Method and apparatus for automatic inspection of moving surfaces

Method for automatic inspection of moving surfaces using at least three different illumination/observation channels, said method comprising the steps of:

• a) illuminating said surface by a beam of light from a light source;
• b) receiving light of a first characteristic reemitted from said surface under a bright field condition by a first light sensitive sensor device to obtain a first signal;
• c) receiving light of a second and a third characteristic, respectively, reemitted from said surface under a dark field condition by a second and a third light sensitive sensor device to obtain a second signal and a third signal, said first, second and third light sensitive sensor devices being spatially separated from each other;
• and
• d) deriving from said first, second and third signals a physical property of said surface.

Apparatus for automatic inspection of moving surfaces, comprising

• a first light source illuminating said surface with light of a first spectral characteristic under a bright field condition;
• a light sensitive sensor device receiving reemitted light of the first spectral characteristic to obtain a first signal;
• a second light source illuminating said surface with light of a second spectral characteristic under a dark field condition, said second spectral characteristic being different from said first spectral characteristic, said light sensitive sensor device receiving reemitted light of the second spectral characteristic to obtain a second signal;
• a third light source illuminating said surface with light of a third spectral characteristic under a dark field condition, said third spectral characteristic being different from said first and second spectral characteristics, said light sensitive sensor device receiving reemitted light of the third spectral characteristic to obtain a third signal;
• and
• means for deriving a physical property of said surface from said first, second, and third signals.

Apparatus for automatic inspection of moving surfaces, comprising

• a light source for illuminating said surface;
• a first light sensitive sensor device receiving light of a first spectral characteristic reemitted from said surface under a bright field condition to obtain a first signal;
• a second light sensitive sensor device receiving light of a second spectral characteristic reemitted from said surface under a dark field condition to obtain a second signal, said second spectral characteristic being different from said first spectral characteristic;
• a third light sensitive sensor device receiving light of a third spectral characteristic reemitted from said surface under a dark field condition to obtain a third signal, said third spectral characteristic being different from said first and second spectral characteristic, said first, second and third light sensitive sensor devices being spatially separated from each other;
• and
• means for deriving a physical property of said surface from said first, second, and third signals.