Device for continuous compensation of stretching of film during drawing applicable on packaging machines

A film stretching compensation device for a packaging machine with intermittent advancement movement, a wrapping material being constituted by a film made of a flexible plastic material, for carrying out a continuous compensation of film stretching during drawing thereof, the machine comprising:

• a sealing station;
• a cutting station;
• a first film drawing unit including motorized first driving rollers;
• a further mobile roller element exerting a given force on the film during advancement thereof;
• a second film drawing unit including motorized second driving rollers arranged downstream of the first film drawing unit group and disposed between the sealing station and the cutting station, where each film drawing unit comprises a second marker sensor for detecting markers located at regular intervals along the film;
• wherein said film stretching compensation device comprises a third film drawing unit and upstream of the sealing station and downstream of the mobile element, located between the first and second film drawing units, the third film drawing unit comprising a third marker sensor, as well as a motor and a roller opening mechanism for automatically controlling a displacement of driving rollers of the third film drawing unit,
• wherein the roller opening mechanism works in a synchronized way with the first drawing group and the second drawing group and contemporaneously compares a signal of the third marker sensor of the third drawing group with the second marker sensor of the second drawing group during drawing the film.