Research On FMCW Laser Interference Embedded System For 3D Motion Platform

Frequency Modulated Continuous Wave(FMCW)laser interferometry is a new optical measurement technology that combines frequency modulation and interference.It can achieve high-precision measurement with a large dynamic range and can be applied in military and modern lithography manufacturing fields.The existing 3D motion platforms require sensors to have high accuracy.Therefore,the main task of this article is to design an FMCW laser interferometric measurement embedded system for three-dimensional motion platforms,achieving high-precision displacement measurement of the measured object.This paper analyzes the principle of frequency modulated continuous wave laser interferometry,adopts the structure of Fabry Perot frequency modulated continuous wave laser interferometer,and takes the saw-tooth wave wave linear frequency modulation as an example to build an interference optical path using fiber devices.Due to the possibility that the beat frequency signal detected by the photo-detector may be too strong or too weak,both of which can affect the measurement accuracy of the FMCW laser interferometer.Therefore,the focus of this project is to design and manufacture an automatic gain control circuit to achieve program control of the voltage amplitude of the beat frequency signal.Through the analysis and comparison of the existing gain control circuits,and considering the characteristics of the embedded digital circuit system,this paper adopts the program controlled digital potentiometer combined with the photoelectric detector’s trans resistance amplifier circuit to realize the automatic gain control of the FMCW interference signal.This method has low noise,high accuracy,and fast response speed,effectively solving the problem of signal intensity changes during the measurement process of the motion platform.In addition,considering the issue of saving system parameters in practical applications,this article also adopts flash for dynamic data storage and reading.Based on the STM32F405VGT6 microprocessor,an embedded system for FMCW laser interference was designed and developed.The hardware part mainly includes STM32 minimum system,I-V conversion circuit,signal acquisition and processing circuit,gain control circuit,serial communication circuit,and PCB layout testing.By using the beat frequency signal demodulation algorithm,high-precision displacement measurement can be achieved,creating a reliable hardware platform for frequency modulated continuous wave fiber displacement sensors.Finally,an experimental platform was established to validate the research topic.The experimental results show that in the measurement environment of a one-dimensional motion platform,the entire system operates within the range of 0-600 mm.After using gain control,the amplitude of the beat signal voltage can be controlled within the range of 1.2V to 1.4V,and the standard deviation of the displacement measurement results for this system is within5 nm.The entire system has high accuracy and simple structure,which is of great significance for use in three-dimensional motion platforms.