A MORE EFFICIENT METHOD FOR PRODUCING THREE-DIMENSIONAL OBJECTS BY MEANS OF A RAPID PROTOTYPING PROCESS

Abstract

The invention relates to a device and a method for the production of three-dimensional objects, in particular of at least parts of dental prosthetic restorations, by a stripping device wiping off plastic material, which protrudes vertically beyond a container, into a collecting container and forms a projection surface. According to the invention, a stripping device and a light source are coupled and simultaneously guided, at a defined distance, across the liquid light-curing plastic material, whereby the stripping device is guided at a defined distance right ahead of the light source and forms the projection surface for the illuminated field of the light source.

Claims

1. Device comprising an assembly (0) with a light source, for production of a three-dimensional object by means of illuminating a liquid light-curing plastic material, having a container for accommodation of a bath of the light-curing liquid plastic material, having a building platform for positioning the object relative to the surface of the bath, wherein the light source and a stripping device are coupleable and in that the stripping device is arranged in front of the light source and/or in front of an illuminated field.

2. Device according to claim 1, wherein an assembly comprising the light source is coupleable to the stripping device and form an entire assembly, whereby the stripping device comprises a coupling device, and a coupling element is assigned to the light source or the assembly and a coupling device is assigned to the light source or the assembly.

3. Device according to claim 2, wherein the coupling element engages the coupling device in detachable manner.

4. Device according to claim 2, wherein the coupling element engages the coupling device in detachable manner and in that the coupling element is formed to be form-fitting with the coupling device, in that the coupling element is coupleable to the coupling device in detachable manner in force-locking, electrical or magnetic manner.

5. Device according to claim 2, wherein the coupling device comprises at least one element and in that the upper end of the stripping device is formed to take the shape of another element, whereby said elements are attached against each other by at least one elastic element and at least one fixation, and, optionally, the coupling element engages the elements laterally in form-fitting manner and is guided through, with a defined force, between the two elements that are attached by an elastic element and a fixation element in force-locking manner.

6. Device according to claim 1, wherein the device has an attenuator that triggers a guiding-through or sliding-through of the coupling element between the two elements of the coupling device.

7. Device according to claim 1, wherein the assembly serves for producing a homogenised distribution of light intensity and comprises an arrangement that comprises a spatially emitting light source, a spatial light modulator, and an optical system, with a lens system, in optionaly, being the optical system.

8. Device according to claim 1, wherein the liquid light-curing plastic material, optionally protruding plastic material of the arched surface, can be transferred into the at least one collecting container by means of a stripping device that can be driven along an axis of the container, whereby, optionally, a surface is formed as projection surface.

9. Device according to claim 1, wherein the drivable stripping device is guided directly along an axis of the container by means of the drive or propulsion of the light source, assembly or entire assembly.

10. Method for producing a three-dimensional object that is generated layer-by-layer, by one layer each being produced as a projection surface of a liquid light-curing plastic material and being polymerised in an illuminated field, at least in part, by light of a light source, that the method comprising: a) generating a layer of the liquid light-curing plastic material on a building platform or on a polymerised layer by guiding a stripping device, which is coupleable to a light source, in a bath of the liquid light-curing plastic material ahead of the illuminated field and/or ahead of the light source, and i) obtaining a layer to be polymerised as projection surface; and ii) polymerizing the layer to be polymerised generated in i) as projection surface of the liquid light-curing plastic material using an illuminated field by means of light of the light source in step a); and, optionally, b) i) in the region of a reversal point of the pathway of the stripping device or of the light source, coupling the stripping device is appropriately coupled to the light source such that the light source again guides the stripping device ahead of itself; and, optionally, ii) in step b), lowering the building platform by one layer thickness and, optionally, generating a layer of the liquid light-curing plastic material above the previously polymerised layer; and, optionally, c) repeating steps a) and b) are repeated at least one to multiple times.

11. Method according to claim 10, wherein steps a) i) a layer to be polymerised is obtained as projection surface; and ii) the layer to be polymerised generated in i) is polymerised as projection surface of the liquid light-curing plastic material using an illuminated field by means of light of the light source take place simultaneously in step a).

12. Method according to claim 10, wherein the drivable stripping device and the light source, optionally the light source of the assembly, form a drivable assembly with a slip clutch, optionally with barrier body clutch.

13. Method according to claim 10, wherein the entire assembly or the assembly for homogenising the distribution of light intensity comprises a spatial light modulator that comprises a multitude of tiltable micro-mirrors that are arranged in rows and columns and can be triggered, in which the light of a spatially emitting light source is projected by means of an optical system and an illuminated field of the projected light source is guided across a projection surface, whereby, towards the middle of the illuminated field, an increasing number of pixels is not being illuminated such that a homogenisation of the light intensity of all pixels that are illuminated on the projection surface is attained when integrating over time.

14. Method according to claim 10, wherein the assembly and thus the illuminated field and the stripping device are simultaneously periodically guided across the projection surface, whereby, optionally, the surface of a liquid light-curing plastic material is used as projection surface.

15. Rapid prototyping method, comprising illuminating a liquid light-curing plastic material by means of a method according to claim 10, optionally with UV light, whereby the stripping device is guided, by means of a coupling device and a coupling element simultaneously and together with the illuminated field ahead of the illuminated field along an axis of the container in order to form the layer to be polymerised of the plastic material as projection surface onto which the illuminated field is projected and on which the plastic material polymerises due to the illumination in the illuminated field.

16. Method for the production of at least parts of a dental prosthetic restoration, comprising using a device according to claim 1.

17. Computer-readable medium on which a computer program for use of a device is stored, which, when executed by a microprocessor, is made operable in order to be able to implement the method according to claim 10.

18. A program element for controlling a device, which, when executed by a microprocessor, is made operable in order to be able to implement the method according to claim 10.

Description

[0083] Exemplary embodiments of the invention shall be illustrated in the following on the basis of schematic figures, though without limiting the scope of the invention. In the figures:

[0084] FIG. 1: shows a device according to the invention having an arched surface 21a made of the polymerisable plastic material.

[0085] FIG. 2: shows a device according to the invention having a planar surface 21b made of the polymerisable plastic material.

[0086] FIGS. 3a, 3b, and 4: show a coupling device and coupling element.

[0087] FIG. 5: shows a a cross-sectional view of a schematic set-up for implementation of a method according to the invention; and

[0088] FIG. 6: shows a schematic comparison of a fully illuminated UV data projector chip according to the prior art (FIG. 6A) and a UV data projector chip operated according to the invention (FIG. 6B).

[0089] FIG. 7a: shows a motif to be printed (13), whereby the light points are shown as black pixels;

[0090] FIG. 7b: shows the images that are projected individually by the light source (1) of the data projector (extracted single images of motif 13a, 13b, 13c, 13d, 13e, 13f) for generation of the motif to be printed (13) during the motion of the light source across the projection surface (with no mask), whereby the light points are shown as black pixels;

[0091] FIG. 7c: shows a motif of the switched-off light points (14) generated by means of a mask or by switched-off light points generated by the spatial light modulator for compensation of illumination differences, whereby the switched-off light points are shown as grey pixels;

[0092] FIG. 7d: shows an addition and/or superimposition of the motif of the switched-off light points (14) generated by the spatial light modulator and/or the mask and the extracted single images of the motif (13a to 13f), whereby the mask with the switched-off light points (14) is shown as grey pixels and the light points are shown as black pixels. The motif of the switched-off light points (14, negative motif) shown as grey pixels is shown statically in all single images of the motif as superimposition and/or subtraction, i.e. of the motif of the permanently faded-out or switched-off light points (14) of the single images of the motif (13a to 13f) of the motif to be printed (13) and shown as superimposition in the single images of the motif to be illuminated (14a, 14b, 14c, 14d, 14e, 14f).

[0093] FIG. 8: shows the entire assembly (0#) comprising a stripping device (20) that can be coupled to and uncoupled from the assembly (0).

[0094] The inventive “Illumination process and procedure of the stereolithography process” involves the regulation of the level of the filling level in the reversal points of the illumination process. During the period of time, in which the illumination unit (assembly 0, entire assembly 0#, FIG. 8) is being decelerated and then accelerated again, the hose pump 19 (FIG. 1, 2) pumps a sufficient amount of resin (polymerisable plastic material, composition comprising monomers) into the container 8. Said amount must be selected appropriately such that a sufficient amount of resin is built up beyond the wall 8a of the container 8. This forms the arched surface 21a (FIG. 1). Due to the surface tension of the resin and/or plastic material, said elevated amount of material is retained until the scraper (stripping device 20) wipes it off and smoothes the surface. The layer (x1, y1) with the projection surface has been formed (FIG. 2).

[0095] Subsequently, the illumination unit (assembly 0, 0#) is being driven and pushes the scraper across the surface and smoothes the surface 21b by wiping off the excess of material. The material leaking over the wall 8a (FIG. 2) is collected in the collecting container (FIG. 2) and is returned to the pump cycle (FIGS. 1 and 2) through a suction opening with a suction line 17a. This ensures that the level always remains constant during the construction process and/or illumination phase.

[0096] The building platform 12 (FIGS. 1 and 2) is lowered by one layer thickness (z1) and the process commences again.

[0097] The horizontal positions of the container 8 and of the scraper 20 do not change during the construction phase and/or method. Said positions are adjusted once and then remain unchanged. The vertical distance with respect to each other is adjusted and aligned by a defined value (this value is 0.1 mm in the first test). The distance mainly serves to maintain a mechanical and vibration-free separation of the two systems (illumination system (assembly, stripping device)=in motion/container system=static). The distance should not be larger than the height that can be attained by the liquid through surface tension. Preferably, the distance is the same or somewhat smaller.

[0098] The wiped-off light-curing plastic material is suctioned into the cycle by means of a suction line 17a and a suction pump 19 (FIG. 1 or 2) and preferably filtered (Filter 18) and returned to the container 8 (trough). The system is tight in order to prevent the ingress of air into the cycle. Inclusions of air interfere with the polymerisation and/or construction process and lessen the quality of the form body/object.

[0099] FIGS. 3a (non-perspective, schematic) and 4 schematically show the coupling device 22 between the assembly 0 or the light source 1 and the stripping device (scraper) 20. According to FIGS. 3a, 3b, and 4, a coupling element 11, such as a sword, is assigned to the light source 1 or the assembly 0 by means of which these can push the stripping device 20 ahead of them by means of the coupling device 22. Arranged in front of the illuminated field 5 of the light source 1, the stripping device is pushed ahead of the illuminated field 5 in the method. The coupling element 11 can be assigned to the assembly on the side of the container or bath, for example the coupling element 11 is connected to the assembly 0 by means of an arm (not shown). For this reason, the coupling element 11 of FIGS. 3a and b is arranged on the side and behind the container rather than above the bath 7 such that the light source 1 (not shown) can reflect an illuminated field 5 on the plastic material 6 in the assembly. The coupling device 22 is provided on the top part of the stripping device and comprises at least one element 20a that is connected to the upper end of the stripping device, which can just as well be present as element 20a, by means of an elastic element, such as a spring mechanism 20c and a fixation 20. An attenuator 23 (FIG. 3b) that decelerates the stripping device 20 can be assigned to the sword 11 in the region of the reversal point of the container. The sword of the assembly 0 or of the light source 1 is then pushed into the recess A between the two elements 20a. Once a certain pressure is reached, the sword pushes the two elements 20a apart and glides through between these elements. The elements 20a are pressed against each other again by the elastic elements 20c. When the direction is changed subsequently (reversal point), the sword again pushes the stripping device ahead of itself across the container. When, in the method according to the invention, the illumination unit/assembly 0, 0# with UV data projector 1 (UV-LED data projector; in assembly 0, 0#) is driven across the surface 21a, 21b symmetrically to the container 8 and at a defined distance and when the illuminated field 5 is guided, preferably horizontally, across the projection surface thus formed, the scraper 20 (stripping device) for smoothing the surface is automatically guided along ahead of the light source 1 or ahead of the illuminated field 5 (drag method). In this embodiment variant, the scraper is connected neither mechanically nor electrically, but simply touches the illumination unit. The scraper is pushed ahead of the illumination unit (assembly 0) or the illuminated field 5 at a distance of 20 to 150 mm. At the start of the illumination process, the illumination unit slowly drives toward the stripping device (scraper) until it contacts the device. Subsequently, the illumination unit accelerates to process speed and pushes the scraper ahead of itself. The illumination step follows next. On the opposite side of the container, the scraper is stopped by an attenuator while the illumination unit drives on. The attenuator builds up pressure until the sword of the illumination unit slips through the coupling device of the scraper once the springs 20c allow the sword to glide through between the plates 20a. The plates 20a and springs 20c are arranged by means of stud bolts 20b. After the illumination unit travelled through said reversal point, the scraper is again positioned on the opposite side of the illumination unit in front of the illumination field 5 and now pushes it back to the starting point accordingly. By this means, two layers can be polymerised. The three-dimensional objects are built up by repeating these cycles. It was possible to significantly reduce the process time by coupling the stripping device to the light source or the assembly 0 and thus to the illuminated field. FIG. 3b shows the illuminated field 5 on top of the plastic material in the container 8. The illuminated field 5 can be projected onto the protection surface by means of a lens 2.

[0100] FIG. 5 shows a schematic cross-sectional view of a set-up for implementing a method according to the invention. An UV-LED data projector 1 emitting ultraviolet light (UV light) is made to emit at a spatial light modulator 4. The UV-LED data projector 1 has a resolution of 1920×1080 pixels that emit as a rectangular area on the surface of a chip of the UV-LED data projector 1. The spatial light modulator 4 comprises a multitude of micro-mirrors that can be triggered and by means of which the light from the UV-LED data projector 1 is reflected and projected onto the surface of a liquid light-curing plastic material 6 by means of a lens system 2. The micro-mirrors are shown in FIG. 1 as small rectangles, differing in orientation, on a surface of the spatial light modulator 4. The liquid plastic material 6 is arranged in a container 8 that is open in an upward direction toward the spatial light modulator 4 and/or the lens system 2. Shown schematically as a simple lens in FIG. 5, the lens system 2 projects the area of the pixels of the UV-LED data projector 1 onto the surface of the light-curing plastic material 6. Using a suitable motor (not shown), the UV-LED data projector 1 is moved across the container 8 and thus the illuminated field is swept across the surface of the light-curing plastic material 6 such that each row of the chip of the UV-LED data projector 1 travels or can travel fully across any point to be illuminated.

[0101] The illuminated field thus generated on the surface of the light-curing plastic material 6 cures the liquid components such that a solid plastic body 10 arises. The solid plastic body 10 is supported as in a bearing on a mounting 12, which is slowly being lowered such that the upper surface of the plastic body 10 is wetted by the liquid light-curing plastic material 6 and a new solid layer can be generated on the plastic body 10 by means of the illuminated field. For details regarding the implementation, reference shall be made to EP 1 880 830 A1 or EP 1 894 705 A2.

[0102] A homogenisation of the illuminated field and therefore of the plastic body 10 thus generated is attained in that the pixels arranged in the middle of the UV-LED data projector 1 are not used, i.e. in that they remain black. For clarity, a use according to the invention and/or a triggering according to the invention of a chip of this type is shown in FIG. 2B and shall be explained in the following.

[0103] FIG. 6 shows a schematic comparison of a fully illuminated UV data projector chip according to the prior art (FIG. 2A) as compared to a UV data projector chip operated according to the invention (FIG. 6B). The UV-LED chip shown for exemplary purposes has only 12×13 pixels to allow the underlying principle of the present invention to be illustrated easily. In a real embodiment, UV-LED data projectors of significantly higher resolution are used, for example 1920×1080 pixels.

[0104] Each of the UV-LED chips has 12 columns and 13 rows. In the fully illuminated UV-LED chip according to the prior art (FIG. 6A), the inner areas of the illuminated field are illuminated with a higher UV intensity than the outer areas. As a result, the highest intensity is produced in the middle column and the intensity decreases towards the outside. Due to scattering effects and other phenomena related to the optical system, the individual pixels of the UV-LED data projector cannot be projected at any desired image sharpness. Accordingly, each pixel also illuminates the areas of the illuminated field that should be illuminated by its neighbouring pixels. As a result, areas of the illuminated field illuminated by the inner pixels receive a higher intensity than the areas of the illuminated field illuminated by the outer pixels.

[0105] This is compensated with respect to the columns (from top to bottom in FIG. 6) in that the UV-LED data projector is driven across the illuminated field along a direction of motion X. The direction of motion X of the UV-LED data projector and/or of the illuminated field is indicated by the arrow in FIGS. 6A and 6B. Accordingly, the image emitted by the UV-LED chips is being moved across the illuminated field in the direction of the rows (from left to right in FIG. 6, i.e. along the arrow X). A DLP® chip made by Texas Instruments can be used for projection.

[0106] The black pixels shown in FIG. 6B, which remain switched-off or are not reflected onto the surface of the liquid light-curing plastic material by the spatial light modulator, progressively reduce the light intensity towards the middle in the different columns of the UV-LED data projector operated according to the invention. As a result, the middle areas of the illuminated field swept along the direction of motion X receive the same intensity of ultraviolet radiation as the outer areas (rows).

[0107] The simplest embodiment of a method according to the invention can be implemented by storing a mask for the data projector that defines which of the pixels are not switched-on and/or used and thus remain black. Alternatively, a spatial light modulator that comprises fewer or blackened mirrors in the middle can be used just as well.

[0108] In FIG. 6B, only the outermost two rows are irradiated by all twelve pixels, whereas one pixel less lights up and/or is projected for each row closer to the middle row. In the middle row, only six pixels are active and/or only six pixels are projected. Sweeping across the illuminated area along the direction of motion X, a mean illumination intensity is generated at the illuminated points of the illuminated field and the mean illumination intensity is directly proportional to the number of pixels of the UV-LED data projector that are used and/or projected. Suitable data projectors can have a resolution of up to 100,000 or up to 1.5 million pixels. Just as well, data projectors projecting in XGA and super-XGA (SXGA) resolution of 1.280×1.024 pixels can be used.

[0109] In order to attain a uniformly homogenised distribution of light intensity on the surface of the light-curing plastic material and/or of the projection surface, the illuminated field is guided across a building platform at a constant velocity. Presently, the building platform is 1,920×20,000 pixels in size (pixel size presently is 50×50 μm). During the motion, image details are constantly reproduced via the illuminated field.

[0110] Once it is defined, the mask stored in the UV data projector generates dead (permanently black) pixels in the individual rows. In this case, the number of pixels in the rows defined to be black increases towards the middle, since the rows in the middle are illuminated more brightly for constructive reasons (due to the optical system).

[0111] The effect is as follows: Due to the motion of the UV data projector, the entire row of the illuminated field is triggered during an illumination. As a result, a maximal amount of UV light of 1080 pixels is generated during the sweep. If fewer pixels are triggered, the power is reduced and the uneven illumination of the optical system can be balanced.

[0112] FIG. 7a shows a motif 13 to be printed, in which the light points are shown as black pixels. FIG. 7b shows the sequence of images that are projected individually by the light source (extracted single images of the motif 13a, 13b, 13c, 13d, 13e, 13f) for generation of the motif 13 to be printed during the motion of the light source or of the arrangement across the projection surface (without motif of the switched-off light points and/or with no mask). The light points are shown as black pixels. FIG. 7c shows the motif of the switched-off light points 14. The motif of the switched-off light points is generated by the spatial light modulator and/or the mask. The switched-off light points are shown as grey pixels. In this manner, light points can be switched-off or deflected by the spatial light modulator in order to balance out differences in illumination.

[0113] FIG. 7d shows the superimposition of the motif of the switched-off light points 14, in particular of the static motif, generated by the spatial light modulator and/or the mask and the extracted single images of the motif 13a to 13f. The motif of the switched-off light points 14 or the mask are shown as grey pixels. The illuminated pixels in the illuminated field are shown as black pixels and form the single images of the motif to be illuminated (14a, 14b, 14c, 14d, 14e, 14f).

[0114] FIG. 8 shows the entire assembly 0# comprising a stripping device 20 that can be coupled to and uncoupled from the assembly 0. For polymerisation of the plastic material 6, the light source 1 or at least the illuminated field 5 of the light source 1 is guided ahead of the entire assembly 0# or the assembly 0 behind the stripping device 20. The stripping device 20 can be mechanically coupled, in particular by means of the coupling device 22, to the light source 1 or to the illuminated field 5 of the light source 1 and is guided ahead of the light source 1 or the illuminated field 5.

[0115] The features of the invention disclosed in the preceding description and in the claims, figures, and exemplary embodiments, can be essential for the implementation of the various embodiments of the invention both alone and in any combination.

[0116] Reference numbers: 0 Assembly comprising light source (1) and/or (A), such as UV-LED data projector (1) or laser system, optical system, in particular lens system (2), spatial light modulator (4); 0# entire assembly and/or entire assembly comprising stripping device 20 and assembly 0 comprising light source 1, such as UV-LED data projector 1 or laser system, optical system, in particular lens system 2, spatial light modulator 4, whereby the stripping device can be coupled to or uncoupled from the assembly 0.

[0117] 1 UV-LED data projector, 2 lens system; 3 arrangement of the spatial light source 1, spatial light modulator 4 and/or lens system/optical system 2; 4 spatial light modulator; 5 illuminated field; 6 light-curing liquid plastic material, in particular mixture comprising monomers, composition comprising dental monomers; 7 bath; 8 container; 10 cured light-curing plastic material/plastic body; 11 coupling element such as sword with the sword preferably having a geometry that is matched to the coupling device and/or recess A′, 12 mounting, building platform;

[0118] 13 motif to be printed, 13a to 13f images projected individually (13a, 13b, 13c, 13d, 13e, 13f) for generation of the motif to be printed; 14 motif of the switched-off light points/motive non-illuminated pixels, 14a to 14f single images of motive to be illuminated having a homogenised distribution of light intensity. Images projected individually (14a, 14b, 14c, 14d, 14e, 14f) for generating the motif to be printed 13, shown as individually projected images (13a, 13b, 13c, 13d, 13e, 13f) for generating the motif to be printed during scrolling with a static superimposition of the motif of the switched-off light points (14)

[0119] 15 feeding device; 16 collecting container; 17 pipeline, 17a suction line, 17b feed line; 18 filter, 19 pump, in particular hose pump; 20 (C) stripping device, scraper; 20a element, in particular plate; 20b fixation, in particular screw; 20c elastic element, in particular spring mechanism (E); 21a surface of bath during overflow of plastic into collecting container; 21b surface of bath corresponding to illumination or after adjustment of the surface by stripping device, in particular planar surface, scraper; 22 coupling device, A′ recess, 23 attenuator; A# direction of motion; D drag method, E compression springs retained by stud bolts, z1: layer thickness; x,y; x1,y1: layer as plane