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Mask Projection micro Stereolithography (MPuSLA) is an additive manufacturing process used to build physical components out of a photopolymer resin. Existing MPuSLA technology cut the CAD model of part into slices by horizontal planes and the slices are stored as bitmaps. A layer corresponding to the shape of each bitmap gets cured. This layer is c...
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In this paper, resin-based photocurable polymer materials for stereolithography (SLA), digital-light-processing (DLP) and polymer-jetting (PJ) additive manufacturing techniques were characterized from 0.2 – 1.4 terahertz (THz) for their comprehensive dielectric properties, e.g. refractive index, absorption coefficient, dielectric constant and loss...
Citations
... With the rapid development of threedimensional microscale components in the field of microelectronics, the additive manufacturing of complex three-dimensional structures at micro and nano scales has become a current research hotspotand difficulty, and has been applied in many fields such as medicine, aerospace, microelectromechanical systems, new energy 5,6 . There are several main methods for additive manufacturing of three-dimensional structures at micro and nano scales: micro stereolithography, twophoton polymerization laser 3D direct writing, and electrochemical deposition technology [7][8][9][10] . ...
... where Hðx i ; y j Þ is the light intensity distribution and H 0 (mW$cm À2 ) is the peak intensity at the center of a pixel ðx i0 ; y j0 Þ, rðx i ; y j Þ is the distance (mm) from the center of the pixel to ðx i ; y j Þ, uðx i ; y j Þ is the directional Gaussian half-width of the intensity distribution. Here, we adopt a simple exposure threshold model, originally derived as a single-pixel DLP model based on Beer-Lambert law of absorption (Zhao, 2009), then modify the relation to account for differences in the degree of irradiation attenuation through uncrosslinked and crosslinked photopolymer. The expression gives exposure, E, vs depth, z, as ...
To address current unmet needs in terms of scalability and material biocompatibility for future photocrosslinking-based additive manufacturing technologies, emergent platform designs are in inexorable demand. In particular, a shift from the present use of cell-damaging ultraviolet (UV) light sources in light-based three-dimensional (3D) bioprinting methods demand new platforms. We adopted an organic light-emitting diode (OLED) microdisplay as a digital visible light modulator to create a 3D printing platform modality that offers scalability and multi-material capability while forgoing the need for UV photocrosslinking. We formulate biocompatible inks that are visible light-crosslinkable with relatively quick photoinitiation rates. We demonstrated successful attachment and rapid growth of primary human dermal fibroblast-adult (HDF-a) cells on biological substrates fabricated using the OLED platform. This platform incites new possibilities by providing a simple-yet-effective means for low-cost, high-throughput, multi-material 3D fabrication of functional structures made of polymers, ceramic composites, and biomaterials.
... Choi et al. [24] developed a more economical and simpler micro-stereolithography technology using a UV lamp as a light source and optical fiber as the light delivery system and photopolymer solidification experiments were conducted to examine the characteristics of the developed microstereolithography apparatus. Zhao et al. [25] developed a thick film mask projection stereolithography to fabricate films on fixed flat substrate and develop a column cure model in which a CAD model of part is discretized into vertical columns instead of being sliced into horizontal layers, and all columns get cured simultaneously till the desired heights. Vatani et al. [26] optimized the exiting slicing algorithms for reducing the size of the files and memory usage of computers to process them. ...
... The build platform is then elevated to introduce an uncured resin for the printer to start building the next layer [1]. This process is repeated with different layer of contour projection depending on the current build height of the STL model until the 3D model is completely printed [1][2][3][4]. Projection mask 3D printing method is known to surpass any other 3D printing technology in terms of accuracy due to its uniform layer curing process [4,5]. This continuous curing process causes the printed part to become monolithic. ...
... This process is repeated with different layer of contour projection depending on the current build height of the STL model until the 3D model is completely printed [1][2][3][4]. Projection mask 3D printing method is known to surpass any other 3D printing technology in terms of accuracy due to its uniform layer curing process [4,5]. This continuous curing process causes the printed part to become monolithic. ...
Projection mask stereolithography is a latest technology in 3D printing industry. It relies on UV projection to cure the photocurable resin layer-by-layer to build the solid 3D object. The projections are generated from tessellated STL CAD model using contour generation algorithm that generates 2D contours as the projection mask. The computational of the algorithm consumes a lot of memory for high-resolution printing. Low-resolution causes the stair-case effect to visibly appear on the printed model. Using real-time contour generation algorithm reduces the memory consumption and retains the high-resolution printing quality and accuracy. Pixel line mapping algorithm is implemented on the generated line segments to scale the line segments with respect to the display resolution of the projection device. Contour loop algorithm connects each of these pixel line segments into multiple closed-loop contours. The algorithms are implemented on an Alien STL model having 150350 facets. It is found that the pixel mapping algorithm correctly scales the model while retaining the aspect ratio of the model. The result of contour loop algorithm shows that the mean contour loop execution time is 0.87 milliseconds which is relevant for real-time application.
... Recently introduced Digital-Light-Processing (DLP) 3D printer utilizes mask projection by DLP projector onto photopolymer resin to cure the liquid form resin into solid model [1][2]. The mask projection is proven to be much faster and it provides uniform curing process due to each layer is being projected at once compared to SLA 3D Printer [3][4] . CAD file such as STereoLithography (STL) is considered as de facto in 3D printing. ...
Owing to the advent of the industrial revolution 4.0, the need for further evaluating processes applied in the additive manufacturing application particularly the computational process for slicing is non-trivial. This paper evaluates a real-time slicing algorithm for slicing an STL formatted computer-aided design (CAD). A line-plane intersection equation was applied to perform the slicing procedure at any given height. The application of this algorithm has found to provide a better computational time regardless the number of facet in the STL model. The performance of this algorithm is evaluated by comparing the results of the computational time for different geometry.
... Primarily due to the complicated nature of ECPL process, no comprehensive control strategy exists yet except for some basic use of offline open-loop process control technology [1,4,5]. This technique relies on characterization experiments to quantify the effects of exposure dose on the cured heights, and adopts open-loop control mode which is error-prone to variations and disturbances in the black/grey box process. ...
... With Jacob's model for ECPL, an empirical process model from experimental data curve fitting is shown as below [5]. We are interested in checking the accuracy of the controller as well as its capability to reject the measurement noise. ...
The Exposure Controlled Projection Lithography (ECPL) is a photopolymerization-based additive manufacturing process, which cures a 3D part by projecting patterned UV light from beneath a stationary and transparent resin chamber. Its application in microfabrication is limited by the current open-loop process control method. The overall research goal is to develop some closed-loop control system for the black / grey box ECPL process. In this paper, we presented two process modeling and control systems for ECPL - a lumped parameters model with an Kalman filter equipped Evolutionary Cycle to Cycle (EC2C) control scheme, and a novel backstepping dynamics model with Adaptive Neural Network Backstepping (ANNB) control method. EC2C and ANNB methods adopt different process models, control approaches and algorithms, and can be applied under different development stages and application scenarios of the ECPL process. Preliminary study concluded that the EC2C and ANNB control methods are capable of tracking the process dynamics, thus are promising to be able to improve the ECPL process precision and robustness.
... Primarily because of the complicated nature of photopolymerization in stereolithogrphy process, no comprehensive control strategy exists yet except for some basic use of offline open-loop process control technology, which relies on characterization experiments to quantify the effects of exposure dose on the cured heights. The ECPL system has been evolving and the process has been continuously improved, resulting in a decreasing fabrication error, from 25 per cent (Zhao (2009)) to 15 per cent (Jariwala (2013)) to recently 10 per cent (Jones et al., 2014). However, to become a more capable micro manufacturing method for wider applications, ECPL still has limited process accuracy. ...
... With Jacob's model, for the DMD-based non-stacking ECPL in this paper, a more true process model could be as below (Zhao, 2009): ...
Purpose
Exposure controlled projection lithography (ECPL) is an additive manufacturing process based on controlled UV photopolymerization. This paper aims to explore an advanced closed-loop control methodology to ECPL.
Design/methodology/approach
This paper proposes an evolutionary cycle to cycle (EC2C) control method, and started with a reduced order EC2C time control to control only the exposure time for given DMD bitmaps, which correspond to target 3D part cross-sections. A preliminary EC2C time control scheme was developed and followed by two types of EC2C time controllers based on two different parameter estimation methods, recursive least squares and L 1 norm minimization (L 1 Min). Both algorithms were in an exponential weighted form, resulting in EWRLS and EWL 1 Min, to weight more on recent data to reflect the current process dynamics.
Findings
EWRLS was found to outperform EWL 1 Min in terms of computation speed and stability. The simulation study demonstrated that the proposed EC2C time control method was capable of adaptively tracking the ECPL process dynamics and updating online the model parameters with real-time measurements. It could control perfectly the exposure time for each bitmap, achieving the desired height for each layer and resulting in a total cured height conforming to the target 3D part height.
Research limitations/implications
The accuracy of EC2C time control method relies heavily on fast and accurate measurement, and this research assumes availability of an adequate real-time metrology. Measurement errors are not considered in this paper and will be explored in future. Only simulation study was performed without physical experiments to verify the EC2C controller.
Practical implications
For implementation, a real-time measurement system needs to be developed and the EC2C control software needs to be programmed and interfaced with the physical system.
Originality/value
It concludes that EC2C control method is very promising for a physical implementation, and could be extended for the development of a more comprehensive closed-loop controller for both exposure time and intensity to improve the ECPL process precision and robustness.
... ECPL systems have been evolving since our first generation prototype in 2008, and the process has been continuously improved, resulting in a smaller and smaller fabrication error, from 25% [2] to 15% [1] to recently 10% [3]. However to become a more capable micro manufacturing method for wider applications, ECPL still has limited process accuracy, which sparks a new study area of interest -advanced process control methods as will be investigated in this paper. ...
... Our group has worked extensively in an effort to realize an automated and precise ECPL system. Zhao (2009) [2] built a process model (Equation 1) relating the exposure dose E to the final cured height Z by curve fitting of measurement data from many cured parts. Experiments were performed beforehand to determine the values of critical exposure E c and penetration depths of liquid (D pL ) and of solid resin (D pS ). ...
... ECPL Open-loop Process Control Scheme by Zhao[2] ...
The DMD based Exposure Controlled Projection Lithography (ECPL) process has promising applications in fabrication of microfluidics and micro optics components. Unlike a conventional layer-stacking projection stereolithography process, ECPL cures a 3D feature by projecting radiation through a stationary, transparent substrate by varying exposure patterns and durations implemented by a sequence of DMD bitmaps. Due to the unavailability of an in situ metrology for cured part dimensions, unmeasurable time-varying disturbances such as oxygen inhibition and light source fluctuations, and the complex chemical & physics interactions in photopolymerization, a common practice in stereolithography process planning is to use experimental characterization and statistics models in an open-loop mode, which yields poor accuracy. This paper reviewed existing process control methods for ECPL and defined a need for advanced control methods. As a first proposal for advanced control methods to mask projection stereolithography, the paper surveyed relevant processes and put forward a hierarchical framework of advanced control methods for ECPL, including evolutionary cycle-to-cycle (EC2C) and adaptive neural network (ANN) backstepping control methods. The goal is to identify some advanced control methods, which are capable of tracking the process dynamics by online updating the model parameters with real-time measurement feedback. Such closed-loop control methods are promising to be able to improve the process precision and robustness.
Les céramiques techniques 3D à géométrie complexe font actuellement l’objet d'une demande croissante pour diverses applications dans des conditions sévères. Elles présentent des propriétés importantes telles qu’une excellente stabilité chimique, une grande résistance à l’oxydation et la corrosion ainsi que des propriétés mécaniques importantes les rendant des composants fiables dans les domaines électronique, aérospatial et biomédical. En particulier, les céramiques à base de Si sont caractérisées par d’excellentes propriétés thermochimiques et une résistance au fluage. La fabrication additive (AM) est la technologie de choix pour concevoir des objets de forme quasi nette avec un contrôle parfait de la géométrie et de la porosité à différentes échelles. Cependant, les poudres céramiques traditionnelles sont difficiles à imprimer à cause de leur dureté et friabilité. Par conséquent, les polymères précéramiques conviennent à l'impression 3D car ils sont facilement modifiables à l'état moléculaire. Dans ce travail, nous avons combiné l'impression 3D avec la chimie des précurseurs (PDCs) pour fabriquer des céramiques à base de Si à géométrie complexe. Deux technologies d’AM ont été investiguées : Fused Deposition Modeling (FDM) basée sur la fusion d'un filament thermoplastique et UV-LCD basée sur la photopolymérisation d’une résine sous rayonnements UVs. La caractérisation des polymères précéramiques et des céramiques qui en dérivent a été systématiquement étudiée. L’influence de la composition chimique et structure du polymère sur son imprimabilité a été présentée. Tout d'abord, nous avons élaboré des céramiques type carbonitrure de silicium (SiCN) et carbure de silicium (SiC) par impression indirecte en couplant la technologie FDM avec une approche de réplique. Nous avons imprimé par FDM des motifs acide polylactique (PLA) en nid d'abeille qui ont été revêtus par le polyvinylsilazane (PVZ) ou l’allylhydrydopolycarbosilane (AHPCS) précurseurs respectifs de SiCN et SiC. Ces polymères ont été chimiquement réticulés avec le dicumyl peroxide. Une pyrolyse ultérieure sous atmosphère contrôlée permet la réticulation thermique des polymères à 130°C, la décomposition du PLA à 320°C et la céramisation à 1000°C. Un rétrécissement volumique a été observé suite à la décomposition du PLA et de la céramisation. SiBC (dérivé de AHPCS modifié par le bore) a également été élaboré pour étudier l'effet du bore sur l’imprimabilité de Si-C. Deuxièmement, nous avons synthétisé des polymères précéramiques photosensibles précurseurs de SiOC, SiC ou SiCN selon deux approches : i) mélange du polymère avec une résine photosensible commerciale et ii) synthèse d'un polymère précéramique sensible aux UVs par fonctionnalisation avec des unités photosensibles. Nous avons procédé ensuite à l’impression 3D par UV-LCD de ces polymères en optimisant plusieurs paramètres : temps d'exposition, épaisseur et nombre de couches. Dans la première approche, deux types de précurseurs de SiOC ont été utilisés : méthyl silsesquioxane (Silres MK) et polyméthylhydrosiloxane (PMHS) qui ont été mélangés avec une résine commerciale photosensible. Un meilleur comportement mécanique de la céramique en forme de pastille est observé avec Silres MK dû à son meilleur rendement céramique. Dans la deuxième approche, Silres MK photosensible est préparée soit par un simple mélange avec des agents photoréticulables type triméthylolpropane triacrylate (TMPTA) et/ou 1,6 hexanediol diacrylate (HDDA), soit par greffage de fonctions triacrylates du 3-(triméthoxysilyl) propyle méthacrylate (TMSPM) sur les fonctions Si-OH du Silres MK. Les céramiques 3D SiOC obtenues après pyrolyse montrent une conservation de la forme de la pastille presque sans fissures. Notre approche a également été appliquée à la fabrication de céramiques non-oxydes SiC et SiCN, prouvant la versatilité de synthétiser des polymères précéramiques photosensibles oxyde et non-oxyde.
A cost-effective stereolithography for medium-scale components is developed to fabricate 3D components with high build speed and resolution from photo-curable resin. The developed SLA utilizes a focused light beam of wavelength range (300 nm – 700 nm) coming from the DLP projector and passes through the objective lens and finally imposed on the platform containing a layer of photo-curable resin. After focusing the light beam on the liquid resin layer, the photo-polymerization reaction occurs and the liquid resin becomes solid. Thus, the 3D object is fabricated layer by layer curing of liquid resin. The photopolymer used in this experimentation is polyethylene glycol di-acrylate and Irgacure 784 as photo-initiator. The Creo 3.0 software is used for modelling of 3D objects. A special MATLAB code is developed for slicing of the 3D model and displaying the sliced image one by one through DLP projector. The Arduino microcontroller with stepper motor and ball screw is used to control the motion of Z-stage platform. The Creation workshop software is also used to control motion of the Z-stage and period to display the sliced images through DLP projector. The medium-scale 3D objects with rectangular, square, and circular cross - sections are obtained by curing the aforementioned photo-curable resin. It is observed that the 3D objects are best cured for two seconds curing time with 0.1 mm curing depth along Z-axis.
