Precision Measurement of Displacement with Two Quasi-Orthogonal Signals for Linear Diffraction Grating Interferometric Sensors

Linear diffraction grating interferometer measures displacement via two orthogonal signals generated from the optical outputs of fringes. Due to noises and regulation errors, two signals are not perfect. This paper presents a precision measurement method of displacement for given two non-orthogonal signals. The phase difference of two signals is first calculated by solving an equation derived from correlation principle. The subdivision value is then obtained with a compensation formula. By further counting the cycle number of periodic signal with an amplitude filtering algorithm, accurate value of displacement is outputted. Experimental results show that the proposed method can measure the displacement expressed with two non-orthogonal signals more reliably and accurately.