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Inkjet Printers

The inkjet printers were available since 1980s but have developed in a significant way since 1990s. They are affordable and produce quality prints.

Hair fine nozzles are used to emit ink on to the print media to build the image. The droplets of ink are produced in different ways. Canon uses the bubble jet technology where tiny resistors create heat. This heat causes the ink to vaporize to a bubble, which expands to form a droplet and gets ejected from the print head. This method is less expensive, hence more commonly used by other manufacturers too. Epson uses the piezo-electric inkjet technology, in which a piezo-electric crystal and electric charge are used to apply the ink. Piezo crystals vibrate when charged with electricity resulting in pulling and then pushing the ink within the nozzle. The size of the ink droplets is varied by varying the strength of the electric charges applied to the piezo crystals.

The driver software of the printer determines the amount of ink to be propelled through these nozzles and also determines when and which nozzle is to be turned on and off. The printer driver acts as an interface software between PC and the printer. It is also the access point that controls the media stock and print quality.

The quality of the prints - resolution - is expressed as dots per inch ( dpi ). Higher the dpi, more the resolution and more the amount of detail in the image, and consequently a larger file size. The other terms commonly used for expressing resolution are

•  ppi-pixels per inch- one pixel is one picture element that represents a single tone of a single point

•  lpi-lines per inch

The advantages of inkjet printers are:

•  cheaper

•  Their advanced inks provide precise detail, gloss uniformity, and consistency in high quality photos

•  4-ink to 9-ink printing is possible helping to achieve wider range of colors, more realistic flesh tones and smoother color transitions

•  Use of individual ink cartridges allows flexibility in replacing only the exhausted ones.

The associated disadvantages are:

•  not many paper handling options

•  higher cost per page, about ten times more expensive than laser printers

•  Ink cartridges are costly and don't last for more than 100 to 200 pages.

Technical Features to be checked prior to buying an inkjet printer:

Resolution - Inkjet printers come with a maximum resolution of 2400 x 1200 dpi, some high end printers come with 4800 x 1200 dpi. Resolution of images printed increases with the quality of paper used.

Ink and paper - Much of the print head is incorporated into the cartridge; replacing the head every time the cartridge is replaced increases the printer life. Most manufacturers produce inkjet printers compatible with a specific type of cartridge causing the price of cartridges to sky rocket. Wrong ink cartridges used can degrade the output and spoil the printers.

Image quality is affected by the quality of the paper used. The brightness of the image is determined by the roughness of the surface of the paper. Smoother paper makes the image printed on it look brighter. Absorption of ink usually by low quality paper produces images that are not sharp. High quality inkjet paper is coated with waxy film that keeps the ink on the surface of the paper, thus giving very high quality images.

Speed - The speed (in pages per minute) mentioned in the specifications of a printer is normally the rate for printing simplest text documents at the lowest resolution. So in reality the mentioned speed is about three times the actual speed that can be actually achieved. High end inkjets have a speed of 20ppm for monochrome and 12ppm for color. Mid-range inkjets have speeds ranging from 8ppm to 16ppm for black and white and 1.2ppm to 12ppm in color.

 



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