Method and a device for checking wrapping material in a packaging machine

A method for checking wrapping material in a packaging machine comprising the steps of:

• supplying a continuous strip of wrapping material to a packaging machine along a feed path upstream of a user station enveloping predetermined products in the wrapping material itself, the continuous strip being supplied through a flow compensating chamber forming a loop expandable to length according to a variable and predetermined range;
• checking the wrapping material along at least one longitudinal wall of the flow compensating chamber by a plurality of emitter devices and detecting sensors arranged in succession along the longitudinal wall of the flow compensating chamber, each emitter device charging a predetermined portion of the loop of the continuous strip electrostatically and each detecting sensor detecting the electrostatic charges;
• electrostatically charging the predetermined portions via use of the emitter devices;
• detecting said electrostatic charges via use of the detecting sensors;
• monitoring continuously any variation in the length of the loop by means of the detecting sensors;
• comparing any variation in the length of the loop monitored with preset maximum and minimum values;
• correcting the length of the loop when the variation in length drifts beyond the preset maximum or minimum value.

A device for checking wrapping material in a packaging machine, wherein the wrapping material is supplied to the packaging machine, comprising;

• electrostatic charge emitter means to charge at least one predetermined portion of the wrapping material electrostatically at a first operative station,
• sensing means to detect the presence of electrostatic charges in the predetermined portion of the wrapping material at a second operative station, and
• discharger means positioned downstream of the emitter means and the sensing means and serving to eliminate the electrostatic charges from the wrapping material;
• a flow compensating chamber through which the wrapping material is advanced along a feed oath and caused to form a loop of lenath variable within a predetermined range,
• wherein the emitter means comprise a plurality of emitter devices ordered along the flow-compensating chamber and the sensing means comprise a plurality of sensors able to detect electrostatic charges. ordered likewise along the flow-compensating chamber and alternated with the emitter devices In such a way as to monitor the variation in length of the loop internally of the chamber;
• a controller acting to control the length of the loop and maintain such length in the predetermined range in response to the monitoring of the variation in length of the loop.