GB2176888A

GB2176888A - Improvements in or relating to x-ray detection apparatus

Info

Publication number: GB2176888A
Application number: GB08515812A
Authority: GB
Inventors: Edwin George Johnson
Original assignee: Goring Kerr PLC
Current assignee: Goring Kerr PLC
Priority date: 1985-06-21
Filing date: 1985-06-21
Publication date: 1987-01-07
Also published as: ES8800433A1; ES556907A0; AU6132086A; GB8515812D0; JPS63500335A; FI870735A; EP0230443A1; FI870735A0; WO1986007638A1

Abstract

In a detector apparatus using x-rays (3), a plurality of light guides (15) each have one end adjacent part of a linear phosphor strip (7). The other ends of the light guides form a circular array. Rotatable means (22) sequentially interrogate the ends of the light guides in circular array and direct light therefrom to a single light sensitive element (24).

Description

SPECIFICATION Improvements in or relating to x-ray detection apparatus The present invention relates to x-ray detection apparatus and more particularly to x-ray detection apparatus suitable for use in quality control procedures, such as in the detection of impurities in food products.

When products such as food are mass-produced the raw materials are delivered to the factory in bulk and are then processed by machines to create the finished food items. From time-to-time impurities are present in the raw materials or in the food items, and the raw materials and the food items must be inspected in some appropriate way so that the raw products or food items containing impurities can be rejected.

It has been proposed to inspect raw materials or food items of this nature by passing them, for example on a conveyor belt, through a vertical downwardly directed fan-shaped beam of x-rays. A linear x-ray detector is located under the conveyor belt, and typically such a detector may comprise a plurality of photo diodes, for example 480 photo diodes, each coated with an x-ray phosphor. In such an arrangement each photo diode must be provided with an individual amplifier, and the outputs of the photo diodes are multiplexed to an appropriate processor adapted to determine whether the item passing through the x-ray beam at any time contains impurities. The processor may operate an appropriate ejector mechanism to eject contaminated raw material or contaminated food items.

Inspection apparatus of this type may be used not only with manufactured products such as loaves of bread, cakes, pots of yoghurt and the like, but may also be utilised to locate the presence of stones and twigs in dried beans, stones in dried peas, and pieces of walnut shell in shelled walnuts, for example.

A problem with the prior art arrangement is that each photo diode has a different response, and thus the apparatus must be calibrated before use.

Also it is expensive to provide a large number of photo diodes each with individual amplifiers, and the multiplexing system that is required is also expensive.

According to one aspect of this invention there is provided a detector apparatus for use in detecting x-rays, said detector comprising a phosphor element, sensitive to x-radiation, a plurality of light guides, each light guide having one end thereof located to receive light emanating from the said phosphor element, the said ends of the light guides being located in a regular linear array, the other ends of said light guides being located in a circular array, rotatable means being provided adjacent the circular array for sequentially interrogating the ends of the light guides in said circular array and directing light therefrom to a single light sensitive element.

Preferably said phosphor element is an elongated strip of phosphor, the said light guides being arranged in a single row extending axially of said strip.

Preferably, said phosphor optic signals from a plurality of points, said apparatus comprising light guides for directing light from said points to a series of positions which constitute a circular array, and rotatable means located adjacent said circular array for sequentially establishing an optical path between each of the said positions which constitute said circular array and a light responsive element.

Preferably said light guides comprise optic fibres.

Conveniently an apertured plate is provided, therebeing means to rotate the aperture plate about an axis passing through the centre of said circular array, the aperture in the apertured plate being coaligned with the ends of the light guides in said circular ray so that light from the light guides can sequentially pass through the aperture, therebeing further light guide means adapted to direct light from said aperture to said light sensitive element.

Preferably the said further light guide means comprise a transparent element having an annular face thereof aligned with the ends of the light guides in said circular array but spaced therefrom by said apertured plate, and having another end thereof in contact with or adjacent the front or inlet face of said light sensitive element.

Advantageously said transparent constitutes an element of transparent material of conical or "funnel" configuration.

Preferably the apertured plate is associated with a further light guide element, one end of which is connected to said aperture and the other end of which is adapted to direct light into the light sensitive device, said further element rotating with said aperture plate.

According to another aspect of this invention there is provided an apparatus for sequentially interrogating optical signals present on a plurality of light guides, said apparatus comprising means to retain the ends of said light guides in a regulator circular array, means adapted sequentially to permit light to pass from each of the light guides to a further light guide arrangement, said further light guide arrangement directing the light to a light sensitive element.

Preferably the light guides are retained in the circular array by being located in an annular element having a plurality of through-going bores adapted to receive the ends of the light guides.

Conveniently the means for sequentially permitting light to pass from the ends of the light guide elements comprises an apertured plate mounted for rotation about an axis which is coincident with the centre of said circular array, the aperture in the plate being so located that as the plate rotates the aperture is sequentially aligned with the ends of said light guides in said circular array.

Advantageously said further light guide arrangement comprises a single element of conical or "funnel" configuration, the element presenting a rim substantially co-aligned with said circular array of light guide elements, and having a narrow end directed towards said light sensitive element.

In order that the present invention may be more readily understood, and so that further features thereof may be appreciated, the invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a diagrammatic perspective view of the essential parts of an apparatus incorporating a sensor in accordance with the invention, with supporting elements and x-ray shielding elements omitted, for the prupose of clarity of illustration; Figure 2 is a partial sectional view through the sensor as shown in Figure 1; and Figure 3 is a perspective view of the structure shown in Figure 2.

Referring to the accompanying drawings Figure 1 illustrates a conveyor belt 1 which is adapted to advance in the direction of the arrow 2. The conveyor belt 1 is adapted to carry raw material or other items intended for inspection.

An x-ray source 3 is mounted in position above the conveyor belt and a masking plate 4 is located immediately beneath the x-ray source 3, the masking plate 4 defining a narrow transverse slip 5 which permits a fan-shaped beam 6 of x-rays to pass from the x-ray source 3 towards the conveyor belt. The fan shaped beam of radiation 6 is vertical and the plane of the beam extends transversely to the direction of travel 2 of the conveyor belt 1.

The conveyor belt is transparent to x-radiation so that the fan-shaped beam 6 can, in normal circumstances, impinge on a strip-like x-ray detector 7 located under the conveyor belt. The detector will be described in more detail hereinafter.

At a position located beyond the detector 7 in the direction of travel 2 of the conveyor belt there is an ejector schematically illustrated at 8. The ejector is adapted to eject from the conveyor belt any contaminated product or material detected by the x-ray detector. Any products not ejected from the conveyor belt by the ejector 8 remain on the conveyor belt for appropriate further packaging or processing etc.

Referring now to Figures 2 and 3 the detector 7 of the present invention is located immediately beneath the conveyor belt 1. The detector consists of a strip 9, which may be of a plastics material, that extends transversely across the conveyor belt 1.

On top of the strip 9 is a layer of phosphor material 10 which is sensitive to x-ray radiation and which thus emits light when excited by x-ray radiation. The phosphor strip is protected by a cover 11 of an appropriate protecting material.

The strip 9 has a plurality of recesses 12 of relatively large diameter formed in the undersurface thereof, each recess 12 communicating with a relatively narrow diameter bore 13 which extends from the recess 12 to the top of the strip 9, that is to say to the undersurface of the phosphor layer 10.

Each recess 12 and associated bore 13 are adapted to receive an end of a optic fibre 14 which is of the same diameter as the bore 13, and which has an opaque outer sheath 15 which has a smaller diameter than the recess 12. The sheath 15 is inserted in the recess and the space between the sheath and the wall of the recess is filled with casting resin.

Thus a plurality of optic fibres 14 are provided which are retained, by the strip 9, with their ends at evenly spaced positions along the phosphor strip 10 which extends tranversely to the direction of travel of the conveyor belt 1. Thus, when the xray source is initially activated the phosphor strip will be evenly irradiated with x-ray radiation and will glow evenly thus providing equal amounts of light to each optic fibre. However, when any items pass between the x-ray source and the detector strip 7 the intensity of light emission of the phosphor strip will be modulated, and thus the intensity of light passing down each optic fibre will be modulated appropriately.

The other ends of the optic fibres 14 are connected to a photo multiplier assembly 16.

The photo multiplier assembly 16 includes an annular optic fibre retaining member 17. On the front face of the annular member 17 are a plurality of evenly spaced recesses 18 of a greater diameter than the outer sheath 15 on each of the optic fibres 14. At the base of each recess 18 is a relatively narrow bore 19, of the same diameter as each optic fibre 14, the bore 19 extending completely through the annular member 17. The ends of the optic fibres 14 are located in the bores 19 with the sheaths 15 located in the recesses 18. The spaces between the sheaths 15 and the recesses 18 are filled with a casting resin. Thus the optic fibres have a uniform linear configuration at one end and a uniform circular configuration at the other end.

A motor 20 is mounted in the centre of the annular member 17, the shaft of the motor being connected to an apertured disc or plate 21 which is located behind the annular member 17, the plate 21 being mounted for rotation in a plane which is parallel to but slightly spaced from the plane of the annular member 17. The disc or plate 21 has a single aperture 22 which is positioned so that, as the disc rotates, the aperture 22 is sequentially coaligned with the through going bores 19. Thus, as the aperture 22 passes each through going bore 19 any light passing down the fibre optic located within the respective through going passage 19 passes through the aperture in the disc. Thus, effectively, the disc serves as a multiplexer which sequentially "interrogates" each of the optic fibres 14.

Located behind the apertured disc 21 is a hollow generally conical or "funnel" shaped element 23 of transparent material such as transparent plastic or glass. The rim of the element 23 surrounding the large open mouth thereof is aligned with the through-going bores 19 in the annular member 17, but is separated therefrom by the apertured disc or plate 21.

The narrow end of the element 23 is in contact with the front or inlet end of a photomultiplier 24, which can be of conventional design.

It is to be appreciated that as the apertured disc 21 rotates each optic fibre 14 is "interrogated" in turn in that, when the aperture 22 in the apertured plate 21 is coaligned with each through-going bore 19 light from the respective fibre optic 14 can pass through the aperture 22, into the element 23 which will serve to guide the light on to the front or input face of the photomultiplier 24. Thus, as the disc 21 completes a single revolution a short pulse of light from each of the optic fibres 14 (assuming that light is passing down all of the optic fibres 14) is sequentially introduced to the element 23 and is thus sequentially introduced to the photo multiplier 24.

The output of the photo multiplier 24 can be fed to any appropriate apparatus adapted to analyse the signals emanating from the photo multiplier or adapted to create and display an image from those signals. If the apparatus analyses the signals it may be adapted to control the ejector 8.

It is envisaged that many modifications may be effected without departing from the scope of the present invention.

For example the element 23 may be replaced by a single light fibre, one end of which is connected to the aperture 22 of the apertured plate 21, the other end of which is located in such a position that light emanating therefrom is directed into the photomultiplier 24. Of course, the light fibre would have to be at supported appropriately for co-rotation with the apertured plate 21.

Whilst a photomultiplier is utilised in the described embodiment of the present invention any appropriate light-sensing element could be utilised provided that the light-sensor produced an electric output signal in response to receipt of light.

It is to be appreciated that, in the preferred embodiments of the invention, it is not necessary to provide a large number of amplifiers, neither is it necessary to provide a multiplexing system.

Claims

1. A detector apparatus for use in detecting xrays, said detector comprising a phosphor element, sensitive to x-radiation, a plurality of light guides, each light guide having one end thereof located to receive light emanating from the said phosphor element, the said ends of the light guides being lo cated in a regular linear array, the other ends of said light guides being located in a circular array, rotatable means being provided adjacent the circu lar array for sequentially interrogating the ends of the light guides in said circular array and directing light therefrom to a single light sensitive element.

2. An appartus according to claim wherein said phosphor element is an elongated strip of phos phor, the said light guides being arranged in a sin gle row extending axially of said strip.

3. An apparatus for repeatedly sequentially sampling optic signals from a plurality of points, said apparatus comprising light guides for direct ing light from said points to a series of positions which constitute a circular array, and rotatable means located adjacent said circular array for sequentially establishing an optical path between each of the said positions which constitute said circular array and a light responsive element.

4. An apparatus according to claim 1 wherein said light guides comprise optic fibres.

5. An apparatus according to any one of the preceding claims wherein an apertured plate is provided, therebeing means to rotate the aperture plate about an axis passing through the centre of said circular array, the aperture in the apertured plate being coaligned with the ends of the light guides in said circular ray so that light from the light guides can sequentially pass through the aperture, therebeing further light guide means adapted to direct light from said aperture to said light sensitive element.

6. An apparatus according to claim 5 wherein the said further light guide means comprise a transparent element having an annular face thereof aligned with the ends of the light guides in said circular array but spaced therefrom by said apertured plate, and having another end thereof in contact with or adjacent the front or inlet face of said light sensitive element.

7. An apparatus detector according to claim 6 wherein said transparent constitutes an element of transparent material of conical or "funnel" configuration.

8. An apparatus according to any one of the preceding claims wherein the light guides are retained in the circular array by being located in an annular element having a plurality of throughgoing bores adapted to receive the ends of the light guides.

8. An apparatus according to claim 5 wherein the apertured plate is associated with a further light guide element, one end of which is connected to said aperture and the other end of which is adapted to direct light into the light sensitive device, said further element rotating with said aperture plate.

9. An apparatus for sequentially interrogating optical signals present on a plurality of light guides, said apparatus comprising means to retain the ends of said light guides in a regulator circular array, means adapted sequentially to permit light to pass from each of the light guides to a further light guide arrangement, said further light guide arrangement directing the light to a light sensitive element.

10. An apparatus according to claim 9 or 10 wherein the light guides are retained in the circular array by being located in an annular element having a plurality of through-going bores adapted to receive the ends of the light guides.

11. An apparatus according to claim 9 or 10 wherein the means for sequentially permitting light to pass from the ends of the light guide elements comprises an apertured plate mounted for rotation about an axis which is coincident with the centre of said circular array, the aperture in the plate being so located that as the plate rotates the aperture is sequentially aligned with the ends of said light guides in said circular array.

12. An apparatus according to any one of claims 9 to 11 wherein said further light guide arrangement comprises a single element of conical or "funnel" configuration, the element presenting a rim substantially co-aligned with said circular array of light guide elements, and having a narrow end directed towards said light sensitive element.

13. An apparatus according to any one of the preceding claims wherein the light sensitive ele ment comprises a photo-multiplier.

14. An apparatus according to any one of the preceding claims and substantially as herein described.

15. Any novel features or combination of features disclosed herein.

Amendments to the claims have been filed, and have the following effect: (a) Claims 3, 4 and 9 to 12 above have been deleted or textually amended.

(b) New or textually amended claims have been filed as follows: (c) Claims 5 to 8, and 13 to 15 above have been re-numbered as 4 to 7 and 9 to 11 and their appendancies corrected.

3. An apparatus according to any one of the preceding claims wherein said light guides comprise optic fibres.