Autonomous unmanned aerial vehicle (UAV) flight generally consist of four steps, take-off, ascent, descent, and finally landing. Among them, autonomous landing is the challenging task due to high risks and reliability problems. In case the landing site where the UAV is supposed to land is moving and oscillating, the situations become more unpredictable and it is the way difficult than landing on a stationary site. For these reasons, the accurate and precise control for autonomous landing control is essentially required. So this thesis ultimately focuses on developing an autonomous landing system of a UAV on top of a moving vehicle which is rolling or oscillating while moving. The system consists of two parts.
Firstly, I proposed a dynamic gimbal control based vision-only based landing algorithm in chapter 2. The conventional camera systems which are applied to the previous studies are fixed as downward facing or forward facing. The main disadvantage of these systems is a narrow field of view (FOV). By controlling the gimbal to track the target dynamically, this problem can be partly solved. Furthermore, the system helps the UAV follow the target faster than using only fixed camera. With the artificial tag on landing pad, the relative position and orientation of the UAV are acquired, and those estimated poses are used for gimbal control and UAV control for safe and stable landing on a moving vehicle.
Secondly, however, the vision-only based algorithm described above is not perfectly trustworthy because of unexpected disturbances, such as a sudden gust of wind, sunlight and etc. So the system proposed in this study approached the solution of autonomous landing in the point of mechanical view as well. In chapter 3, by analyzing the stresses and strains of the conventional landing gears of UAV during landing procedure with finite element analysis (FEA), the weak points are verified. To reinforce those points, the modified landing gears are designed with an attached suspension system on each leg and the results are also verified via FEA using ANSYS.
The simulations using ANSYS show that the modified landing gears decrease the equivalent stress on the critical points, and propose the proper design and parameters to consider for further studies. The outdoor experiment results show that this vision-based algorithm performs fairly well and can be applied to real situations.