Toward Visibility Guaranteed Visual Servoing Control of Quadrotor UAVs

This paper studies the visibility problem in the visual servoing control of quadrotor unmanned aerial vehicles (UAVs). Visual servoing is a useful technique for the inspection, positioning, landing, and tracking of quadrotor UAVs. However, one prerequisite in previous research works is that the visual target stays inside the field of view of the camera for all time. While lose sight of the visual target will result in fatal failure of the task, how to guarantee this prerequisite is often overlooked. In this paper, we aim to achieve reliable visual servoing by deriving a provable solution to guarantee visibility in quadrotor visual serving control. The main idea is to ensure the forward invariance of a set using control barrier functions. The set is constructed as the visible set, which specifies the upper bound of the distance between the center of the image plane and the coordinates of visual features in the image plane. Then, the visibility constraint is developed based on control barrier function. The original control inputs are minimally modified to satisfy the visibility constraint, thus preserving visibility. Finally, some simulations and experimental results are presented to validate this method.