基于IGES的数据交换接口实现

文章通过对IGES中性标准的分析,设计了一个逆向工程数据处理软件数据交互接口的框架。在此框架基础上,实现了重构模型与各种工程设计软件之间的数据信息交换,并应用于相关软件的编制中。     

Experience in design and implementation of an IGES translator

This paper describes a general design concept for an IGES translator. The design allows implementation of IGES translators for different CAD/CAM systems with a minimum of programming effort. It divides the functions of an IGES translator into two categories: those common to implementations of an IGES translator, and those specific to the target system. Allowing user interactions to control entity mappings, the design adds user flexibility to an IGES translator. Different results that can be created for an IGES file are shown and discussed, using a sample implementation.     

Modifying CAD/CAM surfaces according to displacements prescribed at a finite set of points

This article presents a method for modifying CAD/CAM surfaces automatically in accordance with displacements prescribed at a finite set of points in R³, such as node displacements predicted by finite-element analysis. The method is based on the ‘morphing’ approach introduced by Sederberg and Parry in 1986. The input to the process consists of (a) a CAD/CAM model containing trimmed polynomial B-spline surfaces and (b) a set of points and associated displacement vectors in R³. These points are assumed to be close to, but not necessarily on, the objects of the CAD/CAM model. A rectangular volume, enclosing the CAD/CAM model and the input points in R³, is represented as a volume spline, i.e. a trivariate tensor-product spline. A modified volume spline is computed using (a) a least-squares fit based on the given point displacements, and (b) a smoothing functional. The modified CAD/CAM objects are defined as compositions of the original parametric functions and the modified volume spline (i.e. a morphing). In order to ensure compatibility with standard commercial CAD/CAM systems, the modified surfaces are fitted with appropriate splines using any standard, reasonably shape-preserving, fitting procedure applied in the parameter domains of the original surfaces.     

A New Local Control Spline with Shape Parameters for CAD/CAM

Anew local control spline based on shape parameterw with G^3 continuity,called BLC-spline,is pro* posed.Not only is BLC-spline very smoot,but also the spline curve‘s characteristic polygon has only three control vertices,and the characteristic polyhedron has only nine control vertices.The behavior of Iocal control of BLC-spline is better than that of the other splines such as cubic Bezier,B and Beta-spline.The three shape parameters β0，β1and β2 of BLC-spline,which are independent of the control vertices,may be altered to change the shape of the curve or surface.It is shown that BLC-spline may be used to construcet a space are spline for DNC machining directly.That is a powerful tool for the design and manufacture of curves and surfaces in integrated CAD/CAM systems.     

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.     

Initial graphics exchange specification: Successes and evolution

The Initial Graphics Exchange Specification (IGES) arrived on the CAD/CAM stage in late 1979 and has enjoyed substantial attention from a broad set of users and implementors since. As the term initial reflected, the first release was only a beginning and IGES continues to be an active organization, as well as an evolving CAD/CAM specification. This paper reviews some of the key events and efforts of the IGES community in furthering the quality and scope of this important interface standard.     

Constrained curve drawing using trigonometric splines having shape parameters

The problem of drawing a smooth obstacle avoiding curve has attracted the attention of many people working in the area of CAD/CAM and its applications. In the present paper we propose a method of constrained curve drawing using certain C¹-quadratic trigonometric splines having shape parameters, which have been recently introduced in [Han X. Quadratic trigonometric polynomial curves with a shape parameter. Computer Aided Geometric Design 2002;19:503–12]. Besides this, we have also presented a simpler approach for studying the approximation properties of the trigonometric spline curves.     

Databases and cell-selection algorithms for VLSI cell libraries

The issues that must be addressed before commercial database management systems can be used to manage VLSI CAD data are defined. A survey is presented of approaches addressing four of the defined issues: design hierarchies and multilevel representations, design alternatives and version control, common interface between cell libraries and efficient cell selection based on given design constraints. A frame-based model is considered as a case study of the special-purpose design database management system approach. This framework for capturing design data is based on semantic networks. It is well suited for application-specific ICs, yet general enough for other CAD/CAM environments. Benchmark results for the selection algorithms that run on top of the frame-based database system are presented     

基于约束优化的B样条曲线形状修改

B样条曲线广泛应用于计算机辅助几何设计(CAGD),并且与Bézier曲线等其它著名曲线相比,在形状设计方面有其更独特的性质。对曲线的设计和形状的修改是一个重要的课题,也是计算机图形学、CAD/CAM和数控技术领域最重要的研究主题之一。论文运用约束优化的方法,修改均匀B-样条的控制点,使B样条曲线通过调整的控制点,使修改前后曲线的距离范数达到最小,并给出相应的实例说明算法的有效性。     

Automesh for trimmed surface entity of IGES/PDES

IGES/PDES is an internationally accepted standard protocol for transferring the information of a two-dimensional or three-dimensional model between different CAD/CAM software. Any solid model can be constituted by a number of surfaces. Trimmed surface is one of the most important entities used to design a two-dimensional or three-dimensional model in IGES/PDES. The main idea in this article is to extract trimmed surface entity information from an IGES protocol created in a CAD/CAM software. Then, from the extracted information of trimmed surface entity in the model space and in the u–v space, a new u–v space is developed for meshing. After meshing the geometric region in the new u–v space, the meshed geometric region is transformed back to the model space by using a particular transformation. A Fortran code which can be used for pre-processing in Boundary Element Method has been developed by the present authors. Some meshed surface models are presented in this paper as examples.     

Importing mesh entities through IGES/PDES

IGES/PDES is an internationally accepted standard for transferring solid model information between different CAD/CAM software. Most of the information, like geometric entities, mesh entities and drafting entities, for a model generated in a particular software may be imported into another software through the IGES protocol, although either software may have its own internal database structure, radically different from each other. The goal of this article is to outline the basic concepts involved in extracting relevant information from an IGES file produced by a CAD/CAM software. In order to elucidate the process involved, only the mesh entities (nodes and elements) are brought in and a simple F77 code is attached, which could easily be extended to develop a general purpose IGES translator for pre-processing in a Finite Element/Boundary Element based analysis environment.     

Feature-based spline optimization in CAD

In this paper, an advanced method for CAD-based spline structure optimization is investigated. The method is based on the combination of the commonly known parameter-based spline shape optimization and a recently presented feature-based structure variation concept for commercial CAD tools. The aim is to extend common parameter-based spline shape variation by the additional possibility to automatically add and remove control points or entire splines directly in CAD space. Such advanced spline modification provides a new level of flexibility in general geometry-based structural optimization. Using these splines to build CAD models, entirely new structures may be automatically generated during an optimization run through this newly gained flexibility in spline manipulation. The idea is to roughly define a continuous design space by basic splines and to gradually increase their shape complexity by control point number variation during optimization. Thus, operating on a knowledge-lean initialization—a design space bounded by basic splines and filled with material—this combination further extends the search and solution spaces of CAD-based structural optimization. The paper provides an outlook towards automated geometry-based structure creation combining nowadays commercial CAD software and a dedicated variation and optimization framework for geometry-based structural optimization.     

Development of a collaborative CAD/CAM system

This paper presents the development of a collaborative CAD/CAM system (COCADCAM). COCADCAM extends an existing single-location CAD/CAM system to a multi-location CAD/CAM application so that two geographically dispersed CAD/CAM users can work together on a three-dimensional CAD-geometry coediting and CAD-related tasks collaboratively and dynamically. COCADCAM dynamically supports CAD data communication that are not available in traditional single-location CAD/CAM. The dynamic data communication is achieved through the development of networking algorithms and CAD/CAM functions in this paper. The networking algorithms based on UNIX Interprocess Communication (IPC), the Network File System (NFS), and a connection-oriented client and server model under the Transmission Control Protocol/Internet Protocol (TCP/IP) suite. The CAD/CAM functions included surface modelling, simulation of a milling toolpath, and post-processing of an NC program following collaborative CAD-geometry coediting, which are directly or indirectly supported by the Application Programming Interface (API) of the CAD/CAM software. The networking algorithms and CAD/CAM functions together can facilitate an environment for CAD-geometry coediting and related tasks such as design, analysis and manufacture. COCADCAM has been successfully implemented through local area network (LAN) and the Internet; a remote machining cell is also linked so that the generated NC program based on a coedited free-form surface can be used for the physical machining operation. The algorithm proposed by COCADCAM can be referenced for the extension of other single-location CAD/CAM systems to multi-location applications.     

Adaptive CAD model (re-)construction with THB-splines

Computer Aided Design (CAD) software libraries rely on the tensor-product NURBS model as standard spline technology. However, in applications of industrial complexity, this mathematical model does not provide sufficient flexibility as an effective geometric modeling option. In particular, the multivariate tensor-product construction precludes the design of adaptive spline representations that support local refinements. Consequently, many patches and trimming operations are needed in challenging applications. The investigation of generalizations of tensor-product splines that support adaptive refinement has recently gained significant momentum due to the advent of Isogeometric Analysis (IgA) [2], where adaptivity is needed for performing local refinement in numerical simulations. Moreover, traditional CAD models containing many small (and possibly trimmed) patches are not directly usable for IgA. Truncated hierarchical B-splines (THB-splines) provide the possibility of introducing different levels of resolution in an adaptive framework, while simultaneously preserving the main properties of standard B-splines. We demonstrate that surface fitting schemes based on THB-spline representations may lead to significant improvements for the geometric (re-)construction of critical turbine blade parts. Furthermore, the local THB-spline evaluation in terms of B-spline patches can be properly combined with commercial geometric modeling kernels in order to convert the multilevel spline representation into an equivalent – namely, exact – CAD geometry. This software interface fully integrates the adaptive modeling tool into CAD systems that comply with the current NURBS standard. It also paves the way for the introduction of isogeometric simulations into complex real world applications.     

It is time to drop the “R” from NURBS

NURBS were introduced into CAD/CAM systems predominantly for the representation of conventional objects, such as conics and quadrics. Among these, the circle played a critical role in representing a myriad of parts used in the every-day practice. Being the most universally used object, the circle has enjoyed the most popularity in science and engineering. It is an essential entity in both design as well as manufacturing and hence, its representation within CAD/CAM systems requires careful attention. Although the circle enjoys both smoothness as well as a uniform parametrization, its de facto mathematical form, the NURBS form, does not provide either sufficient smoothness or uniform parametrization. On top of all this, NURBS are rational forms requiring homogeneous coordinates in the four-dimensional space, whereas the engineering entity is only Euclidean in 3D. This multiple representational glitch, 3D presence and 4D storage, has given rise to enough headache to warrant reconsideration of the validity of the rational form in engineering design. This paper argues that it is time to drop the “R” from NURBS and to switch to integral splines with approximations where necessary. We also argue that it is time to bury dumb algorithms and consider human-based computing, i.e. our algorithms should be biologically inspired and not based on pure number crunching.     

Subdivision algorithms for the generation of box spline surfaces

This paper proposes a general approach to subdivision algorithms used in interactive computer aided design for splines which are linear combinations of translates of any box splines. We show how these algorithms can be used for efficient generation of the corresponding spline surfaces. Our results extend several known special cases.     

带双形状参数的C-B样条曲线

利用积分方法构造了带双形状参数的C-B样条曲线基函数,这类曲线具有标准C-B样条曲线主要性质,如连续性、凸包性等;根据形状参数的不同取值可以整体或者局部调控曲线形状,由此生成的曲线与曲面,作为一种新的几何造型方法,可应用于CAD/CAM领域。     

基于曲面模型的IGES前后置处理器的设计

符合ＩＧＥＳ标准的曲面模型的输入和输出是大多数ＣＡＤ系统必备的数据接口之一,本文设计了一种基于裁剪ＮＵＲＢＳ曲面片的ＩＧＥＳ曲面模型的前后置处理器,并 详细讨论了Ｂｒｅｐ表示的实体模型和曲面模型的相互转换,在曲央模型到实体模型转换中使用了基于ｏｐｅｎ ｅｄｇｅ结构的曲面拓扑信息重建技术。     

Automatic generation of variants depending on changes of product properties in a flexible manufacturing environment

Competition forces manufacturing systems to be flexible and to increase product variety and process complexity. These tasks depend on the flexible design of a bill of materials (BOM), one of the most important inputs in manufacturing planning and control systems. Product variety forces systems to generate BOMs with regard to product properties through a BOM pattern. A variant bill of materials provides a structure to manage product variability. In this study, an algorithm is designed to build a BOM pattern using computer-aided design and computer-aided manufacturing (CAD/CAM) data, and another algorithm is designed to generate variants with regard to product specifications. Genetic algorithm is used to generate new products to provide high product variability for testing algorithms. After the test, both algorithms are applied to a real industry problem. The BOM pattern is built automatically using CAD/CAM data, and variants are generated with regard to the pattern, and the results are discussed.