Ultrasonic welding system

An ultrasonic welding system for making welds on a strip made of polymeric material, the welding system comprising a supporting structure, N welding equipment mounted on said supporting structure, with integer N at least equal to 1, and a processor, wherein:

• the N welding equipment each comprise a pair of welding heads made of a sonotrode, comprising a sonotrode welding surface, and an anvil, comprising an anvil welding surface;
• in each of the N welding equipment, one movable welding head between the two welding heads of each pair of welding heads is movable with respect to the other welding head of the pair between a non-operating position and a welding position, and vice versa, wherein:
• in the non-operating position, the sonotrode welding surface and the anvil welding surface are spaced apart;
• and
• in the welding position, the sonotrode welding surface and the anvil welding surface are in contact with each other, to engage the strip, and in an alignment condition;
• each of the N welding equipment comprises a control member operatively associated with the respective sonotrode, said control member being configured to vibrate the sonotrode at a nominal ultrasonic vibration frequency and to detect a current value of the vibration frequency of the sonotrode;
• the processor is configured to monitor, for each pair of welding heads, the alignment condition between the sonotrode welding surface and the anvil welding surface;
• and wherein the welding system comprises at least one of the following features:
• the processor is operatively connected to the control member of each of the N welding equipment and is configured to determine, for each pair of welding heads, a presence of a misalignment with respect to the alignment condition if, while the movable welding head is staying in the welding position, the current value of the vibration frequency of the sonotrode detected by the control member is outside a respective acceptable range with respect to the nominal ultrasonic vibration;
• and
• each of the N welding equipment comprises a vibration sensor which is mounted on the movable welding head of the respective pair of welding heads and is operatively connected to the processor, the processor being configured to determine the presence of a misalignment with respect to the alignment condition if vibrations detected by the vibration sensor during a movement of the movable welding head between the non-operating position and the welding position have values outside a respective acceptable range.