CFR Seminar: Integrated Planning and Control for Convex-bodied

Center for the Foundations of Robotics Seminar, May 31, 2006

Title:Integrated Planning and Control for Convex-bodied Nonholonomic Systems Using Local Feedback Control Policies

David C. Conner

Time and Place: 5:00pm NSH 1507

Abstract:
We present a technique for controlling a wheeled mobile robot as it moves ina cluttered environment. The method defines a hybrid control policy that simultaneously addresses the navigation and control problem for aconvex-bodied wheeled mobile robot navigating amongst obstacles. Thetechnique uses parameterized continuous local feedback control policies thatensure safe operation over local regions of the free configuration space;each local policy is designed to respect nonholonomic constraints, bounds onvelocities (inputs), and obstacles in the environment. The hybrid controlpolicy makes use of a collection of these local control policies in concertwith discrete planning tools. This approach allows the system to plan, andre-plan in the face of changing conditions, while preserving the safety andconvergence guarantees of the underlying control policies.The first half of the presentation describes the development of the localcontrol policies for constrained systems. First, we define policyrequirements that all local control policies must satisfy. Next, genericpolicies that meet the policy requirements are developed. These policiesoffer guaranteed performance and are amenable to composition within thehybrid control framework.The second half of the presentation deals with discrete planning within thespace of deployed control policies. The continuous closed-loop dynamicsinduced by the local policies may be represented as a graph of discretetransitions. Two methods for planning on this graph will be discussed.Traditional AI planning (A* and D*) can order the graph to generate aswitching strategy that solves a single navigation problem over the union ofpolicy domains. Experimental results using this first technique will beshown. The second planning strategy uses model checking techniques tospecify sequences of policies that address higher level planning problemswith temporal specifications. This second approach is validated insimulation. The presentation will give an overview of these two approaches,and discuss the relative strengths and weaknesses of the approaches. Thepresentation concludes with suggestions for possible lines of research thatcombine the strengths of the two approaches, thereby making it feasible todo robust high-level behavioral planning for the systems subject to complexinteracting constraints.