| FMCW(Frequency Modulated Continuous Wave)laser radar ranging technology is a high-precision measurement technology that has the characteristics of not touching the object to be measured,measuring the guide rail,and measuring the scene.There must be a high-frequency linearity tunable laser in the ranging,and the position information is extracted by using the beat signal formed by the two-way optical interference.In the actual measurement,the semiconductor laser with linear frequency modulation continuous wave characteristics has inherent frequency modulation nonlinearity,the spectrum of the beat signal is broadened,and the accuracy and resolution of the measurement result are low.Therefore,a high performance laser frequency modulation nonlinearity is developed.The calibration system is of great significance.In this paper,the principle of FMCW ranging is studied based on the ranging model,and the influence of laser frequency modulation nonlinearity on ranging is analyzed.Based on the idea of open-loop correction,a frequency-tuned semiconductor laser frequency nonlinear correction system based on the combination of upper and lower position machines is designed.Ethernet communication is used between the upper and lower machines to ensure reliable data transmission and command transmission.Network calibration of the laser.The iterative correction algorithm is implemented in the host computer based on MATLAB.The algorithm performs Hilbert transform on the beat signal collected by the high-speed data collector.The nonlinear error is obtained by comparing the ideal and actual instantaneous frequency curves to reduce the error.The optimization target is to iterate a new driving current based on the previous driving current,and the upper computer is used to update the waveform table of the lower computer.The arbitrary waveform constant current source circuit is designed independently in the lower position machine,and the laser achieves the effect of linear frequency modulation by outputting specific nonlinear drive current.The lower position machine designs the waveform generation circuit,signal conditioning circuit,constant current source circuit and based on ARM as the core.Network port communication circuit.In addition,in order to achieve automatic correction,a trigger output module is designed in the arbitrary waveform constant current source circuit to control the initial working time of the high speed data collector.The relative error between the output value of the arbitrary waveform constant current source circuit and the rated output value is 0.03%,which lays a foundation for the calibration work.The frequency-modulated linearity before and after laser correction is compared.The results show that the nonlinearity is reduced from 14.3% before uncorrected to less than 0.5% after multiple corrections,and the linearity is improved by more than 30 times.The laser approaches ideal.Linear frequency modulation improves the accuracy and resolution of ranging. |
