Abstract:
A system for sorting articles includes a detector system having a plurality of narrow bandwidth sources of electromagnetic energy sequentially illuminating articles passing through the detector system, the detector system further including a collector for collecting electromagnetic energy reflected from the articles; a deflector for deflecting selected articles toward an alternative destination; and a control system, operably connected to the collector and the deflector, for actuating the deflector in response to a sensed parameter of the electromagnetic energy collected in the collector.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates generally to systems for separating selected articles from a stream of articles, and more particularly, but not by way of limitation, to a system particularly suited for sorting recyclable materials such as different types of plastic containers and paper or cardboard products, including carrier board, from each other.  
         [0003]     2. Description of the Prior Art  
         [0004]     Environmental campaigns and recycling efforts in many areas have generated a substantial supply of recyclable waste paper and like materials. These materials need to be sorted before they can be recycled. For instance, plastic and glass articles need to be sorted from the stream itself and then further by plastic resin type, color, etc. Colored paper stock often needs to be separated from white stock, and cardboard and carrier board needs to be removed from newsprint. In addition, it is sometimes necessary or desirable to separate printed materials from blank materials. Further, separation processes such as screens designed to remove cardboard and plastic and metal containers from paper streams, often miss some of those materials, requiring additional separation steps. Unfortunately, sorting of waste paper and paperboard, etc. is still currently performed almost entirely by manual sorting. Manual sorting of such materials can be time consuming and expensive, which can render the use of recycled paper less economical than virgin paper material. This is even more apparent when so-called carrier board is present in the waste stream. So-called carrier board, commonly understood to be as the paperstock used in, e.g., cereal boxes, soda or beer can carriers, frozen food boxes, etc., must be sorted manually, as there is currently no effective automated method for doing do.  
         [0005]     Numerous automated waste separation techniques are known. However, these techniques are generally designed for the recovery of metals, alloys, municipal waste, mixed recyclables and plastics. Paper (or, more generally, sheeted material) sorting presents unique problems that cannot be overcome by most prior art separation techniques. For instance, the relatively lightweight and flexible nature of paper presents unique problems when sorting is attempted. Indeed, these problems make it difficult to supply paper to a sorting sensor, especially not at a desirable feed rate (usually defined in terms of feet per minute (fpm), but sometimes also in terms of pieces or objects per minute (ppm) or tons per hour (tph)). Without higher speeds, automated sorting systems do not achieve efficiencies substantially greater than manual sorting. The problem is exacerbated where the waste stream includes paper and non-paper waste.  
         [0006]     A number of different sorting systems have been proposed in the prior art for sorting various articles based upon the color of the articles or the characteristics of the reflected or transmitted electromagnetic radiation to which the article is exposed. Such systems have been utilized for sorting glass, plastic, paper, newsprint, fruit and other edible items, and the like. Similarly, a number of arrangements have been provided for carrying the articles through an inspection zone, and for exposing the articles to electromagnetic radiation and then collecting and analyzing the reflected and/or transmitted radiation.  
         [0007]     For example, U.S. Pat. No. 4,131,540 to Husome et al. discloses a color sorting system wherein light is reflected off tomatoes and the reflected light is collected and analyzed as the tomatoes fly through an inspection zone.  
         [0008]     U.S. Pat. No. 4,657,144 to Martin et al. discloses a system for removing foreign material from a stream of particulate matter such as tobacco as it cascades through an inspection zone.  
         [0009]     U.S. Pat. No. 4,919,534 to Reed, discloses a system for determining the color of glass bottles, wherein the light energy is transmitted through the glass bottles.  
         [0010]     U.S. Pat. No. 5,085,325 to Jones et al. discloses a system of a very common type wherein articles are examined as they are supported upon a moving conveyor belt.  
         [0011]     U.S. Pat. No. 5,297,667 to Hoffman et al. discloses a system of utilizing two light sources and a camera to analyze articles as they fly through an inspection zone.  
         [0012]     U.S. Pat. No. 5,314,072 to Frankel et al. discloses a system which analyzes the transmissive characteristics of articles which are exposed to x-ray fluorescence.  
         [0013]     U.S. Pat. No. 5,318,172 to Kenny et al. discloses a system which distinguishes different types of plastic materials based upon their reflected electromagnetic radiation.  
         [0014]     U.S. Pat. No. 5,333,739 to Stelte discloses another system which transmits light through articles, namely glass articles, and analyzes the transmitted light to determine color.  
         [0015]     U.S. Pat. No. 5,443,164 to Walsh et al. discloses a plastic container sorting system which utilizes both transmitted electromagnetic energy and reflected electromagnetic energy to analyze and identify articles.  
         [0016]     U.S. Pat. No. 5,675,416 to Campbell et al. discloses an apparatus which looks at the transmissive properties of articles to separate them based upon the material of the article.  
         [0017]     U.S. Pat. No. 5,848,706 to Harris discloses a sorting apparatus which examines optical characteristics of the articles against a viewing background.  
         [0018]     U.S. Pat. No. 5,966,217 to Roe et al. discloses a system for analyzing articles wherein reflected radiation is split into a plurality of streams which are then filtered and analyzed.  
         [0019]     It has also been suggested to separate carrier board from a newspaper stream via a color-based identification system. However, this approach is not very effective or accurate since color is a secondary feature of these materials, not a fundamental characteristic.  
         [0020]     In a relatively recent and unique approach, Doak et al., in U.S. Pat. No. 6,497,324, disclose a sorting system utilizing a multiplexer to allow a single analyzer unit to be used to analyze electromagnetic signals from each of a plurality of collector units. Although effective, the Doak et al. system requires the operation of complex and highly sensitive software and mechanical components, which can be difficult to maintain.  
         [0021]     In addition, as noted above, another problem encountered by waste sorting systems is the identification and separation of carrier board and coated or waxed board material commonly used as, e.g., beverage cartons, cigarette cartons, etc. from other paper materials. More particularly, the separation of white or printed paper stock from an article stream can be accomplished by recently developed systems, leaving newsprint and carrier board in the article stream. Further separation to provide only newsprint in the stream, however, has proven problematic.  
         [0022]     Thus, it is seen that although there have been many arrangements proposed for the examination of a stream of articles by analysis of reflected and/or transmitted electromagnetic radiation from the articles, there is a continuing need for improved systems, which may simplify the analytical mechanism and permit the identification of materials (such as carrier board) heretofore found difficult to process.  
       SUMMARY OF THE INVENTION  
       [0023]     A system for sorting articles includes a feed conveyor for conveying the articles toward a first destination. A plurality of sources of narrow bandwidth electromagnetic radiation of differing frequencies are provided for shining electromagnetic energy on the articles in seriatim. The sources are preferably arrayed and actuated such that the individual beams of electromagnetic energy from the sources illuminate the same region of the article as it passes through the sensor region. This can be accomplished spatially or through timing, or both. Each of the sources advantageously has a beam spreader associated with it, for spreading the radiation beam across the width of the conveyor (though preferably not along the length of the conveyor, to avoid overlap with adjoining beams). Additionally, the individual sources may be made up of several sources (arranged perpendicular to the flow direction of the articles) with or without beam spreaders such that wide feed streams can be accommodated. A collector is provided for collecting energy reflected from the articles. A deflector is provided for deflecting selected articles toward an alternative destination. A control system is operably connected to the collector and the deflector for actuating the deflector in response to a sensed parameter (such as color) of the energy collected in the collector.  
         [0024]     By providing a series of sources of electromagnetic radiation of narrow bandwidth (i.e., a bandwidth range of from about 5 nm to about 250 nm), the identification and separation of several classes of articles can be accomplished. It is well know that the amount of reflected radiation at specific frequencies varies for differing materials. In the visible range this variation determines the color of an object. In the near infrared range (i.e. from about 680 nm to 2000 nm) the amount of reflected radiation is determined by the molecular structure of the material, and therefore its composition.  
         [0025]     Convention separation systems for recyclable materials typically illuminate the articles with a steady state broadband radiation from a light source such as a halogen lamp. The reflected light is then measured at various frequencies utilizing a spectrometer type system (diffraction grating, etc.) or a system of detectors with individual frequency filter sets. This approach is costly due to the number of expensive optical and detector components required. An improved approach utilizing a multiplexer minimizes the number of detectors and filters required but introduces a mechanical system which limits reliability and throughput speed.  
         [0026]     The improved system utilizes a series of narrow bandwidth sources which can be switched on an off very rapidly such that the amount of reflected radiation can be measured at a number of specific frequencies without the necessity of a broadband light source or a multiplexer. Further the shape of the narrow bandwidth source can be selected or shaped to optimize the resulting reflection intensity differences between differing materials and therefore the identification accuracy.  
         [0027]     For instance, assuming several individual light sources, aligned in the direction of travel of the articles on the conveyor, each actuated sequentially, as an article travels along the conveyor, a pulse of radiation from each of the sources strikes each article sequentially and in substantially the same place. The reflected radiation is collected by multiple collectors. By analyzing the amount of radiation reflected by an article from each differing radiation frequency the article can be identified as for example, polyethylene terephthalate (PET) plastic, newspaper, brown carrier board, white paper, etc.  
         [0028]     Referring to  FIG. 9 , it can be seen that differing materials reflect differing amounts of electromagnetic radiation at different frequencies (PET is illustrated as a solid line, high density polyethylene (HDPE) is illustrated as a dotted line and paper is illustrated as a dashed line). Identification of the differing materials can be made by selecting illuminating frequencies that correspond to a wavelength region with decreases (or “dips” in the spectrum) in the amount of reflected radiation along with illuminating frequencies at an adjacent region. The ratio of the reflected radiation from these two (or three) frequencies will be different than for another material that does not have a decrease in reflection at one of the frequencies.  
         [0029]     For example in  FIG. 9 , taking the ratio of reflected radiation at 1220 nm versus 1300 nm will give approximately equal intensity (a ratio value of about 1) for both frequencies with paper and PET plastic. For HDPE plastic, however, the ratio of the reflected intensity of 1220 nm versus 1300 nm would be on the order of about 2/7 or about 0.29. If in addition one also measured the ratio of the reflected radiation from 1220 nm and 1660 nm, then paper would again be about 1, while PET plastic would be about 5/2 or about 2.5, with HDPE being about 2/6.3 or about 0.32.  
         [0030]     Other methods beside ratiometric calculation can also be used to determine the type of material utilizing the amount of radiation reflected at differing frequencies. These methods include the use of neural net engines, spectrum comparison with predetermined spectrum stored in a look-up table, spectrum stored by training the system with feed materials, or other similar methods.  
         [0031]     The number of different frequencies required depends upon the number of different type of materials in the feed stream and the accuracy of identification required. In a typical feedstream of recyclable materials, it is likely that employing eight different frequencies would provide acceptable accuracy. More frequencies may be utilized to obtain increased accuracy.  
         [0032]     It can be seen in  FIG. 9  that the width of the decreased reflection “dips” varies with material and with wavelength. Current available narrow band radiation sources in general fall into two categories, light emitting diodes (LEDs) and laser diodes. The typical bandwidth of LEDs is shown in  FIG. 10 , and is on the order of 100 nm when measured from the 20% power level. Laser diodes on the other hand have typical bandwidths of less than 5 nm. LEDs are in general less expensive than laser diodes so their use is preferable when possible.  
         [0033]     Laser diodes may be required when the reflection “dip” is very narrow, such as the relatively narrow 940 nm dip for HDPE and the 1660 dip for PET plastic. Contrariwise, the LED radiation bandwidth matches very well with the wider reflection dips of HDPE between 1150 Nm and 1250 nm and between 1375 nm and 1475. To obtain the greatest difference in the ratios of the reflected radiation intensity at different frequencies it is desirable to “match” the illuminated spectrum with the spectrum of the reflected radiation “dip”.  
         [0034]     The power level of available LEDs and laser diodes is limited so matching the illuminator spectrum with the reflected radiation spectrum is advantageous to maximize the signal to noise ratio of the sensor system. Further, laser diodes with acceptable power output are available in fewer frequencies than that of LEDs. Therefore, it may be necessary to modify the output spectrum of an LED at a specific frequency. This can be accomplished, for instance, by placing the appropriate filter between the LED source and the feedstream articles. For example, the PET plastic dip at 1660 is more narrow than a typical LED output spectrum, but wider than that of a typical laser diode. Hence, a filter that limits the LED 20% bandwidth to about 1640 nm to 1690 nm, or 50 nm bandwidth, will result in a better spectrum match than either a laser diode or an LED without a filter.  
         [0035]     In practice the identification process would include:  
         [0000]     1) Sequentially illuminating the same region of the feedstream articles with each of the different frequency sources as the article passes the region of the sensor.  
         [0036]     2) Measuring and storing the reflected radiation levels from each of the sources at a number of positions across the width of the feedstream. The articles are measured in at least 5 places across the feedstream, and are measured often enough that for a given feedstream speed (of say 500 to 1,000 feet per minute), the article is measured in at least five places along the length of the article, or at least such that on average each article is measured in at least 20 to 30 places.  
         [0000]     3) Taking ratios of, or comparing the spectrum to, the measured reflected radiation levels at the various frequencies to determine the type of material for each measured area of the article.  
         [0037]     4) Determining which type of material the article is substantially composed of by examining the measurements for a majority type of material, or type of material in selected regions of the article, or type of material with the highest contiguous counts.  
         [0038]     In another embodiment of the invention, the system is capable of detecting the presence of carrier board (which does not contain lignin) in an article stream having newsprint (which contains lignin) and carrier board by determining the presence of lignin in articles in the stream by measuring the fluorescence of the articles when exposed to electromagnetic radiation at a frequency of about 532 nanometers (nm) (“green” light) and measuring the fluorescence at a frequency between about 600 and 700 nm; articles in which lignin is not detected are deflected to thereby separate carrier board from lignin-containing articles.  
         [0039]     The present invention further includes methods of using the sorting system and its various components.  
         [0040]     It is therefore a general object of the present invention to provide improved apparatus and methods for sorting objects by material and/or color, and particularly for sorting lignin-containing articles from those not containing lignin.  
         [0041]     Still another object of the present invention is the provision of a system for sorting objects wherein the objects are analyzed as they travel along a conveyor.  
         [0042]     Yet another object of the present invention is the provision of a system for detecting multiple classes of articles flowing along a conveyor without the need for a multi-plexer or other complex mechanical systems.  
         [0043]     Other and further objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the following disclosure when taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0044]      FIG. 1  is a side cross-sectional view of one embodiment of the sorting system of the present invention.  
         [0045]      FIG. 2  is a transverse cross-sectional view of the sorting system of  FIG. 1 , facing against the direction of travel of sheeted material, and taken along lines  2 - 2 .  
         [0046]      FIG. 3  is a transverse cross-sectional view of the sorting system of  FIG. 1 , facing against the direction of travel of sheeted material, and taken along lines  3 - 3 .  
         [0047]      FIG. 4  is a perspective schematic view of the detector system of the present invention.  
         [0048]      FIG. 5  is a schematic view of one embodiment of the light collector of the system of  FIG. 4 .  
         [0049]      FIG. 6  is a schematic view of another embodiment of the light collector of the system of  FIG. 4 .  
         [0050]      FIG. 7  is a partial top elevation view of a material  1000  passing through the detector system of the present invention, showing the lines of electromagnetic energy illumination.  
         [0051]      FIG. 8  is a schematic elevation view of a material  1000  passing through the detector system of the present invention, illustrating the sequential illumination of the material  1000 .  
         [0052]      FIG. 9  is a graphical view of the reflection spectra of PET plastic (solid line), HDPE (dotted line) and paper (dashed line), respectively.  
         [0053]      FIG. 10  is a graphical view of the typical bandwidth of LEDs. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0054]     In a preferred embodiment, illustrated in  FIG. 1 , the present invention relates to a sorting system  10  for sorting material  1000 , such as waste paper. Sorting system  10  comprises a path of travel of material  1000 , defined by the travel of a conveyor  20 . Material  1000  can comprise any waste material for which sorting is desired, such as plastics, glass, etc., but preferably includes paper stock, including newsprint, carrier board and the like. Conveyor  20  can comprise any conveyor used for moving material  1000  or the like, such as a roller or conveyor belt and be formed of fabric, mesh, rubber, etc. as would be familiar to the artisan. Advantageously, conveyor  20  is made of a material which provides sufficient friction to maintain material  1000  traveling the path of travel, to the extent possible. Conveyor  20  is typically driven at the desired rate of travel of material  1000  along the path of travel, as discussed in more detail hereinbelow.  
         [0055]     Still referring to  FIG. 2 , sorting system  10  can also comprise a source of entrainment gas  30  which produces a flow of gas, especially air, used to entrain material  1000  traveling along conveyor  20 , and indicated by arrows. Entrainment air provided by source  30  can maintain material  1000  flowing in the proper path along conveyor  20 , even at feed rates as high as 800 fpm, or higher. Indeed, feed rates as high as 1000 fpm and higher can be utilized in sorting system  10  of the present invention.  
         [0056]     In addition to the use of entrainment air, it is also contemplated that other systems can be employed to maintain the sheeted material spread consistently on conveyor  20  and flowing in the proper direction. Exemplary of such a system is that disclosed by Grubbs, Kenny and Gaddis in U.S. Pat. No. 6,250,472, the disclosure of which is incorporated herein by reference.  
         [0057]     Sorting system  10  can further comprise a plurality of receiving bins  40  into which material  1000  traveling along conveyor  20  can be sorted. Receiving bins  40  comprise a “default” receiving bin  42  into which material  1000  will flow if not directed into any of the preceding receiving bins, as well as at least one “selection” bin  44 , and in the embodiment shown in  FIG. 1 , two selection bins  44 A and  44 B, into which selected individual ones of material  1000  can be directed, depending on particular characteristics of the selected material  1000 .  
         [0058]     Selection bins  44 A and  44 B can also have associated therewith a source of directional gas  50 A and  50 B. Directional gas sources  50 A and  50 B comprise conduits for gas (e.g. air) flow in a direction across the top opening of each of selection bins  44 A and  44 B (and indicated by arrows) to ensure that sheeted material  1000  flowing along with the entrainment gas does not inadvertently enter receiving bins  44 A and  44 B. In other words, because the openings of receiving bins  40  would ordinarily cause eddying and other current variations of entrainment gas, it is possible that, without the use of directional gas flow, individual ones of material  1000  may enter one of selection bins  44 A and  44 B when not intended. Directional gas sources  50 A and  50 B provide a directional gas flow to maintain the flow of material  1000  along the flow of entrainment gas. Typically, directional gas sources  50 A and  50 B are powered by fans or blowers (not shown).  
         [0059]     As illustrated in  FIG. 1 , directional gas sources  50 A and  50 B can be arrayed so as to make use of the structures defining the walls of selection bins  44 A and  44 B. For instance, directional gas source  50 A, used for selection bin  44 A, can comprise a conduit running between selection bin  44 A and conveyor  20 . Likewise, directional gas source  50 B, used for selection bin  44 B, can comprise a conduit extending through the structure forming the wall separating selection bin  44 A and selection bin  44 B.  
         [0060]     In addition, the possibility exists on any surface after the termination of conveyor  20  that the flow of material  1000  may be interrupted due to friction. In order to reduce this possibility, in another preferred embodiment, a fluidizing flow of gas can also be created along such surface such as by providing a source of fluidizing gas  60  which creates a fluidizing flow of gas along the surface (indicated by arrows) to keep material  1000  from being hung up. For instance, the gas flow from directional gas source  50 B can be partially diverted to be outletted at a proximate end of the surface  45  between the openings of selection bin  44 A and  44 B, as illustrated in  FIGS. 1 and 3 . This diverted gas flow forms a fluidizing layer of gas along the surface, thus helping to prevent material  1000  from being caught on surface  45 . Moreover, rollers, such as  60 A,  60 B, and  60 C can be positioned to facilitate the flow of material  1000  along the flow path of the entrainment gas, and otherwise to help prevent material  1000  from being caught on corners or other elements of sorting system  10 . Rollers  60 A,  60 B, and  60 C can be driven or passive, but are preferably passive rollers.  
         [0061]     Each of selection bins  44 A and  44 B also has a deflector or sorter  70  associated therewith to direct selected individual ones of material  1000  into the respective selection bin  44 A or  44 B. Sorter  70  preferably comprises an air jet or other like device which, when actuated, will cause the selected material  1000  to pass through any directional gas flow across the opening of the specific selection bin  44 A or  44 B and thereinto.  
         [0062]     More preferably, sorter  70  can comprise a plurality of air jets  72  extending generally across the width of sorting system  10 . In this manner, when individual ones of the material  1000  is arrayed cross the width of conveyor  20  and the path of travel of material  1000 , individual ones across the width of the path of travel of material  1000  can be selected to be directed into one of the selection bins  44 A or  44 B by actuating only those air jets  72  as would direct the selected material  1000  into the respective receiving bin  40 .  
         [0063]     Upstream from the first selection bin  44 A, sorting system  10  comprises a detector system  100  capable of detecting one or more characteristics of material  1000  flowing along conveyor  20 . Characteristics detected by detector system  100  can comprise reflectance (indicative of whiteness), color, presence of printing, presence of lignin or other characteristics of material  1000 . Signals from detector system  100  are provided to a microprocessor  200  which then can provide a control system to sorters  70  to direct sorters  70  to direct individual ones of material  1000  into selection bins  44 A or  44 B provided certain measured criteria are met, or, microprocessor  200  can permit material  1000  to flow past selection bins  44 A and  44 B, by not actuating any of sorters  70 , and thus be directed into default bin  42  if selection criteria are not met, or vice versa.  
       Detector System  
       [0064]     Detector system  100  comprises a plurality of sources of narrow bandwidth electromagnetic energy or radiation  110 , such as lasers  110   a ,  110   b ,  110   c ,  110   d ,  110   e , etc. As noted above, LEDs can also be employed, and/or LEDs having a filter limiting their bandwidth. The number of sources  110  employed and the center frequency of those sources will depend on material  1000  is to be sorted. For instance, if any type of plastic resin is to be sorted from a paper stream fewer frequencies  110  will be required than if the type of plastic resin also has to be sorted as well. For instance, frequencies of interest for plastics identification are 920 nm, 1210 nm, 1425 nm, 1660, 1725 to 2000 nm and 2125 nm. The primary aseptic packaging frequency of interest is 1455 to 1485 nm.  
         [0065]     Sources  110  are positioned above conveyor  20  and sequentially illuminate a section across conveyor  20 . In order to avoid overlap between adjoining illuminated sections, sources  110  preferably illuminate conveyor  20  in a relatively narrow line across the width of conveyor  20 . The width (i.e., thickness of the beam along the direction of travel of material  1000 ) of the line across conveyor  20  illuminated by sources  110  will depend on factors such as how far apart sources  110  are disposed and the rate of travel of material  1000  on conveyor  20 . In a typical example, the lines illuminated across the width of conveyor  20  by sources  110  should be no more than about 1.5 centimeters (cm) in thickness, most preferably no more than about 1.0 cm in thickness.  
         [0066]     Electromagnetic energy from sources  110  illuminates material  1000  and is then reflected into a reflectance collector or detector array  120  to measure the reflected light intensity from material  1000  illuminated by sources  110 . Data from the detector array  120  is processed by a control cabinet  130 , which then actuates sorters  70 . Detector array  120  is comprised of an array of devices which function to collect the light reflected from material  1000  when illuminated by electromagnetic energy from sources  110 , such as photodiodes or a lens array. When lignin detection via fluorescence is desired, the relevant detector array  120  would have two associated photodiodes to enable lignin detection via fluorescence.  
         [0067]     The use of narrow bandwidth sources  110  is especially important to enable both the lignin and the plastics detection and identification. Color identification could be accomplished with a broadband source, but the lignin identification will require a source with a narrow enough bandwidth in the green range so as not to overlap the red fluorescence. Plastics and other material identification in the near infrared range will also require narrow source bandwidths to identify their characteristic sharp absorption dips and/or reflective peaks.  
         [0068]     Lignin content would be detected using illumination of material  1000  with a source  110  comprising a narrow band green laser at 532 nm and then measuring the resulting red fluorescence via a filter and high gain detector. The intensity of the red fluorescence is dependent on the distance between lignin-containing material  1000  and detector array  120 .  
         [0069]     A potential problem with this approach lies in the fact that not all material  1000  lies flat on conveyor  20 . When material  1000  is raised up from the surface of conveyor  20 , such as when material  1000  is “crumpled”, it is thus closer to detector array  120  and can skew the measurement of red fluorescence, since the reflection from material  1000  would be coming from a location closer to detector array  120  than if material  1000  was lying flat on conveyor  20 . A solution to this problem is to factor out the intensity variation by determining lignin content through the ratio of the red fluorescence to the reflected green light, or a ratio with an average of the reflected intensity of the blue, red, and green sources.  
         [0070]     An additional problem associated with lignin detection is the difference in the lignin fluorescence intensity due to the color of the object. Fluorescence from red and green colors tend to have a higher intensity than other colored material containing the same percentage of lignin. One possible solution to this problem is to compensate the calculated lignin content depending on the color of the material being analyzed. This can be accomplished by developing a look-up table which could be determined experimentally for the various colors and shades of colors.  
         [0071]     There are several possible implementations of the lignin portion of the sensing. They all require two photodiode detectors per detection channel  125 , with one diode allowed to receive only the red fluorescence, and potentially longer, wavelengths. In one embodiment, illustrated in  FIG. 5 , two photodiodes,  140   a  and  140   b , are placed next to each other either in or near the focal plane of the lens  120 . Another embodiment, illustrated in  FIG. 6 , is to utilize a dichroic mirror  142  to reflect energy having a wavelength of approximately 600 nm to one diode  140   a  with shorter wavelengths passing through to the other diode  140   b.    
         [0072]     More specifically, the embodiment shown in  FIG. 5  has one of photodiodes,  140   a , covered by a bandpass filter  144  with a center frequency in the range of 650 nm with a bandwidth of 30 to 50 nm. An advantage of this embodiment is simplicity and a disadvantage is a reduction in signal level of 2 or more due to the spread of the image to accommodate the area of the two detectors  140   a  and  140   b.    
         [0073]     In the embodiment of  FIG. 6 , the dichroic mirror  142  reflects all wavelength above the green bandwidths to detector  140   a . Detector  140   b  would measure the blue and the green reflected light. This embodiment would require that the detector  140   b  amplification be variable as the fluorescence signal is on the order of 1000 times less than the reflected green signal so it would likely be about the same for the near infrared (NIR) reflected signals. This embodiment is more complicated than the first one but would likely produce a higher relative signal level.  
         [0074]      FIGS. 7 and 8  show an alternate approach to achieving registration between the different frequencies of sources  110  with a relatively narrow beam width, by sequentially illuminating material  1000  in approximately the same place with each laser beam, designated L 1 -L 5 , respectively. The pulse rate and on time of the source  110  is coordinated to achieve this result.  
         [0075]     Further, in order to reduce noise each pulse from a source  110  would be split into a plurality of short pulses to achieve the effect of a “chopper” system. For instance, source  110   a  would be actuated, for example, for 35 to 40 μsec, the reflected light measured, and then the detector signal measured with no illumination for 10 to 15 μsec. A “train” of such on-off pulses would require about 250 μsec to complete. During this time, if material  1000  were travelling at 1,000 feet per minute, it would have moved about 0.125 cm. Source  110   b  would then be pulsed in the same fashion as above but with the beam offset in the direction of motion by about 0.125 cm. The illumination from each subsequent source  110  would be offset by about 0.125 cm, so that each different frequency source  110  sequentially illuminates the same line across the material  1000 . Sources  110  would be aligned vertically to minimize effects from variation in height of the object. The light collected by detector array  120  would be maximized, as the field of view is approximately 2.5 cm in diameter while material  1000  is illuminated during travel through the center 1.25 cm of the field of view. The beam width from each source  110  would be on the order of about 0.3 cm to 0.63 cm further “averaging” the measurements. If a slower speed for conveyor  20  is used, the on pulse would be lengthened such that the same line across material  1000  is still illuminated by each source  110 . This approach does require that the measurements from each source  110  laser illumination are stored for each detector array  120  until a full set of 8 to 12 measurements are made. Once the full set of measurements is made for each array  120  the appropriate ratios can be calculated and identification made.  
         [0076]     In operation, material  1000  is fed onto conveyor  20  using, e.g., the system disclosed by Grubbs, Kenny and Gaddis in U.S. Pat. No. 6,250,472. Entrainment airflow is also directed in the direction of the flow of travel of material  1000  defined by conveyor  20 , along the direction indicated by the arrows in  FIG. 1 . As material  1000  continues along conveyor  20  as directed by the entrainment gas, material  1000  passes by detector system  100  which detects and/or measures the presence or absence of certain criteria, such as lignin content, whiteness, color, printed matter, etc. Material  1000  then flows across the openings of selection bins  44 A and  44 B as facilitated by the directional gas provided by directional gas sources  50 A and  50 B as well as fluidizing gas provided by source  60  and into default bin  42 . However, when material  1000  meeting certain criteria, such as reflectivity, etc., passes by detector system  100 , a signal is sent from detector system  100  to microprocessor  200  which then actuates one or more sorters  72  to direct individual one of material  1000  into one of the respective selection bins  44 A and  44 B. In this manner, sorting of material  1000  such as carrier board and paper can be accomplished at sufficiently high speeds and with sufficient accuracy and flexibility to be economical.  
         [0077]     All cited patents and publication referred in this application are incorporated by reference.  
         [0078]     The invention thus being described, it will be apparent that it may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the present invention and all such modifications as would be apparent to one skilled in the art are intended to be included within the scope of the following claims.