Computer Aided Drafting & Design. Computer-aided draughting & design

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1 LECTURE #5 Computer Aided Drafting & Design Computer-aided draughting & design Background of CADD Two-dimensional draughting Three-dimensional draughting Software selection CADD functionality Computer graphics Coordinate systems Geometry transformation Graphical kernel system Model display Standards for CAD data exchange 1

2 Computer aided environment CADD systems provides 3D models for these purposes and generate 2D drawing for manufacturing; checking for interference between parts on an assembly; calculations of surface area and mass properties; Stress analysis on components are carried out by the use of numerical methods such as FEA and BEA. Technology Advantage of CAD In 1960 s Mechanism design satisfying several geometric constraints Design parameter optimization Simple 2-D graphics In 1970 s Wireframe modeling Free-form surface modeling mainframe computers Late 1970 s Solid modeling Early 1980 s Turn-key CAD systems CAD/CAM integration Mechanical feature recognition from a CAD database 2

3 Technology Advantage of CAD Middle 1980 s Feature-based CAD system mini and macro computers Parametric design PC s & Turnkey systems (Pro/ENGINEER products) Late 1980 s Design for manufacturing Design for automated assembly Early 1990 s Concurrent engineering design Integrated design, analysis and optimization Present Integrated design, analysis and optimization Virtual-prototyping and automated design optimization Internet based design automation Direct modeling In 1963, Sketchpad in MIT computer program written by Ivan Sutherland Sketchpad Lincoln TX-2 The first computer aided drawing system introduced by IBM. 3

4 Sketchpad the ancestor of modern computer-aided drafting a major breakthrough in the development of computer graphics in general. computer graphics be utilized for artistic and technical purposes a novel method of human-computer interaction. utilize a complete graphical user interface. used an x-y point plotter display as well as the light pen. Sketchpad 4

5 Sketchpad organized its geometric data pioneered the use of "objects" and "instances" in computing and pointed forward to object oriented programming. ran jobs in batch job mode only, using punch cards or magnetic tape. COMPUTER GRAPHICS 5

6 What is engineering graphics is a visual means to develop ideas and convey designs in a technical format. is the dominant means to communication among engineers in industry. Several of the topics that are covered in engineering graphics are listed below: Sketching Geometric Modeling Engineering Drawing/Documentation Assembly Drawing Visualization Rapid Prototyping Computer Graphics Engineering drawing is an essential part of engineer s knowledge. Drawing has evolved into a formal method of communicating ideas by diagrams and pictures. Computers can also pictures for communications, and computer graphics is the art of producing goodquality images on a computer screen. 6

7 Computer Graphics Computer graphics can be thought of as a collection of computer hardware and application programs directed to one specific goal the creation of pictures. The resolution of a graphics display is limited by the number of addressable points (pixels) along each axis. High-resolution : 4096 x 4096 pixels Most graphics terminals have a resolution of 1024 x 1024 pixels. Graphics Standards Several graphics standards have been developed over the years, including q CORE ( ), q GKS (Graphical Kernel System, ), q GKS-3D (Added three-dimensional capabilities), q PHIGS (Programmer s Hierarchical Graphics System, 1984), q PHIGS+ include more powerful 3-D graphics functions, q X-Windows system (1987), and q OpenGL graphics standard is adapted from Unix system. 7

8 Graphics Standards Model for standardization of the graphics environment CAD/CAM Software Architecture Application data structure/model Application program Graphic system Input/Output devices Without graphics standard Graphic Standards Application data structure/ model Application program Kernel (core) system Device handler/ driver Input/Output devices With graphics standard 8

9 Coordinate systems Allows for the mapping of positions andorientations in a 3 dimensional model space. Is required to describe the shape of objectsand for monitoring changes in those shapes. Is used to ensure relevance between 3Dmodeling structures and their real world counterparts. Coordinate systems Cartesian (rectangular) Cylindrical polar Spherical 9

10 Coordinate systems GCS Global Coordinate system WCS World Coordinate system LCS Local Coordinate system 10

11 Working Plane The WP in the prompts and in the picker stands for Working Plane a movable, 2-D reference plane used to locate and orient primitives. By default, the WP origin coincides with the global origin, but you can move it and/or rotate it to any desired position. By displaying a grid, you can use the WP as a drawing tablet. WY WY WX X1 X2 Y1 Y2 WX WP (X,Y) Global Coordinate system The global reference system for the model. May be Cartesian (system 0), cylindrical (1), or spherical (2). For example, location (0,10,0) in global Cartesian is the same as (10,90,0) in global Cylindrical. 11

12 Local Coordinate Systems " A user-defined system at a desired location, with ID number 11 or greater. The location may be: At WP origin [CSWP] At specified coordinates [LOCAL] At existing keypoints [CSKP] or nodes [CS] " May be Cartesian, cylindrical, or spherical. " May be rotated about X, Y, Z axes. Y Y 12 X 12 Y 11 X X 11 Working Plane Coordinate Systems Attached to the working plane. Used mainly to locate and orient solid model primitives. You can also use the working plane to define keypoints by picking. 12

13 Cartesian Coordinate (right-handed) +Z +Y (0,0,0) +X Temporary Coordinate Systems Many also provide for the specification of temporary Local (or User-Defined) Coordinate Systems. Used to simplify input Data input is specified relative to temporary system Data are transformed to absolute reference internally +Z +Y +Z +Y +X +X 13

14 Reference planes Many modelers will allow for thespecification of new local coordinatesystems by specifying a reference (XY) plane May be located with respect to existing model geometry: aligned with existing vertices, edges, surfaces) or to coordinate location (e.g. Z = Z ) Z 1 +Z Y Z=Z +Y X +X Points In 2D a single point can be presented by x y coordinates. [IX IY] = [x y] T IX, IY : integer display coordinates x, y : global life size coordinates T : transformation matrix (2x2) In 3D è [IX IY] = [x y z] T T : 3x2 matix 14

15 Geometric Transformations Modeling systems operate on model entities (and hence the database) through three transformation operations. Translation is a straightforward movement. Rotation does not affect the size or shape of the object. Scaling (dilation) changes the size of the image without changing the shape. Translation Rigid body transformation Every point of entity moved equally a specified distance in a specified linear direction May be specified in terms of: y Initial and final location of a reference point A delta value with respect to the current coordinate system x, y x, y x 15

16 Rotation A rigid body rotation in which every point of an entity is revolved an equal amount about a reference. Requires a rotation axis and angle In the case of a 2D rotation, point view of axis is used y x, y x Dilation (scaling) Alters the absolute size of an entity by multiplying it s geometric coefficients by a scale factor. Scale factor may be applied equally in X, Y and Z directions Entity shape remains the same Scale factor may be applied differently in X,Y or Z Entity shape changes Requires a base point y x, y x 16

17 Rotation Rotation of a triangle through 45º about origin. " cosβ T = $ # $ sin β sin β % ' cosβ &' For point A " % 1/ 2 1/ 2 [ IX IY ] = [ 1 1] $ ' # $ 1/ 2 1/ 2 & ' = " # 0 2 % & For point B " % 1/ 2 1/ 2 [ IX IY ] = [ ] $ ' # $ 1/ 2 1/ 2 & ' = [ ] A(1,1) B(2.5, 1.5) C(1.5, 2.5) C y A B A C B For point C " [ IX IY ] = [ ] $ # $ 1/ 2 1/ 2 1/ 2 1/ 2 % ' & ' = [ ] 0 x Mirror Mirror image about the y-axis. [ IX IY ] = x y [ ] " $ # % ' & C y C B A A B 0 x A(1,1) B(2.5, 1.5) C(1.5, 2.5) 17

18 Homogeneuos Coordinates To enable multiplication, an extra element that can be set to unity is needed: [ IX IY ] =! " x y 1! #% $ % % " m n # & & & $ =! " x + m y + n # $! " An extra coordinate is needed, which is conventionally called H. X Y H! # $ =! " x y 1 #% $ % % " m n 1 # & & & $ =! " x + m y + n 1 # $ 3D Homogeneuos transformations Any point with global coordinates (x y z) can be scaled as (X Y Z H) where x=x/h, y=y/h and z=z/h; thus, for 3D global coordinates, a 4x4 transformation matrix is used. 18

19 Computer graphics (x y z 1) = (X/H Y/H Z/H 1) (X Y Z 1) = (x y z 1) T where! # # T = # # "# a b c p d e f q h i j r l m n s $ & & & & %& The 3x3 matrix produces scaling, shearing and rotation. The 1x3 matrix produces traslation, the 3x1 matrix generates a projection and the 1x1 matrix gives an extra scale factor COMPUTER AIDED DRAWING 19

20 What is CADD?... There are hundreds of CADD programs available in the CADD industry today. CADD is an electronic tool that enables you to make quick and accurate drawings with the use of a computer. Unlike the traditional methods of making drawings on a drawing board, with CADD you can sit back in an easy chair and create wonderful drawings just by clicking the buttons of a keyboard. What is CADD?... Moreover, drawings created with CADD have a number of advantages over drawings created on a drawing board. CADD drawings are neat, clean and highly presentable. Electronic drawings can be modified quite easily and can be presented in a variety of formats. 20

21 Computer-aided drawing a technique where engineering drawings are produced with the assistance of a computer and, as with manual drawing, is only the graphical means of representing a design. a technique where the attributes of the computer and those of the designer are blended together into a problem-solving team. What to Expect from CADD The following are some of the important capabilities that make CADD a powerful tool: " Presentations " Flexibility in editing " Units & accuracy levels " Storage and access for drawings " Sharing CADD drawings " Project reporting " Engineering analysis " Computer Aided Manufacturing (CAM) " Design " Add-on programs 21

22 Computer-aided drawing The advantages of using CADD systems are listed as follow: constant quality drawing saving on repetition creation of database greater accuracy creation of library multicolour drawings use of layers editing functions Universal CAE software model Database contains 2D or 3D geometry of the drawing. (mathematical model) CAE software package Addition and modification input Database output User interface Graphical or text display Hard copy output 22

23 User interface Computer-aided draughting & design Due to the learning difficulties of software, instead of written menus the functions are described by means of icons. Icon menu system are generally popular with CADD users. 23

24 CADD Software selection The size of the company and the amount of investment capital available will be one of the main deciding factors but there are many other questions to be considered: Mainframe or PC/workstation platform? Two dimensions or three? Lines, surfaces or solids? Other analysis tools needed? Will the ability to transfer the geometry to these modelling and analysis systems be needed? Software selection... Compatibility with other systems needed? How good is the maintenance and support from the suppliers? How much, how good and how long is the training? How easy is it to expand the system? 24

25 Computer-aided draughting & design AutoCAD is PC-based CAD software products (late 1982). Mechanical Desktop is an integrated package of advanced 3D modeling tools. Pro/ENGINEER or Pro/E (3D) feature-based, solids model-ing system. It was developed by Parametric Technologies Corporation (PTC) in the late 1980s. SolidWorks is mechanical design automation software I-DEAS (Integrated Design Engineering Analysis Software) is a CAD, CAM, and CAE package. CATIA (Computer Aided Three-dimensional Interactive Application) was created by Dassault Systems of France and is marketed worldwide by IBM. AutoCAD vs. I-DEAS/Pro-E AutoCAD mostly 2D limited 3D modeling limited surface modeling PC-based I-DEAS/Pro-Engineer full 3D solid modeling powerful surface modeling feature-based, parametric solid modeler Workstation-based 25

26 2-D vs. 3-D Documentation A model-centric company may hold a view that the 3D part model contains the master information, and the 2D drawings are only an intermediate form of communication to transmit information to suppliers who need printed drawings. A drawing-centric company may perceive of 3D part models as a preliminary step to create 2D drawings, but the released 2D drawings are archived to document the final design. STANDARDS FOR CAD DATA EXCHANGE 26

27 Model data exchange why is it needed? how it can be accomplished? what formats for transfer? Computer-aided design industry has grown extensively in recent years. Competition between software developers has been high. Many different proprietary CAD packages have been developed and installed. Most use different formats to define the geometric data of model entities. How to implement 1) All use the same CAD package. 2) Use special translator applications to change data from one format to specific one needed. 3) Use a neutral format for data exchange. 27

28 Turnkey System The Solution.! Software and Hardware obtained from one supplier (May prove satisfactory) Suppliers of Turnkey system rarely manufacture all items of system Alternatively User choose specialist software and hardware for best combination which suits to his application Types of Standards for CAD Graphics Standards Data Exchange Standards Communication Standards 28

29 Aim of Graphics Standardisation To provide versatility in the combination of Software and Hardware items of turnkey systems To allow the creation of portable application software package, applicable for wide range of hardware makes and configurations To allow the transfer of graphic data between two or more different companies which may have completely different CAD systems Evolution of Data Standards Interfaces Standardization Organization CAD/CAD CAD/CAM National & European International ISO IGES PDDI PDES ANSI (USA) Product Data Structure SET AFNOR (France) VDA/FS DIN (Germany) STEP CAD*I ESPRIT (EEC) ( A full data model) CIM-OSA ESPRIT (EEC) EDIF USA Electronics Industry??? 29

30 Levels of Graphics Standards Communication Level-1 Comm. b/w Graphics Utility SW & Graphics Output Device (screens, plotters etc) VDI (Virtual Device Interface) or CGI (Computer Graphics Interface) is the most important standard in this category. VDI specifies a standard format for transferring GD between Graphics utility & device drivers Levels of Graphics Standards Communication Level-2 Comm. b/w Application SW & Graphics Utility GKS (Graphics Kernel System) most universally accepted standard developed in W. Germany in GKS provides interface between application package and Graphics utility programs for any CAD system CORE (an American software equivalent to GKS) PHIGS (Programmers Hierarchical Interface for Graphics) has been proposed to eliminate restrictions of GKS 30

31 Levels of Graphics Standards Communication Level-3 Communication between diff. CAD Systems IGES (Initial Graphics Exchange Specification) Developed b/w 1979~1982 Partially adopted by ANSI Standard format of codes for CADCAM data Completely independent of any system supplier Current Situation Translation using IGES is unreliable geometry is corrupted much cleanup required after translation Translation using STEP is not widespread STEP translators only recently available Existing translators lose information parametrics and constraints features and history trees 31

32 Short-term Solutions To avoid data translation problems, many companies have standardized on a single CAD system Ford all suppliers must use I-DEAS Chrysler all suppliers must use CATIA General Motors all suppliers must use Unigraphics A Better Solution A better solution is development of reliable data exchange standards, using a neutral interface. CAD 1 CAD 2 CAE 1 CAE 2 Neutral Interface CAPP PP&C CAM CAQ 32

33 Drawing Exchange Format Depending on the software creating the DXF file, it can either be in an ASCII or a binary format. Almost all CAD (Computer Aided Design) drawings can be represented by a DXF file. Drawing Exchange Format HEADER section General information about the drawing. Each parameter has a variable name and an associated value. CLASSES section Holds the information for application-defined classes whose instances appear in the BLOCKS, ENTITIES, and OBJECTS sections of the database. Generally does not provide sufficient information to allow interoperability with other programs. TABLES section This section contains definitions of named items. Application ID (APPID) table Block Record (BLOCK_RECORD) table Dimension Style (DIMSTYPE) table Layer (LAYER) table Linetype (LTYPE) table Text style (STYLE) table User Coordinate System (UCS) table View (VIEW) table Viewport configuration (VPORT) table BLOCKS section This section contains Block Definition entities describing the entities comprising each Block in the drawing. ENTITIES section This section contains the drawing entities, including any Block References. OBJECTS section Contains the data that apply to nongraphical objects, used by AutoLISP and ObjectARX applications. THUMBNAILIMAGE section Contains the preview image for the DXF file. END OF FILE 33

34 ASCII Code American Standard Code for Information Interchange is a characterencoding scheme. Originally based on the English alphabet, it encodes 128 specified characters into 7-bt binary integers. ASCII was published as ASA X Initial Graphics Exchange Specification (IGES) Established in 1979 and accepted by ANSI in Format consists of a listing of entities and data. Formatted ASCII file format Supports many 2D and 3D CAD entities Has gone through several versions since 1980 Widely supported 34

35 Initial Graphics Exchange Specification (IGES) The IGES file is divided into 5 or 6 sections : 1- The flag section 2- The start section 3- The global section 4- The directory entry section 5- The parameter data section 6- The terminate section IGES Entity Examples Entity # Entity Description 100 Circular arc 108 Plane 110 line 114 Spline surface 118 Ruled surface 126 NURBS curve 150 CSG block 162 Solid of revolution 206 Diameter dimension 35

36 Communication via IGES CADCAM System 1 Preprocessor 1 Postprocessor 2 CADCAM System 2 IGES Database 1 Postprocessor-1 Preprocessor 2 Database 2 IGES format An IGES file is composed of 80-character ASCII records. Text strings are represented in "Hollerith" format. 36

37 Standart for Exchange of Product - STEP STEP is emerging standard ser to replace IGES. The STEP specification is a drawing toghether and unifying of the existing standards. STEP defines the exchange of more than just graphical or topological data. Standart for Exchange of Product - STEP Uses a formal model for data exchange Information is modelled using the EXPRESS language EXPRESS has elements of Pascal, C, and other languages It contains constructs for defining data types and structures, but not for processing data EXPRESS describes geometry and other information in a standard, unambiguous way 37

38 STEP Architecture Layer 3: Application protocols Layer 2: Resource information models Conformance testing & test suites Layer 1: Implementation methods (EXPRESS) Physical files 38

39 STEP Example Continuous Acquisition and Life-cycle Support (CALS) Developed by US Department of Defense Prescribes formats for storage and exchange of technical data Technical publications an important focus 39

40 Important CALS Standards Standard Generalized Markup Language (SGML) developed in 1960s IBM document description language separates content from structure (formatting) uses tags to define headings, sections, chapters, etc. HTML is based on SGML STL Other CAD File Formats 3-D file format used as input for Stereo lithography SAT Solid model file format used by ACIS-based CAD systems Computer Graphics Metafile (CGM) Developed in vector file format for illustrations and drawings All graphical elements can be specified in a textual source file that can be compiled into a binary file or one of two text representations. 40