Optics: measuring and testing – Of light reflection – With diffusion
Patent
1994-06-01
1995-11-28
McGraw, Vincent P.
Optics: measuring and testing
Of light reflection
With diffusion
250226, 356407, G01N 2189, G01N 2149
Patent
active
054713110
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to systems for revealing information about a material by controlled illumination of the material and the monitoring of diffused or scattered transmitted light from the material. The material may be comprised in a physical object or objects but not necessarily so. The invention also relates to establishing information about the properties of, for example, a fluid or flowable material. In particular, however, the invention is based on scanning an object with a point light source and comparing directly reflected light levels with diffused or scattered transmitted light levels.
The invention has a multiplicity of applications. A particular application relates to the detection of defects on individual fruit or vegetable products such as tomatoes for separation out or rejection, and/or to grading the ripeness of such products. A further application of the invention is directed to a sorter for separating extraneous matter from vegetables such as potatoes, in particular at high capacities in excess of 50 tons per hour. The invention may thus be employed in general in the detection of characteristics of organic or living material. The invention may also be applied to the provision of information about the characteristics of inorganic but light-transmitting substances.
BACKGROUND ART
Numerous systems are known for, in particular, classifying articles by optical characteristics, such as their colour. In U.S. Pat. No. 2,678,725, a classification system is described in which two light beams of different colours are directed at articles to be classified. The system is arranged to provide dual outputs, one of which is related to the chromaticity of the articles, this being defined as their redness or blueness, and the second output being related to the brightness of the article, namely its lightness or darkness.
According to U.S. Pat. No. 3,675,769, a mixture of potatoes and stones and soil is conducted beneath a source of visible and invisible light. A detection system responsive to the light reflected by the mixture of materials classifies the material monitored into two categories based upon the ratio of their reflectivities within selected radiant energy bands. Associated sorting means directs useful product into an appropriate collection feature while discarding the unwanted stones and soil.
U.S. Pat. No. 3,776,381 provides a method for sorting products in which light reflected from product is monitored by light-sensitive cells to detect products that are too light, too dark or otherwise defective. U.S. Pat. No. 3,910,701 provides a method and apparatus for measuring light reflectance, absorption and/or transmission, in which light of different wavelengths is directed towards a test piece, and reflected and/or transmitted light from the test piece is monitored by a light-responsive sensor.
U.S. Pat. No. 3,939,983 relates to apparatus for grading and sorting tobacco, in which tobacco leaves are scanned by detectors monitoring the reflectivity of the leaves. Outputs from the detector control an ejection system for separating those leaves having the required reflectivity characteristics from those leaves which are to be discarded. U.S. Pat. No. 4,081,362 is directed to specific mechanical aspects of a fruit sorter, in which a colour sorting system is applied.
In U.S. Pat. No. 4,095,696, a tomato monitoring system making use of three photodetectors, each having a different spectral response, is described. Each detector monitors a different wavelength of light reflected from the tomato. Logic circuitry operating on the outputs of the three detectors enable red tomatoes to be separated from all other articles on the conveyor, including dirt and rocks. U.S. Pat. No. 4,120,402 describes a further product sorter suitable for separating green tomatoes from red tomatoes and also for the removal of foreign objects such as dirt and debris from a flow of tomatoes to be sorted. This system uses two pairs of phototransducers, each having a respective specific colour filter.
U.S. Pat. No. 4
REFERENCES:
patent: 3786266 (1974-01-01), Reid et al.
patent: 4223680 (1980-09-01), Jobsis
patent: 4600105 (1986-07-01), Van Zyl et al.
patent: 4950905 (1990-08-01), Butler et al.
patent: 5190163 (1993-03-01), Anzai et al.
Lane Marvin
Mallon John
van den Bergh Herman
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