Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2002-07-16
2003-05-20
Gordon, Raquel Yvette (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06565194
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an image forming method and an image forming apparatus each for use in a copier, a facsimile, a printer, or the like. In particular, it relates to image formation performed by controlling a developer jumping from a developer holding member to a rear electrode by means of a printhead controlled by an image signal and causing the developer to adhere to an image receiving member positioned between the printhead and the rear electrode.
BACKGROUND ART
With recent improvements in the performance of personal computers and recent advances in networking technology, there have been growing demands for printers with high processing abilities which can handle not only voluminous documents but also color documents. However, an image forming apparatus capable of outputting monochrome and color documents of sufficiently high quality and having a high processing speed is still under development, the advent of which has been expected.
As one of technologies which implement such a high-performance image forming apparatus, there has conventionally been known an image forming technology which causes a toner to jump onto a recording sheet or image-forming means such as an intermediate image holding belt under the effect of an electric field.
As examples of an image forming apparatus of this type, there have been known image forming apparatus disclosed in Japanese Examined Patent Publication No. SHO 44-26333, U.S. Pat. No. 3,689,935 (Japanese Examined Patent Publication No. SHO 60-20747), Japanese Domestic-Phase PCT Patent Application No. HEI 9-500842, and the like.
Referring to
FIG. 12
, a description will be given to an image forming apparatus proposed in the specification and drawings of Japanese Patent Application No. HEI 10-100780 as an example of a similar image forming apparatus. In
FIG. 12
,
31
denotes a grounded toner holding member for holding and transporting a charged toner,
32
denotes a regulating blade for controlling the toner in one to three layers on the toner holding member
31
,
33
denotes a supply roller for charging and supplying the toner to the toner holding member
31
, and
34
denotes a printhead formed with a toner passage hole
35
. A control electrode
36
is formed around the toner passage hole
36
. A voltage corresponding to an image signal is applied from a control power supply
37
, such as a driving IC, to the control electrode
36
.
38
denotes a rear electrode,
39
denotes a power supply for the rear electrode
38
, and
40
denotes receiving means such as a recording sheet transported on the rear electrode
38
.
In the arrangement, the supply roller
33
and the toner holding member
31
are operated such that a uniform toner layer is formed on the toner holding member
31
by means of the regulating blade
32
and transported. Under these conditions, a voltage is applied to the rear electrode
38
and a voltage corresponding to the image signal is applied from the control power supply
37
to the control electrode
36
in synchronization with the movement of the image receiving means
40
while it is moved. Consequently, the toner on the toner holding member
31
passes through the toner passage hole
35
in response to the image signal to jump onto the image receiving means
40
and form a required image thereon.
To form a fine image at, e.g., 600 dpi (a density of 600 dots per inch) on the entire surface of the image receiving means
40
, a plurality of toner passage holes
35
should be formed in the printhead
34
. Even if the toner passage holes
35
are arranged in a row, a fine image as mentioned above cannot be formed so that the toner passage holes
35
and the control electrodes
36
are arranged in a plurality of rows (e.g., eight rows in an example shown in the drawing), as shown in FIG.
13
. The toner passage holes
35
and the control electrodes
36
have, e.g., circular configurations. Connecting electrodes electrically connecting to each of the control electrodes
36
are provided on both sides of the toner holding member
31
to extend along the moving direction thereof for the prevention of mutual interference therebetween. Each of the connecting electrodes is connected to the lead of the control power supply
37
for outputting a control voltage, such as a driving IC.
Although the image receiving means
40
is composed of a recording sheet or the like such that an image is formed directly thereon in the exemplary structure shown in
FIG. 12
, the recording sheet or the like is disadvantageous in that the thickness thereof easily varies, the properties thereof easily change due to humidity, and it is prone to deformation during movement. In the case of color printing, it is difficult to synchronize the timings for image formations in different colors due to inconsistent transportation of the recording sheet so that image quality is likely to be lowered.
To prevent this, there are cases where an intermediate image holding belt is used preferably as the image receiving means
40
so that images formed on the image holding belt are transferred simultaneously onto a recording sheet or the like, as shown in the specification and drawings of, e.g., Japanese Patent Application No. HEI 10-100780.
Referring to
FIG. 14
, a description will be given to a structure using the image holding belt. In
FIG. 14
,
43
denotes an endless image holding belt as the image receiving means
40
which is composed of a resin film having conductive fillers dispersed therein and a resistivity of 10
10
&OHgr;cm. The image holding belt
43
is wound around a pair of rollers
44
a
and
44
b.
45
denotes a pickup roller for feeding out recording sheets
46
on a one-by-one basis from a sheet feed tray
50
.
47
denotes a timing roller for providing synchronism between the fed recording sheet
46
and the position of an image.
48
denotes a transfer roller for transferring a toner image formed on the image holding belt
43
onto the recording sheet
46
. The transfer roller
48
is pressed toward the roller
44
a
with the image holding belt
43
interposed therebetween, while a transfer voltage is applied thereto.
49
denotes a fixing unit for fixing the toner image to the recording sheet
46
by heating and pressing the recording sheet
46
having the toner image transferred thereon.
However, the foregoing image forming apparatus has the problem of so-called clogging. As the apparatus is used for a longer period, toner particles gradually clog the toner passage holes (printhead openings) and hamper precise recording. As a method for preventing clogging, there has been known one which cleans the openings of the printhead by ejecting the toner from the toner holding member (toner supplying member) through the printhead openings.
Specifically, there have been proposed a method of applying an ultrasonic wave to the printhead, a method of applying a voltage to an electrode provided on the printhead, a method of forcibly pressing the toner supplying member onto the printhead, and the like.
However, if the toner ejected for cleaning in accordance with the foregoing conventional methods is large in amount, the toner deposited on the rear electrode reaches the printhead to enter the printhead openings. If the toner is further ejected under this condition, the deposited toner presses the toner in the printhead openings so that the toner solidifies in the printhead openings. This leads to the problem that clogging is caused by the toner ejected for cleaning.
Clogging resulting from the deposition of the ejected toner presents a serious problem not only in the cleaning step but also on other occasions. For example, clogging as described above occurs when a driving system for the rear electrode is out of order or when a driving roller for the intermediate transfer belt skids and the intermediate transfer belt rotates free.
If the toner is ejected in the clogging state, the toner solidifies in the openings, which resultingly damages the printhead.
There is still another problem that, if the toner is deposited on the op
Itoh Taichi
Kitaoka Yoshitaka
Ogawa Katsutoshi
Saegusa Hiroshi
Gordon Raquel Yvette
Harness Dickey & Pierce PLC
Matsushita Electric - Industrial Co., Ltd.
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