Research On Path Following Control For Magnetically Actuated Soft Microrobots

Nature provides a wide range of inspiration for designing microrobots that can navigate through narrow,human-inaccessible environments and perform non-invasive tasks on the environment,such as micro-assembly,cell manipulation,pollutant degradation,minimally invasive treatment,targeted diagnosis,and targeted drug delivery.During the past decade,the field has been transformed in many ways,the most important of which include transitions from hard and rigid micro-structures to soft and flexible architectures,from open-loop control to closed-loop control,from single-mode locomotion mode to multimodal locomotion.Compared with rigid microrobots,soft microrobots that rely on the bending or deformation of functional materials to generate motion show higher adaptability in dynamic and complex environments.However,the fabrication,actuation and motion control of soft micro-robots are challenging because of the complexity of their movement.Therefore,this thesis focuses on the magnetic actuation systems,control systems for multi-degree-of-freedom microrobots,and the design and modeling of soft microrobot with multimodal locomotion.Firstly,a magnetic actuation and control system with friendly user interaction and good performance for multi-degree-of-freedom magnetic soft microrobot was designed,which includes modules such as main control thread,coil drive thread,visual feedback thread,GUI thread,etc.This system can monitor and virtually reconstruct the state of the micro-robot and its surrounding environment in real time.It can also generate a variety of magnetic fields,including constant,rotating,oscillating,cone,pulse,and other magnetic fields,as well as user-defined magnetic fields.The open interface design of the system helps researchers to design actuation and control solutions for magnetic microrobots based on the system.Secondly,a closed-loop control method of soft swimming microrobots for 3D arbitrary path following at low Reynolds numbers by visual servoing was proposed.The 3D arbitrary path is represented by a sequence of key points,and the line segment connected between adjacent points is used as a path sub-segment,which is simpler and more efficient than a complex curve equation.The 3D path following control can be regarded as a combination of multiple sub-segment tasks,which is an iterative process.Different complicated paths drawn by users through a 3D mouse without the input of parametric equations are followed by swimming robots during experiments.Finally,a novel untethered soft millirobot with magnetic actuation in the head and function in the tail is presented via the programmable magnetic field and the soft and elastic body,thereby endowing robots with multimodal locomotion and adaptability in a dynamic,diverse and complex environment.Due to the soft and asymmetric structure,the millirobot not only shows robust multimodal locomotion,including controllable and transformable crawling,swinging and rolling,but also achieves an excellent capability of helical propulsion in water.Moreover,the motion model of the soft microrobot is also analyzed,and a simplified model of dynamics is established.Experiments demonstrate that the soft microrobot passes through a series of obstacles including steps,high walls,low passages,and narrow gaps.Comparative experiments analyze the factors that affect the motion performance of the robot,and verify the accuracy of the dynamics.