Laszlo Techy

Minimum-Time Path Planning for Unmanned Aerial Vehicles in Steady Uniform Winds

This paper is concerned with time-optimal path planning for a constant-speed unmanned aerial vehicle flying at constant altitude in steady uniform winds. The unmanned aerial vehicle is modeled as a particle moving at a constant air-relative speed and with symmetric bounds on turn rate. It is known from the necessary conditions for optimality that extremal paths comprise only straight segments and maximum-rate turns. An essential observation is that maximum-rate turns correspond to trochoidal path segments, as observed from an Earth-fixed inertial frame. The path-planning problem therefore reduces to identifying the switching points at which straight and trochoidal path segments join to form a feasible path and choosing the true minimum-time solution from the resulting set of candidate extremals. The papers primary contribution is a simple analytical solution for a subset of candidate extremal paths: those for which an initial maximum-rate turn is followed by a straight segment and then a second maximum-rate turn in the same direction as the first. The solution is easy to compute and is suitable for real-time implementation onboard an unmanned aerial vehicle with limited computational power. The remaining candidate extremal paths may be found using a simple numerical root-finding routine. The paper also shows that, for some candidate extremal paths, no corresponding Dubins path exists in the (moving) air-relative frame.

Path planning for efficient UAV coordination in aerobiological sampling missions

This paper is concerned with the coordinated flight of two autonomous UAVs to be used for aerobiological sampling of biological threat agents above agricultural fields. The periodic sampling task involves two phases: a sampling interval and an initialization interval. During the sampling interval, both vehicles must employ their aerobiological sampling devices and follow a precise ground track in the presence of sustained winds. During the initialization interval, the vehicles move to their respective initial states to begin the next sampling interval. To maximize the volume of air sampled by the UAVs during an individual sampling mission, the initialization interval must be as short as possible. The paper provides a simple, geometric method for generating candidate time optimal paths in steady winds, based on Dubins¿ well-known results for minimum time paths of bounded curvature. The approach is used to generate paths for both UAVs, which must coordinate their motion along their respective paths in order to avoid collision. The described methods were tested during an aerobiological sampling experiment focusing on the plant pathogen Phytophthora infestans.

Long-baseline acoustic localization of the Seaglider underwater glider

This paper describes a long-baseline underwater acoustic localization system that was developed to provide three-dimensional position information for the Seaglider underwater vehicle. The accurate inertial position of the glider can be used to estimate performance characteristics and to validate novel motion control and path planning strategies in future experiments. The system consists of three acoustic transponders that are placed at known locations at the surface of the water. An extended Kalman filter with RTS smoothing was used to obtain filtered estimates of the states. The filtering methods have been tested both in simulations and in field experiments.

Planar path planning for flight vehicles in wind with turn rate and acceleration bounds

This paper is concerned with path planning for an autonomous flight vehicle operating in a steady, uniform flow-field. We model the vehicle as a particle that travels in the horizontal plane at a constant speed relative to the ambient flow. The vehicle may turn in either direction, subject to symmetric constraints on the turn rate and the turn acceleration. The contribution of the paper is a simple method for generating candidate minimum-time paths from a given initial point and heading to a given final point and heading.

Coordinated Perimeter Patrol with Minimum-Time Alert Response

This paper describes a decentralized feedback framework for coordinated base defense with multiple UAVs. Each UAV is modeled as a constant-speed particle moving in a plane, equipped with steering control and a downward-looking intruder sensor. The feedback framework enables a UAV team flying in a steady, uniform wind to (1) cooperatively patrol a convex perimeter and (2) optimally prosecute intruder alerts. The coordination of patrolling UAVs minimizes coverage gaps in space and time. Each intruder alert is prosecuted by a nearby UAV on a time-optimal path that minimizes response time. After passing over an alert site, the prosecuting UAV resumes the coordinated patrol. This algorithm provides continuous monitoring of a base perimeter and prompt response to intruder alerts with minimal human intervention.

Optimal navigation in planar time-varying flow: Zermelo's problem revisited

This paper is concerned with time-optimal navigation for flight vehicles in a planar, time-varying flow-field, where the objective is to find the fastest trajectory between initial and final points. The primary contribution of the paper is the observation that in a point-symmetric flow, such as inside vortices or regions of eddie-driven upwelling/downwelling, the rate of the steering angle has to be equal to one-half of the instantaneous vertical vorticity. Consequently, if the vorticity is zero, then the steering angle is constant. The result can be applied to find the time-optimal trajectories in practical control problems, by reducing the infinite-dimensional continuous problem to numerical optimization involving at most two unknown scalar parameters.

Unmanned Aerial Vehicle Coordination on Closed Convex Paths in Wind

I N THIS Note we consider the problem of motion coordination of an aerial robotic network in the presence of steady, uniform winds. We present application examples of multivehicle coordination and path planning methods. The control laws we employ are extensions of previous research results on particle coordination and minimum-time path planning in steady, uniform wind. In prior work most relevant to this Note, Lyapunov-based control laws are provided to drive a collective of vehicles to a symmetric pattern along a circular orbit [1], to coordinated patterns on convex curves [2], and to coordinated patterns in the presence of winds [3]. The development of minimum-time path planning algorithms is also relevant [4,5]. The vehicle coordination framework described here may serve as an intermediate layer between low-level vehicle control and highlevel mission planning. We assume that the control signal is the turn rate-of-change, which, in the case of a fixed-wing aircraft, may be controlled by regulating the bank angle.We also assume that the lowlevel controller (the autopilot) can execute the desired turn-rate commands. Similar vehicle models have been frequently used to design kinematic control laws to track targets with aerial vehicles [6– 9]. Coordinated steering laws were presented in [10], where it was shown that collective motion along parallel lines or around the same circle are the only relative equilibria if the particle steering laws depend only on relative positions and headings. Motivated by the need for coordination on curves of arbitrary shapes, Lyapunov-based control laws were presented in [11], in which relative arc lengths between particles were used for coordination, as opposed to relative phases. Leader–follower approaches have also been studied (see, for example, [12,13] and the references therein). The contributions of this Note are twofold: First, we extend an existing motion-coordination framework to the case in which the vehicles travel around strictly convex loops in the presence of a steady, uniform flowfield. Second, we present an approximation method that generates strictly convex curves from convex paths that may contain straight segments. The latter method is important to allow coordination on time-optimal paths, which frequently contain straight segments. This Note also includes simulation results focusing on two application examples: control-volume sampling and perimeter defense. In Sec. II we describe the motion-coordination algorithms. In Sec. III we present the curve-approximation method that enables coordinated control on approximately time-optimal paths. In Secs. IV and V we describe the application examples. Section VI summarizes this Note.

A maneuverable, pneumatic underwater glider

A coastal (100 meter depth) underwater glider has been developed to serve as a platform for testing advanced perception, planning, and control algorithms to improve glider efficiency and performance. The gliders buoyancy engine is pneumatically powered, and capable of generating large changes in buoyancy. Powerful and fast moving mass actuators allow the vehicle to achieve a large range of pitch attitudes and an unrestricted range of roll angles. The ability to complete a full 360 degree roll permits the use of asymmetric geometries like wing camber or dihedral and to assess their performance benefits. In this paper, the mechanical and electrical design of the glider is discussed in detail.

Examples of Augmentation of an Atmospheric Flight Mechanics Curriculum using UAVs

This paper provides an example of stability and control curriculum augmentation with an Unmanned Aerial Vehicle (UAV). Instead of providing a singular experience in one course, three laboratory modules are designed to be integrated during the sophomore, junior, and senior years. By providing providing curriculum augmentation in a vertical sense student exposure and educational impact is enhanced. Cooperative learning is used in a learner{centered approach to design a pedagogical base for the laboratory modules.

Optimal navigation in a planar time-varying point-symmetric flow-field

This paper is concerned with time-optimal navigation for flight vehicles in a planar, time-varying point-symmetric flow-field — such as inside vortices or regions of eddy-driven upwelling/downwelling—where the objective is to find the fastest trajectory between initial and final points. The primary contribution of the paper is the observation that for time-optimality the rate of the steering angle has to be equal to one-half of the instantaneous vertical vorticity. Consequently, if the vorticity is zero, then the steering angle has to be constant. The result can be applied to find the time-optimal trajectories in practical control problems, by reducing the infinite-dimensional continuous problem to numerical optimization involving at most two unknown scalar parameters.