BMFR 4113 – CAD/CAM
LECTURE 4
CAD Standards
Text: PN Rao
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 their
details such as IGES, DXF and STEP
• Dimensional measurement interface specification for
communication between coordinate measuring machine and
the CAD data
STANDARDIZATION IN GRAPHICS
-Necessary to standardise certain elements at each stage to minimize company investment on certain
software 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 (Programmer’s 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)
VARIOUS STANDARDS IN GRAPHICS
PROGRAMMING
GRAPHICAL KERNEL SYSTEM (GKS)
• It is desirable to have programs
interchangeable with a number of systems,
and also to make programmers learn the
system once and then repeatedly use it on
different systems.
Examples are:
Tektronics Plot 10
GINO-F from CAD Centre, Cambridge.
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.
LAYER MODEL OF GRAPHICS KERNEL SYSTEM
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.
• 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
GGDP
Purpose: Output routine. Outputs one of the four generalised
drawing 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 = circle
ldr
Integer*2.
Length of data record
datrec
Character*80
Data record
GRAPHICS PRIMITIVES IN IBM GKS
Other graphic standards
• GKS 3D- maintains compatibility with the 2D
standard.
• PHIGS (Programmer’s Hierarchical Interface
for graphics)
• NAPLPS
5.4 EXCHANGE OF MODELLING DATA
FIG. 5.4 DATA EXCHANGE BETWEEN VARIOUS SYSTEMS
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 the
conversion methodology.
DEVELOPMENTS IN THE DRAWING DATA
EXCHANGE FORMATS
FIG 5.6 DATA INTERCHANGE METHOD BETWEEN TWO
DIFFERENT CAD SYSTEMS USING NEUTRAL DATA FORMAT SUCH
AS IGES OR STEP
FIG. 5.7 COMPONENT DRAWING FOR IGES FILE
GENERATION
PARTIAL LISTING OF THE IGES FILE FOR
DRAWING SHOWN IN FIG. 5.7
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 data
electronically between two different systems.
STEP APPLICATION PROTOCOL AP 203
EXPLICIT DRAUGHTING
STEP APPLICATION PROTOCOL AP207
CONFIGURATION CONTROLLED
DESIGN
EXAMPLE FOR STEP FILE GENERATION SHEET METAL
DIE PLANNING AND DESIGN
3.DRAWING EXCHANGE FORMAT (DXF)
The DXF format has been developed and
supported by Autodesk for use with the
AutoCAD drawing files.
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 objectives – is to provide a bi-directional
communication of inspection data between computer
systems and inspection equipment.
INTRODUCTION OF MEASUREMENT IN
PRODUCT DEVELOPMENT CYCLE
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
.
TOL/CIRLTY
Function:
Specifies a circularity tolerance for
a feature, and assigns to it a label.
Default:
None
Format:
T(label) = TOL/CIRLTY, tolzon,
var_1, F(label)
Where:
var_1 can be: MMC or: LMC
or: RFS label is an
alphanumeric label
Assigned to the tolerance,
and
is up to 10 characters in
length.
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 - ?
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.
THANK YOU