INK JET PRINTERS

6/9/2000

Ink Jet Printers: Printers that print by spraying droplets of ink onto a surface. Continuous stream inkjets are primarily used in industrial processes. A continual string of ink is either sprayed onto the surface to be printed or deflected away when the stream passes over areas not to be printed. Ink jet printers used with personal computers generally create discrete ink droplets (Drop On Demand) as they pass across a page. The droplets are created by squeezing an ink tube or by heating the ink by applying a pulse of current to microscopic heaters embedded in the print head. In most modern printers, the print head is built into the ink cartridge and may contain 50 or more tiny ink nozzles.

Early Ink Jet inks were prone to dry slowly and to smear or produce fuzzy print if special papers were not used. Modern inks dry more quickly and some dry water fast. Special papers are only required for artwork that may lay on heavy coats of ink that might soak and warp ordinary papers. The quality of ink jet printing is generally excellent although the cost per page is rather high compared to laser printing. Color ranges are limited since only three colors are available and color intensity is difficult to modulate. This is frequently exacerbated by the choice of Red, Yellow, Blue rather than Cyan, Magenta, Yellow as printing colors. RYB yields more vibrant colors and is generally preferred for presentation graphics, but CMY produces substantially better color fidelity for photographs. Dithering can be used to create a broader color/intensity range than that from color mixing alone.

The jet nozzles are prone to plug with dry ink. All Ink Jet printers have a provision to seal the print nozzles from air when not in use and contain a mechanism for purging the printhead of dried/drying ink before and after printing. Many inkjets purge the heads during printing, e.g. during page feeds, as well as before and after the printout.

Early ink jets operated, or could operate, in character mode or could emulate high resolution dot matrix printer graphics. More recent models often operate as page printers downloading a description of part or all of a page specified in a format such as PCL then printing it. Ink Jet quality is generally very good except when reproducing photographs. The quality of photograph reproduction is highly variable and often poor or peculiar unless extensive tweaking is done.. Printing is often slow or worse -- more comperable to dot matrix than to laser printing.

ftp://ftp.unina.it/pub/electronics/repairfaq/REPAIR.250a/F_Printer.html

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