Electrophotography – Image formation – Combined or plural functions by single component
Reexamination Certificate
1999-09-22
2001-08-07
Braun, Fred L. (Department: 2852)
Electrophotography
Image formation
Combined or plural functions by single component
C399S176000, C399S357000
Reexamination Certificate
active
06272301
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to an image forming apparatus of an electrophotographic or electrostatic recording type copying machine, printer or the like, more particularly, to an image forming apparatus wherein a step of effecting both cleaning and charging is used.
Heretofore, an image forming apparatus using an electrophotographic type is provided with a rotatable electrophotographic photosensitive member in the form of a drum, for example, as an image bearing member substantially at the center thereof, and the surface of the electrophotographic photosensitive member is uniformly charged by charging means. Thereafter, the surface of the photosensitive member is exposed to a line scanning laser beam, so that the electrostatic latent image is formed in accordance with the image signal on the surface. The electrostatic latent image is visualized at a developing station where the surface of the photosensitive member is faced to a developing device with rotation of the photosensitive member, so that toner image is formed on the photosensitive member. Thereafter, the toner image is electrostatically transferred onto a transfer material by the transfer means, and the toner image is fixed by heat and pressure by a fixing device, so that a permanent image is formed on the transfer material. A cleaning means is provided at a predetermined position to remove untransferred toner from the photosensitive member after the image transfer, so that service of the photosensitive member is cleaned and is reused.
The image forming apparatus performing such a series of process steps, is widely used not only in copying machines but also in printers for outputting means of computers and word processors. The image forming apparatus is used not only in an office but also at home, and economical aspect such as being inexpensive or maintenance-free is important.
In an image forming apparatus having the above described structure, a corona charger is used as the charging means, and a metal wire having an outer diameter of approx. 50 &mgr;m-100 &mgr;m is supplied with a high voltage such as approx. 5 kV-10 kV, so that air therearound is ionized to electrically charge the member to be charged (photosensitive member for example).
However, the corona charger involves the following disadvantages.
The wire per se of the corona charger attracts contamination during the process of the charging operation, and therefore, periodical cleaning and exchange are required. The corona discharge produces ozone.
Recently, a surface hardness of the electrophotographic photosensitive member is increased to increase the printing durability. After repeated use of the photosensitive member surface, the high hardness photosensitive member becomes sensitive to humidity because of the influence of the product of the corona resulting form the ozone produced by the corona charger, with the result that the photosensitive member surface tends to absorb moisture, which causes lateral flow of the charge on the photosensitive member surface and therefore degrading of the image quality due to the resulting image flow.
To avoid these problems, Japanese Utility Model Application Publication No. HEI-1-34205 proposes heating by a heater for the photosensitive member; Japanese Patent Application Publication No. HEI-2-38956 proposes removal of the corona product by a brush formed by cooperation of a magnet roller and magnetic toner; and Japanese Laid-open Patent Application No. SHO-61-100780 proposes the removable of the corona product by an elastic roller from the photosensitive member surface.
However, although rubbing of the photosensitive member surface is used with an amorphous silicon photosensitive member having a very high hardness, the required cleaning device is bulky, against the recent demand for downsizing of the apparatus. Additionally, using the photosensitive member heater for always heating it results in an increase of the electric energy consumption.
The capacity of the heater for the photosensitive member is approx. 15 W-80 W, and the required energy is not so high, but in most of the cases, the energy is supplied always including the night time, the electric energy consumption amount is as large as 5-15% of the entire electric energy consumption of the image forming apparatus in a day.
The above mentioned Japanese Laid-open Patent Application No. SHO-59-111179 and Japanese Laid-open Patent Application No. SHO-62-278577 do not recognize the problem of instability of the name intensity due to the temperature variation of the photosensitive member.
Japanese Laid-open Patent Application No. SHO-63-208878 discloses a charging device of so-called contact charging type wherein a charging member supplied with a voltage is contacted to the surface of the member to be charged (photosensitive member, for example) to electrically charge the surface thereof. Such a charging device of the contact charging type is advantageous over the corona charger in that:
(1] the voltage required to provide the desired potential of the photosensitive member surface can be reduced:
(2) the amount of the ozone produced during the charging process is zero or extremely small, so that necessity of using an ozone removal filter is eliminated, and therefore, the exhausting system of the main assembly of the image forming apparatus can be simplified.
Therefore, the above described drawbacks resulting from the production of ozone and ozone derivative can be avoided.
Therefore, the charging device of the contact charging type is expected as the means replaceable with the corona charger to electrically charge the member to be charged such as a photosensitive member or a dielectric member in an image forming apparatus such as a copying machine, a laser beam printer or an electrostatic recording apparatus.
The following contact charging member usable with the contact charging type charging device have been proposed:
A contact charging member in the form of a magnetic brush of magnetic particles and magnetic materials, as disclosed in Japanese Laid-open Patent Application No. SHO-59-133569:
A contact charging member of a fur brush including electroconductive fibers, as disclosed in Japanese Laid-Open Patent Application No. SHO-57-046265:
A contact charging member in the form of an elastic roller of elastic materials including electroconductive sponge.
FIG. 14
shows a schematic structure of an example of a conventional image forming apparatus using the contact charging type. A electrophotographic photosensitive member
3
(photosensitive member) in the form of a drum is rotated at a predetermined peripheral speed (process speed) in the direction indicated by an arrow x, and the surface thereof is contacted by a charging member
5
which is a contact charging member.
The charging member
5
is supplied by voltage applying means (unshown) with a DC voltage (Vdc) alone or with a DC voltage (Vdc) biased with an AC voltage (Vac), and uniformly charges the outer surface of the photosensitive member
3
which is rotating in the direction indicated by the arrow.
On the other hand, an original G placed on an original supporting platen glass
6
is illustrated with light L emitted by a lamp
71
(exposure means
7
), and the light reflected by the original G is imaged through a mirror system
72
by an imaging lens of a lens unit
73
, and is directed to the surface of the photosensitive member
3
through a mirror
74
, so that image of the original is formed on the surface of the photosensitive member
3
, or the surface of the photosensitive member
3
is scanned by a line scanning laser beam which is modulated in its intensity in accordance with an image signal, so that an electrostatic latent image is formed on the photosensitive member
3
.
The electrostatic latent image is carried to a developing position where the surface thereof is opposed to a developing device
3
, by rotation of the photosensitive member
3
, and the electrostatic latent image is visualized by a developing sleeve
81
coated with a developer charged t
Ehara Toshiyuki
Ishiyama Harumi
Kawada Masaya
Braun Fred L.
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
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