Printronix L5535, Maintenance Manual

Page: 117 / 358

Developing Unit
II–117
Developing Section
In the developing section, toner is attracted to the electrostatic latent image
formed in the exposure step, so that a visible image is formed on the drum
surface. The developing section houses a cartridge that contains toner, a fine
black powder. Whenever the printer senses that it is low on toner, a
mechanism drops toner into the developing unit
auger . The auger holds
carrier beads, which are big, rough and heavy particles. When the printer is
on, toner is constantly rubbing against carrier beads. This combination is
called developing compound. The friction creates an electrostatic field.
The developing compound coats the developing roller, which has a positive
charge. As the photoconductive drum rotates past the developing roller, the
positively charged toner sticks to the negatively charged carrier beads. Recall
that all areas of the drum that were exposed to light from the LEDs hold low
positive charges and thus contain latent images.
The positively charged toner leaves the developing roller and adheres to the
areas of the drum that were exposed by the LEDs. The heavier carrier beads
stay in the developing unit. (Carrier beads are never used up—they recycle.
However, as the developing unit ages, the carrier beads inside it smooth out
and become less effective. When you install new developer, it will, of course,
contain new carrier beads.)
At this point the drum surface contains an image (in the form of toner on the
photoconductive drum surface) of the information or image being printed.
Developing Unit
The developing mechanisms of the printer are integrated into a single unit,
shown in the following figure.
To accomplish ultra-fine developing, the printer uses a two-component fine-
grain developer which consists of a magnetic toner and a carrier. The carrier
is resin-coated to weaken its magnetism. The developing unit is constructed
so that a predetermined amount of toner is always kept in the agitation
chamber, and this toner is replenished as needed from the toner cartridge.
When the toner cartridge is inserted into the developing unit and rotated 180
degrees, the toner in the cartridge falls into the toner hopper.
When the toner density sensor detects insufficient toner density near the
agitation roller, the toner supply roller (sponge) rotates, dropping more toner
into the agitation chamber. The agitation roller then mixes the new toner with
the carrier, and the resultant mixture is fed to the photoreceptor drum surface
via the gap between the developing roller and doctor blade. During this
process, the toner becomes positively charged by the friction between the
toner and carrier.