Dual roll, variable sheet-length, perforation system

A method for intermittently cutting a moving target web, comprising:

• rotating a knife roll having at least one knife member to provide an operative knife-member speed;
• rotating an anvil roll having at least one anvil member to provide an operative anvil-member speed;
• positioning the knife roll and anvil roll to provide an operative nip region therebetween;
• moving a substantially continuous target web at a web speed through the nip region;
• coordinating a rotational positioning of the knife member with a rotational positioning of its cooperating anvil member to provide an operative, cutting engagement between the knife member and its cooperating anvil member to thereby cut the moving web at cut locations which are intermittently spaced along a machine-direction of the web;
• wherein
• a knife encoder has been operatively connected to the knife roll;
• rotational, knife positioning data has been provided from the knife encoder to an operative electronic computer;
• the knife roll has been rotationally driven with a knife servo mechanism which is operatively controlled by the computer;
• an anvil encoder has been operatively connected to the anvil roll;
• rotational, anvil positioning data has been provided from the anvil encoder to the computer;
• the knife roll has been rotationally driven with an anvil servo mechanism which is operatively controlled by the computer;
• to thereby coordinate the rotational positioning of the knife member with the rotational positioning of its cooperating anvil member and provide the operative, cutting engagement between the knife member and its cooperating anvil member;
• a selected amount of cutting interference has been provided between the knife member and its cooperating anvil member in the nip region during the rotating of the knife roll and anvil roll;
• the cutting interference has been maintained at a value of about at least about 0.1 mm;
• the web speed is at least about 100 m/min;
• the knife-member speed is at least about 70% of the web speed of the target web;
• and
• the anvil-member speed is at least about 70% of the knife-member speed.

An apparatus for intermittently cutting a moving target web, comprising:

• a knife roll which has at least one knife member and is rotatable to provide an operative knife-member speed;
• an anvil roll which has at least one anvil member and is rotatable to provide an operative anvil-member speed, the anvil roll positioned to provide an operative nip region between the anvil roll and the knife roll;
• a transport system which moves a substantially continuous target web at a web speed through the nip region;
• a control system which coordinates a rotational positioning of the knife member with a rotational positioning of its cooperating anvil member to provide an operative, cutting engagement between the knife member and its cooperating anvil member to thereby cut the moving web at intermittent locations spaced along a longitudinal, machine-direction of the web.