There has been increased research interest in systems composed of multiple autonomous mobile robots exhibiting collective behavior. Groups of mobile robots are constructed, with an aim to studying such issues as group architecture, resource conflict, origin of cooperation, learning, and geometric problems. As yet, few applications of collective robotics have been reported, and supporting theory is still in its formative stages. In this paper, we give a critical survey of existing works and discuss open problems in this field, emphasizing the various theoretical issues that arise in the study of cooperative robotics. We describe the intellectual heritages that have guided early research, as well as possible additions to the set of existing motivations. 1

Accomplishing useful tasks with a collection of decentralized mobile robots will require control methods that deal effectively with a number of unique problems that impede the system's progress. Reactive control architectures can easily cause the problems of stagnation and cyclic behaviour, both characterized by a lack of progress in achieving a task. In this paper we present one possible solution to stagnation recovery, motivated from the study of group transport in ants and demonstrate its use in a box-pushing task. By using stagnation recovery behaviours, which are triggered by a lack of progress in the task-achieving activity of the system, the collective system can monitor its own advancement in a decentralized manner. A set of such behaviours are progressively ordered using timeouts, with each set designed for a specific recovery strategy. The stagnation recovery behaviours have been tested in simulation with the results to be mapped onto a set of ten autonomous robots presently ...