Research On Method And Key Technologies Of Frequency-Sweeping Polarization-Modulation Ranging

Absolute distance measurement is an important measuring means in space precision measurement.In recent years,with China's rapid development of high-end intelligent manufacturing industry,traditional distance measurement methods may not meet the increasing demand for large-scale and high-precision measurement.Compared with traditional ranging technology,sweep polarization modulation(FSPM)ranging technology has unique technical advantages in measuring principle and method.Research of FSPM is very important to promote China's advanced high-end manufacturing industry.In this paper,sweep polarization modulation ranging technologys are studied and explored in depth.FSPM's measuring principle,main error factors and key error compensation are studied;the optimization,frequency drift compensation experiments and distance measurement experiment are carried out.The main research works are as follows:(1)Aiming at influence of thermally-induced phase delay on frequency measurement,compensation method of measurement error based on bidirectional sweep is proposed.In the method,drift error caused by thermally induced phase delay can be eliminated to some extent by averaging the in-phase frequencies obtained through forward and backward sweep.In the experiment,standard deviation of frequency interval measurement decreased from 5.70×10~4 Hz to 5.80×10~3 Hz with the proposed method,and the ranging error reduced an order of magnitude.Results show that the proposed method can effectively improve the repeatability of frequency measurement and distance measurement without any modification of hardware.(2)An in-phase frequency extraction method based on secondary frequency modulation and digital phase-locked demodulation is presented.In this method frequency of linear sweep modulation signal is modulated sinusoidally,and specific frequency components of the output signal is extracted so that minimum can be converted into zero-crossing of the output,and effectively improves the frequency extraction accuracy.A verification device based on traveling wave phase modulator has been established and in-phase frequency measurement experiment has been conducted.Results proved the effectiveness of the method.(3)Measurement method of wavelength multiple based on multi-frequency interval is proposed.In the method,wavelength multiple is calculated through the in-phase frequencies with interval of u,so the error of frequency interval can be reduced by u times under existing frequency measurement accuracy.(4)Aiming at the frequency measurement error caused by polarization coupling,methods to suppress the polarization coupling errors are proposed from perspective of suppressing the coupling and eliminating the coupling wave interference.Firstly,by establishing a polarization transfer model of the system,main error sources and the influence of polarization coupling across the system are analyzed,then,the optimum film layer and attitude angle range for suppressing polarization coupling are analyzed.Lastly,a suppression method according to depolarization principle based on superluminescent diode is proposed.The mechanism of polarization coupling error suppression is investigated and optimum range of full width at half maximum is analyzed.The effectiveness of this method is proved by experiment of both frequency measurement and absolute distance measurement.Results show that the repeatability error of frequency measurement is decreased from 738 Hz to 25 Hz with super-light emitting diode as light source,and the maximum residual error of absolute distance measurement within 5.2 m reaches 51.7 um.