Method and apparatus for controlling media-to-image registration of a single-pass intermediate transfer member-based printing apparatus

Abstract

An improved printing apparatus provides for very accurate synchronization between cut sheet print media and the unfixed image which is conveyed on an Intermediate Transfer Member (ITM) such as a belt or a drum, and which is targeted for said print media. The printing apparatus is constructed as a single-pass ITM-based electrophotographic (e.g., laser) printer, and the length of the input print media pathway prior to image-to-media transfer is significantly shorter than the sum of the lengths of the image travel along a photoconductive drum and ITM. The print media is typically launched after imaging has been initiated on the photoconductive drum by an imaging apparatus. Variance in the leading edge of the print media with respect to the leading edge of image can be introduced due to phenomena such as pick errors, velocity variation, and uncertainties in the paper stack height. The present invention minimizes this leading edge variance to a tightly targeted specification by accurately sensing the positions of the print media and the ITM image, and correcting the print media's position by controlling the velocity of the print media prior to arriving at the transfer nip. In addition, the present invention detects the presence of print media within the sheet feeder cassette tray before imaging is started in the ITM belt, thereby minimizing the amount of waste toner generated by the printing apparatus. The imaging procedure on the ITM belt typically begins at a time prior to the printer controller having precise knowledge as to the location of the “next” sheet of print media within the combination of the input print media pathway and sheet feeder cassette tray.