  Today, physical Human-Robot Interaction (pHRI) is a very popular topic in the
field of ground manipulation. At the same time, Aerial Physical Interaction
(APhI) is also developing very fast. Nevertheless, pHRI with aerial vehicles
has not been addressed so far. In this work, we present the study of one of the
first systems in which a human is physically connected to an aerial vehicle by
a cable. We want the robot to be able to pull the human toward a desired
position (or along a path) only using forces as an indirect
communication-channel. We propose an admittance-based approach that makes pHRI
safe. A controller, inspired by the literature on flexible manipulators,
computes the desired interaction forces that properly guide the human. The
stability of the system is formally proved with a Lyapunov-based argument. The
system is also shown to be passive, and thus robust to non-idealities like
additional human forces, time-varying inputs, and other external disturbances.
We also design a maneuver regulation policy to simplify the path following
problem. The global method has been experimentally validated on a group of four
subjects, showing a reliable and safe pHRI.
