Multi robot formation control in obstacle environments
Multi robot system has wide applications in both civil and military fields, due to its high efficiency for task completion and robustness with respect to robot failures. Formation keeping, which is one of the fundamental tasks for multi robot control, has been extensively investigated in the past decade, resulting in a large variety of methodologies. However, most of the existing approaches are subject to certain limitations when implemented for addressing real formation control problems, mainly due to practical constraints introduced, such as sensor limitations, obstacle and inter robot collision avoidance in unknown environments, connectivity maintenance, unavailability of global pose measurements and so forth. This thesis deals with formation control problem for real robot applications by taking practical constraints into account. First of all, the virtual structure based formation tracking problem is studied, where obstacle and inter robot collision avoidance as well as connectivity maintenance are explicitly considered. To address this problem, a multi region control scheme is proposed, where three regions, including safe region, dangerous region and transition region, are defined. In different regions, priority is given to different control objectives. In safe region where trajectory tracking holds the priority, the proposed control scheme guarantees the bounded reference tracking for each robot. In dangerous region where avoidance control is the main objective, a new bounded potential function is designed to formulate multiple constraints. By introducing a series of transition functions, smooth switching between trajectory tracking and avoidance Nanyang Technological University Singapore