Gravimetric metering device and control method thereof

A method for controlling a gravimetric metering device (1) which is provided to add an additive material to a polymer material, the gravimetric metering device comprising:

• a hopper (3) configured to contain the additive material,
• a supply member (5), which is provided downstream of the hopper (3) in order to receive the additive material which is discharged from the hopper and to transport it towards a discharge opening (9) which is connected to the polymer material,
• a first weighing element (16) which is associated at least with the hopper (3) and which is provided to detect the weight of the additive material which is discharged from the gravimetric metering device (1) within a first maximum weighing range,
• a second weighing element (17) which is associated at least with the hopper (3) and which is provided to detect the weight of the additive material which is discharged from the gravimetric metering device (1) within a second maximum weighing range which is different from the first maximum weighing range,
• a control unit (11) which is associated with the supply member (5) and with the first and second weighing elements (16, 17),
• wherein the method comprises:
• defining a target flow rate of additive material to be supplied to the polymer material,
• defining a nominal quantity of additive material to be charged in the hopper capable of allowing the metering of the additive material with the target flow rate for an adequate minimum time,
• comparing the nominal quantity of additive material with the first and second maximum weighing ranges and selecting one from the first and second weighing elements (16, 17) as the main weighing element,
• detecting, by means of the main measuring element, the weight of at least the hopper (3),
• determining, by means of the control unit (11), the flow rate of additive material which is discharged from the gravimetric metering device (1) from the weight measurements detected by the main weighing element (16;
• 17), and
• comparing the flow rate of additive material determined by means of the control unit with the target flow rate and consequently regulating the supply member (5).