Abstract:
An ignition system for a smoking machine is disclosed. The ignition system comprises an ignition head ( 12 ) for igniting one end of a smoking article which is held by a smoking machine, a sensor ( 18, 20 ) for detecting a distance between the end of the smoking article and the ignition head ( 12 ) in a direction parallel to the axis of the smoking article, and control means ( 21 ) for automatically adjusting ignition conditions in dependence on the detected distance. The sensor ( 18, 20 ) is arranged to detect the distance across a range of offset positions of the end of the smoking article in a plane perpendicular to the axis of the smoking article, which range is greater than the width of the end of the smoking article.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application is a National Stage filing of International Application PCT/GB2005/004427, filed Nov. 16, 2005, entitled “IGNITION SYSTEM”, claiming priority to United Kingdom Application No. 0426162.4, filed Nov. 29, 2004, entitled “IGNITION SYSTEM”. The subject application claims priority to PCT/GB2005/004427 and to United Kingdom Application No. 0426162.4 and both references are expressly incorporated by reference herein, in their entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates in general to improvements in and relating to smoking machines for smoking articles such as cigarettes, cigars and cigarillos. More particularly, the invention relates to an improved ignition system for igniting smoking articles for smoking by a smoking machine. 
         [0003]    Regular testing of cigarettes on a smoking machine is an important part of any cigarette manufacturing process. A smoking machine serves to create a repeatable standardised environment for the analytical smoking of cigarettes. International and national standards, including ISO standard 3308 (2000), have been put in place for standardising the operation of smoking machines. 
         [0004]    A smoking machine typically comprises at least one holder for a cigarette, and a puffing means for drawing air in controlled fashion through the cigarette in regular short puffs in order to smoke the cigarette. The smoking machine may comprise or be adapted to engage with at least one lighter tool which comprises a heat source such as a resistive coil for lighting the cigarette. The machine usually also comprises or is adapted to engage with a variety of other tools, including tools for measuring or observing particular smoking characteristics, such as puff profile and leak check tools and/or air velocity tools. The tools may be removable for use on a number of different machines. 
         [0005]    It is desirable that the lighter tool should be capable of lighting the cigarette at the first attempt. Multiple attempts at lighting the cigarette may result in pre-charring, which may alter the smoking characteristics of the cigarette or otherwise disrupt any measurements which are to be taken. ISO standard 3308 (2000) indeed requires that a smoking machine should be capable of lighting cigarettes at the first attempt and without pre-charring. Furthermore, the need for multiple attempts at lighting is clearly inefficient. 
         [0006]    The distance separating the heat source of the lighter tool from the cigarette end has a profound effect on the success of ignition. If the heat source is too remote from the cigarette end, then the chances of successful lighting at first attempt will be diminished. On the other hand, if the heat source is too close to the cigarette, then the ignition process may result in heat damage to the cigarette which may alter its smoking characteristics. Actual contact between the heat source and the cigarette during ignition is particularly undesirable and is not permitted under ISO standard 3308 (2000). Typically, a separation of 0.25-0.75 mm between the heat source and the cigarette end at the point of ignition is viewed as desirable. 
         [0007]    Some difficulty has however been encountered in achieving precision positioning (to within about 1.0 mm) of the cigarette and lighter tool. Once a cigarette has been loaded into a smoking machine, the position of the unlit tip with respect to the smoking machine depends primarily upon the length of the cigarette and the depth of insertion of the cigarette into the smoking machine. Owing to the tolerances of manufacturing processes, the lengths of individual cigarettes from a batch typically vary within a range of 1-2 mm, giving rise to a corresponding uncertainty in the predicted length of a cigarette from the batch. Meanwhile, the depth of insertion of a given cigarette into a given smoking machine may also vary by around 1-2 mm, depending primarily on the force with which the cigarette is inserted into the machine. The combined effect of these uncertainties is an overall uncertainty of up to 4 mm in the predicted location of any single cigarette tip with respect to the smoking machine. Precision positioning of the lighter tool with respect to each cigarette tip, based on the predicted location of the cigarette tip, is therefore impossible. 
         [0008]    Co-pending United Kingdom patent application number 0306190.0 in the name of Molins plc, the entire subject matter of which is incorporated herein by reference, discloses a lighter tool with a sensor in order to detect the distance between the lighter tool and the cigarette, and with control means for adjusting the distance between the two so as to enable successful ignition of the cigarette. In particular, it is proposed to provide the lighter tool with a light beam, and to adjust the distance between the lighter tool and the cigarette until the light beam is broken. In this way it can be ensured that the lighter tool and the cigarette are separated by a predetermined distance, so that effective lighting of the cigarette can take place. 
         [0009]    The above arrangement has been found to be effective in dealing with variations in the position of the tip of the cigarette along the axis of the cigarette. However, this arrangement has been found to be less effective in dealing with misalignment of the cigarette in directions perpendicular to the axis of the cigarette. Various causes of misalignment have been discovered, such as mis-insertion of the cigarette into the holder, droop of the cigarette, or accidental knocking of the cigarette. It has been discovered that, if the cigarette is misaligned, then it may not break the light beam, and as a consequence it may not be possible to set the correct distance between the lighter tool and the cigarette. 
         [0010]    According to a first aspect of the present invention there is provided an ignition system for a smoking machine, the ignition system comprising:
       an ignition head for igniting one end of a smoking article which is held by a smoking machine;   a sensor for detecting a distance between the end of the smoking article and the ignition head in a direction parallel to the axis of the smoking article; and   control means for automatically adjusting ignition conditions in dependence on the detected distance;   wherein the sensor is arranged to detect said distance across a range of offset positions of the end of the smoking article in a plane perpendicular to the axis of the smoking article, which range is greater than the width of the end of the smoking article.       
 
         [0015]    By arranging the sensor to detect the distance across a range of offset positions of the end of the smoking article in a plane perpendicular to the axis of the smoking article, the end of the smoking article can be detected with much greater reliability than would otherwise be the case. Thus, even if the smoking article is misaligned, it may still be possible to detect the position of the end of the smoking article and thus to light the smoking article reliably. 
         [0016]    By axis of the smoking article it is preferably meant a line through the middle of the smoking article along its length. Where the smoking article is a rolled article, such as a cigarette, the axis will generally be the axis on which it has been rolled. 
         [0017]    The control means may be arranged to adjust the distance between the ignition head and the smoking article and/or the operation of the ignition head in dependence on the detected distance. For example, once the position of the end of the smoking article has been detected, the control means may move the ignition head in a direction parallel to the axis of the smoking article, so as to bring the ignition head into a position suitable for ignition of the smoking article. Alternatively or in addition the control means may control an amount of heat emitted by the ignition head, or the operation of the ignition head in relation to the puff cycle of the smoking machine. Preferably the control means adjusts ignition conditions so as to enable successful ignition of the smoking article by the ignition head. Successful ignition may denote ignition at the first (or possibly a subsequent) attempt. Furthermore, successful ignition may denote ignition of the smoking article without any undesired heat damage to the article and/or without contact between the smoking article and the ignition head. 
         [0018]    The ignition system may be arranged to carry out a three stage process for igniting the smoking article. In the first stage the ignition system is brought into approximate alignment with the smoking article; in the second stage the distance between the end of the smoking article and the ignition head is detected; and in the third stage the ignition conditions are adjusted in dependence on the detected distance. Thus the ignition system may be arranged to be brought into approximate alignment with the smoking article before the distance between the end of the smoking article and the ignition head is detected. Alternatively the ignition system may be arranged to carry out a two stage or a single stage ignition process where either the tool moves directly to a predetermined position relative to the cigarette without the approximate alignment, or else moves to and at the same time lights the detected smoking article. These processes may be more efficient in terms of time taken to light the smoking article. 
         [0019]    The sensor may comprise an emitter and a detector. Preferably the emitter emits a beam of radiation which is detected by the detector. This can allow the sensor to detect the end of the smoking article by determining whether or not the end of the smoking article interrupts the beam. The ignition system may then be arranged to carry out a “hunting” procedure to detect the end of the smoking article. For example, once the ignition head is in approximate alignment with the smoking article, if it is determined that the smoking article does not interrupt the beam, then the ignition system may be moved closer to the smoking article until the beam is interrupted or partially interrupted. If it is determined that the smoking article does interrupt the beam, then the ignition system may be moved away from the smoking article until the beam is no longer interrupted or is partially interrupted. In either case, once a change in the state of the light beam is detected, there may be a small movement of the ignition system in the opposite direction in order to correct for any overshoot. Thus in this arrangement the step of detecting the distance in effect consists of detecting whether the ignition head is too close to the smoking article, too far from the smoking article, or at the correct distance. 
         [0020]    The emitter may be arranged to emit radiation which covers an area in a plane perpendicular to the axis of the smoking article which has dimensions greater than the depth of the electromagnetic radiation in a direction parallel to the axis of the smoking article. In this way, the sensor may be able to detect the end of the smoking article across a range of offset positions in a plane perpendicular to the axis of the smoking article without compromising resolution of the sensor in the direction parallel to the axis of the smoking article. 
         [0021]    In one embodiment of the invention, the sensor comprises a plurality of emitters which are arranged to emit radiation in a plane perpendicular to the axis of the smoking article. For example, the sensor may comprise 2, 3, 4, 5 or some other number of emitters. This can allow the sensor to cover a greater area than if a single emitter were used. 
         [0022]    The emitters may be arranged in a row such that each emitter emits a beam which runs substantially parallel to the other light beams. Alternatively the emitters may be arranged such that the beams cross each other. For example the emitters may be arranged around part or all of a circle. In either case the beams may be separate or may overlap. 
         [0023]    The or each emitter may be arranged so as to emit a beam which is wider in the direction perpendicular to the axis of the smoking article than it is in the direction parallel to the axis of the smoking article. For example, a slit, a lens, a grating or some other means may be provided in order to make the beam wider in one direction than the other. Where a single emitter is provided, this can enable the sensor to cover an area in the plane perpendicular to the axis which is sufficient to enable detection of the end of the smoking article, without compromising sensitivity in the direction parallel to the axis. This situation may be improved even further by providing a plurality of emitters. 
         [0024]    As an alternative or in addition, the or each emitter may be arranged to scan a beam in a plane perpendicular to the axis of the smoking article. For example, the emitter itself may be moved so as to scan the beam, or a variable beam deflecting means, such as a liquid crystal grating, may be provided in order to scan the beam. In this case, a plurality of detectors may be provided, or a single detector may be provided which can also move or which has a detection area which is sufficient to detect the scanned beam. 
         [0025]    As another alternative, or in addition, the system may further comprise means for moving the ignition system so as to move a beam from the emitter in a plane perpendicular to the axis of the smoking article. In this way the beam is arranged to scan by movement of the ignition system itself. 
         [0026]    The or each emitter may be an emitter of electromagnetic radiation. The radiation may be in any part of the electromagnetic spectrum, such as visible, infrared or ultraviolet light. The emitter may be, for example, an LED (light emitting diode), a laser, a bulb, or any other emitter of electromagnetic or other radiation. 
         [0027]    The sensor may comprise a plurality of detectors. For example, the sensor may comprise a plurality of emitters and a plurality of detectors, and each emitter may be arranged to transmit a beam to a corresponding detector. All of the emitters may be arranged to emit beams at the same time, or the emitters emit beams one or more at a time in a predetermined sequence. In the later case, this can allow the interruption of a beam by the smoking article to be detected with greater certainty, in particular where the beams from two or more emitters overlap. 
         [0028]    All of the emitters may emit radiation of substantially the same type. Alternatively each emitter may be arranged to emit different type of radiation, and each detector may be arranged to detect radiation from the corresponding emitter, but not from other emitters. For example, each emitter could emit radiation of a different wavelength or different polarisation. This may be achieved, for example, by providing different types of emitters, or by adjusting the operation of the emitters, or by providing the emitters with suitable filters or polarisers. The detectors in turn may be arranged only to detect certain types of radiation, or may be provided with suitable filters. This arrangement can prevent a beam from one emitter interfering with that from another, which in turn may allow the interruption of a beam by the end of the smoking article to be detected with greater certainty. 
         [0029]    Preferably the emitters are spaced apart by no more than the width of a smoking article which it is desired to ignite. For example, the emitters may be spaced apart by no more than the width of a cigarette. This can ensure that at least one beam will be broken by the smoking article. However, it may be preferred to arrange the emitters closer together, so that more than one beam will be broken by the smoking article. This can allow the end of the smoking article to be detected with greater certainty, and can compensate for a failed emitter. 
         [0030]    The ignition system may further comprise means for focusing radiation emitted from the or each emitter. For example, each emitter may be provided with a lens in order to focus the radiation into a beam which does not overlap with other beams, or which overlaps to a limited extent. This can allow interruption of a beam by the end of the smoking article to be detected with greater certainty. 
         [0031]    Since the ignition system operates in a smoky environment, it is possible for smoke particles to accumulate on the emitters or detectors, which may reduce the amount of radiation emitted and/or detected. Furthermore, the amount of radiation which is emitted may reduce with ageing of the emitter, and likewise the sensitivity of the detectors may deteriorate over time. Thus the ignition system may be arranged to carry out a test procedure to determine the amount of radiation emitted by the or each emitter and/or detected by the or each detector. For example, where there is a plurality of emitters, each of the emitters may be lit individually in turn, and the amount of radiation received by the corresponding detector may be measured. An amount of radiation emitted by the or each emitter may then be adjusted in dependence on the test procedure. For example, the power supplied to the or each emitter may then be adjusted, or the gain or range or polarisation of the emitters may be adjusted, to ensure that all emitters emit radiation with the desired power. For example all emitters may emit radiation with substantially the same power, or some may emit more radiation than others. Alternatively or in addition the sensitivity of the or each detector may be adjusted in dependence on the test procedure. For example, the gain of the detector may be adjusted though adjustment of electrical gain, or optical filtering or focusing at the detector may be adjusted. 
         [0032]    The ignition head may comprise a heat source, which may emit heat for igniting the end of said smoking article by conduction, by convection or by radiation, or by any combination of conduction, convection and radiation. More typically, the heat source may emit heat by radiation or convection or by a combination of radiation and convection. The heat source may, for example, comprise a heatable coil, such as a resistive coil. Such a coil will emit heat for igniting the end of said smoking article by a combination of electromagnetic radiation and convection of heated air. The power of the coil may be in the region of 30-100 W, such as between 40-60 W, or about 50 W. Alternatively, the heat source may comprise a laser, or a halogen bulb, such as a halogen bulb of about 120-200 W, which will emit heat for igniting the end of said smoking article primarily by electromagnetic radiation. Heat sources of all of these types are known in the art. Said heat source may conveniently be powered by electricity. 
         [0033]    In one embodiment of the invention the ignition head is arranged such that it can ignite the smoking article across a range of offset positions of the end of the smoking article. For example, the ignition head may be of sufficient dimensions, or may emit heat in a sufficiently large area, to ensure that the smoking article is lit even if the smoking article is offset from its anticipated position in a direction perpendicular to the axis of the smoking article. This arrangement has the virtue of simplicity, but may result in unwanted heat being produced due to the need for a relatively large heating area. 
         [0034]    In another embodiment, adjusting means are provided for adjusting the relative position of the ignition head and the smoking article in a direction perpendicular to the axis of the smoking article, in dependence on an output of the sensor. For example, the sensor may detect that the smoking article is offset by a certain amount, and the adjusting means may be arranged to adjust the relative position of the ignition head and the smoking article so as to ensure that the ignition head will ignite the smoking article. This arrangement may provide the advantage that a relatively small ignition head can be provided, which reduces the amount of unwanted heat which is emitted. 
         [0035]    The heat source may be capable of movement with respect to said smoking article, and said control means may be adapted for controlling movement of said heat source, whereby the heat source under the control of said control means can be moved into or halted at a selected position. Alternatively, or in addition, said control means may be adapted for controlling movement of a smoking article held by a smoking machine, whereby said smoking article under the control of said control means can be moved into or halted at a selected position. By thus controlling relative movement of said heat source and/or said smoking article in view of the known position of said end of the smoking article, a predetermined distance separating said heat source from said end of the smoking article may readily be achieved. 
         [0036]    Said sensor may be arranged such as to detect the end of a smoking article when said end is disposed at said predetermined distance from the heat source, or when said end is positioned such that after subsequent movement of said smoking article and/or said heat source along a pre-set locus, said end will be disposed at said predetermined distance from the heat source. Alternatively, said ignition system may be arranged such that following detection of said end of the smoking article by said sensor, said heat source and/or said smoking article are moved under the control of the control means such as to achieve said predetermined distance between said heat source and said end of the smoking article. 
         [0037]    Suitably, said control means may be adapted to ensure that said heat source and said smoking article remain out of contact with one another during emission of heat by the heat source. 
         [0038]    Additionally or alternatively, said control means may be adapted to automatically adjust the operation of said heat source following detection of the end of a smoking article by the sensor, such as to enable successful ignition of said end of the smoking article by the heat source. Parameters of the operation of the heat source which may affect the reliability and success of ignition include the temperature of the heat source; the channelling of heat from the heat source to the end of the smoking article; the level and wavelength range of electromagnetic radiation that is applied by the heat source to the end of the smoking article; the length of time for which heat is applied to the end of the smoking article for igniting the article; and the timing of the application of heat to the end of the smoking article for igniting the article with respect to the “puff cycle” of a smoking machine. By adjusting any or all of these parameters, the control means may serve to enable successful ignition of a smoking article by the heat source without any or any further adjustments in relative movement of the heat source and/or said smoking article. Said control means may therefore be adapted for calculating the type and extent of any adjustments to any of these parameters which may be required for enabling successful ignition, in view of the known position of the end of the smoking article (as detected by said sensor), and for securing the performance of such adjustments. It will be appreciated however that said control means may be adapted for adjusting any or all of the aforementioned parameters of the operation of the heat source in addition to adjusting relative movement of said heat source and/or said smoking article. 
         [0039]    In other embodiment of the invention, the sensor may be adapted to identify the position of said end of the smoking article amongst a range of possible locations. In one possible aspect, therefore, said sensor may comprise a range-finding sensor, such as a laser or radar sensor, which is capable of transmitting signals which are adapted to be reflected from a target, detecting signals reflected from said target, and analysing said reflected signals, whereby the location of said target can be calculated. Said range-finding sensor may be fixed in a known position with respect to said heat source, and may be adapted for identifying the location of said end with respect to said heat source. Alternatively, said range-finding sensor may be adapted to be fixed in a known position with respect to said holding means, and may be adapted for measuring the location of said end of the smoking article with respect to the holding means. In another possible aspect, said sensor may comprise any sensor as hereinabove defined which is capable of detecting the end of said smoking article when said end is in a specified position, which sensor is adapted to be moved with respect to said heat source such as to hunt for said end, and means for identifying the position of the sensor with respect to said heat source, such that the location of said end, once detected by the sensor, can be identified. 
         [0040]    As yet a further alternative, said sensor may comprise a camera type device which is capable of visualising the smoking article and/or a shadow cast by the smoking article, whereby the position of the end of the smoking article may be detected. 
         [0041]    In some embodiments, the arrangement may be such that said end of the smoking article can be selectively shielded from said heat source, such as to prevent substantial transfer of heat from said heat source to said end. Thus, when the heat source and the smoking article are positioned for ignition, said end may be shielded from the heat source and said heat source may be energised without substantial transfer of heat from the heat source to the end during the course of energisation. Once the heat source is fully energised, said end may be exposed to the heat source, thus enabling ignition of the end to take place. 
         [0042]    Accordingly, said heat source may be adapted to move along a pre-set path between a first exposed orientation, in which the heat source is arranged to face said end such that said end is exposed to the heat source, and a second shielded orientation, in which the heat source is arranged to face away from said end such that said end is shielded from said heat source. Alternatively, or in addition, one or more barriers formed from a heat-impermeable material may be provided for selectively shielding said end from said heat source. Said one or more barriers may be adapted to be installed adjacent said heat source for shielding the heat source, and to be removed in order to expose said heat source. 
         [0043]    Said control means may include control hardware which is programmed to control the performance of the functions hereinabove defined. In particular, said control hardware may include processing means for receiving said detection signal and for calculating the type and extent of adjustments which should be made to the components of the ignition system and/or the smoking machine so as to enable successful ignition of said smoking article, and for effecting said adjustments. Said control hardware may be arranged to be located in a smoking machine, and/or in said ignition system. 
         [0044]    Said smoking article may be a rolled smoking article, such as a cigarette, cigar or cigarillo. Suitably, said end of the smoking article may be the end which is ignited by a smoker in use; that is, the non-filter end. 
         [0045]    Preferably, said lighting system and said smoking machine may be capable of satisfying one or more ISO standards including ISO standard 3308 (2000), and/or one or more FTC standards, and/or one or more CORESTA standards, and/or any other applicable national or international standards. Smoking machines suitable for use in conjunction with the present invention are widely available and in common use in the art. 
         [0046]    Said smoking machine may be capable of holding a plurality of smoking articles, and said lighting system may be adapted for igniting each of said smoking articles consecutively. Preferably, said smoking machine may be adapted for moving each smoking article which is to be ignited to a position such that the end of the smoking article is within a small distance, such as to within a few centimetres or a few millimetres, of said ignition head, prior to detection of said end by the sensor and consequent adjustment of the ignition head and/or the position of the smoking article. 
         [0047]    The invention also provides a smoking machine comprising an ignition system in any of the forms described above. 
         [0048]    According to another aspect of the invention there is provided a method of automatically igniting a smoking article held in a smoking machine using an ignition head, the method comprising:
       detecting a distance between the end of the smoking article and the ignition head in a direction parallel to the axis of the smoking article;   adjusting ignition conditions in dependence on the detected distance; and   igniting one end of the smoking article;   wherein said distance can be detected across a range of offset positions of the end of the smoking article in a plane perpendicular to the axis of the smoking article, which range is greater than the width of the end of the smoking article.       
 
         [0053]    Any of the apparatus features may also be provided as method features. 
         [0054]    Preferred embodiments of the invention will now be described, purely by way of example, with reference to the accompanying drawings. 
       BRIEF SUMMARY OF THE INVENTION 
       [0055]    An ignition system for a smoking machine is disclosed. The ignition system comprises an ignition head ( 12 ) for igniting one end of a smoking article which is held by a smoking machine, a sensor ( 18 ,  20 ) for detecting a distance between the end of the smoking article and the ignition head ( 12 ) in a direction parallel to the axis of the smoking article, and control means ( 21 ) for automatically adjusting ignition conditions in dependence on the detected distance. The sensor ( 18 ,  20 ) is arranged to detect the distance across a range of offset positions of the end of the smoking article in a plane perpendicular to the axis of the smoking article, which range is greater than the width of the end of the smoking article. 
         [0056]    One object of the present disclosure is to describe an improved ignition system for a smoking machine. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0057]      FIG. 1  shows parts of a smoking machine for use with embodiments of the present invention. 
           [0058]      FIG. 2  shows a side view of parts of an ignition system in an embodiment of the invention. 
           [0059]      FIG. 3  shows an end view of the ignition system. 
           [0060]      FIG. 4  shows parts of an emitter unit. 
           [0061]      FIG. 5  shows parts of a detector unit. 
           [0062]      FIG. 6  shows parts of the ignition system during a hunting procedure. 
           [0063]      FIG. 7  shows parts of the ignition system during ignition. 
           [0064]      FIG. 8  shows a view of the ignition system during the hunting procedure. 
           [0065]      FIG. 9  shows a view of the ignition system during ignition. 
           [0066]      FIG. 10  shows an exploded view of the ignition system. 
       
    
    
     DETAILED DESCRIPTION 
       [0067]    For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. 
         [0068]    Referring to  FIG. 1 , smoking machine  2  comprises a plurality of cigarette holders  4  for holding cigarettes to be smoked. A suction unit (not shown) is provided for drawing air through the various cigarettes in order to smoke the cigarettes. The suction unit operates under control of a control unit (not shown) in order to smoke the cigarettes in accordance with a particular puff cycle. Smoke from the cigarettes is collected in smoke collection bags (not shown) for analysis. 
         [0069]    The smoking machine  1  is provided with an ignition system  6  for automatically lighting the various cigarettes. In this embodiment the ignition system is mounted on a rail  8  and is driven by a stepper motor to bring the ignition system into approximate alignment with the cigarette it is desired to light. 
         [0070]    Although  FIG. 1  shows a linear smoking machine in which the cigarettes are mounted in a single row, the present invention can be used with any type of smoking machine, including rotary smoking machines and machines in which the cigarettes are mounted in two dimensional or three dimensional arrays. Some machines may have a lighter bar with several lighters on it, but no tool. Rotary machines have a lighting position, but may not have a separate tool, and the present invention can also be applied to such smoking machines. 
         [0071]      FIG. 2  shows a side view of parts of an ignition system  6  in an embodiment of the invention. Referring to  FIG. 2  the ignition system comprises a cylindrical housing  10 , an ignition head  12 , a pair of shutters  14 ,  16 , an emitter unit  18 , a detector unit  20  and a control unit  21 . The ignition head  12  in this embodiment is a resistive coil mounted in a protective holder which is formed from a heat-insulating material such as a ceramic material. The control unit  21  is arranged to control the operation of the ignition head  12 , the emitter unit  18  and the detector unit  20 . The control unit  21  may comprise one or more programmed PCBs. As will be explained below, the emitter unit  18  is arranged to emit a plurality of light beams  22 , and the detector unit  20  is arranged to detect the plurality of light beams. 
         [0072]      FIG. 3  shows an end view of the ignition system. As can be seen, in this embodiment emitter unit  18  emits four light beams  22   1 ,  22   2 ,  22   3 ,  22   4 , and detector unit  20  detects those four light beams. 
         [0073]    The ignition system operates as follows. When it is desired to light a cigarette, the ignition head is first switched on and allowed to reach the correct operating temperature. At this stage the shutters  14 ,  16  are shut to prevent heat from preheating the cigarette. At this stage heat from the ignition head escapes upwards through a vent. The ignition system  6  is then brought into a position in front of the cigarette. This position will be approximately the correct position for ignition of the cigarette. However, due to variations in the length of the cigarette and the depth of insertion of the cigarette, at this stage it is not possible to achieve precise positioning of the lighter tool with respect to the cigarette. 
         [0074]    The ignition system then begins a “hunting” procedure for the end of the cigarette. In this procedure, the ignition system determines whether or not one or more of the light beams  22  is broken. If one or more of the light beams is broken, the ignition system is too close to the cigarette. In this case the ignition system is moved away from the cigarette until the light beam is not broken, or is only partially broken. If however it is determined that none of the light beams are broken, then the ignition system is moved closer to the cigarette until one or more of the light beams is broken, or partially broken. If necessary, overshoot may be corrected by arranging the ignition system to move a small distance in the reverse direction once it has detected the breaking or restoration of the light beam. 
         [0075]    Once the “hunting” procedure is completed, the ignition head  12  is a predetermined distance away from the end of the cigarette  24 . The ignition head  12  is then brought forward towards the cigarette over a distance which will bring it into the correct position for lighting the cigarette. This distance is typically between 0.25 and 0.75 mm away from the end of the cigarette. At the same time the shutters  14 ,  16  are withdrawn to allow the heat from the ignition head to light the cigarette. In this example the shutters are pivoted and movement of the ignition head pivots the shutters into the open position. 
         [0076]    In the first embodiment of the invention, a plurality of light beams  22  are provided in order to detect the position of the end of the cigarette. This can allow the end of the cigarette to be detected with much greater reliability than if a single light beam were provided. For example, if the cigarette is misaligned, then it may not ever break a single light beam, in which case it would be impossible to light the cigarette reliably. However, by providing a plurality of light beams, even if the cigarette is misaligned it may still be possible to detect the position of the end of the cigarette and thus to light the cigarette reliably. 
         [0077]      FIG. 4  shows parts of the emitter unit  18  in more detail. The emitter unit comprises four LEDs (light emitting diodes)  26   1  to  26   4 , each of which emits a respective light beam  28   1  to  28   4 . The LEDs are spaced apart by no more than the width of the narrowest cigarette which it is desired to detect. In practice it may be desirable to space the LEDs closer than this so that two or more beams will be interrupted by a cigarette. This can provide more reliable detection, and may allow detection of a cigarette even if one light beam fails, for example, due to a faulty or dirty LED. The emitter unit is connected by means of cable  30  to control unit  21 . 
         [0078]      FIG. 5  shows parts of the detector unit  20  in more detail. The detector unit  20  comprises four light detectors  32 , to  324  which are arranged to detect the light emitted by the LEDs in the emitter unit. The detector unit  20  is connected by means of cable  34  to the control unit  21 . 
         [0079]    In one arrangement, each LED in the emitter unit  18  transmits a light beam to a single light detector in the detector unit  20 . In this case all of the LEDs are powered at the same time, and interruption of a light beam is detected simply by monitoring the outputs of each of the light detectors. The LEDs may be provided with lenses to focus the light or with masks in order to ensure that the light from one LED does not spill over to the light detector corresponding to another LED. 
         [0080]    In another arrangement the LEDs are lit one at a time in a predetermined sequence under control of the control unit  21 . This can allow the interruption of a light beam to be detected with greater certainty, in particular where the light beams overlap. 
         [0081]    Since the ignition system operates in a smoky environment, it is possible for smoke particles to accumulate on the LED, which may reduce the amount of light emitted by the LED. Furthermore, the amount of light which is emitted by the LED may reduce with ageing of the LED. In order to ensure that sufficient light is emitted by the LEDs, the control unit  21  carries out a test procedure when the ignition system is first switched on, and at other times if desired. In the test procedure, each of the LEDs is lit individually in turn, and the amount of light received by the corresponding light detector is measured. The power supplied to the LED is then adjusted to ensure that all LEDs have substantially the same light output. 
         [0082]      FIG. 6  shows parts of the ignition system during the hunting procedure. Referring to  FIG. 6 , the shutters  14 ,  16  can pivot about pivot points  36 ,  38  respectively. During the hunting procedure the ignition head  12  is withdrawn, and the shutters  14 ,  16  are biased into the closed position by means of springs (not shown). In this way the ignition head  12  is shielded from the cigarette. 
         [0083]      FIG. 7  shows parts of the ignition system when the cigarette is being lit. As can be seen from  FIG. 7 , the ignition head has been moved forward to a predetermined distance from the cigarette. The forward movement of the ignition head  12  causes the shutters  14 ,  16  to pivot about pivot points  26 ,  38 , and thus to open, thereby exposing the ignition head to the cigarette. In this position the cigarette can be lit by the ignition head. 
         [0084]      FIG. 8  shows a view of the ignition system in the hunting position. In this position the ignition head is shielded by shutters  14 ,  16 . The emitter unit  18  emits light beams  22   1 ,  22   2 ,  22   3 ,  22   4  which are detected by the detector unit  20 . The position of the ignition system is adjusted in accordance with the hunting procedure described above until the ignition system is a predetermined distance from the cigarette. At this point the ignition head  12  is moved into the ignition position, as shown in  FIGS. 7 and 9 . 
         [0085]      FIG. 10  shows an exploded view of the ignition system, with corresponding parts given the same reference numerals. 
         [0086]    While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.