Research On Microparts Transportation Based On Magnetic Microrobots At Air-liquid Interfaces

In the field of water quality testing,micropart assembly,and the transfer of MEMS devices,there is a need for a variety of manipulators to accomplish the task of transporting microparts on the liquid surfaces.As the precision and efficiency of micromanipulation become more and more demanding,it has become a challenge for traditional manipulators with complicated structures and big sizes to deliver microparts on liquid surfaces.In contrast,magnetic microrobots working on liquid surfaces have great potential to perform micromanipulation due to their compact structures and flexible locomotion.However,there are still a number of problems in the development of the microrobots on liquid surfaces,such as the single locomotion mode and poor controllability,which restrict their application in the field of microparts transportation.To solve these problems,several propulsion methods of magnetic microrobots with different structures are put forward according to the motion and static properties of these robots,and they are verified by experiments.First of all,to solve the problem that the locomotion mode of the microrobots on the liquid surface is single,a few kinds of locomotion methods are presented.In this thesis,the static properties of the typical microstructure on the liquid surface are investigated,and the positions of the microrobot in different magnetic fields are analyzed.In addition,the environmental forces on the mobile microrobots are also analyzed.This thesis puts forward several strategies to propel the microrobot in rotating,oscillating and precessing fields.Based on the experimental results,the influences of magnetic field parameters on microrobot locomotion are analyzed,which will be helpful for the control of the microrobots on liquid surfaces.Then,for the simple microparts transportation on liquid surfaces,the micropart transporting method is proposed based on the influences of liquid interface deformations,in which the microrobots attract and transport microparts by manipulating the surrounding liquid interface.The fish-and pentagram-shaped single microrobot are designed to accomplish simple microparts transportation based on the proposed method,respectively.According to the structures of the single microrobots,the locomotion modes of the two robots are selected,and the micropart transporting strategies are also put forward.Both microrobots are tested to deliver a microsphere to test their abilities to transport microparts,where the transporting direction can be controlled and the transporting speeds can reach 5 times the diameter of the microsphere.Subsequently,three self-assembled microrobots are designed for microparts transportations that is challenging to be accomplished by single microrobots.Since the self-assembled microrobots are developed based on the dipole-dipole interactions between magnetic microdisks,the magnetic dipole-dipole interactions are analyzed,and the influences of the magnetic field on these interactions are discussed.Micropartners consisting of two steel disks are designed,and their locomotion characteristics under oscillating magnetic fields are investigated.The straight-chain microrobots assembled by several disks are designed,and the characteristics of the paddling motion are also investigated.The characteristic that the straight-chain microrobot reverses its moving orientation at high frequencies is discussed.Nonhomogeneous Janus magnetic disks are designed and fabricated,and the method of constructing different shapes of chain-shaped microrobots is proposed based on different connections of Janus disks.The strategy of controlling the shape of the chain microrobots by adjusting magnetic field strength is also developed.The locomotion mode of the deformable chain-shaped microrobots is selected,and the locomotion characteristics are also discussed.Finally,strategies for the microparts transportation based on the designed selfassembled microrobots are proposed.The methods by which the micropartners grasp and transport microparts are proposed based on the connection and separation of the partners.The micropartners are tested to transport a microwire to verify the transporting methods,and the transporting speed at the level interface can reach 1body length of the microwire per second.The methods by which a single straightchain magnetic microrobot transports microparts are also proposed,and the straightchain microrobot can transport a microball at the speed of 2 body lengths per second.Based on the locomotion characteristics of straight-chain microrobots,strategies for cooperative control of straight-chain microrobots are proposed,and two straightchain microrobots are controlled to cooperate to assemble microparts.Based on the deformation of the chain-shaped microrobots assembled by Janus disks,the methods for the microrobots to encircle,transport,and release microparts are proposed.The locomotion characteristics of deformable chain-shaped microrobots are analyzed during transportation.As indicated above,in order to address the problems that restrict the further use of microrobots on liquid surfaces,including the limited mobility,poor controllability,and poor adaptability to different environments and tasks,several propulsion methods for microrobots of several structures are proposed in the thesis,which can be applied in the microrobot actuation and microparts transportation on liquid surfaces.The single pentagram-and fish-shaped microrobots are designed to transport the microparts such as microballs.In addition,magnetic micropartners,straight-chain microrobots,and deformable chain-shaped microrobots are designed to compensate for the limitations of the single microrobots in microparts transportation.Microparts transporting methods based on these self-assembled microrobots are proposed,which can be used to transport microparts of various structures.Based on these methods,the self-assembled microrobots can accomplish complicated tasks,such as the assembly of microparts.The results of this study are not only useful for the further application of magnetically driven microrobots,such as the assemblies of microparts,but also facilitate the studies of insect movement mechanisms on liquid surfaces and microbial self-assembled principles,which have important scientific value and good application prospects.