内部结构自支撑的三维打印浮体平衡优化算法

为了使浮体能够在熔融挤压式三维打印机中一次成型,提出一种内部结构自支撑的浮体平衡优化算法.首先在给定漂浮姿势的输入模型内部,利用递归细分方法生成自支撑的格子结构,并把输入模型与格子结构组合为初始浮体模型.然后以初始浮体模型中格子单元体积为变量构建平衡优化方程,根据方程解算结果调整初始浮体模型中每个格子单元的体积,从而生成最终的浮体模型.实验结果表明,文中算法生成的浮体模型可以使用熔融挤压式三维打印机直接打印,打印的实体不但能够按照预设的姿势漂浮在液体中,而且具有较好的抗压能力;算法中的递归细分策略能够在模型内部产生较多的格子单元,具有节省打印材料的优势.     

Color laser printer forensic based on noisy feature and support vector machine classifier

Digital forensics in the ubiquitous era can enhance and protect the reliability of multimedia content where this content is accessed, manipulated, and distributed using high quality computer devices. Color laser printer forensics is a kind of digital forensics which identifies the printing source of color printed materials such as fine arts, money, and document and helps to catch a criminal. This paper present a new color laser printer forensic algorithm based on noisy texture analysis and support vector machine classifier that can detect which color laser printer was used to print the unknown images. Since each printer vender uses their own printing process, printed documents from different venders have a little invisible difference looks like noise. In our identification scheme, the invisible noises are estimated with the wiener-filter and the 2D Discrete Wavelet Transform (DWT) filter. Then, a gray level co-occurrence matrix (GLCM) is calculated to analyze the texture of the noise. From the GLCM, 384 statistical features are extracted and applied to train and test the support vector machine classifier for identifying the color laser printers. In the experiment, a total of 4,800 images from 8 color laser printer models were used, where half of the image is for training and the other half is for classification. Results prove that the presented algorithm performs well by achieving 99.3%, 97.4% and 88.7% accuracy for the brand, toner and model identification respectively.     

Interactive Modeling of Cellular Structures on Surfaces with Application to Additive Manufacturing

The rich and evocative patterns of natural tessellations endow them with an unmistakable artistic appeal and structural properties which are echoed across design, production, and manufacturing. Unfortunately, interactive control of such patterns-as modeled by Voronoi diagrams, is limited to the simple two dimensional case and does not extend well tofreeform surfaces. We present an approach for direct modeling and editing of such cellular structures on surface meshes. The overall modeling experience is driven by a set of editing primitives which are efficiently implemented on graphics hardware. We feature a novel application for 3D printing on modern support-free additive manufacturing platforms. Our method decomposes the input surface into a cellular skeletal structure which hosts a set of overlay shells. In this way, material saving can be channeled to the shells while structural stability is channeled to the skeleton. To accommodate the available printer build volume, the cellular structure can be further split into moderately sized parts. Together with shells, they can be conveniently packed to save on production time. The assembly of the printed parts is streamlined by a part numbering scheme which respects the geometric layout of the input model.     

Microstructure Control in 3D Printing with Digital Light Processing

Digital light processing stereolithography is a promising technique for 3D printing. However, it offers little control over the surface appearance of the printed object. The printing process is typically layered, which leads to aliasing artefacts that affect surface appearance. An antialiasing option is to use greyscale pixel values in the layer images that we supply to the printer. This enables a kind of subvoxel growth control. We explore this concept and use it for editing surface microstructure. In other words, we modify the surface appearance of a printed object by applying a greyscale pattern to the surface voxels before sending the cross-sectional layer images to the printer. We find that a smooth noise function is an excellent tool for varying surface roughness and for breaking the regularities that lead to aliasing. Conversely, we also present examples that introduce regularities to produce controlled anisotropic surface appearance. Our hope is that subvoxel growth control in stereolithography can lead 3D printing towards customizable surface appearance. The printing process adds what we call ground noise to the printed result. We suggest a way of modelling this ground noise to provide users with a tool for estimating a printer's ability to control surface reflectance.     

A Rapid Generation Method of Character Doll with Rotatable Limbs Oriented to 3D Printer

Currently, 3D printing of the character dolls is a very practical application for the average person. But the model of doll which can be obtained is static so the posture of the doll is single. On the other hand, the modification of the model is very difficult to non-professions. This paper proposes an rapid generation method of character doll with rotatable limbs, which is through adding the sphere joint to the doll＇s model automatically. After the model is segmented by drawing a line interactively, the sphere joint is created based on the segmentation boundary through entity modeling method. Lastly the two models of the doll and the joint are composited and printed. Some doll＇s model are tested on the FDM（Fused Deposition Modeling） 3D printer using this process. The results are more interesting and the efficiency has been greatly improved compared with modifying the model manually.     

Relating halftone dot quality to paper surface topography

Most printed material is produced by printing halftone dot patterns. One of the key issues that determine the attainable print quality is the structure of the paper surface, but the relation is non-deterministic in nature. We examine the halftone print quality and study the statistical dependence between the defects in printed dots and the topography measurement of the unprinted paper. The work concerns SC paper samples printed by an IGT gravure test printer. We have small-scale 2D measurements of the unprinted paper surface topography and the reflectance of the print result. The measurements before and after printing are aligned with subpixel resolution, and individual printed dots are detected. First, the quality of the printed dots is studied using Self Organizing Map and clustering and the properties of the corresponding areas in the unprinted topography are examined. The printed dots are divided into high and low print quality. Features from the unprinted paper surface topography are then used to classify the corresponding paper areas using Support Vector Machine classification. The results show that the topography of the paper can explain some of the print defects. However, there are many other factors that affect the print quality, and the topography alone is not adequate to predict the print quality.     

Modeling,Evaluation and Optimization of Interlocking Shell Pieces

While the 3D printing technology has become increasingly popular in recent years, it suffers from two critical limitations: expensive printing material and long printing time. An effective solution is to hollow the 3D model into a shell and print the shell by parts. Unfortunately, making shell pieces tightly assembled and easy to disassemble seem to be two contradictory conditions, and there exists no easy way to satisfy them at the same time yet. In this paper, we present a computational system to design an interlocking structure of a partitioned shell model, which uses only male and female connectors to lock shell pieces in the assembled configuration. Given a mesh segmentation input, our system automatically finds an optimal installation plan specifying both the installation order and the installation directions of the pieces, and then builds the models of the shell pieces using optimized shell thickness and connector sizes. To find the optimal installation plan, we develop simulation‐based and data‐driven metrics, and we incorporate them into an optimal plan search algorithm with fast pruning and local optimization strategies. The whole system is automatic, except for the shape design of the key piece. The interlocking structure does not introduce new gaps on the outer surface, which would become noticeable inevitably due to limited printer precision. Our experiment shows that the assembled object is strong against separation, yet still easy to disassemble.     

ZomeFab: Cost-Effective Hybrid Fabrication with Zometools

In recent years, personalized fabrication has received considerable attention because of the widespread use of consumer-level three-dimensional (3D) printers. However, such 3D printers have drawbacks, such as long production time and limited output size, which hinder large-scale rapid-prototyping. In this paper, for the time- and cost-effective fabrication of large-scale objects, we propose a hybrid 3D fabrication method that combines 3D printing and the Zometool construction set, which is a compact, sturdy and reusable structure for infill fabrication. The proposed method significantly reduces fabrication cost and time by printing only thin 3D outer shells. In addition, we design an optimization framework to generate both a Zometol structure and printed surface partitions by optimizing several criteria, including printability, material cost and Zometool structure complexity. Moreover, we demonstrate the effectiveness of the proposed method by fabricating various large-scale 3D models.     

Path smoothing and feed rate planning for robotic curved layer additive manufacturing

Robotic curved layer additive manufacturing (a.k.a. multi-axis 3D printing) has been gaining attention recently owing to its simplicity and unique ability of printing complex shapes without using a support structure. However, as the printing path now is no long planar and the nozzle orientation is no longer fixed but changes continuously during printing, even though it could be smooth when defined in the workpiece coordinate system in both position and orientation of the nozzle, due to the inevitable numerical errors, it typically is unsmooth with many sharp-changing undulations when transformed to the coordinate system of the robot arm. As a result, the feed rate of printing has to be set extremely conservatively lest the printer would chatter or vibrate and seriously jeopardize the printing quality. In this paper, first, we present a practical B-spline based smoothing algorithm for removing sharp corners on the printing path while upholding the required cusp-height threshold on the printed surface. Next, for the smoothed printing path, we propose a feed rate scheduling strategy that will try to maximize the variable feed rate while subject to the kinematic constraints of the six joints of the robot arm. Both computer simulations and physical printing experiments are carried out to assess the proposed methodologies and the results give a positive confirmation on their advantages.     

3D打印模型版权保护技术研究进展

目的 近年来3D打印模型的版权标注和保护引起了研究者的关注,为了全面反映3D打印模型版权保护研究的现状和最新进展,本文对国内外公开发表的主要文献进行了梳理和分析。方法 首先在广泛文献调研的基础上,描述3D打印模型文件和3D打印模型攻击类型,分析3D打印和扫描过程对模型的影响。然后对3D打印模型的版权保护策略进行分类,详细阐述每类方法的基本框架和相关技术特征。最后根据相关文献,将3D打印数字水印方法与传统网格水印算法和抗3D打印—扫描攻击的性能进行比较。结果 基于物理特性的3D模型版权保护技术能对3D打印后的模型嵌入有效的具有一定隐蔽性的版权标识,但在提取微结构体等信息时需要借助一些专用设备,不具有普适性。基于数字水印的方法既能抵抗传统的数字模态下的相似性变换、剪切、噪声、细分、量化、光顺等攻击,又能有效抵抗3D模型的数/模等模态转换攻击,并且高精度的3D打印机和扫描仪能有效提高水印的检测率。结论 3D打印产品是设计者和生产企业的智慧和心血的结晶,包含知识产权。随着3D打印在工业领域的广泛应用,3D打印模型版权保护有着广阔的应用前景和研究价值,但目前针对3D打印模型的版权保护的检测和评估机制存在一些局限性,未来需要构建统一的3D打印模型测试库和3D打印模型水印评测体系。     

Printing 3D microfluidic chips with a 3D sugar printer

This study demonstrated how to quickly and effectively print two-dimensional (2D) and three-dimensional (3D) microfluidic chips with a low-cost 3D sugar printer. The sugar printer was modified from a desktop 3D printer by redesigning the extruder, so the melting sugar could be extruded with pneumatic driving. Sacrificial sugar lines were first printed on a base layer followed by casting polydimethylsiloxane (PDMS) onto the layer and repeating. Microchannels were then printed in the PDMS solvent, microfluidic chips dropped into hot water to dissolve the sugar lines after the PDMS was solidified, and the microfluidic chips did not need further sealing. Different types of sugar utilized for printing material were studied with results indicating that maltitol exhibited a stable flow property compared with other sugars such as caramel or sucrose. Low cost is a significant advantage of this type of sugar printer as the machine may be purchased for only approximately $800. Additionally, as demonstrated in this study, the printed 3D microfluidic chip is a useful tool utilized for cell culture, thus proving the 3D printer is a powerful tool for medical/biological research.     

Saliency‐Preserving Slicing Optimization for Effective 3D Printing

We present an adaptive slicing scheme for reducing the manufacturing time for 3D printing systems. Based on a new saliency‐based metric, our method optimizes the thicknesses of slicing layers to save printing time and preserve the visual quality of the printing results. We formulate the problem as a constrained ?₀ optimization and compute the slicing result via a two‐step optimization scheme. To further reduce printing time, we develop a saliency‐based segmentation scheme to partition an object into subparts and then optimize the slicing of each subpart separately. We validate our method with a large set of 3D shapes ranging from CAD models to scanned objects. Results show that our method saves printing time by 30–40% and generates 3D objects that are visually similar to the ones printed with the finest resolution possible.     

Clean color: Improving multi‐filament 3D prints

Fused Filament Fabrication is an additive manufacturing process by which a 3D object is created from plastic filament. The filament is pushed through a hot nozzle where it melts. The nozzle deposits plastic layer after layer to create the final object. This process has been popularized by the RepRap community. Several printers feature multiple extruders, allowing objects to be formed from multiple materials or colors. The extruders are mounted side by side on the printer carriage. However, the print quality suffers when objects with color patterns are printed – a disappointment for designers interested in 3D printing their colored digital models. The most severe issue is the oozing of plastic from the idle extruders: Plastics of different colors bleed onto each other giving the surface a smudged aspect, excess strings oozing from the extruder deposit on the surface, and holes appear due to this missing plastic. Fixing this issue is difficult: increasing the printing speed reduces oozing but also degrades surface quality – on large prints the required speed level become impractical. Adding a physical mechanism increases cost and print time as extruders travel to a cleaning station. Instead, we rely on software and exploit degrees of freedom of the printing process. We introduce three techniques that complement each other in improving the print quality significantly. We first reduce the impact of oozing plastic by choosing a better azimuth angle for the printed part. We build a disposable rampart in close proximity of the part, giving the extruders the opportunity to wipe oozing strings and refill with hot plastic. We finally introduce a toolpath planner avoiding and hiding most of the defects due to oozing, and seamlessly integrating the rampart. We demonstrate our technique on several challenging multiple color prints, and show that our tool path planner improves the surface finish of single color prints as well.     

Landscaper: A Modeling System for 3D Printing Scale Models of Landscapes

Landscape models of geospatial regions provide an intuitive mechanism for exploring complex geospatial information. However, the methods currently used to create these scale models require a large amount of resources, which restricts the availability of these models to a limited number of popular public places, such as museums and airports. In this paper, we have proposed a system for creating these physical models using an affordable 3D printer in order to make the creation of these models more widely accessible. Our system retrieves GIS relevant to creating a physical model of a geospatial region and then addresses the two major limitations of affordable 3D printers, namely the limited number of materials and available printing volume. This is accomplished by separating features into distinct extruded layers and splitting large models into smaller pieces, allowing us to employ different methods for the visualization of different geospatial features, like vegetation and residential areas, in a 3D printing context. We confirm the functionality of our system by printing two large physical models of relatively complex landscape regions.     

基于深度扫描仪的高辨识度三维人体模型重建方法

3D 照相打印馆人像的打印质量取决于3D 扫描获得的三维人体模型的辨识度。然 而,由于现有3D 人体扫描仪价格昂贵、操作复杂等原因,使得3D 人像打印成本高、耗时长和 打印精度较低。针对这些缺点提出一种基于深度扫描仪重建高辨识度三维人体模型方法。利用 多组深度扫描仪分工协作、优势互补,分别获取高辨识度的人体面部五官点云数据,上半身与 全身表面轮廓点云数据。然后,通过引入特征点和改进的最近点迭代法将采集到的三组点云数 据进行对齐、替换、拼接,将拼接后的无拓扑关系的点云数据进行曲面重构即可获得高辨识度 的三维人体模型。该方法的扫描时间较短,以较低的成本构建了具有高辨识度的三维人像模型。     

Improved Surface Quality in 3D Printing by Optimizing the Printing Direction

We present a pipeline of algorithms that decomposes a given polygon model into parts such that each part can be 3D printed with high (outer) surface quality. For this we exploit the fact that most 3D printing technologies have an anisotropic resolution and hence the surface smoothness varies significantly with the orientation of the surface. Our pipeline starts by segmenting the input surface into patches such that their normals can be aligned perpendicularly to the printing direction. A 3D Voronoi diagram is computed such that the intersections of the Voronoi cells with the surface approximate these surface patches. The intersections of the Voronoi cells with the input model's volume then provide an initial decomposition. We further present an algorithm to compute an assembly order for the parts and generate connectors between them. A post processing step further optimizes the seams between segments to improve the visual quality. We run our pipeline on a wide range of 3D models and experimentally evaluate the obtained improvements in terms of numerical, visual, and haptic quality.     

大幅面DLP型3D打印机错位均摊接缝消除方法研究

针对面曝光模式的数字光处理(Digital light processing, DLP)型3D打印机成型幅面较小问题, 提出一种移动拼接与错位均摊消除接缝痕迹相结合的大幅面技术方案. 该方案首先对三维模型进行均匀切片形成N层切面, 再对切面位图进行错位切分, 使得相邻层的拼接位置错开, 每张切面位图形成M张单元位图, 构成3D打印的数据源; 其次根据错位参数沿着X轴移动投影仪到达对应曝光位, 每层成型M张单元位图, 拼接构成一层切面薄片, 切面薄片的拼接位置逐层错开, 叠加生成三维模型实体. 实际打印结果表明, 该方案能够以较小的附加成本扩大成型尺寸, 提高模型整体质量.     

A wavelet-based multi-dimensional temporal recurrent neural network for stencil printing performance prediction

The solder paste printing (SPP) is a critical procedure in a surface mount technology (SMT) based assembly line, which is one of the major attributes to the defect of the printed circuit boards (PCBs). The quality of SPP is influenced by multiple factors, such as the squeegee speed, pressure, the stencil separation speed, cleaning frequency, and cleaning profile. During printing, the printer environment is dynamically varying due to the physical change of solder paste, which can result in a dynamic variation of the relationships between the printing results and the influential factors. To reduce the printing defects, it is critical to understand such dynamic relationships. This research focuses on determining the printing performance during printing by implementing a wavelet filtering-based temporal recurrent neural network. To reduce the noise factor in the solder paste inspection (SPI) data, this research applies a three-dimensional dual-tree complex wavelet transformation for low-pass noise filtering and signal reconstruction. A recurrent neural network is utilized to model the performance prediction with low noise interference. Both printing sequence and process setting information are considered in the proposed recurrent network model. The proposed approach is validated using practical dataset and compared with other commonly used data mining approaches. The results show that the proposed wavelet-based multi-dimensional temporal recurrent neural network can effectively predict the printing process performance and can be a high potential approach in reducing the defects and controlling cleaning frequency. The proposed model is expected to advance the current research in the application of smart manufacturing in surface mount technology.     

Optimizing Object Decomposition to Reduce Visual Artifacts in 3D Printing

We propose a method for the automatic segmentation of 3D objects into parts which can be individually 3D printed and then reassembled by preserving the visual quality of the final object. Our technique focuses on minimizing the surface affected by supports, decomposing the object into multiple parts whose printing orientation is automatically chosen. The segmentation reduces the visual impact on the fabricated model producing non-planar cuts that adapt to the object shape. This is performed by solving an optimization problem that balances the effects of supports and cuts, while trying to place both in occluded regions of the object surface. To assess the practical impact of the solution, we show a number of segmented, 3D printed and reassembled objects.     

Texture Mapping Real‐World Objects with Hydrographics

In the digital world, assigning arbitrary colors to an object is a simple operation thanks to texture mapping. However, in the real world, the same basic function of applying colors onto an object is far from trivial. One can specify colors during the fabrication process using a color 3D printer, but this does not apply to already existing objects. Paint and decals can be used during post‐fabrication, but they are challenging to apply on complex shapes. In this paper, we develop a method to enable texture mapping of physical objects, that is, we allow one to map an arbitrary color image onto a three‐dimensional object. Our approach builds upon hydrographics, a technique to transfer pigments printed on a sheet of polymer onto curved surfaces. We first describe a setup that makes the traditional water transfer printing process more accurate and consistent across prints. We then simulate the transfer process using a specialized parameterization to estimate the mapping between the planar color map and the object surface. We demonstrate that our approach enables the application of detailed color maps onto complex shapes such as 3D models of faces and anatomical casts.