Hardware of a CAD System

4.1. CAD Output DevicesAssoc.Prof.Dr. Ahmet Zafer enalpe-mail: azsenalp@gmail.com

Mechanical Engineering DepartmentGebze Technical University

ME 521Computer Aided Design14.1. CAD Output Devices CAD Output Devices

PlotterPrinterCRT Display Vector DisplayStorage TubeRaster DisplayLCD DisplayPlazma EkranlarDigital Light Processing-DLPOLEDVirtual RealityRapid Prototyping

Dr. Ahmet Zafer enalp ME 5212Mechanical Engineering Department, GTU Early pen plotters, e.g., the Calcomp 565 of 1959, worked by placing the paper over a roller that moved the paper back and forth for X motion, while the pen moved back and forth on a track for Y motion.Another approach, e.g. Computervision's Interact I, involved attaching ball-point pens to drafting pantographs and driving the machines with motors controlled by the computer. This had the disadvantage of being somewhat slow to move, as well as requiring floor space equal to the size of the paper, but could double as a digitizer. A later change was the addition of an electrically controlled clamp to hold the pens, which allowed them to be changed, and thus create multi-colored output

Hewlett Packard and Tektronix produced small, desktop-sized flatbed plotters in the late 1960s and 1970s. The pens were mounted on a traveling bar, whereby the y-axis was represented by motion up and down the length of the bar and the x-axis was represented by motion of the bar back and forth across the plotting table. Due to the mass of the bar, these plotters operated relatively slowly Plotters are mainly used in CAD applications and drafting .

The advantages of using plotters:High resolutionUsage of large scale paperPlotterDr. Ahmet Zafer enalp ME 5213Mechanical Engineering Department, GTU4.1. CAD Output Devices

PlotterPlotter has either vector or raster graphics property and connected to the computer.

Plotter control languages:

HPGL, HPGL2 (Hewlett-Packard)DMPL (Houston Instruments), Postscript, ps, eps (Adobe)

Ex: pen up=PA, pendown=PD

Dr. Ahmet Zafer enalp ME 5214Mechanical Engineering Department, GTU4.1. CAD Output Devices PlotterPlotters according to structure:

Flatbed plotters Drum plotters

Dr. Ahmet Zafer enalp ME 5215Mechanical Engineering Department, GTU4.1. CAD Output Devices PlotterPen plotters

By moving the pen along the surface of the paper, make drawings. Limited with 2D drawing commands. Cannot draw raster images. Can draw letters but they are slow due to the mechanical movement of the pen. Cannot draw color pictures. They are used for vector graphics. When the computers were slow they were the fastest drawing devices. Different thicknesss pens or color pens can be used. Has to change pens in case of using color pens or pens with different thickness. With the generation of speedy computers, pen plotters disappeared.

Dr. Ahmet Zafer enalp ME 5216Mechanical Engineering Department, GTU4.1. CAD Output Devices Inkjet plotters Work with the same principle with inkject printers Can draw raster pictures. There are also models avilable that can draw photorealisitic pictures. Also used in advertisement sector.

Thermal plottersThey draw on heat sensitive paper or film material by apllying heat.

Plotter

Dr. Ahmet Zafer enalp ME 5217Mechanical Engineering Department, GTU4.1. CAD Output Devices Electrostatic plotters

Draws a raster image to the paper by applying high voltage. This voltage attracts toner and melts on paper by the help of heat. It is fast but more expensive than inkject plotters.

Plotter

Dr. Ahmet Zafer enalp ME 5218Mechanical Engineering Department, GTU4.1. CAD Output Devices Character printers:

First printer type that is similar to typewriter. Characters are pressed similar to typewriter. First samples are in typewriter structure. Later there exists models that type a line at once. This type of printers are not used widely today due t complex electromechanical structures, low speeds and limited printing capabilities.Printer

Dr. Ahmet Zafer enalp ME 5219Mechanical Engineering Department, GTU4.1. CAD Output Devices Line printers:

As the name implies, print an entire line of text at a time.Generally used with mainframe computers.Can print 600-1200 line at a minute. Chain or drum types are available. In drum types charactes are placed on the drum.Printer

chain type line printerDrum type line printersDr. Ahmet Zafer enalp ME 52110Mechanical Engineering Department, GTU4.1. CAD Output Devices Dot-matrix printers :In the general sense many printers rely on a matrix of pixels, or dots, that together form the larger image. However, the term dot matrix printer is specifically used for impact printers that use a matrix of small pins to create precise dots. The advantage of dot-matrix over other impact printers is that they can produce graphical images in addition to text; however the text is generally of poorer quality than impact printers that use letterforms (type).Print quality can be poor-especially for low-density dot-matrix printers. The quality of characters and graphic images often appears to be ragged or unfocused although some high-density dot-matrix printers rival those of letter-quality printers. But, for the most part, dot-matrix printers do not produce high-quality text and graphics. Often, dot-matrix units are used as draft printers. Then, final outputs of higher quality are prepared on letter-quality printersPrinter

Printing head: 5x7 type36x24 typeDr. Ahmet Zafer enalp ME 52111Mechanical Engineering Department, GTU4.1. CAD Output Devices Inkjet Printers:

Ink-jet printers spray tiny drops of ink to form character shapes on paper. Since characters are formed as a pattern of dots, ink-jet printers are technically dot-matrix printers. However the quality of ink-jet output generally is much higher than that of most dot-matrix printers Today inkjet printers have the highest resolution. They are more silent and has small structures than others. According to spraying there are piezoelectric and thermal types available.Printer

Dr. Ahmet Zafer enalp ME 52112Mechanical Engineering Department, GTU4.1. CAD Output Devices Inkjet Printers:

Thermal inkjet printersThe ink droplet that is heated until nearly 300 C in the print head nozzles rooms evaporates and sprayed to the paper with a small explosion with high speed (100 km/hr).Due to the need of heating water based inks are used in this type of printing. Japon Canons inkjet, Bubblejet printers work with this principle. This type of printing is widely used by those who is in need of printing small numbers.

Piezoelectric inkjet printersIn this type of printers, ink spray is made by piezoelectric crystal spray nozzles. Spraying is done in the form of process-induced crystal vibrated spray ink.In this type as no heating is required, there is no limitation in the ink that should be used.Epsons printers use this principle. In commercial and industrial applications generally this kind of inkjet printers are used.PrinterDr. Ahmet Zafer enalp ME 52113Mechanical Engineering Department, GTU4.1. CAD Output Devices Thermal printers:

Thermal printers work by selectively heating regions of special heat-sensitive paper. Monochrome thermal printers are used in cash registers, ATMs, gasoline dispensers and some older inexpensive fax machines. Colours can be achieved with special papers and different temperatures and heating rates for different colours; these coloured sheets are not required in black-and-white output. One example is the ZINK technology.Before the invension of inkjet printers, thermals printers were used widely in CAD applications.

Printer

Dr. Ahmet Zafer enalp ME 52114Mechanical Engineering Department, GTU4.1. CAD Output Devices Laser printers:A laser printer is a common type of computer printer that rapidly produces high quality text and graphics on plain paper. As with digital photocopiers and multifunction printers (MFPs), laser printers employ a xerographic printing process but differ from analog photocopiers in that the image is produced by the direct scanning of a laser beam across the printer's photoreceptor.Latest invented printer type. Silent, high resolution print quality and fast compared to other printers. Basically, use a printing technique similar to photocopy machine. Main feature that differs in laser printers compared to photocopy machines is that: numeric codes from the computer is the source of printing. Signals coming from the computer are drawn on ligth sensitive drum with the help of laser. This operation enables drawn parts on the drum to be charged with electricity. These regions are coated with toner. The coated toner is transfered to the paper. To fix the toner heat is applied between 100-150 C .Color types are slo available. Used widely as fast and economical. Laser printers are also page printers.

Printer

Dr. Ahmet Zafer enalp ME 52115Mechanical Engineering Department, GTU4.1. CAD Output Devices Cutaway rendering of a color CRT:1. Three Electron guns (for red, green, and blue phosphor dots)2.Elektron beams 3. Focusing coils4. Deflection coils5. Anode connection6. Mask for separating beams for red, green, and blue part of displayed image7. Phosphor layer with red, green, and blue zones8. Close-up of the phosphor-coated inner side of the screen

CRT DisplayCRT : Chatode Ray Tube Dr. Ahmet Zafer enalp ME 52116Mechanical Engineering Department, GTU4.1. CAD Output Devices A cathode ray tube (CRT) is a specialized vacuum tube in which images are produced when an electron beam strikes a phosphorescent surface. Most desktop computer displays make use of CRTs. The CRT in a computer display is similar to the "picture tube" in a television receiver.A cathode ray tube consists of several basic components. The electron gun generates a narrow beam of electrons. The anodes accelerate the electrons. Deflecting coils produce an extremely low frequency electromagnetic field that allows for constant adjustment of the direction of the electron beam. There are two sets of deflecting coils: horizontal and vertical. The intensity of the beam can be varied. The electron beam produces a tiny, bright visible spot when it strikes the phosphor-coated screen.To produce an image on the screen, complex signals are applied to the deflecting coils, and also to the apparatus that controls the intensity of the electron beam. This causes the spot to race across the screen from right to left, and from top to bottom, in a sequence of horizontal lines called the raster. As viewed from the front of the CRT, the spot moves in a pattern similar to the way your eyes move when you read a single-column page of text. But the scanning takes place at such a rapid rate that your eye sees a constant image over the entire screen.

CRT DisplayDr. Ahmet Zafer enalp ME 52117Mechanical Engineering Department, GTU4.1. CAD Output Devices Virtually all CRTs today render color images. These devices have three electron guns, one for the primary color red, one for the primary color green, and one for the primary color blue. The CRT thus produces three overlapping images: one in red (R), one in green (G), and one in blue (B). This is the so-called RGB color model.In computer systems, there are several display modes, or sets of specifications according to which the CRT operates. The most common specification for CRT displays is known as SVGA (Super Video Graphics Array). Notebook computers typically use liquid crystal display. The technology for these displays is much different than that for CRTs.

CRT Display

Dr. Ahmet Zafer enalp ME 52118Mechanical Engineering Department, GTU4.1. CAD Output Devices Every pixel on a display is composed of 3 color phosphor droplets. The distance of nearest pixels is called dot pitch. Today CRT monitors have dot pitch values between 0.24 mm and 0.28 mm. When this value is smaller display quality is better. A vector monitor or vector display is a display device used for early computers. It is a type of CRT, similar to the oscilloscope, but typically uses magnetic, rather than electrostatic, deflection. Here, the beam traces straight lines between arbitrary points, repeatedly refreshing the display as quickly as possible.Vector displays for computers did not noticeably suffer from the display artifacts of Aliasing and pixelation, but were limited in that they could display only a shape's outline (advanced vector systems could provide a limited amount of shading), and only a limited amount of crudely-drawn text (the number of shapes and/or textual characters drawn was severely limited, because the speed of refresh was roughly inversely proportional to how many vectors needed to be drawn).Vector displays were used for head-up displays in fighter aircraft, because of the brighter displays that can be achieved by moving the electron beam more slowly across the phosphors. Brightness is critical in this application because the display must be clearly visible to the pilot in direct sunlight.Vector monitors were also used by some late-1970s to mid-1980s arcade games such as Asteroids. Atari used the term Quadrascan to describe the technology when used in their video game arcades.Vector DisplayDr. Ahmet Zafer enalp ME 52119Mechanical Engineering Department, GTU4.1. CAD Output Devices Hewlett-Packard made a large-screen fast vector monitor, which they called an X-Y display. It used a wide-angle electrostatically-deflected CRT that was about as compact as a magnetic-deflection CRT. Instead of the deflection plates of a typical CRT, it had a unique structure they called an electrostatic deflection yoke, with metallized electrodes inside a glass cylinder.Vector Display

Dr. Ahmet Zafer enalp ME 52120Mechanical Engineering Department, GTU4.1. CAD Output Devices Mostly obsolete, a storage tube is a special monochromatic CRT whose screen has a kind of 'memory. When a portion of the screen is illuminated by the CRT's electron gun, it stays lit until a screen erase command is given. Thus, screen update commands need only be sent once and this allows the use of a slower data connection, The two main advantages were:Very low bandwidth needs compared to vector graphics displays, thus allowing much longer cable distances between computer and terminalNo need for display-local RAM (as in modern terminals), which was prohibitively expensive at the time.Storage Tube

Dr. Ahmet Zafer enalp ME 52121Mechanical Engineering Department, GTU4.1. CAD Output Devices Generally speaking, storage tubes could be divided into two categories. In the more common category, they were only capable of storing "binary" images; any given point on the screen was either illuminated or dark. The Tektronix Direct-View Bistable Storage Tube was perhaps the most-famous example in this category. Other storage tubes were able to store greyscale/halftoned images; the tradeoff was usually a much-reduced storage time.Some pioneering storage tube displays were MIT Project MAC's ARDS (Advanced Remote Display Station), the Computek 400 Series Display terminals (a commercial derivative), which both used a Tektronix type 611 storage display unit, and Tektronix's 4014 terminal, the latter becoming a de facto computer terminal standard some time after its introduction (later being emulated by other systems due to this status).

Storage Tube"DVBST" storage tube Tektronix 4014

Dr. Ahmet Zafer enalp ME 52122Mechanical Engineering Department, GTU4.1. CAD Output Devices A liquid crystal display (LCD) is a thin, flat electronic visual display that uses the light modulating properties of liquid crystals (LCs). LCs do not emit light directly.They are used in a wide range of applications including: computer monitors, television, instrument panels, aircraft cockpit displays, signage, etc. They are common in consumer devices such as video players, gaming devices, clocks, watches, calculators, and telephones. LCDs have displaced cathode ray tube(CRT) displays in most applications. They are usually more compact, lightweight, portable, less expensive, more reliable, and easier on the eyes. They are available in a wider range of screen sizes than CRT and plasma displays, and since they do not use phosphors, they cannot suffer image burn-in.LCDs are more energy efficient and offer safer disposal than CRTs. Its low electrical power consumption enables it to be used in battery-powered electronic equipment. It is an electronically-modulated optical device made up of any number of pixels filled with liquid crystals and arrayed in front of a light source (backlight) or reflector to produce images in colour or monochrome. The earliest discovery leading to the development of LCD technology, the discovery of liquid crystals, dates from 1888.[1] By 2008, worldwide sales of televisions with LCD screens had surpassed the sale of CRT units.

LCD Display

LCDs have half life of approximately 50000-70000 hours.Dr. Ahmet Zafer enalp ME 52123Mechanical Engineering Department, GTU4.1. CAD Output Devices 1. Polarizing filter film with a vertical axis to polarize light as it enters.2. Glass substrate with ITO electrodes. The shapes of these electrodes will determine the shapes that will appear when the LCD is turned ON. Vertical ridges etched on the surface are smooth.3. Twisted nematic liquid crystal.4. Glass substrate with common electrode film (ITO) with horizontal ridges to line up with the horizontal filter.5. Polarizing filter film with a horizontal axis to block/pass light.6. Reflective surface to send light back to viewer. (In a backlit LCD, this layer is replaced with a light source.)

LCD Display

ematik sv kristal ekranDr. Ahmet Zafer enalp ME 52124Mechanical Engineering Department, GTU4.1. CAD Output Devices LCD Advantages/DisadvantagesLCD Advantages: Good in stagnant images such as computer display. Quality products have good brightness. Because of dimensions require less space.Has less energy consumption.Has long life. (Approximately 50000- 70000 hr)

LCD Disadvantages: Delay problem. Unnatural view formation when viewing high speed motion. Black levels: In most of the LCDs black cannot be displayed properly. Black is displayed as dark gray.Viewing angle: Perfect display cannot be attained at 1700 viewing angle.Less of the LCDs found in the market have good motion (video) capabilities.Cheap products use cheap panels which do not cause quality displays.In poor quality LCDs dead pixel formation can occur. When dead pixel ratio exceeds 10 % LCD cannot be watched properly. In most of the LCDs unnatural display takes place like digital display.

Dr. Ahmet Zafer enalp ME 52125Mechanical Engineering Department, GTU4.1. CAD Output Devices LCD Display

Dr. Ahmet Zafer enalp ME 52126Mechanical Engineering Department, GTU4.1. CAD Output Devices A plasma display panel is a type of flat panel display common to large TV displays (80cm/30in or larger). They are called "plasma" displays because the pixels rely on plasma cells, or what are in essence chambers more commonly known as fluorescent lamps. A panel typically has millions of tiny cells in compartmentalized space between two panels of glass. These compartments, or "bulbs" or "cells", hold a mixture of noble gases and a minuscule amount of mercury. Just as in the fluorescent lamps over an office desk, when the mercury is vaporized and a voltage is applied across the cell, the gas in the cells form a plasma. (A plasma is a collection of particles that respond strongly and collectively to electromagnetic fields or electrical charges, taking the form of gas-like clouds or ion beams.) With flow of electricity (electrons), some of the electrons strike mercury particles as the electrons move through the plasma, momentarily increasing the energy level of the molecule until the excess energy is shed. Mercury sheds the energy as ultraviolet (UV) photons. The UV photons then strike phosphor that is painted on the inside of the cell. When the UV photon strikes a phosphor molecule, it momentarily raises the energy level of an outer orbit electron in the phosphor molecule, moving the electron from a stable to an unstable state; the electron then sheds the excess energy as a photon at a lower energy level than UV light; the lower energy photons are mostly in the infrared range but about 40% are in the visible light range. Thus the input energy is shed as mostly heat (infrared) but also as visible light. Plasma Displayematik plazma ekranDr. Ahmet Zafer enalp ME 52127Mechanical Engineering Department, GTU4.1. CAD Output Devices Depending on the phosphors used, different colors of visible light can be achieved. Each pixel in a plasma display is made up of three cells comprising the primary colors of visible light. Varying the voltage of the signals to the cells thus allows different perceived colors.Plasma Display

First plasma computer display(1981)ematik plazma ekranDr. Ahmet Zafer enalp ME 52128Mechanical Engineering Department, GTU4.1. CAD Output Devices Plasma DisplayWorking Principle

Dr. Ahmet Zafer enalp ME 52129Mechanical Engineering Department, GTU4.1. CAD Output Devices Plasma Display Advantages/DisadvantagesPlasma Display Advantages: Long life (aproximately 40000-60000 hr of half life)Viewing angle: Has 1800 viewing angle.Plasmas are 4-5 times brillent than CRTs.Has very good contrast.There is no delay or artificial display as in LCDs.Colours are verry close to natural colors.Needs less space.

Plazma Display Disadvantages: There is no size less than 37 inch.Dead pixel formation in less quality products.Consumes more energy than LCDs. Dr. Ahmet Zafer enalp ME 52130Mechanical Engineering Department, GTU4.1. CAD Output Devices CRT-LCD-Plasma ComparisonCRTs are slightly better than LCDs because: cost less. displaying more colors. reacting faster and displaying moving images without smearing or artifacts. using emissive technology (generate their own light) boarder viewing angle.LCDs are better than CRTs because: smaller and lighter. consuming less energy. crisper image because each pixel is displayed by a specific set of LCD cells. reduced eyestrain and fatigue (no flicker) emitting much fewer low-frequency electromagnetic emissions than CRTs. pivoting in landscape or portrait mode. less prone to interference from other devices always perfect image geometry reflecting less glare than most CRTs.Plasma vs. LCDs Plasma will outperform LCD by providing lots of dark and better contrast,but LCD outperforms plasma in brightness and color. (larger screen sizes, burn-in) Dr. Ahmet Zafer enalp ME 52131Mechanical Engineering Department, GTU4.1. CAD Output Devices Digital Light Processing-DLP A semiconductor-based display, from Texas Instruments (1993) A panel of micromirrors are mounted on tiny hinges that enable them to tilt either toward or away from the light source in a DLP projection system (ON/OFF)-creating a light or dark pixel on the projection surface. The white light generated by the lamp in a DLP projection system passes through a color wheel as it travels to the surface of the DMD panel. DLP projection system 1-chip and 3-chip systems

Dr. Ahmet Zafer enalp ME 52132Mechanical Engineering Department, GTU4.1. CAD Output Devices DLP Advantages:Brighter: DLP projectors are among the brightest available because DLP technology brings more light from lamp to screen, resulting in more effective presentations-even when ambient light is difficult to control. Sharper: DLP projection's unique reflective technology comes closest to producing the exact mirror image of an incoming video or graphic signal, resulting in projection that's seamless at any resolution. More Reliable: Display systems using DLP technology are able to recreate their incoming source material with each projection, ensuring a full-impact projection experience that will not fade over time. DLP Disadvantages:In some 1-chip DLPs rainbow effect can be disturbing.They are not slim as LCDs and plasmas.Lamp life is limited (6000-8000 hr).Lamp replacement is expensive (200$-500$) .In 5 -6 years usage can cost 2 times the cost of plasma.Has less viewing angle compared to plasma.Digital Light Processing-DLP Dr. Ahmet Zafer enalp ME 52133Mechanical Engineering Department, GTU 4.1. CAD Output Devices Invented by KodakAn organic light emitting diode (OLED) is a light-emitting diode (LED) in which the emissive electroluminescent layer is a film of organic compounds which emit light in response to an electric current. This layer of organic semiconductor material is situated between two electrodes. Generally, at least one of these electrodes is transparent.OLEDs are used in television screens, computer monitors, small, portable system screens such as mobile phones and PDAs, watches, advertising, information and indication. OLEDs are also used in light sources for general space illumination and in large-area light-emitting elements. Due to their comparatively early stage of development, they typically emit less light per unit area than inorganic solid-state based LED point-light sources.An OLED display functions without a backlight. Thus, it can display deep black levels and can also be thinner and lighter than established liquid crystal displays. Similarly, in low ambient light conditions such as dark rooms, an OLED screen can achieve a higher contrast ratio than an LCD screen using either cold cathode fluorescent lamps or the more recently developed LED backlight.There are two main families of OLEDs: those based upon small molecules and those employing polymers. Adding mobile ions to an OLED creates a Light-emitting Electrochemical Cell or LEC, which has a slightly different mode of operation.OLED Dr. Ahmet Zafer enalp ME 52134Mechanical Engineering Department, GTU4.1. CAD Output Devices OLED displays can use either passive-matrix or active-matrix addressing schemes. Active-matrix OLEDs (AMOLED) require a thin-film transistor backplane to switch each individual pixel on or off, and can make higher resolution and larger size displays possible.Low energy consumtion, thin structure and light weight are the advantages.By time brithness may decrease.Also called as "Organic Electroluminescent Device" (OEL). Generally manufactured on glass but can also be applied to plastics or flexible materials. Universal Displays "FOLED is an example to the application of flexible materials.Has high viewing angles.OLED Dr. Ahmet Zafer enalp ME 52135Mechanical Engineering Department, GTU4.1. CAD Output Devices Schematic of a bilayer OLED

The emissive and conductive layers are made of special organic molecules that conduct electricity. The anode and cathode connect the OLED to the source of electicity.When electricity is applied to an OLED, the emissive layer becomes negatively charged and the conductive layer becomes positively charged. Electrostatic forces cause electrons to move from the positive conductive layer toward the negative emissive layer. This causes a change in the electrical levels and makes radiation that has a frequency in the range of visible light.OLED, as with all diodes, can only work if electricity flows through them in the correct direction. The Anode, connected to the emmisive layer must be at a higher electrical potential (more volts, more positive) than the cathode, connected to the conductive layer, for the OLED to work.

OLED

Cathode ()Emissive LayerEmission of radiationConductive LayerAnode (+)Dr. Ahmet Zafer enalp ME 52136Mechanical Engineering Department, GTU4.1. CAD Output Devices 4.1. CAD Output Devices AdvantagesOLEDs can make more different colors at different levels of brightness than LEDs. Unlike LCDs their colors do not change when viewed at an angle. They are also much cheaper to make. Most LCDs have to have an LED or Cold Cathode Fluorescent Light(CCFL) used as a backlight to be visible. LCDs also need to use filters to work properly. These filters block much of the light created by the LED/CCFL. Because of backlighting and filtering, OLEDs use far less power than LCDs for the amount of light made. OLEDs also react faster (0.01ms) to changes in electricity. They turn on and off much faster than LCDs (2-8 ms).Can be applied to flexible or various material types.

DisadvantagesLEDs will last longer than OLEDs. This is the biggest problem with OLEDs. Organic materials have a life limit of 14000 hours (daily 8 hours makes 5 years) The organic compounds that make up OLEDs are also more easily damaged by water.OLEDAdvantages/Disadvantages Dr. Ahmet Zafer enalp ME 52137Mechanical Engineering Department, GTUOLED

Dr. Ahmet Zafer enalp ME 52138Mechanical Engineering Department, GTU4.1. CAD Output Devices OLED

Dr. Ahmet Zafer enalp ME 52139Mechanical Engineering Department, GTU4.1. CAD Output Devices OLED Dr. Ahmet Zafer enalp ME 52140Mechanical Engineering Department, GTU4.1. CAD Output Devices

Key Technical TermsRefresh Rate of CRTs is refers to how often the screen is redrawn per second. With low refresh rates you can get screen flicker and eye strain. Aim for a rate of 75 Hz for a monitor up to 17 inches in size and 85 Hz for any larger monitor. LCDs are basically flicker free so refresh rates aren't important.

Dot Pitch is the distance in millimeters between phosphors of the same color. The smaller the dot pitch, the sharper the image. Opt for a dot pitch of 0.26 mm or smaller (usually quote horizontal dot pitch).

Brightness: LCD monitors have several backlights that provide illumination. Brightness is measured in units called nits. The majority of LCDs produce 150-200 nits which is fine for most users. The backlights in a LCD are good for 10 to 50 thousand hours of operation. Dr. Ahmet Zafer enalp ME 52141Mechanical Engineering Department, GTU4.1. CAD Output Devices Virtual Reality

Dr. Ahmet Zafer enalp ME 52142Mechanical Engineering Department, GTU4.1. CAD Output Devices Virtual RealityStereopsis : Stereopsis is from the Greek word for "solid sight", and thus refers to perception of three-dimensional shape from any source of depth information.

Personal usageUsage may be disturbing Narrow viewing angle (like a tunnel)Maximum resolution:1280x1024 Tracking is possibleDisplay types: CRT, LCD, OLED, LCOS, FLCOS

Dr. Ahmet Zafer enalp ME 52143Mechanical Engineering Department, GTU4.1. CAD Output Devices