Development and implementation of ℒ₁ gimbal tracking loop onboard of small UAV

This work extends the earlier results of authors on passive vision-based tracking and motion estimation of a non-cooperating ground vehicle. The follower small unmanned air vehicle (UAV) is equipped with a single gimbaled pan/tilt camera and a high bandwidth wireless link for video and command transmitting. The objective is to control the UAV turn rate and gimbaled camera cooperatively to maintain a horizontal circular orbit about the target with a predefined radius, and to keep the target image in the center of the image frame, concurrently providing real-time estimation of the target's position, speed and heading. In this paper, a new ℒ₁ adaptive controller is designed for the gimbal pan control, which provides guaranteed transient performance in the presence of disturbances and model uncertainty. The target velocity estimation problem is formulated such that the recently developed ℒ₁ fast adaptive estimator can be applied. We give a rigorous proof of asymptotic stability for the guidance law for the static target case, and provide a reformulation of the control objective for the moving target case so that the existing controller can be applied naturally. The impact of target loss events on the control and estimation algorithms is also analyzed.