Unwinding apparatus for a wrapping machine

An unwinding apparatus associable with a wrapping machine and arranged to deliver a film of extensible plastic material that is unwound from a reel comprising:

• a first pre-stretching roller and a second pre-stretching roller rotatable about respective longitudinal rotation axes and arranged to unwind and pre-stretch said film;
• a motion transmission system configured to connect said pre-stretching rollers to each other and transmit a rotation motion from said first pre-stretching roller to said second pre-stretching roller with at least one defined transmission ratio, said motion transmission system comprising:
• at least two toothed driving wheels having different respective numbers of teeth, mounted coaxial and integral to each other, and rotated by said pre-stretching roller;
• at least two toothed driven wheels having different respective numbers of teeth, mounted coaxial to said second pre-stretching roller and selectively couplable to said second pre-stretching roller, each toothed driven wheel meshing with a respective toothed driving wheels in order to transmit the rotation motion of the first pre-stretching roller to the second pre-stretching roller with a corresponding transmission ratio when said toothed driven wheel is coupled to said second pre-stretching roller;
• a selector device that can be operated to couple a toothed driven wheel at a time to said second pre-stretching roller;
• wherein said selector device comprises:
• a driven shaft connected to said second pre-stretching roller, rotatably supporting said toothed driven wheels and provided with a longitudinal internal cavity having at least one first lateral through opening and one second lateral through opening suitable for housing respective locking elements;
• a selector pin sliding inside said internal cavity and provided with at least one first transverse protrusion and one second transverse protrusion, said selector pin being movable at least between a first operative position, in which said first transverse protrusion abuts and pushes at least one locking element to protrude externally from said first lateral through opening so as to engage a first seat of said first toothed driven wheel and to couple the first toothed driven wheel to said driven shaft, and a second operative position, in which said second transverse protrusion abuts and pushes at least one locking element to protrude externally from said second lateral through opening so as to engage a second seat of said second toothed driven wheel and to couple the second toothed driven wheel to said driven shaft.