Electrophotography – Control of electrophotography process
Reexamination Certificate
2001-06-12
2003-09-30
Ngo, Hoang (Department: 2852)
Electrophotography
Control of electrophotography process
C399S066000, C399S101000
Reexamination Certificate
active
06628905
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine and the like performing an image formation by an electrophotographic system or an electrostatic recording system.
2. Related Background Art
FIG. 19
is a schematic block diagram showing one example of an image forming apparatus utilizing the conventional electrophotographic system.
This image forming apparatus comprises an electrphotographic photosensitive member (hereinafter referred to as a photosensitive drum) of a drum type as an image bearing member, around the periphery of which are disposed a charging roller
2
, an exposing apparatus
3
, a developing apparatus
4
, a transfer roller
5
and a cleaning blade
6
.
The photosensitive drum
1
is constituted in such a manner that an OPC photosensitive member layer
1
b
is formed on the outer surface of a conductive drum base
1
a
comprising, for example, aluminum and the like, and is rotationally driven by a drive apparatus (not shown) in the arrow direction (clockwise) at a predetermined process speed (a circumferential speed). The drum base
1
a
of the photosensitive drum
1
is grounded to a ground (GND).
The charging roller
2
as contact charging means is formed in a roller shape with a resistantly adjusted elastic layer
2
b
disposed on a metal core
2
a
and is rotated in the arrow direction (anticlockwise direction). The charging roller
2
contacts the surface of the photosensitive drum
1
by a predetermined pressing force, and by a charging bias (a bias in which an alternating voltage is superposed on a direct-current voltage) applied from a charging power source
170
, the photosensitive drum
1
is charged with a predetermined potential of a negative polarity in the present conventional example.
Regarding the exposing apparatus
3
, a modulated laser light according to the time series digital image signal of the image information to be inputted is outputted from a laser output portion (not shown) and performs an image-exposure-L on the surface of the photosensitive drum
1
so that an electrostatic latent image is formed on the surface of the photosensitive drum
1
charged by the charging roller
2
according to the image information.
The developing apparatus
4
allows a developer (for example, a magnetic one component insulating toner t in the present conventional example) borne on a developing sleeve
4
a
to be adhered on the electrostatic latent image formed on the photosensitive drum
1
, and visualizes the latent image as a toner image by a reversal-developing. The non-magnetic developing sleeve
4
a
which is rotated at a speed approximately equal to that of the photosensitive drum
1
is arranged with a minute gap portion (for example, below 200 &mgr;m) disposed against the photosensitive drum
1
and magnetically confines the toner t on the surface of the developing sleeve
4
a
by a magnetic force of a magnetic roll
4
b
fixed and involved in the interior of the developing sleeve
4
a.
The toner t magnetically confined on the developing sleeve
4
a
is regulated to a predetermined layer thickness by a layer thickness regulating blade
4
c.
The developing sleeve
4
a
is applied with a developing bias in which the alternating voltage in a square wave shape is superposed on the direct-current voltage from a developing power source
180
. In this way, an electrical field is generated in the gap portion between the developing sleeve
4
a
and the photosensitive drum
1
, and a toner t on the surface of the developing sleeve
4
a
flies. On this occasion, the portion not subjected to the image-exposure-L in the surface (OPC photosensitive member layer
1
b
) of the photosensitive drum
1
is charged with a negative polarity. The surface potential thereof is reduced lower than the direct-current voltage of the negative polarity of a developing power source
180
and exerts a force on the toner t in a direction to push it back to the developing sleeve
4
a.
Accordingly, by the alternating electrical field of the gap portion generated by the alternating voltage of the developing power source
180
, even when the toner t flies, it is pushed back to the interior of the developing apparatus
4
.
On the other hand, since the portion subjected to the image-exposure-L in the surface (OPC photosensitive member layer
1
b
) of the photosensitive drum
1
is attenuated in a negative charge, that portion becomes higher than the direct-current voltage of the negative polarity of the developing power source
180
(the absolute value of the negative voltage of that surface portion is reduced lower than the absolute value of the direct-current voltage of the developing power source
180
), and exerts a force on the toner t to pull it back to the photosensitive drum
1
. Accordingly, by the alternating electrical field of the gap portion generated by the alternating voltage of the developing power source
180
, the toner t flies and the flied toner t is adhered on the surface of the photosensitive drum
1
.
In this way, the portion subjected to the image-exposure-L in the surface of the photosensitive drum
1
is adhered with the toner t and the portion not subjected to the image-exposure-L in the surface of the photosensitive drum
1
is not adhered with the toner t, so that the toner t is adhered on the electrostatic latent image formed by being subjected to the scan-exposure-L, whereby the toner image is formed.
The transfer roller
5
as contact transfer means is formed in a roller shape with a resistantly adjusted elastic member layer
5
b
disposed on a metal core
5
a
and is rotated in the arrow direction (counterclockwise direction).
The transfer roller
5
forms a transfer nip portion by contacting the surface of the photosensitive drum
1
with a predetermined pressing force and transfers the toner image formed on the surface of the photosensitive drum
1
in the transfer nip portion by a transfer bias (a bias of the (positive) polarity reverse to the toner t) applied from a transfer power source
190
to a transfer material P such as a paper and the like.
Next, the image forming operation by the above described image forming apparatus will be described.
When the image forming is effected, the photosensitive drum
1
is rotationally driven by a drive apparatus (not shown) in the arrow direction at a predetermined circumferential speed and is charged with a predetermined potential by the charging roller
2
applied with a negative polarity charging bias from the charging power source
170
. With the image-exposure-L according to the image information from the exposing apparatus
3
given to the charged photosensitive drum
1
, the potential on photosensitive drum
1
is reduced in the potential of the portion subjected to the image-exposure-L, and the electrostatic latent image is formed according to the inputted image signal.
The toner t, which is charged with the same polarity (negative polarity) as the charged polarity of the photosensitive drum
1
by the developing sleeve
4
a
of the developing apparatus
4
applied with the developing bias of the same polarity of the charged polarity (negative polarity) of the photosensitive drum
1
at a developing position, is adhered on the electrostatic latent image formed on the photosensitive drum
1
and reversal-developed (visualized) as the toner image as described above.
When the toner image on the photosensitive drum
1
reaches the transfer nip portion between the photosensitive drum
1
and the transfer roller
5
, in time for this timing, the transfer material P such as the paper and the like in the interior of a cassette (not shown) is conveyed to the transfer nip portion by a sheet feeding roller (not shown), and by the transfer roller
5
applied with a predetermined transfer bias of the polarity (positive polarity) reverse to the above described toner t, the toner image on the photosensitive drum
1
is transferred on the transfer material P conveyed by the transfer nip port
Hori Kenjiro
Suzuki Koichi
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Ngo Hoang
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