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Title:
A SORTING SYSTEM
Document Type and Number:
WIPO Patent Application WO/2013/005083
Kind Code:
A1
Abstract:
A sorting system wherein transported material is exposed to an incident radio wave signal, preferably at a frequency in excess of 10 GHz, and a detector arrangement which causes the separation of material which, because of its content of a desired characteristic, emits a secondary signal in response to the radio wave signal.

Inventors:
RECH, Gavin (21 Oliveri Place, Schofields, New South Wales 2762, AU)
Application Number:
IB2012/000981
Publication Date:
January 10, 2013
Filing Date:
May 21, 2012
Export Citation:
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Assignee:
COMMODASULTRASORT PTY LTD (Unit 1, 12 Yatala RoadMt. Kuring-Gai,New South Wales 2080, COMMODASULTRASORT PTY LTD, AU)
RECH, Gavin (21 Oliveri Place, Schofields, New South Wales 2762, AU)
International Classes:
B07C5/34; B07B13/10; B65G47/34; G01N23/00; G01N33/24; G01S13/00; H01Q13/00; H01Q15/14
Domestic Patent References:
WO1991014936A1
Foreign References:
US4933075A
GB2211299A
US20100204825A1
Download PDF:
Claims:
CLAIMS

1. A system for sorting material based on the presence of at least one characteristic in the material which includes a mechanism for transporting the material which is to be sorted, at least one signal generator for generating at least one radio wave signal, an antenna arrangement for directing the radio wave signal to be incident at least on some of the material, a detecting arrangement for detecting at least one secondary signal, originating from the material, in response to the incident radio wave signal, a processor for processing at least the secondary signal thereby to determine the presence or absence of the characteristic in the irradiated material and a separator which, in response to the processor, separates the material with the characteristic from the remaining material.

2. A system according to claim 1 wherein the antenna is selected from the following: a parabolic antenna, a spoiled parabolic antenna, a slotted waveguide, a bowtie antenna, a horn antenna and a phased array.

3. A system according to claim 1 or 2 wherein the detecting arrangement includes the antenna which is used for directing the radio wave signal onto the material, and wherein the system includes a duplex arrangement which switches the antenna between transmitting and receiving modes.

4. A system according to claim 1 wherein the secondary signal is at least one of the following: a signal which is reflected by the material and a signal which results from transmission, through the material, of the radio wave signal.

5. A system according to claim 4 wherein the detecting arrangement includes a first detector for detecting a signal reflected from the material and a second detector for detecting a signal resulting from transmission through the material of the incident radio wave signal.

6. A system according to any one of claims 1 to 5 wherein the processor compares the secondary signal to the incident radio wave signal or to reference data established from previous tests, to be representative of the nature of the material to determine the nature of the material.

7. A system according to claim 1 wherein the incident radio signal is in a pulse mode and the duration of each pulse us such that a reflected pulse is distinguishable from an incident pulse.

8. A system according to claim 1 wherein the incident radio signal is a continuous wave which is frequency modulated, and wherein a first antenna is used to transmit the signal and a second antenna is used to receive the secondary signal.

9. A system according to any one of claims 1 to 8 wherein the frequency of the radio wave signal is in the range of from 10 GHz to 300 GHz.

10. A system according to claim 1 wherein a plurality of the radio wave signals are generated which are respectively used to determine the size of a particle to detect a surface characteristic, or the presence of metal content in a particle, and to assess the degree of signal transmissivity of a particle.

Description:
A SORTING SYSTEM BACKGROUND OF THE INVENTION [0001] This invention relates to the sorting of material.

[0002] A number of techniques have been used for the sorting of particulate material based on the presence or absence of one or more defined characteristics. In one case ore from a mine is presented in a particulate stream to suitable sensors which detect the presence or absence of a desired mineral in the particles. This information can then be used together with information relating to the size of each particle to determine the ore grade in each particle and a decision can then be made to accept or reject the particle from the ore stream.

[0003] Similar approaches are used in other fields for example to detect the presence of foreign objects in a food stream, to sort good food from bad food, and so on.

[0004] Various mechanisms are employed to identify particles with particular characteristics. For example a particulate stream may be illuminated with visible light in order to identify contrasting surface characteristics on the particles. Diamondiferous ore could be irradiated with X-rays which produce secondary radiation from diamonds in the ore. Material which inherently possesses an active characteristic can be detected through the use of suitable devices. For example a degree of radio-activity can be detected by the use of Geiger tubes. Sorting decisions can be made in each case on the basis of the information which is generated by the sensors or detectors. [0005] An object of the present invention is to provide a sorting arrangement which can be used with a wide range of materials, particularly particulate materials, and which has the capability of being able to sort at a high rate.

SUMMARY OF THE INVENTION

[0006] The invention provides a system for sorting material based on the presence of at least one characteristic in the material which includes a mechanism for transporting the material which is to be sorted, at least one signal generator for generating at least one radio wave signal, an antenna arrangement for directing the radio wave signal to be incident at least on some of the material, a detecting arrangement for detecting at least one secondary signal, originating from the material, in response to the incident radio wave signal, a processor for processing at least the secondary signal thereby to determine the presence or absence of the characteristic in the irradiated material and a separator which, in response to the processor, separates the material with the characteristic from the remaining material.

[0007] The transport mechanism for the material may be of any appropriate kind and for example may be a conveyor belt. This is exemplary only and non-limiting.

[0008] The material which is to be sorted is preferably in particulate form so that the presence or absence of the at least one characteristic in each particle can be determined.

[0009] The antenna may be of any appropriate type. The nature of the antenna may depend, at least, on the frequency of the radio wave signal and, possibly, on the strength of the radio wave signal. For example the antenna may be a reflective type such as a parabolic antenna, a spoiled parabolic antenna, a slotted waveguide, a bowtie antenna, a horn antenna or the like. [0010] In one preferred form of the invention the antenna is constituted by a phased array. This type of device, known in the art, uses an array of similar aerials or antennas which are spaced physically apart and to which the radio wave signal is applied. The phase of the signal supplied to each individual antenna is however controlled so that the signal is reinforced in one direction and cancelled in other directions. By altering the relative phases of the signals fed to the antennas the resultant beam emitted by the phased array which is directed at the material on the transport mechanism can be caused to scan in an appropriate way across the transport mechanism. This feature can be used to identify, with a substantial degree of accuracy, the size and position of each particle and the presence or absence of a characteristic in the radiated material. This is similar in concept to a radar system.

[0011] The detecting arrangement may be constituted by the antenna which is used for directing the radio wave signal onto the material. To enable the antenna to be used in this way, i.e. as a transmitting and receiving antenna and for the incident signal to be distinguished from the secondary signal, use may be made of a duplex arrangement which switches the antenna between transmitting and receiving modes. Techniques which are known in the radar industry can be used for this purpose. In an alternative arrangement a secondary device is used for detecting the secondary signal. The secondary device may be an antenna which is separate from the antenna which directs the radio wave signal onto the material.

[0012] The secondary signal may be a signal which is reflected by the material or a signal which results from transmission, through the material, of the radio wave signal. In the latter case a receiving antenna which is separate and displaced from the transmitting antenna would normally be used. [0013] In one form of the invention the reflected and transmitted signals are used. Thus the secondary signal has two components and the detecting arrangement includes a first detector for detecting a signal reflected from the material and a second detector for detecting a signal resulting from transmission through the material of the incident radio wave signal.

[0014] The processor may compare the secondary signal to the incident radio wave signal or to reference data to determine the nature of the material.

[0015] The reference data may be established from previous tests, to be representative of the nature of the material.

[0016] A radio wave is reflected in a manner which inter alia is determined by a change in a dielectric or diamagnetic constant. Thus a solid object in air will usually scatter radio waves. The degree of scatter is pronounced for electrically conductive materials such as metal and carbon fibre. Radio wave scatter also depends on the wavelength (frequency) of the radio wave and the shape of the target. More pronounced reflection occurs if a particle size is larger than the wavelength of the incident radiation. The converse applies if the wavelength is longer than the target size, for a reduced degree of reflection is achieved and the target might not be detected.

[0017] Another factor which can affect the extent of reflectivity of a radio wave is the shape of the particle irradiated by the wave. A radio wave with a short wavelength is reflected to a greater degree than a long wavelength signal by curved and corner surfaces on a particle.

[0018] The degree to which a radio wave signal is reflected by a particle can be determined by the energy content of the reflected wave. The remaining energy (i.e. the energy not reflected) enters the particle which is illuminated. The particle will absorb at least some of the energy and the remaining energy will exit the particle, possibly with some degree of angular refraction.

[0019] Additional information which is related to the nature of a particle irradiated with an incident wave and possibly to the presence or absence of a desired characteristic in the illuminated particle can be derived by determining a phase difference between the incident wave and the reflected wave.

[0020] The wavelength, energy content, and so on, of the incident wave can be selected taking into account the nature of the material and the nature of the characteristic to be detected. For example a particle with a high degree of reflectivity will exhibit a low degree of signal transmissivity. A particle which is a poor reflector may have a high degree of transmissivity which can be attenuated by the presence of energy-absorbing constituents in the particle. As stated, the shape of the particle may also play a role in determining in what way the secondary signal is to be processed.

[0021] The nature of polarisation of the radio signal can also have an effect on the degree of reflection. A signal with circular polarisation has a low sensitivity to moisture. Linear polarisation, normally with a change in direction of an electric field caused by reflection, is indicative of a metallic surface on an irradiated particle. Random polarisation in a secondary reflected signal is indicative of a fractal surface e.g. on a rock or on soil.

[0022] The incident radio signal can be in a pulse mode or operate as a continuous wave. Given the nature of a sorting system in which the target particles are relatively close to the signal generator and the transmitting antenna, the duration of each pulse should be correspondingly short if a reflected pulse is to be distinguished from an incident pulse. On the other hand if the secondary signal is produced by an incident radio signal travelling through an illuminated particle then the pulse duration would not normally be a primary consideration.

[0023] Continuous wave operation is based on the use of frequency modulation techniques. The incident radio wave signal is frequency modulated in a predictable way e.g. with a sinusoidal signal at an audio frequency. A first antenna is used to transmit the signal and a second antenna is used to receive the secondary signal. The incident and reflected signals are compared by using a beat frequency modulator that produces an audio frequency signal from the compared signals. The degree of signal frequency shift is related to the distance travelled by the radio wave between the two antennas. This factor enables the amount of frequency shift to be directly related to the distance travelled and this, in turn, can be related to the size and shape of an object.

[0024] Thus, through suitable signal processing techniques and by the correct choice of operating frequency of one or more incident radio waves, it is possible to tailor the sorting system to detect and respond to particle sizes and characteristics in particles and where appropriate, to relate characteristics to particles sizes and volumes. In order to detect small particles and small surface features of the order of 1 mm in size the operating frequency of the incident radio wave should be in the gigahertz range and may be in the range of from 10 GHz to about 300 GHz. These values are exemplary only and non-limiting. It is also to be borne in mind that more than one radio signal can be used in the sorting system. One signal can be used to determine the size of a particle, a second signal, at a different frequency and possibly with a different polarisation, can be employed to detect a surface characteristic or the presence of metal content in a particle (for example), and a third signal at a third frequency can be used to assess the degree of signal tranmissivity of a particle. The invention is not limited in these respects.

BRIEF DESCRIPTION OF THE DRAWING

[0025] The invention is further described by way of example with reference to the accompanying drawing which schematically illustrates a sorting system according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENT

[0026] The accompanying drawing illustrates a sorting system 10 according to the invention which includes an endless belt conveyor 12 which passes over head and tail conveyor drums 14 and 16 respectively. One of the drums is driven by means of an electric motor, not shown, at a constant and known speed. A sensor 20 is used to monitor the belt speed and to feed a signal which is directly proportional to the belt speed to a processor 22.

[0027] A feed hopper 24 is positioned adjacent the tail drum 16. Material 26, to be sorted, is supplied to the hopper using a suitable feed mechanism, not shown. Material flow from the hopper is controlled at a desired rate to create on an upper surface 30 of the belt a continuous stream of material particles 32 which are in a monolayer and which, preferably, are spaced apart from one another. A suitable scraper, not shown, positioned above the belt could be employed to ensure that the monolayer effect is enhanced with adequate particle spacing.

[0028] A signal generator 36, at a convenient location, is used to generate a radio signal. The frequency of the radio signal, its amplitude, its form i.e. pulse and pulse characteristics, or continuous wave and related characteristics such as nature of modulation, nature of polarisation and other attributes, are determined taking into account, at least, the features which have been referred to hereinbefore. For example the signal generator may operate at a frequency of the order of 300 GHz using a suitable oscillator such as a klystron or magnetron. The signal generator is linked to a transmitter 38 by means of a waveguide 40. The transmitter 38, typically, is a suitable antenna which may be parabolic, a spoiled parabola or a slotted waveguide. These antenna types are exemplary only and are non-limiting. It is also possible, as has been outlined hereinbefore, for the antenna 38 to be constituted by a phased array for this considerably facilitates scanning of the emitted signal across the upper surface 30 of the belt.

[0029] A disadvantage of using a frequency of the order of 300 GHz is that normally waveguide techniques are required to handle the signals. Power requirements are also increased. It may be appropriate therefore to work at a lower acceptable frequency, say of the order of 10 GHz. Generally, at this frequency, a cable could be used instead of a waveguide to transmit power or signals.

[0030] A benefit which lies in the use of a low operating power is that digital techniques, for signal processing, can be implemented more readily. At higher powers and frequencies it might be necessary to make use of analogue processing equipment. Alternatively some type of sampling and scaling approach would be required to enable digital techniques to be employed. Apart from signal processing, signal generation is simplified at lower powers and frequencies, in that a digital signal generator and amplifier can be used to produce the irradiating signal.

[0031] In the attached drawing the antenna (transmitter) is shown positioned above the belt. It is possible to position the antenna below the belt and, provided the belt is suitably constructed, the belt would be transparent to the incident wave and to any reflected wave originating from a particle on the belt. The arrangement of the antenna in this way could hold practical benefits in that, inter alia, the antenna is less obtrusive and less likely to be damaged.

[0032] The signal generator is associated with a signal receiver 42. The antenna 38 can be used to receive a signal which is incident on the antenna or a separate antenna (not shown) can be used for this purpose. In the former case a duplexing device 44 is used to switch the arrangement between transmitting and receiving modes so that a single antenna can be used for transmitting and receiving.

[0033] Data which are dependent on the signal produced by the generator 36 and any signal received by the receiver 42 are sent to the processor 22.

[0034] At the head drum 14 a separator 50 is positioned. The separator is responsive to a control signal from the processor 22. The separator may vary according to requirement and in one form of the invention comprises a plurality of individually controllable air blast valves which are rapidly energised, as required, in order to blast selected material from a stream of material leaving the conveyor belt at the head drum. This type of operation, which is known in the art, enables selected particles to be separated from the remaining particles in the particle stream into accept and reject fractions 54 and 56 respectively.

[0035] In use of the system the stream of material particles 32 on the upper surface of the belt are irradiated with at least one incident radio wave signal emitted by the transmitter. A signal reflected from each particle is detected by the receiver 42. The energy content of the signal is determined by the processor 22 and by using suitable algorithms a characterising routine is executed to determine the physical properties of the particle. [0036] In another approach, which can be used alternatively or additionally to processing the reflected signal, a receiver 60 is positioned below the belt. The receiver is responsive to a radio wave which passes through the belt - this will produce a substantially constant output and to a radio wave passing through each particle. The energy content in a wave passing through a particle is indicative of the degree of attenuation of the incident wave by the particle. This can be related to the nature of physical characteristics of the particle. A high degree of attenuation can be linked to a large physical particle size. This aspect can be normalised though, for example by obtaining a measure of the particle size and then correcting the attenuated signal to take account of the particle size.

[0037] Data output by the receiver 60 are applied to the processor 22 which compares input and output signal data to make a determination of the nature of each particle, on a particle-by-particle basis. This is linked to the position of the particle on the belt and the belt speed and by the time a particle reaches the belt at the head drum, in free flight, a decision has been made regarding the acceptance or rejection of the particle.

[0038] The sorting system of the invention is non-invasive. Through the correct choice of operating features the principles which have been described can be used for a wide range of materials.