Abstract:
A particle inspection device includes a feeder configured to drop a particle through an image area. The feeder includes a tray surface having a flat portion and an edge portion disposed above the image area. The inspection device also includes a vibration device configured to vibrate the feeder induce movement of the particle from the flat portion to the edge portion and an image capturing device configured to capture an image of the particle in the image area. The edge portion may be a downwardly curved edge section and configured to maintain the orientation and reduce tumbling motion as the particle slides off the tray and falls through the image area. Alternately or additionally, a landing element is provided having a landing surface disposed in the image area and angled with respect to the flat portion of the tray surface and configured to receive the particle. The image capturing device is configured to capture an image of the particle on the landing surface.

Description:
RELATED APPLICATIONS  
       [0001]     This application is a continuation-in-part of U.S. patent application Ser. No. 10/400,723, filed on Mar. 27, 2003, the entire disclosure of which is hereby incorporated by reference herein. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates generally to inspection systems and particularly to a method and device for inspecting of particles.  
         [0003]     It is often desirable to inspect particles that are produced or created during various industrial processes. Inspection may be useful for determining properties of the particles, including, for example, size, shape, purity, surface roughness, color, and uniformity. The particles may be inspected for a variety of reasons, for example, as part of a quality control process, for sorting, or for identifying particular qualities of the particles including defects.  
         [0004]     Several devices and methods are known for inspecting and analyzing particles. For example, many such methods and devices employ laser diffraction, spectroscopy, and various forms of visual image analysis.  
         [0005]     One known image analysis technique of particle inspection captures a two-dimensional image of particles being inspected as they fall from a feeder through an image area. The captured image is analyzed using software running on a microprocessor to determine certain properties of the particles, such as size and shape. For non-spherical particles, for example, rock fragments and particles produced in mining and aggregate industries, analysis of a two-dimensional image can lead to an incorrect determination of the true size or shape of the particle.  
         [0006]     One known inspection system uses three-dimensional image analysis to inspect the shape of coarse aggregates. That known system relies on the analysis of two separate images taken at right angles from two separate cameras of aggregate particles moving on a conveyor belt. The use of separate cameras and separate images has several disadvantages including additional cost of the inspection device as well problems in calibrating the two separate images. In addition, obtaining high image quality of particles as they are being transported on a conveyor belt can be problematic and can diminish the accuracy and precision of the particle observations and/or measurements.  
       SUMMARY OF THE INVENTION  
       [0007]     An object of the present invention is to provide a method and device for inspection of particles in an efficient and cost effective manner. A further object of the present invention is to provide a method and device that presents particles for inspection in an advantageous way for capturing high quality images of the particles.  
         [0008]     The present invention provides a particle inspection device that includes a feeder configured to drop a particle through an image area, wherein the feeder includes a tray surface having a flat portion and a downwardly curved edge portion disposed above the image area, a vibration device configured to vibrate the feeder so as to induce movement of the particle from the flat portion to the downwardly curved edge portion, and an image capturing device configured to capture an image of the particle in the image area. When capturing an image of a particle falling through the image area, the downwardly curved edge portion helps to minimize tumbling or rotation of the particle as it falls, particularly when oblong-shaped particles are being inspected. Because the particles tend to settle on the vibrating feeder with their largest faces facing the tray surface, the curved edge surface tends to rotate the major face of the particle as the particle slides along the curved surface so that when the particle falls, the major face is aligned perpendicularly with the camera during its fall. This allows the view of the camera to obtain the largest possible circumference of the particle.  
         [0009]     The particle inspection device may also include a first light source disposed opposite the image capturing device and configured to provide backlighting of the particle for the image, and or a second light source configured to provide front lighting of the particle for the image. The flat portion may be disposed at a slight angle from the horizontal so as to encourage movement of the particle from the flat portion to the downwardly curved edge portion when the feeder is vibrated.  
         [0010]     The downwardly curved edge portion preferably includes a first section tangential to the flat portion and a second section tangential to a drop angle of the particle and may define a radius of curvature that is larger than a minimum thickness of the particle. Preferably, the downwardly curved edge portion is configured to enable the particles to slide off the edge of the tray without inducing a rotational movement to the particles.  
         [0011]     The particle inspection device may also include an image processing device in operative connection with the image capturing device and configured to determine a property of the particle, such as a size property, a shape property, a color property, and/or a surface roughness property. The image capturing device defines a sighting axis and may be disposed such that the sighting axis is substantially perpendicular to the drop angle of the particle and preferably at an angle from horizontal.  
         [0012]     The present invention also provides a method for inspecting a particle, that includes providing a feeder having a tray surface that includes a flat portion and a downwardly curved edge portion, disposing the particle on the flat portion, vibrating the feeder so as to induce movement of the particle from the flat portion to the downwardly curved edge portion, sliding the particle over the downwardly curved edge portion and dropping the particle from the downwardly curved edge portion through an image area, and capturing an image of the particle in the image area using an image capturing device.  
         [0013]     Furthermore, the present invention provides a particle inspection device that include a feeder configured to drop a particle through an image area, wherein the feeder includes a tray surface having a flat portion and an edge portion disposed above the image area, a vibration device configured to vibrate the feeder so as to jog the particle from the flat portion to the edge portion, a landing element having a landing surface disposed in the image area and configured to receive the particle, a relative landing angle between the landing surface and the flat portion of the tray being less than 90 degrees, and an image capturing device configured to capture an image of the particle on the landing surface. The landing element is preferably configures to receive the falling particles at an angle so that particle slides down the landing surface with the major face of the particle facing toward the landing surface and at a perpendicular angle to a view of the camera.  
         [0014]     Preferably, the relative landing angle is greater than 30 degrees. The flat portion of the tray surface should be disposed at a slight angle from the horizontal so as to encourage movement of the particle from the flat portion to the edge portion when the feeder is vibrated. The edge portion may be advantageously curved downwardly from the flat portion toward an edge of the tray. The image capturing device defines a sighting axis and may be disposed so that a relative sighting angle between the sighting axis and the landing surface is perpendicular.  
         [0015]     The landing element may be pivotably mounted relative to the feeder so that the relative landing angle is adjustable about a pivot point. A relative distance between the pivot point and the tray surface may be adjustable. A camera mount may be provided and connected at a fixed angle to the landing device. The image capturing device may be mounted on the camera mount so that a relative sighting angle between the sighting axis and the landing surface is unchanged during an adjustment of the landing angle.  
         [0016]     The landing surface may be transparent and a first light source may be disposed behind the landing surface so as to provide backlighting of the particle for the image. The first light may be a back panel light disposed directly adjacent to the landing surface. A second light may be additionally provided and configured to provide front lighting of the particle of the image. A color of the landing device may be chosen to contrast with a color of at least one portion of the particle.  
         [0017]     The present invention furthermore provides a method for inspecting a particle. The method includes providing a feeder having a tray surface that includes a flat portion and an edge portion, disposing the particle on the flat portion, vibrating the feeder so as to induce movement of the particle from the flat portion to the edge portion and dropping the particle from the edge portion through an image area, receiving the particle on a landing surface disposed in the image area at an angle less than 90 degrees from the flat tray surface, and capturing an image of the particle on the landing surface using an image capturing device.  
         [0018]     The feeder preferably includes a tray surface angled downward toward a first end of the feeder disposed above the image area and the particle inspection device preferably also includes a vibration device configured to jog the particle toward the first end of the feeder. The first end of the feeder may advantageously include a downwardly curved edge portion. A first section of the curved edge portion is preferably tangential to the tray surface, and a second section of the curved edge portion is preferably tangential to a drop angle of the particle. The curved portion of the end of the feeder is preferably shaped so as to encourage a translation of the particle and to discourage a rotation of the particle, so that the particle slides off the end of the tray with minimal rotational movement as it falls. If the end of the tray ends abruptly, with no curved transition surface, the particles, particularly oblong-shaped particles, will tend to tumble as they fall through the image area. If the particle is tumbling during its free-fall through the image area, the orientation of the particle with respect to the image capturing device is not well-controlled, and is unlikely to include a principal face of the particle. Particularly when inspecting particles having elongated shapes, it is desirable to have at least one view that shows a principle face of the particle. As the particle vibrates along the tray surface, it will tend to settle in a position such that its principal face is facing downwards against the tray surface. When the particle reaches the curved edge portion, it will tend to slide along the curved edge portion with the principal face facing the surface of the curved edge portion. Thus, as the particle slides down the curved edge surface, the principle face is slowly being rotated so as to be facing the image capturing device as it falls from the end of the curved edge portion and through the image area.  
         [0019]     The method may be performed on a particle having a major diameter between 50 microns and 6000 microns, and/or on a particle has a major diameter between 0.1 inches and 3.0 inches, and/or on a particle having a major diameter greater than 1 inch. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     The present invention will be discussed in the following with reference to the drawings, in which:  
         [0021]      FIG. 1  shows a perspective view of a particle inspection device according to the present invention;  
         [0022]      FIG. 2  shows a perspective view of the imaging assembly of the particle inspection device shown in  FIG. 1 ;  
         [0023]      FIG. 3  shows a schematic view of a portion of the imaging assembly shown in  FIG. 2 ;  
         [0024]      FIG. 4  shows a perspective view of the feeder and vibration device of the particle inspection device shown in  FIG. 1 ;  
         [0025]      FIG. 5  shows a schematic view of an image captured from the particle inspection device shown in  FIG. 1 ;  
         [0026]      FIG. 6  show a perspective view of an exemplary embodiment of a gate mechanism;  
         [0027]      FIG. 7  shows a side view of a further second of a particle inspection device according to the present invention; and  
         [0028]      FIG. 8  shows a perspective view of the second embodiment. 
     
    
     DETAILED DESCRIPTION  
       [0029]      FIG. 1  shows a perspective view of one embodiment of a particle inspection device  10 , which includes housing  20 . Inside the housing, a feeder  11  is suspended from the housing using mounting cables  27 . A vibration device  12  is rigidly connected to the feeder  11  and also suspended from the housing  10  using mounting cables  27 . A particle inlet opening  25  enables particles to be placed into the feeder  11 . In a laboratory setting, a user of the device may place a sample of particles to be inspected through the particle inlet opening  25 . Alternatively, the device could be used in-line so that the particles flow through the opening from a previous process operation.  
         [0030]     The feeder includes a tray surface that is preferably slightly inclined downward from the end proximate the particle inlet opening  25 . When particles are in the feeder  11  and the vibration device  12  is switched on, such as by switching on switch  17 , the feeder is vibrated by vibration device  12 , which jostles the particles so that they may migrate toward the downward end of the feeder  11 , which is adjacent the vibration device  12  in  FIG. 1 . When the particles reach the downward end of the feeder, the particles fall into catch tray  26 . The particles can be removed from the housing through opening  28  in the rear of the housing by the device user. Alternatively, if the inspection device were to be used in-line with a larger production or inspection process, the particles could fall into a chute or otherwise flow to a subsequent process operation. An imaging assembly  30  is mounted to supports  23  and  24 , which each include a plurality of holes, using bolts passing through slots  38  and  39  respectively, of imaging assembly  30 . In this way, the imaging assembly  30  is mounted in a manner such that its position and angle can be adjusted to provide optimal viewing and imaging conditions.  
         [0031]     Imaging assembly  30  is shown in more detail in  FIG. 2 . Two image capturing devices, for example CCD cameras  15  and  16 , are mounted at one end of imaging assembly  30 . At an opposite end, an illumination panel  33  is mounted opposite camera  15  and illumination panel  35  is mounted opposite camera  16 . Image area  31  includes the area in front of illumination panel  33  through which particles fall from the feeder  11  to the catch tray  26 . A second image area  32  includes the area in front of illumination panel  35  through which particles fall from the feeder  11  to the catch tray  26 . Because the particles fall between a camera and illumination pair ( 15  and  33 , or  16  and  35 , respectively), the illumination panels  33  and  35 , when illuminated, provide backlighting for a direct view of the particles from cameras  15  and  16 , respectively. LED panels may be used as the illumination panels.  
         [0032]     Although the embodiment shown includes a pair image capturing devices  15 ,  16  and a pair image areas  31 ,  32 , this is not necessary for the functioning of the invention. An imaging assembly including a single image capturing device  15  and single image area  31  would work as well. The use of two cameras merely increases the rate at which particles can be inspected as two images can be captured of different particles and simultaneously processed.  
         [0033]     In addition, imaging assembly  30  includes reflector  13 , such as a mirror, which is positioned within a field of view of the first image capturing device  15  such that it provides a reflected side view of particles falling through the image area  31  to image capturing device  15 . Illuminated panel  34 , which is oriented 90 degrees with respect to illumination panel  33 , provides backlighting to the reflected side view taken from camera  15 . Similarly, reflector  14  is positioned within the field of view of second camera  16  such that it provides a reflected side view of particles falling through the second image area  32  to second camera  16 . Illuminated panel  36 , which is oriented 90 degrees with respect to illumination panel  35  (and back-to-back with respect to illumination panel  34 ) provides backlighting to the reflected side view taken from camera  16 .  
         [0034]      FIG. 3  shows a schematic view of the components of the imaging assembly  30 . Particles  45  and  46  are shown falling within first image area  31 . Particles  47  and  48  are shown falling within second image area  32 . First camera  15  defines sighting axis  49  and a field of view between boundary lines  41  and  42 . The direct view  43  of the image area  31  taken from camera  15  is shown schematically by arrow  43  and the reflected side view taken from camera  15  is shown schematically by arrow  44 .  
         [0035]     The feeder  11  and vibration device  12  are shown in more detail in  FIG. 4 . Feeder  11  includes two mounting elements  51 . Feeder  11  is rigidly attached to vibration device  12 , which also includes two mounting elements  52 . Mounting elements  51  and  52  each including a loop connected to a spring. Mounting cables  27  are connect to the loops of mounting elements  51  and  52  in order to suspend the feeder  11  and the vibration device  12  from the housing. The springs in mounting elements  51  and  52  provide damping action in order to smooth out the vibrations to feeder  11  and to allow a smoother migration of the particles from one end of the feeder to the other. Feeder  11  includes tray surface  53  at its bottom. Feeder is preferably disposed within housing  20  in such a manner that tray surface  53  slopes downward slightly toward the open end of the feed tray (disposed underneath vibration device  12  in  FIG. 4 ). The slight downward slope coupled with the vibrations induces a migration of the particles from one end of the feeder to the other.  
         [0036]     At its open end, tray surface  53  includes downwardly curved portion  55 . Curved portion  55  provides a smooth transition to the particles as they fall off the edge of tray surface  53  and helps to orient the particles so that a principle surface of the particle is directed toward the camera during free-fall through the image area. Through the vibration of the feeder  11 , the particles, which may include rock fragments or other particles having oblong shapes, will tend to settle into a position with their principle face (i.e. the face having the largest substantially flat surface area) downward. If the tray surface were to include an abrupt edge without a downwardly curved edge portion, the oblong-shaped particles would tend to tumble off the edge of the feeder and rotate end-over-end as they fell through the image area. In effect, the edge would act to flip the trailing edge upward as the leading edge of the particle began to fall. With the curved edge portion  55 , the particles will tend to slide down the edge portion with their principle faces adjacent to the surface of the curved edge portion  55 . Thus, as the particles slide down the curved edge portion, they become oriented such that their principal faces are facing toward image capturing device and in a direction perpendicular to the direction of movement of the particle as it begins to fall from the feeder. The end of the curvature of edge portion  55  is preferably tangential with the initial angle of fall  57  of the particle from feeder  11 . In addition, imaging assembly  30  is preferably mounted within housing  20  so that the sighting axis of the camera is perpendicular to the direction of fall of the particles. In this way, the particles will tend to fall with only minimal rotational movement, if any. During the fall, the principal faces of the particles will be oriented substantially toward the camera. In this way, the direct view of the particle from the camera will show the principle face of the particle, which is useful, especially for size and shape determinations of oblong-shaped particles.  
         [0037]     The direction of fall of the particle will typically not be directly vertical, at least not during the upper portion of its fall. Rather, as it leaves the end of curved portion  55 , the particle will be sliding along in the direction of the angle  57  of the curved portion. The direction of fall will become more vertical later in the fall as gravity accelerates the particle downward. Therefore, as shown in  FIG. 1 , in order to capture an image of the particles perpendicular to their direction of fall through the image area, the imaging assembly  30  is typically mounted in housing  20  at an angle from direct horizontal.  
         [0038]     One variation of the inspection device includes a landing element, which may be a landing tray  106  is shown in  FIGS. 7 and 8 . The landing plate  106  is an additional means of ensuring that the principal face of the particle is directed toward the camera and may work in conjunction with, or instead of, the curved edge portion  55 . As shown schematically in  FIGS. 7 and 8 , landing plate  106  having surface  107  is disposed in the image area beneath the edge  105  of feeder  11  in a tilted orientation. Feeder  11  has a tray surface  53  that includes a flat portion  123  and an edge portion  124 . The edge portion  124  may be flat and coplanar with flat portion  123  or may be downwardly curved such as curved portion  55  in  FIG. 4 . The use of the landing plate  106  is particularly useful for situations of two dimensional viewing (without a side view), since the landing element may interfere with a reflected view of the particles.  
         [0039]     As shown schematically in  FIGS. 7 and 8 , particles  117  are moved along the feeder  11  from the flat portion  123  to the edge portion  124  until they reach edge  125 , where they drop off. Landing element  106 , which can be a landing plate, is disposed beneath the edge  125 . Landing surface  107  of landing element  106  is tilted relative to the flat portion  123  of the tray surface  53 . Preferably, the relative angle is somewhere between 30 degrees and 90 degrees and is set according to the characteristics of the particles being inspected, such as size, weight, density, and degree of bounce. Advantageously, the landing the angle of tilt is chosen so that the particles to land on the surface  107  and achieve and maintain a flat position relative to the camera  15  and lens  110  until the image is taken while the particles are still on the landing plate. The particles then slide down the landing surface  107  and fall into catch bin  120 , which may later be emptied or which may feed the particles to a further processing step. As shown in  FIG. 8 a  recess  109  may be provided in camera mount  112  to allow the particles to pass through to the catch bin  120  after sliding off the bottom edge of landing surface  107 .  
         [0040]     Whether or not edge portion  124  is downwardly curved the landing plate assists in ensuring the optimal orientation of the falling particles for imaging. For example, depending on the characteristics of the particles being measured, some particles may be launched from the feed tray and substantially miss making contact with the curved lip of the tray. The tilted landing plate allows those particles to achieve a flat position with respect to the view of the camera.  
         [0041]     The landing plate  106  is preferably rigidly connected to, or integral with, camera mount  112 , upon which the camera  15  is mounted, at a perpendicular angle, so that the view of the camera  15  is always oriented at a perpendicular angle to the landing surface  107 . The landing plate is mounted in a pivotable manner with respect to landing element support  116 , such as by pivot rod  114  which defines a pivot point about which the landing plate can be pivoted. This the relative angle between the fall direction of the particles and the landing surface  107  may be adjusted according to the characteristics of the particle so as to optimize the view and minimize bounce. Locking pins  113  can be used to lock the angle of the landing plate. Because of the rigid connection between the camera mount  112  and landing plate  106 , the viewing angle of the camera  15  remains the same as the relative landing angle for the particles is adjusted.  
         [0042]     The landing element support  116  and the landing plate  106  are separated from the feeder  11  at a distance. The pivot rod  114  may be mounted on the landing rod so that at least a vertical distance between the landing surface  107  and the edge  125  of the feeder  11  can be adjusted so that the distance of the fall of the particle can be adjusted according to the particle characteristics, so as to reduce bounce on the landing surface, for example.  
         [0043]     Preferably, conditions of background color and light are adjusted for optimal viewing. For example, backlighting may be provided by back panel light  115 , wherein the landing plate  106  itself is transparent. The intensity and color of the light are preferably chosen to optimize the contrast conditions for viewing those characteristics of the particles being viewed. Front lighting may also be provided alternatively or in addition to the backlighting. A color may be selected for the landing surface to contrast optimally with a color of the particle or a color of one portion of the particle in the case of multi-colored particles. This may be performed by placing a colored panel behind the transparent landing plate or by replacing the transparent landing plate with a colored landing plate.  
         [0044]     As shown in  FIG. 4 , tray surface  53  of feeder  11  may also include screened recess  54  at an intermediate portion between the two ends, which may be provided in order to remove particularly fine particles (“fines”) from a particle sample being inspected. In some instances, the volume of fines that are mixed with the larger particles can create a “dirt curtain” through the image area, or otherwise interfere with optimal imaging of the larger particles. Depending on the type of particles being inspected, and the type of analysis being performed, the gage of the screened recess may be adjusted or a feeder without a screened recess may be used.  
         [0045]     A gating mechanism may be optionally used in the feeder with or without a screened recess to separate out particles according to size and/or to control the rate of migration of the particles through the feeder. One example of a gating mechanism, shown in  FIG. 6 , includes a low-profile raised portion  61  of tray surface  53  of the feeder. Raised portion  61  may be a strip of material connected, for example by welding, to tray surface  53 . Raised portion  61  is sized so as to extend above the rest of surface  53  enough to divert fine particles toward the edges of tray surface  53  while enabling larger particles to vibrate over raised portion  61  without being significantly diverted. By diverting the fines to the edges of the tray surface  53 , interference with the imaging of the larger particles is reduced or eliminated. The optimal height of raised portion  61  for diverting fine particles will depend on, among other factors, the size of particles being imaged and the size of fine particles to be diverted.  
         [0046]     For applications in which the fines are an important component of the measurement, the fines can be extracted from the main flow, for example by using the screened recess  54 , and sent down a chute so as to pass through a supplemental image area. A supplemental image capturing device may capture images of the fines and send them to the processor for inclusion in the total analysis of the sample. Flow of fines through a supplemental image area may be viewed with backlighting and/or using a reflector as are the particles through the first and second image areas  31  and  32 .  
         [0047]     An example of an image  100  of particles  45  and  46  (as shown in  FIG. 3 ) is shown in schematic form in  FIG. 5 . The left half of the image  100  shows a direct view  101  of image area  31  and the right half of the image shows a reflected view  102  of image area  31 .  45   d  represents a direct view of particle  45  and  45   r  represents a reflected side view of particle  45 . Likewise,  46   d  represents a direct view and  46   r  represents a reflected side view of particle  46 . As can be seen from two views of the image, particle  45  has a rather flat shape with considerably less thickness than particle  46 . The image  100 , shows an example of the importance of the additional information shown in the reflected side view, especially in determining size or volume of the particles. For example, if only the direct view of the particles were available, the particle  46  may be judged to be only slightly larger than particle  45 . When both views are available, it becomes clear that the volume of particle  46  is substantially greater than the volume of particle  45 .  
         [0048]     In the preceding specification, the invention has been described with reference to a specific exemplary embodiment thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative rather than a restrictive sense.