Research And Implementation Of Linear Frequency Modulation Laser Ranging Algorithms Based On DSP

With the rapid development of aerospace,shipbuilding and other technologies,China has put forward higher requirements for non-contact precision measurement technology of large equipment.Compared with the traditional pulse and phase laser ranging technology,Linear Frequency Modulation(LFM)laser ranging technology has broad application prospects in the field of precision measurement,with the outstanding advantages of high ranging accuracy and strong anti-interference ability.In this thesis,the LFM laser ranging algorithm is studied and implemented with high speed,based on multi-core floating-point DSP.At the same time,a set of LFM laser three-dimensional surface measurement system is built,which can measure large non-cooperative targets with high precision.The main research contents and completed work are as follows:Firstly,this thesis introduces the basic principles of LFM laser ranging and emphatically analyzes the effects of system noise and frequency modulation non-linear error on ranging accuracy.In this thesis,the whole scheme of the ranging system is proposed,and the frequency modulation non-linear error in the signal is compensated by the photoelectric closed-loop feedback circuit,which effectively eliminates most of the non-linear error in the echo signal.Secondly,this thesis illustrates the design and simulation of the laser ranging signal processing algorithm.A frequency non-linear phase error compensation method based on reference channel is designed,aiming at the residual non-linear error in the measurement signal.The ranging accuracy of the system is effectively improved by setting the reference channel to extract the non-linear phase error to compensate the echo signal.In order to reduce the difficulty of extracting signal phase by traditional Hilbert transform,a multi-class IIR filter is designed to convert real signal into complex signal,and the non-linear phase of the reference signal is extracted under the premise of less time and space complexity.As for solving the problem of low precision in frequency estimation by traditional FFT,this thesis uses CZT spectrum thinning method to refine the spectrum of measured signal,which greatly improves the ranging accuracy of the system.Finally,based on the signal processing board of FPGA + DSP,the realization of LFM laser ranging system is completed,including the realization of the acquisition,transmission,processing module of measurement signal and the communication module.In this thesis,serial port is used to complete data interaction between signal processing board and external control board,SRIO high-speed serial interface is adopted to realize data transmission between FPGA and DSP,moreover,Gigabit Ethernet interface is employed to finish communication between DSP and PC.This thesis focuses more on the high-speed implementation of ranging signal processing algorithm based on multi-core floating-point DSP,designs and realizes a multi-core parallel processing framework,meanwhile,optimizes the code in many directions,which effectively improves the speed of data processing.This thesis finally builds a large-scale three-dimensional surface measuring instrument,emphasizes the design and implementation of the focusing module of the system,furthermore,carries out single point ranging experiment on the long rail and three-dimensional scanning test,the experimental results show that the ranging accuracy can reach 20 μm in the range of 2m and 0.5mm in the range of 50 m.