Research On Micromanipulation Methods Using Magnetically Actuated Microrobots At The Liquid Surface

As the micro/nano technology develops recently,micromanipulation has made rapid development.Many strategies for micromanipulation including those at the liquid surface have been proposed,of which many manipulations are actuated by magnetic fields.However,micro-objects capable of being manipulated through the proposed methods are limit to magnetic particles,and the operations are complicated.Referring to manipulations in the liquid environment,the strategy that magnetically actuated microrobot is used to manipulate non-magnetic micro-objects at the liquid surface is proposed,which is easily realized and promising in applications.Here,theoretical models of microrobot in the gradient magnetic field and rotating magnetic field are established respectively based on the statics model of the robot floating at the liquid surface,and the influence of parameters of fields on the motion performance of microrobot is analyzed.Based on statics models of individual microrobot and microsphere floating at the liquid surface,the interaction between microrobot and microsphere is studied,and strategies for micromanipulations are proposed according to the interaction.Theoretical models is established to analyze influences of magnetic fields on performances of manipulation strategies,which is tested in subsequent experiments.First,the statics model of the microrobot,simplified as a circular sheet floating at the liquid surface,is established by analyzing the deformation of liquid surface around the robot,and the shape of liquid level is described by solving the Young-Laplace equation.According to the statics model dynamic models of the microrobot actuated in the gradient magnetic field and uniform rotating magnetic field are established respectively.In the gradient magnetic field the dependence of velocity of the microrobot on magnetic gradient is analyzed.When the microrobot is actuated by rotating magnetic fields,the relationship between the pose of microrobot and pitch of magnetic field is discussed,and dependences of velocity of robot on parameters of the field including rotational frequency and pitch angle are analyzed.Secondly,forces on a microsphere is analyzed and its statics model is established.The lateral capillary force between the microrobot and microsphere is computed,of which the dependence on the center distance between the microrobot and microsphere and the pose of the robot is also analyzed based on statics models of robot and ball.Strategies for manipulation at the liquid surface,including trapping,transporting and releasing,are proposed.Dynamic models of the microrobot and microsphere during transporting in the gradient magnetic field and rotating magnetic field are established respectively,and influences of magnetic gradient and frequency on transporting speed are analyzed based on the models.Furthermore,advantages of the methods for transporting are analyzed by comparing them.The distance of the microsphere during releasing is computed,through which the result of the method for releasing is evaluated.At last,experiments are conducted to verify established dynamic models and proposed strategies for micromanipulations.Methods for producing different magnetic fields are proposed and verified by simulating through the software COMSOL,and the experimental system is established.Experiments are conducted in which the microrobot is actuated by gradient magnetic field and rotating magnetic field respectively and its velocities are measured,and influences of parameters of magnetic fields on velocities are analyzed.Dynamic models are also verified by comparing them with experimental results.Experiments of manipulating solder balls at the liquid surface are also conducted to evaluate proposed strategies,effects of transporting powered by different magnetic fields are compared and analyzed.To present effects of proposed strategies experiments are conducted in which several solder balls are assembled to different pattern.