Driving in urban environments often presents difficult situations that require expert maneuvering of a vehicle. These situations become even more challenging when considering large vehicles, such as buses. We present a path planning framework that addresses the demanding driving task of buses in urban areas. The approach is formulated as an optimization problem using the road-aligned vehicle model. The road-aligned frame introduces a distortion on the vehicle body and obstacles, motivating the development of novel approximations that capture this distortion. These approximations allow for the formulation of safe and nonconservative collision avoidance constraints. Unlike other path planning approaches, our method exploits curbs and other sweepable regions, which a bus must often sweep over in order to manage certain maneuvers. Furthermore, it takes full advantage of the particular characteristics of buses, namely the overhangs, an elevated part of the vehicle chassis, that can sweep over curbs. Simulations are presented, showing the applicability and benefits of the proposed method.

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In this paper, a lateral controller is proposed for an over-actuated vehicle. The controller is formulated as a linear time-varying model predictive controller. The aim of the controller is to track a desired path smoothly, by making use of the vehicle crabbing capability (sideways movement) and minimizing the magnitude of curvature used. To do this, not only the error to the path is minimized, but also the error to the desired orientation and the control signals requests. The controller uses an extended kinematic model that takes into consideration the vehicle crabbing capability and is able to track not only kinematically feasible paths, but also plan and track over non-feasible discontinuous paths. Ackermann steering geometry is used to transform the control requests, curvature, and crabbing angle, to wheel angles. Finally, the controller performance is evaluated first by simulation and, after, by means of experimental tests on an over-actuated autonomous research vehicle.

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Resumo-As redes SDN (Software-defined Networking) vieram introduzir um novo paradigma de controlo nas infraestruturas das redes de comunicação, tendo pois um grande impacto não só na operação da rede em si, mas também em todo o desenvolvimento realizado em torno das mesmas (e.g. serviços de rede, serviços distribuídos, aplicações Internet, etc.). Assim, e por forma a auxiliar os investigadores e profissionais destas áreas, este artigo apresenta um estudo comparativo entre vários controladores SDN existentes no mercado. Numa primeira fase é feita uma análise mais alargada sobre diversos controladores, destacando-se as suas caraterísticas gerais e salientando as áreas onde foram desenvolvidos alguns trabalhos científicos usando cada um dos controladores. Numa segunda fase, é feita uma seleção de alguns controladores, sendo implementados alguns microprojectos ilustrativos, o que permitiu efetuar um estudo comparativo no que que se refere à curva de aprendizagem e algumas das principais APIs suportadas pelos controladores.

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