GB2060870A - Measuring cigarette weight - Google Patents

Abstract

In apparatus for measuring the weight of a section of cigarette rod, the analogue voltage output of a rod weight sensor such as a nucleonic scanner is supplied to a voltage- to-frequency converter whose output is processed, e.g. using a microprocessor, to provide a signal representing the weight per unit length of the rod. A control system comprises a first set of lower level microprocessors (6, 8, 10, 12) each arranged to monitor a specified set of operating characteristics, including the sensor output, and to produce control signals, and an upper level microprocessor (2) arranged to coordinate and control intercommunication between the lower level microprocessors, to receive information from them and activate display means 18. The nucleonic scanner is associated with means for averaging the results of several successive scanning tests with no rod present. The average is compared with a reference to obtain an indication of source decay enabling it to be compensated. <IMAGE>

Description

SPECIFICATION Cigarette weight control system This invention relates to systems for controlling the weight and other quality factors of the cigarette rod made. by a continuous rod cigarette-making machine.

A control system for a continuous rod cigarette making machine according to a first aspect of the invention comprises means for sensing the quantity of tobacco in the rod; a first set of lower level microprocessors each of which is arranged to monitor a specified set of operating characteristics of the machine, including the signal from the said sensing means, and to produce related control signals, and an upper level microprocessor which is arranged to coordinate and control the intercommunication of the set of lower level microprocessors and to receive information from them to activate an information display device or devices.

Preferably, the upper level processor operates a periodic polling system which controls the transfer of information to and from the lower level processors.

Preferably the functions of the lower level processors include: monitoring and control of the rod weight; calculation of target rod weights to achieve desired economy goals; detection of densed ends and indication of their position; and calculation of standard deviation of cigarette weight.

According to a preferred embodiment of the first aspect of the invention, the sensing means comprises a nucleonic cigarette-rod scanning device comprising a nucleonic source positioned on one side of a rod guiding device, and a nucleonic detector for the radiation beam positioned on the other side of the rod guiding device. The rod guiding device may comprise a pass tube immediately upstream of the sensor beam path which may have internal regions arranged to be a sliding fit around the cigarette rod. A suction port communicating with the interior of the guiding device (in particular of the pass tube) is preferably provided so that the rod is restrained against "fluttering" about its axial path; the suction port is preferably upstream of the radiation beam in relation to the path of the rod.

Preferably the pass tube is removably mounted in a fixed housing so that it can be interchanged when rods of different diameters are to be manufactured. Preferably an adjustable guide is provided downstream of the beam path, and may take the form of a support whose height is adjustable for different rod diameters so that the rod is supported by it at the correct height.

Preferably, the apparatus also includes a scanner station checking system of the type described in our co-pending application No. 13741/77 (corresponding to German Offen- legungsschrift No. 2812 702). It will be noted that that application describes, by way of example, a rod weight scanner of the type having a "balance unit" to compensate for source decay effects.However, according to a second aspect of the present invention, there is provided a nucleonic scanner for a rod cigarette making machine comprising a nucleonic source, a nucleonic detector and processing means arranged to average the results of several successive scanning tests with no rod cigarette between the source and detector and to compare the average with a reference to obtain an indication of source decay so that such decay can be compensated; this obviates the need for a compensating "balance chanber", i.e. only a single ionisation chamber is needed. Preferably the processor is also adapted to take account of ambient temperature variations.

According to a third aspect of the present invention there is provided a method of measuring the weight of a section of cigarette rod or cigarette filter rod which method comprises: using a rod weight sensing device to generate an analogue output signal, supplying the analogue signal to a voltage to frequency converter, monitoring the frequency of the output pulses from the converter and processing the monitored frequency data in a microprocessor to provide a signal representing the weight per unit length of the rod.

This signal may be used to indicate the total weight of a cut cigarette rod, and/or to indicate regions in the rod of lower or higher than a required density (i.e. "voids" and "lumps") and/or to detect the position of "densed ends", as is explained in detail below.

According to a further aspect of the invention there is provided apparatus for performing the method of the third aspect.

For a better understanding of the invention and to show how the same may be carried into effect reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a schematic diagram of a microprocessor control system in accordance with the invention; and Figure 2 is a vertical cross-section through a rod-weight scanner; Figure 3 is a block diagram of a timer circuit for use with a microprocessor to determine the speed of a cigarette making machine; Figures 4a, 4b, 4c and 4d are respectively diagrammatic representations of a continuous cigarette rod, the corresponding end-of-cigarette pulses, a series of timing or "clock" pulses, and the output of a timer circuit; Figure 5 is a block diagram of a timer arrangement for detection of low density regions ("voids") in the cigarette rod;; Figures 6a, 6b, 6c and 6d are respectively diagrammatic representations of an averaged "weight frequency" signal, a series of clock pulses, and two different timer output waveforms; Figure 7 is a block diagram of a timer arrangement for detection of high density regions ("lumps").

Figures 8a, 8b, 8c and 8d are respectively diagrammatic representations of an averaged "weight frequency" signal, and three different timer output waveforms; Figure 9 is a block diagram of a timer arrangement for detection of "densed ends" in the tobacco rod; and Figures 1 Oa, 1 Ob, 1 Oc, 7 Od, 1 owe and 1 Of are respectively representations of the continuous cigarette rod, the end-of-cigarette pulses, three different timer output waveforms, and a stream of "weight-frequency" pulses.

Fig. 1 shows the interconnection of the various microprocessor sub-systems which form the machine control system. All intercommunication is controlled by the "Operator Communications" processor 2. Data is transferred using the two-way ten-line data bus 4.

The communications processor operates a one second polling system to avoid the need for upwards interrupts from the lower processors.

One control line is used to define the direction of data transfer while four others are used to provide individual addresses for lower level processors 6, 8, 10 and 12.

Normally the lower level processors operate in the receive mode. They only operate on the data transmitted by the communications processor when their own particular address line is activated. Data is transferred on either of the ten lines of the bus 4. The other two lines are used to provide a handshake sequence to initiate and terminate all messages. The last byte of all messages is a checksum which is compared in the receiving processor with a similar sum which has been calculated from the message received.

The message format is byte orientated subject to a maximum length of 64 bytes. The first byte transmitted indicates the number of bytes in the message not including the checksum but including the first byte itself.

To permit analysis of individual cigarettes, weight information must be transmitted to the individual processors as quickly as possible.

This is achieved by the provision of a special 1 6-line uni-directional data bus 14 which transmits data from the weight processor to the other low level processors. Although this facility is primarily used to carry individual cigarette weight information, it is also used in conjunction with the four bus control lines to provide basic setting data and machine status information during system calibration and commissioning.

The operation of the system of Fig. 1 will now be described with reference to some of the functions which the system can perform.

These functions are explained in further detail later with reference to Figs. 3 to 10.

WEIGHT CONTROL The analogue signal from the scanning head of a nucleonic rod weight measuring device connected to the cigarette rod making machine is applied to a Voltage to Frequency Convertor. The output of the VEC is scaled so that with an average cigarette in the pass tube a frequency of approximately 500 kKz is generated. During normal running this frequency will vary inversely as the density of the rod in the scanning head. The number of pulses occurring during each cigarette period are counted. This count is inversely proportional to the total weight of that particular cigarette. The time period between each cut of the cigarette rod is also measured so that the value can be corrected for variations in machine speed.

When the machine is running at very slow speed the scaling of the VFC may be changed to retain adequate range. This count is processed by the Weight Analysis processor 6 which converts the count into the weight, in milligrams, of the individual cigarettes. This weight is transmitted to the Weight Control processor 8 where the individual cigarette weights are further integrated with a defined cigarette constant. The integration constant is normally 128 cigarettes and is software selectable. This average is then compared with the desired formula weight which has been entered via manually-operated switches 9 or from a higher level in the hierarchy.If the difference exceeds a software established deadband (normally + / - 0.8%) a signal is transmitted to the ecreteur motor of the making machine via solid state relays, i.e. the motor controlling the position of the ecreteur (trimmer) which trims away part of the cigarette filler stream. The sign of the difference is used to direct the direction of the motor so as to correct the calculated error in the rod filling. If the measured mean weight deviates from the formula weight by more than the prescribed limit (4+% nominal) an alarm is generated which causes the making machine to be stopped and a lamp indicates the fault.

The lamp will remain illuminated until the machine is restarted. A Mean Weight Meter is provided to indicate the instantaneous variation of the measured mean weight from the desired formula weight.

The automatic check is carried out during the time between the first rotation of the cutoff and the actuation of the machine "rod break-in" device. This check involves the opening of the source shutter of the nucleonic scanner and the measurement of the output frequency from the VFC., under these circumstances. The system is pre-calibrated so that this frequency should be 1.0MHz providing the pass tube is clean and in good condition.

Any subsequent deviation from 1 .0MHz indicates either paste or debris in the pass tube if the frequency is below 1.0MHz. Occasionally a reduction in this frequency will indicate that the source has decayed sufficiently to warrant recalibration. This will be evident as cleaning of the pass tube will not restore the desired condition.

The principle of checking the nucleonic scanner before a cigarette enters the scanning region has been described in British Application No. 13741/77 and the corresponding German Offenlegungsschrift No. 28 1 2 702 where a signal is derived initially, in the absence of the rod, to detect any dirt in the scanning region. According to the second aspect of the present invention, several successive signals produced in that way are averaged and are compared with a reference to obtain an indication of source decay, so that such decay can be compensated.

If the automatic test is performed and the result is unsatisfactory an alarm will indicate the fault and optionally a machine stop signal can be generated. Once the automatic check is complete the processor closes the shutter and control of the shutter is then restored to the normal machine control system.

DENSED ENDS DETECTION The Weight Analysis processor 6 integrates the density of a software prescribed length of rod one side of the cut-off point. It repeats this operation for a similar length the other side of the cut-off point. These values are independently averaged for 64 individual cigarettes and the averages compared with each other by subtraction to indicate any difference. The difference will be an indication of movement of the Densed Ends from their correct position. A suitably scaled meter driving routine produces a pulse signal which deflects the densed ends indicating meter by an appropriate amount. This routine also ensures that the mean density of these end sections is within the software prescribed range. If the mean density is outside this range an alarm lamp is illuminated and the meter is deflected to one side.

Similar calculations in the Weight Analysis processor ensure that the cigarette rod does not contain any incremental length which has a density lower than a software prescribed value. If such a void is discovered the cigarette which eventually embraces that void may be rejected if required. Similarly, extra light weight cigarettes and/or heavy weight cigarettes may be rejected.

All parameters associated with the above inspection facilities are entered through suitable operator communication facilities, such as a keyboard 16. Alternatively, they can be down loaded from a central computer.

The weight control processor incorporates a routine which calculates standard deviation by nominally dividing the distribution graph into three zones, one for the low side of the distribution, one for the central portion including the mean value, and one for the high side of the distribution. The two dividing lines are shifted until a predetermined percentage of the cigarettes fall between them, so that the width of the central zone is then directly related to the standard deviation.

The use of both sides of the distribution will produce a value which reduces the effect of any "skew". This value is displayed on a special digital display for a simple system or via the operators panel for a full system. It can be displayed either as a percentage or in milligrams. A further calculation examines the difference between the two halves of the distribution and so produces a measure of the "skew". This value is used to aid the diagnosis of machine faults.

The rod weight is arranged to be controlled by the weight control processor in accordance with preset criteria which can be selected by the cigarette manufacturer. In one mode of operation the target weight is arranged to be reduced until a predetermined minimum percentage of the cigarettes produced is above a "quality barrier" weight, i.e. only a small percentage are below the barrier. Not all of these will be rejected; the rejector will be set to reject only those which are abnormally light. Obviously the smaller the standard deviation, or the greater the proportion of light cigarettes which are rejected, the nearer the mean weight can be shifted towards the threshold weight thus saving tobacco.In a more sophisticated mode of operation, it is possible to take into account the cost of recovering tobacco from cigarettes which are rejected as being too light, balanced against the saving which results from being able to progressively reduce the target weight as a higher proportion of light cigarettes are rejected. In a simpler arrangement, the rejector level may be set at a predetermined number of standard deviations below the "brand mean" weight so that the mean weight can be reduced, for a given standard deviation, without causing a larger proportion of undesirably light cigarettes to be produced.

DATA ENTRY AND DISPLAY Except for basic controls and weight related displays all data display and entry is controlled by the Operator Communications processor 2 for a stand-alone equipment. When the equipment is connected to a central computer data can be entered from this source also. All basic operating data as well as limiting values can be entered through this facility.

The full operator facility is based on a 12 line by 40 characters per line display 18 in conjunction with keyboard 16.

When operating an automatic mode, the display will vary according to the status of the machine. The objective is to ensure that the operator has information about machine condition readily available. This is achieved by dividing all available data into sections which are of a size capable of being displayed at one time. These sections are referred to as "pages" One page carries data appropriate to a machine which is running normally. Other pages contain data appropriate to a machine which has just stopped. An index of these pages can be displayed at operator's command. Any page can be selected from this index by use of the keyboard.

Where operator action is required for such things as the entering of stoppage information or indeed for the entering of basic operating data the display acts as a prompt which lists the operator options for that particular section.

The simple digital display which is used for Standard Deviation when only a weight control unit is in use is incorporated as a flexible indicator when the Operator Communications facility is fitted. Any numeric data which the operator wishes to have available for constant observation can be selected from the main display panel to be permanently indicated on the large digital display.

DATA COLLECTION The Data Collection Processor (10) in conjunction with an input buffer card provides an interface for connecting a wide variety of transducers to the data processing system.

The majority of inputs are assumed to be simple two state devices. Three channels are provided to convert analogue signals into digital code.

Each digital input is connected to the processor via a circuit which consists of an optoisolator followed by an integrating Schmitt trigger followed by a latching circuit. The input of the opto-isolator is equipped so that it can accomodate either switch closures requiring an action voltage or active circuits such as photocells which provide either a voltage or current input. These features are hardware set during initial connection. The time constant of integration can also be varied to accommodate signals of different character. Dependent on the nature and timing of the signal, it is necessary to "latch" transient signals. The timing and operation of this latching is critical and this is accommodated within the software programme of the data processor. Longer term status conditions must not be latched and are read into the processor direct.This input technique to the Microprocessor ensures that all occurrences which repeat at cigarette rate or slower will be captured.

Dependent on the purpose of each detector various processing routines will be required as the result of each occurrence. Some detectors will indicate periodic occurrence such as cigarette detectors. The requirement for this type of feature is to count every occurrence and maintain a record of these to-date. Inputs which indicate status generally have signals which last for an appreciable time. The requirement here is to ensure that the signal is a a lasting signal and so verifies the status and then to repeat this condition for use by other processors. Counting of these occurrences may be required. A special routine is required to determine the primary cause of stoppage, otherwise the stoppage inputs are treated as for status.In systems where cigarettes are transported between makers and packers using trays, tray identification codes will be produced which will be treated in a similar way to other status inputs but the tray code is retained in a special storage area, so that it can be fed to a central computer.

The analogue inputs are accommodated by use of a simple voltage to frequency converter system. The output from these converters is stored after suitable integration. The values are monitored to ensure that they remain within prescribed limits.

Some of these detected occurrences requires to initiate the rejection of selected cigarettes. The Data Collection processor uses the occurrence to trigger an appropriate sequence delay and hence to provide an output signal at the time appropriate to the selected rejector. Six separate outputs are provided, any one of which can be selected for any type -of occurrence. The length of delay for each type of occurrence can be varied. The number of cigarettes rejected by each occurrence is also subject to processor control.

SPECIAL FUNCTIONS A processor 12 is provided to permit extra processing to be carried out on any of the data which has been produced or collected by the system. Standard programmes in this Special Function processor provide for batch sampling, zone sampling, histogram plotting and similar facilities. It is possible for other programmes, within the capacity of the processor, to be downloaded from a central computer in the factory. This facility provides for special programmes to be used. The results of these special function programmes are displayed using the standard display features.

The special functions processor can also access the rejection facilities.

Batch sampling permits the selected number of cigarettes to be ejected. These cigarettes can either be equally spaced from a given population or alternatively selected at pseudorandom intervals throughout the population. The standard deviation mean weight and skew of the selected sample is calculated and displayed if required. The ejection can be inhibited if required.

Zone sampling provides the facility for ejecting all cigarettes which lie within a given weight zone. This is particularly useful for checking rejector setting and reliability.

A histogram of weight distribution covering 127 milligrams each side of the formula weight can be generated and displayed on an external device such as an oscillograph or X-Y plotter. Standard deviation of the histogram population is calculated and its mean weight and skew determined. The size of the population may be specified, providing it is limited to avoid any segment of the histogram containing more than 256 cigarettes. This generally allows for populations up to about 15,000 cigarettes.

The average profile of a batch of 64 cigarettes can be generated and displayed in a similar fashion to the histogram. This gives a quantitiative picture of the densing of the ends of the cigarettes and also indicates the way in which the densing is distributed into the rod.

Fig. 2 shows a vertical cross-section through the rod-guiding part of a nucleonic scanning device which comprises a block 20 having a bore 22 with a fixed internal sleeve 24 defining the path of the rod. The sleeve 24 is formed with a window 26 to allow the passage of beta-rays from a source (not shown) on one side of the rod, to an ionisation chamber detector (not shown) on the other side of the rod. In use it will be understood that the signal from the detector is fed to the "weight analysis" processor 6 of Fig.

1, and processed as explained above with reference to that figure.

A removable guide 28 is mounted in the sleeve 24 and is retained in position by a ring-shaped permanent magnet 30 set in a counterbore 32 in the block 20. A screw (not shown) may alternatively be used. The guide is formed with a funnel-like entrance portion 34 whose rear surface contacts the magnet, and the internal surface of the guide is relieved as shown at 36, so that there is a minimum area of contact between the rod and the guide. The guide terminates immediately upstream of the scanning station 26, its end being cut-off at 45 for reasons to be explained below, and an aperture 38 is formed in its extreme end and communicates with a suction source via a conduit 40, so as to hold the rod firmly in position, in use.

Pressure air is supplied to grooves (not shown) in the external surface of the guide member 28 via ports 42, the grooves being cut so as to pass around the aperture 38 and terminate at the base of the end of the guide, to scavenge debris from the scanning station 26. As can be seen from the drawing, the 45 cut at the end of the guide is so oriented that the upper side of the rod, where the wrapper is pasted, emerges from the guide well before the lower side. This helps to prevent any streamers of paste entering the scanning station.

At the exit from the scanner an additional adjustable guide device 44 is arranged to provide further support and positioning for the rod. This guide comprises a sleeve 46 upon which is mounted a split clamp member 48 carrying a rotatable cam-shaped support device 50. The cam 50 is mounted below the path of the rod at right angles to it and is so arranged that by rotating it in its bore in the clamp 48, it can be made to project a variable distance into the internal bore of the sleeve 46. In this way it can be adjusted to provide a supporting surface for the rod at a suitable height for a particular rod diameter, it being understood that it will generally also be necessary to interchange the guide member 28 for different rod diameters. The cam is then retained in the adjusted position by tightening the screw 52 of the clamp member 48.

Fig. 3 shows a timer arrangement for measuring the speed of a cigarette-making machine by measuring the time taken to make each cigarette. This arrangement comprises a first timer/counter 102 which receives clock pulses from a clock pulse timer 104, at 1.024 MHz, and which also receives "end of cigarette" pulses (Fig. 4b) corresponding to the expected position of each cut of the continuous rod (Fig. 4a) from a line 106. When the end-of cigarette pulse is received by counter 102 it generates a delay pulse which is equal to a predetermined number ("a") of clock pulses, as shown in Fig. 4(d), and this pulse is fed to a second timer 108 which also receives clock pulses from line 104. The second counter counts the number of pulses "x" occurring between the end of the delay and the next ECP, and the microprocessor adds (a + x) to give the total time taken to make a cigarette.The delay period "a" is inserted to allow time for the microprocessor to access counter 108 to read the total "x" for the last cigarette, which of course remains fixed whilst counter 102 is measuring the initial delay period "a" for the next cigarette. This measurement of machine speed, in terms of time per unit length of rod, can be used, in conjunction with a count of ''weight frequency" pulses, to determine the weight of any particular length of rod. The "weight frequency" pulses are generated by feeding the signal from the detector of a nucleonic rod weight scanner, which is an analogue voltage, into a voltage-to4requency converter.Since the detector "sees" more radiation from the radiation source when the rod is less dense, the output frequency is inversely related to rod weight so that the weight per unit time can be derived from the number of pulse counts per unit time. Multiplications of this result by the time per unit length gives the weight per unit length.

Fig. 5 shows a counter arrangement for detecting regions of low density ("voids") in the continuous rod. The "weight frequency" signal is fed to a timer acting as a dividing circuit 110 which divides by 32, so as to give an averaging effect, and so that its output appears as shown in Fig. 6(a). The region A, where the pulse frequency is high, indicates the presence of a "void". The output of the divider is fed to a second timer 112 which also receives the stream of clock pulses at 1.024 MHz (Fig. 6b) on line 116 and which times the intervals between the input pulses from the divider, and produces an output pulse only if the intervals are longer than a preset number of clock pulses.If the intervals are shorter than the preset number of clock pulses, the timer is "re-triggered" before it can produce an output pulse and thus no pulse is produced for the period of the void, as can be seen from the waveform of Fig.

6(c). Since an indication of a void is only required if the length of the void is greater than a preset length, the pulse output of timer 11 2 is applied to a further timer 114 which produces an output pulse only if the period between the pulses from timer 112 is greater than a preset period, giving rise to the waveform of Fig. 6d. This causes a "microprocessor interrupt" to occur to signal the presence of a void.

An analogous arrangement is shown in Fig.

7 for the detection of "lumps" (regions of rod which are denser than a prescribed limit), and the corresponding timer waveforms are shown in Fig. 8. The averaged weight signal (i.e.

divided by 32) is shown in Fig. 8a, the region B comprising a "lump" (weight frequency pulses widely spaced). This signal is fed to timer 118 which compares the pulse intervals with a specified number of clock pulses and produces output pulses as shown in Fig. 8b, for the parts of the rod where the pulse frequency is below a specified level as before.

It will be noted that in the waveform 8b pulses occur for the period of the "lump" (instead of appearing for the normal weight portions as in the case of void detection). The output of timer 11 8 is applied to a further retriggerable timer 120 to determine whether the detected region of high density is of sufficient length to be indicated as a "lump", giving rise to the output of Fig. 8c which is a stream of pulses having a gap representing the lump (if it is above the threshold length).

To produce pulses during the period of the "lump" these pulses are applied to a further timer 122 which produces an output only when the period between the pulses of Fig.

8c occur at intervals greater than a prescribed number of clock pulses-that is to say timer 122 is an additional stage which acts purely to "invert" the signal of Fig. 8c from "pulse" to "no pulse" and vice-versa. The output of timer 122 can thus be used as a "microprocessor interrupt" signal.

Fig. 9 shows a timer arrangement for detection of "densed-ends" in a continuous cigarette rod, i.e. regions which are intentionally of greater density at the intended position of the junction between adjacent cigarette lengths, so that the ends will be firm. The rod is shown diagrammatically in Fig. 1 ova, the intended cut positions being indicated at 12lib and the densed region being indicated by the shaded area 126. The densed-end position detection circuit is intended to indicate the position of the densed regions relative to the cut position, which is signalled by the "endof-cigarette" (E.C.P.) pulse (Fig. 10b). The E.C.P. is used to trigger a delay timer 128 (Fig. 9), at the beginning of a sequence of a predetermined number of cigarette lengths.

The delay ("b", Fig. 10c) is initially set to an arbitrary length equivalent to less than the time to produce one cigarette, after which a sample gate timer 130 is triggered. This produces three consecutive negative-going output pulses (Fig. 1 Od) each equal in length to the time for one-third of a cigarette, separated by equal time periods. These pulses are inverted by inverter 132 and the inverted signal (1 0e) is used to gate the weight frequency signal (10f), on line 134, by means of a further timer stage 136. The process is repeated a number of times with the same delay period and the total pulse counts for the first, second, and third samples respectively are computed by the microprocessor and them compared with each other. The lowest density sample (i.e. the one with the highest pulse count) is rejected since this obviously represents a region which is away from the densed end. The whole process is then repeated a number of times but with the initial delay altered (as shown as "c" in Fig. 10) each time by an amount which tends to make the two higher density (i.e. non-rejected) regions more nearly equal, until they are in fact equal, so that they are equi-spaced about a position midway between the densed end. The densed end position, expressed as a percentage of cigarette length, is then equal to (delay~1 /3 ECP time) x 100, and can accordingly be computed by the microprocessor.

Claims (34)

1. A method of measuring the weight of a section of cigarette rod or cigarette filter rod which method comprises: using a rod weight sensing device to generate an analogue output signal, supplying the analogue signal to a voltage to frequency converter, monitoring the frequency of the output pulses from the converter and processing the monitored frequency data in a rnicroprocessor to provide a signal representing the weight per unit length of the rod.

2. A method according to claim 1 comprising counting the output pulses from the voltage to frequency converter over an interval corresponding to the length of the section of rod being measured.

3. A method according to claim 2 comprising supplying signals indicative of rod making machine speed and rod section length to the microprocessor and producing a signal representing the total number of counts per unit length of the rod.

4. A method according to claim 1, 2 or 3 fo measuring the weight of a sample length of cigarette rod comprising: supplying a trigger signal synchronised with the rod cut-off device to a counter which is arranged to then start counting the output pulses from the converter; and supplying a second trigger signal to the counter at the next operation of the cut-off device to stop the counter at a count related to the weight of the sample length.

5. A method as claimed in claim 1, 2, 3 or 4 in which the time taken for the rod making machine to make a sample length of rod is counted by the microprocessor.

6. A method as claimed in claim 5 including the steps of generating clock pulses of known fixed frequency, generating a signal synchronised with the rod cut-off at the beginning of the sample length, generating a delay signal starting at the instant of cut-off, the length of the delay being a known number of clock pulses, starting to count the clock pulses at the end of the delay, stopping the count at the instant of the next cut-off, reading the count into a microprocessor during the succeeding delay period and adding the number of clock pulses in the delay period to the number of clock pulses counted to provide a measurement of the total length of time taken to make the sample length.

7. A method according to any one of claims 1 to 6 for detecting, in a continuous rod produced by a continuous rod making machine, regions in which the density is below or above a defined limit for more than a defined length, which method comprises dividing the output of the voltage to frequency converter by a constant factor, and applying the resultant signal to a re-triggerable counter which is arranged to count clock pulses and to produce an output signal if it is not retriggered before it has counted a predetermined number of clock pulses.

8. A method as claimed in claim 7 wherein said predetermined number is preset to correspond to a desired low density threshold so that an output signal is produced for all regions having a density higher than said low density threshold, and no output signal from the counter is produced for a region having a density lower than said threshold.

9. A method as claimed in claim 7 wherein said predetermined number is preset to correspond to a desired high density threshold so that an output signal is produced for a region of density higher than said high density threshold but no output signal is produced for a region of lower density than said high threshold.

10. A method, as claimed in any one of the preceding claims, for detecting the position of densed-ends in a continuous cigarette rod, comprising: notionally selecting a series of discrete regions within the rod, starting from a predetermined starting-point, these regions being of substantially equal lengths and being substantially equi-spaced from each other, and being positioned so that a rod cutoff point will occur within the total length of the series; counting the number of output pulses from the converter occurring within each region; selecting the two regions having the greatest weight; shifting the position of the starting-point of the whole series until the two selected regions are of equal weight so that they are then equally positioned about the point of maximum densing; and computing the position of this point relative to said cut-off point.

11. A method as claimed in claim 10 wherein the number of said regions is three, each region is equal to one-third of a cigarette length, and the regions are spaced one from an adjacent one by one-third of a cigarette length.

1 2. A method as claimed in claim 10 or 11 comprising measuring over a period corresponding to three cigarette lengths.

13. A method as claimed in claim 12 comprising repeating said measuring a plurality of times and adding the resultant measurements.

14. A method as claimed in any one of claims 10 to 13 wherein the starting-point is determined as the end-point of a variable delay synchronised with the rod cut-off.

15. A method substantially as herein before described with reference to Figs. 3 and 4 or Figs. 5, 6, 7 and 8 or Figs. 9 and 10 of the accompanying drawings.

1 6. Apparatus for measuring the weight of a section of cigarette rod or cigarette filter rod, comprising a rod weight sensing device arranged to supply an analogue output signal to a voltage to frequency converter, means for monitoring the output from the converter and means for processing the monitored frequency data to provide a signal representing the weight per unit length of the rod.

17. Apparatus according to claim 16 comprising a counter arranged to count output pulses from the voltage to frequency converter.

18. Apparatus according to claim 17 comprising means for supplying a trigger signal synchronised with the rod cut-off device to said counter so that the counter counts converter output pulses between rod cut-off points and reaches a count related to the weight of a sample length of rod.

1 9. Apparatus according to any one of claims 16 to 18 comprising means for dividing the converter output by a constant factor, a re-triggerable counter arranged to count clock pulses and to be re-triggered by the divided converter output pulses and to pro duce an output signal if it is not re-triggered before it has counted a predetermined number of clock pulses.

20. A control system for a continuous rod cigarette making machine comprising: means for sensing the quantity of tobacco in the rod; a first set of lower level microprocessors each of which is arranged to monitor a specified set of operating characteristics of the machine, including the signal from the sensing means, and to produce related control signals; and an upper level microprocessor which is arranged to coordinate and control the intercommunication of the set of the lower level microprocessors and to receive information from them to activate an information display means.

21. A control system as claimed in claim 20 wherein said upper level microprocessor is arranged to operate a periodic polling system to control the transfer of information to and from the lower level microprocessors.

22. A control system as claimed in claim 20 or claim 21 wherein said lower level microprocessors are arranged to provide any one or more of the following functions: monitor and control the rod weight; calculate target rod weights to achieve desired economy goals; detect and indicate the position of densed ends; and calculate standard deviation of cigarette weight.

23. A control system according to any one of claims 20 to 22 wherein said sensing means comprises a nucleonic source positioned on one side of a rod guiding device and a nucleonic detector for the radiation beam positioned on the opposite side of the rod guiding device.

24. A control system as claimed in claim 23 wherein a suction port communicating with the interior of the rod guiding device upstream of the nucleonic source and detector is provided to restrain the rod against fluttering about its axial path.

25. A control system as claimed in claim 23 or claim 24 wherein an adjustable guide is provided downstream of the nucleonic source and detector which guide comprises a support whose height is adjustable for different rod diameters.

26. A control system as claimed in any one of claims 23 to 25 wherein said guiding device comprises a removably mounted pass tube immediately upstream of the nucleonic source and detector, the downstream end of the tube sloping in such a way that the upper part of a cigarette rod passing through the pass tube will emerge from the tube before the lower end.

27. A control system for a continuous rod cigarette making machine substantially as herein before described with reference to Fig.

1 and with reference to Figs. 1 and 2 of the accompanying drawings.

28. A nucleonic scanner for a rod cigarette making machine comprising a nucleonic source, a nucleonic detector and processing means arranged to average the results of several successive scanning tests with no rod cigarette between the source and detector and to compare the average with a reference to obtain an indication of source decay so that such decay can be compensated.

29. A nucleonic scanner as claimed in claim 28 wherein said processing means is programmed to take account of ambient tem perature variations in compensating for source decay.

30. A rod cigarette making machine com prising a control system as claimed in any one of claims 20 to 27 in combination with a nucleonic scanner as claimed in claim 28 or claim 29.

31. Apparatus according to any one of claims 16 to 19 substantially as herein before described with reference to Fig. 1, Fig. 2 or Figs. 3 to 10 of the accompanying drawings.

32. Apparatus according to any one of claims 16 to 19 or claim 31 when operated by the method of any one of claims 1 to 15.

33. Apparatus according to any one of claims 16 to 19 or claim 31 or claim 32 in combination with a control system according to any one of claims 20 to 27 and/or in combination with a nucleonic scanner accord ing to claim 28 or claim 29.

34. The subject matter of any preceding claim (ignoring any dependency of one claim on another) considered separately or in combi nation with the subject matter of any one or more of the other claims (again ignoring de pendency).