时变磨损间隙对机构可靠性的动态影响

为克服磨损速率恒定和磨损影响因素随机性假设带来的不足,并准确预测机构磨损可靠性的动态变化过程,利用等效弹簧阻尼接触碰撞力模型和磨损过程离散化方法,建立了关节间隙的时变磨损方程;引入PHI2方法、定义上穿率,将时变磨损方程转变成时变可靠性方程,从而提出了含时变间隙多体系统动力学和PHI2方法相结合的磨损可靠性分析方法。以某星载天线双轴定位机构为例,研究了产品可靠性及参数概率灵敏度的动态变化规律,分析了磨损各参数对产品可靠性的影响。结果表明,在稳定磨损阶段结束以前,接触碰撞力是主导因素,其对可靠性的敏感度是其他因素的10倍以上,此后,间隙将超过接触碰撞力,成为新的主导因素;且间隙存在临界情况,在此之前,间隙的适当增大有利于产品可靠性的提高。相比于现有研究强调磨损随机性、忽略磨损过程的非线性变化和间隙时变对可靠性的影响,所提方法能准确预示磨损及可靠性的动态变化过程。

Dynamic effect of time-variant wear clearance on mechanical reliability

In order to overcome the drawbacks of constant wear rate and wear factors randomness hypothesis and to accurately predict the dynamic process of mechanical wear reliability, a time-variant wear equation of joint clearance is constructed by using a nonlinear equivalent spring-damp contact force model and discretization of wear process. Then, the joint wear evolution equation is converted into a time-dependent reliability equation by introducing a PHI2 method and defining an up-crossing rate. Therefore, a wear reliability analysis method which combines the mechanical multibody dynamics considering time-variant clearance with PHI2 is put forward. At last, by taking a two-axis positioning mechanism of satellite antennas as an example,dynamic reliability of the mechanism, parameters reliability sensitivity and their influence on reliability are studied. Results show that contact force is the dominant factor of reliability which is 10 times sensitive than other factors before the end of the product''s steady wear process stage, while joint clearance will be the new dominant factor of reliability after this stage. What''s more, there is a critical value for joint clearance, and appropriate augmentation of joint clearance before this critical value is propitious to the improvement of product''s reliability. Compared to the current methods where randomness is emphasized, while the nonlinear process of wear and the consequence of concomitant time-variant clearances to product reliability are neglected, the present method could accurately analyze the dynamic process of wear and wear reliability.