Design And Research Of Miniaturized Nanoscale High-Precision Parallel Manipulator

The large transmission electron microscope can achieve nanoscale resolution,and ideal imaging effect requires high image resolution and precise sample control.The mechanical stability of the sample control is also an important factor in determining its image spatial resolution.Conventional sample stages use tandem motion systems,usually consisting of three linear and one tilting motion stage,with low stiffness and slow response times.The parallel manipulator has compact structure,higher multi-axis accuracy and faster response speed,and can achieve high stiffness and high load.In order to achieve high-precision cryo-electron tomography data acquisition,the sample carrying must meet high stability and high resolution,motion.The parallel manipulator with millimeter-level stroke and nano-level resolution is a great challenge.To meet the above requirements,this paper studies a parallel manipulator with small size,large workspace,high stability and high motion resolution.In this paper,a novel high precision 6-DOF parallel manipulator compatible with both 6-P-RR-R-RR and 6-PSS configurations is designed.The structural scheme,kinematic modeling and simulation,testing experiments of the parallel manipulator are systematically carried out.Firstly,this paper presents a detailed design of the parallel manipulator configuration and the whole machine scheme.For both configurations,the large workspace is an important design basis,so the offset hinge and the flexure hinge with a large range of motion are designed respectively.The designed parallel manipulator use piezoelectric motors with large motion range and nano-level precision as actuators,and install the drive assembly on the fixed platform,which can effectively reduce the size of the whole machine and the mass of moving parts,thereby reducing the driving force demand for piezoelectric motors.In this paper,the component structure of the parallel manipulator is designed in detail,and the fundamental frequency and mode shape analysis of the main components are carried out to provide a basis for the subsequent structural optimization design.The selection of components and electrical system scheme are also introduced in detail.Secondly,the 6-P-RR-R-RR parallel manipulator is modeled and simulated.It adopts the offset hinge.As compared to the traditional universal hinge,the rotation axes of the offset hinge are perpendicular to each other in space without intersecting.Thus,the interference risk of the hinge during rotation is effectively reduced,which can increase the workspace of the hinge itself.The offset hinge also has a large load-bearing capacity and is easy to mount and adjust,which can improve the precision,stiffness and workspace of the manipulator.But the kinematics of the parallel manipulator becomes quite complex by the introduction of offset variables for the hinge axis.In this paper,the Denavit-Hartenberg parameter method of the series mechanism is used to analyze the forward and inverse kinematics of the parallel manipulator,and the numerical iteration method is used to solve the problem.The forward and inverse velocity and forward and inverse acceleration are analyzed by means of the differential transformation method,which lays a foundation for the dynamic modeling and analysis.A numerical example is provided,and the correctness of the kinematic model is verified by co-simulation using MATLAB and ADAMS.Then,the modeling and simulation analysis of the 6-PSS parallel manipulator with flexure hinge is carried out.The motion range of the parallel manipulator with flexure hinge depends on the stroke of the actuator and the deformation of the flexure hinge.Common flexure hinges cannot provide large deformation,and in order to achieve multiple degrees of freedom and large deformation,a flexure hinge with omnidirectional incision and large aspect ratio structure is designed in this paper.The flexure hinge can be considered as a slender space beam structure rotating around three axes,thus the precision parallel manipulator with flexure hinge can be regarded as 6-PSS parallel manipulator.In this paper,the flexure hinge with large range of motion is studied from the aspects of flexibility and mode.The stiffness model of the whole parallel manipulator is established by the structural matrix method,and the constraint equilibrium condition for inverse kinematics solution is given.In order to meet the requirements of real-time control,the kinematic mathematical model is further established by the pseudo-rigid body model method,and its approximate center of rotation of the flexure hinge with large range of motion is obtained.Then,based on the three-dimensional model of the parallel manipulator,the rigid-flexible coupling model is established by the finite element method to verify the correctness of the kinematic model established by the pseudo-rigid body model method.Finally,a preliminary experimental research of the parallel manipulator is also carried out in this paper.A test system was built,and the performance indicators such as motion resolution and repeatability of the parallel manipulator were tested using a dual-frequency laser interferometer,which verifies the correctness of the inverse kinematics model and solution method.The research topic provides experience and technology accumulation for the research of parallel manipulator with small size,large workspace,high stiffness and nano-level ultra-high accuracy.