Abstract:
A method for visual inspection of printed matter on moving lids is disclosed. An associated visual inspection system is also disclosed.

Description:
BACKGROUND 
     The present disclosure relates to visual inspection of moving articles. 
     SUMMARY 
     According to the present disclosure, a method for visual inspection of printed matter on moving lids is disclosed. The method includes sensing an image of a lid positioned on and being moved by a conveyor, generating an image signal representative of the image in response to sensing the image, and evaluating the image signal to determine whether printed matter on the lid complies with predetermined criteria. Illustratively, this method is applied to two lanes of lids on the conveyor and to a single lane of lids on the conveyor. Associated dual-lane and single-lane visual inspection systems are also disclosed. 
     Additional features of the disclosure will become apparent to those skilled in the art upon consideration of the following detailed description of illustrative embodiments exemplifying the best mode of carrying out the disclosure as presently perceived. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The detailed description particularly refers to the following figures in which: 
         FIG. 1  is a diagrammatic view showing a visual inspection system for inspecting printed matter on moving lids; 
         FIG. 2  is a perspective view of a dual-lane visual inspection system for inspecting printed matter on lids arranged in two lanes on a conveyor; 
         FIG. 3  is a perspective view of the dual-lane visual inspection system, with portions broken away, showing a pair of image sensors arranged to sense images of the lids for evaluation of the printed matter on the lids to determine whether the printed matter complies with predetermined criteria and showing rejection of defective lids; 
         FIG. 4  is a top plan view, with portions broken away, of the dual-lane visual inspection system; 
         FIG. 5  is a front elevational view, with portions broken away, of the dual-lane visual inspection system; 
         FIG. 6  is a top plan view of a lid showing evaluation of the color content of the printed matter on the lid within an area defined by an imaginary outer circle and showing evaluation of whether the printed matter is concentric with the lid by use of an imaginary inner circle; 
         FIG. 7  is a top plan view of a lid showing printed matter that is off-center from the center of the lid; 
         FIG. 8  is a top plan view of a lid showing evaluation of whether the printed matter is on a predetermined surface of the lid by use of a lid orientation test that determines whether the lid is in a predetermined orientation; 
         FIG. 9  is a sectional view taken along lines  9 — 9  of  FIG. 8  showing application of the lid orientation test when the lid is in the predetermined orientation; 
         FIG. 10  is a top plan view of a lid showing application of the lid orientation test when the lid is not in the predetermined orientation; 
         FIG. 11  is a sectional view taken along lines  11 — 11  of  FIG. 10 ; 
         FIG. 12  is an elevational view showing display of the results of the tests performed in connection with each lid; 
         FIG. 13  is a perspective view of the dual-lane visual inspection system showing inclusion of two additional image sensors for evaluation of a feature of each lid; 
         FIG. 14  is a perspective view showing a single-lane visual inspection system; 
         FIG. 15  is a top plan view of the single-lane visual inspection system; and 
         FIG. 16  is a front elevational view, with portions broken away, of the single-lane visual inspection system. 
     
    
    
     DETAILED DESCRIPTION 
     A visual inspection system  10  is used for visual inspection of printed matter on lids  12  positioned on and being moved by a conveyor  14 , as shown diagrammatically, for example, in  FIG. 1 . System  10  senses an image of each lid  12 , evaluates whether the printed matter on lid  12  complies with predetermined criteria, and rejects lid  12  if the printed matter does not comply with the predetermined criteria. 
     System  10  includes a controller  18 , a lid detector  20 , an image sensor  22 , a lid rejector  24 , and a display  34 . As conveyor  14  moves lid  12  past lid detector  20 , lid detector  20  detects lid  12  and generates a lid-detection signal on electrical line  26  in response to detecting lid  12 . 
     In response to receipt of the lid-detection signal, controller  18  generates a sense-image signal on an electrical line  28  to cause image sensor  22  to sense an image of lid  12 . Image sensor  22  senses an image of lid  12  and, in response to sensing the image, generates on line  28  an image signal representative of the sensed image. Following instructions stored in controller  18 , controller  18  evaluates the image signal to determine whether the printed matter on lid  12  complies with the predetermined criteria. 
     If the printed matter does not comply with the predetermined criteria, controller  18  generates a lid-rejection signal on an electrical line  30  to cause lid rejector  24  to reject lid  12 . In rejecting lid  12 , lid rejector  24  removes lid  12  from conveyor  14  and verifies whether lid  12  has been removed from conveyor  14 . In response to receipt of a display signal from controller  18  over an electrical line  32 , display  34  displays information about the sensed images. 
     A dual-lane visual inspection system  110  shown, for example, in  FIGS. 2–5 , is an example of visual inspection system  10 . System  110  is configured to inspect printed matter  36  on lids  12  which are arranged in two parallel lanes on a conveyor  114 . 
     System  110  includes an enclosure  138  formed to include an interior inspection region  140 , as shown, for example, in  FIGS. 3–5 . Conveyor  114  moves the two lanes of lids  12  through interior inspection region  140  for inspection of lids  12  by system  110 . Enclosure  138  includes a frame  142 , a plurality of panels  144  coupled to frame  142 , and an access door  146  hinged to frame  142  to allow external access to interior inspection region  140 . A handle  148  coupled to door  146  is configured to be used by a person to open and close door  146 . A notch  151  is formed in door  146  to receive a chute  160  when door  146  is closed. 
     System  110  includes a pair of lid positioners  149 , a pair of light sources  150 , a pair of lid detectors  120 , a pair of image sensors  122 , a pair of lid rejectors  124 , and a common controller  118 , as shown, for example, in  FIG. 3 . Each lid positioner  149 , light source  150 , lid detector  120 , image sensor  122 , and lid rejector  124  is associated with one of the two lanes of lids  12 . Controller  118  is coupled to each lid detector  120 , each image sensor  122 , and each lid rejector  124  to control inspection of lids  12  in both lanes so that the inspection process of lids  12  in one lane is independent of the inspection process of lids  12  in the other lane. 
     Each lid positioner  149  is arranged to position the lids  12  of the associated lane in a predetermined position on conveyor  114  in response to movement of conveyor  114  so that lids  12  will enter the field of view of image sensor  122  for inspection by system  110  upon entry into region  140 , as shown, for example, in  FIGS. 3 and 4 . Illustratively, lid positioner  149  is configured as a bar coupled to frame  142  and arranged to move laterally inwardly those lids  12  which are positioned on conveyor  114  too far laterally outwardly upon movement of conveyor  114 . 
     Each light source  150  is coupled to frame  142  and positioned in region  140 , as shown, for example, in  FIG. 3 . Light source  150  is arranged to illuminate each lid  12  in the associated lane and, illustratively, is configured as a ring light. It is within the scope of this disclosure to use a variety of lighting arrangements for illuminating each lid  12 . 
     Each lid detector  120  is arranged to detect the presence of each lid  12  in the associated lane, as shown, for example, in  FIGS. 3 and 4 . Lid detector  120  generates a lid-detection signal and sends that signal to a controller  18  each time it detects a lid  12 . Illustratively, lid detector  120  is a photosensor coupled to a lower side rail  152  of frame  142 . 
     Each image sensor  122  is arranged to sense an image of each lid  12  in the associated lane, as shown, for example, in  FIG. 3 . Controller  118  sends a sense-image signal to image sensor  122  to cause sensor  122  to sense an image of a lid  12  in response to receipt of a lid-detection signal. Image sensor  122  generates an image signal representative of the image sensed and sends the image signal to controller  118  in response to sensing the image. Illustratively, image sensor  122  is a camera coupled to a top rail  154  of frame  142 . 
     Controller  118  evaluates each image signal to determine whether printed matter  36  complies with predetermined criteria. The evaluation process is discussed in more detail below. If printed matter  36  does not comply with the predetermined criteria, controller  118  generates a lid-rejection signal to cause a lid rejector  124  to reject the lid  12  with the non-compliant printed matter  36 . 
     Each lid rejector  124  is arranged to remove the lid  12  with the non-compliant printed matter  36  from conveyor  114  and to verify whether that lid  12  has been removed from conveyor  114 , as shown, for example, in  FIGS. 3–5 . Lid rejector  124  includes, for example, a first air nozzle  156 , a second air nozzle  158 , a chute  160 , a collection bin  162 , a valve assembly  163 , and a lid detector  164 . First air nozzle  156  is coupled to a lane divider  166  of frame  142  and arranged to direct a first pulse  168  of air laterally outwardly at lid  12  to cause lid  12  to move off conveyor  114  and into chute  160 . Second air nozzle  158  is coupled to chute  160  and arranged to direct a second pulse  170  of air at lid  12  to move lid  12  through chute  160  into collection bin  162 . Valve assembly  163  is coupled to frame  142  and controller  118  to control discharge of air pulses from air nozzles  156 ,  158  and includes, for example, four solenoid valves, one for each nozzle  156 ,  158 . 
     Lid detector  164  is coupled to chute  160  to detect each lid  12  that passes through chute  160 . Detector  164  sends a verification signal to controller  118  when it detects a lid  12  to inform controller  118  that lid  12  has been removed from conveyor  114 . Illustratively, detector  164  is a photosensor. 
     Controller  118  performs four tests in connection with each image. The four tests performed are (1) a lid location test (which may be referred to, for example, as a “lid locate test”), (2) a color content test (which may be referred to, for example, as a “graphics inspection test”), (3) a print location test (which may be referred to as an “off-center test”), and (4) a lid orientation test. Each test is discussed in turn. 
     With respect to the lid location test, controller  118  first determines whether the entire lid  12  is present within the image sensed by image sensor  122 —i.e., within the “field of view” of sensor  122 . The entire lid  12  needs to be present within the field of view of sensor  122  for the results of the other three tests to be valid. If lid  12  is outside the field of view, controller  118  generates a lid-rejection signal and lid rejector  124  removes lid  12  from conveyor  114 . 
     In the color content test, controller  118  determines whether the color content of printed matter  36  of a lid  12  complies with predetermined color criteria, as shown, for example, in  FIG. 6 . If printed matter  36  does not comply with the predetermined color criteria, controller  118  generates a lid-rejection signal and lid rejector  124  removes lid  12  from conveyor  114  in response to the lid-rejection signal. 
     To determine whether the color content complies with the predetermined color criteria, controller  118  establishes a “pixel count” area on the image to evaluate the color content of the pixels in the pixel count area. This area is defined by an imaginary outer linear boundary  172  set to match the shape of the perimeter of the image of the lid  12  being evaluated. Illustratively, boundary  172  is circular. 
     Once the pixel count area is established, controller  118  counts the number of pixels of each color of a predetermined set of colors located in the pixel count area. Controller  118  then determines whether the number of pixels of each color of the predetermined set of colors complies with predetermined individual color criteria specific to that color. Lid  12  is rejected if the number of pixels of any color does not comply with the predetermined individual color criteria for that color. 
     Controller  118  employs a “dynamic tolerancing” procedure to establish the individual color criteria for each color. Controller  118  initially uses the color content of the first lid  12  that passes through system  110  after controller  118  receives a commence-inspection signal as a baseline to evaluate the color content of the images of the next few lids  12  that pass through system  110 . The individual color criteria for each color of this initial group of lids  12  is the baseline for that color plus or minus a tolerance. 
     After a predetermined number (e.g., 25) of lids  12  has passed through system  110 , controller  118  determines the individual color criteria for each color of each succeeding lid  12  based on the color content of the printed matter  36  of a predetermined number (e.g., 25) of lids  12  preceding the lid  12  being evaluated. Controller  118  averages the number of pixels of each color of the predetermined set of colors over the predetermined number of lids  12  evaluated before the current lid  12  being evaluated. This average is calculated for each color of each lid  12  evaluated after the initial group of lids  12  and, in conjunction with a tolerance (or “error tolerance percentage”), becomes the predetermined individual color criteria for that color of that lid  12 . The predetermined individual color criteria is thus allowed to change or “float” after the initial group of lids  12  to accommodate real-time variations in the process of applying printed matter  36  to lids  12 . 
     Controller  118  uses the individual color criteria to evaluate each color of each lid  12 . For each color, controller  118  determines the percentage that the color deviates from the baseline (for the initial group of lids  12 ) or the average (for lids  12  after the initial group) and evaluates whether this deviation percentage (or “graphics error percentage) falls within the error tolerance percentage for that color. If it does fall within the error tolerance percentage, that particular color passes the color content test. If it does not fall within the error tolerance percentage, the color does not pass the color content test and lid  12  is rejected. 
     During the print location test, controller  118  determines whether printed matter  36  is located in a predetermined location relative to the center  174  of lid  12 , as shown, for example, in  FIGS. 6 and 7 . Illustratively, the predetermined location is the location of printed matter  36  when it is concentric with center  174 , as shown, for example, in  FIG. 6 . If printed matter  36  is not located in the predetermined location, as shown, for example, in  FIG. 7 , controller  118  generates a lid-rejection signal and lid rejector  124  removes lid  12  from conveyor  114  in response to the lid-rejection signal. 
     To determine whether printed matter  36  is located in the predetermined location, controller  118  establishes an imaginary inner linear boundary  176  and determines whether the pixels located on boundary  176  comply with predetermined location criteria. Illustratively, boundary  176  is circular. Controller  118  categorizes each pixel located on boundary  176  as either a “printed matter” pixel when the pixel represents printed matter  36  or a “non-printed matter” pixel when the pixel does not represent printed matter  36 . Controller  118  calculates the percentage of printed matter pixels relative to the total number of pixels on boundary  176  and compares that percentage to a threshold. If the percentage exceeds the threshold, lid  12  is rejected. 
     Controller  118  employs the lid orientation test to determine whether printed matter  36  is located on a predetermined surface  178  of lid  12 , as shown, for example, in  FIGS. 8–11 . If lid  12  is in the predetermined orientation, as shown, for example, in  FIGS. 8 and 9 , controller  118  determines that printed matter  36  is located on predetermined surface  178 . If, on the other hand, lid  12  is not in the predetermined orientation, as shown, for example, in  FIGS. 10 and 11 , controller  118  determines that printed matter  36  is not located on predetermined surface  178 . Controller  118  generates a lid-rejection signal and lid rejector  124  removes lid from conveyor  114  in response to the lid-rejection signal when lid  12  is determined not to be in the predetermined orientation. 
     During the lid orientation test, controller  118  determines whether a region  179  (e.g., a shadow) of the image having a predetermined size and a predetermined contrast level relative to the lid is present in a predetermined area  180  of the image due to rim  182 . Controller  118  categorizes each pixel in area  180  as either a “white” pixel or a “black” pixel by comparing the brightness level of the pixel with the brightness level of the background color of lid  12 . If the difference between the brightness level of the pixel and the brightness level of the lid background color does not exceed a predetermined contrast level threshold, the pixel is categorized as a white pixel. If the difference between the brightness level of the pixel and the brightness level of the lid background color does exceed the predetermined contrast level threshold, the pixel is categorized as a black pixel. If the number of black pixels in area  180  does not exceed a predetermined black pixel threshold, controller  118  determines that lid  12  is in the predetermined orientation. If the number of black pixels in area  180  exceeds the predetermined black pixel threshold, controller  118  determines that lid  12  is not in the predetermined orientation. 
     Illustratively, lid  12  is in the predetermined orientation when surface  178  faces upwardly away from conveyor  114  and a rim  182  of lid  12  extends downwardly from a panel  184  of lid  12  toward conveyor  114  to rest on conveyor  114 , as shown, for example, in  FIGS. 8 and 9 . Lid  12  is not in the predetermined orientation when surface  178  faces downwardly toward and engages conveyor  114  and rim  182  extends upwardly from panel  184  and away from conveyor  114 , as shown, for example, in  FIGS. 10 and 11 . 
     Light source  150  is used to perform the lid orientation test. Illustratively, light source  150  is one or more ring lights, as suggested, for example, in  FIGS. 8–11 . It is within the scope of this disclosure to use one or more laser(s) and/or one or more infra-red light(s) to perform the lid orientation test. 
     System  112  includes a display  134 , as shown, for example, in  FIG. 12 . Display  134  displays images and information associated with each lane. With respect to each lane, display  134  displays the image  185  which was last sensed and the image  186  which last failed to pass any of the four tests. Regarding image  185 , display  134  displays information  187  such as the product identification number of lid  12 , the maximum graphic error percentage calculated among the colors of lid  12 , and the error tolerance percentage associated with that maximum graphic error percentage. Regarding image  186 , display  134  displays information  188  which sets forth the results of each of the four tests. 
     In some embodiments, system  110  includes two additional image sensors  192  and two additional light sources  193 , as shown, for example, in  FIG. 13 . Each image sensor  192  is used to sense a particular feature (e.g., a net weight statement) on lid  12  and sends an image signal representative of the image sensed to controller  118  for evaluation. Light sources  193  provides supplemental lighting for operation of sensors  192 . 
     A single-lane visual inspection system  210  shown, for example, in  FIGS. 14–16 , is another example of visual inspection system  10 . System  210  is configured to inspect printed matter  36  on lids  12  which are arranged in a single lane on a conveyor  214 . The components of system  210  are similar to components of system  110  so that identical reference numbers refer to similar components. 
     Differences from system  110  relate primarily to modifications for accommodating a single lane of lids  12 . For example, system  210  includes a single lid detector  120 , a single image sensor  122 , and a single lid rejector  124 . A controller  218  is coupled to detector  120 , sensor  122 , and rejector  124  and is configured to evaluate image signals associated with a single lane of lids  12  using the same four tests discussed above. An enclosure  238  is configured for one lane of lids  12  and includes a frame  242 , panels  244  coupled to frame  242 , a hinged access door  246 , and a handle  248  coupled to door  246 . A notch  251  formed in door  246  is configured to receive lid detector  120  when door  246  is closed. Light sources  250  are mounted along side rails  252  and, illustratively, are configured as light bars. 
     A valve assembly  263  shown, for example, in  FIG. 16 , is used to control pulses of air through nozzles  156 ,  158 . Valve assembly  262  includes two solenoid valves  265 , one for each nozzle  156 ,  158 .