Method and apparatus for measuring surface distances from a refe

Details Method and apparatus for measuring surface distances from a refe Method and apparatus for measuring surface distances from a refe

1992-11-16

1994-03-29

Evans, F. L.

Optics: measuring and testing

By polarized light examination

With light attenuation

250561, G01B 1100

Patent

active

052989763

ABSTRACT:
A method of measuring the distance of an examined surface from a reference plane, by: (a) directing a parallel beam of radiation along a first optical path in which the parallel beam is focussed as a spot on the examined surface and reflected therefrom; (b) converting the reflected beam to a parallel beam; (c) directing a part of the reflected parallel beam through a second optical path in which the spot is focussed on a surface of a first detector located such that the position of the spot on the first detector includes both drawback errors caused by variations in reflectivity, scattering, and/or interference in the examined surface; and a plane displacement error, representing the distance between the plane of the examined surface and the reference plane; (d) directing another part of the reflected parallel beam through a third optical path in which the spot is focussed on a surface of a second detector located such that the position of the spot on the second detector includes only the drawback errors; (e) and utilizing the outputs of the first and second detectors for providing a measurement of the distance of the examined surface from the reference plane.

REFERENCES:
patent: 4356392 (1982-10-01), Wittekoek et al.

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