Abstract:
A parts inspection system for automated video inspection for quality control processes. The inspection system is particularly adapted for rotationally symmetrical workpieces including small arms ammunition cartridges. The system provides a first array of light sources oriented radially around the workpiece path presenting zones of illumination on the workpiece at discrete radial positions. A second illuminator is in the form of linear arrays of light emitting elements oriented along linear arrays. A camera oriented to observe images of light provided by the first and second arrays records video images of the workpieces for use in resolving criteria of acceptable and unacceptable parts. An escapement mechanism moves acceptable and rejected parts into different parts streams.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to a video parts inspection system for quality control applications and particularly to such a system adapted for the inspection of rotationally symmetrical parts such as small arms ammunition and other workpieces. 
       BACKGROUND 
       [0002]    In serial production of mass-produced components, quality control systems are often used to assure high-quality final products. For example, in the manufacturing of small arms ammunition such as types for handguns and rifles, it is desired to implement an automated inspection system which can identify defective parts. For example, ammunition cases typically made of brass or other metals can have defects such as nicks, gouges, voids, and discoloration. Numerous other types of rotationally symmetric workpieces such as shafts and pins pose similar inspection requirements. One approach toward providing quality control is the use of human inspectors which observe parts as they move through an assembly line stream. In addition to the cost for implementing such a system, reliability of such inspection is a concern. Numerous approaches toward automating the inspection system have been implemented. Such systems typically rely upon so-called machine vision systems in which the parts are illuminated in some manner and reflected or transmitted light images are evaluated by video cameras or linear detector arrays. Although such systems have been found to operate generally satisfactorily, they are frequently unable to resolve the full range of defects found in such components, limit throughput rate, can be costly to purchase and operate, and give rise to their own significant maintenance requirements. Accordingly there is a need to provide improved systems for such applications. 
       SUMMARY 
       [0003]    In accordance with the present invention an inspection system is provided using arrays of light sources such as LEDs arranged in a radial configuration around a part test section. The light sources are arranged to essentially form stripes of light reflecting from the workpiece. Surface disruptions in the reflected stripes reveal defects. A conveyor system is used to traverse and rotate the parts through the inspection area to enable full coverage of the inspection process. 
     
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
         [0004]      FIG. 1  is a top view of the inspection system in accordance with the present invention; 
           [0005]      FIG. 2  is a left isometric view of the inspection system; 
           [0006]      FIG. 3A  is a right isometric view of the inspection system; 
           [0007]      FIG. 3B  is an enlarged cutaway view from  FIG. 3A  showing the case illuminator: 
           [0008]      FIG. 4  is a side view of the inspection system; 
           [0009]      FIG. 5  is a detailed isometric view of portions of the system; 
           [0010]      FIG. 6A  is an isometric view illustrating gate operation of a defective cartridge; 
           [0011]      FIG. 6B  is a partial plan view of operation of the gate; 
           [0012]      FIG. 7  is an illustration of gate operation for defective and non-defective cartridges; 
           [0013]      FIG. 8  is an end view of the escapement mechanism; 
           [0014]      FIG. 9  is a cross-section through the inspection system showing illumination of a workpiece; and 
           [0015]      FIG. 10  is an illustration of specular reflection lines from a defective workpiece during inspection. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    With particular reference to  FIG. 1 through 4 , a parts inspection system in accordance with the present invention is illustrated which is generally designated by reference number  1 . As illustrated, the inspection system  1  is used in one described application for the inspection of ammunition cartridges  16 . In this description workpieces  16  may alternatively be referred to as a cartridge although, as previously mentioned, other types of workpieces may also be used with the system in accordance with this invention. Preferably such alternative workpieces for inspection are rotationally symmetrical elongated parts which also may be threaded, splined, or fluted. 
         [0017]    Cartridges  16  are moved through an inspection area of system  1  utilizing conveyor  3  in the form of a continuous belt which moves in the direction of the arrows in  FIGS. 1-3  at a diagonal direction from the longitudinal axis of inspection system  1  (axis of the linear movement of the workpieces). Conveyor  3  moves continuously during operation of the device. Components of system  1  are supported by frame  2 . Cartridge  16  is trapped between stop bar  5  and cartridge guide rail  6  and these elements are separated to allow the cartridge to travel along their length. The combined effect of the motion of conveyor  3  and the restraint provided by stop bar  5  causes cartridges  16  which are introduced at the left-hand end of the system (near one edge of conveyor belt  3 ) as illustrated in  FIG. 1  to move from the entrance end toward escapement fence  14  (near an opposite edge of conveyor belt  3 ) and is simultaneously rotated as it moves linearly. The spacing between stop bar  5  and cartridge guide rail  6  is adjustable by a pair of guide rail adjusters  7  which enable precise variation in the spacing as well as the horizontal and vertical positioning of these elements. The figures illustrate cartridge  16  moving along cartridge stop bar  5  and guide rail  6 , with particular reference to  FIG. 7 . 
         [0018]    Cartridge  16  as illustrated is a conventional small arms rifle cartridge of a so-called “bottleneck” (i.e. necked down shell case) configuration. Cartridge  16  forms an elongated body  18  with a reduced diameter neck  19  and a protruding bullet  20 . At the opposite end, cartridge  16  forms case head  21  with extractor groove  22 . Case head  21  forms a head stamp end  23  having a central cavity for the installation of primer  24 . 
         [0019]    Parts inspection system  1  uses two or more different illumination sources provided for illuminating cartridge  16  in a manner to provide a full range of inspection capabilities. Primer illuminator  8  is an annular array of individual LEDs  25  oriented toward cartridge head stamp  23  as the cartridge  16  moves along the inspection axis. Primer illuminator  8  is best shown with reference to  FIG. 3B  is in the form of an array  26  of LEDs  25  around an aperture through which camera  4   a  is oriented. LEDs  25  are mounted to a board which surrounds camera  4   a . Primer illuminator  8  includes LEDs oriented toward cartridge head stamp  23 . A video camera  4   a  is oriented to collect an image of head stamp  23 . These inspection components enable inspection of case defects such as a missing primer  24 . As shown the primer illuminator  8  is oriented to illuminate and record images of the head stamp end of cartridge  16  as it begins its transit toward conveyor  3 . A separate parts handling conveyor  3   a  is provided to transit the parts passed primer illuminator  8 , and toward conveyor  3 . 
         [0020]    An additional series of illuminators is provided to enable evaluation of cartridge body  18 , neck  19 , and bullet  20 . Illuminator  10  is formed by linear arrays  29  of LEDs  25  oriented as illustrated. In a representative embodiment, each linear array  29  is formed by fifteen LED elements  25 . Linear arrays  29  are formed along a cylindrical surface of shell  43  oriented parallel to the longitudinal axis of the workpiece path. The linear arrays  29  form a radial separation angle “c” of 28° and a representative example which is shown in  FIG. 9 . 
         [0021]    Video camera  4  is oriented as shown in the figures and observes the lines of laser light projecting onto cartridge  16  by array  29  through window  44  of shell  43 . This inspection methodology is best described with reference to  FIGS. 9 and 10 . Linear arrays  29  of illuminator  10  cooperate to present lines of light at various angular positions with respect to the longitudinal axis of cartridge  16 .  FIG. 9  illustrates six lines of light  30 ,  31 ,  32 ,  33 ,  34 , and  35  directed onto cartridge  16 . The video image shown in  FIG. 9  shows the use of the lines of light forming images of stripes  36 ,  37 ,  38 , and  39 . As illustrated, these stripes are interrupted in the presence of a defect shown in the figure as a nick or dent clearly observable as deviations of each of the stripes  37 - 39 . Illuminator  10  provides illumination of the stripes on the cylindrical portions of cartridge  16  including body  18  and neck  19 . Shoulder  42  forms a conical surface and shoulder/bullet illuminator  10  produces stripes  36 - 39  on this portion of the cartridge  16 . As shown in  FIG. 9 , camera  4  observes images of stripes  36 - 39  of the cartridge  16 . 
         [0022]    As best illustrated in  FIG. 1  the optical axis  40  of camera  4  is oriented to align with a radial plane of cartridge  16  as it traverses the inspection area. Other types of defects of cartridge  16  are also observable in this manner including discolorations which interrupt the specular reflection of cartridge  16 . In addition to the defects mentioned previously, tears, punctures, holes, and other imperfections of the surface of cartridge  16  are readily detected. 
         [0023]    Images from camera  4  are processed through a processing unit or computer having digital image processing software which enables the detection of defects mentioned previously. 
         [0024]    Escapement/rotary gate  11  is used to change the discharge flow paths of cartridges  16  between those meeting inspection criteria and as those that do not. Stepper motor  15  operates escapement fence  14  through timing belt  12  and timing belt pulleys  13 .  FIGS. 6A and 6B  best illustrate operation of escapement/rotary gate  11 . Those figures illustrate that slots  41  are aligned to cause rejected cartridges  16  to move through the escapement device. For cartridges  16  meeting inspection criteria, escapement  11  is operated to displace cartridges into contact with escapement fence  14  and into the “Accept” parts stream. If a cartridge  16  is deemed to have acceptable quality, the escapement  11  will rotate counterclockwise as illustrated in  FIG. 8  while the cartridge is contained between the ends of the escapement slot  41  (see particularly  FIGS. 6A, 6B, 7 and 8 ). This guides the cartridge  16  in a direction of motion of the conveyor and off the reject-parts track. The cartridge  16  leaves the escapement  11 , and is pulled against the escapement by the motion of the conveyor (see  FIG. 6B ). The cartridge  16  has been held against the fence  14  by the body of the escapement after contacting the fence, the cartridge  16  is pulled forward by the motion of the conveyor, where it enters and Accept parts bin (see  FIG. 9 ). The escapement  11  only completes a partial rotation during this operation, until its next slot  41  is aligned with the reject-parts track. For a rejected part, escapement  11  does not rotate and cartridge  16  is moved to by motion of conveyor  3  in the direction shown in  FIGS. 6A and 6B , along the “Reject” parts stream into a suitable rejected part bin. 
         [0025]    When a workpiece such as cartridge  16  enters the field of view of camera  4 , it begins capturing images at a high frame rate. The frame rate is limited by the image resolution, which must be high enough to resolve defects that must be detected. The part must remain within the field of view of camera  4  long enough to capture images of all sides of the part (i.e. at least one full revolution). The resulting image series is filtered, corrected, and aggregated together, and used to generate several statistical models of the part. These different models reflect different types of image features. 
         [0026]    During initial setup, a collection of pre-inspected acceptable parts are fed through the system  1 . This set of parts must include samples of any manufacturing defects which are deemed acceptable. The resulting models from these acceptable parts are used to generate a “master” model, which reflects the unique aspects of an acceptable part. During normal operation, incoming parts are compared to this master model, and any parts which exceed a user-specified margin of error are directed to a reject-parts bin. 
         [0027]    While the above description constitutes the preferred embodiment of the present invention, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope and fair meaning of the accompanying claims.