Patent Publication Number: US-7896010-B2

Title: Filter cigarette inspection apparatus and inspection method

Description:
TECHNICAL FIELD 
     The present invention relates to a filter cigarette inspection apparatus and a filter cigarette inspection method for measurement of filter ventilation of filter cigarettes as rod-like articles. 
     BACKGROUND ART 
     The filter of a filter cigarette has a rod-like filter material and a wrapping material that envelops the filter material. One of the wrapping materials is a filter having a plurality of perforations. When the filter cigarette with a filter having perforations is smoked, air flows into the filter through the perforations, which dilutes smoke from the cigarette. As a result, nicotine and tar contained in the smoke are reduced, so that the smoker can enjoy a mild flavor. 
     The ratio of an air amount flowing in from the perforations to an amount of the smoke drawn by the smoker is called filter ventilation (hereinafter also simply referred to as V F ). As for the above-mentioned filter cigarettes, if V F  is not fixed constant for each cigarette, the cigarettes do not have a uniform flavor and vary in their qualities. 
     The International Organization for Standardization defines a method of measuring V F , which is carried out by a measurement standard. This measurement standard is used in manufacturing plants of filter cigarettes. More specifically, filter cigarettes are pulled out of the tobacco-manufacturing machine at a constant rate, and the V F  of the pulled-out filter cigarettes is measured by the measurement standard. In short, only some of the manufactured filter cigarettes are subjected to the extraction and the inspection of V F . 
     The method of measuring V F , which is compliant with the ISO, however, is complicated because it is troublesome to install the measurement standard in the tobacco-manufacturing machine. Even if the measurement standard can be installed in the tobacco-manufacturing machine, it takes a lot of time to inspect the V F  of each filter cigarette. Therefore, it is difficult to conduct the inspection of all the manufactured filter cigarettes by this measuring method. 
     The measurement standard is also used in the inspection of undesired holes made in wrapping paper. As to a filter cigarette having great V F , however, an air amount flowing in through perforations is relatively greater than the air amount flowing in through the holes made in the wrapping paper. This makes it difficult to detect the holes made in the wrapping paper without fail by using the measurement standard. 
     The tobacco-manufacturing machine disclosed in Japanese Patent No. 3190132 has an inspection apparatus for inspecting not V F  but total ventilation (hereinafter also simply referred to as V T ) as a control index for a nicotine and tar amount. The V T  is the ratio of an air amount flowing in from the perforations of wrapping paper and filter of the cigarette to an amount of the smoke drawn by the smoker. 
     However, this well-known inspection apparatus is not capable of directly inspecting the V F , and not capable of credibly control the nicotine and tar amount of filter cigarettes. 
     DISCLOSURE OF THE INVENTION 
     An object of the present invention is to provide a new inspection apparatus and a new inspection method capable of measuring filter ventilation of filter cigarettes in a short time. 
     Another object of the present invention is to provide a new inspection apparatus and a new inspection method capable of reliably detecting the formation of undesired holes in wrapping paper. 
     To achieve the objects, according to the present invention, an inspection apparatus for a filter cigarette having a cigarette, a filter that is connected to the cigarette and has a mouthpiece end, and a ventilation area in an outer circumferential surface of the filter for introducing outside air includes a transport path that transports the filter cigarette in a direction orthogonal to an axial direction of the filter cigarette and has an inspection position interposed therein; a filter socket assembly that is disposed on one side of the transport path and is allowed to be connected to the filter cigarette when the filter cigarette passes through the inspection position, the filter socket assembly including a socket that is capable of receiving the filter and defines in the inside thereof a first airtight chamber for enclosing the mouthpiece end of the filter and a second airtight chamber for enclosing the outer circumferential surface of the filter including the ventilation area, a lateral input path for supplying the second airtight chamber of the socket with a compressed fluid of a given pressure, and an output path that outputs a pressure in the first airtight chamber; and a pressure sensor for detecting the pressure outputted from the output path. 
     According to the above-described inspection apparatus, it is possible to inspect filter cigarettes in a transporting process thereof and to find V F  per se, namely the ratio of an air amount flowing in from an outer circumferential surface of the filter to a drawing amount of the smoker. It is also possible to find the V F  on the basis of the given pressure at which the second airtight chamber is supplied with the compressed fluid and the pressure detected by the pressure sensor, which enables a quick inspection. Consequently, the inspection apparatus makes it possible to carry out effective on-machine control on the V F  of each filter cigarette, and to reliably control a nicotine and tar amount in the filter cigarette. 
     According to a specific aspect, the inspection apparatus further has reciprocating means that reciprocates the filter socket assembly toward the filter cigarette in order to receive the filter in the socket removably. In the above-mentioned structure, the cigarette socket assembly includes the pair of seal rings disposed in the socket to be separated from each other in the axial direction and to be reducible in diameters. The seal rings come into tight contact with the filter when reduced in diameters, thereby partitioning the first and second airtight chambers. 
     In the above-described structure, it is preferable that the seal rings be formed of elastically deformable rubber rings, and that the cigarette socket assembly include compression means that is actuated by operating the reciprocating means as a drive source and compresses each of the rubber rings to reduce the diameters thereof. 
     With this structure, the first and second airtight chambers can be formed by using one reciprocating means. Furthermore, since the elastically deformable rubber rings are brought into tight contact with the filter part, the compressed fluid and air are prevented from leaking from between the filter part and the seal rings partitioning the first and second airtight chambers. Consequently, a first pressure sensor is capable of detecting the pressure in the first airtight chamber with accuracy when the second airtight chamber is supplied with the compressed fluid of the given pressure. In other words, it is possible to upgrade reliability of control on the V F  of filter cigarettes, that is, nicotine and tar, with the simple structure. 
     As a preferred aspect, the inspection apparatus further has a cigarette socket assembly that is disposed on the other side of the transport path and is allowed to be connected to the filter cigarette when the filter cigarette passes through the inspection position, the cigarette socket assembly including a cigarette socket that is capable of receiving a tip end of the cigarette and defines a third airtight chamber for enclosing the tip end of the cigarette in the inside thereof, and a forward input path for supplying the third airtight chamber of the cigarette socket with a compressed fluid of a given pressure when the second airtight chamber is in a fluidically closed state, the apparatus in which the lateral input path of the filter cigarette assembly is blocked off while the third airtight chamber is supplied with the compressed fluid. 
     With this structure, it is possible to detect not only the V F  of filter cigarettes but also the formation of undesired holes in wrapping paper in the transporting process of the cigarettes on the basis of the pressure detected by the pressure sensor. In this case, since the second airtight chamber is closed, the formation of holes can be detected without fail regardless of the level of V F  of the filter cigarettes. As a result, defective filter cigarettes can be surely removed. 
     As a specific aspect, the inspection apparatus further has a rotatable drum provided with each of the socket assemblies and including an outer circumferential surface defining the transport path. 
     In order to accomplish the above-mentioned objects, an inspection method for a filter cigarette including a cigarette, a filter that is connected to the cigarette and has a mouthpiece end, and a ventilation area in an outer circumferential surface of the filter for introducing outside air includes the steps of forming a first airtight chamber for enclosing the mouthpiece end of the filter, forming a second airtight chamber for enclosing the outer circumferential surface of the filter including the ventilation area, and measuring a pressure in the first airtight chamber when the second airtight chamber is supplied with a compressed fluid of a given pressure. 
     According to the inspection method, it is possible to directly find the V F  per se, namely the ratio of an air amount flowing in from the outer circumferential surface of the filter to a drawing amount of the smoker. Since the V F  is found on the basis of the given pressure at which the compressed fluid is supplied into the second airtight chamber and the pressure detected by the first pressure sensor, the inspection can be quickly carried out. 
     To be specific, the inspection method is carried out in a process where the filter cigarette is transported in a direction orthogonal to an axial direction thereof. 
     According to the inspection method, it is possible to quickly inspect each of the filter cigarettes, so that the filter cigarettes can be inspected in the transporting process. Therefore, the inspection method makes it possible to carry out effective on-machine control on the V F  of all the filter cigarettes, realizing reliable control on the nicotine and tar amount in the filter cigarettes. 
     Furthermore, to achieve the above-mentioned object, an inspection method for a filter cigarette having a cigarette, a filter that is connected to the cigarette and has a mouthpiece end, and a ventilation area in an outer circumferential surface of the filter for introducing outside air includes the steps of forming a first airtight chamber for enclosing the mouthpiece end of the filter, forming a second airtight chamber for enclosing the outer circumferential surface of the filter including the ventilation area, forming a third airtight chamber for enclosing a tip end of the cigarette, and measuring a pressure in the first airtight chamber when the third airtight chamber is supplied with a compressed fluid of a given pressure. 
     To be concrete, the inspection method is carried out in a process where the filter cigarette is transported in a direction orthogonal to an axial direction thereof. 
     The inspection method makes it possible to detect the formation of undesired holes in the wrapping paper of the filter cigarettes on the basis of the pressure detected by the pressure sensor. Moreover, since the second airtight chamber is closed, it is also possible to detect the formation of the holes without fail regardless of the level of V F  of the filter cigarettes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic depiction showing a filter attachment of one embodiment; 
         FIG. 2  is a side view of a dilution inspection apparatus installed in the filter attachment of  FIG. 1 ; 
         FIG. 3  is a sectional view, taken along line III-III of the dilution inspection apparatus of  FIG. 2 ; 
         FIG. 4  is a sectional view of an assembly included in the dilution inspection apparatus of  FIG. 3 ; 
         FIG. 5  is a part of a cam diagram showing in the dilution inspection apparatus of  FIG. 2 ; 
         FIG. 6  is an explanatory view of operation of the assembly along with rotation of a drum shell in the dilution inspection apparatus of  FIG. 2 ; 
         FIG. 7  is a schematic depiction of filter ventilation measurement in the dilution inspection apparatus of  FIG. 2 ; 
         FIG. 8  is a diagram showing an analogy model of the filter ventilation measurement of  FIG. 7 ; 
         FIG. 9  is a schematic depiction of total ventilation measurement in a conventional dilution inspection apparatus; 
         FIG. 10  is a diagram showing an analogy model of the total ventilation measurement of  FIG. 9 ; 
         FIG. 11  is a schematic depiction of filter ventilation measurement using a measurement standard; 
         FIG. 12  is a diagram showing an analogy model of the filter ventilation measurement of  FIG. 11 ; 
         FIG. 13  is a graph showing response speed in the filter ventilation measurement of  FIGS. 7 and 11 ; 
         FIG. 14  is a schematic depiction of an inspection of holes in wrapping paper, which is carried out by the dilution inspection apparatus of  FIG. 2 ; and 
         FIG. 15  is a histogram of detection pressure in case that the inspection of holes in wrapping paper of  FIG. 14  and a conventional inspection of holes are applied to non-defective and defective articles. 
     
    
    
     BEST MODE OF CARRYING OUT THE INVENTION 
       FIG. 1  diagrammatically shows a filter attachment  10  that attaches a filter to a cigarette. The attachment  10  has a drum line  12  that continues from an upstream side toward a downstream side. The drum line  12  receives a cigarette  2  and a filter  4  on the upstream side (right side in the figure), and attaches the filter  4  to the cigarette  2 . The drum line  12  then performs given inspection with respect to an obtained filter cigarette FT, and allows the filter cigarette FT to be removed from the downstream side (left side in the figure). More specifically, the drum line  12  includes a dilution inspection apparatus  18  interposed between an end checker drum  14  and a carrier drum  16 . 
       FIG. 2  shows both ends of the dilution inspection apparatus  18 . The filter cigarette FT to be inspected is transferred to the dilution inspection apparatus  18  at a start point of a rotation angle region θ 1  from the end checker drum  14  located immediately upstream thereof. Thereafter, the cigarette FT is transported on an outer circumference of the dilution inspection apparatus  18  along a rotating direction R through the rotation angle region θ 1 , a rotation angle region θ 2  and a rotation angle region θ 3 , and is transferred to the carrier drum  16  located immediately downstream at an end point of the rotation angle region θ 3 . 
     In the dilution inspection apparatus  18 , while the filter cigarette is transported through a rotation angle region θ 4  located in the rotation angel region θ 1 , filter ventilation V F  Of the cigarette FT and undesired holes produced in wrapping paper of the cigarette  2  of the cigarette FT are inspected in order. Filter cigarettes FT in which defects are found in a result of the inspection are eliminated from the dilution inspection apparatus  18  in the rotation angle region θ 2 . 
     As illustrated in  FIG. 3 , the filter attachment  10  is provided with a base frame  20  and a sub-frame  22  disposed opposite each other. The inspection apparatus  18  is disposed between the base frame  20  and the sub-frame  22 . 
     To be more specific, the dilution inspection apparatus  18  has a drive shaft  28 , which horizontally extends from the base frame  20  toward the sub-frame  22 . One end portion and an intermediate portion of the drive shaft  28  are rotatably supported by an inner sleeve  34  through a pair of bearings  24 . The inner sleeve  34  horizontally protrudes from a front side of the base frame  20  in a state where one end thereof is fitted into the base frame  20 , and at the same time is fixed to the base frame  20  through a flange  48  located on the one end side thereof. 
     One end of the drive shaft  28  protrudes from the inner sleeve  34  to a backside of the base frame  20 , and a drive gear  30  is fitted to the protruding end through a key  32 . The drive gear  30  is connected to a drive source through a gear line, not shown. The drive shaft  28  can be rotation-driven in the rotating direction R (see  FIG. 2 ) by receiving a driving force from the drive source. A bush  38  is fitted on the drive shaft  28  so as to be located between the bearings  24 . 
     The other end of the drive shaft  28  also protrudes from the inner sleeve  34 . The other end portion is rotatably supported by the sub-frame  22 . More specifically, a cylindrical bearing holder  36  is fitted to the sub-frame  22 , and the other end portion of the drive shaft  28  is supported by the bearing holder  36  through a pair of bearings  44 . A bush  40  is fitted with the other end portion of the drive shaft  28  to be located between the bearings  44 . 
     A control sleeve  56  is fastened onto an outer circumferential surface of the inner sleeve  34  with a screw. One end of the control sleeve  56  is airtightly fitted to a suction duct  52 , and the other end thereof protrudes from the inner sleeve  34 . 
     The suction duct  52  is formed with a cover plate. The cover plate is fixed to a front side of the base frame  20  and accommodates the flange  48  of the inner sleeve  34 . The suction duct  52  forms a suction path  53  in consort with the base frame  20 . The suction path  53  is connected to a suction device, namely a blower. 
     There is formed a circumferential groove in the outer circumferential surface of the inner sleeve  34 . The circumferential groove forms a suction chamber  58  in between the groove and an inner face of the control sleeve  56 . The suction chamber  58  constantly communicates with the suction path  53  through one end side thereof. In other words, in the outer circumferential surface of the inner sleeve  34 , there are formed a plurality of communication grooves that cause the suction chamber  58  and the suction path  53  to communicate with each other. The communication grooves are arranged at intervals in a circumferential direction of the inner sleeve  34 . As a consequence, the suction chamber  58  is constantly supplied with given suction pressure. 
     A suction groove  60  is formed in an outer circumferential surface of the control sleeve  56 . The suction groove  60  communicate with the suction chamber  58  through a plurality of radial holes  62 . To be concrete, the suction groove  60  is positioned on the other end side of the control sleeve  56 , and has given width in the axial direction of the control sleeve  56 . The suction groove  60  extends in a circumferential direction of the control sleeve  56  in the rotation angle region θ 1  and the rotation angle region θ 3 , excluding the rotation angle region θ 2 . One end of each of the radial holes  62  opens in a bottom face of the suction groove  60 . The radial holes  62  are arranged at given intervals in the circumferential direction of the control sleeve  56 . The other end of each of the radial holes  62  opens in the inner circumferential surface of the control sleeve  56 . 
     A drum shell  64  is rotatably fixed to the other end side of the control sleeve  56  in a state where the drum shell partially encloses the outer circumferential surface of the control sleeve  56 . The drum shell  64  is integrally coupled to the drive shaft  28 . More specifically, an outer flange  66  and an inner flange  68  extend from the drive shaft  28  and the drum shell  64 , respectively. The flanges  66  and  68  are joined together with connecting screws. Therefore, the drum shell  64  is rotation-driven integrally with the drive shaft  28 . 
     The drum shell  64  airtightly covers the suction groove  60  of the control sleeve  56 . A great number of transport grooves  70  are formed in an outer circumferential surface of the drum shell  64  at regular intervals in a circumferential direction thereof. Each of the transport grooves  70  extends in the axial direction of the drum shell  64 , and is formed to be shorter than the cigarette  2  of the filter cigarette FT and to have a semicircular cross section. One end of each of suction holes  72  opens at a bottom of each of the transport grooves  70 , and these openings are aligned along the transport grooves  70 . The suction holes  72  extend in a radial inward direction of the drum shell  64 , and the other ends open in an inner circumferential surface of the drum shell  64 . 
     Furthermore, axial holes  74  are formed in the drum shell  64  correspondingly to the respective transport grooves  70 . The axial holes  74  each extend across the suction holes  72  of the respective transport grooves  70  and open in an end face of the drum shell  64  on the inner flange  68  side. 
     There is disposed a control ring  76  outside the inner flange  68  of the drum shell  64 , and the end face of the drum shell  64  is in sliding contact with the control ring  76 . Accordingly, the opening ends of the axial holes  74  are covered with the control ring  76 . The control ring  76  is supported by a fixed cylinder  78  using a pin and a coil spring (both not shown) such that the control ring  76  cannot rotate. The fixed cylinder  78  is fitted to an outer circumferential surface of the bearing holder  36 . The coil spring urges the control ring  76  to press against the end face of the drum shell  64 . The end face of the drum shell  64  and the control ring  76  are in airtight contact with each other. 
     Formed in an inner end face of the control ring  76  is a control groove  80  for elimination. The control groove  80  stretches over the rotation angle region θ 2  (see  FIG. 2 ) so as to have an arc-like shape. A communication hole  82  extends from a bottom of the control groove  80 , and opens in an outer end face of the control ring  76 . Connected to an opening end of the communication hole  82  is one end of an elimination tube  84 . The elimination tube  84  stretches through the fixed cylinder  78 . Therefore, along with rotation of the drum shell  64 , the axial holes  74  are sequentially connected to the elimination tube  84  through the control groove  80 . Although not shown, the elimination tube  84  is connected to a pneumatic source including a compressor and the like through an electromagnetic valve, so that it is possible to supply given elimination pressure through the control groove  80  to the axial holes  74  by switching operation of the electromagnetic valve. 
     Although not shown, in the inner end face of the control ring  76 , there is formed an atmosphere open groove immediately downstream of the rotation angle region θ 3  in the rotating direction R of the drum shell  64 . The atmosphere open groove constantly opens to atmosphere. 
     When the transport groove  70  enters the rotation angle region θ 1 , that is, the suction groove  60 , along with the rotation of the drum shell  64 , the suction pressure is supplied from the suction chamber  58  through the radial holes  62  and the suction holes  72  to the transport groove  70 . As a result, the transport groove  70  is capable of sucking and receiving the filter cigarette FT from the end checker drum  14  of the previous step. Thereafter, the filter cigarette FT is transported while being sucked and held by the transport groove  70  during the period of passing through the rotation angle region θ 1  and the rotation angle region θ 3 . During the period in which the filter cigarette FT passes through the rotation angle θ 2 , the supply of the suction pressure to the transport groove  70  is stopped. Unless the elimination pressure is supplied, however, the filter cigarette FT continues to be sucked and held by the transport groove  70  due to remaining pressure, and is transported passing through the rotation angle region θ 2 . 
     When the transport groove  70  further rotates beyond the rotation angle region θ 3  and is connected to the axial holes  74  of the transport groove  70  to the atmosphere open groove of the control ring  76 , the suction of the filter cigarette FT is cancelled at this point. The released filter cigarette FT is transferred to the carrier drum  16  of the subsequent step, which is located immediately downstream of the inspection apparatus  18 , that is, the drum shell  64 , and continues to be transported. 
     The drum shell  64  is attached with a plurality of pairs of assemblies  86 . Each of the transport grooves  70  is interposed between one pair of assemblies  86  in the axial direction thereof. The assemblies  86  rotate with the drum shell  64 , that is to say, the respective transport grooves  70 . 
     One pair of assemblies  86  can move toward the filter cigarette FT placed on the transport groove  70  and away therefrom along with the rotation of the drum shell  64 . To be concrete, the pair of assemblies  86  is reciprocating-driven between an actuated position where they advance to the filter cigarette FT side and a rest position where they retreat from the actuated position. 
     More specifically, when the pair of assemblies  86  is located at the start end of the rotation angle region θ 1  shown in  FIG. 2 , these assemblies  86  are placed in the rest position. 
     As to the reciprocating drive of the assemblies  86 , the rotation angle region θ 1  is further divided into a rotation angle region θ 4  located at the center in the rotating direction R, and rotation angle regions θ 5  and θ 6  located upstream and downstream of the rotation angle region θ 4 , respectively, to be adjacent to each other. In other words, the pair of assemblies  86  is gradually advanced from the rest position toward the actuated position while passing through the rotation angle region θ 5 , and is held at the actuated position while passing through the rotation angle region θ 4 . Subsequently, the pair of assemblies  86  is gradually retreated from the actuated position toward the rest position while passing through the rotation angle region θ 6 , and is held at the rest position until reaching a start end of the rotation angle region θ 5  again. 
     In  FIG. 3 , the assemblies  86  are shown simply by chain double-dashed lines. Facing into  FIG. 3 , an upper side pair of assemblies  86  is located in the actuated position, and a lower side pair of assemblies  86  in the rest position. 
     Hereinafter, between the assemblies  86  in pair, the assembly  86  positioned on the right side of the transport groove  70  and located in the rest position in  FIG. 3  will be described with reference to  FIG. 4 . Although in  FIG. 4 , the pair of assemblies  86  located in the rest position is placed on an upper side of the drum shell  64  differently from the case shown in  FIG. 3 , this is for the convenience of drawing the figure. 
     As is apparent from  FIG. 4 , the drum shell  64  has small-diameter portions on both ends of the transport groove  70 . A support ring  88  is concentrically fitted on the right small-diameter portion. The support ring  88  is formed to have a large-diameter step on the transport groove  70  side, and has an end wall  90  in contact with the end face of the drum shell  64 . 
     Fixed to the end wall  90  is one end of a guide rod  94 . The guide rod  94  extends in the axial direction of the drum shell  64 . The other end of the guide rod  94  is fixed to a rotation ring  96 . The rotation ring  96  is disposed concentrically with the support ring  88  on the other end side of the drum shell  64 . 
     Two guide pipes  100  and  102  are fixed to the rotation ring  96 . The guide pipes  100  and  102  protrude from the front side of the rotation ring  96  toward the support ring  88  and stretch parallel to the guide rod  94 . The guide pipes  100  and  102  are arranged in a radial outward direction of the support ring  88  with a space therebetween in the order named from the guide rod  94 . In other words, the guide rod  94  and the guide pipe  102  are positioned on their respective sides of the guide pipe  100  in the radial direction. Base ends of the guide pipes  100  and  102  are embedded in the rotation ring, and open in a backside of the rotation ring  96 . 
     The guide pipe  100  is positioned coaxially with the transport groove  70 , that is to say, the filter cigarette FT held by the transport groove  70 , and has a large diameter end  104  at a tip end thereof. 
     A movable sleeve  114  is slidably fitted on the guide pipe  100  from the outside. A slider  108  is attached to an end portion of the movable sleeve  114 , which is located on the rotation ring  96  side. The guide rod  94  pierces the slider  108  with a slide bearing  112  interposed therebetween. The slider  108  is slidably supported by the guide rod  94 . The slide bearing  112  is held in the slider  108  with a snap ring  110  interposed therebetween. A snap ring  122  of the movable sleeve  114  couples the movable sleeve  114  with the slider  108  integrally. Accordingly, the slider  108  is slidably guided by the guide rod  94 , thereby being able to move toward and away from the drum shell  64  in the axial direction thereof together with the movable sleeve  114 . The movable sleeve  114  coaxially contacts/separates with respect to the transport groove  70 , or the filter cigarette FT to be inspected, which is held by the transport groove  70 . 
     An internal diameter of the movable sleeve  114  is enlarged in an end portion  118  on the support ring  88  side. There is secured a tubular chamber  120  between the movable sleeve  114  and the guide pipe  100 . The tubular chamber  120  opens toward the large diameter end  104  side of the guide pipe  100 . An external diameter of the tubular chamber  120  is larger than an external diameter of the large diameter end  104 . 
     When the assembly  86  is placed in the actuated position, the movable sleeve  114  moves closest to the cigarette FT, and the large diameter end  104  of the guide pipe  100  enters the tubular chamber  120  of the movable sleeve  114 . At this moment, an O-ring  106  provided to the large diameter end  104  is in tight contact with an inner end face of the tubular chamber  120 , and the tubular chamber  120  is airtightly sealed by the O-ring  106 . 
     The end portion  118  of the movable sleeve  114  is slidably inserted in a ring-attaching hole  126  of a ring holder  124 . The ring-attaching hole  126  pierces the ring holder  124  and opens in both end faces thereof. A portion of the guide pipe  100  located on the large diameter end  104  side is concentrically disposed in the ring-attaching hole  126 . 
     An end plate  128  is fixed to one end face of the ring holder  124 , which is located on the drum shell  64  side. Formed in the end plate  128  is a slot  130  located concentrically with the ring-attaching hole  126 . The slot  130  has a smaller diameter than the ring-attaching hole  126 . The ring-attaching hole  126  and the slot  130  have respective internal diameters larger than the external diameter of the filter cigarette FT. For this reason, when the assembly  86  moves from the rest position to the actuated position, the filter-side end portion of the filter cigarette FT is insertable into the ring-attaching hole  126  through the slot  130 . 
     In the ring holder  124 , a guide hole  136  is formed parallel with the ring-attaching hole  126 . The guide hole  136  has a closed end on one end face side of the ring holder  124 , and opens in the other end face of the ring holder  124 , that is, an end face on the rotation ring  96  side. A guide pipe  102  is airtightly and slidably inserted into the guide hole  136  from the opening thereof through an O-ring  138 . 
     A radial hole extends from the closed end of the guide hole  136  toward the ring-attaching hole  126 . The radial hole opens in an inner circumferential surface of the ring-attaching hole  126 , and this opening end is located in an intermediate position between the movable sleeve  114  and the end plate  128 . 
     Furthermore, an axial groove  140  is formed in the inner circumferential surface of the ring-attaching hole  126 . The axial groove  140  opens in the other end face of the ring holder  124 . The axial groove  140  is attached with a stopper  142 , and a pin  144  projects from an outer circumferential surface of the movable sleeve  114  into the axial groove  140 . When the assembly  86  is in the rest position, the pin  144  is in contact with the stopper  142  in the axial groove  140 . Additionally, the pin  144  works so as to push back the ring holder  124  through the stopper  142  when the assembly  86  moves from the actuated position to the rest position as described below. 
     Disposed in the ring-attaching hole  126  is an inner cylinder  132 . The inner cylinder  132  is positioned in between the movable sleeve  114  and the end plate  128 . The inner cylinder  132  is brought into slide contact with the inner circumferential surface of the ring-attaching hole  126  and is movable in the axial direction of the ring-attaching hole  126 . The inner cylinder  132  has an internal diameter that is larger than the external diameter of the filter cigarette FT, so that the end portion of the filter cigarette FT can be inserted into the inner cylinder  132  when the assembly  86  is moved to the actuated position. 
     In the inner cylinder  132 , circumferential grooves are formed in inner and outer circumferential surfaces thereof, and there are also arranged in a circumferential direction thereof a plurality of small holes for causing the circumferential grooves to communicate with each other. The outer circumferential groove communicates with the guide hole  136  through the radial hole. Therefore, the guide pipe  102  communicates with the ring-attaching hole  126  through the outer and inner circumferential grooves and the small holes of the inner cylinder  132 . 
     Rubber rings  134  and  135  made of silicone rubber are accommodated in the ring-attaching hole  126  so as to be located on both ends of the inner cylinder  132 . The rubber ring  134  is held between the inner cylinder  132  and the end plate  128 , and the rubber ring  135  between the inner cylinder  132  and the movable sleeve  114 . Accordingly, the rubber rings  134  and  135  are separated away from each other in the axial direction of the ring-attaching hole  126 . Both the rubber rings  134  and  135  are elastically deformable, and they are in a free state when the assembly  86  is in the rest position. In the free state, internal diameters of the rubber rings  134  and  135  are larger than the external diameter of the filter cigarette FT, making it possible to insert the cigarette FT into the rubber rings  134  and  135  without contact. 
     As shown by a chain double-dashed line in  FIG. 4 , when the ring holder  124  is placed in the actuated position, the rubber rings  134  and  135  are compressed between the end plate  128  and the inner cylinder  132 , and between the inner cylinder  132  and the movable sleeve  114 , respectively, in the axial direction of the ring-attaching hole  126  as described below. In this case, since outer circumferences of the rubber rings  134  and  135  are restrained by the ring-attaching hole  126 , internal circumferences of the compressed rubber rings  134  and  135  stretch in a radial inward direction to reduce the diameters of the rings. At this moment, if the filter of the filter cigarette FT has passed through the rubber rings  134  and  135  and has been inserted in the ring-attaching hole  126 , inner circumferential surfaces of the rubber rings  134  and  135  that are reduced in diameters come into tight contact to the outer circumferential surface of the filter of the filter cigarette FT with no space. At this point, a perforation line  6  of the filter cigarette FT is positioned between the rubber rings  134  and  135 . 
     In such a state, the inside of the ring-attaching hole  126  is airtightly sectioned into a surrounding chamber that encircles the outer circumferential surface of the filter in between the rubber rings  134  and  135  in the compressed state, and an end chamber located between the rubber ring  135  and the bottom of the tubular chamber  120 . The perforation line  6  of the filter cigarette FT is positioned in the surrounding chamber, and an end portion of the filter  4  is located in the end chamber ( FIG. 6  clearly shows the surrounding and end chambers). As is apparent from the foregoing, the surrounding chamber communicates with the guide pipe  102 , and the end chamber with the guide pipe  100 . 
     The inner circumferential surfaces of the elastically deformable rubber rings  134  and  135  stretch to be fitted to concaves and convexes of the outer circumferential surface of the filter. Therefore, a satisfactorily sealed state is created between the rubber rings  134  and  135  and the filter. Moreover, it is unlikely that the outer circumferential surface of the filter  4  is overly constricted by the rubber rings  134  and  135  to crinkle the outer circumferential surface of the filter  4 , or tip paper. 
     A stationary ring  146  is in tight contact to a back face of the rotation ring  96 . The stationary ring  146  is disposed coaxially with the rotation ring  96 . As illustrated in  FIG. 3 , the stationary ring  146  is supported by a ring-shaped support plate  148 . The support plate  148  has an inner circumferential portion that is bent and attached to the fixed cylinder  78  to be fastened to the fixed cylinder  78  with a bolt. Although not shown, a spring is interposed between the support plate  148  and the stationary ring  146 . The spring presses the stationary ring  146  toward the rotation ring  96 . 
     The stationary ring  146  is formed of an outer ring  150  and an inner ring  152  that are superposed upon each other. Opening ends of the guide pipes  100  and  102 , which open in the back face of the rotation ring  96 , are airtightly closed by the inner ring  152 . 
     Formed in the inner ring  152  are slots  154 ,  155  and  156  serving as after-mentioned input/output portions of measurement pressure and detection pressure. Among these slots, the slots  154  and  156  extend in a prescribed rotation angle region VF in a circumferential direction of the inner ring  152  in a state where they are detached away from each other in a radial direction of the inner ring  152 . Referring to  FIG. 2 , the rotation angle region VF is defined within the rotation angle region θ 4 . 
     The slot  154  is positioned to be able to fit to the opening end of the guide pipe  100  and has width that is slightly larger than the internal diameter of the guide pipe  100 . The slot  156  is positioned to be able to fit to the opening end of the guide pipe  102  and has width that is slightly larger than the internal diameter of the guide pipe  102 . 
     Although as illustrated in  FIG. 2 , the last slot  155  is formed on the circumference where the slot  154  is positioned, the slots  154  and  155  are separated away from each other in the circumferential direction of the inner ring  152 . The slot  155  extends over a rotation angle region VP, which is defined within the rotation angle region θ 4  to be located downstream from the slot  154 . 
     A plurality of connection holes  158  are formed in the outer ring  150  correspondingly to the slots  154 ,  155  and  156 . The connection holes  158  pierce through the outer ring  150  to communicate with the respective slots  154 ,  155  and  156 . Air tubes  162  are connected to the respective connection holes  158  through respective nipples  160 . 
     The air tube  162  that communicates with the slot  156  is connected to a pressure sensor and a pneumatic source. Therefore, when the guide pipe  102  is connected to the slot  156 , the pneumatic source can supply the measurement pressure to the surrounding chamber through the air tube  162 , the guide pipe  102 , etc., and the pressure sensor monitors the measurement pressure. 
     Pressure sensors are connected to the respective air tubes  162  connected to the slots  154  and  155 . The pressure sensors measure pressure of the end chamber. 
     As illustrated in  FIG. 4 , a roller shaft  164  projects from the slider  108  toward the fixed cylinder  78 . The roller shaft  164  is fastened to the slider  108  with a nut  166 . A roller  168  serving as a cam follower is rotatably supported by the roller shaft  164 . The roller  168  is accommodated in a cam groove  170  of the fixed cylinder  78 . The cam groove  170  is formed in an outer circumferential surface of the fixed cylinder  78  over the entire circumference thereof. Both sidewalls  172  and  172  of the cam groove  170  guide a rolling motion of the roller  168 . 
     In other words, when the assembly  86  rotates outside the fixed cylinder  78  along with the rotation of the drum shell  64 , the roller  168  moves in the axial direction of the fixed cylinder  78 , or the guide rod  94 , along a cam profile of the cam groove  170 . As a result, the slider  108  makes a reciprocating motion while being guided by the guide rod  94 . 
     Once the slider  108  is moved toward the drum shell  64 , the movable sleeve  114  also moves on the guide pipe  100  toward the drum shell  64 . The movable sleeve  114  then presses the end plate  128  of the ring holder  124  through the rubber ring  135 , the inner cylinder  132  and the rubber ring  134 . Consequently, the assembly  86 , or the ring holder  124 , advances to the actuated position in which the end plate  128  comes into contact with the end wall  90  of the support ring  88 . 
     Thereafter, in the state where the ring holder  124  is in the actuated position, once the slider  108  is moved toward the rotation ring  96  together with the movable sleeve  114 , the pin  144  of the movable sleeve  114  pushes back the ring holder  124  through the stopper  142 . The ring holder  124  is thereby returned to the rest position. 
     Even if the ring holder  124  makes the reciprocating motion, the ring holder  124  does not come off from the guide pipe  102 . Connection between the guide pipe  102  and the guide hole  136  of the ring holder  124  is constantly retained. 
       FIG. 5  shows a cam diagram of the cam groove  170 . A horizontal axis indicates a rotation angle of the assembly  86 , and a vertical axis represents a cam lift (namely a reciprocating stroke of the movable sleeve  114 ). As is clear from  FIG. 5 , the cam lift is gradually increased from the point when the assembly  86  passes through the start end of the rotation angle region θ 5 . The ring holder  124  accordingly moves toward the actuated position and reaches the actuated position within the rotation angle region θ 5 . 
     In the process where the assembly  86  further rotates and enters the rotation angle region θ 4 , the movable sleeve  114  further moves forward. At this point, however, the ring holder  124  is in the actuated position, and the forward movement of the ring holder  124  is restricted by the end wall  90  of the support ring  88 . Therefore, the forward movement of the movable sleeve  114  compresses the rubber ring  135  in between the movable sleeve  114  and the inner cylinder  132 , and also compresses the rubber ring  134  in between the end plate  128  and the inner cylinder  132 . As a consequence, the internal diameters of the rubber rings  134  and  135  are reduced at this point. 
     At the same time, the large diameter end  104  of the guide pipe  100  enters the tubular chamber  120  of the movable sleeve  114  together with the O-ring  106 , and the pin  144  of the movable sleeve  114  and the stopper  142  of the ring holder  124  are in the state where they are separated away from each other. 
     When the assembly  86  is in the process of passing through the rotation angle region θ 4 , the cam lift is maintained at a maximum value, and the rubber rings  134  and  135  are kept in the state where they are reduced in their diameters. 
     Subsequently, the assembly  86  moves from the rotation angle region θ 4  to enter the rotation angle region θ 6 . In the process where the assembly  86  passes through the rotation angle region θ 6 , the cam lift is gradually reduced. Accordingly, the compression of the rubber rings  134  and  135  by using the movable sleeve  114  is cancelled, which enlarges the internal diameters of the rubber rings  134  and  135  to the original state. Once the pin  144  of the movable sleeve  114  comes into contact with the stopper  142  of the ring holder  124 , the ring holder  124  moves from the actuated position toward the rest position together with the movable sleeve  114 . 
     After the assembly  86  passes through the rotation angle region θ 6 , the ring holder  124  is maintained in the rest position until the assembly  86  enters the start end of the rotation angle region θ 5  again. 
     The assembly  86  positioned on the left side of the drum shell  64 , facing into  FIG. 4  as viewed, has a similar structure to the assembly  86  on the right side. Therefore, in  FIGS. 2 ,  3  and  4 , members and portions having the same functions are provided with the same reference characters, and explanations thereof will be omitted. Only differences will be described below. 
     First of all, the cam groove  170  in combination with the left assembly  86  is, as is clear from  FIG. 3 , formed in an outer circumferential surface of a fixed cylinder  174 . The fixed cylinder  174  is fixed onto the outer circumferential surface of the control sleeve  56 . The support plate  148  supporting the stationary ring  146  is fixed to a base frame  20 . 
     As illustrated in  FIG. 4 , the left assembly  86  is not provided with the guide hole  136 , the guide pipe  102 , the slot  156  and the inner cylinder  132 . 
     The left assembly  86 , or the ring holder  124 , is provided with the rubber ring  134  only. The rubber ring  134  is disposed between the movable sleeve  114  and the end plate  128 . When the assembly  86  is placed in the actuated position, the rubber ring  134  comes into airtight contact to the end portion of the cigarette  2  of the filter cigarette FT from the outside. In this case, the reciprocating stroke of the ring holder  124 , provided by the cam groove  170 , is set to be virtually half, compared to the ring holder  124  of the right assembly  86 . 
     Accordingly, when the left assembly  86  is in the actuated position, there is formed an end chamber only. The end portion of the cigarette  2  of the filter cigarette FT to be inspected is placed in the end chamber. 
     The slot  154  of the inner ring  152  opens to the atmosphere through the holes formed in the outer ring  150 . Therefore, even if the left assembly  86  is placed in the actuated position, and the end chamber is formed, pressure of the end chamber is maintained to be atmosphere pressure through the slot  154  of the rotation angle region VF. 
     Furthermore, the pneumatic source is connected to the air tube  162  connected to the slot  155  of the left assembly  86  with the pressure sensor. Consequently, as assembly  86  is passing through the rotation angle region VP in which the slot  155  is formed, the pneumatic source can supply the measurement pressure to the end chamber, and the measurement pressure is monitored by the pressure sensor. 
       FIG. 6  diagrammatically shows the operation of one pair of assemblies  86  in the dilution inspection apparatus  18 . 
     According to the inspection apparatus  18 , at the start end of the rotation angle region θ 1  of the drum shell  64 , the filter cigarette FT is transferred from the end checker drum  14  of the previous step into one of the transport grooves  70  (S 100 ). At this moment, the pair of assemblies  86  in combination with the above-mentioned transport groove  70  is in the rest position. The filter cigarette FT is securely received by the transport groove  70  without interfering with the assemblies  86 . The tip end of the cigarette  2  of the filter cigarette FT and the filter  4  project from both the ends of the transport groove  70 . 
     Subsequently, along with the rotation of the drum shell  64 , the filter cigarette FT is transported while being sucked and held by the transport groove  70 . Once the filter cigarette FT enters the rotation angle region θ 5 , the pair of assemblies  86  gradually moves forward from the rest position toward the actuated position, that is, toward the filter cigarette FT on the transport groove  70 . 
     Once the pair of assemblies  86  is placed in the actuated position (S 200 ), both the end portions of the filter cigarette FT are inserted into the ring-attaching holes  126  formed in the right and left ring holders  124  through the slots  130  of the end plates  128 . 
     Thereafter, the rubber rings  134  and  135  in the right and left ring holders  124  each receive a compressive force to be reduced in their diameters, thereby coming into airtight contact onto the outer circumferential surface of the filter cigarette FT. There are formed an end chamber EC and a surrounding chamber SC in the right ring holder  124 , whereas in the left ring holder  124 , there is formed an end chamber EC only (S 300 ). 
     The filter cigarette FT passes through the rotation angle region VF with the pair of assemblies  86  in the state where the end chambers EC and the surrounding chamber SC are formed. During the period in which the cigarette FT passes through the rotation angle region VF, the guide pipe  102  of the assembly  86  located on the filter  4  side (the right side, facing into  FIG. 6  as viewed) is connected to the air tube  162 . As a result, compressed air is fed into the surrounding chamber SC at a pressure monitored by a pressure sensor P 1 , which generates measurement pressure (input pressure) in the surrounding chamber SC. The measurement pressure is applied to the outer circumferential surface of the filter  4  of the filter cigarette FT. Based on the measurement pressure, the compressed air is directed through the perforation line  6  into the filter  4 , and then flows into the end chamber EC from the end face of the filter  4 . Consequently, the pressure that is reduced to be less than the measurement pressure is produced as detection pressure (output pressure) in the end chamber EC. 
     At this point, the guide pipe  100  is connected to a pressure sensor P 2  through the air tube  162 , so that the detection pressure in the end chamber EC is detected by the pressure sensor P 2 . Since the rubber rings  134  and  135  of the right ring holder  124  are in airtight contact to the filter  4  of the filter cigarette FT, the compressed air does not leak out of the surrounding chamber SC and the end chambers EC. Therefore, the pressure sensors P 1  and P 2  are capable of detecting with accuracy the measurement pressure and the detection pressure, respectively. 
     In the rotation angle region VF, the pressure in the end chamber EC of the left ring holder  124  is maintained to the same level as the atmosphere pressure. 
     After passing through the rotation angle region VF, the filter cigarette FT enters the rotation angle region VP with the pair of assemblies  86 . During the period in which the cigarette FT passes through the rotation angle region VP, the guide pipes  100  of the right and left assemblies  86  are connected to the respective air tubes  162  (S 400 ). By so doing, the compressed air is fed into the end chamber EC of the left assembly  86 , and the measurement pressure in the end chamber EC is applied to the cigarette end of the filter cigarette FT. In the right assembly  86 , the guide pipe  102  leading to the surrounding chamber SC is airtightly sealed by the stationary ring  146 . The guide pipe  100  leading to the end chamber EC is connected to a pressure sensor P 3  through the air tube  162 . The pressure sensor P 3  detects the detection pressure (output pressure) in the end chamber EC of the right assembly  86 , which corresponds to the measurement pressure (input pressure) in the end chamber EC of the left assembly  86 . In other words, when the measurement pressure is applied to the cigarette end, the measurement pressure is transmitted to the filter end of the filter cigarette FT while being reduced. The transmitted pressure appears as the detection pressure. 
     Again, the rubber rings  134  and  135  of the ring holders  124  are in airtight contact onto the outer circumferential surface of the filter cigarette FT, so that air does not leak out of the surrounding chamber SC and the end chamber EC. This enables the pressure sensor P 3  to detect the detection pressure with accuracy. 
     Subsequently, when the filter cigarette FT passes through the rotation angle region VP and enters a rotation angle region θ 6 , the internal diameters of the rubber rings  134  and  135  are enlarged into the original state to be detached away from the outer circumferential surface of the filter cigarette FT in the right and left assemblies  86  (S 500 ). The assemblies  86  are moved from the actuated position toward the rest position, and both the end portions of the filter cigarette FT are relatively pulled out of the assemblies  86 . 
     After the right and left assemblies  86 , that is, the ring holders  124 , are detached away from the filter cigarette FT as described above (S 600 ), if the filter cigarette FT is judged to be defective, it is removed in the rotation angle region θ 2 . As a consequence, only non-defective cigarettes FT are transported to a dead end of the rotation angle region θ 3  and transferred from the transport grooves  70  to the carrier drum  16  of the subsequent step to be further transported. 
       FIG. 7  diagrammatically shows a measurement principle performed in the rotation angle region VF in the inspection apparatus  18 . According to this measurement principle, it is possible to find the filter ventilation VF in the filter cigarette FT. The VF is as mentioned the ratio of an air amount flowing in from the perforation line to an amount of smoke drawn by the smoker.  FIG. 8  shows an analogy model in which the measurement principle is replaced with an electric equivalent circuit. According to the analogy model, when the measurement pressure and the detection pressure measured by the pressure sensors P 1  and P 2  are denoted by P 1  and P 2 , respectively, the ratio of the detection pressure P 2  to the measurement pressure P 1 , that is, P 2 /P 1 , is shown by the following equation. 
     
       
         
           
             
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       P 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       2 
                     
                     
                       P 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       1 
                     
                   
                   = 
                   
                     
                       
                         
                           R 
                           P 
                         
                         ⁡ 
                         
                           ( 
                           
                             
                               R 
                               
                                 T 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 1 
                               
                             
                             + 
                             
                               R 
                               
                                 T 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 2 
                               
                             
                             + 
                             
                               R 
                               FF 
                             
                           
                           ) 
                         
                       
                       + 
                       
                         
                           R 
                           
                             T 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                         
                         ⁡ 
                         
                           ( 
                           
                             
                               R 
                               
                                 T 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 2 
                               
                             
                             + 
                             
                               R 
                               FF 
                             
                           
                           ) 
                         
                       
                     
                     
                       
                         
                           R 
                           P 
                         
                         ⁡ 
                         
                           ( 
                           
                             
                               R 
                               
                                 T 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 1 
                               
                             
                             + 
                             
                               R 
                               
                                 T 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 2 
                               
                             
                             + 
                             
                               R 
                               FF 
                             
                             + 
                             
                               R 
                               V 
                             
                           
                           ) 
                         
                       
                       + 
                       
                         
                           R 
                           
                             T 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                         
                         ⁡ 
                         
                           ( 
                           
                             
                               R 
                               
                                 T 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 2 
                               
                             
                             + 
                             
                               R 
                               FF 
                             
                             + 
                             
                               R 
                               V 
                             
                           
                           ) 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     The right side of Equation (1) is identical to a resistance equation (Equation (3)) of the V F  in an after-mentioned measurement standard. In other words, the V F  is a value found by dividing the detection pressure P 2  by the measurement pressure P 1 . It is possible to directly find and monitor the V F  by substituting the measurement pressure P 1  and the detection pressure P 2  in Equation (1). 
     Characters in Equation (1) represent the following matters. 
     R T1 : Equivalent resistance of the cigarette end side, which is created when air flows within the cigarette  2  of the filter cigarette FT. 
     R T2 : Equivalent resistance of the filter side, which is created when air flows within the cigarette  2  of the filter cigarette FT. 
     R FF : Equivalent resistance of the cigarette  2  side, which is created when air flows within the filter  4  of the filter cigarette FT. 
     R FR : Equivalent resistance of the filter end side, which is created when air flows within the filter  4  of the filter cigarette FT. 
     R P : Equivalent resistance created when air flows from the outside of the cigarette  2  into the cigarette  2  through wrapping paper. 
     R V : Equivalent resistance created when air flows from the outside of the filter  4  into the filter  4  through tip paper including the perforation line  6 . 
     Therefore, the inspection apparatus  18  enables effective control of the nicotine and tar of the filter cigarette FT. For example, if a calculating device is connected to the inspection apparatus  18 , and the measurement pressure P 1  and the detection pressure P 2  are inputted to the calculating device to calculate the above-mentioned equation, the V F  can be found immediately. Moreover, if the calculating device is designed to make a judgment as to whether the V F  is defective or not, and the electromagnetic valve of the elimination tube  84  is activated on the basis of the judgment result, it is possible to easily and surely remove the filter cigarettes FT recognized to have defects in the V F  thereof. 
       FIG. 9  diagrammatically shows a measurement principle of dilution performed by a conventional inspection apparatus.  FIG. 10  shows an analogy model thereof, and based on this, the following equation is established according to the ratio between the measurement pressure P 1  supplied to the cigarette end and the detection pressure P 2  taken out from the filter end. 
     
       
         
           
             
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     2 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       
                         P 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                       
                       - 
                       
                         P 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                       
                     
                     
                       P 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       1 
                     
                   
                   = 
                   
                     
                       
                         
                           R 
                           P 
                         
                         ⁡ 
                         
                           ( 
                           
                             
                               R 
                               
                                 T 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 1 
                               
                             
                             + 
                             
                               R 
                               
                                 T 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 2 
                               
                             
                             + 
                             
                               R 
                               FF 
                             
                           
                           ) 
                         
                       
                       + 
                       
                         
                           R 
                           
                             T 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                         
                         ⁡ 
                         
                           ( 
                           
                             
                               R 
                               
                                 T 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 2 
                               
                             
                             + 
                             
                               R 
                               FF 
                             
                             + 
                             
                               R 
                               V 
                             
                           
                           ) 
                         
                       
                     
                     
                       
                         
                           R 
                           P 
                         
                         ⁡ 
                         
                           ( 
                           
                             
                               R 
                               
                                 T 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 1 
                               
                             
                             + 
                             
                               R 
                               
                                 T 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 2 
                               
                             
                             + 
                             
                               R 
                               FF 
                             
                             + 
                             
                               R 
                               V 
                             
                           
                           ) 
                         
                       
                       + 
                       
                         
                           R 
                           
                             T 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                         
                         ⁡ 
                         
                           ( 
                           
                             
                               R 
                               
                                 T 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 2 
                               
                             
                             + 
                             
                               R 
                               FF 
                             
                             + 
                             
                               R 
                               V 
                             
                           
                           ) 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     The right side of Equation (2) is identical to a resistance equation (Equation (5)) of V T  in an after-mentioned measurement standard. This proves that the measurement principle is to find total ventilation V T  of the filter cigarette FT. The total ventilation V T  is as mentioned above the ratio of the air amount flowing in from the wrapping paper and the perforation line to the amount of smoke drawn by the smoker. 
     As in the above-mentioned Equation (1), R T1 , R T2 , R FF , R FR , R P  and R V  represent the equivalent resistance of the cigarette end side and filter end side of the cigarette  2 , the equivalent resistance of the cigarette side and filter side of the filter  4 , the equivalent resistance of the wrapping paper and tip paper, respectively. 
     Although in the cigarette manufacturing industry, the V F , not V T , is generally used as an alternative control target of nicotine and tar, the V F  and the V T  do not always have a fixed relationship. It is therefore difficult to accurately estimate the V F  on the basis of the V T . For this reason, this conventional method is not capable of estimating (predicting) a correct V F , and is not suitable for control of the nicotine and tar of cigarettes. 
       FIG. 11  diagrammatically shows a measurement standard (which is compliant with ISO) that is commonly used in the cigarette manufacturing industry to measure the V F  and the wrapping paper ventilation V P . The measurement using this measurement standard is carried out off-machine with respect to a sampled filter cigarette FT. Characters shown in  FIG. 11  denote the following matters. 
     Q P : Air amount flowing into the chamber surrounding the cigarette  2 . 
     Q F : Air amount flowing into the chamber surrounding the filter  4 . 
     Q: Air amount flowing out from the filter end face. 
     According to this method, the air amounts Q P , Q F , and Q can be measured in a state where negative pressure is supplied to the filter end face of the filter cigarette FT.  FIG. 12  shows an analogy model of this measuring method. Based on the measured air amounts Q P , Q F , and Q, resistance equations (Equations (3), (4) and (5)) of V F , V P  and V T  can be found. 
     
       
         
           
             
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     3 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     V 
                     F 
                   
                   = 
                   
                     
                       
                         Q 
                         F 
                       
                       Q 
                     
                     = 
                     
                       
                         
                           
                             R 
                             P 
                           
                           ⁡ 
                           
                             ( 
                             
                               
                                 R 
                                 
                                   T 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   1 
                                 
                               
                               + 
                               
                                 R 
                                 
                                   T 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   2 
                                 
                               
                               + 
                               
                                 R 
                                 FF 
                               
                             
                             ) 
                           
                         
                         + 
                         
                           
                             R 
                             
                               T 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               1 
                             
                           
                           ⁡ 
                           
                             ( 
                             
                               
                                 R 
                                 
                                   T 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   2 
                                 
                               
                               + 
                               
                                 R 
                                 FF 
                               
                             
                             ) 
                           
                         
                       
                       
                         
                           
                             R 
                             P 
                           
                           ⁡ 
                           
                             ( 
                             
                               
                                 R 
                                 
                                   T 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   1 
                                 
                               
                               + 
                               
                                 R 
                                 
                                   T 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   2 
                                 
                               
                               + 
                               
                                 R 
                                 FF 
                               
                               + 
                               
                                 R 
                                 V 
                               
                             
                             ) 
                           
                         
                         + 
                         
                           
                             R 
                             
                               T 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               1 
                             
                           
                           ⁡ 
                           
                             ( 
                             
                               
                                 R 
                                 
                                   T 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   2 
                                 
                               
                               + 
                               
                                 R 
                                 FF 
                               
                               + 
                               
                                 R 
                                 V 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
             
               
                 
                   
                     V 
                     P 
                   
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                         Q 
                         P 
                       
                       Q 
                     
                     = 
                     
                       
                         
                           R 
                           
                             T 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                         
                         · 
                         
                           R 
                           V 
                         
                       
                       
                         
                           
                             R 
                             P 
                           
                           ⁡ 
                           
                             ( 
                             
                               
                                 R 
                                 
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                                   ⁢ 
                                   
                                       
                                   
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                   ( 
                   4 
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                     T 
                   
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                               R 
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                             ⁡ 
                             
                               ( 
                               
                                 
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                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 1 
                               
                             
                             ⁡ 
                             
                               ( 
                               
                                 
                                   R 
                                   
                                     T 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     2 
                                   
                                 
                                 + 
                                 
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                                   FF 
                                 
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                                   R 
                                   V 
                                 
                               
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                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
     As in the above-mentioned Equations (1) and (2), R T1 , R T2 , R FF , R FR , R P  and R V  represent the equivalent resistance of the cigarette end side and filter side of the cigarette  2 , the equivalent resistance of the cigarette side and filter end side of the filter  4 , the equivalent resistance of the wrapping paper and tip paper, respectively. 
     The measuring method of the V F  using the above measurement standard, however, is performed off-machine, and moreover the method measures a flow ratio Q F /Q. Therefore, this measuring method requires a long period of time (0.1 second or more) as shown in  FIG. 13  to gain a stable measurement result in respect of the V F . 
     By contrast, the inspection apparatus  18  that measures the pressure ratio P 2 /P 1  is capable of finding a highly accurate V F  in a short period time (about 5 ms), thereby actualizing the high-speed measurement of the V F . Consequently, the inspection apparatus  18  having such high-speed response can be applied to the filter attachment  10 , and is capable of inspecting the V F  with respect to all the filter cigarettes FT manufactured by using the filter attachment. In other words, the apparatus  18  is capable of performing continuous measurement of the V F  on-machine. 
       FIG. 13  shows a measurement result in respect of a filter cigarette FT in which the value of V F  is about 60 percent. As to the flow ratio measurement, a flow ratio Q is measured by using a sonic velocity nozzle, and a flow rate Q F  is measured by a differential pressure method using an orifice of φ1.2. 
       FIG. 14  diagrammatically shows the measurement carried out in the rotation angle region VP in the inspection apparatus  18 . According to this measurement, the outer circumferential surface of the filter  4  of the filter cigarette FT is in a closed position due to the surrounding chamber SC, so that the degree of V P  can be judged on the basis of the detection pressure P 3  in the state where the perforation line of the filter is virtually closed. Accordingly this measuring method is capable of making a reliable judgment as to occurrences of undesired tears and holes in the wrapping paper of the cigarette  2  even if the V F  of the filter cigarette FT is great, that is to say, regardless of the V F . 
     For example,  FIG. 15  shows in the form of a histogram a measurement result of the detection pressure P 3 , which was gained by a conventional measuring method in which the outer circumferential surface of the filter  4  was not blocked off, and a measurement result of the detection pressure P 3 , which was gained by the above-described embodiment, with respect to defective filter cigarettes FT in which holes were intentionally made in wrapping paper, and non-defective filter cigarettes FT. 
     It should be noted, however, that the V F  of defective and non-defective filter cigarettes FT was 68 percent. Moreover, the compressed air pressure that was supplied was 1 kPa, and each hole formed in the wrapping paper of the defectives has a diameter of 1 mm. 
     As is apparent from  FIG. 15 , according to the measuring method using the inspection apparatus  18 , distributions of the detection pressures of the non-defectives and defectives are completely separated, which makes it possible to reliably detect the defectiveness of the filter cigarettes FT. As a consequence, defective filter cigarettes FT are surely removed if the calculating device is further designed to make the defective/non-defective judgment. 
     In contrast, according to the conventional measuring method, the perforation line  6  of the filter  4  is not blocked up, so that the compressed air leaks outside the filter cigarette FT through the perforation line  6 . As a result, the detection pressure P 3  is reduced in accordance with the V F . Therefore, in the case of the filter cigarette FT having large V F , the difference of the detection pressure P 3  between the defectives and the non-defectives is small, and it is difficult to detect defectives by the conventional method. 
     The present invention is not limited to the above-described one embodiment, and various modifications can be made. For example, as to the dilution inspection apparatus, the step of measuring the V F  and that of detecting the defectives attributable to tears and holes in wrapping paper may be carried out in reverse order. 
     In the one embodiment, the filter cigarette FT is sucked and held in the transport groove  70  in the rotation angle region θ 4 . In order to improve accuracy in measuring the V F  and accuracy in detecting tears in wrapping paper, however, the suction may be cancelled in the rotation angle region θ 4 . In other words, it is possible to improve the measurement accuracy, etc. by carrying out the measurement in further faithful accordance with the analogy. To that end, for example, the suction groove  60  may be discontinued in whole length of the rotation angle region θ 4 . Again in this case, the filter cigarette FT is securely held on the transport groove  70  in the rotation angle region θ 4  not by suction but by the assembly  86 . 
     Although the material of the rubber ring is silicone rubber, the material is not particularly limited and may be arbitrarily selected from natural rubber, synthetic rubber, gelatinous materials, etc. It is also possible to enhance the adhesion of the rubber ring with respect to the outer circumferential surface of the cigarette and upgrade the sealing ability by forming a slit in the inner circumferential surface of the rubber ring. Furthermore, in the assembly  86  on the filter side, the amount of decreasing the diameter of the rubber ring  134  may be fixed to the same as the rubber ring  135  by making the rubber ring  134  softer than the rubber ring  135 . 
     The present invention is applied to the filter cigarettes having ventilation areas for directing outside air to the filters. Needless to say, however, the arrangement of the perforation lines as ventilation areas is not particularly limited, and the invention may be applied to various rod-like articles that require the dilution inspection, other than the above-mentioned filter cigarettes. The number of surrounding chambers that surround the outer circumferential surface thereof is not limited to one, and a plurality of surrounding chambers may be arranged along the axial direction thereof. The transport path for rod-like articles may be something other than the drum, and the reciprocation mechanism of the assembly and the compression mechanism of the rubber ring are not limited to those illustrated in the drawings. For example, it is also possible to form two adjacent assemblies integrally in the circumferential direction of the drum shell  64  and cause the assemblies to reciprocate at the same time.