Study On Signal Processing Method Of A Laser Synthetic-wavelength Nanomeasurement Interferometer

In recent years, with the micro-electronics, ultra-precision machining and other high-tech rapidly developing, nano-displacement measurement techniques and instruments for large displacement measurement with nanometer accuracy are demanded. This thesis is supported by"The development of a laser synthetic-wavelength nanodisplacement measurement interferometer"(NSFC, No.50827501). A signal processing system of the interferometer based on a complex programmable logic device (CPLD) is designed and developed.Based on the principle of fringe subdivision by using a synthetic wavelength, the method of interferometric signal processing of the interferometer is researched. A novel nanomeasurement method is proposed to compensate the counting errors which usually occur at the oscillation or at the ending position of interferometric fringe during measurment. A hardware system for the signal processing method is designed in detail and realized, including CPLD processing modules, a signal pre-processing circuit, a power circuit, a clock circuit, a JTAG debug circuit and a serial communication circuit. And the software system for the signal processing method is analyzed and designed, which is programmed by using Visual Basic language.In this research work, experiments are done as below:(1) Fractional fringe counting experiment: displacement measurement experiments with 5nm, 10nm and 20nm deplacement increments were carried out, respectively. The experimental results show that the linear correlation coefficient is 0.9991, 0.9998 and 0.9998 with the standard deviations of 1.85nm, 2.54nm and 2.20nm over a range of 200 nm, respectively.(2) Integral fringe counting experiment: In the measuring range of 15μm, the maximum deviation is 0.303μm less than half a wavelength.(3) Combination of integral and fractional fringes counting experiment: displacement measurements with 0.5μm and 1μm deplacement increments were carried out, respectively. In the measuring range of 15μm, the standard deviation is 5.75nm and 8.51nm, respectively. The experiment results show that the designed signal processing system can acheive both large displacement measurement and nanometer measurement accuracy and it has high reliability and practicability.