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Title: Stable Segment Formation Control of Multi-Robot System
Authors: WAN JIE
Keywords: formation control, artificial potential, multi-robot system, nonsmooth analysis, stability,
Issue Date: 7-Jul-2011
Citation: WAN JIE (2011-07-07). Stable Segment Formation Control of Multi-Robot System. ScholarBank@NUS Repository.
Abstract: The aim of this dissertation is to investigate the formation control of multiple mobile robots based on the queue and artificial potential trench method. In general, this thesis addresses the following topics: (1) comparative analysis of two nonlinear feedback controls and study of an improved robust control for mobile robots; (2) real implementation of multi-robot system formation control; (3) extracting explicit control laws and analyzing the associated stability problems based on the framework of queue and artificial potential trench method; (4) zoning potentials for maintaining robot-to-robot distances; (5) stability analysis on attracting robots to the nearest points on the segment and collision avoidance methods; (6) input-to-state stability of formation control of multi-robot systems. A detailed analysis of the qualitative characteristics of two nonlinear feedback controls of mobile robots is presented. The robustness of a tracking control is investigated. Based on the research results, an improved control is proposed. In addition to robustness, the improved method produces faster response. Real implementation of formation control is conducted on a multi-robot system. The triangle and square pattern formations of MRKIT robots are successfully demonstrated. Based on the framework of queue and artificial potential trench for multi-robot formation, we aim to extract explicit multi-robot formation control laws and provide stability analysis for a group of robots assigned to the same segment. A refined definition of artificial potential trench, which allows the potential function to be nonsmooth, is defined and various ways to construct admissible potential trench functions have been proposed. Stability of formation control is investigated through a solid mathematical nonsmooth analysis. We investigate the stability of formation control for multi-robot systems operating as a coordinated chain. In this study, a group of robots are organized in leader-follower pairs with constraints of maximum and minimum separations imposed on a robot with respect to its leader and new stable controls are synthesized. The introduction of the concept of zoning scheme, together with the associated zoning potentials, enables a robot to maintain a certain separation from its leader while forming a formation. Computer simulation has been conducted to demonstrate the effectiveness of this approach. We investigate a generic formation control, which attracts a team of robots to the nearest points on the same segment while taking into account obstacle avoidance. A novel obstacle avoidance method, based on the new concept of apparent obstacles, is proposed to cope with concave obstacles and multiple moving obstacles. Comparison between apparent obstacle avoidance method and other alternative solutions is discussed. An elaborated algorithm dedicated to seeking the nearest point on a segment with the presence of obstacles is presented. Local minima are discussed and the corresponding simple solutions are provided. Theoretical analysis and computer simulation have beenperformed to show the effectiveness of this framework. The input-to-state stability of the formation control of multi-robot systems using artificial potential trench method and queue formation method is investigated. It is shown that the closed-loop system of each robot is input-to-state stable in relation to its leader?s initial formation error. Furthermore, queue formation is robust with respect to structural changes and intermittent breakdown of communication link.
Appears in Collections:Ph.D Theses (Open)

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