Engineering Notes Path Planning and State Estimation for Unmanned Aerial Vehicles in Hostile Environments
Ran Dai, John E. Cochran · 2010
NMANNED aerial vehicles (UAVs) are now widely used in antiterrorism activities and intelligence gathering to enhance mission performance and maximize safety. The susceptibility of these UAVs in hostile environments raises requirements for flight path planning. Path planning strategies in hostile environments are normally composed of two phases [1,2]. The first phase is a Voronoi graph search, which will generate polygonal graphs and will optimize a safety performance index. The second is to use the virtual forces emanated from the virtual field of each surveillance radar site to refine the generated Voronoi graphs. These virtual forces provide information that can be used to reduce the vertices of the Voronoi polygonal and greatly improve the UAV performance. But the curvature continuity of the refined graphs, which plays an important role in the stability of the UAVs’ turning maneuvers, often does not meet the requirements for a continuously flyable path. ManykindsofcurveshavebeenstudiedanddesignedforUAVsto accomplish their mission [3–5]. Dubins curves, first applied in robotics path planning, are curves along which the UAV can move forward. This kind of circle–line–circle curve has a jump discontinuity in curvature at the connection points between the circle and thelinethatwillcausearobottostopattheseconnectionpointswhen traveling through the whole path. Other curves, such as the Reeds– Shepp curves [6,7], also have curvature discontinuities at their joint points. An alternative choice, the composite clothoid–line–clothoid curves, can be well designed with curvature being zero at the joint points to eliminate the discontinuities. This allows one to generate a continuous-curvature path by using different kinds of simply shaped curves, although, under most circumstances, we are expecting more flexibility in the curve shape that will allow more space for change. Shanmugavel et al. [3–5]. proposed quintic Pythagorean hodograph (PH) curves for a flyable path, with ten parameters representing each curve. The PH curves are flexible in design and their curvatures are expressedincontinuouspolynomials.Theparametercalculationofa PH curve is an iterative process in order to satisfy different constraints. Such kinds of curves can be further simplified with fewer parameters and a more efficient optimization algorithm. All the methods discussed leave room for improvement in the area of continuous-curvature path planning.