Direct drive for a printing machine

1. A device for driving a cylinder ( 1 ) of a printing machine, having an electric motor ( 3 ) with a rotor ( 14 ) arranged coaxially with respect to the cylinder ( 1 ) and is connected so as to rotate with the cylinder, and a stator ( 15 ) is held on a frame construction ( 2 ) in which the cylinder ( 1 ) is mounted such that it can be displaced axially, the rotor ( 14 ) and the stator ( 15 ) being dimensioned and coupled to the cylinder ( 1 ) and the frame construction ( 2 ), respectively, so that during any axial displacement of the cylinder ( 1 ) possible during the operation of the printing machine, the gap ( 16 ) formed between stator ( 15 ) and rotor ( 14 ) remains constant both with regard to gap width (s) and with regard to gap length, wherein a housing ( 9 ) of the electric motor ( 3 ) that accommodates the stator ( 15 ) is fixed to an outer ring ( 7 ) of an antifriction bearing ( 5 ) used to mount the cylinder ( 1 ) in the frame construction ( 2 ) wherein the rotor ( 14 ) is guided such that it can be displaced axially relative to the cylinder ( 1 ).

2. A device of claim 1 , wherein a linear guide ( 8 ), by means of which the antifriction bearing ( 5 ) used to mount the cylinder ( 1 ) can be displaced in the frame construction ( 2 ) at right angles to an axis of rotation (A) of the cylinder ( 1 ).

3. A device of claim 2 , wherein an intrinsically safe brake ( 53 ) for braking the assembly comprising cylinder ( 1 ) and rotor ( 14 ).

4. A device of claim 1 , wherein the rotor ( 14 ) has in its radially inner region a bush ( 26 ) which is mounted such that it can be axially displaced on the cylinder ( 1 ) or a journal ( 11 ) fixedly connected to the cylinder.

5. A device of claim 4 , wherein the bush ( 26 ) is fabricated from nonferrous metal.

6. A device of claim 1 , wherein the rotor ( 14 ) is longitudinally displaceably guided relative to the cylinder ( 1 ) by means of an antifriction mounting ( 36 ).

7. A device of claim 1 , wherein a bearing ( 38 ) which fixes an axial position of the rotor ( 14 ) relative to the housing ( 9 ) of the electric motor ( 3 ), irrespective of the axial positioning of the cylinder ( 1 ).

8. A device of claim 7 , wherein the bearing ( 38 ) provided is a grooved ball bearing, whose bearing rings ( 39 , 40 ) are firmly connected to the rotor ( 14 ) and the stator ( 15 ), respectively, of the electric motor ( 3 ).

9. A device of claim 1 , wherein the rotor ( 14 ) is attached to the cylinder ( 1 ) by means of at least one connecting element ( 41 ) which is compliant in an axial direction but at the same time rigid in the circumferential direction and which on one side, in a radially inner region, is connected to the cylinder ( 1 ) or a part ( 11 , 42 ) fixed rigidly to the cylinder, and on another side, in a radially outer region, is connected to the rotor ( 14 ).

10. A device of claim 9 , wherein the connecting element ( 41 ) is springy in the axial direction.

11. A device of claim 9 , wherein the connecting element ( 41 ) is fabricated by means of laser welding and/or connected to the rotor ( 14 ) and/or to the cylinder ( 1 ) or a part ( 11 , 42 ) fixed rigidly to the cylinder.

12. A device of claim 9 , wherein the connecting element ( 41 ) is fabricated from a composite material.

13. A device of claim 12 , wherein the composite material of the connecting element ( 41 ) comprises a metallic material and a polymer material.