Improving Controllers for Formations and Deconfliction among Non-holonomic Vehicles

TitleImproving Controllers for Formations and Deconfliction among Non-holonomic Vehicles
Publication TypeThesis
Year of Publication2011
AuthorsKrontiris, A
Academic DepartmentComputer Science and Engineering at the University of Nevada, Reno
DegreeMS Thesis.
Date Published04/2011
UniversityUniversity of Nevada, Reno
Thesis TypeMS

The first contribution of this work corresponds to a computationally efficient geometric method for simulating formations of systems with non-holonomic motion constraints. The proposed geometric reasoning takes place in curvilinear coordinates, which are defined by the curvature of the leader's reference trajectory, in order to directly satisfy the constraints, instead of the typical rectilinear coordinates. The approach directly provides the feasible controls that each individual robot has to execute for the team to maintain the formation based on the controls of a reference agent, either a real leader or a virtual one. The method’s generality lies on the ability to define dynamic formations so as to smoothly switch between different configurations, where the robots can change both of their relative curvilinear coordinates as they move. It is also possible to acquire a desired formation given an initial random configuration. Simulation results are provided that illustrate the feasibility of the approach. The second contribution corresponds to a motion coordination algorithm, where multiple non-holonomic vehicles are steered in a decentralized manner between assigned start and goal configurations so as to avoid collisions. The approach builds on top of a hybrid control law, known as Generalized Roundabout Policy, which ensures safety, without any communication between the robots. The focus of this work is on improving the performance and liveness features for such problems. Towards this objective, a new hybrid policy that updates the desired direction for each vehicle based on a dynamic priority scheme is proposed. Minimal communication between the various vehicles is employed for the dynamic priority scheme, where vehicles occasionally exchange information with their neighbors. The proposed method can solve decentralized motion coordination problems both faster and with less assumptions, that the Generalized Roundabout Policy, as suggested by simulations presented in this thesis.