Minimalist Multi-Robot Clustering of Square Objects: New Strategies, Experiments, and Analysis

Studies of minimalist multi-robot systems consider multiple robotic agents, each with limited individual capabilities, but with the capacity for self-organization in order to collectively perform coordinated tasks. Object clustering is a widely studied task in which self-organized robots form piles from dispersed objects. Our work considers a variation of an object clustering derived from the influential ant-inspired work of Beckers, Holland and Deneubourg which proposed stigmergy as a design principle for such multi-robot systems. Since puck mechanics contribute to cluster accrual dynamics, we studied a new scenario with square objects because these pucks into clusters differently from cylindrical ones. Although central clusters are usually desired, workspace boundaries can cause perimeter cluster formation to dominate. This research demonstrates successful clustering of square boxes - an especially challenging instance since flat edges exacerbate adhesion to boundaries - using simpler robots than previous published research. Our solution consists of two novel behaviours, Twisting and Digging, which exploit the objects’ geometry to pry boxes free from boundaries. Physical robot experiments illustrate that cooperation between twisters and diggers can succeed in forming a single central cluster. We empirically explored the significance of different divisions of labor by measuring the spatial distribution of robots and the system performance. Data from over 40 hours of physical robot experiments show that different divisions of labor have distinct features, e.g., one is reliable while another is especially efficient

New Models of Self-Organized Multi-Robot Clustering

For self-organized multi-robot systems, one of the widely studied task domains is object clustering, which involves gathering randomly scattered objects into a single pile. Earlier studies have pointed out that environment boundaries influence the cluster formation process, generally causing clusters to form around the perimeter rather than centrally within the workspace. Nevertheless, prior analytical models ignore boundary effects and employ the simplifying assumption that clusters pack into rotationally symmetric forms. In this study, we attempt to solve the problem of the boundary interference in object clustering. We propose new behaviors, twisting and digging, which exploit the geometry of the object to detach objects from the boundaries and cover different regions within the workplace. Also, we derive a set of conditions that is required to prevent boundaries causing perimeter clusters, developing a mathematical model to explain how multiple clusters evolve into a single cluster. Through analysis of the model, we show that the time-averaged spatial densities of the robots play a significant role in producing conditions which ensure that a single central cluster emerges and validate it with experiments. We further seek to understand the clustering process more broadly by investigating the problem of clustering in settings involving different object geometries. We initiate a study of this important area by considering a variety of rectangular objects that produce diverse shapes according to different packing arrangements. In addition, on the basis of the observation that cluster shape reflects object geometry, we develop cluster models that describe clustering dynamics across different object geometries. Also, we attempt to address the question of how to maximize the system performance by computing a policy for altering the robot division of labor as a function of time. We consider a sequencing strategy based on the hypothesis that since the clustering performance is influenced by the division of labor, it can be improved by sequencing different divisions of labor. We develop a stochastic model to predict clustering behavior and propose a method that uses the model's predictions to select a sequential change in labor distribution. We validate our proposed method that increases clustering performance on physical robot experiments