| In the large fusion experimental device,the specific mechanical modules used to construct the experimental path are large in size and of various types,which put forward a high demand for the performance of the supporting tooling.In order to finish the precise installation and calibration of specific mechanical module,Chongqing University has designed a set of special tooling for the lower type specific mechanical module,and the horizontal adjustment unit is the key mechanism to complete the positioning and installation of specific mechanical module in the tooling.The horizontal adjustment unit is essentially a set of 3-DOF spatial parallel mechanism,its design and performance will affect the success or failure of installation and calibration of the specific mechanical module.In this paper,a new horizontal adjustment unit based on the 3-PRS /PSS parallel mechanism is proposed based on the traditional 3-prs institution.This new configuration can better fit the specific module,improve the stability and reduce the size of the lower installation system.By means of theoretical modeling and simulation verification,this paper analyzes and checks the important performance of the new horizontal adjustment unit based on 3-prs /PSS mechanism,so as to verify that this new configuration has better performance compared with the 3-prs mechanism and can meet the actual requirements of installation and calibration of specific machine module.The main contents of this paper are as follows:A novel configuration scheme of horizontal adjustment unit is proposed.Based on the traditional 3-PRS institution to form a four-branch chain,more stable new3-PRS/PSS institution.Using the screw theory to check the degree of freedom of the optimized new configuration,the inverse kinematics model is established and verified by simulation.The stiffness analysis of the horizontal adjustment element is carried out,the stiffness matrix of the mechanism is established,and the stiffness mapping is carried out using MATLAB.The finite element method is used to get the deformation and stress of the mechanism.The calculation and simulation results show that the load-carrying capacity of the new 3-PRS / PSS mechanism is improved compared with that of the 3-PRS mechanism,and it can meet the stiffness requirements of the horizontal adjustment element in the actual installation and calibration.Based on the dynamics analysis of the horizontal adjustment unit by Kane method,a dynamic model of the mechanism with motion pair clearance and flexibility was established on the basis of the multi-rigid body dynamics modeling.Given a practical working condition in the installation and calibration,the driving force of each slider of3-PRS / PSS mechanism and 3-PRS mechanism is solved.It is verified that the dynamic performance of the new horizontal adjustment unit based on 3-prs /PSS parallel mechanism is better,which provides theoretical basis for the dynamic analysis of parallel mechanism at the same time.Based on the matrix method,the static error model of the new horizontal adjustment element is built,the static error modeling of the new horizontal adjustment element and the dynamic error modeling of the component deformation are carried out.The error simulation is carried out in the workspace of the horizontal adjustment unit,and the influence of different static error sources on the accuracy of the mechanism is compared.Given two working conditions,the actual and theoretical trajectories of the new 3-PRS / PSS mechanism and 3-PRS mechanism are compared.Combining dynamic error and static error,it shows that the new horizontal adjustment based on 3-PRS /PSS mechanism has higher accuracy and meets the actual installation and calibration requirements.It also provides a theoretical basis for the accuracy analysis of similar parallel mechanisms. |
