Rating Ruler, also known as grating ruler displacement sensor (grating ruler sensor), is a measurement feedback device using the optical principle of grating.Grating ruler is often used in the closed-loop servo system of CNC machine tools, which can be used to detect linear displacement or angular displacement.The output signal is digital pulse, which has the characteristics of wide detection range, high detection accuracy and fast response speed. For example, in the CNC machine tool is often used to detect the coordinates of the tool and the work piece, to observe and track the tool error, to play a role in compensating the tool motion error.