Abstract:
A high speed high precision laser based alignment sensor system for use on surface mount component placement machines. A laser system is utilized to correctly align and position component parts which range between 0.02 inches and 2.0 inches in size. The laser sensor system consists of a laser light source which is passed through a collimating lens and then through an aperture to create a stripe of collimated laser light which is focused past the component being aligned to strike a multi-element CCD sensor array. The sensor system is mounted directly on the carrying mechanism for the surface mount component placement machine. During transit of the component between the bin of components is to be placed, the component is rotated and the shadow which falls on the detector array is monitored. When the minimum width of shadow is detected, the correct angular orientation is determined, the average of the edges of the shadow when compared with the center of the quill determines the coordinate (X,Y) location of the component on the quill. Two alignments normally occur displayed by 90°. Thereafter, the sensor sends correcting signals to the component placement machine to assure the correct angular orientation and the correct X,Y position for the component to be placed on the circuit board by the component placement machine.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to control system which precisely align electrical components, both as to angular orientation and coordinate (X,Y) location for precise placement via pick-and-place systems such as surface mount component placement machines. More specifically, the invention relates to a non-contact laser based sensor system which precisely determines and allows a pick-and-place system to connect the angular orientation of a component and the coordinate positioning of the component for precise placement of the component by a component placement machine on a circuit board or other work surface. 
     There are two types of component placement machines in common use today, one of which is a cartesian system where one or more vacuum quills are used to travel to a bin, pick up a component, properly orient the component and carry it to a circuit board or other work piece to precisely place the component in its proper location with the leads making proper contact with the circuit connections which are subscribed on the circuit board or work place. Another type of placement system in use is a carousel or turret placement system where components are picked up from the bin and stepped through stations located around the perimeter of a circular component carrying mechanism for placement on the circuit board. It is believed that the present invention will be most useful with cartesian systems which must accurately place components with the highest degree of speed and accuracy. 
     The electrical components must be placed precisely on the circuit board, to ensure proper electrical contact, thus requiring correct angular orientation and lateral positioning. Angular orientation and lateral positioning are most commonly achieved today through mechanical means. A vacuum quill picks up the part to be placed. During travel between the component bins and the circuit board, four jaws or hammers, which are suspended from the fixturing device, travel downwardly and strike the component on all four sides with substantially equal force. The intent of such a mechanical system is to shift the component on the vacuum quill so it achieves the correct angular orientation, 0 degrees deviation, and also to center it on the vacuum quill. The striking of such components can cause damage such as microcracking and other such components. It is also extremely difficult to achieve the very high degree of accuracy both as to angular orientation and lateral position that is required by the design rules in use in today&#39;s technology where lead spacing and widths are only 10-25 mils wide. To accommodate different component sizes, six different sizes of jaws may be required which can lead to high expense. 
     A number of non-contact higher precision methods have been proposed. However, light based systems of the past have had difficulty in achieving the high speed and high accuracy which is required for today&#39;s technology. 
     Vision based systems using a TV camera are capable of achieving high accuracy. However, they are one of the most expensive of systems proposed and they require a deviation in the path of the quill from the bin to the TV station, and then to the work piece or circuit board which substantially slows the process. The laser sensor of the instant invention is connected in a manner to surround the component carrying quill which transports the component directly, without deviation, to the appropriate site on the circuit board to achieve a time saving of approximately a factor of two. In addition, it is sometimes difficult to distinguish the particular parameters of very small components being placed by such systems from the quill upon which the components are mounted. 
     Light sensing systems have also been proposed where a component is interposed in the light path of a collimated beam of light and the intensity of the light is detected by a single photodetector or a pair of photodetectors with a maximum light intensity indicating the narrowest shadow and thus proper angular orientation of the component. However, it is difficult for such systems to handle the range of components that are placed and to achieve the accuracy required for alignment. The dimensions of components to be placed normally vary between 0.02 inch and 2.0 inches. If a single photodetector system is designed large enough to detect shadow variations for a 2.0 inch part, as it must be, the fractional variation caused by rotation of a 0.02 inch part has such little effect on the total light intensity that it is virtually undetectable. For two detector systems, the component part must be precisely aligned between the two detectors with the ratio of light falling on each detector being analyzed to determine edge positions. However, it is extremely difficult to mechanically align photodetectors to make such a measurement. The uniformity of light must be precise and such a system cannot detect component lead positions since shadows of the leads are not distinguishable from shadows of the body of the component. 
     Finally, it has also been proposed that a series of laser light sources be aligned with a series of laser light detectors. Such a design overcomes some of the problems associated with the proposals for a single detector or pair of detectors. However, the degree of accuracy that can be achieved can be no more than the spacing of the individual laser sources one from the other. The minimum spacing would be given by the size of a laser diode source, which is 0.5 millimeter. This minimum spacing still would be too large for reliable component position detection. The required physical spacing will also be negatively affected by diffraction effects to further limit accuracy of such a design. Also, it is believed that the cost of such a system involving many laser sources would also be prohibitively expensive. 
     What is needed to achieve component placement for current technology is a component system which can rapidly, in a few hundred milliseconds, align a range of parts varying between 0.02 inches and 2.0 inches with an angular orientation accuracy of less than 0.03° and with lateral position accuracy of better than 0.001 inches. The present invention is specifically addressed to this current need. 
     SUMMARY OF THE INVENTION 
     The present invention is a laser based system designed to accurately align component parts which range in size from 0.02 and 2.0 inches. To achieve this result, an extremely high speed high accuracy laser based system is secured to the moving placement mechanism. The sensor system includes a laser diode, the light from which is collimated with a collimating lens and passed through a slit aperture. This provides a stripe of laser light which passes by an is blocked by the component whose alignment is being sensed. The shadow can by the component is detected by a linear array detector. Typical spacing between detector elements is 10-14 micrometers. The number of detector elements is chosen to accommodate the largest component to be placed. Data read from the detector array is analyzed to detect the leading edge and the trailing edge of the shadow which is cast upon the detector array. Since only the shadow edges are detected and analyzed, the same degree of accuracy is achieved when aligning a 0.02 inch part as is achieved when aligning a 2.0 inch part. Using data processing algorithms described below, angular orientation can be achieved at much less than 0.03 degrees and lateral alignment can be achieved with an accuracy of less than 0.001 inch. 
     It is also possible to detect not only the orientation and lateral positioning of the component body, but also the electrical leads from the component body which are the actual elements which must be precisely aligned on the circuit board upon which the component is to be placed. 
     It is an object of the invention to accurately and precisely determine angular orientation and lateral position of components for placement by a component placement machine. 
     It is an object of the invention to accurately determine angular orientation of a component to be placed by a component placement machine with an accuracy of better than 0.03 degrees. 
     It is an object of the invention to determine lateral position of a component to be placed by a component placement machine to an accuracy of better than 0.001 inch. 
     It is an object of the invention to determine angular orientation and lateral placement of a component to be placed by a component placement machine in less than 500 milliseconds. 
     It is an object of the invention to accurately determine the angular orientation and lateral position of leads on a component which is to be placed by a component placement machine. 
     It is an object of the invention to determine angular orientation with a degree of accuracy of greater than 0.03 degrees and lateral position to an accuracy of greater than 0.001 inch for a range of component varying in size from 0.02 inch to 2.0 inch. 
     These and other objects, features and advantages of the invention will become obvious to those skilled in the art upon a review of the following description of the preferred embodiment, the drawings and claims appended thereto. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view showing the environment of the invention. Shown in FIG. 1 is a component bin which contains components which are placed by the component placement machine on a circuit board or work piece. Also shown in FIG. 1 is a component being carried by a quill in the shortest route possible between the component bin and the work piece. 
     FIG. 2 is an elevational view showing in greater detail the component carrying mechanism which includes a rotary motor for rotating the component, a placement head control box and a laser alignment sensor. Extending through the laser alignment sensor is the vacuum quill which holds the components. 
     FIG. 3 is an illustration of the basic elements of the invention which include a laser diode and a collimating lens which causes the light beam or stripe to pass across the component to strike a linear array image sensor. For alignment, the component part is retracted into the laser beam and rotated for measurement. 
     FIG. 4 shows a top plan view of a preferred embodiment of the invention. As shown in FIG. 4, the laser beam is directed to a pair of reflecting mirrors through a collimating lens, past the part, through an optical filter and on to the linear CCD array. 
     FIG. 5 is a sectional side view of the laser sensor of FIG. 4 taken along the line  5 — 5 . FIG. 5 illustrates how the optical path between the laser and collimating lens is folded and hence put into a smaller package via a pair of folding mirrors. 
     FIG. 6 is a schematic illustration of the laser light paths from the laser diode through the collimating lens which distributes the light across the measurement area through a slit aperture to create the stripe of light and on to and past the component part to strike the detector array. 
     FIG. 7 is an illustration of the elements of FIGS. 6 when the component part is mis-oriented. FIG. 7 shows the broad shadow that is cast from corner to corner of the component part. Illustrated above the linear array of FIG. 7 is representative data from the linear array. 
     FIG. 8 shows the same components and elements of FIG. 7 when the component is in alignment. As noted, the shadow or dark portion which is cast upon the linear array is narrower than that in FIG.  7 . The corresponding data from the CCD array shows the narrowing of the shadow as well. 
     FIG. 9 shows a component and the laser stripe across the component. The laser stripe can be positioned to read the body only, both leads of the compound and the body, or only the leads of the component part. 
     FIG. 10 illustrates diagrammatically one method for achieving angle orientation and lateral position. As shown in FIG. 10, a discriminator is used to determine when the data falls below a threshold voltage. The discriminator converts the analog data to a digital representation which can then be used to establish angular orientation and edge positions of the component. Illustrated in FIG. 10 are the data points which are identified with the leading edge and trailing edge of the shadow. Also illustrated on the right side of FIG. 10 is a determination of the lead position which can also be discriminated and converted to a digital representation of the lead alignment. 
     FIG. 11 is a block diagram of the electronic elements which are used to identify and detect the leading edge of the shadow and the trailing edge of the shadow as determined from the detector array and to provide signals to the component placement machine indicating the adjustments necessary to put the component in the correct angular orientation and the correct X,Y location on the circuit board or work piece. 
     FIGS. 12a,  12 b, and  12 c illustrate how other part sizes can be analyzed by the sensor system. FIG. 12a illustrates how a part larger than 2 inches can be aligned and positioned via off-center mounting of the detector relative to the component. FIG. 12b shows the use of additional optical elements to reduce the image of a larger part so that the image can be cast on a detector smaller than the component. FIG. 12c shows the use of additional optical elements to enhance the resolution of the measurements. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1 and 2 illustrate the general environment in which the invention is to be used. FIG. 1 illustrates in diagram form a typical surface mount component placement machine in which one or more vacuum quills  24  are used to sequentially pick up components  30  from predetermined bins  32 , transport them as quickly as possible to a circuit board  34  or other surface upon which the component must be precisely aligned, and place the component  30  accurately at the desired location with the proper alignment of the leads  50  of the component  30  to a wiring layout which has been previously created on the circuit board  34 . For high precision placement, an accuracy in angular alignment or orientation of 0.30 degress with positioning error in the X,Y plane of 0.001 inch is required. Component  30  part sizes typically employed in such a system vary between approximately 20 thousands of an inch in size in two inches in size, although in certain cases larger component 30 sizes are required. 
     Angular orientation is important because of the effect misorientation has on placement of the electrical leads. For the largest component size (e.g. 2 inches) a deviation of 0.10 degrees causes the lead positions at the outer edge of the component to be canted or misplaced by approximately 0.002 inches. It is for this reason that alignment accuracy of 0.03° is an object of the invention. 
     Referring to FIG. 2, the component carrier mechanism  40  is disclosed which includes a rotary motor  41 , and placement head control box  43  including a fixturing device for holding, rotating and retracting the vacuum quill  24 . The rotating fixture rotates the quill for purposes of component  30  pickup, alignment, positioning and placement. Also represented in FIG. 2 are the laser sensors  45  and components  30 , the proper placement of which is the subject of this invention. 
     In the component control box  43 , which is of conventional design, are means for retracting the quill to which the component  30  is attached by vacuum pressure, comprising servomotors, a means to create the vacuum to hold the component to the end of the quill  24 , angular position encoders, force sensors force sensors and the like. Attached to the control box  43  is the laser based alignment sensor  45  which has an aperture  48  therein through which the quill  24  extends and into which the component  30  can be retracted for determination of its angular orientation and for alignment with the center of the quill  24 . 
     FIG. 3 is a schematic representation of the components of the laser sensor  45 . For ease of discussion, a line of sight representation is shown from the laser  60  through a collimating lens  61  past the component  30  and quill  24  to the linear array image sensor  65 . In actual practice, a longer focal length is desired and FIGS. 4 and 5 more accurately represent the actual orientation of a preferred embodiment of the laser  60  and other components. In other words, a shown in FIGS. 4 and 5, a preferred embodiment would include a laser diode  60  directed away from the part, two reflecting mirrors  70 , 72  directing the laser light beam through the collimating lens  61  and a slit orifice  75  past the part  30  with that portion of the laser beam or stripe which passes the edge of the component  30  being filtered by optical filter  26  to strike the linear CCD array  65  to provide the data which is to be processed for angular orientation and X,Y location. It is also possible to use a single reflecting parabolic lens (not shown) in place of the mirrors  70 , 72   
     FIGS. 6 through 8 further illustrate diagramatically the components of the laser based component alignment sensor  45  for surface mount component placement machines and its mode of operation. As diagrammed in FIG. 6, a laser source preferably having a short coherence length is directed, or indirectly through reflecting mirrors  70 , 72  to a collimating lens  61  to provide equal light to all portions of the component  30 . The light pattern cast by the component is detected by the multi-element sensor array  65 . A slit aperture  75  is utilized to assure a uniform strip of light (A, B or C in FIG. 9) which is positioned (A) completely across the component  30 , or (B) across the component  30  and its leads  50  or, in special circumstances, (C) across the leads  50  themselves as shown in FIG.  9 . The light which is not blocked by the component  30  passes the component  30  and strikes a linear CCD detector array  65  such as part no. TC104 manufactured by Texas Instruments Corporation which has 3456 elements, each 10.4 micrometers by 10.4 micrometers configured along a line with center to center spacing of 10.4 micrometers. Interposed between the component  30  and the detector array  65  is the optical filter  76  which is outside of the wavelengths of interest. The data  80  thus captured from the detector array  65  is then processed using one or more of the algorithms which are disclosed in more detail below. 
     The laser source  60  with shorter coherence length is preferred to lessen the effect of speckle from dust or dirt which might occur if a monochromatic laser diode were used. The use of 3,456 detector array elements enables large parts to be measured. The elements are spaced at approximately 0.4 mil centers which enables high accuracy. Sensitivity to minute changes in angular orientation and lateral position is increased dramatically over prior art devices. This is because, for a given photodetector element near the shadow edge, the fractional change in light level can be very large for very small angular rotations. 
     Referring now to FIG. 7, the component  30  is shown with its angular orientation out of alignment. As shown in FIG. 7, a relatively large number of detector elements are blocked from the laser because of the angular misorientation of the component  30  creating a shadow  90 . In addition, there are small areas of laser shadow  93 , 94  striking the array  65  created between the bright portion and the dark portion  90  caused by defraction of the light past the edges of the component  30 . In addition, minutely brighter portions  96 , 97  will be detected adjacent to outer edges of the shadow  90  due to diffraction and reflection of light off the outermost edges of the component  30 . Illustrated in FIG. 7 is the data pattern  80  of the data which is read from the CCD array  65  showing portions  102 , 103  of the detector array  65  which receive unblocked light from the laser source  60 , and then an increase in light from reflection  96 , 97 , a decreasing amount of light in the shadow area  93 , 94  caused by refraction, and the dark shadow area  90  with an identical pattern on complimentary sides of the detector array  65 . FIG. 8 illustrates the light pattern and the data  80  when the component is in angular alignment. 
     As will be obvious from a comparison of FIGS. 7 and 8, angular alignment can be assured by determining when the shadow pattern  90  is narrowest as determined by the data  80  from the sensor array  65 . This can be achieved with a minimum of electronic processing means by following and determining the leading edge of the shadow and  110  and the trailing edge of the shadow  112  and by capturing only data  80  which proceeds and follows the edges  110 , 112  of the shadow. 
     FIG. 10 shows a method of processing the data to a high degree of accuracy. The range of part  30  widths which are to be analyzed by the alignment and position sensor  45  normally range from 0.02 to 2 inches and can be larger. It is neither practical nor necessary to retain and analyze all data  80  from the over 3,000 element diode array  65 . It is necessary to obtain and analyze only the data  80  which is relevant to the edges  110 , 112  of the shadow  90  which is cast by the component  30  on the diode array  65 . Referring to FIG. 10, there are two zones, A-B, C-D of primary interest, one A-B is the leading edge  110  of the shadow  90  and the other C-D is the trailing edge  112  of the shadow  90 . In other words the data is zone A-B defines the edge of the shadow caused by one side of the component, and the zone C-D the edge caused by the opposite side. 
     Using the defined edges  110 , 112 , as shown in zones A-B and C-D, the part  30  can be aligned. Initially the component  30  is picked up in a position which is known to be misaligned and will, hence, cast a larger shadow  90 . The component  30  is then rotated by the component placement head  43  and the angular position at which the shadow  90  width is minimized is noted. The edge positions, when the shadow  90  is narrowest and their deviation from the center of the quill  24  are noted as well. These positions allow calculation of the lateral position of the part. The component can then be rotated 90° and the orthogonal lateral position determined, based again on the comparison of the center of the shadow  90  of the component  30 , as determined by the edge  110 , 112  positions, with the center of the quill  24 . 
     Alternatively a second sensor (not shown) could be used which is orthogonally located relative to the first sensor  45  to determine the orthogonal lateral position. 
     As the width of the shadow  90  decreases due to the component  30  being rotated into alignment, a particular photodiode element located on the edge  110  of the shadow  90  will receive increasingly more light, until the point at which the shadow  90  width is minimum. As the component continues to rotate, the shadow width increases and the amount of light falling on the same photo element will begin to decrease. Thus, we are able to accurately orient the component  30  parallel to the laser beam by finding the position at which the output from the photo element which is determined to be on the shadow edge is maximum, that is it is receiving the maximum amount of light. 
     One method which can be used, which is represented in FIG. 10, is the use of a threshold voltage (V TH ) and a comparator or discriminator which converts the analog data  80  from the diode array  65  to a digital representation  120  by detecting when the voltage on each element of the array  65  falls below the threshold voltage V TH  thereby indicating that the shadow  90  of the component  30  has been detected. 
     Preferably each element in the array  65  is sequentially read at a five megahertz data rate and compared with the threshold voltage V TH . The pixel count, where the data  80  reading first fell below the threshold voltage, is used as a latch signal and the number of data readings immediately preceding and immediately following the first occurrence is stored in a data buffer as the leading edge  110  of the shadow. Although any number of data points can be stored, 32 pixels preceding and following the first latch signal (A-B) has been found satisfactory, providing a total of only 128 items of data (A-B, C-D) necessary to analyze the precise angular orientation and lateral position of the component  30 . 
     Similarly, data is read and stored for the trailing edge of the shadow  112  when the data signals first rise above the threshold voltage V TH . This data is then stored as the data for the current shadow edge positions. 
     The quill then incrementally rotates and the next subsequent scan of the data  80  from the diode array  65  is analyzed. Since the data can be read from the array in less than a millisecond and the component  30  rotates through ninety degrees in approximately 150 milliseconds. The rotational movement has a minor effect on accuracy. For fine pitch alignment the part  30  is rotated more slowly through the area where the first pass established the proper angular alignment. On the next subsequent scan, the leading edge  110  of the shadow  90  is again determined by the pixel count of the diode array location where the voltage first dropped below the threshold voltage V TH . If the leading edge  110  of the shadow  90  is detected at a higher pixel count, this indicates that the shadow  90  has narrowed and the previous data is ignored and new data is stored which indicates the present location of the shadow  90 . The above process is repeated until the narrowest shadow  90  is determined which indicates alignment of the component  30 . 
     Basically, the angular orientation can be determined accurately by a number of algorithms. Proper angle orientation can be established at the angle at which the “edge pixel” intensity is maximized. The above algorithm can also be implemented in binary form as shown in FIG. 10 by using a discriminator and threshold voltage V TH . As the shadow  90  narrows, the light falling upon, and, therefore, the voltage read from any certain photo detector elements will rise above the threshold voltage and then, as the component rotates past alignment. fall below the threshold voltage. Using the binary discriminator the angle at which the voltage rose above threshold and the angle at which the voltage fell below threshold can be recorded. Proper alignment can be determined to be midway between the two angles where the voltage, and therefore the light, reached maximum intensity. Multiple “edge pixels” can be analyzed using this binary method to super resolve the angular position. 
     The leading and trailing edges  110 , 112  of the package shadow can be computed using digitized analog video data. The proper angle orientation will be established at the point at which the shadow width  90  is minimized. Interpolation can also be used to super-resolve the angular position. 
     Similar data analysis can be performed to determine the lateral (X,Y) position by similarly applying the analog threshold to the shadow video data. The package width is the distance between the trailing and leading “edge pixels”. The package center is located midway between the two edge pixels. It is also possible to add a correction factor to allow for the finite width of the diffraction pattern. When the video signal is digitized, numerous image processing algorithms exist for computing the edge locations. As will be obvious, the part is rotated 90° to locate the lateral positions in the orthogonal direction. 
     FIG. 10, a discriminator  130  (shown in FIG. 11) is used which can comprise a comparator which compares the data read from the CCD array  65  to the threshold voltage V TH . As illustrated in FIG. 10, there will be a number of data points A-B, C-D which, because of diffraction and reflection, will be present on the leading  110  and trailing  112  edge of the shadow  90 . However, diffraction and reflection will occur uniformly on both the leading edge and the trailing edge of the shadow and therefore both the angular orientation and the lateral position can be accurately established using this method or algorithm. Data  80  will be collected only in the area A-B of FIG. 10 if the stripe of laser light is positioned at location A shown in FIG.  9 . If the stripe is lowered to Position B of FIG. 9, additional data can be collected to establish the location of the leads  50  attached to the compartment  30 . This is important since it is the leads  50  which must be placed most accurately. The leads  50  will cause a drop in data below the threshold voltage when one or more detector  65  elements are blocked and such data can also be converted to binary  172 ,  182  with the discriminator. Thus the precise location of the leads  50  can be ascertained for purpose of placement. In a similar manner, the quill  24  can be retracted further so that the stripe falls only on the leads as shown as position C in FIG.  9 . The finest pitch components  320  can thus be accurately placed. 
     Referring now to FIG. 11, a block diagram is shown of the processing means  200  used to signal the correction for angular orientation and lateral position. The rotary motor  41  which rotates the quill is mechanically coupled to an angular position encoder and monitor  43  which provides the angular orientation of the quill  24  position and thus the component part  30  to a processor  202 . Prior to calculating a component X,Y location, the X,Y location of the quill  24  is located by inserting the quill  24  alone into the laser beam for precise centering. Thereafter, the sensed X,Y location of the component  30  edges is compared to the center of the quill  24  for purposes of precisely placing the component  80  on the circuit board  34 . Similarly, the angular position encoder  43  is initially calibrated to 0 degrees angle deviation. 
     Since it is an objective of the invention to obtain precise angular orientation and lateral position within a few hundred milliseconds, all processing is done at a very high rate of speed. For example, in a preferred embodiment, the pixel clock and array timing  204  speed is at a five megahertz read rate. The pixel clock or count  206  which indicates which sensor element is being read is connected to an analog to digital converter  208  and to a leading shadow edge discriminator  210  and a trailing shadow edge discriminator  212 . As described above, the discriminator can be a voltage comparator  130  comparing the data reading with a threshold voltage V TH  and the same voltage comparator can be used to discriminate both the leading shadow edge and the trailing shadow edge. 
     The pixel clock and array timing  204  is also connected to the photo detector array  65  for purposes of reading the data from the photo detector elements. All data from the analog digital converter  208  is connected to the leading shadow edge data buffer  214  for both temporary and permanent storage when the shadow edge is detected. At the time that the leading shadow edge discriminator  210  detects data which falls below the threshold voltage V TH , the leading edge is indicated and is connected to the leading shadow edge data buffer  214  as a latch signal  220  to store the data  80  which is relevant to the leading edge  110 . In addition, the leading edge detect signal  224  is also connected to the trailing shadow edge discriminator and data buffer  228  to enable it to detect and store in a similar manner the data  80  when detected for the trailing edge  112 . The buffered data is then connected to the processing unit  202  to perform the calculation to the processing unit  202  to perform the calculations for angle orientation and X,Y lateral position. 
     The output  230  of the processor  202  indicating where angular orientation is aligned is then connected to the component placement machine to assure precise angular orientation when the component  30  is placed on the circuit board  34 . In a similar manner, the X,Y location of the edges of the component  30  are compared to the precise center of the quill  24  and this second signal  235  is also connected to the component placement machine to establish the necessary offset in one or both directions for purposes of precise placement of the component  30  on the circuit board  34 . 
     The following table shows the approximate time and extremely high resolution which can be achieved using the invention in less than 300 milliseconds when picking up the part and checking proper alignment, both angular alignment and lateral position in both orthogonal directions. 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE I 
               
               
                   
                   
               
               
                   
                   
                   
                 Angular 
               
               
                   
                 Action 
                 Time 
                 Resolution 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 (1) 
                 Pick up. 
                   
                   
               
               
                 (2) 
                 Rotate to −5°. 
                 32 ms 
                 No data 
               
               
                   
                   
                   
                 collected. 
               
               
                 (3) 
                 Accelerate from −5° to +45°. 
                 73 ms 
                 0.43° 
               
               
                   
                 Read data while going from −5° to +5°. 
               
               
                 (4) 
                 Decelerate from 45° to 95°. 
                 73 ms 
                 0.43° 
               
               
                   
                 Read data in 85° to 95° interval. 
               
               
                 (5) 
                 Assume component alignment was found to 
               
               
                   
                 be at approximately 85.5°. Alignment 
               
               
                   
                 is known to within ±0.43, so a 1″ 
               
               
                   
                 wide zone centered on 85.5 should be 
               
               
                   
                 searched at lower rotational speed to achieve 
               
               
                   
                 0.03°. 
               
               
                 (6) 
                 Rotate from 95° to 86° at high speed. 
                 44 ms 
               
               
                 (7) 
                 Rotate from 86° to 85° at maximum angular 
                 23 ms 
                 0.03° 
               
               
                   
                 velocity of 43°/sec so that 0.03° resolution 
               
               
                   
                 is obtained. 
                   
               
               
                   
                 TOTAL 
                 245 ms  
               
               
                   
               
             
          
         
       
     
     Since the processing speed is much faster than limitation on mechanical movement, the angular position signal  230  and the X,Y location signal  235  can be rapidly and precisely calculated and fed to the component placement machine for precise and accurate placement of the component  30  in its proper position on the circuit board  34 . 
     As shown in FIG. 12a, larger parts  30  can by accommodated by the system by scanning three of the four sides of the component  30  rotating the component  30  through 270 degrees in 90° intervals. FIGS. 12b and 12c show how additional optics can be used. In FIG. 12b the image  90  cast by a larger part is reduced by two lens  229 ,  231 . Similarly, as shown in FIG. 12c higher resolution can be achieved with similar lens,  229 ,  231  by expanding the image on the photo detector array  65 . 
     Using the foregoing embodiments, methods and processes, a very fast high resolution sensing system is achieved which can precisely locate a component for placement of that component on circuit boards which are within the requirements of today&#39;s technology. It will be clear to those skilled in the art that many and varied modifications and variations can be made in the specific embodiment shown and described such as use of an area array instead of a linear array, or even using the same methods or algorithms in conjunction with a TV camera. All such variations and modifications are intended to be within the scope of the appended claims.