evolution of cad/cam

CAD/CAM Module I AM/JA

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Module 1

Evolution of CAD/CAM and CIM segments of generic CIM, computers and workstation, elements of

interactive graphics, input/ output display, storage devices in CAD - an overview of CIM software

2D Graphics: Line drawing algorithms, DDA line algorithm – circle drawing, Bressnham`s circle drawing

algorithm– 2D translation, rotation, scaling – clipping -3D Graphics (basic only).

Design process – CAD process: wireframe, surface, solid modeling; Engineering analysis; design review

& evaluation, automated drafting – CAD hard ware, software, data presentation, CAD software packages

DISCLAIMER

These notes are not the ultimate ‘look-up’ for Model and University exams. Students are advised to read the

references mentioned at the end thoroughly for the exams

INTRODUCTION

CAD- Computer-Aided Design

CAM-Computer-Aided Manufacturing

CIM-Computer Integrated Manufacturing

The use of computers in design and manufacturing applications makes it possible to remove much of the

tedium and manual labor involved.

For example, the many design specifications, blueprints, material lists, and other documents needed to

build complex machines can require thousands of highly technical and accurate drawings and charts. If

the engineers decide structural components need to be changed, all of these plans and drawings must be

changed. Prior to CAD/CAM, human designers and draftspersons had to change them manually, a time

consuming and error-prone process. When a CAD system is used, the computer can automatically

evaluate and change all corresponding documents instantly. In addition, by using interactive graphics

workstations, designers, engineers, and architects can create models or drawings, increase or decrease

sizes, rotate or change them at will, and see results instantly on screen.

CAD is particularly valuable in space programs, where many unknown design variables are involved.

Previously, engineers depended upon trial-and-error testing and modification, a time consuming and

possibly life-threatening process. However, when aided by computer simulation and testing, a great deal

of time, money, and possibly lives can be saved. Besides its use in the military, CAD is also used in civil

aeronautics, automotive, and data processing industries.

CAM, commonly utilized in conjunction with CAD, uses computers to communicate instructions to

automated machinery. CAM techniques are especially suited for manufacturing plants, where tasks are

repetitive, tedious, or dangerous for human workers.


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Computer integrated manufacturing (CIM), a term popularized by Joseph Harrington in 1975, is also

known as autofacturing. CIM is a programmable manufacturing method designed to link CAD, CAM,

industrial robotics, and machine manufacturing using unattended processing workstations. CIM offers

uninterrupted operation from raw materials to finished product, with the added benefits of quality

assurance and automated assembly.

EVOLUTION OF CAD/CAM AND CIM

The story of CAD/CAM was accelerated in early 1950s. Upto year 2011 it has become one of the

supreme technology available on Planet earth. It is being used in almost all the fileds of engineeirng but

primarily in mechanical engineering branches. the development in the field is still gaining speed.

19th century Industrial revolution.

20th century Computer revolution.

CAD/CAM has gone through four major phases.

First phase was at 1950’s.

Era of conceiving interactive graphics.

Demonstration of Numerical Control concept on three - axis milling machine.

Conception of light pen.

Development of Automatically Programmed Tools (APT).

Second Phase 1960s

Sketch pad system was introduced.(tool for create drawings and make alterations)

The term “Computer Aided Design” was appeared.

This leads to extending it beyond basic drafting concepts.

Development of some design modules by General Motors & Lockheed Aircrafts etc.

Development of direct view storage tubes(DVST), it is a display unit.

Third 1970’s

Conference arranged in this era was leads to the development in this area.

3-D concept for drafting and modeling.

Development of mass property calculations, finite element modeling, NC tape generation and

verification.

4th Post 1980

Integrate or automate the various elements of design and manufacturing.

Concentrated on accurate representation of elements.

Analysis and simulation tools.

Development of solid modeling theory.

Development of various 3D CAD softwares.

http://science.jrank.org/pages/5904/Robotics.html


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SEGMENTS OF GENERIC CIM

Nine major elements of a CIM system are in Fig 1.2. They are:

Marketing

Product Design

Planning

Purchase

Manufacturing Engineering Factory

Automation Hardware Warehousing

Logistics and Supply Chain Management

Finance

Information Management

Fig.1.2 Major Elements of a CIM System

i. Marketing: The need for a product is identified by the marketing division. The specifications

of the product, the projection of manufacturing quantities and the strategy for marketing the

product are also decided by the marketing department. Marketing also works out the

manufacturing costs to assess the economic viability of the product.

ii. Product Design: The design department of the company establishes the initial database

for production of a proposed product. In a CIM system this is accomplished through


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activities such as geometric modeling and computer aided design while considering the

product requirements and concepts generated by the creativity of the design engineer.

Configuration management is an important activity in many designs. Complex designs are

usually carried out by several teams working simultaneously, located often in different parts

of the world. The design process is constrained by the costs that will be incurred in actual

production and by the capabilities of the available production equipment and processes. The

design process creates the database required to manufacture the part.

iii. Planning: The planning department takes the database established by the design

department and enriches it with production data and information to produce a plan for

the production of the product. Planning involves several subsystems dealing with

materials, facility, process, tools, manpower, capacity, scheduling, outsourcing, assembly,

inspection, logistics etc. In a CIM system, this planning process should be constrained by

the production costs and by the production equipment and process capability, in order

to generate an optimized plan.

iv. Purchase: The purchase departments is responsible for placing the purchase orders and

follow up, ensure quality in the production process of the vendor, receive the items,

arrange for inspection and supply the items to the stores or arrange timely delivery

depending on the production schedule for eventual supply to manufacture and assembly.

v. Manufacturing Engineering: Manufacturing Engineering is the activity of carrying out the

production of the product, involving further enrichment of the database with performance

data and information about the production equipment and processes. In CIM, this requires

activities like CNC programming, simulation and computer aided scheduling of the

production activity. This should include on- line dynamic scheduling and control based on

the real time performance of the equipment and processes to assure continuous production

activity. Often, the need to meet fluctuating market demand requires the manufacturing

system flexible and agile.

vi. Factory Automation Hardware: Factory automation equipment further enriches the

database with equipment and process data, resident either in the operator or the equipment to

carry out the production process. In CIM system this consists of computer controlled

process machinery such as CNC machine tools, flexible

vii. Warehousing: Warehousing is the function involving storage and retrieval of raw

materials, components, finished goods as well as shipment of items. In today’s complex

outsourcing scenario and the need for just-in-time supply of components and subsystems, logistics

and supply chain management assume great importance.

viii. Finance: Finance deals with the resources pertaining to money. Planning of investment,

working capital, and cash flow control, realization of receipts, accounting and allocation

of funds are the major tasks of the finance departments.

ix. Information Management: Information Management is perhaps one of the crucial tasks in CIM.

This involves master production scheduling, database management, communication, manufacturing

systems integration and management information systems.


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It can be seen from Fig that CIM technology ties together all the manufacturing and related functions

in a company. Implementation of CIM technology thus involves basically integration of all the activities

of the enterprise.

Activities of cim

Engineering design.

Mechanical product design.

Drafting

CAE

Manufacturing engineering.

CAM

CAPP

GT

Simulation

Robotics

Factory production.


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Data collection.

Robots & machine tools.

Quality assurance.

Information management.

Systems integration (customer systems)

Communication

Data base management.

PPC

ELEMENTS OF INTERACTIVE GRAPHICS

Interactive Computer Graphics: Interactive Computer Graphics involves a two way communication

between computer and user. Here the observer is given some control over the image by

providing him with an input device for example the video game controller of the ping pong

game. This helps him to signal his request to the computer. The computer on receiving signals

from the input device can modify the displayed picture appropriately. To the user it appears

that the picture is changing instantaneously in response to his commands. He can give a series

of commands, each one generating a graphical response from the computer. In this way he

maintains a conversation, or dialogue, with the computer.

Block Diagram for elements of Interactive graphics is given below in Figure 1.4

INPUT DEVICES

Keyboard Mouse

CAD keyboard Plotter Templates Space Ball

MAIN SYSTEM

Computer CAD Software

Database

CAD Software Database

OUTPUT DEVICES

Hard Disk Network Printer Network Plotter Plotter

HUMANU DESIGNER


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Figure 1.4 Elements of Interactive Graphics

What is Computer Graphics

Anything to do with visual representations on a computer, including

Text (e.g. Japanese characters 大学)

Computer Images

3D Graphics: CG special effects, games, animations

Scientific Visualization

What is Interactive Computer Graphics?

Creation, storage and manipulation of images and drawing with the control of the user over

digital computer.

Interactive graphics system consist of

input (e.g., mouse, tablet and stylus, scanner, live video streams…)

processing (and storage)

display/output (e.g., screen, paper-based printer, video recorder, etc..)

human being

In passive computer graphics the user dose not have any control over image. Like TV

images.

Image can be created using stroke writing approach & raster graphics approach.

User can do the following functions using ICG.

Modelling. Creation of image by the use of point, line, circle etc.

Storage. Save the image.

Manipulation.

Viewing. Seeing the images (zoom in, zoom out, orthographic view, isometric view

etc….)


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Computer

Figure 1.5 Basic Computer Architecture

Note: Go through the detailed description of Basic Computer Architecture you have studies earlier

CLASSIFICATION OF CAD COMPUTERS

Computers can be generally classified by size and power as follows

Personal computer: A small, single-user computer based on a microprocessor.

Workstation: A powerful, single-user computer. A workstation is like a personal computer,

but it has a more powerful microprocessor and, in general, a higher-quality monitor.

Minicomputer: A multi-user computer capable of supporting up to hundreds of users

simultaneously.

Mainframe: A powerful multi-user computer capable of supporting many hundreds or

thousands of users simultaneously.

Supercomputer: An extremely fast computer that can perform hundreds of millions of

instructions per second.

Supercomputer

Supercomputer is a broad term for one of the fastest computers currently available. Supercomputers

are very expensive and are employed for specialized applications that require immense amounts of

mathematical calculations (number crunching). For example, weather forecasting requires a

supercomputer. Other uses of supercomputers scientific simulations, (animated) graphics, fluid

dynamic calculations, nuclear energy research, electronic design, and analysis of geological data

(e.g. in petrochemical prospecting). Perhaps the best known supercomputer manufacturer is Cray

Research.


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Mainframe

Mainframe is a very large and expensive computer capable of supporting hundreds, or even

thousands, of users simultaneously. The chief difference between a supercomputer and a mainframe

is that a supercomputer channels all its power into executing a few programs as fast as possible,

whereas a mainframe uses its power to execute many programs concurrently. In some ways,

mainframes are more powerful than supercomputers because they support more simultaneous

programs. But supercomputers can execute a single program faster than a mainframe.

Minicomputer

It is a midsize computer. A mini computer is the computer which is referred to as the mid sized

computers and they serve as the same functions as the normal desktop computers. Mini computers

are the one which are found between the main frame computers and the work station computers.

These types of computers are quite easy to be handled and are serving the similar functions as other

computers. This size computer can support a larger range of people. The total numbers of people

who can use the mini computers are from 4-400 users at the same time. At times the mini computers

are often referred to as the multi processing computers which show that the computer can be used to

perform certain tasks at the same time.

The other distinction that exists among the mini computers is that the computer had its own different

types of hardware and software’s. Even at time the operating system unit in the mini computers is

also different this in fact is the major difference among all the other computers and the mini

computers.

Workstation

It is a type of computer used for engineering applications (CAD/CAM), desktop publishing, software

development, and other types of applications that require a moderate amount of computing power

and relatively high quality graphics capabilities. Workstations generally come with a large, high-

resolution graphics screen, at large amount of RAM, built-in network support, and a graphical user

interface. Most workstations also have a mass storage device such as a disk drive, but a special type

of workstation, called a diskless workstation, comes without a disk drive. The most common

operating systems for workstations are UNIX and Windows. Like personal computers, most

workstations are single-user computers. However, workstations are typically linked together to form

a local-area network, although they can also be used as stand-alone systems.

N.B.: In networking, workstation refers to any computer connected to a local-area network. It

could be a workstation or a personal computer.


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Microcomputer

A microcomputer is a computer with a microprocessor as its central processing unit. They are

physically small compared to mainframe and minicomputers. Many microcomputers (when equipped

with a keyboard and screen for input and output) are also personal computers. Monitors, keyboards

and other devices for input and output may be integrated or separate. Computer memory in the form

of RAM, and at least one other less volatile, memory storage device are usually combined with the

CPU on a system bus in one unit. Other devices that make up a complete microcomputer system

include batteries, a power supply unit, a keyboard and various input/output devices used to convey

information to and from a human operator (printers, monitors, human interface devices).

Microcomputers are designed to serve only one user at a time, although they can often be modified

with software or hardware to concurrently serve more than one user. Microcomputers fit well on or

under desks or tables, so that they are within easy access of users.

Hardware Requirements of CAD

Input Devices in CAD

Various devices are available for data input on graphics workstations. Most systems have a keyboard and one

or more additional devices specially designed for interactive input. These include a mouse, trackball, joystick,

tablet light pen etc.

Input Devices

Output Devices

Storage Devices

Analog

Key Board,Mouse

Track ball

Joy Stick

Digital

Light Pen

Tablet

Input Devices

http://en.wikipedia.org/wiki/Computer

http://en.wikipedia.org/wiki/Microprocessor

http://en.wikipedia.org/wiki/Central_processing_unit

http://en.wikipedia.org/wiki/Mainframe_computer

http://en.wikipedia.org/wiki/Minicomputer

http://en.wikipedia.org/wiki/Personal_computer

http://en.wikipedia.org/wiki/RAM

http://en.wikipedia.org/wiki/System_bus

http://en.wikipedia.org/wiki/Power_supply

http://en.wikipedia.org/wiki/Computer_printer

http://en.wikipedia.org/wiki/Computer_display

http://en.wikipedia.org/wiki/Human_interface_device


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Analog IO

Analog input devices sense continuous parameters. The information that they provide is given as a continuous

range of values, not just an on or off indicator. Position will be a continuous outcome.

Digital IO

Digital input devices may be either on or off; they may not hold any other values.

Keyboards

An alphanumeric keyboard on a graphics system is used primarily as device for entering text strings. The

keyboard is an efficient device for inputting such nongraphic data as picture labels associated with a graphics

display. Keyboards can also be provided with features to facilitate entry of screen coordinates, menu

selections, or graphics functions.

Mouse

A mouse is small hand-held box used to position the screen cursor. The main goal of any mouse is to translate

the motion of your hand into signals that the computer can use. Wheels or rollers on the bottom of the mouse

can be used to record the amount and direction of movement. Another method for detecting mouse motion is

with an optical sensor,. For these systems, the mouse is moved over a special mouse pad that has a grid of

horizontal and vertical lines. The optical sensor detects movement across the lines in the grid.

Since a mouse can be picked up and put down at another position without change in cursor movement, it is

used for making relative changes in the position of the screen cursor. One, two, or three buttons are usually

included on the top of the mouse for signaling the execution of some operation, such as recording cursor

position or invoking a function.

Ball Mouse(mechanical)


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The mechanical mouse contains a free-floating ball with rubber coating on the underside which,

when moved on a firm plane surface, is able to follow the movement of the hand. The mot ion of

the ball is resolved into X- and Y-motions by means of the two rollers pressed against the ball.

They, in turn, control the cursor on the screen, which can then be utilized for any desired

applications by means of the clicking of the buttons on the mouse. This can only suffice to point on

the screen but not for giving positional data. Further the mouse is a relative device and not an

absolute pointing device.

Optical Mouse

The main components of the optical mouse are:

Inbuilt optical sensor

High speed camera which can take 1000 pictures at a time

LED

These optical mouses do have an inbulit optical sensor. The optical sensor reads the movements of the optical

mouse (moved by the user) with the help of the light rays which comes out from the bottom. ( The area in

which a light glows). When the user moves the optical mouse, the LED (Light Emitting Diode) present inside

the mouse emits the light according the minute movements. These movements are send to the camera as light

rays. The camera captures the difference in light rays as images. When the camera captures the images, each

and every pictures and compared to one another with the digital technology. With the comparison, the speed

of the mouse and the direction of the movement of the mouse are rapidly calculated. According to the

calculation, the pointer moves on the screen.

Track Ball

Track ball has a ball and socket construction but the ball must be rolled with fingers or the palm of the hand.

The cursor moves in the direction of the roll at a rate corresponding to rotational speed. The user must rely

heavily on the tactile sense when using a trackball since there is no correspondence between the position of

the cursor and the ball. The ball momentum provides a tactile feed back. Trackballs are effective for tracking,

following or pointing at moving elements. Track discs also perform a similar function.

Basically the trackball rolls against a trackball roller which then turns a slotted chopper wheel which is

scanned by an optical sensor which converts your movement into digital information which is then sent to

your computer via a USB connection.


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Joysticks

Joystick is a potentiometric device that contains sets of variable resistors which feed signals that indicates the

device position to the computer. These devices rely on the operator’s sense of touch and hand-eye co-

ordination to control the position of the cursor on the screen. Joystick devices are normally set so that side-to-

side movement produces change in X Co-ordinates and front to back movements produce change in Y Co-

ordinates. Thus they are best suited for pointing in tasks such as menu selection or creating simple schematics.

Many users prefer joysticks because they allow rapid cursor movement for relatively small device movements,

enabling graphic operations to be performed quickly. Three dimensional capability is possible by moving the

handle up and down or by twisting it to provide data entry in the Z axis.

Lightpen

A lightpen resembles a fountain pen in the method of holding, but it wor ks on the principle of light

rather than ink. from which it derives its name. The lightpen is a pointing or picking device that

enables the user to select a displayed graphics item on a screen by directly touching its surface in

the vicinity of the item. The application program processes the information generated from the

touching to identify the selectable item to operate on. The lightpen itself does not emit light but

rather detects it from the graphics items displayed on the screen. Using the emitted lig ht as an

input, it sends an interrupt signal to the computer to determine which was seen by the pen. The

lightpen normally operates as a logical pick in conjunction with a vector refresh display.


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Digitizers

A digitizer is the most widely used input medium by the CAD designer. It is used for converting the physical

locations into coordinate values so that accurate transfer of data can be achieved. A digitizing tablet is

considered as a pointing and locating device. It is a small, low-resolution digitising board often used in

conjunction with a graphics display. The tablet is a flat surface over which a stylus or a puck can be moved by

the user. The close resemblance of the tablet and stylus to paper and pencil contributes to its popularity as an

input device. The puck contains a rectile and at least one pushbutton. The engraved cross-hairs of rectile help

locate a point for digitising. Pressing the pushbutton sends the coordinates at the cross-hairs to the computer.

The sizes of digitising tablets range from 11 x 11 to 36 x 36 inches. The resolution of a tablet is 0.005 inch or

200 dots per inch.

The tablet operation is based on sensitising its surface area to be able to track the pointing element (stylus or

puck) motion on the surface. The surface of the tablet is magnetised and is embedded with wires in the x and v

directions. The physical motion of the stylus is converted by the wires into a digital location signal, which is

then routed to the computer and displayed on the graphics terminal.


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Output Devices

Output Devices

Also audio outputs(but not used in CAD)

Printers

(i).Impact printers: They use small hammers or print heads containing small pins to strike a ribbon to form

dot matrix images. Colors are introduced through the use of multiple ribbons or single ribbons with different

color bands. Color intensity is fixed and creating shades is almost impossible. Because of the low resolution,

copy quality is poor. Impact printers are suitable for high speed, low cost, highvolume hard copies.

(ii) Inkjet printer: Inkjet printers produce images by propelling fine droplets of ink on to the medium to be

printed. Droplets can be generated in continuous streams or pulses. Some of the droplets get charged and are

returned to the reservoir, while uncharged droplets attach to the printing surface to form graphics. The laser jet

printers are capable of giving good quality color prints with shading at reasonable cost.

(iii) Laser printer: Laser printer is one of the most widely used output devices. This type combines high

speed with high resolution and the quality of output is very fine.

Plotters-

2 types- Drum plotter, Flat Bed plotter

Display Devices

Storage Tube

Calligraphic

refresh graphic

displays

Raster Refresh

displays

Hard Copy Devices

Printers

o Impact

o Inject

o Laser

Plotters

o Flat

o Drum

o


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Plotters are special output devices used to produce hard copies of large graphs and designs on paper. Plotters

are often used for the production of cad/cam drawings, engineering drawings, architectural plans and business

charts.

Drum Plotter

A drum plotter is pen plotter that wraps the paper around a drum with a pin feed attachment.

The drum then rotates the paper as pens move across it and draw the image. It was the first

output device used to print graphics and large engineering drawings. There are two types of

drum plotters, external and internal. With an external drum plotter, the paper is wrapped

around its external surface, while the internal drum plotter uses a sheet of paper wrapped

around its internal surface.

Flat-Bed Plotter

A flat-bed plotter is a mechanical drafting device used with many CAD programs for

designers. The paper remains stationary on a flat surface while a pen moves across it

horizontally and vertically. This plotter may use several different colors of pens to create the

graphics. The size of the graphic is limited to the size of the flat-bed plotter's surface.

Pen Movement

in X direction Pen Movement in

Y Direction


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DISPLAY DEVICES

Typically, the primary output device in a graphics system is a video monitor. The operation of most video

monitor is based on the standard cathode-ray tube(CRT) design.

Cathode Ray Tube

A heated cathode emits a high speed electron beam into phosphor coated glass screen.

Electrons energize the phosphor coating , causing it to glow.

Can make an image by focusing the electron beam, changing its intensity, and controlling its point of

contact against the phosphor coating

used in TVs and computer monitors

Factors affecting quality of image

Type of phosphor coating.

Color is required.

The pixel density.

Amount of computer memory available to generate the picture.


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TYPE OF GRAPHICS TERMINALS.

Storage tube display

Calligraphic refresh graphic displays

Raster Refresh displays

Storage Tube Display device

Storage tube refers the ability of the screen to retain the image.(image will be retained for

approximately 2 hours)

Thus avoiding the need to rewrite the image.

For erasing the image the screen is flooded by a particular voltage by flood gun.

The individual lines cannot be selectively removed.

Lowest cost

Capable showing large amount of data.

Lack of animation capability.

Unable to use light pen.

Not used in modern display systems

Calligraphic Refresh Graphic Display


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Image will be regenerated many times per second to avoid noticeable flickering.(approx 50/s), thus

name refresh displays

Screen elements are capable of maintain there brightness for only a short time(in micro sec)

Image is refreshed by Directed beam to retrace repeatedly.

On densely filled screen, it is difficult to avoid the flickering .

Selective erasure and alteration is possible (continually refreshed)

Possible to provide animations.

It is the oldest of modern graphics technologies.

Other names are vector refresh or stroke writing refresh

Display process is as follows- Each time controller checks buffers and give stimulations to vector

generator to produce display in CRT

Display

Refresh rate on a random-scan system depends on the number of lines to be displayed . Picture definition is

now stored as a set of line-drawing commands in an area of memory referred to as the refresh display file.

Sometimes the refresh display file is called the display list, display program, or simply the refresh buffer.

To display a specified picture, the system cycles through the set of commands in the display file, drawing each

component line in turn. After all line- drawing commands have been processed, the system cycles back to the

first line command in the list. Random-scan displays are designed to draw al the component lines of a picture

30 to 60times each second

RASTER REFRESH DISPLAY

Electron beam is trace in zig zag pattern.

It is same as TV screen except the type of input signal

(TV --------------- analog signal,

computer -------- digital signal).

Number of storage space required is depends on number of intensity level.

Quality of the image can be increased by adding color or by increasing the pixel density.

Refresh Buffer

Controller CRT Vector

Generator

Line information

is stored

Checks buffer

before each

refresh display

Commands

electron gun to

move to display

buffer commands


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Two bits required for four intensity level.

Animations are possible.

Color capability.

The screen is divided into small phosphor elements called pixels.

Ranges from 256*256 to 1024*1024.

Each pixel can glow with different brightness.

Color screens provide for pixels to have different colors.

Electron beam sweep along horizontal line on the screen from left to right, it will energize the pixel

during the sweep.

When the sweep of one line is completed it moves to the next line

After sweeping the entire screen the process is repeated at a rate of 30 to 60 scans/sec

Each pixel is either on or off, ie lit or not lit

In a raster- scan system, the electron beam is swept across the screen, one row at a time from top to bottom.

As the electron beam moves across each row, the beam intensity is turned on and off to create a pattern of

illuminated spots. Picture definition is stored in memory area called the refresh buffer or frame buffer. This

memory area holds the set of intensity values for all the screen points. Stored intensity values are then

retrieved from the refresh buffer and “ painted” on the screen one row (scan line) at a time (fig.below). Each

screen point is referred to as a pixel or pel (shortened forms of picture element).

Buffer Electron

Gun

Controller


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Refreshing on raster-scan displays is carried out at the rate of 60 to 80 frames per second, although some

systems are designed for higher refresh rates. Sometimes, refresh rates are described in units of cycles per

second, or Hertz (Hz), where a cycle corresponds to one frame. At the end of each scan line, the electron beam

returns to the left side of the screen to begin displaying the next scan line. The return to the left of the screen,

after refreshing each scan line, is called the horizontal retrace of the electron beam. And at the end of each

frame (displayed in 1/80th to 1/60th of a second), the electron beam returns (vertical retrace)to the top left

corner of the screen to begin the next frame.

CIM Hardware comprises the following:

Manufacturing equipment such as CNC machines or computerized work centers, robotic

work cells, DNC/FMS systems, work handling and tool handling devices, storage devices,

sensors, shop floor data collection devices, inspection machines etc.

Computers, controllers, CAD/CAM systems, workstations / terminals, data entry terminals,

bar code readers, RFID tags, printers, plotters and other peripheral devices, modems, cables,

connectors etc.,

Line Drawing Algorithms


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Primary design criteria for line drawing displays are as follows

Line should appear straight

Line should start and end accurately

Line should have continuous brightness along their length

Display lines should be independent of line length and orientation

Lines should be drawn rapidly

4.3.1 DDA Algorithm

The digital differential analyser generates lines from their differential equations. The DDA worlo

on the principle that x and y are simultaneously incremented by small steps proportional to the

first derivatives of x and y.

Fig. 4.2 The DDA algorithm.

The governing differential equation for a straight line (Figure 4.2) is

where (x1, y1) and (x2, y2) are the end points of the required straight line, and y, is the initial value

for any given step along the line. Equation 4.2 represents a recursion relation for successive

values of y along the required line. For simple DDA algorithm, either Ax or Ay, which ever is

larger, is chosen as one raster unit.

The digital differential analyzer generates lines from their differential equations. The DDA works on

the principle that X and Y are simultaneously incremented by small steps proportional to the first

derivatives of X and Y. In the case of a straight line the first derivatives are constant and are

proportional to DX and DY, where D is a small quantity.


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In the real world of limited precision displays, addressable pixels only must be generated. This can

be done by rounding to the next integer after each incremental step. After rounding, a pixel is

displayed at the resultant X and Y locations. An alternative to rounding is the use of arithmetic

overflow. X and Y are kept in registers that have integer and fractional parts. The incrementing

values which are less than unity are repeatedly added to the fractional part and whenever the result

overflows the corresponding integer part is incremented. The integer parts of X and Y are used to

plot the line. This would normally have the effect of truncating. The DDA is therefore initialized by

adding 0.5 in each of the fractional parts to achieve true rounding.

The symmetrical DDA generates reasonably accurate lines since a displayed pixel is never away

from a true line by half the pixel unit. A Pascal procedure for a simple DDA is given below :

Procedure DDA (X1, Y1, Y2 : X2, integer) ;

length : var ;

i : integer;

X, Y, X-incr, Y-incr : real ;

begin

length : = abs (X2– X1) ;

if abs (Y2–Y1) < length then length: = abs (Y2–Y1);

X - incr : = (X2 – X1) /length ;

Y - incr : = (Y2 – Y1) /length ;

X : = X1 + 0.5 ; Y = Y1 + 0.5 ;

for i : = 1 to length do

begin

plot (trunc (X) ; trunc(Y) ;

X : = X + X - incr ;

Y : = Y + Y - incr ;

end;

end.

It can be noted that lines drawn on a raster display may have a jagged or staircase appearance unless

the lines are vertical or horizontal. This is because the points that are plotted must be pixel grid

points and many of these may not lie on the actual line.

EXAMPLE

To draw a straight line from connecting two points (2, 7) and (15, 10)

X1 = 2, X2 = 15 abs(X2 – X1) = 13


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Y1 = 7, Y2 = 10 abs(Y2 – Y1) = 3

Bresenham’s Line Algorithm(out of syllabus,included as seen in a QP)


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An accurate, efficient raster line drawing algorithm developed by Bresenham, scan converts

lines using only incremental integer calculations that can be adapted to display circles and

other curves.

Keeping in mind the symmetry property of lines, lets derive a more efficient way of drawing

a line.

Choices are(xk +1, yk) and (xk+1, yK+1)

d1 = y – yk = m(xk + 1) + b – yk

d2 = (yk + 1) – y = yk + 1- m(xk + 1) – b

Steps

Input the two end points and store the left end point in (x0,y0)

Load (x0,y0) into the frame buffer (plot the first point)


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Calculate the constants Δx, Δy, 2Δy and 2Δy-2Δx and obtain the starting value for the

decision parameter as

p0 = 2Δy- Δx

o At each xk along the line, starting at k=0, perform the following test:

If pk < 0 , the next point is (xk+1, yk) and

pk+1 = pk + 2Δy

Otherwise

Point to plot is (xk+1, yk+1)

pk+1 = pk + 2Δy - 2Δx

Repeat above step Δx times


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Bresenham Circle ( Xc, Yc, R):

Description: Here Xc and Yc denote the x – coordinate and y – coordinate of the center of the

circle. R is the radius.

1. Set X = 0 and Y = R

2. Set D = 3 – 2R

3. Repeat While (X < Y)


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4. Call Draw Circle(Xc, Yc, X, Y)

5. Set X = X + 1

6. If (D < 0) Then

7. D = D + 4X + 6

8. Else

9. Set Y = Y – 1

10. D = D + 4(X – Y) + 10

[End of If]

11. Call Draw Circle(Xc, Yc, X, Y)

[End of While]

12. Exit

Draw Circle (Xc, Yc, X, Y):

1. Call PutPixel(Xc + X, Yc, + Y)

2. Call PutPixel(Xc - X, Yc, + Y)

3. Call PutPixel(Xc + X, Yc, - Y)

4. Call PutPixel(Xc - X, Yc, - Y)

5. Call PutPixel(Xc + Y, Yc, + X)

6. Call PutPixel(Xc - Y, Yc, + X)

7. Call PutPixel(Xc + Y, Yc, - X)

8. Call PutPixel(Xc - Y, Yc, - X)

9. Exit


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Transformation

A transformation is the process of mapping points to other locations. Changes in orientation, size and

shape are accomplished with geometric transformations that alter the coordinate descriptions of the

objects.

Transformations are used to

position objects

to shape objects

to change viewing positions,

even to change how something is viewed (e.g. the type of perspective that is used).

Use of transformations in CAD

In mathematics, "Transformation" is the elementary term used for a variety of operation such as

rotation, translation, scaling, reflection, clipping etc. CAD is used throughout the engineering

process from conceptual design and layout, through detailed engineering and analysis of components

to definition of manufacturing methods. Every aspect of modeling in CAD is dependent on the

transformation to view model from different directions we need to perform rotation operation. To

move an object to a different location translation operation is done. Similarly Scaling operation is

done to resize the object.

Coordinate Systems In CAD three types of coordinate systems are needed in order to input, store and display model

geometry and graphics. These are the Model Coordinate System (MCS), the World Coordinate

System (WCS) and the Screen Coordinate System (SCS). Model Coordinate System The MCS is defined as the reference space of the model with respect to which all the model

geometrical data is stored. The origin of MCS can be arbitrary chosen by the user.

World Coordinate System As discussed above every object have its own MCS relative to which its geometrical data is stored.

In case of multiple objects in the same working space then there is need of a World Coordinate

System which relates each MCS to each other with respect to the orientation of the WCS. It can be

seen by the picture shown below.


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Screen Coordinate System In contrast to the MCS and WCS the Screen Coordinate System is defined as a two dimensional

device-dependent coordinate system whose origin is usually located at the lower left corner of the

graphics display as shown in the picture below. A transformation operation from MCS coordinates

to SCS coordinates is performed by the software before displaying the model views and graphics.

Viewing Transformations

As discussed that the objects are modeled in WCS, before these object descriptions can be projected

to the view plane, they must be transferred to viewing coordinate system. The view plane or the

projection plane, is set up perpendicular to the viewing zv axis. The World coordinate positions in

the scene are transformed to viewing coordinates, then viewing coordinates are projected onto

the view plane.

The transformation sequence to align WCS with Viewing Coordinate System is. 1. Translate the view reference point to the origin of the world coordinate system.

2. Apply rotations to align xv, yv, and zv with the world xw, yw and zw axes, respectively.


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Transformations

Translation Rotation Reflection Scaling Clipping

TRANSLATION

A translation is applied to an object by repositioning it along a straight line path from one coordinate

location to another. We translate a two-dimensional point by adding translation distances, tx and ty,

to the original coordinate position (x,y) to move the point to a new position (x',y')

The translation distance pair (tx, ty) is called translation vector or shift vector

Matrix representation of translation

This allows us to write the two-dimensional translation equations in the matrix form:

Example: If line A(3,5) , B(4,8) is translated into three units along the positive x-axis and four units

along the positive y axis, find new coordinates of line

Solution

Given A(3,5), B(4,8).

dx=3, dy= 4

The new points are given by A’(x,y)=(3+3, 5+4)=(6,9)

B’(x,y)=(4+3,8+4)=(7,12)


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ROTATION

A two-dimensional rotation is applied to an object by repositioning it along a circular path in the x-y plane. When we

generate a rotation we get a rotation angle (θ) and the position about which the object is rotated (xr , yr) this is known

as rotation point or pivot point. The transformation can also be described as a rotation about rotation axis that is

perpendicular to x-y plane and passes through the pivot point. Positive values for the rotation angle define counter-

clockwise rotations about the pivot point and the negative values rotate objects in the clockwise direction.

Here, r - constant distance of the point from the origin.

Φ - original angular position of the point from the horizontal

θ - rotation angle

we can express the transformation by the following equations

we know the coordinate of x and y in polar form

on expanding and equating we get

The same equations we can write in matrix form as


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Where the rotation matrix R is

Hence it is

the anti-clockwise direction to position P2. The co-ordinates of P2 can be obtained

by multiplying the co-ordinates of P1 by the matrix:

The new coordinates are

SCALING

Scaling is a kind of transformation in which the size of an object is changed. Remember the change is size

does no mean any change in shape. This kind of transformation can be carried out for polygons by multiplying

each coordinate of the polygon by the scaling factor. Sx and Sy which in turn produces new coordinate of (x,y)

as (x',y'). The equation would look like


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or

here S represents the scaling matrix.

NOTE: If the values of scaling factor are greater than 1 then the object is enlarged and if it is less that 1 it

reduces the size of the object. Keeping value as 1 does not changes the object.

Uniform Scaling: To achieve uniform scaling the values of scaling factor must be kept equal.

Differential Scaling: Unequal or Differential scaling is produce incases when values for scaling factor are

not equal.

As per usual phenomenon of scaling an object moves closer to origin when the values of scaling

factor are less than 1. To prevent object from moving or changing its position while is scaling we

can use a point that is would be fixed to its position while scaling which is commonly referred as

fixed point (xf yf).


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REFLECTION Reflection is nothing more than a rotation of the object by 180

o. In case of reflection the image formed is on the opposite

side of the reflective medium with the same size. Therefore we use the identity matrix with positive and negative signs

according to the situation respectively.

The reflection about the x-axis can be shown as:

The reflection about the y-axis can be shown as:

REFLECTION ABOUT A ORIGIN

When both the x and y coordinates are flipped then the reflection produced is relative to an axis that is perpendicular to

x-y plane and that passes through the coordinate origin. This transformation is referred as a reflection relative to

coordinate origin and can be represented using the matrix below.


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REFLECTION ABOUT AN ARBITRARY LINE

Reflection about any line y= mx + c can be accomplished with a combination of translate-rotate-reflect

transformations. Steps are as follows 1. Translate the working coordinate system (WCS) so that the line passes through the origin. 2. Rotate the WCS such that one of the coordinate axis lies onto the line. 3. Reflect about the aligned axis 4. Restore the WCS back by using the inverse rotation and translation transformation.

REFLECTION ABOUT AN ARBITRARY POINT

As seen in the example above, to reflect any point about an arbitrary point P (x,y) can be accomplished by translate-

reflect transformation i.e. the origin is first translated to the the arbitrary point and then the reflection is taken about the

origin. And finally the origin is translated back to its original position.

CLIPPING


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3D TRANSFORMATIONS

HOMOGENEOUS COORDINATES

We have seen that basic transformations can be expressed in matrix form. But many graphic

application involve sequences of geometric transformations. Hence we need a general form of matrix

to represent such transformations. This can be expressed as:

Where P and P' - represent the row vectors.

T1 - is a 2 by 2 array containing multiplicative factors.

T2 - is a 2 element row matrix containing translation terms.

We can combine multiplicative and translational terms for 2D geometric transformations into a

single matrix representation by expanding the 2 by 2 matrix representations to 3 by 3 matrices. This

allows us to express all transformation equations as matrix multiplications, providing that we also

expand the matrix representations for coordinate positions. To express any 2D transformations as a

matrix multiplication, we represent each Cartesian coordinate position (x,y) with the homogeneous

coordinate triple (xh,yh,h),such that

Thus, a general homogeneous coordinate representation can also be written as (h.x, h.y, h). For 2D

geometric transformations, we can choose the homogeneous parameter h to any non-zero value.

Thus, there is an infinite number of equivalent homogeneous representations for each coordinate

point (x,y). A convenient choice is simply to h=1. Each 2D position is then represented with

homogeneous coordinates (x,y,1). Other values for parameter h are needed, for eg, in matrix

formulations of 3D viewing transformations.

Expressing positions in homogeneous coordinates allows us to represent all geometric transformation

equations as matrix multiplications. Coordinates are represented with three element row vectors and

transformation operations are written as 3 by 3 matrices.


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Rotation

Projections

Homogenous factor

Translation Scaling/ Reflection

3D TRANSFORMATION SAMPLE MATRIX

a b c d

e f g h

i j k l

m n o p

.

TRANSLATION

In three-dimensional homogeneous coordinate representation, when a point P is translated to P' with coordinated

(x,y,z) and (x',y',z') can be represented in matrix form as:

Where,

ROTATION Unlike 2D, rotation in 3D is carried out around any line. The simplest rotations could be around coordinate axis. As in

2D, positive rotations produce counter-clockwise rotations. Rotation in term of general equation is expressed as


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Where,

R = Rotation Matrix

Rotation matrix when an object is rotated about X axis can be expressed as:

Rotation matrix when an object is rotated about Y axis can be expressed as:

Rotation matrix when an object is rotated about Z axis can be expressed as:

SCALING Scaling an object in three-dimensional is similar to scaling an object in two-dimensional. Similar to 2D scaling an object

tends to change its size and repositions the object relative to the coordinate origin. If the transformation parameter are

unequal it leads to deformation of the object by changing its dimensions. The perform uniform scaling the scaling factors

should be kept equal i.e.

Where,


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NOTE: A special case of scaling can be represented as reflection.

if the value of Sx, Sy or Sz be replaced by -1 it will return the reflection of the object against the standard plane whose

normal would be either x axis, y axis or z axis respectively.

REFLECTION In 3D-reflection the reflection takes place about a plane whereas 2D reflection it used take place about an axis. The

matrix in case of pure reflections, along basic planes, viz. X-Y plane, Y-Z plane and Z-X plane are given

below:

Transformation matrix for a reflection through X-Y plane is:

Transformation matrix for a reflection through Y-Z plane is:

Transformation matrix for a reflection through Z-X plane is:


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OVERVIEW OF CAD/CAM

What is CAD?

CAD if often defined in a variety of ways and includes a large range of activities. Very broadly it can be

said to be the integration of computer science (or software) techniques in engineering design. At one end

when we talk of modeling, iIt encompasses the following:

Use of computers (hardware & software) for designing products

Numerical method, optimizations etc.

2D/3D drafting

3D modeling for visualization

Modeling curves, surfaces, solids, mechanism, assemblies, etc.

The models thus developed are first visualized on display monitors using avariety of techniques including

wire frame displa, shaded image display, hidden surface removed display and so on. Once the designer is

satisfied, these models are then used for various types of analysis / applications. thus, at the other end it

includes a number of analysis activities. These could be:

Stress (or deflection) analysis, i.e. numerical methods meant for estimating the behaviour of an

artifact with respect to these parameters. It includes tools like the Finite Element Method (FEM).

Simulation of actual use

Optimization

Other applications like

o CAD/CAM integration

o Process planning

These are activities which normally use models developed using one or more of the techniques mentioned

above. These activities are often included in other umbrellas like CAM or CAE. A term often used is CAx

to include this broad set of activities. They all use CAD models and often the kind of application they

have to be used ina determines the kind of amodel to be developed. Hence, in this course I cover them

under the umbrella of CAD. In this course we will strive to give an overview of modelling techniques

followed by some applications, specifically CAM.

Thus there are three aspects to CAD.

Modeling

Display/ Visualization

Applications


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MODELING

Modeling typically includes a set of activities like

Defining objects

Defining relation between objects

Defining properties of objects

Defining the orientations of the objects in suitable co-ordinate systems

Modification of existing definition (editing)

DISPLAY / VISUALIZATION

Displaying the model requires the following:

Mapping objects onto screen coordinates: Models are typically made in a model coordinate

system. this could be the world coordinate system, or a coordinate system local to the object.

these coordinate systems are typically three dimensional in nature. To display the object on a 2D

screen, the object coordinates need to be mapped on to the 2D coordinate system of the screen.

This requires two steps:

o Viewing transformations: The coordinates of the object are transformed in a manner as if

one is looking at the object through the screen. This coordinate system is referred to as

the viewing coordinate system.

o Projections: The object in the viewing coordinate system is then projected onto the two

dimensional plane of the screen.

Surface display or shading / rendering: In displaying the objects on the screen one often likes to

get a shaded display of the object and get a good feel of the three dimensional shape of the object.

This requires special techniques to render the surface based on its shape, lighting conditions and

its texture.

Hidden line removal when multiple surfaces are displayed: In order to get a proper feel of the

three dimensional shape of an object, one often desires that the lines / surfaces which are not

visible should not be displayed. this is referred to as hidden line / surface removal.

APPLICATIONS

Once a model is visualized on the screen and approved by the conceptual designer, it has to go through a

number of analysis. Some of the kinds of usage this model might have to go through are the following:

Estimating stresses / strains / deflections in the objects under various static loading conditions

Estimating the same under dynamic loading conditions

Visualizing how a set of objects connected together would move when subject to external

loading. This leads to a whole set of activities under simulation. These activities would vary

depend upon the application the object is to be subject to.

Optimizing the objects for

o Developing 2D engineering drawings of the object


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o Developing a process plan of the object

Manufacturing the object using NC / CNC machines and generating the programs for these

machines so as to manufacture these objects.

USES OF CAD

To create conceptual product models.

Editing the model for improvement.

Display the model into several colours

Rotate & view the objects.

Create & display all inner details.

Check the clearance between the mating parts.

Prepare the detailed component drawing.

Store the database for modification

BENEFFITS OF CAD

Productivity improvement in design

Shorter lead time.

Flexibility in design.

Improved design analysis.

Fewer of design errors.

Easier visualization of drawings.

Standardization of design, drafting, and documentation.

ENGINEERING DESIGN PROCESS

The engineering design process is a formulation of a plan or scheme to assist an engineer in

creating a product. The engineering design is defined as component, or process to meet desired

needs. It is a decision making process (often iterative) in which the basic sciences, mathematics,

and engineering sciences are applied to convert resources optimally to meet a stated objective.

Among the fundamental elements of the design process are the establishment of objectives and

criteria, synthesis, analysis, construction, testing and evaluation.

http://en.wikipedia.org/wiki/Plan

http://en.wikipedia.org/wiki/Engineer


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Design process Proposed by Shigley

1. Recognition of need: Recognition of need involves the

realization by someone that a problem exists for which some feasible solution is to be found. This

might be the identification of some defects in the present machine design activity by an engineer

or the perception of a new product marketing opportunity by the salesman.

2. Definition of problem: This involves a thorough specification of the item to be designed. This

specification will generally include functional and physical characteristics, cost, quality, performance,

etc. This also involves problems like the cost and the performance like the cooling system,

environmental hazards.

3. Synthesis: During the synthesis phase of the design process various preliminary ideas are

developed through research of similar products or designs in use.

4. Analysis and Optimization: The resulting preliminary designs are then subjected to appropriate

analysis to determine their suitability for the specified design constraints. If the design fails to satisfy

the constraints, they are then redesigned or modified on the basis of feedback from the analysis. This

iterative process is repeated until the proposed design meets the specifications or until the designer is

convinced that the design is not feasible. The components, sub-assemblies or sub-systems are then

synthesized into the final overall system in a similar iterative manner.

5. Evaluation: The assessment or evaluation of the design against the specification established during

the problem definition phase is then carried out. This often requires the fabrication and testing of a

prototype model to evaluate operating performance quality, reliability, etc. Evaluation is the

comparison of actual impacts against strategic plans.

Synthesis

Problem Definition

Recognition of Need

Evaluation

Analysis and Optimization

Presentation


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6. Presentation: The final phase in the design process is the presentation of the design .This includes

documentation of the design through drawings, material specifications, assembly lists and so on.

This involves the re-modeling of the prototype if necessary, the 2D and 3D drawing representation of

the product, the bills of materials, and the complete materials specification

CAD PROCESS

Computer aided Design

GEOMETRIC MODELING

Computer representation of geometry of a component using a software is called geometric

modeling.

Stored in computer as mathematical description.

Three types of commands in modeling

To generate basic models like lines, points, circles etc.

Used for transformations

Used to join various elements to form the shape.

Types.

Wire frame modeling.

Surface modeling.

Synthesis

Problem Definition

Recognition of Need

Evaluation

Analysis and Optimization

Presentation

Geometric Modeling

Automatic Drafting

Engineering Analysis

Design Review and Evaluation


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Solid modeling.

Wire Frame model

Wire-frame model consists only of lines, circles, and curves

Model is represented by its edges.

Wire-frame models represent 3D part shapes with interconnected line elements

Wire-frames contain no information about the surfaces,

No differentiate between the inside and outside of objects

Hidden line elimination is available.

In wire frame modeling the object is represented by its edges. In the initial stages of CAD, wire frame

models were in 2-D. Subsequently 3-D wire frame modeling software was introduced. The wire frame

model of a box is shown in Fig. 6.2 (a). The object appears as if it is made out of thin wires. Fig. 6.2(b),

6.2(c) and 6.2(d) show three objects which can have the same wire frame model of the box. Thus in the

case of complex parts wire frame models can be confusing. Some clarity can be obtained through hidden

line elimination. Though this type of modeling may not provide unambiguous understanding of the

object, this has been the method traditionally used in the 2-D representation of the object, where

orthographic views like plan, elevation, end view etc are used to describe the object graphically.


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The difference between 2D and 3D wire frame model is given below:

Surface modeling

The component is represented by its surface

Can calculate surface area, surface intersections

Automatic hidden line removal

It created by connecting various surface elements.

It can be built from wire frame model.

Represented by

set of plane corss-sectional curves. Eg. Manifolds.

Array of points in space through intersecting curves.


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Irregular mesh of curves.

Required more computational time.

More skill in their construction.

Difficult to interpret without hidden line removal.

Applications

Ship building, automobile body building, cutting out of shoe leather etc.

In this approach, a component is represented by its surfaces which in turn are represented by their

vertices and edges. For example, eight surfaces are put together to create a box, as shown in Fig. 6.3.

Surface modeling has been very popular in aerospace product design and automotive design. Surface

modeling has been particularly useful in the development of manufacturing codes for automobile

panels and the complex doubly curved shapes of aerospace structures and dies and moulds.

Apart from standard surface types available for surface modeling (box, pyramid, wedge, dome, sphere,

cone, torus, dish and mesh) techniques are available for interactive modeling and editing of curved

surface geometry. Surfaces can be created through an assembly of polygonal meshes or using advanced

curve and surface modeling techniques like B-splines or NURBS (Non-Uniform Rational B-splines).

Standard primitives used in a typical surface modeling software are shown in Fig. 6.4. Tabulated surfaces,

ruled surfaces and edge surfaces and revolved are simple ways in which curved geometry could be

created and edited.


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Solid Modeling

Most powerful of 3-D modeling

It will give complete information about the model.

Mass properties such as area, volume, weight, CG, MI can be determined quickly.

It allows the designer to develop & evaluate alternative models.

Cross section can be cut through

Helps to interference checking of moving parts.

Used for technical illustrations.

Approaches to solid model.

Constructive solid geometry (CSG).

Boundary representation.

In CSG models are created by basic elementary shapes known as primitives like blocks,

cylinders, cones, and pyramids.

The boolean operations like union, difference and intersections are used to make the shape.

Easy to construct.

Boundary representation-It is accurate and give internal and external geometric descriptions.

User to draw the out line of various view of (t.v, s.v, f.v etc) the object by the use of input

devices on the CRT.

Then interconnected them

The representation of solid models uses the fundamental idea that a physical object divides the 3-D

Euclidean space into two regions, one exterior and one interior, separated by the boundary of the solid.

Solid models are:

• Bounded

• Homogeneously three dimensional

• Finite

In most of the modeling packages, the approach used for modeling uses any one of the following three

techniques:

i. Constructive solid geometry (CSG or C-Rep)

ii. Boundary representation (B-Rep)

iii. Hybrid method which is a combination of B-Rep and CSG.


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Constructive Solid Geometry (CSG)

In a CSG model, physical objects are created by combining basic elementary shapes known as primitives

–)

primitives, a block and a cylinder which are located in space as shown in Fig.

A “union” operation (A ∪

difference operation (A – B) will create a block with a hole (Fig. 6.5. (D)). An intersection operation (A

Boundary Representation

Boundary representation is built on the concept that a physical object is enclosed by a set of faces which

themselves are closed and orientable surfaces. Fig. 6.6 shows a B-rep model of an object. In this model,

face is bounded by edges and each edge is bounded by vertices.

The entities which constitute a B-rep model are:


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Advantages of Solid Modeling

A solid model is a 3-D representation of an object. It is an accurate geometric description which

includes not only the external surfaces of part, but also the part’s internal structure. A solid model

allows the designer to determine information like the object’s mass properties, interferences, and

internal cross sections.

Solid models differ from wire frame and surface models in the kind of geometric information

they provide. Wire frame models only show the edge geometry of an object. They say nothing

about what is inside an object. Surface models provide surface information, but they too lack

information about an object’s internal structure. Solid models provide complete geometric

descriptions of objects.

Engineers use solid models in different ways at different stages of the design process. They can

modify a design as they develop it. Since computer-based solid models are a lot easier to change

and manipulate than the physical mock-ups or prototypes, more design iterations and

modifications can be easily carried out as a part of the design process.

Using solid modeling techniques a design engineer can modify a design several times while

optimizing geometry. This means that designers can produce more finished designs in less time

than by using traditional design methods or 2-D CAD drafting tools.


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Solid models can be used for quick and reliable design analysis. Solid models apart from

geometric information provide important data such as volume, mass, mass properties and centre

of gravity. The designer can also export models created to other applications for finite element

analysis (FEA), rapid prototyping and other special engineering applications.

Finally designers can generate detailed production drawings directly from the solid model. This

capability increases design productivity considerably. Another important feature of solid

modeling is associatively. Detailed drawings are linked to solid model through the associatively

feature. This is a powerful function - as an engineer modifies a design, the drawings get updated

automatically. In bidirectional associatively, any modifications made to geometry in the drawing

are reflected in the model. In more advanced design and manufacturing environments, solid

models are used for rapid prototyping and automated manufacturing applications.

(ii) ENGINEERING ANALYSIS

. In the formulation of nearly any engint:ering design project some type of analysis is required. The

analysis may involve stress-strain calculations, heat transfer computations or the use of differential

equations to describe the dynamic behaviour of the system designed. CAD systems include engineering

analysis software, which can be called to operate on the current design model.

Two important examples of this type are :

(a) Analysis of mass properties (b) Finite Element Analysis

(a) The analysis of mass properties provides properties of a solid object being analysed such as

the surface area, weight, volume, centre of gravity and moment of inertia. For a plane surface (or a

cross section of a solid object) the corresponding computations include the perimeter, area, and

inertial properties.

(b) The finite element analysis is a powerful feature of the CAD system. With this method, the object

is divided into a large number of finite elements which form an interconnecting net-work of concentrated

nodes. By using a computer with significant computational capabilities, the entire object can be analyzed

for stress-strain, heat transfer and other characteristics by calculating the behavior at each node. By

determining the inter-connecting behaviors at all the nodes in the system, the behavior of the entire object

can be assessed. The output of the finite element analysis is often best presented by the system in

graphical format on the CRT screen for easy visualization by the user. For example, in stress-strain

analysis of an object the output may be shown in the form of deflected shape, superimposed over the

unstressed object. Colour graphics can also be used to accentuate the comparison before and after

deflection of the object. If the finite element analysis indicate behavior of the design which is undesirable,

the designer can modify the shape and recomputed the finite element analysis for the revised design.


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(III) DESIGN REVIEW AND EVALUATION

. Checking the accuracy of the design can be accomplished conveniently on the graphic terminal.

Semiautomatic dimensioning and tolerancing routines which assign size specification to surface indicated

by user help to reduce the possibility of dimensioning error. The designer can zoom the part design details

and magnify the image on the graphic screen for close scrutiny. A procedure called layering is often

helpful in design review.

For Example : A good application of layering involves overlaying the geometric image of the final shape

of the machined part on top of the image of the rough casting. This ensures that to accomplish the final

machined dimensions. This procedure can be performed in stage processing of the part.

(IV) AUTOMATED DRAFTING. Automated drafting involves the creation of hard-copy engineering

drawing directly from the CAD Data base. In some early computer-aided design departments, auto-

mation of the drafting process represent the principal justification for investing in the CAD system.

Indeed, CAD system can increase productivity in the drafting function by roughly five time over manual

drafting.

Representations of CIM


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TQM

Marketing

CIM


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Elements of CIM

Product design.

Establishes the initial database for production of proposed product.

It is accomplished through geometric modeling.

Production planning.

It take the database established by the product design, enriches it with production data.

Produce a plan for the product production.

The cost incurred and production equipment’s capacity will be consider.

Production control.


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Further enriches the output of production planning dept with performance data and information

about production equipment and processes.

In CIM this activity includes

Modeling, simulation, and computer aided scheduling of the production activity.

Continuous optimization of production activity is must.

Production equipment

It enriches the database with equipment and process data and information.

The equipment consist of

computer controlled machines like CNC.

FMS

Robots

Material handling systems

Inspection equipments

Production process.

It create the finished product with the help of the production equipments.

This is done with the help of data information and knowledge resident in the operator or CIM

system.

This process consist of

Material removal.

Material forming.

Automated quality assurance.

Advantages of CIM

Responsiveness to Rapid Changes in Market Demand and Product Modification.

Better Use of Materials, Machinery, Personnel, Reduction in Inventory.

Better Control of Production and Management of the Total Manufacturing Operation.

The Manufacture of High-Quality Products at Low Cost.

Improved competitiveness


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Lower total cost.

High productivity.

Less work in process inventory.

Long time profitability.

PREPARE NOTES FOR SOFTWARES BY YOUR OWN

Suggested extra reading;

http://en.wikipedia.org/wiki/Comparison_of_3D_computer_graphics_software

Principles of Automation and Advanced Manufacturing Systems- Dr K.C. Jain, Sanjay Jain

CAD/CAM-Concepts and Applications- Chennakesava R. Alavala

CAD/CAM- M Groover, E. Zinners

http://en.wikipedia.org/wiki/Comparison_of_3D_computer_graphics_software