4D Printing Of Magnetically Driven Soft Robot And Its Key Theoretical Technology Research

Smart hydrogel is a polymer with three-dimensional network structure,which responds to the stimulation of different factors such as heat,magnetism,electricity,light,p H,etc.Because of its good material properties,it is widely used in many fields such as industry and medicine,etc.Meanwhile,because of the harmlessness of magnetic field and the feature of remote control,magnetically driven hydrogel can be the future research object of smart hydrogel.Soft robots have the characteristics of flexible movement,high degree of freedom and strong environmental adaptability,and hydrogels are widely used in bioengineering,public medical and other fields,and are the most ideal substrate material for soft robots.However,most of the current soft robots are established based on the bionic perspective with a single fabrication method and 3D model.In this paper,we use the self-developed neodymium-iron-boron(Nd Fe B)magnetic hydrogel as the substrate of the soft robot,and use the light-curing 3D printing technology as the preparation means of intelligent hydrogel to prepare the Nd Fe B magnetic hydrogel with good mechanical and magnetic properties,and also study a magnetization drive coil as magnetization and driving device for magnetic hydrogels.The details of the study and the main findings are as follows:(1)By analyzing the magnetization mechanism and the external magnetic field driving mechanism of the magnetic robot after 3D printing,the characteristics of the magnetic medium subjected to magnetic force and magnetic moment in the magnetic field are deduced,the Helmholtz coil is optimized,and the auxiliary coil is added to the original structure to form the magnetization driving coil,so that the magnetization driving coil can generate uniform magnetic field and gradient magnetic field.The Helmholtz coil generates a uniform magnetic field and the additional auxiliary coil generates a gradient magnetic field,and the variations of the magnetic fields of the two coils are used to control various motions of the robot,laying the theoretical foundation.(2)Based on the magnetic field principle,the magnetized drive coil of the magnetic soft robot is designed.The optimal magnetic field control parameters are obtained,and the superimposed magnetic field is simulated and analyzed by using ANSYS-Maxwell,and the distribution law of the superimposed magnetic field is finally derived.The structure and parameters of the designed magnetization drive coil were optimized by using finite element simulation,and it was finally determined that the central magnetic induction strength of the magnetization drive coil could reach1.37 T when the number of turns was 8000 and the distance of the auxiliary coil was70 mm,and then the designed magnetization drive coil was physically built and the test results showed that the central magnetic field could reach 1.34 T with an error of no more than 2% from the simulation.The design was proved to be reasonable and could meet the experimental requirements.(3)The hydrogel matrix mixed with Nd Fe B powder was synthesized by light-curing 3D printing,and its internal structure was uniformly distributed with good mechanical and magnetic properties.The properties of the magnetic gel material were obtained by testing.It was found that the magnetic and mechanical properties of the hydrogel increased with the content of Nd Fe B powder in a certain range,but the high content of Nd Fe B powder would affect its magnetic and mechanical properties.The dissolution rate tends to decrease with the increase of Nd Fe B powder content.Finally,Nd Fe B magnetic hydrogel doped with 50% Nd Fe B powder,with 20 s exposure of base layer and 1.5s curing time of normal layer is selected as the base material of soft robot,which can have good swelling rate,mechanical properties and magnetic properties at the same time.The prepared hydrogel was put into the magnetized driving coil for 1.5h,and the bending angles were measured by taking pictures every half hour,and the bending angles were 251°,267° and 280° at different moments.The experimental results show that the bending deformation of Nd Fe B magnetic hydrogel increases with the increase of placement time,and the more Nd Fe B powder content in the hydrogel,the larger the bending deformation of Nd Fe B magnetic hydrogel.It is also proved that the prepared Nd Fe B magnetic hydrogel can be 4D printed under the action of the applied magnetic field.(4)By calculating and analyzing the magnetic field of the magnetized drive coil and controlling its loaded current,it can make the magnetic soft robot obtain the gradient magnetic force and magnetic torque required for driving,and verify the feasibility of controllable motion of the soft robot.