Unwinding device for reels of web material with dual drive mechanism and relative unwinding method
The device comprises: supports ( 3 A, 5 A; 3 B, 5 B) to support at least a reel (B 1 ) in an unwinding position; at least a peripheral drive mechanism which acts on the cylindrical surface of the reel being unwound and transmits peripherally to said reel a torque to draw it in rotation; and at least a center drive mechanism ( 41 ) which transmits centrally to said reel an auxiliary torque to draw it in rotation together with the torque transmitted by the peripheral drive mechanism.
1. An unwinding device for unwinding reels of web material wound around a central shaft and delivering said web material to a converting line, comprising:
supports to support at least a reel in an unwinding position;
at least a peripheral drive mechanism which acts on a cylindrical surface of the reel being unwound and peripherally transmits to said reel a torque to draw the reel in rotation;
at least a center drive mechanism which transmits centrally to said reel an auxiliary torque to draw the reel in rotation in combination with the torque transmitted by said peripheral drive mechanism;
a control system to reciprocally coordinate operation of said peripheral drive mechanism and of said center drive mechanism; and
a detection system to detect, during unwinding, angular displacement of an outermost web material on the reel in relation to the central shaft of the reel, operation of said center drive mechanism being controlled so as to correct said angular displacement.
2. Device according to claim 1 , wherein said control system controls at least an operating parameter of the center drive mechanism as a function of unwinding conditions.
3. Device according to claim 2 , wherein said control system controls speed of the center drive mechanism.
4. Device according to claim 3 , wherein said control system acts on the speed of the center drive mechanism to correct said angular displacement.
5. Device according to claim 2 , wherein said control system controls the auxiliary torque applied by said center drive mechanism.
6. Device according to claim 5 , wherein said control system is programmed to maintain the auxiliary torque applied by said center drive mechanism within a predetermined interval of values or at a predetermined value.
7. Device according to claim 1 , wherein speed of said peripheral drive mechanism is controlled so as to maintain a set value of tension of the web material delivered by said reel, a tensioning sensor being associated with said control system.
8. Device according to claim 1 , further comprising a first sensor to detect at least a first reference integral with the central shaft of said reel; and a second sensor to detect at least a second reference applied to the web material of the reel.
9. Device according to claim 8 , wherein said second sensor is carried by a supporting arm of the peripheral drive mechanism.
10. Device according to claim 1 , further comprising a sensor to detect a diameter of said reel, associated with said control system.
11. Device according to claim 10 , wherein said control system is programmed to control the center drive mechanism giving the center drive mechanism an angular rotation speed determined as a function of speed of the peripheral drive mechanism and of the diameter of the reel.
12. Device according to claim 11 , wherein said control system is programmed to produce a feedback signal on said center drive mechanism, said feedback signal modifying operation of the center drive mechanism as a function of unwinding conditions.
13. Device according to claim 12 , wherein said feedback signal is a function of said angular displacement.
14. Device according to claim 12 , wherein said feedback signal is a function of a value of the auxiliary torque applied to the reel by said center drive mechanism.
15. Device according to claim 1 , wherein said peripheral drive mechanism comprises a belt and means which press said belt on a cylindrical external surface of the reel being unwound.
16. Device according to claim 1 , wherein said center drive mechanism comprises a shaft equipped with coupling means engageable and disengageable in relation to the central shaft of the reel.
17. Device according to claim 16 , wherein said coupling means comprise a grooved coupling.
18. Device according to claim 16 , wherein said shaft is axially mobile to engage and disengage from the central shaft of the reel.
19. Device according to claim 18 , wherein said shaft is supported in a sleeve which slides axially inside a tubular element, said tubular element constituting a cylinder of a piston-cylinder actuator, of which said sleeve forms a moving piston.
20. Device according to claim 19 , further comprising a first gear splined on said shaft, meshing with a second gear toothing of which has an axial length sufficient to maintain the first gear and the second gear in contact in any axial position of the shaft.
21. Device according to claim 1 , wherein said supports include dual central end supports for at least two approximately axially aligned reels, with the center drive mechanism for one and for another of said reels being disposed between the dual central end supports for the two reels.
22. Device according to claim 1 , wherein said control system is programmed to disconnect one or another of the peripheral drive mechanism and the center drive mechanism.