Research On Flexible North Finder

In recent years, with the development of science and technology, the inertial navigation is not only more and more widely used in military field, but also in various kinds of fields, such as land surveying, tunnel construction, oil mining, mineral exploration, submarine rescue and other civil engineering.According to the requirements, the system should be able to work normally in worse natural condition and in the situations with interferences. The working time should be less than 5 minutes and the error should be less than 0.3 degree. Based on all of these requirements, the North Finder designed is consisted of quartz accelerometer and flexible gyro which is small, high accuracy and low-cost.The CPLD chip is used to generate the sinusoidal excitation signal and three-phase drive signals of gyroscope at first. Then the force feedback loop is designed to make sure the flexible gyro working normally and has sufficient phase margin and amplitude margin. The feedback loop contains following amplifier, phase sensitive demodulation circuit, filters, advanced calibration and power amplifier circuit. Moreover, RS232 and RS422 these two kinds of serial interface circuit and AD sampling circuit were designed under the request.The Nios II processor, SDRAM core, UART core and other hard-core are designed by using SOPCBuilder, which generates the request hardware module. The AD sampling program is programmed under Nios II 8.0 IDE.The paper adopts improved four location north-seeking method, which has proper working time and more accurate. It also analyses the main error of the system. And the experiments are done to prove the stability of the system under the level and slope state. At last, the gyro and accelerometer are calibrated. The experiment shows that the working time is about 4 and a half minute and the error is about 0.2 degree, which satisfied the system requirements.