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1.1 LASER PRINTING
Before you begin learning about your new Star LaserPrinter
4111, you may
find it helpful to know something about laser printing itself.
A laser is actually a beam of light of just one wavelength (Laser is an acronym
for Light Amplification
by Stimulated Emission of Radiation). Such a beam
of light, described as "highly coherent", can be focused very sharply. Lasers,
generated by gases, liquids or semiconductors,
are widely used in applica-
tions ranging from surgery to the visual arts.
Laser printing is a process that uses a laser beam -
in this case, generated
by a semiconductor-
to activate portions of an electrically charged surface.
These activated parts represent the words, numbers, or graphics being sent
from the computer for printing. Other parts of the printer transfer this image
to paper, then clean the surface and prepare it to receive more information to
be printed.
In other words, this process is a type of laser-activated
temporary engraving.
In the Star LaserPrinter 4111, two interconnected
units produce the complete
printing process: the toner cartridge and the printer body.
The toner cartridge contains the drum, which is the rotating surface. In the
darkness of the toner cartridge, the drum holds a negative charge placed on
it by the primary corona wire in the printer. Shutters on the bottom of the toner
cartridge assure that no unwanted light penetrates its interior.
When text or graphics are sent by the computer to the printer, laser beam is
generated by a semiconductor
laser diode. This beam is focused by special
scanning mirrors that turn the light beam into a tool that "writes" or "prints"
on the surface of the drum. The areas of the drum touched by the laser beam
lose their negative charge and contain a reverse image of the information sent
from the computer. As the drum rotates, it passes a developer unit that is also
rotating, but in the opposite direction. The surface of the developer unit is
covered with toner ("ink") which has a negative charge. The neutralized
portions of the drum, containing
the information
to be printed, pick up
negatively charges toner from the developer unit.
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