A method for operating a supply group for supplying a packing band fed from reels with an automatic changing of the reels, for an object-packing machine, wherein the group comprises:
- a supply conveyor (13) along which the packing band (11) runs to a zone of use (45) where the packing band can be applied to an object being packed;
- a first support (17A) for supporting a first reel (12A) of a first band (11A) of packing material and a second support for supporting a second reel (12B) of a second band (11B) of packing material;
- a first entry conveyor (20A) for conveying the first band (11A) from the first reel (12A) to the supply conveyor (13);
- a second entry conveyor (20B) for conveying the second band (11B) from the second reel (12B) to the supply conveyor (13);
- first rollers for advancing (21A) for alternatively introducing and extracting the front end (HA) of the first band (11A) to or from the supply conveyor (13);
- second rollers for advancing (21B) for alternatively introducing and extracting a front end (HB) of the second band (11 B) into or from the supply conveyor (13);
- a central drawing roller (22) operative to be driven in two directions of rotation;
- two idle lateral contrast rollers (23a, 23b), each one disposed on an opposite side of the central drawing roller, and each movably mounted between a first position adjacent from the central roller (22), and a second position spaced from the central roller, wherein when a first of the two idle lateral contrast rollers is moved into the first position, the first band is pressed against the central roller, and when a second of the two idle lateral contrast rollers is moved into the first position, the second band is pressed against the central roller;
- a cutting device for transversally cutting (14) the first band or the second band located at a start of the supply conveyor to form a cut band;
- the method comprising:
- supplying the zone of use with the first band, and keeping the second band stationary, with a front end of the second band located at an entry to the supply conveyor (13);
- when the reel from which the first band unrolls is about to end,
- cutting the first band by the cutting device,
- activating one of the first and second rollers for advancing to extract a front end of the cut band from the supply conveyor (13), and
- activating another of the first and second rollers for advancing to introduce a front end of the second band supplied from the another of the first and second rollers into the supply conveyor (13).