AU632092B2

AU632092B2 - Multichannel sorting apparatus

Info

Publication number: AU632092B2
Application number: AU50000/90A
Authority: AU
Inventors: Barry John Downing; Sean Russell Mercer; Lee Nordin; John David Salter
Original assignee: De Beers Industrial Diamond Division Pty Ltd
Current assignee: De Beers Industrial Diamond Division Pty Ltd
Priority date: 1989-02-20
Filing date: 1990-02-20
Publication date: 1992-12-17
Anticipated expiration: 2010-02-20
Also published as: GB2230099B; GB9003824D0; GB2230099A; AU5000090A

Description

632092 COMMONWEALTH OF AUSTRALIA PATENTS ACT 19S2 COMPLETE SPECIFICATION NAME ADDRESS OF APPLICANT: 00'0t O 0 00~00 0 0 0000 o 0 00.00 0000 o 4 Otto 0 44 De Beers Industrial Diamond Division (Proprietary)Limited 45 Main Street Johannesburg Transvaal Republic of South Africa NAME(S) OF INVENTOR(S): Barry John DOWNING Sean Russel MERCER John David SALTER ADDRESS FOR SERVICE: DAVIES COLLISON Patent Attorneys I Little Collins Street, Melbourne, 3000.

COMPLETE SPECIFICATION FOR THE INVENTION ENTITLED: LA CLc- Y'-c 04'( O 4 4400 0604 O 06 40 0 04 4 4 4 04 0404 4 4 4444 "IThe following statement is a full description of this invention, including the best method t O of performing it known to me/us:- 50000/90' ii

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0 I: 4 044' 4 4' 4 4 14I 2 BACKGROUND TO THE INVENTION THIS invention relates to an apparatus aIImechz4, for sorting particulate material.

It is known that a cavity or chamber of predetermined dimensions will have a certain resonant frequency when electromagnetic signals within a specified frequency range are applied to it. If a particle of material enters the space enclosed by the chamber, the presence of the particle in the chamber will result in a change in the resonant frequency and also in the amplitude of the signal transmitted by the chamber at resonance. The change in resonant frequency may be attributed to a change in the dielectric constant of the space as a result of the presence of the particle while the change in amplitude may be attributed to the electrical loss characteristic of the particle. The electrical loss characteristic is referred to in the art as the loss tangent or tan delta.

The present invention proposes to use this phenomenon in o m- I ada apparatus for sorting particulate materials, such as ores.

-1351 I -3- SUMMARY OF THE INVENTION According to the invention, there is provided a multichannel sorting apparatus for sorting particles into fractions on the basis of dielectric constant or less tangent, the apparatus comprising: a plurality of resonant cavities each of which is split to have spaced apart portions; means for passing a plurality of parallel streams of the particles through the cavities, one stream per cavity; means for subjecting each cavity to a different swept frequency range of electromagnetic radiation; means for detecting and analysing the signals i 15 transmitted by each cavity; and means for separating the particles in each stream into fractions on the basis of detected changes, due to the presence of the particles of the stream in the respective cavity, in the resonant frequency of the cavity and/or in the amplitude of the transmitted signal at resonance.

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4 The means for passing the particles through the or each split cavity may be a conveyor belt which passes through a gap between the portions of the cavity. Alternatively,.

means may be feed means for causing the particles to fall under gravity through such gap or gaps.

pQss In the multi-channel sorter, which uses a conveyor totgar the particles between the portions of the cavities, the cavities are preferably arranged side-by-side across the width of the conveyor, which will typically be a conveyor belt, and are so arranged that one stream of particles passes through each of the cavities, the particles being spaced apart in each stream so that a single particle only is present in a cavity at a time. Suitable channel dividers may be provided between the cavities to shield them one from the other. Furthermore, one portion of each cavity, usually an upper portion disposed above the conveyor, WLa have side walls of which the edges are in close proximity to the belt, the height of the side walls being sufficient to permit passage of the particles on the conveyor. A further refinement is the incorporation of steel or other suitable 6o conductive strips in the conveyor belt at positions it .corresponding to the edges of the side walls of the upper portion of the cavity.

4 0 0 0 sorting particulate material into fractions, method comprising the steps of passing the part s in a stream S° between separate portions of a onant split cavity, subjecting the cavity to s swept frequency range of electromagnetic radia while each particle is inside the cavity, detect* and analysing the signals transmitted by the ca and separating the particles into fractions on f -i"us- BRIEF DESCRIPTION OF THE DRAWINGS One embodiment of apparatus in accordance with the invention will now be described in more detail, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows a diagrammatic plan view of the apparatus; and Figure 2 shows a diagrammatic elevation view of the same apparatus, looking in the direction in which the conveyor belt moves.

SPECIFIC DESCRIPTION Figure 1 shows a conveyor belt 10 which conveys particles 12 in a series of parallel streams 14 in the direction 16. The particles in each stream are spaced apart from one another as illustrated. Conventional particle handling equipment may be used to arrange the particles into streams with the desired spacing between the particles in each stream.

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r r rt r Iri r is I r 920827,phhspe.026,50000-90.spe,5 NT 4x -6 Each stream of particles passes centrally through a resonant cavity 18 which is of split construction. As seen in Figure 2, each cavity has an upper transmitter portion 20 to which a transmission line structure 22 is connected, and a lower receiver portion 24 to which a receiver line structure 26 is connected. The belt 10 passes between the portions and 24 which are totally separate from one another. It will be noted that the upper portion 20 has side walls 28 of which the lower edges are very close to the upper surface of the belt 10. The structures 22 and 26 may be conventional wave guide antennae, the portions 90 and 24 and the wave guide antennae being dimensioned according to well-known microwave principles. Each structure 22 is connected to a microwave generator 30 and the signals transmitted by the cavity 18 and detected by the structures 26 are fed to a microprocessor 32 which also controls the operation of the microwave generators.

The microwave generator in each case continuously subjects each cavity to a swept frequency range of microwave radiation. The signals transmitted by the cavity and detected by the structure 26 are analysed by the microprocesser 32. The microprocessor compares the resonant frequency of the cavity, with the particle inside, i.e.

between the upper and lower portions 20 and 24, with the known resonant frequency with no particle inside and makes a decision as to whether any detected change in such freqency is indicative of the presence of a desired particle.

Alternatively, the comparison may be between signal amplitude at resonance with the particle present and with no particle present, the microprocessor once again deciding whether any change in such signal amplitude at resonance is due to the presence of a desired particle. A still further alternative would be for both such comparisons to be made.

7 Instead of comparing the detected resonant frequency and/or signal amplitude at resonance with the corresponding value for no particle present, the detected value or values may be compared with corresponding values previously determined with a known particle present in the resonant cavity 18.

Irrespective of which comparison is made, the microprocessor, on deciding that a desired particle is present, activates a downstream separation device to remove that particle from its stream. For instance, at a position downstream of the cavities 18, the belt may pass over a head pulley with the result that the particles, after passage through the cavities, are projected in free flight. Having decided that a desired particle is present, the microprocessor activates the appropriate one of a bank of fluid blast ejectors which, at the correct instant, issue a short duration blast of fluid to blast the relevant particle out of its falling stream for collection apart from other particles not selected by the microprocessor.

It will be appreciated that similar operations are being carried out simultaneously for all the streams 12. To 4prevent cross-channel interference, the microwave generators serving the cavities 18 are set to sweep their cavities with different frequency ranges. Furthermore, channel separators or dividers 36 of suitable insulating material are interposed between the cavities.

Although the cavities are split, the majority of the signal applied to them is propagated through them. A part of the signal may be lost through the gaps adjacent the belt and this may cause some local distortions of the electric field.

The gaps should therefore be minimised as far as possible.

However, the maximum attenuation of the signal i.e.

-8reduction in resonant signal amplitude, and the maximum frequency shift will occur at the centre of each cavity, where the field strength is greatest, and it is anticipated that the local field distortions at the gaps will not unduly affect the accuracy of the sort. With the intention of further minimising local distortions and possible resultant inaccuracies in the sort, it is proposed to incorporate strips 40 of steel or other suitable conductive material in the belt at positions corresponding to the edges of the side walls of the upper portions 20 of the cavities 18. These strips will, it is anticipated, go a long way to "closing off" the cavities 18 and to preventing signal losses.

The apparatus described above will be suitable for sorting a wide range of materials either on the basis of their size or their composition. Thus, for instance, similarly composed ooo particles may be differentiated on the basis of differences 00 in their size, i.e. volume, since this will affect their 0006 dielectric constant or loss tangent. On the other hand, .444

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4 ,p similarly sized particles can be sorted on the basis of their different compositions. It would also be possible to .o differentiate between particles of different sizes and different compositions, providing that the apparatus includes means for measuring the size of each individual particle and for applying an appropriate size correction during the analysis step.

The present invention has the advantage that the use of split resonant cavities permits the simultaneous sorting of particles in a number of different streams on a single conveyor, with the result that high throughputs are t possible.

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9 In another embodiment of the invention, the particles are merely projected from a conveyor belt and allowed to fall in parallel streams, under gravity, through the split cavities which in this case would be arranged with their portions and 24 on opposite sides of the particle trajectories.

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Claims

1. A multi-channel sorting apparatus for sorting particles into fractions on the basis of dielectric constant or less tangent, the apparatus comprising: a plurality of resonant cavities each of which is split to have spaced apart portions; means for passing a plurality of parallel streams of the particles through the cavities, one stream per cavity; means for subjecting each cavity to a different swept frequency range of electromagnetic radiation; means for detecting and analysing the signals transmitted by each cavity; and means for separating the particles in each stream into fractions on the basis of detected changes, due to the presence of the particles of the stream in the respective cavity, in the resonant frequency of the cavity and/or in the amplitude of the transmitted signal at resonance.

2. A multi-channel sorting apparatus according to Claim 1 wherein the means for passing the particles through the or each split cavity is a conveyor belt which passes through a gap between the portions of the cavity.

3. A multi-channel sorting apparatus according to Claim 2 wherein the cavities are arranged side-by-side across the width of the conveyor belt.

4. A multi-channel sorting apparatus according to Claim 3 and comprising channel dividers between the cavities to shield them one from the other.

5. A multi-channel sorting apparatus according to any one of Claims 2 to 4 wherein one portion of the cavity has side walls with edges in close proximity to the _1- 11 conveyor belt and wherein the conveyor belt carries conductive strips extending in the direction of movement of the belt in positions corresponding to the positions of the edges of the side walls.

6. A multi-channel sorting apparatus according to any one of Claims 1 to 5 wherein the swept frequencies are in the microwave part of the spectrum.

7. A multi-channel sorting apparatus according to any one of Claims 1 to 6 comprising a transmission line structure for each cavity for transmitting the swept 1 10 one of Clis 1to6 comrsing a tarasmissodng li n frequency range through the cavity, a receiver line structure for each cavity for detecting signals transmitted through the cavity, and a microprocessor for analysing the detected signals from each cavity to determine whether or not they are indicative of the presence in the relevant cavity of a desired particle.

8. A multi-channel sorting apparatus according to Claim 7 wherein the microprocessor compares the resonant frequency of each cavity, with a particle therein, with the resonant frequency of the cavity ir.Ian empty state or with a known particle therein.

9. A multi-channel sorting apparatus according to Claim 7 wherein the microprocessor compares the amplitude of the transmitted signal at resonance, with a particle present in the cavity, with the amplitude of the transmitted signal at resonance with the cavity in an empty state or with a known particle therein. A multi-channel si herein described with drawings. -12- orting apparatus substantially as reference to the accompanying DATED this 27th day of August, 1992. DE BEERS INDUSTRIAL DIAMOND DIVISION (PROPRIETARY) LIMITED By its Patent Attorneys DAVIES COLLISON CAVE i I 920827,phhspe.026,50000-90.spe,12