GB2119509A

GB2119509A - Sorting apparatus and method

Info

Publication number: GB2119509A
Application number: GB08311134A
Authority: GB
Inventors: Shyam Bhaskar Mehta; Joseph Anthony Villanueva
Original assignee: Geosource Inc
Current assignee: Geosource Inc
Priority date: 1982-04-30
Filing date: 1983-04-25
Publication date: 1983-11-16
Also published as: ZA832827B; GB8311134D0; AU1365783A

Abstract

Apparatus (10) for sorting particles (20, 22) which differ from one another only slightly in reflectivity at each of two wavelengths within the visible spectrum includes, for viewing an area through which the particles are passed, a viewer (16) including means (30) to generate first and second colour signals respectively representative of the intensity of light reflected at the two wavelengths from a passing particle. A classifier (46) generates a first classification signal representing the ratio of the first and second colour signals and a second classification signal representing the sum of the first and second colour signals. A comparator (46) compares the first and second classification signals with corresponding first and second reference signals, and a separator (50, 52) generates a separation signal to actuate ejector element (36) via driver (38) if a viewed article causes a preestablished difference between either of the classification signals and its corresponding reference signal. <IMAGE>

Description

SPECIFICATION Sorting apparatus and method This invention relates generally to apparatus and a method for sorting articles which are of various sizes and have only slight differences in reflectivity. More particularly, the invention relates to apparatus and a method for separating oil shale particles from nahcolite particles in mined, nahcolite-bearing oil shale ores.

It is well-known that there are large deposits of oil shale ore in certain geographic locations in the United States and throughout the world. One of the minerals sometimes found in oil shale deposits is nahcolite, which is a naturallyoccurring sodium bicarbonate. Nahcolite may occur throughout the oil shale ore.

In order to extract oil more efficiently from mined oil shale ore, it is preferable to separate the nahcolite particles from the oil shale particles before processing the iatter. Furthermore, the nahcolite fraction of the ore is useful in pollution control, as nahcolite reacts chemically with certain dangerous gases to reduce the harmful effect of the gases.

It would be advantageous to be able to classify and separate the oil shale particles from the nahcolite particles in a mined oil shale ore by means of a bichromatic colour sorting apparatus, such as that described in our United States Patent No. 4,134,498. The apparatus of that patent uses the conventional ratio method for classifying articles either as acceptable or unacceptable.

However, it has been observed that a nahcolite particle or "rock" has only a slightly higher reflectivity than an oil shale "rock" of similar size at each of any two different colour wavelengths in the visible spectrum. Thus, separation of nahcolite and oil shale rocks based solely upon differences in the ratios of light energy reflected at two such wavelengths has not been satisfactory.

The two signals representative of the light reflected at the respective wavelengths may also be summed. There is a substantial difference between the sum of the signals representative of a nahcolite rock and the sum representative of an oil shale rock, as long as the size of the rocks is relativeiy the same.

Where the sizes of the rocks vary, classification based solely upon the addition method results in inaccurate separation. For example, a small white nahcolite rock, which covers only a portion of the background against which the rock is viewed, "looks" substantially like a large, black oil shale rock (assuming that a non-reflective background is used).

According to one aspect of the present invention, apparatus for sorting particles which differ from one another only slightly in reflectivity at each of two wavelengths within the visible spectrum comprises a viewer for viewing a selected area through which the particles are passed, the viewer including means to generate first and second colour signals representative of the intensity of light reflected at respective first and second wavelengths from a particle passing through the selected area; a classifier to generate a first classification signal functionally related to the ratio of the first and second colour signals and a second classification signal functionally related to the sum of the first and second colour signals; a comparator to compare the first and second classification signals with corresponding first and second predetermined reference signals; and a separator to generate a separation signal in response to a pre-established difference between either of said first and second classification signals and its corresponding predetermined reference signal.

The electrical circuitry of the present invention is adapted to be used in conjunction with the apparatus described in U.S. Patent No.

4,1 34,498.

According to another aspect of the invention, a method of sorting particles which differfrom one another only slightly in reflectivity at each of two wavelengths within the visible spectrum comprises conveying a stream of particles to a selected area for viewing; viewing the light energy reflected from the particles at each of said two wavelengths; generating first and second electrical colour signals representative of the respective intensities of the light energy viewed at the two wavelengths; generating a first classification signal functionally related to the ratio of the first and second colour signals; generating a second classification signal functionally related to the sum of the first and second colour signals; comparing the first and second classification signals with corresponding first and second predetermined reference signals; generating a sorting signal responsive to a preestablished difference between either of the first and second classification signals and its corresponding predetermined reference signal; and sorting the particles from the stream in response to the sorting signal.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a partial elevational view and a block diagram of an apparatus for separating articles in accordance with the present invention; Figure 2 is a plan view of part of the apparatus of Figure 1; Figure 3 is a block diagram of electrical circuitry used in the apparatus of Figure 1; Figures 4A and 4B are schematic diagrams of a portion of the electronic circuitry of Figure 3; and Figure 5 is a schematic diagram of a product select network of Figure 3.

Referring first to Figures 1 and 2, a sorting apparatus 10 is operable to separate at least two different types of articles which vary in size and have only slight differences in reflectivity. The apparatus 10 is particularly useful in separating varying sizes of oil shale particles or "rocks" from varying sizes of nahcolite particles or "rocks".

As shown in Figures*1 and 2, the apparatus 10 includes viewing means 1 2 for viewing an illuminated viewed area 14, through which a stream of particles or "rocks" passes, as described in the above-mentioned United States Patent No. 4,134,498 (hereinafter referred to as the "Jones" patent). The viewing means 12 may comprise a plurality of N viewer elements, or viewers, indicated by reference numerals 1 6-1, 16-2,16-3,... 16-N.Theviewers 16-1 1 6-N are disposed in a side-by-side arrangement so as to completely encompass the illuminated area 14 within their field of view.Each of the viewer elements 1 6-1 . 1 6-N is arranged so as to view one of a corresponding plurality of sectors 14-1 . 14-N into which the illuminated, viewed area 14 is divided. The viewed area 14 (comprising the N viewed sectors) has a width commensurate with the transverse width of an upper article conveyor 18. If a conveyor width of 22 inches is utilised, for example, twenty-two viewer elements 16, each assigned to view a one-inch wide sector of viewed area 14, may be used for rock sizes of one-inch or larger. Alternatively, conveyors of other sizes and having different sector width assignments may be used, the sector width assignment being related to the sizes of the particles or rocks to be separated.

Articles to be separated, such as a mixture of varying sizes of oil shale and nahcolite rocks, are disposed across the article conveyor 1 8 in an entirely random fashion. The oil shale rocks and nahcolite rocks are indicated in the figures by reference numerals 20 and 22, respectively.

Before or during conveyance by the conveyor 18, the rocks 20 and 22 are sprayed or otherwise wetted with water.

Articles or rocks 20 and 22 are carried in a direction 24 along upper article conveyor 1 8 to its discharge end, 26. At discharge end 26, articles 20 and 22 fall freely from upper article conveyor 18 toward a second, lower article conveyor 28.

During their free-fall, both oil shale rocks 20 and nahcolite rocks 22 pass through viewed area 1 4.

Each rock 20 or 22 passes through at least one sector 14 ... 14-N of viewed area 14 and is viewed by at least one of viewer elements 1 6-1 ...16-N.

Apparatus 10 includes signal generating means 30 associated with each of the viewer elements to generate a first and a second electrical signal representative of the light energy reflected at first and second predetermined color wavelengths from articles passing through the sector of the viewed area corresponding to the particular viewer element. An illuminator 32 is provided at a convenient location in apparatus 10 to illuminate the article flow. Illuminator 32 provides a source of light energy in the visual spectrum. Electrical signals generated by signal generating means 30 are utilized to classify each article.

Apparatus 10 is operable to prevent either oil shale rocks or nahcolite rocks, depending upon which is selected, from reaching lower conveyor 28. The elimination of unacceptable articles is effected by an ejector 34. Ejector 34 includes a plurality of ejector elements 36, each of which is driven by an associated ejector driver 38. Each ejector element 36 is associated with one of the viewer elements 16, as described in the Jones patent.

As seen in Figure 1, each of viewers 1 6-1 ...

1 6-N is oriented to define a predetermined angle 40 with the horizontal. When no article is within a sector 14-1, 14-2... of the viewed area 14, the corresponding viewer is trained upon a reference region 42 located beneath upper article conveyor 18. This reference region 42 is known as the "black hole", and signal generating means 30 associated with those viewers "seeing" this region generate little or no signal output. The apparatus embodying the teachings of this invention preferably uses "black hole" region 42 as a non-reflective background region against which light energy reflected from articles in the article stream is detected. The black hole region is not utilized to provide a reference signal against which articles are classified.As discussed hereinafter, the articles are compared and classified against reference signals set into comparator arrangements 176 and 198-200 (Figure 4A).

Although the electronic circuitry embodied in apparatus 10 is discussed more fully herein, Figure 1 diagrammatically illustrates a sampling arrangement 44 for sampling the first and second electrical signal outputs from signal generating means 30 operably coupled to viewing means 12.

Sampling arrangement 44 may conveniently be a multiplexer which samples the information input thereto from each of viewers 1 6-1 ... 1 6-N, as described in the Jones patent. Sampling arrangement 44 presents that information over first and second electrical transmission paths 74, 76 to a classification and comparison arrangement 46 for classifying and comparing the sampled electrical signals. Classifier 46 is connected within the transmission paths and generates a plurality of first and second electrical classification signals. The first classification signals are functionally related to the ratio of the first and second electrical signals sampled from the signal generating means 30. The second classification signals are functionally related to the summation of the same first and second electrical signals. Classifier 46 also includes comparator circuitry for comparing the classification signals with predetermined reference signals (as discussed more fully hereinafter) and for generating a separation signal if a rock passing through one of the sectors 141 ... .11 N is classified as unacceptable.

Memory arrangement 50, having a plurality of memory locations therein, is operatively coupled to the classifier 46 to store a separation signal in a memory location corresponding to the particular sector of the viewed area 14, as described in the Jones patent. A separation signal is stored in a particular memory location for a predetermined period of time corresponding to the time required for a rock to pass from viewed area 1 4 to a position near one of ejector elements 36. An actuating arrangement 52 is operatively associated with the memory 50 for actuating the particular one of the ejector drivers 38 associated with the corresponding ejector element 36.

Each of viewer elements 16-1 ... 1 6-N includes a lens arrangement, and signal generating means 30 may include first and second light sensors such as solar cells, which receive the light from the lenses, as described in the Jones patent.

Referring now to Figure 3, a block diagram of the preferred circuitry utilized in apparatus 10 embodying the teachings of this invention is disclosed.

Sampling arrangement 44 comprises a multiplexer, identified by reference numeral 68, which is connected to output lines 72 emanating from the signal generating means 30 associated with each of the viewer elements 1 6. Appropriate preamplification of the signals is provided.

Multiplexer 68 operates to sample, after preamplification, the two electrical signals output from the signal generating means, and presents the sampled signals for transmission over first and second electrical transmission paths, such as output signal lines 74 and 76. The outputs of sampling arrangement 44 are connected to classification and comparing arrangement 46.

More specifically, output signal lines 74 and 76 are connected to a bias network 78. Bias network 78 is, in turn, coupled to a divide network 80 which generates the first classification signals functionally related to the ratio of the electrical signals on lines 74 and 76. Bias network 78 is also coupled to an addition network 81 which generates the second classification signals functionally related to the summation of the electrical signals on lines 74 and 76.

The analog outputs of divide network 80 and addition network 81 are coupled to a ratio comparator network 82 and to an addition comparator network 84, respectively. Connected in parallel with output lines 74 and 76 from multiplexer 68 is a threshold enable network 88.

A first output line 90 of threshold enable network 88 is connected operatively to bias network 78, and a second output line 92 of network 88 is operatively connected to a product select network 93.

A null cycle adjust network 94 is connected in a feedback loop between the output of divide network 80 and addition network 81 and the inputs thereof. Null cycle adjust network 94 is enabled during the "null cycle" of multiplex operation, as described in the Jones patent, to provide a nulling function to divide network 80 and addition network 81.

The output from classification and comparing arrangement 46 is connected to memory 50.

More specifically, the outputs from comparator networks 82 and 84 are connected through a logic network 96 by a line 97 to product select network 93, which is connected to the Data Input terminal of a random access memory element 98.

Memory element 98 contains a plurality of memory locations, corresponding to the sectors 14-1 ... 14-N of viewed area 14, access to which is stepped in synchronism with the stepping action of multiplexer 68 as it is moved through the outputs from each of viewers 1 6-1 ... 1 6-N. Memory 50 is connected to actuating arrangement 52.

Random access memory 98 is connected to a read/write enabling network 100 through a line 102. The output of memory 98 at the DATA OUT terminal is connected through a line 104 to a separate logic demultiplex enable network 106.

Logic network 106 is also coupled to enabling network 100 through a line 108. The output of logic network 106 is coupled to a demultiplexer 110 through lines 112. Demultiplexer 110 actuates the appropriate ejector driver 38 over lines 114. During the time that a multiplexer channel is up, networks 100 and 106 provide means for reading a signal previously stored in a predetermined memory location and for transmitting a signal to the demultiplexer 110 to actuate the appropriate ejector driver 38 if the previously stored signal is a separation signal.

Networks 100 and 106 also provide means for writing the current article classification signals into the addressed memory location while the multiplexer channel is up.

A timing network 11 6 provides master controlling pulses to synchronously direct the stepping function of sampling arrangement 44 (multiplexer 68) and actuating arrangement 52 (demultiplexer 110) with the addressing of memory 50 (the locations within memory element 98). Timing network 11 6 has input thereto a reference clock frequency from which a plurality of binary frequencies are generated. Also, the enabling functions of network 100 are controlled by timing network 11 6 so that the read and write activities may be performed during the time that each individual channel of multiplexer 68, demultiplexer 110, and memory element 98 is addressed, as described in the Jones patent.

Those skilled in the art will appreciate that multiplexer 68 and demultiplexer 110 are synchronously stepped to predetermined channels therein corresponding to each of viewer elements 1 6 at the same time that locations in memory element 98 corresponding to those viewer elements (and therefore corresponding to predetermined sectors of the viewed area) are addressed. The synchronous stepping of multiplexer 68, memory element 98, and demultiplexer 110 is usually, but not necessarily, sequential. As multiplexer 68 is stepped, the signals present at the outputs of signal generators 30 associated with each of viewers 1 6 are sampled, and the first and second classification signals are generated.These classification signals are compared (by comparators 82 and 84) to various levels to determine if the color of the rock indicates an oil shale rock or a nahcolite rock.

During the time that multiplexer 68 has a particular channel up, the memory location synchronously addressed is first read, the information previously stored therein (if a separation signal) generates a signal from enable network 106 to enable demultiplexer 110 to actuate the appropriate ejector driver 38 associated with the viewer element being sampled. After this read-out has occurred, the result of the current classification and comparison operation is entered into the addressed memory location. This current classification and comparison information is stored until the predetermined period of time passes at which time that particular memory location is again addressed, as described in the Jones patent.

Referring now to Figures 4A and 4B, a schematic diagram of the classification and comparing arrangement 46, which includes bias network 78, divide network 80, addition network 81, ratio and addition comparator networks 82 and 84, threshold enable network 88, product select network 93, null cycle adjust network 94, and logic network 96, is shown. Output lines 74 and 76 from green and red multiplexing sections of multiplexer 68, RED MUX OUT and GREEN MUX OUT, are connected to terminals 160 and 162, respectively. Sampled information in an analog voltage format from each of the twentytwo input channels, preceded by a ground signal and followed by nine grounded channels (indicative of the null cycle) are serially presented from the red multiplexing and from the green multiplexing sections through terminals 1 60 and 162, respectively.

Amplifiers 164 and 166 are connected to terminals 1 60 and 162, respectively. The gains of amplifiers 1 64 and 1 66 are set at different levels from one another for compatability with divide, network 80 and addition network 81. The inverted and appropriately scaled signals at the outputs of amplifiers 1 64 and 1 66 are connected to divide network 80 and addition network 81 (Figure 4B).

Divide network 80 operates to provide a real number analog voltage output representing the quotient of the inputs thereto. Divide network 80 is arranged so that an equality of values appearing at the input terminals thereof results in a constant value appearing at the output thereof. The value of the constant is determined and maintained throughout a scan of the twenty-two veiwer channels in accordance with the operation of null cycle adjust network 94. A suitable divide network is that manufactured by Analog Devices, Inc, under model number AD532. Output line 168 of the divide network 80 is connected to ratio comparator network 82 by a line 170.

Line 1 70 is connected to the non-inverting terminal of a comparator 174, such as that manufactured by National Semiconductor under model number LM31 1. A reference voltage is supplied to the inverting input of comparator 174, the reference being adjustably provided from a ratio trip reference network 1 76. Network 1 76 includes resistors 1 78 and 1 80 and a variable resistor 1 82. If the analog output voltage on line 1 70 is more positive than the reference voltage presented to the inverting terminal of comparator 174, a digital logic high pulse appears on an output line 1 84.Output line 1 84 is connected, through a line 186, to logic network 96, which comprises a suitable logic element 188, such as an OR gate. The output of OR gate 188 is coupled to product select network 93 by line 97. Visual indication of an unacceptably colored rock (either an oil shale rock or a nahcolite rock) is provided by the connection of line 1 84 to a network including a resistor 190, an NPN transistor 192, a resistor 194, and a light emitting diode (LED) 196.

Addition network 81 includes a summing amplifier 200, such as that manufactured by PMI, Inc. under model number OP--07. Addition network 81 is connected to addition comparator network 84 over line 202. Comparator network 84 includes comparator 204, such as that manufactured by National Semiconductor under model number LM3 11. Variable resistors 206 and 208 are provided to define a voltage "window" between which the summing trip level may be varied. A variable summing trip level resistor 210 is serially connected between resistors 206 and 208. The variable arm of resistor 210 is, in turn, connected to the inverting input of comparator 204 over a line 212.

If the analog output voltage on line 202 is more positive than the reference voltage presented to the inverting terminal of comparator 204, a digital high pulse appears on an output line 214. Output line 214 is connected to OR-gate 188. Visual indication of an unacceptably colored rock is provided by the connection of line 214 to a network including a resistor 218, an NPN transistor 220, a resistor 222, and a LED 224.

Connected in parallel across the green and red multiplexed inputs to terminals 160 and 162 is a threshold enable network 88. Threshold enable network 88 includes a threshold voltage network 230, including a variable resistor 232 and resistors 234 and 236 (Figure 4A). The voltage set by threshold voltage network 230 is presented through a line 238 to the inverting inputs of comparators 240 and 242, which may be comparators manufactured by National Semiconductor under model number LM3 11. As seen, the non-inverting input of comparator 240 is connected, through a line 244, with a multiplexed output from the GREEN MUX OUT appearing at the terminal 1 62 of amplifier 1 66.

Similarly, the non-inverting input of comparator 242 is connected through a line 246 with the voltage output of the RED MUX OUT appearing at terminal 1 60 of amplifier 1 64. The outputs of comparators 240 and 242 are connected by line 92 to product select network 93 (Figure 5).

The tied outputs of comparators 240 and 242 are connected to a positive voltage source through a resistor 250 and, through a line 252 and a resistor 254, to a transistor logic network 256. Transistor logic network 256 includes a first NPN transistor 258 connected at its base to the outputs of comparators 240 and 242. The collector of transistor 258 is connected to the collector of a second transistor 260, also of the NPN type. The base of transistor 260 is connected, through a resistor 262, to a line 264 leading from null adjust cycle network 94 (Figure 4B).

The tied collectors of transistors 258 and 260 are connected to a positive voltage source through resistors 266 and 268. The base of a PNP transistor 270 is connected between resistors 266 and 268. The emitter of transistor 270 is connected to a positive voltage source while the collector is connected through a line 90 to bias network 78. Bias network 78 operates to present predetermined voltage levels to divide network 80 and addition network 81 in the event that no rock is in the view of any one of the viewer elements and also during the null cycle.

Bias network 78 includes a first voltage divider 280 including resistors 282 and 284 connected between the inverting inputs of amplifiers 1 64 and 1 66. Connected to a node 286 is a second voltage divider 288, including resistors 290 and 292. Resistor 290 is tied to the collector of a PNP transistor 294. The emitter of transistor 294 is tied to a positive voltage source through a resistor 296. A zener diode 298 also is provided. The base of transistor 294 is connected to the positive voltage source by a resistor 300 and to the output of a NOR gate 302 through a resistor 304. The NOR gate 302 is connected at one input to null cycle adjust line 264 by a line 306 and at its second input by a line 308 connected to the output of an inverter 272, the input of which is connected to threshold enable network 88 by line 90.

In operation, during those periods when no rock is in view or during the null cycle, bias network 78 is operative to ensure presentation of the appropriate analog voltages to divide network 80 and addition network 81. At the output of NOR gate 302, the signal is a logic 0 (or digital low) when no article is detected or during the null cycle. With the output of the gate 302 low, transistor 294 is rendered conductive. Zener diode 298 establishes a predetermined voltage VE voits at the emitter of transistor 294. A lower voltage is present at the collector thereof. At node 286, a relatively high bias voltage is applied to amplifiers 164 and 1 66.

Through the operation of bias network 78, as described in the Jones patent, a voltage is introduced to amplifiers 1 64 and 166 that is appropriately valued and scaled for divide network 80 and addition network 81 and that is much greater than any offset from the preamplifiers. Thus, offsets of the preamplifiers are rendered minimal at the input to divide network 80 and addition network 81 by the bias voltages introduced to the inputs to amplifiers 164 and 166 through resistors 282 and 284.

The output of divide network 80 is presented to ratio comparator network 82, and the output of addition network 81 is presented to addition comparator network 84. If a signal indicative of an unacceptably colored rock is presented to either comparator 82 or comparator 84, an appropriate output is presented to logic network 96.

Referring again to Figure 4B, null cycle adjust network 94 is connected from output line 1 68 of divide network 80 and output line 202 of addition network 81 through a normally open switch 318 and through a resistor 320 into the inverting input of an amplifier 322. The amplifier 322 may be that manufactured by Motorola under model number MC741 The output of amplifier 322 is fed back through a capacitor 324 to the inverting input thereof and also through resistors 326 and 328 to ground. The grounded side of resistor 328 is connected in series to resistors 330 and 332, which are in turn connected to a positive voltage source. The non-inverting input of amplifier 322 is connected to a point 334 located between resistors 330 and 332.Switch 31 8 is connected to the collector of an NPN transistor 336, the emitter of which is connected to a negative voltage source. The collector of transistor 336 is connected through a resistor 338 to a positive voltage source, and the base is connected through a resistor 340 to the collector of a PNP transistor 342. The emitter of transistor 342 is connected both to a positive voltage source and to a biasing arrangement comprising resistors 344 and 346. Resistor 346 is connected through diodes 348 and 350 to timing network 116 (Figure 3) and, specifically, to the outputs 23 and 24 thereof. The anodes of each of the diodes 348 and 350 are connected to the NOR gate 302 through the lines 264 and 306.

Null cycle adjust network 94 is operative to activate bias network 78 during selected multiplex channel times, as described in the Jones patent, to provide the appropriate voltages to divide network 80 and addition network 81.

Referring now to Figure 5, a schematic diagram of product select network 93 is illustrated. As shown, two resistors 360 and 362 are connected to the inverting input of comparator 364 over a line 366. The noninverting input of comparator 364 is connected to the output of OR-gate 188 via line 97. The output of comparator 364 is connected to the base of an NPN transistor 368 and to resistor 370 over a line 372. The collector of transistor 368 is connected to a resistor 374 and to a diode 376 via a resistor 378. The collector of transistor 368 is also connected to one input of a NAND-gate 380. The second input to NAND-gate 380 is derived from threshold enable network 88 over line 92.

The output of NAND-gate 380 is connected to the reverse mode terminal of a two-position switch 382. The collector of transistor 368 is connected to the normal mode terminal of switch 382.

Product select network 93 is operative to enable either the ejection of nahcolite rocks (when switch 382 is in the normal mode) or the ejection of oil shale rocks (when switch 382 is in the reverse mode). As the raw separation signal appears at the output of comparator 364, product select network 93 facilitates either operation only when threshold enable network 88 indicates that a rock is being viewed.

In operation, varying sizes of raw oil shale and nahcolite rocks, preferably sized between one and three inches, are washed with water. The wet rocks are fed by means of a vibratory feeder (not shown)' onto conveyor belt 1 8. As the rocks reach discharge end 26 of conveyor 18, they fall freely by gravity through one of the sectors of viewed area 14. As each rock passes through the viewed area, it is classified either as an oil shale rock or a nahcolite rock. If the normal mode is selected, all nahcolite rocks are diverted by ejector 34 from falling onto conveyor 26. If the reverse mode is selected, all oil shale rocks are diverted by ejector 34 from falling onto conveyor 26.

It is to be understood that the oil shale sorter classification circuitry of the present invention may admit of other embodiments. The detailed description is given only to facilitate understanding of the invention by those skilled in the art and should not be construed as limiting the invention.

Claims

1. Apparatus for sorting particles which differ from one another only slightly in reflectivity at each of two wavelengths within the visible spectrum, comprising a viewer for viewing a selected area through which the particles are passed, the viewer including means to generate first and second colour signals representative of the intensity of light reflected at respective first and second wavelengths from a particle passing through the selected area; a classifier to generate a first classification signal functionally related to the ratio of the first and second colour signals and a second classification signal functionally related to the sum of the first and second colour signals; a comparator to compare the first and second classification signals with corresponding first and second predetermined reference signals; and a separator to generate a separation signal in response to a preestablished difference between either of said first and second classification signals and its corresponding predetermined reference signal.

2. Apparatus for separating varying sizes of oil shale rocks from varying sizes of nahcolite rocks, comprising a plurality of viewers for viewing respective sectors of a corresponding plurality of sectors of a viewed area; signal generating means for generating first and second electrical signals respesentative of light energy reflected from a rock at corresponding first and second colour wavelengths; a multiplexer to sample the plurality of first and second electrical signals sequentially and to transmit such signals over first and second electrical transmission paths; electrical classification circuitry connected to the first and second electrical transmission paths to generate a first classification signal functionally related to the ratio of the first and second electrical signals and a second classification signal functionally related to the summation of the first and second electrical signals; electrical comparison circuitry to compare the first and second classification signals with corresponding first and second predetermined reference signals; and electrical separator circuitry to generate a separation signal responsive to a predetermined difference between one of the first and second classification signals and its corresponding predetermined reference signal.

3. Apparatus for separating at least two different types of articles of varying size disposed in an article stream and having only slight differences in reflectivity, the apparatus including a plurality of viewers each to view a respective one of a predetermined plurality of sectors of a viewed area through which the article stream passes; signal generating means associated with each viewer for generating first and second electrical signals representative of light energy reflected at corresponding first and second wavelengths from an article passing through each of the sectors; a multiplexer for sampling each of the first and second electrical signals for transmission over corresponding first and second electrical transmission paths; electrical classification circuitry connected to the first and second electrical transmission paths for generating a first classification signal functionally related to the ratio of each of the first and second electrical signals and a second classification signal functionally related to the summation of the first and second electrical signals; means to compare the first and second classification signals with corresponding first and second predetermined reference signals; and means to produce a separation signal in response to a predetermined difference between one of the classification signals and its corresponding predetermined reference signal.

4. A method of sorting particles which differ from one another only slightly in reflectivity at each of two wavelengths within the visible spectrum, comprising conveying a stream of particles to a selected area for viewing; viewing the light energy reflected from the particles at each of said two wavelengths; generating first and second electrical colour signals representative of the respective intensities of the light energy viewed at the two wavelengths; generating a first classification signal functionally related to the ratio of the first and second colour signals; generating a second classification signal functionally related to the sum of the first and second colour signals; comparing the first and second classification signals with corresponding first and second predetermined reference signals; generating a sorting signal responsive to a preestablished difference between either of the first and second classification signals and its corresponding predetermined reference signal; and sorting the particles from the stream in response to the sorting signal.

5. A method of separating at least two difference types of articles of varying size and having only slight differences in reflectivity, comprising disposing the articles on to a conveyor; conveying the articles through a plurality of sectors of a viewed area viewed by a corresponding plurality of viewers; generating first and second electrical signals representative of light energy at corresponding first and second colour wavelengths reflected from each article passing through one of the sectors of the viewed area; generating a first classification signal functionally related to the ratio of the first and second electrical signals; generating a second classification signal functionally related to the summation of the first and second electrical signals; comparing the first and second classification signals to corresponding first and second predetermined reference signals; and generating a separation signal responsive to a predetermined difference between one of the classification signals and its predetermined reference signal.

6. A method of separating a stream of varying sizes of oil shale rocks and nahcolite rocks, comprising disposing the stream on to a conveyor; conveying the stream through a plurality of sectors of a viewed area viewed by a corresponding plurality of viewers; generating first and second electrical signals representative of tight energy at corresponding first and second colour wavelengths reflected from each rock passing through one of the sectors of the viewed area; generating a first classification signal functionally related to the ratio of the first and second electrical signals; generating a second classification signal functionally related to the summation of the first and second electrical signals; comparing the first and second classification signals to corresponding first and second predetermined reference signals; and generating a separation signal responsive to a predetermined difference between one of the classification signals and its predetermined reference signal.

7. Apparatus as claimed in Claim 1 and substantially as hereinbefore described with reference to the accompanying drawings.

8. A method as claimed in Claim 4 and substantially as hereinbefore described with reference to the accompanying drawings.