Abstract:
The external integrity of cigarettes is verified by a method that involves directing single cigarettes, carried on a conveyor, along a route of which one section affords a monitoring path equipped with a line scan camera; the advancing cigarette can be made selectively to rotate about its longitudinal axis while the camera, a solid state type using CCD arrays, makes a succession of scans on respective closely ordered parallel lines, which are pulsed at a programmed frequency and synchronously with the movement of the cigarette in such a way that each successive scan line will fall on one and the same generator of the cylindrical surface. Repeated scanning of the same limited surface area eliminates quality control errors attributable to the presence of particulates in the space between the cigarettes and the camera.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a method of verifying the external integrity of cigarettes. 
     In particular, the invention is pertinent to a method of the aforementioned type such as can be employed, preferably, in cigarette manufacturing machines. 
     It is standard practice in the art field of cigarette manufacture to verify the external integrity of the finished cigarettes by causing the single cigarettes to advance in succession, with their respective axes disposed transversely to the direction of movement, along a predetermined monitoring path extending past an optical quality control device located following a manufacturing unit in the feed direction. 
     The quality control device in question is designed to sample a limited number of generators delineating the outer surface of each cigarette produced, by reading images of these same sample generators and comparing each registered image with a model or reference image, to the end of indicating any superficial defects of manufacture that might be present (e.g. badly formed and/or obstructed ventilation holes, edges not gummed, incorrect positioning and/or strength of print, etc.) and thus establishing whether or not the cigarette is of acceptable quality. 
     The quality control device consists generally in a solid state camera with a CCD array, familiar to those skilled in the art as a Line Scan Camera, which as the name implies is designed to read an object by scanning a single line. In operation, the scan line falls on a sample generator of the outer surface presented by the cigarette passing in front of the camera at a given moment. 
     It is the usual practice to scan a plurality of sample generators per single cigarette, utilizing a plurality of cameras ranged along the monitoring path: accordingly, the cigarette is made to rotate around its own longitudinal axis while progressing from one camera to the next, so that a different generator will be presented to each camera in turn. 
     A monitoring method of the type outlined above betrays the drawback that in the event of foreign matter (such as specks of dust, particulates, tobacco filler, etc.) occupying the space in between the cigarette and the optical device during the reading operation, this is interpreted by the device as a flaw and the cigarette will be rejected even though perfectly good. In other words, it cannot be guaranteed a priori that an error signal generated by the device effectively indicates a defective cigarette on every occasion. 
     The drawback in question is highlighted especially in dusty surroundings, such as those in which a cigarette manufacturing machine will typically operate. 
     The object of the invention is to provide a method of monitoring the external integrity of cigarettes such as will remain free of the drawback described above. 
     SUMMARY OF THE INVENTION 
     The stated object is realized according to the present invention in a method for monitoring the external integrity of cigarettes that comprises the steps of advancing cigarettes in a predetermined feed direction by means of a conveyor, each accommodated within a respective seat afforded by the conveyor and following a path of which one section is a monitoring path, and examining each cigarette in respect of its external characteristics while in movement along the monitoring path. 
     In the method disclosed, the step of examining the external characteristics of the cigarettes is effected using at least one set of multiline optical scanning means positioned along the monitoring path, such as will execute a plurality of pulsed optical scans at successive intervals. Each scan coincides with one of a cluster of corresponding parallel lines disposed one alongside another, and each cigarette is examined by scanning a given generator of its cylindrical surface more than once on different lines succeeding one another sequentially and synchronously with the movement of the cigarette along the monitoring path in the feed direction. 
     The stated object is realized similarly, according to the invention, in a device for implementation of the method described above. 
     A device according to the invention for monitoring the external integrity of cigarettes comprises a conveyor affording a plurality of seats caused to advance in a feed direction along a predetermined path, of which one section is a monitoring path, each accommodating a respective cigarette disposed with its longitudinal axis transverse to the feed direction, and at least one set of optical scanning means located along the monitoring path and designed to examine the external characteristics of at least one generator presented by each cigarette advancing along the monitoring path. 
     To advantage, the optical scanning means are of a multiline type such as will execute a plurality of discrete scans on a respective plurality of lines disposed parallel with and alongside one another in a cluster; also, the device comprises timing means by which the operation of the optical scanning means is synchronized with the movement of the conveyor so that the plurality of scans will fall on one and the same generator of each advancing cigarette. 
     In a preferred embodiment, optical scanning means will comprise at least one solid state camera using a CCD array and capable of multiline scanning (referred to conventionally as a Time Delay and Integration Line Scan Camera). 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in detail, by way of example, with the aid of the accompanying drawings, in which: 
     FIG. 1 illustrates a preferred embodiment of the monitoring device according to the present invention, viewed schematically and in elevation; 
     FIG. 2 illustrates a detail of the device of FIG. 1, shown enlarged and in successive steps of operation. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the accompanying drawings,  1  denotes a device, in its entirety, for verifying the external integrity of cigarettes  2 ; such a device comprises a cigarette conveyor  3  equipped with a transfer wheel  4  (conventional in embodiment) forming part of a filter tipping machine. The manufactured cigarettes  2  are fed singly and in succession to the transfer wheel  4  by an infeed wheel  5 , then taken up and distanced following verification by an outfeed wheel  6 . The various wheels are driven in rotation about their respective axes by means of conventional embodiment not indicated in the drawings. 
     The transfer wheel  4  incorporates a plurality of peripheral seats  7 , each designed to accommodate and to retain a respective cigarette  2 , advanced by the wheel  4  in a feed direction denoted F 1  (clockwise as viewed in FIG. 1) along a circular path  13  of which one section is a monitoring path  8 . Also forming part of the transfer wheel  4  are means not indicated in the drawings, but of conventional design (for example as disclosed in U.S. Pat. No. 5,287,524, to which reference may be made for a fuller description), such as will engage the two longitudinal extremities of each cigarette  2  occupying a respective seat  7  and induce a rotation F 2  of the cigarette about its own longitudinal axis. Each cigarette  2  is therefore able to describe a controlled trajectory composed of a translational movement in the feed direction F 1  along the monitoring path  8 , and a rotation F 2  about its own longitudinal axis. 
     The device  1  comprises means by which to examine the external characteristics presented by at least one generator  2   a  of each cigarette  2  advancing along the monitoring path  8 . Such means consist in optical scanning means  9  of conventional type such as will execute a plurality of optical readings or scans on respective lines  10  extending parallel to the axes of the cigarettes  2 . 
     The single scan lines  10  are disposed parallel with and alongside one another, forming a cluster generated substantially in alignment with the direction along which the cigarettes  2  advance. The optical scans are discrete, pulsed sequentially and at a predetermined frequency to coincide with each line  10  of the cluster from the first through to the last. As the description will show in due course, the optical scanning means  9  are able to examine a given straight line generator  2   a  of each cigarette  2  several times, the generator for practical purposes being an extremely small portion of the cylindrical surface exhibited by the cigarette  2 , appearing substantially rectangular in plan and having a longitudinal dimension equal to the length of the cigarette  2 . 
     The optical scanning means  9  preferably comprise at least one solid state camera  11  incorporating an array of charge-coupled devices (known to persons skilled in the art as a Time Delay &amp; Integration Line Scan Camera) such as will generate a beam comprising a plurality (typically 96) of discrete scans pulsed in succession and coinciding with the respective lines  10  aforementioned. The width of a single scan line  10  is of the order of just a few micrometers, whilst the overall width of the lines generated by the camera  11  in each burst will be greater than the width of the individual line  10  by a factor of at least one or two. 
     In the solution described and illustrated, use is made of three TDI line scan cameras  11  set apart one from the other along the monitoring path  8 , each camera  11  serving to monitor a relative generator  2   a,    2   b  and  2   c  of the cigarette  2 , as will become clear in due course. 
     The device  1  preferably comprises timing means  14  of conventional embodiment illustrated schematically in FIG. 1, by which the movement of the cigarettes  2  along the monitoring path  8  (that is, to reiterate, translated along the feed direction F 1  by the transfer wheel  4  while in rotation F 2  about their individual longitudinal axes) can be synchronized with the scanning frequency of the cameras  11  in such a way that the cluster of lines  10  scanned in a typical burst by any one camera  11  will always fall substantially on the same generator  2   a  of the cigarette  2  advancing at a given moment past that camera  11 . Thus, the timing means  14  control both the transfer wheel  4  and the means by which the individual cigarettes  2  are made to rotate about their own axis. 
     When, during operation of the device, a given generator  2   a  of an advancing cigarette  2  is rotated exactly into alignment with the first of the cluster of lines  10  relative to the first camera  11 , this same camera will begin scanning. With the cigarette  2  then continuing to advance and to rotate (in the direction denoted F 2 ) the same generator  2   a  (i.e. that already scanned on the first line) will be brought exactly into alignment with the second line  10  of the cluster, whereupon the first camera  11  makes a second scan; and so on for the remaining lines  10  of the cluster. 
     Given that the lines  10  of the cluster are scanned typically at a rate (expressible mathematically as the distance between any two adjacent lines  10  multiplied by the frequency of the scan pulses) faster than the velocity at which the cigarettes  2  advance along the monitoring path  8  in the feed direction F 1 , it follows that if a cigarette  2  were not rotated about its own axis, there would be a built-in delay relative to the scan pulses and each successive scan would therefore fall on a different generator. Precisely in order to avoid such a situation, the cigarette  2  is made to rotate about its own axis in the same direction of rotation as that described by the transfer wheel  4  (see FIG.  2 ), so that the single generator being scanned can keep pace positionally with the pulses. FIG. 2 shows the positions assumed successively by the cigarette  2  in relation to three different scan lines  10  during the burst generated by a given camera  11 . 
     Each image scanned is compared by the device  1  with a reference image in the usual manner. In the event of the space between a given camera  11  and a cigarette  2  being invaded by one or more foreign bodies (specks of dust, particles of tobacco filler, etc.), then certain of the scans made by that camera could produce images dissimilar to the reference image, due to the presence of such matter (and not by reason of any real defect in the cigarette  2 ). This need not necessarily result in the rejection of the cigarette  2 , however, given that the majority of the scans will not be affected by the presence of particulates: indeed the typical size of a particle liable to be detected is much less than the overall width of the cluster of lines  10  scanned by a camera  11  in one burst. 
     The requisite number of scans being completed, the device  1  proceeds to determine the ratio between those resulting “positive”, i.e. reflecting an irregularity in the cigarette  2 , and those which are “negative”; in the event of the ratio exceeding a preset value (reprogrammable), the device  1  responds in conventional manner by generating an output signal that might be utilized, for example, to pilot the operation of a reject device (not illustrated) located further along the manufacturing line. 
     Once beyond the first camera, and before reaching the second camera, the single cigarette  2  can be rotated about its axis (for example through 120°) in such a way that the second camera scans a different generator of the cigarette  2 , denoted  2   b  in FIG. 1, whereupon the cycle of operations described above is repeated. 
     Thereafter, these same operations are again repeated by the third camera on a third generator, denoted  2   c  in the example illustrated. 
     Clearly it would be possible to use a greater number of cameras  11  installed along the monitoring path  8 , so that different generators of each cigarette  2  can be examined, though still with each camera scanning a single generator several times. 
     The facility of causing a cigarette  2  to rotate in the direction denoted F 2  about its own axis serves a dual function: first, the motion of the cigarette  2  can be synchronized with the operation of a camera  11  that is set up to scan a plurality of lines  10 , so that a given generator can be examined repeatedly by the one camera with no need to adopt an excessive peripheral velocity of the transfer wheel  4 ; second, it becomes possible to sample several generators of the same cigarette  2 . 
     Finally, and with a high level of dependability in quality control still as the aim, the sampling of single generators by repeated scanning (as defined in the foregoing description) can be extended in accordance with the present invention to compass any given number of generators, and therefore a portion of any width presented by the cylindrical surface of the single cigarette.