Research On Motion Control Of Trans-medium Multi-rotor Water-air Amphibious Vehicle

Trans-medium water-air amphibious vehicle is a new type of equipment which can both cruise in the air and underwater with the capacity of medium interface crossing.Its amphibious operation ability conforms to the strategic thinking of “Maritime Power” and meets the “Space,Air,Earth and Sea” mission requirements for omnidirectional stereo exploration,which leads to significant research values and broad application prospects.The motion control issues of every mission profiles for a multi-rotor water-air amphibious vehicle were herein studied.The main research contents of the thesis are as follows:(1)Layout design and system modeling: Combined with the layout advantages of quadrotors and ROVs,a layout scheme of hybrid multi-rotor driven amphibious vehicle utilizing “four aerial rotors and four water rotors” was proposed and its working principles were also introduced.The kinematics model was derived based on the spatial coordinate transformation laws,the dynamic model was derived utilizing Newton-Euler method based on its force analysis results,and a reasonable thrust distribution scheme was formulated using the pseudo-inverse method,which lays a theoretical foundation for the subsequent motion control research.(2)Research on single medium motion control: Due to the similarity of the water and air single-medium motions in mathematical models,they were herein unified into one single-medium condition to study.A command filtered backstepping controller based on nonlinear disturbance observer(NDO)was herein designed,the NDO was used to observe external interference and system modeling errors whereas the command filter was used to generate the command signal and its derivative of the virtual control variable to avoid the complex calculation process of analytical derivative,and the simulation results proved that the controller was quite accurate in tracking 3D trajectory.(3)Research on single medium motion control: Based on the comparison results of different medium interface crossing methods,a low-speed vertical way was herein selected.The motion model was simplified into 4DOFs by reasonably neglecting small pitching and rolling motions,and equivalent estimation method of medium parameters(density and dynamic viscosity)based on the feedback altitude signal of the vehicle was also proposed.According to the coupling characteristics,a hierarchical double-loop control structure was herein designed,a full-state constrained controller was designed for the altitude loop whereas a command filtered backstepping controller based on NDO was designed for horizontal fixed-point dynamic positioning loop.Simulation results suggested satisfying performance,especially the full-state constrained controller could effectively limit the vertical movement speed while ensuring the control accuracy,which guaranteed the safety of trans-medium mission.(4)Research on global switching control strategy: Based on former conclusions on motion control and division results of the working space for each mission profile,a global dual-mode hybrid switching control strategy driven by real-time feedback altitude signal of the vehicle was designed,while a dimensional expansion algorithm for the control output of forces and moments was proposed to solve the problem of the output dimension difference between former two control modes.The stability of the switching strategy was analyzed based on dwell time theory,and planning requirements for the desired altitude trajectory of the vehicle was concluded to be “low-frequency low-speed transition”.Simulation results suggested its effectiveness and stability.(5)Prototype development and experiment:Based on the idea of “fly first,dive later” and experience of quadrotors and ROVs,the prototype was built,and the settings and test of ground station software were finished.The thruster performance experiment tested the thrust characteristics of the two selected aerial/water thrusters in each medium,which were capable of missions.The overall test and pool test showed the feasibility of the layout scheme and the effectiveness of the proposed control algorithm.