Regional target surveillance with cooperative robots using APFs

Target surveillance in a bounded environment has been a growing focus in the past few years, particularly with recent world events prompting the need for environmental monitoring using automated surveillance. Scenarios exist where the goal is to be able to track targets within a certain distance and yet maintain a proper distribution of the surveillance units to provide field coverage. Previous works in this area using mobile robots as the surveillance units have made assumptions of a global awareness capability provided by a central controller. Artificial Potential Fields (APFs) have been used in cooperative robots and swarm research for applications such as threat containment and related formation control without as much focus on the surveillance tasks. This thesis aims to extend the use of APFs to the concept of Regional Target Surveillance in a distributed algorithm among cooperative robots, with the utilization of Voronoi cells to aid in coverage control. This investigation proposes a system to utilize only the necessary number of robots with local awareness capability. Each of these robots integrates the use of a centroid force and a target force to provide a balanced coverage and target tracking performance. This is accomplished by implicitly defining three circular regions of responsibility for each robot, namely, the full sensing region, the target tracking region, and the centroid calculation region. The target tracking region is within the full sensing region and encompasses the centroid calculation region. The centroid calculation region is used to define the Voronoi cells and thus the centroid of the responsible field of each robot. By adjusting the relative size of the three regions, the system accomplishes implicit target handoff between robots, and, in turn, provides an overall balance between regional target tracking and environmental coverage for the surveillance goal. Matlab simulation results show that with a proper balance in the tradeoff between the tracking and coverage performance, the algorithm is scalable to larger field sizes with a similar robot density, while successfully accomplishing the surveillance tasks

Information Surfing for Radiation Building

We develop a control scheme for a group of mobile sensors to map radiation over a given planar polygonal region. The advantage of this methodology is that it provides quick situational awareness regarding radiation levels, which is being updated and refined in real- time as more measurements become available. The control algorithm is based on the concept of information surfing, where navigation is done by following information gradients, taking into account sensing performance and the dynamics of the observed proces

Decentralized Learning With Limited Communications for Multi-robot Coverage of Unknown Spatial Fields

This paper presents an algorithm for a team of mobile robots to simultaneously learn a spatial field over a domain and spatially distribute themselves to optimally cover it. Drawing from previous approaches that estimate the spatial field through a centralized Gaussian process, this work leverages the spatial structure of the coverage problem and presents a decentralized strategy where samples are aggregated locally by establishing communications through the boundaries of a Voronoi partition. We present an algorithm whereby each robot runs a local Gaussian process calculated from its own measurements and those provided by its Voronoi neighbors, which are incorporated into the individual robot's Gaussian process only if they provide sufficiently novel information. The performance of the algorithm is evaluated in simulation and compared with centralized approaches.Comment: Accepted IROS 202

A practical search with Voronoi distributed autonomous marine swarms

Submitted in partial fulfillment of the requirements for the degree of Master of Science in Mechanical Engineering at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2022.The search for underwater threats in littoral regions is a problem that has been researched for nearly a century. However, recent developments in autonomy and robotics have made this issue more complex. The advent of capable autonomous underwater vehicles presents a 21st century flare to this traditional problem. These vehicles can be smaller, quieter, and expendable. Therefore, new methods and tactics used to detect and track these vehicles are needed. The use of a swarm of marine robots can increase the likelihood of uncovering these threats. This thesis provides various Voronoi partition-based methods to autonomously control a swarm of identically capable autonomous surface vessels in a limited coverage and tracking problem. These methods increase the probability of interdiction of an adversary vehicle crossing a defined region. The results achieved from Monte Carlo simulations demonstrate how different protocols of swarm movement can improve detection probability as compared to a stationary swarm provided the detection capability does not change. The swarm control algorithms are employed on Clearpath Heron USVs to validate the autonomy algorithms

Range Limited Coverage Control using Air-Ground Multi-Robot Teams

In this paper, we investigate how heterogeneous multi-robot systems with different sensing capabilities can observe a domain with an apriori unknown density function. Common coverage control techniques are targeted towards homogeneous teams of robots and do not consider what happens when the sensing capabilities of the robots are vastly different. This work proposes an extension to Lloyd's algorithm that fuses coverage information from heterogeneous robots with differing sensing capabilities to effectively observe a domain. Namely, we study a bimodal team of robots consisting of aerial and ground agents. In our problem formulation we use aerial robots with coarse domain sensors to approximate the number of ground robots needed within their sensing region to effectively cover it. This information is relayed to ground robots, who perform an extension to the Lloyd's algorithm that balances a locally focused coverage controller with a globally focused distribution controller. The stability of the Lloyd's algorithm extension is proven and its performance is evaluated through simulation and experiments using the Robotarium, a remotely-accessible, multi-robot testbed.Comment: Published at 2021 IEEE International Conference on Robotics and Automation (ICRA