A compact design of optical scheme for a two-probe absolute surface encoders

An improved optical scheme of planar encoder is presented in this paper. The modulation of diffractive beams from scale grating and reference grating is analyzed systematically. Based on this analysis, independent modulation of eight diffractive beams from scale grating and reference grating, with no cross effect between each other, is achieved with an improved design of easy to adjust and simplicity in structure, cost-effectiveness and flexibility in use. Furthermore, in this research, the optical configuration of the planar encoder was divided into three function areas, modulation of diffractive beams, optical subdivision and photoelectric detection. Separate design decreases the coupling relationship between various optical elements, which improves the convenience of optical alignment and reduces the cumulative error in debugging process to a certain extent. In this study, a standard interference ranging system is set up by using a grating with a 1μm period. The typical four path interference signals are collected. The quality of the interference signal verified the feasibility and superiority of the innovative design.