Electrophotography – Control of electrophotography process – Responsive to number of copies or passage of time
Reexamination Certificate
1998-12-23
2001-04-10
Royer, William J. (Department: 2852)
Electrophotography
Control of electrophotography process
Responsive to number of copies or passage of time
C399S071000, C399S148000, C399S149000, C399S150000
Reexamination Certificate
active
06215967
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to an image forming apparatus such as an electrophotographic copying machine and an electrophotographic printer, which is equipped with a charging member, which is placeable in contact with an image bearing member, and to which voltage is applied to charge the image bearing member
FIG. 12
is a schematic vertical section of a conventional image forming apparatus of a transfer type (copying machine, printer, facsimile, and the like), and depicts the general structure thereof.
Reference character
101
designates an electrophotographic photosensitive member (hereinafter, “photosensitive drum”) as an image bearing member, in the form of a rotative drum, which is rotatively driven at a predetermined peripheral velocity in the counterclockwise direction indicated by an arrow mark.
In each image formation cycle, the photosensitive drum
101
is exposed to the light from a pre-exposing device
102
(eraser lamp) across its entire peripheral surface, before it is charged for image formation. This process is carried out to erase the electrical memory which the photosensitive drum
101
might have acquired during the proceeding image formation cycle. Then, the photosensitive drum
101
is subjected to a charging process in which it is uniformly charged to predetermined polarity and potential level by a corona based charging device
103
as a charging means. Then, the charged photosensitive drum
101
is exposed with a beam of image formation light L from an unillustrated exposing means (means for projecting the image of an original onto the photosensitive drum
101
; means for projecting a scanning laser beam modulated with image formation data; and the like means) to form an electrostatic latent image, that is, a latent pattern formed as the electrical charge is selectively removed, or reduced in potential level, from the uniformly charged peripheral surface of the photosensitive drum
101
, by the aforementioned beam of image formation light L. The thus formed electrostatic latent image is developed into a toner image by a toner based developing apparatus
104
as a developing means.
Meanwhile, a piece of transfer medium P (transfer paper) as a recording medium is fed into the image forming apparatus by an unillustrated sheet feeding mechanism, between the photosensitive drum
101
and a corona based charging device
105
as a transferring means, with a controlled timing. As the transfer medium P is passed between the photosensitive drum
101
and the corona based charging device
105
, the transfer medium P is charged to the polarity opposite to the potential of the toner, on the side of the transfer medium P which is not facing the photosensitive drum
101
. As a result, the toner image on the photosensitive drum
101
is electrostatically transferred onto the transfer medium P, on the side which is facing the photosensitive drum
101
.
Next, the transfer medium P is electrostatically separated from the peripheral surface of the rotating photosensitive drum
101
by a conona based charging device
106
, and is introduced into an unillustrated fixing apparatus, in which the toner image is fixed to the transfer medium P. Then, finally, the transfer medium P with the toner image fixed thereto is outputted as a copy or a print, from the image forming apparatus.
In the case of an image forming apparatus which outputs an image of two or more colors, it is equipped with a plurality of image formation stations, each of which is provided with its own processing devices, and each station works in synchronism with the conveyance of the transfer medium to place in layers a toner image of a specific color on the transfer medium, which generally is being conveyed by a dedicated transfer conveying member. After two or more toner images of a specific color are deposited on the transfer medium, the transfer medium is separated from the transfer medium conveying member, and is introduced into the fixing apparatus, in which the toner images are fixed to the transfer medium. Thereafter, the transfer medium with two or more toner images fixed thereto is outputted as a multicolor or full-color copy, or print, from the image forming apparatus.
After the toner image transfer onto the transfer medium, the peripheral surface of the photosensitive drum
101
is cleaned by the cleaning apparatus
107
(cleaner); the toner which remains on the peripheral surface of the photosensitive drum
101
is removed so that the photosensitive drum
101
can be used for the following image formation cycle.
There are various structures for the photosensitive member as the image bearing member, and for the means for carrying out the aforementioned image formation processes, that is, the charging, exposing, developing, transferring, fixing, cleaning, and the like processes. Also, there are various image formation systems.
For example, there is a corona based charging device, which has long been widely used as the charging means
103
. The corona based charging device is positioned immediately next to the photosensitive drum, without any contact with the photosensitive drum, and the peripheral surface of the photosensitive drum is exposed on the corona discharged from this device so that the peripheral surface of the photosensitive drum is charged to predetermined polarity and potential level.
In recent years, however, contact type charging apparatuses have been developed, and some of them have been put to practical use because of advantages such as producing a smaller amount of ozone, and consuming a smaller amount of electric power, compared to the conona based charging apparatus. In the case of the contact type charging apparatus, the peripheral surface of the photosensitive drum is charged to the predetermined polarity and potential level by applying voltage to a contact type charging member placed in contact with the peripheral surface of the photosensitive drum.
There are various contact type charging members, but a magnetic brush type charging member is favorably used because of its reliability. The magnetic brush type charging member comprises a magnetic brush portion, which consists of magnetic particles confined magnetically in the form of a brush. In charging the photosensitive drum, this magnetic brush portion is placed in contact with the peripheral surface of the photosensitive drum.
More specifically, the magnetic brush portion of the magnetic brush type charging member consists of electrically conductive magnetic particles confined magnetically in the form of a brush, directly on the magnet, or on the peripheral surface of a sleeve in which a magnet is disposed. In order to charge the photosensitive drum, the magnetic brush portion of the magnetic brush type charging member, which may be stationary or rotating, is placed in contact with the peripheral surface, and voltage is applied to the photosensitive drum.
There are other contact type charging members which have been used as a desirable contact type charging member; for example, a brush formed of stands of electrically conductive fiber (fur brush type charging member), a roller formed of electrically conductive rubber (charge roller), and the like.
This contact type charging member is remarkably effective when used to charge an organic photosensitive drum, or the object to be charged, the surface layer (charge injection layer) of which is composed of material in which electrically conductive particles have been dispersed, or a photosensitive member based on amorphous silicon, because such a combination makes it possible to charge the peripheral surface of the photosensitive member to a level substantially equal to the potential level of the DC component of the bias applied to the contact type charging member (Japanese Laid-Open Patent Application No. 3921/1994).
A charging method such as the one described above is called “charge injection”. Since this type of charging method (method which directly injects electrical charge into an object to be charged) does not rely on the electrical disc
Gomi Fumiteru
Hashimoto Kouichi
Komiya Yoshiyuki
Takeda Atsushi
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Royer William J.
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