A grating ruler, also known as a grating displacement sensor (grating scale sensor), is a measurement feedback device that works using the optical principle of a grating. The grating ruler is mainly composed of two parts: the ruler grating and the grating reading head, in which the scale grating is generally fixed on the moving parts of the machine tool, the grating reading head is installed on the fixed parts of the machine tool, and the indication grating is installed in the grating reading head. 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.
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 scale facets are placed relatively parallel to each other, a light and dark stripe is formed on the almost vertical grid, which is called "moiré fringe". Moiré stripes have the following characteristics:
When the two gratings are moved relative to each other by one pitch, the moiré fringes are moved by one stripe 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.
Moiré stripes have a magnifying effect. In the case that the angle between the two grating grids is small, there is a specific relationship between the moiré width w and the grating pitch and the busbar angle. When the sin is very small and the moiré width w is much larger than the grating pitch, i.e., the grating plays a magnifying role.
The following points need to be paid attention to when using a grating ruler:
Selection of mounting location: Choose a mounting location that is free of vibration interference and ensure that the installation clearance between the ruler encoder and the encoder readhead is appropriate.
Cable protection: The cable between the connecting ruler encoder and the encoder readhead should be protected from mechanical damage or oil erosion.
Cleaning and maintenance: The encoder should be cleaned and maintained regularly to ensure that it is in good working condition. When cleaning, wipe with a soft cotton cloth and avoid scratching with chemical solvents or hard objects.
Calibration and adjustment: The encoder should be calibrated and adjusted regularly to ensure that its measurement accuracy meets the requirements. Calibration should be carried out using special calibration tools to avoid errors caused by the use of non-standard tools.
Protection and maintenance: Attention should be paid to the protection and maintenance of the grating ruler during use to avoid it being affected by mechanical damage, oil erosion or electromagnetic interference.
In short, the grating ruler is a high-precision measurement feedback device, and its working principle mainly uses the characteristics of moiré fringes to measure displacement. In the process of use, attention should be paid to the selection of installation location, the protection of the connecting cable, cleaning and maintenance, calibration and adjustment, and protection and maintenance, etc., to ensure that it is in good working condition and provides accurate measurement results.
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