Optical inspection apparatus and illumination system particularly useful therein

Claim 1

Inspection apparatus for optically inspecting the surface of a workpiece, comprising: a memory for storing data relating to the desired features of the workpiece surface; an illumination system for illuminating an area of the workpiece surface; an electro-optical sensor for sensing the light reflected from the illuminated workpiece surface, and for outputting electric signals corresponding thereto; and a processor including logic circuitry for analyzing the electric signals outputted by said electro-optical sensor, for comparing them with the data stored in said memory, and for providing an indication of any discrepancies with respect thereto indicating a defect in the inspected workpiece surface; characterized in that said illumination system illuminates an area of the workpiece surface with a sky of illumination which is, with respect to each point in the illuminated area, substantially uniform and circularly symmetric over a solid angle around the optical axis passing perpendicularly through the electro-optical sensor and the workpiece surface; said illumination system comprising: first light producing means producing, within said sky of illumination, a brightfield component of substantially circular configuration and uniform integrity; and second light producing means producing, within said sky of illumination, a darkfield component of substantially annular configuration and uniform intensity around said brightfield component; said second light producing means including a plurality of light sources arranged in an equally spaced circular array around said optical axis and a plurality of reflectors effective to substantially focus the light from said plurality of light sources on the workpiece surfaces, each of said reflectors being formed with an inner knife edge to produce a sharp inner edge of the annular darkfield component of the sky of illumination.