ME6501 COMPUTER AIDED DESIGN L T P C 3 0 0 3 OBJECTIVES ... · Product cycle- Design process- sequential and concurrent engineering- Computer aided design – CAD system architecture-

REGULATION : 2013 ACADEMIC YEAR : 2018-2019

JIT-JEPPIAAR/MECH/Dr.D.MURUGANANDAM & Mr.M.K.KARTHIK/IIIrd Yr/SEM 05/ME6501/COMPUTER AIDED

DESIGN/UNIT 1-5/QB+Keys/Ver1.0

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ME6501 COMPUTER AIDED DESIGN L T P C

3 0 0 3

OBJECTIVES:

• To provide an overview of how computers are being used in mechanical component design

UNIT I FUNDAMENTALS OF COMPUTER GRAPHICS 9

Product cycle- Design process- sequential and concurrent engineering- Computer aided design

– CAD system architecture- Computer graphics – co-ordinate systems- 2D and 3D

transformations homogeneous coordinates - Line drawing -Clipping- viewing transformation

UNIT II GEOMETRIC MODELING 9

Representation of curves- Hermite curve- Bezier curve- B-spline curves-rational curves-

Techniques for surface modeling – surface patch- Coons and bicubic patches- Bezier and B-

spline surfaces. Solid modeling techniques- CSG and B-rep

UNIT III VISUAL REALISM 9

Hidden – Line-Surface-Solid removal algorithms – shading – coloring – computer animation.

UNIT IV ASSEMBLY OF PARTS 9

Assembly modelling – interferences of positions and orientation – tolerance analysis-

massproperty calculations – mechanism simulation and interference checking.

UNIT V CAD STANDARDS 9

Standards for computer graphics- Graphical Kernel System (GKS) - standards for

exchangeimages- Open Graphics Library (OpenGL) - Data exchange standards - IGES, STEP,

CALSetc. - communication standards.

TOTAL: 45 PERIODS

OUTCOMES:

Upon completion of the course, students will be able to use computer and CAD software's for

modeling of mechanical components.

TEXT BOOK:

1. Ibrahim Zeid “Mastering CAD CAM” Tata McGraw-Hill Publishing Co.2007

REFERENCES:

1. Chris McMahon and Jimmie Browne “CAD/CAM Principles", "Practice and

Manufacturing management “ Second Edition, Pearson Education, 1999.

2. William M Neumann and Robert F.Sproul “Principles of Computer Graphics”, McGraw

Hill Book Co. Singapore, 1989.

3. Donald Hearn and M. Pauline Baker “Computer Graphics”’. Prentice Hall, Inc, 1992.

4. Foley, Wan Dam, Feiner and Hughes - "Computer graphics principles & practice"

Pearson Education - 2003.




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Subject Code: ME6501 Year/Semester: III /05

Subject Name: COMPUTER AIDED DESIGN

Subject Handler: Dr.D.Muruganandam & Mr.M.K.Karthik

UNIT I - FUNDAMENTALS OF COMPUTER GRAPHICS

Product cycle- Design process- sequential and concurrent engineering- Computer aided design – CAD

system architecture- Computer graphics – co-ordinate systems- 2D and 3D transformations

homogeneous coordinates - Line drawing -Clipping- viewing transformation

PART * A

Q.No. Questions

1.

Name the design process involved in product cycle. BTL1

• Product concept

• Design

• Drafting and documentation

2

In the product cycle what are the manufacturing processes involved? BTL 1

• Process planning

• Production planning

• Production

• Quality control

• Packaging.

3 Describe design process. (May/June 2016) BTL 2

Design process is an activity that facilitates the realization of new products and process through

which technology, the human needs and aspirants are satisfied.

4 Define clipping. BTL2

If any part of the geometry is not inside the window, it is made invisible by the graphics software

through a process known as clipping.

5

What is viewing transformation? BTL 2

Viewing transformation is capable of displaying generated images the way the user wants to

present .this function set provides the user with the ability to view the image from the desired

angle and at the desired magnification.

6 Define rotation. BTL2

Rotation is also another important transformation. in this transformation, all the points of an

object are rotated about origin (or) about any base point by an angle θ.

7

List out the coordinates used in coordinate representation system. BTL1

• Cartesian coordinate system

• World coordinate system

• Normalized coordinate system

• Device coordinate system

8 What is basic transformation? BTL2.

The transformations are used to reposition and resize two dimensional objects on the displays

(alternatively, in the database).

9 Name the three basic transformation used in computer aided design. BTL1

• Translation




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• Scaling

• Rotation

10 Define translation. BTL2

Translation is one of the important types of transformation. This is used to move the entity. After

moving, all points of new entity are parallel to all points of the old entity.

11 Define scaling BTL2

Scaling of an element is used to enlarge it or reduce it size.

12

Explain the characteristics of concurrent engineering. (Apr/May 2017) BTL 2

• Constant and un-interrupted evaluation of design process and development process.

• Fast and speedy information exchange achieved through internet, LAN, etc..

• Rapid prototyping.

• More attention and concern for satisfying customer needs.

• Focus on new technologies.

13

How are the needs recognized? BTL 2

Needs are recognized by market survey and customer’s demand. After detailed survey there may

be,

• Adoption of existing design

• Modification in the existing design

• Completely new design.

14 Define synthesis. (Nov/Dec 2016) BTL 1

Synthesis is nothing but conceptualization. Synthesis forms a design solution to satisfy the need.

In synthesis the design parameters are adjusted to get perfect fit.

15 What is meant by analysis? BTL1

It is an iterative process and requires good mathematical knowledge. Analysis examines the

already existing or proposed design to judge the suitability for the task.

16

Define optimization. BTL1

Optimization means the best possible solution for the given objectives. All possible solutions are

analyzed and optimum is selected. After every phase of design process, the designer may go to

the previous steps and modify them.

17

List out the different coordinate systems used in the multiple coordinate systems. BTL 2

• World coordinate system.

• Object coordinate system.

• Hierarchical coordinate system.

• Viewpoint coordinate system.

• Model window coordinate system.

• Screen coordinate system.

• Viewport coordinate system.

18 What is concatenation transformation? (Apr/May 2018) BTL1

It is a single transformation by combining many transformation linked one after the other to

perform the final task.

19 Give the flow diagram of concurrent engineering. BTL1




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20

Describe normalized device coordinates. BTL2

An interpreter is used to convert theses coordinates to appropriate pixel values for the particular

display devices. The device independent units are called normalized device coordinates.

PART * B

1

With a neat sketch explain the product cycle. (13M) BTL 2

Answer: Page 1.2 – Dr.G.K.Vijayaraghavan, Dr.S.Sundaravalli

The cycle through which a product goes from development to retirement is called product cycle.

The product undergoes the following two main processes from inception to finished product.

i. Design process[3M]

• Synthesis and Analysis are the two main sub-process

• Working principle, mechanisms implied, functionality and uniqueness of the

product are determined during synthesis process.

• Analysis starts with the careful design of each assembly and each component of

the assembly through top down approach and bottom up approach.

ii. Manufacturing process[3M]

• Process plan is formulated which specifies the sequences of operations to be

carried out to produce the new product.

• The scheduling provides a plan to the company that a certain quantities of the

product should be manufactured within the specified time period.

• The product goes through a series of continuous refinement and improvements,

additions etc., by obtaining feedback from marketing and service leads.




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[7M]

2

What is CAD design process? Draw flow diagram and explain functions. (13M) (May/June

2016, Nov/Dec 2016, Apr/May 2017) BTL 2


The various design related tasks which are performed by modern computer aided design system

can be grouped into four functional areas,

• Geometric modelling: [2M]

It is concerned with the computer compatible mathematical description of geometry of an

object. The geometrical modelling is classified into three types namely wire frame

modelling, surface modelling and solid modelling.

• Engineering analysis: [2M]

Two types of engineering analysis are namely analysis for mass properties and finite

element analysis. The analysis can be done either by user specific program generated for it

or using general purpose software commercially available.

• Design review and evaluation: [2M]

Accuracy of design can be checked and rectified if it is required in the computer screen

itself. Interference checking is another review feature available in design review.

• Automated Drafting: [2M]

It is the process of creating hard copies of design drawing. The important features are

automated dimensioning, scaling of the drawing and capable of generating sectional views,

enlargement of minor parts etc.,




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[5M]

3

Discuss about sequential and simultaneous engineering. (13M) (May/June 2016, Apr/May

2017) BTL 2


SEQUENTIAL ENGINEERING: [3M]

• Three major phases of conventional manufacturing process are design, process planning

and manufacturing. All three phases sequentially carried out.

• There is no interaction which means a communication barrier existing between each

department.

• The other name for the sequential approach is over wall or across the wall approach.

[3M]

CONCONCURRENT ENGINEERING: [3M]

• It is a methodology of restructuring the product development activity in a manufacturing

organization using a cross functional team approach.

• An intensive teamwork between product development, production planning and

manufacturing teams is essential for effective implementation of concurrent engineering.

• The technique is adopted to improve the efficiency of product design and to reduce the

product development cycle time.




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[4M]

4

List out the benefits of CAD. (13M) BTL 2


• Easy editing: Drawing editing and modifications can be easily and quickly done.

• High quality: Created drawings are more neat, precise and sharp.

• Drawings can be plotted quickly in different scales and color.

• Compact storage: Drawings can be plotted quickly in different scales and colors.

• Informations about length, area, perimeter, volume, mass etc are calculated easily.

• Copies of the same drawing can be duplicated without sacrificing image quality.

• Three dimensional drawings can be seen from any viewpoint for better visualization.

• Commonly used components and symbols can be pre-stored in graphics library. [13M]

5

Write the engineering applications of CAD. (13M) BTL 3


• Mechanical engineering: [4M]

i) Applications are usually coupled with manufacturing and forming a CAD/CAM system.

ii) Used for manufacturing and forming a CAD/CAM system such as milling, turning,

wire cut EDM, punching etc.,

• Civil engineering: [4M]

i) Applications range from a simple building design to large scale projects.

ii) They are also used for interior design, static and dynamic analysis.

• Electrical and electronics engineering:[2M]

i)The computer performs all design activities such as electric motor, PCB design, IC

engines etc.,

• Apparel industry: [3M]

i) They have specialized equipment such as large plotters, cutters for patterns and

automatic machines for cutting the fabric.

ii)Their application ranges from fashion designing to manufacturing including pattern

design and lay planning.

6

Draw and explain the CAD system architecture. (13M) (May/June 2016) BTL 2


• Architecture of CAD contains four major components namely,

• Database,

• Operating System,




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• Input- Output System,

• User interface [3M]

• Software is the computer program running with one of the UNIX operating systems and

few with LINUX systems. [2M]

• Application software is CAD modeling and analysis software such as AUTOCAD,

ANSYS, SOLIDWORKS, CATIA, IDEAS etc., [2M]

[6M]

7

Explain homogenous coordinate transformation system and matrix. (13M) BTL 2


• Three dimensional representation of a two dimensional plane is called as homogeneous

representation. [4M]

• The transformation of two dimensional plane is called as homogeneous transformation. [3M]

• It unifies translation, rotation and scaling in one transformation matrix. [3M]

• Conversion of 2D co-ordinate pair into 3D vector can be achieved by represeting the point as

[X,Y,1] [3M]

8

With an example, explain each type of two dimensional transformation. (13M)

(Nov/Dec2017, Apr/May2018) BTL 2


• Translation: Movement of an object from one position to another position.

Adding the distance through which drawing is to be moved. [4M]

• Scaling: Transformation applied to change the scale of an entity.

Achieved by multiplying the co-ordinates of the drawing by enlargement

factor. [3M]

• Rotation: Drawing is rotated about a fixed point.

Position and orientation of geometry is decided by angle of rotation and

base point. [3M]

• Shearing: It produces distortion of an object or entire image

There are two types namely X-shear and Y-shear. [3M]

PART * C

1 Explain the techniques involved in line drawing algorithm. (15M) (Nov/Dec 2016) BTL 4


The following are the requirements for drawing lines: [3M]




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• Lines should appear straight.

• Lines should terminate accurately

• Lines should not have constant density/brightness

• Lines should be drawn rapidly.

Digital Differential Analyzer Algorithm: [6M]

• DDA generates lines from their differential equation.

• The equation of line is expressed as a pair of parametric equations

• Pixel however have only one integer co-ordinates.

• Once the address of all the pixels is determined, it is stored in frame buffer.

• The display driver reads the array of addresses and it illuminates the corresponding pixels.

Bresenham’s Line Algorithm: [6M]

• It eliminates the floating point arithmetic except for initial computations.

• The basic principle is to select the optimum raster locations to represent a straight line.

• The algorithm always increment either x or y by one unit.

• The increment in variable is determined by examining the distance between actual line

location and nearest pixel called as decision variable or error.

2

Explain viewing transformation system. (15M) (Nov/Dec 2016) BTL 3


• Displaying an image of a picture involves mapping the co-ordinates into appropriate co-

ordinates on the device where the image is to be displayed. [3M]

• It is done through the use of co-ordinate transformations called viewing transformations. [3M]

• For viewing transformations, window and viewport are used. [3M]

• The world co-ordinate area selected for the display is called “Window”. [3M]

• An area on a display device to whom a window is mapped is called “ViewPort”. [3M]

3

Explain different types of coordinate representation system. (15M) BTL 2


• World Co-ordinate system (WCS):[2M]

It describes the picture to be displayed with the co-ordinates.

[3M]

• Physical device Co-ordinate system (PDCS): [2M]

It corresponds to a device where the image of a particular is to be displayed.




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[3M]

• Normalized device Co-ordinate system (NDCS): [2M]

It is a system in which display area of virtual display device is to unit square whose lower

left corner is at origin.

[3M]

UNIT II - FUNDAMENTALS OF COMPUTER GRAPHICS

Representation of curves- Hermite curve- Bezier curve- B-spline curves-rational curves-Techniques for

surface modeling – surface patch- Coons and bicubic patches- Bezier and B-spline surfaces. Solid

modeling techniques- CSG and B-rep

PART * A

Q.No. Questions

1. What is meant by cubic polynomial? BTL1

A cubic polynomial is the minimum order polynomial that can guarantee the generation of

these curves.

2

List down the common surface entities used in a surface modeling. BTL1

• Plane surface.

• Ruled (lofted) surface.

• Surface of revolution.

• Tabulated surface.

• Bezier surface.

• B-spline surface

• Coons patch.

• Fillet surface.

• Offset surface.

3 What is called plane surface? BTL1




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The most elementary and simplest form of the surface types is the plane surface which may be

defined between two parallel straight lines through three points or through a point and line.

4

Define fillet surface. BTL1

It is defined as a surface connecting two other surfaces in a smooth transition generally of

constant or smoothly changing radius of curvature.

5

How are synthetic surfaces generated? BTL1

• Tensor method

• Rational method

• Blending method.

6

What do you mean by rational and non-rational curves? BTL1

Rational curves are defined as the ratio of two polynomials whereas the non rational curves is

defined by one polynomial.

7

List the properties of tensor product surface. BTL1

• The rational method develops rational surfaces which is an extension of the rational

curves.

• The blending method approximates a surface by piecewise surfaces.

8

Why B-rep scheme is more widely used? (Nov/Dec 2016) BTL1

• In CSG, the number of basic primitives available is limited but it is not so in B-rep.

• The performance of B-rep scheme is very much superior to that of CSG scheme for

complex engineering models.

• Conversion of CSG to B-rep is possible but the conversion from B-rep to CSG is not

possible.

• Combining the wire frame and surface model is possible only through B-rep solid

representation.

9

Write down the equation for a single parametric cubic spline segment. BTL1

The equation for a single parametric cubic spline segment is given by,

P(u) = ∑ 𝑃4𝑖=1 i u

i-1 0≤u≤1

Where u is the parameter and Pi are the polynomial coefficients.

10

How curve are represented? BTL1

A smooth curve can be obtained from the large number of data points. The two basic curve

representation technique are:

• Analytic curves

• Synthetic curves

11

Write the advantages of analytic curve. BTL 1

• Evaluation of the intermediate points are precise and easy.

• Space taken for the storage of curve is compact.

• Drawing of curve is easy from the storage data.

12

List the disadvantages of synthetic curves. BTL 1

Interpolations techniques are used to obtain intermediate points, which is an inaccurate procedure.

Exact the transformation of the curve become difficult to handle when there are large number of

data points involved. The property of the curve cannot be obtained the irregularity in the shape.

13 What are Hermite curves? BTL2




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Hermite curve is determined by defining positions and tangent vectors at the data points. Hermite

curve is also known as cubic curve. Hermite curve passes through the end points of the curve

segment and possesses first order continuity.

14

How Hermite curves can be notified? BTL 2

• Change in the location of the control points

• Change in the magnitudes of the tangent vectors, keeping the same directions.

• Change in the directions of the tangent vectors, keeping the same magnitudes.

15

What are the observation made in Bezier curves? (Apr/May 2017) BTL2

• The shape of the Bezier curve is obtained or determined by the number of control points.

• They provide local control of the curve shape as opposed to global control by using a

special set of blending functions that provide local influence.

• The positions of the control points and vertices of Bezier characteristics polygon is used to

define the Bezier curve.

• The Bezier curves follows the shape of characteristics polygon.

16

What are the advantages of B-spline curves? BTL2

B-Spline curves also provide the ability to add control points without increasing the degree of the

curve.

17

What is surface modeling? BTL2.

The technique of representation of objects (or) components by surface is called surface

modeling.In this surface modeling, objects can be clearly interpreted by the user (viewer).

18

What are techniques available for surface modeling? BTL1

• Surface patch

• Coons patch

• Bicubic patch

• Bezier surfaces

• B-Spline surfaces

19

What are the different modelling tools? BTL1

• Sketching

• Part creation

• Assembling

• Documentation

20

What is geometric modelling? BTL2

The mathematical description of the geometry of an object using a software is called as geometric

modelling. By this geometric modeling, it is possible to display as well as manipulate the objects

image on a graphical screen.

PART * B

1

Discuss the formulation involved in the Hermite curve. (13M) (Nov/Dec 2016) BTL 2


• Hermite curve - cubic spline - fit smooth curve - designated set - data points - connects

two data points - utilizes cubic equation

P(u) = ∑ 𝑃4𝑖=1 i u

i-1 0≤u≤1 where u parameter - Pi polynomial coefficients.

Expanded form,

P(u) = axu3+bxu

2+cxu+dx 0≤u≤1 [3M]




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• Hermite form - obtained defining positions - tangent vectors - control points. Adjusted

locally - each curve section - only dependent - endpoint constraints. [2M]

• P(u) - parametric cubic point function - curve section between end points Pn and Pn+1 -

boundary conditions - define Hermite curve sections are:

P(0) = Pn ; P(1) = Pn+1 ; P’(0) = P’n ; P’(1) = P’n+1

where P’n and P’n+1 parametric derivatives (slope of the curve) at the end points

Pn and Pn+1 resp. [2M]

• Evaluating four constants a,b,c,d - Hermite matrix ,

MH = 2 -2 1 1

-3 3 -2 -1

0 0 1 0

1 0 0 0 [4M]

• The tangent vector becomes,

P’(u) = Pn(6u2-6u) + Pn+1(-6u2+6u) + P’n(3u2-4u+1)+P’n+1(3u2-2u) [2M]

2

Write short notes on B-Spline curve. (13M) BTL 2


B-Spline Curves:

• B-Spline - non global - each vertex Bi - associated unique basis function - exhibits local

control - order of basis function - single vertex moved - only vertices affected - while rest

remains same. [2M]

• B-Spline curve given by,

P(u) = ∑ 𝑃𝑛𝑖=0 i Bi,k(u) 0≤u≤umax

where Pi - input set of n+1 control points - Bi,k(u) normalized B-spline basis functions.

[2M]

• B-spline functions - properties namely,

• Partition of unity.

• Positivity

• Local support

• Continuity [3M]

3

Discuss in detail about the rational curves. (13M) BTL 2


Rational curves:

• Rational curve - ratio of two polynomials - non-rational curve - defined by one

polynomial - Various rational curves such - rational Bezier curves - rational B-spline - β –

spline curves - rational conic sections - rational cubic been formulated.

[2M]

• Most widely used rational curves used are non-uniform rational B-splines (NURBS)

which is capable of representing in a single form non-rational B-splines and Bezier curves

as well as linear and quadratic analytic curves. [2M]

• The rational B-Spline curve defined by n+1 control points Pi is given by,

P(u) = ∑ 𝑃𝑛𝑖=0 i Bi,k(u) 0≤u≤umax

where the Pi are an input set of n+1 control points for the rational B-spline curve and

Bi,k(u) are the rational B-spline basis function. [2M]

4 What is surface modeling? And discuss the various types of it. (13M) BTL 2




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• Surface - set of related curves. Basis of surface - definition of curve - two dimensions

given plane - swept along another curve- defined another plane.

[3M]

• Surface creation - wire frame entities - lines, curves, points - All analytical, synthetic

curves - used to generate surfaces. Types of surfaces - available in CAD - Flat surface,

Sculptured surface, Analytical surfaces, Sculptured surfaces based on patches.

[2M]

• Various curve generation techniques - Implicit, explicit, parametric forms- extended for

generation of surfaces. It may be treated as the extension of the curve design in parametric

form. [2M]

• Explicit form - surface represented by equation - z=f(x,y).

The implicit form of surface representation is f(x,y,z)=0

Parametric form - surface represented - x=X(u,v) y=Y(u,v) z=Z(u,v)

[3M]

• Parametric polynomial curves - choose degree of curve -Choose high degree - have many

parameters - set form desired shape. [3M]

5

Write short notes on solid modeling and its representation. (13M) (Apr/May 2017) BTL 3


• Solid model representation: wireframe model – surface model – solid model. [2M]

• Solid modeling entities: Block – cylinder- cone – sphere – wedge – torus. [2M]

• Solid modeling approaches: primitive based modeling – feature based modeling. [2M]

• Representation of solid: Rigidity – homogeneous three dimensionality – fitness and finite

description – boundary determinism – closure under rigid motion and Boolean operation.

[4M]

• Representation schemes: half spaces – boundary representation – constructive solid

geometry – sweeping – analytic solid modeling – cell decomposition – spatial

enumeration – octree encoding – primitive modeling . [3M]

6

Discuss interpolation and approximation modelling in computer graphics. (13M) BTL 2


• Polynomial sections – curve passes through – each control point –resulting curve is

interpolate. [4M]

• Polynomials fitted - general control point – without passing through – any control point –

resulting curve – approximate set of control points. [3M]

• Lagrangean polynomial – unique polynomial – degree n passing through n+1 points –

oscillate about control points. [4M]




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• Cubic polynomial – minimum order polynomial – inflection within curve segment –

representation of non-planar three dimensional curves. [2M]

7

Write down the characteristics of the bezier curves. (13M) (Nov/Dec 2016) BTL 2


• Defined on n+1 points – represented parametric polynomial curve degree n.

• Passes through – first and last points .

• Tangent to first and last segments – characteristic polynomial.

• Follows shape of characteristic polygon.

• Degree of polynomial defining curve – one less than number defines polygon points.

• Curves exhibit symmetry property.

• Control point – weighed by blending function.

• Curve lies – convex hull – four control points.

• Exhibits variation diminishing property.

[13M]

8

What are called analytical and synthetic surfaces? Explain them in detail. (13M) (Apr/May

2017) BTL 2


• Two types of surfaces – analytical and synthetic surfaces.

• Analytical surfaces – based on wireframe entities – plane surface, rules surface, surface of

revolution and tabulated cylinder.

• Synthetic surfaces – formed given set of data points – Bezier, b-spline and coons patches.

• Three methods for synthetic surfaces – tensor product method – rational method –

blending method.

• Tensor product – higher dimensionality of surface – properties deduced from underlying

curve schemes.

• Rational method – develops rational surface – extension of rational curves.

• Blending method – approximates surface – piecewise surfaces.

[3M]

PART * C

1

Write short notes on Constructive Solid Geometry (CSG). (15M) (May/June2016,

Nov/Dec2017 ) BTL 4


• Simple primitives – Boolean set operators – Union (U) – Difference (-) – intersection.

Data representation - represented by binary tree – store model – data structure. Any node

– one parent node and two child node.




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• Unbalanced tree and balanced tree – left and right sub-trees – preferred to combine – all

subtracts together – rather than achieving – two subtracts at same time.

• Advantages:

Data stored less – memory less.

Fully valid geometrical solid model

Less skill

Complex shapes – developed easily

User friendly.

2

Define briefly boundary representataio (B-Rep) in solid modeling. (15M) (May/June 2016,

Nov/Dec 2016, Nov/Dec2017) BTL 3


• Physical object bounded set of faces – surface boundaries – vertices, edges and faces –

requires faces convex or triangles – only boundary surfaces stored – volumetric properties

calculated gauss divergence theorem.

• Graph based data structure system – tetrahedron four vertices – edges connected by

vertices – connectivity to form solid called topology




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• Topological information – relationship about vertices, edges and faces – orientation of

edges and faces.

• Geometric information – equations of edges and faces – closed surface – continuous

without break – orientable surface – distinguish two sides using direction of surface

normal.

• Variety of solids – polyhedral solids and curved solids –polyhedral – straight edges like

box, wedge. Curved solids – similar to polyhedral – have curved faces and edges –spheres

and cylinders. [3M]

3

Explain Bezier curve representation. Also discuss its important properties. (15M)

(May/June 2016) BTL 2


• Bezier curves - control polygon - curves in place of points and tangent vectors – case of

cubic splines - section can be fitted - any number of control points - control points be

approximated - relative position determine - degree of the Bezier polynomial.

[3M]

• Mathematically- parametric Bezier curve for n+1 control points - defined by,

P(u) = ∑ 𝑃𝑛𝑖=0 i Bi,n (u) 0≤u≤1

P(u) any point on the curve - Pi control point - describes path - approximating Bezier

polynomial function between P0 and Pn - Bi,n(u) Bezier blending functions - called

Bernstein polynomials. [4M]

• Blending functions - cubic Bezier curve - obtained by substituting n=3,

B0,3 (u) = (1-u)3

B1,3 (u) = 3u(1-u)2

B2,3 (u) = 3u2(1-u)3

B3,3 (u) = u3 [2M]

• Evaluating four constants - Bezier matrix as,

MH = -1 3 -3 1

3 -6 3 0

-3 3 0 0

1 0 0 0 [3M]




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UNIT-III VISUAL REALISM

Hidden – Line-Surface-Solid removal algorithms – shading – coloring – computer animation. PART-A

Q.No Questions

1

What is rendering? BTL2

To represent the visual complexities of the real environment as image attributes i.e., realistic

mage synthesis has been one of the goals in computer graphics research since its inception. The

process of creating realistic images from models is called rendering.

2

On which factors the visibility of parts of objects depends upon? BTL1 The visibility of parts of objects depends on:

• The location of the viewing eye. • The viewing direction. • The type of projection. • The distance of the viewing eye from. • The faces of various objects in the scene.

3

List the various test to determine Visibility. BTL1

• Bounding box or Minimax test. • Containment test. • Back face or depth or Surface test. • Computing silhouettes. • Edge Intersections. • Segment Comparisons. • Homogeneity test.

4

What are Silhouette edges? BTL2 Silhouette edges are boundaries between adjacent front facing (visible) and back facing

(invisible) surfaces with respect to a given viewing direction. The intersection of two visible surfaces form a visible edge but is not a part of the Silhouette.

5

Define Sorting. BTL2 Sorting is the process of arranging items arranging items in some sequence and/or in different sets according to a selected criterion. Sorting is an important tool in computer graphics for problem-solving which greatly improves algorithm’s efficiency.

6

What is Coherence? BTL2

Scenes typically consist of objects whose properties (like geometry, Color, shading, etc.) vary smoothly within a small local region in the scene i.e. there is a tendency for the characteristics of a scene to be locally constant (homogenous).The degree or extent to which the scene or its projection (image) exhibit local similarities is called Coherence.

7

Why removal of hidden line is important? BTL2 When a complex drawing is fully displayed then a large number of lines usually render the picture impossible to perceive. In order to provide an accurate representation of an object and thereby allow the user to correctly interpret the object certain lines must be hidden.

8

State Z-buffer algorithm. BTL1 The depth- buffer algorithm is one of the simplest method to achieve hidden surface removal and is also called the Z-buffer algorithm since object depth is usually measured along the Z-axis of the viewing system.

9

What is ray tracing ? BTL2 Ray tracing is an image space algorithm used to render high quality realistic images of solid objects. It is a technique for generating an image by tracing the path of light through pixels in an




1- 19

image plane and simulating the effects of its encounters with virtual objects. The idea is to trace the light ray for each pixel, from an view point through the pixel and into the scene. The first surface intersected by the ray is the visible surface.

10

What is the basic principle of Ray tracing algorithm? BTL2 Ray tracing is based on the principle of geometric optics. There are infinite number of rays that emanate from the surfaces in a scene and is therefore difficult to trace rays in the direction of light propagation. The method is to trace a light path backward from the viewpoint through each pixel and into the scene.

11

What is Shading? (Apr/May 2017) BTL2 Shading refers to the process of altering the color of an object surface polygon in the 3D scene based or its angle on lights and its distance from lights to create a photorealistic effect.

12

What are the limitation of shaded images? BTL1 The limitations of shaded images are that objects of interest may be hidden or partially obstructed from view and critical geometry such as lines, arcs and vertices are not explicitly shown. To overcome these problems shaded images from different viewpoints may be obtained and techniques such as shaded image/wire frame overlay, transparency, and sectioning can be used.

13

State Lambert’s law. BTL1 Lambert’s cosine law governs diffuse reflection, hence it is also called Lambertian Reflection. The surface brightness depends on the angle between surface normal and the direction to the light source.

14

State the hidden line elimination mechanism in visual realism. BTL1

“For a given three dimensional scene, a given viewing point and a given direction eliminate from

an appropriate two dimensional projection of the edges and faces which the observer cannot see.

”

15

How the visual realism of images can be enhanced? BTL2

The visual realism of images can be enhanced by including shading effects such as • Transparency • Shadows • Surface details • Texture

16

What is a color model? BTL2 A color model or a color space is an abstract mathematical model describing the way

colors can be represented as tuples of numbers, typically as three or four color components. Color models are used to describe color as accurately as possible. Each color is represented by a point

in three dimensional color coordinates system to permit whole range of colors specification within some color range.

17

What is computer animation? BTL2 Computer animation is the use of computers to create animation. Virtual entities may

contain and be controlled by attributes such as location, orientation and scale. Animation is the change of an attribute over time. It generally refers to any time sequence of visual changes in a

scene

18

Mention the various hidden line removal algorithm. (Apr/May 2017) BTL1

• Edge – oriented approach.

• Silhouette originated approach

• Area – oriented approach.

19

What is meant by hidden surface removal? (Apr/May 2018) BTL2

It is the process of eliminating lines of parts of object which are covered by others. It is




1- 20

extensively used for objects represented as wireframe skeletons and it is a bit tracker. Hidden

surface removal does the elimination of parts of solid objects that are covered by others.

20

List down the disadvantages of depth-buffer algorithm. BTL2

• It can only find one visible surface at each pixel position.

• This method requires additional buffer as compared with the depth or priority algorithm

and the overheads is involved in updating the buffer.

• This method is less attractive in the cases where only a few objects in the scene are to be

rendered. PART – B

1

Explain in detail the area-oriented algorithm for removal of hidden line. (13M) (Nov/Dec

2016, Apr/May2018) BTL 2


• Identify silhouette polygons – silhouette computation – description [2M]

• Quantitative hiding values – each edge of silhouette polygons – intersecting silhouette

polygons – using depth test – edges visible – value 0 – edges invisible – value 1. [3M]

• Visible silhouette segment – quantitative hiding values – closed polygon – completely invisible – least hiding values – segment visible. [3M]

• Visible silhouette segment – intersected partially visible faces – partially hide – fully hide non-silhouette – edges partially visible. [3M]

• Display interior – visible or partially visible polygon – all faces lying inside polygon –

stack started visible face. [2M]

2

What is shading? What are the methods of shading? (13M) (Apr/May2018) BTL3


• Process of variation – chromatic or achromatic color – depends on light – reflected from

model of our eye. [1M]

• Lighting model – illumination model – shading model – realistic display of image –

generating perspective projections. [2M]

• Intensity calculations from light model – calculate light intensity – projected pixel

positions – various surfaces in a scene. [2M]

• Constant intensity shading – lambert shading – surface of object – approximated by

polygons – faceted solid. [2M]

• Gourand shading – smooth shading – linearly interpolating color – values matched –

adjacent polygons – among common edges. [2M]

• Phong shading – interpolates normal vectors – normal vector interpolation shading –

shade at each pixel. [2M]

• Half-tone shading – output devices limited intensity range – bilevel monitors and printers

– combining intensity of multiple pixels. [2M]

3

Explain visibility techniques for improving efficiency of algorithms. (13M) BTL 1

Answer: Page 3.6 – Dr.G.K.Vijayaraghavan, Dr.S.Sundaravalli.

• Minimax techniques – compare two polygons – overlap or not – polygon enclosed box –

find maximum and minimum x and y co-ordinates. [2M]

• Containment test – check location of given point – inside or outside given polygon –

convex polygon – x and y co-ordinates – substituted into line equation. [2M]

• Back face/Surface test – surfaces facing the viewer – surfaces opposite to viewer – depth

comparison – remove faces not visible. [2M]




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• Computing silhouettes – edge intersection of one visible face – invisible face called

silhouette – sign of component – viewing direction. [2M]

• Edge intersection – visibility partially visible edges – edge intersection in two dimensions

– point of intersection – segmentation – visibility concepts. [2M]

• Segment comparison – solve hidden surface problems – raster display arranged on display

– top to bottom and left to right. [3M]

4

Explain how position and orientation are interpolated in animation process. (13M) BTL 3

Answer: Page 3.71 – Dr.G.K.Vijayaraghavan, Dr.S.Sundaravalli.

• Interpolation techniques – calculate position and orientation – animate objects three

dimensional space – includes camera and light sources. [5M]

• Position and orientation – object in three dimensional – can be modified – changing

values – transformation matrix – controls translations, rotations and scaling . [4 M]

• When keyframe interpolation techniques used – values in transformation matrix – moving

objects specified – key frames – in between values are interpolated. [4M]

• Most computer animation programs – provide animators- direct ways to edit –

transformation matrix of object – parameter curves. [4M]

5

Explain priority algorithm. (13M) (Nov/Dec 2016, Nov/Dec2017) BTL 2 Answer: Page 3.11 –

Dr.G.K.Vijayaraghavan, Dr.S.Sundaravalli.

• Surfaces of polygon – sorted according – smallest z-coordinate – each surface. [1M]

• Surface – largest z-depth – compared – all other surfaces – list to compare – any overlap

in z-coordinate. [2M]

• Any ambiguities – resolved – splitting polygons – z co-ordinate of polygons – overlap.

[2M]

• If there no overlap – scan converted – fill the frame buffer. [2M]

• Same procedure – followed for all – other surfaces in list – there no overlap. [2M]

• Scan converts – each polygon – ascending order – back to front – terms of z-coordinate.

[2M]

• Priority higher – face coming first – viewing direction – this algorithm called priority

algorithm. [2M]

6

Explain hidden surface removal algorithm. (13M) (May/June 2016, Apr/May 2017,

Nov/Dec2017) BTL 2 Answer: Page 3.18 – Dr.G.K.Vijayaraghavan, Dr.S.Sundaravalli.

• Hidden surface removal – process of eliminating surfaces – covered by other surfaces.

[2M]

• Elimination procedure – object-space algorithm – image space algorithm – hidden surface

removals. [3M]

• Depth buffer or z-buffer algorithm – compares surface depth – at each pixel position on

projection plane. [2M]

• Area coherence or Warnock’s algorithm – elegant divide and conquer – area coherence of

polygons – resolve visibility of many polygons. [2M]

• Scan line or Watkin’s algorithm – one line at a time processed – polygon surfaces

intersecting the line examined. [2M]

• Depth or priority algorithm - Scan converts – each polygon – ascending order – back to




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front – terms of z-coordinate. [2M]

7

Discuss the various animation sofware packages. (13M) BTL 3 Answer: Page 3.73 –


• 2D Modelling: basic tool – almost all software – create basic shapes.

Packages available: Fractal Design Painter – Paintbrush – CorelDraw – Canvas. [2M]

• 3D Modelling and animation tools: objects – rendered – perspective.

Packages available: Macromedia’s extreme 3D – Stratavision’s 3D – Autodesk’s 3D

Studiomax – Specular’s LOGOMOTION – Infini-D C Aligaris Truespace. [2M]

• Image editing tools: create images –scratch – digitize images – scanners – video frame

grabbers.

Packages available: Kai’s power tools from metatool – Adobe Photoshop – Adobe gallery

effects. [3M]

• OCR Software: bitmapped characters – electronically recognizable – ASCII test – text or

graphics – examining texture and density of areas.

Packages available: Perceive – MS Windows OCR application from ocron – omnipage

pro from care. [3M]

• Sound editing programs: both digitized – MIDI – user see music – hear it – representation

of sound – finite increments – cut copy paste.

Packages availabler: Creative wavestudio – soundedit16 from macromedia – alchemy or

audiotax from passport – sound designerII from digi design. [3M]

PART C

1

List down the different color models and explain any two in detail. (15M) (May/June 2016,

Nov/Dec 2016) BTL 4 Answer: Page 3.46 – Dr.G.K.Vijayaraghavan, Dr.S.Sundaravalli.

• Color model – orderly system – whole range of color – two types – subtractive and

additive – additive type result of transmitted light – subtractive type result of reflected

light. [3M]

• Important color models – RGB model – CMY model – YIQ model – HSV model – HSL

model. [2M]

• RGB model – convergence three primary additive colors – red, green and blue – RGB

values are 1 white color produced - RGB values are 0 black color produced.




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[5M]

• CMY model – convergence three primary colors – cyan, magenta, yellow – color in

printing acts subtractive – origin represents white light – equal amount of all primary –

produces gray color – main diagonal of the cube.

[5M]

2

Explain the Warnock’s area subdivision algorithm. (15M) BTL 1 Answer: Page 3.21 –


• John warnock – proposed elegant – divide and conquer hidden surface algorithm – relies

on area coherence of polygons – resolve visibility – many polygons in image space.

[2M]

• Depth sorting – simplified and performed only – cases involving image space overlap –

also called area-subdivision method – process involved division – viewing window into

four equal sub-windows. [3M]

• Classifies polygons – respect to current viewing window – simple or complex cases –

simple case – one polygon in the window or none at all - complex cases overlapping




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polygons. [3M]

• Each subdivision used – reclassifying remaining polygons – recursive procedure

continued – until all polygons classified – simple case – current window reaches pixel

resolution of screen. [3M]

• Polygons readily classified four groups – surrounding surface – intersecting or

overlapping surface – inside surface – outside surface. [2M]

• Alternate subdivision strategies – divide using enclosed polygon vertex – sort polygons by

minimum-z – use front polygon as window boundary. [2M]

3

Explain hidden solid removal algorithm. (15M) (Apr/May 2017) BTL 2 Answer: Page 3.26 –


• Hidden solid removal – process displaying solid models – with hidden lines and surfaces.

[2M]

• Process carried out automatically – completeness and un-ambiguities of solid models.

[2M]

• Complexity of CSG model lines – visibility and combination – primitive solids – one

composite model. [2M]

• Converting CSG model – B-rep model – rendered standard hidden surface removal.

[2M]

• Ray-Tracing or Ray - Casting Algorithm – process of tracking – plotting path taken – rays

of light starting – light source to centre of projection. [2M]

• Shoot a ray from view point – through a pixel – first object which hits – visible at pixel.

[3M]

• Algorithm provides flexibility – handle both flat and curved surfaces – easily modified –

provide realistic shading. [2M]

UNIT-IV ASSEMBLY OF PARTS

Assembly modelling – interferences of positions and orientation – tolerance analysis-mass property calculations – mechanism simulation and interference checking.

Q.No Part*A

1

Why there is a need for assembly modeling? (May/June 2016, Nov/Dec 2016) BTL2

The need for assembly modelling arises due to the following reasons:

• The need for dismantling the assembled component during its service life.

• It is needed when various material combinations are used.

• Sometimes the physical size needs the assembly modelling.• Certain manufacturing process needs the assembly modelling like casting in which pressing

needs assembly.

2

List the main advantages and disadvantages of localized welding. BTL1

The advantages are:

• Localized welding is a fast and low cost welding technique.• This technique is suitable for robot or other automated operation thus result in high volume

production.• This technique does not suffer from distortion because heat input is localized.

• Suitable for sheet metal assemblies.

• Does not require any filler material.




1- 25

The disadvantages are:

• The equipment used is of very high cost.• This technique needs sealing against moisture in joints.

3

Mention the advantages of adhesives techniques. BTL1

• Any type of engineering material can be joined by this technique.

• For assembly purpose it does not require any high temperature operation.

• Varying thickness materials can be joined by this technique.

• This technique does not suffer from any distortion problem.

• Smooth joining is possible by this method.

4

Define tolerance. BTL2

“The tolerance is the permissible variation in the size of a dimension and is the difference between the upper and lower acceptance limits.”

5

Give the disadvantages of Tolerance Analysis. (Apr/May 2017) BTL1

• Helping them study three dimensional relationships within an assembly.

• Giving designers a means of calculating part tolerances.

• Helping Engineers compare design proposals.

• Helping designers produce complete drawings.

6

What is automated assembly? BTL2

The automated assembly implies that there are different components which nares to be assembled by machines. The main difference is that the machines are fearless adaptable than the human counter parts.

7

What are the considerations in designing that facilitates assembly processes? BTL1

• Design for ease of handling

• Design for ease of labelling• Design for ease of testing

8

Why there is need for tolerances? BTL2

It is impossible to manufacture a component with exact size. Hence the designer decides how close to the real size is satisfactory. In recent days, tighter tolerances are possible. As a result of which most of the manufacturer produces interchangeable parts.

9

When do we use geometric tolerances? BTL2

Geometric tolerances to a drawing is very efficient manner of specifying closely the

requirements of the designer. It would, be easy to over-tolerance a component, the result will be an increase in the cost of manufacture. They should be applied for all requirements critical

to the function and interchangeability of parts, except where it is known that the machinery and manufacturing techniques can be relied upon to achieve the required standards of accuracy.

10

How mass property calculation is applied in CAD/CAM? (Nov/Dec 2016) BTL3

It is systems. Mass property one of the major applications implemented in CAD/CAM

calculations involve masses, centroids and inertia properties. They form the basis of study and analysis of rigid and deformable body mechanics. These involve various integrals. For similar

shapes exact evaluation of integrals would occur. Most important property algorithm that utilizes these methods are fully automatic ad require no additional input except mass attributes.

11

Define simulation. BTL2

Simulation is a key technology for designing new products, developing new manufacturing processes and evaluating the performance of mechanisms.

12 What are simulation models? BTL2




1- 26

Simulation models are sets of mathematical equations representing the behavior of the system

in a physical domain of interest. The complexity of the mathematics depends on availability of data and varies in funct6ion of the application and the design state. These simulation models

provide and intuitive representation of the mechanical structure, allowing operator to explore aspects such as type and construction of joints, mobility, etc. The classical teaching method is a

difficult task, which requires operator’s imagination or use of expensive mechanical installations.

13

How are mechanical systems simulated? BTL2 Mechanical systems are described by means of representing them as systems of rigid bodies connected by various kinematical pairs and force elements. Lots of dynamical performances of mechanical systems are available during simulation, such as linear and angular coordinates, velocity and acceleration, active forces and moments, reaction forces, etc.

14

Define motion simulation. BTL2

Motion simulation provides complete, quantitative information about the kinematics –

including position, velocity, and acceleration, and the dynamics – including joint reactions, inertia forces, and power requirements, of all the components of a moving mechanism, In an

additional importance, the results of motion simulation can be obtained virtually at no additional time expense, because everything needed to perform motion simulation has been

defined in the CAD assembly model already, and just needs to be transferred to the motion

simulation program.

15

What is the common mistake made in creating motion simulation models? BTL2

A common mistake made in creating motion simulation models is selecting improper joints to connect bodies. Introducing I proper joints creates and invalid or inaccurate model that does not simulate the true behavior of the mechanical system.

16

List advantages and disadvantages of mechanical simulation. BTL1

Advantage of mechanism simulation:

• Models behavior of a real hardware system using an approximation in software.

• Mathematical formulae are used to emulate and predict physical phenomena.

• Primary method used for evaluation of systems before manufacture.

• Identification and tuning of critical components (optimization) • Time and money are saved by removing faults before manufacture.

Disadvantages of mechanism simulation:

• Building hardware prototypes is impractical for large systems. • Takes too long and costs too much while simulating.

17

Define interference checking. BTL2

Component interference, misaligned and mismatched holes and fasteners and incorrect tolerance of manufactured parts are the main causes of high rework and scrap costs on the assembly floor. When this problem occurs, the components in the assembly have to be modified or redesigned, increasing the cost of production. Interference avoidance modification seeks to access any interference that may exist as a result of basic design and then make proper modifications to remove the interference at the design stage.

18

What are the factors that influence interference checking? BTL2

Interference avoidance modification can be divided into two phases:

• Interference checking to discover existing interference, and then

• Making modifications to remove the interference, if interference does exist. To check




1- 27

interference, geometric and topological data are necessary.

• Any interference between two objects is checked by computer analysis of the data structure

of the model has a strong influence on the efficiency of the interference checking.

19

List out the benefits of the interchangeable parts. BTL2

The benefits of the interchangeable parts are listed below:

• Assembly of parts requires less skilled operators. So it is cheaper and quality is easier to maintain.

• The damaged components can be easily replaced by another component with the same range of dimensions.

• Parts can be made in large quantities with less demand on the skill of operator.

20

Give the relation between tolerance and cost. BTL2

It is known clearly that, as the low tolerance will be with higher accuracy on the other hand cost will be higher. When considering the higher tolerance, it will give low accuracy and cost will also be reduced.

PART*B

1

Describe the various steps in generation of assembly model. (13M) (Apr/May 2017) BTL 1

Answer: Page: 4.2 – Dr.G.K.Vijayaraghavan, Dr.S.Sundaravalli.

• Assembly of product – various methodologies – welding together – fastened together by bolt and nut – barrel and rod in hydraulic cylinder.

• Nature and structure of dependencies – between parts in assembly – sub-components of part are movable.

• Assembly model include – spatial positions and hierarchical relationship among the parts – assembly or mating conditions are important.

• Component geometric models – created and assembly is created – specifying relative location and orientation of parts.

• Assembly of parts – mating and spatial relationship between parts – link between individual and assembly parts created.

• Assembly analysis includes – interference checking – calculation of mass properties – kinematic and dynamic analysis.

(8M)




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(5M)

2

Write short notes on mating conditions. (13M) (Apr/May2018) BTL 3


• Mating conditions – geometric or mathematical rules or restrictions – applied to restrict

the location of parts in assembly model. (3M)

• Basic mating conditions – coincidence – tangent – parallel – concentric – coplanar –

perpendicular. (2M)

• Coincident – applied to planar faces – forces to be in touch with each other – specified by

unit normal vector. (2M)

• Coplanar – applied between to planar faces – forces them to lie in same plane – each face

specified by its unit normal vector. (2M)

• Concentric – also called fit condition – applied between two cylindrical faces –

concentric mating condition – forcing axes to become collinear. (2M)

• Tangent – applicable between planar and cylindrical surface – two cylindrical surfaces –

tangent condition planar face and cylindrical face. (2M)

3

Write short notes on interfernce of position and orientation. (13M) BTL 2 Answer: Page:

4.16 – Dr.G.K.Vijayaraghavan, Dr.S.Sundaravalli.

• Interference of position and orientation – mating parts in assembly – reverse process of

mating condition requirement. (2M)

• The position of mating parts and orientation – found from mating condition implied for

assembly modelling. (2M)

• Process requires computing – 4x4 homogeneous transformation matrix – local

coordinate system is mapped – global coordinate system of assembly using 4x4

homogeneous transformation matrix. (3M)




1- 29

[T1] =

𝑅1𝑥𝑅1𝑦 𝑅1𝑧 𝐿𝑥

𝑅2𝑥𝑅2𝑦 𝑅2𝑧 𝐿𝑦

𝑅3𝑥𝑅3𝑦 𝑅3𝑧 𝐿𝑧

0 0 0 1

= 𝑅 𝐿0 1

(4M)

• Transformation matrix has twelve elements – nine rotational and three translational

elements – twelve variable must be determined for mating conditions. (2M)

4

Explain the concept of tolerance in assembly modelling. (13M) (May/June 2016, Nov/Dec

2016) BTL 4 Answer: Page: 4.30 – Dr.G.K.Vijayaraghavan, Dr.S.Sundaravalli.

• Tolerance analysis – allowance for specific variation – size and geometry of part –

allowable range of variation – design intent in dimension. (3M)

• Tolerancing of machine parts – necessary design functions – variability of all

manufacturing methods. (2M)

• Assignment of upper and lower limits – basic dimensions to account this variability –

allowable amount of dimensional variation – design stage impacts manufacturing cost.

(2M)

• Tolerance analysis – involves modelling of relations – among the variation, tolerance and

cost. (2M)

• Terms used in tolerance analysis – shaft – hole – male and female surface – basic and

actual size – limits of size – maximum and minimum limit – tolerance and allowance.

(2M)

• Maximum material condition – unilateral and bilateral tolerance – tolerance zone –

deviation – upper, lower and actual – zero line – fundamental deviation. (2M)

5

Write short notes on mass property calculations. (13M) (Apr/May2018) BTL 2


• Mass properties of object – useful properties in engineering applications – geometric

models created first – mass properties are calculated using these models. (2M)

• Values evaluated – various integrals using – exact evaluation method or approximation

technique – simple and complex shapes respectively. (1M)

• Formulation of major mass properties – mass, centre of gravity – first moment of inertia

– second moment of inertia. (2M)

• Mass – amount of matter contained in object – depends on volume and density –

calculated initially considering small element – expanded to whole object. (2M)

• Centroid – centre of gravity – location on object – experiences only translation – no

rotation – centre where total mass – assumed to be concentrated. (2M)

• First moment of inertia – moment of area, volume or mass – with respect to given plane –

product of mass and its perpendicular distance from plane. (2M)

• Second moment of inertia – product of mass and square of perpendicular distance –

resistance of object to any rotation about axis. (2M)

6

Describe the techniques involved in mapping constraints to kinematic joints. (13M) BTL 3


• Joint constraints – certain restrictions – components can be assembled – way they move

relative to each other. (3M)

• Each of joint constraints – related to rigid body motion – mating part and degree of




1- 30

freedoms associated with it. (3M)

• Using mating geometric features and principal vectors – one independent principal vector

allows – one rotational DOF and two IPV. (2M)

• Bearing and crank – concentric between hole of bearing and cylindrical surface of lower

shaft of the crank. (3M)

• Coincident mate - between two opposite faces of the two components – two mating

constraints – two principal vectors – parallel one rotational and one parallel. (2M)

7

Write short notes on interference checking. (13M) (Nov/Dec 2016) BTL 5


• Interference checking – process of checking if any parts – pierce each other or not-

interference volume displayed. (2M)

• Interference detected between two parts – CAD system displays – interference should

rectified or eliminated. (2M)

• Designers and manufacturers – check jointly for product assembly – before the product

gets manufactured. (2M)

• Assembly planners – feature mating or interference free techniques – find assembly part

interference interaction. (3M)

• Complete automation of procedure – professional assembly plan – geometrical

information should be automatically taken. (2M)

• Analyzed for interference relationships – designed for utilized assembly analysis tools –

so much time consuming. (2M)

PART*C

1

What is meant by hole basis system and shaft basis system? (15M) BTL 3 Answer: Page:

4.33 – Dr.G.K.Vijayaraghavan, Dr.S.Sundaravalli.

Hole Basis System:

• Hole is kept constant – shaft diameter is changed – to obtain various fits – basic size of

hole – taken as low limit size.

• High limit size of the hole – two limits of size for shaft – then selected to give desired fit.

(4M)

(4M)

Shaft Basis System:

• Shaft is kept constant – hole is varied to get various fits – basic size of shaft taken – one




1- 31

of the limit of size.

• Other limit for shaft – other two sizes for hole – shaft denoted by ‘h’- holes get different

letters to get desired fit. (3M)

(4M)

2

Write short notes on tolerance/cost reationship.(15M) BTL 2


• Cost of part depends on tolerance – manufacturing cost consists – machining cost and

scrap cost. (3M)

• Machining cost contains – labour cost – overhead cost – cost of gages, tools, jigs and

fixtures, inspection. (3M)

• Scarp cost covers – cost of rejected parts – during inspection due to tolerance variations –

defects in manufacturing. (2M)

• Tighter tolerancing results – reduction in manufacturing cost – using less skilled

manpower – lower inspection standards – lower scrap material. (2M)

(5M)

3 Explain Denavit-Hartenberg (D-H) representation in mapping mating constraints. (15M)




1- 32

BTL 4


• After converting mating constraints to kinematic joints – next step is mathematical

construction of kinematic model – commonly assumed all joints have one DOF. (2M)

• Action of each joint can be described – single real number – angle of rotation in case of

revolute joint – displacement in case of prismatic joint – objective to determine the

cumulative effects of entire set of joint variables. (2M)

• Open loop mechanism – n joints and n+1 links – each joint connects two links – first link

is fixed – does not move when joints are actuated. (2M)

• In general link n – not connected back to base link – called as open loop – closed loop

system – link n connects back – any link between 0 and n-2. (2M)

• Using DH convention – considerable amount of streamlining – simplification in

mathematical representation – kinematic model can be achieved. (2M)

• Each homogeneous transformation matrix – represented as product of four basic

transformation matrices.

𝑇1𝑖−1 = 𝑅𝑧(𝜃𝑖)𝑇𝑧(𝑑𝑖)𝑇𝑥(𝑎𝑖)𝑅𝑥(𝛼𝑖)

(5M)

UNIT-V- CAD STANDARDS

Standards for computer graphics- Graphical Kernel System (GKS) - standards for exchange images-

Open Graphics Library (OpenGL) - Data exchange standards - IGES, STEP, CALS etc. -

communication standards.

PART-A

Q.No Questions

1

What are the two methods of exchanging data among the CAD/CAM system? BTL2 The two methods of exchanging the data among the different CAD/CAM systems are direct translators and indirect translators. Direct translators convert data directly in one step. Indirect translators utilize some neutral file format, which reflects the neutral database structure, with each system having its own pair of processor to transfer data to and from this neutral format.

2

What is Graphics Kernal System (GKS) based on? BTL2 GKS is based on a number of elements that may be drawn in an image, known as graphical primitives.

The basic set of primitives are:

• POLYLINE - To draw multi – element line.

• POLYMARKER - To draw points.

• FILLAREA - For Raster fill operations.

• TEXT - Words.

3

When is SET Command used in GKS? BTL2 Display characteristics for primitives, such as line – style and thickness, color, text font and text angle, are defined by attributes, the values of which are set using the SET command. GKS also allows attributes to be bundled, that is grouped together and modified as a single entity.

4

What is bitmap? BTL1 The raster array which converts the CAD system into a series of graphics primitives are represented by a region of computer memory known as bitmap.

5

What is a graphics metafile? BTL1 A graphics metafile is a formatted computer file containing graphics commands and data. It




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may be either a trail of graphics commands used to generate a picture of the elements that make up the picture. A key feature of a metafile is that it is resolution independent, and can therefore be displayed at different sizes and scales and on devices of different resolution.

6

What are metafile standards? BTL1 The important metafile standard is the Computer Graphics Metafile (CGM – ISO 8632, 1992), which allows pictures to be described as collections of graphics primitives including lines, polylines, arcs, ellipse, filled areas, text and markers such as points or crosses.

7

What is the simplest way to store a bitmap? BTL1 The simplest way of storing a bitmap is simply to write the numbers that the pixels represent to the file, together with a header giving information about the file.

8

Define GKS. (Nov/Dec 2016, Apr/May 2017) BTL2 GKS is basically a set of procedures which can be called by user programs to carry out certain generalized functions such as arc, circle and ellipse etc., GKS is defined in terms of number of levels describing the level of support in terms of facilities.

9

What is then advantage of Open Graphics Library? BTL1 It provides a means of drawing and rendering geometric objects like points, line segments, polygons for which specifying how they should be colored, and how they should be mapped from the model space to the screen.

10

What is Open Graphics library? (Apr/May 2017, Nov/Dec2017) BTL2 Open Graphics Libraryis also named as open GL. Windows X offers a powerful device independent means of generating graphical systems and user interfaces, but its device independence and distributed nature means that it can impose a high load on hardware. It has an advantage of the graphics accelerator hardware that has been developed to allow dynamic manipulation of 3-D models with hidden surface removal, shading and texturing.

11

What is CALS? BTL2 (BTL2) Continuous Acquisition and Life cycle support is CALS. This data exchange standard was

produced with an aim of applying computer technology to the process of specifying, ordering, operating, supporting and maintaining the weapons systems used by the US armed forces, although it can be adopted by any industry, not just defense industry.

12

Define start section. BTL2 Start section is setup manually by the person initiating the IGES file. It contains the

information that may help the user at the destination, such as the features of the originating system.

13

Write a short note of error handling? BTL2 While importing an IGES file, Error handling is very much important. There are two major

error sources when processing IGES file: Program errors in the processor and is interpretation

of the IGES standard itself. The way an IGES processor reports error is that preprocessor should report the entity type, number of unprocessed entries, reasons for un processing and

other relevant database information of these unprocessed entities. IGES should also report any invalid or missing data encountered in reading IGES files especially those that were edited.

14

What are fiber optic links? BTL2 It is an alternative to copper connecting wires in LANs. Optical communication offers

the advantage of large transmission bandwidth and relatively immunity from electromagnetic interference or corrosion problems which make them ideal for industrial environments.

15

Write a short note on standards for computer Graphics. BTL2 Computer graphics standards grew from low-level, device-dependent collections of




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subroutines supply by graphics hardware manufacturers into higher-level, device-independent packages designed to introduce a measure of portability to application programs. These packages consist of a series of sub routines to set up graphics windows and viewports and to draw simple graphics primitives within them.

16

Define database. BTL1

Database is a collection of data at a single location to be used by various people for different

applications.

17

Classify CAD standards. (May/June 2016) BTL1

• Graphics and computing standards.

• Data exchange standards.

• Communication standards.

18

What is called topological information? BTL2

Topological information is the information about the product through solid modelling. Next,

features include high level concepts about parts such as hole, flange, web, pocket, chamfer etc.,

19

What is Directory section in IGES? BTL2 Directory section is generated by IGES pre-processor. This section also contains the entry for each entity in the file comprising a code representing the entity type and subtype. Two lines comprising 18 fields of eight characters are used for each entry.

20

State the methods of data exchange. BTL1

• Direct CAD system export/import

• Direct translation software

• Neutral data exchange format.

PART – B

1

Write short notes on database management. (13M) BTL 4Answer: Page 5.2 –


• Database is collection of data – logically related data stored together – set of files

intended to serve one or more applications. [2M]

• Database must have – pre-decided suitable structure – for access, manipulation and

interpretation – based on edges and vertices. [2M]

• Reduces or eliminates redundant data – integrates existing data – provides security –

shares data among users – incorporates changes quickly. [2M]

• Exercises effective control over data – simplifies the method of using data – reduces the

cost of storage and retrieval of data – improves accuracy and integrity of data – also

control of data. [3M]




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[4M]

2

Discuss GKS in CAD standard. (13M) (Nov/Dec2017) BTL 3 Answer: Page 5.8 –


• GKS is basically set of procedures – can be called user programs to carry out certain –

generalized functions such as arc, circle, ellipse. [2M]

• GKS is defined in terms – number of levels describing the level of support – in terms

of facilities –form of computer language – consists of set of commands for graphical

operations. [3M]

• Strong influence by CORE two dimensional graphics – standardized system of

graphical functions – processing graphical data to create and process 2D images -

Defined functions are independent – programming languages applications – types of

devices used – covers three dimensional graphics. [3M]

• GKS implementations made – many hardware manufacturers in many languages – not

acceptable for dynamic graphics - Workstation used as an environment – user which

consists of VDU, printer or plotter – may be identical to programmers. [2M]




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[3M]

3

Describe the logical concepts in IGES. (13M) (May/June 2016, Nov/Dec 2016) BTL 2 Answer: Page 5.32 – Dr.G.K.Vijayaraghavan, Dr.S.Sundaravalli.

• IGES developed by US National bureau of standards – exchanges primarily shape and non-shape data – referred to CAD to CAD exchange. [2M]

• Store a file detail of entities to be transferred between system – allows compressed ASCII format and binary files – will have processor software to translate – from their software to IGES neutral file. [2M]

• Most comprehensive standard – designed to transmit entire product – including manufacturing and any other associated information – essentially specification for structure and syntax of neutral file is ASCII. [2M]

• Generally stable and reliable for exchange – simple geometric entities such as – points, lines, arc and little less - complex entities such as splines – poor for annotation, dimensions and group entities. [2M]

• IGES works at level of application database structure – based on the concept of entities such as points, lines, circles and surfaces etc., Entities – geometric entities –lines, circles, surfaces – annotations entities – dimensions, blocks, additional notes – structure




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entities – description of objects to define how object is made. [3M]

• File sections – flag, start section, global section, directory section, parameter data section, termination section. [2M]

4

Write short notes on OpenGL. (13M) BTL 4 Answer: Page 5.19 –


• OpenGL (Open Graphics Library) cross language – multi-platform application programming interface for rendering 2D and 3D vector graphics – used to interact with graphics processing unit (GPU) – obtain hardware accelerating rendering. [2M]

• Extensively used – fields of CAD, virtual reality, scientific visualization, information visualization, flight simulation and video games – although possible for API – implement entirely in software. [2M]

• Defined as number of functions – called by client program alongside – number of named integer constants – language independent - language bindings such as web GL, WGL, GLX and CGL. [2M]

• Features of OpenGL – based on IRIS GL – Low level – Fine Grained control – Modal – Frame buffer – Not programmable – Geometry and images – purely rendering to provide no API’s. [3M]

• First stage displaying the geometry – second stage effective means for resembling curve – calculating polynomial functions of input data – next stage geometric primitives based on vertices – converted to see the volume required for next stage.

[2M]

• Advantages – Industry standard – stable – reliable and portable – evolving – scalable – easy to use – well documented – simplified software development, speeds time to market – software developers access to geometric and image primitives – lighting and texturing. [2M]

5

Explain elaborately the thrust involved in developing CAD standards. (13M) BTL 4 Answer: Page 5.1 – Dr.G.K.Vijayaraghavan, Dr.S.Sundaravalli.

• Critical concern with CAD and CAM – communication of design and manufacturing data within engineering organization – there was need to create CAD standards – link different hardware and software from vendors. [3M]

• Each computer manufacturer – different operating systems, different rules and protocols – for communication of data between computers – computer to terminals and peripheral devices. [3M]

• Difficulties involved in incompatibility – pressure on data format, hardware, software, database standards – isolate programs and programmers from peculiarities – particular hardware. [3M]




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[4M]

6

Explain in detail about Programmers Heirarchial Interactive Graphics Standard.

(PHIGS). (13M) BTL 3 Answer: Page 5.17 – Dr.G.K.Vijayaraghavan, Dr.S.Sundaravalli.

• Offers extended set of primitives for graphical elements – mainly used for high functional systems – additional features such as hidden lines, surface manipulation and graphics animation etc., [3M]

• Advantage over GKS – ability to handle dynamic graphics changes - support segmentation of graphic displays. [2M]

• Main difference between GKS 3D and PHIGS – better compatibility with 2D images – providing standard acceptable by vendor – combined benefit of 3D animation. [2M]

• Features of PHIGS: very high interactivity – data input hierarchical structure –geometric animation – adaptability to distribute user environment – set of device independent logical concepts. [3M]

• Logical concepts in PHIGS: five basic concepts – structure networks and manipulation – logical input device – search and enquiry – structure transversal and display – graphic output. [3M]

7

Write short notes on continuous acquisition and life-cycle support (CALS). (13M)

(Apr/May 2017) BTL 4 Answer: Page 5.43 – Dr.G.K.Vijayaraghavan, Dr.S.Sundaravalli.

• Developed by US department of defense – prescribes format for storage and exchange of technical data – focuses mainly on technical publications – also known as CALS, CAL, RAS. [3M]

• An attempt to integrate text, graphics and image data – standard document architecture – improve and integrate logistics functions of military and its contractors. [2M]

• All technical publications federal government – must conform to CALS standard – commercial businesses medical, telecommunications, airline and book publishing industries. [2M]

• Structure of two CALS variants – type I and type II – type I consists of following – header , image data – type II contains – document profile, presentation styles, document layout, root layout. [2M]




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• CAL online geometry calculator – evaluate the point, real or integer expressions – existing geometry using object snap functions such as CEN, END and INS. [2M]

• Auto LISP variables inserted – arithmetic expression and assigned – value of the expression back to an Auto LISP variable – arithmetic and vector expressions – used in any command – expects points, vectors or numbers. [2M]

PART C

1

Explain how data is communicated between two CAD systems using IGES. (15M)

(Apr/May 2017) BTL 5 Answer: Page 5.55 – Dr.G.K.Vijayaraghavan, Dr.S.Sundaravalli.

• Level 1: Data communicated between – graphics utility software and graphics output

device – VDI (Virtual Device Interface) or CGI Computer Graphics Interface) – most

important standard in this category – VDI specifies standard format. [3M]

• Level 2: Data communicated between – application software and graphics utility – GKS

(Graphics Kernel System) provides interface – application package and graphics utility

program – PHIGS (Programmers Hierarchical Interface for Graphics). [3M]

• Level 3: Data communicated between – different CAD systems such as – IGES (Initial

Graphics Exchange Specification) and ANSI – completely independent of any system

supplier – enables both graphical and manufacturing data transfer. [3M]

[6M]

2

Write short notes on PDES. (15M) BTL 3 Answer: Page 5.51 – Dr.G.K.Vijayaraghavan,

Dr.S.Sundaravalli.

• PDES is much more comprehensive and complex standard – include all data which are

relevant to entire lifecycle – product, design, analysis, manufacturing, quality

assurance, testing, support. [3M]

• Standard format for exchanging data – between advanced CAD and CAM programs –

complete product including geometric aspects – images and manufacturing features,

material properties and tolerance and finish specifications. [3M]

• PDES methodology contains three layered architecture – reference models, formal

languages and coordination with other standards – application layer, logical layer and

physical layer. [3M]




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[6M]

3

Elaborate the approaches in data exchange format. (15M) (May/June 2016, Apr/May

2017) BTL 2 Answer: Page 5.30 – Dr.G.K.Vijayaraghavan, Dr.S.Sundaravalli.

• Data exchange format can be done – using two approaches such as – shape based

format and product based format. [2M]

• Shape based format: all data exchange files – neutral files – do not have any software

specific function – developed by the US air force Boeing company – example DXE,

IGES – handles simple images as drafting and modelling. [3M]

• Basic sections of DXE file format – header – contains general information about

drawing – table – line type, layers, text style, viewport etc., - block – information about

block and comprising entities – entities – related properties – end – information about

the end of the file. [4M]

• Product based format: three layered architecture – application, logical and physical

layer – application layer – full description about application areas – logical layer –

provide computer independent description of data structures and formats – physical

layer – data structures and formats for file exchange. [3M]




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[3M]

ME6501 COMPUTER AIDED DESIGN L T P C 3 0 0 3 OBJECTIVES ... · Product cycle- Design process- sequential and concurrent engineering- Computer aided design – CAD system architecture-

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