Robot assisted landing of VTOL UAVs on ships: A simulation case study of the touch-down phase

Robot assisted landing means to use a robot manipulator to capture a vertical take-off and landing unmanned aerial vehicle (VTOL UAV) in flight and tow it to a designated landing spot. This procedure enables the VTOL UAV to land on moving surfaces and under side wind conditions. In our previous work, we neglected ship motion, the influence of the UAV on the manipulator, and the torque limits of the robot, which is only valid for light UAVs. Therefore, in this paper, we present a multibody dynamics model of a moving base robot manipulator with a VTOL UAV attached at its end-effector via a ball joint. For the robot, a task space tracking controller with base motion compensation is derived and for the UAV, an active thrust vector control law. We evaluate the effect of heavy UAVs and of base motion compensation on the trajectory tracking performance in a simulation case study using five sets of realistic VTOL UAV model parameters as well as base movements provided by a ship motion simulation at three different sea states. The results clearly show that active thrust vector control is needed in order to comply with the robots joint torque limits.