Investigation Of Phase-demodulation And Frequency Stabilization Techniques In Mechanically Dithered Ring Laser Gyroscopes

As the main research institute of Ring Laser Gyroscopes in China, Teaching and Research Section 208, NUDT, is always puzzled by the problem of null-shift in the process of developing Mechanically Dithered Ring Laser Gyroscopes (MDRLG). The problem is that the MDRLG's null shift equal to the integral times of dither periods when the sample time is set as integer dither periods. The reason for the problem, which consists in some error of the old phase-demodulation circuit, is found out by computer simulation in this dissertation. Then a new phase-demodulation circuit is designed and the problem settled. Again, influence of mechanical dither on gyro frequency stabilization is discussed for the first time. A frequency stabilization circuit is designed and the approach to improve the precision of frequency stabilization is put forward.Firstly, computer model of MDRLG is set up for simulation purpose. By simulation about the two output signals of MDRLG, four basic waveforms between the two signals in lock-in area are found out and the fact is discovered that the old phase-demodulation circuit introduces errors when it is used for demodulating two of the four basic waveforms. Thus the principle to deal with the four basic waveforms is put forward and a new phase-demodulation circuit is designed. Experiments for the two circuits on same gyros are made and they indicate clearly that the MDRLG's null-shift problem consists in the faultiness of the old phase-demodulation circuit. The experiments also show that the new circuit can deal with the four basic waveforms rightly and has the advantage of high resolution, high capability of rejecting noise, simplicity, and so on.Secondly, considering the need of frequency stabilization, MDRLG's light intensity issimulated. The simulations indicate that sharp pulses are produced in the AC light intensity by mechanical dither. As the pulses have a wide frequency spectrum and range over the modulation frequencies of frequency stabilization, mechanical dither may reduce the precision of frequency stabilization.A closed-loop control system for frequency stabilization is designed. After analyzed each part of the loop, the system's open-loop and closed-loop transfer functions are presented and some parameters are optimized to ensure that the system has better stability and response speed.Simulations on light intensity are validated by experiments and influence of mechanical dither on gyro frequency stabilization is studied for the first time. Then it is point out that the key to improve the precision of frequency stabilization is to choose appropriate modulation frequency based on the frequency spectrum of sharp pulses, which is introduced by mechanical dither. Thereafter, Experiments of frequency stabilization under different modulation frequencies are made.In the end, null shift and scale factor of the newly developed MDRLG is tested. Randomwalk of the gyroscope is 0.0163 ? , RMS of drift is less than 0.09 ?h , relative precisionof scale factor is better than 10 PPM. The experiments indicate that the new MDRLG has high precision and the phase-demodulation and frequency stabilizing circuits work fine and stably.