Redundancy, Efficiency and Robustness in Multi-Robot Coverage

Abstract

Abstract-Area coverage is an important task for mobile robots, with many real-world applications. Motivated by potential efficiency and robustness improvements, there is growing interest in the use of multiple robots in coverage. Previous investigations of multi-robot coverage focuses on completeness and eliminating redundancy, but does not formally address robustness, nor examine the impact of the initial positions of robots on the coverage time. Indeed, a common assumption is that non-redundancy leads to improved coverage time. We address robustness and efficiency in a family of multi-robot coverage algorithms, based on spanning-tree coverage of approximate cell decomposition. We analytically show that the algorithms are robust, in that as long as a single robot is able to move, the coverage will be completed. We also show that non-redundant (non-backtracking) versions of the algorithms have a worst-case coverage time virtually identical to that of a single robotthus no performance gain is guaranteed in non-redundant coverage. Moreover, this worst-case is in fact common in realworld applications. Surprisingly, however, redundant coverage algorithms lead to guaranteed performance which halves the coverage time even in the worst case.

Multi-robot forest coverage

“…Recently, STC was generalized to Multi-Robot Spanning Tree Coverage (MSTC), a polynomial-time multi-robot coverage heuristic [5]. MSTC first computes the same spanning tree as STC, and considers the tour that circumnavigates the spanning tree.…”

“…Each robot follows the tour segment clockwise ahead of it, with one exception: To improve the cover time, the longest segment is divided evenly between the two adjacent robots. A few small adjustments, detailed in [5], then ensure that MSTC reduces the cover time of STC by a factor of at least 2 (or 3/2) for k ≥ 3 robots (or two robots, respectively). Each small cell is visited by only one robot, so there are never any collisions or blockages.…”

“…EXPERIMENTAL RESULTS We now compare the cover times of MFC and MSTC experimentally. We implemented the backtracking version of MSTC as described in [5]. We evaluate them on two different tasks, namely coverage ["cover"], and coverage with the additional requirement that all robots return to their initial small cells after coverage ["cover and return"].…”

“…It thus becomes necessary to consider heuristics for solving it. Recently, STC was generalized to Multi-Robot Spanning Tree Coverage (MSTC), a polynomial-time multirobot coverage heuristic [5]. While MSTC provably improves the cover time of STC, it cannot guarantee its cover time to be close to optimal.…”

The giving tree: constructing trees for efficient offline and online multi-robot coverage

“…After such a tree was built, the robot follows the tree around, creating a hamiltonian cycle visiting all cells of the original grid. The idea was first broadened for a multi-robot system in [13], by the family of MSTC algorithms. A different variation on this idea was introduced in [24].…”