Research On Signal Processing Tecnology For 100m Laser Interformeter

With the development of science and technology,processing manufacturing industry of large-scale optical and electromechanical equipment developed rapidly.The size of its components has reached tens of meters or even hectometer.Meanwhile,machining and assembling quality are required to achieve 10-5~10-6 order of magnitude,which puts forward higher requirements for laser range finder and corresponding signal processing technology.This paper is originated from Heilongjiang province science and technology key projects ‘100m Dual-frequency Laser Interferometer',intending to research one large dimension high precision laser interferometer without guide.This paper describes the current status of laser interferometry;analyze the advantage and disadvantage of now existing signal processing techniques for laser ranging.In view of the problems of low precision caused by measured signal bandwidth,mixing signal drift and the high-frequency pulse counting bottlenecks of now existing signal processing techniques,absolute distance measurement laser interferometry signal process technology solution is studied to achieve high resolutions,simple structure and easy integration from the electronic technology and the signal processing area.According to measuring principle of the project calculate the rough and fine frequency for distanse measurement.This subject designs signal generate module to genetate driving signal for AO frequency shifter,meeting the absolute measurement accuracy on the size of the demand for synthetic wavelength.The main research works are as follows:1.Precision phase measurement system designConventional auto-digital phase measurement method using pulse counting incurs lower measurement resolution when the frequency of measured signal is too high.Aiming at this problem,this paper research down conversion technology based on DDS,selecting local oscillator frequency according to different measured signal frequency.Improved phase measurement resolution of pulse counting method by decreasing measured signal frequency.Conventional auto-digital phase measurement method incurs error caused by the frequency drift of a local oscillator or measured signal.Aiming at this problem synchronous digital phase measurement is used.In such an approach,phase difference pulse signal and whole cycle will be filled by standard pulse signals.The phase can be calculated by the ratio of the two counts.This method eliminates the errors on the measurement result caused by the frequency drift of the local oscillator and measured signal.In the method of measure phase with fill-up pulse,phase measurement resolution is limited to standard pulse frequency because of the bandwidth and speed of the electronic component.In this paper FPGA-based precision digital phase measurement module is designed.Improve phase measurement resolution by phase shift and frequency doubling of the standard clock,parallel counting by serial conters whithout increase the system frequency.In view of phase measurement accuracy decline caused by crossing zero error in signal transformation process,fill the positive periodic pulse of the reference signal and measured signal.The counts are usd to compensate the crossing zero error.This method improved phase measurement accuracy on principle.2.Signal generate module designSignal generate module based on DDS is designed to generate sinusoidal signal used for AO frequency shift and local oscillator of mixer.Integrated DDS chip is used to produce initial signal with requied frequency.7-order elliptic filter is designed to filter high frequency spurios signal and high frequency resonance wave.Difference amplifier is designed to amplify the signal and eliminate common-mode noise.Based on the work above,the relevant hardware circuit and software program are designed.The relevant experiments are designed to test precision phase measurement system and signal generate module.Experimental results show that,when the frequency of the signal under 100 MHz,this system can achieved an phase measurement with uncertainty better than ±0.03°,and has a phase measurement resolution of 0.06°.The frequency stability of the signal generate module is better than 10-6.