Laser gauge interferometer and locating method using the same

Abstract

A positional measuring laser interferometer splits a laser beam into a measuring beam and a correcting beam. Each of these beams is further split into a measurement beam and a reference beam. The reference beams travel along a fixed length path of fixed optical properties. Each of the measurement beams travels along respective optical paths in air adjacent each other so that they travel in air having substantially the same changing optical properties, such as the fraction index, preferably with the paths differing in length by a fixed amount regardless of the movement of the object to be measured. The reference beam and measurement beam, for each of the measuring and correcting beams, form an interference pattern that is detected to produce respective outputs correlated to positional information of the object and subjected to positional error due to changing refraction index of air. These two information signals are combined, preferably with a reference refraction index and a reference object position, to obtain a positional information signal of the object that is independent of varying optical characteristics of air. The solid/air interface surface for the interferometer, with respect to the measurement beams, is fixed in position independently of thermal or like expansion of the interferometer by an adjacent abutment surface spring biased into a fixed base abutment surface, which abutment surfaces are generally coplanar with the solid/air interface surface and perpendicular to the path of the measurement beams in air.