Illumination system with incident beams from near and far dark field for high speed surface inspection of rolled aluminum sheet

An apparatus for inspecting surface quality of a moving sheet of metal comprising:

• means for supporting said apparatus in a stationary position relative to a moving sheet of metal to be inspected;
• means for illuminating a surface of a moving sheet of metal to be inspected with at least two incident beams of light;
• means for inspecting said illuminated surface to detect intensity differences in light reflected by such illuminated surface from such at least two incident beams of light;
• said illuminating means is mounted on said support means for directing such at least two incident beams of light in a direction along such moving sheet of metal and said inspecting means being mounted on said support means to receive such reflected light;
• said illuminating means comprises at least two lamps each of which is adapted to emit a respective beam of light where each beam is elongate and narrow in cross-section and of a width at least as wide as a moving sheet of metal to be inspected;
• each of said at least two lamps is positioned on said support means to direct its corresponding beam of light onto an inspection region through which such sheet of metal moves and where each such beam emitted from said at least two lamps is at a different angle of incidence relative to other such beams of light to provide at least two corresponding incident beams from a near dark field and a far dark field;
• means for controlling beam intensity of each of said lamps to permit independent adjustment of beam intensity of each of said at least two lamps;
• said inspecting means comprising means for sensing light reflected by a surface irregularity from at least one of said near dark field and said far dark field of said inspection region;
• said sensing means senses reflected light simultaneously from said at least two lamps while remaining at a single angle of reflection relative to normal for said inspection region;
• means for detecting sensed reflected light from said inspection region which is of an increased intensity greater than a predetermined minimum intensity or less than a predetermined maximum intensity, said detected reflected light of increased intensity or decreased intensity being indicative of an irregularity in surface quality of said moving sheet of metal;
• and
• means for recording location on such moving sheet of metal of a detected irregularity in surface finish quality.