Patent ID: 7050731

Claim:
An image forming apparatus, comprising: at least one image carrier configured to carry toner images and pattern toner images thereon; an endless transfer belt configured to one of directly and indirectly receive the toner images and the pattern toner images from the at least one image carrier, the transfer belt being spanned around a drive roller that drives the transfer belt to rotate and at least one driven roller; and a position shift detector configured to detect positions of pattern toner images formed on the at least one image carrier, wherein assuming that “N” is an integer equal to or greater than 1, pattern toner images are formed on the at least one image carrier at an interval of “1/N” of a circumferential length of the at least one image carrier, and the pattern toner images are transferred from the at least one image carrier onto the transfer belt over one cycle length of the transfer belt, wherein the position shift detector detects positions of the pattern toner images to obtain position shift data, and wherein moving average values of “N” number of the position shift data are calculated, wherein the moving average values are calculated in one cycle length of the transfer belt with elimination of a speed variation component of the image carrier by low pass processing.