Collective robotics: from local perception to global action

Abstract

Does coherent behaviour require an explicit mechanism of cooperation? In this dissertation, the relationship between local perception and global action in a system of multiple mobile robots was examined for a collective box-pushing task. The problem investigated was how local sensing could be used to coordinate the individual motor responses of a system of robots in a coherent manner, using only implicit communication through the task. The task was to move a large box from an initially unknown position to a specified goal location. The central thesis put forward, is that for the box-pushing task a coherent behaviour is possible, without an explicit mechanism of cooperation, by using the mass effect of a system of redundant robots. Preliminary work in collective robotics appeared to lend weight to the hypothesis that collective tasks, by multi-robot systems. are possible without centralized control or explicit inter-robot communications, two common control mechanisms used for cooperation. The goal was to propose and verify a framework for modelling a multi-robot task, such that the system displayed both coherent and coordinated behaviour without centralized control. The result is a coordinated global action by the system similar to group transport behaviour by ants. The result is achieved using the mass effect of a system of redundant robots. The approach to connecting perception and action is through a task description, specified as changes in the environment, and a task decomposition, which describes how a system will achieve those changes. Demonstrated is a framework using a multi-robot box-pushing task and its extension to a directed box-transport task. Steps in the task are modelled as states, and implemented as subtask controllers, with state transitions determined by binary sensing predicates called perceptual cues. A perceptual cue (Q), whose computation is independent from the operation of the controller, is used by a finite state controller, called a Q-machine, to produce an action. Results are presented for a redundant system of physical robots capable of moving a heavy object collectively to arbitrarily specified goal positions.