Electrophotography – Control of electrophotography process – Control of exposure
Reexamination Certificate
2000-01-14
2001-12-11
Lee, Susan S. Y. (Department: 2852)
Electrophotography
Control of electrophotography process
Control of exposure
C399S302000, C399S303000
Reexamination Certificate
active
06330404
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to an image forming apparatus, for example, a copying machine, a printer, a facsimile machine, or the like, which employs an electrophotographic system.
Usually, an image forming apparatus which employs an electrophotographic process comprises: an image formation station in which a latent image is formed with the use of light, magnesium, electric charge, or the like, and a visible image is formed by developing the thus formed latent image; a means for conveying to the image formation station a piece of transfer medium onto which the visible image formed in the image forming station is transferred; and a fixing means for fixing the image having been transferred onto the transfer medium, to the transfer medium.
Each image formation station comprises an image formation medium, a latent image forming means, and a developing means. The image formation medium may be an electrophotographic photosensitive member (image bearing member), or may be different from the electrophotographic photosensitive member in property and shape. The latent image forming means and developing means varies depending on the property and shape of the employed photosensitive drums
As for a means for conveying the transfer medium from the transferring means for transferring an image onto the transferring medium, to the fixing means in a color image forming apparatus, in particular, a color image forming apparatus in which a full-color image is formed by placing in layers a plurality of images formed with the use of a plurality of image formations stations, on a piece of transfer medium, a conveying means which conveys the transfer medium by electrostatically adhering the transfer medium to its surface is widely used because of its superior conveying performance.
The image forming apparatus disclosed by the applicants of the present invention in Japanese Laid-Open Patent Application No. 13976/1990 may be listed a one of the well-known image forming apparatus of the above described type.
FIG. 17
schematically depicts the image forming apparatus disclosed in the aforementioned official gazette.
Referring to
FIG. 17
, the image forming apparatus comprises; three image formation stations I, II and III; a conveying means
139
provided with a conveyer belt
126
for conveying transfer medium; and a fixing apparatus
56
provided with a pair of thermal rollers
56
a
and
56
b
for fixing the image on the transfer medium to the transfer medium. The conveying means
139
is located below the image formation stations I, II and III, and the fixing apparatus
56
is located at the downstream end of the conveying means
139
in terms of the direction in which the transfer medium is conveyed. The image formation stations I, II and III comprise photosensitive drums
111
,
112
and
113
, charging devices
114
,
115
and
116
, developing devices
117
,
118
and
119
, transfer charging devices
120
,
121
and
122
, and cleaner
123
,
124
and
125
, correspondingly.
The conveyer belt
126
is formed of resin. In order to assure that the transfer medium is reliably conveyed, the surface of the conveyer belt
126
is charged with the use of a charging device
133
for adhesion, during the image forming operation, so that the transfer medium is electrostatically adhered to the conveyer belt
126
.
A conveyer belt
126
is suspended by a driver roller
131
as a rotational member, and a follower roller
134
, being stretched with the application of a predetermined amount of tension. The conveyer belt
126
runs at a predetermined conveyance velocity as the driver roller
131
in rotationally driven.
The transfer medium T sent out by the registration roller
49
onto the conveyer belt
126
is electrostatically adhered to the conveyer belt
126
. In order to further assure that the transfer medium T is properly, that is. without becoming wavy, adhered to the conveyer belt
126
, the recording medium is pressed onto the conveyer belt
126
by the follower roller
134
of the transfer medium conveying means
139
, and a presser roller
52
disposed in contact with the follower roller
134
, as the recording medium T is passed between the follower roller
134
and presser roller
52
.
In order to prevent the placement of the recording medium T upon the conveyer belt
126
from being affected by the conveyance velocity of the registration roller
49
, the conveyance velocity of the registration roller
49
is set at a slightly greater velocity than that of the conveyer belt
126
so that the transfer medium T is bent in the form of an arc between the registration roller
49
and presser roller
52
.
In a high temperature-high humidity environment, the conveyer belt
126
fails to be sufficiently charged. and therefore, the transfer medium T sometimes separates, or floats, from the conveyer belt
126
. As the recording medium T flosts, problems occur; for example, an image becomes misaligned with the recording medium T as the former is transferred onto the latter (transfer misalignment, registration misalignment), or certain portions of an image fail to be transferred onto the recording medium T. In order to deal with such problems, an auxiliary roller
200
and an idler roller
203
are provided, which are positioned on the outward and inward sides, respectively, of the conveyer belt loop, in a manner to pinch the conveyer belt
126
.
One of the essential factors which determine the quality of a color image is the alignment among the plurality of monochrome images which form a color image. If the plurality of monochrome images of different color are misaligned in the secondary and/or primary scanning directions, or are not parallel to each other, color misregistration occurs.
In the case of an image forming apparatus such as the one described above, in which each of a plurality of monochromatic images of different color which form a color image is formed at a location different from the locations where other images are formed, the color deviation is more liable to occur, compared to a conventional apparatus in which all the monochromatic images of different color are formed and transferred at the same location.
Paying attention to the color deviation related to the direction of the secondary scanning, there are static and dynamic causes for this type of color deviation. As for the static causes, it is possible to list the difference in the distance between the adjacent two drums, misalignment in exposure position, diameter of a driver roller which determines the velocity at which the transfer medium is conveyed during image transfer. These causes mainly result from assembly errors and impreciseness of components As for the dynamic causes, it is possible to list the fluctuation in the rotational velocities of the image bearing members, and/or belt.
Among the above listed causes for the color deviation, the dynamic causes are generally difficult to rectify. In order to rectify the dynamic causes, the fluctuation in the rotational velocities of the image bearing members and belt must be reduced as much as possible. Therefore, the driving power sources have been devised in various ways in accuracy and control method. For example, the length of each image formation station in terms of the circumferential direction of the belt was set to be equal to a value obtained by multiplying the circumference of the driver roller by an integer so that the eccentricity of the driver roller did not result in the color deviation.
As for the main cause of the aforementioned fluctuation in the rotational velocity of the belt, it is possible to list the nonuniformity in the thickness of the belt.
In the past, the transfer medium conveyer belt, intermediary transfer belt, photosensitive belt, and the like, in other words, the member in the form of an endless belt, were produced by connecting one end of a sheet of belt material to the other end. Thus, these members had a seam, on which an image cannot be formed. Therefore, recently, in order to improve image formation efficiency
Matsui Norio
Munenaka Katsumi
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Lee Susan S. Y.
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