Cooperative Manipulation of an Unknown Object via Omnidirectional Unmanned Aerial Vehicles

This paper addresses the problem of cooperative manipulation and transportation of large and/or heavy unknown objects via a team of aerial robots. In particular, the chosen aerial platform is an omnidirectional quadrotor, which, by exploiting two additional actuators, has the capability to produce an omnidirectional total thrust by changing the orientation of the plane of the rotors. Since it is assumed that the object geometry and dynamic parameters are not known, the devised strategy includes a first stage in which the robots cooperatively estimate the object parameters and a second stage in which such parameters are adopted in an impedance control, aimed at limiting both the contact wrenches, due to the object/environment interaction, and the internal wrenches, due to the robot/object interaction. More in detail, two admittance filters are designed to determine the reference trajectory for the object (external impedance) and for the aerial vehicles (internal impedance). Finally, a simulation case study is developed to provide further insights on the proposed approach.