Classifying – separating – and assorting solids – Sorting special items – and certain methods and apparatus for... – Condition responsive means controls separating means
Reexamination Certificate
1999-07-14
2001-11-06
Walsh, Donald P. (Department: 3653)
Classifying, separating, and assorting solids
Sorting special items, and certain methods and apparatus for...
Condition responsive means controls separating means
C209S577000, C209S578000, C209S579000, C356S301000
Reexamination Certificate
active
06313423
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to the identification and sorting of plastic refuse. Specifically, the invention involves the application of Raman spectroscopy to identification and sorting of post-consumer plastics for recycling.
Society has reaped much benefit from the use of plastics over the past decades. The strength, lightness and versatility of products made from plastic makes their use advantageous over many other materials. Disposal of the products made from plastics, however, has clearly been a problem. Post-consumer plastics have become a tremendous burden upon our waste disposal systems. Plastics constitute only about 9% by weight of municipal solid waste but they occupy approximately 25% of the volume of the waste stream.
Recycling is one major solution to the problem of disposal. Diversion of plastics from landfill to recycling can potentially save the energy equivalent of 60 million barrels of oil annually. In addition, new applications for and products made from recycled post-consumer plastics are being developed each day. Some of these applications and product include the production of fiber for clothing and carpeting, durable goods, consumer goods packaging, and food and beverage packaging.
However, post-consumer plastics recycling is expensive and not cost-effective when the plastics are unsorted. Mixed plastics are of little or no economic value and have limited marketability. To be cost-effective, it is necessary for mixed plastics to be sorted according to chemical composition.
Currently, there are various techniques for identifying and sorting materials by polymer type. Some of these techniques include manual hand sorting, density separation, and various automated “sense/sort” systems. Hand sorting is tedious, expensive, prone to error, and can be unsafe. Density separation of granulated plastics by sink/float in a water bath yields only a float product and a sink product and is not useful for a primary sort of mixed plastics. Sensing methods used in automated sense/sort systems include x-ray analysis, optical inspection using photodiodes or CCD machine vision, and near infrared (NIR) sensing. X-ray analysis is effective only for separating polyvinyl chloride (PVC) plastics from polyethylene terephthalate (PETE) plastics. Optical scanning of post consumer plastics is useful for sorting plastics according to transparency and color but is unable to provide chemical identification of polymers. Application of NIR technology to plastic waste sorting remains largely unproven. A new cost effective technology is needed that can accurately identify and sort plastics by polymer type at high throughput rates.
SUMMARY OF THE INVENTION
The present invention provides the cost effective technique needed in the industry and performs high speed sorting more accurately than any other technology known to the inventors.
The present invention uses Raman spectroscopic sensing and complex identification techniques to identify the polymer type of a sample and to sort accordingly. Research has determined that the Raman spectra within a given group of polymers is very different from the Raman spectra of polymers in another group. This difference is identifiable and can provide the basis of a sort. Through the present invention, the Raman spectra of polymers within a given group, which are not very different, can also be differentiated in most cases. This identification technique in combination with a reliable sorting apparatus results in the breakthrough technology of the present invention for high speed accurate identification and sorting of mixed streams of plastics.
It is a primary object of this invention to provide a high accuracy rapid system for sorting waste plastics by polymer type.
It is a further object of this invention to identify and sort a plurality of materials by polymer type largely independent of sample positioning (depth of field).
It is another object of this invention to identify and sort a plurality of materials by polymer type largely irrespective of the color of the material.
It is still another object of this invention to identify and sort a plurality of materials by polymer type largely irrespective of the existence of contaminants commonly found on the plastic to be sorted.
It is yet another object of this invention to identify and sort a plurality of materials by polymer type even when the material is presented at high speed and thus, for a low exposure time.
Another object of this invention is to identify and sort a plurality of materials by polymer type using data from a broad Raman spectrum of a material sample, instead of from solely a narrow wavelength band, in order to more accurately identify its polymer type.
Other objects, features and advantages of the present invention will become apparent to those skilled in the art from the following detailed description. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration and not limitation. Many changes and modifications within the scope of the present invention may be made without departing from the spirit thereof, and the invention includes all such modifications.
The disclosed invention further employs a sophisticated method for rapid identification and sorting of a plurality of materials by polymer type comprising the steps of:
a) conveying at least one of said plurality of materials;
b) irradiating material conveyed with light from a laser to induce Raman emission;
c) collecting the light reflected from the said material;
d) performing a spectroscopic analysis of the collected light to determine its Raman spectra;
e) identifying the polymer type of said material by comparing said Raman spectra with a database of spectra of at least one known polymer type; and
f) sorting said plurality of materials by identified polymer type.
In the present invention, the step of identifying the polymer type of the material can further comprise the use of baseline correction to reduce the effect of fluorescence and other background noise. The step of identifying the polymer type of the material can also comprise the use of a vector dot product algorithm to perform the comparison of the Raman spectra of the material with the spectra of known polymers in the database.
Also, the inventors disclose a system for rapid recognition and sorting of a plurality of materials by polymer type, said system comprising:
a feed conveyor for conveying said plurality of materials;
a laser diode for providing irradiating light of a determinable frequency;
a probe head, coupled to said laser diode, for irradiating at least a portion of at least one of said conveyed plurality of materials with said irradiating light and inducing Raman emission from the irradiated material and for collecting reflected light energy from the irradiated material;
a spectrograph, coupled to said probe head, for analyzing the collected reflected light to determine its frequency components and outputting data corresponding to said frequency components, and
a microprocessor based controller, coupled to said spectrograph means, for controlling the spectrograph and for processing the said data corresponding to the frequency components of the collected reflected light to identify the irradiated material as a recognized polymer type and to generate a signal to indicate whether the irradiated material should be separated, and
a sorter, coupled to and controlled by said microprocessor based controller, wherein said sorter separates said plurality of materials in accordance with said signal.
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Rich John T.
Sommer Edward J.
Foley & Lardner
National Recovery Technologies Inc.
Schlak Daniel K
Walsh Donald P.
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