Electrophotography – Control of electrophotography process – Control of transfer
Reexamination Certificate
1999-09-08
2001-10-23
Royer, William J. (Department: 2852)
Electrophotography
Control of electrophotography process
Control of transfer
C399S101000, C399S297000, C399S302000, C399S309000
Reexamination Certificate
active
06308019
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 and the like, and more particularly, it relates to an image forming apparatus in which an image on an image bearing member is transferred onto an intermediate transfer member and then the image on the intermediate transfer member is transferred onto a transfer material.
2. Related Background Art
FIG. 9
shows an example of a conventional color image forming apparatus. In
FIG. 9
, a photosensitive drum (image bearing member)
104
is rotated by driving means (not shown) in a direction shown by the arrow and is uniformly charged by a primary charger
105
. Then, a laser beam corresponding to a magenta image pattern is illuminated onto the photosensitive drum
104
from an exposure device
110
to form a latent image on the photosensitive drum
104
. When the photosensitive drum
104
is further rotated in the direction shown by the arrow, among developing devices
107
a
,
107
b
,
107
c
,
107
d
supported by a rotary supporting member
107
e
, a magenta developing device
107
a
containing magenta toner is rotated to be opposed to the photosensitive drum
104
, so that the latent image is visualized by the magenta developing device
107
a
as a toner image.
An intermediate transfer belt (intermediate transfer member)
103
is passed over on three rollers
121
,
122
,
123
and is rotated at a speed substantially the same as that of the photosensitive drum
104
in a direction shown by the arrow. By impressing primary transfer bias to a primary transfer roller
102
, the toner image formed on the photosensitive drum
104
is primary-transferred onto an outer peripheral surface of the intermediate transfer belt
103
.
By repeating the above-mentioned process with respect to a cyan color, an yellow color and a black color by using the developing devices
107
b
,
107
c
,
107
d
, respectively, plural color toner images are formed on the intermediate transfer belt
103
.
Then, a transfer material
113
is fed from a transfer material cassette
113
a
by a pick-up roller
112
at a predetermined timing. At the same time, secondary transfer bias is impressed to a secondary transfer roller
108
, with the result that the toner images on the intermediate transfer belt
103
are transferred onto the transfer material
113
collectively. Then, the transfer material
113
is conveyed, by a conveying belt
120
, to a fixing device
109
, where the toner images are fused and fixed, thereby obtaining a color image.
After the secondary transfer, residual toner remaining on the intermediate transfer belt
103
is charged with opposite polarity by a charging device
101
a
as an intermediate transfer belt cleaning device
101
, with the result that the residual toner is counter-transferred onto the photosensitive drum
104
, thereby cleaning or removing the residual toner. On the other hand, residual toner after primary transfer and counter-transfer toner on the photosensitive drum
104
are removed by a photosensitive drum cleaning device
106
.
Now, the cleaning of the intermediate transfer belt will be fully described.
Residual toner after secondary transfer is subjected to a strong electric field having polarity opposite to that of the toner when the toner is transferred from the intermediate transfer belt
103
to the transfer material
113
, with the result that the residual toner may remain on the intermediate transfer belt
103
in a condition that the residual toner has been charged with polarity (positive polarity in this conventional case) opposite to normal charging polarity (negative polarity in this conventional case) of the toner. However, all toners cannot be reversed to the positive polarity, but there are toners partially neutralized not to have charges and/or toners remaining in negative polarity.
Thus, the charging device
101
a
is disposed at a downstream side of a secondary transfer position, i.e., immediately behind the secondary transfer position in a moving direction of the intermediate transfer belt
103
so that bias obtained by superposing an AC component with a DC component is impressed as a intermediate transfer belt cleaning bias by the charging device
101
a.
The residual toner after secondary transfer is reciprocally moved by the AC component repeatedly so that the toner is charged more uniformly with positive polarity.
The uniformly and positively charged residual toner after secondary transfer is counter-transferred onto the photosensitive drum
104
at a primary transfer nip portion and then is collected by the cleaning device
106
from the photosensitive drum
104
.
In a print operation in which a plurality of transfer materials are continuously printed, the charges of the oppositely charged residual toner after secondary transfer on the intermediate transfer belt
103
and the charges of the normal toner (to be primary-transferred) on the photosensitive drum
104
do not cancel each other by short time contact therebetween. Thus, at the primary transfer nip portion between the photosensitive drum
104
and the intermediate transfer belt
103
, when the primary transfer bias is impressed, the residual toner after secondary transfer and the toner on the photosensitive drum
104
can be substantially simultaneously transferred onto the photosensitive drum
104
and the intermediate transfer belt
103
, respectively. Accordingly, since the residual toner after secondary transfer is not transferred onto the transfer material
113
in the next print, a proper image can be outputted.
When the above-mentioned intermediate transfer belt cleaning device
101
is used, a waste toner container for collecting the residual toner on the intermediate transfer belt
103
can also serve as the photosensitive drum cleaning device
106
so that the apparatus can be made compact and a maintenance ability can be improved.
By the way, in color image forming apparatuses such as the above-mentioned conventional color image forming apparatus, recently, an automatic both-side printing function has frequently been added. As shown in
FIG. 10
, the automatic both-side printing function is realized by optionally adding a both-side unit
130
to the conventional image forming apparatus externally or internally.
In the image forming apparatus having the automatic both-side printing function, there is provided selecting means
111
for selecting between a conveying path for discharging a sheet and a conveying path communicating with the both-side unit
130
, in dependence upon whether the transfer material
113
discharged from the fixing device
109
relates to a first side print or a second side print. Further, the transfer material
113
conveyed to the both-side unit
130
by the selecting means
111
remains within the both-side unit
130
until an image to be printed in the second-side print is prepared on the photosensitive drum
104
, and is re-fed in sync with a second-side image formation.
Several (1 to 3) transfer materials
113
can be stocked within the both-side unit
130
and the transfer material
113
is re-fed in response to a signal from control means (not shown) capable of judging a property of the image (whether a first-side image or a second-side image).
In the both-side print as mentioned above, since electric properties (resistance value, change in electrostatic capacity due to partial adhesion of toner layer and the like) and mechanical properties (rigidity of transfer material, curling condition and the like) of the transfer material to which the first-side image was transferred and fixed are changed, a second-side transferring condition will differ from the first-side transferring condition greatly. As a result, second-side image quality may considerably be worsened in comparison with first-side image quality.
To improve this, there has been proposed a technique in which the second-side image quality is improved by changing the transfer bias in the second-side transferring.
However, in the image
Miyashiro Toshiaki
Tsuruya Takaaki
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Royer William J.
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