Electrophotography – Image formation – Transfer
Reexamination Certificate
2000-05-18
2002-01-08
Chen, Sophia S. (Department: 2852)
Electrophotography
Image formation
Transfer
C399S066000
Reexamination Certificate
active
06337968
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus which is capable of forming high quality of images without causing the jamming of sheets of paper during its conveyance and an image forming method.
2. Description of the Related Art
In an image forming apparatus which is widely used these days, a document image to be copied is exposed on the image carrier after it is electrified to the negative potential. As a result of this exposure, the electric charge on the exposed surface of the image carrier in the background area is neutralized and an electrostatic latent image corresponding to the image area of the document is formed on the surface of the image carrier. This electrostatic latent image formed on the surface of the image carrier is then developed by a developing toner to a visible image. This toner image is transferred on a sheet of paper in the transferring process and then, the sheet of paper with the toner image transferred is separated from the image carrier in the peeling process. The toner image on the separated sheet of paper is heated or pressurized and fixed permanently thereon. After a sheet of paper is separated, the residual toner left on the surface of the image carrier is removed by a cleaner.
In a conventional image forming apparatus using transferring and peeling chargers as described above, in order to satisfactorily transfer a toner image on a sheet of paper and peel off the paper from an image carrier for a long period, an image forming apparatus equipped with an automatic cleaning unit for automatically cleaning wires of transferring and peeling chargers was disclosed in Japanese Laid Open Patent No. 07-92779. The purpose of this automatic cleaning unit is to prevent the paper jamming and an image from becoming defective that are caused from the contamination of the wires of the transferring and peeling chargers resulting from the use of the image forming apparatus for a long period.
In a conventional image forming apparatus which uses transferring and peeling chargers, the wires of the transferring and peeling chargers are contaminated with toner and paper powder floating in the image forming apparatus and adhered to the surfaces of the wires with the increase in the number of copies. Corona discharge current for the transfer and peeling drops gradually from an initial set value when the charger wires are contaminated. When corona discharge current drops, the transfer of a toner image from an image carrier and separation of a sheet of paper from the image carrier, which are the basic functions of the transferring and peeling chargers will become worse.
In particular, as shown in
FIG. 2
, the above-mentioned problems tend to occur in an image forming .apparatus of such type that sheets of paper are ejected in its main body. In other words, in the transfer and peeling areas, a sheet of paper is conveyed upward from the lower part to the upper part as shown in FIG.
2
and the force of gravity of the leading edge of this sheet of paper cannot be used when separating it from the image carrier. The image forming apparatus shown in
FIG. 2
has no margin in the condition of peeling corona current condition for achieving the stabilized paper separating performance when compared with the paper separation performance of the paper conveyance in the horizontal direction in the image forming apparatus shown in FIG.
1
. In order to solve these problems, an image forming apparatus equipped with a cleaning unit for automatically cleaning the surface of the charger wires was disclosed in the above-mentioned Japanese Laid Open Patent No. 07-92779. However, this automatic cleaning unit requires a wire cleaning member, a driving motor for operating the cleaning member, etc. and this system will become very expensive. Further, in order to minimize the required cost, an image forming apparatus that operates a wire cleaning unit manually was also disclosed in Japanese Laid Open Patent No. 10-78692. However, differing from the automatic cleaning unit, this type of cleaning unit is not able to clean a wire periodically and also not able to obtain sufficient reliability for the wire cleaning level and its maintenance is troublesome. In addition, as the image forming apparatus must be stopped whenever the wire is cleaned manually, there was such a problem that a downtime of the apparatus becomes long.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an image forming apparatus and an image forming method which are able to perform the peeling of an image receiving medium such as a sheet of paper from an image carrier after transferring an image formed on an image carrier on the image receiving medium even if a corona wire of a peeling charger, which acts to peel off an image receiving medium from the image carrier, is contaminated as a result of the use for a long period and to perform the high quality image formation.
According to the present invention, there is provided an image forming apparatus comprising image forming means for forming a developer image on the surface of an image carrier; charge means for transferring the developer image from the image carrier on an image receiving medium and after this image transfer, giving electric charge to the image receiving medium so that it is separated from the image carrier; counter means for counting the number of image formations by the image forming means; voltage applying means unit for applying a voltage to the charge means; and control means for controlling voltage applied to the charge means by the voltage applying means so as to vary it according to the number of image formations counted by the counter means.
Further, according to the present invention, there is provided an image forming method comprising the steps of forming a developer image on the surface of an image carrier; transferring the developer image on an image receiving medium from the image carrier and after transferring the developer image, giving electric charge to the image receiving medium by a charger so as to separate the image receiving medium from the image carrier; counting the number of developer image formations; applying a voltage to the charger; and controlling the voltage applied to the charger so as to vary it according to the number of counted developer image formations.
REFERENCES:
patent: 4640606 (1987-02-01), Inamoto
patent: 5049939 (1991-09-01), Koichi
patent: 5526106 (1996-06-01), Katsumi et al.
patent: 5552872 (1996-09-01), Amemiya et al.
patent: 5749039 (1998-05-01), Thomas
patent: 5794097 (1998-08-01), Shinkawa et al.
patent: 6122460 (2000-09-01), Meece et al.
patent: 6173150 (2001-01-01), Suzuki et al.
patent: 7-92779 (1995-04-01), None
patent: 10-78692 (1998-03-01), None
Chen Sophia S.
Foley & Lardner
Toshiba Tec Kabushiki Kaisha
Tran Hoan
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