EP1893996A1

EP1893996A1 - Method and device for detecting foreign matter in a moving solid elongated test object

Info

Publication number: EP1893996A1
Application number: EP06741631A
Authority: EP
Inventors: Philipp Ott; Peter Schmid
Original assignee: Uster Technologies AG
Current assignee: Uster Technologies AG
Priority date: 2005-06-15
Filing date: 2006-06-07
Publication date: 2008-03-05
Also published as: CN101180535A; CN101180535B; JP2008546915A; WO2006133584A1; EP2108949A1

Abstract

The device (1) for detecting foreign matter in a moving solid elongated test object (9), for example a yarn, comprises a sensor (2) for picking up an electrostatic signal from the test object (9). The sensor (2) is suitable for picking up an electrostatic signal from such excess charges that were already previously present on the test object (9). The device (1) also comprises a sensor (2) for picking up a further signal, for example a capacitive signal, from the test object (9). Furthermore, evaluation means (7) are present to evaluate the electrostatic signal and the further signal and to detect foreign matter. The combination of the electrostatic signal and the further signal produces an improvement in selectivity. False alarms are reduced, and greater reliability and sensitivity are achieved.

Description

Method and device for detecting foreign substances in a moving, solid, elongated test material

The present invention is in the field of testing with electrical means of solid, elongated, preferably textile structures such as card sliver, roving, yarn or fabric.

It relates to a method and a device for detecting foreign substances in a moving, solid, elongated

Test material, according to the preambles of the independent claims. A preferred application is the

Yarn monitoring on a spinning or winding machine.

There is a need in the textile industry for reliable detection and eventual quantification of foreign substances such as polypropylene in elongated textile structures such as yarn. Optical means are often used for this purpose. According to WO-98/33061 Al or EP-I '058' 112 Al, a yarn is scanned with ultraviolet or infrared light. Due to the light absorption, foreign substances, in particular polypropylene, can be detected. EP-O '399'945 A2 teaches the illumination of yarn with light of two different wavelengths. This is how two are born Output signals whose difference is determined. Foreign substances such as polypropylene result in a change in the difference signal. All optical measuring principles have the disadvantage that they do not recognize foreign substances which are transparent to the light used, have the same reflectivity ("color") as the test material or are hidden inside the test material and are invisible from the outside.

The shortcomings of optical measuring principles can be circumvented by the use of electrical means. From EP-O '924' 513 Al a method and a device for the capacitive determination of proportions of solids in textile Prüfgut known. The test material is moved through a plate capacitor and exposed to an alternating electric field. Dielectric properties of the test material are determined. From the dielectric properties of two electrical variables are determined and combined, creating a characteristic value that is independent of the mass of the test material. The characteristic value is compared with a previously determined characteristic value for the substances concerned and from this the proportion of foreign substances is determined. A problem with this measuring principle is its strong sensitivity to moisture. In a preferred embodiment of the disclosed in EP-O "924'513 Al device is trying to eliminate caused by humidity interference signals by simultaneously with the actual measuring capacitor, a reference capacitor is used. This can be formed by adding a third, parallel to the two measuring capacitor plates arranged capacitor plate, wherein the three capacitor plates are connected together to form a capacitive bridge. However, this measure does not eliminate interference caused by moisture changes of the test material itself. Therefore, too many wrong responses occur with this measurement principle.

EP-O '301'395 A2 discloses a method and apparatus for detecting asperities on a moving, electrically insulating web. An electrically conductive, transverse to the direction of movement wire is disposed in the vicinity of the web. Electrical charges present on the track surface generate an electrical signal in the wire.

It is also known to monitor a moving thread by passing the thread to be monitored past a stationary electrode. The charges distributed unevenly in the yarn generate a voltage signal in the electrode. Such sensors show z. For example, DE-32'15'695 Al, DE-92'16'181 Ul or DE-195 '35 ^• 177 Al. The signals generated by such sensors. are unreliable and lead to many wrong answers. According to the CH-526'459 A5 becomes a triboelectric

(triboelectric) transducer used to make a

Thread monitoring device to create the two

Surveillance functions: Examination for the presence / absence of the stationary thread

(Presence monitor) and examination for longitudinal movement / standstill (run monitor).

EP-I '037' 047 Al takes up the triboelectric measuring principle. It describes a method and a device for detecting foreign materials in a moving textile material. At first, any existing charges are removed from the textile material by stripping electrodes. A sensor is provided for receiving triboelectric signals from the moving textile material. The output of the probe is compared with a reference value indicative of the textile material without extraneous materials. Based on the result of the comparison, it is determined whether foreign material is present. The removal of the already existing charges by stripping and the application of charges on the textile material causes additional effort and additional space. In addition, this measurement principle also provides too many false responses, mainly caused by electrostatic discharges. The incorrect responses occurring in the prior art are highly undesirable because they lead to unnecessary shutdowns of the production process. This results in production outages for the user. This can be particularly dramatic on spinning machines, where a shutdown takes about 10 minutes. The economic damage of many unnecessary shutdowns is enormous.

It is therefore an object of the present invention to provide a method and a device for the detection of Frexndstoffen in a moving, solid, elongated textile material, which do not have the above disadvantages. In particular, the method and the device should be simple or space-saving. In addition, a better selectivity should be achieved. The shortcomings of the prior art should be significantly reduced, with the same high or higher reliability and sensitivity in the detection of foreign matter.

These and other objects are achieved by the method and apparatus as defined in the independent claims. Advantageous embodiments are given in the dependent claims.

The invention simplifies the methods and devices known, in particular from EP-I '037' 047 A1, by dispensing with the discharge of already existing charges from the test material and the renewed controlled application of charges to the test material. Instead, it presupposes the presence of charges on the test material and uses these charges to obtain information about the test material or any foreign matter components from them. This departure from the measuring principle known hitherto represents a radical change in the detection of foreign substances. It leads to a simplification in the method and a saving of space in the device.

According to the invention, preferably both an electrostatic signal - by charge measurement - as well as another, z. B. capacitive or optical, received signal from the sample, and both signals are used to detect foreign substances. This results in an unexpected improvement in selectivity. It has proved to be particularly advantageous to continuously evaluate the electrostatic signal and to use it as a trigger for evaluating the further signal. The electrostatic signal then provides a coarse measurement, the further signal, if necessary, a fine measurement. Since the electrostatic signal is hardly affected by moisture, incorrect responses caused by humidity fluctuations are eliminated. The further signal refines the measurement and, if necessary, allows the consideration of influences and parameters that the electrostatic signal does not allow. can capture. So z. B. due to the additional signal in addition to impurity levels and the thickness of the test material can be determined. It is particularly advantageous and space-saving if the electrostatic signal and the further signal from one and the same sensor, for. B. a measuring capacitor can be recorded.

Accordingly, the invention includes the use of a sensor to receive an electrostatic signal to detect extraneous matter in a moving, solid, elongated sample. The sensor is capable of picking up an electrostatic signal from those surplus charges that were previously present on the test material. These excess charges can z. B. be applied by friction on machine parts such as balloon limiters, thread tensioner or guide eyelets on the test material.

In the inventive method for the detection of foreign substances in a moving, solid, elongated material to be tested, an electrostatic signal is taken from the test material and used for the detection of foreign substances. The electrostatic signal is thereby absorbed by such surplus charges that were previously present on the test material. In a preferred embodiment, an additional signal is additionally received by the test material, and both the electrostatic signal and the further signal are used for the detection of foreign substances. In another variant of the inventive method for the detection of foreign substances in a moving, solid, elongate test material, the test material is exposed to a high-frequency alternating electric field. Properties of the alternating electric field interacting with the test material are determined by picking up a high-frequency electrical signal and demodulating it with a carrier frequency of the alternating electric field. A second, quasi-static electrical signal originating from the test material is recorded. Both the first and second electrical signals are used for the detection of foreign matter.

The inventive apparatus for detecting foreign substances in a moving, solid, elongate material to be tested includes a sensor for receiving an electrostatic signal from the test material and evaluation means for evaluating the electrostatic signal and for detecting foreign substances. The sensor is suitable for receiving an electrostatic signal from such excess charges that were previously present on the test material. In a preferred embodiment, the inventive device further includes a sensor for receiving a further signal from the test material and evaluation means for evaluating the electrostatic signal and the further signal and for detecting foreign substances. In this document, an "electrostatic signal" is understood as meaning a signal which originates from charges resting on the test specimen, which charges can be tapped off by galvanic contact or detected without contact, for example by influence but their accelerations and velocities are relatively small, so that one can still speak of an electrostatic signal Both cases could alternatively be described by the term "passive charge shift" - in contrast to the active generation of a high-frequency alternating electric field, as described in EP -O '924' 513 Al is taught.

Hereinafter, a preferred embodiment of the invention will be explained in detail with reference to the accompanying drawings. Here are shown schematically:

Figure 1 is an electrical circuit diagram of an embodiment of the inventive device and

FIG. 2 shows a flowchart of an embodiment of the method according to the invention.

An electrical circuit diagram of a device 1 according to the invention is shown in FIG. The device 1 includes a measuring capacitor 2. This is a flat in this embodiment Two-plate capacitor having a first, substantially planar capacitor plate 21 and a second, substantially flat capacitor plate 22. The capacitor plates 21, 22 are each about 0.8 mm thick, consist for. B. made of brass and may, for achieving a higher abrasion resistance z. B. be coated with nickel. The two capacitor plates 21, 22 are separated by an approximately 1-3 mm, preferably about 1.5-2.0 mm thick air gap, which forms a passage opening 26 for a solid, elongated Prüfgut 9. The Prüfgut 9 can z. B. be a yarn. It is preferably moved through the passage opening 26 in the longitudinal direction x.

It is known that textile materials such as the yarn 9 and other materials can charge electrostatically. Such a charge can z. B. come through friction on machine parts such as balloon limiters, thread tensioner or guide eyelets. For example, polypropylene, an undesirable impurity that is an existing need of the textile industry to detect, charges negatively, i. H. in a layer on the surface of the polypropylene is formed

Excess of electrons. The measuring capacitor 2 is now suitable for the detection of such charges. The electric field of

Namely, excess charge causes a potential change on the capacitor plates 21, 22 as soon as the charges in the

Passage opening 26 arrive. This potential change can be effected by means of an output line 27, which, for example, with the second Capacitor plate 22 is connected to be recorded as an electrostatic signal from the yarn 9.

As an alternative to contactless signal recording, it is possible to record the electrostatic signal by means of a contact electrode (not shown) which is in galvanic contact with the yarn. This alternative can have the advantage of being more sensitive. Their disadvantages, however, are the inevitable abrasion of the electrode and yarn, which soils the device and wears the electrode, and the constant contact which is difficult to ensure at high yarn speeds. For this reason alone, the contactless signal recording appears to be more advantageous. Another reason for using the measuring capacitor 2 for recording the electrostatic signal is the usability of the same measuring capacitor 2 for receiving a further, capacitive signal, as will be explained below.

In a preferred embodiment of the present invention, another signal is received by the yarn 9. In the exemplary, non-limiting embodiment of FIG. 1, the further signal is a capacitive signal. The yarn 9 is exposed to a high-frequency alternating electric field in the measuring capacitor 2, and properties of the alternating electric field interacting with the yarn 9 are determined.

- li - In order to reduce interference caused by external influences such as air temperature or humidity, the embodiment of FIG. 1, in addition to the measuring capacitor 2, includes a reference capacitor 3 with two planar capacitor plates 22, 32. The middle capacitor plate 22 is common to both capacitors 2, 3.

Methods and devices for the capacitive detection and quantification of solid foreign substances in textile test material 9 are known from EP-O '924' 513 A1 and can also be adopted for the present invention. EP-O '924' 513 A1 and in particular paragraphs [0022] - [0034] thereof are incorporated by reference into the present specification. By this reference to EP-O '924' 513 Al here is a detailed description of the evaluation methods is unnecessary. For that, only so much is said here that at least two measurement modes are possible. In a first measurement mode is measured with two different excitation or carrier frequencies of the alternating electric field. The two similar output signals, z. B. measured voltages are first detected separately for each of the carrier frequencies and then combined together for evaluation in a suitable manner. In a second measurement mode is measured at a single carrier frequency, but used as output signals output voltage and output current. The phase shift between the voltage and the Current signal supplies the desired information about the yarn 9 after suitable evaluation. A combination of the two measuring modes, ie measurement at several carrier frequencies and measurement of the respective phase shifts between voltage and current signal, is also possible.

For the purpose of capacitive signal recording, the device 1 according to the invention comprises an AC voltage generator 4 for applying a high-frequency AC voltage to the measuring capacitor 2 and the reference capacitor 3. "High frequency" is understood here to mean a frequency between 100 kHz and 300 GHz according to the common usage in electrical engineering. Preferably, the frequency of the applied alternating voltage is between 1 MHz and 100 MHz, eg 10 MHz Thus it can be stated that there is a capacitive voltage divider with two capacitors 2, 3 which can be detuned by the test material 9. With the output line 27 of the capacitors 2, 3 is preferably connected to an impedance converter 5. The impedance converter 5 can be designed, for example, as a collector circuit or as a transimpedance amplifier circuit with an operational amplifier Kon capacitors 2, 3. In the embodiment of Figure 1, the detector circuit 6 essentially performs a multiplication of the output signal of Measuring capacitor 2 with the voltage applied to the capacitors 2, 3 AC signal to demodulate it. The demodulated capacitive measurement signal is fed to an evaluation circuit 7.

Unlike the high-frequency capacitive signal, the electrostatic signal is quasi-static. It can be detected with a bandwidth of, for example, 5 to 10 kHz. In order to extract the quasi-static signal from the high-frequency signal, for example, a peak value rectifier 8 is used, which is electrically connected to the output line 27 of the measuring capacitor 2 and preferably downstream of the impedance converter 5. The output signal of the peak value rectifier 8 is likewise supplied to the evaluation circuit 7.

The evaluation circuit 7 determines from the electrostatic signal and the capacitive signal, the actual result, namely the foreign matter components in the yarn 9, and outputs an output signal on a Ausgangs1eitung 79 of the device. It is possible to determine the quantitative proportion of foreign substances and possibly the material of the foreign substances, as well as other parameters such as the yarn thickness. The evaluation circuit 7 may be formed as an analog electrical circuit or as a digital processor. It can be part of a user-specific integrated circuit (ASIC), on which also other elements like the Impedance converter 5, the detector circuit 6 and / or the peak value rectifier 8 can be integrated. The evaluation circuit 7 may include a first module 71 for the evaluation of the electrostatic signal and a second module 72 for the evaluation of the further signal.

FIG. 2 shows schematically a flow chart of a preferred embodiment of the method according to the invention. Accordingly, an electrostatic signal from the test material 9 is received 101, namely of such excess charges, which were previously already present on the test material. Another signal is taken from the test object, 102. The further signal can be a capacitive signal. The recording 101 of the electrostatic signal can take place by means of the device 1 shown in FIG. 1 and in particular by the measuring capacitor 2, the impedance converter 5 and the peak value rectifier 8. The recording 102 of the further signal can be effected by means of the device 1 shown in FIG. 1 and in particular by the measuring capacitor 2, the impedance converter 5 and the detector circuit 6.

The electrostatic signal is continuously evaluated 103, for example in the first module 71 of the evaluation circuit 7 (see FIG. 1). The result of the evaluation 103 is constantly checked for a particular event 104. What is classified as a "special event" depends on the particular application, there may be a deviation from a target value, an override. or falling below a limit value, a sudden signal change, a signal change whose derivative exceeds or falls below a predetermined value, or be another characteristic of the evaluation result.

The determination 104 of a particular event triggers the evaluation 105 of the further signal, for example in the second module 72 of the evaluation circuit 7 (see FIG. 1). The result of this evaluation 105 is now also checked for a particular event 106, which may be defined according to the same or different criteria as the particular event 104 in the electrostatic signal. If no special event is detected 106, this indicates a false indication of the electrostatic signal, z. B. due to electrostatic discharges, and the Signalaufnähme 101, 102 is continued. If, on the other hand, the evaluation 105 of the further signal also indicates a special event 106, there is a high probability of contamination by foreign substances in the relevant yarn section. In this case, the evaluation unit 7 outputs a foreign substance signal on the output line 79 from 107. The foreign substance signal can be a simple signal that triggers a yarn cut in the sense of a binary yes / no decision, activates a counting step, triggers an alarm or leads to a shutdown of the machine. However, it may also contain information about the type and / or amount of the detected foreign substances, or impurity components. Such impurities can be determined by the evaluation unit 7 on the basis of the evaluations of both signals. Of course, during and / or after the output step 107, the signal recording 101, 102 are continued, which is not shown in FIG. 2 for the sake of simplicity.

Of course, the invention is not limited to the embodiments described above. So it is z. B. not necessary to use measuring capacitors 2 with flat capacitor plates for the measurement of the other signal; other capacitor forms are also possible. The further signal can be electrical, optical or other type. The order of the process steps does not necessarily correspond to that of FIG. 2; the recording 102 of the further signal could, for. B. only after the detection 104 of a particular event in the electrostatic signal. It is also possible first to check the further signal 106 and only then the electrostatic signal 104 for a special event. The signal recordings 101, 102, the signal evaluations 103, 105 and / or the checks 104, 106 can also take place simultaneously. List of reference numbers:

1 device

J

2 measuring capacitor

21 first capacitor plate

22 second capacitor plate

26 _. Passage opening 0 27 Output line

3 reference capacitor

32 capacitor plate

5 4 AC generator

5 impedance converter

6 detector circuit 0

7 evaluation circuit

71, 72 first and second module of

evaluation

79 output line of the device 5

8 peak rectifier

Claims

claims

1. A method for detecting foreign substances in a moving, solid, elongated test material (9), wherein an electrostatic signal from the test material (9) recorded (101) and used for the detection of foreign substances, characterized in that the electrostatic signal of such Surplus charges are recorded, which were previously present on the test material (9).

2. The method of claim 1, wherein a further signal from the test material (9) is received (102) and both the electrostatic signal and the further signal for the detection of foreign substances are used.

3. The method of claim 2, wherein the electrostatic signal is continuously evaluated (103) and results of its evaluation (103) are used (104) to trigger an evaluation (105) of the further signal.

4. The method according to any one of the preceding claims, wherein the further signal is a capacitive signal.

5. The method of claim 4, wherein in the recording (102) of the capacitive signal Prüfgut (9) a High-frequency alternating electric field is exposed and properties of the test material (9) interacting alternating electric field are determined, and in the evaluation (105) of the capacitive signal, these determined properties are used.

6. The method of claim 5, wherein a carrier frequency of the alternating electric field between 1 MHz and 100 MHz, preferably about 10 MHz.

7. The method according to claim 5 or 6, wherein as the properties of the test material (9) interacting alternating electrical field two electrical quantities are determined and combined with each other, that a characteristic value arises which is independent of the mass of the test material (9).

8. The method according to claim 7, wherein the two determined electrical quantities are two voltage signals demodulated with two different carrier frequencies and / or one with a carrier frequency demodulated voltage and one with the same carrier frequency demodulated current signal.

9. The method according to any one of claims 4-8, wherein one and the same sensor, preferably a measuring capacitor (2), is used for the recording of the electrostatic signal (101) and the capacitive signal (102).

10. A method for detecting foreign substances in a moving, solid, elongate test material (9), wherein the test material (9) a high-frequency electrical

Alternating field is exposed and

Characteristics of the test material (9) interacting alternating electric field can be determined by a high-frequency electrical signal is recorded

(102), characterized in that a second quasi-static electrical signal originating from the test material (9) is picked up (101) and both the first and the second electrical signal are used for the detection of foreign substances.

11. The method of claim 10, wherein the second electrical signal is received by such excess charges, which were previously already on ^' the test material (9) were present.

12. The method of claim 10 or 11, wherein the quasi-static signal is evaluated continuously (103) and

Results of his evaluation are used (104) to to trigger an evaluation (105) of the high-frequency signal.

13. The method according to any one of claims 10-12, wherein a carrier frequency of the alternating electric field between

1 MHz and 100 MHz, preferably about 10 MHz.

14. The method according to any one of claims 10-13, wherein as the properties of the test material (9) interacting electrical alternating field two electrical quantities are determined and combined with each other such that a characteristic value arises which is independent of the mass of the test material (9) ,

15. The method according to claim 14, wherein the two determined electrical quantities are two voltage signals demodulated with two different carrier frequencies and / or one with a carrier frequency demodulated voltage and one with the same carrier frequency demodulated current signal.

16. The method according to any one of claims 10-15, wherein one and the same sensor, preferably a measuring capacitor (2), for the reception of the first (102) and the second (101) ^■ electrical signal is used.

17. Device (1) for detecting foreign substances in a moving, solid, elongated test material (9), comprising a sensor (2) for receiving an electrostatic signal from the test material (9) and evaluation means (7) for evaluating the electrostatic signal and Detection of foreign matter, characterized in that the sensor (2) is adapted to receive an electrostatic signal from such excess charges, which were previously already present on the test material (9).

18. The apparatus of claim 17, wherein a further sensor

(2) for receiving a further signal from the test material (9) is present.

19. Device (1) according to claim 18, wherein the sensor (2) for receiving the further signal is a capacitive sensor.

20. Device (1) according to claim 18, wherein the capacitive sensor comprises a measuring capacitor (2) with a passage opening (26) for the test material (9) and the device (1) comprises means (4) for applying a high-frequency alternating voltage to the measuring capacitor (4) for the purpose of acting on the passage opening (26) having a high-frequency alternating electric field.

21. Device (1) according to claim 19 or 20, wherein the sensor (2) for receiving an electrostatic signal and the capacitive sensor (2) in one and the same sensor

(2) are realized.

22. Use of a sensor (2) for receiving an electrostatic signal for the detection of foreign substances in a moving, solid, elongated test material (9), characterized in that the sensor (2) is adapted to receive an electrostatic signal from such excess charges, the previously already present on the test material (9).