Research On Key Technologies Of Phase-shift Laser Radar With Angle Measurement

Compared to interferometry ranging and frequency modulated continuous wave ranging, the phase-shift ranging has a farther distance. Compared to the pulse ranging method, it has higher ranging accuracy. Four-quadrant detector enables to measure the distance and relative position, with small size, light weight and high detection resolution,especially the four quadrants APD(Avanlance Photodiode)with high gain and low noise suitable for medium or long-distance ranging and tracking. Based on phase-shift ranging and four quadrant tracking, this paper designed a phase-shift laser radar systems based on four-quadrant detector, and researchs on several key technologies for ranging and tracking have been done.An important function of the system is ranging and this paper researchs several key techniques influencing on ranging accuracy. Phase-shift measurement algorithm is an important factor impacting on ranging accuracy.For the most commonly used methods –ap FFT(All Phase Fast Fourier Transform) and FFT(Fast Fourier Transform) in phase-shift laser ranging,this paper select FFT algorithm as a phase-shift detection algorithm.by comprehensive comparison of phase accuracy and SNR of output amplitude.The system has four measurement signals and how to extract high-precision distance from four measurement signal has important research value. By analysis and comparison among Atan_Mean algorithm, Mean_Atan algorithm and Max algorithm, this paper proposes an optimization algorithm based on Mean_Atan algorithms and Max algorithms and verifies the superiority of the algorithm.Temperature is another important factor affecting the phase-shift ranging accuracy. At home and abroad some research was done about temperature affecting the phase-shift ranging accuracy.From the temperature characteristic of resistors and capacitors,this paper has studied the effect of temperature on ranging accuracy of the phase-shift method.By experiments it comes to a conclusion: by selecting a low temperature coefficient of resistance and capacitance can improve the phase-shift ranging accuracy.Another important function of the system is tracking,and the paper researchs several key techniques on measuring angles.This paper makes the tracking process reasonable simplification,and proves it feasible and correct to use four signal amplitude based on FFT to get miss distance on the basis of the simplified model.The estimation accuracy of azimuth and elevation directly determine the tracking accuracy, and the miss distance estimation algorithm affects azimuth and elevation estimation accuracy.Based on the traditional equidistant interpolation method,this paper proposes a miss distance estimation algorithm based on the analysis of the characteristic curve and interpolation method.It is obtained by experiments that the maximum errors of the azimuth and elevation of the algorithm are smaller than those of the equidistant interpolation method under the same conditions of the interpolation points.To analyze the impact of amplitude information based on FFT on angles accuracy, this paper has established a miss distance accuracy estimation model.It is obtained through theoretical analysis and simulation that increasing the input SNR, selecting the rectangular window, reducing the frequency offset and increasing the length of the FFT data can improve the estimation accuracy of the miss distance.In order to verify the feasibility of the system, a experimental platform has been established.In order to examine the impact of various modules on ranging accuracy,we respectively have done the appropriate experiment of digital systems, analog circuit board and the whole system.It is obtained the standard error of the distance difference is less than 0.7mm,and less than 0.07 mm by an average of 100 times.This error may be ignored compared to other components in the system. In the difference experiment between the reference channel and measurement channel of analog circuit board, the ranging error standard deviation of this portion is 1.5mm,and is 0.2mm by an average of 100 times. The ranging experiments of high-frequency signal and low-frequency signal have been done in the system testing.In the high-frequency signal experiments, the standard deviation of ranging error is 1cm, and is 0.8cm by an average of 100 times.The peak to peak distance error is 3m in the low-frequency experiments and it meets the convergence condition of the multi-frequency measuring signal. In order to examine the stablishment of the miss distance,we have done a experiment about the miss distance.Experimental results show that standard deviation of the X-axis miss distance normalized is 0.003 and the standard deviationin of the Y axis miss distance normalized is 0.001.