Multi-modal Locomotion And Path Following Control Of Needlelike Nanoparticle Microrobots

The development of microrobot technology provides convenience for human to explore the mysteries of the micro-world.Microbots can move easily in confined spaces and extreme environments and are expected to revolutionize precision machining,targeted drug delivery,minimally invasive surgery,micromanipulation and microassembly,among other fields.However,with the demand upgrading,a single micro-robot in some application scenarios has a single function,poor flexibility,low efficiency and imaging difficulties and other problems.At the micro scale,researchers take inspiration from the collaborative work of biological clusters in nature,using magnetic field forces to aggregate magnetic nanoparticles and move together in a specific motion mode.The self-assembled micro-robots can flexibly change motion modes according to different task scenarios and perform tasks efficiently.In this work,we will start from the basic magnetization and magnetic drive theory of magnetic nanoparticles,describe the formation process of the needle-like nanoparticle microrobot,analyze the multi-modal locomotion of the microrobot by modeling,design the corresponding experimental scenarios for each locomotion mode,and complete the in-plane path following task with each locomotion mode.Fe₃ O₄ suspension is used as experimental material,this paper introduced the basic theory of magnetization and magnetic driving of the magnetic nanoparticles in the magnetic field,the process of forming needle-like microrobots by aggregation and fusion of nanoparticle chains under the combined action of magnetic force,fluid resistance,and friction is analyzed with nanoparticle chains as the smallest unit.In order to verify the above theoretical analysis and to make the subsequent experimental research successful and effective,a set of computer software for magnetic field regulation and microrobot manipulation based on C++Qt framework was designed and developed independently for the 3D Helmholtz coil system.The software is designed with a multi-threaded approach,including a main thread,a visual feedback thread,a center-of-mass tracking and control algorithm thread,and a 3D Helmholtz coil group current regulation thread.It also provides functions such as magnetic field type selection and switching,magnetic field parameter adjustment,3D spatial magnetic field direction indication,microrobot visual monitoring and feedback,target center-of-mass tracking,one-click path following,etc.The interface is good-looking and easy to interact with.Subsequently,the multimodal locomotion of the needle-like nanoparticle microrobot was investigated in this work.By applying different types of magnetic fields,the needle-like microrobot can achieve a total of three different locomotion modes.When different types of oscillating magnetic fields are applied,the microrobot can be moved along its long axis or short axis(referred to as axial or lateral locomotion),and when a rotating magnetic field perpendicular to the horizontal plane is applied,the microrobot can be tumbled.The relationship between the locomotion speed of different locomotion modes and the length of the needle-like nanoparticle microrobot and the frequency of the applied magnetic field is analyzed by theoretical modeling,and the theoretical derivation is verified by velocimetry experiments.In addition,experimental scenarios are designed to demonstrate the flexibility of the needle-like nanoparticle microrobots by combining the locomotion characteristics of each locomotion mode.For example,the experiment of penetrating the non-woven layer of the mask was accomplished by axial locomotion,and the task of overturning the step obstacle was accomplished by tumbling locomotion.Finally,a dual closed-loop path following control algorithm with good mobility for multiple locomotion modes is investigated in this work.The control algorithm takes the optimal position of the nanoparticle microrobot path following as the outer loop and the optimal forward direction as the inner loop.In this study,three locomotion modes,namely axial locomotion,lateral locomotion and tumbling locomotion of the nanoparticle microrobot,are used to complete the path following task of the same"S"reference path in the plane,and the effectiveness and robustness of the closed-loop path following control algorithm are verified.In addition,the experimental results of the path following task performed by each of the above three locomotion modes are analyzed and evaluated in this study.