CH720486A1 - Investigation of a textile fiber structure containing two components - Google Patents

Abstract

A system according to the invention consists of a textile fiber structure (4) containing two components (41, 42) and a device (1) for examining the textile fiber structure (4). The device (1) contains a radiation source (2) for transmitting electromagnetic radiation (3) in a spectral band in the direction of the textile fiber structure (4) and a quantum dot sensor (7) for receiving the electromagnetic radiation (5). A spectral sensitivity of the quantum dot sensor (7) in the spectral band has at least one local maximum and at least one local minimum. The spectral properties of the quantum dot sensor (7) in the spectral band are matched to the spectral properties of the radiation source (2) and each of the two components (41, 24) in such a way that an output signal of the quantum dot sensor (7) is a monotonic function of the mixing ratio of the two components (41, 42). The device (1) is of simple construction and enables an image of the fiber structure (4) with high spatial resolution. The invention further relates to a device and a method for examining a textile fiber structure containing two components and an application of this method.

Description

SPECIALIST AREA

[0001] The present invention is in the field of quality control in the textile industry. It relates to a system consisting of a textile fiber structure containing two components and a device for examining the textile fiber structure, according to the first patent claim. It also relates to a device and a method for examining a textile fiber structure containing two components, according to the further independent patent claims. Preferred applications are the detection of foreign materials in a textile fiber structure such as fiber flakes, fiber fleece, fiber tape, roving, yarn, woven or knitted fabric and the determination of a mixing ratio of two components of such textile fiber structures.

STATE OF THE ART

[0002] Foreign materials in yarn are one of the biggest problems facing spinning mills today. These are materials that are different from the base material of the yarn fibers, e.g. cotton fibers. They can have various origins, such as residues from transport packaging (plastic packaging, strings), pollution from civilization (soot particles, plastic bags) or residues from living beings (human or animal hair, plant stems). Foreign materials lead to thread breakage during spinning and weaving, absorb dye in a different way than the base material and affect the appearance of the final textile product. They significantly reduce the value of the final product. An overview of fabric defects caused by foreign materials and recommendations for reducing them can be found in Section 3.8 of USTER<®>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 possibly eliminated at different stages of the yarn production process, for example in the blow room process and/or in the spinning process.

[0004] The removal of foreign materials follows the manner in which a human would remove the material. It can therefore basically be divided into the following three steps, regardless of the position in the manufacturing process: 1) detection of the foreign material; 2) spatial/temporal localization of the foreign material within the test material; and 3) elimination of the foreign material.

[0005] Detection and localization using detection devices are carried out based on differences in one or more specific properties of the material flow. These include, but are not limited to: reflection and transmission of electromagnetic radiation, fluorescence or density.

[0006] In the simplest applications of machine cleaning, optical detection devices are used to imitate the human eye and analyze the color impression of the material flow, whereby corresponding color differences are recognized. US-6,452,157 B1 discloses a device for detecting contaminants, 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. In addition, a sensor is provided that receives the colors of the light reflected by the fiber material.

[0007] Electromagnetic radiation which appears to be particularly suitable for the examination of textile fibre structures can be assigned to one of the following wavelength ranges: 1) Ultraviolet - approx. 200 nm to approx. 380 nm 2) Visible - approx. 380 nm to approx. 780 nm 3) Short-wave near-infrared - approx. 780 nm to approx. 1400 nm 4) Long-wave near-infrared - approx. 1400 nm to approx. 3000 nm.

[0008] In all cases, the material affiliation is determined based on characteristic signatures (e.g. sequence of specific absorption bands) in the spectrum of the electromagnetic radiation reflected or transmitted by the material. The differentiation of the characteristic signatures becomes more precise the more specific features (e.g. absorption bands) within the signature are used for the differentiation. According to the state of the art, there are no spectrally resolving radiation sensors that achieve spectral resolution without additional optical aids, such as a filter. However, filters can only ever be optimized for specific spectral ranges, e.g. bandpass, low-pass and high-pass filters. Each feature that is to be used to differentiate materials therefore requires a dedicated sensor within the detection device that only responds to the presence or absence of the relevant feature. The more different features are to be used, the more complex the detection device becomes. The input signal must be split accordingly between the various sensors and thus loses intensity.

[0009] In addition, the state of the art does not currently include any spatially resolving sensors for certain features, but only temporally resolving sensors. This requires a device upstream of the detection device that links time and location. Alternatively, the incident electromagnetic radiation must be modulated in time and adapted to the features. However, this is sometimes associated with great effort for the non-visible range of the electromagnetic spectrum.

[0010] If the features are also in different wavelength ranges, this may require different detector technologies. For example, silicon-based radiation sensors can only be used in the wavelength range between 190 nm and 1100 nm; for longer-wave near infrared, indium gallium arsenide-based radiation sensors are usually used.

[0011] When differentiating materials based on color differences, as is common in the spinning process, the features mentioned are in the visible spectral range. Since the color impression is also due to the specific reflection or transmission of certain parts of the irradiated wavelength spectrum, in this case too each feature must be detected individually. To do this, either a temporal color modulation of the input signal can be carried out, or the output signal changed by the yarn must, as already explained, be broken down into the individual features. In the former case, the spatial resolution deteriorates, in the latter the signal-to-noise ratio. The more colors are used, the greater the impact of these disadvantages. For this reason, methods have been established in practice that use only one or a maximum of two colors. A yarn cleaner that scans yarn with several differently colored light components is known from WO-2011/026249 A1.

[0012] WO-2022/198342 A1 discloses a device for determining a mixing ratio of two components of a textile fiber structure. The device includes a radiation source for transmitting electromagnetic radiation in a spectral band in the direction of the textile fiber structure, a radiation sensor for receiving at least part of the electromagnetic radiation and a spectral filter with spectral properties in the spectral band for filtering at least part of the electromagnetic radiation. The transmittance of the spectral filter in the spectral band has at least one local maximum and at least one local minimum. The spectral properties of the spectral filter in the spectral band are matched to the spectral properties of the radiation source and each of the two components 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.

[0013] Bayer sensors in digital color cameras enable the detection of different wavelength ranges with an imaging sensor by distributing the different wavelength ranges - red, green and blue - over different partial areas (pixels) of the flat sensor. This type of variation in local sensitivity requires additional color filters directly above the actual transducers, while the transducers themselves remain broadband sensitive. Bayer sensors have certain disadvantages, particularly with regard to the detection of foreign materials in textile fiber structures. Firstly, the color filters must be applied to the transducers in a separate, downstream process step, which makes the manufacturing process more expensive. Secondly, Bayer sensors are based on silicon technology, which results in high sensitivity in the visible spectral range, but is insensitive in the infrared spectral range. For detection in the infrared, other technologies such as indium gallium arsenide must be used, which are incompatible with silicon technology and expensive. Thirdly, the Bayer sensors with their RGB filters can only detect slight changes in the incoming spectrum to a very limited extent. Fourthly, they have poor spatial resolution because, to produce a complete color image, four neighboring pixels of different colors must be combined to form a "unit cell." Fifthly, the Bayer sensor produces an image for each of the three colors red, green and blue, and these three images must be mathematically combined to form a single color image.

[0014] Quantum dot sensors allow the detection of electromagnetic radiation. The specific spectral sensitivity of the sensors can be adapted to the application by adjusting the size of the quantum dots. As the quantum dot becomes smaller, the spatial localization of the charge carriers increases, which increases the spread of the energy states, i.e. the size of the band gap. In this case, the spectral sensitivity shifts towards higher-energy radiation, e.g. ultraviolet radiation. Quantum dots of different sizes can be combined with one another to enable spectral sensitivity over a broad band or to achieve a specific sensitivity tailored to the application. The relative sensitivity between different spectral bands can be influenced by the number of quantum dots of the corresponding size present. The article “A New Image Sensor Using Quantum Dots Could Replace CMOS” by J. Schneider, PetaPixel, February 10, 2022 (https://petapixel.com/2022/02/10/a-new-image-sensor-usingquantum-dots-could-replace-cmos/) explains quantum dot technology. The datasheet “Emberion VS20 VIS-SWIR Camera GigE & Camera Link”, Emberion Oy, September 23, 2022, gives an example of a commercially available quantum dot camera.

DESCRIPTION OF THE INVENTION

[0015] It is an object of the present invention to provide a system and a device for examining a textile fiber structure containing two components, which avoids the above disadvantages. The system and the device should in particular be of simple construction. They should enable an image of the fiber structure with high spatial resolution. At the same time, the signal-to-noise ratio should be high. A further object is to specify a corresponding method for examining a textile fiber structure containing two components.

[0016] A further object is to provide a system, a device and a method for detecting foreign substances in a textile base material, which avoid the above disadvantages. A still further object is to provide a system, a device and a method for determining a mixing ratio of two components of a textile fiber structure, which avoid the above disadvantages.

[0017] These and other objects are achieved by the system according to the invention, the device according to the invention and the method according to the invention as defined in the independent claims. Advantageous embodiments are specified in the dependent claims.

[0018] The inventor has recognized that quantum dots offer the possibility of covering both the visible spectral range and the near-infrared range with a single detector technology simply by adjusting the sizes of the quantum dots.

[0019] The invention is therefore based on the idea of identifying the spectral features required for the desired application and achieving the corresponding absorption in a quantum dot sensor by mixing quantum dots of different sizes. Quantum dots of different sizes on a pixel-by-pixel basis allow a spatially different spectral sensitivity. A separate evaluation of these pixels then allows the different spectral features to be separated. In contrast to conventional Bayer sensors, however, quantum dots allow different sensitivities on a flat sensor without the need for additional optical components such as color filters.

[0020] The mixture of quantum dots of different sizes on a single readable area (e.g. a pixel) of the quantum dot sensor allows the sensitivity to be adapted to a specific color impression that results from the mixture of two spectral features. The mixture of the absorption of red and green components would in this case result in a particular sensitivity of the quantum dot sensor for yellow objects, while blue objects would not be detected by the quantum dot sensor.

[0021] In the case of material differentiation, the quantum dots are dimensioned based on the specific chemical and/or color signatures of the two components to be separated. As an example, individual features can be enhanced by strong absorption in the quantum dot sensor, while other features are attenuated by low sensitivity of the quantum dot sensor. The combination of amplification and attenuation in the quantum dot sensor enables the generation of a contrast image, whereby the material classes can be separated from one another by differences in contrast.

[0022] The determination of the features in the chemical signatures required for differentiation is carried out using mathematical methods from the field of regression analysis. Principal component analysis and the partial least squares method are not exhaustive.

[0023] The system according to the invention consists of a textile fiber structure containing two components and a device for examining the textile fiber structure. The device includes a radiation source for sending electromagnetic radiation in a spectral band in the direction of the textile fiber structure for interaction with the textile fiber structure. The device also includes a radiation sensor for receiving at least part of the electromagnetic radiation after interaction with the textile fiber structure. The radiation sensor is designed as a quantum dot sensor. A spectral sensitivity of the quantum dot sensor in the spectral band has at least one local maximum and at least one local minimum. The spectral properties of the quantum dot sensor in the spectral band are matched to the spectral properties of the radiation source and each of the two components in such a way that an output signal of the quantum dot sensor is a monotonic function of the mixing ratio of the two components.

[0024] The two components of the textile fiber structure are, for example, two different elements from the following set: cotton, linen, new wool, polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polyester (PES); polyacrylic (PAN); viscose (CV, regenerated cellulose), modal (CMD), lyocell (CLY), polyethylene terephthalate (PET), polystyrene (PS), polyamide (PA), acrylonitrile-butadiene-styrene copolymer (ABS), polymethyl methacrylate (PMMA), polyoxymethylene (POM), elastane (EL), aramid (AR), acetate (CA), cupro (CUP). Preferably, the two components of the textile fiber structure are a pair from the following set: cotton and polyethylene (PE), cotton and polypropylene (PP), cotton and polyvinyl chloride (PVC), cotton and polyester (PES); cotton and polyacrylic (PAN); Cotton and viscose (CV, regenerated cellulose), cotton and polyethylene terephthalate (PET), cotton and polystyrene (PS), cotton and polyamide (PA), cotton and acrylonitrile-butadiene-styrene copolymer (ABS), cotton and polymethyl methacrylate (PMMA), cotton and polyoxymethylene (POM).

[0025] The device according to the invention is used to examine a textile fiber structure containing two components. The device includes a radiation source for sending electromagnetic radiation in a spectral band in the direction of the textile fiber structure for interaction with the textile fiber structure. The device also includes a radiation sensor for receiving at least part of the electromagnetic radiation after interaction with the textile fiber structure. The two components of the textile fiber structure are two different elements from the following set: cotton, linen, new wool, polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polyester (PES); polyacrylic (PAN); Viscose (CV, regenerated cellulose), modal (CMD), lyocell (CLY), polyethylene terephthalate (PET), polystyrene (PS), polyamide (PA), acrylonitrile-butadiene-styrene copolymer (ABS), polymethyl methacrylate (PMMA), polyoxymethylene (POM), elastane (EL), aramid (AR), acetate (CA), cupro (CUP).- The radiation sensor is designed as a quantum dot sensor. A spectral sensitivity of the quantum dot sensor in the spectral band has at least one local maximum and at least one local minimum. The spectral properties of the quantum dot sensor in the spectral band are matched to the spectral properties of the radiation source and each of the two components in such a way that an output signal of the quantum dot sensor is a monotonic function of the mixing ratio of the two components.

[0026] In one embodiment of the device, the two components of the textile fiber structure are a pair from the following set: cotton and polyethylene (PE), cotton and polypropylene (PP), cotton and polyvinyl chloride (PVC), cotton and polyester (PES); cotton and polyacrylic (PAN); cotton and viscose (CV, regenerated cellulose), cotton and polyethylene terephthalate (PET), cotton and polystyrene (PS), cotton and polyamide (PA), cotton and acrylonitrile-butadiene-styrene copolymer (ABS), cotton and polymethyl methacrylate (PMMA), cotton and polyoxymethylene (POM).

[0027] In one embodiment of the system or device, the at least one local maximum is at the wavelength or wavelengths of the electromagnetic radiation at which the absolute value of the difference between the absorption coefficients, the transmission coefficients or the reflection coefficients of the two components has a local maximum.

[0028] In one embodiment of the system or device, 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.

[0029] In one embodiment of the system or device, the spectral band has a width between 100 nm and 1500 nm and preferably between 300 nm and 500 nm.

[0030] In one embodiment of the system or device, the quantum dot sensor includes at least one quantum dot layer located between two electrodes and, for example, several quantum dot layers stacked on top of each other with different band gaps.

[0031] In one embodiment of the system or device, the quantum dot sensor is monolithically integrated on an integrated circuit, which is manufactured, for example, in CMOS technology.

[0032] In one embodiment of the system or device, the spectral properties of the quantum dot sensor in the spectral band are matched to the spectral properties of the radiation source and each of the two components such that an output signal of the quantum dot sensor is a linear function of the mixing ratio of the two components.

[0033] One embodiment of the system or device includes an optical imaging system for imaging the textile fiber structure onto the quantum dot sensor, wherein the quantum dot sensor is spatially resolving and is designed either as a two-dimensional matrix sensor or as a one-dimensional line sensor.

[0034] One embodiment of the system or device includes a time-varying optical imaging system which images different locations of the textile fiber structure one after the other onto the quantum dot sensor, wherein the quantum dot sensor is time-resolved.

[0035] The system or device according to the invention can be used to detect a foreign material in a base material, wherein the foreign material and the base material are the two components of the textile fiber structure.

[0036] The system or device according to the invention can be used to determine a mixing ratio of the two components of the textile fiber structure.

[0037] The method according to the invention is used to examine a textile fiber structure containing two components. Electromagnetic radiation in a spectral band is sent from a radiation source in the direction of 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 interacting with the textile fiber structure. A quantum dot sensor is used as the radiation sensor. A spectral sensitivity of the quantum dot sensor has at least one local maximum and at least one local minimum in the spectral band. The spectral properties of the quantum dot sensor 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 an output signal of the quantum dot sensor is a monotonic function of the mixing ratio of the two components.

[0038] In one embodiment of the method, 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.

[0039] In one embodiment of the method, the spectral band has a width between 100 nm and 1500 nm and preferably between 300 nm and 500 nm.

[0040] In one embodiment of the method, the two components of the textile fiber structure are two different elements from the following set: cotton, linen, new wool, polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polyester (PES); polyacrylic (PAN); viscose (CV, regenerated cellulose), modal (CMD), lyocell (CLY), polyethylene terephthalate (PET), polystyrene (PS), polyamide (PA), acrylonitrile-butadiene-styrene copolymer (AB S), polymethyl methacrylate (PMMA), polyoxymethylene (POM), elastane (EL), aramid (AR), acetate (CA), cupro (CUP). Preferably, the two components of the textile fiber structure are a pair from the following set: cotton and polyethylene (PE), cotton and polypropylene (PP), cotton and polyvinyl chloride (PVC), cotton and polyester (PES); cotton and polyacrylic (PAN); Cotton and viscose (CV, regenerated cellulose), cotton and polyethylene terephthalate (PET), cotton and polystyrene (PS), cotton and polyamide (PA), cotton and acrylonitrile-butadiene-styrene copolymer (ABS), cotton and polymethyl methacrylate (PMMA), cotton and polyoxymethylene (POM).

[0041] The method according to the invention can be used to detect a foreign material in a base material, wherein the foreign material and the base material are the two components of the textile fiber structure.

[0042] The method according to the invention can be used to determine a mixing ratio of the two components of the textile fiber structure.

[0043] The device and method according to the invention avoid splitting the incoming electromagnetic radiation reflected or transmitted by the textile fiber structure into several radiation sensors. The device is simply constructed and allows the fiber structure to be imaged with high spatial resolution. It does not require temporal modulation of the input signal, thereby achieving high spatial resolution. Each pixel of the quantum dot sensor is constructed in the same way, which leads to a higher spatial resolution compared to the Bayer sensor.

LIST OF DRAWINGS

[0044] An embodiment of the invention is explained in detail below with reference to the drawings. For a clearer illustration, an application is described in which a proportion of a foreign material in a base material of a textile fiber structure is determined. However, this should not restrict the generality of the invention. The invention can, for example, alternatively be directed to a textile fiber structure with two desired components. The invention can relate to the detection of a foreign material in a base material or to the determination of a mixing ratio of two components of the textile fiber structure. Figure 1 shows a schematic representation of an embodiment of the system according to the invention and the device according to the invention that works with transmitted light. Figure 2 shows a schematic representation of an embodiment of the system according to the invention and the device according to the invention that works with incident light. Figure 3 shows a schematic representation of the structure of a radiation sensor based on quantum dots. Figure 4 shows various spectra in a common first spectral band, namely: (a) relative intensity distribution of a halogen lamp; (b) absorption level of cotton; (c) absorbance of polyethylene; and (d) spectral sensitivity of a quantum dot sensor. Figure 5 shows a relative intensity distribution of a halogen lamp in a second spectral band. Figures 6-12 show absorbances of the materials cotton, polyethylene, polypropylene, polyester, polyethylene terephthalate, polyacrylic and cellulose, respectively, in the second spectral band. Figure 13 shows a spectral sensitivity of a quantum dot sensor in the second spectral band. Figure 14 shows (a) a grayscale image of a textile sample with different materials and (b) a binary image of the sample after carrying out the method according to the invention and image processing.

IMPLEMENTATION OF THE INVENTION

[0045] A first embodiment of the system according to the invention and of the device 1 according to the invention is shown schematically in Figure 1. The device 1 contains a broadband radiation source 2 for generating electromagnetic radiation 3 in a spectral band. The electromagnetic radiation 3 generated has a spectral intensity distribution in the spectral band that is characteristic of the radiation source 2.

[0046] At least a portion of the electromagnetic radiation 3 generated by the radiation source 2 strikes a textile fiber structure 4 to be examined. The textile fiber structure 4 can be, for example, one or more fiber flakes, a fiber fleece, a fiber ribbon, a roving, a yarn, a woven fabric, a knitted fabric or a fleece. In the example in Figure 1, a fiber flake is schematically shown as the textile fiber structure 4 without restricting generality.

[0047] The textile fiber structure 4 contains at least two different components 41, 42. Without restricting generality, it is assumed here for illustration purposes 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. The foreign material 42 may be, for example, polyethylene. When the electromagnetic radiation 3 strikes the textile fiber structure 4, the electromagnetic radiation 3 interacts with the base material 41 and, if present, the foreign material 42. The interaction changes the spectral intensity distribution of the electromagnetic radiation 3 according to the chemical or color characteristics of the materials. Radiation 5 transmitted through the textile fiber structure 4 thus has a spectral intensity distribution that differs from the intensity distribution of the radiation 3 striking the textile fiber structure 4.

[0048] In the first embodiment of Figure 1, the electromagnetic radiation passes through the textile fiber structure; the examination is thus carried out in transmission.

[0049] After the interaction with the textile fiber structure 4, the radiation 5 hits a radiation sensor 7, which is designed as a quantum dot sensor. A spectral sensitivity of the quantum dot sensor 7 has at least one local maximum and at least one local minimum in the spectral band (see Figure 4(d)). The spectral properties of the quantum dot sensor 7 are specifically matched to the radiation source 2, the base material 41 and/or a type or class of foreign materials 42 in the spectral band such that differences between the base material 41 and the foreign material 42 are amplified in an output signal of the quantum dot sensor 7.

[0050] If the spectral intensity distribution of the electromagnetic radiation 5 impinging on the quantum dot sensor 7 corresponds to that of the base material 41, the output signal should be minimal, for example. If, on the other hand, the spectral intensity distribution of the electromagnetic radiation 5 impinging on the quantum dot sensor 7 corresponds to that of the foreign material 42, the output signal should be maximal, for example. If the spectral intensity distribution of the electromagnetic radiation 5 impinging on the quantum dot sensor 7 has characteristics of both materials 41 and 42, the output signal should correspond to a monotonic and preferably linear function of the mixing ratio of the materials 41 and 42.

[0051] The quantum dot sensor 7 thus converts the incident wavelength-dependent intensity distribution of the radiation 5 into an output signal which is a monotonic and preferably linear function of the mixing ratio of the two components 41 and 42. The output signal is therefore a measure of the mixing ratio. In the example discussed here, it is a measure of the presence and quantity 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.

[0052] The quantum dot sensor 7 is preferably spatially resolving and time-resolving. It can be designed, for example, as a one- or two-dimensional digital quantum dot camera, as is known from the prior art. In this case, the output signal of each image element (pixel) is a measure of the mixing ratio of the two components 41, 42 at the location imaged on the image element. If this location is small enough, it will usually have either only one or only the other component, so that the pixel delivers either a minimum or a maximum output signal.

[0053] If the quantum dot sensor 7 is not spatially resolving, the radiation intensity received by it is a measure of the mixing ratio of the two components 41, 42, averaged over the entire textile fiber structure 4.

[0054] In a preferred embodiment, the quantum dot sensor 7 is spatially resolving, and the textile fiber structure 4 is imaged onto the quantum dot sensor 7 by means of an optical imaging system 6. This also provides information about the number, position, size and shape of the foreign materials 42 present in the textile fiber structure 4. The foreign materials 42 can thus be detected and localized in the textile fiber structure 4. In an image of the textile fiber structure 4 recorded by the quantum dot sensor 7, foreign materials 42 appear bright against a dark background in the present example (cf. Figure 14(b)).

[0055] In an alternative embodiment, the spectral properties of the quantum dot sensor 7 in the spectral band can be matched to the radiation source 2, the base material 41 and/or the foreign material 42 in such a way that the output signal emitted by the quantum dot sensor 7 is maximum when the textile fiber structure 4 consists only of the base material 41, and decreases with increasing proportion of foreign material 42. In this case, foreign materials 42 appear dark against a light background.

[0056] The device 1 can contain optical elements 6 known to the person skilled in the art, such as further lenses, mirrors, apertures, etc. for influencing the radiation 3, 5.

[0057] In one embodiment, the device 1 includes a time-varying optical imaging system which images different locations of the textile fiber structure 4 onto the quantum dot sensor 7 one after the other. This can be implemented mechanically or electronically. An example of such a time-varying optical imaging system is given in EP-1'961'848 A1 and includes a rotatable polygon mirror for scanning the textile fiber structure 4 line by line. This embodiment requires a time-resolving quantum dot sensor 7 and a device for assigning the reception time to the corresponding location on the textile fiber structure 4. For this, the quantum dot sensor 7 does not need to be spatially resolving.

[0058] Figure 2 shows schematically a second embodiment of the system according to the invention and the device 1 according to the invention. The device 1 is analogous to the first embodiment of Figure 1, with the difference that the examination is carried out in reflection. Corresponding elements are designated with the same reference numerals as in Figure 1. Due to the close analogy, the second embodiment does not need to be discussed further.

[0059] A cross section through a part of the quantum dot sensor 7 is shown schematically in Figure 3. Electromagnetic radiation incident on the quantum dot sensor 7 from above is indicated by a wavy arrow 5.

[0060] The quantum dot sensor 7 can be integrated monolithically on an integrated circuit, which can be produced using CMOS technology, for example. The circuit is represented in Figure 3 by a lower electrode 77 and a dielectric 76. It can be used to read out the sensor signals. A structured electrode 75 is located on the circuit. The structuring of the structured electrode 75 represents the actual pixel structure of the quantum dot sensor 7 and allows the spatial localization of the incoming electromagnetic radiation 5.

[0061] At least one quantum dot layer 72-74 is deposited on the structured electrode 75; in the example of Figure 3 there are three quantum dot layers 72-74. The at least one quantum dot layer 72-74 is applied using thin film technology and has no internal structure. The quantum dots in the various quantum dot layers 72-74 differ in their size and thus in the size of the band gap, whereby the spectral sensitivity of the quantum dot sensor 7 is set. The closer the quantum dot layer 72-74 is to the surface, the larger the band gap of the quantum dots. Short-wave radiation, for example ultraviolet or blue radiation, is thus absorbed in a quantum dot layer 72 near the surface of the quantum dot sensor 7. Long-wave infrared radiation, on the other hand, penetrates deep into the quantum dot sensor 7 and is only absorbed in a quantum dot layer 74 near the structured electrode 75.

[0062] On an upper side of the quantum dot sensor 7 there is a light-permeable upper electrode 71, which acts as a counter electrode to the structured electrode 75.

[0063] To read a pixel, a voltage is applied between the upper electrode 71 and the corresponding segment of the structured electrode 75, which creates an electric field between the two electrodes 71, 75. Electrons generated in the quantum dot layers 72-74 are transported by the electric field to the selected segment of the structured electrode 75 and can be converted into an electrical output signal using the circuit. The further processing of the electrical output signals of the various pixels is carried out analogously to the conventional spatially resolving (one- or two-dimensional) semiconductor radiation sensors, e.g. the active pixel sensors (APS) manufactured using CMOS technology.

[0064] In Figure 4(a), the relative intensity of the electromagnetic radiation 3 generated by a halogen lamp 2 is plotted as a function of the radiation wavelength λ in a first spectral band (950 nm ≤ λ ≤ 1400 nm, short-wave near infrared). In this first spectral band, the intensity runs within a relatively narrow range and can thus be considered constant to a first approximation. In another spectral band or with other light sources 2, the intensity spectrum can have a different profile.

[0065] Figures 4(b) and 4(c) show absorption spectra of cotton, which is a typical textile base material 41, and polyethylene, which may be a foreign material 42, respectively. The respective absorption coefficient is again plotted as a function of the radiation wavelength λ in the same spectral band as in Figure 4(a).

[0066] The spectral properties of the quantum dot sensor 7 are determined from the spectral intensity distribution of the radiation source 2 and from spectral properties - absorption coefficient, reflection coefficient and/or transmission coefficient - of the base material 41 and the foreign material 42 to be detected by multidimensional variational calculation. The regression vector resulting from the multidimensional variational calculation contains a weighting for each wavelength in the spectral band under consideration. The weightings correspond to the spectral sensitivity of the quantum dot sensor 7 for the relevant wavelengths. The quantum dot sensor 7 is thus optimized for the detection of a specific foreign material 42 in a specific base material 41 and for determining the mixing ratio of the two materials 41, 42 when illuminated with a specific radiation source 2. Such methods for the design of a spectral filter are known per se; An example can be found in the article “PLS-regression: a basic tool of chemometrics” by S. Wolda, M. Sjöströma and L. Eriksson, Chemometrics and Intelligent Laboratory Systems, Volume 58, Issue 2, October 28, 2001, pages 109-130. They can be applied analogously to the design of a quantum dot sensor 7 .

[0067] Figure 4(d) shows an exemplary spectral sensitivity of a fictitious quantum dot sensor 7 as a function of the radiation wavelength λ in the same spectral band as in Figures 4(a)-4(c). In the example shown, the spectral sensitivity in the spectral band considered (950 nm ≤ λ ≤ 1400 nm) has three local maxima (at wavelengths of approximately λ ≈ 1110 nm, 1210 nm and 1310 nm) and two local minima (at wavelengths of approximately λ ≈ 1145 nm and 1265 nm). The quantum dot sensor 7 amplifies the differences in the absorption of cotton (Figure 4(b)) and polyethylene (Figure 4(c)), which is particularly evident in the respective spectra at wavelengths of approximately λ ≈ 1110 nm, 1210 nm and 1310 nm.

[0068] The spectral sensitivity of the quantum dot sensor 7 is optimized for the two components 41, 42 of the textile fiber structure 4. As a result, those portions of the electromagnetic radiation 5 incident on the quantum dot sensor 7 that result from the interaction of the radiation 5 with the foreign material 42 are absorbed more strongly by the quantum dot sensor 7 than portions that result from the base material 41. An output signal of the quantum dot sensor 7 is thus high for the foreign material 42 and low for the base material 41. If the quantum dot sensor 7 is designed as an image sensor, the foreign material 42 appears as bright image areas and the base material 41 as dark image areas on the image generated by the quantum dot sensor 7 (see Figure 14(b)). Alternatively, the spectral properties of the quantum dot sensor could be selected the other way around.

[0069] The technology for producing a quantum dot sensor 7 with a spectral sensitivity, for example according to Figure 4(d), is available, as mentioned in the introduction. The desired spectral sensitivity of the quantum dot sensor 7 can be adapted to the respective application by suitable selection of the number of quantum dot layers 72-74 and the size of the quantum dots located therein, and thus the size of the band gaps.

[0070] Since the spectrum of the light source 2 in the example of Figure 4 has a relatively constant profile, the light source 2 has practically no influence on the desired spectral properties of the quantum dot sensor 7. However, if the spectrum of the light source 2 were to have pronounced extreme points, its spectral properties would have to be taken into account when designing the quantum dot sensor 7.

[0071] In Figure 5, the relative intensity of the electromagnetic radiation 3 generated by a halogen lamp 2 is plotted as a function of the radiation wavelength λ, in a second spectral band (approximately 1000 nm ≤ λ ≤ 2400 nm, near infrared), which differs from the first spectral band of Figure 4.

[0072] Figures 6-12 show absorption coefficients of the materials cotton, polyethylene, polypropylene, polyester, polyethylene terephthalate, polyacrylic and viscose (regenerated cellulose) in the second spectral band.

[0073] In Figure 13, an exemplary spectral sensitivity of a fictitious quantum dot sensor 7 is plotted as a function of the radiation wavelength λ in the second spectral band. This exemplary quantum dot sensor 7 has two local maxima (at wavelengths of approximately λ ≈ 1725 nm and 2250 nm) and a local minimum (at a wavelength of approximately λ ≈ 2015 nm) in the second spectral band under consideration. The quantum dot sensor 7 of Figure 13 is designed for cotton (Figure 6) as base material 41 and polyethylene (Figure 7), polypropylene (Figure 8), polyester (Figure 9), polyethylene terephthalate (Figure 10), polyacrylic (Figure 11) or polystyrene as foreign material 42. Such use of one and the same quantum dot sensor 7 for two or more different materials 42 is possible provided that the spectra of the materials 42 in the spectral band under consideration have similar characteristics. This is the case for the foreign materials 42 mentioned: As Figures 7-11 show, the absorption spectra of all these foreign materials 42 have pronounced local maxima near the wavelengths λ ≈ 1700 nm and λ ≈ 2300 nm, in contrast to the base material 41 under consideration, cotton (Figure 6). Accordingly, the spectral sensitivity of the quantum dot sensor 7 of Figure 13 has a pronounced local maximum near λ ≈ 1700 nm and another local maximum near λ ≈ 2300 nm.

[0074] Also in the example of Figures 5-13, the spectrum of the light source 2 does not have any pronounced extremal points, so that the spectral properties of the light source 2 can be disregarded when designing the quantum dot sensor 7.

[0075] Figure 14(a) shows a schematic of a fictitious grayscale image of a textile sample with various materials placed on it, such as could be recorded by a conventional infrared camera in a near-infrared spectral range, for example. The base material 41 of the sample can be, for example, a knitted cotton fabric. On top of this lie pieces of film made of the following foreign materials: polystyrene 421, polyethylene 422 and polypropylene 423. The pieces of film 421-423 are transparent in the relevant spectral band and are therefore difficult to recognize in the grayscale image of Figure 12(a). In practice, such foreign materials are even less recognizable in a photographic image in the visible or NIR spectral range. In the example of a fiber cleaning device in a blow room, the base material is not a uniform, flat knit, but a three-dimensional fiber flake with various shadows, and the foreign material is not a large, flat film, but a fiber-like snippet. This is where the invention provides a remedy.

[0076] Figure 14(b) shows an idealized image of the textile sample of Figure 14(a) that could be recorded by a quantum dot sensor 7 of the device 1 according to the invention (see Figure 1). The radiation source 2 can be a halogen lamp with an emission spectrum according to Figure 5. The quantum dot sensor 7 used can have the spectral sensitivity according to Figure 13. In the idealized example of Figure 14(b), the image recorded by the quantum dot sensor 7 is a binary image in which the foreign materials 421-423 are white and the base material 41 is black. In a real image, the difference in brightness between the foreign materials 421-423 and the base material 41 is less pronounced, but the former still stand out clearly from the latter. A binary image according to Figure 14(b) can be generated from the real grayscale image by simple digital image processing by defining a suitable brightness threshold below which the pixels are set to “black” and above which the pixels are set to “white”.

[0077] It is noteworthy that in the example of Figure 14 the same device 1 according to the invention can be used for three different foreign materials 421-423. In other words: a dedicated quantum dot sensor 7 does not need to be designed and built for each foreign material 42; a single radiation source 2 and a single spectral band are also sufficient.

[0078] Of course, the present invention is not limited to the embodiments discussed above. With knowledge of the invention, the person skilled in the art will be able to derive further variants which also belong to the subject matter of the present invention.

LIST OF REFERENCE SYMBOLS

[0079] 1 device according to the invention 2 radiation source 3 electromagnetic radiation generated by the radiation source 4 textile fiber structure 41 base material of the textile fiber structure 42 foreign material in the textile fiber structure 421 polystyrene 422 polyethylene 423 polypropylene 5 radiation incident on the quantum dot sensor 6 optical imaging system, optical element 7 quantum dot sensor 71 upper electrode 72-74 quantum dot layers 75 structured electrode 76 dielectric 77 lower electrode

Claims (22)

1. System, consisting of a textile fiber structure (4) containing two components (41, 42) and a device (1) for examining the textile fiber structure (4), wherein the device (1) contains a radiation source (2) for transmitting electromagnetic radiation (3) in a spectral band in the direction of the textile fiber structure (4) for interaction with the textile fiber structure (4) and a radiation sensor (7) for receiving at least a portion of the electromagnetic radiation (5) after interaction with the textile fiber structure (4), characterized in that the radiation sensor (7) is designed as a quantum dot sensor, a spectral sensitivity of the quantum dot sensor (7) in the spectral band has at least one local maximum and at least one local minimum and the spectral properties of the quantum dot sensor (7) in the spectral band are adapted to the spectral properties of the radiation source (2) and each of the two components (41, 24) are tuned such that an output signal of the quantum dot sensor (7) is a monotonic function of the mixing ratio of the two components (41, 42). 2. System according to claim 1, wherein the two components (41, 42) of the textile fiber structure (4) are two different elements from the following set: cotton, linen, new wool, polyethylene, polypropylene, polyvinyl chloride, polyester; polyacrylic; viscose, modal, lyocell, polyethylene terephthalate, polystyrene, polyamide, acrylonitrile-butadiene-styrene copolymer, polymethyl methacrylate, polyoxymethylene, elastane, aramid, acetate, cupro. 3. System according to claim 2, wherein the two components (41, 42) of the textile fiber structure (4) are a pair from the following set: cotton and polyethylene, cotton and polypropylene, cotton and polyvinyl chloride, cotton and polyester; cotton and polyacrylic; cotton and viscose, cotton and polyethylene terephthalate, cotton and polystyrene, cotton and polyamide, cotton and acrylonitrile-butadiene-styrene copolymer, cotton and polymethyl methacrylate, cotton and polyoxymethylene. 4. Device (1) for examining a textile fiber structure (4) containing two components (41, 42), comprising a radiation source (2) for sending electromagnetic radiation (3) in a spectral band in the direction of the textile fiber structure (4) for interaction with the textile fiber structure (4) and a radiation sensor (7) for receiving at least a portion of the electromagnetic radiation (5) after interaction with the textile fiber structure (4), characterized in that the two components (41, 42) of the textile fiber structure (4) are two different elements from the following set: cotton, linen, new wool, polyethylene, polypropylene, polyvinyl chloride, polyester; polyacrylic; Viscose, modal, lyocell, polyethylene terephthalate, polystyrene, polyamide, acrylonitrile-butadiene-styrene copolymer, polymethyl methacrylate, polyoxymethylene, elastane, aramid, acetate, cupro, the radiation sensor (7) is designed as a quantum dot sensor, a spectral sensitivity of the quantum dot sensor (7) in the spectral band has at least one local maximum and at least one local minimum and the spectral properties of the quantum dot sensor (7) in the spectral band are matched to the spectral properties of the radiation source (2) and each of the two components (41, 24) in such a way that an output signal of the quantum dot sensor (7) is a monotonic function of the mixing ratio of the two components (41, 42). 5. Device (1) according to claim 2, wherein the two components (41, 42) of the textile fiber structure (4) are a pair from the following set: cotton and polyethylene, cotton and polypropylene, cotton and polyvinyl chloride, cotton and polyester; cotton and polyacrylic; cotton and viscose, cotton and polyethylene terephthalate, cotton and polystyrene, cotton and polyamide, cotton and acrylonitrile-butadiene-styrene copolymer, cotton and polymethyl methacrylate, cotton and polyoxymethylene. 6. System according to one of claims 1-3, or device (1) according to claim 4 or 5, wherein the at least one local maximum is at the wavelength or wavelengths of the electromagnetic radiation (3) at which the absolute value of the difference between the absorption coefficients, the transmission coefficients or the reflection coefficients of the two components (41, 42) has a local maximum. 7. Method according to one of the preceding claims, 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. 8. Method according to one of the preceding claims, wherein the spectral band has a width between 100 nm and 1500 nm and preferably between 300 nm and 500 nm. 9. System or device (1) according to one of the preceding claims, wherein the quantum dot sensor (7) includes at least one quantum dot layer (72-74) located between two electrodes (71, 75) and, for example, several quantum dot layers (72-74) stacked on top of one another with different band gaps. 10. System or device (1) according to one of the preceding claims, wherein the quantum dot sensor (7) is monolithically integrated on an integrated circuit, which is manufactured, for example, in CMOS technology. 11. System or device (1) according to one of the preceding claims, wherein the spectral properties of the quantum dot sensor (7) in the spectral band are matched to the spectral properties of the radiation source (2) and each of the two components (41, 24) such that an output signal of the quantum dot sensor (7) is a linear function of the mixing ratio of the two components (41, 42). 12. System or device (1) according to one of the preceding claims, comprising an optical imaging system (6) for imaging the textile fiber structure (4) onto the quantum dot sensor (7), wherein the quantum dot sensor (7) is spatially resolving and is designed either as a two-dimensional matrix sensor or as a one-dimensional line sensor. 13. System or device (1) according to one of the preceding claims, comprising a time-varying optical imaging system which images different locations of the textile fiber structure (4) one after the other onto the quantum dot sensor (7), wherein the quantum dot sensor (7) is time-resolved. 14. Use of the system or device (1) according to claim 12 or 13 for detecting a foreign material (42) in a base material (41), wherein the foreign material (42) and the base material (41) are the two components of the textile fiber structure (4). 15. Use of the system or device (1) according to one of claims 1-13 for determining a mixing ratio of the two components (41, 42) of the textile fiber structure (4). 16. Method (1) for examining a textile fiber structure (4) containing two components (41, 42), wherein electromagnetic radiation (3) in a spectral band is sent from a radiation source (2) in the direction of the textile fiber structure (4), at least a portion of the electromagnetic radiation (3) interacts with the textile fiber structure (4) and at least a portion of the electromagnetic radiation (5) is received by a radiation sensor (7) after the interaction with the textile fiber structure (4), characterized in that a quantum dot sensor is used as the radiation sensor (7), wherein a spectral sensitivity of the quantum dot sensor (7) in the spectral band has at least one local maximum and at least one local minimum and the spectral properties of the quantum dot sensor (7) 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) are coordinated such that an output signal of the quantum dot sensor (7) is a monotonic function of the mixing ratio of the two components (41, 42). 17. The method according to claim 16, 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. 18. The method according to claim 16 or 17, wherein the spectral band has a width between 100 nm and 1500 nm and preferably between 300 nm and 500 nm. 19. Method according to one of claims 16-18, wherein the two components (41, 42) of the textile fiber structure (4) are two different elements from the following set: cotton, linen, new wool, polyethylene, polypropylene, polyvinyl chloride, polyester; polyacrylic; viscose, modal, lyocell, polyethylene terephthalate, polystyrene, polyamide, acrylonitrile-butadiene-styrene copolymer, polymethyl methacrylate, polyoxymethylene, elastane, aramid, acetate, cupro. 20. The method according to claim 19, wherein the two components (41, 42) of the textile fiber structure (4) are a pair from the following set: cotton and polyethylene, cotton and polypropylene, cotton and polyvinyl chloride, cotton and polyester; cotton and polyacrylic; cotton and viscose, cotton and polyethylene terephthalate, cotton and polystyrene, cotton and polyamide, cotton and acrylonitrile-butadiene-styrene copolymer, cotton and polymethyl methacrylate, cotton and polyoxymethylene. 21. Application of the method according to one of claims 16-20 for detecting a foreign material (42) in a base material (41), wherein the foreign material (42) and the base material (41) are the two components of the textile fiber structure (4). 22. Application of the method according to one of claims 16-20 for determining a mixing ratio of the two components (41, 42) of the textile fiber structure (4).