NON-CONTACT HIGH RESOLUTION DISPLACEMENT MEASUREMENT TECHNIQUE

摘要

An apparatus for optically detecting the position of an edge (114) of a workpiece in a sensing plane (110), involving the emission of electromagnetic energy from a known source region (100) in the sensing plane (110) such as to cause the edge (114) to create a shadow having a penumbra in the sensing plane (110). Two detectors (106, 108) are provided for determining the amount of energy which reaches two known detection regions in the sensing plane (110) and wholly within the penumbra. A mathematical derivation shows that the amount of energy detected by one detector (106) determines a first curve in the sensing plane (110) on which the edge must lie, and the amount of energy detected by the other detector (108) determines a second curve in the sensing plane (110) on which the edge (114) must lie. The intersection of these two curves fully determine the position of the edge (114) in the sensing plane (110).