Unit and method for applying opening devices to a web of packaging material

A unit for applying opening devices to a web of packaging material at predetermined areas of said web arranged at a non-zero distance from one another along said web;

• wherein the web fed to the unit is provided with a plurality of pre-laminated holes,
• said unit comprising:
• a feeding group configured for feeding said web along an advancing path;
• at least one first tool, arranged at a first fixed desired position along said path thereby defining a respective first axis fixed along said path, and configured to apply a first opening device to a corresponding first predetermined area arranged at said first desired position;
• wherein said first tool is a first molding station for molding said first opening device onto said corresponding first predetermined area arranged at said first desired position;
• and
• at least one second tool, arranged at a second fixed desired position along said path thereby defining a respective second axis fixed along said path, and configured to apply a second opening device to a corresponding second predetermined area arranged at said second desired position wherein the second tool is a second molding station for molding said second opening device onto said corresponding second predetermined area arranged at said second desired position;
• a buffer portion arranged along said path, downstream of said second tool and upstream of said first tool, and configured to include and/or accumulate a web portion having a number of said predetermined areas which is an integer multiple of the number of tools of said unit;
• a first position sensor, arranged upstream of said first tool along said path, configured to detect the position of said first predetermined area and to generate a first information correlated to the detected position of said first predetermined area;
• a second position sensor, arranged upstream of said second tool along said path, configured to detect the position of said second predetermined area and to generate a second information correlated to the detected position of said second predetermined area;
• and
• a control unit configured to receive said first information and said second information, to compare said first information with a third information correlated to a pre-set nominal position of said first predetermined area along said path, to compare said second information with a fourth information correlated to a pre-set nominal position of said second predetermined area along said path, and to calculate a first position difference value, based on the comparison between said first information and said third information, and a second position difference value, based on the comparison between said second information and said fourth information;
• said feeding group comprising:
• an advancing device configured to advance said first predetermined area towards and at said first desired position, on the basis of said first position difference value, and to feed said web portion to said buffer portion, wherein the advancing device is configured to advance a first pre-laminated hole towards and at a respective desired position, at which an axis of the first pre-laminated hole coincides with the first axis, on the basis of the calculated first position difference value;
• and
• an adjusting device configured to position said second predetermined area at said second desired position, on the basis of said second position difference value, wherein the adjusting device is configured to position a second pre-laminated hole at a respective desired position, at which an axis of the second pre-laminated hole coincides with the second axis, on the basis of the calculated second position difference value.