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

Abstract

For solving the problem of sub-mirror installation and posture monitoring and compensation, an absolute four-degree-of-freedom (DOF) grating encoder that is able to monitor four degrees of freedom's absolute position and pose in the θx, θy, θz, and z-direction is proposed. In this grating encoder, a grating reflector and three quadrant photodetectors (QPD) are employed and an optical path is configured based on the laser autocollimation principle. A model for the solution of the four-DOF motions from outputs of the three QPDs is established. A calibration method for the identification of the relationships between the absolute positions and QPDs outputs is proposed. A prototype four-DOF grating encoder is constructed for verification of this proposal. Test results demonstrated that the method proposed in this research can achieve absolute position distinguishing with a sub-arcsecond and sub-micrometer accuracy in rotation angles and z-direction, respectively.

A Review: High-Precision Angle Measurement Technologies

“…Gratings are currently used in various fields due to their excellent structural dimensional consistency and structural stability thanks to increasingly advanced processing methods [ 180 , 181 , 182 , 183 , 184 , 185 , 186 , 187 , 188 , 189 , 190 , 191 , 192 , 193 ] as a standard device widely used in precision displacement [ 194 , 195 , 196 , 197 ] and orientation measurement [ 178 , 179 , 198 ]. The optical frequency comb output by the mode-locked femtosecond laser can be used to generate an ‘angle standard comb’ as an optical scale for angle measurement.…”

Codes coupling optimization for absolute measurement

“…These advantages make grating interferometers widely applicable in various precision measurement fields, serving as displacement measurement or positioning feedback systems [18]. The research directions for grating interferometers primarily focus on integration [19][20][21][22], multi-degree of freedom [23][24][25][26][27][28][29][30][31], real-time signal processing [32][33][34][35], and absolute positioning research [36][37][38]. Among these, absolute research holds great significance, as traceability of the position helps equipment restore its status more efficiently.…”