Efficient cutting area detection in roughing process for meshed surfaces

Presented in this paper is an efficient cutting area detection algorithm for the layer-by-layer roughing process of the meshed surfaces in stereolithography (STL) format. The algorithm consists of three steps. Firstly, the intersecting model of a spatial triangle facet and a plane is established and formulated. Based on this, all the intersecting segments between the assigned hunting plane and the triangle meshes in the STL model are calculated. These segments are unordered initially, so in the second step, by building a special data structure, an O(nlogn) time-linking procedure is developed to link the unordered intersecting segments into several closed loops, where n is number of intersecting segments. Finally, the cutting area is identified from the obtained loops by inheritance tree analysis. The proposed algorithm has been programed and run on a personal computer. Several STL surfaces have been tested and the results show that the proposed algorithm is fast and stable.     

Machine path generation using direct slicing from design-by-feature solid model for rapid prototyping

This paper explains a new machine path generating system that its output is compatible with different rapid prototyping processes. The basis of this system is direct slicing from design-by-feature solid model. Slicing a computer-aided design (CAD) model through intersecting the model with the XY-plane at each Z increment is a well-known method of path generation. Slicing a CAD model is currently conducted through stereolithography (STL) file slicing, direct slicing, and additive direct slicing. A direct slicing approach inside a design-by-feature solid modeler is proposed. Autodesk Inventor solid modeler, as a design-by-feature solid modeler, is used for 3D solid modeling. The proposed system is implemented by Visual Basic codes inside Inventor. In this approach, first protrusion and subtractive features that form a model are extracted. Then, the intersection of each feature and the XY-plane is identified. Then, the internal and external loops are found. Depending on the specific rapid prototyping (RP) process requirements, internal or external hatch are also computed, respectively. Finally, a continuous path in required format is generated. The system reported in this paper has been successfully tested on several complex 3D models created in Inventor. The system offers customized output for different RP processes that need external or internal hatch pattern. The proposed approach for generating RP machine path through feature recognition inside design-by-feature solid modeler overcomes with the problems that are caused by imperfect STL files. Also, this system is capable of generating code compatible with major rapid prototyping processes.     

上颌窦三维实体模型的重建

使用了一种新的基于CT、MRI等医学影像数据的三维实体模型重建方法.首先对医学影像数据进行阈值分割,提取出需要重建的部分,并重建成为STL格式文件.然后提取出STL文件的顶点得到点云,对点云进行分割,分别重建曲面.最后,将重建得到的曲面进行修剪,并添加所需要的结构,得到三维实体模型.     

Tool-path generation for sheet metal incremental forming based on STL model with defects

Tool-path generation is a key issue in sheet metal incremental forming process, and existing approaches either are prone to computationally expensive or cannot be applied to stereolithography (STL) model including defects. Thus, a new tool-path generation method is presented by adopting the thought of generating cutter-location (CL) data directly from corresponding cutter-contact (CC) data. By analyzing the interference characteristics between fillet-end tool and model surface and considering tangential case and intersection case comprehensively, a discrete computational model is proposed to calculate single-layer interference-free CL contour, instead of computing a precise CL point by checking potential interferences from candidate facet, vertices, and edges, respectively. So this method is more efficient and easier for program implementation. Additionally, a fast recursive search algorithm is developed to identify and extract flat area features, and an efficient 2D invalid loops removal algorithm based on decomposition thought is presented to obtain valid CC contours and CL contours with a near linear time-complexity. Implementation tests prove that the new method is effective and robust for STL model with defects, and tool-path achieved is highly precise. It is also applicable to various tool shapes and suitable for planning various types of tool-paths to meet different SMIF process requirements.     

STL模型切片生成喷漆机器人轨迹的研究

提出了运用STL模型切片技术生成喷漆机器人轨迹的方法.首先估算三角形面片的顶点法向矢量,然后对STL模型进行切片处理获取切片平面上的交点,再对交点进行法向矢量的估算,最后交点沿其法向矢量偏置喷枪到工件的距离以获取喷漆机器人的喷枪运行轨迹.该方法能准确控制喷枪的运行位置、方向以及喷枪与喷涂工件表面之间的距离,提高喷涂质量和效率.     

叠层制造领域中的STL模型平滑处理技术

由于STL格式容易生成且不需复杂的CAD系统支持,已发展为叠层制造领域的数据交换标准,但STL模型的精度与其数据文件的尺寸之间存在严重矛盾。提出并实现了一种既可用更高的精度和平滑度对STL模型截面轮廓进行重构,又可显著减小切片文件数据量的最优双圆弧拟合技术。工艺试验证明:与传统的直线段(圆弧)拟合技术相比,采用了切片轮廓最优双圆弧重构技术的叠层制造系统可加工出具有更高成形精度、表面光滑度的成形件,且无需严格的STL模型毗邻误差。     

分割巨型STL格式形体文件的关键技术

为了避免巨型ＳＴＬ格式文件的读入错误和手工粘接带来的误差,研究了沿垂直于Ｚ向将巨型ＳＴＬ格式文件分割成多个ＳＴＬ格式,连续依次成形的方法,研究了分割面轮廓的拓扑自理和分割的轮廓为三角形的算法。     

Part decomposing algorithm based on STL solid model used in shape deposition manufacturing process

Shape deposition manufacturing is an innovative rapid prototyping technology combining CNC machining and deposition processes and in which if a surface of the part is visible from the build direction it can be directly shaped into desired geometry on part material; if the part features are undercut or face away from the build direction, these part features will be sculptured into the support material in order to form a negative cavity at first, then the part material is deposited into this negative cavity in order to replicate these features into part material. This process is cyclically repeated until all segments have been built. Finally, the sacrificial material is removed, and the finished part is left. This innovative technology has the benefits of commercial rapid prototyping technology; meanwhile, it inherits the accuracy and high surface quality of traditional machining process. For this process to be realized, it is essential to decompose the CAD solid model into a series of manufacturable segments which have no undercut surfaces at the data pretreatment step. In this paper, a solid decomposing strategy is proposed with a detailed discussion on the classification of the segments based on the value of triangle face normal vector, and then an algorithm for auto-decomposing a CAD solid model in STL data format is developed.     

快速成型技术中的光斑半径补偿算法研究

光固化快速成型数据模型切片分层的结果是一系列封闭的多边形截面轮廓,由于光斑（或喷嘴）具有一定的尺寸大小,为了保证零件的制造精度,就需要对多边形截面轮廓进行补偿。为此,简化了补偿矢量计算方法,并针对两种尖角情况,提出了新的处理方法。对多边形轮廓补偿后可能出现的自相交现象,采用基于单调链的平面扫描算法,对自交点进行了求解,并提出了一种无效环的简单判别方法,提高了无效环的去除效率。通过无效环的去除,保证了补偿轮廓的正确性,提高了零件的制造精度。     

三维实体模型到有限元板壳模型的自动转换

针对板壳结构有限元分析的需要,将商用CAD软件生成的板壳结构的三维实体模型用STL文件格式输出。对其进行拓扑关系重构并进行表面网格再划分,在此基础上对单元及面进行分类,从而确定并选取有效三角形面片,并计算面片对应的厚度值及其中面位置。将这些三角形面片移动到中面位置,形成适合有限元分析的板壳中面模型。将这种板壳模型自动转换方案应用到几个实际薄壁构件的实体模型上,成功地抽取了这些板壳的中面模型。结果表明,该方法可大幅度降低生成板壳有限元模型的工作量,提高计算效率。     

复合快速成形中基于STL模型的分层研究

研究了面向分层实体制造与数控铣削复合成形的基于STL模型的三维层生成算法。利用凹边在上下两个方向上的可见性确定分层位置,通过切割平面与各三角面片求交实现STL模型的分割,并把分割面三角网格化生成封闭的三维层。分层的结果可满足复合快速成形工艺要求。     

一种判别空间两线段干涉的快速算法

在多机械手系统中 ,机械手各杆状关节相互之间在运动过程中极易产生机械干涉 ,快速判别两杆状物体互相产生机械干涉的算法对多机械手系统的动态任务规划具有十分重要的意义。一般的研究方法都是把杆状物体简化为空间线段来进行分析和计算他们之间的距离或者具体的交点位置。实际上 ,判断两空间线段是否产生干涉只需要知道两线段是否存在交点 ,而不需具体计算交点的位置以及两空间线段之间的距离 ,就可判别其干涉状态 ,基于此本文提出了一个极为简单的计算方法 ,该方法利用解析几何中的理论 ,提出了几个基本定义 ,将空间的两杆状物体抽象为线段 ,然后投影到笛卡尔空间直角坐标的三个直角投影面 ,通过一些简单的加减乘除计算 ,就可判别两线段干涉状态。     

Topology and kinematic analysis of color-changing ball

The color-changing ball has two stable configurations. Its mechanism is a multiple loop and polygonal mechanism. This paper investigates the mechanism typology and analyzes its structure and configurations during motion. A three-legged mechanism is extracted from this mechanism. The kinematics model of the mechanism is presented and singularity is discussed. The paper further decomposes the mechanism and investigates the platform structure of the intersection between loops. This leads to investigation of the offset of joint intersection at the intersection and its relevant geometry and kinematics. The paper further focuses on the configuration change between two states of the mechanism and investigates kinematics and singularity between two configurations. Based on the analysis, simulation of the color-changing ball is carried out. The topology and kinematics analysis in this paper helps the analysis of this kind of polyhedral linkage mechanism with radial motion. The research could potentially lead to the development of kinematics for design of this kind of mechanism.     

基于STL文件的变密度三维全六面体网格自动生成方法

针对STL文件在传递复杂几何实体模型信息方面具有精度较高的特点，提出了一种基于STL文件变密度三维全六面体网格自动生成方法，给出了STL文件的数据格式及其内容约定，详细阐述了基于STL文件空间CAE模型表面特征自动识别、拓扑关系的生成和变密度栅格法加密信息场的建立等关键技术。实现了在实体模型表面曲率较大和厚度较小的局部区域进行协调加密，可以获得与实体模型边界吻合良好的全六面体协调网格，适合于工程问题的有限元分析计算。若干复杂实体模型算例表明，该算法实用性强，效果良好。     

面向快速成型制造的CAD平台内嵌式通用接口

面向快速成型设备的CAD平台中的内嵌式通用接口，可直接在CAD建模环境下零件模型实施自适应直接切片操作，同时生成以片层结构数据为单位的快速成型接口文件，该接口使用NURBS曲线对各截面的片层结构轮廓进行精确地解析重构；依据重构后的NURBS截面轮廓，自动填充功能可精确地生成快速成型设备的X，Y向栅线扫描路径。实验数据表明，与利用STL模型切片获得的得的多义线轮廓对比，经NURBS解析重构后的自适应直接切片轮廓与原始轮廓间的拟合误差降低98％以上，所需的NURBS线段数目减少77％以上。     

Re-triangulation in STL meshes for rapid prototyping and manufacture

The main objective of this research is to identify ways to simplify the STL meshes, while simultaneously maintaining the accuracy of the STL file. It demonstrates a technique to simplify large and complex STL triangular meshes and to optimise STL shape for rapid prototyping and manufacture. STL mesh re-triangulation can be separated into two processes, i.e., mesh deletion and mesh rearrangement. In the mesh deletion process, two kinds of weighted-value ratio algorithms can be chosen for determining the suitable value of STL mesh deletion. A genetic algorithm that incorporated fitness functions was used for the optimisation of the rearranged STL meshes. Two case studies of STL mesh reconstruction, which examine the effects of the algorithms, are presented. These studies show that optimisation of the shape of the STL file reduces its size, resulting in a reduction of the fabrication time and improvement of the rapid prototyping process.     

Development of a Stereolithography File Interface with ArtCAM™

This paper presents the technique used for converting a 3D ArtCAM™ relief file into the stereolithography (STL) format. This 3D file is obtained from a 2D picture using a 3D CNC engraving software called ArtCAM™. The problem is to convert the 3D relief files into an STL format without compromising the accuracy and details of therelief. This paper discusses the size of the files which have been converted, and steps taken to reduce the file size by reducing the number of triangles or facets in the STL file. The discussion involves the verification of the converted model by comparing it with the original relief. The problems associated with the reduction of triangles when the file has been converted to STL format are also discussed.     

铸件任意剖面的温度场显示

任意剖面的温度场显示是铸件凝固过程数值模拟后处理的重要技术。提出了一套铸件任意剖面求取及高质量彩色云图生成的通用方法，即基于铸件实体模型的STL格式求取剖面轮廓线、对剖面进行三角化，以及利用四面体插值技术求得剖面上的温度场，并采用0penGL的裁剪平面实现任意剖面及其彩色云图的绘制。     

基于STL文件的实体分割算法研究

由于快速成型机加工尺寸的限制,难于制造尺寸较大的零件。针对这一问题本文提出一种基于STL文件格 式的实体分割算法,对STL文件分割过程中的关键问题进行了详细地论述,包括:截面轮廓的生成,截交三角面片的 处理和截面轮廓的三角化算法;通过对STL文件的分割处理,提高了快速成型系统对大尺寸零件的制造能力。     

基于拓扑关系的交线快速生成方法

三角网格是逆向工程中常用的数据模型。由于模型拓扑关系的复杂性，目前在网格模型的交线生成过程中数据点排序与分离存在诸多缺陷。提出了一种利用网格模型拓扑关系的交线生成与分离算法，该算法充分利用了网格模型的拓扑关系，对各种拓扑类型的数据点完成排序、分离，实现任意复杂拓扑关系的交线生成，为逆向工程中曲线框架的构造提供了依据。