EP0747519A2 - Process to avoid the weave in of a broken weft yarn in a woven fabric - Google Patents

Abstract

A method to avoid including a broken weft thread in a weave mfd. on an air jet loom entails detection by a sensor of a thread break caused when a weft thread is inserted into a weaving shed, signalling this occurrence to a loom controller so that the weaving process is stopped and, in contradiction to the normal weaving procedure cut from a repair weft thread which is being held ready. After stopping the weaving process, a known work sequence is introduced wherein the repair weft thread is measured out to such a length on the broken and cut weft thread that the sensor confirms its non-arrival whereupon the weaving process is kept at a standstill.

Description

The present invention relates to a method for avoiding weaving a broken weft thread into a fabric.
Such or similar processes are known, for example, from EP 0 310 804, EP 0 309 013, EP 0 207 470 and US 4,781,221.

Here a weft sensor is provided on the weaving machine opposite the entry nozzle for the weft. This weft sensor checks after each weft entry whether the weft has crossed the shed. If so, the weaving process continues as usual; there is a new weft thread entry after the formation of a new shed.

If the inserted weft thread has not arrived at the weft thread sensor, the machine control triggers an automatic weft break removal procedure. For this purpose, the weaving process is interrupted, the reed is pivoted back into its starting position, and the weft thread that has not passed through the shed is not cut. This method and the steps to be carried out in each case are described in more detail in US Pat. No. 4,781,221 and EP 0 207 470.

Then a new weft thread (repair thread) is inserted on the defective weft thread, which forms a loop, for example. This loop is now carried across the fabric using the relay nozzles and thereby pulls the faulty thread from the fabric stop edge. As soon as the incorrectly inserted weft thread is completely pulled off, it comes into contact with the sensor at the opposite end. This sensor detects the weft thread, activates an appropriate suction and a cutting device that cuts off the weft thread registered for repair; the machine then returns to normal weaving.

If the weft thread used to repair the weft break also gets caught in the shed and therefore does not reach the sensor, the weaving stop will continue to be maintained.

All of the technical solutions disclosed in the publications mentioned at the beginning work according to this method. An important point is that the cutting of the faulty weft thread must be prevented. Otherwise, the faulty weft thread cannot be automatically removed from the fabric stop edge by inserting the repair thread.

However, it has been shown in practice that despite the triggering of the shot break signal, this cutting process cannot always be reliably prevented. There are multiple reasons for that.

For example, a magnetic switch is used relatively often to interrupt the cutting process. The response times of these magnetic switches are usually in the range of a few microseconds, but are subject to certain fluctuations. These fluctuations can account for up to 20% of the response time of the magnetic switches. If a faulty weft entry coincides with a longer response time of a magnetic switch, it is quite possible that the faulty weft thread entered will be cut despite the intended prevention of the cutting process.

Reasons for such fluctuations in the response time include environmental influences such as Temperature, humidity, fluctuations in the mains voltage, vibrations or the like.

Of course, there can also be a simple mechanical error, such as jamming or the like.

In addition, various electrical fields can be used to transmit interference signals to the electrical lines of the control system, which distort or distort the control signals and thus prevent the magnetic switch from responding.

Similar defects can occur not only with magnetic switches, but also with others Actuators that are used to interrupt the cutting process occur.

So far, this problem has not been recognized by experts. In the prior art, a relatively large weft length is entered to remove the defective weft. This thread length is longer than the weft thread length usually entered for weaving. If, therefore, a cut has been made incorrectly, the weft thread entered for repair reaches the area of the weft thread sensor without the faulty weft thread being removed from the fabric stop edge. The sensor then detects the presence of the repair thread, activates the suction of this thread after it has been cut off, and continues the weaving process. The disadvantage here is that the faulty weft thread entered remains in the fabric and the weaving machine is not aware of this error.
It is therefore crucial that, contrary to the state of the art, the broken weft thread is cut off from the repair thread provided contrary to the process. This means that automatic shot break repair in the classic sense is not possible.
In classic weft breakage elimination, the broken weft thread is connected to the weft thread (repair thread) held ready.

It is therefore an object of the present invention to provide a method for air jet looms which reliably prevents a defective (broken) weft thread from being woven into the fabric, the broken weft thread being inadvertently cut off from a prepared weft thread (repair thread).

According to the invention, this object is achieved by the features of claim 1.

It is essential here that a long weft thread is no longer inserted as in the prior art, but rather that in order to avoid weaving in the broken weft thread, a weft thread length (repair thread length) is entered which is smaller than the weft thread length to be entered for weaving.

If the cutting process has now been properly prevented and the defective weft remains connected to the repair thread, the total length of these threads is greater than the weft length usually to be entered for weaving. In this case, the total length of the threads is sufficient for the weft sensor on the opposite side of the fabric to detect the arrival of the weft and for the weft break to be automatically eliminated in a manner known per se.

However, if in an incorrect manner, i.e. if the faulty weft thread has been cut off from the weft thread provided inadvertently or contrary to the procedure, the entered weft thread length is too short to reach the relevant weft thread sensor. In this case, the weaving machine detects the absence of the repair thread and continues to prevent the weaving process. To repair the weft break, the broken weft must be manually removed from the fabric.

An essential advantage of the invention is that when the machine is working correctly, i. if the cutting process is prevented, a reliable shot break repair is given. If, however, an incorrect cut is made, the already cut, defective weft thread can no longer be automatically removed from the fabric stop edge and must be removed manually in any case. This case is also reliably recognized by the machine and processed accordingly. In the prior art, the weaving process has so far been continued, although the defective weft thread was still on the fabric stop edge. This has resulted in tissue defects.

The invention is explained in more detail below with the aid of drawings which illustrate only one embodiment. Here, from the drawings and their description, further features and advantages of the invention that are essential to the invention emerge.

Figur 1:

Schematisch den Zustand der Maschine nach einem Schußfadenbruch;

Figur 2:

die Bildung einer Schlinge zur Behebung des Schußfadenbruch;

Figur 3:

eine Ansicht des Zustands der Maschine nach der Schußfadenbruchbehebung, falls in fehlerhafter Weise geschnitten worden ist;

Figur 4:

die Schußfadenbruchbehebung nach dem Stand der Technik, falls in fehlerhafter Weise geschnitten worden ist.

It shows:

Figure 1:

Schematic of the condition of the machine after a weft break;

Figure 2:

the formation of a loop to repair the weft break;

Figure 3:

a view of the state of the machine after the weft break repair, if cut incorrectly;

Figure 4:

the weft breakage elimination according to the prior art, if it has been cut incorrectly.

Figures 1-4 show schematic representations of an air jet loom in plan view. There are a main nozzle 1 and a plurality of relay nozzles 2 for inserting and transporting the weft thread 3 over the width of the fabric. A cutting device 4 is arranged behind the main nozzle. At the end of the shed 9, a sensor 5 for detecting the weft and a suitable suction 6 are arranged.

In the illustration according to FIG. 1, there is a weft break because the weft thread 3 has not crossed the entire width of the shed 9.
As soon as the weft 3 does not pass through the shed 9 completely, the sensor 5 therefore receives no weft arrival signal. The control of the weaving machine (not shown) recognizes that a weft break is present, whereupon the further weft break elimination procedure described above is carried out. It is essential here that the cutting device 4, which normally separates the weft 3 after its entry, is deactivated.

According to FIG. 2, a repair thread 7 is then entered, the predetermined weft thread length being less than the weft thread length entered for weaving.

If there is still a connection 8 between the repair thread 7 and the defective weft thread 3, the total thread length present is large enough to reach the weft thread sensor 5. In this case, the faulty weft thread 3 is removed from the fabric stop edge; the suction 6 is activated, the thread 7 is cut by the cutting device 4 cut and suctioned through the suction 6.

FIG. 3 shows the state if the cutting process has not been erroneously interrupted after the faulty weft thread 3 has been inserted. It can be seen that the length of the repair thread 7 is dimensioned such that it cannot be recognized by the sensor 5. The machine thus notices that the shot break repair has not been carried out successfully and delivers an appropriate signal. The faulty weft 3 and the repair thread 7 are then removed manually; then the weaving process is started again. A tissue defect has been successfully avoided.

Figure 4 shows a representation of the prior art.
A repair thread 7 is entered here, the length of which is at least as long as the weft thread length usually entered for weaving. If the point 8 has now been cut between the repair thread 7 and the faulty weft thread 3, the faulty weft thread 3 remains on the fabric stop edge. The repair thread is nevertheless recognized by the sensor 5, cut off by the cutting device 4 and removed via the suction 6. The weaving process is then continued, with the defective weft thread 3 still being in the fabric. This leads to a tissue defect.

This tissue defect is successfully avoided with the subject matter of the present invention. There is no increased design effort.

DRAWING LEGEND

1

Main nozzle

2nd

Relay nozzle

3rd

Weft

4th

Cutting device

5

sensor

6

Suction

7

Repair thread

8th

connection

9

Shed

Claims (1)

Method for preventing a broken weft thread from being woven into a fabric to be produced on an air-jet weaving machine, wherein a weft thread is inserted into a shed and the entry thereof leads to a weft break which is detected by a sensor and which signals the detection of the weft break of a weaving machine control. thereupon the weaving process is stopped and the broken weft thread is cut off from a ready-made weft thread (repair thread) contrary to the procedure and after the weakening process has been prevented, a workflow known per se for repairing broken weft is initiated, which consists in the ready-made weft thread (repair thread ) is entered, the length of which is dimensioned such that the sensor detects the absence of the arrival of the weft thread (repair thread) and the weaving process is then still prevented.

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