Patent ID: 8102537

Claim:
An optical displacement gage comprising: a sensing light generating unit to generate a sensing light; a reference surface to reflect a part of the sensing light while transmitting another part of the sensing light toward an object to be measured; a spectroscopic unit to disperse an interference light including a reflection light reflected from the reference surface and reflection light reflected from the object to be measured; an optical intensity distribution generating unit to receive the interference light dispersed by the spectroscopic unit so as to generate an optical intensity distribution with respect to a wave number of the interference light; a light intensity local maximum extracting unit to convert the optical intensity distribution with respect to the wave number into an optical intensity distribution with respect to a spatial frequency of the light intensity for the wave number, so as to extract a local maximum in the optical intensity distribution with respect to the spatial frequency, repeatedly at a predetermined respective time; a phase determining unit to determine a phase of the frequency component corresponding to the spatial frequency at the local maximum in the optical intensity distribution with respect to the wave number; and a displacement amount deciding unit to decide a displacement amount of the object to be measured based on the phase determined by the phase determining unit, wherein the phase determining unit includes a relative phase deciding unit to decide a relative phase of the frequency component within a range of 360 degrees, an absolute phase computing unit to compute an absolute phase by combining the relative phase based on the decision result by the relative phase deciding unit and the past decision result by the relative phase, and a phase reference updating unit to update a reference point of the absolute phase based on a reset instruction, and the displacement amount deciding unit decides the displacement amount based on the absolute phase.