Abstract:
A method, apparatus and system for sorting contaminated glass from a stream of glass particles used light of a wavelength suited to inducing fluorescence in the contaminated glass pieces. Automatic cleaning mechanisms are included in some embodiments to facilitate removal of coatings which would prevent the contaminated particles from fluorescing. The identified particles are then automatically separated from the remaining particles.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The application claims priority to U.S. patent application Ser. No. 11/255,850, for METHOD AND APPARATUS FOR SORTING METAL PIECES, filed on Oct. 21, 2005, which is incorporated herein by reference. The application also claims priority to U.S. Provisional Application Ser. No. 60/728,581, for METHOD AND APPARATUS FOR SORTING CONTAMINATED GLASS, filed on Oct. 20, 2005, also incorporated herein by reference.  
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates generally to methods, techniques and apparata for recycling waste materials, and more particularly relates to methods, techniques and apparata for recycling waste glass, including contaminated glass.  
       BACKGROUND OF THE INVENTION  
       [0003]     CRTs and other obsolete electronics account for a significant and rapidly increasing share of the solid waste generated by many different societies. From current estimates of 75,000 tons per year, the volume of this waste was expected to reach as much as 300,000 tons annually by 2005. The already increasing rates of discard will be exacerbated by the disposal of older units in favor of emerging technologies such as flat panel screens, high definition television (HDTV) and DVD players.  
         [0004]     A cathode ray tube (“CRT”) is the main component in older televisions and computer monitors. The CRT is a specialized vacuum tube in which images are produced when an electron beam internal to the tube is scanned back and forth across a phosphorescent surface on the inside front of the tube. Color CRT&#39;s have phosphor screens using multiple beams of electrons to display millions of colors. The CRT itself appears in the unit as a funnel shaped, leaded glass tube, typically with a metal frame inside. Most CRT&#39;s contain lead, which is well known to be a contaminant in many instances, and some CRT&#39;s can contain up to several pounds of lead, which may be in the form of lead oxide.  
         [0005]     If the lead bearing glass is broken up and the lead oxide is exposed to an acidic environment, lead can be leached out of the glass. Because many CRT units are disposed of in landfills, those landfills may potentially be exposed to high levels of lead, which may leach to the water table and elsewhere in the environment.  
         [0006]     In addition, the interior coatings of older television CRTs may also contain high levels of cadmium compounds, which may also be contaminants. These cadmium compounds can also be released from the CRT, and can contaminate the ground water, among other things.  
         [0007]     CRTs may also contain various other contaminants, as shown in Table 1. It is highly desirable to avoid disposing of CRTs in a landfill by recycling the components. One method for recycling the components of the CRT is to break or shred the units into small pieces which are made of a single material, e.g., metal, plastic, or glass. The shredding can be performed by various means including automatic hammers, saws, blades or similar devices. These smaller pieces are then sorted according to material. For example, the ferrous metal components can be sorted from non-ferrous metals, plastic and glass by magnetic filtration. Other techniques may be used to sort the glass from the other components.  
                                                                   Based on a typical desktop computer and 14″ monitor       weighing ˜60 lbs. Table presented in: Microelectronics       and Computer Technology Corporation (MCC). 1996. Electronics       Industry Environmental Roadmap. Austin, TX.                Content   Actual Weight Content   Recycling       Name   (% of total weight)   (pounds)   Efficiency                    Silica   24.8803   15   0%       Plastics   22.9907   13.8   20%        Iron   20.4712   12.3   80%        Aluminum   14.1723   8.5   80%        Copper   6.9287   4.2   90%        Lead   6.2988   3.8   5%       Zinc   2.2046   1.32   60%        Tin   1.0078   0.6   70%        Nickel   0.8503   0.51   80%        Barium   0.0315   &lt;0.1   0%       Manganese   0.0315   &lt;0.1   0%       Silver   0.0189   &lt;0.1   98%        Beryllium   0.0157   &lt;0.1   0%       Cobalt   0.0157   &lt;0.1   85%        Tantalum   0.0157   &lt;0.1   0%       Titanium   0.0157   &lt;0.1   0%       Antinomy   0.0094   &lt;0.1   0%       Cadmium   0.0094   &lt;0.1   0%       Bismuth   0.0063   &lt;0.1   0%       Chromium   0.0063   &lt;0.1   0%       Mercury   0.0022   &lt;0.1   0%       Germanium   0.0016   &lt;0.1   0%       Gold   0.0016   &lt;0.1   99%        Indium   0.0016   &lt;0.1   60%        Ruthenium   0.0016   &lt;0.1   80%        Selenium   0.0016   &lt;0.1   70%        Arsenic   0.0013   &lt;0.1   0%       Gallium   0.0013   &lt;0.1   0%       Palladium   0.0003   &lt;0.1   95%        Vanadium   0.0002   &lt;0.1   0%       Europium   0.0002   &lt;0.1   0%       Niobium   0.0002   &lt;0.1   0%       Yttrium   0.0002   &lt;0.1   0%                  
 
         [0008]     After the glass has been sorted from the other CRT components, the glass must be sorted based upon either lead content, or upon a similar criteria which may, for example, be based on a different contaminant. Such sorting has, in the past, been largely performed by hand, and therefore is slow and prohibitively costly for most purposes. As a result, there has been a long felt, and growing, need for a system, method and apparatus which is capable of sorting such contaminated glass in a more automated fashion.  
       SUMMARY OF THE INVENTION  
       [0009]     In many applications for recycled glass, glass containing lead oxide cannot be mixed together with non-leaded glass. Therefore, in accordance with the present invention, separation of the contaminated glass, for example leaded glass, is performed using an optical system in which UV light is directed at the glass. The contaminants in the glass typically fluoresce at particular wavelengths, such that glass which is illuminated by appropriate wavelengths emits a characteristic wavelength which can readily be detected by a sensor.  
         [0010]     In a typical arrangement, the glass has deposited thereon one or more layers of coatings. In one embodiment, the glass is cleaned so that at least a small portion of the glass coatings are removed to expose a clean portion of either the surface or a surface edge. The cleaning may be performed by wire brushing, sand blasting, tumbling, chemical etching or cleaning, or any other process suitable for removing the coatings on the glass in at least a portion of the surface. The cleaned glass pieces are then exposed to light of an appropriate wavelength, identified, and removed from the operating surface such as a conveyor belt by an automated means as described in greater detail in the Detailed Description of the Invention, hereinafter. In particular, the glass to be sorted typically contains a portion that will fluoresce upon illumination at the right wavelength, permitting a sensor to detect the glass pieces of interest. The system of the present invention can also include, in at least some embodiments, a mapping system which permits the location of each identified glass piece to be maintained, thereby allowing those pieces to be sorted at a subsequent step.  
         [0011]     These and other aspects of the invention will be better appreciated from the following Detailed Description of the Invention, taken together with the appended Figures as described below. 
     
    
     THE FIGURES  
       [0012]      FIG. 1  shows in top plan view a conveyor carrying thereon an exemplary arrangement of glass pieces, some of which are contaminated.  
         [0013]      FIG. 2  shows in side elevational view the functional blocks of a system for identifying and sorting contaminated glass in accordance with the present invention.  
         [0014]      FIG. 3  shows an automated cleaning module in accordance with one aspect of the invention.  
         [0015]      FIG. 4  shows the cleaning arrangement of  FIG. 3  in greater detail.  
         [0016]      FIG. 5  shows an alternative sorting arrangement in accordance with the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]     With reference to  FIG. 1 , a carrier  221  is shown in top plan view, on top of which rest a plurality of glass pieces of at least two types, indicated by  103  and  105 , waiting to be sorted. The carrier will be, in most cases, a conveyor belt or similar apparatus by which a continuous stream of glass pieces to be sorted is moved below a detection apparatus in accordance with the invention, as described hereinafter. However, for some implementations, the carrier can be implemented in other forms, such as a table, and therefore the carrier is not to be limited to a conveyor belt.  
         [0018]     The glass pieces  103  and  105  typically differ from one another in that at least one of the types of glass pieces contain materials that are cause them to be considered contaminated, or at least different in some material way from the other types of glass pieces resting on the carrier. While only two types of glass pieces are shown in  FIG. 1 , for the sake of simplicity, it will be appreciated that the present invention will work with any number of glass pieces as long as the glass pieces of interest different in some identifiable way from the remainder of the pieces.  
         [0019]     For the sake of simplicity, the present invention is explained in the context of sorting glass which contains lead from glass that does not contain lead. As noted previously, lead can have a deleterious effect on the environment, and leaded glass is frequently considered contaminated. However, it will be appreciated that, while the example of leaded glass will be used hereinafter for purposes of explanation, the use of lead is just an example of one embodiment of the invention, and is not limiting. For purposes of the present disclosure, glass type  103  is designated as not containing lead, while glass type  105  is designated as containing lead.  
         [0020]     It is known that leaded glass  105  contains barium and strontium, and some unleaded glass may have high levels of barium and/or strontium. In response to illumination by UV light (which has a wavelength between 10 nm and 400 nm), barium and strontium in the glass  105  fluoresce by emitting light having a wavelength between 400 and 510 nm. In contrast, most unleaded glass  103  which does not contain either barium or strontium does not fluoresce and so does not emit any light in this wavelength range. Based upon this light output, the pieces of glass  105  that fluoresce can be separated from the non-leaded glass  103 . Visible light has wavelengths between 400 and 750 nm. Because the fluorescence of the glass  105  is in the visible spectrum, it is possible for people to observe the light output from glass pieces  105 . However, this human observation is not recommended without appropriate protection because observing the fluorescent emissions is likely to require exposure to the UV light illuminating the glass. It is well-known that UV radiation can cause serious injury to the eyes and skin. For protection, the carrier can be enclosed within a chamber that prevents UV light from escaping. In addition, because barium and strontium fluoresce in response to UV light of a wavelength on the order of 254 nm, in some embodiments it is desirable to include a notch filter which prevents the emission of UV light not substantially at 254 nm.  
         [0021]     The characteristic of absorbing a first wavelength of light and emitting second wavelength of light that is different than the first wavelength is known as fluorescence. A fluorescent substance converts light in a certain sense before it reradiates it. Following the optical rule of Stokes, the incident first wavelength of light is converted into a second wavelength of light that is larger in wave length. Here the incident ultra-violet light of 254 nm wavelength, which is invisible to humans, is converted into visible light having a longer wavelength 400-510 nm.  
         [0022]     According to quantum theory, fluorescence is linked to a process in the atom, which only occurs when the atom under consideration takes in a definite quantity of energy. If the emitted fluorescent light has the frequency ν a =c/λ a  (c=velocity of light), this energy must be at least be hν a  (h=Planck&#39;s active quantum). If the light irradiated has the wave length λ a , it can only introduce the energy hλ e  into the individual atom, since this is the magnitude of the quanta, out of which the energy of the light of that frequency is composed. Hence, fluorescence can only occur, when hν e &gt;hν a  or when ν e           ν a  and λ e &lt;λ a .  
         [0023]     Referring next to  FIG. 2 , a system in accordance with the present invention can be better appreciated. The pieces of glass of types  103  and  105  rest on carrier  221 , which may for the present example be understood to be a conveyor belt. At an appropriate point on the path of the conveyor  221 , the glass pieces  103  and  105  are illuminated by UV lamps  215 . The glass pieces  103  fluoresce, and that fluorescent emission is detected by optical sensor  207 , which may for example be one or more cameras or one or more optical sensors, and may for example be arranged in an array extending across all or a portion of the carrier  221 . For safety and efficiency, cameras or optical sensors  207  which can be used to detect the leaded glass can include a charge-coupled device (CCD). A CCD is the sensor used in digital cameras and video cameras. The CCD  207  is similar to a computer chip, which senses light focused on its surface, like electronic film. Numerous other types of electronic optical sensors exist, including Complementary Metal-Oxide Semiconductor (CMOS) photodetectors. It will be appreciated that, while specific examples of photosensors are given herein, any form of photodetector suited to detecting the light emitted from the glass type  103  may be used, depending upon the remainder of the implementation. In some implementations, the sensors provide their output to a computer  211  programmed to distinguish different colors and wavelengths of visible light. By imaging a surface with the mixed leaded glass  103  and unleaded glass  105 , the combination of the optical sensor  207  and computer  211  can identify the locations of the leaded pieces  105  on the carrier  221 .  
         [0024]     In an alternative embodiment, a filter is used with the optical sensor  207 . The filter may remove all light that is outside of the 400-510 nm range of wavelengths. Dichroic color filters may be used to block all light outside this range of wavelengths. By filtering the light in this manner, only the light emitted from the leaded glass  105  will be detected by the optical sensor  207 . Thus, when the pieces of glass  103 ,  105  are imaged by the camera  207 , the leaded glass  105  will be illuminated while the unleaded glass  103  will remain dark. This distinction between the leaded glass  105  and unleaded glass  103  simplifies the sorting process because the camera  207  and software do not have to distinguish color and can simply distinguish illuminated from non-illuminated pieces of glass. For example, the leaded glass  105  images are then digitized through a computer program algorithm and converted into a grayscale image at real time at the known 400-510 nm wavelength. The contaminated leaded glass  105  can then identified by the computer and the location of the leaded glass  105  can be determined. In the preferred embodiment, this filter is a notched type filter which only allows light having wavelengths between 400-510 nm to pass through to the camera  207 . In yet another embodiment, several cameras  207  can be used together with different optical filters.  
         [0025]     Once these leaded glass pieces  105  have been identified they are then removed from the surface to separate the leaded glass  103  and unleaded glass  105 . The removal process can be performed by any suitable device, including vacuum, mechanical, pneumatic, hydraulic, and so on. For example, a vacuum hose can be positioned over the detected location of the leaded glass  105  with robotic arms and the vacuum can be actuated to remove the leaded glass piece. Still other alternative embodiments exist, such as: air jets directed at the leaded glass, adhesive contact, grasping with a robotic clamping device, a sweeping mechanism or any other device which can displace the leaded glass  105 . In general, it is more efficient to remove the leaded glass pieces  105  because there are typically more non-leaded glass pieces  103  produced by a shredded or broken CRT tube. However, it is also possible to remove the unleaded glass pieces  103 . After the leaded glass pieces  105  have been separated from a mixture of glass pieces  103 ,  105  on the carrier  221 , the unleaded glass  103  is removed from the surface and a new batch of mixed glass  103 ,  105  is laid out.  
         [0026]     While the arrangement of  FIGS. 1 and 2  can work with a carrier  221  configured as a fixed table, a more efficient approach for sorting the leaded glass pieces  105  is through an automated system that integrates a moving conveyor belt  221  with one or more CCD cameras or other optical sensor(s)  207 , which in some arrangements are configured as an array, a computer  211  and a sorting mechanism. In this embodiment, the mixed glass  103 ,  105  is placed onto the moving conveyor belt  221  which causes the glass pieces  103 ,  105  to travel under the UV light source  215 . The optical sensor  207  is mounted over the conveyor belt and detects moving position of the leaded glass pieces  105 . The positions of the leaded glass pieces  105  are fed to the computer  211 . By knowing the positions of the leaded glass pieces  105  and the speed of the conveyor belt  221 , the computer  211  can determine the time and position across the belt  221  that the leaded glass pieces  105  will travel. For example, the computer  211  can predict when and where a leaded glass piece  105  will fall off the end of the conveyor belt  221 . With this information, the computer  211  can then instruct the sorting mechanism  217  to separate the leaded glass  105  as it falls off the conveyor belt  221 .  
         [0027]     Various sorting mechanisms  217  may be used. In an embodiment, an array of air jets  217  is mounted at the end of the conveyor belt  221 . The array of air jets  217  is mounted above the end of the conveyor belt  221  and has multiple air jets mounted across the conveyor belt  221  width. The computer  211  tracks the position of the leaded glass pieces  105  and transmits a control signal to actuate the individual air jet  217  corresponding to the position of the leaded glass pieces  105  as they fall off the end of the conveyor belt  221 . The air jets  217  deflect the leaded glass pieces  105  and cause them to fall into a leaded glass collection bin  229 . The air jets  217  are not actuated when unleaded glass  103  falls off the conveyor belt  221  and the unleaded glass pieces  103  fall off the end of the conveyor belt  221  into an unleaded glass bin  227 .  
         [0028]     Again, the array of air jets  217  is just one type of mechanism that can be used to sort the glass pieces  103 ,  105 . It is contemplated that various other sorting mechanisms may be used. An array of vacuum hoses may be positioned across the conveyor belt and the computer may actuate a specific vacuum as the leaded glass passes under the corresponding hose. Alternatively, robotic arms with suction, adhesive, grasping or sweeping mechanisms may be used to remove the leaded glass as it moves under a sorting region of the system. An array of small bins may be placed under the end of the conveyor belt and when a leaded glass piece  105  is detected the smaller bin may be placed in the falling path to catch the leaded glass  105  and then retracted. All unleaded glass  103  would be allowed to fall into a lower bin.  
         [0029]     Because UV light is hazardous, in some arrangements the UV light can be contained within a housing to minimize exposure to humans in the vicinity. The housing may be made of any material that is opaque to UV light. For further safety, warning signs can also be posted so that people will not accidentally expose themselves to the UV light from the system of the present invention.  
         [0030]     As discussed above, a small portion of a coating layer on the glass pieces  103 ,  105  can, in some embodiments, be removed to enable more accurate separation of the leaded glass  105  from the unleaded glass  103 . With reference to an embodiment illustrated in  FIG. 3 , the glass  103 ,  105  is passed through a wire brush cleaning system before being exposed to the UV light. The glass  103 ,  105  is placed on a first conveyor belt  331  which drops the glass  103 ,  105  between two wire brush rollers  335 ,  337 . The wire brush rollers  335 ,  337  are cylindrical in shape and have stiff metal bristles. As the glass  103 ,  105  passes between the wire brush rollers  335 ,  337  the bristles scratch through any coating that may exist to expose a small portion of the glass. The glass  103 ,  105  then falls onto a second conveyor belt  339  which transports the glass  103 ,  105  to the inspection conveyor belt  221 .  
         [0031]      FIG. 4  is a more detailed drawing of the wire brush rollers  335 ,  337 . The left wire brush roller  335  rotates clockwise while the right wire brush roller  337  rotates counter clockwise. This rotation draws the glass pieces  103 ,  105  between the wire brush rollers  335 ,  337 . There is a large area between the wire brush rollers  335 ,  337  where the bristles  341  overlap. This overlap forces the bristles  341  against the glass pieces  103 ,  105 . This bristles  341  are typically made of stainless steel and have rough abrasive tips and sides. The force and motion of the abrasive bristles  341  against the glass  103 ,  105  results in scratches in any coatings that have been applied.  
         [0032]     Although the inventive glass sorting system has been described with an array of air jets mounted over the conveyor belt it is also possible to have a similar sorting mechanism with an array of jets mounted under the conveyor belt. With reference to  FIG. 5 , an alternative sorting system includes an array of jets  551  mounted under the conveyor belt  221 . The operation of this sorting system is similar to the system described with reference to  FIG. 2 . The difference between this alternative embodiment is that as the leaded glass pieces  105  fall off the end of the conveyor belt  221 , the computer  211  actuates the array of jets  551  to emit jets that are angled upward to deflect the leaded glass  105  farther away from the end of the conveyor belt  221 . This results in the leaded glass being diverted into a leaded glass bin  229  and the unleaded glass falling into an unleaded glass bin  227 .  
         [0033]     Although an optical leaded glass sorting system has been described above using specific wavelengths of light, it is also possible to perform subsequent separation based upon exposure to alternate wavelengths of light. For example, a subsequent screening can be performed using a 365 nm wavelength light source. The glass containing lead or other contaminants may emit light that the optical sensor may detect. The systems and methods described above may be used to separate glass containing other types of contaminants from uncontaminated glass.  
         [0034]     With the glass sorted by lead content as well as other contaminants, the glass can be properly processed. Both leaded and unleaded glass can be recycled. While leaded glass can tolerate some unleaded glass in the recycling process, it is preferred that only minimal amounts of leaded glass are mixed with the unleaded glass. Thus, the leaded glass sorting algorithm may be adjusted to err conservatively by separating the glass as containing lead even if the observed 400-510 nm signal is weak. Similarly, if this system is used to detect other types of contaminants, it should be configured to err on the conservative side to avoid mixing any contaminated materials with uncontaminated materials. If the glass contains certain types of toxins it may be necessary to dispose of this glass using special hazardous material waste procedures. The inventive separation process allows the hazardous material waste to be properly identified and quantity of the hazardous material to be minimized.  
         [0035]     The inventive system can detect the presence of leaded glass in a few milliseconds by simply detecting the 400-510 nm wavelength visible light. In at least some embodiments, conveyor speeds of up to 400 feet per minute can be used while still accurately separating the leaded and unleaded glass pieces. At these speeds air jets or other high speed sorting devices are necessary to process the volume of glass. Further, because the primary use for the inventive system is to detect glass types which emit visible light, the detection process is very fast and simple and in many if not all embodiments requires only a single scan.  
         [0036]     Having fully described a preferred embodiment of the invention and various alternatives, those skilled in the art will recognize, given the teachings herein, that numerous alternatives and equivalents exist which do not depart from the invention. It is therefore intended that the invention not be limited by the foregoing description, but only by the appended claims.