the slice corresponding to the at least one layer is adapted during the at least one printing step n.

11. The method according to claim 1, wherein the at least one layer is printed depending on a virtual slicing of a remaining structure R.sub.n to be printed, wherein the remaining structure R.sub.n to be printed is determined by a difference of the full three-dimensional optical structure and a structure printed during the printing steps preceding the at least one printing step.

12. The method according to claim 11, wherein the structure printed during the printing steps preceding the at least one printing step n is determined using the predefined true layer shape.

13. The method according to claim 12, wherein the at least one printing step n is the n-th printing step and the remaining structure R.sub.n to be printed is determined as the difference between a remaining structure R.sub.n−1 to be printed of an (n−1)-th printing step and the predefined true layer shape, wherein n>1.

14. The method according to claim 6, wherein multiple line measurements at defined angles are carried out.

15. The method according to claim 5, wherein a height and/or shape of a slice corresponding to the at least one layer is adapted depending on the predefined true layer shape.

16. The method according to claim 15, wherein the at least one layer is printed depending on a virtual slicing of a remaining structure R.sub.n to be printed, wherein the remaining structure R.sub.n to be printed is determined by a difference of the full three-dimensional optical structure and a structure printed during the printing steps preceding the at least one printing step.

17. The method according to claim 16, wherein the structure printed during the printing steps preceding the at least one printing step n is determined using the predefined true layer shape.

18. The method according to claim 17, wherein the at least one printing step n is the n-th printing step and the remaining structure R.sub.n to be printed is determined as the difference between a remaining structure R.sub.n−1 to be printed of an (n−1)-th printing step and the predefined true layer shape, wherein n>1.

19. The method according to claim 6, wherein a height and/or shape of a slice corresponding to the at least one layer is adapted depending on the predefined true layer shape.

20. The method according to claim 19, wherein the at least one layer is printed depending on a virtual slicing of a remaining structure R.sub.n to be printed, wherein the remaining structure R.sub.n to be printed is determined by a difference of the full three-dimensional optical structure and a structure printed during the printing steps preceding the at least one printing step.

21. The method according to claim 20, wherein the structure printed during the printing steps preceding the at least one printing step n is determined using the predefined true layer shape.

22. The method according to claim 21, wherein the at least one printing step n is the n-th printing step and the remaining structure R.sub.n to be printed is determined as the difference between a remaining structure R.sub.n−1 to be printed of an (n−1)-th printing step and the predefined true layer shape, wherein n>1.

23. The method according to claim 19, wherein multiple line measurements at defined angles are carried out.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1 schematically illustrates a printing method according to an exemplary embodiment of the present invention.

[0022] FIG. 2 schematically illustrates the calibration step according to an exemplary embodiment of the present invention.

[0023] FIG. 3 schematically illustrates a printing method according to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION

[0024] 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.

[0025] 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.

[0026] 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.

[0027] In FIG. 1, a printing method according to an exemplary embodiment of the present invention is schematically illustrated.

[0028] According to the state of the art, a three-dimensional structure 1 is virtually sliced into two-dimensional slices. For each of these slices, a layer of printing ink is deposited from the ejection nozzles of a print head of an inkjet printer. Due to the surface tension of the deposited printing ink, the shape of the deposited layer differs from the intended shape defined by the corresponding slice. When printing ophthalmic lenses, for example, the slices are of a cylindrical shape with a top and bottom surface which are flat and parallel to each other. Due to surface tension and viscosity effects, the top surface of the corresponding deposited layer is not flat, however. Generally, a meniscus forms along the edge of the top surface of the deposited layer. Hence, excess printing ink accumulates along the top edge of the layer, forming a ring shaped protrusion on the top surface. This protrusion is accompanied by a ring shaped depression with only an insufficient amount of printing ink. If not accounted for, these deviations accumulate resulting in an error prone three-dimensional optical structure.

[0029] In order to account for these deviations, the method according to the present invention takes into account the true layer shape, i.e. the actual shape of the deposited layers during the printing process, during at least one printing step. The true layer shape is provided in the form of a predefined true layer shape comprising the shape and/or volume characteristics of a typical printed layer. The typical printed layer is specific for a specific printer, printing ink and/or printer settings. It comprises the shape and/or volume characteristics of an average layer of the specific printing ink deposited with the specific printer with the specific printer settings. Preferably, the predefined true layer shape is obtained during a calibration step prior to the at least one printing step, see FIG. 2. During the calibration step, a calibration layer is deposited and the shape and/or volume of the calibration layer is determined at least once. Preferably, multiple calibration layers are deposited and their volume and/or shape measured and averaged, respectively. Particularly preferably, the measured volume or, in case of multiple measurements, the averaged volume is fitted to a predefined volume function. Alternatively or additionally, the measured shape or, in case of multiple measurements, the averaged shape is fitted to a predefined shape function. The shape and/or volume are determined through a two-dimensional measurement. Alternatively, the shape and/or volume are determined through one or multiple one-dimensional, i.e. line, measurements. Line measurements are time and cost saving and particularly suitable for slices with at least one axis of symmetry in the printing plane. For a cylindrical slice as used in printing ophthalmic lenses, a one-dimensional lines measurement suffices to capture the volume and/or shape characteristics of the typical printed layer. In the example depicted in FIG. 2, shape is determined through height measurements of the at least one calibration layer. The height profile can, for example, be determined through confocal height measurements. Here, confocal height measurements of ten calibration layers are carried out and averaged to obtain a height profile of a typical printed layer. As can be inferred from the averaged relative layer height (dotted line), the typical printed layer is not flat. In particular, the top surface of the typical printed layer is non-flat. A protrusion and a neighboring depression forms due to surface tension and viscosity effects. The averaged shape given by the height profile is fitted to a predefined shape function (solid line). The predefined shape function is, for example

[00001]$f\left(x\right)=1-e^{-\mathrm{ax}}.Math.\frac{\sin \left(\mathrm{bx}+c\right)}{\sin \left(c\right)}$

[0030] Here, a, b, c define the parameters to be fitted. The variable x describes the length along a diameter of the calibration layer. A predefined shape and/or volume function allows a compact and efficient means to determine, capture and store the shape and/or volume characteristics of a typical printed layer. The predefined true layer shape is then, for example, provided in the form of the fitted predefined shape function and/or in the form of the fitted predefined volume function. Alternatively, the shape and/or volume characteristics are provided in the form of a lookup table.

[0031] According to the present invention, the three-dimensional optical structure is built up 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 one layer is printed during the corresponding at least one printing step depending on the predefined true layer shape determined during the calibration step as described above. The predefined true layer shape is e.g. provided in the at least one printing step either by a feedforward or a feedback of the corresponding shape and/or volume function. Preferably, the slicing of the structure to be printed during the at least one printing step is adapted depending on the predefined true layer shape. For example, the height and/or shape of the slice corresponding to the at least one layer is adapted during the at least one printing step.

[0032] Preferably, the predefined true layer shape is used to adapt the slicing of multiple layers during the respective printing steps. For example, after an initialization step I during which the initial layers are printed, the predefined true layer shape is provided during at least one printing step through a feedforward FF. The at least one printing step is the n-th printing step, e.g. n=2.

[0033] During the at least one printing step, three substeps S1, S2 and S3 are carried out. First, the remaining structure R to be printed is determined in a substep S1. The remaining structure R.sub.n to be printed in the n-th printing step is obtained as the difference of the remaining structure R.sub.n−1 to be printed in the (n−1)-th printing step and the previously deposited layer.

[0034] The previously deposited layer is taken into account in the form of the predefined true layer shape 2, as depicted in FIG. 3. From the remaining structure R.sub.n−1 the predefined true layer shape 2 is subtracted. Hence, the remaining structure R.sub.n is obtained. The remaining structure R.sub.n is virtually sliced into two-dimensional slices 3 providing the printing data for the n-th printing step. This is done during the true-layer slicing substep S2 of the at least one printing step. Actual printing of the at least one layer is carried out during the substep S3 of the at least one printing step. The layer corresponding to the lowest slice obtained from the true-layer slicing 3 is deposited during the substep S3. Preferably, substeps S1-S3 are repeated for multiple layers. Particularly preferably, substeps S1-S3 are repeated until the three-dimensional optical structure 1 is finished. Substeps S1-S3 are optionally followed by the finalizing step F. The finalizing step F comprises, for example, conventional printing of the remaining layers that need to be printed to finish the three-dimensional optical structure 1 in case not all layers are printed using the true layer slicing 3 and the predefined true layer shape 2. The finalizing step F can also comprise edging, surfacing, coating and other methods needed to finalize the printed three-dimensional optical structure 1.

[0035] KEY TO FIGS. [0036] 1 Three-dimensional optical structure [0037] 2 Predefined true layer shape [0038] 3 True layer slicing [0039] I Initialization step [0040] S1 Determination of remaining structure to be printed [0041] S2 True-layer slicing [0042] S3 Printing step [0043] FF Feedforward of true layer shape [0044] F Finalizing step [0045] R.sub.n Remaining structure to be printed (n-th printing step) [0046] n Number of printing step