Electrophotography – Control of electrophotography process – Of plural processes
Reexamination Certificate
2003-01-23
2004-10-12
Royer, William J. (Department: 2852)
Electrophotography
Control of electrophotography process
Of plural processes
C347S116000, C399S301000, C399S302000
Reexamination Certificate
active
06804479
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 facsimile machine and a printer, for forming an image on a recording material to obtain a hard copy based on an electrophotographic process.
2. Description of the Related Art
In many conventional image forming apparatuses utilizing the electrophotographic process, a corona charger has been employed as means for electrically charging a drum type electrophotographic photoconductor (hereinafter referred to as a “photoconductor”) that serves as an image carrier. The corona charger is arranged in a non-contact and opposed relation to the photoconductor and the photoconductor surface is exposed to discharge corona generated by the corona charger so that the photoconductor surface is electrically charged to a predetermined potential with a predetermined polarity.
On the other hand, a contact charger (direct charger) has recently been put into practical use because of superior advantages over the corona charger, i.e., less ozone and lower power consumption. With a contact charger, a charging member, to which a voltage is applied, is contacted with a photoconductor so that the photoconductor surface is electrically charged to a predetermined potential with a predetermined polarity. A contact charger using a magnetic brush, as the charging member, is employed in many cases because of advantages such as a good charging ability and safety in contact. In a magnetic brush type contact charger, conductive magnetic particles are magnetically retained on a magnet directly or on a sleeve incorporating a magnet to serve as a magnetic brush. The magnetic brush is contacted with the photoconductor surface while the photoconductor is stopped or rotated. By applying a voltage to the magnetic brush in such a condition, charging of the photoconductor is started. Alternatively, a brush made up of conductive fibers (fur brush) or a conductive rubber roll fabricated by forming conductive rubber into a roll shape can also be used as the contact charging member.
As another type of contact charging, an injection charging method is also known in which a charge injection layer is provided in a photoconductor and a charging member, to which a voltage is applied, is contacted with the photoconductor to inject charges into the charge injection layer so that the photoconductor surface is electrically charged to a predetermined potential with a predetermined polarity. With this injection charging method, the photoconductor can be charged to have a surface potential substantially identical to an applied DC voltage (DC bias) regardless of whether or not an AC voltage (AC bias) is applied to the charging member in a superimposed manner. Thus, since the photoconductor is electrically charged without utilizing a discharge phenomenon that occurs in the case of employing the corona charger, the charging can be realized with generation of no ozone and lower power consumption.
Furthermore, in recent years, a so-called cleaner-less system has also been put into practical use for the purposes of reducing the apparatus size, simplifying the construction, and not producing waste toner from the viewpoint of environmental friendliness. In the cleaner-less system, a cleaning device for removing toner from the photoconductor surface remaining after transfer of a toner image onto a recording (transfer) material, e.g., a sheet of paper, is omitted. After recovering the toner remaining after the transfer by a contact charging device, the toner is ejected from the contact charging device to be recovered by a developing device during a period in which an image is not formed.
By employing the cleaner-less system and the injection charging method, a smaller and simpler image forming apparatus generating no ozone, consuming lower power and recovering the leftover toner can be obtained.
FIG. 12
is a schematic view of a laser beam printer as a conventional image forming apparatus. The laser beam printer comprises a photoconductor
1
serving as an image carrier, a magnetic brush
3
serving as a contact charging means, an exposure device
100
, a developing device
4
, and a transfer device
7
serving as transfer means. The components
3
,
100
,
4
, and
7
are successively disposed around the photoconductor
1
in the rotating direction (denoted by arrow A) thereof.
In an image forming mode, the photoconductor
1
is driven by a driving means (not shown) to rotate in the direction of arrow A. During the rotation, the photoconductor surface is uniformly electrically charged (with a negative polarity) by the magnetic brush
3
serving as a contact charging means. Then, the uniformly charged surface of the photoconductor
1
is subjected to exposure of an image by the exposure device (laser scanning device)
100
using a laser beam, whereby an electrostatic latent image corresponding to image information is formed on the photoconductor
1
. The electrostatic latent image is developed into a toner image through a reversal process by the developing device
4
.
When the toner image on the photoconductor
1
reaches a transfer nip
70
between the photoconductor surface and a transfer belt
71
of the transfer device
7
, a recording material P in a cassette
41
is supplied by a sheet supply roller
42
and then fed to the transfer nip
70
by a register roller
43
in a timed relation. Then, charges having a polarity opposite to that of the toner are applied to the backside of the recording material P from a transfer charging blade
74
, to which a transfer bias is applied, whereby the toner image on the photoconductor
1
is transferred onto the front side of the recording material P. The recording material P having the transferred toner image is separated from the surface of the transfer belt
71
with the aid of a separation charger
15
, and then fed to a fusing device
6
. The toner image is fused into a permanently fixed image on the surface of the recording material P by the fusing device
6
, and thereafter the recording material P is ejected from the image forming apparatus.
On the photoconductor
1
having passed the transfer nip
70
, there exists, though in a small amount, toner that has not been transferred onto the recording material P at the transfer nip
70
(i.e., after-transfer remaining toner). The after-transfer remaining toner is electrostatically and physically scraped off by the magnetic brush
3
and is temporarily absorbed by the magnetic brush
3
. As the after-transfer remaining toner accumulates inside the magnetic brush
3
, the resistance of the magnetic brush
3
itself is increased to such an extent that the magnetic brush
3
can no longer sufficiently charge the photoconductor
1
. This produces a potential difference between the magnetic brush
3
and the surface of the photoconductor
1
, whereupon the after-transfer remaining toner so far retained by the magnetic brush
3
is caused to electrostatically move onto the photoconductor
1
. The after-transfer remaining toner having moved onto the photoconductor
1
is electrostatically taken in by the developing device
4
and then consumed in a next cycle of image formation.
On the other hand, toner remaining on the surface of the transfer belt
71
, from which the recording material P has been peeled off, is removed by a transfer belt cleaner
92
constituted by a urethane rubber blade to be ready for a next cycle of image formation.
FIG. 13
is a schematic view of a color laser beam printer as a conventional 4-drum full-color image forming apparatus. In this color laser beam printer, rotary drum type photoconductors
1
a
to
1
d
serving as image carriers are provided in respective image forming stations. Magnetic brushes
3
a
to
3
d
serving as contact charging means, exposure devices
100
a
to
100
d
, developing devices
4
a
to
4
d
, and transfer devices
7
(transfer charging blades
74
a
to
74
d
) are disposed respectively around the photoconductors
1
a
to
1
d.
In an image forming mode, the photo
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