Abstract:
Provided herein is a lens mount system and related process that allow for performing six-axis active alignment with a single joining step. This system and/or process simplifies the lens attachment in a manner that makes such attachment compatible with high volume manufacturing and/or full automation.

Description:
FIELD 
       [0001]    The present disclosure pertains to imaging systems in general and more particularly to methods and systems for mounting an optical axis of an optical lens in an accurate desired alignment with an optical imager. 
       BACKGROUND 
       [0002]    Increasingly, image sensing systems are being used for optical metrology (i.e., measurement) functions. For instance, image sensing systems may utilize various algorithms to calculate, inter alia, the angles, distances, curvatures, speeds, etc. of objects within an acquired image. 
         [0003]    Such image sensing systems typically include a video camera, digital still camera or the like, which are capable of capturing images into digital signals (or potentially analog signals) for storage, manipulation and/or distribution. Such systems ordinarily include a lens or other image-forming element capable of capturing light from a scene/object and focusing/projecting that light onto a surface that is capable of sensing the light. This surface typically comprises an array of photo sensor elements, such as charge-coupled-devices (“CCDs”) or complementary metal oxide semiconductor (“CMOS”) photoreceptors. 
         [0004]    These sensors typically comprise planar, rectangular matrices, or arrays, of photoelectric transducer elements fabricated on the surface of a semiconductor substrate, typically silicon, by various known photolithographic techniques, that are capable of converting the light energy incident upon them into electrical signals on an element-by-element, or pixel-by-pixel, basis. These signals, usually digital in nature, include information pertaining to, e.g., the intensity, color, hue, saturation, and other attributes of the incident light. 
         [0005]    The sensor array substrate(s) is typically disposed on and electrically connected to a base substrate such as a printed circuit board (PCB). A lens structure is disposed over the sensor array typically supports one or more optical elements. This lens structure typically mounts to the base substrate/PCB. The most common method for aligning the lens and optical sensor involves the lens and base substrate having corresponding, complementary mounting features adapted to engage each other such that, when engaged, the optical features of the sensor are aligned with the optical elements of the lens. Typically, the lens includes various projections arranged around its optical axis and the base substrate includes corresponding apertures or pedestals that mate with these projections. 
         [0006]    In order to accurately align the lens and optical sensor, the tolerances of the individual components and the complementary mounting features need to be extremely tight. Maintaining such tight dimensional tolerances is difficult. Separate tolerances are present in the fabrication and assembly of the various components (e.g., optical properties of the lens elements, sensor to PCB mounting tolerances, lens to lens carrier mounting tolerances, etc.) and the final integration of these components (e.g., lens carrier to PCB mounting tolerances). Unless extremely tight dimensional tolerances are specified and maintained, during the fabrication and assembly of all of these components, tolerance stack ups tend to occur. Generally, such tolerance stack up can be maintained to within a few hundred microns in the Cartesian directions (e.g., XYZ directions) and to perhaps slightly more than 1° angularly about one or all of the Cartesian axes. 
         [0007]    While such tolerances are acceptable for many applications, accurate optical metrology (i.e., measurement) functions typically require much tighter tolerances. To provide tighter tolerances, an active alignment process may be utilized where feedback from the optical sensor guides alignment. In such an active alignment method, the sensor is temporarily positioned loosely in about the desired position of alignment with the lens positioned loosely in about the desired position of alignment with sensor. The sensor is temporarily connected to a display to output a test scene or pattern, and the relative position of the sensor or lens is adjusted by a human or machine until the image of the test pattern produced on the display subjectively matches the test pattern, whereupon the position of the sensor relative to the lens is then fixed permanently in place. 
         [0008]    Active alignment typically requires multiple alignment and securing/gluing steps. For instance, one prior design utilizes a two piece lens mount carrier. The first piece is a lens mount with internal threads; the second piece is a mechanical stand-off for attachment to the PCB. First, the lens is focused by being threaded into or out of the lens mount in the Z direction. Then the lens and the lens mount assembly are moved in the XY directions on top of the mechanical stand-off to correct for any lateral misalignment. The process requires a 3-step gluing process that includes tacking the lens inside the threaded mount, tacking the lens mount on the stand-off, and removing the complete assembly from an alignment setup for the final gluing and re-enforcement. 
       SUMMARY 
       [0009]    Provided herein is a lens mount system and related process that allow for performing six-axis active alignment with a single joining step. This system and/or process simplifies the lens attachment in a manner that makes such attachment compatible with high volume manufacturing and/or full automation. 
         [0010]    In a first aspect, a camera module is provided that allows for adjusting the position of a lens assembly in six axes relative to an imager that is mounted on a base substrate such as a PCB. In this aspect, an imager is mounted on a base substrate where the imager has a photo sensor array formed on a planar upper surface. Pluralities of mounting apertures are disposed about the imager and extend through the base substrate between its top surface and a bottom surface. These apertures are sized to receive a corresponding plurality of mounting posts of a lens support mount. Importantly, the size of these apertures is larger than the corresponding dimensions of the mounting posts permitting the mounting posts and the attached lens support mount to move in first and second and/or third Cartesian directions and/or partially rotate about two or more axes. The lens support mount includes a base to which the mounting posts are attached and supports a lens with one or more optical elements. In one arrangement, the lens includes a housing having an axial passageway extending there through. An optical element is disposed within the housing to project an image through the housing along a lens optical axis for disposition on the planar photo sensor array. An elastic gasket is disposed about the imager between the base of the lens supporting mount and the top surface of the base substrate. This elastic gasket separates the lens supporting mount from the top surface of the substrate. The elastic gasket also suspends the mounting post within the mounting apertures. Once the lens optical axis is aligned in a desired orientation with the photo sensor array, the suspended posts are adhered within the apertures fixing the position of the lens supporting mount relative to the PCB and imager. In one arrangement, the lens optical axis is perpendicular/normal to the surface and/or centered on the surface of the imager. However, this is not a requirement. 
         [0011]    The elastic gasket separates the base of the lens support mount from the top surface of the base substrate by a sufficient distance to allow the lens support mount to rotate slightly such that the optical axis may be aligned with the surface of the imager. Further, the gasket permits compression in a direction normal to the surface of the imager. This permits focusing an image plane of the lens on the imager free of adjusting the position of the lens relative to the lens support mount. In one arrangement, the elastic gasket is non permeable gasket that allows for sealing the space between the imager and the lens once the lens support mount is affixed to the surface of the PCB. 
         [0012]    In one arrangement, the gasket includes apertures through which the posts of the lens support extend. In such an arrangement, the gasket may also cover the apertures through the base substrate and thereby provide a glue stop function. 
         [0013]    Typically, the mounting posts of the lens supporting mount are disposed around the optical axes of the lens and the optical imager. The number and spacing of these posts is typically identical to the number and spacing of the apertures within the PCB. The spacing of the posts and apertures may be regular or irregular so long as they correspond. The apertures in the PCB have a larger size than the posts. Typically, corresponding cross dimensions of the mounting apertures are at least 1.1 times the cross dimension of the mounting posts and more commonly at least 1.5 times the cross dimensions of the mounting posts. This permits movement of the lens support mount to align the optical axis of the lens with the photo sensor. 
         [0014]    In another aspect, a method is provided for optically aligning an imager mounted on a base substrate with a lens. The method includes positioning a planar photo sensor surface of an imager mounted on a base substrate relative to a laser beam of a fixed laser. The imager is positioned and/or tilted until the laser beam is positioned in a desired orientation to the planar surface of the imager. Typically, an output image from the imager is utilized for positioning of the imager. Once the imager is correctly positioned, the imager&#39;s position is fixed, and the lens assembly is disposed over the imager such that the laser beam or other light/image source may project through the lens assembly and onto the imager via the lens. At this time, the position of the lens assembly may be adjusted to position the light source (e.g., laser) or image in a desired orientation to the planar surface of the imager. Such adjustment may include tilting the lens assembly in one or more axes to align the optical axis of the lens to be center to and/or normal to the planar surface of the imager. This may further include adjusting the position of the lens assembly in the X, Y and/or Z directions (e.g., substantially parallel to the surface of the base substrate) and/or rotationally about one or more axes. Once the light source or image is repositioned in the desired orientation with the planar surface of the imager, the lens assembly is aligned with the imager and may be moved in a direction normal to the planar surface to focus an image plane of the lens with the imager. This may further include projecting an image through the lens and focusing that image. In one arrangement, the laser or other usable light source may be utilized to project such an image. In any arrangement, once the image is focused, the position of the lens assembly may be fixed relative to the base substrate. 
         [0015]    In one arrangement, the alignment of the lens assembly relative to the imager is performed while the PCB and imager are in a facedown position. In such an arrangement, mounting posts interconnecting the lens assembly relative to the PCB may be partially exposed through a back surface of the PCB, which may facilitate fixing the lens assembly relative to the base substrate. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    For a more complete understanding of the present disclosure and further advantages thereof, reference is now made to the following detailed description taken in conjunction with the drawings in which: 
           [0017]      FIG. 1A  illustrates a perspective view of a camera module. 
           [0018]      FIG. 1B  illustrates an exploded view of the camera module of  FIG. 1A . 
           [0019]      FIG. 2A  illustrates a perspective view of a PCB. 
           [0020]      FIG. 2B  illustrates a perspective view of the PCB of  FIG. 2A , including an imager. 
           [0021]      FIG. 3A  illustrates an exploded view of a lens assembly utilized with a camera module. 
           [0022]      FIG. 3B  illustrates a lens carrier. 
           [0023]      FIG. 3C  illustrates a perspective view of a lens mount subassembly of the lens carrier. 
           [0024]      FIG. 4  illustrates a gasket utilized with the camera module. 
           [0025]      FIG. 5A  illustrates a lens assembly free of the gasket. 
           [0026]      FIG. 5B  illustrates the lens assembly including the gasket of  FIG. 4 . 
           [0027]      FIG. 6  shows a rear view of the PCB once the lens assembly is engaged on the front surface of the PCB. 
           [0028]      FIG. 7  illustrates a flow sheet of an active alignment process. 
           [0029]      FIG. 8  illustrates a 6 axis mounting assembly. 
           [0030]      FIG. 9  illustrates aligning the imager relative to a reference laser. 
           [0031]      FIGS. 10A and 10B  illustrate the output of the imager relative to a reference laser. 
           [0032]      FIG. 11  illustrates aligning a lens assembly relative to the imager. 
       
    
    
     DETAILED DESCRIPTION 
       [0033]    Reference will now be made to the accompanying drawings, which at least assist in illustrating the various pertinent features of the presented inventions. In this regard, the following description is presented for purposes of illustration and description. Furthermore, the description is not intended to limit the disclosed embodiments of the inventions to the forms disclosed herein. Consequently, variations and modifications commensurate with the following teachings, and skill and knowledge of the relevant art, are within the scope of the presented inventions. 
         [0034]    Provided herein are systems and methods for mounting a lens or other image forming element relative to an optical imager/sensor array in precise optical alignment. The provided systems and methods (i.e., utilities) simplify the connection of these elements and substantially eliminates the tolerance stack up issues associated with systems and methods of the prior art. 
         [0035]      FIGS. 1A and 1B  illustrate a perspective and exploded perspective view, respectively, of a camera module  10  for incorporation into various different imaging devices. Such imaging devices include, without limitation, video imaging devices as well as still imaging devices. In this regard, the camera module  10  may be incorporated into various different casings/housings. The module includes a number of major components. These components include a base substrate or printed circuit board  20 , which supports an imager  30 , a lens assembly  50 , and an elastic gasket structure  40 . 
         [0036]      FIGS. 2A and 2B  illustrate the PCB  20  and PCB and imager  30 , respectively. As will be appreciated, the printed circuit board may be formed of any appropriate substrate material as known in the art. For instance, the PCB may be made of ceramic materials, silicon based materials and/or composite materials (e.g., resin and fiberglass). In any arrangement, the PCB  20  typically includes a plurality of conductive traces  26  to which circuitry of the imager  30  is electrically connected by a plurality of fine conductive wires or contact points  28  such as pads on the upper surface of the PCB  20 . These connections carry electrical power and signals between the imager  30  and the circuitry of the PCB. 
         [0037]    The PCB  20  also includes a plurality of various apertures  34  for connecting the PCB to, for example, the camera case. In addition, the PCB includes a plurality of lens mounting apertures  22  that are disposed about the imager  30 . These lens mounting apertures secure the lens assembly  50  relative to the PCB, as discussed herein. 
         [0038]    The bottom surface of the imager may include a plurality of solder pads or balls that connect to corresponding contact points  28  formed on the top surface of the PCB  20 . Such solder balls function as electrical input/output terminals for the imager  30 . The imager is defined by a semiconductor chip that typically has a two-dimensional rectangular sensor array that includes a large number of photo sensors that are each capable of converting light incident upon it into an electrical signal that is proportional to the intensity, and in the case of a color camera or the like, the color and hue of the incident light. The individual photo sensors may be, among others, CCDs or CMOS devices formed by techniques known in the art. Signal processing circuitry (not shown) is typically provided external to the sensor for converting the signals generated thereby into a digital signal capable of being stored, processed or distributed. 
         [0039]    It will be appreciated that while the imager is interconnected to the top surface of the typically planar PCB  20 , the resulting interconnection between these elements  20 ,  30  may result in slight canting of the planar upper surface  32  of the imager  30 . That is, this planar upper surface  32  of the imager  30  may be slightly canted relative to the planar surface of the PCB  20 . To achieve highly accurate imaging, it is desirable to account for such variations when mounting the lens assembly  50  relative to the PCB  20 . 
         [0040]    That is, for the imager to accurately sense images, the sensor array must align with a lens or other image forming device such that the planar upper surface  32  of the imager  30  is substantially coplanar with a focal plane of the lens. Otherwise, the image will be out of focus. Furthermore, the center of the imager will typically be centered on the optical axis of the lens or the image will be off center or only partially sensed. Further, the horizontal and vertical axes X and Y of the rectangular imager  30  will typically be aligned with the horizontal and vertical axes of the scene imaged by the lens, or the scene sensed by the imager may be canted relative to the original scene. However, it will be appreciated that in certain applications it may be desirable to offset the focal plane and/or optical axis of the lens relative to the imager. This may allow, for example, softening hard edges in a sensed image. Therefore, while discussed primarily herein as aligning the optical axis to be centered with and normal to the imager, it will be expressly understood that the systems and methods provided herein allow for aligning the optical axis of the lens in any desired orientation with the imager. 
         [0041]    Generally, the imager optical axis  100  is a reference axis that is centered on the rectangular surface of the imager in the X, Y directions and extends normal (e.g., perpendicular) to the planar surface  32  in the Z direction. See  FIG. 1B . Accordingly, optically aligning the imager  30  with the lens assembly  50  may involve fixing the position of the optical axis  110  of the lens assembly  50  with the optical axis  100  of the imager  30  (or in another desired orientation with the photo sensor). Typically, this requires the controlled positioning of the lens assembly  50  relative to the imager and PCB  20  in six directions of movement, three linear along the X, Y and Z axes and three angular, or rotational, about those three axes. That is, alignment of the optical axes  100 ,  110  and focusing of the lens focal plane with the surface of the imager typically requires movement of the lens assembly  50  in three Cartesian axes (X, Y and Z) as well as the rotational movement about these axes in what may be termed the pitch, yaw and roll directions. In this regard, highly accurate alignment and mounting requires six axis control between the lens assembly  50  and the PCB  20 . 
         [0042]      FIG. 3A  illustrates the lens assembly  50 . As shown, the lens assembly includes a lens mount subassembly  60  and a lens  70 . The lens  70  includes one or more optical elements  72  and an annular housing  74 . As shown, the housing  74  surrounds the optical element(s)  72  and interconnects the lens to the lens mount subassembly  60 . 
         [0043]    The optical element(s)  72  is operative to project an image onto a surface. Stated otherwise, the lens is operative to refract received light onto a focal plane  78 , as illustrated in  FIG. 3B . The lens will focus light reflected or emitted by an element or scene onto the focal plane  78 , which is orthogonal to the optical axis Z of the lens and located a specific distance (i.e., the focal length) behind the optical element or the bottom of the housing (e.g., back focal length). The light reflected or emitted by the element or scene may be thought to align a plane that is defined by two orthogonal axes, horizontal axis X and a vertical axis Y, that intersect at the center of the scene, and to be orthogonal to a third, intersecting axis Z that is perpendicular to the X and Y axes. This plane, may in some embodiments, lie directly on the surface of the optical imager. 
         [0044]    The lens mount subassembly  60  includes a focal tube or barrel  62  that is attached perpendicular to a base  64 . See  FIG. 3C . This barrel has an axial passage running the length thereof and opens through the base. An inside diameter of the barrel  62  is adapted to receive the lower end of the housing  74 . In this regard, the housing  74  has a lower barrel  76  with an outside diameter that substantially matches the inside diameter of the barrel  62 . Again, this lower barrel of the lens  70  is hollow such that the optical element  72  may project light there through. Though illustrated as being circular, it will be appreciated that the upper and lower barrels of the lens and lens mount subassembly may utilize other corresponding shapes, which are considered within the scope of the present disclosure. 
         [0045]    The outside surface of the housing  74  and the lens mount subassembly barrel  62  may include mating threads to allow positioning of the lens  70  relative to the lens mount subassembly  60 . However, aspects of the present disclosure allow for fixedly interconnecting the lens  70  relative to the lens mount subassembly  60  and subsequently adjusting the focal distance of the optical element(s)  72  relative to the underlying imager using a compressible gasket, as is discussed herein. In this regard, the housing  72  may be affixed relative to the subassembly  60  such that the focal length of the optical element(s) is fixed prior to connection of the lens assembly  60  with the PCB  20 . In another arrangement, the upper and lower barrels may be free of threads and provide a friction/slip fit arrangement. In any arrangement, these elements  60 ,  70  may be fixedly connected using adhesives or, for instance, mechanical fasteners (e.g., screws) prior to connecting the lens assembly  50  to the PCB  20 . Generally, the back focal length of the lens will be preset to be substantially equal to the expected distance (i.e., optical length) from the bottom of the lens barrel  74  to the surface of the underlying optical imager  30  when the lens assembly  50  is connected to the PCB  20 . As discussed herein, fine-tune adjustment of this optical length is provided utilizing the elastic gasket  40 . 
         [0046]    The lens mount subassembly  60  engages the lens  70  with the PCB such that the lens may project an image through the internal surface of the lens assembly  50  and onto the attached imager  30 . Further, it is desirable that the lens mount subassembly provide a means for adjusting the position of the optical axis of the lens  70  relative to the optical axis of the imager  30 . In the present arrangement, the lens mount subassembly includes a plurality of mounting posts  66  connected to the base  64 . These mounting posts are adapted for receipt within the lens mounting apertures  22  extending through the PCB  20  as illustrated in  FIGS. 2A and 2B . Generally, these mounting posts  66  extend substantially parallel to the optical axis of the lens  70  and are arrayed around the optical axis. Furthermore, these mounting posts  66  have distal ends that extend beyond the focal plane of the lens. In this regard, the posts are long enough to extend at least partially through the PCB  20  while the focal plane  78  of the lens  70  displays on the surface of the imager  30 . Though illustrated as being circular posts, it will be appreciated that other configurations are possible. 
         [0047]    In the present non-limiting embodiment, the circular mounting posts  66  are adapted for receipt within identically spaced circular mounting apertures  22  of the PCB  20 . Furthermore, the radius of the mounting apertures  22  are equal to the radius of the mounting posts  66  plus the worst case tolerance stack up for all the components involved in the assembly of the camera module  10 . That is, there is play between the mounting posts  66  and the mounting apertures  22  that allows for adjusting the position of the subassembly  60  in the X and Y directions (e.g., laterally) as well as permitting some rotation of the mounting assembly  60  about the three Cartesian axes. Generally, the radius, diameter or other cross-dimension of the mounting apertures will be at least 1.1 times the corresponding dimension of the mounting posts. More typically, the mounting apertures will be at least 1.5 times the corresponding dimension of the mounting posts. Though shown as being regularly spaced about the imager, it will be appreciated that the mounting posts and apertures may have any corresponding spacing (e.g., irregular). Further, the post and apertures need not be circular in cross-section. 
         [0048]    In addition to the mounting posts, a plurality of positioning stops or sidewalls are also interconnected to the base  64  of the lens mount subassembly. See  FIG. 3C . These sidewalls  68  limit the axial positioning (e.g., along the Z axis) of the lens assembly  50  relative to the PCB  20 . That is, the bottom surfaces of these sidewalls  68  may rest on a top surface of the PCB  20  and thereby prevent additional axial movement of the lens assembly relative to the PCB  20 . 
         [0049]      FIG. 4  illustrates an elastic gasket  40  that is adapted for positioning between the lens assembly  50  and PCB  20 . (See also  FIG. 1B ) As shown, the elastic gasket  40  includes a central aperture  42 . This aperture is sized to surround the imager  30  when the gasket  40  is placed on the surface of the PCB  20 . Furthermore, the size of the aperture  42  allows movement of the lens assembly  50  relative to the PCB without contacting the imager  30 . As shown, the elastic gasket  40  also includes a plurality of apertures  44  that are adapted to receive the mounting posts  66  of the lens mount assembly  60 . This is illustrated in  FIGS. 5A and 5B  where the lens assembly is shown without the gasket and with the gasket, respectively. Beneficially, the gasket surrounds the mounting posts and, upon disposition on the base substrate, covers the portion of the apertures in the base substrate around the posts. This provides a glue stop during attachment. In addition, each outside edge surface of the elastic gasket  40  has a recess  46  that receives the sidewall  68  extending down from the base  64  of the lens mount subassembly  60 . In this regard, the gasket is not disposed between the bottom edges of the sidewalls  68  and the top surface of the PCB such that the sidewalls may provide a stop in the Z direction, as discussed above. 
         [0050]    The elastic gasket  40  has a thickness that is greater than the height of the sidewalls  68  that extend from the bottom of the base  64  of the lens mount assembly. In this regard, when the elastic gasket  40  engages the mounting posts  66 , a bottom surface of the gasket extends beyond the bottom surface of the sidewalls  68 . See  FIG. 5B . Once all the components are assembled, as illustrated in  FIG. 1A , the lens assembly  50  floats on top of the elastic gasket  40 , which is sandwiched between the bottom of the lens assembly  50  and the top surface of the PCB  20 . This floating arrangement in conjunction with the use of mounting apertures  22  that have a radius that is greater than the corresponding radius of the mounting posts (i.e., suspended within the apertures) allows for adjusting the pitch, yaw and roll of the lens assembly  50  relative to the imager  30 . That is, if necessary, the lens assembly  50  may be canted relative to one of these axes (e.g., the pitch axis), which is permitted by compressing one side of the elastic gasket  40 . However, when compressing one side of the gasket  40 , the other side of the gasket maintains a seal between the bottom of the lens mount subassembly  60  and the PCB  20 . In this regard, the gasket  40  may act as an environmental seal for the imager  30 . That is, once the lens assembly  50  is interconnected to the PCB  20 , the enclosed area between the lens and the optical imager is sealed from outside contamination. In addition, the gasket may be compressed in an axial direction (e.g., along the imager axis) to adjust the position of the lens focal plane relative to the surface of the imager. 
         [0051]    The gasket may be made of any material that provides a desired compliancy. However, it may be preferable that the gasket be a material that is substantially non-permeable. As noted, in addition to permitting rotational movement about the three Cartesian axes as well as linear movement along at least one axis, the gasket  40  also provides an environmental seal for the imager  30 . Therefore, it is desirable that the gasket be non-permeable to prevent, for instance, moisture infiltration into the area between the imager and the lens. In one arrangement, the gasket is a closed-cell foam. In other arrangements, various neoprene rubbers and/or other materials may be utilized. 
         [0052]    The gasket thickness is such that the optical axis of the lens assembly  50  may be canted at least about ±3° and more typically ±5° relative to the PCB. For instance, in reference to  FIG. 5B , the bottom surface of the gasket  40  may extend beneath the bottom surface of the sidewall  68  to provide the necessary give to permit canting. In any arrangement, this thickness beyond the bottom of the lens assembly is enough to account for the tolerance variation in the manufacture of the optical lens  72  (e.g., the focal length of the lens), as well as the tolerances of the connections between the various different components, including the lens carrier, mounting subassembly and the lens assembly to the PCB. 
         [0053]    Once the gasket, lens assembly and PCB are connected, the four mounting posts  66  of the lens subassembly  60  extend through at least a portion of the lens mounting apertures  22 . See  FIG. 6 . In the present embodiment, the bottom surface of the gasket  40  seals the bottom of the apertures  22 , which limits the amount of adhesive that is utilized to affix the posts  66  within the mounting apertures  22 . As will be discussed herein, upon correctly aligning the optical axis  110  of the lens assembly with the optical axis  100  of the imager, a light curable epoxy or other adhesive may be disposed within the area between the posts and their respective apertures and cured. Once cured, the four posts  66  effectively hold the lens assembly  50  relative to the PCB  20 . In this regard, it will be appreciated that the posts  66  are designed to meet mechanical strength requirements to hold the lens assembly  50  with minimal misalignment throughout the life of the product. 
         [0054]    As noted above, for metrology functions, such as angle, distance, speed and/or curvature measurement, the alignment of the optical axes  100 ,  110  is critical. For instance, it is desirable that the alignment accuracy be less than 10 micrometers in the Cartesian axes and less than 1° in the rotational axes. Accordingly, provided herein is an active alignment system that allows for utilizing an output of the imager  30  during the interconnection process of the lens assembly  50  to the PCB  20  that ensures accurate alignment of the optical axes  100 ,  110 . 
         [0055]    The active alignment process for aligning the optical axis of the imager  30  with the optical axis of the lens assembly is illustrated in  FIG. 7 . As shown, the process includes loading the lens subassembly and the imager board onto mounting apparatuses ( 202 ). The imager is then centered ( 204 ) relative to a reference laser beam. The lens subassembly is then moved into position ( 206 ) underneath the imager such that the laser may project through the lens of the lens assembly. An output of the imager is then monitored ( 208 ) to determine if there is an alignment error between the laser and the imager. Specifically, the determination is made as to whether the laser is disposed normal to the imager after passing through the lens. If not, the lens assembly is moved (e.g., tilted) to correct for pitch or roll error ( 210 ). Once the laser is projecting through the lens and is normal to the surface of the imager, the lens assembly may be moved in the XY directions to center ( 212 ) the laser at the center of the imager. At this time, the lens assembly is positioned such that light received through the lens is centered on the imager and the optical axis of the lens is normal to the surface of the imager. That is, the optical axis of the lens aligns with the optical axis of the imager. 
         [0056]    However, while the optical axis of the lens aligns with the optical axis of the imager, the focal plane of the lens may not be coincident to the surface of the imager. Accordingly, the process further includes focusing the lens. This process ( 214 ) may entail projecting one or more images through the lens and monitoring the output of the imager to properly focus the image. Focusing is achieved by moving the lens assembly along the aligned optical axes. At this time, an adhesive such as an epoxy fixedly interconnects the lens assembly relative to the PCB  20  while the optical axes remain aligned and the lens remains in focus. Once adhered ( 216 ) and cured ( 218 ), the completed assembly may be removed ( 220 ) from the mounting apparatuses. 
         [0057]      FIGS. 8-11  more fully illustrate the process of  FIG. 7 . Initially, the PCB and supported imager  30  are loaded into a PCB mounting chuck  122  as illustrated in  FIG. 8 . Specifically, the PCB  20  and imager  30  are positioned in a facedown position such that the rear side of the PCB  20  is exposed. This facilitates adhesion of the mounting posts  66  of the lens assembly  50  within the mounting apertures  22  of the PCB  20 , as is more fully discussed herein. The PCB mounting chuck  122  is part of a three-axis controllable mounting apparatus  120 . In the present arrangement, the mounting chuck  122  engages the four corner apertures  34  of the PCB  20 . See also  FIG. 2A . In this regard, the PCB is rigidly interconnected with the mounting apparatus  120 . At this time, one or more connections may be made with, for instance, electrical pads  26  on the PCB  20  to provide electrical power and electrical signals to and receive an output signal from the imager  30 . The output signal of the imager may be provided to a display and/or a computer control that may allow for three-axis control of the mounting apparatus  120 . Such control may be manual or fully automated. 
         [0058]    At this time, a circular collimated laser beam from a fixed reference laser  150  is projected onto the surface of the imager  130 . See  FIG. 9 . This laser beam  150  is utilized as an optical reference axis for the imager. For instance, the imager  30  may be centered to the reference laser beam in the X and Y Cartesian directions. That is, the output of the imager is utilized to identify when the laser beam is at a direct center thereof. In addition to determining the center of the imager  30 , the laser beam is also utilized to determine the canting, if any, of the imager relative to the PCB.  FIGS. 10A and 10B  illustrate the output of the imager in relation to the collimated laser. As shown in  FIG. 10A , when the planar surface  32  of the imager  30  is canted relative to the PCB  20 , the circular collimated laser generates a series of elliptical images (i.e., a circular fraction pattern). When measuring the long and short axes of one of the elliptical images, the apparatus  120  may be tilted in one or more directions in order to generate a true circular image, as illustrated in  10 B. That is, once the output generates a circular image that is centered at the center of the imager, the reference axis defined by the laser  150  is perpendicular (i.e., normal) to the imager  30 . That is, the optical axis  100  of the imager is aligned with the laser beam  150  of the fixed reference laser. At this time, the PCB  20  and imager  30  are positioned for receipt of the lens assembly  50 . 
         [0059]    As shown in  FIG. 8 , the lens assembly  50  is also receivable within a lens chuck  142 . This lens chuck  142  is likewise interconnected to a three-axis controllable lens mounting apparatus  140 . This lens mounting apparatus  140  is operative to move in the X, Y, Z directions as well as tilt/rotate about all three Cartesian axes. Once the PCB is properly oriented (i.e., normal to the reference laser), the lens chuck  142  is positioned below the PCB  20  such that the mounting posts  66  of the lens assembly  50  are below the top surface of the PCB  20 . The lens chuck  142  is then advanced in the Z direction to engage the posts  66  through the apertures  22  and the PCB  20 . See  FIG. 11 . In addition, the lens assembly  50  is advanced to a position where the gasket  40  is partially compressed around its periphery. At this time, the laser  150  projects through the lens of the lens assembly  50 . The lens mounting apparatus  140  is then moved in the X and Y directions until the laser is again centered on the optical center of the imager, as well as being perpendicular to the imager plane. In this regard, pitch and roll error correction may be performed first by minimizing the error of a pattern generated by the laser beam similar to that as discussed above. Lateral centering in the X and Y directions is performed by moving the lens assembly until the reference laser is centered in the imager. Necessarily, the mounting posts move laterally within the lens mounting apertures. At this time, the optical axis  110  of the lens is aligned with the imager. However, additional focusing of the focal plane of the lens assembly  50  relative to the surface of the imager  30  may be required. That is, the lens assembly may have to be focused in the Z direction. At this time an image (e.g., a collimated pattern or image with a focal distance of infinity) may be projected (e.g., using the laser or other source) through the lens. This image may be focused by adjusting the Z position of the lens assembly  50  relative to the PCB  20 . Once the focus is maximized, the position of the lens assembly relative to the PCB and imager  30  is accurately aligned. 
         [0060]    Importantly, the compressibility of the gasket allows movement of the lens assembly in the Z direction. Further, as the gasket is initially partially compressed, the gasket permits positive or negative movement along the Z axis. 
         [0061]    In order to maintain the positional relationship between these elements, a light curable epoxy is applied to the backside of the PCB in the mounting apertures  22  around the mounting posts  66 . By exposing the back surface of the PCB  20 , there is nothing in the way of application of this adhesive, and therefore, this application may be automated. Further, in one arrangement, a light curable adhesive permits rapidly curing the adhesive. However, it will be appreciated that other adhesives or other joining methods may be utilized. For instance, welding or soldering may be utilized in various applications. 
         [0062]    The foregoing description of the presented inventions has been presented for purposes of illustration and description. Furthermore, the description is not intended to limit the inventions to the forms disclosed herein. Consequently, variations and modifications commensurate with the above teachings, and skill and knowledge of the relevant art, are within the scope of the present invention. The embodiments described hereinabove are further intended to explain best modes known of practicing the inventions and to enable others skilled in the art to utilize these inventions in such or other embodiments and with various modifications required by the particular application(s) or use(s) of the presented inventions. It is intended that the appended claims be construed to include alternative embodiments to the extent permitted by the prior art.