Patent ID: 8195323

Claim:
A method for controlling advance of a web material having characteristics of extensibility and comprising successive stretches of the web material for the production of respective articles, in which, in the passage from a delivery assembly to a treatment station functioning cyclically, said web material is subjected to extension and in which the stretches of web material are fed in an extended condition to the treatment station in a given phase relationship with respect to the position of the treatment station in the framework of the operating cycle of the treatment station itself, the method comprising: identifying a position of operation of the treatment station to be used as a reference position for said given phase relationship; detecting, for each stretch of said web material, reference marks on the web material to obtain a real position of operation of the treatment station used for feeding the stretch of said web material to the treatment station with said given phase relationship; detecting a position error between said real position of operation and said reference position; controlling operation of said delivery assembly in order to minimize said position error, detecting the real position of operation under the control of a signal sent by a first sensor operating on a non-extended portion of said web material to calculate a first value of average angular position of the treatment station; performing detection of further real positions of operation of the treatment station under the control of a signal sent by a second sensor operating on an extended portion of the web material to calculate a second value of average angular position of the treatment station; comparing the value of the first average angular position to the value of the second average angular position to obtain a coupling error; and adjusting said reference position adaptively on the basis of the coupling error, so as to compensate for the variations of the characteristics of extensibility of said web material.