Rendezvous and Docking of Magnetic Helical Microrobots Along Arc Orbits for Field-directed Assembly and Disassembly

Due to the limited cargo/functional element loading and other capabilities of individual microrobots, assembling them for locomotion and disassembling them as arriving at the target is more effective. An approach called rendezvous and docking is proposed in this paper to control the assembly and disassembly of helical microrobots actuated by a uniform rotating magnetic field. Docking is realized around the intersection of their arc orbits with the assistance of a fluidic field. To adjust the distance between the adjacent helical robots suspending in solution but with a distance beyond the acceptable range of the magnetic interaction, their asynchronized velocities are achieved using the interaction between the robots and fluids. For robots rotating at different speeds around their longitudinal axes at a driving frequency lower than the cut-off frequency, different fluidic flows will be generated. Based on the interaction between the robots and the fluids, the translational trajectory paths may be tuned, causing the adjacent robots to move closer. Docking along the tangential direction of rendezvous arc trajectories avoids the instability of the helical robot rotating around the radial direction and the problem of excessive linear speed at the end during assembly so that the robot can rotate stably around its axis while completing the assembly. Besides these, assembled microrobots can also lower the requirements on the imaging resolution of motion tracking and the forces for driving; hence much lower cost for both imaging and driving equipment.