Stereolithography 3D printing assembly and stereolithography 3D printing method

Abstract

The present invention provides a stereolithography 3D printing assembly, comprising a digital projection system that projects a first digitally defined pattern having a first resolution at a projection location, and a photomask system that projects a second pattern having a second resolution, the second pattern and the first pattern being aligned with each other at the projection location, and the photomask system providing at least one photomask between the digital projection system and the projection location, which provides a high speed 3D printing assembly capable of high resolution detail.

Description

Detailed Description of the Invention

[0001] [Technical field] The present invention relates to a stereolithography 3D printing assembly, a stereolithography 3D printing method, and a computer program product for controlling a stereolithography 3D printing assembly.

[0002] [Background technology] The abstract of U.S. Patent Publication No. 9,733,429 states, "A system and method for forming large thickness micro-grating structures. In one embodiment, a photonomer resin is fixed into a mold having a transparent bottom, the interior surface of which is coated with a mold release agent. A substrate is placed in contact with the top surface of the photonomer resin. The photonomer resin is illuminated from below by one or more collimated light sources through a photomask to form polymer waveguides and micro-grating structures extending to and connected with the substrate. After formation of a layer of the micro-grating structure, the substrate is raised using a translation and rotation system and additional photonomer resin is added to the mold, and the photonomer resin is again illuminated through a photomask to form a further layer of the micro-grating structure. This process is repeated multiple times to form a stacked micro-grating structure."

[0003] The abstract of U.S. Patent Publication No. 9,862,147 states, "The present invention discloses a method for curing a photosensitive resin. The method includes the steps of: generating a sub-pixel pattern having an outer contour region and an inner contour region based on a vector file obtained from a cross-section of a model; providing the sub-pixel pattern to a photomask module, the photomask module including a panel having a pixel matrix, the pixel matrix including a plurality of square pixels, each of the plurality of square pixels including a three-color color-filtered sub-pixel; performing a color fill for each of the color-filtered sub-pixels to distinguish the outer contour region from the inner contour region; and exposing the photosensitive resin to a light source that emits light that passes through the panel."

[0004] The abstract of U.S. Patent Application Publication No. 2018 / 0056605 states, "A 3D printing system includes a build apparatus and an optical projection engine. The build apparatus includes a curing tank, a photocurable material, and a build platform, where the photocurable material and the build platform are disposed within the curing tank. The optical projection engine has a zoom lens that projects an image beam having at least a first pixel size and a second pixel size onto the build platform to cure the photocurable material, where the first pixel size is different from the second pixel size."

[0005] The abstract of US Patent Application Publication No. 2018 / 126647 states, "The present invention relates to an apparatus for correcting a non-uniform intensity distribution of a radiation field generated by a radiation source, in particular a radiation source for an apparatus for generating 3D articles by layer-by-layer solidification of a solidifiable material under the action of radiation at a build surface. The apparatus comprises a correction or filtering device introduced in the radiation path of the apparatus for generating 3D articles by layer-by-layer solidification of a solidifiable material under the action of radiation, between the radiation source and the build surface. Furthermore, an improved method for generating an apparatus for correcting a non-uniform intensity distribution of a radiation field generated by a radiation source, as well as an improved method and apparatus for generating 3D articles, are proposed."

[0006] The abstract of WO2015007772 states, "The invention relates to a method for generating a 3D object (12) by layer-by-layer solidification of a solidifiable material (16) by the action of radiation (14) using an exposure mask (28), in which at least one, preferably a single, digital exposure mask is generated for forming each object layer to be solidified in the object (12) on a build surface (22), by means of which radiation is selectively projected onto the build surface. According to the invention, the method is improved in that 3D objects having improved and smoother surfaces can be conveniently generated by exposing the build surface (22) in an oscillating manner during the exposure time. The invention also relates to an improved exposure mask generation device and an improved device for generating 3D objects."

[0007] In the abstract of "A Novel Low-Cost Process Based on Vector Projection for High-Speed, and Large-Area Stereo Lithography Scanning and Mask High-Accuracy, High-Throughput, Fabrication" by CHI ZHOU et al. (published March 1, 2015), they write, "Photopolymerization-based processes are one of the most common additive manufacturing (AM) processes. The two main configurations of this process are laser-based vector-by-vector scanning (0D) and projection-based layer-by-layer exposure (2D). The highly focused fine laser enables the scanning-based process to achieve very high and precise surface finishes, but the serial nature of the scanning makes this process slow. In contrast to laser scanning, the projection-based process can form all layers in a single exposure, which improves manufacturing efficiency. However, due to the limited resolution of the projection device and various optical shortcomings, it is difficult to fabricate large-area AM processes. For fabrication, the surface quality is significantly degraded. To solve this problem, a new hybrid process combining vector scanning and mask projection is presented. In this process, a laser is focused to a small spot and used to scan the layer boundaries, while projection is focused on a large platform surface to define the inner regions of the layer. An efficient slicing process is proposed to extract the contours for laser scanning. A slice-to-image conversion algorithm is also developed to convert the offset contours into a grayscale image for mask projection. Experimental results demonstrate that the proposed hybrid process can significantly improve the fabrication speed without degrading the surface quality. "

[0008] The abstract of U.S. Patent Application Publication No. 2019 / 084241 states, "A multi-scale multiphoton photolithography system for fabricating 3D objects includes a support structure configured to support a photosensitive composition from which the 3D objects are fabricated; a microscope objective configured to focus light onto the photosensitive composition via an optical path; a first optical assembly configured to provide light of a first wavelength to the microscope objective, the first wavelength being selected to induce single-photon processes in the photosensitive composition; a second optical assembly configured to provide light of a second wavelength to the microscope objective, the second wavelength being selected to induce multiphoton processes in the photosensitive composition; and a second optical assembly configured to focus light of the first and second wavelengths to the microscope objective. and a controller operably coupled to the second optical assembly. The controller includes a processor and a non-transitory computer-readable medium operably connected to the processor, the computer-readable medium including instructions that, when executed by the processor, perform operations including illuminating the photosensitive material with a first wavelength of light through an optical path via the first optical assembly to generate a first region of the 3D object through single-photon photolithography; illuminating the photosensitive material with light of a second wavelength through an optical path via the second optical assembly to generate a second region of the 3D object through multi-photon photolithography; and repeating steps (a) and (b) until the 3D object is completed.

[0009] The abstract of U.S. Patent Application Publication No. 2004 / 019408 states, "The lithography tool includes an exposure chamber and a reticle handler for exchanging reticles to be exposed as defined by a user of the lithography tool. The reticle handler may include a vacuum compatible robot, a vacuum chamber to house the robot, a load lock to load the reticle and transition from atmospheric pressure to vacuum, a processing station to process the reticle, and a reticle library to store at least one additional reticle for swapping during the exposure process. The robot has multiple hand-held grippers and can hold multiple reticles simultaneously. This minimizes swap time by allowing a first hand to remove a first reticle from the reticle stage and a second hand to load a second reticle onto the reticle stage, etc."

[0010] [Summary of the Invention] Among these various methods, one or more drawbacks of the prior art is that they propose a trade-off between resolution and printable object size: methods for printing large objects currently cannot provide sub-μm resolution, and high-resolution printing techniques cannot 3D print objects (volumes of several cubic centimeters) within a reasonable time frame.

[0011] It is therefore an aspect of the present invention to provide an alternative 3D printing method, which preferably further at least partially obviates one or more of the above-mentioned disadvantages.

[0012] Here, a stereolithography 3D printing assembly is provided, comprising a digital projection system that projects a digitally defined first pattern having a first resolution at a projection position, and a photomask system that projects a second pattern having a second resolution, the second pattern and the first pattern being aligned with each other at the projection position, and the photomask system providing at least one photomask between the digital projection system and the projection position.

[0013] There is further provided a stereolithography 3D printing additive assembly for use in a stereolithography 3D printing assembly comprising a digital projection system configured to project a first digitally defined pattern having a first resolution at a projection location, the stereolithography 3D printing additive assembly comprising: at least one photomask for producing at least one microfeature, such as a cavity or a channel, with a second resolution higher than 200 dots per inch, in particular higher than 250 dots per inch, in particular higher than 300 dots per inch; an actuator for displacing a photomask between photocurable layers in a stereolithography 3D printing assembly; and a control unit that controls an actuator to position at least one photomask relative to at least one selected from a digital projection system and a projection position of the stereolithography 3D printing assembly to create at least one micro-feature in the digitally defined first pattern.

[0014] Further, a stereolithography 3D printing method is provided, the stereolithography 3D printing method comprising: - projecting a digitally defined first pattern having a first resolution at a projection location within the resin container using a projection optical system during a stereolithography 3D printing process; providing at least one photomask between the resin container and the projection optical system; - projecting at least one photomask pattern at a projection location using at least one photomask and projecting a second pattern having a second resolution at the projection location to provide the second pattern on the first pattern.

[0015] Further, a computer program product is provided for aligning the stereolithography and photolithography patterns, i.e., the first pattern and the second pattern.

[0016] The combination of polymerization-based 3D printing methods of stereolithography and photolithography allows for high volume and high resolution 3D printing using stereolithography methods. A computer program product is provided for aligning a stereolithography pattern with a photolithography pattern.

[0017] The methods and assemblies described herein comprise a digital illumination system (e.g., digital mirror device, LCD, reflective liquid crystal panel, or laser scanning method) for 3D printing larger features (herein termed macro-patterns) in perfect three-dimensional correspondence. This provides a first pattern. The methods and assemblies also comprise a photomask system with photomask patterns for printing smaller features (herein termed micro-patterns) and a translation or rotation stage for switching between various photomask patterns. This provides a second pattern. The photomask system uses a pattern that is permanently defined on a substrate. The photomask system can use one complete pattern on one substrate. In one embodiment, several basic patterns are each provided on separate substrates. These substrates can be combined to form a second pattern. In yet another embodiment, subsequent patterns can be used on separate substrates to print various fine details of an object.

[0018] For the avoidance of doubt, 3D printing is also referred to as additive manufacturing, which allows the production of 3D objects by the application of layer after layer of material.

[0019] The combination of the two techniques allows the production of parts that are not possible with either method alone (in terms of resolution, scale, and three-dimensional consistency). For example, the shape of a large object (up to 500 x 500 cm using current stereolithography methods) can be produced at low resolution, but at the same time one or more photomask patterns with sub-μm features can be periodically repeated as the piece is printed. This allows the creation of a large part with a regularly repeating microstructure. The macrostructure (i.e. the overall shape of the object) is defined digitally, while the microfeatures are defined by the photomask system.

[0020] Thus, the methods described herein can improve resolution by 100-1000 times compared to conventional stereolithography methods without sacrificing the size of the printed object. Alternatively, the methods reduce printing time by 100-1000 times compared to high-resolution printing methods such as two-photon polymerization. This method is particularly useful when regular repeating microstructures are required while still providing perfectly matched large macrostructures.

[0021] Modern assemblies can be used in a variety of areas, some examples of which are:

[0022] Tissue Scaffolds: Printing porous organ structures to promote cell growth and create custom organs for each patient. In this case, the organ itself is a macro feature with feature sizes greater than 500 μm. Using photomask patterning, it is possible to create a porous lattice with a high surface area to volume ratio to create the micro features required for cell growth.

[0023] Metamaterials: Ultralight and robust lattices known as "metamaterials" have been identified as important applications in high-resolution 3D printing (i.e. feature sizes less than 100 μm). Sectors as diverse as the aerospace industry, furniture design and automotive sectors can benefit from this state-of-the-art assembly and methodology. The limitation of known techniques is the combination of resolution and component size relative to the functional components.

[0024] Liquid chromatography columns: Current liquid chromatography relies on sub-5 μm particles randomly packed into columns. The benefits of 3D printing to produce globally ordered porous media have been demonstrated using simulations and experiments. However, low printing resolution (or long build times in two-photon polymerization) have limited the development of 3D printed columns at a scale applicable for preparative or analytical scale separations. The proposed assembly and methodology allows the fabrication of simple repeating porous grids while meeting the physical requirements of liquid chromatography columns in terms of both resolution and build volume.

[0025] Microfluidic Devices: Microfluidic and lab-on-a-chip devices have traditionally used planar photolithography techniques, which are very time-consuming and often require cleanroom facilities. Known 3D printing offers the opportunity to fully fabricate three-dimensional designs at a fraction of the time and cost. However, the resolution of known stereolithography assemblies is often not compatible with the objective of miniaturization, as it only allows the creation of "millifluidic" devices rather than microfluidic devices. Modern assemblies and methods combine the advantages of both techniques to create complex chip designs with ultra-high resolution at manufacturing times and costs that make the sale of microfluidic devices a commercially attractive proposition. Macrofeatures such as connection ports and solvent reservoirs can be defined with known fabrication process components, while microchannels can be created with proposed additional features.

[0026] In one embodiment of this assembly, the second resolution is at least 10 times higher than the first resolution at the projection position.

[0027] In one embodiment, the first resolution is less than 200 dots per inch and the second resolution is greater than 200 dots per inch, and in a specific embodiment, the first resolution is less than 250 dots per inch and the second resolution is greater than 250 dots per inch. In a more specific embodiment, the first resolution is less than 100 dots per inch and the second resolution is greater than 300 dots per inch. In some embodiments, the first resolution is lower to allow faster printing of certain structures, but the second resolution may be higher, up to 600 dots per inch or more.

[0028] In one embodiment of this assembly, the photomask system comprises at least a substrate having at least a portion of the second pattern permanently defined therein, in one embodiment of which the photomask system comprises a series of substrates, each of the substrates having at least a portion of the second pattern permanently defined therein.

[0029] In one embodiment, the stereolithography 3D printing assembly further comprises an alignment system or adapter for aligning the second pattern and the first pattern to create a combined image for photopolymerization, in one embodiment, the alignment system comprises an alignment provider for the digital projection system and the photomask system, a detector for detecting the alignment provider, and an alignment actuator for aligning the digital projection system and the photomask system relative to each other.

[0030] In one embodiment, the digital projection system comprises an electromagnetic radiation source generating a beam of electromagnetic radiation, a collimating optic downstream of the electromagnetic radiation source for collimating the beam of electromagnetic radiation, a digital mirror device downstream of the collimating optic, and at least one axial translation device for translating the projection position, and a photomask system is provided for positioning at least one photomask in the collimated beam of the collimating optic. In one embodiment, the electromagnetic radiation is in the ultraviolet or visible light range.

[0031] In one embodiment, the digital projection system comprises a light source, a collimating optics downstream of the light source, a digital mirror device downstream of the collimating optics, and at least one axial translation device for translating the projection position.

[0032] In one embodiment, the digital projection system comprises a patterned light source, collimating optics downstream of the patterned light source, and at least one axial translation device for translating the projection position.

[0033] In one embodiment, the stereolithography 3D printing assembly further includes a container containing a photocurable resin and a target surface defining a projection location, the target surface receiving a solidified layer polymerized by radiation from the digital projection system.

[0034] In one embodiment, the photomask system comprises a series of photomasks and a selection system for selecting at least one of the photomasks to generate the second pattern, which makes the assembly more versatile. The micropattern can be decomposed into a combination of base patterns, and photomasks showing those base patterns can be combined, even dynamically, to generate the micropattern. This allows, for example, the micropattern to be modified during processing. In this way, for example, complex 3D-operated channels can be created.

[0035] In one embodiment, the photomask system includes an actuator for displacing at least one photomask during projection of the first pattern to generate a second pattern, and in particular the actuator includes at least one selected from a translation stage and a rotation stage, such that a pattern can be created at a selected location in, for example, the low resolution first pattern.

[0036] In one embodiment, the photomask system is provided as an add-on system to a stereolithography 3D printing assembly, allowing for significant retrofitting of existing stereolithography 3D printing systems.

[0037] Further, a stereolithography 3D printing additive assembly is provided, in particular, the stereolithography 3D printing additive assembly as described above comprises: at least one photomask for producing at least one microfeature, such as a cavity or a channel, in particular with a second resolution of more than 200 dots per inch, in particular more than 250 dots per inch, in particular more than 300 dots per inch; an actuator for displacing a photomask in a stereolithography 3D printing assembly during operation, particularly between photocurable layers; - a control unit that controls an actuator to position at least one photomask relative to at least one selected from a digital projection system and a projection position of the stereolithography 3D printing assembly to generate at least one predetermined micro-feature in the digitally defined first pattern.

[0038] In one embodiment, the stereolithography 3D printing additive assembly comprises a series of said photomasks; a photomask selection system for selecting at least one photomask from a set of photomasks for producing a predetermined micro-feature, such as a superlattice; - a control unit that selects at least one photomask from a set of photomasks for generating at least one micro-feature, and a control unit that controls an actuator that positions the selected at least one photomask, the projection optics, and the projection position relative to each other for generating the at least one micro-feature.

[0039] In one embodiment of this stereolithography 3D printing method, the method further comprises: providing an actuator for displacing at least one photomask; - performing a movement, in particular a movement selected from a rotation, a translation, and a combination thereof, of at least one photomask during the stereolithography printing process together with the projection of the first pattern.

[0040] In one embodiment of the stereolithography 3D printing method, the method further comprises: providing a series of at least one photomask; selecting at least one photomask from a series of at least one photomask; - modifying the second pattern during projection of the first pattern, the modification including at least one selected from removing, adding, substituting, and combinations thereof, at least one of the at least one selected photomask.

[0041] In one embodiment of this stereolithography 3D printing method, at least one photomask including a repeating pattern is provided to generate a second pattern that generates at least one three-dimensional regular lattice having a second resolution.

[0042] Further provided is a computer program product for controlling a stereolithography 3D printing assembly to generate a three-dimensional object, the computer program product, when run on a data processor, comprises: - decomposing the three-dimensional object into individual slices which are projected at projection positions; - decomposing each slice into a first digitally defined pattern having a first resolution; - decomposing each slice into a second pattern having a second resolution; - decomposing the second pattern into a selection of at least one elementary photomask from a series of elementary photomasks, each elementary photomask having an elementary pattern; -Decomposing subsequent slices into displacements of the first pattern, -Decomposing subsequent slices into a second pattern of displacements, providing control instructions to control the digital projection system and the photomask system to simultaneously generate the first and second digitally defined patterns to generate the three-dimensional object;

[0043] Further provided is a computer program product for controlling a stereolithography 3D printing additive assembly to generate a three-dimensional object, the computer program product, when run on a data processor, comprises: - Retrieving a decomposition of the three-dimensional object into individual slices projected at projection positions; - reading out a first pattern having a first resolution and corresponding to each slice; - subtracting the first pattern from the corresponding slice where the correction has been made; - decomposing each corrected slice into a second pattern having a second resolution; - decomposing the second pattern into a selection of at least one elementary photomask from a series of elementary photomasks, each elementary photomask having an elementary pattern; - reading out the displacement of the first pattern for successive slices; -Decomposing successive slices into a second pattern of displacements, providing control instructions to control the photomask system in synchronization with a further stereolithography 3D printing system to simultaneously generate the first pattern and the second pattern to generate a three-dimensional object;

[0044] This computer program product allows for the retrofit of existing assemblies.

[0045] The present invention further relates to a stereolithography 3D printing assembly comprising a digital projection system for projecting a first pattern having a first resolution at a projection location, and a photomask system for projecting a second pattern having a second resolution at the projection location.

[0046] The present invention further relates to a stereolithography 3D printing additive assembly, the additive assembly comprising: at least one photomask for producing at least one microfeature, such as a cavity or a channel; an actuator for displacing a photomask during operation of the stereolithography system; - at least one photomask and a control unit for controlling actuators for positioning the projection optics and the projection location relative to each other to generate predetermined repeating micro-features.

[0047] The present invention further relates to a stereolithography 3D printing additive assembly, the assembly comprising: at least one photomask for producing at least one microfeature, such as a cavity or a channel; an actuator for displacing a photomask during operation of the stereolithography system; a control unit for controlling actuators that position the at least one photomask, the projection optics, and the projection location relative to one another and generate predetermined repeating micro-features;

[0048] The terms "upstream" and "downstream" refer to the location of items and features associated with the propagation of light from a light generating means (here specifically a first light source), such that with respect to a first location in the beam of light from the light generating means, a second location in the beam of light closer to the light generating means is "upstream" and a third location in the beam of light further away from the light generating means is "downstream."

[0049] The term "substantially" as used herein, such as "consisting essentially of", will be understood by those skilled in the art. The term "substantially" is intended to encompass embodiments expressed as "entirely", "completely", "all", etc. Thus, in embodiments, the adjective "substantially" may be omitted. Where applicable, the term "substantially" may relate to 90% or more, such as 95% or more, particularly 99% or more, especially 99.5% or more, including 100%. The term "comprising" also encompasses embodiments where the term "comprising" is used in the sense of "consisting only of".

[0050] The term "functionally" will be clearly understood by and to those skilled in the art. The term "functionally", like "substantially", also encompasses embodiments expressed as "fully", "completely", "all", etc. Thus, in embodiments, the adjective "functionally" may be omitted. When a term is used in a manner such as "functionally parallel", it is understood by those skilled in the art that the adjective "functionally" encompasses the above-mentioned term "substantially". The term "functionally" is specifically understood to encompass configurations of features such that the features are operable as if the adjective "functionally" were not present. The term "functionally" is intended to encompass variations of the features referred to, where the combination of features is operable or functional in the functional application of the feature, possibly in combination with other features to which the feature relates in the invention. For example, when an antenna is functionally coupled or connected to a communication device, electromagnetic signals received by the antenna can be used by the communication device. For example, the term "functionally" in "functionally parallel" is used to encompass strictly parallel, but also encompasses embodiments encompassed by the term "substantially" above. For example, "functionally parallel" is used in reference to embodiments that, during operation, function as if the members were parallel, by way of example, and encompasses embodiments where it would be clear to one of ordinary skill in the art that the members would operate as if they were parallel, within the intended field of use.

[0051] Moreover, the terms first, second, third, etc. in the specification and claims are used to distinguish between similar elements and do not necessarily dictate 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 being practiced in orders other than those described or illustrated herein.

[0052] Devices or apparatus are described herein as being particularly in operation, and as will be apparent to those skilled in the art, the present invention is not limited to methods of operation or apparatus in operation.

[0053] It should be noted that the above-described embodiments illustrate the invention rather than limit it, and that a person skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed in parentheses shall not be construed as limiting the scope of the claims. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention can be embodied by hardware comprising a number of distinct elements, and by a suitably programmed computer. In a device or apparatus claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain means are recited in mutually different dependent claims does not indicate that a combination of these means cannot be used to advantage.

[0054] The invention further applies to an apparatus or device comprising one or more of the characteristic features described in the specification and / or shown in the accompanying drawings.The invention further relates to a method or process comprising one or more of the characteristic features described in the specification and / or shown in the accompanying drawings.

[0055] The various aspects discussed in this patent may be combined to provide further advantages. Further, some of the features may form the basis of one or more divisional applications. [Brief description of the drawings]

[0056] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts and in which the drawings are not necessarily to scale. [Figure 1] FIG. 2 is a schematic side view of one embodiment of the assembly. [Diagram 2] FIG. 2 is a perspective view of FIG. [Diagram 3] FIG. 2 is a cross-sectional view of FIG. [Figure 4] FIG. 2 is an enlarged view of FIG. [Diagram 5] 11 is an alternative setup showing the object being printed. [Figure 6] 1 is a photograph showing a micropatterned object. [Figure 7] A digital photograph of the object in Figure 6. [Figure 8] FIG. 7 is a more detailed photograph of FIG. 6. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0057] 1-4 show a schematic of one embodiment of a stereolithography printing assembly 1. The assembly 1 comprises a digital projection system 2, which is per se known in the art. The light source of the digital projection system may comprise a UV or visible light LED system, or a mercury arc lamp. The projected image can be defined by a digital mirror device (DMD), a laser raster or laser screening, a liquid crystal display (LCD), or a liquid crystal in a silicon-based illumination system.

[0058] The stereolithography printing system 1 comprises a surface 4 defining the projection position. In most cases, such a surface will be a flat surface. This surface is attached to a displacement system 5. Such a displacement system 5 often comprises a so-called Z-axis translation table, by which the surface 4 can be moved up and down, i.e. as shown in FIG.

[0059] The stereolithography printing system 1 further includes a container 6 that contains a polymerizable resin 7 .

[0060] The stereolithography printing system 1 further comprises a photomask system 3. The photomask system 3 comprises a frame holding a first mask 8 and in this embodiment also a second mask 8'. The photomask system 3 further comprises an actuator 9 for translating the masks 8, 8' in the XY plane (as viewed). In one embodiment, the actuator has a micro-translation set for moving or translating the masks 8, 8' by only small amounts, typically in the order of microns, and a macro-translation set for, for example, replacing mask 8 with mask 8' and vice versa.

[0061] The masks 8, 8' used in this photomask system comprise a pattern permanently defined in a substrate. As mentioned above, many options are possible and have been explored. For example, the second pattern can be entirely provided in the substrate. For one printed object, several subsequent second patterns can be used in combination with the first pattern in succession. Obviously, this first pattern can change during the printing of the object. In several alternative embodiments, a series of base patterns can be provided in different substrates, respectively. These base substrates may be combined to form the second pattern, i.e. resulting in the second pattern. For example, this photomask may be made in a substrate known to the person skilled in the art, for example soda lime, quartz or Teflon.

[0062] To 3D print an object, the first and second patterns are aligned to the features defined by the first pattern so that the features defined by the second pattern are in the proper position. This creates a combined image that is photopolymerized. Finally, an alignment system is provided. This can be provided in a number of ways. In one embodiment, one or more alignment features are added to the photomask. In one embodiment, an image detector such as a digital camera records the alignment features on the photomask and the details of the digital projection system. The control system then controls the actuators, for example the photomask system translation table, to set and calibrate the photomask position. Other more simple or complex systems may be used to align and calibrate the digital projection system and the photomask system relative to each other. This creates a combined image slice by slice.

[0063] In Fig. 5 a schematic embodiment of a stereolithography printing system 1 is shown, with an embodiment of a digital projection system 2 shown in detail. In this embodiment a light source and collimating optics 10 is provided to generate a collimated light beam 14. The system 10 projects the beam 14 onto a mirror 11 set at 45 degrees to the surface 4. In this embodiment the mirror 11 is provided with a first pattern 12. Such pattern 12 may be static. In one embodiment the pattern 12 is dynamic, for example comprising an LCD or DMD element capable of varying the pattern 12.

[0064] In figure 5 the formation of an object 13 is shown in one embodiment of the current system, in which the next layer of this object is formed on a projection plane 4', which is in fact one edge of the object 13 being formed.

[0065] The displacement system 5 translates the object in the Z direction, in effect pulling it out of the resin 7. Pulling the object in the Z direction causes new resin to flow between the just-formed new layer of the object 13 and the (optically transparent) bottom 13 of the resin container 6.

[0066] In Figure 6, a photograph of a 3D printed object is shown. The object has a first pattern showing a relatively wide wall on which a second pattern of lower resolution is printed. In Figures 7 and 8, the photographs show the second pattern.

[0067] It should also be clear that the above description and drawings are included to illustrate some embodiments of the present invention, and are not intended to limit the scope of protection. Many more embodiments, including those disclosed herein, will be obvious to those skilled in the art. These embodiments are obvious combinations of the techniques of the prior art and the disclosure of this patent, within the scope and essence of protection of the present invention. [Explanation of symbols]

[0068] Reference Signs List: 1...stereolithography printing assembly, 2...digital projection system, 3...photomask system, 4...printing surface, 5...displacement system (of the object to be printed), 6...container, 7...polymerizable resin, 8,8'...mask, 9...actuator, 10...collimating optics, 11...mirror, 12...first pattern, 13...object being printed, 14...projection beam, 15...optically transparent bottom of resin container

Claims

1. A stereolithography 3D printing assembly comprising: a digital projection system that projects a first digitally defined pattern having a first resolution at a projection location; and a photomask system that projects a second pattern having a second resolution, the second pattern and the first pattern being aligned with each other at the projection location, the photomask system comprising at least one photomask between the digital projection system and the projection location.

2. The stereolithography 3D printing assembly of claim 1 , wherein the second resolution is at least 10 times greater than the first resolution at the projection location. (a) the first resolution is less than 200 dots per inch and the second resolution is greater than 200 dots per inch; (b) the first resolution is less than 250 dots per inch and the second resolution is greater than 250 dots per inch; and (c) the first resolution is less than 100 dots per inch and the second resolution is greater than 300 dots per inch; The stereolithography 3D printing assembly according to claim 1 or 2, which satisfies any one of the above requirements.

4. The stereolithography 3D printing assembly of any one of claims 1 to 3, wherein the photomask system comprises at least a substrate, the substrate having at least a portion of the second pattern permanently defined therein.

5. 5. The stereolithography 3D printing assembly of claim 4, wherein the photomask system comprises a series of substrates, each of the substrates having at least a portion of the second pattern permanently defined thereon.

6. 6. The stereolithography 3D printing assembly of claim 1, further comprising an alignment system having the second pattern and the first pattern, the second pattern and the first pattern being aligned to create a combined image for photopolymerization.

7. 7. The stereolithography 3D printing assembly of claim 6, wherein the alignment system comprises an alignment provider for the digital projection system and the photomask system, a detector for detecting the alignment provider, and an alignment actuator for aligning the digital projection system and the photomask system relative to each other.

8. The stereolithography 3D printing assembly of any one of claims 1 to 7, wherein the digital projection system comprises an electromagnetic radiation source generating an electromagnetic radiation beam, a collimating optical system located downstream of the electromagnetic radiation source and collimating the electromagnetic radiation beam, a digital mirror device located downstream of the collimating optical system, and at least one axial translation device for translating the projection position, and the photomask system is provided for positioning at least one photomask in the collimated beam of the collimating optical system.

9. The stereolithography 3D printing assembly of any one of claims 1 to 8, wherein the digital projection system comprises a light source, a collimating optical system located downstream of the light source, a digital mirror device located downstream of the collimating optical system, and at least one axial translation device for translating the projection position.

10. The stereolithography 3D printing assembly of any one of claims 1 to 9, wherein the digital projection system comprises a patterned light source, collimating optics downstream of the patterned light source, and at least one axial translation device for translating the projection position.

11. The stereolithography 3D printing assembly of any one of claims 1 to 10, further comprising a container for containing a photocurable resin, and a target surface defining the projection location, the target surface receiving a solidified layer polymerized by radiation from the digital projection system.

12. The stereolithography 3D printing assembly of any one of claims 1 to 11, wherein the photomask system comprises a series of photomasks and a selection system for selecting at least one of the photomasks to generate the second pattern.

13. The stereolithography 3D printing assembly of any one of claims 1 to 12, wherein the photomask system comprises an actuator that displaces the at least one photomask during projection of the first pattern to generate the second pattern, the actuator comprising at least one selected from a translation stage and a rotation stage.

14. The stereolithography 3D printing assembly of any one of claims 1 to 13, wherein the photomask system is provided as an additional system to the stereolithography 3D printing assembly.

15. 1. A stereolithography 3D printing assembly for use in a stereolithography 3D printing assembly comprising a digital projection system that projects a digitally defined first pattern having a first resolution at a projection location, the stereolithography 3D printing assembly comprising: - at least one photomask for producing at least one microfeature, such as a cavity or a channel, at a second resolution higher than 200 dots per inch; - an actuator for displacing the photomask between photocurable layers in the stereolithography 3D printing assembly; - a control unit that controls the actuator to position the at least one photomask relative to at least one selected from the digital projection system and the projection position of the stereolithography 3D printing assembly to generate the at least one micro-feature in the digitally defined first pattern.

16. a series of said photomasks; a photomask selection system for selecting at least one photomask from said set of photomasks for producing a predetermined micro-feature, such as a superlattice; - A control unit that selects at least one photomask from the series of photomasks to create the at least one micro-feature, and a control unit that controls the actuator that positions the selected at least one photomask, a projection optical system, and the projection location relative to each other to generate the at least one micro-feature.

17. A stereolithography 3D printing method, comprising: - projecting, using a projection optical system, a first digitally defined pattern having a first resolution at a projection location within the resin container during a stereolithography 3D printing process; - providing at least one photomask between said resin container and said projection optical system; - projecting at least one photomask pattern at the projection location using the at least one photomask, projecting a second pattern having a second resolution at the projection location, and providing the second pattern on the first pattern.

18. A computer program product for controlling a stereolithography 3D printing assembly according to any one of claims 1 to 14 to generate a three-dimensional object, the computer program product being operable when run on a data processor to: - discretizing said three-dimensional object into individual slices projected at said projection locations; - decomposing each slice into said first digitally defined pattern having said first resolution; - decomposing each slice into said second pattern having said second resolution, - decomposing said second pattern into a selection of at least one elementary photomask from a series of elementary photomasks, each elementary photomask having an elementary pattern; - Decomposing subsequent slices into displacements of said first pattern, - Decomposing subsequent slices into said second pattern of displacements; - a computer program product for controlling a stereolithography 3D printing assembly, the computer program product providing control instructions to control the digital projection system and the photomask system to simultaneously generate the first digitally defined pattern and the second pattern to generate the three-dimensional object.

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