Inkjets are often used for good-quality color output and domestic use. They are often combined with other devices (fax or scanner for example).
Operation and Components
An inkjet print head is composed of a series of very small holes or nozzles, behind which can be found a reservoir of ink.
Under normal conditions, the ink cannot flow though the nozzles because the gap is very small, and the ink reservoir is kept at a pressure slightly below that of the ambient pressure.
Characters are formed when a small controlled amount of ink is forced through voltage-charged deflection plates and onto the paper. By synchronizing this action with the movement of the print head across the paper, text and images can be built up in a way similar to that of a dot matrix printer.
Thermal-Shock Print Heads
Hewlett Packard uses thermal print heads, for example on their DeskJet printers. Each ink nozzle has a heating element built around it and when the ink behind the nozzles is heated, it expands and is forced through the holes in a controlled manner, spraying a mark on the paper.
Piezoelectric (or electrostatic) Print Heads
Epson uses piezoelectric print heads, for example in their Stylus printers. A piezoelectric element is built into each nozzle. When an electric charge is applied, it changes shape and acts as a small pump forcing ink out through the nozzle.
In general, thermal inkjet print heads are cheaper and simpler to produce, but the heating elements have a relatively short life. Most thermal printers use a combined print head and ink reservoir. When the ink runs out, the print head is also replaced.
When the first Inkjet printers were introduced, they needed specially coated inkjet paper to produce output of a reasonable quality.
Inkjet-specific paper is still available, but is generally more expensive than standard copier paper, and so should only be used when excellent quality is required. Almost all current inkjet models can be used successfully with standard A4 (US letter) copier paper. Most printer manufacturers provide general guidelines for choosing a paper and suggest the use of paper specifically listed as inkjet-compatible.
If the paper is not sufficiently absorbent, the ink sits on the surface rather than soaking into the paper, causing faint printing.
If the paper is too absorbent, the ink spreads too much, resulting in poorly-defined characters and graphics.
If the paper is rippled, the wetness of the ink causes the fibers of the paper to stretch, resulting in an uneven surface.
Liquid ink is sensitive to the moisture content of the paper. Keep it in its wrapper to prevent it from becoming dry or absorbing moisture.
When the printer fails to produce acceptable output, you may need to replace the ink cartridge. This is often simpler than replacing a dot-matrix ribbon. As a more economical option, you can refill the ink cartridges; however, this process may be messy.
Inkjet print heads are often considered consumable items. In most cases, this is unavoidable because the print head is built into the ink cartridge; for example, as with the HP DeskJet series of printers. Inkjet print heads can be expensive to replace.