Visual servoing of a VTOL vehicle using virtual states

An image-based visual servo (IBVS) control strategy is proposed for a class of under actuated systems. The class of systems considered includes dynamic models of vehicles capable of quasi-stationary flight. The paper extends earlier works that stabilises an aerial vehicle using only direct visual and inertial measurements, and in particular, without a direct measurement of linear velocity. The approach taken is to introduce an additional ´virtual´ state in the control design to compensate for the missing velocity measurement and then apply backstepping control design methodology. Local asymptotic stability of the system is proved and an estimate of the basin of attraction for the closed-loop system is provided. Simulation results are presented to illustrate the closed-loop performance.