Phase laser ranging technology is a significant approach for large-scale and high-precision measurement. Improving the precision of phase ranging by increasing the modulation frequency is considered as one of the most effective methods. However, the maximum sampling frequency of A/D devices limits the sampling rate of high-frequency modulated signals, which means that the modulation frequency cannot be increased infinitely. So, the using of under-sampling for high-speed and highfrequency modulation signals is proposed in this paper. The feasibility of this method is analyzed and verified. For further improvement in ranging precision, the advantage of all phase fast Fourier transform (apFFT) is analyzed by simulation. In addition, Kalman filtering technology is adopted in this paper to suppress noise in the system to improve the precision of phase discrimination. Based on the simulation results, a high-precision phase discrimination system using FPGA is designed in this paper. According to experimental results, when the modulation frequency is 1.616GHz and the sampling frequency is 1.6GHz, the ranging stability of the system can reach ±10.8ߤ݉ and the speed of phase discrimination can reach 2712 times per second.
KEYWORDS: Distance measurement, Cameras, Laser systems engineering, Prisms, Monte Carlo methods, Manufacturing, Laser applications, Imaging systems, 3D modeling
The Six-degree-of-freedom(6-DOF) measurement system based on laser tracking equipment provides a good solution for large-scale industrial measurement. However, there is no unified standard to evaluate the accuracy of attitude measurement system. At present, the accuracy evaluation method of attitude measurement mainly adopts the comparison method of standard parts, which is easily constrained by space dimensions. Aiming at this problems, a homogeneous coordinate transformation method based on spatial distance constraint is proposed to realize the on-site accuracy evaluation of attitude measurement. Firstly, a reasonable control field was arranged, and the distance constraints between the reference points and the measuring points were established. Secondly, the mathematical model which described the relationship between space distance and attitude was established by using homogeneous coordinate transformation matrix. Through the above evaluation method, the accuracy of attitude measurement can be evaluated by tracing the measurement results of attitude angle to the length measuring standards. The simulation results show that the accuracy of the evaluation model decreases linearly with the measurement distance of attitude measurement system. Assuming that the measurement accuracy of the distance constraint is 15μm+6μm/m, the size of the control field is 1.1m*6.4m*5.6m, and the attitude angle range is [-60°, 60°]. The accuracy of the evaluation model can be controlled within [0.34°,3.25°], when the working distance is 3 to 15 meters. This method provide an effective idea for the on-site evaluation of attitude measurement accuracy.
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