Inspection system for sheet material

[0002] 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.

[0003] 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.

[0004] 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.

[0005] 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.

[0006] 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.

[0007] 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.

[0008] FIG. 1 is a schematic side elevational view of an inspection system embodying the present invention.

[0009] FIG. 2 is a schematic front elevational view of the mechanism for receiving and vertically indexing the glass substrate.

[0010] 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.

[0011] 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.

[0012] FIG. 5 is a perspective schematic representation further illustrating the mechanism for horizontally moving the light delivery systems and the cameras in unison.

[0013] FIG. 6 is a schematic elevational view of the sections of the air table.

[0014] FIG. 7 is an enlarged schematic fragmental view of a section of the air table illustrating an air hole pattern.

[0015] FIG. 8 is a schematic illustration of what an actual scanning pattern would look like on the glass sheet.

[0016] 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 12a, middle section 12b, and lower section 12c, 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.

[0017] As shown, the air table 12 has gaps or slots 20aand 20cformed between middle section 12band its associated first and second sections 12a, 12c, 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 20a, 20c. 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 20a, 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 20c. 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.

[0018] 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.

[0019] 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 52afor operating the scanning mechanism 22.

[0020] 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 52aand drive pulley 52bwhich 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.

[0021] 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 12a, middle section 12b, lower section 12cand gaps 20aand 20cis 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 20aand the gap 20b. Each of the gap interfaces is provided with additional air supply holes 64 to compensate for the loss of pressure adjacent the gaps 20aand 20b.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.