  In this paper, an autonomous aerial manipulation task of pulling a plug out
of an electric socket is conducted, where maintaining the stability and
robustness is challenging due to sudden disappearance of a large interaction
force. The abrupt change in the dynamical model before and after the separation
of the plug can cause destabilization or mission failure. To accomplish aerial
plug-pulling, we employ the concept of hybrid automata to divide the task into
three operative modes, i.e, wire-pulling, stabilizing, and free-flight. Also, a
strategy for trajectory generation and a design of disturbance-observer-based
controllers for each operative mode are presented. Furthermore, the theory of
hybrid automata is used to prove the stability and robustness during the mode
transition. We validate the proposed trajectory generation and control method
by an actual wire-pulling experiment with a multirotor-based aerial
manipulator.
