Reliability Analysis Of Cam Mechanisms

Cam mechanism is widely used in automatic machine and automatic control equipment.As the mechanism products are developing toward high speed and high-precision,it puts forward higher request to the dynamics and dynamic performance of the cam mechanism.The motion accuracy and reliability of cam mechanism is more and more valued by the engineering and academic circles.To the cam mechanism,it is obvious that the uncertainty exist inside and outside,such as the cam mechanism's tolerance of spare parts,clearance of hinged joint,and the deformation by stress and thermal and so on.These stochastic uncertainties will inevitably reduce the motion precision and the reliability of the cam mechanism.Therefore,it is of great scientific significance and engineering value to study the theory and method of high-precision and high-reliability of cam mechanism.The research results of the connecting rod mechanism about reliability theory is extended and applied to the cam mechanism in this article.Then it focuses on establishing the time-dependent reliability model,analysis and robust design.The main research contains include establishing the time-dependent reliability model of kinematical accuracy and analyzing the time-dependent reliability under the consideration of the randomness of the dimension errors,and the time-dependent reliability robust optimization based on tolerance-cost.The main innovative points are listed as follows:(1)Firstly,we trace the mechanism's motion reliability,and illuminate the error model of mechanism reliability,the model of point reliability analysis and the time-dependent reliability analysis.Then we introduce the solving algorithm of the point reliability and review the solution strategies and methods of the time-dependent kinematic reliability which is based on the first-passage time theory.(2)Secondly we establish the kinematical error model and analysis of cam mechanism.We take three cam mechanisms which with straight moving,oscillating followers or flat bottomed follower as example.Based on the theoretical derivation of the cam's profile equation,we establish the kinematic error model of cam mechanism.With the direct linearization method,we can Taylor expand the function of output motion error at the mean value,and analyze the mathematical feature statistics.(3)We establish the model of kinematical accuracy reliability of cam mechanism and then analyze the kinematical accuracy reliability.Based on the kinematical error model of cam mechanism,we respectively establish the model of kinematical reliability analysis of the three kinds of cam mechanism mentioned above,including the models of point reliability and time-dependent reliability.We use the first order second moment method to solve the point reliability,and use the mean value first passage method to solve the time-dependent reliability.Then we acquire the reliability or failure probability in the desired range of motion,it provide theoretical basis for the design of high precision cam mechanism.(4)The research of the robust design method of cam mechanism.Based on the model of tolerance-cost,we explore the reliability robust optimization design of cam mechanism.The cam mechanism's manufacturing tolerances of structural parameters is used as design variable and the time-dependent reliability is used as constraints,then we establish the cam's parameters optimization design model which is aimed at manufactural cost.The research indicate that based on the tolerance-cost model and take the time-dependent reliability or failure probability as constraints to design the model.This method can not only notably reduce the tolerance level of the parts of cam mechanism to cut down the manufactural cost,but also ensure the high kinematical precision of the cam mechanism.