The present invention relates to a negative yarn feeder provided with a weft-braking device for locking the unwinding loops of yarn at the final step of the insertion of the yarn into the loom, which step is particularly critical in the case of projectile looms.

As known, the so-called "negative" yarn feeders comprise a stationary drum on which a motorized flywheel winds a plurality of yarn loops forming a weft reserve. Upon request from the loom, the loops are unwound from the drum, then pass through a device for controlling the tension of the yarn, and finally are fed to the loom. The yarn feeders of the above type have the essential aim of maintaining the amount of loops substantially constant on the drum, thereby minimizing the tension of the yarn coming from the drum.

Mainly in the case of projectile looms, the yarn feeder is generally provided with an "anti-balloon" device, which essentially consists of a funnel having the aim of containing the balloon which forms while the yarn is unwound from the feeder. Devices of this type are disclosed, e.g., in EP0719354, EP1094138, and EP1149793. Particularly, in EP1149793 the anti-balloon funnel has a frustoconical profile defmed by a plurality of equally-spaced rods arranged along the generatrices of a frustum of cone, whereby the deposit of dust and the friction against the inner surface of the funnel are reduced.

As known, during the final step of the insertion, yarn loops in excess are liable to unwind from the drum by inertia. In order to contrast this drawback, it is known from US3834635 to provide the feeder with stationary brushes which are arranged in contact with the inner surface of the anti-balloon funnel. The unwinding yarn passes between the brushes and the funnel and, at the end of the insertion, when the loom has finished drawing yarn, it is braked by friction and consequently retained from further unwinding.

A drawback of the above device is that the brushes also brake the yarn during the insertion, when no braking action is required but, on the contrary, the yarn should run as freely as possible. This circumstance affects the smoothness of the yarn-feeding process and leads to a growth of dust generating by friction between the yarn and the brushes, which dust is liable to deposit within the funnel thereby affecting its operation.

US3834635 also discloses the use of air streams for braking the yarn. However, this solution is very complicated and expensive, because air-feeding means must pass through the swivelling, yarn-winding flywheel.

Therefore, it is a main object of the present invention to provide a yarn feeder having a weft-braking device which overcomes the above-cited drawbacks of the known brush-based devices, but which is simpler and cheaper to be manufactured then the pneumatic devices.

The above object and other advantages, which will better appear below, are achieved by the yarn feeder having the features recited in claim 1, while the dependent claims state other advantageous, though secondary features of the invention.

The invention will be now described in more detail with reference to a preferred, non-exclusive embodiment shown by way of non-limiting example in the attached drawings, wherein:

• Fig. 1 is a perspective view of a negative yarn feeder provided with a weft-braking device according to the invention;
• Fig. 2 is a front view of the yarn feeder of Fig. 1;
• Fig. 3 is a partial view in cross-section of Fig. 2 along line III-III;
• Fig. 4 is a longitudinal view of a portion of Fig. 1;
• Fig. 5 is a view in cross-section of Fig. 4 along line V-V, showing a detail to an enlarged scale of the weft-braking device of the invention.

With reference to the above Figures, a negative yarn feeder 10 comprises a stationary drum 12 and a swivel flywheel 14 which is coaxially supported at one end of drum 12 and is driven by a motor 15 for winding loops of yarn F on the drum, thereby forming a stock S. Yam F is unwound from drum 12 upon request from the loom, which in the present invention is preferably a projectile loom (not shown).

A stationary drum 16 longitudinally projects from the motor housing and supports an anti-balloon funnel 18. Anti-balloon funnel 18 consists of a plurality of equally-spaced rods 20 which are arranged along the generatrices of a frustum of cone and have one end attached to a smaller ring 22 defining the smaller base of the frustum of cone, and the opposite end attached to a larger ring 24 defining the larger base of the frustum of cone. A yarn-guide delivery eyelet 25 is arranged at the delivery end of the anti-balloon funnel.

Funnel 18 is coaxially arranged in front of drum 12 with its larger base facing the delivery end 12a of the drum. The inner surfaces of both smaller ring 22 and larger ring 24 are bevelled, and the innermost circumference of larger ring 24 advantageously has a diameter Da smaller than the yarn-winding diameter Dt of drum 12 (Fig. 3). Funnel 18 is attached to a slide 26 (Fig. 4) which is slidable along stationary drum 16 under control of a screw mechanism (not shown) operable by a knob 28, whereby the axial gap between anti-balloon funnel 18 and drum 12 may be changed. By adjusting knob 28, the gap L between the larger base of anti-balloon funnel 18 and the delivery end 12a of the drum may be minimized as a function of the yarn count. This possibility of adjustment partly deriving from the above-defined dimensional relation between the diameter of the drum and the diameter of the innermost circumference of larger ring 24, allows the balloon forming upstream of the funnel to be riduced or even eliminated even without providing anti-balloon funnel 18 with a cylindrical portion surrounding an ending portion of drum 12.

An annular support 30 surrounding drum 12 near its delivery end 12a is attached to stationary drum 16 and holds a pair of movable braking members at diametrally opposite positions (Fig. 5). Each braking member consists of an angular sector of a blistle brush (below, brush 34) which is anchored to the operating rod 36 of a linear, electro-magnetic actuator 37 driven by a microprocessor (not shown). Preferably, the microprocessor which controls the actuators also controls the feeder or the loom. Brush 34 is movable between a resting position spaced from the drum, in which it is received in a respective seat 38 of annular support 30 so that it does not interfere with the unwinding yarn, and an operative position, in which it juts out of seat 38 and engages the outer surface of the drum with the tips of its bristles.The microprocessor is programmed for activating the brushes at a predetermined instant, e.g., as a function of the position degrees of the loom. Programming the times of intervention of the brushes falls within the normal knowledge of the person skilled in the art, therefore no further description will be given about it.

In the operation, during the insertion the brushes 34 are received in the respective seats 38 and do not interfere with the yarn, which consequently may be freely unwound from the drum without coming into contact with them. Funnel 18 adjusted as above prevents the formation of the balloon. During the final step of the insertion, but a few instants before a predetermined ending time, the microprocessor enables the brushes. The latter engage the outer surface of the drum with their tips, brake the unwinding yarn (which yarn runs between the brushes and the outer surface of the drum) by friction, and finally lock it, thereby preventing loops in excess from unwinding from the drum by inertia.

As the person skilled in the art will appreciate, with the device according to the invention the braking action is applied only when required, i.e., at the end of the insertion. Therefore, a smooth insertion is obtained and the formation of dust is limited.

A preferred embodiment of the invention has been described herein, but of course many changes may be made by a person skilled in the art within the scope of the claims. In particular, though the above-described assembly including the anti-balloon funnel and the bristle-based braking system effectively prevents both the formation of the balloon and the unwinding of loops in excess at the end of the insertion, which phenomena are strictly correlated, of course the braking system is capable of operating in association with other conventional anti-balloon funnels. Moreover, although the above-described embodiment is only provided with two braking brushes held by the annular support at diametrally opposite positions, of course a higher number of brushes may be installed, e.g., three or four brushes spaced at equal angles; on the contrary, in certain cases a sole brush could be sufficient. Nevertheless, as will be obvious to the person skilled in the art, the brushes can be operated by conventional actuators of a different type, e.g., electrical actuators.