PPT_ME6501_CAD.ppt

SUBJECT: ME6501 COMPUTER AIDED DESIGN
YEAR / DEPT: III / MECH
UNIT I –FUNDAMENTALS OF COMPUTER
GRAPHICS
Product cycle- Design process- sequential and
concurrent engineering- computer aided design –
6.cad system architecture- computer graphics – co-
ordinate systems- 2d and 3d transformations-
homogeneous coordinates – line drawing -clipping-
viewing transformation
IFETCE/MECH/III YEAR/V
SEM/ME6501/CAD/PPT-VER 1.0
1

1.PRODUCT CYCLE
• Need identification
through Customers
demand and
market demand
Need
• Synthesis
• Analysis
Design process
• Process planning
• Procurement
• programming
Manufacturing
process
2

PRODUCT CYCLE
3

4

DESIGN PROCESS
Starts from customers
and markets.
Synthesis & analysis
The detailed design of
the product is drafted.
Process plan.
production schedule will
be prepared
quality testing and
delivery to the customer
5
Philosophy,
functionality and
uniqueness
Synthesis
Conceptual
design
Analysis
Performance
analysis
Design modeling
& Simulation
What if ?

Time
Profits
Sales
Introductory
Stage
Growth
Stage
Maturity
Stage
Decline
Stage
0
Product Life Cycle
Dollars

Introductory Stage
• High failure rates
• Little competition
• Frequent product modification
• Limited distribution
• High marketing and production
costs
• Negative profits
• Promotion focuses on awareness
and information
• Intensive personal selling to
channels
Full-Scale Launch
of New Products

• Increasing rate of sales
• Entrance of competitors
• Market consolidation
• Initial healthy profits
• Promotion emphasizes brand ads
• Goal is wider distribution
• Prices normally fall
• Development costs are recovered
Offered in more
sizes,
flavors, options
Growth stage

• Declining sales growth
• Saturated markets
• Extending product line
• Stylistic product changes
• Heavy promotions to dealers and consumers
• Marginal competitors drop out
• Prices and profits fall
• Niche marketers emerge
Many consumer
products are in
Maturity Stage
Maturity Stage

• Long-run drop in sales
• Large inventories of
unsold items
• Elimination of all nonessential
marketing expenses
Rate of decline depends on
change in tastes or
adoption of substitute products
Decline Stage

New Product Development
Process
Idea
Generation
Concept
Development
and Testing
Marketing
Strategy
Development
Idea
Screening
Business
Analysis
Product
Development
Market
Testing
Commercialization

Stage 1: Idea Generation
• Brainstorming
– Affinity diagrams
– Osborne's Checklist
– Multivoting
• Morphological Charts
• Delphi Technique
12

Stage 2: Idea Screening
13

• Qualitative Research
• FMEA (Failure Modes and Effects Analysis
• Dot Sticking
• SWOT Analysis
• PMI Analysis
14

2.DESIGN PROCESS
15

(a) Shigley model
In design process, there are six steps to be
followed
16

(b) Earle model
17

Problem identification
18

19
Steps followed in problem identification

Preliminary ideas
20

Design refinement:
• Several of better preliminary ideas are
selected for further refinement.
• Rough sketches are converted to scale
drawings
21

Analysis
• A product must be analyzed to determine its
acceptance by the market before it is released
for production.
• It involves the evaluation of best designs
• general areas of analysis are
(a) Functional analysis.
(b) Human engineering.
(c) Market and product analysis.
(d) Specification analysis.
(e) Strength analysis.
(f) Economic analysis.
(g) Model analysis. IFETCE/MECH/III YEAR/V
22

MORPHOLOGY OF DESIGN
23

3. SEQUENTIAL ENGINEERING
•In the process planning phase, manufacturing instructions are given based on the
method of manufacturing, decoded in the design phase.
•Activities are carried out one after the other. Each phase/activities there is no
interaction between them.
•Over Wall approach. Because Each department complete work and throw to
next There is no interaction i.e. there is a communication barrier between
each department.
24

4. CONCURRENT ENGINEERING
Co-operate work between design and manufacturing and
other specialists has to be made. This is known as Concurrent
Engineering or Simultaneous Engineering.
25

26

Advantage of concurrent engineering:
1.The design decisions - taken by a team of multi
disciplinary experts.
2. Changes and modifications -product design -faster.
3. Shorter lead time -activities related to product design
and Developments -carried out simultaneously.
4. Higher quality.
5. In sequential engineering the number of modifications –
distributed throughout the product development cycle.
concurrent engineering number of
Changes/modifications -maximum at the beginning
27

Characteristics of Concurrent Engineering
1. Product responsibilities lie on team of multi disciplinary
group.
2. Integration of design, process planning and production.
3. Product lead time will be less, because cross-functional
activities are started simultaneously.
4. Most of the modification changes are carried in the
planning stage itself.
5. Frequent review of design and development process.
6. Rapid prototyping.
7. More attention will be given to satisfy the customer needs
and to include newer technologies in product development.
28

ROLE OF COMPUTERS IN DESIGN
29
Geometric modeling
Engineering Analysis
Design Review and
Analysis
Automated Drafting

CAE (Computer Aided Engineering)
CAD
CAD
CAE CAPM
CAM
30
Computer Aided
Production
management
Computer Aided
Design
Computer Aided
Drafting
Computer Aided
Manufacturing

• CAD
– Linkage analysis
– Dynamic & Kinematic analysis
– Design of Machine elements
– Form/shape design of graphic terminals
– Finite element analysis
– Heat transfer problems
– Design of Tools , Dies and fixtures
31

• CAPM
– Material and inventory control
– Plant lay out
– Pay roll
– Process lay out
– CAPP
– Project analysis (PERT/CPM)
– Group technology
– Computer aided Scheduling
32

• CAM
– CNC of machine tools
– Programming/computer aided production of parts
– Graphic simulation of cutter path
– FMS
– Computer controlled CMM/inspection
– Computerised tool selection
– Robotics
33

• CAD (Computer aided drafting)
– 2D drafting of parts
– Assembly of parts
– 3D models
– 3D Shaded images
– Wire frame models
– Hydraulic circuits
– Electrical and electronic circuits
– Animations
– Graphs
34

CAD SYSTEM ARCHITECTURE
35

COMPUTER GRAPHICS
The most common graphics output device is standard cathode ray tube
(CRT)
b) Random Scan
c) Raster Scan
Color CRT Monitors
Direct-View Storage Tubes (DVST-Stores the picture information -a charge
distribution -behind
Light-emitting Diode (LED)- In LED, a matrix of diodes is arranged -form the
pixel positions
Liquid-crystal Displays (LCDs)- produce picture -passing polarized light e
through a liquid
36

CRT
• Electrostatic focusing
• Resolution
• Aspect Ratio
37

b) Raster Scan
• The viewing screen is divided into a large number of discrete
phosphor picture elements, called pixels.
• The matrix of pixels constitutes the raster.
• Might typically range from 256X256 to 1024X1024.
• Each pixel - screen -glow with a different brightness. Color
screen provide for the pixels -different colors & brightness.
• In a raster-scan system, the electron beam is swept across the
screen, one row at a time from top to bottom.
• The beam intensity -turned on and off - create pattern of
illuminated spots.
• Picture definition -stored -memory area -refresh buffer or
frame buffer. IFETCE/MECH/III YEAR/V
38

Raster Scan
39

(c) Random Scan
• Random scan system uses an electron beam -
operates like a pencil -create a line image on the CRT.
• The image is constructed - sequence of straight line
segments.
• Each line segment is drawn on the screen by
directing the beam is defined by its X and Y
coordinates
40

Random Scan
41

Color CRT Monitors
• Beam Penetration Method--electron beam
penetrates into the phosphor layers.
• Shadow Mask Method -One phosphor dot
emits a red light, another emits a green light,
and the third emits a blue light.
42

CO-ORDINATE SYSTEMS
Model coordinate system(MCS)
Working coordinate system (WCS)
Screen coordinate system (SCS)
Model coordinate system (MCS)-Reference space –model-MCS
displayed –computer screen
43

• Origin arbitrary selected-MCS orthogonal
plane &model views to be understood.
• Two possible orientation –
• XY planes in horizontal model in top view-
front view XZ-Right side view YZ
• XY plane front view-XZ plane top view-YZ right
side view
Model coordinate system (MCS)…
44

Working coordinate system(WCS)
MCS –difficult to define inclined model-
convenient to define WCS-Cartesian
coordinate system-XY plane coincides with
plane of construction-Can be established at
any position in space. CAD software
transforms WCS to MCS before storing data
45

Screen coordinate system (SCS)-SCS is defined as 2D
device –origin fixed at the left corner of graphics display-
aspect ratio and type of device (Raster) determine the
range of SCS- used in view related clicks. A 1024 display has
range of (0,0) to ((1024,1024)- center of coordinates
(512,512)-Normalized SCS can also be used range from (0,0)
to (1,1)-Third method drawing size that user defines.
46

2D AND 3D TRANSFORMATIONS
• 2D transformation of primitives
4 main types
• Translations
• Scaling
• Rotation
• Shearing
47

Translations
Point at (x,y)=(2,1)- Translate 3 units right and
1 unit up -(x',y') = (5,2) : (x',y') = (x+3,y+1).
Matrix/Vector Representation of Translations
48

Scaling
Suppose we want to double the size of a 2-D
object.- scaling along each dimension-For e.g.
triangle have been doubled in both width and
height.
49

Rotation
• Consider rotation of a point (x,y) with respect
to origin in the anti clock wise direction. Let
(x’, y’) be the new point after rotation and let
the angular displacement (ie. Angle of
rotation) be θ
50

Shear
• In x direction
In x direction
In y direction
51

HOMOGENEOUS COORDINATES
Complex transformation- combining basic
transformations- Homogeneous coordinates (HC) add
an extra virtual dimension.- 2D HC are actually 3D and
3D HC are 4D. 2D point p = (x,y)- In HC, p= (x,y,1)- An
extra coordinate 1 added - represent translations as
matrix multiplication instead of as vector addition.
52

Composite transformation
• Translations:
If two successive translation vectors (t,x1, tyl)
and (tx2,ty2) are applied to a coordinate
position P, the final transformed location P' is
calculated as
53

• Rotations
54

• Scaling:
55

Composition of 2D transformation
56

57

3D transformations
(i) Perspective transformation.
(ii) Brightness modulation
(iii) Hidden line removal
(iv) Hidden surface removal
(v) Shading
(vi) Movement
58

(i) Perspective transformation
Perspective projection is often used for pictorial
projection of large objects. This enhances the
realism of displayed image by providing the viewer
with a sense of depth. Perspective projection is
used to represent an object that is so large. In
perspective projection the projections converge to
the eye. Therefore it may be generated by first
transforming points to the eye co-ordinate system
using a parallel viewing transformation.
59

(ii) Brightness modulation
Generally parts of the picture near to the
observer are bright while those far away are
dim. During construction of drawing, the
maximum and minimum z co-ordinates are
noted. The z region is the divided into n number
of regions. There are n numbers of visible
brightness levels available in the display system.
The picture is displayed with the appropriate
intensity of brightness along z axis
60

(iii) Hidden line removal
It is also called visible surface determination. It is more
generally an image space process. In this process, an
image of an object is generated at a particular resolution
by manipulating pixels on a raster display, exploding the
ability of raster devices to display shaded areas. A wide
variety of algorithms exists. They include the z-buffer
algorithm, Watkin’s algorithm, Wamock’s algorithm and
Painter’s algorithm
61

LINE DRAWING
• DDA algorithm.
• Bresenham’s Algorithm.
• Parametric representation
62

DDA algorithm
Straight line form the basis for the display of all types
of shapes.
The computer must be able to pick up a number of
other pixels that should be illuminated in addition to
the two end pixels
A popular method uses an algorithm known as the
“Symmetric digital differential analyzer” (DDA).
For a like segment joining two points P1 & P2 a
parametric representation is
u
P
P
p
u
p )
1
2
(
1
)
( 


63

Bresenham’s Algorithm.
In this method, developed by Jack Bresenham,
we look at just the center of the pixels. We
determine d1 and d2 which is the "error", i.e.,
the difference from the "true line."
64

Parametric Equation
Consider u- parameter varies from 0 to 1
P1 is initial point and p2 is the Final point
The above equation defines a line by the
end points p1 and p2 whose associated
parametric values are 0 to 1.
65

66

67

68

9. CLIPPING
Line Clipping-process of removing lines or
portions of lines outside of an area of interest.
Clipping Individual Points-x coordinate
boundaries Xmin and Xmax-y coordinate
boundaries are Ymin and Ymax, inequalities
must be satisfied for a point at (X,Y) to be inside
the clipping rectangle. Xmin < X < Xmax and
Ymin < Y < Ymax.
69

Line clipping
70

Cohen-Sutherland Line Clipping-The algorithm extends window
boundaries to define 9 regions
top-left, top-center, top-right, center-left, center, center-right,
bottom-left, bottom-center, and bottom-right.- (LRBT) for these
four bits
Step1: Compute 4-bit out codes LRBT0 and LRBT1 for each end-
point.
Step2: If both outcodes are 0000, the trivially visible case-
outcodes yields 0000.
Step 3: If both outcodes have 1's in the same bit position- the
trivially invisible case-outcodes is not 0000.
Step 4: the indeterminate case line partially visible or not visible-
compute the intersection of the line with the appropriate
window edges.
71

Liang-Barsky Line Clipping-uses floating-point arithmetic but finds the appropriate
end points with at most four computations-uses the parametric equations for a line
and solves four inequalities-
72

1. Set tmin=0 and tmax=1
2. Calculate the values of tL, tR, tT, and tB (tvalues).
• if t<tmin or t>tmax ignore it and go to the next edge to otherwise
classify the t value as entering or exiting value (using inner
product to classify)
• if t is entering value set tmin=t ; if t is exiting value set tmax=t
1. If tmin<tmax then draw a line from (x1 + dx*tmin, y1 + dy*tmin)
to (x1 +dx*tmax, y1 + dy*tmax)
2. If the line crosses over the window, you will see (x1 + dx*tmin,
y1 + dy*tmin)and (x1 + dx*tmax, y1 + dy*tmax) are intersection
between line and edge
Liang-Barsky Line Clipping-Algorithm
73

10. VIEWING TRANSFORMATION
2D primitives
Vector generation-to use sufficient display lines for the
curve to appear smooth.- The number needed is
controlled by the display tolerance, lines are drawn
between points on the normal curve shape, and
therefore the permissible deviation is inside the curve
74

75

76

(II) WINDOWING AND VIEWING TRANSFORMATION-
It is necessary to view only a portion of the drawing in the full
screen if the drawing is very large and too crowded in the
screen.- Different part of the drawing can thus be selected for
viewing by placing the windows-The window is an imaginary
rectangular frame or boundary through which the user looks
onto the model. The viewpoint is the area on the screen in which
the contents of the window are to be displayed as an image.
Shown in Fig
77

Clipping transformation
Clipping is the process of determining the visible
portion of a drawing lying within a window and
discarding the rest.
78

Reflection transformation-Reflection or mirror
transformation is useful in constructing
symmetric models.
79

Zooming
Zooming transformation is useful for getting
magnified view or enlarged view of particular
part of the drawing. Zooming = Scaling +
translation + Clipping
80

Panning- The panning transformation is used to move
the screen across the work page. i.e. it is used to shift a
drawing across the screen as if it were moving window.
Transmitting information on a network - It is used to
transfer the data from one device to another. For this
purpose the data must be encoded using a protocol.
Graphics libraries- These graphic libraries are used to
avoid unnecessary repeated programs when
programming the operation described above.
81

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