Ink Jet Printers

Although inkjets were available in the 1980s, it was only in the 1990s that prices dropped enough to bring the technology to the high street. Canon claims to have invented what it terms "bubble jet" technology in 1977, when a researcher accidentally touched an ink-filled syringe with a hot soldering iron. The heat forced a drop of ink out of the needle and so began the development of a new printing method.

Ink jet printers have made rapid technological advances in recent years. The three color printer has been around for several years now and has succeeded in making colour inkjet printing an affordable option; but as the superior four color model became cheaper to produce, the swappable cartridge model was gradually phased out.

Traditionally, inkjets have had one massive attraction over laser printers; their ability to produce color, and that is what makes them so popular with home users. Since the late 1990s, when the price of color laser printers began to reach levels which made them viable for home users, this advantage has been less definitive. However, in that time the development of inkjets capable of photographic-quality output has done much to help them retain their advantage in the realm of color.

The down side is that although inkjets are generally cheaper to buy than lasers, they are more expensive to maintain. Cartridges need to be changed more frequently and the special coated paper required to produce high-quality output is very expensive. When it comes to comparing the cost per page, inkjets work out about ten times more expensive than laser printers.

Since the invention of the inkjet, color printing has become immensely popular. Research in inkjet technology is making continual advances, with each new product on the market showing improvements in performance, usability, and output quality. As the process of refinement continues, so the price of an inkjet printers continue to fall.

Inkjet printing, like laser printing, is a non-impact method. Ink is emitted from nozzles as they pass over a variety of possible media, and the operation of an ink jet printer is easy to visualise: liquid ink in various colors being squirted at the paper to build up an image. A print head scans the page in horizontal strips, using a motor assembly to move it from left to right and back, as another motor assembly rolls the paper in vertical steps. A strip 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.

On ordinary inkjets, the print head takes about half a second to print a strip across a page. Since A4 paper is about 8.5in wide and inkjets operate at a minimum of 300dpi, this means there are at least 2,475 dots across the page. The print head has, therefore, about 1/5000th of a second to respond as to whether or not a dot needs printing. In the future, fabrication advances will allow bigger 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 4ppm in colour, 12 to 14ppm in monochrome).

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

The nozzles used in inkjet printers are hair 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.