Research On Frequency Modulated Continuous Wave Laser Interferometric Displacement Measurement System

The frequency modulated continuous wave(FMCW)laser interferometer is a new system of coherent measurement instrument,which can realize non-contact high-precision displacement measurement,and has excellent application prospect in the field of high-end equipment manufacturing.However,the existing frequency modulated continuous wave displacement measurement system adopts frequency division multiplexing to achieve multi-channel measurement will have the problem of harmonic crosstalk.In addition,the low sampling rate of the system and the slow signal processing algorithm lead to the tracking speed of the system on the dynamic target.not tall.Therefore,the main research content of this paper is to realize the multi-channel frequency modulation continuous wave interferometric displacement measurement system of space division multiplexing and further improve the measurement speed of the system.Aiming at the problem of harmonic crosstalk in the frequency division multiplexing measurement method,this paper uses a single light source space division multiplexing method to design a three-channel displacement measurement system.Using the DFB semiconductor laser as the light source,three Fabry-Perot interferometer detection optical paths are built through space division multiplexing,and the measurement optical paths are independent of each other,avoiding the influence of harmonic crosstalk.In order to improve the signal processing speed,three STM32F405 chips are used to sample and process the interference beat frequency signals of the three channels.According to the basic principle of the measurement system,the design and production of the hardware circuit board are completed.In the program,the software synchronous sampling control method and the extreme point phase demodulation algorithm are used to realize the synchronous measurement of each independent channel.Aiming at the problem of slow sampling rate and algorithm phase discrimination speed of existing systems,this paper designs a fast displacement measurement system based on a digital signal processing chip.Built a single-channel frequency modulated continuous wave interferometry optical path,used the TMS320F28377 chip with higher sampling rate and faster signal processing speed for signal processing,wrote the chip peripheral driver,and used the multi-fixed-point peak prediction phase detection algorithm to detect the beat signal fast calculation improves the signal processing speed of the system,and optimizes the direction of the algorithm to further improve the system’s tracking speed of dynamic targets.An experimental platform was built for testing,and the results showed that the two principle prototypes can work effectively.Among them,the synchronization measurement error of the three-channel displacement measurement system principle prototype to the lmm/s moving target is only 0.46nm,and the DSP displacement measurement system principle prototype can The highest modulation frequency is 35KHz,and the tracking speed of the dynamic target is increased to 15mm/s.The standard deviation of the displacement measurement results of the two principle prototypes in the 600mm dynamic measurement range is less than 5nm,and the linear fitting coefficient is above 0.99997,indicating the measurement The system has good measurement accuracy and linearity.The experimental results prove that the frequency-modulated continuous wave laser interferometric displacement measurement system designed in this paper can realize three-channel synchronous displacement measurement and improve the tracking speed of the system to dynamic targets.