  This paper presents a novel quasi-centralized approach for collision-free
path planning of multi-robot systems (MRS) in obstacle-ridden environments. A
new formation potential fields (FPF) concept is proposed around a virtual
agent, located at the center of the formation which ensures self-organization
and maintenance of the formation. The path of the virtual agent is centrally
planned and the robots at the minima of the FPF are forced to move along with
the virtual agent. In the neighborhood of obstacles, individual robots
selfishly avoid collisions, thus marginally deviating from the formation. The
proposed quasi-centralized approach introduces formation flexibility into the
MRS, which enables MRS to effectively navigate in an obstacle-ridden workspace.
Methodical analysis of the proposed approach and guidelines for selecting the
FPF are presented. Results using a candidate FPF are shown that ensure a
pentagonal formation effectively squeezes through a narrow passage avoiding any
collisions with the walls.
