EP0396546B1

EP0396546B1 - Sorting pneumatically conveyed material

Info

Publication number: EP0396546B1
Application number: EP88907557A
Authority: EP
Inventors: Grahame Michael Abbott; Lindsay Alfred Allen; David Michael Johnson
Original assignee: Commonwealth Scientific and Industrial Research Organization CSIRO
Current assignee: Commonwealth Scientific and Industrial Research Organization CSIRO
Priority date: 1987-08-28
Filing date: 1988-08-29
Publication date: 1995-06-28
Anticipated expiration: 2008-08-29
Also published as: HK1006428A1; EP0396546A1; EP0396546A4; NZ225966A; WO1989001832A1; JPH03500021A; JP2672358B2

Abstract

Apparatus for sorting material, for example, fibrous material, as it is pneumatically conveyed in a gas stream includes a duct (12) for the gas stream, and a monitoring station (18, 19) for illuminating the material as it passes in the duct, and for monitoring the intensity of light reflected by the material. There is a lateral opening (22) in the duct, and means (20) responsive to a predetermined change in the intensity caused by a portion of material of darker or lighter shade to deflect such portion through the lateral opening (22). The monitoring station (18, 19) comprises an array (25a, 25b) of substantially monochromatic light sources (26) arranged to illuminate the interior of the duct through a transparent window (27) in the duct, whereby to achieve a substantially uniform diffuse illumination of the passing material in the duct, and a detector (28) responsive to a change in the intensity of reflected light arising from the passage of a portion of the material of darker or lighter shade to generate an output signal which reflects this change. In an alternative construction, any parameter of the material may be monitored and there is means (26) responsive to a predetermined change in the monitored parameter, caused by any specific portions of the material, to discharge a gas pulse transversely of the duct. The pulse is timed and positioned so as to deflect the portion of material through the lateral opening (22). The opening (22) extends across substantially the full width of the duct (12) and is dimensioned to be large enough to accept portions of the material deflected by the gas pulse but not large enough to capture other material in the absence of the pulse.

Description

Field of the Invention

This invention relates to the sorting of pneumatically conveyed material, particularly but not exclusively loose fibrous material such as scoured wool, for example to separate urine stained or otherwise soiled tufts from the bulk of acceptable wool.

Background Art

The wool processing industry presently employs essentially manual techniques to separate out urine stained and otherwise soiled wool, and larger discrete contaminants such as baling twine, after the raw product has been scoured. This manual approach is presently labor intensive and it would be desirable to introduce a degree of automation.
One reason why the sorting of scoured wool has remained essentially a manual operation is the unique nature of the material itself. A mass of wool at this stage comprises tufts of many shapes and sizes, a number of which are loosely intertwined with each other. Although optical sorting has been proposed and employed in connection with a range of different products, the intertwining and size variation of these wool tufts has thus far rendered such an approach for wool either unsuitable or of very low productivity.
Optical sorting arrangements are described, inter alia, in United States Patents 3382975 and 3914601, in European Patent publication 45576 and in an article by Farsaie et al in 1981 Transactions of the American Society of Agricultural Engineers at page 1372. A common feature of these systems is that the observed articles are singulated and move along a predictable path, for example on a conveyor or by being dropped under gravity down a transparent tube. A liquid may be employed as a transport medium, such as with the potatoes of U.S. Patent 3382975. Optically sorted articles to date have been solid and of a substantially predictable size and shape, and are in a substantially predictable position. The actual separation of the unacceptable articles is facilitated by their singulation in a stream of articles, and may be achieved, for example, by a transverse pulse of air.
The most successful technique for high volume transport of a large mass of wool is pneumatic conveyance in a duct. It would be possible to substantially singulate the wool on the basis of discrete stringy tufts, in part by suitably dimensioning the duct, but these tufts are of greatly varying size and will follow unpredictable paths as they travel along the duct. Moreover, it is undesirable to expose the travelling wool to the atmosphere for sorting with air pulses because of dust generation and general difficulties in locating or handling the material in question when it is totally unrestrained by any enclosure.
It has been proposed to divert pneumatically conveyed fibrous material having particular contaminants by operating a flap valve in response to a detector of the contaminant: metal detectors (eg US patent 4171262) and spark detectors have been specifically suggested. However, the slow response time of such flap valves requires, e.g., an 8 to 15 m separation downstream of the detector, and, coupled with the fact that they temporarily divert all material in the duct, would result in an excessive loss of material at higher fault rates. The long separation reduces the reliability of the device where tufts are travelling at different velocities.
It is accordingly an object of the invention to provide a technique for sorting pneumatically conveyed material, for example fibrous material such as wool, in a manner which at least partially alleviates the aforementioned problems in applying sorting techniques to these kinds of materials.
The invention provides apparatus for sorting material, for example, fibrous material, as it is pneumatically conveyed in a gas stream, wherein the material includes portions to be sorted variably disposed across the stream as the material travels with the stream. The apparatus includes:
means defining a duct for the gas stream;
a monitoring station for monitoring a parameter of the material as it passes the station in the duct;
a lateral opening in the duct; and
a chamber in communication with the interior of the duct via the lateral opening.
The apparatus is characterized in that:

the chamber is, apart from the lateral opening otherwise substantially gastight;
there is provided means responsive to a predetermined change in the monitored parameter caused by any of said portions of the material to discharge one or more gas pulses transversely of the duct, the pulse(s) being timed and the pulse discharging means and lateral opening being positioned so that the pulse(s) deflects that portion of the material through the lateral opening into the chamber;
the aforesaid opening extends across substantially the full width of the duct and is dimensioned to be large enough to accept material deflected by the pulse but not large enough to capture material travelling with the gas stream in the duct in the absence of the pulse(s).

There are preferably a plurality of spaced nozzles for discharging the or each gas pulse.
The gastight chamber advantageously includes baffle or other means in the chamber to direct material deflected into the chamber to a collection zone, and means such as a double door gaslock system for periodically or continuously emptying said chamber of its contents without disturbing the gas stream in said duct.
It will be appreciated that the chamber should provide a large enough space to allow the forces associated with the pulse of gas to be dissipated in the chamber without disturbing the flow of material, other than the material to be deflected, along the duct and without creating sufficient turbulence in the chamber to cause any deflected wool to re-enter the duct.
The profile of the downstream edge of said opening should preferably be rounded in order to facilitate immediate shedding of any stringy tufts which could occasionally and/or inadvertently become wrapped around this edge.
The entraining gas stream is preferably air and the gag pulse is preferably a pulse of compressed air.
In a particular application, the material is a loose fibrous material such as wool which is entrained in the gas stream as a sequence of tufts. Other materials to which the invention may be applied include particulate material such as wheat and rice which are of a density which permits pneumatic conveyance and are not unduly susceptible to damage during such conveyance, e.g. by bruising. Preferably, the monitoring station comprises means for illuminating the material as it passes the station in the duct, and for monitoring the intensity of light reflected by the material, which intensity is thereby the monitored parameter. Preferably, the monitoring station comprises an array of substantially monochromatic light sources arranged to illuminate the interior of the duct through a transparent window in the duct, whereby to achieve a substantially uniform diffuse illumination of the passing material in the duct, and detector means responsive to a change in the intensity of reflected light arising from the passage of a portion of the material of darker or lighter shade and to generate an output signal which reflects such change. It will be appreciated that these preferred arrangements rely upon the fact that urine, faeces or other staining, or other contamination, will be evidenced by a portion of region of off-white or dark colouring in the wool.
There are preferably two of said arrays respectively upstream and downstream of the detector means. The detector means may include a photosensitive detector, means to shield the detector from the light sources, and, arranged about the detector, light integrating means to focus the reflected light to the detector.
A further monitoring station is advantageously displaced along the duct from the first mentioned monitoring station, the two stations being on opposite sides of the duct.
Sorting is facilitated if the wool tufts are substantially singulated, i.e. essentially travel along the duct in. single file. The dimensions of the duct are preferably selected to just receive the largest tufts normally formed at the stage of processing involved, typically after scouring and when the wool passes through a lattice feeder. It is found that a duct which meets this requirement, e.g. a duct with a rectangular cross-section of about 90 x 160 mm, has a maximum throughput of 150 to 200 kg of wool per hour. However, a single manual sorter in a mill will typically inspect the 1000 kg/hr of wool output by a scouring machine as the wool passes along a conveyor belt after being scoured and dried. To enlarge the dimensions of the duct to handle this quantity of wool would result in the wool not being singularised to the maximum extent possible. It is therefore desirable to be able to divide pneumatically conveyed wool into multiple streams and multiple ducts. Any division of a duct is liable to very quickly clog up as the stringy lengths of wool lodge on the dividing point and then matt across the duct. United States Patent 4553882 and British Patent 756233 propose the provision of a counter flow source at the dividing point but the present applicant believes that this is a rather expensive and complex proposal.
Accordingly, the apparatus may be included in a duct system having a duct junction provided with a rotationally mounted roller which extends transversely to the direction of material flow and is inclined to rotate in favour of any weight imbalance of wool lodged on the roller. Means may be provided to positively oscillate the roller to dislodge any fibrous material which lodges thereon.
The invention will be further described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic axial cross-section of apparatus constructed in accordance with embodiments of the invention;
Figure 2 is an enlargement of the portion A of Figure 1;
Figure 3 is an enlarged cross-section on the line 3-3 in Figure 2; and
Figures 4, 5 and 6 are cross-sections on the respective lines 4-4, 5-5 and 6-6 in Figure 1 or 2.

The illustrated apparatus 10 was designed for the sorting of stained or otherwise contaminated product from the wool output by a scouring machine. The apparatus includes several ducts 12 along which the wool is pneumatically conveyed in substantially singulated tufts. The wool output by the scouring machine is entrained in an air stream travelling along a primary duct 11 which is divided to form secondary ducts 12 by a series of duct branching junctions, one of which is shown at 14. Each secondary duct 12 is fitted with one or more sorters 16.
Each of the ducts 12 is conveniently of rectangular cross-section dimensioned to just admit the largest typical tufts of the wool and thus to facilitate the aforementioned singulation. A convenient cross-section for admitting and processing an optimum range of wools is found to be 90 x 160mm. A rectangular cross-section is preferred to, e.g., circular, because the resultant narrow section is easier to optically inspect. There is less likelihood of screening of one tuft by another, and the wool is more spread out. In addition, the ejection distance is a minimum for the whole width of the duct.
Each sorter 16 includes a pair of monitoring stations 18, 19, one or more compressed air nozzles 20 located downstream of stations 18, 19 for directing one or more respective pulses 35 of compressed air transversely downwardly across the interior of duct 12, and, generally opposite but extending downstream from the location of nozzles 20, a lateral rectangular opening 22 into an otherwise substantially gastight chamber 24 adjacent and indeed immediately under duct 12.
Monitoring stations 18, 19 are advantageously a co-operating optical arrangement for monitoring the whiteness of the travelling wool and are arranged to inspect the contents of the duct from opposite sides. To achieve high performance, and notwithstanding the substantial singulation of the tufts of wool in the ducts, it is desirable to have more than one optical detector for each duct for those cases where contamination is predominantly evident from only one direction.
Each monitoring station includes a pair of axially separated arrays 25a, 25b of substantially monochromatic light sources 26, typically light emitting diodes and most satisfactorily green or blue light emitting diodes, arranged to diffusely illuminate the interior of the duct through a transparent window 27 on the wide dimension of the duct. These arrays 25a, 25b are disposed so as to uniformly illuminate the area centrally behind the window and to minimise their influence on the opposite monitoring station. The arrays 25a, 25b are substantially identical: a representative elevational view of array 25a is to be found in Figure 3. Diodes 26 are located in holes 40 arranged in offset rows at equispaced intervals in a respective 160 X 70 X 6 mm flat plate 42 of opal perspex for each array.
Green or blue light sources are employed to optimise the contrast between unstained and stained wool. To further enhance this contrast, the interior walls of the duct opposite and adjacent each window 27 are white, thereby placing the acceptable white wool against a white background. Put another way, the aim is to minimise the range of white wool signals ("noise") as much as possible so that (a) signals from stained clumps mostly exceed the dark-side envelope of the white wool noise and (b) when a white and a stained clump are viewed simultaneously, any light signal from the white wool is less likely to swamp that of the stained wool.
At each monitoring station, a photosensitive detector 28, with the aid of a surrounding semi-elliptical mirror 29, or other suitable integrating light collecting arrangement 29, in a light-sealed cavity 31 defined by side walls 33 and mirror 29, monitors the light reflected from the illuminated zone of the duct. The mirror produces a substantially constant signal for a uniformly coloured tuft irrespective of its trajectory along the duct. The detector 28 is of course shielded against direct receipt of light from diodes 26 and is located at one of the foci of the elliptical mirror. If the intensity of the detected integrated light falls below a predetermined threshold, a darkened tuft of wool is considered to have passed and should be ejected from the duct.
As already indicated, monitoring stations 18, 19 are offset from each other along the duct so as to minimise optical interference with each other, and are separated by an internally blackened duct portion 30. The monitoring stations and associated transparent window sections 27 of duct are also shielded to eliminate ambient light.
The sorter is arranged to respond, by control circuitry not shown, to a change in the detected intensity level to a value below the predetermined threshold by actuating nozzles 20. The compressed air pulses 35 are timed and positioned so as to strike the tuft which caused the reduction of intensity and to deflect it through opening 22 into chamber 24. The typical trajectory of such a tuft is shown by a broken lines 32 in Figure 1. There is preferably more than one nozzle. Most preferably, there should be sufficient nozzles 20 to prevent any escape of a detected contaminated tuft past the nozzles: a satisfactory number for a 160 mm wide duct is eight.
It will be understood that the opening 22 should extend substantially the full width of duct 12 and be dimensioned longitudinally of the duct so as to be large enough to accept any tuft deflected by the compressed air pulses, from any transverse position in the duct, but not large enough to inadvertently capture other material entrained in the air stream but not struck by an air pulse from nozzles 20. Chamber 24 also serves to dissipate the forces associated with the pulses of compressed air without disturbing the flow of acceptable wool along the duct or creating such disturbance in the bottom of the chamber as to cause rejected wool to reenter the duct. The rejected contaminated wool which collects in chamber 24 is readily recovered from the chamber by a suitable air lock valve such as rotary valve 34.
The profile of the downstream edge 23 of opening 22 is rounded, at least hemi-cylindrical, in order to facilitate immediate shedding of any stringy tufts which could occasionally and/or inadvertently become wrapped around this edge.
In a typical arrangement, the air stream in duct 12 would travel at about 16m/sec. The entrained wool is transported at about 10m/sec depending or tuft size. The actuating nozzles would typically be supplied with compressed air at 700Kpa pressure. The duration of the pulses at full force is typically 30 msec but this may be extended by the control circuit as the size of the detected clump increases. The response time of the air valves in turning on should be 10 msec or less; the shorter this time is, the closer may nozzles 20 be to the monitoring stations to minimise the adverse effects of the wool tufts travelling at different velocities. This separation may be as little as 80 mm. An added time delay would normally be applied to any actuating signal for the first of the two monitoring stations to compensate for the extra time taken for the tuft to reach the ejection zone. The fast response time and short on-cycle of the nozzles means that the apparatus will typically only reject a small proportion of material traversing the duct, and is therefore much better suited to selective or specific sorting, particularly at higher fault rates, than the slow acting flap valves of the prior art, discussed above. By way of example, for 30 detected faults per minute, the illustrated apparatus will reject about 3% of the total input.
With particular reference to Figure 1, a dividing edge 15 at duct junction 14 would normally provide an ideal edge to snag the long stringy segments which are typical of scoured wool. In a very short time, this snagged wool would matt across the duct with other tufts and completely block one or both ducts.
This dividing edge 15 is fitted with a rotatable roller 40. The roller is disposed in a funnel-like duct segment which is of enlarged cross-section relative to each of the downstream ducts 12, indeed relative to the sum of the cross-sections of ducts 12. Roller 40 need not be driven but should be freely and smoothly rotatable so that the roller will tend to begin spinning as soon as it snags travelling wool and there is any resultant imbalance of weight on one side or the other of the roller. Such an imbalance would generally be inevitable and the subsequent spinning action is found to be sufficient to shed the snagged wool before any significant matting across one or both ducts has occurred. In some cases, especially if the throughput rate is very high, it may be desirable to positively and continuously oscillate the roller by means of an external drive to ensure shedding of snagged wool. It is also helpful for the roller width to occupy only a small proportion of the duct cross-section at the junction, as clearly seen in Figure 6.
It will be appreciated that an oscillatable or oscillated roller such as roller 40 need not be immediately in advance of a dividing edge but may be employed to divide a stream within a single duct into separated flows of wool to either side of the duct.
A roller may also be provided at the downstream edge 23 of ejection opening 22.

Claims

Apparatus for sorting material, for example, fibrous material, as it is pneumatically conveyed in a gas stream, wherein the material includes portions to be sorted variably disposed across the stream as the material travels with the stream, the apparatus comprising:
means defining a duct for the gas stream;
a monitoring station for monitoring a parameter of the material as it passes the station in the duct;
a lateral opening in the duct; and
a chamber in communication with the interior of the duct via said lateral opening,
characterised in that said chamber (24) is, apart from said lateral opening (22), otherwise substantially gastight;
in that there is provided means (20) responsive to a predetermined change in said monitored parameter caused by any of said portions of said material to discharge one or more gas pulse(s) transversely of the duct (12), said pulse(s) being timed and said pulse discharging means (20) and lateral opening (22) being positioned so that said pulse(s) deflects that portion of said material through said lateral opening (22) into said chamber (24); and
in that said opening (22) extends across substantially the full width of the duct (12) and is dimensioned to be large enough to accept material deflected by said pulse but not large enough to capture material travelling with said gas stream in the duct (12) in the absence of the pulse(s).
Apparatus according to claim 1 further characterised in that said responsive means comprise a plurality of spaced nozzles (20).
Apparatus according to claim 1 further characterised in that said substantially gastight chamber (24) includes gaslock means (34) for periodically or continuously emptying said chamber (24) of its contents without disturbing the gas stream in said duct (12).
Apparatus according to claim 1, 2 or 3 further characterised in that the downstream edge (23) of said opening (22) is rounded to facilitate shedding of stringy tufts and the like which became wrapped around said edge.
Apparatus according to any one of claims 1 to 4 further characterised in that said monitoring station (18,19) comprises means (26,28) for illuminating the material as it passes the station in the duct, and for monitoring the intensity of light reflected by the material, which intensity is thereby said monitored parameter.
Apparatus according to claim 5 further characterised in that said monitoring station (18,19) comprises an array (25) of substantially monochromatic light sources (26) arranged to illuminate the interior of the duct (12) through a transparent window (27) in the duct, whereby to achieve a substantially uniform diffuse illumination of the passing material in the duct, and detector means (28) responsive to a change in the intensity of reflected light arising from the passage of a portion of the material of darker or lighter shade and to generate an output signal which reflects said change.
Apparatus according to claim 6 further characterised in that there are two of said arrays (25, 26b) respectively upstream and downstream of said detector means (28).
Apparatus according to claim 6 or 7 further characterised in that said detector means includes a photosensitive detector (28), means to shield the detector from said light sources, and, arranged about said detector, light integrating means (29) to focus said reflected light to said detector (28).
Apparatus according to claim 7, or 8 further characterised in that the interior walls of the duct opposite and adjacent said window (27) are colour matched to said material other than said portions of darker or light shade.
Apparatus according to any one of claims 6 to 9 further characterised in that, in use, said pulses are timed and said pulse discharging means (20) and lateral opening (22) are positioned so that said pulses deflect said portions of darker or lighter shade through said lateral opening (22).
Apparatus according to any preceding claim further characterised by a further said monitoring station (19) displaced along the duct (12) from the first mentioned monitoring station (18), the two stations (18,19) being on opposite sides of the duct.
Apparatus according to any preceding claim further characterised in that said duct is part of a duct system which includes a duct junction provided with a rotationally mounted roller (40) which extends transversely to the direction of material flow and is inclined to rotate in favour of any weight imbalance of wool lodged on the roller.
Apparatus according to claim 12 further characterised by means to positively oscillate the roller to dislodge any fibrous material which lodges thereon.
Apparatus according to any preceding claim further characterised in that, in use, said gas stream is air and/or the gas pulses are pulses of compressed air.