Research On Key Technologies Of INS/DVL Integrated Navigation

Inertial Navigation System(INS)/Doppler Velocity Log(DVL)integrated navigation system has been widely used in underwater navigation due to its complete independence,autonomy,concealment and high precision.Underwater vehicles need to reduce the surfacing times during the missions to improve their efficiency and concealment.Therefore,underwater vehicles require the navigation system to maintain high accuracy positioning as long as possible.INS/DVL integrated navigation system updates the position parameter through dead reckoning method,therefore its positioning error will accumulate with the increase of traveled distance.In this paper,the key technologies of INS/DVL integrated navigation are studied to improve the accuracy of INS/DVL system,thereby realizing the long term autonomous navigation of underwater vehicles.The main contents and innovations of the paper are listed as follows.1.The installation error,the scale factor error,and the constant error of DVL are calibrated by utilizing the Kalman filter based calibration method.In the calibration process,the reason why the calibration cannot be achieved in some maneuvering modes is analyzed and maneuvering modes that can effectively achieve calibration are designed.The model of the DVL measurement error introduced by attitude dynamics is established.Base on the established error model,a correction method for DVL measurement error introduced by attitude dynamics is proposed.In the proposed method,the two effects of the attitude dynamics on the accuracy of DVL measurement are fully considered.The two effects are:(1)the DVL measurement error introduced by the attitude change of Autonomous Underwater Vehicle(AUV)between the DVL signal transmission and reception instant;(2)the DVL measurement error introduced by the lever arm between the DVL installation position and the buoyant center of the AUV.In the proposed method,the correction equation for DVL measurement error indroduced by pitch dynamics,roll dynamics and heading dynamics simultaneously is derived.By utilizing the derived correction equation and the real-time attitude imformation from INS/DVL system,the DVL measurement error introduced by attitude dynamics can be corrected.The performance of the proposed method is examined through semi-physical simulation experiments.2.The technology of DVL-assisted INS initial alignment under moving base conditon is studied.The inertial frame coarse alignment method and the Kalman filter based fine alignment method are used to realize the DVL-assisted INS initial alignment from arbitrary initial misalignment angles.A prior knowledge based observability analysis method is proposed by improving the original observability analysis method.By using the proposed method,the ultimate accuracy of DVL-assisted INS fine alignment under a uniform linear trajectory is analyzed and calculated.The factor that limit the accuracy of fine alignment is determined.Based on the analysis result,a maneuvering mode which can improve the accuracy of fine alignment is designed.Simulation results show that the accuracy of the DVL-assisted INS fine alignment can be improved by designing the maneuvering modes used for fine alignment reasonably.3.The INS/DVL tightly coupled approach is studied and the model of INS/DVL tightly coupled navigation system is established.Based on the tightly coupled approach,a method for INS/DVL integrated navigation with limited DVL beam measurements is proposed.The proposed method is used for the cases that DVL has only limited(less than 3)beam measurements under special circumstances.In these cases,DVL cannot calculate the three-dimensional velocity of the AUV.As a result,the INS/DVL loosely coupled system cannot operate because there is no external reference velocity.The proposed method is based on the INS/DVL tightly coupled approach and gives countermeasures for the cases that DVL only has limited beam measurements.Semi-physical simulation experiments are carried out to evaluate the proposed method and the results show that the INS/DVL integrated navigation system can maintain high accuracy even when the DVL has only one beam measurement by ultilzing the proposed method.Finally,the positioning accuracy of INS/DVL integrated navigation system is analyzed.