Abstract:
Features of the present invention provide an optical layout that can accommodate the relatively strict enclosure requirements for compact component alignment sensor. Specifically, aspects of the present invention provide a single optical component that reduces the degree of divergence, and preferably substantially collimates light from the plurality of divergent light sources prior to entering the sensing field. In this regard, part count is kept low and the physical size of the optical train itself is relatively small.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a Continuation-In-part Application of U.S. patent application Ser. No. 09/767,199 filed Jan. 22, 2001 now U.S. Pat. No. 6,762,847 entitled Laser Align Sensor with Sequencing Light Sources; The application is also a non-provisional application of, and claims priority to, U.S. Provisional Application Ser. No. 60/406,822, filed Aug. 29, 2002 and entitled Multiple Source Laser Align Sensor with Improved Optics. 

   BACKGROUND OF THE INVENTION 
   The present invention relates to control systems which align electrical components for precise placement via pick-and-place machines onto surfaces such as printed circuit boards, hybrid substrates containing circuitry traces, and other carriers of circuit tracings. More specifically, the present invention relates to a non-contact light-based sensor system which precisely determines angular orientation and location (x, y) of components to allow a pick and place machine to correct angular orientation of the component with respect to the pick and place machine&#39;s coordinate system for proper placement. 
   The electronic device assembly industry uses pick and place machines to automatically “pick” components from standardized feeder mechanisms, such as tape reels, and “place” such components upon appropriate carriers such as printed circuit boards. A given printed circuit board may include a large number of such components and thus the automation of component placement upon the printed circuit board is essential for cost effective manufacture. One important aspect of a given pick and place machine is the manner in which component orientation and location are detected prior to placement. Some pick and place machines transport the component to an inspection station where it is imaged by an inspection camera, or the like (i.e. off-head systems). Once imaged, the controller, or other appropriate device, calculates orientation and location information from the component image. One drawback associated with such systems is the added time required to transport the component to the imaging station; to image the component; and to transport the component from the imaging station to the placement location. Another type of pick and place machine uses an “on-head” sensor to essentially image the component while being transported from the component feeder to the placement location. Thus, in contrast to the above example, on-head component inspection systems typically allow higher component throughput and thus lower cost manufacture. 
   Pick and place machines that incorporate on-head sensors are known. One such device is taught in U.S. Pat. No. 5,278,634 issued to Skunes et al., and assigned to the assignee of the present invention. U.S. Pat. No. 5,278,634 discloses an on-head component detector that uses a single light source to direct illumination at and past a component of interest, which illumination then falls upon a detector. The component fits through a fixed size window in the housing of the Skunes &#39;634 sensor. With the light energized, the component is rotated by a vacuum quill while the width of the shadow cast upon the detector is monitored. The minimum shadow width is registered when the sides of a rectangular component are aligned normally with respect to the detector. Associated electronics, sometimes resident in the pick-and-place machine, compute the desired rotational movement of the nozzle (with knowledge of reference axes of the pick-and-place machine). This allows angular orientation of the component, as well as component position to be determined, and corrected for proper placement. 
   Other pick-and-place machines employ sensors with multiple light sources in the sensor, to accommodate components of varying sizes. 
   Although the system taught by Skunes et al. has provided a significant advance to the art of electronic component placement in pick and place machines, an efficient sensor adapted for use with components having a wide range of sizes would provide faster placement and less machine down-time to exchange sensors with different sized windows. 
   SUMMARY OF THE INVENTION 
   Features of the present invention provide an optical layout that can accommodate the relatively strict enclosure requirements for compact component alignment sensor. Specifically, aspects of the present invention provide a single optical component that reduces the degree of divergence, and preferably substantially collimates light from the plurality of divergent light sources prior to entering the sensing field. In this regard, part count is kept low and the physical size of the optical train itself is relatively small. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1A  is a top plan view of a pick and place machine of the present invention. 
       FIG. 1B  is a perspective drawing of a sensor of the present invention. 
       FIG. 2  is a diagrammatic view of a system for detecting component orientation and location in accordance with an embodiment of the present invention. 
       FIG. 3  is a diagrammatic view of a system for detecting component orientation and location in accordance with another embodiment of the present invention. 
       FIG. 4  is a diagrammatic view of a system for detecting component orientation and location in accordance with another embodiment of the present invention. 
       FIG. 5  is a diagrammatic view of a system for detecting component orientation and location in accordance with another embodiment of the present invention. 
       FIG. 6  is a diagrammatic view of a system for detecting component orientation and location in accordance with another embodiment of the present invention. 
       FIG. 7  is a diagrammatic view of a system for detecting component orientation and location in accordance with an embodiment of the present invention. 
       FIG. 8  is a diagrammatic view of a single detector source pair. 
       FIG. 9  is a diagrammatic view of a system for detecting component orientation and location in accordance with an embodiment of the present invention. 
   

   For convenience, items in different figures having the same reference designator number are the same, or serve the same or similar function, as appropriate. 
   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1A  is a top plan view of pick and place machine  150  for which embodiments of the present invention are particularly useful. Although the description of  FIG. 1A  will be provided with respect to pick and place machine  150 , other forms of pick and place machines such as split gantry designs, can be used. As illustrated in  FIG. 1A , machine  150  includes transport mechanism  152  that is adapted to transport a workpiece such as a printed circuit board. Transport mechanism  152  includes mounting section  154  and conveyor  156 . Transport mechanism  152  is disposed on base  158  such that the workpiece is carried to mounting section  154  by conveyor  156 . Feeder mechanisms  160  are generally disposed on either side of transport mechanism  152  and supply electronic components thereto. Feeders  160  can be any suitable devices adapted to provide electronic components. 
   Pick and place machine  150  includes head  162  disposed above base  158 . Head  162  is moveable between either of feeder mechanisms  160  and mounting section  154 . As can be seen, head supports  164  are moveable on rails  166  thereby allowing head  162  to move in the y direction over base  158 . Movement of head  162  in the y direction occurs when motor  170 , in response to a motor actuation signal, rotates ball screws  172  which engages one of head supports  164  to thereby displace the support  164  in the y direction. Head  162  is also supported upon rail  168  to allow head movement in the x direction relative to base  158 . Movement of head  162  in the x direction occurs when motor  174 , in response to a motor actuation signal, rotates ball screw  176 , which engages head  162  and displaces head  162  in the x direction. Other pick-and-place designs, even those which do not operate exclusively in x and y movements, may be adapted for use with the present invention. 
   Head  162  generally includes body  178 , nozzle mount  180 , nozzles  182 , and sensor  184 . Nozzle mount  180  is disposed within body  178  and mounts each of nozzles  182  within body  178 . As used herein, “nozzle” is intended to mean any apparatus capable of releasably holding a component. Each of nozzles  182  is movable in the z direction (up/down), x and y directions, and is rotatable about the z axis by any suitable actuation members, such as servo motors. Sensor  184  is adapted to acquire shadow information related to components held by nozzles  182 . Sensor  184  includes suitable illumination devices and detection devices such that sensor  184  can provide shadow information that varies based upon component orientation and off-set. Sensor  184  can be mounted on head  162 , or alternatively sensor  184  can be mounted at a fixed location with respect to head  162 . The information provided by sensor  184  to processing electronics  34  is used to calculate respective component orientations and offsets. Such information includes calculating offset in the x and y axes as well as rotational offset. 
     FIG. 1B  shows sensor  184  separately, with sources  12 ,  14 ,  15 . Component(s) fit partially within sensing field  31 , and obscure illumination from each of the successively energized sources as it falls onto a detector  24 . Electronics  26  receive a plurality of outputs from the detector as a nozzle (not shown) rotates the component. Electronics  26  may be partially located outside of sensor  184  in a pick-and-place machine. 
     FIG. 2  is a diagrammatic view of component orientation and placement detection system  10  in accordance with an embodiment of the present invention. System  10  includes sources  12 ,  14  which are arranged to direct illumination  16  upon component  18  from at least two different angles. Sources  12 ,  14  can be any suitable light sources as long as they provide illumination of sufficient intensity, as considered from each source. Thus, sources  12 ,  14  can be sources incoherent or coherent illumination. Preferably, sources  12 ,  14  are laser diodes, but in some embodiments, sources  12 ,  14  are light emitting diodes (LED&#39;s). Sources  12 ,  14  can be positioned to provide illumination in substantially the same plane, as defined by either of the sources and two points on the detector (a beginning and an ending pixel on the detector). Although a pair of sources  12 ,  14  are shown, any suitable number of sources, such as three sources, can be used. Illumination  16  from sources  12 ,  14  is blocked, to some extent, by component  18  to thereby generate shadows  20 ,  22 , respectively, on detector  24  which is preferably a linear charge coupled device (CCD) sensor or a Complementary Metal Oxide Semiconductor (CMOS) sensor. Detector  24  includes a number of photoelectric elements, or pixels. Detector  24  essentially captures shadows  20 ,  22  in a brief instant of time and provides data (e.g. detector output) related to the captured shadow image to detector electronics  26  via link  28 . As desired, additional optical components (e.g. lenses, prisms, etc.) may be placed in front of the detector  24  so that the image of the component (the imaged or focused shadow) is incident upon detector  24 , which then provides detector output representative of the shadow image rather than the shadow. As used herein, “shadow” is intended to mean any representation that is generated in part by light of intensity that varies based upon at least partial obstruction by a component of interest. Thus, a shadow may or may not be focussed before falling upon a detector. 
   As component  18  is held, or otherwise affixed to nozzle  30 , component  18  is rotated as indicated by arrow  32  while sources  12 ,  14  are selectively energized. As can be appreciated, during rotation of part  18 , shadows  20 ,  22  will change size and position based upon the cross sectional area of component  18  obstructing a given beam  16  of illumination. The signal from detector  24  is read, and/or stored during rotation of component  18  such that data from detector  24  is used to compute rotational orientation of component  18  as well as location (x, y) of component  18  with respect to nozzle  30 . Detector electronics  26  provides this data to processing electronics  34  via link  36 . As illustrated in  FIG. 2 , processing electronics  34  is also preferably coupled to source control electronics  38  such that processing electronics  34  controls energization of sources  12 ,  14  during rotation of component  18 . Source control electronics  38 , or energization electronics  38 , is mounted within sensor  184  in some embodiments. Processing electronics  34  can reside within a suitable personal computer and includes appropriate software for computing angular orientation and offset. Processing electronics  34  is also coupled to encoder  40  such that processing electronics  34  is provided with a signal from encoder  40  that is indicative of angular orientation of nozzle  30 . Thus, by essentially knowing which sources are energized, knowing the angular orientation of nozzle  30  as indicated by encoder  40 , and by detecting images of the shadows cast by component  30  while rotated, processing electronics  34  computes component orientation and location, given suitable knowledge of the internal geometry of the sensor. 
     FIG. 2  shows a double-edged measurement, as considered with respect to either of sources  12 ,  14 , since shadows of two edges of component  18  fall on detector  24 . 
   Various embodiments of the present invention are designed to be able to extract component information (part size, center offset, and angular orientation, etc.) using either single edge or double edge measurements of the component under inspection. Typically, double edge measurements are used when the dimensions of the component allow the shadows of both component edges to fall upon the detector during the same component measurement time, without overlapping, as illustrated in FIG.  2 . Thus, at least two edges of the component can be shadowed onto the detector by different sources within the same component measurement time. The difference between single edge measurement and double edge measurement is that during the single edge measurement process, only one edge of the component is shadowed by any source onto the detector due to the component being so large that the shadow of the other edge of the component would not fall on the detector. 
   Two or more sources are sequenced to reduce elapsed time before image information is collected for computation. This is particularly advantageous when these sources are spaced separately with respect to the plane that is defined by the sources, and the CCD or imaging array (see, for example, FIG.  1 B). Since the sources are generally at differing angular positions from each other relative to a line drawn from nozzle  30  normal to the surface of detector  24 , each of sources  12 ,  14  will have its principal ray directed at a different angle with respect to this normal line as incident onto component  18 . As used herein, the principal ray is that ray emanating from the center of the illumination generated by the radiation source, nominally referenced from the mechanical axis of the detector body, such that the core of emanated radiation, (which is typically symmetrical) is bisected by the principal ray. This allows the information included in the shadow, such as edge information, to represent a different spatial position of the component, i.e. the edge of one side may be lined up with respect to the source  12  and, in less than 90 degrees of component rotation another side may be lined up with respect to source  14 , as illustrated in FIG.  2 . 
   The light sources  12 ,  14  are sequenced in any suitable manner. For example, sequencing sources  12 ,  14  at the full frame readout rate of detector  24  (e.g. 2 kHz line read-out rate), reduces the amount of time that elapses between these sources being sequenced such that the amount of angular rotation of the component during that interval is relatively small. By sequencing the sources so, shadow images derived from either source individually can be obtained such that the movement of the component between any particular shadow image can be reduced, thus reducing the granularity and enhancing the resolution of the sequence of images from that particular source. Each source allows collection of shadow images from a different rotational position of the component. Based on the different source locations with respect to the component, shadow images from more than one angular position of the component are collected within a relatively small time. The component information can be collected in less time than would be required if a single source, were energized to collect the data since full rotation of the component would be required in order to obtain the angular information. 
   Another important feature of embodiments of the present invention is the ability to create a measurement envelope, or sensing field of varying dimension. As used herein, a “sensing field” is a cumulative space illuminated by the energized sources in the sensor (when all sources are energized), as modified by any mechanical obstruction such as a housing. Thus, a sensing field need not even require a mechanical housing. The sensing field is formed by accommodating a plurality of sources positioned such that a single sensor can sense orientation for components of varying size. For example, if a component is 25 millimeters from side-to-side then one energized source, placed 12.5 millimeters from the nominal center of the component and disposed normal to the detector with its principal ray, would capture the edge of the component that was rotating in the sensing field. This embodiment, in its simplest form, requires only one energized source per component size. The sources have a specified solid cone angle of light emitted from them so the distance from the nominal center and lateral or roughly parallel to, the detector surface as discussed above can be adjusted to account for this divergence of the source light in order to cast a shadow of the edge of the part. However, a source that is placed with its principal ray pointing at, for example, an 8 millimeter position from nozzle  30  and along the diameter of the component  18  parallel to detector  24  would be blocked, depending on the relative orientation of the solid angle of light as well as the position of the source. Based upon the solid angle of each source  12 ,  14 , and the component size, each source will illuminate various sections of the component. It is important to select which one or more of the plurality of sources to energize, since differently sized components mandate the use of different sources to generate even a portion of a shadow. Source control electronics  38  can also provide selective source energization based upon anticipated component size. However, source control electronics can provide varying energization sequences for components of the same size in order to expedite processing, or provide additional information about the components. 
   As components are exchanged from small to larger parts in the same sensor, sources having principal rays that are pointed increasingly further along a line parallel to, or lateral from, detector  24 , but measured from a line normal to detector  24 , through nozzle  30  or the center of rotation of the component will image increasingly large components&#39; edges by selectively sequencing sources  12 ,  14 . (See arrow A in FIG.  1 B). Preferably, sources  12 ,  14  are sequenced to cast shadows from opposite sides of component  18  in the same component measurement time interval (in the case where each source casts a shadow of a side). Selection of an appropriate source allows the source, generally based on a priori knowledge of expected part size, to be turned on such that an edge of component  18  can be imaged onto the detector  24 . This allows components of varying sizes to be imaged on detector  24  without requiring the use of multiple sensors that are of a fixed measurement envelope, or sensing field. 
   Although the description above has focused on embodiments where a single nozzle is disposed within the sensing field, other embodiments can provide any suitable number of nozzles in the sensing field.  FIG. 3  is a diagrammatic view of system  20  for detecting component orientations in accordance with another embodiment of the present invention. System  20  includes many of the same or similar elements as system  10  shown in FIG.  2  and like elements are numbered similarly.  FIG. 3  illustrates that more than one nozzle  30  can be disposed in the sensing field  31 , such that multiple component orientations and the locations can be imaged substantially simultaneously in order to reduce processing time. 
   The sensing field  31  is the area between the radiation (light) sources, and the detector, where components placed upon the nozzles will have light directed upon them. In this embodiment, shadows from the components&#39; edges are cast upon detector  24 . Depending upon the locations of nozzles  30  and sources  12 ,  14 , a particularly sized component  18  is measured by sequencing the various sources  12 ,  14 , etc. such that shadows of the component  18  can be distinguished from shadows of components on other nozzles. Source  12 ,  14  time sequencing is shown in  FIG. 3  where electronics  38  energizes source  12  first, and then energizes source  14 . This has an advantage of allowing more than one component  18  to be measured in the sensing area at essentially the same time. Further, depending upon the spacing of nozzles  30 , the nozzles can hold components of varying sizes, yet still allow measurement of the component to be accomplished while such components are rotated on the nozzles. 
     FIG. 3  is an example of a double edged measurement, as considered with respect to sources  12 ,  14 , since shadows of the two edges of component  18  fall on detector  24 . 
     FIG. 4  is a diagrammatic view of component measurement system  50  in accordance with another embodiment of the present invention.  FIG. 4  illustrates a sensing field  31  where detector  24  comprises two spaced-apart detector portions  24 A,  24 B, each one of which receives light incident from a specific source  12 ,  14 . Detector portions  24 A and  24 B can be disposed adjacent to one another at a variety of angles, since each source detector pair operates independently. The principal axis of detector  24 A need not be in the same plane as the principal axis of detector  24 B. Moreover, detector portions  24 A and  24 B can be arranged to image shadows from different parts of the component. Using separate detector portions allows for the use of smaller detector portions, and, if necessary, allows the detector portions  24 A,  24 B to be packaged separately. In this manner, a very long detector  24  is not required in order to establish the same large component sensing envelope or field  31 . However, sequencing of sources  12 ,  14  is essentially the same as in the previous embodiment. 
     FIG. 4  is an example of a double edged measurement as considered with respect to sources  12 ,  14 , since shadows of two edges of component  18  fall on each of detectors  24 A,  24 B. 
     FIG. 5  is a diagrammatic illustration of component measurement system  60  in accordance with another embodiment of the present invention. System  60  bears many similarities to system  50 , shown in  FIG. 4 , and like components are numbered similarly. The main distinction between systems  60  and  50  is the relative orientations of detector portions  24 A and  24 B. Specifically, referring to  FIG. 4 , faces of detector portions  24 A and  24 B lie in approximately the same plane, and when viewed in two dimensions, appear co-linear. However, system  60 , shown in  FIG. 5 , illustrates detector portions  24 A and  24 B disposed such that the principal axes of detector portions  24 A and  24 B do not lie in the same plane. Thus, detector portions  24 A and  24 B of system  60  do not appear co-linear with respect to each other. Instead, detector portions  24 A and  24 B are disposed normal to a centerline of illumination from the respective source for each detector portion. For example, detector portion  24 A appears to be oriented relative to source  14  such that ends  62  and  64  are equidistant from source  14 . Detector portion  24 A is also disposed in the plane of shadow  20 , and source sequencing operates as shown in the relative timing diagram in FIG.  5 . Although detector portions  24 A and  24 B are shown disposed at a relatively slight angle with respect to each other, any suitable angle such as ninety degrees can be used. 
     FIG. 5  is an example of a double sided measurement, as considered with respect to each source, since shadows of two edges of component  18  fall on each of detectors  24 A,  24 B. 
     FIG. 6  is a diagrammatic view of component measurement and detection system  70  in accordance with another embodiment of the present invention. System  70  is similar to the embodiment shown in FIG.  2  and like elements are numbered similarly. The main distinction between systems  70  and  10 , in  FIGS. 6 and 2  respectively, is the provision of specular reflective surfaces  72 ,  74 . As can be seen, sources  12 ,  14  direct their illumination away from detector  24  initially, which illumination falls upon specular reflectors  72 ,  74 , (typically substantially specular) respectively, and is directed toward nozzle  30  and detector  34 . This embodiment allows for flexibility in placement of sources  12 ,  14 . Detector  24 , as shown in  FIG. 6 , could also incorporate either of the detector layouts shown in  FIG. 4  or  5 . However, in embodiments using split detector portions, and specular reflectors, it is contemplated that one source could utilize a specular reflector while another source could be positioned so that its principal ray is directly incident upon the component, and thus not require a specular reflector. Further, although  FIG. 6  illustrates the use of specular reflectors between sources  12 ,  14  and the component, such specular reflectors could be disposed between the component and detector  34 . 
     FIG. 7  is a diagrammatic view of component measurement and detection system  80  in accordance with an embodiment of the present invention. System  80  is illustrated to show how embodiments of the present invention can be used to detect component offset and rotational orientation for oversized components (e.g. single edge measurements). This discussion is provided to detail computation of rotational and positional (x, y) offsets for single edge measurements, and can be extended to double sided measurements. U.S. Pat. No. 5,559,727 to Deley also provides for computation of rotational and positional offsets for double-sided measurements with a different light source/detector arrangement, and is hereby incorporated by reference herein.  FIG. 7  shows an example of a single sided measurement with respect to either of sources  12 ,  14 , since only one shadow of an edge falls on each of detectors  24 A,  24 B. Such components are generally too large to fit shadows of opposite sides simultaneously upon any single detector portion. 
     FIG. 7  illustrates component  100  casting shadows upon detector portions  24 A and  24 B. However, each detector portion only captures a single shadow, because component  100  is so large that the shadows of its opposite sides do not fall upon detector portions  24 A and  24 B. In this embodiment, detector outputs  28 A and  28 B are monitored while component  100  is rotated in order to detect shadow minimums indicating when respective sides of component  100  are aligned with the a given ray emanating from either of sources  12 ,  14 . For example, in the example shown in  FIG. 7 , slight clockwise rotation will bring edge  102  of component  100  into alignment with a ray emanating from source  14 . Such alignment will generate a local minimum upon detector portion  24 A. Although in  FIG. 7  it appears that the detectors are positioned at right angles to the sources, it will be understood that non-orthogonal positioning may also be employed. 
   To determine the x-axis and y-axis offset, the width of the component, the length of all of the sides of the component, and the rotational offset of the component in  FIG. 7 , consider the analogous example of one source-detector pair of  FIG. 7  shown in FIG.  8 . The length of the minimum width is measured by finding the distance, D 1 , between shadow edge and detector point O 1 . The distance D 1  is related to component dimension L 1  in the following manner.
 
When the distance D 1  is at a minimum: 
                     tan   ⁡     (       α   1     ⁢   _side   ⁢   _a     )       =         L   a       B   1       =         D   1     ·     cos   ⁡     (       ϕ   1     -     90   °       )           A   1                   so               Equation   ⁢           ⁢   1                       L   a     =         B   1       A   1       ⁢     (       D   1     ·     cos   ⁡     (       ϕ   1     -     90   °       )         )                 and               Equation   ⁢           ⁢   2                   α   1     ⁢   _side   ⁢   _a     =     arctan   ⁡     (         D   1     ·     cos   ⁡     (       ϕ   1     -     90   °       )           A   1       )               Equation   ⁢           ⁢   3             
 
   Equations for L c  and α 1— side_a can be derived similarly when side_c is rotated to a similar position as side_a in FIG.  8 . The encoder and encoder electronics captures the encoder rotation, E 1 , the D 1  is at its minimum. If the step size between successive encoder rotations is T, then the part rotation encoder value when side_a is aligned to a reference axis of the pick and place machine is perpendicular to a major axis of detector  24   b , is: 
               E     aligned_side   ⁢   _a       =       E   1     +         ϕ   1     -       α   1     ⁢   _side   ⁢   _a       T               Equation   ⁢           ⁢   4             
 
Where α 1— side_a is the angle formed at point source  12  between the line to O 1  on detector  24   b  and the line to S 1 , and θ 1  is the angle formed at source  12  between the line to O 1  on detector  24   b  and a reference axis in the pick and place machine. The width of the component, W ac , can be calculated as:
 
 W   ac   =L   a   +L   c   Equation 5
 
And the offset of the nozzle axis  30  (the axis of rotation) from the center of the part along the line W is given by: 
               F     a   ⁢           ⁢   c       =         L   c     -     L   a       2             Equation   ⁢           ⁢   6             
 
   The computation process described mathematically by Equations 1-6 can be optionally repeated for the remaining two opposing sides of component  100 , from which orthogonal width and offset can be computed. This process can be iteratively applied to the component  100 , where the values L a , L b , L c , L d , (length of sides of component  100 ) can be derived from any sequence of available minimums cast by sources  12 ,  14  upon detectors  24   b ,  24   a  as determined by the sequencing of energizing of sources  12 ,  14  and the rotation of the component  100  with respect to these sources. 
     FIG. 9  is a diagrammatic view of a component orientation and placement detection system  210  in accordance with an aspect of the present invention.  FIG. 9  is somewhat similar to  FIG. 1 , and like components are numbered similarly. System  210  includes sources  212 ,  214  which are arranged to direct illumination  216  upon component  218  from at least two different angles. Sources  212 ,  214  can be any suitable light sources as long as they provide illumination of sufficient intensity as considered from each source. Thus, sources  212 ,  214  can be incoherent or coherent illumination sources. Preferably, source  212 ,  214  are laser diodes, but in some embodiments, sources  212 ,  214  are light emitting diodes. Sources  212 ,  214  can be positioned to provide illumination in substantially the same plane, as defined by either of the sources and two points on the detector (a beginning and an ending pixel on the detector). 
   Divergent illumination from sources  212 ,  214  passes through optical element  217  which functions to reduce the degree of divergence of the illumination, and preferably substantially collimate, light passing therethrough. As illustrated, illumination passing through element  217  from source  212  forms a first beam  219  having a reduced divergence, while that from source  214  forms a second beam  221  having a reduced divergence. Preferably, optical element  217  is a lens that can be either spherical or cylindrical. However, a cylindrical lens is preferred. The illumination emerging from element  217  is less divergent, providing a more compact ray bundle than would otherwise be present, thereby speeding computation of component alignment, since less component rotation is required. Additionally, those skilled in the art will recognize that optical element  217  is disposed backwards from the optically ideal orientation. In this manner, element  217  provides a flat surface proximate the sensing field  223 . The provision of a flat surface by element  217  proximate the sensing field provides a convenient seal in system  210  against contaminants. 
   In accordance with one aspect of the present invention, filter  225  is disposed proximate detector  224  in order to reduce ambient light falling on detector  224 . Filter  225  can filter based on incident light angles, and/or wavelengths. 
   Those skilled in the art will recognize that for a four-sided component, complete component measurement can be effected in about 225 degrees of rotation (180 degrees to image both edges+45 degrees maximum to image the first edge). This is significantly faster than requiring a complete component rotation. 
   In some cases, the pick-and-place machine may not have any a priori knowledge of component size. In such cases, the machine can perform a “source scan” where a plurality of sources are sequentially energized to determine if any of the sources are disposed relative to the component to cast at least one shadow portion on at least one detector. If such combination is found, component measurement and alignment can be performed with the selected detector/source combination(s). 
   Operation of embodiments of the present invention generally involve the following steps. The first step is calibrating the source, nozzle and detector positions with respect to each other. There are a number of techniques that can be employed for this operation. For example, calculation of the positions of the various sensor components can be performed by placing the sensor with test components fixed in position in a coordinate measuring machine and then using the coordinate measuring machine to identify the relative position of all of the test components such that the position of the ray that is incident from the light source or sources onto the detector is known with respect to the nozzle position and detector position. 
   As a second step, the shadow or shadows from each component cast upon the detector by light incident from the source or sources has a characteristic intensity profile that is processed to extract an edge. The edge position can be interpolated to subpixel position. Such interpolation can be effected using any number of techniques including centroid calculation or curve fitting. This, then, relates a particular edge position to an encoder position and a known source ray position. Then, the defined edge of the shadow provides an (r, θ) pair where θ is the position of the encoder that is on the nozzle shaft or attached to the nozzle shaft indicating its relative angular position, and (r, θ) is the distance from the source to the edge position on the detector that defines the position of the component at that specific point in angular space and time. The (r, θ) pairs are collected during the rotation of the component on the nozzle. These (r, θ) pairs are used to derive, using known geometric techniques as per  FIG. 7  (r, θ, B 1 ) where θ is used with α to calculate angular part orientation, component information including: component width, component length, nozzle off-set of rotation center x, nozzle off-set of rotation center y, and the angular position of a defined frame of reference of the component with respect to the nozzle angular position. With this information, the component location can be translated into the specific pick and place machine&#39;s frame of mechanical reference via software and the component can be properly positioned to be placed upon its target location on the printed circuit board. 
   Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. For example, multiple portions of detector  24  could be placed within the same plane or without the same plane. Further, such detector portions need not be physically adjacent but may be segments of detectors such that the multiple nozzles&#39; position with respect to the light sources and detectors allow components to be imaged on such detector portions based upon selection of sources that are turned on with respect to components and detector portions.