Formation Control of Nonholonomic Multi-Agent Systems

This dissertation is concerned with the formation control problem of multiple agents modeled as nonholonomic wheeled mobile robots. Both kinematic and dynamic robot models are considered. Solutions are presented for a class of formation problems that include formation, maneuvering, and flocking. Graph theory and nonlinear systems theory are the key tools used in the design and stability analysis of the proposed control schemes. Simulation and/or experimental results are presented to illustrate the performance of the controllers. In the first part, we present a leader-follower type solution to the formation maneuvering problem. The solution is based on the graph that models the coordination among the robots being a spanning tree. Our control law incorporates two types of position errors: individual tracking errors and coordination errors for leader-follower pairs in the spanning tree. The control ensures that the robots globally acquire a given planar formation while the formation as a whole globally tracks a desired trajectory, both with uniformly ultimately bounded errors. The control law is first designed at the kinematic level and then extended to the dynamic level. In the latter, we consider that parametric uncertainty exists in the equations of motion. These uncertainties are accounted for by employing an adaptive control scheme. In the second part, we design a distance-based control scheme for the flocking of the nonholonomic agents under the assumption that the desired flocking velocity is known to all agents. The control law is designed at the kinematic level and is based on the rigidity properties of the graph modeling the sensing/control interactions among the robots. A simple input transformation is used to facilitate the control design by converting the nonholonomic model into the single-integrator equation. The resulting control ensures exponential convergence to the desired formation while the formation maneuvers according to a desired, time-varying translational velocity. In the third part, we extend the previous flocking control framework to the case where only a subset of the agents know the desired flocking velocity. The resulting controllers include distributed observers to estimate the unknown quantities. The theory of interconnected systems is used to analyze the stability of the observer-controller system

Modernizing irrigation operations: Spatially differentiated resource allocations.

Water resource management / Irrigation canals / Property rights / Privatization / Social organization / Social participation / Leadership / Land ownership / Farmers' associations / Water users' associations / Equity / Farmer-agency interactions / Pakistan

Autonomous Swarm Navigation

Robotic swarm systems attract increasing attention in a wide variety of applications, where a multitude of self-organized robotic entities collectively accomplish sensing or exploration tasks. Compared to a single robot, a swarm system offers advantages in terms of exploration speed, robustness against single point of failures, and collective observations of spatio-temporal processes. Autonomous swarm navigation, including swarm self-localization, the localization of external sources, and swarm control, is essential for the success of an autonomous swarm application. However, as a newly emerging technology, a thorough study of autonomous swarm navigation is still missing. In this thesis, we systematically study swarm navigation systems, particularly emphasizing on their collective performance. The general theory of swarm navigation as well as an in-depth study on a specific swarm navigation system proposed for future Mars exploration missions are covered. Concerning swarm localization, a decentralized algorithm is proposed, which achieves a near-optimal performance with low complexity for a dense swarm network. Regarding swarm control, a position-aware swarm control concept is proposed. The swarm is aware of not only the position estimates and the estimation uncertainties of itself and the sources, but also the potential motions to enrich position information. As a result, the swarm actively adapts its formation to improve localization performance, without losing track of other objectives, such as goal approaching and collision avoidance. The autonomous swarm navigation concept described in this thesis is verified for a specific Mars swarm exploration system. More importantly, this concept is generally adaptable to an extensive range of swarm applications

Bearing Rigidity Theory: characterization and control of mixed formations and localization

The bearing rigidity theory is applied to mixed formations composed by agents having heterogeneous domains. Necessary and sufficient conditions are provided for the characterization of infinitesimally bearing rigid formations. The stabilization problem for such formations is addressed and a distributed solution proposed and validated through simulations. A location recovery algorithm for fully-actuated formations embedded in SE(3) is presented along with analytical proofs.ope

Utopian Reconfiguration of the Nature/Culture Dualism in Ursula Le Guin’s Always Coming Home

This thesis examines the intersection of utopia and ecology in Ursula Le Guin’s science fiction novel Always Coming Home (1985). As such, the thesis approaches the text from the theoretical frameworks of ecocriticism and utopian studies. By examining the text from these points of view, the thesis presents Le Guin’s novel as a particularly ecological utopian text. Thus, the thesis emphasizes the ways in which the novel’s ecological depictions and worldview influence its utopian speculation while also contributing to the novel’s critical approach to utopia. At the center of the analysis lies an ecocritical examination of the novel’s portrayal of the relationship between its utopian society and its non-human environment. These depictions are examined particularly in terms of their reconfiguration of the anthropocentric, dualistic view of nature and culture. As a result of this reconfiguration, the novel’s ecological worldview emerges as one that emphasizes the interconnectedness and interdependence of the human and the non-human. This ecological worldview is argued to contribute significantly to the novel’s utopian rhetoric. The thesis posits that the novel’s ecological worldview shapes its approach to utopia in two major ways. First, the novel’s ecological worldview is examined as the central feature of the novel’s utopia, and as the foundation for the text’s utopian speculation. Second, the novel’s ecological worldview is presented as limiting the novel’s utopian rhetoric by emphasizing the role of material limits. As a result, the thesis argues that the novel is a specifically ecological utopian text, which situates itself in opposition with present-day ideology primarily through its ecological worldview

A Low-Cost Experimental Testbed for Multi-Agent System Coordination Control

A multi-agent system can be defined as a coordinated network of mobile, physical agents that execute complex tasks beyond their individual capabilities. Observations of biological multi-agent systems in nature reveal that these ``super-organisms” accomplish large scale tasks by leveraging the inherent advantages of a coordinated group. With this in mind, such systems have the potential to positively impact a wide variety of engineering applications (e.g. surveillance, self-driving cars, and mobile sensor networks). The current state of research in the area of multi-agent systems is quickly evolving from the theoretical development of coordination control algorithms and their computer simulations to experimental validations on proof-of-concept testbeds using small-scale mobile robotic platforms. An in-house testbed would allow for rapid prototyping and validation of control algorithms, and potentially lead to new research directions spawned by experimentally-observed issues. To this end, a custom experimental testbed, TIGER Square, has been designed, developed, built, and tested at Louisiana State University. In this work, the completed design and test results for a centralized testbed is presented. That is, the individual robots follow an overarching control entity and are reliant on a global structure, such as a central processing computer. As part of the validation process, a series of formation control experiments were executed to assess the performance of the testbed. In order to eliminate single-point failures, a multi-agent system must be fully decentralized or distributed. This means that the responsibilities of processing, localization, and communication are distributed to each agent. Therefore, this work concludes with the introduction of a prototype localization module that will be integrated into the existing centralized testbed. This initial step allows for the future decentralization of TIGER Square and opens the path to achieve a fully capable multi-agent system testbed