Patent attributes
When images are to be printed on two, front and lower surfaces of a sheet, in order to register the position of the image on the front surface and the position of the image on the back surface highly accurately, an image printing apparatus of this invention includes an image printing section which forms the image for the front surface of the sheet as well as an image of a reference mark on a photosensitive member at one portion in a region outside an image printing region and transfers the images onto the front surface of the sheet, a fixing unit which fixes the transferred images on the sheet, a line sensor which detects the reference mark after fixing printed on the front surface of the sheet, an arithmetic operating section which obtains a shrinkage factor of the sheet on the basis of a size of the reference mark before fixing and a size of the detected reference mark after fixing and calculates a position and magnification of the image to be printed on the back surface on the basis of the shrinkage factor, and a control section which performs control operation to print the image on the back surface of the sheet on the basis of the calculated position and the calculated magnification.
