Weft feeder for eliminating yarn tension peaks

Details Weft feeder for eliminating yarn tension peaks Weft feeder for eliminating yarn tension peaks

1995-06-29

1996-11-26

Falik, Andy

Textiles: weaving

Weft manipulation

Weaving with stationary weft supply

242 4701, D03D 4734

Patent

active

055775365

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a weft feeder for gripper or projectile looms.
2. Description of the Related Art
It is well known to feed weft yarn to machines making use thereof, in particular looms, by feeder devices or "weft feeders". These feeders are devices which are placed between a reel and the loom and which have as their function to store temporarily the weft yarn, facilitating its unwinding from the reel, and to supply it subsequently with preset optimum tension values to picking members.
The basic type of weft feeder which is in universal use today has an arm driven by an electric motor for winding the weft yarn in successive turns onto a winding drum, which is kept motionless.
Devices for controlling the quantity or reserve of weft yarn on the winding drum govern the rate and speed of rotation of the electric motor as a function of the quantity of weft yarn unwound by the loom, thus ensuring that the speed at which the weft yarn is unwound from the reel is kept as uniform as possible.
Where weft feeders are used on gripper or projectile looms, they are provided on their outlet side, for the purpose of imparting to the weft yarn fed to the loom a desired degree of tension, with braking devices downstream of the winding drum on which the reserve is wound. Many of the known braking devices act directly on an outlet end of the drum and are found upstream of an outlet yarn guide provided in order to ensure that the weft yarn is correctly unwound. In many weft feeders, the yarn-braking devices used consist of a plurality of natural or synthetic bristles and are fixed to a support in the form of a closed ring which is carried by a bracket with the possibility of moving along the principal axis of the weft feeder. The plurality of bristles bear, with a variable preloading that can be preset, by adjustment of an axial position of the bracket, on an outer periphery of the winding drum. In other yarn-braking devices, which act directly on the outlet end of the winding drum, a braking element with a varying flexibility is used and comprises a plurality of narrow tongues placed side-by-side on an inclined surface of a frustocone. This braking element is mounted on a cup support with an open base carried by a bracket and has a position which is adjustable along a central longitudinal axis of the drum. Examples of the latter yarn-braking devices comprising tongues in the form of metal drop-wires are illustrated in European Patent Nos. 49,897 and 436,900 belonging to the Applicant, in British Patent No. 1,529,233, and in European Patent No. 330,951.
However, even though the conditions under which the weft yarn is inserted into the loom have been improved in the yarn-braking devices mentioned above, the problem of controlling the tension of the weft yarn fed to the loom at an optimum value has not been fully or effectively resolved.
This problem becomes particularly troublesome during the weft insertion cycle in gripper looms in which the weft yarn is switched mid-shed, during which cycle the yarn must be kept at a high tension as it is gripped by the carrier gripper on entering the shed and as the end of the yarn is passed mid-shed from the carrier gripper to the puller gripper.
So, in the known yarn-braking devices discussed above, it is precisely the tendency which the weft feeders have of allowing the tension of the yarn when switched to fall below the requisite values, which tendency constitutes one of the main drawbacks of such feeders. These drawbacks are overcome by increasing the preset tension in order to maintain a sufficiently high tension at the switch-over point.
However, this increase in the preset tension means increasing the maximum value of the tension when that given by the inertia of the yarn at the time of maximum acceleration of the grippers, before and after the switch-over, is added to the preset tension produced by the braking action.
The resulting tension peaks are clearly not desired since they cause high stresses in the weft ya

REFERENCES:
patent: 4828192 (1989-05-01), Sarfati
patent: 4926912 (1990-05-01), Zenoni
patent: 5123455 (1992-06-01), Maina
patent: 5181544 (1993-01-01), Deiuri

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