Research On Key Technologies Of Phase-shift Laser Range Finder With Multi-frequency Modulation

With the fast development of military, aerospace, ultra-precise processing and measurement, large-scale, high resolution, fast, dynamic distance and velocity measurements are needed in more and more fields, which make new demands on laser range finding.In this paper, some key technologies of phase-shift laser range finding are discussed. A multi-frequency modulation laser range finding system capable of implementing fast, dynamic distance and velocity measurement with high resolution are proposed based on phase-shift laser range finder, the achievement of this paper shows an effective approach to solve the slow measurement, low anti-jamming capacity and incapable of implementing dynamic measurement, which make the designed system in this paper has a broad application prospects in industry, military and aerospace where large-scale distance measurements are needed.After consulting a large number of domestic and foreign related literatures and references, this thesis provided an overview of laser range finder application in industrial, high-precision processing and manufacturing, three-dimensional measurement of large-scale objects, aircraft exterior attitude measurement, spacecraft automated rendezvous and docking and small satellite formation flying. Some key problems of phase-shift laser range finder are summarized in new application occasions and requirements, which laid the foundation of system design and optimization, signal processing and proposing compensation method for nonlinear of APD. And the key problems are in urgent need for solution provides a clear direction for research.Laser range finder system with multi-channel of transmitting and receiving are designed based on multi-DSP parallel processing. For laser range finder with multiple modulation frequency transmitted at the same time, the reference and measurement signals are digitalized by Multiple A/D converters in parallel and were sent to multi-DSP, the phase difference and frequency difference between the reference and measurement signal are calculated by spectrum analysis, the distance and velocity of the target are acquired. The measurement resolution is improved and the anti-jamming capacity is enhanced by digitalized the signals, and the measurement signal with multiple modulation frequency were transmitted, received and processed at the same time, the measurement time is reduced. The temperature control system is designed to guarantee the whole laser range finding system achieving stable, high precision measurement.To improve the phase difference between reflected signal and reference signal, the all phase FFT(apFFT) are introduced in laser range finder as a new spectrum analysis method, the phase estimate accuracy model adopting apFFT in presence of Gaussian white noise is founded, the relationship of accuracy of phase estimate with key factors such as signal-to-noise ratio, normalized frequency leakage error , sampling points,and the window function are discussed in detail. A new frequency correction method are proposed based on apFFT analysis, the Monte Carlo simulation prove that the new method has higher resolution and better stability than Rife-Jane method and centro-baric method.Nonlinearity of APD restrains enhancement of phase-shift laser range finder measurement precision. The relationship among phase measurement error caused by APD'S nonlinear, Multiplication, bias voltage acting on APD, incident light intensity are analyzed. An Active multiplication control unit is designed. Active multiplication controlling and software compensation of phase error are combined to reduce the influence of APD's nonlinear characteristic. Experiment proves that it is an effective way to compress the phase error. For a modulation frequency of 75MHz, the phase error of 4.8013o can be reduced to less than 0.0301o. For a modulation frequency of 7.5MHz, the phase error of 0.5018o can be reduce to less than 0.0291o, a strong increase of the accuracy of distance measurement with the new developed phase error correction method.At last, performance tests and validation experiments on the key technologies discussed in this paper are taken. The experiments are implemented on a precision guide of 3m-long. In the distance stability testing experiment, the distance measurement standard deviation is better than 0.09mm for fixed distance. In the velocity testing experiment, for the target with a contant velocity of 200mm/s, the velocity measurement standard deviation is better than 0.0049m/s when apFFT point number is 4096 and better than 0.0114m/s when apFFT point number is 2048.