考虑运动副间隙的平面函数机构概率分析与综合

发布时间：2019-03-31 07:48

【摘要】：在机械系统中,机构运动副是连接两构件并保持二者有一定相对运动的中间环节。为了保证两构件有相对运动,运动副元件间一般需采用动配合,这就需要存在一定的运动副间隙。保持运动副存在适量间隙是确保机构运转灵活的基础,但运动副间隙的不确定性却已成为严重影响机构动态性能以及可靠性的重要因素。含运动副间隙机构系统的研究已经引起越来越多的关注,虽然其研究已涉及到机构的运动学、动力学各个方面,但现有研究文献显示,对含运动副间隙随机性的机构运动可靠性分析与综合体系尚未完善,需对其相关理论和方法进行深入研究。为此,本文通过考虑尺寸公差和运动副间隙的不确定性,来研究机构运动可靠性分析与综合理论和方法,主要工作体现在以下几方面:(1)为了验证运动副间隙对机构运动可靠性的影响,以曲柄连杆机构为例,综合考虑机构的尺寸公差和运动副间隙不确定性以及机构自身误差,构建误差概率模型。采用概率法对含运动副间隙不确定性的机构运动精度分析的难点是运动副间隙变量的概率建模以及如何处理运动副间隙变量间的统计相关性问题。针对此难点,采用混合降维法(Hybrid Dimension Reduction Method,HDRM)对含运动副间隙不确定性的机构瞬时可靠性进行分析,用一次二阶矩法(First Order Second Moment,FOSM)对考虑随机误差(包括尺寸公差、运动副间隙)的曲柄摇杆机构运动可靠性分析。(2)机构时变可靠度能够提供运动区间上的全部可靠性信息,便于实现风险管理和概率寿命预测。本文提出了一个有效的对函数生成机构的时变可靠性分析方法—包络函数法。文中用混合降维法近似随机变量的运动输出和用包络函数法估算失效概率对时间的依赖性。实例分析表明:所提出的包络函数法是有效的。(3)在对机构可靠性分析的基础上,进一步探讨含运动副间隙不确定性的机构可靠性概率综合,以机构运动失效概率最小为目标函数,并将机构运动失效概率作为约束条件进行概率综合。实例分析表明:所提出的机构概率综合方法能够有效降低机构运动失效概率,提高机构运动的运行安全性。(4)可靠性设计优化和稳健设计是最典型的两种不确定性设计方法。可靠性设计优化和稳健性设计是从不同的角度来提高产品质量,在实际工程中,产品需要同时满足可靠性和稳健性的设计要求。因此,有必要在设计阶段将二者结合起来以期全面提高产品的设计质量和水平。本文提出可靠性稳健设计方法,并进行实例分析,验证可靠性稳健设计的优越性。并在此基础上提出基于成本-质量模型的可靠性稳健综合模型,获取以工程实用的全寿命周期成本最小,满足可靠性和稳健性要求的最优解,为机构设计质量的全面提高奠定基础。
[Abstract]:In the mechanical system, the mechanism motion pair is the middle link that connects the two components and keeps the two parts moving relative to each other. In order to ensure the relative motion of the two components, dynamic coordination is generally needed between the two components, which requires the existence of a certain clearance of the moving pairs. Maintaining proper clearance of motion pairs is the basis for ensuring flexible operation of the mechanism, but the uncertainty of the clearance of motion pairs has become an important factor seriously affecting the dynamic performance and reliability of the mechanism. More and more attention has been paid to the research of mechanism system with kinematic pair clearance. Although the research has involved all aspects of kinematics and dynamics of the mechanism, the existing research literature shows that, The reliability analysis and synthesis system of mechanism with random clearance between motion pairs is not perfect, so the relevant theories and methods need to be studied deeply. In this paper, the kinematic reliability analysis and synthesis theory and method of mechanism are studied by considering the uncertainty of dimension tolerance and clearance of motion pair. The main work is as follows: (1) in order to verify the effect of the clearance of motion pairs on the kinematic reliability of the mechanism, taking the crank-connecting rod mechanism as an example, the dimensional tolerance of the mechanism, the uncertainty of the clearance of the kinematic pair and the error of the mechanism itself are considered comprehensively. The error probability model is constructed. The difficulty of using probability method to analyze the kinematic accuracy of the mechanism with uncertainty of the clearance of the kinematic pair is the probability modeling of the variable of the clearance of the kinematic pair and how to deal with the statistical correlation among the variables of the gap of the moving pair. In order to solve this difficulty, the mixed dimension reduction method (Hybrid Dimension Reduction Method,HDRM) is used to analyze the instantaneous reliability of the mechanism with the uncertainty of the clearance of the kinematic pair. The first order second moment method (First Order Second Moment,FOSM) is used to consider the random errors (including dimensional tolerances). (2) the time-varying reliability of the mechanism can provide all the reliability information in the movement interval, which is convenient for risk management and probability life prediction. In this paper, an effective time-varying reliability analysis method for function generating mechanisms-enveloping function method is proposed. In this paper, the mixed dimension reduction method is used to approximate the motion output of random variables and the envelope function method is used to estimate the time dependence of failure probability. The example analysis shows that the proposed envelope function method is effective. (3) on the basis of the reliability analysis of the mechanism, the probability synthesis of the reliability of the mechanism with the uncertainty of the clearance of the moving pair is further discussed. Taking the minimum probability of kinematic failure of mechanism as the objective function, the probability of kinematic failure of mechanism is considered as the constraint condition for probabilistic synthesis. An example analysis shows that the proposed probabilistic synthesis method can effectively reduce the probability of motion failure of the mechanism. (4) Reliability design optimization and robust design are two typical uncertain design methods. Reliability design optimization and robustness design are to improve product quality from different angles. In practical engineering, the product needs to meet the design requirements of reliability and robustness at the same time. Therefore, it is necessary to combine the two in the design phase in order to improve the quality and level of product design in an all-round way. In this paper, a reliability robust design method is proposed, and an example is given to verify the superiority of reliability robust design. On this basis, the reliability robust synthesis model based on the cost-quality model is proposed, and the optimal solution is obtained, which is based on the engineering practical life cycle cost and meets the requirements of reliability and robustness. It lays a foundation for improving the quality of mechanism design in an all-round way.
【学位授予单位】：西华大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TH112

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