Electrophotography – Control of electrophotography process – Control of developing
Reexamination Certificate
2002-03-08
2004-01-27
Grainger, Quana M. (Department: 2852)
Electrophotography
Control of electrophotography process
Control of developing
C399S044000, C399S048000
Reexamination Certificate
active
06684036
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus, such as a printer, a copy machine, a facsimile and so on.
The conventional image forming apparatus, such as a printer, a copy machine, a facsimile and so on, uses a so-called electrophotographic process, in which the surface of a photo conductor operating as an image carrier is uniformly charged, an image is exposed on the charged photo conductor surface for producing an electrostatic latent image thereon, a developer is supplied to the photo conductor carrying the electrostatic latent image for developing the electrostatic latent image, and a toner image thus formed on the photo conductor is transferred to a sheet of paper, an OHP sheet or a recording body, such as an intermediate transfer body, to obtain a printed image.
In an image forming apparatus of this kind, for the purpose of stably reproducing images with a high image quality over a long period of time, there is a known mechanism in which a patch is formed on the surface of the image carrier body before initiation of the printing operation, after the printing operation or during the printing operation, and various parameters associated with printing are controlled on the basis of the information obtained from the patch. Here, in the patch employed for such control, there are techniques for performing control using a “toner patch” formed by depositing toner on the image carrier body and a technique for performing control using a “potential patch” formed as a latent image, without depositing any toner.
In the case of the toner patch system, since a toner image has to be formed on the image carrier body, an extra amount of toner is consumed. Furthermore, since the toner patch subsequently has to be removed from the image carrier body, the load on the cleaning device of the apparatus tends to be increased.
In contrast to this, in the case of a potential patch, it is sufficient to form the latent pattern on the image carrier body during the charging step and exposure step to solve the problems set forth above. In this type of system, as disclosed in Japanese Patent Application Laid-Open No. Heisei 9 (1997)-230688, it is typical to provide a potential sensor for detecting the potential patch between the exposure device and the developer device for detecting the potential upstream of the developer device. However, when the a printing speed of the image forming apparatus is increased, a greater amount of developer has to be supplied to the image carrier body. As one approach to satisfy this requirement, a multiple stage developing roller system having a plurality of developing rollers has been employed. However, when such a multiple stage developing roller type developing device is employed, which results in an increase in the size of the apparatus, a difficulty is encountered in providing sufficient space for mounting a potential sensor between the exposure device and the developing device.
In addition, mounting the potential sensor between the exposure device and the developing device also is not always appropriate simply from the view point of increasing the printing speed. Namely, it is possible that the potential patch may pass below the potential sensor before the potential of the exposure portion drops down (decays) to the predetermined potential, due to the optical response characteristics of the image carrier body (photo conductor), thereby making it impossible to accurately detect the potential patch.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide an image forming apparatus which restricts disturbance of a potential patch, in the case where a potential sensor for detecting the potential patch is provided on the downstream side of a developing device of a multiple developing roller type, thereby to enable stable reproduction of a high quality image for a long period of time.
In order to accomplish the above-mentioned and other objects, according to a first aspect of the present invention, an image forming apparatus comprises: charging means for charging the surface of an image carrier; exposure means for exposing an image on the charged image carrier for forming a latent image; developing means, including a plurality of developing rollers arranged in opposition with a surface of the image carrier and bias applying means for applying a developing bias to the plurality of developing rollers, for supplying a developer on the image carrier and forming a developed image on the image carrier; transfer means for transferring the developed image formed on the image carrier onto a printing medium; a potential sensor provided downstream in the moving direction of the image carrier relative to the developing means for detecting a potential on the image carrier; and control means for setting the developing bias to a value restricting disturbance of a potential portion, representing an object for potential detection by the potential sensor, by the developer when the potential portion passes across the developing means.
Preferably, setting of the developing bias for the plurality of developing rollers may be performed in sequential order from the developing roller arranged on the upstream side in the moving direction of the image carrier.
According to a second aspect of the present invention, an image forming apparatus comprises: an image carrier; charging means for charging the surface of the image carrier; exposure means for exposing an image on the charged image carrier for forming an exposure portion potential region; developing means, including a plurality of developing rollers arranged in opposition with a surface of the image carrier, bias applying means for applying a developing bias to the plurality of developing roller and a two component developer, for supplying a developer on the image carrier and forming a developed image on the image carrier; transfer means for transferring the developed image formed on the image carrier onto a printing medium; a potential sensor provided downstream in the moving direction of the image carrier relative to the developing means for detecting a potential on the image carrier; and control means for setting the developing bias to a value for restricting deposition of toner on the exposure portion potential region when the exposure portion potential region passes across the developing means.
According to a third aspect of the present invention, an image forming apparatus comprises: an image carrier; charging means for charging the surface of the image carrier; exposure means for exposing an image on the charged image carrier for forming an exposure portion potential region; developing means, including a plurality of developing rollers arranged in opposition with a surface of the image carrier, bias applying means for applying a developing bias to the plurality of developing rollers and a two component developer, for supplying a developer on the image carrier and forming a developed image on the image carrier; transfer means for transferring the developed image formed on the image carrier onto a printing medium; a potential sensor provided downstream in the moving direction of the image carrier relative to the developing means for detecting a charge potential and an exposure potential on the image carrier; and control means for applying the developing bias at a value which restricts the splashing of carrier onto the surface of the image carrier, when the charge potential region passes through the developing means, and sets the developing bias to a value for restricting deposition of toner onto the exposure portion potential region when the exposure portion potential region passes across the developing means.
According to a fourth aspect of the present invention, an image forming apparatus comprises: an image carrier; charging means for charging the surface of the image carrier; exposure means for exposing an image on the charged image carrier for forming an exposure portion potential region; developing means, including a plurality of developing rollers arranged
Akatsu Shinichi
Ishii Masayoshi
Kubota Keisuke
Mabuchi Hiroyuki
Mitsuya Teruaki
Antonelli Terry Stout & Kraus LLP
Grainger Quana M.
Hitachi Koki Co,. Ltd.
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