Chapter 17: Printers^429
Including the toner cartridge, an additional eight standard assemblies exist in a laser
printer. As illustrated in Figure 17-15, these assemblies are as follows:
Drum The drum inside the toner cartridge is photosensitive, which means
it reacts to light. The drum holds an electrostatic charge except where it is
exposed to light. The light source, usually a laser, is reflected onto the surface
of the drum to create a pattern of charged and not-charged dots that form the
image of the page to be printed.
High-voltage power supply The electrophotographic process used in laser
printers applies very high voltage to charge the drum and to transfer and hold
the toner on the paper. The high-voltage power supply converts AC current
into the higher voltages used in the printer.
DC power supply The electronic components of a laser printer use direct current
(DC) power. For example, logic circuits use +/–5 VDC (volts direct current), and
the paper transport motors use +24 VDC. Like a PC’s power supply, the laser
printer’s DC power supply also houses its cooling fan.
Paper transport Inside the laser printer are four sets of rubberized rollers
used to move the paper through the printer, each driven by its own motor.
The four roller sets of the paper transport system are the feed roller or the
paper pickup rollers, the registration rollers, the fuser rollers, and the exit
rollers. The rollers are very much like the platen roller in a typewriter, daisy
wheel printer, or dot matrix printer. They are rubberized to grip the paper
and adjusted to grip only as much as is needed to move the paper along to
the next station. The paper transport system, and particularly the paper feed
rollers, is where most paper jams happen in a laser printer.Figure 17-15. The internal components of the laser printing process