Development of a novel planar encoder for 2D displacement measurement in nanometer resolution and accuracy

This paper presents a novel design of a planar encoder based on the principle of diffractive interferometry. The system is capable of measuring the two-dimensional displacement of the planar grating. It adopts a special design in optical path that can increase the alignment tolerance between the optical head and the grating. Because of the simple optical configuration and the merit of compact size, it can effectively reduce the environmental disturbance and allow higher stability. The signal process circuit and software are also developed that can effectively decrease some major errors. The resolution can reach to 1nm by using the signal subdivision algorithm. Experiment results showed that even in the normal laboratory environment the standard deviation of measured values can be controlled to within 15nm for a long stroke up to 25mm in both axes.