Typewriting machines – Miscellaneous
Reexamination Certificate
1999-02-19
2002-08-27
Hirshfeld, Andrew H. (Department: 2854)
Typewriting machines
Miscellaneous
C347S055000, C347S141000
Reexamination Certificate
active
06439788
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an image forming apparatus for allowing toner to fly in a direction from a toner carrier to a counter electrode so as to directly form an image on a sheet transported between the toner carrier and the counter electrode. The image forming apparatus is applicable to various devices such as a printing section of a digital copying machine and a facsimile device, a digital printer, and a plotter.
BACKGROUND OF THE INVENTION
Conventionally, as an image forming apparatus for forming a visible image in accordance with an image signal on a recording medium such as paper, for example, the apparatus as disclosed in Japanese Unexamined Patent publication No. 211970/1992 (Tokukaihei 4-211970) has been available. The image forming apparatus (electrographic printer) as disclosed in this publication is provided with, as shown in
FIG. 31
, a development roller
102
and a background electrode
103
. The development roller
102
is a carrier for carrying pigment particles
101
such as toner. The background electrode
103
is a counter electrode facing the development roller
102
. To the background electrode
103
is applied a potential for drawing the pigment particles
101
in the direction towards the background electrode
103
. towards the background electrode
103
.
Between the development roller
102
and the background electrode
103
is provided an electrode matrix
104
(control electrode section) having a plurality of passages
105
. The electrode matrix
104
is provided with electrodes, corresponding one to one to the passages
105
, for controlling the electric field between the electrode matrix
104
and the development roller
102
. The passage of the pigment particles
101
through each passage
105
is controlled by these electrodes corresponding to the passages
105
.
Namely, in this type of image forming apparatus, flying of pigment particles
101
is controlled (allowed or prevented) by the electrode matrix
104
under a strong electric field generated between the development roller
102
and the background electrode
103
. This allows the pigment particles
101
held on the development roller
102
to pass through predetermined passages
105
to reach a sheet
106
transported between the electrode matrix
104
and the background electrode
103
, thus directly forming an image made of the pigment particles
101
on the sheet
106
.
Therefore, the above image forming apparatus omits a developing medium, such as a photoreceptor for carrying an electrostatic image or toner image in accordance with an image signal, and a dielectric drum for temporarily carrying a toner image before transfer of the toner image formed on a photoreceptor onto a sheet takes place. This reduces the number of components and simplifies the structure of the apparatus, thus realizing a more compact and less expensive apparatus with ease. Also, because the transfer process from the developing medium to the sheet is omitted, the image is prevented from deterioration, and the reliability of the image forming apparatus is improved.
The following describes the problems associated with the above image forming apparatus. To begin with, two arbitrary electrodes of the electrodes formed on the electrode matrix
104
, corresponding to the passages
105
are electrodes
104
m
and
104
n
. Here, for example as shown in
FIG. 32
, when an image signal is simultaneously applied to the electrodes
104
m
and
104
n
, for example, an ON potential of 150 V is applied to each of the electrodes
104
m
and
104
n
for a predetermined period in synchronization with the image signal, and then, for example, an OFF potential of −200 V is applied to the each of the electrodes
104
m
and
104
n.
Incidentally, at the moment when the ON potential or OFF potential is applied to a single electrode, that is, at the moment when the potential applied to a single electrode is switched to the ON potential or to the OFF potential, typically, a transient current of, for example, about 140 &mgr;A flows through each electrode. Namely, as shown in
FIG. 33
, for example, in the case where the ON potential is simultaneously applied to the two electrodes
104
m
and
104
n
in accordance with the image signal, a total of about 280 &mgr;A of transient current is supplied as a peak current at one instant from a power source.
While such a transient current is minute through one to several electrodes, it amounts to a huge value when the ON potential is simultaneously applied to several hundreds to several thousands of electrodes, as in the case of carrying out solid-black printing for example. More specifically, for example, supposing
2560
electrodes are provided on the electrode matrix
104
, corresponding to the passages
105
, when the ON potential is simultaneously applied to these electrodes, a transient current of 358.4 mA (140 &mgr;A×2560=358400 &mgr;A=358.4 mA) is supplied from the power source at one instant.
Here, it is not generally preferable to adopt a power source having a large current capacity capable of supplying a transient current of, for example, 70 mA or more, as a power source for applying a high voltage such as the ON and OFF potentials to the matrix electrode
104
. This is because when the current capacity is large, in the event of accident, such as a high voltage leak in which the high voltage applied to the electrode matrix
104
is leaked via sheet
106
as the sheet
106
is brought into contact with the electrode matrix
104
when printing, and malfunctioning of the apparatus, the output potential does not drop due to the fact that the current supplying ability of the power source is large, and as a result the high voltage flows into other circuits, causing troubles such as destruction of the circuits. Also, when other devices, such as a computer, are connected to the image forming apparatus, such devices may be destroyed as well. Further, in the worst case, if the user happens to be touching the image forming apparatus, the user may be electrified by the occurrence of such an event.
To prevent such an accident, a high-level insulation may be provided for the parts of the apparatus to which the high-voltage is applied or even for the entire apparatus. Yet, this is not preferable because of the high cost associated with this action.
Thus, the conventional image forming apparatus has the problem that when the number of electrodes on the electrode matrix
104
is large, a transient current exceeding an acceptable value is supplied from the power source, and as a result reliability of the apparatus is lowered.
Also, because a power source having a large current capacity is required, another problem is presented that the size and cost of the apparatus are increased. This problem especially becomes serious when the image forming apparatus is compliant with printing of large sheet
106
or has high resolution. Further, in a high-speed image forming apparatus, the number of times the apply potential is switched per unit time becomes larger, and this necessitates a power source capable of supplying even larger transient current, causing the foregoing problems as well.
SUMMARY OF THE INVENTION
The present invention offers a solution to the above-mentioned problems, and accordingly it is an object of the present invention to provide an image forming apparatus which does not require a power source having a large current capacity even when the number of control electrodes is large, and thus capable of reducing the size and cost of the apparatus and also improving reliability of the apparatus.
In order to solve the above-mentioned problems, an image forming apparatus in accordance with the present invention includes: a carrier for carrying developer particles; a counter electrode positioned so as to face the carrier; a control electrode section having a plurality of passage pores constituting a passage of developer particles flying from the carrier to the counter electrode, and a plurality of gate electrodes formed one to one around the plural
Masuda Kazuya
Wakahara Shirou
Yoshinaga Hajime
Conlin David G.
Dike Bronstein Roberts & Cushman
Hirshfeld Andrew H.
Manus Peter J.
Sharp Kabushiki Kaisha
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