Linear scale is a measuring and feedback device that works on the optical principle of grating. Linear scale is often used in the closed-loop servo system of CNC machine tools and can be used for Linear or angular displacement detection. The measured signal is digital pulse, which has the characteristics of wide detection range, high detection accuracy and fast response. For example, in CNC machine tools are often used to detect the tool and workpiece coordinates, to observe and track the feed error, in order to play a role in compensating the motion error of the tool. Linear scale is composed of a scale grating and a grating reading head. The scale grating is generally fixed on the fixed parts of the machine tool, the reading head of the grating is installed on the moving parts of the machine tool, and the indicating grating is installed in the reading head of the grating.