Measuring device and method for recognizing foreign bodies in tobacco

Translation of description of equivalent WO 2006069720 A2

p0001Hauni Maschinenbau AG, Kurt-A. -Körber-Chaussee 8-32, 21033 Hamburg

p0002Measurement apparatus and method for detecting foreign bodies in a product, in particular in tobacco, cotton or other fiber product

p0003The invention relates to a measuring device for detecting foreign bodies in a product, in particular in tobacco, cotton or other fiber product, according to the preamble of claim 1. The invention further relates to a corresponding measuring method.

p0004For detection of foreign bodies in tobacco, for example, from the documents DE 100 37 180 Cl, DE 101 00 664 Al, EP 1327876 Bl, EP 1330961 Al, the use of microwave measuring devices known. Due to the required high accuracy and the high frequencies used the circuit complexity is high.

p0005The object of the present invention is to provide a structurally simple measuring device for determining foreign body with high accuracy.

p0006The invention solves this problem with the features of claims 1 and 28. The use of a capacitor, in particular, instead of a microwave, and a high frequency field below the microwave range, the circuit complexity can be significantly reduced. In addition, under certain circumstances by a capacitor, a homogeneous field can be generated in the product space as means of a microwave resonator, in which the electric field strength at the peripheral wall disappears.

p0007The term "foreign matter" means any distinct material in which to be tested is the binary system unerwϋnschterweise additionally available. The test binary system is particular product and moisture (or sauce) formed, for example, tobacco and humidity (or sauce), or filter material and triacetin. The invention differs from known capacitive measuring devices in High frequency range for detection of mass or Dichtefehlem example in tobacco, which concern only the two-component system of product and moisture. A foreign body influences due to its different dielectric properties in a specific way the RF field and therefore, the measured variables determined. By suitable evaluation in the evaluation device can be recognized in the product of the determined measured variables a foreign body, particularly if the course of a measurement variable is a caused by the foreign body deviation.

p0008The term "high frequency" will mean in general range in distinction from the microwave, fields with a frequency below 100 MHz, preferably below 10 MHz. As a rule, the frequency is more than 10 kHz, or more than 100 kHz. In a preferred variant the invention, a high-frequency field is used with a frequency less than 5 MHz, preferably below 1 MHz. This is surprising, since it is known with respect to the measurement of the humidity and / or density of the product that, at lower frequencies a sufficiently accurate measurement only is possible in an increasingly limited measuring range, so that a measurement frequency of at least 5 MHz, for example, for tobacco to be appropriate. for the determination of foreign bodies, particularly in tobacco, cotton and other fiber products, but results just at lower frequencies greater measurement sensitivity. a explanation for this is that at lower frequencies the macroscopic conduit has an increasing influence, where this is not of typical non-conductive foreign matter materials (or more generally those with a different macroscopic conductivity) holds, so that the difference in the dielectric constants between the product and foreign object in the measuring range according to the invention is greater than in the microwave range.

p0009As a result of the preferred use of a current high-frequency wave and a substantially non-resonant circuit device, in which therefore the measuring capacitor is not a frequency-determining part of a measuring oscillating circuit, an over temperature influences sensitive oscillating circuit coil can be dispensed fertil on the use. "Substantially" means that resonant field components are not excluded, as long as the measuring principle we sentlichen on a progressive wave is based. Since no resonance condition met for a measuring oscillating circuit must be, the sensing capacitor may have a relation to the prior art reduced capacity of preferably less than 10 pF, which reduces the cost and the size. The described preferred embodiment is therefore different from known capacitive measuring devices in the radiofrequency range for detection of the mass or Dichtefehlem in tobacco, in which a measuring capacitor and a coil are connected as a frequency-determining parts in a high-frequency oscillation circuit, wherein as measured quantities, for example, influenced by the product resonance frequency and resonance amplitude of Hochfrcquenzfeldes be determined.

p0010Preferably, the foreign object detection based on the fact that two independent variables, in particular is dependent on the capacitance of the measuring capacitor variable and one dependent on the loss factor of the measuring capacitor measuring quantity, are in a different time from the expected course ratio. Therefore, the measurement of two independent variables is preferably provided. Advantageously, two dependent on the amplitude and the phase of the high-frequency wave measurement quantities are determined. Basic addition thus the generation of a high-frequency wave is sufficiently what the elaborateness compared with those apparatuses reduced, based on the use of multiple high-frequency waves of different radio frequencies. However, the provision of two independent variables is not mandatory; it is also conceivable to carry out a foreign body detection in the course of only one variable.

p0011The for determining the variables serving part of the circuitry is usually the actual measuring circuit which includes the measuring capacitor. While the measuring circuit having an output for the product of the affect flußte RF field usually has the measurable variables is usually one of the number of relevant variables to be determined number of outlets, preferably therefore two outputs. It is also possible that the measuring circuit and the measurable variables form a unit. The measurable variables is the actual evaluation for Fremdkörperer- detection by evaluating the measurement signal upstream. It is also possible that the measurable variables and the evaluation device form a unit. In a preferred embodiment of determining the measured variable or measured variables serving part of the circuit means is constructed with digital electronics. This allows the use of simple methods for determining the desired measured quantity, for example of the capacitive component and / or the loss component of the output voltage value of the measuring circuit. A particularly simple and therefore preferred method is based on the orthogonality of the sine and cosine fractions and comprises the measurement of a discrete number of N measured values, for example voltage values ​​on each oscillation period of the RF field, separate multiplication of the n measured values ​​with the corresponding sine and cosine values, and separate addition of these sine and cosine products. The totals obtained constitute the measurable variables or can be further processed for determining the measurable variables.

p0012A particularly simple form of a measuring circuit, ie the measuring capacitor comprehensive part processing device of the scarf is a RC member, preferably with an operational amplifier. It is preferably an RC differentiating element, but it may for example also an RC integrator may be used.

p0013In a preferred embodiment, parts of the sensor made of a material with a low coefficient of thermal expansion in order to keep the influence of variations in temperature as low as possible on the measurement accuracy. For the same purpose, the sensor can comprise an additional means for keeping constant the temperature of the measuring capacitor. Also an additional means for measuring the temperature of the measuring capacitor, for example, a temperature sensor is also conceivable to correct the measuring signal accordingly.

p0014Preferably, the condenser is arranged essentially perpendicular to the transport direction of the product. In the case of a plate capacitor so that the capacitor plates are arranged perpendicular to the transport direction. This enables the electrodes at a short distance from each other, for example, below the strand thickness of the product to arrange. This allows an improved resolution with respect to the detection of foreign bodies in the longitudinal direction, and thus an increase of Nachweisemp- sensitivity can be achieved.

p0015The sensor is designed to carry the product through the space formed between the electrodes of the measuring capacitor, in order to allow complete and uniform as possible detection of the product. So it is not preferably a stray field sensor.

p0016Another preferred embodiment relates to the measurement of a relatively wide product, such as a tobacco or tow web or a cotton fleece, or a plurality of adjacent product strands. The sensor comprises a plurality of product across the width of the measuring capacitors arranged. This arrangement allows a simple manner a lateral position of a detected foreign object oriented. The problems associated with the high-frequency field generator electrodes are held at the same potential, for example, simply shorted to minimize crosstalk between the measuring capacitors. For the same purpose also the other electrode are preferably kept virtually respectively by means of an inverting operational amplifier at the same potential.

p0017Further advantageous features are evident from the dependent claims and the following description of case of advantageous embodiments with reference to the accompanying drawings. Show it:

p0018FIG. 1 shows a schematic circuit of an essentially analog measuring device;

p0019FIG. 2: a differentiating measuring circuit for a measuring device;

p0020FIG. 3 shows an integrator circuit for measuring a measuring device;

p0021FIG. 4 is a longitudinal sectional view of a capacitive sensor;

p0022Figure 5 is a cross-sectional view of a capacitive sensor in a further embodiment;. Fig. 6 is a schematic circuit of a substantially digital measuring device;

p0023Figure 7 is a schematic circuit of a Meßvoπϊchtung for the measurement on a wide product;. and

p0024FIG. 8: an operational amplifier for a differentiating measuring circuit for measuring apparatus of FIG. 7.

p0025The capacitive measuring device 10 according to FIGS. 1 to 6 comprises a Hochfrequenzer- generating device 13 for generating a high-frequency wave, which is fed via an input line 14 to a circuit device 28. The circuit means 28 comprises a measuring capacitor 1 1, through which the to be measured, in this case, strand-like product is guided 12th The high frequency wave generated by the high frequency generating means 13 is passed to an electrode 15 of the Meßkondensa- gate 11, to produce therein a high frequency field, which interacts with the product 12th The of the other electrode 16 of the measuring capacitor 11 expiring, influenced by the product 12 high-frequency wave is processed by the circuit means 28 to at least one, preferably two mutually independent of the amplitude and / or phase of be influenced by the product 12 th high-frequency wave to determine dependent variables. These are preferably two of the capacitance and loss factor of the measuring capacitor 11 dependent measured variables. The variables corresponding measurement signals are routed to the evaluation unit 21, for example, a suitably programmed computer.

p0026In the product 12, an unwanted foreign body 90 occur, for example, a plastic or metal particles. Due to variations in dielectric properties of the foreign body 90 influenced in a certain manner the amplitude and phase of the RF wave, and thereby also the measured variables determined. By suitable evaluation in the evaluating device 21 can be detected 90 in the product 12 from the determined measured variables a foreign body, particularly if the course of a measurement variable is a caused by the foreign body 90 deviation. For example, a foreign body 90 deflections (spikes) in a measuring curve caused; the evaluation is then suitably adapted to detect such deflections in the trace. Proven for foreign body detection is the evaluation of the ratio of two independent variables. The evaluation device 21 is able to control optionally a removal means 91 such as a tuyere, for removing a portion of the product 12 in which a foreign body 90 is detected.

p0027The embodiment of FIG. 1 relates to an essentially analogue measuring device. The high frequency generating device 13 includes a harmonic oscillator 22 for generating a high-frequency wave. The voltage amplitude U_e the high-frequency wave generated is preferably kept constant by means of a control unit 23-26, to permit unaffected by variations in the input amplitude measurement. For this purpose, the high-frequency wave generated by the harmonic oscillator 22 is supplied to a controllable amplifier 23rd The output signal of the amplifier 23 is fed to a rectifier 24 whose output signal is passed through the low 25 to a regulator 26th The controller 26 controls the amplifier 23 in such a manner that the amplitude U_e the haπnonischen oscillation at the output of the amplifier 23 has a constant value.

p0028The measuring circuit 27 is directly connected with the measuring capacitor 11 of the circuit means 28 is suitable in this case each measuring circuit which is arranged to generate a sufficient amplitude and phase variation of the high-frequency wave as a result of the current through the measuring capacitor 11 product 12th Two preferred embodiments of the measuring circuit 27 are shown in Figs. 2 and 3, wherein the measuring capacitor 11, a resistor 29 and an inverting operational amplifier 30 are connected in a differentiating arrangement according to FIG. 2 or an integrating arrangement according to FIG. 3. The non-inverting input of operational amplifier 30 is appropriately grounded. When integrating arrangement according to FIG. 3, an additional resistor 31 is provided to prevent, if appropriate, that the output signal passing to the boundary. That the outgoing high-frequency wave output signal corresponding to the measuring circuit 27 undergoes due to the interaction with the product 12 a with respect to the input amplitude U_e amended chipboard voltage amplitude U₃ and a phase shift δ with respect to the input signal.

p0029The current through the measuring capacitor 11 high-frequency wave is on the output line 17 of the measuring circuit 27 directed to the measurable variables 18th The Meßgrößenbestimmungseinrichrung 18 determined from the high-frequency signal suitable measurable. For this purpose, the output of the measurement circuit 27 is a rectifier 32 supplied and smoothed in a low-pass filter 33 in the embodiment of FIG. 1. The signal obtained is proportional to the amplitude U Ausgangsam-_a, The measurable variables 18 is further supplied to the signal generated by the high frequency generating means 13 via the line input signal 34th Generally, it is advantageously a dependent of the generated high-frequency wave signal via an addition to the measuring line through the measuring capacitor 11 provided for line 34, 234 supplied to the circuit means 28, to use the phase information of the input signal for determining the phase shift of the output signal can. In the present case the input signal of the measuring capacitor 11 via the line 34 and the output signal of the measuring capacitor 11 and the measuring circuit 27 is passed via a line 35 to the multiplication amplifier 36 are multiplied by each other and smoothed by means of a low-pass filter 37th The signal obtained is proportional to the output amplitude U₃ times the sine (or cosine) of the phase shift δ. From the course of certain means of measurable variables 18 variables, in particular from an appropriately formed ratio, and compared with an expected course, can be in finding a deviation possible in the product 12 con- tained debris 90 evidence. For corresponding evaluation, the measurement signals on the output lines 19, 20 to the evaluating device 21, in which the evaluation is carried out for example by means of a stored therein computer program.

p0030A preferred embodiment of a high-frequency sensor 38 is shown in Fig. 4. The sensor 38 is constructed substantially rotationally symmetrically about the longitudinal axis L. Through a central longitudinal bore 39 of the sensor 38 is in the transport direction T, which coincides with the longitudinal direction L, the product strand 12, for example a Tobacco rod out. The sensor comprises two rotationally symmetrical, disc-shaped, oriented perpendicular to the longitudinal direction L of the base body 40, 41, which are spaced apart by means of an outer, annular, non-conductive restriction body 44 and each having a central through hole 39 for the product strand. To the perpendicular to the longitudinal direction L-oriented inner surfaces of the base body 40, 41 is in each case an electrode 15, 16 of the measurement capacitor 1 1 in the form of a metallic surface, such as a metallic coating, for example by vapor deposition of gold. The measuring capacitor 11 is therefore designed as a plate capacitor with plate-shaped electrodes 15, 16 that are to the longitudinal L tion oriented circular disk and vertically and have a central opening for passage of the product strand 12th In this arrangement, the field lines extend substantially parallel to the transport direction. Between the base bodies 40, 41 is a field-filled space 45 is formed, which is completed by the Begrenzυngskörper 44 radially outward. The RF field extends into the central product space 46 and When pan is there with the product 12 in interaction. The plates 15, 16 have a smaller radius than the main body 40, 41, to prevent escape of the high-frequency field in the vicinity of the sensor. The plates 15, 16 of the plate capacitor 11 may be arranged in a small distance d from each other to improve the measurement resolution in the longitudinal direction L. The distance d may be in particular were less than the diameter of product strand 12 and, for example less than 8 mm, preferably less than 4 mm. There are still conducting connections 42, 43 of the electrodes 15, 16 are provided with external electrical connections. The base body 40, 41 each have a tubular, axially extending outward comprehensive product strand extension 47, 48th The extensions 47, 48 have a innenwandige metallic surface or coating 49 which is suitably connected to the electrodes 15, 16th The metallic coating 49 forms a metal chimney to prevent leaking of the field of the product through openings of the condenser 11th Furthermore, the product strand 12 immediately surrounding and this leading, over the entire length of the sensor tube extending 50 is provided from non-conductive material, which prevents contamination of the sensor inside by residues. In another disclosed embodiment, the formed between the electrodes 15, 16 field-filled space 45 for positively influencing the field pattern partially or completely, apart from the product space, be filled with a dielectric material.

p0031The body 40, 41, 44 of the sensor 38 are preferably made of non-conductive material with a very low coefficient of thermal expansion, for example, zero-dur to achieve increased dimensional stability of the sensor 38 to temperature effects. Because of the reduced dependence of the capacitance properties of the measuring capacitor 11 from the ambient temperature an improved measurement accuracy can be achieved. To the same end, a regulating device, not shown, is preferably provided for maintaining the temperature sensor. It is also conceivable that the base bodies 40, 41 of the sensor 38 is completely or partially made of metal.

p0032Another embodiment of a sensor 38 is shown in Fig. 5, wherein corresponding parts are designated by like reference numerals-lOOer. The electrodes 15, 16 are formed by plates which are arranged parallel to the oriented perpendicular to the plane of the paper transport direction. The field lines run in this example, substantially perpendicular to the transport direction. The plates 15, 16 are preferably arranged around the product strand 12 around and are preferably curved for this purpose.

p0033A preferred embodiment of a measuring device 10 is shown in Fig. 6, wherein corresponding parts are designated by like 200 series reference numerals. Unlike the embodiment of FIG. 1 which is particularly Meßgrößenbc- determining means 18 constructed with digital electronics. For this purpose, the measurable variables 18 an A / D converter 66, to which the output 27 of the measuring circuit measuring signal is passed. The A / D converter 66 is clocked at a sampling frequency which is a factor n higher than the frequency of the high frequency wave, where n is a natural number greater than 1. The clock signal for the A / D converter 66 is generated by means of the crystal oscillator 222 in the form of a square wave signal having a frequency of for example 50 MHz, so that in the present example n = 10th In general, therefore, the measuring device 10 has a device 222 for generating a sampling signal at a sampling frequency to a factor n higher than the frequency of the high frequency wave. The scanning signal is supplied via the line 70 to the A / D converter 66th

p0034The sampled by the A / D converter 66 measured values ​​61 are passed to the digital processing processing device that is programmed to identify appropriate, of independent variables. In a preferred Meßgrößenermittlungsverfahren each sampled measurement value is multiplied on the one hand with the corresponding value of the sine function and the other part with the corresponding value of the cosine function. For this purpose, the sample signal on the line 70 is applied to the processing device 67 passed. The sine and cosine values, for example, from corresponding tabular Save 68, are taken 69th The thus obtained n sine values ​​and cosine values ​​of n are then separately summed over one period of the high-frequency field, so that two sums are obtained. For this purpose, the RF input signal on the line 234 is applied to the processing device 67 directed so that it works in phase with the high frequency generating means thirteenth From the totals obtained can be due to certain orthogonality the two desired, identify dependent on the amplitude and the phase of the measurement signal influenced by the product 12 measured values ​​clearly. For corresponding evaluation, the values ​​will be on the output lines 19, 20 to the evaluating device 21, in which the evaluation is carried out for example by means of a computer program stored therein.

p0035Conveniently, the signal generated by the RF source 222 optionally also be used to generate the high frequency wave used for the measurement. For this purpose, the signal produced by the RF source 222 by means of the divider stage 60 is by the factor n to a phase-synchronous square-wave oscillation having the measuring frequency of in the present case divided down 5 MHz, and then by means of the PLL circuit 61 in a phase-synchronous sinusoidal signal with the same frequency converted.

p0036The control device 223, 62-64, 226 for keeping constant the voltage amplitude U_e the output from the amplifier 223 high-frequency wave can digitalelek- be executed tronically. In this case, the output signal of the amplifier 223 is fed into a A / D converter 62, which is controlled via a line 65 with the sampling signal of 50 MHz, which are per period generates N samples of the output from the amplifier 223 signal. The sampled by the A / D converter 62 measured values ​​are passed to the digital processing means 63rd In a preferred method each sampled voltage width is multiplied by the corresponding value of the cosine function. For this purpose, the sample signal on the line 65 is passed to the processing means 63rd The cosine values ​​can be taken for example from a corresponding tabular memory 64 are the. The thus obtained n cosine values ​​are then summed over one period of the RF field. For this purpose, the RF input signal is conducted via a line 71 to the processing device 63, so that these works in phase with the high frequency generating means thirteenth The output of the processing device 63 is forwarded to the controller 226, the stronger 223 controls the supply in such a way that the output signal of the processing device 63 and thus the amplitude U_e the vibration at the output of the amplifier 223 has a constant value.

p0037The embodiment of FIG. 7 is used in particular for the measurement on a wide, web-shaped product 312, for example, a tobacco web, a tow web or a cotton fleece, whose width B is substantially greater, for example, at least by a factor of 3, than its height H. A another application relates to the measurement of a plurality of adjacent product lines, such as rolls of tobacco. In Fig. 7, the transport direction is perpendicular to the paper plane. Mess corresponding parts are designated by corresponding reference numerals 300s. In this embodiment, a plurality of measuring capacitors 31 IA, 31 IB, ... is used, here for example six, which are arranged over the width of the product. This arrangement allows a determination of the lateral position of a foreign body, or in a plurality of adjacent product lines, to the debris-containing end product line. The measuring capacitors 31 IA, 31 IB, ... are conveniently powered by the same high frequency generating device. 13 Preferably, all of the input electrode 315 of the measuring capacitors 31 IA, 3 IB I, ... set to the same potential, most simply by shorting the electrodes as shown in Fig. 7 shown. This is the crosstalk between the measuring capacitors 31 IA, 3 IB I ... minimized. The output electrode 316A, 316B, ... of each measuring capacitor 31 IA, 31 IB, ... is ... connected to a measuring circuit 80A, 8OB. The measuring circuit 80A, 80B, ... is preferably as shown in Fig. 8 and then forms, together with the respective measuring capacitor 31 IA, 31 IB, ... a differential measuring circuit 27 as shown in Fig. 2. The use of each of the measuring capacitor 31 IA, 3 IB I ... inverting operational amplifier 330 is particularly advantageous in this embodiment, since this reduces the output electrodes 316A, 316B, ... of all measuring capacitors 31 IA, 31 IB, ... virtually be placed at the same potential, in particular ground. This is the crosstalk between the measuring capacitors 31 IA, 31 IB, ... minimized. The output of each measuring circuit 80A, 80B, ... is expediently, ... connected to a measurable variables 18A, 18B, the particular digital electronic, for example, as shown in FIG. 6, may be implemented. The Meßgrößenbestimmungs- devices 18A, 18B, ... are expediently connected to the Auswerteeirrrichtung 21 for contaminant detection. The corresponding method for determining the measured variables and for the detection of foreign bodies are preferably carried out as previously described.