The grating ruler, also called the grating ruler displacement sensor (the grating ruler sensor), is a measurement feedback device that uses the optical principle of the grating. Grating rulers are often used in closed-loop servo systems of CNC machine tools, and can be used to detect linear or angular displacement. The measured output signal is a digital pulse, which has the characteristics of large detection range, high detection accuracy and fast response speed. For example, it is often used in CNC machine tools to detect the coordinates of the tool and the workpiece, to observe and track the error of the tool, in order to play a role in compensating for the error of the tool. According to different manufacturing methods and optical principles, grating rulers are divided into transmission gratings and reflective gratings.

The key part of the grating detection device is the grating reading head, which is composed of a light source, a condensing lens, an indicating grating, a photoelectric element and an adjustment mechanism. There are many structural forms of grating reading heads. According to the structural characteristics and use occasions of the reading head, it is divided into direct receiving reading heads (or silicon photocell reading heads, mirror reading heads, spectroscopic reading heads, metal grating reflective reading heads).

Reasonably select the grating ruler and use it correctly to make the best possible. There are also contradictory sides. The installation position should be as close to the drive axis as possible, but also as far away as possible from the heat source of the machine tool (such as screw pair). It depends on the machine tool designer, how to compromise and consider various factors, comprehensively consider the selection, design, installation, test and other factors of the grating ruler, to obtain a more reasonable cost performance, and it is bound to achieve a better control and inspection effect. Through the debugging of the above steps, a CNC machine tool can generally obtain good position accuracy (positioning accuracy, repeat positioning accuracy), meet the design requirements of the machine tool, and can easily meet the needs of users. The use of users has extraordinary practical significance.