Wednesday, June 6, 2007

How Inkjet Printers Work.


Although inkjet printers were first mass-produced in the 1980s, it was only in the 1990s that prices dropped low enough for that technology to be brought into the mass consumer market. Canon claims to have invented what it calls 'bubble jet' technology in 1977, when a researcher accidentally touched an ink-filled syringe with a hot soldering iron and the heat forced a drop of ink out of the needle. And so began the development of a new printing method.

Inkjet printers have made rapid technological advances in recent years. First, the three-color printer succeeded in making color inkjet printing an affordable option; but as the superior four-color models became cheaper to produce and sell, it wound up being the standard and users' choice.

Inkjet printing has two chief benefits over laser printers: lower printer cost and color-printing capabilities. But while inkjet printers are priced much less than laser printers, they are actually more expensive to use and maintain. Cartridges need to be changed more frequently and the special coated paper required to produce high-quality output is very expensive. At a cost per page level, inkjet printing costs about 10 times more than laser printing.

Inkjet printing, like laser printing, is a non-impact process. Ink is emitted from nozzles while they pass over media. The operation of an inkjet printer is easy to visualize: liquid ink in various colors being squirted onto paper and other media, like plastic film and canvas, to build an image. A print head scans the page in horizontal strips, using the printer's motor assembly to move it from left to right and back again, while the paper is rolled up in vertical steps, again by the printer. A strip (or row) of the image is printed, then the paper moves on, ready for the next strip. To speed things up, the print head doesn’t print just a single row of pixels in each pass, but a vertical row of pixels at a time.

For most inkjet printers, the print head takes about half a second to print the strip across a page. On a typical 8 1/2"-wide page, the print head operating at 300 dpi deposits at least 2,475 dots across the page. This translates into an average response time of about 1/5000th of a second. Quite a technological feat! In the future, however, advances will allow for larger print heads with more nozzles firing at faster frequencies, delivering native resolutions of up to 1200dpi and print speeds approaching those of current color laser printers (3 to 4 pages per minute in color, 12 to 14ppm in monochrome). In other words, declining costs for improving technology.

There are several types of inkjet printing. The most common is "drop on demand" (DOD), which means squirting small droplets of ink onto paper through tiny nozzles; like turning a water hose on and off 5,000 times a second. The amount of ink propelled onto the page is determined by the print driver software that dictates which nozzles shoot droplets, and when.

The nozzles used in inkjet printers are hairbreadth fine and on early models they became easily clogged. On modern inkjet printers this is rarely a problem, but changing cartridges can still be messy on some machines. Another problem with inkjet technology is a tendency for the ink to smudge immediately after printing, but this, too, has improved drastically during the past few years with the development of new ink compositions.

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