Developing: Stage Four - HP LaserJet II Serie Manual De Instrucciones

HP 33440/HP 33449 COMBINED SERVICE MANUAL
DEVELOPING: Stage Four
At the developing stition, the invisible electrostatic image is developed into a visible image on
the drum when toner from a developer cylinder is transferred to discharged areas on the drum.
The developer consists of a rotating metilic cyfinder, a freed magnet that runs the len~h of the
cylinder, a toner mvity, and a toner-brush-height-control blade. The toner in the toner cavity
is a powde~ substince made of black plastic resin bound to iron particles. The iron in the
toner muses it to be atiracted to the magnet inside the cylinder. As the cylinder rotates, the
bmsh-height-control blade hmits the amount of toner on the cytinder.
The plastic toner particles acquire a negative surface charge by rubbing against the cylinder
which is connected to a negative DC supply (see Figure 5-9). This electrostatic charge causes the
toner particles to be attracted to the areas of the drum which have been exposed to laser light
and repe~ed from the areas not exposed (see Figure 5-9). An AC potential is dso applied to the
developer cytinder to farther assist toner patiicles to overcome the attraction of the magnet and to
pull toner back to the cylinder from unexposed areas, thus improving densi@ and contrast.
The DC bias of the developer cylinder wn be user-adjusted with the Print Densi@ control. This
changes the attractive force between toner and drum, pulling more or less toner to the drum.
+V
o
.100
-600
-v
Developing cylinder surface potent ial
'* Drum surface potential
/
– (ex posed area)
----- -------------- ---
.—— . .
.- _ DC bias
-------- --------- -—
\::::~face
Time (t) _
(unexpo=d area)
, Blade
K
]C
. . . . . . . . . . . . . . . . : :...
. . . . . . . . : , . . . .
E :.
'"""-" ...""
\
2
u
:.. .
: ..'
Y :+.
%
n
.-
I!
---.--
: .: .
0
g}:. .+
: ,.
n .:.
. . ~~
~ ~
+:::::
}
Developing cylinder
9
AC bias
IA
(1600 Vp-P)
#lDCbas
Figure 5-9. Developing an image
Note
The charges making up the latent image shown in Figure 5-9 are negative but
i
they are shown as positive in the illustration because they are less negative than
w
the charges on the toner.
—
—
5-10