Electrophotography – Image formation – Photoconductive member
Reexamination Certificate
2001-07-10
2003-04-29
Grainger, Quana M. (Department: 2852)
Electrophotography
Image formation
Photoconductive member
Reexamination Certificate
active
06556799
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rotation member driving device used for an image forming apparatus adopting an image forming system such as an electrophotographic system, an electrostatic recording system, an ionography, or a magnetic recording system and forming a color or black-and-white image, such as a printer, a copying machine, or a facsimile, and an image forming apparatus using the same, and particularly to a rotation member driving device which can rotate and drive a rotation member such as a photosensitive drum or an intermediate transfer drum with high accuracy and can form a high quality image without distortion and out of color registration as a color or black-and-white image, and an image forming apparatus using the same.
2. Description of the Related Art
Conventionally, as this kind of image forming apparatus adopting an electrophotographic system or the like and forming a color or black-and-white image, such as a printer or a copying machine, ones of various kinds of systems have been proposed and have been put on the market. Especially in recent years, as a personal computer, Internet, digital camera, or the like becomes popular, the development of a color printer is remarkable. In the image forming apparatus such as the color printer, an apparatus for office use, which is capable of forming a color image and satisfies a high speed property, compactness and low cost, similar to those for a black-and-white image, is earnestly demanded.
In the image forming apparatus such as the color printer, in order to form a high quality color image, images of respective colors, such as cyan, magenta, yellow and black, are formed on an image holding member, and it is necessary to improve the accuracy of color registration in superposition of these images of the respective colors.
As the image forming apparatus such as the color printer, there are roughly two types, one adopting a system in which only one photosensitive drum as an image holding member is provided, toner images of respective colors, such as cyan, magenta, yellow and black, are sequentially formed on the one photosensitive drum, and the toner images of the respective colors are multiply transferred onto a recording sheet or an intermediate transfer member, so that a color image is formed, and the other adopting the so-called tandem engine in which image forming units each including a photosensitive drum as an image holding member are provided, the number of the units is made to correspond to the number of colors of toner images to be formed, for example, four in the case of cyan, magenta, yellow and black, toner images of respective colors such as cyan, magenta, yellow and black are continuously formed on the photosensitive drums of the respective image forming units, and the toner images of the respective colors are multiply transferred onto a recording sheet or an intermediate transfer member, so that a color image is formed.
Among these, in the image forming apparatus of the system in which only one photosensitive drum is provided, periodic unevenness of speed of a driving device for driving the photosensitive drum or the intermediate transfer member such as an intermediate transfer drum or an intermediate transfer belt causes the accuracy of the color registration to be degraded. In the image forming apparatus of such system, according to the eccentricity of respect shafts of drive transmission parts of the driving device or the dimension accuracy of a tooth profile of a gear or the like, unevenness of rotation occurs in one rotation period of each of the shafts, and in the case where the photosensitive drum or the intermediate transfer member such as the intermediate transfer drum or the intermediate transfer belt is driven through the drive transmission parts of plural stags, there occurs a speed variation in which the unevenness of the rotation in each of the stages is combined. Thus, in the image forming apparatus of the system, setting is made such that the rotation period of the photosensitive drum is integer times as long as the rotation period of the intermediate transfer drum or the intermediate transfer belt, so that the degradation of the accuracy of the color registration due to the periodic unevenness of speed of a driving device is prevented.
In the latter so-called tandem engine image forming apparatus, since plural (for example, four) image forming units for forming images of respective colors are provided, in order to improve the accuracy of the color registration of the images formed in the respective image forming units, it is necessary to make the positions of the images formed by the respective image forming units coincident with predetermined positions with high accuracy. Thus, the tandem engine image forming unit is constructed such that scan start timing in a main scan direction and a sub-scan direction in an image exposure device for exposing an image by a laser beam onto the photosensitive drum, the phase of a polygon mirror for deflecting and scanning the laser beam, the position of a mirror for guiding the laser beam to the photosensitive drum, and the like are controlled, so that the accuracy of the color registration when the images formed by the respective image forming units are overlapped is improved.
However, the above related art has problems as follows. That is, in the image forming apparatus of the system in which only one photosensitive drum is provided, although it is possible to prevent the accuracy of the color registration from degrading to some degree by setting the rotation period of the photosensitive drum and the rotation period of the intermediate transfer drum or the intermediate transfer belt to have the relation of the integer times, since the image forming apparatus of such system is required to sequentially form the toner images of the respective colors, such as cyan, magenta, yellow and black, for every rotation of the photosensitive drum, there is a problem that it is difficult to satisfy the high speed property required for the color printer for office use, or the like.
On the other hand, in the case of the latter image forming apparatus of the so-called tandem engine, since the toner images of the respective colors, such as cyan, magenta, yellow and black, are continuously formed by the plural image forming units, it is sufficiently possible to satisfy the demand for the high speed property. On the contrary, in this kind of tandem image forming apparatus, in order to improve the accuracy of the color registration, since it becomes necessary to perform correction control of controlling the scan start timing of the image exposure device in the main scan direction and the sub-scan direction, the phase of the polygon mirror, and the position of the mirror for guiding the laser beam to the photosensitive drum, there is a problem that it is difficult to reduce the cost.
Further, in the case of the tandem image forming apparatus, even if the problem of the cost resulting from the correction control of the image exposure device in the respective image forming units is solved, as set forth in “Machine Optimizing Technologies for Color Registration of Electrophotography” (Journal of the Imaging Society of Japan, vol. 38, no. 3 (1999) pp. 175-180), since driving portions of photoreceptor shafts of the respective image forming units are constituted by independent drive transmission parts, it is difficult to improve the accuracy of the color registration by phase alignment of unevenness of one rotation period, the position variation generated by the eccentricity or the like is rather large in view of objective color registration accuracy, and the improvement of the accuracy of the driving part becomes a serious problem, which is pointed out in the publication.
Then, in the tandem image forming apparatus constituted by the independent drive transmission parts for the respective image forming units, in order to improve the accuracy of the driving part, various proposals have been made and actually carried out
Fuji 'Xerox Co., Ltd.
Grainger Quana M.
Morgan & Lewis & Bockius, LLP
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