Title of Invention

A METHOD AND APPARATUS FOR DETERMINING THE PROPORTION OF A FOREIGN SUBSTANCE IN A TEST YARN

Abstract

The invention relates to a method and a device for determining proportions of solid matter in a test material. In order to provide a method and a device of the said type by means of which proportions of solid matter in a test material can be easily and reliably determined, even in the case of transparent matter or matter of a similar colour to the test material, the test material is exposed to an electric field and dielectric properties of the field with, the test material are determined. Two electrical quantities (6Cfl, 6Cf2 or U, cos) are determined from the dielectric properties and combined, resulting in a characteristic value which is independent of the mass of the test material. The characteristic value is compared with a previously determined characteristic value for the matter in question and the proportion of solid matter is determined therefrom. (fig 1)

Full Text

METHOD AND DEVICE FOR DETERMINING PROPORTIONS OF SOLID MATTER IN A TEST MATERIAL The invention relates to a method and a device for determining proportions of solid matter in a test material. One example of the determination of proportions of solid matter in a test material is the detection of foreign matter and foreign fibres in a textile formation. In this case the detection is usually carried out by optical means. For example, foreign matter and foreign fibres are to be detected by their reflection properties, which in the majority of known cases differ from the reflection properties of the pure textile formation. The textile formation is therefore subjected to light. The light absorbed by the test material and/or the reflected light is then detected. Instantaneous or local deviations of the quantity of light received give an indication of the sought proportion of desirable and undesirable matter. A disadvantage of known methods and devices of this kind lies in the failure to detect colourless, transparent or translucent matter such as, for example, polypropylene sheets, or matter of a similar colour, such as cables or cords, which are used when packing raw textile materials such as cotton, etc. This results in parts of such polypropylene sheets, cables and cords being subsequently processed with the raw material, so that these are later enclosed in a yarn, for example. It is also possible to detect solid matter such as polypropylene parts when spun in a yarn. In this respect it is assumed that tjiis matter or these polypropylene parts change (s) the structure of the yarn and, for example,, the hairiness in a section of the yarn in particular. This is detected when measuring the diameter, for example by a change in the mass of the yarn or in the hairiness due to polypropylene parts projecting from the yarn here instead of hairs. Attempts have therefore been made in this case to detect foreign parts by measuring the diameter, the mass or the hairiness. One disadvantage of this detection of proportions of solid matter or of foreign matter by measuring the diameter or the hairiness lies in the fact that a lot of foreign matter is not detected. This is primarily when it is not located at the surface of the test material. As a result, unfavourable proportions of solid matter and foreign matter give rise to an end product which is weakened or comprises defects. However a product of this kind may also be the cause of difficulties during subsequent processing, so that a defect-free end product cannot be produced. The invention as characterised in the claims therefore solves the object of providing a method and a device of the said type by means of which proportions of solid matter in a test material can be easily and reliably determined, even in the case of transparent matter or matter of a similar colour to the test material. This is achieved by exposing the test material to an electric field and determining dielectric properties of the field with the test material. In order to determine the dielectric properties of the field, electrical measurable quantities are measured, from which at least two electrical quantities are determined and combined, resulting in a characteristic value which is independent of the mass of the test material. The characteristic value is compared with comparative values, and information on the proportion of solid matter or the change thereof in the test material is obtained from the comparison. The dielectric properties can be detected on the basis of a plurality of electrical quantities. A first possibility lies, for example, in determining, as an electrical quantity, the change in capacitance caused by the test material or the relative permittivity €r in an electric alternating field at at least two frequencies from measurable quantities such as voltage, current, phase shift between voltage and current and any reference resistances, and forming therefrom a quotient as a characteristic value. A second possibility lies, for example, in determining, as a characteristic value, electrical quantities such as the power factor cos of the change in capacitance caused by the test material and thus of the actual test material from measurable quantities such as voltage, current, phase shift between voltage and current and any reference resistances. The characteristic value determined from the electrical quantities by, for example, forming a quotient, remains constant as long as the proportion of solid matter in the test material remains constant. Should the proportion, change, this is indicated by a corresponding change in the characteristic value. The absolute proportion of solid matter in the test material may also be determined by forming a relation from the constant characteristic value and from the changed characteristic value. The device consists of*at least one precision capacitor, which is disposed in the region of the test material to create an electric field, a frequency generator connected to the capacitor to generate at least one frequency in the electric field, measuring elements connected to the frequency generator for electrical measurable quantities and an evaluation circuit for forming the electrical quantities and the characteristic value and for comparing the characteristic value with predetermined values. In order to be able to cancel out the basic capacitance of the capacitor without the test material, a reference capacitor, connected to the same or to an inverted signal source, may be provided. The frequency generators preferably form a bridge circuit with the precision capacitor and the reference capacitor. The dielectric properties of a field are represented by at least one quantity from a group of electrical quantities comprising capacitance, relative permittivity, loss angle and power factor. The advantages achieved by the invention lie in particular in the fact that it enables the most varied foreign matter, compositions or proportions of solid matter in a test material to be detected, irrespective of whether certain matter is visible, invisible or of a similar colour to the test material or whether it occurs inside or at the surface. The means provided for carrying out the method are of a simple structure and allow it to be combined problem-free with other measuring devices which measure other parameters in pursuit of other objects. The invention is illustrated in detail in the following on the basis of an example and with reference to the accompanying figures, in which: Figure 1 is a diagrammatic and simplified representation of a first device, Figures 2 and 3 are graphical representations of physical relations and Figures 4 to 6 are further constructions of the device according to the invention. Figure 1 shows a first construction of a device according to the invention with a precision capacitor 1 for an elongate test material 2 moved longitudinally such as, for example, a yarn, roving, tape, filament, etc. The precision capacitor 1 is connected on one side via a resistor 3 to a frequency generator 4 and on the other to earth. One output 5 of the precision capacitor 1 is connected via an amplifier 6 to one input 7 of an evaluation circuit 8. The same output 5 is also connected to one input 9 and via the resistor 3 to the other input 10 of an operational amplifier 11, which is connected in parallel with the resistor 3. The output of the operational amplifier 11 forms a further input 12 for the evaluation circuit 8. The inputs 7 and 12 are connected in the evaluation circuit 8 to measuring elements 13, 14, which are known per se, for electrical quantities. The evaluation circuit 8 has an output 15. Figure 2 is a graphical representation with two axes 16 and 17. Values for frequencies of an electric field are plotted along the axis 16 and values for the relative permittivity €r of the same field along the axis 17. Curves 18, 19 and 20 therefore present the relative permittivity er as a . function of the frequency for fields with a test material l of cotton with 68% moisture, of cotton with 47% moisture and of polypropylene., It can be seen here that the relative permittivity for polypropylene according to curve 20 is largely independent of frequency, while the relative permittivity for cotton is highly frequency-dependent, as ) shown by the curves 18 and 19. The frequency dependency increases with the moisture content. As the change in capacitance of the precision capacitor changes proportionally with the relative permittivity, the same relative dependency on frequency applies to'the change in i capacitance. However the change in capacitance is at the same time also influenced by the mass of the test material. Figure 3 is a graphical representation with two axes 21 and 22. Values for frequencies of an electric field are plotted along the axis 21 and values for the power factor cos0 of the test material, for different materials, along the axis 22. Curves 23, 24 and 25 therefore present the power factor cos0 as function of the frequency for cotton with 68% moisture, for cotton with 47% moisture and for polypropylene as the test material. Whereas the power factor of polypropylene is largely independent of frequency, the power factor of cotton is highly frequency-dependent. Here too the dependency increases with the moisture content of the cotton. However the power factor of the change in capacitance of the precision capacitor is independent of the mass of the test material. Figure 4 shows a second construction of a device according to the invention with two precision capacitors 35 and 36 for an elongate test material 37 moved longitudinally such as, for example, a yarn, roving, tape, filament, etc. The precision capacitors 35, 36 are connected on one side via resistors 38, 39 to earth and on the other to a respective frequency generator 40, 41. The precision capacitors 35, 36 are connected via lines 42, 44 and 43, 45 to an evaluation unit 46 which, for example, is formed as a processor and has an output 47. Figure 5 is a simplified representation of a third construction with a precision capacitor 50, a reference capacitor 51 and a frequency generator 52. A tap 53 lies between the capacitors 50 and 51, with each of which an inverting or non-inverting amplifier 54, 55, respectively, is associated. Also provided is an evaluation circuit 57, which is connected via the tap 53 and a line 56. Figure 6 is a simplified representation of a fourth construction with a precision capacitor 60, a reference capacitor 61 and a frequency generator 62. A tap 63 lies between the capacitors 60 and 61, with each of which an inverting or non-inverting amplifier 64, 65, respectively, is associated. Another frequency generator 66 is also connected in series here with the frequency generator 62. The tap 63 leads into an element 61 for frequency separation with two outputs 68, 69. The invention operates in the following mode: In order to determine proportions of solid matter such as, for example, the proportion of polypropylene in a cotton yarn or cotton tape, the test material and hence the cotton yarn or cotton tape is placed in an electric alternating field which is produced with, alternating current of a. certain frequency fl. This produces an electric alternating field whose dielectric properties are determined not just by measurable values such as current, voltage and phase angle, but also by the preset frequency. The dielectric properties may here be expressed in particular by the relative permittivity er and/or the power factor cos#. It is also possible to repeat this operation in further electric alternating fields with further frequencies f2, f3, etc. and then also obtain second, third, etc. differing values for the relative permittivity er and the power factor cos0. If the values which express the dielectric properties for the matter present in the test material are known separately, as represented, for example, in Figures 2 and 3, the proportion of the matter in the test material can be determined from these. There are various possibilities for this. A first possibility lies in determining the change in capacitance AC of the precision capacitor, as a consequence of a test material introduced therein, at at least two frequencies fl, f2, ... of the measuring field in the precision capacitor from the dielectric properties and the quantity of matter. This is effected on the one hand for pure test material such as polypropylene or cotton by calculation with values from Figure 2 and on the other by measuring corresponding values of the dielectric properties at the precision capacitor with actual test material. Assuming that the test material consists of two types of matter, the said change in capacitance of the precision capacitor with a test material consisting of just one of these types of matter in each case can be calculated using values from Figure 2. From this it is possible to determine the change in capacitance of the precision capacitor with pure and with actual test material at two or more frequencies. A quotient can be determined as the characteristic number from the determined changes in capacitance at different frequencies for the test material, this quotient ideally being 1 for polypropylene and > or A second possibility lies in determining in a known manner, from the electrical measurable quantities which characterise an electric field, the power factor cos# of the change in capacitance caused by the test material introduced into the field. However this power factor is independent of the mass of the test material, which is why it is sufficient to determine the power factor for pure test material and the power factor for actual test material. A characteristic number which is proportional to the proportion of one of the types of matter in the test material can be determined from the two power factors according to a formula reproduced in the following and can also be monitored. In the device according to Figure 1 the test material 2 in the precision capacitor 1 is exposed to an electric field with a frequency fl. The precision capacitor 1 is fed with appropriate alternating currents from the frequency generator 4 via the resistor 3, resulting in an alternating field with a frequency fl in the gap in the precision capacitor 1. The voltage at the output 5 of the precision capacitor 1 is amplified in the amplifier 6 and applied to the input 7, so that this voltage is quantified in the measuring element 14 and then fed to the evaluation circuit 8. The voltage across the resistor 3 is amplified in the operational amplifier 11 and fed via the input 12 to the measuring element 13, where it is likewise quantified. As the resistor 3 is known, the evaluation circuit 8 can also calculate the current in the resistor 3 from this. The change in capacitance of the precision capacitor 1 caused by the test material can be determined according to laws which are known per se from this and from the fixed quantities known for the precision capacitor 1. The power factor cos0 is also determined by measuring the phase difference between the current and the voltage. The values for the power factor cos of the change in capacitance are independent of the mass of the test material 2 in the precision capacitor 1. This change in capacitance is determined in the evaluation circuit 8 using values from the measuring elements 13, 14 and other fixed inputs. The evaluation circuit 8 may be formed as an electric circuit or as a computer which digitally processes measured values and inputs. The evaluation circuit delivers via the output 15 a signal which indicates the presence of other solid matter in the test material or a changed proportion of one of the types of matter. A signal of this kind may be continuously delivered by the evaluation unit 8, processed to form mean values therein and compared with mean values of this kind or other reference values. Distinct deviations then point to changes in the composition of the test material 2. In order to quantify the proportion of a solid matter in the test material 2, it is assumed that the matter forming the test material 2 is known. For example, the test material 1 consists of cotton with 47% moisture and possibly polypropylene. Power factors for this matter at arbitrary frequencies fl, f2 can be read from Figure 3. Assuming that the proportions of both types of matter together amount to 100% of the mass of the test material 2, the proportion of the first matter can be determined according to the following formulae (1) and (2). In the device according to Figure 4 the test material is moved through two precision capacitors 35, 36 in succession, these producing fields of different frequencies fl, f2, as produced by a.c. voltages, which are supplied by the frequency generators 40, 41. The evaluation unit 46 therefore receives values for currents and voltages at two different frequencies in parallel via the lines 42 to 45. Changes in capacitance can be calculated from these values and, in turn, a characteristic number from these changes. All the values which 'are represented in Figure 2 are stored as tables in the evaluation unit 46 for this purpose. The proportion of a first matter Kl in the test material is therefore obtained from the formula (1): Kl « (A - F2)/(F1 - F2) . The proportion of the second matter is obtained from the formula (2): K2 = (A - F1)/(F2 - Fl) . Here the values Fl and F2 are the ratios of the relative permittivities of cotton and polypropylene at the first frequency fl and at the second frequency f2. The factors Fl and F2 are therefore obtained by forming a quotient, for example, from the values 26/28 and 27/29 from Figure 2. & corresponds to the quotient of the changes in capacitance .in the precision capacitor for the actual test material or the characteristic number already known. In the device according to Figure 5 an a.c. voltage with a frequency is produced in the frequency generator 52, fed to the two amplifiers 54, 55 and from these applied to both capacitors 50, 51. A phase shift of 180° is produced in the amplifier 55, for example, by delaying the signal, so that the capacitors 50, 51 are each supplied with a signal 70, 71 which cancel each other out. A zero voltage is thus present at the tap 53 at least when there is no test material in the precision capacitor 50. All influences of the empty capacitors are in this way neutralised. The signal at the tap 53 changes as soon as a test material is introduced into the precision capacitor 50. The cosine of the phase angle of the signal is the inverse of the power factor cos0 of the test material in the precision capacitor 50 and independent of the quantity of test material. The mixture ratio of the two types of matter in the test material can be determined from the power factor by a simple rule of alligation with the values from Figure 3 for the frequency of the applied a.c, voltage. This takes place in the evaluation circuit 57, which also receives via the line 56 information on the phase angle of the unamplified signal, which is not influenced by the capacitors 50 and 51, of the frequency generator 52. The operations in the device according to Figure 6 are ) identical to those in the device according to Figure 5, although with the difference that a signal with two superimposed frequencies is applied to the capacitors ,60, 61 by the two frequency generators 62, 66, which signal is resolved into its two frequencies in the element 67. The 5 ratio of the two components in the test material can be determined as is known for the device according to Figure 4. This construction, as well as that according to Figure 5, has the advantage with respect to the construction according to Figure 4 of the influence of the empty capacitor being compensated by the bridge circuit principle. The signal voltage is zero when the precision capacitor is empty and this voltage changes proportionally with the dielectric properties of the test material and the quantity thereof. As this method enables the proportions of solid matter in a test material to be determined, a prerequisite is for proportions of non-solid matter, such as water, in one of the types of matter for measurement to be constant. For example, the moisture in the cotton must be known and constant before measuring takes place. However this is the case in the textile industry anyway, for most operations relating to the processing of raw materials take place in air-conditioned spaces. The capacitive detection of foreign matter and the proportions thereof in a test material may be combined with the measurement, known per se, of other parameters such as, e.g. uniformity, mass, etc., as a signal can be used both for measuring such parameters and for detecting the proportions of foreign matter. As mentioned above, the proportions of foreign matter can be determined by calculating the capacitance at a plurality of frequencies or by calculating the power factor at just one frequency. However it is also possible to do this by calculating the power factor for a plurality of frequencies. Suitable frequencies are, for example, 10 kHz to 100 kHz and 10 MHz. 1. Method for determining proportions of solid matter in a test material, characterised in that the test material is exposed to an electric field, dielectric properties (cos 2. Method according to claim 1, characterised in that, for the dielectric properties, two electrical quantities (ACfl, ACf2) are determined and combined, resulting in a characteristic value which is independent of the mass of the test material. 3. Method according to claim 1, characterised in that, in for the dielectric properties, an electrical quantity (cos0) is determined which forms a characteristic value which is independent of the mass of the test material. 4. Method according to claim 2 or 3, characterised in that the characteristic value is compared with a previously determined characteristic value for the matter in question and the proportion of solid matter is determined therefrom. 5. Method according to claim 1,.characterised in that the electric field is operated with a first frequency and a second frequency, and the proportion is determined from values for dielectric properties which are measured at the first and the second.frequency. 6. Method according to claim 1, characterised in that a respective measured value is obtained from the field-with the first frequency and from the field with the second frequency, and the two measured values are combined to form a signal which is compared with a predetermined value. Method according to claim 6, characterised in that currents, voltages and phase angles are measured as measured values and dielectric properties are determined therefrom. Device for carrying out the method according to claim 1, characterised by a precision capacitor (1) for creating an electric field in the region of the test material (2), a frequency generator (4) for generating at least one electric field with a frequency, measuring elements (13, 14) for electrical measurable quantities and an evaluation circuit (8) for forming a characteristic value. Device according to claim 8, characterised in that a reference capacitor (51) is provided in addition to the precision capacitor (50). Device according to claim 8, characterised in that two frequency generators (62, 66) are provided. Device according to claim 8, characterised in that the frequency generators are connected in series to produce an electric field with two superimposed frequencies. Device according to claim 9, characterised in that the precision capacitor (50) and the reference capacitor (51) form part of a bridge circuit. 13, Method for determining proportions of solid matter in a test material, substantially as herein described, with reference to the accompanying drawings. 14. Device for carrying out the method, substantially as herein described, with reference to the accompanying drawings.

Documents:

2621-mas-1998-abstract.pdf

2621-mas-1998-assignment.pdf

2621-mas-1998-claims duplicate.pdf

2621-mas-1998-claims original.pdf

2621-mas-1998-correspondence others.pdf

2621-mas-1998-correspondence po.pdf

2621-mas-1998-description complete duplicate.pdf

2621-mas-1998-description complete original.pdf

2621-mas-1998-drawings.pdf

2621-mas-1998-form 1.pdf

2621-mas-1998-form 26.pdf

2621-mas-1998-form 3.pdf

2621-mas-1998-form 4.pdf

abs-2621-mas-1998.jpg