Method of and apparatus for ascertaining parameters of cigarette paper and the like

Abstract

The invention relates to a method of and to an apparatus for ascertaining at least one parameter of cigarette paper or the like, such as a running web of cigarette paper at least one side of which carries or should carry longitudinally spaced-apart coatings, e.g., consisting of silicate or cellulose and suitable to serve as so-called burning or combustion stops. A source of electromagnetic radiation cooperates with a polarizer to direct radiation against one side of the running web at an angle of between about 0° and 75° to the plane of the web at the locus of impingement of radiation. The radiation which has penetrated through the web is measured by a photosensitive detector which transmits corresponding signals to an evaluating arrangement serving to ascertain one or more characteristics of the coatings.

Description

CROSS-REFERENCE TO RELATED CASES

[0001] This application is a continuation of the application Serial No. PCT/EP 02/13339 which was filed on Nov. 27, 2002 and which claims the priority of commonly owned German patent application Serial No. 101 60 235.9 filed Dec. 7, 2001.

[0002] The disclosures of the PCT and German patent applications, as well as those of all US and foreign patents and/or patent applications identified in the specification of the present application, are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0003] The present invention relates to improvements in methods of and in apparatus for ascertaining one or more parameters or characteristics of paper or the like, especially paper which is utilized for the confinement of tobacco, filter material for tobacco smoke, inner and/or outer wrapping material for arrays of cigarettes and/or other smokers' products and the like. More particularly, the invention relates to improvements in methods of and apparatus for monitoring paper (hereinafter frequently or mostly referred to as cigarette paper) which involve the steps of and the means for directing electromagnetic radiation from at least one suitable source against one side of the paper at a given angle of incidence, measuring (e.g., with a suitable detector) radiation issuing at the other side of the paper, and ascertaining or determining (e.g., with an evaluation unit) the characteristics of the paper on the basis of the measured radiation.

[0004] U.S. Pat. No. 6,130,438 (granted Oct. 10, 2000 to Torai for “WRAPPING PAPER DETECT INSPECTION APPARATUS FOR A CIGARETTE MANUFACTURING MACHINE”) discloses a cigarette making machine employing an optical system which causes radiation to penetrate through cigarette paper, which evaluates the results of such penetration, and which discards cigarettes having unsatisfactory wrappers. The optical system of this patented arrangement employs lasers which confront suitable photodiodes. The cigarette paper is caused to advance between the diodes. The marginal portions of the cigarette paper are not monitored or must be monitored by an auxiliary system.

[0005] U.S. Pat. No. 6,020,969 (granted Feb. 1, 2000 to Struckhoff et al. for “CIGARETTE MAKING MACHINE INCLUDING BAND INSPECTION” and corresponding to WO 99/02051 and EP 1 011 351 A1) discloses a cigarette making system employing a sensor which is arranged to detect strips in cigarette paper, to detect defects in cigarette paper and to eject (segregate) defective cigarettes. The method which is disclosed in this US patent is based on the principle that infrared radiation issuing from a light emitting diode is reflected by the surface of cigarette paper and the thus reflected light is detected by a radiation-sensitive receiver.

[0006] U.S. Pat. No. 4,845,374 (granted Jul. 4, 1989 to White et al. for “METHOD AND APPARATUS FOR DETECTING THE DEPOSITION OF AN ADHESIVE ON A TRAVELLING WEB”) discloses a method and an apparatus which are designed to ascertain the width of an adhesive strip on an advancing cigarette paper web by resorting to a radiation reflecting arrangement. The radiation issues from a fluorescent tube and is oriented upon the web at a certain angle to a plane which is normal to the paper web; such radiation is reflected by the cigarette paper web to impinge, at a certain angle to the aforementioned plane, upon and to be evaluated by a charge coupled detector device (CCD).

[0007] German patent No. 20 43 876 discloses an arrangement which is designed to, detect defects in transparent webs or strips and employs a position vector consisting of polarized light and serving to scan the web. The web is located in front of a light receiving arrangement when the defective portions of the web, which rotate the polarization plane, rotate the polarization is plane of the light.

OBJECTS OF THE INVENTION

[0008] An important object of the instant invention is to provide a method of ascertaining the characteristics of cigarette paper or the like with a degree of accuracy, reliability and reproducibility which greatly exceeds such parameters of presently known methods.

[0009] Another object of this invention is to provide a relatively simple and compact and relatively inexpensive apparatus which can be utilized for the practice of the improved method and can be installed in or utilized in conjunction with presently known machines for the making, processing, wrapping, packing and/or otherwise manipulating smokers' products including plain and filter cigarettes or the like, packets for groups of rod-shaped smokers' products and/or analogous commodities.

[0010] A further object of the instant invention is to facilitate reliable segregation of defective products from acceptable products in mass producing machines such as modern cigarette, cigarillo or cigar making and packing machines.

[0011] An additional object of the invention is to reduce the number of rejects which are turned out by the machines for the making and/or processing of smokers' products and the like.

[0012] Still another object of the present invention is to take advantage of certain characteristics of cigarette paper or the like in order to enhance the reliability of detection of defects in cigarette paper and/or in material(s) or substance(s) which is(are) carried by cigarette paper during the making, packing and/or other processing of smokers' products.

SUMMARY OF THE INVENTION

[0013] One feature of the present invention resides in the provision of a method of ascertaining at least one parameter or characteristic of paper, especially cigarette paper. The improved method comprises the steps of directing against one side of the ciparatte paper at least one beam or ray of electromagnetic radiation (such as that furnished by a laser) at an incidence angle a which, in accordance with an important feature of the present invention, is between 0° and 75° whereby a. portion of such radiation issues from and at the other side of a cigarette paper, measuring the issuing radiation and ascertaining at least one parameter or characteristic as a function of (e.g., on the basis of) said issuing radiation.

[0014] The angle &agr; can be in the range of between about 5° and 45°, e.g., between about 10° and 20°, and can often equal or approximate 15°.

[0015] That portion of radiation which issues from and at the other side of the cigarette paper can also make a predetermined angle &bgr; with the other side of the cigarette paper. The angle &bgr; is between about 45° and 90°, often preferably between about 70° and 90°.

[0016] It is preferred to resort to electromagnetic radiation which has a predetermined polarized condition.

[0017] In accordance with a presently preferred embodiment of the improved method, the electromagnetic radiation is linearly polarized parallel to the one side of the cigarette paper.

[0018] The improved method can further comprise the step of advancing the cigarette paper in a predetermined direction (lengthwise), and the at least one parameter can involve the presence or absence of essentially periodical coatings or layers provided at least at one side of the running web of cigarette paper; such coatings or layers entail essentially periodical changes of intensity of radiation which issues from the web of cigarette paper at the locus of impingement of electromagnetic radiation against the one side of th advancing web.

[0019] The determining step of the just outlined method can include determining the periods of changes of radiation, and the ascertaining step includes or can include comparing the determined periods of radiation changes with a predetermined period. Such method can further comprise the step of ascertaining the extent of radiation changes, and the predetermined period can include an interval of average value of intensity of radiation which is characteristic of at least one constituent of the material of the coating or layer.

[0020] Another feature of the instant invention resides in the provision of an apparatus for ascertaining at least one parameter or characteristic of paper, such as cigarette paper. The improved method comprises a source of electromagnetic radiation, means for directing a beam of radiation from the source against one side of the paper at an angle &agr; of between about 0° and 75° whereby a portion of such radiation issues from and at the other side of the paper, detector means which is arranged to measure the issuing radiation, and means for ascertaining the at least one parameter of paper as a function of said issuing radiation.

[0021] The angle &agr; can be between about 5° and 45°, often preferably between about 10° and 20°, and often at least close to about 15°.

[0022] It is normally preferred to ensure that the

[0023] radiation issuing from the other side of the paper makes with the paper a predetermined angle &bgr;, and the detector means is or can be positioned to intercept the radiation issuing at such angle &bgr;.

[0024] The angle &bgr; can be between 45° and 90°, often preferably between about 70° and 90°.

[0025] The improved apparatus can further comprise means for polarizing the radiation which issues from the source before the radiation reaches the paper. Such polarizing means can be arranged to polarize the radiation issuing from the source in parallel to the one side of the paper.

[0026] The improved apparatus preferably further comprises means (e.g., one or more rollers or drums) for advancing the paper along a predetermined path, and the detector means can be arranged to monitor the intensity of radiation which issues from the paper. The at least one parameter can include the presence of essentially periodical coatings or layers provided at least at one side of the paper in the path and entailing essentially periodical changes of intensity of radiation which reaches the detector means subsequent to penetration through the web in a predetermined portion of the path. The ascertaining means of such apparatus can comprise a memory which is operatively associated with the is detector means and is arranged to store a predetermined period of changes for comparison with those changes which are represented by the radiation determined by the detector means. The memory can include a table which denotes the extent of changes of radiation, and the predetermined period can include an interval of average value of intensity of radiation which is characteristic of at least one constituent of the material of the coatings.

[0027] The novel features which are considered as characteristic of the invention are se forth in particular in the appended claims. The improved apparatus itself, however, both as to its construction and the modes of assembling, installing and operating the same, together with numerous additional important and advantageous features and attributes thereof, will be best understood upon perusal of the following detailed description of certain presently preferred specific embodiments with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

[0028] FIG. 1 is a somewhat schematic perspective view of a cigarette making machine employing an apparatus which embodies the present invention;

[0029] FIG. 2 is a diagrammatic view of one embodiment of the apparatus which can be employed in the cigarette making machine of FIG. 1; and

[0030] FIG. 3 is a diagram wherein the intensity of radiation penetrating through a travelling web of cigarette paper is measured along the ordinate and the time is measured along the abscissa.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0031] FIG. 1 illustrates certain relevant details od a cigarette rod making machine which can be of the type known as PROTOS distributed by the assignee of the present application. This machine comprises a gate 1 which is arranged to supply batches of shredded and/or otherwise comminuted tobacco leaves into a preliminary distributor 2. A tobacco withdrawing drum 3 serves to draw tobacco particles from the distributor 2 into a magazine 4 in such a way that the supply of tobacco in the latter is or can be maintained at an at least substantially constant level. A preferably automatically controlled elevator conveyor 5 of known design (see, for example, commonly owned U.S. Pat. No. 5,072,742 granted Dec. 17, 1991 to Heitmann for “METHOD OF AND APPARATUS FOR MAKING A FILLER OF SAMOKABLE MATERIAL”) is provided to draw batches of tobacco particles from the magazine 4 and to deliver successive batches into a gathering duct 6 which is installed in the machine frame at a level above a rotary carded drum 7 cooperating with a rapidly rotating so-called picker roller 8 to propel an at least substantially uniform stream of tobacco particles onto the upper reach of a continuously driven constant-speed endless belt conveyor 9.

[0032] The conveyor 9 gathers and advances lengthwise a continuous stream of tobacco particles, and the leader of such stream is propelled against a pneumatic sifter 11 which includes nozzles and/or analogous air discharging and directing devices forming an upright air curtain which is traversed by larger (heavier) tobacco particles but intercepts the lighter particles of the stream being supplied by the belt conveyor 9. The intercepted lighter tobacco particles descend onto the carding of a rotary drum 12 cooperating with a wall 13 to form therewith a funnel 14. The heavier (more satisfactory) tobacco particles which have traversed the air curtain formed by the sifter 11 are propelled by the carding of the drum 12 to enter a channel 16 and to impinge upon and be entrained by the lower reach of a foraminous band conveyor 17. The latter coperates with a suction chamber 18 to attract and advance successive increments of a shower of satisfactory tobacco particles toward a stream trimming or equalizing device 19.

[0033] The equalizing device 19 removes the surplus of tobacco from the stream at the underside of the lower reach of the band conveyor 17 which conveys the thus trimmed stream onto the upper side of a continuously advancing strip or web 21 of cigarette paper or other suitable wrapping material. This web is drawn off a bobbin 22 and moves in the same direction as the lower reach of the band conveyor 17 to advance the equalized tobacco stream into a wrapping mechanism 26 employing a driven endless belt or band 24 known as garniture. Prior to entering the wrapping mechanism 26 including the garniture 24, successive increments of the cigarette paper web 21 advance through a printer 23 which provides successive spaced-apart portions of the web with suitable printed matter (e.g., the trademark(s) of the manufacturer of plain or filter cigarettes).

[0034] The garniture 24 drapes the running web 21 of cigarette paper around the trimmed or equalized tobacco stream (called filler) in such a way that one longitudinal marginal portion of the web extends substantially tangentially of and away from the cylindrical envelope surrounding the confined tobacco stream. The wrapping mechanism 26 further comprises a so-called paster (not shown) which coats one side of the aforementioned one marginal portion of the web 21 with a suitable adhesive, and such marginal portion is thereupon folded over the adjacent portion of the thus finished tubular envelope for the confined equalized tobacco stream or filler of the resulting cigarette rod 28. A plate-like drying device (e.g., a so-called tandem sealer) 27 is provided to promote the setting of adhesive and to thus prevent the envelope from bursting open at the adhesive-coated seam during further processing of the continuous cigarette rod 28.

[0035] Subsequent to leaving the printer 23 but prior to reaching the garniture 24, the web 21 advances through an apparatus 20 which embodies one presently preferred form of the instant invention. The purpose of the apparatus 20 is to ascertain whether or not the web 21 carries a coating or layer. The details of the apparatus 20 will be described in greater detail with reference to FIGS. 2 and 3.

[0036] The rod 28 is caused to advance through a measuring and regulating apparatus 29 on its way to a severing apparatus 31 (known as cutoff) which repeatedly cuts across the advancing rod to convert the latter into a is series of successive plain cigarettes 32 of double unit length. Such plain cigarettes advance into the range of controlled orbiting arms 33 of a transfer unit 34 which delivers the cigarettes 32 onto a drum-shaped receiving conveyor 36 of a filter cigarette making machine 37. The latter comprises a severing device including a drum 38 and a circular knife (not shown) which cooperates with the drum 38 to halve each cigarette 32 into a pair of plain cigarettes of unit length. The filter cigarette making machine 37 can be of the type disclosed in commonly owned U.S. Pat. No. 5,135,008 granted Aug. 4, 1992 to Oesterling et al. for “METHOD OF AND APPARATUS FOR MAKING FILTER CIGARETTES”.

[0037] FIG. 1 further shows two endless belt conveyors 39, 41 which serve to convey surplus tobacco (removed by the trimming device 19) back into the range of the elevator conveyor 5 which supplies such material into the gathering duct 6. More specifically, the conveyor 41 delivers surplus tobacco into a receptacle 42 which is adjacent the path of movement of spaced-apart paddles at the outer side of the endless flexible element of the elevator conveyor 5.

[0038] The aforementioned regulating apparatus 29 of the continuous cigarette rod making machine of FIG. 1 serves to control the operation of the equalizing device. The details of such apparatus are fully disclosed in the commonly owned copending U.S. patent application Ser. No. 10/850,119 filed May 21, 2004 by Andreas Noack for “APPARATUS FOR ASCERTAINING THE TRANSVERSE DIMENSIONS OF ROD-SHAPED ARTICLES”.

[0039] FIG. 2 is a diagrammatic view of the apparatus 20. This apparatus is arranged to direct radiation from a source 40 against one side (42) of the running web 21 and to monitor that percentage or share of radiation which has penetrated through successive increments of the web. The radiation source 40 is assumed to include a laser; however, it is equally within the purview of the present invention to employ other suitable radiation sources. The radiation 40a issuing from the source 40 is focussed by a lens 41 having an optical axis 40b. The locus of impingement of the focussed radiation 40a upon successive increments of the respective side (the underside 42 in FIG. 2) of the advancing web 21 is shown at 50. A polarizing filter 44 is interposed between the focussing lens 41 and the locus 50. The purpose of the filter 44 is to effect linear polarization of the radiation 40a in parallel to the surface 42 of the web 21.

[0040] The optical axis 40b makes an angle &agr;=15° with the respective surface (underside in FIG. 2) of the travelling web 21. The illustrated angle &agr; is but one of numerous suitable angles (e.g., the angle &agr; can exceed 0° and can be less than 75°).

[0041] FIG. 2 shows that the underside 42 of the web 21 is provided with a series of coatings or layers including that shown at 46. It is also possible to turn the advancing web 21 in such a way that the polarized radiation 40a is directed against the uncoated side 48 of the web.

[0042] The illustrated coating 46 consists of discrete paper strips 52 which extend transversely of the web 21 at selected distances from each other. In lieu of employing coatings 52 which constitute paper webs, it is also possible to employ other types of coatings, e.g., silicate.

[0043] The web 21 is advanced lengthwise (in a direction to the right, as viewed in FIG. 2) at a speed v. FIG. 2 shows the web 2 in a position in which the radiation 40a (at the locus 50) impinges upon one of the coatings 52.

[0044] FIG. 2 further shows a detector 54 which constitutes a photosensitive element and is disposed at the upper side of the advancing web 21. The detector 54 is disposed in the path of radiation 58 which has penetrated through the web 21 and the coating or strip 52 at the locus 50 and is focussed by a lens 56 having an optical axis 57 making with the plane of the path for the web 21 an angle &bgr;=85°. The purpose of the detector 54 is to ascertain the intensity of radiation which has penetrated through the running web 21. The angle &bgr; can vary between 45° and 90°.

[0045] The intensity I of radiation (see FIG. 3) which reaches the detector 54 depends upon the presence or absence of a coating 52 at the locus 50 of impingement of radiation 40a upon the web 21. Thus, the intensity I is less pronounced if the radiation 40a must penetrate through the web 21 as well as through one of the coatings 52 The detector 54 is designed to transmit variable-intensity electric signals 60 to an evaluating circuit 62. The amplitudes a of the electric signals 60 being transmitted by the detector 54 to the evaluating circuit 62 are shown in FIG. 3. The intensity I of such signals 60 decreases periodically, namely when the radiation 40a impinges upon a coating 52 at the locus or station 50. Otherwise stated, the amplitude of a signal 60 which is generated when the radiation 40a penetrates solely through the web 21 is higher than the amplitude of that signal 60 which is obtained when the radiation 40a is compelled to pass through the web 21 as well as through one of the coatings 52.

[0046] The evaluating circuit 62 can embody a memory for the storage of a given timing or period of changes of intensity I, and such memorized periods can be compared with the intervals of variations of intensity I which are attributable to the frequency of arrival of successive coatings 52 at the station or locus 50.

[0047] It is also possible to associate the evaluating circuit 62 with a memory for the storage of a table which embodies information denoting at least one extent of change of intensity I attributable to a particular material (such as cellulose) in the coating 46. The evaluating circuit 62 embodying or associated with such table can be designed to furnish information denoting an average value of intensities I within a preselected interval of time t, to furnish information denoting the actual extent a of changes relative to an average value and to ascertain—with reference to the aforementioned stored table—the nature of material (e.g., cellulose) of which the coatings 46 consist. This is possible because different coatings cause more or less pronounced changes of intensity I.

[0048] The polarizing (at 44) of radiation 40a enhances the changes a in comparison with an irradiation of cigarette paper with non-polarized light.

[0049] An important advantage of the improved method and apparatus is that they can be resorted to for a highly reliable ascertaining of one or more selected characteristics of cigarette paper or the like, e.g., the aforediscussed and illustrated presence or absence of coatings or layers 46 as well as the material(s) of such layers. This can be accomplished without it being necessary that the angle &agr; match the angle &bgr;. An advantage of a method and apparatus wherein the angle &agr; need not match the angle &bgr; is that highly accurate results can be achieved without the need for extensive adjustments of the optical, monitoring and evaluating systems.

[0050] As already mentioned hereinbefore, the invention is based on the recognition that the reflection coefficient of coated portions of, cigarette paper is higher than that of the uncoated portions, i.e., the quantity of radiation penetrating through coated portions of a running cigarette paper web is below that which can penetrate through uncoated portions. The utilization of radiation-polarizing means (such as the polarizing filter 44 shown in FIG. 2) enhances the contrast between the coated and uncoated portions of the web 21. Especially if the radiation is linearly polarized parallel to the respective surface or side (42 in FIG. 2) of cigarette paper, the contrast between the irradiated and non-irradiated portions of the web is even more pronounced. Thus, if the running web 21 is irradiated at one (42) of its sides with linearly polarized light issuing from the source 40 or an equivalent thereof, the presence or absence of coatings or layers 46 can be detected with a high degree of accuracy by evaluating the radiation 58 which issues at the other (non-irradiated) side of the running web 21.

[0051] The feature that the radiation source 40 can be installed at either of the two sides (42, 48) of the cigarette paper web 21 brings about the advantage that the improved apparatus 20 can be readily installed at an available location in a cigarette making machine or in any other machine wherein a web of paper or the like (such as cigarette paper) is to be examined for the presence or absence of coatings 46 or the like

[0052] As also already mentioned hereinbefore, the coatings or layers 46 can consist of cellulose or silicate. Such coatings can be utilized as so-called combustion or burning stops which serve to ensure the extinguishment of a cigarette which was unintentionally left in lighted condition for an excessive interval of time. The reason is that, due to the composition of the coatings 46, the respective portions of cigarette paper 21 permit the penetration of lesser quantities of atmospheric air into the tobacco filler of the lighted cigarette. In other words, such coatings effect a reliable extinguishment of a lighted cigarette and thus greatly reduce the likelihood of accidental fires.

[0053] It has been ascertained that the contrast between the intensities of radiation penetrating through the coated and uncoated portions of a cigarette paper web 21 is especially satisfactory if the angle &agr; matches or approximates 15°. By the same token, it is advisable to select a particular angle &bgr; (preferably between about 70° and 90°) because this also contributes to a more pronounced contrast between penetrations of the radiation through coated and uncoated portions of the running web 21. Such contrast, too, can be enhanced if the radiation 40a is linearly polarized parallel to the plane of the cigarette paper web 21 in its path.

[0054] In the machine of FIG. 1, the means for advancing the web 21 lengthwise along the path extending between the polarizing filter 44 and the focussing lens 56 includes the garniture 24. It will be appreciated that other forms of web advancing means can be employed with equal or similar advantage.

[0055] Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic and specific aspects of the above outlined contribution to the art of ascertaining selected parameters of cigarette paper or the like and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the appended claims.

Claims

1. A method of ascertaining at least one parameter of cigarette paper, comprising the steps of:

directing against one side of the cigarette paper at least one beam of electromagnetic radiation at an incidence angle &agr; of between 0° and 75° whereby a portion of said radiation issues from and at the other side of the cigarette paper;

measuring the issuing radiation;

and ascertaining said at least one parameter as a function of said issuing radiation.

2. The method of claim 1, wherein said angle &agr; is between about 5° and 45°.

3. The method of claim 1, wherein said angle &agr; is between about 10° and 20°.

4. The method of claim 3, wherein said angle &agr; is about 15°.

5. The method of claim 1, further comprising the step of detecting said radiation issuing from and at the other side of the cigarette paper at a predetermined angle &bgr; with respect to the other side of the cigarette paper.

6. The method of claim 5 wherein said angle &bgr; is between about 45° and 90°.

7. The method of claim 6, wherein said angle &bgr; is between about 70° and 90°.

8. The method of claim 1, wherein said electromagnetic radiation has a predetermined polarized condition.

9. The method of claim 8, wherein said electromagnetic radiation is linearly polarized parallel to the one side of the cigarette paper.

10. The method of claim 1, further comprising the step of advancing the cigarette paper in a predetermined direction, said at least one parameter involving the presence of essentially periodical coatings provided at least at one of said sides of the cigarette paper and entailing essentially periodical changes of intensity of radiation issuing from the cigarette paper at a locus of impingement of electromagnetic radiation against said one side of the advancing cigarette paper.

11. The method of claim 10, wherein said determining step includes determining the periods of said changes of radiation and said ascertaining step includes comparing the determined periods of said changes of radiation with a predetermined period.

12. The method of claim 11, further comprising the step of ascertaining the extent of said changes of radiation and said predetermined period includes an interval of average value of intensity of radiation which is characteristic of at least one constituent of the material of said coating.

13. Apparatus for ascertaining at least one parameter of cigarette paper, comprising;

a source of electromagnetic radiation;

means for directing a beam of radiation from said source against one side of the cigarette paper at an angle &agr; of between about 0° and 75° whereby a portion of such radiation issues from and at the other side of the cigarette paper;

detector means arranged to measure the issuing radiation; and

means for ascertaining the at least one parameter of cigarette paper as a function of said issuing radiation.

14. The apparatus of claim 13, wherein said angle &agr; is between about 5° and 45°.

15. The apparatus of claim 13, wherein said angle &agr; is between about 10° and 20°.

16. The apparatus of claim 15, wherein said angle &agr; is about 15°.

17. The apparatus of claim 13, wherein said detector means is positioned to intercept radiation issuing from and at the other side of the cigarette paper at a predetermined angle g with respect to the cigarette paper.

18. The apparatus of claim 17, wherein said angle &bgr; is between about 45° and 90°.

19. The apparatus of claim 17, wherein said angle &bgr; is between about 70° and 90°.

20. The apparatus of claim 13, further comprising means for polarizing the radiation issuing from said source before the radiation reaches the cigarette paper.

21. The apparatus of claim 20, wherein said polarizing means is arranged to polarize the radiation issuing from said source in parallel to said one side of the cigarette paper.

22. The apparatus of claim 13, further comprising means for advancing the cigarette paper along a predetermined path, said detector means being arranged to monitor the intensity of radiation issuing from the cigarette paper and said at least one parameter including the presence of essentially periodical coatings provided at least at one of said sides of the cigarette paper in said path and entailing essentially periodical changes of intensity of radiation reaching said detector means subsequent to penetration through the web in a predetermined portion of said path.

23. The apparatus of claim 22, wherein said ascertaining means comprises a memory operatively associated with said detector means and arranged to store a predetermined period of changes for comparison with changes represented by the radiation determined by said detector means.

24. The apparatus of claim 23, wherein said memory includes a table denoting the extent of said changes of radiation and said predetermined period includes an interval of average value of intensity of radiation which is characteristic of at least one constituent of the material of said coatings.