Abstract: A duplex printer has drive motors for driving transfer surfaces carrying toner particle images to transfer stations at which the images are transferred to opposed faces of a substrate web. A web drive motor drives the substrate web through the transfer stations. Sensors sense movement of the transfer surfaces and a control device controls the drive motors in response to signals received from the sensors. Thereby desired registration between the first and second images at a desired location on the substrate web is ensured.

Abstract: The printer has at least two printing stations which cause images to be printed on a substrate. The printer is capable of registration adjustment. First and second patterns of spaced registration marks are printed onto the substrate by operation of the printing stations. The second pattern partially overlaps the first pattern to form a composite pattern of registration marks. The composite pattern is illuminated and the reflectivity thereof is examined at wavelengths complementary to the colors of the first and second patterns to obtain a reflectivity signature for the composite pattern. The reflectivity signature of the composite pattern (120) is compared with a predetermined signature to determine an adjustment factor for the printer.