| Inertial Navigation System(INS)is widely used in civil and military fields,such as aviation,aerospace,navigation and so on,for its advantages of complete autonomy,independent of external information and good concealment.As an important branch of inertial navigation system,orientated north seeking system is widely used in military and civil orienteering.The development of system-level products is toward the direction of high precision,small volume and high reliability.Based on the background of a certain type of ground laser irradiation system,we developed a small two degree of freedom azimuth tracking platform system.It is based on the characteristics of small volume,light weight and easy to be carried by single soldier,combined with the work flow of ground laser irradiation system.Through rapid erection and start-up,the system can complete the north-seeking in a short time and real-time tracking of the target for analyzing the geographic information of the target.According to the requirement of the research background,the system error is analyzed and allocated to provide the basis for sensor selection,and the dynamic tuned gyroscope is adopted to realize the north-seeking function of the gyroscope.The metal leveling bubble is used to replace the traditional accelerometer leveling compensation.The high-precision photoelectric encoder and angle sensor are used as the sensitive devices of azimuth axis and pitch axis to realize the high-precision azimuth tracking measurement.An analog servo loop based on dynamically tuned gyroscope(DTG)is designed for north-seeking gyroscope,including front-discharging circuit,phase-sensitive demodulation,notch,correction network and power amplifier circuit.The theoretical derivation and correction of the transfer functions of each part ensure that the gyroscope has excellent amplitude margin and phase margin,and realize the closed-loop control of gyroscope stability and high precision measurement.In the control circuit of the platform,the dsPIC30F6014 A microcontroller is used as the control core,and the 7V16 kHz excitation,three-phase motor drive,photoelectric encoder and pitch sensor data acquisition and data communication are realized by software programming.Among them,the 7V16 kHz excitation power source abandons the complicated design scheme of discrete component analog circuits.The digital circuit design scheme is realized by using the programmable sine wave generator(ML2035)as the signal source.The power supply of the three-phase motor is realized by using the digital mode of LP624 three-phase motor driver chip and controller for timing control.The high precision 24-bit multi-channel AD7734 chip is used to collect gyroscope and sensor signals instead of the traditional IF circuit with high complexity,thus realizing the miniaturization design of the platform system.In the aspect of algorithm,the two-position algorithm of gyroscope and the tracking and measuring algorithm of north-seeking are studied.The measurement error of gyroscope and the tracking and measuring error of angle are fully considered.Various error factors are separated and the measurement accuracy of the platform system is improved by gyro error coefficient compensation,azimuth axis error compensation and pitch axis error compensation.After the gyro north-seeking is completed,the azimuth tracking measurement method is proposed.The high-precision photoelectric encoder and angle sensor are used as the sensitive devices of azimuth axis and pitch axis to achieve high-precision azimuth tracking measurement.The test and verification show that the autonomous north-seeking time of the system is less than 3 minutes,the north-seeking precision is less than 0.6 degrees,the azimuth tracking precision is 0.02 degrees,and the pitch tracking precision is 0.1 degrees,which meets the requirements of the system development. |
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