INTRODUCTION TO CAD
What is CAD?
–Integration of CS techniques in engineering
design
–Use of computers(hardware & software)for
designing products
–Numerical method, optimizations etc.
–2D/3D drafting
–3D modeling for visualization
–Modeling
curves,surfaces,solids,mechanism,assemblies,
etc.
• ANALYSIS
– Stress (deflection analysis,I.e. numerical
methods,FEM
– Simulation of actual use
– Optimizations
– Applications
– CAD/CAM integration
– Process planning
• DISPLAY VISULIAZITION AIDS
– Display of model objects
– Mapping objects onto screen coordinates
– Surface display,shading
– Projections
– Hidden line removal when multiple
surfaces are displayed
REQUIREMENTS OF
MODELING
• Solids are modeled by storing information of
constituent surfaces
• This help in
– Displaying surfaces(3D)
– Computing solid properties
– Modeling by storing info.on bounding
curves or by storing their geometric
definitions
DATA BASES FOR CAD
Volume
delimits
surface
Is bounded by
Plane surfaces
Warped surfaces
Is boundary of
Has boundary curve
Consist of
Belongs to
Belongs to
curves
Makes up Consist of surface
unit
Is chain of
precedes
succeeds
point
Has end point
Is the end of
Is the start of
Has starting point
Curve segment
Net of curves
patch
LIST OF REFERENCE BOOKS
• Principal of interactive CG by Newman &
sprawl*
• Geometric modeling by Mortenson*
• Fundamental of ICG by Foley & van dam
• Procedural elements of CG by Rogers*
• Mathematical elements of CG by Rogers and
Adams
• Principal of CG by Hearn & baker
• Computer graphics,A programming approach by
Steven & Harrington
• An introduction to FE computations by Hinton
& Owen
• An introduction to FE in engineering* by
Chandrupatla & Belegundu
• Zincowicz (3C)
• Zincowicz & taylor (4C)
Evaluations
•
•
•
•
Minors (I and II) – 30%
Major --- 40%
Labs ---- 20 %
Quizes --- 10%
DISPLAY DEVICES
• Storage tube devices
• Permanent phosphorescence
• For erasing entire screen is flooded with a
particular voltage
• Can draw a line from any point to any point
• CALLIGRAPHIC REFRESH GRAPHICS
DISPLAY
• Picture is refreshed 40-50 times a second
• Display buffer & controller
• Stores INFO about each entity to be displayed
Display
buffer
controller
Vector/character
generator
Repeats whole process 40-50 times a
second
CRT
RASTER REFRESH
GRAPHICS DISPLAY
• SCREEN IS A MATRIX OF POINTS
• Each point (pixel) can be bright/dark
• Lines & curves as series of bright pixels
• Frame buffer stores a bit for each pixel(I if
on, o if off)bit plane
• Additional bit planes for achieving different
gray levels/colors.
• The programmer modifies the frame buffer
• And the display controller refreshes the
screen on the basis of the frame buffer
INPUT OUTPUT DEVICES
• Input devices
– Analog type:mouse (ball type)
–
X-y variable
Resistance
– Track ball
– Joy stick
• Digital type
• Light pen
– Light sensitive diode to point the screen
– Positioned is sensed on basis of when pen
senses light
TABLET AND PEN
Grid of wire
Pen emits radio frequency and intensity received by each
wire tells the position
HARDCOPY AND OUTPUT
DEVICES
• Flat bed plotters
– Pen
– X-drive motor & Y-drive motor
– Pen raise & lower mechanism
– Controller
– Drum plotter
• Pen
• Raise and lower mechanism
• X-drive(for pen) & Y drive(for drum) motors
• Controller
• Printers
– DMP
– Laser
– Inkjet