INSPECTION SYSTEM FOR EDGES OF GLASS

Abstract: An inspection system for the edge of a sheet of glass e.g. automobile glass. The system has at least one laser, with the laser beam directed at the edge of the glass. Light reflected from the edge is recorded e.g. with a camera. The path length from the laser to the glass edge and back to the camera is maintained constant as the glass moves through the apparatus.

Description: TITLE INSPECTION SYSTEM FOR EDGES OF GLASS Field of the Invention The present invention relates to a non-contact inspection system for detection and identification of the type of defects on the edges of sheets of glass, especially the edges of flat automotive glass. The system is intended to operate on a continuous production line at line speed, and to be used for detection and identification of a wide variety of types of defects, including chips, cracks, poor grinding and other edge defects. Background of the Invention In processes for manufacture of glass in sheet form, it is necessary to be able to inspect the sheets of glass for defects. Such defects may be in the form of scratches, bubbles, chips, blemishes and a wide variety of other defects. In addition, the manufacturer of the sheet glass needs to know whether the defects are insignificant e.g. minor in nature and thus acceptable to the customer, or a major flaw such that the sheet would not conform to specifications established by the customer. It is important to able to conduct the inspection on-line in the production process, at production speeds, so that defects may be rapidly identified and communicated to production personnel and/or the sheets with the defects may be readily and quickly separated from sheets meeting quality specifications in an effective manner. Methods have been developed for the inspection of sheets of glass using optical techniques. Apparatus and a method that are particularly intended for use in inspection of sheets of glass in a production line, at production speeds, in a manner that shows the magnitude, type and location of the defects in the sheet of glass are disclosed in Canadian Patent Application No. 2252308 of Adam Weiss and Alexandre Obotnine filed October 30, 1998. Such apparatus and method, referred to herein as viewing area apparatus, are especially intended to be an integral part of a glass processing system. The aforementioned Canadian Patent Application No. 2252308 is directed to a method for the inspection of sheets of glass, in which the sheets of glass are transported through the beams of lasers. Such an inspection is intended to detect bubbles and other defects in the sheet of glass but not defects on the edge of the glass except to the extent that those defects extend from the edge of the glass into the sheet of glass. The lasers are not in a position to inspect the edges of glass. Detection of defects on the edge of the sheet of glass is also important, as such defects may affect both visual and physical properties of the sheet of glass. ι Summary of the Invention Apparatus and a method have now been found for inspection of the edges of sheets of glass in a production line, at production speeds, especially in a manner that shows the magnitude, type and location of the defects. Accordingly, one aspect of the present invention provides an inspection system for the edge of a sheet of glass, comprising: a) means to support and move a sheet of glass in a plane in a first direction, said means to support and move the sheet of glass maintaining the glass in a constant plane; b) a laser that provides a beam of laser light; c) an optical recording device for said laser beam; d) means to direct the laser beam onto said edge of the sheet of glass at an angle to said first direction and to direct light reflected therefrom to said optical recording device, the light reflected from the edge of the sheet being coaxial with light directed onto the edge of the sheet; and e) means to control the total path length of said laser beam from said laser to said edge and from said edge to said optical recording device at a substantially constant length. In preferred embodiments of the apparatus of the present invention, the system additionally comprises software that utilizes information from the light detection system to determine the location, type and magnitude of defects in the edges of the sheet of glass. In a further embodiment, the system additionally has means to record the location, type and magnitude of defects in the edges of the sheets of glass, optionally including a display or a defect map, especially a defect map displayed on a screen. Another aspect of the present invention provides a method for the inspection of the edge of a sheet of glass, comprising: a) supporting and moving a sheet of glass in a plane in a first direction, said sheet of glass being maintained in a constant plane; b) directing a laser beam onto said edge of the sheet of glass at an angle to said first direction and directing light reflected therefrom to an optical recording device, the light reflected from the edge of the sheet being coaxial with light directed onto the edge of the sheet; and e) controlling the total path length of said laser beam from said laser to said edge and from said edge to said optical recording device at a substantially constant length. Brief Description of the Drawings The present invention is illustrated by the embodiments shown in the drawings, in which: Fig. 1 is a schematic representation of the glass edge inspection apparatus of the present invention; Fig. 2 is a schematic representation of a side view of the light system; Fig.s 3 and 4 are schematic representations of perspective views of the light system; Fig. 5 is a schematic representation of a plan view of four units of glass edge inspection apparatus; Fig. 6 is a schematic representation of the plan view of Fig. 5 with accompanying structure; and Fig. 7 is a schematic representation of a perspective view of the apparatus of Fig. 6. Detailed Description of the Invention Techniques for the manufacture of glass are known. For example, glass may be converted to a molten state and then cast onto molten tin metal so that glass with a smooth surface may be obtained. Nonetheless, the glass that has been cast may be subject to a number of defects, including the presence of bubbles, dirt, stones, tin-drip distortion and other defects. Some such defects might arise from raw materials fed to the process while other defects will arise from processing problems, including incorrect temperature or other process parameters and ageing of apparatus, especially of kilns or other apparatus used in the heating of the glass. Subsequent to the casting of the glass, the glass is cut into sheets and then transferred to a manufacturer of glass articles for a particular end-use. In the automobile industry, for instance, the glass articles could be the windows of the vehicle, in which event the manufacturer will shape the glass to a particular size and configuration, prepare ground edges to the glass, cut holes in the glass in locations as required, imprint logos or other writing in the glass and otherwise process the cut glass to a predetermined set of specifications. Despite care in operation of the process, the various steps can result in the formation of chips, cracks, scratches, and other defects that might render the glass unacceptable to a customer. The manufacturer must be able to detect the defects, and separate sheets of glass conforming to specification from those that do not. As noted above, one of the steps in the manufacture of the sheet of glass is the preparation of ground edges to the sheet of glass. The step of grinding may result in a number of defects in the edge of the glass, including shiners viz. sections of the edge of the glass that have not been ground, open shiners viz. shiners in which the section of un-ground glass extends into the top of the sheet of glass, edge chips, V-chips and burns viz. sections of glass that were over-heated during the grinding process. Some of these defects could be a result of defects in the edge of the glass prior to grinding that were not removed in the grinding step. Other defects are the result of the grinding step per se e.g. a mis-aligned grinding wheel, a grinding wheel that has become worn out and/or which causes overheating, or other grinding difficulties. While the glass is generally described herein as a sheet of glass, it is to be understood that in many instances the glass is in the form of a laminated or tempered glass or other glass, to give it strength, shatter resistance or other properties. The processes used to form such glass may add to the potential defects in the edge of the sheet of glass. Fig. 1 shows a schematic arrangement that illustrates apparatus 1 of the inspection system for edges of glass of the present invention. Apparatus 1 has laser beam 2 that has been generated by laser 3. Laser 3 is controlled by laser controller 4 and laser power control 5. Laser beam 2 passes through beam splitter 6 and is reflected by mirrors 7 and 8 in moveable head 9. Laser beam 2 is further reflected at mirror 10 onto edge 11 of glass sheet 12. Light from edge 11 is reflected back to mirror 10 as reflected beam 13. The light reflected from edge 11 of glass sheet 12 being coaxial with the light directed onto edge 11 of glass sheet 12. Reflected beam 13 then passes to mirrors 8 and 7 in moveable head 9 and to beam splitter 6. At beam splitter 6, reflected beam 13 passes to camera 15, which may be in the form of a high-resolution photodiode CCD (charged coupled device) TDI (time delayed integration) device. Camera 15 communicates with computer 17 through cable 16. Computer 17 additionally controls stepping motor control 19 by means of cable 18, which in turn controls motion mechanism 20. Computer 17 further communicates with laser power control 5 though cable 21. Glass edge 11 will undergo lateral movement, as indicated at 22, during inspection of the glass edge, as discussed below. Moveable head 9 will undergo movement in a vertical direction i.e. a direction perpendicular to the movement of glass edge 11 , as indicated at 23. In operation, a sheet of glass 12 is transported into the apparatus for inspection of the edge of the glass. The presence of the glass, and the position of the glass is detected, as is discussed below. Computer 17 activates laser 3 so that laser beam 2 is passed to mirrors 7, 8 and 10 and directed at glass edge 11. It is important that laser beam 2 be in the plane of the sheet of glass 12. As laser beam 2 is at an angle to the direction of travel of sheet of glass 12, laser beam 2 will contact edge 11 at varying positions as sheet of glass 12 moves, traversing along edge 11. If laser beam 2 and edge 11 are not in the same plane i.e. not aligned, then laser beam 2 will not always be in contact with edge 11. Reflected beam 13 passes back from mirror 10 to mirrors 8 and 7 and is redirected at beam splitter 6 to camera 15. Camera 15 communicates with computer 17, so that computer 17 obtains a record of the images reflected from glass edge 11. As is discussed herein, laser beam 2 is normally not directed at an angle that is perpendicular to glass edge 11. In particular, laser beam 2 is directed from mirror 10 towards glass edge 11 at an angle to the direction of travel of glass sheet 12. As glass sheet 12 is continuously moved though apparatus 1 , the distance from mirror 10 to glass edge 11 is constantly varying. During the inspection process, the distance between glass edge 11 and mirror 10 will increase and decrease as each sheet of glass passes though the inspection system. The constantly varying position of the edge of the glass would result in varying intensity and magnification of the reflected beam 13 that passes from glass edge to camera 15, even if there were no changes in the reflected properties of glass edge 11. This causes variations in the intensity of the light and magnification of the image that would be recorded at camera 15. If defects are present on glass edge 11 , such variations in light intensity and magnification caused by the varying distance of glass edge 11 from mirror 10 would result in variations and masking of defects that are present on glass edge 11. To overcome the problem of varying intensity and magnification caused by the varying position of glass edge 11 as sheet glass 12 is inspected, the location of glass edge 11 is detected and predicted using computer 17. Computer 17 then varies the position of moveable head 9 using step motor control 19 and motion mechanics 20. In particular, moving head 9 is moved in a direction perpendicular to the movement of glass sheet 12 so that the distance from laser 2 to glass edge 11 and back to camera 15 is maintained substantially constant. As used herein, "substantially constant" means maintaining the light received by the camera in focus i.e. within the depth of field of focus of the camera. In embodiments, the depth of field may be ± 30 mm. At beam splitter 6, light passing through is split, with part of the light being directed to laser light trap 14. Fig. 2 shows a side, partly in section, view of apparatus 1. Laser 3 is located on frame 30, which also houses beam splitter 6. Camera 15 is located on one end of frame 30, with laser beam stopper 14 located on the opposed end. Beam splitter 6 is intermediate therebetween. Mirrors 7 and 8 are located within moveable head 9, which is shown at the bottom of rails 31 and 32 that extend perpendicular with respect to glass sheet 12. Moveable head 9 moves along rails 31 and 32 on wheels 33, two of which are shown. Stepping motor 34 is located at the upper end of rails 31 and 32. Stepping motor 34 drives pulley 38 around which passes belt 39. Belt 39 extends downwards and is attached to moveable head 9; belt 39 is further shown and described in Fig.s 3 and 4. Guide bar 36 extends from absolute displacement transducer 35 parallel to rails 31 and 32, passing through guide 37. Absolute displacement transducer 35 is used to determine the vertical position of moveable head 9. In operation, stepping motor 34 is controlled by computer 17 (not shown in Fig. 2). Stepping motor 34 causes pulley 38 to rotate in a clockwise or anticlockwise direction, which causes corresponding movement in belt 39. Consequently, moveable head 9 is raised or lowered along rails 31 and 32. Stepping motor 34 is controlled so that the total path length of laser beam, 2, from laser 3 through beam splitter 6, past mirror 7, 8 and 10 to glass edge 11 and as a reflection back through mirrors 10, 8, 7 and beam splitter 6 to camera 15 is maintained substantially constant. Figs. 3 and 4 show camera 15 located on frame 30 and connected to beam splitter 6 by enclosed tube 40, through which reflected beam 13 passes. Mirrors 7 and 8 are shown as enclosed in housings, which are attached to moveable head 9. Mirror 10 as also shown as being enclosed. Belt 39, which is shown as being a stepped belt, passes around pulley 38 of stepped motor 34 and extends downwards to moveable head 9. Although not apparent in Fig. 3, belt 39 also extends downwards from pulley . 39 behind the frame of rails 31 and 32, around spindle 41 and is attached to moveable head 9. Thus, rotation of pulley 39 effects vertical movement of moveable head 9. Fig. 5 shows a plan view of a glass inspection system with four units for inspection of edges of glass. Two sheets of glass are represented. All support and transportation structure has been omitted for clarity. Apparatus 50 of the glass inspection system has four units for inspection of edges, being units 51 A-51 D. Units 51A-51 D are disposed at approximately the corners of a rectangle, with units 51 A and 51 C at opposed ends of one diagonal and 51 B and 51 D at opposed ends of the other diagonal. Units 51 A and 51 C are shown as being aligned, so that the laser beam 52A from unit 51A is directed at and detected by unit 51 C, and vice versa. In this manner, the units can detect the presence or absence of glass between the units. Units 51 B and 51 D are similarly aligned. However, in addition, the position and orientation of the glass should be determined prior to the sheet of glass entering the inspection apparatus, so that the computer can predict arrival of the glass and adjust the mirror position, as discussed herein. Laser beams 52A-52D are aligned in the plane of glass 53, 54 that is transported horizontally past units 51 A-51 D, in the direction of arrows 55. The mechanism for transporting glass 53 and 54 is not shown in Fig. 5. Cameras 56A-56D are located above the plane of the glass. Outer edges 57,58 of glass 54 pass under cameras 56A-56D but in a position such that laser beams 52A-52D will contact glass edge 59 as glass 54 passes by units 51 A-51 D. Glass 54 is of an irregular shape, but such shape is typical of a window for an automobile. As glass 54 passes laser beams 52A-52B, all of edge 59 of glass 54 is traversed at least once by a laser beam. It is important that laser beams 52A-52B be at an angle to the direction of travel 55 in order that all of edge 59 is traversed by at least one laser beam. Fig. 6 shows a plan view of the glass edge inspection apparatus of Fig. 5 with accompanying structure. Glass 54 and 55 is shown as being on support 60. Support 60 has frame sides 61 and 62. Frame side 61 accommodates drive mechanism 63 and 64, which are more clearly seen in Fig. 7. Drive mechanisms 63 and 64 are partially enclosed. Drive mechanism 63 rotates rollers 65 that extend between frame sides 61 and 62. Similarly, drive mechanism 64 rotates rollers 66 that also extend between frame sides 61 and 62. Rollers 65 and 66 are rotated at the same constant speed, and transport glass 53 and 54 through the edge inspection apparatus. One of rollers 66 viz. roller 66A, is directly driven by motor 67, roller 66A in turn effecting rotation of the remainder of rollers 66 by means of drive mechanism 64. A belt (not shown) extends along and within frame side 62 to rotate a roller 65, which in turn effects rotation of the remainder of rollers 65 by means of drive mechanism 63. Thus, rotation of rollers 65 and 66 may be maintained at a constant speed. Fig. 6 shows viewing area camera 70 of apparatus for inspection of the sheet of glass for bubbles, scratches, chips, blemishes and other defects, as disclosed in the aforementioned application of Weiss and Obotnine. Such inspection of the sheet of glass may be and preferably is carried out simultaneously with the edge inspection of the present invention. Viewing area camera 70 has mirror 71 and light source 72. Similarly, viewing area camera 73 has mirror 74 and light source 75. Two viewing area cameras, 70 and 73, are used so that the full width of glass 53,54 may be inspected. Units 51 A-51 D have been described above. It is understood that suitable structure for support of units 51 A-51 D would be required. Such structure has been omitted for clarity. Fig. 7 shows a perspective view of the apparatus of Fig. 6. Only one viewing area camera, 70, is shown in Fig. 7. Drive mechanism 63 and 64 are shown to have belts around a series of pulleys, to drive rollers 65 and 66. The present invention provides a glass inspection system that is capable of automation, and which utilizes laser optics and a computer vision- based system. In preferred embodiments of the invention, the combination provides an advanced image analysis with exceptional inspection accuracy e.g. between 50 μm and 100 μm, as well as the capability to detect and differentiate a wide variety of defects including edge chips, cracks, shiners, V- chips, burns and other edge defects, and identifies the location, type and magnitude of the defects on the glass. A defective area of the edge surface has different light scattering properties than an edge surface that has been ground properly. In particular, defective areas appear as dark spots i.e. areas of low intensity, whereas a surface that is properly ground gives a bright background i.e. an area of high intensity. Detection and measurement of the size of the dark areas provides information on the location, size and type of the defect. The system is capable of being operated at high-speeds e.g. at line speeds of up to 0.3 m/sec, or higher. Thus, the inspection system may be used in-line in many manufacturing processes. The software used in the system may be featured with a menu-based graphical user interface for ease of use, pass/fail specification changes and new model set ups, as well as automatic change over and calibration of the system. In a preferred embodiment, a standard user interface screen with a defect map is used, having coloured icons that represent various types of defects. For examples, circles may be used to represent edge chips, squares to represent V-chips, triangles to represent shiners and so on. The icons may be made to appear at the actual x,y co-ordinates where the defects are located in the sheet of glass. In addition, the icons may be colour coded to represent the size of the defects e.g. the icons could be green to represent a very small defect, yellow to represent a medium defect and red to represent a large defect or reject. Moreover, software may be provided where the user can "click" on any icon to provide characteristics of the defect, including type, size and location. 3-D visualization and mapping of the defects is also possible. Removable surface contaminants such as dust and water, may or may not be not detected by the system, depending on the particular application of the system. It is to be understood that electronic hardware would be interfaced with the detection system. This hardware would provide for control of the detection system, collection of pixel data from the collection system, compression of the data by relaying for further processing only data that is related to areas of interest in the glass sheet, and for pre-processing of pixel data by applying multi-level thresholds and marking transitions between different levels of intensities. A dedicated Peripheral Processor Board (PPB) may be used to further process the data by means of software. The processed data may then be transmitted to a gauge host computer for the purpose of visualization and control, as discussed herein. The detection system may be set to recognize a threshold of illumination that indicates the presence of glass. The transitions that pass through the threshold may be presented on a computer display tube. A sheet of glass cut for a particular end-use, for example the window on the side of an automobile, may be of a complicated shape. The position of the glass within the apparatus is not important, provided that it is located within the width of the laser beam. Moreover, the method of the present invention is capable of being used with curved glass, provided that the edge lays in the plane of the laser beams. Time delayed integration (TDI) techniques may be used in the detection and analysis of the images that are formed and detected. In an embodiment of the invention, the stepping motor provides 2 x 10 4 steps per revolution of the pulley. The distance of the mirror travel per step provided by the stepping motor is 0.051 mm. The mirror position is up-dated at 0.017 seconds. It is preferred that the mirror motion be up-dated for every 5 mm of travel of the glass. The camera depth of field in the embodiment is ± 30 mm and the total path length of the laser beam must be maintained within the depth of field. This may be accomplished by determining the actual mirror position of the movable head by measurement and by calculation based on movement of the glass. The accumulated error between the actual and calculated values must remain within the range of ± 30 mm. As noted above, the location of the glass is tracked as the glass approaches the position of the lasers, for example by counting of encoder pulses. The acceleration of the stepper motor and hence the position of the moveable mirrors is limited. Thus, motion of the mirror should be commenced at an appropriate time prior to arrival of the glass so that mirror speed and glass edge speed can be matched before scanning commences. The present invention provides a versatile apparatus and method for inspection of glass, and which is capable of simultaneously identifying a wide variety of defects by type, magnitude and location, in a manner that not only permits identification of glass that does not meet product specification but also assists in identifying the causes of the defects. The edge inspection system of the present invention may be used inline with a viewing area inspection system of the type described in the aforementioned patent application of Weiss and Obotnine.

Claims: CLAIMS: 1. Apparatus for an inspection system for the edge of a sheet of glass, comprising: a) means to support and move a sheet of glass in a plane in a first direction, said means to support and move the sheet of glass maintaining the glass in a constant plane; b) a laser that provides a beam of laser light; c) an optical recording device for said laser beam; d) means to direct the laser beam onto said edge of the sheet of glass at an angle to said first direction and to direct light reflected therefrom to said optical recording device, the light reflected from the edge of the sheet being coaxial with light directed onto the edge of the sheet; and e) means to control the total path length of said laser beam from said laser to said edge and from said edge to said optical recording device at a substantially constant length. 2. The inspection apparatus of Claim 1 in which the means to control the path length includes a movable housing with mirrors. 3. The inspection apparatus of Claim 1 or Claim 2 in which the means to control the path length includes means to move the movable housing perpendicular to the plane of said sheet of glass. 4. The inspection apparatus of any one of Claims 1-3 in which there is more than one laser. 5. The inspection apparatus of any one of Claims 1-3 in which there are a plurality of lasers, said lasers being directed such that the entire edge of said sheet of glass is inspected. 6. The inspection apparatus of Claim 5 in which there are four lasers. 7. The inspection apparatus of any one of Claims 1-6 in which the glass is automotive sheet glass. 8. The inspection apparatus of any one of Claims 1-6 in which the sheet of glass is planar. 9. The inspection apparatus of any one of Claims 1-6 in which the sheet of glass is non-planar. 10. The inspection apparatus of any one of Claims 1-9 in which the apparatus additionally comprises software to determine the location, type and magnitude of defects in the sheet of glass. 11. The inspection apparatus of Claim 10 in which the apparatus additionally has means to record the location, type and magnitude of defects in the sheets of glass, optionally including a display or a defect map, especially a defect map displayed on a screen. 12. A method for the inspection of the edge of a sheet of glass, comprising: a) supporting and moving a sheet of glass in a plane in a first direction, said sheet of glass being maintained in a constant plane; b) directing a laser beam onto said edge of the sheet of glass at an angle to said first direction and directing light reflected therefrom to an optical recording device, the light reflected from the edge of the sheet being coaxial with light directed onto the edge of the sheet; and e) controlling the total path length of said laser beam from said laser to said edge and from said edge to said optical recording device at a substantially constant length. 13. The method of Claim 12 in which the controlling of the path length includes moving a housing with mirrors, said laser beam being reflected by the mirrors. 14. The method of Claim 13 in which the housing is moved perpendicular to the plane of said sheet of glass. 15. The method of any one of Claims 12-14 in which a plurality of lasers are directed at the edge of the sheet of glass, such that the entire edge of said sheet of glass is inspected. 16. The method of any one of Claims 12-16 in which there are four lasers. 17. The method of any one of Claims 12-16 in which the glass is automotive sheet glass. 18. The method of any one of Claims 12-16 in which the sheet of glass is planar. 19. The method of any one of Claims 12-16 in which the sheet of glass is non-planar. 20. The method of any one of Claims 12-19 in which the location, type and magnitude of defects in the sheet of glass are determined using computer software. 21. The method of any one of Claims 12-20 in which the location, type and magnitude of defects in the sheets of glass are recorded, optionally including a display or a defect map, especially a defect map displayed on a screen.

Inventors: WEISS ADAM, WEISS, ADAM
Applicants: IMAGE PROC SYSTEMS INC, WEISS ADAM, IMAGE PROCESSING SYSTEMS INC., WEISS, ADAM
Application year: 2000
Main classification: G01N21
IPC codes: G01N21