CAD/CAM systems and the concept of interactive

computer graphics. Tools. Tool requirements.

Prof. Dr. Raycho IlarionovAssoc. Prof. Nikolay Madzharov

MSc. Eng. Georgi Tsanev

CAD/CAM systems and the concept of interactive computer graphics

One of the main applications of computer technology is theComputer Aided Design (CAD), side by side with theComputer Aided Manufacturing (CAM).

The term Computer Aided Design characterizes any designactivity which incorporates an electronic computing machinein the process of development, analysis or modification oftechnical design solutions. Modern CAD systems are based onthe vast usage of Interactive Computer Graphics (ICG) tools.

CAD/CAM systems and the concept of interactive computer graphics

The typical system of interactive computer graphics is composed of hardware and software tools. The hardware comprises central processing unit; one or more work stations (incl. graphic display terminals) and a set of peripherals (printers, scanners, digitizers, etc.)

computing environment

application

software

applied

databases

input

output

input

data

operator

output

data

drawing equipment

printer,

plotter

etc.

Advantages of using CAD systems

Increased efficiency of designers` work. It is achieved with the help of thecomputing environment which provides visual presentation of the designedobject, components and specific details.

Higher performance. The CAD systems open up broad opportunities for athorough engineer analysis and examination of a great number of alternativedesign solutions.

Better communication between users. Drawings made with CAD systems areof higher quality, they fully comply with standards` requirementsincorporated within the system and the developed project becomes betterdocumented.

Organizing databases for designing systems. The database contains the wholeinformation required for the successful completion of the design. It may alsoinclude databases created for previous projects with their descriptions.

Technical Tools of CAD Systems

computing

systems

electronic computing

machines,

microcomputers

passive

graphics

plotters,

screen copy tools

messages, commands

alphanumeric keyboards,

displays

graphic

dialogue

digitizers,

interactive

manipulators

data storage

magnetic discs,

optic discs,

magnetic tapes

3D devices

3D scanners,

3D printers

dynamic

graphics

graphic

displays

Computing systems

They involve one or several computingmachines connected in a network. Each of themcan be:

- general purpose computers (universal)

- specialized computers

Data Storage DevicesThey provide the possibility to process a huge amount of information. Recently, devices of high storage capacity (magnetic and optical discs, diskettes, magnetic tapes, USB memory, etc.) are widely introduced and applied. Their usage in CAD systems is determined by a number of factors:

the enormous amount of data that in most cases has to be processed from the design start up to the production stage;

the method of database creation and usage;

the architecture of computer systems’ networks faces the problem of database organization (local data, common data storage for groups or fields, etc.)

Graphic Data Visualization Devicespassive graphic devices: for creating drawings and pictures which cannot be changed;

dynamic graphic devices: for creating graphic objects that can be deleted or changed at any time

Input Data Devices

On the other hand they are subdivided into graphic devices(devices for data transfer as coordinate values) and non-graphic devices (alphanumeric displays and keyboards).

3D devices

Mainly, they are used for developing CAD models. The3D scanners are devices with the help of which therelief of a geographical object can be digitallypresented, while the common scanning devices justcopy the color information of the image.

The 3D printers belong to the class of rapidprototyping devices. They construct the 3D informationin succession, generating interconnected points. Thus aconceptual model of 3D CAD file is quickly createdwithout additional technological tools.

Requirements for Graphic Peripherals

Requirements for Passive Graphics Devices

The category of graphic peripherals includes devices which producegraphic images on a permanent carrier. The distinctive feature is that theproduced image cannot be changed and the carrier should not be re-used. The most widespread devices of this type are plotters. They areautomatic drawing machines converting digitally coded data into imageswithout operator’s direct actions. Depending on the principle of theimage generation plotters are divided into vector or raster type. Classicplotters implement the vector principle for image building in compliancewith the objects’ specification. In fact, the plotter makes a motionaccording to the preset parameters of each vector, and the writing tool(pen) leaves a trace on the carrier equivalent to the motion. Rasterplotters can be classified as mechanical, electro-spark type, electro-chemical type, thermal, optical, magnetic and inkjet type. Depending onthe type of static carriage and the writing pen structure, the vectorplotters are classified as flatbed, drum, roll-on and roller-frictionalplotters.

Regarding functionality plotters are divided into two main groups:

First group – includes the following functions:servo control on two-step or direct-current motors; maintenance of constant drawing speed;writing tool control;linear and circular interpolators;character generator;working with different number of pens;drawing different types of lines;scaling and rotation of drawings to angles multiple of 90;availability of several tables with different characters;characters scaling and rotation to a certain angle;inclined characters drawing;setting up of plotting area and cutting off elements falling outside it;powerful language for program control providing remote access to all foregoing functions.

Second group – includes 17 functions in addition to the above mentioned functions:drawing rotation to a random angle (drawing transformation into the carrier coordinate system);text rotation to a random angle;text writing at adaptable distance between characters;polygon filling in a pattern (full filling, hatching, etc.);exchange different protocols with the computing environment.

Basic technical features of plotters: Drawing size – set up as machine drawing paper sizes (А0 А4) in mm or inches.Resolution – the smallest distance to which the writing element can move. It is measured in mm and is usually within 0,0125 0,1 mm.Accuracy – the error resulting from the movement of the writing tool from point to point at a random distance. It may have positive or negative value. Usually the accuracy varies within 0,05 - 0,25 mm. For some non-flat vector plotter the accuracy is set up separately for X and Y coordinates.Reiteration – the error resulting from the multiple motion of the writing tool to one and the same point.Drawing speed – represents the plotter’s speed and is usually within 25 90 cm/s.Functions:linear interpolator;circular interpolator;character generator;geometric primitives;types of lines;translation;scaling;rotation.Programming languageTypes of interfaces – series RS 232 and parallel IEEE 488.

Requirements for Dynamic Graphics Devices

Displays are devices for showing a generated image that may be subject to further modifications without changing the information carrier.

Displays can be of two types: alphanumeric:- the displayed information is a succession of alphanumeric characters;graphic:- the displayed information is both alphanumeric and graphic.

Displays are characterized by the following parameters: amount of displayed data;size of screen’s working area;number of characters displayed on the screen;image refresh rate;possibility of working with definite number of colors;image display quality;options of screen division into random data zones.

Requirements for Dynamic Graphics Devices

The amount of information for alphanumeric displays is measured by the maximum number of characters set on the screen and it is defined as the product of the maximum number of characters in a line multiplied by the number of lines displayed on the screen. Depending on the type of graphic displays, the amount of displayed information is represented either by the number of address points, or as a summed up length of the graphic image vectors. For alphanumeric displays the number of displayed characters is within 128 – 160. As for graphic displays, the standard set of characters can be extended with specialized symbols which are frequently used in reproducing specific graphic images [5].

According to image regeneration method, graphic displays are divided into vector and raster types.

Requirements for Graphic Data Input

1. Devices which allow data transfer by means of keys(keyboards). Keyboards can be alphanumeric or functional.Functional keyboards represent a set of keys that maycancel relevant operation when pressed, while the numberof the pressed key is conveyed to a computer system. Thesoftware product always prompts the keys which can beused at a given moment .

2. Devices for direct specification of a point on the screen.The light pen is a representative of the group. Theresponse of its operation is the initialization of a specifiedpoint (X, Y) on the screen. The light pen’s accuracy is nothigh and it partially depends on the parallax.

Requirements for Graphic Data Input

3. Devices for indirect specification which allow the setting up of coordinates. This group involves different types of digitizers, tablets, mice and track balls. The last three are also called interactive manipulators.

The process of converting graphic data into digital code includes two stages: reading and encoding.

During the reading process the graphic element (point, line, elementary fragment) is recognized and its coordinates are relevantly specified in the assumed coordinated system. The encoding process performs data conversion into a digital code in accordance with the established rules.

Characteristics of digitizers

1. Working area size – it is set up in accordance with themachine drawing paper size (А0 А4) in millimetersor inches.

2. Resolution – the smallest step of positioningelement’s movement that leads to increase anddecrease in the current coordinates. Most frequentlydigitizers’ resolution is within 0,1 0,025 mm.

Characteristics of digitizers3. Accuracy – the error that occurs during the movement of the

positioning element from one point to another at a random distance in the working area. It may get positive or negative values. Generally the accuracy varies within 0,075 0,625 mm.

4. Speed of coordinate points output – number of points per second (P/s). This parameter conveys information about the device speed, and usually it is within 60 200 points per second.

5. Input mode

6. Functions

7. Programming language

8. Menu

9. Types of interfaces - series RS 232 or parallel

The main technical parameters of scanners

maximum resolution along X and Y axes – it is given by the number of points per inch;

scanning mode – contrast, semi-shaded, etc. depending on the scanner;

contrast control – given with the number of grades;

brightness control – given with the number of grades;

possibility of changing the scanner’s resolution;

maximum scanning speed;

scanning area;

interface for data transfer (SCSI, IEEE-488 - GPIB, RS232).

Requirements for 3D scanner

accuracy – 0,025 mm;

resolution – 0,005 mm;

maximum motion along X, Y and Z axes;

scanning methods (pre-set description of surfaces, or automatic);

contact or contactless scanning method;

scanning speed (number of points per second);

output file format.

Thank you!