GB2060874A

GB2060874A - Cigarette rod optical inspection

Info

Publication number: GB2060874A
Application number: GB8032120A
Authority: GB
Original assignee: Molins Ltd
Current assignee: Mpac Group PLC
Priority date: 1979-10-12
Filing date: 1980-10-06
Publication date: 1981-05-07
Also published as: GB2060874B

Abstract

An inspection device for a continuous cigarette rod comprises a plurality of infra-red emitter-detector units (2) circumferentially spaced around the path of a rod. The light from each unit (2) is focussed onto and collected from a specific area of the rod. Two, or more, axially displaced arrays of units are each arranged to inspect areas of the rod which are staggered in relation to the areas inspected by the other array or arrays. Signals from the units are multiplexed and transmitted to processing circuitry. Instantaneous signals are compared with predetermined values derived for each optical unit as a proportion of the running average of the instantaneous signal. If the instantaneous signal falls below this predetermined value a warning device is operated and the cigarette is ejected. <IMAGE>

Description

SPECIFICATION Cigarette rod optical inspection This invention relates to optical inspection of continuous cigarette rods produced by continuous cigarette making machines or the like. It has previously been proposed to inspect the surface of such rods using an assembly of fibre optic light guides to illuminate the surface of the rod and also to transmit the reflected light back to a transducer or transducers, as shown for example in GB patent specification no. 1135183. The disadvantages of such systems are that they are expensive and require the light guide ends to be fitted very close to the moving rod.

According to the present invention there is provided an inspection device for a continuous cigarette rod comprising means for guiding a continuous cigarette rod through an inspection station at which there are a number of optical units arranged at circumferentially spaced positions around the path of the rod, each optical unit comprising a light emitter and a light detector, the light emitter of each unit being arranged to provide a focussed beam of light directed at a respective area of a rod being inspected, and the light detector of each unit being arranged to receive light from the respective area.

It will be understood that the terms "optical" and "light" as used herein are intended to cover a wider spectrum of electromagnetic wavelengths than just visible light, for example, the units may be infra-red units.

Preferably, the light emitter and detector of each optical unit are packaged as a single unit i.e. an integral part, with a lens in front of each device, so arranged that when the unit is positioned at a suitable distance from the rod, the two devices will both be directed at the same area.

Preferably, output signals from the light detector devices are transmitted from the measuring head to a control unit by means of a multiplexing system, so that a sufficient number of optical units can be arranged around the rod to cover the whole circumference with good resolution, without the necessity for a large number of connections between the head and the measuring circuitry.

According to the invention there is also provided a method of inspecting cigarettes or other continuous rods of the tobacco industry comprising using a plurality of focussed light emitter-detector units spaced circumferentially around a rod being inspected, each unit being arranged to propagate focused light onto a defined surface region of the rod and to receive the light reflected from that surface region and further arranged to generate an electrical signal related to the intensity of the received light, the method including multiplexing the intensity related signals from the various units, transferring the multiplexed signals to a control means, demultiplexing the signals and processing the signal from each unit by continually averaging the signal, comparing the averaged signal with the instantaneous signal from that unit, and generating a fault signal if the instantaneous signal differs from the averaged signals by more than a preset percentage.

One embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a cross-section through an optical inspection device, taken on the line I-I of Fig. 2; Figure 2 is a section on line ll-ll of Fig. 1; Figure 3 is a diagram of a light-source drive circuit and a signal multiplexing circuit; and Figure 4 is a circuit diagram of a demultiplexing and signal processing arrangement.

Referring to Fig. 1, the measuring head of the apparatus comprises a plurality of infra-red sensor units 2 such as the Optron Inc. Type OPB 253A, which each contain a light emitting diode and a phototransistor, positioned behind respective lenses 4 and 6. The lens for the light emitting diode focusses light onto a specific area of a cigarette rod and the lens for the phototransistor collects the light reflected from that area, i.e. "focusses" the reflected light onto the phototransistor. Each unit has a flat casing which is generally wedge-shaped in plan as shown in Fig. 1, with a fixing slot 8 by means of which the unit is fixed in position. The units may be mounted to be readily removable.In the arrangement shown, there are eight units spaced in a circle around the rod, and because of the angle of view seen by each unit, and the shape of the units, it is necessary to arrange a further set of eight units at a position axially displaced from the set shown, which are arranged with their centre-lines offset by 22.5 from those of the first set so that the units of each set inspect areas of rod which are staggered in relation to the areas inspected by the units of the other set, to obtain complete coverage of the surface. More than two sets may be used.

Fig. 2 shows a vertical cross-section through one of the sets of units of Fig. 1, showing the general arrangement for mounting the units relative to the cigarette rod. The units are held within a casing 1 2 having a central aperture 1 4 through which the rod 10 passes, suitable sealing rings 1 6 being located in the joints of the casing and around a glass cylindrical member 1 8 which closes the interior of the casing from the central aperture.

Referring to Fig. 3, the LED's 20 are driven in two banks of eight in series with a d.c.

current source, whilst the photodetectors 22 are all connected in parallel across a 1 SV d.c.

supply. The outputs from the emitters of each group of eight phototransistors are taken to corresponding inputs of respective multiplexers 24, 26 which are driven at a switching speed of 100Khz by a clock generator 28 (Fig. 4) connected to a 4-bit counter 30, via lines 32. The output from each multiplexer is transmitted via a respective amplifier 34 or 36, along lines 3S, 40 to a remotely positioned-measuring circuit, Fig. 4.

The signals received from the two lines 38, 40 at the measuring circuit are applied to respective demultiplexers 42, 44 which are also driven by the lines 32 from the counter 30. Each output 46 corresponding to a respective phototransistor is fed to a network 48 which provides two outputs 50, 52 which are applied to the inputs of a comparator 54. The output 50 of the network is directly proportional to the instantaneous input signal on line 46, whilst the output 52 is averaged. A predetermined value is then determined from this averaged signal for comparison with the instantaneous signal. This predetermined value may, for example, correspond to 85% of the level of a "good" signal.Thus the comparator will give an output if the signal at 50 is less than 85% of the expected signal, and this output will be passed to the "set" input of a latch circuit 56 which will be switched so that it supplies a corresponding output to a respective input of one of a series of four NOR-gates 58 (it will be understood that there is one input corresponding to each phototransistor). The outputs of the NOR-gates are connected to the inputs of a four-input NANDgate 60 whose output will therefore go "LO" in the event of a fault, driving a suitable fault indicator device (not shown) and operating a cigarette ejection facility.

In the example shown the main circuit elements are as follows: Optical sensor units (20, 22): Optron OPB 253A Multiplexers/ demultiplexers (24, 24, 42, 44); Transmission line drivers (34, 36); LM 318 Comparators (54): LM 2901 Latches (56): 4044B Gates (58, 60): 14002, 14501 Counter (30): 1451 6

Claims

1. An inspection device for a continuous cigarette rod comprising means for guiding a continuous cigarette rod through an inspect tion station at which there are a number of optical units arranged at circumferentially spaced positions around the path of the rod, each optical unit comprising a light emitter and a light detector, the light emitter of each unit being arranged to provide a focussed beam of light directed at a respective area of a rod being inspected, and the light detector of each unit being arranged to receive light from the respective area.

2. An inspection device according to claim 1 wherein the light emitter and the light detector of each unit are circumferentially spaced around the path of the rod.

3. An inspection device according to claim 1 or claim 2 wherein each optical unit is formed as an integral part, each unit including a first lens mounted to focus light from the emitter, and a second lens mounted to focus light impinging on the detector.

4. An inspection device according to claim 3 wherein the optical units are wedge shaped and are mounted to taper towards the inspection station.

5. An inspection device according to claim 3 or claim 4 wherein the optical units are arranged in at least two axially spaced circumferential arrays around the path of the rod at the inspection station, the units of each array being arranged to inspect areas of the rod which are staggered in relation to the areas inspected by the units of the other array or arrays.

6. An inspection device according to any one of claims 1 to 5 including a multiplexing system for transferring signals from the detector of each optical unit to a control centre.

7. An inspection device according to any one of claims 1 to 6 including comparator means arranged to sense when the light intensity received by any one of the detectors falls below a predetermined value.

8. An inspection device according to claim 7 including a plurality of comparator means associated with respective optical units, and logic circuitry arranged to produce a signal to operate a cigarette ejection device or a warning device when any one or more of the detectors receives a light intensity below the predetermined value.

9. An inspection device according to claim 7 or claim 8 wherein the output signal of each detector is continually averaged and the predetermined value in relation to that detector is dependent upon the average signal.

10. An inspection device according to any one of the preceding claims wherein the light emitters and detectors are infra-red devices.

11. An inspection device according to any one of the preceding claims wherein the means for guiding a cigarette rod is a transparent tube.

1 2. An inspection device substantially as hereinbefore described with reference to the accompanying drawings.

1 3. A method of inspecting cigarettes or other continuous rods of the tobacco industry comprising using a plurality of focussed light emitter-detector units spaced ciicumferentially around a rod being inspected, each unit being arranged to propagate focused light onto a defined surface region of the rod and to receive the light reflected from that surface region and further arranged to generate an electrical signal related to the intensity of the received light, the method including multiplexing the intensity related signals from the various units, transferring the multiplexed signals to a control means, demultiplexing the signals and processing the signal from each unit by continually averaging the signal, comparing the averaged signal with the instantaneous signal from that unit, and generating a fault signal if the instantaneous signal differs from the averaged signal by more than a preset percentage.

14. A method substantially as hereinbefore described with reference to the accompanying drawings.

1 5. The subject matter of any preceding claim (ignoring any dependency of one claim on another) considered separately or in combination with the subject matter of any one or more of the other claims (again ignoring dependency).