Incremental printing of symbolic information – Electric marking apparatus or processes – Electrostatic
Reexamination Certificate
1997-07-31
2001-03-06
Le, N. (Department: 2861)
Incremental printing of symbolic information
Electric marking apparatus or processes
Electrostatic
Reexamination Certificate
active
06198492
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to an image forming apparatus such as a digital copier, facsimile machine, page printer and the like, in particular relating to an image forming apparatus which forms images by causing developer particles to jump to the recording medium.
(2) Description of the Prior Art
Among image forming apparatuses for outputting image data as a visual image on recording medium such as recording paper etc., one type is known which directly forms a toner image on the recording medium by making toner, the developer, jump onto the recording medium, as has been disclosed in Japanese Patent Application Laid-Open Hei 6 No. 155,798. As shown in
FIG. 1
, the image forming apparatus includes an image forming unit
151
having a toner supplying section
152
and a printing section
153
. In this apparatus, toner
171
is made to jump from toner supplying section
152
and adhere to a sheet of paper
155
, the recording medium. During this, the jumping of toner
171
is controlled in accordance with the image data.
Toner supplying section
152
is composed of a toner reservoir
170
for holding toner
171
as negatively charged developer particles, and a toner support
172
which supports toner
171
on its peripheral surface by magnetic force whilst rotating in the direction of arrow E. Printing section
153
is composed of an opposing electrode
175
of a cylindrical shape and a control electrode
176
which is provided between opposing electrode
175
and toner support
172
. Opposing electrode
175
rotates in the direction of arrow F so that paper
155
is conveyed between opposing electrode
175
and control electrode
176
in the direction of arrow G.
As shown in
FIG. 2
, control electrode
176
has a plurality of gates
179
formed therein, each gate
179
having an annular electrode
177
formed around the edge thereof. As a voltage from a control power source
181
shown in
FIG. 1
is selectively applied to these annular electrodes
177
in accordance with the image data, toner
171
supported on the peripheral surface of toner support
172
is made to jump toward opposing electrode
175
and pass through selective gates
179
hence being made to adhere to paper
155
which is placed between opposing electrode
175
and control electrode
176
.
The image forming apparatus configured as above is one which directly forms the image on the surface of recording medium such as paper etc. Therefore, it is no longer necessary to use a developer medium such as a photoreceptor etc., which was used in conventional image forming apparatuses. Further, the step for transferring the image from the developer medium to the paper can be omitted, thus making it possible to eliminate degradation of the image due to this operation. Moreover, the structure of the apparatus can be simplified needing fewer parts, thus making it possible to reduce the apparatus in size and cost.
Since, in the image forming apparatus directly forming the image by making the toner jump as described above, the toner is selectively made to jump to form an image by controlling the voltage of the control electrode, the controllability of the voltage in the control electrode has a critical influence on the state of the image to be formed. The adherence of the toner bearing static charge is one of the typical causes that degrade the controllability of the voltage in the control electrode. More specifically, the potential of the control electrode on the basis of the toner supported on the toner support varies to a potential different from that applied to the control electrode for image forming, due to the potential which is derived from the static charge on the toner adhering to the control electrode, with respect to the control electrode. For example, if a voltage that allows the passage of toner is applied to the control electrode, the actual voltage may vary or be close to a potential that prohibits the passage of toner, due to the static charge on the toner adhering to the control electrode, and hence no or only an insufficient amount of toner will transfer from the toner support to the paper. Resultantly, the condition of the image formed will be badly deteriorated with image defects, print failure, low contrast and reproduction failure of halftone images.
Adherence of the toner to the control electrode occurs on the surface thereof and the interior of the gates, due to electrically attractive force, typified by ‘image force’, as well as because the friction between the toner surface and the control electrode surface exceeds the electric force exerting on toner particles from the electric fields formed between the control electrode and the opposing electrode or formed between the control electrodes and the toner support. As a result, in order to remove the toner adhering on the control electrode, it is necessary to create a stronger electric field or urging force by a physical method.
In order to create a stronger electric field than that formed between the control electrode and the opposing electrode, it is necessary to apply a greater voltage to the opposing electrode or place the opposing electrode closer to the control electrode. However, creation of a stronger electric field between the control electrode and the opposing electrode requires additional components such as a high-voltage power source and its control circuits. On the other hand, an arrangement of placing the opposing electrode closer to the control electrode requires a device for shifting the opposing electrode toward the control electrode. In either case, it is impossible to avoid sharp increase in the size and cost of the apparatus due to an increased number of parts.
Because of the above reasons, Japanese Patent Application Laid-Open Hei 6 No. 218,981 discloses a configuration in which a bar having an opposing electrode at one end thereof is provided rotatably at the middle part thereof and the other end has a brush roller or scraper to be abutted against the surface of the control electrode. Other configurations than this, are also disclosed such as that having an adhesive tape selectively contacting the surface of the control electrode, that having an air stream generating means for blowing an air stream onto the surface of the control electrode, and that having a vibrating means for vibrating the control electrode.
However, any of the configurations disclosed in Japanese Patent Application Laid-Open Hei 6 No. 218,981 cannot avoid the problem of increase in the size and cost of the apparatus due to an increased number of parts. Further, when adhering toner is removed from the control electrode by blowing an air stream over the surface of the control electrode or vibrating the control electrode, an extensive area other than the control electrode inside the apparatus will be stained with toner.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an image forming apparatus which can reliably avoid deterioration of the condition of formed images, by definitely removing toner adhering to the control electrode by a simple configuration without sharp increase in the size and cost of the apparatus.
The present invention has been devised to attain the above object and is configured as follows:
In accordance with the first aspect of the invention, an image forming apparatus includes:
a supporting medium for supporting the electrified developer;
an opposing electrode spaced a predetermined distance apart from the supporting medium and disposed facing the supporting medium; and
a control electrode disposed between the supporting medium and the opposing electrode and having a plurality of gates which form passage for the developer particles, wherein the image forming apparatus forms a visual image on a recording medium conveyed between the opposing electrode and the control electrode whilst varying the potential applied to the control electrode so as to selectively control transfer of the developer particles through the gates, and is characterized in that
Matsumoto Yoshitaka
Wakahara Shirou
Conlin David G.
Daley, Jr. William J.
Dike Bronstein, Roberts & Cushman LLP
Le N.
Nguyen Judy
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