Ink jet

Inkjet printers are a type of computer printer that operates by propelling tiny droplets of liquid ink onto paper. They are the most common type of computer printer for the general consumer due to their low cost, high quality of output, capability of printing in vivid color, and ease of use.

There are several types of Inkjet printing, which can be classified into the method used to deposit the ink:

Most consumer ink jet printers work by having a print cartridge with a series of tiny electrically-heated chambers constructed by photolithography. To produce an image, the printer runs a pulse of current through the heating elements. A steam explosion in the chamber forms a bubble, which propels a droplet of ink onto the paper (hence Canon's tradename for its inkjets, Bubblejet). The ink's surface tension pulls another charge of ink into the chamber through a narrow channel attached to an ink reservoir.

All Epson printers and most commercial and industrial ink jet printers use a piezoelectric material in an ink-filled chamber behind each nozzle instead of a heating element. When a voltage is applied, the crystal changes shape or size, this generates a pressure pulse in the fluid forcing a droplet of ink from the nozzle. This is essentially the same mechanism as the thermal inkjet but generates the pressure pulse using a different physical principle. Piezoelectric ink jet allows a wider variety of inks than thermal or continuous ink jet but is more expensive.

The continuous ink jet method is used commercially for marking and coding of products and packages. The first patent on the idea is from 1867, by William Thomson. The first commercial model was introduced in 1951 by Siemens. In continuous ink jet technology, a high-pressure pump directs liquid ink from a reservoir through a microscopic nozzle, creating a continuous stream of ink droplets. A piezoelectric crystal causes the stream of liquid to break into droplets at regular intervals. The ink droplets are subjected to an electrostatic field created by a charging electrode as they form. The field is varied according to the degree of drop deflection desired. This results in a controlled, variable electrostatic charge on each droplet. Charged droplets are separated by one or more uncharged “guard droplets” to minimize electrostatic repulsion between neighboring droplets.