Analysis And Optimization Of 3-PPR Mechanism Based On Mixed Joint Clearances

In engineering practice,due to processing,assembly and the wear of component,some clearances inevitably existed the mechanical system.The existence of the clearances can cause many bad influences such as the wear and tear of the component,producing motion errors,and reducing stability,etc.So the influence of the moving pair clearances in the mechanical system cannot be ignored.This article is based on the background of the precision installation and calibration platform in the optical module installation and calibration task of the device construction project.The optical module placed on the precision mounting and calibration platform.To make it have better stability,the effect of the moving pair clearances on the adjustical unit is mainly studied from three aspects: only the prismatic pair clearances,only the revulate pair clearances and the mixed jiont clearances.The main content of the full text is as follows:First,a brief description of the adjustical unit,which is the 3-PPR plane parallel mechanism,and the freedom of the mechanism is simply calculated using the anti-spiral theory.Then this chapter introduces the analysis purpose of clearances and the preliminary layout between the mechanism and the optical module.In the end,this chapter introduces detaily the model of the clearances,the evaluation index of the clearances and the contact force model of the clearances.Kinematics analysis of the 3-PPR planar parallel mechanism without clearances is analyzed,and the displacement curve of the driving slider is used as the input condition of the dynamic analysis later.Then,the Newton-Euler method is used to establish a3-PPR plane parallel mechanism dynamic model without clearances,and the results of simulation with Matlab and Adams software is used to verify the correctness of model.The model provides a basis for the dynamic equation with clearances.Finally,based on the Lankarani-Nikravesh contact force model and the Ambrósio friction force model,the contact force is introduced into the dynamic equation of the 3-PPR plane parallel mechanism with the revulate pair clearances.In the aspect,Comparing and analyzing from three aspects of clearances existence,clearances size and clearances position.And using the comparative simulation analysis of the dynamic characteristics of the mechanism to provide theoretical guidance for the processing and assembly of the revulate pairs of the mechanism.Based on the state of any angular contact in the prismatic pair clearances model,the contact force model and friction model,the dynamic equations of the 3-PPR plane parallel mechanism with the prismatic pair clearances are derived.Comparing and analyzing from three aspects of clearances existence,clearance sizes and clearance positions.And using comparative simulation analysis to provide theoretical support for the assembly of the prismatic pairs of the mechanism.Based on the previous analysis including only the prismatic pair clearances and only the revulate pair clearances of the 3-PPR planar parallel mechanism,the influences of mixed jiont clearances are studied from the three aspects of mixing clearances,different mixing clearance sizes and different mixing clearance positions.Finally,using the results to verify the correctness of the relative layout between the mechanism and the optical module.