Facsimile and static presentation processing – Static presentation processing – Attribute control
Reexamination Certificate
1999-09-02
2002-10-01
Grant, II, Jerome (Department: 2624)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C358S534000
Reexamination Certificate
active
06459502
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image formation device such as a digital copying machine, computer printer, or network printer, and an image processing device for such an image formation device.
2. Description of the Related Art
In most of the image formation devices currently available on the market, such as a digital copying machine, computer printer, or network printer, the electrophotographic system that allows acquisition of a high quality image with a high speed is widely adopted as an image output device.
In the electrophotographic system, the insulated toner and magnetic particles are mixed and rubbed in a developing roller to thereby electrify the insulated toner, the developing agent is formed in a brush on the developing roller by the magnetic force, and the developing agent is supplied onto the photosensitive structure by the rotation of the developing roller, whereby the static latent image is developed on the photosensitive structure. This method is called the two-component magnetic brush developing system, which is widely used in various fields and widely adopted especially in the color image formation device.
However, in the image output unit of this electrophotographic system, specially in the image output unit based on the two-component magnetic brush developing system, the density of the rear end area of the halftone area which borders on the background area decreases due to a non-linear and asymmetric output characteristic of the image output unit, when an outputted image varies from the halftone area to the background area in the sub-scanning direction.
That is, as shown in
FIG. 21A
, when the o utputted image varies from a halftone area
1
to a background area
2
in the sub-scanning direction being the reverse direction to the paper feeding direction, which is perpendicular to the main scanning direction of the laser beam for forming the static latent image on the photosensitive structure, the density of a rear end area
1
B of the halftone area
1
which borders on the background area
2
decreases on the reasons as shown hereunder.
As shown in
FIG. 22
, in the electrophotographic system using the two-component magnetic brush developing system, during the rotation of a photosensitive drum
310
along the direction of an arrow
311
, an electrifier
320
for forming the static latent image electrifies the photosensitive drum
310
, and the laser beam L modulated by an image signal irradiates the electrified photosensitive drum
310
, whereby the photosensitive drum
310
forms the static latent image thereon. The photosensitive drum
310
having the static latent image formed thereon comes in contact with a developing agent layer
337
on the surface of a developing sleeve
335
that rotates in the direction of an arrow
336
at about twice the linear velocity against that of the photosensitive drum
310
. Thereby, the toner in the developing agent layer
337
is affixed to a latent image portion on the photosensitive drum
310
, thereby developing the static latent image on the photosensitive drum
310
into the toner image.
FIG. 22A
illustrates a state at the moment when the irradiation of the laser beam L forms a latent image portion
3
corresponding to the halftone area
1
on the photosensitive drum
310
, and a forward edge
3
f
of the latent image portion
3
comes in contract with the developing agent layer
337
.
FIG. 22B
illustrates a state at the moment when a part slightly before a backward edge
3
b
of the latent image portion
3
comes in contract with the developing agent layer
337
.
FIG. 22C
illustrates a state at the moment when the backward edge
3
b
of the latent image portion
3
comes in contract with the developing agent layer
337
.
The developing sleeve
335
is given the developing bias of, for example, −500 V. The photosensitive drum
310
is electrified at the potential of, for example, −650 V by the electrifier
320
. The latent image portion
3
corresponding to the halftone area
1
is electrified at, for example, −200 V which is lower than the developing bias potential. The electrified potential of a part
4
corresponding to the background area
2
at the back of the halftone area
1
becomes −650 V which is higher than the developing bias.
As shown in
FIG. 22A
, when the forward edge
3
f
of the latent image portion
3
comes in contact with the developing agent layer
337
, a forward electric field for the developing bias is applied to toner tq lying at a position Q where the photosensitive drum
310
comes in contact with the developing agent layer
337
. The toner tq is pulled toward the surface of the developing agent layer
337
, and is affixed on the latent image portion
3
. However, as shown in
FIG. 22B
, when the part
4
corresponding to the background area
2
at the back of the halftone area
1
comes close to the developing agent layer
337
, toner tb lying at a part of the developing agent layer
337
which faces the part
4
is driven away from the surface of the developing agent layer
337
, and dives deep into the developing agent layer
337
.
While the developing sleeve
335
rotates in the direction of the arrow
336
, the toner tb approaches to the position Q where the photosensitive drum
310
comes in contact with the developing agent layer
337
, and moves toward the surface of the developing agent layer
337
due to the lower potential of the latent image portion
3
. However in this movement, there occurs a time delay for the toner to reach the surface of the developing agent layer
337
. Therefore, as shown in
FIG. 22B
, the amount of the toner affixed on the photosensitive drum
310
decreases from the moment when the part slightly before the backward edge
3
b
of the latent image portion
3
comes in contract with the developing agent layer
337
, and as mentioned above decreases the density of the rear end area
1
B of the halftone area
1
which borders on the background area
2
.
When the front of the halftone area
1
is also a background area and the forward edge
3
f
of the latent image portion
3
also comes in contact with the developing agent layer
337
, as shown by toner tf in
FIG. 22A
, some toner is driven away from the surface of the developing agent layer
337
by a part
5
on the photosensitive drum
310
corresponding to the front of the background area.
However, accompanied with the rotation of the developing sleeve
335
in the direction of the arrow
336
, the toner tf quickly moves away from the position Q where the photosensitive drum
310
comes in contact with the developing agent layer
337
. And at the same time, the toner tq pulled close to the surface of the developing agent layer
337
by the lower potential of the latent image portion
3
approaches the position Q immediately, and is affixed on the latent image portion
3
. Therefore, if the outputted image varies from the background area to the halftone area
1
in reverse to the sub-scanning direction, the density of the front end area of the halftone area
1
which borders on the background area does not decrease.
Thus, in the electrophotographic system using the two-component magnetic brush developing system, when the outputted image varies from the halftone area
1
to the background area
2
in the sub-scanning direction, the density of the rear end area
1
B of the halftone area
1
which borders on the background area
2
decreases due to the partial reduction from the average of the toner density on the surface of the developing agent layer
337
overlying the developing sleeve
335
. In this specification, this density reduction is called TED (Trail Edge Deletion).
This TED can be reduced to some extent by approximating the linear velocity of the developing sleeve
335
to that of the photosensitive drum
310
. However, even if the linear velocity of the developing sleeve
335
is made equal to that of the photosensitive drum
310
, it is difficult to completely annul TED and develop the toner with ampl
Hayashi Kazuto
Iwaoka Kazuhiro
Kubo Masahiko
Shinohara Koichiro
Takamatsu Masahiro
Fuji 'Xerox Co., Ltd.
Grant II Jerome
Morgan & Lewis & Bockius, LLP
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