Michael, Nathan
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Publication Bearing-Only Control Laws For Balanced Circular(2008-06-28) Moshtagh, Nima; Michael, Nathan; Jadbabaie, Ali; Daniilidis, KostasFor a group of constant-speed ground robots, a simple control law is designed to stabilize the motion of the group into a balanced circular formation using a consensus approach. It is shown that the measurements of the bearing angles between the robots are sufficient for reaching a balanced circular formation. We consider two different scenarios that the connectivity graph of the system is either a complete graph or a ring. Collision avoidance capabilities are added to the team members and the effectiveness of the control laws are demonstrated on a group of mobile robots.Publication Experimental Testbed for Large Multirobot Teams(2008-03-01) Michael, Nathan; Kumar, Vijay; Fick, JonathanExperimental validation is particularly important in multirobot systems research. The differences between models and real-world conditions that may not be apparent in single robot experiments are amplified because of the large number of robots, interactions between robots, and the effects of asynchronous and distributed control, sensing, and actuation. Over the last two years, we have developed an experimental testbed to support research in multirobot systems with the goal ofmaking it easy for users tomodel, design, benchmark, and validate algorithms. In this article, we describe our approach to the design of a large-scale multirobot system for the experimental verification and validation of a variety of distributed robotic applications in an indoor environment. Our research focusses on decentralized multirobot algorithms that rely on an integrated approach to mobility, perception, and communication, with such applications as environmental monitoring, surveillance and reconnaissance for security and defense, and support for first responders in search and rescue operations [1]. In all of these applications, robots must rely on local sensing, computation, and control and exploit the availability of communication links with other robots whenever possible. To enable scaling up to large numbers, computations must be decentralized, and the systemmust be robust to changes in the numbers of robots and to the dynamic addition and deletion of units. There is also the need to provide some degree of centralization with an interface to one or more human operators for programming, tasking, andmonitoring of the system. These research applications serve as the motivation for our experimental testbed. While there is a rich body of work to build on, there is currently no inexpensive multirobot system that allows users to move easily from conceptual ideas to algorithms and then to experimentation. We begin by motivating design considerations for the testbed in the context of our research and existing multirobot control and experimental architectures.We next arrive at a set of design requirements for the system based on the driving applications as well as practical considerations. Most importantly, we are driven by the pragmatic considerations of ease of use, robustness, flexibility, and scalability to enable the easy inclusion of more robots and sensors with minimal changes to the existing infrastructure. We also review some of the applicable hardware and software options currently available. The experimental testbed is discussed in detail with overviews of the robots, software, and the supporting infrastructure required for multirobot experiments. Since simulation is of great relevance in the experimental process and the testbed design, we discuss its role and detail the transition from simulation to reality. Finally, we present several multirobot experiments for formation control and cooperative manipulation, which demonstrate the capabilities of the system for verification purposes and elucidate the experiment design process with our testbed.Publication Maintaining Connectivity in Mobile Robot Networks(2009-03-28) Michael, Nathan; Zavlanos, Michael M; Kumar, Vijay; Pappas, George JWhile there has been significant progress in recent years in the study of estimation and control of dynamic network graphs, limited attention has been paid to the experimental validation and verification of such algorithms on distributed teams of robots. In this work we conduct an experimental study of a non-trivial distributed connectivity control algorithm on a team of seven nonholonomic robots as well as in simulation. The implementation of the algorithm is completely decentralized and asynchronous, assuming that each robot only has access to its pose and knowledge of the total number of robots. All other necessary information is determined via message passing with neighboring robots. We show that such algorithms, requiring complex inter-agent communication and coordination, are feasible as well as highly successful in enabling a network of robots to adapt to disturbances while preserving connectivity.Publication Controlling Swarms of Robots Using Interpolated Implicit Functions(2005-04-01) Chaimowicz, Luiz; Michael, Nathan D; Kumar, VijayWe address the synthesis of controllers for large groups of robots and sensors, tackling the specific problem of controlling a swarm of robots to generate patterns specified by implicit functions of the form s(x, y) = 0. We derive decentralized controllers that allow the robots to converge to a given curve S and spread along this curve. We consider implicit functions that are weighted sums of radial basis functions created by interpolating from a set of constraint points, which give us a high degree of control over the desired 2D curves. We describe the generation of simple plans for swarms of robots using these functions and illustrate.Publication Vision-Based, Distributed Control Laws for Motion Coordination of Nonholonomic Robots(2009-08-01) Moshtagh, Nima; Michael, Nathan D; Jadbabaie, Ali; Daniilidis, KostasIn this paper, we study the problem of distributed motion coordination among a group of nonholonomic ground robots. We develop vision-based control laws for parallel and balanced circular formations using a consensus approach. The proposed control laws are distributed in the sense that they require information only from neighboring robots. Furthermore, the control laws are coordinate-free and do not rely on measurement or communication of heading information among neighbors but instead require measurements of bearing, optical flow, and time to collision, all of which can be measured using visual sensors. Collision-avoidance capabilities are added to the team members, and the effectiveness of the control laws are demonstrated on a group of mobile robots.