numeral 1 in fig1 indicates a sampling and quality control unit forming part of a manufacturing machine 2 and comprising a conveyor 1a for a succession of cigarettes 3 . conveyor 1a comprises an input roller 4 rotating anticlockwise ( in fig1 ); an intermediate sampling roller 5 rotating clockwise ( in fig1 ) about its axis 6 and in time with roller 4 ; and an output roller 7 rotating anticlockwise ( in fig1 ) and in time with rollers 4 and 5 . roller 5 is tangent to rollers 4 and 7 at respective transfer stations 8 and 9 , which define , along the periphery of roller 5 , a sampling arc 10 forming part of the path 11 along which cigarettes 3 are fed through unit 1 . as they travel along arc 10 , cigarettes 3 are housed inside respective seats 12 equally spaced about the periphery of roller 5 and communicating in known manner with a known suction system 13 . system 13 comprises a fixed distributor 14 , the suction chamber 15 of which extends over the whole of arc 10 with the exception of a small intermediate chamber 16 located along arc 10 at a withdrawal station 17 , and forming part of a diverting device 18 which , when operated , provides for expelling cigarette 3 from the seat 12 communicating with chamber 16 . in addition to chamber 16 , diverting device 18 also comprises a pump 19 for feeding compressed air into chamber 16 under the control of a central control unit 20 . at withdrawal station 17 , roller 5 cooperates with a conveyor device 21 for receiving sample cigarettes hereinafter indicated by 22 -- from roller 5 and feeding them to a control station 23 . conveyor device 21 is substantially tangent to path 11 at station 17 , is a pneumatic conveyor device extending in a direction 24 substantially parallel to axis 6 , and comprises an input portion defined by a substantially u - section spoon 25 oriented parallel to direction 24 and presenting a bottom axial appendix 26 hinged to a fixed support ( not shown ) so as to rotate about an axis 27 parallel to direction 24 . in addition to forming part of conveyor device 21 , spoon 25 also forms part of a catch device 28 which also comprises an actuator 29 connected to appendix 26 and controlled by central unit 20 so as to rotate spoon 25 to and from an operating position wherein its concavity faces upwards and interferes with the path 30 along which sample cigarette 22 travels on leaving seat 12 at station 17 . in addition to spoon 25 , conveyor device 21 also comprises a guide channel 31 parallel to axis 27 and aligned with spoon 25 when this is in the operating position at withdrawal station 17 ; and an ejector nozzle 32 aligned with channel 31 , located upstream from spoon 25 in direction 24 , and connected to pump 19 by a diverting device 33 controlled by central unit 20 so as to direct the delivery of pump 19 towards chamber 16 or towards nozzle 32 . control station 23 is positioned facing the output end of channel 31 , and comprises an optical control device 34 for emitting an output signal s as a function of the surface characteristics of sample cigarette 22 ; and a rotary supporting device 35 aligned with channel 31 , and which provides for supporting sample cigarette 22 and for rotating it about its axis facing optical control device 34 . in the fig1 example , device 35 comprises a pair of side by side rollers 36 supported on respective shafts 37 and rotated in the same direction about their respective axes 38 , parallel to axis 27 , by a device 39 ; and optical control device 34 comprises a linear camera 40 facing rollers 36 and presenting a linear optical detecting system 41 extending along rollers 36 and comprising in known manner an array of photosensors ( not shown ). in actual use , at predetermined time intervals , central control unit 20 operates pump 19 to feed compressed air into chamber 16 and detach a sample cigarette 22 from respective seat 12 as the sample cigarette 22 travels through withdrawal station 17 . at the same time , control unit 20 moves spoon 25 from the idle position clear of station 17 , to the fig1 operating position wherein it interferes with the path 30 travelled by cigarette 22 expelled from seat 12 , so as to catch cigarette 22 and position it in line with channel 31 . at this point , control unit 20 operates diverting device 33 so as to feed compressed air to nozzle 32 which transfers cigarette 22 from spoon 25 to control station 23 along channel 31 . on leaving channel 31 , cigarette 22 is deposited onto rollers 36 which are activated by device 39 to expose the entire surface of cigarette 22 to optical system 41 of camera 40 , and to enable camera 40 to emit signal s which may be used for automatically adjusting the functional and / or structural parameters of machine 2 . in the fig2 embodiment , channel 31 is replaced by a channel 42 which presents a straight input portion 43 parallel to axis 27 , and a tubular output portion 44 perpendicular to portion 43 and connected to it by a curved tubular intermediate portion 45 . more specifically , portion 44 is positioned vertically over a supporting device 46 which comprises three disks 47 defining a cavity 48 with an axis 49 coaxial with tubular portion 44 . disks 47 are connected to a drive device 50 by which they are all rotated in the same direction to rotate a cigarette 22 positioned with one end engaged inside cavity 48 . cigarette 22 is thus rotated about axis 49 and in front of camera 40 which , in this case , is positioned with optical system 41 upright and parallel to axis 49 . in the fig3 embodiment , supporting device 46 is replaced by a supporting device 51 which comprises a fixed plate 52 located beneath the free end of tubular portion 44 , and presenting a vertical sleeve 53 defining a seat coaxial with tubular portion 44 and for receiving the end of cigarette 22 . as supporting device 51 in the fig3 embodiment is fixed , camera 40 is replaced by a camera 54 comprising two matrix optical systems 55 located between output portion 44 of conveyor device 21 and sleeve 53 , and defined in known manner ( not shown ) by respective numbers of photosensors arranged on the surfaces of two dihedrons surrounding cigarette 22 engaged in the seat defined by sleeve 53 .