GB1604200A

GB1604200A - Method of and apparatus for testing rod-like smokable articles for faulty wrappers

Info

Publication number: GB1604200A
Application number: GB2259378A
Authority: GB
Original assignee: Hauni Werke Koerber and Co KG
Current assignee: Koerber AG
Priority date: 1978-01-19
Filing date: 1978-05-25
Publication date: 1981-12-02

Description

(54) METHOD OF AND APPARATUS FOR TESTING ROD-LIKE SMOKABLE ARTICLES FOR FAULTY WRAPPERS (71) We, HAUNI-WERKE KORBER & CO KG., a German Company of Kampchaussee 12-22, 2050 Hamburg 80, Germany (Fed. Rep.), do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to an improvement in or modification of the invention forming the subject of our copending Application No. 49287/77 Serial No. 1596392 (hereinafter referred to as the "main patent").The main patent relates to a method of testing rod-like smokable articles for faulty wrappers which comprise a zone of desired air permeability, during their cross-axial conveyance along a pre-determined path, by forming a pressure drop between a space enclosed by the wrapper and containing a filling, and a space outside the wrapper, and forming a test signal which depends upon the air permeability of the wrapper, wherein each article per se is subjected to a first test by forming a first pressure drop and forming a first test signal, wherein an upper limit value is fixed for the air permeability of the wrapper and a tested article is regarded to be in order when the test signal is located below the upper limit value, and wherein the articles are subjected to a second test with the highest sensitivity in the region of the zone of desired air permeability by the formation of a second pressure drop and the formation of a second test signal, a second test signal for a plurality of articles being formed thereby which corresponds to the mean air permeability of the zone of desired air permeability.Furthermore, main patent relates to an arrangement for testing rodlike smokable articles for faulty wrappers which comprise a zone of desired air permeability, having at least one travelling test conveyor which comprises holders for retaining the articles, and two test devices which comprise sealing means for temporarily separating a space which is enclosed by the wrapper and contains a filling, from a space outside the wrapper of each article, connecting means which connect one of the two spaces to a source of pressure, and have connecting means which connect always one of the two spaces to measuring arrangements which detect pressure differences, the first test device being constructed for forming a first pressure drop between the space within and the space without the wrapper, and the measunng arrangement of which comprises a signal transmitter for a signal delivered when the air permeability lies above an upper limit value, and the second test device the highest sensitivity of which lies in the region of the zone of desired air permeability of the wrapper, being constructed for forming a second pressure drop between the space within and the space without the wrapper, and the measuring arrangement of which comprises a mean value former.

The invention according to the main patent renders it possible to perform a so-called trend watch of the "zone of desired air permeability" (region of the wrapper having an intentional increased Porosity which is usually formed by producing a perforation in the wraPper material). A particular advantage of is trend indication is that after suitable adjustment it can be realised with the test arrangements known at resent.

The present invention is based on the problem to improve in respect of its accuracy the method disclosed in the main patent of indicating the trend for the zone of desired air permeability in smokable articles, so that the trend indication becomes utilisable for control purposes.

This problem is solved according to the invention in that each article per se is subjected to the second test and the second test signal is formed by forming the mean value of a series of successive measuring signals obtained by the second test, wherein exclusively measuring signals of articles are used for forming the mean value which had been found to be in order by the first test. In particular when it is to be tested whether the zone of desired air permeability has a satisfactory minimum air permeability, the accuracy of the trend indication for this zone is distorted by measuring signals which originate from smokable articles the wrapper of which has an additional leakage.If, as is proposed according to the invention, signals are eliminated from the mean value formation which originate from such faulty articles, this mean value already is a fairly accurate statement about the momentary state of the zone of desired air permeability of the smokable articles produced. This mean value becomes even more accurate when, according to a further development, it is formed always from the same number of measuring signals obtained by the second test. Also this mean value may be used better for control purposes, e.g. or ejecting articles detected to be faulty, because the article group for which the respective mean value has been formed is detected and can be observed during its further conveyance of an ejection station.Those articles which effect an increase or a reduction, respectiveliy, of the mean value beyond predetermined limits, may be detected even more accurately when, m accordance with a further embodiment, the mean value is formed continuously, in that the respective youngest measuring signal utilised for forming the mean value is substituted for the respective oldest signal. Thus if in this construction faulty articles are to be ejected, it is no longer necessary to segregate one or more groups each having a defined number of articles, but only those articles at or after the test of which the mean value exceeds the pre-determined limit values.

If merely a minimum air permeability of the zone of desired air permeability is to be ensured, it is sufficient that a lower limit value is fixed for the second testing of the air permeability of the wrapper in the zone of desired air permeability and the tested articles are considered to be in order when the second test signal is located above the lower limit value. However, if it is also to be prevented that the air permeability of the respective zone of the wrapper material is too large, it is proposed that for the second test an upper limit value is fixed for the air permeability of the wrapper in the zone of desired air permeability and the tested articles are considered to be in order when the second test signal is located below the upper limit value.According to a further feature a control signal is formed for ejecting the articles detected to be faulty and/or for influencing a perforation device, when the test signal is located outside the preselected limit values.

The arrangement referred to above is suitable for performing the method described above and is characterised in that the mean value former is connectable to the second test device by means of a switching arrangement, the switching arrangement being connected to the signal transmitter of the first test device and being constructed in such a manner that the transmission of articles the air permeability of which exceeds the upper limit value, to the mean value former is interrupted. For the purpose of forming the mean value of always a defined number of measuring signals, the mean value former is controllable by means of a counter the input of which is connected to the switching arrangement.For the purpose of detecting smokable articles the air permeability of which lie outside predetermined tolerances in the zone of desired air permeability, the measuring arrangement of the second test device comprises a signal transmitter for a signal delivered when the air permeability of the wrapper lies below a lower limit value, and a signal transmitter for a signal delivered when the air permeability of the wrapper lies above an upper limit value.

In order that the two test devices do not influence each other, it is furthermore proposed to arrange the two test devices one behind the other at the test conveyor, in which case then the switching arrangement is preceded by a delay member which is controllable in synchronism with the movement of the test conveyor. The invention renders it possible to connect the measuring arrangement to a control device for removing from their conveyance path articles with a fault in the wrapper.

The invention is explained in detail with reference to the drawing which illustrates constructional examples. There are shown in: Figure I diagrammatically a filter assembly machine for producing filter cigarettes, Figure 2 a section of a test drum of the filter assembly machine of Figure 1, in section, Figure 3 a view from above on a section of the test drum according to Figure 2 Figure 4 a test diagram with two successively arranged test devices for detecting faults in the wrapper of smokable articles for the test drum of Figures 2 and 3, Figure 5 a variant of the test diagram of Figure 4.

Figure 1 illustrates diagrammatically a filter assembly machine of the type MAX S of the Applicant. An inlet drum 1 transfers the cigarettes produced by a cigarette producing machine to two stagger drums 2 which re-arrange the cigarettes supplied in staggered formation and deliver them in rows of always two pieces with a gap between the cigarettes to an assembly drum 3. Filter rods travel from a magazine 4 to a cutting drum 6, are cut by two circular cutters 7 to filter plugs of twice the used length, staggered on a staggering drum 8, aligned by a shifter drum 9 to form a row of plugs disposed one behind the other, and delivered by an accelerator drum 11 into the gaps of the cigarette rows on the assembly drum 3. The cigarette-filter-cigarette groups are pushed together, so that they lie closely against each other. Thereafter they are received by a transfer drum 12.A cover paper strip 13 is drawn off a cover paper reel 14 by means of draft rollers 16. The cover paper strip 13 is guided around a breaker member 17 which comprises a sharp edge. A gumming device 18 for the cover paper strip 13 is preceded by a perforation device e.g. a spark-producing electrical discharge device known per se, by means of which several rows of small holes are produced in the cover paper strip 13 to form a zone of desired air permeability. This zone is exempted from the subsequent gumming, whereupon the cover paper strip 13 is severed on a cover roller 19 by a cutter drum 21. The severed cover sheets are attached to the cigarette-filter groups on the transfer drum 12 and rolled around the cigarettefilter groups on a rolling drum 22 by means of a rolling hand 23.The finished groups of double filter cigarettes are fed by way of a drying drum 24 to a cutting drum 26 and processed to single filter cigarettes thereon by cutting through the centres of the filter plugs, faulty cigarettes being ejected at the same time. A turning device 29 co-operating with a transfer drum 27 and a collecting drum 28 turns one row of filter cigarettes and transfers it simultaneously into the un-turned row of filter cigarettes travelling through by way of the transfer drum 27 and the collecting drum 28. The filter cigarettes travel by way of a test drum 31 to an ejection drum 32 on which moreover a head scanning of the filter cigarettes is effected prior to the ejection process. A depositing drum 34 cooperating with a deceleration drum 33 deposits the filter cigarettes on a support belt 36.

Figures 2 and 3 illustrate diagrammatically the construction of the test drum 31 constructed as a test conveyor. In principle, all known test devices which test pneumatically the wrapper of rod-like smokable articles, may be used after alterations or additions have been effected in accordance with this invention A test device which requires only minor constructional changes for the present invention, is illustrated e.g. in DT OS 2 324 055 and in the corresponding US Patent 3948084 of the Applicant. However, since constructional details of such a test device are not subject of this invention, merely the present diagrammatic illustration has been selected for the explanation of the invention.

A drum body 37 which is drivable to perform a rotary movement is provided with holders 38 for the filter cigarettes Z. The filter cigarettes Z lie upon rails 39 the suction air bores 41 of which are guided to a suction air source through a stationary control ring not visible, for holding the cigarettes.The filter cigarettes can be subjected to test air which is supplied and guided away, respectively, through pipes 48a and 48b, as well as 49a and 49b, through control slots 42a and 42b as well as 43a and 43b arranged one behind the other at the spacing of a pitch of the holders 38, in stationary control rings 44a and 44b, respectively, and sealing means in the form of sealing tubes 46 which can be pushed against the filter ends F of-the filter cigarettes Z against the effect of springs 47 by a mechamcal control element known per se and therefore not illustrated, e.g. a cam guide, Rails 51a and 51b on the drum body 37 have bores 52a and 52b, respectively, which are flush with the holders 38 and co-operate with the control slots 42a and 43a, or 42b and 43b, respectively.The control slot 42a corresponds closely to the pitch division of the holders 38 in respect of its length, whereas the control slot 42b is approximately half as long as the control slot 42a. When the drum body 37 is moved in the direction of the arrow 53 and a bore 52a reaches the control slot 42a, test air flows into the interior of a filter cigarette Z, whereby the same is "blown up", because the bore 52b is still closed by the control ring 44b. When the bore 52b reaches the control slot 42b, the test air flows out of the filter cigarette Z into the control slot 42b and the pipe 48b.

The control slots 43a and 43b are of the same length, so that the bores 52a and 52b reach simultaneously the control slots 43a and 43b, respectively, and test air flows from both ends into the interior of the filter cigarette Z, whereby the same is "blown up". The holes produced in the cover paper B of the filter ends F of the filter cigarettes Z by means of the perforation device 15 are denoted by L.

As illustrated in Figure 4, two test devices 54 and 56 are realisable by means of the construction of the test drum 31 illustrated in Figures, 2 and 3, and each has its own measuring arrangement 57 and 58, respectively, associated therewith.

The test device 54 is constructed in such a manner that test air is supplied to the filter cigarette Z through the pipe 48a which branches off a pipe 61 connected to the pressure side of a pressure source 59 and which contains an adjuster valve 62 and a restrictor 63a. The test air flows through the filter cigarette Z and leaves it through the pipe 48b which comprises a restrictor 63b in front of which is connected the measuring arrangement 57 which detects pressure ferences.The measuring arrangement 57 comprises an electro-pneumatic measuring converter 64 the output end of which is connected to a signal transmitter in the form of a threshold value member 66 which delivers an output signal when the output signal of the measuring converter 64, or when the pressure in the pipe 49b does not reach a pre-determined value, which means that an upper limit value for the air permeability of the wrapper material of a filter cigarette Z has been exceeded. The output end of the threshold value member 66 is connected to an input of an AND-member 67 the other input of which is in connection with a clock pulse transmitter 68 which is drivable in synchronism with the test drum 31.At the output end the AND-member 67 is in connection with the first stage 69a of a shift register 69 which is driven by the clock pulse transmitter 68 and the output of which is connected to a control device 71 for removing from their conveyance path articles with faults in their wrapper.

The control device 71 compnses an amplifier 72 and an electro-magnetic valve 73 which is arranged in pipe 77 which connects a compressed air source 74 to an ejector nozzle 76. This ejector nozzle 76 is associated with the ejector drum 32 of the filter assembly machme illustrated in Figure 1.

In the test device 56, test air is guided into the two end faces of the filter cigarettes Z by a pipe 49 which likewise branches off the pipe 61 and which forms the branch pipes 49a and 49b. The pipe 49 comprises an adjuster valve 78 and a restrictor 79. The pipe 49b comprises a restrictor 81 which is followed by the measuring arrangement 58.

The restrictor 81 in the pipe 49b effects an asymmetric sensitivity of the test device 56, so that the values detected by the measuring arrangement 58 originate in the first place from fluctuations of the air permeability of the cover sheet B provided with holes L of the filter cigarette Z. The measuring arrangement 58 comprises an electropneumatic measuring converter 82 the output end of which is connected to a controllable input a of a mean value former 83.A control input b of the mean value former 83 is connected to the output of a switching arrangement in the form of an ANDmember 84 the input of which is connected on the one hand b way of a NOT-member 86 to an output o the second stage 69b of the shift register 69 (delay member controllable in synchronism with the movement of the test drum 31), and on the other hand to the clock pulse transmitter 68.

A further control input c of the mean value former 83 is connected to an output of a counter 87 the input end of which is likewise connected to the output of the AND-member 84. The mean value former 83 accepts at its input a a signal only when simultaneously a control signal prevails at its input b. A control signal at the input C of the mean value former causes the delivery at the output d of a signal which corresponds to the respective mean value and prepares the mean value former 83 for forming a new mean value by cancelling its content. The output d of the mean value former 83 is connected to two signal transmitters in the form of threshold value members 88 and 89 and to an indicator device 91.The threshold value member 88 delivers a signal when the signal of the mean value former 83 corresponding to the mean value of a number of output signals of the measuring converter 82 exceeds a predetermined value, which means that the air permeability of the wrapper material or the holes L, respectively, of the filter cigarettes Z has dropped below a lower limit value; in contrast the threshold value member 89 delivers a signal when the signal of the mean value former 83 corresponding to the mean value of a number of output signals of the measuring converter 82 drops below a predetermined value, which means that an upper limit value for the air permeability of the wrapper material, or the holes L, respectively, of the filter cigarettes Z has been exceeded.

Manner of operation of the test arrangement described above: In the test device 54 the filter cigarettes Z are penetrated by test air, the air permeability of the entire wrapper material of the filter cigarette Z being monitored by means of the measuring arrangement 57. If a filter cigarette Z has an unacceptable leakage, e.g. in consequence of a seam which is not properly adhesively secured, the threshold value member 66 delivers a signal by way of the AND-member 67 to the shift register 69 in consequence of the pressure drop caused by this leakage and the fact that consequently the nominal pressure in the pipe 48b has not been attained. The test or read-out instant of time is determined by means of the clock pulse transmitter 68 by way of the AND-member 67. The signal inserted in the shift register 69 follows in the shift register the further path of the filter cigarette Z recognised to be faulty, so that the electromagnetic valve 73 is energised by the amplifier 72 at the correct instant of time, namely when this filter cigarette Z reaches the blower nozzle 76 at the ejector drum 32, and the filter cigarette Z is removed from the ejector drum 32 by means of an air stream.

In the test device 56, the filter cigarettes Z are loaded from both ends with test air through the pipes 49a and 49b; because of the asymmetric sensitivity described of this test device, changes of the holes L in the cover paper B have a particularly strong effect on the signal delivered by the measuring converter 82 to the mean value former 83. The instant of time of a signal acceptance into the mean value former 83 is determined by the output signal of the AND-member 84, one input of which is connected to the clock pulse transmitter 68.

If a faulty filter cigarette Z has been detected by the measuring arrangement 57 of the test device 54 which leads by one clock pulse, it is disregarded for forming the mean value in the mean value former 83 of the measuring arrangement 58, in that the AND-member 84 is blocked by means of the output signal of the second stage 69b of the shift register 69, which signal is negatived by the NOT-member 86. Since in this case the counter 87 connected to the AND-member 84 likewise does not receive an input signal, it is ensured that in the mean vaLue former 83 always a mean value is formed from a defined number of filter cigarettes Z which have been detected to be free of faults in the test device 54.The signal issued by the counter 87 and delivered at the output of the mean value former 83 after the predetermined number of filter cigarettes Z to be tested has been reached is indicated by the indicator device 91 on the one hand and is monitored in respect of predetermined limit values by the threshold value members 88 and 89 on the other hand. When these limit values are exceeded or not attained, respectively, the associated signal lam 92 or 93, respectively, is caused to light up the threshold value member 88 or the threshold value member 89. However, output signals of the threshold value members 88 and 89 may alternatively be utilised for influencing the perforation device 15 indicated at the filter assembly machine according to Figure 1, in that e.g. the number or the hole size of the holes inserted in the cover paper strip 13 is changed.

In the variant according to Figure 5, parts which agree with those of Figure 4 are provided with the same reference numerals mcreased by 100 and are not discussed again.

The test device 154 and the measuring arrangement 157 have remained unchanged, whereas a different measuring arrangement 194 is provided for the test device 156. The electro-pneumatic measuring converter 182 is connected to a store 196 which comprises n stages, and the stages a ... n are controllable by an associated counter 187. The counter 187 is connected to the output of the AND-member 184, and it controls the stage a at the counter state 1, the stage b at the counter state 2, and so on, of the store 196 for receiving a signal from the measuring converter 182. Every signal accepted into a stage is stored for one cycle, that is to say until after successive control of all the other store stages, the respective store stage is controlled again for receiving a fresh signal.

At the output end, all stages of the store 196 are continuously connected to a mean value former 197 the output of which in turn is connected to the threshold value members 188 and 189 as well as to the indicator device 191. The threshold value members 188 and 189 are connected to the indicator lamps 192 and 193, respectively, and to inPuts of an OR-member 198 the output ot which is connected to an input of the stage 169b of the shift register 169.

In contrast to the construction of Figure 4, the measuring arrangement 194 consequently does not form periodically, but continuously a mean value from a defined number of filter cigarettes Z tested in the preceding test device 154 and the measuring arrangement 157 thereof and found thereby to be in order. The monitoring of the signal continuously delivered by the mean value former 197, by means of the threshold value members 188 and 189 permits early recognition of the fact that the air permeability in the zone of desired air permeability (holes L) of the wrapper of the filter cigarettes Z strays out of a permitted tolerance range; on the one hand such straying is then indicated by the indicator lamp 192 or 193, and on the other hand a signal is then delivered to the stage 169b of the shift register 169 by way of the OR-member 198.This has the consequence that the filter cigarettes Z which have caused the mean value to increase above or decrease below the permitted tolerance threshold, are ejected from the ejector drum 32 by means of the control device 171 in the manner previously described. The outputs of the threshold value members 188 and 189 led to the inputs of the OR-member 198 may obviously be led alternatively to inputs of a control arrangement for the perforation device 15, so that the waste of filter cigarettes Z may be kept small by appropriate correction of the perforation in the wrapper material of the filter cigarettes z.

WHAT WE CLAIM IS: 1. A method of testing rod-like smokable articles for faulty wrappers which comprise a zone of desired air permeability, during their cross-axial conveyance along a predetermined path by the formation of a pressure drop between a space enclosed by the wrapper and containing a filling, and a space outside the wrapper and formation of

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the filter cigarette Z is removed from the ejector drum 32 by means of an air stream. In the test device 56, the filter cigarettes Z are loaded from both ends with test air through the pipes 49a and 49b; because of the asymmetric sensitivity described of this test device, changes of the holes L in the cover paper B have a particularly strong effect on the signal delivered by the measuring converter 82 to the mean value former 83. The instant of time of a signal acceptance into the mean value former 83 is determined by the output signal of the AND-member 84, one input of which is connected to the clock pulse transmitter 68. If a faulty filter cigarette Z has been detected by the measuring arrangement 57 of the test device 54 which leads by one clock pulse, it is disregarded for forming the mean value in the mean value former 83 of the measuring arrangement 58, in that the AND-member 84 is blocked by means of the output signal of the second stage 69b of the shift register 69, which signal is negatived by the NOT-member 86. Since in this case the counter 87 connected to the AND-member 84 likewise does not receive an input signal, it is ensured that in the mean vaLue former 83 always a mean value is formed from a defined number of filter cigarettes Z which have been detected to be free of faults in the test device 54.The signal issued by the counter 87 and delivered at the output of the mean value former 83 after the predetermined number of filter cigarettes Z to be tested has been reached is indicated by the indicator device 91 on the one hand and is monitored in respect of predetermined limit values by the threshold value members 88 and 89 on the other hand. When these limit values are exceeded or not attained, respectively, the associated signal lam 92 or 93, respectively, is caused to light up the threshold value member 88 or the threshold value member 89. However, output signals of the threshold value members 88 and 89 may alternatively be utilised for influencing the perforation device 15 indicated at the filter assembly machine according to Figure 1, in that e.g. the number or the hole size of the holes inserted in the cover paper strip 13 is changed. In the variant according to Figure 5, parts which agree with those of Figure 4 are provided with the same reference numerals mcreased by 100 and are not discussed again. The test device 154 and the measuring arrangement 157 have remained unchanged, whereas a different measuring arrangement 194 is provided for the test device 156. The electro-pneumatic measuring converter 182 is connected to a store 196 which comprises n stages, and the stages a ... n are controllable by an associated counter 187. The counter 187 is connected to the output of the AND-member 184, and it controls the stage a at the counter state 1, the stage b at the counter state 2, and so on, of the store 196 for receiving a signal from the measuring converter 182. Every signal accepted into a stage is stored for one cycle, that is to say until after successive control of all the other store stages, the respective store stage is controlled again for receiving a fresh signal. At the output end, all stages of the store 196 are continuously connected to a mean value former 197 the output of which in turn is connected to the threshold value members 188 and 189 as well as to the indicator device 191. The threshold value members 188 and 189 are connected to the indicator lamps 192 and 193, respectively, and to inPuts of an OR-member 198 the output ot which is connected to an input of the stage 169b of the shift register 169. In contrast to the construction of Figure 4, the measuring arrangement 194 consequently does not form periodically, but continuously a mean value from a defined number of filter cigarettes Z tested in the preceding test device 154 and the measuring arrangement 157 thereof and found thereby to be in order. The monitoring of the signal continuously delivered by the mean value former 197, by means of the threshold value members 188 and 189 permits early recognition of the fact that the air permeability in the zone of desired air permeability (holes L) of the wrapper of the filter cigarettes Z strays out of a permitted tolerance range; on the one hand such straying is then indicated by the indicator lamp 192 or 193, and on the other hand a signal is then delivered to the stage 169b of the shift register 169 by way of the OR-member 198.This has the consequence that the filter cigarettes Z which have caused the mean value to increase above or decrease below the permitted tolerance threshold, are ejected from the ejector drum 32 by means of the control device 171 in the manner previously described. The outputs of the threshold value members 188 and 189 led to the inputs of the OR-member 198 may obviously be led alternatively to inputs of a control arrangement for the perforation device 15, so that the waste of filter cigarettes Z may be kept small by appropriate correction of the perforation in the wrapper material of the filter cigarettes z. WHAT WE CLAIM IS:

1. A method of testing rod-like smokable articles for faulty wrappers which comprise a zone of desired air permeability, during their cross-axial conveyance along a predetermined path by the formation of a pressure drop between a space enclosed by the wrapper and containing a filling, and a space outside the wrapper and formation of

a test signal which depends upon the air permeability of the wrapper, wherein each article per se is subjected to a first test by forming a first pressure drop and forming a first test signal, wherein an upper limit value for the air permeability of the wrapper is fixed and a tested article is regarded as being acceptable when the test signal is below the upper limit value, and wherein the articles are subjected to a second test having maximum sensitivity in the region of the zone of desired air permeability, by the formation of a second pressure drop and the formation of a second test signal, a second test signal being formed therein for a plurality of articles which corresponds to the mean air permeability of the zone of desired air permeability, wherein each article by itself is subjected to the second test and the second test signal is formed by forming the mean value of a series of successive measuring signals obtained by the second test, wherein exclusively measuring signals of articles which were judged to be in order during the first test, are utilised for forming the mean value.

2. A method according to claim 1, wherein the mean value is formed always from a similar number of measuring signals obtained by the second test.

3. A method according to claim 1 or 2, wherein the mean value is formed continuously in that the respective youngest measuring signal is substituted for the respective oldest signal utilised for forming the mean value.

4. A method according to any one of the preceding claims, wherein for the second test a lower limit value for the air permeability of the wrapper in the zone of desired air permeability is fixed and the tested articles are regarded as being in order when the second test signal is located above the lower limit value.

5. A method according to any one of the preceding claims, wherein for the second test an upper limit value for the air permeability of the wrapper in the zone of desired air permeability is fixed and the tested articles are regarded as being in order when the second test signal is below the upper limit value.

6. A method according to any one of the preceding claims, wherein a control signal is formed when the test signal is outside the fixed limit values.

7. Apparatus for testing rod-like smokable articles for faulty wrappers which comprise a zone of desired air permeability, with at least one travelling test conveyor which comprises holders for retaining the articles, and with two test devices which comprise sealing means for temporarily separatmg a space enclosed by the wrapper and containing a filling, from a space outside the wrapper of each article, connecting means which connect one of the spaces to a source of pressure, and have connecting means which connect always one of the two spaces to measuring arrangements which detect pressure differences, the first test device being constructed for forming a first pressure drop between the space within and the space without the wrapper, and the measuring arrangement thereof comprising a signal transmitter for a signal delivered when the air permeability of the wrapper lies above a preselected upper limit value, and wherein the second test device, the maximum sensitivity of which lies in the region of the zone of desired air permeability of the wrapper, is constructed for forming a second pressure drop between the space within and the space without the wrapper, and the measuring arrangement thereof comprises a mean value former, wherein the mean value former is connectable to the second test device by means of a switching arrangement connected to the signal transmitter of the first test device and so constructed that further delivery of signals from articles of which the air permeability exceeds the upper limit value to the mean value former is inter rupted.

8. Apparatus according to claim 7, wherein the mean claim former is able by means of a counter the input of which is connected to the switching arrangement.

9. Apparatus according to claim 7 or 8, wherein the measuring arrangement of the second test device comprises a signal transmitter for a signal delivered when the air permeability of the wrapper lies below a lower limit value.

10. Apparatus according to any one of claims 7 to 9, wherein the measuring arrangement of the second test device comprises a signal transmitter for a signal delivered when the air permeability of the wrapper lies above a pre-selected upper limit value.

11. Apparatus according to any one of the preceding claims 7 to 10, wherein the two test devices are disposed one behind the other at the test conveyor, and the switching arrangement is preceded by a delay member which is controllable in synchronism with the movement of the test conveyor.

12. Arrangement according to any one of the preceding claims 7 to 11, wherein the measuring arrangements are connected to a control device for removing from their feed path articles having a fault in the wrapper.

13. A method of testing rod-like articles for faulty wrappers which comprise a zone of desired air permeability, substantially as herein described with reference to the accompanying drawings.

14. Apparatus for testing rod-like smok able articles for faulty wrappers which comprise a zone of desired air permeability, substantially as herein described with reference to and as illustrated in the accompanying drawings.