System for feeding portions of material to an injection molding machine

A method for controlling the average weight of each of portion of a plurality of portions of material fed to an injection molding machine from a feeding system that comprises at least a hopper and a weighing device, said method comprising:

• in a first weighing step, weighing said hopper;
• after said first weighing step, dispensing a plurality of portions of material, the plurality of portions being constituted by a given number of portions;
• in a second weighing step, after said dispensing step, weighing said hopper;
• calculating the difference between the weight of said hopper determined in said first weighing step and the weight of said hopper determined in said second weighing step, the difference constituting the loss of weight of said hopper;
• and
• dividing the loss of weight of said hopper by the said given number of said plurality of portions,
• wherein said weighing steps are performed with a weighing device and the given number of portions is equal to at least the number calculated by dividing the sensitivity of said weighing device by an estimated or desired weight of each fed portion, and wherein said estimated or desired weight of each fed portion is smaller than said sensitivity.