基于STL文件的柱状支撑结构自动生成算法

熔融挤压三维打印以热塑性材料为原料逐层打印完成,由于熔丝只能沉积在已存在的物体上层,模型悬空部位需要添加支撑结构。为解决该问题,提出一种基于STL(Stereo Lithography)文件的稀疏柱状支撑结构自动生成算法。算法通过对比三角面片倾斜角度与模型临界角的大小,获取独立的待支撑区域,然后基于边长自适应法和射线与面片相交法得到待支撑点集,自动生成支撑结构。此外为了保证模型表面质量和支撑结构的稳定性,支撑结构不在模型表面生成。调整支撑结构形状,进一步提高支撑结构的稳定性。通过实验证明本文算法比Cura软件节约15%的材料消耗,支撑结构更容易剥离,模型表面质量更好。     

装配体模型优化的免装配打印方法EI北大核心CSCD

针对包含机构语义的装配体模型实施高质量的免装配打印(涉及支撑结构的清除、打印材料的消耗以及机构语义关联表面的打印质量等)不仅困难且仍缺乏自动方法的问题,提出一种装配体模型优化的免装配打印方法.首先基于包围盒剖分和体素关联关系对装配体模型进行体素化;然后采用改进的Bresenham算法快速生成体素路径,并据此快速分析支撑结构的可清除性;提出一种增量式的体素重关联方法,可在零件之间的相对布局改变后避免耗时的模型重体素化;最后以同时满足支撑结构可清除、支撑结构消耗材料量尽量少,以及运动接口面的打印质量尽量好为目标,通过改进粒子群算法确定和调整装配体模型的打印方向及其零件之间的相对布局.在带有典型机构语义的若干装配体模型上进行实验的结果表明,所提方法计算的方向和零件之间的相对布局打印模型的支撑结构均可完全清除,支撑结构所消耗的材料以及机构语义关联表面的粗糙度均大幅度减少(小);与基于八叉树分析支撑结构可清除性的方法以及基于零件布局调整开展免装配机构打印的最新方法相比,该方法对于包含机构语义的装配体模型开展高质量免装配打印具有突出的适用性和优势.     

面向3D打印的自支撑连通性填充结构设计

针对大多数3D打印轻质化填充结构因不能够自支撑而导致模型无法打印成型,额外添加支撑结构又会造成模型内部残留打印材料无法排出的问题,提出一种面向3D打印的自支撑连通性填充结构设计方法.首先,基于每层打印切片构建填充结构;其次,通过调整参数来控制不同层正三角形连续地周期性变化,实现填充结构的自支撑性和连通性;最后,根据每层的几何信息生成可以直接用于打印的G-code文件.通过进行打印实物、打孔灌水和力学测试实验,实验结果表明,该方法可以打印具有不同自支撑角度且包含2个连通区域的填充结构,与5种典型填充结构相比,该填充结构力学性能良好.     

熔丝沉积制造中稳固低耗支撑结构生成

熔丝沉积制造(Fused deposition modeling, FDM)是利用熔融塑料丝的一种3D打印技术,热塑料由喷嘴喷出逐层堆积完成打印.由于熔丝只能沉积在已存在物体的上层,因此需要构造支撑结构以支撑悬空部分.针对现有支撑结构生成算法中存在的或结构不稳固或耗材多的缺陷,提出一种以熔丝为支撑单位的树形稀疏支撑结构.与传统算法计算模型表面支撑区域不同,本算法计算每段熔丝需要支撑的区域,使支撑结构更契合熔丝沉积特点.算法还将支撑结构分为三类,将多约束优化问题分解,降低算法复杂度.实验结果表明,本文算法生成的支撑结构算法耗材少、支撑稳定.     

FDM快速成型支撑结构自动生成算法的研究

FDM系统中零件原形的加工是靠热喷头挤出熔丝逐层堆积而成的。因此,支撑结构的添加对零件原形的制作起着至关重要的作用。针对支撑结构的需求,采用了一种新的支撑自动生成算法。该算法基于STL模型首先需提取待支撑区域,然后添加相应的支撑结构,最后确定待支撑区域的起点和终点。实际应用表明,生成支撑的效果良好。     

基于深度剥离的三维打印模型朝向优化算法

为了提高三维打印产品表面质量且有效节省材料,提出一种面向熔融挤压式三维打印机的模型朝向优化算法.该算法基于深度剥离技术,以打印朝向为自变量构建模型悬空面积及其支撑结构体积的双目标优化函数;利用模式搜索方法设计一个两步走的优化方案来确定最优的打印朝向.实验结果表明,利用深度剥离技术能够较为准确、高效地检测出打印模型悬空区域,并计算出相应的悬空面积和支撑体积;设计的优化方案也能够根据双目标的权重比确定一个较优的打印朝向,不但减少了支撑结构与模型表面的接触范围,还能降低支撑结构的体积.文中算法在提高模型表面质量以及减少支撑结构的材料消耗两方面具有优势.     

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.     

三维形状的自支撑晶体结构的逼近与填充EI北大核心CSCD

针对三维打印无法制造具有悬空杆和悬空节点的晶体结构的问题,提出自支撑晶体结构针对三维形状的逼近与填充算法.首先以菱形六面体为晶体单元,构造晶体单元的几何形状与其自支撑性的函数关系,进一步生成包围三维形状的最小自支撑晶体单元;然后在最短边长与细分次数的约束下,通过晶体单元的迭代细分对三维形状进行逼近;最后,对悬空节点添加支撑杆以保证整体结构的可打印性.另外,通过晶体结构的细分生成三维形状的自支撑填充结构.实验对选自3D ShapeNet数据库的三维模型进行逼近与填充,在VS 2010和MATLAB R2017a平台上进行算法的实现和结果的可视化,结果表明了所提算法对三维形状的逼近与填充的有效性和鲁棒性.     

针对密集点云的快速自适应四边形网格生成算法

为了能够从密集点云直接获得四边形网格,而不需要通过三角形网格重构获得,提出针对密集点直接构造的四边形网格生成算法.首先进行点云数据体素化得到体素模型,建立体素和点云的索引关系,并对体素做精细化操作,以提高映射效果;然后通过体素模型外表面的顶点与原始点云的映射得到四边形网格模型,并对四边形网格进行优化.在斯坦福的数据集上进行实验,并使用MeshLab软件进行效果展示,结果表明,该算法可以基于密集点云直接生成四边形网格模型,同时可以通过调整体素大小来自适应地改变算法效率和四边形网格的大小.     

理想材料零件的锥束CT投影仿真

针对锥束CT在理想材料零件研制中的应用需求,给出了基于拓展体素模型的CT仿真零件材料信息表示方法.在体素模型的投影图像仿真计算中,提出了一种三维射束与体素模型的快速遍历与求交算法,并结合Simpson积分公式实现了投影直线积分的高效高精度计算.实验结果验证了该算法的有效性.     

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%).     

Attribute driven process architecture for additive manufacturing

In additive manufacturing (AM) process, the manufacturing attributes are highly dependent upon the execution of hierarchical plan. Among them, material deposition plan can frequently interrupt the AM process due to tool-path changes, tool start-stop and non-deposition time, which can be challenging during free-form part fabrication. In this paper, the layer geometries for both model and support structure are analyzed to identify the features that create change in deposition modality. First, the overhanging points on the part surface are identified using the normal vector direction of the model surface. A k-th nearest point algorithm is implemented to generate the 3d boundary support contour which is used to construct the support structure. Both model and support structures are sliced and contours are evaluated. The layer contour, plurality, concavity, number of contours, geometric shape, size and interior islands are considered to generate an AM deposition model. The proposed model is solved for minimizing the change in deposition modality by maximizing the continuity and connectivity in the material deposition plan. Both continuity and connectivity algorithms are implemented for model and support structure for free-form object. The proposed algorithm provides the optimum deposition direction that results in minimum number of tool-path segments and their connectivity while minimizing contour plurality effect. This information is stored as a generic digital file format named Part Attributable Motion (PAM). A common application program interface (API) platform is also proposed in this paper, which can access the PAM and generate machine readable file for different existing 3D printers. The proposed research is implemented on three free-form objects with complex geometry and parts are fabricated. Also, the build time is evaluated and the results are compared with the available 3d printing software.     

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。     

Ribbed Support Vaults for 3D Printing of Hollowed Objects

Additive manufacturing techniques form an object by accumulating layers of material on top of one another. Each layer has to be supported by the one below for the fabrication process to succeed. To reduce print time and material usage, especially in the context of prototyping, it is often desirable to fabricate hollow objects. This exacerbates the requirement of support between consecutive layers: standard hollowing produces surfaces in overhang that cannot be directly fabricated anymore. Therefore, these surfaces require internal support structures. These are similar to external supports for overhangs, with the key difference that internal supports remain invisible within the object after fabrication. A fundamental challenge is to generate structures that provide a dense support while using little material. In this paper, we propose a novel type of support inspired by rib structures. Our approach guarantees that any point in a layer is supported by a point below, within a given threshold distance. Despite providing strong guarantees for printability, our supports remain lightweight and reliable to print. We propose a greedy support generation algorithm that creates compact hierarchies of rib-like walls. The walls are progressively eroded away and straightened, eventually merging with the interior object walls. We demonstrate our technique on a variety of models and provide performance figures in the context of fused filament fabrication 3D printing.     

集成数据挖掘知识的可解释最优超球体支持向量机

最优超球体支持向量机(SSLM)是一种典型的黑箱模型, 其运行模式不需要考察被研究对象的内部结构和 机理, 仅利用对象的输入输出数据即能达到认识其功能和作用机制, 因此具有响应快、实时性强等优点, 但也因此 缺乏可解释性和透明性. 鉴于此, 本文研究从SSLM黑箱模型的输入端加入先验知识的方法, 增强其可解释性. 本文 开发了基于数据的非线性圆形知识挖掘算法以及知识的离散化算法, 离散后的数据点不仅包含产生知识的原始数 据点, 还增加了新的数据点. 通过将所挖掘的圆形知识以不等式约束的形式集成至SSLM模型, 构造了可解释 的SSLM模型(i-SSLM). 该模型在训练时要确保知识约束的数据点分类正确, 因此对模型结果有一定程度的预知, 表明模型具有可解释性; 同时, 又由于知识的离散化增加了新的数据信息, 因此, 模型能具有更高的精度. i-SSLM模 型的有效性在10组公共样本集和2组实际高炉数据集上得到了验证.     

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.     

一种提高FDM三维打印系统成型效率的算法

目前,FDM三维打印系统制件加工时间比较长,成型效率较低。在权衡加工时间和加工精度的前提下,从切片层厚和层扫描速度控制的角度,提出了一种基于面积变化率的自适应切片层厚控制和基于周长变化率的自适应层扫描速度控制相结合的算法。首先通过二维轮廓面积变化情况计算每层切片数据的层厚值;然后用获得的层厚数据对模型进行切片,得到每层可打印的真实轮廓;最后计算每层二维多边形轮廓的周长,并根据周长的变化情况确定该层合适的扫描速度。实际打印测试结果表明,该算法可以有效降低打印时间,提高成型效率,验证了算法的有效性。     

基于应力分布的3D打印壳模型构造与优化

近年来,愈发成熟的3D打印技术拉近了模型设计与产品制造的距离.但高昂的材料费用仍是制约其发展的重要因素.因此,如何在不改变模型外观的情况下进行模型结构的优化,以此来减少模型的打印体积、降低打印成本是亟待解决的问题.针对该问题,本文提出一种基于应力分布的壳模型构造和优化算法.该算法首先基于模型的体素化表示构造距离场,提取出初始的均匀厚度壳模型.然后基于顶点的von Mises应力,自适应的向外扩张内表面,调整各部位厚度,直到达到相关约束条件.优化得到的内表面与输入的外表面围成最终的优化模型.实验结果表明,在满足外观不变、力学稳定等约束的同时,优化得到的壳模型体积为输入模型体积的17.2%~24.4%,大幅减少了模型的打印体积,有效降低了打印成本.