AU605209B2 - Improvements in material sorting - Google Patents

Description

N

i~2 P/00/011

SAUSTR

0- PATENTS ACT 1952-1973 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE Form Class: Int. CI: Apolication Number: Lodged: Li~i- A I;.i -rt E a,, 4 iUII~i~L Complete Specification-Lodged: Accepted: Published: Priority: Related Art: SName of Applicant: Address of Applicant: Actual Inventor: Address for Service: TO BE COMPLETED BY APPLICANT ALBERT PETER iAWKINS 36 NEERIM RD, CAULFIELD, VIC, 3162 ALBERT PETER HAWKINS 36 NEERIM RD, CAULFIELD, VIC, 3162 Complete Specification for the invention entitled: IMPROVEMENTS IN MATERIAL SORTING The following statement is a full description of this invention, including the best method of performing it known to me:-- "Note: The description is to be typed in double spacing, pica type face, in an area not exceeding 250 mm in depth and 160 mm in width, on tough white paper of good quality and it is to be inserted inside this form.

11710/76-L C. J. TIOMrPSON. Conimonwcilth Government Primer, Canberra 1 i_ i i 7i IMPROVEMENTS IN MATERIAL SORTING This invention relates to improvements in inspection means for use in automatic sorting machines.

Automatic inspection techniques have been widely used to distinguish between groups of objects or particles being fed through sorting machines. Such machines incorporate means for feeding particles essentially in monolayer form at uniform S velocity or acceleration through inspection means, and subsequently through an ejection region. Here, one or more high pressure air blast valves can be opened to eject particles from normally undeflected trajectory, into a separate product region. Such machines are usually required to operate at high throughput rate,.

In some situations, it is desired to separate essentially opaque objects from translucent objects in as simple a way as possible. One such situation may be the need to remove foreign matter such as burrs, stones and sticks from dried fruit such as sultanas. In this invention, translucent objects can be identified by passing them through a light curtain such as a scanning laser beam, the scanning means usually being a rotating polygon reflector rotating at high speed, with the Slaser beam impinging on the rotating mirror faces.

The translucent object, by multiple internal scatter, tends to glow in a more or less uniform fashion, this emission being i (Signature of Declarant) (IMPORTANT Cross out inapplicable words in the above Form.) that of the light source sr that no surface reflections are detected This enables t ye translucent object to be detected above a preset threshold level, set at such level that opaque sticks, etc., would not be detected. Such detection d.fferences are advantageously large when compared with typical diffuse reflection differences between different species. It has been found that the highest contrast between opaque and translucent objects was found with the plane of the detector view being at about 135 degrees to that of the light curtain.

Often, however, it is the opaque object that is required to be detected and removed. Such a sorter would normally require duplicate detection stations, one to detect the presence of all particles moving through the detection zone (which may be in the form, for example, of a light curtain), and the other to detect which of these objects give a high output by viewing the 2. light scattered in the translucent object.

The invention further described below accomplishes both tasks with only one detection station, thus saving the extra cost and complexity of processing that would occur with the use of the 'i extra station. The simultaneous achievement of both tasks is done by use of a fixed, partially translucent background target, upon which the scanned laser beam impinges in the absense of material passing through the scan zone. The photodetector is arranged to view the background essentially from the opposite side to the laser beam. The background is selected such that with no object in the zone, the photodetector response is approximately equivalent to that with a translucent piece of material of the type being sorted when such material is illuminated by the laser beam in a position near the fixed background.

This background is constructed to be of minimum width in the o o direction transverse to the laser scan direction, slightly 0 0 S wider than the width of the laser beam itself. It is o advantageous that the laser beam should be of minimum width in S0 the region of the background. Consequently, when translucent 0 090 0' material such as dried sultana particles pass through the scan zone, the laser beam is scattered through the extent of the body of the material, this being in the field of view of the 0 4 photodetector. Thus, although the contribution to the photodetector response from background is reduced to a low S value due to obstruction by the object, this is compensated by the detection of scattered light from the translucent object, which is also in the field of view o. the detector.

The principles described above may be extended to the situation where combinations of both types of particles occur, as for example when burrs become attached to sultanas, and pass through the detection region together. In this case, with only a single detection station, the opaque burr must not be fully obscured from the incident laser beam by the translucent sultana for the response to be reduced toward zero in the 3 desired way characteristic of opaque contamination. If it is so obscured, the scattering within the sultana may be sufficient to dominate with the result that the response to the combined parcicles would not be reduced to below the threshold set to reject opaque contaminants. The incorporation of a second identical detection station comprising light curtain, fixed background and photodetector acting on the opposite side of the particle stream to the normal station would overcome th' s problem, thus favouring the rejection of composite sultana/burr pieces, this being usually the prefered outcome rather than the occassional loss of a sultana.

t o a The invention ma be further understood with reference to the figures 1 and 1 below.

Fig. 1 shows a diagrammatic side elevation of the sorting region; Fig. 2 illustrates the form of detector response likely to be obtained with different types of objects passing through the scanning laser beam.

Objects on a conveyor belt are launched into a parabolic trajectory off the end of the belt head pulley, and sometime later, pass through the light curtain consisting of a scanning laser system with HeNe laser (21) as the preferred light source, this scan being accomplished by rotating polygon mirror The rate of scan is sufficient to provide continual spatial coverage over the particle stream consistant with particle velocity through the scanning beam. At 4

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the instant of passing through the beam, the object momentarily stops the beam from impinging on the translucent background The view by the photodetector system of the underside of the translucent background (19) is thus disturbed, and the response (15,16) reduced considerably from its normal value (13) when no objects are in the scan. The angle formed between the photodetector view plane and the light curtain scan plane shown on fig 1 as is preferably about 135 degrees.

If the disturbing object is opaque, as in (11) and then the photodetector output (13) will reduce to essentially zero o level (15) and crossing a fixed low threshold (18) set in the electronic processor This would cause, after a preset delay, a signal to be sent to the appropriate air blast valve to open the valve and pass a rapid jet of air to Sdeflect the particle across the splitter plate into the reject chamber On the other hand, if the disturbing object is translucent, the drop in illumination of the background (19) will be at least partially compensated by the scattered laser illumination in the translucent object thus causing the response (14) to be approximately equivalent to the undisturbed value The threshold (18) is not crossed, and so no ejection is initiated, and the translucent object continues in its normal trajectory into accept chamber Opaque objects can thus be efficiently removed at high speed from particle streams of essentially translucent objects in a sorting system with a simple single detection station as described above.

Claims (4)

1. A sorting process for separating streams composed of partic- ulate matter, based on the degree of translucency of each indi- vidual particle in the stream, by causing the feed stream to interrupt a light curtain consisting of a scanning light beam, with direction of incidence of particle irradiation such that a suitably placed photodetection system behind the particle stream when viewed from the light source does not respond to reflection of the light from its surface, but instead from the light scat- tered within the body of the particle, thus causing large signal differences in the photodetector between translucent and opaque particles.

2. A process according to claim 1 whereby in particle streams with translucent product and opaque contamination, a narrow translucent target is fixed between the photodetector and parti- cle stream such that the detector responds to the translucency of the target or desired particle, but reduces to below a low threshold value when an opaque contamination particle blocks the light beam to the target but, being opaque, produces no scattered light to be seen by the photodetector.

3. A process according to claims 1 and 2 whereby the direction of view of the photodetector is approximately 135 degrees to the plane of the incident light curtain. 1*1'

4. A process according to claims 1 to 3 whereby two complete detectioi stations are used, each said detection station consist- ing of light curtain, fixed translucent background, and system of photodetectors, whereby the respective detectors and their asso- Sciated light sources are on different sides of the particle stream. A process according to claims 1 to 4 whereby the light source used in the scanning light curtain is a low-powered helium neon laser. 1 6. A process according to claims 1 to 5 for the sorting and removal of particulate contamination such as sticks, burrs and stones from dried fruit such as sultanas. S Dated this 6th day of October, 1990 ALBERT PETER HAWKINS APPLICANT nd7 i _1