Patent ID: 6295435
Filing Date: 2001-09-25
Classification: G03G,H04N

Abstract:
A color image forming apparatus comprising:a conveying member for conveying a recording medium in a preselected direction;a plurality of image forming sections arranged side by side along said conveying member, each image forming section forming a toner image of a particular color by an electrophotographic process;a plurality of image transfer units respectively assigned to said plurality of image forming sections for sequentially transferring toner images to the recording medium one upon another;mark forming means for causing said plurality of image forming sections to form respective register marks with toner and transferring said register marks to the recording medium, whereby deviations in a position of said register marks allows deviations of the toner images on said recording medium to be detected;mark sensing means for sensing the position of the register marks;correcting means for correcting the deviations of the toner images on said recording medium on the basis of a signal output from said mark sensing means, including,mark identifying means for specifying from said signal output from said mark sensing means a background level Vs of said conveying member, and determining a point on said signal in excess of a first level Vs+.alpha. or Vs-.alpha., where .alpha. denotes a preselected value, having a peak or a bottom value Vp, respectively, within a preselected section of said signal where a part of the register marks has been sensed,center identifying means for determining a first pair of points coinciding with a second level (Vp-(Vs+.alpha.)).times..beta. or (Vp-(Vs-.alpha.)).times..beta., where .beta. denotes a preselected ratio, said second level lying between the peak or the bottom value Vp and the first level Vs+.alpha. or Vs-.alpha., executing smoothing of said signal to produce a smoothed signal about the first pair of points or about points in proximity to said first pair points, redetermining using the smoothed signal a second pair of points at said second level (Vp-(Vs+.alpha.)).times..beta. or (Vp-(Vs-.alpha.)).times..beta., or a third pair of points in proximity to said second pair of points, and determining a center point between said second or third pair of points to be a center position of one of the register marks,deviation calculation means for calculating the deviation of the register marks based on said center position, andwrite control means for adjusting a timing of a transfer of the toner image in such a manner as to correct for said deviation.