Apparatus and process for detecting the presence of defects on a moving sheet of material

An apparatus for detecting the presence of defects in a moving sheet of material wherein said defects comprise fisheye defects, speck defects and scratches, comprising:

• a first elongated light source having a first longitudinal axis and emitting a first emitted light, said first longitudinal axis oriented substantially perpendicular to the direction of movement of said moving sheet;
• first optical and light processing means for collecting first emitted light after it has passed through said moving sheet, and for converting said collected first emitted light into a first time resolved electrical signal;
• a background having at least one edge, said background located between said first optical and light processing means and said moving sheet such that said edge is oriented substantially parallel to said first longitudinal axis so that said background is imaged in said fisheye defects and said speck defects prevent a portion of said first emitted light from reaching said first optical and light processing means;
• a first shielding enclosure for enclosing said first elongated light source, at least a portion of said first optical and light processing means, and said background so that only first emitted light illuminates said moving sheet and is received in said first optical and light processing means;
• means to pass said moving sheet through said first shielding enclosure;
• a second elongated light source having a second longitudinal axis and emitting a second emitted light, said second longitudinal axis oriented substantially perpendicular to the direction of movement of said moving sheet;
• a second optical and light processing means for collecting second emitted light after it has passed through said moving sheet so that light is image in said fisheye defects and said speck defects prevent a portion of said second emitted light from reaching said second optical and light processing means, and for converting said collected second emitted light into a second time resolved electrical signal;
• a second shielding enclosure for enclosing said second elongated light source and at least a portion of said second optical light processing means so that only light from said second elongated light source is received in said second optical and light processing means;
• means to pass said moving sheet through said second shielding enclosure;
• a third elongated light source having a third longitudinal axis and emitting a third emitted light, said third longitudinal axis oriented substantially perpendicular to the direction of movement of said moving sheet;
• third optical and light processing means for collecting said third emitted light after it has passed through said moving sheet and for converting said collected third emitted light into a third time resolved electrical signal;
• a strip located between said third elongated light source and said moving sheet and between said third elongated light source and said third optical and light processing means and oriented substantially parallel to said third longitudinal axis, such that said third optical and light processing means detects scratches, fisheye defects, and speck defects as brighter than the rest of the moving sheet;
• a third shielding enclosure for enclosing said third light source, at least a portion of said third optical and light processing means, and said strip so that only third emitted light passing around said strip illuminates said moving sheet and is received in said third optical and light processing means;
• means to pass said moving sheet through said third shielding enclosure;
• signal processing means, operationally connected to said first optical and light processing means, said second optical and light processing means and said third optical and light processing means, for analyzing and comparing said first time resolved electrical signal, said second time resolved electrical signal, and said third time resolved electrical signal for determining the kind, location, number and size of defects in said moving sheet.

A method of detecting defects in a sheet of material, wherein said defects comprise fisheye defects and speck defects, comprising the steps of:

• (a) projecting a first beam of light post at least one edge of a background onto a portion of said sheet of material so that said first beam of light passes through said sheet of material and said background is imaged in said fisheye defects in said sheet of material;
• (b) collecting said first beam of light after it passes through said portion of said sheet of material;
• and
• (c) analyzing said thus collected first beam of light to detect said defects.