Principles of CAD

Many books already exist on computer-aided design and manufacture most of which are dedicated to describing the complexities of mathematical modelling and its application to industrial problems. In the experience of the present authors, however, if the subject is to be understood within its true, industrial context it must be taught in relation to the design process. Thus, while this book discusses both modelling and industrial applications, it also tries to provide an insight into design methodology, system selection and usage, and the social relationships that exist within design and manufacturing facilities. The teaching modules which make up the book are the distillation of material used by the authors both for undergraduate courses in CAD at BruneI University, and for seminars given to industrial users. The modules are not intended to be used in isolation, but rather to serve as an introductory survey which will enable students to grasp the broad outlines of the subject. Most aspects ofthe course presented here will need to be supported by further work and reading (see 'Further Reading'). In the authors' own courses much of the geometric and modelling work described in the text is supported by tutorial activities using the university department's commercial and research CAD/CAM systems. These include the Computervision-CADDS4X and Personal Systems.

Section 1 The Design Process.- Module 1.1 The Relationship between Geometry and Function.- Specification of Needs.- Deriving Functions.- Geometric Form.- Geometry-based information.- Module 1.2 The Form of the Design Process.- Interdependency of Design.- Anatomy of Design.- Morphology of Design.- Over-constrained Design.- Under-constrained Design.- Module 1.3 Traditional Drawing Practices.- Communication of Engineering Information.- Drawing Representation by Drafting and CAD.- A Reference for Engineering Information.- Changing Role of the Drawing within CAD.- The Engineering Database.- Module 1.4 The Development of the CAD Industry.- Graphical Displays.- Interactive Drawing.- Styled Surfaces.- Design-based origins of CAD/CAM Systems.- Three-dimesional Modelling.- The Manufacturing Interface.- Current System Availability.- Exercises.- Section 2 System Configuration.- Module 2.1 Workstations.- Vector Display Screens.- Direct-view Storage Screens.- Raster Display Screens.- Special-purpose Facilities.- Cursor Key Input Devices.- Direct Cursor Control Devices.- Direct Pointing Devices.- Tablet and Menu Input Procedures.- Choice of Input Device.- Module 2.2 Computers—Mainframes to Micros.- Time-sharing Facilities.- Mini-computer Turnkey Systems.- Micro-computer Systems.- The Workstation Approach.- Further Changes in Computational Facilities.- Module 2.3 Output Devices.- Pictorial Output.- Terminal Printers and Plotters.- Pen Plotters.- Speed Limitations.- Electrostatic Plotters.- Laser Scanning and Microfilming.- Summary.- Module 2.4 Data Storage.- Management of Data.- Main Design File.- Direct Support Files.- Alternative Design Files.- Personal Files.- Design Approval.- Short-term Storage.- Archiving and Retrieval.- Control of Data.- Module 2.5 Networked Systems.- Independent Workstations.- Network File-handling.- Networks Reflecting the Design Process.- Exercises.- Section 3 Entity Descriptions.- Module 3.1 Points, Lines and Circular Arcs.- Cartesian Coordinates.- Nodes.- Entities.- Node and Entity Lists.- Module 3.2 Basic Geometric Manipulations.- Insertion.- Deletion.- Translation and Rotation.- Move and Copy.- Intersections and Trimming.- Storage and Retrieval.- Module 3.3 Free-form Curves 1.- Explicit and Implicit Functions.- Use of Parameters.- Ferguson Cubics.- Bézier Cubics.- More General Bézier Forms.- Problems of High Degree Curves.- Summary.- Module 3.4 Free-form Curves 2.- Homogeneous Coordinates.- The Bézier Rational Quadratic Form.- B-spline Segments.- B-spline Basis Functions.- An Example.- Some Properties and Local Control.- Module 3.5 Finding Intersections of Free-form Curves.- Iterative Solution of Simultaneous Equations.- Boxes.- Subdivision and the De Casteljau Algorithm.- The Intersection Algorithm.- Summary.- Module 3.6 Surfaces.- Ruled Surfaces.- Bézier and B-spline Patches.- Putting Patches Together.- User Interaction for Surface Creation.- Exercises.- Section 4 View Transformations.- Module 4.1 Two-dimensional Transformations—Pan, Rotate and Zoom.- Zoom.- Pan and Rotate.- Operations on the Node List.- Coordinates for the Display.- Clipping.- Module 4.2 Three-dimensional Transformation Matrices.- View Direction.- Homogeneous Coordinates.- Matrix Transformations.- A Single Form of Transform.- Module 4.3 Axial and Observer Systems.- Line of Sight.- Viewing Rotations.- Observer Coordinates.- Compound Transformations.- Order of Viewing and Display Transformations.- Module 4.4 The Use of Perspective.- The Depth Coordinate.- The Introduction of Perspective.- Matrix Form.- Effects of the Eye Coordinates.- Module 4.5 Multi-view Presentations.- Two-dimensional CAD.- Three-dimensional CAD — Only One Model.- Multiple Views from the Model.- User Interaction with Multiple Views.- Module 4.6 Advanced Viewing Techniques.- Intensity Cueing.- Graphics Processing in the Workstation.- Real-time Transformations.- Stereoscopic Techniques.- Genuine Three Dimensions.- Exercises.- Section 5 Types of CAD Modelling Systems.- Module 5.1 Two-dimensional Drafting Practice.- Orthographic Projection.- Orthogonal Planes.- First and Third Angle Projections.- Standards.- Use of CAD.- Module 5.2 Three-dimensional Wireframe Models.- Problems of Wireframe Representation.- Hidden Line Removal.- Module 5.3 Surface Modelling.- Use of Surface Patches.- Face Lists.- Surfaces Only Where Needed.- Advantages of Surface Modellers.- Module 5.4 Solid Modelling.- Volumetric and Other Properties.- Constructive Solid Geometry.- Boundary Representation.- Comparison of CSG, B-rep and Surface Modelling Approaches.- Speed of Response.- Module 5.5 Display of Solid Models.- Hidden Line and Surface Removal.- Surface Shading.- Need for High Quality Shaded Images.- Exercises.- Section 6 The User Interface.- Module 6.1 User Command Language.- Numeric Input.- Command-driven Programs.- Verb-noun Commands.- Additional Qualifiers.- Command Interpretation.- Module 6.2 Use of Menus.- Menus on the Tablet.- User Configuration of the Menu.- Special Symbols.- Function Boxes.- On-Screen Menus.- Pull-down Menus.- Module 6.3 Graphics Interface Languages.- Graphics Libraries.- Need for Tailoring a CAD System.- Use of Macros of Commands.- Graphics Interface Languages.- Two Examples.- Module 6.4 Use of Parametrics.- Parameters in Design Rules.- Use of the Graphics Interface Language.- Use of the Command Language.- Use of a Journal File.- Summary.- Exercises.- Section 7 System Effectiveness and Organization.- Module 7.1 Information Flow.- Stimulation of Design Activities.- Resource Balance.- Major Resources.- Customer-related Information.- Subcontract-related Information.- Factory output.- Internal Flows.- Downstream Manufacturing Information.- Module 7.2 Establishing Design Needs.- The Drafting Process.- Standards and Codes of Practice.- Social Interaction and Experience.- Assessing Individual Processes.- Establishing Design Needs.- Module 7.3 Identifying Benefits.- Drawing Productivity.- Intitial Savings.- Minimum Staffing Levels.- Downstream Justification.- Product Development Cycle.- Accurate Geometric Description.- Accurate Jigs and Fixtures.- Considering Alternative Designs.- Reduction in Delays.- Other Areas of Benefit.- Individual Justification.- Module 7.4 Training for Operation.- Use of Vendor Training.- Reasons Given for Limiting Training.- Skills Required.- CAD/CAM Awareness.- Training for Simple Interaction.- Full Operator Training.- System Management.- Systems Development.- On-going Training.- Module 7.5 Working Environment.- The Problems.- Air Conditioning and Heating.- Lighting.- Individual Work Areas.- Seating.- Benefits of Good Ergonomics.- Module 7.6 Design and Social Structure.- Need for Planning an Installation.- Processes to be Performed.- Pivotal Activities.- Interacting Factors.- Company Size.- Existing Level of Technology.- Departmental Structure.- Module 7.7 System Management.- Monitoring Use of Correct Procedures.- Using CAD at the Appropriate Time.- Priorities.- Maintaining the System.- System Manager — a Key Company Role.- Exercises.- Section 8 Applications Programs.- Module 8.1 Analysis-centred Applications Programs.- Finite Element Analysis.- Electronic Circuit Analysis.- Kinematic Modelling.- Printed Circuit Board Layout.- Module 8.2 Manufacturing-centred Applications Programs.- Computer-aided Manufacture.- Robotic Assembly.- Mould Design.- Module 8.3 Control-centred Applications Programs.- Expert Systems.- Further Reading.