Ioan SUSNEA, Grigore VASILIU, Adrian FILIPESCU, Adrian RADASCHIN
Department of Automation and Industrial Informatics
“Dunărea de Jos” University, Galaţi, Romania

Abstract: This paper presents a novel implementation of the concept of “virtual pheromones” for controlling autonomous mobile robots. Instead of deploying chemicals, RFID tags, or other traceable marks in the environment, the virtual pheromones are stored in a map of the environment maintained and updated by a “pheromone server”. This map acts like a shared memory for all the agents, each of them communicating with the server via a radio link. No direct communication between agents is required. The pheromone server can be implemented on a regular computer, a portable device, or an embedded controller located on a robot. The technique described is applicable for guiding individual robots and robot swarms. This method can lead to significant simplification and cost reduction of the autonomous agents. Some possible applications are presented.

Keywords: Virtual pheromones, Autonomous Mobile Robots, Path following, Swarm Intelligence, Exo-synapses, Embedded systems.

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CITE THIS PAPER AS:
Ioan SUSNEA, Grigore VASILIU, Adrian FILIPESCU, Adrian RADASCHIN, Virtual Pheromones for Real-Time Control of Autonomous Mobile Robots, Studies in Informatics and Control, ISSN 1220-1766, vol. 18 (3), pp. 233-240, 2009.

1. Introduction

Since 1959, when Karlson and Lüscher ([9]) discovered and described the natural pheromones, and Grassé ([8]) defined the stigmergy, almost 30 years have passed until Deneubourg, Aron et. al. ([3], [4]) noticed the possibility of creating artificial biomimetic agents that communicate and interact with each other by means of a similar mechanism.

In 1989 Beni and Wang ([1]) introduced the concept of swarm intelligence, and, between 1996 and 1999, Dorigo, Bonabeau et al. published several works ([5], [6], [7]) exploring the mechanism of self-organization in swarms, and called “ant colony optimization” (ACO) the process that allows foraging ants to find the shortest path between nest and food sources. Afterwards, a great number of scientific papers propose various methods for creating artificial pheromones. Some researchers propose solutions based on spreading chemicals in the

environment, just like ants do. ([14], [7]). Others ([13]) use short-range infrared transceivers to relay messages between mobile robots, while others ([10], [15]) propose the use of RFID tags, deployed in the environment, to store some data structures, interpreted as digital pheromones.

The term “virtual pheromone” was mainly used in connection with software agents ([17]).

In the experiment described here, virtual pheromones are embedded in a map of the environment, located in the memory of a remote computer, called pheromone server. Robotic agents use their own odometric system to periodically report their position to the pheromone server, via a radio communication link. When the pheromone server receives a data packet containing the current position of a robot, it locates the robot on the internal map, then computes the pheromone concentrations for that particular position, and sends back to the client a response packet containing this data. Thereafter, the robot acts as if it had its own differential pheromone sensors, and adjusts its position so that it gets as close as possible to the pheromone trail.

The system can operate with fixed, predefined paths embedded in the pheromone map, or, when multiple robots are involved, it can modify the pheromone concentrations as if the robots would leave pheromone trails on their way, just like real insects do. In this last case, the pheromone paths stored by the server dynamically change as robots move through the environment, creating a realistic emulation of a natural swarm.