Optics: measuring and testing – By shade or color – Trichromatic examination
Reexamination Certificate
1996-10-28
2001-02-20
Evans, F. L. (Department: 2877)
Optics: measuring and testing
By shade or color
Trichromatic examination
C356S407000, C356S419000, C250S226000, C209S580000
Reexamination Certificate
active
06191859
ABSTRACT:
BACKGROUND TO THE INVENTION
This invention relates to sorting apparatus. It is particularly concerned with such apparatus which grades product according to colour characteristics, and activates an ejection mechanism based on that grading to remove selected product from the stream. The present invention is directed at an optical system for monitoring light at a viewing station in sorting apparatus in order to grade product passing therethrough.
Product can be effectively graded by a colour sorting technique. Various sorting apparatus which grade product according to its ability to reflect light in different wavelength ranges are described in U.S. Pat. Nos. 4,203,522; 4,513,868; 4,630,736; 4,699,273; and 5,538,142, the disclosures of which are incorporated herein by reference. In apparatus disclosed in the '522 and '142 patents for example detectors are responsive to light reflected from a product in different wavelength ranges, and generate signals indicative of different qualities of the product. These signals are compared and analysed, to generate a signal which can activate ejectors to remove the relevant item from the product stream.
In some of the apparatus of the kind described above, the reflected light is monitored by optical systems containing CCD arrays with a plurality of lines of sensing elements. Typically a tri-linear array is used; the three lines of elements view different areas of the product and are filtered to respond to particular wavelength ranges. In order that the colour of an area of the product may accurately be determined it is necessary to compare measurements taken on the three lines of elements at different times. This may be achieved if the speed of the product is constant and is known accurately. However, in practice the speed of the product may vary, the product may move across the stream and it may rotate between sensing positions all of which give rise to difficulties in determining the colour. To avoid the problem it is necessary that the lines of arrays all view the same area of the product simultaneously; i.e. their view is co-incident. Previously this has been addressed by others as detailed in U.S. Pat. No. 5,315,384, by building cameras which split a beam of focussed light from a viewing area into a plurality of paths by use of an arrangement of prisms. The selection of colours in the beams is by filters which are cemented together with the prisms and the arrays. The positioning of the components must be very accurate which makes production of these cameras difficult and expensive, and major colour changes cannot be made to a camera. The introduction of multi-linear CCD arrays offered the possibility of simpler assembly and interchangeability of filters if the problem of the absence of co-incident viewing could be addressed.
SUMMARY OF THE INVENTION
In this invention, light reflected from product at a viewing station in sorting apparatus is monitored by splitting the light received from an area of the product into a plurality of discrete beams, which are then directed onto light sensors, each of which is responsive to light in the visible or infra-red wavelength range required for colour sorting. The beams are directed onto the sensors through a slit which is disposed close to the sensors in such a position that the view of the lines of sensors is co-incident at the viewing station. The light sensors themselves are normally arranged in an array, for example, of charge coupled devices (CCDs), typically a tri-linear array. The beams are filtered into different wavelength ranges by filters positioned in the beams at any position where they follow separate paths. These filters may be changed as required for a particular sorting task without other modifications to the optical assembly being required.
Typically, the light received from a product piece in a viewing station can be split into the plurality of beams by means of a prism section, the split beams then being directed towards the light sensors by a lens. The prism section can consist of two prisms, one on either side of a parallel-sided glass plate disposed on the axis of the lens. The deflection angle of each prism will be very small, for example less than 5° and typically less than 1°, with the result that the split beams remain in close proximity as they pass through the lens Filters are disposed in the path of the beams to restrict the light transmitted in each beam to each sensor to the respective wavelength range, and the filters can be disposed on either side of the prism section, relative to the lens.
In an alternative light splitting mechanism, a variation of a converging lens system is used. Specifically, the portions of a converging lens system between two or more laterally outer sections thereof are reduced, and these outer sections displaced towards the lens axis. The effect is to simultaneously split received light into a plurality of discrete beams in different wavelength ranges by use of filters, and direct the beams onto respective light sensors. The converging lens system may take the form of a simple bi-convex lens, but other suitable assemblies might equally be used. Once again, the light filters can be disposed at any suitable location between the viewing station and the light sensors. This can include coating on the respective active lens surfaces.
Normally, the light emanating from product in the viewing station would be split into beams of light in three discrete wavelength ranges, typically corresponding to those of three specified visible colours, which are known for use in sorting apparatus of this general kind. Alternatively, the wavelength ranges might correspond to those of two specified visible colours, and a third wavelength range in the infra-red. In this configuration, the beams of visible light can be disposed on either side of the beam of infra-red. In one arrangement, the viewing station is illuminated with visible light from the side of which the light sensors are disposed, with light in the third wavelength range being transmitted from the opposite side. The light sensors are thus adapted to monitor reflected light in a visible range, and the light transmitted in the third wavelength range, which may be in the infra-red, being monitored to conduct a “dark” sort and/or monitor the viewing station for the presence or absence of product therefrom, as described in U.S. Pat. No. 5,538,142.
The invention will now be described by way of example and with reference to the accompanying schematic drawings.
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Robinson Laurence John
Winterbottom David Roy
Evans F. L.
Skjerven Morrill & MacPherson LLP
Sortex Limited
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