Patent ID: 6351312
Filing Date: 2002-02-26
Classification: G01B

Abstract:
A length measuring device comprising:a light emitting portion for emitting laser light; an interference system for receiving said laser light, for generating reference light having a first frequency, for outputting the reference light straight, for generating detection light having a second frequency, and for outputting said detection light at a predetermined tilt angle; a moving detection portion for reflecting said reference light and said detection light toward said interference system; a light receiving portion for converting a reference interference wave, which is generated by said interference system, into a first sinusoidal wave electrical signal according to said laser light and for converting a detection interference wave, which is generated from an optical-path-length difference between said reflected reference light and said reflected detection light, into a second sinusoidal wave electrical signal; a signal processing portion for generating a first cosinusoidal wave signal from said first sinusoidal wave signal, for generating a second cosinusoidal wave signal from said second sinusoidal wave signal, and for A/D-converting said first sinusoidal wave signal and said first cosinusoidal wave signal, and said second sinusoidal wave signal and said second cosinusoidal wave signal; and an operation portion for obtaining an electrical angle of said reference interference wave according to a ratio between the A/D-converted first sinusoidal wave data and the A/D-converted first cosinusoidal wave data, for obtaining an electrical angle of said detection interference wave according to a ratio between the A/D-converted second sinusoidal wave data and the A/D-converted second cosinusoidal wave data, for obtaining a phase difference between said reference interference wave and said detection interference wave from said two electrical angles, and for detecting a position of said moving detection portion according to this phase difference and a wavelength of said laser light.