Optics: measuring and testing – By dispersed light spectroscopy – With sample excitation
Reexamination Certificate
2003-01-03
2004-09-21
Smith, Zandra V. (Department: 2877)
Optics: measuring and testing
By dispersed light spectroscopy
With sample excitation
C209S579000
Reexamination Certificate
active
06795179
ABSTRACT:
TECHNICAL FIELD
This invention relates to a system and method for rapidly sorting irregularly shaped scrap metal particles randomly located on a moving conveyor based on the optical analysis of laser-induced plasmas.
BACKGROUND ART
The spectroscopy technique known as Laser-Induced Breakdown Spectroscopy (LIBS), Laser Spark Spectroscopy (LSS), or Laser-Induced Optical Emission Spectroscopy (LIOES) uses a focused laser beam to vaporize and subsequently produce spectral line emissions from a sample material. In this way samples placed at a distance from the analyzing instrumentation, can be analyzed for their chemical composition. It has been shown that a plurality of laser pulses increases the sensitivity of the technique for samples contaminated with paint, dirt, etc., on their surface. Since objects located at a distance could be analyzed rapidly, the method has also been recommended as a possible detection technique in the rapid sorting of mixed scrap metals (see “Analysis of Metals at a Distance Using Laser-Induced Breakdown Spectroscopy.” D. A. Cremers—Appl. Spectroscopy 1987).
Attempts have been made to use laser-induced breakdown spectroscopy (“LIBS”) to analyze metal particles to determine their composition in order to sort the particles. U.S. Pat. No. 5,042,947 discloses utilizing LIBS to sort metal particles. The '947 patent, however, requires the use of a randomly triggerable laser system, such as an excimer laser. Excimer lasers are generally more expensive and less industrially rugged compared to fixed frequency solid-state lasers such as Nd-YAG lasers.
The '947 patent also requires that the metal particles be conveyed into an inspection path where they will each individually pass a fixed inspection point upon which the pulsed laser beam is trained. This process, however, provides for no mechanical means for arranging the moving scrap metal particles in single file, or evenly spacing the particles in a manner expected by the fixed inspection and analysis instrumentation. Experience shows that it is difficult, if not impossible, to arrange and evenly space scrap particles in a high volume production environment. Even if this is possible, the speed of processing would be greatly limited by the speed of orienting each of the scrap particles into a single file so that each of the particles passes the fixed inspection point.
The '947 patent further requires irradiation of the surface of each particle with an initial cleaning pulse and subsequent removal of the plasma produced by the cleaning pulse using an air jet prior to the irradiation of the surface of the particle with an analyzing pulse. An air jet requires a finite time to initiate, and a rapidly moving particle would advance a certain distance during this time. Thus, it would be difficult, if not impossible, to direct more than one pulse to the same target spot of a selected particle. In general, because of the irregular shape of scrap metal particles, it would be difficult, if not impossible, to strike a particle on the same spot when the laser beam is redirected between pulses. Again, even if practically feasible, these additional processing steps would greatly reduce the speed of processing the scrap particles.
It is also known to sort objects located on a moving conveyor by periodically acquiring color images of the objects and discriminating between the objects on the basis of their color. While this method may be employed for sorting certain metal scrap, such as, for example, sorting copper from aluminum, image processing-based color sorting systems are ineffective for sorting randomly oriented scrap metal particles of similar colors, such as aluminum and magnesium, or different aluminum alloys.
It is particularly desirable to efficiently separate scrap into alloy families, since mixed scrap of the same alloy family is worth much more than that of indiscriminately mixed alloys. For example, in the blending methods used to recycle aluminum, any quantity of scrap comprised of similar alloys and of consistent quality, has more value than scrap consisting of mixed aluminum alloys.
DISCLOSURE OF THE INVENTION
One object of the present invention is to provide a system for sorting irregularly shaped scrap metal particles based upon the optical analysis of laser-induced plasmas, as the particles are rapidly transported in random locations on a conveyor.
Another object of the present invention is to provide a system which is capable of rapidly sorting metal scrap particles, such as different aluminum alloy families, which may not be easily differentiated from each other by their color.
Another object of the present invention to provide a LIBS metal scrap sorting system including a scanner system which provides focused laser pulses having uniform power densities along a plane located at the surface of the conveyor.
Another object of the present invention is to provide a LIBS metal scrap sorting system including image detection and processing arrangement that could be used to provide information about a plurality of particles randomly located on a conveyor belt, including location, size, and shape of each particle, to a sorting control system.
Another object of the present invention is to provide a LIBS metal scrap sorting system including an illumination system for image detection that provides uniform controlled illumination of the scrap pieces from a plurality of directions so that the image detected is an actual two-dimensional outline of the particle and is not influenced by the combined effects of particle shape, surface reflectivity, and the geometry of the illumination system.
Another object of the present invention is to provide a LIBS metal scrap sorting system including a fixed frequency laser system configured so as to frequently provide multiple laser pulses during an extremely small interval of time so that all the pulses could be directed to a randomly located scrap particle using a single positioning movement of a laser beam scanner.
In carrying out the above and other objects, the scrap sorting system of the present invention includes a conveyor for conveying the randomly shaped scrap metal particles in a random orientation, an image detector for electronically recording the image of a predefined viewing area through which the scrap particles are conveyed by the conveyor, a position detector for detecting movement of the conveyor, a laser system configured to provide a laser beam including a stream of a plurality of laser pulses within a selected time interval, and at least one laser scanner assembly including a positionable beam deflector to direct the laser pulses at a selected particle at any location in a selected target region on the conveyor and a focusing element mounted downstream of the source of the laser pulses from the beam deflector to focus the beam and provide uniform laser power density along a plane. The system further includes a light collector for collecting light from plasma produced from the particles as they are irradiated by the laser pulses, a light distribution and spectral analyzer system for isolating and measuring at least one selected band from the collected light, a separator to divert particles to different bins based on discriminator signals, and control logic for continuously acquiring an image of the selected viewing area of the conveyor, processing the image to identify and locate the scrap particles as they pass through the viewing area, monitoring the laser system to determine when the next laser pulses will be available, selecting a downstream location on the conveyor at which the next available stream of pulses of radiation may be directed at an identified particle, operating the scanner assemblies as required to direct the pulses at the selected target location, analyzing spectral data collected from the plasma, generating a discriminator signal based at least in part upon the spectral data analysis, and selectably activating the separator as a function of the discriminator signal to sort the analyzed particles.
In one embodiment, the laser beam
Brooks & Kushman P.C.
Huron Valley Steel Corporation
Smith Zandra V.
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