Rewinding machine and method for controlling the speed of the motors in a rewinding machine

1. A rewinding machine for unwinding primary reels of a web material and rewinding said web material in secondary reels, comprising:

a winding station with winding members operated by at least one winding motor;

at least one unwinder with at least one unwinding member operated by at least one unwinding motor;

at least one guide roller along a feed path of the web material;

at least one load sensor associated with the guide roller, the load sensor being configured to detect a parameter proportional to the tension of the web material guided around the guide roller; and

a control unit adapted to modulate a difference in speed between the winding members and the unwinding member as a function of a signal from the load sensor.

2. The rewinding machine of claim 1 , wherein the control unit is configured: to vary the speed of the unwinding member, and therefore of the primary reel in the unwinder, as a function of the signal of the load sensor, so as to maintain the tension in the web material around a desired value.

3. The rewinding of claim 1 , wherein the control unit is configured to perform a winding cycle of secondary reels of web material coming from a primary reel comprising: an acceleration ramp from an initial speed to an operating speed, a winding step at operating speed, and a deceleration ramp from the operating speed to a final speed; and wherein the control unit is adapted to modulate the difference in speed between the winding members and the unwinding member as a function of the signal coming from the load sensor during at least one of said acceleration ramp and said deceleration ramp.

4. The rewinding of claim 3 , wherein the initial speed and the final speed are equal to zero.

5. The rewinding of claim 1 , wherein the control unit is configured to vary the speed of the unwinding member, and therefore of the primary reel in the unwinder, as a function of the signal of the load sensor, so as to maintain the tension in the web material around a desired value that is a function of at least one of: a characteristic of the web material; a winding speed of the web material.

6. The rewinding of claim 5 , wherein the desired value is a function of the winding speed and the desired value for first speeds is greater than the desired value for second speeds, the first speeds being greater than the second speeds.

7. The rewinding of claim 1 , further comprising a cutting device adapted to divide the web material into a plurality of strips, and wherein the winding station is adapted to wind the single strips in respective secondary reels placed side by side to one another.

8. The rewinding of claim 1 , wherein the guide roller, with which said at least one load sensor is associated, is motorized.

9. The rewinder of claim 1 , wherein the web material is a tissue paper web.

10. A method for rewinding a web material, comprising the steps of:

unwinding a primary reel of web material comprising at least one ply of tissue paper by at least one unwinding member controlled by an unwinding motor;

winding the web material in a winding station by at least one winding motor and forming at least one secondary reel in the winding station;

detecting a parameter function of the tension of the web material along the path between the unwinding member and a winding station;

controlling the difference between the speed of the winding motor and of the unwinding motor as a function of said parameter;

inserting at least one winding core into the winding station;

performing an acceleration ramp of the web material coming from the primary reel in the unwinder from an initial speed to an operating speed while winding the web material in the at least one secondary reel in the winding station;

performing winding of the web material around said at least one winding core at the operating speed;

performing a deceleration ramp from the operating speed to a final speed;

interrupting the web material; and

removing said at least one secondary reel from the winding station.

11. The method of claim 10 , wherein said parameter is a signal of a load sensor associated with at least one guide roller around which the web material is guided.

12. The method of claim 10 , comprising the step of modulating the speed of at least one of said unwinding motor and winding motor to maintain the tension of the web material around a given value.

13. The method of claim 10 , comprising the steps of: winding the web material at a winding speed; modulating the unwinding speed as a function of said parameter to maintain the tension of the web material around a given value.

14. The method of claim 13 , wherein the given value is a function of at least one of: a parameter of the web material and the winding speed.

15. The method of claim 14 , wherein the given value first winding speeds is greater than the given value for second winding speeds, the first winding speeds being greater than the second winding speeds.

16. The method of claim 10 , wherein the initial speed and the final speed are equal to zero.

17. The method of claim 10 , comprising the step of modulating the speed of the unwinder as a function of the parameter detected during at least one of said acceleration ramp and said deceleration ramp.

18. The method of claim 10 , comprising the step of dividing the web material into a plurality of strips, and winding the single strips in respective secondary reels placed side by side to one another in the winding station.

19. A start-stop tissue paper rewinding machine for unwinding primary reels of a tissue paper web material and rewinding said web material in secondary reels through successive winding cycles spaced by stops for replacement of the secondary reels with new winding cores, the start-stop tissue paper rewinding machine comprising:

a winding station with winding members operated by at least one winding motor;

at least two unwinders, each unwinder of the at least two unwinders comprising at least a respective unwinding member operated by at least one respective unwinding motor;

for each of the at least two unwinders, at least one respective guide roller along a feed path of the web material unwound from the respective unwinder;

at least one respective load sensor associated with each guide roller, the sensor being adapted to detect a parameter proportional to the tension of the respective web material guided around the guide roller; and

a control unit, adapted to modulate a difference in speed between the winding members and the unwinding member of each unwinder as a function of a signal from the respective load sensor.

20. A method for rewinding tissue paper web materials, from primary reels to secondary reels, through successive winding cycles spaced by stops for replacement of the secondary reels with new winding cores, the method comprising the steps of:

unwinding a first primary reel of tissue paper web material comprising at least one ply of tissue paper by a first unwinding member controlled by a first unwinding motor;

unwinding a second primary reel of tissue paper web material comprising at least one ply of tissue paper by a second unwinding member controlled by a second unwinding motor;

winding the first web material and the second web material in a winding station by at least one winding motor and forming at least one secondary reel in the winding station, wherein a plurality of secondary reels are produced in a sequence of start-stop cycles by winding the first web material from the first primary reel and the second web material from the second primary reel;

detecting a parameter function of the tension of the first web material and of the second web material along the respective path between the first unwinding member and the second unwinding member and the winding station;

controlling a difference between a speed of the winding motor and of each unwinding motor as a function of said parameter function.