Electrophotography – Control of electrophotography process – Control of exposure
Reexamination Certificate
2001-03-26
2003-01-14
Chen, Sophia S. (Department: 2852)
Electrophotography
Control of electrophotography process
Control of exposure
C399S038000, C399S167000, C399S299000, C399S302000
Reexamination Certificate
active
06507713
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an image formation apparatus and a control method thereof, and, more particularly, concerns an image formation apparatus that is provided with a rotary member and belts, such as a belt for transporting paper toward the rotary member or a transfer belt for allowing an image formed on the surface of the rotary member to be transferred on its own surface, and a control method of such an apparatus. Moreover, the present invention also relates to an image formation apparatus provided with a photosensitive drum and a belt, such as a transporting belt for transporting paper or an intermediate transfer belt, and an image formation method of such an apparatus, and a controlling device that is applicable to a mechanism that moves both a rotary member, which normally has eccentricities or deviations in its diameter, and a belt in an integral manner.
BACKGROUND OF THE INVENTION
In recent years, there is an ever-increasing demand for color image formation apparatuses capable of forming color images. One type of image formation apparatuses capable of forming color images at high speeds has an electrophotographic system of a tandem type. With respect to conventional image formation apparatuses of the tandem type, for example, the inventions disclosed in Japanese Patent Application Laid-Open Nos. 63-81373 and 10-246995 have been known.
Each of the inventions disclosed in the above-mentioned publications, Japanese Patent Application Laid-Open Nos. 63-81373 and 10-246995, has four photosensitive drums each of which has a scanning unit for applying a laser light beam to each of the four photosensitive drums so as to write a latent image thereon.
The four photosensitive drums are placed in parallel with each other in the transporting direction of the paper, which is transported by the transporting belt. Each of these is scanned (main-scanning process) in the direction of the rotary axis by a laser light beam directed from the scanning unit, while being rotated, so that a latent image is written thereon. Here, one line of the latent image written by one main-scanning process is hereinafter referred to as a scanning line.
On the surfaces of the four photosensitive drums bearing the latent images written thereon are supplied toners having respective colors of Y (yellow), M (magenta), C (cyan) and K (black) so as to adhere to the respective latent images. Thus, a toner image having one of the colors is formed on each of the surfaces of the four photosensitive drums. A sheet of paper is successively pressed onto the four photosensitive drums on which toner images have been formed. Consequently, the toner images of the respective colors are successively transferred the sheet of paper to form a color image.
In this case, if there is an offset between the scanning lines constituting the toner images of the respective colors in the color image thus formed, a so-called color offset will occur in the color image, resulting in degradation in the image quality. In order to prevent the color-offset, Japanese Patent Application Laid-Open No. 10-246955 has proposed an arrangement in which the photosensitive drums are designed to rotate freely, while an annular transport belt is driven to rotate by a motor so that the transport belt is made to contact the photosensitive drums by press-contact rollers installed below the transport belt. The four photosensitive drums are driven to rotate, following the transport belt. At this time, the four photosensitive drums are subjected to the same rotary force so that they are allowed to rotate at the same angular velocity, thereby making it possible to form a color image that is free from positional offsets between the scanning lines.
However, in image formation apparatuses such as printers and copying machines, there will be ever-increasing demands for high resolution (1200 dpi or more).
In contrast, the technique disclosed in Japanese Patent Application Laid-Open No. 10-246995 fails to meet these demands. In other words, in the technique disclosed in Japanese Patent Application Laid-Open No. 10-246995, the image distortion in the sub-scanning direction due to the eccentricity of the rotary axis of the photosensitive drum is corrected by detecting a outer surface dislocation and using the dislocation information continuously. However, when a high resolution is required, the actual amount of correction tends to deviate from the dislocation information in their correlation as the resolution becomes higher.
Moreover, in general, the photosensitive drum tends to have a slight eccentricity due to the limitation in its assembling precision.
FIG. 43
is a drawing that shows a state in which a transfer belt is made to contact a photosensitive drum
1801
having such an eccentricity by a contact roller. The photosensitive drum
1801
shown in this Figure has a cross-section that is orthogonal to the rotary axis perpendicular to the paper surface, that passes through point O.
The photosensitive drum
1801
having the eccentricity rotates centered on the center axis passing through point O. In contrast, a transport belt
1802
, which has an annular shape, is allowed to move in the direction of arrow A. A contact roller
1803
is made to contact the transport belt
1802
from below while being supported by a spring
1804
so that the transport belt
1802
is made to press-contact the photosensitive drum
1801
. A sheet of paper, not shown, is made to press-contact the photosensitive drum
1801
by the press-contact roller
1803
through the transport belt
1802
. Thus, a toner image formed on the surface of the photosensitive drum
1801
is transferred onto the sheet of paper.
The distance from point
0
to the outer surface of the photosensitive drum
1801
having the eccentricity varies depending on the angle of rotation when observed at a fixed point. For this reason, when the center of gravity of the photosensitive drum
1801
is located at G
7
, the paper and the photosensitive drum
1801
are in contact with each other at press-contact position P
1
, while when the center of gravity of the photosensitive drum
1801
is located at G
2
, they are in contact with each other at press-contact position P
2
.
The press-contact roller
1803
is allowed to move up and down to a certain degree since this is supported by a spring
1804
. Since the press-contact roller
1803
also has an eccentricity, the press-contact position varies in a complex manner, thereby giving greater adverse effects to the angular velocity of the photosensitive drum
1801
.
When the angular velocity of the photosensitive drum
1801
varies, the distance between scanning lines of a latent image to be written on the photosensitive drum
1801
becomes irregular, resulting in a distortion in the image to be formed. Moreover, in the case of a color image formation apparatus of the tandem type having a plurality of photosensitive drums in which multi-color toner images are superposed so as to form a color image, if the angular velocities of the photosensitive drums deviate, offsets occur in the transferring positions of the toner images of the respective colors, resulting in degradation in the image quality of an image to be formed.
Here, another arrangement has been proposed in which: the transferring position of a toner image is estimated through calculations, and based upon the results thereof, the image forming conditions are adjusted so as to make the transferring positions coincident with each other. However, when the angular velocity of the photosensitive drum
1801
varies, it becomes difficult to accurately estimate the transferring positions of the toner images, resulting in failure to adjust the transferring positions of the toner images through adjustments of the image formation apparatus. Therefore, in the image formation apparatus in which the angular velocity of the photosensitive drum varies, it is impossible to improve the image quality by eliminating the offsets in the transferring positions of the toner images through the adjustments of the ima
Chen Sophia S.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
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