Abstract:
An optical imaging apparatus comprising a linear array-based camera, using a positional encoding technique highly insensitive to transient and steady state mechanical tolerances in the mechanical scanning system, with the capacity to capture a three dimensional image of a part with enough precision to allow accurate measurements of the part&#39;s features to be made.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of patent application Ser. No. 09/245,434, filed Feb. 5, 1999, now U.S. Pat. No. 6,160,910 which application claims benefit of provisional application No. 60/110,598 filed Dec. 2, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to high precision cameras of the type which are used to capture a video image of an object with enough precision to allow information to be derived from the video image sufficient to provide accurate measurements of the object for purposes of quality control or other applications requiring accurate dimensional information. 
     2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98 
     Even the human eye with its remarkable ability to capture huge amounts of optical information cannot make measurements with precision and accuracy sufficient for quality control of parts requiring highly precise tolerances. Failure to achieve proper measurements can result in a wide range of problems. For example, failure to maintain dimensional tolerances for parts in an automobile engine may result in problems ranging from decreased system life to increase probability of failure under out of the ordinary conditions. Even where later system testing at a manufacturing facility can detect problems resulting from failure to meet dimensional tolerances, unacceptably high rejection rates on account of defective systems can result. 
     Moreover, even when human eye is capable of performing a required inspection, such factors as fatigue, lighting, distraction and so forth make human inspection unreliable. 
     Today, in an attempt to minimize those applications where human optical inspection is employed, to avoid the sometimes unpredictable problems caused by fatigue, distraction and other factors, industry has turned increasingly toward the implementation of computerized inspection systems. With such systems, however, the resolution of the optical inspection apparatus is far below that of the human eye. 
     Currently, many electronic imaging cameras use two dimensional arrays of light sensitive elements, sometimes of the type known as charged coupled devices (CCD) as photodetectors. The purpose of these devices is to convert an optical image into a video image. There are many relatively low priced color and black and white array CCD detectors available for video imaging, but they produce low quality images, as alluded to above. More particularly, CCD detectors and other video imaging devices suffer from a relatively low pixel count. For example, CCD photodetector arrays have the ability to produce quality images with a resolution of approximately 2048 by 2048 pixels. However, these arrays are presently very expensive. Moreover, these very large arrays tend to have defects such as inoperative pixels, inoperative clusters of pixels, or inoperative lines of pixels. When very high quality images are required this type of electronic imaging system is not only very expensive. Such systems may not even be capable of performing a high-quality, high precision measurement. 
     Linear photodetectors cost much less than array detectors because they have far fewer pixels and thus have correspondingly much higher manufacturing yields. Linear photodetectors, obviously, however, are capable of imaging only one line of information in an image that any given point in time using the single line of photo sensitive devices which they have. Accordingly, the linear photodetector must therefore scan the entire image, line by line. 
     The same is achieved by using a mechanical scanning assembly for moving the linear photodetector across the image plane in the camera. Generally, systems of this type derived image data by 1) relying upon the precision of the steady state operation of the mechanical scanning assembly, 2) assuming identical transient translational movements during the initiation of a scan, and 3) assuming that translational movement is uniform over time. Such a system, while suitable for making high quality digital images for commercial photography, is inappropriate for use in making high precision measurements. 
     More particularly, mechanical irregularities in the scanning assembly make the generation of highly precise image information impossible, thus making the image data captured by such systems on suitable for the purpose of confirming dimensional tolerances in a precision manufacturing environment. 
     Accordingly, it would be advantageous to have a device that will capture a single image of a part with enough precision that accurate measurements can be made of the features of such a part. 
     SUMMARY OF THE INVENTION 
     The invention, as claimed, is intended to provide a remedy. It solves the problem of how to provide a linear array-based camera with the capacity of capturing a three dimensional image of a part with enough precision to allow accurate measurements of part features to be made. Moreover, the same is achieved using a positional encoding technique highly insensitive to transient and steady state mechanical tolerances in the mechanical scanning system. 
     In accordance with the present invention, a positional encoder is coupled to a scanning line array detector. The scanning mechanism moves the linear array along the image plane of a lens. As the linear array moves, each time a predetermined number of resolution steps, corresponding to a resolved distance, are measured by the encoder, the linear array is directed to acquire a line image. In this way, an array of line images, which are precisely spaced, are generated, allowing the precise construction of the entire image on one focal plane. The linear array and focusing optics can then be moved vertically to a different focal plane of the object. The vertical movement of the assembly is in predetermined increments, and also measured by a positional encoder. The scanning process is then repeated on the second focal plane. After repeating the process for all required focal planes, the entire three dimensional image may then be sent to a computer which, using known techniques for detecting object boundaries from digital images, determines the three dimensional position and configuration of the features and compares them to the standard, determining whether the same are within specified tolerances. The focusing optics may be telecentric which may provide for better gauging performance. 
     Alternatively, in accordance with the present invention the linear array can remain stationary while the three dimensional image of the object is captured. This is accomplished by placing the object on a stage in a known position coupled to a horizontal positional encoder, then horizontally moving the stage through the image capture area of the linear array. As the stage moves, the computer will signal the linear array to send an image back to the computer at a predetermined increment. The linear array and focusing optics can then be vertically moved to a predetermined vertical position corresponding to a new focal plane of the image. Then the horizontal imaging process can be repeated for each new focal plane of the image. 
     After repeating the process for all required focal planes, the entire three dimensional image may then be sent to a computer which, using known techniques for detecting object boundaries from digital images, determines the dimensional position and configuration of the features and compares them to the standard, determining whether the same are within specified tolerances. 
     Alternatively, in accordance with present invention the linear array can sequentially acquire an image based on a clock pulse internal to the camera or data acquisition electronics. In this case, the positional encoder is used to precisely control the speed of the scanning mechanism and line image acquisition is synchronized to provide a desired number of pixels per unit length in the direction of scanning, thus achieving high-resolution imaging and the stability needed for precision measurements. 
     More particularly, in order to compensate for repeatable non-linearities and inconsistencies in scanner motion, a high precision optical reticle comprised of a number of fiducial indices is employed. The reticle is optically projected onto a portion of the image plane where the linear array is scanning. More particularly, the reticle may be projected to form an image which coincides with the path of one or more photosensitive elements at one end of the linear detector array. In this way an image of the indices will be present on the captured image. From these indices a computer system can calculate the appropriate pixel to inch ratio for the image and further compensate for any non-linearities and inconsistency in scanning motion. 
     As an alternative to this structure for determining the position of the linear array, an electromagnetic transducer, of the type having printed circuit primary convolutions on a printed circuit scale and secondary convolutions on a printed circuit slider may be employed. 
     An optical illumination system can be coupled to the motion of the scanning linear array detector, such that a suitably intense bar of illumination can be projected only on the area of the part that is currently being imaged onto the linear array. This optical system will typically comprise a point source of light such as a laser or LED coupled to a telecentric lens by a cylindrical optical lens and a beamsplitter placed in front of the scanning linear array. Moreover, the same optics which image a part on the linear photodetector array will function equally well at the same time to project light onto the area of part being scanned by the camera. From the point of view of the point on the part being imaged and within the field of view, the illumination will appear to be coming from the image plane. This illumination bar could also have a repeating pattern that will effectively be focused on the part within the field of view. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     One way of carrying out the invention is described in detail below with reference to the drawings which illustrate one or more specific embodiments of the invention and in which: 
     FIG. 1 is a top view of a precision dimensional camera constructed in accordance with the present invention; 
     FIG. 2 is a side elevational view of the camera illustrated in FIG. 1; 
     FIG. 3 is a block diagram of the control system of the present invention; 
     FIG. 4 is a block diagram of an alternative embodiment of the control system of the present invention; 
     FIG. 5 is a table depicting encoder deviation as taken by a laser inferometer; 
     FIG. 6 is a side view of the present invention depicting an illumination system; 
     FIG. 7 is a side elevational view of an alternative embodiment of the present invention; 
     FIG. 8 is a top view of the movable stage in accordance with an alternative embodiment of the present invention; 
     FIG. 9 is a cross section taken along lines  9 — 9  of FIG. 8; 
     FIG. 10 is a block diagram depicting the control system of an alternative embodiment of the present invention; 
     FIG. 11 is a top view of an inventive illumination system of the present invention; 
     FIG. 12 is a view along lines  12 — 12  of FIG. 11 depicting an inventive illumination system in accordance with the present invention; 
     FIG. 13 is a side elevational view of an alternative embodiment of the present invention; and 
     FIG. 14 is a side elevational view of another alternative embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, a high precision framing camera constructed in accordance with the present invention is illustrated. Line scan camera  10  can be driven by a motor  12  coupled to a gearbox  16  by a drive shaft  14 . Rotation of drive shaft  14  by motor  12  causes gears within gearbox  16  to rotate drive screws  18 . 
     Drive screws  18  are threaded to mate with a tapped block support  20 . Support  20  defines within itself a threaded hole  21 , whose threads mate with the threads on its respective drive screw  18 . Rotation of the drive screws  18  will cause supports  20  to move in the directions indicated by arrow  23 . In accordance with preferred embodiment of the invention, both of the drive screws  18  have identical pitch threads. Accordingly, translational movements of each of the supports  20  are identical to each other. Whether translational movement will be to the right or to the left will depend upon the direction of angular movement of screws  18 . 
     A linear array  22  comprises a plurality of detectors  25 . In accordance with a preferred embodiment, line array  22  has approximately 4096 detectors arranged in a straight line, one adjacent the other. An array suitable for use in the present invention is the CCD array manufactured by Dalsa Inc. of Waterloo, Ontario Canada and sold under its part number IL-PI array. 
     Line array  22  is mounted on and extends between the two supports  20 , whereby translational movement of the supports  20  results in a corresponding translational movement of the array  22 . In accordance with the preferred embodiment of the invention, an elongated light source  24  is also coupled to this assembly, by having each of its ends secured to one of the supports  20 . Because of the proximity of light source  24  to line array  22 , light source  24  is coupled to the same optical system by means of a beam splitter as detailed below. 
     In the embodiment illustrated in FIG. 1, an electromagnetic position transducer is employed to determine the translational position of linear array  22 . A positional encoder  27  comprises a slider  26  is mounted on one of the supports  20 . Slider  26  is electromagnetically coupled with scale  28  to provide a signal which allows precise detection of the position of linear array  22 . Once the linear array has reached each of a set of predetermined points, as determined by slider  26 , at which points line images are to be acquired, the image output of the linear array is downloaded to form a line in the raster image being acquired by the camera. A complete image can then be reconstructed by combining the line images associated with all of the points in the set of predetermined points. The spacing of these lines is based on the distance between reads as determined by slider  26 . 
     For the purpose of focusing an image in the image plane, line scan camera  10  is equipped with a coupling lens  30 , as is illustrated most clearly in FIG. 2. A fifty percent reflective and fifty percent transmissive beamsplitter  32  is positioned below lens  30 . Beamsplitter  32  passes a portion of the light, forming the image of an object  36  being imaged, coming from object  36  through objective lens  34  toward coupling lens  30 . Coupling lens  30  functions to image the object being imaged in image plane  37  where it is captured by the linear array. 
     Beamsplitter  32  also reflects a portion of the light, forming the image of the object being imaged, and coming from object  36  through objective lens  34  to another coupling lens  38 . Coupling lens  38  couples this image to a camera  40 , a standard resolution 768×492 pixel video camera Cohu Model 2100, for viewing by an individual monitoring the system. 
     Generally, the inventive system is controlled by a computer  41  in the control system illustrated in FIG.  3 . Computer  41 , which may be a personal computer, receives positional information from positional encoder  27 . This is information regarding the position of linear array  22 . The positional information is processed by computer  41 . Computer  41  outputs motor control signals to motor  12 . Translational mechanics  43  are mechanically coupled to and driven by motor  12 . Translational mechanics  43  are also mechanically coupled to and move linear array  22  along image plane  37  of object  36 . 
     When linear array  22  is positioned over object  36 , computer  41  signals linear array  22  to trigger a “read” of the detectors contained within linear array  22 . The video information captured by the linear array of detectors is then sent to computer  41  for storage. Motor  12  is then signaled by computer  41  to drive translational mechanics  43  which in turn moves linear array  22  into position for the next “read” of the linear array of detectors. When linear array  22  is in position for the next “read” of the detectors, computer  41  signals linear array  22  to trigger the “read”. 
     Computer  41  processes the positional information provided by positional encoder  27 . When linear array  22  moves a predetermined increment computer  41  will trigger a read of detectors  25 . The predetermined increment is based upon the overall distance the linear array must move to adequately capture the image of object  36 , divided by the width of the image taken by detectors  25 . Therefore if the overall distance is 10 units and the detectors can capture an image with a width of 2 units, there would be 5 incremental divisions at which the computer will trigger a read of the detectors. 
     Once the linear array has been moved over the entire image, or the necessary portion, and detector reads have been performed at the appropriate incremental positions, computer  41  can then assemble each individual read into a composite of the entire image. The reconstructed image can be compared with known dimensional tolerances and the proper precision measurements can be taken. 
     When it is desired to operate the system of the present invention, an object  36  is placed within the field of view by a conveyor or other appropriate method. Light rays emitted by a light source  24  pass through coupling lens  30 , beamsplitter  32 , and objective lens  34  thereby illuminating object  36 . Bundles of light are then reflected by object  36 , represented by a single principle ray  43 , pass back through objective lens  34 , and into beamsplitter  32 . 
     A portion of light ray  43 , represented by ray  45 , is reflected by beamsplitter  32  through coupling lens  38  and into camera  40  for viewing by a user. 
     Another portion of light ray  43 , represented by ray  47 , passes through beamsplitter  32  where coupling lens  30  focuses the image upon image plane  37 . Computer  41  then transmits a read signal to linear array  22 , triggering a read of detectors  25  in the first incremental portion of the image. Video information of the first incremental portion is sent to computer  41  for storage and further processing. Computer  41  then signals motor  12  to drive translational mechanics  43 , which in turn moves linear array  22  to the next incremental position. Positional encoder  27  transmits the positional information of linear array  22  to computer  41 . When computer  41  determines that linear array  22  has been properly advanced to the next incremental position, a read signal is transmitted to linear array  22  thereby triggering a read of detectors  25  in the second incremental portion of the image. Video information of the second incremental portion is sent to computer  41  for storage and further processing. Computer  41  continues this incremental process until the complete image is captured. 
     Once the complete image has been captured, computer  41  can than assemble the entire image by placing each incremental portion of the image in sequential order. The completed image can than be measured by computer  41 . 
     Alternatively, as seen in FIG. 4, signal conditioning electronics can be employed to control the movement of linear array  22 . An encoder  42  which may comprise a slider and a scale sends a raw signal  44  to a signal electronics board  46 . Board  46  comprises signaling electronics which interpret the raw signal and send a pulse  48  to the control board  50  for linear array  22 . The signaling electronics  46  can be programmed to count a certain number of encoder signals before sending the pulse to control electronics  50 . Once control electronics  50  receives pulse  48  from signaled electronics  46  a detector read of line array  22  is initiated. 
     By using encoder signals to trigger a pulse which in turn causes a read of the linear array of detectors the lines can be spatially separated at a variable but well defined rate. This ensures that the distance between images is accurately spaced which enables high precision reconstruction of the entire image. 
     The line image captured by linear array  22  is then sent to imaging electronics  52  which process the image. The image can be reconstructed line by line based upon the distances between each “read”. 
     Any inconsistencies in motion can be compensated for by the use of a high precision reticle, as illustrated in the schematic of FIG. 6 b,  comprised of a number of fiducial indices. A light source  33  can output light rays which can be collimated by use of lens  35 , to provide collimated back light for optically projecting reticle  31  onto a portion of the image plane. Reticle  31  can be optically projected on one edge of the linear array  22  as it is being scanned. If reticle  31  is not touching the linear array of detectors than it must be imaged upon the array. The indices will then be present on the captured image once it is processed by imaging electronics  52 . From these indices a computer system can calculate the appropriate pixel to inch ratio for the image and further compensate for any inconsistencies in scanning due to motion. 
     Alternatively a laser interferometer can be used to compensate for any linear variations in encoder response. These variations can be plotted and observed. This can be accomplished by using a computer to capture the image and compensate for any deviations in measurement accuracy with in a table containing data of encoder response errors. Therefore this invention removes any variability in scanning created by variations in more control, velocity, backlash, or any mechanical irregularities in the motion of the drive screw. 
     In the example shown in FIG. 5, a 1:1 optical system is shown. This assumes the magnification to equal 1. Therefore an object which measures exactly 2.000030 inches we would subtract 0.000030 inches from the measurement to correct it. As can be seen line  54  represents encoder deviation from the laser interferometer reading. 
     An optical illumination system can be coupled to the linear array such that a very intense bar of illumination can be projected only on the area of the object that is currently being imaged on to the line array. As shown in FIG. 6 an optical illumination system  60  can be coupled to linear array  22 . Optical illumination system  60  comprises a beamsplitter  62 , collimating optics  64 , and a laser or other point source of light  66 . 
     In this illumination system laser  66  acts as a point source emitting light rays which pass through collimating optics  64 . Once the light rays pass through collimating optics  64 , they are dispersed along the length of linear array  22 . A transmissive beamsplitter  62  reflects a portion of the light rays onto the portion of object  36  which is within the field of view of detectors  25 . From the point of view of object  36 , the illumination will appear to be coming from image plane  37 . 
     An alternative embodiment is shown in FIGS. 7-9. In this embodiment a optical imaging device  110  is illustrated. The inventive device has a platform  112  which is illustrated in detail in FIGS. 8 and 9. 
     Platform  112  can move horizontally and vertically in relation to a stationary linear CCD array  114 . Horizontal movement of platform  112  is driven by a motor  115  coupled to a gear box  116  by a drive shaft  117 . Rotation of drive shaft  117  by motor  115  causes gears within gear box  116  to rotate drive screws  118 . 
     Drive screws  118  are threaded to mate with a tapped block support  120 . Block support  120  defines within itself a threaded whole  121 , whose threads mate with the threads on its respective drive screw  118 . Rotation above the drive screws  118  will cause block supports  120  to move in the directions indicated by arrows one  23 . In accordance with this embodiment of the invention, both of the drive screws  118  have identical pitch threads. Accordingly, translational movements of each of the block supports  120  are identical to each other. Whether translational movement will be to the right or to the left will depend upon the direction of angular movement of screws  118 . 
     A stage  122  is mounted to block supports  120 . In accordance with the preferred embodiment four block supports are used. However, this number may be increased or decreased depending on the size and weight of stage  122 . Stage  122  may be translucent to allow light to pass through it from the bottom to illuminate or assist and illumination of the object to be viewed. Translational movement of the block supports  120  directly results in a corresponding translational movement on the stage  122 . 
     As illustrated in FIG. 8, an optical position sensing encoder is employed to determine the translational position of stage  122 . Alternatively, a electromagnetic position transducer or other type of position detecting and transmitting device known in the art may be used. A positional encoder  127  comprises a slider  126  mounted on one of the block supports  120 . Slider  126  is electromagnetically coupled with scale  128  to provide a signal which allows precise detection of the position of stage  122 . Once the stage has reached a set of predetermined points, as determined by slider  126 , the image output by linear CCD array  114  is downloaded to form a line and the raster image being acquired by the camera. A complete image can then be reconstructed by combining the line images associated with all of the points and the set of predetermined points. The spacing of these lines is based on the distance between reads as determined by slider  126 . 
     Vertical movement of platform  112  is driven by motor  130  which is coupled to gearbox  132  by a drive shaft  134 . Rotation of drive shaft  134  by motor  130  causes gears within gearbox  132  to rotate vertical drive screws  136 . 
     Vertical drive screws  136  are threaded to mate with tapped vertical block supports  138 . Vertical block supports  138  comprise a threaded hole  140 , whose threads mate with the threats on its respective vertical drive screw  136 . Rotation of vertical drive screws  136  will cause vertical block supports  138  to move in the directions indicated by arrows  142 . In accordance with this embodiment of the invention, all of the vertical drive screws  136  have identical pitch threads. Accordingly, translational movements of each of the vertical block supports  138  are identical to each other. Whether translational movement be up or down will depend upon the direction of a slider  146  movement of the vertical drive screws  136 . 
     Vertical block supports  138  are mounted to a frame  144  which supports the entire horizontal movement assembly earlier described. Frame  144  is mounted on and extends between the vertical block supports  138 . Therefore translational movement of the vertical block supports  138  result and a corresponding transitional movement of the platform  112 . 
     An optical position sensing encoder is preferably employed to determine the vertical translational position of stage  122 . However, a positional encoder which comprises a slider  146  and a scale  128  can be used. Slider  146  is mounted on one of the vertical block supports  138 . Slider  146  is electromagnetically coupled with scale  148  to provide a signal which allows precise detection of the position of stage  122 . Once the stage  122  has reached each of a set of predetermined vertical points, as determined by slider  146 , the image output by the linear CCD array is downloaded to form a line in the raster image being acquired by the camera. A complete image can then be reconstructed by combining the line images associated with all of the points and the set of predetermined points. The spacing of these lines is based on the distance between reads as determined by slider  146 . 
     The illumination of object  150  is provided by light assemblies  170 . Light assemblies  170  consist of a lamp  172 , a fiber optic bundle  174 , a fiber optic light line  175  (preferably of the type manufactured by Fostic Fiberoptics of Auburn, N.Y.), and cylindrical lens  180 . As shown in FIGS. 11-12, light assemblies  170  are placed around object  150 . 
     The process of capturing a three-dimensional image is illustrated in the schematic diagramed and FIG.  10 . When stage  122  positions object  150  in the initial position in the initial horizontal plane, computer  151  signals linear array  114  to trigger a read off the detectors. The video information captured by linear array  114  is then sent to computer  151  for storage. Motor  115  is then signaled by computer  151  to drive translational mechanics  153  and which can turn move stage  122  and object  150  into position for the next read off linear array  114 . When stage  122  and object  150  are in position for the next read, computer  151  signals linear array  114  to trigger the read. 
     Computer  151  processes up a positional information provided by horizontal positional encoder  127 . When stage  122  moves a predetermined increment computer  151  will trigger a read off linear array when  14 . The predetermined increment is based upon the overall distance the linear array must move to adequately capture the image of object when  50 , divided by the width of the image taken by linear array  114 . If the overall distance is 10 units and the detectors can capture and image with a width of two units, there would be five incremental divisions at which the computer will trigger a read of the detectors. 
     Alternatively the system may overlap images captured by linear array  114 . Therefore if the overall distance is 10 units and detectors can capture and image with a width of two units, there would be nine incremental divisions at which the computer could trigger a read of the detectors. The first incremental division would begin at location  0 , 0  and end at location  0 , 2 , width being next incremental division beginning at location  0 ,  1  and ending at location  0 ,  3 . This overlapping of images allows greater pixel density which is interpreted through the use of software by computer  151 . 
     Once linear array  114  and has captured the entire image, or the necessary portion, in the first horizontal plane, computer  151  can then assemble each individual read into a composite of the first horizontal plane. Computer  151  then signals motor  130  to drive translational mechanics  153  which in turn move stage  122  vertically into the correct incremental position for reading the next horizontal plane. Once stage  122  has moved into position vertically, in other horizontal read of the object can take place. This process is then repeated until the entire three dimensional image of the object has been captured. Computer  151  can then assemble each individual horizontal read into a three dimensional composite on the entire image. The reconstructed image can be compared with known dimensional tolerances in the proper precision measurements can be taken. 
     An alternative embodiment of the present invention is illustrated in FIG.  13 . Camera  210  comprises a housing  212  which contains focusing optics  211  which focused the image of an object  213  along in image plane which can be captured by a linear array of detectors  214 . Housing  212  is coupled to a vertical positioning device  216 . Vertical positioning device  216  comprises a support arm  218 , translational mechanics  220  and rigid support member  222 . Translational mechanics  220  is coupled to a positional encoder which can incrementally control the vertical movement of housing  212 . 
     Object  213  is placed upon horizontal positioning device  224 . Horizontal positioning device  224  comprises a motor  226  which is coupled to a gear box  228  by a drive shaft  230 . Rotation of drive shaft  230  by motor  226  causes gears within gear box  228  to rotate drive screws  232 . Drive screws  232  are threaded to mate with a tapped block support which is coupled to a stage  234 . Rotation of the drive screws  232  will cause stage  234  to horizontally move in the directions indicated by arrows  236 . Furthermore, stage  234  may be equipped with another set of translational mechanics, or compound translational mechanics which permit movement along both the x and y axis of the plane in which stage  234  resides. This feature allows stage  234  to move in multiple directions. A horizontal positioning encoder is electromagnetically or optically coupled with a scale to provide a signal which allows the precise positioning of stage  234 . 
     Similar to the earlier illustrated embodiments, when it desired to capture a three-dimensional image in accordance with the present embodiment, the object is moved by horizontal positioning device  224  through the focal point of linear array  214 . A computer signals linear array  214  to send and image of object  213  at predetermined increments. Once the object has been captured at one focal plane the vertical positioning device moves housing  212  and linear array  214  to a new vertical position allowing the process to be repeated and thereby capturing images on a new focal plane. A computer can then reconstruct a three-dimensional image of the object by using images from each focal plane. This three-dimensional image can then be compared to known tolerances to determine whether the same are within the standard tolerances for the object. 
     FIG. 14 illustrates another embodiment of the present invention much like the previous embodiment but differing in that an alternate scanning system is employed. This alternate scanning system may also be employed in any of the other embodiments as well. A three-dimensional representation of object  313  is obtained from a repetitive series of vertical scans instead of horizontal scans. This approach works especially well with an optical system having a relatively high numerical aperture, preferably NA. 0.2 or higher. It is preferred to employ an optical system having a relatively small depth of field. As object  313  is moved along the optical (Z) axis, by positioning device  316  or by translational mechanics within stage  334 , either towards or away from camera/lens assembly  310 , only a small portion of object  313  (small both in terms of displacement parallel to the z axis and small in the plane of focus, which is perpendicular to the z axis) will be in focus on linear array  314 . Scanning repetitively (at different points along the z-axis) along the length of linear array  314  will generate an image of object  313  that amounts to a “Y-Z” or a cross sectional scan. This is achieved by using only those parts of each line scan which represent the highest contrast image for that particular part of the line scan, thus collecting an in focus image segment for the entire line scan using only a small part of each line scan, which small parts when put together form a complete in focus line scan. At the same time, each part has associated with it z axis data, thus giving depth information and effectively a three-dimensional picture of the visible section of the top of object  313  being scanned. This three-dimensional picture is referred to as a cross-section. 
     In this embodiment, housing  312  is coupled to a positioning device  316  capable of vertical and horizontal movement. Vertical positioning device  316  comprises a support arm  318 , translational mechanics  320  and rigid support member  322 . Translational mechanics  320  is coupled to a positional encoder which can incrementally control the vertical and horizontal movement of housing  212 . 
     The surface of object  313  will be indicated on this image by areas of high contrast. Out of focus areas will have much lower contrast where adjacent pixels have very close to the same gray scale values. The sensor for linear array  314 , due to its high data rates, can very quickly generate this cross sectional scan, and a computer can also analyze the image quickly. By mechanically repositioning object  313  on stage  334  relative to camera/lens assembly  310  along an axis orthogonal to the optical axis and using an encoder to precisely control this step interval, a series of these cross-sectional scans may be produced. After completing a series of scans in this fashion, a three dimensional representation of object  313  is derived. 
     A reticle with a series of highly contrasting features may be projected onto object  313  to enhance focus determination by the computer. In particular, in accordance with the invention, one may project a series of narrow bars separated by a distance equal to the line width onto successive linear portions of the object lying along the length of that portion of the object being scanned which lie under the linear array which is generating a picture of a narrow linear region of the object (switch along with other narrow linear region of the object will form an image of the object). For each linear portion of the object, the distance between the linear array and the object is set at a plurality of different distances along the z-axis and depth information is determined artificially by noting the difference in intensity levels between each black bar and its adjacent fully illuminated area. When the difference in intensity is at maximum, it indicates that the corresponding portion of the narrow linear region (for example extending in the direction of the x-axis which is perpendicular to the z-axis) of the object is in focus. Accordingly, a three-dimensional contour can be generated for the particular linear region. After the position along the z-axis has been determined for each part of the particular linear region, an image of that particular part of the particular linear region may then be generated by simple illumination without the projection of bars. The images of all of these particular parts may then be put together and the three-dimensional picture or cross-section of the particular linear region generated. Imaging is then shifted along the y axis (which is perpendicular to the x-axis and the z-axis), and the processes repeated to obtain another three-dimensional picture or cross-section of the next adjacent particular linear region. This is repeated until a complete three-dimensional picture of the object is achieved. If desired, the object may be rotated 180 degrees to achieve a three-dimensional picture of the opposite side of the object. 
     FIG. 14 also illustrates a different embodiment of an system for providing light on object  313 . Linear illuminators  370  are used to enhance the contrast of various features on object  313  and its image, and provide sufficient illumination for camera  310 . Preferably, four illuminators  370  are placed in quadrants spaced at 90-degree intervals. Each illuminator  370  projects a bright line of light unto object  313 . Illuminators  370  are configured to direct light on the particular area of object  313  being imaged by linear array sensor  314 . The illuminators  370  may be independently controlled by a computer to set light levels that enhance image processing for object  313 . 
     While an illustrated embodiment of the invention has been described, it is, of course, understood that various modifications of the invention may be made by those of ordinary skill in the art without departing from the spirit and scope of the invention which is limited and defined only by the appended claims.