Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry
Reexamination Certificate
1997-11-03
2001-05-15
Grant, II, Jerome (Department: 2624)
Facsimile and static presentation processing
Facsimile
Specific signal processing circuitry
C358S461000
Reexamination Certificate
active
06233062
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an image processing device used for a digital copying machine, a computer printer or a network printer and the like, and an image forming apparatus having the image processing device as an image input unit and an image processing unit.
In a large number of image forming apparatuses currently commercialized such as digital copying machines, computer printers or network printers, the electrophotography method capable of obtaining an output image of high quality at high speed as the image output unit (image output device) has widely been employed.
In the electrophotography method, as development means, there is widely used the two-component magnetic brush development in which insulating toner is charged by mixing the insulating toner with magnetic particles and causing friction in a developer unit, developer is formed in a brush shape on a development roll by means of magnetic force, and the developer is supplied on a photosensitive member by the rotation of the development roll to thereby develop an electrostatic latent image on the photosensitive member. This two-component magnetic brush development is more widely used especially for color image forming apparatuses.
However, in the image output unit of this electrophotographic type, especially in the image output unit using the two-component magnetic brush development, when two image portions having different density in the subscanning direction are continuous, there arises a phenomenon in which the density of their one image portion at the boundary portion between it and the other image portion lowers because of the non-linear and asymmetric image output characteristics in the subscanning direction.
This phenomenon has two types, one of which is that when an image outputted changes from a half tone portion
1
to a background portion
2
in a subscanning direction orthogonal to a main scanning direction which is a scanning direction of a light beam for forming an electrostatic latent image on the photosensitive member as shown in FIG.
17
(A), the density at the rear end portion
1
B of the half tone portion
1
in contact with the background portion
2
lowers. Hereinafter, this is referred to as decrease in the density at the half tone portion.
The other is that when an image outputted changes from a low density portion
12
L to a high density portion
13
H in the subscanning direction, the density at the rear end portion
12
W of the low density portion
12
L in contact with the high density portion
13
H lowers as shown in FIG.
17
(B). Hereinafter, this is referred to as decrease in the density at the low density portion.
According to the electrophotography method using the two-component magnetic brush development, as shown in
FIG. 18
, a photosensitive drum
310
is charged by an electrostatic latent image forming charger
320
by the rotation of the photosensitive drum
310
in a direction indicated by an arrow
311
, and laser light L modulated through an image signal is irradiated onto the photosensitive drum
310
thus charged to thereby form an electrostatic latent image on the photosensitive drum
310
. The photosensitive drum
310
, on which the electrostatic latent image has been formed, comes into contact with a developer layer
337
on the surface of a development sleeve
335
which rotates at linear speed approximately twice the linear speed of the photosensitive drum
310
in a direction indicated by an arrow
336
, whereby the toner within the developer layer
337
adheres to a latent image portion on the photosensitive drum
310
so that the electrostatic latent image on the photosensitive drum
310
is developed into a toner image.
FIG.
18
(A) shows a state in the moment a latent image portion
3
of the half tone portion
1
is formed on the photosensitive drum
310
by the irradiation of the laser light L so that its front edge
3
f
comes into contact with the developer layer
337
, FIG.
18
(B) shows a state in the moment a portion somewhat on this side of the rear edge
3
b
of the latent image portion
3
comes into contact with the developer layer
337
, and FIG.
18
(C) shows a state in the moment the rear edge
3
b
of the latent image portion
3
comes into contact with the developer layer
337
.
The developing bias at a potential of, for example, −500 V is applied to the development sleeve
335
. The photosensitive drum
310
is charged at a potential of, for example, −650 V, having a higher absolute value than the developing bias potential by the charger
320
, and the latent image portion
3
of the half tone portion
1
is charged at a potential of, for example, −200 V, a lower absolute value than the developing bias potential. Also, a portion
4
corresponding to the background portion
2
behind the half tone portion
1
is charged at a potential of −650 V having a higher absolute value than the developing bias potential.
When the front edge
3
f
of the latent image portion
3
comes into contact with the developer layer
337
as shown in FIG.
18
(A), a forward development field is applied to toner tq which exists at a position Q where the photosensitive drum
310
comes into contact with the developer layer
337
so that the toner tq is brought close to the surface of the developer layer
337
to adhere to the latent image portion
3
. When, however, a portion
4
corresponding to the background portion
2
behind the half tone portion
1
is brought close to the developer layer
337
as shown in FIG.
18
(B), toner tb which exists in a portion of the developer layer
337
facing to the portion
4
is spaced apart from the surface of the developer layer
337
by the development field in the reverse direction to get into the depths of the developer layer
337
.
By the rotation of the development sleeve
335
in the direction indicated by the arrow
336
, its toner tb is brought closer to the position Q, where the photosensitive drum
310
comes into contact with the developer layer
337
, and at the same time, moves to the surface side thereof because of the low potential at the latent image portion
3
, but some delay occurs to reach the surface of the developer layer
337
. For this reason, when the portion somewhat on this side of the rear edge
3
b
of the latent image portion
3
comes into contact with the developer layer
337
as shown in FIG.
18
(B), the amount of toner adhering to the photosensitive drum
310
starts to decrease so that the density at the rear end portion
1
B of the half tone portion
1
in contact with the background portion
2
lowers as shown in FIG.
17
(A).
If the front of the half tone portion
1
is also the background portion, also when the front edge
3
f
of the latent image portion
3
comes into contact with the developer layer
337
as shown in FIG.
18
(A), there arises, in the toner in the developer layer
337
, toner which is kept away from the surface of the developer layer
337
by a portion
5
on the photosensitive drum
310
corresponding to the background portion ahead as shown by toner tf.
By the rotation of the development sleeve
335
in the direction indicated by the arrow
336
, however, the toner tf is rapidly kept away from the position Q, where the photosensitive drum
310
comes into contact with the developer layer
337
, and at the same time, the toner tq brought close to the surface of the developer layer
337
because of the low potential at the latent image portion
3
approaches the position Q immediately to adhere to the latent image portion
3
. Therefore, even if the image outputted changes from the background portion to the half tone portion
1
on the contrary in the subscanning direction, the density at the front end portion of the half tone portion
1
in contact with the background portion does not lower.
Also, as regards decrease in the density at low density portion, FIG.
19
(A) shows a state in the moment a latent image portion
32
L of the low density portion
12
L is formed on the photosensitive drum
310
by the irradiation
Iwaoka Kazuhiro
Kato Nobuyuki
Kubo Masahiko
Shinohara Koichiro
Takamatsu Masahiro
Fuji 'Xerox Co., Ltd.
Grant II Jerome
Oliff & Berridg,e PLC
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