Absolute measurement has always been one of the important development directions of precision measurement, there are problems that the diffraction and mask working parameters are not considered in the positioning pulse analysis of the absolute code mask at present. Therefore, in order to solve the coupling optimal performance problem of absolute positioning code in actual work, an absolute code should be designed for working in the best parameter-model. In this paper, a multi-parameter model of absolute code working status is established, and the influence of working parameters on its positioning performance is analyzed respectively. The analysis shows that the distance and the angle between the mask and the grating, and the width of the unit code will affect the positioning accuracy. The three parameters restrict each other, and there is a coupling optimal solution. The optimal working state can be obtained through parameter analysis, so as to provide the design and installation parameter guidance of mask. The proposed research can help the practical application of absolute positioning measurement.
Absolute testing for metrology has always been one of the important development directions of precision measurement. The mask with binary code is an important structure for forming absolute positioning pulses in grating encoders. The increase in the number of codes is beneficial to the resolution of positioning, but design of codes has always existed the problem that the optimal design cannot be obtained when the number of codes increases. This paper proposes a design method of binary code based on the genetic algorithm, which can get the required binary code more quickly when the number of codes is greater than 150 or even higher. The specific method can randomly generate binary codes with their fitness factors, and the binary codes enter the algorithm as the parents based on the mutation, crossover, and selection. Then the reproduce binary codes will have higher and higher fitness factor. This method can quickly generate satisfactory binary codes with specified performance, thus providing high resolution at the nanometer level for absolute positioning measurement. This work provides help and reference for future absolute positioning measurements.
Pixelated micro-polarizer array is an attractive polarization imaging device because of its real-time fully detecting capability to Stokes parameters and high integration level. However, this micro-device is commonly fabricated by electron beam lithography, thus is often high-cost. Since periodic unit of this device is a 2×2 array of four types of one-dimensional (1D) gratings with different orientations (0°, 45°, 90°, 135°), a low-cost grating fabrication technique, interference lithography (IL), is possible to be used to fabricate this device. In this research, a four-steps exposure patterning method of micro-polarizer array based on single Lloyd’s mirror interferometer IL is developed. This interferometer is composed by two perpendicular parts: a mirror and a photoresist holder, and a 1D grating parallel with mirror can be fabricated in the exposure region on photoresist through lithography. A Cr-based mask, whose transparent pattern is a square array of square windows with 15×15 μm2 window size and 17 μm window spacing, is introduced and clamped onto the photoresist to cut exposure region. In four exposure steps, each 15×15 μm2 quadrant area of a polarizer array with 2 μm quadrant spacing will be exposed on photoresist, respectively. Between two exposure steps, mask and photoresist substrate need to be simultaneously horizontal rotated, to adjust the orientation of grating fabricated in next exposed quadrant on photoresist. Based on this method, we fabricated the single-state patterned micro-polarizer array, which effectively controls the cost and fabrication cycle. The experimental results show that the photoresist grating within a single window has stable structure, uniform period and good directivity.
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