GB2489587A

GB2489587A - Method and system for producing an endless filter rod

Info

Publication number: GB2489587A
Application number: GB1205421.9A
Authority: GB
Inventors: Dierk Schra Der
Original assignee: Hauni Maschinenbau GmbH
Current assignee: Koerber Technologies GmbH
Priority date: 2011-03-30
Filing date: 2012-03-27
Publication date: 2012-10-03
Anticipated expiration: 2032-03-27
Also published as: GB2489587B; GB201205421D0; DE102011006416B4; DE102011006416A1; ITMI20120367A1

Abstract

The invention relates to tobacco filter rod (24) manufactured from a filter tow (4), wherein a plasticiser is added to the filter tow (4), and after the addition of plasticiser, an endless filter rod (24) is formed from the filter tow, wherein the endless filter rod (24) passes through an HF measurement device (81) and/or a microwave measurement device (37, 64), wherein filter rods (28) of single or several use lengths are then cut from the endless filter rod (24), The method according to the invention is characterised in that individual filÂter rods (28) are removed and supplied to a filter rod measurement station (50), in which at least the mass and pressure drop of the filter rods (28) are measured, percentage by weight of plasticiser and/or moisture in the endless filter rod (24) are determined from the measurements of mass and pressure drop of the filter rods (28) and the measurement with the HF measÂurement device (81) and the microwave measurement device (37, 64) at the endless filter rod (24).

Description

Method and System for Prodcjg amEndless Filter Rod The invention relates to a method for producing at least one endless filter rod of the tobacco processing industry from at least one filter tow, particularly from a filter tow of cellulose acetate, wherein a plasticiser is added to the filter tow, and after the addition of plasticiser, an endless filter rod is formed from the filter tow, wherein filter rods of one or several use lengths are then cut from the endless filter rod, wherein the endless filter rod before cutting the filter rods, passes through an HF measurement device and/or a microwave measurement device. The invention further relates to a corresponding system for producing an endless filter rod.

For the production of filter rods that are cut to length from a previously produced endless filter rod, the constancy of the material properties, and therefore, the con-stancy of the filter properties is vital. Therefore, with the production of endless filter rods, value is placed on consistent quality and composition of the rod material.

These are checked during the production operation. Measurements for quality assur-ance are either made online at the endless filter rod in an endless filter rod machine, or offline at the cut filter rod, for example at so-called filter rod measurement sta-tions.

Filter rods, discharged from the production process on a random basis or systemati- cally, run sequentially through filter rod measurement stations that typically com-prise a series of two or more measurement devices. The discharge and transport to a measurement station is essentially manual, or will be manually requested.

Filter material typically consists of a mixture of substances. Thus, in filters that are produced from a filter tow composed of cellulose acetate (CA), a plasticiser is added, such as triacetin or triethylene glycol diacetate. It makes that the cellulose acetate fibers are dissolved and bonded, and as a result, the filter material is hard- ened. The plasticiser is finely atomised in a dosing device, and spread onto the out-spread filter tow before the tow is formed into a cylindrical endless filter rod. The

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percentage of the plasticiser in the endless filter rod typically amounts to approxi-mately 6% by weight. In addition, the endless filter rod, during the production thereof, absorbs moisture from the surrounding air, similarly also in case of climati-sation in a climatic chamber.

The filter properties of the finished filter rods strongly depend on the percentage by weight of the different substances of the filter rod, particularly on the percentage of the plasticiser. Therefore, the application of plasticiser in relation to the dry mass of the filter tow must be ensured to be as uniform as possible during the production of the endless filter rod.

Different methods are known for determining the mass proportion of plasticiser in an endless filter rod or in filter rods. European patent application EP 1 895 291 Al dis- closes a filter rod measurement station, in which the mass of the plasticiser is deter-mined in a filter rod measurement station, thus offline, in that a resonance frequency shift and a broadening of a resonance curve are measured. The mass and the pressure drop of the filter rod are also measured. The proportion of plasticiser in the filter rod is then computed from these measurement results. The measurements are performed at randomly removed filter rods such that rapidly occurring changes are not always detected.

Online measurements are typically performed in that a microwave measurement is made using a microwave resonator at the finished, formed cylindrical endless filter rod, alternately with and without plasticiser. The difference between the measure-ments provides information about the proportion of plasticiser in the endless filter rod. A disadvantage in this case is the frequent interruption of the filter production due to switching off the application of plasticiser in order to provide a reference for the difference measurement.

The document EP 1 197 746 Al discloses another measurement method performed at the endless filter rod, thus online. In this case, a difference is formed from two mi-crowave measurements which are made before the application of the plasticiser at the open filter tow, and after the application of the plasticiser at the finished, formed endless filter rod. The difference provides information about the proportion of plas-ticiser. A further, corresponding difference measurement by means of microwaves before and after an application of plasticiser is disclosed in the document EP 1 480 532 B!.

These measurement methods which are based on a difference measurement of the microwave resonator measurements before and after the application of plasticiser, require costly calibration. They are tainted with large measurement inaccuracy be- cause the filter tow at the measurement location is non-uniform before the applica-tion of plasticiser. Consequently, the material density at this location fluctuates in the course of the conveyance of the filter tow, and the distribution of the filter tow mass in the resonator chamber changes continuously. The fluctuations in the mate-rial density and material distribution is substantially lower after the formation of the endless filter rod, so that the basis of comparison of the measurements before and after the application of the plasticiser frequently fluctuates.

In contrast, the object of the present invention is to make it possible to continuously determine percentage by weight of a plurality of substances in a filter material in the form of a filter rod and/or an endless filter rod, which is based in particular on cellu-lose acetate, with a lower calibration expenditure than before, and with an increased measurement accuracy.

The object is solved by a method for producing at least one endless filter rod of the tobacco processing industry from at least one filter tow, particularly from a filter tow of cellulose acetate, wherein a plasticiser is added to the filter tow, and after the addition of plasticiser, an endless filter rod is formed from the filter tow, wherein filter rods of single or several use lengths are then cut from the endless filter rod, wherein the endless filter rod before cutting the filter rods, passes through an HF measurement device and/or a microwave measurement device, that is further devel-

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oped in that individual filter rods are removed and supplied to a filter rod measure- ment station, in which at least the mass and pressure drop of the filter rod are meas-ured, wherein a percentage by weight of plasticiser and/or moisture in the filter rods is/are determined from the measurements of mass and pressure drop of the filter rods and the measurement with the HF measurement device and/or the microwave meas-urement device at the endless filter rod. In this context, the mass and pressure drop of the filter rods can be also be continuously determined. The filter rods are removed according to a predetermined system in particular, and supplied automatically to the filter rod measurement station, preferably my means of pressurized air.

The method according to the invention is based on the fundamental idea that the online measurement using an HF measurement device (high frequency measurement device) and/or a microwave measurement device is combined with an offline meas- urement of the mass and pressure drop of the selected filter rods. The mass of plasti- ciser can be determined from this measured data using a simple functional relation-ship. For example, with the use of a microwave measurement device, there is a shift of the resonance frequency, labelled as Af0, and a spread of the resonance curve, la-belled as Ef12. The mass of a filter rod is labelled by M, and the measured pressure drop by PD. The mass of triacetin per unit length results in a good approximation as a linear combination of terms that are respectively proportional to Af0, Af12, M and PD. The moisture content can also be determined as a linear combination of terms that are proportional to M0, Af12 and M. In both cases, there are also constant terms to be considered.

In thc case of moisture, a term that is proportional to M/Af12 can also be considered.

In the case of a measurement with an HF measurement device instead of, or in addi- tion to a microwave measurement device, there is a phase shift and attenuation in- stead of the resonance frequency shift and spread of the resonance curve. The meas-urements in a microwave measurement device and/or an HF measurement device measure variables that are influenced by the quantity and the relative permittivity of

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the substances of the filter material contained in the mixture. If microwaves and HF waves (high-frequency waves), that is electromagnetic waves in the range between kHz and 300 0Hz, are used, it is also possible to exactly determine the percent-ages by weight of the three components of the endless filter rod due to the different frequency-dependencies of the relative permittivities of plasticiser, water and cellu-lose acetate.

The permittivity or dielectric conductivity is a complex variable that depends on the material, frequency and temperature. It describes the transmissibility of a material for alternating electromagnetic fields. It designates the field damping effect of the dielectric polarisation of the medium.

The present invention makes use of the effect that with a combination of measure- ments of the mass and pressure drop of filter rods and with a measurement of vari-ables that are influenced by the dielectric properties of the material of the endless filter rod, it is possible to quickly and accurately determine the content of plasticiser and also the moisture content of a material of an endless filter rod, wherein com- pared to the prior art, a continuous monitoring is possible due to the online meas-urement of the dielectric-influenced variables. Even though the mass and pressure drop of the filter rods are only measured at relatively long time intervals of a few seconds, and therefore, are assumed to be nearly constant for the time period up to the next measurement, changes in the composition of the material of the endless fil-ter rod, for instance changes in the application of plasticiser, appear immediately in the measurement in the microwave measurement device or the HF measurement de- vice. Such a change of the online measurement data, in the case of exceeding prede-termined limits, or limits that can be preset, can lead to the fact that the removal of one or more filter rods and the measurement of the mass and pressure drop thereof is forced, in order to attain a precise determination of the percentages by weight of the substances of the filter matcrial, and thus to attain more thorough information on which to base the decision on whether the affected filter rods must then be removed from the production process. In addition, exceeding the same, or other selected urn- its for the measurement values in the microwave measurement device, or respec-tively the HF measurement device, can already be the basis to remove the affected filter rods from the further production process. These limits can vary depending on the most recently measured values for mass and pressure drop of filter rods.

Because the functional relationships between the percentages by weight of the sub-stances in the filter material and the measured values for the mass, pressure drop and dielectric-influenced variables M0 and AS12, or respectively the corresponding vari-ables in an HF measurement device, are known, and their cross-correlation can also be known or determined, in the case of a change of the online measured measure-ment data for AS0 and Af12, also hypotheses can be made about the change of the mass and the pressure drop, without a direct measurement. With this, the limits for Al'0 and Af12, for example, at which further actions must be initiated upon exceeding or falling below thereof, can also be adapted.

Advantageously, a control of the filter rod production, in particular, a control of the application of plasticiser or of climatisation is carried out, if the determined value of percentage by weight of plasticiser in the endless filter rod and/or moisture of the endless filter rod deviates from predeterminable or preset value or value range, par-ticularly if it deviates from the value or value range by more than a selectable or predetermined amount. For this purpose, both the offline measured values for mass and pressure drop of the filter rods, and also the online measured values from the microwave measurement device and/or the HF measurement device, are combined and supplied to an evaluation and control device which interrupts the filter rod pro-duction so that the desired values for filter rod mass, pressure drop and percentage by weight of the substances remain within the desired parameter range. This control is a closed loop control with components of continuous online measured measure-ment data and discontinuous offline measured measurement data.

Preferably, a phase shift and/or a signal amplitude change are measured in the HF measurement device. In the scope of the present invention, a signal amplitude

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change is a change in amplitude of the resonance frequency voltage. Preferably, a resonance frequency shift and/or a resonance frequency spread and/or a slope change of the resonance curve and/or a change of signal amplitude are measured in the mi-crowave measurement device. This is preferably a microwave resonator. If both an HF measurement device and also a microwave measurement device are used, pref-erably both have the same field geometry and/or the same measurement volume.

This facilitates the mutual calibration.

The method according to the invention, is preferably further improved in that imme-diately before, at, or immediately after the HF measurement device or the microwave measurement device, a temperature of the endless filter rod is measured, wherein in particular, the temperature of the endless filter rod is considered for determining the percentage by weight of plasticiser and/or moisture in the endless filter rod. This way, the fact that the relative perrnittivity of the substances of the endless filter rod are not only frequency dependent, but also temperature dependent, is considered. By considering the temperature of the endless filter rod in the measurement of the di-electric influenced measurement variables, shift effects due to the temperature change can be compensated. This is particularly advantageous during start-up of a machine, wherein the machine warms up significantly within the first minutes of op- eration, which also influences the temperature of the endless filter rod. After ap- proximately 10 minutes, the operating conditions are typically substantially con-stant.

Advantageously, drops of plasticiser and/or foreign bodies in the endless filter rod are detected due to rapid changes in the measurement values in the I-IF measurement device and/or the microwave measurement device. Metallic foreign bodies, in par-ticular, lead to large short-term changes in the dielectric properties of the endless filter rods. In this case, these very significant signals are used to exclude filter rods with corresponding foreign bodies. In the case of drops of the plasticiser, the short-term changes are smaller than those with metallic foreign bodies. The effect that the plasticiser material which is applied in an application chamber typically in a finely

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distributed form onto the filter tow, can collect for example on the cover of the ap-plication chamber and form large drops which subsequently fall onto the filter tow, can also be detected in a microwave measurement device or an lIP measurement de- vice. A part of the filter tow that has received such a drop of plasticiser has signifi-cantly different mechanical properties than the remainder of the finely sprayed filter tow, and is no longer suitable for use in filter rods. Such filter rods are therefore subsequently discharged from the production process.

Preferably, at least two endless filter rods are produced in parallel, and each of the at least two endless filter rods passes through an HF measurement device and/or a mi-crowave measurement device, wherein individual filter rods cut from the at least two endless filter rods are removed, and supplied to a filter rod measurement station or respectively to one of a plurality of filter rod measurement stations. This way, the production speed can be increased.

Preferably, the filter rods that were supplied to the filter rod measurement station are, after the measurement in the filter rod measurement station also supplied to fur- ther production of rod-shaped products provided with filters of the tobacco process-ing industry. This can be performed in that the filter rods that have passed through a filter rod measurement station are inserted into a store of filter rods, or in that they are, particularly together with the remaining filter rods, fed into a downstream filter attachment machine.

The object of the invention is also solved by a system for producing at least one end- less filter rod of the tobacco processing industry from at least one filter tow, particu-larly a filter tow composed of cellulose acetate, with an endless filter rod production machine and at least one filter rod measurement station, wherein the endless filter rod production machine comprises a control unit, an application device for plasti-ciser, a format device for forming an endless filter rod from the filter tow, an HF measurement device and/or a microwave measurement device, and a cutting device for cutting filter rods from the endless filter rod, that is further developed in that a removal device and a conveyor device are provided by means of which individual fitter rods can be removed and can be conveyed to the filter rod measurement sta-tion, wherein the fitter rod measurement station has devices for measuring mass and pressure drop of the filter rods, wherein a data line is provided to transmit measure-ment data from the at feast one filter rod measurement station to the control unit of the endless filter rod production machine, wherein the control unit is designed to determine percentage by weight of plasticiser and/or moisture in the endless filter rod from the measurement data of mass and pressure drop in the filter rods and the measurement data from the HF measurement device and/or the microwave measure-ment device at the endless filter rod. A filter rod measurement station in the scope of the invention is understood to be any device or arrangement that permits offline measurement of weight and pressure drop of filter rods.

The cutting device can be a knife apparatus, for example. The removal device can be designed as a mechanical or pneumatic device, The conveyor device can also be de- signed as a mechanical or pneumatic device. The filter rod production machine ad-vantageously also has a climatic chamber or a moisture chamber for the filter tow.

in an advantageous further development, the control unit is designed to control end-less filter rod production, particularly application of plasticiser and/or climatisation, particularly moisture control, based on the determined percentages by weight of plasticiser and/or the moisture in the endless filter rod.

An acceleration of the production method can be attained if the endless rod machine is advantageously designed as a twin rod machine or as a multiple-rod machine, wherein removed filter rods can be conveyed to a filter rod measurement station, or respectively to one of a plurality of the filter rod measurement stations.

The system according to the invention is advantageously designed to perform a method according to the invention described above.

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The advantages, properties and features named with the individuat subject matters of the invention, i.e. the method according to the invention and the system according to the invention, apply without restriction also to the respective other subject matter according to the invention.

The invention is described below, without restricting the general idea of the inven- tion, using exemplary embodiments with reference to the drawings, whereby we ex-pressly refer to the drawings with regard to the disclosure of all details according to the invention that are not explained in greater detail in the text. The drawings show: Fig. 1 a schematic representation of a system according to the invention, Fig. 2 a schematic cross-sectional representation through a microwave resona-tor, and Fig. 3 a schematic cross-sectional representation through an HF precision ca-pacitor.

In the following figures, the same or similar types of elements or corresponding parts are provided with the same reference numbers so that a corresponding re-

introduction can be omitted.

Fig. 1 schematically shows a side view of one embodiment of a system according to the invention for producing an endless filter rod 24, for example for the production of filter rods 28 for cigarettes and like smokable articles. The represented device for producing filter rods 28 can be a model of the AF/KDF product line sold by the ap-plicant, for example. The device is comprised of two units, a filter tow preparation unit 1, for example of type AF of the applicant, for pulling and preparing an endless filter tow strip 4, and an endless filter rod forming unit 2, for example of the type KDF of the applicant, for producing wrapped filter rods 28. -11 -

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The filter tow preparation unit I has a roller pair 3 for continuously pulling an end-less filter tow strip 4 from a bale 6. The filter tow strip 4, on its way to the roller pair 3, over which it is guided via a redirection roller 5, after being removed from the bale 6, passes two air nozzles 7 and 8 that serve for spreading and breaking up the web of the filter tow strip 4.

A climatic chamber 10, through which the filter tow strip 4 is passed, is used as a climatisation device for the filter tow strip 4, and is located in the movement direc-tion of the filter tow strip 4 after the air nozzles 8 and before the pre-tension roller pair 13. In the climatic chamber 10, the filter tow strip 4 is subjected to water vapor from a water vapor source lOa, or to dry warm air from a warm air source lOb. For controlling the moisture of the filter tow strips 4, the humidity in the climatic cham-ber 10 can be regulated in that the supply of water vapor is controlled by means of a control valve lOc that can be controlled by a closed loop control device 43 and con- trol line tOe, whilst the supply of dry warm air can be controlled by means of a con-trol valve lOd that can be controlled by a closed ioop control device 43 and a control line lOf. The function of the closed loop control device 43 is described further be-low.

After the climatic chamber 10, there is a pre-tension roller pair 13, which has a drive that can be controlled by a control 14, for pretensioning the filter tow strip 4. This pretensioning of the filter tow strip 4 for removing the so-called remaining crimp in the filter tow strip 4 is performed by deflecting the filter tow strip 4 from the move- ment path thereof by a dancer roller 15. The dancer roller 15 is subjected to a de-fined force via a control element 16, controllable by a control 14, so that the tensile stress in the filter tow strip 4 between the pre-tensioning rollers 13 and the roller pair 3 takes on a desired preset value. As a result, the remaining crimp in the filter tow strip 4 is smoothed out. This results in a variable lengthening of the filter tow strip 4, whereby the position of the dancer roller 15 changes. The position of the dancer roller 15 is measured via the control element 16 by the control 14, and is regulated to a constant value by controlling the conveyance speed of the pretension-ing rollers 13. A corresponding method for regulating the tensile stress of a paper strip is described in the document DE 101 52 162 Al by the applicant.

The pretensioning roller pair 13 is followed by three further roller pairs 3, 9 and 11.

The roller pairs 3, 9 and 11 are driven individually. The rotational speed of the roller pair 9 corresponds substantially to the conveyance speed of the endless filter rod forming unit 2. The rotational speed of the roller pair 3 is less than that of the roller pair 9 so that the roller pairs 3 and 9 form a stretching device for the filter tow strip 4. The speed ratio between the roller pairs 3 and 9 specifies a degree of stretching of the filter tow strip 4. The stretching determines the quantity of filter tow per finished filter rod 28. The stretching causes lengthening of the filter tow strip 4, and there-fore a thinning of the density of the filter tow strip 4. The degree of the thinning eventually determines the mass of the filter tow in the finished filter rods 8, and can therefore be adjusted by controlling the conveyor speed of the first roller pair 3. For this purpose, the rotational speed of the roller pair 3 can be changed. The rotational speed of the roller pair 3 can be controlled via a control line 3a from a closed ioop control device 43. The function of the closed loop control device 43 is described fur-ther below.

Between the roller pairs 3 and 9, there is an applicator device 12 for applying plasti-ciser, triacetin for example, on the guided filter tow strip 4 spread out between the roller pairs 9 and 11. In the applicator device 12, the liquid plasticiser is applied in a preset dosing onto the spread out and stretched filter tow strip 4. The plasticiser is supplied to the applicator device 12 by means of a metering pump 33 via a supply line 34 from a plasticiser stock 36. The metering pump 33 can be controlled via a control line 33a from a closed loop control device 43.

The prepared filter tow strip 4, sprayed with plasticiser, arrives from the filter tow preparation unit 1 via the roller pair 11 into an inlet funnel 17 of the endless filter rod forming unit 2 having a housing 2a, in which it is collected and placed on a plugwrap strip 21 pulled from a reel 18 and provided with glue by means of a gluing -13 -device 19 having a glue nozzle. The plugwrap strip 21 and an endless rod of filter material 4a formed by bundling the filter tow strip 4, arrive on a garniture tape 22 which guides both components through a format 23, places plugwrap strips 21 around the endless rod of filter material 4a, and thereby form an endless filter rod 24. The speed of the garniture tape 22 is controlled by a main control 25 via a con-trol line 25a, and matched to the conveyor speed of the stretched filter tow strip 4 determined by the main control 25 by controlling the drives of the roller pairs 9 and 11 according to the arrows 25b and 25c.

The endless filter rod 24 passes through a seam sealer 26 in which the glued seam is dried. Then filter rods 28, continuously cut from the endless filter rod 24 by means of a knife apparatus 27, are transferred by an accelerator 29 into a catcher drum 31 in which they are conveyed in the transverse axial conveyance direction. From the catcher drum 31, the filter rods 28 arrive at a catcher belt 32 out of which they are guided to further processing, or to an intermediate storage.

A microwave measurement device 37, disposed downstream of the seam sealer 26 and upstream of the knife apparatus 27, measures the proportions of the components of the endless rod 24, namely dry filter tow, plasticiser or water.

The microwave measurement device 37 comprises a microwave measurement system with a sensing element, with a microwave source and a microwave detector, which detects the microwaves emanating from the microwave source, penetrating the end-less filter rod 24, for generating two measurement values and supplying them to the evaluation arrangement 42 via a data line 37a. The measurement values allow a statement to be made about the proportion of water and the common proportion of the chemically similar components, namely plasticiser and filter tow, in the endless filter rod 24. A suitable measurement method and a corresponding device can be found in the document, EP 0 791 823 A2, of the applicant, for example.

There can also be an HF measurement device 81, the measurement frequency of -14 -

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which lies in the high-frequency range up to 300 MHz, wherein the HF measurement device 81 is, or can be, connected via a data line 81a to the evaluation arrangement 42.

A closed loop control device 43 is disposed after the evaluation arrangement 42. In the closed loop control device 43, the signals of the evaluation arrangement 42 about the percentages of the components dry filter tow, water, plasticiser are compared as actual values to the preset stored target values by means of an integrated comparison device. In the case of deviation from the target value, the closed loop control device 43 issues a control signal to an assigned control means.

As a control means is provided the metering pump 33 that is influenced by the closed loop control device 43 according to the arrow 33a, in the sense of applying a preset quantity of plasticiser onto the strip of filter material 4. If the comparison de- vice determines that the actual value of the plasticiser percentage in the endless fil-ter rod 24 detected by the evaluation arrangement 42 is too low in comparison to the stored value, then the closed loop control device 43 controls the metering pump 33 to dispense more plasticiser. In contrast, if the comparison device determines that the actual value of the plasticiser percentage in the endless filter rod 24 detected by the evaluation arrangement 42 is too high, then the closed loop control device 43 controls the metering pump 33 to dispense less plasticiser.

The roller pair 3 is a further control means that is influenced by the closed ioop con-trol device 43 via the control line 3a, in the sense of inserting a preset quantity of filter tow into the endless filter rod 24. If the comparison device determines that the actual value of the percentage of the dry filter tow in the endless filter rod 24 de-tected by the evaluation arrangement 42 is too low in comparison to the stored value, then the closed loop control device 43 increases the conveyor speed of the roller pair 3 using the control line 3a via the drive, so that the pair stretches the filter tow strip 4 less strongly so that more filter tow arrives in the endless filter rod 24. In contrast, if the comparison device determines that the actual value of the percentage of filter tow in the endless filter rod 24 detected by the evaluation arrangement 42 is too high in comparison to the stored value, then the closed loop control device 43 decreases the conveyor speed of the roller pair 3 via the drive, so that the pair stretches the filter tow strip 4 more strongly so that less filter tow arrives in the endless filter rod 24, or forms the endless filter rod 24.

Finally, the climatic chamber 10 is provided as a third control means that is influ-ence by the closed loop control device 43 according to the arrows lOe and lOf in the sense of maintaining a preset moisture of the filter tow strip 4 in the endless filter rod 24. If the comparison device determines that the actual value of the percentage of moisture in the endless filter rod 24 detected by the evaluation arrangement 42 is too low in comparison to the stored value, the closed loop control device 43 in- creases the supply of water vapour from the water vapour source 1 Oa into the cli-matic chamber 10 using the control line lOe via the control valve lOc, and lowers the supply of dry warm air from the warm air source lOb, such that the climatic chamber 10 more strongly moisturises the filter tow strips 4 so that more moisture reaches the endless filter rod 24. If in turn, the comparison device determines that the actual value of moisture in the endless filter rod 24 detected by the evaluation arrangement 42 is too high in comparison to the stored value, the closed loop control device 43 decreases the supply of water vapour from the water vapour source 1 Oa into the climatic chamber 10 by means of the control valve lOd, and increases the supply of dry warm air from the warm air source lOb, such that the climatic chamber dries the filter tow strip 4 so that less moisture reaches the endless filter rod 24.

The percentages of dry filter tow, water and plastieiser in the endless filter rod can be controlled independently of each other. Also, it is not necessary to control all three named percentages. It is possible and expedient to control only one or two of the percentages depending on all three percentages, if for example, one or two of the percentages are proven to be non-critical or substantially constant.

Up to this point, Fig. 1 corresponds substantially to a customary filter producing

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machine of type AF/KDF of the applicant. Jn addition, the overall system in Fig. I comprises an additional offline measurement device, or respectively a filter rod measurement station 50. Filter rods are automatically removed from production on a regular or random basis using a removal device and a conveyor device, and as indi-cated by reference number 51, supplied to the filter rod measurement station 50 for offline measurement. Weight, pressure drop and optionally further variables, such as diameter, are measured therein, as shown with the reference numbers 52, 53, and 54.

The filter rods can then be returned again to the production process, as shown with the reference number 55.

The measurement values of the filter rod measurement station 50 are combined in a signal transmission unit 56, and supplied to the evaluation arrangement 42 and closed loop control device 43 via a data line 57. The evaluation arrangement and closed loop control device use the measurement values together with the data from the microwave measurement device 37, in order to determine percentages by weight of the substances of the endless filter rod 24, and to control the processing condi-tions of the endless filter rod machine such that the measurement values remain within desired parameter ranges.

Fig. 2 shows a microwave resonator according to DE 198 54 550 B4 that can be used in the method according to the invention and in the device according to the inven-tion. A partially broken endless filter rod 24 moved in the direction of the arrow 65 is composed of a filter material 62 and a wrapper of a plug wrap 63, passes through a resonator housing 64, to which microwaves are supplied for the purpose of detect-ing the mass and/or the moisture and/or a plasticiscr percentage.

The resonator housing 64 has a cavity in the shape of a hollow cylinder 66, the inner space 67 of which is symmetrical about the endless cigarette rod 24. For closure, a cover 68 is screwed to it. The hollow cylinder 66 and the cover 68 are preferably composed of a material with a very small coefficient of thermal expansion. This re-sults in good constancy of the geometry of the resonator housing 64 and also good constancy of the measurement results. Alternatively or additionally, the temperature of the resonator housing 64 can be controlled wherein the temperature of the resona-tor housing 64 is recorded by a temperature sensor 69. A heating transistor 71 or a heating resistor, or another suitable heating means is controlled using the tempera- ture sensor 69. In this way, the temperature of the housing 64 is maintained substan-tially constant.

The inner space 67 of the resonator housing 66 is preferably vapor coated with a thin layer of gold, which reliably prevents the formation of corrosion that would ad-versely influence the measurement value consistency, and due to good electrical conduction, simultaneously limits the occurrence of a skin effect.

A protective pipe 73 that is preferably composed of a substance from the polyaryl ether ketone group (PAEK), e.g., of poly ether ether ketone (PEEK), serves for the mechanical closure of the inner space 67 with respect to the endless filter rod 24, and from possibly conveyed dirt particles that would impact the measurement re-sults. The protective pipe 73 is widened in the shape of a funnel at one of its ends 73a, at which the endless filter rod 24 enters into the resonator housing 66. Outside of the inner space 67, the resonator housing 64 extends in a tubular shape (66a, 68a) outwards on both sides in the direction of the endless filter rod 24, in order to pre-vent the emission of microwaves from the resonator cavity. It can also extend in a tubular shape (66b, 68b) inwards to some extent.

An antenna 76 insulated from the metal housing 66 by an insulating ring 74 serves for coupling in the microwaves generated by a microwave generator. An antenna 78 insulated by an insulator 77 serves to decouple microwaves which are to be supplied to an evaluation circuit, not shown. A suitable evaluation circuit can be found in the document, DE 197 34 978 Al, for example.

Fig. 3 shows a preferred embodiment of an HF measurement device 81 in the form of an HF precision capacitor. The HF precision capacitor is constructed substantially rotationally symmetric about the longitudinal axis, that is, the central axis of the endless filter rod 24. The endless filter rod 24 is guided through a central bore hole 82 of the HF precision capacitor in the transport direction 65 which coincides with the longitudinal direction. The HF precision capacitor comprises two rotationally symmetric disc-shaped base bodies 83, 84, oriented perpendicular to the longitudinal direction, that are spaced apart from each other by means of an outer annular non-conductive limiting body 85, and which respectively have a central bore hole 82 for the endless filter rod 24.

An electrode 86, 87 of the HF precision capacitor in the form of a metallic surface, for instance a metallic coating, for example by gold vapour deposition, is attached to each inner surfaces, oriented perpendicular to the longitudinal direction, of the base body 83, 84. The HF precision capacitor is therefore designed as a plate capacitor with plate-shaped electrodes 86, 87 that are shaped like circular discs and are ori-ented perpendicular to the longitudinal direction, and have a central bore hole for the endless filter rod 24. In this arrangement, the field lines run substantially parallel to the direction of transport.

A field-filled space 88 is formed between the base bodies 83, 84 and is closed ra- dially outward by the base body 85. The high-frequency field extends into the cen-tral product cavity 89, and interacts there with the endless filter rod 24. The plates 86, 87 have a smaller radius than the base bodies 83, 84, in order to prevent emis- sion of the high frequency field into the surroundings. The plates can also be dis-posed at a small spacing d from each other, in order to improve the measurement resolution in the longitudinal direction. In particular, the spacing d can be less than the diameter of the endless filter rod 24, and for example, less than 8 mm, preferably less than 4 mm.

The electrodes 86, 87 further have conductive connections 90, 91 to external elcctri- cal connectors. The base bodies 83, 84 each have a tubular extension 92, 93, project- ing axially outward, encompassing the endless filter rod, and having a metallic sur-face or coating 95 on the inner walls that is expediently connected to the electrodes 86, 87. The metallic coating 95 forms a metallic flue in order to prevent the field from leaking out of the through openings of the HF precision capacitor.

Furthermore, there is a pipe 94 composed of non-conductive material extending over the entire length of the sensor, directly surrounding and guiding the endless filter rod 24, that prevents contamination of the interior of the sensor by product residues.

The housing parts of the HF measurement device are preferably composed of a non-conductive material with a small coefficient of thermal expansion in order to attain increased shape stability against thermal influences. For the same purpose, there is preferably a control device, not shown, for maintaining a constant sensor housing temperature.

All named features, including those taken from the drawings alone, and individual features, which are disclosed in combination with other features, are considered in-dividually and in combination as essential to the invention. Embodiments according to the invention can be satisfied through individual characteristics or a combination of several characteristics.

-20 -List of reference sypjbol 1 filter tow preparation unit 2 endless filter rod forming unit 2a housing 3 roller pair 3a control line 4 filter tow strip 4a endless rod of filter material redirection roller 6 bale 7, 8 air nozzles 9 roller pair climatic chamber lOa water vapour source lOb warm air source lOc, lOd controllable control valve tOe, lOf control line for controllable control valve 11 roller pair 12 applicator device 13 pre-tension roller pair 14 control dancer roller 16 controllable final control element 17 inlet funnel 18 reel 19 gluing device 21 plugwrap strip 22 garniture tape 23 format 24 endless filter rod

I

main control 25a -25c control line 26 seam sealer 27 knife apparatus 28 filter rod 29 accelerator 31 catcher drum 32 catcher belt 33 metering pump 33a control line 34 feed line 36 plasticiser stock 37 microwave measurement device 37a data line 42 evaluation arrangement 43 closed loop control device filter rod measurement station 51 filter rod removal 52 weight measurement 53 pressure drop measurement 54 measurement of the diameter feedback of the filter rods 56 signal transmission unit 57 data line 62 filter material 63 plug wrap 64 resonator housing transport direction 66 hollow body 66a, 66b tubular extension 67 inner space -22 -68 cover 68a, 68b tubular extension 69 temperature sensor 71 heating transistor 73 protective pipe 73a end of the protective pipe 74 insulation 76 antenna 77 insulation 78 antenna 81 HF measurement device 81a data line 82 through hole 83, 84 disc-shaped base body limiting body 86, 87 electrode

88 field-filled space

89 central production space 90, 91 conductive connection 92, 93 extension 94 pipe metallic coating

Claims

SCLAIMSI. A method for producing at least one endless filter rod (24) of the to bacco processing industry from at least one filter tow (4), particularly from a filter tow (4) of cellulose acetate, wherein a plasticiser is added to the filter tow (4), and after the addition of plasticiser, an endless filter rod (24) is formed from the filter tow, wherein filter rods (28) of single or several use lengths are then cut from the endless filter rod (24), wherein the endless fil- ter rod (24) before cutting the filter rods (28), passes through an I-IF meas- urement device (81) and/or a microwave measurement device (37, 64), char- aeterised in that individual filter rods (28) are removed and supplied to a fil-ter rod measurement station (50), in which at Least the mass and pressure drop of the filter rods (28) are measured, wherein percentage by weight of plasticiser and/or moisture in the endless filter rod (24) are determined from the measurements of mass and pressure drop of the filter rods (28) and the measurement with the HF measurement device (81) and/or the microwave measurement device (37, 64) at the endless filter rod (24).
2. The method according to claim 1, characterised in that there is a control of the filter rod production, particularly control of the application of plasticiser or climatisation, if the determined value of the percentages by weight of plasticiser in the endless filter rod (24) and/or moisture of the end-less filter rod (24) deviate from a pre-determinable, or preset value or value range.
3. The method according to claim 1 or 2, characterised in that a phase shift and/or a change of signal amplitude is measured in the HF measurement device (81).
4. The method according to one of the claims Ito 3, charaeterised in that a shift of the resonance frequency and/or a spread of the resonance curve -24 -Sand/or a change of a slope of the resonance curve and/or a change of signal amplitude is measured in the microwave measurement device (37, 64).
5. The method according to one of the claims ito 4, characterised in that a temperature of the endless filter rod (24) is measured at the endless filter rod (24) immediately before, at, or immediately after the HF measurement device (81) or the microwave measurement device (37, 64), wherein in par- ticular, the temperature of the endless filter rod (24) is considered for deter-mining percentages by weight of plasticiser and/or moisture in the endless filter rod (24).
6. The method according to one of the claims ito 5, characterised in that drops of plasticiser and/or foreign bodies in the endless filter rod (24) are detected based on rapid changes of the measurement values in the HF meas-urement device (81) and/or the microwave measurement device (37, 64).
7. The method according to one of the claims i to 6, characterised in that at least two endless filter rods (24) are produced in parallel, and each of the at least two endless filter rods (24) passes through an HF measurement de- vice (81) and/or a microwave measurement device (37, 64), wherein individ- ual filter rods (28) cut from the at least two endless filter rods (24) are re- moved, and are supplied to a filter rod measurement station (50) or respec-tively to one of a plurality of filter rod measurement stations (50).
8. The method according to one of the claims ito 7, characterised in that the filter rods (28) that were supplied to a filter rod measurement station (50), after the measurement in the filter rod measurement station (50), are supplied to further production of rod-shaped products provided with filters of the tobacco processing industry.
9. A system for producing at least one endless filter rod (24) of the to- -25 -Sbacco processing industry from at least one filter tow (4), particularly from a filter tow (4) composed of cellulose acetate, with an endless filter rod pro-duction machine (1, 2) and at least one filter rod measurement station (50), wherein the endless filter rod production machine (1, 2) comprises a control unit (42, 43), and application device (12) for plasticiser, a format device (17, 22, 23) for forming an endless filter rod (24) from the filter tow (4), an HF measurement device (81) and/or a microwave measurement device (37, 64), and a cutting device (27) for cutting filter rods (28) from the endless filter rod (24), characterised in that a removal device and a conveyor device are provided by means of which individual filter rods (28) can be removed and can be conveyed to the filter rod measurement station (50), wherein the filter rod measurement station (50) has devices for measuring mass and pressure drop of the filter rods, wherein a data line (57) is provided for transmitting measurement data from the at least one filter rod measurement station (50) to the control unit (42, 43) of the endless filter rod production machine (1, 2), wherein the control unit (42, 43) is designed to determine a percentage by weight of plasticiser and/or moisture in the endless filter rod (24) from the measurement data of mass and pressure drop of the filter rods (28) and the measurement data from the HF measurement device (81) and/or the micro-wave measurement device (37, 64) at the endless filter rod (24).
10. The system according to claim 9, characterised in that the control unit (42, 43) is designed to control the endless filter rod production, particularly an application of plasticiscr and/or a climatisation, based on the determined percentages by weight of plasticiser and/or moisture in the endless filter rod (24).
II, The system according to claim 9 or 10, characterised in that the end-less rod machine (1, 2) is designed as a twin endless rod machine or as a multiple endless rod machine, wherein removed filter rods (28) can be con- veyed to a filter rod measurement station (50) or respectively to one of a plu-rality of filter rod measurement stations (50).
12. The system according to one of the claims 9 to 11, characterised in that said system is designed to perform a method according to one of the claims 1 to 8.
13. A method of producing at least one endless filter rod of the tobacco pressing industry substantially as herein described with reference to the ac-companying drawings.
14. A system for producing at least one endless filter rod of the tobacco pressing industry substantially as herein described with reference to accom-panying drawings.