Robust Mechatronic Actuation System for UAV Primary Flight Controls

The paper describes the initial results of a research activity aimed at developing a high integrity mechatronic system for UAVs primary flight controls able to ensure the necessary flight safety and to enhance the system availability by implementing appropriate prognostic functions. In this system a flight control surface is driven by two parallel rollerscrews, on their turn driven by brushless motors equipped with gearhead and clutch; the motors electric drives are controlled by dual redundant electronic units performing closed loop position control as a function of the commands received from the flight control computer. Provisions are taken in the motor drives to provide damping in the event of simultaneous failure of both actuators. The electronic units perform control, diagnosis and prognosis of the actuation system and mutually exchange data via a cross channel data link. System prognosis is made by dedicated algorithms processing the control and feedback signals obtained in flight and during preflight checks. As a whole, a smart mechatronic system is obtained providing high integrity control of an aerodynamic surface with dual mechanical link, dual power source and quadruplex control, similarly to a fly-by-wire hydraulic flight control. The paper first addresses the critical design issues associated with the electromechanical actuation of flight control surfaces, briefly reviews alternative solutions proposed for jam-tolerant electromechanical actuators, then outlines configuration, characteristics and performance of the mechatronic actuation system, and presents a summary of its behaviour under normal, degraded, fault developing and failure conditions.