EP2098624A1 - Weft thread monitoring in a loom - Google Patents

Abstract

The method involves performing an optical motion measurement on a weft thread (5). Movement of the weft thread before a compartment (21) is measured, and a parameter determined from the movement of the weft thread during the insertion of the weft thread is compared with a reference parameter. An operating parameter of a loom i.e. air shuttle loom, is adjusted based on the measured movement of the weft thread, and the measured movement of the weft thread is used to control or regulate speed or insertion of the weft thread during insertion. An independent claim is also included for a loom comprising a weft thread monitor.

Description

The invention relates to a method for weft thread monitoring in a weaving machine and to a weaving machine designed for carrying out this method.

The term weft thread monitoring in the present context means any monitoring of the movement of the weft thread in the weaving machine, including the monitoring of the shooting and the arrival. In particular, these are those methods which characterize or control the entry of the weft thread (i.e., the flight of the weft thread through the shed) or detect or avoid errors in the entry. An important class of weft monitor are those methods which allow a crack of the weft (weft break) to be detected.

Various systems are known that allow monitoring of the weft in a weaving machine with weft detector. In particular, the weft thread can be monitored with a light barrier or the like, as in eg EP 1 502 979 or EP 1 350 878 is disclosed. Also known are triboelectric or piezoelectric sensors, which allow to detect a touch or movement of the weft thread.

However, such methods have several disadvantages. In particular, photoelectric sensors are only able to monitor the weft yarn in a relatively narrow time window, and touch-based methods are material dependent, vibration and noise sensitive, and can interfere with the weft yarn run.

It is therefore the object to provide a method and a weaving machine, which allow a reliable, versatile weft thread monitoring and thereby affect the weft thread running as little as possible.

This object is achieved by the subject matter of the independent claims.

Accordingly, a movement measurement is carried out on the weft thread by means of a non-contact, optical sensor. In particular, the movement of the weft thread in the longitudinal direction of the weft thread is determined.

Motion measurement means the measurement of the velocity or a quantity derived from the velocity (e.g., record length or acceleration).

Preferably, the weft yarn is exposed to at least partially coherent light to produce Doppler interference between scattered and unscattered lightwaves on the weft yarn or between two lightwaves scattered differently on the weft yarn. The Doppler interference is measured and based on the weft monitored.

Doppler interference is the interference between two coherent photons or light waves, of which at least one has been scattered on the weft. If the light waves are brought to overlap, there is a time-varying interference, the interference frequency is a direct measure of the speed of the weft.

Instead of a Doppler interference measurement, it is also possible, for example, to use an optical spatial filter method, as described, for example, in US Pat DE 10 2004 055 561 and the documents cited therein.

The measurement of the speed or of the inserted length of the weft thread makes it possible to measure the speed, the entry length and / or a variable derived therefrom, such as the acceleration, with high accuracy and thus to obtain precise information about the entry process. The measurement is purely optical, ie relatively insensitive to sound or vibration, and non-contact. Furthermore, the entire weft insertion can be monitored until the end which makes it possible, for example, to detect a very late weft breakage.

"Length measurement" in this context means the measurement of the recorded length of the weft thread as a function of time.

Motion measurement should be performed multiple times during a single entry to allow the most accurate monitoring of the entry process.

To monitor the weft thread via Doppler interference, the weft thread monitor of a weaving machine is equipped with a non-contact, optical movement measuring device, in particular a Doppler interferometer, with which the movement of the weft thread is measured. Movement is understood here to mean the speed or a variable derived from the speed.

The invention is suitable for monitoring the weft thread for a variety of applications. For example, it allows the detection of weft breakages, the monitoring or control of the picking speed or the detection of a faulty thread tension due to a deviation of the speed from a Sollwart.

• Fig. 1 eine erste Ausführung eines Doppler-Interferometers,
• Fig. 2 eine zweite Ausführung eines Doppler-Interferometers und
• Fig. 3 eine dritte Ausführung eines Doppler-Interferometers,
• Fig. 4 ein erstes Ausführungsbeispiel einer Webmaschine mit Doppler-Interferometer,
• Fig. 5 ein schematisches Beispiel des Geschwindigkeitsverlaufs des Schussfadens während dem Eintrag,
• Fig. 6 ein zweites Ausführungsbeispiel einer Webmaschine mit Doppler-Interferometer und
• Fig. 7 ein drittes Ausführungsbeispiel einer Webmaschine mit Doppler-Interferometer.

Further preferred embodiments of the invention will become apparent from the dependent claims and from the following description with reference to FIGS. Showing:

• Fig. 1 a first embodiment of a Doppler interferometer,
• Fig. 2 a second embodiment of a Doppler interferometer and
• Fig. 3 a third embodiment of a Doppler interferometer,
• Fig. 4 A first embodiment of a loom with Doppler interferometer,
• Fig. 5 a schematic example of the velocity profile of the weft during the entry,
• Fig. 6 A second embodiment of a loom with Doppler interferometer and
• Fig. 7 a third embodiment of a loom with Doppler interferometer.

definitions:

By "coherent" light is meant in the present context light whose coherence length is so large that it can be used for the purposes of Doppler interference.

The term "course of movement" is understood to mean the time course of the weft speed v (t) or its integral (the entry length x (t)), or its derivative (the acceleration a (t)), as well as all further variables derived unambiguously and reversibly from these quantities ,

Optical Doppler interferometer

Before discussing the application of Doppler interferometry in weft monitoring, some embodiments of Doppler interferometers suitable for measurement on a weft are described below.

In the Fig. 1 illustrated embodiment of a Doppler interferometer 15 has a coherent light source 1, preferably a semiconductor laser, which generates a light beam 2. The light beam 2 strikes a weft thread 3 running at a speed v, where it is partially scattered. A part of the scattered light designated as "first light wave" 4 is scattered at an angle φ and passes into a detector 6 arranged in the corresponding direction. Another part of the light of the light beam 2 passes unchanged to the surroundings of the weft thread 3 and becomes hereafter referred to as "second light wave" 5. The second light wave reaches a deflection mirror 7, from where it is also thrown into the detector 6.

Due to the Doppler shift generated by the movement of the weft thread 3, the frequency of the first light wave 4 is not exactly that of the light beam 2, so that in the region of the superposition of the two light waves 4, 5 at the detector 6 comes to a beat, which as an electrical AC signal ( or alternating voltage signal) of a frequency f can be measured. The magnitude of the frequency f depends directly on the speed v. It also depends on the angle φ, more precisely on the magnitude of the change in momentum experienced by the photons during the scattering in the direction of the velocity vector of the weft thread 3. The corresponding formulas are known to the person skilled in the art and allow the velocity v to be determined directly from the frequency f, given a known geometry of the arrangement and known wavelength of the light of the light source 1.

The intensity of the first light wave 4 will generally be weaker than that of the second light wave 5, since only a relatively small proportion of the light of the light beam 2 is scattered at all, and of which only a part actually falls onto the detector 6, which only observes a small solid angle , As a result, without additional measures, the signal from the detector 6 has a poor contrast, i. It has a high DC component, while the interest actually AC component is much lower. Advantageously, therefore, the second light wave 5 is attenuated before the superposition with the first light wave 4 to improve the contrast. The additional attenuation of the second light wave should preferably be at least 90%.

The attenuation of the second light wave 5 can be effected, for example, by the fact that mirror 7 is a partially transmissive mirror, which is at least 90% of the light output transmitted and reflected only 10% or less.

In the second execution after Fig. 2 the beam 2 of the light source 1 is split at a beam splitter 10 into a first and a second light wave 4, 5. The first light wave strikes the weft thread 3 and is at least partially scattered in a scattered light wave 4 ', which strikes a detector 6. The second light wave 5 is thrown directly onto the detector 6. Again, there is a Doppler interference at the location of the detector 6, whose frequency is directly dependent on the speed v of the weft thread 3.

In principle, it is not necessary for the second light wave 5 to be unscattered light. It can also be formed by scattered light as long as it has experienced a different Doppler shift than the first light wave.

A corresponding design is in Fig. 3 shown. Here the light beam 2 of the light source at the weft thread 3 is scattered into a first and a second light wave 4 or 5, whose photons have experienced different momentum changes in the direction of the velocity v of the weft thread and thus likewise differ in their frequency. An aperture 11 with two openings 12, 13 ensures that only two light waves with respectively well-defined scattering angle φ and -φ are used for the following evaluation. The two light waves 4, 5 pass through a lens 10, which deflects them so that they overlap on the detector 6.

With Doppler interferometry, the sign of velocity v can also be measured by shifting one of the two light waves in frequency (eg with an acousto-optic modulator). As a result, even with unmoved yarn from the detector, an interference signal with a frequency greater than zero is obtained. The frequency shift by the yarn movement can now take place both at higher and lower frequencies, which shows the sign of the speed. Similarly, this result can also be realized with a phase modulator (eg, a Pockels cell, an oscillating mirror, etc.). In Fig. 1 this is illustrated by inserting a Pockels cell 12 in the beam path of the second light wave 5.

Weft watching:

The following describes how a Doppler interferometer can be used to monitor the weft of a loom. In this case, one of the interferometer described in the preceding section, but also a different type of interferometer can be used.

Fig. 4 shows a schematically illustrated loom in a plan view of the woven fabric 20. In this case, the weft thread 5 is introduced into the compartment 21 between the warp threads 22 in a known manner. For this purpose, the weft thread 5 is supplied from a supply point 23, which contains, for example, a thread supply, a weft brake and / or a thread tensioner. The weft thread then passes through a first guide 24, the Doppler interferometer 15 and an insertion device 26. The picking device 26 forms the last guide of the weft thread in front of the compartment 21 and serves to register the weft. Depending on the type of weaving machine (air-jet weaving machine, projectile weaving machine or rapier weaving machine), the feeding device is constructed in a different manner known to the person skilled in the art and does not need to be described in detail here. For the example according to Fig. 4 It is assumed that it is a projectile weaving machine and that feeding device 26 is designed as a projectile launcher.

On the entry device 26 opposite side of the tray 21, a weft receiving device 27 is arranged, which, for example, in a Projectile loom contains a brake mechanism for the projectile.

The measurement of the Doppler interference with the Doppler interferometer 15 is advantageously carried out in front of the compartment 21, since there the movement of the weft thread can be monitored throughout the entry. It can e.g. in the last guide (formed here by the entry device 26), since there the weft thread has a defined position and its speed depends particularly strongly on the course of the entry.

As mentioned, the Doppler interferometer 15 allows the measurement of the time course of the velocity v (t) in the longitudinal direction of the weft thread over the entire duration of the entry, e.g. by measuring the instantaneous frequency of the interferences. By counting the interferences, the integral of the velocity, i. Entry length x (t) are determined, and by deriving the speed, the acceleration a (t). In principle, all of these quantities, as well as other, from the Doppler interference during the weft insertion determined parameters for monitoring the weft thread. In particular, it is also not necessary, e.g. to convert the frequency of Doppler interference (e.g., in Hz) to an absolute velocity (e.g., in m / s), as long as the reference or threshold values in the same units are also detected.

The following examples relate to the measurement of speed, but this is not meant to be limiting.

In Fig. 5 the curve C1 shows a somewhat simplified example of the normal course of the weft speed v (t) during the entry. As can be seen, the speed at the beginning of the entry is 0, then increases rapidly, for example, drops slightly during the entry process, and then quickly goes back to zero when braking the weft. In Fig. 5 is the course of the speed during the entry process shown substantially linear - in practice, however, a deviating, more complicated course is observed, especially in rapier looms.

• Verlauf C2 stellt exemplarisch den Fall dar, wenn der Schussfaden vor dem Abschluss des Eintrags reisst bzw. bricht, und zwar im Falle einer Greifer- oder Projektilwebmaschine. In diesem Fall sinkt die gemessene Geschwindigkeit relativ schnell und vorzeitig auf Null ab.
• Verlauf C3 zeigt ebenfalls den Fall eines Fadenbruchs vor Abschluss des Eintrags, wobei in diesem Fall aufgrund der Fadenspannung, welche zu einer Kontraktion des gerissenen Fadens führt, sogar eine kurze Phase negativer Geschwindigkeit gemessen werden kann.
• Verlauf C4 zeigt den Fall an, wenn ein Faden ganz am Schluss des Eintrags bricht, wenn seine Geschwindigkeit bereits praktisch Null erreicht hat. In diesem Fall kann ebenfalls aufgrund der Fadenspannung unter Umständen noch eine Kontraktion des Fadens beobachtet werden, welche sich durch eine Phase negativer Geschwindigkeit bemerkbar macht.
• Verlauf C5 zeigt den Fall eines zu stark gebremsten oder zu schwach angetriebenen Fadens an. In diesem Fall liegt die Geschwindigkeit etwas tiefer, und die Zeit bis zum Abschluss des Eintrags erhöht sich.
• Verlauf C6 entspricht einem in anderer Wiese gestörten Schusseintrag.

In Fig. 5 are further recorded speed curves C2, C3, ..., as they can occur, for example, in a system error:

• Curve C2 illustrates as an example the case when the weft thread breaks or breaks before the conclusion of the entry, in the case of a rapier or projectile weaving machine. In this case, the measured speed drops relatively quickly and prematurely to zero.
• Course C3 also shows the case of a yarn breakage before the conclusion of the entry, in which case even a short phase of negative speed can be measured due to the yarn tension, which leads to a contraction of the broken yarn.
• History C4 indicates the case when a thread breaks at the very end of the entry, when its speed has already reached practically zero. In this case, due to the thread tension, a contraction of the thread may also be observed which is manifested by a phase of negative speed.
• Course C5 indicates the case of over-braked or under-powered thread. In this case, the speed is slightly lower and the time to complete the entry increases.
• Course C6 corresponds to an otherwise disturbed weft insertion.

How out Fig. 5 As can be seen, the present method can detect all of these malfunctions. For this purpose, depending on the error to be detected or the function to be monitored, at least one parameter determined from the Doppler interference during the weft insertion is to be compared with a suitable setpoint parameter s.

For example, errors of the type described by the curves C2, C3, C5 (and possibly C6) may be determined by comparing the time of the strongest decay of the speed with a desired time, or (for the curves C2 and C3) the integral of the speed ie the entry length is determined until completion of the entry and compared with a desired length. Errors of the kind represented by the curves C3 and C4 can be detected by checking whether the speed drops below zero (or a negative lower limit).

Concretely, e.g. a weft break is detected by detecting an unexpected drop in weft speed.

Die Summe S kann sodann z.B. mit einem Schwellwert verglichen werden. Überschreitet S den Schwellwert, so liegt eine Anomalie vor.Preferably, the course of the movement over the entire entry is analyzed by comparing it with a desired course. For this purpose, the measured parameter p (t) is recorded at a plurality of times t1, t2,..., Where p (t) is, for example, the velocity v (t), the input length x (t) or the acceleration a (t). equivalent. From this, a series of measured values p (t ₁ ), p (t ₂ ),... Is determined. Each of these measured values can then be compared with a corresponding desired value s (t ₁ ), s (t ₂ ),..., Eg by forming the sum S of the quadratic deviations: $$\mathrm{S}\mathrm{=}{\displaystyle \underset{\mathrm{i}}{\mathrm{\Sigma }}}{\left(\mathrm{p}\left({\mathrm{t}}_{\mathrm{i}}\right)\mathrm{-}\mathrm{s}\left({\mathrm{<figure-callout\; id="2"\; label="t\; i"\; filenames="imgf0001.png"\; state="\{\{state\}\}">t\; </figure-callout>}}_{\mathrm{i}}\right)\right)}^{\mathrm{2}}$$

The sum S can then be compared, for example, with a threshold value. If S exceeds the threshold, there is an anomaly.

Instead of S, it is also possible to determine another value (or several values) which indicates the deviation of the actual course of the parameter from the desired course, for example the sum of the absolute deviations from p (t _i ) and s (ti) or a suitably weighted sum the deviations from p (t _i ) and s (ti).

The desired value or desired course described above can be statistically determined, for example, by measuring a multiplicity of weft entries and measuring the parameter or course of movement p (t _i ). From this multiplicity of measurements, a typical parameter value or sequence of movements then becomes p (t _i ) determined, for example by averaging, which then as a desired parameter or desired course s (t _i ) = p (t _i ) can be used. For example, curve C1 in FIG Fig. 5 such a desired course.

However, the described method can not only be used to detect anomalies such as e.g. Detecting a yarn breakage or too slow or too fast a running weft yarn and in this case to issue an alarm and / or stop the machine, but it can also be used to control the movement of the weft yarn during entry.

For example, if a curve of type C5 is detected, i. If the speed is below the desired course and the duration of the entry is therefore too high, then control measures can be initiated which make it possible to remedy this fault condition. The same applies in the case that the speed is above the desired course and the entry duration is too low. In particular, the speed or the picking duration of the weft thread can be suitably controlled so that it again follows the desired course or has the desired value or the entry is terminated at the desired time.

Which control measures are to be taken depends on the type of weaving machine. The measures are generally known to the person skilled in the art.

As an illustration, this is in Fig. 6 an air weaving machine shown in which the weft thread 5 is conveyed with a plurality of air nozzles 28 through the compartment 21. The pressure of the compressed air blown through the nozzles 28 is determined by a pressure control unit 29. This can in turn be controlled by the Doppler interferometer 15, so that increases too deep current speed, the pressure of the air for the nozzle 28 and vice versa at high current speed, the pressure is reduced. In this way, the speed and duration of weft insertion can be very accurately controlled and even controlled by varying the amount of pressurized air, virtually instantaneously. In particular, within a single weft insertion, the speed of the thread may be controlled depending on the Doppler interference measured within the same weft insertion. This makes it possible to control the individual weft threads in such a way that they are completely inscribed at the right time, ie neither too early nor too late. This enables efficient and safe operation regardless of the weft type and other parameters affecting the weft speed. This is particularly advantageous in the case of air-jet weaving machines.

Control of the speed of tail threads is particularly useful in air-jet weaving looms, because the conveying speed in this type of machine depends on the weight and type of weft. In particular, when using different Weft types, it is therefore helpful if the pressure for the compressed air can be adjusted as needed.

With the signals of the Doppler interferometer 15, however, other operating parameters of the weaving machine can be controlled and in particular also regulated, e.g. the launching speed of the projectile in a projectile weaving machine or the braking force of a yarn brake.

The present method is also suitable for use in weaving machines, in which several different weft threads are used. If several weft threads are entered at the same time, then the measurement take place at all simultaneously registered weft threads together. If one of the two weft threads is disturbed or otherwise disturbed in its movement, this leads to a splitting of the frequency spectrum of the Doppler interference, with a frequency which corresponds to the speed of one weft thread and a second frequency which corresponds to the speed of the other weft thread , Thus it can already be recognized due to the frequency splitting that the weft threads do not move evenly and there is an error.

If the weft threads are entered individually and as required, the measurement is advantageously carried out at a location which all weft threads pass through. This is in Fig. 7 shown schematically. Here, several feed points 23a, 23b, 23c, 23d are provided, which provide the weft threads. The weft threads are picked up in a suitable manner and guided by a common guide region 30, which in Fig. 6 is formed at the interferometer 15. This guide area is referred to herein as a "common" guide area because each weft thread is used and guided there in approximately the same way. Thus, this common guide region 30 is particularly suitable for the measurement of Doppler interference. Accordingly, the Doppler interferometer 15 is disposed on the common guide portion 30.

Other measuring methods:

As mentioned above, instead of Doppler interferometry, other non-contact, optical measuring methods can also be used, in particular based on the spatial filtering method. Such methods are based on that an image of the yarn is projected onto an optical sensor, wherein the sensor consists for example of an array of several individual sensors or the sensor is preceded by a transmission grating. The determination of the speed takes place from the resulting spatial frequency. The person skilled in appropriate methods are known, for example from the above-mentioned DE 10 2004 055 561 and the writings quoted there. In principle, they can be used in all of the above-mentioned embodiments instead of Doppler interference.

Claims (15)

Method for monitoring a weft thread (5), in which the weft thread (5) is monitored by optical means, characterized in that an optical movement measurement is carried out on the weft thread (5). The method of claim 1, wherein the motion measurement is performed multiple times during a single entry. Method according to one of the preceding claims, wherein the movement of the weft thread (5) in front of the compartment (21) is measured. Method according to one of the preceding claims, wherein at least one of the movement of the weft thread during a weft insertion determined parameter (a, v, x) is compared with a desired parameter (s). Method according to claim 4, wherein during at least a part of the weft insertion, preferably during the whole weft insertion, a time-dependent course of movement (a (t), v (t), x (t)) is determined from the movement of the weft thread and is calculated with a desired course (s (t)) is compared. Method according to one of claims 4 or 5, wherein the setpoint parameter (s) or setpoint course (s (t)) is determined by determining from the parameter (a, v, x) or the course of motion (a (a) determined in the case of a plurality of weft entries. t), v (t), x (t)), a typical parameter or course of motion is determined and the typical parameter or course of motion is used as desired parameter (s) or desired course (s (t)). Method according to one of the preceding claims, wherein due to the measured movement of the weft yarn, an operating parameter of the loom is regulated. Method according to one of the preceding claims, wherein measured movement of the weft thread is used to control or regulate a speed or picking duration of the weft thread (5) at the entry. The method of claim 8, wherein the weaving machine is an air-jet weaving machine in which the weft thread (5) is forced through the pocket (21) with compressed air, and measured movement of the weft thread is used to increase the speed of the thread in the pocket (21) control, in particular by varying the amount of compressed air. Method according to one of the preceding claims, wherein within a weft insertion the speed of the thread is controlled as a function of the movement of the weft thread measured within the same weft insertion. Method according to one of the preceding claims, wherein the measured movement of the weft thread is used to detect a weft breakage, in particular by detecting from the measured movement an unexpected drop in the weft thread speed. Method according to one of the preceding claims, wherein the weft thread (5) immediately before the entry passes through a last guide (26) in which it is guided, wherein the movement of the weft thread is measured at the last guide. Method according to one of the preceding claims, wherein a plurality of weft threads are entered at the same time, wherein the movement of the weft thread is measured at all simultaneously registered weft threads together. Method according to one of the preceding claims, wherein for measuring the movement of the weft yarn is subjected to at least partially coherent light, wherein a Doppler interference between the weft (5) scattered and unscattered light waves, or between two light waves scattered differently on the weft thread (5), and based on the Doppler interference, the movement of the weft thread (5) is determined. Weaving machine with a weft thread monitor, characterized in that the weft thread monitor has a non-contact, optical movement measuring device, in particular an optical Doppler interferometer (15), for measuring a movement of the weft thread (5).

Images