Printing unit with printing cylinders directly-driven by induction motors

A rotary printing machine with multiple interactively arranged printing cylinders, comprising:

• a frame having two side walls;
• a directly-driven printing cylinder mounted between the two side walls, the directly-driven printing cylinder having a rotatable part rotatable about an axis;
• an interacting printing cylinder adjacent said directly-driven printing cylinder;
• and
• at least one electrically controlled induction motor operable for producing magnetic forces lateral to the rotational axis to directly drive said directly-driven printing cylinder, said induction motor having a rotor connected to the rotating part of the directly-driven printing cylinder and a stator predeterminately spaced from the rotor and fixed to at least one of the side walls for adjusting a radial position of said directly-driven printing cylinder relative to the adjacent interacting printing cylinder through operation of the induction motor using the magnetic lateral forces generated between the rotor and stator, when the induction motor is operated, the rotor and stator being coaxial, said induction motor including means for producing asymmetrical prestress forces, said asymmetrical prestress force producing means normally urging said directly-driven printing cylinder to an off position in which the directly-driven cylinder is radially spaced from the adjacent cylinder, regardless of electric control of the induction motor, eccentrically relative to an on position in which the directly-driven printing cylinder is disposed in contact with the adjacent interacting printing cylinder by the lateral magnetic forces.