Two-agent formation control of magnetic microrobots in two dimensions

This paper presents a new method to control multiple micro-scale magnetic agents operating in close proximity to each other for applications in microrobotics. Controlling multiple magnetic microrobots close to each other is difficult due to magnetic interactions between the agents, and here we seek to control those interactions for the creation of desired multi-agent formations. We use the fact that all magnetic agents orient to the global input magnetic field to modulate the local attraction-repulsion forces between nearby agents. Here we study these controlled interaction magnetic forces for two cases: i) agents with free 3D magnetization, and ii) agents with constrained magnetization to horizontal motion plane. Accordingly, we devise two controllers to regulate the inter-agent spacing, heading and position of the set, for motion in two dimensions. Simulation and experimental demonstrations on two agents in this paper show the feasibility of the idea and its potential for the completion of complex tasks using teams of microrobots. Average tracking error of less than 39 micrometers and 1.45 degrees is accomplished for the regulation of the inter-agent space and the pair heading angle, respectively, for identical spherical-shape agents with nominal radius less than of 250 micrometers operating within several body-lengths of each other.