Transcript Number Systems

11. Computer Peripherals – Part III
Chapt. 10
ITEC 1011
Introduction to Information Technologies
Plan
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Printers
Scanners
Keyboards
Pointing Devices
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Printers
• Four main types:
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Dot matrix †
Laser
Ink jet
Thermal dye transfer and thermal wax transfer
†
Impact (the others are non-impact)
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Introduction to Information Technologies
Impact vs. Non-Impact
• Impact printers physically transfer a dot or
shape to the paper
• Of those in the preceding slide, only dotmatrix uses impact printing
• Non-impact printers spray or lay down the
image with impact
• Impact printers remain important because
they can print multi-part forms
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Introduction to Information Technologies
Printers
• Four main types:
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Dot matrix
Laser
Ink jet
Thermal dye transfer and thermal wax transfer
Introduction to Information Technologies
How it works
A 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 moves
forward, 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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Demo (well, sort of)
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Dot Matrix Print Head
One print wire
Print wires
(e.g., 12)
Front view
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Side view
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Dot Matrix Impact Printing
Paper
Print
wire
Platen
Ribbon
Side view
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Side view
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Front view
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 printed
simultaneously
• Specified as n-part forms (e.g., 4-part forms)
• mtbf
• Mean time between failure (e.g., 6000 hours)
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Introduction to Information Technologies
Noise
• Dot matrix printers are notoriously noisy!
• This is a major disadvantage in many
environments
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Uses
• Primarily two:
• Any situation that requires multi-part forms
• Small printers, such as
• Calculators
• Adding machines
• Point-of-sale terminals
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Dot Matrix Printer Example - 1
Specifications
• 800 cps
• 400 lpm
• 6-part forms (max)
FormsMaster 8000 by Printek, Inc.
http://www.printek.com
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Introduction to Information Technologies
Dot Matrix Printer Example - 2
Specifications
• Printhead wires: 9
• Printhead life: 200 million characters
• Print speed:
• near letter quality: 105 cps
• utility: 420 cps
• high speed draft: 550 cps
• Number of copies: 8
• MTBF: 8000 hours @ 25% duty cycle,
35% density
Pacemaker 3410 by OKI Data, Inc.
http://www.okidata.com
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Introduction to Information Technologies
Printers
• Four main types:
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Dot matrix
Laser
Ink jet
Thermal dye transfer and thermal wax transfer
Introduction to Information Technologies
How it works
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Four steps
1.
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.
Photosensitive
drum
Laser
Spinning
mirror
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Introduction to Information Technologies
Operation of a Laser Printer
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Four steps
1.
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.
Photosensitive
drum
Laser
Spinning
mirror
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Introduction to Information Technologies
Operation of a Laser Printer
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Four steps
1.
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.
Photosensitive
drum
Laser
Spinning
mirror
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Introduction to Information Technologies
Operation of a Laser Printer
2.
As the drum continues to rotate, the charged part of the drum passes
through a tank of black powder called toner. Toner sticks to the drum
wherever the charge is present. Thus, the pattern of toner on the drum
matches the image.
Toner
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Introduction to Information Technologies
Operation of a Laser Printer
3.
A sheet of paper is fed toward the drum. A charge wire coats the
paper with electrical charges. When the paper contacts the drum, it
picks up the toner from the drum
Charge
wire
Paper
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Introduction to Information Technologies
Operation of a Laser Printer
4.
As the paper rolls from the drum, it passes over a heat and pressure
area known as the fusing system. The fusing system melts the toner to
the paper. The printed page then exits the printer.
As the same time, the surface of the drum passes over another wire,
called a corona wire. This wire resets the charge on the drum, to ready
it for the next page.
Corona
wire
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Fusing
system
Specifications
• ppm
• Pages per minute
• Typically 4-10 ppm
• dpi
• Dots per inch
• Typically 600-1200 dpi
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Laser Printer Example
Laserjet 5000 Series from Hewlett Packard Co.
(http://www.hp.com)
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Introduction to Information Technologies
Printers
• Four main types:
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Dot matrix
Laser
Ink jet
Thermal dye transfer and thermal wax transfer
Introduction to Information Technologies
Background
• Inkjet technology was developed in the
1960s
• 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 works
Characters and graphics are 'painted‘ line by line to from a pattern of
dots as a print head scans horizontally across the paper. An ink-filled print
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 for several 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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Inkjet Printer Example
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Introduction to Information Technologies
Printers
• Four main types:
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Dot matrix
Laser
Ink jet
Thermal dye transfer and thermal wax transfer
Introduction to Information Technologies
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 photorealistic, 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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Introduction to Information Technologies
Dithering
Dithering is creating the illusion of new colours and shades by varying
the pattern of dots. Newspaper photographs, for example, are dithered. If
you look closely, you can see that different shades of grey are produced by
varying the patterns of black and white dots. There are no grey dots at all.
The more dither patterns that a device or program supports, the more shades
of grey it can represent. In printing, dithering is usually called halftoning, and
shades of grey are called halftones.
Note that dithering differs from grey scaling. In grey scaling, each
individual dot can have a different shade of grey.
black
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grey
light grey
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white
Plan
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Printers
Scanners
Keyboards
Pointing Devices
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Introduction to Information Technologies
How it works
A scanner works by digitizing an image. A scanning mechanism
consists 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).
ITEC 1011
Introduction to Information Technologies
Scanners
• Three main types
• Flatbed
• Sheet-fed
• Handheld
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Flatbed Scanner Example
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Sheet-fed Scanner Example
OfficeJet Series 700 from Hewlett Packard Co
(http://www.hp.com)
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Handheld Scanner Example
QuickScan GP Bar Code Scanner from PSC, Inc.
(http://www.pscnet.com)
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Introduction to Information Technologies
Plan
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Printers
Scanners
Keyboards
Pointing Devices
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Introduction to Information Technologies
Examples
Natural keyboard by Microsoft
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Internet keyboard by Microsoft
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Keyboard Connectors
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Introduction to Information Technologies
Plan
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Printers
Scanners
Keyboards
Pointing Devices
ITEC 1011
Introduction to Information Technologies
Examples
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Introduction to Information Technologies
Thank you
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ITEC 1011
Introduction to Information Technologies