From ECDL.web

An Epson inkjet printer

An inkjet printer is a type of computer printer that creates a digital image by propelling variable-sized droplets of ink onto paper. Inkjet printers are the most commonly used type of printer and range from small inexpensive consumer models to very large professional machines, that can cost up to thousands of dollars.

The concept of inkjet printing originated in the 19th century, and the technology was first developed in the early 1950s. Starting in the late 1970s inkjet printers that could reproduce digital images generated by computers were developed, mainly by Epson, Hewlett-Packard and Canon. In the worldwide consumer market, four manufacturers account for the majority of inkjet printer sales: Canon, HP, Epson, and Lexmark, a 1991 spin-off from IBM.

[edit] Technologies

There are two main technologies in use in contemporary inkjet printers: continuous (CIJ) and Drop-on-Demand (DOD). Drop-on-demand is further divided into thermal and piezoelectric DOD.

• The continuous inkjet method is used commercially for marking and coding of products and packages. The idea was first patented in 1867, by Lord Kelvin and the first commercial devices (medical strip chart recorders) were introduced in 1951 by Siemens. In continuous inkjet technology, a high-pressure pump directs liquid ink from a reservoir through a gunbody and a microscopic nozzle, creating a continuous stream of ink droplets. The ink droplets are subjected to an electrostatic field created by a charging electrode as they form. The charged droplets pass through an electrostatic field and are directed (deflected) by electrostatic deflection plates to print on the receptor material (substrate), or allowed to continue on undeflected to a collection gutter for re-use. The more highly charged droplets are deflected to a greater degree. Only a small fraction of the droplets is used to print, the majority being recycled.
• Thermal DOD inkjet: most consumer inkjet printers, from companies including Canon, Hewlett-Packard, and Lexmark (but not Epson), use print cartridges with a series of tiny chambers each containing a heater. To eject a droplet from each chamber, a pulse of current is passed through the heating element causing a rapid vaporisation of the ink in the chamber to form a bubble, which causes a large pressure increase, propelling a droplet of ink onto the paper (hence Canon's tradename of Bubble Jet).
• Piezoelectric DOD inkjet: most commercial and industrial inkjet printers and some consumer printers (those produced by Epson) use a piezoelectric material in an ink-filled chamber behind each nozzle instead of a heating element. When a voltage is applied, the piezoelectric material changes shape, which generates a pressure pulse in the fluid forcing a droplet of ink from the nozzle. Piezo inkjet technology is often used on production lines to mark products - for instance the use-before date is often applied to products with this technique; in this application the head is stationary and the product moves past.

[edit] Inkjet head design

Inkjet heads: Disposable head (left) and Fixed head (right) with ink cartridge (middle)

There are two main design philosophies in inkjet head design: fixed-head and disposable head. Each has its own strengths and weaknesses.

• The fixed-head philosophy provides an inbuilt print head that is designed to last for the life of the printer. The idea is that because the head need not be replaced every time the ink runs out, consumable costs can be made lower and the head itself can be more precise than a cheap disposable one, typically requiring no calibration. On the other hand, if a fixed head is damaged, obtaining a replacement head can become expensive.
• The disposable head philosophy uses a print head which is supplied as a part of a replaceable ink cartridge. Every time a cartridge is exhausted, the entire cartridge and print head are replaced with a new one. This adds to the cost of consumables and makes it more difficult to manufacture a high-precision head at a reasonable cost, but also means that a damaged print head is only a minor problem: the user can simply buy a new cartridge.

[edit] Inkjet advantages

Compared to earlier consumer-oriented color printers, inkjets have a number of advantages. They are quieter in operation than impact dot matrix or daisy wheel printers. They can print finer, smoother details through higher printhead resolution, and many consumer inkjets with photographic-quality printing are widely available.

In comparison to more expensive technologies like thermal and laser printers, inkjets have the advantage of practically no warm up time and lower cost per page (except when compared to laser printers).

[edit] Inkjet disadvantages

• The ink is often very expensive.
• Many "intelligent" ink cartridges contain a microchip that communicates the estimated ink level to the printer; this may cause the printer to display an error message, or incorrectly inform the user that the ink cartridge is empty.
• The lifetime of inkjet prints produced by inkjets using aqueous inks is limited; they will eventually fade and the color balance may change. On the other hand, prints produced from solvent-based inkjets may last several years before fading.
• Because the ink used in most consumer inkjets is water-soluble, care must be taken with inkjet-printed documents to avoid even the smallest drop of water, which can cause severe "blurring" or "running." Similarly, water-based highlighter markers can blur inkjet-printed documents.
• The very narrow inkjet nozzles are prone to clogging. The ink consumed cleaning them - either during cleaning invoked by the user, or in many cases, performed automatically by the printer on a routine schedule - can account for a significant proportion of the ink used in the machine.

[edit] Overall expense

Inkjet printers cost less than laser printers, but their costlier ink cartridges means that the ink cost per page is higher. As a result, inkjet printers tend to be more economical in low-volume printing applications, while laser printers tend to be more economical for medium- to high-volume applications.

A common business model for inkjet printers involves selling the actual printer at or below production cost, while dramatically marking up the price of the (proprietary) ink cartridges.

[edit] Professional inkjet printers

Besides the well known small inkjet printers for home and office, there is a market for professional inkjet printers, some being for "page-width" format printing, but most being for wide format printing. Page-width format means that the print width ranges from about 8.5" to 37" (about 20 cm to 100 cm). "Wide format" means that these are printers ranging in print width from 24" up to 15' (about 75 cm to 5 m).

Another specialty application for inkjets is producing prepress color proofs for printing jobs created digitally. Such printers are designed to give accurate color rendition of how the final image will look (a "proof") when the job is finally produced on a large volume press such as a four-colour offset lithography press. A well-known example of an inkjet designed for proof work is an Iris printer, and outputs from them are commonly "iris proofs" or just "irises".

In terms of units, the major supplier is Hewlett-Packard, which supply over 90 percent of the market for printers for printing technical drawings with their DesignJet series. A few other suppliers of low volume wide format printers are Epson, Kodak, Agfa and Canon.