The Kinematic Reliability Analysis And Design Of Globoidal Indexing Cam Mechanism

The globoidal cam mechanisms is a kind of precise mechanism that can realize high speed intermittent indexing.Due to high indexing precision,smooth transmission,accurate positioning,the compact structure and high loading capacity,the globiodal cam mechanisms is widely used in automatic and semiautomatic equipment.However,uncertainties should be reduced the kinematic accuracy of the globoidal indexing cam mechanisms.In this paper,the kinematic reliability and probabilistic design for the globoidal indexing cam mechanisms are studied.Based on the profile equation of the globoidal cam,the kinematic error model of the mechanism is established,and the kinematic reliability and its sensitivity for the cam mechanisms are then analyzed.The probabilistic design of the globoidal indexing cam mechanism is performed with the kinematic reliability.The main contents of this research are as follows:1.According to the machining analysis of the globoidal cam and the theory of spatial meshing,the actual profile equation of the globoidal cam is established.The error transfer coefficient and the error model are then derived by differential method.The MCS method is used to investigate the probabilistic distribution and the statistical properties of the kinematic error for the globoidal indexing cam mechanisms.The results show that the motion output error of the mechanism is following normal distribution when the random parameters of the globoidal indexing cam mechanism obey the normal distribution.2.Considering the influence of the uncertain factors on the kinematic accuracy of the mechanism,the first-order second moment(FOSM)method and the envelope method are used to analyze the point reliability and the interval reliability of the mechanism respectively.The failure probability curves of mechanism kinematic accuracy are obtained by numerical examples.Among them,the failure probability curve corresponding to the point reliability reflects the change of the failure probability of the mechanism at different time during the movement.The failure probability curve corresponding to the interval reliability reflects the change of the failure probability of the mechanism in different motion range.Comparing the two kinds of reliability analysis method,the interval reliability analysis of mechanism can accurately reflect the accuracy of the expected predetermined rules of the whole movement of the mechanism,and the result is more in line with the actual situation.3.Through the reliability sensitivity analysis of the mechanism,the degree of sensitivity of the kinematic accuracy of the mechanism to the error elements can be learned.The numerical example shows that the error of the crossed axes angle between cam and driven plate has the greatest influence on the motion reliability of the mechanism.Therefore,in order to make the movement has sufficient reliability,the crossed axes angle between cam and driven plate should be strictly controlled.And based on reliability sensitivity,robust designwas carried out on the mechanism.The reliability sensitivity is optimized as the objective function.The result of the optimization reduces the sensitivity of the kinematic accuracy of the mechanism to the standard deviation of the random variables,and improves the reliability of the kinematic accuracy of the mechanism.On the basis of the optimization results,a mathematical model of tolerance allocation optimization based on machining cost--tolerance model is established.The optimization results show that the appropriate change of the tolerance of the structural parameters of the globoidal indexing cam mechanism can reduce the manufacturing cost of the mechanism,but also ensure the reliability of the mechanism.