Tissue paper converting line and method

1. A converting line for processing tissue paper, comprising:

an unwinder for unwinding reels of tissue paper;

a rewinding machine for forming rolls of tissue paper;

a feeding path between the unwinder and the rewinding machine, for at least one ply of tissue paper;

along the feeding path, at least one optical detection unit to detect thickness of the tissue paper fed along the feeding path in a feeding direction;

a control system, interfacing with the at least one optical detection unit and adapted to act on at least one production parameter of the converting line according to detected tissue paper thickness;

wherein said at least one optical detection unit comprises at least one light emitter and at least one light receiver, arranged opposite each other, wherein said at least one light emitter is adapted to emit a light beam which intersects a cylindrical surface of a guide roller, around which the tissue paper is driven, and wherein said at least one light receiver is adapted to receive said light beam which is not intercepted by said cylindrical surface.

2. The converting line according to claim 1 , further comprising, between the unwinder and the rewinding machine, an embossing unit comprising at least one embossing roller and at least one pressure roller, the at least one embossing roller and the at least one pressure roller defining an embossing nip, through which at least one ply of tissue paper passes.

3. The converting line according to claim 1 , wherein said at least one production parameter is one or more of: tissue paper tension, tissue paper speed, an embossing condition in an embossing unit of the converting line, length of tissue paper wound on a roll being formed in the rewinding machine, speed of one or more winding members of the rewinding machine, and a pressure of one or more winding members of the rewinding machine on a roll being formed.

4. The converting line according to claim 1 , wherein said at least one optical detection unit is combined with a tissue paper guide roller arranged along the feeding path and around which the tissue paper is driven; the at least one optical detection unit being configured and arranged to detect the thickness of the tissue paper in contact with the guide roller.

5. The converting line according to claim 4 , wherein the control system is adapted to acquire information on the thickness of the tissue paper synchronously with an angular position of the guide roller.

6. The converting line according to claim 1 , wherein the light beam is a laminar light beam.

7. The converting line according to claim 6 , wherein the laminar light beam lies on a plane which is substantially orthogonal to the axis of the guide roller.

8. The converting line according to claim 1 , wherein the at least one light emitter comprises a linear array of light emitters and the at least one light receiver comprises a linear array of light sensors, and wherein the at least one light emitter further comprises a cylindrical condenser.

9. The converting line according to claim 1 , wherein said at least one optical detection unit is configured and arranged to move transversally to the tissue paper and to measure the thickness of the tissue paper along a direction transverse to the feeding path of the tissue paper.

10. The converting line according to claim 1 , wherein the at least one optical detection unit comprises at least two sensors, staggered with respect to each other in a direction transverse to a forward direction of the tissue paper ply and spaced from each other in said transverse direction, so as to detect the thickness of the tissue paper in at least two transversally spaced points of the tissue paper ply.

11. The converting line according to claim 10 , wherein the control system is adapted to act on at least one auxiliary production parameter of the converting line so as to correct an alteration of the thickness of the tissue paper in transverse direction.

12. The converting line according to claim 11 , wherein said at least one auxiliary production parameter is one or more of a pressure profile between two rollers defining a nip through which the tissue paper passes, and a reciprocal inclination between axes of two rollers defining a nip through which the tissue paper passes.

13. The converting line according to claim 12 , wherein said two rollers defining the nip through which the tissue paper passes are rollers of an embossing unit.

14. The converting line according to claim 1 , further comprising two of said at least one optical detection unit, a first of said at least one optical detection unit and a second of said at least one optical detection unit being arranged in two points spaced from each other along the feeding path and each of the at least one optical detection units interface with the control system.