Theses and Dissertations from UMD
Permanent URI for this communityhttp://hdl.handle.net/1903/2
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Motion Planning and Controls with Safety and Temporal Constraints(2016) Zhou, Yuchen; Baras, John S; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Motion planning, or trajectory planning, commonly refers to a process of converting high-level task specifications into low-level control commands that can be executed on the system of interest. For different applications, the system will be different. It can be an autonomous vehicle, an Unmanned Aerial Vehicle(UAV), a humanoid robot, or an industrial robotic arm. As human machine interaction is essential in many of these systems, safety is fundamental and crucial. Many of the applications also involve performing a task in an optimal manner within a given time constraint. Therefore, in this thesis, we focus on two aspects of the motion planning problem. One is the verification and synthesis of the safe controls for autonomous ground and air vehicles in collision avoidance scenarios. The other part focuses on the high-level planning for the autonomous vehicles with the timed temporal constraints. In the first aspect of our work, we first propose a verification method to prove the safety and robustness of a path planner and the path following controls based on reachable sets. We demonstrate the method on quadrotor and automobile applications. Secondly, we propose a reachable set based collision avoidance algorithm for UAVs. Instead of the traditional approaches of collision avoidance between trajectories, we propose a collision avoidance scheme based on reachable sets and tubes. We then formulate the problem as a convex optimization problem seeking control set design for the aircraft to avoid collision. We apply our approach to collision avoidance scenarios of quadrotors and fixed-wing aircraft. In the second aspect of our work, we address the high level planning problems with timed temporal logic constraints. Firstly, we present an optimization based method for path planning of a mobile robot subject to timed temporal constraints, in a dynamic environment. Temporal logic (TL) can address very complex task specifications such as safety, coverage, motion sequencing etc. We use metric temporal logic (MTL) to encode the task specifications with timing constraints. We then translate the MTL formulae into mixed integer linear constraints and solve the associated optimization problem using a mixed integer linear program solver. We have applied our approach on several case studies in complex dynamical environments subjected to timed temporal specifications. Secondly, we also present a timed automaton based method for planning under the given timed temporal logic specifications. We use metric interval temporal logic (MITL), a member of the MTL family, to represent the task specification, and provide a constructive way to generate a timed automaton and methods to look for accepting runs on the automaton to find an optimal motion (or path) sequence for the robot to complete the task.Item Towards a Unified Theory of Timed Automata(2014) Fontana, Peter Christopher; Cleaveland, Rance; Computer Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Timed automata are finite-state machines augmented with special clock variables that reflect the advancement of time. Able to both capture real-time behavior and be verified algorithmically (model-checked), timed automata are used to model real-time systems. These observations have led to the development of several timed-automata verification tools that have been successfully applied to the analysis of a number of different systems; however, the practical utility of timed automata is undermined by the theories underlying different tools differing in subtle but important ways. Since algorithmic results that hold for the variant used by one tool may not apply to another variant, this complicates the application of different tools to different models. The thesis of this dissertation is this: the theory of timed automata can be unified, and a practical unified approach to timed-automata model checking can be built around the paradigm of proof search. First, this dissertation establishes the mutual expressivity of timed automata variants, thereby providing precise characterizations of when theoretical results of one variant apply to other variants. Second, it proves powerful expressive properties about different logics for timed behavior, and as a result, enlarges the set of verifiable properties. Third, it discusses an implementation of a verification tool for an expressive fixpoint-based logic, demonstrating an application of this newly developed theory. The tool is based on a proof-search paradigm; verifying timed automata involves constructing proofs using proof rules that enable verification problems to be translated into subproblems that must be solved. The tool's performance is optimized by using derived proof rules, thereby providing a theoretically sound basis for faster model checking. Last, this dissertation utilizes the proofs generated during verification to gain additional information about the vacuous satisfaction of certain formulae: whether the automaton satisfied a formula by never satisfying certain premises of that specification. This extra information is often obtained without significantly decreasing the verifier's performance.