cad

1. 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.

2. • ANALYSIS
– Stress (deflection analysis,I.e. numerical
methods,FEM
– Simulation of actual use
– Optimizations
– Applications
– CAD/CAM integration
– Process planning

13. 3 ASPECTS OF CAD
• Modeling
• Display/visualization
• Applications
• MODELING
– Definition of objects
– Relation between objects
– Properties
– Orientations in suitable co-ordinate system
– Modification of existing definition
(editing)

14. • DISPLAY VISULIAZITION AIDS
– Display of model objects
– Mapping objects onto screen coordinates
– Surface display,shading
– Projections
– Hidden line removal when multiple
surfaces are displayed

15. 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

16. DATA BASES FOR CAD
Volume
Plane surfaces Warped surfaces
curves
Net of curves patch
point
Is bounded by
Is boundary of
Consist of Belongs to
Belongs to
Consist of surface
unit
Has boundary curve
Is chain of Makes up
precedes
succeeds
Has
starting
point
delimits
surface
Curve segment

17. 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

18. • Display buffer & controller
• Stores INFO about each entity to be displayed
Display
buffer
Vector/character
generator CRT
controller
Repeats whole process 40-50 times a
second

19. RASTER REFRESH
GRAPHICS DISPLAY
• SCREEN IS A MATRIX OF POINTS
• Each point (pixel) can be bright/dark
• Lines & curves as series of bright pixels

20. • 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

21. INPUT OUTPUT DEVICES
• Input devices
– Analog type:mouse (ball type)
–
X-y variable
Resistance

22. – 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

23. TABLET AND PEN
Pen emits radio frequency and intensity received by each
wire tells the position
Grid of wire

24. 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

25. • X-drive(for pen) & Y drive(for drum) motors
• Controller
• Printers
– DMP
– Laser
– Inkjet