Motion Control for Over-Actuated, Non-Affine Aerial Vehicles

Abstract

Remotely piloted aircraft systems (RPASs) have turned out to be an indispensable asset for disaster relief forces. The fact that they possess the abilities to offer a fast scenario overview and to transport vital supplies makes them even more crucial. RPASs with hybrid capabilities are particularly relevant in such instances as they combine the advantages of multicopters and fixed-wing aircraft. They can take off and land vertically, meaning they only require only a small landing area. Their capability for aerodynamic flight makes them much more efficient, enabling long operational airborne time and range. However, this type of airframe is not easy to operate because a large set of actuators must be controlled along with the need to control unstable configurations (mainly during transitioning into forward flight). This study aimed to propose a comprehensive motion control algorithm to resolve the problem of controlling over-actuated, non-affine aerial vehicles. This is exemplified in an application for a tiltrotor aircraft structure. This type of airframe presents nonaffinity in its nacelle control input. The suggested control law is based on the implicit function theorem allowing the integration of the complete set of actuators (motors, control surfaces, and tilting nacelles) into a single-controller structure. With this incorporation, the controller can be seamlessly accommodated into a larger control scheme. In addition, the controller has deterministic properties through the derivation of the control law using the implicit function theorem, although it is fully transparent in its mechanization. These properties are relevant for certification. The methodology involved exploring the use of implicit functions on a general mathematical level and extending the existing theory to be used in over-actuated, non-affine aerial vehicles. The existence of such a comprehensive controller was first proven, and later, an implementation was proposed. The feasibility of the proposed control law was evaluated using a hardware-in-the-loop simulation. In this evaluation, the benefits of the control law (based on implicit functions) were compared with a state-of-the-art variable structure controller.