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.

We claim: 
     
       1. An optical inspection .[.appratus.]. .Iadd.apparatus .Iaddend.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.]. .Iadd.terminate .Iaddend.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 .[.,.]. .Iadd.means producing output signals responsive to said light, .Iaddend.said second set of conductors being divided into angularly spaced groups around said head and adjacent groups leading to separate photosensitive .[.elements.]. .Iadd.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 .Iadd.to form at least two pairs of diametrically opposed groups .Iaddend.and said light picked up and transmitted away from said head by diametrically opposed .[.pairs of said.]. groups .Iadd.of said pairs .Iaddend.are combined either before co-operating with a common photosensitive element of by summation of the outputs of two corresponding photosensitive elements, .Iadd.said photosensitive element or elements forming said photosensitive element means. .Iaddend. 
     
     
       4. Apparatus according to claim 3, wherein said photosensitive .[.elements are.]. .Iadd.element means includes .Iaddend.photoelectric elements from which are produced .[.first.]. .Iadd.output .Iaddend.electrical signals each corresponding to the light received by one of said diametrically opposite .[.pair.]. .Iadd.pairs .Iaddend.of groups of said second set of conductors, .[.there being a.]. .Iadd.and wherein in said .Iaddend.comparator .[.circuit in which.]. .Iadd.means .Iaddend.the level of said .[.first.]. .Iadd.output .Iaddend.electrical signals is compared to .[.a.]. .Iadd.said .Iaddend.datum level and a fault signal is produced if said .[.first.]. .Iadd.output .Iaddend.electrical signals deviate from said datum level by more than a predetermined amount, .Iadd.and wherein said apparatus further includes .Iaddend.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.]. .Iadd.means. .Iaddend. 
     
     
       7. Apparatus according to claim 4, wherein all said photoelectric elements are connected to .[.a.]. common comparator .[.circuit.]. .Iadd.circuitry of said comparator means. .Iaddend. 
     
     
       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.]. .Iadd.means .Iaddend.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.]. .Iadd.monitoring .Iaddend.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. .Iadd. 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. .Iaddend..Iadd. 10. Apparatus according to claim 9 wherein said comparator means comprises common comparator circuitry for all of said photosensitive element means. .Iaddend..Iadd. 11. Apparatus according to claim 9 wherein said signal selection means comprises diode means. .Iaddend.