Initialisation and Decentralised Control for Robotic Control

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This thesis addresses the problem of coordination of a group of mobile robots to get into and maintain a formation with a desired shape. Two issues of particular importance in the coordination problem are formation initialisation and maintenance. Inter-robot collision and communication bandwidth limitations raise certain difficulties and require a thorough treatment. This thesis presents original contributions towards a solution to the formation initialisation and maintenance for multiple mobile robots in an obstacle free environment. In the context of robotic formation control, the commonly-used virtual robot tracking combined with I-I control has limitations in the establishment of a line formation, the possibility of collision between robots, and the singularity cases involved. A new approach called the Virtual Head Robot Tracking (VHRT) and Three Point I-I (3PLL) control incorporated with reactive control schemes is presented. The approach represents an appropriate solution to fonnation control for a group of three mobile robots with singularities alleviated and inter-robot collision completely avoided. For a group of more than three robots, a step-by-step procedure is proposed allowing the robots in turn to participate in the process of formation initialisation, that is based on a predefined control graph, while ensuring inter-robot collision avoidance. An observed-based decentralised control approach is proposed to establish and maintain a desired formation in the condition of a limited information exchange among robots in the group. This suggests the capability of enlarging the size of the platoon of vehicles in practice. The theoretical work of the thesis is evaluated by extensive simulations of multiple mobile robots based on their kinematic models. The results obtained are also experimentally tested, in part, on a group of two Amigo mobile robots.
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