AM-400 (serv.man7). Chapter 3 (Mechanical Description). - Sharp Copying Equipment Service Manual (repair manual). Page 14

AM-400DE

3 – 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
doctor 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 pres-
sure 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-280V 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
exposed 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 con-
tact with the developing roller, any residual toner attached to the OPC
drum is transferred 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.)

The high voltage of DC+3600V plus AC760V (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.

STEP 3 (Development): Toner is attached to the latent electro-

static images on the OPC drum to form 
visible images.

CGL

CTL

OPC drum

Aluminum layer
(Drum base)

Doctor

Toner
supply
roller

DC

-280V

DC-180V

Developing roller

: Toner (Negatively charged)

Exposed area
(exposed
to laser beam)

Non-exposed area
(Not exposed to
laser beam)

Visible images of toner on the OPC drum are 
transferred to the paper.

Transfer roller

DC+3600V
AC760V(P-P)

Paper

CTL

CGL

Aluminum layer
(Drum base)

OPC drum