Measurement of paper speed using laser speckle detection

摘要

In a postage printing device, a printer is employed to print postage indicia on mail pieces. The printer is preferably a noncontact printer such as an ink-jet printer. Printing occurs as the mail piece moves relative to the print head of the printer, which requires that reliable motion information (e.g. a print clock signal) be made available to the electronics driving the print head. The reliable motion is provided in a noncontact way, preferably by directing a laser beam toward the mail piece and detecting a moving speckle pattern in the light scattered from the mail piece. <IMAGE>