Abstract:
A first parameter is detected on a fast moving strip or yarn with a wave field, and a first signal indicating potentially present contaminants or impurities is generated. This first parameter preferably detects reflection properties that can be detected on the surface of the product. A further parameter is detected on the strip or yarn in a field, and a second signal is generated which also indicates contaminants or impurities. This second parameter preferably detects properties such as mass or diameter of the yarn or strip. Evaluations of the first signal and the second signal that occur at the same location on the product are considered together, and labeled to indicate the specific type of impurity or contaminant that they represent. Using empirical analysis, evaluation specifications can be selected to identify a group of impurities which are most likely to include a specific impurity of interest, e.g. non-vegetable contaminants.

Description:
[0001]    This disclosure is based upon Swiss Application No. 1092/00 filed May 31, 2000, and International Application No. PCT/CH01/00293 filed May 14, 2001, the disclosures of which are incorporated herein by reference.  
         FIELD OF THE INVENTION  
         [0002]    The present invention relates to a method and device for detecting impurities in a longitudinally moving thread-like product made of textile fibers.  
         BACKGROUND OF THE INVENTION  
         [0003]    A method and device for detecting contaminants, in particular foreign fibers in elongate textile structures, are known from U.S. Pat. No. 5,414,520. The structure, for example a yarn, is illuminated with light in a first sensor and the extent of the light reflected by the yarn is measured. As a result, contaminants are detected whose color, 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 combined, an impurity signal is produced which is independent of the influence of the mass or the diameter of the structure. The cutting blade of a yarn clearer, or the drive of a spinning machine on which the yarn clearer is provided, is conventionally controlled by this impurity signal, to remove detected contaminants.  
           [0004]    Every removal of a contaminant results in a cut and subsequent 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 affected machines owing to such stoppages. In particular, in spinning machines these losses consist not only of the periods of time required 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 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.  
           [0005]    For these reasons it is desirable, for example, for 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 if he only has the opportunity to set a threshold, beyond which a contaminant is removed or not.  
           [0006]    It is therefore an object of the present invention to provide a method and a device with which contaminants or impurities can be detected and removed on the basis of substantially differentiated criteria.  
         SUMMARY OF THE INVENTION  
         [0007]    In accordance with the invention, a first parameter is detected on a fast moving strip or yarn with a wave field, and a first signal indicating potentially present contaminants or impurities is generated. This first parameter preferably detects reflection properties that can be detected on the surface of the product. In addition, a further parameter is detected on the strip or yarn in a field, and a second signal is generated which also indicates contaminants or impurities. This second parameter preferably detects properties such as mass or diameter of the yarn or strip, which can be ascertained by measuring the shadowing of a wave field or a change in the capacitance in an electrical field. Therefore a variable, optionally belonging to a group of variables, is determined as a second parameter, this group including the mass and diameter of a portion of the product. Separate evaluation criteria, for example limit values, are allocated to the first signal and the second signal, both signals indicating possible contaminants or impurities. Finally, the evaluations of the first signal and the second signal or parameter that occur at the same location on the product are considered together, and labeled to indicate the specific type of impurity or contaminant that they represent. Thus, the type of impurity is associated with the selected evaluation criteria. Using empirical analysis, evaluation specifications can be selected to identify a group of impurities which are most likely to include a specific impurity of interest, e.g. non-vegetable contaminants.  
           [0008]    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 wavelengths 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.  
           [0009]    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. A third signal, for selecting impurities likely to include an impurity of interest, is generated from the first signal and the second signal. Light of a specific color is preferably provided for the first sensor as a wave field, and an electrical field for the second sensor.  
           [0010]    A device for monitoring parameters of a running threadlike yarn is known from EP 0 401 600. In this device, a capacitively operating sensor and an optically operating sensor arranged adjacent to one another 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 fibers, but rather with respect to the reduction in the dependence of foreign influences, such as moisture, material influence, dependence on the shape, etc., during measurement of the uniformity or for the promotion of operator-control. There is no disclosure of differentiated detection of contaminants in this publication.  
           [0011]    A method and a device are known from GB 2,095,828 which are very similar to those from U.S. Pat. No. 5,414,520. Specifically, the reflection and transmission of light on a fiber entanglement are also measured here. The formation of the relationship of the signals from the reflection and 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.  
           [0012]    In a strip or yarn, fibers consisting of plastic material, cords, human and animal hairs, feathers etc., are referred to herein as non-vegetable contaminants or impurities, and are particularly disruptive. With cotton as the base material for the yarn, for example, leaf residue, husk portions, seed portions etc. from the cotton, which constitute vegetable contaminants or impurities, are less disruptive. In other words, vegetable contaminants are those elements originating from the cotton plant. Elements or materials not originating from the cotton plant are called non-vegetable. However, these elements can still be natural products, such as hair or feathers.  
           [0013]    The advantages achieved by the invention can be seen in that, on 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 classification and elimination of selected impurities in accordance with the aforementioned points of view. As an example, a class of impurities which is most likely to contain non-vegetable impurities can be predetermined when detecting contaminants in the form of an evaluation specification for the signals received. This means, for example, that most or all of the non-vegetable contaminants could be removed, while many vegetable contaminants could be left in the yarn. Such a classification results in the advantage that many contaminants do not have to be cut out of the yarn or strip. These contaminants do not impair subsequent processing, for example dyeing, since the vegetable impurities take up the dye equally as well as the cotton. Alternatively, possible original differences in color might be compensated during bleaching. However, such a classification 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. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    The invention will be described in more detail hereinafter with reference to an example and to the accompanying figures, in which:  
         [0015]    [0015]FIG. 1 is a schematic diagram of a device according to the invention,  
         [0016]    [0016]FIG. 2 is a diagram of signals from two sensors of the device in FIG. 1,  
         [0017]    [0017]FIG. 3 is a diagram of dimensions of contaminants and of possible limits for signals connected therewith from the sensors,  
         [0018]    [0018]FIG. 4 is a further diagram of a device according to the invention and  
         [0019]    [0019]FIGS. 5, 6,  7  and  8  are each diagrams of possible evaluation criteria.  
     
    
     DETAILED DESCRIPTION  
       [0020]    [0020]FIG. 1 shows, schematically, a device according to the invention. It includes a first sensor  1 , which can be constructed, for example, as an impurity sensor, as is known from EP 0 761 585. It also includes a second sensor  2  responding specifically to the mass or diameter of the yarn  3 . A sensor  2  of this type is known, for example, from U.S. Pat. No. 5,530,368. 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 classes of impurity, is generated from the first signal and the second signal.  
         [0021]    [0021]FIG. 2 shows a first signal  10  from the first sensor  1  and a second signal  11  from the second sensor  2 . Both signals  10  and  11  are plotted over time axes  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 Δt 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.  
         [0022]    [0022]FIG. 3 shows one known way of organizing 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, transverse to the longitudinal direction of the yarn, are plotted along the axis  19 . The lines  20 - 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.  
         [0023]    [0023]FIG. 4 shows another embodiment of the device according to the invention, 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 ,  29  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.  
         [0024]    [0024]FIG. 5 shows a diagram of evaluation criteria for a classified 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 on the axis  34  indicate values for the change in the capacitance 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  26 ,  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 fibers made of plastic material. The range  36  relates, for example, to strips of plastic material and fiber bundles. The range  37  relates, for example, to human and animal hair. The range  38  relates, for example, to cloth fragments, greasy fiber bundles or larger or coarser contaminants overall.  
         [0025]    [0025]FIG. 6 shows a diagram with measured values for contaminants which are plotted over axes  33 ,  34 , similar to FIG. 5, but here have a different graduation of the numerical values. Each data point in the diagram represents a specific impurity in one or more samples of strips or yarns that are measured by the sensors. The data points labeled F designate impurities that contain undesired foreign fibers. These labels are manually assigned by visually inspecting the strip or yarn samples to determine the type of impurity that is associated with each data point. Since impurities containing foreign fibers are of interest, the specific data points associated with those impurities are identified.  
         [0026]    In the example of FIG. 6, it can be seen that most of the impurities containing foreign fibers are within the class of impurities in which the value on the axis  34  is below 25%. Accordingly, a limit value  39  can be selected which, based on the signals as shown on the axis  34 , indicates this class of impurities.  
         [0027]    [0027]FIG. 7 shows a further diagram with measured values for contaminants for a different set of samples, which are plotted over axes  33 ,  34 , similar to FIG. 5, but here having a different graduation of the numerical values. Undesired foreign fibers are designated by the rectangular symbols. For this example a limit  40  is selected which follows a function y=f(x), where x designates the values along the axis  33  and y the values along the axis  34 . This limit  40  is empirically selected from visual inspection of the labeled data points, to indicate the class of impurities which contain most of the foreign fibers.  
         [0028]    [0028]FIG. 8 shows a further diagram with measured values for contaminants in another set of samples, which are plotted over axes  33 ,  34 , as in FIG. 5, but here having a different graduation of the numerical values. Contaminants of vegetable origin are designated by small rhombusses R, undesired fibers 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″. Again, each of these labels are manually applied as a result of visual inspection of each impurity which generated a data point in the diagram. For this set of samples, a limit  41  is drawn which follows a function y=f(x)+x, where x designates the values along the axis  33  and y the value along the axis  34 . The limit  41  indicates the class of impurities that contain the majority of each of the undesirable types of contaminants.  
         [0029]    FIGS.  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. In other words, all of the impurities are depicted on a common graph, independent of their relative locations in the samples. The circumstance where the values of the signals are vertically superimposed is due to the fact that only certain discrete values are shown for the values of the axis  33 .  
         [0030]    The mode of operation of the device and the method are as follows:  
         [0031]    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 colored fibers or plastic parts suddenly occur in the yarn. The signal produced in the process can, in addition, be modified by a diameter or mass influence and could have a profile as is designated in FIG. 2 by  10 , as known from U.S. Pat. No. 5,414,520. The first parameter is therefore the intensity of the reflected wave field or light, as is drawn, for example, in percent values along the axis  33  in FIGS.  5  to  8  proceeding from a basic value. To neutralize 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 .  
         [0032]    In the second sensor  2  a signal, offset by a time Δt, 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 profile 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 percent values also along the axis  34  in FIGS.  5  to  8  proceeding from a basic value.  
         [0033]    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, the criteria could be the 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 not disruptive if the increase in diameter owing to the fault is large, for example 100%. Therefore, limit values for the first and second signals variables are preset at a level that distinguish a disruptive impurity from a non-disruptive impurity that should simply be disregarded. Such limits are indicated in FIGS. 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 Δt, so in a time segment  42  two signals are simultaneously present for a sufficiently long time.  
         [0034]    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.  
         [0035]    The following table 1, for example, can provide a simple evaluation criteria.  
                                             TABLE 1                                   &gt; Limit value   &gt; Limit value                                        Signal 1   yes   no           Signal 2   yes   no                      
 
         [0036]    Here it can be determined, for example, that events causing both signals  1  and  2  to exceed the limit individually determined for each signal designate an instance of the sought impurity. This can be described in more detail with reference to FIGS.  5  to  8 .  
         [0037]    In the diagram of FIG. 5, ranges  35  to  38  can be detected for impurities or contaminants which are potentially undesirable. If this is the case then a limit, as shown by a line  43 , is valid as an evaluation criterion. In this case only those contaminants are recognized and possibly eliminated which generate signals located below the line  43 , i.e. exceed the basic value in accordance with axis  34  but not the limit in accordance with line  43 . An increase of at least 5% for values of the axis  33  is also demanded. If, however, by way of example, only those contaminants which are located roughly in the region  38  are to be detected, then a line  44  could be provided as a limit instead of the line  43 . Values for the reflection in the wave field are preferably drawn along the axis  33  and values for the increase in the capacity in an electrical field along the axis  34 . If the reflection on the strip or yarn is detected, for example with light of a particular color, then distortions occur as contaminants of the same color will only emit an insufficient signal, so, for example, they are seemingly located in a region  45  instead of beyond the line  43  or  44 . If, however, the second parameter is measured in an electrical field then the contaminant can nevertheless be easily detected by large values along the axis  34 . Therefore insufficiencies of the one sensor can be compensated by the other sensor. For this purpose, it would then also be proper to displace the limits accordingly.  
         [0038]    It can be seen in FIG. 6 that, with the limit value  39  in this case, 89% of the undesirable impurities are selected, but the class identified by the limit value  39  only simultaneously includes 12.8% of the harmless contaminants. This result is obtained by counting out the recorded events.  
         [0039]    It can be seen in FIG. 7 that with the limit  40  in this case virtually all undesirable impurities can be selected with the identified class.  
         [0040]    It can be seen in FIG. 8 that with the limit  41  in this case all undesirable impurities can be selected with the identified class. In addition, about 16% of harmless contaminants per se are simultaneously selected.  
         [0041]    To distinguish between primarily vegetable and non-vegetable contaminants it is advantageous to detect a parameter in an electrical field. With capacitive detection it is namely the mass of the yarn or impurity which influences the signal and it does this to a much greater extent. This can be seen if it is imagined how small a change in mass affects the diameter. For example, with a cylindrical body an increase in the diameter of 10% produces an increase in the mass of 21%. However, this change in mass alone cannot be used to detect impurities as they also influence the surface of the strip or yarn. Therefore a further parameter is investigated and only the joint evaluation of both parameters produces a good result. If the desired classification between desired or tolerated and primarily undesirable impurities exists, the separating stage of a clearer for the strip or yarn can be controlled with the signal in output  9  (FIG. 1).