An Investigation on Simulation and Identification of Diffracted Moire Patterns Within Optical Encoders

Depending on characteristics of high accuracy and resolution combined with a relatively low price, optical encoders as high-precision positioning sensors are broadly utilized in every application field where position and speed measurements are required for position or motion control, such as machine tools, CMM. As for machine tools, optical encoders are the metrology gauge of the measurement system, which quantity the motion displacement of machine tools on the basis of interference fringes named moire patterns. However, due to numerous error factors such as geometric errors, thermal deformation having impact on the spatial distribution of moire patterns, the displacement signals from encoders to CNC system almost contain deviations so that it results in motion error of axes of machine tools. To address this issues, this paper investigates the formation of moire patterns by grating equation and diffractive theory and identifies them through a proposed refining criterion. Theoretical analysis and simulation result show that the research can provide a potential opportunity to assess the influence of error factors of machine tools on the readout of linear encoders.