基于IGES接口的电磁计算模型数据交互

现今武器大多是利用非均匀有理B样条(non-uniform rational B-spline,NURBS)数学表述,在CAD/CAM系统下完成建模和重构.利用电磁计算软件运算武器模型的雷达散射截面(radar cross section,RCS)从而评估其隐身性能,就需要与CAD/CAM系统进行数据交互.通过对基本图形转换规范(initial graphics exchange specification,IGES)数据标准的分析,为电磁计算软件编译了IGES数据接口.该数据接口具备IGES文件数据导入和模型数据导出另存为IGES文件格式的功能,从而实现了自行开发的计算软件CRCS v1.2和CAD系统软件的数据交互,提高了软件处理复杂模型的能力进而使模型重构与计算趋于一体化.     

一类基于ACIS的CAD/CAE数据转换接口实现

基于成熟的商业产品开发CAD/CAE数据转换接口是降低开发成本和周期的有效途径,基于ACIS及数据转换组件InterOp,开发了一类自主知识产权CAE软件高端数字样机（High End Digital Prototyping,HEDP）的CAD数据读写接口,并利用ACIS提供的接口实现了基本的几何修复功能。实验表明,利用算法导入的模型可在HEDP中顺利生成网格,导出的模型可为其他CAD系统正确读入。     

Repairing CAD model errors based on the design history

For users of CAD data, few things are as frustrating as receiving unusable, poor quality data. Users often waste time fixing or rebuilding such data from scratch on the basis of paper drawings. While previous studies use the boundary representation (B-Rep) of CAD models, we propose an approach to repairing CAD model errors that is based on the design history. CAD model errors can be corrected by an interdependency analysis of the feature commands or of the parametric data of each feature command, as well as by a reconstruction of the feature commands through rule-based reasoning of an expert system. Unlike other correction methods based on B-Rep models, our method repairs parametric feature models without translating them to a B-Rep shape, and it also preserves parametric information.     

Direct slicing of STEP based NURBS models for layered manufacturing

Direct slicing of CAD models to generate process planning instructions for solid freeform fabrication may overcome inherent disadvantages of using stereolithography format in terms of the process accuracy, ease of file management, and incorporation of multiple materials. This paper will present the results of our development of a direct slicing algorithm for layered freeform fabrication. The direct slicing algorithm was based on a neutral, international standard (ISO 10303) STEP-formatted non-uniform rational B-spline (NURBS) geometric representation and is intended to be independent of any commercial CAD software. The following aspects of the development effort will be presented: (1) determination of optimal build direction based upon STEP-based NURBS models; (2) adaptive subdivision of NURBS data for geometric refinement; and (3) ray-casting slice generation into sets of raster patterns. The development also provides for multi-material slicing and will provide an effective tool in heterogeneous slicing processes.     

NURBS双向蒙皮造型方法的研究与实现

本文通过对ＮＵＲＢＳ造型方法技术的研究，在自主开发的ＳｕｐｅｒＭａｎＣＡＤ／ＣＡＭ集成系统中成功地实现了基于复杂曲线的ＮＵＲＢＳ双向蒙皮曲面的造型功能，从而建立了完全基于ＮＵＲＢＳ方法的ＣＡＤ／ＣＡＭ系统．通过大量的工程应用和实例验证表明所研究的ＮＵＲＢＳ方法是一种适用于复杂外形产品设计与制造的、灵活有效的造型方法．     

CAD数据交换与互操作性的研究

针对目前三维CAD数据的交换状况,分析了基于标准模型和专用接口等两种主要CAD数据交换技术.以STEP标准为例,阐述了基于标准模型的CAD交换技术的架构和实际交换过程中遇到的数据丢失问题.专用接口是点对点的交换,是最原始的解决CAD数据交换的方法,涉及到各个CAD软件的商业利益,在CAD软件众多的情况下,使得CAD数据交换异常复杂.这两种CAD数据交换方法存在一个重大缺陷,即产生的都是"哑"模型,在非原CAD系统中无法对其进行编辑,极大地阻碍了CAD数据的交换.同步建模技术采用概念设计的理念和非历史特征的建模方法,不仅加速了模型设计,也较好地解决了CAD数据的交换问题.     

Seeking intelligent product development—an integrator environment based on STEP

Rapid Prototyping (RP) is an emerging technology with different applications in the cycle of product and process development used during the conceptual and specification phases. To support it, the usage of a Data Base Management System (DBMS) and an Expert Systems (ES) are important to manage the data, support the identification of errors and check product conformance and production viability during this cycle, seeking intelligent product development. The underlying concept of RP and ES is very straight forward, but still exists a major problem that concerns the integration in the CAD/CAM environment. CAD data can have a variety of formats depending on the model used in the CAD system, as well as on ES' data and knowledge structure, that usually relies on the expert system shell's where it was developed. To support and speed up the integration process of these tools in a manufacturing environment, is essential to have an integrator environment where a standard is adopted for the data and knowledge exchange process, providing the software applications with a neutral format interface, becoming these tools open and standard compliant, ready to be used in any other standard environment. UNINOVA, in the scope of European and National projects, developed a STEP-based Platform for Integration of applications (SIP) to support and aid the software integration in industrial environments using the standard ISO10303-STEP, already used in different industrial domains. This paper addresses the integration aspects using STEP within industrial environments from the technical point of view, and proposes an architecture and a toolkit for the integrator environment, highlighting the implementation efforts required to have RP technology, ES and DBMS focused towards a STEP-based intelligent product development.     

A method to exchange procedurally represented 2D CAD model data using ISO 10303 STEP

Procedural models have the advantage of being easy to edit simply by changing the values of the parameters of their constructional operations. Such models are said to embody design intent, in the sense that modifications to them conform to the method of creation used by their original creator. They also comply with any constraints implied by the particular constructional operations used. This paper introduces the development and standardization process of the ISO 10303-112 specification and describes the concept of procedural 2D modeling, a method of representing procedural 2D CAD models in STEP in harmony with other STEP resources. The feasibility of procedural 2D modeling commands for the exchange of procedurally represented 2D CAD model data is demonstrated through an experiment where procedural 2D CAD model data in neutral form generated with an in-house 2D modeling system are translated to and modified in a commercial 3D mechanical CAD system.     

STL实体模型的拓扑重建及其缺陷修复

STL文件是CAD系统与快速成型制造系统之间进行数据交换的标准格式文件，由于CAD系统在生成STL文件时使用的转换方法不当，使得由STL文件描述的实体模型有许多缺陷，要修复缺陷建立实体模型的拓扑关系是必要的。该文首先对STL实体模型进行了拓扑关系重建，然后修复了一些实体模型中常见的缺陷。     

Reconsideration of T-spline data models and their exchanges using STEP

T-spline is a new approach to define freeform surfaces with relatively less control points than NURBS and is able to represent a model using a single surface without joining errors. Whereas, the complexity of T-spline data models leads numerous difficulties in its programming, which hinders the research and development of T-spline technologies. In addition, the data exchange of T-spline models still remains on a primitive level, and no standardized data format has been published so far. This article gives a reconsideration to the existing T-spline definitions, and proposes a set of redesigned data models which have much more understanding conveniences to both human and computer. Moreover, STEP-compliant data models are designed using the proposed T-spline models to standardize their data exchange between different CAx systems. The combination of T-spline with other product models in ISO 10303 makes it convenient to exchange the versatile resource data in a hybrid neutral file. A prototype system is developed for the validation purpose, which consists of a TSM-to-STEP convertor, a STEP parser and a T-spline kernel. Using the developed prototype system, one can automatically convert a Rhino system exported TSM file to a STEP file in the P21 format, which can be then parsed using the STEP reader and processed by the T-spline kernel. Some testing examples show that the proposed data models are much more efficient in processing and exchanging the T-spline data.     

质量约束的三维模型建模方法

在当今的智能制造和工业软件设计领域,CAD和CAE是极为重要的技术.但现有的CAD和CAE模型表示方法不统一,在数据交换上需要耗费大量时间,造成了计算资源极大的浪费.非均匀有理B样条(NURBS)模型作为一种兼容CAD和CAE的模型表达方式,以样条曲线为基函数,无须进行交换即可进行等几何分析.本文提出了一种基于质量约束...     

基于NURBS的双螺杆制冷压缩机转子CAD系统

双螺杆制冷压缩机在商用制冷与空调领域得到越来越广泛的应用。本文着重介绍了一套双螺杆制冷压缩机转子计算机辅助设计系统，对系统的设计思路进行了阐述，然后详细说明了系统各部分基于NURBS的数学模型和在VC＋＋环境下的实现方法，并对前人的设计思想进行了开拓创新，完成了一套具有自己特色的设计系统。     

基于STEP的三维CAD和PDM系统集成方法研究

研究了基于STEP标准的产品信息模型、CAD数据交换接口、产品数据交换接口,提出了基于STEP中性机制和产品信息模型的三维CAD和PDM系统集成框架,该框架有助于实现广义CAD功能CAD/CAE/CAPP/CAM/CAQ/PDM/ERP之间的系统集成,异地、异构系统在企业间的集成,能够为企业设计和管理信息化提供一体化解决方案.     

A set of standard modeling commands for the history-based parametric approach

The current version of STEP standard cannot exchange the parametric information of CAD models. Only pure boundary representations that cannot be parametrically edited are transferable [Geometric Modeling: Theory and Practice (1997)]. There are two approaches for the exchange of design intents such as parameters, features, and constraints. The first is an explicit approach based on constraints between pre-defined parameters and features. The second is a procedural approach based on the sequence of operations issued to construct the models. The authors have previously proposed a macro-parametric approach [International Journal of CAD/CAM 2 (2002) 23], which is a variation of the procedural approach. In this approach, CAD models can be exchanged in the form of macro files, which include the history of modeling commands. To exchange CAD models using the macro-parametric approach, a set of standard modeling commands should be defined. This paper introduces a set of standard commands and explains the process of developing the set.     

异构CAD系统间中性语义特征数据交换

提出了一种基于中性语义特征转换的异构CAD系统间数据交换方法,该方法采用“中性语义特征转换器”将不同系统间的造型信息转换为统一的数据信息格式,并通过中性语义转换库实现了不同系统间操作命令的4种映射关系。此外,还实现了异构CAD系统间零件的同步协同传输。最后,将该文提到的思想初步应用在理工大学自主开发的HUSTCAIDS与UG间的异构协同设计中,证明该理论的可行性。     

基于NURBS曲面的棉花器官建模

数字农业将工业可控生产和计算机辅助设计的思想引入农业。该文介绍了利用NURBS和OpenGl对虚拟棉花主要器官果枝、铃、主茎叶、果枝叶、花瓣、苞叶等进行建模的方法,得到了逼真的效果。与三维数字化方法相比,省去了大量精确数据的测量和数学表达式的拟合工作。     

Accurate parametrization of conics by NURBS

One argument often given to explain the popularity of NURBS (nonuniform rational B-spline) is that it permits the definition of free-form curves and surfaces (as do most spline models). It also provides an exact representation of conic sections and thus of a large set of curves and surfaces used intensively in CAD: circular arcs, circles, cylinders, cones, spheres, surfaces of revolution and so forth. Nevertheless, few published works discuss the mathematical properties behind the representation of conics by NURBS except for two monographs by Piegl and Tiller (1995) and Farin (1995). The article does not pretend to fill this theoretical lack but rather deals with the following problems: all known NURBS representations of curves and surfaces based on conics have only a C^l continuity. Moreover, no technique exists that would eventually allow us to find a parametrization with a higher level of continuity. The parametrization resulting from the NURBS representation of conics can deviate significantly from the ideal are length (that is, uniform) parametrization. The only known solution to reduce this deviation is to increase the number of control points of the spline by using refinement algorithms, for instance, but such a process converges only slowly to the uniform parametrization. The solution proposed uses an original reparametrization process called zigzag reparametrization, based on a specific family of rational polynomials     

GPU-accelerated minimum distance and clearance queries

We present practical algorithms for accelerating distance queries on models made of trimmed NURBS surfaces using programmable Graphics Processing Units (GPUs). We provide a generalized framework for using GPUs as coprocessors in accelerating CAD operations. By supplementing surface data with a surface bounding-box hierarchy on the GPU, we answer distance queries such as finding the closest point on a curved NURBS surface given any point in space and evaluating the clearance between two solid models constructed using multiple NURBS surfaces. We simultaneously output the parameter values corresponding to the solution of these queries along with the model space values. Though our algorithms make use of the programmable fragment processor, the accuracy is based on the model space precision, unlike earlier graphics algorithms that were based only on image space precision. In addition, we provide theoretical bounds for both the computed minimum distance values as well as the location of the closest point. Our algorithms are at least an order of magnitude faster and about two orders of magnitude more accurate than the commercial solid modeling kernel ACIS.     

A surface based approach to recognition of geometric features for quality freeform surface machining

The paper presents a surface-based approach for geometric feature recognition for the purpose of automating the process planning of freeform surface machining. The proposed approach consists of the following four steps for recognition of the geometric features: conversion and preprocessing of the surface geometry data, subdivision of NURBS surface, reconstruction of surface orientation areas, and recognition of geometric features. The proposed scheme assumes that the input geometry data form is based on an IGES CAD model and the surface model can be represented in the form of trimmed NURBS surfaces. The connectivity relations of the product surfaces are analyzed and each surface is subdivided into orientation regions based on the surface normal vector over a certain point density grid, and then all the connected regions with the same orientation type are grouped into surface orientation areas. After that, the geometric feature will be recognized through the analysis of area connectivity and relationship. The paper describes the developed algorithms on surface orientation region subdivision, surface orientation area reconstruction, and geometric feature recognition. The verified feasibility study of the developed method is also presented.     

异构CAD系统语义信息交换方法研究

传输完整的CAD模型语义信息是协同设计有效进行的关键,提出了一种异构CAD系统语义信息交换方法,该方法通过构建语义转换器实现了常规文件、压缩文件和中性文件三种模型文件的数据转换和翻译,并给出了判定特征相似性的方法,实现了源CAD系统和目标CAD系统的语义互操作,保证了语义传输的完整性和高效性。构建了一个协同资源共享平台,在该平台下实现了Pro/E系统和UG系统之间的语义数据交换,协同传输效率提高了近30%。