EP0790006B1 - Method and apparatus for determining the density of a rod in the tobacco industry - Google Patents

Description

The invention relates to a method according to the preamble of claim 1 and an apparatus according to the preamble of claim 6.

Density measuring devices are used in extruders of the tobacco processing industry used to determine the amount of material and the uniformity of the material distribution in the strand to be monitored and ensured as far as possible in accordance with certain specifications. This applies to the tobacco content in a tobacco rod for the production of smokable Tobacco items such as cigarettes, pillars, cigarillos etc. as well as for the salary of filter material in a filter train. It is known that the strand is evenly filled an important quality criterion for the articles made from the strand. As a measure of that Filling the strand, i.e. for the amount of tobacco or filter material in the strand, will be Density recorded.

Density measuring devices with radioactive are currently known and generally used Radiation - usually with beta radiation from a Strontium 90 preparation (U.S. Patent 4,424,443) - penetrate the strand, the intensity decrease as it penetrates of the strand is measured as a measure of the density of the strand. The one with this measuring device Measurement results obtained are characterized by high reliability, but are because of the required permanent beta emitter with complex security measures bought on the machine.

Recently, a density measuring device has also become known which uses infrared Light works as measuring radiation (US Pat. No. 4,805,641). This device has the advantage that it manages without a radioactive radiation source, but does not quite reach it Reliability of nuclear density measurement.

The use of X-rays as measuring radiation for density measurement is also have already been proposed. US Pat. No. 3,056,026 shows such a measuring device, the basically works like a density measuring head with a nuclear radiation source. The strand penetrating x-rays are detected with an ionization chamber, what the measurement slow and low resolution in the longitudinal direction of the strand.

In US Pat. No. 4,785,830 there is a measuring device on a cigarette rod machine described in which an uncovered tobacco rod in the tobacco channel with X-rays is screened. The radiation penetrating the strand is measured with a sensor array detected to the density of the fiber material in before the cigarette rod to determine different strand height sections separately and thus the density distribution in the strand and to recognize the strand structures. That is a targeted intervention in the Allow strand production for the purpose of optimizing the strand structure. This measurement should also be possible on the wrapped tobacco rod (cigarette rod), which is why the writing does not receive any further details. U.S. Patent 4,865,052 shows also a device for measuring the density of an uncovered tobacco rod, which is conveyed in the tobacco channel of a strand machine, by means of penetrating the strand X-rays. The radiation is detected with a sensor array. From the bottom the measured values of the sensors are summed up to the sum of the tobacco channel reaches a predetermined target value, and the downstream one is correspondingly arranged Excess decrease device set, so that here a default setting of Weight or the density of the strand takes place. For measurements on the cigarette rod is this does not make sense.

The density measurements with X-rays known in the prior art have become not proven in practice and could not be used in industrial cigarette production push through. There is therefore still the desire and the need for a measuring technique to get into your hand that reliably detects the strand density, accurate and high-resolution works and with little effort, especially in terms of safety can be handled and used.

The object of the invention is a further method and a further device of the type described above.

This object is achieved according to the invention in a method of the type specified at the outset by the measures in the characterizing part of claim 1, and in a device of the type specified at the outset with the features which are in the characterizing part of the claim 6 are specified. Continuation, further training and advantageous refinements of the method and the device according to the invention are in the subclaims specified.

The invention offers the advantage of a very fast and accurate high density measurement Resolution. This ensures that the drift phenomena of the detectors or Changes in the intensity of the radiation source do not affect the measurement results can. The invention therefore offers a very reliable strand density measurement. The security-related Difficulties arise from a nuclear beta source not up here. The security effort is low. The dimensions of the X-ray measuring heads according to the invention can be adapted to those of a nuclear measuring head are so that this is exchanged in existing machines for the X-ray measuring head can be.

The invention will now be explained in more detail with reference to the drawing.

Figur 1

eine Prinzipdarstellung einer Meßvorrichtung nach der Erfindung und

Figur 2

eine Blockdarstellung der Meßwertauswertung.

Show it

Figure 1

a schematic diagram of a measuring device according to the invention and

Figure 2

a block diagram of the measured value evaluation.

Figure 1 shows a schematic diagram of a device for determining the density of a Fiber strands of the tobacco processing industry according to the invention. With 1 is a continuous Moving cigarette rod designates a wrapper 2 made of cigarette paper and has a filling 3 of tobacco fibers. The strand can also be one Filter strand of the tobacco processing industry or around a strand for the production of Trade cigarillos, cigars, cheroots, etc.

The strand runs in the longitudinal direction, that is to say approximately perpendicular to the plane of the drawing in FIG. 1 a conveyor section of a cigarette rod machine, which is not shown in the drawing, for example of the type Protos 100 from the applicant, promoted and passes through a tube 6 that is transparent to X-rays in a measuring station 4. This tube can consist, for example, of a thin aluminum or titanium sheet. A polycarbonate (PC), for example, is preferred as the material for the tube MACROLON from BAYER AG or a polyethylene ether ketone (PEEK) with one Wall thickness of about 0.2 mm used. The representation in the drawing is not to scale, so that here the wall thickness of the tube 6 appears too large.

An x-ray radiation source 7 emits x-ray radiation 8, which in FIG is idealized. In fact, the radiation does not go in parallel from the X-ray source out. The limitation of the x-ray radiation 8 is caused by apertures 9 and 9a but that through the gaps 11 and 11a formed by the diaphragms a radiation component penetrates the strand, the radiation course of a parallel radiation course is approximated at least to an extent sufficient for the measurement purpose. As X-ray source comes, for example, an industrial X-ray device of the type MF1-30-2 with a normal focus X-ray tube FK 60-10 W from Rich. Seifert & Co., D-22926 Ahrensburg, in question.

The measurement of the intensity of the X-radiation is carried out by means of an X-ray receiver 12, which is attached behind the gap 11a. This X-ray radiation receiver 12 is designed as a line array 13 with a plurality of X-ray detectors 14.1 to 14.n, which are arranged in a row one behind the other in the array 13. n is the total number of X-ray detectors 14 provided in the array 13. In the exemplary embodiment shown in FIG. 1, n = 11. An embodiment with 16 such X-ray detectors in the array 13, for example of the type CXM-HS 03-16K from CRYSTAL, is preferred ,
i is a serial number between 1 and n. The x-ray-sensitive area of the x-ray detectors is, for example, 1 mm in height, that is to say transversely to the strand direction, and 4 mm in width, that is to say in the strand direction. The gaps 11 and 11a are approximately as wide as the detectors 14.

The X-ray detectors 14.1 to 14.n are all connected separately to an evaluation arrangement 16, which the measurement signals emitted by the X-ray detectors into one Processed density signal 17, which is sent to a control arrangement 18 of an influencing device the strand density is released. Such a device is in a cigarette rod machine for example a device for removing excess from the tobacco rod, with which the amount of tobacco entering the cigarette rod is adjusted becomes. Such devices are known and need no further description here.

In addition to the detectors which detect the intensity of the X-rays penetrating the strand itself, the detector array 13 comprises at least one additional X-ray detector 14.2 which detects a part of the X-rays which does not penetrate the strand. Its measurement signal S ₂ is processed as a reference signal in the evaluation arrangement 16. The detector array 13 also has at least one further X-ray detector 14.1, which is permanently shielded from the radiation from the X-ray source 7. This further detector 14.1 permanently emits a signal S ₁ corresponding to its dark current, which is used in the evaluation arrangement 16 to compensate for drift phenomena in the detectors. Only one additional x-ray detector and another x-ray detector are shown in the drawing. The measurement can be further improved and made more reliable if more detectors each receive the undamped X-rays or generate a signal corresponding to their dark current.

The mode of operation of the evaluation arrangement 16 in the processing of the measurement signals S ₁ to S _n emitted by the detectors 14.1 to 14.n is explained with the aid of the functional diagram shown in FIG.

To prepare the strand density measurement, the measuring device is first calibrated. For this purpose, the X-ray radiation source 7 is switched off or dimmed toward the radiation receiver 12 by means of a shutter (not shown). The measurement signals S ₁ to S _{n of} the X-ray detectors 14.1 to 14.n now represent their dark currents. The measurement signals S ₁ to S _n obtained when the X-ray radiation source is switched off or the X-ray radiation receivers are dimmed are also referred to as dark signals. The dark signals of the X-ray detectors 14.2 to 14.n are processed with the dark signal of the X-ray detector 14.1, which is also referred to as S _D for better identification, to compensation values j _{D, 2} to j _{D, n} which are suitable for later use in density measurement in Storage sections 19.2 to 19.n of the evaluation arrangement 16 are stored as constants. Then, with the X-ray source 7 switched on, the current of the X-ray detectors is measured at full intensity of the radiation without a strand. The resulting measurement signals S ₂ to S _{n of} the X-ray radiation detectors 14.2 to 14.n represent reference measurement values. The reference measurement values S ₃ to S _n are identified with the reference measurement value S _{2 of} the additional X-ray radiation detector 14.2, which is also referred to as S ₀ for better identification as a reference measurement value is processed into reference values j _0.3 to j _{0, n} , which are stored as constants in memory sections 21.3 to 21.n of the evaluation arrangement 16.

For density measurement, a strand 1 is moved through the tube 6 in the measuring station 12, which attenuates the radiation striking the X-ray radiation detectors in accordance with its density. The intensity of the radiation weakened in accordance with the density is detected with the X-ray detectors 14.3 to 14.n, which emit the corresponding measurement signals S ₃ to S _n to the evaluation arrangement 16. The evaluation arrangement compares these measurement signals in the function blocks 22.3 to 22.n with the stored compensation values j _{D, 3} to j _{D, n} corresponding to the dark currents of the X-ray detectors 14.3 to 14.n. The compensation values for their part are corrected in calculation stages 24.3 to 24.n as a function of the respectively current dark signal S _D of the X-ray detector 14.1 which is permanently shielded from the X-rays, thereby compensating for drift phenomena occurring in the detectors. The effect of the aging processes of the detectors or of heat changes in their characteristics is thus reliably eliminated. The comparators 22.3 to 22.n give corrected measurement signals S _{3, k} to S _{n, k} to the downstream calculation stages 23.3 to 23, n, which represent the X-rays which hit the detectors 14.3 to 14.n after passing through the strand, ie correspond to the strand density in the strand height position detected by the respective detector.

At the same time, reference signals I _{3, k} to I _{n, k} are transferred to the calculation stages 23.3 to 23.n. These reference signals result from the reference values j _0.3 to j _{0, n} stored in the memory sections 21.3 to 21.n, which are stored in correction stages 25.3 to 25.n as a function of the current reference measurement signal S ₂ or S ₀ full X-ray illuminated X-ray detector 14.2 can be corrected. A correction signal S _{2, k is} formed by comparison with the reference value j _{D, 2 of} the detector 14.2 in the comparator stage 22.2, which is corrected in the compensation section 24.2 as a function of the dark signal S _{D of} the permanently shielded radiation receiver 14.1 and is stored in the memory section 19.2 as a constant, which is used in correction stages 25.3 to 25.n to correct the reference values j _0.3 to j _{0, n} . Thus, by using the additional detector 14.2, which continuously receives the undamped intensity of the X-ray radiation source 7 and whose measurement signal S _{2 represents} a permanent current reference signal S ₀ , and by the further detector 14.1, which is permanently shielded from the X-ray radiation source 7 and always on Outputs dark current signal S _D as a compensation signal, achieved that the density measurement is independent of fluctuations in intensity of the X-ray source 7, temperature drifts and signs of aging of the detectors.

The corrected measurement signals S _{3, k} to S _{n, k} are processed in the calculation stages 23.3 to 23.n or with the corrected reference signals I _{3, k} to I _{n, k} to separate density signals D ₃ to D _n , each of which is the density in represent an associated string height position. This is done by logarithmizing the ratio (quotient) of the reference signal and the corrected measurement signal. The resulting separate density signals D ₃ to D _n are added in an addition stage 26 and output as a density signal 17 to the connected control arrangement 18. If necessary, the mean value of the separate density signals D ₃ to D _n can also be formed as a density signal representing the strand density. The logarithmization of the individual measured values in the calculation stages 23 has the advantage over the logarithmization of the integrated density value that is common today that a mathematically correct and thus a more reliable and more accurate statement about the strand density in the currently illuminated strand section results.

Another possibility provided according to the invention is the quotients multiply the reference signals and the associated corrected measurement signals first and log the product so formed to the desired density signal to win.

The extent of the radiation sensitive surface of the X-ray detectors is preferably very small. So currently detectors are preferred whose radiation sensitive Area in the longitudinal direction of the strand about 4 mm and across the strand about 1 mm is. The individual detectors thus detect strand sections of very little extent, in which the density is assumed to be at least approximately homogeneous can. This also contributes significantly to the accuracy of the measurement results, because the logarithm of the individual intensity values is a mathematically correct evaluation step, so that falsifications of results are prevented. This training also leads the High resolution detectors.

It is known that the softer radiation components of an X-ray radiation during passage be absorbed more by a mass than the harder ones, making a larger one Proportion of the harder X-rays penetrate the mass. This appearance will also referred to as "curing the X-rays". For a certain fluoroscopic one Material can empirically correct the measured intensities (density signals) assigned, which compensate for the influence of "curing" on the density signals. This results in a further improvement of the strand density measurement according to the Invention.

Claims (14)

1. A method of determining the density of a fibrous strand used in the tobacco-processing industry, in particular a cigarette strand, wherein the intensity of X-radiation penetrating the strand is determined, a measuring signal corresponding to the intensity is formed and the measuring signal is processed to give a density signal representing the density of the strand, characterised in that the intensity of the X-radiation penetrating the strand is determined separately in a plurality of strand height positions, in that measuring signals corresponding to the determined intensities are formed and in that all the measuring signals are processed to give a single density signal.
2. A method according to claim 1, characterised in that, in each strand height position, the intensity of a portion of the X-radiation penetrating a part of the strand with negligible density inhomogeneity is determined.
3. A method according to claim 1 or 2, characterised in that the intensity of a portion of the X-radiation not penetrating the strand is additionally determined separately as reference radiation and a corresponding measuring signal is formed as a reference signal and in that this reference signal is processed with the measuring signals to give a density signal.
4. A method according to any one of claims 1 to 3, characterised in that the measuring signals are processed by summation to give a density signal.
5. A method according to any one of claims 1 to 4, characterised in that the logarithm of the measuring signals is calculated before summation.
6. A method according to any one of claims 1 to 4, characterised in that the measuring signals are multiplied and the logarithm of the product is calculated.
7. A method according to any one of claims 1 to 6, characterised in that at least one X-ray detector is shielded from the X-radiation, in that a dark current of the shielded detector is detected and a corresponding dark signal is generated and in that this dark signal is used to compensate for drift influences during the formation of density signals from the other measuring signals.
8. A device for determining the density of a fibrous strand used in the tobacco-processing industry, in particular a cigarette strand, comprising a measuring station associated with a strand guide and provided with a source of X-radiation and a radiation receiver facing the source of X-radiation for detecting X-radiation penetrating a strand moving in the strand guide and for generating corresponding measuring signals, and an evaluation arrangement connected to the radiation receiver for processing the measuring signals to give density signals representing the strand density, characterised in that the radiation receiver (12) is formed as a linear array (13) with a plurality of X-ray detectors (14.1 to 14.n) arranged in a row for determining the strand density in a plurality of strand height positions and for generating corresponding measuring signals (S₁ to S_n), and in that the evaluation arrangement (16) is formed so as to process the measuring signals to give a density signal (17).
9. A device according to claim 8, characterised in that the linear array (13) has at least one additional X-ray detector (14.2) which detects a portion of the X-radiation not penetrating the strand (1) and generates a corresponding measuring signal (S₂) as a reference signal (S₀), and in that the evaluation arrangement (16) is formed so as to correct the measuring signals (S₃ to S_n) as a function of this reference signal (S₀).
10. A device according to claim 8 or 9, characterised in that the linear array (13) has at least one further X-ray detector (14.1) which is shielded from the X-radiation (8) and generates a dark signal (S_o) corresponding to its dark current, and in that the evaluation arrangement (16) is formed so as to correct the measuring signals (S₃ to S_n) and/or the reference signal (S₀) to compensate for drift influences as a function of this dark signal (S_o).
11. A device according to any one of claims 8 to 10, characterised in that the evaluation arrangement (16) is formed so as to form the sum of the measuring signals (S₃ to S_n) from the detectors (14.3 to 14.n) detecting the X-radiation penetrating the strand (1) and so as to process the sum to give a density signal (17) representing the density of the fibrous strand.
12. A device according to any one of claims 8 to 11, characterised in that the evaluation arrangement (16) is formed so as to calculate, before summation, the logarithm of the measuring signals from at least the detectors (14.3 to 14.n) detecting the X-radiation penetrating the fibrous strand (1).
13. A device according to any one of claims 8 to 11, characterised in that the evaluation arrangement (16) is formed so as to multiply the measuring signals from at least the detectors (14.3 to 14.n) detecting the X-radiation penetrating the fibrous strand (1) and so as to calculate the logarithm of the product.
14. A device according to any one of claims 8 to 13, characterised in that the X-ray detectors (14.1 to 14.n) of the linear array (13) are so small that the density of the strand region detected by each detector appears substantially homogeneous.

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