Discussion on: “Control and navigation in manoeuvres of formations of unmanned mobile vehicles”

Abstract

Control of a multi-agent system has recently triggered a lot of research interest due to the inherently present problem complexity as well as various interesting applications that have become attractive in last few years, in which such an system can be utilized. The coverage problem, persistent monitoring, sensor networks, surveillance, formation control, highway and transportation systems are some of the possible application areas. Some relevant work can be found in the reference lists presented in [1,2]. Formation control has been a focus of the paper and it can be interpreted as a problem in which a set of mobile vehicles follows a reference trajectory while keeping a priori defined formation shape. Such a problem arises in some military applications as well as in applications like the one mentioned in the paper related to the airport snow shoveling. There are currently three different strategies adopted to solve the formation control problem: leader– follower approach, behavioral approach and virtual structure approach. In the paper, the leader–follower strategy is implemented based on a receding horizon control scheme (RHC). Some relevant work on the field of formation control can be found in the reference list presented in the paper. The main contributions of the paper are resulted by some inherent RHC framework features, providing a general approach which takes into account nonholonomic vehicles’ formation stabilization, a trajectory planning which guarantees task completion and a framework which handles dynamic changes in the environment. In addition, the RHC is enhanced by the possibility of the backward movement of the formations of unmanned mobile vehicles. The backward movement is accomplished by extending the leader– follower strategy with the idea of two virtual leaders which seems a reasonable way to solve this problem. Using an RHC scheme to control a formation of unmanned mobile vehicles allows for taking into account local measurements, which in turn makes the control capable of appropriately responding to dynamical changes in the environment during the mission of the mobile robots. The proposed RHC scheme includes mobility, environment and shape of the formation constraints to find suboptimal trajectories toward the target region. An additional term is also used in the objective function to ensure intervehicle collision avoidance. A capability of a backward movement of formations of unmanned mobile vehicles provides a wide range of possible applications in which the proposed control approach can be utilized. Such an additional feature makes the formations of unmanned mobile vehicles more flexible and capable for some complex applications such as the airport snow shoveling mentioned in the paper. However, the surveillance and the persistent monitoring coverage problem with a formation might be certainly enhanced by the backward movement feature. The proposed navigation framework extends the work [3] in that a detailed theoretical overview of the proposed method is covered jointly with some new experimental results. The paper additionally provides the analysis of the task completion, inherently implied by the convergence of the system into the desired target region. In the sequel, some different possible extensions of the