  For guiding the UAV swarm to pass through narrow openings, a trapezoid
virtual tube is designed in our previous work. In this paper, we generalize its
application range to the condition that there exist obstacles inside the
trapezoid virtual tube and UAVs have strict speed constraints. First, a
distributed vector field controller is proposed for the trapezoid virtual tube
with no obstacle inside. The relationship between the trapezoid virtual tube
and the speed constraints is also presented. Then, a switching logic for the
obstacle avoidance is put forward. The key point is to divide the trapezoid
virtual tube containing obstacles into several sub trapezoid virtual tubes with
no obstacle inside. Formal analyses and proofs are made to show that all UAVs
are able to pass through the trapezoid virtual tube safely. Besides, the
effectiveness of the proposed method is validated by numerical simulations and
real experiments.
