Packing Machine Compensating for Errors in Film Printing

Abstract

A packaging machine with a compensation device for film printing errors, having a film unwinder; a drive; a shaper; a number of welders; a number of cutters for separating the successive packages before they are moved to a number of filling and closing stations; a number of photocells for detecting a number of blemish spots printed onto the film; and a compensation device for film printing errors, comprising: two guide rollers and a drive roller fixed to a number of actuation means responsible for moving the same up to a number of positions in which the film defines, between said guide rollers and said drive roller, a loop of variable length to compensate potential film printing errors as it passes through the welders.

What is claimed is: 
     
         1 . A packaging machine with a compensation device for film printing errors, suitable for forming successive packages from a printed, heat-weldable film supplied from a reel, which comprises: a film unwinder; at least one drive for moving the film forwards; a shaper for folding the film along its center lengthways, thus defining two continuous, opposite bands; a number of welders for joining the two bands at a number of closing areas of the packages at the lower end and side ends thereof; a number of cutters for separating the successive packages before they are moved towards the filling and closing stations; a number of photocells for detecting a number of blemish spots printed onto the film and a compensation device for film printing errors; characterized in that said compensation device comprises the following elements between the drive and the unwinder: two free-rotating guide rollers arranged on a first side of the film trajectory and spaced in the forwards moving direction of the film; a free-rotating drive roller, arranged on a second side of the film trajectory, between the two guide rollers and fixed to an actuation means responsible for moving the same transversally relative to the forward direction of the film, up to a number of positions in which the film defines, between the guide rollers and said drive roller, a loop of variable length, suitable for compensating potential printing errors on the film as it passes through the welders. 
     
     
         2 . The packaging machine according to  claim 1 , characterized in that the drive roller actuation means comprise: a servomotor controlled by a PLC assisted by a photocell, which detects the blemish spots printed on the film in an area near to the welders and; a mechanism that transforms the rotary motion provided by the servomotor into transversal linear motion of the drive roller. 
     
     
         3 . The packaging machine, according to  claim 1 , characterized in that it comprises a film tensioner between the unwinder and the welders.