Continuous vat polymerization for three-dimensional printing

Abstract

A system for constructing an article by 3D vat photopolymerization printing is disclosed comprising: a vat having a transparent bottom surface, wherein the vat is configured to hold a photopolymer resin; a building platform configured to elevate upwardly relative to the vat; an objective lens disposed below the transparent bottom surface of the vat; a radiation source disposed below the objective lens and configured to radiate through the objective lens to the vat for curing the photopolymer resin; and the system is configured to produce a continuously changing photomask image that is projected to the photopolymer resin in the vat as the building platform is elevated during 3D printing. The radiation source may comprise: an LCD photomask and a LED disposed. The objective lens and LCD photomask may be configured to move during a printing process as the building platform is moving.

Description

Title: CONTINUOUS VAT POLYMERIZATION FORTHREE-DIMENSIONAL PRINTINGCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to US provisional patent application number 63 / 459,429, titled “CONTINUOUS VAT POLYMERIZATION FOR THREE- DIMENSIONAL PRINTING”, filed April 14, 2023. The ‘429 disclosure is incorporated here by reference in its entirety for all purposes.FIELD

[0002] Disclosed herein are systems, devices, and / or methods for enabling fabrication of articles by three-dimensional printing and, more particularly, continuous vat polymerization three-dimension printing systems, devices, and / or methods constructed for fabricating optical lenses having improved optical and physical properties.BACKGROUND

[0003] Additive manufacturing (AM), also known as three-dimensional (3D) printing, is a known process for fabricating 3D objects by accumulating material at designated locations in a layer-by-layer manner. Benefiting from rapid turnaround and high customizability, additive manufacturing has been widely used in dental, surgical, biomedical, and other applications.

[0004] Among all the AM processes, mask image projection-based vat photopolymerization (MIP-VPP) converts liquid monomers into solid polymers using controlled ultraviolet (UV) light, achieving the micro-scale resolution and centimeter scale fabrication size. MIP-VPP has been a widely used AM process to fabricate parts with high accuracy and surface finish. Many attempts have been made to 3D print optical components using MIP-VPP apparatuses. However, most optical lenses are still not 3D printable due to AM’s resolution limits.

[0005] Conventional AM processes, including MIP-VPP, follow the schema of stacking 2.5D thin sheets layer-by-layer in fabricating 3D products. Laminar sheets generated from the sliced computer-aided design (CAD) model with specific layer thickness are converted into pix elated mask images and projected to the photocurable resin. The curing that results from asliced layer is a 2.5D extrusion of the mask images from that layer. Such conventional AM process has intrinsic discontinuities in pixels and layers that lead to staircase stepping on the printed surface, which deteriorates the 3D objects’ surface quality. An important barrier for AM to overcome is how to reduce pixel size and layer thickness to achieve a high resolution and surface finish that are required by optical lenses.

[0006] Continuous liquid interface production (CLIP) developed by Carbon 3D offers a strategy to reduce the layer thickness to a submicron scale. The CLIP process projects a high-framerate UV mask video onto the building platform while the building platform continuously elevates from the resin vat. The high framerate mask video enables the super slicing of the CAD model to less than 1 pm thin sheets, significantly reducing the staircase stepping. The CLIP process has also been developed that combines grayscale exposure and meniscus coating that fabricates aspherical lenses with surface roughness down to 7 nm after meniscus coating. There also exists a single droplet continuous MIP-VPP that uses the liquid film covering to fabricate contact eye lenses. However, while the layer thickness is significantly reduced in the CLIP processes, the change of mask images is still not smooth, mainly because the pixel size of a mask image defines the smallest projection light change in MIP-VPP. The staircase stepping caused by the discrete change of mask images is at a one- pixel scale (at 10 pm level), which is still not smooth for optical lens fabrication. Thus, the resulting 3D-printed optical lenses need to be post-processed using meniscus coating or polishing to reach a good surface finish. In addition to reducing the manufacturing speed, the post-processing often makes dimensional accuracy uncontrollable.

[0007] It is, therefore, desired that vat polymerization three-dimensional printing systems, devices, and / or methods be developed to facilitate the fabrication of articles such as optical lenses in a manner that provides desired high requirements of feature resolution and high surface finish thereby overcoming the above-described shortcomings associated with fabricating optical lenses using known three-dimensional printing techniques.SUMMARY OF THE INVENTION

[0008] A system for constructing an article by 3D vat photopolymerization printing is disclosed. The system may comprise: a vat having a transparent bottom surface, wherein the vat is configured to hold a photopolymer resin; a building platform disposed in the vat and configured to elevate upwardly relative to the vat; an objective lens disposed below the transparent bottom surface of the vat; a radiation source disposed below the objective lens and configured to radiate through the objective lens to the vat for curing the photopolymerresin: and the system is configured to produce a continuously changing photomask image that is projected to the photopolymer resin in the vat as the building platform is elevated during 3D printing. The radiation source may comprise: an LCD photomask disposed below the objective lens; and a LED disposed below the LCD photomask. The objective lens may be configured to move during a printing process as the building platform is moving. The system may be configured to produce a printed part having a frustum layer with a slant angle for a layer of the printed part. The LCD photomask may be configured to move at a velocity Vied, wherein the building platform is configured to elevate in a continuous manner at a velocity Vh, wherein the objective lens is configured to move at a velocity Viens, and wherein either: (1 ) the slant angle is a function of Vh and Vied; or (2) the slant angle is a function of V and V lens.

[0009] A method for fabricating an article by 3D vat photopolymerization printing process is disclosed. The method may comprise: subjecting a selective region of a volume of photopolymer disposed in a vat and along a transparent bottom of the vat to a radiation source, wherein the selective region is interposed between a transparent bottom region and a movable building platform disposed in the vat; and projecting a continuously changing ultraviolet mask image onto the selective region by using a zooming-focused projection system; wherein during the step of projecting, the building platform is continuously elevated and the selective region cures in the form of a frustum layer, and as the building platform is elevated a new selective region on the existing frustum layer is formed and cured to form another frustum layer that is stacked on the existing frustum layer, and wherein the article comprises a plurality' of stacked frustum layers.

[0010] A system is disclosed comprising: one or more processors; and one or more tangible, non-transitory memories configured to communicate with the one or more processors, the one or more tangible, non-transitory memories having instructions stored thereon that, in response to execution by the one or more processors, cause the one or more processors to perform operations comprising: characterizing each layer of a 3D computer aided design model for a part to be printed, wherein the characterizing includes determining a slant angle for each layer; converting, for each layer, the respective slant angle to a respective ratio of velocities comprising either: (1) Vh and Vied; or (2) Vh and Viens, wherein Vh is the velocity of movement of a build platform, Vied is the velocity' of movement of an LCD photomask, and Viens is the velocity of movement of an objective lens, wherein a 3D printer comprises the build platform, the LCD photomask, and the objective lens; and moving the build platform ata velocity Vh, the LCD photomask at a velocity Vied, and the objective lens at a velocity' Viens to print each layer with the respective slant angle.BRIEF DESCRIPTION OF DRAWINGS

[0011] These and other features, aspects and advantages of the present invention will become better understood with reference to the following description, appending claims, and accompanying drawings where:

[0012] FIG. 1 A illustrates a typical layer based MIP-VPP;

[0013] FIG. IB illustrates a ty pical CLI process;

[0014] FIGS. 1C illustrates a zooming focus MIP-VIP in accordance with various example embodiments;

[0015] FIG. 2 illustrates a block diagram of a zf-MIP-VIP in accordance with various example embodiments;

[0016] FIG. 3 A illustrates in schematic format, a MIP-VIP with an LCD mask and LED array for the radiation source, in accordance with various example embodiments;

[0017] FIG. 3B illustrates in schematic format, a MIP-VIP with DMD for the radiation source, in accordance with various example embodiments;

[0018] FIG. 4 illustrates the difference between layer based stacking and Frustum based stacking, in accordance with various example embodiments;

[0019] FIG. 5 illustrates various steps of the process of 3D printing a zf-MIP-VIP in accordance with various example embodiments;

[0020] FIG. 6A illustrates the error reduction between MIP-VIP and zf-MIP-VIP in accordance with various example embodiments:

[0021] FIG. 6B illustrates relationship between the profile angle and the ratio of velocities in zf-MIP-VIP in accordance with various example embodiments;

[0022] FIG. 7 is a block diagram illustrating an example method of 3D printing using zf- MIP-VIP;

[0023] FIG. 8A is an example image of a layer in zf-MIP-VIP in accordance with various example embodiments;

[0024] FIG. 8B-8C illustrate two steps in zf-MIP-VIP, in accordance with various example embodiments; and

[0025] FIG. 9 illustrates a 3D printing device in accordance with various example embodiments.DETAILED DESCRIPTION

[0026] Disclosed herein is vat polymerization three-dimensional (3D) printing system, device, and / or methods that have been specially developed and engineered for fabricating articles such as optical lenses in a manner providing the desired high requirements of feature resolution and high surface finish. In one example embodiment, the 3D system disclosed herein is one that produces super-sliced frustum layers by continuously changing the mask images on the continuously elevating building platform for optical lens fabrication.

[0027] A zooming-focused MIP-VPP (zf-MIP-VPP) is disclosed herein as a dimensionally accurate and time efficient strategy' to circumvent the critical issues for optical lens fabrication. The zf-MIP-VPP utilizes a moving objective lens to dynamically change the projection images while continuously elevating the building platform. This configuration enables the frustum layer stacking with controlled layer tilting angles. Unlike 2.5D layer stacking, each layer of the frustum layer stacking has a slope for its side surface (defined as a slant angle). Hence, the frustum layer stacking requires not only the information on the cross-sectional image but also the slant angle of the 3D model. As a result, the 3D-printed surfaces by the frustum layer stacking may have three orders of magnitude smaller staircase stepping errors than those by the 2.5D layer stacking under the same layer thickness. By combining frustum layer stacking and the super slicing technique from CLIP, the zf-MIP- VPP improves the surface smoothness to less than ten nanometers, enabling the direct printing of optical lenses with a smooth surface finish and accurate dimension.

[0028] A new continuous zooming-focused mask image projection -based vat photopolymerization (zf-MIP-VPP) process is disclosed that can directly shape polymer materials into optical lenses with high dimensional accuracy and surface finish without additional post-processing. The main idea is to utilize frustum layer stacking instead of the conventional 2.5D layer stacking to eliminate staircase aliasing and enable nanoscale surface roughness. A continuous change of ultraviolet (UV) mask images is achieved using a zooming-focused projection system to generate the frustum layer stacking with controlled slant angles. In an example embodiment, the system uses dynamic control of image size, objective and imaging distance, and light intensity to perform zooming-focused MIP-VPP (zf-MIP-VPP). In an example embodiment, 3D-printed optical lenses with various designs, including parabolic lenses, fisheye lenses, and a laser beam expander, can be fabricated with surface roughness (Rms) of 3.4 nm without post-processing. In an example embodiment, the novel use of frustum layer stacking in 3D printing enables the direct fabrication of an optical lens and similar devices.

[0029] With reference now to FIGS. 1A-1C, 3D printing techniques are compared. FIG. 1A illustrates a conventional part 3D printed using layer-based MIP-VPP. In conventional MIP- VPP additive manufacturing, 2.5D thin sheets are stacked layer-by-layer to 3D print the part. This is done by creating a computer-aided design (CAD) model of an object to be 3D printed. The CAD model has specific layer thickness and dimensions that when stacked approximately replicate the object to be 3D printed. The CAD model layers are converted into pixelated mask images, and these mask images are used to generate the layers as the part is printed. Intnnsic discontinuities in pixels and layers lead to the staircase stepping shown in FIG. 1A. This deteriorates the surface quality of the 3D printed part.

[0030] One attempt to address this staircase stepping was the introduction of Continuous Liquid Interface Production (CLIP), where a high frame-rate UV mask video is projected onto the building platform while the building platform continuously elevates from the resin vat. Stated another way, the mask changes dynamically during the pull. The result is significantly reduced staircase stepping. FIG. IB illustrates a 3D printed part formed by CLIP, indicating the thinner layers possible, and the improvement in the size of the stair-steps associated with the pixel size. Nevertheless. CLIP 3D printing still has pixel size limitations that make the 3D printing unsuitable for some applications such as optical lens fabrication. Thus, even CLIP 3D printed parts need post-processing using meniscus coating or polishing to reach a good surface finish. But the post-processing makes the fabrication take longer, cost more, and introduces a significant level of dimensional accuracy variation. These outcomes are undesirable.

[0031] With reference now to FIG. 1 C, in an example embodiment, 3D printing an object using a zooming-focused MIP-VPP apparatus (zf-MIP-VPP) is disclosed. In an example embodiment, the zf-MIP-VPP utilizes a moving objective lens to dynamically change the projection images while continuously elevating the building platform. This method of 3D printing of a part enables frustum layer stacking with controlled layer tilting angles. Unlike 2.5D layer stacking, each layer of the frustum layer stacking may have a slope for its side surface (a “slant angle'’). Thus, in an example embodiment, each layer may be characterized by not only the cross-sectional image (defined by the mask), but also the slant angle for that layer. While in some embodiments, the slant angle is the same from one layer to the next, in an example embodiment, the slant angle can be different from one layer to the next. This zf- MIP-VPP can produce smaller staircase stepping errors, by as much as 3 orders of magnitude, than typical MIP-VPP of same layer thickness that does not use zooming-focus as described herein. Moreover, combining frustum layer stacking (zf-MIP-VPP) with super slicing technique of CLIP, can improve the surface smoothness to less than ten nanometers. In thismanner, it is possible to 3D print optical lenses that have the requisite surface smoothness, without post processing.

[0032] With reference now to FIG. 2, in an example embodiment, a 3D printing apparatus 200 is disclosed. In an example embodiment, the 3D printing apparatus 200 is an additive manufacturing device. In an example embodiment, the 3D printing apparatus uses zoom- focused mask image projection-based vat photopolymerization (zf-MIP-VPP) to convert liquid monomers into solid polymers using controlled ultraviolet (UV) light. In accordance with various example embodiments, the 3D printing apparatus 200 is configured to generate frustrum stacking, and layers having a slant angle between 10 and 90 degrees.

[0033] In an example embodiment, the 3d printing apparatus 200 comprises a build platform 215, a vat 210. an objective lens 240, and a radiation source 220. The radiation source 220 is configured to project radiation through the lens 240 through the bottom of the vat 210 for curing liquid polymers in the vat 210 as the platform 215 is drawn away from the bottom inside surface of the vat 210. thus forming a 3D printed part. In an example embodiment, the 3d printing apparatus 200 is configured to cure a layer attached to the build platform 215 and move the platform in the negative Z direction to create a cured block that is one or more cured layers thick.

[0034] The 3D printing apparatus 200 may further comprise one or more motors, servos, or the like (described generally as servos (260)) configured to move various components of printing apparatus 200. For example, a first servo 260 may be configured to move the platform 215, a second servo 260 may be configured to move the lens 240 during the pull, as described herein, to effect zoom-focused MIP-VPP, and a third servo 260 may be configured to move the radiation source 220 (e.g.. the LCD or DMD). In an example embodiment, a controller 250 is configured to control the movements of the lens 240 during the pull. The controller may also control the movement of the platform 215, vat 210, and / or the source 220 during the pull. The controller 250 may also control the projection of radiation (e.g., by controlling the intensity7of the light and / or the like).

[0035] In an example embodiment, FIG. 9 illustrates example physical embodiments of a 3D printing apparatus 900.

[0036] FIG. 3A illustrates an example 3D printing apparatus 300 from a side view perspective, in a block diagram form, for showing the relative locations, interaction, and functions of the various components. In an example embodiment, the 3D printing apparatus 300 comprises: a vat 310, a radiation source 320, a build platform 315, and an objective lens 340. In an example embodiment, the 3D printing apparatus further comprises a controller350. In an example embodiment, the radiation source 320 further comprises an LCD mask 330 and an LED array 321.

[0037] In accordance with an example embodiment, the objective lens 340 is configured to move relative to the vat 310. Moreover, in accordance with various example embodiments, the building platform 315 may also move relative to the vat 310, and in this example embodiment, the 3D printing apparatus is configured to move the objective lens 340 relative to the vat 310. In a third example embodiment, the LCD mask 330 may also be configured to move relative to the vat 310. In any of these example embodiments, the 3D printing apparatus is configured to move the objective lens 340 at a zooming speed Vi relative to the platform speed Vh that causes the light projected by a mask to zoom to change the size of the mask at the focused plane (on the top surface of the bottom of the vat in this example embodiment) as the building platform 315 is pulled away from the vat 310. This creates a continuously changing mask during the pull of the part, curing the part with a slant angle to form a frustum layer during the pull of that layer.

[0038] Thus, in an example embodiment, during the movement of the print platform at a velocity Vh, there may also be movement of the objective lens at a velocity Viens, and movement of the light source (e.g. the LCD / LED component) at a velocity Vied or in the case of DMD there may be movement of the DMD at a velocity VDMD. In an example embodiment, the slant angle is a function of the relationship between Vh and Viens. In another example embodiment, the slant angle is a function of the relationship between Vh and Vied. In another example embodiment, the slant angle is a function of the relationship between Vh and VDMD. These may be simultaneously true because, to maintain the focus during the relative movement of the vat, lens, and light source, it is desirable to maintain the focus of the image. In an example embodiment, therefore, the system is configured to maintain a relationship between Viens and Vied. As further disclosed below in the general case the slant angle is a function of Vh and Vi. These slant angle relationships cause the light projected by a mask to zoom to change the size of the mask at the focused plane (on the top surface of the vat in this example embodiment) as the building platform 315 is pulled away from the vat 310.

[0039] The build platform 315 may be configured to move relative to the vat 310, as described further below. In an example embodiment, the 3D printing apparatus 300 is configured for 3D printing of microfluidic devices.

[0040] In an example embodiment, the vat 310 is configured to accommodate a volume of photopolymer resin therein. For example, the vat 310 may comprise a photopolymer resin317 that can be photocured. In accordance with various example embodiments, the resin may comprise fillers such as microscopic particles, ceramics powders, metal powders, ceramic or carbon fibers, etc., and / or mixtures thereof. Stated another way, the photopolymer resin in the vat may be described as a photopolymer slurry comprising a resin and fillers. Moreover, any suitable 3D printing resin may be used. Depending on the resin used, the part formed may be a glass lens, ceramic lens, metal lens, and / or the like.

[0041] In an example embodiment, the vat may be made of any suitable material. In an example embodiment, the vat 310 may comprise a vat bottom portion 31 1. In one example embodiment, the vat bottom portion 311 comprises a transparent bottom surface. For example, the vat bottom portion 311 may be made of transparent glass or acry lic. Moreover, the vat bottom portion 311 may be configured in any suitable way that permits the radiation source 320 to irradiate portions of the resin in vat 310 for curing the resin.

[0042] In an example embodiment, the vat bottom portion 311 may have a vat surface 312 facing the inner portion of vat 310. In an example embodiment, the vat surface 312 has attached to it a thin film. For example, the thin film may comprise a fluorinated ethylene propylene (FEP) film. In another example embodiment, the vat surface 312 is coated with a vat surface coating. For example, the vat surface coating may comprise a Teflon coating, silicone, PDMS, and / or the like. In an example embodiment, the vat surface coating is transparent for permitting irradiation of the resin from the light source. Moreover, any suitable material may be used as the vat surface coating material.

[0043] In an example embodiment, build platform 315 comprises a platform surface 1 16. The platform surface 116 may be a planar surface. The build platform 315 may be configured to pull a 3D printed part from the vat 310, as it is being printed, layer upon layer. The build platform 315 may be configured to move vertically in the vat upwardly and downwardly relative to the transparent bottom surface. In an example embodiment, the build platform 315 may be driven vertically by linear actuators / motors. Moreover any suitable mechanism may be used to move the build platform 315.

[0044] In an example embodiment, the building platform 315 may be made of aluminum, acrylic, poly dimethylsiloxane (PDMS), or glass. Moreover any suitable materials may be used to form the build platform 315. In an example embodiment, the build platform 315 may attach a polymethyl pentene (TPX) film as its surface 116. In an example embodiment, the platform surface 116 may be coated with a platform coating. In one example embodiment, the platform coating is a base layer cured on the platform surface 116 using a photopolymerresin. In other example embodiments, the platform coating comprises a PDMS layer, a silicon layer, and / or the like. Moreover, the platform coating may be any suitable material.

[0045] In an example embodiment, the objective lens comprises an optical device configured to focus the radiation from the radiation source at the top surface of the vat 310. The objective lens may comprise a glass lens or any suitable material. The objective lens may have any suitable shape. In accordance with an example embodiment, the objective lens 340 is configured to move in a vertical direction. The vertical direction is illustrated in FIG. 3A as the Z direction. In an example embodiment, the Z direction is perpendicular to the bottom of the vat. In one example embodiment, the vat 310 is fixed, and the lens 340 moves relative to the vat. However, in other example embodiments, the objective lens may be attached to a fixed reference point, and the relative movement may be due to the movement of the vat and other components of the system. Moreover, in yet another example embodiment, both the vat and the objective lens may move, where the combined movement results in relative movement between the vat and the lens.

[0046] In one example embodiment, an objective lens movement device is operably connected to the objective lens 340 for causing translation of the objective lens 340. In one example embodiment, the movement device is a stepper motor. In other example embodiments, the movement device is a servo, a piezo-driven linear stage, a hydraulic piston, or other mechanisms to achieve the translation of lens 340.

[0047] The photocuring described herein may be implemented using any suitable source of radiation. In an example embodiment, the radiation source is a light source. For example, the radiation source may be a digital light processing (DLP) projector, or a liquid cry stal.

[0048] In one example embodiment, the radiation source 320 comprises an LED array 321 passing light through an LCD mask 330. In this example embodiment, the LED array 321 is configured to provide light to the photopolymer in the vat 310 via the LCD mask 330. In an example embodiment, a homogenizer 331 is located before the LCD mask 330, and is configured to convert parallel UV light into diffuse light to generate uniform light intensity' distribution. In an example embodiment, the liquid crystal display (LCD) mask 330 comprises 4098 * 2560 pixels (4K LCD screen), however any suitable LCD mask may be used. The LCD mask 330 is configured to generate a mask for allowing the radiation from the radiation source to selectively pass through the mask for mask image projection-based vat photopolymerization. Thus, each mask generated by the LCD mask 330 defines the area in the vat that is exposed to the radiation from radiation source 320. In one example embodiment, the mask is a static photomask, wherein the photomask image is constant for theentire time a stack layer is being pulled, then the photomask image is changed and remains constant during the entire time the next stack layer is pulled. In another example embodiment, the mask is a dynamic photomask image, wherein the photomask image changes during the pull for a stack layer, as described above re CLIP techniques. Both schema can be used with the zf-MIP-VPP.

[0049] In another example embodiment, and with reference to FIG. 3B, the radiation source 320 comprises an LED array (or a bulb) 321 and a DMD 322. When turned on. the LED / bulb will generate UV light that is projected on the DMD comprising millions of micromirrors. The DMD can be controlled by a microcontroller to dynamically generate a photomask to define the area in the vat that is exposed to the radiation from the radiation source and the projection light will be focused by the lens onto the vat surface. The LED will generally move with the LCD or DMD, and may be formed in the same physical structure.

[0050] In accordance with an example embodiment, the radiation source is configured to cure at least portions of a liquid resin contained in the vat 310. The radiation source is positioned relative to the vat 310, and / or the build platform 315, so as to direct radiation, through the transparent vat bottom portion 311 and vat surface coating, into a liquid resin 317 contained in the vat 310. In an example embodiment, the radiation source 320 is configured to cure at least portions of the liquid resin in a layer located between a build platform surface and the vat surface coating. In an example embodiment, the radiation source 320 is configured to provide a light that penetrates a predetermined light penetration range of depths. In an example embodiment, the light may be configured to penetrate from 20 pm - 500 pm, or in another example from 100 pm to 300 pm. Moreover, any suitable light penetration depth may be selected. The light penetration depth may be a factor of the w avelength of the light, its intensity, the exposure time, and the vat bottom portion material, the vat surface coating, and / or the resin material selected. In an example embodiment, the radiation source is a 405 nm light source, and the resin is a commercial transparent resin with a light penetration depth of 179.1 pm.

[0051] In an example embodiment, the radiation source 320 is configured to receive software generated mask images configured to cause specific areas of the resin in the vat to be cured and other areas to not be cured corresponding to the mask images projected into the vat.

[0052] Controller

[0053] In an example embodiment, the 3D printing apparatus comprises a controller 350. The controller 350 may be configured to control movement of the objective lens, the build platform, the vat, and / or the radiation source. In particular the controller 350 may beconfigured to control relative movement and / or relative velocity' of two or more of the lens, build platform, vat and radiation source. The controller 350 may further be configured to control operation of the radiation source 320 for constructing a device by the 3D printing apparatus. The controller may comprise any suitable device for providing commands to the motive force devices for moving the build platform. The controller may further provide commands to the radiation source. For example, the controller 350 may provide the desired mask image, and / or any instructions on how long to expose the resin to the radiation / light, the intensity of the light, and or the like. The controller 350 may be collocated at the location of the system 100, or remote therefrom, and / or may be one integrated controller or one or more separate controllers working together to provide the described control.

[0054] In an example embodiment, the slant angle is related to the speed of the platform (Vh) and the speed of lens (Viens) or LCD (Vied) by:. Note Viens and Vied are dependent on each other to achieve the constant focus of the mask image on the vat surface. In an example embodiment. Vi represents the ‘zooming speed’, ‘speed of the mask boundary moving inward’, ‘speed of the mask image change’, etc., with units of mm / s. In an example embodiment, Vi=(Viens*f*D) / (2*f). In another example embodiment, Vi=(Vkd*f*D) / (2(do- f)A2). These are both true because of the focus maintaining relationship between Viens and Vied.

[0055] Here, for a smaller slant angle 0, Vh Vicd (or Vh / Viens) used in the printing process will be reduced accordingly. That is, for the same Vh, Vied will be increased to achieve a smaller slant angle. In an example embodiment, if the controller does not cause the lens to move, i.e., Viens =0, Vied = 0. and Vh is a constant value, then 9 = 90 degree (i.e.. reverting back to the normal layer stacking that is currently used in MIP-VPP).

[0056] In an example embodiment, the LCD mask and the LED array are formed as a single component, and if they move, they move together. In other example embodiments, the LCD mask and LED array may be two separate parts that move together. Therefore, where it may be convenient to only speak herein of the movement of the LCD mask, but it will beunderstood that this typically includes the movement of the LED array together with the LCD mask. In an example embodiment, the LCD mask moves separately from the lens, but the speeds (of the LCD mask and lens) depend on each other to maintain a desired focus. In this example embodiment, moving the LCD mask is related to the moving of the objective lens based on: Viens / Vied = f2 / (do-f)2, which keeps the image in focus.

[0057] In an example embodiment, to achieve a frustum layer the system is configured to continuously move the objective lens, the radiation source, and the platform at the same time. The system is further configured to control the relative speeds of the platform, lens and radiation source to control the slant angle. This is in sharp contrast to any movement of the lens that merely control the position of the lens or radiation source prior to beginning printing (pulling the part). Thus, disclosed herein is a system configured to control relative velocities of the platform, and lens I LCD mask (or DMD) in contrast to moving any of these to a position, fixing that position, and then starting printing.

[0058] In accordance with various example embodiments, the system and methods disclosed herein are configured to control the light intensity during the 3D printing process. During MIP-VPP printing, the light intensity at the printing interface (the polymer material at the bottom of the vat) is constant, and the cure rate is constant throughout the pull. But in zf- MIP-VPP, moving the LCD further from the vat causes a decrease in light intensity, and moving the objective lens changes the focus of the radiation. Changes in the light intensityaffects the photopolymerization behavior of the liquid resin at the printing interface.

[0059] In an example embodiment, using MIP-VPP, e g., with CLIP, the Vh is typically constant and the cure rate is therefore constant. But, with zf-MIP-VPP, as the lens moves to reduce the mask image size on the focus plane, the light intensity of the same mask image increases, and vice versa. Therefore, system is configured to compensate for the change in light intensity that would otherwise occur due to zf-MIP-VPP. The compensation can be by increasing Vh (a faster pull) which compensates for a higher intensity7, or the irradiation system can compensate by dimming the intensity of the LED light or the DMD / LCD pixels’ grayscale values can be reduced, and / or a combination of two or all of the three methods. Thus, in accordance with an example embodiment, the cure rate is based on Vh, or is a function of Vh. This is in contrast to embodiments where Vh is constant in MIP-VPP.

[0060] Therefore, in one example embodiment, the system and method are configured to implement light-intensity compensation to generate a uniform photopolymerization result, the compensation method may comprise: (1) in a first step, a grayscale based mask image compensation is applied to the LCD screen; and (2) in a second step, the printing speed Vh isused to compensate for the light intensity change between different magnification rates. In this second step, the printing speed Vh is increased when the magnification rate decreases and vice versa to get a constant relative energy dosage for a frustum layer. Thus, light intensity uniformity can be achieved by controlling the grayscale mask pattern and the controlled pulling-up speed based on a light distribution model.

[0061] In an example embodiment, the surface roughness, measured for example using atomic force microscopy (AFM) is less than 5 nm, less than 4 nm, and preferably less than 3.5 nm within a 2 pm x 2 pm sampling region, quantified by the root mean square (Rms), and the maximum roughness depth Rmax in the measured region is less than 20 nm.

[0062] In an example embodiment, the systems and methods disclosed herein may be suitable for direct 3D printing of an optical lens. For example, the optical lens could comprise a fisheye lens, parabolic lens, laser beam expander, and / or the like. However, the systems and methods disclosed herein may be used to 3D print any suitable device or structure. In particular the systems and methods disclosed herein may be suitable for 3D printing of devices or structures that require a very’ smooth surface finish. For example, the systems and methods disclosed herein may be suitable for 3D printing of a waveguide horn antenna for use at microwave or millimeter wave frequencies in wireless applications. In an example embodiment, the systems and methods disclosed herein enable 3D printing with a RLMS surface roughness of 3.4 nm or smaller.

[0063] In accordance with other example embodiments, the system is configured to 3D print complex optical lens structures in situ. For example, an in-situ assembled beam expander with a 1:2 expanding ratio could be 3D printed as one part, without subsequent assembly of the parts of the beam expander. Stated another way, devices that typically are assembled can be printed complete without assembly. Thus, the system is configured to provide integrated optical device fabrication. In an integrated optical device comprising two or more optical lenses, the 3D-printed assembly enabled by zf-MIP-VPP may produce high surface quality' and remarkable positioning accuracy over each optical lens. Moreover, because all of the lenses are printed in situ, all assembly error and / or additional calibration effort during the lens manual assembly is avoided. Instead, the assembly error can be controlled by the 3D printing system. In addition to integrated optic structures, mechanical assembly features can be printed with an optical lens or multiple lens.

[0064] In an example embodiment, systems and methods for 3D printing of objects that require a smooth surface involve post processing to achieve the surface smoothness requirements. The post-processing may include a polishing step and / or a step where the partis dipped in a liquid that hardens and fills in the comers to make the surface smoother than it was at the conclusion of the typical layer base printing process. In an example embodiment, the system, devices and methods disclosed herein are able to achieve the requisite surface smoothness without post processing. Stated another way, only the frustrum stacking method is needed to achieve the requisite surface smoothness. Stated yet another way, the desired surface smoothness of 3.4 nm or smaller can be achieved with no further processing steps after the zoom-focused 3D printing described herein.

[0065] With reference to FIG. 5, an example zf-MIP-VPP process is illustrated schematically. In an example embodiment, in step 1, a 3D CAD model of an object (shown at " I ■’) is created. The object or “part"’ may, for example, be an optical lens. In an example embodiment, the 3D CAD model is super sliced into a set of thin frustum layers with a slant angle e and cross-sectional images are correspondingly characterized over the Z direction of the CAD model. This characterizing step is illustrated at '‘2”. In an example embodiment, the data with respect to the slant angle e is converted into relative moving velocity of the objective lens, the LCD photomask, and / or the building platform. This conversion can be done on a layer by layer basis, such that each layer is characterized by its own relative moving velocity. This velocity characterization step is represented by the graph illustrated at “3’". In an example embodiment, the zooming-focused mask image projection is used (represented by ‘"4"’) to create the 3D printed part at “5’". The 3D printed part can be cleaned, using an alcohol bathing and nitrogen flow cleaning, in an example embodiment, and have a surface roughness of less than 3.4 nm without any post processing. The 3D printed part can also have micron-scale dimensional accuracy, in one example embodiment. It is noted that each frustum layer has the same slant angle e around its exterior. Hence, the angle e will generally be symmetric about the Z-axis for each layer.

[0066] In accordance with an example embodiment, and with reference to FIG. 6A, a frustum layer of an optical lens is generated by following three steps: 1) the CAD model is sliced into a series of cross-sectional images under a certain layer thickness dh; 2) the difference between a cross-sectional image and its neighboring cross-sectional images is calculated by di(k) = (1k- lk-i) / 2, where Ik is the characteristic length of the kth layer cross-section image; 3) based on the k* and the (k - l)th cross-sectional images, a frustum layer can be constructed as a linear interpolation of its neighbors, whose slant angle e of the side surface is defined as tan(e) = dh / di.

[0067] By comparison of the CAD models, a large reduction in approximation error is observable. With reference to FIG. 6A, the approximation error 601 (space between the shapeof the CAD model and shape being approximated), assuming the same layer thickness dh for comparison, is illustrated on the left for typical 2.5D layer stacking compared to frustum layer zf-MIP-VPP stacking on the right. This volumetric error (Ek) may be as much as three orders of magnitude smaller for frustum layer zf-MIP-VPP stacking, than for typical 2.5D layer stacking. In an example embodiment, the volumetric error (Ek) for the kth layer is defined as the integral of a metric profile function along that layer's height range [zk-i, zk] as Ek = the integral from zk-i to zk of cp(z) dz. where cp(z) can be written as the area deviation: cp (z) = A(z) - Ao(z). Ao is the designed area of the cross-section at height z, and A is the practical area of the cross-section at height z.

[0068] In accordance with various example embodiments, frustum layer zf-MIP-VPP stacking, i.e.. the printing of a frustum layer with a certain slant angle e may be implemented by controlling Vh and Vi, where Vi is the changing speed of the projection images and Vh is the part printing speed in the Z direction. Vi may further be determined by the velocity of the LCD, Vied , the focal length, the diameter of the mask images on the LCD screen, and the distance between the objective lens and the building platform. Thus, the slant angle e may be governed by the following equation:

[0069] tan(e)= Vh / Vi = -(2Vh(do-f)A2) / (Vlcd*f*D)

[0070] where f is the focal length of the objective lens, D is the diameter of the mask images, and do is the distance between the objective lens and the building platform. In an example embodiment, a desired slant angle e of the frustum layer can be achieved by manipulating the velocity of the LCD photomask Vied and the printing speed Vh. Moreover, any suitable combination of the other variables can be adjusted to achieve a desired slant angle e of the frustum layer.

[0071] An example of motion planning to generate the desired frustum layer stacking of different optical lenses is demonstrated in FIG. 6B, which illustrates, for CAD models of three different parabolic lenses, the slant angles e over the Z height (see 611 curves), which become more shallow7as one reaches the tip of the parabolic lens. The (612 curves) illustrate the calculation for the three example CAD models, calculating based on the slant angle e, the velocity ratio Vied / Vh over the Z height (e.g., using the above tan(e) equation). The value of Vied / Vh increases as the Z height increases from 0 mm to 3 mm (the tip of the parabolic lens of these three CAD models) since the profile slant angle o decreases. At the very7tip of the parabolic lens, Vied / Vh will reach its maximum to fabricate a nearly flat frustum layer.

[0072] With reference now to FIGS. 8A-8C, an example method is illustrated for printing of a frustum layer via zf-MIP-VPP. FIG. 8A illustrates the magnified profile of a designedoptical lens sliced into a frustum layer. Points 1 and 2, are the bottom and the top of the frustum layer. In this example embodiment, the thickness of the frustum layer dh is 1 pm, and the slant angle is e. FIGS. 8B and 8C illustrate the motions of the LCD photomask, the objective lens, and the building platform from point 1 to point 2. The objective lens starts at the position du (i.e., a distance dii from the bottom of the vat), and the LCD photo mask starts at the position doi (i.e.. a distance dii + doi from the bottom of the vat). During the continuous printing, the objective lens moves up at a velocity Viens and the LCD photomask moves down at a velocity Vied to form the slant angle e of the frustum layer at each time moment. The objective lens ends at position di2 (i.e., a distance di2 from the bottom of the vat), and the LCD photomask ends at the position do2 (i.e., a distance di2 + d02 from the bottom of the vat) to finish this frustum layer. Thus, the method is configured to enable the projection image to continuously change its size, during the pull, and consequently, define a frustum layer in the frustum layer stacking.

[0073] With reference now to FIG. 7, in an example embodiment, a method 700 is disclosed for 3D printing an object using a zooming-focused MIP-VPP apparatus (zf-MIP-VPP). In an example embodiment, the method 700 comprises: (710) preparing a 3D CAD model of a part to be 3D printed; and (720) characterization of each layer. The characterization may comprise determining the height of each layer and the slant angle e to create a frustum approximation layer. In an example embodiment, the method 700 further comprises (730) converting, for each layer, the slant angle e to a ratio of velocities of Vh and VLCD.

[0074] In an example embodiment, the method 700 further comprises: (740) moving the build platform vertically upward and away from the transparent bottom surface at a Velocity Vh, while moving the LCD light source downward at a velocity Vied, to generate the slant angle e for respective frustum printed 3D layers. This step may further comprise printing using CLIP technology while implementing zoom-focused 3D printing. The method 700 further comprises: (750) compensating for light intensity to achieve uniform light intensity' during fabrication and compensating for the changes in distances occasioned by the zoomfocus MIP-VPP process.

[0075] In an example embodiment, the hardware and software used may comprise: Hardware: three Motorized linear stages (e g., one for the platform movement, one for the lens movement, and one for the LCD masks movement), Microcontroller board, stepper motor driver with three outputs, photoelectric limit switches, print platform; and Software: Printing file preparation software for DLP / LCD resin printers.

[0076] In this regard, in various embodiments, the controller 350 can comprise one or more processors. The controller 350 may be integrated into a computer system of the printer (e.g., in processor and / or memory). In various embodiments, the controller 350 may be configured as a central network element or hub to various systems and components of the printer. In various embodiments, the controller 350 may comprise a processor. In various embodiments, controller 350 may be implemented as a single processor and associated memory. In various embodiments, the controller 350 may be implemented as one or more processors and / or memories (e.g., a main processor and local processors for various components, a decentralized network of main processors, or the like). The controller 350 can include a general-purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programable gate array (FPGA), or other programable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof. The controller 350 may comprise a processor configured to implement various logical operations in response to execution of instructions, for example, instructions stored on anon-transitory, tangible, computer-readable medium (e.g.. memory) configured to communicate with the controller 350 (e.g., controlling the servos, velocities of the various components, or the like). System program instructions and / or controller instructions may be loaded onto a non-transitory. tangible, computer-readable medium having instructions stored thereon that, in response to execution by a controller, cause the controller to perform various operations. The term “non-transitory” is to be understood to remove only propagating transitory signals per se from the claim scope and does not relinquish rights to all standard computer-readable media that are not only propagating transitory7signals per se.

[0077] Exemplary embodiments of the methods / systems have been disclosed in an illustrative style. Accordingly, the terminology employed throughout should be read in a non-limiting manner. Although minor modifications to the teachings herein will occur to those well versed in the art, it shall be understood that what is intended to be circumscribed within the scope of the patent warranted hereon are all such embodiments that reasonably fall within the scope of the advancement to the art hereby contributed, and that that scope shall not be restricted except in light of the appended claims and their equivalents.

Claims

CLAIMSWhat is claimed is:

1. A system for constructing an article by 3D vat photopolymerization printing comprising: a vat having a transparent bottom surface, wherein the vat is configured to hold a photopolymer resin; a building platform disposed in the vat and configured to elevate upwardly relative to the vat; an objective lens disposed below the transparent bottom surface of the vat; a radiation source disposed below the objective lens and configured to radiate through the objective lens to the vat for curing the photopolymer resin; and wherein the system is configured to produce a continuously changing photomask image that is projected to the photopolymer resin in the vat as the building platform is elevated during 3D printing.

2. The system of claim 1 , wherein the radiation source comprises: a liquid crystal display photomask disposed below the objective lens; and a light emitting diode disposed below the LCD photomask.

3. The system of claim 2, wherein the objective lens is configured to move during a printing process as the building platform is moving.

4. The system of claim 3, wherein movement of the LCD photomask and the objective lens are separately controlled to adjust objective and imaging distances during 3D printing.

5. The system of claim 2, wherein the system is configured to produce a printed part having a frustum layer with a slant angle for a layer of the printed part.

6. The system of claim 5, wherein the LCD photomask is configured to move at a velocity Vkd, wherein the building platform is configured to elevate in a continuous manner at a velocity Vh, wherein the objective lens is configured to move at a velocity Viens, and wherein either: (1) the slant angle is a function of Vh and Vied; or (2) the slant angle is a function of Vh and Vi ens.

7. The system of claim 2, further comprising a light homogenizer interposed between the LCD photomask and the radiation source and configured to convert parallel ultraviolet radiation source light into diffuse light to generate uniform light intensity distribution to the LCD photomask.

8. The system of claim 1, wherein the article is an optical lens comprising a plurality of stacked frustum layers formed during 3D printing from the photopolymer resin as cured by the continuously changing photomask image.

9. The system of claim 2, wherein the LCD photomask image is continuously changed during 3D print to reflect mask images corresponding to different slices of a CAD model of the article.

10. The system of claim 9, wherein each CAD model slice has a thickness of 0.5 pm - 10 pm, and wherein a surface roughness is less than 5 nm without post processing.1 1. A method for fabricating an article by 3D vat photopolymerization printing process comprising: subjecting a selective region of a volume of photopolymer disposed in a vat and along a transparent bottom of the vat to a radiation source, wherein the selective region is interposed between a transparent bottom region and a movable building platform disposed in the vat; and projecting a continuously changing ultraviolet mask image onto the selective region by using a zooming-focused projection system; wherein during the step of projecting, the building platform is continuously elevated and the selective region cures in the form of a frustum layer, and as the building platform is elevated a new selective region on the existing frustum layer is formed and cured to form another frustum layer that is stacked on the existing frustum layer, and wherein the article comprises a plurality of stacked frustum layers.

12. The method of claim 11, wherein during the step of projecting, a mask image in the form of a liquid cry stal display (LCD) photomask disposed below the vat is moved at an LCD velocity (Vied), and an objective lens interposed between the LCD photomask and the vat is moved at a lens velocity (Viens).

13. The method of claim 12, wherein during the step of projecting, the LCD photomask is moved away from the vat at the LCD velocity (Vied), and the objective lens is moved towards the vat at the lens velocity (Viens).

14. The method of claim 12, wherein the building platform is moved at a platform velocity (Vh), wherein the frustum layer has a slant angle, wherein the slant angle is a function of either: (1) the slant angle is a function of Vh and Vied; or (2) the slant angle is a function of Vh and Vi ens.

15. The method of claim 11, further comprising compensating for a relative movement of the building platform, liquid crystal display photomask and objective lens, via a cure rate adjustment to obtain a constant cure rate for the photopolymer.

16. The method of claim 15, wherein adjusting the cure rate adjustment comprises at least one of: adjusting an intensity' of light emitted from a light source comprising light emitting diodes; and adjusting a velocity' of the building platform.

17. A sy stem compri sing : one or more processors; and one or more tangible, non-transitoiy memories configured to communicate with the one or more processors, the one or more tangible, non-transitory memories having instructions stored thereon that, in response to execution by the one or more processors, cause the one or more processors to perform operations comprising: characterizing each layer of a 3D computer aided design model for a part to be printed, wherein the characterizing includes determining a slant angle for each layer;converting, for each layer, the respective slant angle to a respective ratio of velocities comprising either: (1) Vh and Vied; or (2) Vh and Viens. wherein Vh is the velocity of movement of a build platform. Vied is the velocity of movement of an LCD photomask, and Viens is the velocity of movement of an objective lens, wherein a 3D printer comprises the build platform, the LCD photomask, and the objective lens; and moving the build platform at a velocity Vh, the LCD photomask at a velocity Vied, and the objective lens at a velocity Viens to print each layer with the respective slant angle.

Images