The grating ruler, also called the grating ruler displacement sensor or the grating ruler sensor, is a measurement feedback device that works by using 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.
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The grating ruler is composed of two parts: the scale grating and the grating reading head. The scale grating is generally fixed on the movable part of the machine tool, the grating reading head is installed on the fixed part of the machine tool, and the indicating grating is installed in the grating reading head. The structure of the grating detection device 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, which are divided into direct receiving reading heads according to the structural characteristics and use occasions of the reading head.
Take the transmission grating as an example. When a small angle θ is formed between the line pattern on the indicator grating and the line pattern on the scale grating, and the two grating scale facets are placed relatively parallel, under the illumination of the light source, they are located almost perpendicularly. On the grid pattern, light and dark stripes are formed. This kind of fringe is called "moiré fringe". Strictly speaking, the direction of the moiré fringe arrangement is perpendicular to the bisector of the angle between the two grating lines. The distance between two bright lines or two dark lines in the moiré fringe is called the width of the moiré fringe, expressed in W: W=ω /2* sin(θ /2)=ω /θ.