SNS COLLEGE OF ENGINEERING (An Autonomous Institution)
Department of Mechanical Engineering
ME8691 COMPUTER AIDED DESIGN AND MANUFACTURING
ME8691/CADM/BALAMURALI.B/AP/MECH 1 UNIT - 3 CAD STANDARD Topics Covered
• Standards For Computer Graphics • Graphical Kernel System (GKS) • Standards For Exchange Images • Open Graphics Library (Opengl) • Data Exchange Standards • IGES, STEP, CALS
ME8691/CADM/BALAMURALI.B/AP/MECH 2 Standards For Computer Graphics
• A set of guidelines for the way Computer-aided design (CAD) drawings should appear, to improve productivity and interchange of CAD documents between different offices and CAD programs, especially in architecture and engineering.
• Need for graphic standards Need for portability of the geometric model among different hardware platforms. Exchange drawing database among software packages. Need for exchanging graphic data between different computer system. Need for the requirement of graphic data exchange formats and their details such as IGES ,DXF,STEP
ME8691/CADM/BALAMURALI.B/AP/MECH 3 Graphics Standards
ME8691/CADM/BALAMURALI.B/AP/MECH 4 Graphical Kernel System (GKS)
• GKS is basically a set of procedure which can be called by user programs to carry out certain generalized functions such as arc,circle,ellipse etc. • It is a standardized system of graphical functions for processing graphical data to create and process 2D images. • GSK implementations have been made by many hardware manufactures in many languages.
ME8691/CADM/BALAMURALI.B/AP/MECH 5 Features of GKS
• It is an independent device ,it can work with all types of input and output devices. • All text and annotation can be prepared and stored in natural languages. • Graphic functions are defined for both 2D and 3D • GKS defines an international coordinate system called normalized device coordinate system .
ME8691/CADM/BALAMURALI.B/AP/MECH 6 Standards For Exchange Images
ME8691/CADM/BALAMURALI.B/AP/MECH 7 Open Graphics Library (Opengl)
ME8691/CADM/BALAMURALI.B/AP/MECH 8 Data Exchange Standards
• The goal was to define a standard to cover all aspects of a product (i.e. geometry, topology, tolerances, materials, etc.), during its lifetime. • Fundamental difference in IGES and STEP. • The central unit of data exchange in the IGES model is the entity. • The central unit of data exchange in the STEP model is the application, which contains various types of entities. • Data is exchanged between systems it is done in terms of application units.
ME8691/CADM/BALAMURALI.B/AP/MECH 9 IGES, STEP, CALS
• Codes a superset of common entities of all CAD/CAM systems to facilitate the translation between various systems.
ME8691/CADM/BALAMURALI.B/AP/MECH 10 IGES File structure Flag section • Used only with the compressed ASCII and binary format • IGES data in a file can be represented in two formats ASCII and binary • ASCII - American Standard Code for Information Interchange. • ASCII format comprises two types : fixed 80- character record length and compressed format . • Compressed format contains compressed file by eliminating spaces from the records.
Start section • Provides a human –readable description of the file, such as the sending system that generated the original data, the pre-processor ,and the product being described.
11 ME8691/CADM/BALAMURALI.B/AP/MECH Directory Entry section • Is a list of all the entities together with Global section certain of their attributes. • Included information telling the pre- • All product definition data are expressed processor and as a list of predefined entities (geometry information needed by the post –processor and annotation entitles ) . to interpret the • Entry each entity occupies two 80 – files. character records that are divide into a total • Some item specified example : the data of twenty 8-character fields . and time of the file generation . • First and the eleventh field contains entity type number . • Second field contains pointer to the Parameter data entry for the entity in the parameter data section. • Remain entity will contain (line fonts ,layer number, transformation matrix )
ME8691/CADM/BALAMURALI.B/AP/MECH 12 Parameter data section • Section contains the actual data defining each entity listed in the Terminate data section directory entry section . • Section contains a single record which • Example: straight line entity is defined specifies the number of records in each by the 6 coordinates its two end points . of the four preceding sections for • Each entity always has two records in checking purpose the directory entry section and number of records need for each entity in the parameter data section. • Parameter data is placed in free format of columns 1 through 64. • Column 65 left blank. • Columns 66 to 72 on all parameter data records contain the entity pointer specified in the first record of the entity in the data entry section
ME8691/CADM/BALAMURALI.B/AP/MECH 13 Continuous acquisition and life –cycle support (CALS). • It was developed by US department of defense. • It prescribes the formats for storage and exchange of technical data. • Focuses mainly technical publications
Important CALS standards
1.Standard generalized markup language (SGML) is an important standard developed ibn 1960s IBM . It has the document description language.
2.Computer graphics metafile (CGM) is next important standard .developed in 1986 it is used for the vector file format for illustrations and drawings.
ME8691/CADM/BALAMURALI.B/AP/MECH 14 STEP • STEP (Standard for the Exchange of Product model data) is a new International Standard (ISO 10303) for representing and exchanging product model information. • Support any industrial application such as mechanical, electric, plant design, and architecture and engineering construction. • To include all four types of data which is relevant to the entire life- cycle of a product: design, analysis, manufacturing, quality assurance, testing, support, etc.
Three layers of STEP • Application layer –consist of information of various application areas. • Logical layer-provide a consistent , computer-independent description of the data constructs that contain information to be exchanged. • Physical layer –deals with the data structures and data format for exchange file itself. • EXPRESS is a formal data specification language used to specify the representation of product information.
ME8691/CADM/BALAMURALI.B/AP/MECH 15 Thank you
ME8691/CADM/BALAMURALI.B/AP/MECH 16