Hybrid Force/Position Control of Aerial Manipulators in Contact Operation

For the contact operation problem of the aerial manipulator system during moving, a hybrid force and position control framework is applied to controlling the system to contact with the external environment continuously and reliably with a constant force, and implement the desired trajectory tracking during the contact process. Firstly, the workspace is divided into two sub-spaces, i.e. the constrained space and the free-flight space, where the contact force control and position control are adopted respectively. For the force control problem, the closed-loop UAV (unmanned aerial vehicle) system is proven to behave as a spring-mass-damper-like system, and an inverse-dynamics-based controller is designed to implement the contact force control in the constrained sub-space. The motion control in free-flight space depends on trajectory planning and position controllers. Finally, a 1-DOF (degree-of-freedom) aerial manipulator system based on a hex-rotor UAV is developed, and the system is commanded to track a oblique line trajectory in flight mode while contacting with wall surface. The results indicate that the proposed method contributes to maintaining steady motion, and controlling the desired contact force.