A Leader-Follower Control System for a Package-Delivery Drone

This paper proposes a feasible strategy to design a control system to guide drones in delivering packages autonomously. It is shown that the leader-follower control paradigm fulfills all the requirements for the delivery mission, thus being a good strategy for designing the control system. The logic behind the problem is that the quadrotor takes off from a ground vehicle (a delivery truck, for instance) or even from a warehouse, goes to the delivery point, returns to the ground vehicle or warehouse, and lands on it. In each of those steps, the drone should compose a leader-follower formation, meaning it should have a leader and a relative position to such a leader in each step. The advantage of the leader-follower control paradigm is that just one controller is necessary for the delivery drone, the follower. It is required to define the leader in each task step, which is perfectly possible using such a control paradigm, as the paper shows. Such a logic relies on the drone disregarding the ground vehicle as its leader when flying toward the delivery point and resuming its leadership after delivering the parcel. In other words, the delivery drone will follow two leaders at two different moments: the delivery point in the delivery step and the ground vehicle when returning to it. The delivery drone should also avoid obstacles, such as buildings and trees, to which the well-known potential field theory is adopted, which can be easily inserted into the leader-follower control system. Results of an experiment on a lab scale are presented and discussed, which validates the control system designed under the strategy discussed here. Consequently, the correctness of the hypothesis that the leader-follower control paradigm is a feasible solution to control a delivery drone in accomplishing package delivery is confirmed. This is the main contribution of the study. Moreover, a possible generalization of the proposed control system for a set of delivery drones is outlined.