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- 5. L A S Z L O H O R V AT H • I M R E J . R U D A S — — — — — — ....... Modeling and Problem Solving Techniques for Engineers ,!7IA1C6-accfag!:t;K;k;K;k ISBN 012602250X www.books.elsevier.com Modeling and Problem Solving Techniques for Engineers L A S Z L O H O R V AT H • I M R E J . R U D A S Navigate the world of computer-aided engineering with confidence! Today, the majority of engineers in many varied fields must utilize CAD/CAM systems in their work, but due to the increasing number and sophistication of programs and methods avail- able, no one engineer can possibly be an expert in all of them! This book will help, by offer- ing a detailed and comprehensive survey of all the leading computer-aided engineering meth- ods, effectively providing a map to this sometimes confusing world. It is especially written for design and production engineers practicing in the modern industri- al environment, where design, analysis, manufacturing planning, production planning and computer controlled equipment programming are all governed by CAD/CAM systems. The authors, who are engineering professors as well as IT professionals, clearly explain concepts, approaches, principles, and practical methods in purposefully IT-jargon free language, so that engineers will not get lost in a tangle of acronyms. It provides basic theoretical background and examines the relative value of various competitive computer-aided engineering methods, so that engineers will feel confident in making design tool choices, without having to become specialists in the development issues surrounding each system. Topics covered include: integrated product description based modeling technology; knowl- edge assisted group work of engineers; integrated engineering in worldwide-networked sys- tems; human control of model construction processes; and open architecture of modeling systems. Special emphasis is placed on cutting-edge principles and methods, which will be of outstanding industrial significance over the next few years. Other areas considered are modeling of assembly and kinematics, part modeling, finite element modeling and analysis, construction of curve and surface models, and shape model driven associative tool path planning. Application of the introduced virtual technology is not restricted to only traditional mechanical engineering, but includes all industries where sophisticated mechanical parts are applied in configurable variants of products, such as cars, household appliances, and home electronics. COMPUTER ENGINEERING/ INDUSTRIAL ENGINEERING — — —
- 6. Modeling and Problem Solving Techniques for Engineers
- 8. Modeling and Problem Solving Techniques for Engineers by László Horváth and Imre J. Rudas Amsterdam Boston Heidelberg London New York Oxford Paris San Diego San Francisco Singapore Sydney Tokyo
- 9. Elsevier Academic Press 200 Wheeler Road, 6th Floor, Burlington, MA 01803, USA 525 B Street, Suite 1900, San Diego, California 92101-4495, USA 84 Theobald’s Road, London WC1X 8RR, UK This book is printed on acid-free paper. s 1 Copyright ß 2004, Elsevier Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permissions may be sought directly from Elsevier’s Science & Technology Rights Department in Oxford, UK: phone: (þ44) 1865 843830, fax: (þ44) 1865 853333, e-mail: permissions@elsevier.com.uk. You may also complete your request on-line via the Elsevier homepage (http://elsevier.com), by selecting ‘‘Customer Support’’ and then ‘‘Obtaining Permissions.’’ Library of Congress Cataloging-in-Publication Data British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library ISBN: 0-12-602250-X For all information on all Academic Press publications visit our Web site at www.academicpress.com PRINTED IN THE UNITED STATES OF AMERICA 04 05 06 07 08 09 9 8 7 6 5 4 3 2 1
- 10. Table of Contents Preface ix Introduction xv CHAPTER 1 The Magic World of Virtual Engineering 1.1 The Virtual World for Virtual Engineering 2 1.2 Let Us Go into Virtual 8 1.3 A Great Change in Engineering Activities 13 1.4 The Model Space 19 CHAPTER 2 Activities in Virtual Engineering 2.1 Computer Representations for Shape-centered Engineering 24 2.2 Models of Mechanical Units 29 2.3 Integrated Modeling 42 2.4 Entities 46 2.5 Open Architecture Modeling Systems 52 v
- 11. CHAPTER 3 Computer Representations of Shapes 3.1 Geometric Modeling in a Nutshell 58 3.2 Representation of Geometry 82 CHAPTER 4 Representation of Elementary Shapes 4.1 Models of Elementary Lines and Curves 115 4.2 Models of Elementary Surfaces 116 4.3 Offset Geometric Entities 122 4.4 Elementary Solids 126 CHAPTER 5 Models of Shape-centered Products 5.1 Models of Combined Shapes 145 5.2 Assembly Models 157 5.3 Models of Mechanisms 166 5.4 Definition of Dimensions and Tolerances 172 5.5 Animated Shapes 178 CHAPTER 6 Finite Element and Manufacturing Process Models 6.1 Finite Element Modeling 183 6.2 Manufacturing Process Model 196 CHAPTER 7 Creating Curve and Surface Models in CAD/CAM Systems 7.1 Aspects of Model Creation 224 7.2 Curve Models 229 7.3 Construction of Surface Models 258 vi Table of Contents
- 12. CHAPTER 8 Construction and Relating Solid Part Models in CAD/CAM Systems 8.1 Modeling by Form Features 289 8.2 Construction of Sheet Metal Part Models 298 8.3 Creating Assembly Models 303 CHAPTER 9 Creating Kinematic Models in CAD/CAM Systems 9.1 Creating Joints 317 9.2 Analysis of Kinematic Models 318 Bibliography 319 Index 327 Table of Contents vii
- 14. Preface Engineering design is more than an activity of skilled humans in industry: it is also a cultural mission in both common and technical senses. In traditional engineering, abundant time was available for engineers to merge their activity into national and global cultural environments. By the twentieth century the impact of technology and product development accelerated engineering activities. Technology became the prevailing aspect of engineering and the cultural aspect was overshadowed. In the meantime, despite the continued acceleration of product development, the technology- stimulated development of computering has given a great chance for the reintegration of the technical and cultural aspects of engi- neering by the automation of routine activities. Recently, customer demand driven engineering has forced engineers into considering both the cultural and social aspects of engineering. A new style of engineering has been established, where advanced information and computer technologies are applied to handle product related engineering information in computer systems. Engineering activities are done virtually to the greatest extent possible. A virtual technology has emerged, primarily for design, analysis, manufacturing, and human–computer interaction ix
- 15. purposes. The integrated and coordinated handling of information serves engineering activities from the first idea of a product to the last demand for product related information. Engineering model- ing has become one of the activities that has a substantial effect on the achievements of company objectives such as minimal engineer- ing costs, a short product development cycle, effective handling of the minimal number of product changes, reduced time to introduce new products, minimal cost of developing new products, improved quality of products, and advancements in competitiveness. Several characteristics of the present style of engineering mirror recent enhancements of computer based work of engineers. Digital definition and simulation of products and manufacturing processes, and management of product lifecycle information are the main issues in model based engineering. Modeling is supported by CAD/CAM systems. A CAD/CAM system is configured for a well-defined segment of engineering. Advanced computer tools and engineering processes represent one of its typical functionalities. Mechanical parts are defined by application oriented form features with exact boundary-representation of the solid geometry. Local demands for the application of modeling are fulfilled by custom development of open architecture CAD/CAM systems in third party or company environments where domain and application specific knowledge is available. Proven methods are included for capturing, sharing, and reusing corporate knowledge throughout the entire engineering process. Knowledge embedded in models allows less experienced engineers to solve complex problems in product design, analysis, manufacturing planning, and production related engineering activities. Knowledge based modeling enables companies to capture and deploy their best practices through custom-built applications. This reduces the risk of product failure, production inefficiency, market mismatches, and after-delivery compliance costs. Alternative modeling processes and product variants can be handled. By the use of realistic simulation, com- panies can anticipate behaviors of their future products and manufacturing process operations, evaluate multiple design con- cepts, and create design variants from a common concept. Better x Preface
- 16. understanding of product, production, and market by the applica- tion of advanced analysis and simulation, better and more human culture oriented product design, better utilization of earlier design concepts, and fast response to customer demands are also impor- tant effects. The creating, handling, and control of engineering information in modeling systems help to coordinate managing activities in several departments, in a well-organized concurrent engineering system where engineering activities are done simulta- neously and any activity can start immediately when input infor- mation is made available by other engineering activities. Now, all sizes of businesses are covered. Advanced modeling is not a privi- lege of powerful international companies: it is also accessible to small and medium-sized businesses, especially in global collabora- tion. Integrated modeling resources and models offer a powerful background for industrial engineering. In the 1970s and 1980s, huge numbers of excellent computer methods and programs were conceptualized as potential tools to make advancements in actual problem solving for engineering. Most of them remained a dream because of the available com- puter performance and application technology. By the 1990s, advances in computing performance, computer graphics, software technology, and communication in computer systems produced the necessary computer technology for turning earlier dreams into reality. The result was a rapid take-off of industrially applied virtual technology at the end of the twentieth century. Modeling and model based simulation, together with intelligent computing, facilitate handling of the characteristics and behavior of modeled objects so that advanced models as virtual prototypes replace physical prototypes at evaluations of product design. This book is intended to help practicing engineers to get a high level start in engineering modeling. It is also intended to serve as a textbook for undergraduate and graduate students. It serves master students at the great step between bachelor and master courses. The authors were motivated to assist engineers and students who are not computer application specialists in under- standing modeling. Inspired by virtual engineering technology, Preface xi
- 17. new ideas are created by a new generation of engineers. This is why students must be prepared for modeling. Advanced computer methods and tools are also required for experienced engineers to enhance problem solving. Unfortunately, most experienced engi- neers cannot understand modeling to the extent necessary for its efficient application. They cannot utilize the inherent design power of virtual technology in their work. Consequently, they work in one of the conventional ways or their skills and experience are not utilized in engineering activities. This choice of bad and worse can be avoided at companies if experienced engineers are better assisted in understanding the virtual world of advanced computers. Both engineers and employers are motivated by a great chance for improved personal career and business. Numerous excellent and popular books have been written about engineering modeling for beginners and interested people in the past two decades. At the other end of the offerings, excellent books are available for people who are specialists in the develop- ment of modeling procedures and computer aided engineering sys- tems. There is a wide gap between these two important purposes in the recent and presently available choice of books in computer aided engineering. Experienced engineers fail in hunting for books that would help them in understanding modeling and in its practical application for their real world industrial engineering tasks. High level books are not needed with deep explanations of ideas and methods for engineers who just would like to understand and utilize modeling methods and tools and who would not like to be specialists in the theoretical and practical development of modeling and related systems. This textbook is intended to be a contribution to fill the gap. One of the main emphases in this book is on knowledge assisted group work of engineers in integrated, application area oriented, and worldwide networked engineering modeling systems. This style of computer aided engineering utilizes the main results of the development efforts in engineering applications of computer systems during the 1990s. Readers of this book will find text direc- ted toward users of advanced modeling offered by existing, widely xii Preface
- 18. applied, well-accepted, and leading industrial CAD/CAM systems. At the same time, this book does not intend to compete with but refers to excellent books on general CAD/CAM concepts, and on deep mathematical analysis of geometrical models and intelligent computing approaches. Because engineering modeling is so dynamic, the content of this book focuses on up-to-date modeling and cannot devote too much text to the historical pioneering mod- eling methods from the 1970s and 1980s that are not necessary to understand present modeling. Preface xiii
- 20. Introduction Comprehensive application software systems serve virtual engi- neering activities in industrial practice. These systems are called traditionally CAD/CAM (computer aided design/computer aided machining (or manufacture)). They apply advanced computer modeling. The name CAD/CAM refers to their primary applica- tion in the past: geometric model based planning of computer controlled machining. CAD/CAM has developed from several iso- lated or interfaced computer aided engineering activities to inte- grated virtual engineering in local, wide area, or global computer systems. Anyway, the primary purpose of virtual engineering is high level and effective assistance for engineering decisions in an increasingly competitive environment. Engineering design tasks can be considered as a chain of engineering decisions. An engi- neering decision requires information about the complexity of engineering objects, about the effects of earlier decisions on the actual decision, and about the effects of the actual decision on the affected engineering objects. Continuous product development to withstand competition has changed the style of engineering decision making in recent years. Frequent revision of decisions is required by changed or new customer demand, new developments, xv
- 21. and changed company strategy. Decisions often reveal the need for revision of some earlier decisions. Engineering decisions need assis- tance from powerful computer modeling enhanced by intelligent computing where sophisticated model descriptions of objects and their relationships and knowledge based reasoning are available. The growing importance and wide application of virtual engineer- ing need a deep knowledge of modeling by engineers practicing in industry and applying modeling or changing it in the future. Advanced CAD/CAM systems support the coexistence of computer based modeling and engineering design. Not so long ago the prevailing medium for the communication of engineers was engineering drawing in its copied form of the blueprint. By the 1950s and 1960s engineering tasks became increasingly complex in their concepts, details, and considerations. Engineers had won battles in ideas and innovations; however, they had lost battles in information and information processing. Moreover, engineers were under constant pressure to make innovation cycles shorter and shorter. At the same time, ideas and innovative solutions demanded more and more data be described and processed. In the early 1950s the application of modeling became unavoidable. Intricate shapes emerged on parts to be machined by automatically controlled machine tools. They could not be described by conventional engi- neering drawings and blueprints. The only way was mathematical description of the shape and application of this information for the calculation of cutting tool paths. This is considered as the starting point of virtual engineering. Shape and tool path modeling were followed by modeling of other engineering objects as complete parts, assemblies, kinematics, finite elements, etc. Models of mechanical parts have moved into applications far beyond tool path generation. Now, a huge number of analysis tools rely on sophisticated models of analyzed engineering objects, their envir- onments, and simulation processes. The real world of engineer- ing is simulated in an advanced and comprehensive virtual engineering environment. Models as advanced descriptions of engineering objects represent much more than new media that replace blueprints and computer generated drawings. The fantastic xvi Introduction
- 22. development of communication in the past decade has had a strong effect on virtual engineering. Models are exchanged between CAD/ CAM systems in a worldwide integrated engineering environment. At the same time, centralized databases provide services for a lot of engineering workstations in different geographical sites. Remote modeling systems are operated by humans using special browser surfaces opened to the Internet. The utmost purpose of engineering modeling is the product model that covers all the information demanded by all possible engineering activities during the product lifecycle from the first sketch by the designer to recycling. This book covers concepts, approaches, principles, and prac- tical methods for an area of integrated engineering activities where mechanical parts and their structures are conceptualized, designed, analyzed, and planned and programmed for computer controlled manufacturing. Application of the introduced virtual technology is not restricted to traditional mechanical engineering but includes all industries where sophisticated mechanical parts are applied in pro- ducts, such as cars, household appliances, home electronics, sports equipment, furniture, watches, toys, etc. The design, analysis, and manufacturing of shapes and methods for the production of such items are central because they still constitute the majority of engi- neering related computer applications at industrial companies. Because the covered area is so large, special emphasis is placed on principles and methods of outstanding industrial significance anticipated for the next few years. When topics and issues were selected, advanced and proven CAD/CAM systems from industrial practice were considered. Chapter 1 presents a quick glance at the essential concepts of the magic world of computer aided engineering. Chapter 2 intro- duces computer model based engineering activities with a basic package of related knowledge. Chapters 3–6 explain the basic understanding of models for the description of engineering objects. Chapters 7–9 give detailed discussion about computing methods for the creation of model entities that have importance in the pre- sent and future practice of modeling, analysis and manufacturing planning. Introduction xvii
- 24. C H A P T E R The Magic World of Virtual Engineering An engineer is sitting in front of a screen, points to symbols and lines, and types some data. The computer shows a mechanical part in three dimensions allowing the engineer to develop or modify its model or to include it in an assembly structure. All of these activ- ities use the same set of simple interactive functions. Seeing this style of engineering design, one might consider the work of an engi- neer as easy but not very exciting. Others seeing the result may con- sider the engineer as a magician or think of engineering as a simple handling of magic design automata. The truth is that human knowl- edge, skill, and experience are utilized in an interactive communi- cation with a computer system that is capable of creating a model description by utilizing the knowledge, skill, and experience of the engineers who created the computer and the modeling system. As stated in the Introduction, the application of computers by engineers started with the challenging task of the design, manufac- turing planning, and computer controlled manufacturing of intri- cate surfaces, mainly for aerodynamic purposes. The first widely applied computer assistance for engineering served drawing, calcu- lations, data storage, and documentation printing activities during 1
- 25. the 1960s and 1970s. The next milestone was wide acceptance of computer models in the 1980s. The modeling tools1 in industrially applied CAD/CAM systems of the 1970s and 1980s executed direct commands from engineers, mainly for creating line, surface, etc., of geometric model entities. In the 1990s, engineering oriented shape modeling by parametric application features was introduced. Modeling methods also featured in integrated assembly, analysis, and manufacturing planning. In recent years, intelligent features have been given to advanced modeling. Object oriented and knowl- edge supported modeling tools, among others, analyze the behavior of modeled objects, propose alternative solutions, navi- gate interactive model creation, and prevent obviously erroneous results. To do this, sophisticated, integrated, knowledge based,2 and comprehensive sets of modeling tools and models are available for engineers. A new scene of engineering has emerged in computer systems. It is called the virtual world3 and it gives a new and enhanced quality to engineering. 1.1 The Virtual World for Virtual Engineering The virtual world is featured by product and process centered mod- eling in contrast to the task orientation of earlier modeling. Although product models are capable of representing any product related information, they are configured according to the demands of their applications. Despite their potential complexity, product models can range from the description of several modeled objects to the representation of very complex and interrelated structures of various engineering objects. Advanced models act as virtual 1 The phrase ‘‘modeling tool’’ is applied to a procedure that serves a well-defined modeling purpose. 2 Knowledge based modeling utilizes modeling tools that are capable of doing some engineering activities automatically, using built-in knowledge. 3 The word ‘‘virtual’’ refers to a computer resident world. 2 CHAPTER 1 The Magic World of Virtual Engineering
- 26. prototypes. Sophisticated modeling and analysis techniques make it possible to move a great deal of prototype development from expensive machine shops into virtual worlds. Engineers are still the most important participants of virtual worlds. They conduct orchestras of hundreds of modeling procedures through effective graphical human–computer interface actions (HCIs). Engineering objects in the virtual world are described by using methods from virtual technologies such as computer aided modeling, intelligent computing, simulation, data management, multimedia assisted computer graphics, and human–computer interaction. The behavior of engineering objects is assessed under various real-world situations. The dynamic nature of the develop- ment of virtual technologies is the result of their applications in dynamically developing areas of business. Questions concerning the real content of the virtual world for industrial practice will be answered in the subsequent chapters of this text. The virtual world for engineering (Figure 1-1) is constituted of interrelated descriptions of engineering objects as parts, assemblies, kinematics, analysis results, manufacturing processes, production Figure 1-1 Virtual world. 1.1 The Virtual World for Virtual Engineering 3
- 27. equipment, manufacturing tools, instruments, etc. Elements of the descriptions are entities and their attributes. The structure of the descriptions is defined as the relationships between entities, or their attributes. Operated by humans interacting with computer proce- dures, the virtual world communicates with controlled equipment, other computer systems, and other virtual worlds. Production by automatic equipment is controlled by direct application of informa- tion from the virtual world. An implementation of a virtual world is considered as a special computer system. The following is a simple sequence of activities for creating a virtual world as an example from everyday modeling. A part is conceptualized as a set of shape objects. A shape object is described as a form feature entity. It is related to geometric model entities in its representation. Relationships are defined between form features and their dimension attributes. A human controls part model creation procedures by inter- active communication. The model is communicated with a World Wide Web (WWW) site where it is visualized. The purpose of the part model is computer controlled man- ufacturing of a computer numerical controlled (CNC) machine tool. Geometric model entities and their relationships are illus- trated by the example of Figure 1-2. A simple assembly consists of Part 1 and Part 2. During the creation of a model of Part 2, surface entities FS1 and FS2 are related by their common boundary line CE1. Parts are related using relationships referring to geo- metric entities. The contact relationship RC1 defines contact between surfaces FS2 and FS3. A set of geometric entities is avail- able in each modeling system. Construction of a virtual world in the course of engineering activities starts from ideas about the system to be modeled and the engineering objects to be included in it. Typically, objects and their structures are defined. The basic approach to construction may be 4 CHAPTER 1 The Magic World of Virtual Engineering
- 28. top-down, bottom-up, or mixed. Following a pure top-down approach, modeling starts with the definition of a structure, and then objects are created for elements of the structure. Following a pure bottom-up approach, first objects are created and then their structure is defined. A mixed approach represents everyday prac- tice where some objects are available at the start, then structure is defined, and finally the remaining objects are created according to the structure. Examples for predefined elements can be units of computers, integrated circuits, fasteners, bearings, and other standard elements of mechanical and other engineering sys- tems. Typical structures can be predefined, stored, retrieved, and adapted for individual tasks. This text discusses the virtual world where the main charac- teristics of dominating objects are shape related and other objects can be characterized in connection with shape-centered objects. Because real-world shapes are three-dimensional, their computer descriptions should be three-dimensional (3D) for the virtual world. Shapes are described in a space called model space. In Figure 1-3, an object is positioned in a model space. Non-shape features of an object such as stress (ST) and temperature (TE) at a given point of its volume and properties of a surface in Figure 1-2 Relating entities. 1.1 The Virtual World for Virtual Engineering 5
- 29. its boundary are mapped to appropriate shape model entities as attributes. One of the exceptions to shape based engineering objects is an electronic system where active and passive circuit elements are connected by routes but not in a dimensioned space. However, this model of an electronic system is completed with shape models of printed circuit board arrangements and programming of automatic assembly and inspection equipment. At automatic assembly, circuit elements R31, R33, and C33 should be positioned relative to the printed circuit board (Figure 1-4). At automatic inspection, a camera image of the ready assembled printed circuit board is compared with a master image to reveal parts omitted during assembly. Figure 1-5 outlines the description of a mechanical part in a virtual world. A virtual space with dimensions of the real space accommodates objects. The object in this example is a part, one of the product related engineering objects. Shape, position, mate- rial, surface properties, outside relationships, and behavior of the object are described. Outside relationships include connections to other parts such as contact of surfaces, possibilities of movements relative to other parts such as linear movement along a slide, and restraints such as a pin. Behaviors of a part are defined by stress, Figure 1-3 Shape based description of engineering objects. 6 CHAPTER 1 The Magic World of Virtual Engineering
- 30. Figure 1-4 Modeling of electronic circuits. Figure 1-5 Description of an object in the virtual world. 1.1 The Virtual World for Virtual Engineering 7
- 31. strain, temperature, cost, etc., at different effects of the outside world on the object such as loads, etc. The effects of the outside world are modeled to know the behavior of the object. In addition, the virtual world includes production system objects and their relations to product objects. Finally, customers are in connection with production through marketing, demand forecast, and sales services. Humans are involved in the design, manufacturing, and application of products. Engineering is only one but perhaps the largest application area of virtual worlds. Other important application areas are med- ical treatments, flight simulators, and highway traffic control sys- tems, for example. Entertainment applications include live shows, movie and television productions, and theater performances. In addition, virtual arts are emerging. 1.2 Let Us Go into Virtual Competition forces industry to make fast and frequent changes of product design. We can say that the prototype development stage has expanded to the entire life of the product. Times allowed by the market for product changes are too short for expensive and time- consuming physical product prototyping. Creating new or altered physical prototypes is impossible within the available time frame: throughput times and the related manufacturing costs are un- realistic. Conventional physical prototyping cannot cope with the present requirements for product development. The only solution is to move prototyping into the virtual world to the greatest extent. In recent years, companies have converted most of their conven- tional design and prototyping activities for advanced products into virtual technology. Analyses of engineering objects using their cor- rect and sophisticated models are robust enough to replace most physical prototyping. Moreover, the virtual prototype describes much more information about a product than a conventional physical prototype. However, a suitable virtual environment is also expensive, so cost and value analyses are needed to assist 8 CHAPTER 1 The Magic World of Virtual Engineering
- 32. decisions about prototyping technology. Analyses of technical and financial reasons for virtual and physical prototyping generally propose the application of a mixture of them. Changes of the human mind, imagination, and fantasy as a result of creativity as well as fast responses to changes in market, finance, or production conditions change the product through integrated virtual engi- neering activities. The results and experiences from physical pro- totyping are accumulated in virtual prototyping systems and applied to enhance virtual prototyping and to decrease the demand for physical prototyping of similar engineering tasks. It is a standard capability of recent industrial engineering systems to create products from ideas in an automatic, but human governed way. Highly automated engineering and produc- tion require integration of all the actual engineering activities with the related manufacturing process. Integration assumes modeling procedures that communicate a mutual understanding of input and output information, and use the same database and the same user interface (Figure 1-6). Two virtual related concepts in manufacturing are virtual man- ufacturing and virtual controlled manufacturing. Virtual manufac- turing is an assessment of the product and its manufacturing process without any physical manufacturing or measurements. Virtual controlled manufacturing is the control of real-world man- ufacturing equipment by use of information from the virtual world. Figure 1-7 gives a simplified explanation of this scenario. Humans communicate their intents and concepts with a computer system. Procedures translate these concepts into the virtual world, analyze the models, translate the models into control programs and control production equipment. The virtual prototype4 is created and man- ufactured virtually by appropriate analysis of the manufacturability of modeled objects. Finally, virtually controlled manufacturing is applied to create physical prototypes of modeled objects using computer controlled production equipment. 4 The virtual prototype is sometimes cited as the virtual product. 1.2 Let Us Go into Virtual 9
- 33. Figure 1-6 Integration of engineering activities. Figure 1-7 Manufacturing and the virtual world. 10 CHAPTER 1 The Magic World of Virtual Engineering
- 34. Concepts of visual reality and virtual reality are sometimes confused. Virtual reality is a sophisticated computer description of real-world conditions in the virtual world. It cannot commu- nicate directly with humans because it has been developed for the purpose of communication between computer procedures in the form of data structures. Visual reality is the tool that converts these data structures into graphic or other understandable forms in order to visualize computer descriptions for humans. Concepts and intents originate in humans in visual form: visual reality is the tool to translate them into a form understandable by computer procedures. Two-way interactive graphics-based communication is applied. Virtual and visual realities are key techniques for the representation of engineering objects and communication of represented information between humans and procedures in virtual worlds. Figure 1-8 shows the human–computer–human communica- tion chain during engineering modeling. The visual concepts of engineers are translated into model data sets and vice versa. This is why visual computing is one of the main areas of development in computer technology. Data oriented virtual worlds are visu- alized by use of impressive computer graphic tools. Engineers Figure 1-8 Visual reality assisted virtual reality. 1.2 Let Us Go into Virtual 11
- 35. communicate the model-creating procedures by the definition of 3D objects within a construction area on the screen called a view port. Model application procedures visualize the model for humans by 3D reconstruction of modeled objects in the view port. Engineering modeling is highly shape and position intensive. The shape of an engineering object is described mathematically in a model space characterized by a coordinate system (Figure 1-9). Dimension driven modeling was developed during the 1980s for the purpose of shape definition by type and dimensions as well as by dimension definitions on existing shapes. Dimensions may con- trol shapes. Shapes are positioned and oriented in the model space. The position and orientation of a modeled object in the space are defined absolutely or in relation to other modeled objects. Figure 1-9 shows three basic position definitions. The position can be defined in space by coordinates of a characteristic point such as P1 of the Figure 1-9 Shape and position information in models. 12 CHAPTER 1 The Magic World of Virtual Engineering
- 36. modeled object. One of the available position definitions for placing a part in an assembly uses three pairs of planes. Three planes of the other modeled object are in contact with the appro- priate planes of the current modeled object. The third positioning is of the cutting tool in relation to the actual machined surface of the modeled part. 1.3 A Great Change in Engineering Activities The introduction of electronic drawing based computer aided engi- neering signified a great change in engineering activities during the 1960s. No more drawings, blueprints, stacks of books, or finding solutions from old drawings and documents were necessary. No more tedious and time-consuming manual drawing with many repe- titions of the same drawing elements, such as screws, was needed. The introduction of modeling technologies was the next dramatic change in engineering. No more drawings are necessary on paper sheets or screens that accept crazy designs without any reaction. Instead, there is a magic screen with a human governed virtual world behind it. Regiments of computer procedures are ready to fulfill the wishes of engineers. However, wishes must be suitable for processing by the appropriate procedures. Procedures check and sometimes do not accept human decisions on the basis of the intent of the engineers who developed and configured the procedures. An engineer who is not able to understand the computer procedures or cannot interpret actual problems with those procedures is helpless. Engineers often prefer less advanced procedures because they allow creation of models of simpler and even incorrect engineering objects. As a consequence, engineers sometimes are susceptible to accepting less advanced computer procedures and blaming ones that are more advanced but hard to understand for less experienced engi- neers. However, a product intended to compete successfully must be advanced under any circumstances. Similarly to other magic worlds, the virtual world does not work without magicians. 1.3 A Great Change in Engineering Activities 13
- 37. The capabilities of the traditional means of putting ideas on paper manually, on drawing boards using the communication tool of engineering drawing, are summarized in Figure 1-10. Drawings are stored in the form of paper sheets. Archives are hard to handle and demand expensive storage. Documents are copied from paper to paper, traditionally in the form of blueprints. Templates of drawing elements such as circles, ellipses, rectangles, contours of a screw or nut, etc., can be repeated many times. Modifications for the correction or improvement of drawings are done by physical erasing, overwriting, etc. Documents are edited manually or by conventional printing technology. Modified or similar parts need separate drawings for elaboration. The only purpose of drawings is that of communication between humans. Figure 1-10 Manual drawing. 14 CHAPTER 1 The Magic World of Virtual Engineering
- 38. The change to drawing on computer by the use of draw- ing software resulted in a tremendous saving of human work. Drawings are edited on screen by interactive graphics and all modifications are as simple as redefining drawing elements (Figure 1-11). Repeated elements, drawing details, and complete drawings are created, combined, stored, and reused electronically. Plotters and printers produce hard copies. Drawings are visualized on screen. The handling of large and complicated drawings is made easier by zoom and pan functions. Hyperlinks can be defined to any other documents accessible on the Internet. Drawing files can be placed in folders of file systems of operating systems or in data- bases. Special editing programs produce relevant documentation. Figure 1-11 Drawing based computer aided engineering. 1.3 A Great Change in Engineering Activities 15
- 39. Electronic documentation utilizes multimedia. Drawing files are exchanged between different drawing systems in one of the stan- dard formats, or converted between formats of different drawing systems. Translators are available for data conversion between different drawing file formats as building elements of CAD/ CAM systems. Electronic drawing utilizes the conventional symbols of engineering drawing so that it is an excellent commu- nication medium between humans. It is not suitable for commu- nication between modeling procedures, although simple contour information can be extracted for additional processing. Making models of parts, for example, can use contours extracted from electronic drawings. When computer based drawing methods were implemented at industrial companies, paper based drawings were captured in com- puter systems and converted to electronic form (Figure 1-12). This was tedious work so creating new drawings often proved the better solution. Electronic drawings and their hard copies are created Figure 1-12 Conversion between drawings and models. 16 CHAPTER 1 The Magic World of Virtual Engineering
- 40. primarily for people outside of computer systems, for example those in conventional manufacturing, by manually operated machine tools and manual mechanical and electronic assembly. Let us take the first step towards becoming a magician by understanding the world behind the screen of interactive modeling (Figure 1-13). A human develops an idea about the forthcoming object to be modeled, selects appropriate model entity creation procedures, gives values for parameters of procedures, then the procedure creates and combines model entities. Parameters in this context are inputs of entity creation procedures and control opera- tion of these procedures according to the actual model creation task and human intent. Navigators offer suitable values of actual parameters for selection. Model entity data sets are stored in the model data pool temporarily, during the modeling session, and then they are stored in the database as results of the modeling session. Abandoned variants, sketches, etc., are discarded or saved in a separate place for later retrieval and use in other, similar tasks. Model files are exchanged between modeling systems in the original format, in the format of another system, or in one of the standard neutral formats. Except for the first case, translation (conversion) of model data between different formats is necessary. Translation into a neutral format is followed by a second transla- tion into the format understandable by the receiving system. Models are created to facilitate communication between modeling procedures. Humans understand the model during its creation and modification through the interactive graphics user interface. Advanced visualization associated with easy to use prototype mod- eling procedures is often called a digital mock-up. Traditionally, realistic visualization by interactive graphics user interfaces was not a primary objective because of its relatively high demand for computing performance. In recent years, the application of power- ful graphical processors in computer systems has brought a demand for enhanced quality of visualization. Anyway, modeling procedures display on the screen only the information necessary for the actual human interaction. Too much, irrelevant, or badly organized information makes the screen chaotic. 1.3 A Great Change in Engineering Activities 17
- 41. Figure 1-13 Modeling. 18 CHAPTER 1 The Magic World of Virtual Engineering
- 42. 1.4 The Model Space Model descriptions of shape based engineering objects are created in model spaces. A model space, also called a pool (Figure 1-14), is a dedicated temporary data storage that is active during model- ing sessions. The engineer constructs a model using real dimen- sions of the modeled objects. Any position within the model space is defined by the x, y, z model coordinate system, which is a Cartesian type global coordinate system. The model coordinate system is sometimes called a world coordinate system referring to the world of modeling which is defined by the actual model space. For comfortable position and dimension definition, engineers define local coordinate systems on modeled objects or at other appropriate positions in the model space. In Figure 1-14, a local coordinate system (xL, yL, zL) is applied for easy construction of the part model starting from the upper face of the part. Coordinates defined in a local coordinate system are automatically transformed into coordinates in the model coordinate system. Figure 1-14 Model space. 1.4 The Model Space 19
- 43. Objects are reoriented and repositioned in the model space using simple transformations such as translation, rotation, and their combinations. In Figure 1-14 point P is defined by x, y, and z global coordinates. Following this, P is translated to point P0 and the object is rotated in two steps around the y and z axes of the model coordinate system. If a series of transformations of an object is time programmed, the object is animated. Engineers control modeling procedures. They need visualiza- tion of any shape related information of the model under construc- tion, at any time. Communication and interaction between humans and computer procedures (HCI) use a graphical user interface (GUI). Significant computer resources are devoted to interactive vector graphics that visualize shape model representations by graphical entities. 3D objects are projected from the model space to an appropriately positioned two-dimensional (2D) screen area. Elementary graphical entities are lines (vectors), polylines (open and closed chains of vectors), and filled-in surface areas (Figure 1-15). Advanced graphics handle higher-level geometric entities such as curves, surfaces, and solids. During modeling sessions, visualization serves interactions. It concentrates on edges and other characteristic lines of modeled objects (Figure 1-15a). Contour lines of the selected and actual objects are highlighted. Hidden edges often must be visible to allow selection by a point- ing device, as in Figure 1-15a. When hidden edges disturb the clear picture of the object, they can be made invisible (Figure 1-15b). When realistic visualization of an object is needed, its filled surfaces are made visible. Appearance of a surface depends on its color, material properties, and illumination. Illumination of objects in the model space is provided by light source model entities. Figure 1-15c shows uniform color and light intensity on all points of each surface. To achieve a more realistic visualization, the surface must be divided into small areas to show changes of light intensity and color along the surface. The viewpoint of an engineer is often changed during model creation sessions depending on the actual region of the object under work or analysis. In Figure 1-15d, the viewpoint has been 20 CHAPTER 1 The Magic World of Virtual Engineering
- 44. changed to bring surface A to the foreground. A pointing device such as a mouse is used to grip and rotate objects on the screen. This action changes the actual viewpoint of the engineer, but does not change the position and orientation of the object in the model space because the model space rotates with the object. Figure 1-15 Visualization of the model space. 1.4 The Model Space 21
- 46. C H A P T E R Activities in Virtual Engineering The purpose of this chapter is to give an insight into engineering modeling activities by step-by-step explanation, in accordance with emphases in present industrial practice. Basic concepts are explained to prepare readers for Chapters 3–9 that discuss areas of modeling in detail. Computer modeling intensive engineering is applied in a new industrial environment where configurable variants of products are designed, analyzed, manufacturing planned, and production planned and manufactured using leading information and compu- ter technology. Products have changed from heavy and relatively simple mechanical and electric structures to complex mechatronics where styled shapes are accompanied by well-engineered functional elements. Modeling tools are utilized in the continuous, market- demanded improvement of product and production related capabilities. One of the possible groupings of engineering and related com- pany activities is shown in Figure 2-1. The purpose of this grouping is to introduce virtual engineering by the main application areas at industrial companies. Group No. 1 involves engineering activities in 23
- 47. the strict sense of the word. Design of the product is assisted by testing and analysis as well as costing. Product design is done con- currently with manufacturing planning. Manufacturing plans and orders are processed into production plans and schedules by pro- duction planning. Production is controlled by use of these produc- tion plans and schedules. Automatic production equipment is controlled by execution of control programs downloaded into machine shops according to production plans and schedules. Market related activities (Group No. 2) are marketing, distribution of pro- ducts, sales activities, and customer services. Other engineering related activities (Group No. 3) are accounting, financing, environ- mental engineering, and company management. This book focuses on activities bold typed in the Group No. 1 (Figure 2-1). 2.1 Computer Representations for Shape-centered Engineering Shape-centered design, analysis, and manufacturing planning rely on shape description of parts as engineering objects. Shapes are Figure 2-1 Engineering and related company activities. 24 CHAPTER 2 Activities in Virtual Engineering
- 48. organized into structures. Non-shape information is mapped to these structures and the shape descriptions. The shape model is constructed in the model space by the definition of elementary shapes such as contours, elementary surfaces, solid primitives, and form features. Elementary shapes are constructed by a set of lines, curves, and surfaces organized by topological structure. Curves and surfaces are described by mathematical functions. Elementary shapes are combined into complex shapes of parts. Animation is applied to move the resultant shape in the model space according to a time-scheduled program. Contacts and other relationships are defined between parts to describe the rela- tion of parts in assemblies. Finally, relative movements between parts are described by kinematics. The above outlined description of a mechanical system is completed by finite element modeling for the purpose of understanding the effects of loads and restraints on parts, such as stress, strain, and temperature. A mesh of finite elements can be created on the surface or in the volume of a part. Characteristics of part surfaces that affect appearance are also described in the model and are applied by computer graphics as realistic visualization of engineering objects. Figure 2-2 gives a survey of shape-centered models of a mechanical system. Objects O1, O2, and O3 are combined into complex shape O4. O4, O5, and O6 constitute an assembly. C1 in O2 is described as a parametric curve. Parts are in contact at their flat surfaces. O5 is allowed to move relative to O4 along curve C2. Similarly, O6 is allowed to move relative to O4 along line L1. Contacts of the flat surface pairs are not broken during allowed movements. A sequence of three positions of O4 in the model space is described in time by Frames 1–3. Each frame is a discrete posi- tion of the animated object at a given time. The appearance of surfaces of O6 is shown by shading. The virtual world that is established by model based engineer- ing is in close connection with the designed, stored, visualized, and documented worlds (Figure 2-3). The designed world is the phys- ical world to be modeled. Modeling experts sometimes should remember that the final purpose of engineering activities is to 2.1 Computer Representations for Shape-centered Engineering 25
- 49. Figure 2-2 Basic model representations of shape-centered engineering objects. 26 CHAPTER 2 Activities in Virtual Engineering
- 50. Figure 2-3 The scenario of model based design. 2.1 Computer Representations for Shape-centered Engineering 27
- 51. produce a physical world. Data sets generated during modeling are stored and handled for optimal retrieval and utilization of compu- ter resources. One of the main differences between the application of the modeled and stored worlds is that engineers must under- stand the logic of modeling, but the logic of data handling is the competence of computer system managers. Product data manage- ment (PDM) focuses on product structures for variants and hand- ling models in environments where models are created by several different modeling systems in the data organization for a product. The visualized world is for communications and interactions with engineers and applies efficient interactive graphics. Beware of a fantastic visualized world with a poor modeling background! Paper based and electronic documents are needed for both official purposes and the personal use of engineers. Visualization is in direct connection with modeling procedures and modeling is impossible without it while documents, electronic or tradi- tional paper based, are used without any connection to modeling procedures. The designed world includes product and production related engineering objects. Shapes, parts, mechanisms, and materials con- stitute products. The designed world also involves manufacturing and production processes as well as equipment and tools applied to the manufacturing of parts. The designed world is described in computer models. Design is product and production oriented while modeling is computer methodology oriented. In early model based design it was hard to harmonize the mathematical and computing oriented modeling with engineering oriented pro- duct design. This is why application orientation gained great emphasis in the development of modeling during the late 1980s and 1990s. The harmony of the designed and modeled worlds is a recent result of the development of model based engineering. Designs are represented in computers according to the communi- cated intent of design engineers. The designed worlds in the mind of the engineer and the modeled world behind the screen must be harmonized. One of the main purposes of this text is to assist this human related process. The main components of the virtual 28 CHAPTER 2 Activities in Virtual Engineering
- 52. world are given below, as they are grouped and interconnected in Figure 2-3. 2.2 Models of Mechanical Units The term mechanical unit relates to any units that contain parts placed in assemblies and, where applicable, allow movements between pairs of parts with a given degree of freedom. Mechanical units are required in all machines, instruments, cars, domestic appliances, home entertainment devices, etc. The model- ing of mechanical units is applied in the engineering and produc- tion of most industrial products and production equipment as well as in devices for the manufacture of other products. For example, the same geometry is applied to describe curves in car bodies and in tools for making shoes. Although several other geometric model representations pre- vailed in the earlier stages of the development of modeling, the boundary representation became the prevailing shape of modeling in engineering during the late 1980s and 1990s. The boundary geometric model representation uses topology and geometry for the description of shapes and consists of topological and geometrical entities. On the right of Figure 2-4, the shape of a part is visualized. Any point and curve can be computed in the model coordinate system using the mathematical description of the shape. The shape in this example is covered by flat surfaces; it does not contain any curved surfaces or curves on its boundary. Lines and flat surfaces constitute a complete closed boundary of the body. The shape model is based on the principle of boundary representation with surfaces covering the shape and lines at the intersection of surfaces. The analysis of the effect of the change of a geometric entity on other geometric entities needs information about the geometric entities adjoining it. In other words, the model must include infor- mation about connecting curves and surfaces. This information is carried by topological entities of the boundary representation. 2.2 Models of Mechanical Units 29
- 53. Individually described point, curve, and surface geometrical enti- ties are mapped to vertex, edge, and face topological entities, respectively. In Figure 2-4, lines L1–L4, enclosing the surface S1, are mapped to edges E1–E4, respectively. Surface S1 is mapped to face F1. Face F1 is connected to the closed loop of edges LO1. An edge is connected to other edges by vertex topological entities at its ends. A complete outside or inside boundary of a body is called a shell. A shell is a closed and consistent structure of faces, edges, and vertices. If material is defined inside a shell or between shells, the resultant shape model is a solid representation. Some shapes can be unambiguously defined by lines and curves mapped to topological edges. This makes it possible to work with a reduced set of topological and geometrical entities in wireframe models. The reduced set includes point and curve (or line) geometric, and vertex and edge topological entities. Seeing the boundary of a body on the screen with surfaces and their intersection lines, an engineer understands the shape easily. This is not true for computer procedures because these can under- stand and process only predefined data placed in predefined struc- tures. The consequence of any changes of a surface or line is the change of several lines and surfaces in its neighborhood. Figure 2-5 Figure 2-4 Boundary representation of the shape of a part. 30 CHAPTER 2 Activities in Virtual Engineering
- 54. shows two different situations. In Figure 2-5a, change of length of the straight line L1 to L0 1 results in a change of the dimension or position of lines L2 and L3 to L0 2 and L0 3 and flat surfaces S1–S4 to S0 1S0 4, respectively. All geometric entities remain linear. Sometimes construction of the part starts with a simple outline shape then the final shape is created by a sequence of changes of linear entities to curved entities. In Figure 2-5b, the change of line L1 to spatial curve L0 1 changes flat surfaces S1 and S2 to curved surfaces S0 1 and S0 2, respectively. Mechanical parts are defined by dimensions placed in the shape model too. Characteristic dimensions of shapes are used as parameters of entity creation procedures. Dimensions can be also defined on a shape, after its creation, between arbitrary points. Dimensional parameters of a shape or different shapes can be Figure 2-5 Effect of modification of a line mapped to a topological edge. 2.2 Models of Mechanical Units 31
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