Abstract:
A method and apparatus for illuminating the end portions of downwardly extending features of a component without substantially illuminating the body of the component. At least one light source is configured to direct a fan-shaped sheet of light at the downwardly extending features of the component at a low angle of incidence with respect to the component body. A camera or other image capture device captures an image of the illuminate downwardly extending features and signal processing means determine the position of the downwardly extending features from the image thus formed with respect to a desired position.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a method and apparatus for illuminating downwardly extending features on electronic components or mechanical devices. More particularly, the present invention relates to illuminating an end portion of the downwardly extending features without substantially illuminating the body of the component or mechanical device.  
         BACKGROUND OF INVENTION  
         [0002]    In the construction of modern products, automatic assembly, including automatic placement and mounting of electronic components and mechanical devices, has become increasingly popular. However, in recent years, components have become smaller, the average number of leads has increased and the use of non-standard components has increased. Consequently, the use of such automated assembly procedures has become more difficult due to the uncertainty involved in determining the position of the leads or mounting tabs prior to placement. Many modern assembly machines, therefore, include a vision system for determining the exact location of the leads on individual components.  
           [0003]    One type of vision system used in assembly machines utilizes a shade disposed between a light source and the component to illuminate the leads while substantially shading the body of the component. A camera is positioned under the component to obtain an image of the illuminate leads, which is then used to calculate their actual location. Because the shade is positioned between the camera and component, the field of view of the camera is limited by the shade.  
           [0004]    Another type of vision system utilizes two laser beams projected in different directions within a component travel path. The component is moved in a straight-line through the travel path such that the laser beams are sequentially interrupted by the leads of the component. Light sensitive transistors detect when the beams are broken by the leads and the location of the leads is then calculated using a series of complex mathematical equations. When detecting multiple lead configurations, it is important that no lead be obstructed by the other leads because this could produce ambiguous results. Thus, particular care must be taken in selecting the angle between the laser beams for each component to be detected. This results in a reduced flexibility of the system.  
         SUMMARY OF THE INVENTION  
         [0005]    It is, therefore, an object of the present invention to provide a method and apparatus for illuminating the leads of a component.  
           [0006]    It is a further object of the present invention to illuminate the leads of a component without illuminating the body of the component.  
           [0007]    It is another object of the present invention to illuminate the leads of a component without illuminating the body of the component and without the use of a shade.  
           [0008]    It is yet another object of the present invention to determine the location of the leads of a component to be placed by an automated assembly machine.  
           [0009]    The above and other objects are achieved in accordance with the present invention by a method and an apparatus for illuminating an end portion of the leads or other downwardly extending features of a component or mechanical device. One or more light sources  40  project sheets of light at the leads of a component from different angles. Each sheet of light is projected at a low angle of incidence with respect to the body of the component. An image capture device is positioned below the component so as to form an image of the leads. The image capture device is coupled to a computer, which determines from the image the position of the leads within the field of view of the image capture device with respect to a desired position.  
           [0010]    These and other objects, features and advantages of the present invention will be apparent and fully understood from the following detailed description of the preferred embodiments, taken in connection with the appended drawings. While the present invention is described herein in the context of a vision system of a component placement apparatus and components having leads, it should be understood throughout to apply equally to any vision system and the illumination of any downwardly projecting feature, including pins, tabs and solder bumps, of any component or mechanical device. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is a plan view of an illumination system according to the present invention.  
         [0012]    [0012]FIG. 2 is a side elevational view of the illumination system of FIG. 1.  
         [0013]    [0013]FIG. 3 is a side elevational view of a light source from the illuminating system of FIG. 1.  
         [0014]    [0014]FIG. 4 is a rear elevational view of the light source of FIG. 3.  
         [0015]    [0015]FIG. 5 is a plan view of the light source of FIG. 3.  
         [0016]    [0016]FIG. 6 is a plan view of the lens mount from the light source of FIG. 3.  
         [0017]    [0017]FIG. 7 is a side elevational view of the lens mount of FIG. 6.  
         [0018]    [0018]FIG. 8 is a front elevational view of the lens mount of FIG. 6.  
         [0019]    [0019]FIG. 9 is a side elevational view of an alternate illumination system according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]    Referring first to FIGS. 1 and 2, an illumination system  1  according to the present invention is illustrated. The system  1  includes four light sources  40  positioned in the four corners of an imaging area  10 . The light sources  40  each produce a fan-shaped planar sheet of light  14  and direct it towards the center of the imaging area  10 . A CCD camera  20  is mounted at the center of the light sources  40  and is aimed up into the imaging area  10  where the fan-shaped sheets of light  14  intersect. It should be noted that FIG. 2 may be “flipped” and the camera  20  may be mounted above the imaging area  10  and aimed downward.  
         [0021]    As best seen in FIGS. 2 and 3, each sheet of light  14  is relatively thin in the vertical direction. For example, in the illustrated embodiment the sheets  14  are approximately 60-80/1000 of an inch thick. Using this arrangement, the sheets  14  may be precisely aimed in the horizontal plane. Thus, the leads  94  of a component  90  held in the imaging area  10  (e.g., by the pick and placement head of an assembly machine) can be illuminated by the light sources  40  without substantially illuminating the body  92  of the component  90 .  
         [0022]    While a symmetric arrangement of the light sources  40  around the camera  20  provides the greatest flexibility, it should be noted that other arrangements may be utilized depending, in part, on the component  90  being imaged. In addition, fewer or more light sources  40  may be used so long as they are sufficient in number and positioned so as to illuminate all of the desired leads  94  of the components  90  to be placed without substantially illuminating the bodies  92 . For example, if the components  90  in question have only three or four well spaced leads  94 , one light source  40  may be sufficient. However, as the number of component leads  94  increases and/or becomes more dense, the number of light sources  40  used will likely increase to ensure that all of the desired leads  94  are illuminated. Likewise, the reflective characteristics of the leads  94  also affect the required number and arrangement of the light sources  40 .  
         [0023]    Referring now to FIGS.  3 - 5 , each light source  40  includes a laser module  42  and a dispersion assembly  44 . The laser module  42  of the illustrated embodiment is a model LMG6354A5-T distributed by Lasermate Corporation of Monterey Park, Calif. This is a Class IIIa laser diode module which emits a laser beam  12  having a wavelength of 635 nm, a maximum output power of 5 mW and a beam width of approximately 60-80/1000 of an inch. In addition, the laser beam  12  may be pulsed by a control line of the laser module  42 .  
         [0024]    As indicated, each light source  40  also includes a dispersion assembly  44  mounted to the laser module  42 . The dispersion assembly  44  includes an aluminum lens mount  50 , shown in detail in FIGS.  6 - 8 . The lens mount  50  has a cylindrical body  52  having an interior chamber  54  adapted for mounting to the laser  42  (see FIGS. 3 and 4). A bore  58  extends axially through the head  56  of the body  52  to permit projection of the laser beam  12  therethrough.  
         [0025]    The top of the head  56  adjacent the bore  58  has an inclined top surface  60 . This surface  60  permits mounting of a mirror  46  (shown in FIGS.  3 - 5 ) in line with the laser beam  12  to facilitate aiming of the beam  12 , as described below. The inclined surface  60 , and hence the mirror  46  of the illustrated embodiment is oriented at 45° with respect to the horizontal and thereby directs the laser beam  12  out the front of the lens mount  50 . This orientation is selected because the laser modules  42  of the illustrated embodiment are aimed approximately vertically when mounted around the imaging area  10 . Thus, after being reflected by the mirror  46 , the beams  12  of the lasers are directed out the front of the lens mount  50  approximately parallel with the horizontal. The beams  12  may then be adjusted to project at very small angles with respect to the horizontal and, consequently, at very small angles with respect to the component body  92 .  
         [0026]    The adjustment of the laser beam  12  is facilitated through an adjustment groove  62  and two adjustment screws  82 ,  86  in the lens mount  50 . The groove  62  is cut transversely through the head  56  of the lens mount  50  thereby dividing it into a top portion  66  and a bottom portion  72 . The groove  62  extends from the back of the lens mount  50  towards the front, leaving only a small connecting section  64  between the top portion  66  and bottom portion  72  of the head  56  at the front of the lens mount  50 .  
         [0027]    The top portion  66  of the head  56  has two holes  68 ,  70  adjacent one another at the back end for receiving the adjustment screws  82 ,  86 . The first hole  68  is threaded and the second one  70  is not. The bottom portion  72  of the head  56  includes one threaded hole  76  aligned with the non-threaded hole  70  of the top portion  66  of the head  56 . The first adjustment screw, the jacking screw  82 , is screwed into the threaded hole  68  of the top portion  66  and the tip  84  of the screw  82  abuts the top surface  74  of the bottom portion  72 . The second adjustment screw, the locking screw  86 , is inserted through the non-threaded hole  70  of the top portion  66  and is screwed into the threaded hole  76  of the bottom portion  72 .  
         [0028]    When the jacking screw  82  is turned clockwise, the tip  84  pushes against the top surface  74  of the bottom portion  72  of the head  56  and thereby urges the top portion  66  of the head  56  away from the bottom portion  72  at the rear. This decreases the angle of the mirror  46  with respect to the horizontal and lowers the laser beam  12  towards the horizontal. Turning the jacking screw  82  in the opposite direction withdraws the tip  84  from the top surface  74  of the bottom portion  72  and leaves the top portion  66  free to be drawn closer to the bottom portion  72 . This increases the angle of the mirror  46 , and consequently the laser, with respect to the horizontal.  
         [0029]    When the locking screw  86  is turned clockwise, the head  88  of the screw  86  pulls the top portion  66  of the head  56  towards the bottom portion  72  at the rear and locks the top portion  66  in position with the tip  84  of the jacking screw  82  against the top surface  74  of the bottom portion  72 . Thus, the angle of the laser beam  12  may be adjusted and locked by turning the adjustment screws  82 ,  86  to achieve a stable alignment of the beam  12  at a desired angle. It should be noted that other aiming schemes may be employed. For example, the angular relationship of the mirror  46  to the laser beam  12  may be fixed and adjustment may be facilitated by adjusting the mounting orientation of the entire light source  40 . Likewise, the mirror  46  may be mounted at a fixed angular relation to the imaging area  10  and the angle of the laser beam  12  adjusted.  
         [0030]    As described, the laser beam  12  is reflected by the mirror  46  towards the front of the lens mount  50 . The lens mount  50 , therefore, includes a lens aperture  78  at the front to permit the projection of the beam  12  out of the mount  50 . The lens aperture  78  has a ledge  80  on each side for the mounting of a convex dispersing lens  48 . The lens  48  is mounted to the ledge  80  by an adhesive, such as ultraviolet glue.  
         [0031]    The lens  48  of the illustrated embodiment is an LGLI-45 line generating lens (or “cylinder lens”) commercially available from Rolyn Optics, Covina, Calif. The lens  48  is made of an acrylic and is designed to disperse the collimated laser beam  12  in the horizontal direction only into a fan-shaped, planer sheet of light  14 . Thus, the light emitted from the light source  40  remains approximately the same dimension in the vertical direction (see FIG. 3) while at the same time it is fanned out in the horizontal direction (see FIG. 5). In the illustrated embodiment, the sheet of light  14  emitted by the light source  40  is approximately 60-80/1000 of an inch thick in the vertical direction and has a 30° spread angle. Other beam dimensions and shapes may be employed and depend on various factors such as the number of light sources  40  used, laser power, component size, lead count and density and distance to the leads  94 .  
         [0032]    Because of the unique shape of the sheet of light  14  emitted by the light source  40 , it can be aimed very precisely in the horizontal plane. It can, therefore, be aimed to strike multiple leads  94  across a component  90  without substantially illuminating the body  92  of the component  90 . To properly adjust the angle of the sheet of light  14 , the adjustment screws  82 ,  86  are adjusted such that the sheet of light  14  strikes the leads  94  closest to the light source  40  while at the same time not striking the body  92  of the component  90  at the point furthest from the light source  40  (see FIG. 2). This is made possible by the use of a small angle with respect to the horizontal and, consequently, a small angle of incidence with respect to the component body  92 .  
         [0033]    Referring to FIG. 3, it can be seen that by aiming the laser beam  12  at the top portion of the mirror  46 , the sheet  14  may be projected at a very slight angle above the horizontal and still rise to a level above the top of the light source  40  in a relatively short distance. This allows for the use of a very small angle of incidence with respect to the component body  92 , thereby, facilitating the illumination of leads  94  on wider components  90 . Projecting the laser at the top of the mirror  46  also allows the leads  94  of the component  90  to be illuminated without being lowered below the top of the light source  40 . Thus, the component  90  can be passed over the illumination area  10  on its way to being placed without stopping to lower it vertically into the imaging area  10 . By pulsing the light sources  40  at the appropriate time, the CCD camera  20  can capture the image of the leads  94  as the component  90  passes over the imaging area  10 . Alternatively, the camera  20  can include an electronic shutter to be selectively activated in which case the light sources  40  would not need to be pulsed.  
         [0034]    Once the image of the illuminated leads  94  has been captured by the camera  20 , a computer processor  30  is used to calculate and record the location of the leads  94  within the field of view of the camera  20 . These values are then compared with expected or desired locations for the leads  94 . If location of the leads  94  of the component  90  being placed deviate from these expected values, the placement apparatus can either reflect the component or adjust dynamically to compensate for the difference and ensure proper placement of the component  90 .  
         [0035]    The present invention has been described in terms of illustrated embodiments thereof. Other embodiments, features and variations within the scope of the appended claims will, given the benefit of this disclosure, occur to those having ordinary skill in the art. For example, the laser modules  42  may be aimed approximately horizontal, as illustrated in FIG. 9. In such a case, the dispersion lenses  48  are mounted directly in front of the laser modules  42  and the mirrors may be omitted. Aiming of the resulting sheets of light can be facilitated by moving the laser modules  42  and/or the lenses  48 .