Abstract:
An optical inspection apparatus operates at high speed at very high resolution for detecting defects in flat, polished media in a production environment. The configuration of the first embodiment is used to inspect transparent disks such as those used as disk platters in hard disk drives. The configuration of the second embodiment is used to inspect reflective disks. The configuration of the third embodiment is used to inspect transparent flat panels such as those commonly used in Liquid Crystal Display (LCD) panels. All embodiments use a laser providing a light beam directed to a polygon scanner, which provides a linear scan of the beam. The unit to be inspected is moved such that its entire surface passes the scan path of the light beam. The light beam, after contacting the unit to be inspected, is directed to a parallel detector array, which detects changes in the nominal Gaussian distribution of the light beam that correspond to defects above a programmable threshold level. This parallel detection method allows the inspection apparatus to identify defects much smaller than the diffraction limits of the optics used, and will accurately identify changes in the light beam caused by defects in the media. An automatic media handler loads untested units into the apparatus and unloads and sorts tested units according to the results of the inspection.

Description:
RELATED APPLICATIONS 
     This patent application is related to three other U.S. patent applications entitled: “High Speed Optical Inspection Apparatus for a Transparent Disk and Method Therefor”, “High Speed Optical Inspection Apparatus for a Reflective Disk and Method Therefor”, and “High Speed Optical Inspection Apparatus for a Transparent Flat Panel and Method Therefor” which are assigned to the same assignee as this patent application and which are filed on the same date as the date of this patent application. 
    
    
     FIELD OF THE INVENTION 
     This invention generally relates to optical apparatus and methods, and relates, more specifically, to an optical inspection apparatus and method for detecting faults in flat, polished transparent and reflective media, which inspects with high resolution at high speed with automatic handling of the media to allow the apparatus to be used effectively in a production inspection environment. The apparatus of the present invention is well-suited to the inspection of transparent and reflective disks used as platters for hard disk drives, and to the inspection of transparent flat panels such as those commonly used in Liquid Crystal Display (LCD) panels. 
     DESCRIPTION OF THE PRIOR ART 
     Disks for hard disk drives require a surface that is flat to a high degree of accuracy, and that is free from defects such as scratches and chips. Likewise, flat panels also have requirements for flatness and absence of defects. Some optical inspection systems have been used with limited success in inspecting media such as disks and flat panels, but do not provide the accuracy or speed that is needed in a production environment. 
     Dark field microscopes and scatterometers are inspection apparatus well-known in the art. A dark field microscope can somewhat accurately locate surface defects, but takes too long to inspect to be effectively used in a production environment. A scatterometer is faster than a dark field microscope, but has less accuracy (detects fewer defects). Both the dark field microscope and the scatterometer have low detection sensitivity to shallow defects or defects that have a depth less than the wavelength of the light used, which cause a phase shift in the light beam but do not diffuse (scatter) the light in different directions. An interferometer, which is well-known in the art, is suitable to detecting phase shifts, but takes substantial time and effort to set up, limiting its use to laboratory environments. 
     The inherent limitations of the prior art inspection systems have limited their use in industrial production environments. Indeed, the most common inspection method used in a production environment is a manual, visual inspection by human inspectors, which hold the disk or flat panel in their hands and move it in ambient or special light looking for the presence of scratches, chips and other defects. This inspection method is labor intensive, relatively slow, and subject to human errors such as missed defects which the human eye cannot easily distinguish. 
     Therefore, there existed a need to provide a high speed optical inspection system and method which has a high sensitivity to defects which can be used to inspect both transparent and reflective media in a production environment. This inspection system includes automatic handling of the media, high speed inspection, and high resolution to detect defects smaller that the spot size of the beam and/or more shallow that the wavelength of light used. The increased speed of this apparatus increases throughput of the production system, and assures that any mistakes or defects introduced by human inspectors is eliminated. 
     SUMMARY OF THE INVENTION 
     It is an object of this invention to provide a high-speed optical inspection apparatus and method suitable for production testing of transparent disks. 
     It is another object of this invention to provide a high speed optical inspection apparatus and method suitable for production testing of reflective disks. 
     It is a further object of this invention to provide a high speed optical inspection apparatus and method suitable for production testing of transparent flat panels. 
     It is a still further object of this invention to provide a high speed optical inspection apparatus and method which is computer-controlled using an IBM PC-AT computer or equivalent. 
     It is still another object of this invention to provide a high speed optical inspection apparatus and method with surface inspection which has a high speed optical scanner to provide linear movement of the beam across the width of the media, and a media actuator to position each portion of the media in the path of the linear movement of the beam, thereby completely inspecting the entire face surface of the media. 
     It is yet another object of this invention to provide a high speed optical inspection apparatus and method with edge inspection (if required) using a light source and linear Charge-Coupled Device (CCD) cameras which scan the edge of the media as it is moved as needed during surface inspection. 
     It is still another object of this invention to provide a high speed optical inspection apparatus and method which has an automatic media handler for automatically loading the media into the apparatus and for automatically unloading the media from the apparatus. 
     It is a still further object of this invention to provide a high speed optical inspection apparatus and method which detects both phase and amplitude changes of the light beam using multiple detectors to sense changes in the nominal Gaussian distribution of the light beam. 
     It is yet another object of this invention to provide a high speed optical inspection apparatus and method which has a trigger detector within the path of the scanning light beam to provide a signal to synchronize the controlling computer to the scan of the light beam. 
     According to the present invention, an optical inspection apparatus is provided. This inspection apparatus is controlled by an IBM PC-AT computer or equivalent, and has a typical color monitor, printer and keyboard. An Optical Inspection Assembly is provided which comprises a Surface Inspection Assembly and an Edge Inspection Assembly (if required). The Surface Inspection Assembly nominally comprises a laser light source which transmits a light beam, a high-speed Optical Scanner, Scanning Optics, Detection Optics, and a Parallel Detector Array within a Detector. The computer controls the automatic loading and unloading of the media by sending appropriate control signals to the Automatic Media Handler. The computer also controls the movement of the media across the linear scan of the Optical Scanner within the Surface Inspection Assembly to assure the entire surface of the media is inspected. While the media is being moved, both the Surface Inspection Assembly and the Edge Inspection Assembly (if present) simultaneously perform their respective inspections. Surface defects are detected by changes in the nominal light level or in the two-dimensional Gaussian distribution of the detected light beam as explained in more detail below. Edge defects are detected using cameras to monitor the illuminated edges of the media. Any defect detected that exceeds a programmable threshold is reported to the computer, causing the inspection to fail. 
     The Optical Scanner causes a linear scan of the light beam across one axis of the media. After contact with the media the light beam goes to a Parallel Detector Array. This array is typically a matrix of photodiodes or Charge-Coupled Devices (CCDs) upon which the light beam is projected. This matrix configuration provides a two dimensional Gaussian response with respect to light intensity (amplitude). Any defect in the media deflects light from the Parallel Detector Array (causing a change in the nominal light level) or shifts its phase (causing a change in the Gaussian distribution), both of which are detected by the processing electronics coupled to the Parallel Detector Array. Thus the processing electronics simply look for changes in the nominal level or distribution of the Gaussian response provided by the Parallel Detector Array in response to a nominal light beam. Any defect that exceeds a programmable threshold value is reported to the computer, which causes the inspection to fail. Note that the Automatic Media Handler sorts the tested media according to the pass or fail results of the inspection. 
     In the first embodiment of the present invention, the inspection system is used to inspect transparent disks. In this configuration the light beam in the Surface Inspection Assembly originates in the laser, is transmitted through a filter, and is transmitted to the aperture of the Optical Scanner, which reflects the light beam off the moving polygonal scanner head, causing the light beam to sweep across the Scanning Optics. The Scanning Optics make the light beam normal to the surface of the disk and focused at the center of the disk media. On the opposite side of the disk, Detection Optics collimate the light beam and project it onto the Parallel Detector Array, which detects defects in the disk above a programmable threshold. Once the Optical Scanner beam completes one complete scan, the disk is then rotated to the next position, and the scanning continues in like manner until the entire surface of the disk has been inspected. The computer controls the rotation of the disk to assure the entire surface is scanned. At the same time the disk is rotating, the Edge Inspection Assembly simultaneously inspects both the inner and outer edges of the disk for defects above a programmable threshold. If either the Surface Inspection Assembly or the Edge Inspection Assembly detects a defect greater than their programmed thresholds, a fault signal is sent to the computer to indicate the disk failed the inspection. 
     In the second embodiment of the present invention, the inspection apparatus is used to inspect reflective disks. Reflective disks can be scanned using two different configurations of the inspection apparatus of the present invention. In the first configuration the apparatus is used to scan both sides of the reflective disk within the same scan. This is accomplished by placing the disk under test near the center of the scanning beam sweep, with its face normal to the direction of the sweep. Two mirrors are placed at 45 degree angles with respect to the two faces of the disk such that the Optical Scanner beam is reflected onto the two faces. The Scanning Optics and the mirrors focus the Optical Scanner beam on the two faces of the reflective disk. As the Optical Scanner beam begins its scan, the first mirror reflects the beam to the outer edge of the first face of the disk. The reflective face of the disk reflects the beam back to the mirror, which reflects the beam back to the Optical Scanner. This reflected beam is distinguished from the transmitted beam using a beam splitter between the laser and the Optical Scanner. The reflected beam is then projected on the Parallel Detector Array, which detects defects in the disk above a programmable threshold. As the Optical Scanner beam moves, the beam on the disk moves from outside to inside on this first side of the disk. The first side of the disk is completely scanned when the Optical Scanner beam has traveled about half of its scan distance. Near the center of the scan the Optical Scanner beam contacts the outside edge of the disk. As the Optical Scanner beam continues its scan, the second mirror reflects the Optical Scanner beam, beginning at the inside of the disk on the second face of the disk, and moves from inside to outside. By the time the Optical Scanner beam has completed one linear scan, both sides of the disk have been inspected along the scan line. The disk is then rotated to the next position, and the scanning continues in like manner until the entire surface of both sides of the disk have been simultaneously inspected. At the same time the disk is rotating, the Edge Inspection Assembly simultaneously inspects the outer edges of the disk for defects above a programmable threshold. If either the Surface Inspection Assembly or the Edge Inspection Assembly detects a defect greater than their programmed thresholds, a fault signal is sent to the computer to indicate that the disk failed the inspection. 
     In the second configuration of the second embodiment of the present invention, the disk is placed normal to the Optical Scanner beam, in the same position as the transparent disk of the first embodiment of the present invention. The disk reflects the beam, which is distinguished from the transmitted beam using a beam splitter between the laser and the Optical Scanner. The reflected beam is then projected on the Parallel Detector Array, which detects defects in the disk above a programmable threshold. With this configuration, only one side of the disk is inspected at a time, requiring the automatic media handler to turn the disk over after the first side is inspected for inspection of the second side, or requiring two separate scanning systems to inspect both sides simultaneously. 
     In the third embodiment of the present invention, the inspection system is used to inspect transparent flat panels, such as those commonly used in LCD panels. The size of a flat panel can be much greater than the size of disks commonly used in hard disk drives. An inspection system similar to that of the first embodiment could be used for small transparent flat panels where the size of the flat panel is smaller than the size of the Optical Scanner lens. However, many flat panels are larger than a practical lens, making a different method desirable to accommodate larger flat panels. 
     Placing the Optical Scanner at a distance from the Scanning Optics less than the focal length of the Scanning Optics causes the light beam to diverge at the Scanning Optics, making the beam sweep a distance larger than the diameter of the lens. The beam is focused at the center of the transparent flat panel media by the Scanning Optics. On the opposite side of the flat panel is a strip of a spherical mirror which reflects the divergent beam back through the Scanning Optics to the Optical Scanner. This reflected beam is distinguished from the transmitted beam using a beam splitter between the laser and the Optical Scanner. The reflected beam is then projected on the Parallel Detector Array, which detects defects in the disk above a programmable threshold. In this particular application, the flat panel is placed on an actuator that positions the flat panel such that the scanning begins at the top of the flat panel and moves down. Once the Optical Scanner beam completes one scan, the panel is raised to the next position, and the scanning continues in like manner until the entire surface of the flat panel has been inspected. The computer controls the movement of the flat panel to assure the entire surface is scanned. If the Surface Inspection Assembly detects a defect greater than its programmed threshold, a fault signal is sent to the computer to indicate the flat panel failed the inspection. 
     The foregoing and other objects, features and advantages will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the optical inspection apparatus of the present invention. 
     FIG. 1 a  is an enlarged view of the Optical Inspection Assembly shown in FIG.  1 . 
     FIG. 2 is a block diagram of the optical inspection apparatus of FIG.  1 . 
     FIG. 3 is a perspective view of the first embodiment of the present invention for inspecting transparent disks. 
     FIG. 4 is a perspective view of the second embodiment of the present invention for inspecting reflective disks. 
     FIG. 5 is a block diagram of the Surface Inspection Assembly used in the first embodiment of the present invention shown in FIG.  3 . 
     FIG. 6 is a top view of the Optical Scanner and optics function in the Surface Inspection Assembly shown in FIG. 5 for transparent disks. 
     FIG. 7 is a top view of the Optical Scanner and optics function in an alternative configuration of the Surface Inspection Assembly used for inspecting reflective disks. 
     FIG. 8 is a block diagram of the Edge Inspection Assembly used in the first embodiment of the present invention shown in FIG.  3 . 
     FIG. 8 a  is a cross-sectional view of the transparent disk shown in FIG. 8 showing how the waveguide properties of the transparent disk cause illumination of the inner edges with a light source shining on the outer edge. 
     FIG. 9 is a partial perspective view of one particular implementation the outer radius inspection assembly shown in FIG. 8 using a camera having a linear CCD array. 
     FIG. 10 a  is a front view of the transparent disk shown in FIG. 3 showing the scanning in the r direction, and rotation of the disk in the theta direction. 
     FIG. 10 b  is an enlarged view of the scanned portion of FIG. 10 a  showing how the combination of the linear travel of the beam and the rotation of the disk results in complete scanning of the entire surface of the disk. 
     FIG. 11 a  is three dimensional representation of a typical Gaussian (distribution of light intensity (amplitude). 
     FIG. 11 b  is a three dimensional representation of a typical Gaussian distribution of light phase. 
     FIG. 12 is a block diagram of the Surface Inspection Assembly used in the second embodiment of the present invention shown in FIG.  4 . 
     FIG. 13 a  is a top view of the Optical Scanner and optics function in the Surface Inspection Assembly shown in FIG. 11 for reflective disks. 
     FIG. 13 b  is enlarged view of the circle in FIG. 13 a  showing how the beam is focused on the surface of the disk and reflected back. 
     FIG. 14 is a perspective view of the third embodiment of the present invention for inspecting transparent flat panels. 
     FIG. 15 a  is an elevational view of the disk of FIG.  3  and FIG. 4 showing the roller configuration which rotates the disk during inspection. 
     FIG. 15 b  is an elevational view of the disk and rollers of FIG. 15 a  showing how the top roller moves to facilitate loading and unloading of the disk by the Automatic Media Handler. 
     FIG. 15 c  is an elevational view of the disk and rollers of FIG. 15 b  showing how the movement of the roller shown in FIG. 15 b  and the operation of the lifter allow the automatic media handler to load and unload the disk into the apparatus of FIGS. 3 and 4. 
     FIG. 15 d  is a side view of two of the rollers and the disk shown in FIG. 15 a  taken along the line  15   d — 15   d  showing the slot in the rollers for holding the disk in place during rotation. 
     FIG. 16 is a front view of one specific configuration of the Parallel Detector Array which detects changes in the amplitude and/or phase of the Optical Scanner beam. 
     FIG. 16 a  is a front view of another specific configuration of the Parallel Detector Array which detects changes in the amplitude and/or phase of the Optical Scanner beam. 
     FIG. 16 b  is a top view of the optics function of an alternative parallel detection configuration which detects changes in the amplitude and/or phase of the Optical Scanner beam. 
     FIG. 16 c  is a front view of another specific configuration of the Parallel Detector Array which detects changes in the amplitude and/or phase of the Optical Scanner beam. 
     FIG. 17 is a block diagram of the Surface Inspection Assembly used in third embodiment of the present invention shown in FIG.  14 . 
     FIG. 18 is a t view of the Optical Scanner and optics function in the Surface Inspection Assembly shown in FIG. 17 for transparent flat panels. 
     FIG. 18 a  is an enlarged view of the circular area shown in FIG.  18 . 
     FIG. 19 is a flow chart of the control software operation for the apparatus of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows the optical inspection apparatus  40  of the present invention, comprising an IBM compatible PC-AT computer  46  or equivalent, a keyboard  48 , a color monitor  50 , an operator panel  56 , an Optical Inspection Assembly  52  located on table  54 , and an Automatic Media Handler  42  (typically a robot) to automatically load and unload the media to be inspected ( 44 ,  45 , and  47 ) into the Optical Inspection Assembly  52 . FIG. 1 a  is an enlarged view of the Optical Inspection Assembly  52  of FIG. 1, showing the specific configuration used in the first embodiment of the present invention for inspecting transparent disks. FIG. 2 is the block diagram of the apparatus  40  of the present invention, with numbers that correspond to numbers in FIG. 1 representing the same components. The apparatus shown in FIG. 2 includes a printer  58 , and hood switches  60  for detecting when the apparatus  40  is ready for operation. These hood switches  60  act as safety devices, inhibiting operation of the apparatus  40  until the apparatus  40  is in the correct configuration with all hoods secured properly. The Optical Inspection Assembly  52  comprises a Media Movement Driver  62 , a Media Movement Actuator  64 , a Surface Inspection Assembly  66 , an optional Edge Inspection Assembly  68 , and the Unit Under Test  45 . 
     The Automatic Media Handler  42  first loads the Unit Under Test  45  into the Optical Inspection Assembly  52 . The Surface Inspection Assembly  66  then begins its scan of the surface of the Unit Under Test  45 . At the same time the Edge Inspection Assembly  68 , if present, begins inspection of the edges of the Unit Under Test  45 . Both the Surface Inspection Assembly  66  and the Edge Inspection Assembly  68  perform only a linear inspection, and thus depend on the Media Movement Actuator  64  to move the Unit Under Test  45  such that the entire surface is inspected by the Surface Inspection Assembly  66 , and such that the entire edge is inspected by the Edge Inspection Assembly  68  (if present). 
     The Surface Inspection Assembly  66  and the Edge Inspection Assembly  68  both have programmable thresholds that determine the characteristics of allowable defects. If either of these assemblies detects a defect greater than the programmed threshold, a fault signal is sent to the computer  46  to indicate that the inspection failed. The computer  46  causes the Automatic Media Handler  42  to place good units (those that pass inspection) in one place, and to place bad units (those that fail inspection) in a different place. In a fully automated system, an automated cart or conveyer would deliver uninspected units and take away both good and bad inspected units as the apparatus  40  requires. 
     The foregoing discussion applies to all configurations of the apparatus  40  of the present invention. The three distinct embodiments of the present invention relate to the different configurations and combinations of the Surface Inspection Assembly  66  and the Edge Inspection Assembly  68 , which vary according to the physical configuration of the Unit Under Test  45 . Note that the particular configuration shown in FIG.  1  and FIG. 1 a  for illustrative purposes is the first preferred embodiment of the present invention. 
     In the first embodiment of the present invention, the apparatus  40  is used to inspect transparent disks. In this configuration, the Edge Inspection Assembly  68  of FIG. 2 is present, and includes simultaneous detection of defects on both the outer edges and the inner edges of the disk. The Optical Inspection Assembly  52  for this embodiment is shown in FIG. 3. A laser  70  provides the light beam  72  used to inspect the Transparent Disk  74 . The laser  70  must have a minimum spatial and temporal coherence greater than the defects to be measured. The coherence of the laser  70  is related to its optical Signal to Noise (S/N) ratio, while the power of the laser  70  is related to its electrical S/N ratio. The light beam  72  passes through Filter Optics  76 , which increases the spatial coherence of the beam  72  and shapes and directs the beam  72  to the mirror  78 , which directs the beam  72  to an aperture  69  on Optical Scanner  80 . The aperture  69  on Optical Scanner  80  is shown in FIG. 1 a . Referring again to FIG. 3, Optical Scanner  80  has a rotating polygonal head  82  with reflective faces. The beam passes through the aperture (not shown in FIG. 3) onto the rotating polygonal head  82 , which causes the beam  72  to sweep across the Scanning Optics  84 . If the polygonal head  82  rotates clockwise as shown, the sweep of the beam  72  will be from left to right on the Transparent Disk  74 . 
     The Scanning Optics  84  are placed at the precise distance from the polygonal head  82  of Optical Scanner  80  defined by the focal length of the Scanning Optics  84 . The Transparent Disk  74  is placed at this same distance from the Scanning Optics  84 , such that the focal point of the beam is at the exact center of Transparent Disk  74 . After passing through the focal point in the center of Transparent Disk  74 , the beam  72  diverges and contacts Detection Optics  86 , which is placed at a distance from the Transparent Disk  74  that corresponds to its focal length. The Detection Optics  86  cause each point along the beam scan to project on the Parallel Detector Array  88  within Detector  90 , which is also placed at a distance from the Detection Optics  86  that corresponds to the focal length of Detection Optics  86 . 
     One specific implementation of Parallel Detector Array  88  is shown in more detail in FIG.  16 . An array of light sensitive devices  94  is provided, typically a photodiode array. Each light sensitive device  94  provides an electrical signal proportional to the intensity of light it detects. A nominal beam spot  92  is shown, which is smaller than the matrix as shown. This type of a spot  92  of laser light on Parallel Detector Array  88  causes a two-dimensional response with respect to intensity or amplitude, which is represented in FIG. 11 a . Likewise, this type of spot  92  causes a two-dimensional response with respect to changes of phase, which is represented in FIG. 11 b . The changes of phase will create an interference pattern between the center and outer rim of the beam  72 , causing a change in the ideal Gaussian distribution. 
     Note that the light sensitive devices  94  of Parallel Detector Array  88  could also be an array of CCDs, and could be arranged in any physical configuration, such as circular or concentric rings of individual detectors, as shown in FIG. 16 a . In addition, two concentric ring detectors in the configuration shown in FIG. 16 c  could be used to form Parallel Detector Array  88 . Detector  94   a  detects the center portion of the beam, while detector  94   b  detects the outer portion of the beam, which has nominal spot size  92  as shown. 
     FIG. 16 b  shows an alternative arrangement which uses two Parallel Detector Arrays  88 . Beam  72  has a nominal spot size  92  as shown. Beam  72  is projected onto a transparent substrate  87  which has a small reflective portion  89 , and is positioned at a 45 degree angle with respect to the beam  72  as shown. In this manner the center portion  85  of beam  72  is reflected off the reflective portion  89  of transparent substrate  87  to a Parallel Detector Array  88   a  as shown in the figure. The outer portion  83  of the beam  72  passes through the transparent substrate  87  onto a second Parallel Detector Array  88   b . In this manner the two Parallel Detector Arrays  88   a  and  88   b  act in parallel to detect any change in the nominal Gaussian distribution of light within beam  72 . 
     Note that the Parallel Detector Arrays  88   a  and  88   b  shown in FIG. 16 b  could be replaced with a single detector, since the two detectors  88   a  and  88   b  act in parallel, and can therefore detect with only two sensors changes in the nominal Gaussian distribution of the beam  72 . Neither the number, type of device used nor the physical arrangement of these devices is critical to this invention. The primary inventive feature regarding the Parallel Detector Array  88  is the use of more than one optical detector in parallel to detect changes in a nominally Gaussian distribution of light within the spot of the optical beam  72 . 
     By measuring changes in the Gaussian distribution of light, the apparatus  40  of the present invention has a much higher resolution than prior art optical inspection systems, which are limited by the diffraction limits of the optics and specific configuration of the system. By measuring changes in the Gaussian distribution of the beam  72 , the apparatus  40  measures changes in the electromagnetic fields in a general point in space, which therefore removes the classical diffraction limit experienced by prior art systems. Since the Parallel Detector Array  88  can detect changes in both phase and amplitude of the nominal Gaussian distribution of light (phase changes are detected by interference between the center and rim of the beam), a change in the surface characteristics caused by even a very narrow or shallow defect will interfere with the rest of the field, and will be detected. This allows the lateral resolution of the apparatus  40  to be from 100 to 1000 times greater than the diffraction limit, since phase changes are detected as well as amplitude changes. In addition, the longitudinal sensitivity within the diffraction limit is interferometric, while the adjustment sensitivity is only dependent on the depth of field. These features provide for a highly sensitive inspection apparatus  40 , which can detect any changes of the optical characteristics of the inspected surface on the order of {fraction (1/100)} to {fraction (1/1000)} of the diffraction limit in all three axes. 
     Referring again to FIG. 3, rollers  96 ,  98  and  100  comprise the Media Movement Actuator  64  shown in FIG. 2 for this particular embodiment of the present invention. Only one of these three rollers  96 ,  98  and  100  are motor-driven, with the computer  46  controlling the motor drive through communicating with the Media Movement Driver  62  as shown in FIG.  2 . For illustration purposes, it will be assumed that roller  96  is the one roller that is driven by a motor, and that it rotates in a clockwise direction as shown. As the Optical Scanner  80  sweeps the beam  72  repeatedly from left to right on Transparent Disk  74 , the computer  46  causes roller  96  to rotate clockwise, which causes Transparent Disk  74  to rotate counter-clockwise. In this manner the entire surface of Transparent Disk  74  is scanned when it has rotated one revolution. FIG. 3 shows a lifter  99 , which acts in conjunction with the Automatic Media Handler  42  (not shown) to load untested disks into the Optical Inspection Assembly  52  and to unload tested disks from the Optical Inspection Assembly  52 . The detailed operation of the loading and unloading function can be best understood in reference to FIGS. 15 a-c . These three figures illustrate how the Transparent Disk  74  is unloaded from the Optical Inspection Assembly  52  by the Gripping Arm  101  of the Automatic Media Handler  42 . FIG. 15 a  shows a Transparent Disk  74  while it is being rotated under test by rollers  96 ,  98  and  100 . Lifter  99  is positioned away from the Transparent Disk  74  during testing. When testing is complete, the computer  46  stops driving roller  96 , causing the rotation of the rollers  96 ,  98  and  100  to stop. The computer  46  then moves the roller  98  out of the way as shown in FIG. 15 b . Once roller  98  is out of the way, the Gripping Arm  101  of Automatic Media Handler  42  is placed into the proper position, and lifter  99  then lifts the Transparent Disk  74  away from rollers  96  and  98 , to a position where Gripping Arm  101  can close and thereby grip the Transparent Disk  74 , as shown in FIG. 15 c . This process is reversed for loading disks into the Optical Inspection Assembly  52 . FIG. 15 d  shows a side view of the rollers  98  and  100  and the Transparent Disk  74  shown in FIG. 15 a , illustrating the narrow slots or “V” grooves  103  used to hold the disk  74  in the proper position on the rollers  96 ,  98  and  100 . 
     FIG. 5 shows the configuration of the Surface Inspection Assembly  66  shown in FIG. 2 used in the Optical Inspection Assembly  52  for the first embodiment of the present invention, which is used to inspect transparent disks. Note that many of the numbers in FIG. 5 correspond to components shown in FIG.  3 . The laser  70  is powered by a Laser Power Supply  71 , and provides beam  72 , which passes through Filter Optics  76 . The mirror  78  of FIG. 3 is not shown in FIG.  5 . The light beam  72  contacts the Optical Scanner  80 , which provides a linear scanning action of the beam  72  across Trigger Detector  73  and Scanning Optics  84 . Trigger Detector  73  is placed at the beginning position of the scan path of beam  72 , and provides an electrical SYNC signal to the computer  46  when the beam  72  contacts it to synchronize the sweep of beam  72  with the rotation of the Transparent Disk  74  and the output of Detector  90 . Note that the Optical Scanner  80  can be switched on or off by the computer  46  giving the appropriate command to the Scanner Motor Driver  51 , which controls the Scanner Motor  53 . Also note that the Trigger Detector  73  can be mounted anywhere within the scan path of beam  72 . In the configuration illustrated in the figures, Trigger Detector  73  is mounted on the side of the Scanning optics  84 . The Trigger Detector  73  could, in the alternative, be placed in the scan path of beam  72  next to the Transparent Disk  74 . By placing the Trigger Detector  73  next to the Scanning Optics  84 , no optic field of Scanning Optics  84  is taken by Trigger Detector  73 . 
     As shown in FIG. 5, the angle sweep of Optical Scanner  80  is converted by the Scanning Optics  84  to a sweep of parallel beams, each contacting the Transparent Disk  74  normal to its surface. The beam  72  continues through the Transparent Disk  74  to Detection Optics  86 , which directs each beam to the Parallel Detector Array  88  of Detector  90 . The nominal Gaussian output of Parallel Detector Array  88  is processed by analog circuitry in the Analog Process block  91 , which is powered by Power Supply  97 . Analog Process  91  receives a threshold control signal  95  from the computer  46  and detects any change in the Gaussian distribution of beam  72  which corresponds to a defect greater than the programmed threshold. When such a defect occurs, the Analog Process  91  signals the computer  46  that the inspection failed by asserting a Fault signal  93 . The computer  46  will then nominally abort the inspection of the Transparent Disk  74 , and cause the failed disk to be placed in the area of bad disks by the Automatic Media Handler  42 . 
     FIG. 6 clearly represents the operation of the Scanning Optics  84  and the Detection Optics  86 . With the configuration as previously described, the beam  72  is reflected off the Optical Scanner  80 , and first contacts the Trigger Detector  73 , then continues to scan across the Scanning Optics  84 . Beam  72  first comes in contact with Scanning Optics  84  on the left side of the Scanning Optics  84 , as represented by  72 A in FIG.  6 . Scanning Optics  84  focuses the beam to a small spot at the exact center of the Transparent Disk  74  as shown. After passing through the focal point at the center of the Transparent Disk  74 , the beam  72 A begins to diverge. The beam  72 A then contacts Detection Optics  86 , which directs the beam  72 A to the Parallel Detector Array  88  within Detector  90 . Note that Optional Detection Optics  81  may be used to magnify the beam  72 , to correct for wandering of beam  72 , or for other purposes as required. 
     As the Optical Scanner beam  72  continues its sweep, it will come to the position shown by  72 B, and eventually to the position shown by  72 C. Note that for each position of the beam  72 , a different spot on the Transparent Disk  74  is in the path of the beam  72 , and the resulting beam is projected onto the Parallel Detector Array  88  as shown. Note that this method can only be accomplished by placing the Optical Scanner  80  at a distance d from Scanning Optics  84  equal to the focal length of Scanning Optics  84 . The center of the Transparent Disk  74  is located at this same distance from the Scanning Optics  84 . In like manner, Detection Optics  86  is located this same distance from the center of the Transparent Disk  74 , and the Parallel Detector Array  88  is located this same distance from the Detection Optics  86 . In this configuration the size of the beam  72  at the Optical Scanner  80  is nominally the same size as the beam  72  at the Parallel Detector Array  88 . 
     As the scanning of beam  72  takes place along a linear radius of the Transparent Disk  74 , the Transparent Disk  74  is rotated one complete revolution to assure the entire disk surface is inspected. While this rotation of the disk takes place, both the inner and the outer edges of the disk are inspected for defects using the Edge Inspection Assembly  68 , shown in detail in FIG.  8 . The Edge Inspection Assembly  68  is comprised of an Outer Radius Inspection Assembly  128  and an Inner Radius Inspection Assembly  130 . Within Outer Radius Inspection Assembly  128 , a Power Supply  102  powers a light source  104 , which passes through Projection Optics  106  to the outer edge of the Transparent Disk  74  as shown. Each disk nominally has two beveled edges  108  and  110  and a flat edge  109  on its outer edge as shown, and two beveled edges  112  and  114  and a flat edge  113  on its inner edge as shown. As shown in the figure, beveled edge  108  and half of flat edge  109  are inspected by Detector Optics # 1   116 , beveled edge  110  and the other half of flat edge  109  are inspected by Detector Optics # 2   118 , beveled edge  112  and half of flat edge  113  are inspected by Detector Optics # 3   120 , and beveled edge  114  and the other half of flat edge  113  are inspected by Detector optics # 4   122 . Detector Optics # 1   116  and Detector Optics # 2   118  project the image of the edge to be inspected onto detectors, the outputs of which are processed to determine if any defects occur greater than a programmable threshold. This detection and process step is represented by the Detectors and Process block  124 . Likewise Detector Optics # 3   120  and Detector Optics # 4   122  go to a Detectors and Process block  126 . Any defect in either the Outer Radius Inspection Assembly  128  or the Inner Radius Inspection Assembly  130  above their respective programmable thresholds is reported to the computer  46  as a fault, which causes the disk inspection to fail. 
     FIG. 8 a  illustrates how the single light source  104  within the Outer Radius Inspection Assembly  128  can be used to illuminate both the outer edges ( 108 ,  109  and  110 ) and the inner edges ( 112 ,  113  and  114 ) of the Transparent Disk  74  simultaneously. The light source shines through Projection Optics  106 , which illuminates the outer edge of the Transparent Disk  74  as shown. Due to the transparency of Transparent Disk  74 , the light that shines onto the outer edge of the Transparent Disk  74  is transmitted through the transparent disk medium to the inner edges  112 ,  113  and  114 . FIG. 8 a  shows how the Transparent Disk  74  acts as a wave guide, directing the transmitted light to the inner edges of the disk. This feature allows for simultaneous illumination and inspection of both the inner edges ( 112 ,  113  and  114 ) and the outer edges ( 108 ,  109  and  110 ) with only one light source. This is significant since the addition of a second light source to inspect the inner edges would add to the expense and complexity of the apparatus  40 , since this second light source would have to be positioned after the Transparent Disk  74  is loaded for testing, and removed prior to the Transparent Disk  74  being unloaded after testing. 
     Many of the components shown in FIG. 8 are also represented in FIG. 3 in their preferred configurations for the first embodiment of the present invention. Projection Optics  106  is a fiberoptic strand as represented in FIG.  3 . Each of the Detector Optics  116 ,  118 ,  120  and  122  are digital CCD cameras in the first embodiment shown in FIG. 3. A detailed view of the operation of one of the digital CCD cameras is shown in FIG.  9 . For illustrative purposes, inspection of edge  110  and half of edge  109  of the Transparent Disk  74  is shown. The digital CCD camera  132  has a single row of CCDs, known as a Linear CCD Array  136 . The image of the edge  110  and the half of edge  109  of the Transparent Disk  74  to be inspected is focused by the lens  134  of the camera  132  onto the Linear CCD Array  136  as shown. The Processing Electronics  138  then processes the outputs from the Linear CCD Array  136  and asserts a fault signal to the computer  46  if a defect above a programmable threshold value exists. The Linear CCD Array  136  only detects a small portion of the edges as shown in FIG. 9, but the rotation of the disk for one revolution during inspection allows the camera  132  to inspect the entire edge during that one revolution. This occurs simultaneously for all edges  108 ,  109 ,  110 ,  112 ,  113  and  114  shown in FIG. 8, and occurs simultaneously with the inspection of the surface of the Transparent Disk  74  by the Surface Inspection Assembly  66 . 
     Each inspection assembly in the apparatus  40  of the present invention has its own programmable threshold above which a fault will be signaled, causing the disk inspection to fail. In this manner the computer  46  only has to load the disk, rotate the disk, and monitor the outputs of each inspection assembly for faults. If a fault is signaled to the computer  46  prior to a full revolution being completed, the inspection fails and the disk is unloaded by the Automatic Media Handler  42  and placed in the place for “bad” disks. If the computer  46  completes a full rotation of the disk with no fault signal from any of the inspection assemblies, the disk passes the inspection and is unloaded by the Automatic Media Handler  42  and placed in the place for “good” disks. 
     FIGS. 10 a  and  10   b  illustrate how the combination of the scanning of the beam  72  and the rotation of the Transparent Disk  74  provide for a complete inspection of the entire surface of the Transparent Disk  74 . As shown in FIG. 10 a , the beam  72  scans in a line from left to right as shown by the r direction. At the same time the disk rotates in the theta direction shown in the figure. In this manner the disk is inspected in polar coordinates, with the r coordinate representing the position of the beam  72  in its scan path, and the theta coordinate representing the rotational position of the Transparent Disk  74 . 
     The effect of this polar scanning technique is shown in FIG. 10 b.    
     The beam is configured to scan along a radius of the Transparent Disk  74 , from left to right as shown. The beam has a spot size which travels along this scan path. In order for the beam  72  to completely scan the entire surface of the Transparent Disk  74 , the beam  72  must overlap somewhat with the previous scan path. Due to the circular configuration of the disk the outside circumference is significantly greater than the inside circumference, so a rotational change of position causes the outer edge to travel a farther distance than the inner edge. This means that the spot must overlap slightly on the outer edge  140  of the disk, which causes a much greater overlap on the inner edge  142  of the disk, as shown in FIG. 10 b . This difference in overlap between the beam at the outer edge  140  and the inner edge  142  of the Transparent Disk  74  can be corrected using electronics or software to provide for accurate mapping of disk defects. 
     The second embodiment of the apparatus of the present invention is used to inspect a reflective disk. In the system block diagram in FIG. 2, the only difference between this embodiment and the first embodiment is the change in the Optical Inspection Assembly  52 . The Optical Inspection Assembly  52  for the preferred configuration of the second embodiment of the present invention is shown in FIG. 4, with components common to the first embodiment having the same numerical designators. Since the Reflective Disk  75  is reflective, the beam  72  will not pass through Reflective Disk  75 , so the configuration of the first embodiment cannot be used to inspect a Reflective Disk  75 . In this preferred configuration, both sides of the Reflective Disk  75  are inspected simultaneously by using two mirrors  144  and  146  to scan both sides of Reflective Disk  75  in one scan of beam  72 . The mirrors  144  and  146  are placed at 45 degree angles with respect to the two faces of the Reflective Disk  75  so the reflected light beam  77  will be coincident with the transmitted light beam  72 . In this configuration there is no separate Detection Optics, but the light beam  72  is reflected back to the Scanning Optics  84 , which directs the reflected beam  77  (still coincident with the transmitted beam  72 ) to the Optical Scanner  80 , then to a Beam Splitter  79 . The Beam Splitter  79  directs the reflected beam  77  to the Parallel Detector Array  88  within Detector  90 . 
     The Scanning Optics  84  are placed at the precise distance from the polygonal head  82  of the Optical Scanner  80  defined by the focal length of the Scanning Optics  84 . The Reflective Disk  75  is placed at a position such that the path from the Scanning Optics  84  to the face of the Reflective Disk  75  along the entire scan of beam  72  is equal to the focal length of the Scanning Optics  84 . In this manner beam  72  is focused precisely on both faces of the Reflective Disk  75 . 
     FIG. 12 is a block diagram of the configuration of the Surface Inspection Assembly  66  shown in FIG. 2 used in the Optical Inspection Assembly  52  for this first configuration of the second embodiment as shown in FIG.  4 . Note that all the numbers correspond to components shown in FIG. 4 or  5 . The light beam generation, Optical Scanner  80 , and Detector  90  have a configuration identical to that of the first embodiment shown in FIG.  5 . The primary difference is the use of mirrors  144  and  146  to scan both sides of the Reflective Disk  75  in one scan, and the use of the Beam Splitter  79  to direct the reflected beam  77  to the Parallel Detection Array  88  within Detector  90 . 
     FIG. 13 a  clearly represents the operation of the Scanning Optics  84  and the Beam Splitter  79  of the Surface Inspection Assembly  66  shown in FIG.  12 . With this configuration, the beam  72  is reflected off the Optical Scanner  80 , and first contacts the Trigger Detector  73 , then continues to scan across the Scanning Optics  84 . Beam  72  first comes in contact with Scanning Optics  84  on the left side of the Scanning Optics  84 , as represented by A in FIG. 13 a . The beam A contacts the mirror  144  as shown, which focuses beam A on the surface of Reflective Disk  75 , which reflects the beam A back along a path coincident with the transmitted beam A. This is shown in more detail in FIG. 13 b . This reflected beam  77  travels coincident with the transmitted beam  72  until it contacts the Beam Splitter  79 , which directs the reflected beam  77  to the Parallel Detector Array  88  within the Detector  90 . 
     As the Optical Scanner beam  72  continues its sweep, it will come to the position shown by beam B, then to the position shown by beam C, and eventually to the position shown by beam D. Note that for each position of the beam  72 , a different spot on the Reflective Disk  75  is in the path of the beam  72 , and the resulting reflected beam  77  is projected onto the Parallel Detector Array  88  by the Beam Splitter  79  as shown. Note that this method can only be accomplished by placing the Optical Scanner  80  at a distance d from Scanning Optics  84  equal to the focal length of Scanning Optics  84 . The surface of the Reflective Disk  75  is located at this same distance from the Scanning Optics  84  after reflection in mirrors  144  and  146 . In other words, the distance a+b as shown in FIG. 12 must equal the distance d. Since the Scanning Optics  84  also plays the role of Detection Optics due to the reflected beam  77 , the size of the beam  72  at the Optical Scanner  80  is the same as the size of the beam  72  at the Parallel Detector Array  88 . Note that Optional Detection Optics  81  may be used for magnification, to correct beam wandering, or for other purposes as required. 
     FIG. 4 shows only two cameras for edge inspection rather than the four employed by the first embodiment and shown in FIGS. 3 and 8. The difference is that the second embodiment, which deals with a Reflective Disk  75 , can only be inspected on the outer edge as shown in FIG.  4 . Thus, in the Edge Inspection Assembly  68  shown in FIG. 8, only the Outer Radius Inspection Assembly  128  is present, since the Reflective Disk  75  cannot act as a waveguide to shine light on the inner edges  112  and  114  as shown in FIG. 8 a . Inspection of the inner edges  112  and  114  would take a second light source in the Inner Radius Inspection Assembly  130 , which would be positioned after the Reflective Disk  75  is in place. While this is an obvious modification to the apparatus  40  of the present invention, this feature is not shown in the figures. 
     As FIGS. 12 and 13 a  clearly show, this first configuration of the second embodiment allows inspection of both sides of the reflective disk with one scan. In a second configuration of the second embodiment, as shown in FIG. 7, the Surface Inspection Assembly  66  does not have the mirrors that allow the scanning of both sides at once, but the Reflective Disk  75  is inspected one side at a time. When the apparatus  40  completes inspection of one side, it then turns the Reflective Disk  75  and inspects the second side. The operation of all the other features of this second configuration are identical to those explained in relation to FIGS. 12 and 13 a . In addition, two separate scanning systems could be used in the configuration shown in FIG. 7 to accomplish scanning of both sides of the Reflective Disk  75  simultaneously. 
     The operation of rollers  96 ,  98  and  100 , and lifter  99  is identical to that described for the first embodiment, with the difference being the orientation of the rollers to accommodate the Reflective Disk  75 , which must be mounted substantially parallel to the beam  72  if simultaneous inspection of both sides of the disk is desired. 
     In the third embodiment of the present invention, the apparatus  40  is used to inspect transparent flat panels. Referring to FIG. 2, the Edge Inspection Assembly  68  is not required for the inspection of a transparent flat panel. A perspective view of the Optical Inspection Assembly  52  for this third embodiment is shown in FIG.  14 . Note that the Surface Inspection Assembly  66  is the only component of the Optical Inspection Assembly  52  since inspection of the edges of a Transparent Flat Panel  150  is not required. 
     The Surface Inspection Assembly  66  for this third embodiment is shown in FIG.  17 . The operation of all the components in FIGS. 14 and 17 that are the same as those shown in FIGS. 4 and 12 are identical. The primary difference is that the Scanning Optics  84  in FIG. 12 is located at a distance d from the Optical Scanner  80  equal to the focal length of Scanning Optics  84 . This configuration makes the beam exit the Scanning Optics  84  in a direction perpendicular to its face. This method works well for small items such as disks which are not larger than the size of a practical lens. However, a Transparent Flat Panel  150  may be considerably larger than the size of a practical lens. For this reason the Scanning Optics  84  are placed in a position relative to the Optical Scanner  80  which is less than the focal length of Scanning Optics  84 . This relationship is shown in FIG. 18 by the distance b from the Optical Scanner  80  to the Scanning Optics  84  being less than the focal length d of Scanning Optics  84 . This arrangement causes the beam  72  to diverge at the Scanning Optics  84  as shown in FIG. 17, rather than traveling in parallel paths which are perpendicular to the Scanning Optics  84 . This feature allows the Scanning Optics  84  to scan a Flat Panel  150  that is larger than the Scanning Optics  84 . The beam  72  is projected by Scanning Optics  84  at the exact center of Transparent Flat Panel  150 . After the beam  72  passes through Transparent Flat Panel  150 , it begins to diverge, and contacts Spherical Mirror  152 . The Spherical Mirror  152  reflects beam  72 , and this reflected beam  77  is directed back to the Scanning Optics  84 . This is shown in more detail in FIG. 18 a . Referring again to FIGS. 17 and 18, a Beam Splitter  79  is used to distinguish the reflected beam  77  from the transmitted beam  72 , and to direct the reflected beam  77  to the Parallel Detector Array  88  within Detector  90 . The Detector  90  functions the same as for the first and second embodiments. 
     Since the Transparent Flat Panel  150  is rectangular rather than circular, the Media Movement Actuator  64  shown in FIG. 2 for the third embodiment is different than the rollers used for inspecting disks in the first and second embodiments. The Media Movement Actuator  64  for the third embodiment is a lifter  99  as shown in FIG.  14 . The lifter  99  in the first and second embodiment was used to facilitate loading and unloading of the disks into the rollers. The lifter  99  for the third embodiment differs from that used in the first and second embodiment in that it moves the Transparent Flat Panel  150  during the inspection rather than during loading and unloading of the Transparent Flat Panel  150 . For example, during inspection, the lifter  99  positions the Transparent Flat Panel  150  such that the first scan of beam  72  scans the uppermost row of the Transparent Flat Panel  150 . As the beam  72  scans the Transparent Flat Panel  150 , the lifter  99  gradually raises the Transparent Flat Panel  150  such that all portions of the Transparent Flat Panel are scanned by the beam  72 . 
     One advantage of the configuration of these three embodiments of the apparatus  40  of the present invention is that, regardless of the particular configuration of the Surface Inspection Assembly  66  and media, the main control software for computer  46  which controls the apparatus  40  can be identical for all three embodiments. As shown in FIG. 19, the function blocks of the control software are the same regardless of the specific embodiment implemented. The individual device driver software for directing the movement of the Automatic Media Handler  42 , or the Media Movement Driver  62  will vary according to the embodiment implemented, but do not directly affect the operation of the main control software. The specific implementation shown in FIG. 19 assumes that the computer  46  will poll the Surface Inspection Assembly  66  and the Edge Inspection Assembly  68  to determine whether a defect is reported by either of these assemblies. In an alternative arrangement, the Fault output  93  of the Surface Inspection Assembly  66  and the Fault output  93  of the Edge Inspection Assembly  68  are interrupt-driven inputs to computer  46 , which report a fault by interrupting program execution of the computer  46 . In this configuration the computer  46  simply completes the movement of the media, then checks a software flag to determine whether a fault was detected during the scan. 
     The automation of apparatus  40  provided by computer  46  and Automatic Media Handler  42  provides for high-speed inspection of apparatus  40 , which suits the apparatus  40  well to a speed-sensitive production environment. 
     While the invention has been described in its preferred embodiments, it is to be understood that the words which have been used are words of description rather than limitation, and that changes may be made within the purview of the appended claims without departing from the true scope and spirit of the invention in its broader aspects.