Drive of the inking unit in an intaglio printing machine

1. Intaglio printing machine comprising at least a plate cylinder carrying printing plates with engravings corresponding to a specific intaglio structure to be printed on a substrate, and cooperating with an impression cylinder carrying the substrate to be printed, a collector cylinder with at least one blanket on which ink in different colours is deposited by selector cylinders, each selector cylinder receiving ink of a given colour from an associated inking device and having reliefs with contours corresponding to the area of the intaglio structure to be inked with said given colour, wherein said intaglio printing machine further comprises means for varying the length of ink deposited on said collector cylinder by said selector cylinders, said means including drive means for driving the selector cylinders into rotation independently of said collector cylinder.

2. Intaglio printing machine as defined in claim 1 , wherein said drive means comprise at least a motor.

3. Intaglio printing machine as defined in claim 2 , wherein each motor drives the associated selector cylinder through an arrangement of pinions.

4. Intaglio printing machine as defined in claim 3 , wherein each inking device comprises a duct roller which is driven together with the associated selector cylinder by said motor through a second arrangement of pinions.

5. Intaglio printing machine as defined in claim 3 , wherein each inking device comprises a duct roller which is driven together with said collector cylinder through a second arrangement of pinions.

6. Intaglio machine as defined in claim 1 , further comprising means for determining elongation of an individual printing plate, said means including a pattern engraved in said printing plate which is reproduced on the substrate to be printed and allows determination of the elongation of the individual plate and correction of the relative motion of the selector cylinders with respect to the collector cylinder.

7. Intaglio machine as defined in claim 6 , wherein said engraving pattern comprises two sets of parallel lines.

8. Intaglio printing machine as defined in claim 1 , further comprising an optical device for measuring the elongation of the plate and feeding back this elongation for the correction of the relative motion of the selector cylinders with respect to the collector cylinder.

9. A method of inking a plate cylinder in an intaglio printing machine comprising a collector cylinder for inking the plate cylinder and on which ink in different colours is deposited by selector cylinders, wherein said method comprises the step of driving the selector cylinders into rotation independently of said collector cylinder so as to vary the length of ink deposited on said collector cylinder by said selector cylinders.

10. The method as defined in claim 9 , further comprising the steps of determining elongation of a printing plate carried by said plate cylinder and correcting the drive of the selector cylinders to compensate for said elongation.

11. The method as defined in claim 10 , wherein determination of the elongation of the printing plate includes providing the said printing plate with an engraved pattern and determining a shift in the ink deposition on said engraved pattern.

12. The method as defined in claim 11 , wherein said engraved pattern includes a set of parallel lines and only one line among said set of parallel lines is inked, and wherein determination of a shift in the ink deposition includes determining which line among said set of parallel lines is inked.

13. The method as defined in claim 10 , wherein determination of the elongation of the printing plate is performed by an optical device.