Integration of a CAx (Computer Aided x) system throughout the product life
cycle and among different enterprises is a major issue for industrial
competitiveness and collaboration. One of the main successful factors for CAx
system integration is efficient methodology for EPDE (Engineering Product
Data Exchange). Data exchange is the totality of establishing the approach for
and the successful achievement of the transfer of data between two distinct
CAx systems.
Problem Statement:
- Why does an exchanged CAD (Computer Aided Design) model lose some
modelling properties? – Especially losses such as model tree (design
intent) and features.
- What reasons influence that phenomenon?
- How can these losses be minimized?
2. Review state of the art of exchange strategies
The review of exchange strategies is focused on which existing approaches
are in use today, which capabilities are supported by them, which deficiencies
they have, an understanding of state of the art is a precondition for beginning
to deal with of the problem statement.
3. Analysis of modelling capabilities regarding feature
modelling and structure representation
The analysis begins with a short review of existing feature modelling
techniques, which will build up a framework for the analysis process. Three
CAD systems are analysed – Pro/Engineering, I-DEAS and UniGraphics.
Typical models, with the frequently occurring features, are reviewed
depending on the feature modelling method and structural representation.
4. Needs-identification
The results of the analysis of modelling capabilities lead to the improvement
of new methods and techniques. This defines the essential basis for the
building of a concept framework.
5. Requirement definitions
- How can the model-tree to be exchanged?
- How will the exchanged model-tree act?
6. Outline of the thesis
The material is organized in three major sections. The first one, the state of
the art, examines the fundamentals of exchange approaches, the current
state of scientific and commercial exchange approaches and further related
technologies.
The second one, presents the current state of feature modelling techniques
and analyses of three commercial CAD systems according to feature
modelling capabilities and structural representation.
The next section, the concept framework, designs a concept framework fitting
the requirement definitions.
Table of Contents
I. Introduction
1. Problem analysis and requirements definition
2. Review state of the art of exchange strategies
3. Analysis of modelling capabilities regarding feature modelling and structure representation
4. Needs-identification
5. Requirement definitions
6. Outline of the thesis
II. Approaches to the Exchange of CAD Data
1. Outline
2. General Classification of Exchange Approaches
2.1. Direct and Standard-based exchange Approaches
2.2. Horizontal and Vertical Exchange Approaches
2.3. Classification of exchange strategies
3. Capabilities of Scientific Exchange Strategies
3.1. On the Implicit Exchange of Feature-Based Product Model Data
3.2. Exchange of CAD Part Models Based on the Macro-Parametric Approach
3.3. The Unified Approach to Modelling Multidisciplinary Interaction
3.4. An exchange Approach in Conceptual-Based Design System
3.5. Open CAD Environment
4. Capabilities of Exchange Strategies in Commercial Areas
4.1. Vendor Exchange Method
4.2. Native Exchange Method
4.3. Neutral Exchange Method
4.3.1. IGES
4.3.2. VDA-FS
4.3.3. SET
4.3.4. XBF
4.3.5. PDDI
4.3.6. Projects Related to Neutral Exchange Methods
4.3.7. STEP (ISO-10303)
5. Further technologies
5.1. Parts Library
5.2. CAD – Services
5.3. ProSTEP
6. Conclusion
III. Analysis of today’s CAD systems – concepts and capabilities
1. Outline
2. Feature modelling definitions
2.1. Feature definitions
2.2. Feature model definition
2.3. Feature modelling definition
2.4. Feature attributes definition
2.5. Types of features
2.6. Feature properties
2.7. Feature properties classification
2.8. Generic and composite features
2.9. Feature taxonomies
2.10. Feature mapping
3. Analysis of feature modeling methods
3.1. Basic feature creation methods
3.2. Analysis of specific features modeling methods
3.2.1. Interactive feature modeling
3.2.2. Automatic (recognition) feature recognition
3.2.3. Design by feature modeling
3.3. Analysis of structural representation regarding feature modeling methods
3.3.1. Automatic feature recognition
3.3.2. Design by feature modelling
4. Major benefits of feature modelling methods
4.1. Design Intent
4.2. Multilevel structure
4.3. Feature-Kernel
5. Deficiencies as a result of feature data exchange
6. Analysis of commercial systems
6.1. Scope and process of analysis
6.1.1. Analysis of basic feature creation methods
6.1.2. Analysis of modelling kernel
6.1.3. Scope and process of model representation
6.2. Pro/Engineer’s analysis
6.3. I-DEAS’s analysis
6.4. Unigraphic’s analysis
7. Conclusions
IV. Exchange strategy – concept
1. Problem discussion
2. Needs identification on a Feature Model-Tree exchange methodology
3. Requirements definition - sequence of needs identification
3.1. Openness - neutral type of exchange data
3.2. Modularity – structure oriented data
3.3. Optimal Completeness – optimal density of exchange data
4. Requirements list
5. Established and new exchange strategies
6. Concept details
6.1. Fundamental ideas
6.2. General framework
6.3. Detail of the framework
6.4. Translation process
V. Evaluation and outlook
Objectives and Research Themes
The thesis aims to address the challenge of data loss during the exchange of CAD models between different systems, specifically focusing on the loss of "model tree" (design intent) and feature information. It investigates existing scientific and commercial exchange strategies, analyzes feature modelling capabilities in leading CAD software (Pro/Engineer, I-DEAS, Unigraphics), and develops a conceptual framework for a structure-oriented exchange of CAD model data to preserve this critical design information throughout the product life cycle.
- Analysis of CAD feature modelling and structural representation techniques.
- Evaluation of current scientific and commercial data exchange methodologies (e.g., IGES, STEP).
- Comparative analysis of how major commercial CAD systems handle feature and model representation.
- Identification of requirements for preserving model-tree integrity during data transfer.
- Proposal of a new conceptual framework for structure-oriented CAD data exchange.
Excerpt from the Book
3.1. On the Implicit Exchange of Feature-Based Product Model Data
The concept is being funded by the German Research Foundation with participation of H. Tönshoff; F. Krause; R. Baumann and P. Woelk [N]. The concept of an implicit feature model description assumes the use of features such as elementary objects of the product model. A model description consists of two substantial parts: a generic description of the available features and methods (“feature library”) and a structural description of how to create a model out of the features, specified in the feature library (“model history file”). Both the feature library and the model history file define the model.
The feature library, which contains the generic feature description, must be made available to any system that takes part in the information exchange. The syntax for the definition of the feature library is based on EXPRESS. The language allows the definition of the design guidelines and constraints between features and parametric relations. The rules and methods for the transformation of design features into manufacturing features (“feature mapping”) allow systems supporting later stages of the product development process to participate in the information exchange (“vertical information exchange”).
The feature-based model history file is the second essential component of implicit data exchange. It contains the parameter values with which the features are created. Every entity corresponds to an instance of a feature specified in the feature library. The model structure corresponds to the order in which the entities occur in the model history file. A complete implicit description of the model is reached by the combination of the generic feature library and the description of the model history file (Figure 5).
Summary of Chapters
I. Introduction: This chapter establishes the problem statement regarding the loss of design intent during CAD data exchange and outlines the goals and structure of the thesis.
II. Approaches to the Exchange of CAD Data: This section reviews state-of-the-art scientific and commercial data exchange strategies, covering direct, standard-based, horizontal, and vertical exchange methods.
III. Analysis of today’s CAD systems – concepts and capabilities: The author examines fundamental feature modelling concepts and evaluates three specific commercial CAD systems (Pro/Engineer, I-DEAS, Unigraphics) based on their modelling kernels and representation structures.
IV. Exchange strategy – concept: This chapter defines the requirements for a structure-oriented exchange and presents a proposed conceptual framework for preserving model trees.
V. Evaluation and outlook: The author concludes by assessing the feasibility of the proposed concept and identifying areas for future development regarding the full exchange of feature model trees.
Keywords
CAD, Data Exchange, Feature Modelling, Design Intent, Model Tree, Engineering Product Data Exchange, STEP, IGES, Structural Representation, Feature Library, Implicit Exchange, Macro-Parametric Approach, CAD Systems, Product Life Cycle, Interoperability
Frequently Asked Questions
What is the primary focus of this thesis?
The work focuses on developing a methodology for the "structure-oriented exchange" of CAD data, aiming to minimize the loss of design intent and feature-related information when transferring models between different CAx systems.
What are the central thematic areas?
The core themes include CAD system interoperability, feature modelling taxonomies and methods, structural data representation, and the critical analysis of existing exchange standards and scientific strategies.
What is the main research objective?
The primary goal is to specify an overall framework that allows the exchange of "model trees" and design intent, thereby enabling users to modify exchanged CAD models at the feature level in receiving systems.
Which scientific methods are employed?
The thesis utilizes a literature review of existing exchange strategies followed by a deep-dive comparative analysis of three major commercial CAD systems (Pro/Engineer, I-DEAS, and Unigraphics) to identify their underlying modelling kernels and feature creation logic.
What does the main body cover?
The main body systematically reviews exchange technologies, provides a detailed classification of feature modelling, conducts a hands-on technical analysis of selected commercial CAD software, and derives specific requirements for a new, more robust exchange framework.
Which keywords characterize the work?
Essential keywords include CAD, Data Exchange, Feature Modelling, Design Intent, Model Tree, Engineering Product Data Exchange, STEP, IGES, Structural Representation, and Interoperability.
Why do exchanged CAD models often lose their features?
According to the author, models lose features because existing exchange formats often focus on static geometry rather than the design history (the "model tree") or the specific "design intent" and procedural logic used by the original CAD system.
What role does the "Model Tree" play in this research?
The model tree is identified as the key component that captures the design sequence and structural relationships; its loss is defined as a primary failure of current data exchange, and the research specifically aims to enable its transfer.
- Quote paper
- Lubomir Krastev (Author), 2002, Framework for a Structure Oriented Exchange of CAD Data, Munich, GRIN Verlag, https://www.grin.com/document/32714
