Magnetic Force-Propelled 3D Locomotion Control for Magnetic Microrobots via Simple Modified Three-Axis Helmholtz Coil System

Magnetic microrobots are propelled by magnetic fields or magnetic field gradients generated by electromagnetic systems. Generally, 3D Helmholtz coils systems are used for microrobot propulsion, because of their low power consumption, ease of manufacture, and ease of control, for which, only three power supplies are required. Systems of this kind can only generate uniform magnetic fields, which limits their range of applications. However, generating both uniform magnetic fields and gradients typically requires more coils and power supplies, resulting in large expensive energy-intensive systems with complicated control algorithms. Although the aforementioned systems can control magnetic robots with up to 6 degrees of freedom (DOFs), most existing applications at the micro/nanoscale only require 2 rotational DOFs and 1 translational DOF. Here, we propose a new control system capable of producing 3D uniform magnetic fields with 3 DOFs and 3D gradients with 1 DOF. With this system, one pair of coils in a traditional 3D Helmholtz coil system is modified, to enable independent control of the individual coils directing a selected axis, while the configuration of the remaining two pairs of coils is unchanged. This results in a control system with low power consumption, and a simple control algorithm that can be easily applied to existing 3D Helmholtz systems, as it only requires the addition of a power supply. In combination with the developed system, we also propose a new control algorithm applicable to both permanently and temporarily magnetized microrobots, and verify this experimentally.