Dynamic Response And Wear Characteristics Analysis Of Spatial Parallel Mechanism Considering Multi Clearance Effect

With the rapid development of industrial automation,the requirements of efficiency,accuracy and stability of mechanical equipment are gradually improved at home and abroad.Because of the processing and manufacturing factors,there are inevitably clearance between the moving joints in the mechanism system.The clearance is the premise to ensure the normal connection of all joints of the mechanism,but at the same time,the clearance will also cause the mechanism to generate bad vibration and wear,which is the main reason for the decrease of the accuracy and stability of the mechanism.The parallel mechanism is widely used in many fields because of its have good bearing capacity and high precision.The parallel mechanism generally contains many branches,and each branch usually contains many motion joints.Therefore,the stability of parallel mechanism is closely related to the clearance of moving joint.It is of great significance to study the dynamic characteristics of spatial parallel mechanism with multiple clearance of motion joint.In this paper,the 4UPS-RPS spatial parallel mechanism with multiple spherical joint clearances is taken as the research object.The dynamic response,nonlinear characteristics and dynamic characteristics of this mechanism under single and multiple spherical joint clearances are studied in depth.The main research contents are as follows:Firstly,the geometric relationship of the spherical joints clearance is analyzed.On this basis,the kinematic model of the single spherical joint clearance is established,and the normal contact force model of the clearance is established based on the Lankarani-Nikravesh(L-N)contact force model,and the tangential contact force model of the clearance is established by using the improved Coulomb friction force model.On the basis of Newton Euler equation,the dynamic model of 4UPS-RPS spatial parallel mechanism with a single spherical joint clearance is established.The equation is solved by Matlab,and the dynamic response of the mechanism in a single clearance state is obtained.And,Adams is used to simulate the virtual prototype to verify the correctness of the dynamic modeling.The influence of the clearance value on the nonlinear characteristics of the moving platform and the clearance of the mechanism under the condition of single clearance is analyzed by means of phase trajectory diagram,Poincare map and bifurcation diagram.Secondly,based on the kinematic model of single spherical joint clearance,the kinematic model of multiple spherical joint clearances is established,and the contact force model of multiple spherical joint clearances of the mechanism is established according to the L-N contact force model and the improved Coulomb friction model.The dynamic model of 4UPS-RPS spatial parallel mechanism with multiple spherical joint clearances is established by using Newton Euler equation.The dynamic differential equation of 4UPS-RPS spatial parallel mechanism with multiple clearances is solved by using Matlab,and the dynamic response of the mechanism with multiple clearances is studied.According to the phase trajectory diagram,Poincare map and bifurcation diagram,the influence of the clearance value on the nonlinear characteristics of the moving platform and the clearance is analyzed.Finally,according to the dynamic model of the mechanism in the state of multi clearance,a three-dimensional wear calculation model of multiple spherical joints is established based on the Archard wear model,and the worn surface of spherical joints is reconstructed according to the wear depth of multiple spherical joints.The dynamic response of 4UPS-RPS spatial parallel mechanism with multiple worn irregular clearances is studied by using the surface morphology of spherical joint after wear.On this basis,the influence of important parameters like clearance value,friction coefficient and spherical joint radius on the wear dynamic characteristics of the mechanism is further analyzed.It provides a theoretical basis for predicting the actual operation state and life of the mechanism.