Analysis And Optimal Structure Design Of A High-frequency Band6-dof Parallel Manipulator

The hydraulic driving Stewart Platform has been widely used in different kinds ofengineering fields. However the working frequency range of this kind of parallelmanipulator is low due to its structural characteristics, which limits its applications insome high-frequency simulation fields. This paper aims to find the factor which restrictsthe working frequency of Stewart Platform, based on this influence, a new kind of6-dofparallel manipulator is proposed. Then the kinematics and dynamics of this k ind of6-dof parallel manipulator is established, after which the natural frequency of thismanipulator is analyzed.In this thesis, the factor that restricts the working frequency of Stewart Platform isfound out at first. According to the previous experiment, the transverse vibration of thehydraulic cylinder is considered as the restriction. Stewart Platforms usually usehydraulic cylinders as the actuators, and those cylinders are always slender because ofthe platforms’ structure. in this thesis, the slender hydraulic cylinder is simplified as aslender system with consideration of the key parts of the cylinder, and the equations ofthe transverse vibration are derived based on this slender model. After that, the naturalfrequencies and modes of the transverse vibration is calculated and the influences thatthe parameters of the cylinder have on the first-order natural frequency are analyzedusing Matlab. Based on the influences effects, several ways to increase the naturalfrequency can be found. And then the validity of the method in analyzing the transversevibration is verified by comparison with the experiment data and the results of theANSYS simulation.Based on the analysis of the transverse vibration of the hydraulic cylinder, a newkind of6-dof parallel manipulator is proposed, and its potential to achievehigh-frequency motion is discussed. Then the inverse kinematics of this manipulator isderived and its key element: Jacobian, is given. On the basis of kinematics, thedynamics (including single-body dynamics and multi-body dynamics) is established,and Kane’s equation is applied in the process of deriving multi-body dynamics. Thenboth of the kinematics and dynamics are modeled and simulated in Matlab/Simulinkand Adams/View, which verifies the validities of the kinematics and dynamics.After the kinematics and dynamics, the natural frequency of this manipulator isanalyzed. First, the general expression of the rigidity matrix is derived, then togetherwith the mass matrix which can be obtained from the dynamics, the natural frequenciesand modes on the6degrees of freedom of this manipulator when it’s on the neutralconfiguration are calculated. And one can know from the results that the motions ondifferent degrees of freedom are coupled under general situations. In order to eliminate the coupling, the decoupling condition is derived under the situation where themanipulator is on its neutral configuration. And the equations to calculate the naturalfrequencies are derived when the motion is decoupled. And at last, the influences of thestructure parameters on the natural frequencies are analyzed, and together with thedriving forces of the cylinders under different structure parameters, the structureparameters of the manipulator are optimized.This thesis proposed the idea that the transverse vibration of the hydrauliccylinders is the restriction of the working frequency of Stewart Platform, and then thetransverse vibration of the slender hydraulic cylinders are analyzed in detail, whichprovides some help on the design and choice of cylinders. And in the process ofderiving kinematics and dynamic, the modeling method that using vectors is mucheasier than the method that used in the thesis of Tan Qiaoyin from Harbin Institute ofTechnology. The analysis on the natural frequency of the high-frequency6-dof parallelmanipulator is believed to be of some value in the design of this type of manipulator.