Glass Inspection

Abstract

A method of detecting defects in a glass sheet is described, the method including: (i) directing a converging beam from an illumination source onto a surface of the glass sheet to illuminate the defect; (ii) focusing an image capture device onto a first plane to image the defect in the glass sheet; (iii) capturing a first image of the defect; (iv) performing an adjustment step; and (v) capturing a second image of the defect. Each of the first and second images includes a respective first portion from the illuminated defect and a respective second portion due to reflection of a portion of the beam from the glass surface. In the first image of the defect, the first portion is brighter than the second portion, and in the second image of the defect, the first portion is darker than the second portion. An apparatus for performing the method is also described.

Description

[Technical Field]

[0001] The present invention relates to a method for detecting defects in a glass sheet and an apparatus for determining the presence of defects in a glass sheet. [Background technology]

[0002] It is known in the art that glass can be manufactured into sheet form using a variety of forming processes, including float, downdraw, and rolling processes.

[0003] During the manufacture of glass sheets, one or more defects may be introduced into the glass sheet, reducing its optical quality. For example, bubbles and / or refractory particles (often referred to as "inclusions") and / or refractive index changes (often referred to as "ream") may be introduced into the glass sheet as defects, altering its optical quality. The defects may cause one or more optical effects in the glass; for example, refractory particles may be visible to the human eye and / or may cause refractive index changes around the refractory particles that cause optical distortion. Measures may be taken to reduce the number of defects, and there are often predetermined quality standards associated with each type of defect.

[0004] Typically, different defects have different optical effects in the glass sheet, allowing different inspection systems to be used to detect and identify the different defects. Such inspection systems are commercially available from companies such as ISRA VISION AG, Germany (see the following website: https: / / www.isravision.com / en / glass / applications / float-glass / float-glass-for-architecture / ) and Dr. Schenk GmbH, also Germany (https: / / www.drschenk.com / products / glass-inspection / float-glass-inspection.html).

[0005] Other inspection systems for glass sheets are known in the art.

[0006] WO 2000 / 26647 describes a glass sheet inspection system that includes a first laser and a second laser, each of which provides a sheet of light, a cylindrical lens system, and a first optical detection system and a second optical detection system. The first laser is positioned at the focal point of the lens system. The second laser is positioned at a greater distance from the lens system than the first laser and off-axis from the lens system. The first optical detection system receives light from the first laser, and the second optical detection system receives light from the second laser. The inspection system is adapted to position the glass sheet between the lens system and the detection system.

[0007] Korean Patent Publication No. 10-2019-0001789 describes an inspection device for a multi-optical display. The inspection device for a multi-optical display of the present invention includes a curved illuminator that irradiates light onto a curved edge formed on an object to be inspected to indicate defects in the edge, and a camera that captures the object to be inspected and generates a capture image including a curved capture area. The curved illuminator includes a light source and a curved reflector that allows light from the light source to be incident and reflected by the curved edge.

[0008] Chinese Patent Application Publication No. 105259189 describes a glass defect imaging system comprising a first light source, a second light source, and an image collector. Both the first and second light sources are strip-shaped light sources equipped with LED lamp bead module groups. The first light source is positioned below the glass, and the second light source is positioned above the glass. The first and second light sources illuminate the same area of ​​the glass at specific angles, and the transmitted light generated by the first light source and the reflected light generated by the second light source pass parallel to the main optical axis of the camera lens of the image collector. The first and second light sources switch between illumination modes according to a preset system, creating different lighting effects on the glass: bright-field transmission, bright-field reflection, dark-field transmission, and dark-field reflection. The image collector is used to complete glass image collection under all lighting effects during a single system run. This glass defect imaging system can fully utilize the image information from multiple illumination modes to locate defects on the glass surface and comprehensively and accurately determine the types of defects on the glass surface.

[0009] Chinese Utility Model No. 204359710 describes a glass surface defect detection device that includes an upper detection imaging optical path and a lower detection imaging optical path. The upper detection imaging optical path includes an upper bright-field illumination line light source, a dark-field illumination line light source, an upper scanning and imaging objective lens, and an upper linear array image sensor. The lower detection imaging optical path includes a lower bright-field illumination line light source, a backlight illumination line light source, a mirror, a lower scanning and imaging objective lens, and a lower linear array image sensor. The glass surface defect detection device can detect quality issues in cover glass during processes such as electronic product production, processing, and assembly, and can efficiently detect various defects in the cover glass during scanning, strengthen quality control of the cover glass, and improve the overall quality of the cover glass.

[0010] The float process for producing glass sheets is known, in which molten glass is formed into a glass ribbon by floating it on the surface of a bath of molten tin enclosed in a "float bath." The ribbon is then annealed and cut into glass sheets. The forming process, which involves floating molten glass on the surface of molten tin in a float bath, can result in tin defects within or on the formed glass ribbon, which can cause defects within or on the surface of the glass sheet. The tin defects can occur at or near the surface of the glass sheet that is not in contact with the molten tin during forming (this surface is often referred to as the "air surface" or "top surface" of the glass sheet). See, e.g., Ceramic Engineering and Science Proceedings 27(1):19-46 and U.S. Pat. No. 4,236,906.

[0011] A problem with tin defects present on or near the surface of a glass sheet that did not contact molten tin during forming is that this glass surface may also contain other defects, such as dust, dirt, or scratches, after the glass sheet is formed. It is also necessary to distinguish between tin defects that may be on the surface of the glass sheet that contacted molten tin during forming and tin defects that may be on or at least partially beneath the surface of the glass sheet that did not contact molten tin during forming. While both types of defects are "tin defects," they have different impacts on optical quality and may be caused by different conditions during forming. Therefore, it is also important to be able to distinguish between such tin defects so that appropriate corrective action can be taken during forming. Summary of the Invention

[0012] The present invention at least partially addresses the above and provides an alternative method for detecting defects in glass sheets, particularly defects on or near the surface of glass sheets due to particles, such as tin-containing particles, that deposit on the top surface of float-formed glass sheets.

[0013] Accordingly, in a first aspect, the present invention provides a method for detecting defects in a glass sheet, the glass sheet having a first major surface and an opposite second major surface, the method comprising the steps of: (i) directing a beam from an illumination source onto the first major surface of the glass sheet to illuminate defects in the glass sheet, the beam striking the first major surface of the glass sheet being a convergent beam having a first focus; (ii) focusing an image capture device onto a first plane to image the defects in the glass sheet, the image capture device being at a first position relative to the defects; and (iii) capturing a first image of the defects using the image capture device, the first image being captured. (iv) performing an adjusting step; and (v) capturing a second image of the defect using an image capture device, the second image including the first portion from the illuminated defect and the second portion due to reflection of at least a portion of the beam from the first major surface of the glass sheet, wherein in the first image of the defect, the first portion is brighter than the second portion and in the second image of the defect, the first portion is darker than the second portion.

[0014] Preferably, the beam is a beam of electromagnetic radiation comprising electromagnetic radiation having at least one wavelength between 300 nm and 10 μm, preferably between 300 nm and 2500 nm, more preferably between 300 nm and 1500 nm, even more preferably between 300 nm and 1100 nm.

[0015] Preferably, the beam is a light beam comprising electromagnetic radiation having at least one wavelength between 380 nm and 780 nm.

[0016] For the avoidance of doubt, when a glass sheet is defective, this includes defects in the body of the glass sheet, defects on the surface of the glass sheet, and defects that are at least partially below the surface of the glass sheet.

[0017] Depositing particles on the first major surface of a glass sheet as the glass sheet is formed can cause certain defects in the glass sheet. Because the viscosity of the glass when the glass sheet is formed is sufficiently low, depositing particles thereon can cause localized changes in the surface shape of the glass sheet around the particles. As the glass cools, the localized changes in the surface shape of the glass sheet around the particles are essentially "frozen." Thus, defects detected according to the first aspect of the present invention can include particles in the glass sheet and localized changes in the surface shape of the glass surrounding the particles. If the particles that caused the localized changes in the surface shape of the glass surrounding the particles are subsequently removed from the glass sheet after the glass sheet is formed, for example because the particles are not fully embedded in the glass sheet, the defects will still remain in the glass sheet due to the localized changes in the surface shape of the glass that occurred when the particles were initially deposited, as described above.

[0018] In both of the cases described above, the local topographical changes in the surface of the frozen glass sheet cause the path of the beam received by the image capture device to be adjusted, so that the defect (with or without a particle that caused the local topographical changes in the surface of the glass sheet) appears brighter or darker against the surrounding glass background depending on the path from the defect to the image capture device. The present invention exploits this discovery and provides a detection method that can distinguish between different types of defects that may be present in a glass sheet by using an adjustment step in step (iv).

[0019] The adjusting step may be used to adjust the path of the light beam from the illumination source to the defect and / or from the defect to the image capture device.

[0020] Preferably, the adjusting step includes adjusting a first focus of the converging beam to a second focus such that the beam striking the first major surface is a converging beam having the second focus.

[0021] Preferably, the adjusting step includes focusing the image capture device onto the second plane and imaging the defect with the image capture device focused on the second plane.

[0022] Preferably, the adjusting step includes the step of moving the image capture device to a second position relative to the defect.

[0023] As apparent from the above, the adjusting step preferably includes one or more of the following steps: (a) adjusting a first focus of the convergent beam to a second focus such that the beam striking the first major surface is a convergent beam having the second focus, (b) focusing the image capture device on a second plane and imaging the defect with the image capture device focused on the second plane, and (c) moving the image capture device to a second position relative to the defect. Moving the image capture device to the second position relative to the defect may be performed by moving at least one of the image capture device and the defect relative to the other.

[0024] Preferably, in the first image of the defect, the first portion of the first image is surrounded by the second portion of the first image, and more preferably, the first portion of the first image is completely surrounded by the second portion of the first image.

[0025] Preferably, in the second image of the defect, the first portion of the second image is surrounded by the second portion of the second image, and more preferably, the first portion of the second image is completely surrounded by the second portion of the second image.

[0026] Preferably, the first plane is aligned with the first major surface of the glass sheet.

[0027] In step (ii), when the image capture device is in a first position relative to the defect, the image capture device is also in a first position relative to the first plane and in a first position relative to the first and second major surfaces of the glass sheet.

[0028] Preferably, in step (i), positive optical power is added to the beam before it strikes the first major surface of the glass sheet, more preferably, positive optical power of 0.01 diopters to 100 diopters is added to the beam before it strikes the first major surface of the glass sheet, and even more preferably, negative optical power of 0.01 diopters to 50 diopters is added to the beam before it strikes the first major surface of the glass sheet. Preferably, optical power is added to the beam using a lens or mirror before it strikes the first major surface of the glass sheet.

[0029] Preferably, in step (i), a negative optical power is added to the beam before it strikes the first major surface of the glass sheet. Preferably, a negative optical power of between 0.01 diopters and 10 diopters is added to the beam before it strikes the first major surface of the glass sheet. Preferably, the negative power is added to the beam by a lens, more preferably an adjustable lens, even more preferably a computer-adjustable lens, before it strikes the first major surface of the glass sheet.

[0030] Preferably, in step (iv), the image capture device maintains focus on the first plane such that the focus of the image capture device is on the first plane when a second image of the defect is captured by the image capture device during step (v).

[0031] Preferably, in step (iv), the image capture device remains in a first position relative to the defect, and in step (v) a second image of the defect is acquired with the image capture device in the first position relative to the defect.

[0032] Preferably, in step (iv), the first focus of the converging beam is adjusted to a second focus, the second focus being further from the illumination source than the first focus.

[0033] Preferably, in step (iv), positive optical power is added to the beam after it strikes the first major surface of the glass sheet, more preferably, 0.01 diopters to 100 diopters of positive optical power is added to the beam after it strikes the first major surface of the glass sheet, and even more preferably, 0.01 diopters to 50 diopters of positive optical power is added to the beam after it strikes the first major surface of the glass sheet. Preferably, optical power is added to the beam using a lens or mirror after it strikes the first major surface of the glass sheet.

[0034] Preferably, in step (iv), a negative optical power is applied to the beam after it strikes the first major surface of the glass sheet. Preferably, a negative optical power of between 0.01 diopters and 10 diopters is applied to the beam after it strikes the first major surface of the glass sheet. Preferably, the negative power is applied to the beam after it strikes the first major surface of the glass sheet by a lens, more preferably an adjustable lens, even more preferably a computer-adjustable lens.

[0035] Preferably, the defect comprises a localized shape change in the first major surface of the glass sheet, the localized shape change in the first major surface of the glass sheet being caused by particles deposited on the first major surface of the glass sheet during formation of the glass sheet. Preferably, the particles are spherical or substantially spherical.

[0036] Preferably, the defects comprise tin or tin oxides or are caused by particles comprising tin or tin oxides.

[0037] Preferably, the defects detected include spherical or substantially spherical portions.

[0038] Preferably, the defects detected include portions that are at least partially submerged below the first major surface of the glass sheet.

[0039] Preferably, the defect to be detected has a first portion and a second portion, the first portion of the defect being above the first major surface of the glass sheet and the second portion of the defect being below the first major surface of the glass sheet.

[0040] Preferably, the defects detected have a major axis with a length of less than 200 μm, or less than 150 μm, or less than 100 μm, or less than 90 μm, or less than 80 μm, or less than 70 μm, or less than 60 μm, or less than 50 μm.

[0041] Preferably, the defects detected have a major axis with a length greater than 0.5 μm, or greater than 5 μm, or greater than 10 μm, or greater than 20 μm, or greater than 40 μm.

[0042] When the defect includes a spherical or substantially spherical portion, the major axis corresponds to the diameter of the spherical portion.

[0043] Preferably, the first portion of the first image and / or the first portion of the second image are used to determine a parameter related to the shape of the defect. In such an embodiment, the method preferably includes determining a parameter related to the shape of the defect after the first image is acquired and / or determining a parameter related to the shape of the defect after the second image is acquired. This provides an additional step that enables the detected defect to be classified as a target defect. For example, if the target defect is spherical and the parameter related to the shape of the defect is the circularity of the defect, the circularity may be used to determine whether the defect is spherical or a thin line, such as a surface scratch, and thereby determine whether the defect is accurately included in the target defect count.

[0044] Preferably, the parameter related to the shape of the defect is the shape of the defect and / or the shape of the particle that caused the defect.

[0045] Preferably, the image capture device comprises at least a first camera, in particular at least a first digital camera. Preferably, the first digital camera comprises a line scan camera or an area scan camera.

[0046] Preferably, the illumination source emits a range of wavelengths and the beam comprises the same range of wavelengths as the illumination source, or a narrower range of wavelengths than the illumination source. A narrower wavelength range can be produced by appropriately positioning a filter that filters the wavelength range emitted by the illumination source.

[0047] Preferably, the illumination source comprises at least one light emitting diode, in particular an infrared, red, green, yellow or blue light emitting diode.

[0048] Preferably, the illumination source comprises at least one incandescent light source, such as a tungsten filament bulb.

[0049] Preferably, the illumination source comprises at least one laser.

[0050] Preferably, the illumination source has a first hue and the first image and / or the second image are monochromatic images having the same hue at different intensity levels.

[0051] Preferably, the beam is a stopped beam from an illumination source, the stopped beam passing through at least a first aperture located between the illumination source and the first major surface of the glass sheet.

[0052] Preferably, the illumination source comprises an illumination generating portion and a scattering portion for scattering light generated by the illumination generating portion. Preferably, the scattering portion is a body portion and the illumination generating portion is internal to the body portion. The scattering portion may be used to improve illumination of the defect.

[0053] Preferably, the optical axis of the beam strikes the first major surface of the glass sheet at an angle of incidence greater than 45°, preferably between 50° and 140°, more preferably between 80° and 100°, where the angle of incidence is defined relative to a tangent at the point on the first major surface where the optical axis of the beam strikes the first major surface.

[0054] In some embodiments, the beam is a light beam comprising electromagnetic radiation having at least one wavelength between 380 nm and 780 nm.

[0055] Preferably, in step (i), positive optical power is added to the light beam before it strikes the first major surface of the glass sheet, preferably 0.01 to 100 diopters of positive optical power is added to the light beam before it strikes the first major surface of the glass sheet, even more preferably 0.01 to 50 diopters of positive optical power is added to the light beam before it strikes the first major surface of the glass sheet. Preferably, optical power is added to the light beam using a lens or mirror before it strikes the first major surface of the glass sheet.

[0056] Preferably, in step (i), a negative optical power is applied to the light beam before the light beam strikes the first major surface of the glass sheet. Preferably, a negative optical power of between 0.01 diopters and 10 diopters is applied to the light beam before the light beam strikes the first major surface of the glass sheet. Preferably, the negative power is applied to the light beam by a lens, more preferably an adjustable lens, even more preferably a computer-adjustable lens, before the light beam strikes the first major surface of the glass sheet.

[0057] Preferably, in step (iv), the first focus of the convergent light beam is adjusted to a second focus, the second focus being further from the light source than the first focus.

[0058] Preferably, in step (iv), a positive optical power is added to the light beam after it hits the first major surface of the glass sheet, more preferably, a positive optical power of 0.01 diopters to 100 diopters is added to the light beam after it hits the first major surface of the glass sheet, and even more preferably, a positive optical power of 0.01 diopters to 50 diopters is added to the light beam after it hits the first major surface of the glass sheet. Preferably, a lens or mirror is used to add optical power to the light beam after it hits the first major surface of the glass sheet.

[0059] Preferably, in step (iv), a negative optical power is applied to the light beam after it strikes the first major surface of the glass sheet. Preferably, a negative optical power of 0.01 diopters to 10 diopters is applied to the light beam after it strikes the first major surface of the glass sheet. Preferably, the negative power is applied to the light beam after it strikes the first major surface of the glass sheet by a lens, more preferably an adjustable lens, even more preferably a computer-adjustable lens.

[0060] Preferably, the light source comprises a light-generating portion and a light-scattering portion. Preferably, the light-scattering portion is a body portion, and the light-generating portion is internal to the body portion. The light-scattering portion may be used to improve illumination of the defect. A suitable light-scattering portion comprises translucent plastic.

[0061] In some embodiments, the second portion of the first image and / or the second portion of the second image is used to determine the shape of the defect or a parameter related to the shape of the defect.

[0062] In some embodiments, the first plane is aligned with a first major surface of the glass sheet, and the method includes, prior to step (ii), a distance measurement step for determining the relative position of the first major surface of the glass sheet with respect to the image capture device so that the image capture device can be focused on the first major surface of the glass sheet during step (ii).

[0063] In some embodiments, the defect comprises a localized shape change in the first major surface of the glass sheet, wherein the localized shape change in the first major surface of the glass sheet is caused by particles deposited on the first major surface of the glass sheet during formation of the glass sheet, wherein the particles comprise tin or an oxide of tin.

[0064] Preferably, the particles are spherical or substantially spherical.

[0065] Preferably, the particles are at least partially immersed beneath the first major surface of the glass sheet.

[0066] In some embodiments, the defect comprises a localized shape change in the first major surface of the glass sheet, wherein the localized shape change in the first major surface of the glass sheet is caused by a particle deposited on the first major surface of the glass sheet during formation of the glass sheet, and wherein the particle that caused the localized shape change in the first major surface of the glass sheet is not present in the glass sheet when any or all of steps (i), (ii), (iii), (iv), or (v) are performed.

[0067] In some embodiments, the image capture device comprises a first camera and a second camera, preferably a first digital camera and / or a second digital camera.

[0068] Preferably, a first camera is used to capture a first image and a second camera is used to capture a second image.

[0069] In some embodiments, the first image and / or the second image are monochromatic images.

[0070] Preferably, the first image is a monochrome image having the hue of the first image.

[0071] Preferably, the second image is a monochrome image having the hue of the second image.

[0072] Preferably, the hue of the first image is the same as the hue of the second image.

[0073] Preferably, the first image is a grayscale image.

[0074] Preferably, the second image is a grayscale image.

[0075] Preferably, the first image has a pixel depth of at least 8 bits, or at least 10 bits, or at least 12 bits, or at least 16 bits.

[0076] Preferably, the second image has a pixel depth of at least 8 bits, or at least 10 bits, or at least 12 bits, or at least 16 bits.

[0077] In some embodiments, when negative optical power is added to the beam before the beam strikes the first major surface, in step (iv), the image capture device maintains focus on the first plane, and the focus of the converging beam is adjusted from the first focus to a second focus by removing the negative optical power added in step (i).

[0078] In such an embodiment, if during step (i) negative optical power is added to the beam before the beam strikes the first major surface of the glass sheet by using a lens, removing the lens from the beam path removes the negative optical power added to the beam during step (i).

[0079] Alternatively, if during step (i) an adjustable lens having a first focus is used to add negative optical power to the beam before it strikes the first major surface of the glass sheet, then in step (iv) the first focus of the adjustable lens is adjusted to remove some or all of the negative optical power added to the beam during step (i).

[0080] In some embodiments, when the beam is a light beam and negative optical power is added to the light beam before the light beam strikes the first major surface, in step (iv), the image capture device maintains focus on the first plane, and the focus of the converging light beam is adjusted from the first focus to a second focus by removing the negative optical power added in step (i).

[0081] In such an embodiment, if during step (i) negative optical power is added to the light beam before it strikes the first major surface of the glass sheet by using a lens, removing the lens from the light path removes the negative optical power added to the light beam during step (i).

[0082] Alternatively, if during step (i) an adjustable lens having a first focus is used to add negative optical power to the light beam before it strikes the first major surface of the glass sheet, then in step (iv) the first focus of the adjustable lens is adjusted to remove some or all of the negative optical power added to the light beam during step (i).

[0083] In some embodiments, the luminance is determined from a first image and a second image that are monochromatic, with high luminance being white and low luminance being black, with different hues in between.

[0084] Preferably, the images have a pixel depth of at least 8 bits, or at least 10 bits, or at least 12 bits, or at least 16 bits. Pixel depths outside this range, for example, pixel depths greater than at least 16 bits, can be used if desired.

[0085] Suitably, the lowest brightness level of a pixel in an image is 0 and the highest brightness level of a pixel in an image is 2. n -1, where n is the bitrate for the pixel depth.

[0086] Appropriately, the lowest brightness level of a pixel in an image is -(2 n -1) / 2, the highest brightness level of a pixel in the image is +(2 n −1) / 2, where n is the bit rate of the pixel depth.

[0087] Suitably, a monochrome image is a greyscale image, although different hues may be used, for example red, green, blue or combinations thereof.

[0088] In some embodiments, the defect detected is a first defect of a plurality of defects in the glass sheet, the plurality of defects also including at least a second defect, and the first defect is detected by first performing steps (i), (ii), and (iii), and then the second defect is detected by performing steps (i), (ii), and (iii), after which steps (iv) and (v) are performed to detect the first defect, followed by steps (iv) and (v) to detect the second defect.

[0089] Preferably, the first defect or the second defect is detected by moving the glass sheet relative to an image capture device and / or an illumination source.

[0090] Preferably, a first defect is detected by first performing steps (i), (ii) and (iii) with the image capture device in a first position relative to the glass sheet, after which the image capture device is moved relative to the glass sheet, and a second defect is detected by first performing steps (i), (ii) and (iii) with the image capture device in a second position relative to the glass sheet, after which the image capture device and / or the glass sheet are moved so that the image capture device is in the first position relative to the glass sheet to perform steps (iv) and (v) of detecting the defects.

[0091] Preferably, the image capture device and / or the glass sheet are moved so that the image capture device is in a second position relative to the glass sheet to perform steps (iv) and (v) of detecting a second defect.

[0092] Preferably, the distance from the first defect to the image capture device when the first defect is detected is the same as the distance from the second defect to the image capture device when the second defect is detected.

[0093] In some embodiments, the position of the image capture device is fixed relative to the illumination source.

[0094] In some embodiments, the beam illuminating the first major surface shares an optical axis with at least a reflected ray from the first major surface of the glass sheet to the image capture device.

[0095] In some embodiments, the glass sheet is manufactured using a float process, and the first major surface is not in contact with molten tin when the glass sheet is formed.

[0096] It is within the scope of the first aspect of the present invention for steps (iv) and (v) to be performed before steps (i), (ii), and (iii), and for steps (i), (ii), and (iii) to be performed in this order. When the first aspect of the present invention is implemented in this manner, it is preferable that step (v) be performed before step (iv). Also, when the first aspect of the present invention is implemented in this manner, a first image acquired by the image capture device has a first portion that is darker than a second portion, and a second image acquired has a first portion that is lighter than the second portion. This method is not preferable because it is not possible to distinguish the defect in the first acquired image from other defects in the second image that have a first portion that is lighter than the second portion. For example, dust particles on the glass surface may result in a first image in which the first portion is darker than the second portion, and a second image in which the first portion is darker than the second portion. Therefore, when using the present invention in this manner, each defect must be inspected twice to confirm that the defect is the specific defect of interest.

[0097] However, it is preferred to perform the method using steps (i), (ii), (iii), (iv), and (v) in this order, because steps (iv) and (v) need only be performed to determine whether the defect is a target defect when the first image has a first portion that is brighter than the second portion. When the first aspect of the invention is so performed, the first image captured by the image capture device in step (iii) has a first portion that is brighter than the second portion, and the second image captured by the image capture device in step (v) has a first portion that is darker than the second portion.

[0098] In some embodiments, the method comprises steps (i), (ii), (v), (iv), and (iii), in that order, when the first aspect of the invention is so practiced, a first image captured by the image capture device in step (v) prior to adjusting step (iv) has a first portion that is darker than its second portion, and a second image captured by the image capture device in step (iii) after adjusting step (iv) has a first portion that is darker than its second portion.

[0099] In some embodiments, the beam is a light beam and the illumination source is a light source, and such method includes the steps of: (i) directing a light beam from the light source onto a first major surface of the glass sheet to illuminate a defect in the glass sheet, the light beam striking the first major surface of the glass sheet being a converging beam having a first focus; (ii) focusing an image capture device onto a first plane to image the defect in the glass sheet, the image capture device being at a first position relative to the defect; and (iii) capturing a first image of the defect using the image capture device, (iv) performing the adjusting step; and (v) capturing a second image of the defect using an image capture device, the second image of the defect including the first portion due to light from the illuminated defect and the second portion due to light reflected from the first major surface of the glass sheet, wherein in the first image of the defect, the first portion is lighter than the second portion and in the second image of the defect, the first portion is darker than the second portion.

[0100] Preferably, the adjusting step includes adjusting a first focus of the converging light beam to a second focus such that the light beam impinging on the first major surface is a converging light beam having the second focus.

[0101] Preferably, the preparing step includes focusing an image capture device onto the second plane and imaging the defect with the image capture device focused on the second plane.

[0102] The present invention also provides, from a second aspect, an apparatus for determining the presence of a defect in a glass sheet, the glass sheet having a first major surface and an opposite second major surface, the apparatus comprising: an illumination source for illuminating a portion of a surface of the glass sheet containing the defect with a converging beam having a first focus; an image capture device for acquiring a first image of the illuminated defect when the image capture device is in a first position relative to the defect and focused on a first plane; at least one of adjustment means for adjusting the focus of the converging beam to a second focus while maintaining the image capture device focused on the first plane; focusing means for focusing the image capture device on the second plane and imaging the defect with the image capture device focused on the second plane; and movement means for moving the image capture device to a second position relative to the defect.

[0103] Each of the adjusting means, focusing means and moving means may be part of an apparatus alone or in combination with one or two of the others to provide an apparatus capable of carrying out the method according to the first aspect of the invention.

[0104] Preferably, the defect is on or near the first major surface of the glass sheet.

[0105] Preferably, the first major surface of the glass sheet is the air surface of a glass sheet formed by a float process.

[0106] Preferably, the beam has an optical axis arranged to strike the first major surface of the glass sheet at an angle of incidence greater than 45°, preferably between 50° and 140°, more preferably between 80° and 100°.

[0107] Preferably, the illumination source emits electromagnetic radiation having at least one wavelength between 300 nm and 10 μm, preferably between 300 nm and 2500 nm, more preferably between 300 nm and 1500 nm, even more preferably between 300 nm and 1100 nm.

[0108] Preferably, the illumination source emits light comprising electromagnetic radiation having at least one wavelength between 380 nm and 780 nm, i.e. the illumination source is preferably a light source and the beam is a light beam.

[0109] Preferably, the illumination source emits a range of wavelengths and the beam comprises the same range of wavelengths as the illumination source or a narrower range of wavelengths of the illumination source. Preferably, the apparatus comprises a filter positioned to filter the range of wavelengths emitted by the illumination source, such that the beam has a narrower range of wavelengths compared to the range of wavelengths emitted by the illumination source.

[0110] Preferably, the illumination source comprises at least one light emitting diode, in particular an infrared, red, green, yellow or blue light emitting diode.

[0111] Preferably, the illumination source comprises at least one incandescent light source, such as a tungsten filament bulb.

[0112] Preferably, the illumination source comprises at least one laser.

[0113] Preferably, the device comprises at least one aperture device for stopping the illumination source so that the beam is a stationary beam.

[0114] Preferably, the illumination source comprises a diffusing means for increasing the effective size of the illumination source.

[0115] Preferably, the illumination source comprises a lens for providing a converging beam.

[0116] Preferably, the apparatus comprises a beam splitter for directing a beam from the illumination source onto the surface of the glass sheet to be measured.

[0117] Preferably, the image capture device comprises a camera, more preferably a digital camera. Preferably, the digital camera comprises a line scan camera or an area scan camera.

[0118] Preferably, the apparatus comprises a controller for controlling at least one of the illumination source, the image capture device, the adjusting means, the focusing means and the moving means.

[0119] Preferably, the apparatus comprises a computer, and the images acquired by the camera are processed by software installed on the computer to determine a parameter related to the defect. Preferably, the parameter is a parameter related to the shape of the defect. Preferably, the parameter is a parameter related to the brightness of the defect in the image relative to the brightness of the glass surrounding the defect in the image. Preferably, the parameter is a parameter related to the color or hue of the defect in the image relative to the color or hue of the glass surrounding the defect in the image.

[0120] In embodiments in which the apparatus includes a moving means for moving the image capture device from a first position relative to the defect to a second position relative to the defect, the moving means is preferably capable of moving the image capture device in a direction parallel to a normal extending from the first major surface of the glass sheet being measured, either toward or away from the first major surface of the glass sheet being measured.

[0121] The moving means may be configured to move the image capture device from a first position for detecting a first defect in the glass sheet being measured to a second position relative to the first defect for detecting a second defect in the glass sheet, the first defect being different from the second defect.

[0122] The image capture device may be movable and / or the glass sheet to be measured may be mounted on a movable support such that the device further comprises a movable support.

[0123] In some embodiments, the adjustment means for adjusting the focus of the convergent beam to a second focus while maintaining the image capture device focused on the first plane comprises a lens, more preferably a computer-adjustable lens.

[0124] In such an embodiment, the lens is positioned so that the beam from the illumination source passes through the lens before striking the first major surface of the glass sheet being measured.

[0125] In some embodiments, the device comprises a lens, more preferably a computer adjustable lens, for adjusting the focus of the converging beam to a second focus while the image capture device remains focused on the first plane, and a beam splitter.

[0126] In such an embodiment, the lens is preferably between the illumination source and the beam splitter, or alternatively, the beam splitter is preferably between the lens and the illumination source.

[0127] In some embodiments, the apparatus comprises focusing means for focusing the image capture device onto a second plane and imaging the defect with the image capture device focused on the second plane.

[0128] Preferably, the focusing means comprises a lens, more preferably a computer adjustable lens, positioned between the first major surface of the glass sheet to be measured and the image capture device.

[0129] Preferably, the apparatus further comprises a beam splitter for redirecting the beam from the illumination source.

[0130] Preferably, a lens for focusing the image capture device onto the second plane is located between the beam splitter and the image capture device.

[0131] Preferably, a lens for focusing the image capture device onto the second plane is located between the beam splitter and the first major surface of the glass sheet being measured.

[0132] In some embodiments, an apparatus includes a light source for illuminating a portion of a surface of a glass sheet containing a defect with a converging light beam having a first focus; an image capture device for acquiring a first image of the illuminated defect when the image capture device is in a first position relative to the defect and focused on a first plane; at least one of adjusting means for adjusting the focus of the converging light beam to a second focus while the image capture device remains focused on the first plane; focusing means for focusing the image capture device on the second plane and imaging the defect with the image capture device focused on the second plane; and moving means for moving the image capture device to a second position relative to the defect.

[0133] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0134] [Figure 1] 1 shows a schematic cross-sectional view of an apparatus for carrying out the method according to the invention; [Figure 2] 2a and 2b show schematic diagrams of a first image (FIG. 2a) and a second image (2b) of a defect acquired with the apparatus shown in FIG. 1. [Figure 3] 2 shows a series of images of a defect taken with the apparatus shown in FIG. 1 with different levels of light power applied to the system. [Figure 4] 2 shows a schematic isometric view of the apparatus shown in FIG. 1 used to scan the surface of a glass sheet. DETAILED DESCRIPTION OF THE INVENTION

[0135] FIG. 1 shows a schematic cross-sectional view of an apparatus for carrying out the method according to the invention.

[0136] Apparatus 1 includes a light-emitting diode (LED) light source 3 that generates a diverging light beam 5 that is reflected 90° by a beam splitter 7. The reflected light passes through lens 9; a suitable lens 9 is a Nikon EL-Nikkor 50mm F / 2.8 lens. Lens 9 focuses the reflected light beam onto a major surface 11 of glass sheet 13, which is opposite major surface 15 of glass sheet 13. Before striking major surface 11, the light beam focused by lens 9 also passes through a computer-adjustable lens 17. A suitable computer-adjustable lens 17 is an Optotune EL-16-40-TC-VIS-5D-C.

[0137] 1, the apparatus 1 is positioned such that the lens 9 is between the beam splitter 7 and the computer adjustable lens 17. The lens 9 is between the major surface 11 and the beam splitter 7. The computer adjustable lens 17 is between the major surface 11 and the beam splitter 7.

[0138] Beam 5 has an optical axis that strikes major surface 11 at an angle of incidence greater than 45°, preferably between 50° and 140°, and more preferably between 80° and 100°. Preferably, the optical axis of the beam strikes major surface 11 at normal or substantially normal incidence. Shallow angles of incidence are not preferred because such illumination conditions can significantly illuminate defects, such as dust and scratches, on major surface 11, thereby reducing the sensitivity of the method to defects of interest.

[0139] Light reflected by major surface 11 of glass sheet 13 passes back through computer adjustable lens 17 and lens 9, then through beam splitter 7 to digital camera 19. In this example, digital camera 19 is a field, a suitable example of which is the Teledyne Dalsa Genie Nano M1920 digital camera.

[0140] If an infrared emitting solid state device (i.e., an infrared emitting LED) is used instead of the LED light source 3, then a suitable camera sensitive to the infrared radiation emitted by the infrared emitting solid state device is used to capture images of the illuminated defects. As will be readily apparent, any image capture device suitable for capturing images of defects illuminated by a beam from a particular illumination source may be used to carry out the method of the present invention.

[0141] To image defects on or near major surface 11 of glass sheet 13, digital camera 19 is focused on major surface 11.

[0142] In order to focus the digital camera 19 on the main surface 11, the distance between the digital camera 19 and the main surface 11 is required, and this distance is measured using a laser triangulation sensor such as a Micro-Epsilon optoNCDT ILD1420 to enable accurate focusing.

[0143] The distance from the digital camera 19 to the major surface 11 is then used to adjust the computer adjustable lens 17 so that the major surface 11 of the glass sheet 13 remains precisely in focus.

[0144] A controlled amount of negative optical power (e.g., about −0.2 diopters) is then added by computer adjusted lens 17, as it is known that the optical system will be sensitive to distortions in the glass surface around the defect of interest.

[0145] It has been found that the use of focused illumination from lens 9 with additional optical power provided by computer adjustable lens 17 causes images of certain defects acquired by digital camera 19 to appear brighter compared to images of the surrounding glass. It has been found that certain particles, such as tin-containing particles, cause concave local distortions of the glass surface 11 around the particle that can be used to optically determine the presence of such defects, even when the particle itself is small in size, such as less than 50 μm.

[0146] Particles that locally affect the surface profile of a glass sheet around the particle are believed to deposit on the glass surface when the glass sheet is hot enough that the viscosity of the glass is low enough that the deposition of the particle changes the surface shape or profile around the particle. One such example is tin-containing particles or tin particles that can form in a float bath when a glass sheet is formed using the float process. As the viscosity of the glass increases as the glass cools during the forming process, the surface profile around the particle "freezes in," resulting in a defect in the glass sheet. Even if the particle that caused the local change in the surface shape around the particle is later removed (e.g., because the particle was only weakly attached to the surface of the glass sheet), the defect will still exist in the glass sheet due to the change in the local surface profile.

[0147] Dust and dirt that may be present on major surface 11 will typically appear darker than the surrounding image of the glass. Such defects typically accumulate on major surface 11 when the glass is cut into sheets, for example, during handling and / or transport of the glass sheet.

[0148] By scanning the glass sheet 13, suitable image processing software can be used to identify areas of the surface 11 that have bright defects compared to the image of the surrounding glass sheet.

[0149] Advantageously, apparatus 1 is positioned to have a short depth of field so that images captured by digital camera 19 do not show defects on the glass body or opposite major surface 15 of a glass sheet having a thickness of at least about 1.5 mm. Thus, use of the above-described system can be used to detect the presence of defects on or near the surface of major surface 11. Such defects may be at least partially located below major surface 11.

[0150] Once an image is obtained that shows a defect that appears bright compared to the surrounding glass image, the image can be further processed to further determine the type of defect and help distinguish the defect from other types of defects.

[0151] For example, it has been found that under the lighting conditions described above, scratches on major surface 11 also appear brighter than the image of the surrounding glass sheet. To distinguish scratches from other types of defects, further image processing may be used to determine at least one parameter related to the shape of the defect in the image captured by digital camera 19.

[0152] One particularly useful parameter related to the shape of a defect is the aspect ratio. For example, scratches are usually narrow and long. Defects such as tin-containing particles or tin particles are usually spherical, and therefore have a circular profile in an image captured by a camera. The circularity of a defect can also be used as a parameter to distinguish between different types of defects, for example, by using the ratio of the defect's area to the defect's perimeter in an image acquired by a digital camera 19. One measure of circularity is:

[0153]

number

[0154] A perfect circle has a circularity of 1, and the higher the circularity, the less circular the defect. In a digital image of the defect, the perimeter and area of ​​the defect can be determined simply by counting the pixels.

[0155] To further reduce misclassification of a particular defect, the method of the present invention includes the step of removing the controlled level of negative optical power provided by the computer-adjustable lens 17 and acquiring a second image of the defect using, preferably, the same computer-adjustable lens 17 but adding a predetermined amount of positive optical power, such as 0.2 diopters.

[0156] The first and second images containing the same defect are then compared. As noted above, certain defects, such as tin deposited on the surface of the glass during molding or tin-containing defects, locally distort the glass surface (i.e., from flat to concave), and the reflection of light therefrom is adjusted depending on the degree of focus. In a defocused image when negative optical power is applied, the image of the defect appears bright compared to the image of the surrounding glass, but when the defect is in focus or when positive optical power is applied using computer-adjustable lens 17, the image of the defect appears dark compared to the image of the surrounding glass.

[0157] The device 1 may then be used with appropriate image processing steps to make it immune to all other defects except those that locally affect the surface of the glass sheet when deposited on it, such as dust, dirt, scratches, and tin defects or tin containing defects.

[0158] The method of the present invention can be applied to glass that moves relative to the optical system by fixing the relative motion using a short exposure time of the camera and / or a short illumination time of the light source. To cover large areas of the glass, the optical system can be raster scanned over the glass, or multiple optical systems can be used in combination to cover the required area.

[0159] As an alternative to the arrangement shown in FIG. 1, a computer adjustable lens 17 may be located between the beam splitter 7 and the lens 9 .

[0160] In another alternative to the apparatus shown in FIG. 1, a computer adjustable lens 17 may be located between the beam splitter 7 and the digital camera 19 .

[0161] In another alternative to the apparatus shown in FIG. 1, a computer adjustable lens 17 may be located between the beam splitter 7 and the light source 3 .

[0162] The computer adjustable lens 17 provides a quick way to add negative optical power to the light beam illuminating the major surface 11, which is a quicker way to control the degree of defocus of the imaging system, i.e., the digital camera 19.

[0163] To add negative optical power instead of using computer adjustable lens 17, a camera may alternatively be focused on the body of glass sheet 13. However, to adjust the focus to perform the further characteristic step of adding positive optical power, the camera's focus is adjusted to be on major surface 11. Moving the camera's focus is a way to add negative or optical power, but it is more time-consuming than using computer adjustable lens 17.

[0164] A similar effect can be achieved with a lens with a fixed focal length, but changing lenses takes time.

[0165] In other embodiments, the digital camera 19 may be movable towards or away from the first major surface 11 .

[0166] In other embodiments, the light source may be movable towards or away from the beam splitter 7 so that the light path from the light source to the first major surface 11 is adjustable.

[0167] 1, device 1 includes a housing 21 within which are housed LED 3, beam splitter 7, lens 9, computer-adjustable lens 17, and digital camera 19. Also contained within housing 21 is a controller 23 that is used to control the operation of LED 3 and computer-adjustable lens 17. Controller 23 is also used to control the operation of digital camera 19.

[0168] Controller 23 is in electrical communication with LED 3 via cable 25. Controller 23 is in electrical communication with computer-adjustable lens 17 via cable 27. Controller 23 is in electrical communication with digital camera 19 via cable 29. Controller 23 is also in electrical communication with computer 31 via cable 33.

[0169] The computer 31 may be provided with software that controls the operation of the LED 3, the computer adjustable lens 17, and the digital camera 19 via the controller 23. Images captured by the digital camera 19 may be transmitted to the computer 31 via the controller 23 along cables 29, 33. The software may include image processing software to help identify and distinguish defects as described above, for example by determining shape parameters of the defects, such as circularity.

[0170] FIG. 2a shows a schematic diagram of a portion of an image acquired by digital camera 19 of a portion of surface 11 on which spherical tin particles were deposited during the formation of a glass sheet. The spherical tin particles caused a localized change in the shape of the glass surface around the tin particles from flat to concave. In the image, defect 40 has a circular outline. The glass surrounding defect 40 is also included in the image and is labeled 42. In FIG. 2a, defect 40 is brighter than the glass surrounding defect 42, and is from an image acquired with apparatus 1 when digital camera 19 is focused on major surface 11 of glass sheet 13 and a controlled amount of negative optical power of approximately 0.2 diopters is added by computer-adjustable lens 17.

[0171] Using the image of FIG. 2a, computer 31 of FIG. 1 is used to perform additional image processing, as described above, to determine, for example, the circularity of defects in the image. The image processing step may determine that the defect is of a particular type and not another type that is not of interest. For example, when looking for a particular defect due to spherical tin or tin-containing particles deposited on a glass surface, the image processing step may be used to determine whether the defect has a circularity that indicates the defect is round (i.e., spherical) and further inspection is deemed necessary. If the image processing step determines that the defect is a scratch, further inspection may not be necessary.

[0172] Apparatus 1 is then used to acquire another image of the same defect with computer adjustable lens 17 used to provide a positive optical power of approximately 0.2 diopters (instead of being used to add a negative optical power of approximately 0.2 diopters).

[0173] Figure 2b shows a schematic diagram of a portion of an image of a circular defect 40 acquired by digital camera 19 when apparatus 1 is used with a positive optical power of approximately 0.2 provided by computer-adjustable lens 17. All other lighting conditions are the same as those used to acquire the image shown in Figure 2a.

[0174] The circular defect in the image has become darker compared to the surrounding glass. In Figure 2b, the glass surrounding the defect remains labeled 42, but the defect is labeled 40'.

[0175] FIG. 3 shows a series of images (a)-(g) of another defect identified using the apparatus 1.

[0176] In Figure 3(a), apparatus 1 is configured to add 0.3 diopters of negative optical power to the system using a digital camera 19 focused on major surface 11 and a computer adjustable lens 17. As can be seen above, the defect is circular and brighter (a light grey tint) than the image of the glass surrounding the defect.

[0177] In Figure 3(b), apparatus 1 is configured in the same way as when the image in Figure 3(a) was acquired, except that 0.2 diopters of negative optical power has been added to the system using computer adjustable lens 17 (instead of 0.3 negative optical power). As can be seen above, the defect is brighter (a lighter shade of gray) than the image of the glass surrounding the defect.

[0178] In Figure 3(c), the apparatus 1 is configured in the same way as when the image in Figure 3(a) was acquired, except that approximately 0.1 diopters of negative optical power has been added to the system using computer-adjustable lens 17 (instead of the 0.3 negative optical power). The defect is in focus and appears dark compared to the image of the glass surrounding the defect.

[0179] In Figure 3(d), the apparatus 1 is configured in the same way as when the image in Figure 3(a) was acquired, except that no optical power was added to the system using the computer adjustable lens 17. As can be seen above, the defect is darker (a darker shade of grey) than the image of the glass surrounding the defect.

[0180] In Figure 3(e), the apparatus 1 is configured in the same way as when the image of Figure 3(a) was acquired, except that 0.1 diopters of positive optical power has been added to the system using a computer adjustable lens 17. As can be seen above, the defect is darker (a darker shade of grey) than the image of the glass surrounding the defect, and is slightly larger than the image of the defect in Figure 3(d) due to the increased amount of defocus from the glass surface 11.

[0181] In Figures 3(f) and 3(g), the apparatus 1 is configured in the same manner as when the image of Figure 3(a) was acquired, except that 0.2 diopters and 0.3 diopters of positive optical power, respectively, have been added to the system using the computer-adjustable lens 17. As can be seen in both images, the defect is darker (a darker shade of gray) than the image of the glass surrounding the defect. Also, in each image, the image of the defect is slightly larger than the image of the defect in Figure 3(e) due to an increased amount of defocus from the glass surface 11. The image of the defect in Figure 3(g) is larger than the image of the defect in Figure 3(f). This is because more positive optical power was added to the system using the computer-adjustable lens 17 when the image of Figure 3(g) was acquired compared to when the image of Figure 3(f) was acquired.

[0182] The series of images 3(a)-3(g) illustrates how, when the amount of optical power is adjusted from a negative amount of optical power to a positive amount of optical power, the defect of interest can be distinguished from other defects that do not distort the surrounding glass surface and therefore do not appear brighter or darker than the surrounding image.

[0183] As mentioned above, adding optical power to the system using computer adjustable lens 17 is more convenient and quicker than adjusting the focus of digital camera 19 .

[0184] 4 is a schematic diagram showing how apparatus 1 is used to scan an entire glass sheet 13 for defects on or in major surface 11. In this example, glass sheet 13 is rectangular and stationary relative to apparatus 1. In this example, apparatus 1 is as shown in FIG.

[0185] In this example, glass sheet 13 is flat and has a major surface 11, although glass sheet 13 may be curved. On major surface 11 is a first axis 47 and a second axis 48 that is perpendicular to major surface 11. A third axis 49 extends from major surface 11 and is perpendicular to both first axis 47 and second axis 48.

[0186] Preferably, the optical axis of the beam 5 impinging on the major surface 11 is substantially parallel to the third axis 49 .

[0187] Apparatus 1 may capture images of glass sheet 13 using digital camera 19, using a suitable XY stage or robotic arm (not shown) to move the apparatus in the direction of arrow 50. The direction of arrow 50 in this example is parallel to the side edges of glass sheet 13 and parallel to first axis 47.

[0188] The entire glass sheet 13 may be scanned by moving the apparatus 1 in a raster fashion, for example, when the apparatus 1 reaches the end of a first path (labeled 1'), the apparatus may be moved in the direction of arrow 52 to a position shown as 1'' and scanned along the path shown by arrow 54. The paths of arrows 50 and 54 are parallel to each other and both parallel to the first axis 47.

[0189] In images acquired with negative optical power added to the system, areas with bright defects compared to the surrounding glass (e.g., as shown in Figures 2 and 3) are further analyzed to determine how circular the image is and whether the image of the defect changes, as shown in Figures 3(a)-3(g). This can be performed when the defect of interest is identified or after the entire glass sheet has been scanned. In this latter embodiment, the location of each image where a bright defect was identified is recorded so the system can return to that location and perform the steps shown in Figures 3(a)-3(g).

[0190] To speed up the operation, it is possible to use only the computer adjustable lens 17 to provide a predetermined negative optical magnification (e.g., −0.3 diopters) for the first scan, and then use a single predetermined positive optical magnification (e.g., +0.3 diopters) to see if the image of the defect changes as shown in Figures 2a and 2b.

[0191] Instead of apparatus 1 moving across surface 11 of glass sheet 13, glass sheet 13 may be placed on a suitable movable support such that glass sheet 13 moves relative to apparatus 1. Apparatus 1 and glass sheet 13 may each move during the scanning process.

[0192] In another embodiment, apparatus 1 only traverses the glass sheet along a fixed path, with glass sheet 13 moving along a path perpendicular to the path traversed by apparatus 1. Such an embodiment is particularly useful when glass sheet 13 is in the form of a moving glass ribbon, such as formed in a float process over a molten tin bath, whereby apparatus 1 can be located downstream of the molten tin bath and scanned, preferably before cutting the glass ribbon into individual sheets. Apparatus 1 can scan across the ribbon width at a rate dependent on the ribbon speed, such that a scan of the entire ribbon width is performed and then the length of the ribbon can be scanned as the ribbon moves in the transport direction.

[0193] In another embodiment, two or more devices such as that shown in FIG. 1 are used to scan different portions of the glass sheet or ribbon.

[0194] In another embodiment, apparatus 1 is also movable in a direction parallel to axis 49. In such an embodiment, it is not necessary to use computer-adjustable lens 17 to provide positive and negative optical power; instead, apparatus 1 may be moved toward or away from major surface 11 in a direction parallel to third axis 49 to position the image capture device to acquire first and second images of defects in glass sheet 13.

[0195] The present invention is particularly useful for determining the presence of defects in glass sheets on which particles have been deposited when the viscosity of the glass is low enough to locally distort the shape of the glass surface around the deposited particles (i.e., during the formation of the glass sheet). The local shape distortion of the glass surface around the particles adjusts the path of light illuminating the defect differently depending on the convergence of the incident light beam, which can be used to identify this type of defect. The local shape distortion of the glass surface around the particles remains even if the particles are subsequently removed from the glass sheet. Furthermore, the optical effect associated with the local shape distortion of the glass surface around the particles can be used to identify smaller defects because the optical effect is large even when the particles causing the local shape distortion of the glass surface around the particles are small.

Claims

1. 1. A method for detecting defects in a glass sheet, the glass sheet having a first major surface and an opposite second major surface, the method comprising: (i) directing a beam from an illumination source onto the first major surface of the glass sheet to illuminate defects in the glass sheet, the beam striking the first major surface of the glass sheet being a converging beam having a first focal point; (ii) focusing an image capture device onto a first plane to image the defect in the glass sheet, the image capture device being at a first position relative to the defect; (iii) capturing a first image of the defect using the image capture device, the first image including a first portion from the illuminated defect and a second portion due to reflection of at least a portion of the beam from the first major surface of the glass sheet; (iv) performing an adjusting step, the adjusting step including at least one of: adjusting a first focus of the convergent beam to a second focus such that the beam striking the first major surface is a convergent beam having a second focus; focusing the image capture device on a second plane and imaging the defect with the image capture device focused on the second plane; and moving the image capture device to a second position relative to the defect; (v) capturing a second image of the defect using the image capture device, the second image including a first portion from the illuminated defect and a second portion due to reflection of at least a portion of the beam from the first major surface of the glass sheet; Including, In the first image of the defect, the first portion is brighter than the second portion, and in the second image of the defect, the first portion is darker than the second portion. A method for detecting defects in glass sheets.

2. The method of claim 1 , wherein the beam is a beam of electromagnetic radiation comprising electromagnetic radiation having a wavelength between 300 nm and 10 μm.

3. The method according to claim 1 or 2, wherein the beam is a light beam comprising electromagnetic radiation having at least one wavelength between 380 nm and 780 nm.

4. The method of claim 1 , wherein the first plane is aligned with a first major surface of the glass sheet.

5. 5. The method of claim 1, wherein in step (i), positive optical power is applied to the beam before it strikes the first major surface of the glass sheet.

6. 6. The method of claim 1, wherein in step (i), a negative optical power is applied to the beam before it strikes the first major surface of the glass sheet.

7. 7. The method of claim 6, wherein in step (iv), the image capture device maintains focus on the first plane and the focus of the convergent beam is adjusted from the first focus to the second focus by removing the negative optical power added in step (i).

8. 8. The method of claim 1, wherein in step (iv), a negative optical power is applied to the beam after it strikes the first major surface of the glass sheet.

9. 9. A method according to any one of claims 6 to 8, wherein a negative optical power is added to the beam by a lens.

10. 10. The method of claim 1, wherein in step (iv), the image capture device maintains focus on a first plane.

11. 11. The method of claim 1, wherein in step (iv), the image capture device maintains a first position relative to the defect such that in step (v) the second image of the defect is acquired using the image capture device at the first position relative to the defect.

12. 12. The method of claim 1, wherein the defect comprises a localized shape variation in the first major surface of the glass sheet, the localized shape variation in the first major surface of the glass sheet being caused by a particle deposited on the first major surface of the glass sheet during formation of the glass sheet.

13. 13. The method of claim 12, wherein the particles are at least partially immersed beneath the first major surface of the glass sheet, or the glass sheet is free of particles that caused a localized shape change in the first major surface of the glass sheet when any or all of steps (i), (ii), (iii), (iv), or (v) are performed.

14. The method of claim 1 , wherein the image capture device comprises at least a first camera.

15. 15. The method of any one of claims 1 to 14, wherein the first image is a monochromatic image and / or the second image is a monochromatic image.

16. The method of claim 15 , wherein the first image and the second image have the same hue.

17. 17. The method of any one of claims 1 to 16, wherein the defects have a major axis with a length of less than 200 μm, or less than 150 μm, or less than 100 μm, or less than 90 μm, or less than 80 μm, or less than 70 μm, or less than 60 μm, or less than 50 μm, and / or the defects detected have a major axis with a length of more than 0.5 μm, or more than 5 μm, or more than 10 μm, or more than 20 μm, or more than 40 μm.

18. 18. The method according to claim 1, wherein the first portion of the first image and / or the first portion of the second image are used to determine a parameter related to the shape of the defect, or the shape of the defect or the shape of a particle causing the defect.

19. 19. The method of any one of claims 1 to 18, wherein the first plane is aligned with the first major surface of the glass sheet, and prior to step (ii), the method includes a distance measurement step for determining the position of the first major surface of the glass sheet relative to the image capture device such that during step (ii), the image capture device can be focused on the first major surface of the glass sheet.

20. 20. The method of any one of claims 1 to 19, wherein the detected defect is a first defect of a plurality of defects in the glass sheet, the plurality of defects also including at least a second defect, the first defect being detected by first performing steps (i), (ii), and (iii), and then the second defect being detected by performing steps (i), (ii), and (iii), after which steps (iv) and (v) are performed to detect the first defect, followed by steps (iv) and (v) to detect the second defect.

21. 21. The method of any one of claims 1 to 20, wherein the beam illuminating the first major surface shares an optical axis with at least a ray of light reflected from the first major surface of the glass sheet to the image capture device.

22. 22. The method of any one of claims 1 to 21, wherein the glass sheet is manufactured using a float process and the first major surface is not in contact with molten tin when the glass sheet is formed.

23. 23. The method of any one of claims 1 to 22, wherein the illumination source emits a range of wavelengths and the beam comprises the same range of wavelengths as the illumination source or a narrower range of wavelengths relative to the illumination source.

24. 24. The method of claim 23, wherein a filter is positioned to filter a range of wavelengths emitted by the illumination source such that the beam has a narrower range of wavelengths compared to the range of wavelengths emitted by the illumination source.

25. 25. The method according to any one of claims 1 to 24, wherein the illumination source comprises at least one light emitting diode, in particular an infrared, red, green, yellow or blue light emitting diode, or at least one incandescent light source such as a tungsten filament bulb, or at least one laser.

26. 26. The method of claim 25, wherein the illumination source has a first hue and the first image and / or the second image are monochromatic images having the same hue at different intensity levels.

27. 27. The method of any one of claims 1 to 26, wherein the beam is a stop beam from the illumination source, the stop beam passing through at least a first aperture located between the illumination source and the first major surface of the glass sheet.

28. 1. An apparatus for determining the presence of defects in a glass sheet, the glass sheet having a first major surface and an opposite second major surface, the apparatus comprising: an illumination source; an image capture device; and a computer with image processing software; wherein the device is directing a convergent beam from an illumination source onto a first major surface of the glass sheet to illuminate a portion of the first major surface of the glass sheet containing a defect with the convergent beam having a first focus; capturing, with the image capture device, a first image of the illuminated defect while the image capture device is in a first position relative to the defect and focused on a first plane, the first image including a first portion from the illuminated defect and a second portion due to reflection from the first major surface of the glass sheet; performing the adjusting step via at least one of an adjusting means for adjusting the focus of the convergent beam to a second focus while maintaining the image capture device focused on the first plane, a focusing means for focusing the image capture device on the second plane and imaging the defect with the image capture device focused on the second plane, and a moving means for moving the image capture device to a second position relative to the defect; capturing, with the image capture device, a second image of the defect, the second image including a first portion from the illuminated defect and a second portion due to reflection of at least a portion of the beam from the first major surface of the glass sheet; and determining, via the image processing software of the computer, that the first portion of the first image is lighter than the second portion of the first image and that the first portion of the second image is darker than the second portion of the second image to determine the presence of the defect; It is composed of An apparatus for determining the presence of defects in a glass sheet.

29. 30. The apparatus of claim 28, wherein the adjusting means for adjusting the focus of the convergent beam to a second focus while the image capture device remains focused on the first plane comprises a lens, and / or the focusing means for focusing the image capture device on the second plane comprises a lens so as to image the defect with the image capture device focused on the second plane.

30. 30. The apparatus of claim 28 or 29, further comprising a controller for controlling at least one of the illumination source, the image capture device, and means for adjusting the focus of the convergent beam to a second focus while the image capture device remains focused on a first plane.

31. 31. The method of any one of claims 28 to 30, further comprising a computer, wherein images acquired by the image capture device are processed by software installed on the computer to determine parameters associated with the defect.

32. 32. The apparatus of any one of claims 28 to 31, comprising movement means for moving the image capture device from the first position relative to the defect to the second position relative to the defect, and further wherein the movement means can move the image capture device closer to or away from a direction parallel to a normal extending from the first major surface of the glass sheet being measured, and / or the movement means is configured to move the image capture device from the first position to detect a first defect in the glass sheet being measured to the second position relative to the first defect to detect a second defect in the glass sheet.

33. 33. The apparatus of any one of claims 28 to 32, wherein the illumination source comprises a light emitting diode, and / or the illumination source comprises a lens for providing the convergent beam, and / or the apparatus comprises a beam splitter for directing the beam from the illumination source onto the surface of the glass sheet to be measured.

34. 34. Apparatus according to any one of claims 28 to 33, wherein the illumination source emits electromagnetic radiation having a wavelength between 300 nm and 10 μm.

35. 35. Apparatus according to any one of claims 28 to 34, wherein the illumination source emits light comprising electromagnetic radiation having at least one wavelength between 380 nm and 780 nm.

36. 36. An apparatus according to any one of claims 28 to 35, wherein the illumination source emits a range of wavelengths and the beam comprises the same range of wavelengths as the illumination source or a narrower range of wavelengths for the illumination source.

37. 37. The apparatus of claim 36, comprising a filter positioned to filter a range of wavelengths emitted by the illumination source such that the beam has a narrower range of wavelengths compared to the range of wavelengths emitted by the illumination source.

38. 38. Apparatus according to any one of claims 28 to 37, wherein the illumination source comprises at least one light emitting diode, in particular an infrared, red, green, yellow or blue light emitting diode, or at least one incandescent light source such as a tungsten filament bulb, or at least one laser.

39. 39. Apparatus according to any one of claims 28 to 38, comprising an aperture device for stopping the illumination source so that the beam is a stopped beam.

40. 40. Apparatus according to any one of claims 28 to 39, wherein the illumination source comprises diffusing means for increasing the effective size of the illumination source.

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