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Research On Coverage Problem For Mobile Robot

Posted on:2009-02-09Degree:DoctorType:Dissertation
Country:ChinaCandidate:F ZhangFull Text:PDF
GTID:1118360275454635Subject:Control Science and Engineering
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Coverage problem is one of the most challenging research topics in the mobile robotics and control theory, and represents the relationship among mobility, perceptivity and cooperation of robots. Coverage problem is defined as follows: to find a path or paths of the robot or robot groups such that its or their detected region could cover the whole environment with its or their motion. During the process of covering environments, each robot individual can only use the information which could be obtained to decide its motion. For multi-robot or swarm robot, each robot can furthermore obtain the information of its neighbors with finite communication to help its decision, and the whole system shows a collective behavior. The objective of this thesis is to discover the natural relationship between robot models and coverage tasks, to find the natural laws that networked individuals with local interactions can perform different collective behaviors, and to apply these laws to design mobile robot systems and solve problems in practical applications.This thesis provides an in-depth understanding on modeling as well as control method of coverage tasks for single, multi and swarm mobile robot systems, which are fundamental yet challenging issues in this research field. The main contributions in this thesis are divided into the following three aspects:1) For tasks of target detecting and dynamic coverage of single robot, we use mobile robot constrained motion model and reachable region to formulate and solve these problems in a theoretical and algorithmic level. This thesis establishes constrained motion model and sensor model of a mobile robot to represent mobility and perceptivity, respectively, and defines the k step reachable region to describe the states that the robot may reach. We show that the calculation of the k step reachable region can be reduced from that of 2k reachable regions with the fixed motion styles to k + 1 such regions, and provide an algorithm for its calculation. Based on the constrained motion model and the k step reachable region, the problems associated with target detecting and dynamic coverage are formulated and solved. For target detecting, the k step detectable region is used to describe the area that the robot may detect, and an algorithm for detecting a target and planning the optimal path is proposed. For dynamic coverage, the k step detected region is used to represent the area that the robot has detected during its motion, and the dynamic coverage strategy and algorithm are proposed. Simulation results demonstrate the efficiency of the coverage algorithm in both convex and concave environments.2) For the problem of efficiently using finite communication information of multi-robot coverage, we propose an improved market method for task allocation of multi-robot cooperative coverage in an algorithmic and practical level. For the limitation that market-based method only considers costs in the local map of each robot, we update the local maps through fusion of both the local sensor data and the bid information, and thus the extended parts in maps enable robots to calculate costs of other robots'targets. No extra communication is needed. Probability theory is used for occupancy grid maps, uncertain data processing and map update with bids information, which shows the consistency of the whole method. Moreover, we propose a new performance metric, called target point exchanged ratio, to reflect the degree of collaboration. The results of practical robot experiments and simulations demonstrate that the improved method is more efficient than the original market-based approach.3) For the problem of formation and coverage with failed or added robots of swarm robot, we propose a relay switched topology control for mobile robot networks in a theoretical and algorithmic level, which is a novel view of relationship between individuals and the whole system to deal with coverage problem, and becomes a theoretical frame of coopration coverage for large scale of mobile robot systems. Based on the graph and complex network theories, we establish the model of a mobile robot network which combines switched network topologies with an interaction dynamic model for describing the motion of the robots. Correspondingly, the control method is also divided into two levels: in the topology level, we analyze the effect of failed robots and added ones upon the network topology, and propose a relay switched topology control with self-healing ability and scalability; in the individual level, we transform the topology control into individual control algorithm with local interactions. We propose a set of metrics to evaluate control methods, including connectivity, convergence, self-healing ability, scalability, robustness and stability. We show that the proposed algorithm can prevent the network topology from being separated into two or more disconnected parts, and maintain the performance of the network. Based on the Lyapunov exponent, we further provide a criterion of the stability of the network with the proposed distributed control. Finally, we demonstrate the advantages of our method by performing simulations of formation and coverage. The advantages of our approaches over other methods are presented which include lower recovery time, lower power-consumption, more robust against communication failure, and zero blind zones for the coverage task.
Keywords/Search Tags:mobile robot, single robot, multi-robot, swarm robot, coverage
PDF Full Text Request
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