Study On Dither-striping Technology For Mechanically Dithered Ring Laser Gyro

In the output signal of the mechanically dithered ring laser gyro (MDRLG), there is not only external inertial angular rate, but also the angular rate of dithered signal. Therefore, the output signal should be demodulated in order to remove the angular rate of dithered signal. At present, there are mainly two methods to demodulate the mechanically dithered ring laser gyro: full-period demodulation method and high-speed sampling and filtering method. A new demodulation method was studied in this paper: dither-striping technology.Firstly, this paper analyzed the features of laser gyro output pulse signal and dithering sensor feedback voltage signal, as well as the features of pulse differential value and voltage differential value. The simulation results indicated that the dithering parts of the pulse differential value can be simulated by adjusting the phase and the amplitude of the voltage differential value, thus the design idea of dither stripping was put forward. Two problems were encountered during the realization process: one is how much the phase and amplitude of voltage differential value should be adjusted, and the other is how to adjust. Aiming at these two problems, three methods of solving phase difference and amplitude ratio were put forward and simulated respectively. By comparison, it was found that using digital correlation method to solve phase difference and amplitude ratio not only has a high precision, but also has the ability to decrease the noise to some extent. Meanwhile, two phase shifting methods were put forward, and the simulation results indicated that both of the methods can well align the phase between voltage differential value and the dithering part of the pulse differential value.Then, dither-stripping system was designed. Hardware part mainly includes 4-fold frequency phase demodulation counting of the two channels of laser gyro output square wave signals with a phase difference of 90°, data collection for dithering feedback voltage that designed based on DSP and AD976A and the serial communication circuit between DSP and computer. Software implementation includes the DSP program corresponding to the hardware part, and based on LabVIEW, data receiving, solving phase difference and amplitude with digital correlation method, phase shifting and dither-stripping calculation program were designed.Through experimental verifications, the circuits based on DSP operated well with stable property. When dither stripped with mathematical calculation phase shifting method, the dithering parts of the pulse differential value was reduced about 99%, and can be directly applied to the real-time angular rate. After phase-shifting dither-stripping the sampled voltage differential value with FIR band-pass filtering method, the dithering parts of the pulse differential value was reduced by approximately 98%, and then through 15-order FIR low-pass filtering, better measuring results can be obtained. In room temperature and static state, null drift stability tests were performed on the gyro, and the test results indicated that with dither stripping plus 15-order FIR low-pass filtering, both one second RMS and a hundred second RMS of measured null drift value are better than directly filtered with 30-order FIR low-pass filtering. The experimental results showed that with dither stripping method, most of the dithering parts of the gyro output signal can be stripped, filtering order number can be lowered and system demodulation delayed time can be reduced.