Electrophotography – Control of electrophotography process – Of plural processes
Reexamination Certificate
2001-08-29
2003-01-07
Pendegrass, Joan (Department: 2852)
Electrophotography
Control of electrophotography process
Of plural processes
C399S055000
Reexamination Certificate
active
06505012
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus for forming images on recording materials such as sheet materials.
2. Description of the Related Art
A conventional image forming apparatus will be described with reference to
FIG. 8
, which is a sectional view of a conventional color image forming apparatus.
Referring to the drawing, a photosensitive drum
1
serving as an image bearing member is driven in the direction indicated by the arrow by a driving means (not shown); it is charged uniformly by a primary charger
2
.
Then, a laser beam L which is in conformity with an yellow image is applied to the photosensitive drum
1
from an exposure device
3
, whereby a latent image is formed on the photosensitive drum
1
.
As the photosensitive drum
1
further rotates in the direction of the arrow, a developing device
4
a,
containing yellow toner, of four developing devices
4
a
(yellow),
4
b
(magenta),
4
c
(cyan), and
4
d
(black) supported by a rotation supporting means
11
rotates to come to be opposed to the photosensitive drum
1
, and the image is visualized by the yellow developing device
4
a
selected.
An intermediate transfer belt
5
rotates in the direction of the arrow substantially at the same speed as the photosensitive drum. The toner image formed and borne on the photosensitive drum
1
undergoes primary transfer to the outer surface of the intermediate transfer belt
5
by a primary transfer bias applied to a primary transfer roller
8
a.
The above-described process is performed for the four colors: yellow (hereinafter referred to as Y), magenta (hereinafter referred to as M), cyan (hereinafter referred to as C), and black (hereinafter referred to as K), whereby a toner image of a plurality of colors is formed on the intermediate transfer belt
5
.
Next, a transfer material is fed with a predetermined timing from a transfer material cassette
12
by means of pick-up rollers
13
.
At the same time, a secondary transfer bias is applied to a secondary transfer roller
8
b,
and the toner image is transferred from the intermediate transfer belt
5
to the transfer material.
Further, the transfer material is conveyed by a conveyance belt
14
to a fixing device
6
, where fusion and fixing are effected, whereby a color image is obtained.
The toner remaining on the intermediate transfer belt
5
is removed by an intermediate transfer belt cleaner
15
.
On the other hand, the toner remaining on the photosensitive drum
1
is removed by a cleaning device
7
consisting of a well-known blade means.
When using the image forming apparatus described above, maintenance operations, such as toner replenishment, the disposal of waste toner, and the replacement of the photosensitive drum
1
when it has been worn.
In this example, the photosensitive drum
1
, the primary charger
2
, and the cleaning device
7
are integrated into a process cartridge A, and the developing devices
4
a,
4
b,
4
c,
and
4
d
are also in the form of a developing cartridge which is easily detachable with respect to the apparatus main body, so that the maintenance operations can be easily conducted by the user.
Generally speaking, in an electrophotographic image forming apparatus, fluctuations in the density characteristics of the printed image are caused by the fluctuations in characteristics due to the use environment, the developing device, the number of sheets on which printing has been effected by the photosensitive drum, the variation in sensitivity generated at the time of the production of the photosensitive drum, the variation in frictional charging characteristics generated at the time of the manufacturing of the toner, etc.
Although strenuous efforts have been put into stabilizing the characteristics in the variations and fluctuations, no satisfactory result has been achieved yet.
In particular, in a color image forming apparatus, it is necessary to adjust the conditions for the image formation in the four colors of Y, M, C, and K before the user can achieve a desired density and color balance.
In view of this, in the color image forming apparatus of this example, a plurality of toner images for detection are formed on the photosensitive drum
1
by varying the image forming condition stepwise, and the reflection light quantity thereof is measured by a density sensor
9
. On the basis of the result of the measurement, an image forming condition which is likely to provide a desired density (reflection light quantity) is computed by a CPU
17
of the main body for image density control.
Thus, the CPU
17
and the density sensor
9
correspond to image formation condition computing means constituting elements of the present invention used in the embodiment described below.
Next, the density sensor
9
will be described with reference to
FIG. 9
, which is a schematic view of the density sensor applied to the image forming apparatus shown in FIG.
8
.
The density sensor
9
is composed of a light emitting element
91
such as LED, a photoreceptor
92
such as a photo diode, and a holder
93
. Infrared radiation from the light emitting element
91
is applied to a patch P on the photosensitive drum, and the reflected light therefrom is measured by the photoreceptor
92
, whereby the density of the patch P is measured.
The reflected light from the patch P contains a regular reflection component and an irregular reflection component. The light quantity of the regular reflection component undergoes great fluctuations depending on the condition of the photosensitive drum surface underneath the patch and fluctuation in the distance between the sensor and the patch. Thus, when the reflected light from the patch to be measured contains a regular reflection component, the detection accuracy deteriorates to a marked degree.
In view of this, in the density sensor
9
, in order that no regular reflection component from the patch P may impinge on the photoreceptor
92
, the angle at which light is applied to the patch P is set to 45° and the reception angle of the reflected light from the patch P is set to 0° with respect to the normal I, thus measuring only the irregular reflection component.
Next, the image density control in the color image forming apparatus of this example will be described in detail.
First, the photosensitive drum
1
is charged by the primary charger
2
such that its surface potential becomes −600V.
The sensitivity of the photosensitive drum and the exposure amount of the laser are adjusted beforehand such that the potential of the laser exposure portion at normal temperature and normal humidity (23° C., 60% Rh) is approximately −200V.
The developing bias is obtained by superimposing a rectangular wave (with a frequency of 2000 Hz, 1800 Vpp) on a DC voltage, as shown in FIG.
10
. By making the DC voltage component Vdc variable, the toner development amount is controlled.
FIG. 10
is a graph depicting the developing bias applied to the image forming apparatus shown in FIG.
8
.
Further, prior to normal image formation, a plurality of toner image patches of 30 mm square are printed at intervals, as shown in
FIG. 11
, on the portion of the drum corresponding to the density sensor
9
.
FIG. 11
is a schematic diagram showing patches for density detection applied to the image forming apparatus shown in FIG.
8
.
The image patches are each developed by developing biases with different DC voltage components, and reflection light quantity measurement is performed on each of them by the density sensor
9
. In this example, the number of image patches is five, the DC component Vdc of the developing bias being varied from −300V to −500V in steps of 50V.
FIG. 12
shows an example of the result of reflection density measurement.
FIG. 12
is a graph showing the relationship between reflection density and developing bias in the image forming apparatus shown in FIG.
8
.
In this example, the target value of the reflection density of the toner (proper density value) is 1.4, and control is effe
Maebashi Yoichiro
Nakai Tomoaki
LandOfFree
Image forming apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Image forming apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Image forming apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3023076