Abstract:
An illumination source for a machine vision viewer for a sorter that provides a flow of articles along a scan line includes an elongated, cylindrical shroud with illumination sources mounted interior of the shroud. The illumination sources are arranged longitudinally within the shroud and are angularly spaced along the inner circumference of the shroud. Linear slots running parallel with the shroud axis are provided in the shroud for the subject articles to enter and exit the shroud. A linear slot running parallel with the shroud axis is provided for receptors to view the articles passing through the shroud. The cylinder interior is otherwise uniform and light reflecting. An alternative embodiment of the shroud comprises two shroud arc components with openings between the arcs to allow articles to pass between the shroud arc components.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of U.S. Provisional Application No. 60/383,727, filed on May 28, 2002. 

   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not Applicable. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates generally to sorting machines and particularly to an illumination source for a machine vision system. 
   2. Description of the Related Art 
   Sorting machines incorporating machine vision systems typically identify and sort articles by means of reflected energy waves. One of the main components of a vision machine system is the illumination source. The illumination source provides a starting point for the reception quality of the vision system. Typically, the source is required to be uniform and have a high intensity at the object point (sometimes referred to as the scan line) of the vision system. Most inspection systems include some sort of light source. Conventional light sources include incandescent and fluorescent lamps and light emitting diodes. Various optical arrangements have been designed for better illumination, such as ringed lamp arrays, focused filament projectors, and fiber optic emitters. Uneven illumination in conventional illuminators may result in detection of shadows as defects. While the characteristics commonly measured incorporate light sources including human-visible light sources, machine vision systems may measure energy waves outside the human-visible range. 
   U.S. Pat. No. 6,355,897 to Bjork describes an arrangement and method for sorting granules that includes a light detector arranged over a transparent pellet transportation track and a light source arranged on the opposite side of the track. The detector is at one end of a chamber with the light source and track at the other end. The chamber is evenly illuminated and may have a reflective layer. The light source may also illuminate the pellets from above or around the track. Defects are indicated as a lower intensity potential at the detector. 
   U.S. Pat. No. 5,201,576 to Squyres discloses a spherical chamber, which is covered with a reflective interior surface, with a light source within the chamber. A transparent tube extends through an axis of the chamber. The objects to be inspected are transported through the tube. At least two viewing openings are provided in the chamber with inspection cameras oriented through the viewing openings. The patent discloses the use of an acrylic white paint manufactured by Krylon, and claims that product&#39;s capacity to provide reflectivity above 90%. The patent further discloses use of titanium oxide coating as being prior art in optical integrating spheres. 
   The chamber is provided with a circularly tubular lamp, two video cameras and a transparent, cylindrical tube having two open ends. The objects are conveyed through the tube, illuminated by the lamp and examined by the cameras. One problem that may occur in connection with this solution is it may be difficult to adjust the cameras without affecting the light distribution inside the chamber. This is due to the fact that the intensity from the lamp, which is described in the U.S. Pat. No. 5,201,576, will vary inside the chamber, due to the fact that the intensity is higher close to the lamp than at a certain distance from the lamp. Another problem may be that the tube affects the light refraction in the form of reflections, e.g., that a mirror image of the lens may appear. Additionally, this solution is limited to inspecting serial objects, one side at the time. 
   U.S. Pat. No. 6,238,060 to Bourn et al. describes a ring light source of light emission diodes or similar points of light for providing focused, uniform light without shadows on a spot where an object may be inspected. The patent shows many variations; however, none is believed appropriate for a long scan line. 
   U.S. Pat. No. 6,234,317 to Sommer describes a number of light sources each within a light-transmissive cylinder that can be wiped or pneumatically cleaned from time to time. The objects pass between the light-transmissive cylinders during the inspection process. 
   U.S. Pat. No. 5,745,176 to Lebens describes a source having a linear array of lights and a focusing element intermediate the light source and the object to be viewed for producing a focused light on the object. The source has a background that prevents internal reflections that would otherwise interfere with the focused light and produce variations in light intensity from the source. The object that is inspected is not a moving object. 
   U.S. Pat. No. 5,586,663 to Graudejus, et al. describes a rotating background that can be kept clean. However, it is not a cylinder that surrounds the path of the inspected objects. 
   It would be an improvement to the prior art to provide an illumination system for a machine vision system that provides intense, even illumination of the articles to be viewed along a linear or elongated scan line, thereby providing consistent identification of selected characteristics and substantially reducing mis-characterization of articles as having occlusions or other defects genuinely caused by shadows. 
   SUMMARY OF THE INVENTION 
   The present invention comprises an illumination source for a machine vision viewer for a sorter that provides a flow of objects along a scan line. The present invention includes an elongated, cylindrical shroud structure with illumination sources mounted interior of the shroud. Illumination sources may include fluorescent lamps, arc lamps, gas discharge lamps, an array of filament light sources or semiconductor light sources. The sources are arranged longitudinally within the shroud and are angularly spaced along the inner circumference of the shroud. 
   A linear opening is provided in the shroud parallel to the shroud axis for the subject objects to enter the shroud and a second linear opening, parallel to the shroud axis, is provided to allow the objects to exit the shroud. A linear viewing opening, parallel to the shroud axis, is provided for detectors to view the objects passing through the shroud. The cylinder interior is otherwise uniform and light reflecting. 
   The diameter of the cylinder is limited to the minimum size practicable to maximize illumination intensity at the scan line and to allow placement of ejectors as close as practicable to the scan line to allow more accurate rejection of selected articles. However, the cylinder diameter must be large enough to reduce unwanted effects of removed cylinder surface in the area of the openings. 
   To further improve uniformity of illumination, the cylinder may be longer than the required passage area and the shroud ends may be closed. The entire inner surface of the cylinder section and shroud ends are finished using a material that has spectral properties suitable for optimal reflection of the illumination energy within the cylinder section and that provides maximum contrast of the objects to be sorted. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  depicts a machine viewing system including the illumination system of the present invention. 
       FIG. 2  depicts a cross-sectional view of the illumination system of the present invention. 
       FIG. 3  depicts a cross-sectional view of an alternate embodiment of the illumination system of the present invention. 
       FIG. 4  depicts a cross-sectional view of an alternate embodiment of the illumination system of the present invention. 
       FIG. 5  depicts a cross-sectional view of an alternate embodiment of the illumination system of the present invention. 
       FIG. 6  depicts a cross-sectional view of an alternate embodiment of the illumination system of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring first to  FIG. 1 , an illustrative machine vision sorter system  100  including the illumination system  10  of the present invention is depicted. The machine vision sorter system  100  includes a hopper  110 , a conveyor  120 , a vision system  10 , a selector  130 , a container  140  for segregated articles and a bin  150 . 
   The articles to be viewed and sorted by the machine vision sorter system  100  of the present system are retained in hopper  110  and are dispensed onto conveyor  120 . Conveyor  120  may include vibration means (not shown) to segregate individual articles (not shown) to be viewed and sorted. Conveyor  120  may additionally include tracks or channels (not shown) in addition to or as an alternative to the vibration means for segregation of articles. 
   In the exemplary machine vision sorter system  100 , the articles to be sorted are transmitted over a shoulder  122  of the conveyor  120 . The conveyor  120  is structured to provide a flow of articles from conveyor  120  with a velocity such that the articles uniformly pass through illumination system  10 . The flow path of articles through illumination system  10  is represented by article trajectory  102 . The machine vision sorter system  100  of the embodiment disclosed in  FIGS. 1 and 2  provides for free fall of the articles upon ejection from conveyor  120 . Such flow of articles defines article trajectory  102 . 
   The embodiment of machine vision sorter system  100  depicted in  FIG. 3  includes a gravity slide  201 . In such embodiment, the gravity slide  201  is located intermediate a vibratory feeder (not depicted in  FIG. 3 ) and the vision system  10 . In such instance, the free flow of articles from gravity slide  201  defines article trajectory  202 . 
   The articles may be any of a plurality of organic or inorganic objects, such as, for example, grains, nuts, plastic pellets. The articles may be viewed and sorted based on various criteria determined by the user, including size, color, defects and other characteristics. 
   Referring to  FIG. 2 , the illumination system  10  of the present invention includes an elongated, cylindrical shroud  16 . Cylindrical shroud  16  includes shroud wall  18  having an inner reflective surface  20  and a shroud axis  22 . Lines indicating a vertical axis  24  and a horizontal axis  26  are depicted. Such axes  24  and  26  are normal to shroud axis  22 . 
   In an exemplary embodiment of the present invention, conveyor  120  and shroud  16  are configured and operated such that article trajectory  102  passes through shroud  16 . The article trajectory  102  is essentially parallel at any location on the trajectory  102  to shroud axis  22 . 
   Article inlet slot  30  and article outlet slot  32  are provided in shroud  16 . In the exemplary embodiment, inlet slot  30  and outlet slot  32  are elongated openings in shroud wall  18 , each extending parallel to shroud axis  22 . Slots  30  and  32  extend beyond the lateral edges (not shown) of article trajectory  102 . 
   In the illustrative embodiment depicted in  FIG. 1 , inlet slot  30  is located above horizontal axis  26 . Outlet slot  32  is located below horizontal  26  on the opposite side of shroud  16 , as divided by vertical axis  24 , from inlet slot  30 . Locations of slots  30  and  32  on shroud  16  may require adjustment depending on the specific gravity of articles to be viewed. Such adjustments may be achieved by rotation of shroud  16  about shroud axis  22  or by altering placement of the slots  30  and  32 . The width of slots  30  and  32  are maintained at a minimum level to allow unimpeded flow of articles while maintaining maximum reflective surface area of reflective surface  20 . 
   In a preferred embodiment of the invention, inlet slot  30 , outlet slot  32  and article trajectory  102  are arranged such that article trajectory  102  coincides with shroud axis  22 . 
   A scanning slot  34  is provided in shroud wall  18 . In the exemplary embodiment, scanning slot  34  is a linear or elongated opening parallel to shroud axis  22 . Scanning slot  34  is structured to allow a scanning receptor  50  to identify predetermined characteristics of articles to be scanned and sorted. Receptor  50  may comprise a single receptor or a plurality of receptors. 
   Referring to  FIG. 2 , receptor  50  is spaced from scanning slot  34 . Receptor  50  is focused along a scanning axis  38 . The intersection of scanning axis  38  with trajectory  102  identifies a scan line  23  of articles to be inspected. Scan line  23  coincides with or is near to shroud axis  22 . In a preferred embodiment, a plurality of receptors  50  are arranged parallel to scanning slot  34  along the lateral length of article trajectory  102 . 
   A receptor shroud  35  extends intermediate shroud wall  18  and receptors  50 . Receptor shroud  35  provides a closed environment between scanning slot  34  and receptor  50  to limit ingress of environmental light intermediate receptor  50  and scanning slot  34 . Receptor shroud  35  is preferably provided with a non-reflective interior surface  33 . 
   A plurality of light sources  12  are provided within shroud  16 . In the illustrative embodiment depicted, light sources  12  comprise four elongated bulbs aligned parallel to shroud axis  22 . Any number of light sources  12  may occupy the housings consistent with a physical limitation that they not impede flow path  102  or scan axis  38 . 
   Reflective surface  20  is provided on the interior of shroud wall  18 . Reflective surface  20  comprises a reflective coating having spectral properties suitable for optimal reflection of the illumination energy within the shroud  16 . Reflective surface  20  further comprises the background viewed by receptor  50  of the articles to be sorted. The reflective surface  20  coating to be applied in any particular application will be optimized to provide spectral contrast between such background and the characteristics of the material to be viewed taking into account the wavelength emitted by the light sources  12 . 
   The elongated light sources  12  depicted in  FIGS. 2-4  are arranged parallel to shroud axis  22 . Each of light sources  12  is located close to shroud wall  18 , yet sufficiently spaced away from shroud wall  18 , to allow for reflection of light generated by each of light source  12  distal from shroud axis  22  to be reflected by cylinder reflective surface  20 . Light sources  12  are spaced from each other around shroud wall  18  interior of shroud  16 . 
   In the exemplary embodiment, light sources  12  are equally distant from shroud axis  22 . The light sources  12  are not themselves focused in an orientation direction, but instead are high intensity, diffused light sources. The diffused light is thus reflected by the reflective surface  20  to create intense light within shroud  16 . As the light sources  12  project light radially and as the light sources  12  are contained within a cylindrical wall  18 , the light generated by the plurality of light sources  12  will be continuously reflected within cylinder  18 . In the scan line  23  adjacent shroud axis  22 , intense light will accordingly be received from all directions, including light from light sources  12  and reflected light from reflective surface  20 , such that scan line  23  will accordingly receive intense light from all directions. 
   Light sources  12  may include fluorescent tubes, an array of filament lights, arc lamps, gas discharge lamps, or an array of light-producing semiconductors such as light-emitting diodes. In an alternative embodiment incorporating such alternate light sources  12 , the light sources  12  would be arranged near the shroud wall  18  but spaced therefrom and spaced from shroud axis  22 , so as to cumulatively provide intense light at the scan line  23 , such light to include light directly from light sources  12  and reflected light from reflective surface  20 . 
   The diameter of the cylindrical shroud  16  is limited to the minimum size practicable to maximize illumination intensity at the scan line and to allow placement of ejectors as close as practicable to the scan line to allow more accurate rejection of selected particles. However, the cylinder diameter must be large enough to reduce unwanted effects of removed cylinder surface in the area of the slots. 
   To further improve uniformity of illumination, the shroud  16  is constructed longer than the required passage area for articles to be inspected. Shroud wall  18  extends laterally along axis  22  beyond the lateral edges of trajectory  122 , so that there exists ample reflective surface  20  to fully illuminate the end product particles in trajectory  122 . 
   In the exemplary embodiment depicted, cylinder ends  40  are provided at opposed ends of shroud wall  18 . If provided, cylinder ends  40  are each covered with inner reflective surface  20 . 
   In an embodiment comprising elongated bulb light sources  12  as depicted in  FIGS. 1 and 2 , cylinder ends  40  are placed at the termination of the light-producing segment of the bulb with the non-light-producing connector extending outside the cylinder end  40 . Such placements of cylinder ends  40  enhance reflection within shroud  16  and eliminate any adverse effect of the connector or connector base having a differing spectral surface. 
   Referring to  FIGS. 1-3 , in an embodiment of the present invention, selector  130  comprises a series of nozzles  134  for selective intermittent ejection of compressed air  131  into trajectory  102 . Nozzles  134  form a line along article trajectory  102 , such that any individual piece of product (not shown) identified to be sorted may be diverted to trajectory  102   b  without diverting unidentified pieces of product. 
   In operation, upon flow of a quantity of articles along trajectory  102  through vision system  10 , receptor  50  obtains optical data in relation to an article passing along scan line  23  and transmits such data to a processing means for determination whether the acquired data is within a range of acceptable levels or outside such range. If the data is outside an acceptable range, selector  130  is engaged to eject compressed air  131  at articles in trajectory  102  at a particular point along trajectory  102 , thereby changing the trajectory of the identified falling article. For illustration purposes, the trajectory of a rejected article is depicted as  102   b  and the trajectory of an article that is not rejected is depicted as  102   a . In normal operation, selector  130  is timed in relation to article flow past scan line  23  such that the nozzle  134  ejects a short duration blast of compressed air to re-direct the rejected article. 
   The machine vision system  10  of the present invention is useful in a variety of applications to identify measuring characteristics of an article. The high and relatively even intensity of illumination within shroud  16  at scan line  23 , makes the present invention particularly useful in identifying flaws in transparent articles, such as plastic pellets. 
   In an application involving a transparent article such as a plastic pellet, a characteristic to be scanned, and upon which sorting is conducted, is the existence of contaminants in the article. Transparent articles involve a lensing effect wherein light variations exterior to the article may be reflected by the article. The present invention minimizes such lensing effect in part by providing relatively small inlet slot  30 , outlet slot  32  and viewing slot  34 , but more importantly by providing the surrounding cylindrical reflective surface  20  with a plurality of diffuse light sources  12  disposed within the shroud  16  to maintain the intensity of light within the shroud  16 , thereby producing a balanced, multi-directional light at the scan line  23 . 
   A method of determining an opaque contaminant is to determine the deviation of the total quantity of light intensity as measured at receptor  50  as the article passes through scan line  23 . An opaque contaminant absorbs a certain level of illumination resulting in a lower illumination reading by the receptor than the reading for an article that contains no contaminant. The machine vision system  10  of the present invention produces illumination levels at scan line  23  that are not distorted by shadows created by uneven lighting and surface imperfections of the article to be scanned and sorted. 
   Referring now to  FIG. 3 , an alternative embodiment of the present invention is depicted. The embodiment of  FIG. 3  provides an article trajectory  202  of articles that are in free fall from an inclined gravity slide  201 .  FIG. 3  depicts two elongated arc shrouds  216   a  and  216   b , which may be collectively referred to as the shroud  216 . 
   Arc shrouds  216   a  and  216   b  are constructed as arcs of a hollow cylinder and have a common radius. A central axis  222  is defined at the radial center of shrouds  216   a  and  216   b . Article inlet opening  230  and article outlet opening  232  are defined by the open space between adjacent edges of arc shrouds  216   a  and  216   b.    
   A viewing slot  234  is provided in shroud  216   a , along with a receptor  250  aligned to have a viewing axis  238 , as in the embodiment of  FIGS. 1-2 . A scan line  223  is defined at the intersection of viewing axis  238  and article trajectory  202 . As in the embodiment of  FIGS. 1-2 , a plurality of light sources  212  are provided interior of shrouds  216   a  and  216   b . Reflective inner surfaces  220   a  and  220   b  are provided on shrouds  216   a  and  216   b . Light sources  212  are arranged parallel to the scan line  223  and spaced around the interior walls  218   a  and  218   b . In the manner previously described, the light provided by light sources  212  creates an intense level of light from multiple directions at the scan line  223 , including direct light from light sources  212  and reflected light from surfaces  220   a  and  220   b.    
   Referring now to  FIG. 4 , a second alternative embodiment of the present invention is depicted. In the embodiment of  FIG. 4 , the articles to be scanned are supported on a spectrally suitable, clear panel  302 , such as glass, between two elongated arc shrouds  316   a  and  316   b , which may be referred to collectively as shroud  316 . Arc shrouds  316   a  and  316   b  are constructed as arcs of a hollow cylinder and have a common radius. A central axis  322  is defined at the radial center of shrouds  216   a  and  216   b.    
   Article inlet opening  330  and article outlet opening  332  are defined by the open space between the adjacent edges of arc shrouds  316   a  and  316   b . A viewing slot  334  is provided in shroud  316   a  and a receptor  350 , which is aligned to have a viewing axis  338 , as in the embodiment of  FIGS. 1 and 2 . A scan line  323  is defined as the intersection of viewing axis  338  and panel  302 . As in the embodiment of  FIGS. 1-3 , a plurality of high intensity light sources  312  are provided interior of shrouds  316   a  and  316   b , and reflective inner surfaces  320   a  and  320   b  are provided on shrouds  316   a  and  316   b . The light sources  312  are arranged parallel to the scan line  323 , and spaced from the interior walls  318   a  and  318   b . In the manner previously described, the light provided by light sources  312  creates an intense level of light from multiple directions at the scan line  323 , including direct light from light sources  312  and reflected light from surfaces  320   a  and  320   b.    
   Referring to  FIG. 5 , a third alternative embodiment is depicted. This embodiment includes a second scanning slot  434   b  located in shroud  416  on the opposite side of vertical axis  424  from scanning slot  434 . Scanning slot  434   b , like scanning slot  434 , is an elongated opening parallel to shroud axis  422 . Second scanning slot  434   b  is structured to allow a second scanning receptor  450   b  to identify predetermined characteristics of articles to be scanned and sorted. Receptor  450   b  may comprise a single receptor or a plurality of receptors. A plurality of views are provided by receptors  450  and  450   b . The views may be compared using a processor or used individually to identify predetermined characteristics of articles. 
   Receptor  450   b  is focused along a scanning axis  438   b . Receptors  450  and  450   b  are not directly opposed as it is preferred the scanning axes  438  and  438   b  are offset at an angle to avoid interference or reflection between receptors  450  and  450   b.    
   A background opening  436  is located in shroud  416  along scanning axis  438  opposite viewing slot  434 . A second background opening  436   b  is located in shroud  416  along scanning axis  438   b  opposite viewing slot  434   b . Background openings  436  and  436   b  are elongated openings parallel to shroud axis  422 . Background opening  436  provides an opening to a receptor shroud  435   b , which has a non-reflective inner surface  433   b . Thus, receptor  450  has a non-reflective background against which to scan articles. Use of a non-reflective background minimizes any distortion from reflective surfaces when scanning articles. Background opening  436   b  provides an opening to receptor shroud  435 , which also has a non-reflective inner surface  433 . Thus, receptor  450   b  also has a non-reflective background against which to scan articles. 
   Depending upon the angle between scanning axes  438  and  438   b , scanning slot  434  and background opening  436   b  may be combined into a single slot (not shown) to be used for both scanning and providing a non-reflective background. Likewise, scanning slot  434   b  and background opening  436  may be so combined. 
   Although the drawings depict scanning axes  438  and  438   b  intersecting at a single scan line  523 , this embodiment may be practiced with each of the scanning axes  438  and  438   b  of the intersecting the flow of articles at distinct locations on flow line  102 . 
   Referring to  FIG. 6 , a fourth alternative embodiment is depicted. In this embodiment, a background opening  536  is located in shroud  516  along scanning axis  538  opposite viewing slot  534 . Background opening  536  is an elongated opening parallel to shroud axis  522 . Background opening  536  provides an opening to a background shroud  535   b , which has a non-reflective inner surface  533 . Thus, receptor  550  has a non-reflective background against which to scan articles. The non-reflective background minimizes any distortion that may occur when scanning articles. 
   The foregoing disclosure and description of the invention is illustrative and explanatory thereof. Various changes in the details of the illustrated process may be made within the scope of the appended claims without departing from the spirit of the invention. The present invention should only be limited by the following claims and their legal equivalents.