Electrophotography – Control of electrophotography process – Control of exposure
Reexamination Certificate
1997-02-24
2001-01-30
Grainger, Quana M. (Department: 2852)
Electrophotography
Control of electrophotography process
Control of exposure
C399S162000
Reexamination Certificate
active
06181889
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus of an electrophotographic system, such as a copying machine or laser printer, and more particularly, to an image forming apparatus having a belt-shaped photosensitive member.
An electrophotographic apparatus, such as an electrophotographic copying machine or electrophotographic printer, generally comprises; a photosensitive member, such as a photosensitive drum or a photosensitive belt; a charging unit for uniformly charging the surface of the photosensitive member; an exposing unit for exposing the surface of the photosensetive member to light in accordance with image information, thereby forming an electrostatic latent image on the charged surface of the photosensitive member; a transfer unit for transferring a toner image to a recording sheet; and a thermal fixing unit fixing the toner image onto the recording sheet, wherein the recording sheet on which the toner image has been transferred passes through the thermal fixing unit.
In an image forming apparatus of the electrophotographic type using a photosensitive belt, the photosensitive belt has generally a joint so as to be endless. When the joint passes the cleaning unit, the cleaning unit is vibrated due to a difference in level at the joint. Because of the vibration, a photosensitive belt unit is also vibrated. When a latent image is formed by the exposing unit, the latent image is consequently vibrated so that a density variation in a lateral line shape which is perpendicular to the paper conveyance direction occurs on the image. Since the density variation remarkably deteriorates the quality of the image, the vibration of the cleaning unit has to be prevented in order to prevent such a density variation. Therefore, various processing methods for reducing the difference in level at the joint of the photosensitive belt have been conventionally proposed.
For example, Japanese Patent Application Laid-Open No. 1-288860 discloses a method in which the ends of a belt are connected by ultrasonic fusion and an extruded length from the joint portion is set to 1.2 mm or shorter. Japanese Patent Application Laid-Open No. 61-185753 discloses a method of forming a protective film including a solid lubricant in the joint portion.
According to the conventional methods, as mentioned above, the latent image is vibrated by the vibration which occurs when the photosensitive belt passes the cleaning unit due to the joint in the photosensitive belt. The joint is the cause of occurrence of a density variation in the image, so that the joint is processed to reduce the difference in level in order to prevent the vibration. Although the density variation in the image is suppressed by reducing the difference in level by processing the joint, all of the variation is not eliminated. The process cannot be perfectly executed by variation in processing works.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a photosensitive belt which does not cause vibration when a joint of the photosensitive belt passes a cleaning unit and which prevents occurrence of a density variation in an image and also to provide an image forming apparatus having the photosensitive belt.
According to the invention, there is provided an image forming apparatus in which electrostatic latent images are formed into toner image using color toner on an endless photosensitive belt having a photoconductive face on which the electrostatic latent image can be formed, and after that, the latent images are sequentially piled up on an intermediate transfer drum and are simultaneously transferred to a recording sheet. The apparatus comprises a photosensitive belt; a charging unit for uniformly charging the surface of the photosensitive belt so as to have a predetermined potential; an exposing unit for forming an electrostatic latent image on the uniformly charged surface; a developing unit for forming a toner image from the electrostatic latent image using toner; an intermediate transfer drum for sequentially piling up the toner images; and a cleaning unit for removing residual toner after transfer of the toner image, wherein the photosensitive belt has a joint so as to be endless, and when the joint passes the cleaning unit, the latent image is not formed by the exposing unit.
Further, the travel distance of the photosensitive belt from the cleaning unit to the exposing unit is shorter than the distance from the rear end of a print image on the photosensitive belt to the front end of the following print image.
Further, the charging unit for charging the photosensitive belt so as to have a predetermined electric potential, the exposing unit for forming the electrostatic latent image, and the cleaning unit for removing residual toner after the toner image is transferred to the intermediate transfer drum are arranged around one of a plurality of rollers over which the photosensitive belt is stretched.
Further, the charging unit for charging the photosensitive belt so as to have a predetermined electric potential, the exposing unit for forming the electrostatic latent image, and the cleaning unit for removing residual toner after the toner image is transferred to the intermediate transfer drum are arranged around a drive roller which applies a conveyance force to the photosensitive belt.
With the above construction, a latent image with high accuracy can be formed on the photosensitive belt without being influenced by vibration caused when the joint of the photosensitive belt passes the cleaning unit.
REFERENCES:
patent: 4437757 (1984-03-01), Komori et al.
patent: 4596457 (1986-06-01), Peeters et al.
patent: 5258816 (1993-11-01), Haneda et al.
patent: 5341194 (1994-08-01), Haneda et al.
patent: 5652948 (1997-07-01), Sagaguchi et al.
patent: 5666599 (1997-09-01), Miyasaka et al.
patent: 61-185753 (1986-08-01), None
patent: 63-265280 (1988-11-01), None
patent: 1-288860 (1989-11-01), None
patent: 6-95461 (1994-04-01), None
patent: 7-325455 (1995-12-01), None
Akasaki Tetsuro
Hayano Tomio
Terashima Isamu
Ukei Shoji
Wakamatsu Kazuhiro
Antonelli Terry Stout & Kraus LLP
Grainger Quana M.
Hitachi , Ltd.
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