FPGA Implementation Of High Precision Laser Phase Ranging System

Laser has the advantages of strong directionality,good monochromaticity,good coherence,high ranging accuracy and high brightness,which is widely used in cutting,welding,radar,measurement and other fields.At present,the most practical and promising field of laser is measurement.In order to make up for the lack of phase-type large-scale three-dimensional measuring instruments in China,this project proposes a phase-type ranging system with millimeter-level measuring accuracy and million-time measurements per second.It performs three-dimensional imaging of the target by non-contact measurements.This paper mainly studies the phase-type signal processing algorithm,and uses the FPGA in Spartan 6 series to realize the engineering application of the algorithm,and then builds a high-accuracy phase-type ranging system for 3D stereo imaging of non-cooperative targets.The main content of this paper is divided into the following parts:1.Designing ranging algorithm of the phase-type laser: According to the design index of the project,design a phase-type ranging algorithm with millimeter-level measurement accuracy and million-time measurements per second.In order to ensure the requirements of measurement accuracy and measurement range at the same time,select a dual-frequency ruler for distance measurement.The frequency value of the low-frequency ruler is 2MHz and the frequency value of the high-frequency ruler is 107 MHz.2.For the problem that the accuracy of the phase ranging system is affected by the accuracy of the phase calculation algorithm,it is particularly important to choose a phase calculation algorithm that meets the design specifications.Under the same experimental conditions,by comparing the three commonly used algorithms: APFFT phase calculating algorithm,Hilbert transform-based phase calculating algorithm and phase difference method-based phase calculating algorithm,select the phase calculating algorithm based on the phase difference method that meets the design index.3.Considering that the phase ranging board is based on the FPGA and ARM architecture,the corresponding data communication system solution is required to complete the data transmission.In addition,the configuration of the FPGA-side external chip needs to be implemented.First,the AD9959 is used to generate a low-frequency ruler with a frequency of 2MHz and a period of 1ms,and a high-frequency ruler with a frequency of 107 MHz and a period of 1ms.Second,the ADS4225 is used to sample two sampling signals.Third,perform the phase calculation of sampling signals using signal processing algorithms.Fourth,synchronize the phase value and turntable data with the asynchronous FIFO module.Fifth,using the GPMC interface to realize 50 Mbps data transfer,then the data is received by the ARM board card.Sixth,using Gigabit Ethernet to realize data communication between ARM and PC.Finally,display the real-time imaging results on the upper computer interactive platform.4.Joint debugging and testing of the overall system: Connect the phase-type signal processing board card and the turntable module according to the schematic diagram to build a set of high-accuracy phase-type ranging system,and perform single-point and continuous measurement experiments on the ranging system.Through a large number of experimental verifications,it can be known that the phase-type ranging system can achieve the design index of accuracy within 2mm within a 50 m measurement range.