1.The principle of the grating ruler
A grating ruler, also known as a grating displacement sensor (grating scale sensor), is an optical measuring device that uses the optical principle of the grating to work as a measurement feedback device. In the grating scale, a strip of light interferes, forming light and dark stripes that move in sync with another beam. When a beam of light passes over the surface of an object, small changes in the surface of the object cause small shifts in the beam, which are captured by the grating scale and converted into electrical signals. By measuring changes in electrical signals, information such as the shape, position, and size of the surface of an object can be obtained. The working principle of the grating scale can be illustrated by the example of a transmission grating. When a small angle is formed between the line pattern on the indicator grating and the line pattern on the ruler grating, and the two grating scale facets are placed in relative parallel, under the illumination of the light source, they are located on the almost perpendicular grid pattern, forming a light and dark stripe, which is called "moiré fringe". The distance between two bright or two dark lines in a moiré stripe is called the width of the moiré stripe and is denoted by w. w=ω /2* sin（θ /2）=ω /θ 。Moiré fringes have the following characteristics: two gratings are moved relative to each other by one pitch, and moiré fringes are moved by one fringe distance. Due to the diffraction and interference of light, the variation law of Moiré fringes is approximately the positive (co)sine function, and the number of change periods is synchronized with the number of grating spacing of the relative displacement of the grating.
2.Classification and characteristics of grating rulers
Grating rulers are divided into transmission gratings and reflection gratings according to different manufacturing methods and optical principles. It consists of a ruler grating and a raster readhead. In general, the scale is fixed to the moving parts of the machine, and the encoder readhead is mounted on the fixed parts of the machine.
The key part of the grating detection device is the grating readhead, which consists of a light source, a converging lens, an indicator grating, an optoelectronic element and an adjustment mechanism. There are many types of grating readheads, which can be divided into direct receiving readheads (or silicon photocell readheads, mirror readheads, beamsplitter readheads, and metal grating reflection readheads) according to the structural characteristics and applications.
3.Application of the encoder scale
The encoder has the advantages of high precision, high resolution and high sensitivity. Since its operating principle is based on optical interference, it has little influence on environmental factors such as temperature and humidity, and is suitable for measurement in a variety of complex environments. In addition, the grating ruler also has the advantages of large measurement range, fast measurement speed, and non-contact measurement, so it is widely used in precision manufacturing, robotics, aerospace and other fields. It is commonly used in closed-loop servo systems of CNC machine tools and can detect linear or angular displacements.
When using a light grid ruler, care needs to be taken to keep it clean and avoid mechanical shocks. Scales are very sensitive to dust and mechanical vibrations, so it is necessary to keep the environment clean when in use and to take measures to prevent damage to the scale from mechanical shocks. In addition, when installing a light grid ruler, the position and angle of the scale need to be carefully adjusted to ensure the accuracy and reliability of the measurement results.
In short, the grating ruler is a high-precision, high-resolution, high-sensitivity optical measuring device, which is suitable for measurement in various complex environments. Care needs to be taken to keep it clean and avoid mechanical shocks, and to carefully adjust the position and angle of the encoder to ensure the accuracy and reliability of the measurement results.