Computer-aided design incorporates computing systems that help
engineers in developing, modification, analysis and optimizing of various
design solutions. An electronic computing system involves hardware and
software tools which perform specialized functions in the designing process.
Generally, the hardware consists of computers, one or several graphic
displays, keyboards and peripherals including input/output devices of 3D
objects. The software consists of computer programs, ensuring the work with
graphic terminals, and application software which implement design and
construction functions, specific for a definite user. Examples for application
software are the programs for analysis of strength and stresses in elements of
different mechanical structures; calculations of dynamic characteristics of
mechanisms and calculations of heat transfer parameters; analysis and
synthesis of electronic circuits; integral microcircuits design, etc. The set of
specific application software is changed, modified and improved depending
on user’s demands and the available hardware for design implementation.
The term Computer Aided Design characterizes any design activity
which incorporates an electronic computing machine or computer in the
process of development, analysis or modification of technical design
solutions. Modern CAD systems are based on the vast usage of Interactive
Computer Graphics (ICG) tools. The term refers to user-oriented graphic
systems designed for data generation, conversion and visual presentation.
The graphics system user is the designer who defines relevant data
and commands on the computer by means of one of the available data input
devices of the system set. The user interacts with the computer through the
display screen. The designer creates images on the screen applying
commands which address standard subprograms stored in the memory of the
computing environment
.
In most CAD systems the image on the screen is constructed with
standard geometrical elements – points, lines, circles, etc. The generated
image can be further modified by the user with the help of addressed
commands, i.e. the image can be zoomed-in, zoomed-out, moved, rotated
and subjected to other transformations. In the process of executing different
manipulations on the image the user constructs its specific details.
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, digitizers, drawing equipment, etc.).
The software of ICG systems incorporates computer programs for
processing graphical data, and special additional (not included in the system 6
set) application software intended to implement definite design functions as
required by different users
The category of graphic peripherals includes devices which produce
graphic images on a permanent carrier. The distinctive feature is that the
produced image cannot be changed and the carrier should not be re-used.
The most widespread devices of this type are plotters. They are
automatic drawing machines converting digitally coded data into images
without operator’s direct actions. Depending on the principle of the image
generation plotters are divided into vector or raster type.
Classic plotters implement the vector principle for image building in
compliance with the objects’ specification. In fact, the plotter makes a motion
according to the preset parameters of each vector, and the writing tool (pen)
leaves a trace on the carrier equivalent to the motion.
Raster plotters can be classified as mechanical, electro-spark type,
electro-chemical type, thermal, optical, magnetic and inkjet type.
Depending on the type of static carriage and the writing pen structure,
the vector plotters are classified as flatbed, drum, roll-on and roller-frictional
plotters.
Regarding functionality plotters are divided into two main groups:
First group – includes the following functions [1]:
- 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:
1. Drawing size – set up as machine drawing paper sizes (А0 ÷ А4) in
mm or inches.
2. 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.
3. 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 10
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.
4. Reiteration – the error resulting from the multiple motion of the
writing tool to one and the same point.
5. Drawing speed – represents the plotter’s speed and is usually
within 25 ÷ 90 cm/s.
6. Functions:
- linear interpolator;
- circular interpolator;
- character generator;
- geometric primitives;
- types of lines;
- translation;
- scaling;
- rotation.
7. Programming language
8. Types 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.
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
1. Host sets the ReverseRequest line in low level to request a
reverse channel.
2. Peripheral acknowledges reverse channel request by setting the
AckReverse line in low level.
3. Data is set to the data lines by peripheral.
4. Data cycle is selected by peripheral by setting the PeriphAck in
high level.
5. Peripheral indicates valid data by setting PeriphClk signal in low
level.
6. Host sends its acknowledgement of valid data via HostAck going
high. 28
7. Peripheral device sets the line PeriphClk in high level, used to
shift data to the host.
8. Host sends its acknowledgement of the byte by resetting the
HostAck line in low level.
ECP reverse command cycle (Fig. 2.13):
1. Host sets ReverseRequest low to request a reverse channel.
2. Peripheral acknowledges reverse channel request by setting the
AckReverse line in low level.
3. Data is placed on data lines by the peripheral.
4. Command cycle is selected by peripheral by setting the
PeriphAck in high level.
5. Peripheral indicates valid data by setting PeriphClk signal in low
level.
6. Host sends its acknowledgement of valid data via HostAck going
high.
7. The peripheral device sets the line PeriphClk in high level, used
to shift data to the host.
8. Host sends its acknowledgement of the byte by resetting the
HostAck line in low level
This is all i can share about peripheral devices in detail.
engineers in developing, modification, analysis and optimizing of various
design solutions. An electronic computing system involves hardware and
software tools which perform specialized functions in the designing process.
Generally, the hardware consists of computers, one or several graphic
displays, keyboards and peripherals including input/output devices of 3D
objects. The software consists of computer programs, ensuring the work with
graphic terminals, and application software which implement design and
construction functions, specific for a definite user. Examples for application
software are the programs for analysis of strength and stresses in elements of
different mechanical structures; calculations of dynamic characteristics of
mechanisms and calculations of heat transfer parameters; analysis and
synthesis of electronic circuits; integral microcircuits design, etc. The set of
specific application software is changed, modified and improved depending
on user’s demands and the available hardware for design implementation.
The term Computer Aided Design characterizes any design activity
which incorporates an electronic computing machine or computer in the
process of development, analysis or modification of technical design
solutions. Modern CAD systems are based on the vast usage of Interactive
Computer Graphics (ICG) tools. The term refers to user-oriented graphic
systems designed for data generation, conversion and visual presentation.
The graphics system user is the designer who defines relevant data
and commands on the computer by means of one of the available data input
devices of the system set. The user interacts with the computer through the
display screen. The designer creates images on the screen applying
commands which address standard subprograms stored in the memory of the
computing environment
In most CAD systems the image on the screen is constructed with
standard geometrical elements – points, lines, circles, etc. The generated
image can be further modified by the user with the help of addressed
commands, i.e. the image can be zoomed-in, zoomed-out, moved, rotated
and subjected to other transformations. In the process of executing different
manipulations on the image the user constructs its specific details.
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, digitizers, drawing equipment, etc.).
The software of ICG systems incorporates computer programs for
processing graphical data, and special additional (not included in the system 6
set) application software intended to implement definite design functions as
required by different users
The category of graphic peripherals includes devices which produce
graphic images on a permanent carrier. The distinctive feature is that the
produced image cannot be changed and the carrier should not be re-used.
The most widespread devices of this type are plotters. They are
automatic drawing machines converting digitally coded data into images
without operator’s direct actions. Depending on the principle of the image
generation plotters are divided into vector or raster type.
Classic plotters implement the vector principle for image building in
compliance with the objects’ specification. In fact, the plotter makes a motion
according to the preset parameters of each vector, and the writing tool (pen)
leaves a trace on the carrier equivalent to the motion.
Raster plotters can be classified as mechanical, electro-spark type,
electro-chemical type, thermal, optical, magnetic and inkjet type.
Depending on the type of static carriage and the writing pen structure,
the vector plotters are classified as flatbed, drum, roll-on and roller-frictional
plotters.
Regarding functionality plotters are divided into two main groups:
First group – includes the following functions [1]:
- 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:
1. Drawing size – set up as machine drawing paper sizes (А0 ÷ А4) in
mm or inches.
2. 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.
3. 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 10
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.
4. Reiteration – the error resulting from the multiple motion of the
writing tool to one and the same point.
5. Drawing speed – represents the plotter’s speed and is usually
within 25 ÷ 90 cm/s.
6. Functions:
- linear interpolator;
- circular interpolator;
- character generator;
- geometric primitives;
- types of lines;
- translation;
- scaling;
- rotation.
7. Programming language
8. Types 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.
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
1. Host sets the ReverseRequest line in low level to request a
reverse channel.
2. Peripheral acknowledges reverse channel request by setting the
AckReverse line in low level.
3. Data is set to the data lines by peripheral.
4. Data cycle is selected by peripheral by setting the PeriphAck in
high level.
5. Peripheral indicates valid data by setting PeriphClk signal in low
level.
6. Host sends its acknowledgement of valid data via HostAck going
high. 28
7. Peripheral device sets the line PeriphClk in high level, used to
shift data to the host.
8. Host sends its acknowledgement of the byte by resetting the
HostAck line in low level.
ECP reverse command cycle (Fig. 2.13):
1. Host sets ReverseRequest low to request a reverse channel.
2. Peripheral acknowledges reverse channel request by setting the
AckReverse line in low level.
3. Data is placed on data lines by the peripheral.
4. Command cycle is selected by peripheral by setting the
PeriphAck in high level.
5. Peripheral indicates valid data by setting PeriphClk signal in low
level.
6. Host sends its acknowledgement of valid data via HostAck going
high.
7. The peripheral device sets the line PeriphClk in high level, used
to shift data to the host.
8. Host sends its acknowledgement of the byte by resetting the
HostAck line in low level
This is all i can share about peripheral devices in detail.
