Sharp FO-2950M - B/W Laser - All-in-One, Service Manual

Page: 51 / 232

UX-4000MU
FO-2950MU/C
STEP 3 (Development): Toner is attached to the latent electrostatic
images on the O PC d r u m t o form v i s -
i b l e images.
DC
–310V
CGL
CTL
Developing roller
Doctor
: Toner (Negatively charged)
Scraper
Toner supply roller
Grounding sheet
OPC drum
Exposed area
(Exposed to laser beam)
Non-exposed area
(Not exposed to laser beam)
Aluminum layer
(Drum base)
100V
Fig. 14
Toner is transported to the scraper area by the toner supply roller and
the developing roller. The quantity of toner to be transported to the doc-
tor section is controlled by the scraper. Toner transported to the doctor
section is then passed between the developing roller and the doctor to
form a thin toner layer on the developing roller by the pressure applied
by the doctor.
When toner passes between the developing roller and the doctor, it is
charged negatively by friction.
When an area of OPC drum which was exposed to laser beam and lost
its charge comes in contact with the developing roller, toner moves from
the developing roller to the OPC drum surface.
The principle of toner movement from the developing roller to the OPC
drum surface is as follows.
The bias voltage of DC–310V is applied to the developing roller. Toner
is charged negatively by the difference (electrical energy) between the
bias voltage and the OPC drum surface potential and is attracted to the
OPC drum surface which is positively charged.
At that time, the potential of the area of the OPC drum which was ex-
posed to the laser beam and lost its charge is higher than that of the
developing roller.
On the other hand, when an area of OPC drum which was not exposed
to the laser beam and did not lose its charge comes in contact with the
developing roller, any residual toner attached to the OPC drum is trans-
ferred to the developing roller which is more positively charged.
As a result, unnecessary toner on the OPC drum is collected by the
developing unit.
The operating principle for that case is contrary to that for transfer of
toner from the developing roller to the OPC drum surface. (The electric
field energy direction is contrary.)
STEP 4 (Transfer): Visible images of toner on the OPC drum are trans-
ferred to the paper.
The high voltage of DC+3500V plus AC600V (P-P) is applied to the
transfer roller to generate electric discharge between the roller and the
OPC drum, generating positive and negative charges. Positive charges
are attracted to the OPC drum and attached to the paper transported
between the transfer roller and the OPC drum. Therefore the paper has
a strong positive charge.
Negatively charged toner on the OPC drum is attracted by the paper
which is positively charged, and the visible images of toner are trans-
ferred onto the paper.
DC+3500V
AC600V(P-P)
CGL
CTL
OPC drum
Aluminum layer
(Drum base)
Paper
Transfer roller
Fig. 15
3 – 8