Electrophotography – Image formation – Transfer
Reexamination Certificate
2000-05-12
2001-09-25
Pendegrass, Joan (Department: 2852)
Electrophotography
Image formation
Transfer
C250S559440, C347S116000
Reexamination Certificate
active
06295435
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an electrophotographic image forming apparatus and more particularly to a color image forming apparatus capable of accurately detecting positional deviation between images of different colors and correcting the deviation.
The prerequisite with a tandem image forming apparatus extensively used today is that images of different colors be brought into accurate register. Positional deviation between images of different colors is ascribable to various causes including skew, deviation in the subscanning direction, irregular pitch in the subscanning direction, magnification error in the main scanning direction, and deviation in the main scanning direction. While various schemes have heretofore been proposed for obviating positional deviation, none of them can accurately detect deviation to a satisfactory degree.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an image forming apparatus capable of accurately sensing positional deviation between images of different colors and correcting it.
It is another object of the present invention to provide an image forming apparatus capable of accurately sensing positional deviation between images of different colors, correcting the deviation, and executing accurate and rapid calculations for the correction.
It is still another object of the present invention to provide an image forming apparatus capable of easily determining whether or not the result of detection is correct, and reducing a period of time necessary for the decision.
It is a further object of the present invention to provide an image forming apparatus capable of preventing error processing from continuing over a long period of time and causing the operator to feel uneasy.
A color image forming apparatus of the present invention includes a conveying member for conveying a recording medium in a preselected direction. A plurality of image forming sections are arranged side by side along the conveying member each for forming a toner image of a particular color by an electrophotographic process. A plurality of image transfer units are respectively assigned to the image forming sections for sequentially transferring toner images to the recording medium one upon the other. A mark forming device causes the image forming sections to form respective register marks with toner and transfer the register marks to the recording medium. The register marks allow deviation of the toner images on the recording medium to be detected. A mark sensor senses the register marks. A correcting device corrects the deviation on the basis of a signal output from the mark sensor. A mark identifying device specifies a signal output from the mark sensor and representative of the background of the conveying member, and determines a point of the signal above a value Vs+&agr; or Vs−&agr;, where Vs denotes a signal level representative of the background while &agr; denotes a preselected value, and having a peak or a bottom value within a preselected section to be the point where a part of the register marks has been sensed.
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Nakazato Yasushi
Ohshima Kiyoshi
Shinohara Tadashi
Sugiyama Mitsugu
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Pendegrass Joan
Ricoh & Company, Ltd.
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