Textiles: weaving – Weft manipulation – Weaving with stationary weft supply
Patent
1995-08-04
1997-10-07
Falik, Andy
Textiles: weaving
Weft manipulation
Weaving with stationary weft supply
B65H 5122, D03D 4734
Patent
active
056737297
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention concerns a weft yarn feeder for gripper or projectile looms having improved characteristics.
BACKGROUND OF THE INVENTION
It is well known to feed the yarn to machines making use thereof, particularly the weft yarn to looms, by means of feeding devices or yarn feeders: such devices are positioned between the spool and the loom, and are meant to temporarily store the weft yarn, facilitating its unwinding from the spool, and to subsequently feed it to the loom insertion members with optimal and preset yarn tension values.
The type of structure universally adopted at present for such feeding devices involves winding the yarn into successive turns around a drum kept stationary, by means of a winding arm moved by an electric motor. Means for detecting the amount or reserve of yarn present on the winding drum are provided to control the running and rotational speed of the motor of the feeding device according to the amount of yarn drawn by the loom, so as to make the yarn unwinding speed from the spool as uniform as possible.
When weft yarn feeders are used on gripper or projectile looms, they comprise at their outlet end yarn braking means, positioned downstream of the reserve winding drum and meant to feed the yarn to the loom with a specific desired tension. Many of the known yarn braking devices act directly on the outlet end of the drum and are positioned upstream of an outlet yarn guide of the feeder, meant to ensure a correct unwinding of the yarn. Most weft yarn feeders make use of braking devices consisting of a plurality of natural or synthetic bristles, fixed to a support in the form of a closed ring carried by a bracket with the capability to move along the main axis of the weft yarn feeder. The plurality of bristles bear with a variable pressure adapted to be preset by adjusting the axial position of the bracket onto the outer periphery of the reserve winding drum of the weft yarn feeder. Other weft yarn braking devices, which are also widely adopted, and act directly onto the outlet end of the feeder drum, make use of a braking element with varying flexibility. Such braking elements comprises a plurality of thin strips positioned side-by-side onto a frustoconical surface. This braking element is mounted onto a cup support having an open bottom, carried by a bracket of the yarn feeder and whose position is adjustable along the drum axis.
In weft yarn feeders adopting the above-mentioned braking devices, though the conditions of weft insertion into the loom have been improved, it has not been possible to fully and efficiently solve the problem concerning the optimal control of the tension of the weft yarn being fed to the loom.
This problem is particularly felt in the weft insertion cycle in gripper looms with weft yarn exchange at the center of the shed, wherein yarn tension needs to be kept at a high level at the moment in which the yarn is caught by the carrying gripper, at the inlet of the shed, and at the moment in which the leading end of the yarn exchanges from the carrying gripper to the drawing gripper at the center of the shed.
Now, the drawback of weft yarn feeders adopting the known yarn braking devices, considered heretofore, is that they tend to allow yarn tension to drop below the required levels when weft yarn exchange takes place. Attempts have been made to overcome this drawback by increasing the value of the preset tension, but this unfortunately means raising the top tension value when, to the preset tension produced by braking, there is added the tension produced by inertia of the yarn, at the moment of maximum acceleration of the grippers, before and after weft yarn exchange.
The tension peaks determined by the above situation are obviously undesirable, in that they cause high stresses on the weft yarn, which may easily result in its breakage.
Hence, there is a demand for weft yarn feeders which--while keeping the tension of the weft yarn being fed as low as possible, for an efficient working of the loom--are capable of eliminating
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patent: 4068807 (1978-01-01), Jacobsson
patent: 4153214 (1979-05-01), Savio et al.
patent: 4165049 (1979-08-01), Pejchal et al.
patent: 4785855 (1988-11-01), Benz et al.
patent: 4926912 (1990-05-01), Zenoni
patent: 5094275 (1992-03-01), Shaw et al.
patent: 5181544 (1993-01-01), Deiuri
patent: 5316051 (1994-05-01), Zenoni et al.
Bertolone Roberto
Maina Bruno
Falik Andy
Nuova Roj Electrotex S.r.l.
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