High displacement resolution encoder by using triple grating combination interferometer

In this study, the optimal triple gratings combination for a novel displacement sensor was proposed, in which the grating scales of them were 1.616 μm, 3.33 μm, and 3.33 μm, respectively. Theoretical prediction of the optimal sensitivity and resolution can be approximated of 0.72 °/nm and smaller than 0.1 nm, respectively. The experiment results showed that the displacement difference between comparison method and proposed method were within 0.6% and 0.2% for the travel ranges of 1 mm and 50 μm, respectively. The displacement error of the optimal combination of triple gratings was within 10 nm as the measured phase of 360°. Furthermore, the result of the optimal triple gratings combination showed high immunity against environmental disturbance and the smallest displacement variation was better than 1 pm of the optimal triple grating combination.