A Sequence Control System for Onboard Mission Management of an Unmanned Helicopter

Abstract

This paper presents a solution to the onboard mission management problem for UAVs. Inspired by successful approaches from the mobile robotics domain, the proposed architecture achieves hybrid control by combining ideas from the behavior-based paradigm and a three-layered high-level control architectures. A Sequence Control System implements the essential components of this architecture. It is open with respect to its interfaces to other onboard components (e.g. the obstacle avoidance system). Events and commands sent by a remote operator or an onboard component can be integrated into the system in a plug-andfly fashion. A remote operator can send direct commands on different abstraction levels. The solutions to more complex mission problems and events (e.g. onboard trajectory planning or reacting on a data link loss) can be delegated using high level commands. To assure the safe operation of the Sequence Control System, the system is characterized by multiple techniques. First, the event-based decision logic is modeled as a State Chart model. Second, a truth table of valid external commands assures that only permitted commands are accepted by the event handling. Finally, a grammar-based plausibility check avoids illegal behavior commands within a mission plan. The system is implemented onboard the UAVs of the ARTIS program. It is validated in unit tests, and tested in software-in-the-loop and hardware-in-the-loop simulations. As a result, the system allows a robust, deterministic high level control of UAVs. It allows an operator to control a UAV at different levels of autonomy, ranging from common joystick control to execution of prearranged missions.