Maintaining perforation phasing

摘要

In an apparatus for making plastic bags or the like from a continuous film of material comprising a sealing drum having at least one seal bar for imparting transverse seals to the film at regularly spaced intervals and a perforator having a rotatable perforator blade for imparting transverse perforations to the film at regularly spaced intervals, the film comprising print marks appearing thereon at regularly spaced intervals, an apparatus and method are disclosed for tracking the positions of each print mark and each perforation and comparing the difference between these positions to a desired difference and thereafter adjusting the angular position of the perforator blade until the difference between the positions of each print mark and each perforation is equal to the desired difference to thereby maintain a desired spacing between each print mark and each perforation.