Computer Peripherals

Plan

•Printers
•Scanners
•Keyboards
•Pointing Devices



Printers

•Four main types:

•Dot matrix

•Laser

•Ink jet

•Thermal dye transfer and thermal wax transfer

Impact vs. Non-Impact

•Impact printers physically transfer a dot or shape to the paper
•Of those in the preceding slide, only dot-matrix 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

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.

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)

Noise

•Dot matrix printers are notoriously noisy!
•This is a major disadvantage in many environments

Uses

•Primarily two:

•Any situation that requires multi-part forms

•Small printers, such as

•Calculators

•Adding machines

•Point-of-sale terminals

LASER PRINTER



How it works

•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.

Operation of a Laser Printer

•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.

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.

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

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.

Specifications

•ppm

•Pages per minute

•Typically 4-10 ppm

•dpi

•Dots per inch

•Typically 600-1200 dpi

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
•