Abstract:
An inspection system is set forth for the inspection of surface and body defects within glass substrates. The glass is supported by an inclined air table during the inspection process to provide planar stability and minimize vibration. The sheet is indexed a given distance along an oblique axis parallel to the air table and stopped, wherein a scanning mechanism having portions on opposite sides of the air table moves transversely of the sheet in alignment with slots formed in the air table, and the process is repeated until the sheet is completely scanned.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to an inspection system for the inspection of defects in sheet material, and more particularly to an inspection system for the inspection of surface and body defects in glass substrates, such as in LCD glass. The inspection system is particularly adapted to accommodating fairly large size substrates in the order of 550 mm×650 mm and larger, by providing stability to the substrate during inspection through the use of an air support table. 
     Presently, the inspection of such large size glass panels is primarily done by utilizing manual methods. Accordingly, such manual processes introduce a large amount of variability in the outgoing inspection product. Some of the problems encountered with the known inspection systems include the problem of holding a substrate in a manner which minimizes sheet vibration. In addition there has been problems in holding the glass sheet in a strict plane tolerance so as to have consistency in inspection readings. Further, it has been difficult to provide a direct view of all areas of the sheet without interference from supporting structures. That is, most of the known inspection systems rely on some method of holding the sheet by the edge in either a horizontal or vertical orientation, which creates problems of glass sag and vibration during the inspection process. 
     It thus has been an object of the present invention to provide a solution to these problems by utilizing a uniform air support for the entire glass surface of a substrate without physically contacting the surface of the sheet, and while dampening any sheet vibrations and allowing the sheet to move at high speeds during inspection. 
     SUMMARY OF THE INVENTION 
     The present invention sets forth method and apparatus for inspecting surface and body defects in glass substrates. The system includes a dual detector scanning system as well as a brightfield/darkfield imaging system that work together to detect, identify and classify different types of glass defects. The glass is supported in a slightly off-vertical position by an air table during the inspection process to provide stability, particularly for larger size substrates in the order of 550 mm×650 mm and larger. 
     Glass sheets or substrates to be inspected are positioned adjacent a three-piece air table which is tilted by an angle from the vertical. The sheets or substrates are indexed substantially vertically, but along an incline or axis parallel to the tilted air table. Dual light delivery mechanisms and dual detectors are positioned adjacent slots formed within the air table on a slide mechanism that allows them to be moved horizontally along an axis transverse to the oblique axis. The glass substrate is positioned over the slots and held stationary while the dual detector and light delivery systems are swept from one edge of the substrate to the other. The glass is then indexed and this process is repeated until the entire area of the glass substrate has been inspected. 
     Following this initial inspection process, brightfield/darkfield optics can be positioned to review any of the particles or defects detected during the previous scanning process. Scratches, particles and other defects can be identified and accepted or rejected. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic side elevational view of an inspection system embodying the present invention. 
     FIG. 2 is a schematic front elevational view of the mechanism for receiving and vertically indexing the glass substrate. 
     FIG. 3 is a fragmental schematic illustration taken along lines  3 — 3  of FIG. 2 illustrating the V-groove finger for supporting the bottom edge of the glass substrate. 
     FIG. 4 is a schematic front elevational view illustrating the mechanism for vertically indexing at an angle parallel to that of the air support table, and the mechanism for horizontally sweeping the light delivery mechanisms and cameras. 
     FIG. 5 is a perspective schematic representation further illustrating the mechanism for horizontally moving the light delivery systems and the cameras in unison. 
     FIG. 6 is a schematic elevational view of the sections of the air table. 
     FIG. 7 is an enlarged schematic fragmental view of a section of the air table illustrating an air hole pattern. 
     FIG. 8 is a schematic illustration of what an actual scanning pattern would look like on the glass sheet. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to FIG. 1, the scanning portion of an inspection system  10  is schematically shown in elevation. An inclined air table  12  formed in three sections, including upper section  12   a , middle section  12   b , and lower section  12   c , preferably is positioned at an angle to the vertical. A specimen to be examined such as a glass sheet or substrate  14  is supported at its bottom edge  16  by a pair of groove finger supports  18  (see also FIG.  2  and FIG.  3 ). The glass specimen or substrate  14  to be examined or inspected, is maintained parallel to the inclined plane of the air table  12  by means of an air cushion supplied by the air table. As will be explained in more detail hereinafter, the substrate  14  is moved upwardly and downwardly along an oblique Y axis, shown by arrow Y, which is parallel to the plane of the air table  12  and at a desired acute angle from a true vertical. 
     As shown, the air table  12  has gaps or slots  20   a  and  20   c  formed between middle section  12   b  and its associated first and second sections  12   a ,  12   c , respectively. The scanning mechanism  22  of the inspection system  12  is positioned on opposite sides of the glass substrate  14  adjacent the gaps or slots  20   a ,  20   c . The scanning mechanism includes first and second light delivery systems  24 ,  26 , and an optically aligned dual detector system, for example a dual camera system, including first detector  28  and second detector  30 . The light delivery systems  24 ,  26  are positioned on one side of the air table  12 , and the first detector  28  and second detector  30  of the dual detector system are positioned on the opposite side of the table  12 . However, the first light delivery system and the first detector are in optical alignment along optical axis OP- 1  through slot or gap  20   a , whereas the second light delivery system  26  and the second camera  30  are in optical alignment along optical axis OP- 2  through the lower slot or gap  20   c . The scanning mechanism  22  moves in unison along a horizontal X axis (shown by arrow X in FIG. 4) transversely of the glass substrate  14  and the Y axis, as more particularly set forth hereinafter with respect to FIG.  4  and FIG.  5 . The scanning mechanism  22  also includes a third detector  32 , for example, a camera with brightfield/darkfield optics, which is utilized after the initial scanning by the dual detector system to further classify a defect initially located by the dual detector system. The third detector preferably has a higher resolution than the first and second detectors. 
     Referring now to FIGS. 2,  3  and  4 , it can be seen that the grooved finger supports  18  are secured to a carriage plate  34  which is moveable along the oblique Y axis by means of guide rails  36 . A pair of centering pads  38 ,  40  are also secured to the carriage plate  34 . The left centering pad  38  functions as a positioning pad to accommodate different sizes of glass substrates  14  and may be placed in a desired position by means of an actuator, for example, a rotary pneumatic actuator. 
     Referring now more particularly to FIG. 4, both the glass substrate transport mechanism for moving the glass substrate upwardly and downwardly along the oblique Y axis parallel to the air table  12 , and the scanning mechanism  22  for moving the light delivery systems and the dual detector system horizontally along the X axis are driven by motors, for example linear motors through a timing belt, pulley and guide arm system. The glass substrate transport assembly, which includes the finger supports  18 , the carriage plate  34 , guide rails  36  and the centering pads  38 ,  40  is driven by a linear motor  42  through drive pulley  46  and timing belt  48  connected to an arm  44  of the carriage plate  34 . A brake  50 , connected to the drive pulley  46  is provided to prevent the carriage plate  34  from falling along the Y axis when power is lost to the linear motor  42 . A separate linear motor (not shown) is similarly connected to the drive pulley  52  and drive shaft  52   a  for operating the scanning mechanism  22 . 
     Referring now more particularly to both FIG.  4  and FIG. 5, the horizontal movement of the scanning mechanism  22  transversely of the glass substrate  14  can be seen. The scanning mechanism  22  is positioned on opposite sides of the glass substrate transport assembly, which assembly moves the glass substrate  14  substantially vertically along the Y axis. The first detector  28  and the second detector  30  are supported by a detector mount  54 , whereas the first light delivery system  24  and the second light delivery system  26  are supported by a lighting system mount  56 . The mounts  54 ,  56  slide transversely of the sheet  14  along the X axis on rails  58 , such as shown in FIG. 4 for the camera mount  54 . A pair of timing belts  60 ,  62  are connected to the detector mount  54  and the lighting system mount  56 , respectively, for moving the light delivery systems and the detectors in unison along the X axis. The linear motor driving drive pulley  52  and timing belt  60  for moving the cameras along the X axis, also drives the lighting systems along the X axis through a connecting drive shaft  52   a  and drive pulley  52   b  which operates timing belt  62 . A pair of idler pulleys  53  at the opposite ends of the timing belts  60 ,  62  maintain the belts in tension. 
     Referring now to FIGS. 6 and 7, the air table and its hole patterns are shown in more detail. The air table  12  with its upper section  12   a , middle section  12   b , lower section  12   c  and gaps  20   a  and  20   c  is shown in FIG. 6, whereas air supply holes  64  and air exhaust holes  66  are shown in a portion of the table  12  in FIG.  7 . The hole pattern for the air table is specifically designed to provide the required float of the glass sheet  14  off of the table, as well as maintaining flatness of the sheet. In view of the fact that edge portions of the glass sheet will lose or exhaust more air from the sheet surface than centrally of the sheet, exhaust holes are provided centrally of the sheet in order to provide uniform air flow against the surface of the sheet and prevent bowing of the sheet in the center portion thereof. Thus, the flatness of the sheet is provided through a pattern of pressure and exhaust holes, with the exhaust holes being sized, with respect to their location on the table to thereby maintain even pressure to the back of the sheet across the full surface thereof. As noted particularly in FIG. 6, there is a tapered gap interface  68  adjacent the gap  20   a  and the gap  20   b . Each of the gap interfaces is provided with additional air supply holes  64  to compensate for the loss of pressure adjacent the gaps  20   a  and  20   b . 
     As previously mentioned, the inclined air table  12  is tilted at an angle to the vertical so that it is parallel to the oblique Y axis. Preferably the acute angle should be between about 5° and 15° from the vertical. If the angle is much less than 5° from the vertical, the pressure necessary to maintain the glass sheet in a flowing position off of the table must be very carefully controlled, since if too much pressure is applied the sheet will be blown off of the table. Although angles greater than 15° may be utilized, the closer the angle comes to 90°, and the glass sheet is virtually horizontal, the greater are the problems encountered with regard to sagging. Although by no means limiting, an angle of 7½° from the vertical does provide excellent results. 
     In operation, a glass sheet or substrate  14  is positioned with its bottom edge  14  within grooved finger supports  18  on carriage plate  34 . The centering pads  38  and  40  are utilized to center the sheet  14  on the carriage plate  34 . The left centering pad  38  is actuated by a cam action to position the pad in a fixed position relative to the size of the sheet being utilized, and the right centering pad  40  is spring actuated to allow the glass to center. Air is supplied to the air supply holes  64  of the inclined air table  12  so as to position an support the glass sheet  14  along a desired inclined or oblique Y axis which is parallel to the air table  12 . Linear motor  42 , through drive pulley  46  and timing belt  48 , moves the carriage plate  34  along guide rails  36  so as to move the glass sheet  14  along the Y axis parallel to air table  12 . The glass sheet  14  is moved along the Y axis a predetermined distance and is then held in position by the linear motor. The linear motor driving the X axis is then actuated so as to sweep the scanning mechanism  22  across the width of the glass. When the sweep of the scanning mechanism is completed, the glass is moved along the Y axis another predetermined distance so that the detector and optics of the scanning mechanism can make another pass across the glass. This procedure is repeated until the entire sheet of glass has been scanned. The glass may be moved in either an upwardly or downwardly movement during the scanning, and an actual pattern is shown in FIG. 8 when the glass is moved in an upward position. Although the trace  70  of the scanning pattern is shown as a line, the actual field of view of the cameras cover the entire surface between the parallel trace lines. With commercially available optics, a movement along the Y axis of about 1.5 cm between sweeps of the scanning mechanism provides complete coverage of the sheet. The motion along the X and Y axes is controlled by motion control electronics. 
     Following the initial scanning of the sheet, a more detailed scan of the sheet then is effected. Brightfield/darkfield optics are then positioned to further review any of the particles or defects detected during the initial scanning process. To locate a particular X, Y coordinate, the glass is moved vertically a Y distance along the Y axis and the detectors are moved horizontally an X distance along the X axis. The optics of the third detector  32  have a higher magnification than the initial scanning detectors so that the system can find out which surface the particle is on, its size, and also display an image of the particle so it can be further characterized. As will be appreciated by those skilled in the art, algorithms known in the art can be utilized to identify and characterize defects such as scratches and particles in the sheet of material being scanned. Those skilled in the art will appreciate that the algorithm used to accept or reject a defect will be determined by the material being scanned, as well as the acceptable size of the defect for a particular application. 
     Although we have disclosed the now preferred embodiments of the invention, it will be apparent to those skilled in the art that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as set forth in the appended claims.