CAD系统与虚拟装配系统数据转换的研究

提出了信息分解转换法,实现了从计算机辅助设计系统到虚拟装配系统的数据转换,并将计算机辅助设计系统的装配体信息分解为几何信息、拓扑信息和装配信息。利用数据转换接口实现几何信息的转换,通过构造五层次拓扑结构实现拓扑信息的转换,利用数据库技术实现装配信息的转换,三者相互关联,形成系统的体系结构。最后,信息分解转换法在虚拟装配实验系统得到了验证,信息转换准确,显示效果良好。     

基于XML的CAD系统和虚拟装配系统之间的数据转换

针对计算机辅助设计系统和虚拟装配系统之间的模型转换问题,提出了基于特征的统一的产品层次信息模型,采用XML中性文档和三角面片模型文件,通过信息分解的方法,分别将在产品建模系统中建立的产品层次信息模型中的装配信息和几何拓扑信息与三角面片信息通过数据转换接口转换到虚拟装配系统中,并在虚拟装配系统中通过映射关系进行模型重构,较好地解决了计算机辅助设计系统和虚拟装配系统之间信息共享的问题,通过实例验证了研究成果的可行性。     

面向大型复杂产品的虚拟装配技术研究

针对大型复杂产品在装配生产组织形式、人的参与程度、装配工艺流程的优化、装配人员培训和示教等方面的特点,分别进行了虚拟装配关键技术的研究。重点探讨了考虑人体活动的新型虚拟环境技术、CAD系统和虚拟装配系统的数据集成技术、装配工艺的生成及其优化技术、工艺文件生成和现场示教技术等4个方面。最后给出了开发的虚拟装配原型系统在某型号复杂产品中的应用实例。     

基于XML的CAD与XNA的信息转换

针对CAD与虚拟装配环境XNA之间的信息转换问题,提出了一种模型信息转换技术。构建了一种面向虚拟装配的层次化装配信息模型,该信息模型由产品层、子装配体层、零件层、特征层、几何层、三角面片层六层拓扑结构组成;根据模型信息分解方法,将模型信息分解为几何信息、装配信息以及面片信息等,使用Pro/ToolKit二次开发工具实现了对模型装配信息的提取,并通过对模型面片信息的转换,解决了CAD系统与XNA虚拟装配环境间的信息转换问题。利用构建的XNA虚拟装配平台对该技术进行了验证。     

面向虚拟环境的CAD装配模型向运动模型的转换

探讨了在虚拟环境中进行复杂机械产品运动分析时CAD装配模型向机构模型转化的信息识别。首先在总结CAD装配系统提供的各种装配约束类型与其相对应的运动几何元素基础上,给出了平移和旋转自由度的归约规则,根据简单运动副约束与运动自由度及运动几何元素的映射关系,实现从零部件装配信息到运动分析用的构件和简单运动副信息的转换。     

XML-based assembly visualization for a multi-CAD digital mock-up system

Using a virtual assembly tool, engineers are able to design accurate and interference free parts without making physical mock-ups. Instead of a single CAD source, several CAD systems are used to design a complex product in a distributed design environment. In this paper, a multi-CAD assembly method is proposed through an XML and the lightweight CAD file. XML data contains a hierarchy of the multi-CAD assembly. The lightweight CAD file produced from various CAD files through the ACIS kemel and InterOp includes not only mesh and B-Rep data, but also topological data. It is used to visualize CAD data and to verify dimensions of the parts. The developed system is executed on desktop computers. It does not require commercial CAD systems to visualize 3D assembly data. Multi-CAD models have been assembled to verify the effectiveness of the developed DMU system on the Internet.     

A pragmatic system to support interactive assembly planning and training in an immersive virtual environment (I-VAPTS)

Assembly planning for complex products is a difficult task requiring both intensive knowledge and experience. Computer aided assembly planning (CAAP) systems have been the subject of considerable research in recent years without achieving a wide application in manufacturing industry. In this paper an alternative approach to the generation of an optimal assembly planning scheme is presented based on the adoption of immersive virtual reality. A product is assembled from CAD models by providing a CAD interface to transfer assembly constraint information from the CAD system to a virtual environment. In the virtual environment an efficient dynamic recognition and management method based on surface geometry is employed, and a process-oriented assembly task model is established to support interactive assembly planning and evaluation. The system is implemented using an object oriented methodology, and has been successfully applied to train and guide the assembly workers in a pump assembly process.     

支持产品协同设计的隐式特征表达

在产品协同设计过程中，为了使特征在CAD系统内部环境里可编辑，提高实时性，提出基于特征的隐式模型表达，其实质是不交换模型的几何拓扑信息，而只是交换参数化信息，几何拓扑模型由系统通过几何建模引擎实现。通过建立交换特征库来表达形状参数以及特征与其他特征之间的结构化信息，实现基于特征的隐式模型交换。对于操作特征，提出了新的基于坐标引用的持久命名算法以解决引用拓扑实体问题。     

Automatic recognition of machining features using artificial neural networks

We report on the development of an intelligent system for recognizing prismatic part machining features from CAD models using an artificial neural network. A unique 12-node vector scheme has been proposed to represent machining feature families having variations in topology and geometry. The B-Rep CAD model in ACIS format is preprocessed to generate the feature representation vectors, which are then fed to the neural network for classification. The ANN-based feature-recognition (FR) system was trained with a large set of feature patterns and optimized for its performance. The system was able to efficiently recognize a wide range of complex machining features allowing variations in feature topology and geometry. The data of the recognized features was post-processed and linked to a feature-based CAPP system for CNC machining. The FR system provided seamless integration from CAD model to CNC programming.     

Live parametric design modifications in CAD-linked virtual environment

This paper presents a solution to support parametric design modification in a virtual reality (VR) environment. It builds upon a novel computer-aided design (CAD) and VR integration framework, namely, CAD-linked virtual reality environment. With this framework, semantic information in CAD models, such as constraints, design features, and parametric settings can be automatically extracted during the creation of VR environment and be integrated into the virtual assembly (VA) models. Moreover, the persistent naming mechanism originating from feature-based modeling technology is introduced into the CAD–VR integration, based on which a persistent linkage between VA models and their CAD counterparts can be established. Users are able to visualize design features and to access the associated parametric info in VR environment and also to change the parametric settings online whenever necessary. The modified parametric settings are then sent back to the linked CAD models so that parts can be re-evaluated. The modified CAD part can then be reloaded into the VA model under an automated mechanism. Such communications between CAD and VR applications are supported in a live mode utilizing the COM interfaces provided by CAD server. With this solution, a quick return loop from VR to CAD is achieved. Therefore, it provides the possibility to support quick design change review and “what-if” evaluations for applications such as collaborative system design and immersive project review in VR. This constitutes the major contribution of the work to product development process.     

A new type haptics-based virtual environment system for assembly training of complex products

Virtual reality (VR)-based assembly training has been an interesting topic for the last decades. Generally, there are two shortcomings for nowadays virtual assembly training systems. One is that the operators cannot move around the virtual environment in a natural way as people activity in the real world: they are constrained in a fixed position or can only move in a limited space. The other is that most of the virtual assembly training systems are based on geometry constraint modeling only, which lacks haptics feedback. A new type haptics-based virtual environment system for assembly training of complex products is described in this paper. A new low-cost motion simulator is designed and integrated with the virtual environment to realize free walking by human. An automatic data integration interface is developed to transfer geometry, topology, assembly, and physics information from a computer-aided design system to a VR application, and a hierarchical constraint-based data model is rebuilt to construct the virtual assembly environment. Physics-based modeling and haptics feedback are undertaken to simulate the realistic assembly operations. The application examples and evaluation experiments demonstrate that both motion simulator and haptics have great value for training of assembly processes.     

一种基于CT图像反求技术的实体几何造型方法

基于 CT图像的反求是反求工程中的重要内容 ,由 CT图像反求重建出的表面模型只包含了表面几何信息 ,而实体几何模型具有完备的几何和拓扑信息。针对 CAD造型系统中实体模型的特点 ,本文提出一种基于 CT图像反求技术的实体几何造型方法。应用 CT图像反求技术重建出物体的三维表面模型 ,在重建出的拟合曲面三角片序列的基础上 ,采用半边结构来表达重建的表面模型 ,并将该过程作为本研究所开发的特征造型原型系统 3D-Modeler2 .0中的一种造型方法     

Web-based CAD viewer with dimensional verification capability through the STEP translation server

To design a CAD viewer on the Web, a file translation system which converts a native CAD file of a commercial CAD to the simplified CAD file is required. However, commercial CAD viewers have used simplified geometric data similar to the VRML format. Thus, it has been difficult to apply such data to the accurate design and dimension examination procedures, in this paper, a STEP translation server supporting most CAD native formats is devised. To apply the STEP file to the precise CAD viewer, an accurate geometric data extraction method from the STEP file is studied. A STEP translator classifies and defines geometric shapes according to the boundary information. Viewing and measurement functions of the developed system verify the geometries, interferences, dimensional errors, human factors, and form errors of the CAD data. In addition, design modification messages are transferred through the markup functions of the system. Collaborators are able to share their design ideas and opinions rapidly and remotely through the XML (extensible Markup Language) open architecture. The effectiveness of the developed system is confirmed through case studies.     

基于STL模型的逆向工程实体建模技术

针对以STL数据表示的零件模型，在分析结构件模型几何特点的基础上，提出了一种以几何体素分离与拓扑关系重建为基础的STL模型逆向工程实体建模技术。通过对三角面片的合并实现平面、柱面、锥面等基本几何体素的分离，并利用Parasolid系统完成体素重构，进一步提取几何体素之间的布尔关系，从而实现含拓扑关系的产品模型重构。利用这一方法，可以实现RE／RP系统与通用CAD系统之间的快速集成，实现产品数据在不同系统之间顺畅传递。     

Form Feature and Tolerance Transfer from a 3D Model to a Set-up Planning System

Currently, most CAD systems, even the feature-based design systems which were developed for CAPP, cannot provide exact information about an object (e.g. dimensions and tolerances). Some feature-based design systems can provide product data directly or indirectly; however, most CAPP systems still do not have an interface with CAD systems. The product data required by CAPP systems usually has a specific format which is unique to the system. In a CAPP system, it is essential for set-up planning to ensure the precision of the machining processes. Therefore, it is necessary to develop an interface with CAD models, so that the part data file can be obtained directly from the CAD representation. This paper proposes an approach for integrating the set-up planning system with a feature-based CAD system. By using an object-oriented approach – Product Data Translator (PDT), the computer-automated extraction of geometry and complete tolerance information was achieved; and the automated generation of the tool approach direction was developed. RID=" ID=" <E5>Correspondence and offprint requests to</E5>: H.-C. Zhang, Department of Industrial Engineering, Texas Tech University, Lubbock, TX 79409&ndash;3061, USA. E-mail: hzhang&commat;coe.ttu.edu     

基于STEP中性文件的有限元自动建模

直接利用CAD系统的几何造型 ,以STEP中性文件为CAD造型系统与有限元单元剖分系统间的几何和拓朴信息传递媒介 ,实现有限元单元的自动剖分。按STEP/AP2 0 3的语义模型提取STEP中性文件中三维形体的表面信息 ,将该形体的每个表面映射到二维参数平面 ;利用参数平面的边界数据和二维单元自动剖分模块 ,用推进波前法实现表面网络的自动生成 ;然后由表及里实现三维实体单元的生成 ,系统基于STEP中性数据文件 ,可以与多个流行的CAD系统实行连接。     

基于特征的异构CAD模型转换技术研究

提出并实现了一种基于特征的异构CAD模型转换方法。该方法以特征操作为核心,从特征层和几何层访问CAD模型信息并实现其转换。与一般模型转换接口相比,该方法不仅使转换后的模型在几何形状上与原模型相同,而且保证了转换前后模型的特征树、尺寸及约束等信息的一致性。转换后的模型可以在目标系统下进行基于特征的修改和编辑。     

边界表达模型的局部几何更新方法

与历史无关造型技术已成为三维CAD系统令人关注的研究方向之一,对于带有拓扑和几何信息的轻量化模型进行直接编辑是该技术的典型应用。鉴于B-rep模型的变化实际上表现为其内部拓扑和几何的变化,本文基于拓扑结构保持不变的前提,对三维模型一个或多个几何面改变时其相邻边界的几何一致性更新方法进行了研究。提出并分析了适合于多面体模型的边界几何求交方法,并进一步给出了融入模型重构的综合算法。通过实例验证了上述方法的可行性。     

基于SE的BOM信息的自动提取与应用研究

以CAD软件SolidEdge为开发平台,分析研究装配体和包含于装配体内零件的内部信息表达;用Visual Basic作为开发工具,利用SolidEdge的二次开发接口技术及数据库技术,实现SolidEdge装配BOM信息的自动提取,并将其作为基础数据生成中间数据表,应用于PDM和ERP系统集成中;最后,给出了具体应用研究实例.     

从CAD系统到集成虚拟装配环境的数据转换研究

为了完成产品模型从计算机辅助设计系统到集成虚拟装配环境的数据转换,提出了信息提取模型转换法,将计算机辅助设计系统中的模型数据转换分解为信息提取和模型转换两部分,通过计算机辅助设计系统的二次开发和模型转换,得到集成虚拟装配环境所需的模型数据信息。以圆锥破碎机的进料机构为虚拟装配对象,在集成虚拟装配环境中对数据转换结果进行了验证,结果表明,用信息提取模型转换法获得的转换数据完整准确,转换效果良好。