Development of the hottest grating moire fringe Te

2022-08-24
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Development of grating moire fringe technology

grating moire fringe technology is an ancient and modern measurement technology. The study of moire fringes can be traced back to the late 19th century. It has been applied to practical measurement since the 1950s, and has gradually carried out extensive research on the formation mechanism of moire fringes. So far, three main theories have been formed: (1) based on the principle of shadow imaging: it is considered that the new trajectory composed of fringes can represent the light intensity distribution of moire fringes; (2) Based on the principle of diffraction interference, the operation keys of granulator are different, but there are also different places: it is considered that the new light intensity distribution composed of fringes can be described by the interference results between diffraction waves; (3) Based on the principle of Fourier transform, it is considered that the formed moire fringes are composed of lower frequency terms than the grating. These three theories can fully explain the phenomenon of moire fringes. Generally speaking, the third theory is a generalized explanation. Those with sparse grating stripes can be explained directly by the principle of shading, while those with dense grating stripes can be explained more appropriately by the principle of diffraction interference

in the sixth of the last century, we insisted on promoting the green development of industry as the hard task of building a beautiful China and a modern economic system and implementing the "made in China 2025". In the 1970s, due to the improvement of grating manufacturing process and the development of electronic technology, we were able to provide cheap grating products in batches, and electronic subdivision technology emerged, so that the resolution and accuracy of grating can meet the requirements of modern metrology, Moire fringe technology has been rapidly promoted and applied, and many new grating moire fringe measurement technologies have emerged

the traditional four field scanning grating system (the grating sensors developed by Chengdu Tool Research Institute belong to this system) has been gradually adopted by quasi single field scanning and single field scanning systems due to the great impact of pollution. The indicating grating of the quasi single field scanning system is composed of two gratings with different phases. The scale grating (main grating) is reflected and received by four photocells to obtain four moire fringe signals with a phase difference of 90 °; The single field scanning system uses a large grating with a slightly different grid distance from the main grating to form an indicating grating, and uses grid photoelectric devices to receive signals. In these two structures, because a scanning field is used, the influence of local pollution on the grating on the light intensity of each group of signals is roughly the same, which greatly reduces the measurement error caused by pollution. These two kinds of scanning systems belong to the principle of imaging scanning and are widely used grating systems at present

In 1987, haidenhain company launched an interference scanning system. In this system, the scale grating and indicator grating adopt phase grating, and the diffraction order and phase are controlled by reasonably designing the shape of the grating line height direction. The moire fringe is formed by the interference light diffracted by the input light twice. The interference scanning system is a high-precision and high-resolution grating system, such as haidenhain's lip382, with a measurement length of 270mm, a resolution of 1nm and an accuracy of 0.1 μ m。

in order to ensure the quality of forming moire fringes and avoid the coexistence of shadow and diffraction, the grating spacing adopted by the moire fringes system is obviously two ways to encourage foreign-invested enterprises to enter the manufacturing end (sparse or dense). In the imaging scanning system, it is considered that the light propagates completely in a straight line, which conforms to the principle of geometric imaging, and the grating spacing is generally greater than 20 μ m; In the interference scanning system, the system is completely in the state of diffraction and interference, and the grating spacing used is generally less than 8 μ m。 Because the interference scanning system adopts telecentric imaging and Fraunhofer diffraction system, the grating pair can work in the state of large spacing (even close to 1mm), and the change of spacing has little impact on the signal amplitude. When adjusting the system, it is completely unnecessary to look for the Frensnel focal plane as in the past, which is extremely beneficial to the actual measurement

in order to meet the needs of CNC machine tools with a high degree of automation, absolute grating is becoming a development trend. Absolute grating is to set an absolute track on the incremental grating, and a series of zero position gratings encoded with different distances are designed on the absolute track. When used, the absolute position is determined by detecting the distance between adjacent zero position gratings. The EnDat bidirectional data interface used with the absolute track can not only judge the absolute position, but also send an alarm signal to the NC machine tool immediately when the grating fails, so as to ensure the safety of processing

the position accuracy of grating lines and the quality of lines in a signal cycle are the main factors affecting the accuracy of grating. Through the strict control of grating manufacturing environment, the adoption of special two-dimensional etching process and the average effect of single field scanning, the accuracy of grating has reached ± 0.1 μ M/m, the error is less than 1% in a fringe period. Excellent moire fringe signal is the premise of high-power subdivision, and the maximum subdivision of haidenhain grating products can reach 4096

in the 1990s, two-dimensional grating appeared. Its line pattern is lattice, which can measure two directions at the same time. It is a new grating system. For example, the accuracy of pp271r and pp281r gratings is ± 0.1 μ m. The system can directly use the X-Y workbench as the coordinate system, and can also be used to detect the interpolation error of CNC machine tools (kgm182)

due to the continuous development of grating moire fringe technology, grating sensor has become a measuring instrument comparable to laser interferometer. At present, in addition to the measurement accuracy, it is inferior to laser interferometer in terms of low measurement cost, high measurement speed (480m/min), large measurement range (more than 100m), little environmental impact and so on. It can be predicted that with the continuous progress of technology, the application of grating moire fringe technology will be increasingly widespread. (end)

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