EP0436204B1 - Method for obtaining a signal representing a running yarn - Google Patents

Description

The present invention relates to a method for obtaining a thread running signal, in which at least one sensor is attached to the suspension of a thread guide and supplies a signal which, inter alia, reflects the vibrations induced in the thread guide by the thread movement.

A method and a thread sensor of this type are already known from DE-A-29 19 836 and from earlier GB-A-20 23 671 by the same applicant.

The aim in the textile machine industry is to be able to monitor the production on every spindle of a spinning machine. A thread break at a spinning station results in loss of production and subcontracted work and in certain cases can also damage the machine. The main causes of thread breaks are, for example, thin spots in the yarn, poorly maintained parts in the yarn formation process or incorrect setting of the spinning machine.

Known thread monitoring devices record, among other things, parameters such as the ballooning of the thread or the speed of the rotor in a ring spinning machine, the changes over time in the thread thickness of the running thread or the cross section of the thread. However, due to the high manufacturing costs, such devices are only used on a few machines. The aforementioned DE-A-29 19 836 and GB-A-20 23 671 discloses a yarn break sensor which consists of a piezoelectric element which is attached to a part of the yarn guide and whose output signal is further processed to detect a yarn break.

When the thread guide touches the spinning threads, high-frequency vibrations occur on it, which are mixed with mechanical vibrations of the ring spinning machine. As can be read in DE-A-29 19 836, the frequency of the mechanical vibrations is about 1 kHz, while the thread guide vibrates at about 15 kHz. These latter vibrations are evaluated in DE-A-29 19 836 for the detection of thread breaks in such a way that the natural vibrations are discriminated against the mechanical vibrations. More specifically, the two leads of the piezoelectric element are connected to a bandpass filter which receives the natural vibration component in the output signals of the piezoelectric element, i.e. lets through. This natural vibration component is then amplified to a certain value by means of an amplifier. A rectifier filter converts the AC signals into DC signals. With the aid of a voltage comparator, a voltage range is defined in which normal operation is guaranteed, and a corresponding logic output signal is present at the output of the comparator (DE-A-29 19 836, p. 10, lines 29 to p. 11, line. 6).

However, the thread sensor from DE-A-29 19 836 is only able to determine thread breaks, but not to measure the thread tension.

The invention has for its object to provide an inexpensive thread tension measuring device, which can possibly also serve as a thread break detector, is inexpensive to manufacture and can be attached to existing machines that process or generate the thread without the attachment itself causing a change in the thread tension or leads to an undesirable additional stress on the thread.

Proceeding from the known method or sensor, the present invention is characterized in terms of method in that a broadband sensor in the form of a piezo film is used, which is arranged at least essentially in a plane containing the thread running direction or in a plane parallel to it in such a way that the suspension of the thread guide executes elastic movements on both sides (in relation to the thread running direction), that in order to obtain a signal corresponding to the thread tension either the frequency of an element winding the thread and / or harmonics of this frequency are filtered out from the sensor signal and the level of this filtered frequency or Frequencies is measured, the frequency or frequencies filtered out by a filter being well above the fundamental oscillation frequency of the thread guide, ie the natural vibration frequency of the thread guide eyelet or lie, and that the pass frequency of the filter is tracked according to the frequency change of the element winding the thread, the quality of the filter preferably being kept at least substantially constant.

The invention is based on the knowledge belonging to the invention that the output signal of the sensor is a complex analog signal, which among other things also includes the speed of the rotor as a fundamental oscillation in the course of the deflection over time the thread guide as well as harmonic values of this basic vibration and the so-called thread noise contains, in addition to other vibrations such as natural vibrations of the thread guide and vibrations induced by machine vibrations. Furthermore, the invention is based on the inventive finding that both the level of the rotor speed and the level of harmonic frequencies of the rotor speed are a function of the thread tension, so that an evaluation of the thread tension either at the fundamental frequency (f 1) or at the harmonic frequencies (f 2 to f₉) the rotor speed is possible.

The evaluation of the sensor signal can therefore be based on the fact that the level of the thread tension is detected as a value, or that a level comparison is carried out with a reference level. This reference level can depend on machine parameters such as spindle speed, maintenance status, etc. The result of this comparison can then be used to control the corresponding machine, for example to control the spindle speed of a ring spinning machine in the sense of maintaining a predetermined thread tension or a predetermined course of the thread tension using the bobbin forming method.

It should be pointed out here that the amplitude of the natural vibrations of the thread guide, which is evaluated in DE-A-29 19 836 to obtain the thread break signal, is practically independent of the thread tension and therefore does not offer any possibility of evaluating the thread tension.

• a) Das Verfahren bzw. die Vorrichtung erlaubt die quantitative Erfassung der Fadenspannung in einem weiten Frequenz- bzw. Drehzahlbereich, da die schwach ausgebildete Eigenfrequenz oder Resonanzfrequenz des Fadenführers mit Aufhängung unterhalb der Frequenz des Nutzbereiches des Fadenspannungssensors liegt.
• b) Der Fadensensor ersetzt ein bereits vorhandenes Element an der Spinnmaschine, nämlich den Fadenführer, so daß die Verwendung des Fadenspannungssensors keine zusätzliche Belastung für den Faden darstellt.
• c) Der Fadensensor kann preisgünstig hergestellt werden und entweder nur als Fadenbruchsensor oder aber auch als Fadenspannungssensor betrieben werden.
• d) Es kann auch entsprechend der Erfindung ein tragbares Fadenspannungsmeßgerät vorgesehen werden, das insbesondere mit einer Fadenführungsöse in Form eines Sauschwanzerls ausgestattet ist, welche sich um einen laufenden Faden anlegen läßt, ohne das Laufen des Fadens zu unterbrechen.

There are various advantages with the method and the device of the invention:

• a) The method or the device allows quantitative Detection of the thread tension in a wide frequency or speed range, since the weakly developed natural frequency or resonance frequency of the thread guide with suspension is below the frequency of the useful range of the thread tension sensor.
• b) The thread sensor replaces an already existing element on the spinning machine, namely the thread guide, so that the use of the thread tension sensor does not represent an additional load for the thread.
• c) The thread sensor can be manufactured inexpensively and can be operated either only as a thread break sensor or as a thread tension sensor.
• d) It can also be provided according to the invention, a portable thread tension measuring device, which is particularly equipped with a thread guide eyelet in the form of a Sauschwanzerls, which can be placed around a running thread without interrupting the running of the thread.

Particularly preferred variants of the method according to the invention or the device according to the invention, especially with regard to the signal evaluation, can be found in subclaims 2 to 5 and 7 to 18. The design of the moving filter as a filter in the SC version is particularly cost-effective and effective.

When the thread sensor according to the invention is used on a ring spinning machine, the thread guide is preferably designed as a thread guide eyelet, for example in the form of the known bobbin. The thread guide eyelet can be fastened to its holder by means of a leaf spring, the sensor being fastened to the leaf spring. The leaf spring itself should be arranged with its plane essentially parallel to the thread movement. But it is also possible, instead of a leaf spring, to use part of the thread guide or the thread guide eyelet itself as a spring form, the sensor or sensors then being attached to this spring part.

The piezo sensors used in the prior art are piezo crystals which have a pronounced resonance and are therefore not sufficiently broadband for the purpose of the invention.

A particular embodiment of the present invention is characterized in that the piezo film is a so-called PVDF film, which can be obtained particularly inexpensively and is extremely thin. These piezo foils are very broadband and the use of such a piezo foil advantageously does not lead to a falsification of the measured vibrations.

It is also possible according to the invention, as indicated in claims 12 to 15, to provide a non-thread-guiding reference sensor for one or more thread tension sensors which emits a signal which is dependent on the machine vibrations, wherein the thread tension signals can be compared with the reference signal and a difference value can be formed . However, the reference signal can also be used as a threshold value for the generation of binary thread break information. However, it is also possible to use the reference sensor to detect loud environmental noises such as ultrasound of compressed air etc. and to declare thread tension information generated in the same period of time to be invalid.

Fig. 1a

eine Seitenansicht einer Fadenführungsöse einer Ringspinnmaschine, wobei diese Öse mit einem erfindungsgemäßen Fadensensor ausgestattet ist,

Fig. 1b

eine Draufsicht der Ausführung gemäß Fig. 1a,

Fig. 2

eine schematische Darstellung einer Spinnstelle einer Ringspinnmaschine mit der Fadenführungsöse der Fig. 1a und 1b,

Fig. 3a

eine graphische Darstellung der zeitlichen Abhängigkeit der Auslenkung der Fadenführungsöse bei starker Fadenspannung,

Fig. 3b

eine Spektral-Darstellung der Auslenkung bei starker Fadenspannung,

Fig. 4a

eine graphische Darstellung der zeitlichen Abhängigkeit der Auslenkung der Fadenführungsöse bei schwacher Fadenspannung,

Fig. 4b

eine Spektral-Darstellung der Auslenkung der Fadenführungsöse bei schwacher Fadenspannung,

Fig. 5a, 5b und 5c

verschiedene elektronische Sensorsignalbearbeitungsmöglichkeiten,

Fig. 6

eine weitere Ausgestaltung eines erfindungsgemäßen Fadenspannungssensors, und

Fig. 7a

eine schematische Darstellung einer besonderen Ausführung einer Fadenführungsöse, die für die vorliegende Erfindung besonders geeignet ist, wobei die Führungsöse entsprechend den Fig. 1a und 1b eingebaut wird,

Fig. 7b

einen Querschnitt nach der Linie VIIb-VIIb der Fig. 7a,

Fig. 7c

einen Querschnitt nach der Linie VIIc-VIIc der Fig. 7a,

Fig. 8

ein Blockschaltbild eines mitlaufenden Filters in SC-Ausführung,

Fig. 9a und 9b

zwei Möglichkeiten, die von einer Gruppe Fadenspannungssensoren enthaltenen Signale auszuwerten, um Fadenspannungssignale zu erzeugen, und

Fig. 10

eine Möglichkeit, die von einer Vielzahl von Sensoren erhaltenen Signale zu verarbeiten, um reine Fadenbruchsignale zu erzeugen.

The invention is explained in more detail below on the basis of exemplary embodiments with reference to the drawing, in which:

Fig. 1a

a side view of a thread guide eye of a ring spinning machine, this eye with a thread sensor according to the invention is equipped,

Fig. 1b

a plan view of the embodiment of FIG. 1a,

Fig. 2

1 shows a schematic representation of a spinning station of a ring spinning machine with the thread guide eye of FIGS. 1a and 1b,

Fig. 3a

a graphical representation of the time dependence of the deflection of the thread guide eyelet when the thread tension is high,

Fig. 3b

a spectral representation of the deflection with strong thread tension,

Fig. 4a

a graphical representation of the temporal dependence of the deflection of the thread guide eyelet when thread tension is weak,

Fig. 4b

a spectral representation of the deflection of the thread guide eyelet with weak thread tension,

5a, 5b and 5c

various electronic sensor signal processing options,

Fig. 6

a further embodiment of a thread tension sensor according to the invention, and

Fig. 7a

2 shows a schematic illustration of a special embodiment of a thread guide eyelet which is particularly suitable for the present invention, the guide eyelet being installed in accordance with FIGS. 1a and 1b,

Fig. 7b

a cross section along the line VIIb-VIIb of 7a,

Fig. 7c

4 shows a cross section along the line VIIc-VIIc of FIG. 7a,

Fig. 8

a block diagram of a moving filter in SC version,

9a and 9b

two possibilities for evaluating the signals contained by a group of thread tension sensors in order to generate thread tension signals, and

Fig. 10

a way to process the signals received from a variety of sensors to produce pure thread break signals.

In order to facilitate the following explanations, reference is first made to FIG. 2. Fig. 2 shows a side view of a spinning station 10 of a ring spinning machine, in which a thread 12 leaves the outlet rollers 14, 16 of the drafting system and through the thread guide eyelet 18 and an anti-balloon ring 20 leads to a ring traveler 22 rotating on the ring track 21 of the ring rail 23, whereby he is wound on the rotating spindle sleeve 24 to a cop 26. Due to the rotation of the rotor, the thread is guided around the spindle sleeve in such a way that a balloon is formed due to the centrifugal force, which is limited by the anti-balloon or balloon restriction ring 20 and has its tip in the thread guide eyelet. The friction and air resistance of the runner, the air resistance of the thread and the frictional resistance between the thread and the runner and between the thread and the balloon confinement ring produce a thread tension which can be measured at the location of the thread guide.

This thread tension increases with increasing spindle speed.

Of particular interest is a spindle speed range between about 6000 rpm and 20,000 rpm, whereby the thread tension sensor, as described here, easily for spindle speeds or rotor revolutions (which are only 1 or 2% lower than the spindle speeds and can therefore be equated with them ) up to 30,000 rpm and higher.

Touching the tensioned thread in the thread guide eyelet leads to frictional forces that act in both the horizontal and vertical directions.

In the embodiment of the thread sensor according to the invention shown, the horizontal components of this frictional force are used, which are proportional to the thread tension due to the friction coefficient. This thread sensor is shown schematically in FIGS. 1a and 1b. Here the thread guide eyelet 18 is so tapered in the rear part that a bendable, resilient zone 30 with the shape of a leaf spring is formed. The leaf spring-like part 30 is clamped at its end facing away from the thread guide eyelet in a clamping block 35 and is held by means of this clamping block firmly on the frame of the ring spinning machine on a longitudinal rod 37 of the ring spinning machine. On the flat right side 34 of the flexible resilient zone of the leaf spring, a strain-sensitive sensor element 32 is attached, which preferably consists of a PVDF piezo film. This film emits an extension-dependent electrical signal to a downstream electronics (FIG. 5) via the connecting cable 36. The thread 12 runs essentially in a straight line from the pair of delivery rollers 14, 16 to the thread guide 18 and is deflected on the thread guide due to the balloon that is being formed. The rotational movement of the carriage 22 causes the thread to make a circular movement within the thread guide, whereby the forces exerted on the thread guide alternate with the left one and the right side of it. As a result, the leaf spring 30 is also sometimes bent to the left and sometimes to the right (L and R in Fig. 1b), so that the piezo film also performs an alternating movement and generates an alternating voltage. This alternating movement is important for the functioning of the sensor.

Although in the embodiment according to FIGS. 1a, 1b and 2 the piezofilm is arranged in a plane which contains the thread running direction in front of the thread guide, the piezofilm or the leaf spring could also be arranged, for example, laterally offset to the thread guide. This arrangement would also lead to the lateral deflection of the leaf spring on both sides.

It is also possible to form the thread guide eyelet in one piece from shaped sheet metal, as shown in FIGS. 7a, 7b and 7c. The guide eye formed from spring steel is shaped in such a way that it at least essentially retains the originally straight or rectangular cross section (FIG. 7c) of the sheet metal strip in the leaf spring part 32. Upon transition into the actual eyelet 18, this cross-section changes to an arcuate cross-section (Fig. 7b) so that the narrowest passage of the eyelet is formed by the curved central region 18 'of the strip, while the edge regions are further away from the center of the eyelet are. Due to this inexpensive implementation, the thread is always guided by the curved region 18 'of the strip, there is no scraping of the thread at the edges of the strip. The sheet metal strip can be wider in the leaf spring part than indicated in the eyelet part at 34 '.

FIG. 3a first shows the temporal course 38 of the lateral deflection of the thread guide eyelet when the thread tension is high, specifically for an embodiment 1a and 1b. It can be seen that the curve 38 according to FIG. 3a essentially represents a type of sine wave 40 with a superimposed high-frequency oscillation 42 of a complex type. The sine oscillation corresponds to the rotational speed of the ring traveler 22 and the superimposed oscillations contain information about all other vibrations to which the thread guide eye is exposed .

If one carries out a spectral analysis of the sensor signal according to FIG. 3a, one obtains a result, as shown in FIG. 3b. Here you can clearly see the speed f₁ of the rotor as a fundamental vibration in the course of the deflection. The basic vibration harmonic vibrations f₂, f₃, f₄ to f₉ and the so-called thread noise, which ranges from f₁₀ to f₁₁, are assigned. The thread noise is caused on the one hand by the fibrous surface of the thread, and on the other hand by the constantly fluctuating cross-section of the thread (thinning or thickening).

Both the level of the speed f₁ and the level of their harmonics f₂ to f₉ are a function of the thread tension. This makes a comparison between FIGS. 3a and 3b on the one hand and FIGS. 4a and 4b on the other hand clear.

It can be seen from FIG. 4b that the spectral composition of the signal is very similar to the spectral composition of FIG. 3b, but the amplitudes are lower.

An evaluation of the sensor signal is thus possible in both frequency ranges. The evaluation can be based on the fact that the level of the thread tension is recorded as a value, or that only a level comparison with a reference level is carried out. This reference level can depend on machine parameters such as spindle speed, maintenance status, etc. The comparison with a reference level reduces the Thread tension information on a pure thread run or thread break information, which considerably reduces the data transmission and data evaluation effort. It is thus possible to design a ring spinning machine in such a way that only one thread break signal is generated at all spinning positions, but that the thread tension is also measured at some spinning positions. The actual sensor is the same for all spinning positions, only there is a difference in the evaluation of the sensor signal.

The very broadband sensitivity of a thread tension sensor according to the invention, which, according to current determinations, ranges from less than 1 Hz to more than 1 MHz, means that not only does the thread tension of the sensor signal come in, but also machine vibrations, the majority of which come from the area of the spindle or Rotor speed, but also from high-frequency components in the area of thread noise. If a thread runs through the thread guide eyelet, these machine vibrations do not interfere because they are too weak. In the event of thread breakage, however, these vibration signals appear and simulate a very weak thread tension signal.

Therefore, a reference sensor is attached to the machine that works under exactly the same conditions as the thread tension sensor, ie it is also attached to a thread guide, but to one that does not guide a thread. The signal from this reference sensor is processed in a similar manner to the signals from the thread-guiding sensors. The upper reference level is now obtained from the signal from the reference sensor. The reference sensor provides the reference level for one or more thread break sensors. This takes into account local conditions that determine the interference level. A reference sensor is preferably used for groups with 20 to 60 active sensors.

Possible designs of the signal evaluation electronics are shown in FIGS. 5a to 5c.

According to FIG. 5 a, the signal of the sensor applied to the terminal 52 is amplified with one or more amplifiers 54, freed of unwanted signal components with filter 56 and then fed to a rectifier / integrator 58. The filter 56 can be a so-called moving filter, which includes control of a center frequency in accordance with the respective rotor speed. This center frequency can also be asymmetrical in the frequency pass range of the filter. A particularly preferred filter of this type will be described later in connection with FIG. 8.

The output signal of the rectifier / integrator 58, which is present at the terminal 60, is then fed to the circuit according to FIG. 5b as an input signal. The circuit according to FIG. 5a is identified overall with the reference symbol 62.

In FIG. 5 b, the signal present at terminal 60 is converted into a digital signal by means of an analog / digital converter 64, which is analyzed by a subsequent microcontroller 66 in order to obtain the thread tension. The terminal 70 makes it possible to apply a reference voltage to the analog / digital converter, this reference voltage being obtained from the reference sensor mentioned above and also being prepared by a circuit corresponding to the circuit 62 for comparison with the signal present at the terminal 60. The thread tension signal generated by the microcontroller is present at terminal 68 and can be represented in various ways; For example, the thread tension signal can be displayed on a screen as part of a screen display. But it can also Machine control supplied and taken into account here, for example when controlling the rotational speed of the spindle drive.

5c shows an alternative embodiment of the evaluation of the signal present at terminal 60 by a comparator 72, which compares it in analog form with a reference voltage U _Ref which is present at terminal 74 and, as mentioned above, from the reference sensor via a Circuit corresponding to the circuit 62 is obtained. The output signal of the comparator 72 is then further processed by a microcontroller 76 into a thread tension signal which can be tapped at the terminal 78. The thread tension signal can be displayed or evaluated in accordance with the thread tension signal present at terminal 68. 5c, the analog / digital conversion takes place in the microcontroller 76.

Both in FIGS. 5b and 5c, instead of applying a real-time reference voltage to the reference sensor, a predetermined reference voltage U _Ref can be used, which is either constant or whose level can be varied depending on machine operating states.

The. Fig. 6 shows an alternative evaluation which can be used in particular when a reference sensor 80, as explained above, is attached to the machine, i.e. when a reference sensor 80 is attached to a thread guide that does not carry a thread.

6 initially shows a series of input terminals 52, 52.1, 52.2 to 52.n, which each carry the signal from a thread-guiding sensor 32. Each terminal 52 to 52.n leads to a respective circuit 62 according to FIG. 5a and the output terminals 60, 60.1 to 60.n of these circuits 62 applied to an electronic switch 81, which is able to pass the signals successively or in a specific order or in a selected order to a further circuit 82, this further circuit 82 either according to FIG. 5b or according to FIG 5c can be formed. The terminal 52.r carries the voltage from the reference sensor 80, which is likewise amplified, filtered or integrated by means of a circuit 62 in accordance with FIG. 5a. As the arrow 84 shows, the output signal of the circuit 62 associated with the reference sensor 80 forms the reference voltage for the further processing circuit according to FIG. 5b or FIG. 5c.

In other words, the level of the reference sensor 80 is compared with the level of the thread guiding sensors 32, 32.1, 32.2 to 32.n. The difference is then further processed as a pure thread tension signal, for example in accordance with FIG. 5b or 5c. The changeover switch 62 is generally not designed as a mechanical switch, but rather as an electronic circuit, for example using a multiplex method. An arrangement according to FIG. 6 has the advantage that only a complex evaluation circuit is required in order to further process the signals from a large number of yarn break sensors to yarn tension signals.

In the case of a ring spinning machine with several spinning positions, for example 1000 or 1200 spinning positions, a piezofilm sensor is provided for each thread guide, so that a thread break signal can be generated by each of the spinning positions present in total. In addition, the cabling is carried out so that at certain spinning positions, for example every twentieth or every fiftieth spinning position, there is a possibility of measuring the respective thread tension. One or two thread guides are then provided on the machine on each side, which do not carry a thread, but which do exactly the same the other thread guides are formed and are also equipped with piezo film sensors in order to generate the above-mentioned reference signals.

A particularly preferred embodiment of a moving filter is shown in FIG. 8. This is a block diagram which shows the use of a filter in SC design (SC means "switched capacitor"), which is preferably in the form of a chip, namely the chip MF / 10 from National Semiconductors.

Since the pass band of the filter is changed in accordance with the respective rotor speeds, it is necessary to generate a frequency signal which corresponds to the rotor speed. It is known that the rotor speed is only slightly lower than the spindle speed of the ring spinning machine. In the case of a ring spinning machine, the spindle speed can be determined relatively easily, so that instead of the rotor speed, the spindle speed is taken as the guide variable for the filter. The generation of this frequency signal is shown in FIG. 8. This is because the spindles are driven by a main motor 100, via a so-called vertical shaft 102 and belts (not shown), each of which drives four spindles. The exact design of this drive is well known in the prior art, for example from the Rieter ring spinning machines G5 / 1.

In order to generate a signal proportional to the spindle speed, a tachometer generator 104 is mounted on the main shaft of the drive motor. This essentially consists of a gearwheel 106 and an initiator or sensor 108 which counts the gaps 110 present in the gearwheel and generates a signal which is dependent on the speed of the main motor and which is indicated in the drawing as "f-sensor". The exact frequency of this signal depends on the number of teeth on the gear and the speed of rotation of the main motor.

After a translation between the main motor and the spindles of the ring spinning machines, due to the drives connected in between, it is necessary to multiply the frequency signal by a factor in order to achieve the actual spindle speed. But even then the frequency of the signal must be increased even further, since a clock frequency is required to control the filter 56, which is proportional to the spindle speed or rotor speed, but is approximately a hundred times higher in frequency. With a spindle speed of 12000 rpm, which corresponds to 200 Hz, a clock frequency of 20 kHz is required, for example. The circuit indicated in the drawing as multiplier 112 therefore receives the frequency signal of the sensor at its input and delivers the desired higher clock frequency f-clock at its output.

berechnet, wo n das Übersetzungsverhältnis Drehzahlspindel zu Drehzahlhauptmotorantrieb ist.The factor by which the input signal is multiplied to produce the clock frequency signal is given by the equation:

$\text{Factor = 100 xn / number of teeth}$

calculates where n is the ratio of the speed spindle to the speed main motor drive.

This clock frequency is then applied to a two-phase clock generator 114, which is part of the SC filter 56. This two-phase clock generator generates two signals shifted by the phases τ1 and τ2, which serve to actuate two switches via the lines shown as an arrow. These switches serve a capacitor temporarily with the negative terminal of an operational amplifier provided with a further capacitor 122 120 to connect. The clock with which the switches are closed and opened in opposition determines the effective impedance of the capacitance at the input of the OpAmps, which in turn defines the center frequency of the bandpass filter.

The amplified sensor signal coming from the amplifier 54 is therefore applied to the input of the filter, and the filtered signal at the output of the filter 56 is then fed to the rectifier / integrator 58, in accordance with the circuit of FIG. 5a. The described type of thread tension measurement can be carried out at all rotor frequencies that are clearly above the basic oscillation frequency of the thread guide, i.e. the natural vibration frequency of the thread guide eyelet with suspension system. In the normal case, this fundamental oscillation frequency is approximately 10 to 20 Hz and the designation "clearly above" indicates frequencies which are a factor of approximately 4 to 10 or higher. Thus, the thread tension measuring method according to the present invention can with rotor speeds above 100 Hz, i.e. approx. 6000 rpm can be used. Since such speeds are below the useful speeds of interest of the spindles of the ring spinning machine, this lower limit of the voltage evaluation does not represent any restriction in practice.

An advantage of a filter in the SC version is that the bandwidth of the passband of the filter is changed in proportion to the center frequency, in that the quality Q of the filter remains at least essentially constant, which benefits the signal evaluation.

It is important when using the sensor according to the present invention that it is mounted in one plane on the attachment of the thread guide so that the orbital movement of the thread within the thread guide leads to a deflection of the Suspension on both sides and therefore leads to a corresponding expansion and compression of the piezo film on both sides. In other words, the sensor in the form of the piezo film should be arranged in a plane containing the thread running direction or a plane parallel to it in such a way that the suspension of the thread guide executes elastic movements on both sides with respect to the thread running direction. In the ring spinning machine, the thread running direction means, for example, the running direction of the thread between the pair of delivery rollers and the thread guide or the mean running direction of the thread within the thread balloon, which corresponds to the geometric axis of the thread balloon.

At this point it should be clarified that so-called PVDF piezo films are available from various manufacturers, for example from the US company PENNWALT Corporation under the name "KYNAR" (registered trademark). PVDF is an abbreviation for polyvinylidene fluoride, which belongs to the class of piezoelectric polymers. Piezo foils of this type which are suitable for use with the present invention are preferably broad-band with a quality factor Q tending towards zero.

9a shows a particularly preferred embodiment for processing the signals from a group of sensors 52.1 to 52.n and from a reference sensor 52.r by means of a multiplexer which has 16 inputs. For this reason, n will normally have a maximum value of 15 and the further input will be used for the reference sensor. In practice, therefore, a blind thread guide is provided for each group of 15 real thread guides, ie thread guides that actually carry a thread at a spinning position, and the circuit according to FIG. 9a will be duplicated for each group of 15 real thread guides.

The sensor signals, i.e. the signals coming from sensors 52.1 to 52.n are amplified, filtered and rectified in front of the multiplexer 150 by the circuit according to FIG. 5a. The individual channels, i.e. the signals connected from the sensors 52.1 to 52.n and 52.r to the analog / digital converter 152 in turn, the microcontroller 154 determining the sensor address for the multiplexer. The levels of the sensors 52.1 to 52.n are compared in terms of amount with the reference level from the reference sensor 52.r, the difference corresponds to the thread tension and can be present either as a comparison value or after an appropriate calibration as an absolute value.

In this example, the components of the circuit according to FIG. 5a are provided for each sensor and integrated in the holder for the sensor. However, this is somewhat complex and FIG. 9b shows a further improvement, according to which only one respective amplifier is assigned to each sensor, and the filter and the analog / digital converter are arranged after the multiplexer.

In further detail, the signals from sensors 52.1 to 52.n and from reference sensor 52.r are fed to the multiplexer in an amplified form. The microcontroller 154 gives the multiplexer the sensor address to be switched through. The signal is filtered behind the multiplexer, for example by means of a circuit according to FIG. 8, and converted into a digital signal by the analog / digital converter 152. This signal is then fed to the microcontroller 154. If the system, consisting of an analog / digital converter and a microcontroller, does not work quickly enough, a rectifier 156 is inserted between the filter and the A / D converter, which means that frequencies up to 300 Hz no longer have to be converted and evaluated , but only frequencies of approx. 1 Hz have to be measured. At In a more favorable design of the circuit, the individual amplifier stages in / at the sensors can be replaced by a single amplification stage behind the multiplexer. 9a and 9b describe circuit variants which enable the measurement of the thread tension in all sensors.

In contrast, Fig. 10 is concerned with determining whether the thread is broken at the respective spinning positions. The sensor signals are processed in parallel here. They are in turn combined in groups 52.1 to 52.n together with a reference sensor 52.r. In this case, the total number of sensors in a group can be up to 32.

As can be seen from FIG. 10, the signals are first amplified, filtered and rectified and then they are compared in respective comparators, which each correspond to the comparator 72 of FIG. 5c, with the reference signal from the reference sensor 52.r. The output of the respective comparators 72 is actually a digital signal, since the comparator only makes the decision whether the level from an active sensor is higher or lower than the reference level from the reference sensor. All signals are applied to the microcontroller 154 at parallel (port) inputs. The advantage of this variant is that a simple and poorly performing, i.e. low-cost microcontroller can be used (for example, type 80C31 from Intel). A thread tension measurement is excluded here.

It can be seen that the output signals of the individual microcontrollers 154, which are each assigned to a single sensor group, all communicate with a serial data bus, for example of the type RS232 or RS485.

The microcontrollers (approx. 50 units per machine) are advantageous for all circuit variants serial data bus connected to a master controller, which can also be formed, for example, by the component (chip) 80C31 from Intel. This master controller is intended for the evaluation of the thread information and provides the machine control or a process control with compressed data, possibly statistically evaluated.

In machines with over 1000 spindles, it can be advantageous if the microcontrollers are distributed over two serial data buses, for example one data bus for each side of the machine.

It should also be noted that combinations of the circuits of FIGS. 9a, 9b and 10 are possible, and that it is also possible to supply the sensor signals as yes / no information (thread breakage information) in parallel or by multiplexer to the microcontroller while a Sensor per microcontroller group as thread tension meter by A / D converter (which can be an integrated part of the microcontroller) is evaluated.

Claims (18)

1. A method for obtaining a yarn course signal, in which at least one sensor (32) is attached to the suspension (30) of a yarn guide (18) and supplies a signal which represents, among other things, the oscillations induced by the yarn movement in the yarn guide, characterized in that a wide-band sensor in form of a piezofoil is used which is arranged at least substantially in a plane comprising the direction of the yarn course or a plane parallel thereto in such a way that the suspension (30) of the yarn guide (18) carries out elastic movements on either side, that for obtaining a signal representative of the yarn tension, either the frequency (f₁) of an element (22) winding up the yarn and/or the harmonic of this frequency (f₂ to f₉) is filtered out of the sensor signal and the level of said filtered-out frequency or frequencies is measured, whereby the frequency or frequencies filtered out by the filter are clearly above the fundamental frequency of the yarn guide, i.e., the natural oscillation frequency of the yarn guide ring, and that the forward frequency of the filter is followed up according to the frequency change of the element (22) winding up the yarn, whereby the quality (Q) of the filter is preferably at least substantially kept constant.
2. A method as claimed in claim 1, characterized in that the sensor signal is amplified in one or several amplifiers (54), is freed in the filter (56) from the undesirable frequencies and thereafter guided to a rectifier/integrator (58).
3. A method as claimed in claim 1, characterized in that the sensor signal is brought into digital form through an analog-to-digital converter (64) and thereafter is evaluated by a microcontroller.
4. A method as claimed in claim 1, characterized in that the sensor signal is compared with a reference voltage (U_ref), with the level of this reference voltage being either constant or being varied depending on the operating status of the machine.
5. A method as claimed in one of the previous claims, characterized in that a reference signal or the reference voltage is produced by a reference sensor (80) which is attached to the allocated machine and to the yarn guide and which determines machine vibrations, but does not guide yarn itself.
6. A yarn sensor (32), attachable to the suspension (30) of a yarn guide (18), whereby the sensor (32) supplies an electric signal which is representative of the oscillations induced by the yarn movements in the yarn guide, with this signal being filtered and analysed, characterized in that the sensor is a piezofoil whose plane is arranged at least substantially in a plane comprising the direction of the yarn course or a plane parallel thereto in such a way that the suspension of the yarn guide carries out elastic movements on either side, that for filtering the control signals a travelling filter (56) is provided whose forward range is guided according to the frequency (f₁) of an element winding up the yarn at a quality which is substantially constant so as to obtain either the frequency (f₁) of an element (22) winding up the yarn (12) and/or the harmonic (f₂ to f₉) of said frequency (f₁), and that a device (66, 76) measuring the level of the frequency/frequencies which have been filtered out is provided whose output signal corresponds to the yarn tension.
7. A yarn sensor as claimed in claim 6, characterized in that the travelling filter is a filter in semiconductor arrangement, e.g., in the form of the chip under the designation MF 10 supplied by National Semiconductors.
8. A yarn sensor as claimed in one of the claims 6 or 7, characterized in that the frequency bandwidth of the forward range of the filter is in the range of between 5 and 15 %, preferably approx. 10 % of the frequency (f₁) or the selected harmonic frequency (f₂ to f₉) of the element winding up the yarn.
9. A yarn sensor as claimed in claim 8, characterized in that the forward range of the filter with respect to the required frequency (f₁ or f₂ to f₉) of the element winding up the yarn is selected in such a way that said required frequency is situated in the upper part of the forward range.
10. A yarn sensor as claimed in one of the claims 6 to 9, characterized in that the yarn guide is a yarn guide ring in the form of a pig's tail for example, in a ring spinning machine or a portable yarn tension measuring device, for example.
11. A yarn sensor as claimed in one of the claims 6 to 10, characterized in that the suspension (30) of the yarn guide, which may be arranged in one part with the yarn guide (18), is arranged as a leaf spring (30), preferably the part which leads from the guide or ring to the fixing device (35), and that the sensor (32) is attached to the leaf spring, with the leaf spring (30) with its plane extending at least substantially parallel to the direction of the yarn course or the mean direction of the yarn course.
12. A yarn sensor as claimed in one of the previous claims 6 to 11, characterized in that a reference sensor (80) is provided on the machine producing or processing the yarn, which sensor, like the actual yarn measuring sensor (32) or the actual yarn measuring sensors (32, 32.1., ...32.n), is subjected to the vibrations of the machine, but which is hardly influenced or not influenced by a running yarn (12), and that the signal of the reference sensor (80) supplies a reference level (U_ref) for the other sensor (32) or the other measuring sensors (32, 32.1, ..... 32.n).
13. A yarn sensor as claimed in claim 12, characterized in that the yarn tension signals are compared with the reference level in a comparator (72) and that from this comparison a difference signal is formed.
14. A yarn sensor as claimed in claim 12, characterized in that the reference signal (U_ref) is used as threshold value for the production of binary yarn breakage information.
15. A yarn sensor as claimed in claim 12, characterized in that the reference sensor (80) or an evaluation circuit connected thereto recognizes loud ambient noises such as ultransonic sound of compressed air, etc. and that the yarn tension measuring circuit (Fig. 5b; Fig. 5c) is arranged in such a way that yarn tension information produced during the same period is declared invalid.
16. A yarn sensor as claimed in one of the previous claims 6 to 15, characterized in that it is housed in a casing made from metal or plastic which is preferably attached to or on the machine in an acoustically insulated manner, e.g., by means of insulation made from rubber or foam.
17. A yarn sensor as claimed in one of the previous claims 6 to 16, characterized in that the sensor signal is amplified before or after the filtering by one or several amplifiers (54) and that it is supplied to a rectifier/integrator (58) after the amplification and the filtering, from whose output (60) the yarn tension signal can be tapped or at whose output it is further evaluated into a yarn tension signal.
18. A yarn sensor as claimed in claim 17, characterized in that the signal supplied to the output (60) of the rectifier/integrator can be supplied to an analog-to-digital converter whose output is connected to a microcontroller which carries out the evaluation of the signal.

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