Abstract
Method for printing a multifocal lens (1) with a sharp transition region, comprising a base lens (2) and at least one segment lens (3) comprising the following steps:—virtually slicing the three-dimensional shape of the multifocal lens (1) into two-dimensional slices (9), resulting in a number Nbase of slices ji, . . . , jNbase of the base lens (2) and a number Nsegment of slices i1 . . . , iNSegment of the at least one segment lens (3),—providing a number Nfinish of layers printed as surface-finishing layers (4),—printing the base lens (2) in a base-lens printing step and consecutively printing the segment lens (3) in a segment-lens printing step on top of the base lens (2) through a targeted placement of droplets of printing ink at least partially side by side, wherein in the base-lens printing step first Nbase-Nfinish structure layers (5) and then Nfinish surface-finishing layers (6) are printed and in the segment-lens printing step first NsegmentNfinish structure layers (7) and then Nfinish surface-finishing layers (8) are printed.
Claims
1. A method for printing a multifocal lens comprising a base lens and at least one segment lens comprising the following steps: virtually slicing a three-dimensional shape of the multifocal lens into two-dimensional slices, resulting in a number N.sub.base of slices j.sub.1, . . . , j.sub.Nbase of the base lens and a number N.sub.segment of slices i.sub.1, . . . , i.sub.Nsegment of the at least one segment lens; providing a number N.sub.finish of layers printed as surface-finishing layers; printing the base lens in a base-lens printing step and consecutively printing the segment lens in a segment-lens printing step on top of the base lens through a targeted placement of droplets of printing ink at least partially side by side; wherein in the base-lens printing step first N.sub.base-N.sub.finish structure layers and then N.sub.finish surface-finishing layers are printed and in the segment-lens printing step first N.sub.segment-N.sub.finish structure layers and then N.sub.finish surface-finishing layers are printed; and wherein the 2N.sub.finish surface-finishing layers are printed using a printing process defined by droplet size and/or printing speed and/or droplet density that differ from respective properties used in printing the structure layers.
2. The method according to claim 1, wherein the N.sub.segment-N.sub.finish structure layers printed during the segment-lens printing step correspond to the slices i.sub.Nfinish+1, . . . , i.sub.Nsegment-Nfinish of the at least one segment lens and the N.sub.finish surface-finishing layers printed during the segment-lens printing step correspond to the slices i.sub.1, . . . , i.sub.Nfinish of the at least one segment lens.
3. The method according to claim 2, wherein the first surface-finishing layer printed during the segment-lens printing step corresponds to the slice i.sub.Nfinish, the second to the slice i.sub.Nfinish-1 etc. and the last surface-finishing layer printed during the segment-lens printing step to the slice i.sub.1 of the at least one segment lens.
4. (canceled)
5. The method according to claim 1, wherein at least one of the 2N.sub.finish surface-finishing layers is printed in multi-pass mode.
6. (canceled)
7. The method according to claim 1, wherein at least one layer is pin cured through exposition to ultraviolet light, wherein during pin curing, the deposited droplet or droplets are only partially cured.
8. (canceled)
9. (canceled)
10. The method according to claim 1, wherein 4≤N.sub.finish≤12.
11. The method according to claim 1, wherein the multifocal lens is cured through exposure to ultraviolet light after the segment-lens printing step.
12. A multifocal lens printed with a method according to claim 1, comprising a base lens and at least one segment lens on the base lens with a sharp transition between the base lens and the at least one segment lens, wherein the segment lens is printed on a surface-finishing layer.
13. The method according to claim 7, wherein the ultraviolet light is UVA light.
14. The method according to claim 10, wherein N.sub.finish=8.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 schematically illustrates a printing method and a multifocal lens printed with a printing method according to the state of the art.
[0022] FIG. 2 schematically illustrates a printing method and a multifocal lens printed with a printing method according to an exemplary embodiment of the present invention.
DETAILED DESCRIPTION
[0023] 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.
[0024] 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.
[0025] 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.
[0026] In FIG. 1 a printing method and a multifocal lens 1 printed with a printing method according to the state of the art is schematically illustrated. The multifocal lens 1 comprises a base lens 2 and at least one segment lens 3, providing the multifocal lens 1 with at least two areas of differing optical functions. For example, a bifocal lens comprises a base lens 2 and a single segment lens 3. The base lens 2 has a focal point in the far distance, so that the base lens 2 provides a far-view area or far-view field of the multifocal lens 1. The segment lens 3 is for example provided in the lower half of the base lens 2 and has a focal point in reading distance, providing a near-view area or near-view field of the multifocal lens 1. Trifocal or higher multifocal lenses 1 comprise three or more segment lenses 3. Preferably, the segment lens 3 is a convex lens. In a first preparatory step, the three-dimensional shape of the multifocal lens 1 is virtually sliced into two-dimensional slices j.sub.1, . . . , j.sub.Nbase, i.sub.1, . . . , i.sub.Nsegment. Preferably, virtual slicing is carried out on a computer by a corresponding software programme called “Slicer”. The resulting virtual slices j.sub.1, . . . , j.sub.Nbase, i.sub.1, . . . , i.sub.Nsegment serve as input for the printer. Preferably, a slicer software converts the three-dimensional shape of the multifocal lens 1 into a set of slices j.sub.1, . . . , j.sub.Nbase, i.sub.1, . . . , i.sub.Nsegment that is conveyed to the printer in machine code, e.g. G-code. The base lens 2 and the segment lens 3 are hence described by slices N.sub.base slices j.sub.1, . . . , j.sub.Nbase and N.sub.segment slices i.sub.1, . . . , i.sub.Nsegment, respectively. In state of the art printing methods, a number of surface-finishing layers N.sub.finish is defined. Surface-finishing layers endow the printed structure with a smooth surface and .sup.hence the desired optical quality. Preferably, the number N.sub.finish of surface-finishing layers is between four and 12. In a second step, the multifocal lens 1 is printed. Through ejection of droplets of printing ink from nozzles of a print head towards a substrate, layers of printing ink are formed. The printing ink is preferably transparent or translucent and photo-polymerizable, e.g. the printing ink comprises a monomer that polymerizes upon exposure to ultraviolet light. For each slice j.sub.1, . . . , j.sub.Nbase-Nfinish, i.sub.1, . . . , i.sub.Nsegment-Nfinish a structure layer is deposited, such that the structure of the multifocal lens 1 is built up from structure layers. Preferably, first, structure layers corresponding to slices slice j.sub.1, . . . , j.sub.Nbase of the base lens are printed and pin cured before the structure layers corresponding to slices i.sub.1, . . . , i.sub.Nsegment-Nfinish are deposited on top. In a third step, the N.sub.finish surface-finishing layers are printed on the surface of the structure obtained in the previous step. The surface-finishing layers cover the entire surface of the structure deposited so far. The surface-finishing layers are likewise printed through a targeted placement of droplets of printing ink at least partially side by side. These droplets of printing ink are ejected from the ejection nozzles of the print head. The surface-finishing layers are deposited with the aim to create a smooth surface on the printed structure in order to endow the printed structure with the desired optical quality. In the case of a multifocal lens 1 comprising a base lens 2 and at least one segment lens 3, however, a meniscus is created at the border between the base lens 2 and the at least one segment lens 3. The meniscus forms as a result of surface tension of the deposited surface-finishing layers. The transition 10 between the base lens 2 and the at least one segment lens 3 is hence not sharp, but blurred and smoothed out, see the lower panel of FIG. 1. This results in optical aberrations compromising the quality of the printed multifocal lens 1. In current state of the art methods, the printed multifocal lens 1 is cured, e.g. through exposition to ultraviolet light, after deposition of the surface-finishing layers.
[0027] In FIG. 2 a printing method and a multifocal lens 1 printed with a printing method according to an exemplary embodiment of the present invention is schematically illustrated. The printing method differs from the state of the art printing method illustrated in FIG. 1, in the printing step. Prior to print, the shape of the multifocal lens 1 is virtually sliced into two-dimensional slices j.sub.1, . . . , j.sub.Nbase, i.sub.1, . . . , i.sub.Nsegment, which preferably serve as input for the printer. Printing is carried through a targeted placement of droplets of printing ink at least partially side by side such that layers are formed. Printed layers correspond to the two-dimensional slices obtained prior to print. The printing ink is preferably transparent or translucent and photo-polymerizable, e.g. the printing ink comprises a monomer that polymerizes upon exposure to ultraviolet light. A number N.sub.finish of surface-finishing layers is provided. Preferably, 4≤N.sub.finish≤12, particular preferably N.sub.finish=8. Printing of surface-finishing layers is known in the state of the art and serves the purpose of establishing a smooth final surface of the printed three-dimensional optical component, here of the multifocal lens 1. In contrast to prior methodology, in the printing method according to an exemplary embodiment of the present invention, the base lens 2 is printed in a base-lens printing step, followed by a segment-lens printing step during which the segment lens 3 is printed. In the base-lens printing step, first N.sub.base-N.sub.finish structure layers 5 and then N.sub.finish surface-finishing layers 6 are printed and in the segment-lens printing step, first N.sub.segment-N.sub.finish structure layers 7 and then N.sub.finish surface-finishing layers 8 are printed. That means, in contrast to existing methods, in the method according to the present invention, surface-finishing layers 6 are printed prior to printing any of the segment-lens layers 7, 8. The segment lens 3 is printed on surface-finishing layers 6. This advantageously prevents the formation of a meniscus through the deposition of the surface-finishing layers 8 of the at least one segment lens 3. Hence, a sharp transition 10 results as can be seen in the lower panel in FIG. 2. Preferably, the pinning energy of the N.sub.finish surface-finishing layers 6 of the base lens 2 is optimized such that adhesion of the segment lens structure layers 7 and/or the sharpness of the transition 10 between base lens 2 and at least one segment lens 3 is maximized. Preferably, the structure layers 7 of the at least one segment lens 3 correspond to the slices i.sub.Nfinish+1, . . . , i.sub.Nsegment-Nfinish of the at least one segment lens 3 and the N.sub.finish surface-finishing layers 8 printed during the segment-lens printing step correspond to the slices i.sub.1, . . . , i.sub.Nfinish of the at least one segment lens 3. That means, preferably the first N.sub.finish slices of the at least one segment lens 3 are skipped when printing the segment lens structure layers 7. These slices are preferably printed as segment lens surface-finishing layers 8 on top. This advantageously increases the sharpness of the transition 10. A further increase in sharpness is obtained if the order in which the slices are printed as surface-finishing layers 8 is reversed. Preferably, the surface-finishing layer 8 corresponding to the slice i.sub.Nfinish is printed first, followed by the surface-finishing layer 8 corresponding to the slice i.sub.Nfinish-1 etc. and the surface-finishing layer 8 corresponding to the slice i.sub.1 is printed last. The usual application comprises at least one convex segment lens 3. For a convex segment lens 3, the reversed order of printing of the surface-finishing layers 8 implies that the layers are printed in the order of increasing surface. Due to the flow characteristics of the printed layers, a smoother surface of the at least one segment lens 3 advantageously results. In an alternative embodiment, the surface size of the surface-finishing layers 8 is optimized with respect to the sharpness of the transition 10. I.e. the surface-finishing layers 8 are no longer determined by the size of the slices i.sub.1, . . . , i.sub.Nsegment derived from the shape of the multifocal lens 1. Preferably, at least one of the surface-finishing layers 6, 8 is printed in multi-pass mode. Multi-pass printing comprises a decomposition of a single layer 6, 8 into multiple sublayers such that through printing of all sublayers the original single layer 6, 8 is recovered. I.e. each sublayer covers only part of the original single layer 6, 8. Known in two-dimensional printing to eliminate or reduce banding effects, i.e. irregularities in colour density, its application in three-dimensional printing advantageously eliminates or reduces geometrical irregularities such as ripples and waves that otherwise may form on the surface of the printed three-dimensional structure 1, compromising the optical quality of said structure. Preferably, the printing ink and/or printing process defined by printing properties such as e.g. speed and droplet size, used when printing the surface-finishing layers 6, 8 differ from the printing ink and/or printing process and/or printing properties used when printing the structure layers 5, 7, respectively. Preferably, the multifocal lens 1 is cured through exposition to ultraviolet light at the end of the segment-lens printing step.
KEY TO FIGURES
[0028] 1 Multifocal lens [0029] 2 Base lens [0030] 3 Segment lens [0031] 4 Surface-finishing layer [0032] 5 Base lens structure layer [0033] 6 Base lens surface-finishing layer [0034] 7 Segment lens structure layer [0035] 8 Segment lens surface-finishing layer [0036] 9 Slice i.sub.n [0037] 10 Transition
