Hardware Reference
In-Depth Information
on the brand and model; the print engine tells the jets to squirt out ink in different
combinations and proportions for whatever colors are needed. Some photo printers have six
or eight cartridges, because different types of ink are used in some print jobs.
There are two technologies for forcing ink out of the nozzles: thermal and piezoelectric.
Thermal inkjet printers
heat the ink to about 400 degrees Fahrenheit, which creates vapor
bubbles that force out the ink. This creates a vacuum inside the cartridge which, in turn,
draws more ink into the nozzles. This technology is also called
bubble jet
printing. Because
the heat tends to degrade the print heads over time, ink replacement cartridges for these
models often include replacement print heads as well. These cartridges shouldn't be home-
refi lled because, by simply refi lling the ink, you don't get the new print head you need.
In contrast,
piezoelectric inkjet
, or
piezo
, moves the ink with electricity instead of heat.
The nozzles contain piezoelectric crystals, which change their shape when electricity is
applied to them and force out the ink. Piezo technology is easier on the printer because it
doesn't need a heating element, and it's better for the output because the ink is less prone to
smearing.
Inkjet printers are
line printers
; they print the document in a series of horizontal passes
as the print head moves vertically past the print head. Therefore an inkjet printer requires
only a limited amount of RAM—just enough to hold a few fonts and a few lines' worth of
data. Most inkjet printers don't even advertise the amount of RAM they contain because it
isn't important.
Laser Printers
A
laser printer
works much like a photocopier. The main difference is that a photocopier
scans a document to produce an image, whereas the laser printer receives digitized data
from a computer.
A laser printer contains a large cylinder known as a
drum
, which carries a high negative
electrical charge. The printer directs a laser beam to partially neutralize the charge in
certain areas of the drum. When the drum rotates past a toner reservoir, the toner clings
to the areas of lesser charge, and the page image is formed on the drum. Then the drum
rotates past positively charged paper, and the toner jumps off onto the paper. The paper
then passes through a fuser that melts the plastic particles of the toner so that it sticks to
the paper.
Laser printers are available in color or monochrome models. To print in color, a laser
printer must make four passes across the same page, laying down a different color each
time. Such a printer has four separate toner cartridges: cyan, magenta, yellow, and black.
Although you're unlikely to do so, if you spill any toner, let it settle before
you clean it up. Toner is a fine powder and is carcinogenic. A
carcinogen
is
a product that, with long-term continued exposure, may cause cancer. The
most prudent course of action is always to refer to the health and safety
guidelines that come from the manufacturer.
