DETERMINATION OF THE MIXING RATIO OF TWO COMPONENTS OF A TEXTILE FIBER STRUCTURE

Description

SPECIALIZATION

[0001] The present invention lies in the field of quality control in the textile industry. It relates to a method for determining the mixing ratio of two components of a textile fiber structure according to the first claim. A preferred application is the detection of foreign materials in a textile fiber structure such as fiber flakes, fiber fleece, fiber tape, roving, yarn, woven fabric, knitted fabric, or nonwoven fabric. STATE OF THE ART

[0002] Foreign materials in yarn represent one of the major problems in modern spinning mills. These are materials that differ from the base material of the yarn fibers, such as cotton fibers. They can be of various origins, such as residues from transport packaging (plastic packaging, twine), contaminants from human activity (soot particles, plastic bags), or residues from living organisms (human or animal hair, plant stems). Foreign materials lead to thread breakage during spinning and weaving, absorb dye differently than the base material, and affect the appearance of the finished textile product. They significantly reduce the value of the final product. An overview of fabric defects caused by foreign materials and recommendations for their reduction are given in section 3.8 of the USTER® standard. NEWS BULLETIN NO. 47 "The origins of fabric defects - and ways to reduce them", Uster Technologies AG, March 2010.

[0003] Foreign materials can be detected and, if necessary, removed at various stages of the yarn manufacturing process.

[0004] The cleaning process is part of the yarn manufacturing process and precedes the carding process. Its aim is to prepare the raw material so that it can be fed into the carding process in the most consistent quality possible and free of impurities. It includes opening the raw material, feeding it into the processing system, and mixing and coarse cleaning of the incoming material. Depending on the process design, individual steps may be repeated several times or omitted altogether. At this stage, the material is in the form of fiber flakes (for example, in the case of cotton and wool) or shreds (in the case of synthetic fibers). The material is transported by an airflow that connects the various components of the cleaning process.

[0005] The spinning process is another part of the yarn manufacturing process and follows the carding process, either directly or indirectly. In this process, yarn is spun from a fiber ribbon, such as the intermediate product of a carding machine, or from roving. The roving or fiber ribbon is transformed into its final form, yarn, through stretching and twisting. During spinning, the yarn is wound onto spindles. The spindles are then rewound onto large spools. The material is transported in the form of spindles and spools.

[0006] The removal of foreign materials can generally be divided into the following three steps: 1) Detection of the foreign material; 2) spatial / temporal localization of the foreign material within the test specimen; and 3) elimination of the foreign material.

[0007] In the cleaning process, foreign material removal can be carried out manually before the raw material is fed into the automated processing process, or the cleaning can be done mechanically by a suitable system within the cleaning process. Nowadays, mechanical cleaning is the norm.

[0008] In automated cleaning, detection and localization are achieved using detection devices that recognize differences in a specific characteristic within the material stream. These include, but are not limited to, reflection and transmission of electromagnetic radiation or fluorescence. In the simplest applications, optical detection devices mimic the human eye and analyze the perceived color of the material stream, thereby recognizing corresponding color differences. US Patent 6,452,157 B1 discloses a device for detecting impurities, foreign materials, and fibers in textile fiber material. The device has at least two light sources that alternately illuminate the fiber material with different colors. It also includes a sensor that receives the colors of the light reflected by the fiber material.

[0009] However, more sophisticated detection devices are needed to detect foreign materials that are transparent to visible light or have a similar color to the raw material. In this case, the material flow can be analyzed using electromagnetic radiation that is invisible to the human eye (ultraviolet or infrared). The material composition is determined based on characteristic signatures (for example, a sequence of specific absorption bands) in the reflected or transmitted spectrum of the electromagnetic radiation. The more characteristics (for example, absorption bands) within the signature are used for differentiation, the more precise the differentiation of the characteristic signatures becomes.Currently, each characteristic within the signature requires a dedicated sensor within the detection device, meaning it responds only to the presence or absence of that specific characteristic. The more characteristics are required, the more complex the detection device becomes. The input signal must be split across the corresponding number of sensors, resulting in a loss of intensity. Furthermore, for certain characteristics, there are currently only sensors with temporal resolution, not spatial resolution. This necessitates a device upstream of the detection system that links time and location. Alternatively, the incoming electromagnetic radiation can be temporally modulated and adapted to the characteristics. However, this is sometimes very complex and costly for the non-visible portion of the electromagnetic spectrum.

[0010] When differentiating materials based on color differences, as is common in the spinning process, the aforementioned characteristics lie in the visible spectral range. Since the perceived color is also due to the specific reflection / transmission of certain components of the incident wavelength spectrum, each characteristic must be detected individually. This can be achieved either by temporally modulating the input signal with color, or, as already explained, by decomposing the output signal, which is modified by the yarn, into its individual characteristics. In the former case, the spatial resolution deteriorates, and in the latter, the signal-to-noise ratio. The more colors are used, the more pronounced these disadvantages become. Therefore, methods using only one or at most two colors have become established in practice.A yarn cleaner that scans the yarn with several different colored light components is known from WO-2011 / 026249 A1.

[0011] Multivariate optical filters are a special category of optical transmission or reflection filters. The filter properties of multivariate optical filters are tailored to a specific chemical signature. Different characteristics of the signature can be used simultaneously and independently within a single filter. Multivariate optical elements thus allow material identification based on the chemical signature. If the filter's input signal exactly matches the tuned signature, the signal passes through the multivariate optical filter unimpeded. If the input signal deviates from the signature, it is attenuated as it passes through the filter. The greater the deviation, the greater the attenuation. In addition to material differentiation, multivariate optical filters also enable the determination of a mixture ratio based on the chemical signature altered by the mixture.The specific transmission or reflection behavior of multivariate optical filters is obtained from the chemical signatures of the materials to be distinguished using the partial least squares method.

[0012] US Patent 2017 / 0241839 A1 discloses an optical computing device for analyzing a sample. The optical computing device includes a light source for illuminating the sample, several identical integrated computing elements in the form of dielectric interference filters, and a detector. The light emitted by the light source interacts with the sample and the integrated computing elements and is received by the detector. The detection sensitivity of optical computing devices can be improved by combining several integrated computing elements.

[0013] The article “Spectral imaging of chemical compounds using multivariate optically enhanced filters integrated with InGaAs VGA cameras” by RJ Priore and N. Jacksen, Proceedings of SPIE, Vol. 9824, pp. 98240P-1 to 98240P-10, May 12, 2016, presents algorithms and multivariate optical filters for the identification of chemical compounds using high-performance InGaAs VGA detectors.

[0014] From WO-2019 / 051620 A1, a measuring instrument and a corresponding method for determining a fiber blend composition and / or a fiber blend ratio in an input material are known. Electromagnetic radiation sources direct radiation onto the input material at first and second points, and radiation sensors are configured to receive the transmitted or reflected radiation. A control unit processes the sensor signals to determine the fiber blend composition and / or the fiber blend ratio in the input material. PRESENTATION OF THE INVENTION

[0015] The object of the present invention is to provide a method for determining the mixing ratio of two components of a textile fiber structure, which avoids the aforementioned disadvantages. The method should enable high spatial resolution and the use of imaging, spatially resolving radiation sensors. Simultaneously, the signal-to-noise ratio should be high.

[0016] These and other problems are solved by the inventive method as defined in the first claim. Advantageous embodiments are specified in the dependent claims.

[0017] The invention is based on the idea of ​​designing a spectral filter specifically with respect to the components of the textile fiber structure, such that the radiation intensity received by the radiation sensor is a monotonic function of the mixing ratio of the two components. Furthermore, the transmittance or reflectance in the considered spectral band should exhibit at least one local maximum and at least one local minimum, so that several characteristic wavelengths are taken into account. The invention also includes the fact that the aforementioned spectral filter can be designed for the ratio of different characteristics, e.g., color impressions, and thus also makes color differences between similar materials detectable without signal loss.

[0018] The spectral filter is designed based on the specific chemical and / or color signatures of the two components. For example, certain characteristics can be enhanced by high transmission, while others are attenuated by low transmission. The combination of enhancement and attenuation in the spectral filter allows the determination of the mixing ratio of the two components based on the signal exiting the spectral filter. For example, materials and / or colors for which the spectral filter is optimized would produce a high output signal, whereas non-optimized materials and / or colors would result in a low output signal.

[0019] The inventive method serves to determine the mixing ratio of two components of a textile fiber structure. Electromagnetic radiation in a spectral band is emitted from a radiation source towards the textile fiber structure. At least a portion of the electromagnetic radiation interacts with the textile fiber structure. At least a portion of the electromagnetic radiation is received by a radiation sensor after the interaction with the textile fiber structure. At least a portion of the electromagnetic radiation is filtered by a spectral filter with spectral properties in the spectral band before or after the interaction with the textile fiber structure.The spectral filter is selected such that its transmittance or its reflectance in the spectral band has at least one local maximum and at least one local minimum, and its spectral properties in the spectral band are matched to the spectral properties of the radiation source and each of the two components in the textile fiber structure in such a way that a radiation intensity received by the radiation sensor is a monotonic function of the mixing ratio of the two components.

[0020] In one embodiment, one of the two components is a base material from which a predominant part of the textile fiber structure consists, and the other of the two components is a foreign material whose proportion in the textile fiber structure is determined.

[0021] In this method, the spectral band can be located, for example, in the wavelength range between 300 nm and 2200 nm, and preferably in the wavelength range between 700 nm and 1900 nm.

[0022] In this process, the spectral band can, for example, have a width between 200 nm and 500 nm.

[0023] The radiation source can consist of a single radiation element, e.g., a halogen lamp. Alternatively, it can consist of several radiation elements, e.g., a halogen lamp and a mercury vapor lamp.

[0024] In one embodiment, the at least one local maximum is located at the wavelength(s) of the electromagnetic radiation at which the absolute value of the difference in the absorption coefficients, transmittance coefficients or reflectance coefficients of the two components exhibits a local maximum.

[0025] In one embodiment, the transmittance or reflectance of the spectral filter in the spectral band has at least two local maxima and local minima.

[0026] The spectral filter can be designed as a reflection filter or as a transmission filter.

[0027] In one embodiment, the spectral filter is designed as an interference filter.

[0028] In one embodiment, the spectral filter is integrated into the radiation sensor.

[0029] In one embodiment, the radiation sensor is spatially and / or temporally resolved. It can be designed, for example, either as a digital camera with a two-dimensional image sensor or as a one-dimensional line sensor.

[0030] The terms "local maximum," "local minimum," and "monotonic function" used in this document are employed in accordance with their respective mathematical meanings. They are familiar to those skilled in the art, and their definitions can be found in mathematical textbooks or reference works.

[0031] The inventive method allows for a simple yet reliable determination of the mixing ratio of two components of a textile fiber structure. It avoids splitting the incoming electromagnetic radiation, reflected or transmitted by the textile fiber structure, across multiple radiation sensors. The invention does not require temporal modulation of the input signal, thereby achieving high spatial resolution. LIST OF DRAWINGS

[0032] An embodiment of the invention is explained in detail below with reference to the drawings. For clarity, an application is described in which the proportion of a foreign material in a base material of a textile fiber structure is determined. However, this is not intended to limit the generality of the invention, which relates to the determination of a mixing ratio of two components of a textile fiber structure. Figure 1 schematically shows an embodiment of a device for carrying out the method according to the invention. Figure 2 shows various spectra in a common spectral band, namely: (a) relative intensity distribution of a halogen lamp; (b) absorptivity of cotton; (c) absorptivity of polyethylene; and (d) transmittance of a spectral filter. IMPLEMENTATION OF THE INVENTION

[0033] An embodiment of a device 1 for carrying out the method according to the invention is shown schematically in Figure 1 It is shown. It includes at least one broadband radiation source 2 for generating electromagnetic radiation 3. The generated electromagnetic radiation 3 has a spectral intensity distribution 30 characteristic of the radiation source 2. Figure 1 The intensity distribution 30 is shown as a schematic diagram in which the intensity is plotted as a function of the wavelength.

[0034] At least a portion of the electromagnetic radiation 3 generated by the radiation source 2 strikes a textile fiber structure 4 under investigation. The textile fiber structure 4 can be, for example, one or more fiber flakes, a fiber fleece, a fiber tape, a roving, a yarn, a woven fabric, a knitted fabric, or a nonwoven fabric. In the example of Figure 1 Without restriction of generality, a fiber flake is schematically depicted as a textile fiber structure 4.

[0035] The textile fiber structure 4 comprises two different components 41, 42. For illustrative purposes, and without loss of generality, it is assumed here that the textile fiber structure 4 consists of a base material 41, e.g., cotton, and may contain one or more foreign materials 42 that differ from the base material 41. When electromagnetic radiation 3 strikes the textile fiber structure 4, it interacts with the base material 41 and, if present, with the foreign material 42. This interaction alters the intensity distribution 30 of the electromagnetic radiation 3 according to the chemical or color characteristics of the materials. Thus, radiation 5 reflected or transmitted by the textile fiber structure 4 has a spectral intensity distribution 50 that differs from the intensity distribution 30 of the radiation 3 incident on the textile fiber structure 4.The intensity distribution 50 is in . Figure 1 again represented as a schematic diagram in which the intensity is plotted as a function of the wavelength.

[0036] After interacting with the textile fiber structure 4, the electromagnetic radiation 5 interacts in the exemplary embodiment of Figure 1 with a spectral filter 6. The interaction can occur via transmission or reflection at the spectral filter 6. The spectral properties of the spectral filter 6 are specifically tailored to a type or class of foreign materials 42. The spectral filter 6 can, for example, be designed as an interference filter. It modifies the intensity distribution 50 of the electromagnetic radiation 5 interacting with it in such a way that differences between the base material 41 and the foreign material 42 are amplified.

[0037] If the spectral intensity distribution 50 before the spectral filter 6 corresponds to that of the base material 41, then the intensity of the radiation 7 after the spectral filter 6 should be, for example, minimal. If, on the other hand, the spectral intensity distribution 50 before the spectral filter 6 corresponds to that of the foreign material 42, then the intensity of the radiation 7 after the spectral filter 6 should be, for example, maximal. If the spectral intensity distribution 50 before the spectral filter 6 has characteristics of both materials 41 and 42, then the intensity of the radiation 7 after the spectral filter 6 should correspond to a monotonic function of the mixing ratio of materials 41 and 42. This is in Figure 1 schematically represented by a diagram 70, which shows an intensity of the radiation 7 after interaction with the spectral filter 6 as a function of the proportion of foreign materials 42 in the textile fiber structure 4.

[0038] The spectral filter 6 thus converts the incident wavelength-dependent intensity distribution 50 into an intensity distribution 70, which is a monotonic function of the mixing ratio of the two components 41 and 42. The intensity of the electromagnetic radiation 7 after the spectral filter 6 is therefore a measure of the mixing ratio. In the example discussed here, it is a measure of the presence and amount of the foreign material 42 in the textile fiber structure 4 and / or of the degree of color deviation between the base material 41 and the foreign material 42.

[0039] After interaction with the spectral filter 6, electromagnetic radiation 7 is detected by a broadband radiation sensor 8. In a preferred embodiment, the radiation sensor 8 is spatially resolved, and the textile fiber structure 4 is imaged onto the radiation sensor 8 by means of an optical system (not shown).

[0040] This also provides information about the number, size, and shape of the foreign materials 5 present in the textile fiber structure 4. The radiation sensor 8 is preferably time-resolving. It can, for example, be designed as a digital camera.

[0041] In an image of the textile fiber structure 4 taken by the radiation sensor 8, foreign materials 42 appear bright against a dark background in the present example.

[0042] In an alternative embodiment, the spectral properties of the spectral filter 6 can be adapted to the radiation source 2, the base material 41, and / or the foreign material 42 such that the intensity of the radiation 7 after the spectral filter 6 is maximal when the textile fiber structure 4 consists only of the base material 41, and decreases with an increasing proportion of foreign material 42. In this case, foreign materials 42 appear dark against a light background.

[0043] In another embodiment, the spectral filter 6 can be placed in the beam path between the radiation source 2 and the textile fiber structure 4. In this case, the electromagnetic radiation 3 generated by the light source 2 first interacts with the spectral filter 6 and then strikes the textile fiber structure 4. The effect is analogous, and an image of the textile fiber structure 4 recorded by the radiation sensor 8 essentially corresponds to the images recorded according to the embodiments described above.

[0044] In Figure 2(a) The relative intensity of the electromagnetic radiation 3 produced by a halogen lamp 2 is plotted as a function of the radiation wavelength λ. In the spectral band shown (950 nm ≤ λ ≤ 1400 nm, near and short-wave infrared), the relative intensity decreases monotonically with the radiation wavelength λ. The intensity spectrum may look different for other light sources 2.

[0045] Figures 2(b) and 2(c) The absorption spectra of cotton, a typical textile base material 41, and polyethylene, which can be an impurity 42, are shown. The respective absorptivity is again shown as a function of the radiation wavelength λ in the same spectral band as in Figure 2(a) applied.

[0046] The spectral properties of the spectral filter 6 are determined from the spectral intensity distribution 30 of the radiation source 2 and from the spectral properties—absorption, reflection, and / or transmittance—of the base material 41 and the foreign material 42 to be detected, using multidimensional variational calculus. The regression vector resulting from the multidimensional variational calculus contains a weight for each wavelength in the considered spectral band. The weights correspond to the transmittance and reflectance of the spectral filter 6 for the respective wavelengths. Thus, the spectral filter 6 is optimized for the detection of a specific foreign material 42 in a specific base material 41 under illumination with a specific radiation source 2. Such methods for designing a spectral filter are known per se; an example can be found in the article "PLS regression: a basic tool of chemometrics" by S. Wold, M.Sjöström and L.

[0047] Eriksson, Chemometrics and Intelligent Laboratory Systems, Volume 58, Issue 2, October 28, 2001, pages 109-130.

[0048] In Figure 2(d) is an exemplary transmittance of a spectral filter 6 as a function of the radiation wavelength λ in the same spectral band as in the Figures 2(a)-2(c) plotted. In the example shown, the spectral filter 6 has four local maxima (at wavelengths of approximately λ ≈ 1000 nm, 1110 nm, 1213 nm and 1317 nm) and three local minima (at wavelengths of approximately λ ≈ 1055 nm, 1145 nm and 1268 nm) in the considered spectral band (950 nm ≤ λ ≤ 1400 nm). The spectral filter 6 amplifies the differences in the absorption of cotton ( Figure 2(b) ) and polyethylene ( Figure 2(c) ), which is particularly noticeable in the spectra at wavelengths of approximately λ ≈ 1100 nm, 1210 nm and 1320 nm.

[0049] By optimizing the transmission and reflection of the spectral filter 6 for the foreign material 42, those components of the electromagnetic radiation 5 incident on the spectral filter 6 that result from the interaction of the radiation 5 with the foreign material 42 can pass through the spectral filter 6 undamped. Components resulting from the base material 41 are attenuated by the spectral filter 6. The signal on the radiation sensor 8 is therefore high for the foreign material 42 and low for the base material 41. If the radiation sensor 8 is configured as an image sensor, the foreign material 42 appears as bright image areas and the base material 41 as dark image areas in the image generated by the radiation sensor 8.

[0050] Naturally, the present invention is not limited to the embodiments discussed above. A person skilled in the art will be able to derive further variants that also fall within the scope of the invention as defined by the following claims. REFERENCE MARK LIST

[0051] 1 device 2 radiation source 3 Electromagnetic radiation generated by the radiation source 30 Spectral intensity distribution 4. Textile fiber structure 41. Base material of the textile fiber structure 42. Foreign material in the textile fiber structure 5am ​​reflected or transmitted radiation from textile fiber structures 50 spectral intensity distribution 6 spectral filters 7 Radiation after the spectral filter 70 Intensity of the detected radiation as a function of the proportion of foreign materials 8 radiation sensor

Claims

1. Method (1) for detecting a mixture ratio of two components (41, 42) of a textile fiber structure (4), wherein electromagnetic radiation (3) in a spectral band is transmitted from a radiation source (2) in the direction of the textile fiber structure (4), at least a part of the electromagnetic radiation (3) interacts with the textile fiber structure (4), at least a part of the electromagnetic radiation (7) is received by a radiation sensor (8) after interacting with the textile fiber structure (4), and at least a part of the electromagnetic radiation (5) is filtered by a spectral filter (6) with spectral properties in the spectral band before or after interacting with the textile fiber structure (4), characterized in that the spectral filter (6) is selected such that its transmittance or its reflectance in the spectral band has at least one local maximum and at least one local minimum, and its spectral properties in the spectral band are adapted to the spectral properties of the radiation source (2) and each of the two components (41, 42) in the textile fiber structure (4) such that a radiation intensity received by the radiation sensor (8) is a monotonous function of the mixture ratio of the two components (41, 42).

2. Method according to claim 1, wherein the spectral band is in the wavelength range between 300 nm and 2200 nm, and preferably in the wavelength range between 700 nm and 1900 nm.

3. Method according to claim 1 or 2, wherein the spectral band has a width between 200 nm and 500 nm.

4. Method according to one of claims 1-3, wherein one (41) of the two components (41, 42) is a base material of which a predominant part of the textile fiber structure (4) consists, and the other (42) of the two components (41, 42) is a foreign material whose proportion in the textile fiber structure (4) is determined.

5. Method according to claim 4, wherein the base material (41) is cotton and the foreign material (42) is polyethylene.

6. Method according to one of the preceding claims, wherein the at least one local maximum lies at the wavelength or wavelengths of the electromagnetic radiation (3) at which the absolute value of the difference of the absorptance, the transmittance, or the reflectance of the two components (41, 42) has a local maximum.

7. Method according to one of the preceding claims, wherein the transmittance or the reflectance of the spectral filter (6) in the spectral band has at least two local maxima and local minima each.

8. Method according to one of the preceding claims, wherein the spectral filter (6) is designed as a reflection filter or as a transmission filter.

9. Method according to one of the preceding claims, wherein the spectral filter (6) is designed as an interference filter.

10. Method according to one of the preceding claims, wherein the spectral filter (6) is integrated into the radiation sensor (8).

11. Method according to one of the preceding claims, wherein the radiation sensor (8) is spatially resolving and / or time resolving.

12. Method according to claim 11, wherein the radiation sensor (8) is formed either as a digital camera with a two-dimensional image converter or as a one-dimensional line sensor.