EP1188043A1

EP1188043A1 - Method and device for detecting foreign matter in a fibre composite moving in the longitudinal direction

Info

Publication number: EP1188043A1
Application number: EP00925016A
Authority: EP
Inventors: Peter Pirani; Hans Wampfler
Original assignee: Zellweger Luwa AG; Uster Technologies AG
Current assignee: Uster Technologies AG
Priority date: 1999-05-29
Filing date: 2000-05-22
Publication date: 2002-03-20
Also published as: JP2003501623A; CN100387974C; US6771365B1; WO2000073771A1; CN1353811A

Abstract

The invention relates to a method and a device for detecting foreign matter in a fibre composite moving in the longitudinal direction and consisting substantially of wool or cotton fibres. To provide an improved, easier and rapid method of detecting polypropylene in fibres intended for textile products the fibre composite is irradiated with infrared light (2, 3) in a defined wavelength range, the reflected light filtered (13) and the filtered fraction of the light measured (11). Values which significantly deviate from a base value indicate the presence of foreign matter.

Description

METHOD AND DEVICE FOR DETECTING FOREIGN MATERIALS IN A LONG-TERM MOVING FIBER COMPOSITE

The invention relates to a method and a device for detecting foreign substances in a longitudinally moving fiber composite.

Such a method and such a device is known from CH 674 379. A textile fiber material, for example a yarn, is illuminated with multicolored or white light and an image of the yarn is generated on two sensors, each of which is only sensitive to one color. The output signals from the sensors are fed to an electronic differential circuit. Color changes caused by foreign fibers in the yarn lead to a spontaneous change in the output signal from the differential circuit if the color differs from the raw cotton.

Another method and another device are known from EP 0 652 432. Here, a longitudinally moving textile structure is also illuminated by a polychromatic light source and the reflected light is detected simultaneously on at least two wavelengths. Wavelengths in the near infrared range are also to be recorded in order to detect foreign material whose color matches the base color of the yarn to be checked.

A disadvantage of these known methods and devices can be seen in the fact that in the spectral range of visible light, no reliable differentiation from foreign substances such as polypropylene is possible. However, since polypropylene is very common as a packaging material for cotton bales, and the removal of the wrappings for the bales does not always take the necessary care, one must expect that parts of the wrappings made of polypropylene mix with the cotton and occur at any time in the cotton processing process and can affect the product. Processes based on the strong absorption of the CH bond of the plastics are known from the plastics industry. The obvious approach to detect polypropylene in cotton by detecting polypropylene in cotton by absorbing the radiation at 3.43 micrometers is not very revealing, since polypropylene and cotton both appear as dark areas. The correct detection of polypropylene is difficult in these circumstances and can lead to incorrect conclusions about the presence of it. The invention, as characterized in the patent claims, now solves the problem of creating a method and an apparatus which avoid these disadvantages and an improved, simplified and rapid recognition of polypropylene in fibers which are combined as yarn, fleece or flakes , for textile products.

This is achieved by the fact that the different degrees of reflection from fibers made of cotton, wool etc. and from foreign substances such as Polypropylene is used specifically. We rely on the reflection of rays from the actual base materials that make up the fiber composite on the one hand and the foreign substances on the other. This is in contrast to known methods which carry out a recognition based on properties of additives, such as colors. Colors absorb and reflect in different wavelength ranges than the basic materials, such as cellulose or chemical fibers, e.g. Nylon as the basic material for the fibers of the fiber composite. The invention takes advantage of the fact that the reflection of infrared radiation by the fibers and by the foreign substances differs more in certain wavelength ranges than in other wavelength ranges. However, depending on the approach, this succeeds with good or bad success. According to the present invention, it is proposed to bring two different points of view into harmony, so that the desired success is achieved. Firstly, radiation with at least one wavelength should be used, in which the reflection on the base materials of the fibers and on that of the foreign substances gives as different values as possible in order to enable good selection. Secondly, at least one wavelength of the radiation used should advantageously be chosen so that the fibers, which are to be considered here as the basic material, as a carrier or as a kind of background for the foreign substances, reflect as little or no radiation as possible. This then allows the base material to be shown against such a background that does not reflect such radiation. With this procedure, a method is obtained in which the test material is exposed to radiation of a certain wavelength and only the foreign substance, in particular the polypropylene, appears as a light spot. It is no longer possible to differentiate between the background and the test specimen. This means that the radiation is adapted to its base material in such a way that it absorbs it and that polypropylene at least partially reflects the radiation, the background for the sensor appearing dark, like the base body of the fiber composite. This can be achieved, for example, by the background absorbing, reflecting or scattering the radiation in an absorber. An optical element, e.g. a dielectric filter can be used, the reflection of which has been adjusted.

In short, the fiber composite is to be exposed to infrared radiation and the reflected radiation is to be measured from a limited wavelength range, values which differ significantly from a basic value indicating a foreign substance. The restricted wavelength range can be generated by filtering the radiation or directly by a suitable radiation source. The limited wavelength should be adapted to an absorption band of the base material, for example in the case of natural fibers, cellulose. An absorption band around a wavelength of approximately 2.95 micrometers is particularly favorable because cellulose absorbs in this area. In this area, cellulose appears "black" and it is easy to adapt the background, which is necessary for the measurement to be independent of the diameter of the fiber composite. Two wavelengths can also be selected, which are adapted to the basic material of the fibers and the foreign substance, that the foreign substance makes itself felt differently at both wavelengths.

The device according to the invention therefore has a suitable radiation source, a means for restricting the wavelength range and a detector. Such an agent is, for example, a filter that eliminates those portions of the radiation that have an undesired wavelength. An imaging system may or may not be present. A circuit for evaluating the signal that is output by the detector is connected to it.

In a special embodiment, the method according to the invention can also be designed in such a way that the reflected light is divided into at least two beams and filtered, the filtered portion is measured for each beam and the measured values are related to one another or calculated to indicate foreign matter.

The advantages achieved by the invention can be seen, in particular, in the fact that it produces a signal which can be clearly interpreted and which indicates with certainty whether such foreign substances are present or not. The invention also allows the method to be used at different wavelengths and thus to generate two signals which indicate a foreign substance if both signals result in the same deflection or suggest the same conclusion. The measurement at two wavelengths also makes it possible to recognize a foreign substance without adapting the background to the test material. If an adjustment is possible at both wavelengths, this can be an advantage. For example, a high difference in the amount of reflected radiation in the range of a single wavelength and a lesser or an opposite difference in the range of other wavelengths can be offset and used in such a way that a clear statement is also possible. Another advantage is the fact that the device can be put together from components known per se and commercially available. Since the color or an additive to the base material is not to be recorded here, there is no false error message in the case of vegetable foreign matter or contamination if the base material to be reacted to the radiation is the same in the case of vegetables and natural fibers. With this method and the corresponding device, the Foreign substances can be detected on various types of fiber composites, namely on yarns in particular on tapes, fleeces, flakes etc.

The invention is explained in more detail below using an example and with reference to the accompanying figures. Show it:

FIG. 1 shows a schematic illustration of a first embodiment of the device according to the invention,

Figure 2 is a schematic representation of a second embodiment of the device according to the invention.

FIG. 3 shows the reflection behavior of fibers and foreign substances,

FIG. 4 shows a schematic illustration of the characteristic of a filter used in the device,

5 shows a profile of an output signal and

Figure 6 shows a further embodiment of a device according to the invention.

Fig. 1 shows a fiber composite 1, here formed as a yarn, and two radiation sources 2, 3, which act on the fiber composite against a background 4, but do not shine directly behind the fiber composite 1. Limiting elements 5, 6 together form a pinhole 7, which allows radiation 14 reflected on the fiber composite to enter an imaging system 8. This consists of two lenses 9, 10, which direct and focus the beams 14 onto a sensor 11. The lenses 9, 10 generate parallel rays 15 in an intermediate space 12, so that a filter 13 can be arranged there, which works with the parallel rays 15. The rays passed on by the filter 13 strike the sensor 11, which can emit a signal via a line 16 which depends on the intensity of the incident rays and is, for example, proportional to this intensity. An evaluation unit 17, which has an output 18, can be connected to the sensor 11 via the line 16. However, it is also possible to arrange a sensor 11 'with an integrated filter, for example directly behind the pinhole 7, and to provide no imaging system. Or you can also design a sensor 11, 11 'without an integrating filter and arrange the filter directly after the radiation source. However, a narrow-band radiation source, for example an LED, can also be used. FIG. 2 again shows the elements which are already known from FIG. 1 and which are therefore provided with the same reference numerals. However, a beam splitter 19 is inserted between the sensor 11 and the lens 9 here. This also deflects the received beams onto a sensor 21, so that an additional beam path 20 is also generated. A filter 28, 29 is placed in front of both sensors 11 and 21. The sensor 21 is also connected to the evaluation unit 17 via a line 22. The background 4 can also be designed as an absorber or have an absorber 4.

3 shows the reflection coefficient of fiber material as a function of the wavelength of the radiation which acts on it. Therefore, values for wavelengths are plotted along the horizontal axis 23 and values for the reflection coefficient are plotted along the vertical axis 24. 25 shows curves for the reflection coefficient of cotton, 26 of polypropylene and 27 of wool.

FIG. 4 shows a filter characteristic 30 as it is advantageous for the design of the filters 13, 28 and 29. The width of this curve and thus the spectral reflection behavior of the filter must be adapted to the spectral reflection characteristics of the yarn so that on the one hand as much signal as possible gets through and on the other hand only those wavelengths are transmitted whose reflectance is suitable. An optimization can be carried out mathematically after measuring the reflection as a function of the wavelength. Thus, values for wavelengths are provided along a horizontal axis and 35 values for the transmission of the radiation are provided along a vertical axis.

5 shows an example of values that can occur at the output 18 of the evaluation unit 17 or in lines 16, 22 at the output of a sensor. Values for the radiation intensity measured in the sensor, the radiation reflected on the fiber composite, are plotted here over a time axis. In an area 37 which corresponds to the pure fiber material, there is hardly any reflection of radiation, but in an area 38 there is so, so that the signal rises here and indicates a foreign substance which responds to the radiation.

FIG. 6 shows an example of an embodiment with which foreign substances can be recognized in a stream of fiber flakes. For this purpose there is a channel 46 in which flakes 47 are moved in a flow. In addition to a window 48 in the channel 46, radiation sources 49, 50 are arranged which irradiate the flakes 47 through the window 48. The radiation 51 reflected on the flakes 47 is fed to an imaging system 52 and from there also to a detector 53. As radiation sources 49, 50, for example, those for infrared radiation are indicated, which means that the window 48 should be transparent to infrared radiation. The mode of operation of the invention is as follows:

The fiber composite 1 is moved in the device according to FIG. 1 perpendicular to the image plane in its longitudinal direction. He can also move to a small extent in a direction that lies in the image plane. It is illuminated from one side by the radiation sources 2, 3, the radiation falling onto the fiber composite 1. Reflected radiation is laterally limited by the pinhole 7 and directed onto the lenses 10, 9, which also traverses the filter 13. In this filter 13 those portions of the radiation which have undesired frequencies are filtered out and only frequency portions corresponding to the characteristic according to FIG. 4 pass through and reach the sensor 11 in bundles. The sensor 11 only gives a signal in the line 16 if Radiation has passed through the filter 13, which is only the case when radiation is reflected from the fiber composite. If the main axis 33 of the filter 13 is set to approximately 2.95 micrometers, then, according to the curve 25 in FIG. 3, there is an area 39 in which the fiber composite, like the cotton here, absorbs practically all radiation and thus does not emit any radiation. which gives a basic value. In this case, a measured value output by sensor 11 is at least approximately zero. If the background 4 is designed in such a way that it is adapted to the test material, it practically does not emit any signal during the measurement and the cotton or the pure fiber composite cannot be distinguished from the background 4. This can be achieved, for example, by the background 4 being black, i.e. Radiation absorbs or scatters or also consists of cotton or the same fiber material. At point 39 of curve 25 in FIG. 3, it can also be seen that curve 26 deviates significantly from zero and that the foreign material, such as polypropylene, reflects radiation. It is this radiation that can pass through the bandpass filter 13 and is detected in the sensor 11. This case is represented in FIG. 5 by regions 37, 38 of a curve. As the curves 25 and 26 in FIG. 3 show, there is a positive difference between the reflection coefficients of the foreign matter and the fibers in the fiber composite 1, which is just expressed in the areas 38 in FIG. 5.

2, the reflected radiation is filtered in two different filters 28, 29 and recorded in sensors 11, 21, which happens simultaneously and thus affects the same location on the fiber composite. With this device, for example, the filter 28 could have its main axis aligned to a wavelength of approximately 2.3 micrometers and the filter 29 its main axis to approximately 1.5 micrometers. Thus, according to FIG. 3, one now works at points 40 and 41. At both points 40 and 41, significant differences can be seen between the reflection coefficients of the fiber composite and the foreign substance. However, the fibers 1 also reflect radiation that impinges on the sensors 11 and 21. There may also be cases in which, depending on the wavelength range, the fiber composite 1 reflects more than the foreign substance. The evaluation unit 17 continuously calculates the signals recorded in the sensors 11 and 21 Values of radiation, to a final value. As long as only fiber material and no foreign matter is present, this calculation, as shown in FIG. 5, results, for example, in the difference between the values which were measured at points 40 and 41 according to the two curves 26, 26 ". This may already be the case give an output signal according to a curve 42, the section 43 of which gives a basic value, if the background is not completely adapted to the basic material at one or both wavelengths, the signal is also influenced by changes in density, changes in diameter or changes in position of the fiber composite 1. By offsetting the two Signals from sensors 11 and 21 can be used to distinguish the effects of changes in density, changes in diameter or changes in position of fiber composite 1 from a real foreign matter signal, for example at wavelengths such as 2.95 and 2.35, 1.5 and 1 , 7, 1.5 and 1, 2 microns or other combinations of these values to practice.

When using two wavelengths at which the sensor sends a reflection signal from the test material, e.g. who receives cotton or wool and thus recognizes them, either an adaptation of the reflective properties of the background to those of cotton or wool can be made at both wavelengths. Then you get two signals, which are independent of the diameter and each indicate polypropylene. The evaluation of both signals gives more security. If, on the other hand, there is no optimal adaptation to the background at both wavelengths, then the diameter can theoretically be compensated exactly by evaluating the signals. However, it is sufficient that the "reversal of contrast" (one cotton is lighter than polypropylene, the other way round) signals in the presence of polypropylene to go in different directions, while they go in the same direction when the thickness of the yarn fluctuates. The diameter is therefore not complete and exactly compensated, but essentially the sign of the signals is used to distinguish fluctuations in diameter and foreign matter.

These methods are based on the principle that the fiber composite should be detected in wavelength ranges in which the fiber composite or the foreign substance should absorb as much as possible, while the foreign substance or the fiber composite should absorb as little radiation as possible. In one case, the fiber composite gives only a weak signal, but the foreign matter gives a comparatively strong signal or vice versa. The advantage of this is that it is not important how much the fiber composite stands out from the background and is therefore also not a nuisance if the fiber composite changes its density or thickness.

For example, so-called micro incandescent lamps with a lead glass cover can be used as the radiation source. This guarantees that the emitted radiation contains enough infrared. For example, photoconductive lead salt detectors can be used as sensors. However, they have a 1 / f noise, also called flicker noise, flicker noise or sparkling noise. Its strength is inversely proportional to the frequency. Therefore low-frequency signals have to be filtered out. Another embodiment could consist of a commercially available infrared camera, for example a line array or an FPA (Focal Plane Array) with a bandpass filter in front, preferably set to 2.95 micrometers.

Claims

Claims:

1. A method for detecting foreign substances in a longitudinally moving fiber composite (1), characterized in that the fiber composite (1) is subjected to infrared radiation and the reflected radiation (14) is measured from a limited wavelength range, with a basic value (43) being essential deviating values indicate a foreign substance.

2. The method according to claim 1, characterized in that for the limitation of the wavelength range by filtering, a wavelength band is generated, which is adapted to the absorption bands of the base material of the fiber composite.

3. The method according to claim 1, characterized in that the reflected radiation is divided into at least two beams (14, 20) and filtered, the filtered portion is measured for each beam and the measured values are related to each other to indicate foreign matter.

4. The method according to claim 1, characterized in that for each beam portions that significantly exceed and fall below a certain wavelength are filtered out.

5. A device for performing the method according to claim 1, characterized by a radiation source (2, 3), a means for restricting the wavelength range (13) and a sensor (11).

6. The device according to claim 5, characterized by an imaging system (8) which images an area around the fiber composite to be measured on the sensor (11).

7. The device according to claim 5 or 6, characterized in that a beam splitter (19), at least one further bandpass filter (29) and a further sensor (21) is provided, which is connected to an evaluation unit (18).

8. The device according to claim 5 or 6, characterized in that a background (4) is provided for the fiber composite, which absorbs the emitted radiation to approximately the same extent as the fiber composite freed from foreign substances.

9. The device according to claim 5 or 6, characterized in that an optical element with adapted reflection at both wavelengths is used as the background (4).

10. The device according to claim 3, characterized in that the one beam is examined for wavelengths that are examined for the base material of the fiber composite and the other beam for wavelengths that are adapted to the base material of the foreign substance.

11. The device according to claim 1, characterized in that a filtering of the reflected radiation is carried out in a wavelength range.

12. The device according to claim 1, characterized in that radiation from a limited wavelength range is directed onto the fiber composite (1).