Research On New Photoelectric Range Finder And Three Dimensional Imaging

The works in this dissertation are based on the international cooperation between Department of Physics,University of Science and Technology of China(USTC) and Seattle Hardware Division of Microsoft,which includes theoretical and experimental research on one-dimensional(1D) single mode vertical-cavity surface-emitting laser (VCSEL) range finding,two-dimensional(2D) triangulation-based optical rang finding with dual lens and three-dimensional(3D) imaging based on LED array time of flight(TOF) range finding.We have put emphasis on the study of various factors which influence the range accuracy and dynamic range of laser range finder,and emphasized the study of the photoelectric design method for 2D triangulation-based optical rang finder with dual lens,and give in-depth analysis and appropriate remedy on the triangulation ranging error.Also we have proposed a new 3D imaging system based on LED array time of flight(TOF) range finder,analyzed the experimental results in detail and developed a simple Signal Noise Ratio(SNR) model to explain the mutual restriction among the pixel number of depth image,depth measurement resolution and depth measurement speed,which give a good guidance for the optimized design of the 3D imaging system.The main research works and conclusions are as follows:1.We accomplished the theory and system researches of laser range finding by self-mixing effect in a single mode VCSEL,designed the optics and signal processing circuit for the system and builded the protype of the single mode VCSEL laser range finder;We analyzed various factors influencing the system key parameters in theory and experiment,such as ranging accuracy and dynamic range,etc.By applying difference frequency analog phase-locked loop(PLL) instead of Fast Fourier Transform(FFT) to process self-mixing beat signal,choosing the optimum triangular wave frequency and small current to modulate single-mode VCSEL,the signal noise ratio(SNR) of beat signal has been enhanced,which finally makes the ranging accuracy is better than 2 mm and the measurement dynamic range is as large as 50～500 mm. 2.We completed the theory and system researches of the 2D triangulation-based optical rang finding with dual lens,delivered the optics and electronics design for this system in detail,constructed the protype of real-time 2D triangulation-based optical rang finder and gave in-depth analysis and appropriate remedy on the triangulation ranging error.By applying the pinhole imaging instead of normal lens imaging to study 2D ranging,we demonstrated the large visual angle abaxial light aberration of lens is the main reason for the ranging error,and propose an empirical remedy equation based on experiments,which not only simplify the form of theoretical remedy equation but also obviously improve ranging accuracy and speed.The actual work region of this ranging system after remedy is as large as 80 mm×100 mm,the average resolution and ranging error in x and y direction are better than 0.2 mm and 2 mm,respectively.3.We proposed a new 3D imaging system based on LED array time of flight range finder in principle and structure,gave the detail design on the optics and electronics for the 10×10 LED array 3D imaging system,and builded the real time protype.Moreover,we analyzed the experimental results in detail and developed a simple SNR model to explain the mutual restriction among the pixel number of depth image,depth measurement resolution and depth measurement speed,which gives a good guidance for the optimized design of the 3D imaging system.The 10×10 LED array 3D imaging system after optimization can acquire at a rate of 10 frames per second(fps) with a depth resolution better than±5mm in the range of 5～100 cm.The innovative results in this dissertation are as follows:1.Use difference frequency analog PLL to process self-mixing beat signal,so the phase abrupt changes in the beat signal corresponding to the inflection points of the modulation triangular waves have been improved obviously,and the amplitude modulation and distorted waveform has been rejected obviously, which enhance the SNR of beat signal and finally improve,the ranging accuracy and measurement dynamic range.By choosing the optimum triangular wave frequency and small current to modulate single-mode VCSEL, the frequency measurement accuracy of self-mixing beat signal be improved and the ranging error introduced by VCSEL nonlinear modulation can be reduced.2.Based on experiment,we demonstrated the large visual angle abaxial light aberration of lens is the main reason for the ranging error in the 2D triangulation-based optical rang finder with dual lens,which keeps good agreement with the high order distortion theory of imaging lens.We also proposed an experiment-based empirical remedy equation,which not only simplify the form of theoretical remedy equation but also obviously improve ranging accuracy and speed.3.We proposed a new 3D imaging system based on LED array time of flight range finder in principle and structure.The high speed depth measurement can be achieved by employs fast electronic time-division scanning of a two-dimensional array of LED light sources instead of using mechanical scanning,which means no moving or rotating parts are needed in this system. The co-lens method is used to assure the natural registration between the range image and 2D image.The design of fast feedback AGC(FBAGC) circuit obviously reduces the system feedback response time and improves system measurement speed.Based on the theoretical analysis,a simple SNR model is developed to explain the mutual restriction among the pixel number of depth image,depth measurement resolution and depth measurement speed.Finally, the feasibility of implementing a real time large pixels version of the system is also demonstrated.