Electrophotography – Machine operation
Reexamination Certificate
2000-01-21
2001-09-11
Royer, William J. (Department: 2852)
Electrophotography
Machine operation
C399S066000, C399S297000
Reexamination Certificate
active
06289186
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus using an electrophotography technique, such as a copying machine, a facsimile machine or a printer, which forms a toner image on an image holder such as a photosensitive drum and transfers the toner image onto a recording medium, by means of electrostatic attraction.
2. Description of the Related Art
In an image forming apparatus which forms a toner image on an image holder such as a photosensitive drum and transfers the toner image onto a recording medium such as paper, when the apparatus is stopped due to a paper jam or the like, nonfixed toner remains on a photosensitive drum
1
as shown in FIG.
7
. In
FIG. 7
, numeral
2
denotes a transfer belt and numeral
6
a charge roller for charging the transfer belt
2
. Since the photosensitive drum
1
can not stop its rotation immediately upon stoppage of the apparatus due to its inertia, a remaining range of the nonfixed toner becomes correspondingly large. Thus, when restarting the apparatus, the nonfixed toner on the photosensitive drum
1
is separated and recovered by means of a cleaner at a downstream side relative to the rotation of the photosensitive drum
1
.
However, if such a cleaning operation is performed every time the apparatus is restarted, a large load is applied to a blade of the cleaner so that a stable cleaning effect can not be ensured.
In view of this, Japanese Laid-open (unexamined) Patent Publication No. 5-119635 proposes a technique wherein, as shown in
FIG. 8
, when an image forming apparatus is restarted, a transfer belt
2
is caused to abut upon a photosensitive drum
1
and current (although there is no particular explanation in the foregoing publication, it is considered from a context that a value of the current is approximately equal to a value of transfer current which is supplied upon image formation on a recording medium) is fed to a transfer charger such as a charge roller
6
for giving charge to the transfer belt
2
. Thus, the foregoing nonfixed toner on the photosensitive drum
1
is transferred onto the transfer belt
2
and then removed by a cleaner of the transfer belt
2
at a downstream side thereof, while residual toner on the photosensitive drum
1
after the transfer is recovered by a cleaner of the photosensitive drum
1
. Thus, a load applied to the cleaner of the photosensitive drum
1
is reduced. The residual toner recovered by the cleaner of the photosensitive drum
1
is subjected to removal of charge and then returned to a developing unit so as to be recycled for developing a latent image on the photosensitive drum
1
.
However, in the image forming apparatus wherein toner at the developing unit is always in contact with the photosensitive drum, the toner flows out onto the photosensitive drum due to the rotation of the photosensitive drum upon restarting the apparatus even if charge is not applied to the developing unit. The technique of the foregoing publication can not prevent such flowing-out of the toner upon restarting the apparatus.
Further, when the restart of the apparatus due to a paper jam is carried out, paper powder invades the nonfixed toner on the photosensitive drum. The nonfixed toner mixed with the paper powder is separated from the photosensitive drum by the cleaner of the photosensitive drum. However, the nonfixed toner mixed with the paper powder significantly increases abrasion of a blade of the cleaner, thereby to cause replacement thereof and shorten the life duration of the photosensitive drum.
Further, if the toner returned from the cleaner of the photosensitive drum to the developing unit for recycling contains the paper powder, charging of the toner is adversely affected to induce an adverse effect on the print quality.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide an improved image forming apparatus.
According to one aspect of the present invention, there is provided an image forming apparatus characterized by, upon restarting the image forming apparatus, feeding current to all elements each having a charge feeding function, the elements including a transfer charger for charging a transfer member, causing the transfer member to abut upon an image holder, driving the transfer member in a given direction, and cleaning the transfer member at a downstream side of a contact portion between the transfer member and the image holder in the given direction.
FIG. 1
is a diagram for explaining a concept of the present invention. In the figure, upon restarting the image forming apparatus, the current is fed to a transfer charger
6
a
which charges a transfer member
2
a
, as well as an image holder charger
8
a
and a developing unit
9
a
each having a charge feeding function. Nonfixed toner remains on the surface of an image holder
1
a
. In the FIG.,
3
a
denotes a transfer member cleaner,
7
a
a latent image forming unit,
100
a
an image holder cleaner, and
102
a
a return path for returning toner recovered by the image holder cleaner
100
a
to the developing unit
9
a.
The image holder charger
8
a
charges the image holder
1
a
in minus or plus, while the developing unit
9
a
also charges toner in minus or plus. If there is caused no potential difference between the charged image holder
1
a
and the charged toner, repulsion occurs therebetween so that the toner is prevented from flowing out onto the image holder
1
a
due to the rotation of the image holder la. Thus, since the nonfixed toner on the image holder
1
a
is transferred onto the transfer member
2
a
and cleaned by the transfer member cleaner
3
a
and since the flowing-out of the toner onto the image holder
1
a
is prevented, a toner removal load of the image holder cleaner
100
a
can be reduced. For realizing an equipotential state between the charged image holder
1
a
and the charged toner, the latent image forming unit
7
a
should be prohibited from forming a latent image on the image holder
1
a.
According to another aspect of the present invention, there is provided an image forming apparatus comprising an image holder on which an image is formed; a transfer member for conveying a recording medium, the transfer member caused to abut upon the image holder so as to transfer the image formed on the image holder onto the recording medium; a transfer charger for charging the transfer member; a cleaner for cleaning the transfer member at a downstream side of a contact portion between the transfer member and the image holder in a driven direction of the transfer member; a detecting means for detecting restart of the image forming apparatus; and a control means for executing a current feed control, wherein, when the detecting means detects the restart of the image forming apparatus, the control means feeds current to all elements each having a charge feeding function, the elements including the transfer charger, causes the transfer member to abut upon the image holder, and drives the transfer member in a given direction, and the cleaner cleans the transfer member at a downstream side of a contact portion between the transfer member and the image holder in the given direction.
Since the restart of the image forming apparatus requires an initialize process which is normally executed upon turning on a power switch of the apparatus, the detecting means detects an initialize signal as a signal indicative of the restart of the apparatus. The detecting means may be realized by a control box which will be described later.
The elements to be fed with the current by the control means include the transfer charger, an image holder charger and a developing unit. The transfer charger charges the transfer member for transferring nonfixed toner on the image holder onto the transfer member. The image holder charger charges the image holder in minus or plus, while the developing unit also charges toner in minus or plus. If there is caused no potential difference between the charged image holder and the charged toner, repulsion occurs
Armstrong, Westerman Hattori, McLeland & Naughton
Fujitsu Limited
Royer William J.
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