System and associated method for online detection of small defects on/in a glass sheet

An online apparatus for measuring small optical or obstructive defects in a selected area of a glass sheet in a system for fabricating glass sheets including a heating station for heating the glass sheet to a temperature adequate to soften the glass for forming into a desired shape, a bending station wherein the softened sheet is formed to the desired shape, a cooling station wherein the formed glass sheet is cooled in a controlled manner, and one or more conveyors for conveying the glass sheet from station to station during processing, the apparatus including:

• an upstream conveyor and a downstream conveyor, each of which convey each glass sheet in a generally horizontal orientation, wherein the upstream conveyor and downstream conveyor are positioned end-to-end with their adjacent ends spaced apart by a selected size gap such that, as a glass sheet is conveyed from the upstream conveyor to the downstream conveyor, a portion of the glass sheet is unsupported over the gap;
• a background screen including contrasting elements arranged in a pre-defined pattern, wherein the background screen extends across the full dimension of the selected area in the direction transverse to the direction of conveyance;
• a line scan camera for acquiring a set of image data comprising multiple images of the background screen, each image associated with a portion of the selected area of the glass sheet, as the glass sheet is conveyed across the path between the camera and the background screen, the background screen mounted such that the camera may acquire multiple images of the background screen as the unsupported portion of the glass sheet is conveyed therebetween;
• and
• a computer including at least one processor programmed to execute logic for receiving the set of image data, developing an intensity map from the set of image data, and identifying and locating the small defects from the intensity map.

A method for measuring small defects in a selected area of a glass sheet as the glass sheet is conveyed in a system for fabricating glass sheets including one or more processing stations and one or more conveyors for conveying the glass sheet from station to station during processing, the method including at least the steps of:

• providing an upstream conveyor and a downstream conveyor, each of which convey each glass sheet in a generally horizontal orientation, wherein the upstream conveyor and downstream conveyor are positioned end-to-end with their adjacent ends spaced apart by a selected size gap such that, as a glass sheet is conveyed from the upstream conveyor to the downstream conveyor, a portion of the glass sheet is unsupported over the gap;
• providing a background screen including contrasting elements arranged in a pre-defined pattern, wherein the background screen extends across the full dimension of the selected area in the direction transverse to the direction of conveyance of the glass sheet, and wherein the background screen is mounted such that a line scan camera may acquire multiple images of the background screen as the unsupported portion of the glass sheet is conveyed therebetween;
• conveying the glass sheet across the path between the line scan camera and the background screen;
• acquiring from the line scan camera a set of image data comprising multiple images of the background screen, each image associated with a portion of the selected area of the glass sheet, as the glass sheet is conveyed across the path between the camera and the background screen;
• and
• executing logic on a computer including at least one processor for receiving the set of image data, developing an intensity map from the set of image data, and identifying and locating the small defects from the intensity map.