GB2211931A

GB2211931A - Sorting particulate material

Info

Publication number: GB2211931A
Application number: GB8825097A
Authority: GB
Inventors: Neville Eric Brown; David James Hammond
Original assignee: De Beers Industrial Diamond Division Pty Ltd
Current assignee: De Beers Industrial Diamond Division Pty Ltd
Priority date: 1987-11-02
Filing date: 1988-10-26
Publication date: 1989-07-12
Anticipated expiration: 2008-10-26
Also published as: GB2211931B; AU608378B2; GB8825097D0; AU2435788A

Abstract

In a particulate material sorting apparatus, e.g. for sorting diamonds from gangue, light from light-emitting particles 10 is transmitted to a light detection device, such as a PM tube 24, by optical fibres 18. Each fibre 18 views only a small width zone of the stream of particulate material. A motor driven disc 28 with a hole 34 scans the ends of the fibre to determine which fibre transmitted the light. The output of the light detection device controls an ejector (not shown). Filters may be provided in the optical paths. <IMAGE>

Description

"SORTING APPARATUS" BACKGROUND TO TEE INVENTION THIS invention relates to a sorting apparatus.

Most conventional apparatuses for sorting particulate material have a conveyor belt which causes the particles to move successively, usually in free flight, through an excitation zone, a detection zone and an ejection zone. To enable the apparatus to handle a large throughput, the particles are arranged in a wide monolayer on the belt, with a number of particles across the width of the belt.

In the excitation zone, the particles may, for instance, be subjected to X-radiation in a case where diamonds are to be sorted from gangue. Downstream of the excitation zone is a detection zone where a series of photomultiplier (PM) tubes are arranged across the width of the belt to detect luminescence in the particles. Further downstream, a bank of air blast ejectors is arranged. When a luminescing particle is detected at the detection zone, the appropriate ejector is actuated to issue an air blast which deflects the relevant particle out of the main stream.

To ensure that accurate detection and ejection takes place, it is essential that each PM tube and each ejector cover a small area only of the width of the falling stream of particles. If, for instance, the area "seen" by a PM tube is large, an "eject" signal could be issued when any one of a number of particles "seen" by the PM tube is luminescing.

Similarly, if the ejector blasts too large an area, non-luminescing particles could also be ejected.

With continuing research, the sizes of the ejectors have been decreased with the result that they are able these days to cover smaller areas than was hitherto possible. However the cost of small PM tubes has proved to be prohibitive, and the present invention seeks to provide an alternative solution to the detection problem.

SUMMARY OF TEE INVENTION One aspect of the invention provides particulate material sorting apparatus in which light emitted by a particle is transmitted by means of at least one optical fibre for detection by a light detection device.

The apparatus may comprise a plurality of optical fibres for transmitting light emitted from different zones in a stream of particulate material which is to be sorted, one or more photodetectors arranged to receive the transmitted light and means for determining which of the fibres transmitted the light to the photodetector or photodetectors. In one particular embodiment of the invention, the apparatus includes, for each photodetector, a rotatable body located between free ends of the fibres and the photodetector, means for rotating the body and at least one light-transmitting aperture in the body spaced from the axis of rotation, the aperture during rotation of the body passing through successive positions of registry with ends of the fibres and transmitting light through the body. to the photodetector each time it registers with the end of a light-transmitting fibre.

A motor may be provided to rotate the body and processor means which receive signals from the motor and from the photodetector and which analyse such signals and determine which fibre transmitted the detected light and accordingly which width zone of the stream that light was emitted from.

The apparatus may then also include means for actuating downstream separating means for separating from the remainder of the stream a particle or particles occupying the width zone of the stream from which light was emitted.

In one arrangement, a single fibre is provided for each width zone of the stream, while in another arrangment, multiple fibres are provided for each width zone. In the latter case, the fibres are provided with light filters for passing light of different colours.

Either a single bundle of fibres with a single photodetector or a plurality of bundles each with a single photodetector can be provided.

Another aspect of the invention provides a method of sorting particulate material which comprises the step of transmitting light emitted by light-emitting particles through optical fibres to a light detection device.

BRIEF DESCRIPTION OF THE DRAWING The invention will now be described in more detail, by way of example only, with reference to the accompanying drawing which illustrates an apparatus of the invention in diagrammatic fashion, the apparatus being intended for use in sorting diamonds from gangue.

DESCRIPTION OF EMBODIMENTS In the drawing, a wide stream of diamond and gangue particles 10 is illustrated generally with the reference numeral 12. The stream 12 is conveyed on a belt or chute 36. Arranged just above the stream 12 within an enclosure 11 through which the belt or chute passes, is an array of side-by-side lenses 14 each designed to pass light emanating from a small width zone of the stream. Preferably, the width zone will be so small that it can be occupied by a single particle only.

Connected to each lens is one end of an optical fibre 18.

Optical fibre light guides may be provided to connect the lenses to the optical fibres. The fibres 18 are arranged into a bundle within a sheath 20 over the majority of their lengths. The bundle of fibres enters a box 22 in which is located a single PM tube 24 connected to a processing unit 26. The sheath terminates upon entry of the fibre bundle into the box and the fibres are then spread out with their free ends equidistantly spaced in a circular array beneath a disc 28 mounted on a central shaft 30 driven by a motor 32.

The disc 28 has an eccentric aperture 34 which, as the disc rotates, successively registers with the free ends of the fibres. The single PM tube 24 is directed at the upper side of the disc and is able to detect light passing through the aperture irrespective of the position of the aperture.

The operation of the illustrated apparatus is as follows.

Immediately preceding its entry into the enclosure 11, the stream of particles has passed through the excitation zone where it is subjected to incident radiation. Diamond particles in the stream luminesce as a result of this excitation. The light emitted by a luminescing particle is picked up by the relevant lens 14, is then collimated by an appropriate collimator 15, and is transmitted by total internal reflection along the length of the asociated optical fibre 18. At its free end beneath the disc, the light is released from the fibre and is transmitted through the aperture 34 when the aperture registers with that fibre.

The transmitted light is detected by the PM tube 24 which sends an appropriate signal to the processing unit 26.

The processing unit also receives information from the motor and is able to determine, on receipt of a signal from the PM tube 24, the exact position of the aperture 34 when the light was detected. Accordingly, the processing unit is able to determine which fibre 18 transmitted the light and therefore which width zone of the stream 10 the light was emitted from.

The processing unit then sends an actuating signal at the appropriate moment to the appropriate one of a side-by-side array of air blast ejectors (not shown) arranged alongside the stream at a downstream position. Preferably, each ejector will cover the same width zone of the stream as each lens 14 does. When the relevant ejector is actuated by the signal it issues a short duration blast of air which deflects particles in the relevant width zone out of the stream 10 for separate collection.

The major advantage of the illustrated apparatus is the fact that there is a requirement for only one PM tube while it is still possible to determine in which width zone of the stream luminescence took place. In one experimental apparatus constructed by the inventors, there was a total of twenty-one lenses 14 and optical fibres 18, each lens covering a very small width zone only of the stream of particles.

It should be noted that it would be possible to have an even greater number of lenses and fibres, leading to greater accuracy in zone determination. The fibres could, as in the illustrated case, be arranged in a single bundle served by a single PM tube. Alternatively, the fibres could be in different bundles each served by a single PM tube. Even in the latter event, there will still be a relatively small number of PM tubes only.

In the illustrated case, the particles are transported through the enclosure 11 on a conveyor belt 36. In other cases, the particles could be falling in free flight after projection from the end of a conveyor belt. Note also that the invention is not limited in any way to any particular type of separator in the ejection zone. Instead of air blast ejectors, the desired particles could, for instance, be removed from the remainder of the stream by water blasts or by suction means.

Note also that it is within the scope of the invention to use one or more PM tubes for viewing fibres which emanate from the same width zone and which are each fed with a proportion of the light emitted by the particle. This could be achieved, for instance, with the use of a multi-way light splitter associated with the lens 14. In this case, it would be advantageous to use appropriate filters for each fibre. For instance, using the suitable filter, it would be possible to detect diamonds which luminesce in the red part of the visible spectrum and hence to separate those diamonds from other particles.

For security reasons, the optical fibres may be of considerable length. This would enable the particles 10 to be viewed in a security enclosure and for the remaining operations be carried out at an unsecured location.

Claims

CLAIMS:

1.

Particulate material sorting apparatus in which light emitted by a particle is transmitted by means of at least one optical fibre for detection by a light detection device.

2.

Apparatus according to claim 1 comprising a plurality of optical fibres for transmitting light emitted from different zones in a stream of particulate material which is to be sorted, one or more photodetectors arranged to receive the transmitted light and means for determining which of the fibres transmitted the light to the photodetector or photodetectors.

3.

Apparatus according to claim 2 comprising, for each photodetector, a rotatable body located between free ends of the fibres and the photodetector, means for rotating the body and at least one light-transmitting aperture in the body spaced from the axis of rotation, the aperture during rotation of the body passing through successive positions of registry with ends of the fibres and transm.itting light through the body to the photodetector each time it registers with the end of a light-transmitting fibre.

4.

Apparatus according to claim 3 comprising a motor for rotating the body and wherein processor means are provided which receive signals from the motor and from the photodetector and which analyse such signals and determine which fibre transmitted the detected light and accordingly which width zone of the stream that light was emitted from.

5.

Apparatus according to claim 4 comprising means for actuating downstream separating means for separating from the remainder of the stream a particle or particles occupying the width zone of the stream from which light was emitted.

6.

Apparatus according to any one of claims 2 to 5 wherein the fibres are arranged to transmit light emanating from predetermined width zones of the stream of particulate material.

7.

Apparatus according to claim 6 wherein a single fibre is provided for each width zone of the stream.

8.

Apparatus according to claim 6 wherein multiple fibres are provided for each width zone of the stream.

9.

Apparatus according to any preceding claim comprising light filters each for passing light of a different colour.

10.

Apparatus according to any one of claims 2 to 8 comprising lenses and collimators between the fibres and the stream of particulate material.

11.

Apparatus according to any one of claims 2 to 10 comprising a single bundle of fibres whose one ends are spread across the full width of the stream of particulate material, and a single photodetector for receiving light from any fibre in the bundle.

12.

Apparatus according to any one of claims 2 to 10 comprising a plurality of bundles of fibres, and a photodetector for each bundle.

13.

Apparatus according to any one of the preceding claims when used to sort diamonds from gangue.

14.

A method of sorting particulate material which comprises the step of transmitting light emitted by light-emitting particles through optical fibres to a light detection device.

15.

A method according to claim 14 when used to sort diamonds from gangue.

16.

Particulate material sorting apparatus substantially as herein described with reference to and illustrated in the accorppanying drawings.

17.

A method of sorting particulate material substantially as herein described with reference to the accompanying drawing.