Towards the standardized exchange of parameterized feature-based CAD models

The paper describes the status of work aimed at extending the international standard ISO 10303 (STEP) to permit the exchange of parameterized feature-based models between different CAD systems, in terms of the constructional history of the models concerned. Such procedural models have the advantage of being easy to edit following an exchange, by contrast with the models that can be exchanged using current STEP methodology, which prove to be difficult or impossible to edit in the receiving system. The use of the approach described has already been demonstrated in the exchange of realistic procedural shape models of mechanical parts, and the paper includes a brief account of some of the tests performed and the projected benefits of the use of this extension of STEP technology.     

A survey on 3D CAD model quality assurance and testing tools

A new taxonomy of issues related to CAD model quality is presented, which distinguishes between explicit and procedural models. For each type of model, morphologic, syntactic, and semantic errors are characterized. The taxonomy was validated successfully when used to classify quality testing tools, which are aimed at detecting and repairing data errors that may affect the simplification, interoperability, and reusability of CAD models.The study shows that low semantic level errors that hamper simplification are reasonably covered in explicit representations, although many CAD quality testers are still unaffordable for Small and Medium Enterprises, both in terms of cost and training time. Interoperability has been reasonably solved by standards like STEP AP 203 and AP214, but model reusability is not feasible in explicit representations.Procedural representations are promising, as interactive modeling editors automatically prevent most morphologic errors derived from unsuitable modeling strategies. Interoperability problems between procedural representations are expected to decrease dramatically with STEP AP242. Higher semantic aspects of quality such as assurance of design intent, however, are hardly supported by current CAD quality testers.     

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.     

Editing 3D models on smart devices

This study proposes a 3D CAD system available on smart devices, which are now a part of everyday life and which are widely applied in various domains, such as education and robot industry. If an engineer has a new idea while traveling or on the move, or in the case of collaboration between more than two engineers, this 3D CAD system allows modeling to be performed in a rapid and simple manner on a smart device. This 3D CAD system uses the common multi-touch gestures associated with smart devices to keep the modeling operations simple and easy for users. However, it is difficult to input the precise geometric information to generate 3D CAD models by such gestures. It is also impractical to provide a full set of modeling operations on a smart device due to hardware limitations. For this reason, the system excludes several complicated modeling operations. This work provides a scheme to regenerate a parametric 3D model on a PC-based CAD system via a macro-parametrics approach by transferring the 3D model created on a smart device in an editable form to a PC-based CAD system. If fine editing is needed, the user can perform additional work on a PC after reconstruction. Through the developed system, it is possible to produce a 3D editable model swiftly and simply in the smart device environment, allowing for reduced design time while also facilitating collaboration. This paper discusses the first-ever system design of a 3D CAD system on a smart device, the selection of the modeling operations, the assignment of gestures to these operations, and use of operation modes. This is followed by an introduction of the implementation methods, and finally a demonstration of case studies using a prototype system with examples.     

A step toward STEP-compatible engineering data management: the data models of product structure and engineering changes

In an iterative design process, there is a large amount of engineering data to be processed. Well-managed engineering data can ensure the competitiveness of companies in the competitive market. It has been recognized that a product data model is the basis for establishing engineering database. To fully support the complete product data representation in its life cycle, an international product data representation and exchange standard, STEP, is applied to model the representation of a product. In this paper, the architecture of an engineering data management (EDM) system is described, which consists of an integrated product database. There are six STEP-compatible data models constructed to demonstrate the integratibility of EDM system using common data modeling format. These data models are product definition, product structure, shape representation, engineering change, approval, and production scheduling. These data models are defined according to the integrated resources of STEP/ISO 10303 (Parts 41-44), which support a complete product information representation and a standard data format. Thus, application systems, such as CAD/CAM and MRP systems, can interact with the EDM system by accessing the database based on the STEP data exchange standard.     

Pro/E和UG之间三维模型数据交换方法

为了实现CAD系统（Pro/E）和CAM系统（UG）之间三维实体模型数据交换,以卫星零部件为对象,根据系统之间数据交换的机制,在分别研究了IGES标准和STEP标准的基础上,基于这2种标准进行了数据交换实验比较,提出了基于STEP标准实现Pro/E和UG之间实体模型数据交换的方法.     

面向应用协议的CAD／CAM集成模式

本文提出以ＳＴＥＰ为核心，直接支持ＣＡＤ后续各应用系统的特征造型方法和ＣＡＤ／ＣＡＭ集成模式，不仅在一般意义上实现基于ＳＴＥＰ的信息集成，而且是对于ＳＴＥＰ利用应用协议实现ＣＡＤ／ＣＡＰＰ／ＣＡＭ信息集成方法的拓展。     

STEP特征模型及其在集成环境中的应用研究

从STEP特征模型、CAD／CAPP特征建模、STEP工具集的构造、模型映射等角度,论述了STEP技术在CIM领域的应用,在此基础上,阐述了“即插即用”的特征映射及信息集成技术,并讨论了一种在STEP工具集的支持下,以独立于具体系统的方式实现CAD／CAPP特征信息集成的方法。     

A PDES/STEP-based model and system for concurrent integrated design and assembly planning

Product data exchange and interfacing between different CAD/CAM systems are of great importance to the development of concurrent integrated design environments and computer integrated manufacturing systems. This paper presents a STEP-based method and system for concurrent integrated design and assembly planning. An integrated object model for mechanical systems and assemblies is first defined by a hierarchy of structure, geometry and feature. The structure is represented as a component-connector or joint multi-level graph with both hierarchical functional and assembly relations. These hierarchical relation models are then used for uniformly describing their causal relations both for assembly level and feature based single part level. The generic product assembly model is organized according to STEP, using mostly the entities of integrated resources and partly self-defined entities, which are necessary for design and assembly planning. Based on the generic product assembly model, STEP-based strategies and agent concepts are used for agent-based concurrent integration of design and assembly planning. A prototype system, consisting of a CAD system, a product modeling system, an assembly planning system, and an assembly evaluation system is developed, in which product data can be exchanged between these subsystems. Details about the implementation of the system are addressed. The integrated design and assembly planning system can support the introduction of a new product. The results of assembly planning are feedback to the stage of assembly design to improve on the design. A case study is carried out for assembly-oriented design of a gearbox, to illustrate the proposed approach and to validate the developed system.     

基于STEP装配特征的BOM信息提取和多视图映射

为了解决企业信息集成过程中CAD文件物料清单提取问题,提出一种基于STEP装配特征辨识的物料清单信息提取方法,该方法以STEP作为中间数据格式,采用统一建模语言建立实体类映射模型,利用模型的装配特征辨识实体的装配关系,实现异构数据物料清单统一提取。同时,在XMLwebServices框架的网络服务平台上,利用扩展样式表语言转换自动映射机制,有效实现物料清单多视图转换过程集成规范化。在此基础上建立了基于STEP产品物料清单信息管理系统,并给出了该系统在工程机械制造企业产品数据管理中的应用实例。     

基于STEP的集成化CAD／CAM支撑软件系统

本文介绍了由清华大学ＣＡＤ中心等单位开发的集成化ＣＡＤ／ＣＡＭ支撑软件系统，该系统由六个模块组成，它们是用户接口、交互绘图、产品造型、分析与优化、数控加工和数据库管理该系统采用国际标准ＳＴＥＰ作为产品数据表示和交换的中性机制，使用特征造型、变量化设计方法建立产品信息模型，并使产品信息贯穿于设计、装配、分析、工艺、制造等各个阶段，实现系统的集成。     

城市蒸汽管道数字系统设计方法

本文阐述城市蒸汽管道数字系统框架。引入ISO10303国际标准,采用基于实体对象的分布式CAD系统,并说明如何利用该标准进行建模技术研究,讨论建立城市蒸汽数字管道系统的实现方法。通过产品数据管理系统实现虚拟现实技术融合在城市蒸汽数字管道系统。研究表明,所提出的模型易于反复进行计算机仿真试验,在管道工程实际应用中有重要的价值。     

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.     

基于STEP标准的数据交换的研究与实现

文中概述了产品数据表达与交换标准化的发展过程,着重分析了基于STEP产品数据交换接口的设计,为自行研制的可视化系统实现了基于STEP中性文件的数据交换接口,将复杂形体的几何徒刑数据读入并在可视化系统内实现四面体剖分,在复杂数据场的分析和显示方面具有重要的应用价值。     

Mapping 2D midship drawings into a 3D ship hull model based on STEP AP218

Standard for the exchange of product model data (STEP) AP218 has a standard schema to represent the structural model of a midship section. While its schema facilitate the exchange of ship structural models among heterogeneous systems, most shipyards and classification societies exchange information using 2D paper drawings. We propose a feature parameter input method to generate a 3D STEP model of a ship structure from 2D drawings. We have analyzed the ship structure information contained in 2D drawings and have defined a data model to express the contents of the drawing. We also developed a GUI for the feature parameter input. To translate 2D information extracted from the drawing into a STEP AP218 model, we have developed a shape generation library and have generated the 3D ship model through this library. The generated 3D STEP model of a ship structure can be used to exchange information between design departments in a shipyard as well as between classification societies and shipyards.     

A database system of mechanical components based on geometric and topological similarity. Part I: representation

A database of mechanical components is an important issue for some manufacturing activities such as cost estimation, process planning, and design by case-based reasoning. In this paper, we give the representation scheme of the CAD model in such a database. Components are represented using attributed graphs in which the nodes correspond to the surfaces of the component and the links correspond to the edges of the component. The graph is based on the standard for the exchange of product information (STEP) physical file of the component. STEP file should be unique for a single component regardless of the underlying CAD system. The process of creating the graph of a component constitutes two sub-tasks: (i) importing the CAD model from the CAD system in STEP format and (ii) transforming the STEP data into attributed graph-based representation. The graph and its attributes describe the topology of the component completely together with some geometric data that are not dependent on any coordinate system such as surface type and curve type. These geometric data are helpful in the retrieval and matching processes in the database.     

Sketch-Based Procedural Surface Modeling and Compositing Using Surface Trees

We present a system for creating and manipulating layered procedural surface editing operations, which is motivated by the limited support for iterative design in free‐form modeling. A combination of sketch‐based and traditional modeling tools are used to design soft displacements, sharp creases, extrusions along 3D paths, and topological holes and handles. Using local parameterizations, these edits are combined in a dynamic hierarchy, enabling procedural operations like linked copy‐and‐paste and drag‐and‐drop layer‐based editing. Such dynamic, layered “surface compositing” is formalized as a Surface Tree, an analog of CSG trees which generalizes previous hierarchical surface modeling techniques. By “anchoring” tree nodes in the parameter space of lower layers, our surface tree implementation can better preserve the semantics of an edit as the underlying surface changes. Details of our implementation are described, including an efficient procedural mesh data structure.     

大规模城市可计算模型快速构建方法研究

为了给数值模拟计算提供大规模城市的可计算模型,需要具备面向大空间尺度、海量数据、频繁更新的城市的快速可计算建模能力。但是,由于数据采集过程中存在的误差,以及模型处理所做的必要的简化操作,导致直接生成的数字城市模型中存在大量非闭合、相接、相交、悬空等CAD模型缺陷,使得城市模型不可用于数值模拟。而采用商用软件直接修复这些缺陷的代价过高。为此,提出面向大规模城市可计算模型的快速构建方法。通过分析LoD1城市模型中所涉及的CAD模型缺陷,提出了需满足的可计算条件和对应的处理方法。 提出的方法能够直接生成不存在CAD模型缺陷的城市可计算模型。为了提高可计算处理的效率,还提出了面向大规模城市的图形快速检索算法。实验表明,构建710 km2、30余万栋建筑、217万面片的可计算模型仅需约25 min,满足了在大规模城市上进行数值模拟的需求。     

以OOEDB为核心的集成化CAD/CAPP/CAM 系统GS-ICCC的设计与实现

ＧＳ－ＩＣＣＣ是一个以自行研制开发的面向对象工程数据库管理系统ＯＳＣＡＲ为核心的集成化ＣＡＤ／ＣＡＰＰ／ＣＡＭ系统，它的主要特点是按照ＳＴＥＰ标准在全局产品数据模型基础上实现ＣＡＤ，ＣＡＰＰ，ＣＡＭ的信息集成，本文围绕着这一原则介绍了ＧＳ－ＩＣＣＣ的系统总体结构，ＯＳＣＡＲ功能组织，全局产品数据建模框架以系统集成的设计与实现。