GB2057123A - Sorting apparatus - Google Patents

Abstract

Apparatus for sorting bodies according to the infrared radiation reflected from their surfaces includes feeding means 2 for forming the bodies 1 to be sorted into a substantial monolayer moving as a stream 3, a low shadow source 4 of infrared radiation adjacent one side of and extending as a surface across the stream, means 5 for scanning infrared radiation reflected from the bodies and for generating signals in response thereto, signal processing means receiving and converting the scan signals into decision signals, and means 8 for rejecting certain of the bodies in response to the decision signals. There may be a temperature control background target 10 on the opposite side of the stream from the source and shield means 11 defining an elongated window 12 through which the scan plane passes to target 10. There may be a hooded unit for generating and shielding a background target for use in the apparatus. A composite apparatus may have two sets of apparatus as above and with their scan paths coincident. <IMAGE>

Description

SPECIFICATION Sorting apparatus This invention relates to the identification and sorting of bodies according to infrared reflectance of the surface of each body, and more relates particularly to the case where the bodies are rapidly moving as a monolayer stream sequentially past a source of infrared radiation, a scanner for receiving infrared radiation reflected from the surface of the bodies, and a rejection means that rejects bodies out of the stream according to signals received from the scanner.

In the prior art it is well known to identify bodies by surface reflectance when the reflected radiation is in the visible region of the electromagnetic spectrum and some identification has been done when the reflected radiation is in the near infrared region up to 1.2 micrometers.

Hereinafter visible and near infrared radiation will be referred to as prior art radiation. There are, however, classes of objects whose surface reflectance with respect to the prior art radiation does not differ significantly from body to body and thus accurate identification and hence accurate sorting cannot be obtained.

We have found that if use is made of radiation hereinafter referred to as thermal infrared radiation, as exemplified by radiation in the region of 3 to 50 micrometers, then in many of the abovementioned classes of objects, the surface reflectance differs significantly from body to body so that accurate sorting should result. These findings can be applied in laboratory conditions using standard spectrophotometers but unfortunately they cannot be easily applied in practical sorting conditions because of problems which are described in the following pages.

The invention can be applied in any industry requiring high speed identification and sorting of objects moving in a monolayer stream, such as for example in the food processing industry, but it is in the mining industry where the above lack of accuracy probiems are the most acute and the invention is accordingly described hereinafter with respect to the mining industry with the understanding that the invention is not limited thereto.

In the mining industry, high grade deposits are mined before low grade deposits and as the higher grades are depleted so the industry endeavours to mine lower grades which are generally present in much larger quantities. For low grade deposit mining and sorting to be economically successful, one basic requirement is that the bodies must be identified and sorted at a much higher through-put rate than is used for identifying and sorting bodies from higher grades. The invention is particularly suited to the sorting of bodies from low grade deposits or bodies of low unit value because the bodies are formed into a wide high speed monolayer stream from which the bodies are automatically sorted at a high through-put rate.

Another basic requirement for economic success is, of course, that the identification and sorting be performed at low cost and accordingly the equipment used must involve low maintenance and break-down costs.

An ore deposit can be regarded as a collection of separate bodies each containing the mineral being sought in amounts that range from the extremes of zero to one hundred percent. Between these extremes there is a critical amount below which it is not economical to process a body to recover the contained mineral and bodies having such amounts are referred to as waste bodies.

Bodies containing amounts in excess of the critical amount are referred to as valuable bodies and of course bodies containing large amounts are referred to as high value bodies.

The variety of ore body mixes leads to the classification of the grade of a deposit as being high or low. One mix characteristic of a low grade deposit is when the ratio of the number of valuable bodies to the number of waste bodies is low but the value of individual bodies is high. In this case, economic success requires that as many as possible of the valuable bodies shall be recovered from the stream. Another low grade mix is when the ratio is high but the value of individual bodies is low and in this case economic success depends upon the maximum rejection of the waste bodies.

In general, when high speed automatic equipment is used the consequences of inaccuracies rapidly accumulate and when such equipment is used in the mining of low grade deposits the consequences can rapidly make sorting uneconomical. For example, in the mixes discussed above, a failure to recover high value bodies will reduce the overall efficiency of the operation and excessive recovery of waste bodies will reduce the value of the ore recovered. Hence, accuracy is another basic requirement for the economic success of low grade sorting.

Ore bodies may be differentiated from waste bodies according to the surface distribution of the desirable mineral and/or according to differences in surface reflectance between the bodies.

Differentiation becomes more difficult and inaccuracies increase as the grade of the ore body decreases. Moreover, a low grade deposit requires a high through-put but a high through-put accumulates the inaccuracies resulting because of that low grade.

In the prior art sorters, the accuracy problem can in general be solved by increasing the intensity of the source of the radiation that is to be reflected from surfaces of the bodies. This solution, however, cannot be simply applied in the case where the reflected radiation is thermal infrared radiation because the amount of thermal radiation emitted by a source surface rises only slowly as the source surface temperature is raised and a limit is quickly reached above which the surface will melt or burn regardless of its material of construction. Even if the intensity could be increased without damaging the surface, there still rernains a more difficult problem when thermal infrared is used in that bodies are themselves a source of thermal radiation that is received by the scanner to subsequently produce errors in signals identifying the bodies.The relative importance of thermal emission errors can be reduced by increasing the intensity of reflected radiation within the limitations of infrared sources but simply increasing the intensity of the small area sources used in the prior art leads to an intensification of shadows that are always present on surfaces of irregular bodies such as ore bodies.

These shadows then contribute another source of inaccuracies in surface assessment. Under clean conditions such as can be maintained in laboratories, the shadows can be eliminated by the use of optical systems that enlarge the effective area of the source surface but, in the mining industry, such systems cannot be used because they would be quickly rendered ineffective by dust that is always present.

According to the invention there is provided an apparatus for sorting bodies according to infrared radiation reflected from the surface of each body, said apparatus including: (a) feeding means for forming said bodies into a substantial monolayer moving in a direction as a stream, (b) a low shadow source of infrared radiation adjacent to one side of and extending as a surface across said stream, (c) infrared scanner means for receiving said reflected radiation and for generating scan signals in response thereto, (d) signal processing means for receiving and converting the scan signals into decision signals, and (e) rejection means whereby bodies are rejected from said stream as a consequence of said decision signals.

The invention also comprehends a process for identifying and sorting bodies according to the infrared reflectance of the surface of each body (which process may utilise apparatus as above defined), and a unit for generating, and shielding a background target from, infrared radiation for use in sorting bodies according to (thermal) radiation reflected from opposite sides of the surface of each body as said bodies move in a substantially monolayer stream.

In one aspect, such a unit comprises an infrared radiation source extending as a surface and having therein a viewing slot and a hooded shield means that includes (i) a shield plate extending across said radiation surface and having therein a shield window co-extensive with said viewing slot, and (ii) temperature controlled background target walls that include at least two opposing elongated walls intersected by an appropriate scan plane and diverging from a scanner opening to join said shield plate.

In order that the invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawings in which: Fig. 1 is a schematic representation of apparatus for sorting bodies according to one embodiment of the invention, Fig. 2 shows a modification of the background target and shield window, shown in Fig. 1, Fig. 3 is a schematic representation in sectional side elevation of apparatus for sorting bodies according to a second embodiment of the invention, Fig. 4 shows a further modification of the shield in the form of a hood, Fig. 5 is a view similar to Fig. 3 but showing fish-tail shaped shield hood, Fig. 6 is a schematic representation of a further embodiment of the invention, Fig. 7 is a further schematic representation of the embodiment shown in Fig. 1, and Fig. 8 is a further schematic representation of the embodiment of the invention shown in Figs. 3 and 4.

Throughout the specification and claims the term "substantial monolayer" is used to mean a layer such that few bodies overlap other bodies and such that few bodies cast shadows on other bodies. From this meaning it is seen that the height of the layer is related to the shadow casting criteria which in turn is related to angles between monolayer, the radiation source and the scanner means.

As shown in Figure 1, one embodiment of the invention includes a feeding means 2 for fanning the bodies 1 into a substantial monolayer 3 moving in the direction of the arrow. A low shadow source of infrared radiation 4 is located adjacent one side of and extends across the stream 3 as a source surface. An infrared scanner 5 for receiving the radiation reflected in the scan plane 6 and generating scan signals in response to the reflected radiation is positioned on the same side of the stream 3 as the radiation source 4. The scan path 7 extends across the stream 3 and defines with the scanner 5 the scan plane 6.

The signals generated by the scanner are, as will be hereinafter described, converted into decision signals which are applied to the rejection means 8 downstream of the scan path 7 to reject bodies from the stream 3 into reject stream 9.

In performing the invention, any means for feeding the bodies may be used provided the monolayer criteria are observed and, by way of example, one such feeding means can comprise an oscillating tray with feed shute.

The source of infrared radiation, sometimes briefly referred to as an irradiator, can be any source of thermal radiation provided that it is extended as a surface of sufficient area such that shadows on the surface of the bodies being irradiated are eliminated or at least reduced to a level that does not interfere with sorting accuracy.

The expression "low shadow" is used to include the case when shadow has been reduced to zero.

In choosing a particular irradiator, consideration has to be given to the environment of the sorting operation which generally will require an irradiator sufficiently robust to withstand considerable shaking and occasionally impact by misplaced bodies. The irradiator may be a hot metal plate, a perforated body heated by burning gas, or a ceramic body heated by electrical coils embedded therein. The irradiator surface will usually be a plane surface but curved surfaces are possible for special circumstances. For maximum thermal efficiency the radiation flux from the irradiator surface should be uniform.

The total flux from the irradiator must be such that the thermal radiation subsequently reflected by a body surface must be significantly greater than thermal radiation emitted by the body surface as a consequence of the temperature of the body and the emissivity of the body surface. The amount of thermal radiation incident onto a body's surface is dependent upon the temperature of the irradiator, on the emissivity (when appropriate) of the irradiator surface, and on the solid angle subtended by the irradiator at the surface of the body.

Thus, for a particular body temperature there is a desirable set of values associated with the irradiator. For example, for body temperatures below 300C the irradiator temperature should be from 300 to 8000C, the irradiator surface emissivity should be 0.8 to 0.9, and the solid angle should be at least 0.1 steradians.

When prior art sorters are used in dust contaminated atmospheres that are usually part of ore sorting environments, dust collects on the prior art radiation optical systems and decreases the amount of radiation emitted therefrom. Dust is not a problem for the present invention because when the irradiator is a physical surface, the collecting dust soon attains the temperature of the surface and hence from a thermal radiation point of view the dust becomes part of the surface.

The scanner means 5 includes any suitable thermal infrared detectors and any means for collecting thermal radiation from surfaces of the bodies as they cross the scan path 6. One example of a collecting means is an optical system for focussing the monolayer onto the detector. Such an optical system includes a mirror drum that rotates sufficiently fast to ensure that each body surface is scanned at least once and preferably several times during the passage of the body across the scan path, for example between 300 and 2000 times per second.

In an alternative example of a collecting means, a row of adjacent detectors are operated sequentially or in parallel by electronic means and onto which an image of the monolayer is focused.

The scan path 6 is, of course, a strip extending across the monolayer stream from which the thermal radiation is collected and the length of the scan path is dependent upon the width of the monolayer and the scan angle between the scan plane and the direction of the monolayer stream.

The width of the scan path is determined by the optical system which focuses the reflected infrared radiation from the bodies onto the detector. Preferably, the scan angle is chosen to be a right angle and the distance from the scanner to the monolayer is dictated by the design of the optical system. From the above it is seen that the expression "scan plane" only means a two dimensional mathematical plane when in an extreme case the width of the scan path decreases so that for practical purposes it becomes a scan line. Generally, the scan plane is in longitudinal cross-section a triangle having the object being scanned at its apex.

The scanner means generates electrical scan signals in response to received thermal radiation.

It is possible that the radiation may be received in more than one waveband in which case there will be scanner signals for each waveband. The scanner signals and other electrical signals such as timing signals (to indicate the onset of a scan) and reference target signals (referred to later) are combined via amplifiers, digitizers and the like and then fed to a suitable signal processing means such as a digital computer where an appropriate algorithm is used to generate the decision signals.

The algorithm may be any algorithm currently used in sorting machines such as simple threshold, signal difference, signal ratio, surface texture, pattern recognition. The decision signals then pass to the rejection means where bodies are rejected out of the stream according to previously determined criteria based on surface reflectance characteristics.

The rejector means may comprise any means that is appropriate to the nature of the bodies and to the nature of the stream. For example, if the bodies are or include magnetic material then the rejector means could comprise magnetic fields; again if the bodies are food bodies being carried horizontally in pockets by a conveyor then the rejector means could comprise mechanical fingers or suction cups. When the invention is used to sort ore bodies, then the stream is usually freely falling under the influence of gravity and the rejector means comprises a row of air blast valves extending across the stream that deflects bodies as required into one or more alternative stream(s).

To sort economically ore bodies of still lower value higher through-put rates and hence higher levels of accuracy are required. One method of improving accuracy is to increase the intensity of the source radiation. An alternative method is to increase the sensitivity of the detectors but unfortunately this alternative method encounters a background emission problem, similar to the natural emission problem, when thermal radiation is used. This background emission problem results because all physical objects emit thermal radiation and as can be seen in Fig. 1 all radiation originating behind the stream and lying in the scan plane will produce erroneous thermal scanner signals hereinafter called thermal signals.

In order to overcome the background emission problem, the embodiment of the invention described with reference to Fig. 1 includes a temperature controlled background target 10 positioned on the opposite side of the monolayer stream to the scanner means and so located as to intersect the scan plane.

The background target is conveniently made of blackened metal. The purpose of temperature control is not only to limit the temperature rise of the metal, caused by absorption of energy from the irradiators and hence the level of thermal emission, but also to ensure that the emission is spacially constant along the intersection of the target with the scan plane and that the emission remains constant during the sorting period. When the emission is constant then the background target signals are easily differentiated from the signals arising from the bodies being sorted.

Temperature control can conveniently be achieved by water cooling but any method that is appropriate to the sorting environment can be used. The background target may consist of an elongated rectangular target wall having dimensions to contain the scan plane intersection or, as will be seen in later examples, it may consist of several walls.

As previously mentioned, one way of increasing accuracy is to increase the strength of the radiation source but when this is done in conjunction with an extended source then there is a background problem associated with reflection from physical objects behind the stream and in particular from the temperature controlled target.

As the strength of the source and its area increases so this reflection problem increases.

Thus background target reflection gives rise to scan signals that may be difficult to differentiate from scan signals arising from the bodies being sorted.

Background reflection is overcome by means of a shield means 11 which prevents radiation from source 4 reaching the background target 10. The shield means 11 defines an elongated shield window 12 through which scan plane 6 passes to intersect background target 10.

Shield window 12 is schematically shown in Fig. 1 as being bounded on all sides by shield means 11 but this is not necessarily so since the window may be unbounded either at one or both ends.

The main function of shield means 11 is to prevent source radiation from reaching the background target but the shield means may extend to include "hood plates" for the purpose of preventing any other radiation from reaching the background target.

As illustrated in Fig. 2, the background target includes an elongated target wall 13 and hood plates 14 on either side of scan plane 6. The hood plates 14 have inwardly directed shield plates 1 5 that define an elongated shield window 12 unbounded at either end. The background target is cooled by water passing through pipes 16. The target-wall/shield-plate combination shown in Fig. 2 has a cross-section that is rectangular.

The accuracy of the apparatus can be increased by using more than one infrared scanners to scan along the same scan path.

In another embodiment of the invention having an arrangement of two or more of the apparatus described above, the scan paths of all apparatus coincide and the background targets (when present) are arranged so as to not prevent any scanner from receiving radiation in its scan plane.

A particular advantage of this composite embodiment is that it is possible to scan at the same time either the same area of a body's surface from different directions on one side of the stream or different areas of the surface. A particular example of different area scanning is when scanners are located on opposite sides of the monolayer stream so that opposite faces of each body are scanned. In a preferred example of opposite face scanning there is a pair of opposing apparatus arranged so that the scan plane of one coincides with the scan plane of the other and, when background targets are present, there is a scanner opening in each background target through which the opposing scanner receives its radiation.

Fig. 3 illustrates schematically in sectional side elevation the example where background targets are present and a body 1 is in scan path 7 between opposing scanner means 5A and 5B each having its respective scanner plane 6A and 6B in coincidence with the other. The background targets corresponding to each scanner are elongated target walls 1 3A and 1 3B that diverge in pairs from scanner openings 1 7A and 1 7B towards opposite ends of elongated shield windows 1 2A and 1 2B. Irradiators are shown at 4A and 48.

A similar but simpler version of a shield means is shown in Fig. 4 which illustrates how the target walls 1 3B and hood plates 1 4B can be simply combined to form a hood containing shield window 1 2B and scanner opening 1 7B. By a "hood" is meant any one piece configuration of the shield means and the background target that includes a scanner opening and a shield window.

Fig. 5 shows in plan a composite apparatus using fish-tail shaped hoods. This configuration achieves maximum shield effectiveness with minimum overall hood size.

In a still further embodiment of the invention, infrared sources extending as plane surfaces can be combined with a hood to form a hooded unit that is both a generator of and a shielded background target for infrared radiation. Such a hooded unit may be used in the composite embodiment of the invention where the opposing apparatus are arranged with coinciding scan planes. An example of a hooded unit is given in Fig. 6 in which hood 1 8B provides a shielded background target for scanner 5B (not shown) and irradiator 4A is a source of radiation for scanner 5A (not shown) that is positioned to scan sequentially through a viewing slot 22A positioned in irradiator 4A, elongated shield window 1 2B (not shown) and scanner opening 178.

The operation of the single and composite preferred embodiments of the invention will now be described with reference respectively to Figs. 7 and 8 in which the various parts are numbered as in the previous drawings.

In Fig. 7, ore bodies 1 are deposited on a wide path feeding means that includes a feed shute 2 suspended by rigid arms 20 and oscillated by an oscillator means 1 9 (not fully shown) so that the bodies are formed into a substantially monolayer stream 3 freely falling under the influence of gravity sequentially past the upper and lower plates of an electrically heated rectangular irradiator 4 extending in a plane parallel to stream 3, and a rejector means 8 that comprises a horizontal row of air-blast valves adjacent and parallel to the stream that reject identified bodies across a splitter plate 21.An infrared scanner means 5 is positioned so that its scan plane 6 is horizontal and passes through a viewing slot 22, between the upper and lower irradiator plates, to intersect a vertical portion of stream 3 in a scan path that is at right angles to the direction of the stream. The scan plane 6 passes through the elongated shield window 12, defined by upper and lower shield plates 1 5 and between upper and lower hood plates 14 to intersect an elongated target wall 13 that is cooled by means of water carrying pipes 1 6. As the bodies pass across the scan path, radiation reflected from surfaces of bodies in the scan plane is collected by scanner means 5 and converted in the manner previously described into electrical decision signals that are passed to activate air blast valves 8.When bodies are identified for sorting they are blasted across splitter plate 21.

In Fig. 8 the overall sorting process is the same as described with reference to Fig. 7 except that there is a composite scanner means comprising an opposing pair of unity scanner means 5A and 5B so that two sets of identifying signals are obtained in respect to opposite sides of the surface of each body. The sets of signals are combined by the processing means with the various other signals to give the decision signals. Each scanner means is joined to the irradiators by a hood as previously described in reference to Fig. 5. Parallel sets of hood plates 1 4A and 1 4B extend between the upper and lower irradiators into the viewing slots 22A and 22B and define elongated shield windows 1 2A and 12B.

In conclusion, it is reiterated that as long as the basic criteria of the invention are observed, performance matters of detail may be varied in accordance with situational and environmental requirements.

Claims (14)

1. Apparatus for sorting bodies according to infrared radiation reflected from the surface of each body, said apparatus including: (a) feeding means for forming said bodies into a substantial monolayer moving in a direction as a stream: (b) a low shadow source of infrared radiation adjacent to one side of and extending as a surface across said stream; (c) infrared scanner means for receiving said reflected radiation and for generating scan signals in response thereto; (d) signal processing means for receiving and converting the scan signals into decision signals; and (e) rejection means whereby bodies are rejected from said stream as a consequence of said decision signals.

2. Apparatus for sorting bodies according to infrared radiation reflected from the surface of each body, said apparatus including: (a) feeding means for forming said bodies into a substantial monolayer moving in a direction as a stream; (b) a low shadow source of thermal infrared radiation adjacent to one side of and extending as a surface across said stream; (c) infrared scanner means positioned on said one side of the stream for scanning along a scan path that extends across the stream and defines with the scanner means a scan plane so as to receive radiation reflected in the scan plane and to generate scan signals in response thereto; (d) signal processing means for receiving and converting the scan signals into decision signals;; (e) rejection means positioned downstream of the scan path and adjacent the stream whereby selected bodies are rejected from said stream as a consequence of said decision signals.

3. Apparatus as defined in claim 1 or claim 2 including a temperature controlled background target positioned on the opposite side of the stream so as to be intersected by the scan plane.

4. Apparatus as defined in claim 3 including shield means for preventing radiation from said radiation source reaching said background target, said shield means defining an elongated shield window means through which the scan plane passes.

5. The unity apparatus as defined in claim 4 wherein the background target extends as an elongated target wall and further includes hood plates on each side of said scan plane and wherein the shield means is constituted by a shield plate in which said elongated shield window means is positioned.

6. Apparatus as defined in any of the preceding claims wherein the radiation source extends as a plane surface generally parallel to the monolayer stream, wherein the scan path is at right angles to the monolayer stream direction, and wherein the scan plane is perpendicular to the monolayer stream.

7. Composite apparatus for sorting bodies according to infrared radiation reflected from the surface of each body comprising an arrangement of two or more apparatus as defined in any one of the previous claims in which the scan paths of each apparatus coincide with one another and in which background targets when present do not prevent any scanner from receiving radiation in its scan plane.

8. Composite apparatus as defined in claim 7 wherein there is at least one apparatus according to any one of claims 1 to 5 on one side of said monolayer stream opposing at least one other such apparatus on the opposite side of said monolayer stream so that the composite apparatus may receive radiation reflected from opposite sides of the surface of each body.

9. Composite apparatus as defined in claim 8 in which a pair of opposing apparatus is arranged so that the scan plane of one coincides with the scan plane of the other.

10. Composite apparatus as defined in claim 9 wherein the background target of each opposing apparatus includes a scanner opening through which each scanner means receives radiation in its scan plane.

11. Composite apparatus as defined in claim 10 wherein the target walls extend from either side of said scanner openings and diverging generally towards opposite ends of said elongated shield window means.

12. A hooded unit for generating and shielding a background target from infrared radiation for use in sorting bodies according to radiation reflected from opposite sides of the surface of each body as said bodies move in a substantially monolayer stream, said unit comprising: (a) an infrared radiation source extending as a surface and having therein an elongated viewing slot, and (b) a hooded sheild means that includes: (i) a shield plate extending across said radiation surface and having therein an elongated shield window co-extensive with said elongated viewing slot, and (ii) temperature controlled background target walls that include at least two opposing elongated walls diverging from a scanner opening to join said shield plate, the scanner opening and the elongated shield window being so located that a scan plane passing therethrough intersects the opposing elongated walls.

13. A process for identifying and sorting bodies according to the infrared reflectance of the surface of each body comprising the steps of: (a) fanning said bodies into a substantial monolayer moving in a direction as a stream, (b) providing a low shadow source of thermal infrared radiation adjacent to one side of an extending as a surface across the stream, (c) scanning the reflected radiation and generating scan signals in response thereto, (d) processing said scan signals into decision signals, and (e) applying the decision signals to rejection means whereby selected bodies are rejected from the stream as a consequence of the decision signals.

14. Apparatus for sorting bodies according to infrared radiation reflected from the surface of each body substantially as hereinbefore described with reference to the accompanying drawings.

1 5. A hooded unit for generating and shielding a background target from infrared radiation for use in sorting bodies according to radiation reflected from opposite sides of the surface of each body substantially as hereinbefore described with reference to the accompanying drawings.

.16. A process for identifying and sorting bodies according to the infrared reflectance of the surface of each body substantially as hereinbefore described.