Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1998-01-30
2001-01-09
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06170935
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to an image forming apparatus which forms images on the recording medium by causing the developer to jump thereto and can be applied to a printer unit in digital copiers and facsimile machines as well as to digital printers, plotters, etc.
(2) Description of the Prior Art
In recent years, as the image forming means for outputting a visual image on recording medium such as recording paper etc., in response to an image signal, image forming apparatuses have been disclosed in Japanese Patent Application Laid-Open Hei 4 No. 269,563, Japanese Patent Application Laid-Open Hei 6 No. 286,203 and Japanese Patent Application Laid-Open Hei 8 No. 99,433, for example, wherein charged particles are placed in an electric field so that they will jump by electric force to adhere to the recording medium whilst the potential to be applied to the control electrode having a number of passage holes located in the jump passage is being varied, to thereby form a latent image on the recording medium, directly.
In the above prior art, the aforementioned control electrode uses a configuration which has a plurality of electrodes and feeder lines and has an electrode having a function of shielding the electrical influence from the electrodes and feeder line from the toner support, or a configuration in which jumping toner is controlled based on matrix control.
FIG. 1
is a schematic diagram showing main components of a conventional image forming apparatus. This apparatus includes an image forming unit
1
having a toner supplying section
2
and a printing section
3
. Toner supplying section
2
in image forming unit
1
is composed of a toner storage tank
20
for storing toner
21
as the developer, a toner support
22
of a cylindrical sleeve for magnetically supporting toner
21
, a doctor blade
23
which is provided inside toner storage tank
20
to electrify toner
21
and regulate the thickness of the toner layer carried on the peripheral surface of toner support
22
. Doctor blade
23
is placed on the upstream side with respect to the rotational direction of toner support
22
.
Toner support
22
rotates in the direction of arrow A in the figure. Instead of supporting toner
21
bymagnetic force, toner support
22
is configured so as to support the toner by electric force or combination of electric and magnetic forces. Toner
21
supported on the peripheral surface of toner support
22
is made to stand up in ‘spikes’ at the area on the peripheral surface facing control electrode
26
.
Printing section
3
in image forming unit
1
includes: an opposing electrode
25
facing the peripheral surface of toner support
22
; a high-voltage power source
30
for supplying a high voltage to opposing electrode
25
; a control electrode
26
provided between opposing electrode
25
and toner support
22
; a charge erasing brush
28
; a charging brush
8
for charging a sheet of paper
5
; a dielectric belt
24
; support members
16
a
and
16
b
for supporting dielectric belt
24
; and a cleaner blade
19
. Applied between opposing electrode
25
and toner support
22
is a high voltage which produces an electric field needed to make toner
21
carried on toner support
22
jump toward opposing electrode
25
.
Control electrode
26
is disposed in parallel to the tangent plane of the surface of opposing electrode
25
and spreads two-dimensionally facing opposing electrode
25
, and it has a structure to permit the toner to pass therethrough from toner support
22
to opposing electrode
25
. The electric field formed between toner support
22
and opposing electrode
25
varies depending on the potential being applied to control electrode
26
, so that the jumping of toner
21
from toner support
22
to opposing electrode
25
is controlled.
Control electrode
26
is composed of an insulative board
26
a
, a high voltage driver (not shown), independent annular conductors, i.e., annular electrodes
27
and a shield electrode
39
. Board
26
a
has holes forming gates
29
, to be mentioned later, formed therein. Annular electrodes
27
are formed of copper foil, for instance, and are arranged around the individual holes in a predetermined layout. Each opening of the annular electrode forms a passage for toner
21
to jump from toner support
22
to opposing electrode
25
. Hereinbelow, this passage will be termed gate
29
. Shield electrode
39
is also formed of copper foil with an insulative layer
26
b
on the surface thereof, and is disposed on the toner support
22
side with respect to insulative board
26
a
. Configurations having such a shield electrode are disclosed in Japanese Patent Application Laid-Open Hei 4 No. 269,563 and Japanese Patent Application Laid-Open Hei 6 No. 286,203. Japanese Patent Application Laid-Open Hei 8 No. 99,433 disclosed a configuration in which jumping of toner is controlled by the control electrode which is driven by matrix control.
The aforementioned shield electrode
39
is provided to prevent toner
21
adhering to control electrode
26
. Unless control electrode
26
has this shield electrode
39
, it is impossible to avoid adherence of toner
21
to control electrode
26
. If adherence of toner
21
to control electrode
26
occurs, the following defects arise.
In order to illustrate this situation, a control
26
without any shield electrode
39
is illustrated in
FIG. 2
, which is a sectional view of a control electrode having no shield electrode. First, a voltage which inhibits toner
21
from jumping (to be referred to hereinbelow as the OFF potential) is supplied to annular electrodes
27
. In this state, when toner
21
is made to jump to gates
29
, a voltage which causes toner
21
to jump (to be referred to hereinbelow as the ON potential) is applied to make toner
21
jump. In this case, as shown in
FIG. 3
, toner
21
jumps; some toner
21
a
passes through gates
29
, other toner
21
b
jumps to areas other than gates
29
, i.e., toward the surface of control electrode
26
.
Normally, this toner
21
b
will return to toner support
22
when annular electrodes
27
are set at the OFF potential, but some of it, i.e., toner
21
c
as shown in
FIG. 4
remains adhering to the control electrode
26
. If toner
21
c
adheres to control electrode
26
, the apparent potential of control electrode
26
relative to that of toner
21
on toner support
22
varies due to the charge on toner
21
c
. Illustratively, the potential of control electrode
26
tends to vary in such a way as to become close to the voltage for inhibiting toner
21
from jumping, thus making it difficult for the toner to jump. Further, even if a voltage for causing the toner to jump is applied to control electrode
26
, toner
21
on toner support
22
does not receive attraction from the electric field for jumping and the desired transfer of toner will not occur. In this case, the resulting image will not have correct density, presenting a dim, blurred state without contrast. In this condition, a desired reproduction of halftones cannot be obtained, making it difficult to form a correct image. Further, in the case of a color image forming apparatus, proper reproduction of colors cannot be obtained because proper amounts of toners cannot transfer.
Furthermore, if the situation of the toner adherence to control electrode
26
becomes worse, the toner jumping becomes more difficult, and finally in the worst case no toner will jump. This causes image defects and difficulty in reproducing color images in the case of a color image forming apparatus.
Besides, if adhering toner
21
c
has adhered to the gate interior, the gate will become clogged as toner
21
c
builds up, causing physical difficulty in toner jumping. In this state, no dots can be formed causing printing deficiency and/or image defects.
As above, adherence of toner
21
c
at the gates and their vicinity, directly causes the above deficiencies. On the other hand, if toner
21
adheres to the areas other than gates
29
, the following defects
Adachi Katsumi
Honda Iwakazu
Nishio Yukihito
Wakahara Shirou
Barlow John
Conlin David G.
Daley, Jr. William J.
Dike Bronstein, Roberts & Cushman LLP
Gordon Raquel Yvette
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