Abstract: The mapping sensor system of the invention is intended for use with a mechanical arm of an industrial robot which loads and unloads flat circular objects, such as semiconductor wafers, into and from wafer cassettes on operations of processing the semiconductor wafers in stand-alone or cluster machines used in semiconductor production. The mapping system consists of a light source, a light-receiving element, and a light beam shaper. The light source is installed on the front end of the robot arm and directs the light via the beam shaper to the leading edge of the semiconductor wafer. The beam reflected from the wafer edge is sensed by a light-receiving element, such as a photodiode. The shaper modifies the shape and the cross-section of the beam directed towards the wafer so as to provide reflection from the curvilinear surface of the edge, irrespective of the existence of the notch, most optimum for detection by the photodiodes and without generation of false signals.