Grating ruler, also known as optical linear encoder, is a sensor that uses optical principles to achieve high-precision displacement measurement, commonly used for measuring linear position, displacement, and velocity. Applied in the closed-loop servo system of CNC machine tools, the measured output signal is digital pulse, which has the characteristics of large detection range, high detection accuracy, and fast response speed. Grating rulers are divided into transmission gratings and reflection gratings according to different manufacturing methods and optical principles.