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。     

STL文件修补算法研究

:STL文件在计算机辅助设计领域中得到广泛的应用 ,如快速原型制造系统与CAD系统之间的数据交换接口。但是 ,STL文件本身及其创建过程均存在许多问题 ,如裂缝、孔洞、覆盖等。这些缺陷会给后续处理带来许多不便。针对这个问题 ,本文提出了一种 STL文件的修补算法。该算法首先建立三角片之间的拓扑关系 ,然后检查三角片模型是否存在上述缺陷 ,如果存在 ,则对其进行修补。该算法已在“超人CAD/CAM”系统中实现 ,算法稳定可靠 ,且对上述缺陷 ,基本能正确有效地进行检测与修补     

一种基于边界缺陷的STL文件修补算法

STL文件广泛应用于快速成形以及其他领域。对大量STL文件进行分析 ,指出STL文件的缺陷集中发生在实体面与面的交界线处 ,有诸如缝隙、重叠、退化面片、拓扑结构错误等缺陷。现将边界错误作为一种类型统一考虑 ,针对他们的共性设计了相应的修补算法 ,指出修复本质在于面与面的缝合问题 ,提高了修复能力和效率。实践证明修补算法稳定可靠     

Rapid Prototyping Applications in Medicine. Part 1: NURBS-Based Volume Modelling

Rapid prototyping (RP) technology has extended traditional manufacturing applications in areas other than product engineering. Using RP to fabricate custom implants and prostheses for surgical planning and education is now an important area of research. Although, in theory, RP is capable of producing objects of any complexity, designing freeform shapes is difficult using current CAD systems. These CAD systems are geared toward the design of parts manufactured by traditional methods; they do not help designers exploit the extended opportunities offered by RP technology. Medical data cannot be input into these CAD systems directly for further modification and manipulation. The purpose of this project is to explore a new approach for modelling and prototyping biomedical objects. The work extends from volume modelling to RP and medicine. In this paper, Part 1 of two papers, a new approach to modelling complex objects, NURBS-based volume modelling, is proposed. A NURBS representation of volumes is developed to represent not only the surface boundary but also the interior of a 3D object. NURBS-based volume modelling inherits advantages from both NURBS modelling and voxel-based modelling. The key idea of the NURBS-based volume modelling is to exploit the flexibility of NURBS modelling and use the voxelised NURBS volumes as components for constructing complex objects. Part 2 deals mainly with issues of interfacing volume models to RP systems. A new approach to generate STL files through volume modelling and iso-surface extraction is proposed. This approach guarantees the validity of the final STL file inherently. Software development and case studies are also given.     

Rapid Prototyping Applications in Medicine. Part 2: STL File Generation and Case Studies

Rapid prototyping (RP) technology has extended traditional manufacturing applications in areas other than product engineering. Using RP to fabricate custom implants and prosthesis for surgical planning and education is now an important area of research. Although, in theory, RP is capable of producing objects of any complexity, designing freeform shapes is difficult using current CAD systems. These CAD systems are geared toward the design of parts manufactured by traditional methods; they do not help designers exploit the expanded opportunities offered by RP technology. Medical data cannot be input into these CAD systems directly for further modification and manipulation. The purpose of this project is to explore a new approach for modelling and prototyping biomedical objects. The work extends from volume modelling to RP and medicine. In Part 1 of two papers, a new approach to modelling complex objects, NURBS-based volume modelling, is proposed. A NURBS representation of volumes is developed to represent not only the surface boundary but also the interior of a 3D object. NURBS-based volume modelling inherits advantages from both NURBS modelling and voxel-based modelling. The key idea of the NURBS-based volume modelling is to exploit the flexibility of NURBS modelling and use the voxelised NURBS volumes as components for constructing complex objects. This paper, Part 2, deals mainly with issues of interfacing volume models to RP systems. A new approach to generate STL files through volume modelling and iso-surface extraction is proposed. This approach guarantees the validity of the final STL file inherently. Software development and case studies are also given.     

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.     

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.     

NURBS曲线在快速原型制造系统中的应用

大多数快速原型制造系统采用 STL 文件作为与 CAD系统之间的数据交换接口。但是 ,STL 文件是通过用一系列的三角片逼近实际零件表面而产生的 ,STL 文件本身及其创建过程均存在许多问题。要提高模型的精度 ,就必须增加三角片的数量 ,同时减小三角片的尺寸。这必然造成 STL 文件庞大 ,后续处理时间较长 ,而且易产生缺陷 ,使后续处理不能进行。针对上述问题 ,本文分析了 STL文件的不足 ,提出一种 CAD系统与 RPM系统之间新的数据交换方法。该方法对 CAD系统中的真实模型直接切片 ,将切片后所得到的轮廓数据作为 CAD系统与快速原型制造系统之间的数据交换接口。该切片算法已在“超人 2 0 0 0 CAD/ CAM”系统中实现 ,算法表现稳定     

STL文件错误的自动修复算法的研究

目前,对STL文件错误的修复已经进行了一些研究,但这些研究还不能精确实现错误的整体描述,针对这个问题,构造了错误广义表,整体描述了STL文件中的错误,简化了修复过程,并开发了专用的STL文件修复工具.     

An Effective Error-Tolerance Slicing Algorithm for STL Files

Although the STL (stereo lithography) file format is the de facto standard for the rapid prototyping industries, there are always some defects in STL files, many of which are difficult to correct. Instead of correcting the defects of bad STL files by a manual, interactive and complex approach with an STL file correction program, an error-tolerance slicing algorithm for STL files is proposed in this paper. With the detailed analysis of complex defects such as cracks and non-manifold facets, a complete topological structure for the facets model with defects is built and the layer is sliced effectively. The badly sliced contour is processed by crack-tracking and non-manifold facet travelling methods to obtain a correct contour in a relatively easy 2D way.     

基于VC和OpenGL的STL文件的分层和显示

STL文件是快速成型系统的标准文件类型,广泛应用于数控加工、逆向工程和有限元分析等.详细介绍了STL文件的读取和分层算法,并利用VC＋＋6.0平台结合OpenGL编程技术,实现了STL文件格式的读取、分层算法以及STL模型的三维显示、视角变换、缩放、平移和分层显示等功能.为进一步实现数控系统直接使用STL文件进行加工奠定了基础.     

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.     

Direct Slicing from PowerSHAPE Models for Rapid Prototyping

Rapid prototyping processes produce parts layer by layer directly from CAD models. An efficient method is required to slice the geometric model of a part into layers. Several slicing methods are introduced in this paper: slicing from STL files; tolerate-errors slicing; adaptive slicing; direct slicing; adaptive and direct slicing. PowerSHAPE is a powerful package for building models, and it provided macro language and picture files for its secondary development work. To meet rapid proto-typing slicing demands, the author proposes a direct slicing approach based on PowerSHAPE models. In this method, lines, arcs and Bezier curves are used to describe the section contours. This approach can be used in stereolithography, selective laser sintering, fused deposition modelling, and other rapid prototyping processes, e.g. laminated object manufacturing. It may be the future solution to existing slicing problems.     

根据STL文件生成三维四面体网格

STL文件通过记录一系列的三角形集合信息表示实体的边界几何信息。给出了一种从STL文件生成实体的边界一致的符合Delaunay准则的四面体网格的方法，并对生成的四面体网格进行尺度控制及质量优化，从而得到适合于有限元分析的四面体网格。该方法为CAD／CAE的集成提供了一种思路。     

连续性对快速成形制造影响的研究

将实体几何连续性应用于快速分层 ,可以降低内存 ,加快信息提取时间。另外 ,沿垂直于Z向将巨型STL格式文件分割成多个STL格式文件 ,依次成型 ,可以避免巨型STL格式文件的读入错误和手工粘结带来的误差 ,提高了制件精度     

快速成型的切片数据优化

在目前的快速成型系统中，普遍采用STL格式文件来表达CAD模型，因而在切片后截面轮廓含有大量的数据冗余点，影响了插补加工的精度和效率。文章针对直接插补算法，在分析STL文件及切片数据的组成基础上，提出了一种数据冗余点过滤算法，在保证加工精度的条件下，有效地滤除了冗余点。该方法算法简单，运算时间短，有效地提高了后续插补过程的稳定性，在数据优化后仍采用直线插补，既保证了加工精度，又加快了插补速度。     

CSDF:一种基于STL的无锯齿差分网格剖分算法

针对基于差分的铸造CAE系统生成体网格时图像显示呈锯齿状这一问题,提出了一种基于STL面片模型的无锯齿网格剖分算法。算法采用一种新的组件式有符号距离场(CSDF)模型来对多个STL实体进行剖分。该模型采用了一种稳健的容错方法,能够对不封闭、缺点、少面的STL实体进行正确的剖分;使用BSP树来加速计算每个网格中心点距离铸件、砂芯、铸型以及浇注系统等STL几何实体的最小距离,并规定位于内部的中心点的距离为负,外部为正,表面为零,使得每一个网格点有一个表示材质的数据,同时还有几个不同的距离值;材质数据用来表示物理属性,而距离值用来进行STL实体的布尔运算,以实现组件式的网格剖分和几何模型的重建,获得光滑的后处理图像。实例表明:算法可行,可实现组件式的几何实体无锯齿网格剖分,且剖分结果能进行数值计算。     

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。