Electrophotography – Control of electrophotography process – Control of transfer
Reexamination Certificate
2000-03-31
2001-10-23
Brase, Sandra (Department: 2852)
Electrophotography
Control of electrophotography process
Control of transfer
C399S311000
Reexamination Certificate
active
06308020
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrophotographic printer for printing images on a recording medium such as paper. The present invention also relates to a transfer charger incorporated in such a printer for transferring images onto a recording medium.
2. Description of the Related Art
Electrophotographic printers have been widely used for printing desired images on a recording medium such as continuous paper, cut sheets and so on.
FIG. 11
of the accompanying drawings shows the outline of a conventional electrophotographic printer.
As illustrated, the conventional printer includes a photosensitive drum
90
, a latent image forming unit
91
, a developing unit
92
, a transfer charge unit
93
, a fixing unit
95
, a pair of tractors
94
(only one shown) and so on. The tractors
94
are provided for feeding continuous recording paper P along a predetermined paper transfer path. For this purpose, though not illustrated, use is made of paper feed rollers to be operated together with the tractors
94
.
In the conventional printer, electrostatic latent images are formed on the annular surface
90
a
of the drum
90
by the image forming unit
91
. The latent images are developed by the developing unit
92
to produce visible toner images, and then these toner images are transferred onto the paper P by the transfer charge unit
93
. Thereafter, the transferred images are fixed to the paper by the fixing unit
95
.
The conventional transfer charge unit
93
is provided with only one transfer wire
93
a
and one static-eliminating wire
93
b
. The transfer wire
93
a
allows the passage of electric current (referred to as “transfer current” below) of a predetermined polarity for transferring toner images (formed on the drum
90
) onto the paper P. More specifically, the toner images formed on the photosensitive drum
90
are negatively charged, while the transfer wire
93
a
is rendered positive due to the transfer current. Thus, the toner images on the drum
90
will be attracted toward the transfer charge unit
93
to be transferred onto the paper P. In this process, the paper P is positively charged by the transfer current. In this connection, the static-eliminating wire
93
b
serves to eliminate the positive charges on the paper P, thereby preventing the paper P from unduly adhering to the drum
90
. Consequently, the paper P is properly fed along the predetermined paper transfer path.
Though having the above advantage, the conventional printer may suffer from the following problems.
As stated above, the annular surface
90
a
of the drum
90
is negatively charged during the printing operation. Thus, when the paper P is brought to the drum
90
, part of the paper P will adhere to the annular surface
90
a
of the drum
90
. Specifically, as shown in
FIGS. 12 and 13
, the adhering amount or manner of the paper P varies depending on the thickness (stiffness) of the paper P. For instance, when the paper P (p′) is relatively thin (FIG.
12
), a larger area of the paper P′ is stuck to the drum
90
, and the sticking begins at a position N
1
. On the other hand, when the paper P (p″) is relatively thick (FIG.
13
), only a smaller area of the paper p″ is stuck to the drum
90
, and the sticking begins at a position N
2
, which is located downstream of the paper transfer path from the above-mentioned position N
1
.
Keeping the above-described behavior of the paper P in mind, attention is drawn to the transfer charge unit
93
of the conventional printer. As stated above, the conventional transfer charge unit
93
is provided with only a single transfer wire
93
a
fixed at a position facing the photosensitive drum
90
. Even with such an arrangement, it may be possible to perform proper image transfer onto the comparatively thin paper p′ shown in
FIG. 12
, wherein the transfer wire
93
a
is located immediately downstream from the position N
1
.
However, when the comparatively thick paper P″ is used (FIG.
13
), the transfer wire
93
a
is located upstream from the position N
2
, which means that the transfer wire
93
a
faces a portion of the paper p″ which has still not come into engagement with the annular surface
90
a
of the drum
90
. In this state, disadvantageously, the toner images on the drum
90
may fail to be properly transferred onto the paper P″, so that no good printing results are obtainable.
Further, in the conventional printer, the range over which the transfer current is effective for drawing the toner images toward the recording paper is not variable depending on e.g. the type of paper P. Also, the strength of the transfer current may not be readily adjusted. Clearly, these inconveniences tend to be obstacles to proper transfer of toner images onto the recording paper.
SUMMARY OF THE INVENTION
The present invention has been proposed under these circumstances, and its object is to make it possible to perform proper toner image transfer from a photosensitive member to a recording medium, regardless of the type or other properties of the recording medium.
According to a first aspect of the present invention, there is provided a printer comprising:
a photosensitive member on which a toner image is formed;
image transfer means held in facing relation to the photosensitive member and arranged to conduct a transfer current for transferring the toner image onto a recording medium; and
at least one static-eliminating wire for conducting a discharge current for discharging the recording medium;
wherein the image transfer means is provided with a plurality of transfer wires spaced from each other in a feeding direction of the recording medium, the transfer current being selectively conducted through the transfer wires.
The photosensitive member may be a photosensitive drum or belt-like member.
With the above arrangement, it is possible to pass transfer currents through a selected one (or ones) of the transfer wires. In this manner, the locations at which the transfer currents are caused to flow can be altered. Therefore, by changing the above-mentioned locations, the transferring of toner images onto the recording medium is properly performed in accordance with e.g. the thickness of the recording medium. Further, since the number of live transfer wires is variable according to the above arrangement, it is possible to adjust (increase or reduce) the area of the recording medium over which the transfer currents have an effect. It is also possible to adjust the amount of charge to be supplied to the recording medium.
According to a preferred embodiment, the transfer current and the discharge current may be variable.
Preferably, the printer of the present invention may further comprise a common casing for fixing the transfer wires and the static-eliminating wire.
With such an arrangement, the transfer wires and the static-eliminating wire may be collectively handled, which is advantageous in setting these wires in facing relation to the photosensitive member.
According to a second aspect of the present invention, there is provided a printer comprising:
a photosensitive member on which a toner image is formed;
image transfer means held in facing relation to the photosensitive member and arranged to conduct a transfer current for transferring the toner image onto a recording medium;
at least one static-eliminating wire for conducting a discharge current for discharging the recording medium;
a power circuit for supplying the transfer current to the image transfer means;
controlling means for causing the power circuit to selectively supply the transfer current to the image transfect means; and
operation means arranged to be operated in a first manner when a thickness of the recording medium is no greater than a predetermined value, while being operated in a second manner when said thickness is greater than the predetermined value;
wherein the image transfer means is provided with a plurality of transfer wires spaced in a feeding direction of the recording medium, the trans
Fuke Kenji
Tonomoto Yoshihiro
Armstrong Westerman Hattori McLeland & Naughton LLP
Brase Sandra
Fujitsu Limited
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