Distributed unmanned aerial vehicles formation with built-in safety systems

Due to its high manoeuvrability, portable size, high payload capability and good expandability, Unmanned Aerial Vehicle (UAV) is capable of accomplishing varieties of tough missions. In particular, cooperative multiple UAVs can significantly increase the mission efficiency and effectiveness. In some applications with complex environments such as narrow canyon, distributed formation with adjustable shape is required. Moreover, a reliable autopilot safety system is mandatory so that the flight does not pose threats to the surrounding environment. In this research, distributed formation control of multiple UAVs with built-in comprehensive safety features for operation in complex environment is studied. Distributed formation control has been studied in an existing work by integrating proportional control into its path planner. There exists, however, steady state errors when an external reference velocity is applied to a certain UAV. In order to improve the formation control and eliminate the steady-state error, a proportional-integral (PI) controller is proposed. It is shown that the proposed distributed PI controller can stabilize the system and achieve the zero steady-state error. Numerical and hardware in the loop (HIL) simulations and flight tests are conducted to verify the effectiveness of the proposed approach. Since distributed formation is controlled by an on-board autopilot, failures may happen due to system or hardware faults. Hence, safety and robustness of the on-board autopilot become very important. Therefore a comprehensive approach on the implementation of safety operation for multiple UAVs formation in outdoor environments is proposed. A pre-flight UAV status inspection schedule and a hierarchical three layers in-flight safety architecture are developed based on a customized risk assessment matrix.