Electrophotography – Image formation – Photoconductive member
Reexamination Certificate
2000-07-07
2002-05-07
Grainger, Quana M. (Department: 2852)
Electrophotography
Image formation
Photoconductive member
C399S159000
Reexamination Certificate
active
06385417
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to image forming systems such as a color plain paper copy machine (hereinafter referred to as PPC) and a printer for printing/recording information from image information supply apparatuses such as a personal computer (hereinafter referred to as PC) and a digital camera on a plain paper, OHP sheet or other types of paper sheets, and particularly, it relates to a structure for holding an image holding member while a constant fine gap is always maintained on an abutment surface between a photosensitive drum or another image holding member and a developing roller.
An image forming system for use in the aforementioned purpose is provided with an image forming unit for forming an image by using a developing material, a sheet supply portion for supplying a sheet to the image forming unit, a sheet conveying portion for conveying the supplied sheet, and a sheet supplying/conveying controller for controlling the supplying/conveying of the sheet to the image forming unit by the sheet supplying and conveying portions. The image forming unit is provided with an image holding member for converting an optical image formed via an optical system into a latent image and subsequently depositing the developing material thereon to hold the image, a developing unit for developing the latent image held on the image holding member as the image with the developing material, a transferring unit for transferring the developed image to the sheet, and a fixing unit for fixing the transferred image.
In recent years, in a field of image forming system, various color developing/forming methods for forming color images have been proposed, and there are roughly a multiple transferring system and a multiple developing system. The multiple transferring system can be classified into a transferring drum system, a tandem system, an intermediate transferrer system, and the like, and the multiple developing system can be classified to a multiple rotation system and a one pass method. The transferring drum system comprises successively transferring respective color toners on a sheet wound around a transferring drum to obtain the image, and is characterized in that a positioning control is difficult but a degree of freedom in a process design is high. The tandem system is provided with image forming portions for four colors, successively transfers respective color toner images on a conveyed sheet to obtain the color image with one pass, and is high in cost and difficult in the positioning control, but is also provided with an advantage that image formation can be accelerated and a degree of freedom in process design is highest. The intermediate transferrer system comprises successively transferring respective color toner images on an intermediate transferrer, and subsequently collectively transferring the images to the sheet to obtain the color image, and is difficult in the positioning control and low in transfer ratio as compared with the other systems but has advantages that a transferring mechanism portion capacity is relatively small and that curvature separation is also possible.
Moreover, the multiple rotation system in the multiple developing system comprises rotating the photosensitive drum to superposing the respective color toners on the surface, and subsequently collectively transferring the toners to the sheet to obtain the color image, and requires a complicated process control, but is advantageous in miniaturization of a machine body and cost reduction, and has an advantage that the system is also advantageous for positioning. The one pass system is provided with the image forming portions for four colors around a photosensitive member, comprises superposing the toner images on the photosensitive member with one pass to obtain the color image, has difficulty in process arrangement around the photosensitive member and exposure positioning control, easily enlarges an apparatus size, and disadvantageously requires the complicated process control, but has an advantage that image formation can be performed at a high speed.
For the aforementioned image holding member for holding the image in an image forming process, in the aforementioned various image forming systems, concretely, there is one large-diameter photosensitive drum, or there are a plurality of relatively small-diameter photosensitive drums for respective colors in color copy or the like, but any member comprises a single photosensitive drum or a plurality of photosensitive drums as a constituting element of the image forming unit. The photosensitive drum is rotatably supported on a frame constituting a main body of the image forming system via a bearing or the like, and for the single photosensitive drum or the plurality of photosensitive drums a magnet roller for supplying the developing material is also disposed.
The developing magnet roller is disposed in parallel between a developing unit main body case and the photosensitive drum, and is used for attaching a toner as the developing material on an electrostatic pattern to form a visualized image after the electrostatic pattern is formed on the photosensitive drum charged with a static electricity by a charger in accordance with a document pattern by exposure by an optical unit. Therefore, by applying a bias potential of either a positive potential or a negative potential to the developing (magnet) roller to attach the developing material to the peripheral surface of the roller as an electromagnet and rotating the roller opposite to the photosensitive drum with a constant gap immediately before placing the roller in sliding contact with the peripheral surface of the drum, the toner is supplied to the surface of the rotating photosensitive drum which is charged in a predetermined document pattern and on which an electric latent image is formed.
As seen from the aforementioned description, since the photosensitive drum is disposed close to the developing roller to such an extent that the peripheral surfaces are nearly in the sliding contact with each other, a gap control is a big problem to secure an adequate supply amount of the developing material (toner). Particularly, in a recent technique it is a mainstream to integrally forming the photosensitive drum and developing (magnet) roller including the developing unit main body case, and it is very important to control the gap in arranging these components for every unit.
In the conventional image forming system, in order to control the gap between the peripheral surface of the photosensitive drum and the peripheral surface of the developing roller, an adjustment portion for the gap control is disposed in either edge of both ends avoiding a central portion for forming the image in the photosensitive drum, and a gap setting member fixed to a developing roller shaft is disposed opposite to the adjustment portion, and controlled by direct contact in such a manner that a constant distance is always held from the peripheral surface of the photosensitive drum (direct contact system). The gap setting member is provided with a disc shape or a thin cylindrical shape such that the peripheral surface abuts on the adjustment portion disposed on at least one edge of the peripheral surface of the photosensitive drum, and may be constituted, for example, by a bearing comprising an inner race fixed to the developing roller shaft and an outer race rotatably held via a plurality of rollers.
In the conventional image forming system constituted as described above, since the gap between the photosensitive drum and the developing roller is directly adjusted by the surface extended from the surface with the image to be formed thereon, distortion and rattling generated between a rotation drive shaft of the photosensitive drum and the rotation drive shaft of the developing roller, and disturbance forces such as cogging generated in a motor for rotating/driving both drive shafts are applied without being inhibited.
However, according to a conventional image forming device, collision of the peripheral surface of th
Nakatomi Yoshitsugu
Tanaka Toshiaki
Foley & Lardner
Grainger Quana M.
Toshiba Tec Kabushiki Kaisha
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