Research On The Absolute Distance Measurement Technology Based On Sweeping Interference With Double Semiconductor Lasers

The FMCW absolute distance measurement technology has the advantages of no guide rails,non-contact measurement,and measurement of non-cooperative targets.It is an important means to obtain three-dimensional topographic information of large-scale equipment and key components.Since the semiconductor laser can realize current tuning,it has the advantages of fast frequency sweeping,simple and flexible modulation method,small size,and low cost,and has become the first choice for the laser FMCW absolute distance measurement system.This project has designed a dual-channel digital-analog hybrid charge pump optoelectronic phase-locked loop system,which is used to correct the non-linear effects of the tuning of dual-current tuned semiconductor lasers,and uses nonlinearly-corrected current-tuned semiconductor lasers as measurement light sources.The dual-laser laser FMCW absolute distance measurement experiment system uses dual-semiconductor lasers to simultaneously measure the non-cooperative vibration targets and verify the inhibitory effect of the double-sweep on the Doppler error introduced by the relative motion of the measured target.This subject first studied the principle of distance measurement of laser FMCW absolute distance measuring system using current tuned semiconductor laser as the measuring light source,and analyzed the effect of semiconductor laser frequency sweep nonlinearity on ranging resolution and accuracy.The principle of double-semiconductor lasers' synchronous sweep mode to suppress the influence of vibration is studied.Secondly,the method to analyze the nonlinearity of semiconductor laser frequency modulation is introduced,including open-loop pre-correction based on iterative algorithm and real-time closed-loop feedback correction based on charge pump opto-electronic phase-locked loop.The mathematical model and transfer function of the charge-pump optoelectronic phase-locked loop are analyzed in detail,as well as the measurement methods of the important parameters of the photoelectric phase-locked loop and the specific implementation methods of each module.Then,the correction effect of the semiconductor laser frequency-modulated nonlinear correction system was tested and evaluated,and an experimental system based on iterative algorithm pre-correction was built.On the basis of open-loop pre-correction,a stable dual-circuit semiconductor laser was realized by closed-loop correction.Synchronized locking,that is to achieve the FM non-linear correction of the dual semiconductor laser.Finally,a non-linearly calibrated semiconductor laser was used for single-laser frequency sweep and dual-laser synchronous frequency sweep in FMCW ranging experiments.The frequency-modulation parameters of the ranging system were calibrated and used with the displacement measurements of the dual-frequency laserinterferometer.The comparison proves that the semiconductor laser ranging system with non-linearity corrected by the photoelectric phase-locked loop has higher ranging accuracy and repeatability.The non-cooperative vibration targets were measured,and the good measurement results of the dual-laser synchronous sweep mode under vibration environment were verified.