Textiles: weaving – Weft manipulation – Weaving with stationary weft supply
Patent
1995-07-28
1997-09-02
Falik, Andy
Textiles: weaving
Weft manipulation
Weaving with stationary weft supply
139452, D03D 4734
Patent
active
056621485
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method for controlling a thread feed system and to a thread feed system having a measuring feeder which comprises a storage drum and a winding element for winding thread stock onto the storage drum.
DESCRIPTION OF THE RELATED ART
In a method known from EP-A2-0 195 469, the jet-weaving machine works in accordance with the weft mixing principle, i.e., identical threads are alternately withdrawn from at least two measuring feeders. A control device monitors the operation and reacts to failure, for instance thread breakage, in such a manner that the one measuring feeder is controlled such that it assumes the function of the defective measuring feeder or even feeders. In a measuring feeder having a plurality of stop elements distributed over the circumference of the storage drum, the thread length is composed of whole turns and of fractions defined by the spacings of the stop elements. In a measuring feeder comprising one-stop element, the thread length is composed of whole turns and the diameter of the storage drum is adjusted accordingly. Since upon withdrawal of the thread along the thread path a thread tension builds up in the thread and since the thread tension is also felt in the turns in the thread stock on the storage drum, the thread length is adjusted such that the thread tension building up in the thread stock under normal operation is taken into account. When a measuring feeder assumes the function of a defective measuring feeder, the pick frequency will be doubled. The speed level rises. The tension within the thread increases. The original adjustment of the thread length is no longer correct; the thread length of the thread section in its relaxed state within the textile machine will be too short. This will result in short picks. Moreover, when the resistance to withdrawal from the supply bobbin increases, such a risk will even be enhanced.
In other weaving methods using measuring feeders, the thread length is also determined and set in advance. Since the supply bobbin is emptied relatively rapidly and is capable of carrying a considerable amount of thread, the diameter of the thread windings on the supply bobbin also changes considerably from a new supply bobbin to an empty supply bobbin. With a decreasing diameter of the thread windings the winding-on tension, which is the withdrawal tension of the thread being removed from the supply bobbin, increases, as well as the thread tension in the thread stock on the storage drum, so that the set thread length can no longer be maintained. This entails the risk of short picks. The risk is especially great at a high speed level.
To avoid short picks, the thread length has so far been set in advance to the high tension under critical operating conditions, which leads to expensive waste under normal operating conditions. The thread tension which varies in response to the Operating condition, as well as the undesired effect thereof which varies the set thread length are thus taken into account through a corresponding addition in the thread length. Measuring feeders can thus not fulfill the task of keeping a constant thread length in practice, as is actually presupposed in theory.
WO 90/07 600 discloses a thread feed device in which the supply bobbin and the measuring feeder have provided thereinbetween a friction drive which performs an assisting conveying function by means of a driven friction roll in order to avoid undesired great stresses on the thread and to reduce the number of thread breakages. The surface of the friction roll is provided with axially defined surface coatings of different slip tendencies which are arranged side by side and adapted to the thread qualities of different threads, and of which the respectively suited surface coating is used for auxiliary conveyance. The thread follows a fixed thread path over the friction roll.
It is the object of the present invention to provide a method of the above-mentioned kind and a thread feed system with the aid of which the picked thread
REFERENCES:
patent: 4450874 (1984-05-01), Brouwer et al.
patent: 4838319 (1989-06-01), Suwa
patent: 5137059 (1992-08-01), Baeck et al.
patent: 5168903 (1992-12-01), Suwa
patent: 5385310 (1995-01-01), Tholander
Jacobsson Kurt Arne Gunnar
Josefsson Paer
Tholander Lars
Falik Andy
Iro AB
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