STL file generation from digitised data points based on triangulation of 3D parametric surfaces

For the current generation of rapid-prototyping models, laser scanners are currently being used more frequently due to rapid first measuring speed and high precision. Direct generation of an STL file from the digitised points has a great of advantage in that it can reduce time and error during the modelling process. A reduction in the number of point data is important while generating the STL file directly from the measured point data and maintaining precision. A new approach is developed in this paper to generate an STL file directly from point clouds by indicating a tolerance ε to maintain precision. The STL file can be generated directly from scattered points using a new algorithm that reduces and triangulates digitised point data based on triangulation of 3D parametric surfaces. Two experimental examples are presented to demonstrate the effectiveness and efficiency of the proposed algorithm.     

Shape Reconstruction from Unorganized Points Using Voronoi Diagrams

Given only a set of points, without any geometric information such as the adjacency among the points, the scanning order or the scanning direction, it is a difficult problem to reconstruct a surface model corresponding to the original shape. For the reconstruction of open shapes, many effective approaches have been proposed. It is, however, hard to find a robust and effective method for the reconstruction of closed shapes. In this paper, an algorithm is proposed to reconstruct a three-dimensional closed shape from a set of good sample points using the properties of Delaunay triangulation and Voronoi diagrams. The proposed method consists of three steps; (1) constructing a convex hull consisting of mutually exclusive tetrahedra by 3D Delaunay triangulation of input points, (2) generating a Voronoi diagram of input points by utilising the properties of Delaunay triangulation, and (3) extracting the triangles on the shape boundary, defined by input points, after selecting the tetrahedra which are contained inside the shape using the properties of Voronoi diagrams. The proposed method in this paper has some advantages compared to the previous approaches. First, the distance parameter, such as α in the α-shape approach, is not required in the proposed approach. The determination of a proper parameter by trial and error is not appropriate, especially in the automation of shape reconstruction. Secondly, the time complexity of the proposed approach is O(n) since, in a single pass, this algorithm determines whether each tetrahedron is located inside or outside the shape boundary. ID="A1"Correspondance and offprint requests to: Dr K. S. Kim, Department of Industrial Engineering, Pohang University of Science and Technology, San 31, Hyojadong, Pohang, 790–784, Korea. E-mail: kskim@postech.ac.kr     

由断层测量数据直接生成STL文件的方法

提出一种由断层测量数据直接生成 STL 文件的方法 ,其中两端层面的三角剖分符合 Delaunay优化准则 ,而任意两相邻中间层轮廓之间的三角面片连接采用“最小局部极角 "的原则。并给出了算法和算例。     

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.     

离散数据直接映射STL数据文件

在研究反求工程的输出接口与快速成型输入接口标准与技术的基础上,提出了利用离散数据直接三角剖分,实现STL文件格式方法,并给出具体案例,成功的解决了RE／RP系统数据集成的问题。     

RESEARCH ON ADAPTIVE DATA COMPRESSION METHOD FOR TRIANGULATED SURFACES

NC code or STL file can be generated directly from measuring data in a fas re-verse-engineering mode. Compressing the massive data from laser scanner is the key of the new mode.An adaptive compression method based on triangulated-surfaces model is put forwar. Normal-vectoranges between triangles are computed to find prime vertices for removal. Ring data structure isadopted to save massive data effectively. It allows the efficient retrieval of all neighboring vertices andtriangles of a given vertices. To avoid long and thin triangles, a new re-triangulation approach based onnormalized minimum-vertex-distance is proposed, in which the vertex distance and interior angle oftriangle are considered. Results indicate that the compression method has high efficiency and can getreliable precision. The method can be applied in fast reverse engineering to acquire an opimal subsetof the original massive data.     

Interface between CAD and Rapid Prototyping systems. Part 2: LMI — An improved interface

The STL (STereoLithography) file format, as developed by 3D Systems, has been widely used by most Rapid Prototyping (RP) systems and is supported by all major computer-aided design (CAD) systems. However, it is necessary to improve the STL format to meet the development needs of RP technologies. In Part 1, several existing and proposed formats have been discussed. This paper, Part 2, will present an improved interface between CAD and RP systems. The new interface is a file format that supports the STL format, removes redundant information in the STL format and adds topological information to balance storage and processing cost. In addition to supporting facet boundary models, the new interface supports precise models by using the edge-based boundary representation. This paper discusses the design considerations of the new interface and data structures for both facet models and precise models. Finally, a comparison of the new interface and the STL file format will be made.     

基于STL格式数据的网面体碰撞检测方法

在剖析STL网面体模型的数据结构的基础上,用矢量方法对三维空间的STL三角形网面体的相互碰撞检测问题进行了较深入的分析,给出相应的碰撞检测算法,并提出一些基于实践应用经验的改进和优化方法。     

STL文件缺陷分析及修补算法研究

STL(Stereolithography)文件是一种三维实体表述文件,广泛应用于快速成型以及其它领域。这里分析了STL文件的规范以及其缺陷特点,给出了不同类型缺陷的修补策略。特别是针对STL文件不含拓扑信息的特点,引进哈希表构造了一种用于表达STL拓扑信息的数据结构,提高了建立拓扑信息的速度以及识别和修补缺陷的效率。本文对最复杂形式的孔-连环孔进行了研究,彻底解决了孔隙的修补问题。实践证明该修补算法稳定可靠。     

面向快速成形的复杂曲面重建技术研究

针对快速成形工艺特点,提出了一种基于实物的复杂曲面几何重 建的方法。由此直接生成的快速成形机优化STL接口文件,实现了反求容差与模型网格数的 最佳匹配,避免了由通用软件转换存在的错误和繁复,提高了成形设备的前处理效率,并为 反求工程与快速成形技术的有机集成提供了可靠途径。     

The computer-aided design and rapid prototyping fabrication of removable partial denture frameworks

This study explores the application of computer-aided design and manufacture (CAD/CAM) to the process of electronically surveying a scanned dental cast as a prior stage to producing a sacrificial pattern for a removable partial denture (RPD) metal alloy framework. These are designed to retain artificial replacement teeth in the oral cavity. A cast produced from an impression of a patient's mouth was digitally scanned and the data converted to a three-dimensional computer file that could be read by the computer-aided design (CAD) software. Analysis and preparation were carried out in the digital environment according to established dental principles. The CAD software was then used to design the framework and generate a standard triangulation language (STL) file in preparation for its manufacture using rapid prototyping (RP) methods. Several RP methods were subsequently used to produce sacrificial patterns, which were then cast in a chromium-cobalt alloy using conventional methods and assessed for accuracy of fit. This work demonstrates that CAD/CAM techniques can be used for electronic dental cast analysis, preparation, and design of RPD frameworks. It also demonstrates that RP-produced patterns may be successfully cast using conventional methods and that the resulting frameworks can provide a satisfactory fit.     

基于离散点云直接映射STL文件的建模技术

随着计算机技术的发展,反求工程技术和快速原型技术的结合日趋紧密,纯复制的反求工程已不再适应市场发展的需要,在产品的设计和制造阶段都需要具备创新环节的反求工程技术的支持。提出综合优化的方法：对扫描后获取的离散扫描点进行平面的三角剖分及环域间的三角剖分,生成STL文件格式,并结合环域划分风格的特点,使用最小权和最小内角最大化相融合的方法,实现二维优化：当二维坐标释放到空间后会破坏三角形形状,影响模型的质量,用增加点的方法,得到三维优化后的原产品模型的STL文件格式。在布尔运算的基础上,通过对反求模型的三角网格进行任意叠加和任意截取,产生新产品的STL文件格式;对新产品进行总体形状控制、过渡圆角处理等空间优化工作,最终实现新产品创新,缩短了产品的开发周期,降低了开发成本。     

基于Matlab三维数据点三角剖分方法研究

逆向工程中点云数据点三角划分处理,在散乱数据插值曲面构造、快速原型制造以及有限元分析等方面有着重要的应用.根据Delaunay三角划分理论及Lawson优化准则,借助于Matlab中用于点云处理模块快速实现了空间散乱数据点的直接三角划分,给出了数据点三角划分程序代码,并以某小客车车身外表面点云数据处理过程加以验证,给出其外形数据点Delaunay三角划分以及凸壳包络图,由此可以早期发现逆向设计过程中可能存在的问题,从而减少后期修改次数,极大缩短新产品的开发周期,提高了设计精度.     

STL格式文件的拓扑重建方法研究

STL格式文件用三角网格面来描述实体模型,实际应用如逆向工程中需要建立三角形、边和顶点的邻接拓扑关系,其中查找并去除重复顶点是建立拓扑结构的关键.本文通过分析STL格式文件的数据结构特点,建立准确、清晰、简单的拓扑结构,为后续数控加工及STL数据的其他方面的应用提供了极大的方便.     

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.     

义齿加工模型STL文件的数据读取技术研究

STL文件是一种在快速成型加工中经常使用的文件格式。采用Oracle数据库技术读取STL文件中的数据,并对STL中的数据点进行了有效的冗余去除,减小了数据存储量,便于对有用的数据进行加工后处理,提高了处理效率。同时,Oracle技术的使用增强了编程的灵活性和效率。     

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。     

STL模型局部精度补偿方法研究

STL格式文件是RP行业的事实标准,但是STL模型精度与STL文件尺寸之间的矛盾还没有得到有效解决.为此,提出一种局部精度补偿方法,利用该方法重新生成的STL文件保证了模型各部分的精度,同时缩短STL文件尺寸、减少数据计算量.     

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。