Research On The Key Technology Of Frequency-sweeping Distance Absolute Measurement

Compared with the traditional interferometry, with the advantages of no contacting, without guiding, without continuous measurement, the frequency sweeping distance absolute measurement method can make the interferometry better to meet the requirements of practical industrial application and measurement science. It further improves the application range of the existing laser interference ranging system, and has an important theoretical and application value. This thesis researches on system measuring principle, optical path design and building, drive circuit development, synchronous data acquisition system, extremum extraction phase of the frequency sweeping distance absolute measurement method. The main research details can be listed below:Firstly, a set of interferometry system is designed, namely the absolute distance measurement system. This system adopts the frequency sweeping method based on current modulation, and designs a reference interference light path and a measurement interference light path for the synchronous measurement. The interference signal of the reference light path and the measurement light path is received respectively by two single quadrant photoelectric detector, and designs the photoelectric conversion circuit for photoelectric conversion, as the input signal of data processing of an absolute distance. Introduce the current modulation features of LD, design the LD driving circuit of the relatively independent charging and discharging, and introduce the measuring principle of this system.Secondly, designing the phase extraction algorithm of the measurement system, the algorithm uses the extreme value point position of the effective signal to extract the effective signal phase. The fast Fourier algorithm is applied by the analysis of the characteristics of the current modulation mode interference signal. It obtains the about cycle count of effective signals by the fast Fourier algorithm. Employ the two step difference convolution operation to smooth the acquisition signal. Make use of the 3 point interpolation algorithm for the extreme value point. Adopt the maximum and minimum to the maximum and minimum. And then, introduce the relative phase information to the absolute distance computation.Thirdly, the design of synchronous data acquisition system is based on FPGA to implement the collection, storage and transmission of experimental data. The system achieves synchronous data acquisition of interference signals with the AD7812 chip controlled by the FPGA and the data are stored in the FIFO registers of the FPGA. It reads the data and processes data by the Nios II, and displays real-time data by PC.Finally, the design operation based on extremum extraction phase can be used to handle the collection of the valid data, and it is contrasted the laboratory finding with measurement results of the dual-frequency Leaser. It verifies the feasibility of the algorithm and the advantage of the calculation, and it provides a better steadiness and repeatability. In the meantime, the system analyzes the sources of the experiment error.