GB2079580A

GB2079580A - Method and apparatus for tensioning a filter rod

Info

Publication number: GB2079580A
Application number: GB8119819A
Authority: GB
Original assignee: Hauni Werke Koerber and Co KG
Current assignee: Koerber AG
Priority date: 1980-06-27
Filing date: 1981-06-26
Publication date: 1982-01-27
Also published as: IT1136848B; GB2079580B; IT8122481A0

Abstract

The pull upon the running tow of filamentary filter material in a filter rod making machine is maintained at a constant value by monitoring the velocity of the stretched tow and/or a parameter which varies as a function of changes of velocity of the stretched tow, by applying to the tow a retarding force upstream of the location of pull, and by varying the retarding force in response to variations of velocity of the stretched tow so as to maintain the pull at or close to an optimum value. This ensures that the density and draw resistance of the fillers or filter plugs which are obtained from the stretched tow remain unchanged. The retarding force can be applied by one or more idler rolls, by a set of jaws, by one or more driven rolls or by one or more brake shoes. <IMAGE>

Description

SPECIFICATION Method and apparatus for producing a filter rod The present invention relates to a method and apparatus for the production of filter rod sections which can be utilized in the manufacture of filter cigarettes, cigars or cigarillos. More particularly, the invention relates to improvements in a method and apparatus for the production of filter rod sections of the type wherein a converted tow of filamentary filter material constitutes a rod-like filler which is confined in an envelope consisting of cigarette paper, imitation cork or another suitable wrapping material.

It is already known to convert a continuously running tow of filamentary filter material (such as cellulose acetate fibers) into a rod-like filler which is thereupon draped into a continuous web of cigarette paperorthe like to form therewith a continuous filter rod. The latter is severed at regular intervals to yield a file of discrete filter rod sections of desired length (e.g., six or eight times unit length, depending on the nature of the filter tipping machine wherein plain cigarettes, cigars or cigarillos are assembled with filter rod sections to form filter cigarettes, cigars or cigarillos of unit length or multiple unit length).The tow is withdrawn from a bale of densely packed filter material and is subjected to a stretching action which is followed by the application of atomized plasticizer (such as triacetin) before the thus treated tow is caused to advance through a so-called gathering horn and is thereby converted into the aforementioned rod-like filler. The stretching action is carried out while the tow travels lengthwise and while the forward movement of the running tow is opposed by a retarding or braking action which must be overcome by one or more pairs of advancing rolls with attendant stretching of the filamentary filter material. Stretching of filamentary filter material of which the tow consists is desirable and advantageous because, in its initial state, the material is not homogeneous.This is attributable (at least to a considerable degree) to pronounced crimp of filamentary filter material while the material forms a bale consisting of a very large number of flattened and highly compacted loops which together constitute the tow. Another reason for the lack of homogeneousness of filamentary filter material is the absence of regularity in the distribution of filaments within the tow, i.e., the filaments are likely to cross each other, to be partially interlaced with each other, to form bunches of more or less pronouncedly crimped fibers and/or to otherwise contribute to variations of density, as considered in the longitudinal direction of the tow.

On the other hand, predictable density or homogeneousness of the filler in a filter rod is a very important requisite for the production of satisfactory filter rod sections. In other words, the making of filter rod sections should involve such treatment of the tow that the filler of the filter rod will exhibit highly predictable characteristics, especially as concerns the homogeneousness of the filamentary filter material.

A very important characteristic of filter rod sections is their resistance to axial flow of tobacco smoke therethrough. Many manufacturers of filter cigarettes, cigars or cigarillos (hereinafter referred to as filter cigarettes for short) demand that the resistance of filter plugs (i.e., the resistance of filter rod sections of unit length) be maintained within a very narrow range which includes or very closely approximates the optimum or preferred resistance to axial flow of smoke into a smoker's mouth. A smoker expects to encounter a certain resistance which is offered by the filter material and which compels the smoker to exert a certain effort in order to draw a desired quantity of smoke into his or her mouth or lungs.Any deviations from the accustomed resistance are annoying to the smoker, especially if such deviations take place between the filter plugs of filter cigarettes in one and the same pack or in one and the same carton.

The aforementioned resistance to axial flow of tobacco smoke through the filter plug of a filter cigarette depends primarily upon the quantity of filamentary filter material in the plug, i.e., on the density of the filler. The density, in turn, depends upon the extent to which the filaments of the tow are stretched subsequent to withdrawal from the bale and preparatory to contact with atomized plasticizer.

In other words, by changing the stretching or elongating action, it is possible to influence the density of the filler in a filter plug and hence the aforementioned resistance (hereinaftercalled draw resistance) of filamentary filter material within the confines of the tubular envelope forming part of the filter plug.

The stretching or elongating action depends on the force (pull) which is applied to the filaments during travel between the bale and the gathering horn.

Such force or pull, in turn, can be regulated in dependency on changes in the draw resistance of ultimate products (filter cigarettes) and/or on changes in the density of the filler. In other words, by continuously monitoring the draw resistance of filter cigarettes and/or the density of successive increments of the filter rod, one can generate signals which are thereupon utilized to regulate the pull in order to turn out a succession of filter plugs whose characteristics (draw resistance) match or very closely approximate the optimum characteristics.

Reference may be had to German Offenlegungsschrift No. 2,336,005.

The means for stretching the tow of filamentary filter material normally comprises a succession of pairs of drums or rolls. The tow is caused to advance through the nips of successive pairs of rolls. For example, if the stretching means comprises two pairs of rolls, the rolls of the downstream pair are driven at a peripheral speed higher than the peripheral speed of the upstream pair of rolls so that the filaments of the tow are stretched in the region between the two pairs of rolls. In fact, it is not even necessary to drive those rolls which are first to contact successive increments of the tow, i.e., such upstream rolls can constitute idler rolls which offer a certain resistance to rotation under the action of the running tow; this resistance must be overcome by the driven (downstream) rolls.The difference between the peripheral speeds of the two pairs of rolls determines the extent of the stretching or elongating action.

The aforementioned German Offenlegungsschrift No. 2,336,005 discloses a stretching or elongating unit wherein the tow is caused to form a loop between two pairs of driven advancing rolls. The bight of the loop contains a dancer roll whose weight acts upon the filaments of the tow. Such weight can be augmented by an auxiliary weight. To this end, the dancer roll is mounted at the free end of a pivotable leverwhich carries the auxiliary weight in such a way that the latter is movable nearer to or further away from the dancer roll. Thus, the force which the dancer roll applies to and thereby stretches the filamentary material of the tow between the two pairs of driven rolls can be varied by moving the auxiliary weight nearerto the fulcrum forthe leveror nearerto the dancer roll.

A drawback of the just described conventional stretching unitisthatthe roll is mounted ata considerable distance from the locus where the filter rod is severed to yield a succession of discrete filter rod sections of desired length. Therefore, filter rod making machines embodying such stretching units afford ample opportunity for the manufacture of substantial numbers of defective filter rod sections before the deviation of actual draw resistance of filter cigarettes from the desired value is detected and eliminated. This is even more so when the filter rod sections are either stored or transported through considerable distances between the filter rod making machine and the filtertipping machine.In such instances, the filter rod making machine can turn out very large numbers of defective filter rod sections before the defects are detected by monitoring the draw resistance of filter cigarettes issuing from the filter tipping machine. Presently known attempts to indirectly ascertain the draw resistance at a locus ahead of the filter tipping machine have met with outright failure or with highly limited success, i.e., the measurements are accurate in all respects only if they are carried out upon the final products, namely, upon the filter cigarettes rather than upon filter rod sections and/or upon the filter rod.Therefore, the detection of deviations of measured or monitored draw resistance from the desired or optimum draw resistance invariably entails the segregation of a substantial number of defective or presumably defective filter rod sections and/or filter cigarettes which happened to be located between the stretching unit of the filter rod making machine and the monitoring or measuring station of the filter tipping machine at the time a defective filter cigarette was detected and the defect (unsatisfactory draw resistance) was considered to be sufficiently pronounced to warrant an adjustment of the stretching or elongating action.In other words, heretofore known methods and apparatus entail the production of excessive numbers of defective articles because the distance or interval between the locus or time of production of defective articles or portions of defective articles and the locus or time of defection of such defective articles or portions of defective arti cles is rather long.

One feature of the invention resides in the provision of a method of processing a continuous stretchable tow of filamentary filter material which is utilized for conversion into fillers of filter plugs for cigarettes or the like and advances lengthwise in a predetermined direction along an elongated path (such path may but need not be straight); for example, the path may exhibit a pronounced loop and/or may include an arcuate or undulate portion).The method comprises the steps of stretching the tow in a predetermined section of the path including exerting upon the tow a pull ortensional stress in a first portion of the aforementioned section and simultaneously applying to the tow a retarding or advancement-opposing force in a second portion of the aforementioned path section upstream of the first portion, measuring the velocity of the stretched tow (such measurement may involve direct monitoring of velocity of the stretched tow and/or indirect measurement of the velocity by monitoring one or more parameters which vary in dependency on or concomitantly with changes of velocity of the stretched tow), and influencing the retarding or advancement-opposing force in response to changes of measuring velocity so as to maintain the pull at least substantially at a constant value.This ensures that the density of the stretched tow is constant or deviates only negligibly from a desirable optimum value. Predictable density, in turn, ensures predictable draw resistance of the fillers of filter plugs which contain portions of the stretched tow.

As a rule, the retaining force which acts upon successive increments of the advancing tow upstream of the locus of application of pull has several components, and the influencing step may comprise varying at least one of these components as a function of changes of velocity of the stretched tow. For example, one of the components may constitute the resistance to rotation which is offered by one or more idler rolls or jaws engaging the running tow upstream of the locus of application of the pull; such resistance to rotation varies in dependency on the velocity of the tow.Another component may constitute the mass or weight of the idler roll or rolls, and such mass can be varied in dependency on changes of velocity of the stretched tow (for example, by arti ficially increasing or reducing the mass of the idler roll or rolls as a result of shifting one or more auxiliary weights nearer to or further away from the locus of contact between the idler roll or rolls on the one hand and the running tow on the other hand). Alter nativeiy, and especially if the measuring step includes directly monitoring the velocity of the stretched tow, e.g., downstream of the aforementioned section of the elongated path for the running tow, at least one of several components of the retarding force is or can be varied as a function of variations of the velocity of the stretched tow so that the pull remains constant or deviates only negligibly from a desirable optimum value corresponding to optimum density of the stretched tow and to optimum characteristics of products which are obtained on further processing of the stretched tow (such further processing may involve contact with droplets of a suitable atomized plasticizer and con version of the tow into a rod-like filler which is draped into cigarette paperorthe like to form therewith a continuous filter rod ready to be subdivided into filter rod sections of desired length).

The retaining force can be applied to the tow substantially transversely of the aforementioned path section and may include a velocity-dependent first component as well as a velocity-independent second component; the influencing step then preferably includes varying the second component of the retarding force as a function of variations of velocity of the stretched tow. Prior to the application of retarding force substantially transversely of the path section upstream of the locus of application of the pull, the tow is preferably converted into a relatively wide and relatively thin layer, and the retaining force is preferably applied along the full width of such layer.The pull can be applied by a pair of driven rotary elements (such as a pair of driven advancing rolls or drums) which are mounted in or at the first portion of the aforementioned path section in such a way that the filamentary material of the tow advances through the nip of the rotary elements.

The retarding force can be applied, at least in part, by a single tow-engaging element (e.g., a dancer roll) or by a plurality (e.g., a pair) of tow-engaging elements which engage different sides of the tow in or at the second portion of the aforementioned path section.

The pull may be applied by a pair of driven rotary elements in the first portion of the path section, and the retarding force can be applied by a second pair of rotary elements which are rotated by and offer a variable resistance to rotation by the tow. The tow then advances through the nips of the two pairs of rotary elements, and the influencing step then comprises vary the resistance which the rotary elements of the second pair offer to rotation as a function of variations of velocity of the stretched tow. The resistance varying step may include urging the rotary elements of the second pair against the tow therebetween with a force which varies as a function of variations of velocity of the stretched tow or of variations of a parameter which changes proportionally with variations of velocity of the tow.

The aforementioned pull can be said to vary with the velocity of the stretched tow. Therefore, the measuring step may include monitoring the position of at least one tow-engaging element (e.g., a dancer roll, a pair of idler rolls or a pair of jaws) whose position varies as a function of variations of the pull and, if the retarding force has several components, the influencing step then includes varying at least one of these components in dependency on deviations or departure of monitored position of the towengaging element or elements from a predetermined position which denotes a predetermined pull upon the tow. The monitoring step may include measuring the distance between the predetermined position of the tow-engaging element and the actual position of such element.

The step of applying the retarding force may include subjecting the tow to a variable braking action upstream of the tow-engaging element or to a variable braking action which includes the braking action of the tow-engaging element upon the filamentary filter material of the tow. Thus, and if the tow-engaging element is a rotary element which furnishes a portion of the braking action and whose resistance to advancement of the tow varies as a function of variations of velocity as well as a function of changes of area of contact with the tow, the position of the tow-engaging element is preferablyvari- able in and counter two the direction of lengthwise movement of the tow as a function of variations of velocity of the stretched tow (the one component is then the aforementioned portion of the braking action, namely, the portion which is furnished by the tow-engaging element). The influencing step then preferably includes varying the combined braking action as a function of variations of the position of the tow-engaging element.

If the roll oran analogous rotarytow-engaging element offers to advancement of the tow a resistance which varies as a function of variations of velocity of the stretched tow, the measuring step may simply involve monitoring the resistance of the roll.

Such roll may be a non-driven roll which loops the tow between the first and second portions of the path section.

If the retarding force is supplied by several jaws or grippes which bear against the tow with a variable force and are movable in and counter two the direction of lengthwise movement of the tow in response to variations of velocity of the stretched tow, the influencing step may include varying the force of the jaws in dependency on the extent of movement of such jaws from a predetermined position. The just discussed embodiment of the method preferably further comprises the step of monitoring the deviation of the actual position of the jaws from the aforementioned predetermined position.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved stretching apparatus itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawing.

FIG. 1 is a schematic elevational view of a filter rod making machine embodying a stretching apparatus which is constructed and assembled in accordance with one embodiment of the present invention and comprises a dancer roll; FIG. 2 is a larger-scale schematic elevational view of a second stretching apparatus.

FIG. 3 is a similar view of a stretching apparatus which constitutes a modification of the apparatus shown in FIG. 2; FIG. 4 is a schematic side elevational view of a fourth stretching apparatus with a grain gauge; FIG. 5 is a schematic side elevational view of a fifth stretching apparatus constituting a modification of the apparatus shown in FIG. 4; FIG. 6 is a schematic elevational view of a sixth stretching apparatus constituting a further modification of the apparatus which is illustrated in FIG. 2; FIG. 7 is an enlarged axial sectional view of a dancer roll in the stretching apparatus of FIG. 6; FIG. 8 is a schematic elevational view of a seventh stretching apparatus which comprises a series of stationary and mobile brake shoes for the running towoffilamentaryfilter material;; FIG. 9 is a schematic side elevational view of an eighth stretching apparatus which constitutes a modification of the apparatus shown in FIGS. 4 and 5; and FIG. 10 is a schematic elevational view of a ninth stretching apparatus constituting a modification of the apparatus which is illustrated in FIG. 9.

Referring first to FIG. 1, there is shown a filter rod making machine which comprises a first section or unit 2 serving to convert a continuous stretchable running tow 4 offilamentary filter material (such as cellulose acetate fibers) into a continuous rod or filler, and a second section or unit 1 wherein the filler is assembled with a continuous web 7 of cigarette paper, imitation cork or a similar wrapping material to form therewith a continuous filter rod 11 which is subdivided into filter rod sections 11 a of desired length. The machine which is shown in FIG. 1 is similartothose known as"KDF" manufactured bythe assignee of the present application.

The means for converting the running tow into a continuous rod-like filler comprises a so-called gathering horn 3 through which the filaments of the processed (stretched and wetted) tow 4' pass on their way into contact with the running web 7. The web 7 and the filler advance through a wrapping mechanism 6 wherein the web 7 is draped around the filler so that it constitutes a continuous tube whose marginal portions overlap each other to form a seam extending in the longitudinal direction of the resulting filter rod 11. The seam is heated or cooled (depending on the nature of adhesive which coats at least a portion of or an entire side of the web 7) by a so-called sealer 9 before the rod 11 enters a cutoff 12 to be severed at regular intervals so as to yield a file of filter rod sections 1 lea of desired length.Such file of filter rod sections is thereupon converted into one or more rows wherein the sections travel sideways, and the row or rows are transported into a reservoir system, to a pneumatic propelling device which feeds the filter rod sections to one or more filtertipping machines, or directly into the magazine or magazines of one or more filtertipping machines.

Suitable filter tipping machines are produced by the assignee of the present application and are known as MAX and MAX S.

The means for transporting the web 7 and the filler of filamentary filter material through the wrapping station which is defined by the mechanism 6 includes an endless belt conveyor 8 known as garniture. The means for driving the garniture 8 comprises at least one of several pulleys over which the garniture is trained. One such pulley is denoted by the reference character 53, and the shaft which drives the pulley 53 is shown at 52.

The web 7 is drawn off a bobbin 16 by two advancing rolls 14 and is thereupon moved lengthwise by the garniture 8 to advance along a suitable paster 17 having a roller-shaped applicator 17a serving to coat the adjacent side of the running web 7 with one or more strips of suitable adhesive. For example, the applicator 17a can apply adhesive to one or both marginal portions of the web 7 as well as one or more strips of adhesive to the intermediate portion between the marginal portions at the respective side of the web 7. The adhesive which is applied to the marginal portion is used to form the aforementioned seam, and the intermediate strip or strips are used to cause the web 7 to adhere to the filler of filamentary filter material.

The cutoff 12 is followed by a conventional accelerating cam (not shown) which propels successive filter rod sections 11 a of the file into the oncoming flutes at the periphery of a driven row forming drum (not shown) which converts the single file of filter rod sections 11 a into one or more rows wherein the filter rod sections move sideways on their way to the next processing ortransporting station. The flutes of the just mentioned row forming drum are provided with means for braking and arresting successive filter rod sections 11 a so that such sections form one or more rows wherein the neighboring sections are accurately aligned with one another. A suitable row forming drum is shown, for example in commonly owned U.S. Pat. No.3,971,695 granted July 1976 to Hans-Jürgen Block.The disclosure of this patent is incorporated herein by reference.

The first section or unit 2 of the filter rod making machine shown in FIG. 1 comprises a so-called banding device 18 which spreads the filaments of the running tow 4 between a bale 19 and a deflecting roller 21. The bale 19 is confined in a receptacle 1 9a and contains a substantial quantity of filamentary filter material which forms a plurality of closely adjacent and highly compacted loops so that the bale 19 can furnish a very long tow without necessitating replacement of the receptacle 19a with a fresh receptacle. The banding device 19 comprises a pipe 18a which supplies a stream of compressed air to a nozzle 18b having a plurality of orifices (not specifically shown) which direct jets of compressed air against the adjacent side of the running tow 4 so as to separate or untangle the filaments.The jets impinge upon a plate 18e which is installed opposite the nozzle 1 8b and defines with the latter a narrow channel for the travel of expanded tow 4 therethrough and on toward the deflecting roller 21. A second banding device 22 which is preferably identical with or similar to the banding device 18 is installed downstream of the deflecting roller 21, as considered in the direction of lengthwise movement of the tow 4 toward the gathering horn 3.

The second banding device 22 is followed by a stretching means or stretching apparatus 23 wherein the filaments of the stretchable tow 4 are treated in accordance with a first embodiment of the present invention. The stretching apparatus 23 comprises a first pair of rolls 24 or analogous tow-engaging rotary elements, a second pair of rolls 26 or analogous rotary tow-engaging elements, and a ballast or weight 41 constituting a rotary tow-engaging element or dancer roll and defining the bight of an elongated loop 27 between the pairs of rolls 24 and 26. The dancer roll 41 forms part of a looping device which, together with the pair of rolls 24, constitutes the tow retarding or braking means of the stretching apparatus 23. Such retarding means applies to the tow a variable retarding force which opposes the advancement or movement of the tow toward the nip of the rolls 26.The pair of rolls 26 constitutes a tensioning means for exerting upon the running tow 4 a pull in a first portion of that section of the elongated path of the tow which extends between the pairs of rolls 24 and 26. The rolls 26 are followed by a third pair of rolls 28 which serve to effect further spreading or widening of the running tow 4 before successive increments of the tow enter a plasticizer applying or wetting station 29, for example, a station of the type disclosed in commonly owned U.S. Pat.

No.4,132,189 granted January 2, 1979 to Heinz Greve et al. The plasticizer is preferably triacetin or an analogous substance whose finely atomized droplets can melt portions of the filaments and cause such molten portions to adhere to each other so that the filaments of the filler downstream of the gathering horn 3 form a maze of complex paths for the flow of tobacco smoke through the filter plugs. The filaments of the tow 4 which issue from the wetting station 29 are trained about the rolls of a fourth pair of rolls 31 on their way toward the gathering horn 3.

The means for transmitting motion to various moving parts of the machine shown in FIG. 1 comprises a main prime mover 32 (for example, a variable-speed electric motor) whose rotary output element transmits motion to several belt or chain drives including a first drive 34 serving to rotate the lower roll 28, a second drive 33 serving to rotate the lower roll 26, a third drive 36 serving to rotate the lower roll 31, and a fourth drive 38 serving to rotate the input element of a variable-speed transmission 37 for the lower roll 24. The ratio of the transmission 37 can be varied by a reversible electric motor 39.

The prime mover 32 can further transmit torque to the pulley or pulleys for the garniture 8 as well as to the advancing rolls 14 forthe web 7. The moving parts of the cutoff 12 are preferably driven by a discrete electric motor, not shown. The drives 33,34,36 are preferably belt drives or toothed belt drives, and the drive 38 is preferably a chain drive.

The loop forming means of the stretching apparatus 23 includes the aforementioned dancer roll 41 which rests in the bight of the loop 27 between the pairs of rolls 24 and 26 and effects at least some stretching or straightening of crimps which are characteristic of filamentary filter material of which the tow 4 consists and which contribute to the ability of the tow to undergo a stretching action. The peripheral speed of the pair of rolls 26 may but need not match the peripheral speed of the pair of rolls 28.

In the embodiment of FIG. 1, the ratio of peripheral speeds of the pairs of rolls 26,28 is constant owing to lack of adjustability of the torque-transmitting connection between the shaft for the lower roll 28 and the shaft for the lower roll 26. However, it is possible to provide means which allows for or causes rotation of the rolls 28 at a speed exceeding that of the rolls 26 so that the tow 4 is subjected to a further stretching action during travel along the path section between the pairs of rolls 26, 28.

The dancer roll 41 is mounted at the free righthand end of an elongated carrier here shown as a lever or arm 42 which is fulcrumed, as at 43, in the frame F of the filter rod making machine. The shaft for the dancer roll 41 is preferably mounted on or in the arm 42 by interposition of one or more antifriction bearings (not specifically shown) so as to ensure that the friction between the roll 41 and the arm 42 is minimal or negligible. The braking, retarding or advancement-opposing force of the dancer roll 41 is generated primarily by its weight as well as by an auxiliary weight 44 which is reciprocable lengthwise of the arm 42 between the shaft for the dancer roll 41 and the fulcrum 43 in directions indicated by a double-headed arrow 49.The means for reciprocating the weight 44 lengthwise of the arm 42, and for thereby influencing (varying) the braking or retarding action of the dancer roll 41 upon the running tow 4, comprises a reversible electric motor 47 mounted on the left-hand portion of the arm 42 and serving to drive a pinion 48 in mesh with a toothed rack 46 which is connected with the auxiliary weight 44.

Depending on the direction of rotation of the pinion 48, the rack 46 will move the auxiliary weight 44 toward or away from the dancer roll 41 to thereby increase or reduce the retarding force with which the dancer roll 41 opposes advancement of successive increments of the tow 4 toward the nip of the pair of driven rolls 26. The motor 47 may constitute a conventional gear motor. If desired, the pinion 48 can be replaced with a rotary nut in mesh with an elongated feed screw replacing the rack 46 of FIG. 1. Other types of means for reciprocating the auxiliary weight 44 lengthwise of the arm 42 in response to signals which are generated on monitoring of certain characteristics of the filter rod 11 and/or the parameters of one or more constituents of the filter rod 11 can be utilized with equal advantage.The resistance which the non-driven rotary element or elements contacting the running tow 4 offer to lengthwise movement of the tow depends on the velocity of the tow. Otherwise stated, the pull upon the tow 4 (in order to ensure that the tow will advance at a desired speed and the density of the stretched tow will always match or closely approximate a constant value) will depend on the momentary velocity of the tow.

In accordance with a feature of the invention, the filter rod making machine of FIG. 1 comprises means for directly or practically directly monitoring the velocity of the stretched tow 4. In the embodiment of FIG. 1, the monitoring means comprises a signal generating tachometer generator 51 which is operatively connected with the shaft 52 for the pulley 53 shown in the left-hand portion of FIG. 1. The speed of the shaft 52 matches the speed of the garniture 8 and hence the speed of the web 7 as well as the speed of the filler consisting of treated filamentary filter material forming the stretched tow 4'. The output of the tachometer generator 51 transmits signals which are indicative of the speed of the shaft 52 and of the filamentary filler material. Such signals are transmitted to an amplifier 56 by way of conductor means 54, and the output of the amplifier 56 is connected with the input of the reversible electric motor 47 on the arm 42 carrying the dancer roll 41. Thus, signals from the tachometer generator 51 can regulate the total or overall retarding or braking force acting upon the filamentary filter material upstream of the pair of rolls 26. The motor 47, its pion 48 and the rack 46 constitute a means for influencing (varying) the retarding force which is applied by the dancer roll 41 and non-driven (idler) rolls 24.Such force has a velocity-dependent first component (applied by the rolls 24 and 41) which varies automatically as a function of changes of velocity of the stretched tow 4', and a velocity-independent second component which is the mass of the rolls 24,41 pius the effective mass of the weight 44 and is varied exclusively on rotation of the pinion 48, i.e., in response to changes in monitored velocity of the stretched tow 4'. The second component is varied by the influencing means 4648 in response to signals from the monitoring or measuring means 51.

The filter rod making machine of FIG. 1 further comprises means 57 for regulating the size or length of the loop 27. Such regulating means comprises a loop measuring or monitoring means here shown as a potentiometer 58 including a resistor 59 cooperating with a wiper 61 which is connected to the free end portion of the carrier or arm 42 so that the angular position of the wiper 61 with reference to the pivot axis defined by the fulcrum 43 for the arm 42 is indicative of the length or size of the loop 27. The wiper 61 is connected with the input of an operational amplifier 62 which controls the operation of the reversible electric motor 39. As mentioned before, the motor 39 can regulate the ratio of the transmission 37 and hence the speed of the pair of rolls 24. If the speed of the pair of rolls 24 is reduced, the length of the loop 27 is reduced, and vice versa.

The manner in which the wiper 61 connects the amplifier 62 with a source of electrical energy by way of that portion of the resistor 59 which is located below the tip of the wiper, as viewed in FIG. 1, is well known and is not specifically shown in the drawing.

The operation of the filter rod making machine which is shown in FIG. 1 is as follows: The rolls 24 continuously draw the tow 4 from the bale 19, and successive increments of the running tow are banded during travel through the devices 18 and 22 so that the tow is converted into a relatively wide and thin layer wherein all or nearly all of the filaments are accessible forthe application of atomized liquid plasticizer. The tow 4 is thereupon stretched during travel through the stretching apparatus 23 so as to further increase the likelihood of uniform application of atomized plasticizer to the filaments which advance through the wetting station 29.The thus treated (stetched and wetted) tow 4' is then caused to travel through the nip of the rolls 31 and enters the gathering horn 3 to be converted into a rod-like filler wherein the filaments adhere to each other in regions which are contacted by droplets of finely atomized plasticizer during travel through the wetting station 29. The web 7 is draped around the filler during travel through the wrapping mechanism 6, and the resulting filter rod 11 advances past the sealer 9 which heats or cools the aforediscussed seam to reinforce the tubular envelope prior to severing of the rod 11 by the cutoff 12.

The stretching apparatus 23 is designed to effect a predetermined elongation of the tow 4, namely, to effect a stretching which suffices to ensure that the normally irregular crimp of the filaments does not or does not unduly influence the desirable characteristics of filter rod sections 1 lea, especially the density and hence the draw resistance of the fillers of such filter rod sections. The extent of stretching or elongation is determined by the pull which is applied to the filaments of the tow 4 during travel through the stretching apparatus 23. The dancer roll 41 opposes the pull by applying a braking or retarding force which tends to oppose the lengthwise movement of the tow 4 toward the plasticizer applying station 29.

In the stretching apparatus 23 of FIG. 1, the braking or retarding force includes the aforementioned first component K, which is a function of velocity of the tow 4 and is generated (at least in part) by the dancer roll 41, as well as a second component K2 which is independent of the velocity of the tow 4 and is determined (at least in part) by the weight of the parts acting upon the loop 27 between the pairs of rolls 24 and 26. Such weight includes the mass of the dancer roll 41 and the variable effective mass of the weight 44.The weight or mass of the dancer roll 41 remains constant but the effect of the mass of the weight 44 upon the loop 27 varies in dependency on the nature and intensity of signals which are transmitted by the tachometer generato r 51 via conductor means 54 and amplifier 56 to control the operation of the motor 47 which, in turn, influences the position of the auxiliary weight 44 between the fulcrum 43 and the dancer roll 41.

The first component or force K, is determined by frictional forces acting upon the dancer roll 41, i.e., primarily by the frictional forces between the shaft of the dancer roll 41 and the arm 42 (if the shaft rotates with the roll 41) or between the dancer roll 41 and its shaft (if the shaft is held against rotation with the roll 41). Thus, the pull upon the running tow 4 (and hence the extent to which the tow 4 is stretched in the apparatus 23) depends on the velocity of the stretched tow because such velocity determines the force K, namely, the resistance which the dancer roll 41 offers to lengthwise movement of the tow as a result of frictional engagement of its shaft with the arm 42 or as a result of frictional engagement between this dancer roll and its shaft.For the sake of simplicity, it will be assumed that the shaft rotates with the dancer roll 41 so that the force K1 is a function of friction between such shaft and the arm 42.

The structure which is shown in FIG. 1 is capable of compensating for the influence of changes of the velocity of the stretched tow 4' upon the pull and the stretching or elongating action so that the pull will not depend on the velocity at which the tow travels through and beyond the stretching apparatus 23.To this end the tachometer generator 51 monitors the speed of the garniture 8 (and hence the speed of lengthwise movement of the tow 4 in a region downwstream of the rolls 31) and transmits signals denoting the monitored velocity of the running tow via conductor means 54 and on to the amplifier 56 which regulates the operation of the reversible electric motor 47 accordingly, i.e., the auxiliary weight 44 d < ad toward or away from the dancer roll 41, depending on the ascertained velocity of the garniture 8. Thus, the motor 47 can regulate the magnitude of the aforediscussed second component or force K2 which is independent of the velocity of the stretched tow 4'.Therefore, the combined force K1 + K2 which acts upon the running tow 4 in the region between the pairs of rolls 24 and 26 is changed to influence the resistance which the dancer roll 41 (assisted by the auxiliary weight 44) offers to forward movement of the tow. This entails a corresponding change in the intensity of the pull and hence in the stretching or elongating action upon the running tow 4. The changes are such that the stretching or elongating action upon the running tow 4 remains constant or returns to a preselected value in the event of temporary departure from such value. If the velocity of the tow 4 increases, the tachometer generator 51 transmits a signal which causes the motor 47 to effect a movement of the auxiliary weight 44 in a direction to the left, as view in FIG. 1, i.e., toward the fulcrum 43.Thus, the combined weight or mass acting upon the bight of the loop 27 is reduced, and this entails a reduction of resistance which the dancer roll 41 offers to lengthwise movement of the tow 4 toward the nip of the pair of driven rolls 26. It will be seen that the increased velocity of the tow 4 entails an increased resistance to lengthwise movement of the tow (such resistance is offered by the roll 41 ) which, in turn, results in a reduction of the force K2. Such reduction takes place practically without any delay because the detection of increased velocity of the tow is followed, practically immediately, by an adjustment of the position of auxiliary weight 44 with reference to the dancer roll 41 and fulcrum 43.

Inversely, when the velocity of the stretched tow 4' is reduced, the techometer generator 51 transmits a signal which causes the motor 47 to shift the auxiliary weight 44 in a direction toward the dancer roll 41 so that the combined mass of the roll 41 and auxiliary weight 44 increases with attendant increase of the force K2 which, as stated above, is independent of the velocity of the stretched tow. In other words, the braking or retarding force K, + K2 is increased.

Thus, the fact that the resistance which the dancer roll 41 offers to lengthwise movement of the running tow 4 decreases in response to decreasing velocity of the tow 4 is compensated for by increasing the combined mass of the dancer roll 41 and auxiliary weight 44 so that the sum of the forces K1 + K2 remains unchanged even though the force K1 has decreased as a result of deceleration of the tow 4.

Again, the compensation (by changing the combined mass of the dancer roll 41 and auxiliary weight 44) is effected practically instantaneously so that the length of that portion of the tow 4' wherein the density deviates from the optimum density is negligible.

The stretching apparatus 23 of FIG. 1 ensures that the homogeneousness of the filler of the filter rod 11 is not affected by changes of velocity of the stretched tow 4'. Correction of or compensation for any deviations from desired homogeneousness which develop as a result of dependency of pull upon the resistance of the dancer roll 41 (such resistance, in turn, depends upon the velocity of the tow) is not effected subsequent to detection of actual density of the material of the fillers in finished articles (filter cigarettes) but rather after monitoring of the product in the filter rod making machine proper, i.e., close to or in immediate proximity of the stretching or elongating station.As explained above, monitoring of the finished products (filter cigarettes) for the density of the fillers of their filter plugs would entail the production of a large number of defective articles because the number of rod-shaped articles between the stretching apparatus 23 and the outlet or the testing station in a filtertipping machine is or can be very large, especially if the filter rod sections 11 a are stored between the filter rod making machine of FIG.

1 and the filter tipping machine. Otherwise stated, the improved stretching apparatus can compensate for eventual changes in density of the filler practically instantaneously after such changes (deviations from optimum density) develop in the filler rod making machine, i.e., in the machine in which the stretching apparatus is installed.

In orderto ensure that the dancer roll 41 will remain at or close to the optimum level, i.e., that the dimensions of the loop 27 will not fluctuate within an excessively wide range, the dimensions of the loop 27 are controlled by the regulating means 57 so that the distance between the level of the dancer roll 41 and the level of the pairs of rolls 24,26 does not change beyond an acceptable (and relatively narrow) range. Thus, when the velocity of the tow increases, the retaining or braking force is reduced because the tachometer generator 51 transmits a signal which entails a movement of the auxiliary weight 44 toward the fulcrum 43, i.e., the combined mass of the parts 41,44 decreases and the dancer roll 41 drifts to a higher level.This causes the wiper 61 of the potentiometer 58 to move relative to the resistor 59 and to thereby change the voltage which is applied to the input of the operational amplifier 62 forthe motor 39. The motor 39 changes the ratio of the transmission 37 which accelerates the pair of rolls 24 so that the dancer roll 41 descends to a lower level, i.e., closerto the optimum level or exactly to the optimum level.

If the dancer roll 41 descends or drifts to a lower level, i.e., when the velocity of the tow decreases, the motor 39 changes the ratio of the transmission 37 in such a way that the peripheral speed of the pair of rolls 24 decreases and these rolls advance smaller quantities of filamentary filter material per unit of time. This causes the dancer roll 41 to rise to the desired or optimum level. It will be noted that, in the embodiment of FIG. 1, the regulating means 57 does not or need not contribute to adjustment of the pull upon the running tow 4 but merely controls the level of the dancer roll 41, i.e., the dimensions of the loop 27.

FIG. 2 shows a portion of a modified stretching apparatus 23' wherein all such parts which are identical with or clearly analogous to corresponding parts of the apparatus 23 in the filter tipping machine of FIG. 1 are denoted by similar characters. The stretching apparatus 23' of FIG. 2 again comprises a dancer roll 41 which is located in the bight of the loop 27 between the pair of driven rolls 24 and the pair of driven rolls 26. The manner in which the pairs of rolls 24,26 and 28 are driven is or may be the same as shown for the similarly reference pairs of rolls in the machine of FIG 1.The dancer roll 41 is mounted at the free end of an elongated pivotable carrier or arm 42 which is fulcrumed in the machine frame F, as at 43, and an intermediate portion of which is connected to the upper end portion or uppermost convolution of a resilient element here shown as a coil spring 63 tending to pivot the arm 42 in a clockwise direction, as viewed in FIG. 2, i.e., to move the dancer roll 41 to a lower level and to thereby lengthen and tension the loop 27. In this embodiment of the stretching apparatus, the component K2 which is independent of the velocity of the running tow 4 is generated by the weight of the dancer roll 41 and by the force of the tension spring 63. The lowermost convolution or lower end portion of the coil spring 63 is attached to a pin 64 which is mounted eccentically on a rotary disc-shaped holder 66.The shaft 66a of the holder 66 is rotatable in the frame F about a fixed axis, and the holder 66 can be rotated clockwise or counterclockwise (see the double-headed arrow 69) by a reversible electric influencing motor 67 (corresponding to the motor 47 of FIG.1) through the medium of a smooth or toothed belt drive or a chain drive 68. The motor 67 receives signals from a suitable monitoring device (such as the tachometer generator 51 of FIG. 1) via conductor means 54 so that the direction of rotation of its output element, as well as the extent of angular movement of its output element in the clockwise or counterclockwise direction, depends on the velocity of the stretched tow.

When the velocity of the stretched tow increases, the holder 66 is caused to turn in a counterclockwise direction, as viewed in FIG. so that the tension and hence the bias of the spring 63 upon the loop 27 (via dancer roll 41) decreases proportionally with increasing speed of the tow, i.e., proportionally with increasing resistance of the dancer roll 41 to advancement of the tow as a result of increasing friction between the roll 41 and the arm 42. The result is that the pull and the extent to which the running tow 4 is stretched remain unchanged or rapidly reassume the optimum values.When the velocity of the tow 4 decreases, the pin 64 is again caused to move about the axis of the shaft 66a but in a clockwise direction, as viewed in FIG. 2, so that the bias of the spring 63 increases because the distance between the first and second end portions of this spring increases. Such increased bias is added to the reduced force or component K, with the result that the sum of K1 and K2 remains unchanged, i.e., the pull upon the running tow 4 and hence the stretching action upon the filamentary filter material of the tow remains the same.

Athird embodiment of the stretching apparatus (denoted by the reference character 23") is shown in FIG. 3 wherein the reference characters 4, 24, 26, 28, 41 and 42 denote the same parts as in the filter rod making machine of FIG. 1. The lowermost convolution of the coil spring 163 which is attached to an intermediate portion of the carrier or arm 42 is affixed to the frame F, as at 164. In this embodiment of the invention, changes in speed in lengthwise movement of the tow 4 are compensated for by the variable-speed transmission 137 whose input element is driven by the endless belt or chain 138 (corresponding to the belt or chain 38 of FIG. 1) and whose output element rotates the lower roll of the pair of rolls 24.The ratio of the transmission 137 can be varied by a reversible electric motor 139 which, in lieu of being controlled by a regulating means (such as 57 in FIG. 1) which monitors the dimensions of the loop 27, receives signals from an amplifier 156 corresponding to the amplifier 56 of FIG. 1 and receiving signals, via conductor means 154, from a monitoring device (such as the tachometer generator 51 of FIG.

1) serving to ascertain the velocity of the tow 4. Thus, the stretching apparatus 23" of FIG. 3 changes the combined resistance of the dancer roll 41 and spring 163 to forward movement of the tow 4 by changing the level of the roll 41 (i.e., by changing the dimensions of the loop 27). When the velocity of the tow 4 is relatively high, the dancer roll 41 is located at or close to a level S2 which is shown in FIG. 3 by broken lines. This means that the component K2 (force applied by the coil spring 163) is reduced in accordance with an increase of the force K1 (namely, an increase of the force which is attributable to resistance of the dancer roll 41 to advancement of the tow 4, such resistance increasing with increasing speed of the tow).The sum of the components K, and K2 is constant, i.e., the total resistance offered by the dancer roll 41 and the spring 163 is constant to thereby ensure that the stretch or pull upon the filamentary filter material of the tow 4 remains unchanged.

If the velocity of the tow 4 decreases, the dancer roll 41 rises to a second level S, of thereabout whereby the component K2 (bias of the spring 163) increases. This compensates for a reduction of the resistance which is offered by the dancer roll 41 to lengthwise movement of the tow 4 as a result of a reduction of velocity of the tow. Again, the sum of the components K1 and K2 remains unchanged, i.e., the pull upon the filamentary filter material is the same as when the dancer roll 41 is held at or close to the first level S2. The level of the dancer roll 41 changes in response to appropriate adjustment of the ratio of the transmission 137, i.e., in response to signals from the means for monitoring the velocity of the tow 4. The peripheral speed of the pair of rolls 26 (which are or may be driven in the same way as shown in FIG. 1) remains unchanged. The drive 138 is preferably a chain drive or a toothed belt drive, such drive prevents slippage of the driving parts with reference to the driven parts.

It will be noted that, in contrast to the embodiment of FIG. 1, the level of the dancer roll 41 shown in FIG.

3 can be changed on purpose (for reasons other than to maintain the dimensions of the loop 27 within a given range) to thereby ensure that the pull upon the filamentary filter material of the tow 4 will remain unchanged. In the filter rod making machine of FIG.

1, the regulating means 57 serves solely to ensure that the level of the dancer roll 41 shown therein will remain at least substantially unchanged, but such adjustment of the level of the dancer roll does not influence the pull upon the filamentary filter material of the tow 4.

In contrast to the apparatus 23' of FIG. 2, the apparatus 23" of FIG. 3 is designed in such a way thatthe lower end portion (connection 164) of the coil spring 163 is fixed. When the bias of the spring 163 upon the dancer roll 41 is to be changed, the dancer roll 41 moves (with the upper end portion of the spring 163) toward or away from the connection 164. When the pull increases, the drag resistance of the roll 41 also increases and the upper end portion of the spring 163 is moved nearer to the connection 164, and vice versa. Here, again, that component of retarding force which is applied by the spring 163 varies in dependency on changes of velocity of the tow because the drag resistance of the tow is a function of such velocity.

Referring to FIG. 4, there is shown a further embodiment of a stretching or elongating apparatus which is denoted by the reference character 223 and is installed in a filter rod making machine which includes, among others, the pairs of advancing rolls 26 and 28 for the running tow 4. The rolls of the pair of rolls 224 are not driven, in contrast to the rolls 26 which receive motion from the main prime mover of the filter rod making machine, for example, in a manner as illustrated in FIG. 1. The tow 4 travels along an elongated path which includes a straight portion between the pairs of rolls 224 and 26, i.e., the loop 27 is not needed.

The lower roll of the pair of rolls 224 is rotatable about the axis of a shaft 224A at the free end of an elongated carrier or support 72 which is mounted in cantilever fashion in the frame F of the filter rod making machine. The shaft 224B of the upper roll of the pair of rolls 224 is also mounted in or on the carrier or support 72 but in such a way that it can move up and down, i.e., the upper roll of the pair of rolls 224 can move up and down with reference to the lower roll of the pair of rolls 224.The stretching apparatus 223 further comprises means 71 (e.g., a pneumatically or hydraulicaliy operated cylinder and piston unit, a dashpot or the like) for pressing or biasing the upper roll of the pair of rolls 224 with a predetermined force toward the lower roll of the pair of rolls 224 so that the two rolls 224 tend to pinch the tow 4 therebetween and oppose the forward movement of the tow in a direction toward the nip of the pair of driven rolls 26.

The construction of the carrier or support 72 is such that the rolls of the pair of rolls 224 are displaceable in and counter two the direction of forward or lengthwise movement of the tow 4. The position of the pair of rolls 224 is dependent on the pull acting upon the tow 4. When the pull changes, the rolls 224 are caused or allowed to move in or counter to the direction of movement of the tow 4 toward the pair of rolls 26, i.e., the rolls of the pair of rolls 224 are caused or enabled to leave their normal or predetermined positions which can be said to constitute the positions equilibrium or neutral positions.The extent of deviations or departure of positions of the pair of rolls 224 from such neutral positions is monitored because the extent of such deviations or departure is indicative of the extent of deviation of pull upon the tow 4 from a predetermined or optimum value. The monitoring means comprises a signal generating wire strain gauge 73 which is installed in or on the carrier or support 72 and transmits appropriate signals to the amplifier 74 for an adjusting or influencing motor 76 serving to change the bias of the pair of rolls 224 against the respective sides of the running tow 4.

The retaining or braking force of the pair of rolls 224 upon the tow 4 is determined primarily by forces acting at right angles to the direction of travel of the tow 4, i.e., by forces which, in the absence of the tow 4, would urge the peripheral surface of the upper roll 224 against the peripheral surface of the lower roll 224. In accordance with the invention, the strain gauge 73 ascertains the extent of movement of the pair of rolls 224 from their neutral positions and initiates changes of the magnitude of the aforementioned forces which urge the pair of rolls 224 against the respective sides of the tow 4. This, in turn, entails appropriate or commensurate changes of resistance which the rolls of the pair of rolls 224 offer to forward movement of the tow 4 and hence changes of the stretching action upon the filaments in the path portion between the pairs of rolls 224 and 26.The changes of the magnitude of forces with which the rolls of the pair of rolls 224 act upon the tow 4 are intended to compensate for variations of the resistance which the rolls of the pair of rolls 224 offer to travel of the tow 4 as a result of changing velocity of the stretched tow. Thus, the force which is furnished by the pressing or biasing means 71 via rolls 224 is the variable force or component K2, and the force or component K, is the force which varies in automatic response to changes in the speed of the tow 4 and is also applied by the rolls of the pair of rolls 224.

When the velocity of the stretched tow increases, the rolls of the pair of rolls 224 are caused to move in a direction to the left, as viewed in FIG. 4, and the strain gauge 73 transmits corresponding signals to the influencing or adjusting motor 76. The latter allows or causes the biasing means 71 to reduce the pressure between the rolls of the pair of rolls 224 so as to compensate for increasing resistance which the accelerated rolls of the pair of rolls 224 offer to forward movement of the tow 4. The result is that the stretching action upon the filaments in the path portion between the pairs of rolls 224 and 26 remains unchanged or rapidly reassumes its optimum value.

When the velocity of the stretched tow decreases, the rolls of the pair of rolls 224 move in a direction to the right, as viewed in FIG. 4, and the strain gauge 73 transmits signal which causes the influencing or adjusting motor 76 to increase the force which is furnished by the biasing means 71 so that the sum total of retarding forces acting upon the tow 4 is again the same, i.e., the stretching action or pull upon the filamentary filter material of the tow remains unchanged.

It will be noted that, in the stretching apparatus 223 of FIG. 4, the composite retaining force which is applied by the rolls of the pair of rolls 224 but is furnished in part bythe biasing means 71 is influ enced by the pull upon the tow 4 (such pull causes the rolls of the pair of rolls 224 to move toward the pairof rolls 26 or allows the rolls of the pair of rolls 224 to move away from the pair of rolls 26) to countract the effects of changes or velocity of the stretched tow, namely, the influence of changes of velocity of the tow upon the resistance which the rolls of the pair of rolls 224 offer to forward movement of the tow. This again ensures that the pull upon the tow 4 remains unchanged or that such pull practically instantaneously reassumes its optimum value.

The stretching apparatus 323 of FIG. 5 includes two driven rolls 324 located upstream of the two pairs of driven advancing rolls 26, 28 corresponding to the similarly referenced rolls in the filter rod making machine of FIG. 1. The tow 4 is drawn from a bale (such as the bale 19 of FIG. 1) and is caused to advance over a rotary guide member in the form of an idler roller 77. The rolls 26 are driven in the same way as disclosed in connection with FIG. 1. The rolls 324 are rotatably mounted on a plate-like support or carrier 79 which is movable in and counter to the direction of travel of the tow 4 from the idler roller 77 toward the advancing rolls 26. The support 79 thereby stresses or effects a reduction of the bias of a coil spring 78 which is connected to the frame F.

The support orcarrier79 is provided with a wiper 81 forming partofa monitoring means here shown as a potentiometer 83 which further includes a resistor 82 and is in circuitwith an amplifier 84 for a variablespeed electric motor 86. The distance between the rolls 324 is constant and such distance determines the force with which the rolls 324 oppose forward movement of the tow 4 at a given velocity of the filamentary filter material. If the pull upon the tow 4 changes, the torque which the motor 86 transmits to the rolls 324 also changes, and such torque is superimposed upon the torque that ittransmitted by the running tow whenever the balance or equilibrium is destroyed, i.e, whenever the rolls 324 move nearer to or further away from the pair of rolls 26.

This compensates for fluctuations of pull upon the tow 4, especially for those fluctuations which are induced by changes in velocity of the tow.

When the rolls 324 advance toward the pair of rolls 26 in response to increasing pull, the rolls 324 receive torque from the tow 4 as well as an increasing torque from the motor 86. If the rolls 324 are caused to move in a direction to the right to thereby effect a reduction of the stress upon the spring 78, the torque which the motor 86 transmits is reduced in automatic response to movement of the wiper 81 reiative to the resistor 82 of the monitoring potentiometer 83. It will be noted that, in the embodiment of FIG. 5, too, any changes in the pull effectapprop- riate changes in the restraining or braking force for the purpose of ensuring that the pull upon the filamentary filter material reassumes its optimum value.

In the embodiment of FIG. 6, the stretching apparatus 323' comprises a dancer roll 441 in the bight of a loop 27 between the pairs of rolls 24 and 26. These rolls, as well as the rolls 28, can be driven in the same way as described in connection with FIG.

1. The stretching apparatus 323' of FIG. 6 further comprises means for directly ascertaining or monitoring the resistance (braking action) which the dancer roll 441 offers to forward movement of the tow 4, and such resistance is proportional to the vel ocity of the tow. The details of the dancer roll 441 are shown in FIG. 7. This roll comprises a hollow cylin drical tow-contacting body or shell 87 which is rotat able on ball bearings 88 surrounding a shaft 89 mounted in two parallel elongated carriers or arms 42 and 42'. The shaft 89 is rigidly connected with a radially extending pointer or index 91 forming part of a suitable recording or indicating device. To this end, the pointer 91 is turnable in directions indicated by a double-headed arrow 92 (see FIG. 6) with refer ence to a suitable scale which is not specifically shown in the drawing.

The carriers or arms 42,42' are acted upon by coil springs 63 only one of which is shown in FIG. 6 and which tend to pivot the arms 42,42' in a counterc lockwise direction, as viewed in FIG. 6, so as to increase the dimensions of the loop 27. The arms 42 and 42' are pivotally secured to the frame F of the filter rod making machine, and the uppermost convolutions of the springs 63 are connected to inter mediate portions of the respective arms.The lower most convolutions of the springs 63 are attached to pins 64 which are eccentically mounted on rotary discs 66 (only one shown in FIG. 6). Each disc 66 can turn clockwise or counterclockwise as indicated by the double-headed arrow 69 shown in FIG. 6.

When the velocity of the tow 4 increases, i.e., when the resistance of the shell 87 to forward movement of the tow also increases, the pull upon the tow increases whereby the pointer 91 turns in a clockwise direction, as viewed in FIG. 6. This entails ortakes place simultaneously with a counterclock wise rotation of the disc 66 so that the bias of the springs 63 upon the respective arms 42,42' decreases to thus compensate for increasing resis tance of the shell 87 to forward movement of the running tow. In other words, the pull upon the tow4 remains unchanged or rapidly reassumes the optimum value.

When the velocity of the tow 4 decreases with attendant reduction of resistance which the shell 87 offers to forward movement of the tow and to decreasing pull upon the filamentary filter material, the pointer 91 turns in a clockwise direction, as vie wed in FIG. 6. This entails or takes place simultane ously with a clockwise rotation of the disc 66, as viewed in FIG. 6, so that the bias of the spring or springs 63 increases to increase the magnitude of the component K2 for the same reasons and in the same way as described in connection with FIG. 2.

Thus, the sum of the components K1 and K2 remains unchanged and the pull upon the tow 4 also remains unchanged or rapidly reassumes the desired optimum value. The monitoring means (such as a tachometer generator) which ascertains the velocity of the stretched tow and transmits signals to the means (not shown) for rotating the disc 66 of the stretching apparatus 323' is not shown in FIG. 6.

Such monitoring means may include a potentiome ter having a wiper constituting the pointer 91. Alternatively, the pointer 91 may serve solely as a means for indicating the magnitude of braking action which is furnished by the dancer roll 441.

In the apparatus of FIGS. 6 and 7, the dancer roll 441 can be said to constitute the monitoring or measuring means which ascertains changes of velocity of the stretched tow and initiates the transmission of signals which are used to compensate for such changes, i.e., by effecting the transmission of such signals to the means (a reversible electric motororthe like) for changing the angular position of the disc 69 and hence the distance between the two end portions of the spring 63. The roll 441 serves for indirect ascertainment of velocity of the tow 4 because it actually monitors changes of the pull, i.e., of a parameter which is related to velocity of the stretched tow.This exhibits the additional advantage that the cause of defects is eliminated at an even earlier stage, i.e., there is no need to monitor the velocity of the stretched tow downstream of the driven rolls 26 because an equivalent or related parameter (pull upon the tow) can be monitored in the stretching or elongating apparatus proper.

The advantages of the just discussed early ascertainment of possible defects of the stretching action upon the running tow will be readily appreciated by bearing in mind that, in conventional apparatus, the parameterwhich is monitored and which is used to effect an adjustment of the stretching apparatus is the density of the rod 11, the density of filter rod sections 11 a, the density of fillers in filter plugs which are obtained from the sections 11 a and are already combined with plain cigarettes or the like, or the draw resistance of filter cigarettes.The magnitude of force which the roll 441 applies to the loop 27 remains unchanged because, when the drag resistance of the roll 441 increases as a result of increased velocity of the tow, the bias of the spring 63 upon the roll 441 is reduced so that the sum of force that the roll 441 transmits to the tow remains unchanged, and vice versa.

In the stretching or extending apparatus 323" of FIG. 8, the tow 4 is advanced toward the nip of the pair of driven rolls 26 and is trained over a loop form.

ing or dancer roll 96 (primary braking device) which is pivotable about a fixed axis and is mounted at the free end of one carrier or arm 97 of a two-armed lever the other carrier or arm 97a of which supports a counterweight 98. The stretching or extending apparatus 323" further includes a composite secondary braking or retarding device 95 which comprises cylindrical and/or semicylindrical shoes 94a, 94b, 94c, 94d, 94e (of the five shoes which are shown in FIG. 8, the first four are substantially semicylindrical and the last one is a circumferentially complete cyiinder).The shoes 94a to 94e form a file, i.e., they are disposed one after the other, as considered in the direction of travel of the tow 4 toward the nip of the pair of rolls 26, and have convex (cylindrical) surfaces 95a, 95b, 95c, 95d and 95e which are contacted, in this order, by successive increments of the filamentary filter material when the tow 4 is running to advance from the bale (not shown) toward the gathering horn, e.g., in a manner as shown in FIG. 1.

The convex surfaces 95a to 95e together constitute a meandering or sinusoidal (undulate) composite secondary braking surface which is contacted by the tow 4 upstream of the loop forming or dancer roll 96.

The axis about which the dancer roll 96 orbits coincides with the axis of the cylindrical shoe 94e of the secondary braking device 95. The mass of the counterweight 98 on the carrier or arm 97a matches or closely approximates the mass of the braking roll 96 on the carrier or arm 97.

The shoes 94a and 94c are mounted on the legs of a substantially U-shaped shifting member or yoke 99 which is movable in directions indicated by a double-headed arrow 101 so as to move the convex surfaces 95a and 95c into or out of deforming engagement with the tow 4. When the yoke 99 is lifted, as viewed in FIG. 8, the tow 4 engages or can engage only the surfaces 94b, 94d and 95e or only the surfaces 95a, 95c, 95e, depending on the guidance of the tow ahead of the secondary braking device 95.

The carriers or arms 97 and 97a are rigid with a pulley or cam 112 whose axis coincides with the axis of the cylindrical shoe 94e and which is permanently biased in a clockwise direction, as viewed in FIG. 8, by an auxiliary weight 113 suspended on a cord, cable or an analogous flexible element 100. In other words, the auxiliary weight 113 tends to turn the pulley or cam 112 in a direction counter two that in which the running tow 4 tends to rotate the shoe 94e. The latter is rigid with the pulley or cam 112.

The rolls of the pair of rolls 26 exert upon the tow 4 a predetermined pull in the direction of arrow 102 whereby the tow slides along the convex surfaces 95a to 95e of the shoes 94a to 94e before successive increments of its filamentary material engage and rotate the dancer roll 96. The restraining or braking force which acts upon the tow 4 is composed largely of frictional forces which develop between the filaments and the surfaces 95a to 95e. The combined frictional force is selected, by appropriate initial adjustment of the yoke 99, in such a way that any, even minor, changes in angular position of the carrier or arm 97 for the loop forming or dancer roll 96 effect a corresponding change in the pull upon the tow 4.As explained above, adjustments of the yoke 99 entail movements of the shoes 94a, 94c with reference to the adjacent shoes 94b, 94d and hence a change in the combined area of those portions of the surfaces 95a to 95e which come in contact with the running tow 4. In order to increase the extent of frictional engagement between the secondary braking device 95 and the tow 4, the yoke 99 is moved downwardly, as viewed in FIG. 8, to increase the amplitude of waves of the sinusoidal path which is defined by the surfaces 95a to 95e for successive portions of the running tow 4. Inversely, the combined area of contact between the surfaces 95a to 95e and the tow 4 is reduced in response to an upward movement of the yoke 99, as viewed in FIG.

8, i.e., in a direction to flatten the undulations of the sinusiodal path which is defined by the shoes 94a to 94e.

When the yoke 99 is held in the illustrated position (which is assumed to correspond to the position of maximum contact between the tow 4 and the surfaces 95a to 95e), and the tow 4 is advanced at an optimum or preselected speed, the angle (gamma) of contact between the peripheral surface 95e of the cylindrical shoe 95e and the tow is relatively large and the loop forming or dancer roll 96 assumes the position which is indicated by solid lines. This causes the shoe 94e to contribute, to a predetermined extent, to resistance which the secondary braking device 95 offers to lengthwise movement of the tow 4 in the direction of arrow 102.

If the pull upon the tow4 increases for any one of several reasons, the loop forming or dancer roll 96 is moved from the solid-line position toward the broken-line position 96' of FIG. 8 and the pulley or cam 112 is rotated againstthe opposition of the auxiliary weight 113, i.e., in a counterclockwise direction, as viewed in FIG. 8. The counterweight 98 and the auxiliary weight 113 then respectively assume the broken-line positions 98' and 113' of FIG. 8. The corresponding (broken-line) positions of the carriers or arms 97 and 97a are respectively shown at 97' and 97a'. This entails a pronounced reduction of the angle along which the filamentary filter material of the tow 4 contacts the surface 95e of the shoe 94e, namely, the angle gamma is reduced to a fraction of its original size, i.e., to gamma minus alpha.Thus, the length of that portion of the surface 95e (as considered in the circumferential direction of the cylindrical shoe 94a) which contacts the tow 4 is greatly reduced with attendant reduction of resistance which the secondary braking device 95 offers to forward movement of the tow 4. Thie entails a reduction of pull upon the tow 4 so that the pull reassumes its normal or optimum value.

If the pull is reduced below the normal value, the loop forming or dancer roll 96 moves back toward the solid-line position of FIG. 8 and the area of contact between the filamentary filter material and the surface 95e of the shoe 94e increases. This increases the resistance which the secondary braking device 95 offers to forward movement of the tow 4 and the pull upon the tow increases so that it rapidly reassumes the desired value.

It will be noted thatthe stretching apparatus 323" of FIG. 8 also ensures automatic retention of the pull upon the tow 4 at a constant value or within a very narrow range of optimum values. An important advantage of the apparatus which is shown in FIG. 8 is that it not only automatically compensates for those changes of pull which are attributable to changes in velocity of the tow 4 but also for any other changes of pull irrespective of the cause or causes of such changes.

The auxiliary weight 113 constitutes but one form of means for applying to the pulley or cam 112 and shoe 95e a torque in a direction counterto that which is generated by the running tow 4. For example, one can employ atorsion spring one end of which is anchored in the shoe 94e and the other end of which is anchored in the frame of the filter rod making machine and which tends to rotate the shoe 94e in a clockwise direction, as viewed in FIG. 8. Further more, such torque applying means may consist of or may comprise two or more springs including helical springs, torsion springs, leaf springs and/or other types of springs.A single coil spring can be used by connecting one of its end convolutions to an eccentric pin on the pulley 112 or shoe 94e and by connecting the other end convolution to the frame of the filter rod making machine. The pulley 112 may constitute a disc-shaped cam whose peripheral surface (contacted by the flexible element 100) may be selected with a view to influence the regulation of pull upon the tow 4 in response to turning of the cam.

In the stretching apparatus 323" of FIG. 8, the retaining or retarding force acting upon the running tow upstream of the driven rolls 26 is varied in a fully automatic way without necessitating resort to discrete influencing or force varying means. Such influencing means is the roll 96 which can be said to constitute an equivalent of the measuring or monitoring means 51 shown in FIG. 1. In spite ofthe absence of separate influencing means, the apparatus of FIG. 8 can reliably maintain the pull upon the running tow at a constant value (or can rapidly return such pull to the desired value) by the simple expedient ofvarying the area of contact between the members or shoes 94a-94e of the braking device 95 and the running tow. The embodiment of FIG. 8 is one of the presently preferred stretching apparatus.This apparatus exhibits the advantage that the roll 96 performs the function of monitoring means as well as the function of influencing means.

Furthermore, the sensitivity of the apparatus can be regulated in a very simple and efficient way through the medium of the yoke 99. The number of controls in the apparatus of FIG. 8 is negligible because of the dual function of the roll 96.

By utilizing a disc-shaped cam or pulley 112 wherein certain portions of the periphery are located at different distances from the fixed axis about which the roll 96 orbits, it is possible to vary the torque which is applied to the weight 113 through the medium of the flexible element 100. Thus, the influence of the weight 113 upon the roll 96 will vary by changing the angular position of such a cam or pulley 112 because this changes the distance between the fixed axis and the plane of the straight portion of the element 100.

A further embodiment of the invention is illustrated in FIG. 9. In this embodiment of the invention, the pull is also adjusted in automatic response to changes in the velocity of the tow 4. The stretching or expanding apparatus 423 of FIG. 9 comprises a pair of driven rolls 26 and a pair of idler rolls 424. The lower roll 424a of the pair of idler rolls 424 is freely rotatable on an arm 103a of a T-shaped carrier 103 constituting athree-armed lever. The arm 103b of the lever 103 is fulcrumed (at 104) in the stationary frame F of the filter rod making machine by a fulcrum 104; this arm extends substantially at right angles to the arm 103a and is aligned with a third arm 103e of the lever 103. The third arm 103tis articulateiy connected with a two-armed carrier or bell crank lever 106 by a pivot member 109 which is parallel to the fulcrum 104 and extends transversely of the path of movement of the tow 4. The pivot member 109 is located in the region where the arms 106a and 106b of the lever 106 meet. The arm 106a is parallel or nearly parallel to the arm 103a and carries the other or upper roll 242b of the pair of idler rolls 424. The roll 424b is freely rotatable on its shaft at the free end of the arm 106a. The second arm 106b of the lever 106 is coupled to the frame F by a resilient element here shown as a coil spring 107. A second resilient element or coil spring 108 couples the arm 106a of the lever 106 with the arm 103a of the lever 103.

The relationship of forces which are exerted by the springs 107 and 108 is as follows: The force K2 of the spring 107 opposes the force K, of the spring 108.

Furthermore, the force K, of the spring 108 exceeds the force K2 of the spring 107, i.e., the rolls 424a, 424b are biased against each other (and hence against the respective sides of the running tow 4) with a force KA = K, - K2 which offers a certain resistance to lengthwise movement of the tow 4 and compels the pair of rolls 26 to exert a given force in order to advance the tow toward the plasticizer applying or wetting station (not shown in FIG. 9).

If the resistance which the rolls 424a, 424b offer to the movement of tow 4 toward the nip of the pair of rolls 26 increases (for example, in response to increasing velocity of the tow), the levers 103, 106 pivot about the axis of the fulcrum 104 and cause the rolls 424a, 424b to move in a direction to the left, i.e., nearer two the pair of rolls 26.The spring 107 tends to retain the lever 106 in the illustrated angular position, i.e., to cause the lever 106 to pivot about the axis of the pivot member 109 with reference to the lever 103 and to thereby increase the width of the nip of the rolls 424a, 424b. However, and since the force K, of the spring 108 exceeds the force K2 of the spring 107 to an extent which suffices to ensure that the distance between the axes of rotation of the rolls 424a, 424b does not undergo any appreciable changes, the lever 106 shares the angular movement of the lever 103 about the axis of the fulcrum 104 with attendant expansion of the spring 107, i.e., the force K2 increase. Consequently, the force KA (which equals K1 - K2) decreases to entail a reduction of resistance which the rolls 424a, 424b offer to lengthwise movement of the tow 4.Thus, the stretching apparatus 423 of FIG. 9 automatically establishes a new state of equilibrium which takes into account the increased velocity of the tow 4 by reducing the resistance which the rolls 424a, 424b offer to lengthwise movement of the tow. The pull remains unchanged or rapidly reassumes its desired value.

The characteristics of the springs 107 and 108 are selected in such a way that KA (which equals K, - K2) is always a positive force, i.e, that the rolls 424a, 424b always bear against the tow 4 but with a force which varies as a function of changes in angular pos itionsofthe levers 103,106 with reference to the axis of the fulcrum 104. In other words, while the resultant force KA may fluctuate within a certain range, it is always present and prevents the rolls 424a, 424b from becoming disengaged from the running tow 4.

In this manner, the apparatus 424 of FIG. 9 ensures that the pull upon the tow 4 remains constant or unchanged irrespective of possible changes in the velocity of the filamentary filter material. It will be noted that the apparatus 423 of FIG. 9 is evidently capable of automatically adjusting the variable parameter or parameters (in the present instance the force with which the rolls 424a, 424b bear upon the tow 4) to ensure that the pull upon the tow 4 remains unchanged even if certain other parameter or parameters (such as the velocity of the tow) vary within a rather wide range.

FIG. 10 illustrates a modification (423') of the apparatus which is shown in FIG. 9. The principle of operation is the same exceptthatthe rolls424a, 424b of FIG. 9 are replaced with a braking device 111 hav ing a pair of suitably configured jaws 11 1a, 111 b whose convex surfaces bear against the respective sides of the running tow 4 under the action of the spring 108. The force K2 of the spring 107 is weaker than the force K1 of the spring 108 so that the jaws 111 a, 111 b invariably bear against the tow 4 but with a force (KA = K, - KJ which varies in dependency on changes in the velocity of the tow 4 on its way toward the pair of driven advancing rolls 26 so as to ensure that the pull upon the tow 4 remains constant or rapidly reassumes the desired or optimum value.

It will be noted that the adjustment of pull in the stretching apparatus 423' of FIG. 10 is just as automatic as in the apparatus 423 of FIG. 9. This ensures that the filler of the filter rod 11 is homogeneous and the filter rod can yield highly satisfactory filter rod section 11 a whose resistance to axial flow of tobacco smoke therethrough is always within the desired range. Moreover, the apparatus 423 and 423' of FIGS. 9 and 10 also ensure that potential causes of defects (unsatisfactory filter rod sections) are detected as soon as they arise and that such defects are eliminated without any delay.

The parts 103, 104, 106, 109 of the stretching apparatus 423' are identical with or analogous to the similarly referenced parts shown in FIG. 9.

The apparatus 423 of FIG.9 or 423' of FIG. 10 constitute highly advantageous simplified versions of previously described apparatus. The apparatus 423 and 423' need not have any or utilize a minimal number of controls because the system of levers including the levers 103,106 and the springs 107, 108 can be said to constitute the measuring or monitoring means (for the extent of departure of the rolls 424 or jaws 111 from their predetermined or normal position) as well as the influencing or adjusting means which compensate for the effect of those forces that are the cause of departure of rolls 424 or jaws 111 from their normal or predetermined positions. Otherwise stated, the apparatus of FIG. 9 or 10 does not or need not have any pronounced or specifically designed measuring or monitoring means for ascertainment of velocity of the tow. Instead, the apparatus of FIGS. 9 and 10 simply monitor a parameter (departure of the rolls 424 or jaws 111 from their normal or predetermined positions) which is a function of velocity of the tow and the results of such monitoring are automatically utilized to compensate for departure of pull from the desired or optimum value. Another important advantage of the apparatus 423 and 423' is that they can automatically compensate for any and all changes of pull irrespective of their causes, i.e., not only because the velocity of the stretched tow changes but also when any other parameter which influences the pull (and which may but need not be dependent on velocity of the tow) undergoes a change of such proportions as to warrant an adjustment of the stretching apparatus.

The improved apparatus is successible of many additional modifications without departing from the spirit of the invention. For example, the apparatus 423' of FIG. 10 can be modified by replacing one of the jaws lila, ills with an idler roller. Furthermore, the system of levers shown in FIG. 9 or 10 can be replaced with other types of means for carrying the rolls 424 or jaws 111. In the embodiment of FIG. 8, each of the segment-shaped or substantially semicylindrical braking members or shoes 94a-94d can be replaced with a cylindrical braking member, and the distribution of the braking members 94a-94e may be such that they define a substantially arcuate but not necessarily a meandering path for the advancement of tow 4 past the braking device 95 or an analogous braking device.

An important advantage of the improved method and apparatus is that the pull upon the tow is ma intained at or close to a desirable (constant) value in a very simple and reliable way, i.e., by ensuring that at least one component of the retarding force acting upon the tow is regulated in dependency on the velocity of the stretched tow and/or in dependency on a parameter which varies in the same way as (i.e., proportionally with and/or as a function of) changes of velocity of the running tow. As explained above, one of these parameters is the pull upon the tow and another of these parameters is the drag resistance of one or more non-driven rolls or one or more towengaging jaws. The pull depends upon the velocity of the tow because it is related to drag resistance of the retarding means of the stretching apparatus and such drag resistance, in turn, depends upon the velocity of the tow.This renders it possible to compen- sate for undesirable deviations of pull upon the tow as soon as they develop, i.e., while the tow is still untreated (save for banding) and is still located in the filter rod making machine proper, so that such deviations are eliminated without delay with attendant reduction of the number of rejects and a reduction of waste in wrapping material, plasticizer, adhesive, wear upon the cutoff and/or the number of defective smoker's products. In other words, the improved method and apparatus render it possible to ensure the making of acceptable products at a very early stage of treatment of the starting product.Moreover, the apparatus which is used for the practice of the method is very simple, compact, inexpensive and rugged; it can be installed in existing filter rod making machines with a minimum of cost and its space requirements do not exceed those of heretofore known apparatus. The controls which are used in the apparatus are extremely simple and highly reliable.

Thus, and referring for example to FIG. 9 or 10, the controls are practically non-existent because the springs 107 and 108 cooperate to monitor the extent of departure of the rolls 424 or jaws 111 from their predetermined optimum positions and to effect automatic compensation for such departure, i.e., to ensure that the rolls or jaws reassume their predetermined positions with negligible delay as soon as the velocity and/or pull reassumes its normal value.

The invention is further based on the recognition that deviations of pull upon the running tow from a desired or optimum pull, and hence the deviations of stretching action from an optimum value as well as deviations of the characteristics of the final product from optimum characteristics, are often attributable to deviations of operating speed of the filter rod making machine from an optimum or standard speed. In accordance with the method of the invention, changes of velocity (i.e, operating speed of the machine) which greatly influence the pull upon the running tow and hence the stretching action (and the characteristics of the final product) are compensated for at a very early stage and in a highly effective way with the result that the number of rejects is very small and that there is no unnecessary processing of defective portions of the tow. Such compensation at an early stage of processing of the tow, namely, sub sequentto banding but priortothe application of plasticizer, priorto wrapping into cigarette paper or the like, prior to heating or cooling of the seam of the rod 11, priortosubdivisionoftherod 11 into sections 11 a, prior to transport of sections 11 a into storage, into a pneumatic sender or into the magazine of a filter tipping machine, and prior to assembly with plain cigarettes or the like, greatly reduces the cost of the ultimate products because there is no need for expensive processing of useless filter material. The improved apparatus contributes to reliability of the filter rod making machine and ensures a pronounced reduction of the number of rejects in spite of its simplicity, compactness, ruggedness and low cost.

Claims

1. A method of processing a continuous stretchable tow of filamentary filter material which is utilized for conversion into the fillers of filter plugs for cigarettes or the like and advances lengthwise in a predetermined direction along an elongated path, comprising the steps of stretching the tow in a predetermined section of said path, including exerting on the tow a pull in a first portion of said section and simultaneously applying to the tow a retarding force in a second portion of said section upstream of said first portion; measuring the velocity of the stretched tow; and influencing the retaining force in response to changes of measured velocity so as to maintain said pull at least substantially at a constant value.

2. The method of claim 1,wherein said measur- ing step includes indirectly monitoring the velocity of the stretched tow.

3. The method of claim 1, wherein said retaining force has several components and said influencing step comprises varying at least one of said components as a function of changes of velocity of the stretched tow.

4. The method of claim 1, wherein said retaining force has several components and said measuring step includes directly monitoring the velocity of the stretched tow downstream of said section of said path, said influencing step including varying at least one of said components as a function of variations oi the velocity of the stretched tow.

5. The method of claim 1, wherein said retaining force is applied to the tow substantially transversely of said section of said path and includes a velocitydependent first component as well as a velocityindependent second component, said influencing step including varying said second component as a function of variations of velocity of the stretched tow.

6. The method of claim 5, further comprising the step of converting the tow into a relatively thin but wide layer not laterthan on entry into said section of said path, said retaining force being applied to the filamentary filter material along the full width of said layer.

7. The method of claim 6, wherein said pull is applied by a pair of driven rotary elements in said first portion of said section, the filamentary material of the tow advancing through the nip of the rotary elements.

8. The method of claim 1, wherein said retarding force is applied, at least in part, by a plurality of tow engaging elements engaging different sides of the tow in said second portion of said section.

9. The method of claim 1, wherein said pull is applied by a first pair of driven rotary elements in said first portion of said section and said retarding force is applied by a second pair of rotary elements which are rotated by the tow and offer a variable resistance to rotation by the tow, the tow advancing through the nips of such pairs of rotary elements and said influencing step comprising varying said resistance as a function of variations of said velocity.

10. The method of claim 9, wherein said resistance varying step includes urging the rotary elements of the second pair against the tow therebetween with a force which varies as a function of said velocity variations.

11. The method of claim 1, wherein said pull varies with the velocity of the stretched tow and said measuring step includes monitoring the position of at least one tow-engaging element whose position varies as a function of variations of said pull, said retarding force having several components and said influencing step including varying at least one of said components in dependency on deviations of monitored position of the tow-engaging element from a predetermined position denoting a predetermined pull upon the tow.

12. The method of claim 11, wherein the tow- engaging element is a roll.

13. The method of claim 11, wherein said monitoring step includes measuring the distance between said predetermined position and the actual position of the tow-engaging element.

14. The method of claim 11, wherein said step of applying said retarding force includes subjecting the tow to a variable braking action upstream of the tow-engaging element.

15. The method of claim 14, wherein the tow- engaging element is a rotary element which furnishes a portion of the braking action and whose resistance to advancement of the tow varies as a function of variations of velocity and as a function of changes of area of contact with the tow.

16. The method of claim 15, wherein the position of the rotary element is variable in and counter to said direction as a function of variations of velocity of the stretched tow, said one component being said portion of the barking action.

17. The method of claim 16, wherein said influencing step including varying the combined braking action as a function of variations of the position of the rotary element.

18. The method of claim 12, wherein the roll offers to advancement of the tow a resistance which varies as a function of variations of said velocity, and said measuring step includes monitoring the resistance of the roll.

19. The method of claim 18, wherein the roll is a non-driven roll and the roll loops the tow in said section of said path.

20. The method of claim 1, wherein the retarding force is applied by several jaws bearing against the tow with a variable force and being movable in and counter two said direction in response to variations of said velocity, said influencing step including varying said force of said jaws in dependency on the extent of movement of such jaws from a predetermined position.

21. The method of claim 20, further comprising the step of monitoring the extent of deviation of the actual position of the jaws from said predetermined position.

22. Apparatus for processing a continuous stretchable tow of filamentary filter material which is utilized for conversion into the fillers of filter plugs for cigarettes or the like and advances lengthwise in a predetermined direction along an elongated path, comprising means for stretching the tow in a predetermined section of said path including tensioning means for exerting upon the tow a pull in a first portion of said section and retarding means for applying to the tow a variable retarding force opposing advancement of the tow toward said tensioning means in a second portion of said section upstream of said first portion; means for at least indirectly measuring the velocity of the stretched tow; and means for influencing said retarding force in response to changes of measured velocity of the stretched tow so as to maintain said pull at least substantially at a constant value.

23. The apparatus of claim 22, wherein said tensioning means comprises a plurality of driven towengaging rotary elements.

24. The apparatus of claim 22, wherein said retarding means includes means for applying to the tow a composite retarding force having several components including at least one variable component, said influencing means including means for varying said one component.

25. The apparatus of claim 24, wherein said monitoring means includes signal generating means for measuring the velocity of the stretched tow, said influencing means including means for varying said one component in response to signals from said signal generating means.

26. The apparatus of claim 25, wherein said influencing means includes means for varying the effective mass of said dancer roll.

27. The apparatus of claim 22, wherein said retarding means comprises a dancer roll engaging the tow upstream of said tensioning means with attendant formation of a loop.

28. The apparatus of claim 27, wherein said ten sioning means comprises a first set of driven rolls engaging the tow in said first portion of said path section and said retarding means further comprises a second set of driven rolls engaging the tow upstream of said first set, said dancer roll being dis posed between said first and second sets of rolls and further comprising drive means for rotating said first and second sets of rolls so that the peripheral speed of said first set of rolls exceeds the peripheral speed of said second set of rolls.

29. The apparatus of claim 18, wherein said retarding means comprises means for applying to said dancer roll a variable force acting to tension the loop between said first and second sets of rolls, said influencing means comprising means for varying said variable force in'response to changes of velocity of the stretched tow.

30. The apparatus of claim 29, further comprising a mobile carrier rotatably mounting said dancer roll, said variable force applying means including a weight movable with reference to said carrier to thereby furnish a variable contribution to the tensioning action of the dancer roll upon the loop, said means for varying said variable force including means for moving said weight with reference to said carrier.

31. The apparatus of claim 30, wherein said carrier is an elongated arm which is pivotable about a fixed axis and said weight is movable lengthwise of said arm between said fixed axis and said dancer roll.

32. The apparatus of claim 29, wherein said force applying means comprises a resilient element and said influencing means includes means for varying the bias of said resilient element upon said loop through the medium of said dancer roll.

33. The apparatus of claim 32, further comprising an elongated carrier pivotable about a fixed axis and rotatably mounting said dancer roll, said resilient element comprising a tension spring connected with said carrier and said means for varying the bias of said resilient element comprising means for changing the tension of said spring.

34. The apparatus of claim 33, wherein said tension spring is a coil spring having a first end portion connected with said carrier and a second end portion, said tension changing means comprising means for moving said second end portion nearer to or away from said first end portion.

35. The apparatus of claim 28, wherein said drive means comprises a variable-speed transmission for said second set of rolls and said influencing means comprises means for varying the speed ratio of said transmission.

36. The apparatus of claim 35, further comprising means for permanently biasing said dancer roll in a direction to tension said loop with a force which varies as a function of changes of the length of said loop.

37. The apparatus of claim 36, wherein said means for varying said speed ratio includes means for increasing the peripheral speed of said second set of rolls in response to increasing velocity of the stretched tow and vice versa so that the force of said biasing means respectively decreases and increases in response to increasing and decreasing velocity of the stretched tow.

38. The apparatus of claim 22, wherein said measuring means comprises a non-driven element engaging the tow and being movable thereby in said direction from a predetermined starting position in response to increasing pull upon the tow, the magnitude of such pull being a function of the velocity of the stretched tow.

39. The apparatus of claim 38, wherein said influencing means includes means for varying said retarding force as a function of the extent of departure of said element from said predetermined position.

40. The apparatus of claim 39, further comprising meansforyleldably urging said elementto said predetermined position in a second direction counter two said predetermined direction.

41. The apparatus of claim 40, wherein said element includes a single roll.

42. The apparatus of claim 40, wherein said element comprises a plurality of rolls.

43. The apparatus of claim 39, further comprising signal generating means for monitoring the extent of departure of said element from said predetermined position, said means for varying said retarding force comprising motor means connected with said signal generating monitoring means.

44. The apparatus of claim 43, wherein said element is a rotary element and said motor means includes variable-speed motor means arranged to rotate said element at a speed which is a function of said extent of departure of said element from said predetermined position.

45. The apparatus of claim 44, wherein said motor means is arranged to reduce said retarding force in response to increasing departure of said element from said predetermined position, and further comprising means for yieldably urging said element in a second direction counter two said predetermined direction and back to said predetermined position.

46. The apparatus of claim 43, wherein said element comprises a plurality of idler rolls and further comprising means for yieldably urging said idler rolls in a second direction counter two said predetermined direction and back to said predetermined position, said means for varying said retarding force comprises means for pressing said idler rolls against the tow with a force varying as a function of the extent of departure of said idler rolls from said pre determined position.

47. The apparatus of claim 46, wherein said pressing means includes means for reducing the force with which the idler rolls are pressed against the tow in response to increasing departure of said idler rolls from said predetermined position.

48. The apparatus of claim 43, wherein said monitoring means comprises a strain gauge.

49. The apparatus of claim 43, wherein said monitoring means comprises a potentiometer.

50. The apparatus of claim 22, wherein said retarding means comprises a braking device having a tow-engaging braking surface and said measuring means includes a non-driven roll engaging the tow intermediate said braking device and said tensioning means.

51. The apparatus of claim 50, further comprising means for varying the area of contact between said surface and the tow independently of said influencing means.

52. The apparatus of claim 51, wherein said surface consists of several discrete surfaces and said means for varying the area of contact comprising means for moving at least one of said discrete surfaces with reference to each other discrete surface.

53. The apparatus of claim 52, wherein at least some of said discrete surfaces are convex surfaces.

54. The apparatus of claim 52, wherein said discrete surfaces define a substantially undulate path for advancement of the tow past said braking device.

55. The apparatus of claim 50, wherein said roll is movable by the tow between a plurality of positions each corresponding to a different area of contact between the tow and said surface.

56. The apparatus of claim 55, wherein the area of contact between said surface and the tow as well as the position of said roll are functions of the velocity of the stretched tow, said roll constituting said influencing means.

57. The apparatus of claim 56, wherein said roll is arranged to reduce said area in response to movement in said predetermined direction and to thereby reduce said retarding force.

58. The apparatus of claim 57, wherein said roll is arranged to orbit about a fixed axis in and counter to said direction and said surface defines an undulate path for advancement of the tow past said braking device.

59. The apparatus of claim 57, wherein said roll is arranged to orbit about a fixed axis and said surface defines an arcuate path for advancement of the tow past said braking device.

60. The apparatus of claim 59, wherein said braking device comprises a substantially cylindrical member whose axis coincides with said fixed axis, said member having a cylindrical peripheral surface forming part of said braking surface.

61. The apparatus of claim 60, further comprising means for applying to said roll torque tending to orbit said roll counter two said predetermined direction.

62. The apparatus of claim 61, wherein said roll is arranged to respectively increase and reduce the area of contact between the tow and said cylindrical surface in response to orbiting thereof under and countertothe action of said torque.

63. The apparatus of claim 61, wherein said measuring means further comprises a carrier pivotable about said fixed axis and supporting said roll, said torque applying means comprising a pulley affixed to said carrier and a weight acting upon and tending to rotate said pulley counter two the direction in which said pulley tends to rotate as a result of engagement of said roll with the advancing tow.

64. The apparatus of claim 63, wherein said pulley comprises a disc cam and said torque applying means further comprising a flexible element surrounding the periphery of said cam and carrying said weight.

65. The apparatus of claim 64, wherein said cam is rotatable about said fixed axis in response to orbiting of said roll and the periphery of said cam has portions located at different distances from said fixed axis so that the magnitude of said torque is a function of the angular position of said cam.

66. The apparatus of claim 22, wherein said retarding means comprises a plurality of towengaging elements and said influencing means includes adjustable means for pressing said elements against the tow with a variable force, said element being movable by the tow from a predetermined position in response to increasing velocity of the tow and said measuring means including means for monitoring the extent of departure of said elements from said predetermined position.

67. The apparatus of claim 66, wherein said monitoring means includes said influencing means.

68. The apparatus of claim 67, wherein said monitoring means comprises a system of levers.

69. The apparatus of claim 67, wherein said elements include a plurality of jaws.

70. The apparatus of claim 69, wherein said jaws have convex tow-engaging surfaces.

71. The apparatus of claim 67, wherein said elements are non-driven rolls.

72. The apparatus of claim 67, wherein said monitoring means comprises a system of levers and said retarding means further comprises first resilient means acting upon said levers to urge said elements against the tow and second resilient means acting upon said levers to oppose the action of said first resilient means.

73. The apparatus of claim 72, wherein said retarding force equals K1 - K2 wherein K, is the action of said first resilient means, wherein K2 is the action of said second resilient means, and wherein K1 is normally greater than K2.

74. The apparatus of claim 73, wherein at least one of said resilient means is a tension spring.

75. The apparatus of claim 72, wherein said system of levers includes a first lever pivotable about a fixed axis and carrying one of said tow-engaging elements and a second lever pivotally mounted on said first lever and carrying another of said towengaging elements.

76. The apparatus of claim 75, wherein said first resilient element includes a first tension spring connected between said levers to bias said second lever in a first direction and said second resilient element comprises a second tension spring connected with and biasing said second lever in a second direction counter two said first direction.

77. A method of processing a continuous stretchable tow of filamentary filter material which is utilized for conversion into the fillers of filter plugs for cigarettes or the like and advances lengthwise in a predetermined direction along an elongated path, substantially as herein described with reference to the accompanying drawings.

78. Apparatus for processing a continuous stretchable tow of filamentary filter material which is utilized for conversion into the fillers of filter plugs for cigarettes or the like and advances lengthwise in a predetermined direction along an elongated path, substantially as herein described with reference to and as illustrated in the accompanying drawings.