@phdthesis{Saska2009,
  author    = {Saska, Martin},
  title     = {Trajectory planning and optimal control for formations of autonomous robots},
  isbn      = {978-3-923959-56-3},
  doi       = {10.25972/OPUS-4622},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-53175},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2009},
  abstract  = {In this thesis, we present novel approaches for formation driving of nonholonomic robots and optimal trajectory planning to reach a target region. The methods consider a static known map of the environment as well as unknown and dynamic obstacles detected by sensors of the formation. The algorithms are based on leader following techniques, where the formation of car-like robots is maintained in a shape determined by curvilinear coordinates. Beyond this, the general methods of formation driving are specialized and extended for an application of airport snow shoveling. Detailed descriptions of the algorithms complemented by relevant stability and convergence studies will be provided in the following chapters. Furthermore, discussions of the applicability will be verified by various simulations in existing robotic environments and also by a hardware experiment.},
  subject      = {Autonomer Roboter},
  language  = {en}
}
@phdthesis{Hess2009,
  author    = {Hess, Martin},
  title     = {Motion coordination and control in systems of nonholonomic autonomous vehicles},
  isbn      = {978-3-923959-55-6},
  doi       = {10.25972/OPUS-3794},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-46442},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2009},
  abstract  = {This work focuses on coordination methods and the control of motion in groups of nonholonomic wheeled mobile robots, in particular of the car-like type. These kind of vehicles are particularly restricted in their mobility. In the main part of this work the two problems of formation motion coordination and of rendezvous in distributed multi-vehicle systems are considered. We introduce several enhancements to an existing motion planning approach for formations of nonholonomic mobile robots. Compared to the original method, the extended approach is able to handle time-varying reference speeds as well as adjustments of the formation's shape during reference trajectory segments with continuously differentiable curvature. Additionally, undesired discontinuities in the speed and steering profiles of the vehicles are avoided. Further, the scenario of snow shoveling on an airfield by utilizing multiple formations of autonomous snowplows is discussed. We propose solutions to the subproblems of motion planning for the formations and tracking control for the individual vehicles. While all situations that might occur have been tested in a simulation environment, we also verified the developed tracking controller in real robot hardware experiments. The task of the rendezvous problem in groups of car-like robots is to drive all vehicles to a common position by means of decentralized control laws. Typically there exists no direct interaction link between all of the vehicles. In this work we present decentralized rendezvous control laws for vehicles with free and with bounded steering. The convergence properties of the approaches are analyzed by utilizing Lyapunov based techniques. Furthermore, they are evaluated within various simulation experiments, while the bounded steering case is also verified within laboratory hardware experiments. Finally we introduce a modification to the bounded steering system that increases the convergence speed at the expense of a higher traveled distance of the vehicles.},
  subject      = {Robotik},
  language  = {en}
}