Optical inspection apparatus

Abstract

The invention is concerned with an optical inspection apparatus for monitoring a continuously moving rod, such as a tobacco rod. The apparatus comprises a circular head through which the rod passes, a first set of fibre optic conductors the ends of which terminate at an inner peripheral surface of the head and which transmits light from a source to the head to illuminate the rod passing through the head, and a second set of fibre optic conductors the ends of which also terminate at an inner surface of the head to pick up light reflected from the rod passing through the head and transmit that light to a photosensitive element. The second set of conductors are divided into angularly spaced groups around the head and adjacent groups lead to separate photosensitive elements. Preferably the light picked up by diametrically opposite pairs of groups are combined.

Description

The invention is concerned with optical inspection apparatus for monitoring a continuously moving rod, for example a cigarette rod, and for sensing critical variations in the reflective properties of the rod surface for example of a flaw in, or printing on, the surface. In a cigarette rod such a flaw may be produced by an imperfect lap seal of the wrapper or a tear in the paper produced by a particularly hard piece of tobacco stem.

Conventionally, cigarette inspection apparatus involves means for measuring the pressure drop caused by leaks in the surface of the cigarette assembly when air suction or pressure is applied. Methods have also been proposed for inspection by illuminating the rod and detecting the reflected light on a number of photoelectric cells. However, none of these are entirely satisfactory for high speed production.

In accordance with the present invention, an optical inspection device for monitoring a continuously moving rod comprises a circular head through which the rod passes, a first set of fibre optic conductors the ends of which terminate at an inner peripheral surface of the head and which transmit light from a source to the head to illuminate the rod passing through the head, and a second set of fibre optic conductors the ends of which also terminate at an inner peripheral surface of the head to pick up light reflected from the rod passing through the head and transmit that light to a photosensitive element, characterised in that the second set of conductors are divided into angularly spaced groups around the head and adjacent groups lead to separate photosensitive elements to a common comparator circuit 30 via positive diodes 32p and negative diodes 32n which permit only the largest positive and negative signals in the channels to be applied to the corresponding comparator C+ C-.

FIG. 5 illustrates the y-guide characteristic of the reflected light in the head picked up by the light guides 21. The axis A represents the reflected light picked up and the axis B represents the distance d of the rod surface from the inner peripheral surface of the circular head. The portions marked off on the graph represent variations Δd in this distance owing to lateral deviations in the rod relatively to the head. These values will be apparent from FIG. 6 which shows a cigarette rod 31 passing through the head 14. At one position a distance d1 is apparent and at the diametrically opposite position a distance d2. Provided that the distance d is in the substantially straight downward sloping portion of the graph in FIG. 5, the sum of the light picked up by the diametrically opposite guides 21 will be substantially constant irrespective of whether d1 and d2 are equal.

The electrical signal level produced by the phototransistor 23 will be positive or negative and substantially proportional to the difference between the light level picked up by the corresponding pair of guides 21 and a datum level. These positive or negative electrical signals will after amplification all be fed into to the comparator circuit 30, positive pulses from the channel with the most positive signal level passing into comparator C+ and negative pulses from the channel with the most negative signal level into comparator C-. If the signal level is in absolute terms (i.e. irrespective of polarity) greater than a preset allowable level, representing the allowable tolerance in the reflectivity of the rod, and hence a faulty rod portion, fixed amplitude positive going fault pulses are produced at the outputs of the comparators and are combined to produce fault pulses through a logical OR gate G.

The appearance of a fault signal at the gate G sets a first bistable flip-flop B1. The fault signal is transferred to a second bistable flip-flop B2 upon reception of the first subsequent clock pulse P1 through a monostable circuit M1, the clock pulse immediately resetting the first bistable B1 through a second monostable circuit M2. The fault signal is transmitted from the bistable B2 to a third bistable flip-flop B3 upon reception of the next succeeding clock pulse P2 through a third monostable circuit M3.

Immediately afterwards the clock pulse P2 resets the bistable B2 through a fourth monostable circuit M4.

The sequence of operation controlled by the clock pulses P1 and P2 will be apparent from FIG. 4. At the top of FIG. 4 there is indicated diagrammatically the cigarette rod 31 having consecutive rod portions corresponding to cigarettes L1, L2, L3 and L4 passing from right to left successively through the optical inspection apparatus 13 and the nucleonic apparatus 10. The lower part of FIG. 4 represents the various pulse trains to a common time scale.

The separation of the sensing points of the two monitoring apparatus 13 and 10 is indicated as y and the distance x is the distance by which y exceeds one cigarette length. Both the clock pulses P1 and P2 have a period equal to the time it takes for one cigarette length to pass a fixed point. The leading edge of each pulse P2 corresponds to the time that a cut point between adjacent rod portions of the continuous cigarette rod passes the sensing point of the nucleonic apparatus 10 and the leading edge of each pulse P1 is displaced from the corresponding pulse P2 by a time corresponding to the distance y.

FIG. 4 is prepared to represent a case in which a fault signal is produced in the length L1 of the rod by the optical inspection apparatus 13. Thus the fault pulse F is generated and immediately sets the bistable B1. At the next pulse P1 the fault is transmitted to the bistable B2 and at the next pulse P2 the fault signal is transmitted to the bistable B3. It will be seen that the triggering pulse produced by the monostable M3 corresponds with the clock pulse P2 and is immediately followed by the resetting pulse produced by the monostable M4. Similarly, the triggering pulse produced by the monostable M1 coincides with the clock pulse P1 and is immediately followed by the resetting pulse produced by the monostable M2.

The pulses produced by the monostable pulse generators M1, M2, M3 and M4 are very short, for example of the order of 1 microsecond compared with the time interval of a passage of 1 cigarette length which is typically 15 milliseconds or longer.

The effect of the logic circuitry is that the fault signal is delayed in the bistables B1 and B2 whilst the corresponding rod portion in which the fault has been sensed has just completed its passage through the nucleonic apparatus 10. The fault signal is then brought into synchronism with the potential fault signal produced by the nucleonic apparatus 10 so that both potential signals can be stored in a memory store of the apparatus 10 whilst the corresponding rod portion passes to and is cut by the knife 11 prior to deflection by the air jet.

Claims

1. An optical inspection appratus apparatus for monitoring a continuously moving rod, said apparatus comprising a circular head through which said rod passes, a first set of fibre optic conductors the ends of which terminated terminate at an inner peripheral surface of said head and which transmits light from a source to said head to illuminate said rod passing therethrough, and a second set of fibre optic conductors the ends of which also terminate at said inner peripheral surface of said head to pick up light reflected from said rod passing through said head and transmit said reflected light to a photosensitive element , means producing output signals responsive to said light, said second set of conductors being divided into angularly spaced groups around said head and adjacent groups leading to separate photosensitive elements element means, and comparator means coupled to said photosensitive element means for separately receiving the output signals of said photosensitive element means, for comparing the separate output signals of said photosensitive element means with a datum level and for providing a fault signal responsive to said comparison.

2. Apparatus according to claim 1, wherein said ends of said first set of fibre optic conductors terminate in a first annular array at said inner perpheral surface of said head, and said ends of said second set of fibre optic conductors terminate in a second annular array which is axially displaced from said first array at said inner peripheral surface of said head.

3. Apparatus according to claim 1, wherein said second set of conductors are divided into at least four angularly spaced groups to form at least two pairs of diametrically opposed groups and said light picked up and transmitted away from said head by diametrically opposed pairs of said groups of said pairs are combined either before co-operating with a common photosensitive element of by summation of the outputs of two corresponding photosensitive elements, said photosensitive element or elements forming said photosensitive element means.

4. Apparatus according to claim 3, wherein said photosensitive elements are element means includes photoelectric elements from which are produced first output electrical signals each corresponding to the light received by one of said diametrically opposite pair pairs of groups of said second set of conductors, there being a and wherein in said comparator circuit in which means the level of said first output electrical signals is compared to a said datum level and a fault signal is produced if said first output electrical signals deviate from said datum level by more than a predetermined amount, and wherein said apparatus further includes means for storing said fault signal and means for subsequently providing said stored signal at an output for use in operating a rejection mechanism.

5. Apparatus according to claim 4, wherein said photoelectric elements are phototransistors or photodiodes.

6. Apparatus according to claim 4, wherein each photoelectric element is A.C. coupled to the input of an amplifier the output of which is connected to said comparator circuit means.

7. Apparatus according to claim 4, wherein all said photoelectric elements are connected to a common comparator circuit circuitry of said comparator means.

8. Apparatus according to claim 4, which is arranged to be fitted to a continuous rod cigarette making machine and to be used in series with a different rod monitoring apparatus that is also arranged to provide a signal for operating a rejection mechanism for an unacceptable cigarette, wherein said fault signal store of said optical inspection apparatus comprises a first bistable circuit arranged to be triggered by and to hold any fault signal from said comparator circuit means upon the sensing of a fault in a portion of said rod corresponding to a cigarette length, a second bistable circuit which is set by any faults signal held by said first bistable circuit and is triggered to receive and hold said fault signal by a first clock pulse corresponding to completion of passage of said portion through said optical inspection apparatus, said first clock pulse then resetting said first bistable circuit, and a third bistable circuit adapted to be set by any fault signal held by said second bistable circuit and to be triggered to receive and hold said fault signal by a second clock pulse corresponding to said leading edge of said rod portion beginning it's passage through said other monitoroing monitoring apparatus, said second clock pulse then resetting said second bistable circuit whereby said fault signal is available at the output of said third bistable circuit for use in synchronism with a fault signal from said other monitoring apparatus to operate a rejection mechanism for said cigarette produced by cutting off said rod portion. 9. Apparatus according to claim 1 wherein said comparator means includes signal selection means interposed between said photosensitive element means and said comparator means for providing the largest magnitude output signal from said photosensitive element means for comparison with said datum level.

10. Apparatus according to claim 9 wherein said comparator means comprises common comparator circuitry for all of said photosensitive element means.

11. Apparatus according to claim 9 wherein said signal selection means comprises diode means.