Lecture4 Cad Standard-2

8/13/2019 Lecture4 Cad Standard-2

1/30

BMFR 4113CAD/CAM

LECTURE 4

CAD Standards

Text: PN Rao


2/30

Learning Objectives

Need for CAD standard

Understand the graphic kernel system and its extensions for

developing the graphic software systems

Requirement of graphic data exchange formats and theirdetails such as IGES, DXF and STEP

Dimensional measurement interface specification for

communication between coordinate measuring machine and

the CAD data


3/30

STANDARDIZATION IN GRAPHICS

-Necessary to standardise certain elements at each stage to minimize company investment on certainsoftware and hardware without much modification on the newer and different systems.

-This means that there should be compatibility between various software

elements as also between the hardware and software.

-Following are some of the interface standards at various levels;

GKS (Graphical Kernel System)

PHIGS (Programmers Hierarchical Interface for Graphics)

CORE (ACM-SIGGRAPH)

GKS-3D

IGES (Initial Graphics Exchange Specification)

DXF (Drawing Exchange Format)

STEP (Standard for the Exchange of Product Model Data)

DMIS (Dimensional Measurement Interface Specification)

VDI (Virtual Device Interface)

VDM (Virtual Device Metafile) GKSM (GKS Metafile)

NAPLPS (North American Presentation Level Protocol

Syntax)


4/30

VARIOUS STANDARDS IN GRAPHICS

PROGRAMMING


5/30

GRAPHICAL KERNEL SYSTEM (GKS)

It is desirable to have programsinterchangeable with a number of systems,and also to make programmers learn the

system once and then repeatedly use it ondifferent systems.

Examples are:Tektronics Plot 10

GINO-F from CAD Centre, Cambridge.


6/30

The main objectives that were put forward for GKS

are:

1. To provide the complete range of graphical

facilities in 2D, including the interactive

capabilities,

2. To control all types of graphic devices such as

plotters and display devices in a consistent

manner,

3. To be small enough for a variety of programs.


7/30

LAYER MODEL OF GRAPHICS KERNEL SYSTEM


8/30

The coordinate frames available to the user are of three types:

1. World coordinates (WC) which are the user- oriented

drawing coordinates.

2. Normalised device coordinates (NDC) which is a uniform

system for all work stations.

3. Device coordinates (DC) are the actual coordinate

system for the particular work station.


9/30

The GKS is essentially a set of procedures that

can be called by user programs for carrying

out certain generalized functions (such as arc,

circle, ellipse etc.)

GKS is defined in terms of numbers of levels

describing the level of support in term of

facilities


10/30

GGDP

Purpose: Output routine. Outputs one of the four generaliseddrawing primitives.

Format: CALL GGDP (n, px, py, primid, ldr, datrec)

n Integer*2 Number of points

px(n) Real. List of X coordinates (WC)

py(n) Real. List of Y coordinates (WC)primid Integer*2. GDP identifier (Fig. 5.3)

1 = bar

2 = arc

3 = pie slice

4 = circleldr Integer*2. Length of data record

datrec Character*80 Data record


11/30

GRAPHICS PRIMITIVES IN IBM GKS


12/30

Other graphic standards

GKS 3D- maintains compatibility with the 2D

standard.

PHIGS (Programmers Hierarchical Interface

for graphics)

NAPLPS


13/30

5.4 EXCHANGE OF MODELLING DATAFIG. 5.4 DATA EXCHANGE BETWEEN VARIOUS SYSTEMS


14/30

1. INITIAL GRAPHICS EXCHANGE

SPECIFICATION (IGES)

However, the IGES is the most comprehensive

standard and is designed to transmit the

entire product definition including that of

manufacturing and any other associated

information (Fig. 5.6).

A brief description of the IGES version 3.0 is

given below highlighting the philosophy of theconversion methodology.


15/30

DEVELOPMENTS IN THE DRAWING DATA

EXCHANGE FORMATS


16/30

FIG 5.6 DATA INTERCHANGE METHOD BETWEEN TWO

DIFFERENT CAD SYSTEMS USING NEUTRAL DATA FORMAT SUCH

AS IGES OR STEP


17/30

FIG. 5.7 COMPONENT DRAWING FOR IGES FILE

GENERATION


18/30

PARTIAL LISTING OF THE IGES FILE FOR

DRAWING SHOWN IN FIG. 5.7


19/30

2.Standard for the Exchange of

Product model Data (STEP)

The broad scope of STEP is as follows:

1. The standard method of representing the

information necessary to completely define a

product throughout its entire life, i.e., from the

product conception to the end of useful life.

2. Standard methods for exchanging the dataelectronically between two different systems.


20/30

STEP APPLICATION PROTOCOL AP 203

EXPLICIT DRAUGHTING


21/30

STEP APPLICATION PROTOCOL AP207

CONFIGURATION CONTROLLED

DESIGN

EXAMPLE FOR STEP FILE GENERATION SHEET METAL


22/30

EXAMPLE FOR STEP FILE GENERATION SHEET METAL

DIE PLANNING AND DESIGN


23/30

3.DRAWING EXCHANGE FORMAT (DXF)

The DXF format has been developed and

supported by Autodesk for use with the

AutoCAD drawing files.


24/30

DMIS

Dimensional Measurement Interface Specification(DMIS) is a new standard in communication being

established by CAM-I for manufacturing.

This standard tries to establish a means of knowing

what has been made by the CAM process.

The objectivesis to provide a bi-directional

communication of inspection data between computer

systems and inspection equipment.


25/30

INTRODUCTION OF MEASUREMENT IN

PRODUCT DEVELOPMENT CYCLE


26/30

INTRODUCTION OF MEASUREMENT IN

PRODUCT DEVELOPMENT CYCLE

Figure Shows: a circularity tolerance specifies a tolerance zone bounded by two concentric

circles within which the feature must lie.


27/30

TOL/CIRLTY

Function: Specifies a circularity tolerance fora feature, and assigns to it a label.

Default: NoneFormat: T(label) = TOL/CIRLTY, tolzon,

var_1, F(label)

Where: var_1 can be: MMC or: LMC

or: RFS label is analphanumeric label

Assigned to the tolerance, andis up to 10 characters in length.


28/30

Summary

GKS is used to standardise the graphic system calling procedures at the

lowest level so that programmers and program can be easily migrated

between different systems

The neutral CAD database is an important requirement to help with the

transfer of information between various CAD/CAM systems

IGES is used for transferring information between various CAD systems for

modelling as well as drafting data

STEP is being used extensively in view of its varied and better facilities for

exchanging product model data

DXF - ? DMIS - ?


29/30

Review Questions

What is the importance of standards in CADCAM?

Write briefly on any one of the known graphic standards

What is meant by DMIS? Explain its importance in the

manufacturing of mass consumption items

How is IGES different from GKS?

Write a short note about DXF standard

Explain the relevance of IGES in the Malaysian manufacturing

scene.


30/30

THANK YOU

Documents

Lecture4 Cad Standard-2