(^416) PC Hardware: A Beginner’s Guide
charge. Not all of the droplets are charged, only the ones that are selected by the
timing mechanisms for use in printing on paper. After the droplets are charged
they flow over a deflector plate that sends the charged droplets onto the paper
and the uncharged droplets back into the ink supply to be reused. The uncharged
droplets represent white space or unprinted areas of the printed page. Continuous
flow inkjet printers have another major difference to drop-on-demand printers:
the nozzle remains fixed in place and the paper is moved back and forth under
the print head. This prevents the ink from being splashed about, which would
happen if the head were to move.
Piezoelectric Inkjet Technology
Piezoelectric inkjet printers can change the size of the droplet put on the paper by chang-
ing the amount of electricity, which alters the amount of expansion or contraction of the
Piezo crystal. A larger electrical charge causes more expansion in the crystal and forces
more ink from the nozzle.
The advantages of the Piezoelectric approach to inkjet printing are speed and a better
on-page ink quality. A thermal inkjet must cool the ink channel between each droplet, and
the Piezo crystal reacts faster to the electrical charge than the channel can cool. Although the
timesavingsareverysmallfractionsofasecond,theycanaddupoveralargeprintjob.An-
other advantage is that because the ink is not heated, special ink that can withstand high
temperatures is not required, which results in lower prices. Not heating the ink can also re-
sult in truer colors from print to print or even within the same print, a problem common to
the thermal inkjet. Probably the biggest drawback to Piezo technology–based inkjet print-
ers is the cost of the printhead, which can drive up the cost of the printer itself.
A limited number of manufacturers produce Piezoelectric inkjet printers, including
Epson, Xerox, Mutoh, and a few others.
Thermal Inkjet Technology
The thermal type of inkjet printer has its advantages over the Piezoelectric type. First,
thermal inkjets are the most common type in use and its supplies are readily avail-
able—some supermarkets even sell ink cartridges and paper.
The thermal process involves heating the ink in the ink channel between the ink reser-
voir and the printhead’s nozzles. It may sound as if all of the ink in the channel is being
heated.Actually,onlyaboutathirdoftheinkisactuallyheatedandatfullspeed,thetem-
perature gain is only around 30 degrees Celsius.
Thermal inkjet printers are primarily produced by Hewlett Packard, Lexmark, and
Canon, the companies that hold nearly all of the thermal inkjet patents.
The Inkjet Printing Process
The printing process for any type of printer always begins with the PC and its software.
Typically, an application program (such as a word processor like Microsoft Word or Corel