Study On Kinematic Accuracy And Stiffness Characteristics Of 2(3HUS+S) Parallel Manipulator For Hip Joint Motion

With the popularization of artificial joint replacement in modern medicine,hip arthroplasty has become a hot topic.The hip joint manipulator used to evaluate the friction and wear characteristics of artificial hip materials emerged in response to the needs of times.Parallel manipulators are used for the simulation of hip joint motion based on its advantages of high stiffness,high accuracy,high speed,strong bearing capacity,and complex trajectory capability,and makes up for the defects in which the motion simulation and force loading of traditional serial hip joint simulators differ from the actual hip joint motion.This paper presents a study on a 2(3HUS+S)parallel manipulator for the simulation of hip joint motion,which has two moving platforms and can be used to test the friction and wear of two artificial hip joints simultaneously.The kinematic accuracy and stiffness of the manipulator are particularly important in the practical application.Therefore,the kinematic error modeling,parameter calibration,stiffness characteristics and the dimension optimization based on the stiffness and dexterity performances of the manipulator were studied.The correctness and effectiveness of the established models and the proposed methods were validated through the simulations and experiments.The main research contents are presented as follows:1)A kinematic error modeling method of the manipulator was studied and an error analysis was carried out.In order to establish an error model including the geometric error sources of the manipulator in a comprehensive manner,first,a kinematic model of the manipulator was established based on the D-H(Denavit-Hartenberg)transformation matrix.Then,on the basis of the kinematic model,the kinematic error model considering the assembly and manufacturing errors of the manipulator in a comprehensive manner was established based on the perturbation theory.Finally,the main error sources were found out through analyzing the influence of the geometric errors on the attitude errors of the moving platform.It provides a theoretical basis for the calibration modeling and the parameter identification of the main geometric errors.2)A kinematic parameter calibration method of the manipulator was studied and an experimental verification was carried out.First,according to the results of the error analysis,the geometric parameters that need to be calibrated were determined,and an error calibration model containing main geometric error sources was established.Then,the Levenberg-Marquardt iteration algorithm was determined to be used to calibrate the geometric parameters in the calibration model.The multi-group attitude data of the moving platforms were measured,and the parameter identification was carried out.The error compensation of the manipulator was realized according to the identification results.Finally,the numerical simulation of the moving platform attitude errors before and after calibration was carried out through MATLAB software to verify the correctness and effectiveness of the kinematic error model and calibration method.3)The stiffness characteristics of the manipulator were studied and the virtual prototype experiment was carried out.Firstly,a static analysis of the manipulator was carried out,and a static model was established based on the virtual work principle,allowing the relationship between the force and deformation to be obtained.The motion and constraint Jacobian matrices of the manipulator components were obtained according to the kinematic analysis,and the global stiffness matrix model was established.The global and local stiffness performance evaluation indexes and isotropy indexes were defined.The stiffness characteristics of the manipulator were evaluated through analyzing the influence of the attitude parameters and structural parameters on the stiffness indexes.Finally,the structural deformation of the virtual prototype under several typical attitudes was analyzed through the finite element analysis software ANSYS Workbench.The reasonableness of the established stiffness model was verified through comparing the results of the numerical simulation and virtual experiment.4)The dexterity performance of the manipulator was studied and the dimension optimization based on the stiffness and dexterity performances was carried out.First,the dexterity model and performance evaluation index were established,and the numerical simulation analysis was carried out.Combining with the analysis results of the stiffness characteristics of the manipulator,multiple structural parameters were selected as the design variables and the constraint conditions were set up.A linear weighting method was used to convert multiple objective functions into a single objective function based on the stiffness and dexterity performances of the manipulator.Then,the objective function was optimized through the genetic algorithm toolbox in MATLAB,and a set of optimized parameters was obtained.Finally,the optimization results were verified by comparing the stiffness and dexterity performance indexes before and after optimization.