Printing unit for a printing machine

A printing unit (1) for a printing machine, having an image cylinder (2), an image generating device (3) for setting an image on the peripheral surface (4) of the image cylinder (2), and an image transfer cylinder (5) which transfers the image from the image cylinder (2) to a printing substrate (6), the image transfer cylinder (5) having a resilient cover (7) which exhibits a deformation (10, 10′) in respective force transmission areas (8, 9), between the image cylinder and the image transfer cylinder, and the image transfer cylinder and a transport belt (11) that carries the printing substrates (6), and is supported by a back-pressure cylinder (12) driving the image transfer cylinder (5) and the latter driving the image cylinder (2), by friction, comprising:

• a mount for said back-pressure cylinder (12), said mount including a device (13, 14) for selectively displacing said back-press cylinder with respect to the image transfer cylinder (5) with a pressing force (F(S)), a sensor (15) to register the substrate thickness, and a control system (16), the latter determining the pressing force (F(S)) with the aid of the substrate thickness (17) such that the speed of the image cylinder (2) remains constant with respect to changes in the effective radius (r) for driving the image transfer cylinder (5).