Title of Invention

METHOD AND DEVICE FOR DETECTING IMPURITIES IN A LONGITUDINALLY MOVING THREAD-LIKE PRODUCT

Abstract

The invention relates to a method and device for the recognition of impurities in a longitudinally moving thread-like sample of textile fibres. According to the invention, in order to achieve a method and device with which contaminants or impurities can be recognised and removed, based upon essentially differentiated criteria a first parameter should be recorded on the sample, whereby a first signal (10) is generated, which indicates, where it is the case, impurities present. Additionally a further parameter on the sample is recorded, with generation of a second signal (11), which indicates, where it is the case, impurities present. From a combination of the first and second signal at least one particular type of impurity can now be determined.

Full Text

Method and device for detecting impurities in a longitudinally moving thread-like product The invention relates to a method and to a device for detecting impurities in a longitudinally moving thread-like product made .of textile fibres. A method and a device for detecting contaminants, in particular foreign fibres in elongate textile structures is known from US 5,414,520. Here the structure, for example a yarn, is illuminated by light in a first sensor and the extent of the light reflected on the yarn measured. Therefore, in particular, contaminants are detected of which the colour, structure or surface composition differs from that of the base material of the yarn. However, deviations in the mass or diameter of the yarn can also be detected at the same time. To eliminate these deviations the structure is illuminated from the opposite side in the same or in a different sensor, so the sensor accordingly measures the shadowing owing to the structure. If the signal produced by the reflection and the signal produced by the shadowing are now combined an impurity signal is produced which is liberated from the influence of the mass or the diameter of the structure. The blade of a yarn cleaner or the drive of a spinning machine on which the yarn cleaner is provided, is conventionally controlled by this impurity signal. A drawback of this known method and device for detecting contaminants is that every removal of a contaminant results in a cut and also joining of the adjacent portions of a yarn or strip, for example by splicing. If this occurs on a bobbin winding machine the winding head is stopped. If this occurs on a spinning machine the relevant spinning point is stopped. This means that removal of the contaminants, for example from textile yarns, during the production process causes losses in the output of the relevant machines owing to such stoppages. In particular in spinning machines these losses consist not only of periods which it requires to separate the yarn and join it again, other stoppage times can be effected if there is an obligatory pause until the joining apparatus, which conventionally has to service many spinning points, is available and has reached the dubious spinning point. Therefore on the one hand it is desirable to remove impurities or contaminants in order to avoid problems during subsequent processing, such as weaving, dyeing or improving. However, it is not desirable for the power of the machines to be impaired thereby. For these reasons it is desirable for, for example, the manufacturer of a textile intermediate product, such as strip, yarn etc., to be aware of whether and to what extent he wishes to remove contaminants or impurities in the strip or yarn. His possibilities for making a choice are, however, very limited as methods and devices in accordance with the above-mentioned patent only provide the opportunity of setting a threshold, beyond which a contaminant is removed or not. It is therefore an object of the present invention, as indicated in the claims, to create a method and a device with which contaminants or impurities can be detected and removed on the basis of substantially differentiated criteria. This is achieved in that as, for example already known, a first parameter is detected on the fast moving strip or yarn with a wave field, a first signal indicating potentially present contaminants or impurities being generated. This first parameter preferably detects reflection properties as can be detected on the surface of the product. In addition, a further parameter is to be detected on the strip or yarn in a field, a second signal being generated which also indicates contaminants or impurities. This second parameter preferably detects properties such as mass or diameter of the yarn or strip, as can be ascertained by measuring the shadowing of a wave field or the change in the capacity in an electrical field. Therefore a variable, optionally belonging to a group of variables, is determined as a second parameter, this group comprising the mass and diameter of a portion of the product. Separate evaluation criteria, for example limit values, are now allocated to the first signal and the second signal, both signals indicting contaminants or impurities. Finally, a specific type of impurity is ascertained from the evaluations of the first signal and the second signal or parameter, this type resulting from the selected evaluation criteria. Here it is particularly advantageous to ascertain the two parameters in fields which differ greatly owing to their physical properties. Therefore, very different fields can be used, for example light of different wave lengths or light and an electrical field etc. The two parameters or the signals derived therefrom are observed or detected over a predetermined time, possibly integrated and only after this time compared with the evaluation specifications or measured with respect thereto. These evaluation specifications are applied, for example, to distinguish between vegetable and non-vegetable impurities or contaminants in the product. The corresponding device has a first sensor operating with a wave field and a second sensor operating with a field, a processor connected to the first sensor and the second sensor with a memory for time-limited storage of the signals from the first sensor and the second sensor and software for the processor which presets the evaluation specifications for the first and second signals, with which a third signal, distinguishing at least two types of impurity, is generated from the first signal and the second signal. Light of a specific colour is preferably to be provided for the first sensor as a wave field, an electrical field for the second sensor-While a device for monitoring parameters of a running threadlike yarn is known from EP 0 401 600, in which a capacitively operating sensor and an optically operating sensor arranged adjacent to one another are provided and provide measured values derived from the yarn the evaluation of the two signals' is not, however, made with respect to the detection of contaminants or foreign fibres but with respect to the reduction in the dependence of the foreign influences, such as moisture, material influence, dependence on the shape etc., during measurement of the uniformity or for the promotion of operator-control. However, there is no differentiated detection of contaminants in the scope of this publication. A method and a device are known from GB 2,095,828 which are very similar to those from US 5,414,520. This is because the reflection and transmission of light on a fibre entanglement are also measured here. The formation of the relationship of the signals from the reflection the transmission lead to a signal allowing fibrous and vegetable faults to be distinguished. As a result of further investigations of these signals with respect to details on size, transparency to light and shape, a more precise classification of the faults may be made. This very extensive investigation of faults is, however, intended for non-wovens . which are not moved quicker than about 1.5 m/min and which consist of wool, wherein those elements not originating from sheep wool are also to be regarded as contaminants. In contrast, yarns, for example, are moved during spinning at 200 to 400 m/min and during winding at up to 2,500 m/min, so in such cases these complex investigations cannot be carried out in time. In the strip or yarn fibres consisting of plastics material, cords, human and animal hairs, feathers etc., which we are here calling non-vegetable contaminants or impurities, are particularly disruptive. With cotton as the base material for the yarn, for example, the leaf residues, husk portions, seed portions etc, from the cotton, which we are here' calling vegetable contaminants or impurities, are less disruptive. In other words, we are calling vegetable those elements originating from the cotton plant. We are calling elements or materials not originating from the cotton plant non-vegetable. However, these elements can still be natural products, such as hair or feathers. The advantages achieved by the invention can be seen, in particular, in that, on the one hand, the drawbacks during subsequent processing and, on the other hand, the drawbacks during production of the current intermediate product, such as the yarn or strip, can be avoided owing to a purposefully differentiated detection and elimination of the impurities in accordance with the aforementioned points of view. As an important example a distinction can be made between vegetable and non-vegetable impurities which is predetermined when i detecting contaminants in the form of an evaluation specification for the signals received. This means, for example, that only the non-vegetable contaminants could be removed and the vegetable contaminants could be left in the yarn. Such a differentiation results in the advantage that many contaminants do not have to be cut out of the yarn or strip, and these contaminants do not impair subsequent processing, for example dyeing, as the vegetable impurities take up the dye equally as well as the cotton, or as possible original differences in colour are compensated during bleaching. However, such a differentiation also results in the advantage that fewer cuts are made in the yarn and therefore the output of the spinning or bobbin winding machine is not reduced so drastically. The invention will be described in more detail hereinafter with reference to an example and to the accompanying figures, in which: Fig. 1 is a schematic diagram of the device according to the invention, Fig. 2 is a diagram of signals from two sensors of the device in Fig. 1, Fig. 3 is a diagram of dimensions of contaminants and of possible limits for signals connected therewith from the sensors, Fig. 4 is a further diagram of a device according to the invention and Fig. 5, 6, 7 and 8 are each diagrams of possible evaluation criteria. Fig. 1 shows, schematically, a device according to the invention. It consists of a first sensor 1, which can be constructed, for example, as an impurity sensor, as is known from EP 0 761 585. It also consists of a second sensor responding specifically to the mass or diameter of the yarn 3. A sensor 2 of this type is known, for example, from US 5,530r368. The sensors 1 and 2 are connected to a processor 6 via connections 4 and 5. The processor has a memory 7, a computer 8 and an output 9 for a differentiated impurity signal. The processor 6 contains software which presets the evaluation specifications for the first and second signals, with which a third signal 9, distinguishing at least two types of impurity, is generated from the first signal and the second signal."* Fig. 2 shows a first signal course 10 from the first sensor 1 and a second signal course 11 as originates from the second sensor 2. Both signal courses 10 and 11 are plotted over a time axis 12 and 13. Values for the reflection of the wave field on the yarn 3 are plotted over the axis 12 along an axis 14 and values for. the mass or diameter of the yarn 3 are plotted along an axis 15. Markings 16 and 17 indicate a time difference At proportional to the spacing of the two sensors 1 and 2 from one another and the speed at which the yarn is moved. T designates a time during which a signal is stored. Fig. 3 shows a possibility known per se of organising yarn faults, irrespective of whether they are connected with contaminants, in accordance with their length or increase in thickness, in that their size is entered into the field extending between axes 18 and 19. Values for the length of a fault are plotted along the axis 18 and values for the extent of the fault are plotted along the axis 19 transversely to the longitudinal direction of the arm. The lines 2 0, 21 and 22 indicate two of many possibilities as to how limits can be set in the yarn for faults or contaminants in the yarn or generally. Typically, such contaminants or impurities, which owing to their dimensions come to lie above and to the right of the lines 20, 21 or 22, are unacceptable or not desired. Fig. 4 shows a different embodiment of the device according to the invention, here with a strip or yarn 23 crossing a wave field 24 and a further field 25. A first sensor 26 and a second sensor 27 can be seen, the sensor 26 comprising, for example, a transmitter and a receiver for light and the sensor 27 comprising elements 28, 2 9 which are, for example, designed either as transmitter 28 and receiver 29 for light or as capacitor electrodes 28, 29. The two sensors 26, 27 are connected to a processor 6 via lines 30 and 31. An optionally present element 32 can serve to combine the signals from the lines 30 and 31 in order to generate a corrected impurity signal in the line 30. This is particularly the case if the sensor 27 is designed for a transmitted light measurement. Fig. 5 shows a diagram of evaluation criteria for a differentiated assessment of impurities or contaminants. For this purpose, values for the signal deviation in a wave field, such as the wave field 24, are plotted along a horizontal axis 33 and signal deviations in a field, such as the field 25, are plotted along a vertical axis 34. The numbers on the axis 33 relate, for example, to values for the reflection of the wave field on the product and the numbers of the axis 34 indicate values for the change in the capacity in a capacitor or in the transmission of light or waves generally. Here the values 0 represents averages or basic values and the numerical values indicated to the right and upwards are based on percentage deviations, or in particular, increases with respect to the basic values- 35 to 38 indicate ranges for the signals from the two sensors 1, 2 or 2 6, 27 in which certain contaminants or impurities are often located. These ranges 35 to 38 are indicated by value ranges on the two axes 33 and 34. The range 35 relates, for example, to individual fibres made of plastics material. The range 36 relates, for example, to strips of plastics material and fibre bundles. The range 37 relates, for example, to human and animal hair. The range 38 relates, for example, to cloth fragments, greasy fibre bundles or larger or coarser contaminants overall. Fig. 6 shows a diagram with measured values for contaminants which are plotted over axes 33, 34, as are already known from Fig. 5, but here have a different graduation of the numerical values. F designates undesired foreign fibres. For this purpose, a limit value 39 is drawn in which, based on the signals as shown on the axis 34, exceeds the basic value by 25%. Fig. 7 shows a further diagram with measured values for contaminants which are plotted over axes 33, 34, as are already known from Fig. 5, but here having a different graduation of the numerical values. Undesired foreign fibres are designated by the rectangular symbols. For this purpose a limit 4 0 is drawn in which follows a function y = f(x) if x designates the values along the axis 33 and y the values along the axis 34. Fig. 8 shows a further diagram with measured values for contaminants which are plotted over axes 33, 34, as are already known from Fig. 5, but here having a different graduation of the numerical values. Contaminants of vegetable origin are here designated by small rhombusses R, undesired fibres by small squares Q, residues of plastic strips by small triangles D, black hair by further squares Q' and residues of materials by small squares Q,f. For this purpose, a limit 41 is drawn in which follows a function y = f(x) + X if x designates the values along the axis 33 and y the value along the axis 34. Fig. 6 to 8 therefore show signals as can occur in the lines 4 and 5 but wherein here the course over time is not taken into account. The circumstance where the values of the signals are vertically superimposed is only caused where only certain discrete values are shown for the values of the axis 33. The mode of operation of the device and the method are as follows: In the first sensor 1, 26 the strip or the yarn 3, 23 are exposed to a wave field 24, for example, light, for detecting a first parameter and a measurement is made as to how much light or wave energy can be detected again by reflection on the product. Here it is assumed that the reflection changes if impurities occur in the sensor 1, 26 and the signal, produced in the sensor 1, 26, differs from a basic value, determined by the base material. For example, the reflection changes if differently coloured fibres or plastic parts suddenly occur in the yarn. The signal produced in the process can, in addition, as known from US 5,414,520, be modified by a diameter or mass influence and could have a course as is designated in Fig. 2 by 10. The first parameter is therefore the intensity of the reflected wave field or light here, as is drawn, for example, in per cent along the axis 33 in Fig. 5 to 8 proceeding from a basic value. To neutralise the influence of the mass of the strip or yarn in the signal in line 30 (Fig. 4) it is combined in the element 32 in a known manner with the signal from the line 31. In the second sensor 2 a signal, offset by a time At is generated, for example in a capacitively operating sensor 2, 27, which is proportional to the mass or to the diameter of the yarn 3, 23 in the detected portion. The signal resulting in this process (Fig. 2) could have a course as is designated in Fig. 2 by 11. In each case a further parameter is therefore detected on the yarn in the form of an increase in diameter or mass, as is drawn, for example, in per cent also along the axis 34 in Fig. 5 to 8 proceeding from a basic value. The two signals are accordingly input via the lines 4, 5 or 30', 31, into the memory 7 of the processor 6 where they are stored. The time T during which they are stored is dependent on the evaluation criteria used. For example on when, from which length or limit an impurity begins to be perceived to be disruptive. It is known, for example from the yarn test that very short faults are also not disruptive if the increase in diameter owing to the fault is large, for example 100%. Therefore, for the. first and second signals variables also have to be preset above which there is a disruptive impurity and below which there is no disruptive impurity or it should simply be disregarded. Such limits are indicated in Fig. 3 and 5 to 8 and they can be preset for the length and the increase in thickness or mass of the product owing to the impurity, and also for the extent and duration of a reflection deviating from a basic value. This time T should accordingly also exceed at least the time which corresponds to the speed of the yarn multiplied by the length in accordance with the limit (line 21) for the length of the signal or the contaminant. This time T should preferably also be lengthened by the time At, so in a time segment 4 2 two signals are simultaneously present for a sufficiently long time. In principle, only signals exceeding certain limits 20, 21 or 22 (Fig. 3) should be subjected to the evaluation criteria, the limit 22 following a function making the two limits for the length and the thickness mutually dependent. The following table 1, for example, can provide a simple evaluation criteria. Table 1 Here it can be determined, for example, that events allowing both signals 1 and 2 to exceed the limit individually determined for each signal should apply as the sought impurity. This can be described in more detail with reference to Fig. 5 to 8. In the diagram of Fig. 5 ranges 35 to 38 can be detected for impurities or contaminants which are potentially all undesirable. If this is the case then a limit, as can be shown by a line 43, is valid as an evaluation criterion. In this case only those contaminants are recognised and possibly eliminated Claims Method for detecting impurities in a longitudinally moving r;hread-like product (3) made of textile fibres, characterised in that a first parameter is detected on the product in a wave ield, a first signal (10) indicating potentially present -mpurities being generated, in that, in addition, a further parameter is detected on the product in a field, a second signal (11) indicating potentially present impurities being generated, in that separate evaluation specifications are allocated to the i irst signal and second signal for the evaluation thereof, and .in that a specific type of impurity is ascertained from the • valuated first and second signals - Method according to claim 1, characterised in that a variable is determined as the second parameter which optionally lolongs to a group of variables, this group comprising the mass ;nd the diameter of a portion of the product. Method according to claim 2, characterised in that the variables of this group are detected capacitively. ;. Method according to claim 1, characterised in that the . .vadowing and the reflection of the wave field on the product ;re measured to detect the first parameter and in the process • wo signals are produced which combined provide the first signal •'0') . Method according to claim 1, characterised in that the Irst and the second signal are stored over a time (T), and in ■ hat the two stored signals are evaluated, starting from an -valuation specification, and the type of impurity is determined from the evaluation. Method according to claim 1, characterised in that the -valuation specification is designed such that a distinction is eide between vegetable and other impurities. Method according to claim 6, characterised in that the evaluation specification presets a limit (20, 21, 22, 31) for at Least one the two signals, the limit having to exceed the signal t o indicate the one type of impurity. Method according to claim 1, characterised in that' visible ught is used as the wave field. '.-. Device for carrying out the method according to claim 1, :haracterised by a first sensor (1) operating with a wave field, a second sensor (2) operating with a field, a processor (6) connected to the first sensor and the second sensor with a :vomory (7), for time-limited storage of the signals from the :irst sensor and the second sensor and owing to software for the processor presets the evaluation specifications for the first :iid second signals with which a third signal, distinguishing at . east two types of impurity, is generated from the first signal :eci the second signal. "›. Device according to claim 9, characterised in that limits : 9, 4 0, 41, 43) are preset for the signals as evaluation .'pacifications. 11 A method for detecting impurities in a longitudinally moving thread like product nbstantially as herein described with reference to the accompanying drawings.

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