GB2111675A

GB2111675A - Opto-electronic identification of combustion line of wrapper encasing smokable article

Info

Publication number: GB2111675A
Application number: GB08231687A
Authority: GB
Inventors: Dr Dirk Pangritz; Wolfgang Trinkies
Original assignee: BAT Cigarettenfabriken GmbH
Current assignee: British American Tobacco Germany GmbH
Priority date: 1981-11-06
Filing date: 1982-11-05
Publication date: 1983-07-06
Also published as: DE3144189C1; FR2515935A1; FR2515935B1; GB2111675B; CA1197705A; CH660793A5

Abstract

In order to identify the combustion line (2) of the wrapper encasing a smokable article (e.g. the combustion line of cigarette paper, wrapper leaf or synthetic wrapper), the degree of reflectance at the surface of the smokable article (3) is monitored by one or more optical sensors (RL1, RL2). The combustion line (2) can be identified by means of the sudden change in the output signal from the sensors (RL1, RL2) as it registers the transition from ash to wrapper at the combustion line (2). By causing the sensors (RL1, RL2) to move parallel with the advance of the combustion line (2), it is possible to record the path of that combustion line (2). <IMAGE>

Description

SPECIFICATION Procedure for opto-electronic identification of the combustion line of the wrapper encasing a smokable article, and apparatus for carrying out this procedure.

The invention relates to a procedure and an apparatus for identifying the combustion line of the wrapper encasing a smokable article (in particular the combustion line of cigarette paper, wrapper leaf or synthetic wrapper).

DE-OS 2, 947 249 (German Patent Application) describes a method for determining the rate of combustion and/or glow of a smokable article whereby a sensor capable of detecting the radiation from the incandescent zone of the smokable article is made to travel parallel with the movement of that zone, while the exact position of the sensor along the path of travel is plotted in relation of time by means of an electrical signal. By this means it is possible to determine the location of the incandescent zone throughout the period during which the smokable article is being smoked-i.e. during puffs and during the intervals between puffs-thus enabling the rate of combustion and/or glow to be ascertained.

Apart from the rate of combustion and/or glow, a further important parameter for a smokable article such as a cigarette is the behaviour of the wrapper material-for example, cigarette paper, wrapper leaf or synethetic wrapper - during thermal decomposition. The thermal decomposition behaviour can be influenced by the choice of appropriate materials, which in turn have a corresponding influence on the actual line of combustion, i.e.

the point of transition between the ash and the unburnt wrapper material. Among the factors which can be influenced by the thermal decomposition behaviour-and thus by the speed of advance of the combustion line -are the puff resistance of the conical incandescent zone, the degree of ventilation of the burning smokable article, the rate of combustion and the smoke yield.

The recognized method for determining the rate of combustion and/or glow of the incandescent zone is not suitable for plotting the advance of the combustion line due to the fact that the combustion line precedes the area of maximum incandescent-zone temperature by a certain distance, i.e. there is no direct correlation between the rate of combustion and/or glow on the one hand and the advance of the combustion line on the other. In practice, therefore, it has hitherto not been possible to monitor the advance of the combustion line except by purely visual means.

The present invention was therefore devised with the aim or establishing a method and creating an apparatus for identifying the combustion line of a smokable article (in particular the combustion line of cigarette paper, wrapper leaf or synthetic wrapper) in such a way that the movement of the combustion line can be plotted or recorded by fully automatic means.

In particular the invention is designed to determine and record the combustion line throughout the entire smoking process, i.e.

not only in the intervals between puffs but during the puff phases as well.

According to the invention there is provided a procedure for opto-electronic identification of the combustion line of the wrapper encasing a smokable article, wherein the degree of reflectance at the surface of the smokable article can be determined and the combustion line identified by means of the sudden change in the degree of reflectance at the point of transition from ash to wrapper at the combustion line.

The invention also provides an apparatus for opto-electronic identification of the combustion line of the wrapper encasing a smokable article, comprising at least one source and sensor assembly for reflective sensing applications (hereinafter referred to as SSA/SSA unit) and a device for detecting a sudden change in the output signal from the SSA at the point of transition from ash to wrapper at the combustion line.

The benefits of this invention derive from the exploitation of the fact that the wrapper material (e.g. cigarette paper), the combustion line and the ash produced by the burning tobacco in the incadescent zone all posses different reflective characteristics. These characteristics are determined and recorded by a source and sensor assembly for reflective sensing applications (hereinafter referred to as SSA/SSA unit).

An electronic analyzing device records the glow rate of the combustion line during the intervals between puffs, as well as the speed of advance of the combustion line during the puff phases.

By using this apparatus it is therefore possible to carry out investigations into the influence of various wrapper materials-e.g.

cigarette papers to which certain substances have been added-on the thermal decomposition behaviour of the wrapper, as well as investigations into other important parameters for smokable articles.

The degree of reflectance of the surface of the smokable article-i.e. of its wrapper material-is determined by means of a commercially available SSA unit which utilizes a lightemitting diode (LED) operating at infrared frequencies as a transmitter and a suitable phototransistor as a receiver. The measured signal caused by a change in the degree of reflectance of the surface of the smokable article is subject to two disturbance variables, namely a variation in the distance between the surface of the smokable article and the SSA unit, and the infrared emission from the incandescent zone of the smokable article.

The effect of any variations in distance between the SSA unit and the smokable arti cle can be almost entirely offset by utilizing two SSA units mounted side by side and by computing the difference in the signals re ceived by the two units.

The infrared emission from the incandes cent zone of the smokable article influences the opto-electronic receiver of the SSA unit.

However, as the infrared emission from the incandescent zone is continuous, it is possible to compensate for any error by controlling the LEDs of the SSA unit with a sinusoidal AC voltage supply which is shifted upwards by a constant DC voltage.

If the alternating components of the re ceived signals are then isolated and rectified after determination of the difference in signal, the result is a voltage which is proportional to the difference in the degree of reflectance at the points scanned by the two SSA units.

Fluctuations in the performance of the two SSA units result in a phase shift between the two received signals. This phase shift can be offset by means of a phase shifter incorporated in the transmitter circuit of one of the SSA units. If this phase shift is not offset, the difference between the two signals-even if the degree of reflectance at the two points scanned is the same-is sufficient to generate a relatively high output voltage, which in turn results in instrument error.

As the smokable article is normally attached rigidly to the smoking machine, and cannot therefore be moved, the SSA units are mounted in such a way that they can travel forward in accordance with the movement of the combustion line. The SSA units are therefore moved via a rack and pinion gear which is driven by an electric motor.

This motor is controlled in such a way that it moves the two SSA units back and forth over a range within which the analyzed output signal from the two units does not fall below a certain minimum limit. In one preferred design this minimum limit lies above the zerosignal level of the two SSA units.

This constant back-and-forth movement of the motor-and hence of the two SSA units -in the vicinity of the combustion line produces a sufficiently large number of readings for accurate analysis and evaluation.

During the puff phase the infrared emission from the incandescent zone of the smokable article is so powerful that the phototransistor of the SSA unit closest to the incandescent zone exceeds saturation point and therefore ceases to deliver any signal. By means of a time switch the motor is therefore triggered by the smoking machine in such a way that the two SSA units are moved slightly faster during the puff phase than the actual speed of the combustion line.

Immediately after the puff the infrared emission from the incandescent zone falls to a level where the combustion line can once again be identified by the SSA unit directly in line with it.

The position of the motor which moves the two SSA units thus serves to indicate the position of the two SSA units.

A potentiometer coupled to the motor and connected to a reference voltage supply thus delivers an output voltage which is in proportion to the position of the SSA units. This output voltage is then registered by means of an x-t recorder, thus providing a direct indication of the rate of progress of the combustion line.

The incorporation of further switching devices makes it possible to plot the position/time curve to the SSA units, and thus to plot the forward movement of the combustion line at a series of points.

The invention is described in more detail below with reference to a prototype model as specified in the attached graphs and diagrams. These graphs and diagrams are as follows: Figure 1 General view of the apparatus for identifying the combustion line of a cigarette Figure 2 Block writing diagram of the electronic circuitry for the apparatus as shown in Fig. 1 Figure 3 Perspective view of the two SSA units Figure 4 Graphs showing the output signals from the two SSA units without phase shift Figure 5 and 6 The non-rectified difference signal from the two SSA units were the degree of reflectance is the same at the two points scanned Figure 7 The difference signal at the point where the combustion line is identified Figure 8 Time curve for the voltage Urn as the combustion line passes in front of the stationary SSA units Figure 9 Graph representing the fluctuations in the voltage Urn and the limiting values (to be explained subsequently) Figure 10 Graph representing the move ment of the combustion line of a cigarette during smoking Fig. 1 shows the general design of an apparatus for identifying the combustion line of a cigarette. The cigarette consists of an incandescent zone (1), the paper combustion line which is to be monitored (2), the cigarette strand (3) and a filter (4), which is clamped into a standard holder (5). The holder (5) is inserted into a smoking machine (6), which can be programmed to "smoke" the cigarette according to a pattern that simulates the behaviour of a human smoker.

Parallel to the cigarette is a toothed rack (9), on which is mounted a sliding head carrying two SSA units (RL 1, RL2) positioned side by side. The rack (9) can be rotated by means of an electric motor (11), thus causing the two SSA units (RL 1, RL 2) to move parallel with the cigarette. A displacement transducer (10) is connected either to the motor (11) or to the rack (9). The output signal of the displacement transducer (10) is proportional to the rotation of the rack (9)/ electric motor (11) and thus to the position of the SSA units (RL 1, RL 2).

The output signals from the two SSA units, i.e. the received signals, are fed into an ana lyzing device (12), which controls the motor via a control unit (13) and receives the signal from the displacement transducer (10). The analyzing device (12) is connected to a recording device (14).

Fig. 3 shows a perspective view of the two SSA units (RL 1, RL 2), each of which contains a light-emitting diode operating at infrared frequencies as a transmitter, and a suitable phototransistor (FT) which receives the light reflected from the surface of the cigarette. In order to ensure that the points scanned by the two SSA units (RL 1, RL 2) are as close together as possible, an adjusting wedge (35) is positioned between the two units (RL 1, RL 2) in such a way that it maintains the units (RL 1, RL 2) at a predetermined angle to each other. This angle is 1 3, in the case of the apparatus described.

The two SSA units (RL 1 and RL 2) are mounted together on the toothed rack (9) by means of an attachment and can be made to move parallel with the cigarette.

If only one SSA unit were to be used, any variation in the distance between this single unit and the cigarette would result in a corresponding change in the received signal. In order to minimize this effect, the apparatus described utilizes two SSA units (RL 1, RL 2) so that any variations in distance can be almost completely offset by computing the difference between the two signals (E, and E2) received by the two units.

As can be seen from Fig. 2, the two SSA units (RL 1, RL 2) are fed from a constant voltage source (1 5) which supplies a DC voltage (U,) and from a generator (1 6) which supplies a sinusoidal AC voltage. The sinusoidal AC voltage from the generator (1 6) and the DC voltage (U,) are fed into the first subtractor (1 7) so that the LEDs (transmitters) of the two SSA units (RL 1, RL 2) are driven by a sinusoidal AC voltage which is shifted upwards by the DC voltage U,.

The output of the subtractor (17) is linked to a junction (18), which is connected directly to the first SSA unit (RL 1) and via an all-pass network (1 9) to the second SSA unit (RL 2).

This all-pass network compensates for the phase shifts between the two received signals caused by fluctuations in the performance of the two units. Fig. 4 shows the phase shift between the two received signals which occurs when the transmitters of the two SSA units (RL 1, RL 2) are powered directly by the supply voltage. The difference between these two signals-even if the degree of reflectance at the two points scanned is the same-would be sufficient to generate a relatively high output voltage, thus resulting in a faulty reading. For this reason the phase shift must be offset by means of the all-pass network (1 9).

The light emitted from the LEDs (transmitters) is reflected from the surface of the cigarette and picked up by the phototransistors, which generate an output signal in proportion to the degree of reflectance at the surface of the cigarette. The output signals from the phototransistors are then fed into two highpass filters (20 and 21), thus isolating the alternating components of the received signals E, and E2. These signals are then converted.

By feeding the two transmitters with the sinusoidal AC voltage which is shifted upwards by the DC supply voltage U1, it is possible to distinguish between the reflected infrared light and the infrared emission from the incandescent zone, which continuously irradiates the two receivers.

The output signals from the two high-pass filters (20 and 21)-i.e. the alternating components of the signals received by the two SSA units (RL 1 and RL 2)-are fed into a second subtracter (22), which produces the difference between the two output signals.

This difference is then amplified by means of an amplifier (23) and fed into a rectifier (24), the output signal from which represents the actual voltage (Urn), i.e. a voltage which is in proportion to the difference in the degree of reflectance ( at the points scanned by the two SSA units (RL 1, RL 2).

Figs. 5 and 6 show the two received signals E, and E2, i.e. the output signals from the two SSA units (RL 1 and RL 2). In Fig. 5 the two signals are shown in phase, while in Fig. 6 they are in phase opposition. Figs. 5 and 6 also show the non-rectified difference signals, i.e. the difference between the two received singals E, and E2 when the degree of reflectance (g) is the same at the two points scanned.

Fig. 7 shows the non-rectified difference signal for the two received signals (E, and E2) in phase opposition when the combustion line is identified. This signal is the result of the difference in the degree of reflectance of the ash and that of the unburnt paper.

The difference signals shown in Figs. 5 to 7 are thus generated at the output of the second subtracter (22).

After rectification in the rectifier (24), the voltage Urn can be registered by a meter. Fig.

8 shows the curve for the voltage Urn as the paper combustion line passes in front of the two stationary SSA units (RL 1 and RL 2).

The graph shows an obvious peak which marks the transition between the two reflect ing zones, i.e. the ash and the surface of the paper. As expalined above, this sudden transition is due to the different degrees of reflectance ( at the two points scanned.

If the two points scanned by the two SSA units (RL 1 and RL 2) are both located on the ash or the paper surface, the difference signal will fall to zero, or approximately zero, as is shown in Figs. 5 and 6 together with Fig. 8.

Fig. 8 also shows a number of levels (1 L, 2L, 1 H, 2H) on either side of the peak value for Urn. These levels are selected at random on the sole condition that they lie above the apparatus noise threshold.

The output signal from the rectifier (24), i.e.

the voltage Vrn, is applied via two junctions (25 and 27) to two Schmitt triggers (26 and 28). One of these Schmitt triggers (26) is linked via a junction (29) to a third subtracter (31). With the aid of a voltage source U2 (32) the speed of forward and reverse movement can be varied. The output signal from the subtracter (31) is applied via an amplifier (33) to the motor (11).The Schmitt trigger (26) is controlled when the rectified difference between the signals E, and E2 received by the two SSA units (RL 1 and RL 2)-i.e. the voltage Umis less than 2L and greater than 2H (see figures 8 and 9), thus causing the motor (11) to move the two SSA units (RL 1 and RL 2) back and forth in such a way that the voltage (Urn) always remains within the range defined by these two extreme values.

Fig. 9 shows the corresponding switch-over points t2L and t2H, which are dependent on the output voltage Vx2 from the Schmitt trigger (26).

The constant rotation and counter-rotation of the motor (11)-which effects a corresponding back-and-forth movement of the two SSA units (RL 1 and RL 2)-provides a sufficiently large number of readings for accurate evaluation and analysis.

During the puff phase, i.e. while the smoking machine (6) is in operation, the infrared emission from the incandescent zone (1) is so powerful that the phototransistor (FT) of the SSA unit closest to that zone exceeds saturation point and therefore ceases to deliver a measurable signal.

By means of a time switch (not shown) the motor (11) is then triggered by the smoking machine in such a way that it causes the two SSA units (RL 1 and RL 2) to move slightly faster during the puff phase than the actual speed of advance of the combustion line. In Fig. 2 this adaptation is indicated by a transducer (34), which is linked both to the third subtracter (31) and to the smoking machine (6). This transducer (34) serves to trigger the motor (11) via the smoking machine (6) during the puff phases.

Immediately following the end of a puff phase the infrared emission from the incandescent zone falls to a level where the combustion line (2)-with which the SSA units are still aligned-can once again be detected.

The two SSA units are displaced via the toothed rack (9) (indicated in the diagram by a dotted line) by the motor (11), which is controlled accordingly by the voltage Urn and the Schmitt trigger (26). Either the rotation of the motor (11) or the position of the rack (9) therefore serves to indicate the position of the two SSA units (RL 1, RL 2). For this purpose a displacement transducer (10)-e.g. a potentiometer connected to a reference voltage supply-is coupled to the motor (11) or to the rack (9). This potentiometer delivers an output voltage which is in proportion to the position of the two SSA units (RL 1 and RL 2).The output voltage is registered by a recording device (1 4) (e.g. an x-t recorder), thus providing a direct indication of the rate of advance of the paper combustion line.

As explained above, the Schmitt trigger (26) switches between the two values 2L and 2H (see Fig. 8). The second Schmitt trigger (28), which receives the voltage Urn via the junction (27), switches between the values 1 L and 1 H (see Fig. 8), so that the two Schmitt triggers (26 and 28) generate the corresponding output voltages Ux1 and Ux2. These two output voltages Ux1 and Ux2 are then fed into a logic unit (30), either directly via the second Schmitt trigger (28), or indirectly via the first Schmitt trigger (26) and the junction (29).

The logic unit (30) combines the two output signals xl and x2 in accordance with the following logical function: y = x1.x2 The output signal y from the logic unit (30) is then fed to the pen-lift connection of the x-t recorder (1 4).

The logic combination of the two output signals as described makes it possible to present the curve as a series of separate points due to the fact that the pen of the x-t recorder (14) only traces the curve when the two SSA Units (RL 1 and RL 2) are located between the two limiting values 1 L and 2L and are moving towards 2L.

The corresponding switch-over points t" and t1H, which are dependent on the output voltage Ux1 from the second Schmitt trigger, are indicated in Fig. 9.

Finally, Fig. 10 shows the movement of the combustion line of a cigarette, as recorded by the two SSA units (RL 1 and RL 2) moving parallel with the incandescent zone. The breaks in the curve caused by the lifting of the pen can be clearly seen.

Claims

1. A procedure for opto-electronic identification of the combustion line of the wrapper encasing a smokable article, wherein the degree of reflectance at the surface of the smokable article can be determined and the combustion line identified by means of the sudden change in the degree of reflectance at the point of transition from ash to wrapper at the combustion line.

2. A procedure for opto-electronic identification of the combustion line of the wrapper encasing a smokable article substantially as herein described with reference to the accompanying drawings.

3. An apparatus for opto-electronic identification of the combustion line of the wrapper encasing a smokable article, at least one source and sensor assembly for reflective sensing applications (hereinafter referred to as SSA/SSA unit) and a device for detecting a sudden change in the output signal from the SSA at the point of transition from ash to wrapper at the combustion line.

4. An apparatus as set forth in claim 3 in which two SSA units are positioned side by side and move in the direction of travel of the combustion line.

5. An apparatus as set forth in Claim 3 or 4 which comprises a constant voltage source for the generation of the DC supply voltage to the SSA unit or units.

6. An apparatus as set forth in Claim 5 which comprises a generator for the supply of a sinusoidal AC voltage and a subtractor into which the output signal from the generator and the DC supply voltage are fed.

7. An apparatus as set forth in Claim 6 in which an all-pass network is incorporated between the subtractor and an SSA unit.

8. An apparatus as set forth in any of Claims 4 to 7 in which the receiver of each SSA unit is connected to a high-pass filter.

9. An apparatus as set forth in any of Claims 4 to 8 which incorporates a second substracter for the output signals from the receivers of the two SSA units.

10. An apparatus as set forth in Claim 9, which comprises a rectifier for detecting the output signal (amplified if necessary) from the second subtracter and a meter connected to the rectifier which measures the output voltage from the rectifier.

11. An apparatus as set forth in any of Claims 3 to 8 in which a follow-up control system, moves the SSA unit in accordance with the forward movement of the combustion line.

1 2. An apparatus as set forth in Claim 11 in which a motor controlled by the output voltage from the rectifier moves the SSA unit or units back and forth in the vicinity of the combustion line.

1 3. An apparatus as set forth in claim 1 2 which incorporates two Schmitt triggers connected to the output of the rectifier, a logic unit for the output signals from the two Schmitt triggers and a pen-lift connector connected to the output of the logic unit for the pen of the recording device.

14. An apparatus as set forth in Claim 1 3 which incorporates a voltage source for generating the supply voltage to the motor and a third subtracter connected to the voltage source and to the second Schmitt trigger.

15. An apparatus as set forth in any of Claims 1 2 to 1 4 which incoporates a displacement/voltage converter connected to the motor and whose output is linked to the recording device.

1 6. An apparatus as set forth in any of Claims 1 2 to 1 5 for a smokable article placed in a smoking machine in which the motor causes the SSA unit or units to travel at a higher speed during the puff phase than dur-, ing the intervals between puffs.

17. An apparatus as set forth in Claim 1 6 in which a transducer controlled by the smoking machine is connected to a further input of the third subtracter.

1 8. An apparatus for opto-electronic identification of the combustion line of the wrapper encasing a smokable article substantially as herein described with reference to the accompanying drawings.