Printers Chapter 19

Impact Printers Leave an image on paper by physically striking an ink ribbon against the surface of the paper Daisy wheel and dot matrix printers are 2 examples Daisy wheel – single font and only one size

Dot-matrix printers Use an array of pins to strike an inked printer ribbon Downside – need for ongoing maintenance Must keep the platen and print head clean with denatured alcohol Picture (p.481)

Dot-matrix problems White bars on text Dirty or damaged print head Chopped text Print head needs to be adjusted Peppered look Platen is dirty Faded image Move print head closer to the platen Light to dark Platen is out of adjustment

Inkjet Printers Eject ink through tiny tubes. The ink is ejected through tubes by heating the ink with tiny resistors or plates that are at one end of the tube. The resistors literally boil the ink, creating a tiny air bubble that ejects a droplet of ink onto the paper, thus creating portions of the image. (page 483)

Laser printers Parts – most parts are put into the toner cartridge so that small little parts don’t need to be replaced at a regular basis. Photosensitive drum An aluminum cylinder coated with particles of photosensitive compounds Usually contained in the toner cartridge, can be wiped clean if dirty, but if it is scratched every page show the scratch

Laser printers Erase lamp – exposes the entire surface of the photosensitive drum to light, making the photosensitive coating conductive Primary corona wire – located close to the drum, charges the drum Laser – acts as the writing mechanism of the printer, any part of the drum that is struck by the laser is conductive

Laser printers Toner – fine powder made up of plastic particles bonded to iron particles, have charges of between –200 to –500 volts Transfer corona – applies a positive charge to the paper, which draws the negatively charged toner particles to the paper Fuser – 2 rollers that attach the toner to the paper to make the image permanent

The printing process Cleaning(cloning) Conditioning(Connie) Writing(will) Developing(double) Transferring(the) Fusing(fun)

The printing process Cleaning The printing process begins with both physically and electronically cleaning the drum Conditioning (charging) To make the drum more receptive to new images, the primary corona applies a uniform negative charge between –600 to –1000 volts

The printing process Writing The laser writes a positive image on the surface of the drum. For each point contacted on the drum the voltage is reduced. The difference between voltage on the drum represents the image to be printed

The printing process Developing Every particle on the drum hit by the laser release most of its negative charge into the drum. Those particles with a lesser negative charge are relatively positive to the toner particles and will attract them. The toner is attracted to these spots.

The printing process Transferring The transfer corona positively charges the paper, and then the negatively charged toner particles leap from the drum to the paper. Fusing The toner is melted to the paper by the rollers

Printers Laser printers have two power supplies System board – printers have RAM which can be replaced and updated, but make sure you contact your manufacturer to make sure you have the right type Ozone filters – the coronas generate ozone, so the printer has a filter that should be replaced periodically

Printers Read section on Electronics pp Printer languages ASCII (standard printing language) POSTSCRIPT PCL (Hewlett Packard)

Troubleshooting / Disposal It is important to know how to fix certain problems with laser printers Read pp (know this) on common problems with laser printers Don’t throw away toner cartridges - certain companies will pay for them Consult local laws as far as disposal is concerned

Parallel communication Printers work with parallel communication much faster than serial (8 bits at a time rather than 1) Speed of normal parallel ports is 150 KBps Standard for parallel - IEEE 1284

Parallel modes Centronics mode - standard mode Nibble mode - bi-directional (4 bits each way), limited to 50 KBps Byte mode - bi-directional (8 bits each way), limited to 150 KBps

Parallel modes Enhanced Parallel Port (EPP) - high speed communications (500 KBps) software on both sides needs to be compatible and agree to mode Extended Capability Mode (ECP) - good for multi-purpose devices when using fax/printer/scanner devices

Connections and cabling Although there is no true standard, “the standard parallel cable” usually refers to a printer cable with male DB25 on one end and a 36-pin Centronics connector on the other Keep under 6 feet Now printers use USB