PackMerger: A 3D Print Volume Optimizer

We propose an optimization framework for 3D printing that seeks to save printing time and the support material required to print 3D shapes. Three‐dimensional printing technology is rapidly maturing and may revolutionize how we manufacture objects. The total cost of printing, however, is governed by numerous factors which include not only the price of the printer but also the amount of material and time to fabricate the shape. Our PackMerger framework converts the input 3D watertight mesh into a shell by hollowing its inner parts. The shell is then divided into segments. The location of splits is controlled based on several parameters, including the size of the connection areas or volume of each segment. The pieces are then tightly packed using optimization. The optimization attempts to minimize the amount of support material and the bounding box volume of the packed segments while keeping the number of segments minimal. The final packed configuration can be printed with substantial time and material savings, while also allowing printing of objects that would not fit into the printer volume. We have tested our system on three different printers and it shows a reduction of 5–30% of the printing time while simultaneously saving 15–65% of the support material. The optimization time was approximately 1 min. Once the segments are printed, they need to be assembled.     

基于改进粒子群算法的多机器多任务3D打印智能调度方法

针对批量3D打印成本高,多机器多任务的3D打印批次调度复杂的问题,建立以最小单位体积平均成本为目标的优化模型,并提出一种基于改进粒子群算法的智能调度方法求解该模型;首先,分析打印工场、生产流程,构建3D打印单位体积平均成本模型;之后基于改进粒子群算法,以单位体积平均成本为适应度,以调度序列为粒子的位置信息,采用十进制顺序二维编码方式表示问题的解,并在更新策略上应用线性递减权值的动态惯性因子来调整全局与局部的搜索能力;算法迭代后,得到目标函数最优值及对应解集;经实验算例结果表明,该方法较单独打印加工的单位体积平均成本降低了0.101 3GBP/cm3,有效地降低工厂生产的总成本,提高了3D打印机的利用效率。     

面向耗材节省的三维打印路径规划算法研究

为降低三维打印（three-dimensional printing,3D）耗材费用并进一步提高打印效率,给出一种面向熔融沉积制造的三维打印路径规划算法。该方法综合考虑打印耗材、打印效率以及打印表面质量等因素,通过网格模型及其支撑的相邻层片轮廓关系求得可稀疏打印区域;基于多边形扫描线算法以及多边形单调链关系,得到能够连续打印的路径区域;最终通过区域路径稀疏化得到改进的打印路径。通过复杂网格模型的三维打印路径规划实例,验证了算法的有效性。该算法能够降低打印耗材数量,并进一步提高打印效率。     

Deep learning-based optimal segmentation of 3D printed product for surface quality improvement and support structure reduction

Large-sized product cannot be printed as one piece by a 3D printer because of the volume limitation of most 3D printers. Some products with the complex structure and high surface quality should also not be printed into one piece to meet requirement of the printing quality. For increasing the surface quality and reducing support structure of 3D printed models, this paper proposes a 3D model segmentation method based on deep learning. Sub-graphs are generated by pre-segmenting 3D triangular mesh models to extract printing features. A data structure is proposed to design training data sets based on the sub-graphs with printing features of the original 3D model including surface quality, support structure and normal curvature. After training a Stacked Auto-encoder using the training set, a 3D model is pre-segmented to build an application set by the sub-graph data structure. The application set is applied by the trained deep-learning system to generate hidden features. An Affinity Propagation clustering method is introduced in combining hidden features and geometric information of the application set to segment a product model into several parts. In the case study, samples of 3D models are segmented by the proposed method, and then printed using a 3D printer for validating the performance.     

Example-guided segmentation

In this paper, we propose a novel strategy to automatically segment volume data using a high-quality mesh segmentation of an “example” model as a guiding example. The example mesh is deformed until it matches the relevant volume features. The algorithm starts from a medical volume model (scalar field of densities) to be segmented, together with an already existing segmentation (polygonal mesh) of the same organ, usually from a different person. The pre-process step computes a suitable attracting scalar field in the volume model. After an approximate 3D registration between the example mesh and the volume (this is the only step requiring user intervention), the algorithm works by minimizing an energy and adapts the shape of the polygonal mesh to the volume features in order to segment the target organ. The resulting mesh adapts to the volume features in the areas which can be unambiguously segmented, while taking the shape of the example mesh in regions which lack relevant volume information. The paper discusses several examples involving human foot bones, with results that clearly outperform present segmentation schemes.     

Detail control in line drawings of 3D meshes

We address the problem of rendering a 3D mesh in the style of a line drawing, in which little or no shading is used and instead shape cues are provided by silhouettes and suggestive contours. Our specific goal is to depict shape features at a chosen scale. For example, when mesh triangles project into the image plane at subpixel sizes, both suggestive contours and silhouettes may form dense networks that convey shape poorly. The solution we propose is to convert the input mesh to a multiresolution representation (specifically, a progressive mesh), then view-dependently refine or coarsen the mesh to control the size of its triangles in image space. We thereby control the scale of shape features that are depicted via silhouettes and suggestive contours. We propose a novel refinement criterion that achieves this goal and address the problem of maintaining temporal coherence of silhouette and suggestive contours when extracting them from a changing mesh.     

3D conforming power diagrams for radial LGR in CPG reservoir grids

Mesh generation becomes a crucial step in reservoir flow simulation of new generation. The mesh must faithfully represent the architecture of the reservoir and its heterogeneity. In (Flandrin et al. in IJNME 65(10):1639–1672, 2006) a three-dimensional hybrid mesh model was proposed to capture the radial characteristics of the flow around the wells. In this hybrid mesh, the reservoir is described by a non-uniform Cartesian structured mesh and the drainage areas around the wells are represented by structured radial circular meshes. Unstructured polyhedral meshes are used to connect these two kinds of structured grids. The construction of these transition meshes is based on 3D power diagrams (Aurenhammer in SIAM J Comput 16(1):78–96, 1987) to ensure finite volume properties such as mesh conformity, dual orthogonality and cell convexity. In this paper, we propose an extension of this hybrid model to the case where the reservoir is described by a corner point geometry (CPG) grid. At first, the CPG grid is mapped, in a reference space, into a non-uniform Cartesian grid by minimizing the mapping deformation. Then, a hybrid mesh is generated in this reference space using the previous method. Finally, this mesh is mapped back into the real space. Some quality criterions are introduced to measure and improve the quality of the polyhedral transition mesh.     

基于周期性晶格的3D打印模型轻量化方法

为了获得3D打印模型节材效果和优化的物理力学性能,从晶格的形状多变性出发,提出了一种基于晶格的3D打印轻量化结构生成方法,由此产生的轻量化结构用来替代给定模型的实体空间.首先,提出了一种通用的晶格描述方法,进而对晶格的几何和拓扑特征进行个性化设计.其次,通过在模型包围盒内周期性排列晶格单元,构造出了实体建模所依附的拓扑...     

各向同性三角形重新网格化方法综述

三维网格模型的重新网格化是计算机图形学中的重要内容,是许多几何应用的关键组成部分。近年来迅速发展的三维处理技术,如有限元模拟、计算机动画、三维打印等,对网格质量的要求不断提升,促进了三维网格模型重新网格化的持续发展,由此产生了许多新的重新网格化技术。首先介绍了三角形网格质量评估的标准,然后概述了各向同性重新网格化的最新进展,并详细研究和比较了各种重新网格化算法的优缺点,最后对未来的研究提出了新的问题与方向。     

Clever Support: Efficient Support Structure Generation for Digital Fabrication

We introduce an optimization framework for the reduction of support structures required by 3D printers based on Fused Deposition Modeling (FDM) technology. The printers need to connect overhangs with the lower parts of the object or the ground in order to print them. Since the support material needs to be printed first and discarded later, optimizing its volume can lead to material and printing time savings. We present a novel, geometry‐based approach that minimizes the support material while providing sufficient support. Using our approach, the input 3D model is first oriented into a position with minimal area that requires support. Then the points in this area that require support are detected. For these points the supporting structure is progressively built while attempting to minimize the overall length of the support structure. The resulting structure has a tree‐like shape that effectively supports the overhangs. We have tested our algorithm on the MakerBot® Replicator? 2 printer and we compared our solution to the embedded software solution in this printer and to Autodesk® Meshmixer? software. Our solution reduced printing time by an average of 29.4% (ranging from 13.9% to 49.5%) and the amount of material by 40.5% (ranging from 24.5% to 68.1%).     

Parallel computational methods for 3D simulation of a parafoil with prescribed shape changes

In this paper we describe parallel computational methods for 3D simulation of the dynamics and fluid dynamics of a parafoil with prescribed, time-dependent shape changes. The mathematical model is based on the time-dependent, 3D Navier-Stokes equations governing the incompressible flow around the parafoil and Newton's law of motion governing the dynamics of the parafoil, with the aerodynamic forces acting on the parafoil calculated from the flow field. The computational methods developed for these 3D simulations include a stabilized space-time finite element formulation to accommodate for the shape changes, special mesh generation and mesh moving strategies developed for this purpose, iterative solution techniques for the large, coupled nonlinear equation systems involved, and parallel implementation of all these methods on scalable computing systems such as the Thinking Machines CM-5. As an example, we report 3D simulation of a flare maneuver in which the parafoil velocity is reduced by pulling down the flaps. This simulation requires solution of over 3.6 million coupled, nonlinear equations at every time step of the simulation.     

扫掠法有限元网格生成方法

为了提高有限元网格的生成质量,扫掠法生成六面体网格过程中内部节点定位成为关键一步,在研究复杂扫掠体六面体有限元网格生成算法过程中,提出了一种基于扫掠法的六面体网格生成算法,算法利用源曲面已经划分好的网格和连接曲面的结构化网格,用仿射映射逐层投影,生成目标曲面,提出基于Roca算法的内部节点定位的新算法,运用由外向内推进的波前法思想,生成全部的六面体网格。通过实例表明,该算法快速,稳定,可靠,可处理大量复杂2.5维实体六面体网格生成问题。     

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.     

基于三周期极小曲面的三维打印全接触鞋垫建模方法

全接触鞋垫可以降低足底峰值压力来改善和预防糖尿病足群体的神经性溃疡症状,传统全接触鞋垫设计方法操作复杂,本文提出一种新颖的基于三周期极小曲面(TPMS)的三维打印全接触鞋垫建模方法.通过数据采集、全接触模型构建、模型多孔化3个步骤构建基于TPMS结构的全接触鞋垫,使用三维打印技术生产.首先采集用户脚部模型和目标鞋垫模型...     

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。     

A fully 3D adaptive finite element simulation and prototype for gas flow in a porous media

This paper presents a three-dimensional (3D) adaptive finite element solution for gas flow in a porous media. The solution obtained is truly 3D and employs a dynamic h-adaptive refinement technique for efficiency. The adaptive procedure uses a new node-based storage mechanism [Wang GH, Tyler JM, Weltman JS, Callahan JD. Advances in Engineering Software including Computing Systems in Engineering 1999;30:31–41]. This node-based structure substantially reduces the memory necessary to store the finite element mesh. A prototype simulator, written in C++, has been implemented for Eugene Island block 305, a multi-well condensate reservoir off the coast of Louisiana to demonstrate the use of this adaptive procedure. Results, presented in this paper, show dramatic agreement with the actual production data. This prototype simulator uses Windows workstations to support a fully dynamic 3D mesh plus mesh generation.     

NURBS体参数化模型的无支撑打印算法

处理大角度悬垂结构的打印问题是无支撑打印的主要挑战。针对NURBS（non-uniform rational Bspline）体参数化模型的多自由度无支撑三维打印技术,提出一种锥形切片算法。通过对模型的三维文件进行几何映射,利用水平切片算法对其进行切片,得到模型变形后的连续打印路径G-code;然后对得到的G-code进行逆映射,生成适用于六轴机械臂的多自由度连续打印路径。利用锥形切片算法规划打印路径,可以在无须支撑的情况下,依靠自支撑结构实现对悬空结构部分的打印。最后,通过仿真实验和对比实验,验证了锥形切片算法的准确性、可行性和有效性。锥形切片算法的引入为NURBS体参数化模型的无支撑三维打印提供了一种更加高效、经济和环保的解决方案。     

Embedding Pyramids into 3D Meshes

The pyramid architecture is a powerful topology in the area of computer vision. On the other hand, the 3D mesh architecture possesses rich topological features which make it suitable for building scalable parallel processor systems. The usefulness of these two architectures has led us to consider the problem of embedding pyramids into 3D meshes, for which we present two solutions. The first solution, termednatural embedding,maps a pyramid into a 3D mesh such that each level of the pyramid is mapped to a single level of the 3D mesh. The second solution, termedmultiple embedding,allows simultaneous embedding of multiple pyramids into a single 3D mesh. The quality of both solutions is evaluated using dilation and expansion measures. Using the multiple embedding, we are able to obtain an average dilation of 1.26 and a near-optimal expansion of 1.12.     

Generation of 3D mixed element meshes using a flexible refinement approach

This paper describes and discusses the main characteristics and implementation issues of a 3D mixed element mesh generator based on a generalization of the modified octree approach. This mesh generator uses primitive elements of different type as internal nodes, a flexible refinement approach as refinement strategy (primitive elements are not always bisected), and bricks, pyramids, prisms and tetrahedra as final elements. The mesh generation process is divided in several steps: the generation of the initial mesh composed of primitive elements, the refinement of primitive elements until the point density requirements are fulfilled, the generation of a graded mesh between dense and coarse regions, and finally, the recognition of the final elements. The main algorithms and data structures are described in detail for each step of the mesh generation process. As result, examples of meshes that satisfy the Delaunay condition and that can be used with the control volume method are shown.