Electrophotography – Control of electrophotography process – Control of transfer
Reexamination Certificate
2000-08-28
2002-09-10
Grimley, Arthur T. (Department: 2852)
Electrophotography
Control of electrophotography process
Control of transfer
C399S314000, C399S313000
Reexamination Certificate
active
06449444
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine or a printer which uses an electrophotographic system or an electrostatic recording system.
2. Related Background Art
FIG. 11
shows an image forming apparatus of the electrophotographic system.
In the figure, the image forming apparatus includes a drum-shaped electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”)
1
which rotates in a direction indicated by an arrow a (clockwise). A charging roller
2
, an exposing apparatus
3
, a developing apparatus
4
, a transfer roller
5
and a cleaning apparatus
6
are disposed around the photosensitive drum
1
.
Upstream of a transferring nip portion N between the photosensitive drum
1
and the transfer roller
5
in a conveying direction of a transferring material P, a sheet feeding cassette
7
, a sheet feeding roller
8
, a pre-feed sensor
9
, a pair of resist rollers
10
, a top sensor
11
and a transfer guide
12
are disposed. On the other hand, downstream of the transferring nip portion N in the conveying direction of the transferring material P, an electricity erasing needle
13
, a conveying guide
14
, a fixing apparatus
15
and a pair of sheet discharging rollers
16
are disposed.
Also, the image forming apparatus can perform duplex image formation (duplex printing), and a pair of reverse rollers
18
, a pair of sheet re-feeding rollers
19
and a sheet re-feeding sensor
20
for duplex image formation are disposed in a duplex conveying path
17
.
The photosensitive drum
1
is formed of a negatively charged OPC photosensitive member which is rotationally driven in the direction indicated by the arrow a at a given process speed in a conventional example.
The charging roller
2
is brought in contact with a surface of the photosensitive drum
1
by a predetermined pressing force and charges the photosensitive drum
1
to a predetermind polarity and potential by a charging bias applied from a charging bias power supply (not shown).
The exposing apparatus
3
includes a laser diode that emits a laser beam, a collimator lens, a polygon mirror, an f&thgr; lens, etc., not shown, and scans the photosensitive drum
1
, which has been uniformly charged by the charging roller
2
, with an outgoing laser beam L, which has been on/off-controlled in accordance with inputted image information, in a direction perpendicular to the rotating direction of the photosensitive drum
1
and then exposes light. The exposure allows charges on a portion of the photosensitive drum
1
which has been scanned with the laser beam L to be removed, and an electrostatic latent image to be formed on the surface of the photosensitive drum
1
.
The developing apparatus
4
includes a rotatable developing sleeve
4
a
inside of which a magnet roller (not shown) is fixed. The developing apparatus
4
coats a developer (toner) on a developing sleeve
4
a
into a thin layer and attaches the toner onto the electrostatic latent image formed on the surface of the photosensitive drum
1
at a developing position to develop (visualize) the electrostatic latent image as a toner image. The developing sleeve
4
a
is applied with a developing bias from a developing bias power supply (not shown).
The transfer roller
5
is brought in contact with the surface of the photosensitive drum
1
by a predetermied pressing force to form the transferring nip portion N, and transfers the toner image on the surface of the photosensitive drum
1
onto the transferring material P at the transferring nip portion N defined between the photosensitive drum
1
and the transfer roller
5
. The transfer roller
5
is rotated in a direction indicated by an arrow b (counterclockwise).
The fixing apparatus
15
includes a fixing roller
15
a
and a pressure roller
15
b
. The fixing apparatus
15
heats and pressurizes the transferring material P onto which the toner image has been transferred between the fixing roller
15
a
and the pressure roller
15
b
to thermally fix the toner image onto the surface of the transferring material P.
Subsequently, the image forming operation of the above-described image forming apparatus will be described.
Upon the issuance of an image forming operation start signal, the transferring materials P within the cassette
7
are fed one by one by the sheet feeding roller
8
and conveyed up to the pair of resist rollers
10
. During this operation, the conveyance of the transferring materials P is detected by the pre-feed sensor
9
.
On the other hand, the photosensitive drum
1
is rotationally driven in the direction indicated by the arrow a by driving means (not shown) and charged to the predetermined potential by the charging roller
2
. Then, the laser beam L corresponding to an image signal is irradiated onto the photosensitive drum
1
from the exposing apparatus
3
, and the potential on the photosensitive drum
1
at a portion onto which the laser beam L has been irradiated drops to form the electrostatic latent image. Then, the toner is attached onto the electrostatic latent image formed on the photosensitive drum
1
by the developing sleeve
4
a
of the developing apparatus
4
to which the developing bias having the same polarity as the charging polarity (negative polarity) of the photosensitive drum
1
is applied, to thereby visualize the electrostatic latent image as the toner image.
Then, after a leading end of the transferring material P is detected by the top sensor
11
, the transferring material P is fed by the pair of resist rollers
10
to the transferring nip portion N between the photosensitive drum
1
and the transfer roller
5
through the transfer guide
12
in synchronism with the rotation of the photosensitive drum
1
. Then, the transfer roller
5
is applied with a transferring bias having the reverse polarity (positive polarity) of the toner from the transferring bias power supply (not shown), and the toner image is transferred onto the transferring material P from the photosensitive drum
1
.
Then, the transferring material P onto which the toner image has been transferred is electricity-erased by the electricity erasing needle
13
to which charges having the reverse polarity (negative polarity) of the transfer roller
5
are given, and the transferring material P is separated from the photosensitive drum
1
by the own weight of the transferring material P. The transferring material P which has been separated from the photosensitive drum
1
is conveyed to the fixing apparatus
15
through the conveying guide
14
, and the transferred toner image is thermally fixed onto the surface of the transferring material P due to heating and pressurizing by the fixing roller
15
a
and the pressure roller
12
b
of the fixing apparatus
15
. Then, the transferring material P is discharged to the external from the pair of sheet discharging rollers
16
.
On the other hand, a residual toner (untransferred toner) and other attachments are removed from the surface of the photosensitive drum
1
from which the toner image has been transferred and cleaned by the cleaning apparatus
6
, and the photosensitive drum
1
is put to succeeding image formation.
Also, at the time of duplex image formation (double-sided print), the transferring material P which has been discharged from the fixing apparatus
15
after the image has been formed on a first surface (front surface) of the transferring material P is reversed by the reverse rollers
18
and conveyed to the duplex conveying path
17
. Then, the transferring material P is allowed to pass through the sheet re-feeding sensor
20
by the sheet re-feeding rollers
19
and again introduced to the pair of resist rollers
10
. Thereafter, another image is formed on a second surface (back surface) of the transferring material P in the same manner as the first surface.
Note that at the time of the above-described image formation, the transfer roller
5
is applied with a transferring bias Vtr required for transferring th
Fitzpatrick ,Cella, Harper & Scinto
Grimley Arthur T.
Ngo Hoang
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