Study On Magnetic Microrobot Actuation Method Based On Three-Dimensional Adjustable Magnetic Field

Untethered and wirlessly-controlled microrobots have great potential in the fields of biology,medicine,micro-assembly,micro-nano manufacturing.Scientists both at home and abroad are actively engaged in study of wirelessly-controlled microrobot.Many scientists have focused on the method of using the magnetic field which can provide wireless power to actuate microrobot to realize microrobot wireless actuation.From the current research,the proposed electromagnetic actuation(EMA)systems with different shapes and the control methods of microrobot in wet/dry environment show good feasibility and great potentials but far from perfect for the real applications.Research foucs about EMA system is shifting from two-dimensional magnetic actuation to three-dimensional magnetic actuation.The EMA systems not only can produce sufficiently strong magnetic flux density but also ensure larger effective workspace.Faster and accurate control method and the multi-DOF microrobot are also the current hot research.In order to realize the multi-DOF actuation of microrobot as well as compatible with a variety of magnetic actuation methods with a relatively large working space,this paper develops a 3D EMA system compatible with a variety of magnetic actuation modes and proposes magnetic actuation control method for microrobot locomotion in 3D space with five-DOF.The proposed EMA system consists of stationary six-pair coils which include three pairs of Helmholtz coils and three pairs of Maxwell coils in three orthogonal directions.The uniform magnetic field produced by Helmholtz coil and the uniform gradient magnetic field produced by Maxwell coil.This paper established the math modal of 3D EMA system and completed the magnetic field analysis of the EMA system using finite-element-method(FEM)by multi-physics COMSOL software.Based on simulation result,the EMA coil system is designed and manufactured.The proposed three-axis orthogonal Helmholtz and Maxwell coils EMA system can produce magnetic field with different characteristics such as a controllable uniform gradient magnetic field,a rotating magnetic field and a oscillating magnetic field in a three-dimensional space by independently changing the current in each coil.The use of different characteristics of the magnetic field can achieve a variety of magnetic actuation ways.This paper established the 3D motion dynamic equation model of microrobot,and proposed a novel control method for the gravity compensation for the wireless locomotive microrobot.A mapping between magnetic force,magnetic moment and applied currents of each coils is modeled.The magnetic field is controllable in the 3D working space by independently changing the current in each coil.Microrobot is subjected to magnetic force and magnetic torque under the external magnetic field is generated.Simultaneously combining uniform magnetic field with uniform gradient magnetic field ensures that the magnetic force keeps constant to drive the microrobot wirelessly,and the microrobot overcomes the gravity and liquid resistance and achieves stable locomotion in the 3D region of interest(ROI).In the end,we validate the performance of the EMA system and the proposed control method by microrobot locomotion experiments in 2D,3D liquid environment.