The Role of Explicit Alignment in Self-organized Flocking

Flocking is an self-organized behavior that is widely observed in nature from simple organisms such as crickets and locusts to more complex ones such as birds and quadruplets. It can be defined as the coherent and aligned motion of a group of animals at a certain direction. Coherence is the tendency of the individuals to stay together and alignment is a consequence of minimizing collisions at the individual level. In this paper, we study the alignment component of the flocking behavior in a swarm of robots. We implemented two different controllers: one with only a cohesion behavior, namely the no-alignment controller, and the other with both cohesion and alignment behaviors, namely the alignment-enabled controller. In both controllers, only a proportion of robots, called informed robots, are provided with the desired goal direction. In particular, we study the effect of three different parameters on flocking performances. The three parameters are the size of the swarm, noise in the cohesion behavior and the proportion of informed robots. Under the effect of these parameters, we perform a comparative study of the two controllers. We perform simulation-based experiments and evaluate the accuracy of the flock to move in a desired goal direction. The experiments are conducted in stationary and non-stationary environments: in the stationary environment, the goal direction and the informed robots do not change during the experiment, whereas in the non-stationary environment, both the goal direction and the informed robots change over time. The results show that i) the alignment behavior results in a more aligned motion in larger swarms; ii) smaller swarms without an alignment behavior can follow the goal direction more accurately; iii) noise in the no-alignment controller helps to achieve a more aligned motion in large swarms and iv) the swarm needs enough informed robots to follow accurately the goal direction and to adapt to non-stationary environments. Keywords-flocking; self-organization; swarm robotics; swarm intelligence