EP1350878B1 - Method for monitoring the weft thread in a loom - Google Patents

Abstract

A focused light beam (8c) is used for sensing. It is determined whether the weft (1) is at the correct location along the desired path of introduction into the shed, at appropriate positions and instants during the machine cycle. The beam is positioned to be interrupted by the weft, when it is on the right path. The weft is deflected to the side in accordance with the machine cycle, such that it passes through the beam during deflection. The instant at which they intersect, is compared with a desired interval (T1). A fault is deduced, should intersection not occur in interval T1, or if intersection occurs in intervals (T2a) or (T2b) before or after T1. A thread-tensioning deflector (3) moves the weft, in accordance with the machine cycle. The duration of weft intersection is compared with a desired interval, measuring also the deflector motion and arranging the light beam suitably. The loom is a shuttle machine, operated with a similar arrangement. Individual weft measurement times are determined for comparison with measured values.

Description

The invention relates to a method for monitoring the weft thread in a weaving machine according to the preamble of claim 1.

In order to monitor the weft thread in a loom, a thread monitor is usually provided between the thread brake and the tray. Well-known guardians of this kind, as they are eg in CH 651 329 are based, for example based on piezoelectric sensors and detect a movement of the thread. In CH 375 305 and AT 377 795 there are disclosed optical monitoring devices in which the presence of the weft yarn is optically monitored at a particular time at a particular location.

Task of the thread monitor is to determine a thread break in the first place. It turns out, however, that conventional guards do not always reliably detect breaks, especially toward the end of the weft insertion cycle. This is especially true when fine yarn is being monitored and / or there are strong operational vibrations or noise emissions in the area of the yarn monitor, e.g. by compressed air.

It is therefore an object to provide a method of the type mentioned, which allows a reliable monitoring of the weft.

This object is achieved by the method according to claim 1.

Thus, according to the invention, a collimated light beam is provided with which the position of the weft thread can be checked. In this case, it is measured at least one time in the machine cycle and at least one location along the desired path of the weft thread, whether the weft thread is on the desired path.

This method is based on the knowledge that the weft thread in a thread break or another unexpected, abrupt change its Sollweg usually leaves, eg because he loses its tension or because a lateral deflection propagates along the weft.

Here, the light beam is positioned so that it is interrupted by the weft thread when it is at the given time on the target path.

The process is particularly efficient because the weft thread is deflected laterally depending on the machine cycle. Corresponding deflections already take place in today's weaving machines in the area of the thread tensioner or, in the case of rapier weaving machines, in the area of the thread counterparts and the grippers, so that these deflections can be utilized without great interference with the function of the machine.

In the region in which the weft is deflected laterally (the deflection region), the desired path is time-dependent, i. depending on in which part of the machine cycle the loom is located. The light beam is arranged so that the weft thread passes through the light beam when deflected. An error may in this case be e.g. be determined by the time at which the weft thread passes through the light beam is compared with a desired time range.

The present method is also suitable for use in looms with multiple weft threads.

• Fig. 1 schematisch den Aufbau einer Webmaschine,
• Fig. 2 verschiedene Signalzüge,
• Fig. 3 einen zweite mögliche Position der Messanordnung,
• Fig. 4 einen Signalzug für den Aufbau nach Fig. 3 über einen Maschinenzyklus,
• Fig. 5 einen ersten konkreten Aufbau einer Webmaschine im Bereich der Fadenspanner und
• Fig. 6 einen zweiten konkreten Aufbau einer Webmaschine im Bereich der Fadenspanner.

Further preferred embodiments of the method can be found in the dependent claims and the following description with reference to FIGS. Showing:

• Fig. 1 schematically the structure of a loom,
• Fig. 2 different signal trains,
• Fig. 3 a second possible position of the measuring arrangement,
• Fig. 4 a signal train for the structure after Fig. 3 over a machine cycle,
• Fig. 5 a first concrete construction of a loom in the field of thread tensioner and
• Fig. 6 a second concrete construction of a loom in the field of thread tensioner.

In Fig. 1 are the most important parts of a projectile weaving machine shown in the present context, but the invention can also be used in projectile loom types, eg in rapier looms. In the weaving machine shown, the weft thread 1 passes through first a thread brake 2, then a thread tensioner 3 and, as an entry device, a projectile launcher 4. From the projectile launcher 4, the projectile 1 is shot into the compartment 5 of the fabric 6. On the opposite side of the compartment a brake mechanism 7 is provided for the projectile.

The thread tensioner 3 is, as indicated by dashed lines, pivoted in a known manner within a machine cycle to keep the yarn tension at an optimum level. In this case, a time-dependent lateral deflection of the weft thread 1 takes place.

In the deflection area, i. in the region in which the weft thread 1 is laterally deflected by the thread tensioner 3, a measurement arrangement 8, shown schematically as a point, is arranged. This consists essentially of a collimated light beam, preferably a laser beam, which intersects the desired path of the weft thread 1 at the point shown.

Due to the movement of the thread tensioner 3, the weft thread 1 normally passes the light beam at a certain time and interrupts it, which can be detected with a suitable detector. If, before the passage of the weft thread 1 through the light beam, a thread break or loses the projectile the thread, it usually comes very quickly to a lateral deviation of the weft thread 1 of his (time-dependent) desired path, so that the interruption the light beam does not take place at the expected time.

In Fig. 2 this is shown on the basis of some signal trains as a function of time or the machine cycle, whereby the graphic represents only a part of a whole machine cycle. The peaks in the signals indicate the respective interruption of the light beam.

In the following, times and durations are given in seconds or milliseconds or microseconds. However, it will be apparent to those skilled in the art that these values can also be given or evaluated as a position in the machine cycle (e.g., in degrees).

Signal trains a and b were measured in a normal machine cycle without yarn breakage. As can be seen, the signal peaks are in a desired time range T1.

The signal trains c to f were measured at yarn breaks. Since the lateral deflection of the weft thread 1 is uncontrolled in this case, signal peaks may occur before, after or even during the setpoint time range T1. It can also occur several signal peaks when the weft thread 1 moves several times through the light beam. In general, however, it turns out that at least one signal peak occurs in a time interval T2a before the setpoint time range T1 or a time interval T2b after the setpoint time range.

Defining the time intervals T2a and T2b as the absence of time range, so it can be concluded that an error when the light beam is interrupted in this absence period. Furthermore, there is also a fault if the light beam is not interrupted in the set time range T1. Preferably, both of these criteria are checked and an error is displayed if one or both are not met.

The length of the setpoint time range T1 should be selected so that the natural dispersion of the signal peaks without thread breakage is taken into account. In the choice of Length of the time intervals T2a, T2b is to be considered that the weft thread 1 passes through the light beam twice in normal operation per machine cycle, preferably the second regular passage is used for the measurement, since the weft thread 1 during the first regular passage usually not or less tense. The time intervals T2a, T2b should be so short that they do not include the other regular passage not to be detected in a single measurement.

In a concrete example, a favorable length of the setpoint time range T1 was about 1 ms, that of the time intervals T2a, T2b was 5 to 10 ms.

The position of the target time range T1, i. the reference time of the measurement can be e.g. be selected relative to the machine cycle. However, this assumes that the movement of the thread tensioner 3 follows the machine cycle without deviation. For a more accurate measurement and the movement of the thread tensioner 3 can be detected. This can be done with a separate sensor or with the measuring arrangement 8.

If the measuring arrangement 8 is to be used for measuring the movement of the thread tensioner 3, then the in Fig. 3 shown arrangement can be selected. In this case, the measuring arrangement 3 is arranged so that the light beam is also interrupted by the thread tensioner 3 during its movement.

Fig. 4 shows a normal signal train for the device according to Fig. 3 throughout the machine cycle. As can be seen, occur in three signal peaks 10-13, of which the tips 10 and 13 originate from weft 1 and the tips 11 and 12 from the shadow of the thread tensioner 3. In this case, the position of the target time range T1 relative to the second signal tip 12th of the thread tensioner 3, for example, by the target time range at a time Tx after the end of the tip 12 is started. The time Tx can be determined, for example, by test measurements. This can be done (for each yarn) in a test mode, for example, after article change, the control of the loom, the passage times of the yarn by the laser beam and their scattering hold and determine the optimal set time range from each.

In general, as already mentioned, at least one measurement should take place as late as possible in the machine cycle, at a time when the weft thread would have already completely traversed the compartment 5, so that even late fractures can be detected. However, the measurement should not be made so late that the weft thread is already held by the warp threads or edge threads or edge thread clamps.

Fig. 5 shows the specific arrangement of the measuring assembly 8 in a projectile weaving machine with four weft threads 1. In this machine each weft thread 1 occurs before the thread tensioner 3 through a first eyelet 20, then through the eyelet 21 of the thread tensioner 3 and finally through one of the projectile launcher 4 upstream second eyelet 22. The deflection of the weft threads 1 is thus in this embodiment between the first eyelet 20 and the second eyelet 22nd

They are e.g. four thread tensioner 3 is provided, of which one per machine cycle is operated via a cam 23 in the rule.

To the arrangement after Fig. 1 to realize, in the example after Fig. 4 the measuring arrangement with laser 8a, light beam 8c and light detector 8b arranged in the region between the first eyelet 20 and the thread tensioner 3, so that the respective moving weft thread 1 passes through the light beam 8b.

In the execution after Fig. 5 the four lever-shaped thread tensioner 3 are pivotable about a common pivot axis 24 and perform similar movements. This makes it possible, by arranging the light beam 8c approximately parallel to the pivot axis 24, to monitor all the weft threads with only one light beam.

If a joint monitoring of all weft threads by a single light beam is not possible, so a plurality of light beams are provided at appropriate positions accordingly.

In the execution after Fig. 5 is preferably set for each weft 1 an individual target time range T1, since the relative positions of the eyelets 20 and 21 to the light beam are not exactly the same for all weft threads, and also the movements of the thread tensioner 3 may slightly differ.

Fig. 6 shows an embodiment in which the measuring arrangement 8a, 8b, 8c is arranged so that the light beam 8c is interrupted by the thread tensioners 3 during their movement. This arrangement allows a measurement according to Fig. 3 in which the position of the target time range T1 with respect to the movement of the thread tensioner can be set.

As mentioned above, one or more measurements can be taken per machine cycle. Preferably, however, at least one measurement takes place at a time when the thread would have to pass through the tray completely in the correct course of motion. This allows detection of relatively late fractures, e.g. when slowing down the projectile in a projectile loom. Such late fractures can often only be detected unreliably with conventional thread guards because at this time the thread movement is low.

It is also conceivable to use a plurality of light beams or to divide a light beam in order to carry out measurements at different times or at different locations and thus to achieve a more precise monitoring of the weft thread 1 over the machine cycle.

In the examples described so far, the light beam has been arranged in the deflection region of the weft thread, ie in that region in which the desired path of the weft thread changes depending on the point in time in the machine cycle. However, it is also conceivable, for example, a measurement between the yarn brake 2 and the first eyelet 20 or between the second eyelet 22 and the entry device 4 perform. In this case, the measurement is based on the effect that a slight lateral deflection of the weft thread 1 is to be expected in a thread breakage in this area, which can be detected by the light beam. Also in this case, the measurement preferably takes place at one or more fixed times in the machine cycle, in which the weft thread 1 would have to be stretched.

Preferably, in this case, the thread is passed between two laser beams, wherein at a fault of at least one of the beams is interrupted by the deflection of the thread.

The measuring principle described here can also be used in other types of weaving machines, preferably in those types in which a deflection region exists between the brake and the compartment in which the thread is deflected laterally depending on the machine cycle in a defined manner. This is the case in particular with gripper looms with a plurality of weft threads, in which a gripper serves as an entry device. Such a loom is in EP 1 099 784 described, whose FIG. 1 is incorporated by reference herein. There, the weft thread to be introduced into the tray is deflected laterally by thread rippers and by the gripper, so that a deflection area arises in front of and behind the thread rugs, in which it can be checked by a light beam to determine whether the weft thread is at its desired path at a given time.

In order to increase the reliability of the measurements, the thread can be subjected to a lateral air jet in the area of the measurement. This air jet ensures a lateral deflection of the thread in case of failure. In Fig. 1 is a corresponding air nozzle 30 shown in dashed lines. The air nozzle 30 is preferably only in operation during the measurement.

The described method can be used alternatively or in addition to conventional thread guards.

Claims (12)

1. A method for monitoring the weft thread in a weaving machine, in which the weft thread (1) passes along a desired path and through an insertion device (4) into the shed, it being measured with a collimated light beam (8c) at least at one moment in a machine cycle and at at least one location along the desired path whether the weft thread (1) is on the desired path, the collimated light beam (8c) being positioned such that it is interrupted by the weft thread (1) if the weft thread (1) upon measurement is on the desired path, the weft thread (1), dependent on the machine cycle, being deflected laterally in a deflection region so that the desired path is time-dependent, the light beam (8c) being arranged in the deflection region such that the weft thread (1) upon deflection passes through the light beam (8c), characterised in that the weft thread (1) is deflected laterally by a thread tensioner (3) moved dependent on the machine cycle, the collimated light beam being interrupted by the weft thread (1) due to the movement of the thread tensioner (3).
2. A method according to Claim 1, the moment at which the weft thread (1) passes through the light beam (8c) being compared with a desired time range (T1).
3. A method according to Claim 2, it being concluded that there is an error if the light beam (8c) is not interrupted within the desired time range (T1).
4. A method according to one of Claims 2 to 3, it being concluded that there is an error if the light beam (8c) is interrupted in an error time range, the error time range comprising a first time interval (T2a) before the desired time range (T1) and a second time interval (T2b) after the desired time range (T1).
5. A method according to one of the preceding claims, the moment at which the weft thread (1) passes through the light beam (8c) being compared with a desired time range, and the movement of the thread tensioner (3) being measured for determining a position of the desired time range, and in particular the movement of the thread tensioner (3) being measured by arranging the light beam (8c) such that it is interrupted by the thread tensioner (3) along its movement, and by establishing the desired range relative to the interruption of the light beam (8c) by the thread tensioner (3).
6. A method according to one of the preceding claims, the weaving machine being a rapier weaving machine, in which the respective weft thread (1) is supplied to a rapier by a thread holder, the weft thread (1) being deflected laterally by the thread holder and/or the rapier in the deflection region, and the light beam being arranged in the deflection region.
7. A method according to one of the preceding claims, with a plurality of weft threads (1) being monitored, and in particular the weft threads being deflected in succession in the deflection region.
8. A method according to Claim 7, the moment at which each weft thread (1) passes through the light beam (8c) being compared with a desired time range, with an individual desired time range being established for each weft thread (1).
9. A method according to one of Claims 7 or 8, each weft thread (1) being deflected by its own thread tensioner (3), the thread tensioners (3) being pivoted about a common pivot axis (24) and the light beam (8c) extending substantially parallel to the pivot axis (24) in order to be able to detect all the weft threads (1).
10. A method according to one of the preceding claims, with a measurement being made in the machine cycle at least once at a moment when the thread ought to have completely cleared the shed if the path of movement was correct.
11. A method according to one of the preceding claims, the thread being passed through a brake (2) and measurement taking place after the brake (2).
12. A method according to one of the preceding claims, the thread being acted upon at the location by a lateral air jet and in the event of an error being deflected by the lateral air jet.

Images