The Theoretical And Experimental Study On The Errors Of The Ring Laser Goniometer

The ring laser gyro is the ideal angular sensor for the inertial system. Compared to the conventional spinning gyro, it is characteristic of high sensitivity, high accuracy and large dynamic range. The dynamic goniometer system on laser gyro base can bring these features into full play in the process of angle measurement. Beginning with a description of the structure of the ring laser goniometer, this paper has discussed the error sources and the methods to reduce them. It aims at improving the angle measurement accuracy by diminishing the effect of the main error source.Firstly, the components and principle of the ring laser goniometer are introduced. The framework analysis of the double-beam interference-type null indicator is presented. The expressions of the interference light intensity and the electric signal produced by the photodetector are derived too. The null pulses acted as symbols of the angle borders are obtained, which is the basis of dynamic angle measurement.Secondly, the primary error sources of the laser goniometer system are analyzed, including the error from the ring laser gyro, null indicator error, quantization error, mechanical erection error, and so on. The magnitudes of these errors are estimated. The results reveal that the quantization error, which dominates the total angle measurement error, should be reduced in order to increase the angle measuring accuracy.Thirdly, several methods and their realizations to reduce quantization error are discussed. The paper elaborates the signal subdivision method, the pulse subdivision method, the development procedure with FPGA, and the design of gyro pulses counting module. The data acquisition program has also been completed with LabVIEW.Finally, the optimum rotary velocity is obtained from null pulse repeatability and its dynamic responsiveness test. A series of angle measuring experiments are designed, including the 4-fold, 8-fold, 16-fold frequency multiplication experiments based on the signal subdivision method and the experiments with original gyro pulses and 4-fold, 8-fold, 16-fold frequency multiplication pulses based on pulse subdivision. Results show that the quantization error will be diminished effectively by signal subdivision and pulse subdivision methods with the accuracy better than 0.08″, which meets the expecting requirement.