Electrophotography – Control of electrophotography process – Of plural processes
Reexamination Certificate
2001-05-11
2003-01-28
Tran, Hoan (Department: 2852)
Electrophotography
Control of electrophotography process
Of plural processes
C399S072000
Reexamination Certificate
active
06512898
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus, such as an electrophotographic apparatus.
2. Related Background Art
Of the various systems employed for image forming apparatuses, including electrophotographic systems, thermal transfer systems and ink-jet systems, the electrophotographic systems, which, above all, supply higher speeds, better image quality and lower noise, are demonstratively superior to the others and are widely employed.
But among the electrophotographic systems, variations also exist, and include, for example: conventionally known multiple transferring systems and intermediate transferring member systems; multiple developing systems, for superimposing color images on the surfaces of photosensitive members and collectively transferring the images to form final images; and in-line systems, for arranging in series multiple image forming means (process stations) employing different colors and for transferring developed images to transferring materials using transfer belts.
Of these electrophotographic systems, the in-line systems are superior because they provide high processing speeds and because, since they require only a small number of transfer revolutions, there is less deterioration of the quality of the images they produce.
FIG. 20
is a diagram showing the partial configuration of a conventional image forming apparatus that uses an in-line system. In
FIG. 20
, an electrostatic adsorption transfer belt (hereinafter referred to as an ETB)
1
is fitted around a drive roller
7
, an opposite adsorption roller
6
and tension rollers
8
and
9
, and is rotated in the direction indicated by an arrow.
Process stations
201
(yellow),
202
(magenta),
203
(cyan) and
204
(black), which are processors that correspond to components of the invention, are arranged in series, and photosensitive members at the process stations
201
to
204
maintain contact with transferring rollers
3
via the ETB
1
.
An adsorption roller
5
, which is located upstream of the process stations, maintains contact with the opposite adsorption roller
6
. A bias is applied to a transferring material that is passed through a nip formed by the adsorption roller
5
and the opposite adsorption roller
6
, and while electrostatically attracted to the ETB
1
, the transferring material is conveyed in the direction indicated by the aforementioned arrow.
The design of the conventional ETB
1
provides for a surface layer composed of urethane rubber, wherein a fluorocarbon resin such as PTFE, for example, is diffused, to be deposited on a base layer that is formed of a resin film, such as PVdF, ETFE, polyimido, PET or polycarbonate, having a thickness of 50 to 200 &mgr;m and a volume resistivity of 10
9
to 10
16
&OHgr;cm, or on rubber, such as EPDM, having a thickness of 0.5 to 2 mm.
The image forming processing will now be described. First, the image forming process performed by a process station will be explained while referring to FIG.
21
.
FIG. 21
is a diagram showing the configuration of one of the process stations with which the image forming apparatus in
FIG. 20
is equipped. The yellow process station
201
is employed in this explanation; however, the same process is performed by the other process stations.
In the configuration of the process station in
FIG. 21
, a photosensitive member
211
, which is an image bearing member that corresponds to a component of the invention, is uniformly electrified by an electrifier
212
, electrification means that corresponds to a component of the invention. A latent image is formed on the photosensitive member
211
by the emission of a scan light
214
by a light exposure system
213
.
This latent image is developed by a developing roller
215
, which corresponds to a developing device component of this invention, using toner contained in a toner container
216
, and a toner image is formed on the photosensitive member
211
. Residual toner, which is not transferred during a transferring process that will be described later, is scraped off by a cleaning blade
217
and is collected in a waste toner container
218
.
The transferring process will now be described. When an OPC photosensitive member having a negative polarity is employed as the photosensitive member, the commonly employed inverted developing system uses negative toner to develop the light exposed portion. Therefore, a positive transfer bias is applied to the transferring roller
3
by a bias power source
4
. In this case, a low resistant roller is generally employed as the transferring roller
3
.
In the actual printing process, while taking into account the speed at which the ETB
1
moves and the distance between the transferring positions of the process stations, the image forming and transferring process for the process stations and the conveying of the transferring material are performed at a timing whereat the positions of the individual color toner images formed on the transferring material are matched, and after the transferring material has been passed through all the process stations
201
to
204
, a toner image is formed on the transferring material. After the formation of the toner image on the transferring material is completed, the transferring material is passed through a well known fixing apparatus (not shown), and the toner image is fixed thereon.
After the above process has been completed, the ETB
1
is de-electrified by a charging/charge eliminating device
11
, and is ready for the next print process.
The image density varies depending on the temperature and humidity conditions whereunder the image forming apparatus is used, and the usage condition of the process stations. In order to compensate for image density changes, control of image density is exercised. The image density control process will now be described.
To control image density, conventionally, means is employed for forming density patch images of individual colors on the photosensitive member, an intermediate transferring member (hereinafter referred to as an ITB) or the ETB, and for permitting a density sensor
13
, which is a detection means component of the invention, to read the density patch images and feed them back to the process forming condition, such as a high voltage condition or the power for a laser, so that the maximum densities of the individual colors and the halftone characteristics match.
Generally, the density sensor
13
employs a light source to irradiate the density patch, and employs a light receiving sensor to detect the intensity of reflected light. A/D conversion is performed for the signal indicating the intensity of the reflected light, and the obtained signal is processed by a CPU
15
, which constitutes means for controlling detection pattern forming means, which is a component of the invention, and the image forming condition, and the results are fed back to the process forming condition.
The image density control process has the objectives of constantly maintaining maximum individual color densities (hereinafter referred to as Dmax control) and of linearly maintaining the halftone characteristic of an image signal (hereinafter referred to as Dhalf control).
Dmax control can effectively maintain a constant balance between the individual colors, and can prevent dispersion or a color-superimposed character fixing failure due to the piling up of too much toner.
Specifically, in the Dmax control process, multiple density patches formed under different image forming conditions are detected by an optical sensor, a condition wherein a desired maximum density can be obtained is calculated by using the detection results, and the image forming condition is changed. In most cases, it is preferable that the density patch be formed using halftone.
For this reason, when a so-called solid image is detected, the width of a change in the sensor output relative to a change in the toner quantity is reduced, and satisfactory detection accuracy can not be obtained.
During the Dhalf control process, image pro
Fitzpatrick ,Cella, Harper & Scinto
Tran Hoan
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