Optical position encoder based on structured head diffraction grating

Codes coupling optimization for absolute measurement

“…These two solutions possess different measurement benchmark and exhibit different environmental tolerances. Grating interferometers utilize the grating pitch as a reference standard [3][4][5][6][7] for measurement and calculations, which provides greater stability compared to the wavelength reference employed by laser interferometers [8][9][10][11]. Grating interferometers also have the advantage of shorter optical path lengths and are less susceptible to fluctuations in the environment [5,6,12,13].…”

Modeling and test of an absolute four-degree-of-freedom (DOF) grating encoder

“…will destroy the accuracy [10][11][12][13]. The grating interferometer can measure the distance mainly based on the grating pitch (physical structure) and the light path is also shorter than the laser interferometer [14][15][16][17], which means it is more stable [15,18]. The grating manufacturing [19][20][21][22] of the current grating encoder has also made considerable progress, which enables the grating encoder to measure with a smaller and more accurate measurement benchmark, and the accuracy can reach sub nanometer [23,24].…”

An ultra-precision error estimation for a multi-axes grating encoder using quadrant photodetectors

“…Spectral confocal technology is mainly used in single-axis micro-displacement measurement and the topography measurement [16][17][18]; the resolution of laser interferometers can reach picometer level, but the optical path structure of laser interferometers is relatively cumbersome, and the measurement accuracy is relatively dependent on the environment [19][20]. The multi-degree-of-freedom measurement needs to be used in combination, which will bring a certain assembly error to the measurement [21][22][23][24]; compared with the laser interferometer, the resolution of the grating encoder can reach the sub-nanometer, and it has a simpler and more compact optical path structure [25][26][27]. The measurement accuracy is based on the grating pitch used, and the production and processing technology of the grating is related to the manufacturing process of the grating [28][29][30][31], which is less affected by the environment, and has a relatively large advantage in the realization of six-degree-of-freedom measurement.…”

“…Considering the compactness of the measurement structure in the designed scheme of the multi-degree-of-freedom grating encoder, the angle measurement scheme is usually to inject the 0th, +1st and -1st order diffracted lights of the grating into the QPD through the focusing lens, and the principle of autocollimator is used to detect the position change of the light spot on each QPD for angle measurement [36][37]. However, the angle measurement range of the grating encoder based on the traditional QPD linear interval spot positioning method is very limited, which is basically a small angle range [38][39][40], such as the three-axis autocollimator for detection of angular error motions of a precision stage, which has a three-axis measurement range of about 40 arcseconds and is developed by the team of Wei Gao of Tohoku University [41].…”