Apparatus and method for sorting articles

Apparatus and method for sorting scrap metal pieces dependent on the type of metal therein. The apparatus includes a conveyor and a feeding arrangement to feed the scrap metal pieces on to the conveyor, together with an X-ray fluorescence detector to examine each metal piece and determine the type of metal as a result of the characteristic X-rays emitted. A respective control signal is utilized to move pegs on the conveyor so as to permit the respective metal piece to exit from the conveyor along a respective path and to enter a bin for that particular type of metal. In this way scrap metal pieces of different metal are collected in different bins for subsequent processing.

BACKGROUND OF THE INVENTION 
This invention relates to an apparatus and method for sorting articles. 
Embodiments of the invention are particularly concerned with sorting mixed 
metal pieces dependent on the type of metal. 
Methods have previously been proposed whereby articles have been sorted 
manually as they pregressed along a conveyor belt. Once identified, such 
articles would be manually removed from the conveyor belt and deposited in 
appropriately identified receptacles. A method and apparatus is known for 
the separation of uranium bearing rock and this consists of a vibratory 
feeding mechanism together with a translucent conveyor belt. A light 
source device is provided to measure the rock size together with a 
radioactive counter which measures the radiation rate from each rock. From 
the measurements, a product of the rock size and radiation rate is 
computed electronically and a signal is produced to cause actuation of air 
jets which separate the rocks into two categories at the end of the 
conveyor belt. Attempts have been made to utilize this apparatus for 
sorting other items, such as pieces of scrap metal, into different 
categories but such attempts were not successful. 
Apparatus is known for sorting mixed metals using differential melting 
techniques. It is believed that this process is relatively inefficient and 
consumes large amounts of energy. 
As it will be appreciated, apparatus for sorting scrap metal would be 
particularly attractive from a commercial point of view having regard to 
the amount of scrap metal which is presently located in different scrap 
metal yards as, for example, an end product of the automobile industry. 
From one aspect it is an object of the present invention to provide 
apparatus for sorting objects which is applicable to the sorting of scrap 
metal and in which the above-mentioned disadvantages are obviated or 
substantially reduced. 
SUMMARY OF THE INVENTION 
According to this aspect, there is provided conveyor apparatus for 
conveying a plurality of articles along a conveyor in the direction of the 
conveyor and causing different articles to leave the conveyor at different 
exit stations comprising a conveyor having a plurality of keys extending 
transversely across the conveyor and each capable of movement from a 
supporting position to a non-supporting position at a selected exit 
station whereby a respective article is caused to leave the conveyor at 
said selected exit station. 
More specifically there is provided conveyor apparatus for sorting scrap 
metal pieces dependent on the type of metal therein including 
a conveyor, 
feeding means to feed the scrap metal pieces on to said conveyor, 
detector means located adjacent said conveyor to examine said scrap metal 
pieces and determine the type of metal therein and to provide a 
corresponding identifying signal, control means for utilising each 
respective corresponding identifying signal to select one of a plurality 
of paths whereby each scrap metal piece is fed along a selected path in 
dependence on the type of metal determined therein by said detector means. 
From another aspect, it is an object of the present invention to provide a 
method of sorting objects which is particularly applicable to the sorting 
of scrap metal and in which the above-mentioned disadvantages are obviated 
or substantially reduced. 
According to this aspect there is provided a method of sorting scrap metal 
piece dependent on the type of metal therein including the steps of 
feeding the scrap metal pieces on to a conveyor, radiating each scrap 
metal piece with radiation from a radioactive source whereby it emits 
characteristic X-rays dependent on the type of metal therein, detecting 
said characteristic X-rays and producing a corresponding identifying 
signal corresponding to said type of metal, utilising each corresponding 
identifying signal in control means to select one of a plurality of paths 
to feed each piece of scrap metal along a selected path in dependence on 
the type of metal determined therein. 
According to yet another aspect there is provided apparatus for sorting 
objects comprising a conveyor constructed of members extending 
transversely thereacross with a gap between each pair of said member, and 
a reference unit positioned at a fixed location in relation to the 
conveyor whereby the position of objects travelling along the conveyor can 
be measured therefrom.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIGS. 1 and 2, there is diagrammatically illustrated apparatus 
for sorting scrap metal. The mixed pieces of scrap metal travel along a 
conveyor belt system 2 onto a sorter conveyor system 4 arranged in a 
circular manner as illustrated in FIG. 1. The circular or carousel 
conveyor 4 comprises a plurality of individual members or keys adapted to 
support the pieces of scrap metal fed thereon from the conveyor belt 2. In 
use, the carousel conveyor 4 in FIG. 1 moves in a clockwise direction. 
Thus, each piece of scrap metal is supported by one or more members 6, 
dependent on its size, and passes, first of all through an overhead 
detection unit 7 and then through the vertical light beams emanating from 
the light head, unit 8, where the size of the piece may be determined. 
Information signals as to the size of the piece and its presence on the 
carousel conveyor are fed to the computer unit as described below. 
After passing the light head, unit 8, the respective piece of metal 
material continues along the carousel conveyor and under the X-ray 
fluorescence unit 10. This unit determines the elements present in the 
scrap metal and passes this information to the computer unit which then 
analyzes all information signals received and produces resultant output 
control signals. These resultant output control signals are dependent on 
the type of elements determined to exist in the piece of scrap metal and 
also on the size of the piece of metal. The computer's output signals are 
fed to a selected one of a plurality of control stations, dependent on the 
type of metal. The control stations are identified in FIG. 1 as stations 
12,14,16,18 and 20. Each station is adapted to receive scrap metal of a 
particular type, for example, iron, brass, zinc or aluminum. At the 
station where aluminum is deposited a metal detector is provided beneath 
the members 6. Only if the piece of scrap material is determined to be 
metallic, is the piece deposited here. Consequently, non-metallic pieces 
continue along the carousel conveyor to the discard bin. 
The construction of the carousel conveyor 4 will now be considered in 
greater detail, particularly having regard to the construction of the 
individual members or keys 6. Referring to FIG. 1, the carousel conveyor 
consists of a circular wheel, or table, 24 carrying a plurality of metal 
plates, such as 26, rigidly mounted around the periphery of the table 24. 
Each metal plate 26 supports a group of nineteen individual members in a 
manner which will be described in greater detail with reference to FIG. 3. 
Each individual member 6 consists of a plastic key which is ten inches long 
and a quarter-inch square cross section. Each key is supported at its 
inner end on the respective metal plates 26 in a pivotal manner by means 
of a metal rod 28. One such rod is shown in FIG. 3 in a remote location so 
as to indicate how it would be inserted through an aperture in the 
respective member 6 and aligned apertures in finger portions 30 and 32 on 
either side of the respective member 6. Thus, each key is supported at its 
inner end so that it can rotate about the respective metal rod 28. 
The other end of the key portion 6 is normally supported by a smooth metal 
plate 34 which extends around the outer periphery of the carousel conveyor 
4. Thus, the outer end of each member 6 can slide over the smooth metal 
plate 34 during normal rotation of the carousel. 
At the various control stations 12 through 22, the continuity of the smooth 
metal plate 34 is interrupted. The interruption is filled by a slidable 
metal plate 36 (FIG. 3) which can be retracted under control of the 
solenoid device 38 so as to cause the respective member of key 6 to rotate 
about its metal rod or pin 28. Referring particulary to FIG. 4, it will be 
seen that the solenoid device 38 comprises a solenoid coil unit 40 having 
a movable armature 42. Attached thereto is a rod 44 which supports the 
slidable metal plate 36 in the manner illustrated. Energization of the 
coil unit 40 causes the armature 42 to move in the direction A pulling the 
metal plate 36 with it and allowing the respective key 6 to rotate as 
described above. However, as soon as current is removed from the coil unit 
40, the spring memory is effective to cause plate 36 to return to its 
original position where it supports the said members 6 as they move with 
the carousel conveyor. A slidable metal plate 36 and associated solenoid 
device 38 is provided at each of the control stations 12 through 22. The 
operation of the respective solenoid devices is controlled by a computer 
unit, to be described, in dependence on the signals produced by the light 
head unit 8 and the X-ray fluorescence unit 10. 
In FIG. 5, the X-ray fluorescence system is diagrammatically illustrated in 
a little greater detail so as to provide a greater understanding of its 
operation. For convenience, pieces of scrap metal 48 and 50 are shown as 
moving along a standard conveyor 52. The piece 48 has reached the 
examination position and fluorescence is produced by an .sup.125 I source 
54 irradiating the sample of scrap metal 48. Specific X-rays 56 are 
produced and are detected with a Si (Li) detector unit 58 manufactured by 
Kevex Corp. As will be understood, the charge produced in the silicon 
wafer thereof is fed to a pre-amplifier and then is amplified by the Kevex 
Corp. pulse processor within unit 60. An analog electrical signal is 
produced and this is digitized by a Northern scientific analog to digital 
convertor within unit 60. The resultant digital information is then fed to 
a computer unit 62 through a Tracor Northern 1313 Interface within unit 
60. 
The computer unit 62 then analyzes the information received in order to 
produce an output signal on line 68 whereby control of the selected one of 
the control stations 12 through 22 can be effected. In this way, the type 
of metal in a piece of scrap metal can be determined and, at the 
corresponding respective control station, the keys 6 can be caused to 
rotate whereby the piece of metal drops at that control station into a 
chute and, for example, a receiving bin for that particular type of metal. 
At the control station 20 where aluminum is to be deposited, a metal 
detector unit 64 is located below the conveyor as illustrated in FIG. 1. 
This unit overrides the control signal to this station if the material is 
non-metallic so as to prevent the dropping of the members 6. In this way, 
all the scrap metal of a particular type can be collected in a particular 
bin for future processing. 
As will be appreciated, the number of keys 6 which are caused to drop, i.e. 
rotate, by retraction of the respective slidable metal plate 36 (FIG. 3) 
is dependent on the size of the piece of scrap metal. This is determined 
by the light head unit 8 of FIG. 1 which comprises two horizontal metal 
bars, one of which is placed below the position of the keys 6. This metal 
bar incorporates sixteen infra-red omitting light sources (type TIL 32) 
and optical lenses to focus the light whilst the other metal bar is placed 
above the keys 6 and incorporates sixteen solid state infra-red detectors 
(type TIL 63). The sixteen detectors and the sixteen emitters are recessed 
in the respective metal bar so that a light beam from a given emitter is 
received by only the corresponding detector. Fifteen of the light beams 
are utilized in the detection of objects on the conveyor, e.g. pieces of 
scrap metal, whilst one of the light beams, the one closest to the 
perimeter of the wheel, is utilized to provide a pulse to interrupt the 
computer and to provide a pulse to the logic circuits used for test 
purposes. For test purposes, the logic circuits are designed to prevent 
any action being taken merely because successive keys pass through the 
light beam. The logic circuits are designed to respond to the presence of 
pieces of scrap metal. It will be apparent that the circuits to provide 
the interrupt signal and perform the above logic can readily be suitably 
designed. 
In FIG. 6, there is diagrammatically illustrated, in block form the various 
units which are incorporated into the apparatus together with their 
interconnections. The table 24 is associated with the optical detector 
unit 8 as well as the X-ray detector unit 10. An output from the X-ray 
detector unit 10 is fed to a pulse process unit 70, (Kevex Corp. model 
#4532-P), then through an analogue-to-digital converter (ADC) unit 72 
(Northern Scientific model #TN1313) to the computer unit 62. Units 70, 72 
and 74 are indicated in FIG. 5 as the single unit 60, A teletype unit 76 
and a display unit 78 are associated with the computer 62 whilst signals 
pass between the computer 62 and automation module unit 80. The automation 
module unit 80 is operational to receive signals from the optical detector 
unit 8 and pass the information on to the central processor unit for 
analysis. Control signals pass through the automation module unit 80 to 
control a relay unit 82 whereby the selected one of the control stations 
12 through 22 is provided with information signals to initiate its 
operation at a time when the respective piece of scrap metal is over the 
output chute for that particular control station. In FIG. 7, there is 
diagrammatically illustrated, in block form, part of the electronic stages 
which are incorporated in the units illustrated in FIG. 6. It is believed 
that the function and operation of the stages illustrated in FIG. 7 will 
be clear from the labelling thereof and it will be seen that the stages 
have been grouped into the respective groups, data input circuits 84, 
output drive circuits 86 and height reject circuit 83. Thus, the 
illustrated stages may be considered as the electronics for the light head 
stage 10 of FIG. 1 and the driver circuits for the solenoid stages such as 
illustrated in FIG. 4. 
In FIG. 8, there is drawn a schematic outline of the software program when 
the light head stage 8 (FIG. 1) produces an interrupt operation. The 
outline is the main decision-making routine in the computer 62 (FIG. 6) 
which is programmed to control the reaction of the sorting table 24 of 
FIGS. 1 and 6 and its associated apparatus. The simple program normally 
running in the computer displays the X-ray spectrum which is accumulating 
in the computer's memory. When an interrupt occurs as a result of a peg 
pulse, the display program is broken and the sequence of operations 
illustrated occurs. The operation of the outline shown in FIG. 8 will be 
clear to an expert skilled in the art having regard to the labelling used 
thereon. 
In FIG. 9, there is diagrammatically illustrated the light-emitting diode 
sources and the associated optical detectors in the light head 8 (FIG. 1). 
The use of diode sources and the optical detectors permits close spacing 
between the lights beams and this allows objects to be located on the keys 
with a high degree of accuracy. This is of importance in making decisions 
as to whether two objects are located side-by side, or deciding whether an 
object is located in a suitable position so that it will be satisfactorily 
sorted by the detecting unit 10. The light beams are arranged to be 
perpendicular to the axis of the conveyor and each light beam is 
interrupted by the movement of a key under the head. If a beam is 
interrupted within this space, simple counting of the number of keys which 
pass under the head whilst such an interruption continues gives the 
apparatus a measure of the length of the object independently of the speed 
of the conveyor 4. 
As will be appreciated, the movement of the regularly spaced keys through 
the light beam allows the position of a piece of scrap metal to be 
determined as it moves with the carousel conveyor. Since each successive 
pulse which is generated when the beam is broken represents the movement 
of the conveyor 4 by a distance corresponding to one key spacing, the 
position of the object on the table can be located by counting pulses from 
some arbitrary position, the light head. This is completely independent of 
variations in the speed of the conveyor and it has been demonstrated that 
no other method of object location need be provided. 
With reference to FIG. 9, it will be seen that each detector is 
incorporated in a transistor emitter-follower circuit. The low impedance 
output is connected via a multi-conductor cable to an integrated circuit 
amplifier and sixteen separate outputs are selected. These are fed to the 
digital computer which evaluates which of the beams in the series of 
sixteen are occulted at the time that an interrupt pulse is generated. 
To produce a pulse as each key passes through the light beams, the light 
beam closest to the perimeter of the conveyor 4 is emitted, detected and 
then amplified as described above. As the light beam reappears after the 
passage of a key, the voltage step in the light detector is fed to an 
astable multi-vibrator which generates a pulse of a duration approximately 
equal to one-half that of the time for which the light beam will be on. At 
the end of this pulse, a second astable multi-vibrator generates a pulse 
of relatively short duration which is provided to the computer as an 
interrupt signal. It is during this pulse, that the computer reads the 
information about which light beams are occulted. 
The display monitor circuitry displays the signals presented to the 
computer on a set of light-emitting diodes. The outputs are also combined 
through a sequence of gates to activate a light-emitting diode when an 
object is detected between the keys. The status of this indicator only 
changes during the computer-read pulse. 
In FIG. 10 there is diagrammatically illustrated the arrangement for the 
solenoid driver stages, whilst in FIG. 13 the power circuit for the 
solenoid stages is shown. Signals generated by the computer are arranged 
to cause a specific solenoid, like 40 (FIG. 4), at a respective control 
station (FIG. 1) to be activated. These signals are passed by way of a 
connecting cable to a single stage transistor amplifier (FIG. 11), whose 
output is connected to a solenoid driver unit. As will be seen in FIG. 11, 
this comprises a power circuit utilizing an A.C. source, a transformer, a 
full-wave bridge rectifier circuit and a current limiting resistor. The 
power supply charges a capacitor which may be connected across the 
terminals of the solenoid by the imcoming pulse applied to the base of a 
power transistor used in a searching mode. This arrangement provides a 
strong initial pulse to activate the solenoid and a weaker holding current 
appropriate to the permitted power dissipation in the solenoid coil. 
The solenoid driving circuit is repeated in accordance with the number of 
solenoids provided. At one of the control stations, an overide circuit is 
provided utilizing a commercial metal detecter and a Schmidt trigger 
circuit to only activate the solenoid if the object is metallic in nature. 
All other objects are treated as non-metallic and remain on the conveyor 
unit 4 until a discard outlet is reached. 
From the above and with reference to FIG. 5 it will be appreciated that the 
illustrated circuit design has two functions incorporated within it, as 
set forth below 
(a) The provision to the computer of the information which includes: 
(i) An interscript signal to denote the movement of a key under the light 
head unit 10. This pulse forms a peg counter for object location on the 
conveyer 4, and also is utilized to enable the digital computer to alter 
information stored in its internal registers. 
(ii) A series of voltage levels which are high or low depending on whether 
any given light beam is interrupted. These levels are transferred to the 
computer registers only during the above-mentioned interrupt signal. 
(b) The provision of a test facility which includes an illuminated display 
of the status of each light beam and an indicator to show whether any 
light beam is interrupted by an object. This feature is believed to be 
useful for routine testing and setting up of the detector with respect to 
the keys. The front panel lamp display is a set of light-emitting diodes 
which are not illuminated if a beam is broken. If an object is detected by 
any beam, the light-emitting diode is lit and a voltage appears at a test 
point on the front panel. 
After the analysis has taken place, the digital computer changes the 
voltage level within a register appropriate to sorting the metal into a 
particular bin. This level operates a particular solenoid through the 
respective output drive circuit. 
The X-ray fluorescence unit operates to sort non-metallic materials towards 
the bin allocated for aluminium. The solenoid driver circuit for this bin 
is fitted with an over-ride circuit whereby unless a commercial metal 
detector placed immediately in front of the bin is triggered, the material 
will not be sorted and will continue to a discard exit. 
To prevent excessively high pieces of material from damaging the light head 
unit 8 or the detector unit 10, a horizontal light beam in unit 7 (FIG. 1) 
is provided at a set height of approximately three inches above the 
members 6. This is positioned just after the place where the pieces of 
scrap metal come off the feeding conveyor. If the light beam is occulted 
some twenty keys are dropped at a station situated just after this 
horizontal light beam and similar to those of stations 12 to 22. 
Apparatus according to the present embodiment of this invention has been 
described above. Consideration will now be given to the operation and use 
of the apparatus having particular regard to the sorting of shredded 
automobile scrap metal. This is usually non-ferrous but it will be 
appreciated that this embodiment can equally be applied to ferrous scrap 
material. Automobile scrap material can usually be classified into the 
following groups: 
(1) Zinc alloys. 
(2) (a) Copper and brass. (b) Copper wire with some form of insulation. 
(3) Stainless steel. 
(4) Aluminum. 
Using the X-ray fluorescence unit for sorting mixed scrap materials into 
the above catagories, it was concluded that sorting rates of up to 11/2 
tons per hour may be possible with 5% mis-sort or less assuming that the 
material is properly fed to the conveyor 4. 
As mentioned above, soon after a sample arrives on the table from the 
conveyor belt system, it passes through the linear array of infrared light 
beams which are set perpendicular to its path and which are arranged 
vertically so that they can pass between the keys on the rotating wheel. 
If a sample cover part of the opening between two keys, some of the 16 
light beams will be occulted. The position of each light beam occulted is 
passed to the computer. The electronic units necessary to effect this 
transfer can be readily determined from the above description and will be 
seen to consist of an amplifier, a comparator, and a pulse-shaping 
circuit. As mentioned above, the signal from one light beam, on the rim of 
the table is sometimes called a "peg" pulse and is specially treated 
whereby it is delayed approximately seven milliseconds befor being set as 
a relatively short signal to the computer 62 (FIG. 5). All the signals 
pass through the I/O interface within the Tracor Northern 1310 interface 
section within unit 80 and are then fed to the computer. The peg pulse 
causes what is called an "interrupt" in the computer which then accepts 
the information from the light head. The computer determines which of the 
light beams are occulted in each opening between the keys and from this 
information the computer notes: 
(1) where the sample is radially on the keys in order to decide if the 
sample will pass under the X-ray fluorescence detector, 
(2) if there is more than one sample side by side on the table in order to 
cancel the X-ray annalysis and thus prevent mis-sorting, 
(3) the number of openings between keys in which at least one light beam is 
occulted in order to determine the length of the sample. 
The X-ray fluorescence system was described above with reference to FIG. 5 
and it will be understood that when the material is excited by radiation, 
part of the incident energy is lost by the emission of the X-rays which 
have energies characteristic of the elements present in the samples. The 
energy and intensity of such characteristics X-rays serve as a unique 
signature of a given material. 
Radiation from the radioactive source .sup.125 I is incident on the sample 
under investigation which then emits characteristic X-rays. These are then 
detected by a lithium drifted silicon counter unit 58 (FIG. 5). The output 
identifying signals from this counter consists of a series of voltage 
pulses of amplitude proportional to X-ray energy. The pulses are amplified 
and shaped by a standard nuclear electronics stage, and the number of 
pulses corresponding to a given energy (element) are sorted into a 
spectrum and displayed using the computer stage 62. Using this spectrum, 
the minicomputer can make decisions about the type of object presented to 
the detector and provide command control signals to operate the mechanical 
sorting equipment. 
As will be understood, the computer associates with each object an 
identification made by the X-ray detector and prepares subsequent 
components to discharge the respective object at the respective solenoid 
for the particular type of material. The computer keeps track of the 
position of the total number of objects (normally up to thirty) as they 
move around the table by counting the keys as they pass under the optic 
light head. Besides noting the passage of each key the light head, with 
the help of the computer, measures the length of the object by noting the 
number of keys which pass the head whilst one or more of the infrared 
beams is occulated by the respective object. 
As mentioned above, at a number of stations around the outer rim of the 
sorting table there are provided metal slides which can be withdrawn or 
inserted by means of a solenoid. Withdrawing the slides allows the keys to 
rotate about their pinned end to discharge objects off the table at the 
location of the respective solenoid. The operation of these solenoids is 
controlled by the computer. 
As illustrated in FIG. 3, the movable section can be approximately one inch 
long and is on the end of the plunger of a solenoid. When the respective 
section is to be withdrawn, i.e when the first part of a sample to be 
dropped at this station arrives there, the solenoid is simply energized to 
withdraw the support. When all the keys supporting the respective sample 
have dropped through the gap in the supporting surface, the solenoid is 
released and it springs back. Since the keys are somewhat flexible, no 
difficulty was experienced in the operation of the table if one of the 
keys was hit by the returning section of the support surface. 
The energizing of the respective solenoid is effected by the 
above-mentioned computer stage since it monitors were each sample is as it 
moves around the sorting table. 
The computer system which is used in the constructed practical embodiment 
works on the interrupt basis or in real time. Most of the time, it is 
simply displaying an X-ray spectrum it has in its memory. Two types of 
interrupt could occur. One occuring if the ADC has completed digitizing a 
signal from the X-ray detector and the ADC interface (TN1313) interrupted 
the central processor in the computer and directly modified a memory 
location. This is normally referred to as direct memory access (DMA) and 
involves no program steps in the actual transfer if the interface is 
initialized to operate this way. 
The second interrupt occurred when the signal from the peg pulse arrived at 
the computer. It initiated a sequence of events. Firstly the interrupt 
indicated to the computer that a key had passed the light head and 
therefore every sample on the table had moved further along. The computer 
produced a corresponding adjustment in the entry of its memory for each 
sample and caused the appropriate action, e.g. firing a solenoid at the 
appropriate station or starting an analysis at the X-ray fluorescence 
detector etc., to occur, 
If all the light beams were not on, the computer determined which light 
beams were off and whether more than one group of lights was off. This 
information together with similar information from the previous gaps 
between the keys allowed the computer to decide if a single sample was on 
a path going under the X-ray detector and therefore that an analysis 
should be effected when the sample reaches the detector. 
In FIG. 8 there is actually shown the schematic outline of a software 
program when the light head produced an interrupt. This was a main 
decision--making routine in the computer programmed to control action of 
the sorting table. 
As mentioned above, the computer was supplied by Tracor Northern and was 
used to control all functions involved in the sorting operation. It 
collected the data from the X-ray fluorescence detector, decided what type 
of material had passed under the detector, noted the passage of each key 
under the light head and whether a piece of material was sitting on that 
key and subsequently activated the appropriate solenoid as the respective 
object reached it. 
As will be clear, the software (FIG. 8) for performing these operations was 
specially written and consisted of two main parts, the analysis part and 
the table control part. In the first part, the number of counts in several 
regions of the X-ray spectrum was determined after the sample object had 
passed the detector. These regions corresponded to those X-rays which are 
characteristic of Fe, Ni Cu, Zn and a background. If the largest number of 
counts occurs in the Fe or Cu regions, then the sample is said to be iron 
or brass respectively. If the Ni region had the greatest number of counts, 
then the Cu/Ni and Zn/Ni ratios determined whether the sample was brass or 
zinc. If the Zn region had the greatest number of counts, then the 
relative amount of Cu present, i.e. Zn/Cu ratio determined whether the 
sample was zinc or brass. 
If the highest number of counts occured in the background region then the 
material was aluminum or some non-metallic material. Consequently on the 
solenoid for aluminum material, a metal detector was provided to check the 
object for metal content before the solenoid was released. 
The second function of the software was to monitor the position of each 
object as it moved around the sorting table. To do this, information about 
each sample on the table was sotred in a section of the computer's memory. 
This information consisted of (1) the position of the sample relative to 
the light head (2) the length of the sample, in order to drop the correct 
number of keys, and (3) whether the sample had been analysed and, if so, 
the type of material so that the sample would be deposited at the 
appropriate solenoid exit station and exit along a respective selected 
path. 
The digital information from the X-ray detector entered the computer 
through the TN 1313 interface unit 72 whilst the control information, i.e. 
the passage of a key or the status of the solenoids, entered through two 
input-output units in the TN 1310 within unit 80. 
The practical system, including the analysis, the computer and sorting 
table units, were assembled in the form of a commercial unit which was 
tested and found to besatisfactory. The sample of scrap used was unwashed 
and had been shredded into pieces to give a more representative weight 
distribution. The average weight was 44 gms so that a material flow rate 
of one ton/hr. implied a sorting rate of 20,000/hr. or about 5 per second. 
Each piece was approximately 2 inches in size and about 60% of the brass 
and zinc samples were plated. The samples had been hand sorted into 
commercial categories so as to facilitate the investigation. 
Using the X-ray analysis it was found that the materials were well 
characterized by the elements zinc (Zn), brass (Zn, Cu), wire (with lead 
in the insulation), stainless steel (Fe, Cr), aluminium (with no 
characteristic peaks). In the plated samples, only zinc or brass were 
found to be plated and the plating invariably contained nickel (Ni) and 
copper (Cu). Since the technique using 125.sub.I sampled the surface, 
nickel constituted the major detected element for both plated zinc and 
plated brass. However, on the basis of the samples examined, the two 
materials could be distinguished with greater than 90% certainty by 
measurement of the Ni: Cu ratio and the Cu:Zn ratio. By producing the 
results graphically, it was found that plated zinc fell almost exclusively 
above a particular level whilst plated brass had a higher copper content 
and fell below the respective level, i.e. line drawn on the graph. 
The explanation for this resides in the fact that the nickel acts as a 
barrier for those X-rays, characteristic of copper or zinc as they return 
to the detector (FIG. 5). Furthermore, because the characteristic K X-ray 
of zinc has an energy greater than the binding energy of the K electrons 
in nickel while the K X-ray of copper does not, the most abundant X-rays 
from zinc are very strongly absorbed and the discrimination between plated 
zinc and brass is effected. 
It was found that the peaks for all the elements found in the scrap were 
distinct and their heights could be compared in a simple manner. No 
problems were encountered due to dirt, and if the sample of scrap examined 
was representative of the industrial material then no washing would appear 
to be required. 
Experimentally it was estimated that approximately 1000 counts in the whole 
spectum were required in order to make a clear and reliable recognition of 
the material. This figure and the time for which a given specimen is in 
front of the detecting head determines the counting rate required for a 
given speed of operation. 
If scrap material is presented as single pieces separated on 10 cm centres, 
the conveyor system must travel at 0.5 m/s (1.1 mph) for a material 
throughput of 1 ton/hr. A rough estimate suggests that if the sample is 
presented to the detector system for 0.1 sec and 1000 counts are required 
for a decision, then the counting rate is 10,000/s. Standard nuclear 
electronics can operate effectively up to 50,000/s so that the principal 
limitation on counting speed is the strength of the exciting radioactive 
source. 
Sources of a few Curie strength are commercially available and it is to be 
noted that because the radiation is weakly penetrating, it may be easily 
confined by simple radiation shields whereby radiocative hazards are 
minimal. 
It will be appreciated that the categories of brass and zinc could be 
further sub-divided into plated and unplated samples with considerable 
reliability using the apparatus above. Furthermore, the presence of iron 
samples as distinct from stainless steel could also be detected. 
The embodiments of the invention have been described above in regard to a 
particular application, i.e. the separation of mixtures of metallic 
particles. However, it will be appreciated that it can be readily adapted 
to other uses and for some of these applications X-ray fluorescence may be 
a suitable method of analysis. The apparatus can obviously be adapted to 
the separation of alloys of the same class (e.g. the separation of 
stainless steels, brasses nor nickel alloys). Furthermore, other methods 
of analysis could readily be employed with the sorting table and the 
following is a partial list of the measurements which can be made to 
provide the criteria for separation: 
(a) Size and shape 
(b) Mass 
(c) Radioactivity 
(d) Surface features 
(e) Temperature 
(f) Air resistance 
(g) Color 
(h) Pre-marking or Tagging. 
Appropriate combinations of these measurements may also be employed to 
determine the separation critera. 
The sorting table itself may, also be employed for a varity of other 
purposes. It is envisaged that it could be modified in the following ways: 
(a) Size: The keys can be made of any desired length, width and shape to 
accomodate items of appropraite shape and size. 
(b) Configuration: The keys can be incorporated into a table of circular 
design, a linear conveying system or may be stacked. 
(c) Materials of Construction: The sorting system can be constructed in a 
varity of materials to suit the particular operating conditions which 
might, on occasion, involve the immersion of the system in a special 
atmosphere or liquid. 
It will be appreciated that the computer may readily incorporate 
microprocessors or other microcircuit devices. 
(d) Key design: For special purposes the mechanism for key support, release 
and spacing may be redesigned. 
(e) Light Head: The components incorporated within the light head may 
readily be changed for use in other applications as may the number of 
light beams. In the present embodiment of the invention sixteen beams were 
used to facilitate the transfer of information from the light head to the 
sixteen bit computer. 
It will also be appreciated that the sorting mechanism can readily be 
emloyed as a feeding system for particles or manufactured parts. 
While the present invention has been particularly set forth in terms of 
specific embodiments thereof, it would be understood in view of the 
present disclosure, that numerous variations are now enabled to those 
skilled in the art, which variations yet reside within the scope of the 
present invention. Accordingly, the invention is to be broadly construed 
and limited only be the scope and spirit of the claims now appended 
hereto. 
It will be readily apparent to a person skilled in the art that a number of 
variations and modifications can be made without departing from the true 
spirit of the invention which will now be pointed out in the appended 
claims.