Research On And High-resolution Displacement Measurement System Based On Diffractive Grating

With the continuous progress of modern science and technology，nano-scalemeasurement technology has been booming in most areas. Displacement, which isone of the most basic physical quantities, develops toward high-speed,high-resolution, large-range, small-size and low-cost nano-scale measurementdirection. Grating interferometers and laser interferometers are the most importantmeans of measurement in modern precision displacement measurement techniques.Compared with laser interferometers, grating interferometers not only have theadvantages of high-resolution, high-accuracy, and large-range measurement, butalso provide better immunity against environmental factors such as air press, airtemperature and relative humidity for measurement of large range displacement.Also grating interferometers cost lowly and can be microminiaturized easily.Oversea researches on grating measurement have already been quite mature andmassively produced. Although home grating interferometers have developed fast,there are still some gaps compared with foreign researches. Therefore nano-scaledisplacement measurement systems based on diffraction grating are significant.This paper studies a nano-scale displacement measurement system based onreflecting diffraction grating. The system obtains optical quadruple frequency byusing secondary diffraction beams as measuring beams and subdivides orthogonalsignals in160segments. The system achieves sub-nanometric resolution.Based on polarization theory, the system optimizes the frequency-quadrupledoptical sensor model, eliminates the impact of the multiple reflections ofzeroth-order diffracted light in the optical path, and reduces stray light in theinterference field. This paper analyses the structure of the grating by using Fourieroptics and wave optics theory, and the structural parameters of the grating have anideal relationship with the laser light source, which lets the diffraction order energyconcentrate. The optical design software Lighttools analyses the system andachieves deflection tolerance of the grating, location tolerance of the opticalelements and other characteristics. Also the paper analyzes the impact of assemblyerrors of the grating and optical components on the measurement signals based onthe measurement theory.Grating signal processing is completed. Through pre-conditioning circuit, thesystem eliminates effectively the errors of the interference signals, such as DC levelshift, non-orthogonal error, unequal amplitude errors. Then the data acquisition cardcollects the interference signals and obtains the displacement. After integrating and optimizing optical sensors, pre-conditioning circuit anddata acquisition card, building optical architecture platform, and then constructingthe entire displacement measuring system, the performances of each unit of thesystem are tested at the same time in the whole experiment, and experimentalresults of the evaluation system parameters is analyzed. The results show that thesystem good linearity and reproducibility, the measurement resolution better than10nm.