Patent ID: 6303925
Filing Date: 2001-10-16
Classification: B07C,G01N

Abstract:
Apparatus for distinguishing paper from plastic objects, comprising:a coherent light source;a detector arranged to measure an intensity of light that reaches the detector from said light source,wherein when a plastic object and a paper object are respectively positioned between the light source and the detector at a first distance from the detector, the intensities of light measured by the detector for the plastic object and the paper object are approximately equal,wherein when the plastic object is positioned between the light source and the detector at a second distance that is farther from the detector than the first distance, the intensity of light measured by the detector for the plastic object is substantially greater than the intensity of light measured by the detector for the plastic object when the plastic object was at the first distance;wherein when the paper object is positioned between the light source and the detector at a second distance that is farther from the detector than the first distance, the intensity of light measured by the detector for the paper object is substantially less than the intensity of light measured for the paper object when the paper object was at the first distance, andwherein said second distance is selected as a minimum distance from said detector;a device arranged to convey said objects past the detector such that when said objects are between the detector and the light source, said objects are at least said minimum distance from the detector; anda thresholding device connected to said detector for comparing the light intensity measured as the object is moved between the detector and the light source with at least one threshold intensity, said threshold intensity being an intensity either below which the object is determined to be paper or above which the object is determined to be plastic.