Research On High Accurancy Time Measurement For3D Laser Vision System

3D laser vision system is a high-precision, miniaturized, easy-integration complex-environment detection system based on laser. With the advantages of high accuracy, full access to information, fast response,3D laser vision system has wide range of applications in robots,automatic vehicles and others automatic navigation mobile devices, which can promote the explorations of space, ocean and other unknown region. This paper mainly focuses on high-precision3D laser vision systems ranging namely the measurement of time. The main work is as follows:Firstly, this paper analysis the characteristics of direct detection and coherent detection and make the conclusion that the direct detection is the optimal solution for3D laser vision system respect to its applications. The System use a1.55um pulsed fiber laser as light source.Ranging accuracy depends on the measurement accuracy of TOF. With the comparison of the threshold timing, cross-zero timing, constant-fraction timing, centroid timing and the simulation result, this paper conclude that constant-fraction timing is the optimal timing for this system. On the basis of surveys on time interval measurement, this paper present the architecture of the optimal solution namely the time-interpolating counter.Secondly, based on the signal processing demand, this paper design a hardware platform, in which raging information is extracted using high sample rate AD. The clock generating circuit, control interface circuit etc. are carefully designed to provide best performance. The signal integrity issues are studied and rules are applied in the high speed PCB design.Finally, the constant-fraction timing and time interpolating counter are implemented with FPGA. All the parameters are calculated and verified using MATLAB. Modules are designed based on these parameters and tested with data generated by MATLAB. Modules are assembled into the time measuring system. Waveform generator is used to simulating the return pulse and the measuring experiment is conducted. The experiment shows that time measuring accuracy is0.4971ns, namely the ranging accuracy is0.0738m.