These intermediate feeding devices, which are also called weft storage feeders or weft accumulators, play today an important role in the weaving machines where the weft is unwound overhead from the cone and is subjected to abrupt accelerations due to the drawing-off tension exerted by the insertion element (rapier, projectile, fluid). The balloon which is formed at each insertion can cause coil sliding and snarls, owing to the difficulty of braking adequately the yarn and to the high unwinding speed of the yarn from the cone, which results into abrupt stresses, varying with diameter and speed variation. The present weaving speeds made thus absolutely necessary the use of an auxiliary apparatus placed between the cone and the insertion device. This apparatus positions the thread in a way as to favour its unwinding under lower stresses, and at the same time takes off from the package the necessary thread length, also making the most of the dead times between an insertion and the other, therefore with lower unwinding speeds and more continuously.
In the air-jet or water-jet machines, we should better speak of thread length pre-measuring devices, as the feeder has the task of winding on its own drum a thread length which corresponds exactly to an insertion. In modern pre-measuring devices, the thread length wound on the drum is controlled by opto-electronic sensors.
The feeders are supplied together with various outfits and adjustment possibilities, which vary according to the yarn type and count and to the insertion system used. Each of them is equipped with an independent motor, which speed can be modified within a wide range of values. The feeders can also be connected with the driving unit of the weaving machine and interact with it. Their general structure is presented in the scheme as per figure the thread is taken off from the cone by a thread guide 1 composed of an eyelet obtained on a ring which is put in rotation by an electric motor M. The thread guide winds the thread on a drum 2, consisting of a series of fixed segments alternated with a series of oscillating segments. These segments, through their movement, move the coils forward along the surface, positioning them in a regular way and keeping them separated one from the other.
At the moment of the insertion, the thread unwinds from the drum with a torsional movement opposite to the winding movement, passing through a braking system 3 which has the task of bringing the thread tension to the desired value and of maintaining it constant, and finally through another thread guide 4. A photocell system or any other system, suitably adjusted, will bring about the length of the thread reserve which is wound on the feeder’s drum.