Adaptive integrated navigation method of visual positioning/INS in complex multi-medium environment

In view that the autonomous underwater vehicle in the grounded microgravity environment of hybrid suspension has accurate real-time navigation problem in spacecraft rendezvous and docking, an adaptive integrated navigation scheme and algorithm was presented based on visual and inertial measurement system under multi-medium environment. The time synchronization between the data of the inertial measurement unit and that of the visual positioning system (VPS) was realized by fitting the inertial measurement data based on the time tag of VPS and backward inertial navigation calculation. Then an adaptive Sage-Husa integrated Kalman filter was designed based on exponent fading factor system with a real-time estimator for the measurement noise to solve the problem of time-varying measurement noise of VPS. The validity of the proposed algorithm was tested and verified by the experiments, and the results show that, compared with the integrated algorithm with common used Kalman filter and without time synchronization, the accurate real-time navigation can be achieved and the velocity/position estimation errors are reduced by 56% and 64% respectively.