PRINTING SYSTEM AND METHOD FOR PRINTING A THREE-DIMENSIONAL OPTICAL STRUCTURE, PROVIDING REAL-TIME QUALITY CONTROL OF THE PRINTED OPTICAL STRUCTURE

Abstract

A printing system for printing a three-dimensional optical component, including a printing unit having a print head with ejection nozzles for ejecting droplets of printing ink, a measurement unit to measure optical properties of a pre-structure of the three-dimensional optical component, wherein the measurement unit includes at least one light source and at least one light detector, further including a process control unit for determining the difference between the measured optical properties of the pro-structure and target optical properties of the pre-structure. The present teachings further relate to a corresponding method.

Claims

1. A printing system for printing a three-dimensional optical component comprising a printing unit comprising a print head with ejection nozzles for ejecting droplets of printing ink, comprising a measurement unit to measure optical properties of a pre-structure of the three-dimensional optical component, wherein the measurement unit comprises at least one light source and at least one light detector, further comprising a process control unit for determining a difference between measured optical properties of the pre-structure and target optical properties of the pre-structure.

2. The printing system according to claim 1, wherein the measurement unit is a shadowgraph and the measured optical properties of the pre-structure are recorded as an actual shadowgram.

3. The printing system according to claim 1, wherein the measurement unit is a schlieren measurement unit and the measured optical properties of the pre-structure are recorded as an actual schlieren image.

4. The printing system according to claim 1, wherein the printing system comprises at least one UV-light source that emits UV light of differing intensity and/or with differing exposure time and/or wavelength at least two different points on the pre-structure resulting in aspatially varying exposure of the pre-structure to UV light.

5. A method for printing a three-dimensional optical component, wherein the optical component is built up successively by depositing droplets of printing ink side by side and one above the other by means of a print head in several consecutive depositing steps, wherein after at least one depositing step, optical properties of a pre-structure of the optical component built up by the deposited droplets are measured by a measurement unit in a measurement step, wherein during the measurement step the optical properties of the pre-structure are being measured by measuring the properties of light, wherein the light has been emitted from at least one light source and wherein the light has passed through and/or has been reflected from the pre-structure before its properties are being measured by at least one detector and wherein a difference between measured optical properties and target optical properties is determined in a process control step.

6. The method according to claim 5, wherein during the measurement step the optical properties of the pre-structure are being measured through a shadowgraph and the measured optical properties are recorded by the measurement unit as an actual shadowgram of the pre-structure.

7. The method according to claim 6, wherein the target optical properties of the pre-structure are encoded in a target shadowgram and wherein during the process control step the difference between the target optical properties and the measured optical properties is being determined as the difference between the target shadowgram and the actual shadowgram.

8. The method according to claim 5, wherein during the measurement step the optical properties of the pre-structure are being measured through a schlieren measurement and the measured optical properties are recorded by the measurement unit as an actual schlieren image of the pre-structure.

9. The method according to claim 8, wherein the target optical properties of the pre-structure are encoded in a target schlieren image and wherein during the process control step the difference between the target optical properties and the measured optical properties is being determined as the difference between the target schlieren image and the actual schlieren image.

10. The method according to claim 5, wherein the target optical properties of the pre-structure are encoded in a target intensity image which is a projection of the pre-structure, which is three-dimensional, on a two-dimensional plane where a height of the pre-structure is encoded in intensity of image pixels.

11. The method according to claim 10, wherein the optical properties of the pre-structure measured by the measurement unit during the measurement step are translated into an actual intensity image.

12. The method according to claim 11, wherein during the process control step the difference between the target optical properties and the measured optical properties is being determined as the difference between the target intensity image and the actual intensity image.

13. The method according to claim 5, wherein during the process control step a configuration of the print head is adapted depending on the difference between the target optical properties and the measured optical properties of the pre-structure.

14. The method according to claim 5, wherein during the process control step a configuration of the print head is adapted depending on the measured optical properties of the pre-structure.

15. The method according to claim 5, wherein during a preparation step, a support structure that is permeable for visible light is printed on a substrate on top of which the optical component s printed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0092] FIG. 1 illustrates schematically a printing system and a method for printing a three-dimensional structure, in particular an optical component, by depositing droplets of printing ink side by side and one above the other in several consecutive depositing steps by means of a print head according to an exemplary embodiment of the present invention.

[0093] FIG. 2 illustrates schematically a measurement unit and a method for measuring the optical properties of the printed pre-structure by measuring visible light that has either passed through or that has been reflected from the pre-structure with the help of a detector system and a method for printing an optical three-dimensional structure according to an exemplary embodiment of the present invention.

[0094] FIG. 3 illustrates schematically a method and a printing system for printing a three-dimensional structure on top of a support structure.

[0095] FIG. 4 illustrates different steps of the method according to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION

[0096] 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.

[0097] 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.

[0098] 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.

[0099] In FIG. 1, a method and a printing system 1 for printing a three-dimensional structure 2 are schematically illustrated. In the present example, the three-dimensional structure 2 comprises an optical component and in particular an ophthalmic lens.

[0100] The printing system 1 comprises a print head 3 equipped with a plurality of ejection nozzles 4. The ejection nozzles 4 are arranged in parallel on the lower side of the print head 3. Each ejection nozzle 4 is in fluid connection with a reservoir of printing ink (not shown) and comprises piezoelectric crystals to eject a droplet 6 of printing ink from the print head towards a substrate 5. The printing system 1 can therefore also be referred to as DOD (droplets-on-demand) inkjet printer. In each depositing step 14, a volley of several droplets 6 are ejected in parallel and simultaneously towards the substrate 5, so that a layer of deposited droplets 6 arranged side by side onto the substrate 5 is generated. With each following depositing step 14, a further layer of deposited droplets 6 are provided onto the former layer of deposited droplets 6.

[0101] After deposition of the droplets 6, adjacent deposited droplets 6 merge at least partially which each other (the deposited droplets 6 are therefore not illustrated) and are subsequently cured in a curing step 17 by UV-light emitted by LED's (light emitting diodes) 9 of the print head 3. The printing ink comprises a transparent or trans-lucent printing ink, preferably an UV curable liquid monomer becoming a polymer if being cured. The depositing steps 14 and the curing steps 17 are repeated subsequently until a desired three-dimensional structure 2 is built up.

[0102] In order to deposit droplets 6 in certain positions onto the substrate 5, the ejection nozzles 4 are individually controllable by a printing controller of the printing system 1. The horizontal extension of the print head 1 is substantially greater than the horizontal extension of the three-dimensional structure 2 to be printed, so that a movement of the print head 3 relative to the substrate 5 is not necessary to build up the three-dimensional structure 2 in the present example. The print head 3 typically comprises around 100 to 5.000 ejection nozzles 4 arranged in parallel. The print head 3 and the substrate 5 are movable relative to each other. In the present example, movement of the print head 3 relative to the substrate 5 is obtained either by actively driving the print head 3 or by actively driving the substrate 5 respectively by corresponding drive units (not shown).

[0103] The print head 3 and in particular the individual ejection nozzles 4 are controlled by the printing controller in dependency of an intensity image (not shown). The intensity image comprises a two-dimensional patter of different greyscale intensities. The pattern consists of different pixels, wherein each pixel represents a certain position in the three-dimensional structure 2 to be printed. In particular, each pixel represents a certain position of a two-dimensional projection of the three-dimensional structure 2 onto the substrate 5. The intensity in each pixel of the intensity image represents the height of the three-dimensional structure 2 at the corresponding position and therefore the number of droplets 6 to be deposited in this position by the corresponding ejection nozzles 4 in subsequent depositing steps 14. The printing controller now controls each of the plurality of printing nozzles 4 in such a manner that the number of droplets 6 deposited in each position on the substrate 5 corresponds to the intensity of the intensity image after all depositing steps 14 have been subsequently performed. The three-dimensional structure 2 is thereby built up step by step until the amount of printing material deposited in each position corresponds to the intensity of the pixels of the intensity image. In this manner, the droplets 6 are deposited side by side and one above the other in order to generate the desired three-dimensional structure 2. As mentioned above, curing steps 17 are performed optionally between two subsequent depositing steps 14 in order to partially cure the deposited droplets 6 and to avoid that the deposited droplets 6 completely deliquesce after deposition.

[0104] In practice, the ejection characteristics of the ejection nozzles 4 are affected by clogging of printing ink and contamination with e.g. foreign particles and impurities. For this reasons, it happens from time to time that one or few ejection nozzles 4 of the print head 3 eject(s) less amount of printing ink with each droplet 6 in each depositing step 14 or that the ejection direction of the droplet 6 to be deposited is affected. Ejection nozzles 4 with a suchlike ejection characteristic are hereinafter referred to as malfunctioning ejection nozzles 4. Furthermore, it can happen that a certain ejection nozzle 4 ejects more printing ink with each droplet 6 than usual. These ejection nozzles 4 are also hereinafter referred to as malfunctioning ejection nozzles 4. All other ejection nozzles 4 being not clogged and working property are hereinafter referred to as property functioning ejection nozzles 4. As malfunctioning ejection nozzles 4 sometimes open up again (declogging) and properly functioning ejection nozzles 4 get clogged due to unpredictable circumstances, the locations of the malfunctioning ejection nozzles 4 inside the print head 3 changes and cannot be determined or considered upfront before putting the printing system 1 into operation.

[0105] The resulting deviations of the ejection characteristics between malfunctioning ejection nozzles 4 and properly functioning ejection nozzles 4 in the same print head 3 lead to imperfections 7 in the printed three-dimensional structure 2. Examples for imperfections are depressions, indentations and entrapments of air, wherein the depressions, indentations and entrapments are not part of the design of the optical structure. These imperfections sum up with each layer of deposited droplets 6. Usually, these imperfections are so small that no visible and disturbing influences occur. However, in the present example, the three-dimensional structure 2 comprises an ophthalmic lens, wherein even the finest small imperfections lead to serious optical defects disturbing the optical beam path when using the ophthalmic lens. In particular, these imperfections generate unwanted diffractive phenomena.

[0106] In order to avoid these imperfections in the printed three-dimensional structure 2, although the print head 3 comprises malfunctioning ejection nozzles 4 as well as properly functioning ejection nozzles 4, the printing system 1 is provided with a measuring unit 16. In the present example, the measurement unit comprises a light source 9 located below the substrate 5 and two detectors 11 wherein one detector is located above the substrate 5 and one detector is located below the substrate 5. The measurement unit measures optical properties of a pre-structure 2 being built up by droplets 6 deposited in one or more previous depositing steps 14. This measuring step 15 is performed after each depositing step 14 or after at least a predefined number of depositing steps 14.

[0107] In FIG. 2, a measurement unit and a method for measuring the optical properties of a pre-structure 2 being build up during the printing process of a three-dimensional optical structure 2 are schematically illustrated. In the present example, the measurement unit comprises one light source 9 and two detectors 11.

[0108] The measurement unit is preferably configured to measure the optical properties of the pre-structure by measuring the optical properties of light 8 emitted by the light source 9 after having passed through the substrate 5 and pre-structure 2 on a detector 11 placed above the substrate 5 and pre-structure 2 and by measuring the optical properties of light 8 emitted by the light source 9 after having been reflected from the substrate 5 and pre-structure 2 on a detector 11 placed below the substrate 5 and pre-structure 2.

[0109] The measured optical property data are provided by the measurement unit to a process control unit (not shown). The processing unit compared the actual, measured optical properties of the pre-structure with the target optical properties in a process control step 16. The target optical properties are e.g. stored in the process control unit and encode the information on how the optical properties of the pre-structure should theoretically be if all ejected nozzles worked perfectly well and properly and no other irregularities during the printing process occurred. In this way, deviations between the actual optical properties and the target optical properties can be identified and used to initialize compensation measures in at least one of the following depositing steps 14 or in at least one of the following curing steps 17.

[0110] In FIG. 3, a method and a printing system 1 for printing a three-dimensional structure 2 on top of a support structure 12 are schematically illustrated. In the present example, the three-dimensional structure 2 comprises an optical component and in particular an ophthalmic lens.

[0111] The support structure 12 is printed on the substrate 5 in a preparation step 13 wherein the support structure 12 is built up successively by depositing droplets of a second printing ink side by side and one above the other by means of a print head 3 in several consecutive printing steps. The droplets at least partially merge. The droplets are cured using at least one UV light 8 after at least one printing step. If the support structure has reached the desired shape, it is finally hardened in a final curing step. The finally hardened support structure is the end product of the preparation step 13. After the preparation step, the printing process of the three-dimensional optical structure is carried out. The three-dimensional optical structure is built up successively by depositing droplets 6 of printing ink side by side and one above the other by means of a print head 3 on the support structure. The surface of three-dimensional optical structure built up in this way in several consecutive depositing steps that faces the support structure inherits its shape from the support structure.

[0112] In FIG. 4, different steps of the method according to the exemplary embodiment of the present invention are shown. As described above, the method comprises an optional preparation step 13 during which a support structure 12 is printed on the substrate 5, followed by a depositing step 14 of ejecting a plurality of droplets 6 simultaneously and in parallel towards the substrate 5 and/or support structure 12, followed by a measurement step 15 during which the optical properties of the pre-structure 2 built up in the preceding depositing steps 14 are being measured, followed by a process control step 16 during which the difference between the measured optical properties of the pre-structure 2 and target optical properties of the pre-structure 2 is being determined, followed by a curing step 17 during which the deposited droplets are at least partially cured using UV light 8. If the difference between the measured optical properties of the pre-structure 2 and the target optical properties of the pre-structure 2 is above a specified threshold, the print head 3 is adapted depending on the difference between the measured optical properties of the pre-structure 2 and the target optical properties of the pre-structure 2 such that the deviations of the measured optical properties of the pre-structure 2 from the target optical properties of the pre-structure 2 can be compensated in the following depositing step 14. Steps 14-17 are repeated until the difference between the measured optical properties of the pre-structure 2 and the target optical properties of the pre-structure 2 is below the specified threshold in which case final curing is carried out during the final curing step 18.

KEY TO FIGURES

[0113] 1 Printing System [0114] 2 Three-dimensional optical structure [0115] 3 Print Head [0116] 4 Ejection Nozzle [0117] 5 Substrate [0118] 6 Droplet [0119] 7 Imperfection [0120] 8 UV light [0121] 9 Light Source [0122] 10 Light [0123] 11 Detector [0124] 12 Support Structure [0125] 13 Preparation Step [0126] 14 Depositing Step [0127] 15 Measurement Step [0128] 16 Process Control Step [0129] 17 Curing Step [0130] 18 Final Curing Step