Printers

Description about Printers

A printer is an external hardware output device that takes the electronic data stored on a computer or other device and generates a hard copy of it or print something on a paper. For example, if you created a report on your computer you could print several copies to hand out at a staff meeting or to print a very valuable document in a less amount of time. Printers are one of the most popular computer peripherals and are commonly used to print text and photos. The picture to the right is an example of an inkjet computer printer. We Can divide printers as follows….

The four printer qualities of most interest to most users are: Color: Color is important for users who need to print pages for presentations or maps and other pages where color is part of the information. Color printers can also be set to print only in black-and-white. Color printers are more expensive to operate since they use two ink cartridges (one color and one black ink) that need to be replaced after a certain number of pages. Users who don't have a specific need for color and who print a lot of pages will find a black-and-white printer cheaper to operate. Resolution: Printer resolution (the sharpness of text and images on paper) is usually measured in dots per inch (dpi). Most inexpensive printers provide sufficient resolution for most purposes at 600 dpi. Speed: If you do much printing, the speed of the printer becomes important. Inexpensive printers print only about 3 to 6 sheets per minute. Color printing is slower. More expensive printers are much faster. Memory: Most printers come with a small amount of memory (for example, one megabyte) that can be expanded by the user. Having more than the minimum amount of memory is helpful and faster when printing out pages with large images or tables with lines around them (which the printer treats as a large image). We can divide printer into 2 main categories there are Impact – Daisy wheel printers and Dot Metrix printers Non-impact – Inkjet, Thermal and Laser

Daisy Wheel Printers A type of printer that produces letter-quality type. A daisy-wheel printer works on the same principle as a ball-head typewriter. The daisy wheel is a disk made of plastic or metal on which characters stand out in relief along the outer edge. To print a character, the printer rotates the disk until the desired letter is facing the paper. Then a hammer strikes the disk, forcing the character to hit an ink ribbon, leaving an impression of the character on the paper. You can change the daisy wheel to print different fonts. Daisy-wheel printers cannot print graphics, and in general they are noisy and slow, printing from 10 to about 75 characters per second. As the price of laser and ink-jet printers has declined, and the quality of dot-matrix printers has improved, daisy-wheel printers have become obsolete. The daisy wheel print head is mounted to a carriage assembly that is very similar to the assembly used with dot matrix printers. Daisy are slow and limited in the characters printed to those on the wheel. Despite these limitations, they are still used for their ability to print letter quality documents and make carbon copies.

Dot Matrix PrinterThe term of dot matrix refers to form of image using number of dots. In dot matrix image quality will calculate by DPI.

Dot Matrix Printers are invented by Centronics in 1970. These are strike to place 100 to 1000 little dots to form a text or image. It have an ability to print 30 to 550 characters per second (cps), Nowadays these are rarely use because of low quality and can still found on Banks, Institutes, some of supermarkets etc. but still their printout cost is less and more noisy.

How it works? It produced printed images when tiny pins on a print head strike an inked ribbon. When ribbon pressed against the paper, it creates dots that they form characters

and graphics. Rectangular print head contains 7 to 24 vertical column pins. Pins are activating by when the print head moves across the papers and it will form

a dotted image. These can produce carbon copies along with the originals.

Dot Matrix Output

Pin Types

Ink-jet Printer It’s a non-impact printer producing a high quality print. A standard inkjet printer has a resolution of 300dpi. Newer models have further improved dpi. Inkjet printers were introduced in the later half of 1980s and are very popular owing to their extra-ordinary performances. How Inkjet printer works?

1.Print head having four ink cartridges moves. 2.Software instructs where to apply to dots of ink, which color and what quantity to use 3.Electrical pulses are sent to the resisters behind each nozzle. 4.Vapor bubbles of ink are formed by resistors and the ink is forced to the paper through nozzles. 5.A matrix of dots forms characters and pictures. Advantages and Dis-advantages Of Ink-jet Advantages-- 1.High resolution output. 2.Energy Efficient. 3.Many options to select. Dis-advantages-- 1.Expensive. 2.Special paper required for higher resolution output. 3.time consuming in case of graphics printing.

Laser printers

A type of printer that utilizes a laser beam to produce an image on a drum. The light of the laser alters the electrical charge on the drum wherever it hits. The drum is then rolled through a reservoir of toner, which is picked up by the charged portions of the drum. Finally, the toner is transferred to the paper through a combination of heat and pressure. This is also the way copy machines workFuture of Printers

Inkless printing is one of on testing level technology and Xerox was developing the following technology for inkless prints. This technology includes a reusable paper and printer can erase and print the same paper repeatedly.

Future of printing technology may be far differ from the available technology. Because of the day by day printers are up to date and people are looking for more advanced printing methods like 3D printing.

Display Devices

Display types(extended)

A display device is an output device for presentation of information for visual reception. The display systems are often referred to as Video monitor or Video Display Unit(VDU).Display devices are designed to project , show , exhibit display softcopy information.

Display

Analogue Digital Other

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, as illustrated below. The electron gun generates an arrow 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. (In the illustration, only one set of coils is shown for simplicity.) The intensity of the beam can be varied. The electron beam produces a tiny, bright visible spot when it strikes the phosphor-coated screen.

Printers Cathode Ray Tube Display

The illustration shows only one electron gun. This is typical of a monochrome, or single-color, CRT. However, 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.

Features of CRT

The features of a CRT can be split into 4 main sections: 1. Electron gun. 2. Deflection system 3. Fluorescent screen 4. Glass Tube & Base

Features of CRTs 1.Electron Gun The role of this section is to produce electrons at a high, fixed, velocity. This is done through a process known as thermionic emission.

2.Deflection System It consists of Two PERPENDICULAR sets of Electric/Magnetic fields. This allows control over both horizontal and vertical axes. By controlling the Voltage applied to the fields, it is possible to vary the deflection through Electrostatic force/Motor effect.

3.Fluorescent Screen The role of this part is to display where the electrons are hitting the CRT. It is a screen coated with a material that emits light when struck by electrons. Zinc sulfide or Phosphorus are two commonly used materials.

4.Glass Tube & Base The whole assembly is protected in a conical highly evacuated glass tube. Glass tube is a long, clear tube. The CRT uses an evacuated glass envelope which is large, deep, fairly heavy, and relatively fragile. Inside the tube's neck is an assembly that produces a stream of electrons. Electrical connections to these internal components are made through metal pins that extend out through the back of the tube's neck, usually in a circular formation. Vacuum is created inside the glass tube 0.001Pa to 133 nPa.

How CRT work ?

A CRT monitor contains millions of tiny red, green, and blue phosphor dots that glow when struck by an electron beam that travels across the screen to create a visible image. In a CRT monitor tube, the cathode is a heated filament. The heated filament is in a vacuum created inside a glass tube. The electrons are negative and the screen gives a positive charge so the screen glows.

Liquid Crystal DisplayThe heart of all liquid crystal displays (LCDs) is a liquid crystal itself. A liquid crystal is a substance that flows like a liquid, but its molecules orient themselves in the manner of a crystal.

There are three basic types of ordering in liquid crystals which are termed nematic, cholesteric and sematic.

In the cholesteric crystals molecules form planes. A plane has nematic-like structure, but with each plane molecules change their direction. As a result the molecules display a helical twist through the material.

When a nematic liquid crystal material comes into contact with a solid surface molecules become aligned either perpendicular to the surface (homeotropic ordering) or parallel to the surface (homogeneous ordering). These two forms can be produced by suitable treatment of the surface.

The most important electrical characteristic of liquid crystal materials is that the direction of the molecules can be controlled by the electric field. Usually the molecules tend to be orientated along the electric field.

Transmission LCD displays do not have the reflector and must be provided with rear illumination. They operate in a very similar fashion to the reflective displays. Colour displays are possible by incorporating color filters. An LCD cell consumes only microwatts of power over a thousand times less than LED displays. LCDs can operate on voltages as low as 2 to 3 V and are easily driven by MOS IC drivers. LCDs also have their disadvantages. They cannot be seen in the dark, have a limited viewing angle and a limited temperature range.

The left column electrode is at the same potential level as the row electrode. To the right column electrode (red), a different voltage is applied. In this way, an electric field is generated in the right pixel oriented perpendicular to the glass surfaces. On the picture one can see that the rubbing direction of the alignment layers (green) on top and bottom substrate are chosen perpendicular to each other. Due to this choice, the director in the left pixel makes a homogeneous turn of 90°from bottom to top. Therefore, this type of LCD is called a 'Twisted Nematic LCD' (TN-LCD). If a voltage is applied to the electrode, the director reorients to become perpendicular to the surfaces (right pixel).

LED Display • An LED display is a flat panel display, which uses light-emitting diodes as a video display. • A cluster of red, green, and blue diodes is driven together to form a full-color pixel, usually square in shape. • Matrix of diodes is arranged to form pixels and picture definition is stored in refresh buffer. • Information is read from refresh buffer and converted into voltage levels that are provided to diodes, thus producing light patterns in the display. • Three techniques are used in making LED displays Which are ,

1. Edge-Led: -It is done around the rim by using a special diffusion panel to spread the light evenly behind the screen. 2. Full-array Led: - The are arranged behind the screen and their brightness are not controlled individually. 3. Dynamic ‘Local Dimming’ Led: - This type of back-lightning allows dimming of specific areas of darkness on the screen.

Vacuum Fluorescent displaysIf you know how an old-style cathode-ray tube (CRT) television works, understanding a VFD is simple. In a TV like this, there's a hot piece of metal called the cathode whose job is to fire electrons down a glass tube to the screen at the front where the picture is formed. The screen is coated with chemicals called phosphors that glow (or fluoresce) when the electrons crash into them. By steering and focusing the electron beam using magnets and a metal grid with holes in it, we can paint an ever-changing pattern of glowing dots on the screen—and that makes the moving picture you see when you watch TV.

How it works in theory…

A VFD works in similar way to this using three electrical terminals(or electrodes)sealed inside a large glass bulb from which the air has been removed

The cathode is negatively charged (−ve) and each anode is positively charged (+ve), so electrons (yellow arrowed line) tend to flow naturally from one to the other. When electrons strike the phosphor coated anode, it glows with green light. We can stop this happening by making the grid negatively charged, which repels electrons away from the anode. Changing the grid voltage is thus a simple way of switching a segment of the display on or off. It's also a way of controlling the brightness of the display: making the grid more positively charged accelerates the electrons so they rush past and hit the anode with more energy, giving off more light. The higher the positive grid voltage, the brighter the display. (Brightness controls on VFDs are effectively just voltage controls on the grid.)

1. There's a heated filament (the negatively charged cathode) made from tungsten metal whose job is to produce electrons. It's the red bar in our diagram.

2. Each segment of the display (which is a positively charged anode) is coated with phosphor, like the screen of a TV. These phosphor-coated segments glow with light (often a ghostly green color) when electrons hit them.

3. In between the cathode and the anode there's a thin mesh of metal called the grid that can be switched on or off, controlling the flow of electrons from the cathode to the anode

Plasma Display PanelsThe pixel cells in a plasma TV have things in common with both neon lamps and CFLs. Like a neon lamp, each cell is filled with tiny amounts of neon or xenon gas. Like a CFL, each cell is coated inside with phosphor chemicals. In a CFL, the phosphor is the chalky white coating on the inside of the glass tube and it works like a filter. When electricity flows into the tube, gas atoms crash about inside it and generate invisible ultraviolet light. The white phosphor coating turns this invisible light into visible white light. In a plasma TV, the cells are a bit like tiny CFLs only coated with phosphors that are red, blue, or green. Their job is to take the invisible ultraviolet light produced by the neon or xenon gas in the cell and turn it into red, blue, or green light we can actually see

1. Much like the picture in an LCD screen, the picture made by a plasma TV is made from an array (grid) of red, green and blue pixels

(microscopic dots or squares).

2. Each pixel can be switched on or off individually by a grid of horizontally and vertically mounted electrodes (shown as yellow

lines).

3. Suppose we want to activate one of the red pixels (shown hugely magnified in the light gray pullout circle on the right).

4. The two electrodes leading to the pixel cell put a high voltage across it, causing it to ionize and emit ultraviolet light (shown here

as a turquoise cross, though it would be invisible in the TV itself).

5. The ultraviolet light shines through the red phosphor coating on the inside of the pixel cell.

6. The phosphor coating converts the invisible ultraviolet into visible red light, making the pixel light up as a single red square

Electroluminescent DisplayA technology used to produce a very thin display screen, called a flat-panel display, used in some portable computers. An ELD works by sandwiching a thin film of phosphorescent substance between two plates. One plate is coated with vertical wires and the other with horizontal wires, forming a grid. When an electrical current is passed through a horizontal and vertical wire, the phosphorescent film at the intersection glows, creating a point of light, or pixel. Other types of flat-panel displays include LCD displays and gas-plasma displays, both of which are more common than ELDs.

EL displays contain a powdered or thin film phosphor layer sandwiched between x- and y-axis panels. When an x-y coordinate is charged, the phosphor in that vicinity emits visible light.

EL displays are used in rugged, heavy-duty applications