Patent ID: 6011620
Filing Date: 2000-01-04
Classification: G01N

Abstract:
Apparatus for determining defects in an optically transmissive planar object, comprising:(A) a camera having a sensor array for obtaining images of said object, said camera having an optical axis;(B) a light source positioned to direct light at said camera along said optical axis;(C) an object inspection location for receiving said object and disposed between said camera and said light source, said planar object being located at an object plane with said camera being focused at a position that is within the distance of several millimeters from said object plane;(D) a mask positioned in the light path between said light source and said inspection location;(E) said mask having a stripe design selected from the group consisting of a) a narrow clear stripe, for allowing transmission of said light, and straddled by opaque regions which block transmission of said light, b) a narrow opaque stripe straddled by clear regions and c) alternating narrow clear and opaque stripes of a spacing that will cyclically generate a uniform background through interference phenomenon in the region between said mask and said camera;(F) said camera being operable to obtain an image of said object with a selected one of said masks in position; and(G) means for processing said images to obtain indications of said defects.