Hardware Reference
In-Depth Information
Inkjet printers come in two varieties: piezoelectric (used by Epson) and ther-
mal (used by Canon, HP, and Lexmark). The piezoelectric inkjet printers have a
special kind of crystal next to the ink chamber. When a voltage is applied to the
crystal, it deforms slightly, forcing a droplet of ink out of the nozzle. The higher
the voltage, the larger the droplet, allowing the software to control the droplet size.
Thermal inkjet printers (also called
bubblejet
printers) contain a tiny resistor
inside each nozzle. When a voltage is applied to the resistor, it heats up extremely
fast, instantly raising the temperature of the ink touching it to the boiling point
until the ink vaporizes to form a gas bubble. The gas bubble takes up more volume
than the ink that created it, producing pressure in the nozzle. The only place the
ink can go is out the front of the nozzle onto the paper. The nozzle is then cooled
and the resulting vacuum sucks in another ink droplet from the ink tank. The
speed of the printer is limited by how fast the boil/cool cycle can be repeated. The
droplets are all the same size, but smaller than what the piezoelectric printers use.
Inkjet printers typically have resolutions of at least 1200
dpi
(
dots per inch
)
and at the high end, 4800 dpi. They are cheap, quiet, and have good quality, al-
though they are also slow, and use expensive ink cartridges. When the best of the
high-end inkjet printers is used to print a professional high-resolution photograph
on specially coated photographic paper, the results are indistinguishable from con-
ventional photography, even up to 8
10 inch prints.
For best results, special ink and paper should be used. Two kinds of ink exist.
Dye-based inks
consist of colored dyes dissolved in a fluid carrier. They give
bright colors and flow easily. Their main disadvantage is that they fade when
exposed to ultraviolet light, such as that contained in sunlight.
Pigment-based
inks
contain solid particles of pigment suspended in a fluid carrier that evaporates
from the paper, leaving the pigment behind. These inks do not fade over time but
are not as bright as dye-based inks and the pigment particles have a tendency to
clog the nozzles, requiring periodic cleaning. Coated or glossy paper is required
for printing photographs properly. These kinds of paper have been specially de-
signed to hold the ink droplets and not let them spread out.
×
Specialty Printers
While laser and inkjet printers dominate the home and office printing markets,
other kinds of printers are used in other situations that have other requirements in
terms of color quality, price, and other characteristics.
A variant on the inkjet printer is the
solid ink printer
. This kind of printer ac-
cepts four solid blocks of a special waxy ink which are then melted into hot ink
reservoirs. Startup times of these printers can be as much as 10 minutes, while the
ink blocks are melting. The hot ink is sprayed onto the paper, where it solidifies
and is fused with the paper by forcing it between two hard rollers. In a way, it
combines the idea of ink spraying from inkjet printers and the idea of fusing the
ink onto the paper with hard rubber rollers from laser printers.
