Research On Dynamic Accuracy Of A Dynamic Balance Device

As a performance index of parallel mechanism,dynamic accuracy is increasingly important,especially in the application fields of high speed,heavy load and lightweight,dynamic accuracy even directly determines the success or failure of a project.In the production process,there are geometric errors caused by manufacturing and assembly,which greatly reduce the motion accuracy of the parallel mechanism.During the actual motion movement,there are dynamic errors caused by the clearance of the moving pair and the flexibility of the parts,which not only affect the motion accuracy of the mechanism,but also seriously reduce the dynamic performance of the mechanism.Therefore,in view of the above errors,this paper studies the dynamic accuracy of a new 5-PSS/UPU dynamic balance parallel device.(1)First,the kinematics analysis of the parallel mechanism is performed.According to its structural characteristics,an appropriate coordinate system is established,and the vector solution method is used to find the inverse solution expressions of the mechanism position,speed,and acceleration,and the expressions of the Jacobian and Hessian matrix of the mechanism is found.Numerical calculation and prototype simulation tests verified the correctness of the kinematics model,and derived the dynamic regularity in driving displacement,rod speed and acceleration with the movement of the platform.(2)Secondly,the influence of geometric errors on the dynamic accuracy of the parallel mechanism and the error calibration are studied.Based on the analysis of kinematics,the closed vector chain method is used to model the error,and the mapping relationship between the position error of the moving platform and each geometric error source is obtained.The sensitivity of each geometric error is analyzed statistically,and its influence on the dynamic accuracy of the parallel mechanism is analyzed by numerical calculation and simulation experiment.Finally,a vector calibration algorithm suitable for the structural characteristics of the mechanism is proposed,and its correctness is verified by the design variable method.(3)Then the influence of component flexibility on the dynamic accuracy of the parallel mechanism is studied.Based on the finite element method,the fixed connecting rod is divided into an equal-section space beam element model.The Lagrange method is used to establish the element elastic dynamics equation and the vector superposition of the equations is performed using the internal force cancellation,and the elastic dynamic equation of the connecting rod is synthesized.The kinematic constraint relationship of each moving part is listed to realize the assembly of the whole machine's elastic dynamics model,and the Newmark method is used to solve the whole machine's elastic dynamics equation,and the influence of component flexibility on the dynamic accuracy of the parallel mechanism is analyzed.(4)Finally,the influence of joint clearance on the dynamic accuracy of the parallel mechanism is studied.Based on the "contact-separation" two-state model,a kinematics model with spherical joint clearance is established.A modified contact model based on the Flores model and a modified Coulomb friction model are used to calculate the collision and friction forces of spherical auxiliary elements when they are in contact,and converted to the center of mass of the corresponding part.The Newton-Euler equation is used to introduce the Lagrange multiplier,and the dynamic model of the mechanism is established based on the relationship equations of the kinematic constraints of the mechanism.The dynamic accuracy of the parallel mechanism with spherical joint clearance is analyzed by numerical simulation.(5)The research results show that the geometric error has the greatest influence on the dynamic accuracy,but it can be ignored to some extent after being calibrated by an effective calibration algorithm.Comparing the effect of the flexibility of the component and the clearance of the moving pair on the dynamic accuracy of the device,the results show that the effect of the clearance of the moving pair is more significant.Therefore,in the actual design and optimization process,the main design goal is to reduce the effect of the clearance of the moving pair.