Incremental printing of symbolic information – Electric marking apparatus or processes – Electrostatic
Reexamination Certificate
1995-04-07
2001-02-06
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Electric marking apparatus or processes
Electrostatic
Reexamination Certificate
active
06184910
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a color copier, color printer, color facsimile apparatus or similar color image forming apparatus.
A color image forming apparatus of the type leaving a photoconductive belt and an intermediate image transfer belt is conventional. It has been customary with this type of apparatus to provide each belt with a mark or a notch and cause a photosensor or similar sensing member, mounted on the apparatus body, to sense it. This allows position information relating to the belt to be detected.
Japanese Patent Laid-Open Publication No. 4-335665, for example teaches a color image forming apparatus including a photoconductive belt provided with a triangular mark, and mark sensing means for sensing the mark with a laser beam. The mark sensing means senses the mark every time the belt is exposed by a light beam associated with an image forming signal of one color component. The rotation phase of a polygonal mirror and, therefore, the time for starting exposure in the subscanning direction is controlled on the basis of the time when the mark sensing means senses the mark. This kind of scheme is intended to produce a color image free from color displacement. The apparatus sequentially transfers toner images of different colors from the photoconductive belt to an intermediate image transfer belt one above the other, and then transfers the resulting composite image from the intermediate belt to a paper at a time. However, the monocolor images are necessarily displaced from each other because the circumferential length of the intermediate belt and the scanning interval of the polygonal mirror do not have an integral multiple relation Theoretically, therefore, one line of displacement occurs between the consecutive monocolor toner images.
Japanese Patent Laid-Open Publication No. 61-34162 discloses an arrangement wherein a mark for sensing the seam of a photoconductive belt is formed on the belt by the thermal transfer of ink from a thermally fusible ink layer. However, the thermal transfer method is practicable only with limited substances. For example, an intermediate image transfer member made of fluorine-contained resin, e.g., ETFE does not allow the ink to be transferred thereto because it has a non-adhesive surface. Moreover, even when the belt allows the ink to be transferred thereto, the transfer at high temperature is likely to affect the property of the belt.
Further, Japanese Patent Laid-Open Publication No. 60-134274 proposes a photoconductive belt formed with notches for timing detection at opposite edges thereof. The photoconductive belt, having a base made of PET (polyethylene telephthalate), scarcely cracks at the notches or otherwise deteriorates despite the notches. However, the intermediate belt, made of ETFE or similar fluorine-contained resin, would crack at the notches during the course of repeated rotation. Specifically, because the mechanical strength depends on the material, the notch scheme is limited by the material of the belt and not suitable for the intermediate belt.
The intermediate belt made of ETFE exhibits a far more noticeable non-adhesion characteristic than belts made of the other materials. Therefore, it is difficult to form a mark on the ETFE belt by hot stamping, painting, printing or similar technology. Although the mark itself may be adhered to the belt by, for example a two-sided adhesive tape, it is likely that the mark is turned up and disturbs the operation of a photosensor or similar sensing means. In an color image forming apparatus of the type using such an intermediate belt and controlling the registration of colors on the basis of a mark provided on the belt, the contamination, turn-up and other disfigurement of the belt cause the colors to b e displaced from each other and results in irregular colors.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a color image forming apparatus capable of accurately superposing toner images of respective colors by obviating the displacement of an exposing position in the subscanning direction.
It is another object of the present invention to provide a color image forming apparatus having a photoconductive belt or an intermediate image transfer belt to which a position mark can be surely fitted.
It is another object of the present invention to provide a color image forming apparatus which allows a position mark to be simply and firmly affixed to a photoconductive belt or an intermediate image transfer belt.
A color image forming apparatus of the present invention has an image carrier for causing a latent image to be electrostatically formed thereon, a light emitting device for emitting a light beam modulated by each of image signals of respective colors and representative of a document image, a rotatable polygonal mirror for steering the light beam to thereby electrostatically form latent images respectively associated with the image signals on the image carrier, a drive source for causing the polygonal mirror to rotate, a developing device for developing the latent images with developers of respective colors to thereby produce corresponding monocolor toner images, an intermediate transfer body formed with a mark for position detection, and for causing the monocolor toner images to be sequentially transferred thereto from the image carrier, a sensor located at a predetermined position for sensing the mark, a first controller for causing each of the latent images to begin to be formed on the basis of the time when the sensor senses the mark, and a second controller for controlling the rotation phase of the polygonal mirror on the basis of the time when the sensor senses the mark.
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Deki Tsuyoshi
Iwata Nobuo
Motohashi Takeshi
Sasaki Eiichi
Shio Yutaka
Barlow John
Dickens C.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
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