Reliability Optimization Design And Evaluation Of Kinematic Accuracy Of Planar Linkage Mechanism

With the development of machinery towards high accuracy and reliability,the reliability of mechanism motion accuracy,as an important branch of mechanical reliability,has attracted widespread attention and became increasingly prominent.However,for the real mechanisms,there are always uncertainties inside and outside the system,such as link length tolerances and fit clearances,and so on,which lead to the reduction of motion output accuracy,failure and other characteristics.Therefore,in the design stage,considering the uncertainty of the real mechanism output caused by the above factors,the classical mechanisms such as planar four-bar path mechanism,crank-slider mechanism and planar five-bar two-degree-of-freedom metamorphic mechanism were selected to optimize,analyze and evaluate the reliability of kinematic accuracy in this paper.The main research contents are as follows:(1)Aiming at the planar path mechanism,a multi-size probability synthesis method was proposed for the kinematic design of planar linkage with dimension tolerances and joint clearances,Established a probability model of the motion error,Minimizing the maximum failure probability as the objective function,reliability and motion continuity were used as performance probability constraints,then established the reliability-based robust optimization design model of motion accuracy,and the validity of the model was verified.The design parameters such as the length and manufacture tolerances of the links were optimized.The influence degrees of the different fit clearances on the kinematic accuracy reliability were obtained.(2)Aiming at the offset crank-slider mechanism,the prismatic clearance was taken into account.An error analysis method with mixed clearance and multi-dimension tolerance was proposed.The global optimization was carried out for 12 schemes.The actual trajectory and distribution of motion errors of the slider were observed.Aiming at the slider heading interval,the influence degree of the mixed clearances on the reliability of the kinematic accuracy of the mechanism was quantitatively analyzed.(3)Aiming at planar five-bar two-degree-of-freedom metamorphic mechanism.Taking into account the tolerances of link length and rotating clearances as the influencing factors,a multi-objective optimization design model with high accuracy and reliability was established.Quantitative analysis was made on the distribution characteristics of motion errors and failure probabilities at the locus points of differentconfiguration.The cumulative errors in the process of configuration transformation of different schemes were obtained.(4)Based on the manufacturing cost-tolerance function,the costs of different design scheme were predicted for the planar linkage mechanism.Based on the reliability of motion accuracy,the design schemes were comprehensively evaluated.According to the different requirement of design objectives,the optimal design scheme was selected reasonably,which provided a quantifiable evaluation system for the actual engineering design of the mechanism.