Electrophotography – Control of electrophotography process – Of plural processes
Reexamination Certificate
2002-01-22
2004-09-28
Braun, Fred L. (Department: 2852)
Electrophotography
Control of electrophotography process
Of plural processes
Reexamination Certificate
active
06799001
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an image forming apparatus using an electrophotographic system, a cartridge detachably mountable to a main body of the image forming apparatus, which is to say a process cartridge, and to a developing apparatus constructed as a cartridge.
In this case, examples of the electrophotographic image forming apparatus include an electrophotographic copying machine, an electrophotographic printer (for instance, an LED printer, a laser beam printer, and the like), an electrophotographic facsimile apparatus, and the like.
Also, the cartridge detachably mountable to the main body of the electrophotographic image forming apparatus is a cartridge including at least one of an electrophotographic photosensitive body, a charging means for charging the electrophotographic photosensitive body, a developing means for supplying developer to the electrophotographic photosensitive body, and a cleaning means for cleaning the electrophotographic photosensitive body. In particular, the process cartridge integrally combines the electrophotographic photosensitive body with at least one of the charging means, the developing means, and the cleaning means into a cartridge detachably mountable to the main body of the electrophotographic photosensitive body. Alternatively, the process cartridge integrally combines at least the developing means with the electrophotographic photosensitive body into a cartridge detachably mountable to the main body of the electrophotographic image forming apparatus.
2. Related Background Art
An example of a conventional electrophotographic image forming apparatus is shown in FIG.
12
. In this drawing, the image forming apparatus includes a photosensitive drum
101
as an electrophotographic photosensitive body to which an organic photosensitive body (organic photo-conductor) is applied or a photo-conductive body made of A—Si, Cds, Se, or the like on the outer peripheral surface of an aluminum cylinder. This photosensitive drum
101
is driven by an unillustrated driving means in a direction indicated by the illustrated arrow and is uniformly charged at a predetermined potential by a roller charger
102
that is a charging means.
In the upper portion of the main body of the apparatus, there are disposed a laser diode
111
that constitutes an exposing apparatus as an electrostatic latent image forming means, a polygon mirror
109
that is rotatably driven by a high speed motor
108
, a lens
110
, and a return mirror
107
.
When an image signal is inputted into a laser driver
112
, the laser driver
112
causes the laser diode
111
emit light. Then, the light having optical information corresponding to the image signal travels along an optical path
113
and irradiates the photosensitive drum
101
, thereby forming an electrostatic latent image. Further, when the photosensitive drum
101
is rotated in the arrow direction, this electrostatic latent image is developed by a developing apparatus (developing means)
104
, thereby obtaining a toner visible image. The toner visible image obtained by the development is transferred onto transferring paper P, which is a transferring material, by a transferring roller
103
that is a transferring means to which a predetermined bias is applied. The transferring paper P is conveyed by a convey means to a fixing apparatus
105
, and the toner visible image is melted and fixed by the fixing apparatus
105
. In this manner, there is obtained a permanent image.
On the other hand, residual toner on the photosensitive drum
101
is removed by a cleaning apparatus
106
such as a fur brush or a blade means.
By the way, in an image forming apparatus that uses an electrophotographic system and outputs a gradation image, there generally exists a relation between inputted image signals and outputted images, that is, there exists a gradation characteristic, as shown in FIG.
13
. If this default gradation characteristic is used as it is, it is impossible to obtain a high-quality image in the usual cases. Therefore, in actual cases, before being inputted into the laser driver
112
, the image signals are adjusted by referring to a look-up table (hereinafter referred to as the “LUT”) formed in a RAM within a memory
121
so that the gradation characteristic becomes an appropriate relation such as a linear relation. To do so, halftone control is performed by experimentally forming toner images (hereinafter referred to as the “patch patterns”) used to detect image densities on the photosensitive drum
101
from all image signals that can be dealt with, detecting densities of these toner images using an optical density sensor
122
or the like, obtaining a present gradation characteristic of the image forming apparatus from the detection results, and creating an LUT according to the obtained present gradation characteristic. This makes it possible to obtain a desired gradation characteristic with precision.
In more detail, in
FIG. 12
, a CPU
120
inputs signals for forming the patch patterns into the laser driver
112
, and then visualized images are formed on the photosensitive drum
101
. The optical density sensor
122
detects the visualized images, and an LUT is created in the RAM within the memory
121
functioning as a storage means according to the detection results.
By detecting the patch patterns formed on the photosensitive drum
101
using the optical density sensor
122
in this manner, it becomes possible to directly correct the relations between image signals and images formed on the photosensitive drum
101
using the LUT. However, images that are finally obtained the are images transferred from the photosensitive drum
101
onto the transferring paper P. Therefore, in actual cases, with consideration given to a transfer efficiency during this image transfer, correction amounts given by the LUT are determined so that there can be finally obtained correct relations between the image signals and the images on the transferring paper P.
Also, the correction performed using the LUT is a halftone correction and therefore, if the maximum value of a density of an image to be printed varies, it becomes difficult to perform correction using the LUT. In view of this problem, there is used a method with which prior to the halftone correction, a patch pattern used to detect the maximum density is additionally formed on the photosensitive drum
101
and a developing bias voltage applied to the developing apparatus
104
and a bias voltage applied to the charging means
102
for charging the photosensitive drum
101
are adjusted according to a detection result of the patch pattern. In this manner, the maximum density is corrected.
In actual cases, like the halftone correction, this maximum density correction is also performed by determining a target value for the density of the patch pattern on the photosensitive drum
101
with consideration given to the transfer efficiency during the final transfer of the toner image onto the transferring paper P.
However, if the density detection is performed by forming a patch pattern at a place other than the transferring paper P in this manner, when the transfer efficiency to the transferring paper P varies due to endurance, that is, due to an extended period of use of the apparatus, there occurs a problem that even though the toner image density on the photosensitive drum
101
is properly corrected, the final image on the transferring paper varies due to the endurance.
In particular, in the case of a full-color image forming apparatus that forms a full-color image using toner in four colors, variations of halftone densities result in variations of hues. Consequently, the stated problem becomes more serious than in a case of a monochrome image forming apparatus.
As a method of preventing this problem, there is a method with which the halftone correction and the maximum density correction described above are performed by directly transferring the aforementioned patch patterns onto transferring paper and detecting t
Funatani Kazuhiro
Takeuchi Akihiko
Braun Fred L.
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
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