Design and reconfiguration algorithm of Hexbot: A modular self-reconfigurable robotic system

This paper primarily addresses the design and implementation of a planar hexagonal Modular Self-Reconfigurable Robotic System (MSRRS) along with the construction of its reconfiguration path planner and control algorithm. A universal module is carefully designed to be in line with the common goals of MSRRS including homogeneity, cost-effectiveness, fast actuation and quick and strong connections. Although the implemented working prototype is both large and restricted to a planar geometry, it is designed such that its hardware and software can be scaled up in the number of units and down in unit size; similarly, the platform has the potential to be extended for 3D applications. The software infrastructure of this platform is designed in a way that different hierarchies for distributed control and communication can be implemented. The algorithmic design is based on a hierarchical multilayer approach, where upper layers decompose the problem into sub-problems solvable by lower layers. An optimal reconfiguration path planner is developed to minimize the number of module movements during the reconfiguration while enforcing collision avoidance and connectivity constraints in addition to taking into account the kinematic model of the platform. The core of the algorithm relies on a heuristic function and a Markov Decision Process (MDP) optimization to generate a near-optimal reconfiguration path planner and a control algorithm for HexBot shown in Figure 1, a lattice, homogenous, rigid, planar hexagonal MSRRS. Among several novel approaches incorporated in this system, multilayer nature of both hardware and software design provides openness, flexibility and ease of modification or adaptation for other platforms. In this approach each layer is dedicated to perform a specific task and can be modified or enhanced separately while keeping the remaining layers untouched.