Research Of Phase-Shift Absolute Distance Measurement By Use Of Femtosecond Laser

Large equipment manufacturing is moving towards the direction of high-precision and digitalize. The measurement of the position and pose of the work pieceswith high precision and efficiently is the key supporting technologies to ensure thequality and efficiency of manufacturing. Distance is one of the basic constraints todetermine the spatial coordinate. However, conventional measurement methodscannot meet the requirements of measurement in large equipment manufacturing. Thehigh frequency stability and peak energy of laser frequency comb opens thepossibility of high-precision distance measurement in long range. Extracting thestable high frequency microwave signal and obtaining distance by the phase shift isthe method in this thesis. The absolute distance of the target can be achieved afterunwrap the phase by adjusting the repetition frequency of femtosecond laser. Thephase shift measurement error is analyzed and has been determined in the experiment.Basis of theory and technology is put forward for the development of distancemeasurement with laser frequency comb and meeting the new requirements ofmeasurement in large equipment manufacturing. The main work accomplishedincludes:1. The need and characteristics of precision measurement technology in modernadvanced manufacturing are summarized, the conventional measurement methods andcharacteristics are discussed. The source and research significance of the subject, thecharacteristics of femtosecond laser frequency comb and prospects in distancemeasurement application are summarized with application requirements, technologydevelopment and basis of research.2. To meet the requirements of industry application, frequency components inmicrowave frequency comb are extracted by photo-detector from femtosecond laser,and used for the phase shift distance measurement. The key technology of the methodis researched. The method of obtaining high frequency measurement signal with highstability is discussed. Moreover, the non-linear cyclic error in distance measurement isessentially suppressed comparing with the traditional ways.3. According to the contradiction between measurement accuracy andnon-ambiguous range in phase shift method, adjusting repetition frequency to obtain small frequency difference and long non-ambiguous range is put forward formeasurement. Merging results of high-precision measurement and syntheticwavelength measurement to achieve a high-precision distance measurement inlarge-scale.4. According to the ultra-short light pulses of femtosecond laser frequency comb,pulse broadening, amplitude fluctuation and beam pointing fluctuations caused by theair refractive index fluctuation and group velocity dispersion are analyzed, and thefrequency stability attenuation and amplitude fluctuation of microwave signal causedby them are discussed. At last, measurement uncertainty is determined bysynthesizing phase-detecting error, frequency stability error and error of refractionindex of air.5. The experimental platform is established to verify the femtosecond pulserepetition frequency and the analysis of the microwave frequency stability. Thedistance is measured by extracting the microwave frequency signal. High-precisionresults are achieved in large range by adjusting repetition, which verify the feasibilityof the method and the result of error analysis.