Electrophotography – Document handling – Copy
Reexamination Certificate
2000-07-11
2002-02-05
Grainger, Quana M. (Department: 2852)
Electrophotography
Document handling
Copy
C399S068000
Reexamination Certificate
active
06345171
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus to obtain an image by transferring developer images formed on photo-conductive drums on a sheet of paper that is supported and conveyed on a transferring belt and a method to control paper conveying speeds in an image forming apparatus.
2. Description of the Related Art
In an electro-photographic image forming apparatus; for instance, a quadruple tandem full-color printer, a copying machine, etc. to obtain a full color image, an endless transferring belt is used to convey a sheet of paper, etc. to the transferring positions of respective photo-sensitive drums synchronizing with toner images in different colors formed on plural photo-conductive drums which are arranged in parallel. While a sheet of paper is passing the transferring positions on the transferring belt, toner images in different colors are transferred thereto in order from the photo-conductive drums and superposed each other.
On the other hand, at the upper stream side of the transferring belt, there are provided aligning rollers for feeding a sheet of paper to the transferring belt at a prescribed timing after once aligning the leading edge of a sheet of paper supplied from a paper feed cassette, etc. At the downstream side of the transferring belt, there are provided fixing rollers which convey a sheet of paper having a full color toner image formed by superposing plural toner images in different colors while clamping it and fixes it on the sheet of paper.
When conveying a sheet of paper by the aligning rollers, the transferring belt and the fixing rollers and transferring toner images on the sheet of paper, if the traveling speed Vt of the transferring belt is faster than the sheet of paper conveying speed Va of the aligning rollers, the conveying speed of the sheet of paper is accelerated to Vt from Va after the sheet passed through the aligning rollers. In other words, as the conveying speed of the sheet of paper changes (becomes fast) while it is being conveyed on the transferring belt, there are problems that remarkably deteriorate the quality of images because, for instance, a magnification of a transferring image changes or a color distortion is caused although it was intended to prevent a color distortion caused from blurring of transferred images by insuring transferring positions of respective colors by a sensor and adjusting the exposing timings.
Therefore, the sheet of paper conveying speed Va of the aligning rollers was so far set faster than the speed Vt of the transferring belt and as shown in
FIG. 1
, while the conveying force was receiving from the aligning rollers
2
, a difference between both speeds was absorbed by slightly deflecting a sheet of paper
1
at the front of a photo-conductive drum
3
and the sheet of paper
1
was conveyed at the constant speed of Vt of a transferring belt
4
during the conveyance by the aligning rollers and after passing through the aligning rollers.
However, when a difference is provided between the speed Vt of the transferring belt
4
and the sheet of paper conveying speed Va of the aligning rollers
2
, if a sheet of paper is long, an amount of deflection becomes large and the paper may be bent or if a sheet of paper is thick, the paper is not deflected satisfactorily or the transferring becomes poor because the paper is pushed by force on the transferring belt by the conveying force of the aligning rollers
2
. Furthermore, as the force pushing the sheet of paper will be released when the trailing edge of the sheet of paper passed through the aligning rollers, the sheet of paper may cause a vibration and in turn the rotation of the drum becomes uneven and blurring may be caused. These defects may possibly deteriorate the printed quantity of a transferred image.
In addition, when a sheet of paper is conveyed, it may slip on the aligning rollers for the effect of the smooth surface and a thickness of the paper and an accurate conveying speed cannot be obtained. Normally, therefore, it is necessary to set the sheet of paper conveying speed Va of the aligning rollers rather large expecting a sliding. This may make the above defects further worse.
Further, when fixing toner images after transferred them, the transfer is still in operation on the trailing edge of a sheet of paper and according to a difference between the sheet of paper conveying speed by the fixing rollers and the conveying speed of the transferring belt, there is the possibility for the deterioration of the quality of a printed image likewise the above.
Accordingly, in an image forming apparatus that conveys a sheet of paper using a transferring belt, it is desirable to obtain a good transferred toner image by preventing a blurring and vibration when transferring an image by controlling the sheet of paper conveying speeds by the transferring belt, and the aligning rollers and fixing rollers which are provided before and behind the transferring belt.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a highly reliable image forming apparatus that is capable of forming a good transferred image without causing blurring and color distortion by controlling the sheet of paper conveying speeds by a transferring belt, aligning rollers and fixing rollers, preventing blurring and vibration caused by change in the sheet of paper conveying speed while transferring an image.
The present invention provides an image forming apparatus comprising: image forming means for forming a developer image on an image carrier; image transferring means for transferring the developer image developed on the image carrier on an image receiving material; traveling means for traveling to convey the image receiving material toward the image carrier; aligning means for conveying the image receiving material to the traveling means synchronizing with the transfer of the developer image formed on the image carrier; fixing means for fixing the developer image on the image receiving material while conveying the image receiving material which already has the developer image transferred; writing means for writing prescribed inspection mark on the traveling means or the image receiving material conveyed by the aligning means using the image forming means; detecting means for detecting the inspection mark written on the traveling means and the inspection mark written on the image receiving material; and drive control means for controlling the drive of at least one of the traveling means, aligning means and fixing means.
Further, the present invention provides an image forming apparatus comprising: an image forming unit to form a developer image on a photo-conductive drum; a transferring device to transfer the developer image formed on the photo-conductive drum on an image receiving material; a transferring belt that is traveling to convey the image receiving material to the photo-conductive drum; an aligning roller to convey the image receiving material to the transferring belt synchronizing with the transfer of the developer image formed on the photo-conductive drum; a fixing roller to fix the developer image on the image receiving material while conveying the image receiving material that has the developer image transferred thereon; a writing device to write prescribed inspection mark on the transferring belt or the image receiving material that is conveyed by the aligning roller; a sensor to detect the inspection mark written on the transferring belt and the inspection mark written on the image receiving material; and a drive control device to control the drive of at least one of the transferring belt, the aligning roller and the fixing roller according to the result of detection by the sensor.
In addition, the present invention provides a method of controlling the sheet of paper conveying speeds in an image forming apparatus comprising the steps of: traveling a first conveying means to convey an image receiving material toward the image carriers at a prescribed speed; feeding the image receiving
Grainger Quana M.
Toshiba TEC Kabushiki Kaisha
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