CA1174749A - Displacement error correction in sorting systems - Google Patents
Displacement error correction in sorting systemsInfo
- Publication number
- CA1174749A CA1174749A CA000366002A CA366002A CA1174749A CA 1174749 A CA1174749 A CA 1174749A CA 000366002 A CA000366002 A CA 000366002A CA 366002 A CA366002 A CA 366002A CA 1174749 A CA1174749 A CA 1174749A
- Authority
- CA
- Canada
- Prior art keywords
- particle
- correction factor
- dependent
- particles
- displacement
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B07—SEPARATING SOLIDS FROM SOLIDS; SORTING
- B07C—POSTAL SORTING; SORTING INDIVIDUAL ARTICLES, OR BULK MATERIAL FIT TO BE SORTED PIECE-MEAL, e.g. BY PICKING
- B07C5/00—Sorting according to a characteristic or feature of the articles or material being sorted, e.g. by control effected by devices which detect or measure such characteristic or feature; Sorting by manually actuated devices, e.g. switches
- B07C5/34—Sorting according to other particular properties
- B07C5/346—Sorting according to other particular properties according to radioactive properties
Abstract
A B S T R A C T
In radiometric sorting a method of compensating for the count recorded by a detector for an ore particle which is displaced from the centre line of the detector. The compensation is effected by applying one of a plurality of calibration factors to the detector count. The calibration factors are statistically determined and are dependent on the measured displacement and optionally on at least one of the shape, height, volume or mass of the particle.
In radiometric sorting a method of compensating for the count recorded by a detector for an ore particle which is displaced from the centre line of the detector. The compensation is effected by applying one of a plurality of calibration factors to the detector count. The calibration factors are statistically determined and are dependent on the measured displacement and optionally on at least one of the shape, height, volume or mass of the particle.
Description
~ ~ - 2 ~ 1~7~7~
FIELD OF THE INVENTION
This invention relates to sorting systems and particularly to the sorting of radiometric ore.
BACKGROUND TO THE INVENTION
In a radiometric particle-sorter the ore particles are arranged in --a plurality of spaced lines with the individual particles in each line being spaced from one another. ~ach line of particles is directed along a counting channel over a succession of detectors - wh-ich are-hous-ed~ a-lead shield and the radioactive counts recorded by the detectors for each particle are accumulated to obtain a measure of the radioactive content of the particle.
-10 -- Ideally the particles pass down the centre line of the channel and so are exposed under identical conditions to the detectors. In practice, though, due to the requirements of a high tonnage throughput and the limitations of the particle feeding system together with the fact that the sorter must be capable-of--handling particles having a size range of 2 : 1 or possibly 3 : 1 and the necessity of having a counting channel'width within the lead shielding of about 2 to 3 times the nominal maximum particle size to avoid pile-up and jamming of particles within the counting channel, ~~ -~~- -~- ''ma-ny-particles, particularly-smaller-ones, are laterally displaced from the centre line of the counting channel and consequently from the centre line of the scintilla'tion detectors.
The scintillation detectors normally have a scintillation crystal of 75 mm diameter as maximum cross sectional dimensions for several reasons, including minimising the effect of the following and preceding particles at acceptable particle separations and keeping background count low to 25 - maintain sensitivity and selectivity for small low grade particles.
3 - ? 1 ~ 4 7 ~ ~
Many particles are therefore considerably displaced laterally from the centre line of the detectors, and give a considerably reduced count compared to the same particles travelling over the centre line of the detectors, due to the inverse square law attenuati:on,i of radiation and also due to the effect of particle-detector geometry.
Certain sorting machines previously described or built have compensated for this effect by using a single plane projected area volume measuring device to measure the lateral offset of the particle from the centre line, and adjust the reading of the projected area to compensate for the offset in a data processor to derive the particle's grade, i.e. the measured projected area or apparent volume, is reduced to compensate for the lower counts which the particle gives due to its offset. While this method gives acceptable results if only high grade particles giving counts considerably above background counts are being handled, it is not satisfactory when sorting low grade particles with counts only slightly above background counts,~as this correction for lateral displacement by reduction of the apparent mass can result in a barren particle accumulating a background level count being processed to appear as an ore particle.
SUMMARY OF THE INVENTION
, ~
According to the invention a method of compensating for the lateral displacement of a particle from a reference line related to at least one detector which is responsive to a desired property in the particle and - - r~ which produces an output ~ignal which is dependent on the degree to which the particle possesses the property includes the steps of obtaining a measure of the lateral displacement of the particle from the reference line, and applying to the output signal a correction factor which is ~ dependent on the measure of the lateral displacement. - ^
To avoid the apparent upgrading of a barren or very low grade particle the correction factor is applied only if the output signal exceeds a -~predetermined minimu~ he-min~mum may be statistically determined.
- ~ 4 ~ 1 ~ ~ 7 ~ ~
A plurality of correction factors may be predetermined experiméntally with each correction factor being associated with a specific lateral displacement or a lateral displacement within a given range.
Further according to the invention the correction factor is additionaily dependent on a physical characteristic of the particle.
The physical characteristic may be at least one of the shape, height, volume or mass of the particle.
The invention also provides a method of sorting particles which includes the steps of causing the particles to move in line spaced from one another sequentially past a plurality of in-line detectors, the detectors being responsive to the presence of a desired property in the particles and each producing, for each particle, an output signal which is dependent on the degree to which the property is present in the particle, and, for each particle, accumulating the output signals of the detectors, obtaining a measure of the displacement of the particle from the centre line of the detectors, and applying to the accumulation of the output signals a correction factor which compensates for the displacement of the particle from the centre line.
The invention also includes the step of categorizing the particle according to a physical characteristic,the correction factor being dependent on the said characteristic.
BRIEF DESCRIPTION O THE DRAWING
The invention is described by way of example with reference to the accompanying drawings in which:
Figure 1 schematically illustrates a particle travelling off centre over a scintillation counter, Figure 2 illustrates the-reduction in count recorded by the counter as the particle goes off centre, expressed as a percentage of the maximum count recorded for the particle on the centre line of the detector.
~ 4 7 ~ ~
Figure 3 illustrates a circuit diagram of electronic circuitry employed to determine the lateral displacement of a particle, Figure ~ is a'simplified block diagram of a sorting system which incorporates the method of the invention, and - 5 Figure 5 is a flow chart of a programme executed by the system of Figure 4.
DETAILED DESCRIPTION OF THE INVENTION
Figure 1 shows a scintillation detector in an ore sorting machine which includes a crystal 10 surrounded by lead shielding 12. A belt 14 carries particles 16 which are to'be sorted over the crystal.
The shielding 12 is employed to reduce the effects of extraneous radiation, whether background or fringing radiation from adjacent particles, on the count recorded by the crystal of the radioactivity of the particle under test. The shielding however simultaneously makes the crystal more sensitive to direction and consequently if the particle is displaced from the centre line 18 of the crystal the count recorded by the crystal is reduced. This reduction may be combated to some degree though by chamfering the upper rim 20 of the lead shielding thereby increasing the sensitivity of the ~etector to off-sentre particles, but this makes the detector more susceptible to~stray radiation.
The relationship of count reduction to centre line displacement is shown in Figure 2. The curve of Figure 2 is dependent on the shape and size of the particle under test and on the chamfer angle and size but nonetheless exhibits under practically all conditions in operation a sharp reduction 'for recorded count as the distance off-centre increases.
The present invention is based on the adjustment which is dependent on the off-centre displacement of a particle being made to the recorded count for the particle. The circuit illustrated in Figure 3 is employed to determine the lateral displacement of a particle.
~. 17~7~9 The circuit is divided by means o~ a dotted line into upper and lower sections~ The upper section forms the subject of Canadian Patent Application No. 372590, but its working is briefly described hereinafter. The lower section calculates the lateral displacement of a particle from a reference line using the data produced in the upper section.
The arrangementshown in the upper section is intended for the volumetric measurement of a particle 40 projected in free flight from the end of a conveyor belt through a frame 42. The frame carries arrays of light emitting diodes and photo transistors and the numerals 44 and 46 denote horizontal and vertical arrays respectively of light emitting diodes, and the numerals 48 and 50 denote corresponding horizontal and vertical arrays respectively of photo transistor sensors.
The circuitry of the upper section includes a clock oscillator 60, a four bit binary counter 62, two 16 channel analog multiplexers 64 and 66 associated with horizontal and vertical arrays of diodes respectively, high power driver circuits 68, two corresponding 16 -channel de-multiplexers 70 and 72 respectively, retiggerable one-~o shots (astable multivibrators) 74, 76 and 78, AND gates 80 and 81, four bit binary counters 82 and 84, a multiplier 86, a parallel adder 88, a latch 90 and logic units 92 and 94 respectively.
The latter logic unit is used for gating, reset and count ena~le, logic. The former unit is used to detect the length of the particle in its direction of travel. The clock oscillator 60drives the 4-bit binary counter 62 is decoded by the 16 channel analog multiplexer 66 which sequences the diodes in the vertical array 46, and by the multiplexer 64 which sequences the diodes in the horizontal array 44. The outputs of the multiplexers are fed to the high power driver circuits 68 which drive the light emitting diodes ti gi~e very high intensity light pulses.
7 - .
The action of each multiplexer is sequentially to pulse the light emitting diodes in each array as described. The associated light detecting photo transistor outputs are fed in parallel to the 16 channel demultiplexers 72 in the vertical plane and 70 in the horizontal plane. As these demultiplexers are synchronously driven by the binary counter 62 the pulse sequence output of the ~;A demultiplexers corresponds to the sequential pulsing of the respective diode arrays, and a high or low logic pulse is obtained from each photo transistor depending on whether it is obscured or not.
The outputs of the demultiplexers are passed to the retriggerable one shots 76 and 74, respectively, setting the width and height of the particle. The width pulse is used to gate the clock pulse through the AND gate 80 and the height pulse gates the clock pulse through the AND
gate 81. The outputs of the gates are passed to the counter 84 for the vertical plane, and to the counter 82 for the horizontal plane.
The gating-, reset- and count enable logic section 94 resets the binary counters at the beginning of each scan, and stops the binary counters at the end of each scan cycle.
Thus at the end of each scan cycle a count corresponding to the number of photo transistors obscured in-the vertical plane is stored in the binary counter 82 and a count corresponding to the number of photo transistors obscured in the horizontal plane is stored in the binary counter 84. The binary outputs of these counters are fed to -the 4-bit x 4-bit multiplier system 86, and the 16 b1t output of this multiplier, corresponding to the projected cross-sectional area of a 5 mm long slice of the particle is passed to the incremental parallel adder system 88. The incremental adder system is reset to zero by the gating-reset and count enable logic system 84 when an incoming particle is first detected by the photo transistors, and a 16-bit multiplier product representing the cross-sectional area of a 5 mm slice is then added incrementally, or accumulated, at the end of each sequential scan - of the-particle, the total summation over the length of the particle thus being the projected volume of the particle. After the end of the particle has been detected by the particle length logic unit 92, the - 8 ~ 47 ~9 output latch 90 is enabled and the output of this latch representing the projected particle volume is then available for further processing as required.
The lower section of the circuit i.e. the section below the dotted line includes a divide-by-2 flip-flop 100, an AND/OR gate 102, an UP-DOWN preset counter 104, a latch 106, a NOR gate 108, and a multiple input one-shot 110.
The clock pulses, each pulse corresponding to say a 5 mm distance in the upper section i.e. sizer unit, (this being the distance between the pairs of LED's and Phototransistors) are passed to the flip-flop 100.
The direct clock pulses also go to an input B of the gate 102, and the half clock frequency pulses from the flip-flop 100 go to an input A of thP
gate 102. At the beginning of a sizer scan the Q output of retriggerable one-shot 76, representing the particle length, is low, as no particle is obscuring the light beam, and this low output then sets the gate 102 so that the input B is selected and passed from the output to the counter 104. Again, at the beginning of a sizer scan the logic unit 94 output presets the counter 104 to 8 and the trailing negative edge of the preset pulse enables the count-down mode. The counter 104 then counts the clock pulses until a particle obscures a light beam. The output of the one shot 76 then goes high for the width of the particle.
This high input on the gate 102 then selects input A with input at 1/2 clock frequency, and the counter 104 then counts at 1/2 clock frequency for the width of the particle. This high level from the one shot 76 also enable the latch 106 so that the counts on the output of the counter 104 are transferred to the output of the latch 106. The one shot 76 goes low when the sizer scan has passed the edge of the particle, and this low level then latches the output of the latch 106 to hold the counts to the edge of the particle. As the counter 104 was counting at half clock frequency during the width of the particle, and as the counter was preset to count down from 8, the output of the latch 106 then represents the lateral displacement of the centre of the particle from t~e cen~re of the size~ unit in l~nlts of 5 mm.
~ ~47~
g If the particle extends beyond the centre of the sizer unit, or lies wholly beyond the centre, then the counter 104 continues counting down until binary count 0, when the counter's outputs are all low, and therefore the output of the gate 108 goes high.
This triggers the one shot 110 and the output thereof is inhibited when the counter is preset in the count-down mode at the beginning of a sizer scan. As 0 output on the counter is then equivalent to the centre line of the sizer unit, the distance of the output particle from the centre line of the scanner is measured irrespective of the lateral position of the particle.
Figure 4 is a simplified schematic representation of a sorting system wherein corrections are made to compensate for the lateral displacements of the particles.
The particles 200 to be sorted are moved in line from one another on a conveyor belt 202 sequentially past a plurality of in line detectors 204. The radioactivity counts from the detectors associated with each particle are separately totalled in an accumulator 206, for example in the manner described in South African Patent Application No. 78t3198 (published 26 September 20 1979; U.K. counterpart 2022824A). The volume and lateral displacement of each particle are measured, in the manner described, by means of apparatus 208, similar to that shown in Figure 3.
The data from the accumulator 206 and the apparatus 208 is stored 25 in a memory 210 of a processor 212.A read only memory 214, which holds a matrix of empirically determined correction factors pertaining to lateral displacement~ i5 accessible by the processor 212. The correction factors are based on curves o the type shown in Figure 2 and are determined under laboratory conditions by measuring the characteristics of representative ore samples. The particles are categorized according to relevant parameters such as their volume or height, mass or shape. In this respect use may be made of the t~chniques described in the applicant's South African Patent ~pplications Nos~ 80/4250 and 80/4249, entitled 'l~olumetric Measurement" and'l'Grade Determination"
respectively.
j~3 ~ ~47~
- 1 o For each category of particles measurements are made on representati;e detectors to obtain the count reduction/off-centre displacement relation-ship shown in Figure 2. This data is stored in the memory 214.
Each particle on the belt 202 is categorized from the data held in the memory 210 and, when its centre line displacement is known, a look up routine is employed by the processor to locate the appropriate correction factor in the memory 214. If the correction factors are expressed in the same manner as the curve of Figure 2, i.e. as the peak percentage count of a particle related to its distance off centre then the accumulated count output by the accumulator 206 must be multiplied by the inverse of the percentage reduction value. This is easily effected by the processor.
After further, known, calculations to obtain the grade of the particle using the corrected count value an accept/reject decision is made by the processor and known sorting apparatus 216 e.g. an air blast nozzle is actuated accordingly.
A further refinement introduced by the invention is that a correction factor is only applied to an output signal if the output signal is in excess of an empirically determined mimimum dependent inter alia on background levels. This prevents upgrading of barren or very low grade particles.
Figure 5 is largely self explanatory and illustrates a simplified flow chart of the programme executed by the processor 212 to effect the calculations referred to; the preparation of such a programme is well within the capabilities of those skilled in the art and consequently the flow chart is merely by way of illustration and does not purport to be exhaustive.
" 1 1 7 4 7 4 9 In similar vein the circuit elements and arithmetic and logic blocks shown in Figure 3 are all standard circuit elements well known to those skilled in the digital electronic art, so full circuit details are not given.
The system shown comprises a 16 element array, with a corresponding electronic system, but this array can obviously be expanded to arrays with more elements.
"
. ~, )
FIELD OF THE INVENTION
This invention relates to sorting systems and particularly to the sorting of radiometric ore.
BACKGROUND TO THE INVENTION
In a radiometric particle-sorter the ore particles are arranged in --a plurality of spaced lines with the individual particles in each line being spaced from one another. ~ach line of particles is directed along a counting channel over a succession of detectors - wh-ich are-hous-ed~ a-lead shield and the radioactive counts recorded by the detectors for each particle are accumulated to obtain a measure of the radioactive content of the particle.
-10 -- Ideally the particles pass down the centre line of the channel and so are exposed under identical conditions to the detectors. In practice, though, due to the requirements of a high tonnage throughput and the limitations of the particle feeding system together with the fact that the sorter must be capable-of--handling particles having a size range of 2 : 1 or possibly 3 : 1 and the necessity of having a counting channel'width within the lead shielding of about 2 to 3 times the nominal maximum particle size to avoid pile-up and jamming of particles within the counting channel, ~~ -~~- -~- ''ma-ny-particles, particularly-smaller-ones, are laterally displaced from the centre line of the counting channel and consequently from the centre line of the scintilla'tion detectors.
The scintillation detectors normally have a scintillation crystal of 75 mm diameter as maximum cross sectional dimensions for several reasons, including minimising the effect of the following and preceding particles at acceptable particle separations and keeping background count low to 25 - maintain sensitivity and selectivity for small low grade particles.
3 - ? 1 ~ 4 7 ~ ~
Many particles are therefore considerably displaced laterally from the centre line of the detectors, and give a considerably reduced count compared to the same particles travelling over the centre line of the detectors, due to the inverse square law attenuati:on,i of radiation and also due to the effect of particle-detector geometry.
Certain sorting machines previously described or built have compensated for this effect by using a single plane projected area volume measuring device to measure the lateral offset of the particle from the centre line, and adjust the reading of the projected area to compensate for the offset in a data processor to derive the particle's grade, i.e. the measured projected area or apparent volume, is reduced to compensate for the lower counts which the particle gives due to its offset. While this method gives acceptable results if only high grade particles giving counts considerably above background counts are being handled, it is not satisfactory when sorting low grade particles with counts only slightly above background counts,~as this correction for lateral displacement by reduction of the apparent mass can result in a barren particle accumulating a background level count being processed to appear as an ore particle.
SUMMARY OF THE INVENTION
, ~
According to the invention a method of compensating for the lateral displacement of a particle from a reference line related to at least one detector which is responsive to a desired property in the particle and - - r~ which produces an output ~ignal which is dependent on the degree to which the particle possesses the property includes the steps of obtaining a measure of the lateral displacement of the particle from the reference line, and applying to the output signal a correction factor which is ~ dependent on the measure of the lateral displacement. - ^
To avoid the apparent upgrading of a barren or very low grade particle the correction factor is applied only if the output signal exceeds a -~predetermined minimu~ he-min~mum may be statistically determined.
- ~ 4 ~ 1 ~ ~ 7 ~ ~
A plurality of correction factors may be predetermined experiméntally with each correction factor being associated with a specific lateral displacement or a lateral displacement within a given range.
Further according to the invention the correction factor is additionaily dependent on a physical characteristic of the particle.
The physical characteristic may be at least one of the shape, height, volume or mass of the particle.
The invention also provides a method of sorting particles which includes the steps of causing the particles to move in line spaced from one another sequentially past a plurality of in-line detectors, the detectors being responsive to the presence of a desired property in the particles and each producing, for each particle, an output signal which is dependent on the degree to which the property is present in the particle, and, for each particle, accumulating the output signals of the detectors, obtaining a measure of the displacement of the particle from the centre line of the detectors, and applying to the accumulation of the output signals a correction factor which compensates for the displacement of the particle from the centre line.
The invention also includes the step of categorizing the particle according to a physical characteristic,the correction factor being dependent on the said characteristic.
BRIEF DESCRIPTION O THE DRAWING
The invention is described by way of example with reference to the accompanying drawings in which:
Figure 1 schematically illustrates a particle travelling off centre over a scintillation counter, Figure 2 illustrates the-reduction in count recorded by the counter as the particle goes off centre, expressed as a percentage of the maximum count recorded for the particle on the centre line of the detector.
~ 4 7 ~ ~
Figure 3 illustrates a circuit diagram of electronic circuitry employed to determine the lateral displacement of a particle, Figure ~ is a'simplified block diagram of a sorting system which incorporates the method of the invention, and - 5 Figure 5 is a flow chart of a programme executed by the system of Figure 4.
DETAILED DESCRIPTION OF THE INVENTION
Figure 1 shows a scintillation detector in an ore sorting machine which includes a crystal 10 surrounded by lead shielding 12. A belt 14 carries particles 16 which are to'be sorted over the crystal.
The shielding 12 is employed to reduce the effects of extraneous radiation, whether background or fringing radiation from adjacent particles, on the count recorded by the crystal of the radioactivity of the particle under test. The shielding however simultaneously makes the crystal more sensitive to direction and consequently if the particle is displaced from the centre line 18 of the crystal the count recorded by the crystal is reduced. This reduction may be combated to some degree though by chamfering the upper rim 20 of the lead shielding thereby increasing the sensitivity of the ~etector to off-sentre particles, but this makes the detector more susceptible to~stray radiation.
The relationship of count reduction to centre line displacement is shown in Figure 2. The curve of Figure 2 is dependent on the shape and size of the particle under test and on the chamfer angle and size but nonetheless exhibits under practically all conditions in operation a sharp reduction 'for recorded count as the distance off-centre increases.
The present invention is based on the adjustment which is dependent on the off-centre displacement of a particle being made to the recorded count for the particle. The circuit illustrated in Figure 3 is employed to determine the lateral displacement of a particle.
~. 17~7~9 The circuit is divided by means o~ a dotted line into upper and lower sections~ The upper section forms the subject of Canadian Patent Application No. 372590, but its working is briefly described hereinafter. The lower section calculates the lateral displacement of a particle from a reference line using the data produced in the upper section.
The arrangementshown in the upper section is intended for the volumetric measurement of a particle 40 projected in free flight from the end of a conveyor belt through a frame 42. The frame carries arrays of light emitting diodes and photo transistors and the numerals 44 and 46 denote horizontal and vertical arrays respectively of light emitting diodes, and the numerals 48 and 50 denote corresponding horizontal and vertical arrays respectively of photo transistor sensors.
The circuitry of the upper section includes a clock oscillator 60, a four bit binary counter 62, two 16 channel analog multiplexers 64 and 66 associated with horizontal and vertical arrays of diodes respectively, high power driver circuits 68, two corresponding 16 -channel de-multiplexers 70 and 72 respectively, retiggerable one-~o shots (astable multivibrators) 74, 76 and 78, AND gates 80 and 81, four bit binary counters 82 and 84, a multiplier 86, a parallel adder 88, a latch 90 and logic units 92 and 94 respectively.
The latter logic unit is used for gating, reset and count ena~le, logic. The former unit is used to detect the length of the particle in its direction of travel. The clock oscillator 60drives the 4-bit binary counter 62 is decoded by the 16 channel analog multiplexer 66 which sequences the diodes in the vertical array 46, and by the multiplexer 64 which sequences the diodes in the horizontal array 44. The outputs of the multiplexers are fed to the high power driver circuits 68 which drive the light emitting diodes ti gi~e very high intensity light pulses.
7 - .
The action of each multiplexer is sequentially to pulse the light emitting diodes in each array as described. The associated light detecting photo transistor outputs are fed in parallel to the 16 channel demultiplexers 72 in the vertical plane and 70 in the horizontal plane. As these demultiplexers are synchronously driven by the binary counter 62 the pulse sequence output of the ~;A demultiplexers corresponds to the sequential pulsing of the respective diode arrays, and a high or low logic pulse is obtained from each photo transistor depending on whether it is obscured or not.
The outputs of the demultiplexers are passed to the retriggerable one shots 76 and 74, respectively, setting the width and height of the particle. The width pulse is used to gate the clock pulse through the AND gate 80 and the height pulse gates the clock pulse through the AND
gate 81. The outputs of the gates are passed to the counter 84 for the vertical plane, and to the counter 82 for the horizontal plane.
The gating-, reset- and count enable logic section 94 resets the binary counters at the beginning of each scan, and stops the binary counters at the end of each scan cycle.
Thus at the end of each scan cycle a count corresponding to the number of photo transistors obscured in-the vertical plane is stored in the binary counter 82 and a count corresponding to the number of photo transistors obscured in the horizontal plane is stored in the binary counter 84. The binary outputs of these counters are fed to -the 4-bit x 4-bit multiplier system 86, and the 16 b1t output of this multiplier, corresponding to the projected cross-sectional area of a 5 mm long slice of the particle is passed to the incremental parallel adder system 88. The incremental adder system is reset to zero by the gating-reset and count enable logic system 84 when an incoming particle is first detected by the photo transistors, and a 16-bit multiplier product representing the cross-sectional area of a 5 mm slice is then added incrementally, or accumulated, at the end of each sequential scan - of the-particle, the total summation over the length of the particle thus being the projected volume of the particle. After the end of the particle has been detected by the particle length logic unit 92, the - 8 ~ 47 ~9 output latch 90 is enabled and the output of this latch representing the projected particle volume is then available for further processing as required.
The lower section of the circuit i.e. the section below the dotted line includes a divide-by-2 flip-flop 100, an AND/OR gate 102, an UP-DOWN preset counter 104, a latch 106, a NOR gate 108, and a multiple input one-shot 110.
The clock pulses, each pulse corresponding to say a 5 mm distance in the upper section i.e. sizer unit, (this being the distance between the pairs of LED's and Phototransistors) are passed to the flip-flop 100.
The direct clock pulses also go to an input B of the gate 102, and the half clock frequency pulses from the flip-flop 100 go to an input A of thP
gate 102. At the beginning of a sizer scan the Q output of retriggerable one-shot 76, representing the particle length, is low, as no particle is obscuring the light beam, and this low output then sets the gate 102 so that the input B is selected and passed from the output to the counter 104. Again, at the beginning of a sizer scan the logic unit 94 output presets the counter 104 to 8 and the trailing negative edge of the preset pulse enables the count-down mode. The counter 104 then counts the clock pulses until a particle obscures a light beam. The output of the one shot 76 then goes high for the width of the particle.
This high input on the gate 102 then selects input A with input at 1/2 clock frequency, and the counter 104 then counts at 1/2 clock frequency for the width of the particle. This high level from the one shot 76 also enable the latch 106 so that the counts on the output of the counter 104 are transferred to the output of the latch 106. The one shot 76 goes low when the sizer scan has passed the edge of the particle, and this low level then latches the output of the latch 106 to hold the counts to the edge of the particle. As the counter 104 was counting at half clock frequency during the width of the particle, and as the counter was preset to count down from 8, the output of the latch 106 then represents the lateral displacement of the centre of the particle from t~e cen~re of the size~ unit in l~nlts of 5 mm.
~ ~47~
g If the particle extends beyond the centre of the sizer unit, or lies wholly beyond the centre, then the counter 104 continues counting down until binary count 0, when the counter's outputs are all low, and therefore the output of the gate 108 goes high.
This triggers the one shot 110 and the output thereof is inhibited when the counter is preset in the count-down mode at the beginning of a sizer scan. As 0 output on the counter is then equivalent to the centre line of the sizer unit, the distance of the output particle from the centre line of the scanner is measured irrespective of the lateral position of the particle.
Figure 4 is a simplified schematic representation of a sorting system wherein corrections are made to compensate for the lateral displacements of the particles.
The particles 200 to be sorted are moved in line from one another on a conveyor belt 202 sequentially past a plurality of in line detectors 204. The radioactivity counts from the detectors associated with each particle are separately totalled in an accumulator 206, for example in the manner described in South African Patent Application No. 78t3198 (published 26 September 20 1979; U.K. counterpart 2022824A). The volume and lateral displacement of each particle are measured, in the manner described, by means of apparatus 208, similar to that shown in Figure 3.
The data from the accumulator 206 and the apparatus 208 is stored 25 in a memory 210 of a processor 212.A read only memory 214, which holds a matrix of empirically determined correction factors pertaining to lateral displacement~ i5 accessible by the processor 212. The correction factors are based on curves o the type shown in Figure 2 and are determined under laboratory conditions by measuring the characteristics of representative ore samples. The particles are categorized according to relevant parameters such as their volume or height, mass or shape. In this respect use may be made of the t~chniques described in the applicant's South African Patent ~pplications Nos~ 80/4250 and 80/4249, entitled 'l~olumetric Measurement" and'l'Grade Determination"
respectively.
j~3 ~ ~47~
- 1 o For each category of particles measurements are made on representati;e detectors to obtain the count reduction/off-centre displacement relation-ship shown in Figure 2. This data is stored in the memory 214.
Each particle on the belt 202 is categorized from the data held in the memory 210 and, when its centre line displacement is known, a look up routine is employed by the processor to locate the appropriate correction factor in the memory 214. If the correction factors are expressed in the same manner as the curve of Figure 2, i.e. as the peak percentage count of a particle related to its distance off centre then the accumulated count output by the accumulator 206 must be multiplied by the inverse of the percentage reduction value. This is easily effected by the processor.
After further, known, calculations to obtain the grade of the particle using the corrected count value an accept/reject decision is made by the processor and known sorting apparatus 216 e.g. an air blast nozzle is actuated accordingly.
A further refinement introduced by the invention is that a correction factor is only applied to an output signal if the output signal is in excess of an empirically determined mimimum dependent inter alia on background levels. This prevents upgrading of barren or very low grade particles.
Figure 5 is largely self explanatory and illustrates a simplified flow chart of the programme executed by the processor 212 to effect the calculations referred to; the preparation of such a programme is well within the capabilities of those skilled in the art and consequently the flow chart is merely by way of illustration and does not purport to be exhaustive.
" 1 1 7 4 7 4 9 In similar vein the circuit elements and arithmetic and logic blocks shown in Figure 3 are all standard circuit elements well known to those skilled in the digital electronic art, so full circuit details are not given.
The system shown comprises a 16 element array, with a corresponding electronic system, but this array can obviously be expanded to arrays with more elements.
"
. ~, )
Claims
CLAIMS:
1.
A method of compensating for the lateral displacement of a particle from a reference line related to at least one detector which is responsive to a desired property in the particle and which produces an output signal which is dependent on the degree to which the particle possesses the property includes the steps of obtaining a measure of the lateral displacement of the particle from the reference line, and applying to the output signal a correction factor which is dependent on the measure of the lateral displacement.
A method according to claim 1 wherein the particle is caused to pass a plurality of the detectors, the output signals of the detectors being accumulated, and the correction factor being applied to the accumulation of the output signals.
A method according to claim 2 wherein the correction factor is applied only if the accumulation exceeds a predetermined value.
4.
A method according to claim 1 wherein the correction factor is additionally dependent on a physical characteristic of the particle.
5.
A method according to claim 4 wherein the physical characteristic is at least one of the shape, height, volume or mass of the particle.
6.
A method of sorting particles which includes the steps of causing the particles to move in line spaced from one another sequentially past a plurality of in-line detectors, the detectors being responsive to the presence of a desired property in the particles and each producing, for each particle, an output signal which is dependent on the degree to which the property is present in the particle, and, for each particle, accumulating the output signals of the detectors, obtaining a measure of the displacement of the particle from the centre line of the detectors, and applying to the accumulation of the output signals a correction factor which compensates for the displacement of the particle from the centre line.
A method according to claim 6 including the step of categorizing the particle according to a physical characteristic, the correction factor being dependent on the said characteristic.
8. A method according to claim 7 wherein the physical characteristic is at least one of the shape, height, volume or mass of the particle.
9. A method as claimed in claim 6 wherein the or each detector is responsive to radioactivity.
10. A method as claimed in claim 6 wherein a plurality of correction factors are stored in a read only memory and accessed by a processor unit in dependence on the measured displacement of the particle.
11. Apparatus for compensating for the lateral displacement of a particle from a reference line related to at least one detector which is responsive to a desired property of the particle and which produces an output signal which is dependent on the degree to which the particle possesses the property, comprising : means for obtaining a measure of the lateral displacement of the particle from the reference line, means responsive to the measuring means for producing a correction factor dependent on the measure of the lateral displacement, and means for applying the correction factor to the output signal.
12. Apparatus for sorting particles which comprises :
means to cause the particles to move in line spaced from one another sequentially past a plurality of in-line detector means, which detector means are responsive to the presence of a desired property in the particles and each produce, for each particle, an output signal which is dependent on the degree to which the property is present in the particle; means for accumulating the output signals of the detector means; means for measuring the displacement of the particle from the centre line of the detector means;
means responsive to the measuring means for producing a correction factor to compensate for the displacement of the particle from the centre line and means for applying the correction factor to the output of the accumulating means.
1.
A method of compensating for the lateral displacement of a particle from a reference line related to at least one detector which is responsive to a desired property in the particle and which produces an output signal which is dependent on the degree to which the particle possesses the property includes the steps of obtaining a measure of the lateral displacement of the particle from the reference line, and applying to the output signal a correction factor which is dependent on the measure of the lateral displacement.
A method according to claim 1 wherein the particle is caused to pass a plurality of the detectors, the output signals of the detectors being accumulated, and the correction factor being applied to the accumulation of the output signals.
A method according to claim 2 wherein the correction factor is applied only if the accumulation exceeds a predetermined value.
4.
A method according to claim 1 wherein the correction factor is additionally dependent on a physical characteristic of the particle.
5.
A method according to claim 4 wherein the physical characteristic is at least one of the shape, height, volume or mass of the particle.
6.
A method of sorting particles which includes the steps of causing the particles to move in line spaced from one another sequentially past a plurality of in-line detectors, the detectors being responsive to the presence of a desired property in the particles and each producing, for each particle, an output signal which is dependent on the degree to which the property is present in the particle, and, for each particle, accumulating the output signals of the detectors, obtaining a measure of the displacement of the particle from the centre line of the detectors, and applying to the accumulation of the output signals a correction factor which compensates for the displacement of the particle from the centre line.
A method according to claim 6 including the step of categorizing the particle according to a physical characteristic, the correction factor being dependent on the said characteristic.
8. A method according to claim 7 wherein the physical characteristic is at least one of the shape, height, volume or mass of the particle.
9. A method as claimed in claim 6 wherein the or each detector is responsive to radioactivity.
10. A method as claimed in claim 6 wherein a plurality of correction factors are stored in a read only memory and accessed by a processor unit in dependence on the measured displacement of the particle.
11. Apparatus for compensating for the lateral displacement of a particle from a reference line related to at least one detector which is responsive to a desired property of the particle and which produces an output signal which is dependent on the degree to which the particle possesses the property, comprising : means for obtaining a measure of the lateral displacement of the particle from the reference line, means responsive to the measuring means for producing a correction factor dependent on the measure of the lateral displacement, and means for applying the correction factor to the output signal.
12. Apparatus for sorting particles which comprises :
means to cause the particles to move in line spaced from one another sequentially past a plurality of in-line detector means, which detector means are responsive to the presence of a desired property in the particles and each produce, for each particle, an output signal which is dependent on the degree to which the property is present in the particle; means for accumulating the output signals of the detector means; means for measuring the displacement of the particle from the centre line of the detector means;
means responsive to the measuring means for producing a correction factor to compensate for the displacement of the particle from the centre line and means for applying the correction factor to the output of the accumulating means.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| ZA79/6566 | 1979-12-04 | ||
| ZA796566 | 1979-12-04 | ||
| ZA80/4248 | 1980-07-15 | ||
| ZA804248 | 1980-07-15 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1174749A true CA1174749A (en) | 1984-09-18 |
Family
ID=27131847
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000366002A Expired CA1174749A (en) | 1979-12-04 | 1980-12-03 | Displacement error correction in sorting systems |
Country Status (6)
| Country | Link |
|---|---|
| US (1) | US4394907A (en) |
| AU (1) | AU536142B2 (en) |
| CA (1) | CA1174749A (en) |
| DE (1) | DE3045335A1 (en) |
| FR (1) | FR2471225A1 (en) |
| GB (1) | GB2066453B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109789547A (en) * | 2016-11-30 | 2019-05-21 | Abb瑞士股份有限公司 | Battery sorting system based on robot |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| ZA831558B (en) * | 1982-01-27 | 1983-09-30 | ||
| DE3301814C2 (en) * | 1983-01-20 | 1986-11-20 | Kraftwerk Union AG, 4330 Mülheim | Apparatus for removing elongated nuclear instrumentation probes from nuclear reactors |
| US6448564B1 (en) | 2000-05-30 | 2002-09-10 | Gtsd Sub Iii | Apparatus, methods, and systems for assaying materials |
| RU2606414C1 (en) * | 2016-06-02 | 2017-01-10 | Евгений Борисович Пьянковский | Method of monitoring and control over construction materials radiometric parameters |
| RU2764394C1 (en) * | 2020-11-23 | 2022-01-17 | Акционерное общество "Иркутский научно-исследовательский институт благородных и редких металлов и алмазов" АО "Иргиредмет" | Method for x-ray radiometric enrichment of manganese ores |
Family Cites Families (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2717693A (en) * | 1949-09-06 | 1955-09-13 | Fred T Holmes | Method of and apparatus for sorting radiation emissive material |
| US3052353A (en) * | 1958-07-18 | 1962-09-04 | Floyd V Richardson | Ore sorting device |
| US3075641A (en) * | 1959-09-01 | 1963-01-29 | K & H Equipment Ltd | Materials sorting apparatus |
| GB992812A (en) * | 1961-03-14 | 1965-05-19 | Nuclear Materials & Equipment | Continuous object processing apparatus |
| US3242342A (en) * | 1964-02-24 | 1966-03-22 | Fmc Corp | Means for locating the center of a moving article |
| FR1575850A (en) * | 1967-09-08 | 1969-07-25 | ||
| US3588480A (en) * | 1968-12-06 | 1971-06-28 | Fairbanks Morse Inc | Processing control system |
| CA944845A (en) * | 1970-11-05 | 1974-04-02 | Colonial Sugar Refining Company Limited (The) | High speed sorting |
| US3832549A (en) * | 1972-06-22 | 1974-08-27 | Bethlehem Steel Corp | Signal conditioner apparatus for compensating an electronic material gaging signal |
| US3987391A (en) * | 1974-12-02 | 1976-10-19 | Coulter Electronics, Inc. | Method and apparatus for correcting total particle volume error due to particle coincidence |
| CA1110996A (en) * | 1977-09-09 | 1981-10-20 | Reginald H. Clark | Apparatus and method for sorting articles |
| US4194634A (en) * | 1977-12-09 | 1980-03-25 | Leonard Kelly | Method and apparatus for sorting radioactive material |
| ZA783198B (en) * | 1978-06-05 | 1979-09-26 | Sphere Invest | Improvements relating to sorting systems |
| US4246098A (en) * | 1978-06-21 | 1981-01-20 | Sunkist Growers, Inc. | Method and apparatus for detecting blemishes on the surface of an article |
-
1980
- 1980-12-02 DE DE19803045335 patent/DE3045335A1/en active Granted
- 1980-12-03 CA CA000366002A patent/CA1174749A/en not_active Expired
- 1980-12-03 US US06/212,515 patent/US4394907A/en not_active Expired - Lifetime
- 1980-12-03 GB GB8038682A patent/GB2066453B/en not_active Expired
- 1980-12-03 FR FR8025666A patent/FR2471225A1/en active Granted
- 1980-12-04 AU AU65061/80A patent/AU536142B2/en not_active Ceased
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109789547A (en) * | 2016-11-30 | 2019-05-21 | Abb瑞士股份有限公司 | Battery sorting system based on robot |
Also Published As
| Publication number | Publication date |
|---|---|
| FR2471225A1 (en) | 1981-06-19 |
| DE3045335A1 (en) | 1981-07-09 |
| US4394907A (en) | 1983-07-26 |
| AU6506180A (en) | 1981-06-11 |
| FR2471225B1 (en) | 1985-04-05 |
| AU536142B2 (en) | 1984-04-19 |
| GB2066453B (en) | 1984-01-18 |
| GB2066453A (en) | 1981-07-08 |
| DE3045335C2 (en) | 1988-05-05 |
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