Patent ID: 7924480

Claim:
An edge detecting device for detecting a position of an edge of an object, comprising: a measuring circuit for emitting an inspection light to a linear inspecting area including said object, and measuring first light quantity of a reflected light of said inspection light reflected from said inspecting area in a first state and second light quantity of a reflected light of said inspection light reflected from said inspecting area in a second state; a calculation circuit for calculating a difference of said first light quantity and said second light quantity measured by said measuring circuit for each pixel with a first predetermined length, calculating first total differences of reflected lights from pixels with a second predetermined length located adjacent to an objective dot in one direction by totalizing differences between said first and said second light quantity reflected from each of the pixels, and calculating second total differences of reflected lights from the other pixels with said second predetermined length located adjacent to said objective dot in the other direction by totalizing differences between said first and said second light quantity reflected from each of the other pixels; and a judgment circuit for judging said objective dot with the largest variation between the first total differences and the second total differences to be a position of said edge.