| A dual-frequency laser interferometer is one of the most common instruments in modem geometrical precision measurement, and it is also the most authoritative one for measuring displacement and length. Based on the existing dual-frequency laser interferometer with two longitudinal modes, whose laser source is the stabilized-frequency He-Ne laser with thermoregulation, this research has improved the interferometer system, and the main works are as follows:Firstly, the nonlinearity of the existing dual-frequency laser interferometer with two longitudinal modes is theoretically analyzed in detail, and the result is accordant with the observed phenomenon. The influences of nonlinearity to measuring speed and accuracy are determined, and then the quantitative conclusion is followed.Secondly, a solution is proposed to solve the problems of the existing circuit system, such as DC shift of the signal, and the inconvenience of signal observation when adjusting optical path. The signal of frequency v, which is generated by high frequency oscillator of high stability, is divided into two paths by power divider in order to mix measuring signal △v ± △f and reference signal △v . Then measuringsignal |v-△| ± △f modulated by the movement of measuring mirror and reference signal |v-△| can be gained, where △f is Doppler frequency shift. By the aid ofpeak detector circuit, the intensity of measuring signal and the propriety of the optical path adjustment can be known. The measuring and reference signal are imported to AGC and shaping circuit respectively, and then the square-waves areexported, which can be directly calculated by counters. The advantage of this method is that it makes the whole system have the feature of AC system. All kinds of factors, including nonlinearity, that cause DC shift of signals, can be processed by AGC circuit. So it is easy for the system to meet the requirement of normal work.Thirdly, the improved circuit system is expounded, which includes peak detector circuit, Automatic Gain Control circuit based on AD603, and counting circuit based on CPLD.Finally, after design of the circuit and debugging of the software and hardware being finished, experiments of the peak detector circuit and AGC circuit have been carried out. Moreover, the anti-disturbance and the measuring speed of the whole system have been tested.The result shows that the improved dual-frequency laser interferometer with two longitudinal modes can meet the desired goal, and it can work well at the speed of 1000mm/s.
|
PDF Full Text Request