computer peripherals iii

7/29/2019 Computer Peripherals III

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ITEC 1011 Introduction to Information Technologies

11. Computer PeripheralsPart III

Chapt. 10


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Plan

Printers Scanners

Keyboards

Pointing Devices


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Printers

Four main types: Dot matrix

Laser

Ink jet Thermal dye transfer and thermal wax transfer

Impact (the others are non-impact)


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Printers


Laser



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How it worksA print-head moves back-and-forth in front of forms

(paper) on which characters or graphic images are transferred.The print-head contains numerous wires, typically from 9 to

24. Each wire is part of a solenoid-like unit. A pulse applied

to the solenoid creates a magnetic field which forces the wire

to move briefly forward then backward. As the wire movesforward, it presses against a print ribbon containing ink. The

impact transfers an ink dot to the paper. The paper is

supported from behind by a platen.


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Dot Matrix Print Head

Front view Side view

Print wires

(e.g., 12)

One print wire


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Dot Matrix Impact Printing

Print

wire

Ribbon

Paper

Platen

Side view Side view Front view


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Specifications

cps characters per second

Varies by quality of print (e.g., draft vs. final)

lpm

lines per minute (related to cps)

Forms

Maximum number of layers of paper that can by printedsimultaneously

Specified as n-part forms (e.g., 4-part forms)

mtbf

Mean time between failure (e.g., 6000 hours)


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Printers


Laser



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How it works

Four steps1. A laser is fired in correspondence to the dots to be printed. A spinning

mirror causes the dots to be fanned out across the drum. The drum

rotates to the next line, usually 1000th or 1600th of an inch.

The drum is photosensitive. As a result of the laser light, the drum

becomes electrically charged wherever a dot is to be printed.

Laser

Spinning

mirror

Photosensitive

drum


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Specifications

ppm Pages per minute

Typically 4-10 ppm

dpi Dots per inch

Typically 600-1200 dpi


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Printers


Laser



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Background

Inkjet technology was developed in the1960s

First commercialized by IBM in 1976 with

the 6640 printer Cannon and Hewlett Packard developed

similar technology

Also called bubble jet


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How it worksCharacters and graphics are 'painted line by line to from a pattern of

dots as a print head scans horizontally across the paper. An ink-filledprint cartridge is attached to the inkjet's print head. The print head

contains 50 or more ink-filled chambers, each attached to a nozzle. An

electrical pulse flows through thin resistors at the bottom of each chamber.

When current flows through a resistor, the resistor heats a thin layer of ink

at the bottom of the chamber to more than 900 degrees Fahrenheit forseveral millionths of a second . The ink boils and forms a bubble of

vapour. As the vapour bubble expands, it pushes ink through the nozzle to

form a droplet at the tip of the nozzle. The droplet sprays onto the paper.

The volume of the ejected ink is about one millionth that of a drop of

water from an eye-dropper. A typical character is formed by an array of

these drops 20 across and 20 high. As the resistor cools, the bubble

collapses. The resulting suction pulls fresh ink from the attached reservoir

into the firing chamber.


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Printers


Laser



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How it works

Thermal dye transfer printers, also called dye sublimation printers,heat ribbons containing dye and then diffuse the dyes onto specially

coated paper or transparencies. These printers are the most expensive and

slowest, but they produce continuous-tone images that mimic actual

photographs. Note that you need special paper, which is quite expensive.

A new breed of thermal dye transfer printers, called snapshot printers,

produce small photographic snapshots and are much less expensive than

their full-size cousins.

Thermal wax transfer printers use wax-based inks that are melted and

then laid down on regular paper or transparencies. Unlike thermal dye

transfer printers, these printers print images as dots, which means that

images must be dithered first. As a result images are not quite photo-

realistic, although they are very good. The big advantages of these

printers over thermal dye transfer printers are that they don't require

special paper and they are faster.


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Plan

Printers Scanners

Keyboards

Pointing Devices


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How it works

A scanner works by digitizing an image. A scanning mechanismconsists of a light source and a row of light sensors. As light is reflected

from individual points on the page, it is received by the light sensors and

translated to digital signals that correspond to the brightness of each point.

Colour filters can be used to produce colour images, either by providing

multiple sensors or by scanning the image three times with a separate

colour filter for each pass. The resolution of scanners is similar to that of

printers, approximately 300-600 dpi (dots per inch).


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Scanners

Three main types Flatbed

Sheet-fed

Handheld


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Plan

Printers Scanners

Keyboards

Pointing Devices


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Examples

Natural keyboard by Microsoft Internet keyboard by Microsoft


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Keyboard Connectors


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Plan

Printers Scanners

Keyboards

Pointing Devices


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Examples


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Thank you

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