Patent ID: 6496266
Filing Date: 2002-12-17
Classification: G01B,G01D

Abstract:
A measuring device for absolute measurement of displacement, comprising:a first displacement detector for generating a sine wave signal S1A and a cosine wave signal S1B both with a period of P1 in accordance with a displacement L to be detected; a second displacement detector provided in parallel to said first displacement detector for generating a sine wave signal S2A and a cosine wave signal S2B both with a period of P2 different from said period of P1 in accordance with said displacement L to be detected; wavelength composing means for composing said sine wave signals S1A, S2A and said cosine wave signals S1B, S2B from said first and second displacement detectors to obtain a sine wave signal, SxA=S1AÂ·S2Bâˆ’S1BÂ·S2A, and a cosine wave signal, SxB=S1BÂ·S2B+S1AÂ·S2A, both with a period of Px equal to the least common multiple between said periods P1 and P2; phase detecting means for detecting a phase of a fine resolution signal comprising either of output signals obtained from said first and second displacement detectors and a phase of a coarse resolution signal comprising the output signal from said wavelength composing means; and distance arithmetic means for computing said displacement L as an absolute position within said period Px based on phase information detected by said phase detecting means.